A heavy metal-free waterborne anti-rust primer and a preparation method thereof

Abstract

This invention discloses a heavy metal-free water-based anti-rust primer, its preparation method, and its application, relating to the field of water-based metal anti-corrosion coatings. The primer comprises a modified acrylic copolymer emulsion, a modified zinc phosphate-aluminum tripolyphosphate composite pigment, a diatomaceous earth composite filler, and a lignin sulfonate-grafted polycarboxylic acid dispersant. The modified acrylic copolymer emulsion is prepared by copolymerizing four monomers and then modifying them with epoxy silane and amino silane. The modified zinc phosphate-aluminum tripolyphosphate composite pigment is prepared by rare earth lanthanum ion loading and synergistic modification with a dual coupling agent. The diatomaceous earth composite filler is prepared by high-temperature activation, composite with nano-silica, and silane modification. Through the synergistic effect of its components, this invention significantly improves the primer's adhesion, resistance to damp heat, high temperature, kitchen fumes, weak acid resistance in food, and resistance to alkaline media in the kitchen, making it suitable for corrosion protection of various metal components in kitchens and commercial kitchens.

Description

Technical Field

[0001] This invention belongs to the field of water-based metal anti-corrosion coating technology, specifically a heavy metal-free water-based anti-rust primer, its preparation method, and its application. Background Technology

[0002] Water-based acrylic anti-rust primers are widely used for anti-corrosion coating of civil metal components due to their advantages of low VOC, excellent environmental friendliness, and easy application. Metal corrosion protection in kitchens and commercial catering facilities is a crucial part of the daily operation and maintenance of buildings and catering facilities. Numerous metal components in these areas, such as cabinet frames, support brackets, kitchen and bathroom hardware, kitchenware bases, processing equipment frames, and exhaust accessories, are constantly exposed to complex environments with high humidity, frequent temperature changes, oil contamination, and contact with cleaning agents. They are continuously subjected to the combined effects of moisture, temperature variations, and various corrosive media. Therefore, the long-term anti-corrosion capabilities of the metal substrate are subject to stringent requirements.

[0003] Heavy metal-free water-based acrylic anti-rust primers are already commonly used materials for indoor metal corrosion protection. Some products on the market are formulated using only a single anti-rust pigment combined with ordinary acrylic emulsions. Among them, the zinc phosphate and aluminum tripolyphosphate compound system is more suitable for high-humidity corrosive environments due to its complementary anti-corrosion properties and good compatibility with water-based emulsions. However, when conventional primers are used alone to form a film (i.e., without a topcoat), their resistance to damp heat, heat, oil stains, and weak acids and alkalis is generally insufficient, making it difficult to adapt to the harsh conditions of kitchens and commercial kitchens in the long term. Specific problems are reflected in the following aspects: Firstly, the high humidity in the kitchen environment, combined with the degreaser, disinfectant, and food residue from daily cleaning, can intermittently form a weak acid or alkali film on the surface of components. Single rust-preventive pigments offer limited protection, and even with pigment formulations, ordinary primers often lack sufficient density and have numerous micropores, allowing corrosive media to slowly penetrate the metal surface and induce rust. Furthermore, general-purpose acrylic resins typically have limited chemical resistance; prolonged contact with weak acids and alkalis can easily lead to powdering, peeling, and other issues with a single-layer paint film.

[0004] Secondly, daily cooking involves frequent temperature changes and localized high-temperature and high-humidity environments. The normal temperature around the stove is mostly 35-55℃, and the instantaneous temperature near an open flame can reach 70℃. Repeated temperature fluctuations cause the single-layer paint film to be continuously subjected to expansion and contraction stress. In addition, the heat resistance and adaptability of general emulsions are generally poor, and the paint film is prone to softening in warm environments, reducing the overall shielding effect and gradually causing micro-cracks. This further accelerates the penetration of corrosive media and speeds up coating failure.

[0005] Third, commercial kitchens handle large volumes of food and operate for extended periods, causing grease and fumes to condense and adhere to the coating surface, forming a continuous oil film. This disrupts the integrity and density of the single-layer paint film, increasing the penetration rate of corrosive media. In poorly ventilated, damp areas with accumulated grease, mold can easily grow on the coating surface, causing the paint film to become moldy and discolored.

[0006] Because conventional primers have many performance shortcomings when applied in a single layer without a matching topcoat, the industry mostly adopts a two-layer coating solution of primer and topcoat. The topcoat compensates for the shortcomings of a single-layer primer in terms of stain resistance, resistance to various media, and resistance to damp heat. While two-layer coatings can meet the basic requirements of kitchen use, they involve more steps, increase material and labor costs, and lower construction efficiency. Furthermore, two-layer coatings lack flexibility and are not suitable for simple coating applications such as concealed components and supporting frames within the kitchen.

[0007] Therefore, developing a heavy metal-free water-based acrylic anti-rust primer that is suitable for the multiple corrosive environments of kitchens and commercial kitchens, can resist alternating humidity and heat, oil stains, and intermittent corrosion from weak acids and alkalis, and can achieve integrated protection of the base and surface with a single layer of coating, has strong practical application value and market demand. Summary of the Invention

[0008] The purpose of this invention is to provide a heavy metal-free water-based anti-rust primer, its preparation method, and its application, in order to solve the problems of existing water-based anti-rust primers in environments such as high humidity, high temperature, oil fume accumulation, and intermittent corrosion by weak acids and alkalis in kitchens and commercial kitchens, including insufficient adhesion, poor resistance to damp heat, high-temperature re-adhesion and softening, weak resistance to oil fumes and media, easy mold growth, easy cracking and failure of the coating, and inability to achieve single-layer integrated protection of the primer and surface.

