Metal binder for packaging box and preparation method of metal binder

Abstract

The invention provides a metal binder for a packaging box and a preparation method thereof.The metal binder comprises a first component and a second component, and the first component comprises, by mass, 50 parts of modified acrylate emulsion, 5-10 parts of polyvinyl alcohol and 1-3 parts of a trifunctional epoxy cross-linking agent; wherein the modified acrylate emulsion is obtained by initiating emulsion polymerization of acrylate, acrylic acid and unsaturated phosphonic acid through an initiator in the presence of an emulsifier; the second component comprises a divalent metal ion aqueous solution. According to the metal binder, interface component distribution and adsorption behaviors in the bonding process are guided through double-component design, the adhesive capacity of the binder on the surface of a metal base material can be remarkably improved, the structural stability of a composite bonding layer is improved, and therefore the interface adhesive force and the structural stability in a metal-nonmetal composite material are effectively improved.

Description

Technical Field

[0001] The present application relates to the technical field of adhesives, and in particular to a metal adhesive for packaging boxes and a preparation method thereof. Background Art

[0002] In packaging, metal materials are often used as barrier or decorative layers, often combined with non-metallic materials like paper and plastic film to form a multi-layered structure to meet the packaging's multiple requirements for strength, aesthetics, and functionality. To achieve a reliable connection between these dissimilar materials, adhesives are often used to firmly bond the metal substrate to the non-metallic material.

[0003] However, the currently commonly used metal adhesive systems still expose many interface compatibility problems during application. For example, in the prior art, the most widely used metal adhesives are mostly acrylic emulsions, polyurethane dispersions or epoxy water-based adhesive systems. Although these adhesives have good environmental friendliness and certain bonding strength, they still have the following problems in metal-non-metal composite structures: on the one hand, the adhesive has poor adhesion to the metal surface and is prone to interfacial peeling after composite, especially under temperature and humidity changes, which shows a greater risk of interfacial failure, limiting its application in high-reliability packaging structures; on the other hand, the insufficient affinity of the metal surface leads to uneven distribution of the adhesive, and the problem of loose bonding between the coating film layer and the metal interface often occurs. Even if the initial bonding strength is high after film formation, the adhesive layer is prone to fall off when subjected to tensile or peeling tests, and the adhesion fastness is poor; at the same time, the existing adhesives mostly rely on the physical adsorption of the polymer itself or the interfacial wetting behavior during the drying film formation process. They have limited ability to control the microstructure, and the structural uniformity and molecular stability of the bonding interface are insufficient, which is not conducive to the adhesive forming a dense and stable bonding interface on the metal surface.

[0004] In summary, existing metal adhesives still need to be improved in terms of interfacial adhesion ability with metal substrates and structural stability. It is urgent to develop a metal adhesive with stronger interfacial bonding force, more stable structure, and suitable for use in metal-non-metal composite structures, so as to improve its application reliability in high-performance packaging boxes, composite film structures and other occasions. Summary of the Invention

[0005] The present application provides a metal adhesive for packaging boxes and a preparation method thereof, aiming to solve the problem of insufficient interface adhesion of existing metal adhesives in metal and non-metallic material composite materials and unstable bonding layer structure, which leads to easy delamination.

[0006] In the first aspect, the present application provides a metal adhesive for a packaging box, comprising a first component and a second component, wherein the first component comprises the following raw materials in parts by mass: 50 parts of modified acrylate emulsion, 5 to 10 parts of polyvinyl alcohol, and 1 to 3 parts of a trifunctional epoxy crosslinker; wherein the modified acrylate emulsion is obtained by emulsion polymerization of acrylate, acrylic acid and unsaturated phosphonic acid in the presence of an emulsifier, initiated by an initiator; and the second component comprises an aqueous solution of divalent metal ions.

[0007] According to the present application, the metal adhesive guides the interfacial component distribution and adsorption behavior during the bonding process through a two-component design, which can significantly improve the adhesion ability of the adhesive on the surface of the metal substrate and improve the structural stability of the bonding layer after composite, thereby effectively improving the interfacial adhesion and structural stability in metal-non-metal composite materials.

[0008] Specifically, the first component, as the main film-forming body, has excellent interfacial wettability, polar anchoring and hot-pressed film-forming structure stability through the synergistic effect of modified acrylic emulsion, polyvinyl alcohol and trifunctional epoxy crosslinking agent. The emulsion skeleton in the modified acrylic emulsion is mainly composed of acrylic ester monomers, which gives the adhesive good film-forming properties and flexibility; the introduction of acrylic acid can retain an appropriate amount of carboxylic acid groups, which is beneficial to the subsequent cross-linking reaction; at the same time, the unsaturated phosphonic acid further introduced copolymerizes to form a main chain structure during the polymerization process, and its phosphonic acid group has excellent metal affinity, which can form coordination bonds and hydrogen bond adsorption with metal oxides or exposed metal sites on the metal surface through P=O and P-OH functional groups in the early stage of film formation, thereby enhancing the in-situ anchoring ability of the coating to the metal interface. Due to the high polarity of the phosphonic acid group in the molecule, it spontaneously enriches on the metal surface during the film formation process, thereby forming a polar functional group aggregation area at the interface; Polyvinyl alcohol, as a highly polar linear polymer, forms a synergistic network structure with the emulsion system, which not only enhances the initial wettability and film-forming uniformity of the coating on the metal surface, but also provides abundant hydroxyl groups, which is beneficial for subsequent cross-linking and improving interfacial adsorption stability. The trifunctional epoxy crosslinker undergoes a ring-opening reaction with the residual carboxyl or hydroxyl groups in the emulsion and polyvinyl alcohol during the hot pressing process to form a spatial cross-linked network structure, which allows the film layer to further solidify and shape after forming initial adhesion, thereby improving the shear strength and stability of the coating under actual packaging conditions such as hot pressing and high humidity.

