Low-temperature workable PUR hot melt adhesive and preparation method thereof

Abstract

The application discloses a low-temperature workable PUR hot melt adhesive and a preparation method thereof, and belongs to the technical field of adhesives. The hot melt adhesive comprises the following components in parts by mass: 30-50 parts of polyester polyol, 10-20 parts of isocyanate, 5-15 parts of low-melting-point plasticizer, 3-10 parts of reactive diluent, 0.1-0.5 parts of catalyst and 10-25 parts of filler. The low-temperature workable PUR hot melt adhesive is prepared by selecting low-viscosity and low-crystallization-point polyester polyol as a soft segment base, and introducing liquid low-melting-point plasticizer and low-viscosity reactive diluent, so that the melting viscosity of the hot melt adhesive at a working temperature is greatly reduced under the premise that the mechanical properties of a final cured product are not significantly affected, and the hot melt adhesive is still easy to pump, spray or scrape in winter or a low-temperature workshop environment. The hot melt adhesive is particularly suitable for fields, such as automobiles, cold-chain logistics packaging, outdoor buildings in northern regions and the like, which need to be bonded and worked in a low-temperature environment.

Description

Technical Field

[0001] This invention provides a low-temperature-applicable PUR hot melt adhesive and its preparation method, relating to the field of adhesive technology. Background Technology

[0002] Polyurethane reactive hot melt adhesives (PURs) combine the advantages of traditional hot melt adhesives (fast bonding) and reactive adhesives (high strength and high durability). They form an irreversible cross-linked network structure through moisture curing and have been widely used in automotive interiors, wood processing, electronic assembly, and packaging. However, in practical applications, especially in cold climates or workshops without constant temperature conditions during winter, they face a long-standing and unresolved core technical bottleneck: poor low-temperature workability. This stems primarily from two inherent contradictions: First, from a materials rheology perspective, the viscosity of the polyester or polyether polyol that forms the basis of PUR is extremely sensitive to temperature. As the ambient or construction temperature decreases, its melt viscosity increases exponentially, causing the fluidity of the adhesive in hot melt glue machines, pipelines, and spray guns to deteriorate drastically. This not only increases pumping resistance and energy consumption but may also cause blockages, making continuous and stable automated adhesive application difficult. Second, from an adhesive bonding process perspective, even if the adhesive is heated and melted before application, once it comes into contact with substrates such as metals, glass, or plastics with temperatures far lower than its construction temperature, the adhesive will rapidly cool and lose fluidity due to the heat absorption effect of the substrate. This prevents it from fully spreading and wetting the substrate surface, severely affecting the formation of physical anchoring, resulting in low initial tack or even failure, and ultimately damaging long-term bond strength. To improve flowability, existing technologies typically involve adding large amounts of paraffin oil, phthalate-based non-reactive plasticizers, or significantly reducing the molecular weight of the prepolymer. However, these methods often come at a high cost, sacrificing the cohesive strength, heat resistance, aging resistance, and durability of the adhesive layer. They represent a compromise and cannot meet the demands of applications requiring high mechanical properties and reliability. Other studies have attempted to fundamentally reduce viscosity by synthesizing low-viscosity polyethers or polyester polyols with special molecular structures. However, these specialty raw materials are often expensive, have complex manufacturing processes, and offer limited help in improving the instantaneous wetting properties of the adhesive on low-temperature substrates. Therefore, developing a PUR hot melt adhesive that maintains excellent flowability and pumpability at relatively low application temperatures and can quickly establish a high-strength, high-reliability bond after application to low-temperature substrates has become an urgent and highly practically valuable technical challenge in the adhesive field. Summary of the Invention

[0003] To address the above problems, the present invention provides a low-temperature applicable PUR hot melt adhesive, comprising the following components by weight: 30-50 parts polyester polyol, 10-20 parts isocyanate, 5-15 parts low-melting-point plasticizer, 3-10 parts reactive diluent, 0.1-0.5 parts catalyst, and 10-25 parts filler.

