Pre-blackening agent before phosphorization as well as preparation method and application of pre-blackening agent

Abstract

The invention relates to the field of metal surface chemical treatment, and particularly discloses a pre-blackening agent before phosphorization and a preparation method and application thereof.The pre-blackening agent before phosphorization is prepared from, by volume of 1 L, 2-5 g / L of copper sulfate, 5-15 g / L of ammonium molybdate, 5-10 g / L of citric acid, 10-15 mL / L of inorganic acid, 1-3 g / L of a coalescing agent, 3-5 g / L of an accelerant, 3-5 g / L of a complexing agent and a pH regulator, the solvent is water, and the pH value of the pre-blackening agent before phosphorization is 3.0-3.5. The pre-blackening agent before phosphating is excellent in performance and suitable for pre-blackening treatment before steel phosphating treatment, a phosphating film generated when the pre-blackening agent before phosphating is combined with a phosphating solution is uniform and consistent in black appearance, fine and compact in film layer and good in protection performance, and the phenomenon that a steel test piece is corroded is not prone to occurring.

Description

Technical Field

[0001] The invention belongs to the field of metal surface chemical treatment, and particularly relates to a pre-phosphating blackening agent and a preparation method and application thereof. Background Art

[0002] Phosphating technology is widely used in the fields of automobiles, motorcycles, household appliances, mechanical equipment, etc., especially in the field of metal corrosion protection. Phosphating technology is an indispensable main process for phosphating metal surfaces. It can significantly improve the surface corrosion resistance, wear resistance, and decorativeness. It is a key technology to improve metal quality. It can form a protective film with good stability and high density on the surface of metals such as steel, which can effectively resist external erosion. In order to obtain a black and beautiful film layer on the surface of steel, high-temperature boiling and room-temperature blackening processes are generally used, but the corrosion resistance and wear resistance of the film layer are poor, and the blackened film is loose and has poor adhesion; the surface conversion film formed after the phosphating treatment of steel has the advantages of small crystals, denseness, and strong bonding. Therefore, blackening and phosphating treatment are often combined to prepare a black chemical conversion film with better performance.

[0003] There are two types of black film phosphating processes for steel. One of them is the step-by-step method, which is pre-impregnation followed by phosphating. The blackening agent in the pre-impregnation solution is composed of a variety of inorganic salts and acids. During the pre-impregnation process, the steel surface undergoes oxidation-reduction and chemical reactions to generate countless tiny, dense black crystal nuclei. These crystal nuclei combine with phosphate to form a black, firmly bonded, uniform, and delicate black conversion film. Room temperature blackening can be roughly divided into selenium-copper system, selenite-copper salt-phosphoric acid system, copper-sulfur system, molybdenum-copper system, heteropoly acid-copper sulfate system, etc.

[0004] The invention patent with application number 202110759193.9 discloses a highly corrosion-resistant rust-removing pre-blackening agent and its preparation method and application. The highly corrosion-resistant rust-removing pre-blackening agent can complete blackening pretreatment on two or more different materials and different surface states of the same workpiece to obtain a uniform black conversion film; at the same time, it can remove the rust on the surface of the workpiece and has strong corrosion resistance. However, the highly corrosion-resistant rust-removing pre-blackening agent needs to be immersed at 75-85°C for 3-5 minutes, and the heating cost is relatively high; the invention patent with application number 201710058050.9 discloses a method for steel The invention discloses a room-temperature blackening liquid for iron and application thereof. The room-temperature blackening liquid comprises selenouric acid, copper sulfate, nickel sulfate, zinc dihydrogen phosphate, phosphoric acid, citric acid, octylphenol polyoxyethylene ether-10 and water. The room-temperature blackening liquid has high film-forming efficiency, improves the glossiness, bonding strength, density and other properties of the blackened film, solves the problem of poor stability, is simple and easy to use, and is suitable for large-scale promotion. By adding additives, the amount of selenium in the blackening liquid is reduced, and pollution is reduced. However, when the room-temperature blackening agent is used, the blackening temperature is 40-60°C, the blackening time is 10-20 minutes, and the processing time is too long, which is prone to corrosion of steel test pieces.