[0009] The second component is an independently added aqueous solution of divalent metal ions, which can be introduced into the wet film by spraying in the wet film state after the first component is applied. The divalent metal ions use the aqueous phase in the coating as a diffusion medium and migrate from the film surface to the metal interface under the guidance of the polarity gradient formed by the phosphonic acid groups. 2+) When it approaches the metal interface, on the one hand, it can form a complex with the phosphonic acid groups in the polymer chain segment through coordination, thereby enriching the divalent metal ions near the metal interface; on the other hand, the divalent metal ions can undergo Lewis acid-base coordination reaction with the hydroxyl or oxygen anion groups in the oxide layer (such as Al2O3, Fe2O3, etc.) naturally formed on the surface of the metal substrate, forming M 2+ -O type coordination anchor point, to build a stable surface complex structure. Therefore, one end of the phosphonic acid group is connected to M 2+ Forming a coordination structure, the other end is connected to the polymer chain segment, M 2+ Can coordinate and adsorb with the metal surface, thus 2+ The phosphonic acid groups are stably anchored to the polymer chain segments in the binder, thereby enhancing the effective retention and adsorption capacity of the polymer chain segments at the metal interface and improving the overall interface adhesion and structural stability.

[0010] Therefore, the phosphonic acid groups in the first component complete the interface fixation through early adsorption and chain segment enrichment at the metal interface, and the divalent metal ions in the second component subsequently migrate to complete the interface fixation. The two work together to build a stable anchoring structure on the metal surface; at the same time, PVA and the cross-linker construct a controllable film-forming and spatial stabilization mechanism for the overall structure, thereby effectively improving the interface adhesion and structural stability in metal-non-metal composite materials.

[0011] In some embodiments, the modified acrylic ester emulsion is prepared by the following method: 50 parts of butyl acrylate, 25-35 parts of ethyl acrylate, 5-10 parts of acrylic acid, 2-4 parts of unsaturated phosphonic acid, 1-3 parts of sodium lauryl sulfate and 0.5-1 part of ammonium persulfate are reacted in 50-70 parts of water under a nitrogen atmosphere at 70-80° C. for 2-4 hours to obtain the modified acrylic ester emulsion.

[0012] In some of the aforementioned embodiments, the components and conditions of the preparation method synergistically construct a high-performance emulsion adhesive matrix with uniform structure and metal anchoring capabilities. Butyl acrylate, as the primary film-forming monomer, provides good flexibility and film-forming continuity, while ethyl acrylate assists in regulating the cohesive strength and intermolecular forces of the adhesive layer, providing both rigidity and film-forming speed. Acrylic acid, as a hydrophilic monomer, introduces a certain amount of carboxylic acid groups, which react synergistically with the trifunctional epoxy crosslinker during the drying and hot pressing processes to construct an internal crosslinked network within the adhesive, contributing to improved shear strength and durability of the film-forming structure.

[0013] In particular, unsaturated phosphonic acid is copolymerized with the aforementioned monomers into the main chain during polymerization, imparting a controlled distribution of phosphonic acid groups to the emulsion polymer. These phosphonic acid groups not only enhance the binder's initial adsorption to the metal surface but also spontaneously migrate to the metal interface during film formation. They also serve as guides and anchors for the subsequent divalent metal ion spraying, making them key structural units that enhance the binder's adhesion and stability.

[0014] The polymerization process is controlled at 70-80°C under nitrogen protection, ensuring uniform free radical reaction and monomer conversion efficiency, effectively inhibiting hydrolysis and side polymerization of phosphonic acid monomers and maintaining their effective structure. The water content is controlled at 50-70 parts per million to maintain moderate system viscosity and promote emulsion stability.

[0015] Compared with the traditional emulsion binder composed only of acrylate and carboxylic acid monomers, the introduction of unsaturated phosphonic acid as a cooperative monomer can achieve the phosphonic acid group and M 2+ The triple coordination bridge on the metal surface significantly improves the adhesion performance of the film-forming interface layer while maintaining good workability and film continuity.

[0016] In some embodiments, the unsaturated phosphonic acid comprises ethylene glycol methacrylate phosphonate.

