JPH1161493A - Electrodepositon coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrodeposition coating method which is capable of executing stable coating without changing coating quality even by the coating area of materials to be coated, the fluctuation in the kinds of the materials to be coated, etc., and is cost effectively excellent. SOLUTION: This electrodeposition coating method consists in transporting the material 8 to be coated into an electrodeposition vessel 9 in which an electrodeposition coating material 10 is housed and connecting a DC power source 1 between this material to be coated and the electrodes 5, 6 stored in the electrodeposition vessel 9 thereby executing the electrodeposition coating. In such a case, the electrodeposition coating is first started by a preset reference voltage and the coating area and structure of the material to be coated which exists within the electrodeposition vessel are estimated from the change in the current value of the initial period of the electrodeposition coating. The film thickness of the film formed by changing the subsequent voltage is controlled to an adequate value in accordance with the result thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrodeposition coating method, and more particularly to a method of coating without changing a coating quality such as a coating film thickness even by a change in a coating area of an object to be coated and a kind of the object to be coated. The present invention relates to a coating technique that can perform stable coating and is economically excellent.

[0002]

2. Description of the Related Art Conventionally, coating methods include an electrostatic coating method, a spray coating method, an airless coating method, a dipping coating method, and an electrodeposition coating method.

[0003] Among them, the electrodeposition coating method has excellent characteristics in various aspects as compared with other coating methods. For example, the electrodeposition coating method includes a bag-like structure portion of the object to be coated and a space between each part of the object to be coated. It has the feature that painting is possible even at the joints of the above. In addition to the features described above, it is easy to control the film thickness by controlling the amount of electricity, and the workability is good, with no "waki" or "sag" of the coated paint. It has been known.

[0004]

In the electrodeposition coating, the film thickness as described above is generally controlled by an applied voltage.
It is also affected by other factors, such as the coating liquid temperature, the transport speed of the coating object, and the number and type of the coating objects immersed in the coating tank. In other words, even when the coating is performed under a constant voltage, the coating area in the coating tank may fluctuate, or the coating object may be difficult to be formed due to a change in the shape of the coating object to be immersed. However, in such a case, the thickness of the coating film becomes thin, the rust prevention performance of the object to be coated is reduced, and rust is generated early in the obtained product, and the mechanical strength is reduced and the appearance is impaired. turn into.

[0005] In addition, when the conditions are such that the coating film is formed unnecessarily thick, the consumption of the coating material increases, which is not preferable in terms of coating economy.

Conventionally, in the electrodeposition coating method, it has not been carried out to automatically detect a coating area of an object to be coated, a variation in the type of the object to be coated, and to automatically control the voltage for each coating. Even if objects to be coated having various areas and structures (large or small area, flat structure / bag-like structure, etc.) flow to the electrodeposition tank on the same line, electrodeposition coating is always performed under the same voltage conditions. Therefore, there is a problem in that the thickness of the formed electrodeposition coating film cannot be accurately controlled.

As a method of controlling the electrodeposition film thickness in accordance with the number of objects to be coated, Japanese Patent Application Laid-Open No. 62-136527 and the like have proposed such methods. A device is required and the operation is complicated. An example in which the current value during electrodeposition coating is monitored and used for film thickness control is disclosed in JP-A-7-228997. As a possible stage, the energization was stopped, and it was not possible to control a change in the thickness of the formed coating film due to a change in the coating area of the object to be coated and a type of the object to be coated.

Accordingly, an object of the present invention is to provide an improved electrodeposition coating method. The present invention further provides an electrodeposition coating method capable of performing a stable coating without changing the coating quality even if the coating area of the object to be coated, a change in the type of the object to be coated, and the like, is economically excellent. It is an object to provide

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to achieve the above objects, and as a result, objects to be coated in various combinations flow through a coating line and are carried into an electrodeposition tank. When electrodeposition coating is performed, it is found that the behavior of current generation in the initial stage of electrodeposition in the electrodeposition tank containing the electrodeposition paint and the number and type of objects to be coated present in the electrodeposition tank are deeply related, From the current value characteristics in the initial stage of electrodeposition measured in actual electrodeposition coating, an applied voltage (hereinafter, also referred to as “secondary voltage”) in the initial stage suitable for obtaining a desired coating film thickness.
The present invention was completed by devising a method of controlling the secondary voltage to an appropriate value and applying the secondary voltage to this proper value promptly in real time.

