Glossary

Terminology used on this site

Clupak process: A process to make microcrepe paper. Microcreping takes place in the drying stage, when the paper is still wet. The paper passes between a heated roller and a soft, deformable rubber roller or rubber belt and forms tiny creases, and when the paper is dried the creases are ironed into the paper.

Clupak paper: 60-100 g/m2 highly extensible kraft paper used for paper sacks. Longitudinal extensibility is 7-12% and transverse extensibility 4-7%. This greatly increases the dynamic strength, as measured by tensile energy absorption (TEA). Particularly applicable to mechanically-filled sacks with valves, such as sacks for cement, sugar and flour. This valuable property is attained by microcreping of the paper during the drying phase, when dry content is 60-65%. It is also a brand name used by the patentee of a rubber-belt clupak machine.

Semiclupak paper: Clupak paper with lower extensibility.

High-extensible kraft paper: Slightly micro-creped kraft paper with higher extensibility and thus better filling properties.

Kraft (packaging) paper: A type of packaging paper. It is made of bleached or unbleached sulphate cellulose in one or more plies, featuring high strength, toughness and flexibility, with machine finished (MF) or machine glazed (MG) surface, and crisp to touch. Its longitudinal extensibility is less than 2%, in contrast to clupak paper. Used primarily for multi-ply, heavy-duty paper bags and sacks, and the base material for many types of packaging. May be impregnated with wax, ceresin, oil, etc, coated with bitumen, glued to make adhesive strips, creped, etc. Gram weight typically 40-200 g/m2, or 20-60 g/m2 for MG types.

Direct printing: In digital printing, the product is prepared and the printer is directly controlled by a computer publishing editor, thus omitting the usual pre-printing stages. Since there is no need for film, development, mounting or printing plates, it is a faster and cheaper process for low volume production.

Flexographic printing: Relief printing process. The surface of the plate is raised out of the plane. Used widely in the printing and packaging industries. The plate is flexible and in some cases heat-resistant, made of rubber of photopolymer. Very commonly used for newspapers and flexible-wall packaging.