Spray gun type electrostatic paint coating machine

A spray gun type electrostatic paint coating machine which is capable of improving quality of coated surfaces, the coating machine including an air nozzle (8) and a paint nozzle (21) respectively provided at the fore end of a spray gun body (6). The spray gun body (6) and the air nozzle (8) are made of an electrically insulating material, while the paint nozzle (21) is made of a metallic material including a paint spouting orifice (21C) which is projected on the front side through the air nozzle (8). The paint spouting orifice (21C) is connected to ground through a paint supply passage (10) to serve as a grounding electrode. Sprayed paint particles are at the earth potential, so that they are less susceptible to influences of dielectric polarization and negatively charged quickly by the high negative voltage of the external electrode. As a consequence, sprayed paint particles are prevented from depositing on the air nozzle (8) or other negatively charged surfaces and falling down in the form of discrete dot-like driblets to contaminate a coated surface.

TECHNICAL FIELD 
This invention relates to a spray gun type electrostatic paint coating 
machine particularly suitable for use in spray-coating a water-base paint 
or a metallic paint. 
BACKGROUND ART 
Generally, paints which have been in use for electrostatic coating can be 
largely classified into solvent type paints (oil-base paints) which are 
relatively large in electrical resistance and water-base paints (water 
paints) which are relatively small in electrical resistance. Further, 
there have been in use the so-called metallic paints which have metallic 
powder dispersed in a solvent type paint or in a water-base paint. 
Similarly to water-base paints, metallic paints are known to be relatively 
small in electrical resistance. As will be gathered therefrom, the paints 
which are currently in use have different values in electrical resistance 
depending upon the type, necessitating to employ different methods for 
paints of different types in applying voltage thereto in electrostatic 
spray-coating operations. 
More specifically, normally a paint supply passage, a paint tank and a 
color-changer of a coating machine are grounded during coating operations 
from a viewpoint of preventing dangerous situations, although solvent type 
paints have a relatively large electrical resistance. Therefore, in the 
case of a solvent type paint, even if a high voltage is applied to a 
center electrode on a spray gun body directly from an external high 
voltage generator, there is little possibility of the spray gun body being 
grounded to the earth potential through the paint supply passage. For this 
reason, with a solvent type paint spray gun, it has been the usual 
practice to charge paint particles by applying a high voltage directly to 
the spray gun body. 
On the other hand, in the case of a water-base paint or a metallic paint of 
low electrical resistance, if a high voltage is applied directly to a 
center electrode provided on a spray gun body, it is very likely that the 
spray gun body is easily short-circuited to the earth potential, failing 
to charge paint particles to any practical degree. 
In this regard, in the case of a water-base paint or a metallic paint, 
prior art spray gun type electrostatic paint coating machines employ an 
external electrode system having an external electrode body located 
radially outward of a spray gun body which is connected to ground, and 
supplying a high voltage (e.g., of -60 kV to -90 kV) to the external 
electrode through a high resistance and high voltage cable. 
Shown by way of example in FIGS. 8 and 9 is a prior art spray gun type 
electrostatic paint coating machine employing an external electrode of the 
sort as mentioned above. 
In these figures, indicated at 1 is a spray gun type electrostatic paint 
coating machine, which includes a mount member 2 to be fixed on a 
reciprocator (not shown) or the like, a valve mount structure 3 supporting 
thereon paint valves 16 and 17 along with a drain valve (not shown), a 
coating machine head 4 securely fixed on the valve mount structure 3, and 
an external electrode 5 securely fixed at one side of the valve mount 
structure 3 and disposed parallel with and outward of the circumference of 
the coating machine head 4. 
The construction of the coating machine head 4 is shown in detail in FIG. 
9. 
In FIG. 9, the reference 6 denotes a spray gun body of an elongated tubular 
form, which is formed of an electrically insulating synthetic resin 
material such as polytetrafluoroethylene (PTFE) or polyethylene 
terephthalate (PET) or the like. The spray gun body 6 is formed with an 
rearwardly tapered recess at its fore distal end to provide a nozzle 
receptacle 6A which receives a paint nozzle 7, which will be described 
below. The rear or base end of the spray gun body 6 is securely fixed to 
the valve mount structure 3. 
