JPH1071346A - Electrostatic powder coating method for inner surface of can barrel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic powder coating method for the inner surface of a can barrel which can coat the surface efficiently at a desired uniform thickness. SOLUTION: A can barrel 1 one end part of which is narrowed is grounded. First, a charged powdered coating 4 is sprayed from an open end 3 opposite to the narrowed open end 2 of the barrel 1 on the inner surface of the barrel 1, and air is sucked from the narrowed open end 2 on the opposite side to form an air flow to conduct the first process in which the powdered coating 4 is applied mainly to an area on the side of the open end 3 of the inner surface of the barrel 1. Next, the charged powdered coating 4 is sprayed from the narrowed open end 2 of the barrel 1 on the inner surface of the barrel 1, and air is sucked from the open end 3 on the opposite side to form an air flow to conduct the second process in which the powdered coating 4 is applied mainly to an area on the side of the narrowed open end 2 of the inner surface of the barrel 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic powder coating method for an inner surface of a can body, and more particularly to an electrostatic powder coating method for an inner surface of a can body having a reduced diameter at one end and an opening at both ends, such as a neck-in can. Related to the painting method.

[0002]

2. Description of the Related Art Conventionally, beverage cans and aerosol cans have been
Neck-in can body obtained by rolling a metal plate with painted printing on the inside and outside surfaces into a cylindrical shape, overlapping the both edges and welding, then correcting the welding seam, and then neck-in one end A three-piece can with a lid wound around is used. For example, in a neck-in aerosol can, one end of a cylindrical can body having both ends opened is reduced in diameter, and a mountain cup provided with a valve for ejecting the content at the reduced opening end. Are closed and the other end is closed with a bottom cover wound around the other end. The inner surface of such a can body was coated with a solvent-based paint to protect the contents and prevent corrosion of the can due to the contents, and the welded seam was similarly painted in a corrective manner. Despite the need to thicken the coating for cans filled with intense contents, there has been the inconvenience that thick coating is difficult with solvent-based coatings. Therefore, in recent years, it has been considered to perform electrostatic powder coating capable of thick coating using a solvent-free powder coating. When the aerosol can is subjected to electrostatic powder coating as described above, the can body whose one end is reduced in diameter is grounded, and the charged powder paint is directed toward the inner surface of the can body from one open end of the can body. It is conceivable that the powder coating is applied to the inner surface of the can body by spraying and electrostatic effect to perform electrostatic coating.

[0003]

However, in the above-mentioned electrostatic powder coating method, the powder coating is sprayed from one opening end toward the inner surface of the can body in a state where both ends of the can body are open. The sprayed powder paint flows out from the other opening end, and it may be difficult to apply the powder paint thickly and uniformly on the inner surface of the can body.

[0004] In particular, when one end of the can body has a greatly reduced diameter, such as a neck-in can, the slope of the reduced diameter portion becomes large. In order to do this, it is necessary to spray powder paint intensively on this part. However, when the reduced diameter portion is thickly painted, the other portions, particularly the coating near the open end of the end opposite to the reduced diameter end, become thinner, and conversely, the opposite end portion side When the paint is applied from the beginning, the paint near the opening end of the reduced diameter end portion becomes thin, and it becomes difficult to uniformly paint the inner surface of the can body.

[0005] In view of the above-mentioned disadvantages, an object of the present invention is to provide a method for coating the inner surface of a can body with an electrostatic powder, which can uniformly and efficiently coat the inner surface of the can body to a desired thickness.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention relates to a can body having a reduced diameter at one end and an opening at both ends. An electrostatic powder coating method in which powder paint is applied to the inner surface of the can body by spraying from the end toward the inner surface of the can body, and suctioning air from the other open end to form an air flow. A first step of spraying a powder coating from an opening end opposite to the diameter-opened end to electrostatically paint a region mainly on the opposite opening end side of the inner surface of the can body; A second step of spraying a powder coating from the end and electrostatically coating a region of the inner surface of the can body mainly on the side of the reduced opening end is sequentially performed.

