JPS609120B2 - How to replenish electrodeposition paint - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for replenishing silkworm-adhering paint.

In electrodeposition coating, it is desired that the coating be done under the same conditions in order to obtain a product of uniform quality.

In general, the main component of turtle coating paints is polycarboxylic acid resin that forms the coating's stiffness. or water-dispersible ones are used.

However, continuous exposure coating reduces the resin solid content in the coating bath, while residual neutralizing agent used for neutralization accumulates in the bath.

In reality, it is unavoidable that the haze coating composition fluctuates due to continuous painting, and one known method to deal with this fluctuation is to add replenishment paint with a small amount of neutralizing agent. There is.

(Refer to Japanese Patent Publication No. 45-1324.) There are many known methods for replenishing paint, such as '1) Electrodeposition in which a cathode chamber is formed using a diaphragm. There are two methods: using a coating device, diluting the replenishment paint with the liquid in the cathode chamber and supplying it to regular haze paint, and {2} diluting the replenishment paint with an electrodeposition paint grade of electrodeposition coating. .

However, with methods {1} and [2', paints with a low amount of neutralizing agent for the carboxyl groups in the polycarboxylic acid resin (hereinafter referred to as the degree of neutralization) of 0.5 or less, even for replenishment paints, cannot be sufficiently dissolved. This results in the formation of a precipitate, which has the disadvantage that the appearance of the sprayed coating film becomes less glossy and rough. This is because in order to dissolve replenishment paint with a low degree of neutralization as mentioned above, not only a high concentration of neutralizing agent but also a solvent resin content is required. Therefore, there is almost no resin in the cathode chamber solution, and in the case of (2), it is thought that the neutralizing agent concentration is not high enough.

The present invention was made in view of the above-mentioned current situation, and its purpose is to use a special coating device that divides the electrodeposition coating chamber into a catholyte chamber and a paint chamber using a diaphragm that does not allow resin to pass through. To provide a method for replenishing dew paint, which can be easily carried out using a commonly used dew paint apparatus, and can effectively prepare and supply the replenishment paint to dew paint applications.

According to experiments conducted by the present inventors, when the cathode is covered with a masking material such as cotton flannel during lightning coating and continuous decoating is continued, the pH of the tortoise coating within the masking material (hereinafter referred to as the cathode zone) increases. It was found that the concentration of the neutralizing agent was higher than that of the haze coating grade (hereinafter referred to as anode zone), and therefore the concentration of the neutralizing agent was higher.

The present invention has been made based on the above knowledge, and the present invention can be briefly summarized as follows: When applying a paint containing a polycarboxylic acid resin, a neutralizing agent, and a solvent by electrodeposition, a masking material that allows the resin to pass through the inside of an open coating bath is used. The paint near the cathode of the cathode belt is separated into an anode belt and a cathode belt, and the paint is taken out of the electrodeposition coating bath, and the main component is polycarboxylic acid resin with a neutralization degree of 0.1 to 0.5. This is a method for replenishing lightning coating paint, which is characterized by mixing it with a coating material for replenishment and then supplying it to an anode zone.The present invention will be explained based on the accompanying drawings. A masking material 3 is provided on the surface of the cathode 2 installed on the side wall of the haze painting bathtub 1' to cover the surface of the cathode that comes in contact with the paint solution. It is divided into 5 anode zones.

Continuous haze coating causes cathode zone 4 where neutralizing agent has accumulated.
The electrodeposited paint containing a high neutralizing agent concentration is optionally taken out of the coating bath and used for dissolving the replenishing paint 7.

In this case, the mist coating may be taken out from any position within the cathode zone 4 by any method. The timing to take out the electrodeposited paint in the cathode belt castle 4 outside the exposed coating bath depends on the electrical conductivity of the applied paint,
It is preferable to measure the pH and determine the concentration of the neutralizing agent. The exposed paint with a high neutralizing agent concentration taken out of the bathtub can be directly or stored in the dilution tank 8.
and mixed with the lightning replenishment paint 7 to dissolve and dilute the replenishment paint.

The replenishment paint 9 adjusted to a predetermined resin solid concentration can be transferred to the anode belt of the electrodeposition coating bath 1 to adjust the resin solid content, pH, etc. of the electrodeposition paint. By performing the above operations, the replenishment paint can be easily dissolved and diluted.

Furthermore, according to the method of the present invention, the degree of neutralization of the replenishment paint is 0.
This is particularly effective when the value is as low as 1 to 0.5. Therefore, unlike conventional methods, the method of the present invention does not require frequent ion-exchange treatment of exposed paint, makes it possible to minimize compositional fluctuations in exposed paint, and further improves the appearance of the paint film. This makes it possible to stably apply the electric coating that can be removed. To explain the present invention in more detail, a woven fabric or non-woven fabric made of natural or synthetic fibers that transmit resin components is used as a masking material that partitions the interior of the electrodeposition coating bath into a cathode band and an anode band.

Examples of natural fibers that can be used include cotton, silk, wool, and linen, and examples of synthetic fibers that can be used include nylon, polyester t-saran, and polypropylene.

Any commercially available paint that has a polycarboxylic acid resin as the main film-forming component can be used, and a haze paint that has a polycarboxylic acid resin and etherified methylol melamine as its main film-forming component is particularly preferred. .

