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CN-122013166-A - Trivalent chromium surface treating agent for aluminum or aluminum alloy, and preparation method and application thereof

CN122013166ACN 122013166 ACN122013166 ACN 122013166ACN-122013166-A

Abstract

The invention relates to a trivalent chromium surface treating agent for aluminum or aluminum alloy, and preparation and application thereof. The invention provides a trivalent chromium surface treating agent for aluminum or aluminum alloy, which comprises a) hexavalent chromium compound, b) an organic reducing agent, c) hydrofluoric acid and d) inorganic acid, wherein the organic reducing agent contains primary hydroxyl, secondary hydroxyl and/or phenolic hydroxyl, the acidity coefficient pKa of the inorganic acid is smaller than that of the hydrofluoric acid, the ratio of Cr in the hexavalent chromium compound to the maximum electron mole number provided by the theory of the organic reducing agent is 1.0:3.0-5.0, and the trivalent chromium is obtained by in-situ reduction of the hexavalent chromium compound. The hexavalent chromium can be completely and efficiently reduced into trivalent chromium in situ under the low-temperature reaction condition, the formula components are simple, the method has the outstanding advantages of low energy consumption and low raw material cost, the method is used for carrying out surface treatment on an aluminum or aluminum alloy substrate, the formed compact passivation film has good coating adhesion, and the can cover plume can be effectively controlled within 0.1 mm.

Inventors

  • SUN JUNYAO
  • WAN SHENGXING
  • SUN JINGLUN

Assignees

  • 凯密特尔有限责任公司

Dates

Publication Date
20260512
Application Date
20241111

Claims (15)

  1. 1. A trivalent chromium surface treating agent for aluminum or aluminum alloy is characterized in that, The trivalent chromium surface treating agent comprises the following raw materials: a) Hexavalent chromium compounds; b) An organic reducing agent containing primary, secondary and/or phenolic hydroxyl groups; c) Hydrofluoric acid; d) An inorganic acid having an acidity coefficient pKa less than the pKa of hydrofluoric acid; Wherein the ratio of Cr in the hexavalent chromium compound to the maximum electron mole number theoretically provided by the organic reducing agent is 1.0:3.0-5.0, preferably the ratio of the mole numbers is 1.0:3.2-4.8, more preferably the ratio of the mole numbers is 1.0:3.5-4.5; The trivalent chromium is obtained by in-situ reduction of the hexavalent chromium compound.
  2. 2. A trivalent chromium surface treatment agent according to claim 1, wherein, The trivalent chromium surface treatment agent further comprises e) a film forming polymer, further preferably the remainder of the trivalent chromium surface treatment agent is water.
  3. 3. Trivalent chromium surface treatment agent according to claim 1 or 2, characterized in that, The hexavalent chromium compound is selected from one or more of chromium trioxide, chromic acid and/or hexavalent chromates.
  4. 4. A trivalent chromium surface treatment agent according to any one of claim 1 to 3, wherein, The organic reducing agent is selected from one or more than two of glucose, sucrose, gluconic acid, tartaric acid, malic acid, tannic acid, gallic acid, isocitric acid, ascorbic acid, mannitol and/or water-soluble salts thereof.
  5. 5. The trivalent chromium surface treatment agent according to claim 1 to 4, wherein, The molar ratio of Cr in the hexavalent chromium compound to F in the hydrofluoric acid is 1.0:1.8 to 5.0, preferably the molar ratio is 1.0:2.0 to 4.0, more preferably the molar ratio is 1.0:2.2 to 3.5.
  6. 6. The trivalent chromium surface treatment agent according to any one of claims 1 to 5, characterized in that, The acidity coefficient pKa of the inorganic acid is not more than 3.0, preferably the inorganic acid is selected from one or more of phosphoric acid, sulfuric acid, nitric acid, hydrochloric acid, perchloric acid, hydroiodic acid, hydrobromic acid, more preferably the inorganic acid is selected from one or more of phosphoric acid and/or nitric acid.
  7. 7. The trivalent chromium surface treatment agent according to any one of claims 1 to 6, characterized in that, The trivalent chromium surface treatment agent has a pH of less than 3.0.
  8. 8. The trivalent chromium surface treatment agent according to any one of claims 1 to 7, characterized in that, The film-forming polymer is selected from one or more of polyurethane resin, epoxy resin, polyolefin resin, phenolic resin, polyester resin, (meth) acrylic resin and (meth) acrylic urethane resin.
  9. 9. The trivalent chromium surface treatment agent according to any one of claims 1 to 8, characterized in that, The trivalent chromium surface treating agent has no hexavalent chromium residue.
  10. 10. A process for producing a trivalent chromium surface treatment agent for aluminum or aluminum alloys according to any one of the claims 1to 9, comprising, Step A, mixing and dissolving a) hexavalent chromium compound, c) hydrofluoric acid and d) inorganic acid by taking water as a solvent to obtain a mixed solution I; And B), adding the B) organic reducing agent into the mixed solution I under the condition of heating the reaction system without an external heat source, and stirring to perform oxidation-reduction reaction.
  11. 11. The method for preparing a trivalent chromium surface treatment agent according to claim 10, wherein, The preparation method further comprises the following steps: Step C, detecting whether hexavalent chromium exists in the solution, and continuously executing the following steps under the condition that the detection result is negative; And D) mixing the e) film-forming polymer to obtain the trivalent chromium surface treating agent.
  12. 12. The method for preparing a trivalent chromium surface treatment agent according to claim 10 or 11, characterized in that the temperature of the redox reaction of step B) is not higher than 40 ℃, preferably the temperature of the redox reaction is 20-35 ℃.
  13. 13. A surface treatment method of aluminum or aluminum alloy, comprising: the trivalent chromium surface treatment agent for aluminum or aluminum alloy according to any one of claims 1 to 9 is applied to the surface of a substrate made of aluminum or aluminum alloy, and the substrate is heated and dried to form a surface treatment film of aluminum or aluminum alloy.
  14. 14. A surface-treated coating film of aluminum or an aluminum alloy, which is formed by the aluminum or aluminum alloy surface treatment method according to claim 13.
  15. 15. A packaging material having the surface-treated film of aluminum or aluminum alloy according to claim 14, preferably, the packaging material is a packaging material for cans, more preferably, the packaging material is a can lid material.

