Hot melt adhesive film with high bonding strength and preparation method thereof

Abstract

The invention belongs to the technical field of hot melt adhesive films, and particularly relates to a hot melt adhesive film with high bonding strength and a preparation method thereof. The preparation method comprises the following steps: (1) mixing o-vanillin double five-membered cyclic carbonate and phosphorus-containing diamine, and carrying out polymerization reaction under a heating condition to obtain a prepolymer; and (2) carrying out vacuum defoaming treatment on the prepolymer, then coating to form a film, curing, cooling and stripping to obtain the film. An o-vanillin bio-based rigid framework and a Schiff base bond structure in the o-vanillin bio-based rigid framework are used for enhancing cohesive energy and interface interaction, and meanwhile, phosphorus is introduced into a polymer main chain in a covalent bond mode, so that intrinsic flame retardance is achieved. The obtained hot melt adhesive film has high tensile strength, high bonding strength, excellent flame retardance and good heat resistance and water resistance.

Description

Technical Field

[0001] This invention belongs to the field of hot melt adhesive film technology, specifically relating to a hot melt adhesive film with high bonding strength and its preparation method. Background Technology

[0002] Hot melt adhesive films, as a highly efficient and environmentally friendly solid adhesive, achieve rapid bonding by heating and melting, coating, and then cooling and curing. They are widely used in packaging, textiles, electronic assembly, automotive interiors, and composite material lamination. Traditional high-performance hot melt adhesive films mainly rely on petroleum-based raw materials such as polyesters, polyamides, polyolefins, and their derivatives, and achieve excellent flexibility and bonding strength through the reaction of isocyanates with polyols to form a polyurethane structure. However, this technological approach has significant drawbacks: firstly, petroleum-based raw materials are non-renewable, which does not align with the concept of green and sustainable development; secondly, isocyanate monomers are highly toxic and sensitive to moisture, and their use and residues pose potential risks to production safety and the health and environmental impact of end products.

[0003] To address these issues, non-isocyanate polyurethane (NIPU) technology has emerged. NIPU is typically prepared through ring-opening polymerization of cyclic carbonates and polyamine compounds, eliminating the need for isocyanates. The resulting polymer backbone is rich in hydroxyl groups, which are expected to improve adhesion and material toughness through hydrogen bonding. In recent years, researchers have attempted to replace petroleum-based raw materials with bio-based raw materials such as vegetable oils, lignin derivatives, and vanillin to improve the environmental friendliness of products. Meanwhile, to meet the stringent flame retardancy requirements of materials in the electronics, electrical appliances, and transportation industries, flame retardants (such as halogenated, phosphorus-based, nitrogen-based, or inorganic fillers) are often added to adhesives. However, physical blending can easily lead to flame retardant migration and precipitation, resulting in a long-term decrease in flame retardant performance and potentially affecting the transparency, mechanical properties, and interfacial adhesion reliability of the adhesive film.

[0004] While research has yielded progress in bio-based NIPU or flame-retardant adhesives, existing technologies often struggle to simultaneously achieve high bond strength, excellent environmental resistance (temperature and water resistance), and long-lasting, stable inherent flame retardancy. For example, the bond strength of some bio-based NIPU adhesives is insufficient to match that of traditional high-performance products; and the introduction of flame-retardant components often comes at the cost of sacrificing adhesive strength or material flexibility. Therefore, developing a hot melt adhesive film based on renewable resources, with a green and safe synthesis process, and capable of combining high bond strength, long-lasting flame retardancy, and good environmental resistance has become a pressing technical challenge in this field. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a hot melt adhesive film with high bonding strength and a method for preparing the same.

[0006] The objective of this invention is achieved through the following technical solution: The first aspect of this invention provides a method for preparing a hot melt adhesive film with high bonding strength, comprising the following steps: (1) Mix o-vanillin-based bis-pentane carbonate and phosphorus-containing diamine, and polymerize under heating conditions to obtain a prepolymer; (2) The prepolymer is subjected to degassing treatment under reduced pressure, then coated into a film, cured, cooled and peeled off to obtain the hot melt adhesive film with high bonding strength.

