Phosphorus-containing polymer-coated expandable graphite, preparation method thereof and application of phosphorus-containing polymer-coated expandable graphite in fire-retardant coating of fire-fighting pipe network of transformer substation or converter station

Abstract

The invention discloses phosphorus-containing polymer coated expansible graphite, a preparation method thereof and application of the phosphorus-containing polymer coated expansible graphite in a fire-retardant coating of a fire-fighting pipe network of a transformer substation or a converter station, and the preparation method comprises the following steps: mixing trihydroxymethyl phosphine oxide, expansible graphite and a solvent, adding a solution of the solvent of diisocyanate under a heating condition, and stirring uniformly; and after the reaction is finished, filtering, washing and drying to obtain the phosphorus-containing polymer coated expandable graphite. The surface of the expandable graphite is coated with the phosphorus-containing cross-linked polyurethane layer, so that the expansion volume of the expandable graphite is remarkably increased, the expandable graphite is applied to the epoxy resin type expansion fireproof coating, the high-temperature (1200 DEG C) resistant protection performance of the fireproof coating is remarkably improved, and the expandable graphite has good adhesion to steel, is easy to construct and form at one time, and has a good application prospect. The method can be used for fire-resistant protection of a fire-fighting pipe network of a transformer substation (converter station) and improves fire extinguishing reliability.

Description

Technical Field

[0001] The invention relates to the technical field of fireproof coatings, and in particular to a phosphorus-containing polymer-coated expandable graphite, a preparation method thereof, and an application thereof in fireproof coatings for fire protection pipe networks of transformer substations or converter stations. Background Art

[0002] In recent years, large oil-filled equipment in substations (converter stations) have exploded and caught fire one after another. These fire safety accidents have not only caused significant economic losses and adverse social impacts, but more importantly, have caused significant disturbances to the stability of the power grid system. A typical 1000kV UHV AC transformer contains more than 150t of transformer oil in a single-phase body, and a ±800kV UHV converter transformer contains more than 120t of transformer oil in a single-phase body. Due to the large amount of transformer oil, high operating temperature, and high heat, once a fire occurs, it can continue to burn for 10 to 20 hours, and even explode in extreme cases. When a fire accident occurs in large oil-containing equipment, the fire-fighting pipe network can reach a typical temperature of about 1200℃ within tens of seconds when a fire occurs in large oil-containing equipment. Before the fire extinguishing system is started, due to the insufficient anti-dry burning ability of the pipe network, the fire main pipe in the protection area is directly cracked, and some branches and pipelines are damaged by flames. The overall pressure loss of the pipe network leads to the failure of fire extinguishing. Therefore, it is urgent to carry out fire protection and heat insulation research on the fire protection system pipe network of large oil-containing equipment in UHV converter stations and substations.

[0003] Applying fire retardant coating on fire protection pipe network is one of the effective methods to improve the high temperature resistance of fire protection pipe network. Fire retardant coating generally includes intumescent fire retardant coating and non-intumescent fire retardant coating. The fire protection mechanism of intumescent fire retardant coating is that when the coating is heated at high temperature, it burns to form an expanded foam-like carbon layer. This carbon layer has low thermal conductivity and can effectively isolate heat, thereby protecting the substrate under the carbon layer. However, the existing intumescent fire retardant coating is difficult to meet the protection requirements of the fire protection system of the substation (converter station), that is, the existing fire retardant coating is difficult to meet the high temperature protection performance requirements at 1200°C.

