The LDPE film with a higher proportion of the amorphous region has a lower Tf, and the adjacent two layers of the LDPE film can be melted in 0.5 to 2 s, and merged with each other due to the thermal motion of the molecular chain. HDPE is high in crystallinity. If it is to be heat-sealed, it needs to be heated to the crystalline Tm to destroy the crystal lattice before it can be heat-sealed. The process of crystallization is difficult to achieve in 0.5~2s. .
The amorphous structure of CPP generally stands about 40%, so it also has excellent heat sealing performance; however, the heat sealing performance of BOPP is poor, because the crystallinity of BOPP is higher than CPP, and the molecular chain has been oriented, and the orientation is decomposed. Longer relaxation times are required to destroy the crystalline structure.
Similar to BOPP, BOPET has a higher Tf (265 ° C) and higher crystallinity, so it generally does not have heat-sealing properties; if a small amount of third monomer (butanediol or The adjacent poly(dicarboxylic acid) is destroyed by the regularity of the polyester molecular chain formed by the copolycondensation, and the ratio of the amorphous region of the prepared polyester is increased, and the PET copolycondensation product has heat sealability.