The Advantages of Plastics in Series Production

Plastic is in demand in medicine and life science. It all starts with product packaging, such as the outer components of an insulin pen, and extends to diagnostic parts and products that are used in direct contact with patients. Plastics approved for medical products are listed under “Medical Grades”. Basic requirements for medical-grade plastics are:

Complete traceability of the products and raw materials used
Biocompatibility
Chemical resistance
Sterilizability
Reliability of supply

Additional regulations and approvals may apply, depending on the application.

Which plastics are used?

COC plastics are often used in medical technology, especially in diagnostics, as they are highly transparent, have very low optical anisotropies and are biocompatible
PP, PE and PS are inexpensive mass-produced plastics that are used for mass-produced products such as disposable items
POM, PA and PPA are engineering thermoplastics that are used for components with high mechanical requirements (such as the inner workings of insulin pens)
Plastics with high fiber content, such as glass fiber or carbon fiber are used as a substitute for metal parts due to their strength
ABS, PC/ABS, polyamides and PBT are impact-resistant plastics that are suitable for housing parts

Compromises in appearance and design freedom

While plastics dominate in later series production, alternative materials such as glass or silicone are used for basic testing in the laboratory during the development phase. Initially, standard items that are available on the market are used, particularly for reasons of cost and availability. Examples include Petri dishes, titer plates, cuvettes, and glass plates. When analyzing processes in a laboratory using microscopy, camera technology, or fluorescence measurements, transparency is one of the main requirements for the equipment used, which is primarily provided by glass. However, especially transparent variants of plastics, such as COC, are also available, although they do not quite match the transparency of glass.

There are also some limitations with plastics in terms of design freedom, as the components must always be designed in such a way that they can be demolded. This means the walls of the component must be slightly angular, usually by around 0.5 to 3 degrees and in rare cases up to 10 degrees. However, this is nearly imperceptible to the naked eye and is therefore irrelevant for the design, but is essential for the demolding step.

Transparency is one of the most important criteria when selecting plastics for medical components. Transparent lids – stacked as shown here – allow analysis processes using microscopy, camera technology, or fluorescence measurements.

From prototype to series product

When it comes to detailed process development for series production, standard equipment quickly reaches its limits. Complex geometries such as those of lab-on-a-chip cartridges with microfluidic channels require certain plastics. These can be used to produce delicate structures with little energy input.

Initial prototypes can be created using the deep-drawing process or with castings made of silicone or synthetic resin. In these cases, the one-off costs for the molding tools are manageable. In contrast, the production of plastic parts in the laboratory is relatively complex and involves compromises in terms of quality. When series production in injection molding finally starts, the cost ratio is exactly the opposite: The investment in a mold is higher, but the plastic parts can be produced cost-effectively in large quantities.

Tips and tricks for handling plastic

When working with a wide range of plastics, specific technical refinements and processing techniques are required to achieve optimal results with each material. One challenge, for example, may involve extremely small component dimensions that necessitate specialized equipment in injection molding, such as micro-injection units.
Another example is the prevention of yellowing in transparent COC (cyclic olefin copolymer) plastics. COC is highly susceptible to oxygen and tends to react with it during the melting phase, leading to yellow discoloration. To mitigate this, the room can be flooded with nitrogen, effectively displacing oxygen during melting and preventing yellowing.
Additionally, COC is relatively brittle and prone to stress cracking. Therefore, slightly increased draft angles are especially important when working with this material.”

RKT supports process development

RKT specializes in accompanying the process development of medical components through to series production. Ideally, pre-engineering is carried out first and a prototype tool is built in order to evaluate the feasibility of complex geometries in plastic injection molding. Based on the component requirements, advice is given on suitable plastics, which are then selected and tested using the prototype tool. The sample component can then be used to refine and perfect the product. This is how the series tool is finally created. Depending on their complexity, it can produce guaranteed output quantities of millions of components

Plastic injection molding is efficient and adds value

When it comes to producing high-quality medical technology components in accordance with high medical technology standards, plastic injection molding is an efficient method for large quantities and smooth processes. Glass certainly has advantages in terms of transparency for optical testing processes, but plastic has the edge in terms of cost and handling in series production.

Could your product be produced using plastic injection molding? Contact us for advice on industrial implementation.

Stefan Preis
Head of Project Business
S.Preis@rkt.de

Get in touch