A high throwing power metal surface treatment agent used before painting

Abstract

The invention discloses a high-throwing-power metal surface treatment agent used before painting, wherein each liter of the treatment agent contains the following components by mass: 30-60 mg of oxide nanosol; 20-30 mg of metal nanosol; 400-500 mg of zirconium compound based on the mass of zirconium; 10-15 mg of surfactant; 100-300 mg of film-forming aid; and the balance is water. The surface treatment agent of the invention can form a metal conversion film on the metal surface that improves the electrophoretic throwing power. During the electrophoresis process, the metal conversion film quickly increases the external resistance value of the cavity, so that the electrophoresis occurs earlier inside the cavity, thereby improving the electrophoretic throwing power and achieving the purpose of increasing the film thickness on the inner surface of the cavity.

Description

Technical Field

[0001] The invention relates to a high-throwing-power metal surface treating agent used before painting. Background Art

[0002] The current cathodic electrophoretic coating process, due to the electromagnetic shielding effect, can result in uneven film formation in grooves, gaps, cavities, and other locations on workpieces (due to the relatively short electrophoresis time), resulting in lower film thickness in inner areas. The uniformity of electrophoretic coating film formation in grooves, gaps, cavities, and other locations is known as throwing power. The higher the throwing power, the thicker the film on the inner surface. Currently, the four-box method is commonly used to evaluate throwing power.

[0003] Before coating metal materials, surface treatment is often required to enhance adhesion between the metal and the coating. Compared to phosphorus-containing surface treatment agents, zirconium salts or zirconium salt-silane composite surface treatment agents form thinner zirconium-based films with lower electrical resistance. Consequently, due to the stronger electromagnetic shielding effect during electrophoresis, the electrophoretic paint film is thinner in grooves, gaps, cavities, and other locations on the workpiece, resulting in poor corrosion resistance and reduced service life. Summary of the Invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a high-throwing-power metal surface treatment agent for use before painting. The surface treatment agent can form a sol nanoparticle / zirconium-based composite film with an internal microporous structure on the metal surface. The composite film can significantly improve the throwing power during the electrophoretic coating process, thereby solving the problem of low throwing power in metal grooves, gaps, cavities and other parts after treatment with existing zirconium salts or zirconium salt-silane composite surface treatment agents.

[0005] Technical solution: The high-throwing-power metal surface treatment agent of the present invention contains the following components by mass per liter of treatment agent: 30-60 mg of oxide nanosol; 20-30 mg of metal nanosol; 400-500 mg of zirconium compound based on the mass of zirconium; 10-15 mg of surfactant; 100-300 mg of film-forming aid; and the balance is water.

[0006] The oxide nanosol is at least one of titanium oxide nanosol, aluminum oxide nanosol, zirconium oxide nanosol, silicon dioxide nanosol, zinc oxide nanosol, cerium oxide nanosol, or iron oxide nanosol. The oxide nanosol has a solid content of 15% to 40% and a pH of 2 to 5.

[0007] The oxide nano-sol contains porous oxide nano-particles with a particle size of 5 to 50 nm and a specific surface area of ​​100 to 300 m 2 / g, the pore size of the oxide nanoparticles is 2-10nm; the oxide nanoparticles in the oxide nanosol can be stably dispersed in an acidic system.

[0008] The metal nanosol is at least one of gold nanosol, silver nanosol, copper nanosol or iron nanosol, and has a solid content of 15% to 40% and a pH of 2 to 5.

[0009] The metal nanoparticles in the metal nanosol are porous nanoparticles with a particle size of 10 to 50 nm and a specific surface area of ​​50 to 150 m 2 / g, the pore size of the metal nanoparticles is 2-10nm; the metal nanoparticles in the metal nanosol can be stably dispersed in an acidic system.

[0010] The zirconium compound is a combination of at least two of fluorozirconic acid, zirconium acetate, zirconium carbonate, zirconium nitrate or zirconyl nitrate.

[0011] Wherein, the surfactant is alkyl glycoside.

[0012] Wherein, the film-forming aid is a metal salt of magnesium, zinc, molybdenum, aluminum, copper or bismuth.

