Preparation method of water-based epoxy zinc-rich paint

Abstract

The application belongs to the technical field of paint, and particularly relates to a preparation method of water-based epoxy zinc-rich paint. The water-based epoxy zinc-rich paint is prepared from the following raw materials in parts by weight: 80-110 parts of bisphenol A epoxy resin grafting emulsion, 600-800 parts of zinc powder, 2-3 parts of graphene dispersion liquid, 20-25 parts of maleic anhydride modified polyether amine D400, 5-7 parts of wetting dispersant, 15-20 parts of cosolvent and 1-2 parts of defoaming agent; wherein the bisphenol A epoxy resin grafting emulsion is prepared by grafting copolymerization of bisphenol A epoxy resin, hydroxypropyl acrylate and ethyl methacrylate phosphate. Through the synergistic effect of the bisphenol A epoxy resin grafting emulsion, the zinc powder, the graphene dispersion liquid and the modified polyether amine, the conductivity, the adhesion, the barrier property and the construction stability of the paint are improved, and the problems of sedimentation, brittle fracture and corrosion resistance balance of the high-zinc powder coating are solved.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically relating to a method for preparing a water-based epoxy zinc-rich coating. Background Technology

[0002] Waterborne epoxy zinc-rich coatings are waterborne anti-corrosion coatings with waterborne epoxy resin as the matrix and zinc powder as the anti-corrosion filler. They achieve corrosion protection for metal substrates through the film-forming properties of epoxy resin and the cathodic protection of zinc powder, and are widely used in shipbuilding, bridges, construction, marine engineering, and automotive industries. Compared to traditional solvent-based epoxy zinc-rich coatings, the zinc powder in waterborne epoxy zinc-rich coatings provides electrochemical protection through a sacrificial anode matrix, exhibiting excellent salt spray resistance and providing long-lasting corrosion protection. Furthermore, waterborne epoxy zinc-rich coatings have strong adhesion and are easy to apply.

[0003] Existing technologies disclose waterborne epoxy zinc-rich coatings, such as patent CN115286973B, which discloses a waterborne epoxy zinc-rich coating, its preparation method, and its application. This disclosed waterborne epoxy zinc-rich coating has a dry film zinc powder content of over 70%, exhibiting good corrosion resistance, salt spray resistance, damp heat resistance, solvent resistance, and high adhesion. While a dry film zinc powder content of over 70% can ensure cathodic protection, high zinc content leads to decreased coating toughness and a higher likelihood of microcracks, which accelerates the penetration of corrosive media. Furthermore, high zinc powder content easily causes sedimentation during storage, requiring frequent stirring and affecting construction efficiency.

[0004] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing waterborne epoxy zinc-rich coatings, so as to solve the problems existing in waterborne epoxy zinc-rich coatings in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A water-based epoxy zinc-rich coating, by weight, is prepared from the following raw materials: 80-110 parts of bisphenol A epoxy resin grafted emulsion, 600-800 parts of zinc powder, 2-3 parts of graphene dispersion, 20-25 parts of maleic anhydride-modified polyetheramine D400, 5-7 parts of wetting and dispersing agent, 15-20 parts of cosolvent, and 1-2 parts of defoamer; wherein the bisphenol A epoxy resin grafted emulsion is obtained by graft copolymerization of bisphenol A epoxy resin, hydroxypropyl acrylate, and ethyl methacrylate phosphate.

[0008] More specifically, the preparation method of the bisphenol A epoxy resin grafted emulsion includes the following steps:

[0009] S11. Add 600g of bisphenol A epoxy resin and 400g of deionized water to a container, heat to 60℃ and stir at 500rpm to dissolve into a homogeneous phase, then add 250g of hydroxypropyl acrylate and 100g of ethyl methacrylate phosphate at a dropping rate of 10g / min to obtain a pre-emulsified system.

[0010] S12. Dissolve ammonium persulfate in deionized water to prepare a 5 wt% initiator. Add the initiator dropwise to the pre-emulsified system at a rate of 5 g / min. Heat the system to 85 °C and react for 4 h under nitrogen protection.

[0011] S13. Cool to 40℃, adjust the pH to 7.0 with sodium hydroxide, and pass through a 200-mesh sieve to obtain a milky white emulsion, which is the bisphenol A epoxy resin grafted emulsion.

[0012] More specifically, the zinc powder is 800 mesh.

[0013] More specifically, the concentration of the graphene dispersion is 5 wt%.

