Low-molecular weight polymers have been used for decades in release agents for metal die casting. These are mostly long-chain, polyethylene-based molecules that have very good release properties due to their high melt viscosity. They also show very good release properties at the comparatively high temperatures of the Al and Mg die casting processes and burn hardly any residues. Moreover, such polyethylene additives have generally a good lubricating effect, which can reduce wear on moving components of the mold.
Common release agents usually use a combination of modified silicones and low molecular polymers in order to enable a trouble-free die casting process. However, such a formulation is always a compromise, and the negative effects of both additive groups are clearly noticeable during casting as well as in the subsequent processes.
In order to avoid the negative influences described and to increase the economic efficiency of the die casting process, we developed new short-chain polymers which have a completely different structure than the additives used to date. These newly developed polymers are highly polar due to their large number of polar centers in the polymer chain. They exhibit very good adhesion to metal surfaces with simultaneously having a very low melt viscosity. As a result, they spread very quickly on hot surfaces and produce very thin, well-adhering release layers. The high adhesion of these polar additives is based on the interaction of the freely moving electrons of the polar centers with the dipoles of the metal oxides on the mold. Such ultra-thin and well-adhering polar films also exhibit high lubricity and contribute to lower wear on the moving parts of the mold (e.g. on the ejectors). In addition, they show a very high release capacity during the casting process. Any release agent residues remaining after the casting process are washed off during the next application, so that no release agent builds up in the cooler zones of the mold. Also, during subsequent cleaning of the casted parts, small amounts of release agents still adhering can be easily removed with a mild alkaline cleaner and usually do not cause any significant disturbances in downstream coating processes.
Additives from the CPM Concept should, however, be combined with a classic high-molecular additive because in the areas of highest temperatures and flow velocities of the inflowing metal the historical well-adhering additives (polyethylene or mod. polysiloxanes) are still needed. However, their quantity should be limited to the necessary minimum during formulation because they tend to form build-up and residues in the mold. Modified polypropylene dispersions have proven to be a very good alternative to polyethylene additives. Due to its molecular structure, polypropylene is thermally degradable and does not tend to form high-polymer residues compared to polyethylene additives.
Die cast parts made of aluminum, magnesium and zinc alloys are produced in very high quantities due to their low weight and inexpensive manufacturing processes. However, release agent residues from the casting process often lead to major quality problems in subsequent processes such as painting, bonding, electroplating. In addition, release agent residues on the casting molds lead to frequent process interruptions. Keim Additec Surface GmbH has developed specific additives for metal die casting release agents to solve these problems which have been known for decades. Due to the novelty of these aqueous additives (CPM concept) and the release agents produced with them, die casting tests were carried out at the Fraunhofer Institute IFAM in Bremen and the die casting mold as well as the surface of the cast parts were analyzed and evaluated. The tests impressively demonstrated that the additives of the CPM concept reduce the residues on the components to a minimum without any loss of release performance. The use of CPM additives should make die casting significantly more efficient in the future and better meet the increased demands of electromobility.
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