A coating for easy-open lids with excellent processability and its preparation method

Abstract

This invention discloses a coating for the outer wall of an easy-open lid with excellent processability and its preparation method. The coating is composed of film-forming monomer composition, processability modifier, crosslinking curing agent, lubricant, wear-resistant agent, adhesion promoter, polydimethylsiloxane, and propylene glycol methyl ether acetate. The processability modifier uses hexagonal boron nitride as a reinforcing core and is obtained through silica anchoring, phosphorus-nitrogen-zirconium complexation, silane coupling, acrylate grafting, and low-friction lubrication coating treatment. In the preparation process, the film-forming monomer is first prepolymerized, then the processability modifier is added, dispersed, and ground. Crosslinking, lubricating, wear-resistant, and adhesion-promoting components are then compounded, and the viscosity is adjusted before filtration to obtain the finished product. This coating forms a uniform film, adheres firmly, has good scratch resistance and adaptability to edge curling, and is suitable for protective coating of the outer wall of easy-open lids.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically relating to a coating for easy-open lids with excellent processability and its preparation method. Background Technology

[0002] Easy-open lid coatings refer to functional coating materials applied to the outer surface of aluminum or tin-plated easy-open lids, widely used in metal packaging for beverages, food, and canned goods. These coatings typically require multiple processing steps, including coating, baking, printing, stamping, riveting, engraving, flanging, and rolling, maintaining good appearance integrity, adhesion stability, abrasion resistance, and processing adaptability during transportation, stacking, and use. As metal packaging evolves towards high-speed prototyping, lightweighting, refined appearance, and multi-scenario applications, easy-open lid coatings with good film-forming properties, processability, and surface smoothness are receiving increasing attention.

[0003] Existing easy-open can exterior coatings typically use acrylic resin, polyester resin, or epoxy-modified resin as the main film-forming agent, combined with amino resin crosslinking agents, lubricants, wear-resistant fillers, leveling agents, and adhesion promoters to form the coating film. After baking and curing, these coatings can form a continuous protective film on the metal substrate surface, meeting general decorative, protective, and printing compatibility requirements. However, in actual processing, the easy-open can exterior coating is subjected to a combination of bending, stretching, stamping, friction, and edge curling. A good balance needs to be maintained between the coating's flexibility, substrate adhesion, scratch resistance, low friction, and surface integrity. Inorganic wear-resistant fillers can improve the coating's surface hardness and scratch resistance, lubricants can reduce surface friction resistance, and crosslinking curing agents can improve film density and post-processing adhesion stability. The compatibility, distribution, and interfacial bonding of these components affect the coating's dispersion uniformity and film continuity.

[0004] In existing technologies, to improve the processing adaptability and wear resistance of easy-open can outer wall coatings, methods such as improving resin flexibility, adding wax powder or fatty amide lubricants, introducing silica or alumina wear-resistant fillers, and adding silane coupling agents or phosphate ester adhesion promoters are commonly used. However, most of these methods involve single-component modification or simple physical compounding, with limited interfacial bonding and structural synergy between functional components. When the compatibility between inorganic fillers and the resin matrix is ​​insufficient, or when the lubricating components are unevenly distributed in the coating, phenomena such as particle agglomeration, localized stress concentration in the coating film, surface scratches, cracking at the edges, coating peeling, or fluctuations in the coefficient of friction can easily occur, affecting its application in high-speed easy-open can processing and high-quality packaging materials. Therefore, developing an easy-open can outer wall coating system that combines interfacial bonding, composite particle reinforcement, low-friction coating, cross-linking density, and coating continuity is of practical significance for improving the dispersion uniformity, interfacial compatibility, and overall coating processing performance of layered functional fillers in acrylic film-forming systems. Summary of the Invention

[0005] The purpose of this invention is to address the technical problems of existing easy-open can outer wall coatings, which are easily affected by combined stress and friction during high-speed stamping, bending, flanging, and edge rolling processes. This results in difficulties in simultaneously achieving processing integrity, adhesion stability, scratch resistance, and low-friction surface properties. The invention provides an easy-open can outer wall coating with excellent processing resistance and its preparation method. The aim is to improve the dispersion uniformity and interfacial compatibility of layered functional fillers in the acrylic film-forming system through the combination of processing modifiers, crosslinking curing agents, lubricants, wear-resistant agents, and adhesion promoters. This enhances the coating's adhesion, bending resistance, edge rolling integrity, scratch resistance, and low-friction stability during easy-open can processing and use.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A coating for the exterior of an easy-open lid with excellent processability, comprising, by weight, the following raw materials: 30-55 parts of film-forming monomer composition, 1-8 parts of processability modifier, 4-15 parts of crosslinking curing agent, 0.1-1.2 parts of dodecylbenzenesulfonic acid, 0.2-0.8 parts of azobisisobutyronitrile, 0.3-4 parts of lubricant, 0.5-5 parts of wear-resistant agent, 0.3-3 parts of adhesion promoter, 0.1-2 parts of polydimethylsiloxane, and 25-60 parts of propylene glycol methyl ether acetate; Furthermore, the processing modifier is composed of the following raw materials in parts by weight: 10-25 parts hexagonal boron nitride, 8-20 parts tetraethyl orthosilicate, 80-160 parts deionized water, 80-180 parts ethanol, 3-10 parts phytic acid, 1-5 parts zirconium oxychloride, 1-6 parts melamine, 3-9 parts 3-(trimethoxysilyl)propyl methacrylate, 1-5 parts 3-aminopropyltriethoxysilane, 4-12 parts n-butyl acrylate, 3-10 parts 2-hydroxyethyl acrylate, 2-8 parts methyl methacrylate, 0.2-1.2 parts ammonium persulfate, 2-8 parts ethylene bis-stearamide, 4-15 parts pentaerythritol tetrastearate, and 1-6 parts stearic acid.

