There’s a lot going on with the plastics manufacturers. At the end of May, DSM sold off its engineering plastics division to a joint venture of Lanxess and the private equity investor Advent for EUR 3.7 billion. The Dutch company is thus retreating completely from the plastics arena. This sale is the last step in DSM’s restructuring. It was only in April that it divested its fibers business, which went to Avient. The coatings division had already been sold to Covestro in 2020. In the future, DSM wants to concentrate entirely on medical, food and bio technologies.

This transaction is the second big coup in the field of engineering plastics this year. In February, DuPont sold his business unit to its competitor Celanese for USD 11 billion. And the consolidations in this field could continue. Since, even though Lanxess is now acting as a purchaser in the DSM deal, it is not yet clear that the chemical group will continue to produce engineering plastics in the long term. Some parameters of the purchase sound more like a farewell. For example, Lanxess is contributing its own PA and PBT business to the joint venture with Advent, but only retaining a minority shareholding. And Lanxess has the option to sell its shares completely to Advent after three years. Moreover, the company has invested strongly in other chemical sectors in recent years. Lanxess CEO Matthias Zachert wants to reduce the Group’s dependency on economic fluctuations.

In this regard, the automotive industry has been a thorn in the plastic manufacturers’ side in recent times. The auto manufacturers’ weak sales figures have posed particular problems for manufacturers of engineering plastics. After all, the auto industry is one of their biggest markets. In addition, there is also uncertainty due to the shift toward electromobility. That makes the market for technical plastics even more unpredictable. Too unpredictable for Lanxess? In three years’ time, we will know more.

Florian Streifinger [<a href="mailto:Florian.Streifinger@hanser.de">Florian.Streifinger@hanser.de</a>]

16:9

Editorial Streifinger

Streifinger, Florian

The REACH regulation on chemicals is intended to ensure a high level of protection for human health and the environment. Since it came into force, many substances previously used to clean production equipment have been reclassified.

The REACH regulation on chemicals is intended to ensure a high level of protection for human health and the environment. Since it came into force, many substances previously used to clean production equipment have been reclassified. Companies are now required to replace products that are hazardous to employees with environmentally and user-friendly alternatives. Färber & Schmid presents a number of substitutes for the “stalwarts” among solvents. The first part of this two-part series focuses on the cleaning equipment used in PUR processing.

The processing of polyurethane and of resin systems are two particular areas in which NMP (n-methylpyrrolidone), NEP (n-ethylpyrrolidone), DMF (dimethylformamide) and methylene chloride are still occasionally employed as solvents, although they pose a risk to the health of employees. Foremost among these are the cleaning of molds used in the production of molded PUR parts, purging of dosing lines or mixing-and-dosing heads in 2-component systems and the cleaning of encapsulation systems. But solvents are also used in the production of polymer dispersions and adhesives as well as in their removal.

As a result of increasing technical requirements, stricter environmental protection requirements and regulatory provisions, solutions to the various challenges are needed. In most cases, the necessary cleaning work is carried out manually, with brushes, paintbrushes and similar equipment on open and, above all, heated molds or in open production containers and tanks. Work personnel are thus directly exposed to these substances through inhalation, odor and possibly skin contact. Cleaning of closed systems, such as the purging of mixing-and-dosing heads, is somewhat less critical in terms of workplace health and safety. Nevertheless, the same restrictions apply here as for “open” applications. Given the increasingly narrower classifications and labeling of established solvents under REACH, many users and processors are looking for functional alternatives.

Aside from technical functionality, the lowest-possible toxicity, best-possible environmental properties and positive workplace factors are usually at the forefront of this realignment. Färber & Schmid offers a range of cleaning products that serve as alternatives to the critical substances.

These newly developed products offer a price-performance profile comparable to that of established solvents. In many cases, they have already passed their first field tests. In this first part of a series of articles, we look at replacements for NMP, NEP and DMF.

A production company that manufactures polyurethane foam for numerous automotive applications as well as polyurethane elastomers by the hot casting process was using NMP to clean all its molds, hose lines, and containers for prepolymers. While mold cleaning usually involves removing residues of release agent, which in combination with cured isocyanates and polyols usually forms stubborn deposits under pressure and temperature during production, the purging of hose lines and containers for prepolymers calls for a purging agent that has high dissolving power but does not trigger a reaction of the isocyanate-functional compounds. For a long time, the company had been looking for alternatives that were not classified as toxic to the unborn child and that met the technical requirements in a comparable way to NMP. After the customer had described his specific requirements, two suitable products were recommended: Resin-Clean EXP-10/70 and Resin-Clean EXP-10/100. The latter is an aprotic cleaner that has no free OH groups and is therefore ideal for removing reactive premixes. Having passed an initial laboratory test, it underwent production trials under real conditions. The test phase was successful, the results were positive and met with approval, and now the two products are being used to great effect to clean all the machines and mold, at comparable cost and without endangering employees.

Cleaning Mold Parts Overnight in a Bath of Resin-Clean– without NEP

A manufacturer that makes parts for machinery making, special vehicle construction and conveyor technology with its own polyurethane elastomer formulations and Vulkollan had for some time been seeking a suitable replacement product capable of removing stubborn release agent residues. Hot casting of polyurethane elastomers is particularly prone to deposition of release agent residues on the mold surface and these are very difficult to remove because of the high temperatures involved. In the past, a NEP-based cleaner had been used for this. However, as a result of the reclassification of NEP under REACH, the previous supplier had developed a new NEP-free cleaner which it offered as an alternative. Since the molds are generally cleaned cold after production and the new cleaning product failed to match the performance of its predecessor, the production team was very keen to reinstate the latter. This unsatisfactory situation soon led the customer to join the F&S application specialist in testing some cleaning products on site. A few quick tests followed by long-term trials revealed that the product was ideally suited. The company now uses Resin-Clean EXP-3/M-V2, which possesses extremely high dissolving power, especially at room temperature. The customer has purchased a suitable container for soaking the mold parts in the cleaning product overnight. When time is of the essence, manually brushing the parts with the product is an effective way to clean them.