[0005] In view of this, a pre-phosphating pre-blackening agent disclosed in the present invention is particularly important. Summary of the invention

[0006] In view of the defects of the prior art, the present invention provides a pre-blackening agent before phosphating, which is suitable for the pre-blackening treatment of steel before phosphating. When used in combination with the phosphating solution, the generated phosphating film has a uniform black appearance, a fine and dense film layer, good protective performance, and is not prone to corrosion of steel specimens.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] On one hand, the present invention provides a pre-blackening agent before phosphating, which comprises the following raw materials, based on a volume of 1L: 2-5g / L copper sulfate, 5-15g / L ammonium molybdate, 5-10g / L citric acid, 10-15mL / L inorganic acid, 1-3g / L film-forming aid, 3-5g / L accelerator, 3-5g / L complexing agent, and pH regulator. The solvent is water, and the pH value of the pre-blackening agent before phosphating is 2.0-3.5.

[0009] The present application uses copper sulfate and ammonium molybdate as the main blackening components of the pre-blackening agent, utilizes copper ions to deposit on the steel-based surface to generate active copper particles, and simultaneously converts iron into divalent iron ions; while ammonium molybdate accelerates the production of active oxygen under acidic conditions, and directly reacts with copper to generate a black oxide film; the applicant also avoids the phenomenon of reddening of the film layer, unreliable bonding force, and other deterioration of film quality by controlling the mass ratio of copper sulfate and ammonium molybdate.

[0010] In some embodiments of the present invention, the inorganic acid is a mixture of phosphoric acid and acetic acid.

[0011] In some embodiments of the present invention, the mass ratio of phosphoric acid to acetic acid is 1:(0.5-1).

[0012] Preferably, the mass ratio of phosphoric acid to acetic acid is 1:0.8.

[0013] The present invention forms a film layer with good bonding strength at a pH value of 2.0 to 3.5 by adding phosphoric acid to acidify the pre-black liquid. However, due to the generation of brick-red cuprous oxide, the blackened film is translucent brown-black, while the composite addition of acetic acid generates a blackened film with a uniform black appearance. The possible reason is that acetic acid inhibits the generation of brick-red cuprous oxide in the form of a catalyst to a certain extent, and acetic acid acidification also increases the fineness of the blackened film.

[0014] In some embodiments of the present invention, the film-forming aid comprises the following raw materials in parts by weight: 1 to 3 parts of calcium nitrate, 1 to 2 parts of nickel nitrate, 1 to 5 parts of tartaric acid, 0.5 to 2.5 parts of manganese chloride and 2 to 3 parts of boric acid.

[0015] Preferably, the film-forming aid comprises the following raw materials in parts by weight: 2 parts of calcium nitrate, 1.5 parts of nickel nitrate, 3 parts of tartaric acid, 1.5 parts of manganese chloride and 2.5 parts of boric acid.

[0016] The applicant prepared a film-forming aid containing the above raw materials and found that calcium and nickel ions can play a role in refining grains. The possible reason is that calcium and nickel can inhibit the growth of phosphating grains and form short rod-shaped and granular crystals with small particle size, smoothness and close arrangement on the surface of the substrate; in addition, when the pre-blackening agent prepared by the present invention is used as a pre-blackening agent before phosphating treatment with zinc or manganese phosphating liquid, the uniformity of the phosphating film can be significantly improved. The possible reason is that it partially replaces zinc ions or manganese ions, thereby reducing the presence rate of large-size grains; and nitrate ions can also assist ammonium molybdate in the system to oxidize hydrogen into water, play a certain depolarizing role, increase the cathode area, and accelerate the formation. The applicant also found that the film-forming quality of the pre-black liquid with the addition of a film-forming aid was greatly improved, the blackness and thickness were better, and the film layer was denser. The possible reason was that the tartaric acid in the film-forming aid promoted the solubility of other components in water to a certain extent, thereby increasing the content of the effective ingredients of the pre-black agent. On the other hand, manganese chloride reacted with the phosphating liquid of the subsequent phosphating treatment, and the generated manganese hydrogen phosphate was deposited on the steel specimen, which also promoted the film-forming effect of the phosphating liquid to a certain extent. The boric acid in the film-forming aid can form a boric acid-borate buffer system in an acidic solution, which can better control the reaction speed of the film-forming aid and further increase the stability of the pre-black agent film.

