New ASTM Standard Proposed For Film-Thickness Measurement

A newly proposed ASTM International standard for measuring film thickness will help processors produce thinner and higher-quality films. So says Doug Lawrence, an ASTM member helping to write the new standard. Lawrence is president of SolveTech, Inc.., Wilmington, Del., which makes capacitance-based, non-contact gauging equipment.

Lawrence says the proposed non-contact test method will help film processors get precise and accurate measurements on thin films and allow for a reproducible set of data points on film samples that correctly characterizes the extrusion process in both the cross-web and machine directions. Thickness and variability are critical to film performance and good roll formation.

Adds Rob Lawrence, SolveTech v.p. of sales and marketing, “The new standard is necessary because the existing standard, D 6988, focuses on a contacting method. If you are making a 0.5-mil film, for example, the accuracy of the contact measurement is about 10% of your overall thickness. When trying to measure variability of ±10%, a contacting method falls short.”

SolveTech recently concluded a gauging repeatability and reproducibility (R&R) study whose results were independently confirmed by several of its customers. On 0.8-mil blown film, the study compared contact and non-contact technologies, the latter using SolveTech’s PR2000 gauge (photo). Typical thresholds for acceptable R&R are 30%; an R&R below 10% is considered a good result. With the non-contacting gauge, SolveTech achieved an R&R of about 3%, while the contacting micrometer achieved approximately 69%, the company said.

“The existing standard calls for a precision of 1 micron (0.04 mils), but this becomes a significant percentage of the variability of a thin film,” Rob Lawrence states. “Our technology, on the other hand, is precise to better than 0.1 micron (0.004 mils). Now you can get a much better picture of the variability of 0.5-mil film. It is also much less affected by dust and dirt, which is a problem mentioned often in D 6988.”

States Mike Ponting, president of PolymerPlus, Valley View, Ohio, which extrudes high-precision nanolayer films for optical and electronic applications, “Advanced technologies continue to move toward miniaturization, requiring thinner films. We produce films as thin as 0.1 mil. We needed a gauging solution that could handle our high-precision layered films while avoiding issues associated with alternative gauging approaches, including optical reflection or x-ray based techniques. We found that solution with SolveTech’s PR2000, and it helped us create market-leading thin films.”