Effects of Film Forming Conditions on the Strength of a Cross-Oriented Polyethylene Tubular Film

Abstract

Relationship was investigated between the conditions for producing multi-layer film with transversely stretched high density polyethylene tube as the inner layer and vertically stretched polyethylene tube as the outer layer, and various properties such as impact resistance, propagation tear resistance, etc.. Production conditions which will meet the requirements for heavy-duty bag were obtained. The results obtained are summarized as follows:
(1) Low density polyethylene used for the outer layer gave a higher impact resistance and propagation tear resistance compared with high density polyethylene.
(2) With increasing the thickness of the film, the impact and propagation tear resistance increased. Thickness between 100-140 microns will be sufficient for heavy-duty uses. Whether the inner layer thickness should be increased or the whole thickness should be increased will be determined in connection with other properties.
(3) The increase of vinyl acetate contained in ethylene vinyl-acetate co-polymer used as the intermediate layer reduced propagation tear resistance. It is recommended to use ethylene vinyl-acetate co-polymer containing 5-6% vinyl acetate.
(4) With increasing the thickness of the outer layer, impact resistance was lowered. The ratio in thickness of the intermediate to the outer layer should be 7 to 3 in principle.
(5) Increase in draw ratio of the outer layer led to higher propagation tear resistance in the vertical direction. The draw ratio of 1.1 to 1.3 is recommended.
(6) It is suggested that the bond strength of the inner layer with the outer should not be too high in order to increase propagation tear resistance.