Soft Elastic News 08/2019 | Thermoplastic elastomers

Dear Customer,

Thermoplastic elastomers of ACTEGA DS are used in medical technology and in pharmaceutical applications as well as in the consumer goods area.

Optimized adhesion properties
Guaranteed quality

As the demand for hard-soft compounds increases accompanied by an increased prevalence of multi-component technology in this area, the demand for soft-elastic plastics with special adhesive properties is also on the up. The quality of a component manufactured using hard-soft technology is decisively dependent on the adhesive strength of the bond. Within this context, soft-elastic TPE play a major role. 

Against this backdrop, ACTEGA DS offers adhesion-optimized variants of the PROVAMED® TPE portfolio established on the market for medical and pharmaceutical applications and adhesion-optimized SOFT EST.® TPE for consumer goods applications. Thus a variety of applications is possible.

TPE and thermoplastics perfect bonded

Against this background multi-component injection molding is increasingly gaining in economic significance as this technology not only enables integration of component functions during the injection molding process – it also shortens assembly and production times which immediately leads to less expensive manufacturing of parts.

So-called hard-soft compounds represent a high percentage of molded parts designed using multi-component technology, whereby material combinations are realized from thermoplastics with Thermoplastic elastomers. Harder plastics such as polycarbonate (PC), polypropylene (PP) or acrylnitrile-butadiene-styrene (ABS) are combined with a TPE. This process distinguishes between mechanical anchoring (rupture, undercut) and bonding compound.
To generate an adhesion, there are different bonding types, mechanical, chemical and physical. In a bonding compound in e.g. the diffusion model, a soft component overmolds the surface of the hard component which softens enabling diffusion of the molecules in the boundary layer. This is responsible for the quality of such a bond. Important in this procedure is that both phases are geared to each other and the wettability of the surface of the thermoplastic.

But such optimal product functions can only be achieved using the appropriate materials which guarantees this adhesion bond, in other words which displays outstanding adhesion to a variety of plastics. What's more, the adhesive properties must maintained even at continuous media contact and increased temperatures.

Use in medical technology and pharmaceuticals

Hard and rigid plastics such as PC and ABS are often used in the area of medical technology as they are usually distinguished by a high degree of strength, transparency and biocompatibility. They are suitable for manufacturing housings, lids, connecting pieces, syringe plungers, catheter couplings, and functional components, for example. These, in turn, often require seals to prevent liquids from penetrating or liquids and other media leaking. 

On account of their high level of resistance to media contact and the high temperature range covered by many elastomer materials, the classic option of inserting sealing rings made of rubber or silicone has often been relied on in the past. The disadvantage of this process is the fact that the manual or automatic insertion of sealing rings is time-consuming and may even increase the costs associated with the final product.
One alternative is to specifically apply the sealing element by means of injection-molding. In a single manufacturing step – injection of the hard component followed by the soft component – a substance-to-substance compound can be created between the soft elastic seal and the hard component. Accompanied by mechanical strain and media impact, this bonding strength which is achievable by adhesion-compatible plastic combinations is of particular importance as it is also subject to various influential factors, including the polarity of the join partners, the surface structure and quality, and the basic chemical structure of the plastic. As materials such as PC and ABS have not proved ideal in terms of adhesion for soft elastic materials such as TPE, specific tests were conducted to modify this TPE with the aim of optimizing adhesion to these plastics in particular. At the same time, they also need to comply with the respective medical regulations and guidelines prevailing as regards biocompatibility, toxicity, and patient safety in this sensitive industry. The adhesion-optimized variants of the PROVAMED® TPE portfolio meet the core requirements on optics, high strength in combination with PC and ABS, and biocompatibility in accordance with ISO 10993.

Use in the area of consumer goods

Here, too, production in multi-component injection-molding is attributed enormous significance considering the major advantages it offers. High piece numbers are often involved which means that the cost aspect cannot be underestimated. Materials which can be processed economically and swiftly in multi-component injection-molding clearly have some advantages here.

For example, baby pacifiers where both the teat and the ring can be produced in a single step in the 2-component process. While the ring is often produced from polypropylene, the actual teat features TPE. For adhesion bonds with thermoplastics like polyolefins qualifies translucent and natural-colored SOFT EST.® compounds. Furthermore, the special requirements governing baby items also apply.
SOFT EST.® compounds do not, therefore, contain any PAH or BPA components, PVC, or other plasticizers regarded as problematic, silicone or latex. And they are extremely thermally stable. The combination of soft-touch haptics and good grip is of importance for toothbrushes, for example. Color-sorted injection-molding is often applied here, e.g. toothbrushes with a colored soft-touch surface finish as a hard-soft combination with color variants in the soft component. Interdental brushes also usually comprise several components: brushes, wire and substrate. Interdental brushes with fixed or replaceable handles, handles of varying lengths or for plugging on are available for electric toothbrushes. In terms of material, handles and protective casings are usually manufactured from polypropylene (PP) while brush necks are made of a thermoplastic elastomer (TPE) and brushes are made of polyamide (PA).

Please contact us for information on other application possibilities.