Methods and apparatus for conducting electrostatic spray coating

The invention provides methods and apparatus for conducting electrostatic spray coating by which an improved coating layer made uniform in gloss, hardness, weather-tightness, and other characteristics is obtained on an object to be coated. The coating layer is formed with use of a rotary spray head device which is provided with a funnel-like body having an inner wall surface and an open end portion. The rotary spray head device is driven to turn on an axis of rotation surrounded by the inner wall surface of the funnel-like body, and supplied with plural kinds of coating material which are discharged to a substantially common location on the inner wall surface of the funnel-like body simultaneously through respective separate paths so as to form their respective layers superimposed on said inner wall surface of the funnel-like body and move toward said open end portion of the funnel-like body.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to methods and apparatus for 
conducting electrostatic spray coating, and more particularly, is directed 
to an improvement in a method of providing an object to be coated with a 
coating layer thereon through spraying coating material by a rotary spray 
head device and depositing electrostatically the sprayed coating material 
on the object, and also to an apparatus for use in such an improved 
method. 
2. Description of the Prior Art 
There has been proposed adoption of electrostatic spray coating for 
providing a vehicle body with a coating layer which covers uniformly the 
whole outer surface of the vehicle body. Generally, according to the 
electrostatic spray coating, an electrostatic field is formed with a high 
DC voltage supplied between an object to be coated, such as the vehicle 
body, and a spray head device disposed to face the object for spraying 
coating material toward the same, and the coating material sprayed by the 
spray head is charged with electricity in the electrostatic field and 
deposited on the object through electrostatic adsorption effected thereon. 
With use of such electrostatic spray coating the efficiency of deposition 
of the coating material on the object is improved so that a loss of 
coating material is reduced. 
When the object which is subjected to the electrostatic spray coating is 
made of metal, coating of the baking finish type, such as one of various 
kinds of coating of melamine alkyd resin, is ordinarily used for forming a 
coating layer on the object. The coating of the baking finish type 
deposited on the object is dried in a heated ambience of, for example, 
about 140 degrees to be hardened. On the other hand, when the object which 
is subjected to the electrostatic spray coating is made of some material 
with relatively low thermal resistance such as a kind of plastic, a 
coating of the two liquid component type, which comprises a coating base 
of, for example, acrylic resin and a hardening agent, is used for forming 
a coating layer on the object. The coating of the two liquid component 
type disposed on the object is dried in an ambience of ordinary 
temperature to be hardened, so that the coating layer which is expected to 
be securely deposited on the outer surface of the object to have a surface 
thereof with superior gloss, hardness and weather-tightness, is formed on 
the object. 
In general, such coating of the two liquid component type as described 
above is hardened in a relatively short time when the coating base and the 
hardening agent are mixed with each other, and therefore the coating base 
and hardening agent are stored separately and mixed with each other 
immediately before the electrostatic spray coating is conducted. 
Therefore, when electrostatic spray coating is conducted with the coating 
of the two liquid component type, a mixer is provided for mixing the 
coating base with the hardening agent to constitute the coating of the two 
liquid component type, and the coating sent out of the mixer is supplied 
to a spray head device so as to be sprayed thereby. Accordingly, when a 
change of color of the coating base is required, the mixer is to be caused 
to discharge the coating produced therein to the outside therefrom and to 
be washed thoroughly to remove the remaining coating material from the 
inside thereof before a new coating base of different color is supplied to 
the mixer together with the hardening agent. This results in a problem in 
that a relatively long time is wasted for washing the mixer in a 
sequential coating process. 
For the purpose of avoiding such a problem, there has also been proposed an 
apparatus for performing the electrostatic spray coating without using a 
combination of the mixer for mixing the coating base with the hardening 
agent to constitute the coating of the two liquid component type and the 
spray device for spraying the coating, as disclosed in the Japanese patent 
application published before examination under publication number 57-45370 
or 59-228960. Such a previously proposed apparatus is provided with a 
rotary spray head device which is supplied with a high DC voltage and 
operative to rotate at a high speed, and first and second nozzles for 
supplying respectively the coating base and hardening agent, which are 
ingredients of the coating of the two liquid component type, separately 
onto the inner wall surface of the rotary spray head. The coating base and 
hardening agent supplied onto the inner wall surface of the rotary spray 
head device are mixed with each other in the rotary spray head device and 
sprayed from the rotary spray head device due to centrifugal force 
resulting from the rotation of the rotary spray head device. 
Then, the previously proposed apparatus is further provided with a third 
nozzle for supplying a washing agent, such as thinner, to the inside of 
the rotary spray head device. The third nozzle is disposed to have its 
discharging opening positioned in the vicinity of the inner wall surface 
of the rotary spray head device. 
When the change of color of the coating base is carried out, the third 
nozzle is operated to supply the washing agent onto the inner wall surface 
of the rotary spray head device for washing the inside of the rotary spray 
head device after the first and second nozzles are controlled to cease to 
supply the coating base and hardening agent, respectively, so that the 
rotary spray head device is made ready for the change of color of the 
coating base. With such an arrangement, a time spent for the change of 
color of the coating base is effectively saved. 
