Barriers to the Use of UV and EB Technologies

Transcription

1 This paper has been reviewed in accordance with the US. fnvironmentd ProIection Agenws pm and adninistrative review policies and approved for presentation and publication Barriers to the Use of UV and EB Technologies Carlos M. Nufiez US. Environmental Protection Agency National Risk Management Research Laboratory Air Pollution Prevention and Control Divison Research Triangle Park, NC and William L. Blake, C. Jeff Harris, W. Scott Snow, and Jill B. Vitas TRC Environmental Corporation 6340 Quadrangle Drive, Suite 200 Chapel Hill, NC

2 ABSTRACT Surface coating is the process by which paints, inks, varnishes, adhesives, or other decorative or functional coatings are applied to a substrate (e.g., paper, metal, plastic,.wood) for decoration and/or protection. This can be accomplished by brushing, rolling, spraying, dipping, flowcoating, electrocoating, or specialized combinationdvariations of these methods. The substrate and the coating formulation arc two important factors that influence the selection of a coating application process. Once the coating is applied, it is cured or dried using thermal energy or radiation energy in the form of ultraviolet 0 and electron beam (EB). This paper briefly discusses technical, economic, and educational barriers to rahation-curable coatings in each of the three industries studied. 3-4

3 a BACKGROUND AND PURPOSE In support of the Pollution Prevention Act, the Source Reduction Review Project (SRRP), and Maximum Achievable Control Technology (MACT) standards development, EPA's Air Pollution Prevention and Control Division (APPCD) is investigating pollution prevention opportunities for product and material substitutions that help industry to reduce wastc.iz Radiation-curable coatings have been demonstrated to reduce pollution in several specific end-use categorie~.~"~ There are two types of radiation curing processes currently in use: ultraviolet (W) curing and electron beam (EB) curing. W-curing equipment consists of a w lamp suspended above the coated substrate, a light reflector, a radiation shield, and a cooling system. The W-curable coating contains a photoinitiator which initiates the polymerization of the coating to the substrate when exposed to W light. In the EB-curing mechanism, an electron beam excites the electrons in the coating and causes them to crosslink without the aid of photoinitiators. ADHESIVE-COATED AND LAMINATED SUBSTRATE "WFACTURING This industry is the largest source of methyl ethyl ketone and third largest source of toluene emissions.6 Technical Barriers3 Raw material availability and the sensitivity of the curing process to the characteristics of :he coating and the substrate are major barriers. W energy does not penetrate thick,-dark, or colored coatings well, leaving much of the coating uncured. EB electrons cure 100% of solid adhesives, allowing it to be used on a variety of substrates. Many substrates are sensitive to beat and chemical elements making it necessary to modify conventional UV lamps. Since heat is not a concern in EB-curing, it can be successfully used with heat-sensitive substrates. Economic Barriers' Capiral Costs: Information provided by a supplier of EB-curing and thermal machinery indicates. that solvent-based systems (not including emissions control equipment) have higher investment costs. For retrofit, a facility would need to add the EB-curing mechanism; however, a German manufacturer stated that W-curing mechanisms are more affordable than EB systems. Operating Costs: Raw material costs are the primary operating cost for any adhesive coating manufacturer. On an applied-solid basis, the cost of W adhesives is approximately the same as the cost of conventional rubber-based adhesives. The cost of EB adhesives, however, is about 33% more. In the case of conventional acrylic-based adhesives, UV and EB adhesives cost 50% and 888 more, respectively. EB-curable adhesives are best suited for products which require thick coating weights, where they outperform the other conventional and W-curing technologies. 3-5