[0014] More specifically, the preparation method of the graphene dispersion includes the following steps:

[0015] S21. Add 10g of graphite powder with a particle size of 50μm to 1L of 0.5wt% sodium dodecyl thiosulfate aqueous solution and stir to pre-disperse for 30min; add 0.2g of polyethylene glycol PEG-400, mix with magnetic stirring, and then sonicate at 400W and 40kHz for 8h, with water bath temperature controlled at 28℃.

[0016] S23. Centrifuge the sonicated suspension at 3000 rpm for 15 min; collect the supernatant and centrifuge at 12000 rpm for 30 min; collect the precipitate and wash it three times with deionized water;

[0017] S24. Redisperse the washed precipitate in deionized water, add ammonia to adjust the pH to 9.0, disperse with ultrasonic assistance for 30 minutes, and adjust the concentration to 5 wt%.

[0018] More specifically, the maleic anhydride-modified polyetheramine D400 has an amine value of 300-350 mg KOH / g and a viscosity of 800-1200 mPa·s at 25°C.

[0019] More specifically, the preparation method of the maleic anhydride modified polyetheramine D400 includes the following steps:

[0020] S31. Add 100g of polyetheramine D400 and 150mL of toluene to a container, stir and dissolve under nitrogen protection, then heat to 60℃ and add 12g of maleic anhydride at a rate of 1g / min.

[0021] S32. Add 0.5g of p-benzenesulfonic acid, heat to 95℃, reflux for 4h, then cool the reaction solution to 50℃, and remove toluene by vacuum distillation at -0.095MPa and 80℃.

[0022] S33. Add 50 mL of ethyl acetate to dissolve the product, wash three times with 5% sodium bicarbonate solution to remove unreacted maleic anhydride, dry the organic phase with anhydrous sodium sulfate, filter, and remove ethyl acetate by rotary evaporation to obtain a yellow viscous liquid, which is maleic anhydride modified polyetheramine D400.

[0023] More specifically, the wetting and dispersing agent is BYK-190; the cosolvent is a mixture of propylene glycol phenyl ether and dipropylene glycol methyl ether in a volume ratio of 2:1; and the defoamer is BYK-024.

[0024] The present invention also provides a method for preparing the waterborne epoxy zinc-rich coating, comprising the following steps:

[0025] S1. Add the bisphenol A epoxy resin grafted emulsion, zinc powder, and graphene dispersion to the dispersion vessel;

[0026] S2. Add wetting and dispersing agent and defoamer, and disperse at 1500 rpm for 40 min;

[0027] S3. Add maleic anhydride-modified polyetheramine D400 and cosolvent, and stir at 800 rpm for 20 min;

[0028] S4. Pass through a 30μm sieve to obtain the waterborne epoxy zinc-rich coating.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) The bisphenol A epoxy resin of the present invention, after grafting hydroxypropyl acrylate and ethyl methacrylate phosphate into an emulsion, simultaneously possesses the flexible chain segments of hydroxypropyl acrylate and the phosphate groups of ethyl methacrylate phosphate, which can improve the adhesion and impact strength of the coating, and enhance the bonding between the resin and zinc powder through hydroxyl groups; in addition, the phosphate groups actively inhibit corrosion, and the salt spray resistance is significantly improved compared with the ungrafted resin.

[0031] (2) The present invention reduces the amount of high zinc powder used, which helps to reduce the risk of brittleness; in addition, the grafted emulsion forms a chemical bond with zinc powder and metal substrate, which can improve adhesion; secondly, the graft copolymer reduces the zinc powder settling rate through steric hindrance effect.

[0032] (3) The sheet structure of graphene in this invention fills the gaps between zinc powder, reduces the coating resistivity, promotes the uniform sacrificial anode effect of zinc, compensates for the reduction of zinc powder, maintains the cathodic protection efficiency, and the sheet structure also reduces the water vapor permeability of the resin, thus delaying the penetration of corrosive media.

[0033] (4) Polyetheramine D400 introduces carboxyl groups through maleic anhydride and adjusts the amine value to 320 mg KOH / g, which helps to shorten the drying time, match the epoxy groups, and extend the service life. In addition, the modified polyetheramine D400 forms a flexible cross-linked network with the grafted resin, which also helps to improve the impact resistance of the coating.

[0034] Therefore, this invention improves the properties of coatings such as conductivity, adhesion, barrier properties, and construction stability through the synergistic effect of bisphenol A epoxy resin grafted emulsion, zinc powder, graphene dispersion, and modified polyetheramine, and solves the problem of balancing sedimentation, brittleness, and corrosion resistance in high zinc powder coatings. Detailed Implementation

[0035] The technical solution of this invention patent will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0036] In the following examples, the bisphenol A epoxy resin is Nan Ya NPEL-128 bisphenol A type epoxy resin.

