An electrophoretic coating aid, a method for preparing the same, an electrophoretic coating, and a vehicle

Abstract

This application provides an electrophoretic coating additive and its preparation method, an electrophoretic coating, and a vehicle. The electrophoretic coating additive includes a polymer, which comprises a long-chain alkyl-modified phenolic epoxy resin, a chain extender, and a crosslinking agent. The chain extender includes a first amine compound and its derivatives, each containing an active amino site. The crosslinking agent includes a second amine compound and its derivatives, each containing at least two active amino sites. The crosslinking agent provides three-dimensional crosslinking points, giving the polymer a branched structure, resulting in more uniform electrophoretic migration behavior. The long-chain alkyl group provides a hydrophobic anchoring layer, and through the synergy of interfacial anchoring and directional charge migration, the coating particles are electrochemically deposited uniformly on a composite substrate with uneven resistivity under low voltage conditions, improving the uniformity of the paint film.

Description

Technical Field

[0001] This application relates to the field of coating technology, and in particular to an electrophoretic coating additive and its preparation method, electrophoretic coatings, and vehicles. Background Technology

[0002] Electrophoretic coating has been widely used in the surface protection of metal workpieces such as automobile bodies, engineering machinery and parts due to its high coating efficiency, uniform coating, excellent anti-corrosion performance and strong environmental protection.

[0003] However, existing coatings do not perform well on composite metal substrates with large resistivity differences under low voltage conditions. Summary of the Invention

[0004] This application provides an electrophoretic coating additive and its preparation method, an electrophoretic coating, and a vehicle, aiming to solve the problem that existing coatings have poor deposition effects on composite metal substrates with large resistivity differences under low voltage conditions.

[0005] To solve the above problems, this application provides the following technical solution: This application discloses an electrophoretic coating additive, which comprises a polymer, wherein the polymer comprises a long-chain alkyl-modified phenolic epoxy resin, a chain extender, and a crosslinking agent; The chain extender includes a first amine compound and its derivatives, wherein the first amine compound and its derivatives include an active amino site; The crosslinking agent includes a second amine compound and its derivatives; the second amine compound and its derivatives include at least two active amino sites.

[0006] In the embodiments of this application, the active amino groups in the chain extender undergo a chain extension reaction with the epoxy groups in the long-chain alkyl-modified phenolic epoxy resin, thereby enabling the long-chain alkyl-modified phenolic epoxy resin to achieve molecular chain growth or elongation; at least two active amino groups in the crosslinking agent undergo a crosslinking reaction with the remaining epoxy groups in the chain-extended resin to obtain a polymer with a three-dimensional network structure.

[0007] The crosslinking agent provides controllable three-dimensional crosslinking points, giving the obtained polymer a moderately branched structure. This makes it easier for the molecular chains to maintain extension and directional alignment under the influence of an electric field. The improved molecular chain orientation of the polymer results in more uniform electrophoretic migration behavior and more stable stress in the electric field, thereby reducing fluctuations in the migration rate during electrophoresis, improving the uniformity of the coating film, and ultimately achieving a coating film thickness difference of ≤2 micrometers on each substrate surface.

[0008] In addition, long-chain alkyl groups have low surface energy and strong hydrophobicity, which can form a hydrophobic anchoring layer on the surface of metal substrates, effectively blocking corrosive media such as water, oxygen, and chloride ions from penetrating to the substrate interface, and significantly improving the adhesion, water resistance and corrosion resistance of the coating to the metal substrate.

[0009] In summary, the polymers in the electrophoretic coating additives achieve a synergistic effect of interface anchoring and charge-directed migration through precise molecular structure design. This allows for more uniform electrochemical deposition behavior of coating particles on composite substrates with uneven resistivity under low voltage (≤250V) conditions. This enables efficient and uniform deposition of coatings on composite metal substrates with significant resistivity differences even at low voltage. Compared to traditional processes (applied voltage ≥300V), this application significantly reduces electrophoretic energy consumption by ≥20%, avoids electrical breakdown damage to sensitive substrates caused by high voltage, and greatly improves the uniformity of film thickness in the inner and outer cavities and corners of the composite workpiece (corner coverage ≥95%), thus simultaneously meeting the comprehensive requirements of low energy consumption, low substrate damage, and high corrosion resistance.

[0010] Further, the branching factor of the polymer is 1.2 to 1.8; and / or, The number-average molecular weight of the polymer is 3000 Da to 6000 Da; and / or, The polymer has a molecular weight distribution index of less than 2.5; and / or, The amine value of the polymer is 300 mg KOH / g ~ 400 mg KOH / g.

[0011] In this embodiment, the branching factor provides a moderately branched structure for the polymer, enhancing the rigidity of the molecular chain and facilitating its directional alignment and migration in an electric field. Controlling the number-average molecular weight of the polymer within the aforementioned range balances electrophoretic migration efficiency with the polymer's stability in the aqueous phase. The polymer's molecular weight distribution index is less than 2.5, indicating good uniformity of polymer molecular chain length, controllable polymer synthesis, and good batch-to-batch consistency. The amine value indicates that the polymer provides abundant cationization sites, ensuring high charge carrying capacity under low voltage.

[0012] Furthermore, the long-chain alkyl-modified phenolic epoxy resin is obtained by reacting phenolic epoxy resin with a long-chain alkyl organic compound; Wherein, the long-chain alkyl organic compound has ≥8 carbon atoms in the main chain or alkyl side chain; and / or, The epoxy equivalent of the phenolic epoxy resin is 150 g / eq ~ 250 g / eq.

[0013] In the embodiments of this application, the number of carbon atoms is within the above range, which gives the long-chain alkyl-modified phenolic epoxy resin moderate hydrophobicity, which can effectively anchor to the metal surface, but will not precipitate in the aqueous phase; the epoxy equivalent is within the above range, which gives the phenolic epoxy resin a rigid skeleton, providing "hard segments" of the polymer backbone and higher epoxy functionality, which facilitates the construction of a moderately branched network.

[0014] Further, based on mass parts, the content of the phenolic epoxy resin is 15 to 30 parts, the content of the long-chain alkyl compound is 5 to 15 parts, the content of the chain extender is 4 to 7 parts, and the content of the crosslinking agent is 1 to 3 parts.

[0015] In this embodiment, 15 to 30 parts of phenolic epoxy resin serve as the core polymer skeleton, providing sufficient epoxy reaction sites to support polymer rigidity and film strength. 5 to 15 parts of long-chain alkyl compounds impart suitable hydrophobicity to the polymer and form an amphiphilic structure with amino groups. 4 to 7 parts of chain extender regulate the polymer molecular weight and amine value, ensuring sufficient and uniformly distributed cationic sites. 1 to 3 parts of crosslinking agent regulate the branching factor of the polymer, forming a moderately branched structure that balances polymer flexibility and rigidity, thereby improving film density.

[0016] Furthermore, at least one of the following conditions must be met: (1) The phenolic epoxy resin includes at least one of phenolic epoxy resin, cresol phenolic epoxy resin, bisphenol A phenolic epoxy resin, biphenyl phenolic epoxy resin, triphenyl phenolic epoxy resin, dicyclopentadiene phenolic epoxy resin, and naphthol phenolic epoxy resin. (2) The long-chain alkyl organic compounds include at least one of the following: octanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, octadecanoic acid, icosanoic acid, isononanoic acid, isodecanoic acid, isooctanoic acid, oleic acid, linoleic acid, dodecylphenol, tetradecylphenol, hexadecylphenol, octadecylphenol, tert-butylphenol, dinonylphenol, 4-hydroxyphenylalkyl ether, alkylphenol polyoxyethylene ether, di-n-octylamine, N-methyloctadecylamine, N-ethylhexadecylamine, dodecylaniline, and octadecylaniline; (3) The first amine compound and its derivatives include at least one of n-butylamine, n-octylamine, methylbutylamine, ethanolamine, diethylamine, dibutylamine, N-methylethanolamine, diethanolamine, dibutanolamine, and triethylamine salt; (4) The second amine compound and its derivatives include at least one of aminoethylethanolamine, ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, isophoronediamine, polyetheramine, piperazine, N-aminoethylpiperazine, bis(hexamethylene)triamine, ketone imine of aminoethylethanolamine, diethylenetriamineacetone imine, diethylenetriaminebutanone imine, diethylenetriaminemethylisopropyl ketone imine (diethylenetriamine-MIBK condensate), and diethylenetriaminemethylisobutyl ketone imine.

[0017] In the embodiments of this application, the above-mentioned phenolic epoxy resins all contain sufficient epoxy groups and are all commercially mature products, which are readily available, suitable for industrial production, and fully compatible with existing preparation processes; the above-mentioned substances all contain long-chain alkyl groups and active groups such as hydroxyl and amino groups, which can react efficiently with phenolic epoxy resins, and the reaction is mild and easy to control; the first amine compound and its derivatives have one active amino group, which undergoes a ring-opening and chain-extending reaction with the epoxy groups of the prepolymer in the polymer formation reaction, thereby realizing the chain extension of the polymer molecular chain; the second amine compound and its derivatives include at least two active amino groups, and the crosslinking agent can undergo a crosslinking reaction with the remaining epoxy groups in the chain-extended prepolymer to realize the crosslinking of the polymer molecular chain and form a stable branched structure.

