A high adhesion overcoat for pharmaceutical grade aluminum tubing and method of making same

Abstract

The application belongs to the technical field of aluminum hose surface protection, and particularly relates to a high-adhesion outer coating for packaging medicinal-grade aluminum hoses and a preparation method thereof. The coating comprises, by mass fraction, 5-15 parts of catechol-silane modified water-based polyester resin, 35-55 parts of acrylic-polyurethane hybrid emulsion, 9-23 parts of composite anti-rust filler, 0.5-2.0 parts of anti-flash rust agent, 0.5-2.0 parts of adhesion promoter, and additives and deionized water. The modified polyester resin is obtained by grafting a water-soluble saturated polyester resin with a compound containing a catechol group and a silane coupling agent. The composite anti-rust filler is compounded from zinc phytate, titanium white powder and nano-silicon dioxide. The anti-flash rust agent is compounded from phytic acid, tannic acid and molybdate. The obtained coating meets the comprehensive requirements of high adhesion, high flexibility and high protection under the condition of a thin coating layer.

Description

Technical Field

[0001] This invention belongs to the field of aluminum flexible tube surface protection technology, specifically relating to a high-adhesion outer coating for pharmaceutical-grade aluminum flexible tube packaging and its preparation method. Background Technology

[0002] Aluminum flexible tubular tubes are single-layer seamless tubular packaging containers manufactured through stamping and extrusion. Due to their lightweight, good sealing properties, and ease of molding, they are widely used in the packaging of products such as toothpaste, pharmaceuticals, cosmetics, and food. To prevent oxidation and corrosion of the aluminum tubes during storage, transportation, and use, and to impart whiteness and decorative appeal, a white primer coating is typically applied to the outer surface of the tube. After curing, the graphics and text are then printed. The performance of the outer coating directly affects the appearance durability and protective lifespan of the tube.

[0003] For a long time, solvent-based polyester coatings have been the primary coating material for aluminum flexible hoses. These coatings rely on organic solvents as a diluent, resulting in fast drying and good film formation. However, they release large amounts of volatile organic compounds (VOCs) during use, posing a threat to the environment and the health of workers. With increasingly stringent environmental regulations, particularly mandatory national standards that impose higher limits on VOC content and hazardous substances in industrial coatings, water-based coatings that replace organic solvents have become an inevitable path for upgrading aluminum flexible hose coating technology.

[0004] However, the application of water-based coatings in the external coating of aluminum flexible tubes faces many inherent technical obstacles. Aluminum substrates have low surface energy, and the naturally formed oxide film is chemically inert, making it difficult for the polar groups in water-based resins to form effective bonds, resulting in insufficient film adhesion, especially prone to blistering and peeling in humid and hot environments. In subsequent forming processes such as calendering, edge rolling, and sealing, the coating needs to withstand significant bending deformation. If the flexibility is insufficient, it is prone to cracking and peeling at the bending points. Traditional single-aqueous water-based resin systems often struggle to balance flexibility and hardness, resulting in a contradiction of "soft if flexible, brittle if hard." Furthermore, the dry film thickness of aluminum tube external coatings is typically controlled at only ten to twenty micrometers, classifying it as a thin coating system. During the film-forming process, water-based coatings experience slow water evaporation, easily leaving micropores and channels within the film, resulting in poor density and making it difficult to meet long-term protection requirements for salt spray resistance, water resistance, and media resistance. In addition, water-based coatings are prone to flash rusting when applied to aluminum surfaces, further weakening the adhesion between the coating and the substrate.

