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How to refinish plastics.

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Contents.

Plastics: An exemplary career 3

Rough overview of different plastic types 4

Plastics are indispensable 5

Automotive plastic types 6

Acronyms of frequently used plastics 7

Important plastic types in detail 8

Why paint plastics? 10

Plastic parts in the bodyshop 12

Getting paint to adhere on plastics 14

Causes of refinishing flaws 16

Reliable color matching for plastics 18

Technical Data Sheets and refinishing systems 19

Plastics:An exemplary career.

In addition to such terms as the“industrial age”, the „nuclear age“ or the “space age”, our era shouldreally also be described as the“plastics age”, for quite a few achievements would have been virtually impossible without theinvention of plastics.

In 1862, a British scientist, Alexander Parkes, invented a hard ivory-coloredmaterial which he called Parkesin. A long,stony road lay between this first plasticmaterial and the use of modern plastics inmotor cars but that is a different storyaltogether.

The first plastic material was invented 27years before Gottlieb Daimler presentedhis vehicle with steel wheels to the generalpublic and laid the foundations fortoday,s automobile industry.

Plastics have been an indispensable ele-ment in modern motor vehicles for seve-ral decades. For a long time, they wereonly used for the passenger compartmentand such classical external components asbumpers, spoilers or mirror housings, butnowadays they are also used as bodypanels. Doors, wings and bonnets areincreasingly made from different types of plastics and must be repaired whendamaged.

One plastic is not the same as the next, so the challenges facing refinishers areconsequently growing, together with theneed for detailed information on the useof plastics on motor vehicles. The firstquestion to be answered is therefore:“What are plastics?“

A wide variety of terms are used in eve-ryday life to describe one and the samething, such as plastics, rubber and synthe-tics as well as PP/EPDM, polyamide andABS.

Some of these are merely overall termsfor plastic materials in general, while othersrefer to specific plastics with differentproperties. It is exactly these differentproperties which may lead to unpleasantsurprises when refinishing plastics.

As early as the late 1970s, Standox laun-ched a compact yet complete plastics refinishing programme, which has beenimproved and refined over the years inclose cooperation with the automotiveindustry. The programme provides body-shops with proven products that ideallymeet their day-to-day requirements. Inspecial training courses and workshops,refinishers gain valuable knowledge onhow to handle automotive plastics.

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Plastics are made up of individual components known as molecules. Thesemolecules can be strung together in large numbers to form long chainsknown as macromolecules.

Thermoplastics.Thermoplastics is the name given to plastics made up of separate linear orbranched macromolecules which, however,are not linked together.

Due to their many positive properties,thermoplastics are the most commonlyused plastics in vehicle manufacturing.

Thermoplastics can be melted and reusedseveral times. This is an important factorwhere environmental protection is con-cerned. Provided that different types arenot mixed together, thermoplastics areideal materials for recycling, because theoretically new parts can be made from old parts.

Another advantage is that cracks andfractures can be sealed by welding

Elastomers.“Cross-linking“ is the term used whenmacromolecules are linked togethermore or less strongly. When only a smallnumber of individual molecular chains arecross-linked with neighbouring chains,elastomers are formed.

Elastomers cannot be melted and reused,although they can still expand and displayrubber-like properties.

These materials are used for gaskets andspoilers on motor vehicles.

Thermoset materials.As the number of cross-links increases, thematerial becomes harder and more brittle.The numerous molecular chains now forma single network. These extensively cross-linked plastics are known as ThermosetMaterials.

They cannot be welded, dissolved orexpand like elastomers.

Instead, thermoset materials are highlyresistant to heat and this is why they areused for housings in the engine compart-ment, for example.

Rough overview of different plastictypes.

Plastics are indispensable.

There are many reasons for usingplastics in automotive engineering.Most importantly, they help reducevehicle weight without compromisingon safety. In addition to purely func-tional aspects, however, plastics alsoplay a major part with regard to theshape and design of a motor vehicle.

The percentage of plastics used in vehiclemanufacturing has more than doubledsince the 1980s. Researchers and devel-opers assume that by the year 2010 onein six kilogrammes of a vehicle`s weightwill be accounted for by plastics. The per-centage of plastic body parts is growingconstantly due to new materials and com-posites. Instead of producing the spoiler,radiator grill, bumper and wing separa-tely, as in the past, these four parts arenow combined into a single integratedside-and-front element.

