As new auto models are announced in the next two months keep an eye out for a game changer—a roof liner in which printed electronic circuits encapsulated in plastic replace three-dimensional switches.
- The new roof liner will be lighter –by 70%,
- It will be thinner—0.35 inches versus 2.75 inches,
- Switching speeds are 10 times faster,
- It will be more stylish, and
- It will trim costs with an impressive automated in-mold assembly process.
It’s based on proprietary Smart Plastic technology and it has been licensed to an unidentified global automotive OEM. The first production part ships this fall and more than a million units are expected to ship next year.
T-Ink’s Smart Plastic couples printed capacitive sensor/switch technology with film insert molding technology. One of the company’s patents indicates how the process works. Electronics are printed on a high-performance plastic (high heat deflection temperature) film. The film is formed to a desired shape and placed into a mold. The plastic substrate material is injected into the mold to form a rigid structure that incorporates the film.
The patent refers to high-pressure injection molding, but a roof liner would suggest a lower pressure process, such as thermoforming. For injection, it’s preferred that the ink side face away from the injection point. Still, it’s a tough ink that could withstand high injection pressures and temperatures. For polycarbonates, injection molding pressures range from about 8,000 to about 15,000 psi and molding temperatures go from 540 to about 580F.Thermoplastic urethanes (TPUs) are also excellent candidates for the substrate film.
The conductive ink must be formulated to withstand typical injection molding temperatures and blow-off. A suitable conductive ink mentioned in the patent is DuPont Silver Conductor 5096, which is designed for use in thermoforming operations or where extreme crease conditions are employed on flexible substrates.
Here’s how the electronics are printed: A dielectric layer is printed on a ground layer. The dielectric layer is preferably configured to cover the entire ground layer and insulate sensing zones and their electrodes from the ground layer. A switch layer is then printed on the dielectric layer. The switch layer has several sensing zones to detect the presence of an object or finger.
The film switch probably will include LEDs to backlight each of the sensing zones and graphics.
Connector terminals are used to connect in-molded capacitive switches to to electronic devices. The terminals are shaped to match the three dimensional shape of the B-surface of the film switch. In the manufacturing process, terminals are placed in the “moving side” of the injection mold. Terminal ends “press fit” into receiver pockets in the mold.
A conductive adhesive is applied to the connector terminals, then the injection mold closes, and the injection of the substrate begins. As this happens, the terminals and conductive epoxy are pressed onto the silver ink traces on the film switch. The conductive epoxy is cured by the heat of the injection molding process. The part is then ejected, with the terminal secured in the molded plastic part. For headliners, urethanes are a good candidate matrix material, also opening the door to resin transfer molding. For consoles, TPOs are good candidates.
This is a fast process that is said to create secure electronic assemblies. Epoxy adhesives such as epoxies are typically cured at room temperature or through infrared or ultrasonic methods. So cost savings are also very possible through this system.
The patent specifically mentions polycarbonate-based Makrofol and Bayfol films supplied by Bayer Films Americas of Berlin, CT as “exemplary films” for the process. The color, translucence, and/or transparency of film are based on the desired application. The patent example uses a smoked black color that is preferably translucent and which allows graphic indicia printed on one side to be viewed on the other side.
The name of the automotive licensee has not been disclosed, but it is interesting that Will Boddie, the director of T-Ink Transportation is a former VP of Ford Motor and headed Ford’s entire North American engineering group.
T-Ink stands for “Thinking Ink”. The company was formed in 2001.
It’s also interesting to note that Austrian machine builder Engel showed the automotive “cockpit of the future” at its booth at NPE 2012, held in April. No switches—just touch controls. The cockpit was presented in cooperation with Tier One Magna. Functional foils for the exhibit were supplied by plastic electronic GmbH.