Why is Moisture-Cured PU Catalyst Better?

In view of the toxicity of T-12 (dibutyltin dilaurate) and its harm to the environment, the international environmental protection regulations have more and more stricter requirements on its limit, and it have been banned in some fields such as toys and clothing. In the fields where it can still be used, the prepared work should be done in advance for its elimination and substitution. T-12 also has some disadvantages, such as loss of catalytic activity at low temperature, foaming and cracking in application of elastomer.

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WCAT is a series of catalysts developed for many shortcomings of T-12, such as high toxicity, many bubbles, low activity at low temperature, etc. In the application of one-component moisture-cured polyurethane, WCAT has many characteristics, such as reducing viscosity, reducing bubbles, shortening curing time, greatly improving the curing speed at low temperature and fast curing in winter.

Curing process curves of T12 and WCAT-WS8 in one component moisture-cured polyurethane

Two years ago, I wrote in this magazine* about one of the few true innovations in the coatings industry during the last decades. Steelpaint, a German coatings manufacturer specialising in moisture cure polyurethanes, managed to reinvent MCPU technology and extend its life for the next decades to come, explains Perry Poppelaars, director of Recoat UK Ltd, distributor for Steelpaint in the United Kingdom.

What are Moisture Cure Polyurethanes?

Moisture cure polyurethanes (MCPUs) or polyurethane prepolymer is a single-pack coating which utilises ambient moisture as a catalyst to initiate the curing process. The advantages of the technology are well known. MCPU coatings Moisture cure polyurethane coatings provide longer corrosion protection at a lower film thickness, cure down to -5°C without additives and can be applied at relative humidity (RH) up to 98%. They are flexible, resist hair cracks and are surface tolerant. Like all polyurethane coatings, MCPUs contain isocyanates for the curing process.

Isocyanates and other raw materials, such as Bisphenol and Epichlorohydrin used in most epoxy coatings, have been under scrutiny by the health and safety authorities for some time. It seems likely that these raw materials will be phased out one day.

Stelcatec, the next generation in corrosion protection

By introducing Stelcatec, the isocyanate-free moisture cure polyurethane product from Steelpaint, you can see how far this product is ahead of the game. The major step forward compared to traditional moisture cure technology is that Stelcatec does not contain any isocyanates and that VOC levels are very low.

The above-mentioned advantages of traditional MCPU technology are all still valid for Stelcatec. As an extra bonus, drying times are extremely short &#; even when conditions are unfavourable. If required, the individual coats can be spray applied wet-on-wet 15 minutes after each other. This means that the full three-coat system can be applied within one hour and is dry hard in 130 minutes at 10°C. For roller/brush applications the minimum recoat intervals are 40 minutes.

Demonstration

Not long after launching the new product line, a demonstration was given to a delegation from the UK Environment Agency (EA). The purpose of the demonstration was not just to show the impressive drying characteristics of the Stelcatec system, but to present an innovative, timesaving, cost-effective, environment-friendly procedure to perform a full coating refurbishment on existing steel structures.

During the demonstration, the existing coating system, a standard offshore epoxy system, was fully removed by RPR Heat Induction, then the substrate was prepared to St3 standard. The Stelcatec coating system was applied by brush/roller, and was dry and hard before the end of the demonstration. The whole operation from start to finish took less than six hours.

RPR Heat Induction is rust and paint removal by heat induction. Heat induction is the process of heating an electrically conducting object (usually metal) by electromagnetic induction, generated by eddy currents. When heat is generated in the substrate the bonding between the steel and the coating is broken. The coating is then removed in sheets by scraping, without disintegrating and is completely free from contaminating agents, i.e. blast media. This makes disposal and recycling of waste easier and cheaper. Even inside pittings and cracks in the substrate the coating disbonds. There is no noise, which makes it an ideal method around residential areas, and the only chemical waste is sheets of paint instead of tons of grit. As a result, scaffolding can be built lighter because it doesn&#;t have to hold tons of spent grit.

Case Studies in Action

Based on the outcome of the demonstration, it was decided to test the full procedure on some actual projects. We were assigned a series of four Environment Agency river locks to allow evaluation of all the pros and cons of the procedure and set them off against the traditional way of doing these projects. The lock refurbishment projects can only be executed off season, in the Autumn/Winter when there is much less boat traffic. Third-party inspection was implemented, and all participating parties worked to monitor and measure the effect of the process on the programme, such as quality, cost and most importantly risk.

We are two years on and finalising the 14th lock refurbishment &#; we never stopped. The following is a case study of the Irthlingborough Lock, Wellingborough; the first lock in this running project. Based on the results monitored during this pilot project, the same procedure was followed on subsequent locks.

Irthlingborough Lock Case Study

Project                         Irthlingborough Lock on the river Nene, in Northamptonshire, England;

Owner                         UK Environment Agency;

Main contractor          JN Bentley and Jackson;

Link to Yourun Synthetic Material

Paint contractor          Specialist Painting Group;

Paint supplier              Steelpaint/Distributed by Recoat UK;

Independent inspection          Paint Inspection Limited;

Executed                     February to March , duration three weeks;

Contract value                        £ 40,000.

Coating system

Structural framework (C5-M environment)

Stelcatec-L-PR primer at 100 microns

Stelcatec-L-NT intermediate at 80 microns

Stelcatec-L-TC topcoat at 80 microns

Guillotine gate (C5-M environment submerged)

Stelpant-PU Zinc primer at 100 microns

Stelpant-PU Zinc primer at 100 microns

Stelpant-PU Combination 500 intermediate at 100 microns

Stelpant-PU Combination 500 intermediate at 100 microns

Surface preparation   

• High pressure fresh water washing
• RPR Heat Induction
• Mechanical cleaning to St3 standard

Life expectancy

• 15 years to first major maintenance. Due to the reduced surface preparation standard, an extra coat of Stelpant-PU Zinc was specified for the guillotine gate because it is submerged on a regular basis.

Application

• Brush and roller

Challenges

• The EA traditionally utilised abrasive blast cleaning when refurbishing its large portfolio of steel structures. The risks associated with this process of coating removal and surface preparation include contamination of the land or watercourse, creation of large amounts of hazardous waste, exposure of operatives to hazardous substances (particularly lead), reduced annual output costs and standing time costs due to plant rental in times of inclement weather.

Solution

• Specialist Painting Group introduced the EA to the use of RPR Heat Induction as a means of safely removing the existing coating system prior to mechanical preparation, coupled with the application of the Steelpaint moisture coating system.

Key benefits

• 40% reduction in project costs
• 99% reduction in hazardous waste
• 50% reduction in project duration
• Increased number of refurbishments annually

Conclusion

The combination of using RPR Heat Induction and MCPU technology results in significant savings in project costs, hazardous waste removal and project duration. This has freed up budget and time to allow for more projects per season.

Imagine what difference this would make on developments such as. bridge projects. Scaffolding could be built much lighter because it does not have to hold tons of grit, risk of contamination of the environment is immensely reduced and road closure is shortened by 50%. There is also no conditioning required and downtime due to weather conditions is reduced by 90%.

This project has proved that the procedure truly works in practice, which makes it a viable solution to many infrastructure refurbishment projects.

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