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Over the past five years, the drive to

move to an all-polyolefin automotive inte-

rior has led to intense competition be-

tween makers of various plastics, particu-

larly foams. And it makes sense to usesoft polyolefin foams when replacing soft

polyurethane ones.

Recent developments in polyolefin

resin technology make use of new cata-

lyst systems, which enable specific mate-

rial properties to be created, while theproperties necessary to meet the strin-

gent thermal and mechanical require-

ments are maintained. The use of poly-

olefin bead foams for automotive interi-

ors complement the use of TPO (thermo-plastic olefin) skins, which allow for more

flexible part designs. The ability to pro-

duce TPO skins in a single layer, bi-lami-

nate, and even tri-laminate, coupled with

a thermally matched polyolefin beadfoam, enables interior components to be

produced in a single step.

Advances in polypropylene resin devel-

opment have enabled random copolymers

to be created by blending low amounts ofethylene to develop resins with a specific

melt point, melt range, and melt flowall

of which contribute to the property of

expanded bead foams. Development in

the area of polyethylene has led to newblends of LDPE (low-density polyethylene),

LLDPE (linear LDPE), and mLLDPE (metal-

locene LLDPE) resins that allow specific

properties to be obtained in the resulting

expanded bead foams.Expanded polyolefin bead foams have

been used in the automotive industry in

the form of energy-absorbing EPP (ex-panded polypropylene) for more than 20

years in applications such as bumpercores, knee bolsters, and head-impact

pads. Newer applications include instru-

ment panel toppers, door panels, pillars,

and package shelf trays, where the bead

foam has been combined with a TPO skinto produce a finished part. The flexibility

of polyolefin bead foams have enabled

the production of a single-piece door

panel with integrated exterior skin, mold-

ed-in substrate, energy absorber, wireharness clips, fasteners, and structural

framein a single step.

As expanded bead foam technology

evolves, and the availability of specialty-

grade polyolefin resins grows, the ability

to further optimize this single-step opera-

tion will allow for more system integra-tion and more performance optimization.

With market trends favoring part con-

solidation, weight reduction, and in-

creased innovation, the flexibility of

Polyolefin foam on the rise

JSP Internationals laminated ARPRO EPP molding process enables engineers to provide for

specific levels of softness and energy management in localized areas of an all-polyolefin part,as shown in the cross section.

The indentation force deflection test is thestandard one used to evaluate most softfoams. Measured is the load sufficient to

deflect the foam 25%.

The process to produce xEPE bead foam is similar to that used for EPP production.

Extrusion

Base resinsand additives

Expansion &cross-linking

Mini pellets

Molding

SteamAdditives &blowing agent

Bead foam

High-density EPP or xEPE substrate

Low-density EPP or xEPE

PP or PE bonding layer

Center cross-linked PP

In-mold grained TPO skin surface

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0 5 10 15 20 25 30 35 40 45 50 55 60 65

polyolefin bead foams and their ability to perform multiple func-

tions and be integrated into all polyolefin systems make themespecially attractive.

The market for polyolefin foams in automotive interiors has

grown from less than 5% in 1995 to more than 40% in 2002.Of this, a majority of the development has been with polypropyl-

ene in the area of extruded foams and with energy-manage-

ment bead foams. The success of polyolefin bead foam rests inits ability to offer a unique combination of softness, resiliency,

ability to be shape-molded, ability to manage energy, excellent

strength-to-weight ratio, low cost, and low mass. In addition,

polyolefin bead foam is recyclable, contains no volatile blowing

agents, and can be incorporated into a variety of processes. PVC(polyvinyl chloride) foams are becoming obsolete, and neither

that material nor polyurethane foam are well suited for simple

processing methods.

Development of the single-station laminated ARPRO EPP

molding process from JSP Internationalwhereby a TPO skinis vacuum-formed into a female mold, EPP beads injected behind

the skin, and the part steamedhas permitted a thermally

matched all-polyolefin component part to be created without

the use of adhesives, volatile chemicals, or fasteners.

A recent development in the area of polyethylene processinghas permitted the creation of partially cross-linked LDPE and

LLDPE bead foams. This family of lightly cross-linked and closed-

cell polyethylene ARPAK xEPE (cross-linked expanded polyethyl-

ene) bead foams from JSP permits a more targeted approach to

creating a soft foam for use in a traditional EPP molding process.The process is similar to that of the EPP bead production process.

ARPAK xEPE bead foam density ranges from as low as 12 g/L

(0.10 lb/gal) to as high as 45 g/L (0.37 lb/gal). Higher densities

are possible, but like all polyolefin bead foams, there is a clearcorrelation between bead foam density and softness. Once the

This xEPE headrest withintegrated bar was

produced in a single-stepmolding operation.

The shape of the xEPE curve reflects a fairly linear correlationbetween stress and strain in this IFD test graph, which compares thecompression rates of soft xEPE vs. soft PU forms. These properties makexEPE a good choice for both softness at low strain rates and energymanagement at higher strain rates.