[0017] In some of the above embodiments, ethylene glycol methacrylate phosphonate (EGMP) is used as an unsaturated phosphonic acid. On the one hand, it contains a methacrylic acid-type double bond, has high polymerization activity, and has a free radical initiation efficiency that is superior to that of an allyl structure. It can be more stably and fully grafted into the polymer backbone during the emulsion polymerization process, thereby ensuring that the phosphonic acid groups are evenly distributed throughout the polymer and the dosage is controllable, effectively avoiding the problem of low polymerization efficiency of common phosphonic acid monomers. On the other hand, the structure also introduces an ethylene glycol bridge segment as a flexible connecting unit, which gives the phosphonic acid functional group appropriate spatial ductility and conformational freedom, which is beneficial for it to obtain a better coordination configuration when it is enriched at the metal interface during the film formation process, making it easier to achieve M with the metal oxide surface or subsequent migration to the interface. 2+ The multidentate coordination and bridging adsorption between them improve the interface anchoring efficiency and stability.

[0018] Therefore, ethylene glycol methacrylate phosphonate not only has good copolymerization activity and uniform distribution in the emulsion system, but also has better spatial adaptation and coordination capabilities than other unsaturated phosphonic acids with stronger structural rigidity, which can further improve the interfacial adhesion and structural stability in metal-non-metal composite materials.

[0019] In some embodiments, the divalent metal ion aqueous solution includes a zinc ion aqueous solution, and the concentration of zinc ions in the zinc ion aqueous solution is 0.05-0.2 mol / L.

[0020] In some of the above embodiments, Zn 2+ As a divalent metal ion, compared with the common Ca 2+ Mg 2+ 、Fe 2+ Cations such as Zn have higher coordination activity and more stable surface complexing ability. 2+ The ionic radius is moderate, the charge density is high, and it has good Lewis acidity, which can react with phosphonic acid groups and hydroxyl groups / O - The groups form a multi-point coordination structure and collaboratively build a stable anchoring network.

[0021] In contrast, Ca 2+ Mg 2+ Due to its weak polarization ability, the coordination effect between the plasma and the phosphonic acid group or the oxygen group on the metal surface is not significant, making it difficult to form an effective anchoring structure in the interface area, thereby reducing the auxiliary adsorption efficiency; Fe 2+ Although plasma has certain coordination ability, it is easily oxidized or undergoes valence change reaction in an aqueous environment, and has poor stability, which is not conducive to the long-term maintenance of the adhesive interface performance.

[0022] At the same time, Zn 2+ The concentration is controlled in the range of 0.05~0.2 mol / L, which can ensure sufficient Zn 2+ Participate in coordination anchoring, and avoid problems such as ion accumulation and complex imbalance in the emulsion system caused by excessively high concentrations. 2+ It can migrate uniformly to the metal interface in the wet film and coordinate synergistically with the phosphonic acid groups to form a structurally stable anchoring region, thereby further improving the interfacial adhesion and structural stability in metal-non-metal composites.

[0023] In some embodiments, the zinc ion aqueous solution further comprises polyethylene glycol having a weight average molecular weight of 200-600, and the mass percentage of the polyethylene glycol in the zinc ion aqueous solution is 0.1%-0.3%.

[0024] In some of the above embodiments, the introduction of low molecular weight polyethylene glycol (PEG) into the zinc ion aqueous solution can further optimize the Zn 2+ Diffusion behavior and interface anchoring path in the adhesive wet film. The molecular structure of PEG400 contains repeated ether oxygen units, which have certain coordination ability and can 2+ A dynamically reversible complex is formed, thereby improving the dispersion stability of zinc ions in the aqueous phase and inhibiting ion aggregation or crystallization precipitation.

[0025] Compared with the aqueous phase without PEG, PEG can make Zn 2+It exists in the surface of the coating in a stable and mobile complex state, which is conducive to the smooth penetration into the metal interface area under the action of the polarity gradient; when approaching the metal surface, PEG and Zn 2+ The complex between them can be dynamically dissociated to release Zn 2+ Participating in the interface anchoring, it reduces the premature adsorption or retention of zinc ions inside the film layer, allowing them to be efficiently enriched at the interface and assist in building a stable anchoring layer. In addition, PEG, as a medium-polarity fluidity additive, can further improve the spreadability of the spray liquid and the wetting properties of the metal surface during the spraying process, helping Zn 2+ Rapid spreading and uniform penetration on the interface further improve the uniformity and stability of interfacial bonding.

[0026] Therefore, the introduction of low molecular weight polyethylene glycol into the zinc ion aqueous solution not only improves the 2+ The migration efficiency in the wet film also optimizes the stability and consistency of the spraying operation, thereby further improving the interfacial adhesion and structural stability in metal-non-metal composites.

