JP2019002032A - Electrocoating method - Google Patents

Abstract

To provide an electrocoating method capable of reducing a pump power necessary for transferring a coating liquid while preventing a difference in the thickness of coating films formed on the inner and outer faces of a coating object from arising.SOLUTION: The electrocoating method includes: an initial stage of an electrocoating process in which a coating film to be formed on the outer face of a coating object is completed while increasing a relative speed of a coating liquid flowing around a coating object W relative to the coating object; and a later stage of the electrocoating process in which a coating film to be formed on the inner face of the coating object is completed while maintaining the relative speed lower than the relative speed maintained in the initial stage.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrodeposition coating method, and more specifically, in a state where an object to be coated having an internal space whose opening to the outside is restricted is immersed in a coating liquid in an electrodeposition tank, the electrodeposition through the coating liquid. An electrodeposition step of applying a predetermined potential difference for a predetermined electrodeposition time between the electrode in the tank and the object to be counter electrode in the electrodeposition tank; in this electrodeposition process, the periphery of the object to be coated It is related with the electrodeposition coating method which hold | maintains the relative speed with respect to the said to-be-coated article of the said coating liquid which flows through a predetermined relative speed.

  In this type of electrodeposition coating, the electrode in the tank in the electrodeposition tank and the counter electrode immersed in the coating liquid in the tank for a predetermined electrodeposition time (generally 180 seconds to 240 seconds) in the electrodeposition process. By applying a potential difference between the object to be coated as an electrode and electrically fixing the coating film component (in other words, the paint component) contained in the coating liquid to the outer surface and inner surface of the object to be coated, A coating film is formed on each of the outer surface and the inner surface of the object to be coated.

  By the way, in the case of an object to be coated such as an automobile body having an internal space in which the opening to the outside is limited, the inner surface of the object to be coated (that is, the surface of the object to be coated in the inner space) is in the tank compared to the outer surface of the object to be coated. Due to the fact that the current-carrying effect with the electrode is difficult to achieve, a coating film having a large film thickness (that is, a thick coating film) is formed on the outer surface of the object to be coated. Has a problem that a coating film having a small film thickness (that is, a thin coating film) is formed, and the thickness of the coating film is different between the outer surface and the inner surface of the object to be coated (so-called difference in throwing power). .

  On the other hand, as a proposed technique for solving this problem, the following patent document 1 discloses the following electrodeposition coating method.

  As shown in FIG. 5 and FIG. 6, in the surface area and the intermediate area in the electrodeposition tank (1) through which the automobile body (B) as the object passes, the paint is directed toward the object entering tank part. By providing the surface area nozzle (36) and the intermediate area nozzle (37) for ejecting the liquid (L), the coating liquid (L) in the tank in the surface area and the intermediate area is opposed to the moving direction of the object (B). On the other hand, in the bottom area of the electrodeposition tank (1), the bottom area nozzles (29), (35) for jetting the coating liquid (L) toward the substrate outlet tank side. ) So that the coating liquid (L) in the tank in the bottom area flows in the same direction as the moving direction of the article (B).

  Here, the surface area is a tank inner area corresponding to the vicinity of the roof of the automobile body (B) from the liquid level in the height direction, and the intermediate area is a tank corresponding to the side surface of the automobile body (B) in the height direction. The inner area and the bottom area refer to the inner area of the tank corresponding to the vicinity of the floor surface of the automobile body (B) from the bottom wall of the electrodeposition tank (1) in the height direction.

  That is, the direction in which the coating liquid (L) in the tank faces the moving direction of the object to be coated (B) in the surface area and the intermediate area through which the automobile body (B) as the object to be passed passes. To increase the relative speed of the coating liquid (L) flowing around the automobile body (B), which is the object to be coated, with respect to the automobile body (B), for example, to about 0.24 m / s. The reaction gas bubbles and reaction heat generated on the surface of the automobile body (B) due to the electrodeposition coating are effectively removed, and accordingly, between the outer surface and the inner surface of the automobile body (B). The difference in throwing power produced is made small. (See paragraphs [0005], [0012], [0021], [0022], [0052], [0057], [0061], [0062], [0067] of Patent Document 1)

