LSR drops into ​ 3D printing demand

Würzburg, Germany — Two presentations at the biannual SKZ Süddeutsches Kunststoffzentrum Silicone Elastomers conference in Würzburg addressed recently introduced liquid silicone rubber 3D printing systems.

Florian Liesener, manager of the new ACEO 3D printing business unit at Wacker Chemie AG in Burghausen, Germany, classified the company's new drop-on-demand (DOD) material dosing of silicone in viscous paste form.

He pointed out that DOD differs from the commonly used fused filament fabrication (FFF) used in fused deposition modeling (FDM) from extruded plastic filaments.

Samples included a branched blood vessel model and an ear implant, as well as net cube cubic lattice grid structures with crosswise superimposed beams, the latter described as an example of "producing the impossible."

For Wacker, opening the ACEO campus with its Open Print Lab in mid-2016 preceded the world premiere of the company's package of 3D printing LSR materials at K 2016.

Liesener called ACEO "a true system solution" with the ACEO campus functioning as a service provider, also via a worldwide web shop.

Bernd Pachaly, Wacker's silicones research head, said the ACEO research team started developing a 3D printing system for LSR in 2014. The company compared the process to squeezing toothpaste out of a tube, with the LSR material shear thinning for easy flow when under pressure, then sitting firmly in position when higher viscosity returns with removal of shear force.

ACEO prints "voxels" (volume elements) in its contactless DOD system, followed by curing activation of each layer by ultraviolet light in less than one second. The printed part is subsequently post-cured at elevated temperature. A water-soluble support material enables overhangs and cavities and is rinsed away by hand from fully cured parts.

Liesener said ACEO offers LSR materials for 3D printing that result in cured parts between Shore A 10 (soft) to Shore A 80 (hard). A variety of colors are available.

Food contact and biocompatibility test data are expected in the third quarter. Work continues on material developments, with completion dates for optical transparency expected in 2017, adhesion in 2018, media resistance in 2019 and electrical conductivity in 2018/2019, Liesener said.

A presentation by Patrick Beyer and Hans Peter Wolf, silicon rubber R&D managers at Dow Corning Corp. in Wiesbaden, Germany, covered the company's new liquid additive manufacturing (LAM) process.

Dow started LAM development in 2015, together with two Germany-based partners: 3D FFF printing machinery producer German RepRap GmbH in Feldkirchen, and dosing system producer ViscoTec Pumpen- und Dosiertechnik GmbH in Töging am Inn.

ViscoTec has also been assisting Wacker Chemie in its 3D-printed LSR development.

LAM is based around Dow Corning's special LC-335 3D-printable LSR material with Shore A50 hardness. Printed parts exhibit overall 20 percent lower mechanical properties than injection molded LSR, tensile strength being 30 percent lower and tear strength 10 percent lower, Breyer said.

The LC-335 ran live at the SKZ conference, producing transparent shoe inner soles on a German RepRap X400 pre-series modified FDM printer.

The X400 was fitted with a ViscoTec Visco-Duo FDD 4/4 2-component FDD fluid dosing and deposition dispenser. Wolf stressed that the open structure on the X400 would change later to a closed housing based on German RepRap's X500 type of FDM machine.

The X400 running in Würzburg offers build volume of 260 x 320 x 200 mm, building parts in 0.1mm thick layers from a 0.4 mm diameter nozzle at speeds of 10-150 mm per second, with maximum equipment travel speed capable of reaching 300 mm per second. There are also options for 0.2 and 0.3 mm nozzle diameters and a second extruder for the unspecified support material.

Wolf said there is potential for customers to have individual LSR inner soles printed for their shoes in shoe stores.

Oliver Franssen, senior global marketing leader at LSR supplier Momentive Performance Materials GmbH in Leverkusen. Germany, told LSR World that Momentive has been supplying LSR to Sterne SAS in Cavaillon, France, as a silicone processor that has introduced its own LSR printing technology in September 2016.

Sterne's SiO-Shaping 1601 system involves deposition of 100 percent UV-cured transparent and opaque colored silicone in hardness of Shore 30A-60A in minimum layer thickness of 0.25 mm in a printer with maximum build volume of 250 x 200 x 100 mm. Sterne claims the material obtains "100 percent of strength and elongation properties of injection molded LSR."

Sterne General Manger Céline Laget points out that 3D printing plastics does not result in parts with molded LSR properties, and material manager Anthony Pellafol adds that the process can produce complex LSR parts in high precision.

One of the other silicone-based solutions mentioned in passing by Florian Liesener of Wacker Chemie's ACEO business campus in his presentation at the SKZ conference included the Picsima 3D printing system developed by Fripp Design & Research Limited in Rotherham, England. Fripp says its development of 3D printing two-component room temperature vulcanizing (RTV) silicone arose from requests from Manchester Metropolitan University for a process to produce ocular prostheses and from Sheffield University for soft tissue prostheses.

Picsima produces single-softness parts down to Shore A10, with multiple softness also intended in future. The process does not need support materials, Fripp says, claiming uniqueness for the way in which the silicone is polymerized.

Parts have been produced with 0.4 mm layer thickness in a printer with build volume 100 x 100 x 30 mm. Although the company says it wants to sell 3D printers for its process, "it will require a serious injection of working capital to achieve this."

Liesener also referred to Japanese microscope producer Keyence in Osaka offering silicone for 3D printing on its Agilista 3D printers.