Preparation method of surface flame-retardant coating of polystyrene foam board

Abstract

The application discloses a preparation method of a novel flame-retardant coating on a polystyrene foam board surface, which comprises the following steps: first, modifying epoxy resin by using polyurethane; then, performing water-based treatment on the polyurethane modified epoxy resin to obtain water-based polyurethane modified epoxy resin as a coating base material; and simultaneously, selecting inorganic filler aluminum magnesium hydrotalcite and zinc borate as a flame retardant to prepare the novel EPS surface flame-retardant coating. The application can effectively improve the limiting oxygen index and the flame-retardant grade of the polystyrene foam, the flame-retardant layer plays a flame-retardant effect through the combination of gas phase and solid phase flame-retardant, effectively endows the polystyrene foam material with the flame-retardant performance, and the compression strength, adhesion and waterproofness of the polystyrene foam material with the flame-retardant coating are obviously improved. The preparation method is simple, green and environment-friendly, and is easy for industrialized mass production.

Description

Technical Field

[0001] This invention belongs to the field of fire protection materials technology, specifically relating to a method for preparing a flame-retardant coating on the surface of a polystyrene foam board. Background Technology

[0002] Polystyrene foam board (EPS) possesses excellent mechanical properties, corrosion resistance, water resistance, and thermal insulation, making it widely used in construction, chemical, automotive, and many other fields. However, it is flammable and releases large amounts of smoke and toxic gases when burned, posing a threat to human life and property. Therefore, researching the flame retardancy of EPS is of great significance for human life and property safety.

[0003] Currently, common flame-retardant methods for EPS foam include encapsulation, impregnation, polymerization, and surface coating. Surface coating is a simple process that does not damage the internal structure of the foam and ensures its good thermal insulation performance. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a flame-retardant coating on the surface of polystyrene foam board. By comparing the addition ratios of different flame retardants, a composite flame-retardant coating with high flame-retardant properties on the EPS surface is obtained.

[0005] This invention discloses a method for preparing a flame-retardant coating on the surface of polystyrene foam board. First, polyurethane is used to modify epoxy resin. Then, the polyurethane-modified epoxy resin is subjected to waterborne treatment to obtain waterborne polyurethane-modified epoxy resin (WEPU) as the coating base material. Simultaneously, inorganic fillers aluminum-magnesium hydrotalcite (LDH) and zinc borate (ZnB) are selected as a composite flame retardant agent to prepare a novel flame-retardant coating for EPS. Experimental results show that the novel flame-retardant coating WEPU / LDH / ZnB achieves a flame retardancy rating of V-0, with a limiting oxygen index (LOI) greater than 27%.

[0006] The present invention discloses a method for preparing a flame-retardant coating on the surface of polystyrene foam board, comprising the following steps:

[0007] Step 1: Preparation of polyurethane-modified epoxy resin

[0008] Epoxy resin is added to the reactor, followed by defoamer. The temperature is raised to 75-80℃ and stirred evenly. Then, polyurethane prepolymer (commercially available, model: 2151s) is slowly added and reacted at a constant temperature for 2-3 hours to obtain polyurethane modified epoxy resin.

[0009] Step 2: Waterborne application of polyurethane-modified epoxy resin

[0010] First, heat the raw materials and reaction equipment to 40-50℃. Then, pour the polyurethane modified epoxy resin obtained in step 1, the curing agent (commercially available, model: 0705), and the defoamer into the reactor and stir at 200-300 r / min for 30-40 seconds. Add deionized water to the system and continue stirring at 200-300 r / min until the mixture is homogeneous. Then, stir slowly by hand with a glass rod to obtain waterborne polyurethane modified epoxy resin (WEPU).

[0011] Step 3: Coating preparation

[0012] Add hydrotalcite and zinc borate flame retardant to the waterborne polyurethane modified epoxy resin obtained in step 2, stir and disperse evenly, then add curing agent and deionized water, mix evenly to obtain a slurry; coat the obtained slurry onto EPS foam with a coating thickness of 0.5-1mm, and let it stand and air dry at room temperature to obtain EPS foam with a flame retardant coating.