The paint nozzle 7, which is also made of an electrically insulating 
synthetic resin material such as PTFE, PET or the like, is threaded 
centrally into the fore distal end of the spray gun body 6, and internally 
provided with a paint supply passage. In this instance, the paint nozzle 7 
is constituted by a rearwardly tapered fitting portion 7A which fits in 
the nozzle receptacle portion 6A of the spray gun body 6, a valve seat 
portion 7B projected forward from the bottom portion and reduced into a 
smaller diameter toward its fore end for seating and unseating a needle 
valve body 18 as will be described later, a paint spouting orifice 7C 
provided at the fore end of the valve seat portion 7B for spraying a paint 
when the needle valve body 18 is opened, an atomizing air passage 7D 
formed around the outer periphery of the valve seat portion 7B, and an 
annular projection 7E positioned around the outer periphery of the 
atomizing air passage 7D and projected forward in the form of an annular 
ring of a larger diameter and in abutting engagement with a recessed 
portion 8A of an air nozzle 8 which will be described below. 
The air nozzle 8, which covers the fore end of the paint nozzle 7, is 
securely fixed on a fore end portion of the spray gun body 6 through a 
retainer ring 9. The air nozzle 8 is also made of an electrically 
insulating synthetic resin material such as PTFE, PET or the like, and 
constituted by a recessed portion 8A which is held in abutting engagement 
with the above-described annular projection 7E, a front wall portion 8B 
which is formed in such a manner as to cover the front side of the 
recessed portion 8A, forwardly projecting horn portions 8C which are 
provided in radially opposing positions on the upper and lower sides of 
the front wall portion 8B, a nozzle threading hole 8D bored through the 
front wall portion 8B at a position on the center axis of the front wall 
portion to receive a forwardly projected open end of the paint spouting 
orifice 7C, a large number of atomizing air outlets 8E formed in the front 
wall portion 8B around the centrally located nozzle holder hole, and 
patterning air spout holes 8F (only two of which are shown in the drawing) 
which are formed in the horn portions 8C and opened obliquely in an inward 
direction. The air nozzle 8 functions to accelerate atomization of a paint 
which is sprayed forward from the paint spouting orifice 7C of the paint 
nozzle 7, by spurting atomizing air blasts from the nozzle threading hole 
8D and the respective atomizing air outlets 8E, while blowing patterning 
air toward a spray of atomized paint particles from the patterning air 
outlets 8F to shape the spray into an elliptic or oval form. 
Denoted at 10 is a paint supply passage which is formed between the needle 
valve body 18 and the spray gun body 6, and which is connected to a front 
paint valve 16 and a rear paint valve 17 as will be described below. 
Through this paint supply passage 10, the paint is maintained at the earth 
potential. Indicated at 11 is a paint drain passage which connects a fore 
end portion of the paint supply passage 10 to an external drain tank 
through a drain valve (not shown) which is provided in the paint drain 
passage 11. The reference 12 indicates an atomizing air supply passage 
which is bored axially through the spray gun body 6. 
Shown at 13 is an external electrode which is located at a position 
radially outward of the spray gun body 6. The external electrode 13 is 
retained in position by an external electrode holder 14. In this instance, 
the external electrode holder 14 is made of an electrically insulating 
synthetic resin material such as PTFE, PET or the like, and formed in a 
bottle-like shape in outer configuration having a larger diameter portion 
14A and a smaller diameter portion 14B respectively at the rear and fore 
end portions of a rod-like body with a tapered shoulder portion 14C. The 
external electrode 13 is connected to a high voltage generator (not shown) 
through a lead wire 15 which is connected to a rear base end portion of 
the external electrode holder 14. Namely, from a high voltage generator 
which is not shown, a high voltage is supplied to the external electrode 
13 through the lead wire 15. 
Indicated at 16 and 17 are the afore-mentioned front and rear paint valves 
which are provided within the length of the paint supply passage 10 on the 
valve mount structure 3. These front and rear paint valves 16 and 17 are 
connected to a paint tank and a color changing device which are also 
grounded to earth. Further, these paint valves 16 and 17 are arranged as 
spring return type 2-port 2-position pneumatic change-over valves which 
can be switched into desired positions by charging and discharging 
compressed air. As soon as both of the paint valves 16 and 17 are opened, 
a paint is fed to the paint nozzle 7 from an external color changing 
device which is not shown. 
In this instance, the paint valve 16 on the front side has a valve body in 
the form of a needle valve body 18 of a conductive metal as shown in FIG. 
