High-temperature-resistant polyurethane hot melt adhesive and preparation method thereof

Abstract

The invention belongs to the technical field of hot melt adhesives, and discloses a high-temperature-resistant polyurethane hot melt adhesive and a preparation method thereof.The preparation method comprises the following steps that an organic silicon modifier and sulfonyl hydrazide grafted polyester polyol are added into a reaction kettle, heated and stirred, and organic silicon modified polyester polyol is obtained; adding fluorine-containing silicon copolymer modified isocyanate and a catalyst into the organic silicon modified polyester polyol, heating and stirring to obtain a polyurethane solution; adding a latent cross-linking agent into the polyurethane solution, continuously heating and stirring to obtain a polyurethane prepolymer, granulating, and cooling to room temperature to obtain the high-temperature-resistant polyurethane hot melt adhesive. According to the method, the high temperature resistance and chemical resistance of the polyurethane hot melt adhesive are improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of hot melt adhesives, in particular to a high-temperature-resistant polyurethane hot melt adhesive and a preparation method thereof. BACKGROUND

[0002] Polyurethane hot melt adhesive (PU-HMA) is a high-performance adhesive combining thermoplastic process and thermosetting properties. It is based on isocyanate-terminated (-NCO) polyurethane prepolymer, which is coated on the surface of the bonded object after melting by heating, and rapidly forms initial adhesion strength after cooling, and then forms an irreversible crosslinked structure through a moisture curing reaction. This unique mechanism makes it have the convenience of traditional hot melt adhesives and the ultimate performance of reactive adhesives, showing excellent bonding strength, high and low temperature resistance, elastic recovery rate, and excellent oil resistance and vibration fatigue resistance.

[0003] In the field of automobile manufacturing, polyurethane hot melt adhesive has become a key material for achieving lightweight and environmental protection. In the automotive field, polyurethane hot melt adhesive can not only be used for fixing sound insulation pads, but also be used for fixing wire harnesses inside the engine. Sound insulation pads are a very important part of NVH (Noise, Vibration and Harshness) materials, mainly composed of non-woven fabric, PET cotton, foam, PVC sheet and other materials, while the surface of the wire harness is mainly composed of PVC insulation layer, nylon pipe fittings, metal brackets, engineering plastic shell and other materials. These materials have different surface polarities, while the polyurethane hot melt adhesive molecule contains a strong polar urethane bond (-NH-COO-), which can form strong van der Waals forces and hydrogen bonds with the surface of these materials, thereby achieving effective bonding.

[0004] However, during use, the vehicle as a whole is in a high-temperature environment, especially the long-term radiation temperature generated by the engine components during operation can reach 125-150℃, which exceeds the tolerance limit of ordinary polyurethane hot melt adhesive. Continuous high temperature will cause the molecular chain segment to move intensively, resulting in softening deformation and creep, causing the fixed point to relax and lose the binding force, resulting in the phenomenon of delamination; at the same time, the chemical media such as engine oil, transmission oil and coolant existing in the engine compartment will leak during long-term use, eroding the hot melt adhesive layer of the sound insulation pad (such as the firewall facing the engine) and the wire harness, causing swelling or interfacial peeling. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a high-temperature-resistant polyurethane hot melt adhesive and a preparation method thereof, aiming to improve the high-temperature resistance and chemical resistance of the polyurethane hot melt adhesive.

[0006] To solve the above technical problems, the application provides a preparation method of high-temperature-resistant polyurethane hot melt adhesive, which comprises the following steps: S1, the silicone modifier, the sulfonamide hydrazine grafted polyester polyol is added into the reaction kettle, heated and stirred to obtain the silicone modified polyester polyol; S2, the fluorine-containing silicone copolymer modified isocyanate and the catalyst are added into the silicone modified polyester polyol, heated and stirred to obtain a polyurethane solution; S3, the latent crosslinking agent is added into the polyurethane solution, and the heating and stirring are continued to obtain a polyurethane prepolymer, which is granulated and cooled to room temperature to obtain the high-temperature-resistant polyurethane hot melt adhesive.

[0007] In some embodiments, the silicone modifier in step S1 comprises at least one of alpha, omega-dihydroxypolydimethylsiloxane, aminoethyl aminopropyl polydimethylsiloxane, epoxy-terminated polydimethylsiloxane, and methacryloxypropyl-terminated polydimethylsiloxane, and the sulfonamide hydrazine grafted polyester polyol comprises at least one of sulfonamide hydrazine grafted polycaprolactone triol, sulfonamide hydrazine grafted polyphthalate glycerol triol, and sulfonamide hydrazine grafted polyglycerol adipate triol.