[0004] Intumescent fire retardant coatings generally include film-forming substances, intumescent flame retardants, solvents, pigments, fillers and other ingredients. Expandable graphite is a commonly used filler for intumescent fire retardant coatings. After adding an appropriate amount of expandable graphite, the expansion degree of the carbon layer can often be increased, and the heat insulation capacity of the expanded carbon layer can be improved. Therefore, by increasing the expansion degree of expandable graphite, it is possible to increase the expansion degree of the carbon layer, thereby possibly improving the high temperature protection performance of the intumescent fire retardant coating. In order to increase the expansion degree of expandable graphite, the use of coating modification methods is considered. By coating a layer of polymer on the surface of expandable graphite and sealing the decomposition gas, it is possible to increase its expansion degree. In addition, the coating layer can change the inorganic interface and increase the compatibility between expandable graphite and the polymer matrix.

[0005] The Chinese patent application document with publication number CN107880316A discloses a polyurethane-coated expandable graphite flame retardant and a preparation method thereof. The method first stirs polyols and catalysts, then adds expandable graphite to stir, and then adds polyisocyanates to stir. Under the action of a catalyst, polyisocyanates and polyols react on the graphite surface to generate polyurethane, thereby obtaining polyurethane-coated expandable graphite. Its production process does not require solvents, is simple and convenient, and the surface-coated polyurethane accelerates the coking speed and improves the flame retardant properties of the material. The coating of polyurethane improves the compatibility problem of expandable graphite with polymer materials. Compared with the expandable graphite of the same addition amount, the flame retardant ability and mechanical properties of the polyurethane foam prepared by polyurethane-coated expandable graphite are significantly improved. Polyurethane-coated expandable graphite is a non-toxic, environmentally friendly, highly flame-retardant, and compatible flame retardant, but its flame retardant properties are still poor, which limits its application. Summary of the invention

[0006] The technical problem to be solved by the present invention is how to obtain a fire retardant coating that can meet the fire protection pipe network of a transformer substation or a converter station.

[0007] The present invention solves the above technical problems through the following technical means:

[0008] A method for preparing phosphorus-containing polymer-coated expandable graphite comprises the following steps: mixing trihydroxymethylphosphine oxide, expandable graphite and a solvent, adding a solution of diisocyanate in the solvent under heating conditions, then heat-insulating and reacting, and filtering, washing and drying after the reaction to obtain the phosphorus-containing polymer-coated expandable graphite.

[0009] Preferably, the solution of the diisocyanate in the above solvent is added after heating to 60-120° C., and then the reaction is kept warm for 1-12 hours.

[0010] Preferably, the expandable graphite is expandable graphite dried at 60-100° C. for 2-12 hours.

[0011] Preferably, the diisocyanate is selected from diphenylmethane diisocyanate, toluene diisocyanate or a mixture of the two.

[0012] Preferably, the solvent is selected from a mixture of one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and N-methylpyrrolidone.

[0013] Preferably, the molar ratio of the isocyanate group contained in the diisocyanate to the hydroxyl group of trimethylolphosphine oxide is 0.8:1-1.2:1.

[0014] Preferably, the mass ratio of trihydroxymethylphosphine oxide to expandable graphite is 0.05:1-0.3:1.

[0015] Preferably, in the process of mixing trihydroxymethylphosphine oxide, expandable graphite and solvent, the mass ratio of the solvent to the expandable graphite is 6:1-20:1.

[0016] Preferably, in the solution of the diisocyanate in the above solvent, the mass ratio of the solvent to the diisocyanate is 4:1-30:1.

[0017] Preferably, the solvent needs to be freed of moisture before use.

[0018] The invention also provides a phosphorus-containing polymer-coated expandable graphite, which is prepared by adopting the preparation method of the phosphorus-containing polymer-coated expandable graphite.

[0019] The present invention also proposes an application of the phosphorus-containing polymer-coated expandable graphite in fire retardant coatings for fire protection pipe networks in transformer substations or converter stations.

[0020] The present invention also provides a fireproof coating for fire protection pipe network of a transformer station or a converter station, which contains expandable graphite coated with the phosphorus-containing polymer.

