A self-lubricating spot welding sealant for steel plates, its preparation method and application

Abstract

This invention discloses a self-lubricating steel plate spot welding sealant, its preparation method, and its application, belonging to the field of adhesive technology. The spot welding sealant comprises styrene-butadiene rubber, conductive carbon black, and phytic acid-silane-epoxy prepolymer, etc. The prepolymer is prepared by mixing phytic acid, silane coupling agent, and epoxy resin in a mass ratio of 1:0.5~0.8:0.8~1.5. The spot welding sealant uses styrene-butadiene rubber and epoxy resin as the matrix, and innovatively introduces phytic acid-silane-epoxy prepolymer as the core functional component, constructing a dual system of chemical anchoring and interface compatibility. This solves the problem of adhesion failure in self-lubricating steel plates, achieves a balance between flame retardancy and mechanical properties, and the process is suitable for industrialization, exhibiting excellent overall performance.

Description

Technical Field

[0001] This invention belongs to the field of adhesive technology, specifically relating to a self-lubricating spot welding sealant for steel plates, its preparation method, and its application. Background Technology

[0002] Self-lubricating steel sheets, especially those coated with polytetrafluoroethylene or other low surface energy lubricating coatings, are widely used in modern automobile manufacturing, appliance casing stamping, and other industrial fields due to their excellent mold release properties, wear resistance, and corrosion resistance. However, their low surface energy, chemical inertness, and smoothness also make them typical difficult-to-bond materials, posing a significant challenge to subsequent sealing processes.

[0003] Spot welding is a core process for joining metal sheets in the aforementioned manufacturing industries. Spot welding sealant is a functional adhesive applied before the spot welding process and capable of withstanding subsequent spot welding and electrophoretic baking processes; its role is crucial. It not only needs to achieve sealing, rust prevention, and shock absorption between the sheets, but also must meet the extreme requirements of the spot welding process: First, it must possess a certain degree of conductivity to ensure that the spot welding current can effectively pass through the adhesive layer to form a qualified weld; second, it must be able to withstand the high-temperature instantaneous arc thermal shock generated during spot welding, without burning, producing large amounts of smoke, or undergoing carbonization failure.

[0004] Currently, traditional spot welding sealants face the following technical bottlenecks when dealing with self-lubricating steel plates:

[0005] Interfacial adhesion failure: Conventional sealants rely on wetting of the substrate and physical / chemical interactions to form adhesive force. However, the low surface energy and chemically inert surface of self-lubricating steel plates severely hinder the effective wetting of adhesives, resulting in extremely low bond strength and a high susceptibility to interfacial detachment.

[0006] The contradiction between flame retardancy and mechanical properties: To meet the requirements of resistance to instantaneous high temperatures, flame retardants are usually added to the sealant. However, commonly used additive flame retardants (such as inorganic hydroxides and traditional phosphorus-nitrogen flame retardants) have poor compatibility with the polymer matrix and often exist in the form of physical blends. This not only limits the flame retardant efficiency but also leads to severe phase separation and stress concentration, significantly deteriorating the mechanical properties of the sealant, such as making it brittle and reducing its elasticity. At the same time, there is a risk of flame retardant migration and precipitation during long-term use, affecting durability.

[0007] The challenge of multifunctional synergy: A qualified spot welding sealant needs to balance adhesion, flame retardancy, conductivity, processability, and storage stability simultaneously. Existing technologies often achieve this by simply compounding multiple additives, but this complicates the formulation, and the functional components may interact and restrict each other, making it difficult to achieve efficient synergy. For example, increasing the amount of conductive carbon black may affect adhesion and toughness; increasing the flame retardant content may impair processability and mechanical properties.

[0008] Therefore, there is an urgent need in this field for an innovative technical solution that can fundamentally solve the bonding problem of self-lubricating steel plates, while simultaneously endowing spot welding sealants with efficient and long-lasting flame retardancy and balanced comprehensive performance, so as to meet the growing requirements of modern industry for reliability, safety and environmental protection. Summary of the Invention

[0009] To address the aforementioned problems in the prior art, the present invention aims to provide a self-lubricating spot welding sealant for steel plates, the spot welding sealant comprising the following raw materials in parts by weight:

[0010] Styrene-butadiene rubber: 5-10 parts

[0011] Conductive carbon black: 1-2 parts

[0012] Vulcanizing agent: 0.3~1.0 parts

[0013] Vulcanizing aid: 0.2~0.5 parts

[0014] Phytic acid-silane-epoxy prepolymer: 1.8~2.8 parts

[0015] Epoxy resin: 4-10 parts

[0016] Hardener: 0.5~1.0 parts

[0017] Curing accelerator: 0.1~0.3 parts

[0018] Silane coupling agent: 0.2~0.6 parts

[0019] Plasticizer: 25-35 parts

[0020] Filler: 30-35 parts

[0021] And thixotropic agent: 10-15 parts.

[0022] The phytic acid-silane-epoxy prepolymer is prepared from phytic acid, silane coupling agent and epoxy resin. The mass ratio of phytic acid, silane coupling agent and epoxy resin is 1:0.5~0.8:0.8~1.5. Phytic acid and silane coupling agent are reacted at 70~80℃ first, and then epoxy resin is slowly added dropwise at 85℃ to complete the grafting.

[0023] Preferably, the phytic acid-silane-epoxy prepolymer has an epoxy value of 0.20~0.40 eq / 100g, a phosphorus mass fraction of 5.0~9.0%, a nitrogen mass content of 1.0~2.5%, and a viscosity of 5000~50000 mPa·s at 40°C.

[0024] Preferably, the preparation method of the phytic acid-silane-epoxy prepolymer includes: using isopropanol as a solvent and triphenylphosphine as a catalyst;

[0025] First, add dehydrated isopropanol and phytic acid powder, and disperse the phytic acid powder in the dehydrated isopropanol under nitrogen protection.

[0026] Then, add the silane coupling agent, heat to 70-80℃, and react for 1.5-2 hours until the system becomes homogeneous and transparent;

[0027] Then, the temperature is raised to 85°C, and the mixture of epoxy resin and catalyst is slowly added dropwise, controlling the dropping rate to be completed within 1-2 hours. After the addition is completed, the reaction continues for 2-3 hours.

[0028] Then, the temperature was lowered to below 40°C, and the isopropanol solvent was removed by vacuum distillation to obtain phytic acid-silane-epoxy prepolymer.

