利用4种不同厚度的PP薄膜进行超声热合实验，分别得到热合强度最高时相应的超声时间。对封合处的剖面进行显微观测，并对纸板进行同样的超声封合，发现在超声波作用时，材料间摩擦产生的热量是熔融材料实现焊接的主要原因。

PP films of 4 different thicknesses were welded with ultrasonic welding. The ultrasonic welding time corresponds to the peaks of joint strength was obtained. Profile of seal place was observed with microscope. The same ultrasonic welding method was applied to paperboard. It was founded that material friction heat is the main cause of fusion welding.