Coated paper is paper which has been coated by a mixture of materials or a polymer to impart certain qualities to the paper, including weight, surface gloss, smoothness or reduced ink absorbency. Various materials, including Kaolinite, calcium carbonate, Bentonite, and talc can be used to coat paper for high quality printing used in packaging industry and in magazines. The chalk or china clay is bound to the paper with synthetic viscosifiers, such as styrene-butadiene latexes and natural organic binders such as starch. The coating formulation may also contain chemical additives as dispersants, resins, or polyethylene to give water resistance and wet strength to the paper, or to protect against ultraviolet radiation.
Machine-finished coated paper
Machine-finished coated paper (MFC) has a basis weight of 48–80 g/m2. They have good surface properties, high print gloss and adequate sheet stiffness. MFC papers are made of 60–85% groundwood or TMP and 15–40% chemical pulp with a total pigment content of 20–30%. The paper can be soft nip calendered or supercalendered. These are often used in paperbacks.
Coated fine paper
Coated fine paper or woodfree coated paper (WFC) are primarily produced for offset printing:
- Standard coated fine papers
- This paper quality is normally used for advertising materials, books, annual reports and high quality catalogs. Grammage ranges from 90–170 g/m2 and ISO brightness between 80–96%. The fibre furnish consists of more than 90% chemical pulp. Total pigment content are in the range 30–45%, where calcium carbonate and clay are the most common.
- Low coat weight papers
- These paper grades have lower coat weights than the standard WFC (3–14 g/m2/side) and the grammage and pigment content are also generally lower, 55–135 g/m2 and 20–35% respectively.
- Art papers
- Art papers are one of the highest quality printing papers and are used for illustrated books, calendars and brochures. The grammage varies from 100 to 230 g/m2. These papergrades are triple coated with 20–40 g/m2/side and have matte or glossy finish. Higher qualities often contain cotton.
Other types of paper coatings include polyethylene or polyolefin extrusion coating, silicone, and wax coating to make paper cups and photographic paper. Biopolymer coatings are available as more sustainable alternatives to common petrochemical coatings like LDPE (see plastic-coated paper) or mylar.
Printed papers commonly have a top coat of a protective polymer to seal the print, provide scuff resistance, and sometimes gloss. Some coatings are processed by UV curing for stability.
Heat printed papers such as receipts are coated with a chemical mixture, which often contains estrogenic and carcinogenic poisons, such as BPA. It is possible to check whether a piece of paper is thermographically coated, as it will turn black from friction or heat. (see thermal paper)
- "Grades of Paper". paperonweb.com.
- Diana Twede and Susan E. M. Selke (2005). Cartons, crates and corrugated board: handbook of paper and wood packaging technology. DEStech Publications. p. 325. ISBN 978-1-932078-42-8.
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