Description

Trivalent chromium surface treating agent for aluminum or aluminum alloy, and preparation method and application thereof Technical Field The invention relates to the field of metal surface treatment, in particular to a trivalent chromium surface treatment agent for aluminum or aluminum alloy, and preparation and application thereof. Background Aluminum or aluminum alloy has been used in packaging materials in recent years in large amounts, particularly in the industries of foods (such as beverages), medicines, cosmetics, and the like, because of its excellent properties of light weight, easy processing, good thermal conductivity and barrier property, beautiful color, easy recycling, and the like. Taking the beverage industry as an example, the demands of various pop can packaging materials for aluminum or aluminum alloy are increasing dramatically. Aluminum alloy is formed by processing aluminum as a base material and adding a small amount of alloy consisting of magnesium, manganese and copper, for example, 5052 and 5182 aluminum alloy is widely used for producing pop-top can cover products due to high strength and good formability. In order to improve the corrosion resistance of packaging materials of aluminum or aluminum alloys, it is often necessary to subject the substrate of aluminum or aluminum alloys to a surface treatment, in particular a passivation treatment. Passivation is a method of retarding the corrosion rate of metals by converting the metal surface into a state that is less susceptible to oxidation. By passivation, a dense film, which may be referred to as a surface treatment film or passivation film, is formed on the metal surface, which changes the surface state of the metal, and changes the electrode potential of the metal to be a corrosion-resistant passive state. It is common in the industry to passivate aluminum or aluminum alloy substrates with passivating agents. Currently, passivating agents comprise three types, namely a hexavalent chromium passivating agent, a trivalent chromium passivating agent and a chromium-free passivating agent. The hexavalent chromium passivating agent is used as a traditional passivating agent, has outstanding advantages in corrosion resistance and other properties, but the toxicity of hexavalent chromium is harmful to human bodies and the environment, the chromium-free passivating agent is most environment-friendly, but has the problem of insufficient corrosion resistance generally, and the trivalent chromium passivating agent can be relatively environment-friendly and good in corrosion resistance, so that the trivalent chromium passivating agent is more studied and applied in the surface treatment of aluminum or aluminum alloy packaging materials at present. However, trivalent chromium passivation still has some problems aiming at aluminum alloy tank cover products, mainly including insufficient coating adhesion and feather film defects at a tank cover pull opening. For can end products, it is generally necessary to perform cleaning, passivation, coating, curing, stamping, etc. processes, and in order to ensure good appearance and food safety, good adhesion between the coating applied on the aluminum or aluminum alloy substrate and the substrate is required to prevent the coating from falling off. The plume refers to the phenomenon that the coating film and the base material are separated when the edge of the cover is pulled open after the can cover product is pasteurized. The requirements for the film are particularly stringent for pull-open covers (RPTs), and it is generally required to control the film standard to within 0.1mm. Passivation effect is a major factor affecting the plume. The trivalent chromium passivating agent on the market at present can not control the plume to be 0.1mm. Patent document CN108823559a discloses a trivalent chromium passivating agent for pretreatment of can lid packaging material and a preparation method thereof, which adopts a chromic acid reduction method, and components such as organic phosphorus, fluotitanic acid, silane coupling agent, water-soluble polyurethane dispersing agent, water-soluble modified alkyd resin and the like are added into a formula, so that the corrosion resistance and coating adhesion of the passivating agent are improved, and the aluminum alloy can lid plume is effectively controlled within 0.1 mm. However, a conventional chromic acid reduction process is adopted, the system is required to be heated to 80 ℃ and kept for 6 hours, and the energy consumption and the manpower resource are obviously increased in the heating-heat-preserving-cooling process. In addition, the formulation components of this document are complex, increasing the difficulty and cost of production, nor does the document give any experimental data to demonstrate that the disclosed passivating agents have their claimed technical effects. Disclosure of Invention The invention aims to provide a novel trivalent chromium surface