A rotating mould core can induce shear in the tangential direction during injection, which superimposes the injection-induced shear. In the case of fibre-reinforced thermoplastics, this results in a reorientation of the fibres in tangential direction. This paper shows how a rotating mould core influences the fibre orientation and bursting strength of short-fibre-reinforced polypropylene and polyamide respectively. Furthermore, different wall thicknesses and fibre contents are investigated at varying rotational speeds. Regardless of the used material and the wall thickness, strength increases of more than 75 %are possible at the appropriate speed.

Schematic representation of the rotational shear rate due to the rotating tool core

Spritzgießen

Kunststoffverarbeitung: Verfahren

Werkzeugkonstruktion

Dienstleistungen

Werkzeug-, Formen- und Modellbau

Polyamide

Kunststoff Werkstoffe

Thermoplaste

Polypropylen

Faserverbundwerkstoffe

Andere Werkstoffe

Influencing the fibre orientation of polypropylene and polyamide in the injection moulding process by a rotating mould core

Continuous Compression Molding (CCM) technology can be applied to multilayer solutions and is referred to as Continuous Compression Molding Multilayer (CCMM). In addition to the usual benefits of CCM it offers further advantages over competing technologies. In packaging applications, compression technology makes it possible to use minimal quantities of barrier material, thus combining excellent performance with low raw material costs.

EVOH distribution in a compression-molded multilayer capsule produced by CCMM: 1) complete distribution over cross-sectioned capsule, 2) enlargement of two zones (bottom and wall) of the capsule

16:9

Continuous Compression Molding Multilayer of Coffee Capsules

Extrusion

Warmformen / Thermoformen

Kunststoffverarbeitung: Maschinen und Komponenten

Pressen von Kunststoffen

Extrusionsanlagen

Co-Injektion (Barriere-/Sandwich-Spritzgießen)

Paying Attention to Layers in-between

Process technologies for manufacturing multilayer and multicomponent products offer great potential for using reprocessed plastic wastes even for plastic parts that are subject to strict requirements for surface quality, product protection or consumer safety. The key: to place the recycled material in the interior while the surface is made of virgin material. Engel has developed a variant of sandwich injection molding that allows high proportions of recycled material to be used even with complex part geometries.

The sandwich technology (skinmelt) hides the recycled material beneath a virgin material surface – for example in the transport boxes

Engel’s skinmelt Sandwich Process Paves the Way for Increased Use of Recycled Material

Werkstoffprüfung

Messtechnik

Kunststoff-Rezyklat

Recycling that Gets under the Skin

The Circular Economy is not only the theme topic at the K 2019. It is also the “green” thread running through the fair exhibit by Engel, the provider of injection molding machines and integrated system solutions. Industry 4.0 is turning out to be a driving force for recycling. This is a most timely insight, since the branch is in for several economically cool years.

Dr. Stefan Engleder, CEO of the Engel Group: “The plastics industry bears a  global responsibility.”

Engel Supports Strong Involvement by the Plastics Industry in a Circular Economy

Doriat, Clemens, Dr.

Künstliche Intelligenz für die Qualitätssicherung

Industrie 4.0

Industrie 4.0 für die Qualitätssicherung

Folientechnik (IMD, IML, FIM, u.a.)

Digitale Transformation

Wirtschaft

Innovationen und neue Technologie

Verbundwerkstoffe / Werkstoffverbunde

Spritzgießmaschinen

Kunststoff-Recycling

Kunststoff-Aufbereitung

Organobleche (gewebeverstärkte Thermoplast-Halbzeuge)

Halbzeuge und Zwischenprodukte

Kunststoff-Halbzeuge

Ressourcenmanagement

Produktion

A Second Life for Plastics

Single-serve capsules as used, for example, for coffee, are a booming product in the packaging sector. The latest generation of capsules is injection molded and includes an integrated barrier layer to conserve flavor and aroma while saving material compared to alternative manufacturing processes. These complex injection molding parts are produced in high volumes by a Swiss company using Arburg machines.

Two-component injection molding: the single serve capsules conserve the coffee flavor and save material

Lapp Tec Employs Sustainable, Efficient Solutions for Barrier Capsules

Mehrkomponenten-Spritzgießen

Aroma-Tight and Cost-Effective

Once again, the K 2019 in Düsseldorf, Germany, lived up to its claim to be the leading trade show for plastics technology. At least in the field of injection molding, there were exciting global innovations to see – if you looked closely.

