JP2831452B2 - Rust preventive pigment and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a rust-preventive pigment, particularly to a rust-preventive pigment useful for electrocomposite plating of a steel sheet, and a method for producing the same.

[Conventional technology]

Recently, zinc-based alloy-coated steel sheets such as steel sheets for automobiles have been required to be more excellent in corrosion resistance and have been actively developed.

As such a plated steel sheet, a dispersion-type plated steel sheet in which fine insoluble particles such as chromia, alumina, silica, or titania are suspended during electroplating to disperse the fine particles in a plating layer is known. Kaisho 60-2110
No. 94, JP-A-60-211095, JP-A-60-211096
No.).

A method is also known in which a soft-soluble chromate is added to a zinc-based alloy plating bath, and a plating layer containing at least one of alumina sol and Ni ions is formed using a plating bath containing a mixture thereof. JP-A-63-11695, JP-A-63-11696).

In this case, the chromate dispersed and eutectoid in the zinc or zinc-based alloy plating layer acts as a kind of rust preventive pigment, and significantly improves the corrosion resistance of the steel sheet.

As such chromates suitable for rust-preventive pigments for electroplated steel sheets, chromates of metals such as Sr, Ba, Zn, and Pb are known. From the viewpoint of covering properties and the like, barium chromate has attracted attention.

[Problems to be solved by the invention]

However, since barium chromate has a high solubility under acidic conditions, hexavalent chromium (hereinafter referred to as “Cr ⁶⁺ ”) eluted from barium chromate accumulates in the acidic plating solution, and the plating operation is gradually performed. There is a serious problem that it causes instability and causes loss of metallic luster on the plated surface.

As measures to solve this problem, a method of contacting a plating solution with metal particles having a high ionization tendency to reduce Cr ⁶⁺ to Cr ³⁺ and remove the Cr ³⁺ out of the system (JP-A-63-255399) or A method of depositing and coating a fine insoluble metal oxide, silicate or amorphous silica on the surface of barium chromate particles (Japanese Patent Application Laid-Open No. 1-246399) has been proposed.

Among them, the method of reducing and removing Cr ⁶⁺ has a disadvantage that it requires the addition of a special reducing agent and a facility for removing Cr ³⁺ after reduction.

In addition, the method of coating the barium chromate particle surface with a metal oxide, silica, or the like is effective in controlling the solubility of barium chromate under acidic conditions, but by agglomeration of the particles during the coating treatment. There is a drawback that the particles tend to be coarsened and that the dispersibility of the particles in the plating solution or plating layer is reduced.

[Means for solving the problem]

The present inventors have found that the solubility of Cr ⁶⁺ under acidic conditions is suppressed, and that it is used for electro-composite plating of steel sheets, has good dispersibility in plating solutions, and is easily eutectoidized in plating layers. As a result of repeated experiments and studies on the realization of an excellent rust-preventive pigment exhibiting excellent corrosion resistance, by forming a coating of a certain oxyacid salt on the surface of barium chromate particles,
The present inventors have found that desired effects can be obtained, and have completed the present invention.

That is, the rust-preventive pigment according to the present invention is characterized in that acid resistance is improved by depositing and coating fine insoluble oxyacid salt particles on the surface of barium chromate particles.

 Hereinafter, the present invention will be described in detail.

In the rust-preventive pigment according to the present invention, the insoluble oxyacid salt refers to an insoluble oxyacid salt having a solubility at least lower than that of barium chromate as a core material, and because it is deposited and coated on the barium chromate particles. The particles are at least fine particles smaller than the core material particles, and may be either amorphous or crystalline.

Examples of such oxyacid salts include one or more of oxyacid salts such as barium sulfate, nickel chromate, iron chromate, chromium chromate, and lead chromate. Barium sulfate is preferred.

