IMM Focus: Materials

Industrial and product designers from all corners of the globe continue to have a strong affinity for plastics, and with good reason. As raw materials go, plastic heads the list of candidates on several levels. Perhaps most importantly, it can easily be formed into whatever contours and shapes designers imagine. Aesthetic and manufacturing considerations are also addressed. Color can be molded in rather than painted on. It is lightweight and aesthetically pleasing to the eye and touch. Mass production is not only an option, it’s a cost-effective given.

It isn’t surprising, then, to find a wealth of innovative designs based on plastics. The following examples, from the medical, furniture, and automotive industries, are indicative of the many transformations spawned by the close relationship between design and plastics.

Clearly Suited

Chairs designed by Enrico Cionada for Sitland (a major office furniture maker based in Italy) rely on a clear copolyester, Durastar from Eastman Chemical, for both seats and seatbacks. Design requirements included chemical resistance to cleaning solutions and the ability to contact the chairs’ silent rubber blocks without cracking. Dubbed Sit & Move, the chairs also had to be stackable and scratch resistant.

A major factor that helped the copolyester material win over other clear plastics was its ability to flex without fatigue at the area where the rubber contacts the plastic. Chairs were put through a fatigue test to simulate usage, which created friction between the rubber and plastic. PC failed because of hazing, and other clear resins experienced stress cracking. Chemical resistance to cleaning agents was another reason. High impact resistance and moderate tensile modulus allowed enough flexibility to accommodate the user’s comfort.

Cary Clubb, marketing communications director at Eastman, believes that the near future will see greater penetration of clear plastics into furniture. “In Italy, Durastar material is being evaluated for five or six other chairs similar in style,” he says. “Cionada, the designer for Sit & Move, is currently working on a second chair using this polymer.”

Eastman sees the activity in Europe as encouraging, with an overall appearance that the use of clear plastics in the furniture segment and office furniture subcategory is on the rise. Eastman has just signed an agreement to collaborate with Tom Dixon, a well-known furniture designer in Europe and Asia who has worked with Eastman’s ProVista in extrusion applications.

“This is symptomatic of a trend,” says Clubb. “A well-known Japanese furniture designer, Toshiyuki Kita, has already done some injection molded plastic chairs and now has an interest in clear plastics for mass market.”

Aesthetics Without Paint

If you’ve been in an auto dealer’s showroom looking at new cars lately, you’ll notice that engine covers have become serious aesthetic statements, complete with metallized logos and painted surfaces. Glass-filled nylon is the material of choice here, but the surface finish of this material requires a secondary painting operation for appearance purposes.

DSM Engineering Plastics, long a participant in underhood nylon applications, recently devised a high-flow nylon grade that addresses this issue and eliminates the need for paint. Called Akulon KFHGM35, it is a high-flow nylon 6 and has been specified for use in engine covers now in production for Toyota’s Sienna minivans.

When Toyota engineers first viewed the new covers, they were skeptical. “No one could believe it wasn’t painted,” says DSM’s Doug Bosch. “They took out their keys and were scratching the surface, but there wasn’t any paint to take off.”

This material reduced warp and improved aesthetics. The warpage was reduced from 4 to 5 mm over 18 inches to 1 mm. “We have been experimenting with the high-flow material and the alignment of the glass fibers,” says Bosch, “and quite frankly we were very surprised at the finish on these parts.”

According to DSM, engine covers have become a more important element of sales over the past few years. “When the hood is opened on the showroom floor, dealers want some appeal from the increasingly crowded mass of components,” says Bosch.

Melt flow improvements in this material are the result of a proprietary method. In comparison to standard PA6 grades, higher flow translates to cycle time reduction, freedom of design, improved surface appearance, and lower molded-in stress and warpage combined with an excellent retention of mechanical performance levels.

Of course, higher flow means the material is also suited for thin-wall applications. In highly reinforced forms, however, this resin also provides a good alternative in applications where metals are currently used.

Medical Marvels

Thin walls and ultrahigh-volume production were the challenges facing Classic Industries, a custom molder specializing in medical applications, when it received a call from a Fortune 100 medical device manufacturer to produce trocar sleeves. Several years later, Classic supplies the OEM with 7 million surgical trocar sleeves a year from a 24/7 production cell.

Prior to Classic’s involvement, the customer was in a backorder situation, unable to sufficiently supply its product to meet market demands. Today, the OEM has inventory to spare. The change occurred when Classic turned its attention to the total picture, including the material, mold, and process.

Classic’s team examined the resin selected and conducted mold flow analysis of the part. Trocars are complex tools that provide surgeons with a tunnel in which to insert instruments such as laparoscopes for visual examination, specimen removal, and other procedures that involve or use minimally invasive surgery. The thin-walled trocar sleeve relies on a series of external, circumferential barbs for stability during a procedure. Polycarbonate from Dow Chemical is used in a multicavity mold to produce the hollow sleeves, approximately 5 inches long with varying diameters and .020- to .030-inch wall thicknesses.

Bill Larrimer, Classic’s VP of engineering, says, “An obstacle we had to overcome was how to mold polycarbonate in a multicavity mold to make a part with a wall thickness of .030 inch over 5 inches, without flash, and do it consistently.”

After reviewing results of moldfilling analysis, the team agreed that the target material could still be used to produce parts without flash if the molds were reworked and the injection process upgraded. Classic chose high-pressure, high-speed Netstal Synergy machines and Fanuc Roboshot electric machines with high-performance packages for repeatability and speed. “With these machines, the injection time to fill a sleeve is faster than a snap of your fingers, and the process is consistent and stable,” says Larrimer.