The possibilities for shaping and process-ing plastics are virtually unlimited. This not only opens up new possibilities for thedesigners, but also permits considerablesavings in fuel consumption. The weight ofa car door made from composite materi-als is easily 10% lower than the weight ofa „traditional“ metal door. This shows thatplastics make an important contribution toreducing fuel consumption. Rule of thumb:A 100 kg reduction in weight saves 1 litreof fuel over 100 km.

But plastics have even more advantages.Due to the elasticity of the materials, forinstance, minor damage is reduced.Other benefits include greater occupantcomfort, reduced noise emissions and alonger vehicle life.

In view of these positive properties of plas-tics, the trend in vehicle manufacturing istowards body shells that can ideally becombined with plastic body parts.

From market niche to mass market.“Pimp my car“ - the tuning scene is increas-ingly relying on plastic body parts.

It all began in the 1990s, with plastic add-on parts such as spoilers, air scoops andside skirts. Notwithstanding some ups anddowns, this trend remains with us today.Plastics are easily moulded into ever moreextreme body transformations leading tothe development of exotic designs pro-duced in limited – and sometimes tiny –production runs.

green: typical plastic parts such as wheel

covers, bumpers, mirror housings, side

skirts, trims.

blue: optional plastic parts such as bonnet,

mudguards, doors.

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Automotive plastic types.

“Blends” (e.g. PP/EPDM) are fre-quently used in addition to the pureform. A blend is a mixture of diffe-rent plastics and corresponds to an“alloy” in metals.

“Blending“ allows for several desirableproperties to be combined in a new plastic material.

The trade names coined by the individualplastics manufacturers are also commonlyused, but rarely give any direct indicationof the type of plastic involved.

Acronyms of frequently used plastics.

Chemical name Acronym Trade name(s) Automotive parts

Polypropylene/Ethylene- PP/EPDM Stamylan P, Sabic PP, Purell, Bumpers, rear spoilerspropylene-diene-copolymer Novolen, Moplen, Kelburon,

Hifax, Forprene

Acrylonitrile butadiene ABS Bayblend, Relac, Mirror housings, wheel covers, styrene copolymers Magnum, Lustran ABS roof box, front and rear

spoilers

Polyamide PA Minlon, Akulon, Zytel, Wheel covers, fuel filler flapVestamid, Ultramid

Polycarbonate PC Makrolon, Xenoy, Lexan Bumper panels, radiator grilles

Polyphenylene oxide PPO Noryl, Laril Body parts, e.g. mudguards, hatchbacks

Acrylonitrile-styrene- ASA Luran S, Kibilac, Geloy Radiator grilles, front and rear spoilers

Styrene-acrylonitrile SAN Luran, Tyril, Lustran SAN Radiator grilles, front and rear spoilers

Polyurethane PU Bayflex, Baydur, Irogran, Bumper elements, rear spoilers Estane

Polyethylene terephthalate PBT Pocan, Crastin, Ultradur, Body parts, e.g. mudguards, Vestodur hatchbacks

Unsaturated polyester UP Roskydal Hatchbacks, truck add-on parts, sports car parts

Epoxy resin EP Araldit Components for racing cars

Polyvinyl chloride PVC Vestolit, Solvic Tarpaulins, bumper strips

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PP PolypropylenePP/EPDM Ethylene-propylene-

diene-copolymerBody parts made of this material areusually manufactured as blends. Complexinjection-moulding plants are required formanufacturing large parts. For this rea-son, they can be produced particularlycost-efficiently in the large numbersrequired by the automotive industry.

Depending on the composition ineach case, unprimed PP or PP/EPDM can cause problems with regard paintadhesion.

PP was for many years consideredimpossible to refinish by bodyshops onaccount of its non-polar nature. Standoxplayed a pioneering part in solving thisproblem with the development of itsStandoflex system. Thanks to ongoingresearch and development, Standox istoday still regarded as an expert in thefield of plastic refinishing.

ABS Acrylonitrile butadiene styrene

ABS plastics are both tough and rigid.They owe their toughness to the rubbercomponent (butadiene) and their rigidityto the acrylonitrile component.

Parts made of ABS materials should notbe left out-of-doors without protectionand exposed to UV radiation for anylength of time. Like all plastics containingrubber, they gradually lose their tough-ness and become brittle.

PA PolyamideWheel trims are now made almost ent-irely of PA, a tough and resilient materialwith high rigidity and strength. PA is large-ly resistant to most organic solvents.

Molecular water is reversibly bound wit-hin the molecular structure, i.e. it absorbswater from the ambient air and releaseswater to the ambient air. This explainsmany of the material`s positive proper-ties, although it can have an adverseeffect on the adhesion of a coating, asthe water may deposit directly on thesurface.

