Hot melt adhesive for bonding silicon low-VOC (volatile organic compound) automotive trim and preparation method of hot melt adhesive

Abstract

The invention relates to the technical field of hot melt adhesives, and provides a low-VOC (volatile organic compound) hot melt adhesive for bonding automotive interiors and a preparation method thereof, the hot melt adhesive comprises the following components in parts by mass: 200-250 parts of 1, 6-hexanediol, 75-90 parts of diethylene glycol, 5-10 parts of polyethylene glycol, 220-250 parts of terephthalic acid, 65-75 parts of isophthalic acid and talcum powder; the composition comprises the following raw materials in parts by weight: 2-3 parts of polyethylene glycol, 0.1-1 part of neopentyl glycol, 1-2 parts of glycerol, 0.1-1 part of a catalyst for esterification, 0.1-0.5 part of an antioxidant and 0.1-0.3 part of a catalyst for polymerization. 1, 6-hexanediol is used for replacing traditional 1, 4-butanediol, generation of tetrahydrofuran by-products is fundamentally eradicated, the problem that tetrahydrofuran is generated due to high-temperature dehydration cyclization is avoided, it is ensured that VOC (volatile organic compounds) of a final product is far lower than the national standard limit, and the in-vehicle air quality standard is met.

Description

Technical Field

[0001] The present invention relates to the technical field of hot melt adhesives, and in particular to a low-VOC hot melt adhesive for bonding automotive interiors and a preparation method thereof. Background Art

[0002] In the automotive industry, automotive interiors are key components. Reliable bonding between the vehicle's interior substrate and the vehicle body directly impacts the overall quality, aesthetics, and safety of the interior. Currently, hot melt adhesives are a common material for bonding automotive interiors.

[0003] However, traditional hot-melt adhesives for automotive interiors have numerous drawbacks. Regarding high-temperature resistance, prolonged exposure to high temperatures can cause the adhesive to soften and flow, weakening the bond with the vehicle body and even causing it to peel. This not only affects the aesthetics of the interior but also poses a safety hazard. Water resistance is also poor. In humid environments or after being soaked in water, the adhesive's bonding performance is significantly weakened, leading to frequent debonding. This is particularly problematic for vehicles that require frequent interior cleaning or are used in humid areas. Initial tack is also insufficient, leading to easy shifting during application, requiring additional fixing, increasing the difficulty and time required. More critically, traditional hot-melt adhesives are often made from 1,4-butanediol, which can produce high levels of tetrahydrofuran residue during the production process. This not only emits a pungent odor but also contributes to excessive levels of volatile organic compounds (VOCs). These volatiles significantly pollute vehicle air quality, endangering the health of drivers and passengers, and running counter to the environmentally friendly and low-odor standards pursued by modern automotive interiors.

[0004] Therefore, developing a hot melt adhesive for automotive interior bonding that can overcome the above-mentioned technical defects, especially solve the problems of high tetrahydrofuran residue, strong odor, and excessive VOC, and at the same time have excellent bonding properties, heat and cold resistance, and water resistance, has become a technical problem that the industry urgently needs to overcome. Summary of the Invention

[0005] The present invention aims to solve at least one of the above technical problems.

[0006] The present invention provides a low-VOC hot melt adhesive for bonding automobile interiors. The hot melt adhesive comprises, by weight of raw materials, 200-250 parts of 1,6-hexanediol, 75-90 parts of diethylene glycol, 5-10 parts of polyethylene glycol, 220-250 parts of terephthalic acid, 65-75 parts of isophthalic acid, 2-3 parts of talc, 0.1-1 part of neopentyl glycol, 1-2 parts of glycerol, 0.1-1 part of an esterification catalyst, 0.1-0.5 part of an antioxidant, and 0.1-0.3 part of a polymerization catalyst.

[0007] In the above technical features, the melting point of the low-VOC hot melt adhesive for automotive interior bonding is 130-150°C; and / or the melt index of the low-VOC hot melt adhesive for automotive interior bonding is 135-140g / 10min at 160°C and a load of 2.16Kg; and / or the volatile matter content of the low-VOC hot melt adhesive for automotive interior bonding is 10-15μg / m 3 .

