Electro-depositable bio-based coating and preparation method thereof

Abstract

The invention discloses a bio-based coating capable of being electrodeposited, the coating comprises cashew novolac urea-based resin or cashew novolac amide modified epoxy resin, and the emulsion stability is improved by accurately controlling the amine value. The preparation method comprises the following steps: 1) synthesizing a cardanol aldehyde amine curing agent; 2) preparing cashew phenolic amide resin and cashew phenolic urea-based resin; 3) introducing an amino structure, and preparing epoxy resin containing a water-soluble group through a ring-opening reaction and a chain extension reaction; 4) neutralizing amido through a neutralizing agent to form a water-soluble cationic resin emulsion; and 5) adding a cross-linking agent, a cosolvent and a high-boiling-point solvent to form a stable coating emulsion. The invention relates to an electrodepositable coating which is prepared by a green chemical process on the basis of a bio-based material. The coating comprises a method for modifying epoxy resin with cardanol aldehyde urea-based resin or cardanol aldehyde amide, and the emulsion stability is improved by accurately controlling the amine value.

Description

Technical Field

[0001] The invention relates to the technical field of electrodeposition coatings, and in particular to an electrodepositable bio-based coating and a preparation method thereof. Background Art

[0002] Cathodic electrophoretic coatings have been widely used in the coating protection of automobiles and their parts due to their excellent anti-corrosion performance, efficient construction performance and good coating effect on various complex special-shaped workpieces. However, electrophoretic coatings are currently based on petroleum-based raw materials, which cannot be sustainably recycled and do not conform to the green development trend of coatings. With the global emphasis on environmental protection and sustainable development, bio-based materials have received widespread attention due to their renewable, biodegradable and environmentally friendly properties. The development of bio-based materials is in line with the concepts of circular economy and green chemistry and is an important development direction of future materials science. Researchers are developing various bio-based resins, such as epoxy resins and polyurethane resins based on vegetable oils, which can theoretically be used in the formulation of electrophoretic paints. The present invention uses cardanol in cashew nut shell oil, a bio-based raw material, to design and develop a coating that can be used for electrodeposition.

[0003] There are many reports on the application of cardanol-modified resins in coatings: 1) Zheng Jieyuan mentioned in the preparation of cardanol-based epoxy resin that cardanol was used as a raw material to synthesize cardanol-based phenolic resin (CN) under the catalysis of zinc acetate, and then cardanol-based epoxy resin (CNE) was synthesized by catalysis of benzyltriethylammonium chloride (TEBAC), and further modified by silicone to obtain silicone-modified epoxy resin (SICNE). This modified epoxy resin has improved adhesion and hydrophobicity after curing with triethylenetetramine (TETA) (cited from the journal: Zheng Jieyuan et al. Preparation of cardanol-based epoxy resin and its silanization modification [J]. China Adhesives, 2021.1, 30(1): 24-27). 2) The patent of CN117024694A mentions that by introducing an appropriate amount of hydrophilic segments, the cardanol-modified phenolic amide has good water solubility and can be used in combination with water-based epoxy resin emulsions for use in water-based floor coatings and water-based anticorrosive coatings. In addition, this type of curing agent has a fast curing speed, which can improve production efficiency and construction performance. 3) CN110527414A discloses a slow polyurea bottom-to-bottom all-in-one coating and its preparation method, and describes in detail the synthetic polymer A, cardanol-based phenolic amines C and D, and the preparation steps of the final coating, so as to achieve a coating application period of ≥4 hours and a surface drying time of 35 to 60 minutes, which is suitable for metal or concrete substrates, and forms a coating film with fast drying speed, excellent weather resistance and salt spray resistance. However, there is no relevant report on the application of cardanol phenolic amines and derivatives in electrodeposition coatings. The main problem is that cardanol phenolic amines, as curing agents for epoxy resins, will quickly form thermosetting resins and cannot further form water-soluble cationic resins. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing an electrodeposited coating using bio-based cashew oil and its derivatives, which replaces the electrodeposited materials prepared by traditional petroleum-based resins, realizes the bio-based raw materials of electrophoretic paint, and solves one or more of the above-mentioned prior art problems.

[0005] In one aspect, the present invention provides an electrodepositable bio-based coating, which comprises a phenolic urea-based resin or a phenolic amide-modified epoxy resin, and improves emulsion stability by precisely controlling the amine value.