[0018] This application discloses a method for preparing an electrophoretic coating additive, the method being applicable to the aforementioned electrophoretic coating additive, the method comprising: In an inert gas atmosphere, the chain extender and the long-chain alkyl-modified phenolic epoxy resin are mixed and subjected to a chain extension reaction at a first temperature to form a first mixed system. The first mixture and the crosslinking agent are mixed to form a second mixture. The second mixture is subjected to a crosslinking reaction at a second temperature to form the polymer, thereby obtaining the electrophoretic coating additive. The first temperature is lower than the second temperature.

[0019] In this embodiment, segmented amination is employed. First, a chain extender (a first amine compound and its derivatives) is added for initial ring-opening and chain extension to control the molecular weight. Then, a crosslinking agent (a second amine compound and its derivatives) is added for deep crosslinking, forming a polymer with a nonlinear branched structure. This facilitates improved directional migration efficiency in an electric field. The first temperature is controlled to be lower than the second temperature because the multi-claw structure of the crosslinking agent is stable at low temperatures. At high temperatures, it unblocks upon contact with water, restoring the multi-claw crosslinking and thus achieving a high crosslinking density in the polymer.

[0020] Furthermore, the preparation process of the long-chain alkyl-modified phenolic epoxy resin includes: Under an inert gas atmosphere, the phenolic epoxy resin and the long-chain alkyl organic compound are mixed and then subjected to an epoxy ring-opening reaction at a third temperature to obtain the long-chain alkyl modified phenolic epoxy resin.

[0021] In this embodiment, conducting the reaction at a third temperature ensures that the epoxy groups (from phenolic epoxy resin) and carboxylic acids (from long-chain alkyl organic compounds) undergo sufficient epoxy ring-opening reaction to generate a prepolymer with reserved epoxy groups. Controlling the epoxy group conversion rate to ≥95% aims to ensure controllable crosslinking density in subsequent reaction stages, avoiding gelation due to residual epoxy groups or the inability to form a properly branched structure.

[0022] Furthermore, the electrophoretic coating additive obtained according to the polymer further includes: An acid was added to the polymer and a salt-forming reaction was carried out at a fourth temperature; The acid includes at least one of organic acids, inorganic acids, acidic esters, and acidic anhydrides.

[0023] In this embodiment, by adding acid to the polymer, the amine groups in the polymer are converted into quaternary ammonium salts, which gives the polymer water dispersibility. The use of acid can more precisely adjust the conductivity and storage stability of the final electrophoretic coating additive aqueous solution.

[0024] This application discloses an electrophoretic coating comprising the aforementioned electrophoretic coating additives.

[0025] In the embodiments of this application, electrophoretic coating additives are an indispensable key component in electrophoretic coatings, which can play a crucial role in regulating and improving the application performance, bath stability, and overall performance of the final coating film.

[0026] This application discloses a vehicle comprising a coating, the coating comprising the above-described electrophoretic coating, wherein the electrophoretic coating is a cathodic electrophoretic coating.

[0027] In this embodiment, electrophoretic coating is used as a coating on vehicles, which can provide long-term anti-corrosion and anti-rust protection for vehicle bodies and parts, resist external rainwater, salt spray, dust and other erosion, and extend the service life of vehicles. Detailed Implementation

[0028] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0029] Cathodic electrophoretic coating, as a highly efficient anti-corrosion primer coating technology, has been widely used in automobile manufacturing, home appliances, agricultural machinery and other fields since the 1960s due to its excellent penetration, film uniformity and high degree of automation. Its basic principle is to immerse the workpiece to be coated in an aqueous dispersion system containing positively charged paint particles, which serves as the cathode. Under the action of a DC electric field, the paint particles migrate directionally to the workpiece surface and undergo an electrodeposition reaction, forming a dense protective coating. With the rapid development of multi-material lightweight car bodies, the application of workpieces composed of composite materials such as aluminum, galvanized steel, and cold-rolled steel is becoming increasingly common, placing higher demands on the adaptability and coating uniformity of the electrophoretic coating process.

[0030] Traditional cathodic electrophoretic coating processes primarily rely on an external electric field to drive charged resin particles to deposit a film onto the workpiece surface. In actual production, the electrophoretic voltage is typically increased to ensure effective coating deposition on the workpiece surface, especially for composite metal substrates with significant differences in resistivity. For example, composite car body structures made of multiple metal materials such as aluminum alloys, galvanized steel sheets, and cold-rolled steel sheets often employ voltages exceeding 300V to ensure effective coating formation on each substrate surface. The core logic of this process is that aluminum (with a resistivity of approximately 2.65 × 10⁻⁶)... -8 Ω·m), galvanized steel (resistivity approximately 5.92 × 10⁻⁶ Ω·m), -8 (Ω·m) and cold-rolled steel (resistivity approximately 9.71×10) -8 Substrate resistivity (Ω·m) varies significantly. Under the same voltage, low-resistivity substrates (such as aluminum) have a high surface electric field strength and fast deposition rate, while high-resistivity substrates (such as cold-rolled steel) have a relatively weak surface electric field and low deposition efficiency. To obtain a coating thickness that meets corrosion resistance requirements on cold-rolled steel sheets with the highest resistivity, it is necessary to increase the overall process voltage to drive charged particles to deposit in the high-resistivity region. Meanwhile, to mitigate film formation differences between different substrates, the industry often employs auxiliary methods such as segmented voltage control and local shielding to minimize the problem of uneven film thickness distribution.

[0031] However, traditional high-voltage cathodic electrophoresis processes have significant drawbacks and limitations when dealing with multi-metal composite substrates. Due to the significant resistivity differences between aluminum, galvanized steel, and cold-rolled steel, the electric field distribution is severely uneven. While high-voltage coating can meet the film formation requirements of high-resistivity substrates, it significantly increases the energy consumption of the electrophoresis process. Simultaneously, high voltage easily leads to electrical breakdown on the surfaces of low-resistivity aluminum and galvanized steel, damaging the substrate or phosphating film, reducing coating adhesion and corrosion resistance, and making coating failure more likely under harsh testing conditions such as boiling water. Furthermore, this process struggles to ensure uniform film formation across different areas of the workpiece, including planes, edges, and cavities. Over-deposition is common on low-resistivity substrates, while insufficient film thickness occurs in shielded areas such as cavities. More critically, under low voltage conditions of 250V and below, existing coatings show poor deposition performance on composite metal substrates with significant resistivity differences (e.g., inability to deposit uniformly), making it difficult to simultaneously meet the comprehensive requirements of low energy consumption, low substrate damage, and high corrosion resistance, thus limiting its further application in lightweight composite vehicle body coatings.

[0032] Based on the above findings, in order to solve the problem that existing coatings have poor deposition effects on composite metal substrates with large resistivity differences under low voltage conditions, this application provides an electrophoretic coating additive. The electrophoretic coating additive includes a polymer, which includes a long-chain alkyl-modified phenolic epoxy resin, a chain extender, and a crosslinking agent. Among them, chain extenders include first amine compounds and their derivatives, and the first amine compounds and their derivatives include an active amino site; Crosslinking agents include second amine compounds and their derivatives; second amine compounds and their derivatives include at least two active amino sites.

[0033] An active amino site is an amino site that rapidly undergoes a ring-opening addition reaction with an epoxy group (or isocyanate) at room temperature / medium temperature.

[0034] An active amino group is generally considered to be highly reactive if it meets any of the following conditions: Primary amine: -NH; Secondary amine: -NH- (aliphatic, less sterically hindered); It can provide active hydrogen, which can directly participate in the curing reaction.

[0035] The role of active amino sites is that they can directly participate in epoxy curing, contribute crosslinking points, and determine curing speed, exothermic reaction, and glass transition temperature.

[0036] It should be noted that the polymer of this application can be characterized in the following ways: Fourier transform infrared spectroscopy was used with potassium bromide as the pellet, and the scanning range was 4000 cm⁻¹. -1 ~400 cm -14 cm resolution -1 The infrared spectrum of the polymer was obtained, and the specific results are as follows: (1) At 2920 cm -1 ~2930 cm -1 2849 cm -1 ~2859 cm -1 Two strong absorption peaks appeared at the point, corresponding to the stretching vibrations of -CH2- and -CH3 in the long-chain alkyl group, proving the presence of long-chain alkyl groups in the long-chain alkyl-modified phenolic epoxy resin; (2) At 1100 cm -1 ~1150 cm -1 The presence of a strong and broad absorption peak at this point corresponds to the stretching vibration of the COC ether bond, proving that the epoxy groups in the long-chain alkyl-modified phenolic epoxy resin undergo a ring-opening reaction to form an ether bond structure. (3) At 3300 cm -1 ~3500 cm -1 The appearance of a broad absorption peak at this point indicates that the absorption peaks of hydroxyl and amino groups overlap, proving that the chain extender and crosslinking agent participated in the reaction and successfully introduced amino and hydroxyl groups. (4) At 900 cm -1 ~920 cm -1 The absence of obvious absorption peaks (absorbance ≤ 0.05) indicates that the epoxy groups have completely reacted and there are no unreacted epoxy groups remaining.

[0037] In addition, particle size distribution and gel permeation chromatography (GPC) can be used for accurate detection, and amine value determination, conductivity determination and epoxy equivalent determination can be used for auxiliary characterization. The specific characterization methods are described later.

[0038] It should be noted that long-chain alkyl-modified phenolic epoxy resin can also be called prepolymer. The prepolymer mentioned in this article refers to long-chain alkyl-modified phenolic epoxy resin.

