A chromium-free passivating agent for high-temperature resistant retort-type can lids and its preparation method

Abstract

The present invention discloses a chromium-free passivator for a high-temperature resistant retort-type can lid, wherein the raw materials for preparation include, by weight percentage, 0.5-2% organic zirconium, 1-5% inorganic acid, 5-10% film material, 0.5-2% film-forming promoter, 1-5% silane coupling agent, 3-10% auxiliary agent, and pure water to 100%. The main component of the passivation film of the present invention is fluorotitanic acid, and the use of a chromium-free passivation film avoids the potential risks of using a chromium-containing passivator, improves safety in use, is environmentally friendly, and meets modern environmental protection requirements. In addition, a combination of methacrylic zirconium salt, phosphoric acid, and polyacrylic acid is used to increase the adhesion of the passivation film to the aluminum can lid, increase the thickness of the passivation film, and improve the corrosion resistance of the passivation film. The present invention applies the chromium-free passivator to the aluminum can lid strip, which is resistant to water boiling, acid boiling, and sulfur boiling under high temperature conditions.

Description

Technical Field

[0001] The present invention relates to the field of C09D coating compositions, and in particular to a chromium-free passivating agent for high-temperature resistant retort-type can lids and a preparation method thereof. Background Art

[0002] Aluminum can lids are typically made of 3104 aluminum alloy, 5052 aluminum alloy, and 5182 aluminum alloy, and are widely used in food packaging. During the surface treatment of the aluminum can lid strip, the aluminum strip undergoes cleaning, passivation, and coating. Applying a passivator to the inside of the aluminum can lid prevents direct contact between the beverage and the aluminum, preventing aluminum ions from dissolving in the beverage and maintaining the beverage's quality and taste. Existing passivators commonly used in aluminum can lids are mostly chromium (trivalent chromium)-containing passivators, which offer excellent corrosion resistance. While trivalent chromium offers improved food safety compared to hexavalent chromium, as a heavy metal, trivalent chromium still poses significant risks to human health and the natural environment. Therefore, developing chromium-free passivators and maintaining good adhesion between the chromium-free passivator and the can lid are crucial.

[0003] Chinese invention patent CN201410389381.7 discloses a chromium-free composite passivator for hot-dip galvanized steel sheets and its preparation and use methods. First, an organosilane is dissolved in water, stirred until completely dissolved, and then a main salt compound is added. After dissolution, an inorganic acid is added to measure the pH value. Then, sulfate and an inorganic zirconium salt are added while stirring. After complete dissolution, a water-based resin is added. The passivator does not contain chromium and is non-toxic and harmless. The passivation film thickness can reach 8-1.0 mg / m 2 The corrosion resistance of this product approaches that of hexavalent chromium passivation solutions, but it requires the use of resin, making it unsafe for use in beverage packaging. Chinese invention patent CN201410081359.6 discloses a chromium-free composite passivator for galvanized sheet metal in continuous annealing lines at steel mills and its preparation method. The passivator includes a coupling agent, a silicate, an emulsifier, and a corrosion inhibitor. The resulting passivator exhibits a uniform and stable appearance and significantly improved corrosion resistance, but it cannot meet safety requirements for use in food packaging. Summary of the Invention

[0004] In order to develop a chromium-free passivator and maintain good adhesion between the chromium-free passivator and the can lid, the first aspect of the present invention provides a high-temperature resistant cooking can lid chromium-free passivator, the preparation raw materials include, by weight percentage: organic zirconium 0.5-2%, inorganic acid 1-5%, film material 5-10%, film-forming promoter 0.5-2%, silane coupling agent 1-5%, auxiliary agent 3-10%, and pure water supplemented to 100%.

[0005] As a preferred embodiment, the organic zirconium is selected from at least one of zirconium methacrylate, butyl zirconate, zirconium acetylacetonate, zirconium isobutoxide, zirconium acetate, tetraethoxy zirconium, and tetrabenzyl zirconium.

[0006] As a preferred embodiment, the organic zirconium is zirconium methacrylate.

[0007] As a preferred embodiment, the inorganic acid is selected from at least one of phosphoric acid, sulfuric acid, nitric acid, hydrochloric acid, boric acid, and carbonic acid.

[0008] As a preferred embodiment, the inorganic acid is phosphoric acid.

[0009] As a preferred embodiment, the film material is a fluorine compound, and the fluorine compound is selected from at least one of fluorotitanic acid, fluorozirconic acid, ammonium bifluoride, fluoroboric acid, and hydrofluoric acid.

