Self-repairing hot melt adhesive for vehicle headlamp, preparation method and application thereof

Abstract

The application provides a self-repairing hot melt adhesive for vehicle headlamps, a preparation method and application, which is composed of the following components by weight: polyisobutylene 15-40 parts, polyolefin 20-50 parts, butyl rubber 10-30 parts, polyamide modified polymer 10-30 parts, tackifying resin 5-15 parts, filler 1-30 parts, and antioxidant 0.1-2 parts. The modified polyamide is mainly composed of dimer amine and adipic acid, and is prepared by high-temperature polycondensation of pyrimidine and purine compounds, and the molar ratio of dimer amine to adipic acid is 1-2. The pyrimidine-purine multiple reversible hydrogen bonds are used to endow the adhesive layer with the heat-induced self-repairing ability. The polyamide chain segment improves the high-temperature resistance to flow, and the heterocycle improves the bonding strength to PP, PC and PMMA substrates. The system has low volatile matter, and can prevent the vehicle headlamps from fogging. In the preparation, the modified polyamide is first synthesized, and then the raw materials are kneaded at 120-170 DEG C under nitrogen protection and vacuum defoaming to form the adhesive, so that the process is simple and the adhesive is suitable for bonding and sealing of the vehicle headlamps.

Description

Technical Field

[0001] This invention relates to the field of hot melt adhesive technology, specifically to a self-healing hot melt adhesive for automotive headlights, its preparation method, and its application. Background Technology

[0002] As an essential exterior component of automobiles, automotive lights play a vital role in nighttime illumination, traffic signals, fog collision avoidance, and turn signals, ensuring safe driving. In the manufacturing of automotive lights, adhesives are used for bonding and sealing to ensure a tight connection between the lens (usually PMMA or PC) and the lamp housing (usually PP, PBT, ABS, PC / ABS, etc.).

[0003] Hot melt adhesives for automotive lights face harsh working environments: humid conditions, rain, prolonged exposure to light sources, and high operating temperatures (locally exceeding 100°C). Current technologies for automotive light bonding primarily utilize butyl hot melt adhesives, polyurethane hot melt adhesives, or silicone sealants. However, traditional butyl hot melt adhesives suffer from high-temperature flow issues; polyurethane hot melt adhesives offer excellent bonding performance, but disassembly of the lights is often difficult; and silicone sealants have high volatility, affecting the anti-fogging performance of the lights. Furthermore, existing automotive light adhesives generally lack self-healing capabilities; micro-cracks caused by thermal stress and mechanical vibration after long-term use are difficult to heal on their own, impacting the long-term reliability of the light seal.

[0004] Polyamide hot melt adhesives have been extensively studied due to their excellent heat resistance, bonding strength and flexibility, but the compatibility of ordinary polyamides with materials such as butyl rubber and polyisobutylene needs to be improved. Summary of the Invention

[0005] The first objective of this invention is to overcome the shortcomings of existing hot melt adhesives for automotive headlights, such as insufficient high-temperature stability, poor adhesion to low surface energy materials like PP, and lack of self-healing ability, and to provide a hot melt adhesive that combines excellent high-temperature stability, good adhesion performance, and self-healing ability.

[0006] Therefore, the above-mentioned objective of the present invention is achieved through the following technical solution: A self-healing hot melt adhesive for automotive headlights comprises the following components in parts by weight: 15-40 parts of polyisobutylene, 20-50 parts of polyolefin, 10-30 parts of butyl rubber, 10-30 parts of polyamide-modified polymer, 5-15 parts of tackifying resin, 1-30 parts of filler, and 0.1-2 parts of antioxidant; The polyamide-modified polymer is prepared by high-temperature polycondensation reaction of raw materials containing diamine, adipic acid, pyrimidine compounds and purine compounds.

[0007] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions: As a preferred embodiment of the present invention: by weight, the dimeric amine is Priamine 1074, comprising 30-50 parts; the adipic acid comprises 5-15 parts; the pyrimidine compound comprises 1-10 parts; the purine compound comprises 1-10 parts; and the molar ratio of the dimeric amine to the adipic acid is 1-2.

[0008] As a preferred technical solution of the present invention: a catalyst is also used in the high-temperature polycondensation reaction preparation process of polyamide modified polymer, wherein the catalyst is 0.01 to 0.3 parts, and the catalyst is at least one of phosphate, phosphite, and hypophosphite.

