A polyester oligomer toughening agent and its application in solvent-free epoxy fire retardant coating

Abstract

The present invention discloses a polyester oligomer toughening agent and its application in solvent-free epoxy fire-retardant coatings. An epoxidized polyester containing a long carbon chain is synthesized as a toughening agent through a polycondensation reaction, and a flame retardant and a synergist (ammonium polyphosphate / melamine / pentaerythritol / titanium dioxide) are added to prepare a flexible epoxy fire-retardant raw material. By introducing a flexible chain into the epoxy resin through the toughening agent, the behavior of the traditional epoxy resin cross-linked network structure that hinders the expansion of the coating is improved, and the expansion effect and fire-retardant performance under the impact of hydrocarbon flames are improved. At the same time, the resistance to cold and hot cycles is greatly improved, solving the problem of brittleness at low temperatures. At the same time, it does not contain sulfur element, avoiding the production of strong acidic oxides such as sulfur dioxide after combustion, and is an environmentally friendly fire-retardant coating with a full life cycle.

Description

Technical Field

[0001] The invention belongs to the technical field of coatings and relates to a toughening agent-blended epoxy resin-based intumescent fire-retardant coating and a preparation method thereof. Background Art

[0002] Modern buildings often rely on steel structures for support. However, when a fire breaks out, the temperature at the fire scene can quickly exceed the critical temperature for static equilibrium stability of common structural steel. When the temperature rises to 500°C, the steel's strength drops to half its original value. At 650°C, the steel loses all its strength, making the building prone to collapse. Fire-retardant coatings effectively insulate the high temperatures of a fire scene, keeping the steel structure below the critical temperature, significantly extending its fire resistance and effectively reducing fire damage. Using intumescent fire-retardant coatings is an effective method for protecting steel structures from fire. Intumescent fire-retardant coatings typically incorporate ammonium polyphosphate, pentaerythritol, and melamine into the coating formulation. Under heat, the coating decomposes, foams, and carbonizes, providing thermal insulation for the substrate. Ammonium polyphosphate, pentaerythritol, and melamine serve as the acid source, carbon source, and gas source, respectively, commonly known as the "three sources." Based on classical polymer foaming theory and cell growth mechanisms, the intumescent fire-retardant performance of intumescent fire-retardant coatings is closely related to the resin's molecular chain structure, crosslink density, and molecular chain length.

[0003] Intumescent fire retardant coatings primarily use epoxy resins. As a thermosetting material, epoxy resins are corrosion-resistant, highly chemically stable, and have strong adhesion, making them suitable for use in hydrocarbon fire retardant coatings in the petroleum and petrochemical industries. However, as a thermosetting resin, epoxy resins have a highly cross-linked network structure after curing, resulting in poor deformation ability after heating, which affects the foaming and expansion of the coating. Furthermore, their high low-temperature brittleness and poor impact resistance greatly limit their application in some specialized industries, such as offshore oil drilling platforms and LNG tankers, which experience drastic temperature fluctuations. Therefore, improving their low-temperature toughness and overcoming their low-temperature brittleness are technical challenges that the epoxy fire retardant coatings industry needs to address.

[0004] To address these technical challenges, it's necessary to add a suitable toughening agent to epoxy resin fire retardant coatings. Chinese invention patent CN 110903738B, "A flexible solvent-free epoxy fire retardant coating and its preparation method," states that while the resulting flexible solvent-free epoxy fire retardant coating exhibits some crack resistance, the epoxy-modified polysulfide EPS25 used in the preparation process contains sulfur, which, upon combustion, produces sulfur oxides that damage the environment and present certain drawbacks.

