A stripping solution and stripping method for titanium anodic oxidation film of titanium-aluminum composite

Abstract

This invention discloses a stripping solution and method for titanium anodic oxide films on titanium-aluminum composite parts. The stripping solution comprises: an organic compound containing carboxyl groups, an oxidant, an alkali metal salt, and a solvent, wherein the solution pH is 4.5–11. This stripping solution can selectively remove the titanium anodic oxide film from titanium-aluminum composite parts without damaging the aluminum anodic oxide film. The alkali metal ions adsorb onto the titanium metal surface, inhibiting etching of the titanium substrate and resulting in only slow micro-etching with an etching rate less than or equal to 6 nm / min. For workpieces with areas of poor conductivity, the PVD coating on the titanium frame will not exhibit color difference defects. This stripping solution is fluorine-free and heavy metal-free, uses environmentally friendly and inexpensive raw materials, is easy to operate, and has simple waste liquid treatment, resulting in low overall cost and high practical value.

Description

Technical Field

[0001] This invention relates to the field of removing oxide layers from substrate surfaces, and more particularly to a stripping solution and method for titanium anodic oxide films on titanium-aluminum composite parts. Background Technology

[0002] With the iterative upgrades of 3C electronic product technology, mobile phone metal frames typically use titanium and titanium alloys for the frame and aluminum alloys for the middle plate, forming titanium-aluminum composite components. Titanium and titanium alloys have high strength, good corrosion resistance, light weight, and good biocompatibility; aluminum alloys are inexpensive and easy to manufacture into complex structural components. Aluminum alloys undergo anodizing to form an anodic oxide film, overcoming their drawbacks such as poor scratch resistance and susceptibility to corrosion. However, after anodizing, the anodic oxide film also forms on the titanium surface of the titanium-aluminum composite component, which reduces the adhesion of the subsequent PVD coating on the titanium frame, potentially causing the coating to peel off. Current technology removes the titanium anodic oxide film through grinding and sandblasting. For titanium frames with localized poor conductivity, where the anodic oxide film has not formed, grinding, sandblasting, and subsequent PVD coating processes result in uneven color between the poorly conductive areas and other areas, requiring rework.

[0003] Patent CN115679430A discloses a film-removing agent comprising an accelerator, a corrosion inhibitor, and a film-removing agent. The accelerator is nitrate or a nitro compound; the corrosion inhibitor is one or more of quinoline boric acid and its alcohol esters, thioamides, thiazolidinones, thiourea derivatives, imidazoles and their derivatives; and the film-removing agent is selected from at least one of sulfuric acid and sulfates. Before the microporous injection molding of titanium-aluminum composite parts, the titanium anodic oxide film needs to be removed during the step-by-step microporous treatment of titanium and aluminum metals to reduce damage to the aluminum anodic oxide film. Chemical immersion is used for film removal; however, the high concentration of acid in chemical immersion causes significant damage to the aluminum anodic oxide film.

[0004] In existing technologies, a cryogenic electrolytic stripping process is also used. Although low-concentration acid causes little damage to the aluminum anodic oxide film, it does not have a micro-etching effect on the titanium substrate, leaving a pale yellow anodic oxide film. At the same time, the cryogenic electrolytic stripping process has very high requirements for electrolysis equipment and is very costly, making it difficult to commercialize.

[0005] Given the aforementioned deficiencies, it is indeed necessary to provide a low-cost stripping solution that can remove titanium anodized films without damaging aluminum anodized films to solve these problems. Summary of the Invention

[0006] The purpose of this invention is to provide a stripping solution and method for titanium anodic oxide film on titanium-aluminum composite parts, which removes the titanium anodic oxide film on the titanium-aluminum composite parts without damaging the aluminum anodic oxide film. This method is low in cost and easy to operate.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A stripping solution for titanium anodic oxide films on titanium-aluminum composite parts comprises: an organic compound containing carboxyl groups, an oxidant, an alkali metal salt, and a solvent, wherein the solution pH is 4.5–11.

[0009] Preferably, the pH of the solution is 6.5 to 7.5.

[0010] Preferably, by mass percentage, the organic carboxylate or organic carboxylic acid comprises 5-20%, the oxidant comprises 1-5%, the alkali metal salt comprises 2-15%, and the solvent comprises 60-92%.

