Lexmark MX931 Paper and Specialty Media Guide - Page 20

Guidelines for selecting and using paper 20 Some liner materials used in pressure‑sensitive constructions are called label papers. Label papers are either machine finish (MF) or English finish (EF) papers that are calendered, supercalendered, or coated on one side. An MF has varying degrees of surface smoothness. The number of times the paper passes through the rollers (wet or dry) during manufacturing determines the surface smoothness. An EF is uncoated and low gloss in appearance. Label papers may also be used as the face sheet for pressure‑sensitive paper products, such as the materials used in dual web forms construction. Supercalendering produces high gloss surfaces that may be slick. Some supercalendered liners are difficult for printers to pick and feed reliably. We do not recommend using supercalendered liners designed for high‑speed laser printers (50 or more pages per minute). Some pressure‑sensitive constructions use kraft liners or bleached ones. Kraft liners are made from sulfate pulp and are MF or machine glazed (MG). Most MG papers have a high gloss appearance. High gloss, glazed surfaces may increase skew and are more difficult for the printer feed mechanism to handle reliably. Some kraft liners may produce acceptable results; however, we strongly recommend extensive testing of pressure‑sensitive constructions using kraft liners. Tissue‑backed or plain bond liners reduce toner contamination inside the printer and improve feed performance. Slick, non‑porous liners are harder to feed and increase toner buildup in the fuser and on the backup roll. Rough backings can increase paper path friction, which can cause skew and paper jams. The face material of the liner needs to have a melt temperature that can also withstand the fuser temperatures of nearly 225°C (437°F). A stripped area of a maximum of 3 mm (0.12 in.) can expose the face material to these temperatures and could cause melting or contamination in the fuser. Excessive paper dust or chaff associated with the liner may affect print quality. If a liner produces excessive paper dust or chaff during conversion, then the debris may be packaged with the material and end up in the printer. These properties as they feed through the printer may also affect print quality. For more information about liners, see your label supplier. Adhesives There are three basic types of label adhesives: removable, permanent, and semipermanent (cold temp). All types, with proper design, can be used with your printer. Acrylic‑based adhesives are generally preferred for cut‑sheet label printers. The major adhesive‑related printing problem is printer and cartridge contamination. The adhesives are semiliquid and may contain volatile components. If the sheet jams in the fuser, the adhesive can melt, contaminating parts of the printer or releasing fumes. To avoid exposing adhesive to the paper path guides, drive rollers, charge roller, photoconductor drum, transfer roller, and detack fingers, use full label sheets. Zone coating means placing the adhesive only where needed. Paper labels and integrated forms typically use zone coating. In addition, a non‑adhesive border of 1 mm (0.04 in.) around the outside edge of the label sheet generates good results. For more information about designing labels for your printer, see your adhesive manufacturer or label supplier. A stripped edge matrix along the outer border of the stock, combined with adhesive that does not ooze, helps prevent adhesive contamination. This design requires a stiffer backing material to prevent damage when the sheet is aligned on the reference edge. Generally, vinyl and polyester labels are well‑suited for this design. Paper and dual web designs may require testing to determine which backing produces good results. Make sure that the release strength is adequate so labels stay attached to the liner and do not peel off in the printer. Adhesives should withstand pressures up to 25 psi and fuser temperatures of 225°C (437°F) without delaminating, creating hazardous fumes, or oozing around edges of labels, perforations, or die‑cuts. Shear strength should be strong enough to prevent adhesive stringers. For more information, contact your label supplier.