[0007] Furthermore, the preparation method of the processing resistance modifier includes the following steps: S1. Add hexagonal boron nitride to a mixture of deionized water and ethanol, controlling the solid-liquid ratio of hexagonal boron nitride to the mixture to be 1:5-10. Adjust the pH to 8.5-10.5 with ammonia water, disperse at 1200-2000 r / min for 30-60 min, and then sonicate for 15-40 min to obtain a boron nitride dispersion.

[0008] S2. Under stirring conditions of 35-50℃ and 800-1500r / min, tetraethyl orthosilicate is added to the boron nitride dispersion at a dropping rate of 0.2-1.0g / min. After the addition is completed, the reaction continues for 2-5h to obtain a silica-anchored boron nitride dispersion.

[0009] S3. Prepare a phytic acid aqueous solution with a mass fraction of 5-20%, prepare a zirconium oxychloride aqueous solution with a mass fraction of 3-15%, prepare a melamine ethanol dispersion with a mass fraction of 3-12%, and add 3-(trimethoxysilyl)propyl methacrylate and 3-aminopropyltriethoxysilane to ethanol to form a silane mixture; first, add the phytic acid aqueous solution to the silica anchor obtained in step S2 at a dropping rate of 0.1-0.6 g / min. In the solidified boron nitride dispersion, the pH is adjusted to 4.0-6.0, and the mixture is stirred at 40-60℃ for 30-90 min. Then, zirconium oxychloride aqueous solution and melamine ethanol dispersion are added, and the mixture is reacted at 50-75℃ for 1-4 h. Then, the silane mixture is added to the system at a dropping rate of 0.2-0.8 g / min, the pH is adjusted to 7.5-9.5, and the mixture is reacted at 50-70℃ and 700-1200 r / min for 2-4 h to obtain the composite particle dispersion.

[0010] S4. Add n-butyl acrylate, 2-hydroxyethyl acrylate and methyl methacrylate to the composite particle dispersion obtained in step S3. After purging with nitrogen for 20-40 min, raise the temperature to 65-80℃. Prepare an aqueous solution of ammonium persulfate with a mass fraction of 2-10% and add it to the system at a dropping rate of 0.05-0.3 g / min. Perform in-situ grafting reaction at 65-80℃ and 600-1000 r / min for 2-5 h to obtain an acrylate-grafted composite particle dispersion.

[0011] S5. Ethylene bis-stearamide, pentaerythritol tetrastearate, and stearic acid are added to ethanol and pre-dispersed at 70-85℃ and 1200-2200 r / min for 20-60 min to form a lubricating component dispersion. Then, the acrylate grafted composite particle dispersion obtained in step S4 is added and adsorbed and coated at 70-85℃ for 1-3 h to obtain a low-friction coated composite dispersion. The low-friction coated composite dispersion is cooled to 25-40℃, washed 2-4 times with ethanol and deionized water, filtered, and the resulting filter cake is vacuum dried at 60-85℃ for 6-12 h. It is then pulverized and sieved through a 200-500 mesh sieve to obtain a processing modifier.

[0012] Furthermore, the film-forming monomer composition comprises at least one of methyl methacrylate, n-butyl acrylate, 2-hydroxyethyl acrylate, and methacrylic acid.

[0013] Furthermore, the crosslinking curing agent is composed of hexamethoxymethyl melamine and hexa-n-butyloxymethyl melamine in a mass ratio of 1-5:1.

[0014] Furthermore, the lubricant is at least one of stearamide and ethylene bis-stearamide.

[0015] Furthermore, the wear-resistant agent is composed of silicon dioxide, aluminum oxide and boron nitride in a mass ratio of 1-6:0.5-4:0.2-2.

[0016] Furthermore, the adhesion promoter is composed of ethyl dihydrogen phosphate, 3-glycidyl etheroxypropyltrimethoxysilane and tetrabutyl titanate in a mass ratio of 1-4:1-5:0.2-2.

[0017] This invention also provides a method for preparing a coating for the outer wall of an easy-open lid with excellent processability, comprising the following steps: A1. Weigh the film-forming monomer composition, azobisisobutyronitrile, and propylene glycol methyl ether acetate according to the mass ratio. Add the propylene glycol methyl ether acetate to the reaction vessel and heat to 75-85℃ under stirring at 500-900 r / min. Dissolve the azobisisobutyronitrile in the film-forming monomer composition to form a monomer initiation mixture with a mass concentration of 0.4-2.5%. Add the monomer initiation mixture to the reaction vessel at a dropping rate of 0.2-1.0 g / min. After the dropping is completed, keep the reaction at 75-85℃ and 600-1000 r / min for 2-5 hours to obtain the film-forming prepolymer solution.

[0018] A2. Weigh the processing modifier according to the mass fraction, add the processing modifier to propylene glycol methyl ether acetate, and pre-wet it for 10-30 min at 500-1000 r / min to obtain the processing modifier pre-wetted material; add the processing modifier pre-wetted material to the film-forming prepolymer liquid obtained in step A1, and disperse it for 20-50 min at 800-1500 r / min to obtain the processing modifier coarse dispersion.

[0019] A3. Grind the coarse dispersion of the processing modifier obtained in step A2 using a sand mill or basket mill, controlling the grinding temperature at 25-45℃, the grinding speed at 1000-2000 r / min, and the grinding time at 30-90 min, until the fineness is no greater than 15μm, to obtain a refined dispersion.

[0020] A4. Add crosslinking curing agent, lubricant, wear-resistant agent, adhesion promoter and polydimethylsiloxane to the refined dispersion obtained in step A3, and stir for 30-80 minutes at 25-45℃ and 500-1000r / min to obtain coating premix.

