JPH0258360B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a continuous powder electrodeposition coating method for accurately controlling the coating film thickness of various objects to be coated having different horizontal areas and obtaining a uniform finished appearance. An electrodeposition coating method called powder electrodeposition coating method that has been developed and attracts attention in recent years is, for example,
As described in Publication No. 40585, in principle, electrophoresis, electrolysis, and
A coating film is formed on the object by a combination of four phenomena: electrodeposition and electroosmosis, and the paint used partially neutralizes the basic resin containing nitrogen in its molecules with an acidic compound. Powder electrodeposition paint made by using a cationic resin that has been given water dilutability as a water-soluble binder resin, and suspending and dispersing insoluble synthetic resin powder, which is the main component for forming a coating film, in this water-diluted solution. When performing electrodeposition coating using this method, the above paint is diluted with water and the solid content is usually 10 to 20% by weight, pH 4.5 to 6.0, and bath temperature.
A conductive object to be coated is inserted as a cathode into an electrodeposition bath solution adjusted to 20 to 30℃, a stainless steel or carbon electrode is inserted as an anode, and a DC voltage of about 100 to 600V is applied, and the temperature is 5 to 30℃. A coating film is deposited on the object to be coated by applying electricity for seconds, and then the object on which the coating film has been formed is washed with water, drained, dried, and baked to form a tough coating film. It is. By using this powder electrodeposition coating method,
(1) It has high cloning efficiency and can produce a thick coating film in a short time (seconds), (2) It can produce a coating film with high performance and high corrosion resistance, and (3) It is extremely effective in terms of safety and hygiene. On the other hand, the above-mentioned powder electrodeposition coating method has poorer so-called throwing power than ordinary electrodeposition coating methods, and may vary depending on coating conditions, especially the shape of the object to be coated. The coating film formed on the object, that is, the amount of coating, is not uniform on all parts, especially when the object to be coated has a horizontal surface facing the bath liquid surface, the vertical surface of the object and the bottom of the bathtub. The amount of coating on the horizontal surface is considerably smaller than that on the horizontal surface facing the
Therefore, it has disadvantages such as appearance defects. As a method to eliminate the above-mentioned drawbacks, in order to form a coating film to the required thickness for each part of the object to be coated, a plurality of opposing electrodes of the object to be coated, including horizontal parts, are provided in the composition bath, and JP-A-56-13499 discloses a method in which the counter electrode is divided into units consisting of one or more counter electrodes, and energization is conducted by selecting the energizing conditions for each divided unit. Japanese Patent Laid-Open No. 53-134042 proposes a method of controlling the film thickness by arranging the anodes facing each other on a horizontal surface and controlling the amount of electricity flowing through each anode. In addition to the method of converting the predetermined amount of electricity of each anode installed in a time period and stopping the current supply using a circuit breaker, this controls the amount of paint applied.
Similar to the conventional powder electrodeposition coating method shown in Figures 1 and 2, the anode is always immersed in the electrodeposition bath liquid in the electrodeposition bath. Since the anode is left in a non-energized state, a coating film is electrodeposited on a portion of the top of the anode that is not energized due to a so-called polarization phenomenon, and this phenomenon occurs each time each object is electrodeposited. This results in significant contamination of the anode, which reduces the effective anode area, resulting in problems in terms of maintenance and painting. To explain the above polarization phenomenon in the conventional powder electrodeposition coating method using a plurality of auxiliary electrodes (anodes) as shown in FIGS. 1 and 2, as shown in FIG. Since there is a non-energized auxiliary electrode A in the bath solution 2, and the resistance of the electrodeposition solution 2 is significantly higher than the metal resistance of the auxiliary electrode A, for example, a energized side electrode near the auxiliary electrode A is present. S ₁ (+) to automobile body 3 as the object to be coated
When current attempts to flow to (-), the current flows through route a ₁ -> auxiliary electrode A -> a ₂ -> vehicle body 3 rather than through route b ₁ . At this time, the auxiliary electrode A is the third
As shown in the figure, a polarized state is obtained, and a negative (-) charge is accumulated in a portion near the side electrode S ₁ (+), and a paint film 4 is deposited on this portion by electrodeposition. This is the polarization phenomenon. The non-energized auxiliary electrode A, on which the coating film 4 is partially attached, is energized and given a positive charge in order to paint the next object to be coated, the automobile body 30. Since the part to which the coating film 4 is attached does not function as an anode (+), the overall pole area becomes small, and the effective area decreases as described above. In addition, when a positive (+) charge is given to the auxiliary electrode A by energizing, a coating film is electrodeposited on the vehicle body 30 according to the principle of electrodeposition, and at the same time, the following formula is applied on the auxiliary electrode A.
