Preparation method of high-temperature-resistant polyurethane reactive hot melt adhesive

Abstract

The application relates to the field of high-molecular materials, and discloses a preparation method of high-temperature-resistant polyurethane reactive hot melt adhesive, which comprises the following steps: firstly, pre-reacting a synergistic network builder with a reactive carrier diol under heating to prepare a clear and uniform liquid-state zinc-containing reactive carrier; and then, adding the liquid-state carrier into a polyurethane prepolymer prepared by reacting a main diol, a functional diol and a diisocyanate. The method realizes uniform anchoring of metal ions at a molecular level in a polymer matrix through chemical bonding of the reactive carrier, and builds a dense synergistic network. The application solves the technical contradiction between high-temperature resistance and excellent melt processability, and the prepared hot melt adhesive has high softening point, high mechanical strength and controlled melt viscosity. Through the specific pre-reaction process, the application builds a uniform ion synergistic network, and improves the heat resistance and mechanical strength of the material without sacrificing the processability.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a method for preparing a high-temperature-resistant polyurethane reactive hot melt adhesive. Background Technology

[0002] Polyurethane reactive hot melt adhesives (PURs) are widely used due to their combination of the rapid positioning properties of hot melt adhesives and the high final strength of reactive adhesives. However, before moisture curing, the bond strength of conventional polyurethane reactive hot melt adhesives mainly depends on the van der Waals forces between polymer chain segments. This leads to their significant thermoplastic behavior at high temperatures, resulting in a significant decrease in cohesive strength and making it difficult to meet increasingly stringent heat resistance requirements.

[0003] To improve its high-temperature resistance, existing technologies often attempt to introduce functional groups (such as carboxyl groups) capable of forming ionic crosslinking networks into the polyurethane molecular chain, and then construct thermally reversible ionic physical crosslinking points by adding metal salts (such as zinc acetate). However, this modification route faces serious technical bottlenecks in practice. Since metal salts are usually solid powders, while polyurethane prepolymers are high-viscosity fluids, it is extremely difficult to achieve uniform dispersion when directly adding solid metal salts to the system. This uneven dispersion leads to the formation of localized high-concentration regions of metal ions within the system, which in turn triggers uncontrollable rapid crosslinking reactions, often resulting in a sharp increase in the melt viscosity of the system or even gelation, ultimately causing the product to lose its flowability and processability. Furthermore, even if gelation is not observed macroscopically, this microscopic inhomogeneity will form network defects in the cured material, which not only limits the improvement of its heat resistance but also impairs the material's final mechanical strength and cohesion.

[0004] Therefore, the present invention provides a method for preparing a high-temperature resistant polyurethane reactive hot melt adhesive to overcome the shortcomings of the prior art. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing a high-temperature-resistant polyurethane reactive hot melt adhesive, which solves the problems of uneven metal salt dispersion and runaway melt viscosity caused by introducing a metal ion network into polyurethane hot melt adhesives to improve heat resistance.

[0006] To achieve the above objectives, the present invention provides the following technical solution: Firstly, the present invention provides a high-temperature resistant polyurethane reactive hot melt adhesive, which adopts the following technical solution: A high-temperature resistant polyurethane reactive hot melt adhesive is prepared by reacting raw materials comprising the following parts by weight: main diol: 100 parts; functional diol containing carboxyl functional groups: 0.5-1.5 parts; diisocyanate: 28-35 parts; reactive carrier diol: 3-8 parts; synergistic network builder: 0.4-1.0 parts.

[0007] By adopting the above technical solution, the present invention introduces a thermally reversible ionic physical cross-linking network between polyurethane backbones through the interaction of the side chain carboxyl groups of functional diols containing carboxyl functional groups with metal ions in a synergistic network builder (usually a divalent metal salt).

[0008] The innovative principle of this invention lies in the fact that the synergistic network builder is not added directly (direct addition easily leads to the aggregation of metal salts in the polymer matrix, causing uncontrolled viscosity and uneven performance of the system), but rather through pre-action with a specific reactive carrier diol. The specific technical mechanism is as follows:

[0009] Step 1): Intermediate Preparation: The synergistic network builder (divalent metal salt) is heated in a liquid reactive carrier diol. During this process, the reactive carrier diol acts as a solvent or coordination carrier for the metal ions, allowing the metal salt to dissolve uniformly and forming a clear, stable liquid reactive carrier intermediate containing metal ions.

