Application Process of Intumescent Flame Retardant Coatings and Its Influence on the Performance of the Final Layer

YANG Hong-tao1, JIANG Qing-huai2, WANG Ming-qiang2, ZHAO Wei2, LI Zhi-shi2, WANG Hua-jin2

(1. AVIC Xi’an Aircraft Industry (Group) Company Ltd., Xi’an 710089, Shaanxi, China; 2. National Key Laboratory of Marine Coatings,
Marine Chemical Research Institute Co., Ltd., Qingdao 266071, Shandong, China)

Abstract: The application process of intumescent flame retardant coatings will influence the performance of the final layer. In this paper, the influence of different application factors is studied, including water resistance, adhesion strength, flame retardancy, adhesion strength and flame retardancy performance after the water resistance test. The application factors are adjusted through different application cycles, conservation cycles and conservation temperatures. Testing results show that different application techniques have no significant effect on the flame retardant performance of the coatings. Extending the application cycle,
extending the conservation cycle and curing the layer through the drying process will increase the water resistance and adhesion strength of the final layer. Through the investigation, if the equipment permits, a shorter application cycle should be carried out through the drying process; a longer application cycle should be carried out through the conservation process at room temperature. Daily application will make the final layer perform better overall.

0 PrefaceExpansive fire-resistant coatings are often used in buildings for fire protection of steel structures. At the same time, intumescent fire-resistant coatings are also suitable for special fields such as petrochemicals, aircraft, ships, and aviation. Fire-resistant coatings form an expanded carbon layer when exposed to fire. The expanded carbon layer can play the role of flame retardancy and heat insulation, and implement effective fire protection for the substrate. At present, fire-resistant coatings in buildings in China mainly follow the national standard GB 14907-2002 “Steel Structure Fire-resistant Coatings”, which has been issued for more than 10 years. The standard can be divided into indoor type, outdoor type, or ultra-thin, thin and thick type for different application environments of the fire-resistant coating and the characteristics of the coating itself. Except for thick fire-resistant coatings, thin and ultra-thin fire-resistant coatings are intumescent fire-resistant coatings. Due to high density and long service life, the application of thick fire-resistant coatings has gradually decreased. At present, the market is dominated by intumescent fire-resistant coatings.After years of development, the current market mainly includes single-component solvent-based fire-resistant coatings, water-based fire-resistant coatings, two-component epoxy solvent-free fire-resistant coatings, and various types of fire-resistant coatings based on non-use requirements. Although fire-resistant coatings are mature products in the market, there are more studies on fire-resistant properties and smoke-generating properties of fire-resistant coatings, but there is little discussion on the construction process. The construction process parameters of the coating are mainly based on experience and visual judgment. The performance impact of the system is less studied. At the same time, during the construction process, in order to shorten the construction cycle and save time, the influence of the coating construction parameters was studied, and there was no in-depth study on the influence of the coating performance in the later stage.This article focuses on the effects of different construction process parameters on the performance of fire-resistant coatings. Different coating interval, curing temperature, curing period and other parameters were selected to test the coating’s fire resistance, drying time, bond strength, water resistance, and bond strength and fire resistance after the water resistance test. By analyzing the test results, you can choose the appropriate construction process parameters according to the construction conditions.
 1 Experimental part

1.1 Reagents and instruments

Intumescent fireproof coating, special thinner for fireproof coating, Marine Chemical Research Institute Co., Ltd.Spraying equipment high-pressure airless spraying, Graco, X60DL3, spraying pressure 4-6 MPa, spray gun caliber 1.8-2.0 mm.1.2 Experimental methodsThe fireproof coating is applied by spraying, and the thickness of each pass is about 0.15 ~ 0.2 mm, and the thickness of the final coating is controlled to 2 mm. Different construction intervals and drying times are used to adjust the construction process parameters. Construction and storage at room temperature are placed in a constant temperature and humidity room, with a temperature of (25 ± 2) ºC and a humidity of 40% ± 5%. See Table 1 for specific construction parameter adjustments.