When the electrostatic spray coating is conducted with the above described 
apparatus which is equipped with the rotary spray head device and the 
first, second and third nozzles for supplying the coating base, hardening 
agent and washing agent, respectively, each of the coating base and 
hardening agent supplied onto the inner wall surface of the rotary spray 
head device reaches to the open end portion of the rotary spray head 
device so as to be sprayed therefrom in an instant, due to the centrifugal 
force resulting from the rotation of the rotary spray head device. 
Accordingly, it is feared; that the coating base and the hardening agent 
which ar supplied separately onto the inner wall surface of the rotary 
spray head device are sprayed independently from the open end portion of 
the rotary spray head device, and therefore the coating base and hardening 
agent both sprayed by the rotary spray head device are not mixed enough 
with each other. In the case where the coating base sprayed by the rotary 
spray head device is not mixed sufficiently with the hardening agent also 
sprayed by the rotary spray head device, an object to be coated through 
the electrostatic spray coating is provided on its outer surface with a 
coating layer which has partially excess and deficiency of the coating 
base or the hardening agent, and this results in a disadvantage, in that 
the coating layer deposited on the outer surface of the object is lacking 
in uniformity in gloss, hardness, weather-tightness, and other 
characteristics. 
OBJECTS AND SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a method 
and apparatus for conducting electrostatic spray coating which avoid the 
foregoing problems encountered with the prior art. 
Another object of the present invention is to provide a method and 
apparatus for conducting electrostatic spray coating in which a coating 
base and hardening agent to constitute coating of the two liquid component 
type or plural kinds of coating material are supplied separately to a 
rotary spray head device and then sprayed by the rotary spray head device 
toward an object to be coated, and by which the object is provided on its 
outer surface with a superior coating layer which is made uniform in 
gloss, hardness, weather-tightness, and other characteristics. 
A further object of the present invention is to provide a method and 
apparatus for conducting electrostatic spray coating in which a coating 
base and hardening agent to constitute coating material of the two liquid 
component type or plural kinds of coating material are supplied separately 
to a rotary spray head device and then sprayed by the rotary spray head 
device toward an object to be coated in such a manner that the coating 
base and hardening agent, or the plural kinds of coating material are 
mixed sufficiently. 
According to the present invention, there is provided a method of 
conducting electrostatic spray coating which comprises driving a rotary 
spray head device which is provided with a funnel-like body having an 
inner wall surface for guiding coating material and an open end portion at 
the side of larger diameter thereof, to turn on an axis of rotation 
surrounded by the inner wall surface of the funnel-like body, and 
supplying plural kinds of coating material to the inner wall surface of 
the funnel-like body of the rotary spray head device simultaneously 
through respective separate paths so that the plural kinds of coating 
material form their respective layers superimposed on the inner wall 
surface of the funnel-like body and move toward the open end portion of 
the funnel-like body. 
According to the present invention, there is also provided a method of 
conducting electrostatic spray coating which comprises driving a rotary 
spray head device which is provided with a funnel-like body having an 
inner wall surface for guiding coating material and an open end portion at 
the side of larger diameter thereof, to turn on an axis of rotation 
surrounded by the inner wall surface of the funnel-like body, and 
supplying a coating base and a hardening agent both to constitute coating 
of the two liquid component type to the inner wall surface of the 
funnel-like body of the rotary spray head device simultaneously through 
respective separate paths so that the coating base and hardening agent 
form their respective layers superimposed on the inner wall surface of the 
funnel-like body and move toward the open end portion of the funnel-like 
body. 
Also, the present invention provides an apparatus for conducting 
electrostatic spray coating which comprises a rotary spray head device 
provided with a funnel-like body having an inner wall surface for guiding 
coating material and an open end portion at the side of larger diameter 
thereof, a driving device for driving the rotary spray head device to turn 
on an axis of rotation surrounded by the inner wall surface of the 
funnel-like body, and a plurality of nozzles each having its discharging 
opening positioned to be close to the inner wall surface of the 
funnel-like body of the rotary spray head device for supplying plural 
kinds of coating material respectively to the inner wall surface of the 
funnel-like body through respective separate paths so that the plural 
kinds of coating material form their respective layers superimposed on the 
inner wall surface of the funnel-like body and move toward the open end 
portion of the funnel-like body. 
With the method of conducting electrostatic spray coating according to the 
present invention, the coating base and hardening agent to constitute the 
coating of the two liquid component type or the plural kinds of coating 
material are supplied simultaneously through the respective separate paths 
to the inner wall surface of the funnel-like body of the rotary spray head 
device to as to form their respective layers superimposed on the inner 
wall surface of the funnel-like body and move toward the open end portion 
of the funnel-like body. The coating base and hardening agent or the 
plural kinds of coating material forming the respective layers 
superimposed on the inner wall surface of the funnel-like body are 
directly sprayed from the open end portion of the funnel-like body by 
means of the rotation of the funnel-like body so as to form almost 
innumerable sprayed particles each having a double layer or multilayer. 