[0007] Furthermore, the preparation process of the o-vanillin-based bis-pentanone carbonate in step (1) is as follows: (a) o-vanillin and 1,8-octanediamine were added to ethanol and refluxed in the presence of glacial acetic acid to give o-vanillin-based bis-Schiff base diol; (b) Add o-vanillin-based bis-Schiff base diol to epichlorohydrin and carry out a ring-opening reaction in the presence of a phase transfer catalyst, followed by a ring-closing reaction under the action of a strong base to obtain o-vanillin-based diepoxy monomer. (c) Add the o-vanillin-based bisepoxy monomer and catalyst to N,N-dimethylformamide, and pass carbon dioxide through to carry out a cycloaddition reaction to obtain the o-vanillin-based bispentanone carbonate.

[0008] Further, in step (a), the molar ratio of o-vanillin to 1,8-octanediamine is (2-2.2):1; and the reflux reaction time is 6-8 h.

[0009] Further, in step (b), the ratio of o-vanillin-based bis-Schiff base diol, epichlorohydrin, phase transfer catalyst, and strong base is 1 mmol : (3-4) mL : (0.05-0.06) mmol : (2.5-3) mmol; the phase transfer catalyst is tetrabutylammonium bromide; the strong base is sodium hydroxide or potassium hydroxide; the ring-opening reaction is carried out at a temperature of 70-80 °C for 2-3 h; and the ring-closing reaction is carried out at a temperature of 50-60 °C for 4-6 h.

[0010] Further, in step (c), the molar ratio of the o-vanillin diepoxy monomer and the catalyst is 1:(0.05-0.06); the catalyst is tetrabutylammonium bromide; the pressure is maintained at 1.0-2.0 MPa after carbon dioxide is introduced; the temperature of the cycloaddition reaction is 100-110 °C and the time is 12-24 h.

[0011] Furthermore, the preparation process of the phosphorus-containing diamine described in step (1) is as follows: Methylphosphonic acid is added to dichloromethane, and 3-amino-1-propanol and triethylamine are added under ice bath conditions. The mixture is then heated to react and yield the final product.

[0012] Furthermore, the molar ratio of methylphosphonic acid, 3-amino-1-propanol and triethylamine is 1:(2-2.2):(2-2.2); the heating reaction is carried out at a temperature of 40-45 °C for 4-6 h.

[0013] Further, in step (1), the molar ratio of o-vanillin-based bicyclic carbonate and phosphorus-containing diamine is 1:1; the heating temperature is 90-100 °C, and the polymerization reaction time is 12-24 h.

[0014] Furthermore, the curing temperature in step (2) is 110-120 °C and the time is 12-24 h.

[0015] A second aspect of the present invention provides a hot melt adhesive film with high bonding strength, which is prepared by the preparation method described in the first aspect above.

[0016] The present invention has the following advantages over the prior art: This invention utilizes o-vanillin bio-based monomers to replace traditional petroleum-based raw materials through molecular design and combines a non-isocyanate synthesis route. The preparation process is not only green and environmentally friendly, avoiding the use of highly toxic isocyanates, but also endows the film with extremely strong interfacial hydrogen bonding forces and excellent adhesive strength through the large number of side-chain hydroxyl groups generated by the ring-opening of cyclic carbonates and amines. At the same time, o-vanillin provides a rigid aromatic ring structure, restricting molecular chain movement, increasing material rigidity and cohesive strength, thereby improving the shear strength of the film. The Schiff base bonds (-CH=N-) formed in the molecule not only provide additional molecular rigidity, but their polarity and dynamic properties also help to enhance the interfacial interaction between the film and the substrate and improve the toughness of the material. Furthermore, this invention introduces phosphorus into the main chain through covalent bonds, achieving reactive intrinsic flame retardancy, effectively preventing the migration and precipitation of flame retardants, and significantly improving the heat resistance and safety performance of hot melt adhesives by utilizing the phosphorus-nitrogen synergistic effect; while the long-chain 1,8-octanediamine fragment and aromatic ring structure can endow the film with a certain degree of hydrophobicity, hindering the penetration and swelling of water molecules, ultimately obtaining a high-performance green hot melt adhesive film with high bonding strength, flame retardancy, heat resistance and water resistance. Attached Figure Description

