High-temperature shear-resistant packaging adhesive for corrugated case and preparation method of high-temperature shear-resistant packaging adhesive

Abstract

The invention relates to the technical field of adhesives, in particular to a high-temperature shear-resistant packaging adhesive for corrugated cartons and a preparation method of the high-temperature shear-resistant packaging adhesive. The shear-resistant packaging adhesive for the corrugated case comprises an ethylene-vinyl acetate copolymer, boric acid, branched polyethyleneimine, kaolin, water and an auxiliary agent. The boric acid, the branched polyethyleneimine, the kaolin and the ethylene-vinyl acetate copolymer form a dynamically adjustable spatial three-dimensional network structure, so that the strength and the toughness of an adhesive film are favorably improved, and the high-temperature shear resistance of the packaging adhesive is improved.

Description

Technical Field

[0001] The invention relates to the technical field of adhesives, and in particular to a high-temperature shear-resistant packaging adhesive for corrugated paper boxes and a preparation method thereof. Background Art

[0002] Corrugated boxes are often used as the outermost packaging of commodities to ensure the quality of products during transportation and circulation. The last process of its production is to join the overlaps of printed, die-cut and folded cardboards. Since glued cartons have more advantages than nailed cartons, such as material saving, environmental protection, high efficiency and safety, the use of adhesives to glue the overlaps of box cardboards has become the mainstream of the industry. This type of adhesive is also called packaging glue or box glue. The quality of packaging glue directly affects the performance of cartons during production and use. At present, machine gluing has gradually replaced the traditional manual gluing method. Fully automatic or semi-automatic box gluers are used to glue the overlaps of box cardboards, with fast gluing speed and high production efficiency.

[0003] When using a machine to apply glue, it is necessary to control the packaging glue to be liquid at high temperature. At the same time, it is necessary to control the glue liquid to be heated evenly and maintain fluidity at high temperature and mechanical stirring, and to pump the glue liquid to the nozzle and spray it out under pressure. These are all shear conditions. Under such high temperature and shear conditions, the packaging glue commonly used in the prior art has the problem of poor stability and easy breakage of the molecular bonds of its components, which is intuitively manifested in the reduction of the viscosity of the packaging glue and the decrease in the strength of the film, resulting in the deterioration of the performance of the packaging glue. Therefore, a high temperature and shear-resistant packaging glue is urgently needed.

[0004] A patent document with a publication number of CN117384570A discloses such a multi-purpose water-based high-speed packaging glue, which is mainly made of the following raw materials in parts by weight: 72-88 parts of modified VAE emulsion, 10-15 parts of modified polyvinyl alcohol aqueous solution, 0.3-0.5 parts of defoamer, 0.3-0.9 parts of tackifying resin, 1-5 parts of plasticizer, 0.4-1 parts of moisturizer, and 0.2-0.4 parts of preservative; the modified polyvinyl alcohol aqueous solution is obtained by esterification reaction of polyvinyl alcohol aqueous solution and monocarboxylic acid with hydroxyl group. This prior art esterifies polyvinyl alcohol with monocarboxylic acid with hydroxyl group to destroy the structural regularity of polyvinyl alcohol, thereby obtaining better shear stability. However, it only improves the shear resistance of polyvinyl alcohol itself, and then indirectly improves the shear resistance of the system by using the distribution of modified polyvinyl alcohol in the system; however, the amount of modified polyvinyl alcohol is limited, and too much will affect the adhesion of the system, so its improvement on the shear resistance of the system is limited. Summary of the invention

[0005] The present invention aims to solve the above problems and provides a packaging adhesive for corrugated paper boxes which is resistant to high temperature shearing, especially resistant to shearing at a high temperature of 40°C, and a preparation method thereof.

