| 초록 |
The LLDPE is widely used for stretch film applications due to the excellent tensile strength of the LLDPE film. However, LLDPE is not preferred for heat shrinkable film applications due to the poor shrink property of the LLDPE film. The poor shrink property of LLDPE film stems from the linearity of the polymer chain. The pure LLDPE blown films exhibit about 30 to 60 % shrinkage in the machine direction (MD) under a proper shrink condition. In this study, we explored the possibility of utilization of LLDPE in the shrink film applications as a blend with LDPE. The LDPE/LLDPE blends with entire proportion were prepared by dry blending. The blends were extruded into blown films with blowup ratio (BUR) of 2.7. Film shrinkages were determined using ASTM D-2732 at 140℃. When the LDPE portion in the blends was between 30 and 70 % by weight, the shrinkage of films was about 70 to 80% in MD and 10 to 20% in TD. The TD shrinkage of the films increased as the melt index of the blended LDPE decreased. However, the melt index of blending LLDPE was not so effective on the shrinkage of the film as the MI of LDPE. As the BUR was increased, the shrinkage of films in TD was improved linearly but decreased slightly in MD. The shrinkages of films with BUR between 2.5 and 4.0 were about 10 to 30% in TD and 60 to 75% in MD. The shrinkage of films was affected by frost line height (FLH) also. As FLH increased, the shrinkage of films in TD was improved but the shrinkage in MD was deteriorated. The MD/TD shrinkage ratio is varied in accordance to the packaging applications. To satisfy the MD/TD shrinkage, the proportion of LDPE in the blends with the LLDPE can be varied between 30 and 70% by weight. The Films are fabricated at 1∼2 ㎜ die gap and BUR of 2.5 ∼ 4.0. For the shrinkable film application, butene-copolymer LLDPE with MI=1.0 , ρ = 0.919 seems to be suitable to form a useful blend with LDPE because of the easy processibility and economics of the LLDPE resin. These films are being tested in packaging applications of food, drink, and pallet and will substitute LDPE only heat shrinkable films.
|