This results in that the coating base and hardening agent or the plural 
kinds of coating material are sprayed by the funnel-shaped body of the 
rotary spray head device toward an object to be coated so as to mixed 
sufficiently with each other, and consequently the object is provided on 
its outer surface with a superior coating layer which is made uniform in 
gloss, hardness, weather-tightness, and other characteristics. 
Also, with the apparatus of conducting electrostatic spray coating 
according to the present invention, the coating base and hardening agent 
to constitute the coating of the two liquid component type or the plural 
kinds of coating material are supplied separately from the respective 
discharging openings of the nozzles to the inner wall surface of the 
funnel-like body which is driven to turn by the driving device. On such 
occasion, the coating base and hardening agent or the plural kinds of 
coating material discharged from the nozzles impinge upon a common 
location on the inner wall surface of the funnel-like body so as to form 
their respective layers superimposed thereon and move toward the open end 
portion of the funnel-like body. Then, the coating base and hardening 
agent or the plural kinds of coating material forming the respective 
layers superimposed on the inner wall surface of the funnel-like body are 
directly sprayed to an object to be coated from the open end portion of 
the funnel-like body by means of the rotation of the funnel-like body in 
such a manner as to form almost innumerable sprayed particles each having 
a double layer or multilayer. Accordingly, the coating base and hardening 
agent or the plural kinds of coating material sprayed by the funnel-like 
body of the rotary spray head device are mixed sufficiently with each 
other, and therefore the object is provided on its outer surface with a 
superior coating layer which is made uniform in gloss, hardness, 
weather-tightness, and other characteristics. 
The above, and other objects, features and advantages of the present 
invention will become apparent from the following detailed description 
which is to be read in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows an example of apparatus for used in one embodiment of method 
of conducting electrostatic spray coating according to the present 
invention. 
In the apparatus shown in FIG. 1, a rotary spray head device 2 which 
comprises a funnel-like body 4 and a hub member 6 disposed at the center 
of the funnel-like body 4 is provided. The funnel-like body 4 has an open 
end portion 4a with a relatively large diameter, a connecting end portion 
4b with a relatively small diameter, and a middle portion between the open 
end portion 4a and connecting end portion 4b, which is provided with an 
inner wall surface 5 for coming into contact with coating material for 
guiding the same. A plurality of holes 8 is provided at a connecting 
portion between the funnel-like body 4 and the hub member 6 for 
interconnecting a space surrounded by the inner wall surface 5 at the side 
of the open end portion 4a and another space surrounded by the inner wall 
surface 5 at the side of the connecting end portion 4b. A rotary shaft 12 
of an air motor 11 is inserted into the inside of the funnel-like body 4 
through the connecting end portion 4b of the same to be connected with the 
end portion of the hub member 6 close to the connecting end portion 4b. 
The air motor 11 is provided for driving the rotary spray head device 2 in 
its entirety to turn at a high speed on an axis of rotation which is 
surrounded by the inner wall surface 5 and passes through the center of 
the hub member 6 and the center of the rotary shaft 12 of the air motor 
11. 
A bracket 14 is fixed to the air motor 11, and a coating supply nozzle 
portion 16 is mounted on the bracket 14 to have a discharging opening end 
17 thereof which elongates through the connecting end portion 4b of the 
funnel-like body 4 to close to the inner wall surface 5 of the funnel-like 
body 4. One end of each of pipes 20a and 20b for supplying coating bases, 
respectively, and one end of a pipe 20c for supplying a hardening agent 
are coupled with the coating supply nozzle portion 16. The pipe 20a is 
provided with a flow controller 22 and a pump 26 on the way to a coating 
tank 32 to which the other end of the pipe 20a reaches. The pipe 20b is 
also provided with a flow controller 23 and a pump 27 on the way to a 
coating tank 33 to which the other end of the pipe 20b reaches. Further, 
the pipe 20c is provided with a flow controller 24 and a pump 28 on the 
way to a hardening agent tank 34 to which the other end of the pipe 20c 
reaches. 
In the coating tanks 32 and 33, different coating bases or different kinds 
of coating are stored. For example, a coating base composed of acrylic 
resin coating material including red pigment is stored in the coating tank 
32 and a coating base composed of acrylic resin coating material including 
white pigment is stored in the coating tank 33. In the hardening agent 
tank 34, for example, a hardening agent of isocyanate is stored. The flow 
controllers 22, 23 and 24 are operative to adjust independently flow of 
the coating base in the pipe 20a, flow of the coating base in the pipe 
20b, and flow of the hardening agent in the pipe 20c. 
