CELLULOSE IST WEIT MEHR - ALS EINE CHEMIKALIE by zhangyun

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									Lenzinger Berichte, 82 (2003) 76-78


        CIRCULAR KNITS OF MODAL/ELASTANE LYOCELL/ELASTANE

                                                  Egon Duenser a
                                  a
                                      Lenzing AG, Lenzing, e.duenser@lenzing.com

Abstract

Core yarn containing an elasthane core covered                permits a broad range of new variations in the
by cellulosics (Modal, Lyocell) offer new                     production of elastic knitwear [1].
aspects in production of elastic knitted fabric.
As an alternative way to classical plating                    Keywords:
techniques the introduction of elastic core yarns             Modal, Lyocell, core yarn, elasthan, knitting

                     __________________________________________________

Classical plating techniques and new                          pretension do, however, have to be defined with
possibilities using elastic cellulosics core                  the manufacturer of the core yarn. Yarns cannot
elastane yarns                                                be exchanged by the knitter as he sees fit.

The classical plating technique has established               Since core yarns are available to - an increasing
itself in the market as a standard procedure. In              extent sheathed elastane core - an elastic jersey
fact each stitch comprises two single yarns. The              can for example be produced as an alternative
core yarn Spun Modal from Feldkirch spinning                  to the fabrics classically plated (Figure 2, 3).
/ Lenzing AG, Austria) is made with a bare                    When using core yarns only spun fibres are
elastane yarn inside. This conveys permanent                  located on the surface of the yarn. The elastane
elasticity on the fabric.                                     share is hidden on the inside. This means that
                                                              these fabrics have the natural hand of Modal
                                                              and Lyocell fibres even on the skin / inner side,
                                                              and the appearance of the outer side is left
                                                              intact.




Figure 1. Left side of a plated fabric



In this classical structure the Modal/Lyocell
yarn is located on the outer side /showing side               Figure 2. Core yarn of modal, relaxed and with
of the knitted fabric. The elastane is on the skin            pretension for knitting
side as a result of plating.
Yarn components and the desired knit fabric
elasticity can be selected and determined in
agreement with the product from the designer
or knitter. Three-dimensional elasticity can be
obtained. The yarn components and the elastane
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Lenzinger Berichte, 82 (2003) 76-78


                                                         elasticity. The selection of the yarns (fineness
                                                         of twisted thread and stretching) will be
                                                         influenced by the knit you wish to have, the
                                                         machine set-up, the density of the knitted fabric
                                                         and the mass per unit area. There is a
                                                         significant advantage in that with this core yarn
                                                         you have nature next to the skin 100 %
                                                         (Lyocell, Modal fibre fabric), the fish-skin hand
                                                         of the elastane side of the plating goods of
             Elastanseele im Coregarn
             Elastan heart of a Core yarn                former years no longer applies. It might be
                                                         possible to do without dyeing the Dorlastan,
                                                         when the core yarn manufacturer has spun a
Figure 3. Core tread considerably enlarged               super yarn with no elastane peeking out of it
                                                         (Figure 4).
Yarn counts and technical yarn data
                                                         Fabrics can obtain a super-elastic effect with
Most of the processed core yarns comprise a              core yarns even those which have a highly
core of Dorlastan with a count or fineness of 44         irregular yarn /thread consumption /row
dtex and these are covered by spinning with              whereas to date rows always had to be
Micromodal, Lyocell or /cotton of Nm 85 or               constructed with a very regular yarn
100. This results in a twisted thread fineness of        consumption in-between to make the fabric
around Nm 68 or 50.                                      elastic to some extent with an even plating
                                                         effect.
The fineness of the twisted thread depends
enormously on the stretching of the Dorlastan
yarn used as the core. This can and should in
fact be agreed between the knitter and spinner,
respectively with the yarn manufacturer. This
stretching determines the elastic power of the
finished knitted fabric and its mass per unit
area.



                                                         Picture 5 Elastic   fabrics   with   different   thread
                                                         consumption


                                                         Core yarns do not require an investment in
                                                         new machinery

                                                         These can be processed with tape feeders and /
    Small streaks where the elastan is visible           or single feeder. This ensures that the
                                                         machinery can be used in a flexible manner.
                                                         Knitted fabric effects can be achieved with core
Figure 4. Elastic pique made with core yarn              yarns which would barely be possible with
                                                         classical plating techniques.

                                                         The list includes structures, jacquards, jacquard
What yarns suit which knitted fabrics                    and embossed effects (light and heavy). In the
When a fabric is to be made of or with core              same way all drop stitch and rib effects can
yarns, the main task is to make the elastane             now be knitted with a different pattern repeat
disappear, in addition to three-dimensional              and thread consumption (Picture 5 - 7). New
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Lenzinger Berichte, 82 (2003) 76-78


kinds of embossed patterns, elastic and light,
can be knitted with these sheathed yarns in a
3D and much more economic manner.
With Modal and Lyocell core yarns knitted
fabrics become clearer, softer and they have a
smooth and silkier surface. The serviceability,
with structured patterns in particular, improves
enormously since there are no longer any bare
elastane threads on the reverse side of the fabric
as an underlap. These bare elastane yarns are
extremely prone to damage and snagging which
means that knitters frequently had to do without            Picture 7 single jersey with jacquard sculptured design
generous elastane effects such as these.                    effect



                                                            unit area one was aiming for. The adjustment
                                                            should in any case be looser than for classical
                                                            plating products. The knitted fabric becomes
                                                            solid enough after finishing.

                                                            It makes sense to use the same finish as is used
                                                            with conventional plated products. The knitted
                                                            fabric = elastane share should be prefixed prior
                                                            to dyeing.

Picture 6 jacquard single with reverse stitch effect
                                                            References
Processing and finishing                                    1. Dünser E, Melliand Textilberichte 84
                                                               (2003) 176-177.
The tension of the core yarns should be set so
that one obtains approximately the mass per




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