  Moreover, in addition to this, in the electrodeposition coating method disclosed in Patent Document 1, when the automobile body (B) that is the object to be coated is not present in the electrodeposition tank (1), the electrodeposition tank (1 It is desirable from the viewpoint of energy saving to stop the flow of the coating liquid (L) in the electrode), but if the flow of the coating liquid (L) in the electrodeposition tank (1) is stopped, The coating liquid (L) is ejected from the surface area nozzle (36), the intermediate area nozzle (37), and the bottom area nozzles (29), (35) because it is not preferable because the pigment of the liquid settles down. For the pumps (26) and (32), as shown in FIG. 7, when not in operation, the pump power (W1) continuously supplied during operation is intermittently supplied, and otherwise, the pump is supplied during operation. 30% to 60% of pump power (W1) 2) so as to supply, thereby, so that achieve energy saving while preventing the sedimentation of the pigment. (See paragraphs [0004] and [0034] of Patent Document 1)

JP 2002-206195 A

  However, in the electrodeposition coating method disclosed in Patent Document 1, the difference in throwing power generated between the outer surface and the inner surface of the automobile body (B) that is the object to be coated is reduced, and the automobile body (B) Even if the difference between the thickness of the coating film formed on the outer surface and the thickness of the coating film formed on the inner surface can be reduced, the coating liquid is supplied from each nozzle (36), (37), (29), (35). About the electric power required for the operation of the pumps (26) and (32) for ejecting (L), the pump power supplied at the time of non-operation when the coating object (B) is not present in the electrodeposition tank (1) can be reduced. Since the pump power supplied at the time of operation cannot be reduced, the energy saving effect is still low, and there is still a problem that the operation cost of the electrodeposition tank (1) during operation and non-operation is still large.

  In view of this situation, the main problem of the present invention is that the thickness of the coating film formed on the outer surface of the object to be coated and the coating film formed on the inner surface of the object to be coated are taken by adopting a rational electrodeposition coating method. This is in that energy saving can be effectively achieved while effectively suppressing the difference in thickness.

The first characteristic configuration of the present invention relates to an electrodeposition coating method,
In a state where an object to be coated having an internal space whose opening to the outside is restricted is immersed in a coating liquid in the electrodeposition tank, the electrode in the tank and the electrode as the counter electrode in the electrodeposition tank are passed through the coating liquid. An electrodeposition step of applying a predetermined potential difference between the coating and the coating material for a predetermined electrodeposition time;
In this electrodeposition step, an electrodeposition coating method for maintaining a relative speed of the coating liquid flowing around the object to be coated at a predetermined relative speed,
The electrodeposition process is divided into an initial process and a late process,
In the initial step, by increasing the relative speed to be held, the coating film formed on the outer surface of the object to be coated is completed in the initial step,
In the latter step, the coating film formed on the inner surface of the article to be coated is completed in the latter step in a state where the relative speed to be held is smaller than the relative speed to be held in the initial step.

  In other words, in electrodeposition coating, when a potential difference is applied between the electrode in the tank and the object to be coated as the counter electrode in the electrodeposition tank, and the electrodeposition process for a predetermined electrodeposition time is entered, the surface of the object to be coated is applied. As the film precipitates and grows, a large amount of reaction gas (hydrogen gas if the object to be coated is an electrode on the ground side) is generated, and as this reaction gas escapes from the deposited coating in the form of bubbles. Thus, the deposited coating gradually becomes denser and the electrical resistance of the deposited coating gradually increases.

  And, by increasing the electrical resistance, it becomes gradually difficult to electrically attract and fix the coating film component in the coating liquid to the object to be coated. The amount of the generated gas gradually decreases, and finally, at the stage where the dense and highly resistant coating film is completed, the growth of the coating film stops and the generation of the reaction gas is eliminated.

  On the other hand, according to the first characteristic configuration described above, by increasing the relative speed in the initial step, the coating film is generated in large quantities as the coating film precipitates and grows on the outer surface of the object to be coated. The bubbles of the reaction gas that escapes can be quickly removed from the coating by the flow of the coating liquid having a high relative velocity. Can be effectively promoted.

  Therefore, on the outer surface of the object to be coated, it is possible to stop the growth of the film by completing a dense and high electric resistance film at an early stage at an early stage. An excessive thickness can be effectively prevented.

  On the other hand, the inner surface of the object to be coated is not easily affected by the flow of the paint liquid flowing around the object to be coated, so that it is not significantly affected by increasing the relative speed in the initial process. Under the circumstances where the energization effect is difficult and difficult, the deposition and growth of the coating film, the generation of the reaction gas, the densification of the coating film and the increase of the electrical resistance gradually progress through the initial process and the subsequent process. As a result, on the inner surface of the object to be coated, a dense coating film having a large electric resistance is completed in the later stage.

  That is, in this way, an excessive increase in the coating thickness is effectively prevented on the outer surface of the object to be coated, whereas the inner surface of the object is affected by a large relative speed in the initial process. By effectively completing the coating in the later stage, it is possible to effectively prevent the difference between the thickness of the coating formed on the outer surface of the object and the thickness of the coating formed on the inner surface of the object. can do.

