Thursday, August 26, 2010

Scanning Plastic Films for Defects

A new PR blurb from the IKV - Aachen about detecting individual sublayer thicknesses in multilayer films is short on details about the technology used. It's somewhat disappointing, but it really doesn't matter to me as it pretty clear that they have not solved the most fundamental problem in looking for defects on film lines.

Plastic films and the equipment to make them have been around for some time with few significant changes. Whether processed as blown or tentered film, at some point after the orientation is complete, some equipment is used to measure the film thickness. The simplest gauges just measure the overall thickness, while more sophisticated equipment such as is disclosed here, can measure one or more individual layers in a multilayer film. Regardless of the equipment used, they all suffer from a common problem: the equipment only examines a small spot on the film. In an attempt to cover the entire width of the film to look for side-to-side variations, the equipment moves back and forth across the width of the film to look . While this initially seems to be satisfactory, the equipment is only still only examining small section of the film. Let me show this with a picture:In this picture, the newly made film is moving in down the page, and the scanner is moving from first left to right and then back again. Equivalently, the film can thought of as being stationary and the scanner is then moving along the dashed arrows. The dashed areas show the areas of the film that are examined, and conversely, the areas that aren’t. The exact path examined depends on the speeds of both the film and the scanner. The relative velocities of the film and the scanner determine the amount of film examined. The higher the scanner speed, the more the coverage, but you can still see that there will be gaps in the coverage.

The situation would be much improved if the scanner would examine the full width of the film at the same time. Then the area examined would simply be determined by the measurement time and the film speed.

These problems are widely known in the film industry, so if someone had AFFORDABLE equipment to scan the entire width of a film at once, they would be certain to mention it in their press release. Keep in mind that some film operations can produce films that are 8 meters wide, so this is not a small challenge.

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