A reactive polyurethane (PUR) hot melt adhesive and preparation method thereof

Abstract

The present invention relates to the field of polyurethane hot melt adhesives, and specifically to a reactive polyurethane (PUR) hot melt adhesive and a preparation method thereof. A method for preparing a reactive polyurethane hot melt adhesive comprises the steps of adding a bio-based polyol and a tackifying resin into a reactor, vacuum dehydrating, dripping an isocyanate to form a prepolymer, adding a catalyst to react, adding a dual-response cross-linking agent to react, adding a microcapsule repair agent to disperse evenly, adding a viscosity regulator, an inhibitor and a filler to adjust, stopping heating, and discharging the polyurethane hot melt adhesive. The present invention combines microcapsule repair and dual-response cross-linking, utilizing the sensitivity of the dual response to the environment, improving the overall curing depth and uniformity, inhibiting the initial formation and further expansion of cracks, and actively closing cracks when the hot melt adhesive is damaged by containing active prepolymers and catalysts in the microcapsules, restoring the continuity and integrity of the material, achieving internal reinforcement and dynamic repair, and improving the durability and overall strength of the material.

Description

Technical Field

[0001] The invention relates to the field of polyurethane hot melt adhesives, and in particular to a reactive polyurethane (PUR) hot melt adhesive and a preparation method thereof. Background Art

[0002] Reactive polyurethane (PUR) hot melt adhesive is a special adhesive material that is usually solid at room temperature. It melts into a fluid state when heated to a certain temperature, making it easy to apply to the surface that needs to be bonded. After the hot melt adhesive solidifies, it will further come into contact with moisture in the air to cure and cross-link, forming a tougher and more durable polyurethane network structure, thus having better physical properties and durability. It is widely used in situations that require high strength, long-lasting bonding and environmental adaptability.

[0003] However, the existing reactive polyurethane hot melt adhesive still has shortcomings. When the material encounters minor damage, it lacks self-repairing ability, and fine cracks accumulate and expand over time, eventually resulting in a significant attenuation of the bonding interface strength. Secondly, the existing curing often focuses on rapid surface curing, and there will be residual inadequately reacted areas or stress concentration points inside the curing process, which becomes a weak link for the initiation of microcracks. With the passage of time and the action of external stress, cracks are likely to begin to form from these internal defects and gradually spread, further resulting in a reduction in the overall strength and service life of the hot melt adhesive. Therefore, the present invention provides a reactive polyurethane (PUR) hot melt adhesive and a preparation method to solve the above problems. Summary of the invention

[0004] In view of the deficiencies in the prior art, the object of the present invention is to provide a reactive polyurethane (PUR) hot melt adhesive and a preparation method thereof.

[0005] A reactive polyurethane (PUR) hot melt adhesive comprises the following raw material components, measured in parts by weight: 25-40 parts of bio-based polyol, 15-20 parts of isocyanate, 2-5 parts of microcapsule repair agent, 0.5-2 parts of dual-responsive cross-linking agent, 0.1-0.5 parts of catalyst, 5-10 parts of tackifying resin, 3-7 parts of viscosity modifier, 0.05-0.2 parts of inhibitor and 1-3 parts of filler.

[0006] Furthermore, the bio-based polyol includes 15-25 parts by weight of polylactic acid polyol and 10-15 parts by weight of bio-based polyester polyol.

[0007] Furthermore, the isocyanate is one or more of diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, and dicyclohexylmethane diisocyanate.

[0008] Furthermore, the microcapsule repair agent is composed of 90-95% microcapsule shell and 5-10% microcapsule core in a weight ratio, 60-80% of the microcapsule shell is modified starch, and the remaining 15-35% is cellulose acetate. The wall thickness of the microcapsule shell is 0.5-2 μm, 7-9% of the microcapsule core is small molecule prepolymer, and the remaining 1-3% is a catalyst. The small molecule prepolymer is a compound containing unreacted isocyanate or hydroxyl functional groups.

[0009] Furthermore, the dual-responsive cross-linking agent is a copolymer of N-isopropylacrylamide and methacrylate-N,N-dimethylaminoethyl ester.

[0010] Furthermore, the catalyst is one of dibutyltin dilaurate, triethylenediamine, and stannous octoate.

[0011] Furthermore, the tackifying resin is rosin and its derivatives, and the viscosity modifier is microcrystalline wax.

[0012] Furthermore, the polymerization inhibitor is hydroquinone or p-benzoquinone.

[0013] Furthermore, the filler is fumed silica or calcium carbonate.