The neutralization degree of replenishment paint is usually 0.6 to 0. Regarding the degree of affinity, "in order to reduce fluctuations in the concentration of the neutralizing agent commonly used in turtle coating, it is convenient to have a smaller degree of neutralization. By implementing the method of the present invention, the degree of neutralization can be reduced to 0. 1-0.

It can be reduced to 5.

Determination of the neutralizing agent concentration of the misted paint in the cathode zone of the exposed paint bath is done by potentiometric titration with hydrochloric acid, while the pH is determined by p
It can be measured using an H meter.

In either case, it is preferable to carry out automatic measurement so that the liquid can be automatically transferred to a dilution tank or a storage tank when a control point is reached. Examples are shown below to specifically explain the present invention.

Example 1 In this experiment, the coating was carried out using the apparatus shown in FIG.

In Figure 2, 1 is an electrodeposition coating bathtub (capacity 10), 2 is a cathode, and 3 is a cathode.
4 is the masking material, 4 is the cathode zone, 5 is the anode zone, 6 is the overflow tank, 7 is the replenishment paint, 8 is the dilution tank, 9 is the diluted replenishment paint, 1 is the liquid storage tank. Masking is performed by covering the bag with cotton flannel, and the electrodeposition paint inside the masking (cathode band) can be collected outside the silkworm paint bath. , Lightning coating was performed continuously using an anodized aluminum material as an anode.

The exposed paint used was a commercially available acrylic-melamine water-based paint adjusted to a resin solid content of 8% by weight (pH 8.4, degree of neutralization 0.85) (10%).

The coating conditions were as follows.

Treatment area: 4d/time x 75 times (total of 3) -
Haze deposition conditions: Voltage: 150 V, Current application time: 2 minutes, Collection amount of cathode solution: 4 times/time x 75 times (300 discharges in total) The solution collected from the cathode solution was stored in a liquid storage tank.

The cathode band solution has a resin solid content of 5.3% by weight and a pH of 10. &The degree of neutralization was 1.6. At the end of 75 continuous electrodeposition coatings, in order to correct the resin solid content of the adhesive paint, add the replenishment paint (resin** solid content 50% by weight, neutralization degree 0.2) to the dilution tank and use Nawa Azusa. While doing so, the cathode zone solution in the storage tank was gradually added, and after the addition was completed, the addition of one powder was continued.

This replenishment paint is transferred to the anode belt, blended with the electrocoating paint, and further deionized water is added to bring the total amount of the electrocoat to 10%.
Adjusted to the end. Resin solid content, pH, degree of neutralization,
The appearance of the coating film and the change in coating thickness were as shown in Table 1. Table 1 However, ◎...Excellent ○...Good △． ...Slightly inferior ×・．・Inferior XX...Very Inferior Comparative Example 1 In the method of Example 1, the replenishment paint was solubilized using the lightning coating liquid in the anode zone instead of the silkworm coating liquid in the cathode zone. .

The results were as shown in Table 2. Table 2 ◎...Excellent 〇. ．． ．． Good△・． ．． Slightly inferior ×.
．． ．． Poor XX...Very K Poor In addition, the replenishment paint was solubilized using the electrodeposition paint liquid of Anode Otoshi, but the dissolution was insufficient and a precipitate was formed.

Comparative Example 2 A method was implemented in which the method of Example 1 was repeated using an electrodeposition coating device in which the cathode chamber was formed with a diaphragm (cation exchange membrane) instead of the masking material, and the replenishment paint was solubilized with the liquid in the cathode chamber. The results were as shown in Table 3.

Table 3■... Excellent ○・・・Good △・．・Slightly inferior ×
...Poor XX...Very poor In addition, although the replenishment paint was solubilized using diaphragm water, the dissolution was insufficient and a precipitate was formed.

Example 2 and Comparative Examples 3 to 4 Replenishment* paints were added according to the methods of Example 1, Comparative Example 1, and Comparative Example 2, with the degree of neutralization changed as shown in Table 4.

A comparison of the solubility of the replenishment paint and the appearance of the electrodeposited film in the above cases was as shown in Table 4.

Table 4 - Solubility■,.・Excellent 〇． ．． ．． To good condition. −． Slightly difficult to dissolve ×.・．． Precipitate formation ××...Appearance of large amount of precipitate formation ■.・．． Excellent ○・．・Good △・． ．． Slightly inferior ×... Inferior (surface roughness) XX.・．． Large grainy surface

[Brief explanation of drawings]

FIGS. 1 and 2 are explanatory views of one embodiment of the method and apparatus of the present invention, and show a part of a cross-sectional view. DESCRIPTION OF SYMBOLS 1... Lightning coated bathtub, 2... Cathode, 2'... Anode, 330... Masking material, 4... Cathode band castle, 5...
... Anode band castle, 6... Overflow tank, 7... Replenishment paint,
8... Dilution tank, 9... Diluted replenishment paint, 10... Liquid storage tank. Figure 1 Figure 2

Claims (1)

[Claims] 1. When applying a paint containing a polycarboxylic acid resin, a neutralizing agent, and a solvent by electrodeposition, the inside of the electrodeposition coating bath is divided into an anode zone and a cathode zone using a masking material that allows the resin to pass through, and the area near the cathode in the cathode zone is The electrodeposition paint is taken out into and out of the electrodeposition coating bath, mixed and stirred with an electrodeposition replenishment paint whose main component is a polycarboxylic acid resin with a degree of neutralization of 0.1 to 0.5, and then,
A method for replenishing electrodeposition paint, characterized by supplying this to an anode zone.