Replacement for DMF: New Purging Agent for Mixing Heads

A company that manufactures seals of all kinds and molded PUR parts made with Vulkollan and Baytec had, until recently, been purging its mixing heads with the questionable solvent DMF. Toxicological concerns led to the testing of several alternatives, with Resin-Clean HPT-PU 05 ultimately emerging as the product of choice. As the purging agent has since proven itself over the long term and does not require labelling, a line in a newly constructed building at a different location will now also be equipped with the new purging agent.

A lack of viable alternatives has meant that DMF is still in use as a solvent today, especially for the cleaning of rolls in the laminating industry. Since DMF is classified as both acutely toxic and toxic to the unborn child, it poses significant problems for the user in terms of employee health and safety and environmental protection.

In collaboration with a user and a supplier in the textile industry, Färber & Schmid devised a solution for cleaning laminating rolls. The adhesives employed in the laminating process are often exposed to very high thermal stresses that give rise to very stubborn and burnt-in contaminants on the roll. The customer specified that he wanted to be able to dissolve and remove these contaminants with a user-friendly product at room temperature.

The special cleaner Solvetan that was developed for this purpose met the specification in full and impressed the customer over the course of extensive practical tests. Since then, Solvetan has been used to clean flame-laminating rolls and also to remove liquid PUR adhesives in the daily production process.

Tailored Solvents: Adapting to Customer Requirements

The products listed in these practical examples and the products shown in the table are merely a selection of the various options for dissolving and cleaning PUR and other polymer systems. If required, products can be custom developed and manufactured for specific applications. The competitive advantage of customized development products lies in the scope for freely adjusting certain physico-chemical parameters. As a result, even the most stringent requirements imposed on toxicology, ecology, application technology and economy can be targeted. The cleaning products can be used at both ambient and elevated temperatures. Very large parts, with upright mold walls which cannot be immersed, can be treated with thickened (viscous) cleaning products and solvents that cling to them and are highly efficacious. Aside from replacements for the solvents named above, environmentally friendly alternatives to acetone and MEK are also available.

The upper part of the table lists the solvents frequently used in the past while the lower part shows the new substitutes.

This mixing head in PUR production was changed from DMF to a purging agent not subject to labeling requirements..

Name - Hauptartikel

Dipl.-Ing. Holger Schlüter is Head of Division at Färber & Schmid GmbH.

Part two of the series covers replacing methylene chloride and acetone and removing isocyanate and will appear in Kunststoffe international 6/2022.

Read the German version of the article in our magazine Kunststoffe or at <a href="https://www.kunststoffe.de/a/fachartikel/ersatz-von-problemloesemitteln-2044576" target="_blank">www.kunststoffe.de</a>

Werkzeugreinigung, Kunststoffe

Kunststoffverarbeitung: Maschinen und Komponenten

Werkzeuge für die Kunststoffverarbeitung

Reinigung

Betriebsausrüstung / Betriebsmittel

Flame Retardant Polyamides for Electronics

Electrical equipment manufacturers place great importance on representing their brand through a specific color design. This applies to all visible components.

Electrical equipment manufacturers place great importance on representing their brand through a specific color design. This applies to all visible components. However, these do not only have to be visually convincing, but above all, be convincing in terms of mechanical properties and resistance to fire.

The so-called “corporate branding” poses new challenges for the manufacturers of molding compounds for applications in electrical engineering. In addition to signal properties (such as for the switching states ON and OFF), colors should also signal warnings, hazardous areas, or display shutdown options. For example, every emergency stop command element must be reliably recognizable through its red-yellow color scheme – worldwide, in challenging environments and after decades of use.

In addition, there is often the requirement to individually label molded parts with different laser systems. This may require special additives, which in turn may have a retroactive effect on other properties of the final compound. Filling and reinforcing materials of the plastic additionally affect the ability to mark it. The variations possible are limited by the international approvals of the molding compounds – the permissible additive load and an „infrared spectroscopic fingerprint“ of a material stored at licensing organizations set tight limits here.

In order to color fire-protected materials, it requires a thorough understanding of the intrinsic colors of base polymers and fire retardants and also of the colorants. Ascend Performance Materials has a wide portfolio of polyamide materials and color formulas available: From non-fire-protected, standard colored materials to high glass fiber-reinforced compounds in customized coloring, even for low wall thickness. The possible flame retardants range provides cost-effective products with limited performance to additives with capabilities justifying a higher expense.

Electrical appliances have not just been light grey or black for a long time now. Most customers generally closely specify “light grey”. Permissible color deviations are often limited to ΔE ≤ 1.0. This tolerance must be carefully observed across the individual deliveries. Ascend produces well over 100 different color-type combinations (Fig. 1) in the area of grey colors alone. Due to the potentially changing intrinsic color of the base polymer and the different intrinsic colors of different flame-retardant batches, it is essential to be able to readjust the so-called color location over the entire manufacturing process – depending on the production quantity for several hours or even days. Figure 2 shows the color deviations over several production campaigns of a specific color setting over a period of nine months. For such sophisticated compounds, Ascend relies on powder colorants, which allow a rapid color adjustment within the ongoing production process.

The RAL “Classic” color palette includes over 200 different colors between “white” and “black”. Consequently, Ascend produces about 100 white colorations on an ongoing basis, and new ones are constantly added, either to adjust to customer-specific initial colors or, for example, to adjust the color stability for defined thermal profiles throughout different timeframes. These adaptations must neither impair the ignition behavior nor the resistance to fire of the respective molding compound. With applications for the electric power supply of vehicles, orange has established itself as a signal color. Since the signal effect must be ensured until the end of “vehicle life”, the manufacturers demand proof of color stability even after a long-lasting temperature stress. Figure 3 shows the results of a temperature storage test of an unreinforced flame-retardant type with different additive formulations.

The range of flame retardants (FR) used in polyamides ranges from nitrogen-based products to organic phosphorus compounds to red phosphorus (RP). Often times, it is also not possible to avoid relying on halogen-containing FRs.