  In addition, according to the first feature configuration, the relative speed is increased only in the initial process, and the relative speed is decreased in the later process, so that the electrodeposition process is performed as in the electrodeposition coating method disclosed in Patent Document 1 described above. Compared to increasing the relative speed throughout the entire process, the power required for transporting the coating liquid in the electrodeposition process can be reduced by reducing the relative speed in the latter stage process. In combination with reducing the power required for transporting the coating liquid in a non-operating state that does not exist, energy saving and reduction in operating costs can be achieved more effectively.

  According to the first characteristic configuration, the bubbles of the reaction gas are quickly removed from the object to be coated in the initial step, so that the bubbles can be easily and smoothly removed from the coating film. Can be prevented from remaining in the coating film, thereby improving the smoothness of the finished coating film and improving the coating quality of the electrodeposition coating.

The second feature configuration of the present invention specifies an embodiment suitable for the implementation of the first feature configuration.
In the initial step, the relative speed which is at least twice as high as the relative speed held in the latter step is held.

  In other words, the smaller the relative speed held in the initial step, the more difficult it is for the bubbles of the reaction gas to be removed from the object to be coated, so that it is necessary to complete a dense and high electric resistance coating on the outer surface of the object to be coated. Since the time becomes longer and the thickness of the coating film becomes excessive on the outer surface of the object, the relative speed retained in the initial process is less than twice the relative speed retained in the later process. Thus, it becomes difficult to obtain the above-described operational effects by the first characteristic configuration.

  Therefore, while the relative speed held in the later stage process is set to a generally adopted relative speed, the relative speed held in the early stage process should be at least twice the relative speed held in the later stage process. The operational effects of the first characteristic configuration described above can be obtained more remarkably.

The third feature configuration of the present invention specifies an embodiment suitable for the implementation of the first or second feature configuration.
As a nozzle that ejects the paint liquid to the paint liquid in the electrodeposition tank,
A plurality of spray nozzles for spraying spray paint liquid onto each part of the outer surface of the article immersed in the paint liquid;
A plurality of convection nozzles for inducing a convective circulation flow of the coating liquid throughout the electrodeposition tank by the sprayed coating liquid;
In the initial step, the coating liquid is ejected from all the spray nozzles and all the convection nozzles at a rated ejection pressure,
In the latter process, the coating liquid is ejected from all the convection nozzles at a rated ejection pressure, whereas the spray nozzles are
Put all the nozzles for spraying into a state where ejection is stopped,
Or, a part of the nozzles for spraying is stopped, and the coating liquid is ejected from the remaining nozzles for spraying at a rated ejection pressure or an ejection pressure lower than the rated ejection pressure.
Alternatively, the coating liquid is ejected from all the spray nozzles at an ejection pressure lower than a rated ejection pressure.

  That is, in this third characteristic configuration, basically, a plurality of spray nozzles spray a coating liquid onto each part of the outer surface of the object to be coated, thereby ensuring a large relative speed of the coating liquid with respect to the object to be coated. By inducing convective circulation flow of the coating liquid throughout the electrodeposition tank by jetting the coating liquid from the convection nozzle, sedimentation of coating film components such as pigments contained in the coating liquid is prevented.

  Then, in the latter stage, all the spray nozzles are brought into the ejection stop state, or some of the spray nozzles are brought into the jet stop state, and the remaining jet nozzles are operated at a jet pressure lower than the rated jet pressure or the rated jet pressure. By spraying the coating liquid or by spraying the coating liquid at a spray pressure lower than the rated spray pressure from all the spray nozzles, the relative speed of the coating liquid with respect to the object to be coated is reduced from the relative speed in the initial process, Accordingly, the power required for transporting the coating liquid in the electrodeposition process is reduced.

  In addition, for all convection nozzles, the coating liquid is ejected at the rated ejection pressure through the initial process and the late process, so that the settling of coating components such as pigments in the paint liquid is reliably prevented through the initial process and the late process. To do.

  That is, for the convection nozzle, the coating liquid is ejected at the rated ejection pressure through the initial process and the later process, while only the spray nozzle is switched to the ejection stop state or the ejection pressure lowered state in the later process. By changing the relative speed of the liquid, for example, in the electrodeposition coating method disclosed in Patent Document 1 described above, a surface area nozzle (36) or an intermediate area nozzle (37) corresponding to a spray nozzle, and convection Compared to the uniform switching of the coating liquid jetting state of the bottom surface nozzles (29) and (35) corresponding to the nozzles for use between the initial process and the latter process, the deposition of coating film components such as pigments is reduced. The relative speed of the coating liquid can be clearly changed between the initial process and the later process while preventing more reliably through the initial process and the later process.