[0009] As a preferred embodiment of the present invention: the pyrimidine compound is at least one of cytosine, 2,4-diamino-6-hydroxypyrimidine, and triaminopyrimidine; the purine compound is at least one of adenine, guanine, and isoguanine.

[0010] As a preferred embodiment of the present invention, the number-average molecular weight of the polyisobutylene is 1,000 to 150,000. The polyolefin has a number average molecular weight of 5,000 to 100,000 and a softening point of 80 to 140°C. It is an amorphous polyolefin selected from one or more of amorphous polypropylene (APP) and amorphous polyalphaolefin (APAO). The weight-average molecular weight of the butyl rubber is 200,000 to 800,000; As a preferred embodiment of the present invention: the tackifying resin is selected from at least one of terpene resin and C5 / C9 petroleum resin; the filler is selected from at least one of calcium carbonate, talc, and carbon black; and the antioxidant is a compound of hindered phenolic antioxidants (such as 1010 and 1076) and phosphite antioxidants (such as 168).

[0011] As a preferred embodiment of the present invention, the butyl rubber is selected from ordinary butyl rubber or halogenated butyl rubber.

[0012] The second objective of this invention is to provide a method for preparing a self-healing hot melt adhesive for automotive headlights, comprising the following steps: S1. The components are prepared according to the component ratio of the self-healing hot melt adhesive for automotive headlights as described in claim 1; S2. Add butyl rubber, polyisobutylene, polyolefin, polyamide modified polymer, tackifying resin, filler, and antioxidant to a kneader, heat to 120-170°C, and stir and mix for 60-120 minutes under nitrogen protection. Alternatively, butyl rubber, polyisobutylene, polyolefin, tackifying resin and antioxidant are first added to a kneader and mixed, then polyamide modified polymer is added and mixed again, and finally filler is added and mixed; the kneading temperature is 120-170℃, and the mixture is stirred and mixed for 60-120 minutes under nitrogen protection. S3, Vacuum degassing treatment; S4. Discharge, cool, and mold the mixture to obtain self-healing hot melt adhesive for fixing vehicle headlights.

[0013] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions: As a preferred embodiment of the present invention, the polyamide-modified polymer is prepared by the following steps: S1. Add dimelamine and adipic acid to the reaction vessel, heat to 180-220°C under nitrogen protection, and stir for 1-2 hours. S2, add pyrimidine compounds, purine compounds and catalyst, continue heating to 220-260℃, and react under reduced pressure for 3-6 hours; S3. After the reaction is complete, the material is cooled and discharged to obtain the polyamide-modified polymer. Based on weight, the dimelamine is Priamine 1074, comprising 30-50 parts; the adipic acid comprises 5-15 parts; the pyrimidine compound comprises 1-10 parts; the purine compound comprises 1-10 parts; the catalyst comprises 0.01-0.3 parts; and the molar ratio of the dimelamine to the adipic acid is 1-2.

[0014] Another objective of this invention is to provide the application of the self-healing hot melt adhesive for automotive headlights prepared by the preparation method of the self-healing hot melt adhesive for automotive headlights as described above in the bonding of automotive headlights.

[0015] This invention provides a self-healing hot melt adhesive for automotive headlights, its preparation method, and its application, which has the following beneficial effects: 1) By introducing pyrimidine and purine structures into the polyamide molecular chain, and utilizing the multiple hydrogen bond interactions (base pairing principle) between them, a reversible physical cross-linking network is given to the adhesive layer. When microcracks occur in the adhesive layer, the hydrogen bonds can break and absorb energy; at the operating temperature of the vehicle lamp, the hydrogen bonds can reform, realizing the self-repair of cracks and significantly improving the long-term reliability of the vehicle lamp bonding seal.

[0016] 2) This invention utilizes the synergistic effect of polyamide-modified polymers with butyl rubber, polyisobutylene, and polyolefins to give the hot melt adhesive the characteristics of being less prone to flowing when heated and having excellent high-temperature stability. The polyamide component provides heat resistance, effectively avoiding the problem of traditional butyl hot melt adhesives flowing easily in high-temperature environments.

[0017] 3) The pyrimidine / purine structure introduced in this invention contains aromatic heterocycles, which can generate π-π stacking interactions and van der Waals force enhancement effects with the PP surface, improving wettability and adhesion to non-polar materials. Simultaneously, the long-chain alkyl structure in the polyamide-modified polymer has good compatibility with polyolefins and exhibits good adhesion to commonly used automotive lighting substrates (PP, PC, PMMA, etc.).