[0006] Among them: the cardanol aldehyde amide with controllable amine value is selected to introduce some amine groups into the epoxy resin without solidifying the resin. The cardanol aldehyde amide here must be added after the small molecular amine reacts with the epoxy resin first and then reacts.

[0007] In certain embodiments, the cardanol phenol urea-based resin modified epoxy resin is prepared by the following steps:

[0008] 1) using cardanol, formaldehyde and fatty amine as raw materials, synthesizing cardanol aldehyde amine curing agent through Mannich reaction;

[0009] 2) reacting the cardanol aldehyde amine curing agent with fatty acid to dehydrate to obtain cardanol aldehyde amide resin;

[0010] 3) the primary amine and the secondary amine in the phenol aldehyde amine resin react with the isocyanate to form the phenol aldehyde amine urea-based resin;

[0011] 4) Grafting the phenol-formaldehyde urea-based resin onto the epoxy resin to obtain the phenol-formaldehyde urea-based resin modified epoxy resin.

[0012] In certain embodiments, the cardanol aldehyde amide modified epoxy resin is prepared by the following steps:

[0013] 1) using cardanol, formaldehyde and fatty amine as raw materials, synthesizing cardanol aldehyde amine curing agent through Mannich reaction;

[0014] 2) reacting the cardanol aldehyde amine curing agent with fatty acid to dehydrate to obtain cardanol aldehyde amide resin;

[0015] 3) Grafting the phenolic aldehyde amide resin onto the epoxy resin to obtain the phenolic aldehyde amide modified epoxy resin.

[0016] In certain embodiments, the number average and weight average relative molecular weights of the cardanol aldehyde amide resin are both between 1000 and 1500, and have a relatively narrow relative molecular weight distribution.

[0017] In certain embodiments, the amine value of the cardanol aldehyde amine urea-based resin is controlled at 180-250 mgKOH / g.

[0018] In certain embodiments, the amine value of the cardanol aldehyde amide resin is controlled at 150-300 mgKOH / g, preferably 170-250 mgKOH / g.

[0019] On the other hand, the present invention provides a method for preparing an electrodepositable bio-based coating, comprising the following steps:

[0020] 1) Synthetic cardanol aldehyde amine curing agent;

[0021] 2) preparing phenolic aldehyde amide resin and phenolic urea resin;

[0022] 3) introducing an amine structure to prepare an epoxy resin containing a water-soluble group through a ring-opening reaction and a chain extension reaction;

[0023] 4) neutralizing the amine group with a neutralizing agent to form a water-soluble cationic resin emulsion;

[0024] 5) Add crosslinking agent, cosolvent and high boiling point solvent to form a stable coating emulsion.

[0025] In certain embodiments, in step 3), an amino structure is introduced by adding an amine compound, wherein the amine compound is one or more mixtures of diethylamine, dibutylamine, diethanolamine, N-methylethanolamine, diethylenetriamine, triethylenetetramine, ketimine of aminoethylethanolamine, diethylenetriamine methylisobutylketimine or polyamide.

[0026] In certain embodiments, the neutralizing agent in step 4) is a mixture of one or more of lactic acid, glacial acetic acid, formic acid and aminosulfonic acid.

[0027] In certain embodiments, in step 5), the cross-linking agent is a fully blocked isocyanate, and the fully blocked isocyanate is obtained by blocking a polyisocyanate with a blocking agent to obtain a cross-linking agent with complementary reactive functional groups, the polyisocyanate is a mixture of one or more of diphenylmethane-4,4'-diisocyanate, toluene-2,4-diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate, and the blocking agent is a mixture of one or more of alcohol ether solvents, methyl ethyl ketone oxime, alcohols or caprolactam; the co-solvent and high boiling point solvent include monobutyl ether and monohexyl ether of ethylene glycol, phenyl ether of propylene glycol, and monoalkyl ether of ethylene glycol, and the content is preferably 0.5 to 5wt%, which is the mass proportion of the emulsion.

[0028] Beneficial effects: The present invention reduces the amine value of the polymer amine by amidation modification or forming a urea-based resin on the cashew phenol aldehyde amine, selectively grafts it into the epoxy resin, prevents gelation during the polymerization process, and realizes that the aminated resin can form a water-soluble cationic resin emulsion after neutralization. The bio-based electrodeposition coating prepared by the invention has excellent adhesion and moisture and heat resistance, and improves corrosion resistance and mechanical strength. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below through embodiments.

