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TESTING

A vial cap is pierced by a needle of known sharpness to determine the pierce force. (Image courtesy Mark-10)

How do you know whether your product is packaged well enough? How can you quantify it? A product’s packaging should be robust enough to withstand the rigors of transport from the manufacturing site and hold up during a lengthy storage period. The package should be sealed sufficiently to maintain sterility and avoid premature rupture. However, the package must still be easy enough to open the end-user.

In determining the quality of packaging, a force or torque value can represent the effort in opening a package. Force is defined as a push or a pull acting on a body. Typical units of force include pound, kilogram, and newton. Torque (also known as a moment) is defined as a force produced on a lever a distance away from the axis of rotation. Torque is calculated by multiplying the force by the length of the lever. Typical units of torque include pound-inches, kilogram-millimeters, and Newton-centimeters.

In packaging testing, the force or torque value measured during a test is compared with a commonly accepted or internally developed standard. In the case of a syringe package, if a range of 2.5–3.5 lb was specified, a test result of 3 lb would deem the package acceptable. In the case of a pharmaceutical bottle cap, if a range of 10–12 lb-in. was specified, a test result of 15 lb-in. would deem the package unacceptable. Many applications for force and torque tests exist, with some common examples as follows:

90º peel strength of adhesive seals on containers. The force required to peel off foil seals commonly found on containers is important. The foil is typically pulled off a container at a consistent rate of speed, typically at a 90º angle, in conformance with ASTM D6862-03. Extreme difficultulty or ease in opening can have consequences.

180º degree peel test on films. Many pouches, bags, and other packages are heat sealed. The strength of the seal can be determined by subjecting a strip of material to a 180º peel test, where the two loose ends of the material are pulled apart at the seal. Tests are typically performed to conform to ASTM D903 and ASTM F88.

Puncture testing of films and foils. The robustness of a piece of material may be determined by piercing it with a known object and observing the required force. Such testing can approximate real-world conditions in which a package may be accidentally punctured.

Cap removal torque. The cap on a closure is twisted until loosened, and the maximum torque value is measured. Insufficient or excessive opening torque may present a problem. Capping machines used by pharmaceutical packaging plants should be set to tighten the caps sufficiently to prevent accidental loosening, such as through movement during transportation. The cap should still be easy enough for the user to open.

Maximum load usually concerns package testers the most. (Image courtesy Mark-10)

Tensile testing of films. Films, most commonly plastics, should be tensile tested to ensure durability in the field. Material strips are pulled at each end at a controlled rate of speed. A force-versus-deflection curve (typically called a stress-versus-strain curve) is then used to analyze the sample’s performance. Such tests are normally performed in accordance with ISO 527-1/ASTM D638-08.

Commonly available equipment can help accomplish these tests. Among the most basic load-measuring devices available are digital force and torque gauges, which are handheld instruments that integrate a load cell with electronics and display. Gauges are typically used in conjunction with a manually operated or motorized test stand. By regulating the speed of the test, test stands help ensure consistency between samples and batches. A wide range of load capacities for gauges and test stands reflect the great number of different packaging strengths.

Select a gauge with a capacity reasonably close to the expected maximum force, since gauge accuracy is normally specified as a percentage of full scale. Additionally, the resolution decreases with increased load. For example, a 50-lb capacity force gauge may have resolution of 0.02 lb, with accuracy of ±0.2% of full scale. The maximum potential error is 0.1 lb anywhere along the scale from 0 to 50 lb. If the total measured force is only 1 lb, the potential error of 0.1 lb is equal to 10%, which is quite significant.

Force and torque data can yield a wealth of information. The value often of most interest is the maximum load: the force or torque value at which a sample broke, engaged, loosened, etc. This ultimate strength can indicate packaging performance. A less used but important alternative to maximum load is the average load recorded over time.

In many cases more data are desired. Having the proper instrumentation and software is important. Some force and torque measuring instruments are capable of providing a continuous stream of real-time data that can be output to a PC or data collector for further analysis.