Method for detecting thickness of passive film

Abstract

The invention provides a passive film thickness detection method, and belongs to the technical field of detection. According to the invention, the surface of the metal substrate is firstly coated with the induction layer containing the alkaline chromogenic substance, then the passivation layer is coated, and then the alkaline titrating solution is dropwise added to the surface of the passivation layer, and the alkaline titrating solution gradually permeates into the passivation layer to react with the alkaline chromogenic substance in the induction layer, so that the induction layer develops color; the color development time of the sensing layer and the thickness of the passive film are in a linear relation, and the thickness of the passive film can be obtained according to the color development time of the sensing layer and the standard curve. The detection method provided by the invention is economical, practical, simple, rapid and accurate in measurement.

Description

Technical Field

[0001] The present invention belongs to the technical field of detection, and particularly relates to a method for detecting the thickness of a passivation film. Background Art

[0002] Passivation technology is commonly used in the surface treatment of steel coils, including hot-dip galvanized, hot-dip aluminum-zinc, and hot-dip aluminum-magnesium-zinc steel coils. Its main function is to provide a protective film to prevent the oxidation and corrosion of steel coils.

[0003] During the laboratory development and testing of passivation products, the thickness of the passivation film is one of the most basic and important parameters, which directly affects the performance of the product. Therefore, accurately measuring the thickness of the passivation film is crucial.

[0004] The existing methods for measuring the thickness of the passivation film mainly include XRF fluorescence method, infrared film thickness method, and weighing method. However, the XRF fluorescence method requires a very high equipment investment and has radiation hazards; the infrared film thickness method is only applicable to passivation films containing a certain amount of organic resin components and is greatly affected by water vapor and other interferences; the weighing method requires a high-precision 4-digit balance, is sensitive to contamination, has high requirements for the operation process of personnel, and has poor repeatability. Therefore, developing an economic, practical, simple, fast, and accurate method for detecting the thickness of the passivation film is of great significance for the laboratory development and testing of passivation film products. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for detecting the thickness of a passivation film. The detection method provided by the present invention is economic, practical, simple, fast, and accurate in measurement.

[0006] In order to achieve the above invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a method for detecting the thickness of a passivation film, comprising the following steps:

[0008] (1) Mix an alkaline chromogenic substance, a film-forming substance, and a solvent to obtain an induction layer solution;

[0009] (2) Coat the induction layer solution obtained in step (1) on the surface of a metal substrate and then dry it to obtain a metal substrate with an induction layer;

[0010] (3) Coat different amounts of passivation layer solution on the induction layer surface of the metal substrate with an induction layer obtained in step (2) and then dry it to obtain standard plates with different thickness passivation films respectively;

[0011] (4) Use XRF fluorescence method to measure the thickness of the passivation film in the standard plates with different thickness passivation films obtained in step (3), and then drop an alkaline titrant on the surface of the passivation film of the standard plates with different thickness passivation films obtained in step (3), and draw a standard curve based on the color development time of the induction layer and the thickness of the passivation film;

[0012] (5) Mix an alkaline color-developing substance, a film-forming substance and a solvent to obtain an induction layer solution;

[0013] (6) After coating the induction layer solution obtained in step (5) on the surface of the metal substrate and drying, obtain a metal substrate with an induction layer;

[0014] (7) After coating a passivation layer solution on the surface of the induction layer of the metal substrate with an induction layer obtained in step (6) and drying, obtain a metal substrate with a passivation film;

[0015] (8) Drop the same amount of alkaline titrant as in step (4) on the surface of the passivation film of the metal substrate with a passivation film obtained in step (7), and based on the color development time of the induction layer and the standard curve drawn in step (4), obtain the thickness of the passivation film in the metal substrate with a passivation film.

[0016] Preferably, the alkaline color-developing substance in step (5) includes one or more of phenolphthalein, methyl orange, bromothymol blue, litmus, thymol blue, phenol red, bromocresol green, violaxanthin blue, alizarin yellow and indigo sulfonate.

[0017] Preferably, the film-forming substance in step (5) includes one or more of epoxy silane, amino silane, vinyl silane and tetraethyl orthosilicate.

