Low-voc environment-friendly pressure-sensitive adhesive for car body stickers and preparation method thereof

Abstract

The application relates to the technical field of green material engineering, and discloses a low-VOC environment-friendly pressure-sensitive adhesive for a vehicle body sticker and a preparation method thereof, which comprises deionized water, sodium lignosulfonate dry powder, hydrogenated rosin glyceride, an oxidized starch aqueous solution, ammonia water, glucose acid-delta-lactone dry powder and a zirconium ammonium carbonate solution. When the adhesive is prepared, the hydrogenated rosin glyceride is dispersed to form a microemulsion under the shearing field by utilizing the amphiphilic property of lignin, and then the latent acid, the ammonia water and the crosslinking agent are added under the laminar flow state after the hydrogenated rosin glyceride is mixed with the oxidized starch. The physical and chemical coupling mechanism of ammonia water volatilization and glucose acid-delta-lactone acid release under heat is utilized to realize the synchronous homogeneous crosslinking of a thick coating layer, and the cohesion gradient defect is solved; meanwhile, the high-valence zirconium ion is utilized to construct a dynamic reversible coordination dissipation network, the peeling tensile stress is effectively dissipated, the cohesive failure type residual glue is avoided, the VOC and the interface shrinkage risk caused by the small-molecule emulsifier residue are excluded, and the heat-resistant adhesive holding performance is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of green materials engineering technology, specifically to a low-VOC environmentally friendly pressure-sensitive adhesive for vehicle body stickers and its preparation method. Background Technology

[0002] As a special film material used for changing the color of car exteriors and for advertising decoration, the performance of car body wraps mainly depends on the pressure-sensitive adhesive layer on the back. In practical applications, the pressure-sensitive adhesive of car body wraps not only needs to have moderate initial tack to facilitate application and positioning, but also needs to maintain stable tack during long-term outdoor service. More importantly, after the service life ends, it must have the mechanical properties of being easy to peel off without damaging the car paint.

[0003] Currently, most mainstream pressure-sensitive adhesives for vehicle wraps on the market use solvent-based polymer systems. While these adhesives have good weather resistance, they release large amounts of organic solvents during the coating and curing stages, posing a serious problem of volatile organic compound emissions and making it difficult to meet increasingly stringent environmental regulations. To reduce environmental pollution, the industry is gradually shifting towards the development of water-based pressure-sensitive adhesive systems. The conventional preparation method usually relies on adding a large amount of small-molecule surfactants to achieve dispersion and emulsification of the base resin in an aqueous medium.

[0004] However, existing water-based pressure-sensitive adhesive systems still have significant technical shortcomings in vehicle wrap applications. On one hand, the small-molecule emulsifiers added in traditional processes remain in a free state after the film dries, easily accumulating at the interface between the coating and the air or substrate. This leads to coating defects such as pinholes on the coating surface. Furthermore, these residual small molecules can migrate and volatilize again under the high temperatures of outdoor exposure to sunlight, still posing a risk of VOC exceeding standards. On the other hand, considering the coverage and adhesive thickness requirements of vehicle wraps, the coating weight of the pressure-sensitive adhesive is usually large. During conventional thermosetting and drying processes, there are limitations in unidirectional heat and mass transfer. The coating surface heats up quickly and undergoes a cross-linking reaction first, forming a skin layer. This dense skin layer hinders the outward diffusion of moisture and reaction byproducts from the underlying layer, resulting in a large cross-linking density gradient in the thickness direction of the adhesive layer. This heterogeneous curing structure, with a highly cross-linked upper layer and a weakly cross-linked lower layer, causes the overall cohesive strength of the adhesive film's underlying layer to be significantly lower than expected. When car wraps need to be removed after long-term use, the underlying cross-linked network is incomplete and unable to effectively resist and dissipate externally applied mechanical tensile stress. This makes the adhesive film prone to breakage at points of weak internal stress, resulting in a large amount of adhesive residue on the car's paint surface. This cohesive-destructive adhesive residue problem not only severely affects the appearance of the substrate but also greatly increases the cost of subsequent solvent cleaning and the risk of paint damage. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a low-VOC environmentally friendly pressure-sensitive adhesive for vehicle body wraps and its preparation method, solving the problem that existing technologies result in significant free states after the adhesive film dries, leading to coating defects such as pinholes on the coating surface.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: a low-VOC environmentally friendly pressure-sensitive adhesive for vehicle body stickers, made from raw materials comprising the following parts by weight: 100 parts deionized water; 5-20 parts enzymatically hydrolyzed sodium lignosulfonate powder; 15-30 parts hydrogenated rosin glycerol ester; 40-90 parts oxidized starch aqueous solution; ammonia water, the amount of which is added to adjust the pH value of the system to 9.2-9.8; 0.5-3.0 parts glucono-δ-lactone powder; and 1-6 parts zirconium carbonate ammonium solution.

[0007] Preferably, the softening point of the hydrogenated rosin glycerol ester is 85℃-90℃.

[0008] Preferably, the mass fraction of the oxidized starch aqueous solution is 30%, and the degree of substitution of the oxidized starch is 0.05-0.08; The oxidized starch aqueous solution is prepared by the following method: cassava starch is dispersed in deionized water to prepare a starch emulsion. The pH of the system is adjusted to 8.5-9.5 using sodium hydroxide solution. The temperature is raised to 40-45℃. Sodium hypochlorite solution with an effective chlorine mass fraction of 10% is added dropwise at a uniform rate according to 6%-10% of the dry weight of cassava starch and reacted for 2-3 hours. After terminating the reaction by adding sodium sulfite, the temperature is raised to 80-85℃ and kept at that temperature for 45 minutes to gelatinize the starch.

[0009] Preferably, the weight-average molecular weight of the enzymatically hydrolyzed sodium lignosulfonate powder is 3000 Da-5000 Da; The enzymatically hydrolyzed sodium lignin sulfonate powder is prepared by the following method: sulfate-processed alkali lignin is dispersed in a buffer solution, the pH is adjusted to 5.0-5.5, and a complex enzyme system of laccase and xylanase with a mass ratio of 1:1 is added at 1% of the dry lignin mass. The reaction is carried out at 45-50℃ for 4-6 hours. After inactivating the enzyme system by heating, the temperature is lowered to 60℃, and the pH is adjusted to 10.0-10.5 by reverse adjustment using sodium hydroxide solution. Sodium sulfite and formaldehyde aqueous solution are added, and sulfonation reaction is carried out at 85-95℃ for 3 hours. Finally, the powder is spray-dried to obtain the final product.

[0010] Preferably, the pressure-sensitive adhesive is in a uniform and stable water-in-oil mesoscopic emulsion micro-region state before being cured by heat, wherein the hydrogenated rosin glycerol ester is encapsulated and dispersed by the components formed after the enzymatic hydrolysis of sodium lignosulfonate dry powder.

