German foil maker Kurz is developing a technology that will replace in-mold decorating (IMD) with 3D printing for specific applications that create a whole new look of customized decorated and functional plastic parts, including the incorporation of electronics.
In the new Kurz approach, decorative foil ply is clamped (or held with vacuum) to a support with a predefined surface geometry. The ply has a plastic-facing layer with a heat-activated adhesive. Plastic molding compound is applied by a robotically guided 3D print head.
The robot arm carries and guides the print head of the 3D printer to follow the contour of the curved surface.
As more plastic is applied dot-by-dot, the plastic is heated only slightly above its melting temperature, so that it solidifies immediately, eliminating the potential for running. “Thus, a high printing resolution can be achieved,” states the patent, which was published Nov. 14.
“Since the plastic molding compound is successively applied in small quantities, only minimal heating beyond the melting point of the plastic is necessary. In addition, the application of the plastic molding compound is performed in an unpressurized manner.”
As a result, “foil plies having sensitive decorative or functional elements can also be used, which would not survive the pressure and/or temperature conditions during injection molding.”
“The drop-by-drop or layer-by-layer application of the plastic molding compound additionally opens up significantly expanded design possibilities for the molded body in relation to injection molding…The properties of the plastic molding compound, for example, the color or the conductivity of the plastic molding compound, can be varied over the volume of the molded body, for example, to provide further decorative or functional structures inside the molded body.”
Advantages of the approach over insert injection molding include:
· The opportunity for internal decorative or functional (such as magnetized) features, including use of plastics with different optical properties,
· The ability to customize each piece,
· The ability to adapt to rapid design changes,
· Elimination of tool cost, and
· The ability to use sensitive electronic foils that would be destroyed by the high heat and pressure of injection molding.
The cons are also significant and will ensure the continued use of IMD for most production parts. They include higher cost and slower production speed.