Low-temperature impact-resistant polyurethane hot melt adhesive film and preparation method thereof

Abstract

The application discloses a low-temperature impact-resistant polyurethane hot melt adhesive film and a preparation method thereof. The polyurethane hot melt adhesive film comprises the following components in parts by weight: a polyurethane matrix 60-80 parts; a modified auxiliary agent 3-30 parts; a hydroxyl-terminated polydimethylsiloxane 0.5-8 parts; a polycarbodiimide 0.2-3 parts; a light stabilizer 0.05-2 parts; an antioxidant 0.05-1 part; and a rheological modifier 0.05-2 parts. The polyurethane hot melt adhesive film can still maintain good flexibility and impact energy dissipation capacity in a low-temperature environment, effectively reduces the risk of low-temperature bending cracking and brittle fracture, and significantly improves the low-temperature repeated bending performance and impact resistance.

Description

Technical Field

[0001] This invention relates to the field of polyurethane film technology, and in particular to a low-temperature impact-resistant polyurethane hot melt adhesive film and its preparation method. Background Technology

[0002] Hot melt adhesives are gradually replacing traditional needles and glues due to their strong bonding, ease of use, low cost, and lack of pollution. Currently, common hot melt adhesive films include PES, PA, EVA, and TPU. Among them, polyurethane, with its diverse synthetic raw materials and highly customizable formulations, can meet the bonding and application requirements of various substrates. Currently, commonly used industrial hot melt adhesive films mainly include polyester hot melt adhesive films (PES), polyamide hot melt adhesive films (PA), ethylene-vinyl acetate copolymer hot melt adhesive films (EVA), and polyurethane hot melt adhesive films (TPU). Polyurethane hot melt adhesive films, with their abundant raw material sources, adjustable soft and hard segment structure, high degree of molecular design freedom, excellent bonding performance, flexibility, and good adaptability to various substrates, allow for the adjustment of heat resistance, softness, bonding strength, and weather resistance according to different application requirements. Therefore, it has become the most widely used and best-performing type of hot melt adhesive film material.

[0003] However, existing commercially available polyurethane hot melt adhesive films still have significant drawbacks in low-temperature environments. Due to the high glass transition temperature of some soft segments in the polyurethane system, the molecular chain mobility decreases significantly at low temperatures, making the material prone to low-temperature embrittlement. When subjected to external impact or repeated bending in environments at -20°C and below, cracks or even breakage can easily occur, leading to film failure. This makes it difficult to meet the application requirements of outdoor equipment, winter footwear, automotive interiors, and low-temperature composite materials in cold regions.

[0004] Therefore, developing a low-temperature impact-resistant polyurethane hot melt adhesive film that can significantly improve the impact resistance and repeated bending resistance of polyurethane hot melt adhesive film under low-temperature conditions, while also taking into account its hydrolysis resistance, aging resistance and yellowing resistance, and is suitable for industrial-scale production, has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a low-temperature impact-resistant polyurethane hot melt adhesive film and its preparation method.

[0006] This invention provides a polyurethane hot melt adhesive film, characterized in that it comprises the following components in parts by weight: The polyurethane matrix comprises 60 to 80 parts, for example, one or any two of 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, and 80 parts, preferably 65 to 75 parts. The modifying agent is 3 to 30 parts, for example, one or any two of 3, 10, 15, 20, 25, and 30 parts, preferably 10 to 20 parts; Hydroxyl-terminated polydimethylsiloxane, 0.5 to 8 parts, for example, the range of one or any two of 0.5, 1, 2, 3, 4, 5, 6, 7, 8 parts; 0.2 to 3 parts of polycarbodiimide, for example, one or any two of the following: 0.2, 0.5, 1, 1.5, 2, 2.5, or 3 parts; The light stabilizer is used in amounts of 0.05 to 2 parts, for example, one or any two of the following: 0.05, 0.1, 0.5, 1, 1.5, or 2 parts. Antioxidant 0.05 to 1 part, for example, a range of one or both of the following: 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 part; The rheology modifier is used in a range of 0.05 to 2 parts, for example, 0.05, 0.1, 0.5, 1, 1.5, 2 parts or any two of these ranges. The molecular chain of the modified additive contains polytetrahydrofuran ether structural units, polypropylene glycol structural units, hydroxyethyl methacrylate structural units, and hydrogenated rosin ester structural units.