[0009] The objective of this invention is achieved through the following technical solution: In a first aspect, the present invention provides a heavy metal-free water-based anti-rust primer, comprising the following components in parts by weight: 30–45 parts modified acrylic copolymer emulsion, 12–20 parts modified zinc phosphate-aluminum tripolyphosphate composite pigment, 3–8 parts diatomaceous earth composite filler, 2–6 parts film-forming aid, 1–4 parts lignin sulfonate grafted polycarboxylate dispersant, 0.3–1.2 parts hydrophobic associative thickener, 0.5–1.8 parts mildew inhibitor, 0.4–1.5 parts cyclic amine neutralizer, and 18–28 parts deionized water; The modified acrylic copolymer emulsion is prepared by copolymerizing four monomers: butyl acrylate, methyl methacrylate, hydroxyethyl acrylate, and itaconic acid, and then modifying them with epoxy silane KH-560 and amino silane KH-550. The modified zinc phosphate-aluminum tripolyphosphate composite pigment is obtained by combining zinc phosphate and aluminum tripolyphosphate, loading rare earth lanthanum ions, and then modifying it by combining KH-560 and titanate coupling agent NDZ-101. The diatomite composite filler is prepared by uniformly combining porous diatomite with nano-silica after high-temperature activation, and then modifying it with KH-560. The film-forming aid is a compound of ethylene glycol diisobutyrate, tripropylene glycol monomethyl ether, and polyether-modified organosiloxane. The lignin sulfonate-grafted polycarboxylic acid dispersant is obtained by graft copolymerization of lignin sulfonate with acrylic acid and methyl acrylate.

[0010] The heavy metal-free water-based anti-rust primer provided by this invention can improve problems such as moisture absorption and stickiness of the paint film, poor low-temperature film formation, cracking under alternating humidity and heat, oil fume clogging of pores, and slow surface drying and oil adsorption in kitchens and commercial kitchens under high humidity and temperature environments. The functions and mechanisms of each component are as follows: The modified acrylic copolymer emulsion is formed by free radical emulsion copolymerization of four carbon-carbon double bond monomers: butyl acrylate, methyl methacrylate, hydroxyethyl acrylate, and itaconic acid, to form a copolymer backbone structure. Butyl acrylate provides flexible segments to offset the expansion and contraction stress of alternating hot and cold temperatures. Methyl methacrylate increases the hard segment content and heat distortion temperature, solving the problems of film softening and shielding failure when heated. Hydroxyethyl acrylate introduces hydroxyl groups to enhance metal wetting and adhesion. Itaconic acid increases crosslinking points and adhesion, indirectly improving media resistance through high crosslinking density. The four monomers copolymerization and bissilane composite grafting together form a high-density interpenetrating crosslinking network, significantly improving the heat resistance, damp heat resistance, temperature change resistance, and oil fume penetration resistance of the film. Building upon this foundation, a composite grafting modification using epoxy silane KH-560 and amino silane KH-550 is further employed: KH-560 provides epoxy and hydroxyl crosslinking sites, enhancing the crosslinking density and media resistance of the coating film; KH-550 provides interfacial anchoring and crosslinking sites, improving adhesion and water resistance. The combination of these two materials overcomes the defects of excessive crosslinking, poor low-temperature film formation, and easy pinhole formation caused by single silane modification. Simultaneously, silane crosslinking improves the overall water resistance of the coating film, alleviates the increase in hydrophilicity caused by the introduction of carboxyl groups from itaconic acid, and solves the problems of moisture absorption and stickiness, and decreased wear resistance of the coating film in the high-temperature and high-humidity environment of the kitchen.

[0011] The modified zinc phosphate-aluminum tripolyphosphate composite pigment utilizes a dual corrosion inhibition system formed by zinc phosphate and aluminum tripolyphosphate, synergistically achieving dual rust prevention through barrier and passivation. Rare earth lanthanum ions are then introduced to enhance the density of the passivation film and improve its long-term rust prevention. Finally, KH-560 and titanate coupling agent NDZ-101 are used for composite modification. KH-560 improves the pigment's surface hydrophobicity and resin compatibility, preventing powder agglomeration and sedimentation. NDZ-101 enhances the pigment's hydrophobicity and dispersion stability, mitigating the problem of rare earth ion precipitation that leads to whitening of the paint film and rust prevention failure. Simultaneously, it shields the rare earth ions from the thermo-oxidative aging catalytic effect on the resin, solving the problem of paint film yellowing and shortened protective lifespan under long-term high-temperature environments in kitchens. This results in more stable pigment dispersion and longer-lasting rust prevention, making it suitable for the complex working conditions of high humidity and intermittent acid and alkali corrosion in kitchens.

