Ask Joe Powder February 2024: Kitchens and wrinkles

PPCJ’s regular columnist, Kevin Biller AKA Joe Powder, answers readers questions on all things powder coatings. Readers can submit questions to [email protected]

Hi Joe,
I live in Huntington Beach and would like to have my cooker knobs painted red. But I want to keep the lettering (temp, high, low, etc.). Is that possible? I’m trying to find someone in my area who can do it.

Thanks,

Suzanne, California

Hi Suzanne,

I think red oven knobs would be a groovy addition to anyone’s kitchen. Accomplishing this whilst maintaining the lettering will take some precision work.

Let’s talk about the coating first. Cooker knobs will no doubt get splashed with food products and condiments, so a tough coating is requisite. The knobs will require regular cleaning to ensure their spiffiness for your guests to admire. Hence a powder with excellent chemical resistance is mandatory. I suggest either a polyurethane or an appliance-quality hybrid. A garden variety polyester just won’t do.

The surface of your knobs must be perfectly clean before powder application, so I would recommend a thorough scouring with a reasonably strong solvent. Acetone is a very good choice. You’ll want to ensure that there is no residual grease or dirt on the surface. Make sure the solvent has completely evaporated before applying the powder.

As for maintaining the graphics on the knobs, this will require some precision masking with an appropriate tape. Two grades are commonly used – silicone based and polyimide based. I would use the polyimide type because it has higher heat resistance than the silicones.

The tape will have to be surgically sliced to the width of your lettering, which will be no simple task. This will take patience and a steady hand. Make sure that the tape is completely adhered before proceeding to the powder application step.

I would apply the powder and then gel it in the oven. This will take about 5 to 7 minutes at the recommended cure temperature. Remove the knobs from the oven, let them cool, and then carefully detach the masking tape. You probably want to use a hobbyist knife (Exacto™ will do) to accomplish this.

After the tape is removed, pop the knobs back into the oven and cure them fully per the powder manufacturer’s recommendation. The reason for pulling the tape after the powder has gelled, but not cured, is because a fully cured powder will bridge and encapsulate the tape – making it impossible to remove. On the other hand, if you remove the tape while the powder is still in its powder state, the powder will fall back onto the graphics and negate the function of the masking.

I hope this helps you with beautifying your kitchen.

Kind regards,

Joe

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Hey Joe,

What causes a slick glossy appearance in the Black Wrinkle powders? I have tried a few different manufacturers with similar results. Granted, I have substrates with different thicknesses, but issues are not limited to the thicker materials and surrounding areas.

I have been told that the Black Wrinkle begins its “crawl” at a particular temperature and cannot be interrupted during this process or the “slick” undercoating (or what is there before the crawl) will be left. This is a very time-consuming powder that unfortunately has to be used on certain product lines in order to match outsourced products. I have tried a few different primers to help, with no avail. In your opinion, what do you think could be the prominent issue?

Thank you for your time!

Greg, Texas

Greg,

From what you describe, this is probably a polyester-based wrinkle. The wrinkle surface is created by a carefully controlled chemical reaction between the polyester resin and a unique curing agent. This chemical reaction requires a very specific catalyst. Since the wrinkle surface is driven by a chemical reaction, the curing conditions affect the degree of wrinkling, hence a severe undercure will cause the “slick glossy” or “wet look” appearance you describe.

Severe undercure can be ascertained by a simple solvent rub test (acetone or MEK will do). If the coating is easily removed with 10 to 20 double rubs of a solvent-soaked shop rag, then the coating did not see enough heat (time and temperature).

Another condition that influences wrinkling is pH (acidity/alkalinity). The catalyst used to create the wrinkle is acid based, and consequently a substrate surface with high alkalinity will retard the acid catalyst and cause a glossy spot. High alkalinity can occur from substrate contamination, especially from poor rinsing of chemical cleaners.

The concept of wrinkle powder over a primer is an interesting proposition. I have seen wrinkle failure with polyester wrinkle powders applied over fillers. These were repair fillers (putty) and probably occurred due to the alkaline nature of the filler. Many fillers contain high levels of calcium carbonate, which is alkaline in nature.

As for primers, it’s possible that the surface of the primer is alkaline. This could retard the catalysis and cause a glossy instead of wrinkled surface.

I recommend that you try the wrinkle powder over different primers and other more standard powder coatings. If you think the end use of the products you are coating will perform acceptably with a single coat of wrinkle powder, this may be your best bet.

Good luck and let me know how things work out.

Best regards,

Joe