[0021] A5. Add dodecylbenzene sulfonic acid and the remaining propylene glycol methyl ether acetate to the premixed coating solution obtained in step A4, and stir for 20-50 minutes at 25-40℃ and 300-800 r / min to obtain a coating mixture. Adjust the viscosity of the coating mixture at 25℃ to 50-120 s using a Forco-4 cup, and filter it through a 100-300 mesh filter to obtain the easy-open cover coating with excellent processability.

[0022] Furthermore, in step A1, the monomer-initiating mixture is added over a period of 2-4 hours, the reaction temperature is controlled at 78-82°C during the addition process, and the reaction is continued at a constant temperature for 3-4 hours after the addition is completed. During the reaction, the stirring speed is 700-900 r / min.

[0023] Furthermore, in step A4, the stirring time after adding the crosslinking curing agent, lubricant, wear-resistant agent, adhesion promoter and polydimethylsiloxane is 40-70 min, the stirring temperature is 30-40℃, and the stirring speed is 600-900 r / min.

[0024] This invention uses a film-forming monomer composition consisting of methyl methacrylate, n-butyl acrylate, 2-hydroxyethyl acrylate, and methacrylic acid as the main monomer. An acrylate film-forming prepolymer is formed through free radical prepolymerization, and then thermosetting and crosslinking with hexamethoxymethyl melamine and hexa-n-butyloxymethyl melamine in the presence of dodecylbenzenesulfonic acid to form a continuous, flexible, and well-adhesive crosslinked acrylate film matrix. Secondly, hexagonal boron nitride is used as a layered processing-resistant reinforcing core, utilizing its low friction and lamellar reinforcement to improve the coating's slippage performance during stamping, bending, and edge rolling. A silica anchoring layer is formed through in-situ hydrolysis and condensation of tetraethyl orthosilicate, and further, a phosphorus-nitrogen-zirconium complex reinforcement layer is constructed using phytic acid, zirconium oxychloride, and melamine to improve the interfacial bonding and wear resistance of the composite particles. Meanwhile, the introduction of silane coupling agents and acrylate grafting coatings improves the compatibility and dispersion stability of inorganic particles with the resin matrix; combined with additional lubricants, additional wear-resistant agents and adhesion promoters, the processing friction resistance is reduced, and the phenomena of coating scratches, cracking, peeling and flaking are reduced, thereby obtaining an easy-open cover exterior coating with uniform film formation, firm adhesion, good scratch resistance and excellent edge curling processing performance.

[0025] Compared with the prior art, the beneficial effects of the present invention are: 1. This easy-open can outer wall coating with excellent processability, through the synergistic combination of an acrylic film-forming system, a melamine crosslinking system, a composite processability modifier, a lubricating component, abrasion-resistant component, and adhesion-promoting component, enables the coating to have good continuous film-forming properties, metal adhesion, flexibility, scratch resistance, and adaptability to edge-rolling processing. It can maintain the integrity of the coating structure and the stability of the appearance during easy-open can stamping, bending, edge rolling, and subsequent transportation and use.

[0026] 2. This easy-open cover coating with excellent processability uses hexagonal boron nitride as a layered reinforcing core and undergoes silica anchoring, phosphorus-nitrogen-zirconium complexation reinforcement, silane coupling and acrylate grafting treatments. This improves the dispersion stability and interfacial bonding strength of the processability modifier in the coating system, giving the coating better scratch resistance, crack resistance and adhesion retention when subjected to friction, bending and edge curling.

[0027] 3. This easy-open can outer wall coating with excellent processability, through the composite design of low-friction coated composite particles, additional wear-resistant fillers and adhesion promotion system, effectively reduces frictional resistance and local stress concentration during processing contact while ensuring the smoothness of the coating appearance and curing strength. This improves the slippage, wear resistance and processing stability of the coating surface, thus giving the easy-open can outer wall coating excellent processing adaptability, surface protection and long-term reliability. Attached Figure Description

[0028] Figure 1 Fourier transform infrared spectrum of the processing-resistant modifier obtained in Example 1 of this invention. Detailed Implementation

[0029] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Preparation Example 1 Preparation of process resistance modifiers: 1. Raw material weight parts: Hexagonal boron nitride: 18 parts; tetraethyl orthosilicate: 14 parts; deionized water: 160 parts; ethanol: 180 parts; phytic acid: 6 parts; zirconium oxychloride: 3 parts; melamine: 3 parts; 3-(trimethoxysilyl)propyl methacrylate: 6 parts; 3-aminopropyltriethoxysilane: 3 parts; n-butyl acrylate: 8 parts; 2-hydroxyethyl acrylate: 6 parts; methyl methacrylate: 5 parts; ammonium persulfate: 0.8 parts; ethylene bis-stearamide: 5 parts; pentaerythritol tetrastearate: 10 parts; stearic acid: 3 parts.

[0031] 2. Preparation method: S1. Weigh out 63.8 parts of hexagonal boron nitride, 63.8 parts of deionized water and 70 parts of ethanol and add them to the reaction vessel. The solid-liquid ratio of the hexagonal boron nitride to the mixture of deionized water and ethanol is 1:7.78. Disperse the mixture at 1500 r / min for 45 min, adjust the pH of the system to 9.5 with 25-28% ammonia, maintain the temperature at 25℃, and then sonicate for 25 min to obtain a boron nitride dispersion.

[0032] S2. The boron nitride dispersion obtained in step S1 is heated to 45°C. Under stirring at 1200 r / min, tetraethyl orthosilicate is added dropwise to the boron nitride dispersion at a rate of 0.5 g / min for 28 min. After the addition is completed, the reaction is continued at 45°C and 1200 r / min for 3 h to obtain a silica-anchored boron nitride dispersion.

