FR2925072A1 - Fabricating a filament comprising longitudinal channel for transfer of moisture and/or thermal insulation, by extruding polymer through die to form under-filament, and assembling, stretching, cooling and then solidifying the under-filament - Google Patents

Abstract

The process for fabricating a filament comprising a longitudinal channel for the transfer of moisture and/or thermal insulation, comprises extruding a polymer through a die (7) comprising group (6) of openings (1, 2, 3, 4) to form a polymer under-filament, assembling, stretching, cooling and then solidifying three under-filaments to form a filament, and texturizing the obtained filament by false-twist spindle or jet of air. The number of openings is >= 2. The flow speed in output of the die for each under-filament is different from other filaments, and is obtained by polymer extrusion. The process for fabricating a filament comprising a longitudinal channel for the transfer of moisture and/or thermal insulation, comprises extruding a polymer through a die comprising group of openings to form a polymer under-filament, assembling, stretching, cooling and then solidifying three under-filaments to form a filament, and texturizing the obtained filament by false-twist spindle or jet of air. The number of openings is >= 2. The flow speed in output of the die for each under-filament is different from other filaments, and is obtained by the extrusion of the polymer through the openings having a different cross section. Independent claims are included for: (1) an extrusion die; and (2) a filament.

Description

METHOD FOR MANUFACTURING A FILAMENT, EXTRUSION LINE FOR CARRYING OUT SAID MANUFACTURING METHOD AND FILAMENT OBTAINED The present invention is in the technical field of processes for manufacturing a filament comprising on at least a portion of its length at least one longitudinal channel for the transfer of moisture and / or thermal insulation. Filaments or synthetic fibers having longitudinal channels, in particular two-dimensional, are known from the state of the art. This is the case, for example, with the CoolMax fiber marketed by Dupont de Nemours. This fiber has on its surface four rectilinear channels along its longitudinal axis. This configuration gives the CoolMax fiber a greater surface area than the specific surface of an equivalent round-section fiber. By specific surface is meant the actual surface of an element as opposed to its apparent surface. This characteristic gives the fibers having rectilinear channels many properties including improved moisture transfer since the contact surface of the fiber with its surrounding environment is increased. This type of fiber is thus used in particular in the manufacture of sports articles, for example for the manufacture of socks, to accelerate the transfer of moisture to the outside and improve the thermal comfort of the wearer. When these longitudinal channels are internal to the filament, they trap the air and have a significant thermal insulation effect. In order to improve the specific surface, or exchange, of these longitudinal channels, the applicant has sought to obtain longitudinal channels in three dimensions, and in particular longitudinal channels forming a helix along the longitudinal axis of the filament. There are various techniques for obtaining a polymer filament provided with at least one longitudinal channel forming a helix along the longitudinal axis of said filament. One technique is to co-extrude a first elastomeric material with a second material having lower elasticity characteristics, and then after the extrusion step is complete, to relax the resulting filament so that the first and second materials, having different elastic behaviors, balance and create a twist on the wire. In EP 0.233.702, the synthetic filament comprises at least two components: a thermoplastic elastomer forming the central axis of the filament and segments projecting from said central axis, and a thermoplastic polymer of low elasticity, different from said elastomer, forming arranged protuberances at the ends of said segments. After the drawing operation, the filament undergoes a heat relaxation step, during which the segments and protuberances are spirally wound around the central axis of the filament. The forces exerted by each of the segments and protuberances are balanced over the length of the filament. This technique aims to obtain an elastic filament, having good dyeing properties, flexibility and a good feel and easy to implement, especially for knitting. It is not described that the filaments obtained have improved transfer capacity and / or thermal insulation. This technique has the disadvantage that the longitudinal channels formed at the surface of the filament are obtained during the stretch-relaxation step, and not directly at the exit of the die, which implies a subsequent step for forming the three-dimensional channels. Finally, it is necessary to co-extrude at least two materials having elastic properties sufficiently far apart which supposes also distant melting temperatures and therefore residence times in the extruder complex to be managed and flow rates of different materials upstream of the extrusion die. In addition, the properties of the filament obtained are conditioned and therefore restricted by the two polymeric materials used and the relaxation process used. It is thus difficult to obtain a filament having a high tenacity. Also known is a method of manufacturing a filament, described in BE 689.571, in which one or more polymers are extruded through a spinning orifice and the nozzle plate having the spinning hole is rotated around the spinneret. central axis of said orifice and thus communicates torsions to the extruded filament. This method is intended to improve in particular the touch and the inflating said filament. This process is not economically viable. It is not possible to provide such spinning means for each filament, knowing that a multifilament yarn is manufactured continuously and has several hundred filaments. There is a need to improve the absorption and evacuation capacity of synthetic fibers, which by their nature have a low water recovery rate in relation to their weight, less than 10%, and a majority of less than 5% , but thus improved evaporation capacity and thus moisture evacuation compared to natural fibers, such as cotton. The present invention partially addresses the aforementioned problems in that it relates to a method of manufacturing a filament comprising on at least a portion of its length at least one longitudinal channel for transferring moisture and / or thermal insulation comprising a first melt spinning step in which at least one polymer is melted and extruded through a die having a group of spinning orifices to form sub-filaments of said polymer and a second step in which said Sub-filaments are collected, stretched, cooled and solidified to form a filament. Typically, the die having n orifices, with n equal to or greater than 2, during the first step, the outlet flow rate of the die of each given sub-filament is different from that of (n-1) other sub-filaments. Since the flow velocity of the extruded polymer is different from one orifice to another, the cooling time and therefore the rate of solidification are different from one sub-filament to another. The n orifices are sufficiently close in a given group so that the n sub-filaments adhere to each other at the die exit to form a single filament. The sub-filaments at the outlet of the extrusion die are at different stages of their cooling. It is then observed at the exit of the die that the sub-filaments drive between them and balance each other by forming longitudinal channels generally following a helix along the longitudinal axis of said filament. An explanation for this phenomenon, non-limiting, could be that the sub-filament (n-1) being more solidified than the n-th neighbor sub-filament, during its cooling tends to retract and drive the n th sub-filament in rotation.

