Copper casting blackening agent and preparation process thereof

Abstract

The application discloses a kind of blackening agent for cast copper and its preparation process.The blackening agent for cast copper includes the following components by weight: 2-8 parts of selenium dioxide, 6-10 parts of copper sulfate, 5-10 parts of stabilizer, 0.5-1 part of complexing agent, 1-2 parts of wetting agent, 2-5 parts of preservative, 1-2 parts of oxidation promoter and 500-1500 parts of water.The application also provides a preparation process thereof.The process is relatively simple, short and low-energy consumption, and the most important advantage is that the brass castings treated by the process do not have the phenomenon of acid reflux, and the surface of the castings does not appear rust spots, corrosion and other phenomena, and the treated corrosion resistance and wear resistance are better.

Description

Technical Field

[0001] This invention relates to the field of metal plating technology, and in particular to a copper blackening agent and its preparation process. Background Technology

[0002] Blackening processes create a uniform black or near-black hue on the surface of copper artifacts, contrasting sharply with the natural golden luster of copper. This enhances the visual depth and artistic appeal of the artifacts, giving them a more classical and culturally rich feel, catering to diverse aesthetic preferences and decorative styles. For example, blackening can better replicate the texture of ancient bronze artifacts, creating an ancient and mysterious atmosphere. The black surface also better highlights the lines, textures, and carvings of the artifacts, making their shapes more three-dimensional and vivid. The exquisite craftsmanship in the details is fully showcased, enhancing the overall aesthetic value. After blackening, a dense black protective film forms on the surface of the copper artifact. This film, primarily composed of copper oxides such as CuO and Cu2O, effectively isolates the copper substrate from oxygen, moisture, carbon dioxide, sulfides, and other pollutants, preventing further oxidation and rust. This extends the lifespan of the artifact, ensuring it maintains a good appearance and performance under various environmental conditions. Compared to untreated copper surfaces, blackened copper artifacts exhibit significantly improved corrosion resistance. Because the blackening process improves the corrosion resistance and wear resistance of copper handicrafts, it reduces the need for repair and refurbishment due to surface damage, thereby reducing the cost and effort required for long-term maintenance, making them more practical and economical.

[0003] CN109207980A discloses a novel method for blackening brass surfaces through oxidation, primarily encompassing two main stages: surface cleaning and surface blackening. For surface cleaning, a unique ultrasonic cleaning technology is employed, combined with a specially formulated degreasing solvent and pure water for parallel cleaning. Subsequently, a specialized blackening solution prepared from sodium persulfate and sodium hydroxide is used for blackening treatment. This method significantly improves the problem of flaking of the blackened layer on brass parts and greatly enhances the adhesion of the blackened layer.

[0004] CN112111734A discloses a blackening process for copper products, comprising the following steps: degreasing and cleaning to remove surface stains; overflow rinsing to further rinse away residual stains; acid pickling and activation to remove surface oxides; overflow rinsing again; performing the first blackening process to form a light-colored black layer; overflow rinsing; implementing the second blackening process to build a stable black layer; another overflow rinsing; sealing treatment to form an anti-oxidation film on the outside of the finished black layer; continued overflow rinsing; drying; and vibration grinding to remove surface dust and impurities. This process allows the blackened layer of the product to pass long-term salt spray tests without copper leakage, and maintains its color for a long time under continuous tests such as high temperature, high humidity, thermal shock, and low temperature cold shock. The product also possesses excellent anti-reflective and anti-refractive properties.

[0005] The most common blackening techniques for cast copper surfaces on the market mostly employ chemical coloring oxide film preparation methods or manual painting for surface treatment. Traditional blackening processes often use strong acids to generate a black surface film. However, in actual production, it has been found that after blackening the casting surface and then washing with water and drying, acid backflow still occurs, leading to rust spots and corrosion on the casting surface. Furthermore, traditional blackening processes require heating, which is slow and time-consuming. Summary of the Invention

[0006] In view of the above-mentioned deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a blackening agent for cast copper and its preparation process.

[0007] Current blackening processes can be divided into traditional high-temperature alkaline boiling and room-temperature blackening processes. Compared with the former, the latter has a shorter processing time, higher work efficiency, and lower pollution level. This invention provides a blackening agent for cast copper. The blackening process using this agent is relatively simple, has a short process, and low energy consumption. The most important advantage is that brass castings treated with this blackening process do not exhibit acid backflow, and the surface of the castings will not show rust spots or corrosion.