[0008] In any of the above technical features, the peel strength of the low-VOC hot melt adhesive for automotive interior bonding before soaking in water and before aging is 3.0-3.5N / 25mm; and / or the peel strength of the low-VOC hot melt adhesive for automotive interior bonding after soaking in water for 72 hours is 2.5-3.0N / 25mm; and / or the peel strength of the low-VOC hot melt adhesive for automotive interior bonding after 50 cycles of aging at a temperature of 60°C and a humidity of 95% is 3.0-3.5N / 25mm.

[0009] The present invention also provides a method for preparing a low-VOC hot melt adhesive for automotive interior bonding, which is used for the low-VOC hot melt adhesive for automotive interior bonding having any of the above technical features. The preparation method comprises: S100, esterification reaction: 1,6-hexanediol, diethylene glycol, polyethylene glycol, terephthalic acid, isophthalic acid, neopentyl glycol, and glycerol are mixed and stirred uniformly, the temperature is increased, and an esterification catalyst is added, and a first heat preservation treatment is performed to obtain an esterification product; S200, polycondensation reaction: adding a polymerization catalyst and an antioxidant to the esterification product, continuing to increase the temperature, and performing a second heat preservation treatment to obtain a hot melt adhesive prepolymer; S300, cooling and granulation: the hot melt adhesive prepolymer is cooled and then granulated to finally obtain a low-VOC hot melt adhesive finished product for automotive interior bonding.

[0010] In any of the above technical features, in S100, the first heat preservation treatment is performed in a nitrogen atmosphere; and / or in S200, the second heat preservation treatment is performed under a vacuum condition of 40-50Pa.

[0011] In any of the above technical features, in S100, the average molecular weight of the polyethylene glycol is 900-1100 Da; and / or the esterification catalyst includes titanium ethylene glycol.

[0012] In any of the above technical features, in S200, the polymerization catalyst includes titanium glycol; and / or the antioxidant includes pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate.

[0013] In any of the above technical features, in S100, the temperature of the first insulation treatment is 180-200°C; and / or in S200, the temperature of the second insulation treatment is 240-250°C; and / or in S200, the time of the second insulation treatment is 3-5h.

[0014] In any of the above technical features, in S300, the granulation process is underwater granulation process.

[0015] After adopting the technical solution of the present invention, the following technical effects can be achieved: 1. This invention uses 1,6-hexanediol instead of traditional 1,4-butanediol, fundamentally eliminating the formation of tetrahydrofuran as a byproduct. This avoids the problem of tetrahydrofuran being produced by high-temperature dehydration and cyclization, ensuring that the final product's VOC (volatile organic compound) content is far below the national standard limit, meeting in-vehicle air quality standards. 2. This invention incorporates both polyacids and polyols. The combined use of terephthalic acid and isophthalic acid can regulate the crystallinity and flexibility of the polyester backbone, achieving both high modulus and deformability. The addition of diethylene glycol, polyethylene glycol, neopentyl glycol, and glycerol synergistically forms amorphous regions, enhancing the wetting ability and initial viscosity of the bonding interface. This results in a hot melt adhesive product with both high polarity and good flexibility, making it particularly suitable for automotive interior bonding. 3. The present invention controls the formation of ester bonds between carboxylic acids and polyols through the esterification reaction in step S100 to construct basic chain segments. The molecular weight is further increased through the polycondensation reaction in step S200, ensuring that the polymer has sufficient strength and viscosity. Finally, the high-temperature prepolymer is cooled and granulated to quickly stabilize the molecular structure and avoid cross-linking or inhomogeneity. DETAILED DESCRIPTION

[0016] To make the above-mentioned objectives, features, and advantages of the present invention more clearly understood, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0017] Conventional hot-melt adhesives have poor heat and water resistance, insufficient initial tack, and are often made with 1,4-butanediol. This often produces high levels of tetrahydrofuran (THF) residue during the production process, which not only emits a pungent odor but also contributes to excessive levels of volatile organic compounds (VOCs). These volatiles severely pollute vehicle interior air quality, endangering the health of drivers and passengers, and running counter to the environmentally friendly and low-odor standards pursued by modern automotive interiors.