[0030] Cardanol in cashew nut shell oil, a bio-based raw material, is used to design and develop coatings that can be used for electrodeposition. Electrodeposition coatings generally include aqueous dispersions or emulsions, and the electrodeposition coatings are not limited to acrylic resins, polyesters, epoxy resins, and polybutadiene resins. In the cathode electrocoating method, the water-dispersible resin used has a cationic functional group, such as a primary amine, secondary amine, tertiary amine, and / or quaternary ammonium structure portion as a positively charged hydrophilic group. The present invention formally utilizes this property and introduces a bio-based material with an amino structure as a component of the cationic epoxy resin. The specific method is: first, a cardanol aldehyde amine curing agent is synthesized using cardanol, formaldehyde, and aliphatic amine as raw materials through a Mannich reaction. The number average and weight average relative molecular mass of this curing agent are both around 1000-1500, and it has a narrow relative molecular mass distribution. The active hydrogen in the phenol aldehyde amine curing agent can undergo a ring-opening reaction with the epoxy group (COC) in the epoxy resin to form a three-dimensional network structure, which cannot further ionize the aminated resin. However, the phenol aldehyde amine is modified to reduce the number of active hydrogens and control the amine value, thereby reducing the degree of branching in the epoxy amination chain extension process. Therefore, the prepared aminated resin can be protonated and dispersed into an emulsion. The present invention relates to the modification of phenol aldehyde amine, including the preparation of phenol aldehyde amide and phenol aldehyde urea-based resin.

[0031] The main resin of the electro-depositable bio-based coating of the present invention is an epoxy resin, which is a high molecular weight epoxy resin obtained by chain extension of a polyepoxy compound and an appropriate amount of an extender, including polycarboxylic acids, polyols, polyphenols, and an amine having two or more amino hydrogens.

[0032] Epoxy resin can be salt-forming, and hydrophilic groups such as amine, sulfonic group, and phosphorus group need to be introduced. The present invention realizes epoxy resin protonation by introducing amine groups. First, the epoxy resin is ring-opened by two or more mixed amines, and then the remaining epoxy groups can be further extended by diamines, polyamines, polyetheramines, etc. The present invention particularly uses bio-based cashew phenol aldehyde amine derivatives, preferably modified cashew phenol aldehyde amide and cashew phenol aldehyde urea resin, further reacts with epoxy groups, amination chain extension, and prepares a dispersion system with a large enough molecular weight, containing a certain water-soluble group, and can be stably present in water. The amine value of the modified cashew phenol aldehyde amine derivative is controlled at 150-300mgKOH / g, preferably 170-250mgKOH / g. The modified cashew phenol aldehyde amine urea resin has an amine value controlled at 180-250mgKOH / g.

[0033] In the electro-depositable bio-based coating of the present invention, the bio-based resin cardanol aldehyde amine is a curing agent synthesized by using cardanol, formaldehyde and fatty amine as raw materials through Mannich reaction. The number average and weight average relative molecular weight of the curing agent are both about 1000-1500, and has a relatively narrow relative molecular weight distribution.

[0034]

[0035] Where R 1 C 15 H 31-2n, C 9 H 19 ,H;R 2 C 4 H 11 N 2 ,C 6 H 14 N,C 2 H 6 N,C 4 H 9

[0036] The preparation method of the cashew phenol aldehyde amide of the present invention is: cashew phenol aldehyde amide reacts with fatty acid and dehydrates to obtain:

[0037]

[0038] ROOH may be monoacid, dimer acid, tall oil acid, etc. By adjusting the ratio of cardanol aldehyde amine and fatty acid, the amine value of cardanol aldehyde amide is controlled to be 150-300 mgKOH / g, preferably 170-250 mgKOH / g.

[0039] The preparation method of the cashew phenol aldehyde amine urea-based resin of the present invention is: the primary amine and the secondary amine in the cashew phenol aldehyde amine react with isocyanate to generate a urea-based resin, wherein a semi-blocked isocyanate is preferred, to obtain a cashew phenol aldehyde amine resin containing a urea-based structure, and the amine value is controlled at 180-250 mgKOH / g.

[0040]

[0041] The electro-depositable bio-based coating of the present invention comprises an amine compound which is one or more mixtures of diethylamine, dibutylamine, diethanolamine, N-methylethanolamine, diethylenetriamine, triethylenetetramine, ketimine of aminoethylethanolamine, diethylenetriamine methylisobutylketimine or polyamide.