[0018] Preferably, by mass percentage, the induction layer solution in step (5) includes 0.5-5% alkaline color-developing substance, 5-20% film-forming substance and the balance solvent.

[0019] Preferably, the thickness of the induction layer in the metal substrate with an induction layer in step (6) is 0.01-0.15 μm.

[0020] Preferably, by mass percentage, the alkaline titrant in step (8) includes 10-15% inorganic base, 0.9-2.5% sodium polyacrylate, 1-3% organic base, 5-10% ether substance, 15-25% acetone, 15-25% C4-C6 ketone substance and the balance water.

[0021] Preferably, the inorganic base includes one or more of potassium hydroxide, sodium hydroxide, potassium carbonate and sodium carbonate.

[0022] Preferably, the organic base includes one or more of triethanolamine, diethanolamine and monoethanolamine.

[0023] Preferably, the ether substance includes one or more of ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, and ethylene glycol monopropyl ether.

[0024] Preferably, the C4-C6 ketone substance includes one or more of methyl ethyl ketone, methyl isobutyl ketone, and pentanone.

[0025] The present invention provides a method for detecting the thickness of a passivation film, comprising the following steps: (1) mixing an alkaline chromogenic substance, a film-forming substance, and a solvent to obtain an induction layer solution; (2) coating the induction layer solution obtained in step (1) on the surface of a metal substrate and then drying it to obtain a metal substrate with an induction layer; (3) coating different amounts of a passivation layer solution on the surface of the induction layer of the metal substrate with an induction layer obtained in step (2) and then drying it to obtain standard plates with passivation films of different thicknesses; (4) using XRF fluorescence method to measure the thickness of the passivation film in the standard plates with passivation films of different thicknesses obtained in step (3), and then dropping an alkaline titrant on the surface of the passivation film of the standard plates with passivation films of different thicknesses obtained in step (3), and drawing a standard curve based on the color development time of the induction layer and the thickness of the passivation film; (5) mixing an alkaline chromogenic substance, a film-forming substance, and a solvent to obtain an induction layer solution; (6) coating the induction layer solution obtained in step (5) on the surface of a metal substrate and then drying it to obtain a metal substrate with an induction layer; (7) coating a passivation layer solution on the surface of the induction layer of the metal substrate with an induction layer obtained in step (6) and then drying it to obtain a metal substrate with a passivation film; (8) dropping the same amount of alkaline titrant as in step (4) on the surface of the passivation film of the metal substrate with a passivation film obtained in step (7), and obtaining the thickness of the passivation film in the metal substrate with a passivation film according to the color development time of the induction layer and the standard curve drawn in step (4). In the present invention, an induction layer containing an alkaline chromogenic substance is first coated on the surface of a metal substrate, then a passivation layer is coated, and then an alkaline titrant is dropped on the surface of the passivation layer. The alkaline titrant gradually penetrates into the interior of the passivation layer and reacts with the alkaline chromogenic substance in the induction layer to cause the induction layer to develop color. The color development time of the induction layer has a linear relationship with the thickness of the passivation film. The thickness of the passivation film can be obtained according to the color development time of the induction layer and the standard curve. The detection method provided by the present invention is economical, practical, simple, rapid, and accurate in measurement. Description of the Drawings

[0026] Figure 1 Standard curve drawn for step (4) of Example 1;

[0027] Figure 2 Standard curve drawn for step (4) of Example 6. Detailed Description

[0028] The present invention provides a method for detecting the thickness of a passivation film, comprising the following steps:

[0029] (1) Mix an alkaline chromogenic substance, a film-forming substance and a solvent to obtain an induction layer solution;

[0030] (2) Coat the induction layer solution obtained in the step (1) on the surface of a metal substrate and then dry it to obtain a metal substrate with an induction layer;

[0031] (3) Coat different amounts of a passivation layer solution on the surface of the induction layer of the metal substrate with an induction layer obtained in the step (2) and then dry it to obtain standard plates with passivation films of different thicknesses respectively;

[0032] (4) Use the XRF fluorescence method to measure the thickness of the passivation film in the standard plates with passivation films of different thicknesses obtained in the step (3), and then drop an alkaline titrant on the surface of the passivation film of the standard plates with passivation films of different thicknesses obtained in the step (3), and draw a standard curve according to the color development time of the induction layer and the thickness of the passivation film;