According to the present invention, since the inner surface of the can body is painted by spraying powder paint from the opening end toward the inner surface of the can body, a nozzle is inserted into and out of the can body for each can to insert the nozzle. It can be painted in a shorter time than when painting the inner surface.

In the present invention, the inner surface of the can body is divided into two regions, an opening end side having a reduced diameter and an opening end side on the opposite side.
In the first step, the area on the opposite opening end side is mainly electrostatically coated, and in the second step, the area on the reduced opening end side is mainly electrostatically coated. Therefore, since the coating area in one process can be reduced, the entire inner surface of the can body can be uniformly coated with a desired thickness.

Further, in the present invention, after performing the first step of spraying the powder coating from the opposite opening end, a second step of spraying the powder coating from the reduced-diameter opening end is performed.
If the order is reversed and the first step is performed after the second step, the air flow or the powder may be reduced in the subsequent first step because the diameter of the opening end on the intake side is reduced. The flow of the body paint becomes strong, and the powder paint applied near the opening end reduced in diameter in the second step may be peeled off and the coating may become thinner. Absent.

[0010] In the present invention, the first step is carried out in a state in which the tip end of the spray nozzle having an inner diameter slightly larger than the outer diameter of the opposite open end is brought close to the opposite open end. The powder coating is sprayed toward the inner surface of the body, and the air is drawn from the reduced-diameter opening end to form an air flow, so that the powder coating is mainly applied to the region on the opposite opening end side of the inner surface of the can body. The second step is performed in a state where the tip end of the spray nozzle having an inner diameter slightly larger than the outer diameter of the reduced-diameter opening end is brought close to the reduced-diameter opening end. The powder paint is sprayed toward the inner surface of the body, and the air paint is formed from the opposite open end to form an air flow. Is preferably applied.

According to this, in any of the first and second steps, when air is taken in from the opening end on the suction side, the can body is opened from between the opening end on the blowing side and the tip of the nozzle close to the opening end. Since the air flows in the radial direction and the flow amount of the air is small, the airflow toward the opening end on the intake side is weakened. Therefore, the powder coating material diffuses mainly in the vicinity of the opening end on the spray side, and is applied to the inner surface of the can body mainly in the region on the opening end side on the spray side. The inner diameter of the nozzle close to the opening end is slightly larger than the outer diameter of the opening end, but air is drawn into the inside of the opening end by suction from the opposite opening end side. It flows into the inner surface. Therefore, the powder paint sprayed from the nozzle can be applied to the inner surface of the opening end on the spray side, and the powder paint can be prevented from being applied to the outer surface of the can body.

In the present invention, before performing the first step, a step of spraying powder paint from one of the open ends of the can body to electrostatically paint mainly the central area of the inner surface of the can body is performed. It may be performed. According to this, by separately providing a step of electrostatically coating mainly the central region of the inner surface of the can body according to the can body length, even for a can body having a long can body length, the can body inner surface is uniformly formed to a desired thickness. Can be painted. In addition, first, mainly the central area of the inner surface of the can body is electrostatically coated, and then the first
The step mainly applies the electrostatic coating to the opposite opening end area, and finally the second step mainly applies the reduced diameter opening end area, so that the powder applied to each opening end is applied. There is no danger of peeling off the coating and thinning the coating.

In the present invention, the step of electrostatically coating mainly the central region of the inner surface of the can body includes the step of bringing a spray nozzle tip having an outer diameter smaller than the inner diameter of one opening end close to the one opening end. In this state, the powder paint is sprayed toward the inner surface of the can body, and the powder paint is applied mainly to the central region of the inner surface of the can body by forming an airflow by sucking air from the other open end. Is preferred. According to this, when air is taken in from the opening end on the intake side, air flows in the axial direction of the can body from between the opening end on the blowing side and the tip of the nozzle, and the air flows toward the opening end on the intake side. Is formed, the powder paint sprayed from the nozzle enters the vicinity of the central region of the inner surface of the can body along with the air flow, and is applied mainly to the central region of the inner surface of the can body.

