CN102102200A - Phosphorization solution for cathode electrophoresis - Google Patents

Abstract

The invention relates to a phosphating solution for cathodic electrophoresis. A phosphating film with good alkali resistance can be obtained on the steel surface through a dipping or spraying phosphating process, which is suitable for phosphating treatment of iron and steel workpieces before cathodic electrophoresis. The phosphating solution is composed of the following substances: zinc salt 20-50g/L, manganese salt 20-50g/L, phosphoric acid 150-250g/L, hydroxylamine sulfate 20-80g/L, sodium carbonate 15-30g/L, complex Agent 10~20g/L, additive 1~20g/L, and the rest is water. Its characteristics ^are that the phosphating solution does not contain nickel ions, nitrites, nitrates, fluorides and other substances that are harmful to the environment. And the adjustment is simple, the phosphating film is uniform and dense, the crystal is granular, the alkali resistance is good, the P ratio is greater than 90%, and it has a good matching with cathodic electrophoresis.

Description

A kind of phosphating solution for cathodic electrophoresis

technical field

The invention belongs to metal surface chemical treatment technology, in particular to a phosphating solution for cathodic electrophoresis, which is suitable for the phosphating treatment of cathodic electrophoretic coating with high requirements on coating protection.

Background technique

Phosphating of metal parts is an important process in the coating process of automobiles and home appliances, and its purpose is to improve corrosion resistance and coating adhesion. Products subjected to cathodic cathodic electrophoretic coating, such as cars, heavy vehicles, etc., are required to have no rust on the outer plate for 6 years, no perforation corrosion of the outer plate for 10 years, and no rust that damages the structure for 20 years. This requires that the phosphating film matched with the cathodic cathodic electrophoresis has excellent corrosion resistance.

In cathodic electrophoretic coating, the metal to be coated is used as the cathode. Due to the electrochemical results, the pH value of the cathode area of the electric field can reach about 12, which requires that the phosphating film on the metal surface must have good alkali resistance. Cathodic electrophoretic coating also requires the phosphating film to have certain electrical conductivity, so the thickness of the phosphating film must be strictly controlled. At present, the main problems of the phosphating solution used in cathodic electrophoretic coating are: low "P ratio", poor alkali resistance, phosphating solution contains toxic substances such as nitrite, nitrate, nickel ion, fluoride ion, etc. The process is complicated and difficult to control, the working temperature is high, and there are many phosphating residues.

At present, there are patents to provide nickel-free and nitrite-free phosphating solutions, but the patent CN200810228602 "a nickel-ion-free phosphating solution for steel plate treatment" contains nitrates and cobalt ions. CN94193230 "Nickel-free phosphating treatment method" contains fluoride, nitrate, nitrogen-containing organic m-nitrobenzene sulfonate. Nitric acid and sodium chlorate are used in CN200410021272 "low-temperature phosphating solution containing hydroxylamine sulfate accelerator and its preparation method". CN200710034699.3 "Calcium-zinc-manganese-containing ternary cationic phosphating solution for steel plate and galvanized sheet treatment" uses nitrate, sodium m-nitrobenzenesulfonate, and chlorate, and the phosphating temperature is relatively high. Nitrate discharge increases the growth rate of algae and aquatic plants, which can degrade the water quality of streams and lakes. Sodium m-nitrobenzene sulfonate is a nitrogen-containing and benzene-containing organic compound that causes water pollution. Fluoride is a toxic pollutant. Cobalt ion is a toxic heavy metal. Chlorate will generate chloride ions in the phosphating solution, which will affect the corrosion resistance of the phosphating film, and the chloride ions will become a potential source of corrosion after coating.

The invention utilizes the hydroxylamine sulfate accelerator to easily obtain the characteristics of a phosphating film with high Zn ₂ Fe(PO ₄ ) ₂ 4H ₂ O (P phase) content and strong alkali resistance, and adds manganese salt, tungstate and molybdate Further improve the alkali resistance and corrosion resistance of the phosphating film, without using nickel ions, nitrite, nitrate, fluoride and other toxic substances, to obtain a phosphating solution with good alkali resistance and good compatibility with cathodic electrophoresis. The phosphating solution of the invention has a lower phosphating temperature and less phosphating residue; the tank opening liquid and the replenishing liquid are one solution, which is convenient to use.

