A water-based protective agent for nickel-phosphorus alloy coatings, and its preparation method and application

Abstract

The present invention discloses a water-based protective agent for nickel-phosphorus alloy coatings, a preparation method, and applications. The water-based protective agent comprises the following components by weight: 50 to 150 parts of amide, 30 to 100 parts of liquid rosin derivatives, 10 to 100 parts of sebacic acid ester, 5 to 50 parts of organic phosphates, 5 to 50 parts of organic borates, 1 to 20 parts of nonionic surfactants, 0.1 to 10 parts of passivators, and 500 to 900 parts of water. The water-based protective agent can passivate the coating and form a colorless, continuous, dense, hydrophobic, and corrosion-inhibiting thin film on the surface of the coating, sealing the coating pores and significantly improving the salt spray corrosion resistance of the coating without affecting the surface energy and welding performance of the coating. As a water-based system, the overall system is more environmentally friendly.

Description

Technical Field

[0001] The present invention relates to the field of alloy coating protective agents, in particular to an aqueous protective agent for nickel-phosphorus alloy coatings, a preparation method and an application thereof. Background Art

[0002] Chemically plated nickel-phosphorus alloy coatings not only have a bright appearance, but also have excellent hardness, corrosion resistance, wear resistance, certain magnetism and weldability. Therefore, they are widely used in aerospace, military industry, petrochemical industry, automobile and shipbuilding, electronics, communications and other fields. However, nickel-phosphorus alloy coatings are easily oxidized and darkened in humid atmosphere or sulfur-containing environment, which affects the appearance. In particular, for chemically plated nickel-phosphorus alloy coatings with a relatively thin thickness (less than 10 μm), pinholes are inevitable in the coating due to the influence of the substrate material, plating solution composition and process conditions. Nickel-phosphorus alloy coatings are anodic to most substrates such as iron, aluminum and copper. The presence of pinholes can easily cause the oxidizing medium in the external environment to invade the coating, accelerate substrate corrosion, and make the coating lose its protective effect. Therefore, chemically plated nickel-phosphorus alloy coatings usually need to be protected to improve the corrosion resistance and anti-discoloration performance of the coating.

[0003] Traditional nickel-phosphorus alloy coating protection processes use chromate passivation to passivate the surface. While this provides good coating protection, hexavalent chromium ions are highly toxic, carcinogenic, and environmentally harmful, leading to their gradual ban. Currently, chromium-free, environmentally friendly nickel-phosphorus alloy coating protective agents are available in two types: water-based and oil-based.

[0004] Oily protective agents, such as mineral oil or vegetable oil, can form an oil film on the surface of the coating, creating a strong physical barrier and improving the corrosion resistance and anti-oxidative discoloration properties of nickel-phosphorus alloy coatings. However, this oil film can hinder subsequent processing and assembly of workpieces. For example, the corrosion-resistant electroplating protective agent disclosed in patent CN107313090A contains isohexanediol and mineral oil. After sealing the nickel plating, the coating needs to be heated and dried, and the oil film formed by the sealing process is detrimental to subsequent processing steps. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above technical deficiencies, provide an aqueous protective agent for nickel-phosphorus alloy coatings, and a preparation method and application thereof, to solve the technical problems in the prior art of nickel-phosphorus alloy coating protective agents being highly toxic or not conducive to subsequent processing.

[0006] In order to achieve the above technical objectives, the technical solution provided by the present invention is:

[0007] In a first aspect, the present invention provides an aqueous protective agent for nickel-phosphorus alloy plating, the aqueous protective agent comprising the following components in parts by mass: 50 to 150 parts of amide, 30 to 100 parts of liquid rosin derivatives, 10 to 100 parts of sebacic acid ester, 5 to 50 parts of organic phosphate ester, 5 to 50 parts of organic borate ester, 1 to 20 parts of nonionic surfactant, 0.1 to 10 parts of passivating agent, and 500 to 900 parts of water.

[0008] In a second aspect, the present invention provides a method for preparing an aqueous protective agent for nickel-phosphorus alloy plating, comprising the following steps: mixing amide, liquid rosin derivative, sebacic acid ester, organic phosphate ester, organic boric acid ester, nonionic surfactant and passivating agent in sequence, and stirring evenly to obtain the aqueous protective agent.

[0009] In a third aspect, the present invention provides an application of an aqueous protective agent as a protective agent for a nickel-phosphorus alloy coating; the aqueous protective agent acts on the nickel-phosphorus alloy coating by immersion or spraying.