[0008] In some embodiments, step S1 comprises: S1.1, the inhibitor and the sulfonamide hydrazine grafted polyester polyol are added into the reaction kettle in a nitrogen atmosphere, heated to 100-120 DEG C and stirred for 1-2 h to obtain a mixed solution, wherein the mass of the inhibitor is 10-20 wt% of the mass of the polyester polyol, the inhibitor comprises at least one of poly(N-vinylcaprolactam), poly(2-isopropyl-2-oxazoline), and poly(vinyl methyl oxazoline), and the stirring rate is 100-200 rpm; S1.2, the silicone modifier is added into the mixed solution, and the heating and stirring are continued at 100-120 DEG C for 2-4 h to obtain the silicone modified polyester polyol, wherein the molar ratio of the silicone modifier to the polyester polyol is (1.02-1.04):1, and the stirring rate is 200-400 rpm.

[0009] In some embodiments, the fluorine-containing silicone copolymer modified isocyanate in step S2 comprises at least one of fluorine-containing silicone copolymer modified triphenylmethane-4, 4', 4''-triisocyanate, fluorine-containing silicone copolymer modified tris(4-isocyanate phenyl) methane, and fluorine-containing silicone copolymer modified 1, 3, 5-tris(isocyanomethyl) benzene, and the catalyst comprises at least one of dibutyltin dilaurate, stannous octoate, and triethylenediamine.

[0010] In some embodiments, step S2 comprises: S2.1, the fluorine-containing monomer, silicon-containing monomer, hydroxyl-containing monomer and mercaptoethanol, azobisisobutyronitrile are added into ethyl acetate, heated to 70°C, stirred under nitrogen protection for 6-8h to obtain a fluorine-silicon copolymer solution, wherein the fluorine-containing monomer includes at least one of hexafluorobutyl acrylate, trifluoroethyl methacrylate, dodecafluoroheptyl methacrylate, the silicon-containing monomer includes at least one of γ-methacryloyloxypropyl trimethoxysilane, acryloyloxypropyl trimethoxysilane, methacryloyloxypropyl tris(trimethylsiloxy)silane, the hydroxyl-containing monomer includes at least one of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, the mass ratio of the fluorine-containing monomer: the silicon-containing monomer: the hydroxyl-containing monomer: mercaptoethanol: azobisisobutyronitrile is 100:20-50:10-30:1-5:0.5-2; S2.2, the fluorine-silicon copolymer solution is cooled to 40-50°C, isocyanate, dibutyltin dilaurate is added and stirred for 2-3h, then heated to 80-85°C and continued to react for 20-30min to obtain a fluorine-silicon copolymer modified isocyanate, the molar ratio of isocyanate to fluorine-silicon copolymer is 1:(1.02-1.04), the addition amount of dibutyltin dilaurate is 0.01-0.02wt% of the mass of isocyanate; S2.3, the fluorine-silicon copolymer modified isocyanate is added to the silicone modified polyester polyol, heated to 90-110°C and stirred for 1-3h to obtain a polyurethane solution, wherein the molar ratio of the silicone modified polyester polyol to the fluorine-silicon copolymer modified isocyanate is 1:(1.02-1.03).

[0011] In some embodiments, before step S2 is performed, it further includes: The isocyanate monomer is dissolved in anhydrous ethyl acetate, a blocking agent and dibutyltin dilaurate are added at room temperature, and stirred for 2-3h to obtain an isocyanate, wherein the isocyanate monomer includes at least one of triphenylmethane-4,4',4''-triisocyanate, tris(4-isocyanate phenyl) methane, 1,3,5-tris(isocyanomethyl) benzene, the blocking agent includes at least one of butanone oxime, acetone oxime, cyclohexanone oxime, the molar ratio of the isocyanate monomer to the blocking agent is 1:2, and the addition amount of dibutyltin dilaurate is 0.01-0.02wt% of the mass of the isocyanate monomer.

[0012] In some embodiments, the latent crosslinking agent in step S3 includes caprolactam blocked isophorone diisocyanate, caprolactam blocked hexamethylene diisocyanate, and caprolactam blocked 4,4'-dicyclohexyl methane diisocyanate.

[0013] In some embodiments, step S3 includes: S3.1, add a latent crosslinking agent and nano-silica into the polyurethane solution, stir at 90-100 DEG C for 10-20 min, to obtain a polyurethane prepolymer, wherein the concentration of the latent crosslinking agent in the polyurethane solution is 3-10 wt%, and the concentration of the nano-silica in the polyurethane solution is 1-5 wt%; S3.2, granulate the polyurethane prepolymer, and cool to room temperature, to obtain the high-temperature-resistant polyurethane hot melt adhesive, wherein the granulation temperature is 90-100 DEG C.

[0014] Furthermore, a high-temperature-resistant polyurethane hot melt adhesive is provided, which is prepared by the above-mentioned preparation method of the high-temperature-resistant polyurethane hot melt adhesive. In the sizing process, the basic substance is added to the molten polyurethane hot melt adhesive, reacts with the sulfonamide group in the silicone-modified polyester polyol, generates bubbles, and thus forms a porous polyurethane adhesive layer, wherein the addition amount of the basic substance is 0.3-1.0 wt% of the mass of the high-temperature-resistant polyurethane hot melt adhesive, and the basic substance includes at least one of triethanolamine, bis-(p-dimethylaminophenyl) methane, and dicyandiamide. The porous polyurethane adhesive layer can be used for fixing the in-vehicle sound insulation pad, and achieves the effect of heat insulation.