[0033] (5) Mix an alkaline chromogenic substance, a film-forming substance and a solvent to obtain an induction layer solution;

[0034] (6) Coat the induction layer solution obtained in the step (5) on the surface of a metal substrate and then dry it to obtain a metal substrate with an induction layer;

[0035] (7) Coat a passivation layer solution on the surface of the induction layer of the metal substrate with an induction layer obtained in the step (6) and then dry it to obtain a metal substrate with a passivation film;

[0036] (8) Drop the same amount of alkaline titrant as in the step (4) on the surface of the passivation film of the metal substrate with a passivation film obtained in the step (7), and obtain the thickness of the passivation film in the metal substrate with a passivation film according to the color development time of the induction layer and the standard curve drawn in the step (4).

[0037] Unless otherwise specified, the present invention does not have any special limitations on the sources of various substances used in the detection method, and commercially available products well-known to those skilled in the art can be used.

[0038] The present invention mixes an alkaline chromogenic substance, a film-forming substance and a solvent to obtain an induction layer solution.

[0039] In the present invention, the alkaline chromogenic substance preferably includes one or more of phenolphthalein, methyl orange, bromothymol blue, litmus, thymol blue, phenol red, bromocresol green, violophenol blue, alizarin yellow and indigo sulfonate, and more preferably phenolphthalein. In the present invention, the alkaline chromogenic substance can react with an alkaline titrant to show color.

[0040] In the present invention, the film-forming substance preferably includes one or more of epoxy silane, amino silane, vinyl silane, and tetraethyl orthosilicate, and more preferably epoxy silane. As an embodiment, the epoxy silane may specifically be the epoxy silane of Momentive Performance Materials Inc. with the brand name Silquest A-187. In the present invention, the film-forming substance is used to form the induction layer.

[0041] In the present invention, the solvent is preferably an inorganic solvent, and more preferably water. In the present invention, the solvent is used to dissolve the alkaline chromogenic substance and the film-forming substance.

[0042] In the present invention, in terms of mass percentage, the induction layer solution preferably includes 0.5-5% of the alkaline chromogenic substance, 5-20% of the film-forming substance, and the balance of the solvent. As an embodiment, the mass percentage of the alkaline chromogenic substance in the induction layer solution may specifically be 0.5%, 1%, 2%, 3%, 4%, or 5%; the mass percentage of the film-forming substance in the induction layer solution may specifically be 5%, 8%, 10%, 12%, 14%, 16%, 18%, or 20%. By controlling the composition of the induction layer solution within the above range, the present invention can have a better chromogenic effect.

[0043] After obtaining the induction layer solution, in the present invention, the induction layer solution is coated on the surface of the metal substrate and then dried to obtain a metal substrate with an induction layer.

[0044] In the present invention, the metal substrate preferably includes a hot-dip galvanized steel sheet, a hot-dip aluminum-zinc steel sheet, or a hot-dip aluminum-magnesium-zinc steel sheet.

[0045] The present invention has no special limitation on the size of the metal substrate, and it can be selected according to actual needs.

[0046] The present invention has no special limitation on the coating operation, and the coating technical solution well-known to those skilled in the art can be adopted to ensure that the thickness of the induction layer is uniform and within the required range.

[0047] In the present invention, the drying temperature is preferably 280-320°C, and more preferably 300°C; the drying time is preferably 8-12 s, and more preferably 10 s.

[0048] In the present invention, the thickness of the induction layer in the metal substrate with an induction layer is preferably 0.01-0.15 μm. As an embodiment, the thickness of the induction layer in the metal substrate with an induction layer may specifically be 0.01 μm, 0.02 μm, 0.04 μm, 0.06 μm, 0.08 μm, 0.1 μm, 0.11 μm, 0.12 μm, 0.13 μm, 0.14 μm, or 0.15 μm. By controlling the thickness of the induction layer in the metal substrate with an induction layer within the above range, the present invention can have a better chromogenic effect.

[0049] After obtaining the metal substrate with an induction layer, in the present invention, different amounts of a passivation layer solution are coated on the surface of the induction layer of the metal substrate with an induction layer and then dried to obtain standard plates with passivation films of different thicknesses respectively.