The flow velocities are determined for each of the sub-filaments so as to obtain different levels of plasticity and thus different viscoelastic behaviors specific to each sub-filament, which avoid using at least two different polymers such as than in the state of the art. The longitudinal channels having generally a helical direction along the longitudinal axis of the filament are in this process advantageously obtained at the outlet of the die, more precisely it has been observed that the three-dimensional channels are formed at a distance of about 20-30. cm from the extrusion die. The process according to the present invention is of course suitable for synthetic yarns obtained from one or more polymers capable of being melted and extruded. Thus, all the synthetic polymers that can be extruded can be used, and in particular: the family of polyethylene terephthalates, the family of polyamides, the family of polyesters, in particular polybutyleneterephthalate, the family of polyolefins, in particular polypropylene.

In a variant, the difference in flow velocity between the n sub-filaments is obtained by extrusion of said molten polymer through spinning orifices having in cross section different surfaces [mm 2]. This is a known principle regarding the behavior of a constant flow fluid through a given orifice. A specific fluid, fed upstream at a constant rate, in this particular case via the pump feeding the extruder, has a faster flow rate as the size of the orifice decreases. On the other hand, the larger the size of the orifice through which the fluid is fed, the lower the flow velocity of the fluid.

In a variant, during the second step, at least three gathered sub-filaments delimit between them a longitudinal channel internal to the filament. The obtained filament was observed under a cross-sectional microscope that, starting from at least three extruded filaments, an internal channel was formed which could be used to convey the moisture by capillarity and / or to trap the air and thus serve as a thermally insulating material. In a variant, during the first step, at least one molten polymer is extruded through several groups of spinning orifices of a filament bundle die. According to the invention, each group of n orifices corresponds to a filament, and p groups of spinning orifices are arranged in a die to obtain p filaments in the final multifilament yarn. The number of groups of spinning orifices and the cross-sectional area of said orifices, as well as the drawing speeds, make it possible to adjust the titration of the multifilament yarn. In a variant, the second step comprises, after drawing, a texturing operation of the filament or filaments obtained, in particular by false torsion or by air jet. The texturing of a multifilament yarn, in this case a synthetic multifilament yarn, is an operation known to those skilled in the art, a textile specialist. The purpose of the texturing is to give the swelling agent, to improve the qualities of elasticity and mechanical strength of the yarn by subjecting it to a mechanical treatment slightly deforming it concomitantly or before a thermal fixing step. The two preferred methods in the context of the present invention are the fixed false twist process (FTF), a variant of which is also called Helanca) and air texturing, the latter also being called Taslan. The preferred texturing is fixed false twist (FTF) for its reduced cost. The subject of the present invention is, according to a second aspect, an extrusion die for carrying out the manufacturing method according to the second variant, comprising at least one group of n orifices, with n equal to or greater than 2, for the production of a filament, characterized in that, the n orifices being distributed around the central axis of the die from the first to the nth orifice, the surfaces of the cross sections of said orifices are decreasing from the first to the nth orifice.