[0004] Preferably, the polyester polyol comprises a low-crystallinity or amorphous polyester polyol with a number-average molecular weight of 1000-2000 g / mol, a hydroxyl value of 55-112 mg KOH / g, and a viscosity of 2000-5000 mPa·s at 25°C.

[0005] Preferably, the polyester polyol is selected from at least one of polybutylene adipate diol, polyethylene adipate diol, and poly(ε-caprolactone diol).

[0006] Preferably, the isocyanate is selected from at least one of diphenylmethane diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate.

[0007] Preferably, the low-melting-point plasticizer is a plasticizer that is liquid at room temperature and compatible with polyurethane prepolymer, and is selected from at least one of dioctyl phthalate, dioctyl adipate, tributyl citrate, and epoxidized soybean oil.

[0008] Preferably, the reactive diluent is a compound containing active groups that can participate in the polyurethane curing reaction and has a viscosity of less than 100 mPa·s, and is selected from at least one of hydroxyethyl acrylate, hydroxyethyl methacrylate, and glycidyl ether epoxy reactive diluents; the catalyst is an organotin catalyst, and is selected from at least one of dibutyltin dilaurate and stannous octoate.

[0009] Preferably, the filler is a surface-treated ultrafine inorganic filler with a particle size D50 ≤ 5 μm, selected from at least one of calcium carbonate, talc, and fumed silica.

[0010] This invention also provides a method for preparing the above-mentioned low-temperature applyable PUR hot melt adhesive, comprising the following steps: S1. Preparation of terminal isocyanate-based prepolymer: Under inert gas protection, the polyester polyol is heated to 70-90℃ and vacuum dehydrated for 0.5-2 h; then cooled to 60-80℃, isocyanate and catalyst are added, and the reaction is carried out at 70-85℃ for 2-4 h until the NCO content of the system reaches the theoretical value, thus obtaining the terminal isocyanate-based prepolymer; S2. Mixing and molding: Cool the prepolymer obtained in step S1 to 40-60℃, add low melting point plasticizer, reactive diluent and filler in sequence, stir and mix for 0.5-1.5 h under vacuum degree ≤0.095 MPa until the mixture is uniform and the air bubbles are removed; S3. Pour the mixture obtained in step S2 into a mold and seal it at room temperature for 24-72 hours to obtain the low-temperature workable PUR hot melt adhesive.

[0011] Preferably, in step S1, the theoretical value of the NCO content in the reaction is controlled between 3% and 6%; in step S1, the molar ratio of the polyester polyol to the isocyanate, calculated as the ratio of hydroxyl to isocyanate groups (OH:NCO), is 1:1.5-2.2.

[0012] Preferably, in step S2, the mixing and shaping stirring speed is 300-800 rpm.

[0013] Preferably, the low-temperature applyable PUR hot melt adhesive has a melt viscosity ≤8000 mPa·s at 90℃, and when applied to a steel surface at 0℃, its shear strength after curing for 10 minutes is ≥0.8 MPa, and its shear strength after curing for 7 days is ≥5.0 MPa.

[0014] The beneficial effects of this invention are as follows: 1. Excellent low-temperature application fluidity: By selecting low-viscosity, low-crystallization-point polyester polyols as the main body, and coordinating with low-melting-point liquid plasticizers and low-viscosity reactive diluents, the three work together to make the viscosity of the hot melt adhesive significantly lower than that of traditional PUR products under relatively low melting conditions of 90-110℃. This makes it easy to pump and spray, with a wide application window, and is especially suitable for use in winter or in environments without constant temperature workshops.

[0015] 2. Excellent initial tack and final strength on low-temperature substrates: The introduction of reactive diluents is key. During the application stage, it acts as a solvent to effectively reduce the viscosity of the system and improve the wettability on low-temperature substrates. During the curing stage, its active groups, such as hydroxyl groups, participate in the moisture curing reaction and become part of the cross-linking network. This avoids shrinkage and performance degradation caused by the volatilization of small molecules, thus enabling the rapid formation of high initial tack even at low temperatures and ultimately achieving a shear strength of over 5 MPa.

