Surface passivation method for tin-plated plate with extremely low tin content

Abstract

The invention provides a surface passivation method for a tin plate with extremely low tin content, and belongs to the field of tin plate production. Comprising the following steps: carrying out first electrochemical cathode treatment on the tinplate with extremely low tin content after softening treatment in a Ti-containing phosphating solution so as to form a first passivation film on the surface of at least one side of the tinplate with extremely low tin content; and performing second electrochemical cathode treatment on the extremely-low-tin-content tin-plated plate with the first passivation film in a Cr-containing passivation solution so as to form a second passivation film on at least part of the surface of the first passivation film. First electrochemical cathode treatment is carried out in a Ti-containing phosphating solution, so that the first electrochemical cathode treatment is combined with iron on the surface of a tin plate with extremely low tin content, a composite conversion film layer containing Ti, Fe and P is generated, and the situation that the corrosion resistance is affected by an iron leakage area on the surface of the tin plate is avoided; and secondly, chromate cathode passivation is conducted on the treated tin plate, a trivalent chromium passivation film is generated on the surface tin layer part, and therefore the corrosion resistance of the tin plate with the extremely low tin content is improved.

Description

Technical Field

[0001] The present application relates to the technical field of tinplate production, and in particular to a surface passivation method for tinplate with extremely low tin content. Background Art

[0002] Tinplate refers to a cold-rolled low-carbon thin steel plate coated with pure tin on both sides. It combines the strength and mechanical properties of steel with the corrosion resistance and aesthetics of tin. It is a low-cost packaging material with excellent performance. It is currently widely used in the packaging fields of food, beverage, chemical and other industries. However, it has become an industry consensus to reduce the amount of tin on the surface of tinplate. The tinplate commonly used in the industry is 2.8g / m 2 ~11.2g / m 2 In some applications where there is no high requirement for the tin plating amount, a tin plating amount of 2.8g / m is often used. 2 Low tin content tinplate, the tin content is less than 2.8g / m 2 The development and application of extremely low tin content (ultra-thin) tinplate is still relatively small.

[0003] In order to improve the oxidation resistance and corrosion resistance of the tin plate surface, passivation treatment is generally used. The extremely low tin content is due to the small amount of tin plating on the surface, and there are iron leakage gaps in the tin layer. Studies have found that after soft melting treatment, the tin plating amount is less than 2.8g / m 2 There are tin-plated areas, iron leakage and tin-iron alloy areas on the surface of tin-plated sheets. Conventional chromate electrolytic passivation does not perform well on the surface of such complex tin-plated sheets. Although the corrosion resistance is improved after passivation, it still does not meet practical standards. Therefore, it is necessary to develop passivation aspects to improve its corrosion resistance based on the properties of tin-plated sheets with extremely low tin content. Summary of the invention

[0004] The present application provides a surface passivation method for a tinplate with an extremely low tin content, so as to solve the following technical problem: how to improve the surface corrosion resistance of a tinplate with an extremely low tin content.

[0005] The present application provides a surface passivation method for a tin-plated plate with an extremely low tin content, the method comprising:

[0006] The ultra-low tin-content tin-plated plate after the reflow treatment is subjected to a first electrochemical cathode treatment in a Ti-containing phosphating solution to form a first passivation film on the surface of at least one side of the ultra-low tin-content tin-plated plate;

[0007] The extremely low tin content tin-plated plate having the first passivation film is subjected to a second electrochemical cathode treatment in a Cr-containing passivation solution to form a second passivation film on at least a portion of the surface of the first passivation film.

[0008] Optionally, the raw materials of the Ti-containing phosphating solution include: a solvent, titanyl sulfate dihydrate, phosphoric acid, hydrogen peroxide and a surfactant.

[0009] Optionally, the concentration of the titanyl sulfate dihydrate is 1 g / L to 30 g / L, the concentration of the phosphoric acid is 5 mL / L to 100 mL / L, the concentration of the hydrogen peroxide is 5 mL / L to 100 ml / L, and the concentration of the surfactant is 1 μL / L to 10 μL / L.

[0010] Optionally, the pH value of the Ti-containing phosphating solution is 1.0-5.0.

[0011] Optionally, the first electrochemical cathode treatment includes the following parameters: cathode current density is 0.1A / m 2 ~20.0A / m 2 The processing time is 1s~100s, and the processing temperature is 5℃~55℃.

[0012] Optionally, the thickness of the first passivation film is 5 nm to 40 nm, and the first passivation film is a composite conversion film containing Ti, Fe and P.