As shown in (1), 2H ₂ O→2H ₂ +O ₂ ......(1) (-pole) (+pole) Oxygen (O ₂ ) gas is generated and the electrodeposited coating film 4 of auxiliary electrode A is detached. do. Since this detached coating film is composed of agglomerated powder, it is difficult to restore it to a dispersed state in the bath liquid 2, and it adheres to the car body 30 as the object to be coated, resulting in a defective coating film (referred to as spots) 5. will occur. Therefore, in order to make the thickness of the electrodeposited film uniform, as in the electrodeposition method shown in JP-A-52-132051,
An auxiliary electrode is provided facing the object to be coated to make the electric field distribution even.
A flexible electrode is housed in a flexible insulating member like the auxiliary electrode shown in Publication No. 38586, and a connecting wire is connected to the electrode to make the coating thickness uniform and reduce the coating time.
Moreover, a method has been disclosed in which the electrodes can be easily attached and detached from objects with complex shapes and sizes without short circuits, but in the former case, when the shape or size of the object to be coated changes, the It is necessary to change the auxiliary electrode every time, and this cannot be done by mixing various objects having different horizontal area areas in the same electrodeposition bath and performing continuous powder electrodeposition coating. The latter auxiliary electrode is simply used as an auxiliary electrode for parts of objects with complex shapes and sizes where the electric field strength is low, and corresponds to the largest horizontal area of each object to be coated. Since the number of auxiliary electrodes corresponding to the pole area is not connected to the power source, it is not possible to appropriately increase the electric field strength for the horizontal portion of the object to be coated, which changes one after another. In view of the above, the present inventors have conducted research and found that it is possible to control the film thickness of objects to be coated having different shapes and different horizontal areas without causing the polarization phenomenon caused by the anode current cutoff mentioned above, and to obtain a uniform coating film appearance. I found a way to do it. That is, the gist of the present invention is to continuously apply powder electrodeposition to various objects having different horizontal areas in the same electrodeposition bath having a large number of side electrodes by applying a voltage to the side electrodes and the object to be coated. To do this, the number of auxiliary electrodes corresponding to the maximum horizontal area of the object to be coated is connected to a power source, and the object to be coated is exposed to the electrodeposition bath solution in the electrodeposition bath. Prior to immersion in the electrodeposition bath liquid, insert the number of auxiliary electrodes corresponding to the electrode area selected according to the horizontal area of the auxiliary electrodes to be coated into the electrodeposition bath solution and energize them. This powder electrodeposition coating method is characterized in that the other electrodes are placed outside the electrodeposition bath liquid in the electrodeposition tank in a non-energized state. The auxiliary electrode used in the method of the present invention is applied to the side electrode and the object to be coated in the same electrodeposition bath having a large number of side electrodes, so that the auxiliary electrode is the largest one in the object to be coated by powder electrodeposition. Prepare a sufficient number of auxiliary electrodes corresponding to the area of the horizontal part to perform the above-mentioned electrodeposition coating, that is, electrodes of various or the same area, and connect them to a power source. , Insert as many auxiliary electrodes as the pole area selected according to the area of the horizontal part of the object to be coated into the electrodeposition bath liquid of the electrodeposition tank and arrange them close to the horizontal part of the object to be coated. It is. Therefore, the total polar area varies depending on the overall shape of the object to be coated, the required film thickness, etc., but the polar ratio, that is, the area of the auxiliary electrode/the horizontal area of the object to be coated, is 1/1 to 1/1.
