Elastic core yarns based on linen, or hemp, or other materials, and elasticized fabrics therefrom

Abstract

A method is provided for manufacturing an elastic core yarn in which a core comprises an elastic fiber and a continuous yarn arranged along the elastic fiber, and in which a covering yarn of such a natural material as flax, hemp, ramié, bamboo, jute, is helically wrapped about the core. A step of helically wrapping the core with the covering yarn is carried out in such a way that a number T of coils covering yarn is formed about a length unit of the elastic fiber larger than a predetermined minimum value depending on the linear mass density Nm of covering yarn, and that the covering yarn becomes twisted with a final twist direction “S” or “Z” that is opposite to an initial twist direction “Z” or “S”, respectively. The step of wrapping is performed in a wrapping space enclosed within a container.

Claims

1. A method for making an elastic core yarn comprising the steps of: providing a core comprising: an elastic fibre; and a continuous yarn arranged along said elastic fibre; providing a covering yarn made of a natural fibre, said covering yarn having a linear mass density Nm, said covering yarn twisted with an initial twist direction selected between “Z” and “S” and with an initial number of twists per meter; conveying said core towards a collecting bobbin, causing said core to pass through a wrapping space; conveying said covering yarn in said wrapping space; said steps of conveying said core and said covering yarn taking place at respective conveying speeds, helically wrapping said core with said covering yarn in said wrapping space, obtaining said elastic core yarn consisting of said core wrapped by a helix of said covering yarn; and collecting said elastic core yarn on said collecting bobbin, wherein said step of helically wrapping provides: causing said number of twists per meter of said covering yarn to decrease from said initial number of twists per meter to an untwisted condition and afterwards to increase in a direction opposite to the initial twist direction, such that said covering yarn becomes twisted with a final twist direction “S” or “Z” opposite to said initial twist direction “Z” or “S”; and selecting said conveying speeds in order to cause a coil number T of coils, of said helix of said covering yarn wound about one length unit of said elastic core yarn, to be larger than a predetermined minimum value T.sub.0 which depends upon said linear mass density Nm, and wherein said wrapping space is a space enclosed in a container.

2. The method according to claim 1, wherein said covering yarn is selected from the group consisting of: a linen yarn; a hemp yarn; a ramié yarn; a bamboo yarn; a jute yarn; and a combination thereof.

3. The method according to claim 2, wherein said predetermined minimum value T.sub.0, for any value of said linear mass density Nm indicated in a respective line of the following table: TABLE-US-00004 N.sub.m T.sub.0 2 0 3, 5 50 7 150 10 200 15 250 20 350 24 400 26 450 30 470 35 490 40 520 45 540 50 600 60 650 70 700 is the value T.sub.0 written in said respective line of said table, and for values of said linear mass density Nm intermediate between two values indicated in respective contiguous lines of said table, said minimum value T.sub.0 is obtained by linearly interpolating the values T.sub.0 written in said respective contiguous lines of said table.

4. The method according to claim 2, wherein said coil number T per length unit of said elastic core yarn is lower than a maximum value T.sub.1, wherein said maximum value T.sub.1, for any value of said linear mass density Nm indicated in a respective line of the following table: TABLE-US-00005 N.sub.m T.sub.1 2 500 3, 5 750 7 900 10 1000 15 1130 20 1200 24 1250 26 1300 30 1350 35 1450 40 1500 45 1550 50 1620 60 1720 70 1850 is equal to value T.sub.1 written in said respective line of said table, and for values of said linear mass density Nm intermediate between values indicated in respective contiguous lines of said table, said maximum value T.sub.1 is obtained by linearly interpolating the values T.sub.1 written in said respective contiguous lines of said table.

5. The method according to claim 2, wherein said coil number T per length unit, for any value of said linear mass density Nm, is provided by the equations:
T.sub.1=K.sub.1N.sub.m.sup.0.42, if N.sub.m<20 km/kg; and
T.sub.1=K.sub.2N.sub.m.sup.0.42, if N.sub.m≥20 km/kg, where K.sub.1 is a number set between 82 and 348 and K.sub.2 is a number set between 118 and 308.

6. The method according to claim 5, wherein K.sub.1 is set between 120 and 240.

7. The method according to claim 5, wherein K.sub.2 is set between 140 and 220.

8. The method according to claim 1, wherein said steps of conveying said core and said covering yarn comprise: steps of causing said core and said covering yarn to travel through a longitudinal through cavity and along a lateral surface, respectively, of a rotating hollow cylindrical body turning at a predetermined rotation speed, said longitudinal through cavity having an inlet end and an outlet end opposite to each other for said core; and a step of causing said core and said covering yarn to pass through an orifice facing said outlet end of said longitudinal through cavity of said rotating hollow cylindrical body at a predetermined distance therefrom, and wherein said wrapping space is located between said outlet and said orifice, so that said container has an opening at said orifice and said core and said covering yarn pass through said orifice as said elastic core yarn.

9. The method according to claim 1, wherein said elastic fibre is selected from the group consisting of: a natural rubber fibre having a linear mass density set between 22 dtex and 1300 dtex; and a fibre of an elastomeric material having a linear mass density set between 22 dtex and 940 dtex.