[0017] Figure 1 The route diagram for the synthesis of o-vanillin-based bis-pentanone carbonate in Example 1; Figure 2 The route diagram for the synthesis of phosphorus-containing diamines in Example 5; Figure 3 This is a schematic diagram of the polymerization process of vanillin-based bis-pentanone carbonate and phosphorus-containing diamine in Example 1; Figure 4 The image shown is the FT-IR image of the hot melt adhesive film in Example 1. Detailed Implementation

[0018] The technical solution of the present invention will be further described below with reference to specific embodiments. However, those skilled in the art should understand that the following embodiments are only for illustrating the present invention and should not be regarded as limiting the present invention. Specific conditions not specified in the embodiments are performed according to conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the reagents or instruments used are all conventional products obtained through commercial channels.

[0019] Preparation Example 1 A type of o-vanillin-based bis-pentanone carbonate, the preparation process of which is as follows: Figure 1 As shown, the specific steps are as follows: (a) o-vanillin (21 mmol) and 1,8-octanediamine (10 mmol) were added to 50 mL of anhydrous ethanol, and 2-3 drops of glacial acetic acid were added as a catalyst. The mixture was refluxed at 75 °C for 8 h. A yellow precipitate was formed during the reaction. After the reaction was completed, the mixture was cooled to room temperature, and the precipitate was collected by filtration. The filter cake was washed three times with cold ethanol to remove unreacted o-vanillin. The mixture was then dried under vacuum to obtain a yellow powder of o-vanillin-based bis-Schiff base diol with a yield of 90.0%. 1 H NMR (C 24 H 32 N2O4, 400MHz, DMSO-d6) δ 13.55(s, 2H), 8.70(s, 2H), 7.34(d, 2H), 7.01(d, 2H), 6.86(t, 2H), 3.85(s, 6H), 3.71(t, 4H), 1.67-1.62(m, 4H), 1.30-1.25(m, 8H); HRMS(ESI + ): [M+H] + The calculated value is 413.24, and the target compound is found. The above results indicate that this is the target compound.

[0020] (b) The o-vanillin-based bis-Schiff base diol (10 mmol) obtained in step a was added to 35 mL of epichlorohydrin, and then tetrabutylammonium bromide (TBAB, 0.55 mmol) was added as a phase transfer catalyst. The mixture was stirred at 75 °C for 2 h. Then the temperature was lowered to 55 °C, and 20% sodium hydroxide aqueous solution (28 mmol) was added dropwise in portions. The reaction was continued for 5 h to achieve ring closure. After the reaction was completed, excess epichlorohydrin was removed by vacuum distillation. The residue was dissolved in dichloromethane, washed with water until neutral, dried over anhydrous magnesium sulfate, and the solvent was removed by rotary evaporation to obtain the o-vanillin-based diepoxy monomer with a yield of 84.6%. 1 H NMR (C 30 H 40N2O6, 400MHz, DMSO-d6) δ 8.70(s, 2H), 7.50(d, 2H), 7.21(d, 2H), 6.98(t, 2H), 4.19-4.15(m,2H), 3.94-3.90(m, 2H), 3.86(s, 6H), 3.71(t, 4H), 3.06-3.01(m, 2H), 2.61-2.57(m, 2H), 2.36-2.32(m, 2H), 1.67-1.62(m, 4H), 1.30-1.25(m, 8H); HRMS(ESI + ): [M+H] + The calculated value is 525.29, and the target compound is found. The above results indicate that this is the target compound.