[0027] In some embodiments, the weight-average molecular weight of the polyvinyl alcohol (PVA) is between 30,000 and 80,000. Based on these embodiments, controlling the molecular weight of the polyvinyl alcohol (PVA) within this range facilitates the formation of a network structure with a certain degree of linear chain entanglement during the emulsion film-forming process. On the one hand, the higher molecular weight of PVA can enhance the initial adhesion of the binder to the metal surface and the continuity of the coating, improving interfacial wettability and mechanical adhesion. On the other hand, its abundant and evenly distributed hydroxyl groups facilitate subsequent reaction with the epoxy crosslinker to form a spatially crosslinked structure, enhancing the overall strength and thermal hydrolysis stability of the coating. This improves the interfacial adhesion and structural stability of the metal-nonmetal composite material.

[0028] In some embodiments, the trifunctional epoxy crosslinking agent includes at least one of glycerol triglycidyl ether and triglycidyl isocyanurate. Based on the above embodiment, the trifunctional epoxy crosslinking agent can undergo a ring-opening addition reaction with the residual carboxyl groups in the emulsion and the hydroxyl groups in the PVA to form a three-dimensional crosslinked network structure.

[0029] In some embodiments, the raw materials of the first component also include water, and the solid content of the first component is 30% to 40%. Based on the above embodiment, by controlling the solid content of the first component within the range of 30% to 40%, it is possible to ensure the effective film-forming and structural coverage of the polymer component while avoiding the problems of insufficient fluidity or uneven construction under high solid content conditions. In particular, during the divalent metal ion spraying and subsequent interface migration stages, the appropriate water content can provide the necessary diffusion channels and film-forming buffer time, ensuring that the divalent metal ions can smoothly migrate to the interface and participate in coordination anchoring, while preventing the film layer from solidifying too quickly, resulting in ion retention or a decrease in anchoring efficiency.

[0030] In a second aspect, the present application provides a method for preparing a metal adhesive for a packaging box, comprising: Providing raw materials for the first component of the metal binder according to any embodiment of the first aspect, and mixing them to obtain the first component; An aqueous solution of divalent metal ions as the second component in the metal binder according to any embodiment of the first aspect is provided.

[0031] According to the present application, the preparation method is based on the dual-component structure of the metal binder. By preparing the first component and the second component in steps, the structural optimization of film-forming performance and interface anchoring ability can be achieved respectively. On the one hand, the first component, as the main film-forming body, adopts a synergistic ratio of polymer emulsion, polar polymer and cross-linking agent to construct a wet film structure with good wettability, structural stability and functional group directional enrichment ability, providing diffusion channels and anchoring points for subsequent metal ion migration; on the other hand, the second component is an independently prepared metal ion aqueous solution, and its composition can be flexibly controlled, avoiding the pre-polymerization reaction or coordination loss between the metal ions and the emulsion or cross-linking components in the main agent during the preparation stage, thereby improving the system's stability and operating window.

[0032] This method can ensure the functional integrity of key structural units in metal adhesives. The two-component metal adhesive can be optimized with adhesive interface anchoring mechanism and overall structural strength through step-by-step coating and spraying, and is suitable for high adhesion and high stability bonding requirements in industrial composite packaging applications.

[0033] In a third aspect, the present application provides a packaging material comprising: a metal substrate, a non-metallic substrate, and an adhesive layer formed between the metal substrate and the non-metallic substrate, the adhesive comprising the metal adhesive described in any embodiment of the first aspect or the metal adhesive prepared by the method described in any embodiment of the second aspect.

[0034] According to the present application, the packaging material structure achieves stable bonding between the metal substrate and the non-metallic substrate by introducing a bonding layer formed by the metal binder between the two substrates. Through the polar enrichment behavior of the phosphonic acid group and the interface-assisted anchoring mechanism of the divalent metal ions, the binder can form a stable multi-point coordinated adsorption structure on the metal surface, significantly enhancing the adhesion strength of the bonding layer at the interface. Furthermore, the synergistic crosslinking network constructed by PVA and the trifunctional epoxy crosslinker can achieve overall film-forming stability and hot-pressing adaptability of the film layer, thereby ensuring that the bonding structure has excellent mechanical retention and environmental tolerance during subsequent packaging processes such as lamination, die-cutting, and hot pressing.

[0035] This structure is particularly suitable for multi-layer packaging materials with aluminum foil, stainless steel sheets, etc. as metal layers and paper, PET film, polyamide, etc. as non-metallic layers. It is widely used in high-end packaging application scenarios that need to meet barrier properties, mechanical strength and decorative properties at the same time.

[0036] In a fourth aspect, the present application provides a method for preparing a packaging material, comprising: Providing the metal adhesive according to any embodiment of the first aspect or the metal adhesive prepared according to the method of any embodiment of the second aspect; Applying the first component of the metal binder on the surface of the metal substrate to form a wet coating layer, spraying the second component of the metal binder onto the wet coating layer, and drying to form a coating layer; The non-metallic substrate is attached to the coating layer, and the metal substrate and the non-metallic substrate are bonded by a metal adhesive through hot pressing.

