Passive surface conditioning solution for tin-plated steel sheets, tin-plated steel sheets, and methods for producing them.

Abstract

Invention details;

Description

Passivation treatment liquid for tin-plated steel sheet, tin-plated steel sheet and manufacturing method thereof Technical Field

[0001] The present invention relates to a surface treatment liquid and a process, in particular to a surface treatment liquid and a process for tin-plated steel plates. Background Art

[0002] To give metal cans an elegant appearance and excellent corrosion resistance, tinplate sheets generally require surface coating before being made into metal cans. This involves applying one or more layers of organic coating to the surface of the tinplate sheet and curing the coating to form a film. This gives the metal cans an elegant appearance and excellent corrosion resistance. Therefore, coating performance is a very important performance indicator for tinplate sheets.

[0003] In order to give tinplate good coating performance, the surface tin layer of the tinplate needs to be passivated to prevent rapid oxidation of tin and improve coating performance.

[0004] Traditional tinplate surface treatment technology relies on chromate electrolytic passivation. Specifically, the tinplate is placed in a chromate solution and subjected to cathodic electrolysis, forming a passivation film containing chromium oxide on the surface. The chromate used in this process is typically dichromate or chromic anhydride. However, long-term use has shown that this simple chromium oxide passivation film does not provide completely satisfactory finishing properties for tinplate. Defects such as paint cratering and poor paint film adhesion often occur, impacting the proper use of the tinplate.

[0005] In addition, US Patent Document No. US3925171A mentions a method for depositing metallic chromium and chromium oxide on the surface of tin-plated steel sheets, which can improve the paint film adhesion of the tin-plated steel sheets.

[0006] Based on this, the present invention aims to provide a passivation treatment liquid for tin-plated steel sheets. By using the passivation treatment liquid to passivate the tin-plated steel sheets, the coating performance of the tin-plated steel sheets can be improved.

[0007] Summary of the Invention

[0008] One of the purposes of the present invention is to provide a passivation treatment liquid for tin-plated steel sheets, which can give the surface of the tin-plated steel sheets better paint wettability and better paint film adhesion, so as to improve and solve the paintability problems encountered by traditional tin-plated sheets.

[0009] In order to achieve the above object, the present invention provides a passivation treatment solution for tin-plated steel sheets, which comprises the following effective ingredients:

[0010] Chromic anhydride, the content of which is 15-30g / L;

[0011] Metaphosphoric acid and / or metaphosphate, with a content of 5-15 g / L;

[0012] Ammonium bromide, its content is 1-5g / L;

[0013] Nitrogen-containing organic matter, the content of which is 0.2-2g / L.

[0014] In the passivation treatment solution of the present invention, chromic anhydride is the source of chromium in the passivation film on the surface of the tin-plated steel sheet, metaphosphoric acid and its salts are the source of phosphorus in the passivation film, and ammonium bromide and nitrogen-containing organic matter enhance the dispersibility and current efficiency of the passivation solution. The addition of phosphorus can enhance the bonding strength between the tin-plated steel sheet and the paint film.

[0015] Preferably, the content of chromic anhydride can also be 18-28 g / L, or 20-25 g / L, for example 22 g / L; the content of metaphosphoric acid and / or metaphosphate can also be 6-13 g / L, or 8-11 g / L, for example 9 g / L, 10 g / L; the content of ammonium bromide can also be 2-4.5 g / L, or 2.5-4 g / L, or 3-4 g / L, for example 3.5 g / L; and / or the content of nitrogen-containing organic matter can also be 0.5-1.8 g / L, or 0.8-1.5 g / L, or 1-1.2 g / L.

[0016] Preferably, in the passivation treatment solution of the present invention, the nitrogen-containing organic matter includes at least one of thiourea, glycine, and nicotinic acid.

[0017] Preferably, in the passivation treatment solution of the present invention, the metaphosphate is an inorganic salt of metaphosphate, such as potassium salt, sodium salt, etc. of metaphosphate.

[0018] Preferably, in the passivation treatment solution of the present invention, in addition to chromic anhydride, chromic acid and its salts, such as chromic acid, potassium chromate, and sodium chromate, can also be used as a source of chromium.

[0019] Preferably, the pH value of the passivation treatment solution of the present invention is 1.2-3.8. This pH range can be achieved by adjusting the pH using phosphoric acid and sodium hydroxide. The pH value can also be 1.5-3.5, 2-3.2, or 2.5-3.