[0013] Optionally, the Cr-containing passivation solution is a sodium dichromate solution or a chromic anhydride solution, the concentration of the sodium dichromate solution or the chromic anhydride solution is 10 g / L to 25 g / L, and the pH value of the sodium dichromate solution or the chromic anhydride solution is 2.0 to 4.5.

[0014] Optionally, the second electrochemical cathode treatment includes the following parameters: cathode current density is 0.5A / m 2 ~2A / m 2 The processing time is 3s~10s, and the processing temperature is 30℃~50℃.

[0015] Optionally, the thickness of the second passivation film is 5 nm to 40 nm, and the second passivation film is a chromate passivation film.

[0016] Optionally, the method further includes:

[0017] The extremely low tin content tin-plated plate with the second passivation film is washed with water and dried, and the tin content of the extremely low tin content tin-plated plate is ≤2.8g / m 2 .

[0018] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0019] The present application provides a surface passivation method for an extremely low tin tin-plated plate, comprising: subjecting the extremely low tin tin-plated plate after soft melting treatment to a first electrochemical cathode treatment in a Ti-containing phosphating solution to form a first passivation film on the surface of at least one side of the extremely low tin tin-plated plate; subjecting the extremely low tin tin-plated plate having the first passivation film to a second electrochemical cathode treatment in a Cr-containing passivation solution to form a second passivation film on at least part of the surface of the first passivation film. Based on the complex surface properties of the extremely low tin tin-plated plate, a two-step electrochemical cathode treatment process containing Ti is adopted, and the first electrochemical cathode treatment is selected in a Ti-containing phosphating solution, so as to combine with the iron on the surface of the extremely low tin tin-plated plate to generate a composite conversion film layer containing Ti, Fe and P, thereby avoiding the iron leakage area on the surface of the tin-plated plate from affecting the corrosion resistance; secondly, the treated tin-plated plate is subjected to chromate cathode passivation again, so that the surface tin layer partially generates a trivalent chromium passivation film, thereby improving the corrosion resistance of the extremely low tin tin-plated plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0021] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0022] Figure 1 A schematic flow chart of a surface passivation method for a tin-plated plate with an extremely low tin content provided in an embodiment of the present application;

[0023] Figure 2 This is a 3h salt spray test diagram of the extremely low tin content tin-plated plate after passivation treatment provided in Example 1 of the present application;

[0024] Figure 3 This is a 3h salt spray test diagram of the extremely low tin content tin-plated plate after passivation treatment provided in Example 2 of the present application;

[0025] Figure 4 This is a 3h salt spray test diagram of an extremely low tin content tin-plated plate after passivation treatment provided in Example 3 of the present application;

[0026] Figure 5 This is a 3h salt spray test diagram of an extremely low tin content tin-plated plate after passivation treatment provided in Example 3 of the present application;

[0027] Figure 6 This is a 3h salt spray test diagram of the extremely low tin content tin-plated plate after passivation treatment provided in Comparative Example 1 of the present application;

[0028] Figure 7 This is a 3h salt spray test diagram of the extremely low tin content tin-plated plate after passivation treatment provided in Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0030] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0031] In addition, in the description of the specification of the present application, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second", etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. In this article, "at least one" means one or more, and "plurality" means two or more. "At least one", "the following at least one item (items)" or similar expressions refer to any combination of these items, including any combination of single items (items) or plural items (items). For example, "at least one of a, b, or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e. a and b), ac, bc or abc, where a, b, c can be single or plural, respectively.

[0032] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0033] The creative ideas of this application are:

[0034] In the prior art, aluminum dihydrogen phosphate is used as a conversion liquid for immersion treatment or cathode electrolysis treatment, and then dried to form a passivation film. There is also a method of first performing cathode electrolysis and then performing anodic phosphating with a phosphating solution composed of phosphoric acid and trisodium phosphate. Cathode electrolysis can remove oxides on the surface of the tinplate, and anodic phosphating forms a phosphating film with tin phosphate as the main component on the surface of the tinplate, which has certain corrosion resistance and paint film bonding performance. Although the above-mentioned treatment process can improve the corrosion resistance of low-tin tinplate to a certain extent, the overall effect is different from the traditional chromate passivation process.

