JPH0643634B2 - Method for forming laminated phosphate coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a method for forming a laminated phosphate coating, particularly a second phosphorus composed of fine particles on a phosphate coating formed on an iron plate or a galvanized iron plate. The present invention relates to a method for forming a laminated phosphate film having improved corrosion resistance and adhesion by laminating an acid salt film.

[Prior Art] The surface of steel sheets for automobile bodies is subjected to chemical conversion treatment before electrodeposition coating for the purpose of improving corrosion resistance and the like, and phosphate is used as the chemical conversion treatment agent. Zinc phosphate is effective as a phosphate, and in particular, a chemical conversion treatment agent containing zinc phosphate and a nitrate ion, a sulfite ion, a chlorate ion or the like is widely used. In order to improve the adhesion and corrosion resistance of the chemical conversion coating, various modifications have been made to the chemical conversion treatment agent.

Various attempts have been made for the purpose of improving the adhesion and corrosion resistance of this zinc phosphate-based chemical conversion coating. For example, those containing nickel ions in addition to the above components, and JP-A-57-152
As disclosed in Japanese Patent No. 472, there is one in which the metal surface for cationic electrodeposition coating is subjected to phosphate treatment with an acidic phosphate treatment aqueous solution containing manganese ions in addition to the above components. Japanese Examined Patent Publication No. 61-36588 uses a chemical acid treatment solution of acidic phosphate containing manganese ion and fluorine ion in addition to zinc ion, phosphate ion and accelerator to chemically convert the metal surface for cationic electrodeposition coating. A method is disclosed.

In addition, Japanese Examined Patent Publication No. 58-39915 discloses a Fe, Zn, and Mn-based phosphate coating on the surface of weather-resistant steel (due to the first treatment liquid) of 1 mg /
cm ² or less adheres and iron oxide (Fe ₃ O ₄ + Fe
₂ O ₃ ) 3 to 20%, phosphoric acid 0.1 to 3%, Fe, Zn, Mn-based phosphate one or more kinds 0.1 to 10%, Ni, Cu inorganic compounds one or more kinds 0.1 to 2%. 5%, chromic acid, zinc chromate, lead chromate one or more 0.5 to 10%, polyvinyl butyral resin alone or a resin compatible with polyvinyl butyral resin is 3 to 30% in total, and the balance is Weather resistance by applying a treatment liquid (second treatment liquid) consisting of a solvent and a coating auxiliary agent so as to have a dry film thickness of 5 to 100 μm, or forming a weatherproof film on it to 10 to 50 μm A steel surface treatment method is disclosed. Second here
The composition of the coating film formed by applying the treatment liquid of 1. is similar to natural rust, and all the rust generated thereafter by these compounds becomes stable rust and covers the surface and protects the weathering steel for a long time. Has been done.

[Problems to be Solved by the Invention] Phosphate films formed by these chemical conversion treatment methods have excellent corrosion resistance and adhesion, but in recent years, the required level of these properties has become higher and higher for automobiles and the like. It was Regarding the relationship between the water resistant secondary adhesion of the chemical conversion film (adhesion with the coating under wet deterioration conditions) and the particle size of the coating particles, the smaller the particle size, the better the water resistant secondary adhesion. I found out that Therefore, when the particles of the film formed by the conventional zinc phosphate-based treatment agent were examined, it was 2 to 3 μm on the steel surface,
It was about 5 to 6 μm on the zinc surface. It was also found that even when a large amount of manganese ions or the like was added for the purpose of reducing the particles of the coating film on the zinc surface, the particle size was at most about 2 to 3 μm. On the other hand, a thicker film is desirable for corrosion resistance, but as the film becomes thicker, its particles become coarser,
There is a problem that the gaps between the particles are the places where corrosion occurs. For this reason, it has been impossible to form a phosphate film having further improved corrosion resistance and adhesion by the conventional method.

Therefore, it is an object of the present invention to provide a method for forming a phosphate coating having superior corrosion resistance and adhesion to conventional conversion coatings.

