Aqueous high-speed packaging adhesive and preparation method thereof

Abstract

This invention relates to the field of packaging materials technology, specifically to a water-based high-speed packaging adhesive and its preparation method. The packaging adhesive consists of a high-solids-content modified main emulsion, a water-based tackifying resin, a thickener, a defoamer, a preservative and mildew inhibitor, and deionized water. The main emulsion has a solids content of 66%-70%, and its emulsion particles are modified by covalently grafting polyethyleneimine and a composite polyelectrolyte layer. The preparation method includes key steps such as multi-step emulsion polymerization, online shear dispersion, surface grafting modification, and sequential composite polyelectrolyte formation. This invention aims to solve the problems of easy agglomeration, rheological fluctuations, and deterioration of storage performance of high-solids-content water-based adhesives under high-speed shear conditions. The resulting packaging adhesive exhibits excellent dispersion stability, high-speed shear stability, long-term storage stability, and good adhesive strength.

Description

Technical Field

[0001] This invention relates to the field of packaging materials technology, and in particular to a water-based high-speed packaging adhesive and its preparation method. Background Technology

[0002] With the rapid increase in automation in the packaging industry, the operating speeds of box gluing machines and automatic packaging lines are constantly breaking records. To adapt to this high-speed production pace and meet the demands for environmental protection and efficient drying, water-based packaging adhesives are developing towards higher solids content and lower viscosity. High solids content helps reduce the moisture evaporation load after coating and shortens drying time, thereby increasing production line speed. However, when the solids content of the adhesive increases to 65% or even higher, the distance between emulsion particles in the system is extremely compressed, and the traditional electrostatic repulsion or steric hindrance provided by surfactants or protective colloids (such as polyvinyl alcohol) is significantly weakened. In this "crowded" environment, particles are prone to collision and aggregation due to Brownian motion or external shear forces, forming microgels or clumps that are difficult to redisperse. These clumps can lead to uneven adhesive application, adhesive breakage, or stringing during high-speed coating, directly affecting the bonding quality and appearance of the packaging box.

[0003] More challenging is the fact that high-speed coating equipment (such as roller coating and spray coating) itself applies high shear forces to adhesives. These shear forces persist throughout the pumping, circulation, and coating head distribution processes. For high-solids systems, shear forces may temporarily break down weak aggregates, resulting in a temporary decrease in viscosity; however, they may also induce new, irreversible flocculation. Consequently, the rheological properties of the adhesive (such as viscosity and thixotropy) drift significantly with shear history and time, exhibiting unpredictable fluctuations such as insufficient recovery after shear thinning or shear thickening. This rheological instability directly leads to difficulties in controlling coating amount, resulting in significant differences in coating uniformity within the same batch or between different batches, severely impacting the stability and yield of high-speed packaging production.

[0004] From a materials chemistry perspective, existing technologies attempt to improve the stability of emulsion particles at high solids contents through various surface modifications. For example, functional monomers are introduced into the shell layer of emulsion polymerization to impart charge or steric hindrance to the particles. However, many modification methods have limited effectiveness or inherent defects. For instance, relying solely on the introduction of charged monomers (such as carboxyl monomers) and subsequent neutralization to generate electrostatic repulsion is extremely sensitive to pH and ionic strength, and is prone to failure due to charge shielding during high-speed shearing or long-term storage. Furthermore, the steric hindrance provided by the introduction of nonionic hydrophilic segments (such as polyethylene glycol monomers) is insufficient at high solids contents if it fails to effectively enrich the particle surface and form a sufficiently thick and dense hydration layer.

[0005] Furthermore, to further improve initial tack or final bond strength, cationic or anionic polyelectrolytes are often compounded into the emulsion. Improper introduction timing and method can easily lead to instability in the emulsion system. For example, directly mixing polyelectrolytes with opposite charges can easily cause charge neutralization in the bulk phase, forming macroscopic flocs. Even with sequential feeding, if the polyelectrolyte's bond to the emulsion particle surface is weak (e.g., relying solely on physical adsorption), these polyelectrolyte segments may migrate, desorb, or rearrange during high-speed shearing or long-term thermal storage, causing changes in particle surface properties over time, leading to increased viscosity or decreased application performance after storage. Existing technologies often focus on optimizing single properties, failing to systematically address the contradiction between dispersion stability at high solids content, rheological stability under high-speed shearing, and performance consistency during long-term storage. This makes it difficult for the prepared waterborne high-speed packaging adhesives to meet the stringent requirements of high-speed automated production in terms of overall performance. Summary of the Invention

[0006] In view of this, the purpose of this invention is to propose a water-based high-speed packaging adhesive and its preparation method, so as to solve the problem that existing water-based high-speed packaging adhesives are prone to agglomeration of emulsion particles due to compression instability under high solid content and high-speed shear conditions, resulting in rheological fluctuations, uneven coating and performance degradation after long-term storage, which makes it difficult to meet the requirements of high-speed automated production.

[0007] To achieve the above objectives, the present invention provides a water-based high-speed packaging adhesive, which, by weight, comprises the following components:

[0008] 8000 parts of the high-solids-content modified main emulsion described above;

[0009] 1400-2000 parts of the aqueous thickening resin dispersion described above;

[0010] 40-60 parts of the thickener described;

[0011] 18-25 parts of the defoamer described;

[0012] 8-12 parts of the preservative and antifungal agent described;

[0013] 250-500 parts of the deionized water described above;

[0014] The high-solids-content modified main emulsion has a solids content of 66%-70%, and the high-solids-content modified main emulsion comprises emulsion particles. The shell of the emulsion particles contains methoxy polyethylene glycol methacrylate units, [2-(methacryloyloxy)ethyl]dimethyl(3-sulfopropyl)ammonium hydroxide inner salt units, and glycidyl methacrylate units. The surface of the emulsion particles is covalently grafted with polyethyleneimine, and the surface of the emulsion particles is coated with a polyelectrolyte composite layer formed by polydiallyldimethylammonium chloride and sodium polyacrylate.

