These investments are essential ingredients to reduce dirt and to improve quality by eliminating workmanship as a "dirt factor" from the paint lines, and to run consistent and stable processes by the use of automated equipment. OEM coatings technology has progressed from the times when paint formulating was thought of as "alchemy"; the industry today provides scientifically designed products allowing for automated processes. One example of such a sophisticated product is now commercially successful for the first time on an automotive OEM line at BMW Dingolfing, Germany: powder clearcoat.

This article discusses the status of achievements on the Dingolfing lines, described from the view of the paint supplier. Actual work to further optimize and improve product and process efficiency will be discussed, as well as opportunities for car manufacturers regarding process cost savings and simplifications using powder clearcoat technology.

At BMW Dingolfing, more than 1,000 3-,5-, and 7-series bodies are coated daily using powder clearcoat technology (PCC) in a 100%-automated process (see Figure 1). Visitors to the Dingolfing line see the entire topcoat line operating without any workers spraying paint or handling hoods or doors. The few workers present are supervising, programming the equipment or reviewing the excellent finish in the inspection booth.

BMW's three-shift operation was introduced on a continuous basis last year and has been proven to be an easy practice. Where five cleaning cycles/shift are required to ensure consistent operation of a 2K liquid clearcoat production line, PCC only requires one cleaning break per shift to keep first-run capability (FRC) at the high level achieved, leading to fewer repairs throughout the day.

The ability of powder to apply with no sag and run behavior results in a film build varying only within a few microns between horizontals and verticals. This attribute produces a homogeneous and consistent appearance over the entire body.

Production line experience with online recycling of powder overspray was gained at the beginning of the PCC project, and has been in continuous use for more than one year, establishing the entire PCC application as a very stable and dirt-free process.

Introducing a new product or process requires a review of the entire application for all interactions and any potential obstacles or roadblocks. With the launch of powder clearcoat it has been essential to adapt the waterborne basecoats for this technology in order to avoid micropopping, adhesion problems and especially yellowing issues with light colors, which had been a major problem in the beginning.

Today, the basecoat suppliers have successfully adapted their products, and only "powder-compatible basecoats" are used throughout BMW. These basecoats have equal performance qualities when used in combination with PCC in Dingolfing as well as with 2K liquid clearcoats at the Munich and Regensburg plants. The functional quality obtained from the two coatings systems technologies is comparable, and if the owner feedback studies conducted by JD Power & Associates show what the final customer really values (surface quality is a highly visible factor), the BMW vehicles built at Dingolfing are rated among the best in the world.

Avoiding contamination of powder clearcoat has been a user concern from the start. As a preventive measure, the introduction of a clean room practice for powder clearcoat application was extended to also include the manufacture of PCC itself, which required training the employees of the paint manufacturer. These efforts led to new test methods for representative sampling of powder and verifying the efficiency of cleaning procedures. These processes are now well established and have ultimately allowed the customer to reduce the QC check of incoming PCC to a minimum.

Clean room concepts and similar precautions were also required to introduce into practice the online recycling of PCC overspray. Overspray recycling is an important factor to increase the degree of material usage and enable powder clearcoat product to be economically competitive (see Figure 2).

The technical solution realized at BMW collects all overspray and allows it to be re-introduced into the main stream simply after sieving. For each unit sprayed, a corresponding amount of virgin and reclaim in an approximate 70:30 ratio is fed to the circulation system and applied on the body regardless of the surface area - the entire body is considered as a "Class A" surface. Based on known industry practices, the BMW Dingolfing PCC lines are the only OEM clearcoat lines in the world providing online recycling of overspray clearcoat.

Since its start approximately one year ago, experience with continuous online recycling and direct re-use of the overspray has resulted in a total degree of material use of about 95%. Other than the ultrafiltration of electrocoat, no liquid paint system used in automotive OEM is able to compete with this performance.

To guarantee the high product quality level required for use as topcoat, particle size management of the ground PCC chips is required. Unlike the manufacture of most liquid coatings, significant manufacturing "yield loss waste" can result during this conversion step. After intensive testing, re-extrusion recycling of the process fines was line approved and successfully introduced in late fall of 1999, further improving the total ecological benefits of powder clearcoat (see Figure 3).

Another type of powder clearcoat recovery was a result of the learning experience associated with the clean room concept in PCC manufacture. Some trial materials might be rejected because of high dirt or particulate counts leading to line repairs above the accepted level. Material of this nature did not receive a line approval.

These rejected batches have been later successfully re-classified in dedicated PCC equipment, approved and used online without any visible difference. The procedure seems to be more effective than comparable processes for liquids.

This positive experience has encouraged both the customer and the paint supplier to initiate a program targeted to recover even the final 5% of the OEM line waste previously scrapped because of concerns with dirt. Early line trial results indicate feasibility of this goal, and implementation has been started.

The achievements described up to this point indicate some considerable benefits of the PCC system. Some other differences of PCC vs. liquid coatings should not be underestimated: logistics and sludge (see Figure 4).

Even taking into account the difference in container size (PCC packaged in smaller containers), and the space requirements for transportation and storage of waste materials, the associated logistic efforts are significantly reduced with PCC. Also, compared with solventborne coatings, an enormous amount of solvent emissions are eliminated when using powder. A zero-VOC commercial liquid OEM automotive clearcoat product still does not exist.

