Cover Story: The sporting life

While slowed slightly by a front-end slag in this year’s economy, the annual growth rate (6 to 8%) of thermoplastic elastomers over the past five years has nonetheless been impressive. This growth is being driven by expanding applications in a number of key markets. One of the most critical of these has been sports/recreation, where TPEs allow manufacturers and processors to build in comfort, style, light weight and resilience in an ever-expanding array of products.

Finproject, an Italian footwear and sporting goods company with an injection molding facility in Quebec City, uses an exclusive technology and DuPont Dow Elastomers’ Engage polyolefin elastomer to manufacture a kayak seat cushion with a number of design and performance advantages. Through its Quebec-based plant, Finproject has developed a variety of injection-molded foams that capitalize on the polymer’s low molecular weight and processing properties.

“We have a unique technology,” says Andy Reddyhoff, president of Finproject North America. “We blend Engage pellets with blowing agents and crosslinking agents to form a injection-moldable compound.”

Reddyhoff says Engage contributes to the performance of the seat cushion through a combination of toughness and flexibility. The seatback and cushion are molded in one piece with a thinner mid-section to enable it to fold more easily. The low density of the polymer (0.87 g/cc) creates a light cushion that floats easily.

According to France Rochette, business manager, DuPont Dow Elastomers, Canada, Engage is an ideal match for a water-sports application such as the kayak cushion, as well as the technology used by Finproject in its foaming process.

“Because Engage is self-skinning you end up with a very good closed cell structure, which is important in this application,” says Rochette.

Rochette says Engage can be molded with standard injection molding equipment. For best results, Engage should be kept at the minimum melt temperature during injection and cooled very quickly, she says. The polymer, which is made using Dow’s single-site catalyst technology, INSITE, colors easily and has also good impact resistance at low temperatures.

A leading manufacturer of golf clubs, PING, used a highly-filled, high specific gravity thermoplastic elastomer to achieve precise tolerances in its line of custom-fit i3 irons and fairway clubs. The company uses LNP Engineering Plastics’ Thermocomp HSG for inserts in the club heads that adjust the clubs to a desired swing weight. The need for the adjustment occurs because not all clubs are the same weight when they arrive from the factory. The inserts are placed in a molded cavity on the back of the club heads. LNP worked with PING to develop a series of high specific gravity polyurethane compounds to test. The Thernocomp HSG material was chosen, in part, because of its ability to resist “dinging”, which occurs when clubs bang together as a golfer walks or drives around the course.

BUILDING A BETTER FIN

Two different approaches to the design of a swim fin show the broad range of processing methods that can be used with polymers classified as TPEs.

To make its new, innovative Twin Jet fin, Scubapro evaluated a number of different materials, including thermoset rubber, but eventually chose Monoprene TPE supplied by Teknor Apex Co. To ensure that the fin flexes smoothly as the diver’s foot cycles from downstroke to upstroke and back, Scubapro required a material with toughness and elastic memory, revered to as “snap”.

“We looked at EPDM synthetic rubber because of its outstanding weatherability, but it didn’t provide enough snap,” says James McGee, president of Pacific Molding, the company which originally molded the fin. “The same is true for most types of TPE on the market.”

Teknor Apex supplied Pacific with a custom formulation of the Monoprene TPE compound which delivered a high degree of resilience combined with excellent weathering resistance.

The fin is designed with a unique rib or rail along the outer side of each blade. With a thickness close to an inch, a way had to be found to mold, then cool the part without using refrigerated water, which would have affected its surface appearance, according to McGee. Teknor consulted with the molder to optimize processing and eliminate this concern.

To make its new Fab Force swim fin, Force Fin, a company located in Santa Barbara, CA, uses a thermoplastic polyurethane and a patented manufacturing technique that eliminates the need for expensive molds in both prototype and production.

The process starts with sheets of thermoplastic polyurethane supplied by Stevens Urethane. The sheet is cut in the desired pattern and vibration welded together. Next, a castable polyurethane is introduced between the TPU layers. The castable polymer bonds with the TPU and hardens to fill out the product and give the fin its structural form. The TPU sheet serves as both the mold and the outer skin of the finished product.

“Stevens Urethane has really helped us to optimize the design process,” says Susanne Chess, vice president for Force Fin. “Traditionally, you can’t test the product without making a mold, which can cost thousands of dollars. Our process is similar to the fashion industry. If it isn’t what we want, we just change the pattern.”