[0011] A method for preparing a low-VOC environmentally friendly pressure-sensitive adhesive for vehicle body stickers includes the following steps: (1) Add deionized water to a reactor with a high shear dispersion disk and heat it up. Add enzymatically hydrolyzed sodium lignosulfonate powder and stir to dissolve. Then pump in hydrogenated rosin glycerol ester preheated to a molten state to form water-in-oil meso-emulsion micro-regions under high-speed shear. (2) After cooling, pump the oxidized starch aqueous solution into the pump at a constant speed and reduce the speed to maintain the macroscopic turbulent state for continuous stirring and mixing; (3) Continue to cool down and suddenly reduce the stirring speed to laminar flow. Add gluconate-δ-lactone dry powder, ammonia water and zirconium carbonate ammonium solution in sequence. After low shear stirring to ensure homogeneous dispersion, discharge the material to obtain liquid phase adhesive. (4) The liquid phase adhesive obtained in step (3) is coated on the surface of the substrate and then placed in a multi-stage temperature-controlled drying oven for step heating and drying. During this process, an in-situ dynamic coordination crosslinking reaction is triggered. After exiting the oven, the product is compounded and rolled up to obtain the finished product.

[0012] Preferably, in step (1), the heating temperature is 92-98°C, the high-speed shearing speed is 2800-3200 rpm, and the continuous shearing time is 25-35 minutes.

[0013] Preferably, in step (2), the system temperature is reduced to 55-65℃ for pumping, and the stirring speed of the stirring system is simultaneously reduced to 800-1200 rpm, with continuous stirring and mixing time of 20-30 minutes.

[0014] Preferably, step (3) is implemented as follows: Continue cooling until the system temperature stabilizes at 30-35℃. Then, drastically reduce the stirring speed to 50-80 rpm in a laminar flow state. First, add gluconate-δ-lactone dry powder and stir to dissolve. Then, slowly add 25% ammonia water to adjust and lock the pH of the system at 9.2-9.8. After locking in the alkaline environment, finally slowly add the zirconium carbonate ammonium solution and stir under low shear for 15-20 minutes.

[0015] Preferably, in step (4), the temperature gradient set in the multi-segment temperature-controlled drying oven is 90°C to 105°C to 110°C, and the total drying time is 3-5 minutes.

[0016] This invention provides a low-VOC, environmentally friendly pressure-sensitive adhesive for vehicle wraps and its preparation method. It offers the following advantages: 1. In the heating stage of film formation, free ammonia, acting as an inhibitor, is transferred to the gas phase. Simultaneously, gluconic acid-δ-lactone, uniformly dispersed within the system, absorbs heat and undergoes lactone ring hydrolysis, releasing gluconic acid in situ deep within the coating to lower the local microenvironment pH. This physicochemical coupling process solves the curing gradient problem caused by unidirectional heat and mass transfer in thick coatings, allowing the coordination crosslinking activity of ammonium zirconium carbonate to be released synchronously within the film. This avoids premature skinning on the surface and insufficient crosslinking in the underlying layer, resulting in cohesive gradient defects and achieving homogeneous crosslinking of the coating in the thickness direction.

[0017] 2. In this invention, when the pressure-sensitive adhesive is subjected to mechanical peeling force, the coordination bonds in the stress concentration area of ​​the adhesive film preferentially undergo reversible breakage and recombination, converting tensile stress into heat energy dissipation through polymer chain segment movement. This microscopic energy dissipation mechanism prevents the mechanical peeling force from directly damaging the polymer backbone, ensuring that the overall cohesive strength of the coating is always higher than its adhesion force at the substrate interface, thus avoiding the generation of cohesive-damaging residue from the perspective of fracture mechanics.

[0018] 3. This invention uses enzymatically hydrolyzed sodium lignin sulfonate instead of conventional small-molecule surfactants. Utilizing the amphiphilic structure of its skeleton—a hydrophobic phenylpropane unit and a hydrophilic sulfonic acid group—liquid hydrogenated rosin glycerol ester is dispersed into stable oil-in-water mesoscopic latex particles under the action of the hydrodynamic shear field in the reactor. This design not only eliminates the interfacial shrinkage defects and VOC release risks caused by residual small-molecule emulsifiers, but also allows the rigid benzene rings in the lignin structure to act as physical anti-thermal creep nodes after coating curing, thus incorporating them into the crosslinking network and improving the storage modulus and holding power of the pressure-sensitive adhesive system under high-temperature conditions. Attached Figure Description

[0019] Figure 1 This is a flowchart of the process steps of the present invention. Detailed Implementation

[0020] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0022] Cassava starch, CAS No. 9005-25-8, is a commercially available industrial-grade product with an amylose content of 15% to 20% and a moisture content of less than 14%.

[0023] Sulfate-processed alkali lignin, CAS No. 8068-05-1, with a weight-average molecular weight of 10,000 Da to 15,000 Da, a total hydroxyl content of 2.5 mmol / g to 3.5 mmol / g, and a purity greater than 95%.

[0024] Laccase, CAS No. 80498-15-3, is a commercially available solid powder with an enzyme activity greater than 10,000 U / g.

[0025] Xylanase, CAS No. 9025-57-4, is a commercially available solid powder with an enzyme activity greater than 50,000 U / g.

[0026] Hydrogenated rosin glycerol ester, CAS No. 65997-13-9, is a light yellow transparent solid resin obtained by esterification reaction of hydrogenated rosin and glycerol. Its softening point (ring and ball method) is 85℃ to 90℃, its acid value is less than 8mgKOH / g, and its color (Gardner color) is less than 3.

[0027] Zirconium ammonium carbonate solution, CAS No. 68309-95-5, is a homogeneous aqueous solution with a zirconium dioxide mass fraction of 20% and a pH value of 9.0 to 9.5.

[0028] Glucono-δ-lactone, CAS No. 90-80-2, is a white crystalline powder with a purity greater than 99.0%.

[0029] Preparation Example 1: This preparation example provides a method for preparing an aqueous solution of oxidized starch, including the following steps: Cassava starch was dispersed in deionized water to prepare a starch emulsion with a mass fraction of 30%. The pH of the system was adjusted to 8.5 using a 10% sodium hydroxide solution. The system was then heated to 40°C, and a 10% sodium hypochlorite solution with available chlorine was added dropwise at a uniform rate of 6% of the dry weight of the cassava starch to initiate oxidative degradation and carboxylation reactions. After reacting at a constant temperature for 2 hours, 0.5% sodium sulfite (by dry weight of the cassava starch) was added to terminate the reaction of residual free chlorine. Subsequently, the system was heated to 80°C and stirred at this temperature for 45 minutes to completely break down and gelatinize the starch granules. The mixture was then cooled to room temperature to obtain a transparent gelatinized oxidized starch solution with a degree of substitution of 0.05.

