Method and a composition for producing an undercoat layer using dialkyl malonate blocked isocyanates (for electrophotographic applications)
View Patent ↗A method and a composition for the production of surface smoothing polyurethane layers for application to a substrate prior to subsequent application of a charge generation layer for electrophotographic applications by preparing a coating solution containing a dialkyl malonate capped isocyanate or polyisocyanate, a polyol and at least one finely-divided metal oxide, coating the substrate with the coating solution and heating the coating solution to a temperature up to about 140° C.
1. A method for coating an electrophotographic process element adapted to receive an image from a light source with the light image then being converted to an electric charge image with a conductive polyurethane undercoat layer; the method comprising:
a) producing a coating solution comprising a dialkyl malonate capped isocyanate or polyisocyanate, a polyol, a monofunctional alcohol and at least one finely divided metal oxide or mixtures thereof;
b) coating the substrate with the coating solution to produce a coated substrate; and,
c) heating the coated substrate at a temperature up to about 140° C. wherein the at least one metal oxide is present in an amount equal to from about 40 to about 90 weight percent of solids in the polyurethane layer.
2. The method of claim 1 wherein the element comprises a seamless metallic sleeve.
3. The method of claim 1 wherein the element comprises a seamless nickel sleeve.
4. The method of claim 1 wherein the element comprises a seamless plastic sleeve.
5. The method of claim 1 wherein the element comprises a photoelectric film.
6. The method of claim 1 wherein the dialkyl malonate is diethyl malonate.
7. The method of claim 1 wherein the dialkyl malonate contain the alkyl groups containing from 1 to about 12 carbon atoms.
8. The method of claim 7 wherein the alkyl groups contain from 2 to about 6 carbon atoms.
9. The method of claim 7 wherein the alkyl groups of the dialkyl malonate are the same.
10. The method of claim 7 wherein the alkyl groups of the dialkyl malonate are different.
11. The method of claim 1 wherein the isocyanate moiety is hexamethylene diisocyanate biuret.
12. The method of claim 1 wherein the isocyanate moiety is isophorone triisocyanate.
13. The method of claim 1 wherein a mixture of DEM-blocked isophorone triisocyanate and DEM-blocked hexamethylene diisocyanate buret is used.
14. The method of claim 1 wherein the isocyanate and polyol are present in amounts sufficient to provide an OH group to NCO group ratio of from about 1:1 to about 1:5.
15. The method of claim 14 wherein the ratio is from about 1:1 to about 1:3.
16. The method of claim 1 where the polyol is a vinyl polymer made of 81 mole % vinyl chloride, 4-mole % vinyl acetate, 15-mole % hydroxy ethyl acrylate, and hydroxyl value of 59.
17. The method of claim 1 where the polyol is a mixture comprising a vinyl polymer made of 81 mole % vinyl chloride, 4 mole % vinyl acetate, 15 mole % hydroxy ethyl acrylate, and hydroxyl value of 59; and three-fourth pentaerythritol ethoxylated.
18. The method of claim 1 wherein the at least one finely divided metal oxide is selected from the group consisting of metal oxides of titanium, zirconium, indium, antimony, tin, aluminum and mixtures thereof.
19. The method of claim 1 wherein the amount is from about 60 to 80 weight percent.
20. The method of claim 1 wherein the finely divided metal oxide comprises particles of a size less than about 0.1 micron.
21. The method of claim 20 wherein the size is from about 10 to about 50 nanometers.
22. The method of claim 1 wherein the polyurethane layer has a thickness of at least 2 microns.
23. The method of claim 22 wherein the thickness is greater than about 10 microns.
24. The method of claim 1 wherein the mono-functional alcohol is present in an amount from about 10 to about 25-weight percent monofunctional alcohol based upon the weight of the coating solution.