Process for producing electrophotographic composition layer having controlled thickness by dip coating on thin substrate

1. 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.

2. The method of claim 1 wherein said thin substrate has a thickness of less than about 500 microns.

3. The method of claim 2 wherein said thin substrate has a thickness of about 10 microns to about 200 microns.

4. The method of claim 1 wherein said thin substrate is formed from a metal.

5. The method of claim 4 wherein said metal is selected from the group consisting of nickel, aluminum, and steel.

6. The method of claim 5 wherein said metal is nickel.

7. The method of claim 1 wherein said thin substrate is formed from a plastic.

8. The method of claim 1 wherein said thin substrate is a tubular sleeve.

9. The method of claim 1 wherein said controlled temperature is from about 20° C. to about 25° C.

10. The method of claim 1 wherein said controlled humidity is below about 20% R.H.

11. The method of claim 10 wherein said controlled humidity is from about 5% R.H. to about 10% R.H.

12. The method of claim 1 wherein the portion of the coated layer of uniform thickness has a thickness of about 5 μm to about 60 μm.

13. The method of claim 12 wherein the portion of the coated layer of uniform thickness has a thickness of about 10 μm to about 40 μm.

14. The method of claim 13 wherein the portion of the coated layer of uniform thickness has a thickness of about 15 μm to about 30 μm.

15. The method of claim 1 wherein the coated layer includes a controlled portion of non-uniform thickness.

16. The method of claim 1 wherein the coated layer comprises a charge transport agent.

17. The method of claim 1 wherein the coated layer comprises a charge generation agent.

18. The method of claim 1 wherein the coating solution solvent is selected from the group consisting of toluene, tetrahydrofuran, methylene chloride, acetone, methyl ethyl ketone, methyl acetate, ethyl acetate, and mixtures thereof.

19. The method of claim 17 wherein the coating solution solvent is dichloromethane.

20. The method of claim 1 wherein the coating solution solvent has a boiling point below about 100° C.

21. The method of claim 20 wherein the coating solution solvent has a boiling point below about 60° C.

22. The method of claim 21 wherein the coating solution solvent has a boiling point below about 40° C.