10. The method according to claim 1, wherein said elastic fibre is a fibre of an elastomeric material having a linear mass density selected among 22, 44, 78, 100, 156, 310, 470, 620, 940 dtex.

11. The method according to claim 9, wherein said elastomeric material is selected from the group consisting of a polyurethane and a polyether-polyurea copolymer.

12. The method according to claim 1, wherein said continuous yarn is made of a material selected from the group consisting of: a polyamide; a polyester; a ultra-high molecular weight polyethylene; a combination thereof, wherein said continuous yarn is selected from the group comprised of: a continuous one-filament yarn and a continuous multi-filament yarn, said filaments textured or smooth.

13. The method according to claim 12, wherein said polyester is selected among: polyethylene terephthalate; polybutylene terephthalate; polytrimethylene terephthalate; and a combination thereof.

14. The method according to claim 12, wherein said continuous yarn comprises a combination of polyethylene terephthalate and polytrimethylene terephthalate and has a linear mass density set between 22 dtex and 660 dtex.

15. The method according to claim 14, wherein said linear mass density is selected among 22, 44, 83, 167, 330, 660 dtex.

16. The method according to claim 1, wherein said continuous yarn has an arrangement along said elastic fibre selected from the group consisting of: a parallel arrangement, wherein said continuous yarn is arranged parallel to said elastic fibre; an interconnected arrangement, wherein said continuous yarn has connection points to said elastic fibre, said connection points at predetermined distances from one another; a wrapped arrangement, wherein said continuous yarn forms a covering about said elastic fibre.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be now shown with the following description of exemplary embodiments and examples thereof, exemplifying but not limitative, with reference to the attached drawings, in which:

(2) FIG. 1 diagrammatically shows a step of helically wrapping the covering yarn about the core, in order to obtain an elastic core yarn;

(3) FIG. 2 diagrammatically shows an elastic core yarn production equipment configured to carry out the method according to the invention;

(4) FIG. 3 is a diagram showing the minimum, maximum and reference numbers of coils per length unit of the elastic core yarn, and how these numbers change depending on the linear mass density of the covering yarn.

DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENTS

(5) With reference to FIG. 1, a method is described for making an elastic core yarn 50, in which an elastic core 30 is coated by a covering yarn 40 consisting of a natural fibre. Elastic core 30 includes an elastic fibre 10 and a continuous yarn 20 arranged along elastic fibre 10, while covering yarn 40 is made of a natural fibre and is twisted with an initial twist direction 43 that may be “Z” or “S”, but is typically “Z”, i.e., as normally available on the market, as depicted in FIG. 1.

(6) In order to obtain elastic core yarn 50, a step is performed of covering, i.e., helically wrapping covering yarn 40 about core 30. To this purpose, steps are carried out of conveying core 30 and covering yarn 40, at respective speeds v.sub.A, v.sub.C. Core 30 is conveyed towards a collecting bobbin 51 through a wrapping space 35, and covering yarn 40 is conveyed in wrapping space 35, where it reaches core 30 laterally, i.e., tangentially, according to a predetermined angle α between the direction of core 30 and the direction of covering yarn 40, in order to form a substantially helical covering about core 30.

(7) As shown in FIG. 2, the steps of conveying core 30 and covering yarn 40 are controlled by the speed at which elastic core yarn 50 is collected on collecting bobbin 51, while elastic fibre 10, continuous yarn 20 and covering yarn 40 are withdrawn from respective spools, not shown and 41, respectively.

(8) In an exemplary embodiment, before reaching wrapping space 35, core 30 passes through a central recess i.e., longitudinal through cavity 63 of a first cylindrical body 61 turning at a predetermined high speed about its own axis 63′, said longitudinal through cavity 63 having an inlet end 68 and an outlet end 69 opposite to each other. In other words, core 30 follows a substantially linear path. On the contrary, covering yarn 40 is conveyed along an outer surface 62 of first cylindrical body 61, preferably along a guide arranged thereon. Preferably, first cylindrical body 61 is integrally and coaxially housed in a second hollow cylindrical body 64, cylindrical bodies 61,64 forming a conveying unit 60. Bobbin 41 of covering yarn 40 is fixed inside second cylindrical body 64, therefore covering yarn 40 is conveyed through a gap 65 between bobbin 41 and the outer surface of first cylindrical body 61.

(9) In this exemplary embodiment, wrapping space 35 is defined between the outlet end 69 of first cylindrical body 61, at which core 30 enters into wrapping space 35, and an orifice 66, preferably arranged on axis 63′, through which elastic core yarn 50 leaves wrapping space 35 and is drawn to collecting bobbin 51. Container or wall 67 enclosing wrapping space 35 is preferably axisymmetric and converges from the inner surface of second hollow cylindrical body 64 to orifice 66.