9. For example, the needle valve body 18 is made of stainless steel or 
other conductive metallic material. The needle valve body 18 is connected 
to an air-driven actuator at its rear end and extended forward in the 
axial direction of the spray gun body 6 in its fore end portion 
terminating in a fore distal end portion 18A of the needle valve body 18 
to be seated on and off the valve seat portion 7B on the part of the paint 
nozzle 7. Accordingly, when compressed air is supplied to the front paint 
valve 16, the fore distal end portion 18A of the needle valve body 18 is 
unseated from the valve seat portion 7B to open the paint spouting orifice 
7C, permitting the paint in the paint supply passage 10 to spurt out 
forward of the paint nozzle 7. 
In operation, the above-described prior art spray gun type electrostatic 
coating machine 1 functions in the manner as follows. Now, if a high 
voltage of -60 to -90 kV is applied to the external electrode 13, a 
charging electrostatic field zone (an ionizing zone) is formed between the 
external electrode 13 and the paint supply passage 10 which is at the 
earth potential, and at the same time a paint transporting electrostatic 
field zone is formed by lines of electrical forces between the external 
electrode 13 and an article (not shown) to be coated. The paint particles 
sprayed out of the paint nozzle 7 are negatively charged indirectly by 
negative ions while passing through the charging electrostatic field zone, 
and the charged paint particles are transported along the paint 
transporting electrostatic field zone toward and deposited on the coating 
article. 
In this manner, even a water-base paint or a metallic paint, which is 
relatively low in electrical resistance, can be coated on an article by 
the use of a spray gun type electrostatic coating machine with an external 
electrode. 
In this connection, it is to be noted that, in the above-described prior 
art spray gun type electrostatic coating machine 1, sprayed paint 
particles are firstly spouted in the form of liquid threads from the paint 
spouting orifice 7C of the paint nozzle 7 and then divided into fine 
particles by the action of atomizing air blasts from the atomizing air 
outlets 8E, forming a predetermined paint spray pattern under the 
influence of the action of patterning air from the patterning air outlets 
8F. However, under circumstances like this, the atomized paint particles 
are not necessarily subjected uniformly to the energy of atomizing air, 
often developing turbulent flows in outer peripheral regions of the spray 
pattern in addition to temporary stagnation of paint particles around the 
air nozzle 8 off the spray pattern, to a certain degree depending upon 
differences in particle size and traveling speed. 
Besides, the paint nozzle 8 and the air nozzle 7, which are formed of an 
insulating synthetic resin material, each act as a dielectric tending to 
hold negative charges on their surfaces under the influence of the high 
voltage output of the external electrode 13. 
Further, immediately after being sprayed from the paint spouting orifice 7B 
of the paint nozzle 7, the sprayed paint particles undergo the phenomenon 
of dielectric polarization due to a large voltage difference between the 
paint nozzle 7 and the external electrode 13, and therefore the paint 
particles are imparted with a tendency toward positive charging. 
Consequently, a part of the paint particles, just sprayed out from the 
paint nozzle have a tendency toward positive charging and are urged to 
deposit immediately on and around the negatively charged air nozzle 8 to 
cause contamination of the air nozzle 8 and adjacent surfaces. Especially, 
the paint particles which fall off the spray pattern and stagnate 
temporarily around the air nozzle 8 in the manner as mentioned 
hereinbefore, are more likely to be adsorbed on the surfaces of the air 
nozzle 8 because of their tendency toward positive charging instead of 
negative charging. 
These behaviors of sprayed paint particles lead to paint deposition on and 
in the vicinity of the air nozzle 8, which falls off the coating machine 
to deposit on a coated surface of an article as discrete dots of small 
diameters (generally referred to as "paint driblets") which degrade the 
quality of coatings to a considerable degree. 
In view of the above-described problems or drawbacks of the prior art, it 
is an object of the present invention to provide a spray gun type 
electrostatic paint coating machine which is capable of negatively 
charging paint particles quickly as soon as they are sprayed from a paint 
nozzle. 
