Cast copper blackening agent and preparation process thereof

Abstract

The invention discloses a cast copper blackening agent and a preparation process thereof. The cast copper blackening agent comprises the following components in parts by weight: 2-8 parts of selenium dioxide, 6-10 parts of copper sulfate, 5-10 parts of a stabilizer, 0.5-1 part of a complexing agent, 1-2 parts of a wetting agent, 2-5 parts of a preservative, 1-2 parts of an oxidation accelerant and 500-1500 parts of water. The invention also provides a preparation process of the composition. The process for blackening is relatively simple, short in flow and low in energy consumption, and has the most important advantages that the brass casting treated by the blackening process has no acid regurgitation phenomenon, rusty spots, corrosion and the like on the surface of the casting are avoided, and the treated brass casting is better in corrosion resistance and wear resistance.

Description

Technical Field

[0001] The invention relates to the technical field of plating metal materials, in particular to a copper casting blackening agent and a preparation process thereof. Background Art

[0002] The blackening process can make the surface of copper crafts form a uniform black or near-black color, which forms a sharp contrast with the golden luster of copper itself, increases the visual layering and artistic appeal of the crafts, makes them more classical and cultural, and meets different aesthetic needs and decorative styles. For example, some antique bronze crafts can better restore the texture of ancient bronzes after blackening treatment, creating an ancient and mysterious atmosphere. The black surface can better highlight the details such as lines, textures and carvings of the crafts, making the shape of the crafts more three-dimensional and vivid, and the exquisite craftsmanship of the details can be fully displayed, which enhances the overall ornamental value. After the blackening treatment, a dense black protective film will be formed on the surface of the copper crafts. This film is mainly composed of copper oxides such as CuO, Cu2O, etc. It can effectively isolate the oxygen, moisture, carbon dioxide, sulfide, etc. in the air from eroding the copper matrix, preventing the copper surface from further oxidation and rusting, thereby extending the service life of the crafts, so that it can maintain good appearance and performance under different environmental conditions. Compared with the untreated copper surface, the corrosion resistance of the copper crafts after blackening is significantly improved. Since the blackening process improves the corrosion resistance and wear resistance of copper crafts, it reduces the need for repair and renovation work due to surface damage, thereby reducing the cost and energy investment of long-term maintenance, making it more practical and economical.

[0003] CN109207980A discloses a novel method for blackening the surface of brass, which mainly covers two aspects: surface cleaning and surface blackening. When cleaning the surface, a unique ultrasonic cleaning technology is used, with a specially formulated degreasing solvent, and pure water is used for parallel cleaning. Subsequently, a special blackening liquid prepared with sodium persulfate and sodium hydroxide is used for blackening treatment. This method significantly improves the graying phenomenon of the blackening layer on the surface of the brass parts and greatly improves the firmness of the blackening layer.

[0004] CN112111734A discloses a copper product blackening process, the steps are as follows: degreasing and decontamination, removing stains on the product surface; overflow rinsing, further rinsing residual stains; pickling activation, removing oxides on the product surface; overflow rinsing again; performing the first blackening to form a light blackening layer; overflow rinsing; implementing the second blackening to build a stable blackening layer; overflow rinsing again; sealing treatment to form an anti-oxidation film outside the finished product blackening layer; continuing overflow rinsing; drying; vibration grinding to remove dust and impurities on the surface. This process can make the product blackening layer pass the long-term salt spray test without copper leakage, and keep the color unchanged for a long time in continuous tests such as high temperature, high humidity, thermal shock, and low temperature cold shock, and the product has good anti-reflection and anti-refractive properties.

[0005] The commonly used blackening technology for casting copper surface on the market mostly adopts the preparation method of chemical coloring oxide film or manual painting for surface treatment. The traditional blackening process mostly uses strong acid to generate a layer of black surface film on its surface. However, in the actual production process, it is found that after the surface of the casting is blackened, it will still have acid regurgitation after washing with water and drying, and rust and corrosion will appear on the surface of the casting. In addition, the traditional blackening process requires heating reaction, which is slow and takes a long time to process. Summary of the invention

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

[0007] The current blackening process can be divided into the traditional high-temperature alkali boiling and the room-temperature blackening process. Compared with the former, the latter has a shorter processing time, higher working efficiency and lower pollution. The present invention provides a copper casting blackening agent. The blackening process using the process is relatively simple, short in process and low in energy consumption. The most important advantage is that the brass casting treated by the blackening process has no acid regurgitation phenomenon, and no rust spots, corrosion and the like will appear on the casting surface.