[0008] Selenium dioxide is one of the main active ingredients in blackening agents, forming a uniform black copper selenide film on the copper surface. This copper selenide film exhibits excellent adhesion and corrosion resistance, effectively preventing copper oxidation. Copper sulfate and selenium dioxide are the main components involved in film formation. Simultaneously, copper sulfate can form stable complexes with the complexing agent, promoting a uniform reaction. The wetting agent reduces the surface tension of the blackening agent, allowing it to better wet the copper surface and ensuring uniform coverage. The oxidation accelerator accelerates the oxidation reaction on the copper surface, shortening the blackening time and improving blackening efficiency. The adhesion accelerator enhances the adhesion between the blackened layer and the copper surface, preventing the blackened layer from peeling off. Compared to existing blackening agents on the market, this process offers advantages such as rapid blackening at room temperature, accurate blackening color, short processing time, high wear resistance of the blackened film, simple production process, and low cost, enabling mass production.

[0009] Because the currently generated oxide film has poor adhesion to copper, the blackening layer is prone to peeling off and the anti-corrosion and anti-rust effect is also affected. Therefore, this invention provides a corrosion inhibitor that improves the adhesion of polybenzoxazine to the copper surface by modifying it. Moreover, the benzotriazole group in the modifier can also enhance the anti-corrosion performance of the blackening agent. When the modifier contains catechol groups, the catechol groups can form coordination bonds with metal atoms, thus improving the adhesion. The benzotriazole groups can be adsorbed onto the metal surface through van der Waals forces, forming a dense physical barrier that prevents corrosive media (such as water, oxygen, chloride ions, etc.) from contacting the metal. This is not only beneficial for corrosion prevention but also further enhances the adhesion. The nitrogen atoms in the benzotriazole molecule react with metal ions on the metal surface to generate a dense metal-benzotriazole complex. This complex film can prevent further oxidation of the metal, forming a passivated state, thereby achieving the effect of anti-corrosion and anti-rust.

[0010] To achieve the above objectives, the present invention provides a blackening agent for cast copper, comprising the following components in parts by weight: 2-8 parts selenium dioxide, 6-10 parts copper sulfate, 5-10 parts stabilizer, 0.5-1 part complexing agent, 1-2 parts wetting agent, 2-5 parts corrosion inhibitor, 1-2 parts oxidation accelerator, and 500-1500 parts water.

[0011] The method for preparing the preservative includes the following steps:

[0012] X1. Under an inert atmosphere, paraformaldehyde and sodium hydroxide aqueous solution are added to chloroform, heated to 60-70°C, and then polyetheramine is added. Bisphenol A is added after heating to 80-90°C. After stirring for 8-10 hours, the mixture is concentrated and purified for use in the next step.

[0013] X2. Add the product from the previous step to N,N-dimethylformamide, then add the modifier, stir for 1-2 hours, and then concentrate to remove the solvent to obtain the final product.

[0014] Furthermore, the mass ratio of the paraformaldehyde to the sodium hydroxide aqueous solution, chloroform, polyetheramine, and bisphenol A is 1:0.1-0.5:20-50:2-5:1-3.

[0015] Furthermore, the mass ratio of the product from the previous step to N,N-dimethylformamide and the modifier is 1:5 to 15:1 to 3.

[0016] Furthermore, the modifier is one of 2H-benzotriazole-5,6-diol, catechol, or 1-methyl-5-benzotriazole.

[0017] Furthermore, the stabilizer is phosphoric acid.

[0018] Furthermore, the complexing agent is sodium citrate.

[0019] Furthermore, the wetting agent is polyethylene glycol.

[0020] Furthermore, the oxidation promoter is potassium chlorate.

[0021] A preparation process for a copper casting blackening agent includes the following steps:

[0022] Mix all components evenly according to the formula to obtain the copper blackening agent.

[0023] The beneficial effects of this invention are:

[0024] 1. The blackening process using this method is relatively simple, has a short process time, and low energy consumption. The most important advantage is that brass castings treated with this blackening process do not exhibit acid backflow, and the surface of the castings will not show rust spots or corrosion.

[0025] 2. This invention provides a corrosion inhibitor that improves the adhesion of polybenzoxazine to the copper surface by modifying it, resulting in a more corrosion-resistant and wear-resistant film on the cast copper after blackening treatment. Detailed Implementation

[0026] 2H-benzotriazole-5,6-diol, CAS: 95035-38-4.

[0027] 1-Methyl-5-benzotriazolol, CAS: 82132-01-2.

[0028] Polyetheramine, Mw=2000, Hubei Qifei Pharmaceutical & Chemical Co., Ltd.

[0029] Polyethylene glycol, PEG-4000, Lotte Chemicals, South Korea.