[0021] Preferably, the fire retardant coating for fire protection pipe network of substation or converter station comprises raw materials including epoxy resin, intumescent flame retardant, expandable graphite coated with phosphorus-containing polymer and curing agent; the mass fraction of the intumescent flame retardant is 20-60%; the mass fraction of the expandable graphite coated with phosphorus-containing polymer is 1-10%; the molar ratio of NH groups in the curing agent to epoxy groups in the epoxy resin is 0.8:1-1.2:1.

[0022] Preferably, the epoxy resin is selected from bisphenol A diglycidyl ether.

[0023] Preferably, the intumescent flame retardant comprises an acid source, a carbon source and a gas source, and the acid source is selected from ammonium polyphosphate, melamine polyphosphate or a mixture of the two.

[0024] Preferably, the carbon source is selected from pentaerythritol, dipentaerythritol or a mixture of the two.

[0025] Preferably, the gas source is selected from melamine, dicyandiamide or a mixture of the two.

[0026] Preferably, the mass ratio of the acid source, the carbon source and the gas source is 20-80:10-40:10-40.

[0027] Preferably, the curing agent is selected from a mixture of one or more of ethylenediamine, propylenediamine, butylenediamine, pentanediamine and hexamethylenediamine.

[0028] Preferably, if the curing agent is solid at room temperature, it needs to be heated into liquid in advance.

[0029] Preferably, the thickness of the fire retardant coating formed by the fire retardant coating for the fire protection pipe network of the substation or converter station during use is 0.1-10 mm.

[0030] Compared with the prior art, the advantages of the present invention are:

[0031] (1) The present invention can significantly increase the expansion volume of expandable graphite by coating the surface of expandable graphite with a phosphorus-containing polymer. The preparation method of expandable graphite coated with a phosphorus-containing polymer is simple, the raw materials are cheap and readily available (all are commercial products), and the reaction conditions are mild.

[0032] (2) Adding phosphorus-containing polymer-coated expandable graphite to the intumescent fire-retardant coating can significantly improve the high-temperature protection performance of the epoxy resin type intumescent fire-retardant coating under high-temperature flames (1200°C).

[0033] (3) The fire-retardant coating prepared by the coating of the present invention has excellent protection performance at a high temperature of 1200°C, and the coating does not crack or fall off after flame combustion; the fire-retardant coating has good adhesion performance on the steel substrate; the viscosity of the fire-retardant coating material is easy to control, the coating is simple, and it is easy to achieve one-time construction and forming of the coating; the preparation method of the fire-retardant coating is simple, the raw materials are cheap and easy to obtain, and no solvent is required in the preparation process of the coating. The fire-retardant coating prepared by the present invention can be used for the fire protection pipe network of a substation (converter station). BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 These are photos of expandable graphite after expansion, which is uncoated (left picture) / coated with a phosphorus-containing polymer (right picture) in Example 1 of the present invention;

[0035] Figure 2 The test results of the high temperature protection performance of the coatings prepared in Example 2 of the present invention and Comparative Examples 1-2 are as follows;

[0036] Figure 3 The photos of carbon residue after the coatings prepared in Example 2 of the present invention and Comparative Examples 1-2 were tested;

[0037] Figure 4 The present invention illustrates the reaction process of coating expandable graphite using trihydroxymethylphosphine oxide and diphenylmethane diisocyanate as raw materials. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] Unless otherwise specified, the test materials and reagents used in the following examples can be obtained from commercial sources.

[0040] If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the art or according to the product instructions.

[0041] Example 1

[0042] A preparation method of phosphorus-containing polymer-coated expandable graphite comprises the following steps: first, 0.5 g of trihydroxymethylphosphine oxide and 5 g of expandable graphite are added to a round-bottom flask, the expandable graphite is dried at 80° C. for 12 hours before being added, then 40 mL of N,N-dimethylformamide is added to obtain a mixture, and a solution of 1.34 g of 4,4'-diphenylmethane diisocyanate in 20 mL of N,N-dimethylformamide is added dropwise to the mixture at 80° C. After the addition is completed, the reaction is continued for 2 hours, and then filtered. After the filtration is completed, the mixture is washed twice with N,N-dimethylformamide, and the filter cake is dried by forced air at 80° C. for 12 hours to obtain the product phosphorus-containing polymer-coated expandable graphite. The product is a black block solid, which is crushed for use, and the product weighs 5.64 g.

