Preparation method of heat-resistant and flame-retardant foamed hot melt adhesive

Abstract

The present invention belongs to the technical field of adhesives, and particularly relates to a preparation method of a heat-resistant and flame-retardant foamed hot melt adhesive. By mass, the raw materials of the hot melt adhesive include: 40-50 parts of epoxy resin-modified PA6, 5-10 parts of toughening agent, 10-15 parts of flame retardant, 2-4 parts of nucleating agent, 3-5 parts of foaming agent, 1-2 parts of coupling agent, 0.5-1 part of antioxidant, and 0.5-1 part of lubricant. The preparation method includes steps such as mixing, melt blending, granulation, and foaming. The present invention significantly improves the heat resistance and flame retardancy of the foamed hot melt adhesive by optimizing the formula and preparation process, maintains good adhesive strength, and at the same time the raw materials used are environmentally friendly and pollution-free.

Description

Technical Field

[0001] The present invention belongs to the technical field of adhesives, and in particular relates to a method for preparing a heat-resistant and flame-retardant foaming hot-melt adhesive. Background Art

[0002] Foamed hot melt adhesive is a thermoplastic resin that is heated and melted before being coated or injected, solidifying after cooling to form a foam-like structure. This structure not only reduces the weight of the material but also improves its thermal and sound insulation properties. Common foamed hot melt adhesives currently on the market are primarily made from thermoplastic polymers such as polyethylene (PE), polypropylene (PP), and ethylene-vinyl acetate copolymer (EVA). Although these materials exhibit good physical, mechanical, and adhesive properties at room temperature, when used in high-temperature environments, due to the material's inherent heat resistance temperature limitations, they often experience decreased adhesion, deformation, or even melting, seriously affecting the product's performance.

[0003] In certain specific application scenarios, such as the bonding of automotive interior parts, the fixing of internal components of electronic products, the installation of thermal insulation materials for building exterior walls, etc., the foamed hot melt adhesive is required to maintain stable performance at higher temperatures and have a certain flame retardant ability to prevent the occurrence of fire accidents. Traditional modification methods mainly include adding inorganic fillers, organic flame retardants, etc. However, although the heat resistance temperature of most improved foamed hot melt adhesives has been improved, it still cannot meet the application requirements in certain higher temperature environments. In addition, although the addition of some flame retardants can improve the flame retardant grade of the material, due to poor compatibility and other reasons, it often leads to a decrease in the mechanical properties of the material. In addition, the improvement methods of the existing technology are often accompanied by problems such as increased costs, increased processing difficulty, and environmental unfriendliness.

[0004] In summary, developing a foaming hot melt adhesive that can significantly increase the heat resistance temperature and effectively enhance the flame retardant properties, while ensuring that the comprehensive performance of the material is not affected and meets environmental protection requirements, is a technical problem that needs to be solved urgently. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing a heat-resistant and flame-retardant foaming hot-melt adhesive to meet the growing market demand for high-performance adhesives.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for preparing a heat-resistant and flame-retardant foaming hot-melt adhesive, wherein the raw materials include the following components by weight: 40-50 parts of epoxy resin-modified PA6, 5-10 parts of a toughening agent, 10-15 parts of a flame retardant, 2-4 parts of a nucleating agent, 3-5 parts of a foaming agent, 1-2 parts of a coupling agent, 0.5-1 part of an antioxidant, and 0.5-1 part of a lubricant;

[0008] The preparation method includes the following steps:

[0009] (1) Put all raw materials into a mixer for mixing. The rotation speed of the mixer is 1000 - 5000 rpm, and the mixing time is 10 - 20 minutes;

[0010] (2) Add the mixed raw materials into a twin-screw extruder for melt mixing and granulation;

[0011] (3) Add the particles obtained in step (2) into a single-screw extruder for foaming, and cool and shape the foamed material to obtain the heat-resistant and flame-retardant foamed hot melt adhesive.

[0012] Furthermore, the parameters of the twin-screw extruder are set as follows: screw rotation speed: 200 - 300 rpm; feeding section temperature: 175 - 185 °C, compression section temperature: 195 - 205 °C, metering section temperature: 210 - 225 °C, die head temperature: 225 - 230 °C; vacuum degree: -0.05 - -0.1 MPa.

