Hot Melt Adhesives
When evaluating the economics of implementing an alternative adhesive technology, a full range of applicable factors must be taken into account. Conventional tools used to analyze and compare costs and benefits of alternatives leave out a number of important cost factors, such as environmental compliance and future liability. Costs that must be considered for a complete analysis include raw adhesive purchase and transportation; capital equipment; energy consumption; production rates; operator efficiency; and regulatory compliance.
Raw Adhesive Purchasing Costs/Transportation Costs
The purchase prices of hot melt adhesives tend to be more expensive than solvent-based materials. Comparing initial purchase prices, however, does not provide a complete cost picture. Hot melt adhesives are 100% solids and the entire volume is used as an adhesive, while typical adhesives lose 50-70% of their volume during application. A more accurate comparison looks at the raw adhesive purchase cost expressed in pounds of dry solids and the coating thickness yielded per pound. Pound for pound, hot melt adhesives yield more than twice as much coating thickness as solvent-based adhesives. (Ref. 6)
Once the adhesives are purchased, there are transportation costs. Hot melt adhesive freight costs are lower than solvent-based adhesives freight costs, due to the reduced volume of adhesive needed; thus, less hot melt adhesive is purchased and shipped. (Ref. 6)
Capital Equipment Costs
The National Risk Management Research Laboratory published an analysis comparing capital costs of solvent-based and hot melt adhesive systems. This analysis showed, in 1994 dollars, that capital costs for hot melt systems were 50% to 70% less than conventional solvent-based adhesive systems. (Ref. 6) This cost analysis included the need for pollution control equipment for solvent-based adhesive production systems, which are not necessary for hot melt adhesive systems.
Manufacturers considering a switch to a hot melt system must take into account not only the costs of capital, but also operational costs. These operational costs include production costs, energy costs, and regulatory costs, and although they are discussed separately below, these costs often overlap with one another. In addition, overhead operational costs for hot melt adhesives may be lower than costs for solvent-based adhesives due to a reduction in insurance costs, since the risks associated with the solvents are essentially eliminated. (Ref. 6)
One primary advantage that hot melt systems have over solvent-based adhesives is in the curing time of the adhesives. Cure times for hot melt systems are measured in seconds, compared to minutes or hours for solvent-based systems. This is an especially important factor when producing high volumes of products at high speed. Hot melt systems have additional production advantages in terms of floor space and labor requirements. Although the production run of the hot melt system is faster, it is necessary to remember that there will be an initial, one-time production cost resulting from downtime for new maintenance procedures and training.
Table 4 compares average production speed, floor space consumption, and operator requirements for hot melt and solvent-based systems.
Table 4(Ref. 6)
Approximate Productivity/Efficiency/Floor Space Comparisons of
Solvent-based Systems and Hot Melt Systems
Solvent-Based Hot Melts Speed (ft/min) 750 1,800 Length of production line (ft) 150 40 Operators 3 to 4 1 to 2
Although there is little specific data, the literature reports that hot melt adhesive systems have a general energy cost advantage over solvent-based adhesive systems. This is most likely the result of avoiding the costs of operating large drying and curing ovens and pollution control equipment, such as solvent recovery equipment or incineration equipment, both of which are necessary for solvent-based systems. Not having ovens and pollution control equipment avoids the installation and maintenance costs of these systems as well.
By greatly reducing or eliminating emissions of HAPs and other VOCs, hot melt adhesive technologies offer significant savings in avoided emission control equipment costs, permitting fees, and hazardous waste disposal charges. There are also reductions in monitoring costs, since the hot melt systems do not require the stringent monitoring of employee exposure to solvents, or the explosive limits of those solvents.
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