Adhesives Magazine

Measuring Success

November 1, 2006
Eco-efficiency analysis illustrates the benefits of ultraviolet-cured adhesives

One advantage to BASF's acResin UV-cured PSA is its clean removability.


Scheme 1. UV-Curable acResin

Following the devastating effects of Hurricanes Rita and Katrina, government, businesses and consumers are paying closer attention to the environmental impacts of the products that they buy; they are also enacting stronger environmental protection legislation. The pressure-sensitive adhesives (PSAs) business has been - and continues to be - affected by growing environmental concerns, particularly because the U.S. EPA (under the Clean Air Act amendments) regulates it. This business climate means that well-designed PSAs with smaller environmental footprints have competitive advantages in the marketplace and limited liability. Environmentally superior products are popular with consumers who have a "go-green" attitude, which facilitates market entry and success. Furthermore, environmentally superior products help minimize risk by being better situated for the next round of regulation. Many consumers consider environmental impact as a key piece of their buying decision, and the environmental component continues to grow increasingly important. To investigate PSA business options, BASF used eco-efficiency analysis (EEA) and quantified the costs and environmental impacts associated with the production and application of UV-cured - as well as thermally dried - solvent- and waterborne PSAs. The results, which illustrate the benefits of acResin®, a BASF UV-cured PSA, have been used to guide marketing, product development and strategic decisions.

The EEA performed considered the production and application of the three types of PSAs under review, which are all special types of adhesive designed to bond without the use of heat or moisture. They are used in a variety of consumer and commercial products, such as masking tapes, office tape, and labels, and continue to gain market share from mechanical fasteners. PSAs also have specialized industrial applications, such as clear protective films on appliances and automobile components, reflective material on signs, and bonding a variety of similar and dissimilar surfaces, either permanently or temporarily. The adhesives are formulated to meet a specific cost/performance balance through the choice of an elastomer or polymer and other materials, such as tackifying resins, additives, fillers, colorants, and oils. The general categories of elastomers and polymers used in PSAs include natural and synthetic rubbers, acrylics, and silicones. In some cases, more than one resin is used to provide additional properties not available to the single resin formulation (to simplify the EEA study that was conducted, only acrylic resins were considered). Carrier solvents and other additives such as rheology modifiers, defoamers, and stabilizers, are used to influence processing and coating behavior.

Scheme 2. Solvent Acrylic

The application of PSAs is heavily influenced by the solids content and carrier. UV-curable PSAs are extruded with the application of heat directly onto the substrate material (the web), and then UV lamps are used to cure the adhesive, leaving the adhesive on the web. The waterborne dispersion (45% water by mass) is directly applied to the web and then dried to remove the water. The solventborne PSA (53% solvent by mass) is directly applied to the web; the solvent is evaporated through a thermal drying and the vapors are thermally oxidized to meet air regulations. The full processes are summarized in the Schemes 1-3.

Scheme 3. Dispersion Acrylic

Solventborne PSAs use a variety of organic solvents that may include toluene, heptane, MEK, xylene and mineral spirits as solvent carriers, which yield liquids that are easily transported and applied. However, these solvents are flammable liquids that have significantly increased in price in recent years; despite this, they continue to be used in large volumes by the pressure-sensitive tapes and labels sector. In addition to fire and explosion hazards, the U.S. EPA considers them to be volatile organic compounds (VOCs) that can contribute to ambient air quality problems and are, therefore, regulated under the Clean Air Act. Toluene, MEK and xylene are further classified as hazardous air pollutants (HAPs) that can cause adverse health effects. VOCs and HAPs are emitted when solventborne coatings are stirred, applied to the web, and when they dry. The U.S. EPA has additional regulations under development for the Clean Air Act Amendments that will significantly affect the use of HAPs and VOCs by the pressure-sensitive tapes and labels sector.

Figure 1. Eco-Efficiency of PSAs

Eco-Efficiency Methodology and Base Case

Eco-efficiency analysis evaluates the costs and environmental impacts of products and processes over their lifecycle.1 This EEA assessed energy, emissions, toxicity, health effect potential, resource consumption and land use to gauge the environmental impacts of the three different PSAs. The EEA also assessed the total cost of producing and applying PSAs by calculating the cost of materials, manufacturing, waste, energy, and EHS programs. The methodology was created in partnership with an external consultant, has been further developed by BASF, and is based upon the ISO14040 standards for lifecycle analysis, with some additional enhancements that allow for expedient review and decision-making at all business levels. Since its inception in 1996, BASF has completed more than 260 analyses on products ranging from vitamins to building materials and industrial chemicals.

This EEA was focused solely on one type of polymer - acrylics - rather than comparing different types of chemistries. Remaining within the same polymer family discourages potentially uneven performance comparisons and allows the desired focus on the processing differences as a result of the carriers. Furthermore, the study compared UV-curable, solventborne- and waterborne acrylic PSAs slanted toward the specialty performance realm rather than commodities like packaging tape and general-purpose permanent label PSAs.

After having determined the system boundaries (see Scheme 1), the first step was to define the common output or customer benefit (CB) for a uniform measurement of the production and application for each PSA alternative considered. For this EEA, the CB was defined as the application and curing of an acrylic adhesive onto one square meter of web surface. The three acrylic adhesive technologies are shown in Figure 1. The study encompasses the production, transportation, coating/application, drying and finishing of the PSAs.

