DRY FINISHING OF NONWOVEN

                             DRY FINISHING OF NONWOVEN BONDED FABRIC

Shrinkage Finish:

The compaction that accompanies shrinkage is useful in obtaining greater basis weight or GSM (grams per square meter) and density, more bulk, higher strength and improved cleavage properties.

Shrinkage occurs when the fibersare wet or dry depending on the type. Shrinkage by exposure to heat is suitable for a nonwoven fabric made predominantly of synthetic fibers and is especially effective if fibers are prone to shrinkage.

The web is fed through the heating zone on screen driers. They are usually perforated cylinder driers with a rotating over feed, whereby the web is fed faster onto the roll than it is drawn off.

A second shrinkage is carried out if the web contains significant amounts of natural fibers. The web is immersed in a tank of hot water to promote shrinkage and is dried without tension. Some special synthetic fibers shrink both when they are wet and when heated.

A variation of wet shrinkage, which aids in saving energy, is shrinkage in steam.

Needling together two types of webs where one shrinks and the other is shrink-proof results in the formation of decorative raised patterns when shrunk. This technique is used in the production of sculptured wall and floor coverings.

Wrenching Finish:

The Clupak process, invented by Sanford Cluett, is similar to the sanforising process, is used for wet-laid nonwoven bonded fabrics.

The machinery (fig. 1) consists of a continuous rubber belt, about 25 mm thick, with an intermediate woven layer lying on a heated, chromium-plated and polished drying cylinder. The web is pressed against the cylinder at the first point of contact by a non-rotating clamping bar. The rubber cloth is compacted lengthwise, which affects the web between it and the cylinder in the same way thus causing compacting and crimping of the fibers in the web longitudinally.

The web is fed moist, through the gap between the belt and the cylinder. The compacting is fixed by drying.

The outcome of the Clupak method depends on a number of factors. Hydrophilic fibers are more suitable than hydrophobic ones. Polyolefin fibers are not suitable due to their lower moisture absorption and sensitivity to heat.

Webs in which the fibers are oriented lengthwise give a more pronounced effect than cross-laid or random-laid webs.

The degree of wrenching is increased if the moisture content is high - about 20% - but if the bonding agent is more than 50% such increases are unattainable. Thermoplastic bonding agents assist wrenching but the web tends to adhere to the cylinder. Elastomer bonding agents due to their elastic nature almost cancel the wrenching effect.