[0043] Comparative Example 1

[0044] Take 141.9g E44 epoxy resin in a plastic cup and heat it at 50℃ to reduce the viscosity. Then add 18.16g 1,6-hexanediamine (1,6-hexanediamine is solid at room temperature and needs to be heated to melt into liquid). After stirring evenly, the material becomes more viscous after being placed at room temperature for several minutes. At this time, the material is manually coated on a steel plate with a size of 300mm×300mm×2.5mm. The thickness of the coating after curing is controlled to be about 2mm. The high temperature protection performance of the coating is tested after the coating is placed at room temperature for 48 hours.

[0045] Comparative Example 2

[0046] Take 106.4g E44 epoxy resin in a plastic cup and heat it at 80℃ to reduce the viscosity. Then add the intumescent flame retardant and 5.15g uncoated expandable graphite (all pre-dried at 80℃ for 12 hours). The intumescent flame retardant contains 25.7g ammonium polyphosphate, 10.3g dipentaerythritol and 10.3g melamine. After stirring evenly, add 13.6g 1,6-hexanediamine (1,6-hexanediamine is solid at room temperature and needs to be heated and melted into liquid first). After stirring evenly, the material becomes more viscous after being placed at room temperature for several minutes. At this time, the material is manually coated on a steel plate with a size of 300mm×300mm×2.5mm, and the thickness of the coating is controlled to be about 2mm after curing. The high temperature protection performance of the coating is tested after the coating is placed at room temperature for 48 hours.

[0047] Example 2

[0048] The preparation method of the coating in Example 2 is basically the same as that of the coating in Comparative Example 2, except that the uncoated expandable graphite is replaced by the phosphorus-containing polymer-coated expandable graphite prepared in Example 1.

[0049] The test method for the expansion volume of phosphorus-containing polymer coated expandable graphite / uncoated expandable graphite is: put 1g of the sample to be tested into a muffle furnace at 600°C, take it out after 10 minutes and cool it to room temperature, measure the volume after expansion, and the expansion volume is expressed as mL / g. Figure 1 The photo of the sample after the test is completed shows that the volume of the uncoated expandable graphite after expansion is about 60mL, that is, the expansion volume is 60mL / g, and the expansion volume of the phosphorus-containing polymer-coated expandable graphite is about 95mL, that is, the expansion volume is 95mL / g. And it can be seen that the phosphorus-containing polymer-coated expandable graphite generates a larger "worm"-shaped carbon slag after expansion. The phosphorus-containing polymer coated on the surface of expandable graphite generates a dense carbon layer at high temperature, seals the gas released by the heat of expandable graphite, and thus increases the expansion volume. The adhesion of the coating prepared in Example 2 and Comparative Examples 1-2 on the steel plate is tested by ASTM D3359, and the result shows that the adhesion of the coating can reach the highest level.

[0050] The high temperature protection performance of the coating was simulated by a large plate combustion device test: a flame spray gun was used to aim at the center of the coated side of the steel plate, and the flame temperature of the coating surface was tested by a thermocouple on the coating surface, and the flame temperature of the coating surface was kept at about 1200°C, and the temperature of the center of the back-fired side of the steel plate was tested over time (the blank test is the test result of the steel plate without coating). The test results of the high temperature protection performance of the coating prepared in Example 2 and Comparative Examples 1-2 and the blank test are shown in Figure 2. Figure 2 shown.