Further, a nozzle 18 for discharging a washing agent is also mounted on the 
bracket 14 to have a discharging opening 18a thereof which elongates 
through the connecting end portion 4b of the funnel-like body 4 to close 
to the inner wall surface 5 of the funnel-like body 4. One end of a pipe 
35 for supplying the washing agent is coupled with the nozzle 18. The pipe 
35 is provided with a flow controller 36 and a pump 37 on the way to a 
washing agent tank 38 in which, for example, thinner is stored as the 
washing agent and to which the other end of the pipe 35 reaches. 
FIG. 2 shows a part of an embodiment of the rotary spray head device 2 
including the coating supply nozzle portion 16 and the circumference 
thereof. In the embodiment of the rotary spray head device 2, the coating 
supplying nozzle portion 16 comprises nozzles 16a and 16b for discharging 
the coating bases, respectively, and a nozzle 16c for discharging the 
hardening agent. These nozzles 16a, 16b and 16c are connected to the one 
ends of the pipes 20a, 20b and 20c, respectively. Discharging openings 
17a, 17b and 17c of the nozzles 16a, 16b and 16c which form the 
discharging opening end 17, are stacked in the direction perpendicular to 
the axis of rotation of the rotary spray head device 2, that is, in the 
direction along the radius of the funnel-like body 4 of the rotary spray 
head device 2, in the vicinity of the inner wall surface 5 of the 
funnel-like body 4. 
In addition, a high DC voltage is applied between the rotary spray head 
device 2 in its entirety and an object to be coated (not shown in the 
FIGS.) so as to provide the rotary spray head device 2 with a potential 
lower than that of the object to be coated. 
When the apparatus thus constituted is used for putting the embodiment of 
method of conducting electrostatic spray coating according to the present 
invention into practice, first the air motor 11 is driven to rotate at a 
predetermined speed and therefore the rotary spray head device 2 is turned 
at a high speed of, for example, 2,000 to 3,000 r.p.m on the axis of 
rotation which is surrounded by the inner wall surface 5 of the 
funnel-like body 4 and passes through the center of the hub member 6 and 
the center of the rotary shaft 12 of the air motor 11. On this occasion, 
the rotary spray head device 2 is supplied with a negative high DC 
potential of, for example, &lt;90 kV with reference to the potential of the 
object to be coated. 
Then, the pumps 27 and 28 are caused to work so that the coating bases 
stored in the coating tank 33 and the hardening agent stored in the 
hardening agent tank 34 are supplied respectively through the pipes 20b 
and 20c to the nozzles 16b and 16c in the coating supply nozzle portion 
16. Simultaneously with this, the flow controllers 23 and 24 are operated 
to adjust the flow of the coating base in the pipe 20b and the flow of the 
hardening agent in the pipe 20c, respectively, so that the ratio in weight 
of the hardening agent supplied to the nozzle 16c to the coating base 
supplied to the nozzle 16b is set to be one third. 
The coating base supplied to the nozzle 16b and the hardening agent 
supplied to the nozzle 16c are discharged simultaneously from the 
discharging openings 17b and 17c, respectively, to the inner wall surface 
5 of the funnel-like body 4 of the rotary spray head device 2 turning at 
the high speed. Since the discharging openings 17b and 17c of the nozzles 
16b and 16c are stacked in the direction along the radius of the 
funnel-like body 4 of in the vicinity of the inner wall surface 5 of the 
funnel-like body 4, as shown in FIG. 2, the coating base discharged from 
the discharging opening 17b of the nozzle 16b and the hardening agent 
discharged from the discharging opening 17c of the nozzle 16c impinge upon 
a common location on the inner wall surface 5 of the funnel-like body 4 of 
the rotary spray head device 2 turning at the high speed. 
The coating base and hardening agent discharged from the nozzles 16b and 
16c respectively to impinge upon the common location on the inner wall 
surface 5 of the funnel-like body 4 are moved along the inner wall surface 
5 to form their respective streams flowing toward the open end portion 4a 
of the funnel-like body 4 through the holes 8 provided at the connecting 
portion between the funnel-like body 4 and the hub member 6. The streams 
of the coating base and hardening agent flowing along the inner wall 
surface 5 toward the open end portion 4a are affected with centrifugal 
force resulting from the rotation of the rotary spray head device 2 at the 
high speed so as to form thier respective layers Fa and Fi superimposed on 
the inner wall surface 5, as shown in FIG. 1. In such case, the stream of 
the coating base which is larger in specific gravity than the hardening 
agent forms the layer Fa coming into contact directly with the inner wall 
surface 5, and the stream of the hardening agent forms the layer Fi put on 
the layer Fa. That is, the coating base and hardening agent supplied to 
the rotary spray head device 2 are caused to form the layers Fa and Fi 
superimposed on the inner wall surface 5 of the funnel-like body 4 and to 
move toward the open end portion 4a of the funnel-like body 4. 