[0030] Preparation Example 2: This preparation example provides a method for preparing an aqueous solution of oxidized starch, including the following steps: Cassava starch was dispersed in deionized water to prepare a starch emulsion with a mass fraction of 30%. The pH of the system was adjusted to 9.0 using a 10% sodium hydroxide solution. The system was then heated to 42°C, and a 10% sodium hypochlorite solution with available chlorine was added dropwise at a uniform rate at 8% of the dry weight of the cassava starch to carry out oxidative degradation and carboxylation reactions. After reacting at a constant temperature for 2.5 hours, 0.6% sodium sulfite (by dry weight of the cassava starch) was added to terminate the reaction of residual free chlorine. Subsequently, the system was heated to 82°C and stirred at this temperature for 45 minutes to completely break down and gelatinize the starch granules. The mixture was then cooled to room temperature to obtain a transparent gelatinized oxidized starch solution with a degree of substitution of 0.065.

[0031] Preparation Example 3: This preparation example provides a method for preparing an aqueous solution of oxidized starch, including the following steps: Cassava starch was dispersed in deionized water to prepare a starch emulsion with a mass fraction of 30%. The pH of the system was adjusted to 9.5 using a 10% sodium hydroxide solution. The system was then heated to 45°C, and sodium hypochlorite solution with an effective chlorine mass fraction of 10% was added dropwise at a uniform rate according to 10% of the dry weight of the cassava starch to carry out oxidative degradation and carboxylation reactions. After reacting at a constant temperature for 3 hours, sodium sulfite with a mass fraction of 0.8% of the dry weight of the cassava starch was added to terminate the reaction of residual free chlorine. Subsequently, the system was heated to 85°C and kept at a constant temperature with stirring for 45 minutes to completely break down and gelatinize the starch granules. The system was then cooled to room temperature to obtain a transparent gelatinized oxidized starch solution with a degree of substitution of 0.08.

[0032] Preparation Example 4: This preparation example provides a method for preparing sodium lignin sulfonate by enzymatic hydrolysis, including the following steps: Sulfate-processed alkali lignin was dispersed in an acetate-sodium acetate buffer solution to prepare a 15% solids suspension, and the pH of the system was adjusted to 5.0. A complex enzyme system (laccase to xylanase mass ratio of 1:1) was added at 1% of the lignin dry weight, and a directed enzymatic hydrolysis reaction was carried out at 45℃ for 4 hours. The temperature was then raised to 95℃ and incubated for 15 minutes to inactivate the enzyme system. The system was cooled to 60℃, and the pH was reverse-adjusted to 10.0 using a 20% sodium hydroxide solution. Then, 10% sodium sulfite (by weight of lignin dry weight) and 5% formaldehyde aqueous solution (by weight of lignin dry weight) were added to the system, and a sulfonation methylation reaction was carried out at 85℃ for 3 hours. After the reaction, the enzymatically hydrolyzed sodium lignin sulfonate powder was obtained by spray drying. Its weight-average molecular weight was measured to be 5000 Da.

[0033] Preparation Example 5: This preparation example provides a method for preparing sodium lignin sulfonate by enzymatic hydrolysis, including the following steps: Sulfate-processed alkali lignin was dispersed in an acetate-sodium acetate buffer solution to prepare a 15% solids suspension, and the pH of the system was adjusted to 5.2. A complex enzyme system (laccase to xylanase mass ratio of 1:1) was added at 1% of the lignin dry weight, and a directed enzymatic hydrolysis reaction was carried out at 48℃ for 5 hours. The temperature was then raised to 95℃ and incubated for 15 minutes to inactivate the enzyme system. The system was cooled to 60℃, and the pH was reverse-adjusted to 10.2 using a 20% sodium hydroxide solution. Then, 12% sodium sulfite (by lignin dry weight) and 6% formaldehyde aqueous solution (by lignin dry weight) were added to the system, and a sulfonation methylation reaction was carried out at 90℃ for 3 hours. After the reaction, the enzymatically hydrolyzed sodium lignin sulfonate powder was obtained by spray drying. Its weight-average molecular weight was measured to be 4000 Da.

[0034] Preparation Example 6: This preparation example provides a method for preparing sodium lignin sulfonate by enzymatic hydrolysis, including the following steps: Sulfate-processed alkali lignin was dispersed in an acetate-sodium acetate buffer solution to prepare a 15% solids suspension, and the pH of the system was adjusted to 5.5. A complex enzyme system (laccase to xylanase mass ratio of 1:1) was added at 1% of the lignin dry weight, and a directed enzymatic hydrolysis reaction was carried out at 50°C for 6 hours. The temperature was then raised to 95°C and incubated for 15 minutes to inactivate the enzyme system. The system was cooled to 60°C, and the pH was reverse-adjusted to 10.5 using a 20% sodium hydroxide solution. Then, 15% sodium sulfite (by lignin dry weight) and 8% formaldehyde aqueous solution (by lignin dry weight) were added to the system, and a sulfonation methylation reaction was carried out at 95°C for 3 hours. After the reaction, the enzymatically hydrolyzed sodium lignin sulfonate powder was obtained by spray drying. Its weight-average molecular weight was measured to be 3000 Da.

[0035] Example 1: See Appendix Figure 1 This embodiment provides an in-situ dynamic crosslinking pressure-sensitive adhesive for low-VOC environmentally friendly vehicle wraps and its preparation method, including the following steps: (1) In a reaction vessel equipped with a jacketed temperature control and a high-shear dispersion disk, add 100 parts by weight of deionized water and turn on the heater to raise the system temperature to 92°C. Add 8 parts by weight of the enzymatically hydrolyzed sodium lignosulfonate powder prepared in Preparation Example 4 and stir at medium speed until completely dissolved. Pump 18 parts by weight of hydrogenated rosin glycerol ester preheated to a molten state into the vessel, instantly increase the speed of the dispersion disk to 2800 rpm, and continue shearing for 25 minutes to form a uniform and stable water-in-oil mesoemulsion microdomain.

[0036] (2) Turn on the jacket cooling water to reduce the temperature of the material in the reactor to 55°C at a rate of 2°C / min. At this temperature, pump in 50 parts by weight of the oxidized starch aqueous solution prepared in Preparation Example 1 at a uniform rate. Simultaneously, reduce the stirring speed of the stirring system to 800 rpm to maintain macroscopic turbulence and continuously stir and mix for 20 minutes.

[0037] (3) Continue to circulate cooling water to steadily reduce the temperature of the reactor system to 30°C. Reduce the stirring speed to a laminar flow state of 50 rpm, add 0.8 parts by weight of gluconic acid-δ-lactone dry powder and stir to dissolve. Then, slowly add 25% ammonia solution dropwise. Monitor the pH value of the system using an online pH meter and precisely adjust and lock it at 9.2. After locking in the alkaline environment, slowly add 2 parts by weight of ammonium zirconium carbonate solution. Stir for 15 minutes under low shear to ensure homogeneous dispersion, then discharge through a 100-mesh filter to obtain the liquid phase adhesive.