That is, according to the present invention, which achieves the above objects, (1) an object to be coated is transported into an electrodeposition tank containing an electrodeposition coating material, and the object is placed in the electrodeposition tank. In the electrodeposition coating method of connecting a DC power source between the electrodes and performing electrodeposition coating, first, the electrodeposition coating is started by a preset reference voltage, and from the change in the current value of the initial electrodeposition coating, Estimate the coating area and structure of the object to be coated in the electrodeposition tank,
The electrodeposition coating method is characterized by controlling the film thickness of the formed coating film to an appropriate value by changing the voltage based on the result.

Further, the present invention provides that about 1/100 of the total electrodeposition time is required.
3 shows the electrodeposition coating method according to the above (1), wherein the time up to 3 is the initial stage of the electrodeposition coating.

The present invention also provides (3) a method in which, in a coating facility to be used in advance, a coating object having various coating areas and structures is used, and the initial current of the electrodeposition coating at the reference voltage is applied to the coating object. The value characteristic is measured, and a secondary voltage value as a subsequent voltage required to form a coating film having a desired film thickness on such various objects to be coated is determined. The data of the current value characteristic and the secondary voltage value in the various objects to be obtained determined in the following are stored in a voltage control device that controls the DC power supply,
The current value characteristic of the initial electrodeposition coating measured when the actual electrodeposition coating was performed, the secondary voltage value is determined by comparing the data with the data in this voltage control device, and the electrodeposition coating is performed. This shows an electrodeposition coating method according to the above (1) or (2).

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments.

In the electrodeposition coating, when a voltage is applied, the current flowing between the electrode and the object to be coated is substantially proportional to the outer coating area of the object to be coated. Changes depending on the structure of the device. In other words, the current value is affected by the electrodeposition coating equipment structure, the liquid conductivity of the electrodeposition coating material, the applied voltage, and the like, and the outer coating area of the object to be coated. The liquid conductivity of the coating material is generally a constant factor, and if the applied voltage is a predetermined value, the type of the object to be transferred to the electrodeposition tank, the change in the coating area will appear as a change in the current value. . In the present invention, utilizing this, in the electrodeposition coating operation that is performed continuously while changing the type of the object to be coated, the area of the object to be coated, the type of the object to be coated, the coating area existing in the electrodeposition tank, the current value Is measured in almost real time to form a coating film having an appropriate thickness.

In the electrodeposition coating method of the present invention, first,
A reference voltage (a constant voltage that can be applied to an appropriate film thickness when the type of the object to be coated, the coating area, and the like is standard) is set in advance from the characteristics of the electrodeposition coating material of the coating line to be used and the equipment conditions.

Further, in the present invention, the following preliminary experiments are performed prior to actual coating. That is, the current value characteristics of the initial stage of the coating when the electrodeposition coating is performed at the reference voltage set as described above for the sample groups of the coating objects having various types and different coating areas are measured. Further, when the reference voltage is applied throughout the predetermined electrodeposition coating time, the thickness of the coating film formed on the surface of each sample to be coated is measured. Next, based on the measurement result of the coating film thickness,
The applied voltage (secondary voltage) after the initial stage of coating is determined so that a desired appropriate coating film thickness can be obtained for each sample to be coated. The determination of the secondary voltage is based on, for example, a basic experiment in which the applied voltage is variously changed after the initial stage of coating, with an approximate prediction based on the result of the coating film thickness obtained when the reference voltage is applied over the entire coating time. This can be repeated by selecting a voltage value when a desired film thickness is obtained.

The initial time of the electrodeposition coating is as follows:
Desirably, the time is up to about 1/3 of the total electrodeposition time. That is, even if the initial time of the electrodeposition coating is set to be longer than this, the fluctuation of the current value becomes small, and therefore, current value data effective for determining the secondary voltage applied after the initial stage of the coating is hardly generated. However, there is no limitation that the secondary voltage is further adjusted to a tertiary voltage, a quaternary voltage, etc. while measuring the current value for a long time exceeding one third of the total electrodeposition time. Further, making the initial time of electrodeposition coating shorter than about one-third of the total electrodeposition coating time is equivalent to the initial maximum current value in the time-dependent current value change pattern after the start of voltage application as described later. The time at which a characteristic value such as I ₀ is indicated can be set as long as the time is included, but generally, about 1/1 of the total electrodeposition coating time.
Up to about 10 is the limit of shortening.