For a given polymer, extruded and fed at a constant rate, the flow rate thereof is increased as the cross-sectional areas of the spinning orifices are decreasing and thus the degree of solidification is also decreasing. It is thus observed with such a die that the extruded sub-filaments form, at the outlet of the die, and when they adhere to each other a filament having on the surface external channels generally having a helical shape along the longitudinal axis of the filament. . Such a filament has improved characteristics for the transfer of moisture, while maintaining an evaporation capacity close to that of synthetic son known in the state of the art. The multifilament yarns having external longitudinal channels generally having a helical direction along the longitudinal axis of said yarns have an improved moisture transfer capacity of at least 30% compared with multifilament yarns of the same titration and having the same number filaments and external longitudinal channels having a longitudinal direction parallel to that of said son. The moisture transfer capacity is improved by 50% over multifilament yarns of the same size and having the same number of filaments without channels on their surface. The transfer capacity was measured according to the wicking test.

In a variant, the cross sectional area of the nth orifice is less than or equal to 95% of the area of the (n-1) orifice. It has been observed that this degressivity is ideal to obtain a filament having improved properties for the transfer and evaporation of moisture as well as the quality and reproductivity of the continuous spinning of such filaments.

In a variant, the n orifices have an elongated and curved shape, similar to the shape obtained by the displacement of a circular hole along an arc of a circle, the angle at the center of the arc corresponding to the (nth-1 ) orifice is at least 15 ° greater, preferably 30 ° greater than or equal to that of the nth orifice, and the angle at the center of the arc corresponding to the nth orifice is greater than or equal to 90 °. This variant, possibly combined with the preceding, gives the best results concerning the properties of the filament with respect to moisture, close to those of a natural fiber, such as cotton, concerning the water absorption capacity. ; and reproductivity of spinning continuously. The subject of the present invention is also, according to a third aspect, a filament obtained by the use of the die according to one of the embodiments described above in the method according to one of the variant embodiments described above. , characterized in that it is formed of a single polymer and in that it comprises longitudinal channels open on the outside which have a propeller arrangement, in particular for the transfer of moisture. In a variant, the filament comprises an internal longitudinal channel of thermal insulation.

The present invention will be better understood on reading the following exemplary embodiments, cited in a non-limiting manner, and illustrated in the figures below: FIGS. 1 and 2 are photographs of cross sections of cotton and viscose, respectively; FIGS. 3A and 3B are photographs of cross-sections of filaments comprising four longitudinal channels according to the state of the art; FIG. 4 is a schematic representation of an exemplary die according to the present invention comprising a group of four spinning orifices; FIGS. 5A and 5B are photographs of the cross sections of the filaments obtained according to the present invention after various texturing processes. The rate of retention of demineralized water of cotton is of the order of 45% to 55% of its dry weight for 90% to 110% for viscose (regenerated cellulose fiber). The cross sections of these fibers shown in Figures 1 and 2 show, especially for viscose, they have many channels on their surfaces, and are very porous especially for cotton. Cotton and viscose have a water retention capacity due to their structure but also to the many hydrophilic functions, especially hydroxylated (-OH), present along the structures of the macromolecular chains. The water absorption rate of the synthetic fibers is less than 10% by weight of their dry weights. Their low water retention capacity is due to their structure since the synthetic fibers being extruded generally have a substantially oval surface, but also the presence of hydrophobic functions along their macromolecular chains. FIGS. 3A and 3B show cross-sections of synthetic polyester-based tetra lobed filaments, that is to say having at least four external longitudinal channels parallel to the longitudinal axes of the filaments. Figures 3A and 3B show the same filaments, the only difference is the texturing process. In FIG. 3A, the filaments have undergone an air jet texturing process, also known under the Taslan trademark, which is less aggressive, but more expensive, than the fixed false twist method whose filaments obtained are shown in cross section in FIG. 3B. It is said that the filaments are taslanized. The filaments shown in FIGS. 3A and 3B have improved water absorption properties over synthetic fibers having a substantially circular cross-section. Figure 4 shows in cross section a die 7 according to the present invention. The four spinning orifices, referenced 1 to 4, of the group 6 are distributed around the central axis A of the die 7 from the first orifice 1 to the fourth orifice 4. At each spinning orifice corresponds to a sub-filament extruded. The surfaces [mm2] of the cross-sections of the spinning orifices are decreasing in the trigonometrical direction T. The surface of the cross-section of the fourth orifice 4 is less than or equal to 95% of the area of the third orifice 3 and so on until at the second orifice 2 having an area less than or equal to 95% of the area of the first orifice 1. In this specific example, the four spinning orifices 1 to 4 have an elongated and curved shape, similar to the shape obtained by the displacement of a circular hole in a circular arc. Each spinning orifice corresponds to an arc of a circle. Thus for the first port 1, the arc is the curve la. The angle at the center of the arc corresponding to the third orifice 3 is greater by at least 15 °, preferably greater than or equal to 30 ° to that of the first orifice 1. The angle alpha 1 in the center of the arc of circle corresponding to the fourth orifice 4 is greater than or equal to 90 °, in this specific example of the order of 90 °. The spinning orifices thus arranged make it possible to obtain a filament having in cross section the structure represented in FIGS. 5a and 5B. Figure 5B shows taslanized filaments and Figure 5A shows filaments having fixed false twist texturing. FIG. 5A clearly shows the presence of an internal longitudinal channel 5 for each filament that can act as a thermal insulation channel, since each filament has more than three sub-filaments. Furthermore, there are also at least four longitudinal channels open on the outside can be used in particular for the transfer of moisture. It will be noted that the disposition of a given channel opening at the surface of a filament corresponding to an external channel differs from one cross section to the other over the length of the filament, whereby the longitudinal channel has a disposition which is not not parallel to the longitudinal direction of said filament, and a generally helical disposition in the longitudinal direction of said filament. By way of example, the multifilament yarns represented in FIGS. 5A and 5B have a titration of 110 dtex and comprise 68 strands per yarn. The die thus comprises in this specific example 68 groups each having 4 spinning orifices as shown in FIG. 4. Of course, the fineness of the multifilament yarn and the number of filaments are not limited and are determined conventionally according to, in particular, the parameters of the die, the flow rate of the molten polymer and the drawing speed. The structure of these filaments is thus close to that of a natural fiber, such as cotton, hence a strong ability to retain and convey moisture. In addition, the multifilament yarns being obtained from one or more synthetic polymers, they retain a low chemical attractiveness for water and therefore good evaporation properties thereof. The drawing speeds and the twist attributed during the texturing are those known from the state of the art for spinning synthetic multifilament yarns. The present invention thus offers a real industrial advantage because it makes it possible to work in the same industrial conditions as for the spinning of conventional synthetic yarns, which ensures standard productivity and profitability.

