Hot melt adhesive as well as preparation method and application thereof

Abstract

The invention discloses a hot melt adhesive and a preparation method and application thereof, and relates to the technical field of hot melt adhesives, the hot melt adhesive comprises a base resin, a tackifier, a regulator, a plastic additive, a filler, and trimethylolpropane triacrylate and allyl polyoxyethylene ether in a specific ratio. By synergistically introducing two functional additives and optimizing the adding process, a gradient network structure is constructed in the hot melt adhesive, and the problems that an existing product is insufficient in flexibility in a low-temperature environment, unbalanced in mechanical property and poor in durability under damp and hot conditions are effectively solved. On the basis of maintaining good initial bonding and mechanical properties, the low-temperature toughness, mechanical balance and damp-heat aging resistance of the hot melt adhesive are synergistically improved, and the hot melt adhesive is especially suitable for application occasions with strict requirements on comprehensive properties of materials, such as automobile manufacturing, outdoor equipment, low-temperature pipeline sealing and the like.

Description

Technical Field

[0001] This invention relates to the field of hot melt adhesive technology, and in particular to a hot melt adhesive, its preparation method, and its application. Background Technology

[0002] Hot melt adhesives, as an environmentally friendly adhesive, are widely used in many fields, especially in applications requiring low-temperature performance, such as automotive manufacturing, outdoor equipment, and cryogenic pipeline sealing. These applications place higher demands on their low-temperature resistance and flexibility. Existing hot melt adhesives, by combining specific tackifiers such as silicone-modified epoxy resins and polymethyl methacrylate with UV absorbers, can still exhibit certain tensile properties at -50°C. However, with increasingly complex and demanding application scenarios, especially in the combined environment of low temperature and high humidity cycling, existing technologies still face challenges in further improving low-temperature toughness, balancing material strength and elasticity, and ensuring long-term durability. Specifically, how to overcome the bottleneck of low-temperature elongation without sacrificing material bonding strength and processing performance, and significantly improve its performance retention rate in humid and hot environments, is a pressing technical problem to be solved in this field.

[0003] Existing improvement methods often focus on compounding single types of tackifying resins or introducing new polymer components, but they often fail to achieve a synergistic improvement in low-temperature toughness, mechanical strength, and environmental aging resistance. For example, simply increasing the crosslinking density may lead to material brittleness and decreased low-temperature performance; while introducing only flexible segments may weaken the material's cohesive strength and durability. Furthermore, conventional blending processes may result in uneven distribution of functional components at the microscale, failing to fully realize their design potential and causing the material's overall performance, especially its reliability under long-term humid and hot conditions, to fall short of practical application requirements. Therefore, developing a hot melt adhesive that can synergistically optimize the network structure through sophisticated molecular design and process control, thereby maintaining excellent overall performance under harsh conditions, has significant practical implications and application value. Summary of the Invention

[0004] This application provides a hot melt adhesive, its preparation method, and its application, solving the technical problems of insufficient low-temperature flexibility, unbalanced mechanical properties, and poor resistance to humid heat aging faced by existing heat-resistant hot melt adhesives in extreme environments. By synergistically introducing trimethylolpropane triacrylate and allyl polyoxyethylene ether as functional additives and optimizing their combination and addition process, a hot melt adhesive with a gradient network structure is constructed, improving the material's elongation at break and low-temperature flexibility below -50°C, while maintaining excellent performance retention under humid heat aging conditions. This achieves a synergistic breakthrough in low-temperature toughness, adhesive strength, and long-term durability.

[0005] This application provides a hot melt adhesive comprising the following raw materials in parts by weight:

[0006] 100 parts of base resin, wherein the base resin is butyl rubber;

[0007] 70 parts of tackifier, wherein the tackifier is a mixture of silicone-modified epoxy resin, polymethyl methacrylate, syndiotactic polystyrene and polyethylene block copolymer, wherein the molar ratio of silicone-modified epoxy resin, polymethyl methacrylate, syndiotactic polystyrene and polyethylene block copolymer is 6:3:1;

[0008] 15 parts of a regulator, wherein the regulator is paraffin wax;

[0009] Three parts of plastic additives, wherein the plastic additives are organic ultraviolet light absorbers;

[0010] 25 parts of filler, wherein the filler is talc powder;

[0011] 1.0-3.0 parts of trimethylolpropane triacrylate;

[0012] Allyl polyoxyethylene ether, 2.0-5.0 parts;

[0013] The weight ratio of trimethylolpropane triacrylate to allyl polyoxyethylene ether is 1:1.5-1:2.0.

[0014] Furthermore, the organosilicon-modified epoxy resin is prepared by a condensation reaction of bisphenol A propane epoxy resin and dimethyl polysiloxane.

[0015] Furthermore, the allyl polyoxyethylene ether is composed of conventional allyl polyoxyethylene ether and hydrophobically modified allyl polyoxyethylene ether, with a weight ratio of 3:7 to 7:3.

[0016] Furthermore, the conventional allyl polyoxyethylene ether has a molecular weight of 900-1100 Da; the hydrophobically modified allyl polyoxyethylene ether has a molecular weight of 1200-1500 Da, and its hydrophobic end group is an alkyl or trimethylsiloxane with 12-18 carbon atoms.