DISCLOSURE OF INVENTION 
In accordance with the present invention, the above-stated objective is 
achieved by the provision of a spray gun type electrostatic paint coating 
machine which essentially includes: a spray gun body; a paint nozzle 
located at the fore end of the spray gun body and having a paint spouting 
orifice to spray a paint toward an article to be coated; a paint valve 
provided in the spray gun body and having a needle valve body to open and 
close the paint nozzle for opening and stopping supply of the paint to the 
paint nozzle through the paint supply passage; and an external electrode 
located in a position radially outward of the spray gun body; 
characterized in that: the spray gun body is made of an electrically 
insulating material and provided with a grounding electrode at or in the 
vicinity of the paint spouting orifice. 
In accordance with the present invention, there is also provided a spray 
gun type electrostatic paint coating machine which essentially includes: a 
spray gun body; a paint nozzle located at the fore end of the spray gun 
body and having a paint spouting orifice to spray a paint toward an 
article to be coated; an air nozzle securely mounted on the spray gun body 
in such a way as to cover the front side of the paint nozzle while 
exposing the paint spouting orifice to the outside; a paint valve provided 
in the spray gun body and having a needle valve body to open and close the 
paint nozzle for opening and stopping the supply of the paint to the paint 
nozzle through the paint supply passage; and an external electrode located 
in a position radially outward of the spray gun body; characterized in 
that: the spray gun body and the air nozzle are made of an electrically 
insulating material and provided with a grounding electrode in the 
vicinity of the paint spouting orifice. 
The provision of the grounding electrode in the vicinity of the paint 
spouting orifice makes it possible to hold the paint particles 
approximately at the earth potential immediately after they are sprayed 
from the paint spouting orifice, thereby lessening the influences of 
dielectric polarization as would otherwise occur due to a voltage 
difference between the paint spouting orifice and the external electrode, 
letting sprayed paint particles be negatively charged in an accelerated 
manner by the high negative voltage generated by the external electrode. 
In this particular form of the invention, the paint nozzle is made of a 
conductive material to function as a grounding electrode at or in the 
vicinity of the outer end of its paint spouting orifice, utilizing the 
paint spouting orifice of the paint nozzle for the grounding electrode 
which permits to spray paint particles at a potential which is akin to the 
earth potential. 
Alternatively, according to the invention, the needle valve body is 
provided with a grounding electrode which is projected forward through the 
paint spouting orifice of the paint nozzle, similarly permitting to spray 
paint particles approximately at the earth potential and forward of the 
projected end of the paint spouting orifice. 
Further, in accordance with the present invention, the paint nozzle is made 
of a conducting material only at a fore paint spouting end portion, and 
the remainder of the nozzle is made of an electrically insulting material. 
In this case, a paint spouting end portion of the paint nozzle serves as a 
grounding electrode for spraying paint particles forward approximately at 
the earth potential. 
In this instance, the grounding electrode is maintained at the earth 
potential by way of the paint which flows through the paint supply 
passage, more specifically, by way of a water-base paint or other 
conductive paint of low electrical resistance. 
Furthermore, the above-described grounding electrode may be maintained at 
the earth potential by way of a grounding wire which is additionally 
provided on the spray gun body.

BEST MODE FOR CARRYING OUT THE INVENTION 
The present invention is described more particularly by way of its 
preferred embodiments with reference to the accompanying drawings. 
Illustrated in FIG. 1 is a first embodiment of the invention, in which the 
component parts common with the above-described prior art counterpart are 
simply designated by common reference numerals or characters without 
repeating same explanations. 
In this figure, indicated at 21 is a paint nozzle which is employed in this 
embodiment in place of the prior art paint nozzle 7 of an insulating 
synthetic resin material. The paint nozzle 21 is made of a conducting 
metallic material such as brass, stainless steel or the like to serve as a 
grounding electrode as will be described below. 
The paint nozzle 21 is shaped similarly to the prior art paint nozzle 7 
described above, including an internal paint passage and a configuration 
which is tapered toward its rear end. In this particular embodiment, the 
paint nozzle 21 is largely constituted by a fitting portion 21A which is 
fitted in a nozzle receptacle recess 6A on a spray gun body 6, a valve 
seat portion 21B for seating and unseating a needle valve body 18, a paint 
spouting orifice 21C provided at the fore end of the valve seat portion 
21B to spray a paint forward when the needle valve body 18 is opened, an 
atomizing air passage 21D formed around the outer periphery of the valve 
seat portion 21B, and an annular projection 21E in the form of an annular 
ring of a larger diameter located around the outer periphery of the 
atomizing air passage 21D and projected forward into abutting engagement 
with a recess 8A on an air nozzle 8. The paint spouting orifice 21C of the 
paint nozzle 21 is protruded and opened to the outside through a nozzle 
threading hole 8D of the air nozzle 8. 
