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Polyolefin Compounds, Masterbatches and Elastomers
Automotive Design Parameters
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Generally, custom coloured Polypropylene compounds are the preferred option rather than masterbatch addition. This ensures colour consistency and dispersion. PolyPacific can match colour masters or, if necessary use an existing moulding or colour sample to develop a custom colour.
It is important to define the required colour tolerance for production purposes (method of testing, light source, visual or instrumental etc.) especially for touching components where apearance is critical. PolyPacific can also recommend tolerance levels depending upon application, colour and production capability.
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The UV weathering requirement for both exterior and interior components should be clearly specified. Generally this is nominated as a set time at a weathering site (e.g. Allunga, Australia or Arizona, USA etc.) with the component showing no loss of colour or surface degradation and a colour rating, for example, as specified on the AATCC Grey Scale.
As this specified time can be in excess of 12 months, "accelerated" weathering is also specified and the type of weatherometer and conditions should be clearly defined. Typically, the number of hours is specified, with the same pass criteria as for "normal" weathering.
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For interior trim, grained surfaces are preferred and the trend to matt finish is readily achievable with Polypropylene compounds which have the added benefit of sound deadening characteristics compared to the styrenic compounds.
Where possible, the grain surface (type and number) should be specified as this can assist with colour development and initial colour matching. Care should be exercised across the various tools to ensure equal depth of grain and equal degree of polish, as otherwise a difference in colour may be noted from the same batch of material. Also, the tool draft angle should be sufficient to prevent scuffing of grain surfaces during part ejection.
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Interior
Sometimes it is necessary to paint interior trim to either mask off areas (e.g. black surround) or to achieve surface appearance uniformity between different surfaces/material etc. Several paint systems are available and the types depend upon the level of wear that might be encountered.
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Exterior
The major proportion of bumper covers (rubber modified Polypropylene, unfilled and filled grades) are now painted body colour (fully or partially). Several technologies are available to achieve surface finish, durability and conformance to automotive standards.
It should be emphasised that the final paint film performance depends upon the overall "system" used; i.e. the type of base Polypropylene compound influences adhesion, flexibility etc., as well as the cleaning, priming and painting steps.
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© Polypacific Pty. Ltd. 1997-2005. All rights reserved. Disclaimer
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