JPH0788585B2 - Phosphate film treatment agent - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a metal phosphate coating agent, particularly a chemical conversion treatment for forming a phosphate coating having improved adhesion because it comprises fine particles. Regarding agents.

[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 nitrite 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. JP-A-57-152472 discloses a method of phosphating a metal surface for cationic electrodeposition coating with an acidic phosphating aqueous solution containing manganese ions in addition to the above components. In addition, Japanese Examined Japanese Patent Sho 61-3658
No. 8 discloses a method for chemical conversion treatment of a metal surface for cationic electrodeposition coating using an acidic ion acid salt treatment aqueous solution containing manganese ion and fluorine ion in addition to zinc ion, phosphate ion and accelerator. There is.

Further, JP-A-59-43883 discloses that (a) is represented by the formula (XPO ₃ ) n, where n ≧ 3, and X is an alkali metal or alkaline earth metal. An acidic solution for chemical conversion of a metal substrate containing a metal or ammonium water-soluble polyphosphate, (b) an organic chelating agent and (c) zinc ions, the pH of which includes sulfuric acid, hydrochloric acid and nitric acid. It is disclosed that a desired value is obtained by using an inorganic acid selected from the group of inorganic acids. In JP-A-59-43883, it is preferable to select nitric acid because it has an oxidation property that is advantageous for initiating the conversion reaction when adjusting the pH, and as the polyphosphate salt that is a constituent of this solution, In particular, it can be selected from sodium trimetaphosphate, sodium tetrametaphosphate and sodium hexametaphosphate, of which sodium hexametaphosphate or HMPP is described as preferred. As described above, the treatment liquid for a metal substrate disclosed in JP-A-59-43883 contains a metaphosphate and prevents sludge formation to avoid the problem of contamination of the liquid.

[Problems to be Solved by the Invention] When the relationship between the water resistance secondary adhesion of the chemical conversion coating (adhesion with the coating under wet deterioration conditions) and the particle diameter of the coating particles is examined, the smaller the particle diameter is, the smaller the particle diameter is. It was found that the water resistant secondary adhesion was improved. Then, when the particles of the film formed by the conventional zinc phosphate-based treating agent were examined, it was about 2 to 3 μm on the steel surface and 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.

Further, even the chemical conversion film formed by the treatment liquid disclosed in JP-A-59-43883 does not have sufficient adhesion to the coating film.

Therefore, an object of the present invention is to provide a zinc phosphate-based treatment agent capable of forming a fine conversion coating film of particles.

[Means for Solving Problems] As a result of earnest research in view of the above object, it was discovered that particles of a film obtained by adding condensed phosphoric acid to a phosphate film treating agent can be made extremely fine. Then, the present invention was conceived.

That is, the phosphate film treating agent of the present invention has zinc ions of 0.
Containing 2 to 1.5 g /, 5 to 30 g / of phosphate ions derived from orthophosphoric acid and / or orthophosphate (hereinafter referred to as “phosphate ion”), and 1 to 30 g / of condensed phosphoric acid It is characterized by

Examples of the condensed phosphoric acid contained in the phosphate coating agent of the present invention include pyrophosphoric acid, metaphosphoric acid, polyphosphoric acid and salts thereof, and phosphorus pentoxide. Each of these compounds has a structure in which phosphate ions are condensed via 0.

The concentration of condensed phosphoric acid is 1 to 30 g /. If it is less than 1 g /, a film of fine particles is not formed, and if it is more than 30 g /, the effect of further miniaturization of the film particles, that is, thinning cannot be expected. The preferred concentration range is 3 to 15 g /.

As mentioned above, the condensed phosphoric acid can be added in the form of a salt, but as its supply source, alkali salts such as sodium and potassium, ammonium salts, alkaline earth salts, zinc,
There are metal salts such as iron, nickel and manganese.

By adding condensed phosphoric acid, the particles of the obtained film become finer to about 0.1 to 5 μm depending on the concentration.

The concentration of zinc ions is 0.2-1.5 g /. When it is less than 0.2 g /, a uniform phosphate film is not formed on the iron-based surface, and a blue-colored film is partially formed. If it is more than 1.5 g / min, the effect of refining the coating particles cannot be expected. A preferred concentration range is 0.5-1 g /. Sources of zinc ions include zinc oxide, zinc carbonate, zinc nitrate and the like.

