Paper, as that term is used herein, refers to the wide variety of cellulose-based sheet materials used for writing, printing, packaging, and other applications. Paper may be used, for example, but without limitation, in the following applications: as paper money, bank notes, stock and bond certificates, checks, and the like; in books, magazines, newspapers, and art; for packaging, e.g., paper board, corrugated cardboard, paper bags, envelopes, wrapping tissue, boxes; in household products such as toilet paper, tissues, paper towels and paper napkins; paper honeycomb, used as a core material in composite materials; building materials; construction paper; disposable clothing; and in various industrial uses including emery paper, sandpaper, blotting paper, litmus paper, universal indicator paper, paper chromatography, battery separators, and capacitor dielectrics.
Paper is generally produced by pulping a cellulosic material to form a pulp containing cellulosic fibers, amalgamating the cellulosic fibers to form a wet web, and drying the wet web. In the finished paper, the fibers are held together by mechanical interlocking and hydrogen bonding. Pulping may be accomplished in a number of ways, for example: using a chemical process (e.g., the Kraft process), a mechanical process (groundwood), or thermomechanical process (TMP). The amalgamating and drying steps are generally performed using a high speed paper machine.
The most common source of cellulosic fibers is wood pulp from trees. Pulp is also derived from recovered (“recycled”) paper. Vegetable fiber materials, such as cotton, hemp, linen, and rice, are also used. Other non-wood fiber sources include, but are not limited to, sugarcane, bagasse, straw, bamboo, kenaf, jute, flax, and cotton. A wide variety of synthetic fibers, such as polypropylene and polyethylene, as well as other ingredients such as inorganic fillers, may be incorporated into paper as a means for imparting desirable physical properties.
For many applications, it is desirable that paper have high strength and tear resistance, even in very thin sheets, for example, when the paper is used in packaging, in industrial applications, as money, and in other applications that require strength and durability. It is also generally desirable that paper exhibit good printability characteristics, with the particular characteristics depending to some extent on the printing process in which the paper will be used.