Corrosion-resistant transparent coating for welding seam of acid food can

Abstract

The invention discloses a corrosion-resistant transparent coating for a weld joint of an acid food can, and relates to the technical field of corrosion-resistant coating curing coatings. The invention discloses a corrosion-resistant transparent coating for a welding seam of an acid food can. The corrosion-resistant transparent coating is prepared from the following components in parts by mass: 35 to 65 parts of hydroxy acrylic resin, 15 to 30 parts of isocyanate curing agent, 8 to 15 parts of epoxy resin, 0.5 to 3 parts of perfluorobutyl sulfonate, 1 to 5 parts of gamma-glycidyl ether oxypropyl trimethoxy silane, 3 to 8 parts of silicon dioxide, 0.2 to 1 part of flatting agent and 0.1 to 0.5 part of defoaming agent. Through the synergistic effect of the isocyanate curing agent and the perfluorobutyl sulfonate, the high transparency of the coating is kept, meanwhile, the resistance to an acid medium is remarkably enhanced, and the contradiction that a traditional coating cannot give consideration to transparency and corrosion resistance at the same time is solved.

Description

Technical Field

[0001] The invention relates to the technical field of corrosion-resistant coating curing paint, in particular to a corrosion-resistant transparent coating for the weld of an acidic food can. Background Art

[0002] In the food packaging industry, the corrosion prevention of acidic food cans has always been a technical challenge. Acidic foods such as juice, ketchup, and sauerkraut have acidic components that can accelerate the corrosion of can welds, reducing the can's sealing and safety.

[0003] While a variety of anti-corrosion coatings are currently available on the market, they present numerous shortcomings. For one thing, while some coatings offer a certain degree of corrosion protection, their lack of transparency prevents direct observation of the weld condition, hindering the timely detection of potential problems. Furthermore, some transparent coatings have limited corrosion resistance and are prone to peeling and cracking in acidic environments, rendering them ineffective in protecting tank welds.

[0004] Furthermore, the adhesion of existing anti-corrosion coatings needs to be improved. If the coating lacks adhesion to the can surface, it can easily fall off during food processing, transportation, and storage, significantly compromising its anti-corrosion effectiveness. Furthermore, some coatings lack high-temperature resistance and are unable to withstand the high-temperature baking or sterilization conditions of food cans, impacting the coating's stability and service life.

[0005] Furthermore, in practical applications, coating application performance is crucial. Some coatings require complex application processes, specialized equipment and conditions, increasing production costs and operational complexity. Meanwhile, some coatings, while easy to apply, struggle to maintain optimal performance in terms of corrosion resistance, adhesion, and high-temperature resistance.

[0006] In summary, the market is in urgent need of a corrosion-resistant transparent coating for the welds of acidic food cans that can meet the transparency requirements, have excellent corrosion resistance, good adhesion and high temperature resistance, and is easy to construct, so as to solve the many shortcomings of the existing technology and better adapt to the use needs of acidic food cans. Summary of the Invention

[0007] The present invention aims to provide a corrosion-resistant transparent coating for the welds of acidic food cans. The coating has excellent acid resistance, good adhesion and high temperature resistance, and is transparent and easy to construct, so as to solve the problems of insufficient corrosion resistance, poor adhesion, opacity and complex construction of the coating in the prior art.

[0008] To achieve the above object, the technical solution adopted by the present invention is: a corrosion-resistant transparent coating for the weld of acidic food cans, comprising the following components by weight: 35-65 parts of hydroxy acrylic resin, 15-30 parts of isocyanate curing agent, 8-15 parts of epoxy resin, 0.5-3 parts of perfluorobutyl sulfonate, 1-5 parts of γ-glycidyloxypropyltrimethoxysilane, 3-8 parts of silicon dioxide, 0.2-1 parts of leveling agent, and 0.1-0.5 parts of defoaming agent; The isocyanate curing agent has a structure shown in Formula 1: Formula 1; Z1 in Formula 1 is selected from the group consisting of: O, S, N(H), and C(CH3)2.

[0009] Furthermore, the hydroxy value of the hydroxy acrylic resin is 80-120 mg KOH / g.