On the other hand, barium chromate of the core material is not only normal barium chromate but also part of CrO ₄ ^-2 is SO ₄ ^-2 , MoO
^{_{4 -2, PO 4 -3, F}} - may be one which is a solid solution or the like.
In addition, barium chromate should have as fine primary particles as possible due to the properties of the rust-preventive pigment and have good dispersibility. In many cases, the average particle size is preferably in the range of 0.1 to 2 μm.

If the thickness is less than 0.1 μm, the efficiency of coating with the oxyacid salt is low, a large amount of the oxyacid salt needs to be formed, the content of the effective chromate becomes extremely low, and the production becomes difficult. On the other hand, if it is 2 μm or more, it lacks suitability as a rust preventive pigment, and particularly when applied to steel plate plating, not only the precipitation rate in the plating layer becomes low, but also the dispersion in the plating solution and the plating layer becomes poor. Insufficient.

The rust preventive pigment according to the present invention is obtained by depositing and coating fine insoluble oxyacid salt particles uniformly on the particle surface with barium chromate as a core material as described above. It can be easily confirmed by rational means such as electron microscope, ESCA and chemical analysis. In addition, the particle state before and after coating is not different by electron microscope observation,
Since the elution of Cr ⁶⁺ was suppressed, it is considered that the coating formed a uniform film.

The amount of the insoluble oxyacid salt formed on the surface of the barium chromate particles depends on the purpose of use of the rust preventive pigment and the properties of the oxyacid salt, but is preferably 1 to 50% by weight based on the total weight of the rust preventive pigment.

When the amount is less than 1% by weight, the Cr
^The effect of inhibiting ⁶⁺ dissolution is insufficient, while if it exceeds 50% by weight, the content of chromate as an active ingredient exhibiting a rust-preventive effect becomes low and is not practical.

As can be seen from the above, the improvement in acid resistance in the rust preventive pigment according to the present invention means that the solubility of barium chromate, particularly in the acidic region, is reduced to reduce the CrO ₄
^-2 means that the dissolution is controlled.

Such a rust preventive pigment can be industrially advantageously produced by the following method.

That is, sulfuric acid is added to the aqueous slurry of barium chromate,
Aqueous solution of soluble sulfate or at least one soluble metal salt selected from nickel, iron, chromium or lead is slurry pH
Addition reaction is performed at 4 or less to deposit and coat fine insoluble oxyacid salt particles on the surface of the barium chromate particles.

The type of the soluble sulfate in the above is not particularly limited, and examples thereof include alkali sulfate, alkali alkali sulfate, ammonium sulfate, and ammonium sulfate. In addition, as the metal salt such as nickel, iron, chromium, and lead, a water-soluble salt such as sulfate, chloride, and nitrate of the metal can be used.

When these acids or salts are added to and reacted with the aqueous slurry of barium chromate, it is important that the barium chromate particles are well dispersed in advance so as to be as close to the primary particles as possible.

For this purpose, it is preferable to disperse the slurry by high-speed stirring or to perform film agglomeration using a desired dispersing machine by the action of a strong shearing force such as a colloid mill or a homogenizer.

The reaction is carried out by gradually adding the above aqueous solution while stirring at room temperature or in a heated state at a slurry pH of 4 or less.

The reason for setting the slurry pH to 4 or less is to promote an interfacial reaction between barium chromate and an acid or a salt, and to uniformly and densely deposit fine insoluble oxyacid particles on the surface of the barium chromate particles. is there.

After completion of the reaction, aging is continued for a while, followed by solid-liquid separation by a conventional method, washing with water, if necessary, drying and pulverization to finish the product.

(Operation)

The rust preventive pigment according to the present invention is formed by uniformly depositing and coating fine insoluble oxyacid salt particles on the particle surface of barium chromate as a core material.

