Patent ID: 6103313
Filing Date: 2000-08-15
Classification: B05C,B05D,G03C,Y10S

Abstract:
A curtain coating method comprising the steps ofa) forming a composite layer of a plurality of coating compositions;b) forming a freely falling curtain from said composite layer and impinging said freely falling curtain against a continuously moving receiving surface;c) providing said receiving surface with roughness;d) providing an electrostatic field at said impingement point, ande) providing said coating composition forming the layer adjacent to said receiving surface with a viscosity, .eta., measured at a shear rate of 10,000 s.sup.-1, such that, when combined with said roughness, said curtain and electrostatic field, gives a value of specifying parameter .phi..sub.E that is greater than 1,where said specifying parameter, .phi..sub.E, is defined by ##EQU5## wherein, .sigma. is the surface tension (N/m) of the liquid layer adjacent to said receiving surface at impingement,R.sub.z is the surface roughness (m) as defined IN DIN 4768,.eta. is the viscosity (Pa s) measured at a shear rate of 10,000 s.sup.-1 of the composition adjacent to said receiving surface,U is the velocity (m/s) of said curtain at impingement on said receiving surface.theta. is the angle formed between said curtain and the normal to said receiving surface at the point of impingement,.rho. is the lowest density (kg/m.sup.3) of said plurality of coating compositions,Q is the total volumetric flow rate per unit width (m.sup.2 /s) of said curtain,.epsilon. is the dielectric constant of the ambient gas or air,.epsilon..sub.0 is the permittivity of free space (8.854188.times.10.sup.-12 F/m),E is the field strength (V/m) at the surface of said coating composition adjacent to said receiving surface, and ##EQU6## wherein said field strength is at least 3 kV/mm and said curtain height is at least 0.07 m, whereby high coating speeds can be attained.