[0035] In order to solve the above technical problems, the present application starts from the complex surface properties of extremely low tin content tinplate, selects Ti salt-titanic sulfate that does not contain F element, and selects hydrogen peroxide as a stabilizer and film-forming aid for titanic sulfate, phosphoric acid as the main film-forming substance and pH regulator, and surfactants can enhance the wettability of Ti-containing phosphating solution, and combine with the iron on the surface of the extremely low tin content tinplate to form a composite conversion film layer containing Ti, Fe and P, thereby avoiding the iron leakage area on the surface of the tinplate to affect the corrosion resistance; then the treated tinplate is subjected to chromate cathode passivation, so that the surface tin layer partially forms a trivalent chromium passivation film, thereby improving the corrosion resistance of the extremely low tin content tinplate.

[0036] Figure 1 A schematic flow chart of a surface passivation method for a tinplate with an extremely low tin content provided in an embodiment of the present application.

[0037] See also Figure 1 The present application provides a surface passivation method for a tin-plated plate with an extremely low tin content, the method comprising:

[0038] S1, subjecting the extremely low tin content tin-plated plate after the reflow treatment to a first electrochemical cathode treatment in a Ti-containing phosphating solution to form a first passivation film on the surface of at least one side of the extremely low tin content tin-plated plate;

[0039] In some embodiments, the raw materials of the Ti-containing phosphating solution include: a solvent, titanyl sulfate dihydrate, phosphoric acid, hydrogen peroxide, and a surfactant.

[0040] In some embodiments, the concentration of titanyl sulfate dihydrate is 1 g / L to 30 g / L, the concentration of phosphoric acid is 5 mL / L to 100 mL / L, the concentration of hydrogen peroxide is 5 mL / L to 100 ml / L, and the concentration of surfactant is 1 μL / L to 10 μL / L.

[0041] It should be noted that the concentration of hydrogen peroxide was 30%.

[0042] In the above embodiment, titanyl sulfate dihydrate is the main film-forming substance, hydrogen peroxide is the main salt stabilizer and film-forming aid, phosphoric acid is the main film-forming substance and pH regulator, and the surfactant is used to reduce the surface energy of the tinplate and enhance the wettability of the Ti-containing phosphating solution. Exemplarily, the concentration of titanyl sulfate dihydrate can be 1g / L, 5g / L, 10g / L, 15g / L, 20g / L, 25g / L, 30g / L, etc., the concentration of phosphoric acid can be 5mL / L, 10mL / L, 20mL / L, 30mL / L, 40mL / L, 50mL / L, 60mL / L, 70mL / L, 80mL / L, 90mL / L, 100mL / L, etc., the concentration of hydrogen peroxide can be The concentration of the surfactant may be 5mL / L, 10mL / L, 20mL / L, 30mL / L, 40mL / L, 50mL / L, 60mL / L, 70mL / L, 80mL / L, 90mL / L, 100ml / L, etc. The surfactant may be 1μL / L, 2μL / L, 3μL / L, 4μL / L, 5μL / L, 6μL / L, 7μL / L, 8μL / L, 9μL / L, 10μL / L, etc.

[0043] In some embodiments, the pH value of the Ti-containing phosphating solution is 1.0-5.0.

[0044] In the above embodiment, controlling the pH value of the Ti-containing phosphating solution is more conducive to dissolving the Fe element on the surface of the extremely low-tin tin-plated plate under acidic conditions, thereby participating in film formation to form a composite conversion film containing Ti, Fe and P. Exemplarily, the pH value of the Ti-containing phosphating solution is 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, etc.

[0045] In some embodiments, the first electrochemical cathode treatment includes the following parameters: a cathode current density of 0.1 A / m 2 ~20.0A / m 2 The processing time is 1s~100s, and the processing temperature is 5℃~55℃.

[0046] In the above embodiment, the cathode current density of the first electrochemical cathode treatment is controlled, which can accelerate the formation of the Ti-P conversion film on the one hand, and protect the tin layer from being etched by the acidic solution on the other hand; the time and temperature of the first electrochemical cathode treatment are controlled, so that the Ti-P conversion film can be formed on the surface of the tin plate in a short time. For example, the cathode current density is 0.1A / m 2 , 1.0A / m 2 、3A / m 2 , 5A / m2 , 8A / m 2 , 10A / m 2 , 15A / m 2 , 20.0A / m 2 The processing time can be 1s, 3s, 5s, 7s, 9s, 30s, 50s, 80s, 100s, etc., and the processing temperature can be 5°C, 10°C, 15°C, 30°C, 40°C, 50°C, 55°C, etc.

[0047] In some embodiments, the thickness of the first passivation film is 5 nm to 40 nm, and the first passivation film is a composite conversion film containing Ti, Fe and P.