Table 1. Summary of Assumptions for Base Case

Table 1 summarizes data inputs into the analysis of the base case, which included coating and curing processes, transportation, product use, and disposal. For the base case, the environmental impacts and costs were analyzed for the production of 1 m2 of web with a dry coat weight of 20 g/m2 and coating width of 0.8 m, normalized to a total annual production of 76.8 x 106 m2 with a 5% material loss multiplier. No capital investments were included since this study compared costs of using the adhesives and not startup costs. Also, supply-chain costs were assumed to be captured in the purchase price of the adhesives.

Material prices for the three technologies were based on drum amounts in truckload quantities (price represents adhesives with similar performance, i.e., high-end specialty and low-end commodity prices were omitted). Abatement of VOC vapors was handled via a thermal oxidizer (TO), which was based on a recuperative system with a 35% heat recovery and the following operational parameters: process air flow of 30,000 SCFM; process temperature of 200

Table 2. Total Cost of Ownership for Production of 100m2 of Coated Web

Total Cost of Ownership

One advantage of the TCO tool is the ability to make real-time changes to the input parameters. In the following example, the analysis was scaled to reflect the application and curing of 100m2 of PSA onto the web. In this example, the benefits of the UV-cured acResin were demonstrated in reduced energy costs and higher line speeds, which resulted in lower manufacturing costs and increased annual production. The total cost of using the three adhesive technologies was assessed under the conditions of the base case, and included costs for materials, manufacturing, waste, energy, and EHS programs. The results, shown in Table 2, demonstrate that the acResin adhesive has the lowest total cost of ownership, with a 50% cost savings when compared to the dispersion adhesive, and a 30% savings compared to the solventborne adhesive. Energy was a significant differentiator in the cost model. The results show that the acResin process uses more electricity than the other two processes during adhesive preparation, coating, curing and finishing; however, natural gas consumption for the solvent and dispersion during drying and solvent incineration results in higher overall costs for those two technologies. The benefit of the UV-cured acResin is elimination of natural gas consumption for VOC vapor abatement via a thermal oxidizer, which reduces energy consumption by 99% when compared to the dispersion-based adhesive while simultaneously doubling production.

Even though the price per kg as supplied for the acResin adhesive was higher than the solvent or dispersion technologies, the total material cost per 100 m2 of coated web is similar (within 4%) due to higher solids content. The cost for silconized paper and OPP film was the same for all three adhesives. Analysis of manufacturing costs and waste costs showed that the acResin adhesive had lower ownership costs. Labor and operation and maintenance costs were lower due to the faster line speed that results in a higher annual production (m2/yr) and a subsequent lower cost per (100 m2). The acResin process has a line speed of 200 m/min, which produces 20% more coated web annually compared to the solvent process, and 100% more than the dispersion process. The waste costs for the solvent and dispersion adhesives were higher, when compared to the acResin, due to disposal of solvents and wastewater treatment for the dispersion adhesive. Overall, the solvent and dispersion processes are 30% and 50% more expensive than the acResin process, respectively.

Figure 2. Ecological Fingerprint of PSA

Environmental Impacts

Figure 2 shows the relative environmental impact of the PSA in six environmental categories. The most significant differences occur in emissions, energy and resource consumption, land use, and risk potential. The overall health effect potentials for the PSAs are similar.

Figure 3. Energy Consumption

The greatest environmental benefit of UV-cured adhesives is the outstanding efficiency of the curing process. Figure 3 shows the individual energy consumption data megajoules/CB (or MJ/CB), which are summarized on the ecological fingerprint.

Figure 4a. Global Warming Potential

The thermally dried solvent and dispersion adhesives have longer, more energy-intensive curing processes, which consume large quantities of natural gas and result in correspondingly higher environmental impact, utility cost, and longer production times. The primary emissions impact of the longer cure is found in the air emissions. Figures 4a-b show the global warming (GWP) and photochemical oxidant (i.e,. smog) creation potentials (POCP) for the alternatives, respectively. The thermally dried adhesives have the highest GWP, due to the natural gas produced and used for drying.

Figure 4b. Smog Creation Potential

The complete eco-efficiency portfolio consolidates all the individual environmental and economic results into one representation, allowing for an overall picture of which products have the least cost and lowest environmental impact. The most eco-efficient products lie in the upper right-hand quadrant, which corresponds to the lowest environmental and cost impacts.

Figure 5. Eco-Efficiency Portfolio for PSA

Figure 5 shows the portfolio for production and application of 1m2 of a PSA onto a web. The UV-cured acResin adhesive is the most eco-efficient; due to the more-efficient curing processes, they have less overall environmental impact and lower costs than the thermally cured solvent and dispersion adhesives. Also not included in the diagram is the increased revenue generation due to the twofold increase in production.

Conclusion

Environmental concerns are a growing force in business, and the PSA business is no exception. In order to stay competitive, products have to fare well both economically and environmentally. BASF performed an extensive investigation into the PSA business through an eco-efficiency analysis. The analysis revealed that UV-curable PSAs are the best alternative in that they are the lowest cost, have the least environmental footprint and are the best situated to handle stricter air regulations. When the analysis is conducted at higher coating weights typical for PSA tapes (80 g/m2, for example), the acResin products have an even greater positive picture. Having completed the study, BASF has begun marketing the product with a strong emphasis on the low environmental impact, and the company continues to research new products and improvements to its patented class of UV-curable PSAs.

For more information, visit BASF Corp. at BASF Corp.