Nonporous plastic and foil films used in flexible packaging applications provide adhesive manufacturers with a host of challenges as adhesion to the low surface energy materials is often difficult to achieve. In addition, heat seal adhesives must be flexible and durable enough to move with the packaging and withstand distortion of the flexible packaging. Proper resin selection when fromulating a heat seal adhesive is key to maximizing the performance of flexible packaging and overcoming the challenges mentioned above.
Selecting an Adhesive Resin
There are many things that must be considered when selecting a resin for a heat seal adhesive formulation for flexible packaging applications.
Film / Foil type that is to be bonded
How the adhesive will be applied
The required bond strength and preferred failure method
The material being packaged
What type of environment the package will be exposed to
When formulating a heat seal adhesive, care must be taken to select a resin or combination of resins that optimizes the performance of the adhesive based on the end use requirements of the packaging. For example, if a package will be exposed to high heat, the adhesive that seals that package must also be able to withstand those temperatures.
Elvacite® 2044 is the softest, most flexible butyl methacrylate resin available and is preferred for most adhesive applications including heat seal adhesives. Elvacite® 2044 is particularly well suited for bonding polyester films, mylar, polystyrene, and other nonporous plastic films and foils. The starting point formulation listed below is recommended for trial as a heat seal adhesive for polystyrene film to aluminum foil.
The starting point formulation listed above should be prepared by dissolving the vinyl chloride-acetate resin and Elvacite® 2044 in MEK and then diluting with Toluene to the target solids level.
An average peel strength of 500 g/in was measured for this heat seal adhesive. To test peel strength, this formulation was applied with a 1.5 mil Bird application to 1 mil, uncoated, zero-temper, soft aluminum foil. It was air dried for 3 hours and then heat sealed to 4 mil oriented polystyrene film at 250°F under a pressure of 77 psi for 1.5 seconds. Peel strength was then determined for 0.5 in strips on an Instron tensile tester at 2 in/min cross-head speed.
Blending two or more resins in an adhesive formulation is often necessary to achieve optimal performance.The Elvacite® butyl methacyrlate resins are compatible with many other common resin types used in adhesives including epoxy, rosin derivatives, vinyl chlorides, and many others. Elvacite® 2044 and the other butyl methacrylate grades, Elvacite® 2045 and 2046, are often blended with other resins used in heat seal adhesive formulations to provide improved flexibility, adhesion, and toughness.
When formulating a heat seal adhesive, resin selection is of the utmost importance. There are many options available to a formulator that vary in chemistry and performance. Ultimately, resins should be chosen that optimize performance of the adhesive and ultimately the packaging it is being used to seal. Acrylic resins like Elvacite® provide unique benefits to a heat seal adhesive formulation including:
Outstanding adhesion to high slip, nonporous films and foils