The coating base and hardening agent forming the layers Fa and Fi and 
having reached to the open end portion 4a are sprayed from the open end 
portion 4a toward the object to be coated by means of the centrifugal 
force resulting from the rotation of the rotary spray head device 2 at the 
high speed so as to form almost innumerable sprayed particles R, as shown 
in FIG. 1. Since the coating base and hardening agent which form the 
layers Fa and Fi piled on the inner wall surface 5 is directly sprayed 
toward the object to be coated, each of the sprayed particles R has a 
couple of layers formed with the coating base and hardening agent, 
respectively, and therefore the coating base and hardening agent sprayed 
from the open end portion 4a of the funnel-like body 4 are mixed 
sufficiently with each other. As a result, the object to be coated is 
provided on its outer surface with a coating layer which is made uniform 
with the coating base composed of acrylic resin coating material including 
white pigment and the hardening agent of isocyanate which are mixed each 
other with a ratio in weight of the hardening agent to the coating base 
set to be one third. 
In the case where a change of color of the coating base is intended after 
the electrostatic spray coating for the object with use of the coating 
base composed of acrylic resin coating material including white pigment is 
finished as described above, in order to conduct next electrostatic spray 
coating for another object to be coated with use of the coating base 
composed of acrylic resin coating material including red pigment, the 
pumps 27 and 28 are shut off so that the coating base and instead agent 
are prevented from being drawn from the coating tank 33 and hardening 
agent tank 34, respectively, and instead of this the pump 37 provided for 
the pipe 35 for supplying the washing agent is started up. With the 
operation of the pump 37, the washing agent stored in the washing agent 
tank 38 is supplied through the pipe 35 to the nozzle 18. The flow 
controller 36 is operative to adjust the flow of the washing agent in the 
pipe 35 to be appropriate. The washing agent supplied to the nozzle 18 is 
discharged from the discharging opening 18a of the nozzle 18 to the inner 
wall surface 5 of the funnel-like body 4 of the rotary spray head device 2 
so as to wash the inside of the funnel-like body 4. 
After that, the pump 37 is stopped working, and instead the pumps 26 and 28 
are started up so that the coating base stored in the coating tank 32 and 
the hardening agent stored in the hardening agent tank 34 are supplied 
respectively through the pipes 20a and 20c to the nozzles 16a and 16c in 
the coating supply nozzle portion 16 with a ratio in weight of the 
hardening agent to the coating base set to be appropriate by the flow 
controllers 22 and 24. The coating base supplied to the nozzle 16a and the 
hardening agent supplied to the nozzle 16c are discharged simultaneously 
from the discharging openings 17a and 17c, respectively, to the inner wall 
surface 5 of the funnel-like body 4 of the rotary spray head device 2 
turning at the high speed. In this case also, the discharging openings 17a 
and 17c of the nozzles 16a and 16c are stacked in the direction along the 
radius of the funnel-like body 4 of in the vicinity of the inner wall 
surface 5 of the funnel-like body 4, as shown in FIG. 2, and therefore the 
coating base discharged from the discharging opening 17a of the nozzle 16a 
and the hardening agent discharged from the discharging opening 17c of the 
nozzle 16c impinge upon a common location on the inner wall surface 5 of 
the funnel-like body 4 of the rotary spray head device 2 turning at the 
high speed. 
Accordingly, the coating base and hardening agent supplied to the rotary 
spray head device 2 are caused to form their respective layers 
superimposed on the inner wall surface 5 of the funnel-like body 4 and to 
move toward the open end portion 4a of the funnel-like body 4 so as to be 
sprayed therefrom toward the object to be coated. As a result, the coating 
base and hardening agent sprayed from the open end portion 4a of the 
funnel-like body 4 are mixed sufficiently with each other, and the object 
to be coated is provided on its outer surface with a coating layer which 
is made uniform with the coating base composed of acrylic resin coating 
material including red pigment and the hardening agent of isocyanate mixed 
with each other at an appropriate ratio in weight of the hardening agent 
to the coating base. 
With use of the apparatus shown in FIG. 1, it is also possible to cause the 
pumps 26, 27 and 28 to operate simultaneously so that the coating base 
composed of acrylic resin coating material including red pigment and 
stored in the coating tank 32, the coating base composed of acrylic resin 
coating material including white pigment and stored in the coating tank 
33, and the hardening agent stored in the hardening agent tank 34 are 
supplied respectively through the pipes 20a, 20b and 20c to the nozzles 
16a, 16b and 16c in the coating supply nozzle portion 16, and then to 
cause the coating bases supplied to the nozzles 16a and 16b and the 
hardening agent supplied to the nozzle 16c to be discharged simultaneously 
from the discharging openings 17a, 17b and 17c, respectively, to the inner 
wall surface 5 of the funnel-like body 4 of the rotary spray head device 2 
turning at the high speed. The coating bases discharged from the 
discharging openings 17a and 17b of the nozzles 16a and 16b and the 
hardening agent discharged from the discharging opening 17c of the nozzle 
16c impinge upon a common location on the inner wall surface 5 of the 
funnel-like body 4 of the rotary spray head device 2 turning at the high 
speed. 
