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.
Paper sacks are usually made of Kraft paper having the advantage of being soft and strong at the same time. The stretch or elongation increases the energy required to break the material. They easily carry and protect products up to 50 kg, and adapt easily to the nature of their contents and to handling constraints. At the same time sacks are provide an excellent media for promotional messages and sophisticated printing designs.
Paper sacks capacity is variable, each country sets a maximum ground rules such as job security, it comes in a variety of calipers, basis weights, and treatments.
Plastic hazard free paper sacks also called multiwall paper sacks are used for cement, food, chemicals, consumer goods, flour bags etc.
- Yam, K. L., "Encyclopedia of Packaging Technology", John Wiley & Sons, 2009, ISBN 978-0-470-08704-6