[0007] It is understood that when adjustments are made within the above-mentioned numerical range, those skilled in the art can obtain technical solutions with essentially equivalent technical effects through conventional experiments based on the disclosure of this invention, and all such solutions fall within the protection scope of this invention.

[0008] In this invention, both polytetrahydrofuran ether (PTMG) and polypropylene glycol (PPG) structural units have low glass transition temperatures and can be introduced into the polyurethane system as low-temperature flexible segments to lower the overall glass transition temperature of the hot melt adhesive system and improve the molecular chain mobility at low temperatures. The PTMG segments provide good flexibility and mechanical support, while the PPG segments further improve the material's softness and low-temperature elastic recovery. The combination of the two can balance low-temperature impact resistance and repeated bending resistance. The hydroxyl and polar ester groups in the hydroxyethyl methacrylate (HEMA) structural unit enhance the interfacial interaction between the modifier and the polyurethane matrix, improving the compatibility between the two phases. The hydrogenated rosin ester structural unit has both tackifying and stabilizing effects; its cyclic rigid structure enhances intermolecular forces, improves the wetting ability and interfacial adhesion of the polyurethane system to the substrate surface, and effectively reduces the significant decrease in peel strength as the ambient temperature decreases.

[0009] In some embodiments, the mass ratio of the modified additive to hydroxyl-terminated polydimethylsiloxane is (4~15):1. Hydroxyl-terminated polydimethylsiloxane has an extremely low glass transition temperature and a flexible Si-O backbone structure, which can form a flexible, energy-dissipating phase in the polyurethane system. During low-temperature impact or repeated bending, it promotes uniform stress dispersion and reduces local stress concentration, thereby slowing crack propagation and improving the low-temperature impact resistance and repeated bending resistance of the adhesive film. Simultaneously, its terminal hydroxyl groups enhance interfacial compatibility with the polyurethane system, reducing the risk of easy migration and precipitation of ordinary siloxane materials and avoiding a decrease in adhesive strength due to interfacial instability. When the mass ratio of the modified additive to hydroxyl-terminated polydimethylsiloxane is within the range of (4~15):1, a stable and synergistic toughening system can be formed, maintaining the low-temperature flexibility of the polyurethane hot melt adhesive film while ensuring the stability of its adhesive performance.

[0010] In some embodiments, the polyurethane matrix is ​​any one or more of polyester-type polyurethane and polyether-type polyurethane. Different types of polyurethane matrices have different characteristics in terms of low-temperature flexibility, hydrolysis resistance, adhesive strength, and heat resistance. Performance balance and optimization can be achieved through reasonable selection or compounding. Without departing from the concept of this invention, those skilled in the art can also select polyurethane materials with similar structural characteristics and properties for replacement or compounding according to different application scenarios.

[0011] In some embodiments, the light stabilizer is one or more of hindered amine light stabilizers, benzotriazole UV absorbers, and triazine UV absorbers.

[0012] In some embodiments, the rheology modifier is a fatty acid amide rheology modifier or a polyolefin wax rheology modifier.

[0013] In some embodiments, the number average molecular weight of the hydroxyl-terminated polydimethylsiloxane is 1,000 to 10,000; this balances its low-temperature toughening ability, system compatibility, and processing stability, thereby achieving a balanced optimization of the low-temperature impact resistance and adhesion performance of the polyurethane hot melt adhesive film.

[0014] In some embodiments, the modified additive is prepared as follows: S1: Mix polytetrahydrofuran ether glycol and polypropylene glycol, and dehydrate under vacuum at 100~110℃ for 1~2 h to obtain a soft segment mixture; S2: Add aliphatic diisocyanate and catalyst to the soft segment mixture, react at 80~85℃ for 1~2 h, add hydroxyethyl methacrylate and stir evenly, react for 1~2 h to obtain polar modified prepolymer. S3: Add hydrogenated rosin ester to the polar modified prepolymer, react at 80~90℃ for 30~60 min, then add a free radical initiator, and react at 75~85℃ for 0.5~1 h to obtain the modified additive.

