Intumescent flame retardant coating and its use in the production of polyvinyl chloride / polypropylene flame retardant materials

Abstract

The application discloses an intumescent flame-retardant coating and application thereof in preparation of polyvinyl chloride / polypropylene flame-retardant materials and belongs to the technical field of coating. The required coating is obtained by blending flame-retardant powder, bonding resin, solvent, defoaming agent and surfactant through high-speed shearing stirring. The fireproof flame-retardant coating has certain universality, can be also applied to a part of heat-insensitive plastic sheets including PP, has good protection, fast carbon layer expansion, strong bonding force, can effectively improve the flame-retardant grade of PVC and PP sheets, and can meet the requirement of being used as a back plate of a refrigerator.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically relating to an intumescent flame-retardant coating and its application in the preparation of flame-retardant polyvinyl chloride / polypropylene materials. Background Technology

[0002] PVC and PP are commonly used plastics, mainly composed of polyvinyl chloride and polypropylene, respectively. Due to their lightweight, high strength, corrosion resistance, and good insulation properties, they can be used as back panel materials for refrigerators, and are more economical than metal composite panels. Although PVC is a flame-retardant material, it still produces hydrogen chloride gas with a pungent odor when exposed to flame, and it also softens and deforms at high temperatures, leading to structural damage. PP, on the other hand, is flammable, burns violently after ignition, and melts at high temperatures, posing a high fire hazard.

[0003] Generally, PVC and PP sheets require flame-retardant treatment before they can be used as refrigerator back panel materials. However, their flame-retardant rating is still insufficient to withstand prolonged exposure to high-temperature flames, and their fire safety needs improvement. Besides blending flame retardants with PVC and PP materials to enhance their flame retardancy, the flame-retardant rating can also be improved by coating the sheet surface with a flame-retardant coating to form a protective flame-retardant layer. This method of adding an external protective coating can improve the fire safety of the sheet without compromising its various properties, and it is also simpler to implement. However, current literature lacks research on fire-retardant coatings for PVC and PP sheets; therefore, it is necessary to research a highly efficient fire-retardant coating for PVC and PP sheets. Summary of the Invention

[0004] This invention aims to address one of the technical problems in related technologies to a certain extent. Therefore, one objective of this invention is to provide a fire-retardant coating formulation that can effectively improve the flame retardant rating of PVC and PP sheets and reduce their fire hazard.

[0005] The intumescent flame-retardant coating of the present invention is composed of a compound of components including flame-retardant powder, binder, defoamer and surfactant.

[0006] The flame retardant powder is composed of expanded graphite (EG), aluminum dimethyl phosphinate (AHP), metal hydroxide (MOH), and titanium dioxide (TiO2) in a mass ratio of (25~35):(15~20):(45~55):(3~5). A further preferred mass ratio is 30:17:49:4.

[0007] The metal hydroxide is one or more of magnesium hydroxide and aluminum hydroxide.

[0008] The expanded graphite has a mesh size of ≤300 mesh, preferably 200 mesh.

[0009] The adhesive is composed of polyacrylic acid resin and an organic solvent mixed in a mass ratio of (1~2):1. The organic solvent is ethyl acetate or dimethyl carbonate. The preferred mass ratio of polyacrylic acid resin to organic solvent is 1.884:1.

[0010] The defoamer is tributyl phosphate.

[0011] The surfactant is sodium dodecylbenzenesulfonate (SDBS).

[0012] In the intumescent flame-retardant coating of the present invention, the mass ratio of flame-retardant powder, binder, defoamer and surfactant is 1:(2.5~3):(0.01~0.02):(0.005~0.01).

[0013] Furthermore, the mass ratio of flame retardant powder to binder is 1:2.866.

[0014] The present invention relates to the application of intumescent flame-retardant coatings in the preparation of flame-retardant materials for polyvinyl chloride / polypropylene.

[0015] Specifically, the flame-retardant properties of polyvinyl chloride or polypropylene materials are improved by coating the surface of the material with an intumescent flame-retardant coating to form a flame-retardant protective coating.

