Coatings of Polymers and Plastics part 14 pot

ACRONYMS AND DEFINITIONS DT door trim panel EMI electromagnetic induction ESI ethylene styrene interpolymer Haptik German for touch or feel of an interior surface HVAC heating, ventilati

6.3 Coextruded Films

Coextruded, multilayer films to achieve surface decorative effects and providesurface weathering resistance are well established in the appliance, recreationalvehicle, and pool/spa industry

Recently, coextruded films have been applied to automotive surfaces (e.g.,

MY 2002 DaimlerChrysler Neon and the Smart Car) for bumper fascia and roofsurfaces This construction to be used is evolving but is likely to consist of afive-layer structure of surface film/adhesive/color layer/adhesive/thin sheet (TPO

or HDPE) The thin sheet layer is designed to adhere to the injected layer Anextruded layer may be substituted for the injected layer in applications in whichthe entire structure is thermoformed (e.g., adaptation of major appliance andpool/spa fabrication methods)

The initial constructions appear to be capable of offering fabrication costsavings over painted parts such as bumper fascia, but it is too early for a defini-tive economic comparison due to the uncertainties of scrap rate, cycle timeeffects, ability to match metallic colors (on painted metal surfaces), etc

Coatings for polymer substrates offer the automotive OEM a broadened range

of protective, decorative, and tactile capabilities that will develop with the lowing trends:

fol-7.1 Liquid vs Alternative Coatings

Liquid coatings on hard surfaces will come under increasing pressure from:

• In-mold decoration (based on coextruded films and back-printedfilms);

• Molded-in decorative effects; and

• OEM objectives to eliminate coatings from hard and soft interior faces where possible

sur-7.2 Skins

The invisible airbag door will continue to be a key IP skin driver Slush moldingand spray PU will continue to gain share versus vacuum forming Spray PUwill show the greatest short-term gains If TPO slush compounds are developedthat are capable of meeting scratch resistance requirements and are capable ofbeing used without coatings, they could see share gains Skins capable of beingused in in-line processes will be preferred A utilitarian look will gain share for

IP skins and other above-the-belt-line applications

Trends in Coatings for Automotive Plastics and Rubber 315

7.3 Floor Systems/Acoustic Barriers

Noncarpet flooring surfaces, probably based on TPO, will grow in the market,accompanied by lightweight acoustic substrate layers capable of achieving tun-able acoustic properties while saving weight New printing technology willallow patterned floor surfaces, probably coordinated with other interior surfacepatterns Molded-in decorative effects will enter the floor system using the non-carpet skin For carpeted floor systems, PP face yarns will gain share in theNorth American market, further facilitating the all-polyolefins carpet system

7.4 Body/Glazing Seals

The TPEs can be expected to continue their growth in this high-volume marketbased on the desire for color and the potential for systems cost savings Thecoatings on rubber are being adapted to provide adhesion, control surface fric-tion, UV protection, and gloss

7.5 Coated Fabrics

The TPOs have begun penetration of this key PVC interiors sector in Europeand North America Severe price competition and the current, unfavorable eco-nomic conditions are likely to delay this penetration

ACRONYMS AND DEFINITIONS

DT door trim panel

EMI electromagnetic induction

ESI ethylene styrene interpolymer

Haptik German for touch or feel of an interior surface

HVAC heating, ventilation, and air conditioning

IMC in-mold coating

RF radio frequency

TPE thermoplastic elastomer

UEV unsupported expanded vinyl

Zweiglanze coatings that provide a three-dimensional appearance by

differentially altering the peaks and valleys of grainedsurfaces (usually on interior skins)

5 R Eller Growth opportunities for TPOs in auto interior skins, foams, and acousticbarriers SPE Automotive TPO Global Conference, Detroit, MI: October 2000.