[0039] In this embodiment, the active amino group in the chain extender undergoes a ring-opening chain extension reaction with the epoxy group in the long-chain alkyl-modified phenolic epoxy resin, thereby enabling the long-chain alkyl-modified phenolic epoxy resin to achieve molecular chain growth or extension; at least two active amino groups in the crosslinking agent undergo a crosslinking reaction with the remaining epoxy group in the chain-extended resin to obtain a polymer with a three-dimensional network structure.

[0040] Crosslinking agents provide controllable three-dimensional crosslinking points, resulting in polymers with moderately branched structures. These branches create steric hindrance and localized rigid support between molecular chain segments, inhibiting excessive coiling, entanglement, or free creep of the molecular chains. Consequently, the molecular chains are more likely to maintain extension and directional alignment under an electric field. The improved molecular chain orientation leads to more uniform electrophoretic migration behavior and greater stability under stress in an electric field, reducing fluctuations in migration rate during electrophoresis, improving film uniformity, and ultimately achieving a film thickness difference of ≤2 micrometers across different substrates.

[0041] In addition, long-chain alkyl groups have low surface energy and strong hydrophobicity, which can form a hydrophobic anchoring layer on the surface of metal substrates, effectively blocking corrosive media such as water, oxygen, and chloride ions from penetrating to the substrate interface, and significantly improving the adhesion, water resistance and corrosion resistance of the coating to the metal substrate.

[0042] In summary, the polymers in the electrophoretic coating additives achieve synergistic effects of interface anchoring and charge-directed migration through precise molecular structure design. This allows the electrochemical deposition behavior of coating particles on composite substrates with uneven resistivity to become more uniform under low voltage (≤250V) conditions. This enables efficient and uniform deposition of coatings on composite metal substrates with significant resistivity differences under low voltage conditions. Compared to traditional processes (applied voltage ≥300V), this application significantly reduces electrophoretic energy consumption by ≥20%, avoids electrical breakdown damage to sensitive substrates caused by high voltage, and greatly improves the uniformity of film thickness in the inner and outer cavities and corners of the composite workpiece (corner coverage ≥95%). Thus, it simultaneously meets the comprehensive requirements of low energy consumption, low substrate damage, and high corrosion resistance.

[0043] Optionally, in one embodiment, the branching factor of the polymer is 1.2 to 1.8.

[0044] For example, the branching factor of the polymer can be a value in the range of one, two, three, four, five, six, seven, eight, or any two of them.

[0045] It should be noted that the branching factor (BF) can be determined by gel permeation chromatography-multi-angle laser light scattering (GPC-MALS) and is used to quantitatively characterize the degree of branching of long chains.

[0046] In the embodiments of this application, compared with ordinary linear or low-branching auxiliaries (BF≈1.0~1.1), the moderately branched structure of the polymer in this application enhances the rigidity of the molecular chain, which is beneficial for directional arrangement and migration in an electric field, and avoids the problems of easy entanglement and easy brittleness.

[0047] Optionally, in one embodiment, the number-average molecular weight of the polymer is 3000 Da to 6000 Da.

[0048] For example, the number-average molecular weight of the polymer can be one of 3000 Da, 4000 Da, 5000 Da, 6000 Da, or any value in the range of any two.

[0049] It should be noted that the number-average molecular weight of the polymer can be determined by gel permeation chromatography (GPC).

[0050] In this embodiment, controlling the number-average molecular weight of the polymer within the above-mentioned range can balance the electrophoretic migration efficiency and the stability of the polymer in the aqueous phase, avoiding problems such as insufficient final film strength, soaring system viscosity, and increased risk of gelation.

[0051] Alternatively, in one embodiment, the molecular weight distribution index of the polymer is less than 2.5.

[0052] It should be noted that the molecular weight distribution index (PDI) of a polymer can be determined by gel permeation chromatography (GPC). A PDI of less than 2.5 can be used as a "fingerprint" of the polymer structure.

[0053] In the embodiments of this application, the molecular weight distribution index of the polymer is less than 2.5, indicating that the polymer molecular chain length is uniform, the polymer synthesis is controllable, and the batch consistency is good.

[0054] Optionally, in one embodiment, the amine value of the polymer is 300 mg KOH / g ~ 400 mg KOH / g.

[0055] For example, the amine value of the polymer can be one of 300 mg KOH / g, 320 mg KOH / g, 340 mg KOH / g, 350 mg KOH / g, 370 mg KOH / g, 380 mg KOH / g, 400 mg KOH / g, or a range between any two.

[0056] It should be noted that the amine value is determined by potentiometric titration. The specific testing procedure is as follows: Accurately weigh 0.2–0.5 g (accurate to 0.0001 g) of polymer sample into an Erlenmeyer flask, add 50 mL of anhydrous ethanol (or isopropanol) to dissolve, and add 3–5 drops of bromophenol blue indicator to obtain the polymer sample solution; titrate with 0.1 mol / L hydrochloric acid standard solution until the polymer sample solution changes from blue to yellow, and record the volume of hydrochloric acid consumed at this point as V1. Simultaneously perform a blank test, and record the volume of hydrochloric acid consumed in the blank test as V0. The formula for calculating the amine value is:

[0057] In the formula: V1 is the volume of hydrochloric acid consumed by the polymer sample (mL), V0 is the volume of hydrochloric acid consumed by the blank test (mL), C is the concentration of hydrochloric acid (mol / L), m is the mass of the polymer sample (g), and 56.1 is the molar mass of KOH (g / mol). The amine value corresponds to the content of amino groups in the molecular chain, which can be corroborated with the results of infrared spectroscopy characterization.

[0058] In the embodiments of this application, the amine value of the above polymer is much higher than that of ordinary leveling agents or wetting agents (usually <200 mg KOH / g). The polymer has a suitable amine value, which can provide abundant cationization sites. After neutralization and salt formation, it can carry a high density of positive charge, thus still having excellent charge carrying capacity and migration deposition performance under low electrophoresis voltage, ensuring rapid and uniform film formation under low voltage.

[0059] Optionally, in one embodiment, the long-chain alkyl-modified phenolic epoxy resin is obtained by reacting phenolic epoxy resin and long-chain alkyl organic compounds. Among them, the main chain or alkyl side chain of long-chain alkyl organic compounds has ≥8 carbon atoms.

[0060] It should be noted that the number of carbon atoms in the main chain or alkyl side chain of long-chain alkyl organic compounds can be greater than or equal to 8 and less than or equal to 24. For example, the number of carbon atoms can be one of 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 22, 24 or any value in between.

[0061] In this embodiment, the number of carbon atoms is within the aforementioned range, giving the long-chain alkyl-modified phenolic epoxy resin moderate hydrophobicity. This allows it to form an ordered, tightly packed hydrophobic anchoring layer on the metal substrate surface through van der Waals forces and hydrophobic association. This effectively anchors the resin to the metal surface without precipitation in the aqueous phase. In other words, a carbon number greater than or equal to 8 allows for controllable viscosity of the polymer aqueous dispersion, preventing abnormal bath viscosity and meeting the continuous production requirements of industrial electrophoresis, while also improving the storage stability of the bath solution.

[0062] Optionally, in one embodiment, the epoxy equivalent of the phenolic epoxy resin is 150 g / eq to 250 g / eq.

[0063] For example, the epoxy equivalent of the phenolic epoxy resin can be one of, or any combination thereof, 150 g / eq, 160 g / eq, 170 g / eq, 180 g / eq, 190 g / eq, 200 g / eq, 210 g / eq, 220 g / eq, 230 g / eq, 240 g / eq, 250 g / eq.

[0064] It should be noted that the epoxy equivalent was determined using the hydrochloric acid-acetone titration method to demonstrate complete epoxy group reaction, consistent with the characteristic of the epoxy peak disappearing in the infrared spectrum. Furthermore, the epoxy equivalent value can be monitored in real time throughout the polymer formation process, accurately indicating the reaction status of the prepolymer with the chain extender and crosslinking agent.

[0065] The specific testing steps for epoxy equivalent are as follows: Accurately weigh 1–2 g (accurate to 0.0001 g) of phenolic epoxy resin sample into an Erlenmeyer flask, add 25 mL of hydrochloric acid-acetone solution (1 mL of concentrated hydrochloric acid dissolved in 40 mL of acetone), seal and shake well, then let stand in the dark for 1 hour. Add 3–5 drops of methyl red indicator to obtain the phenolic epoxy resin sample solution. Titrate with 0.1 mol / L sodium hydroxide standard solution until a yellow color appears in the phenolic epoxy resin sample solution. The volume of sodium hydroxide consumed at this point is recorded as V1. Simultaneously perform a blank test, and the volume of sodium hydroxide consumed is recorded as V0.

[0066] The formula for calculating epoxy equivalent is:

[0067] In the formula: m is the mass of the phenolic epoxy resin sample (g), V0 is the volume of sodium hydroxide consumed in the blank test (mL), V1 is the volume of sodium hydroxide consumed in the sample (mL), and C is the concentration of sodium hydroxide (mol / L).

[0068] It should be noted that the epoxy group conversion rate was determined using the hydrochloric acid-acetone titration method to ensure that subsequent reactions with chain extenders and crosslinking agents proceed in a controlled manner, avoiding excessive crosslinking. Specifically, this is reflected in: Phenolic epoxy resin is reacted with long-chain alkyl organic compounds to obtain long-chain alkyl-modified phenolic epoxy resin. This reaction process needs to ensure that the epoxy group conversion rate is greater than or equal to 95%, indicating that the long-chain alkyl organic compounds have been basically completely reacted, rather than indicating that a large number of epoxy groups in the phenolic epoxy resin have been consumed.

