November 2015 Roundtable on Inspection and Testing
Global Service Manager
Testing Machines, Inc.
8 years with the company
R. Charles Murray
PPi Technologies Group
Over 20 years with the company
Q: Simply put, if inspection and testing aren’t taken seriously, how dire can the consequences be?
Muchorski: Manufacturing or converting plastic films which do not meet materials specifications can be catastrophic to the success of a business. Materials produced using improper testing techniques or inadequate testing instrumentation will result in losing key business accounts.
Key test measurement parameters such as thickness, hot tack strength, sealing strength and coefficient of friction must be kept within specifications for the material to perform. If, for example, hot tack strength (the force to measure seal strength while the film is still semi-molten) is too low, the film will not perform or run properly during the filling operation and the package may leak product after it is filled.
Hot tack test methods are sensitive seal strength measurements and are critical for package validation. Seal strength data used to measure the performance of medical packages such as sterilized medical devices can be critical to human health if compromised.
It is equally important that the test equipment is calibrated or result data will be compromised. Purchasing testing equipment should not be considered a used car transaction. Having a longstanding relationship with a reputable instrument vendor is also a key to operating and maintaining a successful quality control testing laboratory.
Murray: Complete loss of reputation, financial ruin (and) almost little chance of recovery.
Q: How does inspection/testing offer better quality control?
Murray: Quality control, by description, is the maintenance of quality standards. Frequent testing and monitoring ensures a repetitive in control operation.
Q: Are there alternatives for measuring surface treatment levels of PE Film?
Muchorski: Converters, film extruders and printers need to measure quality and consistency of film treatment to ensure proper liquid-to-substrate adhesion, for applications such as printing water-soluble ink. In most cases, dyne pens are traditionally used to provide this measurement. Surface test fluids such as dyne pens are the most economical and commonly used method to verify surface properties.
However, numerous disadvantages exist with these devices. Test results using a dyne pen are extremely variable due to operator interpretation, have a wide range of inaccuracy from drying out and aging and are likely to become contaminated from improper use.
An alternative test can be accomplished more reliably using a portable contact angle instrument. Using such an instrument eliminates the variability of dyne pens and their undesirable qualities. A dyne pen applies the test liquid which then beads up across the surface. This is what we refer to as the “receding contact angle,” which is the lowest possible contact angle for a given surface. If you gently apply a small liquid droplet on a substrate, it wets out by gravity (small force) and the surface wetting. This is the “advancing contact angle” and the highest contact angle for a given surface. The difference between these two contact angles is referred to as “wetting hysteresis” and is different for different materials. Very hydrophobic surfaces have in general a very low wetting hysteresis.
Dyne pens are easily contaminated as the felt tip/ball easily picks up contaminants from the test surface. This will lower the surface tension of the test liquid inside the pen and this will, in turn, incorrectly indicate a lower contact angle equal higher surface energy equal increased hydrophobicity at the surface. Testing Machines’ Model PGX Pocket Goniometer offers all the advantages of consistent testing with none of the disadvantages of dyne pens.
Q: Talk about your company’s inspection/testing equipment. What has been the most popular?
Murray: We are a machinery manufacture for pre-made and rollstock pouches. Our tests involve checking the seals made using heat and ultrasonics.