[0021] (c) The o-vanillin-based diepoxide monomer (10 mmol) obtained in step b and tetrabutylammonium bromide (TBAB, 0.55 mmol) were added to a high-pressure reactor and dissolved in 25 mL of N,N-dimethylformamide (DMF). CO2 gas was then introduced and the pressure was maintained at 1.5 MPa. The reaction was carried out at 105 °C for 18 h. After the reaction was completed, the pressure was released, the solvent was removed by vacuum distillation, the product was recrystallized from ethanol, and dried under vacuum to obtain o-vanillin-based bis-pentanone carbonate with a yield of 94.5%. 1 H NMR (C 32 H 40 N2O 10 , 400MHz, DMSO-d6) δ 8.70(s, 2H), 7.50(d, 2H), 7.21(d, 2H), 6.98(t,2H), 4.72-4.68(m, 2H), 4.30-4.25(m, 4H), 4.06-4.01(m, 4H), 3.86(s, 6H), 3.71(t, 4H), 1.67-1.62(m, 4H), 1.30-1.25(m, 8H); HRMS(ESI + ): [M+H] + The calculated value is 613.27, and the target compound is found. The above results indicate that this is the target compound.

[0022] Preparation Example 2 A type of o-vanillin-based bis-pentanone carbonate, the preparation process of which is as follows: Figure 1 As shown, the specific steps are as follows: (a) o-vanillin (20 mmol) and 1,8-octanediamine (10 mmol) were added to 50 mL of anhydrous ethanol, and 2-3 drops of glacial acetic acid were added as a catalyst. The mixture was refluxed at 80 °C for 6 h. A yellow precipitate was formed during the reaction. After the reaction was completed, the mixture was cooled to room temperature, and the precipitate was collected by filtration. The filter cake was washed three times with cold ethanol to remove unreacted o-vanillin. The mixture was dried under vacuum to obtain a yellow powder of o-vanillin-based bis-Schiff base diol with a yield of 85.8%.

[0023] (b) The o-vanillin-based bis-Schiff base diol (10 mmol) obtained in step a was added to 30 mL of epichlorohydrin, and then tetrabutylammonium bromide (TBAB, 0.5 mmol) was added as a phase transfer catalyst. The mixture was stirred at 70 °C for 3 h. Then the temperature was lowered to 50 °C, and 20% sodium hydroxide aqueous solution (25 mmol) was added dropwise in batches. The reaction was continued for 6 h to achieve ring closure. After the reaction was completed, excess epichlorohydrin was removed by vacuum distillation. The residue was dissolved in dichloromethane, washed with water until neutral, dried over anhydrous magnesium sulfate, and the solvent was removed by rotary evaporation to obtain the o-vanillin-based diepoxy monomer with a yield of 80.9%.

[0024] (c) The o-vanillin-based diepoxy monomer (10 mmol) and tetrabutylammonium bromide (TBAB, 0.5 mmol) obtained in step b were added to a high-pressure reactor and dissolved in 20 mL of N,N-dimethylformamide (DMF). CO2 gas was then introduced and the pressure was maintained at 1.0 MPa. The reaction was carried out at 100 °C for 24 h. After the reaction was completed, the pressure was released, the solvent was removed by vacuum distillation, the product was recrystallized from ethanol, and dried under vacuum to obtain o-vanillin-based bis-pentane ring carbonate with a yield of 90.7%.

[0025] Preparation Example 3 A type of o-vanillin-based bis-pentanone carbonate, the preparation process of which is as follows: Figure 1 As shown, the specific steps are as follows: (a) o-vanillin (22 mmol) and 1,8-octanediamine (10 mmol) were added to 50 mL of anhydrous ethanol, and 2-3 drops of glacial acetic acid were added as a catalyst. The mixture was refluxed at 80 °C for 6 h. A yellow precipitate was formed during the reaction. After the reaction was completed, the mixture was cooled to room temperature, and the precipitate was collected by vacuum filtration. The filter cake was washed three times with cold ethanol to remove unreacted o-vanillin. The mixture was then dried under vacuum to obtain a yellow powder of o-vanillin-based bis-Schiff base diol with a yield of 88.4%.

[0026] (b) The o-vanillin-based bis-Schiff base diol (10 mmol) obtained in step a was added to 40 mL of epichlorohydrin, and then tetrabutylammonium bromide (TBAB, 0.6 mmol) was added as a phase transfer catalyst. The mixture was stirred at 80 °C for 2 h. Then the temperature was lowered to 60 °C, and 20% sodium hydroxide aqueous solution (30 mmol) was added dropwise in batches. The reaction was continued for 4 h to achieve ring closure. After the reaction was completed, excess epichlorohydrin was removed by vacuum distillation. The residue was dissolved in dichloromethane, washed with water until neutral, dried over anhydrous magnesium sulfate, and the solvent was removed by rotary evaporation to obtain the o-vanillin-based diepoxy monomer with a yield of 82.4%.