Fig. 1. Smart Operation – the machine is operated with only four buttons (© KraussMaffei)

Injection Molding Trends at K 2019

Schaumspritzgießen

Smart Factory

Energieeffizienz

Mikrospritzgießen

Spritzgießmaschinen, allgemein

Spritzgießwerkzeuge

Werkzeuge für die Kunststoffverarbeitung

Fließpressen

Handling, Handhabungstechnik für die spanende Fertigung

Automatisierungstechnik

Handling, Handhabungstechnik

Spritzgieß-Sonderverfahren

Spritzgießsimulation

Software

Simulation

Elastomer-Spritzgießen

Linearroboter für die Kunststoffverarbeitung

Industrieroboter

Montagetechnik

Industrie 4.0 für die Kunststoffverarbeitung

Montage-Spritzgießen

Knickarmroboter

Hybrid-Spritzgießen (Metall / Kunststoff)

Technical Excellence thanks  to Digital Assistance

The state of Upper Austria has recognised Engel Austria´s commitment to building up a circular economy for plastics with the Upper Austrian Environmental Award 2021.

State Councillor Stefan Kaineder (left) congratulating Engel‘s Vice President Marketing Ute Panzer and Günther Klammer, Vice President Recycling at Engel, on winning the State Environmental Award

Kreislaufwirtschaft

Engel´s Skinmelt Technologie Awarded

From their beginnings in the first half of the 20th century until today, polyolefins have taken a long and dynamic path of development and growth. The interactions between customers’ demands and technological developments have left a major mark on this path, and there is no end in sight to the trend. 

Looking Back: Two Centuries of Polyolefins 

Polypropylene (PP) appears to be in surprisingly good shape, even after the financial crisis. Demand for this versatile material has already reached the 2007 level. The greatest impetus for growth is at present coming from Asia. But investments in Europe continue to be worthwhile. New PP variants are increasing productivity, saving resources and giving the end product sought-after properties. 

Dynamic Recovery: Polypropylene (PP) – Part 1 

Low odor and emission long glass-fiber-reinforced PP compounds with excellent mechanical and processing properties are ideal materials for applications in automobile interiors. 

PP-LGF Compounds: Less Odor and Emissions 

Materials for packaging have been optimized for the benefit of customers in terms of savings potential and efficiency. With improved polyolefin grades, pipes can be produced in larger sizes with greater strength than before and their long-term stability can be validated in a very much shorter time. Nearly all producers are answering society’s call for reduced CO2 emissions by offering materials that allow material consumption to be cut, derive from renewable resources or are biodegradable/compostable. 

Polyethylen

Polystyrol

Polyvinylchlorid

Biokunststoffe

Commodity Plastics: Multilayered Development – Not Just in Films 

Contrary to classical surface properties such as scratch resistance or glossiness, it is far more difficult to quantify haptic characteristics. Nonetheless, surface properties with names like Soft Touch, Cool Touch or Silky Touch have gained increasing importance in the plastics industry during recent years. For this reason, a new testing method has been developed that is intended to make research and developments in surface quality more efficient. 

Oberflächentechnik

Surface Quality: Making Sure that Looks Are not Deceiving 

A recently developed polypropylene powder has widened the range of materials processed by laser sintering. This material has just entered the market, and enables processing on most types of usual laser sintering equipment, thus representing a real alternative product to the materials hitherto available for laser sintering at the market. In rapid prototyping, the powder can save certain groups of users the intermediate step of polyamide. 

Rapid Prototyping

Polypropylene Powder for Laser Sintering: A Compounder Breaking New Soil 

Sabic Polymers, Sittard, Netherlands, has introduced in Sabic PP Flowpact FPC 100 a new impact copolymer for its polypropylene series for thin-walled injection molding applications. The material has been developed specifically for the production of thin-wall containers for spreadable fats and packaging dairy products. 

Economical Food Packaging 

Sabic PP Flowpact FPC 100 

After the turbulence caused by the economic crisis, polypropylene is now safely back on the path to growth. Not only its high raw material and energy efficiency and associated good price/performance ratio have been responsible for this, but also a large number of new developments. The traditional cornerstones of the requirements profile – mechanics, optics and ease of processing – are increasingly being supplemented nowadays by demands for purity and freedom from emissions, for sustainability and recyclability. 

On the Path to Growth: Polypropylene (PP) 

Structure-property-relationships for Lightweight Parts Produced via Co-injection Molding and Foam Injection

In this work, foam injection molding is combined with the two-component co-injection molding process to produce hard-soft-combinations with TPS skin and a foamed polypropylene core.

