Automotive applications for powder coating

Automotive Applications for Powder Coating by Sal Lovano, Clearview Consulting,

Lakewood,

owder coatings have been used in North America to coat automotive components since the early 1970s. The initial forces driving this technology change were EPA demands for reducing VOC emissions and for improving corrosion resistance of the lighter weight parts that automotive manufacturers were employing in efforts to reduce overall vehicle weights for increased fuel efficiency.

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APPLICATIONS The first powder applications were on nonappearance, or underbodylunderhood, components that required a tough finish with excellent functional properties. In addition to reducing VOCs, the coating had to be resistant to gasoline and various oils and greases, withstand the constant barrage of road stones and other debris to which the underbody is exposed, have superior flexibility, and offer protection against corrosion from highway deicing salts. Powder coatings emerged as the finish of choice. Since that ignoble beginning as the unseen protector of the undercarriage, powder coatings have evolved to become the finish of choice for many more automotive applications, including interior and exterior trim parts and, most recently, primer/surfacers. It should also be noted that the success of powder coatings in underbodylunderhood applications, and its apparent answer to the EPA demands for reducing VOC emissions, led to both General Motors and Ford setting up pilot lines in the mid-1970s for topcoating automotive bodies with powder coatings. That effort is continuing today with the Low Emissions Paint Consortium (LEPC).

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16,500 metric tons, and usage is expected to reach nearly 25,000 metric tons in 1999. (See Fig. 1 and Table I.) What changes took place that allowed powder coatings to grow and capture a significant share of the trim business and penetrate the primer/surfacer market?

coating applications in the automotive industry is described in Table II. What further changes can be expected as the usage of powder coatings continues to increase in the automotive industry? Table III lists the current areas of application, the technology trends, and what factors are driving the changes.

TECHNOLOGIES In the early 197Os, when powders were first used in automotive applications, the applications were primarily limited to epoxy powders for use on underbody/underhood and interior trim parts. Polyester powders came into existence as viable alternatives for some exterior applications around 1974, and experimental acrylics emerged in 1975. By the late 197Os, there were 15 to 20 powder-coated parts on the average car or light truck manufactured in North America. Advancements in polyester powders, which had the appearance and weatherability necessary to meet exterior trim specifications, allowed that number to increase to approximately 40 powdercoated components by the mid-1980s. Acrylics, although the subject of early experimentation, were not compatible with other powders and did not enter the scene as viable alternatives until the early 1990s. The progression of powder Thousand

UNDERBODYhJNDERHOOD Amide- and phenolic-cured epoxies have dominated this area since powder coatings were first used in automotive applications; however, as shown in Table III, the trend is changing towards epoxy/polyester hybrids. The driving forces behind this technology shift are the economics and better handling properties of the hybrid systems versus the amide and phenolic types. There is also a need for lower cure temperatures, due to the fact that manufacturers would like to coat subassemblies, as well as completely assembled components, that have plastic components, gaskets, and, sometimes, fluids installed in the assemblies. Shock absorbers and gas springs are good examples of potential applications that are currently restricted by the cure temperatures of the dominating technologies.

Metric Tons

30 25 20 15 10

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USAGE

Industry statistics indicate that approximately 8,500 metric tons of powder coatings were used in automotive applications in North America in 1992, but growth is expected to almost double in 1996 with consumption of 20

5 0

1992

1993

1994

1995

1996

1997

1998

1999

Figure 1. North American automotive industry powder coating consumption. 0 Copyright Elsevier Science Inc.

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Table 1. North American Automotive industry-1995 Estimated Powder Coating Consumption Metric Tons

Application Underbodylunderhood Exterior trim Interior trim Wheel colors and primers Wheel clears Primer/surfacer and antichip Total

EXTERIOR

5,200 1,750 1,000 2,000 1,100 2,700 13,750

TRIM

Polyesters and polyester/urethanes are the prevailing technologies for exterior trim applications. Although polyester-based systems have demonstrated good performance over the years, styling changes and increases in quality and performance expectations are driving the change to acrylic technology. The increased UV stability, hardness, and scratch resistance of

acrylic systems, along with advances in solid acrylic resin technology, which now allow powder manufacturers to produce acrylics in several gloss ranges that meet the stringent appearance properties, are making this shift possible. Performance specifications for new models are being rewritten to include the properties available from acrylics. As exhibited in Table III, there are two types of acrylic systems-the GMA, or glycidal methacrylate acrylics, and the HFA, or hydroxyl functional acrylics, that meet the new exterior trim specifications and are starting to replace polyesters for exterior trim applications.