[0014]

Next, an embodiment of the present invention will be described with reference to the drawings. 1A and 1B are explanatory diagrams of a method for coating an inner surface of a can body with electrostatic powder according to this embodiment. FIG. 1A is an explanatory diagram showing a first step, and FIG. 1B is an explanatory diagram showing a second step. In the drawing, a cross section including the center line is described below the center line indicated by a dashed line.

In FIG. 1, a can body 1 of an aerosol can is
The end of the cylindrical metal can body having both ends 2 and 3 open at the opening end 2 side is drawn so that one end 2 is formed in a reduced diameter shape. Reference numeral 4 denotes a powder coating for coating the inner surface of the can body 1. In this embodiment, a thermosetting polyester resin coating having a particle size of 30 to 40 micrometers was used. As other powder coatings, conventionally known thermosetting types,
Thermoplastic powder coating resin, for example, a thermosetting polyester resin, an epoxy resin, a polyamide resin, an acrylic resin, a polyolefin resin, etc., alone or in combination, and if necessary, other additives may be used. Can be.

First, the first step is performed on the can body 1. In this first step, as shown in FIG. 1 (a), a spray nozzle 5 having a hood 6 attached to the tip thereof is arranged close to the opening end 3 on the opposite side of the can body 1, and a suction duct is provided. 7 is arranged close to the reduced-diameter open end 2 of the can body 1. In the first step, the spray nozzle 5 applies the charged powder coating material 4 supplied from a supply device (not shown) to the can body 1.
From the opening end 3 on the opposite side to the inner surface of the can body 1. The spray nozzle 5 has a cylindrical outer shape, and the inner diameter gradually increases from near the center toward the tip. A hood 6 is attached to the tip of the spray nozzle 5. The inner diameter of the hood 6 is rapidly increased at the tip, and the inner diameter of the tip of the hood 6 is larger than the outer diameter of the open end 3 on the opposite side of the can body 1. Are also formed with a slightly larger diameter. Can 1
A slight gap is provided between the opening end 3 on the opposite side to the tip of the hood 6.

Then, the can body 1 is grounded, and the charged powder coating material 4 is sprayed from the opposite opening end 3 toward the inner surface of the can body 1 by the spray nozzle 5, and the diameter of the opening is reduced. Air is sucked in from the end 2 by the intake duct 7, flows into the inside of the can body 1 from the opposite open end 3, and forms an airflow toward the reduced open end 2. At this time, a small amount of the air flowing into the can body 1 flows in a radial direction of the can body from between the opening end 3 on the opposite side and the tip of the hood 6 close to the opening end 3, and thus the diameter is reduced. The airflow towards open end 2 is weak. Therefore, the powder coating material 4 sprayed from the spray nozzle 5 is mainly diffused in the vicinity of the opening 3 on the opposite side, and is applied mainly to the region on the opening 3 on the opposite side. The excess powder paint 4 not applied to the inner surface of the can body 1 is sucked into the intake duct 7 and collected. Further, since the inner diameter of the hood 6 is slightly larger than the outer diameter of the opening 3 on the opposite side, air can be drawn into the inside of the opening 3 on the opposite side while the air is caught inside.
Flows into the interior of. Therefore, the sprayed powder paint 4
Can be applied to the inner surface of the opening end 3 on the opposite side, and the powder paint 4 can be prevented from being applied to the outer surface of the can body 1.

