A single-component zinc-aluminum self-stratifying coating, preparation method and application thereof

Abstract

The present invention discloses a single-component self-stratifying zinc-aluminum bimetallic coating. The single-component self-stratifying zinc-aluminum bimetallic coating comprises, by weight, 20-25 parts of a thermoplastic resin, 5-8 parts of a surfactant, 0.5-1.0 parts of a thickener, 0.2-0.5 parts of a defoamer, 0.5-1 parts of a leveling agent, 5-10 parts of an aluminum-silver paste, 38-40 parts of spherical zinc powder, and 25-30 parts of a mixed solvent; wherein the mixed solvent comprises xylene and ethylene glycol butyl ether. The present invention utilizes mixed solvents of different boiling points and polarities, the compatibility of a single resin with zinc powder, and the incompatibility of the resin with an aluminum powder coating, thereby obtaining a single-component self-stratifying zinc-aluminum bimetallic coating with stable performance, good corrosion protection, and susceptibility to intermetallic electrochemical reactions.

Description

Technical Field

[0001] The present invention relates to the technical field of coatings, and in particular to a single-component self-stratified zinc-aluminum bimetallic coating, a preparation method and applications thereof. Background Art

[0002] In corrosive environments, metal materials are susceptible to oxidation and corrosion, which can lead to performance degradation and shortened lifespan. To address this issue, researchers have developed new coating technologies, such as zinc-aluminum bimetallic anti-corrosion coatings.

[0003] The basic principle of zinc-aluminum bimetallic anti-corrosion coating technology is to protect metal materials by forming a self-layered bimetallic layer of zinc and aluminum on the metal surface. Zinc has excellent corrosion resistance and can be used as a cathodic protection metal material; while aluminum has excellent ductility and shielding properties, shielding against the invasion of corrosive media and providing shielding protection. Due to the different specific gravities of the zinc-aluminum bimetallic, the layers form a dual-protective anti-corrosion coating, improving the corrosion resistance of the metal material.

[0004] Existing zinc-aluminum bimetallic anti-corrosion coatings alloy spherical zinc and aluminum powders before applying them to metal surfaces. This solution can achieve a certain degree of corrosion protection. However, resins have good compatibility with both aluminum and zinc powders, and the zinc-aluminum bimetallic is evenly distributed in the system. As a single-component coating, the coating dries quickly, solidifying before the zinc and aluminum separate. However, there is a certain degree of intercalation between the zinc and aluminum. Due to the different chemical properties of zinc and aluminum, electrochemical reactions between the two metals are likely to occur, resulting in unstable coating performance and unsatisfactory corrosion protection. Summary of the Invention

[0005] In view of the above-mentioned shortcomings that currently exist, the present invention provides a single-component self-stratifying zinc-aluminum bimetallic coating, a preparation method and its application. The present invention is based on mixed solvents with different boiling points and polarities, the compatibility of a single resin with zinc powder, and the incompatibility of the resin with the aluminum powder coating, thereby obtaining a single-component self-stratifying zinc-aluminum bimetallic coating with stable performance, good anti-corrosion effect, and not prone to intermetallic electrochemical reactions.

[0006] In order to achieve the above-mentioned object, the present invention provides a single-component self-stratifying zinc-aluminum bimetallic coating. The formula of the single-component self-stratifying zinc-aluminum bimetallic coating includes, by weight, 20-25 parts of thermoplastic resin, 5-8 parts of surfactant, 0.5-1.0 part of thickener, 0.2-0.5 part of defoamer, 0.5-1 part of leveling agent, 5-10 parts of aluminum-silver paste, 38-40 parts of spherical zinc powder, and 25-30 parts of mixed solvent; wherein the mixed solvent includes xylene and ethylene glycol butyl ether.

[0007] According to one aspect of the present invention, the film-forming temperature of the thermoplastic resin is 35-60° C., and the thermoplastic resin is a high molecular weight thermoplastic phenoxy resin or a high molecular weight thermoplastic epoxy resin.

[0008] It should be noted that the thermoplastic resin of the present invention has a solids content of 50% and a film-forming temperature between 35°C and 60°C. It has wide applicability, excellent compatibility, and excellent adhesion to various substrates. When used in the present invention, it exhibits good compatibility with pigments, fillers, and functional powders, and the cured coating exhibits excellent adhesion to steel.