[0012] In the diatomaceous earth composite filler, high-temperature activation removes impurities, and nano-silica fills the gaps inside the paint film, improves the overall density, and reduces the adsorption of oil fumes and grease in the pores. KH-560 modification further improves the oleophobicity and dispersibility of the filler, which can effectively block the penetration of water vapor, grease, and salt media, while improving the wear resistance and scratch resistance of the paint film, making it suitable for the long-term oil fume adhesion environment in the kitchen.

[0013] The film-forming aid is a compound of ethylene glycol diisobutyrate, tripropylene glycol monomethyl ether, and polyether-modified organosiloxane. Through gradient volatilization and low surface energy synergistic effect, it accelerates the surface drying rate of the paint film, overcoming the defects of slow-drying systems in high-humidity, enclosed kitchen environments, such as slow surface drying, easy adsorption of oil fumes and dust, and sudden drop in adhesion and delamination. At the same time, it eliminates pinholes in the paint film and improves the uniformity of film formation. The organosilicon component reduces the surface energy of the coating, reduces oil fume wetting and adhesion, making the coating more resistant to oil stains and easier to clean, and suitable for environmentally friendly construction requirements in enclosed catering spaces.

[0014] Lignosulfonate-grafted polycarboxylate dispersant uses industrial lignosulfonate as the main chain and grafts polycarboxylate side chains formed by copolymerization of acrylic acid and methyl acrylate, forming an anchored-steric dual dispersion structure. This overcomes the shortcomings of traditional dispersants in terms of temperature resistance, oil resistance, and hydrolysis resistance, and can efficiently and stably disperse composite pigments and fillers, prevent system stratification and sedimentation, and has better storage stability and construction adaptability.

[0015] Hydrophobic associative thickeners rely on hydrophobic segments to form a reversible associative network, giving the system low viscosity and anti-sagging rheological properties during construction. It is suitable for spraying various irregularly shaped metal components in the kitchen, ensuring uniform film thickness and smooth appearance.

[0016] The compound anti-mildew agent effectively solves the problems of mold, discoloration, and contamination of paint films in the damp and oily environment of the kitchen.

[0017] The composite cyclic amine neutralizer provides a wide range of pH buffering capabilities, stabilizing the emulsion system and reducing the impact of acidic components on the substrate.

[0018] In summary, through the synergistic effect of its components, this invention enables the coating to exhibit excellent adhesion, rust prevention, resistance to damp heat, resistance to temperature changes, resistance to oil stains, resistance to mildew, and long-term protection under complex working conditions such as high humidity, alternating temperature and heat, rich oil fumes, and intermittent corrosion by weak acids and alkalis in kitchens and commercial kitchens. It can achieve integrated protection of the bottom and top surfaces with a single layer and is suitable for anti-corrosion coating of various metal components in kitchens.

[0019] As some possible implementations of this application, in the modified acrylic copolymer emulsion, the mass ratio of butyl acrylate, methyl methacrylate, hydroxyethyl acrylate and itaconic acid is 100:(60-80):(15-25):(8-15); the mass ratio of epoxy silane KH-560 and aminosilane KH-550 is (2.5-3.5):1.

[0020] As some possible implementation methods of this application, in the modified zinc phosphate-aluminum tripolyphosphate composite pigment, the mass ratio of zinc phosphate to aluminum tripolyphosphate is (1.2~2.0):1; the total amount of KH-560 and titanate coupling agent NDZ-101 is 1.2~3.8% of the total pigment mass, and the amount of rare earth lanthanum ions added is 0.05~0.3% of the total pigment mass; the mass ratio of KH-560 to titanate coupling agent NDZ-101 is (1.8~2.2):1.

[0021] As some possible implementation methods of this application, in the diatomaceous earth composite filler, the high-temperature activation temperature is 680-760℃; the amount of KH-560 added is 1.8-4.7% of the total mass of the filler.

[0022] As some possible implementations of this application, in the film-forming aid, the mass ratio of ethylene glycol diisobutyrate, tripropylene glycol monomethyl ether, and polyether-modified organosiloxane is (0.8-1.2):(2.8-3.2):(1.0-1.4).

[0023] As one possible implementation of this application, the antifungal agent is a mixture of decanediol and glycerin in a mass ratio of (1.0 to 2.0):1.

[0024] As one possible implementation method of this application, the cyclic amine neutralizing agent is prepared by compounding methylcyclohexylamine and triethanolamine in a mass ratio of 1:(1.2 to 2.0).

[0025] Secondly, this invention provides a method for preparing a heavy metal-free water-based anti-rust primer. First, deionized water, lignin sulfonate grafted polycarboxylate dispersant, and cyclic amine neutralizer are added to a dispersion tank and stirred thoroughly. Then, modified zinc phosphate-aluminum tripolyphosphate composite pigment and diatomaceous earth composite filler are added and stirred thoroughly. Finally, modified acrylic copolymer emulsion, film-forming aid, hydrophobic associative thickener, and mildew inhibitor are added. After dispersion at ≤45℃, the mixture is filtered to obtain the finished primer.

[0026] Thirdly, the present invention provides an application of a heavy metal-free water-based anti-rust primer, which is applied to the protective coating of metal components in kitchen and catering commercial kitchen scenarios. The metal components include cabinet frames, support brackets, kitchen and bathroom hardware, kitchenware bases, processing equipment frames, and exhaust accessories.