INTERIOR

TRIM

There are three categories for interior trim: Type A, which covers locations with high solar exposure, such as dashboards; Type B, for locations at or

Table ii. North American Automotive Industry-Typical

Powder Coating Applications

1970s

1980s

1990s

Oil filters Coil springs A-frames Struts Axles Bumper brackets Trailer hitches Seat frames and glides Wiper motors Emission canisters Voltage regulators Steel sport wheels Light truck wheels Rear window louvers Sun roof frames Window trim

Body trim Pillar posts Mirrors Door handles Running boards Truck bumpers Wheelwell inner liners Seat risers Wiper arms Dashboards Speaker grills Aluminum wheels Heavy truck wheels Roof and deck racks Engine blocks Manifolds Valve covers Radiators

Primer/surfacers Antichip coatings Body clearcoats

Table iii. Automotive Powder Coatings-Technology

Trends and Drivers

Application

Current Technology

TechnologyTrends

Need or Driver

Underbody/ underhood

Epoxy

improved economics

Exterior trim

No change

Improved gloss and color control

Wheel colors Wheel primers Wheel clears

Polyester/ polyurethane Epoxy hybrid, polyester TGIC polyester Hybrids, polyester TGIC polyester

Epoxy hybrid Lower cure temperatures GMA, HFA acrylic

No change No change GMA acrylic

Primer/surfacers Clearcoats

Acrylic/polyester None

Brighter metallic colors Better resistance to outgassing Improved ultraviolet, filiform corrosion, and chemical resistance Improved chip resistance and smoothness Improved smoothness, chip resistance, and acid etch resistance

Interior trim

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hybrid

Acrylic/polyester GMA acrylic

Improved ultraviolet

hybrid

resistance

near the beltline, such as door handles; and Type C, for areas below the beltline, such as seat risers. The category dictates the types of powder that are suitable for the application. For Type A and B surfaces, polyesters are generally used; Type C surfaces are usually epoxy/polyester chemistries. Although there are currently no perceived needs to change technologies, and performance specifications are not being altered due to field failures or product deficiencies, there is a recognized need for powder manufacturers to improve gloss and color control for these applications. Many of the items coated must be exact or very close matches to other components that are not coated, such as plastic trim parts and upholstery fabrics, and precise gloss and color control of the powder coating is necessary to achieve acceptable interior appearances. This has been a difficult task since most of the interior coatings are specified in the 5 to 20” gloss range and slight variances can effect color significantly.

WHEEL COLORS AND PRIMERS The vast majority of powder-coated wheels are the styled aluminum alloy wheels for passenger cars, vans, and light trucks. Powder primers, which are either polyesters or epoxy/polyester hybrids, are applied to provide a smooth surface for the liquid or powder coating color and to improve chip resistance of the finished wheel. Although powder coatings have performed extremely well as primers and color coats for aluminum wheels, and no changes are anticipated in the basic chemistry of these coatings, some improvements are being sought. The first area of concern is outgassing of the aluminum substrate during the powder coating curing cycle, which often results in the wheel having to be hand sanded, and sometimes recoated, before the color coat is applied. Wheel manufacturers are seeking powder primers that are more tolerant of substrate out-gassing that will reduce rejects due this phenomena. The second area of concern is the availability of powder coatings in bright, weatherable, pigmented, and nonpigmented metallic colors. In the past few years, automotive styling has evolved to brighter colors and, thus, METAL FINISHING

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the need for brighter, more intense powder coatings for wheels has arisen. While there are many bright metallic colors available in powder coatings for interior applications, the UV resistance and weatherability of those coatings make them unsuitable for exterior automotive applications. WHEEL CLEARS Due to their extremely good adhesion to aluminum, superb edge coverage, and good weatherability, TGIC polyesters have dominated this segment of the market for the past 15 years; however, with the increasing amount of aluminum wheels being used, field failures due to filiform corrosion and, in the past few years, attack by wheel cleaning chemicals have led to the search for alternative powders. GMA acrylics provide an extra margin of performance in those areas versus TGIC polyesters, as well as offering superior clarity, and are starting to replace them for this application. PRIMER/SURFACERS ANTICHIP COATINGS

