FLOCK
FIBERS
Flock
can be made from natural or synthetic materials such as cotton, rayon, nylon
and polyester. There are two types of flock - milled and cut.
Milled
flock is produced from cotton or synthetic textile waste material. Because of
the manufacturing process, milled flock is not uniform in length, and can vary
from fine (0~ - 0.5 mm) to coarse (0.4 - 1.1 mm). Milled cotton flock has the
advantage of being the lowest in cost and the softest, but has the least
abrasion and wear resistance.
Cut
flock is produced only from monofilament synthetic materials. The cutting
process produces a very uniform length of flock. Lengths can be obtained from
0.3 - 5.0 mm and 1.7-22 dtex in diameter. (One dtex is the measurement of a fiber
that weigh; one gram per 10,000 meters of length.) Rayon is a little bit better
on wear resistance and nylon is the best. For cut flock, rayon is the least
expensive with the least wear resistance. Cut nylon is the best grade of flock
and produces a good feel, but is also the most expensive. Cut polyester is
basically used for industrial applications such as automobile window seals,
glove compartments, and roofing.
Other
flock manufacturing steps:
After
cutting, the flock is cleaned of oils that have accumulated during processing.
It is vat dyed to any number of colors, and then chemically treated to enable
the fibers to accept an electrical charge. Since the fibers are all dielectric,
a certain amount of conductivity must be present for electrostatic flocking
process to occur. When the process is complete the fibers are spin dried and
then oven dried to a specific moisture content. The flocking fibers are never
totally dried, because moisture content adds to their conductivity. Finally,
the flock is packaged in moisture proof bags that maintain proper humidity.
The
fineness of the flock, length of fibers and adhesive coating density determine
the softness of the flocking. However, the fine or short flock is difficult to
work with, because it has a tendency to ball-up during processing.
ADHESIVES
Flock adhesives are available in wide varieties, both single part and two-part
catalysed systems. Adhesives are generally water or solvent based. Some are air
drying, others temperature or catalyst curing. Adhesives are usually applied by
brush, roller, spray or screen printing.
SCREEN
PRINT OF ADHESIVES
Many of the adhesives
have the consistency of plastisol ink. Care should be exercised to select a
stencil emulsion or film that is compatible with the adhesive to be printed.
Proper application of the adhesive is the most important part of the process. A
very heavy deposit of adhesive is required, but at the same time the adhesive
should not be 'squeegeed' through the substrate. Care should also be exercised
not to apply a thin coating. Less adhesive does not give proper adhesion
characteristics for the fibers, which will result in low wear resistance. In
order to achieve the proper deposit of adhesive, the screen should be made from
a 24 - 43 threads/cm (60 - 110 threads/inch) monofilament mesh. Tension should
be at 20 N/cm. Extra face coats of emulsion on the print side of the screen may
be required for mesh counts greater than 36 threads / cm (96 threads/in).
Printing should be off-contact, using a 65 durometer ball-nose squeegee. If
difficulty in getting the proper coverage is experienced then, do not thin the
adhesive to make it more printable. This will only create a thinner deposit by
allowing the adhesive to soak into the substrate. A better solution is to slow
the squeegee stroke down to allow the adhesive time to flow through the screen
and on to the substrate. The flock adhesion can be tested by subjecting the
substrate to the standard textile wash test. If the flocking fibers come loose
or fall off, the adhesive may be too thin or the adhesive is improperly cured.
If the adhesive is properly applied, then the curing temperatures should be
adjusted until the substrate passes the wash test. This is the only safe way to
ensure proper curing of the adhesive.