[0015] Those skilled in the art can make adaptive adjustments to the processing temperature, screw speed, traction speed, and casting parameters according to equipment specifications, production capacity requirements, and product thickness requirements. As long as these adjustments do not substantially deviate from the technical concept of this invention, they all fall within the protection scope of this invention.

[0016] In some embodiments, the catalyst is dibutyltin dilaurate, and the free radical initiator is azobisisobutyronitrile.

[0017] In some embodiments, the thickness of the film is 0.02 to 0.2 mm.

[0018] The present invention also provides a method for preparing the aforementioned low-temperature impact-resistant polyurethane hot melt adhesive film, characterized by comprising the following steps: S1: Weigh out the polyurethane matrix, modifying agent, hydroxyl-terminated polydimethylsiloxane, polycarbodiimide, light stabilizer, antioxidant and rheology modifier according to the mass ratio, and premix them to obtain a mixture; S2: Add the mixture to a twin-screw extruder or internal mixing equipment and melt blend it at 120~180℃ to uniformly disperse the components and obtain a melt rubber compound. S3: The molten adhesive is extruded, cast, and cooled to obtain the polyurethane hot melt adhesive film.

[0019] In some embodiments, the aliphatic diisocyanate is hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), or dicyclohexylmethane diisocyanate (HDI). 12 Any of the following (MDI).

[0020] The polyurethane hot melt adhesive film of the present invention can be applied to shoe material composites, clothing fabric composites, waterproof and breathable membrane composites, automotive interior composites, electronic protective films, outdoor functional materials and low-temperature environment bonding, but is not limited thereto.

[0021] In summary, compared with the prior art, the present invention achieves the following technical effects: 1. This invention introduces a modifying agent containing polytetrahydrofuran ether structural units, polypropylene glycol structural units, hydroxyethyl methacrylate structural units, and hydrogenated rosin ester structural units in its molecular chain. By utilizing low-Tg flexible segments to reduce the glass transition temperature of the system and combining them with a polar anchoring structure to improve interfacial compatibility, the polyurethane hot melt adhesive film can still maintain good flexibility and impact energy dissipation capacity in low-temperature environments. This effectively reduces the risk of low-temperature bending cracking and brittle fracture, and significantly improves the low-temperature resistance to repeated bending and impact resistance.

[0022] 2. This invention utilizes the synergistic effect of polycarbodiimide and the polyurethane system to effectively capture the carboxyl groups formed during polyurethane hydrolysis, inhibiting further degradation of the polyurethane backbone and significantly improving the retention rate of the film's mechanical properties under humid and hot environments. Therefore, while achieving low-temperature toughening modification, it does not sacrifice the original hydrolysis resistance of the polyurethane material, meeting the requirements of humid environments and long-term operating conditions.

[0023] 3. This invention can effectively inhibit the molecular chain degradation and free radical oxidation reaction of polyurethane materials under ultraviolet light and heat-oxygen environment, reduce the generation of chromophores, thereby reducing the risk of yellowing of materials and improving the anti-yellowing performance, weather resistance and long-term service stability of polyurethane hot melt adhesive film, which is especially suitable for outdoor and complex environment use scenarios.

[0024] 4. This invention is prepared using a melt blending-extrusion casting process, with the processing temperature controlled within the range of 120~180℃. It does not require complex reaction equipment or high-cost post-processing. It has the advantages of simple preparation process, wide process window, high production stability, and easy industrial scale-up. It is compatible with existing polyurethane hot melt adhesive film casting production lines and has good prospects for industrial application. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 The image shows the FT-IR infrared spectrum characterization of the modified additive of this invention. Detailed Implementation

[0027] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention are clearly and completely described. 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 should fall within the scope of protection of the present invention.