[0020] Another object of the present invention is to provide a tinplate with excellent coating performance, whose surface has excellent paint wettability and better paint film adhesion, so as to improve and solve the coating problems encountered by traditional tinplate.

[0021] Based on this, the present invention also provides a tin-plated steel sheet with excellent coating performance, comprising a steel substrate and a metal tin layer on the steel substrate, wherein the metal tin layer has a surface passivation film formed by the passivation treatment solution as described above.

[0022] Preferably, the surface passivation film of the tin-plated steel sheet of the present invention contains metallic chromium, trivalent oxide of chromium, tin oxide and phosphorus, and does not contain hexavalent chromium.

[0023] Preferably, the content of metallic chromium in the surface passivation film of the present invention is 0.5-2.5 mg / m 2 , can also be 0.8-2.2mg / m 2 , or 1.1-2 mg / m 2 , or 1.2-1.8 mg / m 2 ; The content of chromium trivalent oxide is 2-7mg / m 2 , can also be 2.5-6.3mg / m 2 , or 3.1-5.6 mg / m 2 , or 3.7-4.8 mg / m 2 , for example 4.5 mg / m 2 ; Phosphorus content is 0.3-5mg / m 2 , can also be 0.6-4.1mg / m 2 , or 1.2-3 mg / m 2 , or 1.7-2.4 mg / m 2 , for example 1.9 mg / m 2 ; The content of tin oxide is 0.5-2mC / cm 2 , can also be 0.9-1.9mC / cm 2 , or 1.1-1.8mC / cm 2 , or 1.3-1.7mC / cm 2 , or 1.4-1.5mC / cm 2 .

[0024] It should be noted that millicoulombs per square centimeter, or "mC / cm 2 " is used to express the content of tin oxide, specifically the amount of reduction required for tin oxide to completely remove the oxide film by cathode electrolysis in a low concentration (e.g. 0.001 mol / L) hydrogen bromide solution.

[0025] Preferably, the paint film adhesion grade of the tin-plated steel sheet of the present invention is grade 1.

[0026] Preferably, the surface contact angle of the tin-plated steel sheet described in the present invention is ≤76°.

[0027] Another object of the present invention is to provide a method for manufacturing tin-plated steel sheets with excellent coating properties. The tin-plated steel sheets manufactured by this method have excellent coating wettability and better paint film adhesion on their surfaces.

[0028] Based on this, the present invention also provides a method for manufacturing tin-plated steel sheets, comprising the following steps: a) pre-treating the tin-plated steel substrate after soft melting to remove the tin oxide film on the surface of the tin-plated steel substrate; b) passivating the pre-treated tin-plated steel substrate, the passivation step comprising immersing the pre-treated tin-plated steel substrate in the above-mentioned passivation treatment solution, and using the tin-plated steel substrate as a cathode for cathodic electrolysis treatment.

[0029] Preferably, in the method of the present invention, the pretreatment step comprises immersing the tin-plated steel substrate after reflow in a chromic anhydride solution, wherein the chromic anhydride content in the chromic anhydride solution is 10-20 g / L.

[0030] The tin-plated steel substrate of the present invention can be prepared by common methods known in the art, preferably by a method comprising the following steps performed in sequence: alkali washing (degreasing) of the steel substrate, pickling (surface activation), electroplating tin on the steel substrate to form a metallic tin layer on the steel substrate, and soft melting (alloying) of the tin-plated steel substrate.

[0031] Preferably, the method of the present invention further comprises cleaning the surface of the tin-plated steel sheet with clean water after the passivation step until no chromate residue is left.

[0032] Since the single-side tin coating amount of tin-plated steel sheet ranges from 0.3 to 15 g / m 2 Therefore, the tin-plated steel substrate is usually subjected to a reflow alloying process, which involves rapidly heating the tin-plated steel substrate to a specific temperature above the melting point of metallic tin (e.g., 240-310°C) to form a tin-iron alloy layer between the steel substrate and the metallic tin layer. Since tin is easily oxidized, this process will produce a large amount of tin oxide on the surface of the tin-plated steel sheet.

[0033] The present invention performs a pretreatment step by immersing the tin-plated and reflowed tin-plated steel substrate in a chromic anhydride solution, thereby removing the tin oxide film on the surface before the passivation step to control the tin oxide content in the finished product.

[0034] Preferably, in the method of the present invention, the pretreatment is performed for 2-10 seconds.

[0035] Preferably, in the method of the present invention, the temperature of the chromic anhydride solution is 30-50°C.

[0036] Preferably, in the method of the present invention, the temperature of the passivation treatment solution is 40-65°C.