Next, a second step is performed on the can body 1. In the second step, as shown in FIG. 1 (b), a spray nozzle 8 having a hood 9 attached to the tip thereof is arranged close to the reduced opening end 2 of the can body 1, The duct 10 is arranged close to the opening end 3 on the opposite side of the can body 1. In the second step, the spray nozzle 8 converts the charged powder coating material 4 supplied from a supply device (not shown) into
It is for spraying from the reduced open end 2 of the can body 1 toward the inner surface of the can body 1 and has a cylindrical outer diameter, and the inner diameter gradually increases from near the center toward the tip. ing. A hood 9 is attached to the tip of the spray nozzle 8,
Like the hood 6, the inner diameter of the hood 9 is rapidly increased at the distal end, and the inner diameter of the distal end of the hood 9 is formed to be slightly larger than the outer diameter of the reduced open end 2 of the can body 1. ing. A slight gap is provided between the reduced-diameter open end 2 of the can body 1 and the tip of the hood 9.

Then, the can body 1 is grounded, and the charged powder coating material 4 is sprayed with the spray nozzle 8 to reduce the diameter of the open end 2.
And the air is blown toward the inner surface of the can body 1, and is sucked from the opposite open end 3 by the intake duct 10, flows into the can body 1 from the reduced-diameter open end 2, and flows into the can body 1. Form an airflow toward At this time, for the same reason as in the first step, the airflow toward the opening end 3 on the opposite side is weak, so that the sprayed powder coating material 4 spreads and spreads mainly near the reduced opening end 2. . Therefore, the powder coating material 4 can be sufficiently applied even to the large inclined portion at the reduced end. The excess powder paint 4 not applied to the inner surface of the can body 1 is sucked into the intake duct 10 and collected. Also, by flowing air into the can body 1 so as to be trapped inside the reduced-diameter opening end, the powder paint is applied to the inner surface of the reduced-diameter opening end 2 and the
Can be prevented from being applied to the outer surface of the device.

In this embodiment, the opening end 3 on the opposite side of the inner surface of the can body 1 is electrostatically coated in the first step, and the opening end 2 whose diameter is mainly reduced is electrostatically coated in the second step. I do. By reducing the coating area in one process as described above, each coating area can be uniformly coated to a desired film thickness, so that the entire inner surface of the can body 1 can be uniformly coated to a desired film thickness. Further, by reducing the spray amount of the powder coating material 4 in one step, the powder coating can be uniformly applied to a thin film. Further, by shortening the spraying time of the powder coating material 4 in one step, the coating time of the entire inner surface 2 of the can body can be shortened.

Further, since the inner surface of the can body 1 is coated by spraying the powder coating material 4 from the opening ends 2 and 3 toward the inner surface of the can body 1, the spray nozzle is provided inside the can body 1 for each can. Can be painted in a shorter time than when the inner surface of the can body 1 is painted by inserting and ejecting the can body.

Next, another embodiment of the present invention will be described with reference to the drawings. 2A and 2B are explanatory diagrams of a method for coating electrostatic powder on the inner surface of a can body of this embodiment. FIG. 2A is an explanatory diagram of a step of electrostatically coating a central region of the inner surface of the can body, and FIG. FIG. 7C is an explanatory view of a step similar to the first step in the example, and FIG. 9C is an explanatory view of a step similar to the second step in the embodiment.

In FIG. 2, the can body 11 of the aerosol can
Is open at both ends 12, 13 and is formed in a shape in which the diameter of one end on the side of the open end 12 is reduced, but the can body length is longer than the can body 1 of FIG. I have. Therefore, in this embodiment, the inner surface of the can body 11 is subjected to electrostatic powder coating by sequentially performing the three steps of FIGS. 2 (a), 2 (b) and 2 (c).

First, a step of electrostatically painting mainly the central region 14 on the inner surface of the can body 11 is performed. In this step, FIG.
As shown in (a), the spray nozzle 15 is arranged in proximity to the reduced-diameter opening end 12 of the can body 11, and the intake duct 16
Is arranged close to the opening end 13 on the opposite side of the can body 11. The outer shape of the spray nozzle 15 is tapered from the vicinity of the center to the tip, and the outer diameter of the tip is smaller than the inner diameter of the reduced opening end 12 of the can body 11.
Further, the inner diameter of the spray nozzle 15 is also formed in a tapered shape corresponding to the outer diameter. There is a slight gap between the tip of the spray nozzle 15 and the reduced-diameter open end 12 of the can body 11.