[0015] The beneficial effects of the present application are: The polyurethane hot melt adhesive formed by the silicone-modified polyester polyol and the isocyanate modified by the fluorosilicon copolymer directly enhances the thermal stability of the polyurethane main chain by the high bond energy of the silicone chain segment (Si-O bond) and the fluorine-containing chain segment (C-F bond), so that it is difficult to be thermally degraded, at the same time, the latent crosslinking agent is activated after being heated during construction, forms a solid three-dimensional crosslinking network with the polyurethane, limits the movement and creep of the molecular chain at high temperature, and thus together ensures that the adhesive still maintains excellent mechanical strength and bonding reliability in a high-temperature environment; at the same time, during the construction of the hot melt adhesive, heating and melting make the polyurethane hot melt adhesive in a low-viscosity liquid state, which provides energy for the movement of the molecular chain; then, in the wet curing stage, the -NCO group at the end of the prepolymer reacts with the moisture in the environment to generate a polyurea structure and release heat, which further increases the temperature of the system and finally makes the adhesive solidify, and in the process of solidification, the low surface energy of the silicone chain segment and the fluorine-containing chain segment will spontaneously and continuously migrate to the surface in contact with the air, and after the solidification is completed, the silicone chain segment and the fluorine-containing chain segment form a dense and chemically inert protective layer on the surface of the adhesive, effectively blocking the penetration and erosion of chemical media such as water vapor, oil, and solvent, thereby improving the chemical resistance of the polyurethane hot melt adhesive. The strong electron-withdrawing sulfonyl group greatly stabilizes the adjacent N-H and N-N bonds through resonance effect, so that the entire group has a high decomposition activation energy; at the same time, the group is highly chemically inert at the polyurethane synthesis temperature, and the activity of the potential nucleophilic site is much lower than that of the hydroxyl and amine groups in the system, and cannot compete with the -NCO or -OH to ensure that the sulfonyl hydrazine group can exist safely during the synthesis below 160 DEG C; at the same time, when the alkaline substance is added, the alkaline substance can catalyze the rapid decomposition of the sulfonyl hydrazine group into water vapor and carbon dioxide, and the water vapor can be used to promote the reaction of the -NCO group of the isocyanate, which promotes curing while producing carbon dioxide, which together with the carbon dioxide obtained by the decomposition of the sulfonyl hydrazine group promotes foaming to form a porous polyurethane adhesive layer. When heat passes through the adhesive layer, it must constantly bypass the bubbles, prolonging the heat transfer path and effectively reducing the heat flow rate. At the same time, the bubbles are wrapped in a tough polyurethane wall, and the size is very small, and the internal air cannot form a large-scale convection, further inhibiting the transfer of heat, thereby achieving the effect of thermal insulation. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 It is the flowchart of the preparation method of the high-temperature-resistant polyurethane hot melt adhesive in an embodiment of the present application. DETAILED DESCRIPTION

[0017] In the description of the present application, it should be noted that the specific conditions are not indicated in the examples, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not indicated by the manufacturer, and are conventional products that can be purchased on the market.

[0018] Please refer to Figure 1 The present application provides a preparation method of a high-temperature-resistant polyurethane hot melt adhesive, which comprises the following steps: S1, an organosilicon modifier and a sulfonyl hydrazine grafted polyester polyol are added to a reaction kettle, heated and stirred to obtain an organosilicon modified polyester polyol; The organosilicon modifier in step S1 includes at least one of alpha, omega-dihydroxy polydimethylsiloxane, aminoethyl aminopropyl polydimethylsiloxane, epoxy-terminated polydimethylsiloxane, and methacryloxypropyl-terminated polydimethylsiloxane, and the sulfonyl hydrazine grafted polyester polyol includes at least one of sulfonyl hydrazine grafted poly (caprolactone) triol, sulfonyl hydrazine grafted poly (phthalate-glycerol) triol, and sulfonyl hydrazine grafted poly (adipic acid-glycerol) triol; The introduction of the organic silicon modifier significantly improves the comprehensive performance of the polyurethane hot melt adhesive through its unique silicon-oxygen bond (Si-O) structure. In terms of heat resistance, the organic silicon segment has higher bond energy and thermal stability, which can effectively inhibit the flow and deformation of the polyurethane soft segment at high temperatures, thereby significantly improving the hot melt adhesive's heat distortion temperature and delaying performance degradation at high temperatures. In terms of chemical resistance, the low surface energy and high hydrophobicity of the organic silicon component spontaneously and continuously migrate to the surface in contact with the air to form a protective barrier, effectively blocking the penetration and erosion of corrosive media such as water molecules, acids, and bases, enhancing the hydrolysis resistance and chemical resistance of the polyurethane hot melt adhesive.