[0005] Therefore, how to achieve strong adhesion to aluminum substrates, integrity during bending processes, and long-term protection in humid and salt spray environments while taking into account environmental protection requirements has become a technical challenge that urgently needs to be overcome in the field of aluminum hose outer coatings. Summary of the Invention

[0006] The purpose of this invention is to provide a high-adhesion outer coating for pharmaceutical-grade aluminum flexible tube packaging and its preparation method. Through formula optimization, the water-based coating forms a strong chemical adhesion to the aluminum substrate at an extremely thin thickness. At the same time, the coating film remains intact during tube end extrusion and bending processes, and has long-lasting salt spray and damp heat protection capabilities, so as to replace high VOC solvent-based coatings and meet the environmental protection and performance requirements of pharmaceutical packaging.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] The first aspect of this invention provides a high-adhesion outer coating for pharmaceutical-grade aluminum tubular packaging, comprising the following components by weight:

[0009] 5-15 parts of catechol-silane modified waterborne polyester resin;

[0010] 35-55 parts of acrylic-polyurethane hybrid emulsion;

[0011] 9-23 parts of composite rust-inhibiting filler;

[0012] Adhesion promoter 0.5-2.0 parts;

[0013] 0.3-0.8 parts of wetting and dispersing agent;

[0014] Defoamer 0.2-0.6 parts;

[0015] Leveling agent 0.3-0.7 parts;

[0016] Anti-flash rust agent 0.5-2.0 parts;

[0017] 15-40 parts deionized water;

[0018] The catechol-silane modified waterborne polyester resin is formed by grafting and modifying a water-soluble saturated polyester resin with a compound containing catechol groups and a silane coupling agent. The compound containing catechol groups is selected from at least one of 3,4-dihydroxybenzaldehyde, 3,4-dihydroxybenzoic acid, and dopamine hydrochloride. The silane coupling agent is selected from at least one of γ-glycidoxypropyltrimethoxysilane (KH-560) and γ-aminopropyltriethoxysilane (KH-550).

[0019] Furthermore, the catechol-silane modified waterborne polyester resin is prepared by the following method:

[0020] Water-soluble saturated polyester resin is reacted with a compound containing catechol groups at 50-80℃ for 1-3 hours, followed by the addition of a silane coupling agent to continue the reaction for 0.5-2 hours.

[0021] Further, the mass ratio of the water-soluble saturated polyester resin, the compound containing catechol groups, and the silane coupling agent is 1:(0.03-0.10):(0.02-0.08).

[0022] Furthermore, the mass ratio of the catechol-silane modified waterborne polyester resin to the acrylic-polyurethane hybrid emulsion is 1:(3-5).

[0023] Furthermore, the acrylic-polyurethane hybrid emulsion is self-crosslinking, with a glass transition temperature of -10°C to 20°C and a solid content of 45-55%.

[0024] The catechol-silane modified waterborne polyester resin incorporates both catechol structural units and hydrolyzable siloxane groups on its molecular side chains. The catechol groups exhibit strong coordination and complexation capabilities for aluminum ions in the aluminum oxide layer, forming multi-point anchoring at the coating-substrate interface. This coordination is relatively stable in an aqueous environment, contributing to improved wet adhesion of the coating under humid and hot conditions. During curing, the siloxane groups condense with hydroxyl groups on the aluminum surface, generating Si-O-Al covalent bonds. Simultaneously, the siloxanes cross-link to form a dense interfacial network, further blocking water molecule penetration along the interface. When this modified polyester resin is compounded with an acrylic-polyurethane hybrid emulsion, the former focuses on building a robust interfacial adhesion layer, while the latter, with its moderate glass transition temperature, provides a flexible framework after film formation, allowing the coating to deform in tandem with the substrate without cracking when the aluminum tube is bent. When the two are combined in an appropriate ratio, a balance can be achieved between interfacial anchoring and bulk flexibility, avoiding processing damage or premature failure caused by excessive rigidity or insufficient adhesion of a single resin system.

[0025] Furthermore, the composite rust-preventive filler is composed of zinc phytate, titanium dioxide and nano silica in a mass ratio of 1:(1.5-3):(0.3-0.8).