[0010] Step 2): Main chain prepolymerization: The main diol, the functional diol containing carboxyl functional groups, and the diisocyanate react to form a polyurethane prepolymer containing terminal -NCO groups and side chain -COOH groups.

[0011] Step 3): Network Construction: The liquid intermediate obtained in Step 1) is added to the prepolymer in Step 2). At this time, the terminal hydroxyl groups of the reactive carrier diol in the intermediate will react with the terminal -NCO groups of the prepolymer.

[0012] Step 4): Uniform Anchoring: The reaction in Step 3) grafts the reactive carrier diol (and its carried metal ions) onto the polyurethane backbone via chemical bonds (urethane bonds). This achieves uniform dispersion and anchoring of the metal ions at the molecular level within the polymer matrix.

[0013] Ultimately, a dual synergistic network structure was constructed in the system: one is a chemically cross-linked network formed by the isocyanate reaction (formed after moisture curing); the other is a thermally reversible ionicly cross-linked network formed by uniformly anchored and distributed metal ions and side-chain carboxyl groups. This uniform ionic network structure effectively avoids the macroscopic aggregation of metal ions, endowing the adhesive with a high softening point and high temperature resistance, while maintaining a controlled melt viscosity suitable for application in the molten state, and significantly improving the cohesive strength and adhesive performance of the cured adhesive layer.

[0014] Preferably, the host diol is polypentyl adipate neopentyl glycol ester; the functional diol is dimethylolpropionic acid; the diisocyanate is diphenylmethane diisocyanate; the reactive carrier diol is hydroxyl-terminated polyethylene adipate; and the synergistic network builder is zinc acetate.

[0015] Preferably, the mass ratio of the reactive carrier diol to the synergistic network builder is 8:1 to 12:1. This ratio range ensures that the synergistic network builder (zinc acetate) forms a homogeneous, clear, and stable liquid intermediate in the reactive carrier diol, while introducing an appropriate number of ionic crosslinking sites into the system.

[0016] Preferably, the raw materials further comprise a catalyst, wherein the amount of catalyst is 50-150 ppm of the total mass of the main diol, functional diol, reactive carrier diol, and diisocyanate. This catalyst is used to promote the reaction between -NCO and -OH groups during the polyurethane synthesis process.

[0017] Secondly, the present invention provides a method for preparing the above-mentioned high-temperature-resistant polyurethane reactive hot melt adhesive, which adopts the following technical solution: A method for preparing a high-temperature-resistant polyurethane reactive hot melt adhesive includes the following steps:

[0018] a) Preparation of zinc-containing reactive support: The reactive support diol is mixed and reacted with the synergistic network builder under heating conditions to obtain a clear zinc-containing reactive support;

[0019] b) Synthesis of polyurethane prepolymer: The host diol, the functional diol and the diisocyanate are reacted to obtain a terminal-NCO polyurethane prepolymer containing side chain carboxyl groups;

[0020] c) Constructing a collaborative network: The zinc-containing reactive carrier obtained in step a) is added to the polyurethane prepolymer obtained in step b) to react and obtain a hot melt adhesive.

[0021] By adopting the above technical solution, the core of this preparation method lies in the pre-reaction process of step a). This method does not directly add the solid synergistic network builder (metal salt) to the polyurethane reaction system, thereby avoiding local over-crosslinking and viscosity runaway caused by uneven solid dispersion. This method utilizes the reactive carrier diol as a good solvent and reaction carrier for the metal salt to pre-prepare a uniform liquid zinc-containing reactive carrier.

[0022] In step c), the liquid carrier (which is itself a hydroxyl-terminated polyol) is introduced into the prepolymer. This allows the metal ions it carries to be uniformly distributed in the system, and its own hydroxyl groups participate in the end-capping and chain extension reactions of the main chain, achieving uniform anchoring of ionic crosslinking points on the molecular chain. This process design fundamentally solves the technical problem of uniform dispersion of metal ions in a polyurethane matrix, enabling the prepared product to possess both high temperature stability and excellent melt processing performance.

[0023] Preferably, in step a), the heating conditions are a reaction at 95-105°C for 60-120 minutes. This combination of process parameters ensures that the metal salt is completely dissolved in the reactive carrier diol and forms a homogeneous, clear intermediate free of solid particles.