Fire-resistant coating construction process parameters

1.3 Performance test

The physical and chemical properties of the fire-resistant coatings are tested in accordance with the requirements for indoor ultra-thin steel structure fire-resistant coatings (NCB) in GB 14907-2002 “Steel Structure Fire-Resistant Coatings”. Table 2 shows the specific test performance and requirements. This article mainly focuses on important performance indicators such as coating drying time, bond strength, water resistance, and fire resistance.

Fire protection coating testing items and technical indicators

The fire performance test uses a small burning furnace. The fire resistance of cellulose fire simulation steel beams is tested on the intumescent fireproof coating. The heating curve conforms to the cellulose fire heating curve. The sample is coated on the surface of the steel plate, and the dry film thickness is 0.8 mm. Heating curve.


 2 Results and discussion

The construction process of the fire-resistant coating will affect the final performance of the coating. Through adjusting the experimental parameters of the construction process, the construction may be easiest to determine the conditions and the optimal performance of the coating.

2.1 Drying time

The surface drying time of the coating meets the requirements, but the surface drying and actual drying time are different. The specific test results are shown in Table 3. Use dry way, it will add the volatile diluent speed, reduce drying time. Meanwhile, two daily administration workers embodiment, although will shorten the construction period, but the coating will be extended curing time. Construction method using drying, for short construction period, maintenance time between long construction requirements.

Surface drying / drying time of fire-resistant coatings under different application conditions

2.2 Bonding strength

Adjust the application interval of the coating so that the coating film can be re-applied under different conditions, including wet-on-wet technology and dry-on-wet technology. Generally speaking, the wet-to-wet technology will increase the interlayer adhesion of the coating, but because the fire-resistant coating is a solvent-based system, the secondary application of incomplete evaporation of the solvent will cause foaming in some areas of the coating and prolonged drying time. problem. The dry-to-wet technology does not have similar problems, but it will prolong the application time of the coating and increase the construction cost. Test the bonding strength of the fire retardant coatings under different application conditions. The test results are shown in Table 4.

Bonding strength of fire-resistant coatings under different construction conditions

According to the test results of the bond strength, the analysis shows that extending the application interval of the coating will increase the bond strength of the coating. Although the wet-on-wet technology will theoretically increase the interlayer adhesion, due to the solvent-based system, the solvent is not completely evaporated. Performing secondary construction will reduce the adhesion between layers. At the same time, high temperature drying will increase the bonding strength of the coating and shorten the construction time. However, due to the need to use drying equipment, energy consumption is increased, and it is not suitable for the construction of larger parts.

2.3 Water resistance

In the case of the same formulation, the water resistance of the coating mainly depends on the sealability of the coating itself, incomplete evaporation of the solvent, and defects in the coating will cause the water resistance of the coating to decrease. The water resistance of the coating under different application conditions is shown in Table 5. The test was terminated after 30 days. Although all of them can meet the requirements of water resistance for 24 hours, the water resistance of the coating is slightly different after the test time is extended. According to the test results, the two-day, normal-temperature drying construction process has a lower water resistance than the one-day, normal-temperature drying construction process, which is because the solvent in the coating has not completely evaporated. At the same time, extending the curing time of the coating to completely evaporate the solvent will increase the water resistance of the coating.

Water resistance of fire-resistant coatings under different application conditions

2.4 Fire performance test

2.4.1 Fire performance test

The fire performance test uses a small combustion furnace. The fire resistance test of the intumescent fire-resistant coating is performed on a simulated steel beam. The heating curve conforms to the cellulose fire heating curve. The sample is coated on the surface of the steel plate with a dry film thickness of 0.8mm. The time when the back temperature of the coated steel plate reaches 500 ℃ is shown in Table 6. From the data obtained, it can be seen that when the coating is dry, different construction processes have no significant effect on the fire resistance of the fireproof coating, and the fire resistance is basically consistent.

