Coatings of Polymers and Plastics part 13 pps

6 AUTOMOTIVE APPLICATIONS WITH ADVANCES IN PROCESS TECHNOLOGY Advances in the extrusion and coextrusion process have resulted in color exterior and interior automotive plastic trim parts

289

trimmed, placed in an injection mold, and “back injected” with a thermoplasticmaterial The film has met the colorfastness, UV weathering, gloss, abrasionresistance, water jet, car wash, crosshatch, and gravelometer tests required byautomobile manufacturers (9) This technology is used for the roof of the Euro-pean “Smart Car” subcompact (10).

There exists advantages of films compared to coating There is easier colormatching between different production sites Allows for rapid color changes

It eliminates the cost and maintenance of a paint line It is environmentallyfriendly

5.8 Extrusion Compression Molding with Film Inserts

A film is placed in a compression mold Plastic is extruded onto the film Oftentimes a reinforcing layer such as glass fiber matt is added The mold is closed.The heat from the extruded plastic will heat the film for forming The filmprovides a class A surface part Films such as polyvinalinedifloride/acrylic,polyester, ionomer, and ASA have been used

The Valyi SFC, Surface Finishing/Compression Molding (SFC) process,has demonstrated the capability to manufacture large structural panels such asautomotive roof tops, hoods, and trunk deck lids (11) The SFC process can beused to manufacture large class A exterior finishes parts at a low clamp force.The precolor matched films offer the part appearance in the mold, thus eliminat-ing painting

5.9 Thermoform Coextruded Sheets

A coextruded multilayer sheet is thermoformed As with films, each layer of thesheet has a specific function The top layer provides the weathering and UVresistance, scratch-and-mar resistance, hardness, and the gloss The color layerprovides the coloring, additional UV resistance, and adhesion The base layerprovides the structural support During the coextrusion process, the materialsare merged using an adapter system and are shaped by a slit die into sheets ofvarying thickness (12) Different thermoplastic materials can be combined usingthis process Also, the regrind from the thermoforming offcuts can be recycled.After the sheets are coextruded, they are cut to size The sheet is then heated,thermoformed, and cooled During thermoforming, the sheet is drawn againstthe thermoform mold by a vacuum The surface quality of the thermoformedsheet can equal that of painted panels (12) It must be noted that the surfaceroughness increases with the depth of thermoforming (12) A thinner residualwall thickness will result in a rougher surface This will lower the gloss of thefinished part Also, for metallic colors, the greater the number and size of theparticles, the rougher the surface (12)

This technology is limited to parts that can be thermoformed Thermoform

tooling is inexpensive Achieving a high-gloss level is difficult with the forming process Body panels made of PMMA/ABS have a proven track record

thermo-on the Ligier small vehicles in Europe (12) Also, the Hotzenblitz, an electriccar in Germany, and the PIVCO, a Norway electric car, have body panels fromPMMA/ABS without painting (9) The PMMA provides the UV and weather-resistant outer layer The impact strength at low-temperature is provided by theABS layer The finished body panels are mounted to a steel framework Theplastic body panels provide a weight savings compared to steel body panels (12)

5.10 Mold-In Color with Clearcoat

General Electric Xenoy PC/PBT with clearcoat polyurethane (PUR) is used tomold body panels for the European “Smart Car.” The clearcoat offers the UVand scratch-and-mar protection Smart Car colors are offered in red, yellow,black, and white straight shades This process still uses a coating, clearcoat.However, it eliminates the primer and basecoat

6 AUTOMOTIVE APPLICATIONS WITH ADVANCES

IN PROCESS TECHNOLOGY

Advances in the extrusion and coextrusion process have resulted in color exterior and interior automotive plastic trim parts For example, extrusionprocess is commonly used for mold-in-color body side moldings Mold-in-colorfascias, claddings, exterior and interior trim parts are manufactured by injectionmolding and co-injection molding Advancement in both film technology andprocessing has allowed the manufacture of parts ranging from applique´s towhole body panels on vehicles

mold-in-7 CONCLUSION

Alternatives to coating automotive plastics have received increased attention indeveloping new materials and process technologies to meet the demands of theautomotive industry These advances have been used successfully in a number

of automotive applications For example, advances in development of new orants and additives has allowed mold-in color to be used in more applicationssuch as mold-in accent color, mold-in straight shade body color, and mold-in-body-color metallics In addition, development of extrusion, injection molding,thermoforming, and insert molding of films processes has allowed OEMs alter-natives to coatings for automotive plastic applications Challenges still remain.For example, color matching is a real concern with mold-in-color plastics bothinitially and after weathering In the future, continuous advances in both materi-als and process technologies will allow alternatives to coatings to make furtherinroads into the automotive plastic applications that are currently coated

alterna-tive to painting of plastic body panels IBEC ’97 Automoalterna-tive Body Painting, pp89–91