[0069] In this embodiment, the epoxy equivalent is within the above-mentioned range, which gives the phenolic epoxy resin a rigid backbone, providing "hard segments" of the polymer backbone and higher epoxy functionality, facilitating the construction of a moderately branched network. The smaller the epoxy equivalent, the higher the epoxy group content in the resin, the stronger the reactivity, and the greater the crosslinking density.

[0070] Optionally, in one embodiment, the content of phenolic epoxy resin is 15 to 30 parts by weight, the content of long-chain alkyl compound is 5 to 15 parts, the content of chain extender is 4 to 7 parts, and the content of crosslinking agent is 1 to 3 parts.

[0071] For example, the content of phenolic epoxy resin can be one of 15 parts, 18 parts, 20 parts, 22 parts, 24 parts, 25 parts, 28 parts, 30 parts, or any combination thereof.

[0072] The content of long-chain alkyl compounds can be one of 5 parts, 8 parts, 10 parts, 12 parts, 15 parts, or any range between two of them.

[0073] The content of the chain extender can be one of 4 parts, 5 parts, 6 parts, or 7 parts, or any range between two of them.

[0074] The content of the crosslinking agent can be one of 1 part, 2 parts, 3 parts, or any range between two.

[0075] In this embodiment, 15 to 30 parts of phenolic epoxy resin serve as the core polymer skeleton, providing sufficient epoxy reaction sites to support polymer rigidity and film strength. 5 to 15 parts of long-chain alkyl compounds impart suitable hydrophobicity to the polymer and form an amphiphilic structure with amino groups. 4 to 7 parts of chain extender regulate the polymer molecular weight and amine value, ensuring sufficient and uniformly distributed cationic sites. 1 to 3 parts of crosslinking agent regulate the branching factor of the polymer, forming a moderately branched structure that balances polymer flexibility and rigidity, thereby improving film density.

[0076] Optionally, in one embodiment, the phenolic epoxy resin includes at least one of phenolic epoxy resin, cresol phenolic epoxy resin, bisphenol A phenolic epoxy resin, biphenyl phenolic epoxy resin, triphenyl phenolic epoxy resin, dicyclopentadiene phenolic epoxy resin, and naphthol phenolic epoxy resin.

[0077] For example, the grades of phenolic epoxy resins include N-740, N-770, N-775, 152, 154, YDPN-638, EPPN-201, EPPN-202, F-44, DEN-431, DEN-438, and DEN-439.

[0078] For example, the grades of cresol-phenolic epoxy resins include N-660, N-665, N-670, N-680, N-695, ESCN001, EOCN-1020, EOCN-1025, EOCN-1027, and Photomer 3701.

[0079] For example, bisphenol A type phenolic epoxy resins include Epon 154, DER-354, and NPEF-170.

[0080] For example, the grades of biphenolic epoxy resins include NC. 3000, NC 3000H, NC 3000P, NC 3100.

[0081] For example, the types of triphenolic epoxy resins include EPPN. 501H, EPPN-502H.

[0082] For example, the models of dicyclopentadiene phenolic epoxy resin include XD. 1000L, EXA7200 H, XD1000.

[0083] For example, the model numbers of naphthol aldehyde type epoxy resins include ESN. 165S, NC 7300L, NC 7300 2L.

[0084] In the embodiments of this application, the above-mentioned phenolic epoxy resins all contain sufficient epoxy groups, which can react efficiently with long-chain alkyl compounds, chain extenders, and crosslinking agents to meet the needs of polymer preparation; and the above-mentioned resins are all commercially mature products, easy to obtain, suitable for industrial production, and fully compatible with existing preparation processes.

[0085] Optionally, in one embodiment, the long-chain alkyl organic compound includes at least one of the following: octanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, octadecanoic acid, icosanoic acid, isononanoic acid, isodecanoic acid, isooctanoic acid, oleic acid, linoleic acid, dodecylphenol, tetradecylphenol, hexadecylphenol, octadecylphenol, tert-butylphenol, dinonylphenol, 4-hydroxyphenylalkyl ether, alkylphenol polyoxyethylene ether, di-n-octylamine, N-methyloctadecylamine, N-ethylhexadecylamine, dodecylaniline, and octadecylaniline.

[0086] In the embodiments of this application, the above-mentioned substances all contain long-chain alkyl groups, and their carbon chain structures can be straight-chain, branched, or cyclic, covering a variety of functional group compounds such as carboxylic acids, phenols, and amines. They can react efficiently with phenolic epoxy resins to obtain long-chain alkyl-modified phenolic epoxy resins. At the same time, they are compatible with existing preparation processes, the reaction is mild and easy to control, and there are no abnormal by-products.

[0087] Optionally, in one embodiment, the first amine compound and its derivatives include at least one selected from n-butylamine, n-octylamine, methylbutylamine, ethanolamine, diethylamine, dibutylamine, N-methylethanolamine, diethanolamine, dibutanolamine, and triethylamine salts. Each molecule contains one amino group based on one nitrogen atom equaling one amino group, and all of the above compounds include one active amino site.

[0088] It should be noted that triethylamine salts include inorganic acid salts and organic acid salts. Inorganic acid salts include triethylamine hydrochloride, triethylamine sulfate, and triethylamine phosphate; organic acid salts include triethylamine formate, triethylamine acetate, triethylamine lactate, triethylamine citrate, triethylamine butyrate, triethylamine isooctanoate, and triethylamine resin carboxylate.

[0089] It should be noted that ethanolamine, N-methylethanolamine, diethanolamine, and dibutanolamine all contain amino and hydroxyl groups. The hydroxyl group is a hydrophilic group, which makes the prepolymer an amphiphilic intermediate that has both hydrophobic long chains and hydrophilic hydroxyl groups, and also has some residual epoxy groups.

[0090] In the embodiments of this application, the first amine compound and its derivatives have active amino groups, which undergo ring-opening and chain-extending reactions with the epoxy groups of phenolic epoxy resin in the polymer formation reaction, thereby achieving polymer molecular chain extension. Some of the first amine compounds and their derivatives contain hydrophilic groups (hydroxyl groups), which help improve the water dispersibility of the polymer.

[0091] Optionally, in one embodiment, the second amine compound and its derivatives include at least one of aminoethylethanolamine, ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, isophoronediamine, polyetheramine, piperazine, N-aminoethylpiperazine, bis(hexamethylene)triamine, ketone imine of aminoethylethanolamine, diethylenetriamineacetone imine, diethylenetriaminebutanone imine, diethylenetriaminemethylisopropylketone imine, and diethylenetriaminemethylisobutylketone imine. The number of amino groups in each molecule is calculated as one nitrogen atom equals one amino group, and all of the above compounds include at least two active amino sites.

[0092] It should be noted that second amine compounds and their derivatives are divided into those that can be used directly and those that require synthesis. Among them, aminoethylethanolamine, ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, isophorone diamine, polyetheramine, piperazine, N-aminoethylpiperazine, and bis(hexamethylene)triamine are all those that can be used directly, are commercially mature, and do not require additional synthesis.

[0093] The ketone imines of aminoethylethanolamine, such as diethylenetriamineacetone imine, diethylenetriaminebutanone imine, diethylenetriaminemethylisopropyl ketone imine, and diethylenetriaminemethylisobutyl ketone imine, are synthetic and not used directly. They are prepared by condensation reaction between the corresponding polyamines and ketones. They are stable in anhydrous conditions and release active polyamines upon contact with water during use.

[0094] In the embodiments of this application, the second amine compound and its derivatives include at least two active amino groups. The crosslinking agent can crosslink with the remaining epoxy groups in the chain-extended prepolymer to achieve crosslinking of the polymer molecular chains and form a stable branched structure.

[0095] First amine compounds and their derivatives, and second amine compounds and their derivatives introduce nitrogen-containing active groups into the polymer chain, thereby endowing polymer materials with new properties, such as toughening, improving reactivity, or improving adhesion.

[0096] This application also proposes a method for preparing an electrophoretic coating additive, applicable to the aforementioned electrophoretic coating additive, the method comprising steps 101-102: Step 101: Under an inert gas atmosphere, the chain extender and long-chain alkyl-modified phenolic epoxy resin are mixed and subjected to a chain extension reaction at a first temperature to form a first mixed system. Step 102: Mix the first mixture system and the crosslinking agent to form a second mixture system, and subject the second mixture system to a crosslinking reaction at a second temperature to form a polymer, thereby obtaining an electrophoretic coating additive; The first temperature is lower than the second temperature.

[0097] It should be noted that the range of the first temperature is 100℃~120℃. For example, it can be one or any two of 100℃, 105℃, 110℃, and 120℃.

[0098] The second temperature range is 120℃~150℃. For example, it can be one or any two of the following: 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, and 150℃.

[0099] It should also be noted that although the first temperature and the second temperature have an overlap of 120℃, in practical applications, it is necessary to ensure that the first temperature is lower than the second temperature. The case where both the first temperature and the second temperature are 120℃ is not taken. For example, the first temperature is 115℃ and the second temperature is 140℃; the first temperature is 120℃ and the second temperature is 150℃, etc.

