JPH05237457A - Method for improving self-precipitation type film - Google Patents

Abstract

PURPOSE:To improve the secondary close adhesiveness of a precipitated resin film composed of a self-preciptation type coating composition. CONSTITUTION:The secondary close adhesiveness of a precipitated resin film composed of a self-precipitation type coating composition is improved by controlling the close adhesiveness of the precipitated resin film to the surface of a metal by setting the concentration of the oxidizing agent H2O2 in the self- precipitated type coating compsn. to 0.04-2.0g/ and measuring the concentration of the oxidizing agent H2O2 by a redox titration method. By this constitution, the coating compsn. can be stably kept and a resin film excellent in secondary close adhesiveness is obtained.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention comprises water dispersible particles,
The present invention relates to a method for improving the secondary adhesion of a deposited resin film by an autodeposition type coating composition capable of forming a resin film on the metal surface by dipping the metal surface.

[0002]

2. Description of the Related Art Conventionally, a composition capable of forming a resin on a metal surface by immersing the metal surface is known as an autodeposition type coating composition.
No. 17630, Japanese Examined Patent Publication No. 52-21006, etc., a coating composition containing a water-dispersible resin, an oxidizing agent such as H ₂ O ₂ and an acid such as HF and having a pH of about 3.8 or less is disclosed. .. The characteristic of the known coating composition is that when the metal surface is immersed in the composition, the chemical action of the composition on the metal surface (eluting from the metal surface by the etching action, the resin particles associate with the metal ion). The resin film can be formed on the metal surface without using external electricity such as electrodeposition, because the resin film can be formed uniformly on the metal surface.

In this way, the deposited resin film formed from the autodeposition type coating composition must be in close contact with the metal surface. In this case, regarding the adhesion between the deposited resin film and the metal surface, not only the adhesion to the metal surface immediately after drying the resin film (hereinafter referred to as primary adhesion), but also the adhesion after a long period of time in a natural environment ( The following secondary adhesion) is also required. The secondary adhesion of the coating resin film to the metal surface is an important characteristic that determines the quality of processed products.

Also with respect to a deposited resin film formed by the autodeposition type coating composition. Improvement of secondary adhesion has been investigated, but it is not sufficient.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems of the prior art and to improve the secondary adhesion of a deposited resin film formed by an autodeposition type coating composition.

[0006]

Means for Solving the Problems The present inventor diligently studied improvement of secondary adhesion of a deposited resin film by an autodeposition type coating composition. As a result, H ₂ O ₂ was used as an oxidant, and the H ₂ O ₂ concentration exceeded 0.04 g / l and was 2.0 g.
It is possible to improve the secondary adhesiveness by controlling the adhesiveness of the deposited resin film to the metal surface by controlling the concentration of H ₂ O _{2 by} a redox titration method. Obviously completed the present invention.

The present invention relates to a method for improving the secondary adhesion of a deposited resin film by an autodeposition type coating composition, wherein the concentration of the oxidizing agent H ₂ O _{2 in} the composition exceeds 0.04 g / l,
The method is provided in the range of 2.0 g / l or less.

Further, in the present invention, in the method for improving the secondary adhesion of the deposited resin film by the autodeposition type coating composition, the concentration of the oxidizing agent H ₂ O _{2 in} the composition is measured by the redox titration method. Thus, there is also provided the above method, wherein the adhesion of the deposited resin film to the metal surface is controlled. The present invention is also characterized in that the autodeposition coating composition is filtered before the operation by the redox titration method.

Next, the structure of the present invention will be described in detail. A known substance is used for the autodeposition coating composition used in the present invention, but it is characterized in that the H ₂ O ₂ concentration as an oxidizing agent is set within a certain range.

The preferred H ₂ O ₂ concentration of the present invention is about 2.0 g.
/ L or less. More preferably, 0.04 g
The range is more than 1.0 liter / liter and less than or equal to about 1.0 g / liter. H ₂ O ₂
When the concentration is about 0.04 g / l or less, the performance of the coating film formed, especially the variation in the secondary adhesion, is observed. About 2.0g
When it exceeds / l, the film formed is thin and has a large amount of roughness, which significantly deteriorates the quality value. Thus, it was not theoretically sufficiently clarified that the secondary adhesion was remarkably improved by setting the H ₂ O ₂ concentration within a certain range, but it was unexpected.

Specific examples of the autodeposition type coating composition that can be used in the present invention include, for example, a dispersion resin and an acid (for example, H
F), ferric fluoride, and a composition having a pH of about 1.6 to 5.0 (Japanese Patent Publication No. 52-35692) which is adjusted by a pigment (for example, carbon black) if necessary. The content of each component in the composition is about 5% of dispersed resin solid content.
~550g / l, HF about 0.4~5g / l, ferric (trihydrate) fluoride about 1 to 50 g / l, oxidizing agents H ₂ O ₂ 0.0
It is preferable to use a pigment having an amount of more than 4 g / l and not more than 2.0 g / l and a pigment containing an appropriate amount depending on a desired color. The dispersion resin is not particularly limited.