[0038] (4) At an ambient temperature of 20°C, the adhesive solution obtained in step (3) is uniformly coated onto the surface of the PET release film substrate using a slot coater, controlling the wet film thickness to be 50 μm. The coated substrate is then placed into a multi-stage temperature-controlled drying oven, with the oven temperature gradient set to 90°C to 105°C to 110°C, and the total drying time is 3 minutes. After exiting the oven, it is hot-rolled and laminated with PVC face material, and then rolled up to obtain the finished product.

[0039] Example 2: This example provides an in-situ dynamic crosslinking pressure-sensitive adhesive for low-VOC environmentally friendly vehicle wraps and its preparation method, including the following steps: (1) In a reaction vessel equipped with a jacketed temperature control and a high-shear dispersion disk, add 100 parts by weight of deionized water and turn on the heater to raise the system temperature to 95°C. Add 12 parts by weight of the enzymatically hydrolyzed sodium lignosulfonate powder prepared in Preparation Example 5 and stir at medium speed until completely dissolved. Pump 22 parts by weight of hydrogenated rosin glycerol ester preheated to a molten state into the vessel, instantly increase the speed of the dispersion disk to 3000 rpm, and continue shearing for 30 minutes to form a uniform and stable water-in-oil mesoemulsion microdomain.

[0040] (2) Turn on the jacket cooling water to reduce the temperature of the material in the reactor to 60°C at a rate of 2.5°C / min. At this temperature, pump in 65 parts by weight of the oxidized starch aqueous solution prepared in Preparation Example 2 at a uniform rate. Simultaneously, reduce the stirring speed of the stirring system to 1000 rpm to maintain macroscopic turbulence and continuously stir and mix for 25 minutes.

[0041] (3) Continue to circulate cooling water to steadily reduce the temperature of the reactor system to 32°C. Reduce the stirring speed to a laminar flow state of 65 rpm, add 1.5 parts by weight of gluconate-δ-lactone dry powder and stir to dissolve. Then, slowly add 25% ammonia solution dropwise. Monitor the pH value of the system using an online pH meter and precisely adjust and lock it at 9.5. After locking in the alkaline environment, slowly add 3.5 parts by weight of ammonium zirconium carbonate solution. Stir for 18 minutes under low shear to ensure homogeneous dispersion, then discharge through a 120-mesh filter to obtain the liquid phase adhesive.

[0042] (4) At an ambient temperature of 22°C, the adhesive solution obtained in step (3) is uniformly coated onto the surface of the PET release film substrate using a slot coater, controlling the wet film thickness at 65 μm. The coated substrate is then placed into a multi-stage temperature-controlled drying oven, with the oven temperature gradient set from 90°C to 105°C to 110°C, and the total drying time is 4 minutes. After exiting the oven, it is hot-rolled and laminated with PVC face material, and then rolled up to obtain the finished product.

[0043] Example 3: This example provides an in-situ dynamic crosslinking pressure-sensitive adhesive for low-VOC environmentally friendly vehicle wraps and its preparation method, including the following steps: (1) In a reaction vessel equipped with a jacketed temperature control and a high-shear dispersion disk, add 100 parts by weight of deionized water and turn on the heater to raise the system temperature to 98°C. Add 15 parts by weight of the enzymatically hydrolyzed sodium lignosulfonate powder prepared in Preparation Example 6 and stir at medium speed until completely dissolved. Pump 25 parts by weight of hydrogenated rosin glycerol ester preheated to a molten state into the vessel, instantly increase the speed of the dispersion disk to 3200 rpm, and continue shearing for 35 minutes to form a uniform and stable water-in-oil mesoemulsion microdomain.

[0044] (2) Turn on the jacket cooling water to reduce the temperature of the material in the reactor to 65°C at a rate of 3°C / min. At this temperature, pump in 80 parts by weight of the oxidized starch aqueous solution prepared in Preparation Example 3 at a uniform rate. Simultaneously, reduce the stirring speed of the stirring system to 1200 rpm to maintain macroscopic turbulence and continuously stir and mix for 30 minutes.

[0045] (3) Continue to circulate cooling water to steadily reduce the temperature of the reactor system to 35°C. Reduce the stirring speed to 80 rpm (laminar flow), add 2.0 parts by weight of gluconate-δ-lactone dry powder and stir to dissolve. Then, slowly add 25% ammonia solution dropwise. Monitor the pH value of the system using an online pH meter and precisely adjust and lock it at 9.8. After locking in the alkaline environment, slowly add 5 parts by weight of ammonium zirconium carbonate solution. Stir under low shear for 20 minutes to ensure homogeneous dispersion, then discharge through a 150-mesh filter to obtain the liquid adhesive.

[0046] (4) At an ambient temperature of 25°C, the adhesive solution obtained in step (3) is uniformly coated onto the surface of the PET release film substrate using a slot coater, controlling the wet film thickness to be 80 μm. The coated substrate is then placed into a multi-stage temperature-controlled drying oven, with the oven temperature gradient set from 90°C to 105°C to 110°C, and the total drying time is 5 minutes. After exiting the oven, it is hot-rolled and laminated with PVC face material, and then rolled up to obtain the finished product.

[0047] Example 4: This example provides an in-situ dynamic crosslinking pressure-sensitive adhesive for low-VOC environmentally friendly vehicle wraps and its preparation method, including the following steps: The difference between the raw material ratio in this embodiment and that in Example 2 is that: 50 parts by weight of the oxidized starch aqueous solution prepared in Example 2, 8 parts by weight of the enzymatically hydrolyzed sodium lignin sulfonate dry powder prepared in Example 5, and 25 parts by weight of hydrogenated rosin glycerol ester are used; the other raw materials and their ratios are exactly the same as in Example 2.

[0048] The preparation method in this embodiment is exactly the same as that in Example 2.

[0049] Example 5: This example provides an in-situ dynamic crosslinking pressure-sensitive adhesive for low-VOC environmentally friendly vehicle wraps and its preparation method, including the following steps: The raw material ratio of this embodiment differs from that of Example 2 in that: 80 parts by weight of the oxidized starch aqueous solution prepared in Example 2, 15 parts by weight of the enzymatically hydrolyzed sodium lignin sulfonate dry powder prepared in Example 5, and 18 parts by weight of hydrogenated rosin glycerol ester are used; the other raw materials and their ratios are exactly the same as those in Example 2.

[0050] The preparation method in this embodiment is exactly the same as that in Example 2.

[0051] Comparative Example 1: Compared with Example 2, the difference is that in step (3), no gluconate-δ-lactone dry powder is added. Instead, before adding the zirconium carbonate ammonium solution, a 10% citric acid aqueous solution is directly added to adjust the pH of the system to the same level. All other aspects are the same.

[0052] Comparative Example 2: Compared with Example 2, the difference is that in step (3), no gluconate-δ-lactone dry powder is added, and homogeneous latent acid is not used at all. The pH value of the system is adjusted by ammonia water and volatilized in the oven. Everything else is the same.

[0053] Comparative Example 3: Compared with Example 2, the difference is that the target temperature for heating in step (1) is set to 75°C (below the softening point of hydrogenated rosin glycerol ester), while the rest are the same.