[0017] Furthermore, the hydrophobically modified allyl polyoxyethylene ether is prepared by the following method: under nitrogen protection, conventional allyl polyoxyethylene ether, dodecyl bromide and sodium hydroxide are added to a reactor in a molar ratio of 1:1.1:1.2, toluene is added to make the concentration of conventional allyl polyoxyethylene ether 25wt%, the reaction is stirred at 90°C for 6 hours, after the reaction is completed, the mixture is cooled, filtered, washed, dried and the toluene is removed by vacuum distillation to obtain hydrophobically modified allyl polyoxyethylene ether with dodecyl ether at the end.

[0018] A method for preparing a hot melt adhesive includes the following steps:

[0019] Step 1, Basic melt mixing: Weigh each raw material according to the weight parts, add butyl rubber and silicone modified epoxy resin to the reactor, heat to 110℃-120℃, melt and stir at 60-120 rpm for 60-100 min, then add talc powder of 70% of the total weight of filler, and continue stirring for 15-30 min to obtain the first-stage mixture;

[0020] Step 2: Mixing thickener and UV absorber: Add polymethyl methacrylate, syndiotactic polystyrene-polyethylene block copolymer and UV absorber to the primary mixture, heat to 130℃-150℃, and stir at 80-150 rpm for 20-40 min.

[0021] Step 3, Synergistic addition of trimethylolpropane triacrylate and allyl polyoxyethylene ether: Trimethylolpropane triacrylate and allyl polyoxyethylene ether are premixed at room temperature and stirred for 10-20 min to form a premix; the premix is ​​added dropwise to the reaction system of step 2 at a rate of 0.5-2.0 parts / min, while maintaining the temperature at 135℃-150℃ and the stirring speed at 120-180 rpm during the dropwise addition; after the dropwise addition is completed, stirring is continued at the same temperature for 30-50 min, and then the temperature is lowered to 100℃-120℃ to obtain a secondary mixture;

[0022] Step 4: Mix the regulator and the remaining filler: Add the regulator and talc powder (30% of the total weight of the filler) to the secondary mixture, and stir at 60-100 rpm for 30-60 minutes at 95℃-115℃.

[0023] Step 5, Molding and Cooling: The mixture obtained in Step 4 is extruded and molded at 90℃-105℃ using an extruder, and then cooled and cured to obtain a hot melt adhesive product.

[0024] Furthermore, the allyl polyoxyethylene ether is composed of conventional allyl polyoxyethylene ether and hydrophobically modified allyl polyoxyethylene ether, with a weight ratio of 3:7-7:3. In step 3, the hydrophobically modified allyl polyoxyethylene ether is first added dropwise to the reaction system at a rate of 0.3-0.8 parts / min at 140℃-145℃, and stirring is continued for 20-30 min after the addition. Then, trimethylolpropane triacrylate is premixed with conventional allyl polyoxyethylene ether and added dropwise to the reaction system at a rate of 0.8-1.5 parts / min, and stirring is continued for 30-50 min after the addition. Then, the temperature is lowered to 100℃-120℃ to obtain a secondary mixture.

[0025] A seal for automobiles, outdoor equipment, or cryogenic pipelines, comprising the hot melt adhesive as an adhesive or sealing material.

[0026] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0027] By synergistically introducing TMPTA and APEG, precise control of the hot melt adhesive polymer network structure was achieved at the molecular design level. TMPTA contributed rigid crosslinking points to enhance network strength, while APEG introduced flexible segments to improve low-temperature flexibility. Through chemical reaction competition and optimized network topology design, the two produced a significant synergistic effect. This synergistic effect not only effectively suppressed the embrittlement problem that easily occurs when TMPTA is used alone, but also showed good compatibility with other components in the original system and generated positive interactions. Ultimately, the resulting hot melt adhesive product maintained excellent adhesive performance while achieving synergistic and significant improvements in low-temperature flexibility, low-temperature elongation at break, and resistance to humid heat aging.

[0028] By combining conventional APEG with hydrophobically modified APEG, precise control and functional design of the chemical structure of hot melt adhesive polymer networks were achieved at the molecular level. Conventional APEG ensured and optimized the basic flexibility of the network, while hydrophobically modified APEG, through its interfacial migration properties, constructed a hydrophobic barrier bonded to the network at the microscopic level. Together with TMPTA as the crosslinking center, they formed a composite crosslinked network structure integrating high strength, high flexibility, and high environmental stability. This synergistic mechanism enabled the prepared hot melt adhesive to maintain excellent initial adhesion, superior low-temperature flexibility, and good mechanical balance, while significantly and synergistically enhancing its water resistance, resistance to damp heat aging, and long-term service reliability in humid environments. This effectively solved the technical problem of insufficient durability of materials in high-humidity application environments.