[0015] Preferably, the aqueous tackifying resin dispersion is an aqueous rosin ester tackifying resin dispersion; and the solid content of the aqueous rosin ester tackifying resin dispersion is 55%.

[0016] Preferably, the thickener is ACRYSOL RM-8W.

[0017] Preferably, the defoamer is BYK-024.

[0018] Preferably, the preservative and antifungal agent is KATHON LX 1.5%.

[0019] Preferably, the pH of the high-solids-content modified main emulsion is 6.

[0020] Preferably, the emulsion particles are obtained by emulsion polymerization of vinyl acetate, n-butyl acrylate, vinyl neodecanoate, acrylic acid, glycidyl methacrylate, methoxy polyethylene glycol methacrylate, and [2-(methacryloyloxy)ethyl]dimethyl(3-sulfopropyl)ammonium hydroxide inner salt in a mass ratio of 3430-3470:800:500:100:50-90:120-200:25-50.

[0021] Preferably, the number-average molecular weight of the methoxy polyethylene glycol methacrylate is 400-600.

[0022] Preferably, the weight-average molecular weight of the polydiallyl dimethyl ammonium chloride is 200,000-350,000.

[0023] Preferably, the sodium polyacrylate has a weight-average molecular weight of 10,000-20,000.

[0024] Furthermore, the present invention also provides a method for preparing a water-based high-speed packaging adhesive, comprising the following steps:

[0025] S1, prepare seed preemulsion, main monomer preemulsion, shell hydrophobic monomer preemulsion, strongly hydrophilic monomer solution and zwitterionic monomer solution;

[0026] S2, the seed pre-emulsion and the main monomer pre-emulsion are sequentially subjected to emulsion polymerization to obtain an intermediate emulsion;

[0027] S3, In the shell polymerization stage, the shell hydrophobic monomer pre-emulsion, the strongly hydrophilic monomer solution and the zwitterionic monomer solution are introduced into the intermediate emulsion to carry out emulsion polymerization, and the resulting emulsion is subjected to devolatilization and online shear dispersion treatment after the reaction is completed.

[0028] S4, polyethyleneimine is added to the emulsion, and the polyethyleneimine undergoes a ring-opening reaction with the epoxy group of the glycidyl methacrylate unit, so that the polyethyleneimine is covalently grafted onto the surface of the emulsion particles.

[0029] S5, first add polydiallyldimethylammonium chloride to the emulsion, then add sodium polyacrylate to the emulsion to form a polyelectrolyte composite layer on the surface of the emulsion particles, then adjust the pH and dehydrate and concentrate to obtain a high solids content modified main emulsion.

[0030] S6, the high solids content modified main emulsion is mixed with water-based tackifying resin dispersion, thickener, defoamer, preservative and mildew inhibitor and deionized water and filtered to obtain water-based high-speed packaging adhesive.

[0031] Preferably, in step S1, the seed pre-emulsion is prepared from the following raw materials in parts by mass: 300 parts deionized water, 10 parts sodium dodecyl sulfate, 800 parts vinyl acetate, 100 parts n-butyl acrylate, and 100 parts vinyl neodecanoate; the main monomer pre-emulsion is prepared from the following raw materials in parts by mass: 500 parts deionized water, 20 parts sodium dodecyl sulfate, 2400 parts vinyl acetate, 600 parts n-butyl acrylate, 400 parts vinyl neodecanoate, and 100 parts acrylic acid; the shell hydrophobic monomer pre-emulsion is prepared from the following raw materials in parts by mass. The following components are prepared: 200 parts deionized water, 10 parts sodium dodecyl sulfate, 230-270 parts vinyl acetate, 100 parts n-butyl acrylate, and 50-90 parts glycidyl methacrylate; the strongly hydrophilic monomer solution is prepared by mass from the following raw materials: 100-180 parts deionized water and 120-200 parts methoxy polyethylene glycol methacrylate; the zwitterionic monomer solution is prepared by mass from the following raw materials: 150-175 parts deionized water and 25-50 parts [2-(methacryloyloxy)ethyl]dimethyl(3-sulfopropyl)ammonium hydroxide inner salt.

[0032] Preferably, in step S3, the rotation speed of the online shearing dispersion is 5000-7000 rpm, the circulation time is 10-20 min, and a 120-mesh filter screen is connected in series at the return port.

[0033] Preferably, in step S4, while maintaining circulation and passing through an online high-shear disperser at 6000 rpm, the diluted polyethyleneimine solution is added uniformly within 10 minutes, and the pH of the emulsion is immediately adjusted to 7.8-8.5 with 28% ammonia water by mass.

[0034] The beneficial effects of this invention are:

[0035] This invention constructs a composite interface layer on the surface of emulsion particles by simultaneously introducing methoxy polyethylene glycol methacrylate and [2-(methacryloyloxy)ethyl]dimethyl(3-sulfopropyl)ammonium hydroxide inner salt during the shell stage of multi-step polymerization. This composite interface layer effectively resists close-range compression between particles under high solids content conditions, significantly reducing the tendency for aggregation caused by van der Waals forces, thereby ensuring that the adhesive still possesses excellent dispersion stability and pumpable flowability at high solids content.