[0030] Paraformaldehyde, purity: 96%, ERCROS, Spain.

[0031] Example 1

[0032] A process for preparing a blackening agent for cast copper includes the following steps, in parts by weight:

[0033] Add 5 parts selenium dioxide, 8 parts copper sulfate, 9 parts phosphoric acid, 0.8 parts sodium citrate, 1.5 parts polyethylene glycol, 3 parts preservative, and 1 part potassium chlorate to 1000 parts water and mix well.

[0034] The method for preparing the preservative includes the following steps, in parts by weight:

[0035] X1. Under a nitrogen atmosphere, 1 part of paraformaldehyde and 0.2 parts of 1 mol / L sodium hydroxide aqueous solution were added to 30 parts of chloroform. The mixture was heated to 65°C and then 3.5 parts of polyetheramine were added. The mixture was heated to 85°C and then 2 parts of bisphenol A were added. After stirring for 8 hours, the mixture was concentrated and purified by column chromatography for the next step.

[0036] X2. Add 1 part of the product from the previous step to 10 parts of N,N-dimethylformamide, then add 2 parts of catechol, stir for 1 hour, and concentrate to remove the solvent to obtain the final product.

[0037] Example 2

[0038] A process for preparing a blackening agent for cast copper includes the following steps, in parts by weight:

[0039] Add 5 parts selenium dioxide, 8 parts copper sulfate, 9 parts phosphoric acid, 0.8 parts sodium citrate, 1.5 parts polyethylene glycol, 3 parts preservative, and 1 part potassium chlorate to 1000 parts water and mix well.

[0040] The method for preparing the preservative includes the following steps, in parts by weight:

[0041] X1. Under a nitrogen atmosphere, 1 part of paraformaldehyde and 0.2 parts of 1 mol / L sodium hydroxide aqueous solution were added to 30 parts of chloroform. The mixture was heated to 65°C and then 3.5 parts of polyetheramine were added. The mixture was heated to 85°C and then 2 parts of bisphenol A were added. After stirring for 8 hours, the mixture was concentrated and purified by column chromatography for the next step.

[0042] X2. Add 1 part of the product from the previous step to 10 parts of N,N-dimethylformamide, then add 2 parts of 1-methyl-5-benzotriazolol, stir for 1 hour, and concentrate to remove the solvent to obtain the final product.

[0043] Example 3

[0044] A process for preparing a blackening agent for cast copper includes the following steps, in parts by weight:

[0045] Add 5 parts selenium dioxide, 8 parts copper sulfate, 9 parts phosphoric acid, 0.8 parts sodium citrate, 1.5 parts polyethylene glycol, 3 parts preservative, and 1 part potassium chlorate to 1000 parts water and mix well.

[0046] The method for preparing the preservative includes the following steps, in parts by weight:

[0047] X1. Under a nitrogen atmosphere, 1 part of paraformaldehyde and 0.2 parts of 1 mol / L sodium hydroxide aqueous solution were added to 30 parts of chloroform. The mixture was heated to 65°C and then 3.5 parts of polyetheramine were added. The mixture was heated to 85°C and then 2 parts of bisphenol A were added. After stirring for 8 hours, the mixture was concentrated and purified by column chromatography for the next step.

[0048] X2. Add 1 part of the product from the previous step to 10 parts of N,N-dimethylformamide, then add 2 parts of 2H-benzotriazole-5,6-diol, stir for 1 hour, and concentrate to remove the solvent to obtain the final product.

[0049] Compare with Example 1

[0050] A process for preparing a blackening agent for cast copper includes the following steps, in parts by weight:

[0051] Add 5 parts selenium dioxide, 8 parts copper sulfate, 9 parts phosphoric acid, 0.8 parts sodium citrate, 1.5 parts polyethylene glycol, and 1 part potassium chlorate to 1000 parts water and mix well.

[0052] Compare with Example 2

[0053] A process for preparing a blackening agent for cast copper includes the following steps, in parts by weight:

[0054] Add 5 parts selenium dioxide, 8 parts copper sulfate, 9 parts phosphoric acid, 0.8 parts sodium citrate, 1.5 parts polyethylene glycol, 3 parts preservative, and 1 part potassium chlorate to 1000 parts water and mix well.

[0055] The method for preparing the preservative includes the following steps, in parts by weight:

[0056] Under a nitrogen atmosphere, 1 part of paraformaldehyde and 0.2 parts of 1 mol / L sodium hydroxide aqueous solution were added to 30 parts of chloroform. The mixture was heated to 65°C and then 3.5 parts of polyetheramine were added. The mixture was heated to 85°C and then 2 parts of bisphenol A were added. After stirring for 8 hours, the mixture was concentrated and purified by column chromatography to obtain the final product.

