New Melt-Phase Process Produces Ultra-Thin Walls

DN Staff

January 11, 2010

5 Min Read
New Melt-Phase Process Produces Ultra-Thin Walls

Thin-wall thermoformed parts are taking aim at injectionmolded parts for critical electronic and medical applications.

A New Hampshirecompany is using old-fashioned Yankee ingenuity to form materials at or abovetheir crystalline melt temperatures to manufacture three-dimensional parts withstress- and pinhole-free thermoplastic walls. Parts with super thin walls arein demand for applications where real estate is at a premium, such as implantablemedical devices and miniature electronics. Typically, the parts protectcomponents against chemicals or act as electrical insulators.

"Sometimes companies can't injection mold parts with somehigh performance thermoplastics because they can't get the materials asconsistently thin as required," says Scott Behner,sales team leader at WelchFluorocarbons in Dover, NH. "They don't have the abilityof making a wall that is 1.0 mil (one thousandth of an inch) thick." Anotherissue is that very thin injection molded walls may have weak spots caused byweld lines, resin impurities, or stresses created by high pressures.Limitations on wall thickness for injection molding vary widely, and aredependent on part design, melt flow characteristics of the resin, and robustnessof the molding machine.

Most of Welch Fluorocarbon's products start with films thatare 0.003-inch to 0.010-inch thick, though the company has formed film as thinas A.50 mil. The films relax as they are heated in a process Welch calls"melt-phase" thermoforming. Special knowledge of the effects of heating andcooling can not only make the walls thin, they can also change the crystallintyof the material, creating properties such as transparency.

Part sizes range from a piece that would fit on the tip of aballpoint pin to a hemisphere with a 14-inch diameter. The machine capacity isan 18-inch square.

Specialized Extrusion
The Welch parts are less susceptible to pinholes caused bymicroscopic residue in plastics used by injection molders. Special compoundingprocesses at companies such as DuPont, Honeywell and Evonik coupled withspecialty film production create very thin films that are gel-free, accordingto Behner. One extruder that specializes in production of gel-free films isSolvay subsidiary Ajedium.

"We get eighty percent of our business from engineers who cometo us because something they're using now doesn't work," says Behner. In oneexample, polycarbonate covers failed to provide water barrier for circuitryinsulators. Welch Fluorocarbon thermoformedprotective liners from polychlorotrifluoroethylene (PCTFE) film. ThermoformedETFE is used as a microwave antenna cover in another example of a productapplication.

The thermoforming process is less costly than injectionmolding due to low tooling costs. Typical tooling materials are aluminum andporous aluminum. Bridge production tools can be manufactured for less than$3,000. Compound die sets for punching slots or holes as small as 0.003-inchand holding tolerances of A plus or minus 0.0005 inch are achievable with tools made by wire EDMequipment.

Welch Fluorocarbons makes several types of insulationsleeves for pacemaker batteries. One is made from 10-mil fluoropolymer film.The part is 0.25 x 0.5 inch, with a depth of 2 inch.

In some cases a thermoformed part is replacing extremelythin vacuum deposition coatings of materials, such as Parylene, the trade namefor polymers that act as moisture barriers and electrical insulators forapplications such as implantable medical devices.

Welch's system is based on single-station vacuum formingmachines using infrared heaters that rapidly take temperatures to more than600F. In one case, Welch took a PCTFE film to a high heat to make it moreeasily formable, then rapidly cooled the material to avoid crystallization. Theresult was transparent, thin, flexible PCTFE parts. They make greatmoisture-protection barriers for electronic parts.

Evan Welchoriginally focused on fluoropolymers when he started the company in 1985. Thecompany now works with polysuflone, polyetherimide, and is developing PEEKparts that can compete with polyimide in critical applications.

Film Replaces PI Tape
In one example of a PEEK application, a medical partrequired a material that did not react with a sensitive battery solutioncontaining lithium. Welch was able to source PEEK film (extruded by Evonik in Germany) as an alternativefor a battery stack insulator. A thermoformed PEEK part can replace polyimidetapes, which are labor intensive.

Laminates don't work well in the Welch melt-phase processbecause of the differing crystalline melt temperatures of multi-ply laminates.Welch; however, has successfully thermoformed some parts with polyethylenelaminated on PCTFE for a disposable medical diaphragm.

The company also specializes in making heat sealed bagswhere chemical or resistance or some other special property is required. Welchspecializes in providing a weld as strong as the material itself, at leasteight pounds of peal strength with FEP, PFA and modified PTFE. The reliabilityof seals was the primary reason NASA chose Welch for manufacturing urinecollection bags for astronauts and cosmonauts in the space shuttle and space station.

The company had a surge in customer base and sales in 2008,when most of the plastic processing industry in the U.S. was buckling underthe recession. Behner says sales rose 50 percent in 2008, and held steady for2009, mostly on the strength of many new medical customers.

One of the company's challenges is moving into productionsizes that can rival injection molding - millions of parts. That will requireof development of more automation in product handling, and improved processcontrol standards.

Three-dimensional parts with ultra-thin thermoplastic walls are competing with injection molding and other processes for applications where real estate is at a premium. Photo:  Welch Fluorocarbons

New Melt-Phase Process Produces Ultra-Thin Walls A

Photo shows a medical device battery sleeve made with Teflon PTFE film. Photo:  Welch Fluorocarbons

New Melt-Phase Process Produces Ultra-Thin Walls B

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