[0016] 3. Excellent performance balance and practicality: The combined use of low-melting-point plasticizers and reactive diluents achieves the goal of easy application at low temperatures. Since both are chemically or physically stable within the adhesive layer, it avoids the softening and durability issues caused by adding inert plasticizers in traditional methods. The use of fillers reduces costs while further adjusting flowability and mechanical properties. The entire formulation is scientifically designed, and the preparation process is simple and stable, suitable for industrial production, effectively solving the technical bottleneck of PUR hot melt adhesives in low-temperature environments. Detailed Implementation

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0019] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the experimental materials used in the following examples are all purchased from commercial channels.

[0020] Example 1

[0021] (1) Prepolymer preparation: In a four-necked flask equipped with a mechanical stirrer, thermometer, nitrogen inlet, and vacuum port, 40 parts by mass of polybutylene adipate diol (hydroxyl value approximately 112 mgKOH / g, viscosity at 25℃ approximately 3500 mPa·s) with a number-average molecular weight of approximately 1000 g / mol was added. Under a nitrogen atmosphere, the temperature was raised to 80℃. The vacuum pump was turned on, and dehydration was carried out at a vacuum of -0.095 MPa for 1 h. Then the temperature was lowered to 70℃, and 15.2 parts by mass of diphenylmethane diisocyanate and 0.15 parts by mass of dibutyltin dilaurate were added at once. The molar ratio of hydroxyl groups to isocyanate groups (OH:NCO) was controlled to be 1:1.8. The reaction system was heated to 80°C and kept at this temperature for 3 hours. During this period, samples were taken periodically and the NCO content was determined by di-n-butylamine titration. The reaction was stopped when the NCO content reached 4.5%, and a clear and viscous NCO-terminated prepolymer was obtained.

[0022] (2) Mixing and Degassing: The prepolymer was transferred to a heatable and stirred mixing vessel and cooled to 50°C. 10 parts by weight of dioctyl phthalate, 5 parts by weight of hydroxyethyl acrylate, and 20 parts by weight of light calcium carbonate with an average particle size (D50) of 2 μm, treated with stearic acid, were added sequentially. The vacuum system was turned on at a stirring speed of 500 rpm, maintaining a vacuum degree ≤0.095 MPa, and the mixture was stirred for 1 h until the filler was uniformly dispersed and no obvious bubbles were observed in the system.

[0023] (3) Curing and molding: Pour the evenly mixed adhesive into a square shallow dish coated with polytetrafluoroethylene, place it in a desiccator, seal it at room temperature for 48 hours to allow it to cure initially, and after demolding, you will get block-shaped low-temperature workable PUR hot melt adhesive.

[0024] Example 2

[0025] (1) Prepolymer preparation: In a four-necked flask equipped with a mechanical stirrer, thermometer, nitrogen inlet, and vacuum port, 35 parts by mass of polyethylene adipate diol (hydroxyl value approximately 75 mg KOH / g, viscosity at 25℃ approximately 4200 mPa·s) with a number-average molecular weight of approximately 1500 g / mol and 10 parts by mass of poly(ε-caprolactone diol) (hydroxyl value approximately 112 mg KOH / g, viscosity at 25℃ approximately 3000 mPa·s) with a number-average molecular weight of approximately 1000 g / mol were added. Under a nitrogen atmosphere, the temperature was raised to 85℃. The vacuum pump was turned on, and dehydration was carried out at a vacuum of -0.095 MPa for 1.5 h. Then the temperature was lowered to 75℃, and 13 parts by mass of hexamethylene diisocyanate and 0.2 parts by mass of stannous octoate were added at once. The molar ratio of total hydroxyl groups to isocyanate groups (OH:NCO) was controlled to be 1:2.0. The reaction system was heated to 75°C and kept at this temperature for 3.5 h. During this period, the NCO content was measured periodically. When the NCO content reached 5.2%, the reaction was stopped to obtain the NCO-terminated prepolymer.