PC PolycarbonateThis thermoplastic material features seve-ral outstanding properties, some of whichare also obtained with other plastics, butwhich are only found in their entirety inpolycarbonates. These properties include:· High mechanical strength, even at very

low temperatures (down to –100 °C).· Good resistance to weathering.

ASA Acrylonitrile-styrene-acrylate

ASA forms a brilliant and scratch-resis-tant high-quality surface and can also bemade transparent. Matt surfaces can beproduced with the addition of mattingagents.

ASA is characterised by excellent resis-tance to liquid substances includingaggressive chemicals. ASA is also highlyresistant to oils, fats, etc.

Important plastic types in detail.

PU PolyurethaneAll these plastics are structural foams, thehardness and flexibility of which can bevaried extensively. Structural foams havea cellular core that becomes more andmore compact the further it is from thecentre and which is virtually sealed onthe surface.

Flexible PU foam has an extremely elasticcore with very high resilience, i.e. thematerial will return to its original shapeeven after an extended period of defor-mation.

TPU Thermoplastic polyurethane

RTPU TPU, Reinforced thermoplastic polyurethane

RTPU and TPU are recyclable thermo-plastics. This is an increasingly importantadvantage for the automobile industry,particularly in times of strict recyclingregulations.

Parts made from these thermoplasticsdisplay all the various properties charac-teristic of every polyurethane:· High rigidity.· Dimensional stability under heat.· Good low-temperature impact

strength.· Can be coated.· Resistant to corrosion.

UP Unsaturated glass-fibre-reinforced polyester

BMC Bulk Moulding Compound

SMC Sheet Moulding Compound

UP-GF was better known as GFK (glass-fibre-reinforced plastic) for a long time.However, these materials must now bedifferentiated more accurately, sincenumerous plastics are reinforced withglass fibre.

The use of glass-fibre-reinforced UP forlarge body parts, such as bonnets, bootlids or wings, is common practice forlow volume production and in the tuningsector.

SMC and BMC are the most commonlyused processes employed by the auto-motive industry.

BMC comprises chalked-filled UP resinand chopped strands. The plastic partsmade from this material are injection-moulded under high pressure and hightemperature.

SMC are sheets and panels of polyesterresin with two-dimensional glass fibrereinforcement, which are moulded underpressure and at high temperatures.

Carbon fibre is characterised by its highstrength and low weight as well as by itsattractive appearance. Due to the highmanufacturing costs, carbon fibre isnormally used only in motor sports andfor premium priced cars.

PVC Polyvinyl chloridePVC is one of the most versatile plasticsdue, not least, to the fact that it can beproduced with a wide variety of proper-ties, from rigid to rubbery.

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On the one hand, plastics must be paint-ed for aesthetic reasons:

· Individual coloring to match the paint-work of the vehicle body.

· More gloss or color brilliance byadding.

· Elimination of manufacturing defects.

At the same time, the plastic materialmust be protected, because it is exposedto the elements day after day and willage as a result.

It is almost impossible to imagine plasticscorroding or degrading, but like mostother materials, they also age anddegrade when exposed to moisture andUV light.

Factory-finishing plastics by the automotiveindustry or its suppliers is a standard,high-volume operation using parts identicalin shape and made of the same plastic

material. Refinishers, on the other hand, are faced with a number of basic problems:

· The parts are not identical or evensimilar; they are always made of different types of plastics with different design and functions.

· Bodyshop conditions and resourcesmay vary considerably.

· The parts are presented in differentconditions, i.e. as new or repairedparts.

Since the 1980s, plastic components havebeen marked on the back in accordancewith VDA Recommendation 260*. Theacronyms used are standardised in DINEN ISO 1043-1 and DIN ISO 1629.

Why paint plastics?

Although plastics can now be produced in all colors and with a matt or a glossy surface, in many cases they still have to be painted.

*) Distributor:

DOKUMENTATION KRAFTFAHRWESEN e.V. (DKF)

Ulrichstr. 14, D-74321 Bietigheim-Bissingen

Now that the type of plastic is identified,it has become easier to draw up specificrecommendations for painting the plasticconcerned.

Consult the practical section for furtherinformation on how to deal with oldervehicles containing unidentified plastics.

In some cases, the carmakers specify thatcertain components must not be coatedfor functional reasons. Such restrictionsmust always be observed.

Example: Motorcycle helmets:Many helmets are made from polycarbo-nate (PC), a highly shock-resistant plasticthat can be coated using suitable paintmaterials.

