Roll Coating

인쇄 공정 중 산업에서는 종종 인쇄면에 잉크를 전달하고 적용하는 롤 코팅(roll coating) 이라고 불리는 기술을 사용합니다. 이 공정에서 통상적으로 잉크 유액은 두 개의 회전하는 실린더 사이의 좁은 갭(gap)으로 흘러 들어갑니다.

 

롤 코팅 공정 앞쪽의 시뮬레이션, air entrainment 있고(상단) 없고(하단), 공기방울의 존재는 유액 물성과 표면의 contact angle, roller의 속도에 의존합니다. Courtesy Institute of Fluid Mechanics (LSTM), Universitat Erlangen.

Validating the Forward Roll Coating Process

 

The computed splitting distance was 0.50cm versus the asymptotic analysis result of 0.509cm, a very good agreement for a computation that only took 172s of CPU time.

 

In a well known paper by Coyle, Macosko and Scriven (J.Fluid Mech., (1986), V.171, p.183) an asymptotic analysis is presented for the splitting distance, i.e., the distance from the minimum gap location to the downstream position of the free surface on the centerline between the cylinders. Here we use this prediction as a validation test for FLOW-3D. The rolls have radii of 2.54cm and a minimum separation of 0.02cm. Their tangential speed in the gap is U=2.0cm/s. A dimensionless flow rate in the gap of 1.3 was specified as an inflow boundary condition. The liquid has a viscosity of μ=0.2poise and surface tension of σ=2.0dyne/cm, resulting in a Capillary number of μU/σ=0.2. Because of symmetry, only the top half of the flow region was simulated. The complete flow region could easily have been simulated and included rolls with different radii and/or different speeds. The final steady results are shown in the figure above, where only every other velocity vector is displayed to avoid overcrowding. The blue region shows where the horizontal velocity is negative, indicating a pair of counter rotating vortices at the splitting point.