The driving force behind new developments for manufacturing car interior parts is producing high-quality soft trim with product weight reductions while, at the same time, minimizing costs.
Current, common manufacturing methods of laminating adhesives to polypropylene substrates involve open-flame preheating. Although flame pretreatment is typical in automotive door panels, artificial lumber, boat hulls and other applications, there are inherent safety risks. High-tech solutions such as low-pressure plasma treatment or fluorination are expensive, however, making flame treatment the most common choice regardless of fire risks and quality concerns.
A global adhesive developer manufactured a polyolefin hot melt adhesive, and its development allowed for the creation of flame-free polypropylene bonding technology. Together, they create a highly efficient in-mold graining, or IMG process. The adhesive offers green strength while curing and immediately after lamination. (Green strength is the ability of an adhesive to be managed and manipulated prior to curing.)
A Tier One OEM supplier of door panels and other car parts to many automotive companies needed a new manufacturing approach and a flame-free lamination process. Research led them to the polyolefin hot melt adhesive and the in-mold graining process. Research into curing methods showed the best solution for the application was to use a medium-wave infrared emitter at specific electromagnetic wavelengths (figure 1). The adhesive, which is applied to the fabric in the door panel application, possesses properties that make both the adhesive and the fabric suited to absorb infrared. Additionally, the in-mold graining process permits laminating (or forming) without grain stretch, creating a superior surface.
The lamination press (figure 2) for the car door panels is designed with a movable upper tool and a stationary, water-chilled bottom tool. The adhesive is applied to the fabric with a roll coater prior to being placed onto the tool. Fabric is placed onto the bottom tool and a substrate “board” is held in place by vacuum on the upper tool.
A retractable shuttle-mounted infrared emitter radiates infrared energy upward at the substrate while simultaneously heating the adhesive and fabric on the bottom tooling. It directs energy to both substrates and is programmable to specific energy densities and wavelengths. The infrared emitter’s purpose is to elevate the temperature of the adhesive to the point where its high-strength cure properties are activated for optimum quality of lamination.
The energy density and infrared wavelength are preset to specific parameters to optimize the absorption of the emitter’s infrared energy. The infrared emitter module is indexed into position for approximately 30 seconds and then retracted. The tools then clamp the substrates to the activated coated surface of the fabric to form the various shaped and designed interior door panel inserts. The laminating press is loaded and unloaded manually. The complete laminating process cycle takes approximately 55 sec.
This technology brings cost savings to the Tier One supplier and OEMs. With the success of this flameless lamination technology, research is continuing to improve efficiencies, cycle times and product quality with many other automotive soft parts.
Seat Cover Application
In another automotive application, infrared curing is used during the production of seat covers.
Automotive seat covers begin as substrates on an unwind roll at the entrance to the system (figure 3). Automotive seats are required to handle hundreds of thousands of lifetime impressions. The seating material usually is fabric or leather backed by polyurethane foam. The two are bonded together, typically using a polyamid web adhesive for good strength, temperature resistance and longevity of bond.
A turret system unwinds the adhesive web. The foam is unwound from a roll onto a conveyor and the web adhesive film is placed onto it. The combined web goes through an infrared oven, where the web adhesive melts and flows into the foam. Three zones in the machine direction and three zones across ensure uniform heating of the web. Optical pyrometers, non-contact temperature measuring devices, are used to precisely control the web temperature.
At the exit of this oven, the face web (fabric or leather) comes down vertically and is heated to 150°F (65°C) to remove the moisture from the fabric. Following preheating, the fabric is conveyed into a nip consisting of a steel roll and a rubber-covered roll. The two webs are pressed together and bonded. The nip station — a manufacturing station where two substrates are pinched or compressed together — permanently laminates the substrates, producing a 72" fabric and foam laminate. The line runs at 90 ft/min and the finished product is wound onto large diameter rolls. These rolls then are fed to the die-cutting machines, where different parts of the seat are die cut and then sewn together to form the seat.
The fast, targeted heating zones possible with infrared heating make this process heating technology an essential part of many automotive finishing applications.