Bio-based waterborne polyurethane anticorrosive paint primer and preparation method thereof

Abstract

The invention provides a bio-based waterborne polyurethane anticorrosive paint primer and a preparation method thereof. The primer consists of a waterborne additive and a curing agent, the water-based auxiliary agent is prepared from the following components in parts by mass: 38 to 52 parts of self-emulsifying water-based vegetable oil-based polyurethane dispersion, 1 to 8 parts of nano zinc oxide, 3 to 8 parts of zinc phosphate, 15 to 25 parts of anti-rust pigment, 0.5 to 2 parts of water-based wetting dispersant, 0.1 to 0.5 part of water-based defoaming agent, 10 to 20 parts of filler and 8 to 12 parts of water; the self-emulsifying type water-based vegetable oil-based polyurethane dispersion is prepared from 15 to 25 parts of vegetable oil-based polyol, 10 to 18 parts of polycarbonate diol, 2 to 2.5 parts of a hydrophilic chain extender and 20 to 25 parts of diisocyanate through a reaction. The water-based anti-corrosion primer provided by the invention has excellent anti-corrosion performance and environment-friendly characteristic, and has important technical significance and market value.

Description

Technical Field

[0001] This invention belongs to the field of waterborne coating technology, specifically relating to a waterborne polyurethane anticorrosive coating primer with bio-based materials as the main raw material and its preparation method. Background Technology

[0002] Metal corrosion is a global problem causing enormous economic losses, with direct economic losses due to metal corrosion accounting for approximately 3%-5% of GDP annually. Anti-corrosion coatings are a crucial means of metal protection, and their performance directly affects protective effectiveness and service life. Traditional solvent-based anti-corrosion coatings are mostly based on petroleum-based raw materials, consuming non-renewable resources and releasing large amounts of volatile organic compounds (VOCs) during production and use, causing environmental pollution. Waterborne polyurethane coatings, using water as the dispersion medium, have advantages such as low VOC content, non-toxicity, and non-flammability, representing an important development direction for environmentally friendly coatings. However, traditional waterborne polyurethane coatings are generally inferior to solvent-based coatings in terms of anti-corrosion performance, water resistance, and mechanical strength, limiting their application in heavy-duty anti-corrosion fields. The core challenges are: the high latent heat of vaporization of water leads to poor film formation; the high surface tension of water affects the wetting of substrates and pigments / fillers; furthermore, while providing water dispersibility, the hydrophilic groups in waterborne resins can also become channels for corrosive media penetration, reducing the barrier properties and corrosion resistance of the coating. In recent years, the application of bio-based materials in the coating field has received widespread attention. Vegetable oils, as a renewable resource, contain abundant active functional groups (such as hydroxyl groups, ester groups, and carbon-carbon double bonds), and can be chemically modified to prepare polyols for use in the synthesis of waterborne polyurethanes. Compared with petroleum-based raw materials, bio-based materials have advantages such as wide availability, renewability, and environmental friendliness. However, although some current bio-based waterborne polyurethane coatings use vegetable oil modification, they suffer from problems such as complex preparation processes for vegetable oil-based polyols, high pollution (e.g., traditional epoxidation processes use organic acid anhydrides, generating large amounts of waste liquid), and poor compatibility between the nano-anticorrosion system and the resin, resulting in insufficient salt spray resistance of the coating (mostly below 600 h).

[0003] Therefore, developing a waterborne anti-corrosion primer that combines bio-based materials with waterborne polyurethane technology, while also taking into account excellent anti-corrosion performance and environmental protection characteristics, has significant technical importance and market value. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a bio-based waterborne polyurethane anti-corrosion coating primer, composed of waterborne additives and a curing agent; the waterborne additives comprise the following components in parts by weight: 38-52 parts of self-emulsifying waterborne vegetable oil-based polyurethane dispersion, 1-8 parts of nano zinc oxide, 3-8 parts of zinc phosphate, 15-25 parts of anti-rust pigment, 0.5-2 parts of waterborne wetting and dispersing agent, 0.1-0.5 parts of waterborne defoamer, 10-20 parts of filler, and 8-12 parts of water; The self-emulsifying waterborne vegetable oil-based polyurethane dispersion is prepared by reacting 15-25 parts of vegetable oil-based polyol, 10-18 parts of polycarbonate diol, 2-2.5 parts of hydrophilic chain extender and 20-25 parts of diisocyanate.