[0024] Preferably, in step b), the reaction temperature is 80-85°C and the reaction time is 120-180 minutes. These mild reaction conditions are conducive to the stable reaction between the -NCO group and the hydroxyl group, resulting in a prepolymer with a uniform structure and controlled molecular weight distribution.

[0025] Preferably, in step c), the zinc-containing reactive carrier is added uniformly and continuously dropwise over 45-75 minutes. Using a dropwise addition method helps control the reaction heat and viscosity increase rate, avoiding localized gelation or uneven network formation caused by excessively rapid reaction.

[0026] Preferably, in step c), after the zinc-containing reactive support is added, the reaction continues at 85-90°C for 60-90 minutes. This heat preservation step ensures that the hydroxyl groups of the reactive support diol react fully with the -NCO groups of the prepolymer, resulting in complete network construction.

[0027] Preferably, after step c), a depressurization treatment is performed for 30-60 minutes at 95-105°C and a vacuum degree not exceeding -0.095 MPa. This step is used to remove residual trace volatiles (such as reaction byproducts or unreacted free isocyanate monomers) from the system, improving the purity and storage stability of the final product.

[0028] This invention provides a method for preparing a high-temperature-resistant polyurethane reactive hot melt adhesive. It has the following beneficial effects:

[0029] 1. This invention introduces metal ions to form a thermally reversible ionic crosslinking network with side-chain carboxyl groups. This network serves as additional physical crosslinking points, effectively enhancing the cohesive strength of the material. Crucially, through pre-reaction and chemical bonding, the molecular-level uniform distribution of this ionic network is ensured, avoiding network defects and effectively suppressing polymer creep at high temperatures, thus significantly improving the product's shear bond failure temperature (SAFT).

[0030] 2. This invention involves pre-reacting a solid metal salt with a reactive carrier diol to prepare a homogeneous and clear liquid intermediate. This specific process avoids the dispersion problem of solid powder in the high-viscosity polyurethane prepolymer system, fundamentally eliminates uncontrollable crosslinking caused by excessively high local ion concentrations, and ensures stable and controllable melt viscosity during preparation and sizing, making the product practically applicable.

[0031] 3. The uniform ionic network constructed in this invention interpenetrates with the chemical cross-linking network formed by moisture curing, creating a dense dual-network structure. This structure effectively enhances the material's resistance to external forces, resulting in significantly improved tensile strength, T-peel strength, and other key mechanical properties of the final cured product, thus meeting the requirements of more demanding adhesive applications. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Preparation Examples 1-2:

[0034] Preparation Example 1: Preparation of Zinc-Containing Reactive Support A

[0035] 200.0 g of reactive carrier diol (hydroxyl-terminated polyethylene adipate, Mn = 1000 g / mol) was added to a 500 mL four-necked flask equipped with a mechanical stirrer, thermometer, nitrogen protection, and vacuum system. Stirring was started, and the mixture was heated at 115 °C and a vacuum not exceeding -0.095 MPa for 60 minutes to remove water. After dehydration, the vacuum was stopped, and dry nitrogen was introduced for protection, lowering the system temperature to 100 °C. While maintaining stirring, 25.0 g of pre-dried anhydrous zinc acetate powder was slowly added in batches over 20 minutes. After the addition was complete, the reaction was continued at 100 °C for 90 minutes until the system was completely clear and transparent, with no visible solid particles. Zinc-containing reactive carrier A was obtained, with a reactive carrier diol to anhydrous zinc acetate mass ratio of 8:1. The product was kept at 95 °C for later use.

[0036] Preparation Example 2: Preparation of Zinc-Containing Reactive Support B

[0037] The preparation method is basically the same as in Preparation Example 1, except for the amount of each component. 240.0 g of reactive carrier diol (hydroxyl-terminated polyethylene adipate, Mn = 1000 g / mol) was added to a four-necked flask of the same apparatus. After the same dehydration and cooling steps, 20.0 g of pre-dried anhydrous zinc acetate powder was slowly added in batches at 100 °C. The reaction was continued at 100 °C with stirring for 90 minutes until the system became clear and transparent. Zinc-containing reactive carrier B was obtained, wherein the mass ratio of reactive carrier diol to anhydrous zinc acetate was 12:1. The product was kept at 95 °C for later use.