[0100] In specific implementation, in step 101, under inert gas protection (nitrogen gas is introduced into the system), a first amine compound and its derivatives (chain extender) and a solvent (the solvent includes at least one of hydrocarbon solvents, alcohol solvents, alcohol ether solvents, ketone solvents, and ester solvents, as detailed below) are added and stirred until uniform. Long-chain alkyl-modified phenolic epoxy resin is added dropwise at a time of 1 to 2 hours and controlled at a first temperature (100℃ to 120℃) to induce a chain extension reaction and form a first mixed system. In step 102, a second amine compound and its derivatives (crosslinking agent) are added to the first mixed system to form a second mixed system. The second mixed system is subjected to a crosslinking reaction at a second temperature (120℃ to 150℃) for 2 to 6 hours until the viscosity of the system stabilizes, which is the endpoint of the reaction, to form a polymer.

[0101] It should be noted that the crosslinking agent used in this application can be a diethylenetriamine-MIBK condensate, wherein the amines in the diethylenetriamine-MIBK condensate are derived from diethylenetriamine, and the ketones in the diethylenetriamine-MIBK condensate are derived from methyl isobutyl ketone. The diethylenetriamine-MIBK condensate is a relatively stable intermediate, so that the highly reactive polyamine can be released again under the high-temperature conditions of the subsequent second temperature, thereby achieving precise control of the crosslinking reaction.

[0102] It should be noted that the first temperature is controlled to be lower than the second temperature because the multi-claw structure of the crosslinking agent is stable at low temperatures, but at high temperatures, it is unsealed by water, restoring the multi-claw crosslinking, thereby achieving a high crosslinking density of the polymer.

[0103] In this embodiment, segmented amination is performed, that is, firstly, a chain extender (a first amine compound and its derivatives) is added to perform preliminary ring-opening chain extension to control the molecular weight, and then a crosslinking agent (a second amine compound and its derivatives) is added to perform deep crosslinking to form a polymer with a nonlinear branched structure, which facilitates the improvement of directional migration efficiency in an electric field.

[0104] Taking diethanolamine as the first amine compound and its derivatives, and diethylenetriamine methyl isopropyl ketone imine (diethylenetriamine-MIBK condensate) as the second amine compound and its derivatives, the specific process is explained as follows: The first stage of segmented amination: Adding diethanolamine initiates preliminary ring-opening and chain extension. The reaction principle is that both the secondary amino and hydroxyl groups on diethanolamine can react with the epoxy groups, primarily the amino groups reacting first to open the epoxy ring and attach the diethanolamine molecules to the prepolymer. This has the following effects: 1. Introducing hydrophilic groups: Diethanolamine has two hydroxyl groups, which are hydrophilic groups. This step introduces hydrophilicity into the originally hydrophobic and oily prepolymer, preparing it for the water solubility of the final electrophoretic coating additive.

[0105] 2. Molecular chain growth (chain extension): Diethanolamine acts like a small bridge, connecting or extending the prepolymer molecular chains through a reaction, thus initially increasing the molecular weight.

[0106] 3. Introduction of reactive sites: After the reaction, in addition to the original epoxy groups, the system contains many newly generated hydroxyl groups.

[0107] The prepolymer became an amphiphilic intermediate with both hydrophobic long chains (contributed by long-chain alkyl organic compounds) and hydrophilic hydroxyl groups (contributed by diethanolamine), and also retained some epoxy groups.

[0108] The second stage of segmented amination: By adding diethylenetriamine-MIBK condensate for deep crosslinking modification, residual epoxy groups remain in the system after the first stage of segmented amination. The reaction principle is that the diethylenetriamine-MIBK condensate has a "multi-claw" structure, which releases multiple highly reactive primary amino groups under reaction conditions. These primary amino groups undergo a rapid and efficient crosslinking reaction with the residual epoxy groups in the system. Specific effects are as follows: 1. Constructing branched structures: A "multi-claw" amine molecule can react simultaneously with epoxy groups on multiple different prepolymer chains, linking them together to form a three-dimensional network or highly branched structure.

[0109] 2. Increase amine value: Diethylenetriamine itself is rich in nitrogen atoms, and its introduction contributes a large number of potential cationization sites (tertiary amine groups) to the polymer.

[0110] 3. Enhanced molecular rigidity: The cross-linking points formed restrict the free movement of molecular chains, enhance the rigidity of the entire molecule, make it easier for it to orient itself in an electric field, and make it less prone to curling up, thereby improving the electrochemical mobility index (EMI).

[0111] The final product was a highly branched, amino-rich cationic polymer with an amphiphilic structure.

[0112] In practice, diethanolamine is first added to the reactor and heated. Then, the prepolymer is slowly dripped into the reactor using a reverse addition method, ensuring that the amine remains in excess throughout the reaction. In this environment, each dripped prepolymer molecule is rapidly surrounded by a large number of amine molecules, allowing its epoxy groups to react gently and uniformly with the diethanolamine, thus avoiding runaway reaction or explosive polymerization caused by excessively high local epoxy group concentrations.

[0113] In this process, diethanolamine acts as a "chain extender." Through the reaction of its functional groups with the epoxy groups on the prepolymer, it links the originally relatively independent, low-molecular-weight prepolymers together, forming polymer chains with significantly increased molecular weight. This stage precisely controls the base molecular weight of the final product. The molecular weight cannot be too low, otherwise an effective network structure cannot be formed; nor can it be too high, otherwise the system viscosity will be too high, hindering the uniform introduction and deep crosslinking of the subsequent crosslinking agent. Only after this basic chain growth step is complete, the molecular weight reaches the design expectation, and the system viscosity stabilizes, can the crosslinking agent be added for crosslinking. This allows for the precise introduction of branching points onto the already constructed, well-organized framework, ultimately obtaining the target branching factor without performance failure due to insufficient framework strength or structural disorder.

[0114] Optionally, in one embodiment, the preparation process of the long-chain alkyl-modified phenolic epoxy resin includes: In an inert gas atmosphere, phenolic epoxy resin and long-chain alkyl organic compounds are mixed and then subjected to an epoxy ring-opening reaction at a third temperature to obtain long-chain alkyl modified phenolic epoxy resin.

[0115] It should be noted that the logP value of long-chain alkyl organic compounds is approximately 3.0. The logP value refers to the logarithmic ratio of the partition coefficient of a substance in n-octanol (oil) and water, reflecting the distribution of the substance in the oil and water phases. logP > 0 indicates a preference for the oil phase, hydrophobicity, and lipophilicity. Therefore, long-chain alkyl compounds are hydrophobic and can effectively anchor to metal surfaces.

[0116] It should be noted that the range of the third temperature is 100℃~150℃. For example, it can be one or any two of the following: 100℃, 120℃, 130℃, 140℃, and 150℃.

[0117] In practice, under inert gas protection (replacing air in the system until the oxygen content is <0.5%), phenolic epoxy resin, solvent, and long-chain alkyl organic compound are added sequentially to the reactor. After stirring and mixing evenly, the temperature is raised to 50℃~95℃, and then a catalyst is added. The mixture is kept at 100℃~150℃ for 2 to 6 hours to carry out the epoxy ring-opening reaction (since this process forms a prepolymer, it can also be called a prepolymerization reaction). At the same time, the epoxy equivalent in the reaction system is measured. When the epoxy equivalent is greater than or equal to 95%, the reaction is complete. The temperature is then lowered to 40℃~60℃ for later use, and the long-chain alkyl modified phenolic epoxy resin, i.e., the prepolymer, is obtained.

[0118] The catalyst includes at least one of amines, imidazoles, imidazolines, and organophosphorus compounds. The amount of catalyst added is 0.01 to 0.03 parts. For example, the catalyst includes triethylamine, N,N-dimethylbenzylamine, triethanolamine, tetramethylammonium chloride, triphenylphosphine, triethylamine salt, dimethylimidazolium, tetramethylimidazolium, tetraethylammonium bromide, and N,N-dimethylethanolamine. The catalyst catalyzes the ring-opening reaction of epoxy groups, exhibiting high activity and good selectivity.

[0119] The solvent includes at least one of hydrocarbon solvents, alcohol solvents, alcohol ether solvents, ketone solvents, and ester solvents. The amount of solvent added is 10 to 20 parts. For example, hydrocarbon solvents include toluene, xylene, and trimethylbenzene; alcohol solvents include methanol, ethanol, n-butanol, isopropanol, isooctanol, ethylene glycol, and propylene glycol; alcohol ether solvents include ethylene glycol ethyl ether, diethylene glycol ethyl ether, ethylene glycol butyl ether, diethylene glycol butyl ether, ethylene glycol hexyl ether, diethylene glycol hexyl ether, propylene glycol methyl ether, propylene glycol phenyl ether, and diethylene glycol dibutyl ether; ketone solvents include acetone, butanone, methyl isobutyl ketone, cyclohexanone, isoflurane, and acetylacetone; and ester solvents include ethylene glycol ethyl ether acetate and ethylene glycol butyl ether acetate. The solvent has a moderate boiling point, which is beneficial for controlling the reaction temperature.

[0120] In this embodiment, conducting the reaction at a third temperature ensures that the epoxy groups (from phenolic epoxy resin) and carboxylic acids (from long-chain alkyl organic compounds) undergo sufficient epoxy ring-opening reaction to generate a prepolymer with reserved epoxy groups. Controlling the epoxy group conversion rate to ≥95% aims to ensure controllable crosslinking density in subsequent reaction stages, avoiding gelation due to residual epoxy groups or the inability to form a properly branched structure.