[0029] Preferably, the styrene-butadiene rubber is a carboxyl-terminated solution-polymerized styrene-butadiene rubber with a Mooney viscosity range of 55-65 and an organic acid content of 4.0-6.0%.

[0030] Preferably, the vulcanizing agent is a peroxide vulcanizing agent DCP and / or BIPB; the vulcanizing aid is p-benzoquinone dioxime; and the epoxy resin is a bisphenol A type epoxy resin E-44 and / or E-51 with an epoxy value of 0.4~0.55 eq / 100g.

[0031] Preferably, the curing agent is one or more of dicyandiamide, sebacic acid dihydrazide, or adipic acid dihydrazide; the curing accelerator is an organic urea accelerator; and the silane coupling agent is one or more of KH550, KH560, or KH580.

[0032] Preferably, the conductive carbon black is acetylene black; the filler is heavy calcium carbonate and / or talc; and the thixotropic agent is one or more of nano-calcium carbonate with a particle size of less than 100 nm, organic bentonite, or kaolin.

[0033] The second objective of this invention is to provide a method for preparing a self-lubricating spot welding sealant for steel plates, the method comprising:

[0034] S1. Styrene-butadiene rubber is put into a kneader. Under low-speed stirring at 60-80°C, about half of the plasticizer is added in batches and kneaded for 20-30 minutes.

[0035] S2, without stopping the machine, adds conductive carbon black, filler and thixotropic agent to the kneader in sequence. Under a vacuum of -0.06 to -0.08 MPa, mix at low speed for 10 minutes, then switch to medium speed kneading for 30 to 40 minutes.

[0036] S3 lowers the kneader temperature to 40~50℃, adds phytic acid-silane-epoxy prepolymer, epoxy resin, silane coupling agent and remaining plasticizer, and kneads at medium speed under vacuum for 20~30 minutes.

[0037] S4. Reduce the temperature of the kneader to below 40°C, add vulcanizing agent, vulcanizing aid, curing agent and curing accelerator, and stir at low speed under vacuum for 15~20 minutes.

[0038] S5 takes out the mixed paste material from the kneader and refines it 2-3 times using a three-roll mill, with the gap between the rollers decreasing each time; then, the refined material is stirred and degassed at low speed for 20-30 minutes under a vacuum of -0.095MPa or higher.

[0039] The third objective of this invention is to provide an application of a self-lubricating steel plate spot welding sealant, characterized in that the sealant is first applied and then spot welded, followed by a curing process.

[0040] Preferably, the curing process adopts a stepped heating method, with the first stage being treated at 80°C for 40 minutes, the second stage at 130°C for 60 minutes, and the third stage at 150°C for 30 minutes.

[0041] The self-lubricating steel plate spot welding sealant of this invention effectively solves the technical pain points of traditional sealants through the core role of phytic acid-silane-epoxy prepolymer. It achieves this by chelating phosphate groups with metal ions in the steel plate and hydrolyzing siloxy groups to form Si-O-Fe covalent bonds. Combined with epoxy segments integrated into the matrix crosslinking network, it constructs a dual system of chemical anchoring and interface compatibility, improving wettability and adhesion strength to low surface energy steel plates and solving the problem of interface adhesion failure. Simultaneously, phosphorus and silicon in the prepolymer form a reactive synergistic flame retardant; phosphoric acid catalyzes char formation, and silicon is converted into SiO2 to support the char layer, preventing high-temperature damage during spot welding. Furthermore, it chemically addresses the phase separation and migration problems of additive flame retardants. The long silane chains and phytic acid branches alleviate the rigidity of the epoxy, forming a rigid-flexible interpenetrating network with the styrene-butadiene rubber, balancing flame retardancy and mechanical properties. In addition, the prepolymer integrates adhesion, flame retardancy, compatibility, and corrosion protection functions, simplifying the formulation, avoiding additive constraints, and achieving comprehensive improvements in adhesion, conductivity, flame retardancy, processability, and stability. Detailed Implementation

[0042] The following description includes certain specific details to provide a comprehensive understanding of the various disclosed embodiments. However, those skilled in the art will recognize that embodiments can be implemented without employing one or more of these specific details, but using other methods, components, materials, etc.

[0043] Unless otherwise required by the present invention, throughout the specification and the following claims, the words “comprising” and “including” shall be interpreted in an open-ended, inclusive sense, meaning “including but not limited to”.

[0044] Throughout this specification, the terms "an embodiment," "an embodiment," "a preferred embodiment," or "some embodiments" refer to including, in at least one embodiment, a specific reference element, structure, or feature associated with that embodiment. Therefore, the phrases "in an embodiment," "in a preferred embodiment," or "in some embodiments" appearing in different places throughout the specification do not necessarily all refer to the same embodiment. Furthermore, specific elements, structures, or features may be combined in one or more embodiments in any suitable manner.

[0045] According to a first aspect of the present invention, a self-lubricating spot welding sealant for steel plates is provided, the spot welding sealant comprising the following raw materials in parts by weight:

[0046] Styrene-butadiene rubber: 5-10 parts

[0047] Conductive carbon black: 1-2 parts

[0048] Vulcanizing agent: 0.3~1.0 parts

[0049] Vulcanizing aid: 0.2~0.5 parts

[0050] Phytic acid-silane-epoxy prepolymer: 1.8~2.8 parts

[0051] Epoxy resin: 4-10 parts

[0052] Hardener: 0.5~1.0 parts

[0053] Curing accelerator: 0.1~0.3 parts

[0054] Silane coupling agent: 0.2~0.6 parts

[0055] Plasticizer: 25-35 parts

[0056] Filler: 30-35 parts

[0057] And thixotropic agent: 10-15 parts.

[0058] The phytic acid-silane-epoxy prepolymer is prepared from phytic acid, silane coupling agent and epoxy resin. The mass ratio of phytic acid, silane coupling agent and epoxy resin is 1:0.5~0.8:0.8~1.5. Phytic acid and silane coupling agent are reacted at 70~80℃ first, and then epoxy resin is slowly added dropwise at 85℃ to complete the grafting.

[0059] The low surface energy and chemical inertness of self-lubricating steel plates make it difficult for sealants to wet and form effective bonds. This invention effectively solves the problem of interfacial adhesion failure in existing technologies by constructing a dual-action system of chemical anchoring and interface compatibility.

