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    Bonding Packaging Films

    Nowadays, many consumer goods in are packaged in formats such as flexible packaging that require the use of adhesives. These adhesives, specifically called "laminating adhesives" play a role in the construction of flexible packaging by bonding films and foils together that each impart functional properties to the package.  Some examples of these properties range from serving as an oxygen and moisture barrier to being a receptive substrate for printing inks to facilitating the final sealing of the package.    

The nonporous plastic films and metal foils used in these flexible packaging applications, however, tend to be made of low surface energy materials.  This causes a host of challenges for laminating adhesive manufacturers when applying their adhesives to these materials.


On top of that, laminating adhesives must be flexible and durable enough to maintain their bonds throughout any distortion of the packaging encountered during customer handling.  Proper resin selection when formulating a laminating adhesive is thus key to maximizing the performance of flexible packaging to overcome these challenges.  

Selecting an Adhesive Resin

Several factors must be considered when selecting a resin for laminating adhesive formulation for flexible packaging applications:  

 

  • Specific film/foil material that is to be bonded
  • How the adhesive will be applied
  • The required bond strength  
  • The type of goods being packaged
  • The type of environment the packaging will be exposed to

 

Based on the above, care must be taken when formulating a laminating adhesive to select a resin or combination of resins that optimize 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 which seals that package must also be able to withstand those temperatures.  

Elvacite® Acrylic Adhesive Resins

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Elvacite® is a line of acrylic resins which are polymers or copolymers of methyl methacrylate or other acrylic monomers that are essential in formulating solvent-based acrylic adhesives that have ideal toughness, flexibility, and adhesion qualities.  

In particular, Elvacite® 4345 is the softest, most flexible butyl methacrylate resin available and is preferred for laminating adhesives applied to packaging films.  Elvacite® 4345 is particularly well suited for bonding polyester films, mylar, polystyrene, and other nonporous, low surface energy plastic films and metal foils.  Additionally, this acrylic resin complies with FDA 21 CFR 175.105 for laminating adhesives used in the food and beverage industry.

Formulation Guidance with Elvacite® Acrylic Adhesive Resins

The starting-point formulation listed below is recommended as a one-part acrylic laminating adhesive for polystyrene film to aluminum foil.

    Ingredients
    % by Weight
    Elvacite® 4345
    36.00
    Methyl Ethyl Ketone
    54.00
    Vinyl Chloride-Acetate Resin
    4.01
    Toluene
    5.99

This formulation should be prepared by dissolving the vinyl chloride-acetate resin and Elvacite® 4345 acrylic resin in MEK and then diluting the solution with Toluene to the target solids level.  
 
An average peel strength of 500 grams/inch was measured for this acrylic adhesive.  To test peel strength, this formulation was applied using a 1.5-mil Bird film applicator to a 1-mil, uncoated, zero-temper, soft aluminum foil.  The acrylic adhesive was then air dried for 3 hours and subsequently 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 post-cure for 0.5-inch strips on an Instron tensile tester at 2-inch/minute crosshead speed.

Blending Resins

Blending two or more resins in an adhesive formulation is often necessary to achieve optimal performance.  Elvacite® 4345 and other butyl methacrylate grades, such as Elvacite® 2045 and 2046, are compatible with many other common resin types used in adhesives, including epoxy, rosin derivatives and vinyl chlorides.  When Elvacite® acrylic resins are blended with different resins used in heat seal adhesive formulations, they provide improved flexibility, adhesion, and toughness.  

Conclusion

When formulating a laminating 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 to optimize both the performance of the adhesive and the packaging it is being used to seal.  Acrylic resins like Elvacite® provide unique benefits to a laminating adhesive formulation- including:

 

  • Outstanding adhesion to high-slip, low surface energy nonporous films and foils
  • Excellent flexibility
  • Resistance to UV degradation and yellowing
  • Resistance to harsh environments and chemicals
  • Resistance to discoloration from heating

 

Contact us today using the link below to discuss an acrylic resin for your adhesive application.  

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