[0018] 4) The hot melt adhesive of this invention uses a high molecular weight polymer system with low volatile content, which effectively avoids the corrosion and optical pollution problems of internal components of car lights caused by the volatilization of small organic molecules in traditional hot melt adhesives.

[0019] 5) The hot melt adhesive of this invention can be applied using conventional hot melt adhesive processing equipment, making it suitable for continuous automated production and meeting the industrialization needs of automotive lighting manufacturing. Detailed Implementation

[0020] The present invention will be described in further detail with reference to specific embodiments.

[0021] I. Experimental Examples Example 1 Synthesis of polyamide-modified polymer: 40 parts of Priamine 1074 (amine value 202~212 mg KOH / g) and 9 parts of adipic acid were added to a reactor. The mixture was heated to 200℃ under nitrogen protection and stirred for 1.5 hours. Then, 3 parts of cytosine, 3 parts of adenine, and 0.1 parts of sodium hypophosphite catalyst were added, and the temperature was raised to 220℃. The reaction was carried out under vacuum for 4 hours. After the reaction was completed, the product was discharged to obtain the polyamide-modified polymer (denoted as PA-M1).

[0022] Preparation of hot melt adhesive: Take 15 parts of butyl rubber (IIR), 15 parts of polyisobutylene (PIB, molecular weight 2400), 10 parts of polyisobutylene (PIB, molecular weight 50000), 30 parts of amorphous polyolefin (APAO), 18 parts of PA-M1, 8 parts of C5 petroleum resin, 2 parts of calcium carbonate, 0.8 parts of antioxidant 1010, 0.4 parts of antioxidant 168, and 1 part of carbon black, add them to a kneader, mix at 140℃ for 90 minutes under nitrogen protection, and then vacuum knead for 30 minutes. Discharge the material to obtain the hot melt adhesive sample for automotive lights (denoted as HM-1).

[0023] Example 2 Synthesis of polyamide-modified polymer: 45 parts of Priamine 1074 and 11 parts of adipic acid were added to a reactor. The mixture was heated to 190°C under nitrogen protection and stirred for 2 hours. Then, 2 parts of 2,4-diamino-6-hydroxypyrimidine, 5 parts of guanine, and 0.3 parts of sodium hypophosphite were added. The temperature was raised to 240°C, and the reaction was carried out under reduced pressure for 5 hours. The product was discharged to obtain the polyamide-modified polymer (denoted as PA-M2).

[0024] Preparation of hot melt adhesive: Take 20 parts of butyl rubber (IIR), 10 parts of polyisobutylene (PIB, molecular weight 1300), 10 parts of polyisobutylene (PIB, molecular weight 80000), 25 parts of amorphous polyolefin (APAO), 20 parts of PA-M2, 10 parts of terpene resin, 5 parts of talc, 0.6 parts of antioxidant 1076, 0.3 parts of antioxidant 168, and 2 parts of carbon black, add them to a kneader, mix at 150℃ for 80 minutes under nitrogen protection, and then vacuum degas and knead for 30 minutes. Discharge the material to obtain the hot melt adhesive sample for automotive lights (denoted as HM-2).

[0025] Example 3 Synthesis of polyamide-modified polymer: The same method as in Example 1 was used, but the amount of pyrimidine / purine was adjusted to 5 parts cytosine and 5 parts adenine, while the rest remained unchanged, to obtain the polyamide-modified polymer (denoted as PA-M3).

[0026] Preparation of hot melt adhesive: Take 25 parts of butyl rubber (IIR), 20 parts of polyisobutylene (PIB, molecular weight 2400), 20 parts of polyisobutylene (PIB, molecular weight 50000), 40 parts of amorphous polyolefin (APAO), 25 parts of PA-M3, 8 parts of C9 petroleum resin, 10 parts of calcium carbonate, 0.8 parts of antioxidant 1010, 0.4 parts of antioxidant 168, and 5 parts of carbon black, add them to a kneader, mix at 140℃ for 90 minutes under nitrogen protection, and then vacuum degas and knead for 30 minutes. Discharge the material to obtain the hot melt adhesive sample for automotive lights (denoted as HM-3).