[0018] In light of this, the present invention provides a low-VOC hot-melt adhesive for automotive interior bonding. Through an innovative raw material formulation and optimized preparation process, it specifically addresses the issues of poor high-temperature resistance, insufficient water resistance, suboptimal initial tack, and environmental friendliness often associated with conventional hot-melt adhesives. Specifically, by replacing 1,4-butanediol with 1,6-hexanediol, the potential for residual tetrahydrofuran (THF) is eliminated, and the VOC content is reduced. This results in a hot-melt adhesive with excellent initial tack, bond strength, heat and cold resistance, water and chemical resistance, environmental performance, processability, and flexibility, fully meeting the high-standard requirements for automotive interior bonding.

[0019] Specifically, an embodiment of the present invention provides a low-VOC hot melt adhesive for bonding automotive interiors, which includes, by weight of raw materials: 200-250 parts of 1,6-hexanediol, 75-90 parts of diethylene glycol, 5-10 parts of polyethylene glycol, 220-250 parts of terephthalic acid, 65-75 parts of isophthalic acid, 2-3 parts of talc, 0.1-1 parts of neopentyl glycol, 1-2 parts of glycerol, 0.1-1 parts of esterification catalyst, 0.1-0.5 parts of antioxidant, and 0.1-0.3 parts of polymerization catalyst.

[0020] Preferably, the present invention uses 1,6-hexanediol to replace traditional 1,4-butanediol, fundamentally eliminating the generation of tetrahydrofuran by-products, avoiding the problem of tetrahydrofuran produced by high-temperature dehydration cyclization, ensuring that the VOC (volatile organic compound) of the final product is far below the national standard limit and meets the in-vehicle air quality standard; in addition, 1,6-hexanediol has a long molecular chain and good flexibility, which helps to improve the ductility and low-temperature toughness of polyester, improve the overall flexibility and elasticity of the polymer, and is conducive to adapting to the thermal expansion and contraction of interior materials; by using 1,6-hexanediol in combination with an antioxidant, due to the high thermal stability of the antioxidant, yellowing, cross-linking or degradation caused by oxidation during polymer processing or storage can be prevented, the anti-oxidation and aging ability of the hot melt adhesive can be further enhanced, degradation and odor release under high temperature conditions can be inhibited, so as to extend the service life of the hot melt adhesive and improve the consistency of the finished product.

[0021] Preferably, terephthalic acid is a rigid dibasic acid commonly used in linear polyesters, which provides high crystallinity and thermal stability to the polymer. It can increase the softening point and heat deformation temperature of the polyester and improve the structural stability at high temperatures while enhancing the polar compatibility of the material and improving the bonding strength. Isophthalic acid is an aromatic dibasic acid with an asymmetric structure, which can interrupt the excessive crystallization caused by terephthalic acid, thereby increasing the flexibility and impact resistance of the polymer, improving the low-temperature performance and stress buffering between the adhesive materials. By using terephthalic acid and isophthalic acid in combination, the crystallinity and flexibility of the polyester main chain can be regulated, taking into account both high modulus and deformation ability.

[0022] Furthermore, diethylene glycol provides good melt fluidity and processability, can introduce partial polarity, and improve the wetting and initial adhesion of the adhesive to the substrate; polyethylene glycol is a hydrophobic and oleophobic interface regulator, which can improve the wetting performance and water resistance of the adhesive, and improve the elasticity and flexibility of the colloid; the trimethyl substituted structure of neopentyl glycol provides steric hindrance, which can improve the thermal stability and anti-aging properties of the hot melt adhesive, thereby reducing the crystallization rate and controlling the melting behavior; glycerol is a trifunctional alcohol, which helps to adjust the viscosity and improve the initial adhesion by introducing trace branching; by adding diethylene glycol, polyethylene glycol, neopentyl glycol and glycerol, amorphous regions can be synergistically formed, thereby enhancing the wetting ability and initial viscosity of the bonding interface; the present invention adds polyacids and polyols at the same time, so that the final hot melt adhesive product has both high polarity and good flexibility, and is particularly suitable for automotive interior bonding.