[0054] Comparative Example 4: Compared with Example 2, the difference is that in step (3), the stirring speed is not suddenly reduced to 65 rpm to a laminar flow state, but the macroscopic turbulent high-speed shear state of 1000 rpm is maintained throughout until the material is discharged. The rest are the same.

[0055] Comparative Example 5: Compared with Example 2, the difference is that in step (1), instead of adding enzymatically hydrolyzed sodium lignosulfonate powder, it is directly replaced with an equal part by weight of conventional small molecule emulsifier (sodium dodecylbenzenesulfonate), and the rest are the same.

[0056] Test Example 1: Room Temperature Pot Life and Rheological Stability Test of Adhesive Solution This test example is used to determine the rheological stability and pot life of the liquid phase adhesives obtained in each embodiment and comparative example at room temperature. The specific experimental steps are as follows: 1. Take 500g of each of the liquid phase adhesive samples prepared in Examples 1 to 5 and Comparative Examples 1 to 5, put them into standard wide-mouth glass bottles and seal them.

[0057] 2. Place the sealed samples in a constant temperature incubator set at 25℃ ± 1℃ for static storage.

[0058] 3. The initial viscosity of each sample was tested using a rotational viscometer. The rotor model and rotation speed were set and fixed according to the initial fluid state.

[0059] 4. On days 3, 7, 14, and 28 of storage, samples were removed from the incubator and allowed to stand at 25°C for 2 hours. Their absolute viscosity was then measured using the same viscometer and test conditions. No high-shear stirring of the samples was performed before testing.

[0060] 5. Observe and record the appearance of the sample. When the absolute viscosity of the sample exceeds 200% of its initial viscosity (i.e., the viscosity doubles), or when irreversible gelation, agglomeration, or severe phase separation occurs macroscopically, it is determined to be past its service life, and the number of days to reach the failure state is recorded. If the viscosity growth rate is less than 100% and there is no gelation after 28 days, the service life is recorded as greater than 28 days.

[0061] Table 1. Test results of viscosity and shelf life at room temperature for each example and comparative example.

[0062] According to the data in Table 1, after the adhesive solutions of Examples 1 to 5 were stored at 25°C for 28 days, although the viscosity of the system increased slowly, the overall growth rate was controlled between 35% and 45%, which is completely within the operable window required for industrial coating leveling, demonstrating excellent room temperature liquid-phase stability. This proves that the liquid-phase inhibition mechanism of the present invention is completely feasible. The alkaline environment (pH 9.2 to 9.8) constructed by ammonia water in the reactor effectively inhibited the coordination crosslinking activity of zirconium ions in ammonium zirconium carbonate. At the same time, the hydrolysis rate of the added gluconate-δ-lactone was extremely low at room temperature of 25°C and in the current pH buffer system, and did not cause a significant decrease in the macroscopic pH value. The crosslinking reaction was in a completely closed latent state.

[0063] In Comparative Example 1, gluconate-δ-lactone was removed and citric acid was directly added to adjust the pH. The initial viscosity was abnormally high, and gel solidification occurred within one day of storage. This indicates that the direct addition of external free acid disrupted the alkaline inhibition environment of the liquid phase, causing a sharp drop in both local and macroscopic pH values. This prematurely triggered the coordination crosslinking reaction between ammonium zirconium carbonate and the carboxyl groups of oxidized starch and the hydroxyl groups of lignin, resulting in the loss of leveling properties and pot life of the adhesive.

[0064] The viscosity of Comparative Example 3 showed an irregular and explosive increase on the third day, accompanied by macroscopic phase separation. This was because its emulsification temperature was 75°C, which is lower than the softening point of hydrogenated rosin glycerol ester, making it impossible to utilize the amphiphilicity of lignin to construct stable mesoscopic oil-in-water emulsion microdomains. The thermodynamically unstable physical dispersion state rapidly underwent microphase recombination and resin precipitation at room temperature, losing its rheological stability.

[0065] Comparative Examples 2, 4, and 5 also maintained a service life of more than 28 days at room temperature, indicating that using only ammonia to suppress flow, altering the shear flow field, or using conventional emulsifiers does not compromise the chemical stability of the liquid phase at room temperature. However, based on the aforementioned mechanism, the lack of latent acid in Comparative Example 2 leads to incomplete internal cross-linking during solid-phase drying, the high shear in Comparative Example 4 disrupts the coordination network structure, and the absence of rigid nodes in Comparative Example 5 weakens its heat resistance. These performance defects in the solid-phase film formation stage will be confirmed in subsequent high-temperature mechanical and peel tests.

[0066] Test Example 2: Variable Temperature Rheological Scan Test This test example is used to determine the changes in the rheological behavior of the liquid phase adhesives obtained in each embodiment and comparative example during the heating process, and to determine the abrupt change points of the crosslinking network of the system. The specific experimental steps are as follows: 1. A rotational rheometer with a heating and temperature control system and a normal force sensor was used, and a parallel plate testing system with a diameter of 25 mm was selected. An appropriate amount of adhesive sample was placed in the center area of ​​the lower test plate.

[0067] 2. Slowly lower the upper test plate and precisely set the test gap between the two plates to 1.0 mm. Scrape off any excess adhesive squeezed out from the edges, and apply a thin layer of low-viscosity methyl silicone oil to the edge of the test fixture to seal the volatile interface of the sample and prevent excessive moisture evaporation in the early stage of the test from interfering with the phase change data.

[0068] 3. Set the rheometer to oscillating temperature scanning mode, fix the test frequency at 1Hz, and fix the strain amplitude at 1%. This strain amplitude parameter was confirmed to be completely within the linear viscoelastic region of the sample through the previous amplitude scanning program.

[0069] 4. Start the program heating control panel, set the initial test temperature to 25℃, the target endpoint temperature to 110℃, and strictly control the heating rate to 5℃ / min.

[0070] 5. The instrument continuously acquires and records the characteristic curves of the storage modulus G' and loss modulus G'' of the system as a function of temperature during the heating process. The temperature at which the G' and G'' curves intersect is extracted as the gel point temperature, and the peak storage modulus data reached by the sample at 110℃ is extracted.

[0071] Table 2. Test results of variable-temperature rheological characteristic parameters for each embodiment and comparative example.

[0072] According to the data in Table 2, in the programmed temperature rise tests of Examples 1 to 5, the gel point temperatures were concentrated in the range of 89.4℃ to 94.7℃, and the storage modulus of the system reached a relatively high level of 134500Pa to 181300Pa when the temperature was raised to 110℃. This confirms the thermodynamic kinetic process of the cross-linking-triggered push-pull synergistic mechanism. When the ambient temperature rises to the critical range, the coordination state suppressed by ammonia in the system undergoes a phase transfer. The volatilization of ammonia provides the de-inhibition push, and the simultaneously heated gluconic acid-δ-lactone breaks through the hydrolysis activation energy and releases gluconic acid in situ to provide the pull. This precisely controlled microenvironment pH drop forcibly removes the alkaline seal of ammonium zirconium carbonate, and the high-valence zirconium ions undergo three-dimensional complexation with the polydentate coordination groups of oxidized starch and lignin in a short time, rapidly constructing a dynamic coordination network structure with extremely high storage modulus.