[0028] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, all materials and reagents used are commercially available.

[0029] I. The main sources of raw materials are as follows: Polytetrahydrofuran ether diol: Industrial grade 99%, Boxuan Chemical (Shandong) Co., Ltd.

[0030] Polypropylene glycol: PPG-400, Anyi Chemical.

[0031] Aliphatic diisocyanates: Hexamethylene diisocyanate, Hongyao Chemical.

[0032] Hydroxyethyl methacrylate: Longhui Chemical.

[0033] Hydrogenated rosin ester: KE-100, Haolong Chemical.

[0034] Polyurethane matrix #1: Polyester type, C85A, BASF, Germany.

[0035] Polyurethane matrix #2: Polyether type, C78A, BASF, Germany.

[0036] Hydroxyl-terminated polydimethylsiloxane: molecular weight 2,000~3,500, Andisil OH-70, Silicones.

[0037] Polycarbodiimide: Huaxiang Kejie Biotechnology.

[0038] The same substance was used in parallel experiments for light stabilizers, antioxidants, and other raw materials.

[0039] II. Preparation of Modifying Additives: S1: Take 6.7 kg of polytetrahydrofuran ether glycol and 3.3 kg of polypropylene glycol, mix them evenly, and put them into a vacuum drying oven. Dehydrate them under vacuum conditions of 105℃ and vacuum degree ≤-0.09 MPa for 1.5 h to completely remove the adsorbed water and trace free water in the raw materials. After dehydration, cool to room temperature to obtain a soft segment mixture. Seal it for later use to avoid re-absorbing moisture and affecting the subsequent polymerization reaction and the hydrolysis resistance of the product.

[0040] S2: The soft segment mixture prepared above was added to the reactor, and nitrogen gas was continuously introduced to isolate oxygen. The stirring speed was controlled at 250 r / min. Then, 1.6 kg of aliphatic diisocyanate and 8 g of dibutyltin dilaurate catalyst were added. After uniform dispersion, the temperature was raised to 82℃ and stirred at a constant temperature for 1.5 h. After the reaction was completed, 1.4 kg of hydroxyethyl methacrylate was slowly added dropwise to the system. The mixture was stirred continuously until uniform and the temperature was maintained at 82℃ for another 1.5 h to obtain the modified prepolymer.

[0041] S3: Add 4.5 kg of hydrogenated rosin ester to 10 kg of modified prepolymer, maintain stirring speed at 320 r / min, heat to 85℃ and stir for 45 min; then dissolve 0.03 kg of azobisisobutyronitrile free radical initiator uniformly in a trace amount of anhydrous solvent, and slowly add it dropwise to the reaction system. After the addition is complete, adjust the system temperature to stabilize at 80℃ and react for 0.8 h; after the reaction is completed, stop heating, cool to room temperature under continuous nitrogen protection, and remove trace amounts of residual monomer and solvent under vacuum to obtain the target product.

[0042] The target product was characterized by infrared spectroscopy, such as Figure 1 As shown, the test scan wavenumber range is 4000 cm⁻¹. -1 ~400 cm -1 The absorption peak characteristics of each band are as follows: 3320 cm⁻¹ -1 A broad absorption peak for the NH stretching vibration of carbamate was observed; 2935 cm⁻¹ -1 2858cm -1 A double peak appears at 1728 cm⁻¹ due to the strong stretching vibrations of saturated methylene and methyl CH. -1 A strong, sharp carbonyl C=O stretching vibration absorption peak appears at 1110 cm⁻¹. -1 The appearance of an extremely strong and broad peak is a characteristic peak of the asymmetric stretching vibration of the COC ether bond in the polyether structure.

[0043] Example 1 The polyurethane hot melt adhesive film of this embodiment has the following components in parts by weight: Polyurethane matrix #1 70 parts, modifying agent 16 parts, hydroxyl-terminated polydimethylsiloxane 2 parts, polycarbodiimide 1.2 parts, light stabilizer 622 0.8 parts, antioxidant 1010 0.4 parts, N,N'-ethylene bis-stearamide 0.6 parts.