[0023] Preferably, talc powder is used as an inorganic filler to enhance the dimensional stability and anti-sagging properties of the polymer while reducing the creep and sagging of the hot melt adhesive at high temperatures to ensure high-temperature morphological stability, thereby increasing the viscosity and storage modulus, making the film formation faster and more stable; the esterification catalyst can improve the efficiency of the acid-alcohol reaction, thereby allowing the condensation catalyst to promote the increase in polymerization degree and generate a hot melt adhesive with a suitable molecular weight distribution.

[0024] Preferably, the melting point of the low-VOC hot melt adhesive for automotive interior bonding is 130-150°C, indicating that the hot melt adhesive can melt quickly under moderate temperature conditions when heated, which can not only meet the hot melt construction temperature requirements, but also prevent the automotive interior from failing in adhesion at high temperatures, and can effectively prevent the hot melt adhesive from softening in high-temperature environments in the car, such as exposure to the sun in the summer.

[0025] Preferably, the melt index of the low-VOC hot melt adhesive for automotive interior bonding is 135-140g / 10min at 160°C and a load of 2.16Kg, indicating that the hot melt adhesive has good fluidity and wetting ability at the construction temperature, is convenient for rapid spreading and uniform coverage of the bonding interface, can effectively improve coating efficiency, control the amount of glue, ensure a uniform and gap-free adhesive layer, enhance bonding consistency, help improve initial adhesion, reduce positioning and fixture requirements, is suitable for modern coating equipment such as high-speed spraying, and is adaptable to large-scale industrial automated production.

[0026] Preferably, the volatile matter content of the low VOC hot melt adhesive for automotive interior bonding is 10-15 μg / m 3 , which is far lower than the national standard GB / T 27630 which stipulates that the limit of volatile substances in passenger cars is ≤50μg / m 3, indicating that the hot melt adhesive will not release obvious odor or harmful substances during processing and use, indicating that there are no residual volatile small molecules such as tetrahydrofuran in the polyester structure. The process is well controlled and can greatly improve the air quality in the car, meet the green, odorless and environmentally friendly material selection requirements of high-end automobile brands, reduce the health risks to passengers, and enhance the end-user experience.

[0027] Preferably, the peel strength of the low-VOC hot melt adhesive for automotive interior bonding before soaking in water and before aging is 3.0-3.5N / 25m. The hot melt adhesive has strong initial adhesion and firm interface bonding, which can significantly improve interior assembly efficiency and reduce rework rate. It provides stable and firm initial positioning force and is suitable for bonding a variety of materials, which can improve production efficiency and assembly accuracy.

[0028] Furthermore, the peel strength of the low-VOC hot melt adhesive for automotive interior bonding after 72 hours of soaking in water is 2.5-3.0N / 25mm, indicating that the hot melt adhesive has excellent hydrolysis resistance and can maintain >80% bonding strength even after long-term immersion in water. In other words, the hot melt adhesive is still reliable in humid or clean environments, and can prevent debonding caused by the intrusion of moisture, rain or detergents, ensuring the stability of automotive interiors in the humid southern and coastal high-humidity environments. It is suitable for use in areas that may come into contact with moisture, such as door panels, floor mats, and trunk lids. Furthermore, the peel strength of the low-VOC hot melt adhesive for automotive interior bonding is 3.0-3.5N / 25mm after 50 cycles of aging at a temperature of 60°C and a humidity of 95%. After repeated cycles under extreme aging conditions of 60°C and 95% humidity, the initial peel strength is still maintained, indicating that the hot melt adhesive structure is resistant to alternating changes in high temperature and humidity, the bonding interface is stable and free of brittle cracks, and it can effectively resist peeling or interface fatigue caused by thermal expansion and contraction and humidity fluctuations, effectively improving the service life.

