By far, plastic pouches are the cheapest of all styles of containers used for packaging liquids or liquid food, as the weight of these pouches is generally 1/3-1/10 of rigid and semi-rigid containers.
The “integrity of the package” is the primary concern facing the packager of liquids that utilizes plastic pouches. Both the seals and the packaging wall must not only be 100% leak-proof, they must also successfully withstand the mechanical stress faced during product distribution. The packager also supports the pouch on a frequent basis through the use of a paperboard carton as the outside container. The “bag-in-box” arrangement is the most frequently used version of this system.
Unsupported Plastic Pouches
The VFFS system has already been adapted to successfully package milk and other fluid-based food products. Notably, the machine, the material of which should be stainless steel and run in a sterile environment, typically operates in the same manner as described/indicated above for dry/free-flowing products.
Apart from hygiene-related prerequisites, the other key difference lies in the film’s requirements. It is necessary for both the top and bottom seals to be created using a film of liquid which contains substantial quantities of fat on a frequent basis. This implies that the film needs to be sealed reliably and hermetically under some very trying conditions, something that most plastics are unable to withstand.
The packaging of small amounts of fluid-based products like mayonnaise, mustard, relish and ketchup are usually done in four-side-seal pouches on a vertical machine to which two webs of film are fed. Both webs come into contact at their edges before being sealed. It is possible to make a number of small pouches at the same time by sealing both webs collectively at intervals across their width, before eventually cutting them apart at the mid portion of each overlapping seal.
This distinctly specialized technique of packaging is used for extremely viscous yet pumpable products – including specific kinds of processed cheeses and meat, bread dough and cookie – as well as explosives in the form of a gel or paste. As with the more frequently used VFFS equipment, a stream of product and roll of plastic end up feeding these packaging machines.
After the plastic passes over a forming head wherein a side seam seal creates a tube, the tube is closed using a plastic clip or a metal (rather than a heat seal) to accommodate the product that is subsequently metered in. Thereafter, the top portion of the filled package is clipped off in the same sequence of steps that involves slitting the next tube’s bottom portion.
Plastic Pouches Supported by a Box (Bag in Box)
By using a paperboard box to provide support to the plastic pouch containing the fluid product, packagers are able to leverage the bag-in-box system for filling much higher quantities of products than an unsupported pouch system can accommodate.
Currently, individual bag-in-box packages that contain up to 330 gallons of liquid products, which primarily consist of foods, are being utilized. The packager benefits from significant savings through these light weight packages.
During the process of bag-making, the bag-in-box package contains a plastic bag attached using a spout, which, is assembled as an important component of the bag. After the spout fills the bag with liquid, atypically as part of a different procedure, it is subsequently capped off using a molded plastic valve via which the liquid contents can be dispensed at a later stage.
Generally, the bag is essentially a lamination comprising of two distinct films. One of these is an inner layer which establishes contact with the food contents, whereas the other one provides the necessary barrier to gases.
While packaging liquid foods inside such containers, it becomes important to use machinery that is specifically designed for providing sterile conditions. To this end the inside portion of the bag is sterilized by the heat generated during the process of making bags.
Capping off the bag while it remains hot allows these conditions to be maintained. Meanwhile in cases when the bag is filled during a distinct operation that is not part of the bag-making process, chlorine or steam must be used to sterilize its outer surface. On the other hand, if product filling, bag making and film making are all undertaken within the same operation, the heat created during the process of film-making is strong enough to get the entire bag sterilized.