FIG. 3 shows an example of a change pattern of the current value during the elapsed coating time. The current value rises to the initial maximum current value I ₀ immediately after the start of the voltage application, and then falls after a while. It approaches a constant current value and starts to stabilize. Since it depends on the magnitude of the applied reference voltage, etc., it cannot be specified unconditionally. For example, it takes about 1 to 30 seconds from the start of application until the initial maximum current value I ₀ is reached, and furthermore, the initial maximum current value the current than I ₀ starts to stably descends in the order of about 5 to 90 seconds after reaching the initial maximum current value I _0.

The initial maximum current value I ₀ increases as the coated area of the object to be coated increases, and after a predetermined time elapses after reaching the initial maximum current value I ₀ (for example, after a lapse of about 5 to 90 seconds as described above). The current value I ₁ at the time when the current value starts to stabilize)
Is influenced by the shape of the object to be coated, and tends to increase as the ratio of the bag-like structure or the like increases. Therefore, if these current values I ₀ and I ₁ are determined for the coating object sample and the coating sample groups having various coating areas, and compared with the values obtained in actual coating as described later, the actual It is possible to certify the type of the object to be coated and the area of the coating in the coating.

The time required to reach the initial maximum current value I ₀ and the time required until the current value starts to stabilize thereafter are as follows:
Since it can be easily known by the basic experiment, each measurement time is determined from the result of the basic experiment, and the current values measured at each measurement time are regarded as I ₀ and I ₁ , respectively. The measured value of I ₀ may have a slight difference from the true value of I ₀ , but the measured value of the measured value in the sample group of the workpiece to be compared is measured before the actual coating. If the measurement time at the time of actual painting is matched, the current value measured at the time of actual painting is compared with the current value measured at the sample group, and the There is no particular problem in determining the coating area and the type of the object to be coated.

The method of measuring the current value at the initial stage of the electrodeposition coating is not limited to the method of measuring the current value at two points as described above. The current value of the object sample is measured, the current value data of the object sample group at these three or more measurement points is created, and compared with the current value measured at the same measurement point at the time of actual coating, Naturally, it is possible to determine the coating area and the type of the object to be coated during the actual coating. Further, the current value is continuously measured in the initial stage of the electrodeposition coating for each of the workpiece samples, and the waveform analysis data of the change in the current value in the initial stage of the electrodeposition coating of the workpiece sample group is prepared, and the actual data is prepared. At the time of painting, the state of change of the current value obtained by performing the same continuous current value measurement at the beginning of electrodeposition coating is compared with this waveform analysis data, the coating area of the object to be coated at the time of actual coating, It is also possible to determine the type of the object to be coated.

According to such preliminary experiments, the type of the object to be coated,
Current value characteristic data at the initial stage of coating for a group of workpieces with different coating areas and data of the secondary voltage to be applied to obtain the desired proper coating film thickness for each workpiece sample Once obtained, both data are stored in the voltage control device.

Then, the actual painting operation is started. In actual coating, an object to be coated composed of various combinations can be flowed into a coating line, carried into an electrodeposition tank, and subjected to electrodeposition coating. When a certain type of the object to be coated or a combination of a plurality of the same or different types of the object to be coated enters the electrodeposition tank, first, a reference voltage is applied to start the electrodeposition coating. Then, at the above-mentioned predetermined point in time of the initial electrodeposition, the value of the current flowing in the tank is measured.

The measured current value is immediately sent to a voltage control device as an electric signal. In the voltage controller, the judgment program is operating, and the measured current value sent is
In comparison with the data of the current value characteristics of the coated object sample group obtained by the preliminary experiment stored above, the sample having the most similar current value characteristics in the data is selected from the secondary voltage data. The secondary voltage value for this sample is found as a solution. If necessary, an appropriate correction is made to the solved secondary voltage value based on the degree of dissociation of the current value characteristic closest to this data and the actually measured current value characteristic. It is also possible to execute various correction programs together. The voltage controller issues a command to the DC power supply so that the secondary voltage value thus determined is subsequently applied in the electrodeposition bath. Thus, a desired secondary voltage is applied in the subsequent electrodeposition coating time, and the electrodeposition coating is performed.