[0033] S3. Weigh phytic acid and dilute it with 54 parts of deionized water to prepare a 10% phytic acid aqueous solution; weigh zirconium oxychloride and dissolve it with 27 parts of deionized water to prepare a 10% zirconium oxychloride aqueous solution; weigh melamine and disperse it with 37 parts of ethanol to prepare a 7.5% melamine ethanol dispersion; weigh 18 parts of 3-(trimethoxysilyl)propyl methacrylate, 3-aminopropyltriethoxysilane and ethanol, and mix them to form a silane mixture. First, phytic acid aqueous solution was added to the silica-anchored boron nitride dispersion obtained in step S2 at a dropping rate of 0.3 g / min. After the addition was completed, the pH was adjusted to 5.2 with ammonia water, and the mixture was stirred for 60 min at 50 °C and 900 r / min. Then, zirconium oxychloride aqueous solution and melamine ethanol dispersion were added, and the mixture was reacted for 2.5 h at 65 °C and 900 r / min. Subsequently, silane mixture was added to the system at a dropping rate of 0.5 g / min, the pH was adjusted to 8.5 with ammonia water, and the mixture was reacted for 3 h at 60 °C and 900 r / min to obtain a composite particle dispersion.

[0034] S4. Add n-butyl acrylate, 2-hydroxyethyl acrylate, and methyl methacrylate to the composite particle dispersion obtained in step S3, and stir at 700 r / min for 20 min; purge the system with nitrogen for 30 min and then raise the temperature to 72℃; dissolve ammonium persulfate in 15.2 parts of deionized water to prepare a 5% (w / w) ammonium persulfate aqueous solution, and add it to the system at a dropping rate of 0.15 g / min for 107 min; after the dropping is completed, perform an in-situ grafting reaction at 72℃ and 800 r / min for 3.5 h to obtain an acrylate-grafted composite particle dispersion.

[0035] S5. Weigh 55 parts of ethylene bis-stearamide, pentaerythritol tetrastearate, stearic acid, and ethanol, add them to a dispersion container, and pre-disperse them at 80℃ and 1800 r / min for 40 min to form a lubricating component dispersion. Add the lubricating component dispersion to the acrylate grafted composite particle dispersion obtained in step S4, and adsorb and coat it at 80℃ and 1000 r / min for 2 h to obtain a low-friction coated composite dispersion. Cool the low-friction coated composite dispersion to 30℃, then filter it to obtain a wet filter cake. Wash the wet filter cake twice with ethanol, each time using 100 parts of ethanol, and then wash the wet filter cake twice with deionized water, each time using 100 parts of deionized water. The ethanol and deionized water used for washing are post-treatment media and are not included in the above raw material mass percentages. The filter cake obtained after washing was vacuum dried at 75℃ for 10 hours with the vacuum degree controlled at -0.08MPa. After drying, it was crushed and sieved through a 300-mesh sieve to obtain a processing modifier.

[0036] The infrared spectrum of the processing resistance modifier obtained in Preparation Example 1 is shown below. Figure 1 As shown. By Figure 1 It can be known that 2920cm -1 The absorption peaks around 1700 cm⁻¹ can be attributed to the CH stretching vibration in the organic chain segment. -1 The nearby absorption peak corresponds to the C=O stretching vibration of the ester group, 1600-1500 cm⁻¹ -1 The absorption peaks in this region are related to melamine or NH-related vibrations, 1250-1000 cm⁻¹ -1 The absorption peaks in this range are mainly related to bond vibrations such as Si-O-Si, PO, and CO, and are located in the 800-600 cm⁻¹ range. -1 The absorption in the region can reflect the vibration of the inorganic filler and the BN skeleton.

[0037] Comparative Preparation Example 1 The preparation of the processing modifier was carried out by referring to the preparation method in Preparation Example 1, except that 18 parts by mass of hexagonal boron nitride were replaced with 18 parts by mass of molybdenum disulfide, and the rest remained the same as in Preparation Example 1.

[0038] Comparative Preparation Example 2 The preparation of the processability modifier was carried out by referring to the preparation method in Preparation Example 1, except that 14 parts by mass of tetraethyl orthosilicate was replaced with 14 parts by mass of silica sol, and the rest remained the same as in Preparation Example 1.

[0039] Comparative preparation example 3 The preparation of the processing modifier was carried out by referring to the preparation method in Preparation Example 1, except that 3 parts by mass of zirconium oxychloride were replaced with 3 parts by mass of zirconium oxynitrate hydrate, and the rest remained the same as in Preparation Example 1.

[0040] Comparative preparation example 4 The preparation of the processing modifier was carried out by referring to the preparation method in Preparation Example 1, except that 3 parts by mass of 3-aminopropyltriethoxysilane were replaced with 3 parts by mass of 3-glycidoxypropyltrimethoxysilane, and the rest remained the same as in Preparation Example 1.

[0041] Comparative preparation example 5 The processability modifier was prepared by referring to the preparation method in Preparation Example 1, except that 6 parts by mass of 2-hydroxyethyl acrylate was replaced with 6 parts by mass of 2-hydroxyethyl methacrylate, and the rest remained the same as in Preparation Example 1.

[0042] Comparative preparation example 6 The processability modifier was prepared by referring to the preparation method in Preparation Example 1, except that 10 parts by mass of pentaerythritol tetrastearate was replaced with 10 parts by mass of oleamide, and the rest remained the same as in Preparation Example 1.

[0043] Comparative preparation example 7 The preparation of the processing modifier was carried out by referring to the preparation method in Preparation Example 1, except that 6.0 parts by mass of phytic acid was replaced with 6.0 parts by mass of phosphoric acid, and the rest remained the same as in Preparation Example 1.