[0005] The use of dibasic acids and diols to synthesize flexible polyesters as toughening agents for epoxy resins is a common practice in the industry. To obtain highly flexible polyesters, it is usually necessary to select dibasic acids with a larger number of carbon atoms between the two carboxyl groups and a slightly longer carbon chain, such as suberic acid, azelaic acid, sebacic acid, and dodecanedioic acid. However, these longer carbon chains are prone to crystallization, resulting in a high viscosity of the resulting polyester at room temperature, which has a significant impact on the workability of epoxy resin coatings. The amount of diluent that needs to be added will increase the VOC emissions of the epoxy coating, which does not meet the requirements of environmentally friendly coatings. How to overcome the crystallinity of polyesters obtained from long-chain dibasic acids and reduce their viscosity is another technical challenge in the industry. Summary of the Invention

[0006] To address the above-mentioned issues, the present invention uses a polycondensation reaction to react azelaic acid, dodecanedioic acid, and diethylene glycol to obtain a preliminary product, which is then further subjected to an exothermic reaction with an epoxy resin under certain conditions to produce an epoxidized linear polyester oligomer. By compounding dibasic acids with different odd and even carbon numbers, and selecting different epoxy compounds for epoxidizing the polyester, the structural symmetry and regularity of the polyester molecular chain are disrupted, its crystallinity is inhibited, and its viscosity is reduced. The resulting toughening agent, prepared by regulating the ratio of epoxy resin to linear polyester oligomer, can be used in intumescent fire-retardant coatings to address the problems of epoxy intumescent fire-retardant coatings, such as insufficient expansion height when resistant to hydrocarbon flames, insufficient fireproofing performance, and brittleness at low temperatures.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] The epoxy resin-based intumescent fire retardant coating is composed of components A and B by weight. Component A contains 2-22 parts of epoxy resin, 2-20 parts of linear polyester oligomer toughening agent, 4-5 parts of epoxy diluent, 25-30 parts of ammonium polyphosphate, 8-10 parts of melamine, 8-10 parts of pentaerythritol, and 7-10 parts of titanium dioxide. Component B contains 8-14 parts of polyamide curing agent JD-814.

[0009] The linear polyester oligomer toughening agent has the following synthesis reaction equation:

[0010]

[0011] Among them, n is preferably 1 or 2.

[0012] A preparation method of a solvent-free polyester toughened flexible epoxy fire retardant coating is as follows:

[0013] (1) Synthesis of linear polyester oligomer toughening agent: Calculate the required theoretical mass of dibasic acid and diol according to the preferred total amount of substance of 2:1. Pour it into a four-necked round-bottom flask, and equip the flask with a stirring and dehydration device. Then add the catalyst monobutyltin oxide to carry out polycondensation reaction. Heat the contents of the flask to 110-130℃ and maintain it under nitrogen for 20-30 minutes to fully melt the contents of the flask. Heat the reactant to 170-180℃ (5 hours and 15 minutes), remove the distillate (water), and check its acid value. The reactant is kept at 170-180℃ for another 2.5 hours until all the hydroxyl groups in the diethylene glycol are reacted and the acid value reaches about 210-230 mg KOH / g.

[0014] The reactants were cooled to 95-105° C., 1,4-butanediol diglycidyl ether, epoxy resin EP-51, and triphenylphosphine were added, followed by a mild exothermic reaction. The reaction temperature was adjusted to 85-95° C. and maintained for 5-6 hours. At this time, the acid value was 0.23 mg KOH / g, and a linear polyester oligomer toughening agent was obtained.

[0015] Furthermore, the dibasic acids are azelaic acid and dodecanedioic acid. Using either acid alone or replacing it with another acid increases the viscosity, raises the glass transition temperature of the coating, and reduces the expansion and fireproofing properties. A 3:1 molar ratio of dodecanedioic acid to azelaic acid is preferred, as it provides low viscosity and optimal results.

[0016] Furthermore, the diol includes one or more of diethylene glycol, triethylene glycol and dipropylene glycol.

[0017] Furthermore, the addition amounts of the above components are as follows, calculated by weight: 6 to 7 parts of azelaic acid, 22 to 23 parts of dodecanedioic acid, 6 to 7 parts of diethylene glycol, 0.07 to 0.09 parts of monobutyltin oxide, 17 to 18 parts of 1,4-butanediol diglycidyl ether (LS-622), 49 to 50 parts of epoxy resin, and 0.2 to 0.3 parts of triphenylphosphine.