[0006] The technical solution of the present invention to solve the problem is: first , providing a shear-resistant packaging adhesive for corrugated boxes, including ethylene-vinyl acetate copolymer, boric acid, branched polyethyleneimine, kaolin, water and additives. In this application, ethylene-vinyl acetate copolymer (EVA) emulsion is first used as the basic adhesive liquid, which has the advantages of permanent softness, water resistance, weather resistance, low temperature resistance, fast bonding speed, high bonding strength and non-toxic use. However, for corrugated paperboard packaging glue, a single EVA emulsion has poor shear resistance, especially poor shear resistance at high temperature, and the effect of carton lamination is not ideal. Therefore, EVA is secondly modified by high temperature shear resistance through boric acid, branched polyethyleneimine and kaolin. The specific principle is speculated to be: the borate ions of boric acid react with the hydroxyl groups in the EVA emulsion to form borate ester bonds as crosslinking points; the amine groups of the branched polyethyleneimine react with the vinyl acetate groups or vinyl groups in the EVA emulsion to form a spatial three-dimensional network structure. On this basis, kaolin is physically crosslinked to the spatial three-dimensional network structure through its adsorption, filling and dispersibility, thereby forming a spatial three-dimensional network structure with both chemical crosslinking and physical crosslinking. Based on the reversibility of physical cross-linking, the spatial three-dimensional network structure has dynamic adjustability, so that it can maintain good stability under high temperature shear.

[0007] in, For Ethylene Vinyl Acetate (EVA) , its solid content further affects the performance of the packaging glue. For example, if the solid content is too high, the viscosity of the packaging glue may increase, which is not convenient for gluing on the one hand, and requires greater shear force to be provided during stirring, so that the packaging glue is more easily sheared and destroyed. The stability; if the solid content is too low, the viscosity of the packaging glue may be insufficient, which may cause splashing during the gluing process on the one hand and affect the adhesion on the other hand. As a preferred embodiment of the present invention, the solid content of the ethylene-vinyl acetate copolymer is 16% to 50%, and the viscosity is 2000 to 2500 mPa·s. For example, the solid content can be 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%; preferably 30% to 50%, and more preferably 50%.

[0008] For branched polyethyleneimine, its molecular weight and degree of branching further affect the performance of the packaging glue. For example, when the degree of branching is the same, the branched polyethyleneimine with a larger molecular weight has a longer molecular chain, which can form more cross-linking points with EVA, thereby increasing the density and strength of the cross-linking network, and then improving the heat resistance and shear resistance of the packaging glue; but the solubility and dispersibility of the branched polyethyleneimine with a molecular weight that is too large are poor, and its diffusion rate in the system is reduced, which may affect the cross-linking reaction. When the molecular weight is the same, the branched polyethyleneimine with a larger degree of branching has more cross-linkable branches and higher activity, thereby increasing the density and strength of the cross-linking network; but too high a branching degree may also cause the molecular chain to be too complex, making the reaction site difficult to approach, thereby reducing the reaction rate to a certain extent and affecting the cross-linking result. Therefore, as preferred in the present invention, the molecular weight of the branched polyethyleneimine is 800-2200, for example, it can be 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200; preferably 1200-2000, more preferably 1500. The degree of branching of the branched polyethyleneimine is 0.3-0.55, for example, 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.4, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.5, 0.51, 0.52, 0.53, 0.54, 0.55; preferably 0.35-0.45, more preferably 0.4.

