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Film Criteria for Vertical Form/Fill/Seal Applications

Vertical form/fill/seal operations depend on the right films for optimal performance.

Vertical Form Fill Seal Machine

As noted in last month’s column “Vertical Form/Fill/Seal 101: Key Considerations”, vf/f/s is a process where roll film is formed into a tubular package, filled, and sealed, repeatedly, in a vertical orientation. It then stands to reason that the characteristics of the film impact machine efficiency and packaging quality.

The term film herein is used to denote any vf/f/s substrate, including those that incorporate coatings, foil, and metallizing. A film must meet product requirements (for example, barrier properties) when a decision-maker chooses among a monolayer, a coextrusion, or a lamination. Optimal productivity and cost-effectiveness, however, can’t be achieved unless the film also meets machine requirements. Each of the three operations imposes requirements that set film criteria.

Form. A film requires stiffness to withstand enacted forces, starting with the tension exerted by the unwinding of the roll. Forces continue as the film is pulled upward, around, and over sets of rollers. A film also requires a sufficiently low coefficient of friction (COF), enabling it to slide over the forming collar and filling tube as it’s made into the desired shape. At the same time, the film requires pliability as it’s wrapped and folded around the collar and tube. Stiffness again comes into play as the formed package is pulled downward by driving belts. Also reasserting itself is the COF, this time needing to be low enough to accommodate the grip of the driving belts.

Lacking these properties, a film is subject to splitting, breaking, bunching, creasing, and sticking, among other undesirable effects. All of them can affect package registration, which refers to the package’s being in the proper orientation for a given purpose. It’s particularly important for pre-printed film; the graphics of which have to be properly aligned, typically with an electronic eye. It’s equally important for in-line coding, e.g., batch numbers, expiration dates, etc. Depending on package type, proper package registration also is essential for the location of features such as tear notches, zipper strips, and punched holes for display hanging.

FILL. Product flows down into the packages from fillers that weigh and dispense. However, the physical effects differ, in accordance with product properties, e.g., dry, granular, pellet, wet, liquid, etc. The package must be able to endure any imposed bulging, for example. A related concern is that the product’s shape, weight, and density may puncture the package. The film’s thickness plays a part, along with properties such as tensile strength, tear resistance, elongation, and modulus of elasticity, among others.

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