[0121] Taking a phenolic epoxy resin as dicyclopentadiene phenolic epoxy resin, a long-chain alkyl organic compound as isooctanoic acid, a first amine compound and its derivative as diethanolamine, and a second amine compound and its derivative as diethylenetriamine methyl isopropyl ketone imine (diethylenetriamine-MIBK condensate) as an example, the specific process is explained as follows: The first stage is the prepolymerization reaction: In this stage, dicyclopentadiene phenolic epoxy resin reacts with isooctanoic acid. The carboxyl groups on the isooctanoic acid open some of the epoxy groups and attach them, introducing a hydrophobic long chain. However, phenolic epoxy resin is multifunctional, with multiple epoxy groups originally present in the molecule. The goal of this stage is to consume only a small portion of these epoxy groups, for example, 15% to 20% of the initial total epoxy groups, thus retaining the vast majority (approximately 80% to 85%) for subsequent reactions with chain extenders and crosslinking agents. An epoxy group conversion rate of ≥95% indicates that the isooctanoic acid has reacted almost completely, not that a large number of epoxy groups have been consumed. Therefore, after the prepolymerization reaction, the system has a very sufficient number of reserved epoxy groups.

[0122] The second stage is the first stage of segmented amination: After the addition of diethanolamine, the amino and hydroxyl groups on the diethanolamine react with some of the reserved epoxy groups, which serves to introduce hydrophilic groups and initially extend the chain. The key control point at this stage is that the epoxy groups must not be completely consumed; some must be reserved for crosslinking by the crosslinking agent in the next step.

[0123] Experiments show that after the first stage of reaction, the optimal percentage of reserved epoxy groups in the system is between 10% and 20% of the initial total epoxy groups. If the reserved epoxy groups exceed 20%, the excessive crosslinking sites after the addition of the crosslinking agent will lead to runaway reaction, rapidly forming an insoluble gel, rendering the entire batch of product unusable. If the reserved epoxy groups are less than 10%, the crosslinking agent cannot provide enough epoxy group sites to react with, failing to effectively connect multiple molecular chains to form a branched structure. The final product tends to be linear, the branching factor cannot be increased to 1.2-1.8, and the electrochemical mobility index is difficult to reach above 0.85, thus hindering efficient and uniform deposition under low voltage.

[0124] The reaction process is set with the first temperature lower than the second temperature, and the system viscosity is stabilized as the reaction endpoint. The fundamental purpose is to precisely control the reserved epoxy groups after the first stage of reaction within the golden window of 10% to 20%, so as to prepare for the next step of appropriate crosslinking.

[0125] The third stage is the second stage of segmented amination: After the first stage of reaction, the content of reserved epoxy groups in the system is precisely controlled between 10% and 20% of the initial total epoxy groups. This is crucial in determining whether the final polymer can form a moderately branched structure. Only when the reserved epoxy groups are controlled within the golden window of 10% to 20% can the crosslinking agent molecules have the opportunity to moderately connect with 2 to 3 different polymer chains to form a three-dimensional network structure that is neither linear nor dense gel. This allows for the controllable improvement of BF and the achievement of the target amine value (300 mg KOH / g to 400 mg KOH / g), while ensuring a stable reaction process.

[0126] Optionally, in one embodiment, the electrophoretic coating additive, based on the polymer, further includes: An acid was added to the polymer, and a salt-forming reaction was carried out at a fourth temperature. Among them, acids include at least one of organic acids, inorganic acids, acidic esters, and acidic anhydrides.

[0127] For example, organic acids include formic acid, acetic acid, lactic acid, propionic acid, butyric acid, caprylic acid, valeric acid, hexanoic acid, benzoic acid, dimethylolpropionic acid, N-acetylglycine, N-acetyl-β-alanine, acrylic acid, methacrylic acid, aminosulfonic acid, maleic anhydride, 2-sulfobenzoic anhydride, methanesulfonic acid, and hydroxyethylsulfonic acid.

[0128] Inorganic acids include boric acid, phosphoric acid, hydrochloric acid, and sulfuric acid.

[0129] Acidic esters / acidic anhydrides include maleic anhydride, diisopropyl malonate, and 2-sulfobenzoic anhydride.

[0130] It should be noted that the amount of acid added is 0.2 to 0.8 parts. For example, it can be one or any two of the following: 0.2 parts, 0.4 parts, 0.5 parts, 0.6 parts, and 0.8 parts.

[0131] It should be noted that the fourth temperature range is 50℃~70℃. For example, it can be one of 50℃, 60℃, and 70℃ or any two of them.

[0132] In practice, after the polymer is formed, the reaction system is cooled to 50℃~70℃. Acid is added to the polymer and the mixture is kept at 50℃~70℃ for 0.5~1 hour to carry out a salt formation reaction. Finally, pure water is added twice at 30-minute intervals to dilute the mixture, controlling the final solid content to 30%±2%. The mixture is then filtered through a 200-mesh filter to obtain the electrophoretic coating additive. It is important to monitor the conductivity of the system during the reaction to confirm whether the reaction is complete.

[0133] This application selects to add a mixed acid, such as formic acid and acetic acid, wherein formic acid is a strong acid that can be quickly neutralized and provide initial conductivity; acetic acid is a weak acid that can finely adjust the pH and buffer the stability of the system.

[0134] Stepwise water addition helps avoid polymer precipitation or micelle structure damage caused by excessively low local concentrations. A 200-mesh filtration removes gel particles or foreign impurities that may be generated during synthesis, ensuring product purity and storage stability.

[0135] The electrophoretic coating additive is a uniform and transparent liquid with a pH of 6.0~8 at 25℃ and a conductivity of 4000µS / cm~8000µS / cm at 25℃. The conductivity reflects the degree of ionization of the additive. Within this range, the conductivity of the bath solution can be optimized without affecting the stability. The storage stability is no stratification or precipitation after 7 days at 50℃.

[0136] The electrophoretic coating additives were also characterized by their electrochemical migration index (using an electrochemical testing device) and dynamic contact angle (using a contact angle meter on galvanized steel sheets). The results showed that the electrochemical migration index (EMI) of the electrophoretic coating additives was greater than or equal to 0.85, quantifying the efficiency with which the additives carried pigment particles to the cathode under an electric field, while the EMI of ordinary additives was typically <0.6. The dynamic contact angle of the electrophoretic coating additives was ≤30°, indicating that the additives could significantly reduce the wetting angle of the coating liquid on low surface energy substrates, which is beneficial for initial adsorption.

[0137] In this embodiment, by adding acid to the polymer, the amine groups in the polymer are converted into quaternary ammonium salts, giving the polymer ionicity and water dispersibility or water solubility. The use of acid can more precisely adjust the conductivity and storage stability of the final electrophoretic coating additive aqueous solution.

[0138] This application obtains a cationic polymer aqueous solution with high positive charge density (Zeta potential +35 to +50 mV) by adding acid. The Zeta potential is measured by a dynamic light scattering instrument. The high positive charge potential is a direct reflection of the high amine value and efficient cationization of the electrophoretic coating additive, ensuring efficient electrophoretic migration under low voltage.

[0139] In addition, polymers can also be measured by particle size distribution and crosslinking density.

[0140] The characteristic particle size distribution of the polymer was measured using a laser particle size analyzer. The results showed a bimodal distribution, with the main peak at 80 nm to 120 nm and the secondary peak at <20 nm. The principle behind this is that the polymer has an amphiphilic branched structure, with the molecular chain containing both hydrophilic groups and hydrophobic long-chain alkyl groups. During aqueous dispersion, due to the self-assembly of hydrophilic and hydrophobic groups and the spatial association of branched segments, small-diameter micelles and large-diameter aggregates easily coexist, resulting in a bimodal particle size distribution, which is a typical characteristic of this type of amphiphilic branched polymer.

[0141] The crosslinking density of the polymer was measured by the swelling method (xylene), and the results showed that the crosslinking density of the polymer was 3.0 × 10⁻⁶. -4 mol / cm 3 ~4.5×10 -4 mol / cm 3 The crosslinking density is determined by the controllable branching brought about by the crosslinking agent, ensuring that the coating formed by the electrophoretic coating additives has excellent mechanical properties and chemical resistance.

[0142] This application also proposes an electrophoretic coating, which includes the above-mentioned electrophoretic coating additives.

[0143] In the embodiments of this application, electrophoretic coating additives are an indispensable key component in electrophoretic coatings, which can play a crucial role in regulating and improving the application performance, bath stability, and overall performance of the final coating film.

[0144] Furthermore, the electrophoretic coating additives of this application are highly compatible with existing electrophoretic coating systems and are suitable for high-requirement coating fields such as automotive bodies.

[0145] This application also proposes a vehicle that includes a coating comprising the aforementioned electrophoretic coating.

[0146] In practice, the above-mentioned electrophoretic coating additives are added to the commercial cathodic electrophoretic coating bath at 2% of the total solids content. Electrophoretic coating is performed on a composite test plate made of aluminum plate, galvanized plate, and cold-rolled steel plate at a bath temperature of 30℃±1℃ and a voltage of 250V for 3 minutes, followed by baking at 70℃ for 20 minutes to form a coating.

[0147] In this embodiment, electrophoretic coating is used as a coating on vehicles, which can provide long-term anti-corrosion and anti-rust protection for vehicle bodies and parts, resist external rainwater, salt spray, dust and other erosion, and extend the service life of vehicles.

[0148] While ensuring the coating quality of all parts of the composite body, the operating voltage is significantly reduced, thereby saving energy, reducing coating defects, and improving production safety and efficiency.