[0037] Hydroxypropyl acrylate was purchased from Liaoning Kelong Fine Chemical Co., Ltd. (purity: 99.5%).

[0038] Ethyl methacrylate phosphate is Solvay SIPOMERPAM4000 ethyl methacrylate phosphate;

[0039] Polyetheramine D400 is Huntsman polyetheramine D400;

[0040] Maleic anhydride was purchased from Wuhan Jixin Yibang Biotechnology Co., Ltd. (purity: 99%).

[0041] Example 1

[0042] A water-based epoxy zinc-rich coating is prepared from the following raw materials in parts by weight: 1000g of bisphenol A epoxy resin grafted emulsion, 6000g of 800-mesh zinc powder, 20g of 5wt% graphene dispersion, 40g of maleic anhydride-modified polyetheramine D4002 with an amine value of 320mg KOH / g, 60g of BYK-190 wetting and dispersing agent, 150g of cosolvent prepared by mixing propylene glycol phenyl ether and dipropylene glycol methyl ether in a volume ratio of 2:1, and 15g of BYK-024 defoamer.

[0043] Example 2

[0044] The preparation method of the bisphenol A epoxy resin grafted emulsion in Example 1 includes the following steps:

[0045] S11. Add 600g of bisphenol A epoxy resin and 400g of deionized water to a container, heat to 60℃ and stir at 500rpm to dissolve into a homogeneous phase, then add 250g of hydroxypropyl acrylate and 100g of ethyl methacrylate phosphate at a dropping rate of 10g / min to obtain a pre-emulsified system.

[0046] S12. Dissolve ammonium persulfate in deionized water to prepare a 5 wt% initiator. Add the initiator dropwise to the pre-emulsified system at a rate of 5 g / min. Heat the system to 85 °C and react for 4 h under nitrogen protection.

[0047] S13. Cool to 40℃, adjust the pH to 7.0 with sodium hydroxide, and pass through a 200-mesh sieve to obtain a milky white emulsion, which is the bisphenol A epoxy resin grafted emulsion.

[0048] Example 3

[0049] The preparation method of the graphene dispersion in Example 1 includes the following steps:

[0050] S21. Add 10g of graphite powder with a particle size of 50μm to 1L of 0.5wt% sodium dodecyl thiosulfate aqueous solution and stir to pre-disperse for 30min; add 0.2g of polyethylene glycol PEG-400, mix with magnetic stirring, and then sonicate at 400W and 40kHz for 8h, with water bath temperature controlled at 28℃.

[0051] S23. Centrifuge the sonicated suspension at 3000 rpm for 15 min; collect the supernatant and centrifuge at 12000 rpm for 30 min; collect the precipitate and wash it three times with deionized water;

[0052] S24. Redisperse the washed precipitate in deionized water, add ammonia to adjust the pH to 9.0, disperse with ultrasonic assistance for 30 minutes, and adjust the concentration to 5 wt%.

[0053] Example 4

[0054] The preparation method of maleic anhydride modified polyetheramine D400 in Example 1 includes the following steps:

[0055] S31. Add 100g of polyetheramine D400 and 150mL of toluene to a container, stir and dissolve under nitrogen protection, then heat to 60℃ and add 12g of maleic anhydride at a rate of 1g / min.

[0056] S32. Add 0.5g of p-benzenesulfonic acid, heat to 95℃, reflux for 4h, then cool the reaction solution to 50℃, and remove toluene by vacuum distillation at -0.095MPa and 80℃.

[0057] S33. Add 50 mL of ethyl acetate to dissolve the product, wash three times with 5% sodium bicarbonate solution to remove unreacted maleic anhydride, dry the organic phase with anhydrous sodium sulfate, filter, and remove ethyl acetate by rotary evaporation to obtain a yellow viscous liquid, which is maleic anhydride modified polyetheramine D400. The amine value was measured to be 320 mg KOH / g, and the viscosity at 25℃ was 1100 mPa·s.

[0058] Example 5

[0059] The preparation method of the waterborne epoxy zinc-rich coating in Example 1 includes the following steps:

[0060] S1. Add the bisphenol A epoxy resin grafted emulsion, zinc powder, and graphene dispersion to the dispersion vessel;

[0061] S2. Add wetting and dispersing agent and defoamer, and disperse at 1500 rpm for 40 min;

[0062] S3. Add maleic anhydride-modified polyetheramine D400 and cosolvent, and stir at 800 rpm for 20 min;

[0063] S4. Pass through a 30μm sieve to obtain the waterborne epoxy zinc-rich coating.