[0014] The method for preparing the reactive polyurethane (PUR) hot melt adhesive comprises the following steps:

[0015] S1: adding bio-based polyol and tackifying resin into a stirred reactor, stirring at 100-120°C and 100-120rpm, and vacuum dehydrating to remove moisture and volatiles in the raw materials for 30-60min to obtain a premix;

[0016] S2: Slowly drop the isocyanate into the premix under vacuum, control the dropping speed, and carry out the dropping process at 60-75°C with continuous stirring. After the dropping is completed, continue to stir under vacuum at 80-90°C for 1-2h to form a prepolymer;

[0017] S3: Add a catalyst to the prepolymer, continue to react at 80-90°C for 0.5-1h, then slowly add a dual-responsive crosslinking agent, while controlling the temperature at 80-90°C, react for 1-2h, and form a crosslinked prepolymer;

[0018] S4: After the reaction reaches the predetermined time, the temperature is reduced to 50-70°C, and the microcapsule repair agent is gradually and slowly added and dispersed evenly, with a stirring speed of 50-100rpm; then the viscosity regulator, polymerization inhibitor and filler are added, and stirring is continued for 20-40min under vacuum to obtain a polyurethane hot melt adhesive premix;

[0019] S5: Stop heating, fill nitrogen into the reactor, and discharge the material at a temperature below 50° C. After discharge, the hot melt adhesive is morphologically processed by extrusion or granulation.

[0020] The beneficial effects achieved by the present invention are as follows: 1. The present invention combines microcapsule repair and dual-response cross-linking. The active prepolymer and catalyst contained in the microcapsule can be accurately released when the hot melt adhesive is damaged, actively triggering self-healing, effectively closing cracks, and restoring the continuity and integrity of the material. At the same time, the sensitivity of the dual response to the environment can be used to drive the curing reaction deep into the material, making up for the incomplete curing problem under single curing, thereby improving the overall curing depth and uniformity. Even if tiny cracks are generated inside the material, the initial formation and further expansion of the cracks can be suppressed due to the denser overall structure and better internal connectivity. The repair agent can repair the damage in time, realize internal reinforcement and dynamic repair, which not only solves the problem of insufficient curing depth, but also provides a second line of defense by actively repairing cracks, thereby improving the durability and overall strength of the material.

[0021] 2. The present invention uses a dual-responsive cross-linking agent to enhance the initial bonding strength. Through its sensitivity to the environment, it promotes deep cross-linking reactions and achieves multi-level control of the curing process. The dual response not only accelerates the formation of the initial cured network, but also during long-term use, under dynamic loads or environmental changes, the material structure can be continuously optimized and reinforced, thereby improving the overall bonding strength and stability.

[0022] 3. The present invention ensures that the hot melt adhesive has good rheology and operability in a wide temperature range by adjusting the types and proportions of additives, broadens its application range on objects of different materials and complex shapes, and improves production efficiency.

[0023] 4. The present invention uses bio-based and recyclable components as viscosity modifiers and fillers, effectively reducing VOC emissions while maintaining high performance of the product, meeting the requirements of sustainable development.

[0024] 5. The present invention comprehensively considers factors such as heat resistance, weather resistance, and aging resistance, while ensuring basic bonding performance, while enhancing the stability and functionality of the hot melt adhesive under extreme conditions, such as introducing special fillers to improve flame retardancy, conductivity, or reduce weight. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The figure is a schematic flow chart of a method for preparing a reactive polyurethane (PUR) hot melt adhesive used in an embodiment of the present invention. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below with reference to specific embodiments.

[0027] Example 1: A reactive polyurethane (PUR) hot melt adhesive comprises the following raw material components, in parts by weight: 30 parts of bio-based polyols (20 parts by weight of polylactic acid polyols and 10 parts by weight of bio-based polyester polyols), 17 parts of isocyanates (diphenylmethane diisocyanate), 3 parts of microcapsule repair agents, 1 part of dual-responsive cross-linking agents (copolymer of N-isopropylacrylamide and methacrylate-N,N-dimethylaminoethyl ester), 0.3 parts of catalysts (dibutyltin dilaurate), 7 parts of tackifying resins (rosin), 5 parts of viscosity modifiers (microcrystalline wax), 0.1 parts of inhibitors (hydroquinone), and 2 parts of fillers (fumed silica).

