Two-component water-based acrylic cathodic electrodeposition paint for metal alloy and preparation method thereof

Abstract

The present application relates to the technical field of environment-friendly water-based metal coating, and discloses a two-component water-based acrylic cathode electrodeposition paint for metal alloy and a preparation method thereof, which is composed of 580-620 parts of cationic hydroxy acrylic resin solution, 150-190 parts of aliphatic blocked isocyanate curing agent, 15-21 parts of organic acid neutralizer, 3-5 parts of leveling agent, 2-4 parts of defoaming agent and 190-220 parts of deionized water in terms of mass fraction. The cationic hydroxy acrylic resin is prepared by gradient dropping polymerization of methyl methacrylate, butyl acrylate, hydroxyethyl methacrylate and dimethylaminoethyl methacrylate in a specific ratio. The paint film has high hardness (2H) and excellent flexibility (no cracking after 50 cm impact), can withstand neutral salt spray for 120 hours, the scratch corrosion is less than or equal to 0.8 mm, the working solution is free of precipitation and gel after standing at room temperature for 8 months, the VOC content is less than or equal to 50 g / L, and is suitable for electrodeposition coating of zinc alloy / aluminum alloy workpieces.

Description

Technical Field

[0001] This invention relates to the field of environmentally friendly water-based metal coatings, and in particular to a two-component water-based acrylic cathodic electrodeposition paint for metal alloys and its preparation method. Background Technology

[0002] Cathodic electrodeposition is a special coating process in which the metal workpiece to be coated is used as the cathode (negative electrode) and immersed in a paint solution while an electric current is applied. The positively charged paint particles are then uniformly "swimmed" to the surface of the workpiece under the influence of the electric field and deposited to form a paint film. This method can perfectly cover workpieces with complex shapes and produce a uniform coating thickness.

[0003] Water-based acrylic cathodic electrodeposition paint has gradually replaced traditional solvent-based coatings and is widely used in the hardware surface treatment industry due to its advantages such as low VOC content, high degree of automation in coating, uniform and dense paint film, and good edge and corner coverage.

[0004] However, existing commercially available products have the following significant technical defects for zinc alloy and aluminum alloy substrates:

[0005] 1. Imbalance in mechanical properties: It is difficult to balance the hardness and flexibility of the paint film. If the hardness is too high (≥2H), it will easily crack upon impact. If the flexibility is good, the pencil hardness is insufficient (≤H), which cannot meet the wear-resistant and scratch-resistant requirements of hardware parts.

[0006] 2. Poor stability of working solution: The resin has a wide molecular weight distribution (PDI>2.5) and a high residual monomer content. Precipitation and gelation occur in the working solution after standing at room temperature for 1-2 months, requiring frequent tank cleaning and solution replacement, which greatly increases production costs.

[0007] 3. Insufficient corrosion resistance: Ordinary products can only achieve 24-48 hours of neutral salt spray without being scratched. After being scratched, corrosion is prone to spread, which cannot meet the mandatory 72-hour salt spray requirement under special circumstances.

[0008] 4. Curing process defects: Curing agents are often added directly, which can easily lead to premature agglomeration of the curing agent, resulting in problems such as pinholes, sagging, and uneven gloss in the paint film, and a low yield rate.

[0009] Therefore, improvements are needed to address the aforementioned shortcomings. Summary of the Invention

[0010] The main objective of this invention is to provide a two-component waterborne acrylic cathodic electrodeposition paint for metal alloys and its preparation method, specifically a two-component waterborne acrylic cathodic electrodeposition paint for zinc alloys / aluminum alloys and its preparation method.

[0011] To achieve the above objectives, this invention proposes a two-component waterborne acrylic cathodic electrodeposition paint for metal alloys, which, by weight, comprises the following components: 580-620 parts of cationic hydroxyl acrylic resin solution, 150-190 parts of aliphatic blocked isocyanate curing agent, 15-21 parts of organic acid neutralizer, 3-5 parts of leveling agent, 2-4 parts of defoamer, and 190-220 parts of deionized water.

[0012] Specifically, the cationic hydroxy acrylic resin, by weight, comprises the following components: 200-240 parts methyl methacrylate, 120-160 parts butyl acrylate, 90-130 parts hydroxyethyl methacrylate, 55-75 parts dimethylaminoethyl methacrylate, 6-10 parts azo initiator, 1.5-2.5 parts thiol chain transfer agent, and 430-480 parts alcohol ether reaction solvent.

[0013] Specifically, the organic acid neutralizer is glacial acetic acid, the leveling agent is a high-transparency polyether-modified silicone leveling agent, and the defoamer is a non-silicone polyether defoamer.

[0014] Specifically, the azo initiator is azobisisobutyronitrile, the thiol chain transfer agent is tert-dodecyl mercaptan, and the alcohol ether reaction solvent is propylene glycol methyl ether.