[0051] Figure 2It shows that when the blank test was not coated, the temperature of the back of the steel plate rose rapidly under the impact of a 1200°C flame, and soon stabilized at about 493°C. After coating the coating in Comparative Example 1, the back temperature stabilized at about 335°C after 1 hour, indicating that the coating in Comparative Example 1 has certain high temperature protection performance. After coating the coating in Comparative Example 2, the back temperature stabilized at about 173°C after 1 hour. Compared with the coating in Comparative Example 1, the coating in Comparative Example 2 added an intumescent flame retardant (ammonium polyphosphate, dipentaerythritol and melamine) and uncoated expandable graphite, and their addition significantly improved the high temperature protection performance of the coating. After coating the coating in Example 2, the back temperature stabilized at about 152°C after 1 hour. Although the back temperature stability value was only reduced by 21°C, the lower the temperature, the more difficult it is to reduce, and such a reduction is already very significant. Compared with the coating in Comparative Example 2, the coating in Example 2 replaces the uncoated expandable graphite with expandable graphite coated with a phosphorus-containing polymer, indicating that the coating of the expandable graphite with the phosphorus-containing polymer significantly improves the high temperature protection performance of the coating.

[0052] Figure 3 It is a top view and a side view of the coating after testing in Example 2 and Comparative Examples 1-2. This figure shows that when the coating prepared only by cured epoxy resin in Comparative Example 1 is tested, the coating area directly contacted by the flame is burned out, exposing the steel plate under the coating, and the high temperature protection performance of the coating is very poor. After adding the intumescent flame retardant and the uncoated expandable graphite, the coating in Comparative Example 2 is heated to form an intumescent carbon layer, and this carbon layer remains until the end of the test. After replacing the uncoated expandable graphite with the expandable graphite coated with a phosphorus-containing polymer, the coating in Example 2 also forms an intumescent carbon layer, and this carbon layer remains until the end of the test. Although the intumescent carbon layer of the coating of Example 2 has a small amount of cracks, it has a significantly higher degree of expansion than the carbon layer of Comparative Example 2. After the phosphorus-containing polymer is coated on the expandable graphite, on the one hand, the expansion degree of the expandable graphite is increased, and the expansion of the expanded carbon layer is promoted. On the other hand, the phosphorus-containing polymer has a flame retardant effect and can form a synergistic flame retardant effect with the phosphorus and nitrogen in the expandable flame retardant, suppressing the flame in the gas phase and improving the quality of the expandable carbon layer (increasing the carbonization rate and improving the high-temperature stability of the carbon layer), thereby effectively improving the high-temperature protection performance of the fire-retardant coating. Figure 3 It can also be seen that the coating of Comparative Example 2 fell off the steel plate after the test was completed (test time was greater than 1 hour), but the coating of Example 2 did not fall off. In addition, the material viscosity of the coatings of Example 2 and Comparative Examples 1-2 is easy to control and easy to apply, and the coating can be formed in one construction.

[0053] Example 3

[0054] A preparation method of phosphorus-containing polymer-coated expandable graphite comprises the following steps: first, 0.5 g of trihydroxymethylphosphine oxide and 5 g of expandable graphite are added to a round-bottom flask, the expandable graphite is dried at 80° C. for 12 hours before being added, then 40 mL of N,N-dimethylformamide is added to obtain a mixture, and a solution of 1.072 g of 4,4'-diphenylmethane diisocyanate in 20 mL of N,N-dimethylformamide is added dropwise to the mixture at 80° C. After the addition is completed, the reaction is continued for 2 hours, and then filtered. After the filtration is completed, the mixture is washed twice with N,N-dimethylformamide, and the filter cake is dried by forced air at 80° C. for 12 hours to obtain the product phosphorus-containing polymer-coated expandable graphite.

