Cure conditions, inductive

Table I. Comparative Fluidity Values for vs. Inductive Cure Conditions. "Normal"...

They are placed between parts to be bonded, they melt during the oven cycle and bond the parts together. They may also act as a potting and encapsulating product. The epoxy formulation may also contain conductive particles in order to allow cure by induction or high frequency. Curing conditions are those of the one-component epoxy adhesives, i.e. from 15 to 60 min at temperatures ranging from 120 to 160°C. 

Polyamides. Polyamides are formed by the condensation reaction of polyamines with dimeric fatty acids. They are available from a number of suppliers in a large variety of viscosities and molecular weights. Many products are available in the form of adducts which provide good compatibility with epoxy resins without the need for an induction period and give a better cure under adverse conditions compared with standard polyamides. Polyamide curing agents offer a number of desirable features, as follows (Dow Chemical Company, undated b) ... 

Immunosuppression has concomitant risks of opportunistic infections and secondary tumors. Therefore, the ultimate goal of research on organ transplantation and autoimmune diseases is to induce and maintain immunologic tolerance, the active state of antigen-specific nonresponsiveness. If attainable, tolerance would represent a true cure for conditions discussed above without the side effects of the various immunosuppressive therapies. The calcineurin inhibitors prevent tolerance induction in some, but not aU, preclinical models. In these same model systems, sirolimus does not prevent tolerance and may even promote tolerance induction. 

A step change of viscosity at critical conditions to infinity (3) is a convenient model for investigating the flow of a curing liquid. The simplest model employs the most important physical property of the process. In a number of papers [83-87], the dependence of the induction period t, the time during which a reactive substance retains the ability to flow, on the rate of shear y is studied. 

In all these cases, the condition of gelation (curing) for non-isothermal flow was generalized with the help of a goieralized criterion similar in structure to the well-known criterion (according to Baily) of long-term strength imder a variable load operation [90]. At a temperature Tq and induction period t, it is assumed that under arbitrary temperature conditions T(t) the value of the induction period tf is expressed as an upper int ral limit in the formula... 

To cure thin coatings in contact with air, it is therefore necessary to work under intense illumination in order to consume rapidly the O2 dissolved in the sample and shorten the exposure time during which atmospheric oxygen diffuses into the coating. This is not a problem anymore in adhesive applications which are performed under oxygen diffusion-free conditions (laminates). After a short induction period during which the dissolved O2 is consumed by the initiator radicals, the polymerisation of the acrylate double bond proceeds as fast in the laminated sample as in an inert atmosphere and much faster than for a coating, as shown in Fig. 2 for a polyurethane-acrylate resin. 

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