[0036] This invention introduces glycidyl methacrylate as a reactive site in the shell layer and enriches it on the particle surface, providing a covalent bonding basis for subsequent anchoring of polyethyleneimine. Polyethyleneimine is firmly grafted onto the particle surface covalently via an epoxy-amine ring-opening reaction, forming a cationic anchoring layer that is difficult to migrate and desorb. This covalent anchoring layer provides the system with durable and stable positive charge and interface modification, effectively avoiding the desorption and failure of cationic modifiers that rely solely on physical adsorption during high-speed shearing or long-term storage, significantly improving the long-term storage stability and anti-aging properties of the system.

[0037] This invention innovatively employs a spatiotemporal synergistic process of online high-shear dispersion and polyelectrolyte modification. During the addition of polyethyleneimine solution, the high-intensity mechanical action of an online high-shear disperser instantly breaks down any potential micro-agglomerates into native particles, while simultaneously enabling polyethyleneimine to undergo a uniform and rapid covalent anchoring reaction on the newly exposed particle surface. This mechanical deagglomeration and instant surface locking process not only eliminates existing agglomerates but also kinetically inhibits the re-agglomeration of particles in high-solids environments, achieving fundamental control over the problem of emulsion particle agglomeration.

[0038] This invention designs a specific polyelectrolyte composite sequence: first, covalently anchored polyethyleneimine is introduced to form a primary cationic layer; then, polydiallyldimethylammonium chloride is introduced for cationic reinforcement; finally, sodium polyacrylate is introduced to form a stable polyelectrolyte composite shell layer, and the pH is adjusted to a weakly acidic state at the end. This sequence effectively avoids the instantaneous neutralization and flocculation that occurs in the bulk phase when polyelectrolytes with opposite charges come into direct contact, promoting the layer-by-layer, uniform adsorption and composite of polyelectrolytes on the particle surface, forming a thin and dense core-shell structure. This structure can better withstand high-speed shearing, ensuring that the rheological properties of the adhesive remain highly consistent before and after shearing and between batches, thereby ensuring the extreme uniformity and stability of the high-speed coating process. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0040] Example 1:

[0041] The polyvinyl alcohol used in this embodiment is Kuraray POVAL 22-88, with a 4% aqueous solution having a viscosity of 23 mPa·s and a degree of alcoholysis of 88 mol%; methoxy polyethylene glycol methacrylate is Sigma-Aldrich product 447943, with a number average molecular weight of approximately 500 (including polymerization inhibitor); the polyethyleneimine aqueous solution is Sigma-Aldrich product 408700, with a mass fraction of 50% and a weight average molecular weight of approximately 1800; the polydiallyl dimethyl ammonium chloride aqueous solution is Sigma-Aldrich product 409022, with a mass fraction of 20% and a weight average molecular weight of approximately 200,000-350,000; the sodium polyacrylate aqueous solution is Sigma-Aldrich product 416037, with a mass fraction of 35% and a weight average molecular weight of approximately 15,000; and the waterborne tackifying resin is Lawter's SNOWTACK SE780G. SA is a water-based rosin ester thickening resin dispersion with a solid content of 55%. The thickener is Dow Chemical's ACRYSOL RM-8W; the defoamer is BYK's BYK-024; and the preservative and mildew inhibitor is LANXESS's KATHONLX 1.5%.

[0042] Step S1: Mix 300g deionized water, 10g sodium dodecyl sulfate, 800g vinyl acetate, 100g n-butyl acrylate, and 100g vinyl neodecanoate, and disperse using a shear disperser at 8000 rpm for 10 min to obtain a seed pre-emulsion; mix 500g deionized water, 20g sodium dodecyl sulfate, 2400g vinyl acetate, 600g n-butyl acrylate, 400g vinyl neodecanoate, and 100g acrylic acid, and disperse using a shear disperser at 8000 rpm. After 15 min, a pre-emulsion of the main monomer was obtained; 200 g deionized water, 10 g sodium dodecyl sulfate, 250 g vinyl acetate, 100 g n-butyl acrylate, and 70 g glycidyl methacrylate were mixed and dispersed at 8000 rpm for 10 min using a shear disperser to obtain a pre-emulsion of the shell hydrophobic monomer; 150 g deionized water and 150 g methoxy polyethylene glycol methacrylate were mixed and stirred at 300 rpm for 10 min to obtain a strongly hydrophilic monomer solution; 170 g deionized water and 30 g [2-(methacryloyloxy)ethyl]dimethyl(3-sulfopropyl)ammonium hydroxide inner salt were mixed and stirred at 300 rpm for 20 min until completely dissolved to obtain an amphoteric monomer solution;

[0043] Step S2: Add 800g of deionized water, 2000g of 14% polyvinyl alcohol aqueous solution, 20g of sodium bicarbonate, and 20g of sodium dodecyl sulfate to the reactor equipped with reflux condenser, thermometer, and nitrogen introduction. Start stirring at 250 rpm and introduce nitrogen for 30 minutes to remove dissolved oxygen. Then raise the temperature to 78°C and keep it constant.

[0044] Dissolve 20g of ammonium persulfate in 200g of deionized water to prepare an initiator solution. Add all 220g of the initiator solution to the reactor at once under conditions of 78°C and 250rpm. Then, add 1210g of seed pre-emulsion dropwise over 20min. After the addition is complete, continue the reaction at this temperature for 30min. Dissolve 40g of ammonium persulfate in 360g of deionized water to prepare another initiator solution. Under conditions of 78°C and 250rpm, simultaneously add 4020g of main monomer pre-emulsion and 400g of initiator solution dropwise over 180min. After the addition is complete, continue the reaction at this temperature for 60min.

