Introduction
This report encompasses some of the most interesting
processes of forming composite elastic nonwoven webs. Elasticity is a desired
property in nonwoven webs to be used in bandages, diapers for a tight yet
comfortable fit, garment linings for a body-hugging fit, bandages that should
be stretchable to cover the wound well and several other applications where it
may be needed 1). There are multiple processes of making an elastic
nonwoven composite. Hence, this report looks into the different processes from
the product perspective. The general principle of forming an elastic nonwoven
composite is to make two different webs, of which one of the webs is elastic
and bonding them together keeping the elastic web stretched while bonding takes
place.
How the two webs are bonded makes the processes different
from one another. The following section discusses the different processes of
forming such webs using different bonding techniques.
The Processes:
1. By Chemical Bonding 2)
In this process, the product is manufactured by passing a
longitudinally oriented nonwoven material over a roller so as to apply an
adhesive to one surface of the nonwoven material. At the same time, a
polyurethane web is heated and longitudinally stretched and adhered to the nonwoven
material. Thereafter, a second nonwoven material is adhered to the other
surface of the polyurethane web to form a laminate consisting of a stretched
inner polyurethane core and outer un-stretched nonwoven fabric layers adhered
to the core by the adhesive. Next, the laminate is passed through a moistening
device which results in a relaxing of the engagement between the nonwoven
fabric outer layers and the adhesive connecting the outer layers to the
stretched polyurethane core layer. This allows the stretched polyurethane layer
to return to substantially its original length which results in the outer
nonwoven layers being buckled or undulated to form wrinkles.
Another patent 3) discusses a composite nonwoven
elastic web which is composed of a nonwoven elastic web that is joined to a
fibrous nonwoven gathered web. This process produces a composite nonwoven
elastic web which, in its relaxed, non-stretched state, is composed of a
gathered nonwoven fibrous web that is joined to a nonwoven elastic web with the
nonwoven elastic web having been relaxed from a stretched length to a relaxed,
non-stretched length so as to gather the fibrous nonwoven gathered web. An
important feature of the process is that the fibrous nonwoven gatherable web is
formed directly onto a surface of the nonwoven elastic web while the nonwoven
elastic web is maintained in a stretched and elongated condition. The nonwoven
elastic web may be formed by a melt-blowing process or any other process for
forming a nonwoven elastic web. For example, the nonwoven elastic web could be
an apertured web of an elastic film as opposed to a melt-blown fibrous nonwoven
elastic web. The formed nonwoven elastic web has a normal relaxed, non-stretched,
nonbiased length. Thereafter, the nonwoven elastic web is elongated by being
stretched to a stretched, biased length.
2. By Needle Punching 4)
In this method, a nonwoven textile layer and a layer of
generally elastic material having inherent resilience are positioned to form
superposed layers. The superposed layers are then needle punched to make a
composite of the two layers. The spacing of the needles and plurality of needle
punching locations are predetermined. The superposed needle punched composite
is then drafted in the machine direction by means of nip rolls within the
elastic limits of the generally elastic layer thereby permanently stretching
the nonwoven textile layer. The composite is then allowed to relax. This
permits the generally elastic layer to recover its original dimensions
substantially in response to its inherent resilience whereas the bulk of the
nonwoven textile fabric increases between the points of needle punching. The
draft ratio is selected keeping in mind the desired amount of bulking in the final
composite. The draft ratio applied to the laminate is limited by two factors:
the elastic limit of the generally elastic layer as well as the capability of
the nonwoven textile layer to be drafted while maintaining its structural
integrity. The draft ratios can vary between 1:1 to 4:1 while the most typical
ones lie between 1.5:1 to 2:1.