Polycarbonate is highly sensitive to solvents.Unsuitable cleaners or paint materialsmay harm the polycarbonate and leadto microcracks in the plastic material. Asa result, the protective function of thehelmet may be affected and the helmetmay break in a crash.

Abbreviation for the main component contained

in the plastic.

Filler or reinforcing materials, possibly proportion

of filler or reinforcing material.

Painted old parts.Old parts which have already been coatedmust be carefully examined:

· Is the part damaged?· Does the paint film adhere

everywhere?· Are there any cracks to be seen?· Is the paint resistant to solvents?

It goes without saying that any defectsfound must be repaired before continu-ing, provided that the effort requireddoes not exceed the cost of a new part.This is then followed by: cleaning, sand-ing, renewed cleaning and finally appli-cation of the paint.

Repairing damaged plastic parts:Special repair kits approved by carmakers for repairing damaged plasticparts are available for most materials.Minor scratches can be eliminated quicklyand easily with a suitable fine stopper.

Plastic-welding is the ideal method forrepairing thermoplastics, although tho-rough training and a detailed knowledgeof this technology are essential.

Unpainted old parts.Such parts constitute the most critical substrates, since their history will alwaysremain unknown to the refinisher.What has happened to the plastic sincethe vehicle was delivered to its owner?

· Has it been looked after?· If so, what care agents were used and

how?· Has the plastic material absorbed wax

or silicone from polishes or preserva-tives?

· Can these agents be removed?

These questions cannot always beanswered retrospectively, with the resultthat adhesion of the refinish may beimpaired in spite of thoroughly preparing

the part and ensuring that it is apparentlyas clean as possible.

The risks of old plastic parts relate totheir unknown history. Utmost careand great experience is required to avoid mistakes when refinishingsuch parts.

Plastic parts in the bodyshop.

Before starting to refinish a part, the refinisher should observe a few important basic rules and thoroughly inspect theplastic part concerned. Is it an old or a new part? Painted, primed or untreated? Answers to all these questions andmore can be found in the following paragraphs.

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Uncoated new parts.The most important rule to be observedis that:

The substrate must be free from releasethe agents!

Clean the parts thoroughly in accordancewith the Standox TDS recommendations.Standox can offer the ideal tailor-madeor universal systems for the subsequentcoating process. For more tips on how to remove the different release agents, please see the following pages.

Coated new parts.If the existing coating is found to beintact, coated new parts can be refin-ished without difficulty.

After sanding and carefully cleaning thepart, it can be coated directly withStandox topcoat or Standox clearcoat.Topcoats and clearcoats should be plasti-cised by adding the respective additivesto match the flexibility of the plasticmaterial.

Primed new parts. The primers used here differ considerably,and their composition and suitability forsubsequent processing remain unknown.Preliminary tests are recommended andthe manufacturer`s instructions (e.g. thoseenclosed with the product) can proveuseful.

If unknown primers from other manufac-turers have been used and informationfor further processing is not enclosedwith the plastic part, it is impossible tomake any reliable assessment of whetheror not certain criteria are met, such as:

· Adhesion between primer and plastic.· Suitability for coating with primer

fillers, topcoats or other Standox products.

· Appearance in the paint system, e.g.sinkage or lifting.

· Elasticity in the paint system.· Redissolving when cleaned.

In this case, please note the manufactu-rer s refinishing recommendations.

The release agent used to free plastic parts from the mould will also release your paint coating from the plastic. Plasticparts are primarily injection-moulded or reaction injection-moulded with the aid of complex moulds and presses, as wellas other highly sophisticated tools. Very high production rates can be achieved in this way. Release agents are used to ensure that many parts can be taken from one mould without difficulty. Some of these release agents stubbornlyadhere to the plastic. Release agents come in three different types and can make life difficult for the refinisher.

External release agents.· Conventional release agents are based

on wax and oil, dissolved in organicsolvents. They can be removed in thebodyshop with suitable organic thin-ners and a sanding pad.

· Water-thinnable emulsions of releaseagents are based on wax and oil, i.e.emulsified in water. These can beremoved in the bodyshop with suitableorganic thinners and a sanding pad.Water-thinnable release agents cannot be dissolved in water.

Internal release agents.Self-release products contained in theplastics blend are used in what is knownas the IMR process.Zinc stearate is the main chemical con-cerned. Parts must be conditioned beforebeing cleaned. Can be cleaned withorganic solvents or thinners and a sand-ing pad.

Release paints.Chemically speaking, release paints are apolyvinyl alcohol dissolved in water. Suchparts are only encountered in negligiblepercentages and are easily identified bythe wavy rear. These parts must alwaysbe cleaned with water first. Polyvinyl alcohol can only be re-moved with water and is insoluble inorganic solvents.