[0045] Step S3: Dissolve 20g of ammonium persulfate in 180g of deionized water to prepare an initiator solution. Under conditions of 78°C and 250rpm, simultaneously add 630g of shell hydrophobic monomer pre-emulsion, 300g of strongly hydrophilic monomer solution, 200g of zwitterionic monomer solution, and 200g of initiator solution dropwise into the reactor over 40 minutes. After the addition is complete, continue the reaction at this temperature for 60 minutes. After the reaction is complete, lower the reactor temperature to 60°C and maintain stirring at 200rpm. Reduce the pressure to 30kPa and maintain this pressure for 30 minutes to remove residual volatile monomers and some water. Then restore the pressure to atmospheric pressure and cool to 35°C. Connect the reactor to an online high-shear disperser via pipeline circulation, set the speed to 6000rpm, and circulate for 15 minutes. Simultaneously, connect a 120-mesh filter in series at the reflux port to trap occasional gels / foreign matter. After circulation, return the solution to the reactor and maintain stirring at 250rpm.

[0046] Step S4: At 35°C, add 200g of deionized water and 40g of 50% polyethyleneimine (by mass) to the reactor and premix for 5 minutes to obtain a diluted polyethyleneimine solution. Then, while maintaining circulation and passing through an online high-shear disperser (6000rpm), add 240g of the diluted polyethyleneimine solution at a uniform rate through the feed port at the inlet of the disperser over 10 minutes, and immediately adjust the pH of the emulsion to 8 with 28% ammonia (by mass). After the addition is complete, stop the online shearing and react at 35°C and 250rpm for 180 minutes.

[0047] Step S5: Premix 100g of a 20% (w / w) aqueous solution of polydiallyldimethylammonium chloride with 100g of deionized water to obtain 200g of diluted polydiallyldimethylammonium chloride solution. Add the solution to the reactor at a uniform rate over 10 minutes at 35°C and 250 rpm, and continue stirring for 30 minutes after addition. Premix 120g of a 35% (w / w) aqueous solution of sodium polyacrylate with 180g of deionized water to obtain 300g of diluted sodium polyacrylate solution. Add the solution to the reactor at a uniform rate over 30 minutes at 35°C and 250 rpm. During the dropwise addition, the pH of the emulsion was maintained at 8 using 28% ammonia water by mass. After the dropwise addition was completed, the emulsion was circulated again through an online high-shear disperser and sheared at 6000 rpm for 5 minutes before being returned to the reaction vessel. Then, the pH of the emulsion was adjusted to 6 using glacial acetic acid and stirred for another 20 minutes. The temperature was then raised to 60°C and stirred at 200 rpm. The pressure was reduced to 25 kPa, and samples were taken to determine the solid content while dehydrating. The pressure was reduced until the solid content (measured at 105°C to constant weight) reached 68%, at which point the pressure was stopped and the emulsion was cooled to 25°C to obtain a high-solids-content modified main emulsion.

[0048] Step S6: Add 8000g of high solids content modified main emulsion, 1500g of water-based tackifying resin dispersion, 50g of thickener, 20g of defoamer, 10g of preservative and mildew inhibitor, and 420g of deionized water to the mixing tank. First, stir at 200rpm for 20min, then stir at 300rpm for 10min to remove bubbles and filter through a 120-mesh filter to obtain water-based high-speed packaging adhesive.

[0049] Example 2:

[0050] Compared to Example 1, in step S1, the glycidyl methacrylate in the pre-emulsion of the hydrophobic shell monomer was adjusted from 70g to 90g, while the vinyl acetate was adjusted from 250g to 230g, and the deionized water remained at 200g, sodium dodecyl sulfate at 10g, and n-butyl acrylate at 100g. In the strongly hydrophilic monomer solution, the deionized water was adjusted from 150g to 120g, and the methoxy polyethylene glycol methacrylate was adjusted from 150g to 180g. In the zwitterionic monomer solution, the deionized water was adjusted from 170g to 160g, and the [2-(methacryloyloxy)ethyl]dimethyl(3-sulfopropyl)ammonium hydroxide inner salt was adjusted from 30g to 40g. In step S4, the diluted polyethyleneimine solution was obtained by premixing 185g of deionized water with 55g of 50% polyethyleneimine for 5 minutes, and the pH of the emulsion was adjusted to 8.3 with 28% ammonia. In step S5, the diluted polydiallyldimethylammonium chloride solution was obtained by premixing 130g of a 20% (w / w) aqueous solution of polydiallyldimethylammonium chloride with 70g of deionized water. The diluted sodium polyacrylate solution was obtained by premixing 160g of a 35% (w / w) aqueous solution of sodium polyacrylate with 140g of deionized water. During the dropwise addition, the pH of the emulsion was maintained at 8.2 using 28% (w / w) ammonia water. After the dropwise addition was completed, the emulsion was circulated through an online high-shear disperser and sheared at 6500 rpm for 6 minutes before being returned to the reactor. The final solid content at the vacuum dehydration endpoint was 69%. In step S6, the aqueous thickening resin dispersion was 1700g, the thickener was 60g, the defoamer was 20g, the preservative and mildew inhibitor was 10g, and the deionized water was 350g. The remaining conditions were the same as in Example 1.

