Viscoelastic properties and peel strength of water-borne acrylic PSAs for labels

The use of acrylic emulsion pressure-sensitive adhesives (PSAs) in labels continues to increase due to their environmental friendliness, good aging resistance and excellent processability during coating process. This study has investigated the acrylic emulsion/tackifier blend systems by examining their thermal properties as indicated by the glass transition temperature (T _g), by conducting optical microscopy to determine their structure, by exploring their viscoelastic properties with the advanced rheometric expansion system (ARES), and by measuring their peel strength with the 180° peel test. The acrylic emulsion/tackifier blends with low softening point and low molecular weight exhibited only a single T_g. However, the acrylic emulsion/tackifier blends with high softening point and high molecular weight showed two T_g values. Microscopic observation of blends with miscible tackifier did not show any evidence of tackifier traces, whereas the microscopic structures of blends with immiscible tackifier showed dispersed tackifier particles. As the tackifier content increased, the rubbery plateau region decreased for the miscible blends but increased for the immiscible blends. The 180° peel strength of the miscible blends was dependent on the viscoelastic properties and was influenced by incorporation of tackifiers in the PSA systems. However, the peel strength of the immiscible systems did not depend on the viscoelastic properties at low tackifier content, but it decreased as the tackifier content increased in accordance with the increase of the storage modulus G′.