Testing of Preforms
PET has many benefits over other forms of packings. It is cost effective, durable and sustainable. Due to its light weight and easy moulding properties, it is very much preferred over other materials like paper, CFB, flex pack, etc. Manufactures can easily create packing which is aesthetically rich and durable at the same time, without compromising on anything. Moreover, this form of packing doesn’t add too much cost to the end product. It has non-reactive properties which make it fit to use for packing consumables and pharma products. To make packing that last long and withstand different environmental and handling conditions, preforms are tested strictly according to test standards. Testing devices like Polariscope, Wall thickness gauge, Colorimeter, etc. are some commonly used devices.
For durable PET products, the first step is to conduct testing on preforms. If there are defects in the preforms, the end product will definitely fail when subjected to filling line or top load. Polariscope is used to determine any defects in the preforms. It can easily detect the crystallinity in the preforms. An incident light is made to pass through the test sample, which usually allows the light to pass completely through it. If there is any defect, the incident light will refract from its path creating molecular birefringent flow lines in colour. If not this, it shows black isoclinic lines when observed parallel to the polarised axis.
PET is tested at two points; one after the blow moulding and second at the filling (if used for packing). After blow moulding, there are chances that there is the uneven thickness of the wall or deformity at the neck or base. If not tested right after this point, the defective PET comes into usage cycle and may fail in actual working conditions. Wall thickness gauge (Magna-Mike 8600) can be used for quantifying uniformity of the bottle. Base clearance tester is another device used for testing the base of the bottle. All these tests determine the stability and balancing.
Again, PET storage bottles and jars are tested with a top load tester. In this test, a specific load is applied from the top on the test material until buckling appears. The load is considered as a standard for that specific lot. Another benefit of top-load testing is that it identifies the defect observed consistently throughout the faulty batch. For instance, deformity always appear around the neckline of the bottle, this helps the quality managers to estimate that preform design and specifications need to be reconsidered. This is usually possible if preform testing using polariscope is skipped.