[0013] Furthermore, the parameters of the single-screw extruder are set as follows: screw rotation speed: 50 - 70 rpm; feeding section temperature: 175 - 185 °C, compression section temperature: 195 - 205 °C, metering section temperature: 210 - 225 °C, die head temperature: 225 - 230 °C; foaming pressure: 8 - 12 MPa.

[0014] Furthermore, the preparation method of the epoxy resin-modified PA6 includes the following steps:

[0015] (i) Mix 40 - 50 parts of PA6, 2 - 5 parts of epoxy resin, 0.1 - 0.3 parts of triphenylphosphine, and 0.1 - 0.2 parts of antioxidant, and then put them into a twin-screw extruder for melt grafting reaction to obtain a graft copolymer;

[0016] (ii) Cool and granulate the graft copolymer obtained in step (i) to obtain epoxy resin-modified PA6.

[0017] Furthermore, the epoxy resin is selected from one or more of bisphenol A-type epoxy resin, aliphatic epoxy resin, and amino acid-type epoxy resin.

[0018] Furthermore, the antioxidant is selected from one or more of antioxidant 1010, antioxidant 168, dilauryl thiodipropionate, diphenylamine, and antioxidant 1076.

[0019] Furthermore, the toughening agent is maleic anhydride grafted polypropylene (MAH-g-PP) and ethylene-octene copolymer (POE), and the mass ratio of the two is 1:(0.8 - 1.2).

[0020] MAH-g-PP can form chemical bonds with the matrix resin through maleic anhydride groups, enhancing the interfacial bonding force, improving the compatibility with epoxy resin-modified PA6, forming a continuous phase interface, and thus improving the overall performance of the material. POE is an elastomer with excellent flexibility and tear resistance. It can effectively disperse stress and prevent crack propagation, thereby improving the toughness of the material. The combination of MAH-g-PP and POE can produce a synergistic toughening effect. MAH-g-PP enhances the interfacial bonding through chemical bonding, while POE improves flexibility through physical dispersion. This synergistic effect enables the material to better disperse stress when subjected to external forces, preventing the generation and propagation of cracks. By adjusting the mass ratio of MAH-g-PP and POE, other properties of the material (such as heat resistance and flame retardancy) can be maintained while improving toughness. The combination of MAH-g-PP and POE can also improve the heat resistance of the material. MAH-g-PP enhances the interfacial bonding through chemical bonding, improving the heat resistance stability of the material, and the elasticity of POE can prevent brittle fracture at high temperatures, thus improving the overall heat resistance performance.

[0021] Further, the flame retardant is a mixture of melamine phosphate, modified expanded graphite, and red phosphorus, and the mass ratio is (4-6):(3-4):(1-2).

[0022] Further, the preparation method of the modified expanded graphite includes the following steps:

[0023] (a) Mix expanded graphite with sulfuric acid with a mass concentration of 98%, immerse the expanded graphite completely in the sulfuric acid, and place the mixture in an ice-water bath;

[0024] (b) Drop nitric acid with a mass concentration of 65% into the mixture. After dropping, continue to stir in the ice-water bath for 20-40 minutes, then transfer to room temperature and continue to stir for 50-70 minutes;

[0025] (c) After the reaction in step (b) is completed, centrifuge the solid product, wash the solid product with deionized water until the filtrate is neutral;

[0026] (d) Redisperse the washed solid product into deionized water, perform ultrasonic treatment to ensure uniform dispersion, add silane coupling agent KH550, continue ultrasonic treatment, transfer the ultrasonically treated mixture to a water bath, heat to 50-70 °C, and stir and react to obtain a modified expanded graphite suspension;

[0027] (e) Dry, grind, and sieve the modified expanded graphite suspension through a 100-mesh sieve to obtain the modified expanded graphite.

[0028] Further, the mass-volume ratio of the expanded graphite to 98% sulfuric acid is 1 g : (4 - 6) mL, and the mass-volume ratio of the expanded graphite to 65% nitric acid is 1 g : (1 - 2) mL.

[0029] Further, in step (d), the mass of the silane coupling agent KH550 is 15 - 25% of that of the expanded graphite; after adding the silane coupling agent KH550, ultrasonic treatment is continued for 20 - 40 minutes; the stirring reaction time in step (d) is 1.5 - 2.5 hours.