[0048] In the above embodiment, the thickness of the first passivation film is controlled to provide corresponding corrosion resistance for the extremely low tin content tin-plated plate. Exemplarily, the thickness of the first passivation film can be 5nm, 10nm, 20nm, 30nm, 35nm, 40nm, etc.

[0049] S2. Subjecting the extremely low tin content tin-plated sheet having the first passivation film to a second electrochemical cathode treatment in a Cr-containing passivation solution to form a second passivation film on at least a portion of the surface of the first passivation film.

[0050] In some embodiments, the Cr-containing passivation solution is a sodium dichromate solution or a chromic anhydride solution, the concentration of the sodium dichromate solution or the chromic anhydride solution is 10 g / L to 25 g / L, and the pH value of the sodium dichromate solution or the chromic anhydride solution is 2.0 to 4.5.

[0051] In some embodiments, the second electrochemical cathode treatment includes the following parameters: a cathode current density of 0.5 A / m 2 ~2A / m 2 The processing time is 3s~10s, and the processing temperature is 30℃~50℃.

[0052] In some embodiments, the thickness of the second passivation film is 5 nm to 40 nm, and the second passivation film is a chromate passivation film.

[0053] In the above embodiment, the present application uses a Ti-containing two-step electrochemical cathode treatment process to first form a composite conversion film containing Ti, Fe and P in the iron leakage gaps in the tin layer of the extremely low tin content tin-plated plate, and then continue to generate a trivalent chromium passivation film on it, thereby improving the corrosion resistance of the extremely low tin content tin-plated plate. Exemplarily, the thickness of the second passivation film can be 5nm, 10nm, 20nm, 30nm, 35nm, 40nm, etc.

[0054] In some embodiments, the method further comprises:

[0055] S3, washing and drying the extremely low tin tin-plated plate with the second passivation film, wherein the tin-plated amount of the extremely low tin tin-plated plate is ≤2.8g / m 2 .

[0056] In some embodiments, the drying is drying at 60° C. for 30 to 60 minutes or placing under ventilation conditions for more than 24 hours.

[0057] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to industry standards. If there is no corresponding industry standard, then the conditions recommended by the manufacturer are followed.

[0058] Example 1

[0059] This embodiment provides a surface passivation method for a tinplate with an extremely low tin content, comprising the following steps:

[0060] 1) First, the extremely low tin content tin plate (tin content is 0.5g / m 2 , the thickness of the tin layer is 0.1 μm) in a Ti-containing phosphating solution containing 5 g / L titanium sulfate dihydrate, 25 ml / L hydrogen peroxide (30%), 20 ml / L phosphoric acid, and 5 μL / L surfactant OP-10 for the first electrochemical cathode electrolysis treatment; the process parameters of the first electrochemical cathode electrolysis treatment are: cathode current density 2A / m 2 The treatment time is 5s, the treatment temperature is room temperature (25°C), and it is rinsed with clean water after treatment. The thickness of the first passivation film formed is 30nm;

[0061] 2) Immerse the extremely low tin content tinplate obtained in step 1 in a passivation solution containing 25 g / L sodium dichromate and a pH value of 4.2 for a second electrochemical cathode electrolysis treatment; the process parameters of the second electrochemical cathode electrolysis treatment are: a passivation temperature of 40°C, a current density of 1 A / m 2 , the passivation time is 4s, rinse with clean water after treatment, blow dry at room temperature, and the second passivation film formed is 20nm;

[0062] 3) After the treatment in step 2, place the extremely low tin content tin-plated plate in ventilation conditions for 24 hours to allow it to dry completely. The 3-hour salt spray test of the extremely low tin content tin-plated plate after passivation treatment is shown in the figure below: Figure 2 shown.

[0063] Example 2

[0064] This embodiment provides a surface passivation method for a tinplate with an extremely low tin content, comprising the following steps:

[0065] 1) First, the extremely low tin content tin plate (tin content is 0.5g / m 2 , the thickness of the tin layer is 0.1 μm) in a Ti-containing phosphating solution containing 5 g / L titanium sulfate dihydrate, 55 ml / L hydrogen peroxide (30%), 25 ml / L phosphoric acid, and 5 μL / L surfactant OP-10 for the first electrochemical cathode electrolysis treatment; the process parameters of the first electrochemical cathode electrolysis treatment are: cathode current density 2A / m 2 The treatment time is 3s, the treatment temperature is room temperature (25°C), and it is rinsed with clean water after treatment. The thickness of the first passivation film formed is 40nm;