[0027] Compared with the prior art, the beneficial effects of the present invention are: This invention effectively improves the problems of insufficient adhesion, poor resistance to damp heat, easy re-adhesion and softening at high temperatures, weak resistance to oil fumes and weak acids and alkalis, easy mold growth, and weak long-term protective properties of water-based anti-rust primers on metal substrates in kitchen and commercial kitchen environments through the synergistic effect of quaternary copolymer modified acrylic emulsion, rare earth and dual coupling agent composite modified anti-rust pigments, diatomaceous earth composite filler, film-forming aids, and lignin-grafted polycarboxylate dispersant. The initial adhesion of the obtained primers is ≥5.2MPa, and they have excellent interfacial bonding strength with metal substrates. They show no obvious abnormalities in resistance to 500h of damp heat, 70℃ / 240h of high temperature, and 168h of kitchen oil stains. They are stable in resistance to weak acid food and alkaline kitchen cleaners. They show no rust or spread in resistance to 500h of neutral salt spray. The low-temperature flexibility at -10℃ is 1.8-2.3mm. The mildew resistance is ≤1. They show no obvious abnormalities in resistance to 50 cycles of hot and cold cycling. After 30 cycles of comprehensive accelerated aging in the kitchen, they only lose slight gloss, without blistering, cracking, or peeling, and the residual adhesion still maintains a stable protective level. This primer can be applied directly as a single-layer base and topcoat, or used in conjunction with the topcoat. It can meet the long-term protection requirements of kitchens without the need for multiple coats. It can better adapt to the complex service conditions of kitchens, such as high humidity, high temperature, rich oil fumes, intermittent acid and alkali corrosion, and frequent temperature changes. It has better overall protective stability and application applicability. It does not contain heavy metal components and is suitable for anti-corrosion coating of various metal components in kitchens and commercial catering kitchens with low food contact risk. Detailed Implementation

[0028] Example 1 1. Preparation of modified acrylic copolymer emulsion: By mass ratio, butyl acrylate: methyl methacrylate: hydroxyethyl acrylate: itaconic acid = 100:70:20:12 were mixed evenly to obtain mixed monomers; 3.0% sodium dodecylbenzenesulfonate emulsifier and 100% deionized water were added to the mixed monomers and stirred and dispersed at 800 r / min for 25 min to prepare a pre-emulsion; the temperature was raised to 75℃, and 0.1% ammonium persulfate and 10% pre-emulsion were added first, and the mixture was kept warm and stirred for 30 min to form a seed emulsion; the remaining 90% pre-emulsion and 0.4% ammonium persulfate aqueous solution were mixed evenly and added dropwise over 2 h. After the addition was completed, the mixture was kept warm and stirred for 2 h to obtain the copolymer emulsion.

[0029] Separately, epoxy silane KH-560 and amino silane KH-550 were mixed at a mass ratio of 3:1, and 3 to 5 times the total mass of the silane was added to deionized water. The pH was adjusted to 4.0 to 5.0 with acetic acid, and the mixture was pre-hydrolyzed for 20 min. The hydrolyzed silane solution was then added dropwise to the copolymer emulsion, with the total amount added being 3.5% of the total mass of the mixed monomers. The mixture was stirred and reacted for 2 h at 65℃ and 600 r / min. After cooling to below 40℃, the pH was adjusted to 7.0 to 7.5 with ammonia water to obtain the modified acrylic copolymer emulsion.

[0030] 2. Preparation of lignin sulfonate grafted polycarboxylate dispersant: A mixture of lignin sulfonate (weight average molecular weight 10000, sulfonation degree 1.0 mmol / g), acrylic acid, and methyl acrylate was prepared at a mass ratio of 100:40, with the mass ratio of acrylic acid to methyl acrylate being 1:1. Deionized water was added to prepare an aqueous solution with a solid content of 30%, and the pH was adjusted to 8.0. The mixture was heated to 85℃, and 0.6% (by mass of the total mass of acrylic acid and methyl acrylate) of ammonium persulfate initiator was added. The mixture was stirred at 500 r / min for 3 h to carry out the graft copolymerization reaction. After cooling to room temperature, the pH was adjusted to 7.0–7.5 to obtain the lignin sulfonate grafted polycarboxylate dispersant.

[0031] 3. Preparation of modified zinc phosphate-aluminum tripolyphosphate composite pigment: Zinc phosphate and aluminum tripolyphosphate were mixed evenly in a mass ratio of 1.6:1 to obtain composite pigment powder. Lanthanum nitrate was prepared into a 5% (w / w) aqueous solution using deionized water. This solution was sprayed evenly using a high-pressure atomizing nozzle at a spray pressure of 0.4 MPa and a flow rate of 6 mL / min. Simultaneously, a tumbling mixer was used to continuously stir the pigment at 70 r / min, controlling the lanthanum ion addition to 0.1% of the total pigment mass. Stirring and adsorption continued at 400 r / min for 30 min, followed by drying at 100–120℃. Then, a compound surface modifier (2.5% of the total pigment mass) pre-mixed with KH-560 and titanate coupling agent NDZ-101 in a mass ratio of 2:1 was added, and the mixture was stirred at 800 r / min for 40 min to obtain the modified zinc phosphate-aluminum tripolyphosphate composite pigment.