[0010] Compared with the prior art, the present invention has the following beneficial effects:

[0011] The water-based protective agent of the present invention passivates the coating and forms a colorless, continuous, dense, hydrophobic, and corrosion-inhibiting film on the surface of the coating, sealing the coating's pores and significantly improving its salt spray corrosion resistance. Furthermore, the protective agent does not affect the coating's surface energy or welding properties, ensuring the coating's appearance, conductivity, and weldability. Furthermore, the water-based protective agent of the present invention does not contain highly toxic hexavalent chromium ions, making it a water-based system and more environmentally friendly. After treatment with the water-based protective agent of the present invention, the coating can be air-dried before subsequent processing, reducing energy consumption and improving production efficiency. DETAILED DESCRIPTION

[0012] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0013] The present invention provides an aqueous protective agent for nickel-phosphorus alloy coatings, which is used to solve the problem of insufficient salt spray corrosion resistance of the coating in the prior art. At the same time, the present invention also provides a method for preparing the aqueous protective agent. The aqueous protective agent of the present invention can passivate the coating and improve the corrosion resistance of the coating itself. At the same time, it can also form a transparent adsorption film on the surface of the coating, close the pores on the surface of the coating, improve the protection of the coating to the substrate, and thus improve the overall salt spray corrosion resistance of the product. In addition, the aqueous protective agent of the present invention can also neutralize the acidic plating solution remaining on the surface of the coating and improve the surface state of the coating. The colorless passivation film formed by passivation and the colorless adsorption film formed by closure can also enable the coating to obtain excellent anti-discoloration and anti-fingerprint properties, so that the bright appearance of the coating can be maintained for a long time even in harsh environments; at the same time, the aqueous protective agent of the present invention does not contain highly toxic hexavalent chromium ions, is a water-based system, and is more environmentally friendly as a whole; the protective film formed on the nickel-plated surface can be naturally dried in the air without affecting subsequent processing.

[0014] In a first aspect, the present invention provides an aqueous protective agent for nickel-phosphorus alloy plating, wherein the aqueous protective agent comprises the following components in parts by weight: 50 to 150 parts of amide, 30 to 100 parts of liquid rosin derivatives, 10 to 100 parts of sebacic acid ester, 5 to 50 parts of organic phosphate ester, 5 to 50 parts of organic borate ester, 1 to 20 parts of nonionic surfactant, 0.1 to 10 parts of passivating agent, and 500 to 900 parts of water.

[0015] The main mechanism of action of the present invention is as follows: adding a passivating agent to the aqueous protective agent can increase the oxidation potential of the coating, achieve a passivating effect, and improve the corrosion resistance of the coating itself. The reason for adding amide to the aqueous protective agent is, firstly, that the added amide has a weak alkalinity, which can play a role in regulating and stabilizing the pH of the working solution, and also helps to remove acidic plating solution residues on the surface of the coating. Secondly, the added amide has solubilizing properties, which can increase the solubility of liquid rosin derivatives and sebacic acid esters in water. Liquid rosin derivatives and sebacic acid esters are the main film-forming substances of the above-mentioned aqueous protective agent, which can form a thin and dense protective film on the surface of the coating, improving the salt spray corrosion resistance of the coating without changing the metallic luster of the coating. The surfactant added to the aqueous protective agent can enhance the wettability and dispersibility of the aqueous protective agent. The organic phosphate in the aqueous protective agent acts as a penetrant, which can penetrate into the pores of the nickel-phosphorus coating and improve the sealing effect of the protective agent on the pores. The organic borate in the water-based protective agent acts as a corrosion inhibitor, which can not only improve the corrosion resistance of the coating, but also enter the pores under the action of the penetrant to improve the corrosion resistance of the substrate.

[0016] In general, the aqueous protective agent of the present invention can passivate the coating and form a bright and transparent adsorption film on the surface of the nickel-phosphorus alloy coating, thereby sealing the pores on the surface of the coating and significantly improving the salt spray corrosion resistance of the electroplating layer.

[0017] The operating temperature of the above-mentioned aqueous protective agent is in the range of 40 to 80°C, preferably in the range of 60 to 70°C.

[0018] The aqueous protective agent can be applied to the nickel-phosphorus alloy plated workpiece by immersion or spraying, preferably by immersion, with the immersion time being in the range of 1 to 10 minutes, preferably in the range of 2 to 5 minutes.