[0008] Selenium dioxide is one of the main active ingredients in the blackening agent, which can form a uniform black copper selenide film on the copper surface. The copper selenide film has good adhesion and corrosion resistance, and can effectively prevent copper oxidation. Copper sulfate and selenium dioxide are the main components of film formation. At the same time, copper sulfate can form a stable complex with the complexing agent to promote the uniform reaction. The wetting agent can reduce the surface tension of the blackening agent, so that it can better wet the copper surface and ensure that the blackening agent is evenly covered on the copper surface. The oxidation promoter can accelerate the oxidation reaction on the copper surface, shorten the blackening time, and improve the blackening efficiency. The adhesion promoter can enhance the adhesion between the blackening layer and the copper surface and prevent the blackening layer from falling off. Compared with the existing blackening agents on the market, this process can quickly blacken at room temperature, with positive blackening color, short time, high wear resistance of the blackening film, simple production process, low cost and other advantages, and can achieve mass production.

[0009] Since the oxide film currently generated has poor adhesion to copper, not only is the black layer easy to fall off, but also the anti-corrosion and anti-rust effect is affected. Therefore, the present invention provides an anticorrosion agent, which improves its adhesion to the copper surface by modifying polybenzoxazine, and the benzotriazole group in the modifier can also improve the anti-corrosion performance of the blackening agent. When the modifier has a catechol group, since the catechol group can form a coordination bond with the metal atom, the adhesion can be improved, and the benzotriazole group can be adsorbed on the metal surface through the van der Waals force to form a dense physical barrier to prevent the corrosive medium (such as water, oxygen, chloride ions, etc.) from contacting the metal, which is not only beneficial to anti-corrosion, but also can further improve the adhesion. The nitrogen atoms in the benzotriazole molecules react with the metal ions on the metal surface to generate a dense metal-benzotriazole complex. This complex film can prevent further oxidation of the metal and form a passivation state, thereby achieving the anti-corrosion and anti-rust effect.

[0010] To achieve the above-mentioned purpose, the present invention provides a copper casting blackening agent, comprising the following components in parts by weight: 2 to 8 parts of selenium dioxide, 6 to 10 parts of copper sulfate, 5 to 10 parts of a stabilizer, 0.5 to 1 part of a complexing agent, 1 to 2 parts of a wetting agent, 2 to 5 parts of a preservative, 1 to 2 parts of an oxidation promoter and 500 to 1500 parts of water.

[0011] The preparation method of the preservative comprises the following steps:

[0012] X1. Under an inert atmosphere, add paraformaldehyde and sodium hydroxide aqueous solution to chloroform, heat to 60-70°C and then add polyetheramine, heat to 80-90°C and add bisphenol A, stir for 8-10 hours, concentrate, purify and use in the next step;

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

[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 of the previous step to N,N-dimethylformamide and the modifier is 1:5-15:1-3.

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

[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 of a copper casting blackening agent comprises the following steps:

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

[0023] Beneficial effects of the present invention:

[0024] 1. The blackening process is relatively simple, short process and low energy consumption. The most important advantage is that the brass castings treated by the blackening process will not have acid reflux phenomenon, and there will be no rust or corrosion on the surface of the castings.

[0025] 2. The present invention provides an anticorrosive agent, which improves the adhesion between polybenzoxazine and the copper surface by modifying the polybenzoxazine, so that the cast copper film after blackening treatment is more anticorrosive and wear-resistant. DETAILED DESCRIPTION

[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 Chemical, South Korea.

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

[0031] Example 1

[0032] A preparation process of a copper casting blackening agent comprises the following steps, measured in parts by weight:

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

[0034] The preparation method of the preservative comprises the following steps, measured in parts by weight:

[0035] X1. Under nitrogen atmosphere, add 1 part of paraformaldehyde and 0.2 parts of 1 mol / L sodium hydroxide aqueous solution to 30 parts of chloroform, heat to 65°C and then add 3.5 parts of polyetheramine, heat to 85°C and add 2 parts of bisphenol A, stir for 8 hours, concentrate, purify by column chromatography and use in the next step;

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

[0037] Example 2

[0038] A preparation process of a copper casting blackening agent comprises the following steps, measured in parts by weight:

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

[0040] The preparation method of the preservative comprises the following steps, measured in parts by weight:

[0041] X1. Under nitrogen atmosphere, add 1 part of paraformaldehyde and 0.2 parts of 1 mol / L sodium hydroxide aqueous solution to 30 parts of chloroform, heat to 65°C and then add 3.5 parts of polyetheramine, heat to 85°C and add 2 parts of bisphenol A, stir for 8 hours, concentrate, purify by column chromatography and use in the next step;

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

[0043] Example 3

[0044] A preparation process of a copper casting blackening agent comprises the following steps, measured in parts by weight:

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

[0046] The preparation method of the preservative comprises the following steps, measured in parts by weight:

[0047] X1. Under nitrogen atmosphere, add 1 part of paraformaldehyde and 0.2 parts of 1 mol / L sodium hydroxide aqueous solution to 30 parts of chloroform, heat to 65°C and then add 3.5 parts of polyetheramine, heat to 85°C and add 2 parts of bisphenol A, stir for 8 hours, concentrate, purify by column chromatography and use in the next step;

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

[0049] Comparative Example 1

[0050] A preparation process of a copper casting blackening agent comprises the following steps, measured in parts by weight:

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

[0052] Comparative Example 2

[0053] A preparation process of a copper casting blackening agent comprises the following steps, measured in parts by weight:

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

[0055] The preparation method of the preservative comprises the following steps, measured in parts by weight:

[0056] Under a nitrogen atmosphere, add 1 part of paraformaldehyde and 0.2 parts of 1 mol / L sodium hydroxide aqueous solution to 30 parts of chloroform, heat to 65°C and then add 3.5 parts of polyetheramine, heat to 85°C and add 2 parts of bisphenol A, stir for 8 hours, concentrate and purify by column chromatography to obtain the product.

[0057] Test Example 1

[0058] The surface of the brass casting is polished to remove the surface oxide layer and oil stains, and then it is polished with 1000 mesh fine sandpaper; then rinse it with clean water and blow it dry, hang the casting in the blackening agent, blacken it for 5 minutes, take it out and rinse it with clean water, then rub it with a scouring pad to remove the surface oxide dust, put it in the oven, and bake it at 140℃ for 20 minutes. After taking it out, rub it and bake it at 160℃ for 20 minutes. The treated parts are immersed in clear oil and sealed, and dried to obtain the blackened brass casting.

[0059] The corrosion resistance of the blackened brass castings was tested with reference to QB / T3824-1999 "Test Method for Chemical Protective Layer of Ferrous Metals of Light Industrial Products - Immersion Drip Method". The blackened samples were rinsed in clean water, then cleaned with anhydrous ethanol, and immersed in a 3% copper sulfate solution. The corrosion resistance of the blackened film was measured by the time the surface of the brass blackened film did not change.

[0060] Table 1 Corrosion resistance test results of brass castings after blackening

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

[0062] By immersing the ferrous metal sample with a chemical protective layer in a specific corrosive medium or dripping a corrosive liquid on its surface, observing whether there are signs of corrosion (such as rust, discoloration, pitting, etc.) on the metal surface and the degree of corrosion within a specified time, the ability of the chemical protective layer to resist the corrosive environment of the ferrous metal is evaluated. During the test, if there are pores, cracks or other defects in the chemical protective layer, the corrosive medium will more easily penetrate into the surface of the metal substrate and cause a corrosion reaction. In the immersion drip test, if the coating has a weak bonding force with the ferrous metal substrate, the coating may blister and peel off under the action of the corrosive medium. Therefore, this method can also indirectly reflect the bonding strength between the coating and the substrate to a certain extent. Ensuring good bonding between the coating and the metal substrate is one of the key factors to ensure product performance.

[0063] It can be seen from Table 1 that the addition of preservatives can significantly improve the corrosion resistance of the samples after blackening treatment. The time for the sample in Control Example 1 to change is significantly shorter than that in the embodiment. Although the preservative is added in Control Example 2, the prepared polybenzoxazine has certain corrosion resistance, but due to its rigidity, the adhesion to the substrate is poor, so the corrosion resistance time is short. In the embodiment, by adding a modifier, the catechol group and the benzotriazole group in the modifier can interact with the metal surface. The catechol group can form a coordination bond with the metal atom, so the adhesion can be improved, and the benzotriazole group can be adsorbed on the metal surface through van der Waals force to form a dense physical barrier to prevent corrosive media (such as water, oxygen, chloride ions, etc.) from contacting the metal, which is not only beneficial to corrosion protection, but also can further improve the adhesion. The nitrogen atoms in the benzotriazole molecule react with the metal ions on the metal surface to form a dense metal-benzotriazole complex. This complex film can prevent further oxidation of the metal and form a passivated state. While Examples 1 and 2 have catechol and benzotriazole groups respectively, Example 3 has both catechol and benzotriazole groups, so Example 3 has the longest corrosion resistance time. This may be because the preservative has the best adhesion to the surface of the brass casting, and the physical adsorption of benzotriazole and the passivation layer of the complex jointly play a good anti-corrosion role.

