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Diving into Inks: Digital, Analog and UV-Curable

by Dianna Brodine, managing editor

Consumer demands and technology advances in both equipment and substrate materials add challenges for inks used in industrial plastic decoration. Ink developers are in a constant scramble to meet end-user needs for scratch resistance, weatherability, color fastness and more. Add in advanced decorating equipment with faster throughput capabilities – which require faster ink drying times – and a substrate base with varying percentages and types of additives, recycled content and performance characteristics … well, let’s just say inks are in the spotlight.

Whether intended for use in digital printing applications, more traditional analog screen or pad printing applications or with ultraviolet (UV) or electron beam (EB) curing, today’s inks need to meet more requirements than ever before and handle a wider variety of applications.

Application variety

From interior automotive components and medical syringes to cellphone cases and food containers, plastics are everywhere – and each of these applications have specific requirements for heat resistance, abrasion resistance, chemical resistance, solvent resistance, ability to withstand extreme weather conditions and color fastness.

Marabu, a manufacturer of screen, digital and pad printing inks, as well as liquid coatings, detailed some of the challenges in these areas1:

  • Automotive applications place high demands on printing inks: they must be resistant to extreme climatic chamber tests; must be highly opaque; must exhibit resistance to sweat, abrasion and cleaning products; and adhere well to polycarbonate.
  • Bottle crates and transport containers of PE (polyethylene) or PP (polypropylene) often have a long lifetime and are subject to high chemical and mechanical stress during this period of time. Additionally, there are often extreme climatic conditions.
  • Printed designs on audio, electronic and household devices must withstand chemical, thermal and mechanical stress day in, day out.
  • Safety is the most important factor in terms of labelling medical products. Therefore, printing inks must be sterilization-resistant and follow specified guidelines of sensitive products. Apart from this, ingredients must not immigrate into the human body.
  • Technical markings on audio, electrical and household products must be resilient in the face of heat, exposure to chemicals and general wear and tear. Icons, scales and other markings on electrical switches, nameplates and dials are important sources of information and guidance.

In addition, new applications emerge – and thrive – with incredible speed. A few years ago, the wearables market was a blip on the radar; now, consumers with Apple watches and Fitbits abound. IDTechEx’s most recent report on wearable technology predicts an “increasingly diverse market for wearable devices will reach over $150 billion annually by 2026.”2 The daily use stressors for the decorators for these products – headphones, fitness trackers, medical devices and others – are immense: chemical resistance to hair products; scratch resistance for items that, when worn on the wrist, are banged against counters, desks and walls; and water resistance for sweaty fitness device users. Not only does wearables decoration need to withstand multiple challenges to its lifespan, but it also requires a high degree of quality. “Printed wearables are held in hand by consumers and subject to very close visual inspection. Alphanumeric text may be six points or smaller. To avoid visible artifacts and ensure readability, high-resolution printing is required,” according to Scott Sabreen, president, The Sabreen Group.3

Substrate and contents

Environmental and chemical factors aside, the substrate itself creates difficulty for ink adherence: a wide variety of grades and formulations exist, all with different levels of additives, plasticizers and recycled plastic content. “More and more plastics are being produced by regrinding scrap or older material,” said Chuck McGettrick, North American sales manager for Marabu North America.

Then, the type of product itself can interfere – is the product to be decorated flexible or rigid? Is the surface flat, curved or textured? If the product – for instance, a container – has been pretreated, how long ago was the pretreatment process done? If the containers have been sitting in storage in a warehouse that isn’t climate controlled, the pretreatment may be less effective – or not effective at all. All of these affect the ink and its ability to adhere.

“One of the most common occurrences we’re asked to problem-solve is adhesion,” explained McGettrick. “This is seen in both solvent and UV applications. The main issue, more often than not, is the surface tension of the substrate. This is where proper pre-treatment is needed to ultimately allow the ink to adhere to problematic and low-surface-energy substrates.”

Jack Knight, global business development director, Rigid Packaging, for INX International Ink Co., concurred: “Surface tension and adhesion are issues we face when ensuring an ink performs to the customers’ requirements.” However, Knight mentioned that the product exterior isn’t the only challenge to inks: “When looking at food containers, we need to be mindful of the regulations governing the raw materials approved for these to insure public safety.”

As plastics are increasingly used in the packaging applications, both in rigid and flexible film formats, the contents of a container become the focus. Will the packaging hold a liquid or solid product? What outside forces (extreme temperatures, long periods of time on a shelf) will the product come in contact with frequently? Is there a risk of product contamination, if the ink should leach through the packaging barrier? Then, as Knight mentioned, ink adherence is no longer the primary concern, but rather safety regulations for the food and medical industries.

Technology changes

In addition to adhesion concerns and the wide variety of applications ink must adapt to, updates to equipment, graphics and ink formats add another layer of complexity.

“With the advances that have been seen in the graphics area with HD images, the inks need to be fast curing with low dot gain to insure the designer's vision is captured as intended,” Knight explained. “With the speed of the printers increasing, the cure rates of the inks needed to be addressed as well."

UV- and EB-curable inks often are the answer when faster cure times are needed. “The cure time with UV is much faster and almost immediate versus conventional solvent curing,” said McGettrick. “This helps with packaging a product almost minutes after it printed.”

In addition, UV- and EB-curable inks have other advantages on products intended for use by a customer base concerned with sustainability and environmental issues. “UV inks are a great green alternative for the environmentally conscious individual vs. using conventional solvent or ceramic frit inks. UV inks require less energy output while in production, thus leaving a smaller footprint in the environment,” said McGettrick. “Curing with UV or LED light also is significantly more cost effective than running large ovens for curing solvent-based inks.”

Ink formulations also much keep up with the changing equipment technology. “We’re seeing a migration toward digital printing, especially with membrane switches, glass and cylinder printing,” said McGettrick. “Technology is changing in the ways that products are being decorated and the equipment is being built – it’s opening more doors and allowing people to print more quickly than they’ve traditionally been able to do.”

“Digital is the hot topic for all rigid containers segments,” Knight agreed. Digital printing allows for customization and quick changes in graphics, text and appearance to meet changing consumer desires, but the trend has created challenges for inks. “Ensuring that all food regulations are met when formulating digital inks is key to having a product that can be used for this application,” he continued.

However, digital isn’t the right solution for every situation. Screen printing and pad printing with analog ink technology still have their place, particularly when inks need to be applied to hard-to-reach areas. “Specialty inks for special effects and shaping of the packaging are things that the digital inks are still challenged by. The speed of analog technology and cost of digital conversions are the biggest factors that keeps many out of this arena,” Knight said.

Adhesion challenges, an ever-changing substrate base and rapidly advancing technology mean decorators can find themselves in a bind when their customers demand a quick turnaround. The solution for plastics decorators, as always, is to work closely with ink manufacturers to find the right solution for every application.

References

  1. www.marabu-northamerica.com
  2. Wearable Technology 2016-2026 Markets, players and 10-year forecasts; James Hayward, Dr. Guillaume Chansin and Dr. Harry Zervos; July 2016, http://www.idtechex.com/research/reports/wearable-technology-2016-2026-technologies-markets-forecasts-000427.asp
  3. Industrial Inkjet Printing onto Wearables; Scott R. Sabreen, The Sabreen Group, and Dene Taylor, Ph.D., SPF-Inc.; Plastics Decorating, July/August 2015