[0011] Preferably, the carboxylate-containing organic compound is at least one selected from sodium citrate, citric acid, potassium sodium tartrate, tartaric acid, tetrasodium ethylenediaminetetraacetate, trisodium aminotriacetate, malonic acid, p-tert-butylbenzoic acid, oxalic acid, sodium oxalate, and sodium acetate.

[0012] Preferably, the oxidant is at least one selected from potassium persulfate, sodium persulfate, urea peroxide, hydrogen peroxide, sodium perchlorate, potassium iodate, sodium metavanadate, sodium stannate, sodium tungstate, and sodium molybdate.

[0013] Preferably, the alkali metal salt is a water-soluble alkali metal salt.

[0014] Preferably, the alkali metal salt is at least one of lithium, sodium, and potassium salts of silicic acid, phosphoric acid, and carbonate.

[0015] Preferably, the solvent is pure water.

[0016] The present invention also provides a method for removing titanium anodic oxide film from titanium-aluminum composite parts, comprising the following steps:

[0017] (1) Place the titanium-aluminum composite part in the above-mentioned stripping solution, the temperature of which is 20-50℃;

[0018] (2) After removing the titanium anodic oxide film, rinse twice with pure water and dry with compressed air.

[0019] The beneficial effects of this invention are as follows:

[0020] (1) The stripping solution of the present invention can selectively remove the titanium anodic oxide film of titanium-aluminum composite parts. Under the action of the oxidant and organic carboxylic acid ions in the stripping solution, the titanium anodic oxide film generates soluble titanium metal ions. At the same time, during the stripping process, since the acidity and alkalinity of the stripping solution are relatively mild, the aluminum anodic oxide film will not be damaged.

[0021] (2) After removing the titanium anodic oxide film, the alkali metal ions of the stripping solution of the present invention will be adsorbed on the titanium metal surface, inhibiting the etching of the titanium substrate, and only slow micro-etching will occur. The etching rate is less than or equal to 6 nm / min, which can completely remove the titanium anodic oxide film.

[0022] (3) For workpieces with localized poor conductivity, after removing the titanium anodic oxide film, the titanium frame PVD coating will not show color difference defects after grinding, sandblasting and PVD coating processes.

[0023] (4) The stripping solution of the present invention is free of fluorine and heavy metals, the raw materials are environmentally friendly and inexpensive, the stripping operation is simple, the waste liquid is easy to treat, the overall cost of use is low, and it has high practical value. Detailed Implementation

[0024] To make the technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] According to a first aspect of the present invention, the present invention provides a stripping solution for titanium anodic oxide films on titanium-aluminum composite parts, characterized in that it comprises: an organic compound containing carboxyl groups, an oxidant, an alkali metal salt, and a solvent, wherein the solution pH is 4.5 to 11.

[0026] In one embodiment of the present invention, the solution pH is 6.5–7.5. The acidity or alkalinity of the stripping solution is related to whether the stripping solution will damage the aluminum anodic oxide film during use. When there is a high concentration of acid, the stripping solution will cause significant damage to the aluminum anodic oxide film. The stripping solution of this application uses a relatively mild acidity or alkalinity, which can remove the titanium anodic oxide film without damaging the aluminum anodic oxide film.

[0027] In one embodiment of the present invention, the organic carboxylate or organic carboxylic acid comprises 5-20% by mass, the oxidant comprises 1-5%, the alkali metal salt comprises 2-15%, and the solvent comprises 60-92%.

[0028] In one embodiment of the present invention, the carboxylate-containing organic compound is at least one selected from sodium citrate, citric acid, potassium sodium tartrate, tartaric acid, tetrasodium ethylenediaminetetraacetate, trisodium aminotriacetate, malonic acid, p-tert-butylbenzoic acid, oxalic acid, sodium oxalate, and sodium acetate. The stripping solution of the present invention uses organic carboxylic acids or organic acid salts, replacing traditional fluorine-containing inorganic strong acids, which can quickly remove the titanium anodic oxide film without damaging the aluminum anodic oxide film, ensuring dimensional accuracy requirements during precision part processing.