Getting paint to adhere on plastics.

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Conditioning.Conditioning (i.e. warming up) the partsbefore they are cleaned can be usefulfor the following reasons:· The heat helps the part “sweat out“

release agent (particularly important inthe case of PU materials).

· Stresses in the plastic material arerelieved in order to prevent cracking.

· Voids (trapped air) can be identifiedand treated (opened and filled withstopper) BEFORE the part is coated.

If necessary, the parts must be supportedin order to avoid deformation.

Cleaning.Repeated cleaning is imperative.Intensive, repeated cleaning with pad,brush and fresh cleaning agent is absolutely essential in the bodyshop.

Simply wiping clean once is rarely suffi-cient, even if the recommended cleaningagents are used.

Textured parts must be cleaned moreintensively. Release agents and dirtmust be removed from textured plasticparts using a soft brush or high-pressurecleaner.

After cleaning the plastic parts, it is abso-lutely essential that the cleaning agentsevaporate entirely before further process-ing.

How to remove release agents from plastic parts.

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Inadequate preparation (condition-ing, cleaning).Inadequate preparation is the common-est mistake and can have various conse-quences. For example:

· Surface defects due to release agentresidues.

· Chipping, since the coating is appliedto a release agent which is designed to prevent adhesion.

· Cracking if stresses present in the plastic material are not relieved.

Any time saved by not conditioning orcleaning a part correctly will often be lost by expensive rework. And this is notcounting the loss of goodwill from acomplaining customer.

Unsuitable cleaning agents.Highly corrosive cleaning agents candamage plastics such as ABS, PC, PPO,etc., which are not resistant to solvents,and lead to cracks or even destroy them

entirely. Standox has developed speciallytested cleaning products to prevent thishappening.

Applying the coating too soon aftercleaning.The solvents absorbed by the plasticmaterial when it is cleaned must beremoved completely before the coating is applied, otherwise they will cause abuild-up of vapour pressure between the plastic and the coating, ultimatelyreducing the adhesion. The risk of solventpopping and pinholing is also increased.

Causes of refinishing flaws.

Mistakes are made everywhere, but knowing where to look cuts down onproblems and complaints. Remember that rework costs a lot of time andmoney.

Unsuitable coupling agents.It has repeatedly been mentioned in thepreceding chapters that there are manydifferent plastic materials and that eachmaterial has specific properties.

Standox has the experience and the pro-ducts needed not only for refinishing jobsin the bodyshop, but also for high-volumefactory finishes, possibly with preciselydefined specifications to meet.

Too little plasticiser.Topcoats and clearcoats must contain theright amount of plasticiser. Too little andcoatings usually crack under mechanicalstrain. In any case, please note theTechnical Data Sheets.

right: Orange peel caused by unsuitable

solvent combination.

beneath: Poor adhesion caused by insufficient

cleaning or unsuitable adhesion promoters.

above: Pinholes are caused when the paint is

applied too soon.

left: Lifting caused by improper isolation

and/or through-sanding.

Tip: The Standothek brochure entitled“Identifying and Eliminating PaintDefects“ provides an overview of themost common defects and tips on how to assess and avoid them.

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Plastic add-on parts on modern cars areusually painted in the same color as thecar. In this case, the same color can beused with the addition of a plasticiser.The situation is not that easy when add-on parts are coated in a different color,which is often the case on old cars orwith decorative parts of current models.

In the case of a smooth, glossy surface,Genius and Standowin help refinishersdetermine exactly the right color shade.Based on precise electronic measurement,Standowin will offer the best matchingcolor formulation.

If and when no electronic colorimeter isavailable, refinishers may use the colorinformation on the Standowin CD or thecolor search on the Internet, which isaccessible via the Standox website ofeach country. Here, they will find specialprograms to suggest the right color for-mulation for each model and the respect-ive add-on parts.

Tip: The Standothek brochure entitled“The quick way to a perfect colormatch“ provides valuable information on how to find the right color sheet.

Reliable color matching for plastics.

A perfect refinish on plastic components is the result of skilful workmanship,correct preparation and the exact choice of color. Standox offers refinishersmany useful aids for precise color matching.

Technical Data Sheets and refinishing systems.Please contact your Standox representativefor the latest Technical Data Sheets andother information on the Standox refinishing systems. The current DataSheets are also available on the nationalStandox websites.

Standox GmbH · Postfach · D-42271 Wuppertal · Germany D11

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