Coated paper (also known asenamel paper,gloss paper, andthin paper[1]) is paper that has been coated by a mixture of materials or apolymer to impart certain qualities to the paper, including weight, surface gloss, smoothness, or reduced ink absorbency. Various materials, includingkaolinite,calcium carbonate,bentonite, andtalc,[2] can be used to coat paper for high-quality printing used in thepackaging industry and in magazines.
Thechalk orchina clay is bound to the paper with syntheticviscosifiers, such asstyrene-butadienelatexes and natural organic binders such asstarch. The coating formulation may also contain chemical additives asdispersants,resins, orpolyethylene to give water resistance andwet strength to the paper,[3] or toprotect against ultraviolet radiation.
Coated papers have been traditionally used for printingmagazines.[4]
Machine-finished coated paper (MFC) has abasis 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 orthermomechanical pulp (TMP) and 15–40%chemical pulp with a totalpigment content of 20–30%. The paper can be soft nipcalendered orsupercalendered.[5] These are often used inpaperbacks.[citation needed]
Coated fine paper orwoodfree coated paper (WFC) are primarily produced foroffset printing:[6]
Plastic-coated paper includes types of paper coatings;polyethylene orpolyolefinextrusion coating,silicone, andwax coating to makepaper cups andphotographic paper.Biopolymer coatings are available as more sustainable alternatives to commonpetrochemical coatings likelow-density polyethylene (LDPE) ormylar.[7] It is most used in thefood and drinkpackaging industry.[citation needed]
The plastic is used to improve functions such as water resistance, tear strength, abrasion resistance, ability to beheat sealed, etc. Some papers are laminated by heat or adhesive to aplastic film to provide barrier properties in use. Other papers are coated with a melted plastic layer:curtain coating is one common method. 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 byUV curing for stability.[citation needed]
Most plastic coatings in the packaging industry arepolyethylene (LDPE) and to a much lesser degreePET.Liquid packaging board cartons typically contain 74% paper, 22% plastic and 4%aluminum.Frozen food cartons are usually made up of an 80% paper and 20% plastic combination.[8][better source needed]
The most notable applications for plastic-coated paper aresingle use (disposable food packaging):[9]
Plastic coatings or layers usually make paper recycling more difficult. Some plastic laminations can be separated from the paper during the recycling process, allowing filtering out the film.[10][11] If the coated paper is shredded prior to recycling, the degree of separation depends on the particular process. Some plastic coatings are water dispersible to aid recycling and repulping. Special recycling processes are available to help separate plastics.[12][13][14] Some plastic coated papers areincinerated for heat orlandfilled rather than recycled.
Most plastic coated papers are not suited tocomposting,[15] but do variously end up in compost bins, sometimes even legally so. In this case, the remains of the non-biodegradable plastics components form part of the globalmicroplasticswaste problem.[9]
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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 byUV curing for stability.
Arelease liner is a paper (or film) sheet used to prevent a sticky surface from adhering. It is coated on one or both sides with arelease agent.
Heat printed papers such as receipts are coated with a chemical mixture, which often contains estrogenic and carcinogenic poisons, such asbisphenol A (BPA). It is possible to check whether a piece of paper is thermographically coated, as it will turn black from friction or heat. (seeThermal paper)
Paperlabels are often coated with adhesive (pressure sensitive or gummed) on one side and coated with printing or graphics on the other.
Book paper is divided into uncoated paper (also calledoffset paper), coated paper (also called art paper, enamel paper, gloss paper and slick paper) and text paper.