The fire behavior of solid, non-foamed plastics in so-called “small applications” is often grouped into different performance classes in accordance with the requirements of UL 94. Here, “HB” describes a non-fire-protected material, whereas a material that meets the requirements of class “V-0/5VA” has passed a test with a 500 watt gas burner, among other things.

While FRs based on nitrogen and organic phosphorus compounds are color neutral, products with red phosphorus can only be produced in dark red, which is characteristic of red phosphorus, or in dark grey/black colors.

The different flame retardants are incorporated into the compound at concentrations between about 5 and 25 percent by weight, which affects the material properties more or less significantly, depending on the FR type. An example: The stiffness of a Polyamide reinforced with 25 % glass fibers is reduced by more than 30 % as a result of moisture absorption. Whereas in a brightly colored, fire-protected version only by less than 20 %. Color formulations that are not ideally selected may have additional–in some cases significantly negative– effect on the compound properties here.

Ascend offers the entire range of flame retardants suitable for Polyamides in technical applications in the various types of the “Starflam” product range (Fig. 4). The ideal balance between the various requirements must be established through close communication between the customer and the molding compound manufacturer. Here, too, the use of powder-shaped input materials expands the possible variations. The advantages and limitations of various flame retardants are shown in Figure 5.

Frequently, molded parts made from fire-protected molding compounds are used to manufacture applications which are later used in the scope of the regulations of Underwriters Laboratories (UL). In this case, the characteristic properties of the respective formulation are stored at UL and the variation possibilities of the molding compound manufacturer are extremely limited.

As is so common, the benefits of powder input materials must be “bought” in the color adjustment through compromises elsewhere: Dosing the relatively small amounts of required formulation components is more complex and cleaning the systems is more labor-intensive than, for example, using color concentrates (“Colorant Masterbatches”). It can be more attractive for customers to secure lower-cost solutions with compromising color consistency by using batches.

Functional additives and colorants may significantly affect the electrical properties of a molding compound. For example, the Comparative Tracking Index (determined according to IEC 60 112) is a integral characteristic for dimensioning geometric distances in electrical devices. The use of unsuitable additives may reduce the Tracking Resistance and consequently the Comparative figure of creep path formation (CTI) of a molding compound to such an extent that a given design no longer meets the relevant standards. In such a case, the manufacturer of a device may face significant liability. Additives with a negative influence on the Comparative Tracking Index can be, for example, flame retardants or their synergists, or also compounds used to increase the contrast in the laser markability of plastics.

The production of flame-retardant molding compounds is concentrated in the Fosses plant (France). Among others, an in-house laser laboratory enables the targeted optimization of the laser markability of custom colors, while the simultaneous monitoring of the other properties that are critical for the respective application ensures the required overall performance. This includes, for example, incorporated lubricants used to minimize friction and the resulting wear. Ascend uses the entire range of additives provided by the upstream industry to offer molding compounds with the desired property profiles. With the acquisition of Poliblend (Mozzate, Italy), competence and capacity were acquired to be able to supply such formulations, some of which are customer-specific, in small and large quantities.

Use of Radiation Crosslinkable  Materials

Molding compounds produced with a special chemical can be crosslinked molecularly by means of radiation through electrons (“beta radiation”) or electromagnetic waves (“gamma radiation”). This significantly affects the properties of polymers.

Molded parts made of radiation crosslinkable materials will no longer melt after radiation crosslinking. While the strength and toughness typical for polyamide is retained, the original melting point is eliminated. While Polyamide 66 melts at 260 °C, cross-linked polyamides retain their shape for several minutes even at temperatures well above 300 °C. Such temperature peaks occur, for example, in electrical switching devices. When currents are switched off, light arcs are created, with temperatures reaching several thousand degrees. Such light arcs are appearing in for example industrial switching devices or in DC-power circuits of electrically-driven motor vehicles.

Traditionally, such temperatures could only be handled with thermoset materials, which in turn require numerous compromises. The list is by no means complete, and can include high wall thicknesses, long curing and thus long cycle times, deburring, limited ductility and high wear on moving parts.

Radiation-crosslinked Polyamides can also substitute thermosets for applications in metal welding systems in where plastic parts are required to withstand metal particles having >100 °C. Particularly for molded parts with small dimensions required to resist repeated temperature peaks, radiation crosslinkable Polyamides (according to the standard ISO 1043, marked by an “-X” after the molding compound designation) can offertheir advantages.

In addition to increasing the peak temperature resistance, radiation crosslinking also brings significant improvements in creepage and friction behavior. Ascend’s range of crosslinkable compounds extends here from unreinforced material to highly glass fiber-reinforced, halogen-free, fire-protected molding compounds. These products can also be colored according to customer specifications. From the “stable” color, which does not change due to the irradiation, to the formulation with targeted color change, various customer requests can be achieved. The UL recognition, of course, is maintained even after the crosslinking process.

Test with an 850 °C hot glow wire on a switching device: If a fault in the connection of an electrical device causes a cable to become overheated, for example, then a potential flame must extinguish by itself.

Fig. 1. A very small selection from the  range of constantly produced grey tones for electrical applications.

Fig. 2. Color variations for various production campaigns of a flame retarded PA66 compound.

Fig. 3. Sample body in orange color after temperature storage test.

Fig. 4. Overview of flame retardants in polyamide molding compounds.

Fig. 5. Advantages and restrictions of various flame retardants.

Ascend - KU 2022-07 - Special

Thilo Hindert has been in charge of the electrical applications at Ascend Performance Materials since 2020 as an Application Development Engineer.

Ascend Performance Materials is one of the world’s largest fully backwards-integrated Polyamide 66 manufacturers. Headquartered in Houston/Texas, with three production sites in Europe (Netherlands, France, and Italy), it allows for serving customers from a wide range of industries with high-volume standard materials as well as with customized compounds based on PA6 and PA66. PA6.10 and PA6.12 compounds are manufactured under the brand name HiDura. With several acquisitions over the past two years, the company is maintaining its strong growth trend despite the crises worldwide. The two recent acquisitions in Mexico and India underline the claim of being a global partner with manufacturing facilities throughout the world.