[0060] In this invention, the phosphate groups in the phytic acid-silane-epoxy prepolymer have strong coordination ability, which can form stable chelates with metal ions exposed by microscopic defects on the surface of the self-lubricating steel plate, forming chemical anchors and enhancing the interfacial adsorption force between the sealant and the self-lubricating steel plate. At the same time, the siloxane groups of the silane coupling agent in the prepolymer can be hydrolyzed to generate silanol under the action of trace amounts of moisture in the matrix, and then dehydrated and condensed with the hydroxyl groups on the steel plate surface to form Si-O-Fe covalent bonds, upgrading physical adsorption to chemical bonding. Furthermore, the epoxy segments in the prepolymer and the epoxy resin components in the sealant matrix work together to integrate into the cross-linking network of the matrix, which helps to avoid the formation of a weak interfacial layer and ensures uniform bonding strength transfer.

[0061] Meanwhile, the multifunctional structure of phytic acid-silane-epoxy prepolymer can effectively adjust the surface energy matching between the adhesive layer and the self-lubricating steel plate, improve the wettability of the adhesive layer on the substrate, and avoid bonding failure caused by excessive contact angle and inability to spread.

[0062] In existing technologies, sealants mainly rely on additive flame retardants to achieve flame retardant effects. However, additive flame retardants suffer from drawbacks such as poor compatibility, phase separation, embrittlement of the adhesive layer, and flame retardant migration. This invention achieves a balance between flame retardancy and mechanical properties by employing reactive phosphorus-silicon synergistic flame retardancy and a rigid-flexible network balanced design.

[0063] In this invention, the phosphate groups in phytic acid catalyze the dehydration and carbonization of epoxy resin and styrene-butadiene rubber molecular chains during combustion, forming a dense carbon layer to block oxygen and heat transfer. Simultaneously, the silicon in the silane coupling agent can be converted into silicon dioxide at high temperatures, uniformly dispersed in the carbon layer to form a skeletal support, improving the high-temperature resistance of the carbon layer and thus preventing carbon layer cracking caused by the instantaneous high temperature during spot welding. The phytic acid-silane-epoxy prepolymer utilizes the reactivity of epoxy groups to incorporate phosphate groups and silane coupling agents into the cross-linked network of the sealant matrix, fundamentally solving the phase separation problem and avoiding the risk of flame retardant migration.

[0064] Meanwhile, the long organic chains of silanes and the multi-branched structure of phytic acid are flexible, which can alleviate the internal stress of the rigid epoxy crosslinking network, prevent embrittlement, and make it more conducive to forming a rigid-flexible interpenetrating network with the elastic network formed by styrene-butadiene rubber, balancing mechanical properties, and helping to solve the industry contradiction that flame retardancy inevitably leads to embrittlement.

[0065] In this invention, the phytic acid-silane-epoxy prepolymer not only helps to ensure the uniformity and stability of the multiphase system (rubber, epoxy, inorganic filler, conductive carbon black), but also simultaneously undertakes four major functions: adhesion strengthening, flame retardancy, compatibility optimization, and corrosion prevention. This simplifies the formulation system, avoids mutual constraints between multiple additives, and achieves a comprehensive improvement in adhesion, conductivity, flame retardancy, processability, and stability.

[0066] In a preferred embodiment of the present invention, the phytic acid-silane-epoxy prepolymer has an epoxy value of 0.20~0.40 eq / 100g, a phosphorus mass fraction of 5.0~9.0%, a nitrogen mass content of 1.0~2.5%, and a viscosity of 5000~50000 mPa·s at 40°C.

[0067] In this invention, an epoxy value of 0.20~0.40 eq / 100g can control the crosslinking density and balance rigidity and toughness. If the epoxy value is <0.20 eq / 100g, the adhesive layer is prone to low strength due to insufficient crosslinking; if the epoxy value is >0.40 eq / 100g, the adhesive layer is prone to embrittlement due to excessive crosslinking. A moderate epoxy group content can also improve the compatibility of the prepolymer and avoid system delamination caused by too few or too many epoxy groups.

[0068] A phosphorus content of 5.0% to 9.0% ensures a highly efficient synergistic effect between flame retardancy and corrosion prevention. If the phosphorus content is <5.0%, the prepolymer is prone to insufficient char formation, resulting in poor flame retardancy. If the phosphorus content is >9.0%, excessive phytic acid can lead to overly polar prepolymers, reducing compatibility with styrene-butadiene rubber and making phase separation more likely. Furthermore, the phosphate groups within this range can react with metal ions (Fe2+) on the steel plate surface. 2+ Zn 2+ Phosphorus forms a stable phytate protective film, which inhibits anodic oxidation; insufficient phosphorus content can easily lead to an incomplete protective film, while excessive phosphorus content can cause phosphate groups to easily absorb water, which will accelerate corrosion.

[0069] A nitrogen content of 1.0-2.5% can form PN bonds with phosphorus during flame retardancy, improving the thermal stability of the char layer and suppressing smoke release, thus compensating for the insufficient flame retardancy efficiency of phosphorus alone.

[0070] When the prepolymer has a viscosity of 5000~50000 mPa·s at 40℃, it is more conducive to the uniformity of dispersion and process compatibility with the sealant matrix. Combined with precise control of phosphorus and nitrogen content, it can synergistically prevent phase separation or functional group migration, thereby extending the sealant's shelf life. When the viscosity is too low, it easily leads to uneven concentration of functional groups; when the viscosity is too high, it easily leads to dispersion difficulties, forming local agglomerates, and thus causing performance fluctuations. At the same time, within this viscosity range, the prepolymer, plasticizer, and thixotropic agent synergistically adjust the overall viscosity of the sealant, which is beneficial for meeting the flowability and anti-sagging requirements of automated coating processes.

[0071] In a preferred embodiment of the present invention, the method for preparing the phytic acid-silane-epoxy prepolymer includes: using isopropanol as a solvent and triphenylphosphine as a catalyst;

[0072] First, add dehydrated isopropanol and phytic acid powder, and disperse the phytic acid powder in the dehydrated isopropanol under nitrogen protection.

[0073] Then, add the silane coupling agent, heat to 70-80℃, and react for 1.5-2 hours until the system becomes homogeneous and transparent;

[0074] Then, the temperature is raised to 85°C, and the mixture of epoxy resin and catalyst is slowly added dropwise, controlling the dropping rate to be completed within 1-2 hours. After the addition is completed, the reaction continues for 2-3 hours.

[0075] Then, the temperature was lowered to below 40°C, and the isopropanol solvent was removed by vacuum distillation to obtain phytic acid-silane-epoxy prepolymer.

