Multiwall paper sacks have been used as a way of packaging products for over 100 years. The multiwall paper sack has proven itself to be a strong, economical, cost effective and acceptable means of packaging. Sacks can be manufactured in a size range from 5kg to 50kg. Containerisation has increased there popularity and paper sacks are widely used to export an increasing range and volume of products.
Principally there are two main types of paper sack.
Open Mouth sacks, flat or gusseted made from a flush cut tube. This style of sack is supplied with a closed bottom. The top is then closed after the sack has been filled with product by either sewing, taping, stapling or heat sealing. This type of sack is easily filled using simple equipment. They are suitable for the packing of powders, granular products, grains and cereals. This type of sack can also have an inner polyethylene bag or ply as a moisture barrier, for protection of the product.
Valve Pasted Sacks
This type of bag is closed at both ends with a small opening called a valve in one corner, through which the sack is filled with product, using a specialised packaging equipment. The use of a flush cut tube is the simplest way to produce a sack with folded and pasted ends. The ends are usually capped with a rectangular piece of paper to give added strength to improve sift-proofing and to give a flat surface which may be used for the addition of extra identification data. This type of sack may have an inner ply of polyethylene for product protection. Valved multiwall sacks are now used extensively in a wide range of industries. Some of the most commonly seen sacks are used to pack Cement, Lime, Plaster, Tile Adhesives, Sugar, Milk Powder, Flour, Starch and Potatoes just to name a few.
The valves that may be incorporated into sacks are many and varied. They may be internal or external and may be closed by gravity, by manual folding or heat-sealing. If necessary some valves may be narrower than the sack end. Colquhoun’s staff can advise on the best valve to suit your product.
Types of Sack Paper
The type of sack paper and the number of plies and grammage to be used depends on different factors as to the characteristics of the product, the weight and filling conditions. Colquhoun’s can advise on the best construction to be used for your product. Some major points to consider: (1) Packing Weight. (2) Product Density. (3) Main Flow Characteristics of the product. (4) How will the sack be filled and closed. (5) Sack size relative to the size of pallet being used. (6) What are the print requirements for the sack. (7) Total weight that will be packed onto a pallet.