An important point in the present invention is that H in the composition
_A redox titration method is used as a method for measuring the ₂ O ₂ concentration. The titration method may be any known redox titration method,
The method is not particularly limited. The titrant is also not particularly limited.

During continuous use of the autodeposition type coating composition, for example, when the metal to be coated contains an iron-based metal, excess ferrous iron ions accumulate in the coating composition, resulting in a film formed. However, there is a problem in that the composition becomes unstable and the composition itself becomes unstable.
No. 28461 discloses a continuous use stabilizing method (hereinafter referred to as continuous use) in which ferric ion (FeF ₃ ) is added to the composition from the beginning. Also. like this,
As a management method for dealing with the problem, for example, Japanese Patent Publication No. 59-275 can be cited as a prior art. Japanese Patent Publication No. 59-275 discloses a composition in which a known H ₂ O ₂ is added to an autodeposition coating composition containing known organic resin particles, hydrofluoric acid and ferric fluoride (FeF ₃ ). A management method has been proposed, which is characterized by monitoring the concentration of ferrous ions in a substance by the redox potential.

However, in order to improve the secondary adhesion of the deposited resin film by the autodeposition type coating composition of the present invention, the redox potential method is unsuitable for the following reason, and the present inventors As a result of intensive studies, they found that the measurement of the H ₂ O ₂ concentration by the redox titration method is optimal.

The redox potential (hereinafter referred to as ORP) method cannot directly grasp the concentration of the oxidant. For example, when the metal to be coated is iron, ORP is expressed by the following equation.

ORP value = E ^o +0.059 log [Fe ³⁺ ] / [Fe ²⁺ ] (Nernst's formula) E ^o = 0.4 V VS NHE (standard ORP of iron fluoride complex)

The effect of the oxidizing agent is expressed by the following equation. H ₂ O ₂ → O ₂ + 2H ⁺ + 2e 2Fe ²⁺ + 2H ⁺ → 2Fe ³⁺ + H ₂

As described above, the management by ORP does not directly grasp the oxidant concentration but manages the balance of Fe ³⁺ and Fe ²⁺ . Therefore, the concentration of the oxidizing agent cannot be directly grasped.

In the ORP method, as the concentration of the oxidant increases, the ORP value changes less, and the correlation between the ORP value and the oxidant concentration cannot be maintained.

In order to prove the above facts, the present inventor measured the concentration of the oxidizing agent H ₂ O ₂ by the redox titration method of the present invention (H ₂ O ₂ concentration = KMnO ₄ titration amount).
Then, for each H ₂ O ₂ concentration, OR by the conventional ORP method
The P value was measured and the correlation was calculated. The result is shown in FIG.

As can be seen from FIG. 1, the ORP value gradually disappears from the region where the H ₂ O ₂ concentration exceeds about 0.1 g / l. Further, at a high H ₂ O ₂ concentration, the curve becomes horizontal and fluctuates. It disappears and approaches a certain value. That is, as the concentration becomes higher, the ORP value and the H ₂ O ₂ concentration become less correlated. As described above, in the present invention, the optimum range of the H ₂ O concentration for improving the secondary adhesion is such an OR.
It can be said that the ORP method is unsuitable for measuring and controlling the H ₂ O ₂ concentration in the present invention because it includes the range in which the P value is not changing.

The ORP method causes destabilization of the coating composition. In the continuous use of the autodeposition type coating composition, the ORP value often decreases sharply due to the change in the treated area of the article to be coated, and in order to prevent it, the ferrous ion should be kept low, that is, H ₂ O. _If you try to manage ₂ to a high level, the management accuracy will suddenly deteriorate, and OR will be performed in an area with high management accuracy.
This causes destabilization of the P management coating composition.

In other words, the ORP control has a problem that the oxidant concentration cannot be directly grasped, the control cannot be performed in a region where the oxidant concentration is relatively high, and the coating composition becomes unstable. It has drawbacks. On the other hand, in the method of the present invention, the concentration of the oxidant H ₂ O ₂ can be directly grasped, and
_It is possible to control even in a high concentration range of ₂ O ₂ , and the coating composition can be used stably. As a result, the adhesion of the deposited resin film to the metal surface can be controlled, and the secondary adhesion of the deposited resin film can be improved.

An important point in the present invention is that when the coating composition is continuously used, a part of the coating composition is filtered through a polymer membrane or the like, and the H ₂ O ₂ concentration is determined by redox titration using the filtration. To quantify. H ₂ O ₂ by redox titration
In the quantitative determination of, when the coating composition is directly subjected to titration,
It was difficult to judge the end point of titration by the resin or pigment in the coating composition. However, the resin and pigment components can be removed by passing a part of the coating composition through a polymer membrane, and the end point can be easily determined by subjecting the filtrate to redox titration.

In continuous use of the coating composition, if necessary, addition of a dispersion resin (including pigments) and HF
Etc. acid component is added. The dispersed resin is managed by periodical measurement of solid text. In the case of acid components such as HF,
The line guard 101 meter control disclosed in U.S. Pat. No. 3,329,585 can be preferably used. Alternatively, the acid concentration in the coating composition can be easily quantified by neutralization titration of the filtrate filtered through a polymer membrane or the like.