[0149] The above-described electrophoretic coating and vehicle embodiments include the aforementioned electrophoretic coating additives and achieve the same technical effects. To avoid repetition, they will not be described again here. For relevant details, please refer to the description of the electrophoretic coating additive embodiments.

[0150] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention is further described below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0151] The present invention will be described in detail below through embodiments.

[0152] Test method: (1) Thickness testing of aluminum sheet film, galvanized sheet film, and cold-rolled steel sheet film The thickness of aluminum sheet film, galvanized sheet film, and cold-rolled steel sheet film were measured in accordance with GB / T 13452 "Determination of film thickness of paint and varnish".

[0153] The thickness difference of the composite film is calculated based on the thickness of the aluminum sheet film, galvanized sheet film, and cold-rolled steel sheet film.

[0154] (2) Testing of working voltage The operating voltage parameters are obtained through a DC power supply.

[0155] (3) Corner coverage test Take the sample after electrophoretic coating, cut a cross section along the vertical direction of the corner, and after inlaying, grinding and polishing, observe the cross section with a metallographic microscope, measure the coating thickness at the plane and corner positions, observe the coating continuity and whether the substrate is exposed, and determine whether the corner coverage is qualified.

[0156] (4) Coulomb efficiency test The electrophoretic coating solution is placed in an electrolytic cell, and the test panel is electrophoretically coated under a constant voltage. The amount of electricity consumed in depositing the coating is recorded by a coulometric meter. The mass change of the test panel before and after electrophoresis is measured, and the mass of the coating deposited per unit amount of electricity is calculated, which is the coulometric efficiency.

[0157] (5) Adhesion test Adhesion tests were conducted in accordance with GB / T 9286-2021 "Cross-cut test for paints and varnishes".

[0158] (6) Boiling water resistance test The boiling water resistance test at 100℃ was conducted in accordance with GB / T 1733-1993 "Determination of Water Resistance of Coating Film".

[0159] (7) Impact resistance test Impact resistance was tested according to GB / T 1732-2020 "Test Method for Impact Resistance of Coating Film" (500g weight, 50cm height).

[0160] (8) Cupping test The cupping test was conducted in accordance with GB / T 9753 "Cupping Test for Paints and Varnishes".

[0161] (9) Salt spray resistance test Salt spray resistance was tested in accordance with GB-T 1771-2007 "Determination of resistance to neutral salt spray in paints and varnishes".

[0162] (10) Stone impact resistance test Stone impact resistance test was conducted in accordance with DIN 55996-1 "Test of stone impact resistance of painted coatings".

[0163] Example 1 (1) Preparation of long-chain alkyl-modified phenolic epoxy resin Under an inert gas atmosphere (nitrogen), 20 parts of phenolic epoxy resin (dicyclopentadiene phenolic epoxy resin XD-1000L), 15 parts of solvent (methyl isobutyl ketone), and 8 parts of long-chain alkyl organic compound (isooctanoic acid) were added to the reactor and mixed. The mixture was stirred at 200 rpm for 30 minutes until homogeneous. The temperature was first slowly preheated to 95°C, and then 0.02 parts of catalyst (triphenylphosphine) were added. The epoxy ring-opening reaction was carried out at a third temperature (120°C) for 4 hours. The epoxy conversion rate was monitored in real time. When the epoxy conversion rate was ≥95%, the reaction was stopped to obtain long-chain alkyl modified phenolic epoxy resin (prepolymer). The mixture was then cooled to 50°C and sealed for storage.

[0164] (2) Preparation of electrophoretic coating additives In a separate reaction vessel, under the protection of an inert gas atmosphere (nitrogen), add 7 parts of chain extender (diethanolamine) and 3 parts of methyl isobutyl ketone solvent, stir and mix evenly, and add the above prepolymer dropwise at the first temperature (110℃) for 1-2 hours to allow the chain extension reaction to occur. During the dropwise addition process, control the viscosity fluctuation of the system to be <10% to form the first mixed system. Then, 3 parts of crosslinking agent (diethylenetriamine-MIBK condensate) were added to the first mixture to form the second mixture. The second mixture was subjected to a crosslinking reaction at a second temperature (140°C) for 5 hours until the viscosity of the system stabilized, which was the endpoint of the reaction, and a polymer was formed.

[0165] The reaction system was cooled to 60°C, and 0.5 parts of formic acid and 0.3 parts of acetic acid were added to the polymer. The mixture was stirred at 150 rpm for 30 minutes and kept at the fourth temperature (60°C) for 1 hour to carry out the salt formation reaction. During this period, the conductivity of the system was monitored to confirm that the reaction was complete. 20 parts of pure water at 50°C were added to the system and the mixture was kept at this temperature for 1 hour.

[0166] Finally, 35 parts of pure water were added in two batches for dilution, and the mixture was filtered through a 200-mesh filter to obtain electrophoretic coating additive A with a solid content of 30% ± 2%.

[0167] (3) Preparation of coating Add the above-mentioned electrophoretic coating additive A at 2% of the total solids to the commercial cathodic electrophoretic coating (CS8830) bath solution. Under the conditions of bath temperature 30±1℃ and voltage 250V, electrophoretic coating is performed on the composite test plate spliced ​​from aluminum plate, galvanized plate and cold-rolled steel plate for 3 minutes. Finally, it is baked at 70℃ for 20 minutes to obtain the coating (paint film).

[0168] Examples 2-3 The difference between Examples 2 and 3 and Example 1 is that... In Examples 2 and 3, the chain extender in the preparation of the electrophoretic coating additive in step (2) was adjusted to N-methylethanolamine and dibutanolamine, respectively.

[0169] The remaining steps and dosages are the same as in Example 1, and a coating is obtained.

[0170] Examples 4-5 The difference between Examples 4 and 5 and Example 1 is that... In Examples 4 and 5, the crosslinking agents in the preparation of the electrophoretic coating additives in step (2) were adjusted to aminoethylethanolamine and diethylenetriaminemethylisobutyl ketone imine, respectively.

[0171] Diethylenetriamine methyl isobutyl ketone imine is prepared from the corresponding amine and ketone.

[0172] The remaining steps and dosages are the same as in Example 1, and a coating is obtained.

[0173] Examples 6-7 The difference between Examples 6 and 7 and Example 1 is that... In Examples 6 and 7, in the preparation of long-chain alkyl modified phenolic epoxy resin in step (1), the phenolic epoxy resin was adjusted to cresol phenolic epoxy resin N-680 and phenolic epoxy resin N-770, respectively.

[0174] The remaining steps and dosages are the same as in Example 1, and a coating is obtained.

[0175] Examples 8-9 The difference between Examples 8 and 9 and Example 1 is that... In Examples 8 and 9, in the preparation of long-chain alkyl modified phenolic epoxy resin in step (1), the long-chain alkyl organic compounds were adjusted to dodecylphenol and di-n-octylamine, respectively.

[0176] The remaining steps and dosages are the same as in Example 1, and a coating is obtained.

[0177] Examples 10-11 The difference between Examples 10 and 11 and Example 1 is that... In Examples 10-11, the content of phenolic epoxy resin in step (1) of preparing long-chain alkyl modified phenolic epoxy resin was adjusted to 15 parts and 30 parts, respectively.

[0178] The remaining steps and dosages are the same as in Example 1, and a coating is obtained.

[0179] Examples 12-13 The difference between Examples 12 and 13 and Example 1 is that... In Examples 12-13, the content of long-chain alkyl compounds in the preparation of long-chain alkyl modified phenolic epoxy resin in step (1) was adjusted to 5 parts and 15 parts, respectively.

[0180] The remaining steps and dosages are the same as in Example 1, and a coating is obtained.

[0181] Examples 14-15 The difference between Examples 14-15 and Example 1 is that... In Examples 14-15, the contents of chain extender and crosslinking agent in the preparation of electrophoretic coating additives in step (2) were adjusted to 4 parts and 1 part, respectively.

[0182] The remaining steps and dosages are the same as in Example 1, and a coating is obtained.

[0183] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that, Comparative Example 1 did not add any electrophoretic coating additives, but only used the same commercial cathodic electrophoretic coating (CS8830) to coat the same composite test panel at 300V to obtain a coating (film).

[0184] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that... Comparative Example 2: 2% of a commercially available general-purpose electrophoretic coating wetting and leveling agent was added to the same commercial cathodic electrophoretic coating (CS8830), and the composite test panel was coated at 250V to obtain a coating.

[0185] The polymers obtained in Examples 1-15 all had branching factors in the range of 1.2-1.8; the number average molecular weight of the polymers was 3000 Da to 6000 Da; the molecular weight distribution index was less than 2.5; and the amine value of the polymers was 300 mg KOH / g to 400 mg KOH / g.

[0186] The electrophoretic coating additives obtained in Examples 1-15 are all uniform and transparent liquids with a pH of 6.0-8 at 25°C, an electrical conductivity of 4000µS / cm-8000µS / cm at 25°C, and a storage stability of no stratification or precipitation after 7 days at 50°C. The electrochemical migration index (EMI) is ≥0.85.

[0187] The thickness, working voltage, edge coverage, and coulombic efficiency of the electrophoresis processes of each embodiment and comparative example were tested for aluminum plate film, galvanized plate film, and cold-rolled steel plate film. The results are shown in Table 1.

