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(11) | EP 1 162 292 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Polyolefin fibers having high and permanent hydrophile characteristics and extrusion and spinning process thereof |
(57) Polyolefin fibers having high and permanent hydrophile characteristics obtained from
a mixture of a polyolefin and a polyamide. Such fibers are produced by extrusion through
the holes of a die and by spinning comprising the following steps:
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[0001] The present invention relates to polyolefin fibers having high and permanent hydrophile properties and the related process of extrusion and spinning thereof.
[0002] More particularly, the present invention relates to polyolefin fibers having high and permanent hydrophile properties, suitable to be used in the health sector for the production of sanitary napkins and in the technical sector for works carried out with extremely quick cards.
[0003] By the expression "sanitary napkin", as used in the present invention and the claims, there is intended to indicate any porous structure having a high absorbing capacity, in the form of tampons, towels, diapers and the like, generally used for intimate hygiene of women, newborn babies, and those affected by incontinence.
[0004] As is known, napkins are constituted of an inner absorbent layer, generally made from cellulose fibers, and a covering external gauze or nonwoven fabric. The properties required of such gauze or nonwoven fabric are those of being soft, absorbent and non-irritating, of insulating the inner layer, keeping dry the skin of the user with which it in contact.
[0005] Polyolefin fibers allow to obtain all these properties, which is why they are widely used for this purpose.
[0006] However, they are not free from drawbacks among which the most important one is the wet or humid sensation users feel in the presence of an absorbed body fluid, especially after some time of permanence.
[0007] In order to solve this drawback it has been proposed to treat the fibers with special finishing products that facilitate the leak of the liquid from the external covering layer, the liquid being then absorbed by the underlying cellulose layer.
[0008] However, also this solution proved not to be exempt from drawbacks, especially because it is not a permanent one; in fact, such finishing products are easily removable upon the contact with the liquid.
[0010] In particular, object of the present invention is to provide a polyolefin fiber suitable for the production of gauze or nonwoven fabric for napkins which, besides being soft, hydrophile and not irritating, gives users a permanent sensation of dryness even after a long period of use and contact with the internal wet layer.
[0011] A further object of the present invention it to provide an extrusion and spinning process such as to allow to markedly increase the production power of each extruding unit, up to values exceeding 100 kg/h, with remarkable savings of energy and fabrication costs.
[0012] Under a first aspect of the present invention, these and other objects, that will clearly result from the following description, are achieved by employing a polyolefin fiber constituted of a mixture of a polyolefin and a polyamide.
[0013] The polyamide contents in the mixture is not critical for the purposes of the present invention; it may range from 5 to 50% by weight and preferably from 15 to 45% by weight based on the mixture.
[0014] The term "polyolefin" as used in the present description and the claims, comprises polyethylene and thermoplastic copolymers thereof, polypropylene and thermoplastic copolymers thereof, and mixtures of polyethylene, polypropylene and/or copolymers thereof, in any mutual ratios.
[0015] Polypropylene, and in particular the high fluidity one for extrusion, is preferred. This type of polypropylene is available on the market, for instance by the commercial names FINAPRO PPH 10069S and PPH 10080, produced and sold by the FINA Chemicals company. They have a Melt Flow Index of 35 g/min, as determined according to the norm ASTM D 1238, and a melting temperature range of 160-165°C.
[0016] Any known polyamide may be used for the production of the fibers of the present invention. By way of example, we mention nylon 6, nylon 6,6, nylon 6,10, etc. All these polyamides are known and available on the market. By way of example, we remember the polyamide known by the commercial name ULTRAMID BS 700, produced and sold by BASF company.
[0017] A second aspect of the present invention is the extrusion and spinning process that allows to obtain fibers starting from the polyolefin-polyamide mixture, at a high spinning speed and to very contained costs.