[0019] In an embodiment, the method for preparing the sulfhydryl hydrazine grafted polyester polyol is as follows: The carboxyl-containing sulfhydryl hydrazine substance and the polyester polyol are mixed in anhydrous acetone at 0-5°C, and a dicyclohexyl carbodiimide-containing anhydrous acetone solution is added dropwise while stirring. After the dropwise addition is complete, the temperature is raised to 50-60°C, and the reaction is carried out for 5-6 hours. The precipitate is removed by filtration to obtain the sulfhydryl hydrazine grafted polyester polyol. The concentration of the carboxyl-containing sulfhydryl hydrazine substance in anhydrous acetone is 20-50 wt%, the molar ratio of the carboxyl-containing sulfhydryl hydrazine substance to dicyclohexyl carbodiimide to polyester polyol is 1.02-1.04:1.04-1.05:1, and the mass of dibutyltin dilaurate is 0.01-0.02 wt% of the mass of the diisocyanate. The carboxyl-containing sulfhydryl hydrazine substance includes at least one of 4-carboxybenzenesulfonyl hydrazine, 3-carboxybenzenesulfonyl hydrazine, and 2-carboxyethylsulfonyl hydrazine, and the diisocyanate includes at least one of isophorone diisocyanate, hexamethylene diisocyanate, and toluene diisocyanate.

[0020] By adding dicyclohexyl carbodiimide, the esterification reaction between the carboxyl group of the carboxyl-containing sulfhydryl hydrazine substance and the hydroxyl group of the polyester polyol can be efficiently promoted, the covalent grafting of the sulfhydryl hydrazine molecule to the polyester chain is achieved, and the sulfhydryl hydrazine grafted polyester polyol is obtained. In this reaction process, the water molecules generated by esterification can be quickly absorbed by dicyclohexyl carbodiimide and converted into dicyclohexyl urea, which is insoluble in organic solvents and precipitates. This mechanism not only removes the byproduct through simple filtration, greatly simplifying the purification process, but also effectively avoids the adverse effects of water molecule residues on the stability of the product and subsequent applications.

[0021] Step S1 includes: S1.1, under nitrogen atmosphere, the inhibitor, sulfonamidografted polyester polyol is added into a reaction kettle, heated to 100-120℃ and stirred for 1-2h to obtain a mixed solution, wherein the mass of the inhibitor is 10-20wt% of the mass of the polyester polyol, the inhibitor includes at least one of poly(N-vinyl caprolactam), poly(2-isopropyl-2-oxazoline) and poly(vinyl methyl oxazoline), and the stirring rate is 100-200rpm; In the early high temperature (>100°C) sizing stage, they are dissolved in the polyester polyol matrix in a hydrophilic extended chain conformation, effectively inhibiting the premature migration of silicone by increasing the system viscosity and steric hindrance; when the temperature cools down below the lower critical solution temperature (60-80°C) of the polymer, the polymer chain undergoes a conformational transition, and the compatibility of the polymer with the polyester polyol matrix decreases sharply, resulting in phase separation and precipitation from the matrix. The phase separation process generates strong interfacial energy driving force, and the polymer aggregates can effectively drive the low surface energy silicone segments to migrate to the surface of the colloid during the migration process, and the two work together to achieve enrichment.

[0022] S1.2, the silicone modifier is added to the mixed solution, and the heating and stirring are continued at 100-120℃ for 2-4h to obtain a silicone-modified polyester polyol, wherein the molar ratio of the silicone modifier to the polyester polyol is (1.02-1.04):1, and the stirring rate is 200-400rpm; The slight excess of the silicone modifier ensures that it reacts fully with the hydroxyl groups at the ends of the polyester polyol chain, improves the grafting efficiency and modification degree, avoids the residual unmodified segments due to the excess of the polyester polyol, and thus ensures the uniformity and stability of the product performance; the reaction temperature of 100-120℃ provides sufficient heat energy to activate the reaction molecules and accelerate the reaction rate, and at the same time, this temperature range is higher than the boiling point of most small molecular byproducts (such as water), which is beneficial to the evaporation and escape of the byproducts, promotes the movement of the reaction equilibrium towards the generation of the target product, and can avoid the degradation of the polyester or silicone segments caused by excessively high temperature. The stirring rate of 200-400rpm ensures that the reaction system, especially the materials which may be in a heterogeneous system, is in a fully mixed and uniform state, enhances the mass and heat transfer efficiency, prevents local overheating or uneven concentration, ensures that the reaction proceeds uniformly at the molecular level, and thus obtains a product with consistent modification degree; the reaction time of 2-4h provides sufficient process guarantee for the above condensation reaction, ensures that the reaction can be close to complete, and makes the silicone segments effectively grafted onto the polyester molecular chain to form a stable chemical structure, which is a key time window to achieve the expected modification effect.