[0027] Comparative Example 1 Without adding polyamide-modified polymer, the remaining components are basically the same as in Example 1: 15 parts of butyl rubber (IIR), 15 parts of polyisobutylene (PIB, molecular weight 2400), 10 parts of polyisobutylene (PIB, molecular weight 50000), 48 parts of amorphous polyolefin (APAO), 8 parts of C5 petroleum resin, 2 parts of calcium carbonate, 0.8 parts of antioxidant 1010, 0.4 parts of antioxidant 168, and 1 part of carbon black are added to a kneader and mixed at 140°C for 90 minutes under nitrogen protection, followed by vacuum kneading for 30 minutes. The material is then discharged to obtain the automotive headlight hot melt adhesive sample (denoted as HM-D1).

[0028] Comparative Example 2 The polyamide-modified polymer was synthesized without the addition of pyrimidine and purine compounds. It was obtained by polycondensation of 45 parts Priamine 1074 and 11 parts adipic acid with a catalyst to obtain ordinary polyamide (PA-D2). The hot melt adhesive formulation was the same as in Example 2, but PA-D2 was used instead of PA-M2. The preparation method was the same as in Example 2, resulting in a hot melt adhesive sample for automotive lights (denoted as HM-D2).

[0029] Comparative Example 3 During the synthesis of the polyamide-modified polymer, 40 parts of Priamine 1074 and 4 parts of adipic acid were added, with the other components remaining the same as PA-M1, to obtain ordinary polyamide PA-D3. The hot melt adhesive formulation was the same as in Example 1, but PA-D3 was used instead of PA-M1, and the preparation method was the same as in Example 1, to obtain HM-D3.

[0030] Comparative Example 4 During the synthesis of the polyamide-modified polymer, 40 parts of Priamine 1074 and 15 parts of adipic acid were added, with the other components remaining the same as PA-M1, to obtain ordinary polyamide PA-D4. The hot melt adhesive formulation was the same as in Example 1, but PA-D4 was used instead of PA-M1, and the preparation method was the same as in Example 1, to obtain a hot melt adhesive sample for automotive lights (denoted as HM-D4).

[0031] Comparative Example 5 During the synthesis of the polyamide-modified polymer, 40 parts of Priamine 1074 and 9 parts of terephthalic acid were added, with the rest being the same as PA-M1, to obtain ordinary polyamide PA-D5. The hot melt adhesive formulation was the same as in Example 1, but PA-D5 was used instead of PA-M1, and the preparation method was the same as in Example 1, to obtain a hot melt adhesive sample for automotive lights (denoted as HM-D5).

[0032] Comparative Example 6 During the synthesis of the polyamide-modified polymer, 10 parts hexamethylenediamine and 9 parts terephthalic acid were added, with the other components remaining the same as PA-M1, to obtain ordinary polyamide PA-D6. The hot melt adhesive formulation was the same as in Example 1, but PA-D6 was used instead of PA-M1, and the preparation method was the same as in Example 1, to obtain a hot melt adhesive sample for automotive lights (denoted as HM-D6).

[0033] II. Performance Testing The hot melt adhesives prepared in Examples 1-3 and Comparative Examples 1-6 were subjected to performance tests, and the test methods are as follows: Bond strength test: Hot melt adhesive was applied between the PP substrate and the PC substrate, and the samples were pressed together. Tensile shear strength was tested using a universal testing machine (tensile speed 50 mm / min), and the bond strength (MPa) was recorded.

[0034] High temperature stability test: The hot melt adhesive is placed in a 100℃ oven and heated for 24 hours. Observe whether it flows and measure the flow distance to evaluate the high temperature stability.

[0035] Self-healing performance test: The separated sample was placed in an 80℃ oven for 4 hours and then left to stand at room temperature for 24 hours. The bonding strength was tested again and the strength retention rate was calculated (strength after repair / initial strength × 100%).

[0036] Aging resistance test: The sample was placed in a 200℃ oven for 3 days for aging. After being taken out, the bonding strength was tested and the strength retention rate was calculated.