[0044] Example 1

[0045] A coating for easy-open lids with excellent processability: 1. Raw material weight parts: Film-forming monomer composition: 45.0 parts, consisting of 15.0 parts methyl methacrylate, 20.0 parts n-butyl acrylate, 8.0 parts 2-hydroxyethyl acrylate and 2.0 parts methacrylic acid.

[0046] Processing modifier: 4.5 parts, which is the processing modifier prepared in Preparation Example 1.

[0047] Crosslinking curing agent: 9.0 parts, consisting of 6.75 parts hexamethoxymethyl melamine and 2.25 parts hexa-n-butyloxymethyl melamine.

[0048] Dodecylbenzenesulfonic acid: 0.6 parts.

[0049] Azobisisobutyronitrile: 0.5 parts.

[0050] Lubricant: 2.0 parts, consisting of 1.2 parts stearamide and 0.8 parts ethylene bis-stearamide.

[0051] Wear-resistant agent: 2.5 parts, consisting of 1.5 parts silicon dioxide, 0.7 parts aluminum oxide and 0.3 parts boron nitride.

[0052] Adhesion promoter: 1.5 parts, consisting of 0.6 parts of ethyl dihydrogen phosphate, 0.75 parts of 3-glycidyl etheroxypropyltrimethoxysilane, and 0.15 parts of tetrabutyl titanate.

[0053] Polydimethylsiloxane: 0.5 parts.

[0054] Propylene glycol methyl ether acetate: 45.0 parts.

[0055] The silica was purchased from Hubei Huifu Nanomaterials Co., Ltd., and is model HL-200 hydrophilic fumed silica with a specific surface area of ​​200±20m². 2 / g The alumina was purchased from Shanghai McLean Biochemical Technology Co., Ltd., model A750299, with an average particle size of 100nm.

[0056] The boron nitride was purchased from Shanghai McLean Biochemical Technology Co., Ltd., model B802370, with a particle size of 1-2μm.

[0057] The polydimethylsiloxane was purchased from Hubei Kefule Materials Technology Co., Ltd., and is model CFS-F(M)-1000 medium viscosity polydimethylsiloxane with a viscosity of 1000±50 mm. 2 / s.

[0058] 2. Preparation method: A1. Weigh approximately 65 wt% of the total amount of propylene glycol methyl ether acetate and add it to a reaction vessel. Stir at 700 r / min under nitrogen protection and heat to 80 °C. Add azobisisobutyronitrile to a film-forming monomer composition consisting of methyl methacrylate, n-butyl acrylate, 2-hydroxyethyl acrylate, and methacrylic acid. Stir until the azobisisobutyronitrile is completely dissolved to obtain a monomer initiation mixture. Add the monomer initiation mixture dropwise to the reaction vessel at a rate of 0.25 parts by mass / min. After the addition is complete, keep the reaction at 80 °C and 800 r / min for 3.5 h to obtain a film-forming prepolymer.

[0059] A2. Weigh the processing modifier obtained in Preparation Example 1, add it to propylene glycol methyl ether acetate, and pre-wet it for 20 min at 25°C and 800 r / min to obtain the processing modifier pre-wetted material; add the processing modifier pre-wetted material to the film-forming prepolymer obtained in step A1, and disperse it for 35 min at 25°C and 1200 r / min to obtain a coarse dispersion.

[0060] A3. Grinding and refining: Place the coarse dispersion obtained in step A2 into a sand mill and grind it for 60 minutes at 35℃ and 1500r / min. Control the material temperature to not exceed 45℃ during the grinding process and grind it to a fineness of not more than 12μm to obtain a refined dispersion.

[0061] A4. Add hexamethoxymethyl melamine, hexa-n-butyloxymethyl melamine, stearamide, ethylene bis-stearamide, silica, alumina, boron nitride, ethyl dihydrogen phosphate, 3-glycidyl etheroxypropyltrimethoxysilane, tetrabutyl titanate and polydimethylsiloxane to the refined dispersion obtained in step A3 in sequence, and stir at 35°C and 800 r / min for 55 min to obtain the coating premix.

[0062] A5. Add dodecylbenzene sulfonic acid and propylene glycol methyl ether acetate to the premixed coating solution obtained in step A4, stir for 35 minutes at 30°C and 500 r / min, and then filter through a 200-mesh filter to obtain an easy-open cover exterior coating with excellent processability.

[0063] Example 2

[0064] The preparation of an easy-open cover coating with excellent processability is carried out by referring to the preparation method in Example 1, except that the mass fraction of the film-forming monomer composition is replaced with 55 parts, and the rest remains the same as in Example 1.

[0065] Example 3

[0066] The preparation of an easy-open cover coating with excellent processability is carried out by referring to the preparation method in Example 1, except that the mass part of the processability modifier is replaced with 8 parts, and the rest is the same as in Example 1.

[0067] Example 4

[0068] The preparation of an easy-open cover coating with excellent processability is carried out by referring to the preparation method in Example 1, except that the mass fraction of the crosslinking curing agent is replaced with 15 parts, and the rest is the same as in Example 1.

[0069] Example 5

[0070] The preparation of an easy-open cover coating with excellent processability is carried out by referring to the preparation method in Example 1, except that the mass fraction of the lubricant is replaced with 4 parts, and the rest is the same as in Example 1.

[0071] Example 6

[0072] The preparation of an easy-open cover coating with excellent processability is carried out by referring to the preparation method in Example 1, except that the mass fraction of the wear-resistant agent is replaced with 5 parts, and the rest is the same as in Example 1.

[0073] Comparative Examples 1-7 The preparation of an easy-open cover coating with excellent processability is carried out by referring to the preparation method in Example 1, except that the processability modifier is replaced with the processability modifier prepared in Comparative Preparation Examples 1-7, and the rest is the same as in Example 1.

