Bowing Phenomenon of Double Bubble Tubular Film Process for Nylon6 Film
Masao Takashige, Toshitaka KANAI, Toshiro Yamada
Idemitsu Petrochemical Co., Ltd.
Japan

Keywords: Double Bubble Tubular Film, Nylon6, Bowing

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This report discussed the bowing phenomenon and the sag elimination tension for biaxially oriented nylon6 film process which consists of double bubble tubular film process and heat set tentering one.
The bowing phenomenon does not occur in the heat set of the triple bubble tubular process. However, there is a problem of the bubble stability when the sufficient heat set by the tubular process is carried out. The bowing phenomenon arises when the heat set is carried out by the tenter method. Bowing ratio becomes large when the heat set temperature is high and film relaxation ratio is large.
It is possible to reduce the bowing ratio when it is heat-treated in the two steps of tenter process. Shrinkage stress of the stretched film was relaxed in the heat treatment of the first step, and then the bowing ratio in the heat treatment of the second step, whose temperature is higher than the first one, was able to be decreased compared with the one step heat treatment.
When the bowing phenomenon occurs, shrinkage percentage in hot water changes along the cross-direction of the film. The humidity expansion coefficient in the film increases with increasing hot water shrinkage percentage which is related to the orientation of the molecule.�@
The sag also increases with increasing the bowing ratio. The bowing ratio and the sag elimination tension have the proportional relation. It is necessary to decrease the sag of film in order to carry out smooth and clear printing. Nylon6 film is easy to absorb moisture, so the bowing ratio should be low