[0027] (c) The o-vanillin-based diepoxy monomer (10 mmol) and tetrabutylammonium bromide (TBAB, 0.6 mmol) obtained in step b were added to a high-pressure reactor and dissolved in 25 mL of N,N-dimethylformamide (DMF). CO2 gas was then introduced and the pressure was maintained at 2.0 MPa. The reaction was carried out at 110 °C for 12 h. After the reaction was completed, the pressure was released, the solvent was removed by vacuum distillation, the product was recrystallized from ethanol, and dried under vacuum to obtain o-vanillin-based bis-pentane ring carbonate with a yield of 92.8%.

[0028] Preparation Example 4 Preparation Example 4 is basically the same as Preparation Example 1, except that steps (a) and (b) are omitted, and the o-vanillin diepoxy monomer in step (c) is replaced with bisphenol A diglycidyl ether with an epoxy value of 0.48-0.54 mol / 100g. The product obtained is a bisphenol A type bispentanone carbonate.

[0029] Preparation Example 5 A phosphorus-containing diamine, the preparation process of which is as follows: Figure 2 As shown, the specific steps are as follows: Methylphosphonic acid (10 mmol) was dissolved in 30 mL of dichloromethane. A mixed solution of 3-amino-1-propanol (21 mmol) and triethylamine (21 mmol, as an acid-binding agent) was slowly added dropwise under ice bath cooling. After the addition was complete, the temperature was raised to 45 °C and the reaction was carried out for 5 h. After the reaction was completed, the generated salt was removed by filtration, the solvent was removed by rotary evaporation of the filtrate, and the solution was dried under vacuum to obtain a viscous phosphorus-containing diamine with a yield of 80.1%. 1 H NMR (C7H) 19 N2O3P, 400MHz, DMSO-d6) δ 4.08-4.05(t, 4H), 4.00 (s, 4H),2.79-2.74 (t, 4H), 1.76-1.71 (m, 4H), 1.21 (s, 3H); + ): [M+H] +The result is 211.12, and the target compound is found. The above results indicate that it is the target compound.

[0030] Preparation Example 6 A phosphorus-containing diamine, the preparation process of which is as follows: Figure 2 As shown, the specific steps are as follows: Methylphosphonic acid (10 mmol) was dissolved in 30 mL of dichloromethane. A mixed solution of 3-amino-1-propanol (22 mmol) and triethylamine (22 mmol) was slowly added dropwise under ice bath cooling. After the addition was complete, the temperature was raised to 50 °C and the reaction was carried out for 4 h. After the reaction was completed, the generated salt was removed by filtration, the solvent was removed by rotary evaporation of the filtrate, and the solution was dried under vacuum to obtain a viscous phosphorus-containing diamine with a yield of 78.3%.

[0031] Preparation Example 7 A phosphorus-containing diamine, the preparation process of which is as follows: Figure 2 As shown, the specific steps are as follows: Methylphosphonic acid (10 mmol) was dissolved in 30 mL of dichloromethane. A mixed solution of 3-amino-1-propanol (20 mmol) and triethylamine (20 mmol) was slowly added dropwise under ice bath cooling. After the addition was complete, the temperature was raised to 40 °C and the reaction was carried out for 6 h. After the reaction was completed, the generated salt was removed by filtration, the solvent was removed by rotary evaporation of the filtrate, and the solution was dried under vacuum to obtain a viscous phosphorus-containing diamine with a yield of 77.2%.