In such a case as described above, the coating bases discharged from the 
nozzles 16a and 16b and the hardening agent discharged from the nozzle 16c 
are caused to form their respective layers superimposed on the inner wall 
surface 5 of the funnel-like body 4 and to move toward the open end 
portion 4a of the funnel-like body 4 so as to be sprayed therefrom toward 
an object to be coated. As a result, the object to be coated is provided 
on its outer surface with a coating layer which is made uniform with the 
coating base composed of acrylic resin coating material including red 
pigment, the coating base composed of acrylic resin coating material 
including white pigment, and the hardening agent of isocyanate mixed with 
one another at an appropriate ratio in weight of the hardening agent to 
the coating bases. 
It is further possible to have the coating tanks 32 and 33 in the apparatus 
shown in FIG. 1 stored, for example, red coating and white coating both 
being of melamine alkyd resin, and to conduct electrostatic spray coating 
for an object to be coated with use of both the red and white coating in 
accordance with the method of the present invention. 
In this case, first, the pumps 26 and 27 are started up so that the red 
coating stored in the coating tank 32 and the white coating stored in the 
coating tank 33 are supplied respectively through the pipes 20a and 20b to 
the nozzles 16a and 16b in the coating supply nozzle portion 16 with a 
ratio in weight of the white coating to the red coating set to be 
appropriate by the flow controllers 22 and 23. Then, the red coating 
supplied to the nozzle 16a and the white coating supplied to the nozzle 
16b are discharged simultaneously from the discharging openings 17a and 
17b, respectively, to the inner wall surface 5 of the funnel-like body 4 
of the rotary spray head device 2 turning at the high speed. The red 
coating discharged from the discharging opening 17a of the nozzle 16a and 
the white coating discharged from the discharging opening 17b of the 
nozzle 16b impinge upon a common location on the inner wall surface 5 of 
the funnel-like body 4 of the rotary spray head device 2 turning at the 
high speed. 
Accordingly, the red coating and white coating supplied to the rotary spray 
head device 2 are caused to form their respective layers superimposed on 
the inner wall surface 5 of the funnel-like body 4 and to move toward the 
open end portion 4a of the funnel-like body 4 so as to be sprayed 
therefrom toward the object to be coated. As a result, the object to be 
coated is provided on its outer surface with a coating layer which is made 
uniform with the red coating and the white coating mixed with each other 
at an appropriate ratio in weight of the white coating to the red coating. 
Now, in relation to the case where two different kinds of coating are 
caused to impinge upon the inner wall surface 5 of the funnel-like body 4 
of the rotary spray head device 2 turning at a high speed and sprayed from 
the open end portion 4a of the funnel-like body 4 toward an object to be 
coated, such as mentioned above, the relation between a coating condition 
on the object to be coated and a distance L between locations on the inner 
wall surface 5 of the funnel-like body 4 upon which the two different 
kinds of coating impinge respectively, will be set forth below with 
reference to FIG. 3. FIG. 3 shows experimental results for the 
nonuniformity in color of coating disposed on the object on a graph which 
has the ordinate representing color difference .DELTA.E between each of 
coating layers disposed on the object and a reference color coating, and 
the abscissa representing the distance L. 
As apparent from FIG. 3, the color difference .DELTA.E is very small when 
the distance L is zero or close to zero, and the color difference .DELTA.E 
increases according as the increase of the distance L. This means that the 
object is provided on its outer surface with a coating layer having 
superior uniformity when the two different kinds of coating material are 
caused to impinge respectively upon locations close to each other on the 
inner wall surface 5 of the funnel-like body 4. Accordigly, it is to be 
clearly understood that the above mentioned object which is subjected to 
the electrostatic spray coating conducted with use of the red coating and 
white coating which are caused to impinge upon the common location on the 
inner wall surface 5 of the funnel-like body 4 in accordance with one 
embodiment of the method of -the present invention, is provided thereon 
will a coating layer superior in color uniformity. 
FIGS. 4 and 5 show parts of other embodiments of rotary spray head device 2 
each including the coating supply nozzle portion 16 and the circumference 
thereof. 
In the embodiment of rotary spray head device 2 shown in FIG. 4, a coating 
supply nozzle portion 16 comprises nozzles 50a and 50b for discharging 
coating bases, respectively, and a nozzle 50c for discharging a hardening 
agent. The nozzles 50a, 50b and 50c are connected respectively to the 
pipes 20a, 20b and 20c shown in FIG. 1 and each of the nozzles 50a, 50b 
and 50c has a compressed end portion in which each of discharging openings 
51a, 51b and 51c is provided. The discharging openings 51a, 51b and 51c 
which form a discharging opening end 17 are stacked in the direction along 
the radius of a funnel-like body 4 in the vicinity of an inner wall 
surface 5 of the funnel-like body 4. In the case of such embodiment, a 
coating base and a hardening agent or two different kinds of coating 
supplied thereto to be discharged to the inner wall surface 5 are 
facilitated to form their respective layers superimposed on the inner wall 
surface 5. 