[0044] The polyurethane hot melt adhesive film preparation steps in this embodiment are as follows: Step 1: Accurately weigh each raw material according to a fixed weight ratio. First, put the polyurethane matrix resin and self-made modified additives into a high-speed mixer and premix at 650 r / min for 3 minutes to achieve initial homogenization of large-particle resin. Then, add liquid hydroxyl-terminated polydimethylsiloxane, powdered polycarbodiimide, light stabilizer, antioxidant, and rheology modifier in sequence, and continue high-speed stirring for 5 minutes. The total premixing time is 8 minutes to ensure that the liquid additives uniformly coat the resin surface and that the powdered additives do not agglomerate or accumulate in dead corners, thus obtaining a dry, homogeneous mixture.

[0045] Step 2: The premixed material is fed into the twin-screw extruder at a uniform speed. A segmented gradient heating and melting process is adopted, and the specific temperature parameters of each segment are as follows: The temperature of the feeding section is set at 130℃ to preheat and soften the material at a low temperature, ensuring stable material conveying and avoiding local overheating and degradation; the temperature of the melting and plasticizing section is set at 160℃ to fully plasticize and shear the material at a high temperature, so that the self-made modified additives and functional additives can be molecularly compatible and dispersed with the polyurethane matrix, preventing component agglomeration and stratification; the temperature of the die head section is kept constant at 170℃ to achieve constant temperature and pressure discharge from the die head, ensuring stable melt viscosity and uniform overall fluidity; the screw speed of the equipment is fixed at 110 r / min, and the total melting and blending time is 5 min.

[0046] Step 3: Extrude the molten adhesive through an extrusion die with a die gap of 0.12 mm and a casting traction speed of 9 m / min; the melt is bonded to a 25°C cooling roller for shaping, and then pulled by a traction roller at 25°C and a tension of 0.8 N / mm, and wound into a master roll at a tension of 0.5 N / mm and a speed of 9 m / min; then cut into finished rolls with a width of 100 mm and an outer diameter of φ200 mm at a speed of 12 m / min and a winding tension of 0.6 N / mm, to obtain a polyurethane hot melt adhesive film with a thickness of 0.10 ± 0.005 mm.

[0047] Example 2 The polyurethane hot melt adhesive film of this embodiment has the following components in parts by weight: Polyurethane matrix #1 60 parts, modifying agent 3 parts, hydroxyl-terminated polydimethylsiloxane 0.5 parts, polycarbodiimide 0.2 parts, light stabilizer 622 0.05 parts, antioxidant 1010 0.05 parts, N,N'-ethylene bis-stearamide 0.05 parts.

[0048] The preparation steps of the polyurethane hot melt adhesive film in this embodiment are the same as in Embodiment 1.

[0049] Example 3 The polyurethane hot melt adhesive film of this embodiment has the following components in parts by weight: Polyurethane matrix #1 80 parts, modifying agent 30 parts, hydroxyl-terminated polydimethylsiloxane 8 parts, polycarbodiimide 3 parts, light stabilizer 622 2 parts, antioxidant 1010 1 part, N,N'-ethylene bis-stearamide 2 parts.

[0050] The preparation steps of the polyurethane hot melt adhesive film in this embodiment are the same as in Embodiment 1.

[0051] Example 4 The polyurethane hot melt adhesive film of this embodiment has the following components in parts by weight: Polyurethane matrix #1 70 parts, modifying agent 13.5 parts, hydroxyl-terminated polydimethylsiloxane 4.5 parts, polycarbodiimide 1.2 parts, light stabilizer 622 0.8 parts, antioxidant 1010 0.4 parts, N,N'-ethylene bis-stearamide 0.6 parts.

[0052] The preparation steps of the polyurethane hot melt adhesive film in this embodiment are the same as in Embodiment 1.

[0053] Example 5 The polyurethane hot melt adhesive film of this embodiment has the following components in parts by weight: Polyurethane matrix #2 70 parts, modifying agent 16 parts, hydroxyl-terminated polydimethylsiloxane 2 parts, polycarbodiimide 1.2 parts, light stabilizer 622 0.8 parts, antioxidant 1010 0.4 parts, N,N'-ethylene bis-stearamide 0.6 parts.