[0050] In the present invention, the passivation layer solution is preferably a chromium-free passivation layer solution.

[0051] The present invention has no special limitation on the composition and source of the passivation layer solution, and commercially available products well-known to those skilled in the art can be used.

[0052] As an implementation manner, in terms of mass percentage, the composition of the passivation layer solution can specifically be: 70-80% of water, 1-5% of amino silane, 1-5% of silicate ester, 0.1-1.0% of acetic acid, 0.5-2.0% of phosphoric acid, 0.5-1.5% of fluotitanic acid, and 15-20% of acrylic resin emulsion. In the examples of the present invention, the passivation layer solution is UNICHEMCOAT8803.

[0053] The present invention has no special limitation on the coating operation, and the coating technical solutions well-known to those skilled in the art can be adopted to ensure that the thickness of the passivation layer is uniform.

[0054] The present invention has no special limitation on the coating amount of the passivation layer solution, as long as the thicknesses of the passivation films are different.

[0055] In the present invention, the drying temperature is preferably 280-320 °C, more preferably 300 °C; the drying time is preferably 18-22 s, more preferably 20 s.

[0056] In the present invention, the number of standard plates with passivation films of different thicknesses is preferably 7-9, more preferably 8. The present invention controls the number of standard plates with passivation films of different thicknesses within the above range, which can further improve the detection accuracy.

[0057] As an implementation manner, the thicknesses of the passivation films in the standard plates with passivation films of different thicknesses can specifically be 0.40 g / m 2 , 0.51 g / m 2 , 0.76 g / m 2 , 1.03 g / m 2 , 1.22 g / m 2 , 1.55 g / m 2 , 1.79 g / m 2 and 2.01 g / m 2 .

[0058] After obtaining the standard plates with passivation films of different thicknesses, the present invention uses XRF fluorescence method to measure the thickness of the passivation films in the standard plates with passivation films of different thicknesses, and then drops an alkaline titrant on the surface of the passivation films of the standard plates with passivation films of different thicknesses, and draws a standard curve according to the color development time of the induction layer and the thickness of the passivation film.

[0059] In the present invention, the XRF fluorescence method is preferably a high-precision XRF fluorescence method. The present invention has no special limitation on the operation of using the XRF fluorescence method to measure the thickness of the passivation films in the standard plates with passivation films of different thicknesses, and the XRF fluorescence method well-known to those skilled in the art can be used.

[0060] In the present invention, by mass percentage, the alkaline titrant preferably comprises 10-15% inorganic base, 0.9-2.5% sodium polyacrylate, 1-3% organic base, 5-10% ether substance, 15-25% acetone, 15-25% C4-C6 ketone substance and the balance water.

[0061] By mass percentage, the alkaline titrant preferably comprises 10-15% inorganic base. As an implementation manner, the mass percentage of the inorganic base can specifically be 10%, 11%, 12%, 13%, 14% or 15%.

[0062] In the present invention, the inorganic base preferably comprises one or more of potassium hydroxide, sodium hydroxide, potassium carbonate and sodium carbonate, and more preferably potassium hydroxide. In the present invention, the inorganic base provides an alkaline environment.

[0063] By mass percentage, the alkaline titrant preferably further comprises 0.9-2.5% sodium polyacrylate. As an implementation manner, the mass percentage of the sodium polyacrylate can specifically be 0.9%, 0.96%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4% or 2.5%.

[0064] In the present invention, the average molecular weight Mw of the sodium polyacrylate is preferably 3500-4500, and more preferably 4000. In the present invention, the sodium polyacrylate is used to control the penetration rate of the alkaline titrant, and further control a suitable color development time to make it at a relatively reasonable level, which can not only distinguish passivation films of different thicknesses, but also does not need to wait too long.

[0065] By mass percentage, the alkaline titrant preferably further comprises 1-3% organic base. As an implementation manner, the mass percentage of the organic base can specifically be 1%, 1.5%, 2%, 2.5% or 3%.

[0066] In the present invention, the organic base preferably includes one or more of triethanolamine, diethanolamine, and monoethanolamine, and more preferably triethanolamine. In the present invention, the organic base assists the inorganic base to provide an alkaline environment together.