It should be noted that the program incorporated in the voltage control device is not limited to the configuration as exemplified above, and the current value characteristic data and the secondary voltage value obtained by the preliminary experiment are obtained. Any data may be used as long as the desired secondary voltage value can be determined from the measured current value by the data, or furthermore, a function formula derived from these data. In addition, any voltage control device may be used as long as it can execute the above-described program.
For example, it can be configured by incorporating one or more arithmetic devices such as a microcomputer, a personal computer, and an office computer. In addition, without using such a voltage control device, the current value characteristic data and the secondary voltage value data obtained by the preliminary experiment and the current value at the initial stage of the coating obtained in the actual coating operation are manually set. Although it is possible to determine an appropriate secondary voltage value and change the DC power supply voltage, it is naturally desirable to automatically control the secondary voltage by a voltage control device.

As described above, in the present invention, an appropriate coating film thickness can be obtained by controlling the subsequent voltage from the current value during the initial fixed period in the electrodeposition coating.

FIG. 1 schematically shows the configuration of a cationic electrodeposition coating apparatus which is an example of the apparatus configuration for performing the electrodeposition coating method according to the present invention. In this apparatus, the electrodeposition tank 9 is filled with the electrodeposition paint 10, and the object 8 is conveyed onto the electrodeposition tank 9, and
The hanger 7 which can immerse is provided.

In the electrodeposition bath 9, a plurality of groups of opposed electrodes 6 for the object to be coated are arranged, and each electrode 6 is electrically connected to the anode side of the DC power supply 1. On the other hand, a coating object 8 can be electrically connected to the cathode side of the DC power supply 1.

An electrode 5 for measuring current characteristics is arranged in the electrodeposition tank 9 near the end of the electrodeposition tank 9 on the side of the object to be coated. The power supply 1 is electrically connected to the anode side.

The DC power source 1 for the current characteristic measuring electrode 5
An ammeter 3 is arranged in the middle of the connection circuit to the, and the ammeter 3 can measure a current flowing between the current characteristic measuring electrode 5 and the article 8 to be coated. In the course of the connection of the electrode 6 to the DC power supply 1
The current meter 2 can measure a current flowing between the electrode 6 for the object to be coated and the object 8 to be coated.

Further, each of the ammeters 2 and 3 is electrically connected to an input side of a secondary voltage controller 4 composed of a microcomputer or the like, and the currents measured by these ammeters 2 and 3 are measured. The electric signal is input to the secondary voltage control device 4. Further, a DC power supply 1 is electrically connected to an output side of the secondary voltage control device 4, and the DC power supply 1 can change an applied voltage by a command signal issued from the secondary voltage control device 4. It has such a configuration.

The configuration of the electrodeposition coating apparatus that can be used in the electrodeposition coating method of the present invention includes at least a current flowing between an electrode installed in the electrodeposition tank and an object to be coated (opposite electrode). The apparatus is not limited to the example shown in FIG. 1 as long as it has a configuration capable of measuring a value and controlling an applied voltage based on the measured current value. For example, in the apparatus configuration shown in FIG. 1, the wall surface of the electrodeposition tank 9 is connected to the DC power supply 1 instead of the electrode 6 for the object to be coated arranged in the electrodeposition tank 9, thereby forming a tank inner wall electrode. In the apparatus configuration shown in FIG. 1, various modifications are possible, such as a configuration in which the current characteristic measuring electrode 5 and the object to be coated electrode 6 are respectively connected to separate DC power supplies.

An outline of the case of carrying out the electrodeposition coating method of the present invention using the apparatus shown in FIG. 1 will be described. First, an object 8 to be coated is placed in an electrodeposition tank 9 and a reference voltage is first set. Start electrodeposition coating. Then, the value of the current flowing between the current characteristic measuring electrode 5 and the object 8 to be coated in the initial stage of the coating is measured by the ammeter 3. The current value measured by the ammeter 3 is sent to the secondary voltage control device 4 as an electric signal. In the secondary voltage control device 4, an appropriate secondary voltage value is determined from the obtained measured current value in the initial stage of coating as described above, so that the voltage generated from the DC power supply 1 becomes the secondary voltage value. A command signal is sent to the DC power supply 1. The DC power supply 1 is automatically transformed from the reference voltage value to a predetermined secondary voltage value by the command signal, and the surface of the workpiece 8 moving in the electrodeposition tank 9 by being transported by the hanger 7 has An electrodeposition coating film having a desired film thickness is deposited during the remaining period of the electrodeposition coating that passes between the electrodes 6 for applying a secondary voltage.

[0034]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples.

Electrodeposition coating was carried out using a cationic electrodeposition coating apparatus as shown in FIG.

As shown in Table 1, the substrates to be used are a substrate A (plate-shaped substrate) and a substrate B (bag-shaped structure).
Was used in one kind or in a combination of two kinds, and the number of objects to be coated was such that the index of the total coating area of the objects to be coated was 0.5 to 1.5.

