Various Paper Grades
School writing paper is a machine-finished, highly sized paper with a basis weight of 60–80 g m–2.
Air mail paper is light-weight (25–30 g m–2) wood-free, often rag-containing pa¬per with high opacity.
Carbon copy paper is well sized, has a basis weight between 23 and 30 g m–2 and is used in the copying of letters and manuscripts.
Carbonless copy papers contain color forming reagents, which produce a contour-true copy when subjected to pressure (exerted on underlying sheets).
Correspondence envelope paper can be made from a wide range of stocks, from 100 % recycled fibers to 100 % virgin fibers. This paper is used exclusively in the production of envelopes and mailing bags.
Kraft paper is used to make envelopes and mailing bags and is made from unbleached or bleached kraft pulp.
Envelope lining tissue is an intensely colored, sometimes dip dyed, wood-free tissue paper with a basis weight of 22–30 g m–2. It is used for the lining of ex¬pensive envelopes.
Base paper for diazotype is wood-free, has a basis weight of 55 to > 200 g m–2 and is used in the making of blueprint papers.
Copying papers are used for copying and nonimpact printing. Basis weight varies between 70 and 90 g m–2 and ISO brightness between 80 and 96 %. The most important properties for a copying paper are smooth run in a copy machine and good dimensional stability. It must not show curling or cockling and retain dust when copying. It is mainly made of 90–100 % virgin chemical pulp fibers, but it may contain recycled fibers up to 100 %. The recycled fibers used are mainly from recovered newspaper, magazines and copying paper. Total filler content varies be¬tween 10 and 25 %.
Digital printing papers (synonymous with electronic printing papers) are a rapidly growing group predominantly made from chemical pulp. They are mainly un¬coated, but increasingly coated, fine paper grades. The bulk of this paper is deliv¬ered in sheets.
The major categories of nonimpact printing the papers have to suit are electrical charge based methods, magnetic methods, thermal methods and ink-jet methods. The requirements vary by printing method. In electrophotography, the runnability of the paper is critical. The electrical conductivity as well as the electrical resistivity of the paper should be sufficient. Moisture content and friction are also important properties. Other required characteristics are good dimensional stability to avoid curl and cockle for example, surface strength and surface smoothness, especially for high resolution printing. Chemical properties of the paper surface such as surface energy are important for fixing the toners to the paper. In ink-jet printing,
papers require characteristics that are matched with the inks and the ink drop size. First, ink-jet papers must be smooth. They must have sufficient and uniform po¬rosity, with small pores, in order to absorb the solvent quickly and to counteract the spreading tendency. Dimensional stability is also important to avoid cockling and curling. Typical uses for digitally printed products are manuals, price lists, and various direct mail materials, but also low-volume paperbacks and hard-cover books. Black-and-white applications cover more than 80 % of digital paper needs at present. Basis weights vary a lot, from 40 to as much as 400 g m–2
Copy base papers are wood-free. They can be finished to e. g., thermocopy, and photocopy papers with a wide basis weight range of 50 to 180 g m–2.
Base papers for offset films are predominantly wood-free papers that are used for making paper offset plates.
Carbonizing base papers are carrier papers for a wax-bearing color mass. They are used for the production of carbon and blue papers (basis weight range of the coating is 10 to 14 g m–2).
One-time carbon (OTC) base paper is used in the productio
n of one-time carbon paper (basis weight range is 16 to 24 g m–2).
Multiple carbon base papers are used in the production of multiple carbon or blue papers.
Base papers for nonimpact printing processes are predominantly wood-free and are specially suitable for nonimpact printing processes (thermosensitive, electrosensi¬tive, thermostatic papers). Basis weights range from 50 to 180 g m–2.
Blotting papers are wood-containing or wood-free, white or colored, and some¬times have veined fibers. They possess a very high absorbency and wetability. Basis weight range is from 35 to 350 g m–2.