[0051] Example 3:

[0052] Compared to Example 1, in step S1, the glycidyl methacrylate in the pre-emulsion of the hydrophobic shell monomer was adjusted from 70g to 60g, while the vinyl acetate was adjusted from 250g to 260g, and the deionized water remained at 200g, sodium dodecyl sulfate at 10g, and n-butyl acrylate at 100g. In the strongly hydrophilic monomer solution, the deionized water was adjusted from 150g to 180g, and the methoxy polyethylene glycol methacrylate was adjusted from 150g to 120g. In the zwitterionic monomer solution, the deionized water was adjusted from 170g to 175g, and the [2-(methacryloyloxy)ethyl]dimethyl(3-sulfopropyl)ammonium hydroxide inner salt was adjusted from 30g to 25g. In step S3, after the reaction, the conditions of the circulating online high-shear disperser were adjusted to: a rotation speed of 5000rpm and a circulation time of 10min, while the other depressurization and filtration conditions remained unchanged. In step S4, the diluted polyethyleneimine solution was obtained by premixing 205g of deionized water with 35g of 50% polyethyleneimine for 5 minutes, and the pH of the emulsion was adjusted to 7.8 with 28% ammonia. In step S5, the diluted polydiallyldimethylammonium chloride solution was obtained by premixing 90g of 20% polydiallyldimethylammonium chloride aqueous solution with 110g of deionized water, and the diluted sodium polyacrylate solution was obtained by premixing 120g of 35% sodium polyacrylate aqueous solution with 180g of deionized water. During the dropwise addition, the pH of the emulsion was maintained at 7.8 with 28% ammonia. After the dropwise addition was completed, the emulsion was circulated through an online high-shear disperser at 5500 rpm for 4 minutes and then refluxed back to the reactor. The final solid content of the dehydrated emulsion under reduced pressure was 67%. In step S6, the aqueous thickening resin dispersion is 1400g, the thickener is 45g, the defoamer is 18g, the preservative and mildew inhibitor is 10g, and the deionized water is 500g. The remaining conditions are the same as in Example 1.

[0053] Example 4:

[0054] Compared to Example 1, the conditions of the circulating online high-shear disperser after the reaction in step S3 were adjusted as follows: the rotation speed was set to 7000 rpm and the circulation time was 20 min, while the 120-mesh filter in series at the reflux port remained unchanged. In step S4, the diluted polyethyleneimine solution was obtained by premixing 195 g of deionized water with 45 g of 50% polyethyleneimine for 5 min, and the pH of the emulsion was adjusted to 8.5 with 28% ammonia water. In step S5, the diluted polydiallyldimethylammonium chloride solution was obtained by premixing 110g of a 20% (w / w) aqueous solution of polydiallyldimethylammonium chloride with 90g of deionized water. The diluted sodium polyacrylate solution was obtained by premixing 140g of a 35% (w / w) aqueous solution of sodium polyacrylate with 160g of deionized water. During the dropwise addition, the pH of the emulsion was maintained at 8.0 using 28% (w / w) ammonia water. After the dropwise addition was completed, the emulsion was circulated through an online high-shear disperser and sheared at 7000 rpm for 5 minutes before being returned to the reactor. The final solid content at the vacuum dehydration endpoint was 70%. In step S6, the aqueous thickening resin dispersion was 1600g, the thickener was 50g, the defoamer was 20g, the preservative and mildew inhibitor was 12g, and the deionized water was 300g. The remaining conditions were the same as in Example 1.

[0055] Example 5:

[0056] Compared to Example 1, in step S1, the glycidyl methacrylate in the pre-emulsion of the hydrophobic shell monomer was adjusted from 70g to 50g, while the vinyl acetate was adjusted from 250g to 270g, and the deionized water remained at 200g, sodium dodecyl sulfate at 10g, and n-butyl acrylate at 100g. In the strongly hydrophilic monomer solution, the deionized water was adjusted from 150g to 100g, and the methoxy polyethylene glycol methacrylate was adjusted from 150g to 200g. In the zwitterionic monomer solution, the deionized water was adjusted from 170g to 150g, and the [2-(methacryloyloxy)ethyl]dimethyl(3-sulfopropyl)ammonium hydroxide inner salt was adjusted from 30g to 50g. In step S4, the diluted polyethyleneimine solution was obtained by premixing 180g of deionized water with 60g of 50% polyethyleneimine for 5min, and the pH of the emulsion was adjusted to 8.0 with 28% ammonia. In step S5, the diluted polydiallyldimethylammonium chloride solution was obtained by premixing 140g of a 20% (w / w) aqueous solution of polydiallyldimethylammonium chloride with 60g of deionized water. The diluted sodium polyacrylate solution was obtained by premixing 170g of a 35% (w / w) aqueous solution of sodium polyacrylate with 130g of deionized water. During the dropwise addition, the pH of the emulsion was maintained at 8.0 using 28% (w / w) ammonia water. After the dropwise addition was completed, the emulsion was circulated through an online high-shear disperser and sheared at 6000 rpm for 8 minutes before being returned to the reactor. The final solid content at the vacuum dehydration endpoint was 66%. In step S6, the aqueous thickening resin dispersion was 2000g, the thickener was 40g, the defoamer was 25g, the preservative and mildew inhibitor was 8g, and the deionized water was 250g. The remaining conditions were the same as in Example 1.

[0057] Comparative Example 1:

[0058] The difference from Example 1 is as follows: In step S1, instead of adding 150g of methoxy polyethylene glycol methacrylate to the strongly hydrophilic monomer solution, only 300g of deionized water is added; to achieve an equal substitution and maintain the total monomer amount added simultaneously in step S3, the vinyl acetate in the shell hydrophobic monomer pre-emulsion in step S1 is adjusted from 250g to 400g, and the deionized water is adjusted from 200g to 50g, while the sodium dodecyl sulfate 10g, n-butyl acrylate 100g, and glycidyl methacrylate 70g remain unchanged. All other conditions are the same as in Example 1.

[0059] Comparative Example 2:

[0060] The difference from Example 1 is as follows: In step S1, instead of adding 30g of [2-(methacryloyloxy)ethyl]dimethyl(3-sulfopropyl)ammonium hydroxide inner salt to the zwitterionic monomer solution, only 200g of deionized water is added; to achieve an equal volume substitution and maintain the total monomer amount added simultaneously in step S3, the vinyl acetate in the shell hydrophobic monomer pre-emulsion in step S1 is adjusted from 250g to 280g, and the deionized water is adjusted from 200g to 170g, while the sodium dodecyl sulfate 10g, n-butyl acrylate 100g, and glycidyl methacrylate 70g remain unchanged. All other conditions are the same as in Example 1.