[0019] In one embodiment of the present invention, the amide is one of formamide, acetamide, and dimethylformamide;

[0020] The nonionic surfactant is at least one of polyethylene glycol 400, Tween 40, and Span-80.

[0021] Preferably, the amide is acetamide; and the nonionic surfactant is polyethylene glycol 400.

[0022] Acetamide is added to the aqueous protective agent to stabilize the pH of the working solution and help neutralize any residual acidic plating solution on the surface of the coating. Compared to other amides, acetamide is the most effective and more compatible with the overall coating. Polyethylene glycol 400, added to the aqueous protective agent, acts as a surfactant, enhancing its wettability and dispersibility. Compared to other surfactants, polyethylene glycol 400 offers the best wetting and dispersing properties and is more compatible with the overall coating.

[0023] In one embodiment of the present invention, the liquid rosin derivative is one or more of tall oil fatty acid, tall oil fatty acid sodium, and tall oil fatty acid amide.

[0024] In one embodiment of the present invention, the sebacic acid ester is dioctyl sebacic acid, dibutyl sebacic acid or diisooctyl sebacic acid.

[0025] Liquid rosin derivatives and sebacic acid esters are the main film-forming substances in water-based protective agents. They can form a thin and dense protective film on the surface of nickel-phosphorus coatings, improving the coating's salt spray corrosion resistance without changing its appearance. Among them, the combination of tall oil fatty acid amide and di-2-ethylhexyl sebacic acid ester is the most effective, and the resulting protective film has the best salt spray corrosion resistance.

[0026] In one embodiment of the present invention, the passivating agent is one or more of salicylic acid, phytic acid, and sodium ethylenediaminetetramethylenephosphate. Adding a passivating agent to the aqueous protective agent can increase the oxidation potential of the coating, achieving a passivating effect and improving the corrosion resistance of the coating itself. Compared to other passivating agents, salicylic acid has a better passivating effect, enabling the coating to achieve a higher oxidation potential and superior corrosion resistance.

[0027] In one embodiment of the present invention, the organic borate is selected from trimethyl borate, triethyl borate, and triisopropyl borate. The organic borate in the aqueous protective agent acts as a corrosion inhibitor, participating in film formation. This not only improves the corrosion resistance of the coating but also, through the action of a penetrant, penetrates pores and enhances the corrosion resistance of the substrate. Overall, triethyl borate exhibits the best corrosion inhibition, resulting in a film with superior corrosion resistance.

[0028] In one embodiment of the present invention, the organic phosphate comprises one of diphenyl phosphate, diethyl phosphate, and phenol ether phosphate. In general, diethyl phosphate has the best penetration effect, forms a denser film, and has the best salt spray corrosion resistance.

[0029] In a second aspect, the present invention provides a method for preparing the above-mentioned water-based protective agent, comprising the following steps:

[0030] Step 1: Add amide and liquid rosin derivative into a container in sequence and stir until clear;

[0031] Step 2: Add sebacic acid ester, organic phosphate ester, and organic borate ester to the container in sequence, stirring until the solution is clear after each addition of the raw materials;

[0032] Step 3: Dissolve the nonionic surfactant and passivating agent in the required amount of deionized water, add them to the container, and stir until the solution is clear and uniform.

[0033] The main advantages of the present invention are:

[0034] (1) The preparation method of the water-based protective agent of the present invention is suitable for industrial large-scale production and has low requirements for production equipment. The container for preparing the above-mentioned water-based protective agent is generally made of stainless steel, polypropylene, polyvinyl chloride, Teflon, etc.

[0035] (2) Compared with existing coating protective agents, the aqueous protective agent prepared by the preparation method of the present invention can firstly remove acidic plating solution residues on the surface of the electroplated layer, improving the cleaning effect and improving the surface condition of the coating; secondly, it can passivate the coating and improve the corrosion resistance of the coating itself; and finally, it can form a colorless, continuous, dense, hydrophobic and corrosion-inhibiting thin film on the surface of the coating, sealing the pores of the coating. The synergistic effect of these three factors significantly improves the salt spray corrosion resistance of the coating, making the salt spray resistance time of the coating reach more than 120 hours.

[0036] (3) Compared with existing oil-based nickel plating protective agents, the water-based protective agent prepared by the preparation method of the present invention is a water-based system, which is more environmentally friendly overall, and does not affect the appearance, welding performance, and electrical conductivity of the coating. The protective film formed by the water-based protective agent on the nickel-plated surface can be dried naturally in the air.