[0030] Further, in step (e), the drying temperature is 60 - 70 °C, and the drying time is 20 - 30 hours.

[0031] The modified expanded graphite of the present invention can rapidly expand at high temperatures to form a porous carbon layer. This carbon layer can effectively isolate oxygen and heat, prevent the spread of flames, and improve the flame retardancy of the material; the formed carbon layer has good heat insulation performance, can significantly reduce the temperature inside the material, and prevent the pyrolysis and combustion of the internal material; the formed carbon layer can also physically shield the flame and prevent the flame from directly contacting the substrate, thereby improving the fire resistance of the material. Through the modification with silane coupling agent, the compatibility between the modified expanded graphite and the matrix resin is greatly improved, the interfacial bonding force is enhanced, and the flame retardant effect is improved. The combination of melamine phosphate, modified expanded graphite and red phosphorus can produce a synergistic effect and jointly improve the flame retardant performance of the material. Melamine phosphate and red phosphorus form a carbonized layer through chemical action, and the modified expanded graphite forms a heat insulation layer through physical expansion. The three complement each other to form a multiple flame retardant mechanism. Reasonable design of the ratio of the three can simultaneously improve the heat resistance, flame retardancy and mechanical properties of the material. In addition, red phosphorus, melamine phosphate and modified expanded graphite are more environmentally friendly than halogen-based flame retardants and do not produce toxic gases during combustion, meeting the environmental protection requirements.

[0032] Further, the nucleating agent is selected from one or more of nano-silica, talcum powder, calcium carbonate, sodium diphenylacetate, mica powder.

[0033] [[ID=!5]]Further, the blowing agent is selected from one or more of azodicarbonamide, sodium bicarbonate, citric acid, sodium nitrite.

[0034] Further, the coupling agent is selected from one or more of silane coupling agents, titanate coupling agents, aluminate coupling agents.

[0035] Further, the antioxidant is selected from one or more of antioxidant 1010, antioxidant 168, dilauryl thiodipropionate, diphenylamine, antioxidant 1076.

[0036] Further, the lubricant is selected from one or more of zinc stearate, calcium stearate, polyethylene wax, polypropylene wax.

[0037] The heat-resistant and flame-retardant foaming hot-melt adhesive of the present invention uses epoxy resin-modified PA6 as the matrix resin. The introduction of epoxy groups can further improve the chemical bonding and physical adsorption between the hot-melt adhesive and the substrate surface, thereby enhancing the bonding performance of the hot-melt adhesive. In addition, epoxy resin can improve the toughness of PA6, making it not easy to break when subjected to impact or tension. When epoxy resin-modified PA6 is used as the matrix resin, it can cooperate with the flame retardants (a mixture of melamine phosphate, modified expanded graphite, and red phosphorus) of the present invention to further improve the flame retardant effect. The modified expanded graphite is treated with a silane coupling agent and can form chemical bonds with the epoxy groups in the epoxy resin, further enhancing the interfacial bonding force and improving the compatibility. The active groups in melamine phosphate and red phosphorus can react with the epoxy groups in the epoxy resin to form a stable network structure, improving the overall performance of the material. The addition of MAH-g-PP and POE can further improve the cohesion and toughness of the material. Through the synergistic effects such as chemical bonding, physical dispersion, and multiple flame retardant mechanisms among the components in the formula of the present invention, the heat resistance, flame retardancy, mechanical properties, and processing properties of the material are significantly improved.

[0038] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0039] The present invention provides a preparation method of a heat-resistant and flame-retardant foaming hot-melt adhesive. By optimizing the formula and preparation process, the heat resistance and flame retardancy of the material are significantly improved. Compared with traditional foaming hot-melt adhesives, the product of the present invention has a higher softening point and stronger flame retardant performance at high temperatures, while maintaining good bonding performance and having environmental protection characteristics. In addition, through reasonable formula design and preparation process, the present invention reduces the production cost and improves the market competitiveness of the product. Detailed implementation manners

[0040] 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. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

[0041] Unless otherwise specified, the raw materials used in the embodiments are all ordinary commercially available products. The following is an exemplary description:

[0042] Polyamide 6 (PA6) was purchased from Zhejiang NHU Company Limited, PA6-1013;