[0016] Furthermore, the thickness of the intumescent flame-retardant coating on the surface of the PVC or polypropylene material is 250-750 μm. After coating, the material is dried in a circulating hot air oven at 25-50°C for 12 hours. Then, the dried material is pressurized and held at 40-50°C for 10-20 seconds using a flat vulcanizing machine to obtain PVC or polypropylene material with a fire-retardant coating.

[0017] As a preferred option, the intumescent flame retardant coating is applied to the surface of polyvinyl chloride or polypropylene material with a thickness of 500 μm.

[0018] As a preferred option, the hot-pressing conditions are maintained at 50°C and 2MPa pressure for 20s.

[0019] Furthermore, the polyvinyl chloride / polypropylene flame-retardant material is used as a material for household appliances, especially for refrigerator back panels.

[0020] The beneficial effects of this invention are as follows: This invention provides a fire-retardant coating suitable for PVC and PP sheets through a simple blending preparation method. The raw materials are halogen-free and non-toxic, inexpensive, and the preparation process is easy to control, requiring minimal production equipment. The finished coating exhibits good dispersion stability and can be stored for extended periods. When exposed to high-temperature flames, the fire-retardant coating of this invention can absorb heat and rapidly form an expanding carbon layer, exhibiting excellent heat insulation capabilities and effectively protecting the substrate. Attached Figure Description

[0021] Figure 1 The images are of four PVC sheets with protective coatings in Example 1 after UL-94 5VA testing. (a), (b), (c), and (d) correspond to the test results of coatings #1, #2, #3, and #4, respectively.

[0022] Figure 2 The images show the SEM images of the expanded carbon layers of the four types of PVC sheets with protective coatings in Example 1 after UL-94 5VA testing. Figures (a), (b), (c), and (d) correspond to the expanded carbon layers produced by coatings #1, #2, #3, and #4, respectively.

[0023] Figure 3 These are photos of the three types of PVC sheets with protective coatings from Example 2 after undergoing the UL-94 5VA test.

[0024] Figure 4 The following are EDS elemental distribution diagrams of the protective carbon layer in Example 2, where (a) is an electron scanning image, (b) is an elemental combination distribution diagram, and (c), (d), (e), and (f) are the distribution diagrams of Al, P, C, and O elements, respectively.

[0025] Figure 5 These are photos comparing the PVC sheet with and without coating protection before and after the UL-94 5VA test in Example 3.

[0026] Figure 6 These are photos comparing the PP sheet with and without coating protection before and after the UL-94 5VA test in Example 4.

[0027] Figure 7 The figures are (a) TG and (b) DTG of PVC sheet and PP sheet in air atmosphere.

[0028] Figure 8 The graphs show the results of cone calorimeter tests on PVC sheets and PP sheets. (a) shows the HRR curve over time, (b) shows the THR curve over time, (c) shows the TSR curve over time, and (d) shows the CO release rate curve over time.

[0029] Figure 9 Photographs of PVC sheets (a) (b) and PP sheets (c) (d) after cone calorimeter testing.

[0030] Figure 10 The images show the #6 coating from Example 2 and the coatings from Comparative Examples 1, 2, and 3 after standing for 72 hours. Detailed Implementation

[0031] The following describes preferred embodiments of the present invention. It should be understood that these embodiments are for better explanation of the present invention and are not intended to limit the present invention. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0032] Example 1: Preparation of PVC sheet protected by fire-retardant coating

[0033] (1) 40g of expanded graphite EG, 54g of aluminum dimethylphosphinate AHP and 6g of titanium dioxide were put into a high-speed mixer and mixed evenly to obtain group a flame retardant powder.

[0034] (2) 27g of expanded graphite EG, 67g of aluminum hydroxide ALH and 6g of titanium dioxide were put into a high-speed mixer and mixed evenly to obtain group b flame retardant powder.

[0035] (3) 20g of expanded graphite EG, 54g of aluminum hydroxide ALH, 22g of aluminum dimethylphosphinate AHP and 4g of titanium dioxide were put into a high-speed mixer and mixed evenly to obtain group C flame retardant powder.