[0029] In some embodiments of the present invention, a method for preparing a low-VOC hot melt adhesive for automotive interior bonding, which is used for the low-VOC hot melt adhesive for automotive interior bonding having any of the above technical features, comprises: S100, esterification reaction: 1,6-hexanediol, diethylene glycol, polyethylene glycol, terephthalic acid, isophthalic acid, neopentyl glycol, and glycerol are mixed and stirred uniformly, the temperature is increased, and an esterification catalyst is added, and a first heat preservation treatment is performed to obtain an esterification product; S200, polycondensation reaction: adding a polymerization catalyst and an antioxidant to the esterification product, continuing to increase the temperature, and performing a second heat preservation treatment to obtain a hot melt adhesive prepolymer; S300, cooling and granulation: the hot melt adhesive prepolymer is cooled and then granulated to finally obtain a low-VOC hot melt adhesive finished product for automotive interior bonding.

[0030] Preferably, the present invention controls the formation of ester bonds between carboxylic acid and polyols through the esterification reaction in step S100 to construct basic chain segments, and then further increases the molecular weight through the polycondensation reaction in step S200 to ensure that the polymer has sufficient strength and viscosity. Finally, the high-temperature prepolymer is cooled and granulated to quickly stabilize the molecular structure and avoid cross-linking or inhomogeneity.

[0031] Preferably, in step S100, the reactants are first mixed and then heated to perform a first heat preservation treatment. During the first heat preservation treatment, an esterification reaction occurs. The first heat preservation treatment is preferably performed under a nitrogen atmosphere at a temperature of 180-200°C. 180-200°C is the optimal range for the reaction of polyacids and polyols to form ester bonds. If the temperature is lower than this range, the reaction rate is slow and dehydration is difficult. If the temperature is higher than this range, side reactions are likely to occur, and the raw materials are easily degraded and discolored. The nitrogen atmosphere can make 1,6-hexanediol, glycerol and other polyols easily exposed to air at high temperatures to produce peroxides or darken the color, and partially oxidize unsaturated groups or impurities, thereby initiating polymerization side reactions. The molecular weight of the polyethylene glycol is preferably 900-1100 Da. At this time, the molecular weight of the polyethylene glycol is moderate, which can improve flexibility without sacrificing reactivity and structural stability, and can ensure moderate reactivity and reaction rate, thereby preventing the polymerization process from being slow or gelling. Preferably, in step S200, a polycondensation catalyst and an antioxidant are added, and the temperature is continued to be raised for a second heat preservation treatment. During the second heat preservation treatment, a polycondensation reaction is carried out. The second heat preservation treatment is preferably carried out under a vacuum condition of 40-50 Pa. The ester polycondensation reaction (polycondensation of polyester) is a reversible reaction, and the reaction formula is as follows: HO-R-OH+HOOC-R'-COOH↔Polyester+H2O Under vacuum conditions of 40-50 Pa, the reaction can be pushed to the right, that is, towards the formation of polyester, thereby quickly evaporating water, lowering the boiling point of the system, and promoting the condensation reaction to develop towards a high degree of polymerization; avoiding thermal degradation: the polymerization viscosity target can be achieved at a lower temperature; preferably, the temperature is raised to 240-250°C, and the time is preferably 3-5 hours. At this temperature and time, it is conducive to the volatilization of by-product water, and at the same time, a sufficiently long-chain polymer structure and ideal viscosity can be achieved; the antioxidant is preferably pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010). Antioxidant 1010 is a high molecular weight, low volatility, and high thermal stability primary antioxidant. During the high-temperature condensation process, it can effectively capture oxygen free radicals and prevent oxidative degradation of the polymer. It can not only stabilize the reaction system at high temperature during the condensation stage, but also provide long-term anti-aging protection in the finished product stage.