800

700

600

500

400

300

200

100

0

3500

3000

2500

2000

1500

1000

500

0

Molded xEPE 20 g/L (IFD=225)

Glued bead xEPE 34 g/L (IFD=170)

Flexible PU 86 g/L (IFD=85)

Seating PU 50 g/L (IFD=50)

Compression, %

N lb

Force

Circle 303

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104 OCTOBER 2004 aei

It may look like any other valve spring, butCorus believes this is something special.

xEPE bead foam is produced, it can be

steam-chest-molded to densities ranging

from 20 g/L (0.17 lb/gal) to 60 g/L (0.50

lb/gal). The properties achieved by the

molded xEPE bead foam offer a good

balance of density, tensile strength, andtensile elongation, as well as tear

strength, compression-set resistance, and

softness (as measured by the indentation

load deflection test).

The development of the soft foamxEPE technology allows for a unique set

of properties exhibited by both polyolefin

and polyurethane foams. The shape of

the stress-strain curve is more like that of

the soft polyurethane foams, but with

better stress-to-density (weight) ratio. The

elongation (75% for 20 g/L molded xEPE)

is also similar to that of the soft polyure-

thane foams, but with better tear

strength.

As is the case with EPP, both the soft-ness and the energy-management capa-

bility of a molded xEPE part is a direct

function of its molded density. Multiple

densities can be strategically located

within a given molded part in a one-stepor multi-step process in order to meet

specific customer requirements.

This article was written by Steven R. Sopher,

JSP International.

Corus springs a surprise

Piston ring coating from DanaA new piston ring coating from Danaisdesigned to reduce emissions and oil con-

sumption while improving the durabilityof diesel engines.

The PCF-480 coating is based on PCF-

380 technology currently used for heavy-

duty engines. The new formula, geared

for use on the milder duty cycle of pas-senger-car diesels, was designed for de-

creased wear on the bore and ring sur-

faces to provide a superior seal. The ther-

mally applied coating fills the groove on

the piston ring face.

Internal coating strength is improved

compared to standard thermally applied

coatings, and the new coating produces a30% harder surface and is less porous

than previous light-duty ring coatings,

resulting in better wear characteristics,

said Mike Kestner, Director of R&D,

Danas Perfect Circle Division. Becausethermally applied coatings offer more

design flexibility than electroplated piston

rings, the shape and sharp-edge profiles

provide improved emissions performance

and reduced oil consumption.The PCF-480 coating process is also

friendlier to the environment than tradi-

tional electroplated coatings, Kestner

added.

Patrick PonticelDanas thermally applied coating shown inthe groove of the piston ring face.

One of the most demanding applications

of steel in a car is valve springs. Steelproducer CorusAutomotive has just

completed the first fatigue tests of a

new grade of steel manufactured to

meet valve spring requirements.

It produced a trial quantity of the mate-rial, which was sent to a Swedish specialist

in the manufacture of valve spring wire,

Haldex-Garphyttan, which subjected it

to a continuous fatigue test program over

three months and reported that it hadbeen impressed by the performance of the

steel. Further trials will be held.

It is likely to be at least 24 monthsbefore the new steel is fully approved for

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aei OCTOBER 2004 105

valve spring applications and enters full

production, said Coruss Wire Rod

Director Peter Hogg. If successful, we

would become one of only a handful of

integrated steel manufacturers in the

world to supply this quality of steel.It was Coruss successful manufacture

of steel rod for tire cord that initially gave

the company the confidence to develop a

new grade of steel. The same steel com-

position that is used for valve springs canalso be used in clutch and suspension

springs. Corus has supplied further trial

quantities to leading wire drawers for

testing in the production of these other

spring types.Stuart Birch

All thatglistens may bealuminumA gold finish for metallic automotive trim

parts may not be to mass aesthetic taste,but there is some demand for it. A dif-

ficulty, though, may be to achieve a color

wholly consistent with the gold effects

needed. Now, BASFhas come up with a

patented process for coloring aluminum

in baths containing methanesulphonicacid which, it says, makes it possible to

obtain a realistic gold finish on alumi-

num surfaces.

Typically, gold effects can be achieved

on aluminum via anodizing followed bythe application of color. But BASF says that

dyes have limited performance; shades

and lightfastness may be unsatisfactory.

So, instead of dyes, the company uses

finely divided metal crystals deposited inthe aluminum oxide layer. This results in a

realistic gold finish with excellent light

fastness, said Helmut Witteler, BASFsHead of Development and Applications

Technology for Surface Finishing. Themetal crystals are deposited very evenly if

the bath is based on methanesulphonic

acid, and this does not depend on the po-

sition of the parts in the bath. The re-

quired shades are said to be achievable

even on complex shapes, the BASF process

enabling aluminum to be colored up to

50% more quickly than other processes.Methanesulphonic acid is readily bio-

degradable, and, according to BASF, can

be employed in all processes in metal

finishing in which acids are used. Its ad-

vantage over sulphuric acid and ordinary,

less pure grades of methanesulphonic

acid is that tin, silver, and copper com-

pounds can be prevented from formingsludge, which saves money and energy.

Stuart Birch

Gold out of abottle? BASF tellshow it is done.

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