[0010] Furthermore, the isocyanate curing agent is any one of the following structures: ; .

[0011] Furthermore, the epoxy equivalent of the epoxy resin is 175-200 g / mol.

[0012] Furthermore, the perfluorobutanesulfonate is potassium perfluorobutanesulfonate.

[0013] Furthermore, the leveling agent is polydimethylsiloxane.

[0014] Furthermore, the defoaming agent is sodium dodecylbenzenesulfonate.

[0015] A method for preparing a corrosion-resistant transparent coating for the weld of an acidic food can comprises the following steps: (a) mixing and dispersing the hydroxy acrylic resin, epoxy resin and silica at 40-50° C. for 30 minutes; (b) adding the γ-glycidyloxypropyltrimethoxysilane and reacting at 60° C. for 1 hour; (c) cooling to below 35° C. and adding the isocyanate curing agent; (d) adding perfluorobutanesulfonate, leveling agent, and defoaming agent in sequence; (e) Filtering with a filter screen to obtain a transparent corrosion-resistant transparent coating for the welds of acidic food cans.

[0016] Furthermore, the reaction in step (b) is carried out under nitrogen protection.

[0017] Furthermore, the corrosion-resistant transparent coating for the weld of an acidic food can is applied to the weld area of a tinplate with a wet film thickness of 8-12 μm and cured by baking at 200-220° C. for 60-90 seconds.

[0018] The isocyanate curing agent of the present invention contains a heteroaromatic ring structure, which has a highly conjugated π electron system, forming a stable planar structure, which can effectively resist the erosion of acidic media (such as organic acids in food); the electron cloud density of the conjugated system is evenly distributed, reducing the interaction with H + The reaction activity of heteroatoms can form coordination bonds through lone pairs of electrons, thereby enhancing adhesion to metal substrates; the hydrophobic aromatic ring structure hinders the penetration of moisture and ions, slowing down electrochemical corrosion; the high bond energy of the large conjugated aromatic ring makes it stable at the coating baking temperature and avoids decomposition. The isocyanate curing agent described in the present invention contains an isocyanate group (-NCO), which can react with the hydroxyl group (-OH) of the hydroxy acrylic resin to form a polyurethane bond and construct a three-dimensional cross-linked network. This reaction gives the coating high hardness, wear resistance and adhesion. The heteroaromatic ring provides a rigid skeleton, while the fatty chain connected by isocyanate imparts moderate flexibility to avoid brittle cracking of the coating. The large-volume heteroaromatic ring structure slows down the reaction rate of the -NCO group and improves stability during the construction period. The heteroaromatic ring can adsorb the fluorocarbon chain of perfluorobutane sulfonate through π-π stacking, promote its uniform dispersion in the coating, and enhance the anti-permeability.

[0019] The hydroxylated acrylic resin and isocyanate curing agent described in this invention create a corrosion-resistant cross-linked backbone. The hydroxylated acrylic resin provides active hydroxyl (-OH) groups that react with the -NCO groups of the isocyanate curing agent to form a dense polyurethane cross-linked network, imparting high hardness, wear resistance, and toughness to the coating. The rigid heteroaromatic ring backbone combines with the flexible polyurethane segments to prevent brittle cracking of the coating. The heteroaromatic rings adsorb perfluorobutanesulfonate through π-π stacking, promoting its uniform dispersion and improving anti-permeation efficiency.

[0020] The epoxy resin + γ-glycidyloxypropyltrimethoxysilane described in the present invention: Enhances adhesion and interfacial stability. The epoxy resin provides epoxy groups, which react with the epoxy groups of the silane to form an interpenetrating network, improving the density of the coating; the silane coupling agent generates silanol (Si-OH) through a hydrolysis reaction, forming a Si-O-Sn covalent bond with the Sn-OH on the surface of the tinplate; the epoxy groups react with the resin to achieve a strong chemical bond between the "inorganic substrate and the organic coating." The epoxy resin and silane form an interpenetrating network, filling the gaps in the polyurethane crosslinking and blocking the penetration path of the acidic medium; the silane improves the dispersibility of the silica filler in the resin.