[0037] In summary, the aqueous protective agent of the present invention can passivate the coating and form a colorless, continuous, dense, hydrophobic, and corrosion-inhibiting film on the coating surface, sealing the coating pores and significantly improving the coating's salt spray corrosion resistance. Furthermore, the coating's appearance, weldability, and electrical conductivity are preserved. After treatment with the aqueous protective agent of the present invention, the coating can be air-dried before subsequent processing, improving production efficiency.

[0038] The present invention is further described in detail below through specific examples.

[0039] Example 1

[0040] The invention provides an aqueous protective agent for nickel-phosphorus alloy plating. The aqueous protective agent comprises the following components in parts by weight: 100 parts of amide, 70 parts of liquid rosin derivative, 50 parts of sebacic acid ester, 30 parts of organic phosphate, 30 parts of organic boric acid ester, 10 parts of nonionic surfactant, 5 parts of passivator, and 705 parts of water.

[0041] Specifically, the amide is acetamide;

[0042] The liquid rosin derivative is tall oil fatty acid amide;

[0043] The sebacic acid ester is dioctyl sebacic acid ester;

[0044] The organic borate ester is triethyl borate;

[0045] The organic phosphate is diethyl phosphate.

[0046] The surfactant is polyethylene glycol 400;

[0047] The passivating agent is one or more of salicylic acid, phytic acid, sodium ethylenediaminetetramethylenephosphate, etc.

[0048] The preparation process of the above-mentioned water-based protective agent is as follows:

[0049] Step 1, adding amide to a container;

[0050] Step 2: Add liquid rosin derivative and stir until clear;

[0051] Step 3: Add sebacic acid ester and stir until clear;

[0052] Step 4: Add organic phosphate and organic borate, and stir until clear;

[0053] Step 5: Add the required amount of deionized water, surfactant and passivating agent to another container, and stir to clarify;

[0054] Step 6: Add the solution in step 5 to the container in step 4 and stir until clear.

[0055] Examples 1 to 3 and Comparative Examples 1 to 4

[0056] The specific compositions of the aqueous protective agents of Examples 1 to 3 and Comparative Examples 1 to 4 are shown in Table 1, and the preparation steps are the same as those of Example 1.

[0057] Table 1 Specific composition of aqueous protective agents of Examples 1 to 3 and Comparative Examples 1 to 4

[0058]

[0059]

[0060] The specific types and proportions of raw materials used in Examples 1 to 3 are different.

[0061] Compared with Example 1, Comparative Example 1 and Comparative Example 2 omitted sebacic acid ester and liquid rosin derivative respectively in terms of raw materials.

[0062] Compared with Example 1, Comparative Examples 3 and 4 omitted the organic borate and organic phosphate, respectively, in terms of raw materials.

[0063] Comparative Example 5

[0064] The chromium-free passivation described in the literature (Tang Feng, Hu Guanghui, Huang Hua'e, et al. Research on chromium-free passivation process of chemical nickel plating layer [J]. Electroplating and Finishing, 2012, 34(5): 28-33.) has a passivation solution composition of: 10 g / L sodium hydroxide, 15 g / L sodium carbonate, 50 g / L sodium phosphate, 5 g / L sodium silicate, and 1 g / L potassium permanganate.

[0065] Comparative Example 6

[0066] The test materials were not subjected to any protective treatment.

[0067] The test materials used in Examples 1 to 3 and Comparative Examples 1 to 6 were all carbon steel substrates coated with a 10 μm electroless nickel-phosphorus coating. Examples 1 to 3 and Comparative Examples 1 to 5 all employed an immersion treatment for protection, while Comparative Example 6 did not undergo any protection. The specific process is shown in Table 2.

[0068] Table 2 Treatment conditions of the test pieces with aqueous protective agents of Examples 1 to 3 and Comparative Examples 1 to 6

[0069]

[0070] After being treated with the aqueous protective agent of Examples 1 to 3 and Comparative Examples 1 to 5, the coatings were naturally dried or washed and blown dry, and then the neutral salt spray resistance time of the coatings was evaluated using GB5938-86 "Test Methods for Corrosion Resistance of Metal Coatings and Chemically Treated Coatings of Light Industrial Products".

[0071] The performance test results of the water-based protective agents of Examples 1 to 3 and Comparative Examples 1 to 6 are shown in Table 3.

