A look at the status of UV/EB curing

An expert in the field assesses the current state of ultraviolet and electron beam curing.

RadTech '96 North America, the fifth biennial UV/EB Processing Conference and Exhibition, was held April 28-May 2, 1996, in Nashville, TN. The event, produced by RadTech International North America, offered 24 sessions covering a wide-ranging spectrum of technology and issues in ultraviolet and electron beam curing.

Topics included materials, equipment, processing, health and safety, marketing/economics, government affairs, and an international perspective.

To obtain conference proceedings, or for information on RadTech membership, upcoming events (RadTech 1998 will be held in Chicago April 19-23), publications, etc., contact the association at 60 Revere Dr., Ste. 500, Northbrook, IL 60062; ph: 847/480-9576; fax: 847/480-9282.

An excellent overview presentation, "The Status of UV/EB Curing in North America - 1996," was offered by Kenneth Lawson, president, DSM Desotech Inc., Elgin, IL.

Lawson explained that in 1991, 1993, and 1995 he chaired studies conducted by members of RadTech International North America to assess the markets for UV- and EB-curable products. The studies involved a representative cross section of end users and suppliers of equipment, raw materials, and services.

The paper presented at RadTech 96 utilized a modified "Delphi" technique with the input of more than 30 industry participants who shared an update of their experience during 1995 and early 1996. After each round of questions, the participants compared their impressions with those of other participants and then had the opportunity of adjusting their own estimates or "holding fast." The result, Lawson noted, was a consensus of opinion that represents the reality of the current market's status and provides a reasonable projection of the growth and opportunities ahead. Portions of his update are presented here.

The actual increase of UV/EB curing has been slightly more rapid than was projected in the 1991 study. The current panel indicated that 1995 growth was 12%. However, there was a wide variation in the perception of the members that varied from 7% to 12%. Average growth in the past five years has been about 12% per year, and the total North American market now uses more than 45,000 metric tons of UV- and EB-curable products. By comparison, this represents more than 2% of the industrial coatings market (solids basis) and is about 40% the size of the powder coatings tonnage in North America. Continued growth is anticipated at a rate of about 13% for each of the next five years, as the motivators for the use of these highly productive, environmentally friendly products will continue to grow.

Graphic Arts

Clear overprint coatings for paper and paperboard comprise the largest market for UV- and EB-curable products. As a group, materials used in graphic arts and converting industries comprise about one-half of the total volume. The more mature overprint coatings have captured a significant share of the market for high-gloss finishing of point-of-purchase signage, folding cartons, magazines, and pocket book covers.

Nevertheless, new application techniques (flexo) and the continued growth of offset and screen printing techniques have resulted in recent expansion of about 7% per year.

In 1995 there was a leveling of growth in this segment caused by some conversion of UV-cured overprint coatings for magazine coatings to much less expensive water-based acrylic coatings. This loss was partly offset by the growth of flexographic coatings. There may have also been some reduction of letterpress inks as these continue to be replaced by newer printing techniques.

The growth of UV/EB-curable inks has been strong, particularly in the area of flexography, where a number of wide web machines have joined thousands of narrow web presses that have used UV-curable inks and overprint coatings for more than a decade. In 1995 there was not the increase in wide web machines that was expected. However, this is anticipated to be a temporary setback. Growth of UV-curable inks was about 25% in 1995, with growth in both offset and flexo applications.

Electronic/Opto-Electronics

Photo-resist materials and optical fiber coatings are two examples of applications in which "special properties" have been responsible for the adoption of photo-curable materials. In the early stages of development, optical fibers were coated with two-component, heat-curable silicones with line speeds of about 2 m/sec, using ovens as hot as 600 deg C. Using UV-curable coatings, line speeds have been increased to 10-20 m/sec using "ovens" of about the same length.

Photo-resists make possible the manufacture of integrated circuits using positive or negative photo-resists to transfer circuit patterns, which are later etched and plated, forming very thin, small, compact circuits in a stepped manner. The photo-resist process is vital to manufacturing, and the technology has become so complex and specialized for the semiconductor market that this use of radiation curing is generally not considered to be part of the UV/EB-curable market.

Water-Reducible Products

Water-reducible, UV/EB-curable formulations have been developed for a number of markets. Water dilution of a compatible resin system provides lower viscosity; application of thinner films; improved flow and leveling; lower applied costs; and reduction/elimination of monomers and solvents.

This technology is being directed toward numerous applications, including flexo and gravure inks. The use of water as a viscosity reducer can minimize or eliminate the use of lower-molecular-weight diluents that tend to be skin irritants. Some work has indicated that small amounts (1%) of water can reduce the viscosity of oligomers substantially, and larger amounts of water can be used as a formulation tool to vary gloss and reduce web temperatures in critical applications.

Disadvantages include the time/energy required to remove any added water, as well as the effects of water on the drying/curing system and the substrate to which it is applied. If cured before the water is fully evaporated, film properties will be reduced.

Motivators for Use

UV and EB curing applications are still referred to as niches of specialty businesses, and there remain very few markets using more than 1,000 tons of product per year. Nevertheless, the advantages of UV curing lead many users into successful and often extremely profitable applications. Although the cost per kg of these products is usually higher than that of the conventional products they replace, the overall applied cost per unit is almost always lower, and new products are often made possible, as UV/EB-curable products provide properties not otherwise achievable with conventional materials.

Much has been said about the "green advantages" of UV/EB curing. While it's true that the curing emits little volatile organic compounds (VOCs) to the atmosphere, and it is energy-efficient, the motivators driving increased use are more often related to lower unit costs, which include faster production rates, rapid curing at near-ambient temperatures, and less required space.

However, it must be noted that in the past three years there has been a great deal more active interest in using UV/EB-curable materials in order to meet the ever tightening regulations regarding the emission of VOCs.

While many of the barriers to the use of UV/EB-curable materials have been overcome or eliminated by the thousands of successful users of the technology, prospective users must study the limitations - and determine how to eliminate them - before they can make a successful switch in technology.

Costs

When evaluated on a cost-per-liter (gallon, kg, or pound) basis, UV/EB-curable raw materials and formulated products are almost always more expensive than their conventionally cured counterparts. The cost premium is the result of several factors:

* Materials are generally purchased without solvent, i.e., high solids;

* Volumes are lower (specialty products);

* There is minimal economy of scale;

* Manufacture of monomers and oligomers is a relatively complex, multistage, batch process;

* There is less competitive intensity;

* It is a newer technology and not fully depreciated;

* There is a higher research and development cost component per unit sold.

The panel believes that the cost differences will moderate but will continue to remain higher than most alternative technologies. However, applied costs of UV/EB-curable products are already competitive for many applications.


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