The influence of butyl acrylate/methyl methacrylate/2-hydroxy ethyl methacrylate/acrylic acid latex properties on pressure sensitive adhesive performance

Pressure sensitive adhesives (PSAs) were produced using latexes synthesized via a starved seeded semi-batch emulsion polymerization process with butyl acrylate (BA), methyl methacrylate (MMA) and sometimes additional monomers, 2-hydroxy ethyl methacrylate (HEMA) and/or acrylic acid (AA). For the BA/MMA comonomer latexes, the amount of cross-linker (allyl methacrylate), monomer emulsion and initiator solution feeding times, and the BA/MMA weight ratio were manipulated to vary the polymer properties. The performance of PSA films cast from these latexes was evaluated by tack, peel strength and shear strength. The effect of polymer properties on PSA performance was related to the viscoelastic properties of the PSAs. For BA/MMA latexes, it was not possible to greatly improve the peel strength even at great sacrifice of shear strength for PSAs with gel contents of ∼60 wt% or higher. This was because the ratio of the loss modulus at debonding frequency to the storage modulus at bonding frequency did not vary significantly for the conditions studied. The addition of HEMA provided a significant influence on latex polymer properties as well as PSA performance for both high (>60 wt%) and low (∼20 wt%) gel contents. For some cases, tack, peel strength and shear strength were simultaneously and greatly improved by the addition of HEMA. Adding both AA and HEMA while decreasing the amount of emulsifier, also resulted in a PSA with much better performance (i.e., higher tack, peel strength and shear strength) than a BA/MMA PSA with similar gel content (∼60 wt%).