[0072] Table 3 Performance test results of water-based protective agents of Examples 1 to 3 and Comparative Examples 1 to 6

[0073]

[0074] As can be seen from the data in Table 3, Comparative Example 6 is unprotected and has a neutral salt spray resistance time of only 48 hours. The neutral salt spray resistance time of the coatings treated with the protective agent in Examples 1 to 3 all reaches more than 120 hours, indicating that the protective agent of the present invention can significantly improve the corrosion resistance of the coating.

[0075] In addition, the surface of the coating treated with the protective agent in Examples 1 to 3 and Comparative Examples 1 to 4 still maintains a bright appearance and has the same conductivity and solderability as the bare coating.

[0076] Compared with Example 1, Comparative Example 1 and Comparative Example 2 reduced one of the liquid rosin derivative and sebacic acid ester respectively, and their corrosion resistance was significantly reduced, indicating that the liquid rosin derivative and sebacic acid ester have a synergistic film-forming effect, and the synergistic film formation of the two can provide a denser and safer protective film for the coating.

[0077] Compared with Example 1, Comparative Examples 3 and 4 reduced one of the organic borate and organic phosphate, respectively, and their corrosion resistance was significantly reduced, indicating that organic borate and organic phosphate also have a synergistic protective effect. As a corrosion inhibitor, organic borate can enter the pores of the coating under the synergistic action of the penetrant organic phosphate, thereby improving the corrosion resistance of the substrate.

[0078] Comparative Example 5 is another chromium-free passivation treatment, and the neutral salt spray resistance time is 96 hours, which shows that the corrosion resistance of the protective agent of the present invention is significantly better than that of the chromium-free passivation agent described in Comparative Example 5.

[0079] In summary, the raw materials of the water-based protective agent of the present invention include amide, liquid rosin derivative, sebacic acid ester, organic phosphate, organic boric acid ester, non-ionic surfactant, passivating agent and water; the preparation method is to mix the various raw materials in order and then stir them until they are uniform. The present invention solves the problem of poor corrosion resistance of the coating in the prior art. The prepared water-based protective agent can not only neutralize the plating solution residue on the surface of the coating and improve the cleaning efficiency, but also passivate the coating on the surface of the coating and improve the corrosion resistance of the coating itself. It can also form a colorless, transparent, continuous, dense, hydrophobic and corrosion-inhibiting thin film on the surface of the coating, seal the pores of the coating, and thus improve the salt spray corrosion resistance and color change resistance of the coating. In addition, the protective agent of the present invention does not affect the appearance, conductivity and solderability of the coating. Therefore, the present invention effectively overcomes the various shortcomings of the prior art such as chromate passivation being carcinogenic and chromium-free passivation having insufficient corrosion resistance, and has high industrial utilization value.

[0080] The specific embodiments of the present invention described above do not limit the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A water-based protective agent for nickel-phosphorus alloy coating, characterized in that: The aqueous protective agent comprises the following components by weight: 50 to 150 parts of amide, 30 to 100 parts of liquid rosin derivative, 10 to 100 parts of sebacic acid ester, 5 to 50 parts of organic phosphate, 5 to 50 parts of organic boric acid ester, 1 to 20 parts of nonionic surfactant, 0.1 to 10 parts of passivating agent, and 500 to 900 parts of water; The amide is formamide, acetamide or dimethylformamide; The liquid rosin derivative is one or more of tall oil fatty acid, tall oil fatty acid sodium, and tall oil fatty acid amide; The sebacic acid ester is dioctyl sebacic acid, dibutyl sebacic acid or diisooctyl sebacic acid; The organic borate ester is trimethyl borate, triethyl borate or triisopropyl borate; The organic phosphate is diphenyl phosphate, diethyl phosphate or phenol ether phosphate; The passivating agent is one or more of salicylic acid, phytic acid and sodium ethylenediaminetetramethylenephosphate.

2. The aqueous protective agent for nickel-phosphorus alloy coating according to claim 1, characterized in that: The nonionic surfactant is at least one of polyethylene glycol 400, Tween 40 and Span 80.

3. The method for preparing the aqueous protective agent according to any one of claims 1 to 2, characterized in that: The following steps are involved: The amide, liquid rosin derivative, sebacic acid ester, organic phosphate, organic boric acid ester, nonionic surfactant and passivating agent are mixed in sequence and stirred evenly to obtain the water-based protective agent.

4. Use of the aqueous protective agent according to any one of claims 1 to 2 as a protective agent for nickel-phosphorus alloy coatings.

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