The above-described paint supply passage 10 is maintained approximately at 
the earth potential by way of a metallic or water-base paint of low 
electrical resistance, which flows through the paint supply passage 10, 
and the paint valves 16 and 17 which are grounded through respective paint 
tanks and a color changing device (which are not shown). Therefore, the 
paint nozzle 21 which is made of a conducting material is maintained at 
the earth potential through the paint supply passage 10, so that the paint 
spouting orifice 21C of the paint nozzle 21 can serve as a grounding 
electrode. Further, the needle valve body 18 which is likewise made of a 
conducting metallic material contributes to maintain the paint nozzle 21 
at the earth potential in cooperation with the paint supply passage 10. 
In a manner similar to the prior art counterpart described hereinbefore, 
the electrostatic paint coating machine of this embodiment with the 
foregoing arrangements is operated to spray paint particles forward from 
the paint spouting orifice 21C. The sprayed paint particles are negatively 
charged in a charging electrostatic field zone (an ionizing zone) formed 
between the external electrode 13 and the paint nozzle 21, which serves as 
a grounding electrode at or in the vicinity of the paint spouting orifice 
21C. The negatively charged paint particles are then urged to travel 
toward and deposit on a coating article, through a paint transporting 
electrostatic field zone which is formed between the external electrode 13 
and the coating article. 
In this regard, according to the above-described embodiment of the 
invention, the spray gun body 6 and the air nozzle 8 are made of an 
insulating synthetic resin material while the paint nozzle 21 is made of a 
metallic material and has its paint spouting orifice 21C projected forward 
of the front wall 8B of the air nozzle 8. Therefore, in a coating 
operation, the paint nozzle 21 is grounded by way of the paint of low 
electrical resistance, which flows through the paint supply passage 10, so 
that it serves as a grounding electrode at or in the vicinity of the paint 
spouting orifice 21C. 
Therefore, the paint spouting orifice 21C is capable of spraying paint 
particles forward approximately at the earth potential, thereby 
suppressing the influences of dielectric polarization which would 
otherwise occur due to a voltage difference between the paint spouting 
orifice 21C and the external electrode 13. It follows that the sprayed 
paint particles, just coming out of the paint spouting orifice 21C, are 
still electrically in a neutral state (at the earth potential) instead of 
picking up a tendency toward positive charging, and can be negatively 
charged promptly in the negatively charging electrostatic field zone which 
is formed by the external electrode 13. In this case, it is possible to 
effect the negative charging even to those paint particles which fall off 
the spray pattern and tend to stagnate around or in the vicinity of the 
air nozzle 8. 
As a consequence, since the air nozzle 8 and the spray gun body 6 are made 
of an insulating synthetic resin material, it becomes possible to 
negatively charge sprayed paint particles in an accelerated manner even in 
a case where surfaces of the air nozzle 8 are constantly in a negatively 
charged state under the influence of the high voltage from the external 
electrode 13, thereby preventing contamination of the air nozzle 8 by 
deposition of paint particles, which would eventually drop on a coated 
surface to form the so-called driblets or similar dot-like defects 
thereon. Accordingly, there can be obtained finish coatings of improved 
quality, free of contamination as caused by falling paint driblets. 
In place of the needle valve body 18 of a metallic material which is 
employed for the paint valve 16 in the foregoing first embodiment 
similarly to the prior art counterpart, a needle valve body 31 of an 
insulating synthetic resin material may be used as shown in the 
modification of FIG. 2. In this case, the paint nozzle 21 also functions 
as a grounding electrode through a paint of low electrical resistance 
which flows through the paint supply passage 10, producing substantially 
the same effects as in the first embodiment. 
Referring now to FIG. 3, there is shown a second embodiment of the 
invention, which is characterized by the provision of a grounding 
electrode which is embedded in the needle valve body of the front paint 
valve 16 in such a manner as to project through the paint spouting 
orifice. In the following description of this embodiment, the component 
parts identical with the corresponding parts in the foregoing first 
embodiment are simply designated by the same reference numerals or 
characters to avoid repetition of the same explanations. 
In FIG. 3, indicated at 41 is a needle valve body which is employed in this 
embodiment in place of the needle valve body 18 of the first embodiment. 
