Paper sack

A paper sack is shipping container made of high quality and weight paper, 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 [1] and coated papers are sometimes used as inner layers to provide a moisture barrier, and resistance to rodents and insects.

Cement Sacks

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.[2]

Paper sack are produced on paper sack machine consisting of tuber and a bottomer.[3]

Sack Paper manufacturing
Main articles: Kraft process and Paper machine

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.[2] Machine direction elongation can be further improved by pressing between very elastic cylinders causing more microcrepping.[2] 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.

Properties
Main article: Brown paper

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.

Testing

Filled bags or sacks can be evaluated in the field by careful observation. Laboratory package testing is often conducted using drop testing,[4] shock table testing,[5] puncture testing, etc.

Applications

Plastic hazard free paper sacks also called multiwall paper sacks are used for cement, food, chemicals, consumer goods, flour bags etc.

References
  1. Fiscus, D M (2004). "METALLOCENE LLDPE FILMS FOR HEAVY-DUTY SACK APPLICATIONS". Journal of Plastic Film & Sheeting. 20 (2): 105–148. doi:10.1177/8756087904047212. S2CID 136923401.
  2. Paulapuro, Hannu (2000). "5". Paper and Board grades. Papermaking Science and Technology. 18. Finland: Fapet Oy. pp. 121–122. ISBN 978-952-5216-18-9.
  3. Industrial Bags Production, Mondi Group
  4. "EFFECT OF DROP TEST UNITS ON CORRELATION OF SACK PERFORMANCE WITH PAPER PROPERTIES" (PDF). Institute of Paper Chemistry. 16 October 1962. Retrieved 3 December 2018.
  5. Packaging and Marking Specifications - FOR THE PURCHASE OF COMMODITIES IN 25 KG BAGS FOR USE IN EXPORT PROGRAMS - APPENDIX 2 (PDF), USDA, 2005, retrieved 3 December 2018
  • Yam, K. L., "Encyclopedia of Packaging Technology", John Wiley & Sons, 2009, ISBN 978-0-470-08704-6
  • Steven P. Miteff and Diana Twede. 1990. Open-Ended Bag Problems; An Investigation of Multiwall Paper CSB Bag Closure Failures Reported in India and Recommended Solutions. MSU School of Packaging Project 1 Special Report No 27.
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