[0042] The crosslinking agent in the electro-depositable bio-based coating of the present invention is a fully blocked isocyanate, which is combined with a salifiable resin before being dispersed in water. The fully blocked isocyanate that can be unblocked at high temperature is blocked with a polyisocyanate by a blocking agent to obtain a crosslinking agent with complementary reactive functional groups, the polyisocyanate is a mixture of one or more of diphenylmethane-4,4'-diisocyanate, toluene-2,4-diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate, and the blocking agent is a mixture of one or more of alcohol ether solvents, methyl ethyl ketone oxime, alcohols or caprolactam.

[0043] In the electro-depositable bio-based coating of the present invention, the neutralizing agent is a mixture of one or more of lactic acid, glacial acetic acid, formic acid and aminosulfonic acid.

[0044] The electrodepositable bio-based coating of the present invention contains a small amount of co-solvent and high boiling point solvent, such as monobutyl ether and monohexyl ether of ethylene glycol, phenyl ether of propylene glycol, monoalkyl ether of ethylene glycol, preferably about 0.5 to 5 wt%.

[0045] Example 1, Preparation of Cardanophenol Aldehyde

[0046] A cardanol aldehyde amine is prepared from the following raw materials in mass percentage: 67% cardanol, 20% diethylenetriamine, and 13% paraformaldehyde. Cardanol and diethylenetriamine are added into a reaction kettle according to mass percentage, stirred to make the materials evenly mixed, and the temperature is raised to 60°C; the measured paraformaldehyde is added into the reaction kettle in 8 times, each time with an interval of 15 minutes; after all the paraformaldehyde is added, the temperature is raised to 85°C and kept warm for 2 hours; the water generated by the reaction is removed by vacuum under stirring to obtain a cardanol aldehyde amine curing agent with a number average molecular weight of 1250 and an amine value of 350 mgKOH / g.

[0047] Example 2, Preparation of Cardanophenol Aldehyde Amide

[0048] The cashew phenol aldehyde amine and tall oil acid in Example 1 were mixed in a mass ratio of 3:1, and the temperature was raised to 170-180° C. and kept warm for 3 hours. After the mixture was finished, it was vacuum dehydrated at 90° C. for 40 minutes under stirring to obtain cashew phenol aldehyde amide with an amine value of 210 mgKOH / g.

[0049] Example 3, Preparation of cashew phenol urea resin

[0050] The cashew phenol aldehyde amine and isocyanate in Example 1 are prepared in a mass ratio of 5:1: the cashew phenol aldehyde amine is put into a reaction kettle, the temperature is raised to 80°C, and the semi-blocked isocyanate is added dropwise into the kettle (the semi-blocked isocyanate is obtained by reacting 1 mol of TDI and 0.5 mol of isooctyl alcohol). After the addition is completed, the reaction mixture is kept at 80°C for 1 hour to obtain a cashew phenol urea-based resin having an amine value of 180 mgKOH / g.

[0051] Example 4. Preparation of cross-linking agent

[0052] 523g of diphenylmethane diisocyanate MDI (Wanhua PM200, NCO equivalent of 135g / eq) and 1g of dibutyltin dilaurate were added to a 2-liter round-bottom four-necked flask equipped with a stirrer, a condenser, a temperature probe, and a nitrogen feed line, and the mixture was stirred and heated to 60°C. 200g of diethylene glycol butyl ether and 314g of ethylene glycol butyl ether were added dropwise to the reaction bottle at a uniform rate, and the addition was completed within 2 hours. The addition temperature was controlled between 60-80°C, and the temperature was raised to 100°C and kept warm until the NCO value was less than 0.3%. 120g of methyl isobutyl ketone was added and diluted to a crosslinking agent with a solid content of 90%.

[0053] Example 5. Preparation of Electrodepositable Biobased Dispersion A

[0054] In a 2-liter round-bottom four-necked flask equipped with a stirrer, a condenser, a temperature probe, and a nitrogen feed line, 223 g of NPEL128 epoxy (Nanya Epoxy, EEW=188 g / eq), 94 g of bisphenol A and 18 g of methyl isobutyl ketone solution were added in sequence, and the temperature was slowly raised to 130°C for melting. After complete melting, 0.4 g of triphenylphosphine was added, and heat was released by itself, and the maximum temperature was controlled not to exceed 175°C. After the heat release was completed, the material was cooled to 145°C until the epoxy equivalent reached 840 g / eq, and 40 g of methyl isobutyl ketone was added. Stirring and cooling to 70°C, 9.9 g of methylethanolamine and 14.4 g of diethanolamine were added, and the temperature was raised to 100-110°C and stirred for 1 hour. After the insulation is completed, 20g of ethylene glycol butyl ether is added, 10g of ethylene glycol hexyl ether is cooled to below 100°C, and then 204g of a cross-linking agent (prepared in Implementation 4) and 72g of cashew phenol aldehyde amide (prepared in Example 2) are added, and the mixture is stirred at 90-100°C for 2 hours. After the insulation is completed, 14.6g of glacial acetic acid is added, and the mixture is stirred at 80-90°C for 1 hour. After the insulation is completed, 960g of pure water is slowly added for stirring and emulsification. At 40-50°C, the solvent is vacuum extracted to remove the residual methyl isobutyl ketone solution in the emulsion to obtain an emulsion with a solid content of 35% and a pH of 5.8.