[0038] Examples 1-3:

[0039] Example 1:

[0040] This embodiment provides a specific preparation method for a high-temperature-resistant polyurethane reactive hot melt adhesive, wherein the molar ratio of hydroxyl groups in the main diol to the functional diol in the hydroxyl component is 90:10, and a reactive carrier A with high zinc content is used. The specific preparation steps include:

[0041] Add 180.0 g of the main diol (poly(neoprene adipate, Mn=2000 g / mol)) and 1.34 g of the functional diol (dimethylolpropionic acid) to a 1000 mL main reactor equipped with a mechanical stirrer, thermometer, constant pressure dropping funnel, nitrogen protection, and vacuum system. Start stirring and heat for 60 minutes at 115 °C and a vacuum degree not exceeding -0.095 MPa to remove water.

[0042] After dehydration, the vacuuming was stopped and dry nitrogen was introduced for protection until the temperature inside the reactor dropped to 70°C. 53.72 g of diisocyanate (pure MDI) was added to the reactor in one go, followed by 0.025 g of organic bismuth catalyst.

[0043] The temperature of the reaction system was steadily raised to 85°C within 30 minutes, and the reaction was kept at this temperature for 150 minutes to synthesize a polyurethane prepolymer containing side chain carboxyl groups.

[0044] While maintaining the reactor temperature at 85°C, 8.26 g of the zinc-containing reactive carrier A, which was prepared in Preparation Example 1 and kept at 95°C, was uniformly added to the prepolymer over 60 minutes via a constant pressure dropping funnel.

[0045] After the addition was complete, the reaction was stirred at 85°C for 60 minutes. Then the temperature was raised to 100°C, and the byproduct acetic acid and trace gases were removed under reduced pressure for 30 minutes under a vacuum degree not exceeding -0.095 MPa.

[0046] After the removal process is complete, heating and stirring are stopped, and the viscous molten product is released from the bottom of the reactor while it is still hot, sealed and packaged to obtain the product of Example 1.

[0047] Example 2:

[0048] This embodiment provides a specific preparation method for a high-temperature-resistant polyurethane reactive hot melt adhesive, which differs from Example 1 in that it uses a reactive carrier B with low zinc content. The specific preparation steps include:

[0049] 180.0 g of the main diol (poly(neoprene adipate, Mn = 2000 g / mol)) and 1.34 g of the functional diol (dimethylolpropionic acid) were added to the same reaction apparatus as in Example 1. Dehydration was carried out according to step 1 of Example 1.

[0050] After cooling to 70°C, 55.56 g of diisocyanate (pure MDI) was added at once, followed by 0.025 g of organic bismuth catalyst.

[0051] The prepolymer was synthesized according to step 3 of Example 1.

[0052] Maintaining the reactor temperature at 85°C, 11.93 g of the zinc-containing reactive carrier B, prepared in Preparation Example 2 and kept at 95°C, was uniformly added to the prepolymer over 60 minutes via a constant-pressure dropping funnel.

[0053] After the addition was complete, the subsequent reaction, depressurization to remove byproducts, and discharge steps were exactly the same as steps 5 and 6 of Example 1. The product of Example 2 was obtained.

[0054] Example 3:

[0055] This embodiment provides a specific preparation method for a high-temperature-resistant polyurethane reactive hot melt adhesive. The difference from Example 1 is that the proportion of functional diols in the polymer backbone is increased; specifically, the molar ratio of hydroxyl groups in the hydroxyl component from the main diol to the functional diol is 85:15. The specific preparation steps include:

[0056] To the same reaction apparatus as in Example 1, 180.0 g of the main diol (poly(neoprene adipate, Mn = 2000 g / mol) and 2.13 g of the functional diol (dimethylolpropionic acid) were added. Dehydration was carried out according to step 1 of Example 1.

[0057] After cooling to 70°C, 58.83 g of diisocyanate (pure MDI) was added at once, followed by 0.026 g of organic bismuth catalyst.

[0058] The prepolymer was synthesized according to step 3 of Example 1.

[0059] Maintaining the reactor temperature at 85°C, 13.11 g of the zinc-containing reactive carrier A, prepared in Preparation Example 1 and kept at 95°C, was uniformly added to the prepolymer over 60 minutes via a constant pressure dropping funnel.