[0010] As a preferred embodiment, the membrane material is fluorotitanic acid.

[0011] During experiments, the applicant discovered that using fluorotitanic acid as the primary film-forming component also resulted in a coating with a certain degree of adhesion on the surface of aluminum can lids, making it a viable alternative to chromium-containing passivators and improving safety in beverage packaging. This may be due to the fact that chromium-containing passivators typically contain trivalent chromium, which can convert to hexavalent chromium when the passivation film structure becomes unstable, making it unsafe for use in beverage packaging. Furthermore, chromium-containing passivators still pose significant environmental hazards. Therefore, using fluorotitanic acid as the primary film-forming component can avoid the use of chromium and improve safety. However, chromium-free passivators still exhibit some shortcomings in their adhesion to the aluminum lid during the film-forming process.

[0012] As a preferred implementation, the film-forming promoter is a high-valent metal compound, and the high-valent metal compound is selected from at least one of ammonium tungstate, ammonium heptamolybdate, ammonium tetramolybdate, and ammonium heptatungstate.

[0013] As a preferred implementation, the film-forming promoter is ammonium tungstate or ammonium heptamolybdate.

[0014] As a preferred embodiment, the silane coupling agent is an aminosilane coupling agent or an acyloxysilane coupling agent, wherein the aminosilane coupling agent is selected from at least one of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyl-trimethoxysilane, and N-(β-aminoethyl)-γ-aminopropyl-methyl-trimethoxysilane. The acyloxysilane coupling agent is γ-methacryloxypropyltrimethoxysilane.

[0015] As a preferred embodiment, the silane coupling agent is selected from at least one of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and γ-methacryloxypropyltrimethoxysilane.

[0016] As a preferred embodiment, the auxiliary agent includes at least one of a stabilizer and a wetting and dispersing agent, the stabilizer is polyacrylic acid, and the average molecular weight of the polyacrylic acid is 2000-5000 Da.

[0017] During experiments, the applicant discovered that introducing zirconium methacrylate and phosphoric acid into a polyacrylic acid system could improve the adhesion of the passivation film to the substrate and increase the thickness of the passivation film. The possible reason is speculated to be that in the polyacrylic acid system, the zirconium methacrylate reacts with phosphoric acid to form a suspension of nanoparticles. These nanoparticles create slight protrusions on the surface of the fluorotitanium passivation film, increasing the roughness of the passivation film and improving adhesion to the smooth substrate surface. Furthermore, the polyacrylic acid system contains a large number of polar groups, further enhancing adhesion to aluminum can lids. Furthermore, the nanoparticles generated by the reaction of zirconium methacrylate and phosphoric acid increase the thickness of the passivation film, making the structure of the passivation film more stable and improving its corrosion resistance.

[0018] However, the generated nano-particle suspension is prone to precipitation during storage. The weight ratio of zirconium methacrylate, phosphoric acid, and polyacrylic acid is (0.5-2): (1-5): (3-8), which can increase the dispersibility of the passivator system, avoid precipitation during storage, and improve the storage stability of the passivator system.

[0019] As a preferred embodiment, the wetting and dispersing agent is a nonionic surfactant, and the nonionic surfactant is a hyperbranched surfactant with a central hydrophilic group.

[0020] As a preferred embodiment, the wetting and dispersing agent is BASF WE 3323.

[0021] During experiments, the applicant discovered that using ammonium tungstate or ammonium heptamolybdate as a film-forming accelerator and adding an aminosilane coupling agent can accelerate the film formation of the passivating agent, improve the corrosion resistance of the passivating film, and impart certain high-temperature and water resistance to the passivating film. Possible reasons for this are speculated to be: ammonium tungstate or ammonium heptamolybdate can accelerate the film formation of the passivating agent under acidic conditions. As high-valent metal compounds, ammonium tungstate or ammonium heptamolybdate can achieve multivalent state conversion, thereby improving the corrosion resistance of the passivating film. Furthermore, the use of an aminosilane coupling agent can reduce the drying temperature of the passivating film. When the aluminum strip passes through a drying plate, a film can be rapidly formed at 60-65°C. The passivating film exhibits good bonding to the aluminum strip at low-temperature film formation, resulting in a passivating film that is resistant to water boiling, acid boiling, and high-temperature vulcanization.