[0032] 4. Preparation of diatomaceous earth composite filler: Porous diatomaceous earth was placed in a muffle furnace and activated at 720℃ for 2 h using a mass proportioner. After cooling, nano-silica was mixed with it at 16% of the mass of the activated diatomaceous earth and stirred at 600 r / min for 30 min to achieve uniform composite. Then, KH-560 at 3.2% of the total filler mass was added and stirred at 800 r / min for 40 min to modify the diatomaceous earth composite filler.

[0033] 5. Preparation of film-forming aid: Ethylene glycol diisobutyrate, tripropylene glycol monomethyl ether, and polyether-modified organosiloxane were mixed evenly at a mass ratio of 1:3:1.2 and stirred at 500 r / min for 15 min to obtain the film-forming aid.

[0034] 6. Preparation of antifungal agent: Decanediol and glycerin are mixed evenly at a mass ratio of 1.5:1 to obtain an antifungal agent.

[0035] 7. Preparation of cyclic amine neutralizer: Methylcyclohexylamine and triethanolamine are mixed evenly at a mass ratio of 1:1.6 to obtain the cyclic amine neutralizer.

[0036] 8. Preparation of heavy metal-free water-based anti-rust primer: By weight, add 23 parts deionized water, 2.5 parts lignin sulfonate grafted polycarboxylate dispersant, 1.0 part cyclic amine neutralizer, and 0.5 parts Nalin FA179 corrosion inhibitor to a dispersion tank and stir at 900 r / min for 6 min; add 16 parts modified zinc phosphate-aluminum tripolyphosphate composite pigment and 5 parts diatomaceous earth composite filler, heat to 38℃, and disperse at 1300 r / min for 18 min; reduce the speed to below 800 r / min, add 38 parts modified acrylic copolymer emulsion, 4 parts film-forming aid, 0.7 parts hydrophobic associative thickener (hydrophobic modified polyurethane associative thickener), and 1.2 parts mildew inhibitor, and disperse at 800 r / min for 12 min, controlling the system temperature ≤45℃ throughout the process; after dispersion, filter through a 150-mesh filter to obtain the finished primer.

[0037] Example 2 Compared to Example 1, only the following parameters were adjusted; all other processes, parameters, rotation speed, temperature, and time remained exactly the same as in Example 1. The specific adjustments are as follows: 1. Preparation of modified acrylic copolymer emulsion: Modified acrylic copolymer emulsion: Butyl acrylate: Methyl methacrylate: Hydroxyethyl acrylate: Itaconic acid = 100:60:15:8, KH-560:KH-550 = 2.5:1.

[0038] 2. Preparation of modified zinc phosphate-aluminum tripolyphosphate composite pigment: Zinc phosphate:aluminum tripolyphosphate = 1.2:1; the amount of rare earth lanthanum ions added is 0.15% of the total pigment mass; the total amount of compound surface modifier is 1.2% of the total pigment mass, KH-560:NDZ-101 = 1.8:1.

[0039] 3. Preparation of diatomaceous earth composite filler: The high-temperature activation temperature is 680℃; the amount of nano-silica added is 12% of the mass of activated diatomaceous earth; the amount of KH-560 added is 1.8% of the total mass of the filler.

[0040] 4. Preparation of film-forming aid: Ethylene glycol diisobutyrate: tripropylene glycol monomethyl ether: polyether-modified organosiloxane = 0.8:2.8:1.0.

[0041] 5. Preparation of antifungal agent: Decanediol: Glycerol = 1.0:1.

[0042] 6. Preparation of cyclic amine neutralizing agent: Methylcyclohexylamine: Triethanolamine = 1:1.2.

[0043] 7. Preparation of primer formulation: 30 parts modified acrylic copolymer emulsion, 12 parts modified zinc phosphate-aluminum tripolyphosphate composite pigment, 3 parts diatomaceous earth composite filler, 2 parts film-forming aid, 1 part lignin sulfonate grafted polycarboxylate dispersant, 0.3 parts hydrophobic associative thickener, 0.5 parts mildew inhibitor, 0.4 parts cyclic amine neutralizer, 0.2 parts Nathan's NALZINFA179 corrosion inhibitor, and 18 parts deionized water.

[0044] Example 3 Compared to Example 1, only the following parameters were adjusted; all other processes, parameters, rotation speed, temperature, and time remained exactly the same as in Example 1. The specific adjustments are as follows: 1. Preparation of modified acrylic copolymer emulsion: butyl acrylate: methyl methacrylate: hydroxyethyl acrylate: itaconic acid = 100:80:25:15, KH-560:KH-550 = 3.5:1.

[0045] 2. Preparation of modified zinc phosphate-aluminum tripolyphosphate composite pigment: Zinc phosphate:aluminum tripolyphosphate = 2.0:1; the amount of rare earth lanthanum ions added is 0.2% of the total pigment mass; the total amount of compound surface modifier is 3.8% of the total pigment mass, KH-560:NDZ-101 = 2.2:1.

[0046] 3. Preparation of diatomaceous earth composite filler: The high-temperature activation temperature is 760℃; the amount of nano-silica added is 20% of the mass of activated diatomaceous earth; the amount of KH-560 added is 4.7% of the total mass of filler.

[0047] 4. Preparation of film-forming aid: Ethylene glycol diisobutyrate: tripropylene glycol monomethyl ether: polyether-modified organosiloxane = 1.2:3.2:1.4.

[0048] 5. Preparation of antifungal agent: Decanediol: Glycerol = 2.0:1.