First, the types of the substrates to be coated shown in Table 1 (A1 to A
5, AB1 to AB5, B1 to B5) were subjected to electrodeposition coating under a reference voltage (240 V).

At this time, the current was measured by the ammeter 3, and the current reached the maximum value about 15 seconds after the start of voltage application. So 15
The current value I _{0 in} seconds and the current I ₁ 25 seconds after the current starts to decrease
Was measured. After the completion of the electrodeposition, the thickness of the outer plate of the object to be coated was measured. Table 2 shows the results.

Next, the secondary voltage (the voltage applied from 30 seconds after the start of voltage application to the end thereof) was adjusted so that the thickness of the outer plate after electrodeposition became 20 μm (target value), and electrodeposition was performed. Table 3 shows the results. As shown in Table 3, it can be seen that by setting the secondary voltage, the thickness of the outer plate can be made constant at 20 μm.

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

[Table 3]

FIG. 2 illustrates the relationship between the current values I ₀ and I ₁ and the secondary voltage. The current value I ₀ increases as the painting area increases, and the current value I ₁ increases as the ratio of the bag-like structure increases. The secondary voltage has a current value I ₀ , I ₁
The larger is the higher. In the embodiment, the ammeter 3
The current values I ₀ and I ₁ were read, and a proper secondary voltage was determined by the voltage control device 5, and the secondary voltage generated from the DC power supply 1 was automatically controlled. FIG. 3 shows the relationship between the elapsed time at the time of coating, the current change, and the applied voltage, taking the case of the type A3 as an example.

[0044]

As described above, in the coating method of the present invention, the current value during the initial fixed period in electrodeposition coating is
By controlling the subsequent voltage, an appropriate coating film thickness can be obtained. Also, since the electrodeposition coating can always be performed with an appropriate film thickness without being influenced by the type, shape, etc. of the object to be coated, there is no need to consume an excessive amount of the coating material, and the device configuration to be further used. Since it is simple, it is advantageous in terms of coating economy.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a structure of an example of an electrodeposition coating apparatus used in carrying out the electrodeposition coating method of the present invention in a use state;

FIG. 2 is a graph showing a relationship between current values I ₀ and I ₁ and a secondary voltage obtained in an example of the electrodeposition coating method of the present invention;

FIG. 3 is a graph showing a time-dependent change in a current value during electrodeposition coating obtained in one embodiment of the electrodeposition coating method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... DC power supply, 2,3 ... Ammeter, 4 ... Voltage control device, 5 ... Electrode for current characteristic measurement, 6 ... Electrode for coating object, 7 ... Hanger, 8 ... Coating object, 9 ... Electrodeposition tank, 10 ... Electrodeposition paint

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenshiro Shima, Nissan Motor Co., Ltd., 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Prefecture (72) Inventor Yoshinobu Tamura 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Prefecture, Nissan Motor Co., Ltd.

Claims (3)

[Claims] An object to be coated is transported into an electrodeposition tank containing an electrodeposition coating material, and a DC power source is connected between the object and an electrode stored in the electrodeposition tank. In the electrodeposition coating method of performing the electrodeposition coating, first, the electrodeposition coating is started by a preset reference voltage, and from the change in the current value at the initial stage of the electrodeposition coating,
The coating area and structure of the object to be coated present in the electrodeposition tank are estimated, and based on the result, the subsequent voltage is changed to control the film thickness of the formed coating film to an appropriate value. Electrodeposition method. 2. The electrodeposition coating method according to claim 1, wherein a period of time up to about 1/3 of the total electrodeposition coating time is set as the initial time of the electrodeposition coating. 3. In advance, in a coating facility to be used, by using objects to be coated having various coating areas and structures, the current value characteristics of the initial stage of electrodeposition coating at the reference voltage for these objects to be coated are measured. Further, a secondary voltage value as a subsequent voltage required for forming a coating film having a desired film thickness on such various objects to be coated is determined in advance, and various values obtained in this manner are determined. The data of the current value characteristic and the secondary voltage value in the object to be coated are stored in a voltage control device that controls the DC power supply, and the initial electrodeposition coating measured during actual electrodeposition coating is performed. The electrodeposition coating method according to claim 1, wherein the secondary voltage value is determined by comparing the current value characteristic of the voltage control device with the data in the voltage control device, and the electrodeposition coating is performed.