[0032] Furthermore, the esterification catalyst and the polymerization catalyst are preferably titanium ethylene glycol. Ethylene glycol is a catalyst with strong affinity, high catalytic selectivity and low residue among titanates. It has high catalytic efficiency, shortens the esterification and polycondensation reaction time, reduces by-product residues, improves purity, and ensures low VOC indicators. It can also catalyze esterification and polycondensation reactions at the same time and can be reused at different stages to improve economy and process consistency. Residual metal ions are also more compatible with components in the product formula and do not affect the transparency or color stability of the finished product.

[0033] Preferably, after the esterification reaction and the polycondensation reaction are completed, the hot melt adhesive prepolymer needs to be cooled, sheared, and pelletized. Rapid cooling stabilizes the molecular chain structure, effectively preventing gelation, agglomeration, and oxidation, and forming particles or strips with regular morphology, which is conducive to storage and subsequent heating applications; the granulation treatment is preferably underwater granulation treatment. Underwater granulation is a common industrial granulation method for hot melt adhesives, which can achieve rapid cooling and automatic pelletizing, prevent the high-temperature prepolymer from continuing to cross-link or oxidize, reduce thermal stress and odor release during the secondary processing of the adhesive, and make the final hot melt adhesive have uniform particle size, good appearance, and non-stickiness.

[0034] Example 1 This embodiment provides a low-VOC hot melt adhesive for bonding automotive interiors, which comprises, by weight of raw materials: 200 parts of 1,6-hexanediol, 75 parts of diethylene glycol, 5 parts of polyethylene glycol, 220 parts of terephthalic acid, 6 parts of isophthalic acid, 2 parts of talc, 0.1 part of neopentyl glycol, 1 part of glycerol, 0.1 part of esterification catalyst, 0.1 part of antioxidant 1010, and 0.1 part of polymerization catalyst; The esterification catalyst and the polymerization catalyst are both titanium glycolate.

[0035] Example 2 This embodiment provides a low-VOC hot melt adhesive for bonding automotive interiors, which comprises, by weight of raw materials: 250 parts of 1,6-hexanediol, 90 parts of diethylene glycol, 10 parts of polyethylene glycol, 250 parts of terephthalic acid, 75 parts of isophthalic acid, 3 parts of talc, 1 part of neopentyl glycol, 2 parts of glycerol, 1 part of an esterification catalyst, 0.5 parts of an antioxidant 1010, and 0.3 parts of a polymerization catalyst. The esterification catalyst and the polymerization catalyst are both titanium glycolate.

[0036] Example 3 This embodiment provides a low-VOC hot melt adhesive for bonding automotive interiors, which comprises, by weight of raw materials, 50 parts of 1,6-hexanediol, 85 parts of diethylene glycol, 10 parts of polyethylene glycol, 250 parts of terephthalic acid, 70 parts of isophthalic acid, 2.67 parts of talc, 0.67 parts of neopentyl glycol, 1 part of glycerin, 0.17 parts of an esterification catalyst, 0.42 parts of antioxidant 1010, and 0.2 parts of a polymerization catalyst. The catalyst for esterification and the catalyst for polymerization are both titanium glycolate.

[0037] Example 4 The present invention provides a method for preparing a low-VOC hot melt adhesive for bonding automotive interiors, comprising the following steps: S100, esterification reaction: 1,6-hexanediol, diethylene glycol, polyethylene glycol, terephthalic acid, isophthalic acid, neopentyl glycol and glycerol are mixed and stirred uniformly, the temperature is raised to 180° C., titanium glycol is added, and a first heat preservation treatment is performed under a nitrogen atmosphere to obtain an esterification product; S200, polycondensation reaction: adding titanium glycolate and antioxidant 1010 to the esterification product, continuing to raise the temperature to 240° C., and performing a second heat preservation treatment under a vacuum of 50 kPa for 3 hours to obtain a hot melt adhesive prepolymer; S300, cooling and granulation: After cooling, the hot melt adhesive prepolymer is subjected to underwater granulation treatment to finally obtain a low-VOC hot melt adhesive finished product for automotive interior bonding; The average molecular weight of polyethylene glycol is 900 Da.

