Adhesion improvement of the acrylic pressure-sensitive adhesive to low-surface-energy substrates using silicone urethane dimethacrylates

The acrylic pressure-sensitive adhesive (acrylic PSA) shows satisfactory adhesion to high-surface-energy substrates, such as glass, metal, and SUS, but it shows very low adhesion to low-surface-energy substrates, such as polyethylene, polypropylene, and polydimethylsiloxane (PDMS). To increase the adhesion strength of PSA to the low-surface-energy substrates, silicone dimethacrylate (SiDMA) was added to decrease the surface energy of the PSA, but it induced degraded peel strength due to plasticization and miscibility problems. In this study, various types of silicone urethane dimethacrylates (SiUDMAs) were synthesized by controlling the ratio of diisocyanate to PDMS to overcome the miscibility problem. As the ratio increased, their molecular weight and viscosity decreased, but their surface energy increased due to the reduced PDMS content. With the addition of SiUDMA2.0, which has a similar molecular weight to SiDMA, PSA showed 4- and 6-times higher loop tack and peel strength, respectively, on the PDMS substrate without UV curing. All types of SiUDMAs lowered the surface energy of the PSA and significantly increased the loop tack and peel strength on the PE, PP, and PDMS substrates. On the PDMS substrate, PSA that was modified with 20 wt% of SiUDMA2.0 and cured at 200 mJ/cm² showed a peel strength of 520 g_f/25 mm, which was more than 3 times higher than that of the control PSA (138 g_f/25 mm). The shear adhesion failure test showed that SiUDMA2.0-modified PSA endured a temperature of 70 °C, which is higher than the 46.5 °C of the control PSA.