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Medical Plastics: Machines which meet the sector's challenges

By Lou Reade
Posted 6 February 2013

 

There is an increasing trend for system integration within plastics production, in which the machinery and its ancillary components work more harmoniously together.   This helps to control costs, as well as ensuring more consistent quality – which are both vital to the production of medical plastic parts.

Late last year Sumitomo (SHI) Demag launched its ActiveCell, a self-contained injection moulding clean room, for manufacturing pharmaceutical and medical components to ISO 7 (class 10,0000) standards.

The system is available in an all-electric turnkey format, and contains everything needed for production of sterile parts: platen-mounted six-axis robot, laminar airflow cabinets to ensure particle-free air in the mould-space area and integral packaging equipment.

When installed, it is fully compliant with GAMP and FDA requirements and DQ, IQ and OQ documentation. The company says that it offers low-investment entry into cleanroom manufacturing.

“For many medical and pharmaceutical manufacturers, a cleanroom facility is a significant investment,” says Nigel Flowers, managing director of Sumitomo (SHI) Demag UK. “It’s not always essential for their production needs and can be cost-prohibitive when looking to expand into niche markets. ActiveCell is designed to address current market requirements for a low investment alternative with complete flexibility at a fraction of the cost of a full cleanroom.”

The system is available in 100, 160, 220 and 280 tonne formats, and helps manufacturers expand into ISO class 7 manufacturing.

The compact cell, which is fully guarded, incorporates a platen-mounted robot – making it only 500mm wider than a standard machine. It combines technologies from Sumitomo (SHI) Demag’s UK technology partners Motoman (robotics), AVT (packaging) and Max Petek (laminar flow hood). The system maintains its ISO 7 class 10,000 cleanroom environment thanks to laminar air flow systems that flood the mould surface and part handling areas with HEPA-filtered air.

A six-axis robot transfers moulded parts to the conveyor system, chute or packaging system.

“The robot also offers secondary operations including assembly and palletising – a value-add for manufacturers looking for expansion options and fast pay back,” says Flowers.

The final element of the system is an AVT packing system, which bags multiple products in the controlled conditions before they exit the machine.

Sumitomo (SHI) Demag operates as a system integrator to oversee the process of installation.

Combination process

Meanwhile, a collaboration between Austrian machinery specialist Engel and Italian mould maker Cantoni has led to a technology that combines injection and blow moulding in a single process.

Inject2blow uses a single mould, in which the two processes are combined. The technique can be used to cut the cycle time for a range of products, including pharmaceutical containers. For example, a wide-necked jar can be made in less than 14 seconds on a 90-tonne Engel Victory machine in a special 2+2-cavity mould from Cantoni.

The process can be used to process a range of thermoplastics including PE, PP, polycarbonate and PET.

Preforms are traditionally made by injection moulding, and then later processed on a blow moulding machine. The new method allows small, ready-to-use containers to be made in a single, combined process. This combination method is the first of its kind available on the market, say the developers.

Potential benefits of integrating these processes include: lower system investment costs; reduced energy bills; a smaller footprint; higher system availability; simpler quality control; and no maximum clamping force.

In addition to the Engel injection moulding machine – from either its Victory or e-Victory series – the system comprises a Cantoni sliding table mould and Viper linear robot, which removes finished parts from the mould. Both the injection moulding and blow moulding processes are controlled via a CC 200 control unit.

The tiebarless injection moulding machines offer plenty of free space for the sliding table mould. Because the mould clamping platens of tiebarless machines can be used up to their edges, or even beyond, large moulds can fit on comparatively small machines. This means that machine size can now be decided on the required clamping force, rather than the size and movement radius of the mould. This helps to reduce investment and operating costs.

The barrier-free mould area also simplifies the automation process, because the robot can access the mould from the side without being hindered.

Engel claims that the process consumes less energy than the traditional ‘two stage’ process: preforms do not have to be re-heated, it says, and the Ecodrive energy-saving option also reduces consumption.

Cavity inserts make it easier to change from one product to another, and the production of small batches economical. As the inject2blow process is based on standard injection moulding machines, the system can also be used with moulds for classic injection moulding products.

