Fast cure intumescent coating for passive fire protection

Dimitri Leroy/Stefan Priemen – HUNTSMAN

With legislation regarding building safety becoming increasingly stringent, demand for construction materials that have effective fire protection properties is growing fast. Among the many choices available to specifiers in the construction sector are intumescent coatings, which can provide fire resistance capabilities across a wide range of applications. Designed to expand and insulate when exposed to heat or fire, intumescent coatings are made up of carefully engineered chemical compounds. These combined elements undergo a transformation when faced with heat and / or fire, forming a thick and robust, insulating char layer.

The creation of this char layer serves two purposes. First and foremost, the char delays the spread of flames – protecting the material inside by cutting off the oxygen supply necessary for combustion. Secondly, the char shields the underlying substrate, safeguarding its structural integrity from thermal stress and reducing the risk of a structure flexing and / or collapsing due to heat fatigue.

Fig. 1 
Back side temperature evolution of side two steel substrates, one with Polyresyst® IC6005 and one with a standard polyurethane coating

As a result of these features, interest in intumescent coatings is rising across several sectors where fire poses a risk. In mission critical industries, which are dependent on highly engineered structures – for example in infrastructure projects – there is considerable demand for coatings that can protect the beams, columns, sections, and trusses of bridges in the event of fire. Similarly, in industrial and domestic buildings, incorporating intumescent coatings into building fixtures, fittings, and structural components such as lintels, rolled steel joists (RSJ) and i-beams, can give occupants extra evacuation time during fire incidents. Moreover, the use of intumescent coatings can afford firefighters crucial additional minutes to carry out their duties.

Huntsman has recently applied its polyurethane know-how to the field of intumescent coatings. The result is a novel two-component system with advanced capabilities. Dimitri Leroy, Platform Manager for Coatings at Huntsman, explained more: “Historically, epoxy-based systems have dominated the intumescent coatings area, accounting for more than half of global revenue in this field in 20221. “We saw an opportunity to introduce a polyurethane coating that could overcome some of the limitations presented by incumbent systems”.

“With demand for intumescent coatings that can be applied in a factory setting on the rise, our brief was clear. We wanted to develop an intumescent polyurethane technology for the construction sector that could be applied to multiple substrates. We wanted a coating that would be easy to apply – using existing equipment. Crucially, we also wanted a coating that would cure fast – reducing any downtime required between layers”.

After in-depth research and development, the team created Polyresyst® IC6005 system – an innovative fast curing intumescent coating that: Provides passive fire protection – Cures fast – Is easy to apply – Can be used for a range of different substrates – Is tough and flexible – It is a 100% solids, low VOC, low emissions system – Has good weatherability.

Passive fire protection
Stefan Priemen, Technical Coatings Expert at Huntsman, said: “When it comes to passive fire protection, Polyresyst® IC6005 system delivers a robust performance at high temperatures. As the graph below shows, when applied to a steel substrate, and exposed to a 1100-degree Celsius flame, the system will reach a maximum temperature of 250 degrees Celsius after thirty minutes. This is in stark contrast to a steel substrate coated with a standard polyurethane coating, which would reach 400 degrees Celsius in less than five minutes.”The thermal insulating properties of the system are further demonstrated in the thermograph below, which shows the result of a furnace test conducted according to DIN 4102-8 – the German DIN norm that classifies building materials according to their flammability.

Front side steel substrates with Polyresyst® IC6005 exposed to a 1100-degree Celsius flame

Fig. 2
Front side steel substrates with Polyresyst® IC6005 exposed to a 1100-degree Celsius flame

The thermograph illustrates what happened in a laboratory to a 2mm metal plate, coated with Polyresyst® IC6005 system at 2.3 mm and 4.5 mm respectively, when exposed to a 1100 degrees Celsius flame from a gas burner.  The red line shows the normal heating curve seen during a furnace test conducted according to DIN 4102-8 – with the temperature reaching more than 500 degrees Celsius after just a few minutes. In contrast, the blue line shows that a metal substrate coated with 2.3 mm of the system will heat up much more slowly – only reaching 500 degrees Celsius after more than 70 minutes. The numbers are even more impressive on the yellow line – with a 4.5 mm thick the system coating taking more than an hour and a half to reach a similar temperature.

A fast fix
With fire performance and application of the coating covered, Huntsman’s next step was to differentiate its intumescent coating in the most striking way possible – giving it quick cure capabilities, which sets it apart from other intumescent solutions currently available. Stefan Priemen said: “One of the key issues with epoxy intumescent coatings is the amount of time you must leave them to cure. Typically, after spraying, epoxy-based intumescent coatings take several days to cure – if left to their own devices. This timeframe can be reduced to hours with the use of a curing oven. However, in a busy manufacturing environment – where every minute counts and time is money – that’s just not practical. Waiting several hours while a coating dries in an energy-intensive oven, before you can apply another layer, is inefficient on many levels. Polyresyst® IC6005 system overcomes this issue”.

“With snap cure capabilities built into the system, you can literally spray the coating and watch it dry in front of your eyes. The coating has a tack free time of just two seconds, meaning there is very little dripping or sagging. This in turn reduces waste”. “Crucially, with such a rapid cure, users can also spray additional layers almost immediately – building up the desired final dry film thickness in one go. This is a game changer in high throughput, automated manufacturing environments, with Polyresyst® IC6005 opening the door to substantial time and money savings”.

Fig. 3 
Performance of a 2 mm metal plate, coated with Polyresyst® IC6005 system at 2.3 mm and 4.5 mm respectively, when exposed to a 1100-degree Celsius flame from a gas burner

Additional layers of benefits
The system also has other benefits. A 100% solids system – with no added solvents and low levels of volatile organic compounds – the coating has a lower impact on air quality, human health, and environment.  The system is also robust enough to be used at low temperatures. Even at temperatures below zero degrees Celsius, the system can create the same tough and flexible surface, with the same quick cure properties. This is in stark contrast to epoxy intumescent coatings that are susceptible to cold shock and generally break at around zero degrees Celsius.

Commenting, Stefan Priemen said: “While our Polyresyst® IC6005 system was predominantly designed to satisfy the requirements of structures being sprayed in factory settings, the technology will, obviously, also be applied in situ – outdoors on building and construction sites. Ensuring that the coating could be applied easily, regardless of temperature or humidity was therefore crucial. This also makes the system an ideal choice for use in the northern hemisphere where severe weather has – in the past – restricted the use of coatings and caused a delay to projects”.

Fig. 4
Polyresyst® IC6005 sprayed on cardboard, cures in just a few seconds

The toughness and flexibility of the system continues to be felt once it has been applied. According to ASTM G154 (Standard Practice for Operating Fluorescent Ultraviolet (UV) Lamp Apparatus for Exposure of Materials), the system was successfully cycled between cold and warm and humid and dry conditions – with no decline in performance over time.

Fig. 5
Polysesyst® IC6005 shown during an elongation test

Concluding, Dimitri Leroy said: “For many years, specifiers of intumescent coatings have had to work with slow-curing coatings. With Polyresyst® IC6005 we’ve created an intumescent coating that cures in seconds, delivers comparable levels of fire and mechanical performance, and is flexible enough to be applied in all kinds of conditions. In a world where fire safety remains a significant concern, and intumescent coatings are growing in popularity, this kind of progress will benefit everyone – further increasing the adoption of coatings that can help protect people and assets from the risks presented by fire”.


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