[0037] According to the present application, the preparation method can guide the distribution, positioning and anchoring structure construction of the functional components of the binder on the metal surface by first coating the first component of the metal binder and then spraying the second component. The first component acts as the main bonding layer, forming a polar coating containing phosphonic acid groups and hydroxyl groups on the metal surface, which has good wettability and interfacial adsorption foundation; the divalent metal ions in the second component, in the wet film state, use the water phase as a diffusion medium, and migrate directionally from the film surface to the metal interface under the action of the polarity gradient formed by the phosphonic acid groups, and coordinate with the phosphonic acid groups in the interface area to synergistically construct a stable anchoring structure.

[0038] In this application, the second component is sprayed after the first component is applied to ensure that the divalent metal ions can penetrate into the metal interface area along the polar functional group guide, thereby completing directional anchoring. If the second component is pre-applied to the metal surface and then the first component is overcoated, due to the high water content of the first component and the uniform distribution of phosphonic acid groups in the first component, the divalent metal ions diffuse into the coating and complex with the phosphonic acid groups under the drive of the concentration gradient, so that the phosphonic acid groups and the divalent metal ions are more easily fixed in the film layer, rather than enriched near the metal interface, thereby affecting the overall interface adhesion.

[0039] After spraying, divalent metal ions on the surface penetrate directionally due to concentration and polarity gradients, becoming complexed and enriched by phosphonic acid groups near the metal interface. During the hot-press lamination stage, crosslinking reactions in the coating proceed simultaneously with interfacial curing, forming a spatially stable adhesive structure. The resulting packaging material offers strong interlayer bonding and adhesion, making it suitable for metal-non-metal composite packaging structures requiring high bonding reliability.

[0040] In some embodiments, the coating amount of the first component is 10-20 g / m 2 The spraying amount of the second component is 0.5~2mL / m 2 .

[0041] In some of the above embodiments, the coating amount of the first component is controlled to be 10-20 g / m 2 , can form a wet film structure of moderate thickness on the surface of the metal substrate, on the one hand, to ensure that the polar groups and functional components in the binder can be fully distributed and evenly formed into a film, on the other hand, to avoid the film layer being too thick to cause M 2+ The migration path is extended and the interface anchoring efficiency is reduced.

[0042] At the same time, the spraying amount of the second component is controlled at 0.5~2mL / m 2 The spraying amount is too low, which will lead to insufficient zinc ion content and unclear bonding enhancement effect. The spraying amount is too high, which may cause local dilution of the emulsion system, thereby affecting the density of the bonding layer and the uniformity of film formation.

[0043] Therefore, the above coating and spraying amounts are helpful to achieve a metal-non-metal bonding structure with high adhesion and high reliability under actual industrial process conditions.

[0044] In some embodiments, the interval between applying the first component and spraying the second component is 0.5 to 2 minutes. Based on the above embodiment, this interval allows the phosphonic acid groups in the first component to adsorb to the metal interface, thereby forming a polarity gradient, which facilitates the diffusion and enrichment of divalent metal ions to the metal interface. It also prevents the formation of a dry membrane shell on the wet membrane surface, which can affect the penetration of divalent metal ions.

[0045] In some embodiments, the drying conditions include drying at 20-30°C for 2-5 minutes, followed by hot air drying at 50-70°C for 10-15 minutes. Based on the above embodiments, the initial standing at room temperature facilitates the directional migration of divalent metal ions; the subsequent heating and drying process promotes rapid film formation of the emulsion and initially stabilizes the film structure, preventing premature reaction of the crosslinker or excessive flow of the wet film, thereby ensuring uniform film formation and structural stability.

[0046] In some embodiments, the hot pressing conditions include hot pressing at 110-130°C and 0.2-0.4 MPa for 5-15 seconds. Based on the above embodiment, this temperature and pressure can activate the trifunctional epoxy crosslinker to undergo a ring-opening crosslinking reaction with residual hydroxyl and carboxyl groups in the film layer without damaging the metal or non-metal substrate, thereby constructing a spatially crosslinked network structure. Simultaneously, the closed compaction effect of the hot pressing process further enhances the density of the bonding layer, thereby significantly improving the interfacial stability of the metal-non-metal structure during subsequent processing and use.

[0047] Compared with the prior art, the present invention has the following advantages: 1. By introducing unsaturated phosphonic acid monomers to construct a modified acrylic emulsion with phosphonic acid groups, the initial adsorption capacity and interfacial anchoring strength of the adhesive on the metal substrate surface are significantly improved; 2. Using divalent metal ions as interfacial synergistic components, they are induced to migrate to the metal interface under the drive of polarity gradient by post-spraying, forming a stable multi-point coordination anchoring structure with phosphonic acid groups and metal surface, thus enhancing metal adhesion; 3. Polyvinyl alcohol and trifunctional epoxy crosslinking agent are used to synergistically construct a spatial crosslinking network to improve the film density and structural stability of the film layer. The adhesive layer maintains good mechanical properties under complex conditions such as hot pressing and high humidity. 4. Through the two-component structure and step-by-step coating process, the component enrichment behavior and interface positioning effect of the adhesive can be regulated, overcoming the problems of weak interface adsorption and easy detachment of the adhesive layer of traditional adhesives, and achieving higher interface adhesion strength and composite stability. DETAILED DESCRIPTION

[0048] The various embodiments or implementation schemes in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments.