[0018] (2) Preparation of fire retardant coating: Ammonium polyphosphate, melamine, pentaerythritol, titanium dioxide, epoxy resin, 1,4-butanediol diglycidyl ether, and linear polyester oligomer toughening agent were mixed and uniformly dispersed in a high-speed disperser at a speed of 1000 r / min for 20 min. Polyamide curing agent JD-814 was added to the dispersed slurry.

[0019] Furthermore, the epoxy resin is a bisphenol A diglycidyl ether epoxy resin, and the epoxy value is 0.48 to 0.54 eq / 100 g.

[0020] Furthermore, the curing agent is added in an amount according to the ratio of active hydrogen equivalent to epoxy equivalent of 1:1.

[0021] Compared with the prior art, the advantages of the present invention are:

[0022] The toughening agent prepared by the present invention uses azelaic acid and dodecanedioic acid as raw materials to synthesize epoxidized linear polyester oligomers. This degrades the crystallinity of the polyester and reduces its viscosity. The resulting epoxy fire-retardant coating can be used as a toughening agent for preparing solvent-free epoxy fire-retardant coatings. The resulting epoxy fire-retardant coating film has a moderate glass transition temperature, allowing the paint film to exhibit suitable deformation capacity upon heating without affecting the foaming and expansion of the intumescent flame retardant system. This significantly improves the expansion effect and fireproofing properties of the epoxy resin-based intumescent fire-retardant coating, while overcoming the drawback of epoxy resin fire-retardant coatings, which are prone to brittle cracking at low temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The hydrogen nuclear magnetic resonance spectra of the polyester toughening agents in Examples 1-3 and Comparative Examples 1-2 are shown.

[0024] Figure 2 1-3 and 1-2. 4-11-12 are Fourier transform infrared spectra of the linear polyester oligomer toughening agents in Examples 1-3 and Comparative Examples 1-2.

[0025] Figure 3 The following are DSC curves of paint films with different formulations under nitrogen atmosphere.

[0026] Figure 4 This is the ultimate fire resistance test curve.

[0027] Figure 5 The following are TGA / DTG diagrams of paint films with different formulations under nitrogen atmosphere.

[0028] Figure 6 This is the SEM image of the residual carbon layer of the fire retardant coating after the fire test. DETAILED DESCRIPTION

[0029] The present invention will now be further described with reference to specific examples. The following examples are intended to illustrate the present invention rather than to further limit the present invention.

[0030] The raw materials used in the present invention are all commercially available industrial products, and the testing methods used are as follows:

[0031] 1 H-NMR spectrum analysis: The determination was carried out using an ARX-400 nuclear magnetic resonance spectrometer from Bruker, Germany, with deuterated acetone as solvent.

[0032] Glass transition temperature (T g ) Test: The measurement was performed using a Pyris 8500 differential scanning calorimeter (Perkin Elmer, USA) in a nitrogen atmosphere at a heating rate of 20°C / min.

[0033] Ultimate Fire Resistance Test: The coating's fire resistance is tested using the Q / 6S2153 fire resistance time tester developed by AVIC Bermuda. The ultimate fire resistance time is the time it takes for the substrate backplane to reach 580°C. This test is based on the standards Q / 6S 2138-2007 and GB / T 9978.

[0034] Thermogravimetric analysis: The thermal decomposition curves of fire retardant coatings with different formulations were measured using a TG 209F3 thermogravimetric analyzer from NETZSCH, Germany, in a nitrogen atmosphere at a heating rate of 20°C / min from 30°C to 800°C.

[0035] Basic performance test of paint film: gloss of paint film is tested according to GB / T 9754-2007, hardness of paint film is tested according to GB / T 6739-2006, adhesion of paint film is tested according to GB / T 9286-1998, and impact resistance of paint film is tested according to GB / T 1732-1993.

