Off the Coater and Out the Door! Streak-free, on-color production from a PVC plastisol coating line every time.

Too good to be true? Let's start by examining some real color measurement data showing what is possible. Consider the following graphs. This first graph represents color plot data from nine separate production runs of a PVC plastisol product coated on a casting paper carrier. Each lot is represented by a different color/symbol combination and the individuals within each group are various roll samples taken throughout the run. Note the presence of a "flyer" in just about every case. These were always from the first testing sample taken at the start of the first roll. This insignificant deviation is caused by some residual color from the prior job and is only detected through very accurate measurement. The fact of its presence is excellent evidence of the color stability present in this coating system.

DH vs DC Production Batches

Delta Hue vs. Delta Chroma is plotted using the visually weighted DH*/Sh and DC*/Sc components of the CMC equation used to calculate Delta E CMC versus the standard. Note that all samples seem to be 0.10 unit or less from the standard and fairly well centered making the maximum spread among these samples 0.20 units or less. This phenomenon is not by chance or accident - very sophisticated curve shifting techniques were used to create the drift standard used as the color target for this production. Additionally, very tight tolerances around this target were required and machines, not people determined when the batches were close enough.

Here is another chart for the same production except this time we plot the same DC*/Sc from above along with the lightness function DL*/Sl exhibiting a somewhat larger spread by being slightly over 0.20 units from the standard. As before, it is fairly well centered with respect to the standard.

DH vs DC Production Batches

This is 2+ times more deviation than for hue and chroma but the most commonly accepted method for calculating DE CMC weights the lightness as being half the effect of the other parameters. Taking into account that humans are more visually tolerant to lightness variations would seem to suggest both graphs being visually equivalent. DE CMC2:1 = [(DL*/ 2 Sl) 2 + (DC*/Sc) 2 + (DH*/Sh) 2 ] 1/2 . Note the 2 in denominator of the DL*/Sl term that cuts the lightness contribution in half. Assuming the highest DL*/Sl to be 0.27 and applying this equation gives a maximum DE CMC2:1 = [(0.27/2) 2 + (0.10) 2 + (0.10) 2 ] 1/2 = 0.20. How about that? Nine separate production runs over 2 months or so and every single sample within 0.20 DE CMC2:1 of the standard. And maybe even more importantly, all samples within 0.40 of each other!

How is this type of color precision achieved? Does such a system exist at present? Not likely.

It took two plus years of research and development to progress to the point described above and there was still a lot of work left yet undone in all of the steps, plus additional engineering and mechanical issues yet to be resolved. However, on September 17, 2001, the Monday following 911, my job, along with 35 or 40 others, was eliminated under the guise of softening conditions in the automotive market coupled with knee jerk reactions of impending economic gloom and doom. I'm sure the project died after my departure.

Strangely enough, few people grasp the economic significance of being able to produce precise colors at the coating line. Most likely, due to years of having to overprint much of the coated production for other reasons, so why be concerned about the color of a product that's going to be covered anyway. I have to admit, I once felt the same way and was not 100% sold on the project myself at its inception.

After struggling about half way through the project, and quite by accident, I discovered that, after 35 years working with coating of plastisols, I had misdiagnosed the true root causes of many of the defects requiring overprinting. The project moved along quite well after that "Eureka Event". Up to then, we (pigment suppliers, dispersion houses, surfactant experts, compounders, resin suppliers, etc. helping with this project) had produced some of the worst cases of flotation, flooding, pigment streaking, and color drift I had ever seen!

I'm now a believer. I know that perfect color, color perfect or whatever you want to call it, is achievable simultaneously with significant absence of these other problems. Hundreds of thousands of dollars can be saved in excessive pigment and coloring costs. My dream would be to use a combination of grained paper and/or inline embossing coupled with some inline finishing process to produce a product that goes from the coater directly to the customer!