[0029] By implementing a step-by-step sequential addition process, the performance of hot melt adhesives, especially their resistance to damp heat aging and low-temperature toughness, is synergistically and significantly improved. Experimental results show that, with identical formulation components, materials prepared using this process retain over 96% of their damp heat aging performance, further reducing the low-temperature flexibility temperature to -76.8°C, and simultaneously increasing the elongation at break at -50°C, while maintaining excellent basic adhesion and mechanical properties. This process synergistically improves the low-temperature toughness, mechanical balance, and resistance to damp heat aging of hot melt adhesives, making them particularly suitable for applications with stringent requirements for comprehensive material performance, such as automotive manufacturing, outdoor equipment, and low-temperature pipeline sealing. Detailed Implementation

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0031] Example 1: A hot melt adhesive, composed of the following raw materials in parts by weight:

[0032] Base resin: 100 parts, wherein the base resin is butyl rubber;

[0033] Tackifier: 70 parts, wherein the tackifier is a mixture of silicone-modified epoxy resin, polymethyl methacrylate, syndiotactic polystyrene and polyethylene block copolymer, wherein the molar ratio of silicone-modified epoxy resin, polymethyl methacrylate, syndiotactic polystyrene and polyethylene block copolymer is 6:3:1;

[0034] Modifier: 15 parts, wherein the modifier is paraffin;

[0035] Plastic additives: 3 parts, wherein the plastic additives are ultraviolet light absorbers, preferably organic ultraviolet light absorbers;

[0036] Filler: 25 parts, wherein the filler is talc powder;

[0037] Trimethylolpropane triacrylate (TMPTA): 1.0-3.0 parts;

[0038] Allyl polyoxyethylene ether (APEG, molecular weight 900-1100 Da): 2.0-5.0 parts;

[0039] The weight ratio of TMPTA to APEG is 1:1.5-1:2.0.

[0040] The organosilicon-modified epoxy resin is prepared by a condensation reaction of bisphenol A propane epoxy resin and dimethyl polysiloxane.

[0041] The preparation of the hot melt adhesive specifically includes the following steps:

[0042] Step 1, Basic melt mixing:

[0043] Weigh each raw material according to the specified weight proportions, add butyl rubber and silicone-modified epoxy resin to the reactor, heat to 110℃-120℃, and melt and stir for 60-100 minutes at a stirring speed of 60-120 rpm. Then add 70% of the total weight of filler talc powder and continue stirring for 15-30 minutes to obtain the first-grade mixture.

[0044] Step 2: Mix the tackifier and UV absorber:

[0045] Add polymethyl methacrylate, syndiotactic polystyrene-polyethylene block copolymer and ultraviolet light absorber sequentially to the primary mixture, raise the temperature to 130℃-150℃, and stir and mix for 20-40 minutes at a stirring speed of 80-150 rpm.

[0046] Step 3: Synergistic addition of TMPTA and APEG:

[0047] Trimethylolpropane triacrylate (TMPTA) and allyl polyoxyethylene ether (APEG) were premixed at room temperature and stirred for 10-20 minutes to form a homogeneous premix.

[0048] The premixed liquid is slowly added dropwise to the reaction system of step 2, with the dropping rate controlled at 0.5-2.0 parts / min. During the dropping process, the temperature is maintained at 135℃-150℃, and the stirring speed is 120-180 rpm. After the dropping is completed, the mixture is stirred and mixed for another 30-50 minutes at the same temperature. Then, the temperature is lowered to 100℃-120℃ to obtain the secondary mixture.

[0049] Step 4: Mix the conditioner with the remaining filler.

[0050] Add paraffin wax as a regulator and talc powder (30% of the total weight of filler) to the secondary mixture, and stir at 95℃-115℃ for 30-60 minutes at a stirring speed of 60-100 rpm.

[0051] Step 5, Molding and Cooling:

[0052] The mixture obtained in step 4 is extruded through an extruder at an extrusion temperature of 90℃-105℃. The extrudate is then cooled and solidified to obtain a hot melt adhesive product.

[0053] Experiments were conducted on the technical solution of this embodiment to verify the effects of TMPTA and APEG on the properties of hot melt adhesive.

[0054] I. Experimental Formulation Design: The following components were fixed in weight parts: base resin (butyl rubber): 100 parts, tackifier: 70 parts (42 parts of silicone-modified epoxy resin, 21 parts of polymethyl methacrylate, 7 parts of syndiotactic polystyrene and polyethylene block copolymer, molar ratio 6:3:1), regulator (paraffin): 15 parts, plastic additives (organic ultraviolet light absorber): 3 parts, filler (talc): 25 parts;

[0055] Six experimental groups were designed, with three parallel samples in each group. The experimental groups are shown in Table 1 below:

[0056] Table 1 Experimental Groups and Amounts of TMPTA and APEG Added

[0057]

[0058] II. Preparation process parameters: All groups follow the unified preparation process of this embodiment, and the specific process parameters are as follows:

[0059] Step 1: Basic Melt Mixing: Weigh each raw material according to the specified weight proportions. Add butyl rubber and silicone-modified epoxy resin to the reactor, heat to 115℃ and maintain this temperature. Start stirring, set the speed to 90 rpm, and continue melting and stirring for 80 minutes. At the 60-minute mark of stirring, add talc powder (17.5 parts), accounting for 70% of the total filler weight, to the system. After adding the filler, continue stirring for 20 minutes. After this process, the materials are uniformly mixed, yielding a primary mixture.