[0023] S2, the fluorine-containing silicone copolymer modified isocyanate and the catalyst are added to the silicone-modified polyester polyol, and heated and stirred to obtain a polyurethane solution; The isocyanate modified by the fluorine-containing silicon copolymer in step S2 includes at least one of fluorine-containing silicon copolymer modified triphenylmethane-4, 4', 4''-triisocyanate, fluorine-containing silicon copolymer modified tris (4-isocyanate phenyl) methane, fluorine-containing silicon copolymer modified 1, 3, 5-tri (isocyanate methyl) benzene, and the catalyst includes at least one of dibutyl tin dilaurate, stannous octoate and triethylenediamine.

[0024] The modification of isocyanate by the fluorine-containing silicon copolymer introduces the unique properties of fluorine and silicon elements into the polyurethane hard segment, and cooperatively improves the heat resistance and chemical resistance of the hot melt adhesive. In terms of heat resistance, the fluorine-containing segment (C-F bond) has extremely high bond energy and thermal stability, combined with the rigid aromatic ring structure of triphenylmethane and the like, which significantly enhances the molecular rigidity and thermodynamic strength of the hard segment, greatly improves the glass transition temperature (Tg) and thermal decomposition temperature of the material, so that it can effectively resist softening and deformation in high temperature environment, and maintain excellent bonding strength; in terms of chemical resistance, the fluorocarbon chain migrated to the surface of the material has extremely low surface energy and the hydrophobicity of the siloxane chain, which together build a dense and chemically inert barrier, which can excellently resist the infiltration, swelling and corrosion of various chemical media such as water, oil, solvent, acid and alkali, thereby improving the chemical resistance of the polyurethane hot melt adhesive.

[0025] Step S2 includes: The isocyanate monomer is dissolved in anhydrous ethyl acetate, and a blocking agent and dibutyl tin dilaurate are added at room temperature, and the reaction is stirred for 2-3 h to obtain the isocyanate, wherein the isocyanate monomer includes at least one of triphenylmethane-4, 4', 4''-triisocyanate, tris (4-isocyanate phenyl) methane and 1, 3, 5-tri (isocyanate methyl) benzene, the blocking agent includes at least one of butanone oxime, acetone oxime and cyclohexanone oxime, the molar ratio of the isocyanate monomer to the blocking agent is 1: (2.02-2.04), and the addition amount of dibutyl tin dilaurate is 0.01-0.02wt% of the mass of the isocyanate monomer. The molar ratio of the isocyanate monomer to the blocking agent is 1: (2.02-2.04), so that the blocking agent is slightly excessive relative to the theoretical amount (1:2) of completely blocking two -NCO groups, which ensures that the reaction proceeds fully and maximizes the reaction of two -NCO groups with the blocking agent, thereby preferentially generating the double-blocked (i.e. monofunctional) target product and inhibiting the generation of triple-blocked by-products; the addition of 0.01-0.02wt% of dibutyl tin dilaurate as a catalyst can efficiently catalyze the blocking reaction of the oxime blocking agent and the -NCO group, improve the reaction rate and the selectivity of the double-blocked product, and at the same time, due to its extremely low addition amount, avoid excessive catalysis or initiation of gelation and other side reactions.

[0026] S2.1, the fluorine-containing monomer, silicon-containing monomer, hydroxyl-containing monomer and mercaptoethanol, azobisisobutyronitrile are added into ethyl acetate, heated to 70 DEG C, stirred under nitrogen protection for 6-8h, to obtain a fluorine-containing silicon copolymer solution, wherein the fluorine-containing monomer includes at least one of hexafluorobutyl acrylate, trifluoroethyl methacrylate, dodecafluoroheptyl methacrylate, the silicon-containing monomer includes at least one of gamma-methacryloxypropyl trimethoxysilane, acryloxypropyl trimethoxysilane, methyl methacryloxypropyl tris (trimethylsiloxy) silane, the hydroxyl-containing monomer includes at least one of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, the mass ratio of fluorine-containing monomer: silicon-containing monomer: hydroxyl-containing monomer: mercaptoethanol: azobisisobutyronitrile is 100:20-50:10-30:1-5:0.5-2; The mass ratio of each monomer (100:20-50:10-30) regulates the relative content of fluorine, silicon and hydroxyl functional groups in the copolymer molecular chain, ensuring that fluorine and silicon elements are sufficient to enrich on the material surface to provide sufficient shielding protection, while the moderate proportion of hydroxyl ensures sufficient subsequent reactivity and avoids excessive crosslinking of the final polyurethane, resulting in decreased flexibility; mercaptoethanol is used as a chain transfer agent, which can effectively control the molecular weight of the copolymer, prevent the molecular chain from growing indefinitely during polymerization, and thus prevent the molecular weight from being too large or gelling, thereby ensuring that the final copolymer solution has good solubility and processing fluidity and can be uniformly dispersed in the polyurethane system; azobisisobutyronitrile as an initiator can efficiently decompose to generate free radicals at 70 DEG C, initiating copolymerization, and its amount ensures a moderate reaction rate and high monomer conversion.

