trend report automotive 65

Trend Report AUTOMOTIVE 65

Kunststoffe international 9/2018 www.kunststoffe-international.com

One sure way to save weight is still to reduce the density of materials. That

this also applies to foams that are light-weight anyway, was demonstrated exem-plary by an instrument panel (Fig. 1) at this year’s congress for Plastics in Automotive Engineering PIAE at Mannheim, Germany. It was developed by Covestro AG of Leverkusen together with Volks wagen AG of Wolfsburg, both Germany, [1] and consists of a molded skin surface, cush-ioning foam, and a thermoplastic carrier.

This type of instrument panel is pro-duced in three steps:

W 1. The molding skin is placed in the lower half of the mold and the injec-tion molded carrier in the upper half.

W 2. The fluid foam components are in-troduced by a mixing head, usually by robot control, into the open mold which is subsequently closed.

W 3. The mixture foams up, it is very sticky in this phase, fills the space be-tween molded skin and carrier (while

compensating for tolerances), and by the end of reaction time forms a stable sandwich – the instrument panel blank that can be removed from the open mold.

The latest generation of Bayfill semi-hard foams is capable of reducing the foam molded skin’s density of 150 kg/m³, which already seems quite low, to only 120 kg/m³ without entailing any disadvantages somewhere else. The significance of this approx. 20 % lighter version is ampli-

[VEHICLE ENGINEERING] [MEDICAL TECHNOLOGY] [PACKAGING] [ELECTRICAL & ELECTRONICS] [CONSTRUCTION] [CONSUMER GOODS] [LEISURE & SPORTS] [OPTICS]

Cockpit of the 5 series BMW with high-gloss natural wood trim panels lacquered in

one-step-technology for self-healing scratch resistant surface (© BMW)

»

Plastics for the Mobility of Tomorrow

New Polymers, Efficient Processes, and Advanced Parts for the Automotive Industry

Digitalization, electromobility, energy and resource efficiency are making their mark on future vehicles. These

trends were also reflected at this year’s PIAE, the branch’s get-together in Germany. Plastics are an important

key to mastering ecological and economic challenges in the coming years.

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------© 2018 Carl Hanser Verlag, Munich, Germany www.kunststoffe-international.com/archive Not for use in internet or intranet sites. Not for electronic distribution.

66 AUTOMOTIVE Trend Report

© Carl Hanser Verlag, Munich Kunststoffe international 9/2018

compared to PVC-P enables additional weight savings of 5 to 10 %. Bayflex spray skin can, like the classic spray skin of Rec-ticel N. V., be produced in two tones by a masking technique. However, the use of an isocyanate crosslinking agent in the 2-component in mold coating lacquer from iSL-Chemie GmbH & Co. KG of Kürten, Germany, requires regular appli-cation of a releasing agent. 2-component IMC lacquers with carbodiimide crosslink-ing [2] or 1-component IMCs as practiced by BMW AG get along with permanent crosslinking agents on the mold surface (“Galvano”) for the most part.

New Alternatives among Thermoplastics

Under the brand name Xiran [3], Poly-scope Polymers B. V. of Geleen, Nether-lands, develops and sells copolymers

fied when we consider that the weight of the foamed material layer is about the same as that of the molded skin.

Reduced foam density offers even more advantages when combined with the widely used molded skins made from plasticized polyvinyl chloride (PVC-P). The foam mass is reduced together with its receptivity for softeners. This helps in-crease the aging resistance of the com-pound, thus preserving the low-tempera-ture flexibility required for crash safety.

At the same time, Covestro was able to decisively reduce acetaldehyde emissions as required in the Asian market which is very important for car sales in China.

Even in the molded skin, weight-sav-ing potential was found by the partners [1]. The PVC slush skin with which VW has been setting benchmarks for quality for more than ten years is being replaced by an IMC spray skin. PU’s lower density

Fig. 1. Schematic

instrument panel

construction from

IMC-PU spray mold-

ed skin, cushioning

foam and a thermo-

plastic injection

molded carrier

(© Covestro)

from styrene and maleic acid anhydride (SMA). At the end of the 1990s, these poly-mers replaced the previously dominant PC+ABS blends as carrier material for in-strument panels with foam-backed mold-ed skins. The hydrolysis sensitivity of poly-carbonate (PC) in particular with contact with PU foams and lacquers raised too great a risk of field losses.

