Simultaneous extrusion of polyvinyl chloride profiles with a PS foam core is challenging due to the different processing conditions and has not been performed before. A trial plant for researching this process has now been set up at the SKZ.

Fig. 1. The foaming of PS was investigated in a test system developed for this purpose 

Method for the Simultaneous Extrusion of Window Profiles with a Foam Core

Extrusion

Kunststoffverarbeitung: Verfahren

Schaumstoffe und Vorprodukte

Kunststoff Werkstoffe

PVC-Profile

Halbzeuge und Zwischenprodukte

Kunststoff-Halbzeuge

Schaumstoffe

Polystyrol

Thermoplaste

Polyvinylchlorid

Dichtungsschäumen

Schäumen / Reaktive Verarbeitung

Rohr- und Profilextrusion

Foamed and Still Extruded  in One Step

Before the direct extrusion of profiles made of polyvinyl chloride was developed, it was previously necessary to produce a dry blend. This process is expensive and energy-intensive and, in contrast to direct extrusion, discontinuous. The direct extrusion of PVC using planetary roller extruders promises an improvement. In addition to soft PVC, rigid PVC can also be processed in this way with a few adjustments.

The direct extrusion of PVC profiles on planetary roller extruders can save costs and energy and simplify the process

Extrusion of Rigid PVC without Dry Blend Production

Kunststoff-Profile

Granulat, PVC- (Compound)

Andere Werkstoffe

Werkstoffe für additive Verfahren

Kunststoff

Bauwesen

Baustoffe

Extrusionsanlagen

Kunststoffverarbeitung: Maschinen und Komponenten

Direct Route to the PVC Profile

Electromobility in particular, but also many other electrical applications, are asking for ever higher demands regarding the electrical properties of thermoplastics. This raises the question of whether the polymers commonly used in this area can still meet these demands. The plastics manufacturer, Lanxess, has now investigated how suitable, for example, polyamide and polybutylene terephthalate are for use at higher voltages and temperatures.

16:9

How Suitable Are PA and PBT for High-Voltage Applications?

Polybutylenterephthalat

Elektronik

Elektromobilität

Mobilität

Polyamide

Leistungselektronik

Technische Kunststoffe

Against the Current

DSM sells its Engineering Polymers business to Lanxess and the financial investor Advent. In return, the two companies are setting up a joint venture to which Lanxess is also contributing its PA and PBT business.

Lanxess is outsourcing its engineering plastics business to the joint venture.

Streifinger, Florian

Wirtschaft

Lanxess and Advent to Buy DSM‘s Engineering Plastics Business

A focal point of the Lanxess booth at the show this year will be materials for electromobility.

The demonstrator of a near-series- production housing for electric vehicle batteries is one of the highlights at  the Lanxess booth.

Messe K-Kunststoffmesse

kunststoffe-international.com

kunststoffe.de

Demonstrator for EV Battery Housings

The global market for PBT has recovered well from the aftermath of the corona pandemic. However, there is a lot going on among manufacturers at the moment.

PBT compounds are very much in demand for electromobility, including for parts of the battery, electric transmission and the charging infrastructure.

Polybutylene Terephthalate (PBT): Demand for Products with Added Benefits

Electromobility and Sustainability Are Driving Growth

Production of PVC pipe in Bitterfeld, Germany, in 1935 ushered in the use of plastics for pipe production. This required exact knowledge of material properties, life expectancy and permissible loads. This was recognized from the very beginning and pursued systematically. 

Qualitätsnachweise

Looking Back: Materials for Pipes – Meeting Changing Requirements 

After a few selective modifications, the production of PVC-based WPC dryblends in a heating-cooling mixer and the subsequent processing to form profiles can be copied from PVC processing. Attention has to be paid, however, to the influences of formulation, process technology and process parameters during the production of the mixture. 

Verbundwerkstoffe / Werkstoffverbunde

Wood Plastic Composites (WPC): From the Formulation to the Finished Product 

PA66 and PBT considerably expand the field of applications for laser sintering by showing better properties than classic PA11 and PA12 materials in most cases.

As a temperature-resistant and flame-retardant material with high mechanical properties, PA66 opens up new application possibilities for laser sintering, such as its use as a sensor holder

PA66 and PBT for Laser Sintering

Selektives Lasersintern von Kunststoff, Metall, Keramik

Verfahren für die additive Fertigung

Pulverbettverfahren

Additive Fertigung

From Injection Molding to  Additive Manufacturing

Alternative powertrains, autonomous driving and the urge for more sustainability impact the vehicle design and driving experience.

 The USB connector system enables space saving of up to 60 %. The used PBT allows tight tolerances regardless of the ambient conditions.