[0076] In this invention, the preparation method specifically includes:

[0077] The mass ratio of dehydrated isopropanol to phytic acid is 4-7:1, and the mass of triphenylphosphine is 0.5-0.8% of the mass of epoxy resin. KH550 is preferably used as the silane coupling agent, and E-51 is preferably used as the epoxy resin.

[0078] The isopropanol was dehydrated using a molecular sieve to obtain dehydrated isopropanol. Phytic acid powder was added to the dehydrated isopropanol and stirred at 300-500 rpm for about 30 minutes to ensure that the phytic acid powder was fully dispersed.

[0079] After adding the silane coupling agent, the temperature is slowly raised to 70~80℃, and the reaction is carried out at this temperature for 1.5~2 hours. The reaction system gradually changes from an opaque suspension to a homogeneous and transparent solution.

[0080] The system temperature was raised to 85℃, and the epoxy resin and triphenylphosphine catalyst were premixed evenly. Then, the mixture was slowly and uniformly added to the reaction system over 1-2 hours using a constant pressure dropping funnel. After the addition was complete, the reaction was maintained at 85℃ for another 2-3 hours.

[0081] After the reaction was complete, the system was cooled to below 40°C. Then, a rotary evaporator was used to remove the isopropanol solvent and the water generated in the reaction by vacuum distillation under a 60°C water bath and a vacuum degree of -0.095 MPa or higher. A viscous, pale yellow to amber phytic acid-silane-epoxy prepolymer was obtained and stored in a sealed container for later use.

[0082] In a preferred embodiment of the present invention, the styrene-butadiene rubber is a carboxyl-terminated solution-polymerized styrene-butadiene rubber with a Mooney viscosity range of 55-65 and an organic acid content of 4.0-6.0%, preferably Chimei SSBR PR-1205.

[0083] In this invention, carboxyl groups can react with vulcanizing auxiliaries to form carboxylate salts, which serve as active centers for rubber vulcanization, accelerating the cross-linking of rubber molecular chains initiated by the vulcanizing agent and making the vulcanization network denser. Simultaneously, carboxyl groups can form covalent / ionic cross-links of "rubber-epoxy-prepolymer" with epoxy resin and phytic acid-silane-epoxy prepolymer. The carboxyl groups are highly polar and can form coordination bonds with trace amounts of metal ions exposed on the surface of the self-lubricating steel plate, or form hydrogen bonds with hydroxyl groups on the steel plate surface, supplementing the chemical anchoring effect of the phytic acid-silane-epoxy prepolymer and further strengthening the interfacial bonding between the adhesive layer and the substrate. A Mooney viscosity of 55-65 facilitates rapid swelling and dispersion of the rubber in the plasticizer, and moderate molecular chain entanglement ensures sufficient elastic recovery of the vulcanized adhesive layer, which is beneficial for absorbing stress generated by steel plate vibration and thermal expansion and contraction, achieving dynamic sealing, while avoiding adhesive layer collapse due to excessively low viscosity or increased assembly resistance due to excessively high viscosity.

[0084] Simultaneously, it can synergize with phytic acid-silane-epoxy prepolymers. The carboxyl groups of the rubber form multiple interactions with the amino and phosphate groups of the prepolymer, further strengthening the interpenetrating network of the rubber-epoxy-prepolymer and improving the integrity of the adhesive layer. It can also synergize with fillers / conductive carbon black. The carboxyl groups can adsorb onto the surfaces of fillers and conductive carbon black, reducing their surface energy and helping the prepolymer improve dispersion uniformity, avoiding performance fluctuations caused by agglomeration. In synergy with vulcanization / curing systems, the temperature windows of rubber vulcanization and epoxy curing are matched. The presence of carboxyl groups can simultaneously activate the vulcanization and curing reactions, enabling the two networks to form a synchronously cross-linked and mutually supportive structure, balancing elasticity and rigidity.

[0085] In a preferred embodiment of the present invention, the vulcanizing agent is a peroxide vulcanizing agent DCP and / or BIPB; the vulcanizing aid is p-benzoquinone dioxime; and the epoxy resin is a bisphenol A type epoxy resin E-44 and / or E-51 with an epoxy value of 0.4~0.55 eq / 100g.

[0086] In this invention, the peroxide vulcanizing agent and the vulcanizing aid p-benzoquinone dioxime synergistically activate styrene-butadiene rubber to form a high-temperature-resistant C-bond crosslinking network, and achieve simultaneous vulcanization-curing reaction with bisphenol A type epoxy resin with an epoxy value of 0.4~0.55eq / 100g; the epoxy resin co-crosslinks with rubber and phytic acid-silane-epoxy prepolymer to form a rigid-flexible interpenetrating structure, which ultimately improves the high-temperature resistance of the sealant (suitable for instantaneous high temperature during spot welding) and mechanical balance (combining rigidity and flexibility), optimizes the system compatibility and storage stability, and adapts to industrial production processes, enhancing the sealing and corrosion resistance durability.

[0087] In a preferred embodiment of the present invention, the curing agent is one or more of dicyandiamide, sebacic acid dihydrazide, or adipic acid dihydrazide; the curing accelerator is an organic urea accelerator; and the silane coupling agent is one or more of KH550, KH560, or KH580.

[0088] In this invention, organic urea accelerators can efficiently activate curing agents such as dicyandiamide and sebacic acid dihydrazide, enabling them to undergo co-crosslinking reactions with epoxy resin (E-44 / E-51) and phytic acid-silane-epoxy prepolymers, accelerating the formation of a dense, rigid network. Silane coupling agents such as KH550, KH560, and KH580 can form chemical bridges with the steel plate surface and various components of the adhesive layer through functional groups such as amino and epoxy groups, synergistically strengthening the interfacial bonding with the prepolymer. Ultimately, this not only improves the curing efficiency and crosslinking density of the sealant but also significantly enhances the bonding reliability to self-lubricating steel plates. Simultaneously, it optimizes system compatibility and storage stability, further ensuring corrosion resistance durability and compatibility with spot welding processes.

[0089] The preferred silane coupling agent in the raw materials described in this invention is KH560, which is an additional silane coupling agent added to the formulation, distinct from the raw materials used in the preparation of phytic acid-silane-epoxy prepolymers. KH560 can form a dual interface reinforcement with the prepolymer; its silanol groups condense with the silanol groups of the prepolymer to form a continuous siloxane network, and the epoxy groups interact with the trace polar defects of the lubricating coating, further filling the interfacial gap between the prepolymer and the coating.