[0017] In some embodiments of the present invention, the pH adjuster is sodium hydroxide and / or potassium hydroxide.

[0018] Preferably, the pH adjuster is potassium hydroxide.

[0019] In some embodiments of the present invention, the complexing agent is at least one of tartaric acid, sodium tartrate and potassium sodium tartrate.

[0020] Preferably, the complexing agent is sodium tartrate.

[0021] In some embodiments of the present invention, the promoter is a mixture of an oxidant containing chlorate ions and an aromatic nitro compound.

[0022] In some embodiments of the present invention, the oxidant containing chlorate ions is potassium chlorate, and the aromatic nitro compound is sodium nitrobenzene sulfonate.

[0023] Preferably, the concentration ratio (g / L) of the oxidant containing chlorate ions to the aromatic nitro compound is (0.2-0.6):1.

[0024] Further preferably, the concentration ratio (g / L) of the oxidant containing chlorate ions to the aromatic nitro compound is 0.4:1.

[0025] The applicant ensured the effect of the pre-blackening agent at room temperature by optimizing and regulating the concentration ratio of potassium chlorate and sodium nitrobenzene sulfonate, while accelerating the reaction speed. When the pre-blackening agent is used in combination with zinc or manganese phosphating solution, it can accelerate the growth of crystal nuclei and improve stability.

[0026] On the other hand, the present invention also provides a method for preparing a pre-blackening agent before phosphating, comprising the following steps: adding water to copper sulfate, ammonium molybdate, citric acid, inorganic acid, film-forming aid, promoter, and complexing agent until dissolved, mixing and stirring evenly, and adjusting the pH to 2.0-3.5 with a pH regulator to obtain the pre-blackening agent before phosphating.

[0027] In another aspect, the present invention also provides an application of a pre-blackening agent before phosphating in phosphating treatment of steel.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The present invention provides a pre-blackening agent before phosphating, which is suitable for pre-blackening treatment before steel phosphating treatment. When used in combination with a phosphating solution, the phosphating film generated has a uniform black appearance, a fine and dense film layer, good protective performance, and is not prone to corrosion of steel specimens;

[0030] (2) The pre-blackening agent before phosphating provided by the present invention is a pre-blackening agent before phosphating with a copper-molybdenum blackening system, with copper sulfate and ammonium molybdate as the main blackening components of the pre-blackening agent, using copper ions to deposit on the steel base surface to generate active copper particles, while ammonium molybdate accelerates the generation of active oxygen under acidic conditions, directly reacting with copper to generate a black oxide film; at the same time, the mass ratio of copper sulfate and ammonium molybdate is controlled to avoid the phenomenon of reddening of the film layer, unreliable bonding force and other film quality degradation phenomena;

[0031] (3) The present invention acidifies the pre-black liquid by adding a composite inorganic acid of phosphoric acid and acetic acid, and forms a black film with good bonding strength and uniform black appearance at an acidity of pH 2.0 to 3.5, while increasing the fineness of the black film;

[0032] (4) The present invention prepares a new film-forming aid, which plays a role in refining grains and improving the uniformity of the phosphating film; on the other hand, it assists the ammonium molybdate in the system to oxidize hydrogen into water, accelerates the film-forming speed, and avoids the corrosion of the steel substrate; on the other hand, it improves the film-forming quality of the pre-black liquid, and its blackness and thickness are improved, and the film layer is denser, further increasing the stability of the pre-black agent film; and it also has a certain promoting effect on the film-forming effect of the phosphating liquid;