(10) The direction of the rotation of conveying unit 60 is selected so that the sense of the helix is opposite to the initial twist direction 43 of covering yarn 40 and therefore covering yarn 40 becomes twisted with a final twist direction 44, e.g. “S”, opposite to the initial twist direction 43, e.g. “Z”, in the step of helically wrapping core 30. During the wrapping step, the absolute number of twists per metre of covering yarn 40 initially decreases down to an untwisted configuration 45, and then increases again in the opposite direction.

(11) Conveying speeds of core 30 and covering yarn 40, as well as the rotation speed of conveying unit 60 are selected so that a number of coils T of covering wrapper 40 is wound on each length unit of elastic core yarn 50 as manufactured, the number T being larger than a predetermined minimum value T.sub.0 that depends on the linear mass density Nm of covering yarn 40.

(12) Wrapping space 35 is enclosed in a container 67, in order to avoid friction between free air, on the one hand, and the conveyed materials, and elastic core yarn 50 being formed, on the other hand. As discussed above, covering yarn 40 would lose its consistence, and could even break, while turning from initial twist direction 43 to opposite final twist direction 44.

(13) In particular, the material of covering yarn 40 is a stiff material, for example one among linen, hemp, ramié, bamboo, jute, or a combination thereof.

(14) FIG. 3 is a diagram showing the predetermined minimum value T.sub.0 of the coils that must be wrapped per length unit of elastic core yarn 50, for any value of linear mass density Nm of covering yarn 40, as a curve 81. Curve 81 is obtained by interpolating the values of table 1, described above.

(15) The diagram of FIG. 3 also shows a curve 82 indicating, for any value of linear mass density Nm of covering yarn 40, a maximum coil number T.sub.1 that should not be exceeded in order to obtain good elastic properties of elastic core yarn 50, as experience has shown. Curve 82 is obtained by interpolating the values of table 2, described above.

(16) Advantageously, the coil number T per length unit of elastic core yarn 50, for any value of the linear mass density Nm of covering yarn 40, is provided by the equations:
T.sub.1=K.sub.1N.sub.m.sup.0.42, if N.sub.m<20 km/kg;
T.sub.1=K.sub.2N.sub.m.sup.0.42, if N.sub.m≥20 km/kg,
where K.sub.1 and K.sub.2 can range between a minimum value, respectively 82 and 118, and a maximum value, respectively 308 and 348. Curves 83 and 84 corresponds to the couples of values (K.sub.1,K.sub.2)=(82,118) and (K.sub.1,K.sub.2)=(308,348), respectively. Preferably, K.sub.1 is set between 120 and 240, and K.sub.2 is set between 140 and 220.

(17) The diagram of FIG. 3 also shows a band 85 corresponding to preferred values of number of coils T per length unit of elastic core yarn 50. For any value of the linear mass density Nm, these preferred values are set between ±10% a central reference value T.sub.2 that is obtained by interpolating the values of table 3, corresponding to curve 86.

(18) In some exemplary embodiments, elastic fibre 10 of core 30 is a natural rubber fibre having linear mass density Nm set between 22 dtex and 1300 dtex.

(19) In other exemplary embodiments, elastic fibre 10 of core 30 is a fibre made of a synthetic elastomeric material having linear mass density Nm set between 22 dtex and 940 dtex. In particular, linear mass density Nm can be selected among 22, 44, 78, 100, 156, 310, 470, 620 and 940 dtex. The elastomeric synthetic material is preferably a polyurethane or a polyether-polyurea copolymer.

(20) Continuous yarn 20 can be a polyamide yarn, or a polyester such as polyethylene terephthalate, polybutylene terephthalate, and polytrimethylene terephthalate. In this case, continuous yarn 20 can be made of a single polyester or of a combination of these polyesters, in particular a combination of polyethylene terephthalate and polytrimethylene terephthalate commercially known as “T400”.

(21) Such a combination of polyethylene terephthalate and polytrimethylene terephthalate used to make continuous yarn 20 has preferably a linear mass density Nm set between 22 dtex and 660 dtex, in particular, linear mass density Nm is selected among 22, 44, 83, 167, 330, 660 dtex

(22) As an alternative, continuous yarn 20 can be an ultra-high molecular weight polyethylene yarn. Finally, continuous yarn 20 can comprise any combination of the above-mentioned materials. Each of these yarns can be smooth or texturized.

(23) Moreover, even if the FIG. 1 shows a substantially parallel arrangement of continuous yarn 20 and elastic fibre 10, this is not a limitation. On the contrary, a wrapped arrangement is also possible, in which continuous yarn 20 forms a covering about elastic fibre 10, and/or a interconnected arrangement, in which elastic fibre 10 and continuous yarn 20 are mutually connected in connection points at predetermined distances from one another.

(24) It falls within the scope of the invention also an elastic core yarn 50 obtained through the method described above, as well as an elasticized fabric, not shown, made at least in part at least of elastic core yarn 50 obtained through the method described above. More in detail, elastic core yarn 50 can be used for either warp or weft yarn.

(25) The foregoing description of embodiments and of examples of the invention, and of the way of using the apparatus, will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt for various applications such embodiment without further research and without parting from the invention, and, then it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiment. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and, therefore, not of limitation.