Speciality Thermoplastics

At TBA Protective Solutions we manufacture speciality thermoplastics for a variety of applications Fire Safe, Anti – Microbial, Low Friction, Magnetically Detectable, Bespoke Colours, Fibre Reinforced Engineering Compounds, Thermally Conductive , Electrostatic Conductive, Electrostatic Dissipative + EMI/RFI Shielding.

Our foundational products are the last three in that list, our first product, ECP 104 conductive PP was developed in the mid 1980’s for electronics packaging, storage applications and explosive handling applications. Based on standard carbon black additives, this is still produced to this day at our Rochdale site as well as a highly conductive variant ECP 104/4264 for EMI Shielding applications, which shows what can be done with a standard carbon black. Over time we expanded the range, including a PP extrusion grade, HDPE LDPE, HIPS, EVA + Nylon 6.

By the late 80’s the limitations of carbon blacks were evident, they’re dirty (you can write your name with a plastic moulding based on high loadings of carbon black) , colour is limited to black and are difficult to make electrostatic dissipative.

At the same time electrostatic dissipative thermoplastics were becoming more desirable, as it was realised in the industry that these materials reduce the energy of an electrostatic discharge (ESD), there was also a desire for colourable and clean room compatible materials.  Using ICP’s (Intrinsically Conductive Polymers) TBA PS developed a range of thermoplastics that were permanently static dissipative and genuinely colourable.

 

ECP 104 conductive box

ICP’s do have issues at elevated process temperatures, restricting the range of polymers, although with PP, HDPE, ABS and PC/ABS available the range covers a lot applications. ICP materials proved to expensive for electronic packaging applications, despite the technical advantages on offer there was little uptake of these materials in these applications. However, they found their niche in ATEX applications such as instrument housings and process control enclosures.

                                                                ECP 2200 Static Dissipative PP

Although, TBA PS started manufacturing conductive thermoplastics for Electro Static Discharge applications, an ESD is also an Electro Magnetic Interference (EMI) event, as a result we began to look at EMI Shielding thermoplastics. Our first product for the National Coal Board, ECP 108 – a carbon fibre /carbon loaded PP- was for the enclosure for a lift control unit. This grade gave both EMI Shielding and ATEX compliance, both necessary below ground, and it’s performance as the graph below shows was very good.

 

Although a high performing grade, it is only available in black and being a compound there are minimum runs, customers requirements increasingly were for colours, frequently short runs and a variety of materials. As a result TBA PS developed a range of stainless steel fibre masterbatches for PP, TPE, HDPE, PA6, 6,6, 12, ABS, PC, PC/ABS, Acetal and more. Masterbatch quantities of as little as 1kg could now be supplied (added at 10% by weight) and a limited range  of colours made available, blues, greys, greens, greys and darker reds were now options although white, yellow orange and similar were heavily compromised.

ECP 1015 was another carbon fibre grade but also incorporating glass fibre, a PBT grade, it had excellent physical properties and dimensional stability and was conductive enough to be classed as shielding material and found good applications in radar antennae for yachts.

 

EMI Shielding performance was certainly good enough for a large number of applications as per graph below

Shielding effectiveness measured using shielded room test to MIL STD 285 3mm thick plaque.

Left: SS Fibre Masterbatch Mouldings

Although the Shielding Effectiveness is not quite as good as ECP 108, there are advantages, more material choices, some colours and smaller quantity purchases.

Moving into the late noughties and early tens of the 21st century two new carbon based additives became available Carbon Nano Tubes (CNT’s) and Graphene, these nanotech and two dimensional materials offered technological advantages but also challenges.

The advantages are theoretically highly conductive ( 1000x that of copper has been quoted) and diamond strength (diamond being another form of carbon), the challenges are many but the key ones for thermoplastics and this article are cost of the additives and dispersing them into a thermoplastic to obtain the full properties of the additives.

Initially it was thought that CNT’s of themselves would be conductive enough to provide EMI Shielding properties, however, Shielding Effectiveness figures of only around 30dB were achieved (40dB and above are needed for EMI Shielding), that said the volume and surface resistance made them ideal for ESD applications in electronics handling, ATEX etc. Importantly. using CNT’s opened up opportunities to produce high quality conductive engineering thermoplastics e.g. PBT, PPS etc, using carbon blacks this was difficult to impossible, any resulting conductive compounds in these materials had physical properties that were heavily compromised.

This resulted from the much lower loadings required to make conductive compounds using CNT’s, the lower loadings also help offset the additional cost of the additives.

Still pursuing, EMI Shielding performance, we looked at combinations with SS fibre masterbatch and carbon fibres and the results were excellent very high levels of EMI Shielding were delivered, the reflectance test below on such a material gives 93% reflectance of the incident wave, equating to a Shielding Effectiveness of greater than 70dB.

We have continued to explore this hybrid approach and we are now incorporating graphene into this family of materials with great success, they are particularly effective in thin sections. As many of the base materials are high temperature engineering materials it opens up under the bonnet applications, rail and aviation as well as the usual applications for shielding thermoplastics.