[0033] (5) The present invention optimizes and regulates the mass ratio of potassium chlorate and sodium nitrobenzene sulfonate so that the pre-blackening agent can be used within room temperature and the reaction speed is accelerated. When the pre-blackening agent is used in combination with a zinc or manganese phosphating solution, the growth of crystal nuclei can be accelerated and the stability can be improved. DETAILED DESCRIPTION

[0034] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following embodiments are examples of the present invention and are only used to illustrate the present invention, but not to limit the present invention. Other combinations and various modifications within the concept of the present invention may be performed without departing from the spirit or scope of the present invention.

[0035] Unless otherwise specified, the reagents used below can be easily obtained from commercial companies. Q235 steel was purchased from Suzhou Ou Tian Board Industry Co., Ltd., and manganese phosphating solution was from Shanghai Shouxuan Surface Technology Co., Ltd.

[0036] Example 1

[0037] A pre-blackening agent before phosphating, which comprises the following raw materials based on a volume of 1 L: 3.5 g / L copper sulfate, 10 g / L ammonium molybdate, 7.5 g / L citric acid, 6.9 mL / L phosphoric acid, 5.6 mL / L acetic acid, 2 g / L film-forming aid, 1.1 g / L potassium chlorate, 2.9 g / L sodium nitrobenzene sulfonate, 4 g / L sodium tartrate, potassium hydroxide, and the solvent is water;

[0038] Each part of the film-forming aid contains the following raw materials in parts by weight: 2 parts of calcium nitrate, 1.5 parts of nickel nitrate, 3 parts of tartaric acid, 1.5 parts of manganese chloride and 2.5 parts of boric acid;

[0039] The preparation method of the pre-blackening agent before phosphating of this embodiment comprises the following steps: adding water to copper sulfate, ammonium molybdate, citric acid, phosphoric acid, acetic acid, a film-forming aid, potassium chlorate, sodium nitrobenzene sulfonate, and sodium tartrate until dissolved, mixing and stirring evenly, and adjusting the pH to 3 with potassium hydroxide to obtain the pre-blackening agent before phosphating.

[0040] Example 2

[0041] A pre-blackening agent before phosphating, which comprises the following raw materials based on a volume of 1L: 2g / L copper sulfate, 5g / L ammonium molybdate, 5g / L citric acid, 6.9mL / L phosphoric acid, 5.6mL / L acetic acid, 1g / L film-forming aid, 0.9g / L potassium chlorate, 2.1g / L sodium nitrobenzene sulfonate, 3g / L sodium tartrate, potassium hydroxide, the solvent is water, and the pH value is 2.0-3.5;

[0042] Each part of the film-forming aid contains the following raw materials in parts by weight: 2 parts of calcium nitrate, 1.5 parts of nickel nitrate, 3 parts of tartaric acid, 1.5 parts of manganese chloride and 2.5 parts of boric acid;

[0043] The preparation method of the pre-blackening agent before phosphating in this embodiment comprises the following steps: adding water to copper sulfate, ammonium molybdate, citric acid, phosphoric acid, acetic acid, a film-forming aid, potassium chlorate, sodium nitrobenzene sulfonate, and sodium tartrate until dissolved, mixing and stirring evenly, and adjusting the pH to 2.0 with potassium hydroxide to obtain the pre-blackening agent before phosphating.