[0018] Such process is characterized in that the polyolefin-polyamide mixture at the molten state, before the extrusion · through the holes of a die of a spinning head, is mixed in a diffusion chamber comprising a set of prismatic elements, symmetrically arranged with respect to each other, filled with diathermic oil and heated to a temperature higher than the melting temperature of the mixture by at least 10°C, and in that the spinning heads are arranged in a closed box filled with diathermic oil, and heated to a temperature than the temperature of mixture melting higher by at least 10°C.
[0019] In particular, the process of extrusion through the holes of a die and of spinning of the present invention comprises sequentially the following steps:
- mixing the polyolefin with the polyamide in a mixer,
- feeding the so obtained mixture to an accumulation chamber by means of a pump formed by parallel, cooperating, rotary and grooved cylinders;
- melting the mixture in a melting chamber provided with heating means;
- mixing the molten mixture in a diffusion chamber, and subsequently,
- extruding the molten mixture through the holes of a die of a spinning head;
[0020] The heating of the prismatic elements and the spinning heads is carried out with resistors arranged in their inside.
[0021] The polyolefin-polyamide mixture in the form of grains coming from a mixer is loaded in a hopper and pushed by the pump first in am accumulation chamber, afterwards towards the outlet wherein the dies are located, passing through a melting chamber and a diffusion chamber.
[0022] In the accumulation chamber, there is obtained the pressure necessary to force the mixtures, once it is molten in the melting chamber, to come out from the die holes.
[0023] The cylinders of the feeding pump have preferably a diameter of 450 mm and a length of 1000 mm.
[0024] The arrangement of the cylinders of the feeding pump, perpendicular to the axis of the die holes, allows to uniformly distribute the pressure on the whole length of the die.
[0025] The use of a pump with cylinders having the aforesaid diameter and length values allows to use a melting chamber having a mouth surface of about 500,000 mm2.
[0026] The use of prismatic elements in the diffusion chamber allows to reduce the mass to be heated markedly.
[0027] Each of these elements is filled with diathermic oil and contains in its inside a tubular resistor having a very small diameter compared with the internal one of each element.
[0028] The various prismatic elements are closed in a box filled with diathermic oil, so that the diffusion chamber will be entirely full of oil in its inside. Resistors heat oil and the latter transmits simultaneously the heat to the parts forming the diffusion chamber. This involves a remarkable energy saving to heat the entire diffusion chamber.
[0029] A length of the pump cylinders of about 1000 mm allows to use an extruding unit formed by 19 spinning heads and therefore 10 dies.
[0030] · Each die can have a useful work section of 20,000 mm2, allowing a better cooling of the filaments for the subsequent crystallization.
[0032] Each spinning head comprises, in the feed direction of the polymer:
- a drilled plate, that acts as a pressure homogenizer of the molten mass coming from the prismatic elements of the diffusion chamber;
- a temperature mixer and homogenizer, composed of prismatic and cylindrical ducts having different diameters, symmetrically arranged and oriented in the polymer feed direction;
- a further drilled plate, in order to resists the passage of the molten mass and to better homogenize pressure;
- a false die, and following this,
- the die.
[0033] The prismatic and cylindrical ducts having different diameters have the function of compressing and expanding the molten material, so that the current of parallel flow in the direction of the die tends to expand in each cylinder, creating an internal turbulence that contributes to a better mixing of the mixture components.
[0034] Each mixer is drilled in the inside to allow the passage of diathermic oil in its inside. Diathermic oil is heated by tubular resistors. This contrivance allows to markedly reduce energy consumption for the heating of all the extrusion heads.
[0035] The ten heads of each extruding units are contained in a sealed box filled with diathermic oil heated by resistors located in the inside of said box.
[0036] The extrusion and spinning process of the present invention can be applied with the same success for the production of fibers from mixtures of a polyamide with polypropylene, copolymers or mixes thereof, in any ratio by means of a simple adjustment of work temperature and change of dies.
[0037] Based on the knowledge of the applicant, up to today no extruding unit was available that could be used both for extruding and spinning polypropylene, polyethylene, copolymer and mixes thereof.
[0038] Besides, the process of the present invention allows to reach yields of 300 kg/h of polymer, each extruding unit being formed by ten dies, and the yield of each die can be of 30 kg/h, with a title range that oscillate between 1 and 150 deniers.
