| 摘要 |
Multi-walled paper sacks for powder products, notably plaster, have a porous paper inner wall surrounded by a paper outer wall and a vapour barrier separate from the paper inner wall. The vapour barrier may be a coating on the inside face of the outer paper wall. Perforations through the vapour barrier are substantially confined to either or both of the broad faces of the sack. During filling of the sacks air is able to vent through the inner wall and then through the perforations in the vapour barrier, allowing filling by high speed machinery. Deterioration of the product as a result of moisture perforation is unexpectedly just as good, and sometimes superior, to that encountered with alternative sacks. Consequently the improvement in filling is not encumbered by a reduction in shelf life of the product.
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