[0054] The preparation steps of the polyurethane hot melt adhesive film in this embodiment are the same as in Embodiment 1.

[0055] Example 6 The polyurethane hot melt adhesive film of this embodiment has the following components in parts by weight: Polyurethane matrix #1 70 parts, modifying agent 16 parts, hydroxyl-terminated polydimethylsiloxane 2 parts, polycarbodiimide 1.2 parts, light stabilizer 622 0.8 parts, antioxidant 1010 0.4 parts, N,N'-ethylene bis-stearamide 0.6 parts.

[0056] The polyurethane hot melt adhesive film preparation steps in this embodiment are as follows: Step 1: Accurately weigh each raw material according to a fixed weight ratio. First, put the polyurethane matrix resin and self-made modified additives into a high-speed mixer and premix at 500r / min for 5 minutes to achieve initial homogenization of large-particle resin. Then, add liquid hydroxyl-terminated polydimethylsiloxane, powdered polycarbodiimide, light stabilizer, antioxidant, and rheology modifier in sequence, and continue high-speed stirring for 5 minutes. The total premixing time is 8 minutes to ensure that the liquid additives uniformly coat the resin surface and that the powdered additives do not agglomerate or accumulate in dead corners, thus obtaining a dry, homogeneous mixture.

[0057] Step 2: The premixed material is fed into the twin-screw extruder at a uniform speed. A segmented gradient heating and melting process is adopted, and the specific temperature parameters of each segment are as follows: The temperature of the feeding section is set at 120℃ to preheat and soften the material at a low temperature, ensuring stable material conveying and avoiding local overheating and degradation; the temperature of the melting and plasticizing section is set at 150℃ to fully plasticize and shear the material at a high temperature, so that the self-made modified additives and functional additives can be molecularly compatible and dispersed with the polyurethane matrix, preventing component agglomeration and stratification; the temperature of the die head section is kept constant at 180℃ to achieve constant temperature and pressure discharge from the die head, ensuring stable melt viscosity and uniform overall fluidity; the screw speed of the equipment is fixed at 80 r / min, and the total melting and blending time is 8 min.

[0058] Step 3: Extrude the molten adhesive through an extrusion die with a die gap of 0.12 mm and a casting traction speed of 9 m / min; the melt is bonded to a 25°C cooling roller for shaping, and then pulled by a traction roller at 25°C and a tension of 0.8 N / mm, and wound into a master roll at a tension of 0.5 N / mm and a speed of 9 m / min; then cut into finished rolls with a width of 100 mm and an outer diameter of φ200 mm at a speed of 12 m / min and a winding tension of 0.6 N / mm, to obtain a polyurethane hot melt adhesive film with a thickness of 0.10 ± 0.005 mm.

[0059] Comparative Example 1 The amounts of each component in the polyurethane hot melt adhesive film of this comparative example, by weight, are as follows: Polyurethane matrix #1 86 parts, hydroxyl-terminated polydimethylsiloxane 2 parts, polycarbodiimide 1.2 parts, light stabilizer 622 0.8 parts, antioxidant 1010 0.4 parts, N,N'-ethylene bis-stearamide 0.6 parts.

[0060] The preparation steps for the polyurethane hot melt adhesive film in this comparative example are the same as in Example 1.

[0061] Comparative Example 2 The amounts of each component in the polyurethane hot melt adhesive film of this comparative example, by weight, are as follows: Polyurethane matrix #1 72 parts, modifying agent 16 parts, polycarbodiimide 1.2 parts, light stabilizer 622 0.8 parts, antioxidant 1010 0.4 parts, N,N'-ethylene bis-stearamide 0.6 parts.

[0062] The preparation steps for the polyurethane hot melt adhesive film in this comparative example are the same as in Example 1.