[0066] 2) Immerse the extremely low tin content tinplate obtained in step 1 in a passivation solution containing 25 g / L sodium dichromate and a pH value of 4.2 for a second electrochemical cathode electrolysis treatment; the process parameters of the second electrochemical cathode electrolysis treatment are: a passivation temperature of 40°C, a current density of 1 A / m 2 , the passivation time is 4s, rinse with clean water after treatment, blow dry at room temperature, and the second passivation film formed is 40nm;

[0067] 3) After the treatment in step 2, place the extremely low tin content tin-plated plate in ventilation conditions for 24 hours to allow it to dry completely. The 3-hour salt spray test of the extremely low tin content tin-plated plate after passivation treatment is shown in the figure below: Figure 3 shown.

[0068] Example 3

[0069] This embodiment provides a surface passivation method for a tinplate with an extremely low tin content, comprising the following steps:

[0070] 1) First, the extremely low tin content tin plate (tin content is 0.5g / m 2 , the thickness of the tin layer is 0.1 μm) in a Ti-containing phosphating solution containing 2 g / L dihydrated titanium sulfate, 15 ml / L hydrogen peroxide (30%), 15 ml / L phosphoric acid, and 5 μL / L surfactant OP-10 for the first electrochemical cathode electrolysis treatment; the process parameters of the first electrochemical cathode electrolysis treatment are: cathode current density 1 A / m 2 The treatment time is 5s, the treatment temperature is room temperature (25°C), and it is rinsed with clean water after treatment. The thickness of the first passivation film formed is 20nm;

[0071] 2) Immerse the extremely low tin content tinplate obtained in step 1 in a passivation solution containing 25 g / L sodium dichromate and a pH value of 4.2 for a second electrochemical cathode electrolysis treatment; the process parameters of the second electrochemical cathode electrolysis treatment are: a passivation temperature of 40°C, a current density of 1 A / m 2 , the passivation time is 4s, rinse with clean water after treatment, blow dry at room temperature, and the second passivation film formed is 20nm;

[0072] 3) After the treatment in step 2, place the extremely low tin content tin-plated plate in ventilation conditions for 24 hours to allow it to dry completely. The 3-hour salt spray test of the extremely low tin content tin-plated plate after passivation treatment is shown in the figure below: Figure 4 shown.

[0073] Example 4

[0074] This embodiment provides a surface passivation method for a tinplate with an extremely low tin content, comprising the following steps:

[0075] 1) First, the extremely low tin content tin plate (tin content is 0.5g / m 2 , the thickness of the tin layer is 0.1 μm) in a Ti-containing phosphating solution containing 3 g / L dihydrated titanium sulfate, 25 ml / L hydrogen peroxide (30%), 25 ml / L phosphoric acid, and 5 μL / L surfactant OP-10 for the first electrochemical cathode electrolysis treatment; the process parameters of the first electrochemical cathode electrolysis treatment are: cathode current density 1 A / m 2 The treatment time is 8s, the treatment temperature is room temperature (25°C), and it is rinsed with clean water after treatment. The thickness of the first passivation film formed is 20nm;

[0076] 2) Immerse the extremely low tin content tinplate obtained in step 1 in a passivation solution containing 25 g / L sodium dichromate and a pH value of 4.2 for a second electrochemical cathode electrolysis treatment; the process parameters of the second electrochemical cathode electrolysis treatment are: a passivation temperature of 40°C, a current density of 1 A / m 2 , the passivation time is 4s, rinse with clean water after treatment, blow dry at room temperature, and the second passivation film formed is 20nm;

[0077] 3) After the treatment in step 2, place the extremely low tin content tin-plated plate in ventilation conditions for 24 hours to allow it to dry completely. The 3-hour salt spray test of the extremely low tin content tin-plated plate after passivation treatment is shown in the figure below: Figure 5 shown.

[0078] Comparative Example 1

[0079] This comparative example provides a surface passivation method for a tinplate with an extremely low tin content, comprising the following steps:

[0080] Use 25g / L sodium dichromate solution as the passivation solution to passivate the extremely low tin content tin plate (tin content of 0.5g / m 2 , tin layer thickness is 0.1μm) at a temperature of 40℃ cathode electrolytic passivation for 4s, the pH value of the passivation solution is 4.2, and the passivation current density is 1A / dm 2 The thickness of the passivation film is about 20nm. The 3h salt spray test of the extremely low tin content tin-plated plate after passivation treatment is shown in the figure below. Figure 6 shown.

