Silicone is the ideal material for oral hygiene applications. It is flexible, free of plasticizers, biocompatible and rugged. Liquid silicone rubber (LSR) makes it possible to map structures that are fine enough to penetrate even the tightest spaces, while also being soft and thus gentler on the gums than the bristles of small brushes.
An insightinto manufacturing at TePe.
TePe, a Swedish family-owned company, makes use of these features for its product known as EasyPick, the innovative 21st century toothpick. TePe has been specialized in the field of oral health since its founding in 1965 and currently ships its products to over 60 countries. The core competencies of design, development and production (including 50 injection molding machines) are located entirely in Malmö. This gives the company control over the entire value chain. Including its seven international subsidiaries, TePe has 370 employees and its annual earnings are approximately 80 million euros.
Challenging two-component part made of PBT and LSR
TePe has been taking advantage of KraussMaffei's silicone expertise for the EasyPick since 2015. The two-component part consists of a white base body made of PBT (weight: 15 grams) with a conical tip overmolded with just under four grams of colored silicon. Orange indicates size S and blue indicates size M. EasyPicks always come in sets of six, connected via thin break-off points. This makes it easy to detach one for use.
From S to M:The color depends on the size
The manufacturing itself uses the transfer method: The lower, cooled mold-half includes the thermoplastic component. After the mold opens, an LRX linear robot removes these molded articles and places them in the (hot) silicone half. In this process, the thin PBT pins are centered, but free in the cavity, allowing them to be encapsulated uniformly from all sides—at wall thicknesses of just 200 µm, manufacturing with maximum precision is essential. The silicone that is used is a self-adhesive formulation suitable for food contact and with reduced volatile silicone content. In addition, the material is mechanically anchored—after all, the two components of the EasyPick have to stay firmly bonded together, even during vigorous use.
Customized system solution from a single source
KraussMaffei provided the complete production systems, including the SilcoSet equipment, automation, mixing and metering unit and packaging line. TePe's Product Developer Alexander Dingizian recalls the project start well, saying: "The machine set-up was correct from the beginning, and we could get our production up and running quickly. We were particularly impressed by the startup of the LSR components. After just three shots in semi-automatic mode, we were able to launch fully automated production."
Ready for production quickly:The CX system at TePe.
For the CXL 160 machines used, the all-electric second unit is attached on the non-operator side in an L-connection. The CX has a large daylight, even in standard models. Based on the modular design, the daylight has been enlarged by an additional 200 millimeters. This also provides easy access to the non-operator side, despite the L-injection unit. The mold clamping platens have also been widened and the maximum mold installation height has been likewise expanded. The parts removal takes place after separating the sprue in the lengthwise direction downstream of the machine. However, thanks to the cantilever clamping unit, it would also be possible to attach a conveyor belt below the clamping unit bed.
Minimal standard deviation for part weight
By the time the low-viscosity LSR flows into the evacuated cavity, the corresponding dye pigments have been added to it earlier in the mixing block. This is always a tricky matter in the reactive process, if for no other reason than that the silicone individual components are generally also subject to significant batch fluctuations. If too much dye is added, decreased viscosity of the material—which is already like water—is the result, and along with it the possibility of overmolding.
The perfect colorsucceeds with LSR.
With APC plus, every part is a good part
For a two-component part made of thermoplastic and silicone—for which even the counter-rotating temperature control in the plasticizing unit and mold is complex—the APC plus machine function from KraussMaffei provides particular benefits. Based on the measured melt viscosity and stored material parameters, such as compression, it controls the shot weight in each and every cycle. This is done by adapting the changeover point and the holding pressure level. For silicones that expand in the cavity, the focus is on the changeover point. APC plus makes even the thermoplastic preforms extremely weight-constant, providing the basis for perfect multicomponent articles.
APC plus for non-thermoplastics then controls the challenging silicone process. The finer the structures to be mapped, the tighter the tolerance band that can be selected. Once machine, mold and peripherals have been tuned to each other optimally, the user generates a reference shot (or multiple shots) and stores it in the mold data record.
The TePe EasyPick shows how useful the bond of thermoplastic and silicone can be. Rugged support element and soft layer that is gentle on the gums: With the KraussMaffei SilcoSet, nothing gets in the way of a brilliant smile.