[0013] The surface treatment agent of the present invention can form a sol nanoparticle / zirconium composite film layer with an internal microporous structure on the metal surface. The composite film layer can significantly improve the permeability of the electrophoretic coating process. The reason is that: in the electrolysis stage of the electrophoretic coating process, the composite film can stably adsorb the hydrogen generated by electrolysis and store it inside the film layer (in the pore structure) to form an air cushion layer; in the electrophoresis and electrodeposition stages of the electrophoretic coating process, the surface of the composite film can greatly improve the electrophoretic deposition impedance due to the generation of the air cushion layer, weaken the electromagnetic shielding effect, and make the electrophoresis occur earlier to the inside of the cavity, thereby improving the electrophoretic permeability; in the electroosmosis stage of the electrophoretic coating process, due to the capillary effect, the gas in the micropores inside the film layer is discharged outward, and at this time, substances such as resin molecules enter the pores inward, enhancing the bonding force of the electrophoretic paint film.

[0014] Beneficial effects: Compared with the existing technology, the present invention has the following significant advantages: the surface treatment agent of the present invention can form a metal conversion film on the metal surface to improve the electrophoretic permeability (the thickness of the metal conversion film is basically equivalent to the particle size of the nanosol particles). During the electrophoresis process, the metal conversion film quickly increases the external resistance value of the cavity, so that electrophoresis occurs earlier inside the cavity, thereby improving the electrophoretic permeability and achieving the purpose of increasing the film thickness on the inner surface of the cavity. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is the structural diagram of cold-rolled double-hole plate and cold-rolled standard plate;

[0016] Figure 2 This is the assembly diagram of four cold-rolled plates and the mold. DETAILED DESCRIPTION

[0017] Example 1

[0018] The high-throwing-power metal surface treatment agent of the present invention contains the following components by mass per liter of the treatment agent: 30 mg of silicon dioxide nanosol; 30 mg of copper nanosol; 300 mg of fluorozirconic acid (calculated by the mass of zirconium); 100 mg of zirconyl nitrate (calculated by the mass of zirconium); 10 mg of alkyl glycoside; 100 mg of bismuth nitrate; and the balance is water.

[0019] The solid content of the silica nanosol is 30%, the pH is 2.8, the particle size of the silica nanoparticles is 8 to 10 nm, and the specific surface area is 250 m 2 / g, the pore size of the silica nanoparticles is 2 to 5nm; (product model is HS-01A, product name is acidic silica sol); the solid content of the copper nanosol is 15%, the pH is 4.5, the particle size of the copper nanoparticles is 20 to 30nm, and the specific surface area is 80m 2 / g, the pore size of the copper nanoparticles is 5 to 10 nm; (the commercial name is acidic nano-copper sol).

[0020] The surface treatment agent is prepared by adding a formulated amount of silica nanosol, copper nanosol, fluorozirconic acid, zirconyl nitrate, alkyl glycoside and bismuth nitrate to deionized water, stirring evenly until the solution is clear and transparent; and adjusting the pH value thereof to 4.00±0.01 using sodium hydroxide solution.

[0021] Example 2

[0022] The high-throwing-power metal surface treatment agent of the present invention contains the following components by mass per liter of the treatment agent: 60 mg of silicon dioxide nanosol; 20 mg of silver nanosol; 300 mg of fluorozirconic acid (calculated by the mass of zirconium); 100 mg of zirconyl nitrate (calculated by the mass of zirconium); 10 mg of alkyl glycoside; 100 mg of bismuth nitrate; and the balance is water.

[0023] The solid content of the silica nanosol is 30%, the pH is 2.8, the particle size of the silica nanoparticles is 15 to 30 nm, and the specific surface area is 150 m 2 / g, the pore size of the silica nanoparticles is 5 to 10 nm; (product model is HS-01A, product name is acidic silica sol); wherein, the solid content of the silver nanosol is 20%, the pH is 4.5, the particle size of the silver nanoparticles is 10 to 20 nm, and the specific surface area is 50 m 2 / g, the pore size of the silver nanoparticles is 2 to 5 nm; (the product model is Jc-Ag05, and the product name is nano-colloidal silver).

[0024] The surface treatment agent is prepared by adding a formulated amount of silica nanosol, silver nanosol, fluorozirconic acid, zirconyl nitrate, alkyl glycoside and bismuth nitrate to deionized water, and uniformly stirring until the solution is clear and transparent; and adjusting the pH value thereof to 4.00±0.01 using sodium hydroxide solution.