[0026] (2) Mixing and Degassing: Transfer the above prepolymer to a heatable and stirred mixing vessel and cool to 45°C. Add 8 parts by weight of dioctyl adipate, 8 parts by weight of hydroxyethyl methacrylate, and 15 parts by weight of hydrophilic fumed silica (specific surface area 200 m²). 2 / g). At a stirring speed of 600 rpm, turn on the vacuum system and maintain the vacuum degree ≤0.095MPa. Mix and stir for 1.2 h until the filler is evenly dispersed, the system is a uniform paste and there are no air bubbles inside.

[0027] (3) Curing and molding: Pour the evenly mixed adhesive into a square shallow dish coated with polytetrafluoroethylene, place it in a desiccator, seal it at room temperature for 72 hours to allow it to cure initially, and after demolding, you will get block-shaped low-temperature workable PUR hot melt adhesive.

[0028] Example 3

[0029] (1) Preparation of prepolymer: In a four-necked flask equipped with a mechanical stirrer, thermometer, nitrogen inlet, and vacuum port, 45 parts by mass of polybutylene adipate diol (hydroxyl value approximately 56 mgKOH / g, viscosity at 25℃ approximately 4800 mPa·s) with a number-average molecular weight of approximately 2000 g / mol was added. Under a nitrogen atmosphere, the temperature was raised to 90℃. The vacuum pump was turned on, and dehydration was carried out at a vacuum of -0.095 MPa for 2 h. Then the temperature was lowered to 80℃, and 18 parts by mass of isophorone diisocyanate and 0.3 parts by mass of dibutyltin dilaurate were added at once. The molar ratio of hydroxyl to isocyanate groups (OH:NCO) was controlled to be 1:1.5. The reaction system was heated to 85℃ and kept at this temperature for 2.5 h. During the reaction, the NCO content was measured periodically. When the NCO content reached 3.8%, the reaction was stopped to obtain the NCO-terminated prepolymer.

[0030] (2) Mixing and Degassing: Transfer the prepolymer to a heatable and stirred mixing vessel and cool to 60°C. Add 12 parts by weight of tributyl citrate, 3 parts by weight of hydroxyethyl acrylate, 3 parts by weight of 1,4-butanediol diglycidyl ether, and 25 parts by weight of talc (particle size D50 ≤ 5 μm) sequentially. With the stirring speed at 400 rpm, turn on the vacuum system and maintain a vacuum degree ≤ 0.095 MPa. Mix and stir for 1.5 h until the system is homogeneous and bubbles are removed.

[0031] (3) Curing and molding: Pour the evenly mixed adhesive into a square shallow dish coated with polytetrafluoroethylene, place it in a desiccator, seal it at room temperature for 24 hours to allow it to cure initially, and after demolding, you will get block-shaped low-temperature workable PUR hot melt adhesive.

[0032] Comparative Example 1 (1) Preparation of prepolymer: In a four-necked flask equipped with a mechanical stirrer, thermometer, nitrogen inlet, and vacuum port, 40 parts by mass of polyethylene terephthalate diol (hydroxyl value of approximately 112 mg KOH / g, solid at room temperature) with a number-average molecular weight of approximately 1000 g / mol and high crystallinity were added. The temperature was raised to 80℃ under a nitrogen atmosphere. The vacuum pump was turned on, and dehydration was carried out for 1 h under a vacuum of -0.095 MPa. Then the temperature was lowered to 70℃, and 15.2 parts by mass of diphenylmethane diisocyanate and 0.15 parts by mass of dibutyltin dilaurate were added at once. The molar ratio of hydroxyl to isocyanate groups (OH:NCO) was controlled to be 1:1.8. The reaction system was heated to 80℃ and kept at this temperature for 3 h. During the reaction, the NCO content was measured periodically. The reaction was stopped when the NCO content reached 4.5%, and the NCO-terminated prepolymer was obtained.

