Mold Cleaning Agents in the Polyurethane Molding Cycle
Polyurethanes are produced by molding in automotive, furniture and shoe industry. These molds are most of the time made up of aluminum alloys, steel and in some cases epoxy or polyester.
Polyurethane is injected or poured in to mold by means of dosing machine, that has a mixer head. This mixer head mixes component A that consists of polyols, chain extenders, catalysts etc. and component B, that is isocyanate prepolymer.
This mixture is very sticky at first 10 to 20 seconds and release agents has to be used to prevent sticking to the molds. Release agents are mixtures of non-polar film formers and lubricating oils and/or particles in water or in hydrocarbon solvents.
Most of the time lubricating oils and particles taken at out of the mold on polyurethane piece, but film forming polymers stays in the mold and building up with each molding cycle. Mold built-up consist of film forming polymers and trace amount of polyurethane.
Polyurethane molding cycle is like this:
• New/clean mold is taken into production area, usually mounted to rotary polyurethane machine.
• Molds are heated to target temperature that is determined by polyurethane system houses.
• Mold release agent is applied, usually by spray and sometimes by brush.
• For clean molds, mold release agents are applied several more times to have sufficient release film.
• Certain amount of polyurethane is poured or injected into the mold by dosing machine.
• Reaction completes usually in 3-6 minutes and formed polyurethane piece is demolded.
• After reapplying release agent, cycle starts again.
• After many cycles of molding , film forming polymers built up and started to affect quality of polyurethane pieces, and mold is taken into cleaning process.
Mold cleaning is done physically or chemically or sometimes both ways.
Depending on the size and structure physical cleaning is done by sanding, dry ice, or by steel wool or just by green and hard size of dish foam. Dry ice blasting is most common used method for cleaning molds physically. Specially designed machines blasting solid CO2 into the molds and ice particles do the cleaning and then evaporates. This method has similar benefits of sanding but way much cleaner. Big molds are usually cleared by this method.
When cleaning molds chemically, DMF ( n,n-dimethylformamide, CAS# 68-12-2) is the solvent used traditionally and widely. When cleaning molds chemically, traditional way is heating molds to 60 - 80°C and applying DMF by brush, another traditional chemical is NMP (1-methyl-2-pyrrolidone, Cas#872-50-4). But both of these chemicals are very toxic and listed in SVHC list.
These chemicals are hepatotoxic and harming fetus. In Turkey, these chemicals are still in use because of lack of regulations and their efficiency. New healthier mold cleaning agents are developed and can replace these toxic chemicals. These mold cleaners are not as
efficient and fast performing as DMF or NMP, but they are much less toxic and easy to use. With these new generation cleaners and carefully planning of production molds can be cleaned safely.
A mold cleaner should have these properties:
• Cleaning ability in a reasonable time,
• Long shelf-life,
• Thixotropic viscosity to be able to be used on vertical surfaces,
• Without SVHC listed chemicals,
• REACH compliant,
• Not corrosive to molds.
Teknik Kimya has developed new mold cleaner with a name Armaclean 0555 that has all properties listed above.
References
1. http://echa.europa.eu
2.http://www.lyindustrial.com/kuru-buzla-temizlik/
3. http://www.icebergkurubuz.com
4. Merck, MSDS, 1-metil-2-pirolidon
5. Merck, MSDS, n,n-dimetil formamid
6. Kilo, S., Göen, T., & Drexler, H. (2016). Cross-sectional study on N, N dimethylformamide (DMF); effects on liver and alcohol intolerance. International archive 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