[0055] Example 6. Preparation of Electrodepositable Biobased Dispersion B

[0056] In a 2-liter round-bottom four-necked flask equipped with a stirrer, a condenser, a temperature probe, and a nitrogen feed line, 223 g of NPEL128 epoxy (Nanya Epoxy, EEW=188 g / eq), 96 g of bisphenol A and 18 g of methyl isobutyl ketone solution were added in sequence, and the temperature was slowly raised to 130°C for melting. After complete melting, 0.4 g of triphenylphosphine was added, and heat was released by itself, and the maximum temperature was controlled not to exceed 175°C. After the heat release was completed, the material was cooled to 145°C until the epoxy equivalent reached 890 g / eq, and 40 g of methyl isobutyl ketone was added. Stirring and cooling to 70°C, 18 g of diethylenetriamine ketimine (73% solid content) and 14.4 g of methylethanolamine were added, and the temperature was raised to 110-120°C and stirred for 2 hours. After the insulation is completed, 20g of ethylene glycol butyl ether is added, 10g of ethylene glycol hexyl ether is cooled to below 100°C, and then 216g of a cross-linking agent (prepared in Example 4) and 78g of a cashew phenol urea-based resin (prepared in Example 3) are added, and the mixture is stirred at 90-100°C for 2 hours. After the insulation is completed, 18.0g of glacial acetic acid is added, and the mixture is stirred at 80-90°C for 1 hour. After the insulation is completed, 1080g of pure water is slowly added for stirring and emulsification. At 40-50°C, the solvent is vacuum extracted to remove the residual methyl isobutyl ketone solution in the emulsion to obtain an emulsion with a solid content of 36% and a pH of 6.0.

[0057] Example 7. Preparation of electrophoresis bath

[0058] 2000 parts by weight of Example dispersions A and B were mixed with 400 parts by weight of HS-2516G mortar of Haolisen and 2600 parts by weight of deionized water to prepare electrophoresis baths A and B. After aging at 30°C for 48 hours, the plates were made.

[0059] Electrophoresis sample preparation:

[0060] Pretreatment agent: Chemetall 9810 silane treatment liquid;

[0061] Workpiece sample: 100mm*200mm*0.8mm cold-rolled steel plate;

[0062] Electrophoresis conditions: bath temperature 28-30°C, stirring speed 500rpm, electrophoresis soft start time 15s, electrodeposition time 120s, voltage adjustable between 150V-320V.

[0063] Baking conditions: 180℃ / 15 minutes.

[0064] The test results of electrophoresis bath A and electrophoresis bath B are shown below:

[0065] Electrophoresis bath A:

[0066] Water resistance: 25℃, no gloss loss for 480 hours, adhesion level 0;

[0067] Resistance to moisture and heat: At 40°C and 98% humidity, after 240 hours of moisture and heat testing, there is no obvious expansion and no peeling.

[0068] Electrophoresis bath B:

[0069] Water resistance: 25℃, no gloss loss for 480 hours, adhesion level 0;

[0070] Resistance to moisture and heat: At 40°C and 98% humidity, after 240 hours of moisture and heat testing, there is no obvious expansion and no peeling.

[0071] It can be seen that the present invention can achieve electrodeposition through the electrophoretic coating process, and both electrophoretic bath A and electrophoretic bath B can achieve electrodeposition, and after curing, a paint film with excellent anti-corrosion performance and good appearance is obtained, especially having good performance in water resistance and moisture and heat resistance.

[0072] In summary, the present invention reduces the amine value of the polymer amine by amidation modification or forming a urea-based resin on the cashew phenol aldehyde amine, selectively grafts it into the epoxy resin, prevents gelation during the polymerization process, and realizes that the aminated resin can form a water-soluble cationic resin emulsion after neutralization. The bio-based electrodeposition coating prepared by the invention has excellent adhesion and moisture and heat resistance, and improves corrosion resistance and mechanical strength.

