Лако-красочные материалы — производство

Peel-and-stick labels provide a quick and easy way to apply labels to almost any surface. Die cut and supplied on release papers, they can be printed in computers for addresses, while preprinted labels for an enormous range of applications, particularly difficult sub­strates such as polyolefins or cold, moist containers make labeling a pleasure compared with traditional wet-applied systems such as dextrines or caseins. Pressure-sensitive label stock provides reliable bonding, is easy to use and virtually instantaneous, and offers a choice of properties, including permanence or easy removal, high-temperature resistance, or low-temperature flexibility. Large or small labels can be easily stored and handled, and applied by hand, hand-held applicators, or semiautomatic or fully automatic industrial labelers.

Labels are generally regarded as falling into three classes: permanent label stock, removable labels, and labels for use at low temperatures. In addition, specialty applica­tions include delayed-action labels, high-temperature applications, and decals. Permanent label stock is the mainstay of the label market. Label stock is invariably paper, and the labels, which are usually preprinted, are supplied on a release paper backing, leading to their popular name, “peel-and-stick” labels. Adhesives for permanent stock have high shear strength, and attempts to remove them will usually damage the label. Applications range from price stickers and address labels to inventory labels, shipping labels, warning signs, and labels for bottles, buckets, or drums.

By contrast, peelable or removable labels use adhesives with relatively low tack and shear strengths. On removal, no residue must remain on the surface from which the label was removed. Some removable labels use a water-soluble adhesive, permitting easy clean­ing of the surface. These labels are used for temporary labeling or where they will fre­quently be replaced. Freezer labels use adhesives that have very good low-temperature flexibility to allow labels to be applied and remain adhered at temperatures down to —20°C or lower. They are characterized by very low glass temperatures, typically in the range —60 to —80°C.

Label adhesives are seldom solvent based. The majority are prepared using water-based adhesives, although hot melts are taking an increasing segment of this market. Important adhesive characteristics include the ability to be dye cut cleanly, low tendency to make the paper curl, coupled with ability to conform to the surface to which they are applied, very quick grab and good resistance to yellowing, and loss of tack with age. Acrylic dispersions, either with or without additional tackifiers, are the most widely used adhesives.

Production of label stock makes severe demands on the release paper. Since transfer coating is a common application method, the adhesive must wet the release paper adequately and yet transfer cleanly to the label when label and backing are united. The release paper must remove quickly and easily in use, but must remain firmly adhered during storage. Use of silicone releases is virtually universal, invariably requiring the use of wetting agents in the formulation to ensure that the adhesive wets the surface. There must be no transfer of the release coating to the adhesive surface, however, as this will destroy the tack of the adhesive.