[0009] According to one aspect of the present invention, the aluminum-silver paste is flaky aluminum powder coated with sodium stearate.

[0010] It should be noted that the aluminum paste of the present invention is a flaky aluminum powder coated with sodium stearate. The particles of the flaky aluminum powder are flat, similar to thin sheets or foil. This shape gives the flaky aluminum powder a large surface area and a high specific surface area. After film formation, the flaky aluminum powder is stacked together, significantly extending the intrusion path of corrosive media.

[0011] According to one aspect of the present invention, the mass ratio of xylene to ethylene glycol butyl ether is 1:1 to 1:2.

[0012] According to one aspect of the present invention, the leveling agent includes any one or both of an organosilicon leveling agent and an acrylic leveling agent.

[0013] It should be noted that the organosilicon leveling agent in the present invention contains a certain amount of siloxymethyl groups, which can reduce surface tension. The acrylic leveling agent in the present invention contains intermediate substances and has good compatibility with the high-molecular-weight thermoplastic phenoxy resin. The combination of the two improves the fluidity and smoothness of the coating, allowing the coating to flow evenly during application and form a smooth surface. This can reduce the surface tension of the coating and reduce wrinkling and flow marks.

[0014] According to one aspect of the present invention, the spherical zinc powder is spherical zinc powder with a mesh size of 1000 or more; and the particle size of the aluminum-silver paste is 3 μm-7 μm.

[0015] It should be noted that the spherical zinc powder of the present invention is spherical zinc powder with a mesh size of 1000 or above, and has a higher specific gravity than flaky aluminum powder. When the film forming time is long enough, the zinc powder descends faster in the resin due to gravity than flaky aluminum powder.

[0016] According to one aspect of the present invention, the surfactant is a condensate of octylphenol and ethylene oxide; the thickener includes any one or more of polyurea, sodium polyamide, and bentonite; and the defoamer is a polyether siloxane copolymer emulsion containing fumed silica.

[0017] It should be noted that the surfactant of the present invention, the condensate of octylphenol and ethylene oxide, has an HLB value of about 15, a milky white to light yellow paste appearance, and good emulsifying, wetting, diffusing, and solubilizing properties.

[0018] It should be noted that the thickener of the present invention - polyurea, sodium polyamide or bentonite - plays the role of adjusting viscosity, improving suspension, improving rheological properties and enhancing hiding power in the coating; by using a thickener, the present invention can make the coating easier to apply, improve the performance and stability of the coating, and thus obtain a better coating effect.

[0019] It should be noted that the defoamer of the present invention—a polyether siloxane copolymer emulsion containing fumed silica—is highly effective in suppressing and defoaming. The defoamer prevents bubbles and foam from forming in the coating, improving its fluidity and coatability. It breaks down the surface tension of the liquid, allowing bubbles to escape smoothly from the coating and reducing surface defects.

[0020] Based on the same inventive concept, the present invention also provides a method for preparing the above-mentioned single-component self-stratified zinc-aluminum bimetallic coating, comprising the following steps:

[0021] Step 1: Put aluminum paste and surfactant into a grinder and grind them thoroughly to obtain a paste-like hydrophilic aluminum paste with high floating value;

[0022] Step 2: Add xylene to the paste-like hydrophilic high-floating value aluminum-silver paste and stir evenly, add thickener and stir evenly, add defoamer and stir evenly, add leveling agent and stir evenly, add thermoplastic resin and stir evenly, add spherical zinc powder and stir evenly, add ethylene glycol butyl ether and stir evenly, continue to disperse evenly for a certain period of time to obtain a single-component self-stratified zinc-aluminum bimetallic coating.

[0023] Based on the same inventive concept, the present invention also provides an application of any of the above-mentioned single-component self-stratifying zinc-aluminum bimetallic coatings or the single-component self-stratifying zinc-aluminum bimetallic coatings prepared by the above-mentioned preparation method, comprising the following steps: using the mixed solvent to dilute the single-component self-stratifying zinc-aluminum bimetallic coating to a suitable viscosity, and spraying it onto a sandblasted steel plate.

[0024] According to one aspect of the present invention, the sprayed film thickness is 80 μm.

