JPS6247595B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an apparatus for coating the inner surface of a side weld seam of a metal can body with a resin powder coating. More specifically, when the metal can body is used as a can body for foods, etc., the metal can be prevented from leaching into the contents of the food etc. due to the exposed part of the metal material present in the joint at the inner weld part of the welded can. The present invention also relates to a device for coating the inner surface of a weld joint with a resin powder coating in order to prevent corrosion of the metal material caused by contact between the contents and the exposed portion of the metal material. (Prior Art) Solder cans and adhesive cans have been widely used as cans having side seams, but recently welded cans have also come into use. In the case of solder cans, the cut end surface of the tin plate is partially covered by the solder that is formed during pressure bonding, so it is easy to completely cover it by spraying paint or applying paint using a paint roller, etc. It is. In addition, in the case of adhesive cans, the cut end of the metal material can be bonded by wrapping the cut end of the metal material with adhesive tape, or by bonding the cut end of the metal material by embedding it in the adhesive layer. can prevent exposure. On the other hand, in the case of welded cans, the cut end surface of the welded seam remains as a welding step, and furthermore, since the welded part is generally a rough surface, even if liquid paint is applied to this part with a roller or spray, no paint will be applied. It was difficult to coat the welded part in such a way that it would flow and evenly eliminate the level difference in the welded part. Japanese Patent Publication No. 48-4428 and Japanese Patent Publication No. 50-31179 are methods for covering the steps of the side welded seams of such welded cans.
As proposed in the above publication, an apparatus is known in which resin powder is sprayed onto a weld seam to electrostatically adhere it thereto, and then the adhered resin powder is melted to cover the weld seam. However, when these devices are used, the following problems occur when the resin powder is ejected and electrostatically adhered to the welded seam. In other words, when the resin powder is ejected downward and electrostatically adheres to the weld seam, the resin powder is electrostatically attracted toward the weld seam and the velocity of the ejection is added to the resin powder, causing it to collide with the weld seam. It is unavoidable that the resin powder layer irregularly bounces off and adheres, resulting in an uneven layer of resin powder. Furthermore, the resin powder adheres to the periphery of the resin powder ejection hole or to the corona discharge pin provided close to the ejection hole, forming a lump of resin powder, which falls from time to time and forms a conspicuously thick part of the adhering resin powder layer. Form. If the resin powder layer that adheres to the weld seam becomes thick or thin in this way, the resin powder will not melt uniformly (in the case of thermoplastic resins) or flow harden (in the case of thermosetting resins), resulting in The properties of the paint film vary depending on the location, and during flange processing and neck-in processing performed after the resin paint film is formed, cracks and peeling occur in the resin paint film, exposing the metal material at the weld seam, and the metal content remains the same as in the conventional case. It becomes difficult to prevent elution into objects and corrosion of welded seams. Furthermore, since the resin powder is ejected and adhered to the metal can body that is continuously transported, immediately after passing through the metal can body, some particles collide with the inner surface of the metal can body and bounce back, while others are thrown out of the metal can body. These resin powders not only scatter and contaminate the surrounding area, but also
There is an inconvenience that it adheres to the inner and outer surfaces of the metal can body. (Problems to be Solved by the Invention) The purpose of the present invention is to eliminate the drawbacks of the conventional methods, prevent unnecessary resin powder from adhering to the inner surface of the weld seam of the metal can body being transported, and It is an object of the present invention to provide an apparatus for uniformly depositing resin powder and heating and melting it for protective coating. Another object of the present invention is to remove the powder paint that adheres to the vicinity of the nozzle hole and the corona discharge pin and falls from time to time when the resin powder paint is electrostatically adhered to the inner surface of the weld seam of the metal can body. This method prevents unnecessary powder paint from adhering to the inner surface of the metal can body, coats the inner surface of the weld seam uniformly with powder paint, and prevents scattering of powder paint that occurs at cuts in the metal can body being transported. The objective is to provide a device that can reliably prevent this. (Means for Solving the Problems) For this purpose, the present invention provides a transfer device that transfers the side weld seam of a metal can body upward, and a transfer device that transfers the side weld seam of the metal can body toward the inner surface of the weld seam of the metal can body being transferred. A resin powder paint ejecting device having an ejection hole facing diagonally upward with respect to the direction of travel, a corona discharge pin provided near the ejection hole for charging the resin powder paint to be ejected, and the ejection hole and the corona. a powder paint recovery device connected to a vacuum suction device provided surrounding the discharge pin; a semicylindrical powder paint recovery cover that covers the top of the recovery device and is longer than the distance between the metal can bodies and connected to the vacuum suction device; and a heating device for melting the powder coating material adhering to the inner surface of the weld seam of the metal can body. (Example) An example of implementing the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 indicates a metal can body which is gradually formed into a cylindrical shape by a guide rail 2 having a Z-shaped cross section, and whose ends are overlapped. Reference numerals 3 and 4 denote a pair of upper and lower welding rolls for welding both overlapping edges of the metal can body 1, and the welding rolls 3 and 4 are provided with copper wire electrodes 5 and 6 to weld the overlapping ends. The copper wire electrodes 5 and 6 are pressed together and an alternating current welding current is applied to the copper wire electrodes 5 and 6 to cause heat-generating welding. 