[0029] In one embodiment of the present invention, the oxidant is at least one selected from potassium persulfate, sodium persulfate, urea peroxide, hydrogen peroxide, sodium perchlorate, potassium iodate, sodium metavanadate, sodium stannate, sodium tungstate, and sodium molybdate. Under the combined action of the oxidant and organic carboxylic acid ions, the titanium anodic oxide film generates soluble titanium metal ions, and the stripping solution can quickly remove the titanium anodic oxide film.

[0030] In one embodiment of the invention, the alkali metal salt is a water-soluble alkali metal salt. The alkali metal salt needs to be dissolved in the stripping solution to generate alkali metal ions, which are adsorbed onto the titanium metal surface in subsequent reactions to inhibit etching of the titanium substrate.

[0031] In one embodiment of the present invention, the alkali metal salt is at least one of lithium, sodium, or potassium salts of silicate, phosphoric acid, and carbonate. The alkali metal ions adsorb onto the titanium metal surface, inhibiting etching of the titanium substrate and resulting in only slow micro-etching at a rate less than or equal to 6 nm / min, which can completely remove the titanium anodic oxide film.

[0032] In one embodiment of the present invention, the solvent is pure water.

[0033] According to a second aspect of the present invention, the present invention also provides a method for removing titanium anodic oxide film from titanium-aluminum composite parts, comprising the following steps:

[0034] (1) Place the titanium-aluminum composite part in the above-mentioned stripping solution, the temperature of which is 20-50℃;

[0035] (2) After removing the titanium anodic oxide film, rinse twice with pure water and dry with compressed air.

[0036] The present invention will be further described below through specific embodiments. These specific embodiments are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0037] Example 1

[0038] (1) Take a stripping solution with a mass percentage of 8% trisodium aminotriacetate, 4% urea peroxide, 2% sodium silicate and 86% pure water, and a solution pH of 9.3. Take two sets of titanium-aluminum composite sample pieces with dimensions of 30×120×1.5mm, suspend one half in the stripping solution with an immersion area of ​​30×60mm, and suspend the other half in the air without contacting the stripping solution. The temperature of the stripping solution is 40℃.

[0039] (2) After removing the titanium anodic oxide film, rinse twice with pure water and dry with compressed air.

[0040] Example 2

[0041] Unlike Example 1, the stripping solution was prepared with 6% citric acid, 3% sodium perchlorate, 5% sodium carbonate, and 86% pure water by mass, and the pH of the solution was 5.1.

[0042] The rest is the same as in Example 1, and will not be repeated here.

[0043] Example 3

[0044] Unlike Example 1, the stripping solution was prepared with 10% by mass of p-tert-butylbenzoic acid, 5% by mass of hydrogen peroxide, 5% by mass of sodium silicate, and 80% by mass of pure water. In addition, the pH of the solution was 11.

[0045] The rest is the same as in Example 1, and will not be repeated here.

[0046] Comparative Example 1

[0047] Unlike Example 1, the stripping solution was prepared with 8% by mass of trisodium aminotriacetate, 3% by mass of urea peroxide, 2% by mass of sodium hydroxide, and 87% by mass of pure water. In addition, the pH of the solution was 13.7.

[0048] The rest is the same as in Example 1, and will not be repeated here.

[0049] Comparative Example 2

[0050] Unlike Example 1, the stripping solution was prepared with 8% by mass of trisodium aminotriacetate, 2% by mass of sodium silicate, and 90% by mass of pure water. In addition, the pH of the solution was 9.3.

[0051] The rest is the same as in Example 1, and will not be repeated here.

[0052] Comparative Example 3

[0053] Unlike Example 1, the stripping solution was prepared with 8% citric acid, 4% urea peroxide, 2% sodium silicate, and 86% pure water by mass, and the solution pH was 3.2.

[0054] The rest is the same as in Example 1, and will not be repeated here.

[0055] After the film removal was completed, the aluminum anodized surfaces of Examples 1-3 and Comparative Examples 1-3 were subjected to zebra pen sealing level tests, while the other group was subjected to titanium micro-etching rate measurement experiments.

