TT Talk - Assessing waterborne paints
The replacement of solvent based paints with environmentally friendlier waterborne paints will have a number of consequences to container owners.
The Chinese Government has introduced a new 'self-discipline Convention' covering air pollution, stipulating the responsibilities of coating enterprises and the penalties for violation. The Convention permits the use of zinc rich primers so long as the manufacturer accepts regular auditing and that the emissions are within acceptable limits. However, other coats are required to be waterborne based.
Since there are severe penalties for both the container manufacturer and the paint supplier, new solvent free painting facilities are being installed. CIMC has estimated that the associated cost will amount to three times the cost of a traditional solvent line (up from US$9 million to US$27 million). Assuming the costs are written off over 10 years and without government subsidies, this would add just over US$5 per TEU.
The running costs of the waterborne paint line are also going to be higher. Factories need to install temperature and humidity controlled air conditioning with a resultant energy cost penalty. Again, CIMC stated that this could be between US$10 and US$20 per TEU, plus additional unit costs of up to US$20 due to pre-heating of the container in the winter and for longer periods for factories in higher latitudes (such as Dalian). Finally, the costs of curing the waterborne paint are reported to increase; required additional curing ovens could add an estimated US$50 per TEU.
Such cost increases are clearly unwelcome, but must be seen in a broader context. In the period September 2016 to May 2017, the price of cold rolled steel rose by US$80 per tonne (approximately US$160 per TEU including waste). Thus, a container unit cost increase from US$1,300 to US$2,200 over the same period cannot be seen a purely a consequence of waterborne paint.
Impact on productivity
Reportedly, the application of waterborne paints has also adversely affected productivity. Part of the huge cost of the new production lines is to increase the number and size of the curing ovens. If it takes 20 hours to cure waterborne paints and only four for solvent based paints then the ovens need to be five times longer, in order to maintain the line speed while accommodating the longer dwell time. MCI reported that they have achieved target outputs that represent the equivalent line speed and quality as when using solvent based paints within two months. However, like CIMC, MCI has had to adopt long curing ovens capable of handling more than five containers at any one time.
Waterborne paint processes also preclude 'wet on wet' applications. This historical practice enabled the primed container to move directly to the second coat booth, applying the intermediate coat over the still wet primer. With waterborne paint, the primer coat has to be dried before the intermediate coat may be applied.
"Waterborne paint processes also preclude 'wet on wet' applications"
There is a benefit here, with plenty of time to check the application of the primer coat avoiding a common fault in the past of this coat being very thin or missing altogether. Poor primer coating can substantially reduce the life of the container; use of waterborne coatings means that there is less opportunity to miss the primer coat as the container must be held for curing.
"Producing a quality finish must be the objective of the container manufacturer"
Producing a quality finish must be the objective of the container manufacturer, and MCI have reported that the frequency of defects has reduced significantly to an acceptable level through training, line management and improved worker skills. Of course, improved working conditions required by waterborne paints will also increase productivity. Furthermore, the heavy investment requirement in building new paint lines, plus the higher material cost, are likely to encourage automation, which in turn will reduce wastage and overspray.
There is still work to be done to improve the surface anti-abrasive properties and cracking, but with the increasing use of waterborne paint is motivation for paint suppliers to invest in improving the quality of their product and reducing the cost.
We gratefully acknowledge the assistance in the preparation of this article of Bill Brassington of ETS Consulting.
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Risk Management Director, TT Club