7 and 8 are devices having several rows of inert gas ejection holes 9 and cooling the inner and outer surfaces of the welded portion of the metal can body 1 in an inert gas atmosphere to prevent oxidation of the inner and outer surfaces of the welded portion. Reference numeral 10 denotes a resin powder paint spraying device for coating the inner surface of the welded seam of the metal can body 1 sent out by the transfer device 11 that transfers the welded metal can body 1 with the welded seam facing upward. The spouting hole 12 of the powder coating spouting device 10 is located on the inner surface of the welded seam of the metal can body being transferred, facing diagonally upward with respect to the direction of travel of the welded seam. It is connected to a source (not shown) that pumps the powder coating with a stream of dry air. Reference numeral 13 denotes a corona discharge pin provided close to the ejection hole 12, which negatively charges the powder paint ejected from the ejection hole 12. 14 is the jet hole 12 and the corona discharge pin 13
Powder paint receiver 1 that surrounds and opens upward
5 and is connected to a vacuum suction device (not shown). 16 is a contact that also serves as a transfer guide for grounding the metal can bodies 1 being transferred, and 17 is a contact element for collecting powder paint that is ejected between the metal can bodies 1 that are continuously transferred. A surplus powder paint recovery device 19 has a semi-cylindrical powder paint recovery cover 18 that is longer than the distance between the metal can bodies 1 and 1 and is connected to a vacuum suction device (not shown). A heating device is shown for melting deposited powder paint. Both end edges are overlapped at the upper position by the guide rail 2 and formed into the can body 1, and the welded seam welded by the welding rolls 3 and 4 is transported while being prevented from oxidation by the weld part oxidation prevention devices 7 and 8. It is sent out by the device 11. The jetting hole 1 of the resin powder paint jetting device 10 is applied to the inner surface of the welded seam of the metal can body 1 being transferred.
The powder paint ejected from the corona discharge pin 1
3, it is charged and discharged obliquely upward toward the inner surface of the welding seam, forming a streamline that touches the inner surface of the welding seam, becoming floating at a position close to the inner surface of the welding seam, and electrostatically adhering to the inner surface of the welding seam. . The inner surface of the weld seam is therefore uniformly coated with the adhering powder coating. Next, the powder paint adhering to the welded seam is heated by the heating device 19 and melted to form a coating film of uniform thickness covering the welded seam. As mentioned above, when the powder coating is sprayed and adhered to the inner surface of the weld seam of the metal can body 1 being transferred, the powder coating also adheres to the vicinity of the injection hole 12 and the corona discharge pin 13 over a long period of time. As lumps of powder paint fall from time to time, the powder paint receiver 15 receives them, prevents them from adhering to the metal can body 1, and collects them in the powder paint recovery device 14. Prevents local thickening. Immediately after passing the continuously transported metal can body,
The powdered paint that tends to scatter into and out of the metal can body as described above is reliably collected by the powdered paint collection device 14 and the powdered paint collection cover 8, and is prevented from scattering. In the above-mentioned embodiment, in order for the powder coating material jetted from the jet hole 12 to adhere to the weld seam in a floating state in the form of a streamline contacting the weld seam of the metal can body, the jet hole 12 must be placed on the inner surface of the weld seam. The inclination θ made with respect to the direction of movement is required to be 20° to 80°, preferably 40° to 60°, and the distance between the inner surface of the weld seam and the jet hole 12 is 3 to 30°.
mm, preferably 5 to 10 mm. Also, the voltage applied to the corona discharge pin 13 is
If it is less than 1KW, the adhesion force of the powder coating to the inner surface of the weld seam is too weak, and if it exceeds 50KV, electric discharge will occur between the corona discharge pin 13 and the metal can body 11, which is undesirable. However, 5 to 30 KV is suitable. The resin powder coating used in the present invention is heated to a temperature of 150 to 300℃.
It is preferable to use a material that melts or fluidizes and hardens in several seconds to several tens of seconds at a temperature of 100 to 100 seconds, and thermoplastic nylon, polyester, polyolefin, thermosetting epoxy, polyester, acrylic resin, etc. are preferable. Hereinafter, the coating according to the present invention will be compared with a comparative example in which the powder coating is electrostatically adhered to the welded seam under the same conditions and at the same injection speed, and the coating is heated and melted. It was as shown in Table 1.

