Bio-based 3D printing
3D printing is beginning to make more of an impact on the footwear industry as new ideas and materials continue to come to market. The most recent, launched in June, comes from American company Carbon Inc, based in Redwood City, California.
Called EPU 44, it is a 40% bio-based production-grade elastomeric 3D printing resin that has been developed to be especially well-suited for lattice structures where high resilience is called for. It is said to have superior latticing performance, to print faster, use less material and have a higher green strength than previous resins and offers greater protection for delicate designs. Carbon says that this proves it is possible to have highly-sustainable materials without sacrificing performance.
The new product is a sustainable, bio-based material developed by the company for its Digital Light Synthesis (DLS) technology. This is a resin-based 3D printing process that uses digital light projection, oxygen-permeable optics and dual-cure liquid resins to manufacture products and component parts with exceptional mechanical properties, resolution and surface finish. The process allows engineers and designers to iterate faster and radically rethink products by making it possible to consolidate parts and create structures that are beyond the capabilities of moulding technologies.
Dual-cure materials combine UV curable resins that react with and solidify with UV light, and thermally curable resins which react in the same manner as two-component resin adhesives. These two separate chemistries can be blended and then mixed prior to loading into a 3D printer. The printer then solidifies the part being printed by using UV chemistry. In this way, an initial network is formed by the UV printing process entrapping the thermal chemistry into that part or product that has been formed. This is then removed from the printer, cleaned and put into an oven where the thermally curable chemistry embedded within it is activated. This sounds like very clever technology and, indeed, it is.
Bio content
The company used a polymer derived from plants instead of petroleum by-products to create the necessary building blocks for EPU 44 to achieve a reduced carbon footprint and make it a more sustainable option. One of these materials, known as PO3G, forms the backbone of the long polyurethane chain involved. The monomer for this material is Susterra produced from corn sugars by DuPont Tate & Lyle Bio Products. Carbon says that this results in a much lower carbon footprint as it is essentially a case of taking CO2 from the air and sunshine to make plants and then, in turn, using them to make the building blocks of the final polymer. This 40% bio-content has also resulted in a lower viscosity resin that prints faster.
Lattice structures made using EPU 44 have a non-linear material response with a high resistance to failure and are said to offer gains in regard to quality, cost and performance, all of which are so important in high-volume production where industrial-class dispensing, cleaning and baking is present. The company says that its new resin is particularly well-suited for the production of elastomeric lattice geometries and offers more advantages compared to traditional foam materials. This is because its tear strength, energy return and elongation rates offer superior cushioning, impact absorption and comfort. Combined with its lattice generation software tool Design Engine, the company says components can be created that exceed the capabilities of those produced using foam.
Working with adidas
To give an example of the possibilities EPU 44 and Carbon’s technology can achieve, the company partnered with adidas to manufacture high-performance midsoles for running shoes, including the 4DFWD line of products. Combining athletes’ data, EPU 44 and Carbon DLS technology, adidas 4D footwear offers the possibility to fine tune midsoles to specific patterns of movement so that athletes can experience precision performance with every step.
Specifically, the new printing resin enables a unique ‘bow-tie’ lattice, designed by adidas, to be produced which is able to convert vertical force into horizontal motion to improve the wearer’s running performance. The 4DFWD is recognised as being the first performance shoe where the midsole has been designed and produced entirely with the aid of 3D printing. It has been claimed that by using EPU 44 combined with Carbon’s spin cleaning technology, the generation of an average of 203 metric tons of Isopropyl alcohol (IPA) waste and 74 metric tons of resin waste was prevented. This only goes to show what can be achieved through the adoption of modern technologies of this kind.
New directions
As product teams look for fresh applications of elastomeric lattices they will need to innovate in new directions that call for characteristics that were previously unattainable. However, many materials currently on the market constrain design geometries which, in turn, constrain performance. Soft elastomeric photopolymers can restrict the design space for strut-based lattices due to how delicate the structures are while printing. These photopolymers also take a long time to print and can pose significant challenges in managing supply and quality. Additionally, the vast majority of photopolymers on the market do not meet the requisite durability requirements needed for high performance footwear products such as running shoes.
There are many opportunities for growth and development when it comes to sustainability by the use of additive manufacturing. Parts can be made on-site or at a time when they are needed, thus reducing transportation costs and the environmental impact of shipping. Companies can also benefit from a lower inventory or cloud-based inventory as an alternative to warehouses filled with polymeric parts that require humidity and temperature regulation, and are often discarded after their expiration dates. Companies can now manufacture these products locally and on-demand. Another major benefit of additive manufacturing is the ability to reduce material content and weight by using lattices and other types of geometric design that are not possible with traditional manufacturing processes.
Widespread adoption of additive manufacturing is nevertheless still in its early stages, but the role it can play in making manufacturing more sustainable and innovative is immense. Materials such as EPU 44 can help the footwear industry reimagine what is possible using bio-based materials that do not sacrifice durability, aesthetics and cost.
The adidas 4DFWD shoe features a 3D printed lattice midsole in EPU 44 resin from Carbon Inc.
All Credits: ADIDAS