The concentration of phosphate ion is 5 to 30 g /. If it is less than 5 g /, a uniform film is not formed, and the condensed phosphoric acid decomposes quickly. On the other hand, if it exceeds 30 g /, the corresponding improvement in effect cannot be expected, and it is uneconomical because the amount of chemical used increases. A preferred concentration range is 10-20 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, the concentration is 0.01 ~ 0.2 g /, preferably 0.01 ~ 0.1 g /
Is. 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 0.5-10 g /, and the chlorate ion concentration is 0.0.
It is 5 to 2 g /. Sources of nitrate ions include sodium nitrate, ammonium nitrate, zinc nitrate, manganese nitrate,
There are 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 0.3 to 3 g /, and the concentration of manganese ions is 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. Nickel carbonate as a source of nickel ions,
There are nickel nitrate, nickel chloride, nickel phosphate and the like, and sources of manganese ions include manganese carbonate, manganese nitrate, manganese chloride and manganese phosphate.

Next, the chemical conversion treatment using the treatment agent of the present invention will be described.

First, the chemical conversion treatment with the phosphate coating agent 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-based surface include those subjected to hot dip galvanizing, hot dip galvanizing, electrogalvanizing, alloying electrogalvanizing, and the like.

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 the phosphate coating agent of the present invention, and it is preferable to use the dipping method. The temperature of the processing liquid is 25 ~
The temperature is 60 ° C, preferably 30 to 50 ° 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 15 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 the body of an automobile, practically, it is first immersed for 15 seconds or longer, preferably for 30 to 90 seconds, and then for 2 seconds or longer, preferably for 5 seconds. Spray for 45 seconds. In order to wash off the sludge attached during the dipping treatment, it is preferable that the spraying treatment be performed for as long as possible.

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] In the phosphate film treating agent of the present invention described above, it is considered that the addition of condensed phosphoric acid suppresses the etching during the chemical conversion treatment and reduces the particle growth rate of the film. Condensed phosphoric acid and orthophosphoric acid form metal ions and metal salts at the interface, but PH at the interface rises only slightly in the vicinity, so the crystal grains precipitated on the metal surface have low crystallinity (amorphous). ) It becomes fine. Therefore, since the obtained film is dense, it has excellent adhesion and corrosion resistance. The obtained film is presumed to be a zinc phosphate film containing condensed zinc phosphate.

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

Examples 1 to 8 and Comparative Examples 1 to 6 Electrogalvanized steel sheets and cold-rolled steel sheets were used as the metals to be treated, and the following treatments were applied to the respective metals.

(1) Degreasing An alkaline degreasing agent with a concentration of 2% by weight (Rd manufactured by Nippon Paint Co., Ltd.
53) was used, and immersion treatment was performed 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% by weight concentration) was used for immersion treatment at room temperature for 20 seconds.

(4) Chemical conversion treatment Using a phosphate-treated aqueous solution having the composition shown in Table 1 below,
Immersion treatment was performed at 43 ° C. for 2 minutes.

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

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

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

The appearance and weight of each of the chemical conversion coatings thus obtained were measured. Scanning electron microscope (SE
M) (1500 times and 10000 times) to observe the coating particles.

(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 180 V, energization time 3 minutes) and baked at 180 ° C. for 30 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” made by Nippon Paint Co., Ltd.) was applied to the remaining electrodeposition coated plate to a film thickness of 40 μm, and then a top coating (“Olga G-65 White” made by Nippon Paint).
Was coated to a film thickness of 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) A cross cut was put in each electrodeposition coated plate, 5% salt water was sprayed, and the blister width (mm) outside the cross cut was evaluated. The spray time was 500 hours (electrogalvanized steel sheet) and 1000 hours (cold rolled steel sheet), respectively.

(B) Water resistance adhesion test After immersing the coated plate in deionized water at 40 ° C for 10 days, 1 mm intervals and 2 mm intervals of cross-cuts (100 pieces) were formed on each surface with a sharp cutter, and each surface was formed. After sticking the adhesive tape, these were peeled off, and the number of grids remaining on the coated plate was counted.