It is best to set it to 30. The present invention provides continuous powder electrodeposition coating for various objects having different horizontal areas as described above in the same electrodeposition bath having a large number of side electrodes by applying an electric current to the side electrodes and the object to be coated. To do this, the number of auxiliary electrodes corresponding to the maximum horizontal area of the object to be coated is connected to a power source, and the object to be coated is exposed to the electrodeposition bath solution in the electrodeposition bath. Prior to immersion in the electrodeposition bath liquid, insert the number of auxiliary electrodes corresponding to the electrode area selected according to the horizontal area of the auxiliary electrodes to be coated into the electrodeposition bath solution and energize them. This powder electrodeposition coating method is characterized by placing the other auxiliary electrodes outside the electrodeposition bath liquid in the electrodeposition bath in a non-energized state, so it is possible to coat many objects with different horizontal areas. In the same electrodeposition bath having side electrodes, when applying power to the side electrodes and the object to be coated to perform powder electrodeposition coating continuously, correspond to the maximum horizontal area of the object to be coated. By connecting each of the auxiliary electrodes to the power supply in a number that corresponds to the maximum area, even if various objects with different horizontal areas flow continuously through the powder electrodeposition coating line, the line will not be disturbed. It is possible to immediately respond to each object to be coated, which improves production efficiency, and also, prior to immersing the object to be coated in the electrodeposition bath liquid in the electrodeposition bath, it is possible to immediately respond to each object to be coated. Insert as many auxiliary electrodes as the selected electrode area into the electrodeposition bath liquid in the electrodeposition bath and energize them, and place the other electrodes outside the electrodeposition bath liquid in the electrodeposition bath in a non-energized state. As a result, the coating film thickness of the object to be coated can be accurately controlled, and furthermore, there is no polarization phenomenon in unused auxiliary electrodes, and therefore, problems such as the above-mentioned "bumps" as defective coating films are not caused. This has the effect of providing stable coating quality. The present invention will be explained below with reference to Examples. In addition,
All parts and percentages are by weight. The powder electrodeposition paint bath used here was prepared in the following manner. [How to adjust the bath liquid] The water-dilutable cationic resin is Epicoat #1001.
(Trade name: epoxy resin, Ciel product) 488 parts,
105 parts of diethanolamine and 250 parts of inpropyl alcohol were reacted under reflux at 80°C to 85°C for 3 hours to obtain a liquid aminoepoxy resin. Also, as a synthetic resin fine powder, Epicoat #1004
(manufactured by Ciel) 40 parts, Adduct B-1065 (manufactured by Hueva) 30 parts, Titanium oxide R-550 (manufactured by Ishihara Sangyo) 29
and 1 part of Carbon Black MA-100 (manufactured by Mitsubishi Kasei Corporation) were melted and kneaded in an extruder using a conventional method for manufacturing powder coatings, and then pulverized in an impact pulverizer to obtain an epoxy resin with an average particle size of 7μ. A fine powder was obtained. 6.2 parts of glacial acetic acid and 500 parts of deionized water were added to 143 parts of the above cationic resin as a binder, thoroughly stirred with a dissolver, and then 280 parts of the above fine powder was added.
After stirring and mixing with a dissolver for 30 minutes, the mixture was dispersed and diluted with deionized water until the solid content was 15% by weight. This solution had a pH of 5.2 and a fine powder solid content/cationic synthetic resin solid content ratio of 2.8/1. This was used in the following examples and comparative examples. Example 1 An automobile body was used as the object to be coated, and the horizontal area of the roof was A1.4 m ² , B2.5 m ² and C3.2, respectively.
