Radiation-Curing
Technologies
Kerry Pianoforte, Editor
Radiation-curable formulations, including coatings, inks, adhesives and electronics, are cross-linked by high-inten- sity 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 com-
posites. “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 coat-
ing applications there are a number of unique considerations.
“The main difficulty is always in the combination of the dif-
ferent 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 diversifica-
tion 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