[0049] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with an embodiment or example is included in at least one embodiment or example of the present application. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0050] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. Throughout the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0051] In the description of this specification, unless otherwise specified, "parts" refer to "parts by mass".

[0052] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0053] Ethylene glycol methacrylate phosphonate, CAS No. 24599-21-1; Vinylphosphonic acid, CAS No. 1746-03-8.

[0054] Preparation Example 1 Preparation of modified acrylic emulsion: 50 parts of butyl acrylate, 30 parts of ethyl acrylate, 7 parts of acrylic acid, and 3 parts of ethylene glycol methacrylate phosphonate were uniformly mixed to obtain 90 parts of a monomer premix solution for later use; 0.8 parts of ammonium persulfate was dissolved in 10 parts of water to obtain 10.8 parts of an initiator solution for later use; 50 parts of water and 2 parts of sodium lauryl sulfate were added to a reactor, stirred and heated to 75°C, 9 parts of monomer premix and 2 parts of initiator solution were added under a nitrogen atmosphere, and the mixture was reacted at 75°C for 15 minutes to obtain seed latex particles, 81 parts of monomer premix and 8.8 parts of initiator solution were simultaneously added dropwise to the reaction within 1 hour, and the temperature of the reactor was maintained at 75°C during the addition. After the addition was completed, the mixture was kept warm for 2 hours and cooled to room temperature to obtain modified acrylate emulsion A.

[0055] Preparation Example 2 The modified acrylate emulsion B was obtained in a manner substantially the same as that in Preparation Example 1, except that vinylphosphonic acid was used instead of ethylene glycol methacrylate phosphonate.

[0056] Comparative Preparation Example 1 Preparation of modified acrylic emulsion: 50 parts of butyl acrylate, 30 parts of ethyl acrylate, and 10 parts of acrylic acid were mixed to obtain 90 parts of a monomer premix solution for later use; 0.8 parts of ammonium persulfate was dissolved in 10 parts of water to obtain 10.8 parts of an initiator solution for later use; 50 parts of water and 2 parts of sodium lauryl sulfate were added to a reactor, stirred and heated to 75°C, 9 parts of monomer premix and 2 parts of initiator solution were added under a nitrogen atmosphere, and the mixture was reacted at 75°C for 15 minutes to obtain seed latex particles, 81 parts of monomer premix and 8.8 parts of initiator solution were simultaneously added dropwise to the reaction within 1 hour, and the temperature of the reactor was maintained at 75°C during the addition. After the addition was completed, the mixture was kept warm for 2 hours and cooled to room temperature to obtain modified acrylate emulsion C.

[0057] Comparative Preparation Example 2 Preparation of modified acrylic emulsion: 50 parts of butyl acrylate, 30 parts of ethyl acrylate, and 10 parts of ethylene glycol methacrylate phosphonate were uniformly mixed to obtain 90 parts of a monomer premix solution for later use; 0.8 parts of ammonium persulfate was dissolved in 10 parts of water to obtain 10.8 parts of an initiator solution for later use; 50 parts of water and 2 parts of sodium lauryl sulfate were added to a reactor, stirred and heated to 75°C, 9 parts of monomer premix and 2 parts of initiator solution were added under a nitrogen atmosphere, and the mixture was reacted at 75°C for 15 minutes to obtain seed latex particles, 81 parts of monomer premix and 8.8 parts of initiator solution were simultaneously added dropwise to the reaction within 1 hour, and the temperature of the reactor was maintained at 75°C during the addition. After the addition was completed, the mixture was kept warm for 2 hours and cooled to room temperature to obtain modified acrylate emulsion D.

[0058] Example 1

[0059] Preparation of metal adhesive for packaging boxes: 50 parts of modified acrylic emulsion A, 7 parts of polyvinyl alcohol with a weight-average molecular weight of about 50,000, and 2 parts of propylene glycol triglycidyl ether were mixed evenly, and then diluted with water to a solid content of 35 wt % to obtain a first component; PEG400 and zinc chloride were dissolved in water to obtain a second component, wherein the zinc ion concentration was 0.1 mol / L and the mass percentage content of PEG400 was 0.2%.

[0060] Preparation of metal-non-metal composite packaging materials: Take a clean and dry aluminum foil (thickness of 20μm) as the metal substrate, and use an anilox roller to evenly coat the first component on its surface with a coating amount of 15g / m 2 , forming a wet coating film; After the first component is applied, let it stand for 1 minute, then use an aerosol spray gun to spray the second component onto the wet film surface with a spraying volume of 1mL / m 2 , so that the surface is evenly moistened; After spraying, let it stand at room temperature (about 25°C) for 3 minutes, then place it in a 60°C forced air oven to dry for 10 minutes to complete the initial film formation and structural curing; Place a piece of coated paper (surface density of about 180g / m 2 ) is laid on the surface of the dried film layer and hot pressed in a hot press at 120℃ and 0.3MPa pressure for 10s to make the paper and the aluminum foil substrate firmly adhere to each other. After cooling, the metal-non-metal composite packaging material is obtained.