[0027] S2.2, the fluorine-containing silicon copolymer solution is cooled to 40-50 DEG C, isocyanate and dibutyltin dilaurate are added and continue to stir for 2-3h, then heated to 80-85 DEG C and continue to react for 20-30min, to obtain a fluorine-containing silicon copolymer modified isocyanate, the molar ratio of isocyanate to fluorine-containing silicon copolymer is 1: (1.02-1.04), and the addition amount of dibutyltin dilaurate is 0.01-0.02wt% of the mass of isocyanate; 40~50℃'s temperature, isocyanate and fluorine-containing silicon copolymer using 1: (1.02~1.04) molar ratio, fluorine-containing silicon copolymer slightly excess, in the activation reaction, ensure that the hydroxyl group at the end of fluorine-containing silicon copolymer and isocyanate group addition reaction, rather than directly initiate isocyanate itself self-polymerization, thereby efficiently generating the target urethane bond (-NHCOO-), realize copolymer oriented grafting, avoid residual unmodified isocyanate, thereby ensure the uniformity and stability of the final product performance; 0.01~0.02wt% dibutyltin dilaurate catalyze the addition reaction of the above hydroxyl and isocyanate group, improve the grafting efficiency, at the same time, due to its extremely low amount, avoid unnecessary catalytic isocyanate dimerization, trimerization and other side reactions. Subsequently, the temperature is raised to 80~85℃ for 20~30min to evaporate and remove the residual solvent (ethyl acetate) and other impurities in the reaction system, thereby purifying the product, preventing these impurities from causing side reactions in the subsequent polyurethane synthesis, affecting the final product performance.

[0028] S2.3, the fluorine-containing silicon copolymer modified isocyanate is added to the silicone modified polyester polyol, heated to 90~110℃ and stirred for 1~3h to obtain a polyurethane solution, wherein the molar ratio of silicone modified polyester polyol to fluorine-containing silicon copolymer modified isocyanate is 1: (1.02~1.03); The reaction temperature is set at 90~110℃, this temperature range not only ensures that the reaction system is in a molten homogeneous state, providing sufficient heat energy to promote the reaction, more importantly, the temperature is higher than the de-blocking temperature of the blocking agent (usually above 80~90℃), which makes the blocked -NCO groups on the fluorine-containing silicon copolymer modified isocyanate first de-block, releasing free -NCO groups with high reactivity, and then these activated -NCO groups can react with the terminal hydroxyl groups of the silicone modified polyester polyol to generate urethane bonds, thereby realizing chain growth; the molar ratio of silicone modified polyester polyol to fluorine-containing silicon copolymer modified isocyanate is 1: (1.02~1.03), making the isocyanate component slightly excess, aiming to ensure that the hydroxyl groups at the end of the polyester polyol can be completely consumed, promoting the reaction to generate high molecular weight polymers, ensuring that the molecular weight and mechanical properties of the final polymer meet the expectations.

[0029] S3, adding a latent crosslinking agent to the polyurethane solution, continuing to heat and stir to obtain a polyurethane prepolymer, granulating, cooling to room temperature to obtain a high-temperature resistant polyurethane hot melt adhesive; The latent crosslinking agent in step S3 includes caprolactam blocked isophorone diisocyanate, caprolactam blocked hexamethylene diisocyanate, and caprolactam blocked 4,4'-dicyclohexyl methane diisocyanate.

[0030] The latent crosslinking agent remains chemically inert during the processing and storage of the hot melt adhesive, but during the subsequent heat curing after hot melt construction, the blocking agent dissociates and releases active isocyanate groups, which react with urea groups, carbamate groups on the polyurethane chain or external moisture, forming a solid three-dimensional crosslinked network between the molecular chains, thereby limiting the movement ability of the molecular chains at high temperature, significantly improving the thermal deformation temperature of the material, preventing softening, creep or melting at high temperature, and thus maintaining the long-lasting bonding strength; in terms of chemical resistance, the presence of crosslinking points in the dense crosslinked network makes it difficult for molecular chains to be pushed away by solvent molecules, greatly reducing the swelling degree, thereby improving the chemical resistance of the polyurethane hot melt adhesive.

[0031] Step S3 comprises: S3.1, adding the latent crosslinking agent and nano-silicon dioxide into the polyurethane solution, stirring at 90-100 DEG C for 10-20 min to obtain a polyurethane prepolymer, wherein the concentration of the latent crosslinking agent in the polyurethane solution is 3-10 wt%, and the concentration of the nano-silicon dioxide in the polyurethane solution is 1-5 wt%; With the cooling and solidification of the system, the polyurethane matrix shrinks and the polarity increases, and the affinity of nano-silicon dioxide with silicone becomes much greater than that with the polar polyurethane matrix, and the thermodynamic drive forces the nanoparticles to act together with silicone and migrate to the surface, and finally, the nano-silicon dioxide particles are embedded in the silicone-rich layer, which can provide physical support and make the silicone protective layer more stable and wear-resistant.