Read the German version of the article in our magazine Kunststoffe or at <a href="https://www.kunststoffe.de/a/fachartikel/grau-aber-genau-2739060" target="_blank">www.kunststoffe.de</a>

Elektrotechnik, Elektronik allgemein

Elektrotechnik, Elektronik

Pigmente

Kunststoff Werkstoffe

Additive

Farbstoffe und Pigmente

Kunststoffe

Photonik

Optik

Flammschutzmittel

Simulating Surface Defects in Parts Using Effect Pigments

Effect pigments can be used to injection mold thermoplastic parts with a shiny metallic surface. However, non-uniform pigment orientation can lead to optical defects. Suitable simulation methodology enables defects to be predicted and prevented.

Effect pigments can be used to injection mold thermoplastic parts with a shiny metallic surface. As electroplating and painting are eliminated, the savings potential is huge. However, non-uniform pigment orientation during production can lead to optical defects on the part’s surface. Using a suitable simulation methodology enables such surface defects to be predicted and prevented.

Various surface-finishing processes, such as electroplating and painting, are used to give plastic automotive parts a metallic appearance. As a rule, however, these processes are cost-intensive and make subsequent recycling difficult. The use of metallic effect pigments for automotive parts therefore offers substantial advantages in terms of both economy and sustainability. Mold-in-color (MIC) is a technology in which the effect pigments are added to the pellets. These are then injection molded to produce parts that have a shiny metallic surface. At Audi, this technology is employed for bumper parts, for example (Fig. 1).

The challenge posed by this technology is how to avoid optical defects on the part’s surface. These stem from the orientation imposed on the metallic effect pigments by the manufacturing process (Fig. 2). Non-uniform pigment orientation gives rise to differences in light reflection. Parts having areas where there are flow lines and weld lines usually show up dark. The scope for influencing pigment orientation and the resulting defects via the process parameters is limited. This makes it all the more important for the part’s design and the mold concept to be optimized early in the vehicle development process.

New Simulation Method Developed in a Collaborative Project

One problem, however, is that a simulation methodology capable of predicting pigment orientation and thus defects does not as yet exist. So, Audi, the Plastics Engineering Group (PEG), and Darmstadt Technical University, Germany, are collaborating on developing such a method. This involves simulating the injection molding process with the aid of Moldflow Insight software from Autodesk.

If the surfaces of the effect pigments are aligned parallel with the part’s surface, it may be assumed that light reflection is uninterrupted. However, if they are disposed at an unknown angle to the surface, the likelihood is that the reflected light will be interrupted and that an optical defect exists. Program implementation is based on calculating a differential angle between the surfaces of the effect pigments (flake normals) and the part’s surface (element normals) and thus affording a way of evaluating possible optical defects via a differential angle (Fig. 3). The basic procedure is divided into three steps:

<ul><li>Generation of the CAD geometry to be studied.</li><li>Design and execution of the injection molding simulation using orientation, calculation and adjusted aspect ratio.</li><li>External defect simulation and re-import into Moldflow for graphical evaluation.</li></ul>

The approach will utilize the fiber-orientation models contained in Autodesk Moldflow Insight and the results which they generate will be evaluated in downstream postprocessing. All fiber-orientation models in Autodesk Moldflow have free parameters for adapting simulation results to, for example, experimental results. The fiber-orientation models that are available reveal the scientific advances that have been made in this area:

<ul><li>The Folgar-Tucker model (FT) [1] and the introduction of second-order tensors to describe orientation distributions [2] present the user with two model parameters in Moldflow. These are, on one hand, the aspect ratio and, on the other, the interaction coefficient, which describes the interaction of filler particles with each other.</li><li>The Reduced Strain Closure model (RSC) [3], which was expanded with a further parameter to account for the slower orientation kinetics in the edge region, provides a total of three parameters.</li><li>The current standard model, the Moldflow Rotational Diffusion (MRD), offers three new coefficients instead of the coefficient.</li></ul>

In all these models, the orientation distribution through the part wall thickness can be influenced via the model coefficients. By contrast, the aspect ratio describes the geometry of the particles contained in the polymer. Here, L is the length of an ellipsoid and D is its diameter (Fig. 4). The usual use case for orientation models provides for an aspect ratio of between 10 and 40. As a result, the ellipsoid starts to approximate a chopped glass fiber in shape. If the aspect ratio is set to a value much smaller than 1, the original long half-axis becomes very short, relative to the diameter. The ellipsoid becomes flatter and it starts to resemble a platelet in shape. From the data supplied by the manufacturer of the effect pigments employed at Audi, a mean aspect ratio of 0.001 was calculated and used in all the simulations.

Parameter studies also carried out on simple plate geometry revealed that the RSC model is capable of yielding the best results. As already mentioned, the outcome of a Moldflow simulation is a second-order orientation tensor that describes the orientation distribution of the flakes in the part. This orientation tensor is used to determine the differential angle between flake and surface normal. At the moment, the study is only addressing the uppermost element layer of the injection molding simulation model. The extent to which deeper-lying flakes contribute to defect formation is unclear and is currently being examined.

Differential Angle Calculation:  What Is Needed for This

Two vectors are required for the calculation of the differential angle under the planned methodology. First, those elements of the injection molding mesh on the part’s surface which have three nodes are identified and are therefore deemed surface elements. For that side of the elements lying between the three identified nodes, the normal vector is calculated. Once this first step is complete, all element numbers for the surface elements and the corresponding normal vectors are now available.

For the identified surface elements, the second-order orientation tensors, calculated from the Moldflow simulations, are also known. As the orientation tensor is expressed in terms of the part’s coordinate system, a transformation into the principal axis system must be applied before it can be used (for information about the properties of second-order orientation tensors, see [2]). It can be deduced that the eigenvalues of the tensor describe the degree of orientation and the associated eigenvectors describe the corresponding direction. Initial results visualizing just the calculated differential angle between surface normal and eigenvector (Fig. 5) reveal very small differences between the two. Multiplying the differential angle by the corresponding eigenvalue markedly improves the quality of the visualization.