[0037] Preferably, in the method of the present invention, the charge density of the cathode electrolysis treatment is 15-60C / dm 2 .

[0038] Preferably, the method of the present invention further comprises squeezing the cleaned tin-plated steel sheet after passivation with a squeezing roller, and then drying the surface of the tin-plated steel sheet with hot air not lower than 80°C; and the dried tin-plated steel sheet is conventionally coated with DOS oil (dioctyl sebacate) to obtain a finished product.

[0039] Compared with the prior art, the passivation treatment solution, the tin-plated steel sheet obtained and the manufacturing method thereof of the present invention have the following beneficial effects:

[0040] The chromic anhydride used in the passivation treatment solution of the present invention has a low concentration and does not contain fluorine, thereby reducing the corrosiveness to production equipment, and reducing the environmental load and the environmental protection treatment cost of chromate wastewater.

[0041] The tin-plated steel sheet obtained by using the passivation treatment liquid and manufacturing method described in the present invention has very excellent coating performance, is more conducive to the full spreading and wetting of the paint on the surface of the tin-plated steel sheet, and forms a strong bonding force between the paint film and the tin-plated steel sheet after the paint is cured, which can significantly reduce the quality risks of paint dewetting and poor paint film adhesion, and is more conducive to controlling the amount of tin oxide on the surface of the tin-plated steel sheet at a low level, extending the aging resistance of maintaining good coating performance, and will not cause a decrease in coating performance even after long-term storage. DETAILED DESCRIPTION

[0042] The passivation treatment solution, tin-plated steel sheet and manufacturing method thereof described in the present invention will be further explained and illustrated below in conjunction with specific embodiments. However, such explanation and illustration do not constitute an undue limitation to the technical solution of the present invention.

[0043] Examples 1-9 and Comparative Examples 1-3

[0044] The tin-plated steel sheets of Examples 1-9 of the present invention were manufactured according to the following steps:

[0045] (1) Alkaline washing of the steel substrate;

[0046] (2) pickling;

[0047] (3) Electroplating tin on the steel substrate to form a metallic tin layer, wherein the tin plating amount is 2.8g / m 2 ;

[0048] (4) Soft melting of the tinned steel substrate;

[0049] (5) Pretreatment: Immerse the tinned steel substrate after reflow in a chromic anhydride solution with a chromic anhydride content of 10-20 g / L and a temperature of 30-50°C for a pretreatment time of 2-10 seconds;

[0050] (6) Passivation: The pretreated tin-plated steel substrate was immersed in the passivation treatment solution listed in Table 2. The pH value of the passivation treatment solution was adjusted to 1.2-3.8 with phosphoric acid and sodium hydroxide. The temperature of the passivation treatment solution was 40-65°C. The tin-plated steel plate was used as the cathode for cathodic electrolysis. The cathode electrolysis charge density range was 15-60C / dm 2 After passivation treatment, clean the surface of the tinplate with clean water until there is no chromate residue; squeeze the cleaned tinplate with a squeeze roller, and then dry the surface of the tinplate with hot air at not less than 80°C;

[0051] (7) Apply DOS oil.

[0052] It should be noted that, in order to demonstrate the effect of the present invention, comparative examples 1-3 do not undergo a pretreatment step, and their passivation steps also adopt a traditional process, and the passivation solution used is a 25 g / L sodium dichromate solution, and the passivation solution of the present invention is not used.

[0053] Table 1 lists the specific process parameters of the pretreatment process of Examples 1-9.

[0054] Table 1.

[0055] Table 2 lists the component contents of the passivation treatment solution of Examples 1-9 of the present invention and Comparative Examples 1-3.

[0056] Table 2.

[0057] Table 3 lists the process parameters of the passivation step of Examples 1-9 of the present invention and Comparative Examples 1-3.

[0058] Table 3.

[0059] In order to verify the implementation effect of the present invention, the inventors detected the components in the surface passivation films in Examples 1-9 and Comparative Examples 1-3, and listed them in Table 4.

[0060] In addition, a coating performance evaluation test was conducted on Examples 1-9 and Comparative Examples 1-3, which included:

[0061] (1) Surface wettability test

[0062] The wettability of the surfaces of the tin-plated steel sheets of the Examples and Comparative Examples was measured using a contact angle tester, with water as the test medium. The surface wettability of the surfaces of the Examples and Comparative Examples is listed in Table 4.