The fourth characteristic configuration of the present invention specifies an embodiment suitable for the implementation of any of the first to third characteristic configurations,
In the initial step, the potential difference smaller than the potential difference applied between the in-tank electrode and the object to be coated in the latter step is provided between the in-tank electrode and the object to be coated.

  In other words, since the amount of reaction gas generated is particularly large at the beginning of the electrodeposition process, even if the relative speed of the coating liquid is increased in the initial process to promote the removal of bubbles due to the flow of the coating liquid, When the generation rate exceeds the bubble removal rate, the object to be coated is temporarily covered with the reaction gas bubbles, which hinders the completion of the coating on the outer surface of the object to be coated. There is a case.

  On the other hand, in the fourth characteristic configuration, the generation amount of the reaction gas is suppressed by making the potential difference applied between the electrode in the tank and the object to be coated smaller than the potential difference applied in the later step in the initial step. The bubble removal load is reduced, thereby compensating for the rapid removal of reaction gas bubbles from the object to be coated by the flow of the coating liquid whose relative speed is increased in the initial step.

  Therefore, according to the fourth feature configuration, a dense and high electrical resistance coating film can be surely completed early in the initial process stage on the outer surface of the object to be coated. It can suppress more reliably that a difference arises in the thickness of the coating film formed, and the thickness of the coating film formed in the inner surface of a to-be-coated article.

In addition, the potential difference applied between the electrode in the tank and the object to be coated in the latter process is changed to a generally adopted potential difference, whereas it is applied between the electrode in the tank and the object to be coated in the initial process. As to how much the potential difference is to be made smaller than the potential difference applied in the later stage process, the correlation between the applied potential difference in the initial process and the bubble state around the object to be coated may be confirmed by experiments or the like.
In the implementation of the fourth characteristic configuration, the change in the electrical resistance of the coating film formed on the outer surface of the object to be coated is detected in the initial process, and the electrode in the tank and the object to be coated are detected in the initial process based on the detected information. The potential difference applied to the object may be automatically adjusted to an optimum value.

The fifth characteristic configuration of the present invention specifies an embodiment suitable for implementation of any of the first to fourth characteristic configurations,
The electrodeposition time is determined according to the condition of the coating liquid,
The time for the initial step is that the time is within a range of 1/6 to 1/2 of the electrodeposition time.
That is, the electrodeposition time should be determined according to the conditions of the coating liquid, and the time of the initial process is preferably a time within the range of 1/6 to 1/2 of the electrodeposition time. Specifically, it is appropriate to set the initial process time to about 30 seconds to 120 seconds.

Side view showing schematic structure of electrodeposition tank Plan view showing schematic structure of electrodeposition tank A graph showing the correlation between paint liquid relative speed and coating film smoothness Schematic diagram showing conventional coating film structure Side view of electrodeposition tank explaining electrodeposition coating method of Patent Document 1 Cross-sectional view of an electrodeposition tank explaining the electrodeposition coating method of Patent Document 1 A graph of pump power explaining the electrodeposition coating method of Patent Document 1

  1 and 2 show an electrodeposition tank in which an automobile body W before assembly is an object to be coated. This electrodeposition tank 1 has a boat shape, and a coating film component is contained in the tank. The coating liquid L is stored.

  Electrodes in the tank (not shown) are arranged on both side walls 1a of the electrodeposition tank 1 in a state of being immersed in the coating liquid L in the tank. Maintains the state of being electrically grounded as a counter electrode with respect to the electrode in the tank, and the whole is immersed in the coating liquid L in the tank.

  That is, in this electrodeposition tank 1, as an electrodeposition process for the automobile body W, the electrode in the tank and the counter electrode are provided via the paint liquid L in the tank while the automobile body W is immersed in the paint liquid L in the tank. By applying a predetermined potential difference E to the object W as a coating over a predetermined electrodeposition time t, the coating film component in the coating liquid L is electrically attracted to the outer surface and the inner surface of the object W to be coated. By fixing, a coating film is formed on each of the outer surface and the inner surface of the workpiece W.

  The automobile body W is immersed in the coating liquid L in the tank at the inlet tank portion 1A at one end in the longitudinal direction of the electrodeposition tank 1 by the transport apparatus 2 along with the transport in the suspended form by the transport apparatus 2. Then, in the state where the immersion state in the coating liquid L is maintained following this entrance tank, the process proceeds in the tank toward the exit tank part 1B at the other end in the longitudinal direction of the electrodeposition tank 1, The above-described electrodeposition process is carried out over a predetermined electrodeposition time t.