4 Educational Barriers' The cost of newly installed radiation-curing equipment should approximate that of new thermal-curing machinery without control equipment. The productivity of the radiation-curing equipment exceeds that of the thermal system, resulting in lower costs and higher profits. Employees must be trained to properly handle these coatings. Although non-hazardous, radiationcurable coatings can cause allergic responses. METAL CAN MANUFACTURING This industry emitted over 16,000 tons (14,500 tonnes) of air pollutants in Technical Barriers' ' Product Perfonname: The product performance problems of ink pick off, poor abrasion resistance, yellowing overvarnish, and off-shade whites were experienced. The W-curable coatings used by Coors Brewing Co. achieve a level of abrasion resistance high enough to meet the standards of other can manufacturers. Another barrier is the lack of an FDA (Food and Drug Administration)-approved W- curable coating for direct contact with food, including beverages. Ball Corporation claimed that * components of the exterior W-curable coatings migrated to the interior of the cans after the cans exited the W-curing oven. However, Coon conducted 3 months of analyses using Fourier Transform Infrared technology and gas chromatography/infrared detection instruments and found no volatile components from exterior inks or coatings on the internal coating of its cans. Tests have shown a loss of coating weight in the internal coating ovens, indicating that waterbased external coatings also may have a migration problem. Healrh and Safev: Through recent advances in monomer chemistry, hazards associated with radiation-curable coatings have decreased significantly. There are concerns with human skin becoming sensitized when in direct contact with radiation-curable coatings, and workers are required to wear appropriate personal protective equipment. Economic Barriers' Capital Invesmenr: The most common deterrent, when initially considering a W-curing system, is capital cost. However, when adding additional capacity, a plant may consider a W-curing oven because the thermal system is a larger capital investment. The can manufacturing business operates on low margins and high volume. Therefore, line speed is a critical element to be considered when evaluating new technologies., Material and Operating Costs: For Coors Brewing Co., the energy savings from its UV-curing oven compensated for the higher price of W-curable materials. However, due to increased material consumption and, therefore, increased costs, the Wcuring alternative was not economically feasible for Ball Corporation. Another cost barrier is the availability of materials because ink suppliers consider UV-curable products to be a "specialty" line with a limited market. Coors believes that, if other can manufacturers used these products, material costs would fall. I 3-6

5 Educational Barriers' One of the most pressing barriers involves the perception of the word "radiation." Although UV-curing ovens harness radiant energy used to cure the coatings, many people are still hesitant about using such equipment. Another perceived problem is worker sensitization to acrylate compounds in the inks and coatings. A previous difficulty that has since been overcome involves oxygen inhibition. Molecular oxygen would react with free radicals in the coating, forming a peroxide. The reactions would deplete the number of free radicals available for polymerization during the curing process, leading to incomplete curing. Coors suppliers have resolved the oxygen inhibition problem through i-mproved coating formulations. Many industry personnel believe that W systems are not cost effective; however, the capital expense for a UV-curing oven is no more than for a new thermal line. Studies indicate that W curing oven maintenance and energy costs are less than those for thermal systems. Increase of raw materids costs may be offset by savings in emissions fees due to fewer releases of volatile organic compounds and hazardous air pollutants. COMMERCIAL PRINTING Commercial printing accounted for over 1,300 tons (1.180 tonnes) of total air releases in This paper focuses on wide-web flexographic printing and screen printing Flexographic Printing Flexographic printing is the leading printing process in the packaging industry and is gaining ground in other segments of the printing industry, including newspaper and book printing. The focus of this section is on wide-web flexography, typically defined as flexographic printing on substrates that are 36 in. (91 cm) wide or wider. Materials Availability. W-curable flexographic'inks have only recently been commercially produced. One major concern is meeting the FDA criteria for direct contact with food. Manufacturers are working with FDA to develop W-curable inks that meet FDA criteria. Product and Ink Pe$ormance. Print quality, the most important property in printing, is determined by several parameters, such as color density, adhesion to substrate, and dot gain. Except in glossy printing, W-curable inks perform as well as or better than solvent-based inks. Health and Safev. Recent advances in monomer chemistry have significantly reduced the ' hazards associated with W-curable flexographic inks. The monomers have a high molecular weight which reduces volatility and removes almost any danger associated with vapor inhalation. 3-7