[0005] Further, the method for preparing the plant oil-based polyol is as follows: 30 parts of plant oil, 0.1-0.5 parts of alkaline catalyst and 5-8 parts of epoxy compound are mixed and reacted. After the reaction is completed, phosphoric acid is added to neutralize the system to pH=6.5-7.2. After standing and separating into layers, the plant oil-based polyol is obtained by vacuum distillation. The epoxy compound includes at least one of ethylene oxide or propylene oxide.

[0006] Furthermore, the epoxy compound also includes a siloxane with an epoxy group, preferably γ-glycidoxypropyltrimethoxysilane; the amount of the siloxane with an epoxy group added is 0.8%-2% of the weight of the vegetable oil.

[0007] This invention also provides a method for preparing a bio-based waterborne polyurethane anti-corrosion coating primer, comprising the following steps: S1. Preparation of vegetable oil-based polyols: S1-1. Mix vegetable oil and alkaline catalyst, and dehydrate under vacuum; S1-2, Add an epoxide compound to step S1-1 to carry out the reaction; S1-3. After the reaction is complete, cool down and add phosphoric acid dropwise to neutralize. Post-treatment yields vegetable oil-based polyols. S2. Preparation of self-emulsifying aqueous plant oil-based polyurethane dispersion: S2-1, vegetable oil-based polyols react with polycarbonate diols, isocyanates, and chain extenders until the NCO content of the system reaches the theoretical value; S2-2, Add neutralizing agent to step S2-1 for neutralization, and after neutralization, add water to emulsify and disperse; S2-3. Add ethylenediamine to step S2-2 to extend the chain and obtain a self-emulsifying waterborne vegetable oil-based polyurethane dispersion; S3. Preparation of water-based main agent: A self-emulsifying waterborne vegetable oil-based polyurethane dispersion, nano zinc oxide, zinc phosphate, rust-preventive pigment, water, waterborne wetting and dispersing agent, waterborne defoamer, filler, and additives are mixed and dispersed evenly to obtain the waterborne main agent. S4. Mix the water-based main agent and the curing agent to obtain a bio-based water-based polyurethane anti-corrosion coating primer; The epoxy compound includes at least one of ethylene oxide or propylene oxide.

[0008] Furthermore, the epoxy compound also includes a siloxane with an epoxy group. Specifically, S1-2 involves adding ethylene oxide or propylene oxide to S1-1 and reacting at 95-105°C for 3-5 hours; then cooling to 65-80°C, adding a siloxane with an epoxy group, and maintaining the temperature for 2-3 hours.

[0009] Furthermore, the vegetable oil is tung oil or castor oil, preferably castor oil; the hydroxyl value of the vegetable oil-based polyol is 150-180 mgKOH / g.

[0010] Further, the chain extender in S2-1 is at least one of dimethylolpropionic acid or dimethylolbutyric acid; the isocyanate is an HDI trimer; and the neutralizing agent in S2-2 is at least one of triethylamine, ammonia, diisopropanolamine, and trimethylolpropane.

[0011] Furthermore, the anti-rust pigment is one or more of mica iron oxide, zinc phosphate, or aluminum tripolyphosphate; The filler is at least one of barium sulfate, talc, silica powder or mica powder.

[0012] Furthermore, the additives include aqueous ultraviolet absorbers, aqueous light stabilizers, and aqueous leveling agents.