The phosphating solution used for cathodic electrophoresis of the present invention is realized by the following technical solutions, and the content of each composition in one liter of aqueous solution is:

Zinc salt is the sum of one or two of zinc oxide and zinc dihydrogen phosphate, and the dosage is 20-50g;

Manganese salt is the sum of one or two kinds of manganese dihydrogen phosphate and manganese carbonate, and the dosage is 20-50g;

The dosage of phosphoric acid is 150~250g;

The dosage of hydroxylamine sulfate is 20-80g;

The dosage of sodium carbonate is 15-30g;

The additive is sodium tungstate, sodium molybdate or the sum of two kinds, the dosage is 1-20g;

The complexing agent is one or both of citric acid and tartaric acid, and the dosage is 10-20g;

The rest is water.

A kind of preparation method of cathodic electrophoresis phosphating solution of the present invention:

Take a specified amount of zinc salt and manganese salt, add water and a specified amount of phosphoric acid, and stir until dissolved; add a specified amount of complexing agent, sodium carbonate, hydroxylamine sulfate, and additives, and add water to the specified volume after fully dissolving.

A kind of cathodic electrophoresis phosphating liquid phosphating liquid using method of the present invention:

According to the concentration of phosphating solution 100ml/L, add water to prepare phosphating working solution, measure and adjust the free acidity of phosphating working solution at 0.8-1.5, and the total acidity at 20-30 points. The heating temperature is 25-45°C, and the phosphating time is 2-6 minutes.

Using the phosphating solution for cathodic electrophoresis to carry out phosphating treatment, the phosphating film forming speed is fast, the phosphating film has fine crystals and excellent alkali resistance. The phosphating film is immersed in 0.1mol/L NaOH solution at (30.0±0.5)°C for 5 minutes, and the weight loss of the phosphating film per unit area is less than 5%, which is equivalent to the high-nickel phosphating film. Therefore, the phosphating film obtained by the invention has excellent alkali resistance, and has excellent compatibility with cathodic electrophoretic coating.

Detailed ways:

Implementation example 1:

Zinc oxide 20g/L, manganese dihydrogen phosphate 30g/L, phosphoric acid 150g/L, citric acid 10g/L, hydroxylamine sulfate 20g/L, sodium tungstate 10g/L, sodium molybdate 1g/L, sodium carbonate 15g/L L, all the other are water.

The free acidity of the phosphating solution is 8 and the total acidity is 220. Phosphating at 40°C for 3 minutes, the obtained phosphating film has a uniform and dense appearance, phosphating crystals are granular, the film weight is 2.8mg/m ² , the alkali resistance of the phosphating film is 2.6%, and the P ratio is 96%.

Implementation example 2:

Zinc oxide 30g/L, manganese carbonate 20g/L, phosphoric acid 170g/L, tartaric acid 10g/L, hydroxylamine sulfate 50g/L, sodium tungstate 20g/L, sodium carbonate 22g/L, and the rest is water.

The free acidity of the phosphating solution is 12 and the total acidity is 280. Phosphating at 35°C for 4 minutes, the obtained phosphating film has a uniform and compact appearance, phosphating crystals are granular, the film weight is 1.6mg/m ² , the alkali resistance of the phosphating film is 4.8%, and the P ratio is 91%.

Implementation example 3:

Zinc oxide 10g/L, zinc dihydrogen phosphate 40g/L, manganese dihydrogen phosphate 50g/L, 85% phosphoric acid 250g/L, tartaric acid 10g/L, citric acid 10g/L, hydroxylamine sulfate 80g/L, sodium tungstate 15g/L, sodium molybdate 5g/L, sodium carbonate 30g/L, and the balance is water.

The free acidity of the phosphating solution is 10 and the total acidity is 250. Phosphating at 25°C for 6 minutes, the obtained phosphating film has a uniform and dense appearance, phosphating crystals are granular, the film weight is 2.1mg/m ² , the alkali resistance of the phosphating film is 3.8%, and the P ratio is 92%.

Implementation example 4:

Zinc oxide 15g/L, zinc dihydrogen phosphate 20g/L, manganese carbonate 10g/L, manganese dihydrogen phosphate 10g/L, phosphoric acid 200g/L, citric acid 5g/L, tartaric acid 10g/L, hydroxylamine sulfate 20g/L, Sodium molybdate 5g/L, sodium carbonate 27g/L, the rest is water.

