High-performance polymers for 3D printing

The influence of the pandemic is radically transforming the habits of production and design of artefacts. According to Context World, which is in charge of analyzing technology markets, 2020 has defined what may be the new industrial scenarios for 3D printing. It has become clear that 3D printing can be leveraged easily and quickly to print when you need almost everything you need. You can get a component without waiting for delivery times or the complex supply chains associated with traditional manufacturing techniques. Items can also be crafted in the region (or even in the same building) where they will be used or assembled. This awareness has led to renewed interest from new markets with a forecast of growth in 3D printer sales of 15% in 2021.

The use of 3D printers is also changing. From a use closely related to the making of prototypes and single objects, new technologies and new polymeric and composite materials are destined to drive the growth of the 3D printing industry and see a development in series production.

3D printing, also called AM (additive manufacturing), born in the 1980s, has consolidated overtime for the rapid creation of prototypes and has found great use in the study of new products and customized pieces. However, prototyping is only one of the applications, because new materials and technologies can use 3D printers in mass production. This is an important transformation in the world of industrial production. One of the main reasons that prevented this production technique from gaining ground was the greater convenience in terms of time and materials of traditional moulding. More sophisticated and faster technologies are catching on alongside more widespread FDM (filament deposition) mode. Systems such as powder bed fusion (called SLS) or tub photopolymerization (SLA) are faster and enable large-scale production.

The technology usually used in additive manufacturing is FDM, which uses a molten polymer filament extruded onto a plate by a head which, with overlapping layers, replicates the object designed by the software. The polymer used is a polyamine and the times are determined by the thickness of the layers and the steps required to get to the finished object. The higher the definition, the thinner layers and therefore the longer the execution time. Moreover, if the classical moulding technique has about 3,000 types of materials available, which can satisfy the demands of all fields of application, for 3D printing there are only 30. Among them, polyamide, which is already widely used in scale productions, adds nothing to traditional products.

Polymers in FDM additive printing

With the introduction of polyurethane and polycarbonate in additive printing methods, the range of possibilities in terms of performance and properties such as hardness, heat resistance, transparency and flexibility is enriched. The polyurethane and polycarbonate used in one of the most common printing methods such as FDM have also shown advantages over conventional materials and methods and reduce the costs of moulds and development times. Not to mention the freedom of design which translates into increasingly sophisticated solutions that meet market demands. Studies conducted in Covestro research centres have shown that the polyurethane used in place of polyamide is particularly versatile and has advantages even in industrial-scale production.

Both flexible and rigid thermoplastic polyurethanes (TPUs) or high-strength polycarbonate (PC) have proven to be particularly suitable for 3D printing. Their behaviour in melting and hardening produces a permanent bond between the applied layers. The characteristics of the two polymers are maintained: resistance to abrasion and elasticity, as well as high resistance to impact or combustion and great thermal stability.

Thermoplastic polyurethanes in the SLS printing technique

SLS (selective laser sintering) is an additive printing technology in which a localized energy source, usually a high-power laser, selectively melts a bed of powder layer by layer to obtain the desired component. The SLS process is ideal for parts with complex geometries, especially when they have internal details or thin walls. SLS moulded parts have excellent mechanical properties and strength similar to those of injection moulded parts. Thermoplastic polyurethane (TPU) powders have strength and elasticity advantages over other polymers.

New generation resins for SLA additive manufacturing

Invented in the 1980s, stereolithography (SLA) is one of the most popular 3D printing technologies in the industry. SLA technology uses a laser or a projector to transform the liquid polymer into a solid plastic through the photopolymerization process. Of all 3D printing technologies, stereolithography is the one that produces pieces with the highest resolution and precision, with defined details and a quality surface finish. Here the high-tech polyurethane resins give hardness, flexibility and resistance to atmospheric and chemical agents superior to polyamine. Mixtures with isocyanates and polyols are possible, which make the resin respond to all the applications and properties required by production.

High-tech resins have increasingly higher advantages and characteristics that can successfully replace the traditional moulding. They can have properties that satisfy every need in high-tech productions where there is a need for:

• high chemical resistance and resistance to atmospheric agents
• solid colours over time
• perfect transparency if required by the project
• low shrinkage and compliance with established measures
• modularity of the compound with the creation of customized blends.

SLA 3D printing is used successfully in very specialized fields such as reconstructive medicine and oral and maxillofacial surgery.

Could additive printing make the green industrial revolution possible? Surely there are some aspects of 3D printing that manage to profoundly change the usual ways of production. And if at the same time conscious choices are made in line with the principles of the circular economy, significant sustainability of the manufacturing industry. The first revolution is certainly the logistics one. 3D printing starts with a file that you can send anywhere. You can create what you need, when and where you need it, without the need for warehouses, obsolete parts left in stock. With the decrease in transport, fuel consumption and therefore CO₂ emissions into the atmosphere are also reduced.

By definition, compared to traditional moulding, 3D printing is a production process that does not produce waste. The objects are created by the addition of raw material and only what is necessary for their realization is used. Furthermore, 3D printers use little energy with benefits for the environment and economic savings for businesses. Ecological raw materials also contribute to sustainability. Covestro laboratories have developed TPU-based filaments and powders with a component of biological origin that reaches 50% that can be used with standard 3D printing machines If this sustainable technology is to develop, it is essential to create polymeric materials that are adaptable to any type of printer. As Lukas Breuers, Covestro's marketing manager, says:

3D printing is showing its full potential in the various sectors where it is already bringing great innovations in the field of clothing, automotive and construction.