High-acid-resistance water-based baking varnish as well as preparation method and application thereof

Abstract

The invention discloses high-acid-resistance water-based baking varnish as well as a preparation method and application thereof. The water-based baking varnish is prepared from the following raw material components: water-based polyester resin, amino resin, filler, auxiliaries and water, the waterborne polyester resin comprises hydroxyl polyester resin containing a benzene ring structure and / or an alicyclic structure; the auxiliaries comprise an adhesion promoter, a pH regulator and a wetting agent; the amino resin comprises methyl etherified amino resin; the filler comprises hydrophobic modified flaky filler. According to the invention, the waterborne polyester resin is matched with the high-activity methyl etherified amino resin, and high-temperature heat energy is utilized to drive hydroxyl and methoxyl to generate copolycondensation reaction, so that the hidden dangers of self-corrosion and water absorption of a baking varnish film caused by residual acid catalyst are eliminated. Meanwhile, the hydrophobic modified flaky filler can form chemical bonding with the organic resin, micro gaps existing between the filler and a resin interface are eliminated, and a physical defense line is established for concentrated acid. The baking varnish disclosed by the invention has chemical and physical double defense lines on concentrated acid, and has extremely high concentrated acid resistance.

Description

Technical Field

[0001] This invention relates to the field of baking paint technology, and in particular to a highly acid-resistant water-based baking paint, its preparation method, and its application. Background Technology

[0002] Galvanized steel pipes and Q235 carbon steel pipes are widely used in industrial transportation, building structures, and chemical facilities. In many applications, these pipes need to withstand acidic environments, such as chemical acid mist environments or contact with specific acidic cleaning solutions. Traditional anti-corrosion coatings mainly use solvent-based epoxy or acrylic systems, but with increasingly stringent environmental regulations, low-VOC water-based coatings are becoming the development trend.

[0003] Currently, water-based industrial baking paints on the market are mainly based on acrylic amino or ordinary polyester amino systems. However, existing technologies have the following significant drawbacks: First, the baking paint formulation often contains a large amount of acidic catalysts such as p-toluenesulfonic acid (p-TSA). The residual acidic substances not only reduce the water resistance of the paint film, but also easily induce self-corrosion inside the paint film. Second, the ester bonds of ordinary polyester resins are easily hydrolyzed under the attack of strong acids (such as 6 mol / L hydrochloric acid), leading to blistering and peeling of the paint film. Finally, existing baking paints have difficulty achieving excellent adhesion on both inert galvanized surfaces and reactive carbon steel surfaces.

[0004] Therefore, there is an urgent need to provide a baking paint that can achieve dense curing without acid catalysts and can withstand the corrosion of high concentrations of hydrochloric acid. Summary of the Invention

[0005] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, the object of the present invention is to provide a highly acid-resistant water-based baking paint. A second object of the present invention is to provide a method for preparing this highly acid-resistant water-based baking paint. A third object of the present invention is to provide applications of this highly acid-resistant water-based baking paint.

[0006] The inventive concept of this invention is as follows:

[0007] This invention uses a hydroxyl-containing polyester resin with benzene ring and / or alicyclic structures as the main body, combined with a highly active amino resin containing methoxy groups. High-temperature thermal energy drives the self-condensation reaction between hydroxyl and methoxy groups, eliminating the need for traditional acid catalysts and removing the potential for hydrophilicity within the paint. The rigid benzene ring and / or alicyclic structure in the waterborne polyester resin provides significant steric hindrance, significantly increasing the glass transition temperature (Tg) and cohesive strength of the paint. This highly sterically hindered structure effectively protects the ester bonds in the polyester backbone, effectively blocking hydrogen ion attack on the ester bonds, significantly reducing the ester bond hydrolysis rate under concentrated acid conditions, and improving the paint's acid and corrosion resistance.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a highly acid-resistant water-based baking paint, the raw material components of which include water-based polyester resin, amino resin, filler, additives and water; the water-based polyester resin includes hydroxyl polyester resin containing benzene ring structure and / or alicyclic structure; the additives include adhesion promoter, pH adjuster and wetting agent; the amino resin includes methyl etherified amino resin; the filler includes hydrophobically modified flake filler.

[0009] In this invention, waterborne polyester resin is combined with highly active methyl etherified amino resin, utilizing high-temperature thermal energy to drive the co-condensation reaction between hydroxyl and methoxy groups, eliminating the need for traditional acid catalysts and removing the potential hydrophilicity issue within the paint film. Simultaneously, the waterborne polyester resin in this invention contains benzene ring and / or alicyclic structures. The rigid benzene ring and alicyclic structures provide significant steric hindrance, significantly increasing the glass transition temperature (Tg) and cohesive strength of the paint film. This highly sterically hindered structure effectively protects the ester bonds of the polyester backbone, greatly reducing the ester bond hydrolysis rate under concentrated acid conditions, constructing a chemical defense against concentrated acid, and improving the acid and corrosion resistance of the paint film. Furthermore, the filler in this invention includes hydrophobically modified sheet fillers. The modified sheet fillers have a hydrophobic surface, enabling them to form chemical bonds with the organic resin, eliminating microscopic gaps at the filler-resin interface that are easily utilized by acid. Moreover, the high aspect ratio of the sheet fillers creates a "maze effect" in the paint film, constructing a physical defense against concentrated acid and greatly extending the acid penetration path. The paint of this invention has both chemical and physical protection against concentrated acids, and has extremely high acid and corrosion resistance.

[0010] Preferably, by weight, the raw material components include 40-60 parts of waterborne polyester resin, 8-15 parts of amino resin, 5-18 parts of filler, 1.2-4.0 parts of adhesion promoter, 0.2-0.5 parts of pH adjuster, 0.3-0.8 parts of wetting agent and 6-45 parts of water.

[0011] More preferably, the waterborne polyester resin is in the form of 42-58 parts by weight; even more preferably, the waterborne polyester resin is in the form of 44-56 parts by weight; and even more preferably, the waterborne polyester resin is in the form of 45, 47, 49, 51, or 53 parts by weight.

[0012] More preferably, the amino resin is in the form of 8.5-14.5 parts by weight; even more preferably, the amino resin is in the form of 9-14 parts by weight; and even more preferably, the amino resin is in the form of 10, 11, 12, 13 or 14 parts by weight.

[0013] More preferably, the filler is 5-15 parts by weight; even more preferably, the filler is 5-13.5 parts by weight; and even more preferably, the filler is 5, 7, 8, 10 or 13 parts by weight.

[0014] More preferably, the adhesion promoter is present in 1.4-3.8 parts by weight; even more preferably, the adhesion promoter is present in 1.6-3.6 parts by weight; and even more preferably, the adhesion promoter is present in 1.8-3.3 parts by weight.

[0015] More preferably, the pH adjuster is 0.2-0.48 parts by weight; even more preferably, the pH adjuster is 0.2-0.42 parts by weight; and even more preferably, the pH adjuster is 0.25 parts, 0.32 parts, 0.38 parts or 0.42 parts by weight.

