Preparation method of environment-friendly coating type temporary protective conversion film

Abstract

The application discloses an environment-friendly coating type temporary protective conversion film preparation method. The method only needs to coat a conversion liquid on the surface of a steel workpiece after oil removal and rust removal, so that the conversion film with the protective performance is generated, and the conversion film can be completely removed by soaking in an alkali solution with pH 12-14 for a period of time. The conversion liquid mentioned in the application has very low phosphorus concentration, the steps required for preparing the film are simple, the film forming speed is fast, the loss caused after the film removal is small, the workpiece size change is small, and the method is suitable for temporary protection of steel workpieces.

Description

Technical Field

[0001] This invention belongs to the field of metal surface treatment, and particularly relates to an environmentally friendly method for preparing a coating-type temporary protective conversion film. Background Technology

[0002] Steel components, from the time they leave the factory until final processing and assembly, are exposed to the natural environment and require temporary protective measures to prevent direct contact between their surfaces and the external environment, reducing the risk of corrosion and damage. The most common method is surface phosphating, as described in Chinese invention patent application number 202211442673.3. However, this method has several drawbacks: firstly, the traditional phosphating process involves cumbersome steps including alkaline washing to remove oil, rinsing, acid pickling to remove rust, rinsing, activation, phosphating, and deionized water rinsing; secondly, traditional surface phosphating requires film formation at temperatures above 90°C, resulting in significant energy consumption. Chinese invention patent application number 201710606794.X discloses a low-temperature phosphating process, requiring only the pre-treated steel to be placed in a phosphating solution at 25-30°C. However, this process requires large quantities of raw materials such as phosphoric acid, which is environmentally unfriendly. Chinese invention patent application number 201410551424.7 has the following drawbacks: it discloses a low-phosphorus concentration chemical solution, but requires a long reaction time to form a uniform conversion film, greatly increasing the production cycle; in addition, precipitates and scale often form in the conversion tank, requiring regular cleaning and maintenance, increasing the complexity of the process and the difficulty of operation, thus affecting production efficiency. Moreover, the film removal process is cumbersome and generally contains highly toxic hexavalent chromium, requiring the film removal solution composed of CrO3 and H2SO4 to be heated to 70°C and soaked for more than 15 minutes to complete the film removal.

[0003] Therefore, there is a need to find a more efficient, energy-saving and environmentally friendly method for preparing temporary protective conversion films, while also ensuring that the film removal process is simple. Summary of the Invention

[0004] The purpose of this invention is to address the above-mentioned technical problems by providing an environmentally friendly method for preparing a coating-type temporary protective conversion film. This method only requires degreasing and derusting the steel workpiece to be treated, followed by applying a conversion solution to the surface to generate a protective conversion film. Furthermore, the formed conversion film can be completely removed by immersing it in an alkaline solution with a pH of 12-14 for a period of time. The conversion solution mentioned in this invention has an extremely low phosphorus concentration, the steps required for film preparation are simple, the film formation speed is fast, and the loss after film removal is minimal, with small changes in workpiece dimensions, making it suitable for temporary protection of steel workpieces.

[0005] This invention adopts the following technical solution: a method for preparing an environmentally friendly coating-type temporary protective conversion film, comprising the following steps:

[0006] Step 1: After degreasing, derusting and washing the steel to be treated, the pretreated steel workpiece is obtained.

[0007] Step 2: Apply the conversion solution to the surface of the pretreated steel workpiece at room temperature.

[0008] Step 3: After 2-5 minutes, blow away or wipe clean any excess solution from the surface of the steel workpiece.

[0009] The conversion solution includes the following components at the following concentrations:

[0010]

[0011] Furthermore, the organophosphonic acid is one or more of hydroxyethylidene diphosphonic acid, aminotrimethylphosphonic acid, and ethylenediaminetetramethylphosphonic acid.

[0012] Furthermore, the zinc salt is one of zinc dihydrogen phosphate, zinc oxide, or zinc carbonate.

[0013] Furthermore, the accelerator is one or more of sodium nitrite, hydrogen peroxide, copper nitrate, and sodium perborate.

[0014] Furthermore, corrosion inhibitors are commonly used in this field, such as one or more of benzotriazole, ammonium molybdate, sodium citrate, and sodium gluconate.

[0015] Furthermore, the thickener is one or more commonly used in the field, such as hydroxymethyl cellulose, hydroxyethyl cellulose, xanthan gum, and polyvinyl alcohol.

[0016] Furthermore, the preparation of the environmentally friendly coating-type temporary protective conversion membrane involves coating at room temperature; the membrane formation speed is fast; the phosphorus content of the conversion solution is extremely low, resulting in low wastewater treatment costs; the formed conversion membrane can be completely removed after soaking in an alkaline solution with a pH of 12-14 for a period of time; the membrane removal process is simple, and the losses caused after membrane removal are minimal.