This coating, when barium chromate in the core material to elute Cr ⁶⁺ gradually dissolved in water or acidic solution, difficulties intervention to spread the movement of Cr ⁶⁺ between the core material and the liquid The elution is controlled by performing, the thickness of the coating layer,
The dissolution of Cr ⁶⁺ can be suppressed to an arbitrary degree by appropriately setting the kind, the density, and the like. Thus,
It can be long-term granted stable rust action of the metal based on Cr ⁶⁺ the release of controlled Cr ^6+.

As a mechanism of such coating formation, the type and content of the reaction performed in the production of the rust preventive pigment of the present invention differ depending on the type of acid or salt to be added, and the effect of coating slightly differs.

For example, the reaction between barium chromate and sulfuric acid or a sulfate is a kind of ion substitution reaction, and the following formulas (1) and (2)
Indicated by

In these reactions, the release of Ba ⁺⁺ based on the dissolution of barium chromate by the acid is rate-determined and proceeds from near the surface of the barium chromate particles, and a dense coating made of ultrafine BaSO ₄ is formed.

Further, in the following reactions (3) and (4) of barium chromate and Ni salts, fine particles of nickel chromate which are extremely insoluble and tend to have a positive surface potential are formed to form a coating.

In the reaction (4), the reaction (1) also occurs to form a coating composed of nickel chromate and barium sulfate.

Furthermore, the reaction of barium chromate and FeSO ₄ at pH 4 or lower proceeds via the following oxidation-reduction reaction (5), and is a complicated reaction comprising poorly soluble iron (III) chromate, chromium chromate, barium sulfate, etc. A coating having an appropriate composition is formed.

Cr ⁶⁺ + 3Fe ²⁺ → Cr ³⁺ + 3Fe ³⁺ ... (5) Nickel chromate, iron chromate, chromium chromate, etc. generated by these reactions are easily charged positively in the plating solution, and are rustproof. When used as a pigment in a dispersion plating material, it is presumed that barium chromate facilitates eutectoid deposition in the plating layer.

〔Example〕

In the following Examples, the dissolution of Cr ^{6+ in} the acidic region of the rust preventive pigment was evaluated by the following test method.

A 5 g sample of a rust-preventive pigment is placed in 100 ml of a sulfuric acid aqueous solution having a pH of 2 ± 0.1, and the mixture is stirred and mixed at 20 ° C. for 1 hour with a magnetic stirrer.
The concentration (mg /) of chromium (as CrO ₃ ) is determined by colorimetry.

Example 1. After sufficiently dispersing 500 parts of an aqueous slurry containing 100 parts of barium chromate having an average particle size of 0.5 µm, 18 parts of sulfuric acid (48% of H ₂ SO ₄ ) was added to the slurry, and the mixture was stirred. 1 at 60 ° C
Allowed to react for hours.

The reaction product was washed, washed, dried and pulverized by a conventional method to obtain 95 parts of a rust-preventive pigment.

This rust-preventive pigment has a barium sulfate coating on the surface of barium chromate particles, the average particle size of which is 0.6 μm, and when observed under an electron microscope, particles almost identical to the original barium chromate particles. Condition.

Example 2 After sufficiently dispersing 600 parts of an aqueous slurry containing 100 parts of barium chromate having an average particle size of 0.5 μm, 400 parts of an aqueous nickel sulfate solution (NiSO ₄ 23 g /) was added to the slurry, and a further small amount was added. After adjusting the pH value to 2 by adding sulfuric acid, the mixture was reacted at 80 ° C. for 1 hour with stirring.

The reaction product was filtered, washed with water, dried and pulverized in a conventional manner to obtain 104 parts of a rust preventive pigment.

Although this rust-preventive pigment has a coating of nickel chromate and barium sulfate, it shows the average particle size and Cr ⁶⁺ elution property in the acidic region shown in Table 1, and the surface potential in a sulfuric acid acidic aqueous solution (pH 2) is positive. Met.

Example 3 Instead of an aqueous solution of nickel sulfate, an aqueous solution of iron sulfate (22 g of FeSO ₄
/) The reaction and post-treatment were carried out in the same manner as in Example 2 except that 400 parts were added and the reaction was carried out at 80 ° C for 1 hour.
I got 5 copies.

