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PHYSICAL CROSSLINKING OF ACRYLIC HOT-MELT PRESSURE-SENSITIVE ADHESIVES USING ACID/BASE INTERACTION [2006]

Audrey A. Sherman, Albert I. Everaerts, and Ken Zieminski
3M Company
St. Paul, MN, USA

Hot-melt pressure-sensitive adhesives advantageously reduce or eliminate the use of organic solvents in adhesives and their processing. Among hot-melt adhesive chemistries, tackified block copolymers and, more recently, (meth)acrylates are two of the most prominent. To provide for easy processing and good coating quality, hot melt PSAs typically are relatively low in molecular weight. The inherent physical crosslinking of block copolymers results in a good balance of cohesive strength and processibility. Unfortunately, for acrylic PSAs this low molecular weight results in limited cohesive strength and the need for a final processing step to cure or crosslink the polymer after the coating process. Ionic crosslinking, electron beam or UV initiated crosslinking have all been employed for various applications [1-4]. Each type of crosslinking has its own set of advantages and disadvantages.

One way to effectively improve cohesive strength of an adhesive is by ionic crosslinking. Ionic crosslinking may offer the following benefits:

• No need for special curing equipment.
• No interference from pigments or fillers.
• Thickness of the adhesive is not limiting the curing efficiency or process speed.
• Crosslinking may be thermally reversible.

Ionic crosslinking may be achieved by introducing metal ions into an acid-containing adhesive or by generating acid/base interaction between polymer chains. This paper focuses on the use of acid/base interaction, its effect on PSA performance, and the rheological behavior of the material.