In this work, foam injection molding is combined with the two-component co-injection molding process to produce hard-soft-combinations with TPS (thermoplastic elastomer based on SEBS) skin and a foamed polypropylene core. For the first time the potential for weight reduction of this highly integrated processing technology is analyzed by systematic evaluation of the part thickness and the physical blowing agent content.

Hard-soft combinations are of interest for numerous applications like handles or handholds in the automotive interieur. In this study foam injection molding is combined with co-injection molding to achieve two-component parts with a foamed core and a haptic skin. This highly integrated and efficient processing technology enables the manufacture of products with high potential for lightweight design. In contrast to the overmolding process (realized for example via turning table technology) a complete encapsulation of the core component by the skin component is possible.

Katharina Krause, Michelle Hartbauer, Thomas Neumeyer, Volker Altstädt;

Neue Materialien Bayreuth GmbH, Universität Bayreuth

Structure-property-relationships for Lightweight Parts Produced via Co-injection Molding and Foam Injection Molding

In this work, foam injection molding is combined with the two-component co-injection molding process to produce hard-soft-combinations with TPS (thermoplastic elastomer based on SEBS) skin and a foamed polypropylene core. Due to the fast solidification of the melt at the cavity wall, an increasing part thickness leads to an increasing foamable melt volume. Increasing the part thickness leads to a higher temperature for a longer time in the center of the part. Thus, for thicker parts, an extended period of time is available for the foaming process, contributing to a further weight reduction. Especially for high blowing agent (N2) contents of 0.70 %, the finger flow (non-uniform flow of the core melt into the skin melt) is clearly pronounced at the end of the core flow front, due to instabilities of the polymer flow. For the first time the potential for weight reduction of this highly integrated processing technology is analyzed by systematic evaluation of the part thickness and the physical blowing agent content.

Struktur-Eigenschafts-Beziehungen von Leichtbauteilen produziert durch Co-Injektion und Schaumspritzgießen

In dieser Arbeit werden die Prozesse Schaumspritzgießen und Co-Injektion vereint, um Hart-Weich-Verbunde aus TPS (Thermoplastisches Elastomer auf SEBS-Basis) und geschäumtem Polypropylen herzustellen. Da die Randschicht schnell an der Werkzeugwand einfriert, erhält man mit zunehmender Bauteildicke ein größeres Schmelzevolumen im Kern des Bauteils, welches aufgeschäumt werden kann. Die Temperatur in der Mitte des Bauteils liegt daher für einen längeren Zeitraum über der Erstarrungstemperatur. Somit steht bei höheren Bauteildicken ein längeres Zeitfenster für das Schäumen zur Verfügung und die Gewichtsreduktion kann gesteigert werden. Insbesondere bei hohem N2-Gehalt (0,70 %) ist der Fingerfluss (ungleichmäßiges Fließen der Kernschmelze in die Hautschmelze) am Ende der Kernfließfront deutlich ausgeprägt, was auf Instabilitäten des Polymerschmelzeflusses zurückzuführen ist. Erstmals wird das Potenzial zur Gewichtsreduzierung dieses hochintegrierten Prozesses durch systematische Auswertung des Einflusses von Bauteildicke und Treibmittelgehalt analysiert.

Structure-property-relationships for Lightweight Parts Produced via

Co-injection Molding and Foam Injection Molding

K. Krause, M. Hartbauer, T. Neumeyer, V. Altstädt

As soft component TPS (thermoplastic elastomer based on SEBS) is used in this study, due to its advantages in processability and its high compatibility to PP as core component. By a systematic variation of the skin / core volume ratio in the part, the potential for weight reduction by changing the part thickness is analyzed for the first time. In addition, the influence of the injected melt volume and the blowing agent content was studied. A maximum portion of the foamed core with homogeneous spread in the part as well as a fine-celled homogeneous foam morphology are targeted. As the skin component is a soft-touch material, it plays a minor role for the mechanical properties. For high specific (density-related) bending stiffness mainly the core component with its sandwich structure (foam core surrounded by a compact layer) is relevant.

In the process of foam injection molding, a blowing agent (supercritical fluid) is dissolved in the plastic melt in the plasticizing unit of the injection molding machine. As long as the melt in the cylinder of the injection molding unit is under pressure (up to approx. 200 bar), the blowing agent remains in solution. When the melt is injected into the mold, there is an abrupt drop in pressure to ambient pressure and the gas dissolves from the solution, causing the polymer to foam [1], see Figure 1. Cooling of the melt increases the viscosity of amorphous plastics, and in the case of semi-crystalline plastics, the plastic solidifies by crystallization and the foam cells are stabilized. In the foam injection molding process, the temperature control of ungleichmäßiges Fließen der Kernschmelze in die Hautschmelze the mold and the part thickness are decisive for the stabilization of the cells. The thermal conditions in the cavity lead to a sandwich structure, shown in Figure 2, consisting of compact outer layers and a large number of foam cells. Thus, with this process, foam injection molded parts with high specific bending stiffness and less material consumption can be produced [2–4]. Depending on the processing technology, raw material and component geometry, up to weight-70 % polymer can be saved [1,5–7].