[0074] Comparative Example 8 The preparation of an easy-open cover coating with excellent processability is the same as in Example 1, except that no processability modifier is added.

[0075] Comparative Example 9 The preparation of an easy-open cover coating with excellent processability is the same as in Example 1, except that the crosslinking curing agent is not added.

[0076] Comparative Example 10 The preparation of an easy-open cover coating with excellent processability is the same as in Example 1, except that no lubricant is added.

[0077] Comparative Example 11 The preparation of an easy-open cover coating with excellent processability is the same as in Example 1, except that no wear-resistant agent is added.

[0078] Performance testing: The coatings obtained from Examples 1-6 and Comparative Examples 1-11 were applied to the outer surface of degreased aluminum easy-open cover substrates, with the wet film thickness controlled at 12-18 μm. The substrates were baked at 180°C for 10 min and then cooled to room temperature to obtain test samples. The test samples were then placed in an environment of 23±2°C and 50±5% relative humidity for 24 h before performance testing.

[0079] 1. Adhesion Test: Using a cross-cut adhesion tester with a blade angle of 15°-30°, make 1mm-spaced intersecting cuts on the coating surface of the test sample. The blade should penetrate the coating to the metal substrate surface in one stroke, forming 100 squares. After marking the squares, gently brush away any coating debris generated during the marking process. Using pressure-sensitive adhesive tape conforming to GB / T 9286-2021 (peel strength ≥10N / 25mm), firmly adhere the tape to the marked area, roll it back and forth three times with a rubber roller to ensure full contact, hold for 60±10s, and then quickly peel it off at a 180° angle to the coating surface. Observe the coating peeling in the marked area visually (observation distance 30-50cm) under a standard light source (D65). The coating is graded according to the area of ​​peeling: no coating peeling is grade 0; peeling area not exceeding 5% is grade 1; peeling area exceeding 5% but not exceeding 15% is grade 2; peeling area exceeding 15% but not exceeding 35% is grade 3; peeling area exceeding 35% but not exceeding 65% is grade 4; and peeling area exceeding 65% is grade 5. The lower the grade, the better the adhesion between the coating and the metal substrate. The results are shown in Table 1.

[0080] 2. T-bend / Edge Rolling Performance Test: T-bend performance test: The test sample is cut into pieces with a width of 25mm and a length of 100mm. The coated side is placed on a T-bend machine for T-bend testing. 0T, 1T, 2T, and 3T bends are performed at different locations on the sample, and larger T-value bends are performed if necessary. 0T represents a bend with an inner radius R=0, 1T represents an inner radius R=1 times the plate thickness, 2T represents an inner radius R=2 times the plate thickness, and 3T represents an inner radius R=3 times the plate thickness. After bending, the coating condition in the bending area is observed using a 10x magnifying glass, and the bending area is peeled using pressure-sensitive tape conforming to GB / T 9286-2021. The minimum T-value corresponding to no cracking, no exposed substrate, and no peeling at the bend is taken as the T-bend performance result. The smaller the T-value, the better the coating's resistance to bending.

[0081] Edge-rolling performance test: The coated easy-open lid substrate was edge-rolled using the same actual easy-open lid edge-rolling mold. The mold was a laboratory edge-rolling mold adapted for aluminum easy-open lids, with an edge-rolling wheel radius of 1.0 mm, an edge-rolling pressure of 0.35 MPa, an edge-rolling speed of 30 times / min, and a single edge-rolling time of 2 seconds. At least 5 samples were tested for each type of product. After rolling, a 5x magnifying glass was used for preliminary observation of the coating at the edge, checking for cracks, peeling, flaking, exposed substrate, or obvious scratches. Simultaneously, under a fixed light source with an illuminance of 800 lx and a fixed shooting distance of 100 mm, at least 10 observation areas were evenly selected along the circumference of the edge for image acquisition, with each observation area being 4.0 mm². 2 The image acquisition device is a digital microscope with scale calibration function; a unified threshold image analysis method is used to count the defect area. After the image is grayscaled, the average grayscale value of the undamaged coating area is used as the benchmark, and areas with grayscale differences exceeding 25% and continuous areas not less than 0.02 mm are excluded. 2 Cracking, peeling, flaking, exposure of the substrate, and continuous obvious scratches were recorded as defect areas. The defect area and the total area of ​​the observation area were counted, and the curling defect area ratio was calculated according to the following formula: Curling defect area ratio = Total defect area / Total area of ​​observation area × 100%. The average value of all test results for each sample was taken as the curling defect area ratio. The lower the curling defect area ratio, the better the integrity of the coating curling process. The results are shown in Table 1.

[0082] 3. Scratch Resistance Test: The scratch resistance of the coating was determined according to the method specified in GB / T 31591-2015. The test sample was fixed on the platform of the scratch resistance testing equipment, and a scratch test was performed using an arc-shaped scribing needle. The load was gradually increased (the load increment was 1N), and the critical load (N) at which continuous visible scratch marks appeared on the coating surface was recorded. Each sample was tested three times, and the average value was taken. The higher the critical load, the better the scratch resistance of the coating. The results are shown in Table 1.

[0083] 4. Friction Coefficient Test: Under conditions of 23±2℃ and 50±5% relative humidity, the dynamic friction coefficient of the coating surface was determined using a coating friction coefficient tester. The test sample was fixed on a horizontal test platform. The grinding part was a 304 stainless steel slider (surface roughness Ra≤0.4μm), with a slider mass of 200g. The test speed was 100mm / min, and the test stroke was 100mm. During the test, the average friction force F of the slider during the stable sliding stage on the coating surface was recorded. The dynamic friction coefficient was calculated according to the formula μ=F / N, where μ is the dynamic friction coefficient, F is the average friction force (N) during the stable sliding stage, and N is the normal load (N) of the slider. The results are shown in Table 1.