  The automobile body W that has reached the exit tank 1B through the electrodeposition process is pulled up from the coating liquid L in the tank along with the transport by the transport device 2, and is sent to the subsequent process section following this discharge tank.

  A liquid processing apparatus 3 is provided outside the electrodeposition tank 1, and this liquid processing apparatus 3 overflows from the electrodeposition tank 1 to the auxiliary tank 4 on the outlet tank 1 B side together with floating dust and the like. A dust removal process and a temperature adjustment process are performed on the liquid L and the coating liquid L extracted together with sedimentary dust from the bottom of the electrodeposition tank 1 on the outlet tank 1B side.

  The tank of the electrodeposition tank 1 is equipped with a number of nozzles 5A and 5B for jetting the coating liquid L into the tank, and the nozzles 5A and 5B have paints jetted from the nozzles 5A and 5B, respectively. As the liquid L, the coating liquid L processed by the liquid processing apparatus 3 is fed by the spray pump Pa and the convection pump Pb.

  That is, the coating liquid L in the tank is circulated and used while being subjected to dust removal processing and temperature adjustment processing in the liquid processing apparatus 3, and is reduced by the amount of the coating liquid L that is reduced by being taken out of the electrodeposition tank 1 together with the automobile body W. The new coating liquid L is supplied to the electrodeposition tank 1 through the supply path.

  The multiple nozzles 5A and 5B are divided into a plurality of spray nozzles 5A connected to the spray pump Pa and a convection nozzle 5B connected to the convection pump Pb for the purpose, and the spray nozzle 5A is an electrodeposition tank. 1, the convection nozzle 5B is disposed at the bottom of the electrodeposition tank 1 in such a posture that the coating liquid L is jetted toward the outlet tank 1B.

  That is, the paint liquid L is ejected from the convection nozzle 5B, and the paint liquid L in the tank in the electrodeposition tank 1 is guided by the thick paint arrow in the figure by the induction of the paint liquid L in the tank by the sprayed paint liquid L. As shown in the figure, the bottom of the electrodeposition tank 1 flows along the tank bottom from the inlet tank part 1A toward the outlet tank part 1B, and the upper part of the coating liquid L in the tank of the outlet tank part 1B. In a convective flow form that flows from the side toward the inlet tank 1A, it is made to circulate and flow over the entire tank of the electrodeposition tank 1, and thereby, coating film components such as pigments in the coating liquid L In addition to preventing sedimentation, foreign substances such as floating and sedimentary dust mixed into the coating liquid L by being brought into the tank together with the automobile body W are discharged from the tank together with the coating liquid L, and the liquid processing apparatus. 3 is promoted.

  On the other hand, the nozzle 5A for spraying includes nozzle rows Ra to Rc in which the nozzles 5A for spraying are arranged at predetermined intervals in the advancing direction in the tank of the vehicle body W, the upper nozzle row Ra, the middle nozzle row Rb, and the lower nozzle row Rc. The spray nozzles 5A are respectively arranged at a predetermined angle (for example, 15 °) with respect to the side wall 1a of the electrodeposition tank 1. The coating liquid L is disposed in a state in which the coating liquid L is ejected to the side of the tank 1 </ b> A in an obliquely inclined posture inclined only toward the inside of the tank.

  The upper nozzle row Ra is disposed at a height corresponding to the roof outer surface wr of the automobile body W that travels in the tank, and in parallel, the automobile body W travels in the tank, The coating liquid L ejected from the spray nozzle 5A of the upper nozzle row Ra is sprayed on the roof outer surface wr, which is an upward outer surface portion of the automobile body W, in a spraying manner along the roof outer surface wr.

  Further, the middle nozzle row Rb and the lower nozzle row Rc are arranged at heights corresponding to the upper and lower portions of the side part outer surface ws of the automobile body W traveling in the tank. In parallel with traveling in the tank, the coating liquid L ejected from the spray nozzle 5A of the middle nozzle row Rb and the lower stage are formed on the upper and lower sides of the side part outer surface ws which is a laterally outer surface part of the automobile body W. The coating liquid L ejected from the spray nozzle 5A of the nozzle row Rc is sprayed.

  Therefore, in this electrodeposition tank 1, the relative speed V of the coating liquid L flowing around the automobile body W traveling in the tank with respect to the automobile body W is guided by the coating liquid L ejected from the convection nozzle 5B and flows in the tank. The combined speed of the flow speed of the coating liquid L flowing convectively, the traveling speed of the automobile body W traveling in the tank, and the spraying flow speed of the coating liquid L sprayed to each part of the automobile body W by each spray nozzle 5A. It becomes.