[0036] (4) 30g expanded graphite EG, 49g aluminum hydroxide ALH, 17g aluminum dimethylphosphinate AHP and 4g titanium dioxide were put into a high-speed mixer and mixed evenly to obtain group d flame retardant powder.

[0037] Then, 144g of polyacrylic acid resin was mixed and diluted with 76g of ethyl acetate. Then, 100g of flame retardant powder, 1g of tributyl phosphate and 0.5g of sodium dodecylbenzenesulfonate of different groups prepared above were added to the mixed resin. The mixture was then mixed in a high-speed shear disperser at 1200r / min for 15min to obtain 4 different fire-retardant coatings. The coatings corresponding to powder group a and a are numbered #1 to #4 in sequence.

[0038] Fire-retardant coatings were applied to the surface of PVC sheets with a thickness of 0.4 mm and a coating thickness of 500 μm. The coated sheets were then placed in a circulating hot air oven and dried at 40°C for 12 hours. After drying, the sheets were then subjected to a pressure of 2 MPa at 50°C for 20 seconds using a flat vulcanizing machine, resulting in four types of PVC sheets with fire-retardant coating protection.

[0039] Example 2: Preparation of PVC sheet protected by fire-retardant coating

[0040] First, put 30g of expanded graphite (EG), 49g of aluminum hydroxide (ALH), 17g of aluminum dimethylphosphinate (AHP), and 4g of titanium dioxide into a high-speed mixer and mix them evenly to obtain flame retardant powder.

[0041] (1) Preparation of fire-retardant coating with a mass ratio of flame retardant powder to binder of 1:3: 196g of polyacrylic acid resin and 104g of dimethyl carbonate were mixed and diluted. Then, 100g of flame retardant powder, 1g of tributyl phosphate and 0.5g of sodium dodecylbenzenesulfonate were added to the mixed resin. The mixture was then mixed in a high-speed shear disperser at 1200r / min for 15min to obtain fire-retardant coating No. #5.

[0042] (2) Preparation of fire-retardant coating with a mass ratio of flame retardant powder to binder of 1:2.87: 187g of polyacrylic acid resin was mixed and diluted with 100g of dimethyl carbonate. Then, 100g of flame retardant powder, 1g of tributyl phosphate and 0.5g of sodium dodecylbenzene sulfonate were added to the mixed resin. The mixture was then mixed in a high-speed shear disperser at 1200r / min for 15min to obtain the fire-retardant coating numbered #6.

[0043] (3) Preparation of fire-retardant coating with a mass ratio of flame retardant powder to binder of 1:2.5: 163g of polyacrylic acid resin and 87g of dimethyl carbonate were mixed and diluted. Then, 100g of flame retardant powder, 1g of tributyl phosphate and 0.5g of sodium dodecylbenzene sulfonate were added to the mixed resin. The mixture was then mixed in a high-speed shear disperser at 1200r / min for 15min to obtain the fire-retardant coating numbered #7.

[0044] A fire-retardant coating was applied to the surface of a 0.4 mm thick PVC sheet, with a coating thickness of 500 μm. The coated sheet was then placed in a circulating hot air oven and dried at 40°C for 12 hours. After drying, the sheet was then subjected to a pressure of 2 MPa at 50°C for 20 seconds using a flat vulcanizing machine to obtain a PVC sheet with a fire-retardant coating.

[0045] Example 3: Preparation of PVC sheet protected by fire-retardant coating

[0046] (1) 30g of expanded graphite EG, 49g of magnesium hydroxide MH, 17g of aluminum dimethyl phosphinate AHP and 4g of titanium dioxide were put into a high-speed mixer and mixed evenly to obtain flame retardant powder.

[0047] (2) Mix 187g of polyacrylic acid resin with 100g of dimethyl carbonate and dilute. Then add 100g of flame retardant powder, 1g of tributyl phosphate and 0.5g of sodium dodecylbenzene sulfonate to the mixed resin. Mix in a high-speed shear disperser at 1200r / min for 15min to obtain a fire-retardant coating with a mass ratio of flame retardant powder to binder of 1:2.87, numbered #8.