[0063] Comparative Example 3 The amounts of each component in the polyurethane hot melt adhesive film of this comparative example, by weight, are as follows: Polyurethane matrix #1 71.2 parts, modifying agent 16 parts, hydroxyl-terminated polydimethylsiloxane 2 parts, light stabilizer 622 0.8 parts, antioxidant 1010 0.4 parts, N,N'-ethylene bis-stearamide 0.6 parts.

[0064] The preparation steps for the polyurethane hot melt adhesive film in this comparative example are the same as in Example 1.

[0065] Comparative Example 4 The amounts of each component in the polyurethane hot melt adhesive film of this comparative example, by weight, are as follows: Polyurethane matrix #1 70 parts, modifying agent 35 parts, hydroxyl-terminated polydimethylsiloxane 2 parts, polycarbodiimide 1.2 parts, light stabilizer 622 0.8 parts, antioxidant 1010 0.4 parts, N,N'-ethylene bis-stearamide 0.6 parts.

[0066] The preparation steps for the polyurethane hot melt adhesive film in this comparative example are the same as in Example 1.

[0067] Comparative Example 5 The amounts of each component in the polyurethane hot melt adhesive film of this comparative example, by weight, are as follows: Polyurethane matrix #1 70 parts, modifying agent 16 parts, hydroxyl-terminated polydimethylsiloxane 10 parts, polycarbodiimide 1.2 parts, light stabilizer 622 0.8 parts, antioxidant 1010 0.4 parts, N,N'-ethylene bis-stearamide 0.6 parts.

[0068] The preparation steps for the polyurethane hot melt adhesive film in this comparative example are the same as in Example 1.

[0069] Test methods 1. Low-temperature bending resistance: According to GB / T 13934-2006 standard, the test conditions were -25℃, bending angle 180°, and reciprocating bending frequency 60 times / min. The samples were cut into strips 150 mm long and 20 mm wide, and placed in a low-temperature test chamber for 2 hours to ensure the overall temperature of the samples reached -25℃. The samples were then clamped on a flexural testing machine and repeatedly bent at 180°. The number of bends at which cracking, fissures, and fracture occurred was recorded. Five samples were tested in parallel for each group, and the average value was taken. The higher the value, the better the low-temperature impact resistance / flexural strength.

[0070] 2. Hydrolysis resistance: According to GB / T 1690-2010 standard, the test conditions were: temperature 50℃, relative humidity 95% RH, duration 1000 h. The test method was as follows: the film sample was placed in a constant temperature and humidity chamber and continuously placed at 50℃ and 95% relative humidity for 1000 h; after removing the sample, it was allowed to thaw at 23℃ and 50% relative humidity for 2 h, and the tensile strength was tested according to GB / T 528-2009.

[0071] Tensile strength retention rate = (Tensile strength after aging ÷ Original tensile strength) × 100%.

[0072] 3. Resistance to yellowing (xenon lamp aging) Referring to GB / T 16422.3-2014 standard, the test conditions were: continuous xenon lamp irradiation, with an irradiance of 0.51 W / (m²). 2 • 340nm), black standard temperature 60℃, relative humidity of the chamber 50%, total irradiation time 500 h. Yellowing evaluation: The yellow index (YI) of the samples before and after aging was tested according to GB / T 2409-2021, and the yellow index after aging was used as the evaluation index; 3 points were tested for each group of samples, and the average value was taken. The smaller the value, the stronger the resistance to yellowing.

[0073] The test results are shown in Table 1.

[0074] Table 1 Performance test results of the examples and comparative examples

[0075] Table 1 shows that the polyurethane hot melt adhesive film of the present invention exhibits excellent performance in terms of low-temperature flexural resistance, hydrolysis resistance, and yellowing resistance. The present invention, through a multi-component synergistic system, balances interfacial adhesion stability and long-term durability, effectively overcoming the problems of traditional polyurethane hot melt adhesive films being prone to brittleness and cracking during low-temperature environments, as well as hydrolysis and yellowing during long-term use. When the mass ratio of the modifying agent to hydroxyl-terminated polydimethylsiloxane is controlled within the range of (4~15):1, the two can form a stable synergistic effect, enabling the adhesive film to possess both low-temperature flexibility and stable adhesive strength, thereby significantly improving low-temperature flexural resistance.