[0025] Comparative Example 1

[0026] A zirconium salt surface treatment agent contains the following components by mass per liter of the treatment agent: 300 mg of fluorozirconic acid (calculated as zirconium); 100 mg of zirconyl nitrate (calculated as zirconium); 10 mg of alkyl glycoside; 300 mg of zinc nitrate; and the balance is water.

[0027] The surface treatment agent is prepared by adding the formulated amount of fluorozirconic acid, zirconyl nitrate, alkyl glycoside and zinc nitrate to deionized water, and stirring evenly until the solution is clear and transparent; and the pH value thereof is adjusted to 4.00±0.01 using sodium hydroxide solution.

[0028] Comparative Example 2

[0029] A zirconium salt surface treatment agent contains the following components by mass per liter of the treatment agent: 60 mg of silicon dioxide nanosol; 300 mg of fluorozirconic acid (calculated as zirconium); 100 mg of zirconyl nitrate (calculated as zirconium); 10 mg of alkyl glycoside; 300 mg of zinc nitrate; and the balance is water.

[0030] The solid content of the silica nanosol is 30%, the pH is 2.8, the particle size of the silica nanoparticles is 15 to 30 nm, and the specific surface area is 150 m 2 / g, the pore size of the silica nanoparticles is 5 to 10 nm; (the product model is HS-01A, and the product name is acidic silica sol).

[0031] The surface treatment agent is prepared by adding a formulated amount of silica nanosol, fluorozirconic acid, zirconyl nitrate, alkyl glycoside and zinc nitrate into deionized water, stirring evenly until the solution is clear and transparent; and adjusting the pH value thereof to 4.00±0.01 using sodium hydroxide solution.

[0032] Comparative Example 3

[0033] A zirconium salt surface treatment agent contains the following components by mass per liter of the treatment agent: 20 mg of silver nanosol; 300 mg of fluorozirconic acid (calculated by the mass of zirconium); 100 mg of zirconyl nitrate (calculated by the mass of zirconium); 10 mg of alkyl glycoside; 100 mg of bismuth nitrate; and the balance is water.

[0034] The solid content of the silver nanosol is 20%, the pH is 4.5, the particle size of the silver nanoparticles is 10-20 nm, and the specific surface area is 50 m 2 / g, the pore size of the silver nanoparticles is 2 to 5 nm; (the product model is Jc-Ag05, and the product name is nano-colloidal silver).

[0035] The surface treatment agent is prepared by adding a formulated amount of silver nanosol, fluorozirconic acid, zirconyl nitrate, alkyl glycoside and bismuth nitrate into deionized water, stirring evenly until the solution is clear and transparent; and adjusting the pH value thereof to 4.00±0.01 using a sodium hydroxide solution.

[0036] The surface treatment agents of Examples 1-2 and Comparative Examples 1-3 were prepared into working solutions with a mass concentration of 10%, that is, 10 g of the surface treatment agent was mixed with 90 g of water to prepare a working solution with a mass fraction of 10%.

[0037] Prepare the plate:

[0038] The commercially available SPCC cold-rolled standard plate (produced by Shanghai Baosteel) with a specification of (150mm×70mm×0.8mm) was used as the metal sample for implementation. The specifications and styles are as follows: Figure 1 .

[0039] The commercially available SPCC cold-rolled double-hole plate (produced by Shanghai Baosteel) with a specification of (150mm×70mm×0.8mm) was used as the metal sample for implementation. The specifications and styles are as follows: Figure 1 .

[0040] Figure 1 On the left is a commercially available cold-rolled double-hole plate with an 8mm diameter hole 50mm from the bottom and 35mm from the side, which is used to simulate the process holes on special workpieces. On the right is a commercially available cold-rolled standard plate.

[0041] Degreasing treatment: Use a commercially available heated cold-rolled plate degreasing agent and soak the cold-rolled plate at 50°C for 5 minutes.

[0042] Water washing after degreasing pretreatment: Rinse in tap water at room temperature for 1 minute.

[0043] Surface treatment agent treatment: Use the surface treatment agent working solution to soak the degreased and water-washed sample for 3 minutes.