[0067] In terms of mass percentage, the basic titrant preferably further includes 5-10% of an ether substance. As an embodiment, the mass percentage of the ether substance can specifically be 5%, 6%, 7%, 8%, 9%, or 10%.

[0068] In the present invention, the ether substance preferably includes one or more of ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, and ethylene glycol propyl ether, and more preferably ethylene glycol monobutyl ether. In the present invention, the ether substance acts as a coupling agent and a stabilizer to ensure good compatibility between other components and water.

[0069] In terms of mass percentage, the basic titrant preferably further includes 15-25% of acetone. As an embodiment, the mass percentage of the acetone can specifically be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, or 25%.

[0070] In the present invention, the acetone is used to dissolve the passivation film, so that the basic titrant can penetrate through the passivation film and then undergo a color reaction with the sensing layer.

[0071] In terms of mass percentage, the basic titrant preferably further includes 15-25% of C4-C6 ketone substances. As an embodiment, the mass percentage of the C4-C6 ketone substances can specifically be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, or 25%.

[0072] In the present invention, the C4-C6 ketone substances include one or more of methyl ethyl ketone, methyl isobutyl ketone, and pentanone, and more preferably methyl ethyl ketone. In the present invention, the C4-C6 ketone substances and acetone act together to dissolve the passivation film.

[0073] In terms of mass percentage, the basic titrant preferably further includes the balance of water. In the present invention, the water is used to dissolve other components.

[0074] By controlling the composition of the basic titrant within the above range in the present invention, the basic titrant can have an appropriate penetration rate and color reaction effect.

[0075] The present invention has no special limitation on the preparation method of the basic titrant. It is only necessary to mix the various components evenly by using the technical scheme of material mixing well-known to those skilled in the art.

[0076] In the present invention, during the preparation process, sodium polyacrylate is preferably added in the form of an aqueous solution of sodium polyacrylate; the solid content of the aqueous solution of sodium polyacrylate is preferably 45-50 wt%, more preferably 48 wt%. In the examples of the present invention, the aqueous solution of sodium polyacrylate is specifically Shanghai Daochuang Deceen 801A.

[0077] In the present invention, the sodium polyacrylate in the alkaline titrant is based on the sodium polyacrylate in the aqueous solution of sodium polyacrylate, and the water in the aqueous solution of sodium polyacrylate is calculated into the remaining water.

[0078] In the present invention, the addition amount of the alkaline titrant is preferably 0.4-0.6 mL, more preferably 0.5 mL.

[0079] The present invention has no special limitation on the dropping position of the alkaline titrant, as long as it is ensured that the alkaline titrant does not fall out of the passivation film. As an implementation manner, the alkaline titrant is dropped to the center position of the passivation film.

[0080] The present invention preferably observes the color development time of the sensing layer from directly above the passivation film.

[0081] The present invention has no special limitation on the operation of drawing a standard curve according to the color development time of the sensing layer and the thickness of the passivation film, and the operation of drawing a standard curve well-known to those skilled in the art can be adopted.

[0082] After obtaining the standard curve, the present invention mixes an alkaline color-developing substance, a film-forming substance and a solvent to obtain a sensing layer solution.

[0083] In the present invention, the composition of the sensing layer solution is the same as that of the above-mentioned sensing layer solution, and will not be elaborated here.

[0084] After obtaining the sensing layer solution, the present invention coats the sensing layer solution on the surface of the metal substrate and then dries it to obtain a metal substrate with a sensing layer.

[0085] In the present invention, the operation of coating the sensing layer solution on the surface of the metal substrate and then drying it to obtain a metal substrate with a sensing layer and the thickness of the sensing layer are the same as those of obtaining a metal substrate with a sensing layer above, and will not be elaborated here.

[0086] After obtaining a metal substrate with a sensing layer, the present invention coats a passivation layer solution on the surface of the sensing layer of the metal substrate with a sensing layer and then dries it to obtain a metal substrate with a passivation film.

[0087] In the present invention, the composition of the passivation layer solution, the drying temperature and time are the same as those of the above-mentioned passivation layer solution, and will not be elaborated here.

[0088] The present invention has no special limitation on the coating amount of the passivation layer solution, and any coating amount can be used.