[0061] Comparative Example 3:

[0062] The difference from Example 1 is that, in step S1, instead of adding 70g of glycidyl methacrylate to the pre-emulsion of the shell hydrophobic monomer, only 320g of vinyl acetate is added for equal-volume substitution (200g of deionized water, 10g of sodium dodecyl sulfate, and 100g of n-butyl acrylate remain unchanged, and the total amount of the pre-emulsion of the shell hydrophobic monomer remains 630g). All other conditions are the same as in Example 1.

[0063] Comparative Example 4:

[0064] The difference from Example 1 is that in step S4, instead of maintaining circulation and adding the diluted polyethyleneimine solution through the feed port at the inlet of the online high-shear disperser, 240g of diluted polyethyleneimine solution is directly added to the reactor at 35°C and 250rpm without passing through the online high-shear disperser, and the addition is completed within 10 minutes. Immediately after addition, the pH of the emulsion is adjusted to 8 with 28% ammonia water by mass, and the reaction is carried out at 35°C and 250rpm for 180 minutes. The remaining conditions are the same as in Example 1.

[0065] Comparative Example 5:

[0066] The difference from Example 1 is that the order of adding polydiallyldimethylammonium chloride and sodium polyacrylate in step S5 is reversed. First, 300g of diluted sodium polyacrylate solution is added uniformly over 30 minutes at 35°C and 250 rpm, maintaining the pH of the emulsion at 8 using 28% ammonia solution during the addition, and stirring continues for 30 minutes after the addition is complete. Then, 200g of diluted polydiallyldimethylammonium chloride solution is added uniformly over 10 minutes at 35°C and 250 rpm, and stirring continues for another 30 minutes. All other conditions are the same as in Example 1.

[0067] Performance testing:

[0068] Sample preparation: Waterborne high-speed packaging adhesives were prepared according to Examples 1-5 and Comparative Examples 1-5, respectively; simultaneously, samples were taken at the end of step S5 of each sample to obtain the corresponding high-solids content modified main emulsion. All samples were tested after standing at 25°C for 24 hours.

[0069] Viscosity determination: The single-cylinder rotational viscometer method in GB / T 2794-2022 was used. Each water-based high-speed packaging adhesive sample was conditioned in a 25°C constant temperature water bath for 30 min and degassed for 10 min. A rotational viscometer with a No. 3 rotor was used at a speed of 20 rpm. After shearing for 30 s, the stable viscosity value (mPa·s) was read. Each sample was measured 3 times and the average value was taken. The ambient temperature during the test was controlled at (25±1)°C.

[0070] High-speed shear stability (viscosity retention after shearing): Based on viscosity measurement. 200g of water-based high-speed packaging adhesive sample was placed in a 500mL stainless steel cup and continuously sheared at 6000rpm for 30min using an online high-shear disperser. During shearing, a circulating cooling water jacket was used to control the sample temperature at (25±2)°C. Viscosity was measured before and after shearing, and the viscosity retention rate after shearing R = (viscosity after shearing / viscosity before shearing) × 100% was calculated. Two parallel shearing samples were prepared for each sample, and the average value was taken as the result.

[0071] Storage stability: Tested according to GB / T 11175-2021. Each water-based high-speed packaging adhesive sample was sealed in a polyethylene bottle and stored in a constant temperature chamber at (50±2)°C for 7 days; after removal, it was placed at (25±1)°C for 24 hours; viscosity was measured, and the viscosity change rate after storage was calculated as K=[(viscosity after storage - initial viscosity) / initial viscosity]×100%. Each sample was measured twice in parallel and the average value was taken.

[0072] Freeze-thaw stability: Performed according to GB / T 11175-2021. Each water-based high-speed packaging adhesive sample was placed in a sealed container and placed in a -10°C low-temperature chamber for 16 hours, then transferred to a 25°C constant-temperature chamber for 8 hours, completing one freeze-thaw cycle; a total of 3 cycles were performed. After the cycle, the sample was allowed to stand at 25°C for 2 hours, and the viscosity was measured. The viscosity change rate after freeze-thaw was calculated as L = [(viscosity after freeze-thaw - initial viscosity) / initial viscosity] × 100%. Each sample was measured twice in parallel, and the average value was taken.

[0073] Paperboard - Tensile shear strength (10-min early strength): Tested according to GB / T 7124-2008. Take coated white cardboard (basis weight 250 g / m²). 2 Cut the sample into 100mm × 25mm pieces; apply water-based high-speed packaging adhesive evenly to the overlap area (12.5mm × 25mm) to achieve a wet application rate of 35g / m². 2(Verified by weighing method), then after an opening time of 30s at 25°C, the two specimens were overlapped and pressed together for 10s under a pressure of 0.20MPa; after pressing, they were placed at (25±1)°C and (50±5)% relative humidity for 10min before tensile shear testing was performed. The clamping distance of the testing machine was 50mm and the loading speed was 50mm / min; the maximum load was recorded and the 10min tensile shear strength (MPa) was calculated. Five specimens were prepared for each sample and the average value was taken.

[0074] Paperboard-to-paperboard tensile shear strength (24h final strength): conducted according to GB / T 7124-2008. The specimen size, overlap size, glue application amount, pressing pressure, and pressing time were consistent with the paperboard-to-paperboard tensile shear strength (10min early strength) test; the difference was that after pressing, the specimens were cured at (25±1)°C and (50±5)% relative humidity for 24h before tensile shear testing, with a loading speed of 50mm / min; the 24h tensile shear strength (MPa) was recorded, and five specimens were prepared for each sample, with the average value taken; the test results are recorded in Table 1.