[0013] In step 2, the solid content of the waterborne polyurethane modified epoxy resin emulsion is 50%.

[0014] The amounts of each raw material added, by mass parts, are as follows:

[0015] 2.5-5 parts epoxy resin, 2.5-5 parts polyurethane prepolymer, 1-2 parts curing agent, 1.5-6 parts aluminum magnesium hydrotalcite, 3-6 parts zinc borate, and 1-2 parts defoamer.

[0016] The amount of curing agent added here is the total amount added in steps 2 and 3. Each addition is half of the total amount.

[0017] The amount of defoamer added here is the total amount added in steps 1 and 2. Each time, half of the total amount is added.

[0018] The beneficial effects of this invention are reflected in:

[0019] Epoxy resins, due to their dense network structure formed after curing, possess excellent adhesion but exhibit brittleness, low toughness, and poor impact resistance. Polyurethane, on the other hand, boasts high elasticity and toughness, and exhibits good compatibility with epoxy resins. Their interaction results in a high-performance interpenetrating network structure. However, polyurethane resin coatings release significant amounts of black smoke and toxic gases upon combustion. Water-based treatment of polyurethane-modified epoxy resins can reduce pollution and carbon emissions. LDH possesses a wider thermal decomposition temperature range and better flame retardant properties. During combustion, LDH removes interlayer free water and hydroxyl condensation water from the layers, carrying away some heat; CO3... 2-The thermal decomposition of anions generates CO2, which dilutes the oxygen concentration in the air and produces aluminum oxide and magnesium oxide. This can promote the thermo-oxidative cross-linking reaction of polymers and form a carbonized film covering the surface of combustibles. ZnB loses its water of crystallization at high temperatures, which has an endothermic and cooling effect. At the same time, some zinc elements exist in the gaseous form of zinc oxide or zinc hydroxide, which dilutes the combustible gas. ZnB can promote carbonization and play a role in smoke suppression.

[0020] This invention verifies its excellent flame-retardant effect through experiments such as cone calorimeter measurement, weight loss rate determination, and LOI index measurement. Simultaneously, the polystyrene foam material with added flame-retardant coating exhibits significantly improved compressive strength, adhesion, and water resistance. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the preparation process of the flame-retardant EPS of this invention.

[0022] Figure 2 Vertical combustion test experiments were conducted on polystyrene foam raw materials and Examples 1-7. Detailed Implementation

[0023] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, so as to better understand the content of the present invention.

[0024] Experimental materials:

[0025] Epoxy resin, model 6101, Yueyang Petrochemical Resin Plant; Curing agent, model 0705, Yueyang Petrochemical Resin Plant; Polyurethane prepolymer, model 2151s, Shandong Aolilong Chemical Co., Ltd.; Magnesium aluminum type hydrotalcite (LDH), Shandong Yousuo Chemical Technology Co., Ltd.; Zinc borate, Zhengzhou Juepai Chemical Products Co., Ltd.

[0026] Example 1:

[0027] The epoxy resin type polystyrene foam surface flame retardant coating is a sample prepared by using polystyrene foam as raw material, 5 parts epoxy resin, 2 parts curing agent, and 1 part deionized water as flame retardant coating.

[0028] The preparation method is as follows: First, add 2 parts curing agent to 5 parts epoxy resin, then add 1 part deionized water, place it on a magnetic stirrer, stir for 30-40 minutes at room temperature, apply the prepared flame retardant coating slurry to the prepared EPS foam with a brush, the coating thickness is about 0.5-1mm, let it stand and air dry at room temperature to obtain EPS foam with EP flame retardant coating.

[0029] Example 2:

[0030] The flame-retardant coating on the surface of waterborne polyurethane modified epoxy resin polystyrene foam is prepared from polystyrene foam, 5 parts waterborne polyurethane modified epoxy resin, 2 parts curing agent, and 1 part deionized water.