[0016] More preferably, the wetting agent is 0.35-0.75 parts by weight; even more preferably, the wetting agent is 0.38-0.7 parts by weight; and even more preferably, the wetting agent is 0.4-0.6 parts by weight.

[0017] More preferably, the water content is 7-40 parts by weight; even more preferably, the water content is 7-35 parts by weight; and still more preferably, the water content is 8-30 parts by weight.

[0018] Preferably, the raw materials for preparing the waterborne polyester resin include polybasic acid, polyol, hydrophilic monomer, and neutralizing agent; the polybasic acid includes at least one selected from isophthalic acid, terephthalic acid, trimellitic anhydride, phthalic anhydride, 1,2-cyclohexanedicarboxylic anhydride, 1,4-cyclohexanedicarboxylic acid, and adipic acid; the polyol includes at least one selected from hydrogenated bisphenol A, 1,4-cyclohexanediethanol, neopentyl glycol, and pentaerythritol; the hydrophilic monomer includes dimethylolpropionic acid (DMPA); and the neutralizing agent includes triethylamine or aminomethylpropanol.

[0019] More preferably, the raw materials for preparing the waterborne polyester resin include, by weight, 230-270 parts of polyacid, 260-300 parts of polyol, 45-65 parts of hydrophilic monomer, and 30-40 parts of neutralizer.

[0020] Preferably, the hydroxyl value of the waterborne polyester resin is 45-70 mgKOH / g; more preferably, the hydroxyl value of the waterborne polyester resin is 48-68 mgKOH / g; and even more preferably, the hydroxyl value of the waterborne polyester resin is 50-60 mgKOH / g.

[0021] Preferably, the acid value of the waterborne polyester resin is 25-45 mgKOH / g; more preferably, the acid value of the waterborne polyester resin is 28-42 mgKOH / g; and even more preferably, the acid value of the waterborne polyester resin is 30-38 mgKOH / g.

[0022] Preferably, the glass transition temperature of the waterborne polyester resin is 50-80°C; more preferably, the glass transition temperature of the waterborne polyester resin is 55-75°C; and even more preferably, the glass transition temperature of the waterborne polyester resin is 60-70°C.

[0023] Preferably, the solid content (the proportion of the polyester resin by mass in the solid state) of the waterborne polyester resin is 40%-50%; more preferably, the solid content of the waterborne polyester resin is 42%-48%.

[0024] Preferably, the methyl etherified amino resin includes at least one of methyl etherified melamine resin, methyl etherified urea resin, methyl etherified benzoic melamine resin, methyl etherified glycourea resin, and methyl etherified cocondensation resin; more preferably, the methyl etherified melamine resin includes hexamethoxymethylmelamine resin (HMMM).

[0025] Preferably, the waterborne polyester resin and the amino resin can undergo a co-condensation reaction; more preferably, the waterborne polyester resin and the amino resin undergo a co-condensation reaction at a high temperature; wherein, the high temperature is preferably 190-200°C; even more preferably, the high temperature is 195-200°C.

[0026] In this invention, methyl etherified amino resin, under acid-free catalyst conditions, can undergo a complete co-condensation reaction with the hydroxyl groups of waterborne polyester resin through high-temperature baking, thereby forming a dense hydrophobic crosslinked network. This invention avoids the formation of hydrophilic ions in the paint film after the residue of traditional acid catalysts, eliminating the risk of ion-induced self-corrosion and hydrolysis, and further improving the overall acid and solvent resistance of metal pipes coated with this paint film.

[0027] Preferably, the filler comprises hydrophobically modified sheet filler and acid-resistant inert filler; the hydrophobically modified sheet filler comprises sheet filler modified with a first silane coupling agent; the aspect ratio of the sheet filler modified with the first silane coupling agent is greater than 50:1; the particle size of the acid-resistant inert filler is <1μm. Since the surface of the unmodified sheet filler contains hydrophilic hydroxyl groups, it easily becomes a channel for acid penetration. This invention grafts a first silane coupling agent onto the sheet filler, making the filler surface hydrophobic and enabling it to chemically bond with the resin matrix, thereby sealing interfacial gaps, preventing acid penetration, and achieving highly efficient physical barrier against concentrated acids.

[0028] More preferably, the first silane coupling agent includes at least one of γ-glycidoxypropyltrimethoxysilane (KH-560), phenyltrimethoxysilane, 3-aminopropyltriethoxysilane, and 3-methacryloyloxypropyltrimethoxysilane.

[0029] More preferably, the aspect ratio of the first silane coupling agent modified sheet packing is greater than 60:1; even more preferably, the aspect ratio of the first silane coupling agent modified sheet packing is greater than 80:1; even more preferably, 100:1 < aspect ratio of the first silane coupling agent modified sheet packing < 200:1. The first silane coupling agent modified sheet packing has a high aspect ratio, which can form a labyrinth structure and extend the acid permeation path.

[0030] More preferably, the particle size D50 of the first silane coupling agent modified sheet filler is 5-20 μm; more preferably, the particle size D50 of the first silane coupling agent modified sheet filler is 8-18 μm; and even more preferably, the particle size D50 of the first silane coupling agent modified sheet filler is 10-15 μm.

[0031] Preferably, the acid-resistant inert filler comprises ultrafine barium sulfate.

[0032] More preferably, the particle size of the acid-resistant inert filler is <1μm; even more preferably, the particle size of the acid-resistant inert filler is <0.8μm; and even more preferably, the particle size of the acid-resistant inert filler is 0.1μm < 0.8μm.

[0033] More preferably, the first silane coupling agent modified sheet filler comprises wet-process sericite powder modified with the first silane coupling agent surface and / or glass flakes modified with the first silane coupling agent surface.

[0034] Preferably, the adhesion promoter includes a phosphate ester adhesion promoter and a second silane coupling agent.

[0035] More preferably, the second silane coupling agent comprises a silane coupling agent containing an amino functional group; even more preferably, the silane coupling agent containing an amino functional group comprises at least one of 3-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane.

[0036] More preferably, the mass ratio of the phosphate ester adhesion promoter to the second silane coupling agent is (3-5):1; even more preferably, the mass ratio of the phosphate ester adhesion promoter to the second silane coupling agent is (3.5-4.5):1.

[0037] In this invention, a specific ratio of phosphate ester adhesion promoter and second silane coupling agent is used to achieve non-obvious coupling with the metal and the host resin, respectively, in a high-temperature, acid-free catalyst crosslinking system. Specifically, the phosphate ester groups in the phosphate ester adhesion promoter can form dense, hydrolysis-resistant chemical coordination bonds (anchoring I) with zinc ions on the surface of the zinc plating layer, thereby forming a stable chelate. The inorganic end (hydrolyzed Si(OH)3) of the second silane coupling agent forms MO-Si bonds with the metal substrate (zinc plating or Q235), while its organic end's amino functional groups ( At high temperatures of 190-200℃, NH2 directly participates in the condensation and crosslinking reaction of the main polyester resin and amino resin, achieving interfacial bridging through coupling. This coupling ensures that the second silane coupling agent molecule becomes part of the final paint film network structure and also forms covalent bonds (anchoring II) that run through the paint film to the metal interface. This three-in-one structure of "crosslinking network-interfacial coupling agent-substrate" ensures a high degree of match between interfacial strength and the cohesive force of the paint film, enabling it to maintain Grade 0 adhesion to various metal substrates in harsh environments with high concentrations of acid corrosion.