Then, the can body 11 is grounded, and the powder coating material 4 charged by the spray nozzle 15 is sprayed toward the inner surface of the can body 11 from the reduced opening end 12.
The air is taken in by the air intake duct 16 and the diameter of the open end 12 is reduced.
Then, air flows into the interior of the can body 11 to form an air flow toward the opening end 13 on the opposite side. At this time, the tapered tip of the spray nozzle 15 and the reduced opening end 1
2, air flows in the axial direction of the can body 11, and a large air flow toward the opening end 13 on the opposite side is formed. Therefore, the powder paint 4 sprayed from the spray nozzle 15
The central region 14 of the inner surface of the can body 11 is
It diffuses in the vicinity and is mainly applied to the central region 14. Excess powder paint 4 is sucked into the intake duct 16 and collected.

Next, with respect to the can body 11, the first
A step similar to the step is performed. In this step, FIG.
As shown in FIG.
8 can be arranged close to the opening end 13 on the opposite side of the can body 11, and the suction duct 19 can be arranged close to the reduced opening end 12 of the can body 11. The structures of the spray nozzle 17, the hood 18, and the intake duct 19 are the same as those of the spray nozzle 5, the hood 6, and the intake duct 7 in FIG.

Then, the can body 11 is grounded, and the charged powder coating material 4 is sprayed toward the inner surface of the can body 11 from the opening end 13 on the opposite side by the spray nozzle 17.
Air is taken in from the opening end 12 reduced in diameter by the intake duct 19. At this time, as in the case of FIG. 1A, the airflow toward the reduced-diameter opening end 12 is weakened, and thus the powder coating material 4 sprayed from the spray nozzle 17 mainly emits the opposite opening end. Spread around 13 and apply. Excess powder paint 4 is sucked and collected by the intake duct 19.

Finally, a process similar to the second process of the above embodiment is performed on the can body 11. In this step, FIG.
(C) As shown in FIG.
1 with the open end 12 of the can body 11 having a reduced diameter.
And the intake duct 22 is connected to the can body 11.
Is arranged close to the opening end 13 on the opposite side of the above. The structures of the spray nozzle 20, the hood 21, and the intake duct 22 are the same as those of the spray nozzle 8, the hood 9, and the intake duct 10 in FIG. 1B, respectively.

Then, the can body 11 is grounded, and the charged powder coating material 4 is sprayed toward the inner surface of the can body 11 from the reduced opening end 12 by the spray nozzle 20, and the opposite side is provided by the suction duct 22. Is taken in from the open end 13. At this time, as in the case of FIG. 1B, the airflow toward the opening end 13 on the opposite side is weak, so that the sprayed powder coating material 4 mainly diffuses near the opening end 12 whose diameter has been reduced. To wear. Excess powder paint 4 is sucked and collected by the intake duct 22.

According to this embodiment, the can body 1 having a long can body length
With respect to 1, also, the inner surface of the can body is divided into three regions in accordance with the length of the can body 11, and each region is subjected to electrostatic coating in three steps, so that the inner surface of the can body can be uniformly formed to a desired thickness. Can be painted. Also, first, the central area 14 of the inner surface of the can body 11 is electrostatically coated, then the area mainly on the opposite opening end 13 side is electrostatically coated, and finally, the diameter of the opening end 12 side mainly reduced in diameter is applied. Since the area is coated, there is no possibility that the powder coating 28 applied to both open ends is peeled off to make the coating thin.