[0031] The preparation method is as follows: 250 parts of epoxy resin are poured into a three-necked flask, an appropriate amount of defoamer is added, and the flask is placed in a water bath. The temperature is gradually raised to 75-80℃, and after stirring evenly, 250 parts of polyurethane prepolymer are slowly added. The mixture is reacted at a constant temperature for 2 hours to obtain polyurethane-modified epoxy resin. The polyurethane-modified epoxy resin, water, curing agent, and the necessary beakers, glass rods, and molds are kept at a constant temperature of 40℃. The polyurethane-modified epoxy resin and curing agent are poured into a beaker. The beaker is placed on a magnetic stirrer and stirred at a speed of about 200-300 r / min for about 30 seconds. One part of deionized water is added according to the ratio of 50% of the emulsion solid content of the waterborne polyurethane-modified epoxy resin. The mixture is stirred at high speed until it is evenly mixed, and then stirred slowly by hand with a glass rod to obtain the waterborne polyurethane-modified epoxy resin. The prepared flame-retardant coating slurry is applied to the prepared EPS foam with a brush. The coating thickness is about 0.5-1mm. The coating is left to air dry at room temperature to obtain EPS foam with WEPU flame-retardant coating.

[0032] Example 3:

[0033] The flame-retardant coating on the surface of waterborne polyurethane modified epoxy resin / hydrotalcite type polystyrene foam is prepared from polystyrene foam, 5 parts waterborne polyurethane modified epoxy resin, 6 parts hydrotalcite, 2 parts curing agent, and 1 part deionized water.

[0034] The preparation method is as follows: Accurately weigh 5 parts of polyurethane-modified epoxy resin into a beaker using an electronic balance and stir until homogeneous. Then add 6 parts of hydrotalcite flame retardant to the beaker (when the amount of LDH in the solution increases to 8 parts, the solution becomes extremely viscous and cannot be stirred, preventing successful coating onto the EPS surface; therefore, the maximum amount of LDH is selected as 6 parts). Place the beaker on a magnetic stirrer and stir at high speed for 25-30 minutes. Then add 2 parts of curing agent and 1 part of deionized water, stirring until homogeneous to obtain the coating slurry. Apply the prepared flame-retardant coating slurry to the prepared EPS foam using a brush, with a coating thickness of approximately 0.5-1 mm. Allow it to air dry at room temperature to obtain the WEPU / LDH flame-retardant coated EPS foam.

[0035] Example 4:

[0036] The waterborne polyurethane-modified epoxy resin / zinc borate type flame-retardant coating for polystyrene foam is prepared from polystyrene foam, 5 parts waterborne polyurethane-modified epoxy resin, 6 parts zinc borate, 2 parts curing agent, and 1 part deionized water.

[0037] The preparation method is as follows: Accurately weigh 5 parts of polyurethane-modified epoxy resin into a beaker using an electronic balance, stir until homogeneous, then add 6 parts of zinc borate flame retardant to the beaker (when the amount of ZnB is 6 parts, some ZnB particles have already precipitated and settled in the solution, and the solubility of ZnB in the solution has reached its limit, so the maximum amount of ZnB used for a single factor is selected as 6 parts). Place the beaker on a magnetic stirrer and stir at high speed for 25-30 minutes. Then add 2 parts of curing agent and 1 part of deionized water, stir until homogeneous, and obtain the coating slurry. Apply the prepared flame-retardant coating slurry to the prepared EPS foam with a brush, the coating thickness is about 0.5-1 mm, and allow it to air dry at room temperature to obtain WEPU / ZnB flame-retardant coated EPS foam.

[0038] Example 5:

[0039] The waterborne polyurethane modified epoxy resin / hydrotalcite / zinc borate-1 type polystyrene foam surface flame retardant coating is prepared from polystyrene foam, 5 parts waterborne polyurethane modified epoxy resin, 3 parts hydrotalcite, 3 parts zinc borate, 2 parts curing agent, and 1 part deionized water.