[0049] 6. Preparation of cyclic amine neutralizing agent: Methylcyclohexylamine: Triethanolamine = 1:2.0.

[0050] 7. Preparation of primer formulation: 45 parts modified acrylic copolymer emulsion, 20 parts modified zinc phosphate-aluminum tripolyphosphate composite pigment, 8 parts diatomaceous earth composite filler, 6 parts film-forming aid, 4 parts lignin sulfonate grafted polycarboxylate dispersant, 1.2 parts hydrophobic associative thickener, 1.8 parts mildew inhibitor, 1.5 parts cyclic amine neutralizer, 0.8 parts Nasal NALZINFA179 corrosion inhibitor, and 28 parts deionized water.

[0051] It is worth noting that the modified acrylic copolymer emulsion, lignosulfonate-grafted polycarboxylate dispersant, modified zinc phosphate-aluminum tripolyphosphate composite anti-rust pigment, diatomaceous earth composite functional filler, and finished water-based metal anti-rust primer prepared in Examples 1-3 above have the following physicochemical characterization and microscopic performance parameter ranges: ① Modified acrylic copolymer emulsion: solid content 44.0%~46.0%, kinematic viscosity at 25℃ 2250~2750 mPa·s, average particle size of emulsion 95~120 nm.

[0052] ② Lignosulfonate grafted polycarboxylate dispersant: solid content 30.0%~33.0%, grafting rate of total components of acrylic acid and methyl acrylate 28.0%~36.0%.

[0053] ③ Modified zinc phosphate-aluminum tripolyphosphate composite anti-rust pigment powder: average particle size 2.8~4.5 μm, oil absorption value 27.0~32.0 g / 100g, water surface contact angle 98.0°~110.0°.

[0054] ④ Diatomaceous earth composite functional filler: average particle size 3.2~6.0 μm, actual loading rate of nano silica 14.0%~18.0%, water surface contact angle 103.0°~112.0°.

[0055] ⑤ Finished water-based metal anti-rust primer: 25℃ system viscosity 900~1350 mPa·s.

[0056] Comparative Example 1 Compared with Example 1, the modified acrylic copolymer emulsion was prepared without the addition of itaconic acid, while the remaining components, proportions, processes, rotation speed, and temperature were exactly the same.

[0057] Comparative Example 2 Compared with Example 1, the modified acrylic copolymer emulsion was prepared using only KH-560 for modification, without adding KH-550 or performing compound modification. The other components, proportions, and processes were exactly the same.

[0058] Comparative Example 3 Compared with Example 1, the modified zinc phosphate-aluminum tripolyphosphate composite pigment does not introduce rare earth lanthanum ions, does not use NDZ-101, and only uses KH-560 for modification. The other components, proportions, and processes are exactly the same.

[0059] Comparative Example 4 Compared with Example 1, the modified zinc phosphate-aluminum tripolyphosphate composite pigment was prepared without NDZ-101, using only KH-560 for modification, while the other components, proportions, and processes were exactly the same.

[0060] Comparative Example 5 Compared with Example 1, the diatomaceous earth composite filler was not activated at high temperature of 680~760℃ during preparation, and no nano-silica was added. Only ordinary diatomaceous earth was modified with KH-560. The other components, proportions and processes were exactly the same.

[0061] Comparative Example 6 Compared to Example 1, the lignin sulfonate-grafted polycarboxylate dispersant was replaced with a conventional ungrafted ordinary polycarboxylate dispersant, while the remaining components, proportions, and processes were exactly the same.

[0062] Experimental Example The heavy metal-free water-based anti-rust primers obtained in Examples 1-3 (denoted as S1-S3) and Comparative Examples 1-6 (denoted as D1-D6) were uniformly coated onto the surface of cold-rolled steel sheets (substrate size 100mm×100mm×1mm). The samples were coated, formed, and cured for 7 days in a standard environment (temperature 23±2℃, relative humidity 50±5%), with the dry film thickness controlled at 100±10μm. After curing, performance tests were conducted on each group of samples as follows, and the test results are recorded in Table 1. Three parallel samples were set up for each group, and the average value of each performance test result was taken, with a relative standard deviation not exceeding 5%. Specific test indicators and methods are as follows: (1) Adhesion test: The adhesion of the coating is tested using a pull-off tester. The unit is MPa. The test results are used to characterize the interfacial bonding strength between the coating and the metal substrate.

[0063] (2) Moisture and heat resistance test: The sample was placed in an environment with a temperature of 47±1℃ and a relative humidity of 96±2% for 500 hours. After the test, the surface condition of the coating was observed and the blistering, corrosion, whitening, cracking and peeling were recorded.

[0064] (3) High temperature resistance test: The sample was placed in a 70℃ constant temperature oven for 240 hours to simulate the high temperature working conditions of the kitchen stove. After the test, the coating was observed to see if it became sticky, soft, lost its gloss, yellowed and cracked.

[0065] (4) Kitchen oil stain resistance test: Mix edible vegetable oil and animal oil at a mass ratio of 1:1 to prepare simulated oil fume condensate, and apply it evenly to the coating surface; place the sample in an environment of 60℃ for 168 hours, take it out and wipe it clean with a lint-free cloth; observe whether the coating loses its gloss, changes color, bubbles, wrinkles and peels off.

