While far less common than multi-wall paper bags, millions of polyethylene (aka PE, poly, or plastic) valve bags are filled and transported each year. Southern Packaging has become a leading supplier of PE block bottom valve bags and supports a wide variety of manufacturers across North America with this unique bag style.
What is a Poly Valve Bag?
A poly valve bag is a common industrial package style made from 100% polyethylene film. Valve bags are packed on equipment that deposits material into the bag via horizontal filling spout. After filling, forces generated by the product inside the bag allow the valve opening to self-seal.
Poly valve bags self-seal in the same manner as a paper or woven valve bag. A woven valve bag (aka AD*STAR block bottom bag or WPP valve bag) is another type of plastic valve bag that will be discussed below. For a detailed review of the AD*STAR Woven valve bag, visit our blog post here.
Although their functionalities are very similar, polyethylene valve bags offer numerous benefits vs traditional multi-wall paper valve bags.
The benefits of Poly Valve Bags include:
Excellent water/ moisture resistance
Excellent sift resistance
High quality printing capabilities
High strength / durability
Minimal Lead Time
What types of products do we see packed in Poly Valve Bags?
PE and PVC Resin
What Valve Types are available on a Poly Valve Bag?
Available valve types on a poly valve bag are very similar to a paper valve bag. Valve Types include:
Standard Internal Valve
Extended Tuck-In Sleeve
Sonic Seal Sleeve
How does a Polyethylene Block Bottom Valve Bag differ from an AD*STAR Woven Block Bottom Valve Bag?
The basic functionality of a PE valve bag and WPP valve bag are the same. The main differences are in the material and how they are made.
Raw Material – PE valve bags are made from Polyethylene, whereas woven valve bags are made from Polypropylene.
Construction – PE valve bags are made with flat PE film (sheet) that is tubed, cut, and welded to form a bag. PE film bags have a back seam. WPP valve bags are made by weaving thin polypropylene tapes to form a continuous tube. The tube is then cut, folded, and welded to form a bag. Woven PP valve bags do not have a back seam.
Lamination – PE film bags are made with 3-5 layers of Coex PE film. They are not laminated. However, PE film is nearly waterproof. Woven bags are laminated (i.e. coated) with PP film to give the bag an extra layer of moisture protection and sift resistance.
Anti-Skid – Plastic valve bags are inherently more slick than paper bags. Both PE and WPP valve bags can be embossed, but the embossing is done in significantly different ways. PE bags can be equipped with a “sanded” finish for added slip resistance.
Perforation – PE and WPP valve bags can both be perforated for air release. PE valve bags are inherently less permeable than WPP valve bags. Customers must understand that they may need to make adjustments to their packing equipment before changing from paper to a poly valve bag.
Printing – both bags are capable of full process printing (up to 8 colors)
Lead Time – PE valve bags can be made much faster than woven bags. Southern Packaging sources PE valve bags from the U.S., Mexico, and South America. We source WPP valve bags from Turkey and India. Lead time for PE valve bags is typically 6-8 weeks. WPP valve bags are generally 16 weeks or more.
Cost – PE valve bags are a premium product and are considerably more expensive than paper or Woven PP valve bags. In many cases a PE film valve bag will be 50-100% more expensive than a paper or woven PP bag. Nevertheless, customers packing sensitive products should strongly consider the performance capabilities of the polyethylene valve bag.
Can Poly Valve Bags be designed to melt for batch inclusion applications?
Yes! PE film bags can be made with sophisticated resin blends to melt at specified temperatures. Many of our carbon black customers use low-melt bags for batch inclusion applications. Read more about batch inclusion valve bags here.