[0036] The fire retardant coating film resistance to cold and heat shock test is to place the paint film sample in a -20℃ environment for 4 hours, 60℃ environment for 4 hours, and 23℃ environment for 16 hours as one cycle. The cycle test is carried out continuously for several cycles until the paint film cracks, falls off, etc., which is considered to be failure and the test is stopped.

[0037] Expanded carbon layer structure testing and characterization: A digital camera was used to analyze the macroscopic appearance of the expanded carbon layer, and a JEOL JSM-6360LA scanning electron microscope was used to observe the internal microstructure of the expanded carbon layer. Nano Measurer, a particle size distribution calculation software, was used to analyze and calculate the internal pore size of the carbon layer.

[0038] Example 1:

[0039] (1) Calculate and weigh the required theoretical mass of azelaic acid, dodecanedioic acid, and diethylene glycol (23.5 g azelaic acid, 26.5 g diethylene glycol, and 86.25 g dodecanedioic acid) according to the ratio of acid to alcohol in a ratio of 2:1, add them to a four-neckedioic acid round-bottom flask, and then add 0.27 g monobutyltin oxide to carry out polycondensation reaction. Heat the contents of the flask to 120°C for 30 minutes to fully melt the contents of the flask, start stirring, and pass nitrogen. Heat the reactants to 175°C for 5.5 hours and remove water. Keep the reactants at 175°C for 2.5 hours until the acid value reaches 217 mg KOH / g. At this time, cool the reactants to 100°C, and add 65 g 1,4-butanediol diglycidyl ether, 188 g epoxy resin E-51, and 1.13 g triphenylphosphine. A mild exothermic reaction was then carried out, and the temperature of the reactants was adjusted to 90°C and maintained for 5.5 hours. At this time, the acid value was 0.23 mg KOH / g, and a linear polyester oligomer toughening agent ADPE was obtained. Its viscosity at 25°C was measured to be 12000 mPa.s. The results of nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy were shown in Figure 2. Figure 1 and Figure 2 shown.

[0040] (2) According to the formula in Table 1, epoxy resin E-51 and toughening agent ADPE were mixed in a ratio of 7:3. The theoretical mass of epoxy resin, toughening agent ADPE, diluent 1,4-butanediol diglycidyl ether, ammonium polyphosphate, melamine, pentaerythritol, and titanium dioxide were mixed and dispersed evenly using a high-speed disperser at a speed of 1000 r / min for 20 minutes. Then, polyamide curing agent JD-814 (commercially available, Changzhou Kingdee Chemical Co., Ltd.) was added and mixed evenly. The coating was applied to the steel substrate with a brush. The average thickness of the coating sample was maintained at about 2 mm and measured by a thickness gauge. The coating was cured at room temperature for 7 days. The test results of the fire retardant coating are shown in Table 3.

[0041] At the same time, in order to verify the toughening effect of the toughening agent on epoxy resin, a solvent-free varnish was also prepared without any flame retardant ingredients, that is, only epoxy resin, toughening agent ADPE, diluent 1,4-butanediol diglycidyl ether and curing agent JD 814. The solvent-free varnish was used to prepare a sample, and its basic properties were tested as shown in Table 4.

[0042] Example 2:

[0043] (1) The synthesis steps of linear polyester oligomer toughening agent ADPE are the same as step (1) in Example 1.

[0044] (2) According to the formula in Table 1, the epoxy resin and toughening agent ADPE are mixed in a ratio of 5:5, the flame retardant content is controlled to account for 50% of the total components, and the curing agent content is calculated. The other steps are the same as step (2) of Example 1.

[0045] Example 3:

[0046] (1) The synthesis steps of linear polyester oligomer toughening agent ADPE are the same as step (1) in Example 1.

[0047] (2) According to the formula in Table 1, the epoxy resin and toughening agent ADPE were mixed in a ratio of 3:7. The other steps were the same as step (2) in Example 1.

