A nano-silica modified flame retardant coating and its preparation method

Abstract

The present invention provides a nano-silica modified flame retardant coating, which comprises the following components by weight: 35-50 parts of an aqueous epoxy resin emulsion, 10-15 parts of modified silica, and 5-10 parts of carbon nanotubes; the modified silica is a mesoporous silica / polydopamine composite; in the mesoporous silica / polydopamine composite, polydopamine is loaded on the pore surface of the mesoporous silica; the pore diameter of the mesoporous silica is 10-20 nm. This flame retardant coating uses a combination of modified silica and carbon nanotubes, effectively improving the flame retardant performance of the aqueous coating without affecting other properties of the flame retardant coating.

Description

Technical Field

[0001] The invention belongs to the technical field of coatings, and in particular relates to a nano silicon dioxide flame retardant coating and a preparation method thereof. Background Art

[0002] Flame retardant coating is an important material that can reduce casualties and property losses. When a fire occurs, it can form a protective layer, making the surface of the coated object difficult to burn or difficult to catch fire, which plays a role in delaying the spread of the fire and allowing firefighters enough time to carry out fire fighting and rescue. Secondly, flame retardant coatings also have the function of reducing the release of harmful substances. The smoke and harmful gases produced by fire are one of the main causes of casualties, and the use of flame retardant coatings can slow down the speed of combustion and reduce the amount of smoke and harmful gases produced to a certain extent. Therefore, the flame retardant properties of flame retardant coatings are of great significance for fire prevention. They can effectively resist fires caused by natural disasters and human factors, prevent the spread and spread of fires, and reduce casualties and property losses.

[0003] At present, halogenated compounds are still the most effective gas phase flame retardants, and their mechanism of action is to inhibit ignition and slow down the spread of flames. However, due to the potential environmental hazards of halogenated compounds, in the past 20 years, the attention of polymer industry researchers has been focused on the modification of new environmentally friendly halogen-based flame retardant coatings and existing halogen-based flame retardant coatings. Based on the deepening of environmental protection concepts in my country and even the world, halogen-free flame retardant coatings have been greatly developed in recent years. These halogen-free coatings are mainly flame retardant coatings based on N, P, and Si formulas. However, in many reports on these flame retardant coatings, research on certain halogenated systems is still involved.

[0004] In addition, most flame retardants in existing coating systems are non-water-soluble and have relatively complex molecular structures. When added to water-based coatings, the flame retardants and water-based coatings are incompatible, which not only affects the flame retardant effect of the water-based coatings, but also has a certain impact on the properties of the water-based coatings themselves.

[0005] Water-based coatings are of great significance to environmental protection, and water-based coatings are the future development trend. Therefore, how to prepare a halogen-free, environmentally friendly, water-based flame-retardant coating with good dispersibility is of positive significance. Summary of the invention

[0006] In order to solve the problems and shortcomings in the prior art, the present invention provides a nano-silicon dioxide flame retardant coating and a preparation method thereof. The flame retardant coating adopts a combination of modified silica and carbon nanotubes, which effectively improves the flame retardant properties of water-based coatings without affecting other properties of the flame retardant coating.

[0007] The present invention provides a nano-silica modified flame retardant coating, which comprises the following components in parts by weight: 35-50 parts of an aqueous epoxy resin emulsion, 10-15 parts of modified silica, and 5-10 parts of carbon nanotubes; the modified silica is a mesoporous silica / polydopamine composite; in the mesoporous silica / polydopamine composite, polydopamine is loaded on the pore surface of the mesoporous silica; the pore diameter of the mesoporous silica is 10-20 nm.