[0033] (2) Mixing and Degassing: Transfer the prepolymer to a heatable and stirred mixing vessel and cool to 50°C. Add 10 parts by weight of dioctyl phthalate, 5 parts by weight of hydroxyethyl acrylate, and 20 parts by weight of light calcium carbonate with an average particle size (D50) of 2 μm, treated with stearic acid. Stir at 500 rpm, turn on the vacuum system, maintain a vacuum level ≤0.095 MPa, and mix for 1 h until the filler is uniformly dispersed.

[0034] (3) Curing and molding: The uniformly mixed rubber material is poured into a square shallow dish coated with polytetrafluoroethylene, placed in a desiccator, sealed and placed at room temperature for 48 h, and after demolding, a control sample rubber block is obtained.

[0035] Comparative Example 2 (1) Preparation of prepolymer: exactly the same as step (1) in Example 1.

[0036] (2) Mixing and Degassing: Transfer the prepolymer to a heatable and stirred mixing vessel and cool to 50°C. Add 5 parts by weight of hydroxyethyl acrylate and 20 parts by weight of light calcium carbonate with an average particle size (D50) of 2 μm, treated with stearic acid. Do not add dioctyl phthalate. Stir at 500 rpm with a vacuum system maintained at ≤0.095 MPa for 1 h until the filler is uniformly dispersed.

[0037] (3) Curing and shaping: exactly the same as step (3) in Example 1.

[0038] Comparative Example 3 (1) Preparation of prepolymer: exactly the same as step (1) in Example 1.

[0039] (2) Mixing and Degassing: Transfer the prepolymer to a heatable and stirred mixing vessel and cool to 50°C. Add 10 parts by weight of dioctyl phthalate and 20 parts by weight of stearic acid-treated light calcium carbonate with an average particle size (D50) of 2 μm. Do not add hydroxyethyl acrylate. Stir at 500 rpm with the vacuum system activated, maintaining a vacuum level ≤0.095 MPa, and mix for 1 h until the filler is uniformly dispersed.

[0040] (3) Curing and shaping: exactly the same as step (3) in Example 1.

[0041] Comparative Example 4 (1) Preparation of prepolymer: exactly the same as step (1) in Example 1.

[0042] (2) Mixing and Degassing: The prepolymer was transferred to a heatable and stirred mixing vessel and cooled to 50°C. 10 parts by weight of dioctyl phthalate, 5 parts by weight of toluene (as a non-reactive solvent), and 20 parts by weight of stearic acid-treated light calcium carbonate with an average particle size (D50) of 2 μm were added sequentially. The vacuum system was turned on at a stirring speed of 500 rpm, maintaining a vacuum level ≤0.095 MPa, and the mixture was stirred for 1 h. Subsequently, the temperature of the mixing vessel was raised to 80°C, and stirring continued for 2 h under the same vacuum level in an attempt to remove the toluene.

[0043] (3) Curing and shaping: exactly the same as step (3) in Example 1.

[0044] Comparative Example 5 (1) Preparation of prepolymer: In a four-necked flask equipped with a mechanical stirrer, thermometer, nitrogen inlet, and vacuum port, 40 parts by mass of polybutylene adipate diol with a number-average molecular weight of approximately 1000 g / mol were added. The temperature was raised to 80°C under a nitrogen atmosphere. The vacuum pump was turned on, and dehydration was carried out at a vacuum of -0.095 MPa for 1 h. Then the temperature was lowered to 70°C, and 8.9 parts by mass of diphenylmethane diisocyanate and 0.15 parts by mass of dibutyltin dilaurate were added at once. The molar ratio of hydroxyl to isocyanate groups (OH:NCO) was controlled to be 1:1.05. The reaction system was heated to 80°C and kept at this temperature for 4 h. During the reaction, the NCO content was measured periodically. The reaction was stopped when the NCO content reached 1.5%, and a high molecular weight NCO-terminated prepolymer was obtained.

[0045] (2) Mixing and degassing: exactly the same as step (2) in Example 1.