[0026] Zinc phytate is an organic chelating rust-inhibiting pigment. Its multiple phosphate groups on the phytate ions can form a stable chelate film with aluminum ions on the aluminum substrate surface and in the corrosion micro-regions, providing chemical passivation and corrosion inhibition at the interface, thus delaying the occurrence and spread of corrosion. Titanium dioxide, as the main pigment in the coating, provides the necessary whiteness and hiding power to meet the appearance requirements of the aluminum tube. Furthermore, its inert, lamellar particles, arranged in a layered manner within the coating, inherently possess a certain physical shielding effect, extending the path of corrosive media to the substrate. Nano-silica, with a particle size much smaller than the previous two fillers, can fill the microscopic gaps between the titanium dioxide and zinc phytate particles, increasing the packing density of the pigment fillers and the overall compactness of the coating. This reduces the micropores and capillary channels formed during film formation, thereby enhancing the coating's barrier ability against corrosive media such as water, oxygen, and chloride ions. The three pigments complement each other in particle size distribution and function, enabling the coating to simultaneously meet the comprehensive requirements of covering decoration, chemical corrosion inhibition, and physical barrier even in a thin layer of only a few micrometers.

[0027] Furthermore, the anti-flash rust agent is composed of phytic acid, tannic acid and molybdate in a mass ratio of 1:(0.4-1.0):(0.2-0.5).

[0028] Phytic acid can rapidly adsorb onto the aluminum surface during the initial wetting stage of water-based coating application, forming a stable chelate film with aluminum ions. This provides immediate flash rust inhibition before the coating is fully cured. Tannic acid, containing numerous phenolic hydroxyl groups, can also complex and adsorb onto the aluminum surface, forming a dense organic passivation adsorption layer at the interface with phytic acid, compensating for potential coverage defects associated with single components. Molybdate, as an inorganic corrosion inhibitor, exhibits a certain self-repair tendency in its passivation film when localized corrosion occurs. Molybdate ions can migrate to the corrosion micro-area and participate in the replenishment and deposition of the passivation film, thereby inhibiting further corrosion propagation. When these three components are combined in the aforementioned proportions, the anti-flash rust effect can be maintained throughout the entire coating drying and film formation process.

[0029] Furthermore, the adhesion promoter is γ-aminopropyltriethoxysilane (KH-550).

[0030] The second aspect of this invention provides a method for preparing the above-mentioned high-adhesion outer coating for pharmaceutical-grade aluminum flexible tube packaging, comprising the following steps:

[0031] (1) Add 40-60% of the total amount of deionized water to the dispersion vessel, and add 40-60% of the total amount of wetting and dispersing agent and defoamer in sequence under stirring. After dispersing for 5-10 minutes, add the composite rust-preventing filler, disperse at high speed for 20-30 minutes, and then grind until the particle size is ≤20μm to obtain the composite rust-preventing filler slurry.

[0032] (2) Add acrylic-polyurethane hybrid emulsion and catechol-silane modified waterborne polyester resin to the composite rust-preventive filler slurry and stir for 15-20 minutes.

[0033] (3) Add adhesion promoter, leveling agent, anti-flash rust agent, and the remaining amount of defoamer and deionized water to the system obtained in step (2), continue stirring for 10-15 minutes, adjust the pH value to 7.0-8.0, filter, and the high adhesion outer coating for pharmaceutical grade aluminum flexible tube packaging is obtained.

[0034] Furthermore, the high-speed dispersion speed in step (1) is 1200-1500 r / min, and the stirring speed in steps (2) and (3) is 200-400 r / min.

[0035] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0036] This invention utilizes a compound of catechol-silane modified waterborne polyester resin and acrylic-polyurethane hybrid emulsion. The catechol groups' ortho-diol structure forms a stable coordination anchor with the aluminum surface, while the silane coupling agent provides Si-O-Al covalent bonds, enabling the coating to maintain high adhesion even in humid and hot environments. This solves the problem of poor adhesion of waterborne coatings to aluminum substrates and easy peeling upon contact with water. The modified polyester resin and hybrid emulsion are mixed in a specific ratio, balancing interfacial anchoring density with overall coating flexibility. The coating can be bent synchronously with the substrate without cracking during aluminum tube calendering, edge rolling, and sealing processes. In the composite rust-preventive filler, zinc phytate replaces conventional zinc phosphate. Its phytate groups form a chelated passivation film on the aluminum surface, synergistically enhancing the physical shielding of titanium dioxide and the microporous filling of nano-silica, resulting in excellent barrier and anti-corrosion capabilities even in thin-layer conditions. The anti-flash rust agent uses a ternary compound of phytic acid, tannic acid, and molybdate. Phytic acid and tannic acid quickly form an organic adsorption layer in the early stages of coating application to inhibit flash rust, while molybdate provides long-lasting corrosion inhibition and self-repair function when corrosion occurs. The three components work synergistically to improve the stability of coating application and the reliability of the coating during service. In addition, the coating formulation does not contain toxic anti-flash rust components such as nitrites, and all raw materials are selected based on compliance requirements for food contact or pharmaceutical packaging, with low VOC content, in line with the trend of green environmental protection. Attached Figure Description