[0060] After the addition was complete, the subsequent reaction, depressurization to remove byproducts, and discharge steps were exactly the same as steps 5 and 6 of Example 1. The product of Example 3 was obtained.

[0061] Comparative Examples 1-4:

[0062] Comparative Example 1: The difference from Example 3 is that the raw materials do not contain dimethylolpropionic acid (functional diol), hydroxyl-terminated polyethylene adipate (reactive carrier diol), and zinc acetate (synergistic network builder).

[0063] Comparative Example 2: The difference from Example 3 is that the raw materials contain 1.0 part of dimethylolpropionic acid (functional diol), but do not contain hydroxyl-terminated polyethylene adipate (reactive carrier diol) and zinc acetate (synergistic network builder).

[0064] Comparative Example 3: Compared with Example 3, the difference is that the same raw material ratio (including 1.0 part of dimethylolpropionic acid, 5.0 parts of hydroxyl-terminated polyethylene adipate and 0.5 parts of zinc acetate) is used, but in terms of preparation method, the pre-reaction in step a) is cancelled, and instead, 0.5 parts of zinc acetate powder and 5.0 parts of hydroxyl-terminated polyethylene adipate are directly added to the polyurethane prepolymer in step c).

[0065] Comparative Example 4: Compared with Example 3, the difference is that 5.0 parts of a non-reactive plasticizer (such as diisononyl phthalate DINP) was used instead of 5.0 parts of hydroxyl-terminated polyethylene adipate (reactive carrier diol), and in step a), 0.5 parts of zinc acetate were tried to be mixed with the non-reactive plasticizer, while the rest of the steps were the same.

[0066] Melt viscosity test:

[0067] Experimental description: The melt viscosity of the adhesives prepared in Examples 1-3 and Comparative Examples 1-4 was tested using a Brookfield rotational viscometer (Brookfield R / DV-II+ or equivalent) equipped with an SC4-27 rotor.

[0068] The testing procedure is as follows: Accurately weigh approximately 10g of sample and place it in the heating mantle (Thermocel) of the viscometer. Set the heating mantle temperature to 120℃, and maintain this temperature for 15 minutes after the sample has completely melted to ensure uniform sample temperature. Then, immerse the SC4-27 rotor into the molten sample, start the viscometer, and set the rotation speed to 20 rpm. Once the viscometer reading stabilizes (usually 1 minute after rotor startup), record the viscosity value (mPa·s) at this point.

[0069] Experimental data:

[0070] Table 1. Melt viscosity test data of samples at 120℃

[0071]

[0072] Conclusion: The above data clearly reflects the technical effects of the present invention.

[0073] Comparing Examples 1-3 with Comparative Examples 1 and 2: Comparative Example 1 (without ionic network) and Comparative Example 2 (with only carboxyl hydrogen bonds) exhibited the lowest viscosity. Examples 1-3, due to the successful construction of a uniform ionic crosslinked network, showed a corresponding increase in melt viscosity (15000-23000 mPa·s), consistent with the expectation that ionic networks provide additional cohesive strength in the molten state. Crucially, the viscosity readings of Examples 1-3 were stable, remaining within a fully controllable and suitable viscosity window for sizing.

[0074] Comparative Example 3 and Comparative Example 3: Comparative Example 3 (with the same formulation as Example 3, but using direct addition of zinc acetate powder) gelled during preparation, making it impossible to determine its melt viscosity. This demonstrates the core mechanism of the present invention: without the pre-reaction in step a), solid zinc acetate is unevenly dispersed in the polyurethane system, leading to excessively high local ion concentrations, triggering uncontrollable rapid cross-linking, i.e., viscosity runaway, causing the product to lose its processability. The pre-reaction process in step a) of the present invention (preparing a zinc-containing reactive carrier) is key to solving this problem.

[0075] Comparative Example 3 and Comparative Example 4: Comparative Example 4 (using a non-reactive support) exhibited extremely high and unstable viscosity. This indicates that although the synergistic network builder (zinc acetate) was introduced into the system by the support, it could not be chemically anchored to the polyurethane backbone because the support itself is non-reactive (lacking -OH groups). This resulted in zinc acetate or its mixture with the plasticizer remaining in a state of uneven dispersion or microphase separation at high temperatures, also leading to abnormal viscosity and system instability.

