Kraft Paper Bags
Paper is widely used as the bag material in the bagging of powders. It is the standard for many kinds of bags, due to cost, strength, ease of handling, and other features.
Polyvinyl-Kraft Paper Bags
A layer of plastic is inserted between layers of kraft paper. This type of bag features high resistance to moisture and is used for bagging materials that deteriorate in quality on contact with air.
Inner Laminated Paper Bags
These are kraft paper bags laminated with an innermost layer of plastic or other material. Inner laminate bags raise the level of hygiene as the powder does not contact paper. They are highly airtight and resistant to humidity.
PP-Cross Internal-Layer Bags
From outer to inner, these bags have layers of PP-Cross, paper, and film. They are used particularly for exporting, and other situations where high bag strength is required.
Slit Polyvinyl-Kraft Paper Bags
The plastic film in this bag is slit to allow air to escape more easily while maintaining a certain level of humidity resistance. Cement bags are usually this type of inner-valve bag.
These bags use only plastic. They may be single- or double-layered and can be in many shapes and sizes.
Many layering variations of the bag types and materials outlined here are possible. For example, a bag might have three layers of kraft paper, and that bag could then be combined with a vinyl bag. Or, to reduce costs, a certain layer might be made of recycled paper.
Sizes of Bags & Valves
Even with the same materials and layer compositions, bags can have an infinite variety of valves and sizes. In the case of valve bags, the diagram below shows how bags are measured according to length (L), breadth (W), and flat width (D). Although the volume of the bag is roughly set by length and breadth, the flat width is crucial when bagging. This is because the valve size is in many cases decided by the flat width. As the AMO Packer inserts a nozzle into the valve, the valve size must be selected to match the nozzle.