[0038] Preferably, the pH adjuster comprises an organic amine adjuster; more preferably, the organic amine adjuster comprises at least one selected from 2-amino-2-methyl-1-propanol, N,N-dimethylethanolamine (DMEA), 2-dimethylamino-2-methyl-1-propanol, ammonia, triethylamine, cyclohexylamine, and 4-morpholinoethylamine.

[0039] Preferably, the pH of the water-based baking paint is 8.0-9.0; more preferably, the pH of the water-based baking paint is 8.2-8.8; and even more preferably, the pH of the water-based baking paint is 8.3-8.6.

[0040] In this invention, a pH adjuster is used to precisely control the pH of the baking paint system within 8.0-9.0, which effectively inhibits the corrosion and dissolution of the zinc layer to form "zinc soap", ensures the durability of the phosphate ester group and zinc ion chelate, and overcomes the problem of easy adhesion failure of traditional water-based baking paint on zinc plating.

[0041] Preferably, the wetting agent comprises at least one of polyether-modified polydimethylsiloxane, polyether-modified polymethylalkylsiloxane, polyester-modified polydimethylsiloxane, acetylenic diol and its ethoxylates, fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, polyether-modified polyacrylate wetting agent, and fluorocarbon surfactant.

[0042] More preferably, the acetylidene glycol and its ethoxylated derivatives include at least one of Surfadol 541, Surfadol 400, Surfadol 600, Surfadol 500, and Surfadol 300.

[0043] More preferably, the fluorocarbon surfactant includes at least one of TEGO Twin 4100, TEGO Wet 270, and SURFYNOL 104BC.

[0044] Preferably, the additives further include at least one of leveling agents, defoamers, color pastes, and thickeners.

[0045] More preferably, the leveling agent is present in an amount of 0.2-0.6 parts by weight; even more preferably, the leveling agent is present in an amount of 0.25-0.55 parts by weight; and even more preferably, the leveling agent is present in an amount of 0.3-0.5 parts by weight.

[0046] More preferably, the defoamer is present in an amount of 0.1-0.5 parts by weight; even more preferably, the defoamer is present in an amount of 0.2-0.4 parts by weight; and even more preferably, the defoamer is present in an amount of 0.2-0.3 parts by weight.

[0047] More preferably, the color paste is 4-8 parts by weight; even more preferably, the color paste is 4.5-7 parts by weight; and even more preferably, the color paste is 5-6.5 parts by weight.

[0048] More preferably, the thickener is 0.5-1.2 parts by weight; even more preferably, the thickener is 0.5-1.1 parts by weight; and even more preferably, the thickener is 0.5-1.0 parts by weight.

[0049] Preferably, the leveling agent includes at least one of silicone leveling agents, acrylate leveling agents, and fluorocarbon leveling agents; more preferably, the leveling agent is selected from at least one of BYK 346, EFKAFL 3772, and SN3760.

[0050] Preferably, the defoamer includes at least one of polysiloxane-based defoamer and mineral oil-based defoamer; more preferably, the defoamer includes at least one of TEGO Foamex 810, BYK030, and Dispelair CF245.

[0051] Preferably, the color paste comprises an aqueous color paste.

[0052] Preferably, the thickener includes at least one of a polyurethane thickener and an alkali-swellable thickener; more preferably, the thickener includes at least one of Elementis 299, TAFIGEL® PUR 65RHEOVIS AS 1130, and RHEOLATE 150.

[0053] Preferably, by weight, the raw material components of the water-based baking paint include 40-60 parts water-based polyester resin, 8-15 parts amino resin, 5-18 parts filler, 1.2-4.0 parts adhesion promoter, 0.2-0.5 parts pH adjuster, 0.3-0.8 parts wetting agent, 0.2-0.6 parts leveling agent, 0.1-0.5 parts defoamer, 4-8 parts color paste, 0.5-1.2 parts thickener, and 0.1-45 parts water.

[0054] More preferably, by weight, the raw material components of the water-based baking paint are 40-60 parts water-based polyester resin, 8-15 parts amino resin, 5-18 parts filler, 1.2-4.0 parts adhesion promoter, 0.2-0.5 parts pH adjuster, 0.3-0.8 parts wetting agent, 0.2-0.6 parts leveling agent, 0.1-0.5 parts defoamer, 4-8 parts color paste, 0.5-1.2 parts thickener and 0.1-45 parts water.

[0055] In a second aspect, the present invention provides a method for preparing the water-based baking paint described in the first aspect. The method comprises mixing raw material components other than amino resin and adhesion promoter, then adding amino resin and adhesion promoter and mixing again to obtain the water-based baking paint.

[0056] Preferably, the mixing method is stirring in a disperser; more preferably, the speed of the disperser is 500-2000 r / min; even more preferably, the speed of the disperser is 500-1500 r / min. This invention does not rely on complex instruments; the instrument used is a disperser, a conventional piece of equipment that is simple and easy to operate.

[0057] Preferably, the mixing time is 20-50 minutes; more preferably, the mixing time is 25-45 minutes.

[0058] Preferably, the preparation method includes the following steps: S1: Mix water-based polyester resin, pH adjuster and some water to adjust the pH value to 8.0-9.0; S2: Add wetting agent and filler to S1 and mix; S3: Add amino resin, adhesion promoter and remaining water to S2 to obtain water-based baking paint.

[0059] Preferably, the mixing method in S1 is to stir in a disperser with a speed of 500-800 r / min; more preferably, the speed of the disperser is 550-700 r / min.

[0060] Preferably, the mixing method in S1 is to stir in a disperser for 10-20 minutes; more preferably, the stirring time is 12-18 minutes.

[0061] Preferably, the mixing method in S2 is to stir in a disperser with a speed of 1000-1500 r / min; more preferably, the speed of the disperser is 1100-1300 r / min.

[0062] Preferably, the mixing method in S2 is to stir in a disperser for 20-40 minutes; more preferably, the stirring time is 25-35 minutes.

[0063] Preferably, the mixing method in S3 is to stir in a disperser with a speed of 500-800 r / min; more preferably, the speed of the disperser is 550-700 r / min.

[0064] Preferably, the mixing method in S3 is to stir in a disperser for 15-25 minutes; more preferably, the stirring time is 18-22 minutes.

[0065] Preferably, the ratio of water in S1 to water in S3 is 1:(0.4~0.8).

[0066] In some specific embodiments of the present invention, the raw materials also include a defoamer, which is added in S2.

[0067] In some specific embodiments of the present invention, the raw materials also include color paste, which is added in S2.

[0068] In some specific embodiments of the present invention, the raw materials also include a thickener, which is added in S3.