[0032] Example 1 A method for preparing a hot melt adhesive film with high bonding strength includes the following steps: (1) The o-vanillin-based bicyclic carbonate obtained in Preparation Example 1 and the phosphorus-containing diamine obtained in Preparation Example 5 were mixed in an equimolar ratio. The mixture was placed in a reactor and polymerized at 95 °C for 18 h to obtain a prepolymer. (2) The prepolymer is subjected to degassing under reduced pressure, then poured onto a preheated plate covered with release paper. A uniform film is then coated using a scraper or coating machine. The film is then cured at 115 °C for 15 h to allow the cyclic carbonate and amine groups to react completely, forming a polyhydroxy polyurethane network. The polymerization process is as follows: Figure 3 As shown; after the reaction is complete, cool to room temperature, and peel the cured hot melt adhesive film off the release paper to obtain the hot melt adhesive film with high bonding strength; the number average molecular weight of GPC test is 6200 g / mol.

[0033] This embodiment also provides a hot melt adhesive film with high bonding strength, which is prepared by the above-described method.

[0034] Example 2 A method for preparing a hot melt adhesive film with high bonding strength includes the following steps: (1) The o-vanillin-based bicyclic carbonate obtained in Preparation Example 2 and the phosphorus-containing diamine obtained in Preparation Example 6 were mixed in an equimolar ratio. The mixture was placed in a reactor and polymerized at 90 °C for 24 h. After cooling, the prepolymer was obtained. (2) The prepolymer is subjected to degassing treatment under reduced pressure, and then poured onto a preheated plate covered with release paper. It is then coated into a film of uniform thickness using a scraper or coating machine. The film is then cured at 110 °C for 24 h to allow the cyclic carbonate and amine groups to react completely and form a polyhydroxy polyurethane network. After the reaction is complete, the film is cooled to room temperature and the cured hot melt adhesive film is peeled off from the release paper to obtain the hot melt adhesive film with high bonding strength. The number average molecular weight measured by GPC is 6500 g / mol.

[0035] This embodiment also provides a hot melt adhesive film with high bonding strength, which is prepared by the above-described method.

[0036] Example 3 A method for preparing a hot melt adhesive film with high bonding strength includes the following steps: (1) The o-vanillin-based bicyclic carbonate obtained in Preparation Example 3 and the phosphorus-containing diamine obtained in Preparation Example 7 were mixed in an equimolar ratio. The mixture was placed in a reactor and subjected to polymerization at 100 °C for 12 h. After cooling, a prepolymer was obtained. (2) The prepolymer is subjected to degassing treatment under reduced pressure, and then poured onto a preheated plate covered with release paper. It is then coated into a film of uniform thickness using a scraper or coating machine. The film is then cured at 120 °C for 12 h to allow the cyclic carbonate and amine groups to react completely and form a polyhydroxy polyurethane network. After the reaction is complete, the film is cooled to room temperature and the cured hot melt adhesive film is peeled off from the release paper to obtain the hot melt adhesive film with high bonding strength. The number average molecular weight measured by GPC is 6100 g / mol.

[0037] This embodiment also provides a hot melt adhesive film with high bonding strength, which is prepared by the above-described method.

[0038] Comparative Example 1 The content of Comparative Example 1 is basically the same as that of Example 1, except that the phosphorus-containing diamine in step (1) is replaced with 1,8-octanediamine, and in step (2), triphenyl phosphate with the same phosphorus content as in Example 1 is physically added to the prepolymer before degassing under reduced pressure.

[0039] Comparative Example 2 The content of Comparative Example 2 is basically the same as that of Example 1, except that the vanillin-based bicyclic carbonate in step (1) is replaced with the bisphenol A type bispentancyclic carbonate of Preparation Example 4.

[0040] Experimental Example 1 FT-IR analysis was performed on the hot melt adhesive film obtained in Example 1, and the results are as follows: Figure 4 As shown. From Figure 4 It can be seen that 1780-1800 cm -1 No cyclic carbonate carbonyl bands were observed nearby, but at 1710 cm⁻¹ -1 The strong absorption peak at -C=O bond indicates that the cyclic carbonate group has successfully reacted with the diamine, leading to the formation of a carbamate bond; 3200-3600 cm⁻¹ -1 The broad peak at 1460 cm⁻¹ represents the stretching vibrations of -OH and -NH. -1 The point is characterized by NH bending vibration, 2850-2930 cm. -1 This is a CH stretching vibration, 1650 cm. -1 It is a C=N stretching vibration, 1590-1638 cm. -1 It is a C=C stretching vibration of the aromatic ring; 1032 cm -1 1078 cm -1 1140 cm -1 and 1200-1260 cm -1 The characteristic spectral bands appearing at these locations can be attributed to the stretching vibrations of COC, CO, and P=O, respectively.

