US 7,547,461 Process for producing electrophotographic composition layer having controlled thickness by dip coating on thin substrate
A method for controlling the thickness and uniformity of a dip coated layer, using a coating apparatus under conditions of controlled temperature and controlled low humidity, includes the following steps: under normal coating conditions of ambient temperature and relative humidity, forming on a metal substrate having a thickness of at least about 500 microns a series of coated layers 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, the coated layer being formed on a thin substrate under coating conditions of controlled temperature and controlled low humidity; 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), the coated layer being formed on a thin substrate under coating conditions of controlled temperature and controlled low humidity.