Coating
Coating is a covering that is applied to the surface of an object, usually referred to as the substrate. In many cases coatings are applied to improve surface properties of the substrate, such as appearance, adhesion, wetability, corrosion resistance, wear resistance, and scratch resistance. In other cases, in particular in printing processes and semiconductor device fabrication (where the substrate is a wafer), the coating forms an essential part of the finished product.
Coating and printing processes involve the application of a thin film of functional material to a substrate, such as paper, fabric, film, foil or sheet stock. This article discusses what is frequently termed 'roll-to-roll' or 'web-based' coating. A roll of substrate, when wound through the coating machine, is typically called a web.
Coatings may be applied as liquids, gases or solids. Coatings can be measured and tested for proper opacity and film thickness by using a drawdown card.
Functions
- Printing (text or decoration) such as on paper, fabric, and flexible packaging
- Self adhesive properties such as for tape, labels and packaging
- Melt-adhesive properties such as for vacuum seal and heat seal applications
- "Release" coatings such as the liner of a double-sided tape or vinyl stickers
- Low surface energy coatings to act as a non-stick surface
- Optical properties such as tint, color, anti-reflection, and holographics
- Photo-sensitivity such as for photographic film and paper
- Electronic properties such as passivity or conduction as with flexible circuits
- Magnetic properties such as for magnetic media like cassette tapes and floppy disks
- Water-resistant or water-proof coatings, such as for fabrics or paper, or on wood surfaces such as outdoor furniture, patio decks, yacht hulls and decks.
- Scent properties such as scratch and sniff stickers and labels
Coating processes
Coating processes are classified as follows:
Chemical vapor deposition
Physical vapor deposition
Chemical and electrochemical techniques
Spraying
Optical coatings
Other
Roll-to-roll coatings
Common roll-to-roll coating processes include:
The main coating and varnishes for the printing industry include:
Standards
- ISO 1461 Hot dip galvanized coatings on fabricated iron and steel articles—Specifications and test methods
- ISO 4042 Fasteners—Electroplated coatings
- ISO 10683 Fasteners—Non-electrolytically applied zinc flake coatings
- ISO 10684 Fasteners—Hot dip galvanized coatings
- ISO 12944 Paints and varnishes—Corrosion protection of steel structures by protective paint systems—Part 6: Laboratory performance test methods
See also
References
- Titanium and titanium alloys, edited by C. Leyens and M. Peters, Wiley-VCH, ISBN 3-527-30534-3, table 6.2: overview of several coating systems and fabriction processes for titanium alloys and titanium aluminides (amended)