[0090] In a preferred embodiment of the present invention, the conductive carbon black is acetylene black; the filler is heavy calcium carbonate and / or talc; and the thixotropic agent is one or more of nano-calcium carbonate with a particle size of less than 100 nm, organic bentonite, or kaolin.

[0091] In this invention, acetylene black, with its highly conductive structure, requires only a small amount to form a continuous conductive path, ensuring the conduction of spot welding current. Heavy calcium carbonate / talc powder bonds tightly with the adhesive matrix, enhancing mechanical strength and providing a physical barrier against corrosion. Nanoscale thixotropic agents, through the formation of a three-dimensional network, impart excellent anti-sagging properties to the adhesive layer, while maintaining uniform dispersion without compromising system compatibility. The synergistic effects of each component with the phytic acid-silane-epoxy prepolymer and the rubber-epoxy system ensure high spot welding success rate and balanced mechanical properties of the sealant, while also optimizing coating processability and storage stability, further enhancing corrosion resistance and durability, thus meeting the industrial application requirements of self-lubricating steel plates.

[0092] According to a second aspect of the present invention, a method for preparing a self-lubricating spot welding sealant for steel plates is provided, the method comprising:

[0093] S1. Styrene-butadiene rubber is put into a kneader. Under low-speed stirring at 60-80°C, about half of the plasticizer is added in batches and kneaded for 20-30 minutes.

[0094] S2, without stopping the machine, adds conductive carbon black, filler and thixotropic agent to the kneader in sequence. Under a vacuum of -0.06 to -0.08 MPa, mix at low speed for 10 minutes, then switch to medium speed kneading for 30 to 40 minutes.

[0095] S3 lowers the kneader temperature to 40~50℃, adds phytic acid-silane-epoxy prepolymer, epoxy resin, silane coupling agent and remaining plasticizer, and kneads at medium speed under vacuum for 20~30 minutes.

[0096] S4. Reduce the temperature of the kneader to below 40°C, add vulcanizing agent, vulcanizing aid, curing agent and curing accelerator, and stir at low speed under vacuum for 15~20 minutes.

[0097] S5 takes out the mixed paste material from the kneader and refines it 2-3 times using a three-roll mill, with the gap between the rollers decreasing each time; then, the refined material is stirred and degassed at low speed for 20-30 minutes under a vacuum of -0.095MPa or higher.

[0098] In this invention, in step S1, the low-speed stirring speed is 30-50 rpm, which can prevent the rubber from locally heating up due to excessive shear force. Approximately half of the plasticizer used is about 12.5-17.5 parts, added in 3-4 batches, with an interval of 3-5 minutes between each batch. Each batch of plasticizer is added only after the previous batch has been completely absorbed by the rubber (no free liquid remains). After adding the plasticizer, maintain a temperature of 60-80°C and knead for 20-30 minutes until the rubber is completely swollen into a soft lump, with no hard particles to the touch and a uniform appearance.

[0099] In step S2, maintain the kneader temperature at 60-80℃ without stopping the machine. Add acetylene black, filler, and thixotropic agent sequentially. After each powder is added, stir at a low speed of 20-30 rpm for 5 minutes until no dust is emitted before adding the next powder. Then close the feed port, start the vacuum system, and evacuate to a vacuum level of -0.06 to -0.08 MPa to remove air and prevent air bubbles from forming when the powder agglomerates. First, set the speed to low (20-30 rpm) and mix for 10 minutes to initially disperse the powder in the rubber matrix. Then adjust the speed to medium (60-80 rpm) and continue kneading for 30-40 minutes until no obvious powder particles are visible, no powder adheres to the inner wall of the kneader, and the material is a uniform gray paste without white or black spots. Starting with low speed and then medium speed prevents powder from agglomerating due to sudden excessive shear force, while medium speed provides sufficient shear force to break up secondary agglomerations.

[0100] In step S3, the cooling jacket of the kneader is activated to lower the material temperature to 40-50°C, preventing premature reaction of epoxy groups or decomposition of the prepolymer due to excessive temperature. Phytic acid-silane-epoxy prepolymer, epoxy resin, silane coupling agent, and remaining plasticizer are added sequentially. Maintain a vacuum of -0.06 to -0.08 MPa and knead at a medium speed of 50-70 rpm for 20-30 minutes until the material forms a homogeneous, viscous paste.

[0101] In step S4, the material is further cooled to below 40°C, preferably 35°C, to prevent the peroxide vulcanizing agent and curing agent from decomposing prematurely due to high temperature. The vulcanizing agent, vulcanizing aid, curing agent, and curing accelerator are added sequentially. A vacuum of -0.06 to -0.08 MPa is maintained, and the mixture is stirred at a low speed of 20 to 40 rpm for 15 to 20 minutes. Low-speed stirring reduces the temperature rise of the system, ensuring uniform dispersion of the additives and preventing premature reaction, thus guaranteeing the storage stability of the sealant.

[0102] In step S5, the three-roll mill is preheated to 30-40°C, and the roller speed ratio is set to 1:3:9, with the front roller slowest and the rear roller fastest. The initial roller gap is 0.5mm. The kneaded paste-like material is fed into the inlet and ground once to remove large agglomerates. Then, the roller gap is adjusted to 0.3mm for a second grinding pass. The roller gap can also be adjusted to 0.1mm for a third grinding pass. The three-roll mill further refines powder agglomerates through extrusion and shearing, especially hard agglomerates of conductive carbon black and nano-thixotropic agents, ensuring a continuous conductive network and stable thixotropic properties.

[0103] The refined material is then transferred to a vacuum degassing machine. The equipment is started and the stirring speed is controlled at 10~20 rpm. The vacuum is then drawn to above -0.095 MPa, and degassing is performed for 20~30 minutes. High vacuum degassing above -0.095 MPa can effectively remove residual microbubbles in the material, preventing bubbles from disrupting the current path during spot welding and causing poor weld joints.

[0104] Finally, stop the machine, unload the material, seal it in packaging, and store it in a cool, dark place.

[0105] According to a third aspect of the present invention, an application of a self-lubricating steel plate spot welding sealant is provided, characterized in that the sealant is first applied and then spot welded, followed by a curing process.

[0106] In a preferred embodiment of the present invention, the curing process adopts a stepped heating method, with the first stage being treated at 80°C for 40 minutes, the second stage being treated at 130°C for 60 minutes, and the third stage being treated at 150°C for 30 minutes.