[0009] For Kaolin, which is clay or clay rock based on kaolinite clay minerals, and its main components are aluminum oxide and silicon oxide. In the present application, kaolin can fill the gaps between emulsion molecules, increase the solid and thickening of low-solid emulsions, and at the same time improve the rigidity of the chain segments, so that the cohesive strength and heat and chemical resistance of the glue are improved. The particle size of kaolin further affects the performance of the packaging glue. For example, kaolin with a smaller particle size has a larger specific surface area, can effectively fill the gaps between emulsions, form more cross-linking points, and can be more tightly wrapped in a three-dimensional network structure in space to form a protective layer to prevent the material from denaturing under high-temperature shear; but if the particle size is too low, there may be agglomeration problems, which will affect its combination effect with molecular weight. Therefore, as a preferred embodiment of the present invention, the kaolin is an ultrafine kaolin of 2000~6000 mesh, and for example, it can be 2000 mesh, 2500 mesh, 3000 mesh, 3500 mesh, 4000 mesh, 4500 mesh, 5000 mesh, 5500 mesh, and 6000 mesh. Further preferred is 4000 mesh. Ultrafine kaolin has unique high dispersibility and chemical inertness. The particle size of 4000 mesh is 2~4μm, which makes it easy to mix with the glue and fully fill the gaps in the glue to enhance solidification and thickening. The ultrafine nanoparticles have a high specific surface area and can effectively construct physical cross-linking points, which is beneficial to improve the high-temperature shear resistance of the modified emulsion; it can also enhance density, improve cohesive strength, and play a role in reinforcement and cost reduction.

[0010] For additives , any commonly used auxiliary agent in packaging adhesive can be selected, such as defoamer, plasticizer, stabilizer, flame retardant, etc. In the present application, based on the above-mentioned dynamically adjustable spatial three-dimensional network structure, the plasticity and stability of the packaging adhesive can be well adjusted. Therefore, as a preferred embodiment of the present invention, the auxiliary agent can be a defoamer. The defoamer can reduce the surface tension of the adhesive, promote the rupture and disappearance of bubbles, and ensure the uniformity and stability of the packaging adhesive. The selection of the defoamer is not limited. For example, it can be at least one of a polyether defoamer, a mineral oil, and a silicone.

[0011] As a preferred embodiment of the present invention, the auxiliary agent is a polyether defoamer. In addition to playing a defoaming role, the polyether defoamer can improve the dispersibility of ultrafine kaolin particles in the EVA emulsion matrix, reduce the viscosity of the slurry or colloid, improve the rheology, and does not affect the production process.

[0012] The selection of polyether defoamers is not limited, and for example, it can be aliphatic polyether defoamers, polyoxyethylene polyether defoamers, alcohol polyether defoamers, silicone polyether defoamers, etc.

[0013] The amount of each component in the packaging glue of the present application further affects the density and strength of the dynamically adjustable spatial three-dimensional network structure. As a preferred embodiment of the present invention, the packaging glue includes 0.01-0.4wt% boric acid, 0.001-0.004wt% branched polyethyleneimine, 1.89-7.9wt% kaolin, 3.77-11.9wt% water, 0.09-0.4wt% additives, and the rest is ethylene-vinyl acetate copolymer.

[0014] For example, boric acid can be 0.01wt%, 0.05wt%, 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt%, 0.4wt%; branched polyethyleneimine can be 0.001wt%, 0.002wt%, 0.003wt%, 0.004wt%; kaolin can be 1.89wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 7.9wt%; water can be 3.77wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 11.9wt%; and the auxiliary agent can be 0.09wt%, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%.

[0015] As a preferred embodiment of the present invention, the packaging glue comprises 0.09 wt % of boric acid, 0.001 wt % of branched polyethyleneimine, 1.89 wt % of kaolin, 5.6 wt % of water, 0.14 wt % of auxiliary agent, and the rest is ethylene-vinyl acetate copolymer.

[0016] Secondly Another object of the present invention is to provide a method for preparing the high temperature shear resistant packaging adhesive for corrugated paper boxes, comprising the following steps: S1. mixing the boric acid and the branched polyethyleneimine to obtain a shear resistant accelerator; S2. Under stirring conditions, the auxiliary agent, kaolin, shear accelerator and water are sequentially added to the ethylene-vinyl acetate copolymer to obtain a packaging adhesive.

[0017] In the preparation process of the present application, by reasonably allocating the order of addition, strengthening first and then thickening, the reduction of mixing efficiency caused by excessive viscosity is avoided, which is conducive to uniform mixing of different components. The whole process is simple to operate and easy to control.

