フェノール樹脂・ポリビニルブチラール混合系塗膜の誘電特性と粘弾性

Abstract

As the useful properties of the phenol resin-polyvinyl butyral mixed coating materials are due to the cured form of its two ingredients, it appears desirable to understand the resulting dispersed state and the plasticizing effect of the polyvinyl butyral (PVB) on the phenol resin. However, the explanation based on the experimental results has not appeared. In order to ascertain these facts, the dielectric properties of the phenol resin-polyvinyl butyral system cured at high temperature have been measured over a temperature range of -70 to 170°C and a frequency range of 0.3 to 106cps, while these dynamic mechanical properties have been also measured over a temperature range of -70 to 200°C by means of the vibrating reed method at about 50cps.In the phenol resin-polyvinyl butyral system, the two dielectric absorptions, i.e., the higher and lower temperature absorptions, can be observed. These two absorptions are also detected by the dynamic measurement as the mechanical loss peaks at 100 and -42°C, respectively. The dielectric absorption locates in higher temperature region (30-170°C) for the mixed systems may be expected to the glass transition of the PVB which is to be heterogeneous state in the mixed system. Another dielectric absorption locates in lower temperature region (-70-30°C) for the mixed systems, whose PVB contents are from 0 to 60%, is supposed to be caused mainly by the movement of local parts as side groups, especially unreacted methylol and amino groups in the phenol resin molecules.For the mixed systems, the temperature of ε"-maximum at 1cps and the apparent activation energy ΔH* of the dielectric absorption in higher temperature region decrease with increase of the PVB content. From these results, it is suggested that the restriction of segmental motions of the PVB molecules in the mixed system gradually becomes stronger with increase of the phenol resin content.In lower temperature region, ΔH* of the dielectric absorption for the mixed systems is almost independent of the PVB contents and only the dielectric relaxation time τ at any finite temperature decreases with increase of the PVB content: The former seems to be characteristic in such cases where polymers are used as plasticizers, of which the glass transition temperatures are far higher than the temperature of the measuring region. The latter may be due to the reason that the PVB molecules mixed are attached to the phenol resin molecules, keeping them apart and thus enabling the side groups of phenol resin molecules easier to slide over each other.The results of dielectric measurement on this mixed system could successfully be used to argue about the estimation of the mechanism in the mechanical dispersion, because these two properties are found to be intrinsically correlated with each other.