Seikei-Kakou

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Polypropylene (PP) films with β-form nucleating agent were prepared by T-die film extrusion at various T-die temperatures. The relationship between heat-sealability and crystal structure of the film was studied. The following results were obtained. When the T-die temperature was 220°C or 250°C, the crystal structure was not influenced by the amount of β-form nucleating agent. The effect of amount of β-form nucleating agent on the heat-sealability of the films was found to be small. On the other hand, in the case of T-die temperatures of 280°C, the β-form crystal content largely depended on the amount of β-form nucleating agent. β-Form crystals began to appear at 0.05wt% addition of nucleating agent and with the addition of 0.10wt% of nucleating agent, the β-form crystal content reached 0.87. As a result, the heat-sealability of film was improved greatly, and heat-sealing became possible even at 144°C. When β-form nucleating agent was increased further to 0.20wt% or 0.40wt%, the content of β-form crystal decreased and the heat-sealability of films obtained deteriorated. It was found that there is an optimum content of, β-form nucleating agent for enhancing the heat-sealability of PP films.

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Polypropylene (PP) films with β-form nucleating agent were prepared by T-die film extrusion. The relationship among extrusion conditions, crystal structure of the films and heat-sealability was studied. The following results were obtained: Fine crystallites formed more easily in films prepared at a chill-roll temperature of 25°C than in those at 75°C. The heat-sealabilities of the former films were better than those of the latter ones in a low heat-seal temperature range from 140°C to 144°C. The heat-sealability of PP film without additive prepared at a chill-roll velocity of 2.5m/min was better than that at 1.0m/min because of smaller size crystallites. On the other hand, the heat-sealability of the PP film with 0.10wt% β-form nucleating agent, prepared at 1.0m/min, was better than that at 2.5m/min due to the higher β-form crystal content. Accordingly, it may be said that the smaller sizes of α- and β-form crystals and the higher content of the β-form crystals both cause better heat-sealability due to the lower melting point of the crystals. It was also found that the air-gap distance negligibly affects the crystal structure and hence the heat-sealability of film.

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In this study, we investigated the forming technology of large seamless-belts. The influence of the rotational molding method and the flow behavior of the liquid materials on the distribution of thickness and the anisotropy of orientation in the belt have been examined. The results are as follows.
The low-speed (S) spray method was negligibly influenced by the form and the position tolerance of the mold, even when using liquid materials without a yield stress. Seamless-belts with accurate thicknesses were successfully produced by casting with a centrifugal force about the same as gravity. Furthermore, it was shown that the S method of the centrifugal effect Z=1.2 can attain a thickness accuracy of 95±5 micrometers even when forming belts exceeding 2 meters in circumference.

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