6 SEBS, TPV, and TPO-type thermoplastic elastomers markets, economics, nology, intermaterials competition and the role of metallocene resins MulticlientStudy, Robert Eller Associates, Inc., 2000

tech-7 R Eller TPE intermaterials competition in auto interiors in north america and rope SPE Automotive TPO Global Conference, Detroit, MI: October 2001

Eu-8 R Eller Acoustic barriers—material substitution and industry structure drivers tomotive and Transportation Interiors, 46, November 1999

Au-9 R Miel Plastics News August 13, 2001, p 1

10 European Instrument Panel Photo/Supplier Database, Multiclient Study, Robert ler Associates, Inc., 2001

El-11 Automotive interior skins and foams intermaterials competition, technology andglobal markets Multiclient Study, Robert Eller Associates, Inc., 1998

12 R Eller Automotive interiors impact of new fabrication technology and als Le Havre, France: JEMA, February 2, 2000

materi-13 R Eller Polypropylene usage in auto interior textile applications The PP ogy Conference, Clemson University, August 1998

Technol-14 Elastome`res Thermoplastiques a l’interface de caoutchouc SNCP Meeting,Paris, June 21, 2000

Automotive Plastic Coatings in Europe

Hans Christian Gruner

DuPont Performance Coatings, Cologne, Germany

317

role The use of plastic components has also been observed as a substitute formetal in body applications like wings, fenders, and tailgates Both off-line coat-ing and on-line coating techniques are used to coat this type of small parts.While some car companies have built their own bumper coating lines oreven injection molding lines, more than 80 percent of the coated plastic compo-nents are provided suppliers and most of these do both jobs molding and coating

to deliver complete assembled components to the automotive industry

The European market volume for coatings for automotive plastic nents is in the range of 50,000 tons for the year of 2000 (Fig 1) and is expected

compo-to reach 60,000 compo-tons by 2004 (1)

2 CHARACTERISTICS OF THE PLASTIC COATINGS PROCESS

A typical bumper fascia plant in Europe has a capacity of about 3,000 bumpersper day The plant is comprised of robotized spray booths for primer, basecoat,and clearcoat, and includes an 80°C oven (Fig 2) Optional elements found insome plants include power wash, a pretreatment unity, and a primer oven.For optimum appearance and part quality, the bumpers are positioned on

an under floor conveyor skid in the position equal to the assembling of the carbody (Fig 3) This is done in order to avoid any color deviation (azimuth)between the plastic part and the car body The conveyor speed is 2–3.5m/min(6–11.5 ft/min) and skids are loaded with 2–6 parts parallel to the conveyordirection

Most paint spray booths are configured for two robots, with both on oneside of the conveyor line or staggered opposite each other, depending on thepart positioning on the skid The paint is atomized when sprayed through pneu-

F IG 1 Coatings for automotive exterior plastics: overall paint sales in the Year

2000 in European countries

F IG 3 Bumper coating robotic process.

matic guns or through electrostatic high rotation bells Although limited, somecoaters still apply paint through handheld guns

In France and south Europe, a complete wet-on-wet process consisting ofprimer, basecoat, and clearcoat is quite popular and is used in conjunction with

a final 80°C oven In Germany, the primer is baked at 80°C in which the primeroven is typically integrated Low temperatures around 80°C are used to cure thepaint and avoid distorting the part Higher oven temperatures would result insignificant part distortion Unlike that used in North America, high curing tem-peratures (121°C) are only used to cure plastic parts with high dimensionalstability, like sheet molding compound (SMC) or thermoplastics such as GeneralElectric’s Noryl GTX

Automotive Plastic Coatings in Europe 321

Due to the low paint curing temperatures for thermoplastic automotivemolded parts, two component or two pack clearcoats are typically used All thepaint used needs to provide sufficient flexibility to ensure high-impact perfor-mance of the molded part even at low temperature (2) If a clearcoat is highlyflexible and exhibits a hard surface to easily polish defects caused by coatingimpurities, it has attributes that empirically appear to contradict one another.However, through today’s advanced resin chemistry, products are available thatoffer both ambient temperature polishing capability and excellent flexibility, asmeasured through low-temperature impact

2.1 Ecological Considerations

In addition to cost reduction and higher quality standards (wave scan, colormatching), the main driving force for innovation has been and continues to beecology Until the late 1990s, most coating materials for automotive plasticcomponents continue to be solvent based This is quite surprising given thatwater-based basecoats for plastics were introduced as early as 1985, and water-based basecoats clearly dominate on the car body The reason for the slowprogress in plastic coatings was that legislation focused on newly built plantsand implemented more stringent ecological standards on these plants The plantsfor painting plastic parts were much older, and in some cases, less sophisticated