[0028] The microcapsule repair agent is composed of 90% microcapsule shell and 10% microcapsule core in a weight ratio, wherein the microcapsule shell part is 75% modified starch and the remaining 25% cellulose acetate. The microcapsule shell wall is 1 μm thick, and the microcapsule core part is 8% small molecule prepolymer and the remaining 2% catalyst; the small molecule prepolymer is the biuret of hexamethylene diisocyanate, which is formed by self-polymerization of hexamethylene diisocyanate and retains active isocyanate groups in the structure.

[0029] Preparation method of reactive polyurethane (PUR) hot melt adhesive, such as Figure 1 As shown, the following steps are included:

[0030] S1: adding bio-based polyol and tackifying resin into a stirred reactor, stirring at 110°C and 110 rpm, and vacuum dehydrating to remove moisture and volatiles in the raw materials for 45 minutes to obtain a premix;

[0031] S2: slowly drop the isocyanate into the premix under vacuum, control the dropping speed, and carry out the dropping process at 65°C with continuous stirring. After the dropping is completed, continue to stir under vacuum at 85°C for 1.5 hours to form a prepolymer;

[0032] S3: Add the catalyst to the prepolymer, continue to react at 85°C for 0.5h, then slowly add the dual-responsive crosslinking agent, while controlling the temperature at 85°C, react for 1.5h to form a crosslinked prepolymer;

[0033] S4: After the reaction reaches the predetermined time, the temperature is reduced to 60°C, and the microcapsule repair agent is gradually and slowly added and dispersed evenly, with a stirring speed of 60 rpm; then the viscosity regulator, polymerization inhibitor and filler are added, and stirring is continued for 30 minutes under vacuum to obtain a polyurethane hot melt adhesive premix;

[0034] S5: Stop heating, fill nitrogen into the reactor, discharge the material at 50°C, and after discharge, perform morphological treatment on the hot melt adhesive by extrusion.

[0035] Example 2: A reactive polyurethane (PUR) hot melt adhesive comprises the following raw material components, in parts by weight: 40 parts of bio-based polyols (25 parts by weight of polylactic acid polyols and 15 parts by weight of bio-based polyester polyols), 20 parts of isocyanates (toluene diisocyanate), 5 parts of microcapsule repair agents, 2 parts of dual-responsive cross-linking agents (copolymer of N-isopropylacrylamide and methacrylate-N,N-dimethylaminoethyl ester), 0.5 parts of catalysts (stannous octoate), 9 parts of tackifying resins (rosin glycerol ester), 6 parts of viscosity modifiers (microcrystalline wax), 0.2 parts of inhibitors (hydroquinone), and 3 parts of fillers (fumed silica).

[0036] The microcapsule repair agent is composed of 92% microcapsule shell and 8% microcapsule core in a weight ratio, wherein 80% of the microcapsule shell is modified starch and the remaining 20% ​​is cellulose acetate. The wall thickness of the microcapsule shell is 1.5 μm. 7% of the microcapsule core is small molecule prepolymer and the remaining 1% is catalyst. The small molecule prepolymer is a prepolymer of polyether diol and toluene diisocyanate, which is generated by the partial reaction of polyether diol and toluene diisocyanate and contains unreacted isocyanate groups.

[0037] Preparation method of reactive polyurethane (PUR) hot melt adhesive, such as Figure 1 As shown, the following steps are included:

[0038] S1: adding bio-based polyol and tackifying resin into a stirred reactor, stirring at 110°C and 110 rpm, and vacuum dehydrating to remove moisture and volatiles in the raw materials for 45 minutes to obtain a premix;

[0039] S2: slowly drop the isocyanate into the premix under vacuum, control the dropping speed, and carry out the dropping process at 65°C with continuous stirring. After the dropping is completed, continue to stir under vacuum at 85°C for 1.5 hours to form a prepolymer;

[0040] S3: Add the catalyst to the prepolymer, continue to react at 85°C for 0.5h, then slowly add the dual-responsive crosslinking agent, while controlling the temperature at 85°C, react for 1.5h to form a crosslinked prepolymer;

[0041] S4: After the reaction reaches the predetermined time, the temperature is reduced to 60°C, and the microcapsule repair agent is gradually and slowly added and dispersed evenly, with a stirring speed of 60 rpm; then the viscosity regulator, polymerization inhibitor and filler are added, and stirring is continued for 30 minutes under vacuum to obtain a polyurethane hot melt adhesive premix;

[0042] S5: Stop heating, fill nitrogen into the reactor, discharge the material at 50°C, and after discharge, perform morphological treatment on the hot melt adhesive by extrusion.