[0056] Zebra Pen Sealing Grade Test: A 5mm diameter dot is made on the workpiece using a Zerba black oil-based pen (made in Japan). After drying for 10 seconds, the dot is repeatedly wiped with a cotton pad soaked in pure water under pressure of approximately 5 kgf. The degree of black dot residue is observed to determine the sealing grade. The test results are divided into six grades from 0 to 5, with grade 0 indicating the best sealing performance, showing no damage to the workpiece surface, and grade 5 indicating the worst performance, showing severe damage to the workpiece surface.

[0057] Experiment to determine the micro-etching rate of titanium: First, the workpiece after removing the titanium anodized film was weighed, with the result accurate to 0.0001 g. Then, half of the sample with the removed titanium anodized film was suspended and immersed in the stripping solution, while the other half was suspended in the air without contact with the stripping solution. After immersion for 2 hours, it was rinsed twice with pure water, dried with CDA, and weighed again, with the result accurate to 0.0001 g. The mass loss of titanium per hour Δm (g / h) was measured, and the density of titanium was 4.51 g / cm³. 3 The formula for calculating the micro-etching rate on a titanium substrate is: V(nm / min)=(Δm / 4.51)×10 7 ÷(30×60×0.01×60). This gives us the micro-etching rate of the stripping solution on titanium.

[0058] The test results are shown in Table 1:

[0059] Table 1

[0060]

[0061]

[0062] The experimental results of Example 1 and Comparative Example 1 show that the stripping solution of Comparative Example 1 causes severe damage to the aluminum anodic oxide film, with a zebra pen sealing grade of 5 and a micro-etching rate of up to 120 nm / min on titanium. This indicates that the alkali metal ions of the alkali metal salt used in this experiment are adsorbed on the surface of titanium metal, inhibiting the etching of the titanium substrate and only causing slow micro-etching with an etching rate of less than or equal to 6 nm / min. Furthermore, it maintains a relatively mild solution pH and does not damage the aluminum anodic oxide film. However, a higher alkalinity will damage the aluminum anodic oxide film.

[0063] The experimental results from Example 1 and Comparative Example 2 show that the stripping solution of Comparative Example 2 cannot remove the titanium anodic oxide film. This indicates that only through the synergistic effect of the organic carboxylic acid ions and the oxidant in the stripping solution can soluble titanium metal ions be generated with the titanium anodic oxide film, thereby removing the titanium anodic oxide film.

[0064] The experimental results of Example 1 and Comparative Example 3 show that the stripping solution of Comparative Example 3 damaged the aluminum anodic oxide film, and the zebra pen sealing level test was 2. This indicates that the stripping solution of Example 1 maintains a relatively mild solution pH and will not damage the aluminum anodic oxide film, while a higher acidity will damage the aluminum anodic oxide film.

[0065] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A stripping solution for titanium anodic oxide films on titanium-aluminum composite parts, characterized in that, include: Organic compounds containing carboxyl groups, oxidizing agents, alkali metal salts, and solvents, wherein the solution pH is 4.5–11; By mass percentage, the organic compound containing carboxyl group is 5-20%, the oxidant is 1-5%, the alkali metal salt is 2-15%, and the solvent is 60-92%. The organic compound containing carboxylate is at least one of sodium citrate, citric acid, potassium sodium tartrate, tartaric acid, tetrasodium ethylenediaminetetraacetate, trisodium aminotriacetate, malonic acid, p-tert-butylbenzoic acid, oxalic acid, sodium oxalate, and sodium acetate. The alkali metal salt is at least one of the lithium, sodium, and potassium salts of silicic acid, phosphoric acid, and carbonate.

2. The film-removing solution according to claim 1, characterized in that, The solution has a pH of 6.5 to 7.

5.

3. The film-removing solution according to claim 1, characterized in that, The oxidant is at least one selected from potassium persulfate, sodium persulfate, urea peroxide, hydrogen peroxide, sodium perchlorate, potassium iodate, sodium metavanadate, sodium stannate, sodium tungstate, and sodium molybdate.

4. The film-removing solution according to claim 1, characterized in that, The solvent is pure water.

5. A method for removing titanium anodic oxide film from titanium-aluminum composite parts, characterized in that, Includes the following steps: (1) The titanium-aluminum composite is placed in the stripping solution of any one of claims 1-4, wherein the temperature of the stripping solution is 20~50℃; (2) After removing the titanium anodic oxide film, rinse twice with pure water and dry with compressed air.

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