[0066] (5) Food weak acid resistance test: A 5% acetic acid solution was used as the test medium to simulate the weak acid environment of food such as vinegar and fruit juice; the acetic acid solution was dripped onto the coating surface and kept at room temperature for 24 hours. After the time was up, it was wiped clean with a lint-free cloth; observe whether the coating showed whitening, loss of gloss, blistering and corrosion.

[0067] (6) Resistance to kitchen alkaline cleaners test: A 5% sodium carbonate solution was used as the test medium to simulate the environment of edible alkali and kitchen alkaline cleaners; the sodium carbonate solution was dripped onto the coating surface and kept at room temperature for 24 hours. After the time was up, it was wiped clean with a lint-free cloth; observe whether the coating showed whitening, loss of gloss, blistering and corrosion.

[0068] (7) Neutral salt spray resistance test: Place the sample in a salt spray test chamber for 500 hours continuously; observe the corrosion of the coating after the test. Judgment criteria: No obvious abnormalities means no corrosion and no spread; slight corrosion means a small number of corrosion points appear and the unidirectional spread width of corrosion is ≤2mm; obvious corrosion means a large corrosion area and the spread width is ≤3mm; severe corrosion means large-area corrosion and coating failure.

[0069] (8) Low temperature flexibility test: The sample was placed in a -10℃ low temperature environment for 4 hours to allow the coating to reach a low temperature equilibrium state; the cylindrical bending method was used for testing, and the minimum bending radius at which the coating did not crack was recorded.

[0070] (9) Anti-mold performance test: The samples were uniformly sprayed with a mixed suspension of Aspergillus niger, Aspergillus flavus, Chaetomium globulus, Trichoderma viride, and Bacillus subtilis spores; the samples were then placed in an environment with a temperature of 28±2℃ and a relative humidity of 90±5% for 28 days, and the growth of mold on the paint film surface was observed and the anti-mold level was evaluated. Anti-mold level judgment criteria: Level 0: No mold growth on the coating surface, no colonies at all; Level 1: A small number of mold spots on the coating surface, with a mold coverage area of ​​<10%; Level 2: A significant increase in mold on the coating surface, with a coverage area of ​​10% to 30%.

[0071] (10) Resistance to thermal cycling test: The thermal cycling cycle was completed by “baking at 70℃ for 2 hours → freezing at -10℃ for 2 hours”, and a total of 50 cycles were performed. After the test, the coating was observed to see if cracking, wrinkling, powdering and peeling occurred.

[0072] (11) Comprehensive accelerated aging test of the kitchen: The test was conducted using a multi-factor combined accelerated aging method. A single cycle included: 2h of wet heat treatment at 60℃ and 90% relative humidity → 2h of simulated oil fume coating and 2h of placement at 60℃ → 1h of contact with 5% acetic acid solution at room temperature → 1h of contact with 5% sodium carbonate solution at room temperature → 1h of freezing treatment at -10℃; 30 cycles were performed continuously under the above conditions. After the cycle, the appearance of the coating was observed and the residual adhesion of the coating was tested.

[0073] Table 1: Performance Test Results It is worth noting that the " / " in Table 1 indicates that no relevant experiments were conducted. Due to the weak performance of individual tests in the early stage, no subsequent experiments or comprehensive aging tests were carried out.

[0074] As shown in Table 1, Examples 1-3 effectively improved the problems of insufficient adhesion, poor resistance to damp heat, easy re-adhesion and softening at high temperatures, weak resistance to oil fumes and weak acids and alkalis, easy mold growth, and weak long-term protective properties of water-based anti-rust primers in kitchen and commercial kitchen environments. Specifically, all three exhibit initial adhesion ≥ 5.2 MPa, demonstrating excellent interfacial bonding strength with metal substrates; they show no significant abnormalities in resistance to 500 hours of damp heat, 70℃ / 240 hours of high temperature, and 168 hours of kitchen grease; they demonstrate stable resistance to weak acid food and alkaline kitchen cleaners; they show no rust or spread after 500 hours of neutral salt spray; their low-temperature flexibility at -10℃ is between 1.8-2.3 mm; their mildew resistance is ≤ 1 level; and they show no significant abnormalities after 50 cycles of alternating hot and cold temperatures; after 30 cycles of accelerated aging in a comprehensive kitchen environment, they only experience slight loss of gloss, without blistering, cracking, or peeling, and their adhesion remains ≥ 3.3 MPa, maintaining stable protective capabilities. They are suitable for the complex service environment of kitchens characterized by high humidity, high temperature, abundant oil fumes, intermittent acid and alkali corrosion, and frequent temperature changes.