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

The results are shown in Tables 2 and 3. Further, SEM photographs of Example 1 are shown in FIG. 1A (on Zn, 1500 times) and FIG. 1B (on Zn,
10000 times), Figure 2A (on Fe, 1500 times) and Figure 2B (Fe
Above, 10,000 times). As a further comparison, S of Comparative Example 1
EM photographs are also shown in Fig. 3A (on Zn, 1500 times) and Fig. 3B (Zn, respectively).
Top, 10,000 times), Figure 4A (on Fe, 1500 times) and Figure 4B (F
e, 10000 times).

As is clear from the above results, the chemical conversion treatment using the phosphate coating agent of the present invention provides a uniform, dense and sufficiently thin chemical conversion film, and the particle size of the coating particles is as small as submicron. I understand. Further, the corrosion resistance and the water-resistant secondary adhesion after forming the coating were also good. On the other hand, a treating agent to which condensed phosphoric acid has not been added (Comparative Example 1), one having an excessively small content of condensed phosphoric acid (Comparative Example 2), and one containing no Zn ion (Comparative Example 3) , which does not contain phosphate ions (Comparative example 4), nO ₂ ^- those not containing (Comparative example 5), and the high concentration of those (Comparative example 6) both the characteristics of Zn ions I was not satisfied.

Example 9 The same treatments and tests as in Example 1 were carried out except that 0.8 g / manganese ion was added to the phosphate film treating agent of Example 1. As a result, the appearance of the chemical conversion film is uniform and dense,
The coating weight was 0.61 g / m ² and the particle size was 0.7 μm. In addition, the corrosion resistance (SST) of the electrodeposition coated plate is 5 mm, and the water-resistant secondary adhesion after overcoating is 10 in both 2 mm and 1 mm cross-cut tests.
It was 0/100.

[Effects of the Invention] As described in detail above, since the phosphate coating agent of the present invention contains condensed phosphoric acid, the particles of the chemical conversion coating are made finer to submicron size. Therefore, the water-resistant secondary adhesiveness when electrodeposition coating is performed on the chemical conversion film is remarkably improved, and the corrosion resistance of the film is equal to or higher than that containing no condensed phosphoric acid. Further, the treatment agent of the present invention is suitable for treating the iron surface and the zinc surface at the same time, and the chemical conversion treatment can be performed at a lower temperature as compared with the case where the condensed phosphoric acid is not contained, which is economical.

[Brief description of drawings]

FIGS. 1A and 1B are scanning electron microscopes (SEM) showing the crystalline appearance structure of a chemical conversion coating formed on an electrogalvanized steel sheet using the phosphate coating agent of the present invention (Example 1).
FIG. 2A and FIG. 2B are photographs (1500 times and 10000 times, respectively), and the crystalline appearance of the chemical conversion coating formed on the cold-rolled steel sheet using the phosphate coating agent of the present invention (Example 1). 3A and 3B are scanning electron microscope (SEM) photographs showing the structure (1500 times and 10000 times, respectively), and FIGS. 3A and 3B show electrogalvanizing using a treatment agent containing no condensed phosphoric acid (Comparative Example 1). SEM photographs showing the crystalline structure of the chemical conversion coating formed on the steel sheet (1500 each)
4A and 4B are SEM photographs showing the crystalline appearance structure of the chemical conversion coating formed on the cold-rolled steel sheet using the treating agent containing no condensed phosphoric acid (Comparative Example 1). (1500 times and 10000 respectively
Times).

Claims (5)

[Claims] 1. Zinc ion 0.2 to 1.5 g / and phosphate ion derived from orthophosphoric acid and / or orthophosphate 5 to 30 g /
And a condensed phosphoric acid 1 to 30 g /, a metal phosphate coating agent. 2. The phosphate coating agent 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 phosphate coating agent, characterized in that it is one kind or two or more kinds. 3. A phosphate film treating agent according to claim 1 or 2, further comprising at least one oxidizing agent. 4. The phosphate film treating agent according to claim 3, wherein the oxidizing agent is a nitrate ion or a chlorate ion. 5. The phosphate film treating agent according to claim 1 or 2, further comprising nickel ion of 0.1.
3 to 3 g /, nitrate ion 0.5 to 10 g /, manganese ion 0.6
-3 g / and one or more of chlorate ion 0.05-2 g / are contained, and a phosphate film treating agent characterized by the above-mentioned.