Why can fire retardant coatings stop the spread of fire?

Fire retardant coatings. It is by brushing the paint on the surface of those flammable materials, which can improve the fire resistance of the material, slow down the spread of flames, or stop the combustion within a certain period of time, this kind of paint is called fire retardant coating, or flame retardant coating.

Fire retardant coating is a special coating used on the surface of flammable substrates, which can reduce the flammability of the surface of the coated material, block the rapid spread of fire, and improve the fire resistance limit of the coated material. It is applied to the surface of a flammable substrate to change the combustion characteristics of the material surface and prevent the rapid spread of fire; or applied to building components to improve the fire resistance limit of special coatings, called fire retardant coatings. The fire protection mechanism of fire retardant coatings can be roughly summarized into the following five points:

1) The fire-retardant coating itself is flame retardant or non-combustible, so that the protected substrate is not in direct contact with the air, delaying the object to catch fire and reducing the speed of combustion.

2) In addition to the flame retardant or non-combustible coating, it also has a low thermal conductivity.

It is possible to delay the flame temperature.

Transfer to the substrate to be protected.

3) The fireproof coating is heated and decomposes into non-combustible inert gas.

Dilution of flammable gases decomposed by heat of the protected object.

Make it less flammable or burn slower.

4) The nitrogen-containing fireproof coating is heated to decompose NO, NH3 and other groups, and organic free radicals.

compounding, interrupting the chain reaction, lowering the temperature.

5) The intumescent fireproof coating expands and foams when heated, forming a carbonaceous foam insulation layer to seal the protected object, delay the transfer of heat and the substrate, and prevent the object from catching fire and burning or reducing the strength caused by the increase in temperature.

To put it simply, fire-retardant coating refers to a type of coating that is applied to the surface of an object to prevent fire, prevent the spread of fire or isolate the source of fire, prolong the ignition time of the substrate or increase thermal insulation to delay the time of structural damage.

We know that there are three conditions for combustion: first, there must be combustible substances; the second is to have sufficient oxygen; The third is to have a certain temperature. All three are indispensable. Fire retardant coatings are designed for them.

First of all, the composition of this coating is, of course, the use of non-flammable or non-flammable materials (such as certain non-flammable resins) as the main composition. Once on fire, it releases a gas that extinguishes the flame. The auxiliary ingredients it uses, such as pigments, should also be non-combustible.

Secondly, add a fire retardant to the paint. When it is subjected to the heat of a flame, it decomposes gases such as carbon dioxide, which does not burn, isolate oxygen from the burning things, and extinguish them due to lack of oxygen. Some coatings also add phosphoric acid, silicone oil and other foaming agents.

When burned, they produce a large amount of foam, like the foam sprayed by a foam fire extinguisher, forming a barrier layer that envelops the flame and extinguishes it. Some paints also add some materials with low melting points that do not burn, such as glass powder and so on. They will be melted under the heat of the flame, flowing over the burning things, creating an insulated fire layer.

These are the reasons why fire-retardant coatings can stop the spread of fire.

The basic components of thick-coated steel structure fireproof coatings are: cementing material (Portland cement, magnesium chloride or inorganic high-temperature binder, etc.), aggregate (expanded vermiculite, expanded perlite, aluminum silicate fiber, mineral wool, rock wool, etc.), chemical additives (modifiers, hardeners, waterproofing agents, etc.), water. Portland cement, magnesium chloride cement and inorganic binders for steel structure fire retardant coating base materials, commonly used inorganic binders include alkali metal silicates and phosphate substances.

However, there are often free alkali metal ions in alkali metal silicates, and acidic gases and CO2 in the air will react with them. If alkali metal silicate is used as the binder of the coating alone, the coating film will not be water-resistant, moisture-resistant, and has poor weather resistance, and the coating is prone to cracking, depowdering and other undesirable phenomena. Therefore, if alkali metal silicate is used as the binder of fire retardant coating for steel structures, the first key problem to be solved is to modify it, that is, to solve the problem of inhibition of free alkali metal ions.

Formal and qualified solvent-based fireproof coatings are strictly forbidden to contact fire sources when they are not completely dry.

Before the solvent-based fireproof coating is completely dried, it is strictly forbidden to contact the fire source, and any fire source is easy to cause fire, ** and other disasters. Here's why:

The thinner used in solvent-based fire retardant coatings is flammable and can burn quickly in case of fire. Solvent-based fire-retardant coatings are applied to the protective surface after a certain period of time and the solvent gradually volatilizes, and then it can really play a role in fire prevention.

The film-forming substance in solvent-based fire-retardant coating is organic resin, which must be diluted with diluent to add flame retardants, refractory materials and other substances to form fire-retardant coatings. Among them, resins and thinners are combustibles.

It is necessary that solvent-based fireproof coatings are strictly prohibited from contacting fire sources during storage, transportation and construction.