The aim of the experimental study is to validate the methodology on a complex part geometry under the boundary conditions of series production. To this end, a part measuring 400 mm x 375 mm was selected that contains different design elements, such as wall thickness variations, ribs, snap-in hooks, breakthroughs and weld domes (Fig. 6). These influence the filling process and thus pose a challenge for the use of MIC material. Gating is done centrally on the top of the part, with Rotec Acrylic PMMA Compound AC-MA 50001 (manufacturer: Romira) being used in addition to the polypropylene (PP) Hifax TYC 459P (manufacturer: LyondellBasell). Preliminary tests had shown that the occurrence of surface defects depended substantially on the injection speed. High injection speeds improve part quality. Fewer flow lines are produced. For this reason, the injection time was varied in several steps during the study (Table 1).

To evaluate the quality of the method’s predictions, the results of the simulation were compared with those of experimental studies (Fig. 7). For more-accurate defect evaluation, three characteristic sections of the part were examined in detail. In one section of the part, the wall thickness in some areas was reduced (Fig. 8, top). These areas show clearly visible optical defects in the form of dark flow lines. The simulation result, too, reveals marked color variation in these areas. The presence of a defect and the area of the defect can be predicted with good accuracy. However, the length and the exact path of the flow line cannot be evaluated in the simulation.

The simulation is also able, with an acceptable degree of fuzziness, to localize defects in those areas of the part that feature weld domes and breakthroughs (Fig. 8, center and bottom). A breakthrough in a part (experiment) is always followed by a fine, dark weld line whose path usually extends as far as the edge of the part (the end of the flow path). In the simulation, a breakthrough is followed by a marked color variation. Thus, the existence of a defect can be correctly predicted. The direction of the flow line can usually be determined, too. However, the extent of the defect in terms of manifestation, thickness and length of the flow line cannot always be clearly determined. In the region of the weld domes, the existence of defects is correctly predicted if the orientation distribution is examined. However, the exact position and the path of the defects cannot be visualized here either. The simulation tends to predict slightly more defects than are found on the actual part.

Overall, the methodology possesses great potential for predicting defects that is open to further optimization. One promising approach might be to calculate and visualize the gradient of the differential angle. The rationale for this is that, when the differential angle changes slowly and continuously, the color change is not perceived as a defect. An abrupt change, on the other hand, is clearly perceptible and should be amenable to visualization via the gradient, in particular.

[1] Folgar, F. und Tucker, C. Orientation Behavior of Fibers in Concentrated Suspensions. Journal of Reinforced Plastics and Composites 3. 1984, pp. 98–119.

[2] Advani, S. und Tucker, C. The Use of Tensors to Describeand Predict Fiber Orientation in Short Fiber Composites. Journal ofRheology 31. 1987, pp. 751–784.

[3] Wang, J., O`Gara, J. und Tucker, C. An objective model forslow orientation kinetics in concentrated fiber suspensions: Theory andrheological evidence. Journal of Rheology 52. 2008, pp. 1179–1200.

[4] Belgeli, Cigdem. Weiterentwicklung und Validierung einer neuen Methode zur Vorhersage von optischen Fehlstellen in thermoplastischen Bauteilen mit Effektpigmenten. Darmstadt : TU Darmstadt, Institut für Statik und Konstruktion, 2020.

[5] Schlachter, Jonas. Praktikumsdokumentation, Konstruktion eines Versuchsbauteils. s.l. : Hochschule Augsburg, 2020.

[6] Phelps, J. und Tucker, C. An anisotropic rotary diffusion modelfor fiber orientation in short- and long-fiber thermoplastics. Journalof Non-Newtonian Fluid Mechanics 156. 2008, pp. 165–176.

[7] Cintra, J. und Tucker, C. Orthotropic closure approximationsfor flow-induced fiber orientation. Journal of Rheology 39. 1995, pp. 1095–1122.

[8] Advani, S. und Tucker, C. Closure approximations for threedimensional structure tensors. Journal of Rheology 34. 1990, pp. 367–387.

There is huge demand for automobiles that have metallic finishes. Plastic parts are often painted or electroplated for this purpose. Metallic effect pigments constitute an alternative. Audi and PEG are working on a simulation process for these pigments with a view to ruling out surface defects. 

Fig. 6. CAD model of the part shown from different perspectives: in order to test the method on different parts, the latter are designed with elements such as ribs, breakthroughs and weld domes.

Fig. 7. Comparison between experiment and simulation for the entire part.

Fig. 8. Comparison between experiment and simulation in three detailed views: flow lines at wall-thickness variations (top), flow lines after weld domes (center), weld line after breakthroughs (bottom). All three examples illustrate the simulation’s accuracy at predicting defects. However, when it comes to predicting the exact position and shape of the defects, the methodology still needs to beimproved.

Table 1. Test parameters for the two materials used.

Fig. 1. Audi uses metallic effect pigments for the shiny metallic surfaces of various parts in its vehicles. They are found, for example, in the skid plate of the A4 Allroad.

Fig. 2. Schematic diagram of pigment orientation in one area without a defect (left) and in one area that already has a flow line (right): the orientation of the pigments gives rise to differential light reflection, creating the impression of a surface defect.

Fig. 3. In the simulation, the orientations of the various pigments are predicted and the  differential angle between their surfaces and the part’s surface is calculated. This information is used to predict possible defects.

Fig. 4. The shape of the simulated pigment varies with the chosen aspect ratio.

Fig. 5. Differential angle (left) and scaling of the differential angle via eigenvalue (right): the latter leads to much better visualization.

KUint5-22_PEG - Hauptartikel

Simulation

Software

Farbstoffe

Effektpigmente

How the Particle Size of Fillers Influences Color Intensity

Fillers and additives are used for targeted modification of the properties of plastics. Apart from the additive’s nature, also its particle size as well as its aspect ratio play an important role.

Fillers and additives are used for targeted modification of the properties of plastics. Apart from the additive’s nature, also its particle size as well as its aspect ratio play an important role. For example, the particle size of hexagonal boron nitride influences color intensity in heat-conducting plastics.