18: February 2001

In-Mold Film Brochure, 1997

News 25(9):30, 1998

and car body parts made of fiberglass-reinforced polyurethane The Senoplast Mold Film Brochure, 1997

part production without painting ANTEC 2654, 2000

Trends in Coatings for Automotive Plastics

and Rubber in North America and Europe

Robert Eller

Robert Eller Associates, Inc., Akron, Ohio, U.S.A., and Bordeaux, France

1 INTRODUCTION AND OBJECTIVES

In this chapter we examine the forces driving the selection of coatings andassociated process technology for the modification of plastics and rubber sur-faces Primary emphasis is on the North American auto industry Where thetechnology and trends are applicable to (or derived from) nonauto markets, wehave so indicated

1.1 Geographic Coverage

The need to be competitive in the global marketplace has made the barriers totechnology transfer quite transparent We have therefore indicated and, in somecases, quantified material substitution trends in Japan or Europe likely to affectNorth American coating technologies and the associated demand

1.2 Trends

We have sought to present a view of the future as seen from the perspective ofour recent work in the automotive sector Where the current implication of fu-ture trends is not clear we have so indicated and sought to define the decisivefactors

1.3 Substrate Type

Coatings for both plastics and thermoset rubber are included Because the face between thermoset rubber and plastics is becoming blurred by the use of

inter-293

thermoplastic elastomers (TPEs), we have included these materials in the scope

of the automotive polymers to be coated

1.4 Definitions

We have used the term coating to include not only liquid coatings and paints

but also skins, textiles, and other materials designed to modify the surface erties and characteristics of automotive polymers in interior soft trim and exte-rior applications A summary of the abbreviations used and a list of references

prop-is given in the glossary at the end of the chapter Non-Englprop-ish terms (usuallyGerman or French) are commonly used without translation to characterize sur-face qualities Their definitions are also included in this chapter’s glossary

2 THE DYNAMICS OF COATING SELECTION

Dry films (e.g., wood grain)

Elimination is major research and developmentobjective

Mold release

Source: Robert Eller Associates, Inc., 2001.

2.2 The Plastic Processor’s Perspective

For the plastics processor, the application of coatings to the surface of moldedparts adds cost, the uncertainties of adding liquids and the associated “wet chem-istry,” and an additional operation that increases capital investment and broadensthe quality control requirements

Some (usually large) plastic processors have turned this burden into acompetitive advantage by installing high-volume, highly automated, closelycontrolled spray booths, which contribute to profitability and provide an entrybarrier against smaller competitors (Bumper fascia fabricators are an example

of such large volume molder/coatings suppliers.) Roll goods manufacturers applycoatings to skins or coated fabrics using spray or reverse roll coating

2.3 The Automotive Coatings Market

Liquid coating materials, process technologies, and performance requirementsare reviewed in other chapters of this book The dynamics and economics ofplastic and rubber parts manufacturing require that the design engineer examinealternatives to liquid coatings such as:

• Molded-in color (see Chapter 1);

• Surface skins, textiles, and coated fabrics applied off-line (see ing discussion); and

follow-• In-mold decoration using films, carpet, textiles (see following sion)

discus-The auto polymer coatings market has been (1) defined in terms of strate type (hard/soft), substrate material (polymer type), and module (instru-ment panel [IP], door trim [DT], floor) A summary of the applications that useliquid coatings and the alternatives is presented in Figure 1 The target zones ininteriors and exteriors for coatings are summarized in Table 2

sub-2.4 The Measurement Problem

The driver typically spends 40,000 hours at the steering (2) wheel facing theinstrument panel The choice of surface treatment (hard, soft, textile, patterned,colored, etc.) is therefore critical to the auto original equipment manufacturer(OEM)

Physical and chemical tests quantify technical performance (scratch/mar,ultraviolet (UV) resistance, oil resistance, color shift, etc.) Despite the eco-nomic importance of surface treatment selection, techniques for the quantifica-tion of sensorial attributes of the interior surface to measure their importance tothe consumer have not been developed Renault and other OEMs (3,4) haveemployed techniques derived from methods used in the agro-business sector to

F IG 1 Automotive plastic coating alternatives Note: (*) indicates liquid coatingsopportunity target (Courtesy of Robert Eller Associates, Inc., 2001.)

identify and quantify the sensorial attributes and their perception by humans Thetechniques are in the early stages of development and only vaguely quantified,but appear to represent a starting point to the response to such questions as:

• What is the perceived value to justify the cost penalty for substituting

a skin for hard substrate?

• Do the customers care about exact grain matching as much as theinterior trim designer?

• What is the role of color and pattern matching between modules?

• What is the value of the utility function (e.g., washable, noncarpetfloor module surfaces)?

• What is the value of touch (“haptik”) in consumer quality perception?

• What is the role of olfactory perceptions (some OEMs are seekingzero smell interiors)?