[0060] Step 2: Mixing the tackifier and UV absorber: Add the remaining components of the tackifier to the primary mixture sequentially. First, add polymethyl methacrylate and mix for 10 minutes while maintaining a stirring speed of 115 rpm. Then, add the syndiotactic polystyrene-polyethylene block copolymer and continue stirring for 10 minutes. Finally, add the UV absorber. During this process, gradually raise the system temperature to 140°C. After adding the UV absorber, continue stirring for 10 minutes at 140°C and 115 rpm to ensure thorough mixing and initial reaction of the components.

[0061] Step 3, Synergistic addition of TMPTA and APEG: The operation of this step varies depending on the experimental group, but all are carried out at the same starting temperature of 140℃, and the stirring speed is uniformly increased to 150 rpm.

[0062] Comparative Example A: Without adding TMPTA and APEG, after completing step 2, the material was directly cooled to 110°C to obtain a secondary mixture.

[0063] Comparative Example B: TMPTA was added only. TMPTA was added dropwise to the reaction system at a rate of 1.0 parts / min, and the addition process took 2 min. After the addition was complete, the mixture was stirred continuously at 140°C for 40 min, and then cooled to 110°C.

[0064] Comparative Example C: APEG only. APEG was added dropwise to the reaction system at a rate of 1.17 parts / min, and the addition process took 3 minutes. Subsequent stirring and cooling operations were the same as in Comparative Example B.

[0065] Experimental groups 1, 2, and 3: TMPTA and APEG were added simultaneously. The two were premixed according to the formulation ratio at room temperature and mechanically stirred for 15 min to form a homogeneous premix. Then, the premix was added dropwise to the reaction system at specific rates: Experimental group 1 (total addition 3.0 parts) had a dropping rate of 1.0 parts / min for 3 min; Experimental group 2 (total addition 5.5 parts) had a dropping rate of 1.1 parts / min for 5 min; and Experimental group 3 (total addition 8.0 parts) had a dropping rate of 1.14 parts / min for 7 min. After the addition was complete, all experimental groups were stirred at 140℃ for 40 min, then cooled to 110℃ to obtain a secondary mixture.

[0066] Step 4: Mixing the regulator and remaining filler: Add all the regulator (15 parts paraffin) and the remaining 30% talc powder (7.5 parts) to the cooled secondary mixture. Maintain the system temperature at 105℃, adjust the stirring speed to 80 rpm, and mix for 45 minutes.

[0067] Step 5, Molding and Cooling: Transfer the final mixture obtained in Step 4 to a single-screw extruder. Set the extruder temperature to 95-100℃ and the screw speed to 30 rpm, and use a 2mm thick sheet die for extrusion molding. The extruded hot melt adhesive sheet is then air-cured at room temperature (25℃). Finally, the cooled sheet is cut into standard test strips that meet the requirements of various performance tests for later use.

[0068] III. Performance Testing Standards and Methods:

[0069] 1. Adhesion test: The hot melt adhesive strip was peeled from the copper substrate at 180° according to the GB / T 2791 standard. The sample width was 25 mm. The peel strength was determined at a loading speed of 100 mm / min under the standard ambient temperature of 23±2℃. The results are expressed as Newtons per 25 mm (N / 25 mm). Five samples were tested in parallel for each group.

[0070] 2. Low-temperature flexibility test: Referring to the test principle of ASTM D3111, the specimen in a non-stretched state is placed in a programmable temperature-controlled environment and cooled at a rate of 2℃ / min. The temperature at which the specimen first shows visible cracks or breaks is observed and recorded. This temperature is defined as the low-temperature flexibility temperature of the material.

[0071] 3. Elongation at break test: The test was conducted at a low temperature of -50℃. Type IV dumbbell specimens were prepared according to ASTM D638 standard. The elongation at break was tested in a low temperature test chamber at a tensile speed of 50 mm / min. The elongation at break was calculated as follows: Elongation at break = (gauge length at break - original gauge length) / original gauge length × 100%.

[0072] 4. Tensile properties test at room temperature: According to ASTM D638 standard, the tensile strength and elongation at break of the type IV dumbbell specimens were tested at room temperature of 23±2℃. The loading speed was set to 50 mm / min to obtain the basic mechanical properties of the material under normal use conditions.

[0073] 5. Damp heat aging performance test (damp heat aging retention rate): The test was conducted according to the relevant methods of GB / T 1690-2010. The dumbbell samples were placed in a constant temperature and humidity test chamber at 85℃ and 85% relative humidity for 168 hours (7 days). After aging, the samples were restored to standard environmental conditions (23℃, 50%RH) for 24 hours, and then their tensile strength and elongation at break were tested again. The tensile strength retention rate and elongation at break retention rate were obtained by calculating the ratio of the properties before and after aging. The tensile strength retention rate (%) = (tensile strength after aging / tensile strength before aging) × 100%, and the elongation at break retention rate (%) = (elongation at break after aging / elongation at break before aging) × 100%.

[0074] The performance test results are shown in Table 2 below:

[0075] Table 2 Results of hot melt adhesive performance tests for each experimental group

[0076]

[0077] Experimental results show that the addition of TMPTA and APEG significantly affects material properties. Adding TMPTA alone improves room temperature tensile strength but impairs low-temperature flexibility and toughness, and results in poor aging resistance. Adding APEG alone improves low-temperature performance and aging resistance but reduces room temperature strength. When both are added synergistically in an appropriate ratio (e.g., 1:1.5-1:2.0), the embrittlement problem caused by using TMPTA alone can be effectively solved, and the low-temperature performance, mechanical balance, and aging resistance of the hot melt adhesive can be comprehensively optimized.

