Holding it together: Two-component wet-in-wet moulding process prevents freeze-cracking
Martin Manka, Arburg senior sales manager, medical describes how a two-component wet-in-wet moulding process prevents freeze-cracking of blood sample tubes and how Arburg plays a key role within this process.
The French Blood Donor Centre, and other institutions within Europe, the United States and Australia come to Jako Meditec, Szekszárd, Hungary, for tubes, closures and racks used to store blood samples.
Their requirements are quite specific stating that each tube and the blood sample inside it must be uniquely identifiable, and the tubes must also withstand storage at -35⁰C for three years. To meet those demands, Jako worked with Arburg and a German mould maker to develop a unique two-component moulding process they refer to as wet-in-wet moulding.
The process yields transparent tubes made from polypropylene (PP) with a black PP base that can be laser marked with a unique data matrix (DM) code that meets the traceability requirement.
However, Jako found they couldn’t use a rotary or sliding split mould which is the conventional approach to two component injection moulding, because injecting the two materials sequentially created a weld line that was prone to cracking during the thawing of the blood samples. This problem led to the development of the wet-in-wet process.
Instead of injecting sequentially, explains Stephan Hauri, Jako project manager for plastic injection moulding, “both components are injected almost simultaneously into the mould. Here, they flow towards each other and fuse together when they meet.”
This sophisticated innovation was jointly implemented with Arburg Hungary and the German mould manufacturer Polar-Form,” says Joachim Koch, who, along with his brother, Andreas Koch, founded Jako Group 20 years ago and formed Jako Meditec in 2015. The two share the title of managing director. Their father, senior partner Adam Koch came up with the idea for the wet-in-wet process and Jako also had the support of the Arburg application technology group during the development and implementation stages of the project.
Joachim Koch states that the Arburg control system “operates with a precision down to a hundredth of a second during injection.” Such precision is necessary because the amount of clear and black material needs to be consistent so that the black section which gets the DM marking is the right size.
The first 8-cavity mould performed well, producing in excess of two million shots. Today, a moulding cell docked to a class 8 clean room is used to produce the tubes. The centrepiece of the cell is a 2,200-kN (245-ton) hydraulic allrounder 570 S, which is fitted with two size-170 (3.7-oz) injection units and a 32-cavity mould.
In the clean room, the tubes are stored temporarily until they are labelled, assembled, and inspected according to customer specifications. “For this purpose, we work with island solutions,” explains Hauri.
In total, Jako operates five Allrounders and around 20 moulds with between one and 32 cavities are in operation to produce the appropriate screw caps, thermoplastic rubber or elastomer (TPE) plugs and seven different rack types. Joachim Koch says Jako expects “to produce around 1.5 million tubes per month.”
Andreas Koch concludes by saying, “The Arburg machines have been in continuous operation very reliably since the start of production and have proven extremely well suited to their task.”