More Questions and Answers
Q: Why would I use a valve bag instead of an open-mouth bag?
A: Wayne Revell, Taylor Products, says:
Valve bags are quick and don't require a sealer or sewing machine to close the bag, saving you the cost of a sealing conveyor and bag-top closer. Valve bags usually cost a little more per package, but the up-front equipment savings is significant. Valve bags also stack very well, as they are more of a block than most open-mouth bags.
Normal valve bags have an internal passive valve—a thin poly flap that is held shut by the product—but the closure isn't sealed and thus can open and allow leakage. So if you need a tamper-evident seal that meets food-grade standards, or if you just don't want leakage, open-mouth bags are usually the correct choice.
Pinch-bottom open-mouth bags have a paper exterior, commonly with a laminate liner, and the top of the bag has pre-applied dry glue that is reactivated by a heat sealer and folded over to close. They're also available as just a poly-plastic bag or woven poly construction. Some open-mouth bags must be sewn shut.
Valve bag technology has advanced, and there are now valve bags with extended sleeves that can be sealed closed. However, this slows down the fill cycle time and is therefore usually undesirable.
Some products that are commonly packaged in valve bags include seeds and grains, aggregates, industrial minerals, chemicals, and plastics—but rarely foods.
Open-mouth bags are usually chosen for food products and are also commonly used for bulky or sticky products that don't feed well through the spout-style valve-bag filling equipment. Bulk seeds and feeds are traditionally packaged in less expensive, woven open-mouth bags and sewn closed, mostly because of bag cost. In contrast, pet foods are usually packaged in more expensive, high-end-graphic open-mouth bags because they appear attractive on the shelf and are easy to use.
In any case, the choice between valve and open-mouth bags depends on product characteristics, rate and accuracy production requirements, dust control, package cost, equipment cost, and, most often, end-product acceptance. Ultimately the consumer may drive the package style as much as any other factor, because end users expect certain products, from pet food to cement mixes, to appear in traditional packages.
Taylor Products is a Kansas-based supplier of bulk bag filling systems, robotic palletizing systems, and packaging automation systems.
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