[0107] In this invention, in the first stage, the vulcanizing agent begins to decompose slowly. Its decomposition products, activated by the vulcanizing accelerator, generate a small number of free radicals, initiating preliminary cross-linking of the styrene-butadiene rubber molecular chains and forming a low-crosslink density elastic network. Simultaneously, the curing accelerator activates the curing agent, causing a preliminary ring-opening reaction with the epoxy groups of the epoxy resin and the phytic acid-silane-epoxy prepolymer. The first stage's low-temperature start-up at 80°C allows for a gentle initial reaction, avoiding localized burst polymerization caused by direct high temperatures and laying a uniform foundation for subsequent deep reactions.

[0108] In the second stage at 130℃, the vulcanizing agent completely decomposes, and the rubber molecular chains undergo deep cross-linking to form a complete elastic network. The reaction between the epoxy resin and the curing agent reaches its peak, interpenetrating with the rubber elastic network to form a continuous structure that combines rigidity and flexibility. The chelation reaction between the phosphate groups of the phytic acid-silane-epoxy prepolymer and the metal ions of the steel plate, as well as the silanol condensation reaction of the silane coupling agent, are fully carried out in this stage, resulting in stable interfacial chemical bonds. This temperature represents a synergistic reaction window for rubber vulcanization and epoxy curing. The matching reaction rates of the two processes avoid the contradiction of internal stress caused by rubber vulcanization and setting before epoxy curing, or the limitation of rubber vulcanization by epoxy curing first. This ensures that the two networks are tightly bonded, effectively improving interfacial delamination.

[0109] In the third stage, the remaining small amount of epoxy groups react completely with the curing agent, further densifying the cross-linked network. Weak cross-linking points in the rubber vulcanization network (such as locally unreacted segments) rearrange at high temperatures, improving network uniformity. Phosphoric acid produced from phytic acid decomposition further catalyzes the stabilization of the matrix carbonization layer, and the silicon-oxygen network can further condense at high temperatures, enhancing temperature resistance. The high-temperature treatment in the third stage is mainly used to eliminate residual stress within the system and improve the dimensional stability of the adhesive layer; simultaneously, it strengthens the flame-retardant and corrosion-resistant barriers, and the high temperature promotes the fusion of the phytic acid passivation film and the silicon-oxygen network.

[0110] The total curing time is 130 minutes, which is suitable for the pace of automobile manufacturing production lines.

[0111] The present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0112] In the following embodiments, unless otherwise specified, all raw material components are commercially available products.

[0113] Example 1

[0114] The raw material formula for the spot welding sealant in Example 1 is as follows:

[0115] Styrene-butadiene rubber: 7 parts, using Chimei SSBR PR-1205, Mooney viscosity (ML1+4 100℃) is 55~62, organic acid content is 4.2~5.8%;

[0116] Conductive carbon black: 1.5 parts, using acetylene black, specific surface area 850 m² 2 / g, particle size 30nm;

[0117] Vulcanizing agent: 0.6 parts, using DCP;

[0118] Vulcanizing aid: 0.3 parts, using p-benzoquinone dioxime;

[0119] Phytic acid-silane-epoxy prepolymer: 2.2 parts;

[0120] Epoxy resin: Use E-51, 7 parts;

[0121] Hardener: 0.8 parts, using dicyandiamide;

[0122] Curing accelerator: 0.2 parts, using complexed high-tech HUA5050;

[0123] Silane coupling agent: 0.4 parts, using KH560;

[0124] Plasticizer: 30 parts, using DOP;

[0125] Filler: 20 parts heavy calcium carbonate, 15 parts talc;

[0126] Thixotropic agent: 12 parts, nano-calcium carbonate, particle size 60~80nm.

[0127] Preparation method:

[0128] 1. Preparation of phytic acid-silane-epoxy prepolymer

[0129] In the preparation of phytic acid-silane-epoxy prepolymer, KH550 is used as the silane coupling agent and E-51 is used as the epoxy resin.

[0130] The ingredients are prepared according to the mass ratio of phytic acid:KH550:E-51=1:0.6:1.2, with 10g of phytic acid, 6g of silane coupling agent, 12g of epoxy resin, 60g of dehydrated isopropanol, and 0.08g of triphenylphosphine.

[0131] Under nitrogen protection, phytic acid was dispersed in dehydrated isopropanol and stirred at 300 rpm for 30 min.

[0132] Add a silane coupling agent and react at 75°C for 1.8 h until the system becomes transparent;

[0133] Heat to 85℃, add a mixture of epoxy resin and triphenylphosphine dropwise over 1.5 hours, and maintain the temperature for 2.5 hours.

[0134] The solvent was removed by vacuum distillation below 40°C to obtain phytic acid-silane-epoxy prepolymer.

[0135] The epoxy value was determined by hydrochloric acid-acetone titration according to GB / T 1677-2008, and the value was 0.30 eq / 100g; the phosphorus content was determined by molybdenum blue spectrophotometry according to GB / T 9874-2001, and the value was 7.2%; the nitrogen content was determined by Kjeldahl nitrogen determination according to GB / T 17767.1-2008, and the value was 1.8%; the viscosity at 40℃ was determined by rotational viscometer (rotor No. 2, 6 rpm) according to GB / T 2794-2013, and the value was 25000 mPa·s.

[0136] 2. Preparation of spot welding sealant

[0137] S1: Put the styrene-butadiene rubber into a kneader, stir at a low speed of 40 rpm, add 15 parts of plasticizer in three batches at 70°C, with an interval of 4 minutes between each batch, and then knead for 25 minutes.

[0138] S2: Maintain the kneader temperature at 70℃. Without stopping the machine, add acetylene black, filler, and thixotropic agent in sequence. After adding each powder, stir at a low speed of 25 rpm for 5 minutes before adding the next one. Then, under a vacuum of -0.06 to -0.08 MPa, first set the speed to low 25 rpm and mix for 10 minutes, then adjust the speed to medium 70 rpm and continue kneading for 35 minutes.

[0139] S3: Cool down to 45℃, add phytic acid-silane-epoxy prepolymer, epoxy resin, silane coupling agent and remaining plasticizer, and knead at medium speed for 25 minutes under vacuum of -0.06~-0.08MPa.

[0140] S4: Cool to 35℃, add vulcanizing agent, vulcanizing aid, curing agent and curing accelerator, and stir at 30 rpm for 18 min under a vacuum of -0.06~-0.08MPa.

