Formulation technology for nickel-free medium-temperature sealing agents for aluminum and aluminum alloys

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This post was last edited by hechuanjishu on 2020-4-3 at 14:51. Among the various surface treatment methods for aluminum alloys, sealing treatment is an essential post-treatment step following anodization; it enhances the wear resistance and corrosion resistance of the aluminum surface, or imparts other functional or decorative properties to it. Moreover, the surface retains its metallic luster after this treatment, preserving its metallic texture. The anodized film is covered with micropores; the newly formed layer is highly reactive and prone to absorbing contaminants and becoming contaminated. Sealing the anodized film can reduce its tendency to absorb contaminants and improve its corrosion resistance and electrical insulation properties ； Abroad, nickel salts are primarily used as sealants; among these, nickel acetate sealants for high temperatures from Japan and those for normal temperatures from Europe and the United States are the most common ； The normal-temperature sealing method using the nickel-fluorine system is currently the most widely used sealing process in China. As global environmental problems become increasingly severe and various environmental protection regulations are introduced, more and more products are developing in a more environmentally friendly direction. The medium-temperature nickel-free sealer is a specialized product used for sealing aluminum alloys after anodization; it contains unique sealing salts, as well as dispersants, complexing agents, and pH buffers, and can quickly seal the micropores on the surface of aluminum alloys. II. Project features: 1) It is a nickel- and fluorine-free liquid that is not very sensitive to changes in typical sealing parameters ； Reduced gravity leads to better results, and the aging time is significantly shortened; after sealing, the aluminum retains its original color, effectively preventing the discoloration of the coating layer ； 2) Good sealing effect, wide temperature range, no white frost formation ； 3) Excellent salt spray resistance – it does not cause the oxide film to yellow, and there are no stains on the surface; 4) The use of a new type of surfactant not only helps to prevent powder formation but also promotes sealing of the surface ； 5) Use high-quality tap water to prepare the sealer in order to ensure its quality ； 6) The treatment solution contains no toxic substances such as nickel, cobalt, or other heavy metals; the wastewater is non-toxic and harmless, and can be discharged without treatment. 7) The closed process is easy to control, saving 30% of energy. There will be no gloom. Extend the lifespan of the bath solution ； III. Value of Project Development 1. Technical Challenges: 1) How to address issues such as the fading of the oxide film color after sealing, insufficient hardness, an uneven surface after sealing, stickiness, lack of smoothness, and long sealing times? 2) How to address the poor frost resistance of medium-temperature sealing agents? 3) How to achieve a nickel- and fluoride-free formulation, ensure product stability, and prevent dust accumulation after sealing? 4) How to achieve good weight loss with a short aging time? 2. Market value: 1) High-end sealing agents are under long-term technical monopoly by well-known foreign companies; it is therefore particularly important for domestic enterprises to carry out independent development and technological innovation ； 2) Most sealant manufacturers and research institutions have been engaged in the research and development of this technology for a long time ； And due to its many shortcomings, it failed to achieve any technical breakthroughs ； Therefore, this project has high development value ； 3) The R&D center of Kogawa Chemical has independently developed new surfactants that effectively solve the problems associated with thick-film sealing and coloring film sealing ； IV. Physical Properties
Product Name/Model: Medium-temperature nickel-free sealer
Appearance: Colorless (light yellow) transparent liquid
Physical Stability: Remains stable at room temperature over long periods; does not decompose or deteriorate.
Density: 1.15±0.05 g/cm3
pH Value: 6.0–6.5 (for the original liquid)
Toxicity and Harmfulness: Contains no Ni2+ or Co2+.

V. Application Areas
Suitable for sealing sulfuric acid or oxalic acid anodized coatings on aluminum and aluminum alloy products; particularly effective for sealing colored coatings. It is also used for sealing aluminum alloy components in buildings. It is widely employed to prevent fading or discoloration of colored aluminum anodized coatings, offering excellent performance in this regard. VI. Process Parameters and Precautions
Process Parameters:
1. Sealing agent concentration: 5–10 g/l
2. Sealing temperature: 65–95°C
3. Sealing time: Determined by the thickness of the anodized film; 2 minutes per μm for indoor components, 3 minutes per μm for outdoor components. 4. To extend the lifespan of the tank fluid, it is recommended to install a continuous filtration unit with filter element pore sizes of 10–15 μm. The filtration volume per shift (8 hours) should be at least 3 times the volume of the tank. 5. Quality of membrane sealing: ISO2143 (appearance, dye resistance test, acid dissolution test). Dilution process: Add pure water to a clean sealing tank; prepare the solution in the tank using deionized water. If it is necessary to increase the pH value, use 1N NaOH solution, and if it is necessary to decrease the pH value, use 1N acetic acid solution. Ensure that the pH value of the solution remains between 6.5 and 7.5. Precautions: 1. To ensure the best sealing effect, the parts to be sealed must not overlap each other ； Additionally, the sealing liquid should be tested regularly on a daily basis, and when its concentration is insufficient, it should be replenished promptly. 2. When the sealer has been used for too long and the concentration of impurity ions in the sealing solution is too high, it is necessary to replace the sealing solution. It depends on the condition of the sealed workpiece; generally, the replacement cycle is 2 to 5 months. 3. Do not allow this product to come into contact with the eyes. If it accidentally gets into the eyes, lift the eyelids and rinse thoroughly with flowing water or saline solution ； If swallowed accidentally, seek medical attention promptly. VII. Reference formula for nickel-free sealer (for reference only) Component mass percentage: Calcium (magnesium) acetate tetrahydrate 14–17; Benzoic acid/sodium benzoate 0–1; Auxiliary chelating agent 0–1; Isopentanol 0–1; Composite surfactant (wetting and ash suppression) 1–3; Water, remainder. To maintain the confidentiality of core technical information, the data have been modified and are provided for reference only. This entity assumes no legal responsibility for any losses resulting from the direct copying of formula data ； VIII. Example Photos