In this embodiment, when performing the step of electrostatically coating mainly the central region of the inner surface of the can body 11, the powder coating material 4 is sprayed from the reduced opening end 12 by the spray nozzle 15, and From the side open end 13 to the intake duct 16
, But this is reversed and the opposite open end 1
The spray paint may be sprayed from 3 by a spray nozzle 15, and the air may be sucked in from the reduced-diameter opening end 12 by the suction duct 16.

Further, another embodiment of the present invention will be described with reference to the drawings. 3A and 3B are explanatory views of a method for electrostatic powder coating of the inner surface of a can body of this embodiment. FIG. 3A is an explanatory view of a step of electrostatically coating a central region of the inner surface of the can body, and FIG. FIG. 7C is an explanatory view of a step similar to the first step in the example, and FIG. 9C is an explanatory view of a step similar to the second step in the embodiment.

In FIG. 3, the can body 30 of the aerosol can
Is formed in such a shape that both ends 31, 32 are open and one end on the side of the open end 31 is reduced in diameter. However, as compared with the can body of the embodiment of FIGS. The neck of the reduced diameter end is longer, and the inclined shoulder of the reduced diameter end is located closer to the center of the can body 30. In this embodiment, the inner surface of the can body 30 is subjected to electrostatic powder coating by sequentially performing the three steps shown in FIGS. 3 (a), 3 (b) and 3 (c).

First, a step of electrostatically coating mainly the central region 33 on the inner surface of the can body 30 is performed. In this step, FIG.
As shown in (a), the spray nozzle 34 is arranged close to the reduced-diameter open end 31 of the can body 30,
Is disposed close to the open end 32 on the opposite side of the can body 30. The structure of the spray nozzle 43 and the intake duct 35 is the same as the structure of the spray nozzle 15 and the intake duct 16 in FIG.

Then, the can body 30 is grounded, and the charged powder coating material 4 is sprayed from the opening end 31 reduced in diameter by the spray nozzle 34 toward the inner surface of the can body 30. Air is taken in from the open end 32. At this time, as in the case of FIG. 2A, a large air flow is formed toward the opening end 32 on the opposite side. It diffuses and coats near the region 33. Extra powder paint 4
Is sucked and collected by the intake duct 35.

Next, with respect to the can body 30, the first
A step similar to the step is performed. In this step, as shown in FIG. 3B, a spray nozzle 36 having a hood 37 attached to the tip thereof is arranged close to the opening end 32 on the opposite side of the can body 30. The can body 30 is arranged close to the reduced-open end 31. Spray nozzle 3
6, the structure of the hood 37 and the intake duct 38 are respectively shown in FIG.
The structure is the same as that of the spray nozzle 17, hood 18, and intake duct 19 shown in FIG.

Then, the can body 30 is grounded, and the charged powder coating material 4 is sprayed toward the inner surface of the can body 30 from the opening end 32 on the opposite side by the spray nozzle 36.
Air is taken in from the open end 31 reduced in diameter by the intake duct 38. At this time, as in the case of FIG. 2B, since the airflow toward the reduced-diameter opening end 31 is weak, the powder coating material 4 is spread and applied mainly near the opening end 32 on the opposite side. Excess powder paint 4 is sucked and collected by the intake duct 38.

Finally, the same process as the second process of the above embodiment is performed on the can body 30. In this step, FIG.
The hood 40 is attached to the tip of the spray nozzle 39 as shown in FIG. 3 and placed close to the reduced opening end 31 of the can body 30, and the intake duct 41 is connected to the opening end 32 on the opposite side of the can body 30. It is arranged close to. Spray nozzle 39,
The structures of the hood 40 and the intake duct 41 are the same as those of the spray nozzle 20, the hood 21, and the intake duct 22 in FIG. 2C, respectively.

Then, the can body 30 is grounded, and the charged powder coating material 4 is sprayed from the opening end 31 reduced in diameter by the spray nozzle 39 toward the inner surface of the can body 30. Air is taken in from the open end 32. At this time, as in the case of FIG. 2C, the airflow toward the opening end 13 on the opposite side is weak, so that the powder coating material 4 is diffused and applied mainly near the opening end 31 whose diameter is reduced. Excess powder paint 4 is sucked and collected by the intake duct 41.