[0061] Example 2

[0062] Preparation of metal adhesive for packaging boxes: The process is substantially the same as Example 1, except that modified acrylate emulsion B is used instead of modified acrylate emulsion A in the first component.

[0063] Preparation of metal-non-metal composite packaging materials: It is substantially the same as Example 1, except that the metal binder prepared in Example 2 is used.

[0064] Example 3

[0065] Preparation of metal adhesive for packaging boxes: The process is substantially the same as Example 1, except that calcium chloride is used instead of zinc chloride in the second component.

[0066] Preparation of metal-non-metal composite packaging materials: It is substantially the same as Example 1, except that the metal binder prepared in Example 3 is used.

[0067] Example 4

[0068] Preparation of metal adhesive for packaging boxes: The process is substantially the same as Example 1, except that magnesium chloride is used instead of zinc chloride in the second component.

[0069] Preparation of metal-non-metal composite packaging materials: It is substantially the same as Example 1, except that the metal binder prepared in Example 4 is used.

[0070] Example 5

[0071] Preparation of metal adhesive for packaging boxes: The process is substantially the same as Example 1, except that ferrous chloride is used in place of zinc chloride in the second component.

[0072] Preparation of metal-non-metal composite packaging materials: The process is substantially the same as Example 1, except that the metal binder prepared in Example 5 is used.

[0073] Example 6

[0074] Preparation of metal adhesive for packaging boxes: The process is substantially the same as Example 1, except that PEG400 is not added to the second component.

[0075] Preparation of metal-non-metal composite packaging materials: The process is substantially the same as Example 1, except that the metal binder prepared in Example 6 is used.

[0076] Comparative Example 1 Preparation of metal adhesive for packaging boxes: The process is substantially the same as Example 1, except that modified acrylate emulsion C is used instead of modified acrylate emulsion A in the first component.

[0077] Preparation of metal-non-metal composite packaging materials: The process is substantially the same as Example 1, except that the metal binder prepared in Comparative Example 1 is used.

[0078] Comparative Example 2 Preparation of metal adhesive for packaging boxes: The process is substantially the same as Example 1, except that modified acrylate emulsion D is used instead of modified acrylate emulsion A in the first component.

[0079] Preparation of metal-non-metal composite packaging materials: The process is substantially the same as Example 1, except that the metal binder prepared in Comparative Example 2 is used.

[0080] Comparative Example 3 Preparation of metal adhesive for packaging boxes: 50 parts of modified acrylic emulsion A, 7 parts of polyvinyl alcohol with a weight average molecular weight of about 50,000 and 2 parts of propylene glycol triglycidyl ether were mixed evenly, and then diluted with water to a solid content of 35 wt % to obtain a metal adhesive.

[0081] Preparation of metal-non-metal composite packaging materials: Take a clean and dry aluminum foil (thickness of 20μm) as the metal substrate, and use an anilox roller to evenly coat the metal adhesive on its surface with a coating amount of 15g / m 2 , forming a wet coating film; After coating, let it stand at room temperature (about 25°C) for 3 minutes, then place it in a 60°C forced air oven to dry for 10 minutes to complete the initial film formation and structural curing; Place a piece of coated paper (surface density of about 180g / m 2 ) is laid on the surface of the dried film layer and hot pressed in a hot press at 120℃ and 0.3MPa pressure for 10s to make the paper and the aluminum foil substrate firmly adhere to each other. After cooling, the metal-non-metal composite packaging material is obtained.

[0082] Test section The 180° peel strength σ (kN / m) between the metal material and the non-metallic material in the metal-non-metal composite packaging materials obtained in each embodiment and comparative example was tested with reference to GB / T 2790-1995 "Test method for 180° peel strength of adhesives - Flexible material to rigid material". The results are shown in Table 1, specifically including: Cut the test sample into strips of 25 mm × 200 mm, with the peeling direction along the length of the composite material; Fix the metal substrate on the tensile testing machine and peel the paper end backward in a 180° direction; The test speed was set to 100 mm / min, and the average value of the stable tension section during the peeling process was recorded; Three specimens were tested in each group and the average value was taken in kN / m.

[0083] Table 1

[0084] According to Table 1, each embodiment shows a higher 180° peel strength than Comparative Examples 1 to 3, indicating that the metal adhesive provided by the present application constructs a more stable interface anchoring structure between the metal and the non-metallic substrate, significantly improving the interface adhesion and bonding strength. The possible reasons are: in Comparative Example 1, the modified acrylic emulsion does not introduce a phosphonic acid group, lacks an effective coordination adsorption mechanism for the metal substrate, resulting in insufficient anchoring ability of the adhesive at the metal interface and low peel strength; in Comparative Example 2, although an unsaturated phosphonic acid monomer is used, a monomer containing a carboxylic acid functional group such as acrylic acid is not introduced, and the system lacks sufficient polar segments and cross-linking sites, resulting in insufficient film density and stability, and excessive phosphonic acid group content may induce interchain association, which is not conducive to the anchoring of the phosphonic acid group at the metal interface, resulting in low peel strength; in Comparative Example 3, the second component is not used, thereby lacking the interface coordination adsorption mechanism induced by divalent metal ions, and the interface anchoring ability is weak, relying only on the initial adsorption of the phosphonic acid group, resulting in low peel strength.

