Process for glueing two non-metallic substrates by means of an a

Details Process for glueing two non-metallic substrates by means of an a Process for glueing two non-metallic substrates by means of an a

1994-04-22

1995-09-05

Barry, Chester T.

Adhesive bonding and miscellaneous chemical manufacture

Methods

Surface bonding and/or assembly therefor

B32B 3100

Patent

active

054475929

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a process for glueing two non-metallic substrates by means of an adhesive with the aid of a hot-polymerizable resin.
It has already been proposed to add ferromagnetic or ferrimagnetic fillers to hot polymerizable resins in order to heat them by induction.
If this kind of heating process is to have commercial value relative to heating in a furnace, in which the resin substrate assembly is brought progressively to the higher temperature of polymerization of the resin, this heating must make it possible to put the entire mass of resin, and above all the resin/substrate interface, at the temperature of polymerization within a period of less than 1 minute, with the temperature of polymerization not dropping below the lower limit of polymerization. This heating time must not involve very high frequencies, whose use on an industrial scale presents excessive problems, both in terms of equipment and of safety; it must no longer involve overly high proportions of fillers, at the cost of impairing the mechanical properties of the resin. Given the poor thermal conductivity of both the resin and the substrate that are to be glued, the temperature of the particles heated by induction must not substantially exceed the upper temperature of polymerization, at the cost of spoiling the resin in contact with the particles by excessive temperature. In other words, the rise in temperature of the particles must be relatively slow, to enable diffusion of the heat to the resin and the substrate. The heating is interrupted as soon as the upper polymerization temperature is reached. If this rise in temperature is overly rapid, then it must also be interrupted as soon as the upper polymerization temperature is reached, to enable the heat to diffuse, but the alternating induction field must then be re-applied until the energy necessary for the polymerization has been transmitted.
It is known that the thermal energy generated by induction in a magnetic field may be the result of three types of losses: Foucault current losses, which increase with the dimensions of the conductor element, and which are higher, the lower the resistivity; hysteresis losses, which are virtually independent of the size but are dependent on the shape of ferromagnetic or ferrimagnetic particles, and which are greater than the Foucault current losses in the case of fine particles; and residual losses, which involve phenomena such as dielectric losses or "magnetic viscosity", which represent a major part of the losses in the case of ferrites. The Foucault current losses and hysteresis losses increase with the square of the frequency, and the frequency, respectively.
In the case of heating of a resin by incorporating fillers capable of heating by induction, hysteresis losses have already been a preoccupation in the prior art, and particles capable of rising to temperature more rapidly thanks to these losses have therefore been sought.
This is the teaching in particular of European Patent Disclosure EP 82 403 276, in which particles have been sought that have high coercive magnetic fields associated with magnetic induction fields of from 1 to 15 times the coercive force of the heating particles. This leads to a choice of very fine particles, less than 1 .mu.m in size, with very high resistivity in high concentration, and to the employment of magnetic fields that may range as high as 480 kA/m. No information whatever is provided about the mechanical properties obtained when this process is used to glue two nonmetallic substrates with the aid of an induction-heated resin.
U.S. Pat. No. 5,075,034 relates to a version in which conductive carbon black is associated with ferromagnetic or ferrimagnetic particles in an adhesive composition. The purpose of the carbon black is to lower the volumetric resistivity of the adhesive mixture in order to enable rapid induction heating at relatively low frequency, doubtless by Foucault current. This version leads to the use of a relatively large proportion of solid matter in the resin, which is likel

REFERENCES:
patent: 5129977 (1992-07-01), Leatherman

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