[0025] Beneficial effects of the present invention:

[0026] (1) The single-component self-stratifying zinc-aluminum bimetallic coating of the present invention uses spherical zinc powder and flaky aluminum powder to enhance the self-stratification effect. The larger the mesh size of the spherical zinc powder, the smaller the particle size, and the faster the sinking speed; the smaller the particle size of the flaky aluminum powder, the higher the floating value;

[0027] (2) After the aluminum paste of the single-component self-stratified zinc-aluminum bimetallic coating of the present invention is fully ground with a surfactant, a paste-like hydrophilic aluminum paste with a high floating value is obtained. The paste-like hydrophilic aluminum paste with a high floating value is mixed and dispersed with xylene, a thickener, a defoamer, a leveling agent, a thermoplastic resin, and spherical zinc powder. Due to the hydrophilic and oleophobic properties of the aluminum paste and its thin, flaky, and high floating value characteristics, the aluminum paste floats on the upper layer and is not easily miscible with other substances.

[0028] (3) The single-component thermoplastic resin of the present application is lipophilic, while the aluminum-silver paste is hydrophilic after being modified with a surfactant (i.e., the resin is incompatible with aluminum). Under the action of a mixed solvent (xylene and ethylene glycol butyl ether), the resin, zinc powder, and aluminum-silver paste all have a certain degree of cross-linking. However, according to the compatibility principle, the cross-linking degree between the resin and zinc powder is greater than that between the aluminum-silver paste. During the drying process of the coating, the zinc powder layer contains more resin than the aluminum powder layer. Since the specific gravity of zinc powder is three times that of aluminum powder, and the zinc powder cross-links more resin, eventually, under the action of gravity, the zinc powder layer gradually sinks, and the aluminum powder layer floats upward to achieve the effect of self-stratification. In addition, the resin is unevenly distributed in the vertical direction, i.e., there is more resin in the lower layer and less resin in the upper layer.

[0029] (4) The present application adds a mixed solvent, and when the mixed solvent evaporates, the flaky aluminum powder is pushed upward, thereby causing the flaky aluminum powder to float; and since the ethylene glycol butyl ether in the mixed solvent is a high-boiling point solvent, the volatilization rate of the mixed solvent in the coating is controlled, so that the coating dries slowly, thereby causing the zinc and aluminum to be completely stratified.

[0030] (5) The aluminum-silver paste of the present application is flaky aluminum powder coated with sodium stearate, thereby separating the aluminum powder and zinc powder to avoid electrochemical reactions between the metals. DETAILED DESCRIPTION

[0031] To make the present invention easier to understand, the present invention is further described below with reference to specific examples. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Unless otherwise defined, the professional terms used below are consistent with the meanings understood by professional and technical personnel in this field; unless otherwise specified, the raw materials and reagents involved in this article can be purchased from the market or prepared by known methods.

[0032] To address the technical problems mentioned in the background art, the present invention provides a single-component, self-layering zinc-aluminum bimetallic coating. The formula of the single-component, self-layering zinc-aluminum bimetallic coating comprises, by weight, 20-25 parts of a thermoplastic resin, 5-8 parts of a surfactant, 0.5-1.0 parts of a thickener, 0.2-0.5 parts of a defoamer, 0.5-1 parts of a leveling agent, 5-10 parts of an aluminum paste, 38-40 parts of spherical zinc powder, and 25-30 parts of a mixed solvent; wherein the mixed solvent comprises xylene and butyl glycol ether. Preferably, the thermoplastic resin has a film-forming temperature of 35-60°C, and the thermoplastic resin is a polymeric thermoplastic phenoxy resin or a polymeric thermoplastic epoxy resin. Preferably, the aluminum paste is flaky aluminum powder coated with sodium stearate, and the mass ratio of xylene to butyl glycol ether is 1:1 to 1:2. Preferably, the leveling agent includes either or both of a silicone leveling agent and an acrylic leveling agent. Preferably, the spherical zinc powder is 1000 mesh or larger; and the aluminum-silver paste has a particle size of 3 μm to 7 μm. Preferably, the surfactant is a condensate of octylphenol and ethylene oxide; the thickener includes either or both of polyurea, sodium polyamide, and bentonite; and the defoamer is a polyether siloxane copolymer emulsion containing fumed silica.

[0033] For example, the polymer thermoplastic phenoxy resin is RT8180 produced by Guangdong Ruitu Fine Chemicals; and the polymer thermoplastic epoxy resin is 8180 produced by Hualian Polymer.

[0034] Exemplarily, the condensate of octylphenol and ethylene oxide is OP-15.