[0022] A second aspect of the present invention provides a method for preparing a chromium-free passivating agent for a high-temperature resistant retort-type can lid, comprising the following steps:

[0023] S1: Dissolve the inorganic acid in pure water, start the disperser, control the reaction temperature, slowly add the silane coupling agent, continue to disperse for 20-30 minutes, adjust the pH, and disperse again for 20-40 minutes to obtain mixed solution I;

[0024] S2 accelerates the dispersion of mixed solution I, controls the reaction temperature, adds additives, disperses for 5-15 minutes, slowly adds organic zirconium, and continues to disperse for 1-3 hours;

[0025] S3 slows down and disperses, cooling to room temperature;

[0026] S4 slowly adds membrane material and film-forming accelerator and disperses for 20-40 minutes.

[0027] As a preferred embodiment, the dispersion speed of step S1 is 300-400 r / min, and the dispersion speed of step S2 is 800-1000 r / min.

[0028] As a preferred embodiment, the pH of step S1 is 2-3; the reaction temperature of step S1 is 15-25°C.

[0029] As a preferred embodiment, the speed of adding the silane coupling agent in step S1 is 3-7% of the formula amount of the silane coupling agent per minute.

[0030] As a preferred embodiment, the reaction temperature in step S2 is 35-40° C., and the rate of adding the organic zirconium in step S2 is 1-2% of the formulated amount of the organic zirconium per minute.

[0031] As a preferred embodiment, after the dispersion in step S2, the solution is slightly turbid, and a sample is taken and cooled to room temperature and allowed to stand for 20-40 minutes until there is no obvious floating matter or precipitation in the solution.

[0032] As a preferred embodiment, the film material and film-forming accelerator are added at a rate of 10-15% of the formulated amount per minute in step S4.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The chromium-free passivation agent for the high-temperature cooking-resistant can lid of the present invention has a passivation film whose main component is fluorotitanic acid. The use of a chromium-free passivation film avoids the potential risks of using a chromium-containing passivation agent, improves safety in use, does not pollute the environment, and meets modern environmental protection requirements.

[0035] (2) The chromium-free passivator for high-temperature cooking-resistant can lids of the present invention adopts a combination of zirconium methacrylate, phosphoric acid and polyacrylic acid, which can improve the adhesion of the passivation film to the aluminum can lid, increase the thickness of the passivation film, and improve the corrosion resistance of the passivation film.

[0036] (3) The chromium-free passivator for the high-temperature resistant retort-type can lid of the present invention uses ammonium tungstate or ammonium heptamolybdate as a film-forming promoter, and also includes an aminosilane coupling agent, which can accelerate the film formation of the passivator, improve the corrosion resistance of the passivation film, and make the passivation film have certain high-temperature resistance and water resistance.

[0037] (4) The chromium-free passivator for high-temperature cooking-resistant can lids of the present invention uses a hyperbranched surfactant with a central hydrophilic group as a wetting and dispersing agent, which can increase the wetting speed of the passivator on the substrate, make the microparticles evenly dispersed, maintain the stability of the system, and prevent the passivator from polymerizing, precipitating, or cross-linking under normal temperature conditions.

[0038] (5) The high-temperature boiling-resistant can lid chromium-free passivator of the present invention is applied to the aluminum can lid strip, and has excellent water boiling resistance, acid boiling resistance, and sulfur boiling resistance under high temperature conditions. DETAILED DESCRIPTION

[0039] Example

[0040] A chromium-free passivating agent for high-temperature resistant retort can lids, the raw materials for preparation are shown in Table 1 below in terms of weight percentage:

[0041] Table 1

[0042]

[0043] KH-792 is N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane; KH-550 is γ-aminopropyltriethoxysilane; and KH-570 is γ-methacryloyloxypropyltrimethoxysilane. The average molecular weight of the polyacrylic acid is 2000-5000 Da, and its CAS number is 9003-01-4.

[0044] A method for preparing a chromium-free passivating agent for a high-temperature resistant retort-type can lid comprises the following steps:

[0045] S1: Dissolve the inorganic acid in pure water, start the disperser, control the reaction temperature, slowly add the silane coupling agent, continue to disperse for 20 minutes, adjust the pH, and disperse again for 30 minutes to obtain mixed solution I;

[0046] S2 accelerates the dispersion of mixed solution I, controls the reaction temperature, adds additives, disperses for 10 minutes, slowly adds organic zirconium, and continues to disperse for 2 hours;

[0047] S3 slows down and disperses, cooling to room temperature;

[0048] S4 slowly adds membrane material and film-forming accelerator and disperses for 30 minutes.