Figure 2: Morphology of foam injection molded part

A major process-specific advantage of foam injection molding is the so-called internal holding pressure which is created by the volume expansion of the foaming melt. This pressure obsoletes the holding pressure applied by the injection molding machine and enables the production of parts with high wall thicknesses without sink marks. On the other hand, the pressure drop at the flow front causes premature outgassing, which leads to the typical surface defects known as silver streaks and swirls [8]. To overcome this obstacle, a second component can be used for coverage: foam injection molding is combined with an overmolding process. By using thermoplastic elastomers as second component, soft-touch properties can be achieved.

An alternative way of producing parts from two thermoplastic components is the co-injection process, which is the focus of this work. In the co-injection molding process, two melts are injected into a mold through the same gate [9].

The co-injection process can be subdivided firstly according to the injection (sequential or simultaneous) and secondly according to the processing technology. In sequential co-injection, the skin component is injected first. Then, the core material is injected into the cavity through the same gate and spreads within the skin component until the entire part is filled. This sub-form of co-injection can be carried out with all processing technologies. In simultaneous co-injection molding, a smooth transition between the skin and core components is realized by controlling shut-off nozzles. When differentiating by processing technology, one should mention co-injection using shut-off nozzles and the mono co-injection molding. The designation „mono“ indicates that both melts are injected through only one injection molding cylinder. This means that the materials are always injected one after the other (sequentially) and at the same cylinder temperature. The injection speed, on the other hand, can differ by setting an injection profile in the system control. The co-injection process is much more flexible when co-injection nozzles or co-injection intermediate plates are used, see Figure 3. In addition to sequential co-injection, simultaneous co-injection with smooth transition between the skin and core components is also possible by controlling the shut-off nozzles. With these two process variants, the process parameters can also be adapted more specifically to the two individual materials, since it is possible, for example, to select different cylinder temperatures for the skin and core components [9].

The quality (e.g. optical and mechanical properties) of co-injected parts is usually defined by the distribution of the core component in the skin component, which is directly influenced by the rheological and thermal properties of the melt as well as the compatibility of the individual components and the mold geometry. The most common defects are the breakthrough of the core component at the flow front and the instability of the interface between skin and core (formation of „finger flow“) [9,10].

The core content (vol.%) has the greatest influence on the material distribution in the resulting component. For simple geometries, a core content of up to 70% is achievable, while for complex geometries a core content of 30% is desirable [11]. In addition to the volume ratio, the processing parameters of co-injection molding also have a significant influence on the morphological structure of the component [12–14].

The viscosities of the skin and core materials used have a direct effect on the flow behavior and the formation of the skin/core structure [10]: if the shear rate dependant viscosity ratio ?core/?skin is too large, the core material remains only in the region close to the gate. If the viscosity ratio is too small, the core material tends to break through the skin material [15,16]. A desired and uniform thickness of the core material can only be achieved with a suitable viscosity ratio (e.g. between 0.5 and 2 [15,16,22]). In this work, co-injection molding is combined with foam injection molding. Relevant literature of this process combination is summarized hereafter.

Table 1 summarizes the available literature about co-injection molding with a foamed core. Skin and core component, as well as type of blowing agent and main findings are listed.

Higher specific bending stiffness compared to foam injection molded part

Fine-celled foam morphology (by adding chemical blowing agent as nucleating agent) realizable

Only minor effects of chemical blowing agent on skin/core-structure: longer core flow path when adding blowing agent (compared to compact injection molding).

No change in viscosity detectable in online viscosimeter.

Optimized surface quality and 13 – 25 % higher tensile strength compared to foamed specimens without skin layer

02012023_ NEUKunststofftechnik.pdf

01012023_FIN-348 Krause

Authors Katharina Krause, Michelle Hartbauer, Thomas Neumeyer, Volker Altstädt; Neue Materialien Bayreuth GmbH, Universität Bayreuth

Published in Zeitschrift Kunststofftechnik / Journal of Plastics Technology, 01/2023, page: 27– 51 © Carl Hanser Verlag GmbH & Co. KG ISSN 1864 – 2217