[0040] The preparation method is as follows: Accurately weigh 5 parts of polyurethane-modified epoxy resin into a beaker using an electronic balance, stir until homogeneous, then add 3 parts of hydrotalcite and 3 parts of zinc borate flame retardant to the beaker. Place the beaker on a magnetic stirrer and stir at high speed for 25-30 minutes. Then add 2 parts of curing agent and 1 part of deionized water, and stir until homogeneous to obtain the coating slurry. Apply the prepared flame-retardant coating slurry to the prepared EPS foam using a brush, with a coating thickness of approximately 0.5-1 mm. Allow it to air dry at room temperature to obtain EPS foam with a WEPU / LDH / ZnB flame-retardant coating.

[0041] Example 6:

[0042] The flame-retardant coating on the surface of waterborne polyurethane modified epoxy resin / hydrotalcite / zinc borate-2 type polystyrene foam is prepared from polystyrene foam, 5 parts waterborne polyurethane modified epoxy resin, 2 parts hydrotalcite, 4 parts zinc borate, 2 parts curing agent, and 1 part deionized water.

[0043] The preparation method is as follows: Accurately weigh 5 parts of polyurethane-modified epoxy resin into a beaker using an electronic balance, stir until homogeneous, then add 2 parts of hydrotalcite and 4 parts of zinc borate flame retardant to the beaker. Place the beaker on a magnetic stirrer and stir at high speed for 25-30 minutes. Then add 2 parts of curing agent and 1 part of deionized water, and stir until homogeneous to obtain the coating slurry. Apply the prepared flame-retardant coating slurry to the prepared EPS foam using a brush, with a coating thickness of approximately 0.5-1 mm. Allow it to air dry at room temperature to obtain EPS foam with a WEPU / LDH / ZnB-2 flame-retardant coating.

[0044] Example 7:

[0045] The waterborne polyurethane modified epoxy resin / hydrotalcite / zinc borate-3 type polystyrene foam surface flame retardant coating is prepared from polystyrene foam, 5 parts waterborne polyurethane modified epoxy resin, 1.5 parts hydrotalcite, 4.5 parts zinc borate, 2 parts curing agent, and 1 part deionized water.

[0046] The preparation method is as follows: Accurately weigh 5 parts of polyurethane-modified epoxy resin into a beaker using an electronic balance, stir until homogeneous, then add 1.5 parts of hydrotalcite and 4.5 parts of zinc borate flame retardant to the beaker. Place the beaker on a magnetic stirrer and stir at high speed for 25-30 minutes. Then add 2 parts of curing agent and 1 part of deionized water, and stir until homogeneous to obtain the coating slurry. Apply the prepared flame-retardant coating slurry to the prepared EPS foam using a brush, with a coating thickness of approximately 0.5 mm. Allow it to air dry at room temperature to obtain EPS foam with a WEPU / LDH / ZnB-3 flame-retardant coating.

[0047] Vertical burning tests were conducted on the polystyrene foam raw materials and those from Examples 1-7, and the burning conditions at 1s and 10s are as follows. Figure 2 As shown.

[0048] Since EPS is originally a polymer material with an LOI value of only 17.8%, it is extremely flammable and will be quickly engulfed when exposed to a fire source.

[0049] Examples 2 and 3 are EPS samples coated with epoxy resin and WEPU resin. Both samples burned rapidly after being ignited. This is because epoxy resin itself is a highly flammable material and produces a large amount of dense smoke when burning. The modified WEPU resin did not increase flame retardant properties and could not protect the EPS matrix. Therefore, flame retardants need to be added to make it flame retardant.