[0141] S5: Preheat the three-roll mill to 35℃, set the roller speed ratio to 1:3:9, with the front roller at its slowest and the rear roller at its fastest. Initially, set the roller gap to 0.5mm and feed the kneaded paste-like material into the inlet. Grind once to remove large agglomerates. Then adjust the roller gap to 0.3mm and grind a second time; finally, adjust the roller gap to 0.1mm and grind a third time.

[0142] The refined material is then transferred to a vacuum degassing machine. The machine is started and the stirring speed is controlled at 15 rpm. The vacuum is drawn to above -0.095 MPa and degassed for 25 minutes.

[0143] 3. Application curing

[0144] Test sample: a self-lubricating steel plate with a polytetrafluoroethylene coating, 1.5 mm thick, with a coating thickness of 20 μm and a surface energy of 18~20 mN / m, measuring 100 mm × 50 mm; the test sample was cleaned of floating dust, and the surface of the steel plate was wiped twice with anhydrous ethanol-soaked lint-free cloth to remove rolling oil, fingerprints and other oil stains, and then dried.

[0145] Apply adhesive to one of the test samples to a thickness of 0.4 mm. Then, place another test sample on top of the adhesive-coated steel plate, ensuring that the two steel plates are aligned. Finally, spot weld the samples at a current of 10000A and a pressure of 1MPa.

[0146] Then, a stepped temperature curing process is carried out: In the first stage, the spot-welded steel plate assembly is placed in an 80℃ oven, the oven door is closed, the blower is turned on (wind speed 1m / s), and the temperature is maintained for 40 minutes.

[0147] Second stage: Raise the oven temperature to 130℃ (heating rate 5℃ / min, to avoid sudden temperature rise causing the adhesive layer to crack), and keep it at this temperature for 60 minutes;

[0148] Third stage: Raise the oven temperature to 150℃ (heating rate 5℃ / min) and keep it warm for 30 minutes.

[0149] After curing, turn off the oven, remove the steel plate assembly, and allow it to cool naturally at room temperature (25°C) for 30 minutes.

[0150] Example 2

[0151] The difference between Example 2 and Example 1 is that in the preparation of the phytic acid-silane-epoxy prepolymer, the ingredients are prepared according to the mass ratio of phytic acid:KH550:E-51=1:0.5:0.8, with 10g of phytic acid, 5g of KH550, 8g of E-51, 50g of dehydrated isopropanol, and 0.06g of triphenylphosphine. After the reaction is completed, the phytic acid-silane-epoxy prepolymer is obtained with an epoxy value of 0.25eq / 100g, a phosphorus content of 8.5%, a nitrogen content of 1.5%, and a viscosity of 18000mPa·s at 40℃. Other properties are the same as in Example 1.

[0152] The preparation and curing process of the spot welding sealant are the same as in Example 1.

[0153] Example 3

[0154] The difference between Example 3 and Example 1 is that in the preparation of the phytic acid-silane-epoxy prepolymer, the ingredients are prepared according to the mass ratio of phytic acid:KH550:E-51=1:0.5:1.5, with 10g of phytic acid, 5g of KH550, 15g of E-51, 80g of dehydrated isopropanol, and 0.12g of triphenylphosphine. After the reaction is completed, the phytic acid-silane-epoxy prepolymer is obtained with an epoxy value of 0.38eq / 100g, a phosphorus content of 5.8%, a nitrogen content of 2.2%, and a viscosity of 45000mPa·s at 40℃. Other properties are the same as in Example 1.

[0155] The preparation and curing process of the spot welding sealant are the same as in Example 1.

[0156] Example 4

[0157] The difference between Example 4 and Example 1 is that the styrene-butadiene rubber used in the raw material formulation of the spot welding sealant is SBR1009C, while the others are the same as in Example 1.

[0158] The preparation of phytic acid-silane-epoxy prepolymer, the preparation of spot welding sealant, and the application curing process are the same as in Example 1.

[0159] Example 5

[0160] The difference between Example 5 and Example 1 is that in the raw material formulation of the spot welding sealant, KH550 is used as the silane coupling agent, while the rest is the same as in Example 1.

[0161] The preparation of phytic acid-silane-epoxy prepolymer, the preparation of spot welding sealant, and the application curing process are the same as in Example 1.

[0162] Example 6

[0163] The difference between Example 6 and Example 1 is that in the raw material formulation of the spot welding sealant, E-44 epoxy resin is used, while the rest is the same as in Example 1.

[0164] The preparation of phytic acid-silane-epoxy prepolymer, the preparation of spot welding sealant, and the application curing process are the same as in Example 1.

[0165] Example 7

[0166] The difference between Example 7 and Example 1 is that in the raw material formulation of the spot welding sealant, 1.8 parts of phytic acid-silane-epoxy prepolymer are used, while the rest are the same as in Example 1.

[0167] The preparation of phytic acid-silane-epoxy prepolymer, the preparation of spot welding sealant, and the application curing process are the same as in Example 1.

[0168] Example 8

[0169] The difference between Example 8 and Example 1 is that in the raw material formulation of the spot welding sealant, 2.8 parts of phytic acid-silane-epoxy prepolymer are used, while the rest are the same as in Example 1.

[0170] The preparation of phytic acid-silane-epoxy prepolymer, the preparation of spot welding sealant, and the application curing process are the same as in Example 1.

[0171] Example 9

[0172] The difference between Example 9 and Example 1 is that the curing process used is constant temperature curing at 120℃ for 2 hours, while the rest is the same as Example 1.

[0173] The raw material formulation, preparation process of phytic acid-silane-epoxy prepolymer, and preparation process of spot welding sealant are the same as in Example 1.

[0174] Comparative Example 1

[0175] Phytic acid-silane-epoxy prepolymer is not used; instead, aluminum hydroxide with a particle size of 1 μm is used as a flame retardant.

[0176] In the raw material formulation of the spot welding sealant, 9.2 parts of epoxy resin E-51 and 10 parts of aluminum hydroxide are used, and the rest are the same as in Example 1.

[0177] The preparation and curing process of the spot welding sealant are the same as in Example 1.

[0178] Comparative Example 2

[0179] Instead of using phytic acid-silane-epoxy prepolymer, it uses the traditional phosphorus-nitrogen flame retardant MPP.

[0180] In the raw material formulation of the spot welding sealant, 9.2 parts of epoxy resin E-51 and 8 parts of traditional phosphorus-nitrogen flame retardant MPP are used, and the rest are the same as in Example 1.