[0048] Comparative Example 1:

[0049] (1) The synthetic ratio, reaction conditions and steps of the polyester oligomer were the same as those of step (1) of Example 1, except that only azelaic acid was used as the dibasic acid, and the total molar amount of the dibasic acid was consistent with the molar amount of the dibasic acid in Example 1, to obtain an epoxidized linear polyester oligomer toughening agent APE, which had a viscosity of 14,000 mPa.s at 25°C (Table 2), which was significantly higher than the viscosity of the polyester obtained by combining dodecanedioic acid and azelaic acid.

[0050] (2) According to the ratio of epoxy resin to toughening agent APE of 7:3, the theoretical mass of epoxy resin, toughening agent APE, 1,4-butanediol diglycidyl ether, ammonium polyphosphate, melamine, pentaerythritol and titanium dioxide were mixed and evenly dispersed in a high-speed disperser at a speed of 1000r / min for 20min. Then, polyamide curing agent JD-814 was added and mixed evenly. The coating was applied on the steel substrate with a brush. The average thickness of the coating sample was kept at about 2 mm and measured by a thickness gauge. The coating was cured at room temperature for 7 days. The formula of the fire retardant coating is as shown in Table 1, Comparative Example 1. The formula of the varnish is as shown in Table 1, Comparative Example 1, without adding APP, MEL, PER and TiO2.

[0051] Comparative Example 2:

[0052] (1) The synthetic ratio, reaction conditions and steps of the polyester oligomer were the same as those of step (1) of Example 1, except that only dodecanedioic acid was used as the dibasic acid, and the total molar amount of the dibasic acid was consistent with the molar amount of the dibasic acid in Example 1, i.e., only dibasic acids with an even number of carbon atoms were retained, to obtain an epoxidized linear polyester oligomer toughening agent DPE, which had a viscosity of 14200 mPa.s at 25°C.

[0053] (2) According to the ratio of epoxy resin to toughening agent DPE of 7:3, the theoretical mass of epoxy resin, toughening agent DPE, 1,4-butanediol diglycidyl ether, ammonium polyphosphate, melamine, pentaerythritol and titanium dioxide were mixed and evenly dispersed using a high-speed disperser at a speed of 1000r / min for 20min. The coating was applied to the steel substrate with a brush. The average thickness of the coating sample was maintained at about 2 mm and measured by a thickness gauge. The coating was cured at room temperature for 7 days. The formula of the varnish is as shown in Table 1, Example 2, without APP, MEL, PER and TiO2. The formula of the fire retardant coating is as shown in Table 1, Example 2.

[0054] Comparative Example 3:

[0055] Without adding any toughening agent, only epoxy resin was used. The coating preparation and operation process were the same as in Example 1. The formula is shown in Table 1. The theoretical mass of epoxy resin, 1,4-butanediol diglycidyl ether, ammonium polyphosphate, melamine, pentaerythritol, and titanium dioxide were mixed and evenly dispersed using a high-speed disperser at a speed of 1000 r / min for 20 minutes. The coating was applied to the steel substrate with a brush. The average thickness of the coating sample was maintained at approximately 2 mm and measured using a thickness gauge. The coating was cured at room temperature for 7 days.

[0056] Comparative Example 4:

[0057] The molar ratio of azelaic acid to dodecanedioic acid was adjusted to 1:1, and the other steps were the same as step (1) of Example 1 to prepare a linear polyester oligomer toughener ADPE1, which had a viscosity of 13600 mPa.s at 25°C (Table 2), which was higher than the viscosity when the ratio of azelaic acid to dodecanedioic acid was 1:3, and was not suitable for application in solvent-free epoxy fire retardant coatings.

[0058] Comparative Example 5:

[0059] The synthetic ratio, reaction conditions and steps of the polyester oligomer are the same as those of step (1) of Example 1, except that azelaic acid and 1,4-butanediacid are used as dibasic acids in a molar ratio of 1:3, and the total molar amount of the dibasic acid is consistent with the molar amount of the dibasic acid in Example 1, thereby obtaining an epoxidized linear polyester oligomer toughening agent ATPE, which has a viscosity of 14600 mPa.s at 25°C (Table 2), which is higher than the viscosity of the polyester obtained by combining dodecanedioic acid and azelaic acid, and is not suitable for application in solvent-free epoxy fire retardant coatings.