A large number of sets of three types of car bodies having a size of cm ² were continuously immersed in an electrodeposition bath solution in an electrodeposition tank to perform electrodeposition coating. As an auxiliary electrode (anode) for the horizontal surface of the car body as the object to be coated, one electrode of 10 cm x 20 cm was connected to a power source and prepared outside the tank. During electrodeposition coating, insert the necessary number of auxiliary electrodes so that the pole ratio to the area of each of the horizontal parts is about 1/20 (specifically shown in Table 1), facing each other on each of the horizontal parts. However, unnecessary auxiliary electrodes (redundant auxiliary electrodes) were drawn out from the electrodeposition bath solution in the electrodeposition bath each time and electrodeposition was performed. These auxiliary electrodes were immersed in the bath solution for the time required to electrodeposit the required film thickness when electricity was applied to the bath solution each time from outside the tank, and were installed so that they would function as anodes as soon as they were immersed. The other outer panels of the vehicle body, that is, the bottom and side surfaces, were always immersed in the bath liquid and placed so that the electrode ratio was 1/1 with the facing side electrode (anode). The distance between the vehicle body as the object to be coated and the auxiliary electrode is at least 30cm, and the current conditions are 25℃, 500V, 30cm.
Seconds. The object to be coated is treated with zinc phosphate (ET
#3118) was used. Painting is done as a whole with the above three types of car bodies as one set.
Table 1 shows the coating results after ² consecutive electrodeposition coatings of 14,000 m. Note that FIG. 5 is an explanatory diagram schematically showing an embodiment of the present invention, in which the auxiliary electrode (anode) corresponding to the maximum horizontal area of the vehicle body 300 as the object to be coated is 1.
If only piece B is used, the auxiliary electrode A, which is not energized,
C shows a working state in which electrodeposition coating is being performed with the electrodeposition tank 1 placed outside the surface of the solution 2 in the electrodeposition tank 1. S indicates a side electrode (anode) provided in the electrodeposition bath liquid 2 of the electrodeposition tank 1. Comparative Example 1 Using the same electrodeposition bath liquid and object to be coated as in Example 1,
Electrodeposition was carried out under the same energizing conditions as in Example 1, with eight auxiliary anodes each measuring 10 cm x 20 cm as in Example 1 kept immersed in the bath solution. However, the pole ratios for A, B, and C, which have different horizontal areas, are as shown in Example 1.
Only the number of auxiliary electrodes (anodes) necessary to achieve the same number as in each case was energized, and the other auxiliary electrodes remained immersed and only the energization was interrupted. Similar to Example 1
14000m 1st coating result after ² consecutive electrodepositions
Shown in the table. As is clear from Table 1, in Example 1, the film thickness on the horizontal surface of the object to be coated was controlled both at the initial stage of painting and after continuous painting, and the finished appearance was good, but in Comparative Example 1, after continuous painting, The film thickness on the horizontal surface was not controlled, and the finished appearance was also somewhat poor.

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 is a schematic side view of a powder electrodeposition coating device using a conventional powder electrodeposition coating method, FIG. 2 is an enlarged side view of the main parts of the electrodeposition coating device, and FIG. 3 is a schematic side view of a powder electrodeposition coating device using a conventional powder electrodeposition coating method. FIG. 4 is an explanatory diagram showing the occurrence of defective coating film (bumps) in the electrodeposition coating apparatus, and FIG. 5 is an explanatory diagram schematically showing an example of the present invention. be. 1: Electrodeposition bath, 2: Electrodeposition bath liquid, 3: 30,30
0: Automobile body as object to be coated, 4: Paint film attached to non-energized auxiliary electrode, 5: Defective paint film (pieces), A,
B, C: auxiliary electrode (anode), S: side electrode (anode).

Claims (1)

[Claims] 1. When applying powder electrodeposition to various objects with different horizontal areas in the same electrodeposition bath having a large number of side electrodes by applying a voltage to the side electrodes and the object, A number of auxiliary electrodes having a polar area corresponding to the maximum horizontal area to be coated on the object to be coated are each connected to a power source, and before the object to be coated is immersed in the electrodeposition bath liquid in the electrodeposition bath. A number of auxiliary electrodes corresponding to the area of the horizontal part to be coated in the above auxiliary electrodes are inserted into the electrodeposition bath liquid of the electrodeposition tank and energized, and the other electrodes are energized. A powder electrodeposition coating method characterized by placing the powder in a non-electrodeposition state outside the electrodeposition bath solution in a deposition tank.