[0008] Inorganic silica has excellent flame retardant properties, but inorganic silica generally belongs to micro-nano materials and has poor dispersibility in both aqueous and oil-phase systems, which affects the exertion of its flame retardant properties and others. Compared with ordinary silica particles, mesoporous silica has the characteristics of larger specific surface area and higher activity, and is widely used in various fields. However, mesoporous silica still has the problem of poor dispersibility, which also affects the exertion of its performance. First of all, in the present invention, polydopamine is modified on the surface of mesoporous silica. Firstly, polydopamine contains a large number of amino groups and phenolic hydroxyl groups, which can improve the dispersibility of mesoporous silica in aqueous coatings and promote the exertion of the flame retardant properties of mesoporous silica; secondly, polydopamine is a nitrogen-containing polymer and also has certain flame retardant properties. When it is loaded on the surface of mesoporous silica, it can synergistically enhance the flame retardant properties of mesoporous silica and improve the flame retardant properties of aqueous coatings. Secondly, the mesoporous silica / polydopamine composite can further form a point-line interpenetrating network structure with carbon nanotubes. Carbon nanotubes have excellent mechanical and thermodynamic properties. The mesoporous silica / polydopamine composite and carbon nanotubes can further play a synergistic role, which can effectively improve the structural stability of the coating while further enhancing the flame retardant properties of the coating. In addition, mesoporous silica has a large specific surface area and high activity, and the polydopamine loaded on its surface is more firm and compact, making the synergistic effect of these two substances more obvious and the flame retardant properties more excellent; at the same time, more and more firmly and compactly loaded polydopamine in the pores of mesoporous silica is also beneficial to improving the structural strength of mesoporous silica itself and ensuring that the mechanical properties and other properties of the coating will not decline. In addition, in the aqueous epoxy resin emulsion, the epoxy resin is also modified with more active groups, which is beneficial to the full contact and dispersion of the mesoporous silica / polydopamine composite and carbon nanotubes in the epoxy resin, and improves the denseness of the coating. And the mesoporous silica / polydopamine composite and carbon nanotubes will not affect the exertion of other properties of the original aqueous epoxy resin coating, but can further improve the comprehensive performance of the aqueous epoxy resin coating and further optimize the corrosion resistance and mechanical strength of the coating.

[0009] In addition, controlling the pore diameter of mesoporous silica within the above range can not only ensure that polydopamine has sufficient space to enter the pores of mesoporous silica and be successfully loaded, but also avoid the instability of the mesoporous silica structure caused by too large pores and deteriorate the coating performance.

[0010] Preferably, the particle size of the mesoporous silica / polydopamine composite is 150 - 250 nm. At this particle size, the mesoporous silica / polydopamine composite can be well dispersed in the waterborne epoxy resin coating, can fully exert the synergistic effect of mesoporous silica and polydopamine, and at the same time can form a tight interpenetrating network structure between the composite particles and carbon nanotubes, optimizing the flame retardant performance of the coating, etc.

[0011] Preferably, the diameter of the carbon nanotubes is 30 - 50 nm and the length is 3 - 7 μm. Carbon nanotubes with this length can effectively enhance the mechanical properties of the coating while being well dispersed in the waterborne epoxy resin coating, ensuring the performance of themselves and further optimizing the flame retardant performance of the coating, etc.

[0012] Preferably, the carbon nanotubes are carboxylated carbon nanotubes. Carboxylated carbon nanotubes can be more uniformly dispersed in the waterborne epoxy resin coating, which is beneficial to the synergistic effect between carbon nanotubes and the mesoporous silica / polydopamine composite, optimizing the flame retardant performance and mechanical properties of the coating, etc.

[0013] Preferably, the specific operation for preparing carboxylated carbon nanotubes is as follows: place the carbon nanotubes in a mixed acid solution, reflux and react at 80 - 90 °C for 12 h, then filter, wash, and dry; the mixed acid solution is prepared by mixing 98% concentrated sulfuric acid and 30% H 2 O 2 solution, and the volume ratio of concentrated sulfuric acid to H 2 O 2 solution is 3:1.

[0014] Preferably, the preparation of the mesoporous silica / polydopamine composite includes the following steps:

[0015] S1. Dissolve the template agent in water, then adjust the pH of the solution to 10 - 12, add tetraethyl orthosilicate dropwise thereto and react for 3 - 5 h, then carry out hydrothermal reaction on the resulting mixed system at 120 - 140 °C for 18 - 24 h, wash and dry to obtain mesoporous silica; S2. Disperse the mesoporous silica in a tris(hydroxymethyl)aminomethane - hydrochloric acid buffer solution, then add dopamine hydrochloride thereto, react at 30 - 40 °C for 16 - 20 h, wash and dry to obtain the mesoporous silica / polydopamine composite; the pH of the tris(hydroxymethyl)aminomethane - hydrochloric acid buffer solution is 8.5 - 10.5. By controlling the above reaction conditions, on the one hand, it is beneficial to obtain mesoporous silica / polydopamine composite particles with uniform particle size, and on the other hand, it is beneficial for polydopamine to be fully loaded onto the mesoporous silica to form mesoporous silica / polydopamine composite particles with stable structure, giving full play to the role of the composite particles in improving the flame retardant performance of the coating.