[0069] In some specific embodiments of the present invention, the filler includes hydrophobically modified sheet filler, and the preparation method of the hydrophobically modified sheet filler is as follows: the sheet filler is mixed with a first silane coupling agent and heat-treated to obtain the hydrophobically modified sheet filler.

[0070] Preferably, the first silane coupling agent accounts for 1%-3% of the mass percentage of the sheet packing; more preferably, the first silane coupling agent accounts for 1.2%-2.5% of the mass percentage of the sheet packing; even more preferably, the first silane coupling agent accounts for 1.5%-2.0% of the mass percentage of the sheet packing. Preferably, the heat treatment temperature is 110-130℃; more preferably, the heat treatment temperature is 112-125℃; and even more preferably, the heat treatment temperature is 115-120℃.

[0071] Preferably, the heat treatment time is 30-60 min; more preferably, the heat treatment time is 35-55 min; and even more preferably, the heat treatment time is 40-50 min.

[0072] In some specific embodiments of the present invention, the waterborne polyester resin is prepared by the following method: esterification reaction of polyacid and polyol is carried out. After the acid value is less than 40 mg KOH / g, hydrophilic monomer is added to continue the reaction. After the acid value is less than 35 mg KOH / g, a neutralizing agent is added to neutralize, thereby obtaining the waterborne polyester resin.

[0073] In this invention, the defined polyacid and polyol undergo an esterification reaction at high temperature to obtain a hydroxyl polyester resin containing a benzene ring structure and / or an alicyclic structure. This resin is then further reacted with a hydrophilic monomer to carry carboxyl groups on the side chains of the polyester resin, providing sites for subsequent water solubility. A neutralization reaction is then carried out using a neutralizing agent to convert the carboxyl groups into ammonium carboxylate salts, thereby achieving dispersion of the polyester resin in water and obtaining an aqueous polyester resin.

[0074] In some specific embodiments of the present invention, the temperature of the esterification reaction is 220-240°C; in some specific examples of the present invention, the temperature of the esterification reaction is 225-235°C.

[0075] The present invention also provides the application of the water-based baking paint described in the first aspect.

[0076] Thirdly, the present invention provides a paint film formed by curing an aqueous baking paint comprising the first aspect.

[0077] Preferably, the curing temperature is 190-200℃; more preferably, the curing temperature is 192-200℃; and even more preferably, the curing temperature is 195-200℃.

[0078] Preferably, the curing time is 15-25 min; more preferably, the curing time is 18-23 min; and even more preferably, the curing time is 20-22 min.

[0079] Preferably, the thickness of the paint film is 20-40 μm; more preferably, the thickness of the paint film is 22-38 μm; and even more preferably, the thickness of the paint film is 25-35 μm.

[0080] Fourthly, the present invention also provides a metal pipe, the metal pipe comprising a metal pipe and the paint film described in the third aspect on the surface of the metal pipe.

[0081] Preferably, the metal pipe includes at least one of galvanized steel pipe and carbon steel pipe.

[0082] Fifthly, the present invention provides the application of the water-based baking paint described in the first aspect, the paint film described in the third aspect, and the metal pipe described in the fourth aspect in industrial transportation, building structures, or chemical facilities.

[0083] The beneficial effects of this invention are: (1) The waterborne polyester resin in the waterborne baking paint provided by this invention includes a hydroxyl polyester resin containing a benzene ring structure and / or an alicyclic structure, combined with a highly active methyl etherified amino resin. High-temperature thermal energy drives the hydroxyl groups and methoxy groups to undergo a co-condensation reaction, eliminating the need for traditional acid catalysts and removing the risk of self-corrosion and water absorption in the baking paint film caused by residual acid catalysts. This significantly improves the density and long-term corrosion resistance of the coating. Simultaneously, the rigid benzene ring and alicyclic structure in the waterborne polyester resin provides significant steric hindrance, significantly increasing the glass transition temperature and cohesive force of the baking paint. This highly sterically hindered structure effectively protects the ester bonds of the polyester backbone, greatly reducing the ester bond hydrolysis rate under concentrated acid conditions and improving the acid and corrosion resistance of the baking paint film. Furthermore, the filler in this invention includes hydrophobically modified sheet filler. The modified sheet filler has a hydrophobic surface, enabling it to form chemical bonds with organic resins. This eliminates microscopic gaps at the filler-resin interface that are easily utilized by acids. The hydrophobically modified sheet filler also has a high aspect ratio, creating a "maze effect" within the paint film, thus constructing a physical defense against concentrated acids and significantly extending the acid penetration path. The paint of this invention provides both chemical and physical defense against concentrated acids, exhibiting extremely high acid and corrosion resistance.

[0084] (2) The water-based baking paint preparation method provided by the present invention is simple and easy to operate. The instruments and equipment used are all conventional equipment, which does not rely on complex equipment and the raw material cost is controllable. The preparation process of the present invention has strong controllability and high repeatability. The process parameters (temperature, speed, time, pH, etc.) can be precisely controlled, the batch-to-batch consistency is high, and the product quality is stable.

[0085] (3) The water-based baking paint provided by the present invention has strong adhesion to metal pipes and high interface strength. The paint film formed by curing at high temperature can maintain 0-level adhesion to different metal pipes in the harsh environment of concentrated acid corrosion. It has extremely strong acid and corrosion resistance and can be well applied in industrial transportation, building structures or chemical facilities. Attached Figure Description

[0086] Figure 1 This is the infrared spectrum of the aqueous polyester resin synthesized in this invention. Detailed Implementation

[0087] To enable those skilled in the art to better understand this application, the present invention will be further described in detail below with reference to embodiments. However, it should be understood that the following embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims.

[0088] In the description of this invention, it should be noted that unless specific conditions are specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available products. Furthermore, to better illustrate this invention, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this invention can be practiced even without certain specific details. In some embodiments, raw materials, methods, and means well known to those skilled in the art are not described in detail in order to highlight the main points of this invention.

[0089] Some of the raw materials used in this invention are as follows: Amino resin: Grade: Cymel 303, purchased from ZX Resins (China) Co., Ltd.; Phosphate ester adhesion promoter: Brand: Lencolo 4051, purchased from Guangdong Lancolo New Materials Co., Ltd.; First silane coupling agent: γ-glycidoxypropyltrimethoxysilane, a conventional commercially available product; Second silane coupling agent: 3-aminopropyltriethoxysilane, a commercially available product; Wetting agent: Model: TEGO Twin 4100, Brand: Evonik. Defoamer: Model: TEGO Foamex 810, Brand: Evonik. Thickener: Model: Elementis 299, Brand: Haimingsi; Water-based pigments: purchased from Kedi Pigment.