[0050] Example 4 is a combustion test of a flame retardant coating filled with 6 parts of aluminum-magnesium hydrotalcite in WEPU resin. It can be seen that the sample can achieve self-extinguishing after the flame is removed after 10 seconds of combustion, but the matrix is ​​deformed and the coating is cracked, and it can be seen that the internal matrix has been pyrolyzed. After the flame is removed after a second 10 seconds of combustion, the coating does not extinguish immediately, but the flame is significantly reduced, and the flame retardant performance is significantly improved. The sample achieves self-extinguishing within 60 seconds, and dripping occurs as combustion progresses, with the flame retardant rating reaching V-2. However, when the LDH content reaches the maximum, its flame retardant rating still does not meet the national standard for flame retardant materials.

[0051] Example 5 is a combustion test of a flame retardant coating filled with 6 parts of zinc borate in WEPU resin. The sample can self-extinguish after 10 seconds of ignition, and the matrix does not change significantly. After a second 10 seconds of combustion, it does not self-extinguish immediately after the flame is removed, but it does self-extinguish within 60 seconds, and there is no dripping. Its flame retardant rating reaches V-1. However, when the amount of ZnB used reaches the maximum, its flame retardant performance still does not meet the national standard for flame retardant materials.

[0052] Examples 6, 7, and 8 respectively tested the flame retardant coatings filled with WEPU resin using 3 parts hydrotalcite + 3 parts zinc borate, 2 parts hydrotalcite + 4 parts zinc borate, and 1.5 parts hydrotalcite + 4.5 parts zinc borate, respectively. After two 10-second burning cycles, the EPS samples coated with the flame retardant coating were immediately self-extinguishing after the ignition source was removed, with no dripping material. Their flame retardant effect reached V-0 level. This indicates that LDH and ZnB have a certain synergistic effect, greatly improving the flame retardant performance of the coating. Among them, the charring phenomenon on the surface of the EPS / WEPU / LDH / ZnB-1 sample was slightly more obvious, while the charring phenomenon on the surface of the EPS / WEPU / LDH / ZnB-3 sample was relatively mild.

[0053] The LOI oxygen index, thermogravimetric analysis, cone calorimeter analysis, and smoke density tests were performed on all samples in the examples. The specific experimental results are shown below:

[0054]

[0055] The above values ​​show that:

[0056] After coating with epoxy resin, the LOI value did not increase significantly. After coating with WEPU resin, the LOI value did not change significantly because the modified polyurethane did not add flame retardant properties to the epoxy resin. Adding LDH alone increased the LOI value of EPS. Adding ZnB alone, during combustion, generates boron oxide that covers the EPS matrix surface, isolating oxygen and also increasing the LOI value. When LDH and ZnB are combined, they crosslink and catalyze char formation, resulting in a more significant flame retardant effect and greatly increasing the LOI value. The LOI values ​​of all composite flame retardant coatings were greater than 27%, with EPS / WEPU / LDH / ZnB-3 showing the best flame retardant effect, reaching an LOI value of 38.8%.

[0057] The original EPS coating had a char residue of 0.14%, indicating complete combustion of the substrate. After coating with epoxy resin, the char residue did not change significantly compared to the original EPS. However, after coating with WEPU resin, the char residue was slightly higher than that of the epoxy resin coating. Adding LDH significantly improved the char residue, and adding ZnB resulted in a char residue of 42.72%. When ZnB and LDH are combined, both act as catalysts for char formation, synergistically improving the char residue of the coating. Among the composite flame-retardant coatings, EPS / WEPU / LDH / ZnB-3 exhibited the best charring performance, achieving a char residue of 46.43%.

[0058] The peak heat release rate of the EPS sample coated with epoxy resin was 438.42 kW / m³. 2 Compared to the original EPS's peak heat release rate of 388.38 kW / m², 2 Significant improvements were observed. However, the EPS sample coated with WEPU, due to the lack of flame-retardant properties in polyurethane, showed a peak heat release rate similar to that of the epoxy resin coating, both exceeding that of the original EPS. The addition of LDH reduced the PHRR value. Similarly, the addition of ZnB significantly reduced the PHRR value. The composite flame-retardant coating WEPU / LDH / ZnB showed a significant decrease in both peak heat release rate and total heat release, indicating a synergistic effect between LDH and ZnB. The EPS / WEPU / LDH / ZnB-1 sample exhibited the lowest total heat release at 4.03 MJ / m³. 2 .

