Significant enhancements to a broad range of engineering and thermoplastic materials have been introduced over the past few years. This article focuses on two types of innovations, a range of new high flow specialised thermoplastics, and a look at aesthetics. A Oosterlaken, B. Havenith and H G Schoot report.

The expansion of engineering thermoplastic materials options has offered designers a similar expansion of design freedom. Growth has been along three paths. The first consists of new kinds of materials, which offer everything from low-cost options to new kinds of high-end material performance properties. The second has explored enhancements to existing resins, typically extending their applicability in products that demand new kinds of material behaviours. The final path is one that we can call aesthetics and identification – the use of colour, effects, and markings to enhance the attractiveness of products or to differentiate them from similar competitive products.

These enhancements have emerged from R&D activities in the past two or three years, and each one provides new elements of design freedom. The first is a new material, an ultra-soft copolyester elastomer (COPE). The second is a group of engineering materials in new high flow types. Finally, we look at new additives for laser marking.

While the COPE materials offer soft touch and enhanced aesthetics, a number of applications with more practical needs have arisen. For example, in today’s

ever-smaller electronic devices, components such as connectors and device packaging, have increasingly tended toward miniaturisation. With ever higher circuit densities in ever smaller envelopes, the need has arisen for resins that exhibit high flow during moulding for high pin- or contact-count, stiff and strong components.

In the past, enhancing a resin to produce high flow during moulding would often mean serious reduction in mechanical properties of the component after moulding. Recent research, however, has focused on the molecular make-up of a range of thermoplastic resins, including polyamides (PA) and PC. Focused on both melt viscosity and component functionality, this research has resulted in an array of high flow materials designed for such applications as high-performance/high-density connectors, parts with extremely complex geometries, thin wall mouldings and the like.

For example, one polyamide 4,6 (PA46) compound, Stanyl Super Flow, offers very high flow in a material that retains the heat-resistance characteristics of PA46. With a heat deflection temperature (HDT) of 290°C, the  material can withstand exposure to lead-free soldering temperatures. At the same time, it can be readily moulded into parts that are relatively large with ultra-thin sections, such as notebook computer components, down to 0.06mm. This material also offers production with good weld-line strength (see Fig.1).

A second example, XantarMX1000 series, is a high-flow, flame resistant polycarbonate which is tailored for the requirements of such office equipment as computer and monitor housings and other electrical equipment, where aesthetics and thin section design must combine with stiffness and break resistance. The new material is also excellent for such electronics applications as chargers, junction boxes and cartridges. In addition to high flow, good impact and compliance with UL94 V-0 at 1.5mm, these grades also meet glow wire testing at 960°C at 1.5mm as well as ball pressure test at 125°C, and exhibit good colour stability in office environments.

A third example is an ultra high-flow polyamide 6 (PA6), Akulon Ultraflow, that exhibits all the mechanical properties of conventional PA6 with up to 80percent greater flow and a 40percent reduction in injection moulding cycle times. At the same time, in highly reinforced grades, it offers better surface appearance than conventional PA6 with lower reinforcement levels. It has shown good applicability to large, thin components like automotive engine covers, air inlet manifolds, pedals and levers, and a variety of consumer durable goods, tool and furniture applications.

Overall, these new materials lend themselves to a range of tools, business equipment, and electrical and electronic applications.

There has been strong growth of products and components that combine a tough, engineered core with a soft touch overlay or skin, yielding a product that combines functional performance with a touch pleasant to human users. The effect is similar to historical high-end finishes, such as coach and carriage interiors, fine furniture and the like. However, instead of requiring a painstakingly built-up sandwich of hand-formed wood, layers of padding, and fine fabric or leather, the modern approach takes advantage of an ability to produce a stiff, self-supporting underlayer and a soft touch outer layer in a single, mouldable product in virtually any shape or colour.