The needle valve body 41 is extended axially toward the fore end of the 
spray gun body 6, the needle valve body 41 having a fore end portion 41A 
to be seated and unseated on and off the valve seat portion 7B of the 
paint nozzle 7 which is formed of an insulating synthetic resin material. 
Denoted at 42 is a grounding electrode which is provided axially within the 
needle valve body 41, the grounding electrode 42 having its base end 
grounded through an air-driven actuator of the front paint valve 16 and 
its fore end 42A projected forward of the front wall portion 8B of the air 
nozzle 8. 
In the case of the electrostatic paint coating machine of this embodiment 
with the above-described arrangements, paint particles sprayed forward 
from the paint spouting orifice 7C are also negatively charged in the 
charging electrostatic field zone formed between the external electrode 13 
and the fore end 42A of the grounding electrode 42 which is retained at 
the earth potential. Charged paint particles are transferred toward and 
deposited on an article to be coated, through the paint transporting 
electrostatic field zone which is formed between the external electrode 13 
and the coating article. 
Further, according to this embodiment employing the grounding electrode 42 
which has its fore end 42A projected outward through the paint spouting 
orifice 7C, paint particles just sprayed out through the paint spouting 
orifice 7C stay approximately at the earth potential by contact with the 
fore end 42A of the grounding electrode 42. Being almost at the earth 
potential, the sprayed paint particles are less susceptible to the 
influences of dielectric polarization which occurs due to a voltage 
difference between the paint spouting orifice 7C and the external 
electrode 13, and readily undergo negative charging by the charging 
electrostatic field zone which is formed by the external electrode 13. As 
a result, even if the air nozzle 8 of insulating synthetic resin material 
holds negative charges on its surfaces, freshly sprayed paint particles 
are prevented from depositing on the air nozzle 8 to ensure higher finish 
quality of coated surfaces free of contamination by falling paint driblets 
as would result from paint deposition on the air nozzle 8. 
Further, according to the invention, in place of the metallic needle valve 
body 41 of the paint valve 16 in the above-described second embodiment, 
there may be employed a needle valve body 51 of an insulating synthetic 
resin material as shown in FIG. 4, the needle valve body 51 similarly 
having its fore end portion 51A so shaped as to be seated and unseated on 
and off the valve seat portion 7B of the paint nozzle 7 and holding a 
grounding electrode 52 which is outwardly projected at its fore end 52A to 
produce the same effects as in the second embodiment. In the second 
embodiment, if desired, the grounding electrode 42 may be formed as an 
integral part of the needle valve body 41 of a conducting metallic 
material. 
Referring to FIG. 5, there is shown a third embodiment of the invention, 
which is characterized by a paint nozzle which is made of a combination of 
an insulating synthetic resin material and a conducting metallic material. 
In the following description of the third embodiment, those component 
parts which are common with the foregoing first embodiment are simply 
designated by common reference numerals or characters without repeating 
same explanations. 
In FIG. 5, indicated at 61 is a paint nozzle which is employed in this 
embodiment, the paint nozzle 61 being constituted by a fitting portion 
61A, a valve seat portion 61B and an atomizing air passage 61D, which are 
made of an insulating synthetic resin material as will be described later, 
and a paint spouting orifice 61C which is made of a conducting metallic 
material separately from other parts of the paint nozzle. 
With regard to the shape, the paint nozzle 61 is internally formed with a 
paint passage in the same manner as the prior art paint nozzle 7, and 
constituted by a fitting portion 61A which is tapered off toward its rear 
end to fit tightly in the nozzle receptacle portion 6A on the spray gun 
body 6, a valve seat portion 61B for seating and unseating the needle 
valve body 18, a paint spouting orifice 61C of a conducting metallic 
material which is projected forward of the valve seat portion 61B to spray 
the paint when the needle valve body 18 is opened, an atomizing air 
passage 61D which is formed around the outer periphery of the valve seat 
portion 61B, and an annular projection 61E which is located around the 
outer periphery of the atomizing air passage 61D and projected forward in 
the form of an annular ring of a larger diameter on the front side and in 
abutting engagement against the recessed receptacle portion 8A of the air 
nozzle 8. 
As described above, in this embodiment, the paint spouting orifice 61C 
alone is made of a conducting metallic material, and integrally joined 
with the remainder of the nozzle by resin molding, more specifically, 
integrally with the fitting portion 61A, valve seat portion 61B and 
annular projection 61E which are made of an insulating synthetic resin 
material. 
