Procter & Gamble continues to build an interesting intellectual property portfolio for its recently established venture into injection molding—a Hamilton, Ohio-based company called iMFLUX.
The newest patent is for a mechanism for pressurizing molten plastic prior to injection into a mold. The patent also covers an injection element for advancing the molten plastic from the melt holder through a nozzle and into the mold.
The goal of the technology is to mold container walls less than 1 mm thick without molded-in stresses or use of expensive equipment and molds. In conventional molding, the injected plastic material adjacent to the walls of the cavity immediately begins to “freeze,” or solidify. This “boundary” layer continues to thicken, eventually closing off the path of material flow. Just increasing pressure is not a good approach because the plastic may have molded-in stress. Plus special equipment is needed.
The pressure-regulating valve and pressure relief valve in the newly patented iMFLUX technology can prevent overpressurization of the mold.
The iMFLUX inventors say that shear-thinning thermoplastics may be injected into the mold at low, substantially constant, pressure without any significant adverse effects.
“It is believed that injecting the molten thermoplastic material into the mold at low, substantially constant, pressures creates a continuous flow front of thermoplastic material that advances through the mold from a gate to a farthest part of the mold cavity,” the patent states. “By maintaining a low level of shear, the thermoplastic material remains liquid and flowable at much lower temperatures and pressures than is otherwise believed to be possible in conventional high pressure injection molding systems.”
In another important feature, reduced pressure helps reduce damage to seals, parting lines, and moving mold mechanisms.
Examples of shear-thinning plastics are polypropylene, polyethylene, thermoplastic elastomers, polyester, polystyrene, polycarbonate and polyacetals.
Parts molded at low, substantially constant, pressures exhibit some superior properties compared to the same part molded at a conventional high pressure, according to iMFLUX.
The iMFLUX approach is a direct contradiction to conventional wisdom within the industry that teaches higher injection pressures are better.
Another benefit of the iMFLUX technology is the ability to mold “thick-to-thin” flow wall thicknesses.