As an example, the German “TA Luft” regulation of 1986 limits the vent concentration to 150 mg/m3

sol-for automated spraybooths and 50 mg/m3

foroven exhaust To meet this limitation, two paths were used Firstly, by recircu-lating the spraybooth air, volatile solvents could be concentrated while beingcontinuously extracted and a percentage cleaned using thermal incinerationequipment Secondly, water-based materials could be used to reduce solventemmission and pollution Unlike in the continental countries, beginning in theearly 1990s Great Britain adopted legalisation similar to that of the North Amer-ican regulations comprising of a volatile organic compounds (VOC) concept forall paint materials

In order to harmonize the regulations for solvent emission in the EuropeanUnion (EU) member countries and to enhance ecologically friendly coatings inboth new and existing plants, the EU states have agreed to a regulation currently

in force This “Council Directive 1999/13/EC” of March 1999 is based on thelimitation of emissions of VOC due to the use of organic solvents in certainactivities and installations (3) From this legislation, a great reduction in VOCthrough the period 2004 to 2007 is expected This regulation states that thesolvent concentration for plants using more than 15 tons/annum of solvents islimited to 75 mg C/m3

in the EU with a lower level of 50 mg C/m3

beingallowed in Germany If this is not achievable at that point in time, a reductionplan can be approved by the authority, according to the EU guidance document

titled “IPPC-Integrated Pollution Prevention and Control.” It is remarkable thatall activities are supported that apply best available techniques (BAT) Althoughthe EU regulation does not set solvent limits per unit of paint material, single

EU members allow for compliance of the regulation by meeting VOC limits.For example, in Germany, the general limit is 250g/l, although higher valuesmay be set for specific applications (4,5)

3 COATING OF TPO BUMPERS/FASCIA

When coated bumpers were introduced by the European automotive industry inthe early 1980s, compounds of polypropylene homopolymer (PP) with thermo-plastic ethylene-propylene rubber (EPR), or ethylene-propylene-diene rubber(EPDM) dominated (6) Using highly specific metallocene catalysts, it wasfound possible to polymerize PP in an isotactical structure with the requiredmolecular weight The function of the rubber phase (post blended, post ex-truded) was to improve low-temperature impact resistance but in addition to this

it was effective to improve paint adhesion and allowed for a coating withoutpretreatment The EPR phase is embedded in the continuous PP phase in form

of spheric domains and dissorted (elongated) inclusions near to the moldingsurface

Due to cost reduction needs of late, these blends have been substituted byreactor blends using stepwise propylene- and ethylene-propylene copolymeriza-tion techniques in the gas phase Thus the rubber elastifier is introduced in alow-cost one-step process Rubber contents as high as 50 percent can be pro-vided It was quickly seen that TPO produced by this manufacturing methodgave more problems with paint adhesion than that seen in traditional PP-EPDMcompounds

In France and Italy, very often copolymers of propylene and ethylene areused These materials are characterized by a homogeneous phase character with-out any distinct rubber phase Therefore, complete and accurate pretreatment iscrucial to get the expected adhesion with these materials When higher stiffnessand temperature resistance is required, high modulus TPOs with 10 percent ormore of talc extender is quite common for bumpers The added talc has theadditional benefit of enhancing adhesion of the coating to the plastic

Due to the thermal properties of the TPO and the thin-walled molding thatvery often is as low as 2.5 mm, the temperature limit for paint curing is 90°C(194°F) provided the part is fully supported on the painting skid Typically,therefore two component primers and clearcoats are used along with one compo-nent basecoats

Attention has to be paid to the variable degree of cristallinity of the PPphase that depends on the polymer (stereo regularity), the blend formula, and

Automotive Plastic Coatings in Europe 323

T ABLE 1 Examples of TPO Moldings/Related to the Coating Process

for a Reactor-Blend and a Reinforced Compound

Shrinkage (mold plus coating) 1.8% 0.9%

Surface tension (not flamed) 25–30 dynes/cm 25/30 dynes/cm

Source: Refs 6 and 7.

