US 7,544,382 : Dip coating process for producing electrophotographic composition layer having controlled thickness
A method for controlling the thickness and uniformity of a dip coated layer, using a coating apparatus in a normal coating environment, includes the following steps: forming under normal coating conditions of ambient temperature and relative humidity a series of coated layers on a metal substrate having a thickness of at least about 500 microns, using variations in coating solution viscosity m, coating substrate withdrawal speed v, capillary number Ca, coating solution surface tension S, and boiling point bp (a correlative of evaporation rate)of the coating solution solvent, a coated layer including at least a portion of uniform thickness T(even) and, optionally, a portion of non-uniform thickness L (uneven); statistically analyzing measurements carried out on the series of coated layers and generating the constants, a, b, c, d, and e for Equations 2, 3, and 4:
T(even)=a+b(m*v) (Equation 2)
L(uneven)=c+d*(v*bp)+e*(Ca*bp) (Equation 3)
v(even)=−c/bp*(d+e*m/S) (Equation 4)
using Equation 4, determining the coating speed v(even) producing the maximum thickness of a coated layer having a completely uniform thickness for a given set of coating solution characteristics; and using Equation 2, determining the thickness T(even) of the portion of the coated layer having uniform thickness for a given set of coating solution characteristics and the coating speed determined in step (c).