[0078] The technical solutions described in the embodiments of this application have at least the following technical effects or advantages:

[0079] This embodiment introduces trimethylolpropane triacrylate (TMPTA) and allyl polyoxyethylene ether (APEG) to overcome the bottleneck of low-temperature toughness improvement and insufficient long-term durability in the original system. By constructing a more refined and controllable polymer network structure, while maintaining excellent initial adhesion performance, it synergistically improves the material's low-temperature flexibility, mechanical balance and resistance to humid heat aging.

[0080] Trimethylolpropane triacrylate, a trifunctional acrylate monomer, undergoes a free radical addition reaction during the reaction process. The three acrylate double bonds on its molecule can be initiated by free radicals generated from the thermal decomposition of the UV absorber, reacting with the unsaturated bonds on the butyl rubber molecular chain and the active groups of the silicone-modified epoxy resin. This process introduces additional, uniformly distributed chemical crosslinking points into the system, effectively increasing the crosslinking density of the polymer network, thereby improving the bulk strength, modulus, and shape stability of the material.

[0081] Allyl polyoxyethylene ether is a functional monomer containing terminal allyl groups in a long-chain polyether structure. Its function is twofold: first, the terminal allyl groups can participate in the free radical copolymerization reaction of the system, thereby grafting flexible polyoxyethylene long chains onto the polymer backbone; second, its polyoxyethylene segments possess excellent segmental mobility and flexibility, maintaining a certain degree of mobility even at low temperatures. Its introduction contributes long-range flexible connecting segments to the material network, helping to lower the glass transition temperature of the material and significantly improving its deformation capacity and resistance to brittleness under low-temperature conditions.

[0082] The synergistic effect of TMPTA and APEG is based on the complementarity and optimization of chemical reactivity and network construction. Specifically: First, during the free radical reaction, the allyl group of APEG and the acrylate double bond of TMPTA compete for reaction. This competition can moderately divert active free radicals, thereby inhibiting the self-aggregation tendency between TMPTA molecules and improving its efficiency as an effective network crosslinking point. Second, and more importantly, TMPTA, as a rigid multifunctional crosslinking center, combined with the flexible long chains provided by APEG, guides the formation of a composite network topology with alternating distributions of rigid crosslinking points and flexible connecting chains at the microscopic level. This structure allows stress to be transmitted and dissipated more uniformly within the material, achieving a balance between high strength and high toughness at the macroscopic level, and significantly improving the flexibility and tensile properties of the material at extreme low temperatures.

[0083] This synergistic system also exhibits positive interactions with other substances in the raw materials. The polyether segments of APEG and the siloxane segments in the silicone-modified epoxy resin have a certain degree of polar compatibility, which can improve the interfacial bonding of the multiphase system, reduce phase separation, and thus further enhance the uniformity and durability of the material. The talc filler pre-existing in the system can be partially coated or interact with by the flexible segments of APEG, improving the interfacial properties between the filler and the polymer matrix, enabling stress transfer during deformation, and positively impacting the final product's resistance to humid heat aging.

[0084] Example 2: The above examples, through the synergistic introduction of TMPTA and APEG, achieved precise control over the network structure of the hot melt adhesive polymer at the molecular design level. TMPTA contributed rigid crosslinking points to enhance network strength, while APEG introduced flexible segments to improve low-temperature flexibility. The two produced a significant synergistic effect through chemical reaction competition and optimized network topology design. This synergistic effect not only effectively suppressed the embrittlement problem easily caused by using TMPTA alone, but also showed good compatibility with other components in the original system and generated positive interactions. Ultimately, the resulting hot melt adhesive product maintained excellent adhesive performance while achieving synergistic and significant improvements in low-temperature flexibility, low-temperature elongation at break, and resistance to damp heat aging. To further improve its overall performance, further improvements were made based on Example 1.

[0085] The APEG is composed of conventional APEG and hydrophobically modified APEG, with a weight ratio of 3:7-7:3. The conventional APEG is an allyl polyoxyethylene ether with a molecular weight of 900-1100 Da, one end of which is allyl and the other end of which is hydroxyl.

[0086] The hydrophobically modified APEG is a product obtained by chemically modifying the terminal hydroxyl groups of conventional APEG to hydrophobic end. The hydrophobic end groups are preferably alkyl or trimethylsiloxane groups with 12-18 carbon atoms, and the molecular weight is 1200-1500 Da.

[0087] The preparation method of the hydrophobically modified APEG is as follows: Under nitrogen protection, conventional allyl polyoxyethylene ether (APEG) with a molecular weight of 1000±100 Da, dodecyl bromide, and sodium hydroxide powder are added to a reactor at a molar ratio of 1:1.1:1.2, and toluene is added to make the concentration of APEG 25 wt%. The mixture is stirred at 90°C for 6 hours. After the reaction is completed, it is cooled to room temperature, and the generated sodium bromide solid is removed by filtration. The filtrate is washed successively with 5 wt% dilute hydrochloric acid and deionized water until neutral. The organic phase is separated, dried with anhydrous sodium sulfate, and then distilled under reduced pressure at 60°C and -0.09 MPa to remove toluene, thereby obtaining hydrophobically modified APEG with dodecyl ether at the end.