In this embodiment, the inner surface of the can body 30 is divided into three regions and the respective regions are subjected to the electrostatic coating in three steps also for the can body 30 having a long neck portion at the reduced diameter end.
It can be uniformly coated with a desired thickness.

Although the present invention has been described with reference to the example of the can body of an aerosol can, it is needless to say that the present invention can also be applied to a method for coating the inside of a can body of a three-piece welded can or beverage can. In general, a welding can body has to be subjected to correction painting of a welding seam portion, and conventionally, a coating nozzle is arranged inside the can body to paint the inner surface of the welding seam portion. Therefore, the welded can body that can be manufactured is limited to those having a large can body diameter into which a welding nozzle can be inserted. However, according to the present invention, since the inner surface can be coated from the outside of the can body, the present invention can be applied to a small-diameter can which could not be used conventionally because a coating nozzle could not be arranged.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of one embodiment of the present invention.

FIG. 2 is an explanatory diagram of another embodiment of the present invention.

FIG. 3 is an explanatory view of still another embodiment of the present invention.

[Explanation of symbols]

1, 11, 30 ... can body, 2, 12, 31 ... reduced-diameter open end, 3, 13, 32 ... opposite open end, 4 ... powder paint, 5, 8, 15, 17, 2
0, 34, 36, 41 ... spray nozzle, 9, 1
8, 21, 37, 40 ... food, 7, 10, 1
6, 19, 22, 35, 38, 41 ... intake duct,
14, 33 ... central area

Claims (4)

[Claims] 1. A charged powder coating material is sprayed from one open end of a can body toward the inner surface of the can body, and the other open end is applied to a can body having a reduced diameter at one end and open at both ends. Is an electrostatic powder coating method in which a powder paint is applied to the inner surface of a can body by forming an airflow by inhaling the powder paint from the opening end opposite to the reduced-diameter opening end. A first step of spraying and electrostatically coating a region mainly on the opposite open end of the inner surface of the can body, and spraying powder paint from the reduced-diameter open end to mainly form the inner surface of the can body. And a second step of electrostatically coating the reduced-diameter opening end side region in order. 2. The method according to claim 1, wherein the first step is performed by bringing a spray nozzle tip having an inner diameter slightly larger than an outer diameter of the opposite opening end close to the opposite opening end. The powder coating is sprayed toward the opening and the air is drawn from the reduced-diameter opening end to form an airflow, so that the powder coating is applied mainly to the region on the opposite opening end side of the inner surface of the can body. In the second step, the spray nozzle tip having an inner diameter slightly larger than the outer diameter of the reduced-diameter opening end is brought close to the reduced-diameter opening end, and the inner surface of the can body is The powder paint is sprayed toward the container body, and the air paint is formed by suctioning air from the opposite open end, thereby applying the powder paint mainly to the region of the inner end surface of the can body on the reduced diameter open end side. The method for coating electrostatic powder on the inner surface of a can body according to claim 1, wherein the coating is performed. 3. The method according to claim 1, wherein a step of spraying a powder coating material from one of the open ends of the can body to electrostatically paint mainly a central region of the inner surface of the can body before performing the first step. 3. The method according to claim 1, wherein the inner surface of the can body is coated with an electrostatic powder. 4. The step of electrostatically coating mainly the central area of the inner surface of the can body includes the step of bringing the tip end of the spray nozzle having an outer diameter smaller than the inner diameter of one open end close to the one open end. By spraying the powder paint toward the inner surface of the can body, and by suctioning air from the other open end to form an airflow, the powder paint is applied mainly to the central region of the inner surface of the can body. The method for coating electrostatic powder on the inner surface of a can body according to claim 3.