[0090] The aqueous polyester resin used in the embodiments of this invention is prepared by the following method: 180g of isophthalic acid, 70g of adipic acid, 130g of 1,4-cyclohexanediol, 150g of neopentyl glycol, and 5g of pentaerythritol were added to a reaction vessel. Under nitrogen protection, the mixture was heated to 230℃ for esterification until the acid value was less than 40 mgKOH / g. The temperature was then lowered to 180℃, and 55g of dimethylolpropionic acid was added to continue the reaction until the acid value reached 35 mgKOH / g. The temperature was then lowered to 90℃, and 34g of triethylamine was added for neutralization. Water was added for high-speed dispersion to obtain an aqueous polyester resin with a solid content of 45%. The synthesis of waterborne polyester resins includes the following three stages: 1. Synthesis of polyester prepolymer: Polymerization reaction of polybasic acids (isophthalic acid and adipic acid) with polyols (cyclohexanediol, neopentyl glycol and pentaerythritol) to form hydroxyl-terminated polyester; 2. Introduction of hydrophilic groups (modification with dimethylolpropionic acid): The hydroxyl groups in dimethylolpropionic acid react with the residual carboxyl groups in the system, or dimethylolpropionic acid is introduced into the polyester main chain through transesterification, so that the polyester side chains or ends have free carboxyl groups. 3. Neutralization reaction: A neutralizing agent (triethylamine) is introduced to neutralize the free carboxyl groups, converting them into carboxylates to obtain waterborne polyester resin.

[0091] Infrared spectrum of waterborne polyester resin, such as Figure 1 As shown. Figure 1 Middle, 3519cm -1 With 3426cm -1 (Strong, broad peak) Attributable to free hydroxyl groups or hydroxyl groups associated with hydrogen bonds, indicating that the waterborne polyester resin has active sites (hydroxyl groups) that react with amino resins; 2945 cm⁻¹ -1 Stretching vibrations attributed to saturated alkyl groups (such as -CH2-, -CH3) indicate the successful introduction of aliphatic structures from neopentyl glycol, adipic acid, and 1,4-cyclohexanediethanol (CHDM) into the waterborne polyester resin; 1731 cm -1 The extremely strong peak is attributed to the C=O stretching vibration of the ester carbonyl group and is a characteristic peak of polyester, indicating that the acid and alcohol successfully formed an ester bond through esterification. Figure 1 The peak position is very standard (no obvious conjugation shift occurred), indicating the prevalence of aliphatic ester structures in the main chain of the synthesized waterborne polyester resin; 1635 cm⁻¹ -1 The HOH bending vibration attributed to residual moisture indicates that in waterborne polyester resins, even after drying, hydrogen-bonded water around the groups often presents a signal at this location. Additionally, if neutralization is incomplete, the asymmetric stretching vibration of the carboxylate group (-COO-) may also be superimposed here; 1308 cm⁻¹ -1 With 1248cm -1 This is attributed to the asymmetric stretching vibration of COC in the ester group, which is related to 1731 cm⁻¹. -1 The corresponding C=O peak further confirms the formation of the ester bond. The benzene ring is located at 700-800 cm⁻¹. -1 The region exhibits characteristic absorption at 732 cm⁻¹. -1 The out-of-plane bending vibration of CH belonging to the benzene ring indicates that the benzene ring structure in isophthalic acid (IPA) has been successfully introduced into the backbone of waterborne polyester resin.

[0092] It should be noted that this invention only provides a method for preparing a waterborne polyester resin, and does not mean that the paint raw material in this invention can only use this waterborne polyester resin. Commercially available (such as TPR-W7903 sold by Guangdong Jiayuan New Materials Co., Ltd., and TH-2306 of Zhejiang Tianhe Resin) and other hydroxyl polyester resins containing benzene ring structure and / or alicyclic structure synthesized by other methods can all be used as waterborne polyester resins in this invention.

[0093] Example 1 A highly acid-resistant water-based baking paint, by weight, comprises 50.0 parts water-based polyester resin, 12.5 parts amino resin, 8.0 parts hydrophobically modified flake filler, 5.0 parts ultrafine barium sulfate, 2.0 parts phosphate ester adhesion promoter, 0.5 parts second silane coupling agent, 0.3 parts N,N-dimethylethanolamine (DMEA), 0.5 parts wetting agent, 0.2 parts defoamer, 6.0 parts water-based color paste, 1 part thickener, and 14.0 parts deionized water.

[0094] The highly acid-resistant water-based baking paint is prepared using the following method: (1) Preparation of hydrophobic modified sheet filler: 1 kg of 1250 mesh wet sericite powder (aspect ratio > 50) was put into a high-speed mixer and dried at 110℃ for 30 min; 20 g of first silane coupling agent was dissolved in 100 g of ethanol and sprayed into the mixer and stirred at high speed for 15 min; the temperature was raised to 120℃ and kept at that temperature for 1 hour, and the material was cooled and discharged to obtain hydrophobic modified sheet filler; (2) Under the condition that the speed of the disperser is 600 r / min, 50 parts of waterborne polyester resin, 0.3 parts of DMEA and 7 parts of deionized water are mixed, the pH is adjusted to 8.5 and stirred for 15 min; 0.5 parts of wetting agent, 0.2 parts of defoamer, 8.0 parts of hydrophobic modified flake filler, 5.0 parts of ultrafine barium sulfate and 6.0 parts of color paste are added, the speed is increased to 1200 r / min, and the mixture is ground and dispersed for 30 min until the fineness is ≤15μm; (3) Reduce the rotation speed to 600 r / min, add 12.5 parts of amino resin, 2.0 parts of phosphate ester adhesion promoter and 0.5 parts of second silane coupling agent, stir for 20 min; add 0.8 parts of thickener and the remaining deionized water to adjust the viscosity to 50s (measured by Forecast cup 4, temperature 25℃), and filter to obtain high acid resistance water-based baking paint.

[0095] Example 2 A highly acid-resistant water-based baking paint, by weight, comprises 45.0 parts water-based polyester resin, 10.0 parts amino resin, 12.0 parts hydrophobically modified flake filler, 4.0 parts ultrafine barium sulfate, 1.5 parts phosphate ester adhesion promoter, 0.3 parts second silane coupling agent, 0.2 parts DMEA, 0.4 parts wetting agent, 0.2 parts defoamer, 5.0 parts water-based color paste, 0.8 parts thickener, and 20.6 parts deionized water.

[0096] The preparation method in this embodiment is the same as in Embodiment 1.

[0097] Example 3 A highly acid-resistant water-based baking paint, by weight, comprises 55.0 parts water-based polyester resin, 14.0 parts amino resin, 4.0 parts hydrophobically modified flake filler, 6.0 parts ultrafine barium sulfate, 2.5 parts phosphate ester adhesion promoter, 0.8 parts second silane coupling agent, 0.4 parts DMEA, 0.6 parts wetting agent, 0.3 parts defoamer, 7.0 parts water-based color paste, 0.4 parts thickener, and 9 parts deionized water. The preparation method of this embodiment is the same as that of Example 1.

[0098] Example 4 A highly acid-resistant water-based baking paint, by weight, comprises 48.0 parts water-based polyester resin, 11.5 parts amino resin, 6.0 parts hydrophobically modified flake filler, 4.5 parts ultrafine barium sulfate, 1.8 parts phosphate ester adhesion promoter, 0.4 parts second silane coupling agent, 0.3 parts DMEA, 0.5 parts wetting agent, 0.2 parts defoamer, 6.0 parts water-based color paste, 0.7 parts thickener, and 20.1 parts deionized water.