Heat-conducting plastics are gaining in importance in the lighting, electro, and automotive fields. Important trends in these sectors are miniaturization, lightweight construction, and more complex geometries. In such applications, plastics – which generally exhibit very low thermal conductivity – usually come to their limits very soon. However, by using heat-conducting fillers such as boron nitride (BN), the thermal conductivity of plastics and thereby their functionality are greatly improved. Compared with the widely-used metallic heat conductors, BN fillers offer many advantages. These include simple processability, low density and hardness, plus high electrical insulating capability. Particularly in the field of electromobility, thermal conductance, and electrical insulation play an important role. The requirements for components in electrically powered vehicles are high and will rise further. As true multi-talents, they must exhibit heat-conducting and flame retardant properties, and frequently have a rich orange color. In electric vehicles, orange (mostly RAL 2003) serves to mark high-voltage components such as connectors, cable insulation, and battery cell holders.

Boron Nitride Not Only Improves Thermal Conductivity

BN is mainly used as filler in such components to improve thermal conductivity, but also influences the component’s mechanical properties and its color intensity. In the field of thermal management, the family-owned company Henze BNP offers various BN powder qualities as filler. They differ in morphology and in other specific characteristics, which results in different influences in a compound’s processability, coloring, and thermal conductivity. Together with Kunststoff-Zentrum SKZ, Henze has investigated the effect of particle size on the coloring of a compound. In view of current developments in the electromobility field, an orange color body was used for the analysis.

To investigate the effects of particle size on the color of an epoxy resin, three BN powders with different particle sizes were selected. Powder 1 has a medium particle size (D50) of 35 µm, powder 2 a size of 12 µm, and powder 3 a size of 4 µm. For the measurements conducted by SKZ, comparable sample bodies were produced (Fig. 1). The recipe of the sample bodies was kept constant, and only the BN type and thereby the particle size varied. For production, a 2-component epoxy resin, an inorganic orange color body with RAL 2000, and 30 wt. % for each of the BN powders 1 to 3 were used. The overall loading ratio was 20 vol. % – distributed as 19 vol. % BN and 1 vol. % colorant. For the plastic matrix, Araldit G2 casting resin with the associated Aradur H2 hardener from Carl Roth was used.

In the first step, resin, BN, and color body were mixed and de-aerated in a mixer (type: Speedmixer DAC.600.2 VAC-P, manufacturer: Hausschild). In the second step, the hardener was worked into the filled compound under the same conditions. Subsequently, the sample was cured at room temperature for 6 h, and finally hardened at 60 °C for further 12 h. To ensure a homogeneous surface and thereby a uniform color measurement, the measurement surfaces of the sample bodies were polished.

The cured colored sample bodies were analyzed at the SKZ by means of a Ci7860 spectrophotometer (manufacturer: X-Rite). For the measurement, the di:8°-mode with inclusion of the gloss component, a 25 mm aperture, D65 standard lighting, and the 10° viewer mode were used. Color platelets with the reference color RAL 2003 served as reference. Due to the translucence of the platelets, two platelets were always placed on top of each other for the measurements, so that opacity was ensured. Measurements were made at two measurement points per platelet, and the values averaged over three platelets. The epoxy resin samples with and without BN were opaque, and three measurement points per sample were averaged via dual measurements (results are shown as CIELAB color values in the Table 1).

It was shown that, when compared with the reference color RAL 2003, the RAL 2000 colorant used without BN exhibited a slight deviation on the color axes (a* and b*), but in the epoxy resin it has a lower lightness (L* axis) (Fig. 2). If BN is added, the values for lightness as well as the color axes are changed. The increasing values on the lightness axis, as well as the decreasing values on the color axes indicate that the BN leads to increased scatter. For the observer, this results in the impression of a color reduction. But the larger the particles are, the more intensive the color remains.

The measurements illustrate the influence of BN particles on the colorant’s color value in the epoxy resin – particularly the influence of BN particle size. The smaller the particles, the less intensive does the orange of the sample bodies appear. Presumably, this is because the BN acts as white pigment, whose hiding power decreases with increasing particle size. This means that the colorant’s saturation increases with increasing particle size, whereby more intensive orange tones can be achieved. However, the color value of reference color RAL 2003 cannot be fully achieved with the colorant used.

Apart from a rich color, the use of large BN particles offers further benefits. Processing is simplified due to a lower increase of the compound’s viscosity, and a larger aspect ratio increases thermal conductivity. Moreover, it is likely that the mechanical and electrical properties are also improved by the use of larger particles. But these influences must still be verified and investigated.

Table 1. Results of the color measurements on color bodies with and without boron nitride: RAL 2003 was used as reference color.

Fig. 1. Depending on particle size of the BN powder, the orange tone of the manufactured sample bodies can vary.

Fig. 2. Sample values on the color axes and the lightness axis: without BN, the values on the color axes deviate less from the reference. But with the filler, the lightness values are closer to the reference. 

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Hexagonal boron nitride (BN) – isoelectronic with graphite – is a high-performance technical ceramic with a special combination of properties. It combines good separating and lubricating effects, very good thermal conductivity, low thermal expansion, thermal shock resistance, plus low density and hardness with good electrical insulation. Thanks to these properties, BN is used in many different fields: in sintered form for precision components in high-temperature furnaces and PVD plants, as powder in suspensions – e.g. as coating for aluminum processing – and as filler in plastics. With the latter, the main focus is on improved thermal conductivity.

Colors can turn plastics products into real eye-catchers. Kunststoffe asked colorant manufacturers to predict which colors will be trending in the coming year.

Colors can turn plastics products into real eye-catchers. But choosing the wrong color can cause sales to flag. And impact a product’s recyclability. Kunststoffe asked colorant manufacturers to predict which colors will be trending in the coming year. One of the exciting findings: current supply bottlenecks are impacting the range of available colors.