[0037] Figure 1 This is a photograph of the coating obtained in Example 1.

[0038] Figure 2 This is a photograph of the coating effect after the coating from Example 1 was applied to the surface of an aluminum hose and cured. Detailed Implementation

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise specified, the raw materials used in the embodiments are all commercially available products.

[0040] Example 1

[0041] This embodiment provides a pharmaceutical-grade aluminum tube packaging high-adhesion outer coating, comprising the following components by weight:

[0042] 10 parts of catechol-silane modified waterborne polyester resin;

[0043] Acrylic-polyurethane hybrid emulsion (JN AA-3442d) 40 parts;

[0044] 16 parts of composite rust-preventive filler;

[0045] Adhesion promoter (KH-550) 1.0 part;

[0046] Wetting and dispersing agent (BYK-190) 0.5 parts;

[0047] Defoamer (FoamStar® ED 2528) 0.4 parts;

[0048] Leveling agent (TEGO® Glide 450) 0.5 parts;

[0049] 1.2 parts of anti-flash rust agent;

[0050] 30.4 parts of deionized water;

[0051] The composite rust-preventive filler is composed of zinc phytate, titanium dioxide and nano silica in a mass ratio of 1:2:0.5, and the average particle size of the nano silica is 80nm.

[0052] The anti-flash rust agent is a compound of phytic acid, tannic acid and sodium molybdate in a mass ratio of 1:0.6:0.3;

[0053] The catechol-silane modified waterborne polyester resin is prepared by the following method: water-soluble saturated polyester resin (WR80292 type) is reacted with 3,4-dihydroxybenzaldehyde at 65°C for 2 hours, and then KH-560 is added to continue the reaction for 1 hour. The mass ratio of water-soluble saturated polyester resin, 3,4-dihydroxybenzaldehyde and KH-560 is 1:0.06:0.05. After cooling, the catechol-silane modified waterborne polyester resin is obtained.

[0054] The acrylic-polyurethane hybrid emulsion is self-crosslinking type, with a glass transition temperature of 5°C and a solid content of 50%.

[0055] The preparation method of the coating described in this embodiment is as follows:

[0056] (1) Add 50% (15.2 parts) of the total amount of deionized water to the dispersion vessel, and add 0.5 parts of wetting and dispersing agent BYK-190 and 50% (0.2 parts) of the total amount of defoamer FoamStar® ED 2528 in sequence under stirring. After dispersing for 8 minutes, add 16 parts of composite rust-preventive filler and disperse at a high speed of 1350 r / min for 25 minutes. Grind until the particle size is ≤15 μm to obtain composite rust-preventive filler slurry;

[0057] (2) Add 40 parts of acrylic-polyurethane hybrid emulsion and 10 parts of catechol-silane modified waterborne polyester resin to the slurry obtained in step (1), and stir at 300 r / min for 18 min.

[0058] (3) Add 1.0 part of adhesion promoter KH-550, 0.5 part of leveling agent TEGO® Glide450, 1.2 part of anti-flash rust agent, 0.2 part of the remaining defoamer and 15.2 parts of the remaining deionized water to the system obtained in step (2). Continue stirring at 300 r / min for 12 min, adjust the pH value to 7.5, and pass it through a 250 mesh filter to obtain the high adhesion outer coating for pharmaceutical grade aluminum tube packaging.