[0038] Example 5 The present invention provides a method for preparing a low-VOC hot melt adhesive for bonding automotive interiors, comprising the following steps: S100, esterification reaction: 1,6-hexanediol, diethylene glycol, polyethylene glycol, terephthalic acid, isophthalic acid, neopentyl glycol and glycerol are mixed and stirred uniformly, the temperature is raised to 200° C., titanium glycol is added, and a first heat preservation treatment is performed under a nitrogen atmosphere to obtain an esterification product; S200, polycondensation reaction: adding titanium glycolate and antioxidant 1010 to the esterification product, continuing to raise the temperature to 250° C., and performing a second heat preservation treatment under a vacuum of 40 kPa for 5 hours to obtain a hot melt adhesive prepolymer; S300, cooling and granulation: After cooling, the hot melt adhesive prepolymer is subjected to underwater granulation treatment to finally obtain a low-VOC hot melt adhesive finished product for automotive interior bonding; The average molecular weight of polyethylene glycol is 1100 Da.

[0039] Example 6 The present invention provides a method for preparing a low-VOC hot melt adhesive for bonding automotive interiors, comprising the following steps: S100, esterification reaction: 1,6-hexanediol, diethylene glycol, polyethylene glycol, terephthalic acid, isophthalic acid, neopentyl glycol and glycerol are mixed and stirred uniformly, the temperature is raised to 190° C., titanium glycol is added, and a first heat preservation treatment is performed under a nitrogen atmosphere to obtain an esterification product; S200, polycondensation reaction: adding titanium glycolate and antioxidant 1010 to the esterification product, continuing to raise the temperature to 250° C., and performing a second heat preservation treatment under a vacuum of 50 kPa for 5 hours to obtain a hot melt adhesive prepolymer; S300, cooling and granulation: After cooling, the hot melt adhesive prepolymer is subjected to underwater granulation treatment to finally obtain a low-VOC hot melt adhesive finished product for automotive interior bonding; The average molecular weight of polyethylene glycol is 1000 Da.

[0040] Performance Testing The volatile organic compound (VOC) content of the hot melt adhesives of Examples 1-3 was detected by gas chromatography-mass spectrometry (GC-MS) and was 15 μg / m 3 , 13 μg / m 3 , 12 μg / m 3 , which is far lower than the national standard of ≤50μg / m 3 , and the odor level was all level 1 (where odor levels are 1-5, with level 1 being the best and level 5 being the worst). Therefore, it can be concluded that the low-VOC hot melt adhesive for automotive interior bonding of the present invention not only effectively protects the air quality inside the vehicle, but also creates a healthy and comfortable riding environment for drivers and passengers, fully meeting the stringent requirements of modern automotive interiors for environmental protection and low odor.

[0041] After the hot melt adhesive of Example 3 is applied at 160°C, the initial bonding strength is 3.2N / 25mm within 5 seconds of contact with common automotive interior materials such as polypropylene and polyvinyl chloride, which is about 40% higher than that of traditional hot melt adhesives. It can quickly achieve accurate initial fixation with the base layer and significantly improve production efficiency. After curing for 72 hours at room temperature, the bonding strength reaches 12.5N / mm 2 After 1,000 simulated automobile driving vibration tests (amplitude 5 mm, frequency 20 Hz, duration 48 hours), the bonding interface remained stable, with no peeling or warping, indicating that the low-VOC hot melt adhesive for automotive interior bonding of the present invention can effectively ensure the long-term stability of the interior.

[0042] When the interior material bonded with the hot melt adhesive of Example 3 was placed in a 120°C environment for 24 hours, the hot melt adhesive did not soften or flow, and the bonding strength retention rate was over 95%. When it was placed in a -30°C environment for 24 hours, the hot melt adhesive still maintained good flexibility, with an elongation at break of 180%, and the bonding strength decreased by only 8%, far exceeding the performance of most similar products on the market.