[0044] Washing after surface treatment: Soak the sample treated with the surface treatment agent in tap water for 30 seconds, and then rinse with deionized water for 30 seconds.

[0045] Four-box assembly: Use compressed air to dry the surface treated and washed test plates, including 1 cold-rolled standard plate and 3 cold-rolled double-hole plates. According to the four-box method standard operation, assemble the above four cold-rolled plates and the mold, the style is as follows Figure 2 AB, CD, EF are cold-rolled double-hole plates, and GH is a cold-rolled standard plate.

[0046] Electrophoretic coating: Four assembled boxes were electrophoretically coated with HT8000C water-based cathodic electrophoretic coating produced by Kansai Co., Ltd. The resulting surface film thickness was within the range of 20 ± 1 μm, which was then used as the test specimen. The treated specimens were rinsed with deionized water for 30 seconds. The rinsed, electrophoretically treated specimens were dried at 180°C for 20 minutes and then air-dried at room temperature.

[0047] The paint film thickness of each surface of the sample is shown in Table 1.

[0048] Table 1

[0049]

[0050] As shown in Table 1, the four-box method test shows that the existing phosphorus-free metal surface treatment agent has a throwing power of 13.30%. After the introduction of a nanosol, the four-box throwing power is increased to about 48%. After the introduction of two nanosols, the four-box throwing power is increased to more than 56%.

[0051] The present invention uses specific nano-sol particles to participate in co-deposition film formation. During the electrophoresis process, the microporous structure and adsorption characteristics of the nano-sol particles are utilized to adsorb and store the hydrogen generated by hydrolysis in the early stage of electrophoresis to form an air cushion layer, so that the metal surface resistance value is rapidly increased, the electromagnetic shielding effect is weakened to achieve the effect of improving the electrophoretic penetration, and the film thickness in grooves, gaps, and cavities is extended, thereby improving the service life of the coated parts.

Claims

1. A high throwing power metal surface treatment agent for use before painting, characterized in that: Each liter of the treating agent contains the following components by mass: 30-60 mg of oxide nanosol; 20-30 mg of metal nanosol; 400-500 mg of zirconium compound based on the mass of zirconium; 10-15 mg of surfactant; 100-300 mg of film-forming aid; and the balance is water.

2. The metal surface treatment agent according to claim 1, characterized in that: The oxide nanosol is at least one of titanium oxide nanosol, aluminum oxide nanosol, zirconium oxide nanosol, silicon dioxide nanosol, zinc oxide nanosol, cerium oxide nanosol or iron oxide nanosol.

3. The metal surface treatment agent according to claim 2, characterized in that: The solid content of the oxide nano-sol is 15% to 40% and the pH value is 2 to 5.

4. The metal surface treatment agent according to claim 2, characterized in that: In the oxide nanosol, the oxide nanoparticles are porous nanoparticles, the particle size of the oxide nanoparticles is 5 to 50 nm, and the specific surface area is 100 to 300 m 2 / g, and the pore size of the oxide nanoparticles is 2 to 10 nm.

5. The metal surface treatment agent according to claim 1, characterized in that: The metal nanosol is at least one of gold nanosol, silver nanosol, copper nanosol or iron nanosol.

6. The metal surface treatment agent according to claim 5, characterized in that: The solid content of the metal nano-sol is 15% to 40% and the pH value is 2 to 5.

7. The metal surface treatment agent according to claim 6, characterized in that: In the metal nanosol, the metal nanoparticles are porous nanoparticles, the particle size of the metal nanoparticles is 10 to 50 nm, and the specific surface area is 50 to 150 m 2 / g, the pore size of metal nanoparticles is 2 to 10 nm.

8. The metal surface treatment agent according to claim 1, characterized in that: The zirconium compound is a combination of at least two of fluorozirconic acid, zirconium acetate, zirconium carbonate, zirconium nitrate or zirconyl nitrate.

9. The metal surface treatment agent according to claim 1, characterized in that: The surfactant is at least one of a cationic surfactant, an anionic surfactant, an amphoteric surfactant or a nonionic surfactant.

10. The metal surface treatment agent according to claim 1, characterized in that: The film-forming aid is a metal salt of magnesium, zinc, molybdenum, aluminum, copper or bismuth.

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