Intumescent Paints. Formulation, Function and Fire Protection

Transcription

1 Intumescent Paints Formulation, Function and Fire Protection

2 Intumescent Paints Formulation, Function and Fire Protection The use of intumescent coatings is classified as passive fire protection. The purpose of this passive fire protection measure is to: Insulate the structural member, e.g. steel or other metallic products and wood in the event of a fire. Increase the time before the steel loses its structural strength The intumescent coating acts to: Prevent the passage and spread of smoke and fire. Allow safe escape for building occupants. Prevent and reduce the amount of damage to the structure of the building. Sales of intumescent paints have grown strongly over the past 15 years due to building regulation requirements, the growth in steel framed construction and the need to protect other systems in the building such as electrical ducting. Growing consumer awareness of fire hazards in areas such as loft conversions has lead to these systems being specified in wider field of construction including plasterboard, wood trim and stud partition. Intumescent Mechanism of Action Intumescent coatings derive their name from the Latin verb tumescere, which means to begin to swell. The intumescent or swelling mechanism is classed as a condensed phase reaction as opposed to gas phase reactions typically seen with halogens. The key steps in the mechanism are: 1. The water based binder melts at the right temperature to allow further chemical reaction to take place. 2. The acid source i.e ammonium polyphosphate decomposes to form polyphosphoric acid. 3. The polyphosphoric acid reacts and catalyses the decomposition of the carbon source i.e. pentaerythitol. 4. The esters formed during step 3 decompose to form a carbon matrix. 5. The blowing agent, typically melamine, decomposes to release inert gases that cause the carbon matrix to foam and expand to provide an insulating barrier.

3 The insulating char/barrier not only shields the substrate from the heat source but also hinders the passage of combustible gases. Xyntra have developed binder systems which are ideally suited to the formulation of intumescent coatings. Xynpol VO5023AF and Xynpol VO505L are colloid stabilised, APEO free VA/VeoVa copolymer dispersion. Xynpol VO5023AF has a high degree of stabilisation necessary to accept the combination of raw materials in the mill base and forms a high but stable char in the applicationrecommended for general purpose application. Xynpol VO505L is similarly stabilised but is a more hydrophobic system which confers advantages in some applications where a high level of stability is required both in the wet paint and in the applied film, where it tends to confer better performance in damp conditions. The ultimate performance of the system depends amongst other factors on the height and strength of the char. A char with too low a height will not provide sufficient insulation whereas a char which is too high will lack strength and will not stay in place on the substrate. Xynpol VO505L tends to yield a slightly tighter char (lower height) with good substrate adhesion. When formulated correctly these binders contribute to the reactions that allow a sustainable insulating barrier to be formed. Intumescent coatings based on the binders when applied at approx 1mm dry film thickness, and exposed to temperatures of greater than 250 ºC will increase in volume by 10 to 100 times* to develop a char barrier that insulates the substrate. *formulation dependent Other key features of the product include: Good pigment compatibility High pigment binding High water/alkali resistance Tough tack free films Xynpol VO505L and VO5023AF are compatible with the key components of an intumescent system such as the: Acid Source, typically Ammonium Polyphosphate Carbon Source - Pentaerythtritol Blowing agent, typically Melamine

4 As well the above components the binders are also compatible with a range of standard emulsion paint components such as: Dispersants Pigments Plasticisers Preservatives Foam control agents The effectiveness of the insulating properties of an intumescent coating based on the binders can be seen in the graph below, followed by an illustration of the char achieved with Xynpol VO5023AF in duplicate. The paints are made up then coated onto 1mm galvanised steel plates, about 3 coats to achieve a 1mm dry thickness, measured with a thickness gauge. Formulation This starting point formulation was used in the test regime: Component Description % Water 30.8 Tylose H10000YP Thickener 0.6 Xyndisp 4500AD Buffer/co-dispersant 0.1 Xyndisp XA100HP Dispersant 0.3 Biocide Biocide 0.2 Xynburst 9615 Antifoam 0.2 Pentaerythritol Carbon Source 11.5 Melamine Blowing Agent 11.5 Ammonium Polyphosphate Acid Source 21.0 Titanium Dioxide Pigment 4.6 Xyntrol DBE-B Coalescing Solvent 1.0 Xynwet 4000BW Wetting agent 1.0 Xynpol VO5023AF Binder 17.2 Total 100.0

5 In the test commissioned by Xyntra, samples were then tested in a muffle furnace two at a time. The furnace was initially preheated to 500 ºC, once the samples are offered to the furnace the temperature is increased by about 100 ºC per 10 minutes for a total of 1 hour, with a final temperature of 1000 ºC, and removed to cool down. The graph below shows the insulating effect of the formed char (below) on the plate temperature. Fire test, temperature increase Temperature ( C) Time (minutes) Furnace Temperature Coated plate temperature The pictures below give an indication of the char developed from an applied film of 1mm dry film thickness (dft): All information is based on our present state of knowledge. We cannot accept liability for any damage, loss or patent infringement resulting from the use of this information.

6 Registered Office and main contact Xyntra Chemicals B.V. Achterdijk 13 E NL-5705 CB Helmond The Netherlands Main Production site Resiquimica S.A. Rua Francisco Lyon de Castro, MEM MARTINS Portugal T: F: info@xyntra.com