By Tony Ring, technical director Fielco Adhesives. Huntingdon Valley, PA
In the March issue we discussed ways to use specialized instruments – the Brookfield cone-plate digital rheometer and the Aquastar titrator – for answering specific customer concerns. Continuing with this series, this article discusses two more instruments, the dielectric analyzer and the differential scanning calorimeter. In each case, a high technology product required a specific test with these instruments. The series will conclude in the October issue.
Differential Scanning Calorimeter
The differential scanning calorimeter measures both the temperature and heat flow associated with material transitions. The operator determines heat and temperature values required by a specific manufacturing operation and then sets the instrument, which works as a small, precise oven. This oven can be used to control chamber conditions from -170ºC to 725ºC, within 0.1º. We have used this equipment often to determine the glass transition of a polymer, which is the point where the material changes from a rigid piece to a rubbery material. This value is an excellent indicator of the temperature range in which the mechanical properties of a test material will remain constant.
Fielco uses this instrument to analyze samples of finished product that are not performing to spec. Mechanical problems that seem to be temperature related can be correlated to fundamental properties such as glass transition temperatures. For example, we found that the high temperature shear strength of our Masterweld 5970A/ 42B was related to the glass transition temperature. As a result, we were able to make very specific recommendations for the product – that it should only be used at certain grinding temperatures of 175ºF or less. For significantly higher temperatures, we would recommend a different material with a higher glass transition temperature and the associated high crosslinking density.
The dielectric analyzer (DEA) measures resistance to electrical current as well as the storage of an electrical charge in materials. The instrument functions by rapidly oscillating a charge difference between two parallel plates and measuring the time lag for the change to occur in the sample materials between the two plates. From this time lag, it is possible to determine the values of the material’s dielectric constant or energy storage from a material sample. The DEA can be operated at a constant temperature or frequency or across a broad range of temperatures and frequencies. A sample can be measured, cycled through temperature ranges and remeasured to test intended operating conditions. Alternately, a product can be measured, removed, exposed to temperature and humidity cycling, and remeasured to establish performance limits for a final product.
The DEA can be used for technical service when customers have problems with electronic potting materials. For example, one customer had difficulties with signal loss with a specific batch of potting material. The DEA was used to verify that the dielectric constant was high on the customer’s defective material, while showing normal properties on freshly mixed material. Based on this data and an abnormal DSC test, the customer’s meter-mix dispensing equipment was examined and the problem identified as an improper mix ratio, too high in curing agent. Materials testing is a critically important aspect of quality control, especially given the exacting tolerances of electrical materials. We invested in these instruments to pinpoint problems and lead the way to fast effective solutions. AA
For more information please contact Fielco at 215-674-8700 or visit our web site at http://www.fielco.corn.
AA REPRINTED FROM ADHESIVES AGE, JUNE 1998