- May 01, 2002, David J. Bentley, Jr., RBS Technologies
Many things in everyday life can be good or bad, depending on circumstance and use. We need food to sustain ourselves, but too much leads to obesity and often to subsequent health problems. Penicillin has saved many lives, but excessive use of it has resulted in many bacteria that have changed over the years to develop a resistance to the antibiotic.
The converting industry contains examples of items that can be good or bad. Offset powder is one. Offset powder is a material used in printing operations to facilitate the subsequent drying of inks. Inks applied onto the surface of a substrate undergo drying. Before winding this printed substrate into a roll or slitting and stacking it, a printer “dusts” the inked surface with an offset powder.
Offset powder is a particle of starch that has a relatively large size. The starch can be tapioca, wheat, maize, or potato. When sprinkled over the printed surface, it prevents the front or printed side of a substrate from intimately contacting the back or unprinted side of a substrate. The starch particles act as spacers so air can enter from the sides and between the front and back of the substrate. This free flow of air across the inked surface allows inks that “dry” or cure by surface oxidation to receive exposure to oxygen in the air. The ink then cures to its final oxidized state.
From this description, offset powder obviously plays a very important role in a converting application that uses inks requiring oxidation to reach their final properties. The powder can come in a variety of types. Some have approval under specific regulations promulgated by the FDA. Certain offset powders have use with paper; others are for different substrates. Offset powders to separate materials also can have a coating to impart specific properties necessary in some applications.
Although offset powders are very beneficial, they sometimes can contribute detrimental characteristics. In applications in which a printed substrate undergoes further converting when perfect surface appearance is a requirement, use of offset powders may not be appropriate.
Consider the case of a printed substrate that will undergo lamination with an adhesive to a clear film. The application may be a label on which gloss and an optically perfect appearance are necessary. The dusting of offset powder acts like a sprinkling of dirt or other contaminant: It will produce surface imperfections in the laminate and seriously detract from the final appearance. They become entrapped in the lamination and contribute a “hills-and-valleys” appearance. This may be on a very small scale, but it is often enough to lead to an unsatisfactory appearance on close inspection.
Another application in which the use of offset powder may not be appropriate is on a printed substrate used to make labels for the in-mold label (IML) process. In this process, a label printed on a paper or plastic substrate becomes an integral part of an injection- or blow-molded container during the molding operation. IML products are used in a variety of applications, many of which involve the packaging of health and beauty care items for expensive products requiring excellent optical properties. For the popular “no-label” look, the optical characteristics must be such that the consumer cannot see the label under any circumstances. Specks of offset powder, dust, or anything similar would detract from the appearance of such a label and make it unsatisfactory.
Thus, people in the converting industry must be careful to avoid the use of offset powder on a printed surface when it could cause a problem in a subsequent operation. Using an ink that does not require an oxidation step to cure is one way to avoid offset powder — an example of a good material that sometimes can be bad.