[0064] Test Example 2

[0065] The surface of the brass casting is polished to remove the surface oxide layer and oil stains, and then it is polished with 1000 mesh fine sandpaper; then rinse it with clean water and blow it dry, hang the casting in the blackening agent, blacken it for 5 minutes, take it out and rinse it with clean water, then rub it with a scouring pad to remove the surface oxide dust, put it in the oven, and bake it at 140℃ for 20 minutes. After taking it out, rub it and bake it at 140℃ for 20 minutes. The treated parts are immersed in clear oil and sealed, and dried to obtain the blackened brass casting.

[0066] Place a layer of sandpaper on the blackened sample, put a 100g weight on the sandpaper, drag the sandpaper back and forth on the surface of the sample and rub it until a certain point of the sample leaks out of the matrix. The actual number of frictions is used to measure the friction resistance of the blackened film.

[0067] Table 2 Friction test results of brass castings after blackening

[0068] Experimental protocol Friction resistance / times Example 1 263 Example 2 220 Example 3 214 Comparative Example 1 151 Comparative Example 2 182

[0069] The friction test can directly evaluate the surface wear resistance of the black film. If the black film can remain intact after multiple frictions, it means that it has good wear resistance, can resist physical wear in actual use, and protect the base material from damage. The friction test can indirectly evaluate the adhesion between the black film and the base. Good adhesion is the key factor for the coating to remain intact and effectively protect. If the black film easily falls off during the friction process, it means that the adhesion is insufficient; if the black film can withstand multiple frictions without falling off, it means that the adhesion is good and can effectively adhere to the base surface.

[0070] It can be seen from Table 2 that the brass casting after blackening treatment in the embodiment of the present invention has better friction resistance. This may be because the preservative can interact with the metal surface after modification, and the catechol group can form a coordination bond with the metal atom, thereby improving the adhesion. The benzotriazole group can be adsorbed on the metal surface through the van der Waals force to form a dense physical barrier to prevent the corrosive medium (such as water, oxygen, chloride ions, etc.) from contacting the metal, which is not only beneficial to corrosion protection, but also can further improve the adhesion. Therefore, the film formed by blackening can better adhere to the surface of the brass casting.

[0071] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A copper casting blackening agent, characterized in that: The invention comprises the following components in parts 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.

2. The copper casting blackening agent according to claim 1, characterized in that The preparation method of the preservative comprises the following steps: X1. Under an inert atmosphere, add paraformaldehyde and sodium hydroxide aqueous solution to chloroform, heat to 60-70°C and then add polyetheramine, heat to 80-90°C and add bisphenol A, stir for 8-10 hours, concentrate, purify and use in the next step; X2. Add the product of the previous step into N,N-dimethylformamide, then add the modifier, stir for 1 to 2 hours, and then concentrate to remove the solvent.

3. The copper casting blackening agent as claimed in claim 2, characterized in that 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.

4. The copper casting blackening agent as claimed in claim 2, characterized in that The mass ratio of the product of the previous step to N,N-dimethylformamide and the modifier is 1:5-15:1-3.

5. The copper casting blackening agent as claimed in claim 2, characterized in that The modifier is one of 2H-benzotriazole-5,6-diol, catechol or 1-methyl-5-benzotriazole alcohol.

6. The copper casting blackening agent according to claim 1, characterized in that: The stabilizer is phosphoric acid.

7. The copper casting blackening agent according to claim 1, characterized in that The complexing agent is sodium citrate.

8. The copper casting blackening agent according to claim 1, characterized in that The wetting agent is polyethylene glycol.

9. The copper casting blackening agent according to claim 1, characterized in that The oxidation promoter is potassium chlorate.

10. The process for preparing the copper casting blackening agent according to any one of claims 1 to 9, characterized in that: The steps include: The selenium dioxide, copper sulfate, stabilizer, complexing agent, wetting agent, preservative, oxidation accelerator and water are uniformly mixed according to the formula to obtain the cast copper blackening agent.