[0181] Performance testing:

[0182] Shear strength: GB / T 7124-2008;

[0183] Oxygen index: GB / T 2406-2021;

[0184] Elongation at break / tensile strength: GB / T 528-2009;

[0185] Salt spray test: GB / T 10125-2021 (5% NaCl solution, record the time of rust occurrence as the salt spray test life);

[0186] Storage stability: GB / T 7123.2-2002, sealed storage at 40℃, record the number of days with viscosity change rate exceeding 30%.

[0187] The performance test data of Examples 1-9 and Comparative Examples 1-2 are shown in Table 1.

[0188] Table 1 Performance test data of Examples 1-9 and Comparative Examples 1-2

[0189] .

[0190] As shown in Table 1, this invention fundamentally solves four major industry pain points—bonding failure, flame retardant embrittlement, insufficient corrosion protection, and short shelf life—by replacing traditional additive flame retardants with phytic acid-silane-epoxy prepolymers. Examples 1-9 exhibit shear strength ≥1.69 MPa, oxygen index ≥28%, salt spray life ≥650 h, and shelf life ≥24 days, fully meeting the industrial requirements for spot welding and sealing of self-lubricating steel plates in the automotive and home appliance industries. Process adaptation: The combination of stepped temperature curing, carboxyl-terminated styrene-butadiene rubber, and bisphenol A epoxy resin can further optimize performance and provide clear parameter references for industrial production.

[0191] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, nor does it mean that the present invention must rely on the above process steps for implementation. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A spot-weld sealant for self-lubricating steel plates, characterized by comprising: The spot welding sealant comprises the following raw materials in parts by weight: Styrene-butadiene rubber: 5-10 parts Conductive carbon black: 1-2 parts Vulcanizing agent: 0.3~1.0 parts Vulcanizing aid: 0.2~0.5 parts Phytic acid-silane-epoxy prepolymer: 1.8~2.8 parts Epoxy resin: 4-10 parts Hardener: 0.5~1.0 parts Curing accelerator: 0.1~0.3 parts Silane coupling agent: 0.2~0.6 parts Plasticizer: 25-35 parts Filler: 30-35 parts And thixotropic agent: 10-15 parts; The phytic acid-silane-epoxy prepolymer is prepared from phytic acid, silane coupling agent and epoxy resin. The silane coupling agent used in the preparation of the prepolymer is KH550. The mass ratio of phytic acid, silane coupling agent and epoxy resin is 1:0.5~0.8:0.8~1.

5. Phytic acid and silane coupling agent are reacted at 70~80℃ first, and then epoxy resin is slowly added dropwise at 85℃ to complete the grafting. The phytic acid-silane-epoxy prepolymer has an epoxy value of 0.20~0.40 eq / 100g, a phosphorus mass fraction of 5.0~9.0%, a nitrogen mass content of 1.0~2.5%, and a viscosity of 5000~50000 mPa·s at 40℃.

2. The self-lubricating steel plate spot welding sealant as described in claim 1, characterized in that, The preparation method of the phytic acid-silane-epoxy prepolymer includes: Isopropanol was used as a solvent and triphenylphosphine was used as a catalyst. First, add dehydrated isopropanol and phytic acid powder, and disperse the phytic acid powder in the dehydrated isopropanol under nitrogen protection. Then, add the silane coupling agent, heat to 70-80℃, and react for 1.5-2 hours until the system becomes homogeneous and transparent; Then, the temperature is raised to 85°C, and the mixture of epoxy resin and catalyst is slowly added dropwise, controlling the dropping rate to be completed within 1-2 hours. After the addition is completed, the reaction continues for 2-3 hours. Then, the temperature was lowered to below 40°C, and the solvent was removed by vacuum distillation to obtain phytic acid-silane-epoxy prepolymer.

3. The self-lubricating steel plate spot welding sealant as described in claim 1, characterized in that, The styrene-butadiene rubber is a carboxyl-terminated solution-polymerized styrene-butadiene rubber with a Mooney viscosity of 55-65 and an organic acid content of 4.0-6.0%.

4. The self-lubricating steel plate spot welding sealant as described in claim 1, characterized in that, The vulcanizing agent is a peroxide vulcanizing agent DCP and / or BIPB; the vulcanizing aid is p-benzoquinone dioxime; the epoxy resin is a bisphenol A type epoxy resin E-44 and / or E-51 with an epoxy value of 0.4~0.55 eq / 100g.

5. The self-lubricating steel plate spot welding sealant as described in claim 1, characterized in that, The curing agent is one or more of dicyandiamide, sebacic acid dihydrazide, or adipic acid dihydrazide; the curing accelerator is an organic urea accelerator; and the silane coupling agent is one or more of KH550, KH560, or KH580.

6. The self-lubricating spot welding sealant for steel plates as described in any one of claims 1-5, characterized in that, The conductive carbon black is acetylene black; the filler is heavy calcium carbonate and / or talc; the thixotropic agent is one or more of nano-calcium carbonate with a particle size of less than 100 nm, organic bentonite, or kaolin.

7. The method for preparing the self-lubricating spot welding sealant for steel plates according to any one of claims 1-6, characterized in that, The preparation method includes: S1. Styrene-butadiene rubber is put into a kneader. Under low-speed stirring at 60~80℃, half of the plasticizer is added in batches and kneaded for 20~30 minutes. S2, without stopping the machine, adds conductive carbon black, filler and thixotropic agent to the kneader in sequence. Under a vacuum of -0.06 to -0.08 MPa, mix at low speed for 10 minutes, then switch to medium speed kneading for 30 to 40 minutes. S3 lowers the kneader temperature to 40~50℃, adds phytic acid-silane-epoxy prepolymer, epoxy resin, silane coupling agent and remaining plasticizer, and kneads at medium speed under vacuum for 20~30 minutes. S4. Reduce the temperature of the kneader to below 40°C, add vulcanizing agent, vulcanizing aid, curing agent and curing accelerator, and stir at low speed under vacuum for 15~20 minutes. S5 takes out the mixed paste material from the kneader and refines it 2-3 times using a three-roll mill, with the gap between the rollers decreasing each time; then, the refined material is stirred and degassed at low speed for 20-30 minutes under a vacuum of -0.095MPa or higher.

8. The application of the self-lubricating steel plate spot welding sealant as described in any one of claims 1-6, characterized in that, First, apply the sealant and then spot weld it, followed by a curing process.

9. The application of the self-lubricating steel plate spot welding sealant as described in claim 8, characterized in that, The curing process employs a stepped heating method: the first stage is at 80°C for 40 minutes, the second stage is at 130°C for 60 minutes, and the third stage is at 150°C for 30 minutes.