[0073] The above description is only a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this field, several modifications and improvements can be made without departing from the creative concept of the present invention, and these should also be regarded as within the scope of protection of the invention.

Claims

1. A bio-based coating that can be electrodeposited, characterized in that: The coating contains phenolic urea-based resin or phenolic amide-modified epoxy resin, and the emulsion stability is improved by precisely controlling the amine value.

2. The electro-depositable bio-based coating according to claim 1, characterized in that: The cashew phenol urea resin modified epoxy resin is prepared by the following steps: 1) using cardanol, formaldehyde and fatty amine as raw materials, synthesizing cardanol aldehyde amine curing agent through Mannich reaction; 2) reacting the cardanol aldehyde amine curing agent with fatty acid to dehydrate to obtain cardanol aldehyde amide resin; 3) the primary amine and the secondary amine in the phenol aldehyde amine resin react with the isocyanate to form the phenol aldehyde amine urea-based resin; 4) Grafting the phenol-formaldehyde urea-based resin onto the epoxy resin to obtain the phenol-formaldehyde urea-based resin modified epoxy resin.

3. The electro-depositable bio-based coating according to claim 1, characterized in that: The cardanol aldehyde amide modified epoxy resin is prepared by the following steps: 1) using cardanol, formaldehyde and fatty amine as raw materials, synthesizing cardanol aldehyde amine curing agent through Mannich reaction; 2) reacting the cardanol aldehyde amine curing agent with fatty acid to dehydrate to obtain cardanol aldehyde amide resin; 3) Grafting the phenolic aldehyde amide resin onto the epoxy resin to obtain the phenolic aldehyde amide modified epoxy resin.

4. An electrodepositable bio-based coating according to claim 2 or 3, characterized in that: The number average and weight average relative molecular weights of the cardanol aldehyde amide resin are both between 1000 and 1500, and the relative molecular weight distribution is relatively narrow.

5. The electro-depositable bio-based coating according to claim 2, characterized in that: The amine value of the cashew phenol aldehyde amine urea-based resin is controlled at 180-250 mgKOH / g.

6. The electro-depositable bio-based coating according to claim 2, characterized in that: The amine value of the cardanol aldehyde amide resin is controlled at 150-300 mgKOH / g, preferably 170-250 mgKOH / g.

7. A method for preparing an electrodepositable bio-based coating as claimed in any one of claims 1 to 6, characterized in that: The following steps are involved: 1) Synthetic cardanol aldehyde amine curing agent; 2) preparing phenolic aldehyde amide resin and phenolic urea resin; 3) introducing an amine structure to prepare an epoxy resin containing a water-soluble group through a ring-opening reaction and a chain extension reaction; 4) neutralizing the amine group with a neutralizing agent to form a water-soluble cationic resin emulsion; 5) Add crosslinking agent, cosolvent and high boiling point solvent to form a stable coating emulsion.

8. The method for preparing the electrodepositable bio-based coating according to claim 7, characterized in that: In step 3), an amine structure is introduced by adding an amine compound, wherein the amine compound is one or more mixtures of diethylamine, dibutylamine, diethanolamine, N-methylethanolamine, diethylenetriamine, triethylenetetramine, ketimine of aminoethylethanolamine, diethylenetriamine methylisobutylketimine or polyamide.

9. The method for preparing the electrodepositable bio-based coating according to claim 7, characterized in that: Step 4) the neutralizing agent is a mixture of one or more of lactic acid, glacial acetic acid, formic acid and aminosulfonic acid.

10. The method for preparing an electrodepositable bio-based coating according to claim 7, characterized in that: In step 5), the crosslinking agent is a fully blocked isocyanate, wherein the fully blocked isocyanate is obtained by blocking a polyisocyanate with a blocking agent to obtain a crosslinking agent with complementary reactive functional groups, wherein the polyisocyanate is a mixture of one or more of diphenylmethane-4,4'-diisocyanate, toluene-2,4-diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate, and the blocking agent is a mixture of one or more of an alcohol ether solvent, methyl ethyl ketone oxime, alcohols, or caprolactam; the cosolvent and the high boiling point solvent include monobutyl ether and monohexyl ether of ethylene glycol, phenyl ether of propylene glycol, and monoalkyl ether of ethylene glycol, and the content is preferably 0.5 to 5wt%.

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