[0099] The preparation method in this embodiment is the same as in Embodiment 1.

[0100] Example 5 A highly acid-resistant water-based baking paint, by weight, comprises 52.0 parts water-based polyester resin, 13.0 parts amino resin, 10.0 parts hydrophobically modified flake filler, 5.5 parts ultrafine barium sulfate, 2.2 parts phosphate ester adhesion promoter, 0.6 parts second silane coupling agent, 0.4 parts DMEA, 0.6 parts wetting agent, 0.3 parts defoamer, 6.5 parts water-based color paste, 0.9 parts thickener, and 8.0 parts deionized water.

[0101] The preparation method in this embodiment is the same as in Embodiment 1.

[0102] Example 6 A highly acid-resistant water-based baking paint, by weight, comprises 50.0 parts water-based polyester resin, 12.5 parts amino resin, 8.0 parts hydrophobically modified flake filler, 5.0 parts ultrafine barium sulfate, 2.0 parts phosphate ester adhesion promoter, 0.5 parts second silane coupling agent, 0.3 parts DMEA, 0.5 parts wetting agent, 0.2 parts defoamer, 6.0 parts water-based color paste, 0.8 parts thickener, and 14.2 parts deionized water.

[0103] The preparation method in this embodiment is the same as in Embodiment 1.

[0104] Example 7 A highly acid-resistant water-based baking paint, by weight, comprises 46.0 parts water-based polyester resin, 11.0 parts amino resin, 7.0 parts hydrophobically modified flake filler, 4.0 parts ultrafine barium sulfate, 1.6 parts phosphate ester adhesion promoter, 0.3 parts second silane coupling agent, 0.3 parts DMEA, 0.4 parts wetting agent, 0.2 parts defoamer, 5.5 parts water-based color paste, 0.6 parts thickener, and 23.1 parts deionized water.

[0105] The preparation method in this embodiment is the same as in Embodiment 1.

[0106] Example 8 A highly acid-resistant water-based baking paint, by weight, comprises 54.0 parts water-based polyester resin, 12.5 parts amino resin, 8.0 parts hydrophobically modified flake filler, 6.0 parts ultrafine barium sulfate, 1.4 parts phosphate ester adhesion promoter, 0.7 parts second silane coupling agent, 0.4 parts DMEA, 0.6 parts wetting agent, 0.3 parts defoamer, 5.5 parts water-based color paste, 0.4 parts thickener, and 10.2 parts deionized water.

[0107] The preparation method in this embodiment is the same as in Embodiment 1.

[0108] Example 9 The difference between this embodiment and Embodiment 1 is that this embodiment does not contain phosphate ester adhesion promoters, the weight of deionized water is 16.2 parts, the weight of thickener is 0.8 parts, and the rest are the same as in Embodiment 1.

[0109] Example 10 The difference between this embodiment and Embodiment 1 is that this embodiment does not contain a second silane coupling agent, the weight of deionized water is 14.7 parts, the weight of thickener is 0.8 parts, and the rest are the same as in Embodiment 1.

[0110] The composition of the paint raw materials in Examples 1-10 is shown in Table 1, in parts by weight.

[0111] Table 1. Raw material components and dosage in Examples 1-10

[0112] Comparative Example 1 The difference between this comparative example and Example 1 is that this comparative example uses ordinary unhydrophobic modified wet-process sericite powder instead of the hydrophobic modified sheet filler in Example 1, while the rest is the same as Example 1.

[0113] Comparative Example 2 The difference between this comparative example and Example 1 is that the filler in this comparative example does not contain hydrophobically modified sheet filler, and is entirely ultrafine barium sulfate. That is, the filler in this comparative example is 13.0 parts of ultrafine barium sulfate, and the rest is the same as in Example 1.

[0114] Comparative Example 3 This comparative example uses a common waterborne polyester resin (model: 399A-2, Miki). The waterborne polyester resin does not contain benzene ring structure or alicyclic structure, and all other aspects are the same as in Example 1.

[0115] Comparative Example 4 The difference between this comparative example and Example 1 is that no wetting agent is used in this comparative example; instead, an equal amount of water is used. Everything else is the same as in Example 1.

[0116] Comparative Example 5 The difference between this comparative example and Example 1 is that 0.5 parts by weight of p-toluenesulfonic acid catalyst are added in this comparative example, and the weight of deionized water is reduced by 0.5 parts. All other aspects are the same as in Example 1.

[0117] The differences in setup and verification objectives of Comparative Examples 1 to 5 are shown in Table 2.

[0118] Table 2. Setup Instructions for Comparative Examples 1-5

[0119] Performance testing The water-based baking paints of Examples 1-10 and Comparative Examples 1-5 were sprayed onto hot-dip galvanized steel sheets and Q235 steel sheets, respectively. After flash drying for 10 minutes, they were cured at high temperature at 195°C for 20 minutes. After the baking paints were fully cured, a paint film with a thickness of 30±5μm was formed on the hot-dip galvanized steel sheets and Q235 steel sheets, respectively.

[0120] Examples 1-10: Water-based paint was sprayed onto hot-dip galvanized steel sheets to obtain galvanized pipes, experimental groups 1-10 respectively; Examples 1-10: Water-based baking paint was sprayed onto Q235 steel plates to obtain Q235 pipe experimental groups 1-10; Comparative Examples 1-5 were sprayed with water-based baking paint onto hot-dip galvanized steel sheets to obtain galvanized pipes; Control Groups 1-5 were also used. Comparative Examples 1-5 were sprayed with water-based baking paint onto Q235 steel plates to obtain Q235 pipes, respectively; Control Groups 1-5; In addition, a group was set up to spray the water-based paint of Example 1 onto hot-dip galvanized steel sheet and Q235 steel sheet, flash dry for 10 minutes and then cure at high temperature. The curing conditions were 170°C for 20 minutes, resulting in galvanized pipe control group 6 and Q235 pipe control group 6 respectively.

[0121] Test items: 1. Acid resistance: Galvanized pipe experimental groups 1-10 and galvanized pipe control groups 1-6 were immersed in 6 mol / L hydrochloric acid and the bubbling time was observed; Q235 pipe experimental groups 1-10 and Q235 pipe control groups 1-6 were immersed in 6 mol / L hydrochloric acid for 24 hours and the bubbling time and whether there was any peeling or discoloration were observed.

[0122] 2. Adhesion test: Refer to the cross-cut test method of GB / T 9286-2021 "Paints and Varnishes" to test the adhesion of galvanized pipe experimental groups 1-10, Q235 pipe experimental groups 1-10, galvanized pipe control group 1-6, and Q235 pipe control group 1-6 respectively. Grade 0 is the best and grade 5 is the worst.