[0073] Comparative Example 2, by removing gluconate-δ-lactone, significantly delayed the gel point temperature to 107.5℃, with a storage modulus of only 41200 Pa at 110℃. In the absence of the internal acid-releasing pull from the homogeneous latent acid, the activation of the crosslinking centers was entirely dependent on the natural diffusion rate of ammonia towards the interface. Macroscopically, this manifested as a delayed crosslinking reaction and insufficient network construction, directly leading to gradient collapse of the cohesive force within the polymer network system, preventing the formation of a dense, high-strength coordination dissipative network.

[0074] Comparative Example 4 did not undergo the process of abruptly reducing the rotational speed to laminar flow. Its gel point temperature remained at 91.9℃, but the storage modulus at 110℃ significantly decreased to 78500Pa. The mechanical breaking energy provided by the strong shear flow field exceeded the binding energy of the initial formation of zirconium-oxygen coordination bonds. The macroscopic hydrodynamic turbulence continuously disrupted the dynamically reversible coordination bonds that were being assembled, hindering the extension of the three-dimensional spatial network in the mesoscopic phase region, resulting in a lack of cohesion in the final cured film.

[0075] Comparative Example 5 used sodium dodecylbenzene sulfonate instead of enzymatically hydrolyzed sodium lignin sulfonate. Although its crosslinking temperature was normally triggered at 89.8℃, its storage modulus at 110℃ was only 56300 Pa. The small molecule surfactant could not participate in the crosslinking construction of the polymer backbone, and the system completely lost the physical heat-resistant creep anchor provided by the rigid phenylpropane units in the lignin structure. The single oxidized starch flexible backbone faced severe segmental thermal slippage under high-temperature conditions, and the heat-resistant rigidity of the coordination network experienced a precipitous decline.

[0076] Test Example 3: Gradient Test of Macroscopic Gel Rate Depth of Coating This test example is used to determine the differences in crosslinking degree distribution of the coatings obtained in each embodiment and comparative example along the thickness direction (Z-axis) to verify the effectiveness of the homogeneous crosslinking mechanism in the solid-phase film formation stage. The specific experimental steps are as follows: 1. Take the pressure-sensitive adhesive products obtained from each embodiment and comparative example through complete coating and oven curing processes, and cut them into standard test blocks of 100mm×100mm.

[0077] 2. Place the test sample in a liquid nitrogen environment for 5 minutes to induce a glass transition in the adhesive layer. While frozen, use a microtome with micron-level scale adjustment to scrape off approximately 1 / 3 of the thickness of the top layer adhesive sample and approximately 1 / 3 of the thickness of the bottom layer adhesive sample close to the substrate.

[0078] 3. Place the collected surface and bottom gel samples in a vacuum drying oven to remove condensed moisture. Accurately weigh each group of gel samples and record the initial mass W1.

[0079] 4. Wrap the weighed gel samples separately in pre-treated 300-mesh stainless steel mesh bags, seal them tightly, and weigh them as a whole.

[0080] 5. Place the mesh bag containing the sample in a Soxhlet extractor and add tetrahydrofuran as the extraction solvent. Reflux continuously for 24 hours in a water bath to fully dissolve uncrosslinked resin, starch, and other free components.

[0081] 6. After extraction, remove the stainless steel mesh bag and dry it in an 80℃ vacuum drying oven until constant weight. Weigh the total mass of the mesh bag containing the sample after extraction, subtract the mass of the mesh bag, and obtain the mass of the cross-linked network residue, which is recorded as the final mass W2.

[0082] 7. Calculate the surface gel rate and the bottom gel rate respectively according to the formula gel rate = (W2 / W1) × 100%, and calculate the difference between the two.

[0083] Table 3. Gel rate test results of the coating substrate in each embodiment and comparative example.

[0084] According to the data in Table 3, the gelation rates of both the surface and bottom layers of the coatings in Examples 1 to 5 remained at a high level, and the difference between the upper and lower layers was strictly controlled within a very small range of 1.6% to 3.3%. This proves that the push-pull synergistic mechanism constructed in this invention achieves three-dimensional homogeneous cross-linking during the solid-phase film formation stage of the thick coating. During the curing heating process, gluconic acid-δ-lactone absorbs heat energy in situ inside the adhesive layer and undergoes lactone ring hydrolysis, releasing gluconic acid that simultaneously lowers the pH value of the microenvironment deep within the coating. Since the latent acid is homogeneously dispersed at the molecular level, the active release of ammonium zirconium carbonate at the cross-linking center does not depend on the penetration and diffusion of external substances into the interior, thereby completely overcoming the mass and heat transfer obstacles caused by the thickness of tens of micrometers and ensuring the synchronous construction of the coordination network between the upper and lower layers.

[0085] Comparative Example 2, lacking the addition of gluconate-δ-lactone, exhibited a surface gelation rate as high as 88.3%, while the bottom layer gelation rate was only 42.1%, resulting in a significant gelation rate gradient difference of 46.2%. Driven solely by the unidirectional mechanism of ammonia evaporation, the coated surface layer directly contacts hot air, leading to the rapid de-inhibition crosslinking of the surface layer due to the initial phase transfer of free ammonia. This prematurely formed dense surface polymer network constitutes a physically sealed layer, severely blocking the diffusion channels of ammonia and moisture from the bottom layer to the gas phase. The bottom layer remains in a high-ammonia-concentration alkaline inhibitory microenvironment for an extended period, preventing the dissociation of coordinating zirconium ions, ultimately resulting in severe macroscopic defects such as an externally dry but internally moist environment and a collapsed cohesive gradient.

[0086] Although the gelation rate difference in Comparative Example 4 was low, its overall crosslinking degree decreased significantly to around 50%. This indicates that unreasonable flow field control directly interfered with the crosslinking thermodynamic process. The hydrodynamic turbulence introduced by high shear throughout the process broke the dynamic coordination bonds in the early stages of growth, resulting in a significant decrease in the effective crosslinking network density. Comparative Example 5, lacking the core polyhydroxy rigid framework of enzymatically hydrolyzed sodium lignin sulfonate, relied solely on the coordination of oxidized starch monomers with zirconium ions. This resulted in a reduced density of crosslinking reaction sites, a loose overall network structure, and increased swelling loss during extraction, similarly leading to an overall decrease in the macroscopic gelation rate.

[0087] Test Example 4: Macroscopic Coating Leveling and Appearance Evaluation This test example is used to evaluate the film-forming and leveling ability of the liquid phase adhesives obtained in each embodiment and comparative example on the substrate surface, as well as the distribution of macroscopic defects in the coating after curing and drying. The specific experimental steps are as follows: 1. In a cleanroom with an ambient temperature of 23℃ and a relative humidity of 50%, each liquid phase adhesive sample was coated onto the surface of a corona-treated PET film with a thickness of 50μm using an automatic bar coating machine. The wet film thickness was uniformly controlled to 60μm by changing the bar type.