[0021] The potassium perfluorobutanesulfonate of the present invention: directional migration corrosion protection and synergistic barrier. The sulfonate group is hydrophilic, and the fluorocarbon chain is hydrophobic, driving the molecules to migrate to the coating / metal interface; forming a hydrophobic fluorocarbon layer at the interface and releasing K+ Combines with metal corrosion products to form stable precipitates, inhibiting the spread of corrosion.

[0022] The silica described in this invention enhances wear resistance and structural stability. It fills the gaps in the cross-linked network, improving coating hardness and scratch resistance. It also forms an inorganic-organic hybrid structure with silane, reducing internal stress in the coating and preventing cracking during high-temperature baking.

[0023] The leveling agent (polydimethylsiloxane) and defoamer (sodium dodecylbenzenesulfonate) described in this invention ensure both workability and surface performance. The leveling agent reduces surface tension, ensuring uniform coating spread across welds; the defoamer suppresses bubbles during mixing and application, ensuring coating density. The combination of these two ensures a stable wet film thickness, eliminates defects such as pinholes and fisheyes after curing, and maintains transparency and uniform corrosion protection.

[0024] Compared with the prior art, the present invention has the following beneficial effects: 1. Synergistic improvement of corrosion resistance and transparency: Through the synergistic effect of isocyanate curing agent and perfluorobutane sulfonate, the coating's resistance to acidic media is significantly enhanced while maintaining high transparency, solving the contradiction between traditional coatings' difficulty in balancing transparency and corrosion resistance.

[0025] 2. Enhanced adhesion and structural stability: Epoxy resin and γ-glycidyloxypropyl silane form an interpenetrating network, combined with the filling effect of silica, which greatly improves the chemical bonding force and mechanical strength of the coating and the tinplate substrate, effectively avoiding cracking and shedding of the coating under high-temperature baking or acidic environment.

[0026] 3. Optimized high-temperature resistance and construction performance: Isocyanate curing agents impart excellent thermal stability to the coating, making it suitable for high-temperature baking processes in food cans. The precise ratio of leveling agent and defoamer ensures uniform wet film spread across the weld area, simplifying the construction process and reducing coating defects. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The isocyanate curing agent 1 of the present invention 1 HNMR spectrum. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solution of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] Synthesis example 1 Synthesis of isocyanate curing agent 1: ; The first step: Under nitrogen protection, 20g of raw material 1, 16.26g of raw material 2, 14.61g of sodium tert-butoxide, 2.09g of tris(dibenzylideneacetone)dipalladium, 0.8g of tri-tert-butylphosphine and 200g of toluene were added to the reaction system in sequence, stirred evenly, heated to 110°C, and refluxed for 11h; after the reaction was completed, the temperature was slightly lowered, filtered using diatomaceous earth, the filtrate was cooled to room temperature, washed three times with water, the organic phase was retained, and the aqueous phase was extracted with ethyl acetate; after the organic phases were combined, they were dried with anhydrous magnesium sulfate, filtered, spin-dried, and chromatographed on a silica gel column using a mixture of petroleum ether and ethyl acetate as an eluent to obtain 21.17g of intermediate 1.

[0030] Step 2: Under nitrogen protection, 21.17 g of intermediate 1, 20.80 g of raw material 3, 31.29 g of potassium phosphate trihydrate, 0.07 g of pyridine-2-carboxylic acid, 0.55 g of CuI and 220 g of DMSO were added to the reaction system in sequence, and heated at 85 ° C for 16 h; after cooling, the reaction mixture was extracted with an ammonia solution and methyl tert-butyl ether, and the organic phase was washed five times with water and then washed twice with a saturated NaCl solution; finally, the combined organic phase was dried over anhydrous magnesium sulfate, filtered, spin-dried, and subjected to silica gel column chromatography using a mixture of petroleum ether and ethyl acetate as eluent to obtain 27.50 g of isocyanate curing agent 1.