[0046] (3) Curing and shaping: exactly the same as step (3) in Example 1.

[0047] All samples were tested using the following methods, and the results are shown in Table 1.

[0048] Detection method: Melt viscosity: A Bollerfeld rotational viscometer equipped with a small sample adapter and an SC4-27 rotor was used. Samples were heated to specified temperatures (90°C, 100°C, 110°C) and held at that temperature for 10 min, followed by melting at a shear rate of 10 s⁻¹. -1 The viscosity value is measured in mPa·s.

[0049] Shear strength (low-temperature construction): Refer to GB / T 7124-2008. Place two sandblasted low-carbon steel sheets (100 mm × 25 mm × 1.5 mm) in a 0℃ constant temperature chamber for 2 hours to pre-cool. Melt the hot melt adhesive at 110℃ and quickly apply it to the bonding surface of one of the pre-cooled steel sheets (approximately 150 g / m²). 2 Immediately overlap the bonded sample with another pre-cooled steel sheet (overlap area 12.5 mm × 25 mm) and apply a pressure of 0.5 MPa. Immediately return the bonded sample to a 0°C environment. Remove the sample after 10 min and 7 days of curing, and test its tensile shear strength at room temperature using a universal tensile testing machine at a rate of 10 mm / min. The result is the average of five samples, in MPa.

[0050] Elongation at break: Referring to GB / T 528-2009, the hot melt adhesive was made into a 2 mm thick sheet and stamped into a dumbbell-shaped specimen. After curing the specimen under standard conditions (23℃, 50%RH) for 7 days, it was tested using a tensile testing machine, and the elongation at break was calculated, in percentage.

[0051] Low-Temperature Workability Evaluation: Practical Operation Evaluation. Hot melt adhesive granules were added to a commercially available manual hot melt glue gun set to 110℃. After preheating for 20 minutes, continuous extrusion was attempted onto a glass plate at 0℃. The smoothness of extrusion, the continuity of the adhesive strip, and the leveling and spreading on the glass plate were observed. The evaluation was divided into three levels: Excellent (smooth, continuous, good spreading), Good (can be extruded, slightly discontinuous), and Poor (difficult to extrude, severe strip breakage, unable to spread).

[0052] As can be seen from the above results, Examples 1-3 of the present invention successfully solved the core problem of poor workability of traditional PUR hot melt adhesives at low temperatures through the combined effect of three core technical features: the selection of low-crystallization-point / low-viscosity polyester polyols, the synergistic combination of low-melting-point plasticizers and reactive diluents, and the control of the NCO content of the prepolymer within a moderate range of 3-6%. At the critical low-temperature construction temperature of 90℃, the melt viscosity of the examples can be controlled at around 8000 mPa·s, which is much lower than that of Comparative Example 1 and Comparative Example 5. This makes the adhesive of the examples smooth to extrude in a manual glue gun and spread well on a substrate at 0℃, achieving excellent or good workability evaluations. In contrast, Comparative Examples 1 and 5 were evaluated as poor due to excessively high viscosity, making them difficult to apply in practice. More importantly, the excellent flowability directly translates into outstanding wetting ability on low-temperature substrates. Combined with the physical plasticizing effect provided by the reactive diluent in the early stages of curing and its later integration into the cross-linking network through chemical reaction, the example achieved an initial tack strength exceeding 0.78 MPa within 10 minutes in the highly challenging 0°C substrate curing test, ensuring rapid positioning. After 7 days of curing, the final shear strength reached over 4.9 MPa, fully meeting the strength requirements of structural bonding. In contrast, Comparative Example 3, due to insufficient low-temperature wetting, had an initial tack strength of only 0.45 MPa. Although Comparative Example 4 underwent post-treatment to remove the solvent, it inevitably led to porosity and shrinkage in the adhesive layer, severely degrading its final strength. This powerfully demonstrates the irreplaceable role of reactive diluent technology in balancing workability and final performance. Comparative Example 2, lacking a low-melting-point plasticizer, was slightly inferior to the example in viscosity and workability, indicating that the plasticizer clearly contributes to improving processing flowability. Furthermore, the embodiments achieved excellent low-temperature workability and bond strength while maintaining an elongation at break of over 510%, demonstrating good flexibility and impact resistance potential. In contrast, Comparative Example 5, due to the excessively large molecular weight of the prepolymer, resulted in brittle colloid, with an elongation at break of only 150%. In summary, this invention, through the compatibility of multiple components and precise control of process parameters, synergistically achieves a series of goals that are difficult to simultaneously attain in traditional technologies, including low application viscosity, excellent low-temperature substrate wettability, high initial tack, high final strength, and good toughness.