For the third year in a row, the Covid 19 pandemic is shaping color trends in plastics. Like last year, colors that symbolize an end to restrictions on movement and freedom remain hugely popular. Jessica Knoch, Director of Marketing at Lifocolor, a masterbatch manufacturer, says that vibrancy is in demand: “After various lockdowns and restrictions during the pandemic, garish colors are set for a strong comeback in the year ahead. A new-found joie de vivre, a perceived sense of freedom and an enthusiasm for experiencing and showing off colors are going to be celebrated in all their glory.”

She thinks that the dominant shades will be turquoises, purples, oranges, blues and reds, owing to the heavy influence of fashion circles and designers who are adopting colors and style elements from the 1980s and 1990s. Earthy and natural shades such as khaki green, dark gray and warm reddish brown will feature prominently, she adds. These trends, too, have their origins in the pandemic, she believes, brought on by the massive changes which many consumers see happening around the world. Both trends are evoking a desire among customers for more originality, reflection and a sense of home. The need for greater environmental protection is playing a role, too, she notes.

Lifocolor is working closely with Renolit to identify current color trends. Every year, the plastics film and products manufacturer gets together with trend research institutes and experts to produce its “Color Road” predictions for trending colors. After all, color trends in plastics never occur in isolation, but emerge from the wishes of customers in those consumer industries which receive particularly high attention from customers. “In the plastics industry, the colors setting the tone are usually those divined and identified by international trend researchers, color experts and designers for future-focused consumer-goods sectors, e.g. fashion, automotive, cosmetics or architecture,” explains Knoch.

Are Raw Materials Bottlenecks Influencing the Color Range?

Dirk Schmitz, Head of Coloristic at Lanxess Performance Materials, addresses another factor governing the range of available colors. He believes that the current supply bottlenecks have condemned color trends to play a lesser role in many development projects right now than they did in the past. For him, in light of the current situation, plain rather than garish colors are on the rise: “Plain colors such as grays, blues and greens are growing in popularity. This seems to be an effect of the availability issue, because the necessary colorants are still available in sufficient quantity.” At Lanxess, they expect demand for safety orange in electric vehicles to keep growing into the future. Orange is used to identify high-voltage components.

Schmitz believes that the burgeoning interest in making more energy-efficient production has implications for the color sector. Any process that helps to reduce or completely eradicate post-processing of products can help achieve this goal. “A major candidate here is direct coloring – even for metal-effect colors – because it renders downstream painting superfluous,” he explains.

Colorant manufacturers also need to give more thought to colorants that offer greater sustainability, believes Anne Stelzer, Head of Global Marketing for the Colorant Additives business unit at Lanxess Polymer Additives. Demand for these is growing very strongly right now, she says. Lanxess has responded by developing halogen-free colorants and is currently working on deploying environmentally sound solvents in production.

That there is demand for more sustainable colorants is corroborated by Andrea Hanke, Marketing Manager at Lifocolor. “We have seen a noticeable rise in the number of inquiries about recycled, bio-based and biodegradable colorants.” This means that Lifocolor has to keep an eye not only on the colorants themselves, but also on the matrix material employed in its masterbatches. To prove that attractive color batches can be produced from recycled materials, Lifocolor has made masterbatches for the colors contained in the Renolit “Colour Road” trend report based on a matrix of 100 % recycled polypropylene (rPP). Hanke points out, however, that the coloring of recycled plastics is a very complex matter, chiefly because of their own intrinsic colors. In the case of light-colored plastics, achieving the desired color is easy and the range of possible colors is greater. But the darker the material, the more difficult coloring becomes and the narrower the spectrum of attainable colors becomes. Added to which, the heterogeneous nature of the input material is a huge problem.

Hanke believes that masterbatch manufacturers need to sensitize their customers to this issue. “Because there are all sorts of recycled plastics of different intrinsic color on the market and because the requirements vary, projects involving them are highly complex. As masterbatch manufacturers, it is incumbent on us to utilize our know-how and to raise awareness. We need to explain which color is feasible with which particular PCR or bio-grade and which properties are possible,” she says. Lifocolor has enjoyed success with biodegradable polymers in the area of more sustainable colorants. The company claims that its masterbatches contain colorants which do not harm the environment when they degrade. Its Bio-C range allegedly decomposes under home-composting conditions to yield just water, CO2 and minerals.

An ongoing major headache for colorant manufacturers when it comes to plastics recycling is the widespread use of carbon black. This is employed for pigmenting black plastics, but it prevents polymers from being sorted accurately in plastics waste recycling facilities. Plastics pigmented with carbon black elude detection by the near-infrared (NIR) sensors commonly employed in the facilities. “The first thing is to ensure that the various plastics can be sorted. Carbon black is always problematic, because it hampers the use of NIR-detection methods,” says Dirk Schöning, Sales Director at AF-Color, a masterbatch manufacturer. This has led manufacturers to develop NIR-detectable black pigments that are not based on carbon black. It is claimed that these ensure better sortability of plastics waste.

Aside from the foregoing issues, most manufacturers currently have concerns about the difficult supply situation and raw materials bottlenecks, which have recently led to delays in deliveries and to higher costs. “Although we managed to run our production at full capacity, bottlenecks in the logistics chain constrained our ability to supply customers, and this led to delivery delays for our products. This situation was exacerbated by the rocketing prices of freight transport,” says Stefano Bartolucci, Global Market Segment Manager Plastics, Paper and Specialties at Lanxess Inorganic Pigments. Andreas Wingartz, Head of Market and Corporate Development at Lifocolor agrees. The masterbatch manufacturer has had to look for new raw materials sources in some cases, he says. “We are being forced to qualify some alternative raw materials sources so that we can secure the high quality of our products over the long term.” Neither Wingartz nor Bartolucci sees the situation easing any time soon. Both expect energy and transportation costs to keep rising. In contrast, Dirk Schöning from AF-Color paints a more positive picture: “The bottlenecks haven’t affected us at all so far.”

The matrix of Lifocolor’s masterbatches colored in current trend colors consists of 100 % recycled PP.

