Dip Molding-An Ancient Process Turned Modern
by Jenny Knodell, IQS Editor
Believe it or not, the manufacturing process that creates plastic products like plugs, handles and caps is one of the oldest known human professions. The ancient art of candle making, which dates back as early as 3,000 BC, used the process of dip coating to make candles out of beeswax and animal fat. Since then, it surprisingly hasn’t changed much. Plastic wasn’t widely used until the 20th century, but soon after it started replacing materials like glass and ivory, manufacturers experimented with melting down thermoplastics like Plastisol. They found that by applying the candle dip coating method to modern day products, melted plastic resins provide a strong, resistant and protective coating that is used in dozens of industries.
Candle Dip Coating
The dip coating process is very simple, and creates products like coated fencing or wires. The object being dipped must be able to withstand the extreme temperatures required for melting plastic to molten form. This method is so simple it could easily be done at home. Plastic materials like PVC and vinyl are heated until they melt, and the product is slowly dunked down into the plastic at a consistent speed. The longer the product stays in the plastic, the thicker the coating will be. This is called the dwell time. After it’s slowly taken out of the plastic, voila! A dip coated product. Chances are, you grab a plastic dip coated product just about everyday. Gas pump handles, tool handles and fitness equipment are all dipped in plastic to increase gripping ability and cut down on blisters. They also provide electrical safety—wires and cords are dip coated to provide electrical insulation, which prevents electrocution when animals and small children get curious.
Ever wonder how small hollow plastic products are made? Along the same vein as plastic dip molding lies the slightly more complex process of dip molding. The idea is the same, only instead of dunking products, manufacturers plunge hollow molds into vats of melted plastic to create products like caps, latex gloves, handle grips and the most popular and widely used—condoms. The molds, called mandrels, are never totally submerged in the plastic, to provide a way of removing the part after it has dried. Since the plastic materials always exhibit at least some elasticity, even tight, complex parts can be pushed off of the mold easily. These products are available in any color of the rainbow and can be made with a smooth, satin finish or rough to the touch.
Photo courtesy of U.S. Plastic Coatings Corp.
Latex glove dip molding
Because molten plastic has such a fast drying time, these processes take no longer than 2 minutes per batch. And due to their simplicity, most dip molded or coated product manufacturing is fully automated, requiring almost zero labor costs. These products are used all over the place—in plumbing, commercial product manufacturing, electrical and medical applications, and they are preventing blisters and slipping everyday. So the next time you go to grab that gas pump handle, admire its smooth plastic coating and be glad you aren’t clutching cold metal.
Plastic dip coated gas pump handle