The description is a solvent-based fire-retardant coating (oil-based fire-retardant coating), which is flammable when exposed to fire before it is completely dried. Therefore, fireworks are strictly prohibited in the process of production, transportation and construction.

Fire protection principle of fire retardant coatings:

1. Intumescent fireproof coatings (ultra-thin, thin, veneer, cable fireproof coatings) are coated on the surface of components The principle of fireproof coating is that the fireproof coating layer expands and foams when it is fired, forming foam, and the foam layer not only isolates oxygen, but also has good thermal insulation performance because of its loose texture, which can delay the speed of heat transfer to the protected substrate; According to the analysis of physical and chemical principles, the process of foaming the foam layer produced by the expansion of the coating shows an endothermic reaction because of the expansion of the volume, which also consumes the heat during combustion, which is conducive to reducing the temperature of the system.

Second, the non-intumescent fireproof coating (thick steel structure, fireproof embankment, tunnel fireproof coating) coated on the component of the fireproof coating of the fireproof coating is that the fireproof coating basically does not change in volume when the fireproof coating is fired, but the thermal conductivity of the coating is very low, which delays the speed of heat transfer to the substrate to be protected, and the coating of the fireproof coating itself is non-combustible, which acts as a barrier and prevents thermal radiation on the component, and avoids the direct attack of the flame and high temperature on the component to play an efficient fireproof and thermal insulation protection on the steel. In addition, when the fireproof coating of this kind of component is fired, the coating does not change in volume to form a glaze-like protective layer, which can play the role of isolating oxygen, so that oxygen can not be protected by the flammable substrate contact, so as to avoid or reduce the combustion reaction. However, the glaze-like protective layer produced by this type of coating often has a large thermal conductivity and poor thermal insulation effect.

In order to achieve a certain fireproof and thermal insulation effect, non-intumescent fireproof coatings are generally thicker to meet certain fireproof and thermal insulation performance requirements.

The main fire protection principle of fire retardant coatings is to improve the fire resistance time of building components through their own flame retardant properties and low thermal conductivity.

1. Fire retardant coating: It is inherently flame retardant or non-combustible, so that the protected flammable substrate is not in direct contact with the air, so the ignition time of the substrate is delayed.

2. The fireproof coating decomposes non-combustible inert gas when heated by fire, so that the combustible gas decomposed from combustibles is diluted with oxygen in the air and inhibits combustion.

3. The chain reaction that prevents the ignition reaction and the combustion reaction of the decomposition gas are free radical reactions, and the fireproof coatings containing nitrogen, phosphorus, bromine, etc. decompose some active genes; It binds to combustible free radicals and interrupts the chain reaction, thereby reducing the combustion rate.

4. The fire-retardant coating expands and foams when exposed to fire, forming a layer of foam thermal insulation to seal the protected substrate and prevent the base layer from burning.

In addition, some fire-retardant coatings decompose when exposed to fire, resulting in a strong endothermic reaction, which inhibits the temperature rise and delays the spread of fire.

Top 10 causes of fire retardant coating cracking.

1. It is not suitable for the bottom and surface coating;

2. Immediate construction after painting anti-rust paint, resulting in the mixing reaction of the coating, will also cause cracking of the coating film of the fireproof coating;

3. The volume concentration of pigment (PVC) in the topcoat is high;

4. The primer coating is not dry and the topcoat is too thick;

5. The treatment of the substrate of the fireproof coating is unqualified, and the cracking of the base layer of the fireproof coating will also be affected, and the cracking of the substrate will also cause the cracking of the coating film of the fireproof coating;

6. If the substrate of the fireproof coating is too dry, it will also cause the adsorption of moisture in the fireproof coating, so that the fireproof coating will dry too quickly, and the fireproof coating will crack;

7. The fireproof coating is not stirred evenly, and the moisture is uneven, which may also make the painted fireproof coating film crack;

8. During construction, the fireproof coating is exposed to sunlight, so that the fireproof coating film dries quickly, so that the cracking phenomenon occurs;

9. During construction, you should wait for the previous fireproof coating film to dry, and then paint another one to prevent the fireproof coating from drying because the painted fireproof coating is not dry, and a layer of fireproof coating is painted, so that the two layers of fireproof coating are mixed, and the fireproof coating cracks occur;

10. If the fireproof coating is not properly maintained, there will be strong winds, sun exposure, etc., which will also make the fireproof coating film dry quickly and crack.

The curing of fireproof coatings for thick steel structures can be maintained in appropriate ways such as covering wet sacks, wet straw, plastic sheeting and spraying curing agents. When the ambient temperature is too high, it should not be simply watered and cured to prevent the surface of the coating from sand and cracking, resulting in the decline of the performance of the fireproof coating.

Samples of fire retardant coatings.

1.When the staff used the fireproof coating, its topcoat matching and products were not adaptable.

2.When applying fireproof coatings, it mixes with other coatings.

3.The fire retardant coating used by the user has a significantly higher pigment volume concentration in its own topcoat.