Blister Packaging, a versatile pre-formed plastic packaging material, is used in a number of different industries including consumer goods, electronics, and pharmaceuticals.
A thermo forming process is used to create a cavity or pocket made from a formable transparent plastic web, the size and shape of which is determined by the product for which it is required. This cavity or pocket is typically heat sealed onto an adhesive coated cardboard or foil to trap the contents in place underneath creating a typical blister pack.
There are many types and variations of blister packs that are used, selected according to the product requirements. Some types like face seal blisters incorporate a flanged blister to surround the product, which is heat sealed onto piece of cardboard, the seal therefore is only on the flange while the rest of the cardboard stays uncovered (usually printed).
Others like the clamshell blister pack incorporates the blister in a hinged two half container that opens and closes, due to its robustness it is therefore suitable for heavy products.
Whichever type of blister packaging is used, clear undistorted visibility of the contents is essential, not only from and aesthetic point of view of the product underneath, but in
pharmaceutical applications critical to allow the pharmacist to visually check markings on the individual doses of medication.
The thermo forming method used to create the cavity is therefore a critical stage in the process as there are several factors that can influence the optical quality of the blister.
Material selection, forming temperature and mould condition all need to be correctly controlled to prevent substandard end products being produced.
Due to the complex shape of this type of packaging, visual quality checks of the blister windows have mostly been used as it has been impossible to perform measurements using traditional sphere-based transmission hazemeters.
The complex shape of the blister material did not present any problems during measurement as there was sufficient coverage of the material over the measurement graticule of the Rhopoint ID.
Each sample was measured 4 times over the surface area to obtain results for Haze (HASTM) and Sharpness (S). Sharpness quantifies the loss of perceived detail for objects viewed through a material.
Measurement Results
A total time of 20mins was taken to measure all samples (4 times x 5 samples –20 measurements) each of which were manually manipulated during measurement.
Images were then analysed to identify changes in optical quality. Average results were calculated and used for the purpose of this report.
Observations of results
Analysing the results, the variation of Haze and Sharpness across the samples could be observed.
Looking in detail at the images for Samples 3 – 5 there appeared to be a texture present on the surface causing a distortion (when viewed at the point where the black and white areas of the measurement graticule meet). This texturing appears higher on Samples 3 & 4 (resulting in a higher haze and lower sharpness) due to the smaller size of the texture whilst on Sample 5, due to the texturing being larger, the haze is lower and sharpness higher.
The ability to obtain numeric and image data allows visual confirmation of the data. The measurement of these samples, due to their shape and size, would have been impossible using a traditional hazemeter.
Rhopoint Instruments
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