Caractérisation diélectrique de colles industrielles en fonction de la fréquence et de la température en vue d’une réticulation par micro-ondes

Industrial bonding with microwaves. dielectric characterization of glues as a function of frequency and temperature

Laboratoire Master (Modélisation Avancée des Systèmes Thermiques et Ecoulements Réels), Groupe de physique expérimentale et micro-ondes, Université de Bordeaux 1, Talence

Abstract

When heating glues with microwaves it is necessary to know their behaviour as reticulation is progressing in order to make the best profit of the energy sent into the product. Actually we can notice that the absorbed power evolves significantly as temperature increases. Some products go into an exothermic rate which comes from a sudden increase in dielectric parameters, this may result in a degradation and even a destruction of the glue. For solving these problems we have perfected methods for measuring permittivity according to temperature in order to foresee the behaviour of glues used in the wood industry. Among these methods two of them are often applied at 2.45 GHz:

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  the first one is based on the method of small perturbations in resonant cavities. The product is injected into a 1.15 mm diameter cylindrical thermal glass tube which is placed inside a rectangular cavity used in transmission and operating in TE₀₁₃ mode.

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  the second one uses an open-ended coaxial cell, in reflection, in TEM mode.

The measurements are often made through an automatic network analyser HP 8752A. The temperature variation can range from 20 to 130°C and the frequency from 300 kHz to 3 GHz. Thus we have been able to compare the reactivity of five vinyl glues at 2.45 GHz from 20°C to 90°C. We provide variation curves of dielectric parameters according to frequency and temperature as well as mechanical results derived from test pieces submitted to mechanical shear stress.