By Olivia Cahoon
Part 1 of 2
While UV LED curing systems provide instant cure speeds for digitally printed applications, using these systems in manufacturing is still a relatively new concept. Improvements in ink equipment costs, ink formulation, curing technology, and even wavelengths remain for successful implementation.
Equipment costs are one of several areas that can be improved to help UV LED curing systems integrate into manufacturing environments. System costs vary depending on the power output, specialty features, cure area size, and wavelength. These factors affect the system’s speed as well as cure quality and form factor.
“The premium for LED-based solutions in comparison to conventional UV has narrowed as technology has continually improvedoduct manager, OmniCure UV curing solutions, Excelitas Technologies Corp.
In many cases, return on investment for an LED curing solution can be short with significantly lower electrical, operating, and maintenance costs as well as a longer lifetime—offsetting higher acquisition costs, shares Lee. “As the market continues to adopt UV LED curing systems, pricing for equipment will further decline.”
In 2018, UV LED consumption continued with high growth. According to Simon Reissmann, technical marketing engineer, digital inkjet, Phoseon Technology, the market demonstrated it is converting from traditional curing technologies to UV LED. With this increase in sales volume, UV LED manufacturers lowered prices per single LED—leading to more affordable systems.
Jeffrey Stines, director of marketing, American Ultraviolet, agrees. “Current UV LED pricing is still somewhat higher than conventional UV curing systems, but as with all technological development and increasing user acceptance, the pricing tends to drop over time.” Differences between UV curing and UV LED systems is often reflected in price, but more importantly in the device’s functionality.
In recent years, UV LED curable inks have become more compatible as well as widely available. Despite this, improvements can be made to photoinitiators to promote the use of UV-curable inks in cautious markets like food packaging.
Traditionally, ink formulators were accustomed to devising products that respond to the broad band emission of medium pressure UV lamps, which typically output 200 to 400 nanometers (nm). “This gives the opportunity to ensure the optimum overlap between the photoinitiator packages and the output of the UV lamp curing system,” says Dawn Skinner, application development manager, Europe, Heraeus Noblelight.
Photoinitiators work around the absorption pigment profile to ensure the fastest possible reactivity for a given ink product. There are several constraints for photoinitiator selection, including low odor and low migration properties, which food packaging end users demand. “The performance of such photoinitiators has improved over the years and allow reasonable formulation options. Legislations such as REACH drives other limiting factors facing formulations,” offers Skinner.
UV LED curing lamps provide several benefits to digitally printed applications, such as instant on/off curing that doesn’t require a warm-up time. Inks offer fast-drying capabilities that produce high-quality images.
These systems are now adopted into a range of applications since undergoing rigorous testing and validation processes. “It goes to say that the quality of cure has been proven to be sufficient in those processes,” shares Lee. However, it’s also worth noting that there are challenges in curing technology that need to be addressed, like surface tackiness.
According to Lee, free radical formulations are susceptible to tacky curing when exposed to air. To improve the surface cure, a number of techniques are implemented including formulation modification, high irradiance curing, and exposure to short wavelength UV.
Chemical and physical processes can also mitigate tacky surfaces from air exposure. For example, Skinner suggests incorporating specific molecules, which can react with the peroxy radicals and neutralize their adverse effects on the polymerization process. Other options include removing oxygen from the UV curing atmosphere with nitrogen inerting. “In some applications, a combination of UV LED lamps and medium pressure UV lamps can also be effective.”
Reissmann sees UV-C LEDs—ranging from 200 to 280 nm—as potentially improving surface curing. To do so, he says manufacturing capabilities need to improve and prices for individual UV-C LEDs must drop to a more economical level. “Early prototypes show that UV-C curing systems might lead to improvements in curing performance in combination with UV-A in a hybrid setup.”
Wavelengths & Knowledge
UV LED curing systems are available in a variety of wavelengths, often ranging from 365 to 405 nm.
Generally, short wavelength UV LED output is not developed to a level high enough to meet industrial printing production rates. However, it is expected that adding shorter wavelength output from UV LEDs widen the formulating opportunities and enable inks to reach a higher surface cure degree, which helps several industrial print applications, shares Skinner. As this process is ongoing, she says it’s important to understand the specific wavelengths and the output levels in the UV-B/UV-C needed to make significant improvements to either reactivity or cured properties.
In addition to wavelengths, improvements can also be made to industry and technology knowledge. “The impression is that we all really don’t understand the power that is required when dealing with LED technology,” admits Stines.
The market’s current focus is to get the highest irradiance possible. However, he believes education needs to improve to match chemistry to wavelength while research should focus on understanding how irradiance numbers affect the properties and reactions of photoinitiators and oligomers. “Not requiring an extremely high irradiance could overcome many issues, such as LED heat management, LED life, cost, and available wavelengths among other things.”
Designed for Industrial Use
Before UV LED curing systems are fully integrated into manufacturing environments, improvements should be made to ink formulation, curing technology, wavelengths, and equipment costs. Addressing these issues will further promote the implementation of UV LED curing systems into manufacturing.
In the second part of this series we provide roundup of available UV LED curing systems.
Mar2019, Industrial Print Magazine