[0088] 2. Place the coated PET film sample flat and transfer it to a forced convection hot air circulating oven. Then, heat and cure the film in stages by holding it at 90°C for 1 minute, 105°C for 1.5 minutes, and 110°C for 1.5 minutes.

[0089] 3. Remove the sample and let it cool and stand at room temperature for 30 minutes. Then cut three test areas with an area of ​​100mm×100mm along the coating longitudinal direction.

[0090] 4. Visually observe the sample under transmitted and reflected light in a standard D65 light source box, and record leveling defects such as orange peel, pinholes, and coating streaks on the coating surface.

[0091] 5. Using a 10x magnifying glass with a graduated grid, count the number of macroscopic gel particles and undispersed resin clumps with a diameter greater than 0.5 mm in each test area, and record the arithmetic mean of the three test areas.

[0092] Table 4 Evaluation results of appearance and leveling defects of the cured coatings in each example and comparative example.

[0093] According to the data in Table 4, the cured films of Examples 1 to 5 exhibited a smooth and uniform appearance with an extremely low number of macroscopic particle defects. This confirms the effectiveness of the liquid-phase stabilization and mesoscopic emulsification mechanism of this scheme from a rheological macroscopic perspective. In the buffer system constructed by sodium hydroxide and ammonia, the crosslinking activity of ammonium zirconium carbonate was inhibited, and the liquid-phase adhesive maintained normal fluid properties during the shear stage of coating, achieving sufficient leveling time. The sodium lignosulfonate prepared by the composite enzymatic hydrolysis process utilizes a polyhydroxy and phenylpropane amphiphilic framework to disperse molten hydrogenated rosin glycerol esters into stable oil-in-water mesoscopic latex particles within the high shear field of the reactor, avoiding macroscopic precipitation of the resin phase.

[0094] The liquid-phase system in Comparative Example 1 completely lost the leveling properties required for coating operations. Directly adding a 10% (w / w) citric acid aqueous solution to the system disrupted the uniform alkaline environment. The extremely high local acid concentration instantly neutralized the ammonia, forcing ammonium zirconium carbonate to rapidly release zirconium ions in this local micro-region. These ions then undergo vigorous coordination crosslinking with starch carboxyl groups and lignin hydroxyl groups, forming a large number of crosslinked dead glue blocks, leading to the direct failure of the process.

[0095] Comparative Example 3 exhibited a large number of hard clumps larger than 0.5 mm in diameter on its coating surface, accompanied by severe coating tailing. The process-set heating temperature of 75°C was below the softening point range of 85°C to 90°C for hydrogenated rosin glycerol ester, preventing the resin from undergoing a thermodynamic phase change and melting, thus maintaining a rigid solid state. The high-speed shearing of the dispersion disc could not overcome the cohesive energy of the solid phase, and sodium lignosulfonate could not encapsulate it at the solid-liquid interface. Ultimately, a large number of undispersed resin particles remained directly in the adhesive, forming tailing scratches during wire rod extrusion, completely destroying the coating smoothness.

[0096] In Comparative Example 5, sodium dodecylbenzenesulfonate, a conventional small-molecule emulsifier, replaced sodium lignosulfonate, resulting in a rapid decrease in the surface tension of the system and a severe tendency to foam. During the thermodynamic mass transfer process of coating and drying, the rupture and escape of internal bubbles were hindered, leaving dense micro and macro pinholes on the surface of the film.

[0097] Test Example 5: Evaluation of 180° peel strength and residual adhesive content This test example is used to determine the peel mechanical properties and cohesive failure of the adhesive film systems obtained in each embodiment and comparative example on a standard metal substrate. The specific experimental steps are as follows: 1. Under constant temperature and humidity conditions (temperature 23±1℃, relative humidity 50±5%), the finished tapes (face material is PVC film) of each embodiment and comparative example after hot roller lamination were cut into standard test strips with a width of 25mm and a length of 250mm.

[0098] 2. Select a SUS304 stainless steel test plate with a surface roughness conforming to GB / T2792 standard. Before testing, wipe the surface of the stainless steel plate clean with anhydrous ethanol and allow it to stand in a standard environment for 15 minutes to evaporate until completely dry.

[0099] 3. Peel off the PET release film from the test strip and attach the PVC strip with the exposed adhesive layer to the center of the stainless steel test plate. Use a standard electric pressure roller with a mass of 2 kg to roll back and forth on the strip 3 times at a speed of 300 mm / min to remove air bubbles at the interface and ensure that the adhesive layer in the test area is evenly compressed.

[0100] 4. Place the bonded test components horizontally in the above constant temperature and humidity environment for 24 hours to allow the macromolecular chain segments at the pressure-sensitive adhesive interface to be fully wetted and reach thermodynamic equilibrium.

[0101] 5. Fix the test component in the upper and lower clamps of the computer-controlled electronic universal testing machine, keeping the peel angle at 180°. Start the testing machine and peel at a constant tensile speed of 300 mm / min. The software automatically records the force curve during the peeling process. Take the average force value of the effective peeling range as the 180° peel strength, in N / 25 mm.

[0102] 6. After the peel test is completed, a transparent film with a standard grid scale is attached to the peeled area of ​​the stainless steel test plate. The percentage of residual adhesive area to the total bonded area is calculated and recorded as the residual adhesive rate. The failure type (interfacial failure, cohesive failure, or mixed failure) is also recorded.

[0103] Table 5. Test results of 180° peel strength and residual adhesive content for each example and comparative example.

[0104] According to the data in Table 5, the 180° peel strength of Examples 1 to 5 remained stable between 13.7 N / 25 mm and 17.1 N / 25 mm, with stable peel force and zero residual glue rate. The failure type exhibited standard pure interface failure. This verifies the effectiveness of the dynamic reversible coordination network dissipation mechanism of the present invention at the solid-state mechanics level. The high-valence zirconium ions released by ammonium zirconium carbonate, together with the carboxyl groups, polyhydroxy groups, and phenolic anions on oxidized starch and enzymatically hydrolyzed sodium lignin sulfonate, formed a high-density coordination bond network. When a 180° mechanical peel force was applied, a huge stress concentration occurred at the peel front. Since the bond energy of the Zr-O coordination bond is lower than that of the carbon-carbon covalent bonds in the polymer backbone, some coordination bonds preferentially under stress undergo reversible breakage, converting the concentrated stress into heat dissipation energy of the polymer chain segments. This microscopic stress dissipation mechanism avoids the direct tearing of the polymer skeleton by mechanical tension, ensuring that the overall cohesive force of the coating is always greater than the interfacial adhesion force of the substrate, thus eliminating the most fatal cohesive destructive residue problem in car body sticker applications from the root of fracture mechanics.