[0039] The extrusion and spinning process of the present invention will be better understood from the following description, wherein reference is made to an extruding unit illustrated by way of non-limiting example in the figures of the attached drawings, wherein:
Figure 1 shows a transversal perspective view of an extruding unit for the production of polyolefin textile fibers according to the process of the present invention;
Figure 2 shows a longitudinal perspective view of the extruding unit of Figure 1, and
Figure 3 shows a longitudinal perspective view from top downwards and in enlarged scale of one of the spinning heads of the extruding unit of the preceding figures.
[0040] With reference to the figures, the extrusion and spinning process for the production of polyolefin fibers of the present invention consists essentially in the introduction of the polyolefin-polyamide mixture, already produced in a mixer and in the form of grains, into a hopper (1) provided with a feeding or extruding pump constituted of two parallel, grooved, cooperating, rotary cylinders (2), arranged perpendicularly to the axis of the holes of the dies.
[0042] The rotation sense of the cylinders (2) is the one marked with harrows in Figure 2 and their surface is grooved with such a form that, by working in synchrony with each other, it causes grains to be first pushed towards the melting chamber, and afterwards towards the die for the extrusion.
[0043] The mixture is pushed by the feeding pump to an accumulation chamber (3), having preferably a truncated trapezoid section, wherein the grain mixture is compressed, and the pressure accumulates that is necessary to cause the material, molten in the melting chamber, to come out from the holes of a die (10).
[0044] As the distance between the two rotation axes of the cylinders (2) of the feeding pump is of 450 mm and their length of 1000 mm, the mouth of the accumulation chamber (3) can be of 450,000 mm2 and its base of about 500,000 mm2.
[0045] · From the accumulation chamber (3) the grains of the mixture are pushed by the feeding pump into the subsequent melting chamber comprising resistors (5) homogeneously distributed in its inside. The melting chamber is heated to a temperature preferably comprised between 280 and 340°C.
[0047] From the melting chamber, the molten mix passes into the subsequent diffusion chamber comprising a plurality of elements having a prismatic shape (6) symmetrically arranged with respect to each other. These prismatic elements (6) are filled with diathermic oil and contain a resistor (7). Said prismatic elements (6) are contained in a sealed box (12) heated in its inside with resistors (7). This structure of the diffusion chamber allows to obtain a better distribution of heat energy and a remarkable energy saving.
[0049] The molten mixture is distributed through distribution means (8) towards the spinning heads (9).
[0051] Each extruding unit contains 10 spinning heads (9), having each a useful work section of 20,000 mm2, allowing thereby a better cooling of the filaments.
[0052] The spinning heads (9) are contained in a sealed box (13) filled with diathermic oil heated by resistors (11).
[0054] With reference to Figure 3, each spinning head (9) comprises sequentially: a first drilled plate (14), a mixer (15), a second drilled head (16), a false die (17), and the die (10).
[0055] The first drilled head (14) has the task of distributing the pressure and the molten material coming from the diffusion chamber before entering the mixer (15).
[0056] A mixer (15) comprises several prismatic ducts (18) having a rectangular section and other ones having a cylindrical section circumscribed by drilled separators for the passage of diathermic oil into their inside, so as to distribute temperature uniformly and save much electric energy.
[0057] The drilled plates (14, 16) and mixer (15) are arranged in a sealed box (13), filled with diathermic oil and heated by means of resistors (11). With this system, a better homogenization of the components of the mixture and a better distribution of heat in the molten mass, with ensuing energy saving, are achieved.
[0058] The second drilled plate (16) is like the first one (14) and has the task of improving pressure distribution.
[0059] The false die and the die are of a known type and selected depending on the polymer to be spun and extruded and the type of fiber desired.
[0061] Each extruding unit can bear 10 dies with a maximum yield per die of 30 kg/h; to total maximum yield per extruding unit is therefore of 300 kg/h. The expected consumption is of 0.4 kw per each kg of fabricated fiber, starting from a production of 900 kg/h.