  By the way, when an object to be coated such as an automobile body W having an internal space in which an opening to the outside is restricted is electrodeposited, the inner surface of the object to be coated (that is, the surface of the object to be coated in the internal space) Compared to the outer surface, the effect of energization between the electrodes in the tank is difficult and the film thickness of the coating film formed on the outer surface of the coating object is less than that of the coating film formed on the inner surface of the coating object. There is a problem that the film thickness becomes small (a so-called difference in throwing power).

  On the other hand, in the electrodeposition tank 1 of this example, the electrodeposition process of a predetermined electrodeposition time t (for example, 3 minutes) for each automobile body W is performed at an initial process and a late process at a predetermined time ratio (for example, 1: 2). In the initial step, the coating liquid L is ejected at the rated ejection pressure from all the spray nozzles 5A and all the convection nozzles 5B by adjusting the outputs of the spray pump Pa and the convection pump Pb. The electrodeposition tank 1 is operated in the “speed increase mode”.

  On the other hand, in the latter process, the coating liquid L is ejected from all the convection nozzles 5B at the rated ejection pressure following the initial process by adjusting the output of the convection pump Pb, whereas the spray pump 5A “Relative speed reduction mode” in which all the spray nozzles 5A are stopped by stopping Pa (or lower than the rated jet pressure from all the spray nozzles 5A by reducing the output of the spray pump Pa) The electrodeposition tank 1 is operated in the “relative speed reduction mode” in which the coating liquid L is ejected at the ejection pressure.

  In other words, in the initial process, the coating liquid L is ejected from all the spray nozzles 5A at the rated ejection pressure, so that the relative speed V of the coating liquid L with respect to the automobile body W is at least twice the relative speed V that is maintained in the latter process. This increases the thickness of the coating on the outer surface of the automobile body W so that a dense coating with high electrical resistance is completed on the outer surface of the automobile body W early in the paragraph of the initial process. To prevent.

  Further, in the latter process, all the spray nozzles 5A are stopped from being ejected (or the paint liquid L is ejected from all the spray nozzles 5A at an ejection pressure lower than the rated ejection pressure), and the paint liquid for the automobile body W is obtained. By reducing the relative speed V of L, the pump power required in the electrodeposition process is reduced.

  Then, on the inner surface of the automobile body W where the influence of the flow of the coating liquid L is difficult to be applied, a coating film is gradually formed through the initial process and the latter process regardless of the change in the relative speed V, and the coating is dense and has high electric resistance. The film is completed in a later step, thereby suppressing the difference between the thickness of the coating film formed on the outer surface of the automobile body W and the thickness of the coating film formed on the inner surface of the automobile body W. .

  Furthermore, regarding the potential difference E applied between the electrode in the tank and the vehicle body W in the electrodeposition process, the potential difference E applied in the initial process is limited to a potential difference smaller than the potential difference E applied in the latter process, In the initial stage of the electrodeposition process in which a large amount of reaction gas is generated, it is avoided that the automobile body W is temporarily covered with the reaction gas bubbles, so that the coating on the outer surface of the automobile body W is applied in the initial process. Ensure the completion of the membrane.

  By the way, the coating liquid L is composed of pigment particles a having an average particle size of about 0.1 to 10 μm and fine main component resin particles b having an average particle size of about 20 to 100 nm as the main component of the coating. However, the pigment particles a have a specific gravity larger than that of the main component resin particles b and are likely to settle.

  For this reason, the pigment particle a sinks downward along the side portion outer surface ws on the side portion outer surface ws of the automobile body W (that is, the laterally facing outer surface portion of the object to be coated), and thus is mainly caused by electric attractive force. There are few pigment particles a fixed on the outer surface ws of the side portion together with the component resin particles b, and as a result, as shown schematically in FIG. 4A, the pigment particles a are almost completely within the assembly of the main component resin particles b. A coating film T in a state of being buried in is formed on the side portion outer surface ws.

  On the other hand, on the roof portion outer surface wr of the automobile body W (that is, the upward outer surface portion of the article to be coated), the pigment particles a settle and deposit on the roof portion outer surface wr, so that the roof portion outer surface wr together with the main component resin particles b. As shown schematically in FIG. 4 (b), there are many pigment particles a that are not completely filled in the aggregate of the main component resin particles b. The coating film T of the form to form is formed in the roof part outer surface wr.

  For this reason, in electrodeposition coating, the coating film T formed on the roof outer surface wr of the automobile body W is rougher than the coating film T formed on the side outer surface ws of the automobile body W. Thus, the smoothness of the coating film T on the roof portion outer surface wr tends to be lower than the smoothness of the coating film T formed on the side portion outer surface ws.