[0013] Furthermore, the mass ratio of the water-based main agent to the curing agent is (5-10):1.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: It boasts significant environmental advantages: using water as the dispersion medium, its VOC content is less than 50 g / L, far lower than that of traditional solvent-based coatings; at the same time, it uses renewable vegetable oil raw materials, resulting in a high bio-based content.

[0015] Excellent corrosion resistance: Through the synergistic anti-corrosion effect of nano zinc oxide and zinc phosphate, and the dense film-forming properties of waterborne polyurethane prepared from castor oil-based polyol, the salt spray resistance time can reach more than 800 hours.

[0016] Good mechanical properties: The coating adhesion reaches over 4.5 MPa, especially after grafting siloxane onto castor oil-based polyols, the coating adhesion can reach 5.4 MPa.

[0017] Construction is safe and convenient: Water is used as the dispersion medium, which is non-toxic and non-flammable, ensuring high construction safety; the surface drying time is ≤60 minutes, resulting in high construction efficiency. Detailed Implementation

[0018] The embodiments of the present invention will be described in detail below with reference to the examples. The following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.

[0019] Example 1 (1) Preparation of castor oil-based polyols: Add 30 kg of refined castor oil (iodine value ≤ 85 g I2 / 100 g, acid value ≤ 0.5 mg KOH / g) and 0.3 kg of alkaline catalyst (potassium hydroxide, purity ≥ 98%) to a dry 50 L high-pressure reactor. After stirring evenly, purge the air in the reactor three times with nitrogen (nitrogen pressure 0.2 MPa each time, held for 5 min). Raise the temperature to 120 °C and dehydrate under vacuum for 1.5 h (vacuum degree -0.095 MPa) to remove trace amounts of moisture from the raw materials. Then lower the temperature to 80 °C and slowly add 6 kg of ethylene oxide (purity ≥ 99.5%) dropwise at a stirring speed of 300 rpm, controlling the dropping rate to ensure the pressure inside the reactor does not exceed 0.4 MPa. After the addition is complete, raise the temperature to 100 °C and maintain the reaction temperature for 4 h. After the reaction was completed, the temperature was lowered to 60℃, and phosphoric acid (concentration 85%) was added to neutralize the system to pH=7.0. The system was allowed to stand and separate into layers to remove salt residue. Then, the low-boiling substances were removed by vacuum distillation (110℃, -0.098MPa) to obtain a pale yellow transparent castor oil-based polyol with a hydroxyl value of 160 mgKOH / g (test standard GB / T 12008.3-2009).

[0020] (2) Preparation of self-emulsifying aqueous plant oil-based polyurethane dispersion: 20 kg of the above-mentioned castor oil-based polyol (hydroxyl value 160 mg KOH / g), 15 kg of polycarbonate diol (molecular weight 2000), 2 kg of dimethylolpropionic acid (DMPA, chain extender), and 24 kg of HDI trimer (NCO content approximately 23.5%, Desmodur N 3900) were added to a reactor. Under nitrogen protection, the reaction was carried out at 80°C until the NCO content of the system reached 4.2% (test standard GB / T 12009.4-2016); the final solid content of the aqueous polyurethane dispersion was 40.3% (test standard GB / T 1725-2020). The temperature was lowered to 45°C, and 1.5 kg of triethylamine was added for neutralization for 20 minutes. 120 kg of deionized water was added under 2000 rpm shear for emulsification and dispersion, while 1.2 kg of ethylenediamine aqueous solution was added dropwise for chain extension. Finally, vacuum distillation was used to remove any remaining solvents such as acetone, yielding an aqueous polyurethane dispersion with a solid content of approximately 40%.