[0018] In step S1, as a preferred embodiment of the present invention, specifically: dissolve boric acid in water to a concentration of 3 to 10 wt%, then add branched polyethyleneimine, and stir evenly. For example, the concentration of boric acid can be 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, preferably 5 wt%.

[0019] In step S2, as preferred in the present invention, the stirring speed is 1000-1500 rpm / min. For example, it can be 1000 rpm / min, 1100 rpm / min, 1200 rpm / min, 1300 rpm / min, 1400 rpm / min, 150 rpm / min, preferably 1200 rpm / min.

[0020] In step S2, as the preferred embodiment of the present invention, specifically: pre-stir the ethylene-vinyl acetate copolymer at a stirring speed of 1000-1500 rpm / min; then add the auxiliary agent and stir for 5-10 minutes; then add kaolin and stir for 1-3 hours until no solid powder appears in the glue sample; then add the shear accelerator and stir for 1-2 hours; finally, add water and stir.

[0021] For example, the stirring time of the auxiliary agent can be 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, preferably 8 min. The stirring time of kaolin can be 1 h, 1.5 h, 2 h, 2.5 h, 3 h, preferably 2 h. The stirring time after the shear resistant accelerator is added can be 1 h, 1.5 h, 2 h, preferably 2 h.

[0022] As a preference of the present invention, the shear resistant accelerator is slowly added by dripping or pouring in succession during stirring, and the adding time is ≥10 min to control the crosslinking reaction rate.

[0023] Beneficial effects of the present invention: 1. The present application provides a high temperature shear resistant packaging adhesive for corrugated boxes, which forms a dynamically adjustable spatial three-dimensional network structure with boric acid, branched polyethyleneimine, kaolin and EVA, which helps to increase the strength and toughness of the adhesive film and improve the high temperature shear resistance of the packaging adhesive. Specifically: by adding a high temperature shear resistant agent, the auxiliary agent is composed of a certain ratio of boric acid and branched polyethyleneimine. Among them, boric acid can react with the hydroxyl groups on the glue molecules, and the borate ions react with the hydroxyl groups in the glue to form borate ester bonds, and the amine groups of the branched polyethyleneimine can react with the vinyl acetate groups or vinyl groups in the EVA emulsion to cross-link, and then construct a modified packaging latex space three-dimensional network structure by dynamically adjusting the cross-linking reaction, which is beneficial to the modified emulsion to improve the high temperature shear resistance, form a stable covalent bond, limit the slippage of the latex particles, and do not need to add a rheological regulator. The ability to resist shear deformation during roller coating on the machine is enhanced, and the viscosity of the glue is increased. In addition, by cooperating with ultrafine kaolin particles, the ultrafine nanoparticles have a high specific surface area and can effectively construct physical crosslinking points. The polymer chains in the EVA emulsion can be entangled with each other and form a mesh structure to enhance the overall performance of the material, forming a physical crosslinking network, which can further improve the stability of the EVA emulsion in high temperature and shear environments. This packaging glue is suitable for full / semi-automatic box gluing machines, has good bonding effects and no flying glue, and can also effectively reduce production costs.

[0024] 2. The present application provides a method for preparing the above-mentioned packaging adhesive. By reasonably allocating the order of addition, the adhesive is first strengthened and then thickened, thereby avoiding the reduction in mixing efficiency due to excessive viscosity, facilitating uniform mixing of different components, and the whole process is simple to operate and easy to control. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 1 is a bar graph of the film strength of the packaging adhesive obtained in Example 1 and the blank example at 25° C. and 40° C. respectively. DETAILED DESCRIPTION

[0026] The following are specific implementations of the present invention, and in conjunction with the accompanying drawings, the technical solutions of the present invention are further described, but the present invention is not limited to these embodiments.

[0027] Example 1 A high-temperature shear-resistant packaging adhesive for corrugated paper boxes comprises 0.09 wt% of boric acid, 0.001 wt% of branched polyethyleneimine, 1.89 wt% of kaolin, 5.6 wt% of water, 0.14 wt% of an auxiliary agent, and 92.279 wt% of ethylene-vinyl acetate copolymer.

