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Perhaps the oldest form of packaging and one that is still growing in use with renewed popularity, is the bag. It performs all the basic functions of packagingcontainment, protection, and communicationgenerally at the lowest possible cost. It is created in a wider range of sizes and materials than any other packaging form. It is used for virtually every type of product from liquids and powders to solids and, therefore, offers a versatility unmatched by any other type of product container.
The bag got its start in the form of sewn animal skins and bladders used by ancient man for carrying water, wine, cheese, and other subsistence items. In more recent times with the advent of textiles and then papers and plastic films formed on high-speed machines, bags have become so generally available they are staple household and industrial items. It is estimated that annual U.S. usage of all papers, plastics, and foils in such flexible containers approached 6 billion lb (2.7 billion kg) in 1995 [1]. Of this total, film bags account for about 4.2 billion lb (1.9 billion kg), paper requires another 1.5 billion lb (680 million kg), and foil makes up the balance of 235 million lb (106 million kg). The number of bags obviously runs to many billions per year.
While textile bags have largely been overtaken by other materials, burlap and cotton still are used to form sacks for seeds, grains, and granular products. For export shipment of more moisture-sensitive products like sugar, the cloth can be laminated to PE for added barrier properties, but more likely is used with a liner.
More recently, material choices have broadened to include nonwovens where plastic fibers are compressed and bonded together in a process simi-
lar to felting. Another recent development is the use of woven strands of plastic, particularly polypropylene (PP), for giant flexible sacks, which have pallet-sized footprints, but range in height from 12 in. (30.5 cm) to about 6 ft (183 cm) with capacities up to 6,000 lb (2,722 kg). Rectilinear or tubular in shape, the big bags can have either an open or closed top fitted with a woven filling spout. The bottom can be solid and is slit to dispense product or fitted with a woven discharge spout or even a fully openable bottom flap closed with ties (see Figure 5.1) [2]. Loops at the top enable transport on fork-truck tines. Properly loaded and handled, the big bags can stand alone and be stored in warehouse racks.
The bag structure can be porous, coated, or film-lined depending on barrier requirements. Some designs have heavy-duty, removable film liners, which can contain liquids. Depending on the product for which they are used and the nature of the liners, the sacks may be reusable. However, most are one-way containers that occupy less space in disposal areas than comparable rigid containers. Although relatively new, big bags already are used for a wide range of food, chemical, and pharmaceutical products and the business is growing more than 20 percent per year, say suppliers.
Before proceeding further, it is necessary to define terms. A bag has been described as a preformed container created from a tube of paper, plastic film, textile, or nonwoven material with one or both ends closed and an opening for loading product.
Bags either have one open end (open-mouth bag) or are closed at both ends and filled through a small opening at the side of one end called a valve. In recent years, bags also have been created with closures mounted in the face surface. These generally are used in conjunction with a paperboard or corrugated box (bag-in-box). Note also that some bag structures have gussets (pleats) in the sides that provide more filling room in the same width and length.
Consumer bags contain a standard unit of merchandise and serve as a shelf package at the retail level. These small bags generally are limited to weights up to 20 lb [3]. Larger industrial bags, particularly 50 lb and above, are termed shipping sacks.
A specialized design is the baler bag, usually a satchel-bottom or selfopening structure used to hold several smaller bags of product.
A pouch is a small flexible container made from paper, plastic, or foil materials, which is formed, filled, and sealed on a single machine. While still generally true, these definitions have been somewhat modified by development of single machines that form, fill, and seal industrial-size plastic pouches from rollstock and by machines that fill and seal small preformed paper and plastic bags that are constructed like pouches.
An envelope is defined as a die-cut flexible container with two faces that is joined by three flaps to form a three-sided enclosure that is open on the fourth edge for filling and can be closed by a gummed flap, tie string, or clasp. Because of the die-cut flaps, envelopes are folded differently from bags and are made on a completely different type of machine. Some envelopes are multilayer, containing a thick inner cushion of pulp paper or bubble-plastic. Such envelopes are used as packages in the rapid-delivery mailing systems mostly for small items or small quantities of product. Common envelopes often are used to hold instructions for packaged products of all sizes.
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