  On the other hand, when the correlation between the relative speed V and the smoothness of the coating film formed on each part of the outer surface of the automobile body W was studied, the side surface outer surface ws of the automobile body W was shown in the graph of ◆ in FIG. As shown in FIG. 3, the smoothness of the coating film does not change so much even if the relative speed V changes, whereas the roof outer surface wr of the automobile body W is shown by the graph of ■ in FIG. In addition, when the relative speed V is increased, the smoothness of the coating film is greatly improved. (Note: Since the vertical axis in FIG. 3 represents the smoothness of the coating film by the roughness of the coating film, the lower the vertical axis, the smaller the coating film roughness and the higher the smoothness of the coating film. It is shown that)

  The tendency is that, on the outer side surface ws of the side part, there are many pigment particles a that have settled downward along the outer side surface ws of the side part. The amount of the pigment particles a fixed on the side portion outer surface ws does not change so much. On the roof portion outer surface wr, when the relative speed V of the coating liquid L increases, the sedimentation and deposition of the pigment particles a on the roof portion outer surface wr occurs. This is presumably because the amount of pigment particles a that are blocked and fixed on the outer surface wr of the roof portion together with the main component resin particles b is greatly reduced.

  Therefore, as described above, in the initial step in the electrodeposition step, the relative velocity V and the smoothness of the coating film on the outer surface ws of the side portion are maintained in order to maintain the relative velocity V larger than the relative velocity V retained in the latter step. And the correlation between the relative speed V and the smoothness of the coating film on the roof outer surface wr, the smoothness of the coating film obtained on the side portion outer surface ws and the smoothness of the coating film obtained on the roof portion outer surface wr The arrangement of the nozzle 5A for spraying and the rated ejection pressure are set so that the relative speed V close to the equivalent common relative speed Vx (specifically, about 45 cm / s) is maintained in the initial step.

  That is, this suppresses the occurrence of a difference between the thickness of the coating film formed on the outer surface of the automobile body W and the thickness of the coating film formed on the inner surface of the automobile body W as described above. About the coating film formed in the side part outer surface ws of the body W, and the coating film formed in the roof part outer surface wr of the motor vehicle body W, the smoothness of the coating film formed in those outer surfaces is also made uniform.

  In addition, the relative speed V close to the common relative speed Vx at which the smoothness of the coating film obtained on the side portion outer surface ws and the smoothness of the coating film obtained on the roof portion outer surface wr are equal is specifically, The relative speed V (0.7 Vx ≦ V ≦ 1.3 Vx) within the range of 30% decrease to 30% increase of the common relative speed Vx is desirable, and more preferably, the common relative speed Vx is decreased by 20% to A relative speed V (0.8 Vx ≦ V ≦ 1.2 Vx) within a 20% increase range is desirable.

  Further, in the latter stage of the electrodeposition process, the coating liquid L is ejected from all the convection nozzles 5B at the rated ejection pressure, whereas when all the spray nozzles 5A are brought into the ejection stop state, the electrodeposition process. Even in a situation where the coating liquid L is ejected from all the convection nozzles 5B at the rated ejection pressure as in the latter process, all the spraying nozzles 5A are brought into the ejection stop state, Even in a situation where the electrodeposition process is not performed, the power required for transporting the coating liquid is reduced while preventing sedimentation of coating film components such as pigments.

  Also, in the latter stage of the electrodeposition process, the coating liquid L is ejected from all the convection nozzles 5B at the rated ejection pressure, whereas the coating liquid L is ejected from all the spray nozzles 5A at an ejection pressure lower than the rated ejection pressure. When the electrodeposition process is not performed, the coating liquid L is ejected from all the convection nozzles 5B at the rated ejection pressure, whereas all the spraying nozzles 5A are stopped. This further reduces the power required for conveying the coating liquid while preventing sedimentation of coating film components such as pigments in a situation where the electrodeposition step is not performed.

[Another embodiment]
Next, other embodiments of the present invention will be listed.

  In the above-described embodiment, the coating liquid L is ejected from all the spray nozzles 5A at the rated ejection pressure in the initial process of the electrodeposition process, whereas in the latter process of the electrodeposition process, all the spray nozzles 5A are ejected. The coating liquid L is ejected at a stop state or at an ejection pressure smaller than the rated ejection pressure from all the spray nozzles 5A. Instead of this, all the spray nozzles 5A are used in the initial step of the electrodeposition process. While the coating liquid L is ejected from the nozzle at the rated ejection pressure, in the latter stage of the electrodeposition process, a part of the spray nozzles 5A is stopped and the remaining spray nozzles 5A have the rated ejection pressure or rating. The coating liquid L may be ejected at an ejection pressure lower than the ejection pressure, and the relative speed V of the coating liquid L may be switched between the initial process and the later process in the electrodeposition process.