[0043] Epoxy resin was purchased from Baling Petrochemical, E-51;

[0044] Maleic anhydride grafted polypropylene (MAH-g-PP) was purchased from the New Materials Research Institute of Beijing University of Chemical Technology, MAH-g-PP-100;

[0045] Ethylene-octene copolymer (POE) was purchased from Shanghai Petrochemical Co., Ltd., POE-8150;

[0046] Ethylene-vinyl acetate copolymer (EVA) was purchased from Jiangsu Sierbang Petrochemical Co., Ltd., EVA-1102;

[0047] Talc powder was purchased from Liaoning Haicheng Talc Group Co., Ltd., HT-100, with a particle size of about 1 μm;

[0048] Melamine phosphate was purchased from Zhejiang Longsheng Group Co., Ltd., MPP-100, with a particle size of about 5 μm;

[0049] Red phosphorus was purchased from Shandong Ruifeng High Polymer Materials Co., Ltd., RF-RP-100;

[0050] Expanded graphite was purchased from Qingdao Huagao Graphene Technology Co., Ltd., HG-EG-100, with a particle size of about 10 μm and an expansion ratio of ≥200 times.

[0051] Example 1

[0052] This example provides a preparation method of a heat-resistant and flame-retardant foamed hot melt adhesive, and its raw materials include the following components by mass: 45 parts of epoxy resin-modified PA6, 8 parts of toughening agent (MAH-g-PP and POE with a mass ratio of 1:1), 13 parts of flame retardant, 3 parts of nucleating agent (talc powder), 4 parts of foaming agent (azodicarbonamide), 1.5 parts of coupling agent (KH550), 0.8 part of antioxidant (antioxidant 1010), and 0.8 part of lubricant (zinc stearate).

[0053] The preparation method of the epoxy resin-modified PA6 includes the following steps:

[0054] (i) Mix 45 parts of PA6, 4 parts of epoxy resin (Epoxy Resin E-51), 0.2 part of triphenylphosphine, and 0.1 part of antioxidant 1010, and then put them into a twin-screw extruder for melt grafting reaction. The screw speed is 200 rpm, and the temperatures of each zone are: feeding section 180 °C, compression section 200 °C, metering section 220 °C, and die head temperature 230 °C to obtain a graft copolymer;

[0055] (ii) Cool and pelletize the graft copolymer obtained in step (i) through a water-cooled pelletizer to obtain epoxy resin-modified PA6.

[0056] The flame retardant is a mixture of melamine phosphate, modified expanded graphite, and red phosphorus, with a mass ratio of 5:3.5:1.5.

[0057] The preparation method of the modified expanded graphite comprises the following steps:

[0058] (a) Add 10 g of expanded graphite into a clean beaker, then add 50 mL of sulfuric acid with a mass concentration of 98% thereto, so that the expanded graphite is completely immersed in the sulfuric acid, and place the beaker in an ice-water bath;

[0059] (b) Dropwise add 15 mL of nitric acid with a mass concentration of 65% into the beaker, the dropping time is about 5 minutes, after the dropping is completed, continue to stir in the ice-water bath for 30 minutes, then transfer the beaker to room temperature and continue to stir for 60 minutes;

[0060] (c) After the reaction in step (b) is completed, centrifuge and separate the solid product, and wash the solid product repeatedly with deionized water until the filtrate is neutral;

[0061] (d) Redisperse the washed solid product into 100 mL of deionized water, perform ultrasonic treatment for 10 minutes to uniformly disperse the solid product in the deionized water, add 2 g of silane coupling agent KH550, continue ultrasonic treatment for 30 minutes, transfer the mixture after ultrasonic treatment to a water bath, heat to 60 °C, and stir and react for 2 hours to obtain a modified expanded graphite suspension;

[0062] (e) Dry the modified expanded graphite suspension at 60 °C for 24 hours, grind it using a grinder, and pass through a 100-mesh sieve to obtain the described modified expanded graphite.

