Printing Coating – FAMOUS TYPES

Coating of printing matters surfaces could provide the best surface properties and protection for printed surfaces. When coatings are applied as an off-line process over dry ink, they create a bold effect, but when applied as an on-line process, they create a much more subtle effect over ink that is still wet. Among the most popular coatings are overprint varnishes, aqueous coatings, UV coatings, and EB coatings.

Overprint Varnish
Applied during the printing process or as an off-line process, overprint varnish is much like a solvent-based ink. The different varieties are usually colorless, but sometimes they are tinted to achieve a desired effect. Varnish can be applied as an all-over coat or in spots to highlight a specific area of a printed piece.

Overprint varnish is available in glossy, dull, or satin finishes. Gloss varnish creates a smooth surface over the paper, filling in any voids or irregularities that may be on the surface. Dull varnish also fills in irregularities to form a smooth surface, but it diffuses light that reflects back to the eyes, which creates a dull appearance. A nearly 3-D effect can be created by applying gloss varnish to a subject and dull or satin varnish to the background. The subject will appear to jump off the page. In addition to applying varnish as a solid coat, it can also be printed as a halftone (series of dots) in order to provide subtle effects and to provide printed objects with an increased dimensional appearance. The effects that can be achieved are endless when using different combinations of varnish, paper, and ink.

Besides design effects, another important aspect of varnish is the protection it provides. A coating of varnish over a printed piece protects it from the wear and tear that is part of every day handling, allowing the document to remain intact for a longer period. An all-over coat of satin varnish will protect the printed surface without drawing attention to the fact that varnish was used for protection purposes.

A disadvantage of varnish is that many of them are solvent-based. Solvent-based means that they emit VOCs while they are being applied, which can be a health hazard for the press operator unless the proper safety precautions are followed. Another disadvantage is that varnishes tend to yellow over time if they are formulated with tung or linseed oil. Varnishes with alkyd formulations will not yellow, but they are not as glossy or as hard as tung or linseed oil.

The use of varnishes on print applications should be planned early in the design process. They should not be applied as an afterthought in order to try to cover-up a poor choice in paper, ink, or design.

Aqueous Coating
An aqueous coating is usually applied during the printing process and can be applied as an all-over coat or in patterns or spot coatings. Like varnishes, an aqueous coating offers protection for the printed document and provides numerous effects for print applications. Aqueous coatings are available in gloss, matte, and satin finishes. Among the advantages that aqueous coatings have over solvent-based varnishes is that they will not yellow over time and they are less toxic and emit fewer VOCs.

UV Coating
UV coatings come in a liquid or paste form and remain as a liquid or paste until exposed to ultraviolet light. The printed page is covered with the UV coating and is then exposed to the UV light, which causes photoinitiators within the coating to immediately react, creating a hard protective finish. Ingredients called monomers give the coating its gloss and hardness characteristics. UV coating, which is also known as an Energy Curable coating, provides the best surface properties and protection for printed surfaces. Some benefits of UV Coating include:
- Greater opacity, Color stability, Deeper and more vibrant colors and color tones.
- Sharper graphics, Higher gloss, Uniform surface to give labels a more vibrant look.
- Scuff resistance, Instantaneous curing, Allows for in-line die cutting.
- Chemical resistance, Better outdoor endurance.
- Environmentally safe - No VOCs (Volatile Organic Compounds) are produced.

EB Ink / Coating
Like UV inks/coatings, EB (Electron Beam) is an energy curable coating, but it is hardened with the use of a concentrated beam of high energy electrons. EB inks/coatings do not contain photoinitiators because the high energy electron beam is all that is necessary to cure the surface.

Other Coatings
Other types of coatings include clay coatings to add strength and gloss to paper, whitewash coatings which are used as a finish coat for such items as Kraft paper, and grease resistant coatings used on applications for industrial and scientific uses.

More...