the molding conditions (speed of cooling) This affects both shrinkage propertiesand adhesion of coatings Shrinkage, depending on filler load, takes place notonly in the molding process but also to a certain degree in the thermal steps ofthe painting process This is to be considered in automotive “no gap” bodyapplications Also important for no-gap applications is the thermal elongationcoefficient that ranges from 60µm/mK to 120µm/mK for reinforced and nonre-inforced TPOs respectively With respect to the coating properties, high crystal-linity negatively influences paint adhesion

New highly crystalline, higher modulus (HCPP) TPO grades have beendeveloped without the need for a high filler loading and without the need for acompounding step In the past, high modulus TPO has been widely achievedthrough obtaining the desired specific gravity and by compounding the polymerwith inorganic extenders In the future, HCPP grades will be more commonlyoffered in the marketplace

To broaden the area of TPO applications to the low modulus side offeringplastics with elastomeric properties, compounds with both a thermoplastic PPmatrix and vulcanized domains of ethylene butylene rubber (EBR) have beenintroduced These offer a route to rubber-like materials that can easily be pro-duced through injection molding As a special feature, these thermoplastic elas-tomers (TPE) can be sequentially co-injected with “normal” TPO to give partswith specific functional zones

3.1 The Coating Process for TPO Moldings

In some cases, the parts are coated without going through a washing process asthey come out of the injection-molding machine This is fairly rare as most partspass through a four-phase aqueous power wash and a dryer After cleaning,usually a pretreatment step follows to ensure paint adhesion before the paintingprocess of primer, basecoat, and clearcoat is applied

T ABLE 2 Pretreatment Methods for

Automotive TPO Moldings

Mostly flaming booths are robotized and integrated in the conveyor line.While simply shaped parts get good overall treatment and can be coated evenwith standard plastic primers, other parts, due to their complex three-dimen-

T ABLE 3 Flame Pretreatment/Chemical Effects

Surface-tension

(polar/dispersive) Atom—

36 (15/21) dynes/cm 8–9% Borderline (mostly weak)

45 dynes/cm 12–16% Good (solvent-based paints)

55–75 dynes/cm >16% Good (water-based paints)

55–75 dynes/cm >16% Peel off paint/degraded TPO Overflame,

TPO melting

Source: Ref 8.

Automotive Plastic Coatings in Europe 325

T ABLE 4 Flame Pretreatment/Examples of Flaming Parameters

Excess of oxygen For air: propane 26:1 by volume

Source: Refs 6 and 8.

sional geometry, cannot be sufficiently treated Typical defects are poor paintadhesion, for example, on bumpers in lamp-openings or grille areas due to devi-ations in positioning of the skids to the flaming robot Therefore, for optimumresults, most painters often combine flaming with use of an adhesion-promotingprimer (usually chlorinated polyolefin) Once the process is established by pre-trials and testing, the flame treatment provides optimum adhesion to meet eventhe toughest specifications and the primer ensures good adhesion for perfor-mance in practical use even on zones not treated properly

4.2 Low-Pressure Plasma

In some cases, in Europe automotive components are pretreated by low-pressureplasma As this process is more costly than flame treatment, it is used lessfrequently However, it is an attractive process for flaming complex parts thatcannot be effectively treated due to their size, shape, or the presence of recessedareas The more consistent plasma process can alter the surface of the entirepart and often allows the application of topcoat direct, without the use of andcost associated with a primer Various systems are offered for plasma treatment.They mainly differ in the high-frequency wavelength that is used to generatethe plasma (10,11)

4.3 Fluorine Treatment

In addition to flame treatment and low-pressure plasma treatment, fluorine ment has gained some importance as an alternative method (12) This method isvery effective and even gives excellent results on polyethylene or polypropylenehomopolymer even when flaming does not provide sufficient adhesion Manyautomotive parts such as interior door handles and interior switches have beensuccessfully treated by this method For the fluorination process to work effec-tively, the parts need to be positioned in a reactor to which a vacuum is applied.After approximately 20 seconds or so, the parts are exposed to 10 percent fluo-rine gas in air at 500 mbar (7.0 psi) pressure The excess of fluorine and the