11.2 Types of Paper, Board and Cardboard
Supercalendered writing papers are wood-containing natural papers that are sized and supercalendered. They can also be made from recycled fibers.
Machine-finished offset papers are supplied in sheets or rolls.
Wood-containing coating base papers and boards are intended to be further proc¬essed into coated papers or boards.
18.104.22.168.3 Wood-free Natural Printing Papers
Wood-free natural printing papers consist almost exclusively of chemical pulp. The proportion of fibers from mechanical pulp should not exceed 5 %. Wood-free print¬ing papers do not yellow to any appreciable extent and have a high strength. This is the main difference between these papers and the wood-containing grades de¬scribed above. The papers are uncoated and normally leave the paper machine in a machine-finished state. For certain printing processes these papers can be ma-chine-finished or further calendered on a supercalender. This group of papers includes:
Wood-free, machine-finished natural printing papers with basis weights of ) 80gm–2 (Group 1), 81–149 g m–2 (Group 2) and * 150gm–2 (Group 3).
Wood-free, supercalendered natural printing papers with basis weights as described for machine-finished papers.
Letterpress printing papers are particularly suitable for books (specific volume is
* 1.4 fold).
Wood-free bible, thin printing papers and thin letter papers can be rag-containing or rag-free. They are highly filled to give good opacity. The basis weight is in the range below 40 g m–2.
Coating base papers for printing papers and boards are intended to be further proc¬essed into coated papers or boards.
22.214.171.124.4 Coated Printing Papers
These represent the largest group within the printing and press papers. Here the base paper is finished by the application of one or more layers of coating color to both sides of the paper web, which imparts a closed surface to the printing papers (see Chapter 7). These papers are supercalendered and supplied with a dull or glossy surface. They are described as wood-containing or wood-free, depending on the raw materials used. The wood-containing, coated printing papers represent the largest part and the LWC papers (light weight coated), in turn, make up the main part of this subgroup. Basis weight varies for LWC from 35–80 g m–2, for MWC (medium weight coated) from 70–130 g m–2 and for HWC (high weight coated) from 130–170 g m–2 (basis weight figures include base paper plus coating weights if not stated differently).
Wood-containing, two-sided coated papers. Typical coating application is 5–13 g m–2 per side. Base paper basis weight is 29–36 g m–2. Main areas of appli¬cation are magazines, catalogs, and job printing with total basis weight of 39 g m–2 (ULWC).
Wood-containing LWC paper is coated on both sides; basis weight is ) 80gm–2. It is suitable for gravure printing and roller offset printing.
High weight coated (HWC) papers differ from other coated, mechanical pulp dom¬inated paper grades in their higher coat weight. Traditionally they are produced at a basis weight of 100–135 g m–2. They compete with coated fine papers in such end use areas as high-quality magazines, catalogs, and magazine covers as well as in the area of direct advertising. HWC papers can be double or triple coated.
Wood-containing consumer papers, coated on both sides have a minimum ground¬wood content of 50 % and typical coat weight of 3–14 g m–2.
Wood-free, two-sided coated papers (WFC). The coating application is 3–14 gm–2 per side and the basis weights vary between 55 and 170 g m–2. The fields of appli¬cation are magazines, catalogs, books, direct mail, labels.
Wood-free medium weight coated paper (MWC) is coated on both sides and has a basis weight of 72–120 g m–2 and typical coat weight of 12–25 g m–2.
Art papers represent one of the highest quality printing papers and are used for illustrated books, calendars, and brochures. The basis weight varies from 100 to 230gm–2. Art papers are produced with matt or glossy finish. The coat weight varies from 20 to > 40 g m–2 per side. Art papers are almost exclusively available in sheets. They are triple coated, usually first with a precoater and thereafter with a double blade coater.
Pigmented papers, film coated offset (FCO), have a coat application of 5–10 g m–2 per side and basis weights of 45–65 g m–2. Wood-containing or wood-free coating base paper can be used for their manufacture.