[0021] (3) Preparation of water-based main agent: Under low-speed stirring at 400 rpm, the following components were added sequentially to 50 kg of the above-mentioned self-made aqueous polyurethane dispersion: 0.3 kg water-based defoamer, silicone defoamer (model BYK-024); 8 kg of deionized water; 1.0 kg of water-based wetting and dispersing agent; polycarboxylate dispersant (model BYK-190) 15 kg of mica iron oxide (800 mesh); 10 kg talc powder (800 mesh); 5 kg of nano zinc oxide aqueous dispersion, zinc oxide content 50% (particle size 50nm, model VK-ZnO-50) 5 kg zinc phosphate (1000 mesh); 3 kg of water-based functional additives: UV absorber UV-1130 (20%) + light stabilizer 770 (30%) + leveling agent BYK-333 (50%) After each component is added, increase the speed to 800 rpm and stir for 15 minutes to ensure uniform dispersion. After all components are added, stir at high speed of 1200 rpm for 30 minutes, and control the slurry fineness to ≤35 μm to obtain the water-based main agent.

[0022] (4) Coating preparation and performance testing: The obtained water-based main agent and curing agent (Bayhydur XP 2487 / 1) were mixed at a mass ratio of 6:1, cured at 25°C for 10 minutes, and then coated and tested. The test results are shown in Table 1.

[0023] Example 2 (1) Preparation of castor oil-based polyols: Following the same steps (1) as in Example 1, castor oil-based polyols were obtained.

[0024] (2) Preparation of self-emulsifying aqueous plant oil-based polyurethane dispersion: 22 kg of the above-mentioned castor oil-based polyol (hydroxyl value 160 mg KOH / g), 12 kg of polycarbonate diol (molecular weight 2000), 2.2 kg of dimethylolpropionic acid (DMPA, chain extender), and 25 kg of HDI trimer (NCO content approximately 23.5%, Desmodur N 3900) were added to a reactor. Under nitrogen protection, the reaction was carried out at 80°C until the NCO content of the system reached 4.5%. The temperature was then lowered to 45°C, and 1.6 kg of triethylamine was added for neutralization for 20 minutes. 110 kg of deionized water was added under 2000 rpm shear for emulsification and dispersion, while 1.0 kg of ethylenediamine aqueous solution was added dropwise for chain extension. Finally, any residual solvents such as acetone were removed by vacuum distillation to obtain an aqueous polyurethane dispersion with a solid content of 40.1%.

[0025] (3) Preparation of water-based main agent: Under low-speed stirring at 400 rpm, the following components were added sequentially to 55 kg of the above-mentioned self-made aqueous polyurethane dispersion: 0.3 kg of water-based defoamer, polyether-modified siloxane defoamer (model TEGO Foamex 810); 10 kg of deionized water; 1.2 kg of water-based wetting and dispersing agent, phosphate ester dispersant (model EFKA-4010) 6 kg of nano zinc oxide aqueous dispersion, zinc oxide content 50% (particle size 50nm, model VK-ZnO-50) 18 kg zinc phosphate (1000 mesh); 12 kg barium sulfate (800 mesh); 3 kg of water-based functional additives: UV absorber UV-327 (25%) + light stabilizer 622 (35%) + leveling agent TEGO Glide 410 (40%) After each component is added, increase the speed to 800 rpm and stir for 15 minutes to ensure uniform dispersion. After all components are added, stir at high speed of 1200 rpm for 30 minutes, and control the slurry fineness to ≤35 μm to obtain the water-based main agent.

[0026] (4) Coating preparation and performance testing: The obtained water-based main agent and curing agent (Bayhydur XP 2487 / 1) were mixed at a mass ratio of 6:1, cured at 25°C for 10 minutes, and then coated and tested. The test results are shown in Table 1.

[0027] Example 3 (1) Preparation of castor oil-based polyols: Unlike Example 1, after adding ethylene oxide and reacting at 100°C for 4 hours, and before adding phosphoric acid at 60°C, an additional step was added: the temperature was lowered to 70°C, 0.35 kg of KH560 (γ-glycidoxypropyltrimethoxysilane) was added, and the reaction was maintained for 2 hours; the rest was the same as step (1) of Example 1, to obtain siloxane-grafted castor oil-based polyol.