[0016] Preferably, in S1, the template agent includes at least one of cetyltrimethylammonium bromide, dodecyltrimethylammonium bromide, sodium dodecyl sulfonate, and sodium dodecyl sulfate.

[0017] Preferably, in S1, the template agent is a compound of cetyltrimethylammonium bromide and sodium dodecyl sulfate. The template agent obtained by compounding these two materials is beneficial to better controlling the shape and size of the formed mesoporous silica, making the formed mesoporous silica have uniform particle size and pore size, which is beneficial to the subsequent loading of polydopamine.

[0018] Preferably, in S1, the mass ratio of the template agent to tetraethyl orthosilicate is 1:2 - 4.

[0019] Preferably, in S1, the pore size of the mesoporous silica is 10 - 20 nm. Controlling the pore size of the mesoporous silica within the above range can not only ensure that polydopamine has sufficient space to enter the pores of the mesoporous silica and be successfully loaded, but also avoid the instability of the mesoporous silica structure caused by too large pores and deteriorate the coating performance.

[0020] Preferably, in S2, the mass ratio of the mesoporous silica to dopamine is 1:1 - 3.

[0021] Preferably, the above nano-silica modified flame retardant coating, calculated by weight, further includes 10 - 30 parts of inorganic filler, and the inorganic filler includes at least one of barium sulfate, titanium dioxide, and feldspar powder.

[0022] Preferably, the above nano-silica modified flame retardant coating is prepared according to the following steps:

[0023] Mix the waterborne epoxy resin emulsion, modified silica, carbon nanotubes, thickener, wetting agent, and water evenly, then add the inorganic filler, dispersant, defoamer, and preservative to it and mix evenly. Finally, add the waterborne epoxy resin curing agent, film-forming aid, and PH regulator and mix evenly to obtain the nano-silica modified flame retardant coating. Specific embodiments

[0024] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0025] Example 1

[0026] 1. Preparation of mesoporous silica / polydopamine composite

[0027] Prepared according to the following steps:

[0028] S1. Dissolve cetyltrimethylammonium bromide and sodium dodecyl sulfate in water, then adjust the pH of the solution to 11, dropwise add tetraethyl orthosilicate thereto and react for 4 h, and then hydrothermally react the obtained mixed system at 130 °C for 20 h, wash and dry to obtain mesoporous silica; the mass ratio of cetyltrimethylammonium bromide, sodium dodecyl sulfate, and tetraethyl orthosilicate is 0.5:0.5:3;

[0029] S2. Disperse the mesoporous silica in a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with a concentration of 12 - 15 mmol / L, then add dopamine hydrochloride thereto, react at 350 °C for 16 - 20 h, wash and dry to obtain a mesoporous silica / polydopamine composite; the pH of the tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution is 9.5; the mass ratio of dopamine hydrochloride to mesoporous silica is 1:2.

[0030] In the above S1, the average pore diameter of the mesoporous silica is 15 nm, and it can be observed that the boundaries between the pores of the mesoporous silica are relatively clear, the particle size is relatively uniform, and the average particle size is 180 nm; in the above S2, the average particle size of the mesoporous silica / polydopamine composite is 200 nm.

[0031] 2. Preparation of the flame retardant coating

[0032] Calculated by weight, mix 40 parts of epoxy resin emulsion, 12 parts of the above mesoporous silica / polydopamine composite silica, 7 parts of carbon nanotubes, 2 parts of thickener, 0.8 part of wetting agent, and 20 parts of water evenly, then add 15 parts of inorganic filler (including 10 parts of titanium dioxide and 5 parts of barium sulfate), 1 part of dispersant, 0.5 part of defoamer, and 0.4 part of preservative and mix evenly, and finally add 50 parts of waterborne epoxy resin curing agent, 0.8 part of film-forming aid, and 0.5 part of pH regulator and mix evenly to obtain a nano-silica modified flame retardant coating.

[0033] Among them, the average diameter of the above carbon nanotubes is 35 nm and the average length is 2.5 μm; and the carbon nanotubes are carboxylated carbon nanotubes. The specific operation is as follows: place the carbon nanotubes in a mixed acid solution, reflux and react at 80 - 90 °C for 12 h, and then filter, wash and dry; the mixed acid solution is prepared by mixing 98% concentrated sulfuric acid and 30% H 2 O 2 solution, and the volume ratio of concentrated sulfuric acid to H 2 O 2 solution is 3:1.