[0059] A photograph of the actual coating obtained in this embodiment is shown below. Figure 1 As shown. After the coating of Example 1 was uniformly applied to the outer surface of the aluminum hose and cured into a film, as shown... Figure 2 As shown, the coating surface is smooth and clean, with good whiteness, and it is tightly bonded to the aluminum substrate.

[0060] Example 2

[0061] This embodiment provides a pharmaceutical-grade aluminum tube packaging high-adhesion outer coating, which, by weight, consists of the following components:

[0062] Eight parts of catechol-silane modified waterborne polyester resin;

[0063] Acrylic-polyurethane hybrid emulsion (JN AA-3442d) 40 parts;

[0064] 14 parts of composite rust-preventive filler;

[0065] Adhesion promoter (KH-550) 1.2 parts;

[0066] Wetting and dispersing agent (BYK-190) 0.6 parts;

[0067] Defoamer (FoamStar® ED 2528) 0.3 parts;

[0068] Leveling agent (TEGO® Glide 450) 0.4 parts;

[0069] Anti-flash rust agent 1.0 part;

[0070] 34.5 parts deionized water;

[0071] The composite rust-preventive filler is composed of zinc phytate, titanium dioxide and nano silica in a mass ratio of 1:1.8:0.4, and the average particle size of the nano silica is 80 nm.

[0072] The anti-flash rust agent is a compound of phytic acid, tannic acid and ammonium molybdate in a mass ratio of 1:0.8:0.4;

[0073] The catechol-silane modified waterborne polyester resin is prepared by the following method: water-soluble saturated polyester resin (WR80292 type) is reacted with dopamine hydrochloride at 70°C for 1.5 h, and then KH-550 is added to continue the reaction for 1.5 h. The mass ratio of water-soluble saturated polyester resin, dopamine hydrochloride and KH-550 is 1:0.08:0.04. After cooling, the catechol-silane modified waterborne polyester resin is obtained.

[0074] The acrylic-polyurethane hybrid emulsion is self-crosslinking type, with a glass transition temperature of 5°C and a solid content of 50%.

[0075] The preparation method of the coating described in this embodiment is as follows:

[0076] (1) Add 55% (about 19.0 parts) of the total amount of deionized water to the dispersion vessel, and add 0.6 parts of wetting and dispersing agent BYK-190 and 50% (0.15 parts) of the total amount of defoamer FoamStar® ED 2528 in sequence under stirring. After dispersing for 6 minutes, add 14 parts of composite rust-preventive filler and disperse at a high speed of 1400 r / min for 20 minutes. Grind until the particle size is ≤18 μm to obtain composite rust-preventive filler slurry;

[0077] (2) Add 40 parts of acrylic-polyurethane hybrid emulsion and 8 parts of catechol-silane modified waterborne polyester resin to the slurry obtained in step (1), and stir at 250 r / min for 20 min.

[0078] (3) Add 1.2 parts of adhesion promoter KH-550, 0.4 parts of leveling agent TEGO® Glide450, 1.0 part of anti-flash rust agent, 0.15 parts of the remaining defoamer and 15.5 parts of the remaining deionized water to the system obtained in step (2). Continue stirring at 250 r / min for 15 min, adjust the pH value to 7.2, and filter through a 200 mesh screen to obtain the high adhesion outer coating for pharmaceutical grade aluminum tube packaging.

[0079] Comparative Example 1

[0080] The difference between this comparative example and Example 1 is that the catechol-silane modified waterborne polyester resin is replaced with a silane modified waterborne polyester resin, and its preparation method is as follows:

[0081] Water-soluble saturated polyester resin (WR80292 type) was reacted with KH-560 at 65℃ for 3 hours, wherein the mass ratio of water-soluble saturated polyester resin to silane coupling agent was 1:0.05. After cooling, silane-modified waterborne polyester resin was obtained.