[0049] The dispersion speed of step S1 is 350 r / min, and the dispersion speed of step S2 is 900 r / min.

[0050] The pH of step S1 is 2.5; the reaction temperature of step S1 is 20°C.

[0051] The speed of adding the silane coupling agent in step S1 is 5% of the formula amount of the silane coupling agent per minute.

[0052] The reaction temperature in step S2 is 37.5° C., and the rate of adding the organic zirconium in step S2 is 1% of the formulated amount of the organic zirconium per minute.

[0053] After dispersion in step S2, the solution is slightly turbid. Samples are taken and cooled to room temperature and allowed to stand for 30 minutes until there is no obvious floating matter or precipitation in the solution.

[0054] The film material and film-forming accelerator are added at a rate of 10% of the formulated amount per minute in step S4.

[0055] Comparative Example

[0056] A chromium-free passivating agent for high-temperature resistant retort can lids, the raw materials for preparation are shown in Table 2 below in terms of weight percentage:

[0057] Table 2

[0058]

[0059] A method for preparing a chromium-free passivating agent for high-temperature resistant retort-type can lids, the specific implementation method is the same as that of Example 1.

[0060] Performance Testing

[0061] The passivating agents prepared in the examples and comparative examples were diluted 6 times with deionized water, coated on the inner side of the can lid by a roller, and dried at a plate temperature of 60° C. to obtain a passivation film.

[0062] Tests were conducted according to the internal coating requirements of "YS / T726-2010 Aluminum Alloy Sheet and Strip for Can Lids and Ring Pulls." The test results are shown in Table 3.

[0063] High temperature sterilization: 121℃, 30min distillation, if the coating does not turn white, lose gloss, peel or fall off, it is qualified;

[0064] Acid resistance: 121℃, 32min acid etching, the coating is qualified if there is no whitening, loss of gloss, peeling or falling off;

[0065] Sulfur resistance: 121℃, 31min sulfur corrosion, the coating is qualified if there is no whitening, loss of gloss, peeling or falling off;

[0066] Adhesion level 1 (no peeling or falling off in the coating 100-grid test) is qualified.

[0067] Table 3

[0068]

Claims

1. A chromium-free passivating agent for high-temperature resistant retort can lids, characterized in that: The raw materials for preparation include, by weight percentage: organic zirconium 0.5-2%, inorganic acid 1-5%, membrane material 5-10%, film-forming accelerator 0.5-2%, silane coupling agent 1-5%, auxiliary agent 3-10%, and pure water to 100%; The organic zirconium is zirconium methacrylate; The inorganic acid is phosphoric acid; The film-forming accelerator is ammonium tungstate or ammonium heptamolybdate; The silane coupling agent is selected from at least one of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and γ-methacryloxypropyltrimethoxysilane; The auxiliary agent includes a stabilizer and a wetting and dispersing agent. The stabilizer is polyacrylic acid with an average molecular weight of 2000-5000 Da. The weight ratio of methacrylate zirconium salt, phosphoric acid and polyacrylic acid is (0.5-2): (1-5): (3-8).

2. The chromium-free passivator for high-temperature resistant retort can lids according to claim 1, characterized in that: The membrane material is a fluorine compound, and the fluorine compound is selected from at least one of fluorotitanic acid, fluorozirconic acid, ammonium bifluoride, fluoroboric acid, and hydrofluoric acid.

3. The chromium-free passivator for high temperature resistant retort can lids according to claim 1, characterized in that: The wetting and dispersing agent is a nonionic surfactant, and the nonionic surfactant is a hyperbranched surfactant with a central hydrophilic group.

4. A method for preparing the chromium-free passivating agent for high-temperature resistant retort can lids according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1: Dissolve the inorganic acid in pure water, start the disperser, control the reaction temperature, slowly add the silane coupling agent, continue to disperse for 20-30 minutes, adjust the pH, and disperse again for 20-40 minutes to obtain mixed solution I; S2 accelerates the dispersion of mixed solution I, controls the reaction temperature, adds additives, disperses for 5-15 minutes, slowly adds organic zirconium, and continues to disperse for 1-3 hours; S3 slows down and disperses, cooling to room temperature; S4 slowly adds membrane material and film-forming accelerator and disperses for 20-40 minutes.

5. The method for preparing the high temperature resistant retort type can lid chromium-free passivating agent according to claim 4, characterized in that: The dispersion speed of step S1 is 300-400 r / min, and the dispersion speed of step S2 is 800-1000 r / min.

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