Lesson 15 E

15.18 Flexible Packages

  • Flexible packages are made from combination of flexible materials.
  • These include the basic substrate, laminating adhesives, protective or decorative coatings, and decorative inks.
  • There are literally millions of possible combinations.
  • By selecting appropriate components and tailor-making a laminate, it is possible to meet the packaging needs of a particular product.
15.19 Wrappers

  • Flexible packages are made from materials whose final shape conform to and are governed by the product enclosed, as opposed to rigid packages which require the product to conform to the shape of the container.
  • The simplest flexible package is a wrapper which may be loose or tight and may be sealed shut by using heat or various types of adhesives.
  • Some wrappers are left unsealed as is done on stick chewing gum wrappers; others are partly sealed to hold them in place as is done with carton overwraps.
  • The simplest wrappers are sheets of paper, metal foil or plastic film with or without decoration.
  • Many films can be heat sealed but paper and foil require coatings in order to make them heat sealable.
  • Early types of paper wrappers were glued shut.
  • The earliest types of heat - seal coating were waxes.
  • Many advances have been made in wax formulations and hot melt so that today some wrappers can be sealed with pressure alone (cold tack adhesives).
  • The advent of plastic resin coatings such as the vinyls, nitrocelluloses, sarans and polyolefins made it possible not only to add heat seal properties but also to substantially improve strength and barrier properties of laminates of paper and plastics.
  • Metal foil is in itself an excellent barrier. Coating and other substrates serve only to add strength, decoration and heat sealability.
  • A wrapper that comes in direct contact with a food such as candy or a loaf of bread is called an intimate wrap whereas if it wraps an inner package such as a carton it is called an overwrap.
  • Wraps may be purchased as roll stock or as precut sheets. The latter are usually used for hand or semi automatic production.
  • Other variations of wrappers include labels which wrap only part of a rigid package and serve primarily to identify the contents. Some completely wrapped around labels on paper containers contribute barrier protection also.
  • Another variation of a wrapper is a bundling overwrap which combines several smaller packages into one larger unit. Plastic film shrink wraps serve this function. The ultimate is extremely large pallet overwraps where a plastic film stabilizes an entire pallet load of smaller packages.
  • There are at least 13 distinct types of twists and folds by which wrapper may be closed neatly before sealing. Over wrapping machinery has been developed for each type of wrap and fold and for specific products.
15.20 Preformed Bags or Envelops

  • A flexible container which is open at one end is broadly called a "bag". Although in any size it can also be called a "sack", this term is usually reserved for very large bags holding 25 kgs or more.
  • An 'envelope' is usually but not necessarily smaller than a bag, envelopes are die-cut and are folded differently from bags.
15.20.1 Sacks
  • Multiwall sacks are either 'sewn' across the top and bottom or are of 'pasted' construction.
  • The side seams in either case are glued.
  • If only one of the ends is closed, the container is called an 'open mouth’ sack.
  • In other cases both ends are closed except for a small valve in one corner, which may have an extended 'sleeve' that is folded in after filling or may depend on the check valve action of an internal sleeve for a tight closure. The folded sleeve in a pasted bag will give the least amount of sifting.
15.20.2 Bags
  • Plastic bags and paper bags require completely different type of equipment, both for manufacturing and for sealing.
  • Plastic bags may be made from plastic tubing or from a flat web that is folded and joined in 'back-seam' construction.
  • Either of these can be 'flat' or they can be 'gusseted', the ends are generally heat -sealed to complete the closure.
  • In some cases a web of film is folded and heat - sealed to give a 'side-seam' bag.
  • The folded edge forms the bottom and can be accordion-folded if a bottom gusset is desired.
  • The top edge usually has a lip for easy opening when filling which is one advantage of a side seam bag over the other types, which must be flush - cut. Advantages & disadvantages of bags

1. The paper bag is lowest in unit cost,

2. It keep shipping costs to a minimum since they have the lowest - tare weight ratio.

3. They are essentially dust - tight and protect the contents from outside contaminations.

4. They can be tailored to fit snugly around the products they contain.

5. They adjust to any shift in the shape of the contents

6. A fluffy product which tends to settle at bottom, will take up less space in storage.

7. Bags take minimum of space in storage and shipment, both before and after filling

8. Size can be made to suit almost any conceivable product.


1. Non - supporting and hence do not stand neatly on shelf

2. Wrinkles and folds may be unattractive for some product

3. Stacking may pose problem

4. Durability is usually borderline

5. A bulky low - cost product is often put into minimum of packaging for economic reasons.

Last modified: Thursday, 11 October 2012, 9:48 AM