This news article was originally written in Spanish. It has been automatically translated for your convenience. Reasonable efforts have been made to provide an accurate translation, however, no automated translation is perfect nor is it intended to replace a human translator. The original article in Spanish can be viewed at Desarrollo de elastómeros termoplásticos - TPE con características innovadoras

Cromado Selective of unions of hard and soft materials (TPE)

Development of thermoplastic elastomers - TPE with innovative characteristics

Avendaño, V. & Gerald Görich et.al.18/02/2014

Up to now, the cromado of plastic pieces realizar with hard materials and alone elastomers could realizar through a costly process and technologically demanding that consisted of several stages. The new compounds of TPE Allruna that resist the bathrooms of cromado without metallising , offer freedoms previously irrealizables for the design of pieces, in addition to clear savings of costs of process.

The surfaces of plastic cromadas have big acceptance in the market because of his big optical quality and to the pleasant tactile feeling. Pieces of plastic with these finishings can find in numerous sectors and applications. Up to now, the cromado selective of compound pieces by unions of soft hard / materials realizar through a costly process and technologically very demanding that involved multiple stages. The individual steps of the process illustrate in the Figure 1.

Once that the hard component has been molding by injection, is metallised. To continuation plants the piece already cromada again in the mould of injection to realizar the injection of the soft material. This process involves several complications due to the fact that the common types of thermoplastic elastomers - TPE do not adhere to the surfaces metallised.

The new range of materials TPE Allruna allows to realizar the cromado selective of compound pieces by hard and soft materials in an alone step.

Problem and aims

The cromado in an alone step of compound pieces by hard and soft materials was until the day of today a difficult process to realizar by several reasons. On the one hand, the soft component is severely damaged by the galvanic bathroom and shows the fault of lines nítidas in the zone of transition of the hard component to soft. Equally this zone sees affected by the learning of halos and/or of an excessive growth of the metallised (Figures 2 and 3).

Fig. 1. Comparison of current processes (left) and the new process of cromado selective (right).

Fig. 2. Learning of halo in the hard component; Fig. 3. On growth in the elastomer

On the other hand, the galvanic bathrooms are damaged by compounds dissolved from the soft materials likewise observes that the soft component absorbs substances of the bathroom of galvanised that with hindsight they migrate.

The figure 4 sample some plates of essay of commercial thermoplastic elastomers, in combination with ABS / PC, that have been subjected to a classical process of cromado. All the TPE independently of the chemical base developed a clear discoloration. In the types of base of polyester (TPC) observed in the surface footprints of “carbonización”. In one of the types of TPS (base estirénica) is visible the learning of a halo.

The main disadvantage of the current solution is, first of all, his high cost, since several tasks only can carry out manually. Besides, this process imposes requirements very elevated in the moulds, as well as in the individual steps of the necessary process to avoid the high costs by mermas. This requires a dispendioso retouching of the moulds and the use of at least three different plastics, to end to ensure the reliability of the process. What results in high costs of investment, as well as high risks of error during the sequence of processing

Fig. 4. Plates of ABS/PC and TPE before (arrive) and after the bathroom of cromado (down). TPE Of different bases.

Therefore, the aim of this project was to develop a new material elastómerico for the technician of cromado selective. So that it can realizar initially an injection multi-component of the soft hard/unions and to continuation cromar of selective way the complete piece. This method has to allow a stabilisation of this process, the reduction of the time of manufacture and a substantial reduction in the tax of rejections of the cromado of the unions of hard materials-soft. Equally, has to avoid the sour attack in the TPE during the process of decapado. The revestimiento metallised has to cover only the hard component and finish clearly with clear-cut lines in the zone of transition of the TPE.

Modification of the thermoplastic elastomer (TPE)

In the first place investigated the chemical resistance of diverse commercial types of TPE in diverse galvanic bathrooms (Fig. 4). Later to these pieces realizar them proofs of aging in an oven of warming to establish in what measured the macromolecular structure of the soft materials had been damaged.

Basing in this information, realizar the corresponding modifications to the materials elastoméricos and adapted for the process of electroplating. Using combinations of different materials and processes, examined the procesabilidad and the applicability on a large scale for pieces manufactured at present in series.

Criteria of evaluation

The pieces that were injected with hard and soft materials and later cromadas were examined chord to some criteria of evaluation defined:

Realizar a visual proof of the soft component that consisted of a general examination of the piece, as well as an analysis of the condition of the surface. Afterwards of the process of cromado realizar essays of the behaviour of the low soft components effort. Equally, it evaluated the metallic finishing of the hard component, being of big importance the definition of the zone of transition between the hard and soft components (Fig. 5).

After the process of metallised, the complete piece was subjected to an essay of thermal sensors aging (125 °C/96 h) and evaluated visualmente the damage.

With the end to establish any change in the strength of adhesion, did proofs of adherencia between the thermoplastic material and the TPE in function of the path of flow, before and after the cromado.

To allow that the material use in the applications of personal and cosmetic care, were significant the proof of inocuidad toxicológica, as well as the analyses of resistance to means of contact. These analyses also included the comprobación of waste of chromium in the soft material.

Likewise, evaluated the solidity of the colour in the material after the process of electroplating, to end to avoid the discoloration after the process.

Fig. 5. Lines nítidas in the zone of transition of the hard material (ABS/PC) and the elastomer ALLRUNA.

Conclusion

The process of investigation indicates that now it is possible produce pieces of hard metallised compounds-soft by means of moldeo by injection multi-component and his back cromado. Since the process is significantly shorter in comparison with the current state of the technology, results a big potential of saving in terms of costs of moulds and manufacture, as well as in logistics (see fig. 1). The requests of work and the risk of error reduce considerably, so that the mermas of the process of cromado could reduce to <3%. Other additional advantages to the reduction of costs derive of the possibility to integrate functions, such like switches of membrane.

This method improved can give access to new areas of application in a wide variety of fields. The possibility of the use of these new thermoplastic elastomers offers a wide range of applications from coatings for cromado until the freedom for new designs, p.And. Special effects of light through the use of transparent elastomers; possible effects of depth, decoration, stamped and new configurations of colours…

The cromado selective has turned into an economically viable option in front of other alternatives of metallic coatings like the lacado, offering terminations of big quality and additional advantages of design.

Authors

Procter & Gamble AG, Kronberg, Germany: