FLEXIBLE PACKING LAMINATE IN THE FORM OF SHEETS OR OF A WEB, A METHOD FOR THE MANUFACTURE OF THE LAMINATE AND PACKING CONTAINERS MANUFACTURED FROM THE LAMINATE

摘要

In the manufacture of packing containers by means of folding of laminate in the form of sheets or of a web of the type which comprises a relatively thick carrier layer of paper or cardboard and a gas-tight, thin metal foil the laminate is subjected to stresses which, particularly within folding regions comprising multiple material thicknesses, may be so strong that crack formations occur in the metal falls protecting against gas which are senstive to tension, thus entailing the risk of the intended gas barrier characteristica of the packing container being impaired or wholly lost. To counteract this risk the packing laminate is provided with a layer of ethylvinyl alcohol laminated between the metal foil and the carrier layer which for one thing is mechanically sufficiently durable to withstand the external stresses during the folding of the laminate, and for another has sufficiently good gas barrier properties to compensate for the loss in gas tightness which thus may arise if the integrity of the metal foil is lost during the manufacture of the container. Preferably the laminate is provided also with a further layer of a material permeable to moisture which is laminated between the ethylvinyl alcohol layer and the carrier layer and which is adapted to let through moisture whihc from the liquld-filled inside of the container might be able to penetrate into the ethylvinyl alcohol layer through such crack formations in the metal foil . As a result the moisture content in the ethylvinyl alcohol layer can be kept at a sufficiently low level so as not to have a negative effect on the gas barrier characteristics of the ethylvinylalcohol layer which otherwise diminish with increasing moisture content.