Patent ID: 7547461

Claim:
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, said method comprising: (a) 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, coating solution surface tension S, and boiling point bp of coating solution solvent, at least a portion T(even) of a coated layer being of uniform thickness and, optionally, a portion L(uneven) of said coated layer being of non-uniform thickness; (b) statistically analyzing measurements carried out on said series of coated layers and generating the constants, a, b, c, d, and e for the following Equations 2, 3, and 4: (i) Equation 2, which predicts the thickness T(even), in cm, of the portion of the coated layer having uniform thickness T (even)= a+b ( m*v ) (Equation 2) where a and b are constants, m is the dynamic viscosity, in poise, of the coating solution, and v is the substrate withdrawal speed in cm/sec, (ii) Equation 3, which predicts the length L(uneven), in cm, of a sloping portion of the coated layer having non-uniform thickness L (uneven)= c+d* ( v*bp )+ e* ( Ca*bp ) (Equation 3) where c, d, and e are constants, v the substrate withdrawal speed in cm/sec, bp is the boiling point of the coating solvent in ° C., and Ca is the capillary number, (iii) Equation 4, which predicts the substrate withdrawal coating speed v(even), in cm/sec, required for the maximum thickness of a coated layer having a completely uniform thickness, which occurs when L(uneven)=0: v (even)=− c /( bp* ( d+e*m/S )) (Equation 4) where c, d, and e are constants, bp is the boiling point in ° C. of the coating solvent, m is the dynamic viscosity, in poise, of the coating solution, and S is the surface tension, in dyne/cm, of the coating solution; (c) using Equation 4, determining the coating speed v(even) producing the maximum thickness of a coated layer having completely uniform thickness for a given set of coating solution characteristics, said coated layer being formed on a thin substrate under coating conditions of controlled temperature and controlled low humidity; and (d) using Equation 2, determining the thickness T(even) of the portion of a coated layer having uniform thickness for a given set of coating solution characteristics and the coating speed determined in step (c), said coated layer being formed on a thin substrate under coating conditions of controlled temperature and controlled low humidity; and (e) using the v(even) and T(even) values determined in (c) and (d) to control the thickness and uniformity of a dip coated layer on a thin substrate using a coating apparatus under conditions of controlled temperature and controlled low humidity.