[0082] Comparative Example 2

[0083] The difference between this comparative example and Example 1 is that the catechol-silane modified waterborne polyester resin is replaced with acrylic-silane modified waterborne polyester resin, and its preparation method is as follows:

[0084] Water-soluble saturated polyester resin (WR80292 type) was reacted with acrylic acid at 70°C for 2 hours, and then KH-560 was added to continue the reaction for 1 hour. The mass ratio of water-soluble saturated polyester resin, acrylic acid, and silane coupling agent was 1:0.06:0.05. After cooling, acrylic acid-silane modified waterborne polyester resin was obtained.

[0085] Comparative Example 3

[0086] The difference between this comparative example and Example 1 is that the coating comprises the following components by weight:

[0087] 20 parts of catechol-silane modified waterborne polyester resin;

[0088] Acrylic-polyurethane hybrid emulsion (JN AA-3442d) 40 parts;

[0089] 12 parts of composite rust-preventive filler;

[0090] Adhesion promoter (KH-550) 1.0 part;

[0091] Wetting and dispersing agent (BYK-190) 0.5 parts;

[0092] Defoamer (FoamStar® ED 2528) 0.4 parts;

[0093] Leveling agent (TEGO® Glide 450) 0.5 parts;

[0094] 1.2 parts of anti-flash rust agent;

[0095] 25 parts deionized water.

[0096] Comparative Example 4

[0097] The difference between this comparative example and Example 1 is that zinc phytate in the composite rust-preventive filler is replaced with zinc phosphate.

[0098] Comparative Example 5

[0099] The difference between this comparative example and Example 1 is that the anti-flash rust agent does not contain tannic acid, but is only composed of phytic acid and sodium molybdate in a mass ratio of 1:0.5.

[0100] Performance testing

[0101] The coatings obtained in Examples 1-2 and Comparative Examples 1-5 were uniformly coated on the surface of degreased aluminum plates, baked at 100°C for 15 minutes to cure, and the dry film thickness was controlled at 15μm±2μm. After cooling to room temperature, various performance tests were performed.

[0102] VOC content: The determination was carried out in accordance with GB / T 23986.2-2023 "Determination of volatile organic compounds (VOC) and / or semi-volatile organic compounds (SVOC) in paints and varnishes - Part 2: Gas chromatography".

[0103] Adhesion: The adhesion was tested according to GB / T 9286-2021 "Paints and Varnishes Cross-cut Test", and the results were rated on a scale of 0-5, with 0 being the best.

[0104] Flexibility: The test shall be conducted in accordance with GB / T 30791-2014 "T-bend test for paints and varnishes", and shall be expressed as the minimum T-bend grade that does not cause the coating to crack or peel off.

[0105] Salt spray resistance: The test shall be conducted in accordance with GB / T 10125-2021 "Salt spray test for corrosion in artificial atmosphere", and the time when the coating shows signs of rust or blistering shall be recorded.

[0106] Water resistance: The test was conducted according to the immersion test method in GB / T 1733-1993 "Test Method for Water Resistance of Coating Film". After soaking for 72 hours, the coating was removed and the abnormal changes such as whitening, blistering, peeling, loss of gloss, and wrinkling on the coating surface were observed and recorded.

[0107] The test results are shown in Table 1.

[0108] Table 1 Performance Test Results

[0109]

[0110] The performance test results above show that both Examples 1 and 2 achieved environmental protection standards with VOC content below 50g / L, adhesion reached grade 0, T-bend tests showed no cracking at 1T and 0T respectively, salt spray resistance exceeded 900h, and water immersion showed no peeling or whitening after 72h. All performance characteristics are superior to existing water-based aluminum pipe coating technologies, simultaneously meeting the comprehensive requirements of high adhesion, high flexibility, and high protection under thin coating conditions. Comparative Example 1, using only silane modification and lacking the coordination anchoring effect of catechol groups, resulted in decreased interfacial bonding strength between the coating and the aluminum substrate, leading to deterioration in all performance aspects. In Comparative Example 2, replacing catechol with acrylic acid modification weakened the carboxyl group's complexation ability on the aluminum surface compared to the multidentate coordination effect of the ortho-diol structure, resulting in decreased adhesion and localized whitening in water resistance. In Comparative Example 3, excessive use of modified polyester resin led to excessively rigid coating with insufficient flexibility, causing cracking in the 3T T-bend test. In Comparative Example 4, after replacing zinc phytate with zinc phosphate, the passivation film density and chelating corrosion inhibition ability of zinc phosphate were inferior to those of zinc phytate, resulting in a decrease in salt spray resistance time and adhesion. In Comparative Example 5, after removing tannic acid, the anti-flash rust agent system lacked the film-forming assistance and synergistic passivation effect of tannic acid. Slight flash rust spots appeared after coating application, and the T-bend and salt spray resistance performance deteriorated.