[0055] Example 4

[0056] A preparation method of phosphorus-containing polymer-coated expandable graphite comprises the following steps: first, 0.5 g of trihydroxymethylphosphine oxide and 5 g of expandable graphite are added to a round-bottom flask, the expandable graphite is dried at 80° C. for 12 hours before being added, then 40 mL of N,N-dimethylformamide is added to obtain a mixture, and a solution of 1.608 g of 4,4'-diphenylmethane diisocyanate in 20 mL of N,N-dimethylformamide is added dropwise to the mixture at 80° C. After the addition is completed, the reaction is continued for 2 hours, and then filtered. After the filtration is completed, the mixture is washed twice with N,N-dimethylformamide, and the filter cake is dried by forced air at 80° C. for 12 hours to obtain the product phosphorus-containing polymer-coated expandable graphite.

[0057] Example 5

[0058] A preparation method of phosphorus-containing polymer-coated expandable graphite comprises the following steps: first, 0.25 g of trihydroxymethylphosphine oxide and 5 g of expandable graphite are added to a round-bottom flask, the expandable graphite is dried at 80° C. for 12 hours before being added, then 40 mL of N,N-dimethylformamide is added to obtain a mixture, and a solution of 0.67 g of 4,4'-diphenylmethane diisocyanate in 20 mL of N,N-dimethylformamide is added dropwise to the mixture at 80° C. After the addition is completed, the reaction is continued for 2 hours, and then filtered. After the filtration is completed, the mixture is washed twice with N,N-dimethylformamide, and the filter cake is dried by forced air at 80° C. for 12 hours to obtain the product phosphorus-containing polymer-coated expandable graphite.

[0059] Example 6

[0060] A preparation method of phosphorus-containing polymer-coated expandable graphite comprises the following steps: first, 1.5 g of trihydroxymethylphosphine oxide and 5 g of expandable graphite are added to a round-bottom flask, the expandable graphite is dried at 80° C. for 12 hours before being added, then 40 mL of N,N-dimethylformamide is added to obtain a mixture, and a solution of 4.02 g of 4,4'-diphenylmethane diisocyanate in 20 mL of N,N-dimethylformamide is added dropwise to the mixture at 80° C. After the addition is completed, the reaction is continued for 2 hours, and then filtered. After the filtration is completed, the mixture is washed twice with N,N-dimethylformamide, and the filter cake is dried by forced air at 80° C. for 12 hours to obtain the product phosphorus-containing polymer-coated expandable graphite.

[0061] Example 7

[0062] A method for preparing a fire retardant coating for a fire protection pipe network of a substation or a converter station comprises the following steps: 106.4g of E44 epoxy resin is taken in a plastic cup and heated at 80°C to reduce the viscosity. Then an intumescent flame retardant and 3.39g of phosphorus-containing polymer-coated expandable graphite prepared in Example 1 are added (all dried at 80°C for 12 hours in advance). The intumescent flame retardant comprises 25.7g of ammonium polyphosphate, 10.3g of dipentaerythritol and 10.3g of melamine. After stirring evenly, 13.6g of 1,6-hexanediamine (1,6-hexanediamine is solid at room temperature and needs to be heated and melted into a liquid first) is added. After stirring evenly, the material becomes relatively viscous after being placed at room temperature for several minutes to obtain the fire retardant coating for the fire protection pipe network of the substation or the converter station. At this time, the material is manually coated on a steel plate with a size of 300mm×300mm×2.5mm, and the thickness of the coating is controlled to be about 2mm after curing. The coating is obtained after being placed at room temperature for 48 hours.