[Means for Solving Problems] As a result of earnest research in view of the above object, after a phosphate film is once formed on an iron plate or a galvanized iron plate, an extremely fine particle is formed by a phosphate treatment agent containing condensed phosphoric acid. It was discovered that a phosphate coating consisting of particles was laminated, and thus a laminated phosphate coating having excellent corrosion resistance and adhesion was obtained.
The present invention was conceived.

That is, according to the method for forming a laminated phosphate coating of the present invention, an iron plate or a galvanized iron plate on which a phosphate coating is applied with a treating agent that does not substantially contain condensed phosphoric acid is used for zinc ion 0.1-1.
5 g / and phosphate ion derived from orthophosphoric acid and / or orthophosphate (hereinafter, simply referred to as “phosphate ion”
5 to 30 g /, and condensed phosphoric acid 1 to 30 g /
It is characterized in that it is treated with a film treating agent containing and.

In summary, the method of the present invention forms a laminated phosphate coating having a phosphate coating of relatively large particles and a phosphate coating of fine particles. The fundamental difference between the two coatings is that the former contains substantially no condensed phosphoric acid, while the latter does. The other components may be the same. Therefore, the latter film will be mainly described below.

Examples of the condensed phosphoric acid contained in the phosphate coating agent of the present invention include pyrophosphoric acid, metaphosphoric acid, polyphosphoric acid and phosphorus pentoxide. Each of these compounds has a structure in which phosphate ions are condensed via oxygen.

The concentration of condensed phosphoric acid is 1 to 30 g /. If it is less than 1 g /, a coating film made of fine particles is not formed on the existing phosphate coating, and if it is more than 30 g /, further reduction of the coating particles, that is, the effect of thinning cannot be expected. A preferred concentration range is 5 to 20 g /.

Condensed phosphoric acid can be added in the form of a salt, but its source is an alkali salt such as sodium or potassium,
Ammonium salt, alkaline earth salt zinc, iron, nickel,
There are metal salts such as manganese.

By the addition of condensed phosphoric acid, the particles of the obtained film become finer to about 0.1 to 1.5 μm depending on the concentration.

The concentration of zinc ions is 0.1 to 1.5 g /. 0.
When it is less than 1 g / g, a uniform phosphate film is not formed on the iron-based surface, and a blue-colored film is partially formed. If it is larger than 1.5 g / g, the effect of refining the coating particles cannot be expected. The preferred concentration range is 0.5 to 1 g /. As a source of zinc ions, zinc oxide, zinc carbonate,
For example, zinc nitrate.

The concentration of phosphate ions is 5 to 30 g /. 5 g /
If it is less than 1, a uniform film is not formed and the condensed phosphoric acid decomposes quickly. On the other hand, if the amount exceeds 30 g / g, the corresponding improvement in effect cannot be expected, and it is uneconomical because the amount of chemicals used increases. A preferred concentration range is 5 to 20 g /. Sources of phosphate ions include phosphoric acid, zinc phosphate, zinc dihydrogen phosphate, and the like.

The phosphate film treatment agent of the present invention further contains a film formation accelerator. Nitrite ion, m as film formation accelerator
-Nitrobenzene sulfonate ion and hydrogen peroxide are good, and their concentration is 0.2 g / or less, preferably 0.01
~ 0.1 g /. The concentration of the film formation accelerator is related to the decomposition rate of condensed phosphoric acid, and the smaller the better. However, its role is important for the primary rust prevention of iron surfaces. Sources of nitrite ions include sodium nitrite and ammonium nitrite.

Further, the phosphate film treating agent of the present invention may contain an oxidizing agent such as nitrate ion or chlorate ion. The nitrate ion concentration is 0.5 to 10 g /, and the chlorate ion concentration is 0.05 to 2 g /. Sources of nitrate ions include sodium nitrate, ammonium nitrate, zinc nitrate,
There are manganese nitrate, nickel nitrate and the like, and sources of chlorate ions include sodium chlorate and ammonium chlorate.