[0064] Example 6: Effect of different raw materials on the performance of waterborne epoxy zinc-rich coatings

[0065] The raw materials are shown in Table 1. Refer to the test items and methods of HG / T 3668-2020 "Zinc-Rich Primer" and supplement the tests for zinc powder settling rate, resistivity and water vapor transmission rate.

[0066] Table 1 Raw materials for preparing water-based epoxy zinc-rich coatings

[0067]

[0068] In Table 1, A grafting refers to grafting bisphenol A epoxy resin with only hydroxypropyl acrylate; B grafting refers to grafting bisphenol A epoxy resin with only ethyl methacrylate phosphate; A+B grafting refers to grafting bisphenol A epoxy resin with both hydroxypropyl acrylate and ethyl methacrylate phosphate, as described in Example 2; modified polyetheramine D400 refers to modifying polyetheramine D400 with maleic anhydride, as described in Example 4.

[0069] Table 2 Test Items, Test Methods, Basis and Explanation

[0070]

[0071] Table 3. Effects of different raw materials on the performance of waterborne epoxy zinc-rich coatings

[0072]

[0073] As shown in Table 1, in terms of salt spray resistance, C4 achieves a salt spray resistance of 3250h through the synergistic effect of active corrosion inhibition by double-grafted resin and the barrier effect of graphene, which is significantly higher than C3 and C5; C7 has the worst salt spray resistance due to the lack of modified curing agent and graphene.

[0074] In terms of adhesion and impact strength, C4 has the best adhesion and impact strength at the interface of hydroxypropyl acrylate-grafted reinforced resin and zinc powder; C1 has the lowest adhesion without grafting; and C7 has the worst impact strength due to its dual defects.

[0075] Regarding zinc powder settling rate and resistivity, C4-modified D400 improves dispersibility, with a settling rate of only 2.3%; graphene forms a conductive network, resulting in a resistivity as low as 8.0 × 10⁻⁶. 2 Ω·cm; C7 unmodified D400 and the absence of graphene resulted in the highest sedimentation rate and the highest resistivity.

[0076] In terms of drying time and workability, the modified D400 of C4 has a high amine value, a surface drying time of 18.5 min, and excellent workability. The unmodified D400 of C6 and C7 cures slowly, with a surface drying time of ≥50 min, and shows obvious sagging during construction.

[0077] In summary, the bisphenol A epoxy resin emulsion grafted with hydroxypropyl acrylate and ethyl methacrylate phosphate possesses both the flexible segments of hydroxypropyl acrylate and the phosphate groups of ethyl methacrylate phosphate, which can improve the adhesion and impact strength of the coating, and enhance the resin-zinc powder interface bonding through hydroxyl groups; in addition, the phosphate groups actively inhibit corrosion, and the salt spray resistance is significantly improved compared with the ungrafted resin.

[0078] Reducing the amount of high-zinc powder helps to lower the risk of brittleness; in addition, the grafted emulsion forms chemical bonds with zinc powder and metal substrate, which can improve adhesion; secondly, the graft copolymer reduces the zinc powder settling rate through steric hindrance effect.

[0079] The sheet structure of graphene fills the gaps between zinc powder, reduces the coating resistivity, promotes the uniform sacrificial anode effect of zinc, compensates for the reduction in zinc powder, maintains cathodic protection efficiency, and the dense structure of the sheet-forming barrier resin reduces water vapor permeability and delays the penetration of corrosive media.

[0080] Polyetheramine D400 introduces carboxyl groups through maleic anhydride, adjusting the amine value to 320 mg KOH / g, which helps to shorten drying time, match epoxy groups, and extend the pot life. Furthermore, the modified polyetheramine D400 forms a flexible cross-linked network with the grafted resin, which also helps to improve the impact resistance of the coating.

[0081] Therefore, this invention improves the properties of coatings such as conductivity, adhesion, barrier properties, and construction stability through the synergistic effect of bisphenol A epoxy resin grafted emulsion, zinc powder, graphene, and modified polyetheramine, and solves the problem of balancing sedimentation, brittleness, and corrosion resistance in high zinc powder coatings.