[0048] (3) Apply fire-retardant coating to the surface of PVC sheet with a thickness of 0.4 mm and a coating thickness of 500 μm. Place the coated sheet in a circulating hot air oven and dry it at 40°C for 12 h. Then, use a flat vulcanizing machine to pressurize the dried sheet at 50°C for 2 MPa for 20 s to obtain PVC sheet with fire-retardant coating protection.

[0049] Example 4: Preparation of PP sheet protected by fire-retardant coating

[0050] The preparation process of the fire-retardant coating is the same as in Example 3. The fire-retardant coating is applied to the surface of a hollow PP sheet with a total thickness of 1 mm and a coating thickness of 500 μm. The coated sheet is then placed in a circulating hot air oven and dried at 40°C for 12 h. After drying, the sheet is then subjected to a pressure of 2 MPa at 50°C for 20 s using a flat vulcanizing machine to obtain a PP sheet with a fire-retardant coating.

[0051] Comparative Example 1:

[0052] The preparation of fire-retardant coatings includes the following steps:

[0053] (1) 30g expanded graphite EG, 49g aluminum hydroxide ALH, 17g aluminum dimethylphosphinate AHP and 4g titanium dioxide were put into a high-speed mixer and mixed evenly to obtain flame retardant powder.

[0054] (2) Mix 187g of polyacrylic acid resin with 100g of dimethyl carbonate and dilute. Then add 100g of flame retardant powder and 1g of tributyl phosphate to the mixed resin. Mix at 1200r / min for 15min in a high-speed shear disperser to obtain a fire-retardant coating with a mass ratio of flame retardant powder to binder of 1:2.87, numbered #9.

[0055] Comparative Example 2:

[0056] The preparation of fire-retardant coatings includes the following steps:

[0057] (1) 30g expanded graphite EG, 49g aluminum hydroxide ALH, 17g aluminum dimethylphosphinate AHP and 4g titanium dioxide are put into a high-speed mixer and mixed evenly to obtain flame retardant powder.

[0058] (2) Mix 187g of polyacrylic acid resin with 100g of dimethyl carbonate and dilute. Then add 100g of flame retardant powder, 1g of tributyl phosphate and 0.5g of octylamine to the mixed resin. Mix at 1200r / min for 15min in a high-speed shear disperser to obtain a fire-retardant coating with a mass ratio of flame retardant powder to binder of 1:2.87, numbered #10.

[0059] Comparative Example 3:

[0060] The preparation of fire-retardant coatings includes the following steps:

[0061] (1) 30g expanded graphite EG, 49g aluminum hydroxide ALH, 17g aluminum dimethylphosphinate AHP and 4g titanium dioxide are put into a high-speed mixer and mixed evenly to obtain flame retardant powder.

[0062] (2) Mix 187g of polyacrylic acid resin with 100g of dimethyl carbonate and dilute. Then add 100g of flame retardant powder, 1g of tributyl phosphate and 0.5g of stearic acid to the mixed resin. Mix at 1200r / min for 15min in a high-speed shear disperser to obtain a fire-retardant coating with a mass ratio of flame retardant powder to binder of 1:2.87, numbered #11.

[0063] Performance testing:

[0064] (1) UL-94 5VA test: The sheets prepared in Examples 1-4 and the uncoated PVC and PP sheets were tested. The test results are shown in Table 1.

[0065] (2) Cone calorimeter test: Take the sheets from Examples 3-4 and the uncoated PVC and PP sheets, cut them into 10cm*10cm samples, put them into the cone calorimeter for testing, and the test results are shown in Table 2.

[0066] (3) Tensile shear strength test: According to GB / T 33334-2016 "Test method for tensile shear strength of single lap joint of adhesive (composite material to composite material)", the coating No. 6 in Example 2 and the pure adhesive resin were tested using a universal tensile testing machine. The coatings were applied to the surface of PVC sheet and PP sheet respectively to test their shear strength. The test results are shown in Table 3.