Once the automobile suppliers had mastered activating the surface of PP compounds, long-term stable sandwich-es arose between formally incompatible PU and glass fiber-reinforced PP. These materials established themselves quickly due to weight and cost advantages. Though, the semi-crystalline PP is at a dis-advantage compared to amorphous SMA and PC blends. The increased shrink ten-dency of most highly filled materials can only be compensated by additional design measures. However, the loss of stiffness at higher temperatures is also causing more problems.

Chemical modification [4] of the SMA to styrene-maleic anhydride-N-phenyl-maleicamide terpolymer (SMI) results in a highly heat resistant transparent plastic. It is capable of resisting temperatures up to almost 200 °C, depending on the com-position of the monomer components. Since the weakly polar styrene molecules and highly polar maleic acid derivatives in the chain make it compatible, SMI is also mixed with many engineering plastics as a “Heatbooster” (Polysclope brand name). In this way, the use temperature of ABS, ASA, or PMMA, for example, can be in-creased up to 30 K.

As a highlight at this year’s PIAE, Poly-scope presented an entirely new class of polymers as a further development of its Xibond products [5]. Here the develop-ers succeeded in creating a chemical bond between both thermoplastic worlds, the amorphous and the semi- crystalline. When compounded, the amino end groups of polyamide 6 (PA6) react chemically in the extruder with the maleic acid groups in the SMI chain with dehydration (Fig. 2). In this way, a wide-meshed network arises, depending on the components and processing condi-tions selected. By contrast with purely physical blends, this coupling keeps the mechanical characteristics picture con-stant over a very wide temperature range and acts as a modification for im-pact toughness. This material provides

Fig. 2. Chemical crosslinking of styrene-maleic anhydride-N-phenylmaleicamide terpolymer

with Polyamide 6 to a polymer blend from amorphous and semi-crystalline components (source:

Polyscope)

-H2O

H2O

H2O

Linked molecular chains with SMI and PA6 (schematical)

CH2

CH2

N

H H

5

CH

CH–HCCH–HC

CH–HC CH–HC

C

C NH

O

C

CO OC C

OO O

CH2 5

CH2

N

HH

CH

C C

C O

OCC

O OO

Imide branching

SMI chain

PA6 chain

© Kunststoffe



space [7]. This calls for the further develop-ment of the DirectCoating process formed to serial application in recent years and known as ColorForm (KraussMaffei Tech-nologies GmbH, Munich, Germany) and ClearMelt/ColorMelt (Engel Austria GmbH, Schwertberg, Austria, and Hennecke GmbH, Sankt Augustin, Germany) [8].

designers with additional options for highly heat resistant, impact tough, and creep resistant parts such as found in conventional engine rooms or in the field of power electronics of electric drives or power LEDs, as well.

Traditionally, in addition to materials development and production, the clos-ing of materials cycles has top priority at Polyscope, especially for high-quality production wastes. Together with Wipag Deutschland GmbH of Neuburg a. d. Donau, Germany (since 2018 in the Albis Group), their long-standing recycling partner [6], the recycling of such thermo-plastic foam sandwiches by composite separation is also included in the devel-opment in order to keep this high quality material in the cycle.

Interiors of the Future

The interior of the future will be character-ized by entirely new concepts. The idea is to transform the interior of autonomous vehicles into a multi-functional living

In a reactive 2C injection molding process, a thermoplastic carrier made from a transparent thermoplastic opti-mized for the process is flooded with a 2-component PU-RIM or a 2-component PUA-RIM system. The surface of the light-fast (aliphatic) lacquer called PUx (short-age of polyurethane or polyurea) is

Fig. 3. By including shiny and microstructured surface areas as well as different layer thickness in

the mold, a 3D effect was generated on the part surface in the RIM process (© Rühl)

»





loading and overtaxing passengers and driver. Taking a smart trunk lid, Rehau KG & Co. of Rehau, Germany, has demon-strated how various optical pieces of in-formation can be exchanged. Much of this ought to be transferable to the in-terior.