[0044] Example 3

[0045] A pre-blackening agent before phosphating, which comprises the following raw materials based on a volume of 1 L: 5 g / L copper sulfate, 15 g / L ammonium molybdate, 10 g / L citric acid, 6.9 mL / L phosphoric acid, 5.6 mL / L acetic acid, 3 g / L film-forming aid, 1.4 g / L potassium chlorate, 3.6 g / L sodium nitrobenzene sulfonate, 5 g / L sodium tartrate, potassium hydroxide, the solvent is water, and the pH value is 2.0-3.5;

[0046] Each part of the film-forming aid contains the following raw materials in parts by weight: 2 parts of calcium nitrate, 1.5 parts of nickel nitrate, 3 parts of tartaric acid, 1.5 parts of manganese chloride and 2.5 parts of boric acid;

[0047] The preparation method of the pre-blackening agent before phosphating in this embodiment comprises the following steps: adding water to copper sulfate, ammonium molybdate, citric acid, phosphoric acid, acetic acid, a film-forming aid, potassium chlorate, sodium nitrobenzene sulfonate, and sodium tartrate until dissolved, mixing and stirring evenly, and adjusting the pH to 3.5 with potassium hydroxide to obtain the pre-blackening agent before phosphating.

[0048] Example 4

[0049] A pre-blackening agent before phosphating, which comprises the following raw materials based on a volume of 1 L: 3.5 g / L copper sulfate, 10 g / L ammonium molybdate, 7.5 g / L citric acid, 6.9 mL / L phosphoric acid, 5.6 mL / L acetic acid, 2 g / L film-forming aid, 1.1 g / L potassium chlorate, 2.9 g / L sodium nitrobenzene sulfonate, 4 g / L sodium tartrate, potassium hydroxide, the solvent is water, and the pH value is 2.0-3.5;

[0050] Each film-forming aid comprises the following raw materials in parts by weight: 1 part calcium nitrate, 1 part nickel nitrate, 1 part tartaric acid, 0.5 part manganese chloride and 2 parts boric acid;

[0051] The preparation method of the pre-blackening agent before phosphating in this embodiment has the same specific preparation steps as in Example 1.

[0052] Example 5

[0053] A pre-blackening agent before phosphating, which comprises the following raw materials based on a volume of 1 L: 3.5 g / L copper sulfate, 10 g / L ammonium molybdate, 7.5 g / L citric acid, 6.9 mL / L phosphoric acid, 5.6 mL / L acetic acid, 2 g / L film-forming aid, 1.1 g / L potassium chlorate, 2.9 g / L sodium nitrobenzene sulfonate, 4 g / L sodium tartrate, potassium hydroxide, the solvent is water, and the pH value is 2.0-3.5;

[0054] Each film-forming aid contains the following raw materials in parts by weight: 3 parts of calcium nitrate, 2 parts of nickel nitrate, 5 parts of tartaric acid, 2.5 parts of manganese chloride and 3 parts of boric acid;

[0055] The preparation method of the pre-blackening agent before phosphating in this embodiment has the same specific preparation steps as in Example 1.

[0056] Example 6

[0057] A pre-blackening agent before phosphating, which comprises the following raw materials based on a volume of 1 L: 3.5 g / L copper sulfate, 10 g / L ammonium molybdate, 7.5 g / L citric acid, 12.5 mL / L phosphoric acid, 2 g / L film-forming aid, 1.1 g / L potassium chlorate, 2.9 g / L sodium nitrobenzene sulfonate, 4 g / L sodium tartrate, potassium hydroxide, the solvent is water, and the pH value is 2.0-3.5;

[0058] Each part of the film-forming aid contains the following raw materials in parts by weight: 2 parts of calcium nitrate, 1.5 parts of nickel nitrate, 3 parts of tartaric acid, 1.5 parts of manganese chloride and 2.5 parts of boric acid;

[0059] The preparation method of the pre-blackening agent before phosphating in this embodiment has the same specific preparation steps as in Example 1.

