From The Standard, Volume 3, 2009, courtesy of Sappi North America.
Anilox Coating Process • A hard roller made of steel or aluminium coated with industrial ceramic is etched on the surface with a predetermined number of cells that act as carriers of exact quantities of coating to the printing plate. During the printing process, the anilox roller is immersed in coating, then a sharp “doctor blade” scrapes excess coating off the surface, leaving an exactly measured amount in each cell. The roller then makes contact with the flexographic printing plate, which transfers the coating onto paper. Anilox is used for special UV and aqueous coating applications, including pearlescent, metallics, and spot coating. (Editor’s note: Anilox coating may also be used with inline coating units on offset and other, non-flexographic presses, particularly in packaging applications.)
Aqueous Coating • Aqueous is a fast-drying, water-based protective coating that can be applied inline on press from a coating tower. It is particularly noted for providing excellent smudge resistance. It also does not yellow with age. Aqueous coating comes in gloss, satin, dull, and many custom finishes (pearlescent, metallics, touch coatings). It can be flooded onto the entire sheet or spot coated.
BCM per Square Inch • BCM stands for “billion cubic microns,” which is the volume measurement for each pocket, or cell, on an anilox roller. BCM expresses the amount of ink or solids that each cell holds. In commercial printing, BCMs per square inch typically range from 9 to 40 BCMs.
Coatings • Press coatings (aqueous or UV) are applied to protect the printed sheet from fingerprinting, scratches, and smudges, as well as exposure to moisture and temperature extremes. They are also better than varnish at protecting against long-term fading. Choice of coating finish can improve the look of the printed piece and can be used as a technique to achieve different visual effects.
Color Shift • In four-color printing, image colors change to some degree depending on ink densities, dot gain, paper choice, and coating finish. Generally speaking, a gloss-finish coating tends to result in more saturated colors, particularly intensifying blacks and darker shades. Satin coating tends to be the most color neutral. Dull coating tends to minimize the contrast between darks and lights, resulting in a softer look.
Cyrel® Plate • This is the photopolymer plate used in the flexographic printing process. It develops thermally, without any need for solvents or drying time, and is suitable for fine screen, line, and solids work. Spot aqueous and UV coatings require the use of a Cyrel plate or peelable coating blanket. (Editor’s note: Cyrel plates may also be used with inline coating units on offset or other non-flexographic presses.)
Dry Trap • Printing over dry ink, as opposed to wet trap. This requires the printed piece to go through the press a second time. It offers more creative flexibility and greater ink/coating holdout, but costs more and takes more time than inline processes.
Dull Finish • Dull varnish and coatings do not add sheen to the printed sheet. Their non-glare surface is known for enhancing readability.
Flood Coating • This process involves applying a finishing coating (aqueous, UV, or varnish) to an entire press sheet as one flat coating.
Gloss Finish • Available in varnish and aqueous and UV coatings, gloss has a high reflective finish that gives the sheet a shiny appearance.
Inline • This includes any process done on a printed piece while it is on the press. The ability to do everything in one operation saves time and money. (Editor’s note: Inline processes can include the printing of multiple colors, the application of coatings or varnishes, and most cutting and binding operations.)
Offline • This includes any process done after a printed piece has come off the press.
Overprinting • Also called surprinting, this is a technique where one ink, varnish, or coating is printed directly over another, without knocking out the image behind it.
Pearlescent Finish • This specialty pigment, made from crushed mother-of-pearl particles, is used to add iridescent highlight and depth to defined printed areas.
Raised UV Coating • An anilox cylinder is required to create a raised surface. The deeper the BCM cell depth on the anilox cylinder, the higher the raised surface.
Reticulation Effect • A wrinkled look created by increasing the viscosity of the coating to a point where it cannot be spread evenly onto the paper. The surface semi-rejects the coating film, causing it to bead and leaving a snakeskin look.
Sandpaper Finish • Grainy particles are suspended in coating to create a tactile sandpaper texture.
Satin Finish • This smooth finish is not as shiny as gloss finish and not as matte as dull finish.
Scented Finish • Scents microencapsulated in pigments are added to coating and applied to the sheet. When rubbed the microcapsules break, releasing the fragrance.
Soft-Touch Coating • This special-effects coating imparts a unique, rubbery, leather-like feel with a matte appearance. It can be applied inline through a coating tower and does not require any secondary or offline treatment.
Strike Through(also known as Contrast Varnish) • This is a method of simulating a perfect-image trap by taking advantage of a chemical reaction between varnish and coatings. A dull varnish is first put down in the areas intended to stay matte, then an overall flood gloss coating is applied. The gloss coating is “neutralized” in the varnished areas, which remain dull while the rest of the image goes glossy.
Textured Finish • This coating creates a surface that looks like it was textured by a ball-peen hammer. Also known as a hammertone finish.
Thermochromatic Coating • This is a reaction caused by dyes that are heat sensitive. The heat from a finger will cause the color to change.
UV (Ultraviolet) Coating • UV coating is a clear liquid coating that can be cured instantly with an ultraviolet light, leaving a gloss, satin, or dull finish. Since UV coating is cured by light not heat, the application process emits no solvents into the atmosphere.
Varnish • A liquid coating applied to a sheet via an ink unit, either inline or offline. Varnishes can be gloss, satin, or dull. They can also be tinted with pigment for interesting effects. Although varnish protects the sheet from scuffing, it tends to yellow over time.
Wet Trap • When varnish or ink is printed over wet ink.