Bag-in-box, dry product
When the bag-in-box concept is applied to dry products, it generally involves a bag inside a folding carton (see Cartons, Folding). In order to appreciate the impact of the bag-in-box (BIB) concept for dry products, one must understand the history of the folding carton. The turn of the century marked the first use of the folding carton as a package when National Biscuit Company introduced the ‘‘Uneeda Biscuit’’ (soda cracker). Instead of opting for the conventional bulk method of selling crackers, Nabisco decided to prepackage in smaller boxes, using a system that would prolong freshness. The paperboard carton shell with creased score line flaps had recently been developed, along with a method for bottom and top gluing on automatic machinery (see Cartoning machinery).Waxed paper (see Paper; Waxes) was to be added manually to the inside of the carton. So was born the ‘‘lined carton.’’
The evolutionary process eventually culminated in two basic methods of producing lined cartons. The first was a machine to automatically open a magazine-fed sideseamed carton and elevate it around vertically indexed mandrels where glue is applied to the bottom flaps and folded up against the end of the mandrel with great pressure. The result is a squarely formed open carton with a very flat bottom surface capable of being conveyed upright to a lining machine that plunges a precut waxedpaper sheet into it by a system of reciprocating vertical mandrels. The lining is overlapped at the edges and sealed together to form an inner barrier to outside environmental factors. It protrudes above the carton top score line by a sufficient amount of paper to be later folded and sealed at a top-closure machine. Straight-line multiple-head filling machines are used to fill premeasured product into the carton. Initial fill levels are often above the carton-top score line and contained within the upper portion of the lining, which eventually settles with vibration before top sealing takes place. This fact has relevance with respect to the bag-in-box concept.
The second method involves the use of a double-package maker (DPM), which combines the carton forming/ gluing operation with a lining feed mechanism that wraps the lining paper around a solid mandrel prior to the carton feed station. In this instance the carton blank is flat and is side-seamed on the DPM. The lined carton is then discharged upright onto a conveyor leading to the filler and top closing machine.
These packaging lines are typically run at up to 80 packages per minute (in some special cases 120/min). They are considered to be very complex machines requiring skilled operating personnel and are usually restricted up to a single size.
Although the time reference is rather vague, it would appear that the bag-in-box concept began with the refinement of vertical form/fill/seal (VFFS) machinery in the 1950s (see Form/Fill/Seal, Vertical). Packaging machinery manufacturers and users saw an alternative to the DPM in the horizontal cartoner coupled with VFFS equipment. The idea of automatically end-loading a sealed bag of product into a carton offers the following important advantages compared to lined cartons: simplicity (i.e., fewer and less-complicated motions); flexibility (i.e., size changes more easily and quickly accomplished); higher speed (i.e., up to 200 packages per minute is theoretically possible with multiple VFFS machines in combination with a continuous-motion cartoner); lower packaged cost (i.e., higher speeds and lower-priced machinery); improved package integrity (i.e., bags are hermetically sealed using heat-seal jaws); reduced personnel (i.e., possible for one operator to run line); requires less floorspace (i.e., more compact integrated design); and wider choice of packaging materials (i.e., unsupported as well as supported films can be handled).
Although bags are sometimes inserted manually, the high-speed methodology (see Figure 1) employs multiple VFFS machines stationed at right angles to the cartoner infeed, dropping filled and sealed bags of product onto an inclined conveyor that carries themto a sweep-arm transfer device for placement into a continuously moving bucket conveyor. The VFFSmachines are electrically synchronized with the cartoner, and the transfer device is mechanically driven by the bucket conveyor. When the bag reaches the carton-loading area, it is gradually pushed out of the bucket by cammed push rods through guides and into the open mouth of the box which is contained within chain flights traveling at the same speed adjacent to the bucket. A guide plate drops into the bucket fromoverhead to confine the bag during insertion into the box. Once the bag is in the box, the end flaps are glued and rail closed before entering compression belts for discharge to the case packer.
When difficulties occur in this system, it is usually at the insertion station, caused by misshaped or rounded bags with a girth larger than the carton opening. An attempt is made to condition the bag on the inclined conveyor by redistributing the product within the bag more evenly and, once in the bucket, by vibrating tampers to flatten it. However, if there is too much air entrapment in the bag, or a high product fill level, or an improperly shaped bag, these devices become futile. Increasing the carton size would be a simple solution, but the packager is often not free to do this. Marketing departments are generally reluctant to change the size of a carton that has been running satisfactorily on DPM equipment. The main problem is that the BIB manufacturer must allow more clearance of bag to box than is required on a closefitting lining. The usual BIB bag-sizing rule of thumb is a gusseted bag having a width 3/6 in. (9.53mm) less than the carton face panel and 1/4 in. (6.4mm) less than carton thickness. This can vary somewhat, but the bag must be small enough to transfer positively into the bucket and subsequently into the box without interference.