In the case of the electrostatic paint coating machine of this embodiment 
employing the above-described arrangements, i.e., employing the paint 
nozzle 61 with the paint spouting orifice 61C of a conducting metallic 
material formed separately from the fitting portion 61A, valve seat 
portion 61B and annular projection 61E of an insulating material, the 
paint nozzle 61 is retained substantially at the earth potential at the 
paint spouting orifice 61C. Consequently, in the same manner as in the 
foregoing embodiments, paint particles still remain at the earth potential 
at the instant when they are sprayed out through the paint spouting 
orifice 61C, and therefore positively charged immediately in the charging 
electrostatic field zone which is formed by the external electrode 13, 
also making it possible to enhance the quality of coatings. 
Although the needle valve body 18 of the paint valve 16 in the 
above-described third embodiment is made of a metallic material as in the 
prior art coating machine, it may employ a needle valve body 31 of an 
insulating synthetic resin material as in the modification shown in FIG. 
6. In this case, the paint spouting orifice 61C of the paint nozzle 61 can 
also function as a grounding electrode through a paint of low electrical 
resistance which flows through the paint supply passage 10, producing 
substantially the same effects as in the third embodiment. 
Further, the paint nozzle 21 is maintained at the earth potential by way of 
a paint of low resistance which flows through the paint supply passage 10. 
However, the present invention can be realized by other means, for 
example, by the use of a grounding wire 71 which is provided on the spray 
gun body 6 as shown in FIG. 7. Alternatively, a similar grounding wire may 
be provided on the spray gun body 6 if desired. 
Furthermore, although the coating machine 4 in each of the foregoing 
embodiments employs an air atomization type spray gun, the present 
invention is similarly applicable to a spray gun of a hydraulically 
atomizing type using a lip-shaped nozzle tip for spouting out and 
atomizing a paint under high pressure. 
INDUSTRIAL APPLICABILITY 
As described in detail hereinbefore, the present invention employs a 
grounding electrode at or in the vicinity of a paint spouting orifice and 
in combination with a spray gun body and/or an air nozzle which are made 
of an insulating material, thereby making it possible to spray paint 
particles from the paint spouting orifice substantially at the earth 
potential and to let the sprayed paint particles be negatively charged 
quickly by the high negative voltage generated by the external electrode, 
substantially free of the influences of dielectric polarization which 
would otherwise take place due to a voltage difference between the paint 
spouting orifice and the external electrode. Consequently, it becomes 
possible to prevent contamination of the spray gun body and air nozzle of 
insulating material while improving the quality of coatings on articles. 
In this case, by making the paint nozzle of a conducting material, the 
paint spouting orifice of the paint nozzle can be used as a grounding 
electrode which serves to hold the paint approximately at the earth 
potential at the instant when it is sprayed in the form of atomized 
particles. Accordingly, as soon as the paint is sprayed out, paint 
particles are negatively charged readily by the high negative voltage from 
the external electrode, allowing the operator to carry out a coating work 
without being troubled by contamination of the spray gun body or air 
nozzle. 
Further, a grounding electrode may be provided on the needle valve body of 
the paint valve in such a way as to project on the front side through the 
paint spouting orifice of the paint nozzle, thereby holding paint 
particles approximately at the earth potential when they are sprayed 
forward from the paint spouting orifice and letting them undergo negative 
charging by the high negative voltage from the external electrode 
immediately as soon as they come out of the paint spouting orifice. As a 
consequence, the operator is similarly allowed to carry out a coating 
operation free of contamination of the spray gun body and air nozzle. 
Furthermore, a grounding electrode may be provided at the paint spouting 
orifice of the paint nozzle by making the paint spouting orifice of a 
conducting material while making the remainder of the paint nozzle of an 
insulating material, thereby spraying paint particles almost at the earth 
potential and similarly letting them undergo negative charging by the high 
negative voltage from the external electrode immediately as soon as they 
come out of the paint nozzle. 
On the other hand, in accordance with the present invention, the grounding 
electrode itself is maintained at the earth potential by way of a 
conducting water-base paint or a paint of low resistance which flows 
through the paint supply passage. 
Moreover, according to the present invention, the grounding electrode can 
be maintained at the earth potential by way of a grounding wire which is 
provided additionally on the spray gun body.