Trim parts have to have some degree of transparency in order for signals to be transmitted through them. Classic lac-quers are already the first obstacle. How-ever, most of the thermoplastics in use, especially those with fillers, are also non-transparent. It is especially difficult in the case of the platelet-shaped fillers very frequently used in PP. Therefore, a rather spherical, coated filler was select-ed for the transparent trim parts to ensure that the mechanical properties level remains at the required level (Fig. 4). At the same time, the filler particle can, if suitably coated, continuously adapt the transition of the refractive index be-tween the optically differently dense materials, thereby lessening scatter at the phase boundary and having a posi-tive effect on screening.

Self-Healing Surfaces

Glossy interior surfaces such as the very popular piano black, are the pride of every new-car owner. Unfortunately, they often don’t last very long. Glossy black surfaces often are dust magnets and make the slightest fingerprint visible. This provokes very frequent cleaning, even with unsuit-able means. Thus, the search has been long for a way to ameliorate this.

Previously, the solution was to make the surface ever harder in order to increase scratch resistance. PMMA is known to be the hardest thermoplastic, and its limits are quite well known. Many metals and above all (mineral) dust are notably hard and break particles from the brittle surface (Fig. 5, top right). Tough- hardened or semi-crystalline plastics such as polyamide behave differently. Locally impacting energy causes local melting of the crystallite and displaces surface materials, thus increasing surface energy. Above glass transition tempera-ture, this deformation can once again re-gress more or less and approximate the low-energy original state (Fig. 5, bottom).

The effect of viscoelastic recovery has been utilized by Rühl Puromer GmbH, Friedrichsdorf, together with Novem Car Interior Design GmbH, Vorbach, both Germany, in its PU systems for a two-step ClearCoatMolding process (CCM) with wooden trim parts. This development has reached a temporary peak in a one-step process (ColorForm), in which real wood veneers are back injected and sub-sequently flooded in a second cavity with a PU system that is set for easy demolding by an internal release agent. For the first time, Novem has introduced this technology to serial production with the wooden trim panels on doors and instrument panel of the current BMW 5 series (Title figure).

Scratch Resistance Remains a Challenge

By reducing the friction coefficient at the surface, the scratching medium glides over the surface and cannot introduce its destructive force into the material – “it slides off”. This approach is used, some-times unintentionally, by trim parts manu-facturers. Remnants of the finish from the final polishing process or traces of pro-cessing aids, such as removal aids, lower

shaped by the mold. This offers the ad-vantage that even 3D contours and matt or very glossy surface structures can be precisely and reproducibly imaged next to and simultaneously with each other (Fig. 3).

The combination of back foamed décor and function film (wood veneers) (Title figure) or LED integration + capacitive switching functions and disappearance effect enables the single-step production of a decorated and functional part. Com-patible printed PC films with correspond-ing surface coating against scratch, UV, and cosmetics resistance have already proven successful with this Film Insert Molding (FIM) technology. This technolo-gy simultaneously enables simple diversi-fication, since only a new print design has to be produced in order to generate the corresponding inserts.

Optically Functional Trim Parts

The temporary use of trim parts would be an additional option for transporting the mass of information without over-

Fig. 4. Modification of thermoplastics to improve the optical transparency of trim parts

(source: Rehau)

Light input

PP-EPDM T20/30(Standard)

ABS + PC withspecial filler

Lightoutput

Talcum

10 µm Light input

LightoutputFiller requirements:

• No platelet shapes• Low light absorption• Refractive index (light scatter)• No inherent color

© Kunststoffe

Fig. 5. Schematic

damage from

scratching (top) and

self-healing of

scratches on ductile

plastics (bottom)

Plastic displacement Brittle fracture, material removal

Plastic deformation Viscoelastic recovery

Restoring forces

© Kunststoffe




are almost identical with those of the basic types, thereby simplifying their use considerably.

Another factor involved in scratch re-sistance is the processing in itself [11].

Scratch resistance is the higher, the freer the part is from stress during production: high mass and mold temperatures are also helpful, as is low sheer from injection speed and gate design.

Fig. 6. Influence from various surface pretreatments on the adherence of steel-PP-GMT hybrid

structures (source: Kömmerling)

14

MPa

10

8

6

4

2

0Degreasing Pressurized

air blastingFine laser

structuringCoarse laserstructuring

KöratacHL400

KöratacHL403

0

2.6

6.87.2

11.712.1

Tens

ile sh

ear s

tren

gth

© Kunststoffe

»

the friction coefficient of the part surface and thus hinder or reduce scratch dam-age. However, this approach has several disadvantages:

W The amount of “scratch protection” is quite undefined.