[0082] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. An aqueous epoxy zinc-rich coating, characterized by, Prepared from the following raw materials by weight parts: bisphenol A epoxy resin graft emulsion 80-110 parts, zinc powder 600-800 parts, graphene dispersion liquid 2-3 parts, maleic anhydride modified polyether amine D400 20-25 parts, wetting dispersant 5-7 parts, cosolvent 15-20 parts and defoamer 1-2 parts; wherein the bisphenol A epoxy resin graft emulsion is prepared by graft copolymerization of bisphenol A epoxy resin, hydroxypropyl acrylate and ethyl methacrylate phosphate.

2. The aqueous epoxy zinc-rich coating of claim 1, wherein, The preparation method of the bisphenol A epoxy resin graft emulsion comprises the following steps: S11, 600g of bisphenol A epoxy resin and 400g of deionized water are added to a container, heated to 60℃ and stirred at 500rpm to dissolve uniformly, then 250g of hydroxypropyl acrylate and 100g of ethyl methacrylate phosphate are added at a dropping speed of 10g / min to obtain a pre-emulsion system; S12. Ammonium persulfate is dissolved in deionized water to prepare an initiator with a concentration of 5wt%, and the initiator is added to the pre-emulsion system at a dropping speed of 5g / min, heated to 85℃, and reacted for 4h under nitrogen protection; S13. Cool to 40℃, adjust the pH value to 7.0 with sodium hydroxide, pass through a 200 mesh screen to obtain a milky white emulsion, which is the bisphenol A epoxy resin graft emulsion.

3. The aqueous epoxy zinc-rich coating of claim 1, wherein, The zinc powder is 800 mesh.

4. The aqueous epoxy zinc-rich coating of claim 1, wherein, The concentration of the graphene dispersion liquid is 5wt%.

5. The aqueous epoxy zinc-rich coating of claim 4, wherein, The preparation method of the graphene dispersion liquid comprises the following steps: S21. 10g of graphite powder with a particle size of 50μm is added to 1L of 0.5wt% sodium dodecyl sulfonate aqueous solution, and stirred for 30min for pre-dispersion; 0.2g of polyethylene glycol PEG-400 is added, and after magnetic stirring and mixing, ultrasonic treatment is carried out at 400W and 40kHz for 8h with water bath temperature control at 28℃; S23. The suspension after ultrasonic treatment is centrifuged at 3000rpm for 15min; the supernatant is collected and centrifuged at 12000rpm for 30min; the precipitate is washed with deionized water for 3 times; S24. The washed precipitate is re-dispersed in deionized water, ammonia water is added to adjust the pH to 9.0, and ultrasonic assisted dispersion is carried out for 30min to adjust the concentration to 5wt%.

6. The waterborne epoxy zinc-rich coating of claim 1, wherein, The maleic anhydride modified polyether amine D400 has an amine value of 300-350mg KOH / g and a viscosity of 800-1200mPa·s at 25℃.

7. The aqueous epoxy zinc-rich coating of claim 6, wherein, The preparation method of the maleic anhydride modified polyether amine D400 comprises the following steps: S31. 100g of polyether amine D400 and 150mL of toluene are added to a container, stirred and dissolved under nitrogen protection, then heated to 60℃, and 12g of maleic anhydride is added at a speed of 1g / min; S32. Add 0.5g of p-toluene sulfonic acid, heat to 95℃, and reflux for 4h, then cool the reaction liquid to 50℃, remove toluene under reduced pressure at a vacuum degree of-0.095MPa and a temperature of 80℃; S33. Add 50mL of ethyl acetate to dissolve the product, wash with 5% sodium bicarbonate solution for 3 times to remove unreacted maleic anhydride, dry the organic phase with anhydrous sodium sulfate, filter and remove ethyl acetate by rotary evaporation to obtain a yellow viscous liquid, which is the maleic anhydride modified polyether amine D400.

8. The waterborne epoxy zinc-rich coating of claim 1, wherein, The wetting and dispersing agent is BYK-190; the cosolvent is a mixture of propylene glycol phenyl ether and dipropylene glycol methyl ether in a volume ratio of 2:1; the defoamer is BYK-024.

9. A process for the preparation of the aqueous epoxy zinc-rich coating according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Add the bisphenol A epoxy resin grafted emulsion, zinc powder, and graphene dispersion to the dispersion vessel; S2. Add wetting and dispersing agent and defoamer, and disperse at 1500 rpm for 40 min; S3. Add maleic anhydride-modified polyetheramine D400 and cosolvent, and stir at 800 rpm for 20 min; S4. Pass through a 30μm sieve to obtain the waterborne epoxy zinc-rich coating.

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