[0088] Based on Experimental Group 2 of Example 1 (2.0 parts TMPTA, 3.5 parts APEG, ratio 1:1.75), this embodiment maintains the same TMPTA addition of 2.0 parts and total APEG addition of 3.5 parts. The APEG component is adjusted to a mixture of conventional APEG and hydrophobically modified APEG (terminated dodecyl ether) prepared by the above method to verify the effectiveness of this improved scheme. A total of 5 experimental groups were designed, with 3 parallel samples prepared in each group. The specific groupings are shown in Table 3 below.

[0089] Table 3 Experimental Groups and APEG Composition

[0090]

[0091] The performance test results are shown in Table 4 below:

[0092] Table 4. Test results of hot melt adhesive properties under different ratios of conventional APEG and hydrophobically modified APEG.

[0093]

[0094] Experimental results show that, based on the TMPTA and APEG synergistic system, optimizing the APEG component into a combination of conventional APEG and hydrophobically modified APEG is an effective improvement scheme. When the two are used in a 1:1 weight ratio (experimental group 5), the prepared hot melt adhesive maintains and even optimizes its core low-temperature toughness, mechanical strength, and adhesive properties, while achieving a significant and synergistic improvement in resistance to humid heat aging. Therefore, introducing hydrophobic functional segments through molecular design can specifically address the durability problem of materials in humid environments without sacrificing the main properties.

[0095] The technical solutions described in the embodiments of this application have at least the following technical effects or advantages:

[0096] This solution further improves the APEG component to a combination of conventional APEG and hydrophobically modified APEG. The core objective of this design is to specifically enhance the water resistance and hygrothermal aging stability of the hot melt adhesive while maintaining and optimizing the existing low-temperature flexibility and mechanical balance of the system. This addresses the performance degradation issue that occurs when the material is used for a long time in high-temperature and high-humidity environments, thereby broadening its application reliability in humid and harsh environments (such as outdoor, automotive chassis, and high-humidity industrial settings).

[0097] The role of hydrophobically modified APEG (through hydrophobic end-capping of the hydroxyl groups of conventional APEG) is dual: firstly, the retained allyl groups ensure that it can also participate in the aforementioned free radical copolymerization reaction, becoming part of the polymer network; secondly, the hydrophobic long-chain alkyl or siloxane groups at its ends, due to thermodynamic incompatibility with the hydrophilic polyether segments and polar matrix, tend to undergo interfacial migration during the reaction process. Specifically, these hydrophobic segments are more likely to accumulate in the interfacial region between the inorganic filler (talc) and the organic polymer matrix, and to some extent form hydrophobic microregions within the polymer phase.

[0098] The two types of APEG play complementary and synergistic physicochemical roles in polymer network construction. Conventional APEG participates in copolymerization through its terminal allyl groups, introducing hydrophilic and flexible long-chain polyoxyethylene segments into the network, primarily responsible for ensuring the material's chain mobility and basic toughness. While also participating in the copolymerization reaction, the hydrophobically modified APEG's terminal hydrophobic long-chain alkyl groups, due to their thermodynamic incompatibility with the polar matrix, spontaneously migrate and accumulate at the filler-matrix interface and phase domain interface during processing. This process microscopically forms local barriers composed of chemically bonded hydrophobic segments within the network. These hydrophobic regions effectively block the penetration and diffusion of water molecules into the material's interior, particularly protecting the ester crosslinking sites formed by TMPTA and the hydrophilic polyether segments from water swelling and hydrolytic erosion, thereby fundamentally improving the network's hygrothermal stability.

[0099] The two types of APEG and the multifunctional crosslinking agent TMPTA exhibited a deeper synergistic effect. TMPTA constructed a rigid three-dimensional crosslinked network framework, providing strength and shape stability; conventional APEG filled the spaces between the framework with flexible connections, ensuring toughness; and hydrophobically modified APEG added hydrophobic protection to the entire network, especially at the filler interfaces where stress is easily concentrated and environmental corrosion is susceptible. The combined effect of these three agents achieved an integrated improvement in network strength, toughness, and durability. Furthermore, the modification of the filler interface by hydrophobically modified APEG enhanced the interfacial compatibility and bonding force between the filler and the polymer matrix, further improving stress transfer efficiency and the integrity of the overall structure.

[0100] Example 3: Example 2 above, by combining conventional APEG and hydrophobically modified APEG, achieved precise control and functional design of the hot melt adhesive polymer network chemical structure at the molecular level. Conventional APEG ensured and optimized the basic flexibility of the network, while the hydrophobically modified APEG, through its interfacial migration properties, constructed a hydrophobic barrier bonded to the network at the microscopic level. Together with TMPTA as the crosslinking center, they formed a composite crosslinked network structure integrating high strength, high flexibility, and high environmental stability. This synergistic mechanism enabled the prepared hot melt adhesive to maintain excellent initial adhesion, superior low-temperature flexibility, and good mechanical balance, while significantly and synergistically enhancing its water resistance, resistance to damp heat aging, and long-term service reliability in humid environments, effectively solving the technical problem of insufficient durability of materials in high-humidity application environments. To further improve its overall performance, further improvements were made based on Example 2.

