One-shot footwear: A dream becoming reality

Since the advent of the PVC Wellington Boot design, one shot shoe production has remained a footwear manufacturing dream, Jane Denny looks at the possibilities the future holds.

Crocs, Wellies and jellies - although not necessarily made using polyurethane - all fall under the same category and have emerged immensely successful types of footwear or brands. Such easy to produce, one-shot shoe design innovation could support the re-globalisation of shoe manufacturing.

SATRA’s head of communications, Jake Locke, said: “The simplicity of the moulded process gives the potential for low cost production depending on the tooling cost of the moulding machines and moulds.

“Moulding produces the footwear in a single step saving the need to join together, in a sequence of operations, component parts of different materials which must themselves be pre-formed. It provides a footwear item without joins or stitch holes, ideal for waterproof products.

“However, the footwear cannot breathe, unless it is a sandal, and will not break in (adapt to the wearer’s own foot) as fabricated shoes usually do.”

Despite what Locke regards as limitations, both BMS and Huntsman have formed partnerships with footwear experts to produce prototype PU shoes around the one shot process idea.

For the chemical manufacturers, the advantage of the process stems from the drastic reduction in material selection for shoes – its swaps the maximum 300 components for just one material, or, in some cases, varying grades of one material. The ability to produce a pair of shoes with an injection moulding technique adds to the attractiveness of their respective systems.

Huntsman describe its prototype as a “radical thermoplastic polyurethane manufacturing system” and claims that it paves the way for footwear innovation.

Huntsman teamed up with German footwear company Footwear Concept and Design to create the one-shot, single unit, shell shoe for cyclists from injection moulded TPU. Eliminating the need for any stitching after demoulding as upper and sole are attached automatically during the injection moulding process.

Alfons Tremml, commercial manager footwear, Huntsman,  said this type of shoe production provides a “unique sales advantage” due to the range of polyester and polyether grades the company has available.

Scope for customisation

“It offers outstanding scope for customisation,” he added.

From a collaboration between BMS and DESMA, a similarly influenced innovation was presented in 2014 with the QuadWrap shoe.

In creating the shoe, a stabilising layer is firstly moulded directly onto a carrier fabric. At the same time, outsole pads are created by micro-pouring. The outsole is directly moulded on top of the pads. A fourth layer completes it while adding three-dimensionality.

The shoe’s cast elastomer production process uses Baytec PE for the more rigid elements of the shoe and Bayflex S for its sole and shaft elements. Muller said Bayflex S is a low density PU – of density 220g/l – which can be produced either through the use of a physical blowing agent – for smaller production schedules – or through CO₂ lightweight technology.

The innovation also uses a newly designed last-mould combination, two sets of moulds and allows production on a single machine. The polyurethane was tailored to meet the requirements of each shoe element’s function.

The tensile strength of the first layer allows for comfortable fastening, while the outsole pads are slip and abrasion resistant. This dual density system combines to make the trainer’s external structure extremely lightweight, flexible and shock absorbent.

Using less glue

The trainers can be made without additional adhesives and the process is highly automated.

According to Yafang Li, Desma PR representative, “many” of the shoe machinery maker’s customers showed interest in the design concept.

David Dixon, Rocky Brands, said: “I showed a sample Quadwrap shoe to our development department and they were very impressed. It definitely started them thinking of ways to incorporate this into our hunting or hiking concepts.

“The idea of making a complete polyurethane shoe with little to no labour required for lasting or finishing is very appealing, especially in higher wage markets such as the US,” added Dixon.

According to SATRA, a certain degree of component grouping is typical to the industry. Locke said number of shoemakers “group grade heels, stiffeners and box toes using a mid-size to cover those around it.” He added that “a range of styles may use the same last, thus allowing the shoemaker to use one insole for all those models.

SATRA and the future of shoemaking

SATRA undertakes research and testing for companies all over the world. The organisation, which has around 1,700 members from the footwear and leather industries, also publishes the technical handbook, Basic Shoemaking.

The handbook’s popularity, “reflects the international demand for solid shoemaking knowledge and skills,” said Locke, SATARA's  head of communications.

“Interest in footwear design and manufacture is alive and well almost everywhere you turn, not just in the usual places in Asia and Europe.”

Early in 2015, the organisation hosted its second International SATRA PPE Innovation Awards.

According to Locke, the awards provide a window on “ideas’ initial or experimental” stage, thanks to SATRA’s willingness to invest in technical innovation.

Locke said: “One thing we saw that could be quite exciting is adaptive materials technology for example, materials that adapt to the environment. Such technology could bring huge benefits to the user in levels of comfort, performance and safety.

Innovation gives the edge

“Companies that develop and supply the next generation materials are likely to gain a competitive edge in certain markets,” he added.

Locke also told Urethanes Technology International, that the organisation’s global foot scanning project “proved interesting.”

Carried out in 2014, the initiative’s data is still being reviewed by the organisation said Locke.

“A pattern is emerging that suggests there are subtle differences between the shape and size of feet in the UK, US and China. Such information when qualified could be of advantage to any company making and supplying footwear for these markets,” he added. Locke said foot sizing information will be of particular interest to Chinese and international companies looking to supply footwear to the vast Chinese market – a market that he said, “appears to be growing towards a level double that of the United States.”

SATRA Technology Services, the organisation’s operation in Dongguan, China will use the sizing information as part of a consultancy and problem-solving service to help ensure footwear is designed and manufactured for optimum fit and comfort and better match with the Chinese consumer, he said.

Locke also said that import and export figures for 2012 – statistics that are included in SATRA’s World Footwear Markets report – are “encouraging.”

He said: “The figures would seem to confirm the global footwear industry has finally moved on from the shadow of the previous recession and is showing signs of development in new and potentially exciting places.

“Many established footwear producing regions, rather than stagnating, are bringing fresh thinking and innovation to the footwear business. We have seen a significant rise in the number of companies wishing to become SATRA members, which we think reflects optimism for the future,” he added.

SATRA, based in Kettering, United Kingdom, has a 1,200m² humidity and temperature-controlled footwear and leather testing laboratory.

The organisation’s testing processes measure a shoe’s durability, slip resistance fitting and comfort as standard. SATRA also undertakes evaluations on a shoe’s breathability, chemical composition – to rule out the use of banned substances – cushioning, sole bond adhesion, strap strength and water resistance among others.

For safety footwear, the organisation tests to standards EN ISO 20345, 20346 and 20347 (European Union Notified Body for Personal Protective Equipment PPE).