Kfz-Elektronik

Steckverbinder

Elektromechanik

Smaller, Faster, Lighter

Biogasoline fuels such as E10 and improved fuel injection systems to reduce consumption have changed the specifications for gasoline fuel lines. As a result, extractables from conventional components of the fuel system can clog injection nozzles in individual cases and lead to critical situations. To eliminate this, new low-extractable multilayer tubes for fuel lines were developed. 

Development, Testing and Processing Low-Extractable Multilayer Tubes for Fuel Lines 

Beschichten von Kunststoffen

Purity Requirements for Fuel Lines 

Manufacturers of standard extruders sometimes incorporate oversized drives into their machine designs in order to be able to cover a wide range of requirements. In times of high energy prices, however, this is no longer economical. An extruder should be equipped with a drive package that is matched to the gearbox and the processing unit. But what are the requirements governing the design of the drive system?

Drives on the test bench: this type of motor test bench is used by Veka to collect experience about the operation of some 700 twin-screw extruders and 300 single-screw extruders used in production facilities worldwide at the most favorable operating point

Process-Oriented Design of the Main Drive for the Extruder

Elektrische Antriebe

Antriebe

Flachfolien- und Plattenextrusion

Extruder

Ingenieurwissenschaften

Elektrotechnik

Energieeffizienz

Energy-Efficient Use of Drives

New polymer composites for the production of multi-layer small tubes are being developed to give products specific functions. With suitable co-extrusion dies and a thermal barrier option, even complex layer composites with melt temperature differences of more than 50 °C can be processed reliably and in high quality.

CV-T 5-layer co-extrusion die in pilot plant operation: tubes with small cross-sections that fulfill a multitude of demands can be produced by  co-extrusion

Combining Polymers with Very Different Processing Temperatures

Temperiergeräte

Gießanlagen

Temperiertechnik

Baugewerbe (Hoch- und Tiefbau)

Medizintechnik (KU)

Kunststoffverarbeitung

Bautechnik, Sanitär

Extrusionswerkzeuge

Werkzeuge für die Kunststoffverarbeitung

Extruder-Folgeeinrichtungen

Extrusions-Zubehör

Automotive

Fahrzeugbau

Co-Extrusion with Thermal Control

In the area of pipe and profile extrusion, the focus remains on increasing efficiency. In addition to energy-saving systems, the focus on efficiency increasingly includes flexibilization of plants and processes, as well as reproducibility of quality in production.

Optimization of Components and Expansion of Plant Control Systems Offer Potential  for Improvement

Kreislaufwirtschaft

Efficiency Remains the Order of the Day

Enhancing mixed bottle flakes by turning them into extrudable recycled crystalline polyethylene terephthalate (rCPET) was the goal of a joint development project looking to close the gap in the PET recycling system. By successfully producing a sheet made from recycled material suitable for high-quality applications such as thermoformed food trays, Gneuss, Sukano and Illig have demonstrated that this approach is indeed possible.

Thermally stable rCPET food trays made from multicolor APET bottle flakes

Upcycling of Mixed APET Bottle Flakes into Thermally Stable rCPET Food Trays

Farbstoffe und Pigmente

Additive

Schmelzefilter

Kunststoff-Aufbereitung

Anlagen Lebensmittel

Anlagen für die Additive Fertigung

Anlagen Additive Fertigung / 3D-Druck, andere

Filteranlagen

Farbstoffe

Flakes

Kunststoff-Rezyklat

Kunststoff-Recycling

PET: From A to C

Co-Extrusion of PVC with Modified PBT Blend Improves Profile Mechanics

Profiles made of rigid PVC have many advantages: they are easily extrudable, inexpensive, and with suitable additives, they exhibit good UV resistance. However, regarding its mechanical and thermal properties, PVC occasionally reaches its limits. This shortcoming can be evaded by co-extrusion with a PBT blend.

PVC is widely used for extruded profiles. Typical applications are the profiles for windows, roller blinds, cable ducts, and other technical products. But in a few cases, the mechanical and thermal properties of PVC are inadequate for certain applications. A possible solution is to stiffen the profiles with metal. However, it would be preferable to find a material that combines the positive properties of PVC in terms of extrudability, UV resistance, weldability, flexibility in profile design, and costs with the outstanding mechanical properties of a highly reinforced technical plastic.

This can be achieved by co-extruding PVC with technical plastics. Previously, this was not possible, because the processing temperatures of technical plastics are significantly higher than those of PVC. Consequently, both polymers could not be guided simultaneously through a mold as a melt.