[0034] Example 2

[0035] 1. Preparation of the mesoporous silica / polydopamine composite

[0036] The preparation of the mesoporous silica / polydopamine composite in this example is the same as that in Example 1.

[0037] 2. Preparation of the flame retardant coating

[0038] In the preparation of the flame retardant coating in this example, the difference from Example 1 is that the average length of the carbon nanotubes used is 9 μm, and the rest is the same as that in Example 1.

[0039] Example 3

[0040] 1. Preparation of the mesoporous silica / polydopamine composite

[0041] The preparation of the mesoporous silica / polydopamine composite in this example is the same as that in Example 1.

[0042] 2. Preparation of the flame retardant coating

[0043] In the preparation of the flame retardant coating in this example, the difference from Example 1 is that the average length of the carbon nanotubes used is 1 μm, and the rest is the same as that in Example 1.

[0044] Example 4

[0045] 1. Preparation of the mesoporous silica / polydopamine composite

[0046] In the preparation of the mesoporous silica / polydopamine composite in this example, the difference from Example 1 is that in S1, the template used is cetyltrimethylammonium bromide, the average pore diameter of the obtained mesoporous silica is 12 nm, but it can be observed that there are a few connections between the pores of the mesoporous silica, the particle size difference is relatively large, the average particle size is also 180 nm, and the particle size of the final mesoporous silica / polydopamine composite is also 200 nm; the rest is the same as that in Example 1.

[0047] 2. Preparation of the flame retardant coating

[0048] The preparation of the flame retardant coating in this example is the same as that in Example 1.

[0049] Example 5

[0050] 1. Preparation of the mesoporous silica / polydopamine composite

[0051] In the preparation of the mesoporous silica / polydopamine composite in this example, different from Example 1, in S1, the template agent used is cetyltrimethylammonium bromide + sodium dodecyl sulfate (mass ratio 1:1). The average pore diameter of the obtained mesoporous silica is 20 nm, but it can be observed that there are more connections between the pores of the mesoporous silica, with a large difference in particle size. The average particle size is also 180 nm, and the particle size of the final mesoporous silica / polydopamine composite is also 200 nm; the rest is the same as in Example 1.

[0052] 2. Preparation of the flame retardant coating

[0053] The preparation of the flame retardant coating in this example is the same as in Example 1.

[0054] Example 6

[0055] 1. Preparation of the mesoporous silica / polydopamine composite

[0056] In the preparation of the mesoporous silica / polydopamine composite in this example, different from Example 1, in S1, the template agent used is cetyltrimethylammonium bromide + sodium dodecyl sulfate (mass ratio 1:1). The pore diameter of the obtained mesoporous silica is 20 nm, but it can be observed that there are more connections between the pores of the mesoporous silica, with a large difference in particle size. The average particle size is also 180 nm, and the particle size of the final mesoporous silica / polydopamine composite is also 200 nm; the rest is the same as in Example 1.

[0057] 2. Preparation of the flame retardant coating

[0058] The preparation of the flame retardant coating in this example is the same as in Example 1.

[0059] Example 7

[0060] 1. Preparation of the mesoporous silica / polydopamine composite

[0061] In the preparation of the mesoporous silica / polydopamine composite in this example, different from Example 1, in S1, the template agent used is dodecyltrimethylammonium bromide + sodium dodecyl sulfate (mass ratio 1:1). The pore diameter of the obtained mesoporous silica is 18 nm, but it can be observed that there are a few connections between the pores of the mesoporous silica, with a large difference in particle size. The average particle size is also 180 nm, and the particle size of the final mesoporous silica / polydopamine composite is also 200 nm; the rest is the same as in Example 1.

[0062] 2. Preparation of the flame retardant coating

[0063] The preparation of the flame retardant coating in this example is the same as in Example 1.

[0064] Example 8

[0065] This example is different from Example 1 in that when preparing the flame-retardant coating, the carbon nanotubes used are not carboxylated; the rest is the same as Example 1.