[0081] Comparative Example 2

[0082] Use 16.8g / L chromic anhydride solution as the passivation solution to passivate the extremely low tin content tin plate (tin content of 0.5g / m 2 , tin layer thickness is 0.1μm) cathode electrolytic passivation at a temperature of 40℃ for 4s, the pH value of the passivation solution is 2.5, and the passivation current density is 1A / dm 2 The thickness of the passivation film is about 20nm. The 3h salt spray test of the extremely low tin content tin-plated plate after passivation treatment is shown in the figure below. Figure 7 shown.

[0083] The extremely low tin content tin-plated sheets obtained in Examples 1 to 4 and Comparative Examples 1 to 2 after passivation treatment were subjected to a 3-hour salt spray test. The results are shown in Table 1.

[0084] Table 1 3h salt spray test results of extremely low tin content tinplate after passivation treatment

[0085] Comparative Example 1 Comparative Example 2 Example 1 Example 2 Example 3 Example 4 Salt spray level 4 2 9 9 10 9

[0086] In addition, one or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0087] In the embodiment of the present invention, starting from the complex surface properties of the extremely low tin content tinplate, a Ti salt-titanic sulfate that does not contain the F element is selected, and hydrogen peroxide is selected as a stabilizer and film-forming aid for titanic sulfate, phosphoric acid is used as the main film-forming substance and pH regulator, and the surfactant can enhance the wettability of the Ti-containing phosphating solution, and combine with the iron on the surface of the extremely low tin content tinplate to form a composite conversion film layer containing Ti and P; then the treated tinplate is subjected to chromate cathode passivation, so that the tin layer partially forms a trivalent chromium passivation film, thereby improving the corrosion resistance of the extremely low tin content tinplate.

[0088] In the embodiment of the present invention, the salt spray grade of the ultra-low tin content tin-plated plate after passivation treatment in a 3h salt spray test is ≥ grade 9.

[0089] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A surface passivation method for extremely low tin content tinplate, characterized in that: The method comprises: The ultra-low tin-content tin-plated plate after the reflow treatment is subjected to a first electrochemical cathode treatment in a Ti-containing phosphating solution to form a first passivation film on the surface of at least one side of the ultra-low tin-content tin-plated plate; The extremely low tin content tin-plated plate having the first passivation film is subjected to a second electrochemical cathode treatment in a Cr-containing passivation solution to form a second passivation film on at least a portion of the surface of the first passivation film.

2. The method according to claim 1, characterized in that The raw materials of the Ti-containing phosphating solution include: solvent, titanyl sulfate dihydrate, phosphoric acid, hydrogen peroxide and surfactant.

3. The method according to claim 2, characterized in that The concentration of the titanyl sulfate dihydrate is 1 g / L to 30 g / L, the concentration of the phosphoric acid is 5 mL / L to 100 mL / L, the concentration of the hydrogen peroxide is 5 mL / L to 100 ml / L, and the concentration of the surfactant is 1 μL / L to 10 μL / L.

4. The method according to claim 2, characterized in that: The pH value of the Ti-containing phosphating solution is 1.0-5.

0.

5. The method according to claim 1, characterized in that The first electrochemical cathode treatment includes the following parameters: cathode current density is 0.1A / m 2 ~20.0A / m 2 The processing time is 1s~100s, and the processing temperature is 5℃~55℃.

6. The method according to claim 1, characterized in that The thickness of the first passivation film is 5nm-40nm, and the first passivation film is a composite conversion film containing Ti, Fe and P.

7. The method according to claim 1, characterized in that The Cr-containing passivation solution is a sodium dichromate solution or a chromic anhydride solution, the concentration of the sodium dichromate solution or the chromic anhydride solution is 10 g / L to 25 g / L, and the pH value of the sodium dichromate solution or the chromic anhydride solution is 2.0 to 4.

5.

8. The method according to claim 1, characterized in that The second electrochemical cathode treatment includes the following parameters: cathode current density is 0.5A / m 2 ~2A / m 2 The processing time is 3s~10s, and the processing temperature is 30℃~50℃.

9. The method according to claim 1, characterized in that: The thickness of the second passivation film is 5 nm to 40 nm, and the second passivation film is a chromate passivation film.

10. The method according to claim 1, characterized in that The method further comprises: The extremely low tin content tin-plated plate with the second passivation film is washed with water and dried, and the tin content of the extremely low tin content tin-plated plate is ≤2.8g / m 2 .

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