[0031] Product structure identification: MS [MS+H] of intermediate 1 + :361; MS[MS+H] of isocyanate curing agent 1 + :575; Isocyanate curing agent 1 1 HNMR-Chloroform d: δ7.77-7.70(m,1H),7.60(dd,1H),7.43-7.28(m,1H),7.34-7.25(m,2H),7.18(q,1H),7.02(d,1H),6.98-6.86(m, 2H),6.62-6.55(m,1H),4.33(m,1H),4.13-4.02(m,1H),3.70(m,1H),2.52(m,1H),2.33-2.20(m,10H),1.48(s,6H).

[0032] Synthesis Example 2-Synthesis Example 4 In Synthesis Examples 2 to 4, isocyanate curing agent 2 to isocyanate curing agent 4 were synthesized in sequence, referring to the synthesis method of Synthesis Example 1, replacing raw material 1 therein, and remaining the same as Synthesis Example 1. Specific structures of raw material 1, isocyanate curing agent 2 to isocyanate curing agent 4, MS [MS + H] + See Table 1 for data.

[0033] Table 1. Structure of raw material 1, isocyanate curing agent 2-isocyanate curing agent 4, and MS [MS+H] involved in Synthesis Examples 2-4 + data.

[0034]

[0035] Example 1 This embodiment provides a corrosion-resistant transparent coating for the weld of an acidic food can and a preparation method thereof. The specific steps are as follows: 1. Raw material ratio (by mass): 50 parts of hydroxyl acrylic resin (hydroxyl value 100 mg KOH / g), 22 parts of isocyanate curing agent (isocyanate curing agent 1 synthesized in Synthesis Example 1), 12 parts of epoxy resin (epoxy equivalent 185 g / mol), 1.8 parts of potassium perfluorobutylsulfonate, 3 parts of γ-glycidyloxypropyltrimethoxysilane, 5 parts of silicon dioxide (particle size 20 nm), 0.6 parts of polydimethylsiloxane (leveling agent), and 0.3 parts of sodium dodecylbenzenesulfonate (defoaming agent); 2. Preparation method: (a) Adding a hydroxylated acrylic resin, an epoxy resin, and silica to a reaction kettle, heating the mixture to a constant temperature of 45° C., and stirring and dispersing the mixture at 800 rpm for 30 minutes; (b) adding γ-glycidyloxypropyltrimethoxysilane to the system, passing nitrogen protection, and heating to 60° C. for 1 hour; (c) cooling to 30° C., adding isocyanate curing agent 1, and stirring at low speed to mix evenly; (d) adding potassium perfluorobutylsulfonate, polydimethylsiloxane, and sodium dodecylbenzenesulfonate in sequence, and stirring at 400 rpm for 15 minutes; (e) filtering the mixture through a 30-mesh filter to obtain a transparent and uniform corrosion-resistant transparent coating liquid for the welds of acidic food cans.

[0036] Example 2-Example 4 A corrosion-resistant transparent coating for the weld of an acidic food can is prepared by referring to the preparation method of Example 1, except that the isocyanate curing agent therein is replaced with isocyanate curing agent 2 to isocyanate curing agent 4 prepared in Synthesis Examples 2-4, and the rest remains the same as Example 1.

[0037] Comparative Example 1 A corrosion-resistant transparent coating for the weld of an acidic food can is prepared by referring to the preparation method of Example 1, except that the isocyanate curing agent is replaced by comparative compound 1, and the rest of the process remains the same as that of Example 1.

[0038] Comparative compound 1: .

[0039] Comparative Example 2 A corrosion-resistant transparent coating for the weld of an acidic food can is prepared by referring to the preparation method of Example 1, except that the isocyanate curing agent is not added, and the rest of the steps remain the same as in Example 1.

[0040] Comparative Example 3 A corrosion-resistant transparent coating for the weld of an acidic food can is prepared by referring to the preparation method of Example 1, except that the mass ratio of potassium perfluorobutanesulfonate is replaced with 8 parts, and the rest remains the same as in Example 1.

[0041] Performance testing: Sample preparation: Spray the prepared coating (a corrosion-resistant transparent coating for the weld of acidic food cans prepared in the examples and comparative examples) on the weld area of the tin-plated steel plate, control the wet film thickness to 10 μm, and bake in an oven at 210°C for 75 seconds to cure.