[0032] S3.2, granulating the polyurethane prepolymer and cooling it to room temperature to obtain a high-temperature-resistant polyurethane hot melt adhesive, wherein the granulation temperature is 90-100 DEG C; Granulation at 90-100 DEG C makes the prepolymer in a molten state with suitable fluidity and viscosity, so that it can be smoothly cut or extruded into particles of uniform size, ensuring good processability and use convenience of the final product, and more importantly, this temperature is lower than the deblocking temperature of the latent crosslinking agent used, ensuring that the crosslinking agent will not be prematurely deblocked and crosslinked during the granulation process, thereby avoiding adhesion and clumping between the particles and ensuring the storage stability of the product; at the same time, the temperature is also higher than the glass transition temperature of the system, so that the molecular chains have sufficient activity, which is beneficial to the preliminary orientation and distribution adjustment of the nano-silicon dioxide particles and fluorosilicon segments in the melt, laying a preliminary foundation for the subsequent full migration and surface enrichment of the functional segments.

[0033] The application provides a high-temperature-resistant polyurethane hot melt adhesive prepared by the above-mentioned preparation method. The high-temperature-resistant polyurethane hot melt adhesive adds an alkaline substance to the molten polyurethane hot melt adhesive during the gluing process, and the alkaline substance reacts with the sulfonamide groups in the silicone-modified polyester polyol to generate bubbles, thereby forming a porous polyurethane adhesive layer, wherein the alkaline substance is at least one of triethanolamine, bis-(p-dimethylaminophenyl) methane, and dicyandiamide, and the amount of the alkaline substance added is 0.3-1.0wt% of the mass of the high-temperature-resistant polyurethane hot melt adhesive. The porous polyurethane adhesive layer is used for fixing the sound insulation pad in the vehicle and achieves the effect of heat insulation. Compared with the ordinary polyurethane adhesive layer, when heat passes through the porous polyurethane adhesive layer, it must constantly bypass the bubbles, prolonging the heat transfer path and effectively reducing the heat flow speed, and the bubbles are wrapped in the tough polyurethane wall and have a very small size, and the air inside cannot form a large-scale convection, further inhibiting the transfer of heat, thereby achieving the effect of heat insulation.

[0034] The above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited by the above embodiments, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application should be equivalent replacement methods, and are all included in the protection scope of the present application.

Claims

1. A method for preparing a high-temperature resistant polyurethane hot melt adhesive, characterized in that, The preparation method includes the following steps: S1. Add organosilicon modifier and sulfonyl hydrazine-grafted polyester polyol into a reaction vessel, heat and stir to obtain organosilicon-modified polyester polyol. S2. Fluorosilicone copolymer modified isocyanate and catalyst are added to organosilicon modified polyester polyol, and the mixture is heated and stirred to obtain a polyurethane solution. S3. Add a latent crosslinking agent to the polyurethane solution, continue heating and stirring to obtain a polyurethane prepolymer, granulate, and cool to room temperature to obtain a high-temperature resistant polyurethane hot melt adhesive.

2. The method for preparing a high-temperature resistant polyurethane hot melt adhesive according to claim 1, characterized in that, In step S1, the organosilicon modifier includes at least one of α,ω-dihydroxy polydimethylsiloxane, aminoethylaminopropyl polydimethylsiloxane, epoxy-terminated polydimethylsiloxane, and methacryloyloxypropyl-terminated polydimethylsiloxane. The sulfonyl hydrazine-grafted polyester polyol includes at least one of sulfonyl hydrazine-grafted polycaprolactone triol, sulfonyl hydrazine-grafted polyphthalic acid-glyceride triol, and sulfonyl hydrazine-grafted polyadipate-glyceride triol.

3. The method for preparing a high-temperature resistant polyurethane hot melt adhesive according to claim 1 or 2, characterized in that, Step S1 includes: S1.1 In a nitrogen atmosphere, the inhibitor and sulfonyl hydrazine-grafted polyester polyol are added to a reaction vessel, heated to 100-120°C and stirred for 1-2 hours to obtain a mixture. The mass of the inhibitor is 10-20 wt% of the mass of the polyester polyol. The inhibitor includes at least one of poly(N-vinylcaprolactam), poly(2-isopropyl-2-oxazoline), and poly(vinylmethyloxazoline). The stirring rate is 100-200 rpm. S1.2 Add organosilicon modifier to the mixture and continue heating and stirring at 100~120℃ for 2~4h to obtain organosilicon modified polyester polyol, wherein the molar ratio of organosilicon modifier to polyester polyol is (1.02~1.04):1, and the stirring speed is 200~400rpm.

