Aqueous print coatings and UV (Ultraviolet) print coatings are types of coatings applied to printed materials to enhance their appearance, durability, and other functional properties. First and foremost both Aqueous (water-based) and UV coatings have achieved widespread use in the Graphic Arts Industry as competing top coats. Both offer aesthetic enhancement and protection, adding value to a variety of printed products.
Aqueous Coatings require water components to evaporate for curing.
Fundamentally, the drying or curing mechanisms of the two are different. Aqueous coatings dry when the coatings’ water component (as much as 60%) is forced to evaporate, or is in part absorbed into a porous substrate. This allows the coatings’ other ingredients to coalesce to form a thin, dry to the touch, film.
UV Coatings cure 100% of the components
The difference is that UV coatings are formulated so that all of the ingredients in the coating, become a part of the cured coating. 100% of the components of the coating form the final cured, solid coating film. Curing takes place when the coating’s ingredients are exposed to ultraviolet (UV) light.
Equipment Differences in Coatings
In terms of application equipment, both low-viscosity aqueous & UV coatings can be effectively applied using the last inker in flexo & gravure liquid ink printing processes. In contrast, web and sheet-fed offset litho paste ink printing processes require that a press-end coater be added to apply aqueous or UV low-viscosity coatings. Screen processes also are used to apply UV coatings as are off-line coaters.
Flexo and gravure printing presses have the necessary solvent & aqueous ink drying capacity already installed to effectively dry aqueous coatings. Web offset heat set printing processes also have been shown to have the necessary drying capability to dry aqueous coatings.
However, it’s another matter when considering the sheet-fed offset litho printing process. Here the use of aqueous coatings requires the installation of special drying equipment consisting of infrared emitters, hot air knives, and air extraction devices. Extended delivery is also recommended to provide extra drying time.
Specialty Drying Equipment used in Aqueous Coating process
When considering the drying (curing) of UV coatings or inks, the difference is in the type of special drying (curing) equipment required. UV curing systems primarily supply UV light sourced from medium-pressure mercury arc lamps or more and more from (LED’s) light-emitting diodes.
Aqueous coatings are fast drying and attention must be paid to clean-up during any press stoppage. The difference is UV coatings stay open on press as long as there Is no exposure to UV light. UV inks, coatings and varnishes do not dry or plug anilox cells. There is no need to clean- up between press runs or over a week end, reducing down-time and waste.
Differences in Coating Qualities
Aqueous coatings dry with the clarity of water. Both aqueous & UV coatings can offer high transparency, and a range of finishes from high gloss, through satin to matte. The difference is UV coatings can offer a significantly higher gloss finish with a discernible depth.
Aqueous coatings generally offer good rub, mar, and blocking resistance. Specifically formulated aqueous coating products can also provide grease, alcohol, alkali and moisture resistance. The difference is UV coatings typically go a step further offering far greater rub, abrasion, mar, blocking, chemical and product resistance.
The difference is UV coatings typically go a step further offering far greater rub, abrasion, mar, blocking, chemical and product resistance.
Productivity Improvements
Aqueous coatings for sheet-fed offset litho were developed to in-line wet trap over slow-drying paste inks, minimizing or eliminating the need for spray powder used to prevent ink offsetting. Pile temperature needs to be maintained in the range of 85-95° F to avoid softening of the dried coating at higher temperatures, and the potential for setoff & blocking.
Advantageously, productivity is improved as coated sheets can be further processed sooner. The difference is UV coatings applied in-line, wet trapping over UV inks, are both cured at press-end, and sheets may be further processed immediately.
When UV coating over conventional litho inks is considered, aqueous primers are recommended to seal and adhere to the inks to provide a base for the UV coating. Hybrid UV/conventional inks can be used to negate the need for a primer.
Best Available Control Technology
Aqueous coatings offer clean air, low VOC, zero alcohol, low odor, non-flammability, non-toxicity, and non-polluting properties. Similarly, UV coatings produce no solvent emissions, zero VOCs, and are non-flammable. The difference is wet uncured UV coatings contain reactive components that may have a sharp odor, and can range from slight to severe as irritants, which can cause allergic reactions in some people. Skin and eye contact should be avoided. In a positive note, UV curables are designated as “Best Available Control Technology” (BACT) by EPA, reducing VOC’s, CO2 emissions, and energy needs.
Aqueous coatings are susceptible to consistency changes throughout a press run due to evaporation, and Ph influence. The difference is UV coatings maintain consistency on press as long as there is no exposure to UV light.
Dried aqueous coatings are recyclable, biodegradable, and repulpable. The difference is while cured UV coatings are recyclable and repulpable, they are slower to biodegrade. This is because curing produces both high physical and chemical resistant properties.
Aqueous coatings are able to conform with FDA regulations for both dry and/or wet greasy food contact.
Aside from differences, aqueous & UV coatings share many benefits, to varying degrees. For example, particular formulations can offer heat, grease, alcohol, alkali, and moisture resistance.
Additionally, they can offer gluability or glue resistance, a range of COF, imprint ability, hot or cold foil acceptability, the ability to protect metallic inks, increased productivity, in-line processing, work-and-turn capability, energy savings, no set off, and in sheet fed offset, the elimination of spray powder.
What Coatings to choose?
Choosing between Aqueous and UV print coatings depends on factors such as the desired finish, durability requirements, budget, and environmental considerations. Each type has its own advantages and is suited for different printing applications.
Our business at Cork Industries is the development and formulation of Aqueous, energy-curing Ultraviolet (UV), and Electron Beam (EB) specialty coatings and adhesives. Cork thrives on its ability to formulate novel, useful specialty products that offer the graphic arts industry printer/coater a competitive advantage.