[0041] Experimental Example 2 The following performance tests were performed on the hot melt adhesive films prepared in Examples 1-3 and Comparative Examples 1-2: Mechanical properties: Tensile tests were conducted on a universal testing machine at a speed of 10 mm / min, and the tensile strength and elongation at break were recorded. The results are shown in Table 1. Adhesion performance: Each hot melt adhesive film was directly sandwiched between two aluminum substrates (100 mm × 25 mm × 5 mm), with an overlap area of ​​20 mm × 15 mm. The samples were hot-pressed in a hot press at 150℃ and 0.3 MPa for 5 min, cooled to room temperature and left for 24 h. Then, the bonded samples were subjected to uniaxial tensile tests at 20℃ and a rate of 5 mm / min. The tensile shear strength was tested according to GB / T 7124-2008 to evaluate the bond strength. The results are shown in Table 1. Heat resistance: The bonded sample was placed in a 150℃ oven for hot air aging for 24 h. After being removed and placed at room temperature for 24 h, the tensile shear strength was tested again to measure the heat resistance performance. The results are shown in Table 1. Water resistance: The bonded sample was immersed in deionized water for 24 h, and then the tensile shear strength was tested again to measure the water resistance. The results are shown in Table 1. Flame retardant performance: The flame retardant rating of each sample was determined according to the standard UL94 vertical burning test method. The sample size was 100 mm × 25 mm × 5 mm. The flame retardant rating increased progressively from HB, V-2, V-1 to V-0. The results are shown in Table 1.

[0042] As shown in Table 1, the hot melt adhesive film prepared by the present invention has high bonding strength as well as excellent mechanical properties, heat resistance, water resistance and flame retardant properties.

[0043] Compared to the examples, Comparative Example 1 replaced the reactive phosphorus-containing diamine of the present invention with a physically additive small molecule flame retardant, and Comparative Example 2 replaced the o-vanillin-based bis-pentanone carbonate of the present invention with a bisphenol A-type bis-pentanone carbonate. Lacking the o-vanillin rigid skeleton and Schiff base bond structure, the properties of the films obtained in Comparative Examples 1-2 all showed varying degrees of decline.

[0044] In terms of mechanical properties, the tensile strength of Example 1 was significantly higher than that of Comparative Examples 1 and 2, while maintaining a moderate elongation at break. This indicates that the present invention achieves a balance between high strength and good toughness through the synergistic effect of the rigid framework of the o-vanillin Schiff base and the reactive phosphorus-containing diamine.

[0045] Regarding adhesion performance, the tensile shear strength of Example 1 was significantly higher than that of Comparative Example 1 and Comparative Example 2. This is attributed to the large number of side-chain hydroxyl groups generated by the ring-opening of cyclic carbonate and amine, which endow the film with extremely strong interfacial hydrogen bonding forces and excellent adhesion strength. It also shows that the Schiff base bonds in the o-vanillin backbone can enhance intermolecular forces and interfacial interactions with the substrate, while the reactive phosphorus-containing diamine structure, as part of the main chain, can further enhance the cohesive strength.

[0046] In terms of weather resistance, after being treated at 150 ℃ or immersed in water for 24 h, the bonding strength retention rate of Example 1 was higher than that of Comparative Example 1 and Comparative Example 2. This proves that the physical addition of flame retardants will seriously damage the heat resistance and water resistance stability of the film, while the reactive phosphorus-containing structure and hydrophobic design of the present invention can effectively resist the erosion of high temperature and moisture.

[0047] In terms of flame retardant performance, Example 1 can achieve the UL94 V-0 rating, while Comparative Example 1 is only V-1, and may further decline after long-term use. This indicates that the physical addition of flame retardants is not as effective as the present invention in terms of flame retardant efficiency and durability by covalently incorporating phosphorus into the main chain.

