Custom binder system set to commercialize

Developing a new binder for PIM has a lot in common with the art of formulations, according to Karl-Heinz Schofalvi, technical director at Stanton Advanced Materials. His experience in developing adhesives at H.B. Fuller, along with an academic background in chemistry and macromolecular science, were part of the inspiration for Stanton’s Apex P/M binder system. These materials and associated compounding services will become commercially available in Q1 2000 at a new facility.

“The interface between the particle and binder is critical,” says Schofalvi. “Binder formulas must solve the incompatibility between the organic binder and the inorganic particle. This surface coupling determines both flow characteristics and dimensional stability of the molded part.”

Schofalvi’s approach led to a binder system consisting of wax, polymer, and a surface agent package formulated specifically for ideal electrostatic coupling. “The surface of every particle has an electrostatic charge, either positive, negative, or amphoteric,” he explains, “which is associated with the particle’s isoelectric point, or IEP. We have developed five systems that are tailored to the ranges of IEP for ceramic and metal powders, including ferrous and nonferrous metals such as titanium and tungsten. By tailoring the binder to the IEP, the system optimizes electrostatic coupling.”

In fact, because of the targeted surface coupling, Apex feedstocks can be compounded with 5 to 10 percent higher loading by volume than standard thermoplastic binders. Higher concentrations of metal or ceramic powders, in turn, reduce the potential for part defects.

Processing with Apex feedstocks also benefits from the surface agents, which fully wet out fine particles for better flow and reduced differential shrinkage upon debinding. Even at 65 percent volume loading, molding temperatures remain a relatively cool 90C. “While processing parameters will depend on powder type and loading levels,” notes Schofalvi, “you can generally run Apex materials at lower temperatures and pressures than industry standard systems.”

Thermal debinding takes place in one step, and can be performed in several types of furnaces—air, hydrogen, nitrogen, or vacuum—because the binder system provides its own oxygen. Major decomposition products are carbon dioxide and water. Because the binder formula contains no alkali metal-oxides, it burns cleanly and leaves nearly zero ash. When pyrolized, the polymer component creates only 40 ppm char, while the entire system leaves less than 100 ppm. Schofalvi believes his development team will be able to lower this figure to 10 ppm by next year.

Because levels of oxygen and carbon in the char are so low, the binder system can be used with oxidation-sensitive materials. “We recently compounded our first batch of titanium,” says Schofalvi, “and although it had a higher-than-recommended level of contaminant, we were able to mold prototype parts for medical and electronic components successfully.”

Stanton will spin off Apex P/M Binders this quarter, and will market the binders in several ways. Customers may send MIM- or CIM-capable powder for Apex to compound using one of its five IEP-tailored binders, or they may buy the binder, which requires the use of a twin-screw compounding extruder to create feedstock.

Stanton also has a prototyping program, in which customers can send their powder and receive prototype quantities of feedstock. Beta site testing is also welcome.