Mold Cleaners in Polyurethane Molding Cycles

Polyurethane is molded and used in the automotive, furniture and footwear sectors. The molds used generally consist of metals such as aluminum alloys and steel, and in some cases materials such as epoxy and polyester. Polyurethane is obtained by pouring into molds using a dosing machine with a mixing head, where component A contains polyol mixtures and various additives such as chain extenders, crosslinkers and catalysts, and component B contains isocyanate prepolymers. Mold release agents are used to prevent the polyurethane mixture, which has a highly tacky structure in the first 10-20 seconds, from sticking to the molds. Mold release agents consist of non-polar film-forming polymers in water or hydrocarbon solvent and lubricating oils and/or particles that provide slip. The lubricating oils and/or particles contained in the mold release agent leave the mold together with the molded part, while the film-forming polymers remain on the mold surface. This film layer necessary for mold release causes contamination as it accumulates in the mold over time during the production cycle. Mold contamination consists of the film created by the mold release agent and partially accumulated polyurethane particles in the mold. The polyurethane molding cycle is outlined as follows: • A new or cleaned mold is brought to the production area and attached to the polyurethane machine. • The molds are brought to the mold temperature recommended by the polyurethane manufacturer. • The mold release agent is applied to the mold generally by spray, sometimes by brush. On clean molds this operation is performed 3-4 times to condition the mold and ensure adequate film formation by the mold release agent. • A predetermined amount is poured into the mold using the polyurethane machine and the mold is closed. • After the reaction, which is generally completed within 3-6 minutes, the molds are opened and the part is removed from the mold. • The cycle is continued by applying mold release agent again. • At the end of these cycles, the mold is sent for cleaning when the mold surface becomes contaminated by accumulated mold release agent film that affects the pattern and the surface of the finished part begins to deteriorate. Mold cleaning can be performed by physical or chemical methods, sometimes by both physical and chemical methods. Physical methods are performed depending on the structure and size of the mold using sandblasting, dry ice, steel wool with abrasive surface or the hard green side of dishwashing sponges. Dry ice application is among the most commonly used physical cleaning methods. Carbon dioxide ice particles with sublimation properties are sprayed onto the mold using machines specially designed for this purpose. While this process achieves results similar to sandblasting, it provides much cleaner cleaning than sandblasting, and large molds are generally cleaned this way. In mold cleaning using chemical methods, the conventional and most effective method is performed by applying DMF to molds between 60°C and 80°C and allowing it to soak, with NMP being another effective chemical. However, these chemicals are highly toxic and are on the SVHC list. These chemicals harm the fetus and are hepatotoxic to the liver. In our country, these chemicals are still frequently used due to their effectiveness and lack of legal regulation. Formulas containing much safer chemicals have been developed to replace these effective but extremely toxic chemicals. While this group of cleaning materials does not act as quickly as DMF (n,n-dimethyl formamide, CAS#68-12-2) and NMP (1-methyl-2-pyrrolidone, CAS#872-50-4), they have much less toxic content and are easy to use. With good production planning, molds can be cleaned safely. Properties that should be present in mold cleaners: • Ability to clean the mold within reasonable timeframes, • Long shelf life, • Thixotropic effect when necessary (especially in vertical applications), • No prohibited substances content, • No corrosive effect on the mold. Armaclean 0555, newly developed by Teknik Kimya, is a next-generation mold cleaner that possesses all these properties, contains no SVHC, and is REACH compliant.

Sources / References:

1. http://echa.europa.eu 2.http://www.lyindustrial.com/kuru-buzla-temizlik/ 3. http://www.icebergkurubuz.com 4. Merck, MSDS, 1-methyl-2-pyrrolidone 5. Merck, MSDS, n,n-dimethyl formamide 6. Kilo, S., Göen, T., & Drexler, H. (2016). Cross-sectional study on N, N dimethylformamide (DMF); effects on liver and alcohol intolerance. International archives of occupational and environmental health, 89(8), 1309-1320. 7. Jyothi, K., Kalyani, D., & Nachiappan, V. (2012). Effect of acute exposure of N, N dimethylformamide, an industrial solvent on lipid peroxidation and antioxidants in liver and kidney of rats. 8. TDS, Armaclean 0555

 

İlker Akça Chemist Technical Director Teknik Kimya