[0123] 3. Solvent resistance test: Galvanized pipe experimental group 1-10 and galvanized pipe control group 1-6 were repeatedly wiped with methyl ethyl ketone (MEK). Q235 pipe experimental group 1-10 and Q235 pipe control group 1-6 were also tested. The higher the number of solvent resistance wiping cycles, the better the cross-linking degree.

[0124] The performance test results of galvanized pipe experimental groups 1-10 and galvanized pipe control groups 1-6 are shown in Table 3.

[0125] Table 3

[0126] The adhesion test results of Q235 pipe experimental groups 1-10 and Q235 pipe control group 1-6 are shown in Table 4.

[0127] Table 4

[0128] As shown in Tables 3 and 4, the water-based baking paint of Examples 1-10 of the present invention, after being sprayed onto hot-dip galvanized steel plates and Q235 steel plates and cured to form metal pipes covered with a paint film, all exhibit good appearance, strong acid resistance, good adhesion to metal pipes, and solvent wiping resistance. In a 6 mol / L hydrochloric acid solution, experimental groups 1-10 of galvanized pipes showed no blistering after immersion for more than 6 hours. Experimental groups 1-10 of Q235 pipes showed no blistering, peeling, or discoloration after immersion in a 6 mol / L hydrochloric acid solution for 24 hours, and all exhibited solvent wiping resistance greater than 80 times.

[0129] Compared to Examples 1-8, the adhesion of the galvanized pipe obtained with the water-based baking paint in Example 9 was slightly reduced from grade 0 to grade 2 because no phosphate ester adhesion promoter was added. This indicates that the phosphate ester adhesion promoter has a chelating effect on the zinc layer and can improve the adhesion of the water-based baking paint on galvanized steel sheets. Compared to Examples 1-8, the adhesion of the Q235 pipe obtained with the water-based baking paint in Example 10 was slightly reduced from grade 0 to grade 2 because no second silane coupling agent was added. This indicates that the second silane coupling agent can improve the adhesion of the water-based baking paint on the surface of reactive carbon steel.

[0130] Therefore, in the embodiments of this invention, the phosphate ester adhesion promoter and the second silane coupling agent have a synergistic effect. With the pH of the water-based baking paint system adjusted to 8-9 by a pH adjuster, the phosphate ester groups react with the Zn on the surface of the zinc plating layer of the metal substrate through a chelation reaction. 2+ It forms dense, hydrolysis-resistant chemical coordination bonds, inhibiting the corrosion and dissolution of the zinc layer to form "zinc soap," ensuring the durability of the chelate bonds, and overcoming the problem of easy adhesion failure of traditional water-based baking paints on zinc plating. Simultaneously, the inorganic end of the second silane coupling agent forms MO-Si bonds with the metal substrate, while its organic end contains amino functional groups ( At high temperatures of 190-200℃, NH2 directly participates in the condensation and crosslinking reaction of the main polyester resin and amino resin, achieving interfacial bridging through coupling. This coupling ensures that the second silane coupling agent molecule becomes part of the final paint film network structure and also forms covalent bonds that run through the paint film substrate to the metal interface. The phosphate ester adhesion promoter and the second silane coupling agent work synergistically to construct a three-in-one structure of "crosslinking network-interfacial coupling agent-substrate," resulting in a high degree of matching between the interfacial strength and the cohesive force of the paint film substrate. This enables the film to maintain Grade 0 adhesion to various metal substrates in harsh environments with high-concentration acid corrosion.

[0131] Compared to Example 1, the acid resistance and solvent wiping ability of the resulting metal pipes (galvanized pipes and Q235 pipes) decreased because unmodified wet-process sericite powder was used in the paint raw materials of Comparative Example 1. In a 6 mol / L hydrochloric acid solution, bubbling occurred in less than 3 hours. This is because the wet-process sericite powder modified with the first silane coupling agent in Example 1 eliminated the microscopic gaps at the filler-resin interface, thus improving the acid resistance of the metal pipes.

[0132] Compared to Example 1, the acid resistance of the metal pipes (galvanized pipes and Q235 pipes) obtained by the water-based baking paint in Comparative Example 2 decreased because the filler in Comparative Example 2 only contained ultrafine barium sulfate and did not contain the sheet-like filler wet-process sericite powder. In a 6 mol / L hydrochloric acid solution, bubbling occurred in less than 1.5 hours. This is because the high aspect ratio of the sheet-like filler can form a labyrinth structure, which can effectively extend the acid penetration path and improve the acid resistance of the metal pipes.

[0133] Therefore, the embodiments of the present invention modify the sheet-like filler to make its surface hydrophobic, so that while maintaining the labyrinth structure of the sheet-like material, it can chemically bond with the resin matrix, thereby sealing the interface gaps and preventing acid penetration, thus achieving a highly efficient physical barrier against concentrated acid.

[0134] Compared to Example 1, the aqueous polyester resin in Comparative Example 3 lacks benzene ring and alicyclic structures. Consequently, the acid resistance of the resulting metal pipes (galvanized pipes and Q235 pipes) significantly decreased; bubbling occurred within 1 hour of immersion in a 6 mol / L hydrochloric acid solution. This is because the benzene ring and alicyclic structures of the aqueous polyester resin in Example 1 provide significant steric hindrance. This highly sterically hindered structure effectively protects the ester bonds of the polyester backbone, significantly reducing the ester bond hydrolysis rate under concentrated acid conditions, constructing a chemical defense against concentrated acid, and improving the acid and corrosion resistance of the metal pipes.

[0135] Compared to Example 1, Comparative Example 4, which lacks a wetting agent, exhibited pinholes in its corresponding metal pipes (galvanized pipes and Q235 pipes), and both acid resistance and adhesion of the galvanized pipes showed a significant decrease. This is because the lack of a wetting agent prevents the paint from penetrating to the bottom of the micro-rough surface of the substrate, forming micro-gaps (pinholes) that provide penetration channels for the acid and prevent the adhesion promoter from effectively accumulating at the interface and forming chemical anchoring points. Furthermore, pinholes cause a sharp reduction in the local thickness of the paint film, damaging its integrity. Concentrated acid can quickly penetrate the weak points of the paint film. Pinholes also cause surface flow, disrupting the parallel orientation of the hydrophobic modified lamellar filler, leading to the loss of the anti-corrosion "maze effect," thus significantly reducing acid resistance.

[0136] Compared to Example 1, Comparative Example 5 added a toluenesulfonic acid catalyst. Although the pipes obtained in Comparative Example 5 (galvanized pipes and Q235 pipes) showed better solvent wiping resistance (indicating a higher degree of crosslinking), their acid resistance decreased. This is because the toluenesulfonic acid catalyst added in Comparative Example 5 is an acidic catalyst, and its residue in the system reduces the long-term acid resistance of the pipes. Therefore, in the waterborne baking paint raw materials of this invention, the methyl etherified amino resin can undergo a complete co-condensation reaction with the hydroxyl groups of the waterborne polyester resin under acid-free catalyst conditions through high-temperature baking. This avoids the formation of hydrophilic ions in the paint film after the residue of traditional acidic catalysts, eliminates the risk of ion-induced self-corrosion and hydrolysis, and improves the acid resistance of the pipes.