AND

This segment of the market has been the fastest growing automotive application for powder coatings in the 1990s. Although first introduced at the General Motors plant in Shreveport, La. in the early 198Os, powdered primer/surfacers did not find significant use until the early 1990s. Now, both Chrysler and General Motors are applying powdered primer/surfacers at several plants and new installations are in the planning stages. The powders serve a dual purpose, acting as both a primer/surfacer for the entire body and as an antichip coating on specific areas of the vehicle. Some plants use the same powder for both applications, and simply increase the film thickness in the antichip zones (generally below the beltline and on the leading edges of the hood), while other plants use two different powders for these areas. No sanding of the powder coating is done, except to repair areas that have surface defects so, in either case, the finish must be smooth enough to accept the color coat without sanding. Three chemistries are currently being used as primer/surfacers and anti-

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chip coatings-GMA acrylic, polyester, and epoxy/polyester hybrid. While each of these technologies has achieved acceptable results, further improvements are necessary for powders to continue to grow in this application. Film thicknesses of the primer/ surfacer must be reduced from the current 2.5 to 3.5 mils to an average of 2.0 mils in order to meet economic criteria. Smoothness and chip resistance must also be improved so there is no trade-off for the lower film thickhybrids, nesses. Acrylic/polyester which offer better flexibility (for chip resistance) than GMA acrylics and better UV resistance than polyesters (for use under translucent color coats), appear to have the attributes necessary for increasing performance and may well be the technology of the future for this application; however, polyester resin suppliers are developing materials specifically designed for use as primer/surfacers and antichip coatings that offer better economics than acrylic/polyester hybrids, and the future will most likely be determined by cost/ performance benefits.

which precludes coatings of some plastic components, and there are some shortcomings in all areas that must be overcome if powder coatings are to continue to enjoy growth in this segment of the market. Several powder manufacturers and resin suppliers have research and development programs under way to develop new materials that address the problem areas, and coatings offering lower curing temperatures with improved smoothness, chip resistance, and acid rain etch resistance can be expected in the near future. SUMMARY Powder coatings have come a long way in automotive applications since the early 1970s. The success of the technology has been continuous improvement in raw materials, formulatand manufacturing ing techniques, processes. Powder is here to stay, and there is still room for significant growth in the automotive market as long as the technology continues to advance. The carrot is big enough, the rewards are substantial, and competition will ensure the success of powder coatings.

BODY CLEARCOATS Powder coatings are not currently being used in North America as fullbody clear coats, and are not expected to come into use for that application until after the year 2000. The LEPC began evaluating powder coating earlier this year at its new 60,000 ft2. facility in the Ford Motor Company assembly plant at Wixom, Mich. The Consortium’s mission is to evaluate all low emission coatings, as well as new equipment and processes, with low emission potentials, and present their findings to the program sponsors (Chrysler, Ford, and GM). The program will take several years to complete, and liquid clear coat technologies will also be evaluated, but powder coatings are expected to emerge as a viable alternative for body clearcoats. The current technology employed for this application by powder coatings manufacturers is the GMA acrylic chemistry since no other technology offers the same combination of flow and leveling, clarity, and chemical resistance. Nonetheless, cure temperatures are still higher than desired,

Biography Sal Lovano has a total of 34 years of experience in the coatings and plastics industries. He spent 29 years with Ferro Corp., a multinational producer of organic coatings, inorganic coatings, plastics and specialty chemicals, where from 1990 to 1996 he held the position of General Manager, North American Powder Coatings Operations. His previous positions at Ferro included International Business Manager for Powder Coatings; Division Manager, Powder Coatings, Ferro (Great Britain) Ltd.; Director of Sales and Marketing, North American Powder Coatings Operations; Technical Service Manager, Powder Coatings; and Mid-South Area Operations Manager for the Plastics Division. Prior to his employment at Ferro, he held sales and technical positions at the Wagenman Paint Co. and Knight Brothers Inc. Lovano is a member of the Association for Finishing Processes, Society of Manufacturing Engineers, and serves on the industry communications committee of the Powder CoatMF ings Institute.

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