[0063] Example 8

[0064] A method for preparing a fire retardant coating for a fire protection pipe network of a substation or a converter station comprises the following steps: 106.4g of E44 epoxy resin is placed in a plastic cup and heated at 80°C to reduce the viscosity. Then an intumescent flame retardant and 18.5g of phosphorus-containing polymer-coated expandable graphite prepared in Example 1 are added (all dried at 80°C for 12 hours in advance). The intumescent flame retardant comprises 25.7g of ammonium polyphosphate, 10.3g of dipentaerythritol and 10.3g of melamine. After stirring evenly, 13.6g of 1,6-hexanediamine (1,6-hexanediamine is solid at room temperature and needs to be heated and melted into a liquid first) is added. After stirring evenly, the material becomes relatively viscous after being placed at room temperature for several minutes to obtain the fire retardant coating for the fire protection pipe network of the substation or the converter station. At this time, the material is manually coated on a steel plate with a size of 300mm×300mm×2.5mm, and the thickness of the coating is controlled to be about 2mm after curing. The coating is obtained after being placed at room temperature for 48 hours.

[0065] Example 9

[0066] A method for preparing a fire retardant coating for a fire protection pipe network of a substation or a converter station comprises the following steps: 106.4g of E44 epoxy resin is placed in a plastic cup and heated at 80°C to reduce the viscosity. Then an intumescent flame retardant and 5.15g of phosphorus-containing polymer-coated expandable graphite prepared in Example 1 are added (all dried at 80°C for 12 hours in advance). The intumescent flame retardant comprises 17.4g of ammonium polyphosphate, 6.95g of dipentaerythritol and 6.95g of melamine. After stirring evenly, 13.6g of 1,6-hexanediamine (1,6-hexanediamine is solid at room temperature and needs to be heated and melted into a liquid first) is added. After stirring evenly, the material becomes relatively viscous after being placed at room temperature for several minutes to obtain the fire retardant coating for the fire protection pipe network of the substation or the converter station. At this time, the material is manually coated on a steel plate with a size of 300mm×300mm×2.5mm, and the thickness of the coating is controlled to be about 2mm after curing. The coating is obtained after being placed at room temperature for 48 hours.

[0067] Example 10

[0068] A method for preparing a fire retardant coating for a fire protection pipe network of a substation or a converter station comprises the following steps: 106.4g of E44 epoxy resin is placed in a plastic cup and heated at 80°C to reduce the viscosity. Then an intumescent flame retardant and 5.15g of phosphorus-containing polymer-coated expandable graphite prepared in Example 1 are added (all dried at 80°C for 12 hours in advance). The intumescent flame retardant comprises 104.3g of ammonium polyphosphate, 41.7g of dipentaerythritol and 41.7g of melamine. After stirring evenly, 13.6g of 1,6-hexanediamine (1,6-hexanediamine is solid at room temperature and needs to be heated and melted into a liquid first) is added. After stirring evenly, the material becomes relatively viscous after being placed at room temperature for several minutes to obtain the fire retardant coating for the fire protection pipe network of the substation or the converter station. At this time, the material is manually coated on a steel plate with a size of 300mm×300mm×2.5mm, and the thickness of the coating is controlled to be about 2mm after curing. The coating is obtained after being placed at room temperature for 48 hours.

[0069] In the preparation process of the phosphorus-containing polymer-coated expandable graphite of the present invention, the hydroxyl group of trimethylolphosphine oxide reacts with the isocyanate group of diisocyanate to form a phosphorus-containing cross-linked polyurethane coating layer on the surface of the expandable graphite. The reaction process is shown in FIG. Figure 4 shown.

[0070] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing expandable graphite coated with a phosphorus-containing polymer, characterized in that: The following steps are involved: The trihydroxymethylphosphine oxide, expandable graphite and solvent are mixed, and a solution of diisocyanate in the solvent is added under heating conditions, followed by heat preservation and reaction. After the reaction is completed, the expandable graphite coated with the phosphorus-containing polymer is obtained by filtering, washing and drying.

2. The method for preparing expandable graphite coated with phosphorus-containing polymer according to claim 1, characterized in that: After heating to 60-120° C., add the solution of diisocyanate in the above solvent, and then keep the temperature to react for 1-12 hours.

3. The method for preparing expandable graphite coated with phosphorus-containing polymer according to claim 1, characterized in that: The diisocyanate is selected from diphenylmethane diisocyanate, toluene diisocyanate or a mixture of the two.