[0028] The molecular weight of the branched polyethyleneimine is 1500, the branching degree is 0.4, the kaolin is 4000 mesh ultrafine kaolin, the auxiliary agent is a polyether defoamer, and the solid content of the ethylene-vinyl acetate copolymer is 50%.

[0029] This corrugated paper box is prepared by the following steps: S1. Boric acid and water are mixed in a mass ratio of 1:20 to obtain a boric acid solution; then branched polyethyleneimine is added and stirred evenly to obtain a shear resistance accelerator.

[0030] S2. Add EVA emulsion into the reactor and start stirring at a speed of 1200 rpm / min; then add polyether defoamer at a speed of 1200 rpm / min and stir for 8 minutes; then add ultrafine kaolin at a speed of 1200 rpm / min and stir for 2 hours until no solid powder appears in the glue sample; then add shear accelerator by dropwise addition at a stirring speed of 1200 rpm / min, and add the shear accelerator within 10 minutes; then continue stirring at a speed of 1200 rpm / min for 1.5 hours; finally add the remaining water at a stirring speed of 1200 rpm / min to obtain packaging glue.

[0031] Embodiment 2~5 Examples 2 to 5 are substantially the same as Example 1, except that the solid contents of the ethylene-vinyl acetate copolymers are different, as shown in Table 1 below.

[0032] Table 1. Embodiment 6~9 This embodiment is basically the same as embodiment 1, and the only difference is that the molecular weight of the branched polyethyleneimine is different, as shown in Table 2 below.

[0033] Table 2. Embodiments 10 to 13 This embodiment is basically the same as embodiment 1, and the only difference is that the branching degree of the branched polyethyleneimine is different, as shown in Table 3 below.

[0034] Table 3. Embodiments 14 to 17 This embodiment is basically the same as embodiment 1, and the only difference is that the mesh size of kaolin is different, as shown in Table 4 below.

[0035] Table 4. Embodiment 18 This embodiment is basically the same as Embodiment 1, the only difference being that the auxiliary agent is silicone oil.

[0036] Embodiment 19 This embodiment is basically the same as Embodiment 1, and the only difference is that: A high-temperature shear-resistant packaging adhesive for corrugated paper boxes comprises 0.4wt% boric acid, 0.004wt% branched polyethyleneimine, 7.9wt% kaolin, 11.9wt% water, 0.4wt% auxiliary agent, and 79.396wt% ethylene-vinyl acetate copolymer.

[0037] The molecular weight of the branched polyethyleneimine is 1500, the branching degree is 0.4, the kaolin is 4000 mesh ultrafine kaolin, the auxiliary agent is a polyether defoamer, and the solid content of the ethylene-vinyl acetate copolymer is 50%.

[0038] Embodiment 20 This embodiment is basically the same as Embodiment 1, and the only difference is that: A high-temperature shear-resistant packaging adhesive for corrugated paper boxes comprises 0.01 wt% of boric acid, 0.002 wt% of branched polyethyleneimine, 5.15 wt% of kaolin, 3.77 wt% of water, 0.09 wt% of an auxiliary agent, and 90.978 wt% of ethylene-vinyl acetate copolymer.

[0039] The molecular weight of the branched polyethyleneimine is 1500, the branching degree is 0.4, the kaolin is 4000 mesh ultrafine kaolin, the auxiliary agent is a polyether defoamer, and the solid content of the ethylene-vinyl acetate copolymer is 50%.

[0040] Blank example A high-temperature shear-resistant packaging adhesive for corrugated paper boxes comprises 100 wt% of ethylene-vinyl acetate copolymer, wherein the solid content of the ethylene-vinyl acetate copolymer is 50%.

[0041] Comparative Example 1 This comparative example is substantially the same as Example 1, except that it contains only EVA, kaolin, water and additives.

[0042] Specifically, it includes 1.89wt% kaolin, 5.6wt% water, 0.14wt% additive, and 92.37wt% ethylene-vinyl acetate copolymer.