[0015] To achieve the above objectives, the present invention also proposes a method for preparing a two-component waterborne acrylic cathodic electrodeposition paint, comprising the following steps:

[0016] S1. Neutralization and emulsification: Add the cationic hydroxy acrylic resin solution to the reactor, start stirring, slowly add the neutralizing agent, stir for 10-20 minutes to neutralize, then slowly add deionized water, stir for 25-35 minutes to emulsify;

[0017] S2. Adding additives and curing agents: Add defoamer and leveling agent in sequence, stir for 10-20 minutes, then slowly add aliphatic blocked isocyanate curing agent, controlling the dripping time at 15-25 minutes, and continue stirring for 25-35 minutes after the dripping is completed.

[0018] S3. Filtering and Packaging: After standing and defoaming, filter twice with a 180-220 mesh filter and store in a sealed container.

[0019] The technical solution of this invention balances the hardness and flexibility of the paint film by using a precisely proportioned cationic hydroxy acrylic resin solution to improve the corrosion resistance of the paint film. At the same time, the working fluid has extremely strong stability, good compatibility, and an environmental safety factor. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, top, bottom, inside, outside, vertical, horizontal, longitudinal, counterclockwise, clockwise, circumferential, radial, axial, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0022] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0023] One embodiment of this invention is a two-component waterborne acrylic cathodic electrodeposition paint for metal alloys, which, by weight, consists of the following components: 580-620 parts of cationic hydroxyl acrylic resin solution, 150-190 parts of aliphatic blocked isocyanate curing agent, 15-21 parts of organic acid neutralizer, 3-5 parts of leveling agent, 2-4 parts of defoamer, and 190-220 parts of deionized water.

[0024] The cationic hydroxy acrylic resin solution is prepared by mixing 200-240 parts by weight of methyl methacrylate, 120-160 parts by weight of butyl acrylate, 90-130 parts by weight of hydroxyethyl methacrylate, 55-75 parts by weight of dimethylaminoethyl methacrylate, 6-10 parts by weight of azo initiator, 1.5-2.5 parts by weight of thiol chain transfer agent, and 430-480 parts by weight of alcohol ether reaction solvent.

[0025] In the preparation of the cationic hydroxy acrylic resin solution, the azo initiator used is azobisisobutyronitrile, the thiol chain transfer agent is tert-dodecyl mercaptan, and the alcohol ether reaction solvent is propylene glycol methyl ether.

[0026] Preferably, the mixture comprises 220 parts of methyl methacrylate, 140 parts of butyl acrylate, 110 parts of hydroxyethyl methacrylate, 65 parts of dimethylaminoethyl methacrylate, 8 parts of azobisisobutyronitrile, 2 parts of tert-dodecyl mercaptan, and 455 parts of propylene glycol methyl ether.

[0027] The preparation method of cationic hydroxyl acrylic resin solution includes the following five steps:

[0028] S1. Preparation before reaction: Purge nitrogen into the reactor for 15 minutes to completely replace the air inside the reactor; mix all monomers evenly to prepare a mixed monomer solution; dissolve the initiator and chain transfer agent in 50 parts of propylene glycol methyl ether to prepare an initiator solution;

[0029] S2. Initial Heating: Add the remaining 405 parts of propylene glycol methyl ether to the reactor; start stirring and adjust the speed to 300 rpm; heat to 78-82℃ and keep the temperature stable.

[0030] S3. Gradient Dropping Reaction: Simultaneously and uniformly add the mixed monomer solution and the initiator solution; the mixed monomer is added over 3-4 hours, and the initiator solution is added over 3.5-4.5 hours; maintain the reaction temperature at 78-82℃ throughout the dropping process.

[0031] S4. Incubation Reaction: After the initiator solution is completely added, continue the reaction at 78-82℃ for 1.5-2.5 hours; after the incubation period, take a sample for testing, and the solid content should reach 48-52%.

[0032] S5. Cooling and Discharging: After the reaction is complete, turn off the heating and cool down to below 40°C by passing cooling water; discharge the material to obtain a cationic hydroxy acrylic resin solution with a solid content of 50±1%, which is a colorless to slightly yellow transparent liquid with no mechanical impurities.

[0033] After obtaining a cationic hydroxyl acrylic resin solution with a solid content of 50%, a two-component waterborne acrylic cathodic electrodeposition paint can be prepared, as follows:

[0034] S1. Neutralization and emulsification: Add the cationic hydroxy acrylic resin solution to the reactor, start stirring, slowly add the neutralizing agent, stir for 10-20 minutes to neutralize, then slowly add deionized water, stir for 25-35 minutes to emulsify;

[0035] S2. Adding additives and curing agents: Add defoamer and leveling agent in sequence, stir for 10-20 minutes, then slowly add aliphatic blocked isocyanate curing agent, controlling the dripping time at 15-25 minutes, and continue stirring for 25-35 minutes after the dripping is completed.

[0036] S3. Filtering and Packaging: After standing and defoaming, filter twice with a 180-220 mesh filter and store in a sealed container.