[0066] Comparative Example 1

[0067] 1. Preparation of mesoporous silica / polydopamine composite

[0068] The preparation of the mesoporous silica / polydopamine composite in this comparative example is different from that in Example 1 in that in S1, the mass ratio of the template agent to tetraethyl orthosilicate is 1:1, the pore diameter of the obtained mesoporous silica is 6 nm, and it can be observed that there are a few connections between the pores of the mesoporous silica, and the average particle size is 200 nm, so that the particle size of the final mesoporous silica / polydopamine composite is 215 nm; the rest is the same as Example 1.

[0069] 2. Preparation of flame-retardant coating

[0070] The preparation of the flame-retardant coating in this comparative example is the same as that in Example 1.

[0071] Comparative Example 2

[0072] 1. Preparation of mesoporous silica / polydopamine composite

[0073] The preparation of the mesoporous silica / polydopamine composite in this comparative example is different from that in Example 1 in that in S1, the mass ratio of the template agent to tetraethyl orthosilicate is 1:4, the pore diameter of the obtained mesoporous silica is 22 nm, and it can be observed that there are a few connections between the pores of the mesoporous silica, and the particle size is 165 nm, so that the particle size of the final mesoporous silica / polydopamine composite is 180 nm; the rest is the same as Example 1.

[0074] 2. Preparation of flame-retardant coating

[0075] The preparation of the flame-retardant coating in this comparative example is the same as that in Example 1.

[0076] Comparative Example 3

[0077] This comparative example is different from Example 1 in that when preparing the flame-retardant coating, the mesoporous silica / polydopamine composite is not added; the rest is the same as Example 1.

[0078] Comparative Example 4

[0079] This comparative example is different from Example 1 in that when preparing the flame-retardant coating, carbon nanotubes are not added; the rest is the same as Example 1.

[0080] Comparative Example 5

[0081] This comparative example is different from Example 1 in that when preparing the flame-retardant coating, mesoporous silica / polydopamine composite and carbon nanotubes are not added; the rest is the same as in Example 1.

[0082] Comparative Example 6

[0083] This comparative example is different from Example 1 in that when preparing the flame-retardant coating, the mesoporous silica / polydopamine composite is replaced by mesoporous silica, that is, the mesoporous silica is not modified by polydopamine; the rest is the same as in Example 1.

[0084] Test Example

[0085] 1. Experimental construction method

[0086] The coatings prepared in the above examples and comparative examples were tested for flame retardancy, acid and alkali resistance, tensile strength, and elongation at break.

[0087] (1) Flame retardancy test: Mainly test the vertical burning performance and limiting oxygen index (LOI) of the coating.

[0088] The vertical burning performance was tested according to the GB / T2408-2008 standard. The test specimen size was 130mm×13mm×1.6mm. The specimen was placed vertically, clamped at the upper end, adjusted so that the lower end was 300mm from the absorbent cotton, and the Bunsen burner was adjusted to produce a 20mm blue flame. The flame was directed at the middle of the lower end face of the specimen to ignite. After the first combustion for 10s, the Bunsen burner was removed and the afterglow and smoke time were recorded: Immediately after the first combustion extinguished, it was applied for 10s, and then the Bunsen burner was removed and the afterglow and smoke time were recorded. According to the afterglow and smoke time of the first and second times, the flame retardancy of the material was divided into three grades: V-0, V-1, and V-2, as shown in Table 1.

[0089] Table 1 Vertical burning level

[0090]

[0091] Limiting oxygen index (LOI): Tested according to the GB / T2406-2009 standard. The specimen size was 100mm×10mm×3mm. The specific criteria are shown in Table 2.

[0092] Table 2 Limiting oxygen index (LOI) measurement standard

[0093]

[0094] Top surface ignition: Ignite the specimen on the top surface for 30s, and check whether it is in a burning state by moving it away every 5 seconds.

[0095] Diffusion ignition: Move the igniter down from the top surface to the vertical surface by 6 mm and ignite for 30 seconds. Move it away every 5 seconds to check if it is in a burning state.

[0096] (2) Tensile strength and elongation at break test: Conduct the test with reference to JGT 172-2005.

[0097] (3) Acid and alkali resistance test: Conduct the test with reference to GB / T 9274-1988.

[0098] 2. Experimental results

[0099] The test results of the flame retardancy, acid and alkali resistance, tensile strength, and elongation at break of the coatings prepared in the above examples and comparative examples are shown in Table 3-1 and Table 3-2.