  In the above-described embodiment, an example in which the automobile body W is an object to be coated has been shown. However, the electrodeposition coating method according to the present invention is not limited to the electrodeposition coating of the automobile body W, and the opening to the outside is limited. As long as it has an internal space, various objects such as casings for electrical products, building materials, vehicles other than automobile bodies, and vehicle parts can be used as objects to be coated.

  In the above embodiment, the case where the electrodeposition time t, which is the execution time of the electrodeposition process, is set to 3 minutes and the time ratio between the initial process and the later process is set to 1: 2, the electrodeposition time t is It is not limited to 3 minutes, and an appropriate electrodeposition time t may be adopted depending on the situation, and the time ratio between the initial process and the later process is not limited to 1: 2, but depending on the situation. An appropriate time ratio may be adopted.

  The relative speed V of the coating liquid L retained in the initial process is not limited to the relative speed of about 45 cm / s, but the relative speed at which the coating film on the outer surface of the article such as the automobile body W is completed in the initial process. In addition, the relative speed V of the coating liquid L retained in the later process is also completed in the later process by gradually forming the coating film on the inner surface of the object such as the automobile body W through the initial process and the later process. Any relative speed to reach

  In the initial process, in some cases, such as when the reaction gas bubbles can be sufficiently removed simply by increasing the relative velocity V of the coating liquid L, it is applied between the electrode in the tank and the object to be coated such as the automobile body W. The potential difference E to be maintained may be kept at the same potential difference in the initial process and the later process.

  The present invention can be used for electrodeposition coating of various articles in various fields as long as the article has an internal space in which the opening to the outside is limited.

W Auto Body (Coating)
1 Electrodeposition tank L Paint liquid E Potential difference t Electrodeposition time V Relative speed 5A Spray nozzle 5B Convection nozzle

Claims (5)

In a state where an object to be coated having an internal space whose opening to the outside is restricted is immersed in a coating liquid in the electrodeposition tank, the electrode in the tank and the electrode as the counter electrode in the electrodeposition tank are passed through the coating liquid. An electrodeposition step of applying a predetermined potential difference between the coating and the coating material for a predetermined electrodeposition time;
In this electrodeposition step, an electrodeposition coating method for maintaining a relative speed of the coating liquid flowing around the object to be coated at a predetermined relative speed,
The electrodeposition process is divided into an initial process and a late process,
In the initial step, by increasing the relative speed to be held, the coating film formed on the outer surface of the object to be coated is completed in the initial step,
The electrodeposition coating method in which, in the latter process, the coating film formed on the inner surface of the object to be coated is completed in the latter process in a state where the relative speed to be held is smaller than the relative speed to be held in the initial process.   2. The electrodeposition coating method according to claim 1, wherein in the initial step, the relative speed is maintained at least twice as high as the relative speed held in the latter step. As a nozzle that ejects the paint liquid to the paint liquid in the electrodeposition tank,
A plurality of spray nozzles for spraying spray paint liquid onto each part of the outer surface of the article immersed in the paint liquid;
A plurality of convection nozzles for inducing a convective circulation flow of the coating liquid throughout the electrodeposition tank by the sprayed coating liquid;
In the initial step, the coating liquid is ejected from all the spray nozzles and all the convection nozzles at a rated ejection pressure,
In the latter process, the coating liquid is ejected from all the convection nozzles at a rated ejection pressure, whereas the spray nozzles are
Put all the nozzles for spraying into a state where ejection is stopped,
Or, a part of the nozzles for spraying is stopped, and the coating liquid is ejected from the remaining nozzles for spraying at a rated ejection pressure or an ejection pressure lower than the rated ejection pressure.
The electrodeposition coating method according to claim 1 or 2, wherein the coating liquid is ejected from all the spray nozzles at an ejection pressure lower than a rated ejection pressure.   The said initial process WHEREIN: The said potential difference smaller than the said potential difference provided between the said electrode in a tank and the said to-be-coated object in the said latter process is provided between the said electrode in a tank and the to-be-coated object. 4. The electrodeposition coating method according to any one of 3 above. The electrodeposition time is determined according to the condition of the coating liquid,
The electrodeposition coating method according to any one of claims 1 to 4, wherein the time for the initial step is set to a time within a range of 1/6 to 1/2 of the electrodeposition time.

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