JPH02282499A - Coating method by cationic electrodeposition - Google Patents

Abstract

PURPOSE:To form a coating film even in a gap of <=500mum width in a body to be coated by supplying electric current in many steps at a prescribed temp. of a coating material bath and a prescribed voltage between electrodes to carry out coating by cationic electrodeposition. CONSTITUTION:A body having a gap of <=500mum width is coated by cationic electrodeposition under the conditions of 10-23 deg.C temp. of a coating material bath and 50-150V voltage between electrodes. By this first-step coating, a coating film having resistance is formed at the inlet of the gap. Electric current is then supplied in many steps at >=250V voltage between the electrodes in at least one of the steps to carry out coating by cationic electrodeposition.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides a cationic electrodeposition coating method using a multi-stage energization method, which can form a coating film in the gaps of an object to be coated, which has a complex structure such as an automobile body. Regarding.

(Prior art and its problems) Electrodeposition coating is a method in which a coating film is deposited and formed on the surface of an object to be coated by electrophoresis or the like by applying a voltage. For example, when there is a spot welded gap, if the conventional method is used, for example, cationic electrodeposition at a bath temperature of 30°C and a voltage between electrodes of 300V, the coating film will be concentrated on the edges and protrusions such as the gap area. The inlet of the gap is blocked, and the inside of the gap cannot be coated properly. For this reason, in order to cover the rust prevention properties of areas that cannot be painted, wax is applied inside the gaps or rust-proof steel plates are used, but these methods have the problems of being costly and requiring a lot of man-hours. there were.

(Means for Solving the Problems) The present invention has developed a cationic electrodeposition paint as a result of intensive research aimed at improving coating properties in the cationic electrodeposition coating method in order to form a coating film over a wide range within the gap. In the method of electrodeposition coating using a multi-stage energization method, the temperature of the paint is lowered and the first stage voltage of the multi-stage energization method is lowered, and the voltage is increased in the subsequent electrodeposition process to reduce the current density at the entrance of the gap in the early stage of electrodeposition. The present inventors have discovered that the paint film can be formed over a wide area within the gap without being blocked because there is no abnormal precipitation of the coating film in the gap population, and the present invention has been completed.

That is, the present invention provides a method for cationic electrodeposition coating of objects having a gap of 500 μm or less using a multi-stage energization method, in which the coating temperature is 10 to 23°C, and the voltage between electrodes in the first stage electrodeposition coating is The present invention relates to a cationic electrodeposition coating method characterized in that the electrode voltage is 50 to 150V, and the interelectrode voltage in at least one stage after the second stage is 250V or more.

In the present invention, the bath temperature of the cationic electrodeposition paint bath is set at 10 to 2
It is necessary to maintain the bath temperature at 3°C, and if electrodeposition coating is performed at a bath temperature exceeding 23°C, the coating film tends to be abnormally deposited at the entrance of the gap of 500 μm or less, which may cause blockage of the entrance of the gap. It becomes easier.

On the other hand, if the bath temperature of the electrodeposition paint bath is less than 10° C., it is not preferable because it becomes difficult to build up a film thickness.

In the present invention, it is necessary that the interelectrode voltage in the first stage electrodeposition coating of the multistage electrodeposition method be in the range of 50 to 150 . If the interelectrode voltage exceeds 150 V, abnormal deposition of the coating film occurs at the entrance of the gap in the early stage of electrodeposition, which tends to cause stiffness and blockage of the entrance.

On the other hand, if the voltage is less than 50V, the film formed in the first stage will not only be thin and inefficient (in the second stage and subsequent electrodeposition coating processes, when painting by increasing the voltage between electrodes, Since the film thickness at the entrance of the gap formed in the first stage is too thin and the coating resistance is too low, there is a risk that abnormal deposition of the coating film will occur at the entrance.

In the present invention, in the first stage of the multi-stage electrodeposition method, it is possible to form a coating film having coating resistance at the entrance of the gap without clogging the gap entrance due to abnormal deposition of the coating. It is essential.

In the present invention, after the first stage electrodeposition coating, the electrode voltage in at least one stage after the second stage is set to 250.
By setting the interelectrode voltage to 250 V or more, preferably 250 to 500 V, it is possible to form an electrodeposited coating film over a wide range inside the gap, and also to provide the required voltage in the general area. A thick electrodeposition coating can be formed. The voltage between electrodes at this time is 25
If it is less than 0 V, it becomes difficult to form an electrodeposition coating over a wide area inside the gap, and the resulting electrodeposition coating tends to be thin, which is not preferable.

In the present invention, the inter-electrode voltage is increased to 25% in the second and subsequent stages.
Even if the voltage is raised to 0V or higher, the interstitial population will not be blocked, but
This is because a coating film is formed at the entrance of the gap in the first stage and has coating resistance to prevent abnormal deposition of the coating film even if the voltage between the electrodes increases.

The cationic electrodeposition paints used in the electrodeposition paint bath in the present invention are conventionally known epoxy resin-based, acrylic resin-based,
Any resin system can be used, such as polybutadiene.

(Function and Effects of the Invention) According to the method of the present invention, the current density at edges and protrusions where current tends to concentrate can be controlled, so that in the case of objects to be coated that have gaps of 500 μm or less, abnormal deposition of the coating film causes blockage of the gap entrance. This phenomenon does not occur, and an electrodeposition coating film can be formed over a wide range even inside the gap.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Nireclone 9600 manufactured by Kansai Paint Co., Ltd. (electrodeposition paint containing polyester modified epoxy resin, blocked diisocyanate, and nonionic acrylic resin as resin components) was applied in an electrodeposition bath with a solid content of 18% by weight and a pH adjusted to 6.4. , Two cold-rolled steel plates with a thickness of 0.8 m/m and a size of 70 mm x 150 mm are stacked on each other with two 300 μm thick 1010 x 150 spacers sandwiched between both ends so that the gap (clearance) is 300 microns. The object to be coated was immersed in an electrodeposition bath, and cationic electrodeposition coating was performed under the following conditions.

1 condition Bath = 312 PVC bat electrode area ratio: A/C is 2/1 Distance between electrodes: 15cm Bath temperature: 20°C Electrification Varnish roll start 20 seconds (total 3 minutes 30 seconds) 1st stage molding 100VX 1.5 minutes voltage increase 1
0 seconds 2nd stage mold application 400VX 1.5 minutes mold application After painting, the object to be coated was dismantled and the coating height on the inner surface was examined and found to be 35 mm, and no clogging of the gap population occurred.

Examples 2 to 4 and Comparative Examples 1 to 4 The electrodeposition conditions were the same as in Example 1 except that the bath temperature and electrode voltage during energization were as shown in Table 1.

Test results such as coating height are shown in Table 1.

Claims (1)

[Claims] In a method of cationic electrodeposition coating of objects having a gap of 1,500 μm or less using a multi-stage energization method, the coating temperature is 10 to 23°C, and the voltage between electrodes in the first stage electrodeposition is 50 to 23°C. 150V, at least 1 from the second stage onwards
A cationic electrodeposition coating method characterized in that the voltage between electrodes in two stages is 250V or more.