[0037] At this point, the proportions of the components added by weight are as follows:

[0038] 600 parts of cationic hydroxyl acrylic resin solution with a solid content of 50%; 170 parts of HDI-type aliphatic blocked isocyanate curing agent with a solid content of 75%; 18 parts of glacial acetic acid with an NCO content of 12% and a purity of ≥99.5%; 4 parts of analytical grade high-transparency polyether modified silicone leveling agent with 100% active ingredient; 3 parts of non-silicone polyether defoamer; and 205 parts of deionized water with a conductivity of <5μS / cm.

[0039] After the electrodeposition paint is prepared, it is formulated into a working solution with 10% solids. The zinc alloy workpiece is then subjected to electrodeposition coating treatment using a standard process at 150V for 2 minutes. After the electrodeposition coating is completed, the zinc alloy workpiece is baked and cured at 160℃ for 20 minutes. Finally, the zinc alloy workpiece is inspected.

[0040] The test results are shown in the table below:

[0041]

[0042] Example 2: The amount of curing agent was adjusted to 160 kg, and other properties were the same as in Example 1. The test results were: pencil hardness 1.5H, neutral salt spray test for 60 hours, and other properties were the same as in Example 1.

[0043] Example 3: The amount of curing agent was adjusted to 180kg, and the rest was the same as in Example 1; the test results were: pencil hardness 2.5H, neutral salt spray test for 75 hours, slightly brittle paint film, and no cracking at 40cm impact test.

[0044] In addition, this experiment also provides a comparative example: a commercially available ordinary cationic acrylic resin (solid content 50%) was used to prepare a finished paint according to the electrodeposition paint formulation process of Example 1; the test results were: pencil hardness 1H, neutral salt spray test for 48 hours, precipitation after 1 month in the working solution, and other properties were the same as in Example 1.

[0045] In summary, this invention employs a precise monomer ratio of 22:14:11:6.5 between methyl methacrylate, butyl acrylate, hydroxyethyl methacrylate, and dimethylaminoethyl methacrylate, perfectly balancing the hardness (2H) and flexibility (no cracking after 50cm impact), solving the long-standing industry problem of "hard and brittle, soft and easy to scratch," and demonstrating its excellent mechanical properties.

[0046] Meanwhile, it achieves no red rust or blistering after 120 hours in neutral salt spray without scratches, and the width of scratched corrosion is ≤1mm, which greatly enhances corrosion resistance.

[0047] A resin with a narrow molecular weight distribution (PDI<1.8) and residual monomer content of <0.5% was obtained by gradient drop polymerization. The working solution showed no precipitation or gelation after standing at room temperature for 6 months, and its service life was more than 3 times that of ordinary products, greatly improving the stability of the working solution.

[0048] The one-step mixing process avoids premature agglomeration of the curing agent, resulting in a uniform paint film free of pinholes and sagging. Existing electrodeposition coating production lines can be used directly without any modifications, thus improving their process compatibility.

[0049] The water-based system has a VOC content of ≤50g / L, meets the latest national environmental protection standards, and has a high environmental safety factor.

[0050] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A two-component water-based acrylic cathodic electrodeposition paint for metal alloys, characterized in that, By weight, it consists of the following components: 580-620 parts cationic hydroxy acrylic resin solution, 150-190 parts aliphatic blocked isocyanate curing agent, 15-21 parts organic acid neutralizer, 3-5 parts leveling agent, 2-4 parts defoamer, and 190-220 parts deionized water.

2. The two-component water-based acrylic cathodic electrodeposition paint for metal alloys according to claim 1, characterized in that, The cationic hydroxy acrylic resin, by weight, comprises the following components: 200-240 parts methyl methacrylate, 120-160 parts butyl acrylate, 90-130 parts hydroxyethyl methacrylate, 55-75 parts dimethylaminoethyl methacrylate, 6-10 parts azo initiator, 1.5-2.5 parts thiol chain transfer agent, and 430-480 parts alcohol ether reaction solvent.

3. The two-component waterborne acrylic cathodic electrodeposition paint for metal alloys according to claim 1, characterized in that, The organic acid neutralizer is glacial acetic acid, the leveling agent is a high-transparency polyether-modified silicone leveling agent, and the defoamer is a non-silicone polyether defoamer.

4. The two-component water-based acrylic cathodic electrodeposition paint for metal alloys according to claim 2, characterized in that, The azo initiator is azobisisobutyronitrile, the thiol chain transfer agent is tert-dodecyl mercaptan, and the alcohol ether reaction solvent is propylene glycol methyl ether.

5. A method for preparing a two-component waterborne acrylic cathodic electrodeposition paint as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Neutralization and emulsification: Add the cationic hydroxy acrylic resin solution to the reactor, start stirring, slowly add the neutralizing agent, stir for 10-20 minutes to neutralize, then slowly add deionized water, stir for 25-35 minutes to emulsify; S2. Adding additives and curing agents: Add defoamer and leveling agent in sequence, stir for 10-20 minutes, then slowly add aliphatic blocked isocyanate curing agent, controlling the dripping time at 15-25 minutes, and continue stirring for 25-35 minutes after the dripping is completed. S3. Filtering and Packaging: After standing and defoaming, filter twice with a 180-220 mesh filter and store in a sealed container.

Images