[0043] Example 3: A reactive polyurethane (PUR) hot melt adhesive comprises the following raw material components, in parts by weight: 30 parts of bio-based polyols (20 parts by weight of polylactic acid polyols and 10 parts by weight of bio-based polyester polyols), 17 parts of isocyanates (diphenylmethane diisocyanate), 3 parts of microcapsule repair agents, 1 part of dual-responsive cross-linking agents (copolymer of N-isopropylacrylamide and methacrylate-N,N-dimethylaminoethyl ester), 0.3 parts of catalysts (dibutyltin dilaurate), 7 parts of tackifying resins (rosin), 5 parts of viscosity modifiers (microcrystalline wax), 0.1 parts of inhibitors (hydroquinone), and 2 parts of fillers (fumed silica).

[0044] The microcapsule repair agent is composed of 95% microcapsule shell and 5% microcapsule core in a weight ratio, wherein the microcapsule shell is 75% modified starch and the remaining 25% cellulose acetate. The wall thickness of the microcapsule shell is 1 μm. The microcapsule core is 8% small molecule prepolymer and the remaining 2% catalyst. The small molecule prepolymer is a compound containing unreacted isocyanate or hydroxyl functional groups.

[0045] Preparation method of reactive polyurethane (PUR) hot melt adhesive, such as Figure 1 As shown, the following steps are included:

[0046] S1: adding bio-based polyol and tackifying resin into a stirred reactor, stirring at 120°C and 100 rpm, and vacuum dehydrating to remove moisture and volatiles in the raw materials for 55 min to obtain a premix;

[0047] S2: slowly drop the isocyanate into the premix under vacuum, control the dropping speed, and carry out the dropping process at 70°C with continuous stirring. After the dropping is completed, continue to stir under vacuum at 90°C for 1 hour to form a prepolymer;

[0048] S3: Add a catalyst to the prepolymer, continue to react at 90°C for 1 hour, then slowly add a dual-responsive crosslinking agent while controlling the temperature at 90°C for 1 hour to form a crosslinked prepolymer;

[0049] S4: After the reaction reaches the predetermined time, the temperature is reduced to 50°C, and the microcapsule repair agent is gradually and slowly added and dispersed evenly, with a stirring speed of 70 rpm; then the viscosity regulator, polymerization inhibitor and filler are added, and stirring is continued for 35 minutes under vacuum to obtain a polyurethane hot melt adhesive premix;

[0050] S5: Stop heating, fill nitrogen into the reactor, discharge the material at 40°C, and after discharge, the hot melt adhesive is granulated for morphological treatment.

[0051] Verification Example: The reactive polyurethane (PUR) hot melt adhesives prepared in Examples 1 to 3 were tested for bonding strength, heat resistance, self-healing efficiency, and long-term stability;

[0052] 1. Adhesion strength: Aluminum alloy plates of standard size were selected as the test substrates. Each embodiment was a group of samples. Each group of samples included two substrates, with the polyurethane hot melt adhesive of the corresponding embodiment coated in the middle and cured at room temperature for 24 hours.

[0053] In accordance with ASTM D1002 standard, a universal material testing machine was used to perform tensile shear tests at a test rate of 5 mm / min. The maximum breaking load (N) of each group of samples was recorded to evaluate the strength grade of the bonding strength.

[0054] 2. Heat resistance: Each embodiment is a group of test samples. According to ASTMD648 standard, the samples are placed in a constant temperature oven at 85°C for a thermal weight loss test for 7 days. The samples are taken out every day, cooled to room temperature, and then the weight change is measured. The data is recorded, and the initial weight is compared with the final weight to calculate the mass loss rate and evaluate the thermal stability.

[0055] 3. Self-healing efficiency: Cut a straight crack of about 0.5 mm deep and 2 cm long on the surface of the cured hot melt adhesive sample with a blade, place the cracked sample in an environment of 40°C and 80% relative humidity to simulate the conditions that promote self-healing, and observe for 72 hours;

[0056] An optical microscope was used to observe the crack closure process, and a scanning electron microscope examination was performed at the end of the self-healing process to evaluate the microstructural recovery. Finally, a tensile shear test was performed to compare the bonding strength of the samples before and after self-healing, and the self-healing efficiency was evaluated by the degree of crack closure and the recovered bonding strength as a percentage of the original strength.

[0057] 4. Long-term stability test: Accelerated aging: According to the ASTM G154-23 method, a QUV ultraviolet aging box was used to subject each example sample to a continuous 8-hour ultraviolet light (using a UVA-340 lamp), 4-hour condensation, and 4-hour dark cycle for a total of 500 hours;

[0058] The bond strength of the samples was measured after 500 h and compared with that of the unaged benchmark samples. The long-term stability was evaluated by the bond strength retention rate.