The free acidity of the phosphating solution is 12 and the total acidity is 230. Phosphating at 30°C for 5 minutes, the phosphating film obtained is uniform and compact in appearance, the phosphating crystal is granular, the film weight is 2.3mg/m ² , the alkali resistance of the phosphating film is 2.4%, and the P ratio is 94%.

Implementation example 5:

Zinc dihydrogen phosphate 50g/L, manganese carbonate 10g/L, manganese dihydrogen phosphate 20g/L, phosphoric acid 150g/L, citric acid 20g/L, hydroxylamine sulfate 80g/L, sodium tungstate 10g/L, sodium carbonate 15～ 30g/L, the rest is water.

The free acidity of the phosphating solution is 15 and the total acidity is 270. Phosphating at 40°C for 2 minutes, the obtained phosphating film has a uniform and dense appearance, phosphating crystals are granular, the film weight is 3.0mg/m ² , the phosphating film has an alkali resistance of 2.2%, and a P ratio of 96%.

Implementation example 6:

Zinc dihydrogen phosphate 50g/L, manganese carbonate 30g/L, phosphoric acid 200g/L, tartaric acid 20g/L, hydroxylamine sulfate 80g/L, sodium tungstate 15g/L, sodium molybdate 3g/L, sodium carbonate 25g/L, The rest is water.

The free acidity of the phosphating solution is 13 and the total acidity is 250. Phosphating at 45°C for 3 minutes, the obtained phosphating film has a uniform and dense appearance, phosphating crystals are granular, the film weight is 1.6mg/m ² , the phosphating film has an alkali resistance of 3%, and a P ratio of 95%.

Implementation example 7:

Zinc nitrate 40g/L, manganese dihydrogen phosphate 30g/L, phosphoric acid 200g/L, citric acid 5g/L, tartaric acid 5g/L, hydroxylamine sulfate 50g/L, hydroxylamine sulfate 30g/L, sodium tungstate 15g/L, molybdenum Sodium bicarbonate 1g/L, sodium carbonate 30g/L, and the rest is water.

The free acidity of the phosphating solution is 9 and the total acidity is 255. Phosphating at 30°C for 4 minutes, the obtained phosphating film has a uniform and dense appearance, phosphating crystals are granular, the film weight is 1.5mg/m ² , the phosphating film has an alkali resistance of 4.5%, and a P ratio of 92%.

Implementation example 8:

Zinc oxide 10g/L, zinc dihydrogen phosphate 10g/L, manganese carbonate 10g/L, manganese dihydrogen phosphate 40g/L, phosphoric acid 150g/L, citric acid 15g/L, tartaric acid 5g/L, hydroxylamine sulfate 60g/L, Sodium tungstate 18g/L, sodium molybdate 1g/L, sodium carbonate 28g/L, and the rest is water.

The free acidity of the phosphating solution is 12 and the total acidity is 240. Phosphating at 40°C for 3 minutes, the obtained phosphating film has a uniform and dense appearance, phosphating crystals are granular, the film weight is 2.6mg/m ² , the alkali resistance of the phosphating film is 3.3%, and the P ratio is 95%.

Implementation example 9:

Zinc oxide 10g/L, zinc dihydrogen phosphate 10g/L, manganese carbonate 20g/L, manganese dihydrogen phosphate 10g/L, phosphoric acid 180g/L, citric acid 5g/L, tartaric acid 15g/L, hydroxylamine sulfate 50g/L, Sodium molybdate 2g/L, sodium carbonate 29g/L, the rest is water.

The free acidity of the phosphating solution is 12 and the total acidity is 250. Phosphating at 35°C for 5 minutes, the phosphating film obtained is uniform and dense in appearance, the phosphating crystal is granular, the film weight is 1.6mg/m ² , the alkali resistance of the phosphating film is 4.7%, and the P ratio is 91%.

Implementation example 10:

Zinc dihydrogen phosphate 20g/L, manganese carbonate 10g/L, manganese dihydrogen phosphate 40g/L, phosphoric acid 150g/L, tartaric acid 20g/L, hydroxylamine sulfate 60g/L, sodium tungstate 18g/L, sodium molybdate 2g/L L, sodium carbonate 26g/L, all the other are water.

The free acidity of the phosphating solution is 8 and the total acidity is 260. Phosphating at 45°C for 5 minutes, the obtained phosphating film has a uniform and dense appearance, phosphating crystals are granular, the film weight is 2.8mg/m ² , the phosphating film has an alkali resistance of 2%, and a P ratio of 97%.

