As electronic devices become smaller and faster, their sensitivity to electrostatic charges is increased and electronic packaging has been provided to improve electrostatically dissipative properties. Electronics packaging is designed to prevent the build-up of static electrical charges and the consecutive electrostatic discharge (ESD) which can be responsible of serious damages to sensitive electronics and result in product defects and high scrap rates.
In order to ensure ESD protection, insulating polymers may be rendered conductive or dissipative by incorporating conductive fillers allowing effective dissipation of static electrical charges.
Currently conductive or dissipative plastics are mainly prepared with carbon black which is cheaper than other conductive fillers such as carbon fiber, carbon nanotubes, metal fiber, metal powder or metal-coated carbon fiber. The carbon black content within the material must be sufficiently high so that the carbon black particles create a conductive pathway through the materials. In consequence, high levels of carbon black, e.g. 15-30% are required. Such high levels alter the mechanical properties of the material such as impact strength, elongation, and compound viscosity.
When using other fillers instead of carbon black, these properties need to be preserved at a low content of said fillers to provide a non-costly alternative. Conductive compositions containing carbon nanotubes are known. Production of polymer-CNT composites can be done by physically mixing the polymer powder and the CNT by shear mixing techniques or by grinding. However, an inconvenient of these mixing methods is that the carbon nanotubes are not well dispersed in the polymer since carbon nanotubes tend to form agglomerates within the polymer matrix. These agglomerates induce poor mechanical properties and the need to consider higher CNT content than in the case of well-dispersed CNT. Due to the high cost of CNT, this latter consequence is economically unfavorable.
Another problem encountered with a poor dispersion of the CNT in composite material is that they affect the final aspect of the article made from this material, especially when this article is thin for example when the article is a film. Thus there is a need for composite material comprising a low content of CNT, good electrical properties as well as good dispersion of the CNT and in particular few and little agglomerate of CNT.
It is known from EP2028218 a process for preparing a resin composition comprising blending carbon nanotubes with poly(hydroxyl carboxylic acid) to form a composite and then blending the composite with a polyolefin to form the composition. This document discloses the use of poly(hydroxyl carboxylic acid) as compatibiliser to blend carbon nanotubes into polyolefins.
It is known from WO2015/014897 masterbatches for preparing conductive composites materials comprising carbon nanotubes and produced from amorphous polymers such as polystyrene.
USPTO Backgrounds
USPTO Backgrounds