[0063] The preparation method of the heat-resistant and flame-retardant foaming hot-melt adhesive comprises the following steps:

[0064] (1) Weigh the raw materials according to the ratio, put all the raw materials into a mixer for mixing, set the rotation speed of the mixer to 2000 rpm, and the mixing time to 15 minutes to ensure that each component is fully dispersed;

[0065] (2) Add the mixed raw materials into a twin-screw extruder for melt mixing. The following parameters are set for the twin-screw extruder: screw rotation speed: 240 rpm; feeding section temperature: 180 °C, compression section temperature: 200 °C, metering section temperature: 220 °C, die head temperature: 230 °C; vacuum degree: -0.08 MPa. The material after being mixed by the twin-screw extruder is pelletized by a water-cooled pelletizer to obtain particles with uniform particle size;

[0066] (3) Add the particles obtained in step (2) into a single-screw extruder for foaming. The parameters of the single-screw extruder are set as follows: screw rotation speed: 60 rpm; feeding section temperature: 180 °C, compression section temperature: 200 °C, metering section temperature: 220 °C, die head temperature: 230 °C, foaming pressure: 10 MPa. Cool and shape the foamed material through a cold water bath. Control the water temperature at 20 °C and the cooling time at 1 minute to ensure complete curing of the material. Cut the cooled material into the required size and shape to obtain the heat-resistant and flame-retardant foamed hot melt adhesive.

[0067] Example 2

[0068] This example provides a preparation method of a heat-resistant and flame-retardant foamed hot melt adhesive. The difference from Example 1 is that the raw materials include the following components by mass: 50 parts of epoxy resin-modified PA6, 5 parts of toughening agent (MAH-g-PP and POE with a mass ratio of 1:1), 13 parts of flame retardant, 3 parts of nucleating agent (nano-silica), 4 parts of foaming agent (sodium bicarbonate), 1.5 parts of coupling agent (KH550), 0.8 parts of antioxidant (antioxidant 1010), and 0.8 parts of lubricant (polyethylene wax). The flame retardant is a mixture of melamine phosphate, modified expanded graphite, and red phosphorus with a mass ratio of 5:4:1. The rest is the same as in Example 1.

[0069] Comparative Example 1

[0070] This comparative example provides a preparation method of a heat-resistant and flame-retardant foamed hot melt adhesive. The difference from Example 1 is that epoxy resin-modified PA6 is replaced with EVA (ethylene-vinyl acetate copolymer), and the rest is the same as in Example 1.

[0071] Comparative Example 2

[0072] This comparative example provides a preparation method of a heat-resistant and flame-retardant foamed hot melt adhesive. The difference from Example 1 is that the toughening agent is 8 parts of POE, and the rest is the same as in Example 1.

[0073] Comparative Example 3

[0074] This comparative example provides a preparation method of a heat-resistant and flame-retardant foamed hot melt adhesive. The difference from Example 1 is that the flame retardant is a mixture of melamine phosphate, modified expanded graphite, and red phosphorus with a mass ratio of 5:1:1, and the rest is the same as in Example 1.

[0075] Comparative Example 4

[0076] This comparative example provides a preparation method of a heat-resistant and flame-retardant foamed hot melt adhesive. The difference from Example 1 is that the flame retardant is a mixture of decabromodiphenyl ether, aluminum hydroxide, and zinc borate with a mass ratio of 5:3.5:1.5, and the rest is the same as in Example 1.

[0077] Comparative Example 5

[0078] This comparative example provides a method for preparing a heat-resistant and flame-retardant foamed hot melt adhesive, which is different from Example 1 in that: the expanded graphite in the flame retardant is not modified, and the rest is the same as in Example 1.

[0079] Comparative Example 6

[0080] This comparative example provides a method for preparing a heat-resistant and flame-retardant foamed hot melt adhesive, which is different from Example 1 in that: the epoxy resin-modified PA6 is replaced with unmodified PA6, and the rest is the same as in Example 1.

[0081] Performance Test

[0082] Test the peel strength, softening point, and oxygen index of the hot melt adhesives prepared in Examples 1-2 and Comparative Examples 1-6.

[0083] Test method for peel strength: Coat the hot melt adhesive to be tested between two standard stainless steel plates of 25 mm × 200 mm, with a thickness of about 1 mm. After pressing, cure at room temperature (25 °C) for 24 hours. Fix the specimen on an electronic universal testing machine, set the peel speed to 100 mm / min, record the peel force, and calculate the peel strength.