[0137] Furthermore, as shown in the control groups 6 for galvanized pipes and Q235 pipes, using the same paint from Example 1, the acid resistance, adhesion, and solvent resistance of the resulting metal pipes significantly decreased due to the reduced curing temperature of 170°C. In particular, the number of solvent wiping cycles decreased to 25. This is because at 170°C, the raw materials in the paint from Example 1 could not achieve complete cross-linking, thus failing to form a dense and stable paint film on the surface of the metal pipe.

[0138] In summary, the water-based baking paint of this invention has the following four core mechanisms: (1) High-rigidity acid-resistant resin skeleton (core chemical defense line): Waterborne polyester resin contains rigid benzene rings and / or alicyclic structures, which have huge steric hindrance, which can significantly improve the glass transition temperature and cohesive force of the coating film. In addition, this high steric hindrance structure effectively protects the ester bonds of the polyester backbone, greatly reduces the hydrolysis rate in the 6 M concentrated hydrochloric acid environment, and achieves basic acid resistance.

[0139] (2) "Interface sealing" (core physical defense line) of hydrophobically modified sheet filler: The sheet filler is modified with a first silane coupling agent to make the surface of the sheet filler hydrophobic and form a chemical bond with the organic resin, which completely eliminates the microscopic capillary gaps at the interface between the traditional filler and the resin matrix that are easily utilized by acid. At the same time, the hydrophobically modified sheet filler has a high aspect ratio and can form a labyrinth structure, which prolongs the acid penetration path and further improves the acid resistance of water-based baking paint.

[0140] (3) High-temperature dense cross-linking mechanism without acid catalyst (high durability guarantee): Under the condition of no acid catalyst, methyl etherified amino resin can undergo complete co-condensation reaction with the hydroxyl groups of waterborne polyester resin through high-temperature baking, thereby forming a dense hydrophobic cross-linking network. This avoids the hydrophilic ions formed in the paint film after the residue of traditional acid catalysts, eliminates the risk of ion-induced self-corrosion and hydrolysis, and further improves the overall acid resistance and solvent resistance of the pipe.

[0141] (4) Non-obvious synergistic mechanism of dual chemical anchoring (adhesion level 0 on multi-metal substrates): Phosphate ester adhesion promoters and second silane coupling agents are formulated in a specific ratio, wherein the phosphate ester groups react with the Zn on the surface of the zinc plating layer of the metal tube through a chelation reaction. 2+ The first step involves forming dense, hydrolysis-resistant chemical coordination bonds (Anchoring I) to improve adhesion to galvanized metal pipes. The inorganic end of the second silane coupling agent reacts with the metal substrate, while the organic end participates in the polycondensation and crosslinking reaction of the main polyester-amino resin at high temperatures (Anchoring II), forming a crosslinked network. This dual anchoring creates a three-in-one structure of "crosslinked network - interfacial coupling agent - metal substrate," resulting in a high degree of matching between interfacial strength and the cohesive force of the paint film, enabling it to maintain Grade 0 adhesion to various metal substrates even in harsh environments with concentrated acids.

[0142] Therefore, through the above four mechanisms, the embodiments of the present invention achieve high crosslinking degree, high acid resistance and excellent adhesion to multi-metal pipes for water-based polyester baking paint under acid-free catalyst conditions.

[0143] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A water-based baking paint, characterized in that, The raw material components of the water-based baking paint include water-based polyester resin, amino resin, filler, additives and water; the water-based polyester resin includes hydroxyl polyester resin containing benzene ring structure and / or alicyclic structure; the additives include adhesion promoter, pH adjuster and wetting agent; the amino resin includes methyl etherified amino resin; the filler includes hydrophobically modified flake filler.

2. The water-based baking paint according to claim 1, characterized in that, By weight, the raw material components include 40-60 parts of waterborne polyester resin, 8-15 parts of amino resin, 5-18 parts of filler, 1.2-4.0 parts of adhesion promoter, 0.2-0.5 parts of pH adjuster, 0.3-0.8 parts of wetting agent and 6-45 parts of water.

3. The water-based baking paint according to claim 1, characterized in that, The raw materials for preparing the waterborne polyester resin include polybasic acid, polyol, hydrophilic monomer, and neutralizing agent; the polybasic acid includes at least one selected from isophthalic acid, terephthalic acid, trimellitic anhydride, phthalic anhydride, 1,2-cyclohexanedicarboxylic anhydride, 1,4-cyclohexanedicarboxylic acid, and adipic acid; the polyol includes at least one selected from hydrogenated bisphenol A, 1,4-cyclohexanediethanol, neopentyl glycol, and pentaerythritol; the hydrophilic monomer includes dimethylolpropionic acid; and the neutralizing agent includes triethylamine or aminomethylpropanol.

4. The water-based baking paint according to claim 1, characterized in that, The methyl etherified amino resin includes at least one of methyl etherified melamine resin, methyl etherified urea resin, methyl etherified phenyl melamine resin, methyl etherified glycourea resin, and methyl etherified cocondensation resin.

5. The water-based baking paint according to claim 1, characterized in that, The filler includes hydrophobically modified sheet filler and acid-resistant inert filler; the hydrophobically modified sheet filler includes sheet filler modified with a first silane coupling agent; the diameter-to-thickness ratio of the first silane coupling agent modified sheet filler is greater than 50:1; the particle size of the acid-resistant inert filler is <1μm.

6. The water-based baking paint according to any one of claims 1 to 5, characterized in that, The additives also include at least one of leveling agents, defoamers, color pastes, and thickeners; And / or, the adhesion promoter comprises a phosphate ester adhesion promoter and a second silane coupling agent; the mass ratio of the phosphate ester adhesion promoter to the second silane coupling agent is (3-5):1; And / or, the pH adjuster includes at least one of 2-amino-2-methyl-1-propanol, N,N-dimethylethanolamine, 2-dimethylamino-2-methyl-1-propanol, ammonia, triethylamine, cyclohexylamine, and 4-morpholinoethylamine; And / or, the wetting agent includes at least one of polyether-modified polydimethylsiloxane, polyether-modified polymethylalkylsiloxane, polyester-modified polydimethylsiloxane, acetylenic diol and its ethoxylates, fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, polyether-modified polyacrylate wetting agent, and fluorocarbon surfactant.

7. The method for preparing the water-based baking paint according to any one of claims 1 to 6, characterized in that, First, mix all raw material components except amino resin and adhesion promoter, then add amino resin and adhesion promoter and mix again to obtain the water-based baking paint.

8. A paint film, characterized in that, It is formed by curing the water-based baking paint according to any one of claims 1 to 6.

9. A metal pipe, characterized in that, It includes a metal tube and a paint film as described in claim 8 on the surface of the metal tube.

10. The application of the water-based baking paint according to any one of claims 1 to 6, the paint film according to claim 8, or the metal pipe according to claim 9 in industrial transportation, building structures, or chemical facilities.

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