[0084] Table 1. Results of performance test data

[0085] The data in the table show that the coatings obtained in Examples 1-6 maintain a good overall balance in terms of adhesion, T-bend processability, edge integrity, scratch resistance, and low surface friction. In Comparative Examples 1-7, the replacement of a single functional component in the processability modifier leads to changes in the interfacial structure, dispersion state, or lubrication coating stability of the composite particles, resulting in a corresponding decrease in the coating's processability, scratch resistance, and friction performance. Comparative Examples 8-11, lacking processability modifier, crosslinking curing agent, lubricant, or wear-resistant agent respectively, show a more direct decline in their corresponding performance, indicating that these components respectively play roles in stress dispersion, crosslinking densification, friction reduction lubrication, and surface reinforcement in the coating system.

[0086] This invention employs hexagonal boron nitride as the functional component of the layers, and uses tetraethyl orthosilicate to form an in-situ silica anchoring structure. Combined with phytic acid-zirconium coordination, melamine modification, silane coupling, and acrylate grafting, it improves the interfacial compatibility and dispersion stability between inorganic particles and the acrylic resin matrix, reducing localized stress concentration during coating bending, curling, and scratching. The crosslinking curing agent increases the crosslinking density and structural compactness of the cured coating, while the lubricant and polydimethylsiloxane reduce the surface contact friction resistance. The additional wear-resistant system composed of silica, alumina, and boron nitride strengthens the coating surface and provides scratch resistance. It should be noted that although Comparative Example 9 contains a processing modifier, the lack of a crosslinking curing agent reduces the crosslinking density of the coating film, resulting in weaker bonding between hard particles and the matrix. During the scratching process, the particles are prone to detachment, inducing localized wear. Therefore, its critical scratch resistance load is lower than that of Comparative Example 8, which, despite lacking a processing modifier, can still form a crosslinked coating film. This result indicates that the processing modifier needs to work in conjunction with the crosslinking curing network to stably exert its scratch resistance effect. When key structural or functional components are replaced or omitted, interfacial bonding, structural density, dispersion stability, or surface reinforcement are affected, resulting in an increase in the T-bend throughput, a higher area ratio of curling defects, a lower critical scratch resistance load, or an increased coefficient of dynamic friction.

[0087] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A coating for the outer wall of an easy-open lid with excellent processability, characterized in that, The coating, by weight, is prepared from the following raw materials: 30-55 parts of film-forming monomer composition, 1-8 parts of processing modifier, 4-15 parts of crosslinking curing agent, 0.1-1.2 parts of dodecylbenzenesulfonic acid, 0.2-0.8 parts of azobisisobutyronitrile, 0.3-4 parts of lubricant, 0.5-5 parts of wear-resistant agent, 0.3-3 parts of adhesion promoter, 0.1-2 parts of polydimethylsiloxane, and 25-60 parts of propylene glycol methyl ether acetate; The processing modifier is composed of the following raw materials in parts by weight: 10-25 parts hexagonal boron nitride, 8-20 parts tetraethyl orthosilicate, 80-160 parts deionized water, 80-180 parts ethanol, 3-10 parts phytic acid, 1-5 parts zirconium oxychloride, 1-6 parts melamine, 3-9 parts 3-(trimethoxysilyl)propyl methacrylate, 1-5 parts 3-aminopropyltriethoxysilane, 4-12 parts n-butyl acrylate, 3-10 parts 2-hydroxyethyl acrylate, 2-8 parts methyl methacrylate, 0.2-1.2 parts ammonium persulfate, 2-8 parts ethylene bis-stearamide, 4-15 parts pentaerythritol tetrastearate, and 1-6 parts stearic acid. The dry powder of the processing modifier is a solid powder obtained after washing, filtering, drying, pulverizing and sieving. Its amount is based on the mass of the dried powder. The deionized water, ethanol and washing ethanol used in the preparation of the processing modifier are not included in the mass of the dry powder of the processing modifier in the finished coating.