An honest discussion of the benefits of OEM automotive powder clearcoat should mention a very real actual deficiency: on a material-only basis, PCC itself is actually significantly more expensive than a state-of-the-art 2K liquid clearcoat.

This cost disadvantage should not delay any favorable decision for PCC, because the following saving potentials are obvious (see Figure 5).

• The introduction of thin film PCC, which is expected to take place later this year, will result in a 15% improvement in direct material cost if the today¿s film build average of 65u(greek mu)m is reduced to 55u(greek mu)m.
• As commercial implementation of PCC is in the beginning of its life cycle, cost reductions in raw materials and manufacturing conversion can be expected similar to those that have followed the commercialization of competitive liquid technologies. Achievable savings of approximately 20% within the next 2¿3 years are forecasted.

Automation usually requires increased investments, no matter whether for liquid or powder. The decision to implement powder clearcoat is of particular monetary benefit if a new paint shop is built.

Even when a larger retrofit of an existing paint shop is planned, the potential listed in Figure 6 should be taken into consideration, especially regarding energy savings as shown in Figure 7. If automation and controlled processes, which require constant conditions, are assumed to be in place as they would be with analogous high-performance paint systems, the apparent extra costs for temperature and humidity control of the PCC application are relatively balanced by the reduced demands for conditioned air, and eliminating the need for destruction of VOC emissions.

In the overall assessment, BMW Dingolfing has realized actual annual energy cost savings of approximately 25%.

As shown, general information was used to highlight the saving potential of powder clearcoat. The basis for the following comparisons are average figures from detailed investigations by industry experts. The investments in the material application itself are comparable for liquid and powder, the major saving potentials refer to booth air supply equipment and the waste and emission treatment (see Figure 8).

Beneficial for powder clearcoat in terms of annual costs is not only the reduced depreciation expense related to the difference in facility investments, but also the elimination of certain indirect materials and their associated operating costs (see Figure 9). Also included is the absence of those operational costs, which do not exist because the associated facility capital investment was avoided. Of course, this chart does not provide a fair picture as long as costs for direct materials are not included.

A simple stand alone graph with actual costs might disappoint any potential powder clearcoat user who may plan for a new or retrofitted paint shop. The data in Figure 10 is given as cost per unit, based on actual consumption of 1.6-kg PCC vs. 2.4-kg liquid 2K-CC blend.

The short-term saving potential of reduced film builds and expected cost reduction in raw material and manufacture were already described, so the only variable in this graph is referred to as "economy of scale." As well known, the Dingolfing plant is the pioneer of OEM automotive powder clearcoat technology. The figure illustrates the potential cost impact when gaining a second customer of the same size.

Based on figures provided some time ago by an automotive manufacturer, the cost structure for the entire paint process in OEM is shown in Figure 11.

Assuming general validity of this data for the clearcoat process, the achievements for PCC as discussed before are reflected in the second column, giving the real status: total costs actually are very nearly equal. This analysis is in good accordance with BMW findings as reported in other papers.

The third column takes into account the savings described in the previous chart and suggests a short term savings potential for the PCC process of about 15%.

As usual, beneficial effects from a more stable process and higher FRC are not easy to predict and therefore not included.

To summarize the OEM automotive powder clearcoat experience discussed in this article, the triangle shown in Figure 12 compares the overall performance of PCC vs. liquid clearcoat where 2K-CC was the internal benchmark.

The total process cost of powder clearcoat is today already equal to liquid - providing an excellent potential to support automotive makers in improving their processes with a clearcoat that perfectly fits in clean room concepts, satisfies customer requirements regarding automation, simplifies handling and waste treatment, provides better workability and improved process stability - and last but not least, provides an excellent finish at competitive costs.

Implementing clean room practices and enhanced automation increases system complexity (and costs) no matter what coatings technology is used. To compensate against these additional expenses, non-value-added processes and equipment should be identified and eliminated (e.g., waste) and no commercial system other than powder clearcoat will provide better possibilities.

From the view of the paint supplier, this technology has the potential to gain 50% or more of the OEM clearcoat market share in the long term. The only alternative for those who would like to stay with liquid for whatever reason, will be a zero-emission waterborne paint, which would require accepting the system deficiencies already discussed.

Experience with powder primer and clearcoat suggests that these innovative materials can be combined for use in highly automated paint shops. The idea of powder basecoats is not unrealistic: working prototypes of powder color changers are already being tested with powder primer. Even color monocoat as well as a metallic type powder basecoat can be seen on European roads already in the form of the "SMART" car.

Precoated steel substrates have proven to simplify assembly processes, robots are applying sealer, and more attention is given to sprayable sound deadeners as they allow for further automation and practice of the clean room concept as well.

Our customers will eventually determine the viability of powder basecoat combined with powder clearcoat, but for sure, as paint suppliers we are investing into improved automotive powder coating technologies and perhaps we will be able to see these new concepts in North American showrooms soon.

This paper was originally presented at Powder Coating Europe 2000 January 19-21 in Amsterdam, The Netherlands.