JPH0657443A - Composition of zinc phosphate film chemical conversion agent - Google Patents

Abstract

PURPOSE:To obtain a treating solution small in the generation of sludge and excellent in stability by incorporating dicyclohexylammonium nitrite in a solution for forming a zinc phosphate chemical film mainly containing phosphoric acid, nitric acid and zinc. CONSTITUTION:The zinc phosphate chemical film is formed by using the treating solution mainly containing phosphoric acid, nitric acid and zinc and, if necessary, into which components such as a fluorine compound, an organic acid, NBS soda, nickel, manganese, calcium or the like are added, on the surface of the metal. In the zinc phosphate film chemically treating method, dicyclohexylammonium nitrite is incorporated as an accelerator for forming chemical film in the treating solution. The adequate adding quantity is about 0.2-0.3 g/m<2>. As a result, the generation of sludge is reduced and the stability of the treating solution is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composition of a zinc phosphate film chemical forming agent for forming a rust preventive film of zinc phosphate on a metal surface such as steel and zinc as a pretreatment for coating.

[0002]

2. Description of the Related Art A zinc phosphate film is formed on the surface of steel, zinc or other metal for the purpose of enhancing the adhesion of the coating material and adding corrosion resistance. In such a metal surface treatment step, a method for forming a zinc phosphate conversion film is known, and its composition is phosphoric acid, nitric acid, zinc as a main component, a fluorine compound, an organic acid, a chelating agent, nickel, manganese, Cobalt, calcium, etc. are added according to the purpose. A general zinc phosphate film chemical conversion agent of the above composition is at room temperature or 3
A zinc phosphate film is formed on the surface of a metal such as steel or zinc by heating at a temperature of about 0 to 70 ° C. and dipping or spraying. This film forming agent is generally used by continuously adding a nitrite or a halogen acid salt or by blending as a component to be used as a film forming accelerator. By using this accelerator, low temperature and short time of zinc phosphate film chemical conversion treatment are realized.

[0003]

Although the halogenate salt is relatively stable in the zinc phosphate coating solution, it is not possible to control the film thickness depending on the film formation conditions, and it is difficult to balance the consumption amount and the supply amount. However, there is a factor that causes a large amount of sludge due to its strong oxidizing power. Nitrite has the effect of promoting the formation of a zinc phosphate conversion film, but it promotes the hydrolysis of the treatment bath solution and causes a large amount of sludge similarly to the halogenate. In the formation of a zinc phosphate film, when a metal comes into contact with a film forming solution, free phosphoric acid in the solution first acts on the treated metal surface to start etching. When the metal tries to diffuse into the solution by etching, the pH rises and the insoluble third
Phosphate is formed and precipitates as crystals on the metal surface. Nitrite and halogenate rapidly oxidize nascent hydrogen generated by the reaction of metal and phosphoric acid, accelerate the dissolution of the metal, and accelerate the rise of pH at the interface. The eluted metal is partially incorporated into the chemical conversion film, but the excess amount reacts with the zinc phosphate in the bath and is deposited as sludge in the bath. Since nitrite decomposes and volatilizes in an acidic solution, it must be continuously added separately in order to always exist in the zinc phosphate film forming solution at a concentration of 200 to 400 mg / L, and the concentration is always controlled. Must. These conventionally used accelerators often generate sludge and have a problem in the stability of the zinc phosphate treatment bath.

[0004]

[Means for Solving the Problems] As a result of intensive studies conducted by the present inventors in the above-described method for forming a zinc phosphate film under the circumstances, dicyclohexylammonium nitrate was used instead of nitrite or in combination with nitrite. By including light in the film forming solution, less sludge,
We have found a zinc phosphate film formation method with excellent stability.

[0005]

[Function] When dicyclohexylammonium nitrite is used as an accelerator for the film-forming agent, an appropriate amount is temporarily added to show a promoting effect in the process of spontaneous decomposition,
There is no need to perform strict concentration control. It is considered that this is because dicyclohexyl ammonium nitrite undergoes the following decomposition reactions in the zinc phosphate film forming agent.