[0057] Test Example 1

[0058] The surface of the brass casting is ground and polished to remove the oxide layer and oil stains, then sanded with 1000-grit sandpaper. It is then rinsed with clean water and dried. The casting is then immersed in a blackening agent for 5 minutes, removed, rinsed with clean water, and scrubbed with a scouring pad to remove surface oxide dust. It is then placed in an oven and baked at 140℃ for 20 minutes. After removal, it is rubbed and baked at 160℃ for 20 minutes. The treated part is then immersed in a clear oil solution to seal it and allowed to air dry, resulting in the blackened brass casting.

[0059] The corrosion resistance of blackened brass castings was tested according to QB / T3824-1999, "Test Methods for Chemical Protective Coatings of Ferrous Metals in Light Industrial Products - Immersion Drop Method". The blackened samples were rinsed thoroughly with clean water, then cleaned with anhydrous ethanol. The samples were then immersed in a 3% copper sulfate solution, and the corrosion resistance of the blackened film was measured by the time it took for no change to occur on the surface of the blackened film.

[0060] Table 1. Corrosion resistance test results of blackened brass castings.

[0061] Experimental protocol Corrosion resistance time / min Example 1 11 Example 2 9 Example 3 8 Compare with Example 1 4 Compare with Example 2 6

[0062] The ability of a chemically protected ferrous metal sample to resist corrosive environments is assessed by immersing it in a specific corrosive medium or by applying corrosive solutions to its surface. The presence and extent of corrosion (such as rust, discoloration, pitting) on ​​the metal surface are observed within a specified time. During testing, if the chemically protected layer has pores, cracks, or other defects, the corrosive medium can more easily penetrate the metal substrate and trigger a corrosion reaction. In the immersion drop test, if the adhesion between the coating and the ferrous metal substrate is weak, the coating may blister or peel off under the influence of the corrosive medium. Therefore, this method can also indirectly reflect the bonding strength between the coating and the substrate to some extent. Ensuring good adhesion between the coating and the metal substrate is one of the key factors in ensuring product performance.

[0063] As shown in Table 1, the addition of preservatives significantly improves the corrosion resistance of the samples after blackening treatment. The sample in Comparative Example 1 showed a significantly shorter change time than the example. Although preservatives were added in Comparative Example 2, the prepared polyphenyloxazine, while possessing certain anti-corrosion properties, had poor adhesion to the substrate due to its rigidity, resulting in a shorter corrosion resistance time. In the examples, the addition of modifiers allowed the catechol and benzotriazole groups to interact with the metal surface. The catechol groups formed coordinate bonds with metal atoms, thus improving adhesion. The benzotriazole groups adsorbed onto the metal surface through van der Waals forces, forming a dense physical barrier that prevents corrosive media (such as water, oxygen, chloride ions, etc.) from contacting the metal. This not only improves corrosion resistance but also further enhances adhesion. The nitrogen atoms in the benzotriazole molecule reacted with metal ions on the metal surface to generate a dense metal-benzotriazole complex. This complex film prevented further oxidation of the metal, forming a passivated state. Examples 1 and 2 contain catechol and benzotriazole groups, respectively, while Example 3 contains both catechol and benzotriazole groups. Therefore, Example 3 has the longest corrosion resistance time. This may be because the corrosion inhibitor has the best adhesion to the surface of the brass casting, and the physical adsorption of benzotriazole and the passivation layer of the complex work together to provide good corrosion protection.

[0064] Test Example 2

[0065] The surface of the brass casting is ground and polished to remove the oxide layer and oil stains, then sanded with 1000-grit sandpaper. It is then rinsed with clean water and dried. The casting is then immersed in a blackening agent for 5 minutes, removed, rinsed with clean water, and scrubbed with a scouring pad to remove surface oxide dust. It is then placed in an oven and baked at 140℃ for 20 minutes. After removal, it is rubbed and baked at 140℃ for another 20 minutes. The treated part is then immersed in clear oil for sealing and air-dried to obtain the blackened brass casting.

[0066] Place a layer of sandpaper on the blackened sample, put a 100g weight on the sandpaper, and drag the sandpaper back and forth on the sample surface until the substrate is exposed at a certain point on the sample. The abrasion resistance of the blackened film is measured by the actual number of abrasions.

[0067] Table 2. Results of abrasion resistance test on blackened brass castings.