[0075] Table 1 Performance Test Results

[0076] sample Viscosity at 25°C (mPa·s) Viscosity retention after shearing / % Viscosity change rate after storage / % Freeze-thaw viscosity change rate / % 10-minute tensile shear strength (MPa) 24-hour tensile shear strength (MPa) Example 1 4350 96.7 5.7 6.9 0.5 0.98 Example 2 5280 98.4 3.6 4.5 0.55 1.03 Example 3 3720 95.1 6.8 8.4 0.44 0.92 Example 4 5050 98.9 3.1 3.9 0.53 1.08 Example 5 4820 97.8 4.4 5.6 0.58 1.05 Comparative Example 1 4680 88.4 18.6 22.4 0.33 0.78 Comparative Example 2 4520 90.9 14.9 19.5 0.38 0.84 Comparative Example 3 4410 90.1 15.8 19.8 0.37 0.81 Comparative Example 4 4590 89.6 16.8 21.0 0.35 0.8 Comparative Example 5 4710 86.9 20.9 24.8 0.31 0.74

[0077] Data Analysis:

[0078] As can be seen from the data in Table 1, the water-based high-speed packaging adhesive prepared by this invention maintains a suitable application viscosity while exhibiting minimal viscosity change after shearing. Furthermore, it maintains a relatively stable rheological state after heat storage and freeze-thaw cycles, simultaneously demonstrating an increasing trend in both early and final bond strength. This may be due to the following: methoxy polyethylene glycol methacrylate accumulates outside the emulsion particle shell to form a steric hydration layer; the [2-(methacryloyloxy)ethyl]dimethyl(3-sulfopropyl)ammonium hydroxide inner salt constructs a zwitterionic strong hydration interface, thereby reducing particle proximity and re-agglomeration in the high-solids system; simultaneously, the epoxy reaction sites provided by glycidyl methacrylate allow for covalent anchoring of polyethyleneimine; combined with the charge regulation process of first adding polydiallyldimethylammonium chloride and then sodium polyacrylate, the particle surface state is further stabilized; and the online high-shear dispersion process achieves sufficient depolymerization and immediate surface locking of the aggregates, resulting in a more uniform coating process, which in turn facilitates the high-speed and stable operation of box gluing and automatic packaging lines.

[0079] As can be seen from the data in Table 1 for Example 1 and Comparative Examples 1 and 2, when the shell stage lacks methoxy polyethylene glycol methacrylate or the inner salt of [2-(methacryloyloxy)ethyl]dimethyl(3-sulfopropyl)ammonium hydroxide, the viscosity retention after shearing decreases, the viscosity change after heat storage and freeze-thaw cycles increases, and the adhesive strength decreases. This may be because the lack of a sterically hindered hydration layer or a zwitterionic strong hydration interface makes the emulsion particles more prone to adhering and re-aggregating under high solids content conditions, leading to rheological fluctuations and uneven coating. This indicates that the superposition of the two types of hydrophilic layers has an unexpected synergistic effect on interfacial anti-adhesion and stable dispersion.

[0080] As can be seen from the data in Table 1 for Example 1 and Comparative Example 3, when glycidyl methacrylate is not introduced into the hydrophobic monomer of the shell, the viscosity stability of the system decreases after shearing and aging, and the final bond strength is also affected. The main reason is that after the epoxy reaction sites provided by glycidyl methacrylate are lost, polyethyleneimine is difficult to form a stable covalent anchoring layer on the particle surface and relies more on charge adsorption. Under high-speed shear and temperature change conditions, this adsorbed layer is more likely to migrate or become locally unbalanced, causing the repulsive effect between particles to decay over time and inducing re-aggregation. Therefore, the covalent anchoring of epoxy sites and polyethyleneimine has a key synergistic contribution to long-term stability and strength maintenance.

[0081] As can be seen from the data in Table 1 for Example 1 and Comparative Example 4, when polyethyleneimine was added directly to the reactor with stirring instead of through the inlet of an online high-shear disperser in synergy with circulating shear, the viscosity retention after shearing and storage / freeze-thaw stability both deteriorated, and the bond strength decreased. This may be because the synergistic process of mechanical depolymerization and immediate surface locking was lacking, making it difficult to fully disperse the formed agglomerates. Polyethyleneimine was also more prone to localized over-adsorption and the formation of gelation regions, resulting in uncontrollable rheological response under subsequent processing shear. These results indicate a significant synergistic scale-up effect between the process pathway and chemical modification.

[0082] As can be seen from the data in Example 1 and Comparative Example 5 in Table 1, when the order of addition of sodium polyacrylate and polydiallyldimethylammonium chloride is reversed, both viscosity stability and adhesive strength deteriorate further, and the viscosity retention rate after shearing is the lowest. This may be because adding sodium polyacrylate first causes the charge state of the system to be dominated by sodium polyacrylate initially. When polydiallyldimethylammonium chloride is added subsequently, it is more likely to undergo strong adsorption and aggregation in the bulk phase, weakening its role in forming an effective regulating layer at the emulsion particle interface, leading to the destruction of the particle-scale dispersion structure. Therefore, it is evident that the charge regulation path of adding polydiallyldimethylammonium chloride first and then sodium polyacrylate, combined with the aforementioned hydrophilic layer and covalent anchoring, is necessary to achieve a balance between stability and strength.