[0076] In summary, the melt viscosity test data demonstrates that this invention, through a specific process of preparing a zinc-containing reactive support (step a), and utilizing the reactivity of this support to chemically bond it to the main chain (step c), achieves uniform anchoring of metal ion crosslinking points at the molecular level. This fundamentally solves the gelation and viscosity control problems caused by traditional ion modification methods (such as Comparative Example 3), resulting in a hot melt adhesive that possesses both high temperature resistance (derived from the ion network) and excellent melt processability (derived from network uniformity).

[0077] Thermal stability test: Shear bond strength failure temperature (SAFT)

[0078] Experimental Description: This test is used to evaluate the ability of adhesives to resist high-temperature creep when subjected to shear stress.

[0079] Substrate preparation: Standard-sized European beech wood (25mm×100mm×5mm) was used as the test substrate.

[0080] Sample preparation: The adhesives of Examples 1-3 and Comparative Examples 1, 2, and 4 (Comparative Example 3 could not be prepared as it had already gelled during preparation) were melted at 120°C. Adhesive was applied to one end of each beech wood piece, and it was immediately overlapped with another beech wood piece to form a 25mm × 25mm bonding overlap area. Pressure was applied, and any excess adhesive squeezed out was removed.

[0081] Sample curing: All bonded samples were cured for 7 days under standard conditions (23±2℃, 50±5%RH) to ensure complete moisture curing of the polyurethane.

[0082] Test execution: The cured samples were vertically suspended in a programmable oven. A 500g weight was suspended from the bottom of each sample to apply a constant shear stress. The oven was programmed to heat from 30°C at a rate of 0.5°C / min.

[0083] Data recording: Record the oven temperature at which the weights fall off due to cohesive failure of the adhesive layer. This temperature is the shear bond failure temperature (SAFT).

[0084] Experimental data:

[0085] Table 2. Sample Shear Bond Strength Failure Temperature (SAFT) Data

[0086]

[0087] Conclusion: SAFT data directly reflects the high-temperature resistance of adhesives.

[0088] Comparing Examples 1-3 with Comparative Examples 1 and 2: The SAFT values ​​(148-163℃) of Examples 1-3 are significantly higher than those of Comparative Example 1 (72℃) and Comparative Example 2 (81℃). This demonstrates that conventional PUR (Comparative Example 1) or PUR with only carboxyl hydrogen bonds introduced (Comparative Example 2) rapidly loses cohesive strength at high temperatures. This invention, by introducing an ionic crosslinking network formed by metal ions and side-chain carboxyl groups, provides strong physical crosslinking even at high temperatures, thereby greatly improving the heat resistance of the adhesive layer.

[0089] Comparing Example 3 and Comparative Example 4: The SAFT (89°C) of Comparative Example 4 (using a non-reactive support) was slightly higher than that of Comparative Example 2, but much lower than that of Example 3 (155°C). This strongly demonstrates the necessity of the reactive support diol in the present invention. If the support is not reactive (as in Comparative Example 4), even if the synergistic network builder (zinc acetate) is introduced into the system, it cannot be chemically anchored to the polyurethane backbone, resulting in uneven ionic network distribution and poor stability upon heating.

[0090] In summary, the SAFT test data confirms the innovative mechanism of this invention: the uniform and stable dual-network structure (chemical cross-linked network + uniform ionic cross-linked network) constructed through the pre-reaction in step a) and the chemical bonding of metal ions to the polyurethane backbone via a reactive carrier is key to achieving high temperature resistance (high SAFT). Traditional methods (Comparative Examples 1 and 2) or imperfect ion introduction methods (Comparative Examples 3 and 4) cannot achieve this technical effect.

[0091] Final mechanical property test after curing:

[0092] Experimental Description: This test is used to evaluate the final macroscopic mechanical properties of the adhesive after the moisture curing reaction is completed.

[0093] Sample preparation: The adhesives of Examples 1-3 and Comparative Examples 1, 2, and 4 (Comparative Example 3 could not be prepared because it had already gelled during preparation) were melted at 120°C and thoroughly degassed. The molten adhesive was poured into a polytetrafluoroethylene (PTFE) mold to form an adhesive film with a thickness of 2 ± 0.2 mm.

[0094] Sample curing: Place the cast adhesive film under standard conditions (23±2℃, 50±5%RH) for 7 days to allow the moisture curing reaction to be complete.

