Coated paper

Last updated October 18, 2023

Coated paper (also known as enamel paper, gloss paper, and thin paper^[1]) is paper that 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,^[2] can be used to coat paper for high-quality printing used in the 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,^[3] or to protect against ultraviolet radiation.

Coated papers have been traditionally used for printing magazines.^[4]

Varieties

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 thermomechanical pulp (TMP) and 15–40% chemical pulp with a total pigment content of 20–30%. The paper can be soft nip calendered or supercalendered.^[5] These are often used in paperbacks.

Coated fine paper

Coated fine paper or woodfree coated paper (WFC) are primarily produced for offset printing:^[6]

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 paper grades are triple coated with 20–40 g/m²/side and have matte or glossy finish. Higher qualities often contain cotton.

Plastic coatings

Plastic-coated paper includes types of paper coatings; 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 low-density polyethylene (LDPE) (see plastic-coated paper) or mylar.^[7]

Others

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.

A release liner is a paper (or film) sheet used to prevent a sticky surface from adhering. It is coated on one or both sides with a release agent.

Heat printed papers such as receipts are coated with a chemical mixture, which often contains estrogenic and carcinogenic poisons, such as bisphenol A (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)

Paper labels are often coated with adhesive (pressure sensitive or gummed) on one side and coated with printing or graphics on the other.

Related Research Articles

Filter paper is a semi-permeable paper barrier placed perpendicular to a liquid or air flow. It is used to separate fine solid particles from liquids or gases.

Paperboard is a thick paper-based material. While there is no rigid differentiation between paper and paperboard, paperboard is generally thicker than paper and has certain superior attributes such as foldability and rigidity. According to ISO standards, paperboard is a paper with a grammage above 250 g/m², but there are exceptions. Paperboard can be single- or multi-ply.

<span class="mw-page-title-main">Kraft paper</span> Paper or paperboard produced from chemical pulp produced in the kraft process

Kraft paper or kraft is paper or paperboard (cardboard) produced from chemical pulp produced in the kraft process.

Inkjet paper is a special fine paper designed for inkjet printers, typically classified by its weight, brightness and smoothness, and sometimes by its opacity.

A Yankee dryer is a pressure vessel used in the production of machine glazed (MG) and tissue paper. On the Yankee dryer, the paper goes from approximately 42–45% dryness to just over 89% dryness. In industry, MG cylinders or Yankee dryers are primarily used to remove excess moisture from pulp that is about to be converted into paper. The Yankee cylinder can be equipped with a doctor blade and sprayed with adhesives to make the paper stick. Creping is done by the Yankee's doctor blade that is scraping the dry paper off the cylinder surface thereby crêping the paper. The crinkle (crêping) is controlled by the strength of the adhesive, geometry of the doctor blade, speed difference between the yankee and final section of the paper machine and paper pulp characteristics.

Printing and writing papers are paper grades used for newspapers, magazines, catalogs, books, notebooks, commercial printing, business forms, stationeries, copying and digital printing. About 1/3 of the total pulp and paper marked is printing and writing papers. The pulp or fibers used in printing and writing papers are extracted from wood using a chemical or mechanical process.

Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, rags, grasses, or other vegetable sources in water, draining the water through a fine mesh leaving the fibre evenly distributed on the surface, followed by pressing and drying. Although paper was originally made in single sheets by hand, almost all is now made on large machines—some making reels 10 metres wide, running at 2,000 metres per minute and up to 600,000 tonnes a year. It is a versatile material with many uses, including printing, painting, graphics, signage, design, packaging, decorating, writing, and cleaning. It may also be used as filter paper, wallpaper, book endpaper, conservation paper, laminated worktops, toilet tissue, currency, and security paper, or in a number of industrial and construction processes.

Deinking is the industrial process of removing printing ink from paperfibers of recycled paper to make deinked pulp.

Liquid packaging board is a multi-ply paperboard with high stiffness, strong wet sizing and a high barrier coating, e.g. plastic. Only virgin paper fibers are used. The barrier coating must hold the liquid and prevent migration of air and flavors through the paperboard.

A variety of tests are used to determine ink and paper and paperboard quality, and to measure their interactions. They are necessary to balance print quality, cost, and wear on the press. Some of the important paper and ink tests are listed here:

<span class="mw-page-title-main">Electrical insulation paper</span> Paper used as electrical insulation

Electrical insulation papers are paper types that are used as electrical insulation in many applications due to pure cellulose having outstanding electrical properties. Cellulose is a good insulator and is also polar, having a dielectric constant significantly greater than one. Electrical paper products are classified by their thickness, with tissue considered papers less than 1.5 mils (0.0381 mm) thickness, and board considered more than 20 mils (0.508 mm) thickness.

Lamination paper is a paper used for laminates. Normally on particle or fiberboards giving a good-looking and resistant surface for use as furniture, decoration panels and flooring.

Woodfree uncoated paper (WFU), uncoated woodfree paper (UWF) or uncoated fine papers are manufactured using wood that has been processed into a chemical pulp that removes the lignin from the wood fibers and may also contain 5–25% fillers. Both softwood and hardwood chemical pulps are used and a minor part of mechanical pulp might be added. These paper grades are calendered.

Special fine paper is a classification of paper used for copying and digital printing.

Air-laid paper is a textile-like material categorized as a nonwoven fabric made from fluff pulp.

Fine papers are printing and writing paper grades based mainly on chemical pulps. Normally the content of mechanical pulps are below 10% and the amount of fillers in the range 5–25%.

<span class="mw-page-title-main">Greaseproof paper</span>

Greaseproof paper is paper that is impermeable to oil or grease, and is normally used in cooking or food packaging. It is usually produced by refining the paper stock and thus creating a sheet with very low porosity. This is then passed between hard pressure rollers (supercalendered) to further increase the density, creating a paper called glassine. The glassine is treated with starches, alginates or carboxymethyl cellulose (CMC) in a size press to fill pores or treat the paper chemically to make it fat repellent. Basis weights are usually 30–50 g/m².

The wet strength of paper and paperboard is a measure of how well the web of fibers holding the paper together can resist a force of rupture when the paper is wet. Wet strength is routinely expressed as the ratio of wet to dry tensile force at break.

Magazine papers are paper grades generally used in printing of magazines.

The surface chemistry of paper is responsible for many important paper properties, such as gloss, waterproofing, and printability. Many components are used in the paper-making process that affect the surface.

References

↑ Mark Beach (1993). Getting it Printed . North Light Books. p. 178. ISBN 978-0-89134-510-7. Book paper is divided into uncoated paper (also called offset paper), coated paper (also called art paper, enamel paper, gloss paper and slick paper) and text 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.
↑ "How to buy paper for magazines". holmen.com. Retrieved 10 October 2023.
↑ Paulapuro, Hannu (2000). "1". Paper and Board grades. Papermaking Science and Technology. Vol. 18. Finland: Fapet Oy. p. 35. ISBN 978-952-5216-18-9.
↑ Paulapuro, Hannu (2000). "1". Paper and Board grades. Papermaking Science and Technology. Vol. 18. Finland: Fapet Oy. pp. 38–39. ISBN 978-952-5216-18-9.
↑ Khwaldia, Khaoula; Elmira Arab-Tehrany; Stephane Desobry (2010). "Biopolymer Coatings on Paper Packaging Materials". Comprehensive Reviews in Food Science and Food Safety. 9 (1): 82–91. doi: 10.1111/j.1541-4337.2009.00095.x . PMID 33467805.