[0053] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0054] The present invention and its embodiments have been described above. This description is not restrictive, but merely one embodiment of the present invention, and the actual application is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar methods and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A low-temperature applicable PUR hot melt adhesive, characterized in that, The product comprises the following components by weight: 30-50 parts polyester polyol, 10-20 parts isocyanate, 5-15 parts low melting point plasticizer, 3-10 parts reactive diluent, 0.1-0.5 parts catalyst, and 10-25 parts filler.

2. The low-temperature applicable PUR hot melt adhesive according to claim 1, characterized in that, The polyester polyols include low-crystallinity or amorphous polyester polyols with a number-average molecular weight of 1000-2000 g / mol, a hydroxyl value of 55-112 mgKOH / g, and a viscosity of 2000-5000 mPa·s at 25°C.

3. The low-temperature applyable PUR hot melt adhesive according to claim 2, characterized in that, The polyester polyol is selected from at least one of polybutylene adipate diol, polyethylene adipate diol, and poly(ε-caprolactone diol).

4. The low-temperature applyable PUR hot melt adhesive according to claim 1, characterized in that, The isocyanate is selected from at least one of diphenylmethane diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate.

5. The low-temperature applyable PUR hot melt adhesive according to claim 1, characterized in that, The low-melting-point plasticizer is selected from at least one of dioctyl phthalate, dioctyl adipate, tributyl citrate, and epoxidized soybean oil.

6. The low-temperature applyable PUR hot melt adhesive according to claim 1, characterized in that, The reactive diluent is selected from at least one of hydroxyethyl acrylate, hydroxyethyl methacrylate, and glycidyl ether epoxy reactive diluents; the catalyst is selected from at least one of dibutyltin dilaurate and stannous octoate.

7. The low-temperature applyable PUR hot melt adhesive according to claim 1, characterized in that, The filler is selected from at least one of calcium carbonate, talc, and fumed silica.

8. A method for preparing a low-temperature applyable PUR hot melt adhesive according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Preparation of terminal isocyanate-based prepolymer: Under inert gas protection, the polyester polyol is heated to 70-90℃ and vacuum dehydrated for 0.5-2 h; then cooled to 60-80℃, isocyanate and catalyst are added, and the reaction is carried out at 70-85℃ for 2-4 h until the NCO content of the system reaches the theoretical value, thus obtaining the terminal isocyanate-based prepolymer; S2. Mixing and molding: Cool the prepolymer obtained in step S1 to 40-60℃, add low melting point plasticizer, reactive diluent and filler in sequence, stir and mix for 0.5-1.5 h under vacuum degree ≤0.095 MPa until the mixture is uniform and the air bubbles are removed; S3. Pour the mixture obtained in step S2 into a mold and seal it at room temperature for 24-72 hours to obtain the low-temperature workable PUR hot melt adhesive.

9. The preparation method according to claim 8, characterized in that, In step S1, the theoretical value of the NCO content in the reaction is controlled between 3% and 6%; in step S1, the molar ratio of the polyester polyol to the isocyanate is 1:1.5-2.2 based on the ratio of hydroxyl to isocyanate groups.

10. The preparation method according to claim 8, characterized in that, In step S2, the mixing and shaping stirring speed is 300-800 rpm.

Images