[0017] The beneficial effects of this invention are:

[0018] (1) Coating to form a film not only reduces energy costs, but also greatly reduces maintenance costs because it does not produce sludge or scale;

[0019] (2) The phosphorus content in the conversion liquid is extremely low, resulting in good environmental protection and low wastewater treatment costs;

[0020] (3) A conversion film with excellent protective properties can be generated by treating at room temperature for 2 to 5 minutes;

[0021] (4) The film can be removed by soaking in an alkaline solution with pH 12 to 14 for a period of time. The operation process is convenient and causes little loss to the dimensions of steel workpieces.

[0022] (5) By combining phosphonic acid groups with iron oxides, a self-assembled film with protective properties is formed. This film is applied to the surface of steel workpieces to generate a light blue conversion film with protective properties. The protective effect is further enhanced by zinc salts and corrosion inhibitors. The film is easy to remove. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to embodiments. It should be noted that the embodiments described below are intended to facilitate understanding of the present invention and are not intended to limit it in any way. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions.

[0024] The following is a detailed description of a method for preparing an environmentally friendly coating-type temporary protective conversion film provided by the present invention. Contents not described in detail in the embodiments of the present invention are prior art known to those skilled in the art. To more clearly demonstrate the technical solution provided by the present invention and its resulting technical effects, a detailed description of a method for preparing an environmentally friendly coating-type temporary protective conversion film provided by the present invention is provided below with specific embodiments.

[0025] Example 1

[0026] A method for preparing an environmentally friendly coating-type temporary protective conversion film includes the following steps:

[0027] Step A1: After removing the surface grease of the Q235 steel workpiece with alkaline degreasing solution, remove the surface oxides with acidic rust remover, and then rinse it clean with deionized water.

[0028] Step A2: Apply the conversion solution (formula A) evenly to the surface of the pretreated Q235 steel workpiece and wait for 4 minutes;

[0029] Step A3: Blow away or wipe clean any excess solution from the surface of the Q235 steel workpiece.

[0030] Step A4: Immerse the Q235 steel workpiece after film formation in a sodium hydroxide solution with a pH of 13, wait for 3 minutes, and then rinse it clean with deionized water.

[0031] The environmentally friendly coating-type conversion solution formulation A includes the following components at the following concentrations:

[0032]

[0033]

[0034] Example 2

[0035] A method for preparing an environmentally friendly coating-type temporary protective conversion film includes the following steps:

[0036] Step B1: Use sandblasting to remove oil and rust from Q235 steel workpieces, and then rinse them clean with deionized water; the remaining steps and the environmentally friendly coating conversion solution are the same as in Example 1. Figure 1 To process the appearance of the sample, Figure 2 This is the appearance of the sample after the film has been removed.

[0037] Example 3

[0038] A method for preparing an environmentally friendly coating-type temporary protective conversion film includes the following steps:

[0039] Step C1: After removing the surface grease of the 30CrMnSiA steel workpiece with alkaline degreasing solution, remove the surface oxides with acidic rust remover, and then rinse it clean with deionized water.

[0040] Step C2: Apply the conversion solution (formula C) evenly to the surface of the pretreated 30CrMnSiA steel workpiece and wait for 3 minutes;

[0041] Step C3: Blow away or wipe clean any excess solution from the surface of the 30CrMnSiA steel workpiece.

[0042] Step C4: Immerse the 30CrMnSiA steel workpiece after film formation in a sodium hydroxide solution with a pH of 13, wait for 3 minutes, and then rinse it clean with deionized water.

[0043] The environmentally friendly coating-type conversion solution formulation C includes the following components at the following concentrations:

[0044]

[0045] Example 4

[0046] A method for preparing a commercially available high-temperature phosphating film includes the following steps:

[0047] Step D1: After removing the surface grease of the 30CrMnSiA steel workpiece with alkaline degreasing solution, remove the surface oxides with acidic rust remover, and then rinse it clean with deionized water.

[0048] Step D2: Immerse the pretreated 30CrMnSiA steel workpiece in a conversion solution (formula D) at 90°C and wait for 25 minutes.

[0049] Step D3: Rinse the surface of the 30CrMnSiA steel workpiece with deionized water to remove excess solution.

[0050] Step D4: Immerse the 30CrMnSiA steel workpiece after film formation in a 75℃ stripping solution (formula D') and wait for 15 minutes, then rinse it clean with deionized water.

[0051] The high-temperature phosphating solution formulation D includes the following components at the following concentrations:

[0052] Zinc dihydrogen phosphate 30g / L;

[0053] Zinc nitrate 50g / L;

[0054] Phosphoric acid 10 g / L.

[0055] The high-temperature phosphating stripping solution formula D' comprises the following components at the following concentrations:

[0056] Chromium trioxide 125 g / L;

[0057] Sulfuric acid 2g / L.

[0058] Comparative Example 1

[0059] The steps used are the same as in Example 1, except that ammonium molybdate in Formulation A of the environmentally friendly coating conversion solution is removed.

[0060] Comparative Example 2

[0061] The steps used are the same as in Example 1, except that zinc oxide in Formulation A of the environmentally friendly coating conversion solution is removed.