[0100] Table 3-1 Test results of the flame retardancy of the coatings in the examples and comparative examples

[0101]

[0102] It can be seen from Table 3-1 that by using the synergistic effect of the mesoporous silica / polydopamine composite provided by the present invention and carbon nanotubes, the flame retardancy of the waterborne epoxy resin coating can be effectively improved. Referring to Examples 1 to 8, the coatings provided by these examples all have good flame retardancy, can be extinguished within 8 s, with only 1 to 2 drops of molten droplets or even none, and the limiting oxygen index reaches more than 27%, having better flame retardancy. The reason for the above phenomenon may be that, firstly, in the mesoporous silica / polydopamine provided by the present invention, polydopamine is loaded on the surface of mesoporous silica, which can synergistically enhance the flame retardancy of the waterborne epoxy coating; secondly, the mesoporous silica / polydopamine composite can further form a point and line interpenetrating network structure with carbon nanotubes, and these two substances can further play a synergistic role to further improve the flame retardancy of the coating.

[0103] Observing Comparative Examples 1 and 2, the ratio of the template agent to tetraethyl orthosilicate was changed in these two comparative examples, resulting in a change in the controlled size of mesoporous silica. If the pore diameter of mesoporous silica is too small, it is not conducive to the full loading of polydopamine, and the loading amount of polydopamine on the pore surface of mesoporous silica is too small, resulting in an insignificant synergistic effect of mesoporous silica / polydopamine and deteriorating its flame retardancy. If the pore diameter of mesoporous silica is too large, there will still be some voids after the pore surface of silica is loaded with polydopamine, which is also not conducive to the stability of the overall structure of mesoporous silica. During the flame retardancy process, there are many voids in the mesoporous silica / polydopamine particles, which is also not conducive to the full exertion of the flame retardancy effect.

[0104] When observing Comparative Examples 3 to 6, no mesoporous silica / polydopamine composite was added in Comparative Example 3, no carbon nanotubes were added in Comparative Example 4, no mesoporous silica / polydopamine composite and carbon nanotubes were added in Comparative Example 5, and the mesoporous silica in Comparative Example 6 was not modified with polydopamine. These situations all led to a significant decrease in the flame retardant properties of the water-based epoxy coating, which shows that the mesoporous silica / polydopamine composite and carbon nanotubes have a strong synergistic effect, and only the simultaneous presence of these two substances can effectively improve the flame retardant properties of the water-based epoxy resin coating.

[0105] Further, observing Examples 1, 2, and 3, the carbon nanotubes used in Examples 2 and 3 are too short and too long, all of which lead to a slight decrease in the flame retardant properties of the coating, which is manifested as a longer extinguishing time and a lower limiting oxygen index. This is because too short carbon nanotubes are not conducive to forming a more closely connected point and line interpenetrating network structure with the mesoporous silica / polydopamine complex, which is not conducive to the synergistic effect of the two, thus causing a slight decrease in the flame retardant properties of the coating. In addition, too long carbon nanotubes have poor dispersibility in water-based coatings, are not conducive to the interaction between carbon nanotubes and mesoporous silica / polydopamine complexes, and are not conducive to the performance of carbon nanotube performance, thus also reducing the flame retardant properties of the coating.

[0106] Observing Examples 1, 4, 5, 6, and 7, we can find that the type of template agent and the ratio of template agent to tetraethyl orthosilicate will affect the size and morphology of the mesoporous silica finally formed, and further affect the load of polydopamine on mesoporous silica, thereby affecting the performance of the flame retardant properties of the mesoporous silica / polydopamine composite in the coating. For example, the template agent is changed in Examples 4, 5, 6, and 7, resulting in changes in the size of the mesoporous silica, and at the same time, there are a few or more connections between the pores of the mesoporous silica, which affects the load of polydopamine on the mesoporous silica, thereby causing the degradation of the flame retardant properties of the mesoporous silica / polydopamine composite in the coating. Observing Example 8, the carbon nanotubes in Example 8 are not carboxylated, resulting in poor dispersibility of the carbon nanotubes in the water-based coating, which deteriorates the performance of its flame retardant properties.