[0035] For example, the thickener containing bentonite is Hemmings BENTONE 27, the thickener containing sodium polyamide is Aiox AT-720, and the thickener containing polyurea is Anjeka 4410.

[0036] For example, the polyether siloxane copolymer emulsion containing fumed silica is Tegofoamex 810 produced by Evonik Chemicals.

[0037] For example, the flaky aluminum powder coated with sodium stearate is Haofeng Aluminum's high-floating aluminum-silver paste 2510.

[0038] For example, the silicone leveling agent is AFCONA-3758, and the acrylic leveling agent is AFCONA-3771.

[0039] In order to solve the technical problems mentioned in the background technology, the present invention also provides a method for preparing the above-mentioned single-component self-stratified zinc-aluminum bimetallic coating, comprising the following steps:

[0040] Step 1: Put aluminum paste and surfactant into a grinder and grind them thoroughly to obtain a paste-like hydrophilic aluminum paste with high floating value;

[0041] Step 2: Add xylene to the paste-like hydrophilic high-floating value aluminum-silver paste and stir evenly, add thickener and stir evenly, add defoamer and stir evenly, add leveling agent and stir evenly, add thermoplastic resin and stir evenly, add spherical zinc powder and stir evenly, add ethylene glycol butyl ether and stir evenly, continue to disperse evenly for a certain period of time to obtain a single-component self-stratified zinc-aluminum bimetallic coating.

[0042] Specifically:

[0043] Step 1: Add surfactant to high-floating aluminum-silver paste and disperse at a stirring rate of 400-600 rpm for 10 minutes;

[0044] Step 2: Add xylene to step 1 in sequence at a stirring rate of 600-800 rpm, disperse for 1-2 minutes, and stir evenly;

[0045] Step 3: Add the thickener to step 2 in sequence at a stirring rate of 600-800 rpm, disperse for 2-3 minutes, and stir evenly;

[0046] Step 4: Add the defoamer to step 3 in sequence at a stirring rate of 600-800 rpm, disperse for 2-3 minutes, and stir evenly;

[0047] Step 5: Add the leveling agent to step 4 in sequence at a stirring rate of 600-800 rpm, disperse for 2-3 minutes, and stir evenly;

[0048] Step 6: Add the resin to step 5 at a stirring rate of 800-1000 rpm, disperse for 2-3 minutes, and stir evenly;

[0049] Step 7: Add zinc powder to step 6 at a stirring rate of 800-1000 rpm, disperse for 2-3 minutes, and stir evenly;

[0050] Step 8: Add ethylene glycol butyl ether to step 7 in sequence at a stirring rate of 600-800 rpm, disperse for 1-2 minutes, and stir evenly;

[0051] Step 9: Maintain the rotation speed above 1500 rpm and disperse evenly for 15 minutes to obtain a zinc-aluminum bimetallic coating.

[0052] To address the technical problems mentioned in the background art, the present invention further provides a method for applying any of the aforementioned single-component, self-stratifying zinc-aluminum bimetallic coatings or a single-component, self-stratifying zinc-aluminum bimetallic coating prepared by the aforementioned preparation method, comprising the steps of: diluting the single-component, self-stratifying zinc-aluminum bimetallic coating to a suitable viscosity using the aforementioned mixed solvent, and spraying the coating onto a sandblasted steel plate. Preferably, the sprayed coating has a thickness of 80 μm.

[0053] The following further describes the details in conjunction with specific embodiments.

[0054] Example 1

[0055] A single-component self-stratifying zinc-aluminum bimetallic coating comprises the following components in parts by mass: 20 parts of a thermoplastic resin, 5 parts of a surfactant, 1.0 part of a thickener, 0.5 part of a defoamer, 1 part of a leveling agent, 8 parts of an aluminum-silver paste, 39.5 parts of spherical zinc powder, and 25 parts of a mixed solvent; wherein the mixed solvent comprises 12.5 parts of xylene and 12.5 parts of ethylene glycol butyl ether.

[0056] Among them, the above-mentioned thermoplastic resin is a high molecular thermoplastic epoxy resin (8180 from Chemical Link Polymer); the above-mentioned surfactant is a condensate of octylphenol and ethylene oxide (OP-15); the above-mentioned thickener is a thickener containing sodium polyamide (Aiox AT-720); the above-mentioned defoaming agent is a polyether siloxane copolymer emulsion containing fumed silica (Tegofoamex 810 from Evonik Chemical); the above-mentioned leveling agent is a silicone leveling agent (AFCONA-3758); the above-mentioned spherical zinc powder is a 1000-mesh spherical zinc powder; and the above-mentioned aluminum paste is a flaky aluminum powder coated with sodium stearate (high-floating aluminum paste 2510).