W The duration of the effect is limited, since the layers can be removed by mechanical loading and cleaning pro-cesses in particular with means not permitted for this coating.

W Depending on the position in the ve-hicle and its type, photo-oxidative degradation also takes place, making these materials soluble in water, or at least dispersible and thus easily re-movable.

For some time, Evonik Industries AG, Essen, Germany, has been offering its Plexiglas compounds in inherently scratch resistant form, as well [9]. The lubricants [10] from the company are al-ready firmly fixed in the compound, thereby providing defined surface prop-erties that can resist common loads mark-edly better. The other property levels of the scratch-resistance equipped TX series




Heat and Light Resistance

Lighting technology on and in the auto-mobile presents its own challenge. The enormous luminance of modern high- performance LEDs for large-area ambi-ent lighting and ever larger displays causes considerable heat to develop near the LED. Due to its higher thermal dimensional stability, this has led to the use of optical polycarbonate (PC). How-ever, in practice we see that PC tends to yellow under long-term thermal loading, ultimately leading to color change and loss of transparency. In Pleximide, a poly-methyl methacrylimide (PMMI), Evonik has a more heat resistant relative of PMMA in its portfolio that almost reach-es the transparency of PMMA and some-what exceeds that of PC. Both meth-acrylic polymers have excellent UV resis-tance and even after long-term thermal load exhibit only a low yellowing ten-dency as well as loss of transparency. Both classes have “potential for optical self-healing” under the influence of strong light streams. The yellow value sinks thereby, and transmission loss un-der long-term thermal loading falls to

less than half in the presence of strong light streams. [11]

Hybrid Structures and Auxiliary Materials

To adapt to the improved production of hybrid parts that have crystallized at the PIAE as a decisive element for essentially lightweight there are joining technolo-gies with surface pretreatment, adhesion promoters, and glues.

The importance of thermoplastic fiber- composite materials (TP-FCP) contin-ues to grow. This is due on the one hand to low materials costs compared to the widely used duromers and versatile high-ly-automated processing technology, and on the other to considerably simpler recy-cling in closed cycles. But at the same time, the basic tenor at this year’s PIAE congress was that pure FCP sheeting can neither economically nor technically fulfill all necessary requirements. Hybrid struc-tures from metal and plastics – with and without fiber reinforcement – are current-ly the most promising technologies.

These materials combinations in re-turn, however, require joining technolo-gies to create the desired composites. In their accompanying exhibit [12], Kömmer-ling Chemische Fabrik GmbH of Pirma-sens, Germany, demonstrated a hybrid joining technology developed together with the Institut für Verbundwerkstoffe GmbH of Kaiserslautern, Germany, as a key to efficient lightweight construction (Fig. 6). In the first step, metal surfaces are coated with thermally polymerizable ad-hesion promoters that Kömmerling origi-nally developed for PP (brand name: Köratac). Additional TP-FCP combinations are already in development. The required layer thicknesses there are less than 35 µm. The next step is joining the FCP (in this case PP based) by the easily automat-able induction welding method (Fig. 7).

This process virtually fulfills several requirements for hybrid lightweight in serial automobile production:

W High strength connection between FCP and metal by adhesion promoter.

W Low investment costs for system tech-nology,

W energetically very efficient joining pro-cess, and

W heat generation directly in the part, i. e., high thermal efficiency and no damage to fiber structure. W

Fig. 7. Induction welding head for the automated joining of metal to GMT-PP for lightweight

hybrid parts (© Institut für Verbundwerkstoffe)

The AuthorBernhard Klein is an expert for reactive surface technology, materials develop-ment and processing mainly for the automotive industry at PolymerConsult-ing & Service of Neuburg a. d. Donau, Germany; [email protected]

ServiceReferences & Digital Version

B You can find the list of references and a PDF file of the article at www.kunststoffe-international.com/6715848

German Version B Read the German version of the

article in our magazine Kunststoffe or at www.kunststoffe.de


trend report automotive 65

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