[0101] The conventional APEG and the hydrophobically modified APEG are added in steps 3, specifically as follows:

[0102] Step 3.1: Maintain the reaction system temperature from Step 2 at 140℃-145℃. Slowly add the hydrophobically modified APEG from the formulation to the reaction system at a rate of 0.3-0.8 parts / minute. After the addition is complete, continue stirring the reaction at this temperature for 20-30 minutes.

[0103] Step 3.2: After completing Step 3.1, maintain the system temperature at 140℃-145℃. Premix trimethylolpropane triacrylate (TMPTA) from the formulation with conventional APEG at room temperature and stir for 10-20 minutes to form a homogeneous premix. Add this premix dropwise to the reaction system at a rate of 0.8-1.5 parts / minute. After the addition is complete, continue stirring and mixing at the same temperature for 30-50 minutes. After the reaction is complete, lower the system temperature to 100℃-120℃ to obtain the secondary mixture.

[0104] Based on Experiment 5 of Embodiment 2, this embodiment's technical solution is tested as Experiment 8. The difference between Experiment 8 and Experiment 5 is that in Experiment 8, standard APEG and hydrophobically modified APEG are added separately in step 3. The specific steps are as follows:

[0105] Under stirring conditions of 140℃ and 150 rpm, hydrophobically modified APEG (1.75 parts) was slowly added dropwise to the reaction system at a rate of 0.5 parts / min. After the addition was completed, stirring was continued at 140℃ for 25 minutes.

[0106] TMPTA (2.0 parts) and conventional APEG (1.75 parts) were premixed at room temperature and mechanically stirred for 15 minutes. Maintaining the system temperature at 140°C and the stirring speed at 150 rpm, the premix was added dropwise to the reaction system at a rate of 1.1 parts / minute. After the addition was complete, stirring was continued at 140°C for 40 minutes. The system temperature was then lowered to 110°C to obtain the secondary mixture.

[0107] The test results are shown in Table 5 below:

[0108] Table 5. Effect of step-by-step sequential addition process on hot melt adhesive properties

[0109]

[0110] Experimental results show that, under the premise of the exact same formula, the step-by-step sequential addition process has a positive and significant regulatory effect on the overall performance of hot melt adhesive compared with the traditional one-time premixing addition, especially in terms of moisture heat aging resistance and low temperature toughness.

[0111] The technical solutions described in the embodiments of this application have at least the following technical effects or advantages:

[0112] By implementing a step-by-step sequential addition process, a synergistic and significant improvement in the performance of hot melt adhesives, particularly in resistance to damp heat aging and low-temperature toughness, was achieved. Experimental results show that, under the premise of identical formulation components, materials prepared using this process exhibit a performance retention rate of over 96% after damp heat aging, a further reduction in the low-temperature flexibility temperature to -76.8°C, and a simultaneous increase in elongation at break at -50°C, while maintaining excellent basic adhesion and mechanical properties.

[0113] The underlying technology lies in the precise control of the reaction sequence, enabling the gradient and ordered construction of the polymer network microstructure. Specifically, the process first introduces hydrophobically modified APEG separately in the early stage of the reaction. This allows the terminal allyl groups to preferentially graft onto the active sites on the filler surface, silicone epoxy resin, and butyl rubber chains, minimizing competitive reaction conditions. Simultaneously, its hydrophobic long-chain alkyl groups, driven by thermodynamics, spontaneously and fully migrate and anchor at the interface between the filler and the matrix, thus forming a chemically bonded, dense, endogenous hydrophobic interface layer. Subsequently, the TMPTA and conventional APEG premix added in the second step undergo large-scale free radical copolymerization and crosslinking reactions on the established framework of the hydrophobic interface layer, constructing a main network that provides overall strength and bulk flexibility. This sequential reaction, prioritizing the interface and then the bulk, effectively avoids the complex competition and mutual interference of multiple functional monomers in a single reaction, optimizing the spatial distribution of the hydrophobic protective phase at the interface and the rigid-flexible structural phase in the bulk.

[0114] The result of this process is the formation of a composite cross-linked network structure with a clear functional gradient and excellent stability. It fundamentally solves the performance bottlenecks caused by uneven dispersion of hydrophobic components, insufficient interfacial modification, and entanglement interference of functional segments in traditional blending processes. The presence of a dense hydrophobic interfacial layer significantly hinders the penetration and diffusion of water molecules, thereby effectively protecting the easily hydrolyzed ester bonds (from TMPTA) and hydrophilic segments in the network. This is the direct reason for the breakthrough improvement in resistance to humid heat aging. Simultaneously, the construction of rigid cross-linking points and flexible segments in the bulk network is more ordered due to the reduction of physical interference from hydrophobic long chains, allowing for a greater release of chain mobility at low temperatures, resulting in a simultaneous improvement in low-temperature flexibility and toughness. Therefore, this stepwise addition process, by controlling the spatiotemporal sequence of molecular reactions, successfully transforms the chemical potential of the formulation design into more superior and balanced macroscopic properties, providing an effective technological solution to overcome the challenge of long-term durability of materials under low-temperature and high-humidity environments.

