MATERIALS FOR FLOCKING

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.