【table】

[Table] (Effects of the Invention) From the above results, it is clear that according to the present invention, the metal can body can be transported with the welded seam facing upward, and the direction of movement is toward the inner surface of the welded seam. Using a resin powder coating spraying device with an injection hole facing diagonally upward, the powder coating is sprayed upward in a streamline that touches the inner surface of the welded seam of the metal can body being transported. It can be electrostatically uniformly deposited on the inner surface of the weld seam in a suspended state, and the powder coating can therefore be melted by means of a heating device to evenly coat the weld seam. Furthermore, when the resin powder paint is electrostatically attached to the welding joint, the powder paint that adheres to the vicinity of the nozzle hole and the corona discharge pin etc. and falls as a lump is removed from the powder paint that surrounds the nozzle hole and the corona discharge pin. Since the powder paint is removed by a powder paint recovery device installed at Since the powder paint collected is collected by the powder paint collection device and the powder paint collection cover, it is possible to provide an apparatus in which unnecessary powder paint does not adhere to the inside or outside of the metal can body.

[Brief explanation of the drawing]

What is illustrated is a diagram showing an example of the implementation of the present invention, and showing a coating process and a coating apparatus. 1...Metal can body, 10...Powder paint ejection device,
11...Transfer device, 12...Ejection hole, 13...Corona discharge pin, 14...Powder paint recovery device, 18
...Heating device.

Claims (1)

[Claims] 1 A transfer device that transfers the side weld seam of a metal can body upward, and a resin powder that has an ejection hole facing diagonally upward with respect to the direction of movement toward the inner surface of the weld seam of the metal can body to be transferred. A paint ejecting device, a corona discharge pin provided close to the ejection hole for charging the ejected resin powder paint, and a powder paint connected to a reduced pressure suction device provided surrounding the ejection hole and the corona discharge pin. a recovery device, and a semi-cylindrical powder paint recovery cover that is longer than the distance between the metal can body and covers the top of the recovery device and is connected to a vacuum suction device;
1. An apparatus for coating the inner surface of a welded seam of a welded can body, comprising a heating device for melting the powder coating material adhering to the inner surface of the welded seam of the metal can body.