Issue link: https://www.e-digitaleditions.com/i/398011
The force-decay method is quick and simple in princi- ple and can detect holes as small as 10 microns, depend- ing on the type of blister material. However, it requires a means of testing the force in each blister cavity. This might limit its flexibility in testing a range of package for- mats and, as with vacuum-decay testing, require expen- sive tooling. Laser testing.Laser testing machines such as the BlisterScan [2] detect weak seals and holes as small as 7 microns in blister packaging. The packages are placed in product-specific nests in a vacuum chamber where a laser scans them. A vacuum is then applied and the laser scans the package again to measure movement within the cavities. A cavity with a large hole will show no movement, whereas one with a small hole will deflate slowly. A third laser scan detects these small holes. The test is non-subjective and offers a high degree of sensitiv- ity. However, special package-specific tooling is required, so it is generally best suited to higher-value products. Vision scanning.Vision scanners, such as the one my company offers [3], are similar in many ways to laser scanners. The packages are placed in a vacuum chamber and a high-resolution camera captures a baseline datum image. A vacuum is then applied, which causes defect- free pockets to "deflect" or swell. Then a second image is taken and compared against the first. Blisters with large holes do not swell and are thus readily apparent. To check for small holes, the vacuum is reduced and a third image is taken. If there is a small hole, it will allow air to slowly enter the cavity, causing it to return to its baseline size (Figure 2). The test is sensitive to holes as small as 15 microns. The vision method allows multiple packs to be tested in a single cycle and, unlike laser scanning, requires no special tooling. Software compares the images automati- cally and determines irregularities and defects based on a pre-determined, validated recipe for the product being tested. Leakage information about each blister cavity is given as an unambiguous pass/fail result, eliminating the guesswork inherent to the blue-dye test. Furthermore, this batch data can be saved and exported as part of the QC process in accord with CFR 21 Part 11. Since vision scanning relies on the movement of lid- ding material to identify good pockets, it may not be suit- able for blisters that remain rigid under changes in pres- sure, such as those with especially thick lidding or a minuscule volume of air inside the cavity. However, if the cavity changes shape enough for a camera to detect it, vision scanning will work. The initial investment in vision scanning technology is higher than that of blue-dye test- ing, but many companies can expect a return on invest- ment within 1 to 2 years. T&C References 1. Code of Federal Regulations 21 Part 211.166. 2. BlisterScan, Sepha, Belfast, UK. 3. VisionScan, Sepha, Belfast, UK. Philip Stevenson is product manager at Sepha, Unit 25 Carrowreagh Business Park, Dundonald, Belfast, UK. Its representative in North America is Service Industries, 3885 Industrial Ave., Rolling Meadows, IL. Tel. 847 392 1652, fax 847 392 0276. Website: www.serviceindustries.biz. 32 October 2014 Tablets & Capsules Figure 2 Vision scanning test method Datum (baseline) Comparison 1 Vacuum Reduced vacuum } Comparison 2 }