[0043] Comparative Example 2 This comparative example is substantially the same as Example 1, except that it contains only EVA, boric acid, water and an additive.

[0044] Specifically, it includes 0.09wt% boric acid, 5.6wt% water, 0.14wt% auxiliary agent, and 94.17wt% ethylene-vinyl acetate copolymer. Comparative Example 3 This comparative example is substantially the same as Example 1, except that it contains only EVA, branched polyethyleneimine, water and an auxiliary agent.

[0045] Specifically, it includes 0.001wt% branched polyethyleneimine, 5.6wt% water, 0.14wt% auxiliary agent, and 94.259wt% ethylene-vinyl acetate copolymer.

[0046] High temperature shear resistance test The viscosities of the packaging adhesives obtained in the examples, blank examples and comparative examples were tested at 25° C. and 40° C., respectively, and the high-temperature shear resistance was represented by the viscosity decrease rate.

[0047] According to GB / T 33334-2016 Adhesive Single Lap Tensile Shear Strength Test Method, the shear strength (film strength) of the packaging adhesives obtained in the examples, blank examples and comparative examples at 25°C and 40°C was tested, and the high temperature shear resistance was expressed by the decrease rate of the film strength. The test results are shown in Table 5.

[0048] Table 5. As shown in Table 5, Comparative Example 1 and Blank Example, and Figure 1 It can be seen that the addition of boric acid, branched polyethyleneimine, kaolin, water and polyether defoaming agent to ethylene-vinyl acetate copolymer in the present application can effectively improve the viscosity of the adhesive and the film strength at room temperature and high temperature of 40°C, and reduce the reduction rate of the viscosity and film strength of the adhesive at a high temperature of 40°C, thereby improving the high-temperature shear resistance of the adhesive.

[0049] On this basis, by continuing to compare comparative examples 1, 2, and 3, it can be seen that although kaolin, boric acid, and branched polyethyleneimine can reduce the viscosity reduction rate of the adhesive and the film strength at a high temperature of 40°C to a certain extent when used separately in EVA, kaolin, boric acid, and branched polyethyleneimine are mixed for use in Example 1, and the reduction rate can be further reduced. This shows that kaolin, boric acid, and branched polyethyleneimine work synergistically to further improve the high-temperature shear resistance of the adhesive, which may be related to the spatial three-dimensional network structure with both chemical crosslinking and physical crosslinking and dynamic adjustability obtained in the present application.

[0050] In addition, it can be seen from the comparison in the examples that the specific selection of component ratio, EVA, kaolin, branched polyethyleneimine and defoamer also has a certain influence on the high temperature shear resistance of the packaging glue. For example, by comparing Example 1 with Examples 2 to 5, it can be seen that within an appropriate range, the solid content of EVA has an effect on the reduction rate of the viscosity and film strength of the packaging glue at a high temperature of 40°C, but the effect is not significant; when the solid content of EVA is too high, the high temperature shear resistance of the packaging glue will be significantly reduced. This may be because the excessively high EVA content causes part of the EVA to fail to be cross-linked and unable to form a spatial three-dimensional network structure, and the molecular bonds are broken under high temperature and shear; when the EVA content is too low, although it has little effect on the high temperature shear resistance of the packaging glue, it will cause the viscosity and film strength of the packaging glue to be significantly reduced, which is not suitable for actual production packaging.

[0051] By comparing Example 1 with Examples 6 to 9, it can be seen that within an appropriate range, the molecular weight of the branched polyethyleneimine has an effect on the reduction rate of the viscosity and film strength of the packaging adhesive at a high temperature of 40°C, but the effect is not significant. When the molecular weight of the branched polyethyleneimine is too high, it may lead to poor dispersibility and affect the cross-linking reaction; when the molecular weight of the branched polyethyleneimine is too low, it may lead to insufficient cross-linking sites; this will affect the density and strength of the three-dimensional network structure, so that the high-temperature shear resistance of the packaging adhesive is reduced.