[0059] The original flue gas emission rate of EPS reached its peak at around 100s, at 0.0733m. 2 / s, the total flue gas release is 7.44m³. 2 After coating with a composite flame-retardant coating, LDH and ZnB work synergistically, promoting each other to form a denser char layer that isolates heat and oxygen, absorbs fine particles in the air, and reduces smoke release, thus significantly reducing smoke production. Among them, EPS / WEPU / LDH / ZnB-2 showed the best smoke suppression effect, with a total smoke release of 3.61m³. 2 This is 3.83m lower than the original EPS. 2 .

[0060] After coating with epoxy resin and WEPU resin, the samples began to produce smoke almost instantly upon ignition, with the peak smoke density even exceeding that of the original EPS sample. After blending with LDH and ZnB, the smoke density was significantly reduced. Among them, the sample EPS / WEPU / LDH / ZnB-1 had the lowest smoke density rating, at 25.83.

[0061] All samples from the examples underwent compressive strength testing, adhesion testing, pencil hardness testing, and water resistance testing. The specific values ​​are shown below:

[0062]

[0063] The mechanical properties of the flame-retardant EPS samples blended with LDH and ZnB were significantly improved compared to the original EPS samples. Among them, EPS / WEPU / LDH / ZnB-3 exhibited the best mechanical properties, with a compressive strength reaching 1627.6 kPa. The adhesion between WEPU / LDH / ZnB and the substrate reached a 5B level, and the surface hardness reached a 6H level. Furthermore, after seven days of water immersion, the coating of the flame-retardant EPS samples showed no peeling or detachment, remaining tightly adhered to the EPS substrate surface, indicating that the flame-retardant EPS samples have good waterproof performance.

[0064] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for preparing a flame-retardant coating on the surface of a polystyrene foam board, characterized in that... Includes the following steps: Step 1: Preparation of polyurethane-modified epoxy resin Epoxy resin is added to the reactor, followed by defoamer. The temperature is raised to 75-80℃, and after stirring evenly, polyurethane prepolymer is slowly added. The reaction is carried out at a constant temperature for 2-3 hours to obtain polyurethane modified epoxy resin. Step 2: Waterborne application of polyurethane-modified epoxy resin Pour the polyurethane modified epoxy resin, curing agent and defoamer obtained in step 1 into the reactor, stir at a speed of 200~300r / min for 30-40s, add deionized water to the system, continue stirring while maintaining the stirring speed, mix evenly, and then manually stir slowly with a glass rod to obtain waterborne polyurethane modified epoxy resin. Step 3: Coating preparation Add aluminum magnesium hydrotalcite and zinc borate flame retardant to the waterborne polyurethane modified epoxy resin obtained in step 2, stir and disperse evenly, then add curing agent and deionized water, mix evenly to obtain a slurry; coat the obtained slurry onto EPS foam with a coating thickness of 0.5-1mm, and let it stand and air dry at room temperature to obtain EPS foam with a flame retardant coating. By weight, the amount of epoxy resin added is 2.5-5 parts, the amount of polyurethane prepolymer added is 2.5-5 parts, the amount of curing agent is 1-2 parts, the amount of aluminum magnesium hydrotalcite added is 1.5-6 parts, and the amount of zinc borate added is 3-6 parts.

2. The preparation method according to claim 1, characterized in that: The solid content of the waterborne polyurethane modified epoxy resin obtained in step 2 is 50%.

3. The preparation method according to claim 1, characterized in that: The mass ratio of epoxy resin to polyurethane prepolymer is 1:

1.

4. The preparation method according to claim 1, characterized in that: The total amount of aluminum-magnesium hydrotalcite and zinc borate added was 6 parts.

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