The silicone resin-modified epoxy resin-based flame retardant thermal insulation coating was prepared from epoxy resin as the main film-forming agent, silicone resin diluted with isopropanol as a copolymerization modifier, ammonium polyphosphate (APP) as dehydration catalyst, melamine (MEL) as foaming agent, pentaerythritol (PER) as char forming agent, and palygorskite and sepiolite as fillers. The effect of silicone resin on the flame retardancy, physicochemical properties and mechanical properties of the coatings were investigated by large plate combustion, ultimate limiting oxygen index (LOI), vertical combustion, cone calorimetry, X-ray diffraction (XRD), Fourier infrared analysis, thermogravimetric differential scanning calorimetry analysis, N2 absorption and desorption test, scanning electron microscopy (SEM), and tensile, flexural, compressive strength tests. The addition of silicone resin not only accelerated the thermal reaction of the coating when exposed to heat, but also improved the thermal stability and oxidation resistance of the coating. The silica generated by the decomposition of silicone resin not only increased the residual char content of the coating but also optimized the structure of the coating. The surface of residual char was denser, and the internal pore structure was finer and high-density, which effectively reduced the smoke emission of the coating, enhanced the anti-ablation effect, improved the insulation effect, and increased the mechanical performance. Through comprehensive comparison, when the amount of silicone resin added was 20[Formula: see text]wt.%, the performance of E80S20 coating was the best. After 2[Formula: see text]h of butane flame ablation, the backside temperature was just 198.8∘C with no molten pits. The peak heat release rate (PHRR), total heat release (THR), total smoke production (TSP), and peak smoke production rate (PSPR) were significantly improved, with 17.3%, 33.8%, 32.0%, and 49.2% lower than those of blank sample E10S0. The LOI value of E80S20 was 32.5%, while that of the blank sample was just 20.8%. After combustion, the mass of the residual char and the Brunauer–Emmet–Teller (BET) surface area of E8020 was 15.8% and 256% higher than those of E10S0. Besides, the tensile, bending and compressive strengths of E80S20 were 23.7, 36.2, and 79.3[Formula: see text]MPa, which were 3%, 2.6%, and 13.1% higher than those of E10S0. Corrosion resistance tests show that the coating is suitable for aqueous environments but not for acidic or alkaline environments. Finally, the flame retardant mechanism of E80S20 coating is summarized into four types: cooling insulation, vapor phase flame retarding, condensed phase flame retarding, and reinforced flame retarding.