Therefore, BASF developed a new material: Ultradur B4040 G11 HMG HP. Ultradur is the company’s trade name for a partially crystalline thermoplastic polyester based on polybutylene terephthalate (PBT). PBT is an established material for high-grade and highly stressed technical components in numerous industrial fields. Apart from its very good thermal stability, low moisture absorption, and good resistance to many chemicals, PBT features high stiffness. The melting point of PBT is usually 223 °C. However, the melting point of the material developed by BASF is 198 °C and therefore 25 °C lower. This permits co-extrusion with PVC in the classical processing window, thereby opening up a new, very interesting application area.

Customized Melting Point plus  High Stiffness

Aim of the development was a product that offers very high stiffness in addition to the customized melting point. A high elastic modulus and a low coefficient of expansion are required to meet the properties necessary for the profile. Thanks to a specific PBT blend plus a 55 % proportion of chopped glass fibers by weight, the required properties were achieved.

Frequently, the mechanical and thermal limits of PVC are as follows:

<ul><li>Post-shrinkage, as soon as the material is heated once above 60 °C – in case of one-sided heating, this leads to a permanent curvature of the profile.</li><li> High thermal expansion coefficient – with uneven temperature distribution, this also results in curvature.</li><li> Temperature-dependent stiffness (elastic modulus) – even with slightly increased temperatures, the elastic modulus of PVC drops strongly.</li><li>Creep tendency of the material.</li></ul>

The properties of classical rigid PVC and the newly developed Ultradur type are compared in Table 1. The values for stiffness and tensile strength were measured on injection-molded samples acc. to ISO 527. Extrusion results in lower values, because the fibers are less aligned in the manufactured product. However, a well-designed mold permits 70 % of the initial value to be achieved.

In the co-extruded product, PVC and PBT with their respective cross sections jointly dissipate the mechanical or thermal loads, whereby PBT frequently dominates. This is illustrated very well by analyses of the remaining post-shrinkage of different profiles. For this, pure PVC profiles, pure PBT profiles, and co-extruded hybrid profiles were examined. Hereby, the temperature was maintained at 50 °C for 16 hours, and then reduced to 23 °C, and the remaining shrinkage measured. Subsequently, the cycle was repeated with the profiles, but with increasingly higher holding temperatures up to max. 100 °C (Fig. 1).

The PVC profile exhibits very strong post-shrinkage of up to 1.2 %. With a value of 0.015 %, post-shrinkage of the pure PBT profile across the entire temperature range is comparatively low. At maximum temperature, the co-extruded profile exhibits a shrinkage of just 0.13 %, which is considerably lower than that of the pure PVC profile. This clearly improved behavior of co-extruded profiles can be used to notably reduce permanent curvatures, for example in dark window frames subjected to intensive solar radiation, without resorting to a metal insert. Similarly, the co-extrusion with PBT also reduces the longitudinal thermal expansion of PVC significantly, as well as a possibly resulting curvature.

Processing with Single-Screw or  Twin-Screw Extruders?

The PBT developed by BASF for this purpose can be processed in both mono and co-extrusion. Important for processing is a low moisture content, which should lie below 0.03 %. If the value is higher, e.g. with open containers, pre-drying of the material is recommended. Among the different drying systems, the dry-air drier has proved to be superior, both technically and economically. Typical drying times are two to four hours at 80 to 120 °C.

Single-screw extruders as well as counter-rotating twin-screw extruders can be used for processing Ultradur. With single-screw extruders, single-flight, three-zone shallow screws with a length of 22 to 25 D should preferably be used. Hereby, a compression ratio between 2.5 and 3 is recommended. The compression zone length should be about 4 to 5 D. Barrier screws and shearing/mixing devices are less advisable, because they can damage the glass fibers. Single-screw extruders should be of the flat-bore type without a grooved bush. A melt temperature range of 210 to 220 °C should be aimed for, with a moderate screw speed as far as possible.

Counter-rotating twin-screw extruders, both parallel and conical, are the preferred choice in the PVC industry. They are also suitable for processing PBT. Disadvantageous is the higher purchasing price compared with single-screw extruders. But the frequently present degassing and pressure build-up (chamber feeding) can be advantageous. Suitable wear protection (barrel and screw) should be observed with single as well as twin-screw extruders. As with all glass fiber-reinforced polymers, processing of Ultradur requires that shear is kept as low as possible to prevent the glass fibers being damaged or shortened. The challenge hereby is to ensure complete melting of the material at the lowest possible temperature, so that the PVC is not affected negatively during convergence. The temperatures in the co-extrusion mold must be selected so that the PBT can flow without freezing, while preventing damage to the PVC at the same time.