[0188] Table 1

[0189] In all embodiments, the operating voltage was less than or equal to 250V, and the aluminum plate film thickness and surface were intact. However, in Comparative Example 1, without the addition of electrophoretic coating additives, local breakdown points were observed, and the operating voltage was greater than or equal to 300V. In Comparative Example 2, using commercial leveling agents, although the operating voltage could reach 250V, the film thickness was less than 20 micrometers. Furthermore, the range of film thickness in the composite plates of the embodiments was less than or equal to 2 micrometers, while the range of Comparative Examples 1 and 2 was greater than 5 micrometers. This demonstrates that the electrophoretic coating additive of this application, through precise molecular structure design, achieves a synergistic effect of interface anchoring capability and charge directional migration capability, thereby enabling the film thickness to be maintained at low voltages (≤200V). Under 50V conditions, the electrochemical deposition behavior of coating particles on composite substrates with uneven resistivity tends to be uniform. This allows for efficient and uniform deposition of coatings on composite metal substrates with large resistivity differences under low voltage conditions, resulting in a coating thickness difference of ≤2 micrometers on the surface of each substrate. Compared with traditional processes (applied voltage ≥300V), this application significantly reduces electrophoresis energy consumption by ≥20%, avoids electrical breakdown damage to sensitive substrates caused by high voltage, and greatly improves the uniformity of film thickness in the inner and outer cavities and corners of composite workpieces (corner coverage ≥95%), thus simultaneously meeting the comprehensive requirements of low energy consumption, low substrate damage, and high corrosion resistance.

[0190] The coatings prepared in each embodiment and comparative example were subjected to adhesion test, boiling water resistance test, impact resistance test, cupping test, salt spray resistance test, and stone impact resistance test, provided that the film thickness reached 20 micrometers ± 2 micrometers (the film thickness of comparative example 2 was less than 20 micrometers, so no further test was conducted). The results are shown in Table 2.

[0191] Table 2

[0192] As shown in Table 2, the coatings of each embodiment showed a boiling water resistance of 0% and an adhesion of 0% after 6 hours, while the coating of Comparative Example 1 showed bubbles and decreased adhesion after 2 hours. The cupping of the coatings of each embodiment was higher than that of the comparative example, indicating that the coating obtained in this application has better flexibility and resistance to deformation, and is less prone to cracking and peeling during deformation. The salt spray resistance of the coatings of each embodiment was greater than or equal to 1000 hours, and the unilateral erosion of scratches was <2 mm, while the salt spray resistance of Comparative Example 1 was greater than or equal to 920 hours, and the unilateral erosion of scratches was <2.5 mm, indicating that the salt spray resistance (corrosion resistance) of this application is superior to that of the comparative example.

[0193] This application utilizes a rigid phenolic epoxy resin and introduces long-chain alkyl groups. Its rigid cyclic structure provides "hard segments" for the polymer backbone, giving the molecular chain spatial conformation stability. Its abundant hydroxyl groups can form strong chemical bonds with the substrate surface, improving coating adhesion and interfacial hydrolysis resistance. After boiling in water at 100°C for 6 hours, the coating still maintains an adhesion rating of 0, enhancing coating adhesion and durability. At the same time, low-voltage operation fundamentally avoids the risk of electrical breakdown of aluminum and galvanized plates, protecting sensitive substrates and improving product quality and reliability.

[0194] By precisely controlling the proportions of phenolic epoxy resin, long-chain alkyl organic compounds, chain extenders, crosslinking agents, and acids—that is, the synergistic effect of "rigid resin skeleton, moderately hydrophobic anchoring chains, crosslinking agents, and acids"—the target structure of "high branching, high amine value, and high EMI" is precisely achieved. This forms a polymer system with suitable molecular weight, conductivity, and stability, ensuring high migration efficiency at low voltages, moderate crosslinking density after film formation, and excellent mechanical properties and corrosion resistance. The coating obtained at low voltages exhibits hardness, flexibility, impact resistance, chemical resistance, and salt spray resistance (≥1000h) that meet or exceed the levels of traditional high-voltage processes. This solves the core problem of uniform and efficient coating of composite substrates at ≤250V. In other words, the electrophoretic coating additive of this application fundamentally solves the industry problem of uneven film thickness caused by differences in substrate resistivity.

[0195] Furthermore, the electrophoretic coating additives of this application can be directly compounded with commercially available electrophoretic coatings without modifying existing coating lines, offering a wide process window and making them easy to control and promote.

[0196] Terminology Explanation In this application, "multiple" refers to two or more.

[0197] The terms “first,” “second,” “third,” “fourth,” etc., in this application (if present) are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0198] In this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, in this application, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0199] Unless otherwise specified, all steps in this application may be performed sequentially or randomly. For example, if the method includes steps A and B, it means that the method may include steps A and B performed sequentially, or it may include steps B and A performed sequentially. For example, if the method may also include step C, it means that step C may be added to the method in any order. For example, the method may include steps A, B, and C, or it may include steps A, C, and B, or it may include steps C, A, and B, etc.

[0200] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An electrophoretic coating additive, characterized in that, The electrophoretic coating additives include polymers, which include long-chain alkyl-modified phenolic epoxy resins, chain extenders, and crosslinking agents; The chain extender includes a first amine compound and its derivatives, wherein the first amine compound and its derivatives include an active amino site; The crosslinking agent includes a second amine compound and its derivatives; the second amine compound and its derivatives include at least two active amino sites.

2. The electrophoretic coating additive according to claim 1, characterized in that, The branching factor of the polymer is 1.2 to 1.8; and / or, The number-average molecular weight of the polymer is 3000 Da to 6000 Da; and / or, The polymer has a molecular weight distribution index of less than 2.5; and / or, The amine value of the polymer is 300 mg KOH / g to 400 mg KOH / g.

3. The electrophoretic coating additive according to claim 1, characterized in that, The long-chain alkyl-modified phenolic epoxy resin is obtained by reacting phenolic epoxy resin with long-chain alkyl organic compounds. Wherein, the long-chain alkyl organic compound has ≥8 carbon atoms in the main chain or alkyl side chain; and / or, The epoxy equivalent of the phenolic epoxy resin is 150 g / eq ~ 250 g / eq.

4. The electrophoretic coating additive according to claim 3, characterized in that, The phenolic epoxy resin comprises 15 to 30 parts by weight, the long-chain alkyl compound comprises 5 to 15 parts by weight, the chain extender comprises 4 to 7 parts by weight, and the crosslinking agent comprises 1 to 3 parts by weight.

5. The electrophoretic coating additive according to claim 3, characterized in that, At least one of the following conditions must be met: (1) The phenolic epoxy resin includes at least one of phenolic epoxy resin, cresol phenolic epoxy resin, bisphenol A phenolic epoxy resin, biphenyl phenolic epoxy resin, triphenyl phenolic epoxy resin, dicyclopentadiene phenolic epoxy resin, and naphthol phenolic epoxy resin. (2) The long-chain alkyl organic compounds include at least one of the following: octanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, octadecanoic acid, icosanoic acid, isononanoic acid, isodecanoic acid, isooctanoic acid, oleic acid, linoleic acid, dodecylphenol, tetradecylphenol, hexadecylphenol, octadecylphenol, tert-butylphenol, dinonylphenol, 4-hydroxyphenylalkyl ether, alkylphenol polyoxyethylene ether, di-n-octylamine, N-methyloctadecylamine, N-ethylhexadecylamine, dodecylaniline, and octadecylaniline; (3) The first amine compound and its derivatives include at least one of n-butylamine, n-octylamine, methylbutylamine, ethanolamine, diethylamine, dibutylamine, N-methylethanolamine, diethanolamine, dibutanolamine, and triethylamine salt; (4) The second amine compound and its derivatives include at least one of aminoethylethanolamine, ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, isophoronediamine, polyetheramine, piperazine, N-aminoethylpiperazine, bis(hexamethylene)triamine, ketone imine of aminoethylethanolamine, diethylenetriamineacetone imine, diethylenetriaminebutanone imine, diethylenetriaminemethylisopropyl ketone imine, and diethylenetriaminemethylisobutyl ketone imine.

6. A method for preparing an electrophoretic coating additive, characterized in that, The preparation method is applicable to the electrophoretic coating additives according to claims 1-5, and the preparation method includes: In an inert gas atmosphere, the chain extender and the long-chain alkyl-modified phenolic epoxy resin are mixed and subjected to a chain extension reaction at a first temperature to form a first mixed system. The first mixture and the crosslinking agent are mixed to form a second mixture. The second mixture is subjected to a crosslinking reaction at a second temperature to form the polymer, thereby obtaining the electrophoretic coating additive. The first temperature is lower than the second temperature.

7. The preparation method according to claim 6, characterized in that, The preparation process of the long-chain alkyl-modified phenolic epoxy resin includes: Under an inert gas atmosphere, the phenolic epoxy resin and the long-chain alkyl organic compound are mixed and then subjected to an epoxy ring-opening reaction at a third temperature to obtain the long-chain alkyl modified phenolic epoxy resin.

8. The preparation method according to claim 6, characterized in that, The electrophoretic coating additive obtained from the polymer further comprises: An acid was added to the polymer and a salt-forming reaction was carried out at a fourth temperature; The acid includes at least one of organic acids, inorganic acids, acidic esters, and acidic anhydrides.

9. An electrophoretic coating, characterized in that, The electrophoretic coating includes the electrophoretic coating additives according to any one of claims 1 to 8.

10. A vehicle, characterized in that, The vehicle includes a coating, the coating including the electrophoretic coating of claim 9, wherein the electrophoretic coating is a cathodic electrophoretic coating.

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