Although we wouldn’t presume to usurp the formulating expertise of a coatings manufacturer nor the expertise of the experienced user, the item in your July 2002 column piqued our interest. You may recall that a small shop producing plastisol coated parts in Mexico was complaining about “drop-like” flaws. Your response that this is “normal” is wrong. It is only normal if this is the expectation from one’s plastisol supplier and/or your operating conditions.
There are many excellent plastisols on the market, which when applied appropriately, do not exhibit sag or drips. We strongly recommend that your reader contact his plastisol manufacturer to request a solution to his problem either in the form of process improvement suggestions or a change to a different plastisol.
The key to a no sag/drip plastisol is the use of an appropriate sag control agent incorporated into the original formulation that is stable and predictable across the entire use and cure cycle of the plastisol. Many plastisol producers use colloidal silica or organic treated clay additives and achieve a fair level of success with this challenge. To achieve the highest level of thixotropic viscosity control over all of the temperatures the plastisol encounters, my company recommends the addition of a couple of its additives at a level of about 1-3% . This must be added at the plastisol manufacturing step by the coating supplier. In short, the end user must demand a high-quality product that provides the performance he needs at a fair price. S.R.
Maybe there is help available for R.E. If so, he should get it. For the record, let me restate his question: “We dip racks with preheated (300-350F for 3-4 min) small sheet metal hook-like pieces about 2.5 inches long by 1 inch wide into a tank of cold plastisol. Next, we take the racks out of the tank and let them drip. Then we send them to an oven (300-350F for 6-7 min) to get vulcanized. This is when we recognize a similar problem with all the pieces. There is a drop-like flaw that forms on the lower part of each piece, and we cannot get rid of it.”
I will be glad to forward your e-mail to R.E. If there is help available, he can’t get it without knowing which supplier uses your material in his formulation. Remember, if he is a small user, he won’t mush help from most suppliers. If he is interested, he will contact you. Hopefully, you will provide him with a list of your customers. That’s the only way he can solve his problem. Looking back on my own career, I made sure I was aware of the latest technology from resin, pigment, solvent and additive suppliers, including your company. That was 15-20 years ago, and probably before your time. Consequently, my company’s products were always coated with the best available materials.