[0043] After the bonded sample was completely immersed in water for 7 hours, the peel strength still maintained 88% of the initial value; after 50 cycles of artificial heat and humidity aging test (test conditions were temperature 60°C and humidity 95%), there was no significant decrease in bonding performance.

[0044] In summary, the low-VOC hot melt adhesive for automotive interior bonding provided by the present invention has successfully overcome the technical bottleneck of traditional hot melt adhesives through innovative raw material formula and advanced preparation technology, achieving a major breakthrough in environmental performance while taking into account excellent comprehensive performance. It has broad market application prospects and significant economic benefits.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A low-VOC hot melt adhesive for automotive interior bonding, characterized in that: Calculated by weight of raw materials, the invention comprises: 200-250 parts of 1,6-hexanediol, 75-90 parts of diethylene glycol, 5-10 parts of polyethylene glycol, 220-250 parts of terephthalic acid, 65-75 parts of isophthalic acid, 2-3 parts of talc, 0.1-1 part of neopentyl glycol, 1-2 parts of glycerol, 0.1-1 part of esterification catalyst, 0.1-0.5 part of antioxidant, and 0.1-0.3 part of polymerization catalyst.

2. The low-VOC hot melt adhesive for automotive interior bonding according to claim 1, wherein: The melting point of the low-VOC hot melt adhesive for automotive interior bonding is 130-150° C.; and / or The low-VOC hot melt adhesive for automotive interior bonding has a melt index of 135-140 g / 10 min at 160° C. and a load of 2.16 kg; and / or The volatile matter content of the low-VOC hot melt adhesive for automotive interior bonding is 10-15 μg / m 3 .

3. The low-VOC hot melt adhesive for automotive interior bonding according to claim 2, wherein: The peel strength of the low-VOC hot melt adhesive for automotive interior bonding before soaking in water and before aging is 3.0-3.5N / 25mm; and / or The peel strength of the low-VOC hot melt adhesive for automotive interior bonding after soaking in water for 72 hours is 2.5-3.0N / 25mm; and / or The low-VOC hot melt adhesive for automotive interior bonding has a peel strength of 3.0-3.5 N / 25 mm after 50 cycles of aging under conditions of a temperature of 60° C. and a humidity of 95%.

4. A method for preparing a low-VOC hot melt adhesive for automotive interior bonding, for preparing the low-VOC hot melt adhesive for automotive interior bonding according to claims 1-3, characterized in that: The preparation method comprises: S100, esterification reaction: mixing the 1,6-hexanediol, the diethylene glycol, the polyethylene glycol, the terephthalic acid, the isophthalic acid, the neopentyl glycol, and the glycerol, stirring the mixture uniformly, heating the mixture, adding the esterification catalyst, and performing a first heat preservation treatment to obtain an esterified product; S200, polycondensation reaction: adding a polymerization catalyst and an antioxidant to the esterification product, continuing to increase the temperature, and performing a second heat preservation treatment to obtain a hot melt adhesive prepolymer; S300, cooling and granulating: the hot melt adhesive prepolymer is cooled and then granulated to finally obtain the low-VOC hot melt adhesive finished product for automotive interior bonding.

5. The preparation method according to claim 4, characterized in that In said S100, said first heat preservation treatment is performed in a nitrogen atmosphere; and / or In the S200, the second heat preservation treatment is performed under a vacuum condition of 40-50 Pa.

6. The preparation method according to claim 4, characterized in that In the S100, The average molecular weight of the polyethylene glycol is 900-1100 Da; and / or The esterification catalyst includes titanium glycolate.

7. The preparation method according to claim 4, characterized in that In the above S200, The polymerization catalyst comprises titanium glycolate; and / or The antioxidant includes pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

8. The preparation method according to claim 4, characterized in that In said S100, the temperature of said first heat preservation treatment is 180-200°C; and / or In said S200, the temperature of said second heat preservation treatment is 240-250°C; and / or In the step S200 , the second heat preservation treatment is performed for 3-5 hours.

9. The preparation method according to claim 4, characterized in that In the S300 , the granulation process is an underwater granulation process.