Further, nickel ions and manganese ions may be contained. The concentration of nickel ions is preferably 0.3 to 3 g /, and the concentration of manganese ions is preferably 0.6 to 3 g /. By using nickel ions and manganese ions in combination, the performance of the chemical conversion coating is further improved, and the adhesion and corrosion resistance after electrodeposition coating are improved. Sources of nickel ions include nickel carbonate, nickel nitrate, nickel chloride and nickel phosphate, and sources of manganese ions include manganese carbonate, manganese nitrate, manganese chloride,
There are manganese phosphate and the like.

In addition, one or more oxo acid ions of Cr, V, Mo, W, and Zr may be contained if necessary.

Next, the method for forming the laminated phosphate coating of the present invention will be described.

First, the method for forming a laminated phosphate film of the present invention can be applied to an iron-based surface, a zinc-based surface, or a metal surface having both an iron-based surface and a zinc-based surface. Examples of the zinc surface include hot dip galvanized, alloy hot dip galvanized, electrogalvanized, and galvannealed electrogalvanized.

These metal surfaces are first degreased. Degreasing treatments include solvent degreasing and alkaline degreasing.For solvent degreasing, use solvents such as trichloroethylene, perchlorethylene, gasoline, and hexane.For alkaline degreasing, sodium hydroxide, sodium carbonate, sodium silicate, phosphoric acid. Use a cleaning solution such as sodium.

The degreased metal surface is washed with water and immersed in a surface conditioner.

Next, a chemical conversion treatment is carried out with a phosphate film treating agent which does not substantially contain condensed phosphoric acid. The treating agent may have a known composition and contains Zn ions, PO ₄ ions and an accelerator. If necessary, Ni ions, Mn ions, etc. may be added. It is preferable to use a dipping method for this chemical conversion treatment, and the temperature of the treatment liquid is 25 to 65 ° C, preferably 30 to 5 ° C.
It is 0 ° C. Immersion treatment time is 15 seconds or more, preferably 3
It is 0 to 120 seconds. If the treatment time is too short, a film having a desired thickness cannot be obtained.

This gives a coating of orthophosphate (zinc phosphate).

Next, a chemical conversion treatment is performed with a phosphate film treating agent containing condensed phosphoric acid, which is also preferably the dipping method. The temperature of the treatment liquid is 10 to 60 ° C., preferably 20 to 4
It is 0 ° C. If the temperature is too low, the film-forming property is low, and long-time treatment is required. On the other hand, if the temperature is too high, the condensed phosphoric acid is hydrolyzed and the concentration balance of the treatment liquid is disturbed.

The immersion treatment time is 5 seconds or longer, preferably 30 to 120 seconds. If the treatment time is too short, a film having a desired particle size cannot be obtained.

When treating a steel sheet having a complicated shape such as an automobile body, both the treating agent containing no condensed phosphoric acid and the treating agent containing condensed phosphoric acid should be sprayed after the dipping treatment. Preferably. For example, in each case, first, the immersion treatment is performed for 15 seconds or longer, preferably 30 to 90 seconds, and then the spray treatment is performed for 2 seconds or longer, preferably 5 to 45 seconds. In addition, it is preferable that the spray treatment is performed as long as possible in order to wash off the sludge attached during the dipping treatment.

By the above chemical conversion treatment, lamination of a phosphate film consisting of large particles and a phosphate film consisting of fine particles (composite)
A film is formed.

After chemical conversion treatment, it is washed with water and dried. An undercoat is applied to the surface to be subjected to the chemical conversion treatment, and it is particularly preferable to apply a cationic electrodeposition coating to the surface subjected to the chemical conversion treatment with the treatment agent of the present invention.

[Operation] By the chemical conversion treatment with the treating agent containing condensed phosphoric acid, the metal and the existing orthophosphate film are simultaneously etched and dissolved, and fine particles having low crystallinity are deposited. It is considered that these fine particles are made of zinc phosphate containing condensed zinc phosphate, and the particle size is as small as submicron. On the other hand, since the particle size of the zinc orthophosphate coating is relatively large, such as iron micron, there are some gaps between the particles, but the fine particles are densely formed on and between the large zinc orthophosphate particles. become. Therefore, not only can the gap between the particles that cause corrosion be sealed and the corrosion resistance can be improved, but also the adhesion can be improved by the fine particles.