[0067] (4) Coating dispersion stability test: Coatings numbered #6, #9, #10, and #11 were placed in transparent plastic bottles and left to stand at room temperature for 72 hours. The layering of the coatings was observed. The results are shown in the figure. Figure 10 .

[0068]

[0069]

[0070]

[0071] Figure 1 These are photographs of the four sheets from Example 1 after undergoing UL-94 5VA testing. The test results show that, with the improvement of the fire-retardant coating powder formulation, the pores produced in the combustion test became smaller and smaller.

[0072] For the coating system formulated with group A flame retardant powder, the protective coating formed will have the expanded graphite rapidly expand after being exposed to fire, thus providing a heat insulation effect. At the same time, aluminum dimethylphosphinate will decompose, and while absorbing a small amount of heat, it will promote the carbonization of the resin and matrix in the coating and generate phosphorus free radicals to inhibit the combustion chain reaction in the gas phase, thereby protecting the substrate. However, due to the high temperature of the spray gun flame, the temperature rises very rapidly after contacting the sheet, and the protective coating cannot generate a sufficiently dense expanded carbon layer in time, resulting in insufficient heat insulation. This causes the PVC sheet to be burned through during the second flame burn. Figure 2 Figure (a) shows that the protective carbon layer formed by the coating is relatively broken and sparse, resulting in poor heat insulation.

[0073] For the coating system formulated with group B flame-retardant powder, the protective coating formed, upon exposure to fire, will cause the aluminum hydroxide to decompose and absorb a large amount of heat, releasing water vapor to lower the system temperature. This allows more time for the expanded graphite to expand and form a heat-insulating char layer, resulting in a char layer with good heat insulation, thus protecting the substrate. However, during the third flame burn, because the aluminum hydroxide in the system has almost completely decomposed, the heat absorption protection is lost. The char layer formed by the expanded graphite alone is insufficient to withstand the high temperature of the flame, causing the PVC sheet to burn through. Figure 2 As can be seen from Figure (b), the graphite in the protective carbon layer is more intact, but still relatively sparse, resulting in insufficient heat insulation.

[0074] For the coating system formulated with group C flame-retardant powder, the protective properties of the coating are significantly improved by combining the good heat insulation effect of expanded graphite, the heat absorption protection of aluminum hydroxide, and the char-promoting effect of aluminum dimethylphosphinate, allowing it to withstand five flame burns. After modifying the proportions of the flame-retardant powder, the coating formulated with group D powder can protect PVC substrates through the UL-94 5VA test, maintaining the integrity and density of the char layer. Figure 2 As can be seen from Figures (c) and (d), the protective carbon layer formed by the coatings obtained by combining EG, ALH and AHP is denser, and the carbon layer corresponding to the powder in group d is more complete. This is because the heat insulation effect of expanded graphite is the key performance of fireproof and flame-retardant coatings. After appropriately increasing the proportion of graphite, the efficiency of forming the expanded carbon layer is higher and the heat insulation is better.

[0075] Figure 3The images show the three types of sheets from Example 2 after undergoing the UL-94 5VA test. When the ratio of flame retardant powder to binder was 1:3, the PVC sheet with coating protection cracked during the UL-94 5VA test and failed. This was because the proportion of flame retardant powder in the coating was too low, resulting in insufficient coating protection. However, when the ratio of powder to binder was increased to 1:2.5, the PVC sheet with coating protection could pass the UL-94 5VA test smoothly. Further adjustments to the powder to binder ratio, reaching a mass ratio of 1:2.87, resulted in sufficient coating protection for the PVC sheet to pass the UL-94 5VA test. From an economic cost perspective, the proportion of binder can be appropriately increased to reduce costs, while the coating still provides sufficient protection.

[0076] Figure 4 This indicates that the various elements in the expanded carbon layer produced by the protective coating are evenly distributed, suggesting that the flame retardant powder did not agglomerate in the coating and that the coating composition is uniform.

[0077] Figure 5 These are photos comparing the PVC sheet with and without coating protection before and after the UL-94 5VA test in Example 3.