[0052] By comparing Example 1 with Examples 10 to 13, it can be seen that within an appropriate range, the degree of branching of branched polyethyleneimine has an effect on the reduction rate of viscosity and film strength of packaging adhesive at a high temperature of 40°C, but the effect is not significant. When the degree of branching of branched polyethyleneimine is too high, it may lead to complex molecular chains, difficult to access reaction sites, and affect the cross-linking reaction; when the degree of branching of branched polyethyleneimine is too low, it may lead to insufficient cross-linking sites; this will affect the density and strength of the three-dimensional network structure, so that the high-temperature shear resistance of the packaging adhesive is reduced.

[0053] By comparing Example 1 with Examples 14 to 17, it can be seen that within an appropriate range, the particle size of kaolin has an effect on the reduction rate of the viscosity and film strength of the packaging adhesive at a high temperature of 40°C, but the effect is not significant. When the particle size of kaolin is too large, it may cause a reduction in physical cross-linking sites; when the particle size of kaolin is too small, kaolin may have agglomeration problems; this will affect the density and strength of the three-dimensional network structure, resulting in a decrease in the high-temperature shear resistance of the packaging adhesive.

[0054] By comparing Example 1 and Example 18, it can be seen that the polyether defoamer can further improve the high-temperature shear resistance of the packaging rubber compared with mineral oil. This may be because the polyether defoamer, in addition to playing a defoaming role, can also improve the dispersibility of ultrafine kaolin particles in the EVA emulsion matrix and improve the cross-linking effect of kaolin in the three-dimensional network structure.

[0055] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A high temperature shear resistant packaging adhesive for corrugated paper boxes, characterized in that: The invention comprises ethylene-vinyl acetate copolymer, boric acid, branched polyethyleneimine, kaolin, water and additives.

2. The high temperature shear resistant packaging adhesive for corrugated paper boxes according to claim 1, characterized in that: The solid content of the ethylene-vinyl acetate copolymer is 16% to 50%.

3. The high temperature shear resistant packaging adhesive for corrugated paper boxes according to claim 1, characterized in that: The molecular weight of the branched polyethyleneimine is 800-2200.

4. The high temperature shear resistant packaging adhesive for corrugated paper boxes according to claim 1, characterized in that: The branching degree of the branched polyethyleneimine is 0.3-0.

55.

5. The high temperature shear resistant packaging adhesive for corrugated paper boxes according to claim 1, characterized in that: The kaolin is ultrafine kaolin with a mesh size of 2000-6000.

6. The high temperature shear resistant packaging adhesive for corrugated paper boxes according to claim 1, characterized in that: The auxiliary agent is selected from at least one of polyether defoamer, mineral oil and silicone.

7. The high temperature shear resistant packaging adhesive for corrugated paper boxes according to claim 6, characterized in that: The auxiliary agent is a polyether defoamer.

8. The high temperature shear resistant packaging adhesive for corrugated paper boxes according to claim 1, characterized in that: The invention comprises 0.01-0.4wt% of boric acid, 0.001-0.004wt% of branched polyethyleneimine, 1.89-7.9wt% of kaolin, 3.77-11.9wt% of water, 0.09-0.4wt% of auxiliary agent, and the rest is ethylene-vinyl acetate copolymer.

9. A method for preparing the high temperature shear resistant packaging adhesive for corrugated paper boxes according to any one of claims 1 to 8, characterized in that: The steps include: S1. mixing the boric acid and the branched polyethyleneimine to obtain a shear resistant accelerator; S2. Under stirring conditions, the auxiliary agent, kaolin, shear accelerator and water are sequentially added to the ethylene-vinyl acetate copolymer to obtain a packaging adhesive.

10. The method for preparing a high temperature shear resistant packaging adhesive for corrugated paper boxes according to claim 9, characterized in that: In step S2, the shear resistance promoter is slowly added by dripping or pouring in succession during stirring, and the adding time is ≥10 min.

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