Development of Pressure-Sensitive Adhesives Degradable on Ultrasonic Irradiation

We have developed novel pressure-sensitive adhesives (PSAs) which could be peeled off easily on ultrasonic irradiation as external stimuli. The PSAs were composed of acid degradable polyurethanes and microcapsules containing a thermal acid generator (TAG). Three layered (w/o/w) type microcapsules containing a TAG were prepared by coacervation method. Generation of acid from the microcapsules and PSA layers on ultrasonic irradiation in water was confirmed by pH changes. Peel strength of PSAs containing the microcapsules decreased from 10 to 1 N/20mm on ultrasonic irradiation in water at 28 kHz for 20 min. The peel strength of PSAs containing the microcapsules was constant on heating up to 80 degrees C for 1 h, while that decreased on heating above 80 degrees C. These results suggest that acid was generated but kept in microcapsules on heating up to 80 degrees C, and the acid was released from microcapsules when PSAs were ultrasonic irradiated or heated above 80 degrees C.