[0060] Example 7

[0061] A pre-blackening agent before phosphating, which comprises the following raw materials based on a volume of 1L: 3.5g / L copper sulfate, 10g / L ammonium molybdate, 7.5g / L citric acid, 12.5mL / L acetic acid, 2g / L film-forming aid, 1.1g / L potassium chlorate, 2.9g / L sodium nitrobenzene sulfonate, 4g / L sodium tartrate, potassium hydroxide, the solvent is water, and the pH value is 2.0-3.5;

[0062] Each part of the film-forming aid contains the following raw materials in parts by weight: 2 parts of calcium nitrate, 1.5 parts of nickel nitrate, 3 parts of tartaric acid, 1.5 parts of manganese chloride and 2.5 parts of boric acid;

[0063] The preparation method of the pre-blackening agent before phosphating in this embodiment has the same specific preparation steps as in Example 1.

[0064] Example 8

[0065] A pre-blackening agent before phosphating and a preparation method thereof, the specific implementation manner is the same as that of Example 1, except that 0.67 g / L of potassium chlorate and 3.3 g / L of sodium nitrobenzene sulfonate are added.

[0066] Example 9

[0067] A pre-blackening agent before phosphating and a preparation method thereof, the specific implementation manner is the same as that of Example 1, except that 1.6 g / L of potassium chlorate and 2.4 g / L of sodium nitrobenzene sulfonate are added.

[0068] Example 10

[0069] A pre-blackening agent before phosphating and a preparation method thereof, the specific implementation manner is the same as that of Example 1, except that 8.9 mL / L of phosphoric acid and 3.6 mL / L of acetic acid are added.

[0070] Embodiment 11

[0071] A pre-blackening agent before phosphating and a preparation method thereof, the specific implementation manner is the same as that of Example 1, except that 6.0 mL / L of phosphoric acid and 6.5 mL / L of acetic acid are added.

[0072] Performance Testing:

[0073] Q235 steel with a size of 20mm×14mm×8mm was polished on a metallographic sample grinder and polisher with water-resistant sandpaper, from 150#→400#→600#→800# in sequence, and then wiped with absorbent cotton dipped in ethanol, and then immersed in the pre-phosphating blackening agent solution (the mass ratio of the pre-blackening agent to water is 1:5) prepared in the above embodiment, the blackening temperature was controlled at 25°C, the blackening time was 4.5min, and then immersed in a manganese phosphating solution for 15min, and naturally dried to obtain a black phosphating film, and the following performance tests were performed respectively. The test results are shown in Table 1.

[0074] (1) Corrosion resistance test: The corrosion resistance is tested by the copper sulfate drop test in accordance with GB6807-86 "Technical conditions for phosphating treatment of steel workpieces before painting". The method is to drop a drop of copper sulfate drop test solution (copper sulfate 41g·dm -3 ; Sodium chloride 35g·dm -3 ; 0.1mol·dm -3 Hydrochloric acid 13mL·dm -3 ), start the stopwatch at the same time, and observe the time it takes for the droplet to change from sky blue to light yellow or light red, which is the copper resistance time. The longer the copper resistance time, the better the corrosion resistance;

[0075] (2) Film bonding strength test: Use clean filter paper to rub the surface of the black phosphate film back and forth until the steel substrate appears at a certain point. Record the number of frictions. The higher the number of frictions, the stronger the film bonding strength.

[0076] (3) Film appearance inspection: Observe the appearance of the black phosphate film with the naked eye. The evaluation criteria are whether it is uniform and whether the color of the black phosphate film is pure black. Bright black is the best and matte black is the worst.

[0077] Table 1

[0078] project Copper resistance time / s Friction times Film appearance Example 1 360 250 Uniform, bright black Example 2 355 250 Uniform, bright black Example 3 345 245 Uniform, bright black Example 4 335 235 Uniform, bright black Example 5 327 230 Uniform, bright black Example 6 332 225 Uneven, bright black Example 7 329 220 Uneven, bright black Example 8 320 214 Uneven, foggy black Example 9 315 212 Uneven, foggy black Example 10 340 237 Uneven, brown-black Embodiment 11 341 235 Uneven, bright black