This rust-preventive pigment has a coating of iron chromate, chromium chromate, and barium sulfate, but shows the average particle size shown in Table 1 and the Cr ⁶⁺ elution property in an acidic region, and is used in a sulfuric acid solution (pH 2). Had a positive surface potential.

Example 4. An aqueous solution of chromium sulfate (Cr ₂ (SO ₄ ) instead of nickel sulfate)
_The reaction and post-treatment were carried out in the same manner as in Example 2 except that 400 parts of ₃ 20 g /) was added and reacted at 60 ° C. for 1 hour to obtain 104 parts of a rust preventive pigment.

This rust preventive pigment showed a coating of chromium chromate and barium sulfate shown in Table 1, and had a positive surface potential in an aqueous sulfuric acid solution.

Example 5 An aqueous solution of lead nitrate (Pb (N
O ₃ ) ₂ 49 g /) 400 parts were added, and the reaction and post-treatment were carried out in the same manner as in Example 2 except that the reaction was carried out at 80 ° C for 2 hours.
101 parts of rust preventive pigments were obtained.

This rust preventive pigment mainly has a lead chromate coating,
Table 1 shows the average particle size and Cr ⁶⁺ elution property in the acidic region.

When the particle characteristics of the rust preventive pigment obtained in each of the above Examples were examined, the results shown in Table 1 were obtained.

As shown in Table 1, the rust-preventive pigment according to the present invention has a significantly reduced Cr ⁶⁺ elution property in an acidic region as compared with barium chromate before the coating treatment (comparative example). Met.

Anticorrosive pigments according to the present invention [Effect of the Invention are, Cr ⁶ in order that suppresses the solubility by coating fine particles of an insoluble oxyacid salts on the particle surfaces of barium chromate, especially acidic region ⁺
The rust-preventing effect of the metal based on Cr ⁶⁺ is remarkable because the release of the metal is stable and mild.

Therefore, the rust-preventive pigment according to the present invention is not only suitable as an additive for electro-composite plating particularly for improving the corrosion resistance of a steel sheet, but also in place of the conventionally used sink chromate, a rust-preventive paint or electrodeposition. It can be used relatively safely as a rust preventive pigment for painting.

In addition, the above rust-preventive pigments can be arbitrarily designed for the type and thickness of the film or the surface potential according to the application by the production method according to the present invention to set the release and particle characteristics of Cr ⁶⁺ , and therefore, industrially This can advantageously be obtained.

Continuing from the front page (72) Inventor Kazuhiko Sano 1-2-2 Harumi-cho, Tokuyama-shi, Yamaguchi Pref. Japan Chemical Industry Co., Ltd. Tokuyama Plant (72) Inventor Nobuo Takagi 9-15-1, Kameido, Koto-ku, Tokyo Japan Chemical Industry (72) Inventor Minoru Yokoyama 3-36-5 Sakashita, Itabashi-ku, Tokyo Toho Pigment Industry Co., Ltd.

Claims (4)

(57) [Claims] 1. A rust preventive pigment having improved acid resistance by depositing and coating fine insoluble oxyacid salt particles on the surface of barium chromate particles. 2. The rust preventive according to claim 1, wherein the fine insoluble oxyacid salt is one or more selected from barium sulfate, nickel chromate, chromium chromate, lead chromate and iron chromate. Pigment. 3. The rust preventive pigment according to claim 1, wherein the average particle size is in the range of 0.1 to 2 μm. 4. An aqueous slurry of barium chromate with sulfuric acid,
One or two or more aqueous solutions selected from soluble metal salts or soluble metal salts of iron, nickel, chromium or lead are added and reacted at a slurry pH of 4 or less to form fine insoluble metal oxyacids on the barium chromate particle surface. A method for producing a rust preventive pigment, comprising depositing and coating salt particles.