[Examples] The present invention will be described in more detail by the following examples.

Examples 1 to 6 and Comparative Examples 1 to 5 An electrogalvanized steel sheet and a cold rolled steel sheet were used as the metals to be treated, and the following treatments were applied to each.

(1) Degreasing An alkaline degreasing agent with a concentration of 2% by weight (R made by Nippon Paint Co., Ltd.
d53) was used for immersion treatment at 60 ° C. for 2 minutes.

(2) Washing with water Using tap water, washing was performed at room temperature for 15 seconds.

(3) Surface conditioning Surface conditioning agent (Nippon Paint Co., Ltd. "Fixogen 5N-
5 ", 0.1 wt% concentration) was used for 20 seconds at room temperature.

(4) Chemical conversion treatment (1) A zinc orthophosphate film was formed on each metal surface with a phosphate treating agent having the following composition.

Zn ion 1 g / PO ₄ ion 16 g / Ni ion 0.3 g / NO ₂ ion 0.06 g / NO ₃ ion 4 g / (5) Washing with water Using tap water, washing was performed at room temperature for 20 seconds.

(6) Chemical conversion treatment (2) Using a condensed phosphoric acid-containing phosphate treating agent having the composition shown in Table 1 below, immersion treatment was performed at 40 ° C. for 2 minutes.

Comparative Example 1 is an example not treated with the condensed phosphate-containing treatment agent, and Comparative Example 2 is an example treated with a treatment agent having the same composition as the coating of the first layer.

(7) Washing with water Using tap water, washing was performed at room temperature for 20 seconds.

(8) Washing with pure water Using ion-exchanged water, immersion treatment was performed at room temperature for 20 seconds.

(9) Drying It was dried with hot air at 100 ° C for 10 minutes.

The particles of the chemical conversion treatment film thus obtained were observed with a scanning electron microscope SEM (1500 times and 10000 times).

As a result, it was found that the coatings of Examples 1 to 4 were of a laminated type, whereas Comparative Examples 1 to 5 were of a single layer type. In Comparative Example 2, it was confirmed that the single layer (zinc orthophosphate layer) was etched. Furthermore, in Comparative Examples 3 to 5, the second layer was not formed even if the condensed phosphoric acid-containing treatment agent was used, and the degree of etching was weak → medium → strong → in the order of Comparative Examples 3 to 5. Was there.

SEM photograph of Example 2 (1500 times and 10000 times)
1A and 1B (on Zn), and 2A and 2
The results are shown in FIG. B (on Fe), and SEM photographs (1500 times and 10000 times) of Comparative Example 1 are shown in FIGS. 3A and 3B (on Zn) and FIGS. 4A and 4B (on Fe), respectively. Show.

(8) Coating A cationic electrodeposition coating (“Power Top U-50 Gray” manufactured by Nippon Paint Co., Ltd.) was coated to a film thickness of 20 μm (voltage 18
It was baked at 180 V for 30 minutes at 0 V for 3 minutes. A part of the thus obtained plurality of electrodeposition coated plates was subjected to a salt spray test.

Next, an intermediate coating (“Olga S-93 gray” manufactured by Nippon Paint Co., Ltd.) was formed to a film thickness of 40 μm on the remaining electrodeposition coated plate, and then a top coating (“Olga G-65 White” manufactured by Nippon Paint Co., Ltd.) was formed. It was coated to 40 μm to obtain a coated plate with 3 coats and 3 bake as a whole. This was subjected to an adhesion test.

Each test method was as follows.

(A) Salt spray test (JIS-Z-2871) Put a cross cut on each electrodeposition coated plate and spray 5% salt water,
The blister width (mm) outside the cross cut was evaluated. The spray time was 500 hours (electrogalvanized steel sheet) and 1000 hours (cooled steel sheet), respectively.

(B) Water resistance adhesion test A coated plate was immersed in deionized water at 40 ° C for 10 days, and then a grid pattern (100 pieces) with a 1 mm interval and a 2 mm interval, respectively.
Was formed with a sharp cutter, and an adhesive tape was attached to each surface thereof, and then these were peeled off, and the number of crosses remaining on the coated plate was counted.

