Martha K. Raymond
Staff Editor
Luxury-based demands and environmentally based needs are driving the growth in adhesive use in the automotive industry. In fact, North American consumption of adhesives, coatings, and sealants in automotive applications is valued at more than $5 billion, and demand is expected to increase by 2% annually during the next five years, as reported in a study “Coatings, Adhesives and Sealants in Automotive,” conducted by Skeist Inc., Whippany, N.J.
Industry trends
Other trends pushing the increase in adhesive use include automotive companies’ ongoing development of lighter, more efficient, and more technologically advanced automobiles. These changes, combined with updated product design, generate growth opportunities for the adhesives industry.
Continued growth for adhesives applications for automakers will continue, according to a report, “North American Automotive Coatings and Adhesives Technologies,” conducted by Frost & Sullivan, Mountain View, Calif. It forecasts that total market revenue for advanced materials will grow 1.2 to 1.5% through 2003.
Data in the report also underscores the importance of adhesives to the environment. Many coatings, adhesives, and sealant manufacturers are replacing solvent-based products with high-solids and water-based products to reduce emissions of volatile organic compounds. And while water-based products cost less per gallon, more gallons are required. As always, automakers are demanding stringent cost-to-performance ratios from adhesive suppliers to go along with their designs.
“One way automakers are cutting costs is by using modular engine designs, which makes component matching between different sized engines easier,” says Joe Ballantine, marketing manager of Loctite Corp.’s Automotive Group, in Rocky Hill, Conn. “To facilitate the change, a bedplate was added, which meant an additional sealing area.” The metal-to-metal design required liquid sealants instead of a rigid gasket.
Luxury for all
Consumers with a yen for plushness and opulence are forcing automakers to include contoured parts and luxurious materials inside their cars and sport utility vehicles. In automotive interiors adhesives are used for headliners, instrument panels, flooring systems, consoles, visors, wheel covers, and steering wheels. They’re also used to laminate, bond, and edgewrap components, and most adhere to vinyl while resisting plasticizer migration and high temperatures.
As automakers make more and more changes in the design and materials used for interior components, their use of adhesives is also increasing. For example, contoured parts and sculpted interiors are popular, but the joint where the door panel meets the instrument panel must be smooth for the overall look to be effective. It almost forces designers to use adhesives systems for assembly because mechanical fasteners could mar the sleekness.
“It also takes new adhesives when we change materials. As materials and cloths become more luxurious, they require new adhesive systems for laminating them to the foam in the seats,” says Chris White, automotive marketing manager at Bostik Automotive & Industrial Div., Troy, Mich.
“In the past, a door panel was layered with a piece of cardboard and a sheet of vinyl on top. Now, construction methods are much more exotic and the ergonomics much more dramatic as far as the design of the contours. There’s really only one way to assemble those components, and that’s with adhesives,” says White.
Door panel material changes were cost-cutting measures made by automakers. Previously ABS was the material of choice, but they now use a less-expensive polypropylene, a lower surface energy material, according to Paul Moran, transportation market manager of Avery Dennison Specialty Tape Div. Automotive Group, Troy, Mich. The surface energy of a material dictates an adhesives sticking strength, so a change in surface energy generally requires a new adhesive.
Besides surface energy, adhesives properties are usually specified such as viscosity, specific gravity, flash point, coefficients of thermal expansion and conductivity, as well as breakaway and prevailing torque. However, automakers retained the same adhesives specs for the higher surface energy ABS. Finding a match to fit the spec and the actual material was a challenge, but a UHA adhesive worked to bond carpet to door panels.
Another material change reflecting a change in adhesives was in a headliner. The new adhesive had to bond to new materials, and withstand temperature extremes such as heat generated inside a car parked in the summer sun and winter cold. Engineers chose web and powder hot melts to hold the headliners together.
Types of adhesives
Powder hot melts or web adhesives, which come in continuous rolls of either polyolefins, polyamide, or polyester and in a range of basic weights and made-to-order widths, bond upholstery or headliner laminates, while film adhesives are used for vinyl trim. The water-based or solvent-based liquids provide adhesion of vinyl trim stock to ABS and fiberboard door and dash panels.
Hot melt adhesives include linear saturated polyesters, polyamides, compounded polyolefin, and formulated block copolymers. They help create great looking, highly durable upholstery. Hot melts are 100% nonvolatile adhesives that are solid at room temperature, liquefy upon heating, and resolidify with cooling.
Film adhesives are high-performance, solvent-free bonding agents. They carry a thin layer of pressure-sensitive, thermosetting, or heat-activated thermoplastic adhesive supported on a peelable backing. More complex versions, such as dual-coated films are also available.
Another type of adhesive, foam barrier tape, resists hostile temperature extremes like heat from the engine and moisture, as well as chemicals such as brake fluid, hydraulic fluid, and gasoline. “Typically, vehicles have about 13 to 15 pounds of tape,” says Larry Cascino, manager of research and development, Gaska Tape Inc., Elkhart, Ind.
Other trends to watch in the automotive industry that may impact adhesives companies are the development of new materials to replace metals, part-consolidation for weight reduction, noise control for improved acoustics, additional energy absorbtion requirements for passenger safety, and longer bond life to meet increased warranty periods.
Adhesives cut gasketing costs
An anaerobic adhesive from Loctite Corp., Rocky Hill, Conn., provides leak-free sealing on critical bed-to-block joints for two new Chrysler engines. The challenge in this application was that the bedplate-to-block joint bisects the main journal bearing and undergoes heavy crankshaft loading. The joint must be extremely rigid and maintain zero clearance for proper bearing clearances and minimal vibrations.
Conventional pressed-in-place or compression O-ring gaskets for these engines would have required machining a contoured groove, and adding a low-tolerance gasket to avoid shimming the bedplate out of position. O-ring machining is time consuming and requires a special CNC machine for close tolerances to seal the joint while avoiding shimming. The cost of a specialized O-ring gasket, plus the cost of processing, raised the total sealing costs to more than two dollars per engine. The anaerobic gasket solution, on the other hand, costs less than 20 cents per engine and streamlines assembly.
When using the anaerobic gasket process, the block and the bedplate are machined and bolted together. Main bearing bores are machined as an assembly, and the bedplate is removed to install the crankshaft
A 42-in. adhesive bead is applied by a CNC robot which traces the skirt. Cycle time is less than 30 sec. Bead geometry assures the exact amount of sealant is consistently applied around the joint edges. The bedplate is then bolted into place.