Low VOC emission standards for vehicle interiors propel polyacetal development

Automakers want to reduce that characteristic odor new car buyers may love. And one way of achieving this is employing grades of resin that emit less volatile organic compounds (VOCs).

Resin suppliers are developing such grades of polyacetal (POM) resin that feature such low emissions. For example Asahi Kasei Plastics (Tokyo) offers POM grades with VOC emissions of 2, 5 and 10 ppm, depending on the requirements of the automaker. Nowadays, Japanese automakers have some of the strictest requirements among global automakers for VOC emission standards.

Global polyacetal suppliers are also developing such low VOC emission grades to differentiate themselves from emerging Chinese suppliers of POM. Typically coal companies, these suppliers are employing coal seam gas (methane) as a feedstock and entering the business with large plants. Blue Star, for example, expanded capacity from 40,000 tonnes/yr to 60,000 tonnes/yr in 2o12, while Tianye Chemical, Shenhua Ningmei, Tianjin Bohua, and Yancon Lunan have all started up new world-scale plants since 2011 and the industry is mired in overcapacity. These Chinese suppliers, however, generally target commodity applications such as fasteners and lack the capability to supplier low-VOC grades.

New grades

Celanese (Dallas, TX) offers XAP low-emission technology for its Hostaform acetal copolymer (POM) to assist automakers achieve their global engineering emission standards for molded parts located in a vehicle's interior.

"Driven by international legislation, air quality in automobiles is receiving renewed focus. Celanese is helping to set the global standard for low-emission engineered materials with its Hostaform XAP and XAP2  POM grades that help the auto industry reduce part emissions in vehicles," says Scott Klingler, Celanese global original equipment manufacturer (OEM) manager.

Lower VOC  emission standards are driving development of new POM grades.

Hostaform has bee identified by one of world's largest automakers as the preferred material in a specification standard for POM. Hostaform UV270Z XAP2 reportedly meets OEM performance requirements for automotive cockpit applications with a combination of high flow, UV stability, colorability, scratch resistance, and impact strength.

One automotive interior application for the use of this Celanese engineered material is speaker grills. Hostaform UV270Z XAP2 can be injection molded in one shot, and then snap-fitted or ultrasonically inserted in the support element. One recent set of front and rear door speaker grills posed specific challenges since they required a perfect fusion of function and form to ensure excellent sound transmission, as well as aesthetics.

"This grill pattern design, with its small and thin pattern and small and tight holes, pushed the material and processing envelope," says Craig Dlugos, Celanese application development engineer. "The engineered material needed a high-flow characteristic because the small design created significant sheer and molding issues."

Another challenge involved color matching. The Celanese color technology team needed to adapt the formulation to match interior colors without losing any of the low-emission properties. Formulating a color-matched material to meet the OEM color approval process required numerous formulation iterations and molding trials," says Bruce Mulholland, Celanese global color technology manager. "The hole pattern in these particular speaker grills significantly changed the appearance of these colors in the actual part."

Colorants were specifically selected to match each color. All colors were approved with the first submission in plaque form to the design studio. The challenge came in translating a solid molded plaque to a speaker grill with hundreds of holes on the appearance surface. Offsets to the official master were developed in the laboratory and trialed in the actual part until part appearance approval was achieved.

"Part placement in the vehicle was also challenging for these colors," adds Mulholland. "Color harmony in the vehicle had to be achieved between solid plastic trim, soft leather trim and these speaker grilles with holes and curvature."

Components such as door modules or seatbelt pre-tensioning systems increasingly call for low-emission materials. Other potential applications include head rests and lumbar support, fastening solutions in the door area and trim for door elements, instrument panels and center consoles.

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