Claims (10)

A method of manufacturing a filament comprising on at least a portion of its length at least one longitudinal channel for moisture transfer and / or thermal insulation comprising a first melt spinning stage in which at least one polymer is melted and extruded through a die (7) having a group (6) of spinning orifices (1, 2, 3, 4) to form sub-filaments of said polymer and a second step in which said sub-filaments -filaments are collected, stretched, cooled and solidified to form a filament, characterized in that, the die having n orifices (1,2,3,4), with n equal to or greater than 2, during the first step, the outlet flow rate of the die (7) of each given sub-filament is different from that of the (n-1) other sub-filaments. 2. Method according to claim 1, characterized in that the difference in flow velocity between the n sub-filaments is obtained by extrusion of said molten polymer through spinning orifices (1,2,3,4) having in section cross-section of different surfaces [mm2]. 3. Method according to either of claims 1 and 2, characterized in that during the second step, at least three sub-filaments together delimit between them an internal longitudinal channel (5) to the filament. 4. A method of manufacturing a multifilament yarn according to any one of claims 1 to 3, characterized in that during the first step, at least one molten polymer is extruded through several groups (6) of orifices spinning (1, 2, 3, 4) of a filament die (7). 5. Manufacturing process according to any one of claims 1 to 4, characterized in that the second step comprises, after drawing, a texturing operation of the filament or filaments obtained, in particular by false twist or air jet . 6. extrusion die (7) for carrying out the manufacturing method according to claim 2, comprising at least one group (6) of n orifices (1, 2, 3, 4), with n equal to or greater than 2, for the manufacture of a filament, characterized in that, the n orifices being distributed around the central axis (A) of the die (7) from the first to the nth orifice, the surfaces of the cross sections of said orifices are decreasing from the first to the nth orifice. 7. Spinneret (7) according to claim 6, characterized in that the cross sectional area of the nth orifice is less than or equal to 95% of the surface of the (n-1) orifice. 8. Die (7) according to either of claims 6 and 7, characterized in that the n orifices (1, 2, 3, 4) have an elongated and curved shape, comparable to the shape obtained by the moving a circular hole in a circular arc, in that the angle at the center of the arc corresponding to the (n-1) orifice is greater than at least 15 °, preferably greater than or equal to 30 ° ° to that of the nth orifice, and in that the angle at the center of the arc corresponding to the nth orifice is greater than or equal to 90 °. 9. Filament obtained by the implementation of the die (7) according to any one of claims 6 to 8 in the method according to one of claims 2 to 5, characterized in that it is formed of a only polymer and in that it comprises longitudinal channels open on the outside which have a propeller arrangement, in particular for the transfer of moisture. Filament obtained by carrying out the process according to one of claims 3 to 5, comprising an internal longitudinal channel (5) for thermal insulation.