[0048] In summary, this invention has prepared a hot melt adhesive film with excellent overall performance through the synergistic design of a specific Schiff base-containing ortho-vanillin rigid framework, a reactive phosphorus-containing diamine structure, and a non-isocyanate polymerization pathway.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. The basic principles and main features of the present invention have been described above with specific implementation schemes. Based on the present invention, some modifications or substitutions can be made, but these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of protection claimed by the present invention.

Claims

1. A method for preparing a hot melt adhesive film with high bonding strength, characterized in that, Includes the following steps: (1) Mix o-vanillin-based bis-pentane carbonate and phosphorus-containing diamine, and polymerize under heating conditions to obtain a prepolymer; (2) The prepolymer is subjected to degassing treatment under reduced pressure, then coated into a film, cured, cooled and peeled off to obtain the hot melt adhesive film with high bonding strength.

2. The method for preparing a hot melt adhesive film with high bonding strength according to claim 1, characterized in that, The preparation process of the o-vanillin-based bis-pentanone carbonate in step (1) is as follows: (a) o-vanillin and 1,8-octanediamine were added to ethanol and refluxed in the presence of glacial acetic acid to give o-vanillin-based bis-Schiff base diol; (b) Add o-vanillin-based bis-Schiff base diol to epichlorohydrin and carry out a ring-opening reaction in the presence of a phase transfer catalyst, followed by a ring-closing reaction under the action of a strong base to obtain o-vanillin-based diepoxy monomer. (c) Add the o-vanillin-based bisepoxy monomer and catalyst to N,N-dimethylformamide, and pass carbon dioxide through to carry out a cycloaddition reaction to obtain the o-vanillin-based bispentanone carbonate.

3. The method for preparing a hot melt adhesive film with high bonding strength according to claim 2, characterized in that, The molar ratio of o-vanillin to 1,8-octanediamine in step (a) is (2-2.2):1; the reflux reaction time is 6-8 h.

4. The method for preparing a hot melt adhesive film with high bonding strength according to claim 2, characterized in that, In step (b), the ratio of o-vanillin-based bis-Schiff base diol, epichlorohydrin, phase transfer catalyst, and strong base is 1 mmol : (3-4) mL : (0.05-0.06) mmol : (2.5-3) mmol; the phase transfer catalyst is tetrabutylammonium bromide; the strong base is sodium hydroxide or potassium hydroxide; the ring-opening reaction is carried out at a temperature of 70-80 °C for 2-3 h; and the ring-closing reaction is carried out at a temperature of 50-60 °C for 4-6 h.

5. The method for preparing a hot melt adhesive film with high bonding strength according to claim 2, characterized in that, In step (c), the molar ratio of the o-vanillin diepoxy monomer to the catalyst is 1:(0.05-0.06); the catalyst is tetrabutylammonium bromide; the pressure is maintained at 1.0-2.0 MPa after carbon dioxide is introduced; the cycloaddition reaction is carried out at a temperature of 100-110℃ for 12-24 h.

6. The method for preparing a hot melt adhesive film with high bonding strength according to claim 1, characterized in that, The preparation process of the phosphorus-containing diamine mentioned in step (1) is as follows: Methylphosphonic acid is added to dichloromethane, and 3-amino-1-propanol and triethylamine are added under ice bath conditions. The mixture is then heated to react and yield the final product.

7. The method for preparing a hot melt adhesive film with high bonding strength according to claim 6, characterized in that, The molar ratio of methylphosphonic acid, 3-amino-1-propanol and triethylamine is 1:(2-2.2):(2-2.2); the heating reaction is carried out at a temperature of 40-45 °C for 4-6 h.

8. The method for preparing a hot melt adhesive film with high bonding strength according to claim 1, characterized in that, The molar ratio of o-vanillin-based bicyclic carbonate and phosphorus-containing diamine in step (1) is 1:1; the heating temperature is 90-100℃, and the polymerization reaction time is 12-24 h.

9. The method for preparing a hot melt adhesive film with high bonding strength according to claim 1, characterized in that, The curing temperature in step (2) is 110-120 ℃ and the time is 12-24 h.

10. A hot melt adhesive film with high bonding strength, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

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