[0078] Figure 6 These are photos comparing the PP sheet with and without coating protection before and after the UL-94 5VA test in Example 4. For PP sheets that melt upon contact with a flame, the fire-retardant coating provides significant protection, effectively preventing the PP sheet from being melted and burned through.

[0079] Figure 7 The figures show the TG and DTG curves of PVC and PP sheets with and without flame-retardant coatings obtained in Examples 3-4. The test results indicate that, in an air atmosphere, the curve trends of the coated substrates are basically the same as those of the original samples, and the coating does not change the thermal stability of the sheets.

[0080] Figure 8The results of cone calorimeter tests on PVC and PP sheets are shown in Table 2. Based on the data, under the protection of the fire-retardant coating, the HRR of PVC and PP sheets decreased by a maximum of 16.2% and 14.3%, respectively. Furthermore, the heat release peak of the coating appeared first, followed by the combustion peak of the sheet, indicating a delayed combustion time for the sheet, suggesting that the coating provided good protection for the substrate. The smoke release rate (SPR) of the coated PVC sheet decreased by 46.2%, while the change in PP sheet was not significant. However, the coating protection significantly delayed the smoke release time of both PVC and PP sheets, while the TSR did not change significantly, indicating that the fire-retardant coating did not exacerbate smoke generation. Moreover, the CO release of both types of sheets was delayed, and the CO yield of PP sheet decreased by 11.1%.

[0081] Figure 9 The photos show the results of cone calorimeter tests on PVC and PP sheets. The original sheets without fire-retardant coatings left very little residue after the test, especially the PP sheets, which left almost no residue after burning. In contrast, the samples with coating protection had a very obvious expanded char layer, and the amount of char residue was significantly increased.

[0082] Table 3 shows the adhesive shear strength test results of the coating No. 6 prepared in Example 2. Compared with the pure adhesive without flame retardant powder, the coating with flame retardant powder has only a small loss in shear strength. The coating still has good adhesion and can cope with the common scratches and bends of the refrigerator back panel without the problem of coating cracking.

[0083] Figure 10 Images show the #6 coating from Example 2 and the #9, #10, and #11 coatings from the comparative examples after standing for 72 hours following preparation. The three coatings prepared in the comparative examples all showed varying degrees of stratification, indicating that their dispersibility needs improvement. A suitable surfactant is needed in the coating system to maintain its dispersibility. Experiments showed that adding an appropriate amount of sodium dodecylbenzenesulfonate to the coating system can effectively improve its dispersibility. In subsequent standing tests, the fire-retardant coating #6 maintained system stability for a long time, making it suitable for long-term storage.

Claims

1. The application of an intumescent flame-retardant coating in the preparation of flame-retardant materials of polyvinyl chloride or polypropylene, characterized in that: The flame retardant properties of polyvinyl chloride (PVC) or polypropylene (PP) materials are improved by coating the surface of the PVC or PP material with an intumescent flame retardant coating to form a flame retardant protective coating. The coating thickness of the intumescent flame retardant coating on the PVC or PP material surface is 250-750μm. After coating, the material is placed in a circulating hot air oven and dried at a temperature of 25-50℃ for 12 hours. After drying, the material is pressed and held at 40-50℃ for 10-20 seconds using a flat vulcanizing machine to obtain PVC or PP material with fire-retardant coating protection. The intumescent flame-retardant coating is composed of a compound of flame-retardant powder, binder, defoamer and surfactant; The flame retardant powder is composed of expanded graphite, aluminum dimethylphosphinic acid, metal hydroxide and titanium dioxide in a mass ratio of 30:17:49:4; The metal hydroxide is one or more of magnesium hydroxide and aluminum hydroxide; The surfactant is sodium dodecylbenzenesulfonate; The mass ratio of flame retardant powder, binder, defoamer and surfactant is 1:(2.5~3):(0.01~0.02):(0.005~0.01).

2. The application according to claim 1, characterized in that: The polyvinyl chloride or polypropylene material with fire-retardant coating protection is used as a material for household appliances.

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