[0028] (2) Preparation of self-emulsifying aqueous plant oil-based polyurethane dispersion: Unlike Example 1, 22 kg of the above-mentioned siloxane-grafted castor oil-based polyol, 12 kg of polycarbonate diol and 25 kg of HDI trimer were added to the reactor and reacted at 80°C for 30 min under nitrogen protection. Then, 2.2 kg of dimethylolpropionic acid was added to continue the reaction until the NCO content reached the theoretical value. The rest was the same as step (2) of Example 2, and an aqueous polyurethane dispersion with a solid content of 40.1% was obtained.

[0029] (3) Preparation of water-based main agent: Following the same steps (3) as in Example 1, an aqueous main agent is obtained.

[0030] (4) Coating preparation and performance testing: The obtained water-based main agent and curing agent (Bayhydur XP 2487 / 1) were mixed at a mass ratio of 6:1, cured at 25°C for 10 minutes, and then coated and tested. The test results are shown in Table 1.

[0031] Example 4 The difference from Example 2 is that the castor oil-based polyol was replaced with tung oil-based polyol (hydroxyl value 155 mgKOH / g), and the rest was the same as in Example 2. The preparation method of the tung oil-based polyol was as follows: 30 parts of tung oil and 0.2 parts of potassium hydroxide catalyst were mixed, vacuum dehydrated at 120°C for 1.5 h, cooled to 85°C and 7 parts of propylene oxide were added dropwise, the reaction was kept at this temperature for 4 h, and after cooling, the mixture was neutralized with phosphoric acid to pH=6.8-7.0. After standing and separating into layers, the low-boiling substances were removed by vacuum distillation to obtain the tung oil-based polyol.

[0032] Comparative Example 1 The difference from Example 2 is that the castor oil-based polyol is replaced with castor oil, otherwise it is the same as Example 2.

[0033] Table 1

[0034] The data above show that the present invention, using nano-zinc oxide aqueous dispersion and zinc phosphate as composite anti-corrosion additives, can improve the salt spray resistance of coatings. The adhesion, salt spray resistance, and impact resistance of the examples are significantly better than those of the comparative examples. This is related to the controllable hydroxyl value and high hydroxyl activity of the vegetable oil-based polyol. The castor oil-based polyol provided by the present invention can effectively optimize the crosslinking structure of the coating, improving its adhesion and salt spray resistance. Example 3: Based on the ethylene oxide-modified castor oil of Examples 1 and 2, KH560 was grafted onto it. The resulting coating has a dual structure of polyurethane crosslinking network and siloxane crosslinking network. Simultaneously, KH560 with flexible segments bonds to fillers, substrates, and groups on the polyurethane via -Si-OH, further improving the mechanical properties, salt spray resistance, and impact resistance of the coating.

Claims

1. A bio-based waterborne polyurethane anticorrosive primer, characterized in that, The water-based auxiliary agent and the curing agent; the water-based auxiliary agent comprises the following components by mass fraction: 38-52 parts of a self-emulsifying water-based vegetable oil-based polyurethane dispersion, 1-8 parts of nano zinc oxide, 3-8 parts of zinc phosphate, 15-25 parts of anti-rust pigment, 0.5-2 parts of water-based wet dispersant, 0.1-0.5 parts of water-based defoaming agent, 10-20 parts of filler, and 8-12 parts of water; The self-emulsifying water-based vegetable oil-based polyurethane dispersion is prepared by reacting 15-25 parts of vegetable oil-based polyol, 10-18 parts of polycarbonate diol, 2-2.5 parts of hydrophilic chain extender, and 20-25 parts of diisocyanate.