4. The method for preparing expandable graphite coated with phosphorus-containing polymer according to claim 1, characterized in that: The solvent is selected from a mixture of one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and N-methylpyrrolidone.

5. The method for preparing expandable graphite coated with a phosphorus-containing polymer according to any one of claims 1 to 4, characterized in that: The molar ratio of the isocyanate group contained in the diisocyanate to the hydroxyl group of trimethylolphosphine oxide is 0.8:1-1.2:

1.

6. The method for preparing expandable graphite coated with a phosphorus-containing polymer according to any one of claims 1 to 4, characterized in that: The mass ratio of the trihydroxymethylphosphine oxide to the expandable graphite is 0.05:1-0.3:

1.

7. The method for preparing expandable graphite coated with a phosphorus-containing polymer according to any one of claims 1 to 4, characterized in that: In the process of mixing trihydroxymethylphosphine oxide, expandable graphite and solvent, the mass ratio of the solvent to the expandable graphite is 6:1-20:

1.

8. The method for preparing expandable graphite coated with a phosphorus-containing polymer according to any one of claims 1 to 4, characterized in that: In the solution of the diisocyanate in the above solvent, the mass ratio of the solvent to the diisocyanate is 4:1-30:

1.

9. A phosphorus-containing polymer coated expandable graphite, characterized in that: The method for preparing expandable graphite coated with a phosphorus-containing polymer as described in any one of claims 1 to 8 is used for the preparation.

10. Use of the phosphorus-containing polymer-coated expandable graphite as claimed in claim 9 in fire retardant coatings for fire protection pipe networks in transformer substations or converter stations.

11. A fire retardant coating for fire protection pipe network of a transformer substation or converter station, characterized in that: Contains the phosphorus-containing polymer-coated expandable graphite as claimed in claim 9.

12. The fire retardant coating for fire protection pipe network of a transformer substation or converter station according to claim 11, characterized in that: Its raw materials include epoxy resin , an intumescent flame retardant, the phosphorus-containing polymer coated expandable graphite and a curing agent; the mass fraction of the intumescent flame retardant is 20-60%; the mass fraction of the phosphorus-containing polymer coated expandable graphite is 1-10%; the molar ratio of the NH groups in the curing agent to the epoxy groups in the epoxy resin is 0.8:1-1.2:

1.

13. The fire retardant coating for fire protection pipe network of a transformer substation or converter station according to claim 12, characterized in that: The epoxy resin is selected from bisphenol A diglycidyl ether.

14. The fire retardant coating for fire protection pipe network of a transformer substation or converter station according to claim 12, characterized in that: The intumescent flame retardant comprises an acid source, a carbon source and a gas source, wherein the acid source is selected from ammonium polyphosphate and melamine polyphosphate or a mixture of the two.

15. The fire retardant coating for fire protection pipe network of a transformer substation or converter station according to claim 14, characterized in that: The carbon source is selected from pentaerythritol, dipentaerythritol or a mixture of the two.

16. The fire retardant coating for fire protection pipe network of a transformer substation or converter station according to claim 14, characterized in that: The gas source is selected from melamine, dicyandiamide or a mixture of the two.

17. The fire retardant coating for fire protection pipe network of a transformer substation or converter station according to claim 14, characterized in that: The mass ratio of the acid source, the carbon source and the gas source is 20-80:10-40:10-40.

18. The fire retardant coating for fire protection pipe network of a transformer substation or converter station according to any one of claims 12 to 17, characterized in that: The curing agent is selected from a mixture of one or more of ethylenediamine, propylenediamine, butylenediamine, pentanediamine and hexamethylenediamine.

19. The fire retardant coating for fire protection pipe network of a transformer substation or converter station according to any one of claims 11 to 17, characterized in that: The thickness of the fire retardant coating formed during use is 0.1-10mm.

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