[0115] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A hot melt adhesive, characterized in that, Including the following parts by weight of raw materials: 100 parts of base resin, wherein the base resin is butyl rubber; 70 parts of tackifier, wherein the tackifier is a mixture of silicone-modified epoxy resin, polymethyl methacrylate, syndiotactic polystyrene and polyethylene block copolymer, wherein the molar ratio of silicone-modified epoxy resin, polymethyl methacrylate, syndiotactic polystyrene and polyethylene block copolymer is 6:3:1; 15 parts of a regulator, wherein the regulator is paraffin wax; Three parts of plastic additives, wherein the plastic additives are organic ultraviolet light absorbers; 25 parts of filler, wherein the filler is talc powder; 1.0-3.0 parts of trimethylolpropane triacrylate; Allyl polyoxyethylene ether, 2.0-5.0 parts; The weight ratio of trimethylolpropane triacrylate to allyl polyoxyethylene ether is 1:1.5-1:2.

0.

2. The hot melt adhesive as described in claim 1, characterized in that, The organosilicon-modified epoxy resin is prepared by a condensation reaction of bisphenol A propane epoxy resin and dimethyl polysiloxane.

3. The hot melt adhesive as described in claim 1, characterized in that, The allyl polyoxyethylene ether is composed of conventional allyl polyoxyethylene ether and hydrophobically modified allyl polyoxyethylene ether, with a weight ratio of 3:7-7:

3.

4. The hot melt adhesive as described in claim 3, characterized in that, The conventional allyl polyoxyethylene ether has a molecular weight of 900-1100 Da; the hydrophobically modified allyl polyoxyethylene ether has a molecular weight of 1200-1500 Da, and its hydrophobic end group is an alkyl or trimethylsiloxane with 12-18 carbon atoms.

5. The hot melt adhesive as described in claim 4, characterized in that, The hydrophobically modified allyl polyoxyethylene ether was prepared by the following method: under nitrogen protection, conventional allyl polyoxyethylene ether, dodecyl bromide and sodium hydroxide were added to a reactor in a molar ratio of 1:1.1:1.

2. Toluene was added to make the concentration of conventional allyl polyoxyethylene ether 25 wt%. The reaction was stirred at 90 °C for 6 hours. After the reaction was completed, the mixture was cooled, filtered, washed, dried and the toluene was removed by vacuum distillation to obtain a hydrophobically modified allyl polyoxyethylene ether with dodecyl ether at the end.

6. A method for preparing a hot melt adhesive, characterized in that, Includes the following steps: Step 1, Basic melt mixing: Weigh each raw material according to the weight parts, add butyl rubber and silicone modified epoxy resin to the reactor, heat to 110℃-120℃, melt and stir at 60-120 rpm for 60-100 min, then add talc powder of 70% of the total weight of filler, and continue stirring for 15-30 min to obtain the first-stage mixture; Step 2: Mixing thickener and UV absorber: Add polymethyl methacrylate, syndiotactic polystyrene-polyethylene block copolymer and UV absorber to the primary mixture, heat to 130℃-150℃, and stir at 80-150 rpm for 20-40 min. Step 3, Synergistic addition of trimethylolpropane triacrylate and allyl polyoxyethylene ether: Trimethylolpropane triacrylate and allyl polyoxyethylene ether are premixed at room temperature and stirred for 10-20 min to form a premix; the premix is ​​added dropwise to the reaction system of step 2 at a rate of 0.5-2.0 parts / min, while maintaining the temperature at 135℃-150℃ and the stirring speed at 120-180 rpm during the dropwise addition; after the dropwise addition is completed, stirring is continued at the same temperature for 30-50 min, and then the temperature is lowered to 100℃-120℃ to obtain a secondary mixture; Step 4: Mix the regulator and the remaining filler: Add the regulator and talc powder (30% of the total weight of the filler) to the secondary mixture, and stir at 60-100 rpm for 30-60 minutes at 95℃-115℃. Step 5, Molding and Cooling: The mixture obtained in Step 4 is extruded and molded at 90℃-105℃ using an extruder, and then cooled and cured to obtain a hot melt adhesive product.

7. The method for preparing hot melt adhesive as described in claim 6, characterized in that, The allyl polyoxyethylene ether is composed of conventional allyl polyoxyethylene ether and hydrophobically modified allyl polyoxyethylene ether, with a weight ratio of 3:7-7:

3. In step 3, the hydrophobically modified allyl polyoxyethylene ether is first added dropwise to the reaction system at a rate of 0.3-0.8 parts / min at 140℃-145℃, and stirring is continued for 20-30 min after the addition. Then, trimethylolpropane triacrylate is premixed with conventional allyl polyoxyethylene ether and added dropwise to the reaction system at a rate of 0.8-1.5 parts / min, and stirring is continued for 30-50 min after the addition. Then, the temperature is lowered to 100℃-120℃ to obtain a secondary mixture.

8. A seal for automobiles, outdoor equipment, or cryogenic pipelines, characterized in that, It includes the hot melt adhesive as described in any one of claims 1 to 3 as an adhesive or sealant.

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