[0062] Comparative Example 3

[0063] The steps used are the same as in Example 1, except that aminotrimethylenephosphonic acid in formulation A of the environmentally friendly coating conversion solution is replaced with phosphoric acid.

[0064] Comparative Example 4

[0065] The steps used are the same as in Example 4, except that the film formation time is shortened to 3 minutes.

[0066] Comparative Example 5

[0067] The steps used are the same as in Example 4, except that step D4 is changed to immersing the 30CrMnSiA steel workpiece after film formation in a sodium hydroxide solution with a pH of 13.

[0068] Comparative Example 6

[0069] The steps used are the same as in Example 4, except that step D2 is changed to application at room temperature.

[0070] Comparative Example 7

[0071] The steps used are the same as in Example 4, except that the phosphorus content in Formula D is reduced to be the same as in Formula A.

[0072] The test results of the steel workpieces protected by the conversion film are shown in Table 1 below.

[0073]

[0074] The results in Table 1 show that:

[0075] (1) The test results of Examples 1, 2 and 3 show that the prepared conversion membrane is light blue, has good protective performance and is easy to remove;

[0076] (2) The test results of the comparison with Example 1 show that the lack of a slow-release agent will reduce the protective performance of the conversion membrane;

[0077] (3) Comparing the test results of Example 2, it can be seen that when the conversion solution does not contain zinc ions, the conversion film is grayish-white and rust spots will appear after long-term storage.

[0078] (4) The test results of the comparative example 3 show that organophosphorus, as an important component of coating conversion film, can not only change its protective effect, but also affect the film removal result.

[0079] (5) The test results of Examples 1, 4, and Comparative Example 4 show that the commonly used high-temperature phosphating process requires a long film-forming time, and shortening the time will not achieve the expected protective effect. However, the organic phosphating conversion film of this patent only requires 3 minutes to form a film.

[0080] (6) The test results of Examples 1, 4, and Comparative Example 5 show that the stripping solution of commonly available high-temperature phosphating films has complex composition and high requirements. However, the stripping solution of the organic phosphating conversion film of this patent has simple composition and requires simple conditions.

[0081] (7) The test results of Examples 1, 4 and Comparative Example 6 show that the common high-temperature phosphating process on the market requires a high film-forming temperature, and a conversion film cannot even be formed when applied to the metal surface at room temperature.

[0082] (8) The test results of Examples 1, 4 and Comparative Example 7 show that commercially available high-temperature phosphating solutions can only form a conversion film under high phosphorus content conditions. However, the organophosphorus conversion solution of this patent has an extremely low phosphorus content.

[0083] The embodiments described above provide a detailed explanation of the technical solutions of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, or equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an environmentally friendly coating-type temporary protective conversion film, characterized in that: Includes the following steps: Step 1: After degreasing, derusting and washing the steel to be treated, the pretreated steel workpiece is obtained. Step 2: Apply the conversion solution to the surface of the pretreated steel workpiece at room temperature. Step 3: After 2-5 minutes, blow away or wipe clean any excess solution from the surface of the steel workpiece. The conversion solution includes the following components at the following concentrations: Organophosphonic acid 1.5~2.0 g / L; Zinc salts: 2.0~2.5 g / L; Accelerator 0.2~0.4 g / L; Corrosion inhibitor 0.1~0.5 g / L; Thickener 0.1~0.5 g / L; pH 3.0~4.5; The remainder is water; The preparation of environmentally friendly coating-type temporary protective conversion membrane involves coating at room temperature; the membrane formation speed is fast; the conversion solution has a low phosphorus content, resulting in low wastewater treatment costs; the formed conversion membrane can be completely removed after soaking in an alkaline solution with a pH of 12-14 for a period of time; the membrane removal process is simple, and the losses after membrane removal are minimal.

2. The method for preparing an environmentally friendly coating-type temporary protective conversion film according to claim 1, characterized in that: Organophosphonic acids are one or more of hydroxyethylidene diphosphonic acid, aminotrimethylidene phosphonic acid, and ethylenediaminetetramethylphosphonic acid.

3. The method for preparing an environmentally friendly coating-type temporary protective conversion film according to claim 1, characterized in that: Zinc salts are one of zinc dihydrogen phosphate, zinc oxide, and zinc carbonate.

4. The method for preparing an environmentally friendly coating-type temporary protective conversion film according to claim 1, characterized in that: The accelerator is one or more of sodium nitrite, hydrogen peroxide, copper nitrate, and sodium perborate.

5. The method for preparing an environmentally friendly coating-type temporary protective conversion film according to claim 1, characterized in that: Corrosion inhibitors are commonly used in this field, such as one or more of benzotriazole, ammonium molybdate, sodium citrate, and sodium gluconate.

6. The method for preparing an environmentally friendly coating-type temporary protective conversion film according to claim 1, characterized in that: Thickeners are one or more of hydroxymethyl cellulose, hydroxyethyl cellulose, xanthan gum, and polyvinyl alcohol.

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