抄録
The curing process of urea resin adhesive was studied by the change of fluidity measured with Koka Flow Tester.
The flow test was operated under the fixed testing conditions of pressure (10kg/cm2), orifice dimensions (0.2mmφ×1mm), and temperature (20°C). The volumetric flow rate was calculated at several points on the auto-recorded flow curves. And the relative fluidity-decay curves were obtained by plotting in the form Q(t)/Q(0), where Q(t) was the efflux rate at time t, and Q (0) the initially measured efflux rate, versus log t for each sample.
In order to express the character of fluidity in curing urea resin as a function of time and hydrogen ion concentration, experiments were made with resins adjusted to various pH's. It seems that the change in pH removed the fluidity-decay curve horizontally along the logarithmic time axis. The slope of the curve, however, was affected by the condensation degrees of the resin.
To find any possible influence of chemical components of resin in the shape of the fluidity-decay curve, further experiments were carried out by using several different resins.
As the resins used were prepared under different conditions, they were subjected to analysis to determine the amounts of free and combined formaldehyde (methylol, methylene, and dimethylene ether groups). The results revealed that the shape of the fluidity-decay curve was remarkably varied with the amount of the aldehyde groups. It seems that the fluidity-decay curve represents the condensation process of the urea resin.