[0060] Comparative Example 6:

[0061] Adipic acid, dodecanedioic acid, and diethylene glycol were weighed and calculated to achieve a 2:1 molar ratio (18.25 g adipic acid, 86.25 g dodecanedioic acid, and 26.5 g diethylene glycol). The mixture was then added to a four-necked round-bottom flask, followed by 0.27 g monobutyltin oxide for a polycondensation reaction. The flask contents were heated to 120°C for 30 minutes to fully melt. Stirring was initiated and nitrogen flowed through the flask. The reaction mixture was heated to 175°C for 5.5 hours, with water removed. The reaction mixture was maintained at 175°C for an additional 2.5 hours until the acid value reached 217 mg KOH / g. At this point, the reaction mixture was cooled to 100°C, and 65 g 1,4-butanediol diglycidyl ether, 188 g epoxy resin E-51, and 1.13 g triphenylphosphine were added. A mild exothermic reaction then proceeded, with the temperature adjusted to 90°C for 5.5 hours. The acid value reached 0.23 mg KOH / g, yielding a linear polyester oligomer toughening agent, AAPE. The viscosity of AAPE was measured to be exceptionally high, at 80,000 mPa·s, making it unsuitable for use in the preparation of solvent-free epoxy fire retardant coatings.

[0062] Table 1 Fire retardant coating formula

[0063]

[0064] Table 2 Molecular weight and viscosity of polyester toughening agents

[0065]

[0066] Table 3 Ultimate fire resistance time of fire retardant coating

[0067]

[0068] Table 4 Basic properties of solvent-free varnish

[0069]

[0070]

[0071] As shown in Table 4, the impact strength of Examples 1-3 is higher than that of Comparative Example 3. The overall performance of the varnish without epoxy diluent is relatively poor. Without affecting the pencil hardness and adhesion, the overall performance of Example 2 is better.

[0072] Table 5 Resistance to thermal shock

[0073]

[0074] It can be seen from Table 5 that the thermal shock resistance of the embodiments is significantly higher than that of the comparative examples, and among them, the thermal shock resistance of Examples 2 and 3 is relatively good.

[0075] Figure 1It is the nuclear magnetic resonance hydrogen spectrum of the linear polyester oligomer toughening agent in Example 1-3 and Comparative Example 1-3, wherein the peak a at δ=6.85ppm and δ=7.28ppm is the proton peak of the benzene ring in the epoxy resin, the peak b at δ=3-4.2ppm is the CH2 peak of diethylene glycol, the peak c at δ=2.5-3ppm is the CH2 peak of azelaic acid, and the peak d at δ=1.3-1.5ppm is the CH2 peak on dodecanedioic acid.

[0076] Figure 2 The infrared spectra of the linear polyester oligomer toughening agent in Examples 1-3 and Comparative Examples 1-3 are shown in FIG. -1 The absorption peak of ester group is at 831cm. The appearance of ester group indicates that the acid and alcohol have undergone esterification reaction, indicating that polyester has been successfully synthesized. -1 The peak at 2928cm is the bending vibration peak of epoxy group. -1 、2856cm -1 The peak of CH2 stretching vibration is 1607cm -1 、1509cm -1 It is the C=C stretching vibration peak on the benzene ring.

[0077] Figure 3 The DSC curves of different varnish cured films under nitrogen atmosphere are shown in Figure 2. As the toughening agent content increases, the T g Gradually decreases. When the T g When T is too high or too low, the carbon layer obtained in Comparative Examples 2 and 3 has large pores or is difficult to foam, the foaming ratio is relatively low, and the fire-resistant time is not long enough. g The size is moderate as in Example 2, and the softening speed and viscosity after heating are appropriate, and it can cooperate well with other components in the system to foam into carbon.