(C) Particle size measurement It was evaluated by a scanning electron microscope (SEM) photograph (10000 times).

The results are shown in Table 2.

As is clear from the above results, in the laminated phosphate coating formed by the method of the present invention, fine particles of submicron size are densely formed on orthophosphate particles having a relatively large particle size and in the gaps between them. There is. Therefore, the corrosion resistance and adhesiveness after forming the coating film were remarkably improved. On the other hand, none of the laminates (Comparative Examples 1 to 5) were not satisfactory in the above characteristics.

Example 7 The same treatment and test as in Example 1 were performed except that the treating agent obtained by adding 0.8 g / manganese ion to the pyrophosphoric acid-containing treating agent of Example 1 was used and the test plate was an electrogalvanized steel sheet. It was The obtained laminated film had a structure in which fine particles were densely formed on and between large particles as in Example 1. The corrosion resistance (SST) of the electrodeposition coated plate is 3.5 mm, and the adhesion after top coating is 2 mm and 1 mm.
All were 100/100 in the cross-cut test.

[Effect of the Invention] As described in detail above, in the method of the present invention, since the second phosphate film containing condensed phosphoric acid is formed on the phosphate film, the obtained film has large particles. A layer and a fine particle layer of about submicron are laminated. Therefore, the corrosion resistance and the adhesiveness when the electrodeposition coating is performed on the chemical conversion film are remarkably improved. The method of the invention is also suitable for treating iron and zinc surfaces simultaneously. Further, there is an advantage that the chemical conversion treatment with the condensed phosphoric acid-containing treatment agent can be performed at a relatively low temperature.

[Brief description of drawings]

FIGS. 1A and 1B are scanning electron microscope (SEM) photographs (1500 × and 1,500 ×, respectively) showing the crystal appearance structure of a laminated phosphate coating formed on an electrogalvanized steel sheet by the method of the present invention (Example 2). 10000 times), and FIGS. 2A and 2B are scanning electron microscope (SEM) photographs showing the crystalline appearance structure of the laminated phosphate coating formed on the cold-rolled steel sheet by the method of the present invention (Example 2). (1500 times and 10000 times, respectively), and FIGS. 3A and 3B show the crystal appearance structure of the chemical conversion film formed on the electrogalvanized steel sheet using the treating agent containing no condensed phosphoric acid (Comparative Example 1). 4A and 4B are SEM photographs (1500 times and 10000 times, respectively) showing the above, and FIGS. 4A and 4B show the chemical conversion formed on a cold-rolled steel sheet using a treating agent containing no condensed phosphoric acid (Comparative Example 1). SEM photographs (each 1500 representing the crystal appearance structure of the coating
And 10000 times).

Claims (5)

[Claims] 1. An iron plate or a galvanized iron plate coated with a phosphate coating with a treating agent substantially free of condensed phosphoric acid, containing 0.1 to 1.5 g of zinc ions and orthophosphoric acid and / or orthophosphoric acid. 5 to 30 g / of salt-derived phosphate ions,
A method for forming a laminated phosphate coating, which comprises treating with a coating treatment agent containing 1 to 30 g of condensed phosphoric acid. 2. The method for forming a laminated phosphate coating according to claim 1, wherein the condensed phosphoric acid is selected from the group consisting of pyrophosphoric acid, metaphosphoric acid, polyphosphoric acid and salts thereof, and phosphorus pentoxide. A method for forming a laminated phosphate coating, comprising one or more selected types. 3. The method for forming a laminated phosphate coating according to claim 1 or 2, wherein the coating treatment agent further contains at least one oxidizing agent. Method of forming acid salt film. 4. The method for forming a laminated phosphate film according to claim 3, wherein the oxidizing agent is nitrate ion or chlorate ion. . 5. The method for forming a laminated phosphate coating according to claim 1 or 2, wherein the coating treatment agent further comprises 0.3 to 3 g of nickel ion / 0.5 to nitrate ion. 10 g /, manganese ion 0.6 to 3 g /
And a chlorate ion of 0.05 to 2 g / one or more, and a method for forming a laminated phosphate film.