One manufacturer has attempted to deal with the problem by wrapping the carton blank around the bucket after the bag has been top-loaded into it (see Figure 2). In wraparound cartoning, flat blanks are used and glue is applied to the manufacturer’s joint and side-seamed against the mandrel by rotating-compression bars. The mandrel/bucket is withdrawn, leaving the bag in the box ready for flap gluing and closing. This approach is more forgiving than end-loading, but is still susceptible to bag-sizing problems because additional clearance must be allowed to compensate for the gauge of the three-sided bucket walls. Speeds of r140 per minute are possible.
The vertical load concept has gone a long way toward overcoming bag insertion problems (see Figure 3). It relies on simple gravity and special bag-shaping techniques to drop the bag directly into the box from a film transportbelt- driven type of VFFS machine. The carton shell is formed from a flat blank and bottom glued on a rotary four-station mandrel carton former. The upright carton is conveyed to a starwheel-timed flighted chain indexing device to position it squarely under the VFFS rectangular forming tube. Two VFFS machines with electronically synchronized motor drives operate independently of the carton former. A prime line of empty cartons initiates the operation of each VFFS machine.
The bag-forming parts consist of a rectangular-forming shoulder and tube that has been manufactured to produce a bag with cross-sectional dimensions 1/4 in. (6.4mm) less than carton face panel and 1/6 in. (3.2mm) less than the side panel. This very close fit is made possible by a combination of several mechanisms. First a gusseting device creates a true flat-bottom bag using fingers that fold in the film from the sides as contoured cross-seal jaws close on the bag. The bottom of the rectangular forming tube is within 1/4 in. (6.4mm) of the seal jaws and acts as a mandrel around which the bag bottom is formed. The bag is thereby given a sharply defined rectangular shape, which is maintained as it is filled with product and lowered through a shaperetaining chamber. This chamber is vibrating so as to present a moving surface to the bag to reduce frictional contact and, more important, to settle the product before the top seal is made. Since the bag is confined and not allowed to round out, headspace between product and top seal is kept to a minimum, thereby reducing air entrapment to manageable levels. Flap spreaders ensure that there is unobstructed access into the box.
The shaped filled bag slips freely into the box, allowing the four corners of the bag to settle snugly into the bottom, making maximum use of available volume. The bag cutoff is determined by product fill level and, if necessary, can be made so that the top seal protrudes over the score line by several inches. (centimeters) when fully seated in the box, which is neatly pressed down at the next station. While the carton is contained in the flighted chain, it is indexed through a top sealer where hot-melt glue is applied to the flaps, which are railed over before passing under compression rollers. The top sealer is integrated mechanically and electrically with each VFFS machine, and because the operation is performed immediately after bag insertion, the carton never has a chance to bulge, which is eventually important for efficient case packing.
This packaging system is rated at up to 100 cartons per minute, and two lines can be mirror-imaged for higher speeds. A recent adaptation of the vertical-load system integrates a carton erector for side-seamed blanks with one VFFS and a top-and-bottom gluer into a single compact module rated at up to 50 boxes per minute.
Another BIB system close-couples a carton former (preglued or flat blanks) with a pocket conveyor that indexes the box to a series of bag insertion, filling, sealing, and carton top/bottom gluing stations. The bag is formed using vertical form/fill techniques utilizing a rectangular forming tube. A unique gripping mechanism engages the bottom seal of the bag and pulls it into the box from underneath. The bag top is left open to be filled with product at succeeding stations. This system offers the advantages of multiple-stage filling for optimum accuracy, checkweighing, and settling before the bag top is sealed. This is a very effective way of dealing with the problem of high fill levels. Outputs of 65–80 packages per minute are claimed for this type of machinery.
RELATED CONCEPTS
A field that has grown is institutional bulk packaging of large quantities of product in 10 to 20-lb (4.5 to 9.1-kg) sizes which usually require corrugated-box materials (see Boxes, Corrugated). The VFFS unit is an expanded machine capable of producing large deeply gusseted bags and is usually set up for vertical bag loading. Speeds are in the range of 15–30 cartons per minute. In a related process, not technically ‘‘bag-in-box,’’ horizontal pouch (three-sideseal) machines are close-coupled to a cartoner to automatically insert one or multiple pouches into a carton at high speeds.