[0063] (2) Paint film adhesion performance

[0064] The evaluation method for the paint film adhesion performance refers to the paint film adhesion evaluation method used in QB / T 2763-2006 "Coating of Tin (or Chrome) Thin Steel Sheets". The paint is a commercially available epoxy phenolic paint, which is applied to the tin-plated steel sheet involved in the examples and comparative examples. The dry film weight of the paint film is 10 g / m 2 The coating adhesion performance was evaluated according to the paint film shedding area ratio, and the paint film adhesion performance of the tin-plated steel sheets of the embodiments and comparative examples is listed in Table 4.

[0065] Table 4.

[0066] As can be seen from Table 4, since the pretreatment step of the present invention was not adopted, the tin oxide in the passivation film of the tin-plated steel sheets of Comparative Examples 1-3 was all higher than the upper limit of 2 mC / cm 2 , while the tin oxide content in the passivation film of the tin-plated steel sheets of each embodiment of the present invention is relatively low.

[0067] Furthermore, due to the use of the passivation treatment solution of the present invention, the passivation film of the tin-plated steel sheet of the present invention contains metallic chromium and phosphorus, while none of the comparative examples 1-3 contain these. Furthermore, the contact angles of the examples 1-9 of the present invention are significantly smaller than those of the comparative examples 1-3, and the paint film adhesion grade is Grade 1. This demonstrates that the present invention has superior surface wettability and paint film adhesion performance.

[0068] It should be noted that the prior art within the scope of protection of the present invention is not limited to the embodiments given in this application document. All prior art that does not contradict the solutions of the present invention, including but not limited to prior patent documents, prior publications, prior public uses, etc., can be included in the scope of protection of the present invention.

[0069] In addition, the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0070] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therefrom that can be directly derived from or easily conceived by those skilled in the art based on the disclosure of the present invention are intended to fall within the scope of protection of the present invention.

Claims

DEPCT6925 / 09 / 25681. Passivation treatment solution for tin-plated steel sheets, in which the passivation treatment solution contains the following active ingredients: chromic anhydride in the amount of 15-30 g / L; metaphosphoric acid and / or metaphosphate in the amount of 5-15 g / L; ammonium bromide in the amount of 1-5 g / L; nitrogen-containing organic compounds in the amount of 0.2-2 g / L.

2. Passivation treatment solution according to claim 1, in which the active ingredients 3. An organic compound containing nitrogen, including at least one of the following: thiourea, glycine, or niacin.

4. A passivation surface conditioning solution according to claim 1, where the passivation surface conditioning solution has a pH of 1.2-3.

8.

5. A tin-plated steel plate consisting of a steel substrate and a layer of tin on the steel substrate, where the tin layer has a passivation film on its surface, and where the passivation film is formed by one of the passivation surface conditioning solutions according to claims 1-3.Tin-plated steel sheets under Patent 4 where the surface passivation film consists of chromium, chromium oxide valence tri, tin oxide, and phosphorus, and is free of chromium valence hex.

6. Tin-plated steel sheets under Patent 5 where in the surface passivation film the amount of chromium is 0.5-2.5 mg / m², the amount of chromium oxide valence tri is 2-7 mg / m², the amount of phosphorus is 0.3-5 mg / m², and the amount of tin oxide is 0.5-2 mg / cm².

7. Tin-plated steel sheets under Patent 4 where the tin-plated steel sheet has a lacquer film adhesion level of grade 1.

8. Tin-plated steel sheets under Patent 4 where the tin-plated steel sheet has a surface contact angle less than or equal to 76 degrees.9.The method for producing tin-plated steel sheets includes the following steps: a) pre-conditioning of the tin-plated steel sheet substrate after reflowing to remove the tin oxide film on the surface of the tin-plated steel sheet substrate; b) passivation of the pre-conditioned tin-plated steel sheet substrate, where the passivation step includes immersion of the pre-conditioned tin-plated steel sheet substrate in a passivation surface conditioning solution as specified in one of the claims 1-3, and introduction of the substrate.

10. The method under claim 9 in which the pretreatment includes immersion of the tin-plated steel substrate after reflow in a chromic anhydride solution containing 10-20 g / L of chromic anhydride.

11. The method under claim 9 in which the pretreatment is performed for a duration of 2-10 seconds.

12. The method under claim 10 in which the chromic anhydride solution is heated to 30-50°C. 13.The method under claim 9 in which step b) the surface conditioning solution is subjected to a passivation temperature of 40-65 degrees Celsius.

14. The method under claim 9 in which step b) the cathodic electrolysis process has a cathodic current density of 15-60 coulombs / square decimeter;