Patent ID: 7544382

Claim:
A method for controlling the thickness and uniformity of a dip coated layer using a coating apparatus in a normal coating environment, 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 viscositym, 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) measuring the thickness of the coated substrate at various positions along the full length of the coated substrate; (c) generating a plot of the thickness vs. axial position; (d) measuring the length of the uneven thickness portion of the coated layer L(uneven); (e) measuring the thickness of the uniform thickness portion of the coated layer T(even), and statistically analyzing the L(uneven) measurements as a function of (m*v), where m is the viscosity in poise and v is the coating withdrawal speed in cm/sec to generate Equation 2, T (even)= a+b ( m*v ) (Equation 2) which predicts the thickness T(even), in cm, of the portion of the coated layer having uniform thickness; (f) statistically analyzing the L(uneven) measurements as a function of (v*bp) and (Ca*bp), where v is the coating speed in cm/sec, bp is the boiling point of the coating solvent, Ca is equal to (m*v)/S, a dimensionless number, where m is the viscosity of the coating solution in poise, v is the coating speed in cm/sec5 and S is the surface tension of the coating solution to generate Equation 3, L (uneven)= c+d *( v*bp )+ e* ( Ca*bp ) (Equation 3) which predicts the length L(uneven), in cm, of a sloping portion of the coated layer having non-uniform thickness; (g) obtaining Equation 4 v (even)=− c/bp *( d+e*m/S ) (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 by setting L(uneven) =0; (h) using Equation 4, detennining the coating speed v(even) for producing the maximum thickness of a coated layer having completely uniform thickness for a given set of coating solution characteristics; and (i) 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 v(even) determined in step (h); and (j) using the v(even) and T(even) values determined in (h) and (i) to control the thickness and uniformity of a dip coated layer using a coating apparatus in a normal coating environment.