Radiation-Curing Technologies

By Kerry Pianoforte, Editor | April 8, 2016

Radiation-curable formulations, including coatings, inks, adhesives and electronics, are cross-linked by high-intensity ultraviolet (UV) light or electron beam (EB) energy sources. Radiation-curable products are used in a wide variety of applications. According to data from research firm IHS, in North America, the graphic arts sector, which includes overprint varnishes and inks predominates, with coatings, adhesives, and other industries being of lesser importance. In Europe, IHS reported that the wood coatings and graphic arts markets account for about 80 percent of demand. In Asia, radiation-curable film resists, printing plates, semiconductor resists and color filter resists are used extensively for semiconductors, printed circuit boards, printing plates and other components. In Asia (except for China), these uses account for 30-40 percent of the total market for radiation-curable products. In China, the major uses of radiation-curable products are in wood, bamboo, paper, and plastics coatings, accounting for approximately 60 percent of the total market.

IHS analysts predict that over the next five years, government regulations in the U.S. and Europe, especially those concerning air pollution, will continue to be a driving force behind the adoption of new, low-pollution coating technologies such as radiation-cured coatings. However, radiation-curable coatings have other desirable properties such as speed of cure; extremely hard, chemically resistant finishes; ambient curing; small application equipment footprint; high productivity; and nonflammability. Because of the high costs associated with their use, radiation-cured products tend to be adopted in specific applications only where they exhibit advantages over conventional coatings. Currently radiation-curable coatings account for two percent of the total global market for industrial coatings.

There are a number of suppliers offering specific raw materials for the radiation-curable market.

Allnex is a leading global supplier of resins for UV/EB coatings. “The resin in general is one of the key components of the coating that will provide most of the chemical (stain resistance) and mechanical (impact, scratch resistance) properties of the final coating as well as some haptic effect (gloss or dead matte effect, soft touch feeling),” said Gregory Gerin, global marketing director radcure, Allnex.

Allnex’s resin portfolio includes several hundred different grades, covering applications mainly in industrial coatings, packaging coatings and inks, consumer electronics and industrial plastics, as well as other markets such as composite, gel nails and 3D printing.

RAHN offers a comprehensive line of products for UV/EB formulations, including coatings, inks, adhesives and composites.  “Those products are a full range of reactive diluent monomers, oligomers from all common acrylate classes – epoxy, polyester, polyether, urethane, photoinitiators, both traditional and polymeric, synergists, stabilizers, ‘co-resins’ and additives specifically for adhesion and/or property modification,” said Michael Gould, technical key account manager EnergyCuring USA, RAHN USA Corp.

 When developing products and technologies for UV/EB coating applications there are a number of unique considerations.

“The main difficulty is always in the combination of the different properties that are required,” said Gerin. “Developing the performance of a resin on one specific property usually requires trade-offs on one or several other properties, for example soft feel effect and hardness are usually antithetical. Therefore the success of a resin often lies in the capacity of our chemists to develop/invent new resins with a limited need for trade-offs. Moreover, an industry trend we see across most applications is the diversification of substrates versus the traditional substrates such as wood and paper. In these cases, adhesion to substrate, again without limiting the other properties of the resins, is a real challenge.”

“Challenges that must be met in developing new products include ensuring adhesion – always a challenge because of the shrinkage that occurs with cure and the variety of substrates needing to be coated – achieving sufficient reactivity with new curing methods such as LED, keeping viscosity as low as possible while maintaining all other properties and providing a balance of cost and performance as new applications emerge,” said Gould. “Perhaps the biggest and most daunting of challenges that we face as an industry is the greater scrutiny these chemicals are under and the more onerous labeling with which we have to comply on a nearly monthly basis.  Traditional coating chemistries most often utilize high molecular weight polymers that are crosslinked with heat or which coalesce and dry by releasing solvent and/or water.  UV/EB coatings utilize highly reactive, lower molecular chemical compounds which, by their reactive nature, tend to be aggressive to the skin and eyes.  Advantages in utilizing UV/EB formulas for packaging are met with equal or greater challenges in proving that small molecules and fragments cannot leach from coatings and contaminate food or sensitive products, such as medical devices.  Finding an effective balance among ‘verifiable low migration’ performance, cost, labeling and all other physical performance requirements is daunting.” 

Although radiation-curable products represent a relatively small percent of the overall coatings market, there are a number of areas for potential growth. “Perspective on the UV/EB market is that 3D printing/rapid prototyping and digital inkjet printing are the two biggest areas of growth in the near term,” said Gould. “While we see significant interest in the automotive sector, traditional coating technologies are entrenched as qualified incumbents and very difficult to displace.  Performance and/or cost benefits must be realized in order to achieve significant growth in this sector.  Electronics is a high value market space, but the rapid and constant metamorphosis of devices and applications makes product development difficult in this area where material cost and performance requirements change almost daily.  Across market segments, the growth of UV/EB adhesives appears to be robust, though labeling issues with raw materials complicates growth here.”

According to Gerin, the radcure coatings grows faster than the coating industry in general, around four percent per year. Growth areas depend on the region but two fast growing applications Allnex sees double digit growth in inkjet and automotive interior applications.

Suppliers to the radcure coatings market must stay ahead of impending legislation by developing more sustainable products.

“As global supplier of radiation curable resins, Allnex continuously improves its product offerings to the coatings market.  “The existing product portfolio is being adapted ahead of legislation limiting chemicals of concern, by improving sustainability (increasing use of biobased raw materials), by reducing potential migration species in packaging ink resins,” said Gerin. 

“Furthermore, several R&D projects are targeting new curing and new application technologies requiring lower viscous resins.”

“New applications emerge when the value proposition of the UV/EB coatings (productivity, superior properties, low VOC content) versus the other technologies (mainly solventborne and waterborne coatings) becomes interesting and profitable for our clients or the end user,” Gerin continued. “As an example, a few years ago, UV gel nails took a sizeable share of the market, mainly because of the rapidity of the process – reduced number of layers and quicker drying time. The question every coating user should ask him/herself is always the same: what is the gain provided by a superior coating / quicker process versus the limited investment needed to cure UV/EB coatings? In some cases, the gain comes from the quality of the coating, which allows our clients or the clients of our clients to sell their products with a premium. In other cases, the gain comes from the productivity, the capacity to produce on demand, the reduced inventory level, the capacity to replace the current substrate by a less expensive one. The opportunities are infinite.” 

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