塗膜の硬化速度解析:水性ベース塗料中のアミンがクリア塗料の硬化に及ぼす影響

摘要

溶剤型クリアを水性べース上に積層して一括焼付けすると，ベース層に含有されるアミンが焼付け中に移動してクリア層の硬化速度に影響するか調べた。硬化速度は，ナイフエッジを支点とし，試料膜と接した状態で振動する剛体振り子の運動から粘弾性を測定する振り子式粘弾性測定装置で評価した。測定原理に基づいて各層の寄与を見積もった結果，上記装置の測定結果は実質的にクリア層のみの硬化挙動をあらわすことがわかった。積層系で硬化速度定数を測定した結果，クリア塗料が酸エポキシ架橋の場合には硬化促進，メラミン架橋の場合には硬化阻害の影響があり，イソシアネート架橋の場合は影響が認められなかった。これらは各クリア塗料にアミンを添加した場合と定性的に同じ結果であった。上記の手法で積層系での硬化速度を定量的に評価できることが明らかになった。%A viscoelasticity measurement device for measuring complex moduli of coatings films during cure process was applied to multi-layer systems. The device is equipped with a pendulum and the fulcrum of it is a knife edge as a probe for coatings moduli. Theoretical consideration predicts that the contribution of the upper layer to measurement is dominant so that the modulus measurement deviation by assuming single layer of clear-coat will be7% in a typical case. Three clear-coats with different curing chemistry were laminated on common waterborne base-coat in 2C1B process and cure rate constants were examined. As waterborne base-coat contains amine, curing measurements were also applied to single layers of amine-added clear-coats and neat clear-coats. The curing rate of acid-epoxy clear-coat was increased in 2C1B and amine-added single layer, whereas the curing rate of melamine curing clear-coat was decreased. No effect was observed in the case of isocyanate curing clear-coat. Accordingly, it is possible to quantitatively discuss the influence of amine migration from base-coat on clear-coat curing.