In the embodiment of rotary spray head device 2 shown in FIG. 5, a coating 
supply nozzle portion 16 comprises nozzles 52a and 52b for discharging 
coating bases, respectively, and a nozzle 52c for discharging a hardening 
agent. The nozzles 52a, 52b and 52c are connected respectively to the 
pipes 20a, 20b and 20c shown in FIG. 1. The nozzle 52c has its end portion 
which is provided with a discharging openings 53c and inserted through an 
opening 40 provided on the nozzle 52b into an end portion of the nozzle 
52b in which a discharging opening 53b is provided. Further, the end 
portion of the nozzle 52b is inserted through an opening 42 provided on 
the nozzle 52a into an end portion of the nozzle 52a in which a 
discharging opening 53a is provided. The discharging openings 53a, 53b and 
53c are arranged concentrically to form a discharging opening end 17 and 
have respective portions stacked in the direction along the radius of a 
funnel-like body 4 in the vicinity of an inner wall surface 5 of the 
funnel-like body 4. 
In the case where one of the embodiments of rotary spray head device 2 
shown in FIGS. 2, 4 and 5 is used for the apparatus shown in FIG. 1, the 
coating supply nozzle portion 16 is provided to elongate in substantially 
parallel with the axis of rotation of the rotary spray head devices 2, and 
therefore it is feared that a fluid of the coating base and hardening 
agent or two different kinds of coating is discharged from the coating 
supply nozzle portion 16 to impinge upon the hub member 6 and a pulsation 
stream of the fluid arises on the inner wall surface 5, when the fluid is 
discharged in large quantities from the coating supply nozzle portion 16. 
Such pulsation stream of the fluid may give rise to a disadvantage that 
the coating base and hardening agent or the two different kinds of coating 
sprayed from the open end portion 4a of the funnel-like body 4 are not 
mixed uniformly with each other. 
When it is intended to avoid such disadvantage as mentioned above, a 
further embodiment of rotary spray head device 2 as shown in FIGS. 6A and 
6B is employed in the apparatus shown in FIG. 1. 
In the embodiment of rotary spray head device 2 shown in FIGS. 6A and 6B, a 
coating supply nozzle portion 16 comprises nozzles 54a and 54b for 
discharging coating bases, respectively, and a nozzle 54c for discharging 
a hardening agent. The nozzles 54a, 54b and 54c are connected respectively 
to the pipes 20a, 20b and 20c shown in FIG. 1 and each of the nozzles 54a, 
54b and 54c has an end portion which is provided therein with each of 
discharging openings 55a, 55b and 55c and bent toward the inner wall 
surface 5 of the funnel-like body 4 so as to cause each of discharging 
openings 55a, 55b and 55c to face the inner wall surface 5 of the 
funnel-like body 4. The discharging openings 55a, 55b and 55c which form a 
discharging opening end 17 are arranged in the direction, along the axis 
of rotation of the rotary spray head device 2, as shown clearly in FIG. 
6B. Incidentally, each of the end portions of the nozzles 54a, 54b and 54c 
is bent at such an angle that the coating base, hardening agent or coating 
material discharged therefrom is caused to impinge upon the inner wall 
surface 5 of the funnel-like body 4 with an incident angle of less than 45 
degrees measured with reference to a normal for the inner wall surface 5 
of the funnel-like body 4. 
In the case of such embodiment, the coating base and hardening agent or two 
different kinds of coating discharged from the nozzles 54a, 54b and 54c 
impinge directly upon the inner wall surface 5 of the funnel-like body 4 
even when the coating base and hardening agent or two different kinds of 
coating are discharged in large quantities from the nozzles 54a, 54b and 
54c. Accordingly, any pulsation stream of the coating base and hardening 
agent or two different kinds of coating are prevented from arising on the 
inner wall surface 5 of the funnel-like body 4. 
In relation to the case where two different kinds of coating are caused to 
impinge upon the inner wall surface 5 of the funnel-like body 4 of such a 
rotary spray head device 2 as shown in FIGS. 6A and 6B to be sprayed from 
the open end portion 4a of the funnel-like body 4 toward an object to be 
coated, the relation between a coating condition on the object to be 
coated and an incident angle .theta. to a normal for the inner wall 
surface 5 of each of the two different kinds of coating, will be set forth 
below with reference to FIG. 7. FIG. 7 shows experimental results for the 
ununiformity in color of coating deposited on the object on a graph which 
has the ordinate representing color difference .DELTA.E between each of 
coating layers deposited on the object and a reference color coating, and 
the abscissa representing the incident angle .theta. and in which a solid 
line .alpha., broken line .beta. and dot-dash line .gamma. stand for 
results obtained under discharging quantities of 300 ml/min, 200 ml/min 
and 50 ml/min, respectively. As apparent from FIG. 7, the color difference 
.DELTA.E is relatively large regardless of the discharging quantity under 
the situation in which the incident angle .theta. is more than about 60 
degrees, is relatively small only when the discharging quantity is small 
under the situation in which the incident angle .theta. is more than about 
45 degrees but less than about 60 degrees, and is relatively small 
regardless of the discharging quantity under the situation in which the 
incident angle .theta. is less than about 45 degrees. 