[0076] Compared with Example 1, Comparative Example 1 did not add the self-made modifying agent, lost the core low-temperature toughening unit, and only had 75 bending cycles, highlighting the problem of low-temperature brittleness; Comparative Example 2 lacked hydroxyl-terminated polydimethylsiloxane, and the synergistic toughening system was missing, resulting in significantly worse low-temperature performance; Comparative Example 3 did not add polycarbodiimide, and the polyurethane molecular chains rapidly hydrolyzed and degraded under humid and hot conditions, with a strength retention rate of only 56%; Comparative Examples 4 and 5 had compatibility issues, and their bending resistance decreased simultaneously.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A polyurethane hot melt adhesive film, characterized in that, Based on parts by weight, it comprises the following components: 60-80 parts of polyurethane matrix; Modifying additives: 3-30 parts; Hydroxyl-terminated polydimethylsiloxane 0.5-8 parts; 0.2-3 parts of polycarbodiimide; Light stabilizer 0.05~2 parts; Antioxidant 0.05~1 part; Rheology modifier 0.05~2 parts; The molecular chain of the modified additive contains polytetrahydrofuran ether structural units, polypropylene glycol structural units, hydroxyethyl methacrylate structural units, and hydrogenated rosin ester structural units.

2. The polyurethane hot melt adhesive film according to claim 1, characterized in that, The mass ratio of the modified additive to the hydroxyl-terminated polydimethylsiloxane is (4~15):

1.

3. The polyurethane hot melt adhesive film according to claim 1, characterized in that, The polyurethane matrix is ​​any one or more of polyester-type polyurethane and polyether-type polyurethane.

4. The polyurethane hot melt adhesive film according to claim 1, characterized in that, The light stabilizer is one or more of the following: hindered amine light stabilizers, benzotriazole UV absorbers, and triazine UV absorbers.

5. The polyurethane hot melt adhesive film according to claim 1, characterized in that, The rheology modifier is a fatty acid amide rheology modifier or a polyolefin wax rheology modifier.

6. The polyurethane hot melt adhesive film according to claim 1, characterized in that, The number average molecular weight of the hydroxyl-terminated polydimethylsiloxane is 1000~10000.

7. The polyurethane hot melt adhesive film according to claim 1, characterized in that, The preparation method of the modified additive is as follows: S1: Mix polytetrahydrofuran ether glycol and polypropylene glycol, and dehydrate under vacuum at 100~110℃ for 1~2 h to obtain a soft segment mixture; S2: Add aliphatic diisocyanate and catalyst to the soft segment mixture, react at 80~85℃ for 1~2 h, add hydroxyethyl methacrylate and stir evenly, react for 1~2 h to obtain polar modified prepolymer. S3: Add hydrogenated rosin ester to the polar modified prepolymer, react at 80~90℃ for 30~60 min, then add a free radical initiator, and react at 75~85℃ for 0.5~1 h to obtain the modified additive.

8. The polyurethane hot melt adhesive film according to claim 7, characterized in that, The catalyst is dibutyltin dilaurate, and the free radical initiator is azobisisobutyronitrile.

9. The polyurethane hot melt adhesive film according to claim 1, characterized in that, The thickness of the film is 0.02~0.2mm.

10. The method for preparing the low-temperature impact-resistant polyurethane hot melt adhesive film according to any one of claims 1 to 9, characterized in that, Includes the following steps: S1: Weigh out the polyurethane matrix, modifying agent, hydroxyl-terminated polydimethylsiloxane, polycarbodiimide, light stabilizer, antioxidant and rheology modifier according to the mass ratio, and premix them to obtain a mixture; S2: Add the mixture to a twin-screw extruder or internal mixing equipment and melt blend it at 120~180℃ to uniformly disperse the components and obtain a melt rubber compound. S3: The molten adhesive is extruded, cast, and cooled to obtain the polyurethane hot melt adhesive film.

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