[0042] 1. Alkali resistance: The alkali resistance of the sample was tested with reference to GB / T9274-1998. The data is shown in Table 2.

[0043] 2. Acid resistance: The acid resistance of the sample was tested with reference to GB / T9274-1998. The data is shown in Table 2.

[0044] 3. Paint film appearance: Evaluate the paint film appearance of the sample. See Table 2 for the data.

[0045] Table 2. Performance test data of the sample plates sprayed with a corrosion-resistant transparent coating for the weld seam of acidic food cans prepared in the examples and comparative examples.

[0046]

[0047] The embodiments are superior in acid and alkali resistance and paint film appearance, with good coating stability (no obvious failure such as blistering and wrinkling), and all remain transparent. The performance of the comparative examples is significantly reduced. The acid and alkali resistance of comparative example 1 (replacement of curing agent) and comparative example 2 (missing curing agent) are seriously deteriorated (blistering, wrinkling, discoloration), and the paint film is turbid or cracked. The acid resistance of comparative example 3 (excessive perfluorinated salt) is reduced (blistering, wrinkling), and the paint film is slightly whitish. The formula of the present invention is superior to the adjusted comparative example in corrosion resistance and appearance stability, verifying the necessity of the key components.

[0048] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A corrosion-resistant transparent coating for the weld of acidic food cans, characterized in that: Contains the following components by weight: 35-65 parts of hydroxy acrylic resin, 15-30 parts of isocyanate curing agent, 8-15 parts of epoxy resin, 0.5-3 parts of perfluorobutyl sulfonate, 1-5 parts of γ-glycidyloxypropyltrimethoxysilane, 3-8 parts of silicon dioxide, 0.2-1 parts of leveling agent, and 0.1-0.5 parts of defoaming agent; The isocyanate curing agent has a structure shown in Formula 1: Formula 1; Z1 in Formula 1 is selected from the group consisting of: O, S, N(H), and C(CH3)2.

2. The corrosion-resistant transparent coating for the weld of an acidic food can according to claim 1, characterized in that: The hydroxy value of the hydroxy acrylic resin is 80-120 mg KOH / g.

3. The corrosion-resistant transparent coating for the weld of an acidic food can according to claim 1, characterized in that: The isocyanate curing agent is any one of the following structures: ； 。 4. The corrosion-resistant transparent coating for the weld of an acidic food can according to claim 1, characterized in that: The epoxy equivalent weight of the epoxy resin is 175-200 g / mol.

5. The corrosion-resistant transparent coating for the weld of an acidic food can according to claim 1, characterized in that: The perfluorobutanesulfonate is potassium perfluorobutanesulfonate.

6. The corrosion-resistant transparent coating for the weld of an acidic food can according to claim 1, characterized in that: The leveling agent is polydimethylsiloxane.

7. The corrosion-resistant transparent coating for the weld of an acidic food can according to claim 1, characterized in that: The defoaming agent is sodium dodecylbenzenesulfonate.

8. The corrosion-resistant transparent coating for the weld of an acidic food can according to claim 1, characterized in that: The corrosion-resistant transparent coating for the weld seams of acidic food cans is coated on the weld seam area of the tinplate with a wet film thickness of 8-12 μm and is cured by baking at 200-220° C. for 60-90 seconds.

9. A method for preparing a corrosion-resistant transparent coating for the weld of an acidic food can according to any one of claims 1 to 8, characterized in that: The following steps are involved: (a) mixing and dispersing the hydroxy acrylic resin, epoxy resin and silica at 40-50° C. for 30 minutes; (b) adding the γ-glycidyloxypropyltrimethoxysilane and reacting at 60° C. for 1 hour; (c) cooling to below 35° C. and adding the isocyanate curing agent; (d) adding perfluorobutanesulfonate, leveling agent, and defoaming agent in sequence; (e) Filtering with a filter screen to obtain a transparent corrosion-resistant transparent coating for the welds of acidic food cans.

10. The method for preparing a corrosion-resistant transparent coating for the weld of an acidic food can according to claim 9, characterized in that: The reaction in step (b) is carried out under nitrogen protection.

Images