Upward curve

Within medical extrusion, the need for a greater diversity of tubing continues – whether it is smaller diameter, higher specification or greater durability. US-based extrusion machinery supplier American Kuhne has managed to extrude Peek tubing on a vertically upward extrusion line.

The company found that the tube can be annealed, by passing it through an oven placed above the die head. This allows the outer diameter and ovality to be precisely controlled.

The outer diameter can be kept to a tolerance of 0.0007in (0.18mm), and the ovality to less than 0.001in (0.25mm). Annealing gives Peek the time to crystallise uniformly as it cools, to give optimum physical properties.

Discovering the vertically upward extrusion and in-line annealing process followed previous unsuccessful attempts to extrude Peek horizontally and vertically downwards. The horizontal attempt, performed with a 24in (61cm) gap between die head and quench bath, resulted in a semi-crystalline tube – but with inconsistency in outer diameter (OD) and ovality.

It also led to non-uniform crystallinity between the top and the bottom of the tube. The vertically downward attempt resulted in a ‘snake-like’ product with bends and kinks in the tube, because the Peek had insufficient melt strength to hold the weight of the extrudate. There is a patent pending on the technology.

At the same time, Cincinnati Milacron says that its M-Pak range of single screw extruders has been designed to meet the stringent clean processing applications of the medical industry.

The machines are optimised for processing small precision tubing, including multi-lumen tubing of the type used in catheters, vascular intervention and dialysis. The extrusion lines can manufacture a wide range of multi-lumen tubing, which can have multiple lumens of two or more within the same extrusion. This is achieved with a specialised multi-cavity die technology, which produces multiple working channels and high mechanical performance with accuracy and precision.

The barrel and screw are built from stainless steel, and have a low-profile, modular design and smaller capacity hopper to fit better into clean rooms. The machines have stainless steel barrel covers, feed hoppers and high-efficiency sealed AC vector direct coupled drives.

Cincinnati Milacron focuses on two main areas: small precision tubing for minimally invasive procedures; and larger bore diameter high speed tubing for more general medical applications.

For very specialised requirements, a second extruder can provide a co-extruded outer layer. The M-Pak range uses the Mosaic PLC – a control system that can operate other upstream or downstream equipment, for complete control of the extrusion line.

Culture shock

German medical specialist Zellwerk has developed several cell culture technologies, and recently relied on injection moulded components from UK-based Proto Labs in its latest device.

Its ZRP technology allow cell cultures to be grown outside the body, and then re-implanted. This technique is commonly used in some cancer treatments.

“The patented system is a revelation in regenerative medicine, and the dream of biomedical scientists,” says Hans Hoffmeister, CEO. “It takes a sample from the patient, isolates the immune cells, cultures them outside the body in large quantities, and leads them back to fight tumour cells.”

The system comprises an incubator, located in the sterile work chamber of a bioreactor, and a special adapter. An external control unit monitors, controls and documents everything.

“It is critical that laminar flow is created in the plastic reactor,” says Hoffmeister.

To ensure repeatability, it was vital to create a special surface in the reactor that had the optimum amount of friction – not too smooth and not too rough.

The firm’s construction manager, Rainer Mausolf, says that the choice of plastic was crucial because Zellwerk needed to maintain constant chemical and physical conditions in the reactor.

“We tried several common plastics but had difficulty in finding a material that was resistant to sterilisation by gamma-rays. Finally, with the help of Proto Labs, we found the optimum resin for our system,” he says.

All the bioreactors and probe adapters (in different versions) were manufactured using the Protomold rapid injection moulded parts service. Finished parts were delivered within 10 days of transferring the 3D model – though were sometimes delivered within five days.

“The process was simple: I uploaded my 3D SolidWorks model to the Protomold website,” he says. “Almost immediately my quote arrived, and shortly after I was contacted with tips on implementation. Within days we had received the first reactors and adapters made using our special plastic.”

Although many medical products are made in huge quantities, there is often a need for precision parts that are produced in more modest volumes. The flexibility of modern production methods means that both scenarios can be catered for in plastics – which is often the most appropriate material for the job.


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