Fire performance of fire-resistant coatings under different construction conditions

2.4.2 Fire resistance test after water resistance for 7 days

After 7 days of water resistance, the fire-resistant coating samples were taken out and left for 24 hours at room temperature for fire resistance test. The fire resistance was compared with the samples before the water resistance test.

Fire resistance test of fire retardant coating before and after water resistance

According to the test results, after 7 days of water resistance, the fire resistance of the fire-resistant coating decreased slightly. At the same time, the bond strength of the samples was tested after water resistance. After the water resistance test, the samples were placed at room temperature for 24 h and 7 d. After the water resistance test, the bond strength of the coatings decreased. After 7 days at room temperature, the adhesion The strength has picked up. May be due to the evaporation of the water immersed in the coating, the denseness inside the coating is restored, and the bonding strength is increased, but it cannot always be increased to the bonding strength before the water resistance test.

Table 7 Performance of Flame Retardant Coatings under Different Application Conditions after Water Resisting Tests

The expanded carbon layer of the No.1, No.4, No.7, and No.9 samples before and after water resistance test is shown in Figure 2.

Expanded carbon layer of fire-resistant coating before and after water resistance

After the water-resistant coating is water-resistant, the height of the expanded carbon layer decreases, the uniformity of the carbon layer remains unchanged, and the height of the expanded carbon layer decreases, resulting in a decrease in fire resistance. The reason for the analysis is that due to the intumescent flame retardant system used in fire-resistant coatings, ammonium polyphosphate is easily soluble in water, and it will be a solvent during the water resistance test, reducing the content in the coating, resulting in a decline in the final fire resistance.

2.5 Comparison of Comprehensive

ResultsThe performance of fire retardant coatings under different application conditions is shown in Table 8. It can be seen from the data in Table 8 that different construction conditions have an impact on the drying time, bond strength, and water resistance of the fire-resistant coating, and have no significant effect on the fire-resistant performance of the coating. After 7 days of water resistance, the fire resistance and bond strength of the fire-resistant coatings have decreased, but the bond strength will increase with time.

Table 8 Comprehensive Comparison of the Testing Results of Flame Retardant Coatings under Different Application Conditions

Comparing different construction conditions, among samples 1 to 6 cured at room temperature, the bond strength, water resistance, and adhesive strength after water resistance of sample 3 (1 course per day and 21 d curing at room temperature) all perform well, which proves that at room temperature In the curing construction process, extending the coating application interval and increasing the curing time will improve the coating performance. Among the samples No. 7 to No. 10 using the drying process at 60 ℃, the bonding strength and the water-resistant cohesive strength of the No. 8 sample (1 pass per day and drying at 60 ℃ for 2 h) performed well. Application interval, increase drying time, the coating will show better performance.Based on the results of the above data, for the construction process of the intumescent fireproof coating, extending the coating interval and extending the curing period will increase the performance of the coating. Adopting the curing process at normal temperature requires prolonging the curing time, which will increase the construction period. The drying curing process can shorten the construction period, but it will increase the energy consumption and require equipment support. Therefore, in the case of complete equipment, a short construction period is suitable for the drying process, and a long construction period can be selected for the normal temperature curing process.
 

3 Conclusion

This article mainly discusses the effects of different construction processes on the performance of intumescent fire-resistant coatings. By adjusting the performance conditions such as the construction cycle, curing cycle, and curing temperature, attention is paid to the performance of fire-resistant coatings. The test results show that different construction processes have no significant effect on the fire resistance of the coating, and have an effect on the water resistance and bond strength of the coating. Prolonging the coating interval and the curing period of the coating will increase the performance of the coating. At the same time, the drying process can shorten the construction period and obtain better coating performance. When the equipment allows, the short construction period is suitable for the drying process, and the long-term construction period can be used at room temperature curing process. One application per day will make the coating have better comprehensive performance.

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