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Read the German version of the article in our magazine Kunststoffe or at <a href="https://www.kunststoffe.de/a/fachartikel/knallig-oder-doch-gezwungen-schlicht-2739054" target="_blank">www.kunststoffe.de</a>

Masterbatches

Farben, flüssig

Keeping Setting Parameters  under Control

Simple Determination of Process Windows and Quality beyond Parameter Limits

Engel’s new “Parameter Limits” feature provides a remedy. It supports injection molders in keeping the parameters constant within a process window.

The prerequisite for a stable production process and a constant high product quality is the correct setting of all process parameters on the injection molding machine. But errors also often occur. Engel’s new “Parameter Limits” feature provides a remedy. It supports injection molders in keeping the parameters constant within a process window.

The quality of the parts is crucial for an injection molding company’s competitiveness. A modern interpretation of the quality concept requires looking at the topic in a holistic way. Not only the measurable product quality of the part is important, but additionally also an integrated quality assurance and comprehensive quality management (Fig. 1). Quality stands for the quality of all processes that lead to manufacture of the part, starting with a survey of customer requirements, part development and mold design, through organization of the production process, to continuous process optimization.

The relationship between the injection molding process and part quality is physically based. However, the complexity of this process allows for hardly any simple correlations between individual process parameters and the quality criteria of the part. In addition, it must be taken into account that the running injection molding process is influenced by different factors. They include fluctuations of the raw material properties, wear in the mold and on the injection molding machine, as well as changes in ambient conditions [1]. The consequences are deviations in the process and also as regards part quality. In general, various process parameters correlate with the quality data of the part. For example, the warpage of a part is determined by, among other things, the injection velocity, holding pressure, melt temperature and mold temperature, moreover the part geometry and material also decide how greatly the process settings impact the part warpage.

To ensure a constant high quality during injection molding, various methods are available. The oldest is the control of defined quality criteria on the part. For some applications, 100 % control is specified by customers or by law. Though control of the finished part is a very reliable method, it has a number of disadvantages. Thus, not all aspects of the part quality can be tested; in addition, the method is expensive because it requires either complicated automation or high personnel costs. In addition, the quality problems can only be ascertained if bad parts have already been produced, which cannot be reconciled with the requirement for sustainable energy- and resource-efficient production.

Another method that has been used for many years is monitoring of the actual values of the production process. This method is economical, provides rapid information about the current process quality and allows the relationships between the injection molding process and part quality to be better understood. With the process data protocol, Engel offers, for example, an option with a proven track record over many years. However, it is disadvantageous that it is difficult to produce a quantitative relationship between process actual values and part quality, since the process parameters often do not correlate with the part quality and, when they do, not in a linear way [1, 2].

The more recent methods include active compensation of process fluctuations through the adaptive control of the injection molding process. For example, with the iQ weight control assistance system, Engel offers the possibility of keeping the shot weight constant from cycle to cycle by adjusting the injection profile, the changeover point and the holding pressure. This allows compensation of fluctuations of the raw material properties and the ambient conditions, as well as of influences due to mold and machine wear [2].

A new method targets the basis of the process setting, the preset setpoint values of the injection molding process. By means of the Parameter Limits feature, it ensures that the setpoint values lie within a defined process window at any time and therefore the quality criteria of the part do not fall outside the specified limits. This method can be easily combined with the actual value monitoring as well as the complete product testing.

A process window describes the range within whose limits the process must run in order to attain the part quality required by the customer. In the optimization of the injection molding process, the setpoint values are set on the injection molding machine in order to come as close as possible to the quality optimum (100 %) (Fig. 2). The much easier method would be to define a concrete process point, however this has proved impracticable. Because of continuous changes, for example in the raw material and ambient conditions, the process values often have to be adjusted in order to ensure the quality. As long as these adjustments take place within a process window, the high demands on quality can be ensured in the great majority of cases.

Quantitatively, the relationship between setpoint values and part quality can be determined by means of a statistical design of experiments (DoE). Here, the setpoint values of individual process parameters are systematically varied and the resulting part quality is recorded. A statistical analysis is performed to determine from which values the part quality no longer meets the required specification. In Figure 2, for example, this is the case if the quality values lie below 95 %. The process window then results from the lower and upper setpoint values of a parameter that still allow the required part quality to be reached.

Precise Measuring of the Process Window and the Permitted Tolerance

In practice, it is defined in the design of the part what dimensional deviations can be tolerated so that the functional and aesthetic requirements can still be met. Based on this, the injection mold is often designed with a certain geometrical and material-dependent reserve in order to compensate the warpage that is to be expected. If the warpage at a place on the part is a critical quality criterion, it is determined in the DoE which parameters have how much influence on it. Those parameters that, because of experience and the physical process understanding, have the biggest influence are systematically varied and the manufactured components are measured. This is then used to calculate the process window for the parameters considered in the DoE. A DoE is the centerpiece of a process validation, as specified, for example, in medical technology and also increasingly required in other industries, too.

Once the process window is defined, this information must be available at the injection molding machine on production start. The operating personnel conventionally have access to the threshold values – if at all – as a print out or in digital form outside the injection molding machine control. It is not always known to the machine operator where the limits of the process window currently are. Thus, despite elaborate preparatory work, it may be that rejects are produced unnoticed for a long time.

As a solution for this, Engel has developed the Parameter Limits feature in order to enter the process window directly on the injection molding machine and ensure that the threshold values are reliably maintained during operation of the machine in production. For up to 150 individually selectable process parameters, a process window can be specified by means of the software in the CC300 operating panel in Engel injection molding machines. All numerical process parameters whose setpoint values can be varied by the machine operator come into consideration.

All the selected parameters are displayed to the machine operator on a summary page (Fig. 3). They are subdivided into four groups analogous to the phases of the injection molding process, and individual groups can be added. The setpoint value currently set for each parameter is displayed. In addition, the value obtained from the process optimization or validation is entered for which the optimum part quality was obtained. This value serves as a reference for the permitted deviations that are entered as absolute or percentage tolerance. Alternatively an upper and lower threshold value can be directly entered, according to which the tolerance is automatically calculated. The operator can thus keep an eye on the entire process window, the currently set values and the associated reference value.

Saving the Process Window in the Settings Data Record