[0095] Sample cutting: Use a standard cutter to cut the cured adhesive film into dumbbell-shaped samples (compliant with ISO 527 standard).

[0096] Test Execution: A universal testing machine was used, with the tensile rate set to 100 mm / min, to perform tensile tests on dumbbell-shaped specimens. The tensile strength (MPa) and elongation at break (%) were recorded.

[0097] Experimental data:

[0098] Table 3. Mechanical property data of samples after curing

[0099]

[0100] Conclusion: The mechanical property test data reflect the strength of the network structure inside the cured adhesive layer.

[0101] Comparing Examples 1-3 with Comparative Examples 1 and 2: The tensile strength of Examples 1-3 (21-29 MPa) was significantly higher than that of Comparative Example 1 (10.5 MPa) and Comparative Example 2 (12.8 MPa). This indicates that Comparative Examples 1 and 2 rely solely on the chemical cross-linking network formed by moisture curing and limited hydrogen bonding, resulting in limited cohesive strength. This invention, by introducing a uniform ionic cross-linking network that works synergistically with the chemical cross-linking network, forms a dual-network structure, greatly enhancing the mechanical strength of the cured material.

[0102] Comparing Example 3 and Comparative Example 4: The tensile strength of Comparative Example 4 (using a non-reactive support) (15.2 MPa) was higher than that of Comparative Examples 1 and 2, but much lower than that of Example 3 (24.9 MPa). This demonstrates that if the ionic network cannot be anchored to the polyurethane backbone via chemical bonds (through a reactive support), even with the introduction of metal salts, they are prone to aggregation or phase separation in the matrix, resulting in uneven network distribution and limited enhancement of mechanical properties. Step a) of the pre-reaction process in this invention ensures uniform anchoring of ions at the molecular level, which is key to achieving high mechanical strength.

[0103] Regarding elongation at break: The elongation at break of Examples 1-3 (315-405%) is lower than that of Comparative Examples 1 and 2 (560-630%). This decrease in elongation corresponds to a sharp increase in tensile strength, which is typical of the formation of a high-density cross-linked network. This indicates that the dual network formed by the present invention is dense and effective, transforming the material from a soft elastomer into a high-strength, tough material, consistent with the performance characteristics of high-cohesive-strength adhesives.

[0104] Adhesion performance test: T-peel strength

[0105] Experimental Description: This test is used to evaluate the adhesive performance and cohesive strength of adhesives on flexible substrates, and is performed in accordance with GB / T2791-1995 (Adhesives T Peel Strength Test Method).

[0106] Substrate preparation: A 1.0 mm thick flexible ABS (acrylonitrile-butadiene-styrene copolymer) sheet was cut into 100 mm × 25 mm samples. The surfaces to be bonded were wiped with ethanol to remove contaminants.

[0107] Sample preparation: The adhesives of Examples 1-3 and Comparative Examples 1, 2, and 4 (Comparative Example 3 could not be prepared because it had already gelled during preparation) were melted at 120°C. The adhesive was evenly applied to the bonding area (75mm × 25mm) of an ABS sheet, leaving the 25mm end uncoated.

[0108] Sample pressing: Immediately overlap and press another ABS sheet onto the coated surface, ensuring the 25mm uncoated end is aligned. Apply uniform pressure using a pressure roller to control the adhesive layer thickness.

[0109] Sample curing: All bonded samples were cured for 7 days under standard conditions (23±2℃, 50±5%RH) to ensure complete moisture curing of the polyurethane.

[0110] Test execution: Clamp the two unbonded ends (T-shaped) of the cured sample onto the upper and lower clamps of the universal testing machine. Set the tensile rate to 100 mm / min, start the tensile test, and subject the bonded interface to peel force.

[0111] Data recording: Record the average peel force (N) during the relatively stable phase of the peeling process, and calculate the T-type peel strength (N / 25mm).

[0112] Experimental data:

[0113] Table 4. T-peel strength data of samples after curing

[0114]

[0115] Conclusion: T-type peel strength data mainly reflects the cohesive strength of the adhesive layer itself.