[0037] The test results are shown in Table 1 below: Table 1 Examples 1, 2, and 3 all used a rubber matrix with the specified ratio of the present invention plus a polyamide modified polymer containing pyrimidine / purine hydrogen bonding units. Only the amount of polyamide monomer added, the rubber combination, and the types of tackifying resin and filler were slightly adjusted. The three groups of samples showed excellent overall performance and stable performance within a certain range, as shown in Table 1. 1) Adhesion strength: HM-1 is 2.8 MPa, HM-2 reaches 3.1 MPa, and HM-3 is 2.9 MPa. HM-2 uses terpene resin with an appropriate ratio of butyl rubber, resulting in stronger π-π interaction between the aromatic heterocyclic resin and the PP substrate, leading to optimal adhesion strength. In HM-3, increasing the amount of pyrimidine and purine increases the number of hydrogen bonding sites, resulting in a slight improvement in adhesion strength. This demonstrates that within the composition range of this invention, adjusting the amount of tackifying resin and heterocyclic monomer can slightly optimize interfacial adhesion, and the formulation adjustment window is wide.

[0038] 2) High-temperature stability: No flow was observed in any of the three groups of samples after 24 hours in a 100℃ oven. The rigid segments of polyamide form an interpenetrating network with butyl rubber and polyolefin, inhibiting the slippage of rubber molecular chains at high temperatures. This completely solves the high-temperature creep and flow defects of traditional pure butyl hot melt adhesives, meeting the requirements of long-term operation of automotive lights above 100℃.

[0039] 3) Self-healing performance: The self-healing strength retention rate is 89.8%–93.2%. HM-3 has the highest content of pyrimidine and purine, the highest density of hydrogen bond pairing sites, and the best crack healing effect. At high temperature, the reversible hydrogen bond breakage between pyrimidine and purine dissipates stress, and after cooling, the hydrogen bonds recombine, realizing the self-repair of microcracks in the adhesive layer and significantly extending the life of the automotive headlight seal.

[0040] 4) Heat aging durability: After aging at 200℃ for 3 days, the strength retention rate is higher than 92%. The polyamide-modified polymer heterocyclic structure synergistically combines hindered phenol / phosphite antioxidants to inhibit the thermal oxidative degradation of rubber, resulting in outstanding heat aging resistance.

[0041] Compared to Example 1, Comparative Example 1 (HM-D1, without polyamide-modified polymer) completely removed the polyamide-modified polymer, retaining only polyisobutylene, butyl rubber, and polyolefin base compounds. HM-D1 exhibited a bond strength of only 1.6 MPa, flowed to 2 mm at 100°C, had a self-healing retention rate of 62.4%, and an aging retention rate of 78.4%, all four indicators being inferior to HM-1.

[0042] Comparative Example 2 (HM-D2, polyamide without pyrimidine and purine) differs from Example 2 in that the polyamide synthesis process does not involve the addition of pyrimidine or purine hydrogen-bonding monomers, while the remaining formulation and process are identical to Example 2. High-temperature stability showed no significant difference, but the adhesive strength decreased to 2.4 MPa, the self-healing retention rate was only 71.3%, and the heat aging retention rate decreased to 89.3%.

[0043] Compared to Example 1, Comparative Examples 3 and 4 (with altered dimelamine / adipic acid molar ratios) showed that Example 1 controlled the dimelamine / adipic acid molar ratio to be 1.23; HM-D3 had insufficient adipic acid (molar ratio 2.76), while HM-D4 had excessive adipic acid (molar ratio 0.74). HM-D3 exhibited a slightly higher bond strength of 3.2 MPa, but flowed 2 mm at 100°C, with a self-healing retention rate of only 80.1%. Excessive terminal amino groups improved interfacial adhesion, but the low molecular weight and insufficient chain rigidity of the polyamide resulted in decreased high-temperature creep resistance, uneven hydrogen bond distribution, and poorer repair performance. HM-D4 did not flow at high temperatures, but maintained a self-healing retention rate of 69.6% and an aging retention rate of 70.5%.

[0044] Compared with Example 1, Comparative Example 5 (HM-D5, terephthalic acid instead of adipic acid) uses rigid terephthalic acid to replace flexible adipic acid in the synthesis of polyamide. The adhesive strength of HM-D5 is reduced to 1.9 MPa, and the self-healing retention rate is 68.7%.

[0045] Comparative Example 6 (HM-D6, where small molecule hexamethylenediamine replaces long-chain dimelamine) Compared with Example 1, small molecule hexamethylenediamine replaced long-chain Priamine 1074 dimelamine. HM-D6 had an adhesive strength of 2.1 MPa, flowed 5 mm at 100°C, and had a self-healing retention rate of only 56.8%, which was the lowest among all samples.