2. A bio-based waterborne polyurethane anticorrosive primer according to claim 1, characterized in that, The vegetable oil-based polyol is prepared by mixing 30 parts of vegetable oil, 0.1-0.5 parts of alkaline catalyst, and 5-8 parts of epoxy compound, and then reacting, adding phosphoric acid to neutralize the system to pH=6.5-7.2 after the reaction is completed, and obtaining the vegetable oil-based polyol by static layering and reduced pressure distillation. The epoxy compound comprises at least one of oxirane or oxetane.

3. A bio-based waterborne polyurethane anticorrosive primer according to claim 2, characterized in that, The epoxy compound further comprises siloxane with an epoxy group, preferably gamma-glycidoxypropyltrimethoxysilane; the siloxane with an epoxy group is added in an amount of 0.8%-2% of the mass of the vegetable oil.

4. A process for the preparation of a bio-based waterborne polyurethane anticorrosive primer coating characterized in that, The method comprises the following steps: S1, preparation of vegetable oil-based polyol: S1-1, mix vegetable oil and alkaline catalyst, and perform vacuum dehydration; S1-2, add epoxy compound to step S1-1 to perform reaction; S1-3, after the reaction is completed, add phosphoric acid dropwise for neutralization after cooling, and obtain vegetable oil-based polyol after post-treatment; S2, preparation of self-emulsifying water-based vegetable oil-based polyurethane dispersion: S2-1, react vegetable oil-based polyol, polycarbonate diol, isocyanate, and chain extender until the NCO content of the system reaches the theoretical value; S2-2, add neutralizing agent to step S2-1 for neutralization, and add water for emulsification and dispersion after the neutralization is completed; S2-3, add ethylenediamine for chain extension to step S2-2 to obtain self-emulsifying water-based vegetable oil-based polyurethane dispersion; S3, preparation of water-based main agent: Mix self-emulsifying water-based vegetable oil-based polyurethane dispersion, nano zinc oxide, zinc phosphate, anti-rust pigment, water, water-based wet dispersant, water-based defoaming agent, filler, and functional auxiliary agent, and uniformly disperse to obtain water-based main agent; S4, mix water-based main agent and curing agent to obtain bio-based water-based polyurethane anticorrosive coating primer. The epoxy compound comprises at least one of oxirane or oxetane.

5. A process for the preparation of a bio-based waterborne polyurethane anticorrosive primer according to claim 4, characterized in that, The epoxy compound further comprises siloxane with an epoxy group, and S1-2 specifically comprises: adding oxirane or oxetane to S1-1, reacting at 95-105°C for 3-5h; then cooling to 65-80°C, adding siloxane with an epoxy group, and reacting for 2-3h.

6. A process for the preparation of a bio-based waterborne polyurethane anticorrosive primer according to claim 4, characterized in that, The vegetable oil is castor oil or ricinus communis oil, preferably ricinus communis oil; the vegetable oil-based polyol has a hydroxyl value of 150-180 mgKOH / g.

7. A process for the preparation of a bio-based waterborne polyurethane anticorrosive primer according to claim 4, characterized in that, The chain extender in S2-1 is at least one of dimethylol propanoic acid or dimethylol butanoic acid; the isocyanate is HDI trimer; and the neutralizing agent in S2-2 is at least one of triethylamine, ammonia, diisopropyl alcohol amine, and trimethylol methylamine.

8. A process for the preparation of a bio-based waterborne polyurethane anticorrosive primer according to claim 4, characterized in that, The rust-proof pigment is one or more of iron oxide mica, zinc phosphate or aluminum tripolyphosphate; The filler is at least one of barium sulfate, talcum powder, silicon powder or mica powder.

9. A process for the preparation of a bio-based waterborne polyurethane anticorrosive primer according to claim 4, characterized in that, The functional auxiliary agent includes an aqueous ultraviolet absorber, an aqueous light stabilizer and an aqueous leveling agent.

10. A process for the preparation of a bio-based waterborne polyurethane anticorrosive primer according to claim 4, characterized in that, The mass ratio of the aqueous main agent to the curing agent is (5-10):1.

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