| 摘要 |
<p>In the manufacture of non-returnable packages for milk and other beverages the laminated packing material is sealed to itself along linear sealing zones by causing outer thermoplastic layers of the packing material to fuse together. The strength of the seal obtained depends upon the thermoplastic surface being free of impurities, e.g. oxide coatings or residues of the contents of the package. In spite of the presence of impurities a strong seal can be obtained if the thermoplastic layers, within a limited region of the sealing zone, are pressed against each other with such a force that molten thermoplastic material is made to flow to adjoining regions (15), since in this case the thermoplastics are blended to such a degree that the seal-preventing layer of impurities is broken.</p> |