[0089] After obtaining the metal substrate with a passivation film, the present invention drops the same amount of alkaline titrant on the surface of the passivation film of the metal substrate with a passivation film as that when drawing the standard curve, and based on the color development time of the induction layer and the drawn standard curve, the thickness of the passivation film in the metal substrate with a passivation film is obtained.

[0090] In the present invention, the composition of the alkaline titrant is the same as that of the alkaline titrant when drawing the standard curve, and details are not repeated here.

[0091] The present invention has no special limitation on the operation of obtaining the thickness of the passivation film in the metal substrate with a passivation film based on the color development time of the induction layer and the drawn standard curve. The thickness of the passivation film can be obtained from the standard curve by using a technical solution well-known to those skilled in the art.

[0092] In the present invention, an induction layer containing an alkaline chromogenic substance is first coated on the surface of the metal substrate, then a passivation layer is coated, and then an alkaline titrant is dropped on the surface of the passivation layer. The alkaline titrant gradually dissolves the passivation film and penetrates into the interior of the passivation layer to react with the alkaline chromogenic substance in the induction layer, causing the induction layer to develop color. The color development time of the induction layer has a linear relationship with the thickness of the passivation film. The thickness of the passivation film can be obtained based on the color development time of the induction layer and the standard curve. The detection method provided by the present invention is economical, practical, simple, fast and accurate in measurement.

[0093] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without making creative efforts belong to the scope of protection of the present invention.

[0094] Example 1

[0095] A method for detecting the thickness of a passivation film is as follows: (1) Mix phenolphthalein, epoxy silane (Momentive Performance Materials Inc., brand name Silquest A-187) and water to obtain an induction layer solution. In terms of mass percentage, the induction layer solution consists of 3% phenolphthalein, 10% epoxy silane and the balance of water;

[0096] (2) Coat the induction layer solution obtained in step (1) on the surface of a metal substrate (hot-dip galvanized steel sheet, model HDG), and dry it at 300 °C for 10 s to obtain a metal substrate with an induction layer. The thickness of the induction layer is 0.1 μm;

[0097] (3) On the surface of the induction layer of the metal substrate with an induction layer obtained in step (2), different amounts of chromium-free passivation layer solution (UNICHEMCOAT 8803) were coated, and dried at 300 °C for 20 s to obtain standard plates with passivation films of different thicknesses respectively;

[0098] (4) The thickness of the passivation film in the standard plates with passivation films of different thicknesses obtained in step (3) was measured by using high-precision XRF fluorescence method. Then, 0.5 mL of alkaline titrant (by mass percentage, the alkaline titrant consists of 15% potassium hydroxide, 1.44% sodium polyacrylate (Mw is 4000), 3% triethanolamine, 8% ethylene glycol monobutyl ether, 25% acetone, 25% methyl ethyl ketone and the balance of water) was dropped at the center of the surface of the passivation film of the standard plates with passivation films of different thicknesses obtained in step (3). A standard curve was plotted based on the color development time of the induction layer and the thickness of the passivation film. Among them, the thicknesses of the passivation films were 0.40 g / m 2 , 0.51 g / m 2 , 0.76 g / m 2 , 1.03 g / m 2 , 1.22 g / m 2 , 1.55 g / m 2 , 1.79 g / m 2 and 2.01 g / m 2 respectively, and the corresponding color development times were 3 s, 5 s, 7 s, 9 s, 11 s, 13 s, 15 s and 17 s;

[0099] (5) A metal substrate with an induction layer was prepared by the same method as in steps (1) to (2), and the thickness of the induction layer was 0.1 μm;

[0100] (6) A chromium-free passivation layer solution (UNICHEMCOAT 8803) was coated on the surface of the induction layer of the metal substrate with an induction layer obtained in step (5), and dried at 300 °C for 20 s to obtain a metal substrate with a passivation film;

[0101] (7) The same alkaline titrant with the same composition and the same amount as in step (4) was dropped at the center of the surface of the passivation film of the metal substrate with a passivation film obtained in step (6). The color development time of the metal substrate with a passivation film was observed, and based on this color development time and the standard curve plotted in step (4), the thickness of the passivation film in the metal substrate with a passivation film was obtained.