Accordingly, it is to be clearly understood that an object to be coated 
which is subjected to the electrostatic spray coating conducted with use 
of the embodiment of the rotary spray head device shown in FIGS. 6A and 6B 
in which each of the coating base and hardening agent or two different 
kinds of coating is caused to impinge upon the inner wall surface 5 of the 
funnel-like body 4 with the incident angle of less than 45 degrees in 
accordance with one embodiment of method of the precent invention, is 
provided thereon the coating layer superior in color uniformity. 
In the case where one of the embodiments of rotary spray head device 2 
shown in FIGS. 2, 4, 5, 6A and 6B is used for the apparatus shown in FIG. 
1, the discharging openings forming the discharging opening end 17 are 
close to one another and therefore it is feared that the hardening agent 
will act upon the coating base so as to harden the same at the location of 
the discharging opening end 17 and as a result the coating base and 
hardening agent will be prevented from being discharged properly from the 
discharging opening end 17 the inner wall surface 5 of the funnel-like 
body 4. 
When it is intended to avoid such a problem, a still further embodiment of 
rotary spray head device 2 as shown in FIGS. 8A and 8B is employed in the 
apparatus shown in FIG. 1. 
In the embodiment of rotary spray head device 2 shown in FIGS. 8A and 8B, a 
coating supply nozzle portion 6 comprises nozzles 56a and 56b for 
discharging coating bases, respectively, and a nozzle 56c for discharging 
a hardening agent. These nozzles 56a, 56b and 56c are connected 
respectively to the pipes 20a, 20b and 20c shown in FIG. 1. Discharging 
openings 57a, 57b and 57c of the nozzles 56a, 56b and 56c, which form the 
discharging opening end 17, are stacked with a space between each adjacent 
two thereof in the direction along the radius of the funnel-like body 4 of 
the rotary spray head device 2 in the vicinity of the inner wall surface 5 
of the funnel-like body 4. Further., an end portion of each of the nozzles 
56a, 56b and 56c, in which each of the discharging openings 57a, 57b and 
57c is provided, is bent toward the inner wall surface 5 of the 
funnel-like body 4 so as to cause each of the discharging openings 57a, 
57b and 57c to face the inner wall surface 5 of the funnel-like body 4. 
In the case of such embodiment, since the discharging openings 57a, 57b and 
57c of the nozzles 56a, 56b and 56c are arranged with the space between 
each adjacent two, the hardening agent discharged from the discharging 
openings 57c is prevented from acting upon the coating base discharged 
from at least one of the discharging openings 57a and 57b so as to harden 
the same at the locations of the discharging openings 57a, 57b and 57c, 
and the coating base discharged from at least one of the discharging 
openings 57a and 57b and the hardening agent discharged from the 
discharging opening 57c meet each other in the air to impinge together 
upon the inner wall surface 5 of the funnel-like body 4. 
Although the discharging openings 57a, 57b and 57c of the nozzles 56a, 56b 
are stacked in the direction along the radius of the funnel-like body 4 of 
the rotary spray head device 2 in the embodiment of rotary spray head 
device 2 shown in FIGS. 8A and 8B, it is possible to arrange the 
discharging openings 57a, 57b and 57c of the nozzles 56a, 56b and 56c with 
a predetermined space between each adjacent two thereof in the direction 
along the circumference of a circle around the axis of rotation of the 
rotary spray head device 2, in such a manner as shown as discharging 
openings 59a, 59b and 59c of nozzles 58a, 58b and 58c in FIG. 9. 
FIG. 10 shows a further different embodiment of rotary spray head device 2 
for use in the apparatus shown in FIG. 1. This embodiment of rotary spray 
head device 2 is intended to have reduced flow resistance at the inside 
thereof. 
In the embodiment of rotary spray head device 2 shown in FIG. 2, an inner 
wall surface 5 of a funnel-like body 4 is covered by a surface treating 
layer 44 which contributes to reduce flow resistance against a coating 
base and hardening agent or coating on the inner wall surface 5. The 
surface treating layer 44 is formed with a layer of fluoridated resin, a 
plating layer including nickel and fluoridated resin, flame coating layer 
of molybdenum, or the like. The inner wall surface 5 which is covered by 
the surface treating layer 44 is previously processed to have surface 
roughness reduced sufficiently, for example, such surface roughness as 
containing the maximun height less than 0.5 .mu.. 
Although the coating supply nozzle portion 16 is constituted to include the 
nozzle for discharging a hardening agent in addition to the nozzles for 
discharging coating bases or different kinds of coating material in the 
embodiments described above, it is to be understood that another coating 
supply nozzle portion which does not include a nozzle for discharging the 
hardening agent may be employed in place of the coating supply nozzle 
portion 16.