[0068] Experimental protocol Abrasion resistance / times Example 1 263 Example 2 220 Example 3 214 Compare with Example 1 151 Compare with Example 2 182

[0069] The abrasion resistance test can directly evaluate the surface abrasion resistance of the blackened film. If the blackened film remains intact after multiple abrasions, it indicates good abrasion resistance, capable of resisting physical wear in actual use and protecting the substrate material from damage. The abrasion resistance test can also indirectly evaluate the adhesion between the blackened film and the substrate. Good adhesion is a key factor in maintaining the integrity of the coating and providing effective protection. If the blackened film easily detaches during abrasion, it indicates insufficient adhesion; if the blackened film can withstand multiple abrasions without detaching, it indicates good adhesion and effective bonding to the substrate surface.

[0070] As can be seen from Table 2, the brass castings treated with blackening in the embodiments of the present invention have better abrasion resistance. This may be because the modified corrosion inhibitor can interact with the metal surface. The catechol group can form a coordinate bond with the metal atom, thus improving the adhesion. The benzotriazole group can be adsorbed on the metal surface by van der Waals forces to form a dense physical barrier, preventing corrosive media (such as water, oxygen, chloride ions, etc.) from contacting the metal. This is not only beneficial for corrosion protection, but can also further improve the adhesion. Therefore, the film formed by blackening can better adhere to the surface of the brass castings.

[0071] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A blackening agent for cast copper, characterized in that, It comprises the following components in parts by weight: 2-8 parts selenium dioxide, 6-10 parts copper sulfate, 5-10 parts stabilizer, 0.5-1 part complexing agent, 1-2 parts wetting agent, 2-5 parts preservative, 1-2 parts oxidation promoter, and 500-1500 parts water. The method for preparing the preservative includes the following steps: X1. Under an inert atmosphere, paraformaldehyde and sodium hydroxide aqueous solution are added to chloroform, heated to 60~70℃ and then polyetheramine is added. Bisphenol A is added after heating to 80~90℃. After stirring for 8~10 hours, the mixture is concentrated and purified for use in the next step. X2. Add the product from the previous step to N,N-dimethylformamide, then add the modifier, stir for 1-2 hours, and then concentrate to remove the solvent to obtain the final product. The modifier is one of 2H-benzotriazole-5,6-diol, catechol, or 1-methyl-5-benzotriazole.

2. The copper blackening agent as described in claim 1, characterized in that, The mass ratio of paraformaldehyde to sodium hydroxide aqueous solution, chloroform, polyetheramine, and bisphenol A is 1:0.1~0.5:20~50:2~5:1~3.

3. The blackening agent for cast copper as described in claim 1, characterized in that, The mass ratio of the product from the previous step to N,N-dimethylformamide and the modifier is 1:5~15:1~3.

4. The copper blackening agent as described in claim 1, characterized in that, The stabilizer is phosphoric acid.

5. The blackening agent for cast copper as described in claim 1, characterized in that, The complexing agent is sodium citrate.

6. The blackening agent for cast copper as described in claim 1, characterized in that, The wetting agent is polyethylene glycol.

7. The blackening agent for cast copper as described in claim 1, characterized in that, The oxidation promoter is potassium chlorate.

8. The preparation process of the copper blackening agent according to any one of claims 1 to 7, characterized in that, Includes the following steps: Selenium dioxide, copper sulfate, stabilizer, complexing agent, wetting agent, preservative, oxidation accelerator, and water are mixed evenly according to the formula to obtain the copper casting blackening agent.

9. The preparation process of the copper blackening agent as described in claim 8, characterized in that, The steps include the following, in parts by weight: Add 5 parts selenium dioxide, 8 parts copper sulfate, 9 parts phosphoric acid, 0.8 parts sodium citrate, 1.5 parts polyethylene glycol, 3 parts preservative, and 1 part potassium chlorate to 1000 parts water and mix well to obtain the final product. The method for preparing the preservative includes the following steps, in parts by weight: X1. Under a nitrogen atmosphere, 1 part of paraformaldehyde and 0.2 parts of 1 mol / L sodium hydroxide aqueous solution were added to 30 parts of chloroform. The mixture was heated to 65°C and then 3.5 parts of polyetheramine were added. The mixture was heated to 85°C and then 2 parts of bisphenol A were added. After stirring for 8 hours, the mixture was concentrated and purified by column chromatography for the next step. X2. Add 1 part of the product from the previous step to 10 parts of N,N-dimethylformamide, then add 2 parts of catechol, stir for 1 hour, and concentrate to remove the solvent to obtain the final product.