The core material in the modern, moulded component typically includes such tough or

break-resistant resins as polycarbonate (PC), polycarbonate blends, polyesters, and acrylonitrile butadiene styrene (ABS). Providing these materials with a soft skin has posed some dilemmas in the past. Many soft-to-the-touch materials exhibit one or more drawbacks – they are difficult to bond to the tough base material, or they disintegrate under human skin salts and oils, or they are too tender to stand up to abrasion. Many also posed aesthetic problems, in that their natural colour (often an unattractive yellowish or brown hue) made it difficult or impossible to achieve pure, matched colours in such applications as automotive interiors, hand tools, or office equipment.

Except for softness, traditional COPE materials have long offered properties for overmoulding on PC, polyesters and ABS and other polar materials. COPE bonds well to these substrates, and it offers outstanding chemical resistance in general – in particular to hydrocarbons and skin oils. While ideal in a chemical or a mechanical sense, COPE materials have until recently resisted formulation into a truly soft material.

Recent research has changed this through molecular enhancement, resulting in a COPE product that is quite soft to the touch, yet well-suited for such overmoulding techniques as 2K moulding, which offers efficient, relatively low-cost production. With a hardness of 25ShoreD (75ShoreA), the new material is well within the Shore range perceived as soft, which goes as high as 30ShoreD. It is one of the lowest Shore ratings of any COPE material on the market. At the same time, it has proven to be relatively easy to mould, and it adheres well to polar materials. It readily takes surface textures, which can be designed to increase the soft feel, grippability, or appearance.

This new COPE material offers excellent abrasion resistance and high friction, useful in tool handles and other implements that must both stand up to rough handling and offer a surface that can be held securely in hand. At the same time, the material is FDA compliant for direct contact with food and water. Finally, it is supplied in a pure white form, easily and accurately coloured for a variety of applications that require a close match to surrounding materials and finishes.

Table1 shows selected properties of the new material compared to other thermoplastic elastomers (TPEs) used in soft-touch applications.

Laser marking

In addition to conventional colours and effects, a growing number of resin formulations are becoming available which radically change colour or appearance when exposed to laser light energy. One solution, called Micabs, is a new additive technology that offers the advantages of dark laser marking on thermoplastics over traditional printing techniques without introducing changes in base polymer attributes.

Micabs masterbatch granulate can be added to a wide range of polymers to yield photo-quality, dark laser marks on light backgrounds. It can be used in a wide range processing techniques and applications, and can be used with various laser systems.

Micabs is fundamentally different from conventional additives. The latter absorb laser light, transform the absorbed light into heat, and carbonise the thermoplastic matrix.

The quality of the mark depends on the carbonising ability of the matrix, which is often insufficient to meet the designer’s demands.

For dark marking, the Micabs process is totally different. Micabs is a granulate that is dispersed in the polymer using compounding or dry blending. Upon processing, a dispersion of well-defined laser active particles is obtained in the matrix. During laser irradiation, these particles absorb the laser energy and change from light to dark. The laser mark is activated inside the Micabs particle and is independent of the carbonising ability of the matrix. With Micabs it is thus possible to laser mark traditionally ‘impossible’ to mark thermoplastics such as polyoxymethylene copolymer (POM), polyethylene (PE) or polypropylene (PP).

The laser marking performance of other polymers, like polyamide (PA), polybutylene terephthalate (PBT) or thermoplastic polyurethanes elastomers (TPU), can be improved.

The high-definition, micro-marking capability, useful in security and credit card applications (Fig.2), is but one facet of the new technology. High contrast combined with high marking speeds makes Micabs a good fit with mass production of MCBs and electronics connectors. 

Further, polyoefinic, polyester and PA films can be marked without influencing processing conditions. 

A Oosterlaken, DSM Engineering Plastics, is based in Geleen, The Netherlands; B Havenith, Engineering Plastics, is based in, Sittard, The Netherlands; H G Schoot, DSM Innovation Center, is based in Geleen, The Netherlands, For more information vist www.dsmep.com or www.micabs.com