Process for predicting gloss of low gloss coating by wet color measurement
The present invention is directed to a process for process for predicting gloss of a coating resulting from a wet layer of a low gloss coating composition, such as automotive OEM or refinish paint. The process includes measuring reflectance of the layer of the coating composition applied over a test substrate and then allowing the layer to dry and/or cure into a coating. Thereafter, its gloss is measured with a gloss meter. The process is repeated with varying amounts of one or flatting agents added to the composition and the reflectance vs. gloss is plotted on a graph and by using a curve fitting equation a gloss prediction curve is obtained. By measuring the reflectance of a wet layer of a target low gloss coating composition the gloss of a coating that would result from such a layer is then predicted by using the gloss prediction curve. The process is most useful during the manufacture of coating compositions, such as automotive OEM and refinishes paints.
1. A gloss prediction process comprising:
(a) dispensing on a test substrate a L 0 layer of a substantially uniform thickness of a coating composition through a vessel of a gloss prediction device containing said coating composition, wherein said thickness is controlled by a gap between a slot provided on said vessel and said substrate;
(b) projecting on said L 0 layer a beam of light of a preset intensity at a preset angle of incidence from a light source;
(c) measuring B 0 reflectance of said beam reflected from said L 0 layer at a preset angle of reflectance by an optical measurement instrument;
(d) curing or drying said L 0 layer into a C 0 coating;
(e) measuring Y 0 gloss of said C 0 coating at a preset gloss angle by a gloss meter;
(f) storing said B 0 reflectance of said L 0 layer and said Y 0 gloss of said C 0 coating in a computer usable storage medium of a computer;
(g) repeating said steps (a) through (f) for S 1 to S n coating compositions respectively comprising F 1 to F n parts by weight of one or more flatting agents based on 100 parts by weight of said coating composition to determine B 1 to B n reflectance of L 1 to L n layers and Y 1 to Y n gloss of C 1 to C n coatings wherein n ranges from 4 to 20;
(h) subtracting said B 0 reflectance of said L 0 layer from said B 1 to B n reflectance of said L 1 to L n layers to determine ΔB 1 to ΔB n of said L 1 to L n layers respectively;
(i) locating intersecting points on a graph where said ΔB 1 to ΔB n of said L 1 to L n layers on X-axis of said graph intersect with said Y 1 to Y n gloss of said C 1 to C n coatings on Y-axis of said graph;
(j) using a curve fitting equation to produce a gloss prediction curve on said graph;
(k) dispensing on said test substrate a L T layer of said substantially uniform thickness of a target coating composition through said vessel of said wet gloss prediction device containing said target coating composition further comprising said flatting agent;
(l) projecting on said L T layer a beam of light at said preset intensity and at said preset angle of incidence from said light source;
(m) measuring B T reflectance of said beam reflected from said L T layer at said preset angle of reflectance by said optical measurement device;
(n) subtracting said B 0 of said L 0 layer from said B T of L T layer to determine ΔB T of said L T layer;
(o) locating said ΔB T of said L T layer on said X-axis of said graph;
(n) locating an intersecting point on said gloss prediction curve that intersects with said ΔB T on said X-axis of said graph; and
(p) predicting gloss at said preset gloss angle of a target coating resulting from said target layer by locating Y T on said Y-axis of said graph that intersects with said intersecting point on said gloss prediction curve that intersects with said ΔB T on said X-axis of said graph.
2. The process of claim 1 wherein said optical measurement device is a spectrophotometer.
3. The process of claim 1 wherein said optical measurement instrument is in communication with said computer.
4. The process of claim 1 wherein said gloss meter is in communication with said computer.
5. The process of claim 1 wherein said opening is a slot adjacent to said test substrate such that a resulting gap between said slot and said test substrate controls the thickness of said L 0 and said L 1 to L n layers.
6. The process of claim 1 wherein said L 0 and said L 1 to L n layers are of the same thickness ranging from 6 micrometers to 2300 micrometers.
7. The process of claim 1 wherein said test substrate is a disc positioned substantially vertically on a support frame of said gloss prediction device.
8. The process of claim 1 wherein said curve fitting equation is a second degree polynomial equation.
9. The process of claim 8 wherein said second degree polynomial equation is of the formula:
Gloss Y =a (Δ B n ) 2 +b (Δ B n )+ c
R 2 =Z
wherein said constants a, b, c and Z are determined by a curve fitting process.
10. The process of claim 1 comprising displaying said predicted gloss of said target coating on a CRT monitor.
11. The process of claim 1 comprising communicating said predicted gloss of said target coating from said computer to a remote computer.
12. The process of claim 1 wherein said coating composition is an automotive OEM or refinish paint.
13. The process of claim 12 wherein said flatting agent is talc, silica, or barium sulfate.
14. The process of claim 13 wherein said F 1 is 10 parts and said F n is 90 parts by weight of one or more flatting agents based on 100 parts by weight of said coating composition.