Hot Runners Tri-layer hot runner systems complement co-injection

Editor: Eric Culp

Mold-Masters says its Iris co-injection system is well-suited to the beverage, caps and closures, food container and medical industries, and the company’s proprietary hot runners play a central role in the technology.

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The replaceable nozzle tip splits the skin flow into two separate streams and then brings the barrier flow front in between them.
The replaceable nozzle tip splits the skin flow into two separate streams and then brings the barrier flow front in between them.
(Source: Mold-Masters)

Iris is a compact co-injection nozzle manifold technology that combines melt streams and provides balanced fill-valve gate control of the opening and closing movements of the servo-actuated valve gate pins to achieve fast cycle times and precise cavity fill, according to Mold-Masters. The co-injection results are obtained by a precise, integrated control of dosing, flow and the pressure of the two melt streams.

Process, range of applications continue to evolve

The Iris co-injection technology is currently available for 32- or 48-cavity tools and further application possibilities are continually evolving. According to Mold-Masters, the Iris technology is ideal for use in beverage caps and closures, food containers, and medical applications. Wherever barrier layers are required to prevent permeation of oxygen and migration of CO2 or stop the entry of moisture for medicine or food containers, the Iris system is said to provide a comprehensive solution for process optimisation and cost reduction.

Balanced filling critical for successful co-injection

The company explained that this co-injection technology can create a 3% barrier layer encased in a skin through the controlled interaction of core technologies within the hot runner.

The molten plastic for both the skin and core layers is conveyed to the patent-pending hot runner nozzles using Mold-Masters iFlow manifold technology, the company said. By using multi-piece manifolds, brazed together using a proprietary process, the melt is conveyed in the same rheological condition and in equal measure to each nozzle, it explained. The valve gates are controlled throughout their entire stroke using a servo-driven synchro-plate system, called E-Drive. The E-Drive ensures that each gate opens at the same time and that the valve pin in each nozzle is in exactly the same position during the critical injection sequence.

Patented nozzle creates the desired flow front

The two streams of molten plastic are brought together in the patent-pending nozzle tip, Mold-Masters explained. The replaceable nozzle tip splits the skin flow into two separate streams and then brings the barrier flow front in between them. The valve pin assists in developing the three flow streams and ensures that the melt flows do not mix.

The barrier material is injected into the hot runner via the mould-mounted electric injection unit called E-Multi. This all-electric injection unit is mounted in close proximity to the hot runner to ensure accurate and responsive injection of very small amounts of plastic into each cavity.

System said to suit virtually all injection moulding equipment

All functions in the Iris system are centrally controlled from a master CPU and a single HMI. The injection of the skin material and barrier material, as well as valve pin movement, temperature control and sensors, are all visible in conveniently arranged screens. according to Mold-Masters. The interaction of these different control elements is optimised and fine tuned via special Iris software and controls.

The supplier noted that an Iris system can be easily integrated into any injection moulding machine as well as with any mould maker’s tool design. This flexibility allows users to continue to work with their established suppliers of machinery and moulds, the company said.

Technology offers attractive alternative for the food packaging industry

Suitable for the production of food packaging containers for products such as diced fruit, pet food, coffee pods, sauces, soups, beer and baby food, Iris provides an attractive alternative to glass, metal, multi-layer thermoforming or multi-piece assemblies to achieve a functional barrier. The system produces a net-shape part with no waste or additional processes.

Injection moulding goes head-to-head with thermoforming processes

The company noted that one featured application shows advantages over typical thermoformed thin-walled parts which have foil or label barriers. An injection-moulded part with an EVOH barrier offers 30 times the protection against oxygen or other gases, according to Mold-Masters. The recyclability of the part is also improved due to the elimination of tie layers and the low percentage of barrier (<5%). The containers can be deposited into existing higher-value recycling waste streams, the company added.

Closure molders can also take advantage of barrier layers

The technology allows caps to have a directly co-injected EVOH barrier, which merely constitutes a proportion of 3-6% of the total cap, the supplier explained. The co-injection process is said to simplify the production of the closure where a barrier layer is required, and it eliminates the previous requirement for multi-piece assemblies. The result is a simple but 100% sealed cap, which can be used directly in the packaging process, the company noted.

Mold-Masters outlined one current closure produced with the application, a tamper-evident, linerless, 38-mm hot-fill HDPE cap for a beverage container with an integrated oxygen and CO2 barrier.

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