[0078] Figure 4 The maximum fire resistance test curve is shown in Table 2, and the data obtained from the fire resistance test is shown in Table 2. The maximum fire resistance time is the time required for the substrate backsheet to reach 580°C. As can be seen from the figure, the maximum fire resistance time of Comparative Example 3 is the shortest, at 38 minutes; the maximum fire resistance time of Comparative Example 2 is 42 minutes, and the maximum fire resistance times of Examples 1-3 are 46, 49, and 47 minutes, respectively. The maximum fire resistance time of Example 2 is higher than that of the other examples, indicating that Example 2 has the best fire resistance performance.

[0079] Figure 5 The following are TGA graphs of different formulations under a nitrogen atmosphere. The graphs show that the epoxy resin-based intumescent fire retardant coatings prepared with different toughening agents all undergo a similar decomposition process. Compared with the comparative example, Examples 1-3 exhibit better fire resistance without sacrificing a large residual carbon content. Overall, Examples 2 and 3 exhibit the best fire resistance.

[0080] Figure 6 Figures a and b show the microscopic carbon layer morphologies of the fire-retardant coatings prepared in Example 2 and Comparative Example 3, respectively. Compared to the carbon layer in Comparative Example 3, which has an average pore size of 8.87 μm, the carbon layer of the fire-retardant coating prepared using the linear polyester oligomer toughening agent ADPE exhibits improved density and continuity. The carbon layer in Example 2 exhibits the best morphology, with small, dense pores and an average pore size of 4.28 μm. This dense, continuous carbon layer structure significantly isolates heat transfer to the steel substrate.

Claims

1. A linear polyester oligomer toughening agent with a flexible segment, characterized in that: The polyester oligomer toughening agent is prepared by firstly subjecting azelaic acid, dodecanedioic acid and diol to a condensation reaction to obtain a polyester oligomer, and then reacting the polyester oligomer with an epoxy resin and 1,4-butanediol diglycidyl ether to obtain a linear polyester oligomer toughening agent; the molar ratio of azelaic acid to dodecanedioic acid is 3:

1.

2. The linear polyester oligomer toughening agent with a flexible segment according to claim 1, characterized in that: The preparation method of polyester oligomer toughening agent is: (1) In a reaction vessel, add 6-7 parts of azelaic acid, 6-7 parts of diol, 22-23 parts of dodecanedioic acid, and then add 0.07 parts of monobutyltin oxide to carry out polycondensation reaction, heat to 110-130 ° C, keep nitrogen flow for 20-30 minutes, then start stirring to melt the materials and collect the reactants; (2) The reactants were heated to 170-180 °C for dehydration, and then the temperature was maintained at 170-180 °C until the acid value reached 210-230 mg KOH / g. The reactants were cooled to 95-105 °C, 17-18 parts of 1,4-butanediol diglycidyl ether, 49-50 parts of epoxy resin and 0.2-0.3 parts of triphenylphosphine were added, and the temperature of the reactants was adjusted to 85-95 °C and maintained for 5-6 h to obtain a linear polyester oligomer toughening agent.

3. The linear polyester oligomer toughening agent with flexible segments according to claim 2, characterized in that: The epoxy resin is bisphenol A diglycidyl ether epoxy resin with an epoxy value of 0.48~0.54 eq / 100 g.

4. The linear polyester oligomer toughening agent with a flexible segment according to claim 2, characterized in that: The diol includes one or more of diethylene glycol, triethylene glycol and dipropylene glycol; the total mass ratio of the dibasic acid to the diol is 2:

1.

5. Use of the linear polyester oligomer toughening agent with flexible segments according to any one of claims 1 to 4 in solvent-free epoxy fire retardant coatings, characterized in that: The raw materials of the fire retardant coating are calculated by weight and are composed of components A and B, wherein component A is as follows: 2 to 22 parts of epoxy resin, 2 to 20 parts of linear polyester oligomer toughening agent, 4-5 parts of epoxy diluent, 25 to 30 parts of ammonium polyphosphate, 8 to 10 parts of melamine, 8 to 10 parts of pentaerythritol, and 7 to 10 parts of titanium dioxide; component B is: 8 to 14 parts of curing agent.

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