The automobile steel plate is subjected to phosphating treatment and cathodic electrophoretic coating through the phosphating solution of the present invention, and the thickness of the cathodic electrophoretic coating is 20 μm. The test results are as follows:

1. The morphology of phosphating film was detected by scanning electron microscope (SEM)

It can be seen from Figure 1 of the specification that the crystallization of the phosphating film is granular, with a particle diameter of about 2 μm, and the particles are uniform and fine.

2. Use X-ray diffractometer (XRD) to analyze the composition of the phosphating film and calculate the P ratio

It can be seen from Figure 2 of the specification that there are Zn ₂ Fe(PO ₄ ) ₂ 4H ₂ O (P phase) and iron phases in the phosphating film. The iron phase appears because the phosphating film is thin and the iron matrix participates in the diffraction. The amount of Zn ₃ (PO ₄ ) ₂ 4H ₂ O (H phase) in the phosphating film is very small, almost undetectable. The P ratio is the ratio of the diffraction intensity of the P phase to the sum of the diffraction intensities of the P phase and the H phase.

3. Phosphating film alkali resistance test

After phosphating, the test plate is accurately weighed (W ₁ ), immersed in 0.1mol/L NaOH solution, immersed at (30.0±0.5)°C for 5 minutes, washed with deionized water, dried and cooled, and then accurately weighed (W ₂ ), calculate the weight loss ratio: (W ₁ -W ₂ )/S×100%, less than 5%.

4. According to GB/T9286-1998, the paint film adhesion test is carried out by the cross-cut method, and it reaches level 1.

5. Conduct salt spray test according to GB/T10125-1997 salt spray test method

The paint film has passed the 400-hour salt spray test, and there is no bubbling phenomenon of the paint film. Draw a diagonal line on the paint film and penetrate to the surface of the metal substrate. After 48 hours of salt spray test, the corrosion depth is less than 0.5mm.

6. Output of phosphating slag:

Prepare 2L of bath solution, treat the steel plate with an area of 1m ² , then filter the phosphating solution, dry the filter residue at (120±5)°C for more than 2 hours to constant weight, put it into the desiccator and calculate the output of phosphating residue to be less than 2g/m ² .

Claims (8)

1. phosphatization liquid that ability cathode electrophoresis is used, it is made up of following material: zinc salt 20～50g/L, manganese salt 20～50g/L, phosphatase 11 50～250g/L, oxammonium sulfate 20～80g/L, yellow soda ash 15～30g/L, complexing agent 10～20g/L, additive 1～20g/L, all the other are water.

2. the phosphatization liquid that a kind of ability cathode electrophoresis according to claim 1 is used is characterized in that zinc salt is one or both sums in zinc oxide, the primary zinc phosphate.

3. the phosphatization liquid that a kind of ability cathode electrophoresis according to claim 1 is used is characterized in that manganese salt is one or both sums in manganous carbonate, the phosphate dihydrogen manganese.

4. the phosphatization liquid that a kind of ability cathode electrophoresis according to claim 1 is used is characterized in that complexing agent is one or both sums in citric acid, the tartrate.

5. the phosphatization liquid that a kind of ability cathode electrophoresis according to claim 1 is used is characterized in that additive is one or both sums in sodium wolframate, the Sodium orthomolybdate.

6. a kind of ability cathode electrophoresis according to claim 1 is characterized in that: get zinc salt, the manganese salt of specified amount, add the phosphoric acid of entry and specified amount, be stirred well to dissolving with the compound method of phosphatization liquid; The complexing agent, yellow soda ash, oxammonium sulfate, the additive that add specified amount respectively fully add water to prescribed volume after the dissolving.

7. a kind of ability cathode electrophoresis according to claim 1 phosphatization liquid using method, it is characterized in that: add water by the concentration of phosphatization liquid hold-up 100ml/L and be mixed with the phosphatization working fluid, measure and adjust phosphatization working fluid free acidity 0.8～1.5, total acidity 20～30 points.Be heated to specified temperature and can carry out bonderizing.

8. a kind of ability cathode electrophoresis according to claim 1 is characterized in that: 25～45 ℃ of phosphatization temperatures, phosphating time 2～6 minutes with phosphatization liquid phosphating process parameter.

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