Innovation Eases Overmolding of Decorated Gun Stocks

Good news for recreational hunters: A new molding technology makes it substantially easier to mold soft grips on decorated hard-plastic stocks.

Jim Ryan, president of Polymer Injection Molding (Monson, MA), explains: “We’ve been overmolding plastic parts for years. Razor, toothbrush, pen and screwdriver companies all use it to add value. It was a natural for gun manufacturers to get into adding value through overmolding. We did our first overmolded stock for a gun manufacturer over ten years ago. It wasn’t long before everybody wanted to camo and overmold the same stock. That proved to be easier said than done. Masking the overmolded part makes a horrible mess and overmolding directly over camo (without our process) has big adhesion problems. We experimented for a long time before coming up with a process that worked. We overmold over camo day-in and day-out without any problem. It looks great and holds up as well as direct overmolding applications”.

The US Patent Office recently awarded Patent 8,062,736 to the company for its innovative approach.

As explained in the patent, a gun stock or bow component is first molded from a rigid thermoplastic and then dipped in a chemical bath to seal the molding. The next step is application of a primer that provides a surface that accepts and adheres well to a patterned ink layer. The patterned layer may be applied by taking a transfer film bearing an ink pattern and applying the film to the article by immersing the article in a liquid bath to transfer the ink to the surface of the article.

A polyurethane outer is then applied over the preceding layers and allowed to set. Then the piece goes back into the molding machine and is overmolded with a thermoplastic elastomer to provide a soft, firm grip. The preferred elastomer for the application is thermoplastic vulcanizate (TPV) because it bonds well with the polyurethane.

The big innovation is the ability to overmold the camo decoration.

Here’s how it works without the new approach. The overmolded areas have been typically masked and unmasked by hand and then the camouflage is applied to the exposed un-overmolded surface areas. However, the edges  where the overmolding and the camouflage meet are often not well defined. Also, there may be exposed areas with no camouflage near the edge.

The masking and unmasking are labor intensive, time consuming, costly and require skilled workers.

For a description of the process used to apply camouflage to gunstocks, see www.immersiongraphics.com, and www.tarjac.com.

Craig Dougherty, Polymer’s director of marketing, says: “The ultimate added value is to decorate with camo and overmold the grip areas with a complementary color. We’ve done a lot of basic black over camo but overmolded tan, gray and green grips really punch it up. Now that our technology is protected, we expect to be doing more variations for our valued customers”.

 

About Doug Smock

Former Chief Editor at Plastics World and Senior Technical Editor Design News

Comolding, Design, Elastomers, Insert Molding, North America, Sports

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