By applying the method of the present invention, it is possible to stably maintain the coating composition and obtain a resin film having excellent secondary adhesion. Hereinafter, the present invention will be described in detail with reference to examples.

[0027]

EXAMPLE The composition of the coating composition used in the present invention is shown below. Ingredients Amount (g / L) Daran SL-143 (54% solid content) 90.17 Newcol 261A (45%) emulsifier 0.30 Aquablak 255 (carbon black dispersion) 3.87 Ferric fluoride 3.00 Foot Hydrochloric acid 0.75 Total amount of 1 L with deionized water As the metal surface coated with the above aqueous coating composition, a cold rolled steel plate (7 × 15 cm) was used. Before painting, clean with alkaline degreasing and wash with water. After coating, it was washed with water, dried in an oven at 110 ° C. for 25 minutes, and then subjected to a test.

Example 1 Using 1 L of the above aqueous coating composition, H ₂ was added to the coating composition.
Treatment was carried out with the composition to which 0.10 g of O ₂ was added.
The performance of the coated plate is shown in Table 1. In the treatment, the H ₂ O ₂ concentration in the composition was determined by redox titration, and the HF concentration was determined by neutralization titration. At the same time, the oxidation-reduction potential was measured (the values are shown at the time of composition preparation (A) and at the time of treatment of the coated object of 8.4 × 10 ⁻² m ² (B)). The results are shown in Table 2.

Examples 2-4 and Comparative Examples 5-7 1 L of the aqueous coating composition was used, and H ₂ was added to the coating composition.
O ₂ is 0.20, 0.50, 1.00, 0.02,
Treatment was performed with the composition added with 0.04 and 2.20 g. The performance of the coated plate is shown in Table 1. In the treatment, the H ₂ O ₂ concentration, the HF concentration, and the redox potential in the composition were measured in the same manner as in Example 1. The results are shown in Table 2.

[Determination of H ₂ O ₂ Concentration of Coating Composition] A part of the coating composition was filtered through a polymer membrane having an average pore size of less than 0.1 μm, and the filtrate was subjected to redox titration. The redox titration was carried out by the following operation. Collect 10 mL from the filtrate, add 5 mL of 50% sulfuric acid, and add 0.025 NKMn.
Titrate with aqueous O ₄ solution. The end point is the time when the collected filtrate becomes slightly red. 0.025NKM required to finish
The H ₂ O ₂ concentration in the coating composition was determined from the titration amount of the nO ₄ aqueous solution.

[Quantification of HF Concentration of Coating Composition] The HF concentration was determined by neutralization titration using a filtrate as described above. The titration operation is shown below. 10 mL is collected from the filtrate, an indicator (bromophenol blue) is added, and titration is performed with a 0.1 N NaOH aqueous solution. The end point is when the collected filtrate turns pink. The HF concentration in the coating composition was determined from the titration amount of 0.1N NaOH aqueous solution required until the end point.

[Measurement of Redox Potential] The potential of the coating composition was measured using a Pt / AgCl (saturated) electrode. (Temperature RT20 ℃)

Test Method and Criteria 1. Appearance of coating The coating after coating and drying was visually evaluated. ○: No abnormality, △: Pinhole present, ×: Pinhole and grainy

2. Coating Adhesion 40 pieces of 40 ° C. × 240 hours Each test plate before and after hot water immersion was carved with 100 squares of 1 mm square, the tape was peeled off, and the number of remaining marks of the coating was measured. The pre-immersion is indicated by the primary adhesion, and the post-immersion is indicated by the secondary adhesion.

[0035]

As a method of improving the secondary adhesion of the deposited resin film by the autodeposition type coating composition, the oxidizing agent H ₂ in the composition is used.
By controlling the concentration of O ₂ within a certain range and measuring the concentration of the oxidizing agent by a redox titration method, the adhesion of the deposited resin coating to the metal surface can be controlled, and the coating composition can be stabilized. It is possible to obtain a resin film that can be maintained and has excellent secondary adhesion.

[0036]

[Table 1]

[0037]

[Table 2]

[Brief description of drawings]

FIG. 1 is a correlation diagram between a redox potential method value and a hydrogen peroxide quantitative value.

Claims (3)

[Claims] 1. A method for improving the secondary adhesion of a deposited resin film by an autodeposition type coating composition, wherein the concentration of the oxidizing agent H ₂ O _{2 in} the composition exceeds 0.04 g / l and 2. 0 g /
The method is characterized in that it is in the range of 1 or less. 2. A method for improving the secondary adhesion of a deposited resin film by an autodeposition coating composition, comprising measuring the concentration of an oxidizing agent H ₂ O _{2 in} the composition by a redox titration method. The above method, wherein the adhesion of the deposited resin film to the surface is controlled. 3. The improved method according to claim 2, wherein the autodeposition coating composition is filtered before the operation by the redox titration method.