[0107] Table 3-2 Test results of acid and alkali resistance, tensile strength and elongation at break of coatings in Examples and Comparative Examples

[0108]

[0109]

[0110] As can be seen from Table 3-2, the waterborne epoxy coating provided by the present invention also has relatively excellent acid and alkali resistance, tensile strength and elongation at break performance, and is a waterborne epoxy flame retardant coating with excellent comprehensive performance, such as Examples 1 to 8. And it can be seen from Comparative Examples 1 and 2 that the pore size of mesoporous silica has little influence on the acid and alkali resistance and mechanical properties of the coating. Therefore, the coatings in Comparative Examples 1 and 2 still have good acid and alkali resistance and mechanical properties. However, in Comparative Example 2, the pore size of mesoporous silica is too large, and the structural stability is a little worse, resulting in the mechanical properties of the coating being worse than those in Comparative Example 1. But observing Comparative Examples 4 and 5, these two comparative examples do not contain carbon nanotubes, resulting in a significant decrease in the tensile strength and elongation at break of the coating, and the acid and alkali resistance will also decrease significantly. In Comparative Example 3, the mesoporous silica / polydopamine composite is not added, which will also cause a slight decrease in the mechanical properties of the coating. In Comparative Example 6, the mesoporous silica is not modified by polydopamine. The mesoporous silica has many pores and relatively poor structural stability, and cannot effectively enhance the mechanical properties of the coating. The test results of doctors also show that when using the mesoporous silica / polydopamine composite and carbon nanotubes to enhance the flame retardant performance of the coating, the coating can also have excellent acid and alkali resistance and mechanical properties.

[0111] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced, but these modifications or replacements are all within the protection scope of the present invention.

Claims

1. A nano-silicon dioxide modified flame retardant coating, It is characterized in that Calculated by weight, it includes the following components: 35-50 parts of waterborne epoxy resin emulsion, 10-15 parts of modified silicon dioxide, and 5-10 parts of carbon nanotubes; The modified silica is a mesoporous silica / polydopamine composite; In the mesoporous silica / polydopamine composite, polydopamine is loaded on the pore surface of the mesoporous silica; the pore size of the mesoporous silica is 10 to 20 nm; The preparation of the mesoporous silica / polydopamine composite comprises the following steps: S1. The template is dissolved in water, and then the pH of the solution is adjusted to 10-12, and ethyl orthosilicate is added dropwise thereto for reaction for 3-5 hours, and then the resulting mixed system is subjected to a hydrothermal reaction at 120-140° C. for 18-24 hours, washed, and dried to obtain mesoporous silica; S2. dispersing the mesoporous silica in a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer, then adding dopamine hydrochloride thereto, reacting at 30-40° C. for 16-20 hours, washing and drying to obtain the mesoporous silica / polydopamine complex; the pH of the tris(hydroxymethyl)aminomethane-hydrochloric acid buffer is 8.5-10.5; In S1, the mass ratio of the template to the tetraethyl orthosilicate is 1:3; In S2, the particle size of the mesoporous silica / polydopamine composite is 200 nm.

2. The nano-silicon dioxide modified flame retardant coating as claimed in claim 1, Features: The carbon nanotube has a diameter of 30-50 nm and a length of 3-7 μm.

3. The nano-silicon dioxide modified flame retardant coating according to claim 1, Features: In S1, the template agent includes at least one of hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, sodium dodecyl sulfonate, and sodium dodecyl sulfate.

4. The nano-silicon dioxide modified flame retardant coating as claimed in claim 3, Features: In S1, the template is a compound of hexadecyltrimethylammonium bromide and sodium dodecyl sulfate.

5. The nano-silicon dioxide modified flame retardant coating as claimed in claim 1, Features: In the S2, the mass ratio of the mesoporous silica to the dopamine is 1:1-3.

6. The nano-silicon dioxide modified flame retardant coating as claimed in claim 1, Features: Calculated by weight, the invention further includes 10 to 30 parts of inorganic filler, wherein the inorganic filler includes at least one of barium sulfate, titanium dioxide and feldspar powder.

7. The nano-silicon dioxide modified flame retardant coating as claimed in claim 1, It is characterized in that Prepared according to the following steps: The water-based epoxy resin emulsion, the modified silicon dioxide, the carbon nanotubes, a thickener, a wetting agent and water are mixed evenly, and then an inorganic filler, a dispersant, a defoaming agent and a preservative are added thereto and mixed evenly, and finally a water-based epoxy resin curing agent, a film-forming aid and a pH regulator are added thereto and mixed evenly to obtain the nano-silica modified flame retardant coating.

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