UV Ink in Flexo Printing
Updated: Nov 18, 2022
Ink has several components, but an ink has a color or pigment along with a base (water, etc.) that transports from the fountain to the substrate. Other components and additives are included in the ink formula to maintain the distributive process, fix pigments on the substrate, and bring out the desire traits of the image.
Water and Solvent-Based Inks
Traditional water and solvent-based inks require a dryer to apply heat to the web. The ink dries via an evaporative process that can remove roughly 30-40% of the ink volume. In short, there is a need to deliver 40% more volume to the substrate with water or solvent ink to obtain the appropriate color.
Solvent-based inks have been widely utilized for decades and achieve fantastic results on nonabsorbent surfaces like films. All of that is changing rapidly. We are bearing witness to growing environmental awareness and intolerance for environmental negligence. Waste disposal is a major factor in decisions made by manufacturers and print shops. Environmental Protecting Agency (EPA) regulation are becoming strict when it comes to the disposal of solvent substances.
Environmental Concerns and Printing Ink Statistics
Environmental concerns and regulations have had a major impact on printers, and they opt to use water-based ink as often as possible. Water-based ink is well known for being difficult to work with on film. If it is left in open exposure, water-based ink will dry within the anilox cells, which greatly impacts usable cell volume and requires the roll to be removed from the press for cleaning.
It makes perfect sense why cell clogging has become such a common occurrence, especially when you consider the pressure on component manufacturers. Printers are tasked with adding color. Printers also want to lay as much ink as possible. That is why they want the inks to dry faster so they can maintain fast press speeds. Inks should dry quickly and have a static registration throughout the entirety of the printing process. There is also a need to bring out specific traits in the print target such as resilience and protection from rub.
Flexo Ink Vendors
Ink vendors are doing everything within their power to meet their customers’ requirements. They are constantly researching and improving formulations to a variety of inks. This did not come without drawbacks. If the ink dries quickly on substrate, then the anilox roller is being affected similarly. You can expect to have clogged anilox cells. If the ink is more resilient when applied to the substrate, it will be just as resilient when attempting to clean it from the cells.
This issue becomes even more pronounced to anilox roll manufacturers as they become challenged in similar ways to ink vendors. Mechanical engravings with depthless cells have since been upgraded to steep-walled laser engraved cells. Cell volumes have changed. Anilox cell openings have been reduced as screen lines have improved. The demand is for maintaining or increasing ink density while simultaneously providing finer distribution. Deeper cells do not typically release ink as well and finer engravings provide greater cell wall surface area for the ink to hold.
In the pursuit of achieving greater printing results, printers and support vendors alike have created terrible complications as well. The result is the expensive and annoyingly complicated removal of ink resin. The propagation of equipment, supplies, methods, and vendors for cleaning anilox serves as an example of what the impact of plugged cells has done to our industry.
The good news? UV ink does not require air to dry. Thus, it minimalizes the problem with plugged cells. There is no component that requires evaporation, so there is very little maintenance during a press run. A press could feasibly be left unattended for 24 hours or more and be ready to go!
The Many Benefits of UV Ink
UV ink behaves very similarly to liquid plastic. As the component is exposed to a UV light, a reaction occurs that causes photo-initiators to bond the ink into a solid. There is no waste. Almost all the delivered volume is used to color the substrate. When comparing UV ink to water-based ink, you require about 35% less ink coverage with UV when comparing the two.
UV inks are usually extremely thick. Lower viscosities do exist, but UV inks are typically within a range of 1000-5000 centipoise (when compared to water-based inks within a range of 100 centipoise). A reasonable assumption could be made concerning water or solvent ink where it is more readily transferred from cell to the substrate. This does not diminish the fact that printers are able to achieve excellent results when using anilox rollers with specifications compatible with water and solvent inks. Pre-existing anilox rollers can almost always be utilized for printing UV and serve as a means of determining specifications for new anilox roll engravings. Leaving out transfer rate, the thickness of UV ink can be used to greatly enhance the quality of a printing job by diminishing color bleed and dot gain creating vastly sharper images.