[0105] Comparative Example 2, lacking glucono-δ-lactone, exhibited abnormally high and drastically fluctuating peel strength values, accompanied by a residual adhesive rate as high as 68%, indicating a shift to severe cohesive failure. Combined with the aforementioned macroscopic gelation depth gradient test results, it is evident that the absence of homogeneous latent acid prevented the synchronous decrease of pH in the coating's internal microenvironment during curing, resulting in extremely uneven crosslinking network construction. The surface layer formed a dense, high-modulus crosslinked skin due to the preferential volatilization of free ammonia, while the underlying layer remained in a high-ammonia alkaline inhibition state, with macromolecular chains in an uncrosslinked or weakly crosslinked state. Under peel stress, the mechanically weak underlying layer was completely unable to resist external shear and tensile stress, causing the adhesive layer to fracture and tear directly from within, leaving a large amount of adhesive residue on the stainless steel substrate surface.

[0106] Comparative Example 4 did not drastically reduce the stirring speed to laminar flow; instead, it maintained macroscopic turbulent high-speed shear throughout the process. Its peel strength decreased to 10.5 N / 25 mm, and a 34% residual adhesive rate was observed. The continuously supplied high shear mechanical energy exceeded the binding energy of some initial dynamic coordination bonds, disrupting and destroying the pre-assembly of the three-dimensional spatial network within the mesoscopic emulsion microdomains at the hydrodynamic level before the material was discharged from the reactor. The overall decrease in the density of the coating crosslinking network led to a reduction in the system's cohesive strength, making it unable to effectively dissipate peel stress, thus triggering cohesive failure.

[0107] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A low-VOC environmentally friendly pressure-sensitive adhesive for vehicle body stickers, characterized in that, It is made from the following raw materials in parts by weight: 100 parts deionized water; 5-20 parts enzymatically hydrolyzed sodium lignosulfonate powder; 15-30 parts hydrogenated rosin glycerol ester; 40-90 parts oxidized starch aqueous solution; ammonia water, the amount added is the effective amount to adjust the pH of the system to 9.2-9.8; 0.5-3.0 parts glucono-δ-lactone powder; 1-6 parts ammonium zirconium carbonate solution; The softening point of the hydrogenated rosin glycerol ester is 85℃-90℃; The preparation method of pressure-sensitive adhesive includes the following steps: (1) Add deionized water to a reactor with a high-shear dispersion disk and heat it up. Add enzymatically hydrolyzed sodium lignosulfonate powder and stir to dissolve. Then pump in hydrogenated rosin glycerol ester preheated to a molten state to form water-in-oil mesoscopic emulsion microregions under high-speed shear. The heating temperature is 92-98℃, the high-speed shearing speed is 2800-3200rpm, and the shearing time is 25-35 minutes. (2) After cooling, pump the oxidized starch aqueous solution into the pump at a constant speed and reduce the speed to maintain the macroscopic turbulent state for continuous stirring and mixing; (3) Continue to cool down and suddenly reduce the stirring speed to laminar flow. Add gluconate-δ-lactone dry powder, ammonia water and zirconium carbonate ammonium solution in sequence. After low shear stirring to ensure homogeneous dispersion, discharge the material to obtain liquid phase adhesive. (4) The liquid phase adhesive obtained in step (3) is coated on the surface of the substrate and then placed in a multi-stage temperature-controlled drying oven for step heating and drying. During this process, an in-situ dynamic coordination crosslinking reaction is triggered. After exiting the oven, the product is compounded and rolled up to obtain the finished product.

2. The low-VOC environmentally friendly pressure-sensitive adhesive for vehicle body stickers according to claim 1, characterized in that: The oxidized starch aqueous solution has a mass fraction of 30%, and the degree of substitution of the oxidized starch is 0.05-0.

08. The oxidized starch aqueous solution is prepared by the following method: cassava starch is dispersed in deionized water to prepare a starch emulsion. The pH of the system is adjusted to 8.5-9.5 using sodium hydroxide solution. The temperature is raised to 40-45℃. Sodium hypochlorite solution with an effective chlorine mass fraction of 10% is added dropwise at a uniform rate according to 6%-10% of the dry weight of cassava starch and reacted for 2-3 hours. After terminating the reaction by adding sodium sulfite, the temperature is raised to 80-85℃ and kept at that temperature for 45 minutes to gelatinize the starch.

3. The low-VOC environmentally friendly pressure-sensitive adhesive for vehicle body stickers according to claim 1, characterized in that: The weight-average molecular weight of the enzymatically hydrolyzed sodium lignosulfonate powder is 3000 Da-5000 Da. The enzymatically hydrolyzed sodium lignin sulfonate powder is prepared by the following method: sulfate-processed alkali lignin is dispersed in a buffer solution, the pH is adjusted to 5.0-5.5, and a complex enzyme system of laccase and xylanase with a mass ratio of 1:1 is added at 1% of the dry lignin mass. The reaction is carried out at 45-50℃ for 4-6 hours. After inactivating the enzyme system by heating, the temperature is lowered to 60℃, and the pH is adjusted to 10.0-10.5 by reverse adjustment using sodium hydroxide solution. Sodium sulfite and formaldehyde aqueous solution are added, and sulfonation reaction is carried out at 85-95℃ for 3 hours. Finally, the powder is spray-dried to obtain the final product.

4. The low-VOC environmentally friendly pressure-sensitive adhesive for vehicle body stickers according to claim 1, characterized in that: Before being cured by heat, the pressure-sensitive adhesive is in a uniform and stable water-in-oil mesoscopic emulsion micro-region state, wherein the hydrogenated rosin glycerol ester is encapsulated and dispersed by the components formed after the enzymatic hydrolysis of sodium lignosulfonate dry powder.

5. The low-VOC environmentally friendly pressure-sensitive adhesive for vehicle body stickers according to claim 1, characterized in that: In step (2), the system temperature is reduced to 55-65℃ for pumping, and the stirring speed of the stirring system is simultaneously reduced to 800-1200rpm. The continuous stirring and mixing time is 20-30 minutes.

6. The low-VOC environmentally friendly pressure-sensitive adhesive for vehicle body stickers according to claim 1, characterized in that: The specific implementation method of step (3) is as follows: Continue cooling until the system temperature stabilizes at 30-35℃. Then, drastically reduce the stirring speed to 50-80 rpm in a laminar flow state. First, add gluconate-δ-lactone dry powder and stir to dissolve. Then, slowly add 25% ammonia water to adjust and lock the pH of the system at 9.2-9.

8. After locking in the alkaline environment, finally slowly add the zirconium carbonate ammonium solution and stir under low shear for 15-20 minutes.

7. The low-VOC environmentally friendly pressure-sensitive adhesive for vehicle body stickers according to claim 1, characterized in that: In step (4), the temperature gradient of the multi-segment temperature-controlled drying oven is set to 90°C to 105°C to 110°C, and the total drying time is 3-5 minutes.

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