6 There are concerns with human skin becoming sensitized when in direct contact with W-curable flexographic inks, Also, the potential exists for the ink to be slightly undercured leaving a residual odor as well as residual unreacted monomers on the~printed product. Together, industry and the EPA are working to develop an acceptable maximum residual monomer level. Economic Barriers The primary economic barriers to switching to Wtured flexographic printing are the capital cost of new equipment and ink costs. Most Wcurable inks are comparable in price to solvent-based inks on a cost per unit area covered basis. However, white UV-curable inks are more expensive than any other W-curable inks, while white solvent-based inks are the cheapest. Educational Barriers The Print Manager at a German firm using W-curable flexography noted that about 3 to 4 weeks of on-the-job training is required to train a standard solvent-based press operator operate a W-cured press. Screen Printing The best known application is printing designs on textiles; however, screen printing is also used on numerous non-textile substrates; e.g., point-of-purchase advertising material, fleet graphics, specialty decorations, and fine art. Use of UV-curable inks offers substantial economic, process, and environmental benefits including: (1) reduction in required floor space - large hot-air dryers and drying racks are unnecessary ;(2) increased throughput -- drying is essentially instantaneous; (3) reduction in health and safety hazards for workers exposed to screen printing inks; and (4) reduced cost per unit area printed (UV-curable screen printing inks are applied in thinner layers). Technical Barriers Because of curing difficulties, it is necessary to use inks which achieve the proper opacity with a thin layer of ink. Substrates with deeply textured surfaces may present barriers to screen printing with UV-curable inks. Ink in the deep recesses of surfaces not exposed to sufficient light may not cure properly, resulting in poor adhesion of the ink layer to the substrate. W- curable inks do not stand up well to finishing procedures after printing, such as die-cutting and molding. Another banier is the lack of FDA-approved UVcurable inks for packaging that contacts food. Many signs and labels must withstand extended outdoor exposure or harsh industrial environments. One of the largest markets of this type is fleet graphics, or the large signs that are placed on the sides of tractor-trailer trucks. W-curable inks are not capable of meeting the expected standard of a 6- to 7-year ink life. I Economic Barriers Many U.S. screen printers are medium- to small-sized shops, employing less than 50 people and can not afford the capital investment required to converto W-curable inks. A shop 3-8

7 with only one or two production lines would lose a significant percentage of its production capacity during conversion. Benefits of larger printers may not be realized in printing small runs on semi-automatic presses. Educational Barrier8 Although the Screen Printing Association International provides information on UVcurable materials, the availability of the information to small shops may be limited. CONCLUSIONS Many barriers must be overcome before radiation-curable coatings can penetrate the industry categories discussed. Many of the barriers Similar ~C~OSS the categories so that the improvements may be &sferred from one' industry category to another. EPA is developing the Adhesives Alternatives Guide (AAGE), which will provide facilities with a computerized system to assist in the evaluation of alternative adhesives. Working through the Design for the Environment Program, EPA is investigating alternative iaks for flexographic printing REFERENCES Pollution Prevention Act of 1990,42 U.S.C. $ et seq. U.S. Environmental Protection Agency. Source Reduction Review Project. Office of the Administrator, Pollution Prevention Policy Staff, Washington, x. EPA- loo/r March Vita, J.B., G.D. McMinn, and W.L. Blake, Jr.. Evaluarion ofbarriers to the Use of Radiarion-Cured and Hor Melr Coarings in Coated and Laminated Substrate' Manufacturing, EPA-600/R (NTIS PB ), U.S. Environmental Protection Agency, Research Triangle Park, NC, March McMinn, B.W. and S.R. Church, Evaluation,of Barriers to the Use of Radiarion-Cured Coarings in Can Manufacruring, EPA-600/R (NllS PB lo), U.S. Environmental Protection Agency, Research Triangle Park, NC, April Harris, C.J., and J.D. Winkler, Evaluation of Barriers to the Use of Radiarion-Cured Coatings in Screen Printing, EPA-600R (NTIS PB f;U.S. Environmental Protection Agency, Research Triangle Park, NC, April U.S. Department of Health and Human Services, Toxic Chemical Release Inventory Database. National Institutes of Health, National Library of Medicine. Bethesda, MD. Toxicology Information Program Online Services TOXNET@ Files

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9 ABSTRACT ENVIRONMENT AND TECHNOLOGY TEAMED FOR ECONOMIC SUSTAINABILITY by K. P- MST Great Lakes Manufacturing Technology Center (GLMTC) 4600 Prospect Avenue Cleveland, OH : Emphasis of waste minimization methodologies merged with advanced technologies to improve both the environment and the bottom line. Proactive activities in pollution prevention require commitment and vision much like the commitment to develop and implement new and emerging technology. This is'a Case of the * linking of both environmental focus and advanced technology to produce not only an environmentally sound practice but an economically advantageous one. A waste reduction assessment was conducted at a medium-sized producer of specialized screen printing products. The company occupies about 40,000 ft2 (3,700 m2) and employs 200 people. The sclf-adhesive products are used for identification, decorative trim, and screen printed circuitry for electronic products. With programs in place to produce products with little or no solvent content and efforts to reduce production wastes, the company actively began to implement opportunities identified in the assessment. The aggressive engagement to implement these opportunities has provided realized savings large enough to improve profits by $188,000 per year. These opportunities were found in changes in cleaning procedures for silk screens, the deployment of ultraviolet curable inks, and the development and use of waterbased adhesives and inks. The work described in this paper was not funded by the US. Environmental Protection Agency. The contents do not necessarily tdlect the views of the Agency and no off icid endorsement should be infared

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