[Chemical 1]

Dicyclohexyl ammonium nitrite is originally used as a rust preventive for steel and zinc, and its rust preventive action is based on the following reaction in the case of steel. That is, the metallic hydrogen of the dicyclohexyl ammonium nitrite molecule undergoes a substitution reaction with iron and is adsorbed on the iron surface to suppress the etching of iron. By this action, first, excessive dissolution of iron in the film forming bath is suppressed and the etching amount is reduced. After that, dicyclohexylammonium nitrite is decomposed in the acidic zinc phosphate film forming solution to complete its inhibitory action, and the decomposed nitrite ion produces an effect as a film forming accelerator. When used in combination with a halogenate or a nitrite, dicyclohexylammonium nitrite suppresses the base metal, suppresses etching appropriately, and reduces sludge generation. In the experiment, dicyclohexylammonium nitrite can continuously maintain good film formation by adding 0.2 g per 1 m ² . In addition, a treatment of 3.6 m ² was carried out for 14 days in a state of containing 1 g / L at the time of building the bath, but a good chemical conversion film was formed throughout. The amount of dicyclohexylammonium nitrite dissolved in water at 0 ° C. is 30 g / L. The amount dissolved in the zinc phosphate film chemical conversion agent was about 10 g / L at 30 to 40 ° C. with respect to the zinc phosphate film chemical conversion treatment liquid having a pH of 3.0, as measured by the inventor. From the above, the addition of dicyclohexylammonium nitrite may be added depending on the treatment amount of the object to be treated, and the addition amount is 0.2 to 0.3 g per 1 m ² .
As an upper limit value, an excess of 30 g / L of dicyclohexylammonium nitrite was added to the zinc phosphate film chemical conversion agent for treatment, but there was no effect on the chemical conversion film. In this case, the insoluble dicyclohexyl ammonium nitrite was in a state of floating on the surface of the treatment liquid.

[0007]

EXAMPLES Specific examples of the present invention will be shown below together with comparative examples with the conventional method. JIS. G. 314
1: SPCC-SD (0.8 × 70 × 150 mm) steel plate was sprayed with a commercially available alkaline degreasing detergent (Kemicoat Co., Ltd., Chemcoat No. 130, 2%, 50 ° C.) for 2 minutes at 1 kg / cm ² . After washing and then rinsing sufficiently with tap water, a regulator for forming a zinc phosphate film of colloidal titanium (Chemicoat No., manufactured by Chemicoat Co., Ltd.).
S-2, 0.2%, room temperature) for 0.5 minutes, 1 Kg / cm
^I sprayed ^two . After that, spray treatment is performed with a zinc phosphate film chemical conversion treatment solution of the components shown in Table 1 at 35 ° C. for 2 minutes at 0.6 Kg / cm ² , and the amount of sludge generated and material etching amount, film weight, adhesion after coating, salt resistance The water sprayability was evaluated. In this example, 1 m ² was treated per 1 L of the treatment liquid, component analysis was performed on the way, and the treatment was performed while adjusting the amount of the display component so that the fluctuation of the initially set component was within 10%. The adhesion of the coating film was subjected to a cross-cut test according to JIS K-5400, and the corrosion resistance was evaluated according to JIS-Z-2371 (salt spray test) for 96 hours. Amino Alkyd resin type DELICON 300 manufactured by Dainippon Paint Co., Ltd. was applied at a thickness of 20 to 25 μm. The baking temperature at this time is 120 ° C, 30
Went in minutes.

[0008]

[Table 1] After carrying out the above test, after standing for 7 days in the composition of the example, the steel was treated under the same conditions as in the initial stage without adjusting the components of dicyclohexylammonium nitrite, but a good zinc phosphate chemical conversion film was obtained. I was able to.

[0009]

When dicyclohexylammonium nitrite is used as an accelerator for zinc phosphate film formation, the amount of sludge generated can be reduced and the stability of the treatment liquid can be reduced as compared with the case where conventional nitrites and halogenates are used as accelerators. Will get better.

Claims (1)

[Claims] A treatment liquid for forming a zinc phosphate conversion film on a metal surface, in addition to known components such as phosphoric acid, nitric acid, a fluorine compound, an organic acid, NBS soda, zinc, nickel, manganese, and calcium, dicyclohexyl ammonium nitrate. A zinc phosphate film chemical conversion treatment method characterized by containing light.