[0059] The performance test results of the reactive polyurethane (PUR) hot melt adhesives prepared in Examples 1 to 3 of the present invention are shown in Table 1, wherein the maximum destructive loads of the three embodiments are all above 2000N, and the bonding strengths of Examples 1 and 3 are the strongest; the mass loss rates of the three embodiments are not much different and the loss is very small; the crack closure degree and the bonding strength recovery rate of the three embodiments are all above 65%, and the self-healing efficiency of Example 2 is the lowest; the long-term stability of the three embodiments is all above 80%, that is, using the reactive polyurethane (PUR) hot melt adhesive and preparation method of the present invention, the obtained hot melt adhesive has good bonding strength, heat resistance, self-healing efficiency and long-term stability.

[0060] Table 1 Test results of bonding strength, heat resistance, self-healing efficiency and long-term stability

[0061]

[0062] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A reactive polyurethane (PUR) hot melt adhesive, characterized in that: The raw material components include, by weight: 25-40 parts of bio-based polyol, 15-20 parts of isocyanate, 2-5 parts of microcapsule repair agent, 0.5-2 parts of dual-response cross-linking agent, 0.1-0.5 parts of catalyst, 5-10 parts of tackifying resin, 3-7 parts of viscosity modifier, 0.05-0.2 parts of inhibitor, and 1-3 parts of filler; The overall weight of the microcapsule repair agent is 100%, of which 90-95% is a microcapsule shell, 5-10% is a microcapsule core, 60-80% of the microcapsule shell is modified starch, and the remaining 15-35% is cellulose acetate, the microcapsule shell has a wall thickness of 0.5-2 μm, 7-9% of the microcapsule core is a small molecule prepolymer, and the remaining 1-3% is a catalyst, and the small molecule prepolymer is a compound containing unreacted isocyanate or hydroxyl functional groups; The dual-response cross-linking agent is a copolymer of N-isopropylacrylamide and methacrylic acid-N,N-dimethylaminoethyl ester.

2. A reactive polyurethane (PUR) hot melt adhesive according to claim 1, characterized in that: The bio-based polyol includes 15-25 parts by weight of polylactic acid polyol and 10-15 parts by weight of bio-based polyester polyol.

3. A reactive polyurethane (PUR) hot melt adhesive according to claim 1, characterized in that: The isocyanate is one or more of diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, and dicyclohexylmethane diisocyanate.

4. A reactive polyurethane (PUR) hot melt adhesive according to claim 1, characterized in that: The catalyst is one of dibutyltin dilaurate, triethylenediamine and stannous octoate.

5. A reactive polyurethane (PUR) hot melt adhesive according to claim 1, characterized in that: The tackifying resin is rosin and its derivatives, and the viscosity modifier is microcrystalline wax.

6. A reactive polyurethane (PUR) hot melt adhesive according to claim 1, characterized in that: The polymerization inhibitor is hydroquinone or p-benzoquinone.

7. A reactive polyurethane (PUR) hot melt adhesive according to claim 1, characterized in that: The filler is fumed silica or calcium carbonate.

8. A method for preparing a reactive polyurethane (PUR) hot melt adhesive according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1: adding bio-based polyol and tackifying resin into a stirred reactor, stirring at 100-120°C and 100-120rpm, and vacuum dehydrating to remove moisture and volatiles in the raw materials for 30-60min to obtain a premix; S2: Slowly drop the isocyanate into the premix under vacuum, control the dropping speed, and carry out the dropping process at 60-75°C with continuous stirring. After the dropping is completed, continue to stir under vacuum at 80-90°C for 1-2h to form a prepolymer; S3: Add a catalyst to the prepolymer, continue to react at 80-90°C for 0.5-1h, then slowly add a dual-responsive crosslinking agent, while controlling the temperature at 80-90°C, react for 1-2h, and form a crosslinked prepolymer; S4: After the reaction reaches the predetermined time, the temperature is reduced to 50-70°C, and the microcapsule repair agent is gradually and slowly added and dispersed evenly, with a stirring speed of 50-100rpm; then the viscosity regulator, polymerization inhibitor and filler are added, and stirring is continued for 20-40min under vacuum to obtain a polyurethane hot melt adhesive premix; S5: Stop heating, fill nitrogen into the reactor, and discharge the material at a temperature below 50° C. After discharge, the hot melt adhesive is morphologically processed by extrusion or granulation.

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