Hot Melt Adhesive Vs EVA
Carton closure hot melt packaging hot melt adhesive using ethylene vinyl acetate (EVA) polymer systems have been used for decades due to their availability, formulation latitude and performance attributes. Packaging adhesive formulations typically contain polymer, tackifier resin and wax.
Packaging adhesives using EVA can be formulated using a variety of tackifier systems, including rosin esters, hydrocarbon resins (C5, C9, C5/C9), terpene resins and hydrogenated hydrocarbon resins. However, for premium packaging adhesive applications where clarity, thermal stability and temperature resistance are critical, EVA-based packaging adhesives are often formulated with hydrogenated hydrocarbon tackifiers.
The hot melt adhesive industry has recently trended toward high-quality packaging adhesives due to cost benefits and improved performance characteristics. This has prompted the development of aromatic pure monomer resins (PMRs) as synergetic tackifier additives for EVA-based premium packaging adhesives.
PMRs are produced from pure aromatic monomer streams, especially styrene and alkyl styrene derivatives. Compared to other aromatic crude C-9 resins, major advantages of PMRs include light color (water white), excellent thermal stability, temperature resistance (similar to hydrogenated hydrocarbon resins) and controlled molecular weight.
In this study, the effect of different PMRs and their benefits in performance attributes when used in premium EVA hot melt packaging adhesives are described. It was determined that packaging adhesives containing PMRs can effectively improve adhesive and cohesive performance characteristics while maintaining other performance attributes of the adhesive. PMR-containing adhesives also exhibit good thermal stability and temperature resistance.
Typical properties of selected hydrogenated hydrocarbon resin and PMRs are an average of typical samples and should not be interpreted as product specifications. For this study, a packaging adhesive control formulation was prepared with a hydrogenated hydrocarbon resin. Four different PMRs with hydrogenated hydrocarbon resins were evaluated at two different addition levels (4.5 and 9 wt %).
These formulations were prepared using an in-can mixer with mechanical agitation (a paddle-type agitator controlled by a variable speed motor) in pint-sized cans with a heat block set at 177°C. The polymer and antioxidants were introduced into the can and heated up to 177°C under a nitrogen blanket. Resin followed by wax was then introduced into the can after the polymer was melted. This was agitated for 30 min until the mixture was completely homogenous.
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