Plastisol Drips

Question:

Just read your comment and response to C.O. in the January 2003 issue, Re: Plastisol Drips. I’m with you. We prime and plastisol coat small hardware on an automated machine. The parts are not touched once they are racked up and automatically proceed through the primer dip, pre-baked, plastisol dipped and then post baked. To eliminate plastisol drips, we have tried everything from raising the pre-heat cycle (primer bake) to varying the plastisol viscosity - running the plastisol at room temperature to installing a hot water heating coil in the external plastisol reservoir tank (which auto feeds to the dip tray) - slowing the machine down and increasing machine speed. Nothing we have tried has eliminated the dripping - 98% of the product dipped will have a “drip” at the bottom of the part anywhere from 1 to several millimeters long. If we could get 100% to stay within 0.5-1.0 mm, this would be very satisfactory but, this is not the case. I didn’t get to read the article mentioned in the July 2002 issue from R. E. and would be interested in obtaining this article. R.T.

Answer:

R. E. has a small shop in Mexico where he dips racks of parts preheated to 300-350 F for 3-4 min. into a tank of cold plastisol. After removing, he lets the parts drip, then sends them to an oven for 6-7 min at 300-350 F. This is when he recognized a drop-like flaw that forms on the lower part of each piece.

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In my answer I told R. E., I was sorry I couldn’t help him and that his product was normal. Most parts dipped in plastisol have a drip or drop-like flaw on the bottom edge. This forms when the parts are dipped and withdrawn. The same thing happens when parts are dip-coated in paint. I also told him that molding the parts will solve the problem. What I forgot to tell him was, powder coating the parts will also solve the problem. My good friend Nick Liberto will be proud of me for saying that.

As to obtaining a copy of the article, please visit pfonline.com in the article archives.