Calendaring and Pressing:
These methods are
used to improve the surface characteristics of the fabrics, the most important
features being smoothing and patterning. The processes used are continuous and
usually involve one or several pairs of rollers operating under pressure.
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| Calendaring and Pressing |
i. Moire or
goffering calender: The calenders are common in nonwoven finishing and are used in the
compacting of the webs made of natural and synthetic fibers. This type of
calendering can be considered to be both a bonding and finishing process.
Webs composed of longitudinally
oriented cotton or viscose fibers with a GSM of about 10-30
g/m2 can be
stiffened and compacted sufficiently by passing them through a goffering
calender when slightly damp.
Hot embossing of
synthetic fiber webs, even when the fibers are longitudinally oriented,
produces a product remarkably strong due to the fibers melting at the embossed
areas.
The embossing
effect is used to obtain special effects such as leather graining, simulated
weave, plaster, brush strokes, cord and mock tiling. Another area in which
heated calenders are used is in the manufacture of laminates.
Here thermoplastic
fibers, layers of thread or film are placed between two layers of non-plastic
web and are fused together by heat and pressure. Such laminates are used as
tablecloths, seat and cushion covers. Calenders are also used in the transfer
printing of the bonded webs.
ii. Roller
presses: The oldest form of improving the surface of nonwoven bonded fabrics is
the pressing of wool felts, especially felts for collar linings. This gives a
smoother surface finish and also improves strength and luster.
Miscellaneous
Dry Finishing:
Perforating:
The Artos method is a method of perforating in which the web, which has
been bonded by using chemicals, is perforated with hot needles. This process
not only punches holes but also reinforces as a result of crosslinking and
condensation of the bonding agent.
Slitting: Slitting,
originally developed to improve the softness and drape of films was used by the
Breveteam company for interlinings, in particular for adhesive fixable
interlinings.
The slitting is
accomplished by a roller with small blades mounted on it.
Splitting: When
nonwovens are substituted for leather, the thick layer of needled fabric is
split similar to the splitting of leather to make thinner fabrics. The fabrics
used are thick, high strength, firmly bonded, closely needled and usually
shrunk. Splitting is done by machines in which a continuous rotation hoop knife
is guided with great precision in the gap between two conveyor rollers, the
distance between them depending on the thickness and type of fabric required.
Grinding
and Velouring: Splitting is followed by either ironing and friction calendering or
moire calendering and possibly also grinding and polishing to make the surface
even, giving the fabric the appearance of velour or suede. The process is known
as velouring.
Singeing: It belongs
to the category of a dry finishing process. It is essentially the burning off
of protruding fibers from nonwoven fabrics, particularly needled fabrics. The
process is exactly the same as traditional singeing and is carried out on
gassing frames where the fabric is passed over an open gas flame. The surface
is made smoother, which simplifies the dusting of filter fabrics.
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