2. The easy-open lid outer wall coating with excellent processability according to claim 1, characterized in that, The preparation method of the processing resistance modifier includes the following steps: S1. Add hexagonal boron nitride to the mixture, and control the solid-liquid ratio of hexagonal boron nitride to the mixture to be 1:5-10. Adjust the pH to 8.5-10.5 by adding ammonia water with a mass fraction of 25-28% dropwise. Disperse the mixture at 1200-2000 r / min for 30-60 min, and then sonicate it for 15-40 min to obtain a boron nitride dispersion. S2. Under stirring conditions of 35-50℃ and 800-1500r / min, tetraethyl orthosilicate is added to the boron nitride dispersion at a dropping rate of 0.2-1.0g / min. After the addition is completed, the reaction continues for 2-5h to obtain a silica-anchored boron nitride dispersion. S3. Prepare a phytic acid aqueous solution with a mass fraction of 5-20%, prepare a zirconium oxychloride aqueous solution with a mass fraction of 3-15%, prepare a melamine ethanol dispersion with a mass fraction of 3-12%, and add 3-(trimethoxysilyl)propyl methacrylate and 3-aminopropyltriethoxysilane to ethanol to form a silane mixture; first, add the phytic acid aqueous solution to the silica anchor obtained in step S2 at a dropping rate of 0.1-0.6 g / min. In the solidified boron nitride dispersion, the pH is adjusted to 4.0-6.0, and the mixture is stirred at 40-60℃ for 30-90 min. Then, zirconium oxychloride aqueous solution and melamine ethanol dispersion are added, and the mixture is reacted at 50-75℃ for 1-4 h. Then, the silane mixture is added to the system at a dropping rate of 0.2-0.8 g / min, the pH is adjusted to 7.5-9.5, and the mixture is reacted at 50-70℃ and 700-1200 r / min for 2-4 h to obtain a composite particle dispersion. S4. Add n-butyl acrylate, 2-hydroxyethyl acrylate and methyl methacrylate to the composite particle dispersion obtained in step S3. After purging with nitrogen for 20-40 min, raise the temperature to 65-80℃. Prepare an aqueous solution of ammonium persulfate with a mass fraction of 2-10% and add it to the system at a dropping rate of 0.05-0.3 g / min. Perform in-situ grafting reaction at 65-80℃ and 600-1000 r / min for 2-5 h to obtain an acrylate-grafted composite particle dispersion. S5. Ethylene bis-stearamide, pentaerythritol tetrastearate, and stearic acid are added to ethanol and pre-dispersed at 70-85℃ and 1200-2200 r / min for 20-60 min to form a lubricating component dispersion. Then, the acrylate grafted composite particle dispersion obtained in step S4 is added and adsorbed and coated at 70-85℃ for 1-3 h to obtain a low-friction coated composite dispersion. The low-friction coated composite dispersion is cooled to 25-40℃ and washed 2-4 times by weight with ethanol and deionized water, respectively, wherein the amount of ethanol or deionized water used each time is 80-120 parts by weight of hexagonal boron nitride. The mixture is filtered, and the resulting filter cake is vacuum dried at 60-85℃ for 6-12 h, pulverized, and sieved through a 200-500 mesh sieve to obtain a processing modifier.

3. The easy-open lid outer wall coating with excellent processability according to claim 1, characterized in that, The film-forming monomer composition comprises at least one of methyl methacrylate, n-butyl acrylate, 2-hydroxyethyl acrylate, and methacrylic acid.

4. The easy-open lid outer wall coating with excellent processability according to claim 1, characterized in that, The crosslinking curing agent is composed of hexamethoxymethyl melamine and hexa-n-butyloxymethyl melamine in a mass ratio of 1-5:

1.

5. The easy-open lid outer wall coating with excellent processability according to claim 1, characterized in that, The lubricant is at least one of stearamide and ethylene bis-stearamide.

6. The easy-open lid outer wall coating with excellent processability according to claim 1, characterized in that, The wear-resistant agent is composed of silicon dioxide, aluminum oxide and boron nitride in a mass ratio of 1-6:0.5-4:0.2-2.

7. The easy-open lid outer wall coating with excellent processability according to claim 1, characterized in that, The adhesion promoter is composed of ethyl dihydrogen phosphate, 3-glycidyl etheroxypropyltrimethoxysilane and tetrabutyl titanate in a mass ratio of 1-4:1-5:0.2-2.

8. A method for preparing a coating for the outer wall of an easy-open lid with excellent processability as described in any one of claims 1-7, characterized in that, Includes the following steps: A1. Weigh the film-forming monomer composition, azobisisobutyronitrile, and propylene glycol methyl ether acetate according to the mass ratio. Add the propylene glycol methyl ether acetate to the reaction vessel and heat to 75-85℃ under stirring at 500-900 r / min. Dissolve the azobisisobutyronitrile in the film-forming monomer composition to form a monomer initiation mixture with a mass concentration of 0.4-2.5%. Add the monomer initiation mixture to the reaction vessel at a dropping rate of 0.2-1.0 g / min. After the dropping is completed, keep the reaction at 75-85℃ and 600-1000 r / min for 2-5 h to obtain the film-forming prepolymer solution. A2. Weigh the processing modifier according to the mass fraction, add the processing modifier to propylene glycol methyl ether acetate, and pre-wet it for 10-30 min at 500-1000 r / min to obtain the processing modifier pre-wetted material; add the processing modifier pre-wetted material to the film-forming prepolymer liquid obtained in step A1, and disperse it for 20-50 min at 800-1500 r / min to obtain the processing modifier coarse dispersion. A3. Grind the coarse dispersion of the processing modifier obtained in step A2 using a sand mill or basket mill, controlling the grinding temperature at 25-45℃, the grinding speed at 1000-2000 r / min, and the grinding time at 30-90 min, until the fineness is no greater than 15μm, to obtain a refined dispersion. A4. Add crosslinking curing agent, lubricant, wear-resistant agent, adhesion promoter and polydimethylsiloxane to the refined dispersion obtained in step A3, and stir for 30-80 minutes at 25-45℃ and 500-1000r / min to obtain coating premix; A5. Add dodecylbenzene sulfonic acid and the remaining propylene glycol methyl ether acetate to the premixed coating solution obtained in step A4, and stir for 20-50 minutes at 25-40℃ and 300-800 r / min to obtain a coating mixture. Adjust the viscosity of the coating mixture at 25℃ to 50-120 s using a Forco-4 cup, and filter it through a 100-300 mesh filter to obtain the easy-open cover coating with excellent processability.

9. The method for preparing the easy-open lid outer wall coating with excellent processability according to claim 8, characterized in that, In step A1, the monomer-initiating mixture is added over a period of 2-4 hours. During the addition process, the reaction temperature is controlled at 78-82°C. After the addition is completed, the reaction is kept at a constant temperature for another 3-4 hours. During the reaction, the stirring speed is 700-900 r / min.

10. The method for preparing the easy-open lid outer wall coating with excellent processability according to claim 8, characterized in that, In step A4, the stirring time after adding the crosslinking curing agent, lubricant, wear-resistant agent, adhesion promoter and polydimethylsiloxane is 40-70 min, the stirring temperature is 30-40℃ and the stirring speed is 600-900 r / min.

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