1. A polyolefin fiber having high and permanent hydrophile properties constituted of
a mixture of a polyolefin and a polyamide.
2. The fiber according to claim 1, wherein the polyolefin is high fluidity polypropylene
for extrusion.
3. The fiber according to claim 2, wherein polypropylene has a Melt Flow Index of 35
g/min, as determined according to ASTM D 1238 norm and an interval of melting temperature
of 160-165°C.
4. The fiber according to any of the preceding claims, wherein polyamide is selected
from: nylon 6, nylon 6,6 and nylon 6,10.
5. The fiber according to any of the preceding claims, wherein the amount of polyamide
in the mixture is comprised between 5 and 50% by weight.
6. An extrusion process through the holes of a die and of spinning for the production
of fibers constituted by a mixture of a polyolefin with a polyamide according to any
of the preceding claims, characterized in that the mixture of molten polyolefin and polyamide, before the extrusion through the
holes of a die of a spinning head is mixed in a diffusion chamber comprising several
prismatic elements symmetrically arranged with respect to each other, filled with
diathermic oil and heated to a temperature higher than the melting temperature of
the mixture by at least 10°C, and in that the spinning heads are arranged in a sealed box, filled with diathermic oil, and
heated to a temperature higher than the melting temperature of the mixture by at least
10°C.
8. The extrusion and spinning process according to claim 8, comprising sequentially
the following steps:
- mixing the polyolefin with the polyamide in a mixer,
- feeding the so obtained mixture to an accumulation chamber by means of a pump formed by parallel, cooperating, rotary and grooved cylinders;
- melting the mixture in a melting chamber provided with heating means;
- mixing the molten mixture in a diffusion chamber, and subsequently,
- extruding the molten mixture through the holes of a die of a spinning head;
characterized in that cylinders (2) of the feeding pump are arranged perpendicularly to the dies; the diffusion chamber comprises a plurality of prismatic elements (6) symmetrically arranged with respect to each other, filled with diathermic oil and heated to a temperature higher than the melting temperature of the mixture by at least 10°C, and the spinning heads (9) are arranged in a box filled with diathermic oil, and heated to a temperature higher than the melting temperature of the mixture by at least 10°C.9. The extrusion and spinning process according to claims 7 or 8, wherein the prismatic
elements (6) and the spinning heads are heated by resistors (7, 11) arranged in their
inside.
10. The extrusion and spinning process according to any of claims 7-9, wherein the prismatic
elements (6) are contained in a sealed box (12) heated in the inside by resistors
(7).
11. The extrusion and spinning process according to any of claims 7-10, wherein each
spinning head (9) comprises sequentially: a first drilled plate (14), a mixer (15),
a second drilled head (16), a false die (17), and the die (10); said mixer and the
drilled plates being contained in a sealed box (13), filled with diathermic oil and
heated by resistors (11).
12. The extrusion and spinning process according to any of claims 7-11, wherein the mixer
(15) comprises several · prismatic ducts (18) having a rectangular section and other
ones having a cylindrical section circumscribed by drilled separators for the passage
of diathermic oil.
13. The extrusion and spinning process according to any of claims 7-12, wherein the melting
chamber is heated to a temperature comprised between 280 and 340°C, the diffusion
chamber to a temperature comprised between 230 and 300°C, the spinning head to a temperature
comprised between 220 and 280°C, and each die to a temperature comprised between 210
and 270°C.
14. The extrusion and spinning process according to any of claims 7-13, wherein each
cylinder (2) of the feeding pump has a diameter of 450 mm and a length of 1000 mm;
the accumulation chamber (3) has a truncated trapezoid section with a mouth having
a surface of 450,000 mm2 and a base of 500,000 mm2; and each extrusion unit comprises 10 spinning heads (9), each die having a useful
working section of 20,000 mm2.
15. A sanitary napkin comprising an external covering constituted of a gauze or nonwoven
fabric of polyolefin-polyamide two-component fibers having high and permanent hydrophile
properties as claimed by any whatever of claims 1-6.