リバースロールコーターにおける塗布安定条件に関する基礎検討

摘要

Reverse roll coating is widely used to coat a thin liquid layer onto a moving substrate. The metered liquid layer is created within the gap between a pair of co-rotating rolls. To avoid roll damage due to roll run-out, substrate caliper change or splice passage, when gap between rolls is small, one of the rolls will have a compliant polymer cover. The existence of a deformable cover in the gap between metal roll and rubber roll creates a elastrohydrodynamic flow field in that region. As the liquid passes through the coverging-diverging section within the gap it generates pressure, this pressure can deform the elastic roll surface, which in turn, alters the geometry of the gap and the flow. Therefore the uniformity of coating is effected differently than what is observed in the case, when only rigid rolls are used. In this study, visualizations of the flow between a reverse deformable roll and solid stainless steel roll are done to determine how the uniformity of coating is effected by operating parameters: the speed ratio, roll diameter and liquid properties. The wavelength of ribbing is investigated to verify the effect of speed ratio, wet thickness and viscosity. The roll coating apparatus is used with 4 inch diameter rolls installed one above the other for these experiments. The ribbing wavelength is measured from images. The uniformity of coating and its dependence on capillary number is evaluated. Numerical simulation of the flow between 2rolls leading to prediction of ribbing wavelength is conducted.%近年，鋼板表面上に絶縁性，耐食性，塗装性などの機能を付与することにより，高級化を図った表面処理鋼板の需要が拡大している。また，連続的に走行する基材へ薄い皮膜をコーティングするプロセスとしてロールコーターが幅広い分野で適用されている。ロールコーターでは，パン皿に保持した塗布液をロールによりくみ上げ，所定の膜厚に調整した後に，基材表面へ塗布液を塗布するプロセスとなっており，一般的には複数のロールを用いて膜厚を所定量に調整している。また，ロールの回転方向によりフォワード方式（ロールの回転方向が接触部で同一方向）とリバース方式（ロールの回転方向が接触部で反対方向）に分けられる。