4. The method for preparing a high-temperature resistant polyurethane hot melt adhesive according to claim 1, characterized in that, In step S2, the fluorinated silicone copolymer modified isocyanate includes at least one of fluorinated silicone copolymer modified triphenylmethane-4,4',4''-triisocyanate, fluorinated silicone copolymer modified tris(4-isocyanatophenyl)methane, and fluorinated silicone copolymer modified 1,3,5-tris(isocyanate methyl)benzene, and the catalyst includes at least one of dibutyltin dilaurate, stannous octoate, and triethylenediamine.

5. A method for preparing a high-temperature resistant polyurethane hot melt adhesive according to claim 1 or 4, characterized in that, Step S2 includes: S2.

1. Fluorine-containing monomers, silicon-containing monomers, hydroxyl-containing monomers, mercaptoethanol, and azobisisobutyronitrile are added to ethyl acetate, heated to 70°C, and stirred under nitrogen protection for 6-8 hours to obtain a fluorine-containing silicone copolymer solution. The fluorine-containing monomers include at least one of hexafluorobutyl acrylate, trifluoroethyl methacrylate, and dodecafluoroheptyl methacrylate; the silicon-containing monomers include at least one of γ-methacryloyloxypropyltrimethoxysilane, acryloyloxypropyltrimethoxysilane, and methacryloyloxypropyltris(trimethylsiloxy)silane; and the hydroxyl-containing monomers include at least one of hydroxyethyl acrylate, hydroxypropyl acrylate, and hydroxyethyl methacrylate. The mass ratio of fluorine-containing monomers: silicon-containing monomers: hydroxyl-containing monomers: mercaptoethanol: azobisisobutyronitrile is 100:20-50:10-30:1-5:0.5-2. S2.2 Cool the fluorinated silicone copolymer solution to 40-50℃, add isocyanate and dibutyltin dilaurate, and continue stirring for 2-3 hours. Then heat to 80-85℃ and continue the reaction for 20-30 minutes to obtain fluorinated silicone copolymer-modified isocyanate. The molar ratio of isocyanate to fluorinated silicone copolymer is 1:(1.02-1.04), and the amount of dibutyltin dilaurate added is 0.01-0.02 wt% of the isocyanate mass. S2.3 Add the fluorinated silicone copolymer modified isocyanate to the organosilicon modified polyester polyol, heat to 90~110℃ and stir for 1~3h to obtain a polyurethane solution, wherein the molar ratio of organosilicon modified polyester polyol to fluorinated silicone copolymer modified isocyanate is 1: (1.02~1.03).

6. The method for preparing a high-temperature resistant polyurethane hot melt adhesive according to claim 5, characterized in that, Before proceeding to step S2, the following is also included: Isocyanate monomers are incorporated into anhydrous ethyl acetate, and a capping agent and dibutyltin dilaurate are added at room temperature. The mixture is stirred for 2-3 hours to obtain isocyanate. The isocyanate monomers include at least one of triphenylmethane-4,4',4''-triisocyanate, tris(4-isocyanatophenyl)methane, and 1,3,5-tris(isocyanate methyl)benzene. The capping agent includes at least one of butanone oxime, acetone oxime, and cyclohexanone oxime. The molar ratio of isocyanate monomers to capping agents is 1:2, and the amount of dibutyltin dilaurate added is 0.01-0.02 wt% of the mass of the isocyanate monomers.

7. The method for preparing a high-temperature resistant polyurethane hot melt adhesive according to claim 1, characterized in that, The latent crosslinking agents in step S3 include caprolactam-blocked isophorone diisocyanate, caprolactam-blocked hexamethylene diisocyanate, and caprolactam-blocked 4,4'-dicyclohexylmethane diisocyanate.

8. The method for preparing a high-temperature resistant polyurethane hot melt adhesive according to claim 1, characterized in that, Step S3 includes: S3.1 Add the latent crosslinking agent and nano-silica to the polyurethane solution and stir at 90~100℃ for 10~20 min to obtain the polyurethane prepolymer. The concentration of the latent crosslinking agent in the polyurethane solution is 3~10wt%, and the concentration of nano-silica in the polyurethane solution is 1~5wt%. S3.

2. Granulate the polyurethane prepolymer and cool it to room temperature to obtain a high-temperature resistant polyurethane hot melt adhesive, wherein the granulation temperature is 90~100℃.

9. A high-temperature resistant polyurethane hot melt adhesive, characterized in that, It is prepared by the method of any one of claims 1-8 for preparing a high-temperature resistant polyurethane hot melt adhesive; During the application process, an alkaline substance is added to the molten polyurethane hot melt adhesive to react with the sulfonyl hydrazine group in the organosilicon-modified polyester polyol, generating bubbles and forming a porous polyurethane adhesive layer. The amount of alkaline substance added is 0.3~1.0 wt% of the mass of the high-temperature resistant polyurethane hot melt adhesive. The alkaline substance includes at least one of triethanolamine, bis-(p-dimethylaminophenyl)methane, and dicyandiamide. The porous polyurethane adhesive layer can be used to fix the sound insulation pads inside the vehicle and achieve a heat insulation effect.

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