[0084] Test method for softening point: Heat the hot melt adhesive to a flowing state, pour it into a standard ring mold, demold after cooling to room temperature to obtain a specimen. Place the prepared specimen on the bracket of a softening point tester, ensure good contact between the bottom of the specimen and the bracket. Set the water bath temperature of the tester to an initial temperature of 5 °C, place the steel ball in the ball holder above the specimen, turn on the tester, and uniformly heat the water bath at a rate of 5 °C / min. Observe and record the temperature at which the steel ball passes through the specimen and touches the bottom steel plate, which is the softening point of the hot melt adhesive.

[0085] Test method for oxygen index: Make the hot melt adhesive to be tested into a standard specimen with dimensions of 150 mm × 10 mm × 3 mm. Fix the specimen in the fixture of an oxygen index tester, ensure the specimen is vertically suspended. Set the oxygen concentration of the tester to an initial value of 21%. Use a lighter to ignite the upper end of the specimen, observe and record the combustion situation of the specimen. If the specimen continues to burn for more than 3 seconds after removing the lighter, increase the oxygen concentration. If the specimen extinguishes immediately after removing the lighter, decrease the oxygen concentration. Gradually adjust the oxygen concentration until a critical value is found such that the specimen can just continue to burn for 3 seconds after removing the lighter. Record this critical oxygen concentration, which is the oxygen index of the hot melt adhesive.

[0086] The test results are shown in Table 1.

[0087] Table 1 Performance Test Results

[0088] Sample Peeling strength (N / mm) Softening point (℃) Oxygen index (%) Example 1 4.5 120 32.6 Example 2 4.3 118 31.9 Comparative Example 1 3.3 105 31.4 Comparative Example 2 3.7 112 31.6 Comparative Example 3 4.5 110 29.3 Comparative Example 4 4.6 92 24.0 Comparative Example 5 4.2 102 27.1 Comparative Example 6 3.9 109 28.2

[0089] From the above test results, it can be seen that the hot melt adhesive prepared by the present invention has excellent adhesive strength, heat resistance and flame retardancy. In Comparative Example 1, the epoxy resin-modified PA6 was replaced with EVA. EVA has poor compatibility with other components, resulting in a weak interfacial bond, which leads to a decrease in peel strength and flame retardancy; EVA has a lower melting point than PA6, resulting in a decrease in softening point. In Comparative Example 2, the toughening agent was changed from a mixture of MAH-g-PP and POE to a single POE. MAH-g-PP enhances the interfacial bond through chemical bonding, while POE mainly provides flexibility and lacks chemical bonding. The mixture of MAH-g-PP and POE can improve the cohesion of the material, while a single POE cannot provide the same effect, resulting in a decrease in peel strength; MAH-g-PP can promote the crystallization of epoxy resin-modified PA6 and improve heat resistance. MAH-g-PP can also promote the dispersion of the flame retardant and improve the flame retardant effect, while POE has little effect on the crystallinity and the dispersion of the flame retardant. In Comparative Example 3, the mass ratio of each component of the flame retardant was changed, especially the amount of modified expanded graphite was reduced. Modified expanded graphite expands at high temperature to form a protective layer, improving heat resistance and flame retardancy. Reducing its amount will significantly affect heat resistance and flame retardancy. In Comparative Example 4, the type of flame retardant was replaced, and the heat resistance and flame retardancy were significantly reduced, indicating that the effect of decabromodiphenyl ether, aluminum hydroxide and zinc borate as flame retardants is significantly inferior to that of the flame retardant of the present invention. In Comparative Example 5, unmodified expanded graphite was used. The compatibility and interfacial bond between unmodified expanded graphite and epoxy resin-modified PA6 are poor, and the expansion effect at high temperature is poor, and an effective protective layer cannot be formed. Therefore, the adhesive performance, heat resistance and flame retardancy are all poor. In Comparative Example 6, unmodified PA6 was used, and its flame retardancy was significantly reduced. The reason is that the interfacial bonding force between unmodified PA6 and the flame retardant is weak, and it is easy to undergo interfacial separation at high temperature, resulting in the detachment or failure of the flame retardant, thereby reducing the flame retardant performance. This further proves that the flame retardant of the present invention and the matrix resin need to be used simultaneously to produce better effects.