[0111] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-adhesion outer coating for pharmaceutical-grade aluminum flexible tube packaging, characterized in that, By weight, it includes the following components: 5-15 parts of catechol-silane modified waterborne polyester resin; 35-55 parts of acrylic-polyurethane hybrid emulsion; 9-23 parts of composite rust-inhibiting filler; Adhesion promoter 0.5-2.0 parts; 0.3-0.8 parts of wetting and dispersing agent; Defoamer 0.2-0.6 parts; Leveling agent 0.3-0.7 parts; Anti-flash rust agent 0.5-2.0 parts; 15-40 parts deionized water; Catechol-silane modified waterborne polyester resin is prepared by the following method: The water-soluble saturated polyester resin was reacted with a compound containing catechol groups at 50-80℃ for 1-3 hours, followed by the addition of a silane coupling agent and the reaction continued for 0.5-2 hours; the mass ratio of the water-soluble saturated polyester resin, the compound containing catechol groups, and the silane coupling agent was 1:(0.03-0.10):(0.02-0.08). The compound containing a catechol group is selected from at least one of 3,4-dihydroxybenzaldehyde, 3,4-dihydroxybenzoic acid, and dopamine hydrochloride, and the silane coupling agent is selected from at least one of γ-glycidoxypropyltrimethoxysilane and γ-aminopropyltriethoxysilane. The composite rust-preventive filler is composed of zinc phytate, titanium dioxide, and nano-silica in a mass ratio of 1:(1.5-3):(0.3-0.8). The adhesion promoter is γ-aminopropyltriethoxysilane; The anti-flash rust agent is a compound of phytic acid, tannic acid and molybdate in a mass ratio of 1:(0.4-1.0):(0.2-0.5).

2. The high-adhesion outer coating for pharmaceutical-grade aluminum flexible tube packaging according to claim 1, characterized in that, The mass ratio of the catechol-silane modified waterborne polyester resin to the acrylic-polyurethane hybrid emulsion is 1:(3-5).

3. The high-adhesion outer coating for pharmaceutical-grade aluminum flexible tube packaging according to claim 1, characterized in that, The acrylic-polyurethane hybrid emulsion is self-crosslinking, with a glass transition temperature of -10°C to 20°C and a solid content of 45-55%.

4. The method for preparing the high-adhesion outer coating for pharmaceutical-grade aluminum flexible tube packaging according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Add 40-60% of the total amount of deionized water to the dispersion vessel, and add 40-60% of the total amount of wetting and dispersing agent and defoamer in sequence under stirring. After dispersing for 5-10 minutes, add the composite rust-preventing filler, disperse at high speed for 20-30 minutes, and then grind until the particle size is ≤20μm to obtain the composite rust-preventing filler slurry. (2) Add acrylic-polyurethane hybrid emulsion and catechol-silane modified waterborne polyester resin to the composite rust-preventive filler slurry and stir for 15-20 minutes. (3) Add adhesion promoter, leveling agent, anti-flash rust agent, and the remaining amount of defoamer and deionized water to the system obtained in step (2), continue stirring for 10-15 minutes, adjust the pH value to 7.0-8.0, filter, and the high adhesion outer coating for pharmaceutical grade aluminum flexible tube packaging is obtained.

5. The preparation method according to claim 4, characterized in that, The high-speed dispersion speed in step (1) is 1200-1500 r / min, and the stirring speed in steps (2) and (3) is 200-400 r / min.

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