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paper sack ''A ''paper sack is a packaging made of paper high quality and weight, usually kraft virgin fiber, which is normally used for transporting powder materials, such as flour, cement, animal feed, etc. Multi-wall paper bags usually have several layers of heavy duty kraft paper, sometimes with a highly printed paper on the outside. Plastic films and coated papers are sometimes used as inner layers to provide a moisture barrier, and resistance to rodents and insects. Usually consists of several layers to provide strength, with high elasticity and high tear resistance, designed for packaging products with high demands for strength and durability and resistant outer surface where instructions are printed, trademark, etc. ==Paper sack manufacturing==
Wood pulp for sack paper is made from softwood by the kraft process. The long fibers provides the paper its strength and is added wet strength chemicals to even further improve the strength. Both white and brown grades are made. Sack paper is then produced on a paper machine from the wood pulp. The paper is microcrepped to give porosity and elasticity. Microcrepping is done by drying with loose draws allowing it to shrink. This is causing the paper to elongate 4% in machine direction and 10% in cross direction before busting.〔 Machine direction elongation can be further improved by pressing between very elastic cylinders causing more microcrepping.〔 The paper may be coated with polyethylene (PE) to ensure an effective barrier against moisture, grease and bacteria. A paper sack can be made of several layers of sack paper depending on the toughness needed.
抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「paper sack」の詳細全文を読む
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