[0085] Examples 1 and 2 show that modified acrylate emulsions obtained using different types of unsaturated phosphonic acids have a certain impact on the bonding performance of metal adhesives. Changing only the structure of the unsaturated phosphonic acid, using ethylene glycol methacrylate phosphonate, yielded the highest peel strength. This suggests that ethylene glycol methacrylate phosphonate, due to its excellent polymerization activity and spatial configuration flexibility, can more effectively graft onto the backbone and achieve targeted coordination enrichment, thereby forming a stronger interfacial anchoring network.

[0086] According to the comparison between Example 1 and Examples 3 to 5, it can be seen that the use of different types of divalent metal ions has a certain influence on the bonding performance of the metal adhesive. 2+ Due to its moderate charge density, stable Lewis acidity and good coordination structure adaptability, it can effectively synergistically complex with phosphonic acid groups and metal oxide interfaces; while other ions have weak coordination ability or poor chemical stability, making it difficult to form a stable anchoring structure.

[0087] According to the comparison between Example 1 and Example 6, whether PEG is added to the second component has a certain influence on the bonding performance of the metal adhesive. When PEG400 is not added, the peel strength drops to 1.73 kN / m, indicating that PEG400 can form Zn in the spray liquid. 2+ The complex improves its migration ability and distribution uniformity, which helps Zn 2+ Stable diffusion in the film layer to the interface, thereby improving the final interface adhesion.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A metal adhesive for packaging boxes, characterized in that: The method comprises a first component and a second component, wherein the first component comprises the following raw materials in parts by weight: 50 parts of modified acrylic emulsion, 5-10 parts of polyvinyl alcohol, 1-3 parts of trifunctional epoxy crosslinking agent; The modified acrylate emulsion is obtained by emulsion polymerization of acrylate, acrylic acid and unsaturated phosphonic acid in the presence of an emulsifier and an initiator; The second component includes an aqueous solution of divalent metal ions.

2. The metal adhesive according to claim 1, characterized in that The modified acrylate emulsion is prepared by the following method: 50 parts of butyl acrylate, 25-35 parts of ethyl acrylate, 5-10 parts of acrylic acid, 2-4 parts of unsaturated phosphonic acid, 1-3 parts of sodium lauryl sulfate and 0.5-1 part of ammonium persulfate are reacted in 50-70 parts of water at 70-80° C. under a nitrogen atmosphere for 2-4 hours to obtain a modified acrylate emulsion.

3. The metal adhesive according to claim 2, characterized in that The unsaturated phosphonic acid includes ethylene glycol methacrylate phosphonate.

4. The metal adhesive according to claim 1, characterized in that The divalent metal ion aqueous solution includes a zinc ion aqueous solution, and the concentration of zinc ions in the zinc ion aqueous solution is 0.05-0.2 mol / L.

5. The metal adhesive according to claim 4, characterized in that The zinc ion aqueous solution further comprises polyethylene glycol with a weight average molecular weight of 200-600, and the mass percentage of the polyethylene glycol in the zinc ion aqueous solution is 0.1%-0.3%.

6. The metal adhesive according to any one of claims 1 to 5, characterized in that The metal binder satisfies at least one of the following conditions: 1) The weight average molecular weight of the polyvinyl alcohol is 30,000 to 80,000; 2) the trifunctional epoxy crosslinking agent comprises at least one of glycerol triglycidyl ether and isocyanuric acid triglycidyl ester; 3) The raw materials of the first component also include water, and the solid content of the first component is 30% to 40%.

7. A method for preparing a metal adhesive for a packaging box, characterized in that: include: Providing raw materials for the first component of the metal adhesive according to any one of claims 1 to 6, and mixing them to obtain the first component; Provided is a divalent metal ion aqueous solution as the second component in the metal binder according to any one of claims 1 to 6.

8. A packaging material, characterized in that: include: A metal substrate, a non-metal substrate and a metal binder according to any one of claims 1 to 6 or a metal binder arranged between the metal substrate and the non-metal substrate The bonding layer formed by the metal adhesive prepared according to the method of claim 7.

9. A method for preparing a packaging material, characterized in that: include: Provide the metal adhesive according to any one of claims 1 to 6 or The metal binder prepared by the method according to claim 7; Applying the first component of the metal binder on the surface of the metal substrate to form a wet coating layer, spraying the second component of the metal binder onto the wet coating layer, and drying to form a coating layer; The non-metallic substrate is attached to the coating layer, and the metal substrate and the non-metallic substrate are bonded by a metal adhesive through hot pressing.

10. The method according to claim 9, characterized in that The coating amount of the first component is 10~20g / m 2 The spraying amount of the second component is 0.5~2mL / m 2 .

Images