[0102] The standard curve plotted in step (4) of Example 1 is as Figure 1 shown, and the corresponding standard equation is: y = 0.1204x - 0.0454, where y is the film thickness in g / m 2 , and x is the color development time in s.

[0103] In Example 1, the color development time in step (7) is 16.6 s, and the thickness of the passivation film in the metal substrate with the passivation film is 1.95 g / m 2 The thickness of the passivation film in the metal substrate with the passivation film prepared in step (6) of Example 1 is measured by high-precision XRF fluorescence method to be 1.93 g / m 2 .

[0104] Examples 2 to 5

[0105] They are different from Example 1 only in that the coating amount of the chromium-free passivation layer solution in step (6) is different, and other parameters are the same as those in Example 1.

[0106] In Examples 2 to 5, the color development times in step (7) are 13.1 s, 10.7 s, 7.4 s, and 5.9 s in sequence, and the thicknesses of the passivation films in the metal substrates with the passivation films obtained are 1.53 g / m 2 , 1.24 g / m 2 , 0.85 g / m 2 and 0.66 g / m 2 . The thicknesses of the passivation films in the metal substrates with the passivation films prepared in step (6) of Examples 2 to 5 are measured by high-precision XRF fluorescence method to be 1.55 g / m 2 , 1.26 g / m 2 , 0.83 g / m 2 and 0.68 g / m 2 .

[0107] The thicknesses of the passivation films in the metal substrates with the passivation films measured in Examples 1 to 5, the thicknesses of the passivation films in the metal substrates with the passivation films measured in Examples 1 to 5 by high-precision XRF fluorescence method, and the relative errors are shown in Table 1.

[0108] Table 1 The thicknesses of the passivation films in the metal substrates with the passivation films measured in Examples 1 to 5, the thicknesses of the passivation films in the metal substrates with the passivation films measured in Examples 1 to 5 by high-precision XRF fluorescence method, and the relative errors

[0109]

[0110] As can be seen from Table 1, the relative error between the thickness of the passivation film in the metal substrate with the passivation film measured by the detection method of the present invention and the thickness of the passivation film in the metal substrate with the passivation film measured by high-precision XRF fluorescence method is within ±3%, which proves that the detection method of the present invention has good accuracy.

[0111] Example 6

[0112] A method for detecting the thickness of a passivation film is as follows: (1) Mix phenolphthalein, epoxy silane (from Momentive Performance Materials Inc., grade Silquest A-187), and water to obtain an induction layer solution. By mass percentage, the induction layer solution consists of 1.5% phenolphthalein, 10% epoxy silane, and the balance water;

[0113] (2) Coat the induction layer solution obtained in step (1) on the surface of a metal substrate (hot-dip galvanized aluminum-magnesium steel plate), and dry it at 300°C for 10 s to obtain a metal substrate with an induction layer. The thickness of the induction layer is 0.1 μm;

[0114] (3) Coat different amounts of chromium-free passivation layer solution (UNICHEMCOAT 8803) on the induction layer surface of the metal substrate with an induction layer obtained in step (2), and dry it at 300°C for 20 s to obtain standard plates with passivation films of different thicknesses;

[0115] (4) Use a high-precision XRF fluorescence method to measure the thickness of the passivation film in the standard plates with passivation films of different thicknesses obtained in step (3). Then, drop 0.5 mL of an alkaline titrant (by mass percentage, the alkaline titrant consists of 10% potassium hydroxide, 2.4% sodium polyacrylate (Mw = 4000), 2% triethanolamine, 8% ethylene glycol monobutyl ether, 15% acetone, 15% methyl ethyl ketone, and the balance water) at the center of the passivation film surface of the standard plates with passivation films of different thicknesses obtained in step (3). Draw a standard curve based on the color development time of the induction layer and the thickness of the passivation film, where the thicknesses of the passivation film are 0.75 g / m 2 、0.98 g / m 2 、1.15 g / m 2 、1.35 g / m 2 、1.60 g / m 2 、1.86 g / m 2 and 2.05 g / m 2 , and the corresponding color development times are 6 s, 9 s, 11 s, 13 s, 17 s, 19 s, and 21 s;

[0116] (5) Use the same method as in steps (1) to (2) to prepare a metal substrate with an induction layer. The thickness of the induction layer is 0.1 μm;

[0117] (6) Coat a chromium-free passivation layer solution (UNICHEMCOAT 8803) on the induction layer surface of the metal substrate with an induction layer obtained in step (5), and dry it at 300°C for 20 s to obtain a metal substrate with a passivation film;

[0118] (7) Add the same alkaline titrant as in step (4) with the same composition and the same amount dropwise to the center of the passivation film surface of the metal substrate with the passivation film obtained in step (6), observe the color development time of the metal substrate with the passivation film, and obtain the thickness of the passivation film in the metal substrate with the passivation film according to the color development time and the standard curve drawn in step (4).