[0057] Comparative Example 1

[0058] The difference between this comparative example and Example 1 is that no surfactant is added, the mixed solvent is 30 parts, wherein the mixed solvent contains 15 parts of xylene and 15 parts of ethylene glycol butyl ether. Other parameters and steps are the same as Example 1.

[0059] Comparative Example 2

[0060] The difference between this comparative example and Example 1 is that the mixed solvent contains 20 parts of xylene and 5 parts of ethylene glycol butyl ether. Other parameters and steps are the same as those in Example 1.

[0061] Performance check and result analysis:

[0062] The coatings prepared in Example 1 and Comparative Examples 1-2 were sprayed onto sandblasted steel plates using the same method. The thickness of the coatings was 80 μm. The sandblasted steel plates sprayed with the coatings were placed in the open air for one week before testing their relevant properties. The relevant properties are shown in Table 1 below:

[0063] Table 1:

[0064]

[0065]

[0066] As shown in Table 1, the corrosion resistance of Comparative Examples 1 and 2 is inferior to that of Example 1, and the coatings prepared in Comparative Examples 1 and 2 both failed the 2000-hour salt spray test. This indicates that the single-component, self-stratified zinc-aluminum bimetallic coating of the present application has superior corrosion resistance compared to Comparative Examples 1-2.

[0067] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A single-component self-stratified zinc-aluminum bimetallic coating, characterized in that: The formula of the single-component self-stratified zinc-aluminum bimetallic coating includes, in parts by mass: 20-25 parts of thermoplastic resin, 5-8 parts of surfactant, 0.5-1.0 part of thickener, 0.2-0.5 part of defoamer, 0.5-1 part of leveling agent, 5-10 parts of aluminum-silver paste, 38-40 parts of spherical zinc powder, and 25-30 parts of mixed solvent; wherein, the mixed solvent includes xylene and ethylene glycol butyl ether; wherein, the film-forming temperature of the thermoplastic resin is 35-60°C, and the thermoplastic resin is a polymer thermoplastic phenoxy resin or a polymer thermoplastic epoxy resin; the aluminum-silver paste is flaky aluminum powder coated with sodium stearate; the mass ratio of xylene and ethylene glycol butyl ether is 1:1 to 1:2; the leveling agent includes any one or two of a silicone leveling agent and an acrylic leveling agent; and the surfactant is a condensate of octylphenol and ethylene oxide.

2. The single-component self-stratifying zinc-aluminum bimetallic coating according to claim 1, characterized in that: The spherical zinc powder is spherical zinc powder with a mesh size of 1000 or more; the particle size of the flaky aluminum powder is 3 μm-7 μm.

3. The single-component self-stratified zinc-aluminum bimetallic coating according to claim 1, characterized in that: The thickener comprises any one or more of polyurea, sodium polyamide, and bentonite; and the defoamer is a polyether siloxane copolymer emulsion containing fumed silica.

4. The method for preparing a single-component self-stratified zinc-aluminum bimetallic coating according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step 1: Put aluminum paste and surfactant into a grinder and grind them thoroughly to obtain a paste-like hydrophilic aluminum paste with high floating value; Step 2: Add xylene to the paste-like hydrophilic high-floating value aluminum-silver paste and stir evenly, add thickener and stir evenly, add defoamer and stir evenly, add leveling agent and stir evenly, add thermoplastic resin and stir evenly, add spherical zinc powder and stir evenly, add ethylene glycol butyl ether and stir evenly, continue to disperse evenly for a certain period of time to obtain a single-component self-stratified zinc-aluminum bimetallic coating.

5. Use of the single-component self-stratifying zinc-aluminum bimetallic coating according to any one of claims 1 to 3 or the single-component self-stratifying zinc-aluminum bimetallic coating prepared by the preparation method according to claim 4, characterized in that: The following steps are involved: The single-component self-stratified zinc-aluminum bimetallic coating is diluted to a suitable viscosity by using the mixed solvent, and then sprayed onto a sandblasted steel plate.

6. The use according to claim 5, characterized in that The sprayed film thickness was 80 μm.

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