[0079] As can be seen from Table 1, the pre-phosphating pre-blackening agent provided by Examples 1-3 of the present invention is a highly efficient pre-blackening agent with excellent corrosion resistance, strong film bonding strength, no metal substrate disappearing after repeated rubbing for 245 to 250 times, and uniform and bright black black phosphating film; Examples 4 and 5 change the component ratio of the film-forming aid, and compared with Example 1, it can be shown that the film-forming aid added in the preferred ratio of the present invention plays a role in refining the grains and improving the uniformity and quality of film formation; and the ammonium molybdate in the system plays a synergistic role, avoiding corrosion to the steel substrate; Examples 6 and 7 change the type of inorganic acid that plays an acidifying role in the pre-phosphating pre-blackening agent, and Examples 10 and 11 change The addition ratio of inorganic acid is changed. Compared with Example 1, it can be explained that the preferred compounding of phosphoric acid and acetic acid and controlling their mass ratio in the present invention increases the uniformity and fineness of the black appearance of the blackened film, and the properties are better. When phosphoric acid or acetic acid is used alone, it has an adverse effect on the binding force of the blackened film, and at the same time affects the synergistic effect with the phosphating solution, resulting in a decrease in the quality of the blackened phosphating film; Examples 8 and 9 change the addition ratio of potassium chlorate and sodium nitrobenzene sulfonate in the accelerator. Compared with Example 1, it can be explained that the accelerator added in the preferred ratio of the present invention can effectively play a role in balancing the growth of crystal nuclei and stability, and ensures the comprehensive performance of the blackened phosphating film when used in combination with a manganese phosphating solution.

[0080] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A pre-blackening agent before phosphating, characterized in that, Calculated by volume of 1L, the pre-blackening agent before phosphating comprises the following raw materials: 2-5g / L copper sulfate, 5-15g / L ammonium molybdate, 5-10g / L citric acid, 10-15mL / L inorganic acid, 1-3g / L film-forming aid, 3-5g / L accelerator, 3-5g / L complexing agent, pH regulator, the solvent is water, and the pH value of the pre-blackening agent before phosphating is 2.0-3.

5.

2. A pre-blackening agent before phosphating according to claim 1, characterized in that, The inorganic acid is obtained by mixing phosphoric acid and acetic acid.

3. A pre-blackening agent before phosphating according to claim 2, characterized in that, The mass ratio of the phosphoric acid to the acetic acid is 1:(0.5-1).

4. A pre-blackening agent before phosphating according to claim 1, characterized in that, The film-forming aid comprises the following raw materials in parts by weight: 1 to 3 parts of calcium nitrate, 1 to 2 parts of nickel nitrate, 1 to 5 parts of tartaric acid, 0.5 to 2.5 parts of manganese chloride and 2 to 3 parts of boric acid.

5. A pre-blackening agent before phosphating according to claim 1, characterized in that, The pH regulator is sodium hydroxide and / or potassium hydroxide.

6. A pre-blackening agent before phosphating according to claim 1, characterized in that, The complexing agent is at least one of tartaric acid, sodium tartrate and potassium sodium tartrate.

7. A pre-blackening agent before phosphating according to claim 1, characterized in that, The promoter is obtained by mixing an oxidant containing chlorate ions and an aromatic nitro compound.

8. A pre-blackening agent before phosphating according to claim 7, characterized in that: The oxidant containing chlorate ions is potassium chlorate, and the aromatic nitro compound is sodium nitrobenzene sulfonate.

9. A method for preparing a pre-blackening agent before phosphating according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: adding water to copper sulfate, ammonium molybdate, citric acid, inorganic acid, film-forming aid, accelerator and complexing agent until dissolved, mixing and stirring evenly, and adjusting the pH to 2.0-3.5 with a pH regulator to obtain the pre-blackening agent before phosphating.

10. Use of the pre-blackening agent before phosphating according to any one of claims 1 to 8 or the pre-blackening agent before phosphating obtained by the preparation method according to claim 9 in phosphating treatment of steel.