[0119] The standard curve drawn in step (4) of Example 6 is as Figure 2 shown, and the corresponding standard equation is: y = 0.0856x + 0.2173, where y is the film thickness in g / m 2 , and x is the color development time in s.

[0120] In summary, the detection method provided by the present invention is economical, practical, simple, fast and accurate in measurement.

[0121] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for detecting the thickness of a passivation film, comprising the following steps: (1) Mix an alkaline chromogenic substance, a film-forming substance and a solvent to obtain an induction layer solution; (2) Coat the induction layer solution obtained in step (1) on the surface of a metal substrate and then dry it to obtain a metal substrate with an induction layer; (3) Coat different amounts of a passivation layer solution on the surface of the induction layer of the metal substrate with an induction layer obtained in step (2) and then dry it to obtain standard plates with passivation films of different thicknesses respectively; (4) Use XRF fluorescence method to measure the thickness of the passivation film in the standard plates with passivation films of different thicknesses obtained in step (3), and then drop an alkaline titrant on the surface of the passivation film of the standard plates with passivation films of different thicknesses obtained in step (3), and draw a standard curve according to the color development time of the induction layer and the thickness of the passivation film; (5) Mix an alkaline chromogenic substance, a film-forming substance and a solvent to obtain an induction layer solution; (6) Coat the induction layer solution obtained in step (5) on the surface of a metal substrate and then dry it to obtain a metal substrate with an induction layer; (7) Coat a passivation layer solution on the surface of the induction layer of the metal substrate with an induction layer obtained in step (6) and then dry it to obtain a metal substrate with a passivation film; (8) Drop the same amount of alkaline titrant as in step (4) on the surface of the passivation film of the metal substrate with a passivation film obtained in step (7), and obtain the thickness of the passivation film in the metal substrate with a passivation film according to the color development time of the induction layer and the standard curve drawn in step (4).

2. The detection method according to claim 1, wherein The alkaline chromogenic substance in step (5) includes one or more of phenolphthalein, methyl orange, bromothymol blue, litmus, thymol blue, phenol red, bromocresol green, violophenol blue, alizarin yellow and indigo sulfonate.

3. The detection method according to claim 1, wherein The film-forming substance in step (5) includes one or more of epoxy silane, amino silane, vinyl silane and tetraethyl orthosilicate.

4. The detection method according to claim 1, wherein By mass percentage, the induction layer solution in step (5) includes 0.5 - 5% alkaline chromogenic substance, 5 - 20% film-forming substance and the balance solvent.

5. The detection method according to claim 1, wherein The thickness of the induction layer in the metal substrate with an induction layer in step (6) is 0.01 - 0.15 μm.

6. The detection method according to claim 1, wherein By mass percentage, the alkaline titrant in step (8) includes 10 - 15% inorganic base, 0.9 - 2.5% sodium polyacrylate, 1 - 3% organic base, 5 - 10% ether substance, 15 - 25% acetone, 15 - 25% C4 - C6 ketone substance and the balance water.

7. The detection method according to claim 6, wherein The inorganic base includes one or more of potassium hydroxide, sodium hydroxide, potassium carbonate and sodium carbonate.

8. The detection method according to claim 6, characterized in that The organic base includes one or more of triethanolamine, diethanolamine and monoethanolamine.

9. The detection method according to claim 6, wherein The ether substance includes one or more of ethylene glycol monobutyl ether, diethylene glycol monobutyl ether and ethylene glycol propyl ether.

10. The detection method according to claim 6, wherein The C4 - C6 ketone substance includes one or more of butanone, methyl isobutyl ketone and pentanone.

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