2.5 Requirements for Interiors and Exteriors

Liquid coating technologies used on interior and exterior plastic surfaces aresomewhat similar The range of nonliquid coating surface treatments and perfor-mance requirements for interior and exterior automotive surfaces is considerablydifferent as shown in Table 3

3 DRIVING FORCES AND TRENDS IN COATING USAGE

The macro-economic, automotive technology and module fabrication ogy driving forces and trends affecting coating use and intercoating competitionare reviewed in Table 4 (1)

opportunities

increased by growth

of telematics Liquid coating on X

metal applications)

Tactile requirement X

Dominant substrate ETP, PP (solid/foam), TPO (fascia),

TPE, skins, coat thermosets, ETPs fabrics

NVH requirements Important Not important

Surface parts X (More X (Highly integrated)

integration opportunities)

Metallic pigments X (Minor) X (Major)

opportunity Skin/foam/substrate X

Source: Robert Eller Associates, Inc., 2001.

3.1 ELV Legislation and PVC Substitution

PVC is widely used in North American vehicles A quantification by applicationhas been previously reported (5) The implications for PVC in auto interior appli-cations from existing or anticipated European legislation has been discussedpreviously (5,6) European End-of-Life (ELV) legislation has been among themain drivers for the search for PVC substitutes in interior applications.The General Motors announcement in mid-1999 of their intention to mini-mize PVC in interiors by Model Year (MY) 2004 has prompted substitution forPVC in instrument panel and door trim skins See discussion of intermaterialscompetition in skins below (Section 4.1) PVC compounds are becoming moresophisticated (higher flow, better color control, improved compression set) andare gaining share in some applications (e.g., glazing encapsulation, blow-moldedinterior components) Also, PVC remains a highly cost effective competitor, andthis has resulted in considerable difference in the policies of automotive OEMswith regard to PVC substitution policy

In mid-2001, German OEMs and legislators reached an agreement on anELV automotive recycling bill that is more severe than the previous EuropeanUnion (EU) directive In particular, it shifts the responsibility for dismantlingand recycling to the automakers rather than the vehicle owner The implications

of the revised German legislation on interior substitution have been reviewed

by the author (7) Ryntz reviewed recycling implications on coatings in Chapter

7 of this book

3.2 Economics as Coating Substitution Driver

The high capital investment and operating cost burden of coatings can doublethe cost of molded parts (e.g., bumper fascia and IP substrates) Substitutes forcoatings thus have a wide economic window in which to seek profitable materialsubstitutions

3.3 Acoustics

Acoustic performance has often been an afterthought rather than an integral part

of the initial vehicle design A broad range of acoustic materials is used (8).This has often resulted in messy solutions with high systems costs (e.g., asphalt-based floor module acoustic barriers) Increased use of telematics, improvedacoustic profiling techniques, and a better understanding of acoustic perfor-mance as well as increased pressure for weight reduction are creating opportuni-ties for new acoustic materials combinations

Weight savings assume increased importance in a high fuel cost ment A weight increase of 100 kg increases fuel consumption by 0.6 liters/100

environ-km This has stimulated the development of below-the-surface acoustic barriers

that provide acoustic performance (especially in floor modules) with less weightaddition These lightweight acoustic barriers have been introduced by Collinsand Aikman, Lear, and Rieter (1).

Coating selection contributes to interior acoustic performance (1,9) creased use of telematics has made characterization of acoustic behavior a per-formance parameter for the selection of interior coatings

In-3.4 Instrument Panel Fleet Shares

A quantification of the shares of instrument panel production is given in Table

5 Hard (nonskinned) surfaces have typically represented 30 to 40 percent ofvehicle production (1,10) Hard IPs represent substantial cost savings versus softIPs (11) and are used at the lower end of the trim range The recent trend toward

a more utilitarian look in smaller vehicles (compact sedans, compact SUVs) andcost pressures from a deflationary economic environment suggest that the share

of hard IPs in the fleet will remain at least at the present level This creates

an opportunity for coating treatments capable of providing improved sensorialappreciation and acoustic performance without the need for skins The trendtoward soft-touch paint as a low-cost alternative to skins (e.g., Ford Focus) hasnot gained much momentum to date

3.5 Role of the Interior Soft Trim Fabrication Process

Soft interior trim typically consists of a three-layer sandwich of skin (or textile),foam, and substrate Off-line processes that combine these three layers to pro-duce interior soft trim are complex, multistep, wasteful, and labor intensive Therate of change of interior module fabrication processes during the past twentyyears has been slow (10–12) but is accelerating and will influence the choice

of skin material and process technology The relationship between fabricationprocess technology and skin type is shown in Figure 2 The off-line technologiesare currently predominant The trend is toward the in-line technologies In-lineprocesses with fewer, more efficient operations have been slow to be acceptedfor instrument panels but have gained share in door-trim manufacture Theseinclude:

• Low-pressure molding (combining skin and substrate in the injectionmold);

• Two-shot molding (also starting to be used in exterior trim, e.g., rockerpanels in European models);

• Negative forming to improve grain quality of vacuum-formed skins; and

• In-mold coated (IMC) cast skins that combine the formation of a slushmolded (or PU spray skin) with subsequent PU-RIM molding in thesame mold to form the substrate layers