[0090] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle described in the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a heat-resistant and flame-retardant foamed hot melt adhesive, the raw materials of which include the following components by mass parts: 40-50 parts of epoxy resin-modified PA6, 5-10 parts of toughening agent, 10-15 parts of flame retardant, 2-4 parts of nucleating agent, 3-5 parts of foaming agent, 1-2 parts of coupling agent, 0.5-1 part of antioxidant, and 0.5-1 part of lubricant; The preparation method includes the following steps: (1) Put all the raw materials into a mixer for mixing, the rotation speed of the mixer is 1000-5000 rpm, and the mixing time is 10-20 minutes; (2) Add the mixed raw materials into a twin-screw extruder for melting and mixing, and granulate; (3) Add the particles obtained in step (2) into a single-screw extruder for foaming, cool and shape the foamed material to obtain the heat-resistant and flame-retardant foamed hot melt adhesive; The preparation method of the epoxy resin-modified PA6 includes the following steps: (i) Mix 40-50 parts of PA6, 2-5 parts of epoxy resin, 0.1-0.3 parts of triphenylphosphine, and 0.1-0.2 parts of antioxidant, and then put them into a twin-screw extruder for melt grafting reaction to obtain a graft copolymer; (ii) Cool and granulate the graft copolymer obtained in step (i) to obtain epoxy resin-modified PA6; The toughening agent is maleic anhydride-grafted polypropylene and ethylene-octene copolymer, and the mass ratio of the two is 1:(0.8-1.2); The flame retardant is a mixture of melamine phosphate, modified expanded graphite and red phosphorus, and the mass ratio is (4-6):(3-4):(1-2); The preparation method of the modified expanded graphite includes the following steps: (a) Mix expanded graphite with sulfuric acid with a mass concentration of 98% so that the expanded graphite is completely immersed in the sulfuric acid, and place the mixture in an ice-water bath; (b) Drop nitric acid with a mass concentration of 65% into the mixture. After dropping, continue to stir in the ice-water bath for 20-40 minutes, then transfer to room temperature and continue to stir for 50-70 minutes; (c) After the reaction in step (b) is completed, centrifuge to separate the solid product, and wash the solid product with deionized water until the filtrate is neutral; (d) Redisperse the washed solid product into deionized water, perform ultrasonic treatment to ensure uniform dispersion, add silane coupling agent KH550, continue ultrasonic treatment, transfer the ultrasonically treated mixture to a water bath, heat to 50-70 °C, and stir and react to obtain a modified expanded graphite suspension; (e) Dry, grind, and sieve the modified expanded graphite suspension through a 100-mesh sieve to obtain the modified expanded graphite.

2. The preparation method according to claim 1, characterized in that, The epoxy resin is selected from one or more of bisphenol A-type epoxy resin, aliphatic epoxy resin, and amino acid-type epoxy resin.

3. The preparation method according to claim 1, wherein The mass-volume ratio of the expanded graphite to 98% sulfuric acid is 1 g:(4-6) mL, and the mass-volume ratio of the expanded graphite to 65% nitric acid is 1 g:(1-2) mL.

4. The preparation method according to claim 1, characterized in that, The mass of the silane coupling agent KH550 described in step (d) is 15-25% of the expanded graphite; after adding the silane coupling agent KH550, ultrasonic treatment is continued for 20-40 minutes; the stirring reaction time described in step (d) is 1.5-2.5 hours.

5. The preparation method according to claim 1, wherein, The drying temperature described in step (e) is 60-70 °C, and the drying time is 20-30 hours.

6. The preparation method according to claim 1, characterized in that, The nucleating agent is selected from one or more of nano-silica, talcum powder, calcium carbonate, sodium diphenylacetate, mica powder; the foaming agent is selected from one or more of azodicarbonamide, sodium bicarbonate, citric acid, sodium nitrite; the coupling agent is selected from one or more of silane coupling agents, titanate coupling agents, aluminate coupling agents; the antioxidant is selected from one or more of antioxidant 1010, antioxidant 168, dilauryl thiodipropionate, diphenylamine, antioxidant 1076; the lubricant is selected from one or more of zinc stearate, calcium stearate, polyethylene wax, polypropylene wax.

7. A heat-resistant and flame-retardant foamed hot melt adhesive prepared by the preparation method according to any one of claims 1-6.