[0046] The above specific embodiments are used to explain and illustrate the present invention, and are only preferred embodiments of the present invention, not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A self-healing hot melt adhesive for automotive headlights, characterized in that, It contains the following components in parts by weight: 15-40 parts of polyisobutylene, 20-50 parts of polyolefin, 10-30 parts of butyl rubber, 10-30 parts of polyamide-modified polymer, 5-15 parts of tackifying resin, 1-30 parts of filler, and 0.1-2 parts of antioxidant; The polyamide-modified polymer is prepared by high-temperature polycondensation reaction of raw materials containing diamine, adipic acid, pyrimidine compounds and purine compounds.

2. The self-healing hot melt adhesive for automotive headlights according to claim 1, characterized in that, Based on weight, the dimelamine is Priamine 1074, comprising 30-50 parts; the adipic acid comprises 5-15 parts; the pyrimidine compound comprises 1-10 parts; the purine compound comprises 1-10 parts; and the molar ratio of the dimelamine to the adipic acid is 1-2.

3. The self-healing hot melt adhesive for vehicle headlights according to claim 1 or 2, characterized in that, A catalyst is also used in the high-temperature polycondensation reaction of the polyamide-modified polymer. The catalyst is 0.01 to 0.3 parts and is at least one of phosphate, phosphite, and hypophosphite.

4. The self-healing hot melt adhesive for vehicle headlights according to claim 1 or 2, characterized in that, The pyrimidine compound is at least one of cytosine, 2,4-diamino-6-hydroxypyrimidine, and triaminopyrimidine; the purine compound is at least one of adenine, guanine, and isoguanine.

5. The self-healing hot melt adhesive for automotive headlights according to claim 1, characterized in that, The number-average molecular weight of the polyisobutylene is 1,000 to 150,000. The polyolefin has a number-average molecular weight of 5,000 to 100,000 and a softening point of 80 to 140°C. The weight-average molecular weight of the butyl rubber is 200,000 to 800,000.

6. The self-healing hot melt adhesive for automotive headlights according to claim 1, characterized in that, The tackifying resin is selected from at least one of terpene resin and C5 / C9 petroleum resin; the filler is selected from at least one of calcium carbonate, talc, and carbon black; and the antioxidant is a compound of hindered phenolic antioxidant and phosphite antioxidant.

7. The self-healing hot melt adhesive for automotive headlights according to claim 1, characterized in that, The butyl rubber is selected from ordinary butyl rubber or halogenated butyl rubber.

8. A method for preparing a self-healing hot melt adhesive for automotive headlights, characterized in that, The method includes the following steps: S1. The components are prepared according to the component ratio of the self-healing hot melt adhesive for automotive headlights as described in claim 1; S2. Add butyl rubber, polyisobutylene, polyolefin, polyamide modified polymer, tackifying resin, filler, and antioxidant to a kneader, heat to 120-170°C, and stir and mix for 60-120 minutes under nitrogen protection. Alternatively, butyl rubber, polyisobutylene, polyolefin, tackifying resin and antioxidant are first added to a kneader and mixed, then polyamide modified polymer is added and mixed again, and finally filler is added and mixed; the kneading temperature is 120-170℃, and the mixture is stirred and mixed for 60-120 minutes under nitrogen protection. S3, Vacuum degassing treatment; S4. Discharge, cool, and mold the mixture to obtain self-healing hot melt adhesive for fixing vehicle headlights.

9. The preparation method according to claim 8, characterized in that, The polyamide-modified polymer is prepared by the following steps: S1. Add dimelamine and adipic acid to the reaction vessel, heat to 180-220°C under nitrogen protection, and stir for 1-2 hours. S2, add pyrimidine compounds, purine compounds and catalyst, continue heating to 220-260℃, and react under reduced pressure for 3-6 hours; S3. After the reaction is complete, the material is cooled and discharged to obtain the polyamide-modified polymer. Based on weight, the dimelamine is Priamine 1074, comprising 30-50 parts; the adipic acid comprises 5-15 parts; the pyrimidine compound comprises 1-10 parts; the purine compound comprises 1-10 parts; the catalyst comprises 0.01-0.3 parts; and the molar ratio of the dimelamine to the adipic acid is 1-2.

10. The application of the self-healing hot melt adhesive for automotive headlights prepared by any one of claims 1-7 or by the preparation method of the self-healing hot melt adhesive for automotive headlights according to claim 8 or 9 in the bonding of automotive headlights.

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