Summary for x-rite lab readings Discussion
The thread asks whether X-Rite L,a,b readings on powder-coated parts should change with powder thickness, since one supplier claims a good powder should not vary within 2 to 4 mils. The poster reports that a batch is passing at 2 mils and below, but the L value fails above 3 mils while a and b remain acceptable. In response, one contributor says that, based on years using an SP-68, he did not see paint thickness affect readings when the coating was opaque to under 6 mils, though he relied on Delta E rather than individual L*a*b* values. He recommends contacting X-Rite tech support and checking whether the instrument and standard have been re-certified on schedule. He also notes that batch-to-batch powder stability problems could explain the variation. The overall advice is that thickness alone should not normally drive color change in a good powder, but equipment calibration and powder consistency should be verified.
Q. Hi experts,
I’m here again, trying to help my supplier and also to gain solid knowledge on powder coating with your help.
Recently, we have some issues with color variances on some powder coated parts of my supplier, we have rejected because we have seen color variances visually and also using spectrophotometer(x-rite).
Powder coat guys even came here in Philippines from Korea to discuss their issue. One of the issues in discussion that my supplier strongly believe in is that: a good powder doesn’t change the L,a,b readings within 2 to 4 mils thickness. This is our specs. However, the affected batch of this powder has shown to be changing in readings within this range of thickness. above 3 mils are not passing on the L values (a and b are ok). If we now check 2 mils and below, the L value is within specs and so with a and b.
Can you guys please give some thoughts on this? Thanks.
Newton
manufacturing – Philippines
2005
adv (affil link): Color matching spectrophotometers on
and
Amazon
A. Hello, I used an SP-68 for years and never came across the issue of the paint thickness (opaque to < 6 mils) changing the readings, but I used the Delta-E as my standard, not the individual L*A*B*’s. X-Rite does have a tech support site that you need to contact and get some of your questions about the machine answered, has it been re-certified at the proper intervals? Has the standard been re-certified?
It would certainly explain a lot of things if the paint has a batch to batch stability problem. I agree with the assessment that a good powder won’t change color based on the thickness, but I have seen noticeable color differences(Delta E readings) between batch’s at times. I can’t say that I’ve ever dealt with a supplier that stated that the color would be met as long as I held a certain paint thickness, that’s a little odd.
Sheldon Taylor
supply chain electronics
Wake Forest, North Carolina
A. Colour control is not dependent directly on film thickness as it is on the hiding quality of the pigments used. I am quite familiar with the X-rite and colour control is one of my main areas of expertise, both paints and inks. Pigments such as black have very good hiding. Other pigments such as extenders and many organics have very poor hiding. Many are translucent. If problems are suspected with a batch the X-rite has a contrast ratio feature that in conjunction with black and white Leneta charts can be used to determine hiding. I’m not familiar enough with powder coating to help you develop a methodology.
Ronald Zeeman
Coil coating – Brampton