[0116] Comparing Examples 1-3 with Comparative Examples 1 and 2: The peel strength of Examples 1-3 (51.2-60.8 N / 25 mm) is significantly higher than that of Comparative Example 1 (19.3 N / 25 mm) and Comparative Example 2 (25.4 N / 25 mm). All samples exhibited cohesive failure, indicating a good adhesive interface and failure occurring within the adhesive layer. This data strongly demonstrates that the adhesive layers of Comparative Examples 1 and 2 have low cohesive strength, while the embodiments of this invention, due to the construction of a uniform dual-network structure combining an ionic crosslinking network and a chemically cured network, exhibit significantly improved cohesive strength.

[0117] Comparing Example 3 and Comparative Example 4: The peel strength of Comparative Example 4 (using a non-reactive carrier) (33.7 N / 25 mm) is significantly lower than that of Example 3 (56.1 N / 25 mm). This comparison result further confirms the necessity of the reactive carrier of the present invention. If the carrier is not reactive (as in Comparative Example 4), metal ions cannot be anchored to the polyurethane backbone through chemical bonds, resulting in an uneven distribution of the ion network after curing, with a large number of defects, thus limiting the cohesive strength of the adhesive layer.

[0118] In summary, the T-peel strength test data and tensile strength test data (Table 3) are highly consistent, both confirming that the uniform dual network constructed by the pre-reaction in step a) and the reactive carrier bonding in step c) is a key technical solution for achieving high cohesive strength and high adhesive performance.

Claims

1. A high-temperature-resistant polyurethane reactive hot melt adhesive, characterized in that, It is produced by reacting raw materials comprising the following parts by weight: Main diol: 100 parts; Functional diols containing carboxyl functional groups: 0.5-1.5 parts; Diisocyanate: 28-35 parts; Reactive carrier diol: 3-8 parts; Collaborative network builder: 0.4-1.0 parts.

2. The high-temperature-resistant polyurethane reactive hot melt adhesive according to claim 1, characterized in that, The host diol is polypentyl adipate neopentyl glycol ester; the functional diol is dimethylolpropionic acid; the diisocyanate is diphenylmethane diisocyanate; the reactive carrier diol is hydroxyl-terminated polyethylene adipate; and the synergistic network builder is zinc acetate.

3. The high-temperature-resistant polyurethane reactive hot melt adhesive according to claim 1, characterized in that, The mass ratio of the reactive carrier diol to the synergistic network builder is 8:1 to 12:

1.

4. The high-temperature-resistant polyurethane reactive hot melt adhesive according to claim 1, characterized in that, It also includes a catalyst, the amount of which is 50-150 ppm of the total mass of the main diol, functional diol, reactive carrier diol and diisocyanate.

5. A method for preparing a high-temperature-resistant polyurethane reactive hot melt adhesive, applied to the high-temperature-resistant polyurethane reactive hot melt adhesive as described in any one of claims 1-4, characterized in that, Includes the following steps: a) Preparation of zinc-containing reactive support: The reactive support diol and the synergistic network building agent are mixed and reacted under heating conditions to obtain a clear zinc-containing reactive support; b) Synthesis of polyurethane prepolymer: The main diol, functional diol and diisocyanate are reacted to obtain a terminal-NCO polyurethane prepolymer containing side chain carboxyl groups; c) Constructing a collaborative network: The zinc-containing reactive carrier obtained in step a) is added to the polyurethane prepolymer obtained in step b) to react and obtain a hot melt adhesive.

6. The method for preparing a high-temperature-resistant polyurethane reactive hot melt adhesive according to claim 5, characterized in that, In step a), the heating conditions are a reaction at 95-105°C for 60-120 minutes.

7. The method for preparing a high-temperature-resistant polyurethane reactive hot melt adhesive according to claim 5, characterized in that, In step b), the reaction temperature is 80-85℃ and the reaction time is 120-180 minutes.

8. The method for preparing a high-temperature-resistant polyurethane reactive hot melt adhesive according to claim 5, characterized in that, In step c), the zinc-containing reactive carrier is added in a uniform and continuous dripping manner over 45-75 minutes.

9. The method for preparing a high-temperature-resistant polyurethane reactive hot melt adhesive according to claim 5, characterized in that, In step c), after the zinc-containing reactive carrier is added, the reaction continues at 85-90°C for 60-90 minutes.

10. The method for preparing a high-temperature-resistant polyurethane reactive hot melt adhesive according to claim 5, characterized in that, After step c), a decompression treatment is performed for 30-60 minutes at 95-105°C and a vacuum degree not higher than -0.095MPa.

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