A good mold, combined with a functioning extrusion process, must ensure the following properties:

<ul><li>effective implementation of the PBT’s mechanical properties (suitable positions and cross sections),</li><li> high forward orientation of the glass fibers in the PBT – this leads to a high elastic modulus, higher strength, a lower expansion coefficient, and even lower creep behavior,</li><li>specified wall thicknesses in all areas of the geometry,</li><li>no curvature of the extruded profile,</li><li>high haul-off speed,</li><li>permanent serviceability, and</li><li>plannable time from ordering to delivery of the molds.</li></ul>

However, the development requires more expertise than for classical co-extrusion molds, which are mostly used to process materials with comparable properties.

In the present case, the flow channels in the mold must be designed for two materials with different flow behaviors (PVC: wall slippage, PBT: wall adherence). The two materials also differ in viscosity and velocity profile in the channel.

Moreover, it is advantageous if the glass fibers are shortened as little as possible, and have a maximum forward orientation. After all, the PBT should freeze in a suitable position.

During mold design, it must be taken into account that PVC tends to swell considerably. If possible, the thickness of the Ultradur profile should not be less than 1.5 mm, to minimize glass fiber damage.

Several molds for this material combination have already been developed and are in series production. Greiner Extrusion, an Austrian mold maker, has already built several successful molds.

Weldability of Co-Extruded  Profiles Ensured

In some applications, e.g. for PVC widow frames, the profiles are cut at a 45° angle and then welded. Simultaneous welding is also possible with co-extruded profiles made of PVC and Ultradur, because both materials can be processed in the same temperature window. To obtain high strength, it must be ensured that PVC butts against PVC, i.e. there is no PBT melt in between. Due to the glass fibers in Ultradur, a higher wear of welding foil has been observed during butt welding. However, the cycle time remains practically the same.

Recycling: Easy Separation of PVC  and PBT

Recycling is gaining in importance, and has become firmly established in the PVC window frame industry for years. Also co-extruded profiles made of PVC and PBT can be recycled easily. Hereby, the coloring of the plastics is helpful during treatment. Ultradur B4040 G11 HMG HP is available in a non-colored and in a green-tinted version, which simplifies sorting of the window frame profiles in the recycling procedure at the end of their service life.

After the profile has been disintegrated into small particles in a mill, Ultradur can be separated from the PVC using different methods. This works most effectively with color sorters, because other green-colored plastics are not used in the window making business. In case of similar coloration of PVC and Ultradur, use of an NIR sorter or an electrostatic sorter is possible. Should traces of Ultradur remain in the PVC, these can be removed by means of a melt filtration. Subsequently, the recycled PVC and Ultradur fractions can be reused. Their recyclability has been confirmed in plants that are customary in the industry.

If a PVC profile does not meet the mechanical requirements, co-extrusion with Ultradur B4040 G11 HMG HP can be an intelligent alternative. This is shown by various application examples developed jointly with BASF (Figs. 2, 3, and 4). Other possible applications are folding shutters, roller blinds and their housings, gutters, fence and balcony profiles, house cladding panels, and rods for agricultural use.

BASF SE  

https://www.basf.com

Ausgabenartikel

Fig. 1. Permanent post-shrinkage of profiles made of rigid PVC and the PBT Ultradur from BASF, as well as hybrid profiles of PVC and PBT after heating to a certain temperature: shrinkage of hybrid profiles is significantly lower than with pure PVC profiles. On average, the measured hybrid profiles contain about 18 % PBT.

If the properties of pure PVC profiles are inadequate, PBT co-extruded versions are an option. For example, their thermal expansion and post-shrinkage when heated are lower.

Table 1. Properties of a classical rigid PVC and an Ultradur PBT type.

Fig. 3. Ultradur B4040 G11 HMG HP can be used instead of steel to stiffen rigid PVC profiles. The result is a lower permanent deflection after one-sided heating. Moreover, thermal conductance is reduced. This permits large, energy-saving windows, also with dark-colored profiles.

Fig. 4. Door profile of a chest freezer: hereby, Ultradur replaces a metal stiffener, which eliminates the need for an electrical heater in the profile to prevent condensate formation on the outer surface. This improves the freezer’s energy efficiency.

Fig. 2. This co-extruded profile replaces a steel profile in certain window frames. The lower thermal conductance increases the energy efficiency.

KUint1_BASF_Brockmüller - Hauptartikel

Dr. Wenke Wollny works for BASF in product development in the PBT field.

Dr. Norbert Effen is specialist for extrusion, compounding, and screws, and works for BASF in the technical plastics field.

Dr. Kay Brockmüller supports BASF customers in the development of new applications; <a href="mailto:kay.brockmueller@basf.com">kay.brockmueller@basf.com</a>