In the 1970s, one of the first major energy crunches occurred, spurring the development of solventless adhesive technology for packaging to replace the commonly used solvent-based adhesives. The same issues exist today: high energy costs, high raw material costs, higher labor costs, environmental concerns and the need to supply finished and safe laminate in ever shorter time.
The current state of solventless adhesive development favors all of these issues. While converters are paying more for energy and raw materials, retailers and consumer product goods manufacturers are trying to drive prices down. There are many advantages to using solventless adhesives today, based upon the current economic and reglulatory conditions.
Relative Costs
The adhesive is the least costly part of the lamination construction, between 1 percent and 5 percent of raw material cost (substrates, inks, coatings) but involves the most costly wastepoor adhesion, or lack of performance in the intended use, usually results in total scrap of the construction. When the cost of the competing adhesive types, solvent-based, water-based and solventless, are compared, there is a clear advantage for solventless. Table 1.
The solventless adhesive also has some cost advantage simply due to applied weight. Solventless adhesive is generally applied at lower weight on average. Table 2.
Machine Requirements
Solventless adhesives require a dedicated coating head, consisting of three or four smooth application rolls for the adhesive. A conventional gravure, offset gravure, or flexographic coating system can not be used effectively. In addition, superior tension control of the substrates is required due to low bond and low shear of the solventless adhesive. Current dedicated solventless machines cost much less than similar laminators dedicated to water or solvent based adhesives, or a combination of solventless/water/solvent based with interchangeable coating heads. Table 3.
Energy Efficiency
Over the last five years, the cost of natural gas has increased 50 percent and the cost of crude oil has increased by more than 246 percent (U.S. Energy Information Administration). In todays economy, there is more to the cost of an adhesive than just the delivered cost to the converter or energy consumed to use it. There is also the need to consider the Life Cycle Inventory (LCI). This is an analysis of the energy required to make and use an adhesive, as well as water consumption and carbon dioxide emissions associated with manufacture and use of an adhesive.
Chart 1 compares the energy LCI of the various adhesive types and shows much lower energy consumption for solventless adhesives. Note that energy used for transportation is much lower for solventless because fewer drums are shipped. This also means the converter uses less warehouse space, and has fewer drums to handle/dispose of/recycle.
Product Categories
Adhesives encompass the categories of general purpose (low demand/low performance), medium performance (demanding bonds and performance) and high performance (elevated temperature and specialty/aggressive content performance). Current solventless adhesives cover the full range of lamination use, having the capability to be used in place of water based and solvent based adhesives. Solventless adhesives can be used across all the current substrates commonly used in packaging. Table 4.
Currently, available solventless adhesives cure more quickly than older versions without the need for energy cure assist, extended hot room acceleration cure, special handling and equipment. Chart 2 details bond development of select solventless adhesives.
FDA Regulations
For food packaging adhesives, there are very specific regulations in Title 21 of the Code of Federal Regulations (CFR) under parts 170 to 199, under the Food and Drug Administration (FDA). Of the many parts, the three that are most pertinent are:
- Part 175.105 - Adhesives (for use up to 120 F).
- Part 177-1390 - Laminate structures for use at temperatures of 250 F and above.
- Part 177.1395 - Laminate structures for use at temperatures between 120 F and 250 F.
A reputable solventless adhesive supplier will list the FDA Regulations to which the adhesive complies, as well as appropriate recommendations for intended use to ensure safety in the packaging for food supply. Table 5. 