[0083] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A water-based high-speed packaging adhesive, characterized in that, It consists of the following components by mass parts: 8000 parts of the high-solids-content modified main emulsion described above; 1400-2000 parts of the aqueous thickening resin dispersion described above; 40-60 parts of the thickener described; 18-25 parts of the defoamer described; 8-12 parts of the preservative and antifungal agent described; 250-500 parts of the deionized water described above; The high-solids-content modified main emulsion has a solids content of 66%-70%, and the high-solids-content modified main emulsion comprises emulsion particles. The shell of the emulsion particles contains methoxy polyethylene glycol methacrylate units, [2-(methacryloyloxy)ethyl]dimethyl(3-sulfopropyl)ammonium hydroxide inner salt units, and glycidyl methacrylate units. The surface of the emulsion particles is covalently grafted with polyethyleneimine, and the surface of the emulsion particles is coated with a polyelectrolyte composite layer formed by polydiallyldimethylammonium chloride and sodium polyacrylate.

2. The water-based high-speed packaging adhesive according to claim 1, characterized in that, The aqueous tackifying resin dispersion is an aqueous rosin ester tackifying resin dispersion; and the solid content of the aqueous rosin ester tackifying resin dispersion is 55%.

3. The water-based high-speed packaging adhesive according to claim 1, characterized in that, The thickener is ACRYSOL RM-8W; the defoamer is BYK-024; and the preservative and mildew inhibitor is KATHON LX 1.5%.

4. The water-based high-speed packaging adhesive according to claim 1, characterized in that, The pH of the high-solids-content modified main emulsion is 6.

5. The water-based high-speed packaging adhesive according to claim 1, characterized in that, The emulsion particles are obtained by emulsion polymerization of vinyl acetate, n-butyl acrylate, vinyl neodecanoate, acrylic acid, glycidyl methacrylate, methoxy polyethylene glycol methacrylate, and [2-(methacryloyloxy)ethyl]dimethyl(3-sulfopropyl)ammonium hydroxide inner salt in a mass ratio of 3430-3470:800:500:100:50-90:120-200:25-50.

6. The water-based high-speed packaging adhesive according to claim 1, characterized in that, The number-average molecular weight of the methoxy polyethylene glycol methacrylate is 400-600; the weight-average molecular weight of the polydiallyl dimethyl ammonium chloride is 200,000-350,000; and the weight-average molecular weight of the sodium polyacrylate is 10,000-20,000.

7. A method for preparing an aqueous high-speed packaging adhesive according to any one of claims 1-6, characterized in that, Includes the following steps: S1, prepare seed preemulsion, main monomer preemulsion, shell hydrophobic monomer preemulsion, strongly hydrophilic monomer solution and zwitterionic monomer solution; S2, the seed pre-emulsion and the main monomer pre-emulsion are sequentially subjected to emulsion polymerization to obtain an intermediate emulsion; S3, In the shell polymerization stage, the shell hydrophobic monomer pre-emulsion, the strongly hydrophilic monomer solution and the zwitterionic monomer solution are introduced into the intermediate emulsion to carry out emulsion polymerization, and the resulting emulsion is subjected to devolatilization and online shear dispersion treatment after the reaction is completed. S4, polyethyleneimine is added to the emulsion, and the polyethyleneimine undergoes a ring-opening reaction with the epoxy group of the glycidyl methacrylate unit, so that the polyethyleneimine is covalently grafted onto the surface of the emulsion particles. S5, first add polydiallyldimethylammonium chloride to the emulsion, then add sodium polyacrylate to the emulsion to form a polyelectrolyte composite layer on the surface of the emulsion particles, then adjust the pH and dehydrate and concentrate to obtain a high solids content modified main emulsion. S6, the high solids content modified main emulsion is mixed with water-based tackifying resin dispersion, thickener, defoamer, preservative and mildew inhibitor and deionized water and filtered to obtain water-based high-speed packaging adhesive.

8. The method for preparing the water-based high-speed packaging adhesive according to claim 7, characterized in that, In step S1, the seed pre-emulsion is prepared from the following raw materials in parts by weight: 300 parts deionized water, 10 parts sodium dodecyl sulfate, 800 parts vinyl acetate, 100 parts n-butyl acrylate, and 100 parts vinyl neodecanoate; the main monomer pre-emulsion is prepared from the following raw materials in parts by weight: 500 parts deionized water, 20 parts sodium dodecyl sulfate, 2400 parts vinyl acetate, 600 parts n-butyl acrylate, 400 parts vinyl neodecanoate, and 100 parts acrylic acid; the shell hydrophobic monomer pre-emulsion is prepared from the following raw materials in parts by weight. The solution comprises: 200 parts deionized water, 10 parts sodium dodecyl sulfate, 230-270 parts vinyl acetate, 100 parts n-butyl acrylate, and 50-90 parts glycidyl methacrylate; the strongly hydrophilic monomer solution is prepared by mass fraction from the following raw materials: 100-180 parts deionized water and 120-200 parts methoxy polyethylene glycol methacrylate; the zwitterionic monomer solution is prepared by mass fraction from the following raw materials: 150-175 parts deionized water and 25-50 parts [2-(methacryloyloxy)ethyl]dimethyl(3-sulfopropyl)ammonium hydroxide inner salt.

9. The method for preparing the water-based high-speed packaging adhesive according to claim 7, characterized in that, In step S3, the rotation speed of the online shearing dispersion is 5000-7000 rpm, the circulation time is 10-20 min, and a 120-mesh filter screen is connected in series at the return port.

10. The method for preparing the water-based high-speed packaging adhesive according to claim 7, characterized in that, In step S4, while maintaining circulation and passing through an online high-shear disperser at 6000 rpm, the diluted polyethyleneimine solution is added uniformly over 10 minutes, and the pH of the emulsion is immediately adjusted to 7.8-8.5 with 28% ammonia water by mass.