[0075] In Comparative Example 1, because itaconic acid was not added to the emulsion, the resistance to weak acids and the integrity of the crosslinking of the paint film decreased, resulting in slight whitening, softening, and loss of gloss. Adhesion and resistance to media were significantly reduced. In Comparative Example 2, because the emulsion was modified with only KH-560 and not compounded with KH-550, the crosslinking gradient and interfacial anchoring effect were insufficient, leading to re-adhesion, whitening, and decreased resistance to media in the paint film, resulting in reduced overall protective stability. In Comparative Example 3, because the composite pigment did not introduce rare earth lanthanum ions and was not synergistically modified with NDZ-101, the rust prevention and passivation effect and the heat resistance of the paint film decreased, resulting in blistering, yellowing, and slight cracking. Salt spray resistance and temperature change resistance were significantly weakened. In Comparative Example 4, because the composite pigment was modified with only KH-560 without NDZ-101, the stability of rare earth ions and pigment dispersibility were insufficient, leading to blistering, whitening, and decreased resistance to media in the paint film, resulting in reduced rust prevention and aging resistance. In Comparative Example 5, because the diatomaceous earth was not activated at high temperature and was not combined with nano-silica, the density and shielding effect of the paint film decreased significantly, resulting in obvious blistering, softening, whitening, and corrosion. Its resistance to damp heat, salt spray, and mechanical deformation also deteriorated significantly. In Comparative Example 6, because a conventional ungrafted polycarboxylate dispersant was used, the dispersion stability of the pigments and fillers was insufficient, leading to slight sedimentation and loss of gloss in the system. Its salt spray resistance and storage compatibility were also reduced.

Claims

1. A water-based anti-rust primer free of heavy metals, characterized in that, Includes the following components by weight: 30–45 parts modified acrylic copolymer emulsion, 12–20 parts modified zinc phosphate-aluminum tripolyphosphate composite pigment, 3–8 parts diatomaceous earth composite filler, 2–6 parts film-forming aid, 1–4 parts lignin sulfonate grafted polycarboxylate dispersant, 0.3–1.2 parts hydrophobic associative thickener, 0.5–1.8 parts mildew inhibitor, 0.4–1.5 parts cyclic amine neutralizer, and 18–28 parts deionized water; The modified acrylic copolymer emulsion is prepared by copolymerizing four monomers: butyl acrylate, methyl methacrylate, hydroxyethyl acrylate, and itaconic acid, and then modifying them with epoxy silane KH-560 and amino silane KH-550. The modified zinc phosphate-aluminum tripolyphosphate composite pigment is obtained by combining zinc phosphate and aluminum tripolyphosphate, loading rare earth lanthanum ions, and then modifying it by combining KH-560 and titanate coupling agent NDZ-101. The diatomite composite filler is prepared by uniformly combining porous diatomite with nano-silica after high-temperature activation, and then modifying it with KH-560. The film-forming aid is a compound of ethylene glycol diisobutyrate, tripropylene glycol monomethyl ether, and polyether-modified organosiloxane. The lignin sulfonate-grafted polycarboxylic acid dispersant is obtained by graft copolymerization of lignin sulfonate with acrylic acid and methyl acrylate.

2. The heavy metal-free water-based anti-rust primer according to claim 1, characterized in that, In the modified acrylic copolymer emulsion, the mass ratio of butyl acrylate, methyl methacrylate, hydroxyethyl acrylate and itaconic acid is 100:(60-80):(15-25):(8-15); the mass ratio of epoxy silane KH-560 and amino silane KH-550 is (2.5-3.5):

1.

3. The heavy metal-free water-based anti-rust primer according to claim 1, characterized in that, In the modified zinc phosphate-aluminum tripolyphosphate composite pigment, the mass ratio of zinc phosphate to aluminum tripolyphosphate is (1.2~2.0):1; the total amount of KH-560 and titanate coupling agent NDZ-101 is 1.2~3.8% of the total pigment mass, and the amount of rare earth lanthanum ions added is 0.05~0.3% of the total pigment mass; the mass ratio of KH-560 to titanate coupling agent NDZ-101 is (1.8~2.2):

1.

4. The heavy metal-free water-based anti-rust primer according to claim 1, characterized in that, In diatomaceous earth composite fillers, the high-temperature activation temperature is 680–760℃; the addition amount of KH-560 is 1.8–4.7% of the total mass of the filler.

5. The heavy metal-free water-based anti-rust primer according to claim 1, characterized in that, In the film-forming aid, the mass ratio of ethylene glycol diisobutyrate, tripropylene glycol monomethyl ether, and polyether-modified organosiloxane is (0.8-1.2):(2.8-3.2):(1.0-1.4).

6. The heavy metal-free water-based anti-rust primer according to claim 1, characterized in that, The antifungal agent is a compound of decanediol and glycerin in a mass ratio of (1.0-2.0):

1.

7. The heavy metal-free water-based anti-rust primer according to claim 1, characterized in that, The cyclic amine neutralizer is a compound of methylcyclohexylamine and triethanolamine in a mass ratio of 1:(1.2 to 2.0).

8. The method for preparing a heavy metal-free water-based anti-rust primer according to any one of claims 1 to 7, characterized in that, First, add deionized water, lignin sulfonate grafted polycarboxylic acid dispersant, and cyclic amine neutralizer to the dispersion tank and stir thoroughly. Then, add modified zinc phosphate-aluminum tripolyphosphate composite pigment and diatomaceous earth composite filler and stir thoroughly. Finally, add modified acrylic copolymer emulsion, film-forming aid, hydrophobic associative thickener, and mildew inhibitor. After dispersion at ≤45℃, filter to obtain the finished primer.

9. The application of the heavy metal-free water-based anti-rust primer according to any one of claims 1 to 7, characterized in that, Protective coating for metal components used in kitchens and commercial catering back kitchens, including cabinet frames, support brackets, kitchen and bathroom hardware, kitchenware bases, processing equipment frames, and exhaust accessories.

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