GB1596023A

GB1596023A - Coating containers

Info

Publication number: GB1596023A
Application number: GB5647/77A
Authority: GB
Original assignee: Metal Box PLC
Current assignee: Crown Packaging UK Ltd
Priority date: 1977-02-10
Filing date: 1977-02-10
Publication date: 1981-08-19
Also published as: JPS53121040A; ZA78350B; NL7801498A; BE863884A; FR2380114A1; FR2380114B3

Description

(54) COATING CONTAINERS (71) We, METAL BOX LIMITED, of Queens House, Forbury Road, Reading RG1 3JH, Berkshire, a British Company, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to the curing of a coating on a container body and more particularly but not exclusively to the curing of a side stripe applied to the side seam of a can body, said side strip being of a coating material curable by ultra violet radiation.

In a known method of applying a side stripe to the side seam of a can body, a stripe of solvent based lacquer is applied to the side seam and the can body is conveyed past heaters which drive off the solvent and cure the lacquer. A typical conveyor is twelve feet long to allow sufficient travelling time for the side stripe to cure. Conventional lacquers have as much as 80% solvent which has to be driven off. Not only is the energy required to drive off the solvent costly but it is inflammable. Therefore curable lacquers, which are actuated by ultra violet light have been developed which permit curing of the lacquer substantially without the emission of solvents. The ionic curing lacquer systems are particularly suitable because curing may be initiated by a flash of ultra violet radiation of short duration. Apparatus, suitable for curing lacquers by ultra violet radiation is described in British Patent No. 1457785, in which specification the curing of external coatings is described.

In the first aspect, this invention provides a method of coating an internal surface a container body, said method including the steps of applying a coating material, curable by ultra violet radiation, to an internal surface of the container body and exposing the internal surface coating to a source of ultra violet radiation. The source of radiation may be continuous or alternatively may be pulsed intermittently. In a preferred method the source is a pulsed Xenon Lamp, in which the radiation emitted is synchronised with the location of the can body in the path of the radiation. The radiation may be directed onto the coating from a source within the container or alternatively may be directed from a source outside the container.

The coating may be, if required, be further cured or hardened by an application of heat.

In another aspect the invention provides apparatus for coating an internal surface of a container body, the apparatus including means to apply a coating material, curable by ultra violet radiation, onto an internal surface of the container, a source of ultra violet radiation; and means to direct ultra violet radiation from the source onto the coating material, The source of ultra violet radiation may be continuous or alternatively may be intermittent or pulsed to subject the can body to a plurality of flashes.

The ultra violet radiation may be directed from a source located outside the can body.

Alternatively the source of radiation may be surrounded by the can body. In order to cure an internal coating or side stripe a heating means may be provided to further cure the coating if necessary.

In one embodiment the apparatus comprises a can body maker having means to weld a side seam, a roller adapted to apply a lacquer curable by ultra violet radiation to the surface of the side seam inside the body, a source of ultra violet radiation and means to convey the can body from the welder, past the coating roll to the source of ultra violet radiation.

In a further aspect the invention provides a can body coated by a method or by means of apparatus according to the invention.

Various embodiments of the invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a diagrammatic side elevation of a can body maker, including side stripping means, a conveyor and a source of ultra violet radiation outside the path of the can bodies; Figure 2 shows diagrammatically the light distribution from a source of Figure 1 onto a pair of can bodies: Figure 3A is a graph of intensity of radiation received by the side stripe of Figure 1 plotted against the distance along the side stripe, during a first exposure; Figure 3B is a like graph to Figure 3A showing the dose accumulated on the side stripe after a second exposure; Figure 4 is a diagrammatic side elevation of an alternative embodiment of the apparatus in which the can body to be irradiated surrounds the source of radiation: Figure 5 is a diagrammatic side elevation of the embodiment of Figure 4 modified to permit irradiation of the whole interior surface of a can body; and Figure 6 is a diagrammatic plan view of a free standing apparatus for irradiating can bodies in which the spokes bearing the can bodies rotate in the horizontal plane about a central pivot.

In Figure 1 the apparatus comprises a can body maker 1 having means 2 to apply an internal side stripe 3 of a lacquer, curable by ultra violet radiation, and a conveyor 4 which conveys each can body to a source of ultra violet radiation 5. In Figure 1 two sources 5 and 6, of radiation are shown by way of example in order to show that a plurality of sources may be used if prolonged exposure times are desired. Each source 5, 6 is outside the can bodies and the ultra violet radiation shines onto the side stripe 3, on the inside of each can body by passing through the gap between adjacent can body such as those denoted 7 and 8.

In a preferred embodiment of the apparatus of Figure 1 the source of irradiation is a Xenon tube 5 which is controlled to fire at the time when the can bodies such as 7 and 8, are suitably positioned, as shown in Figures 1 and 2, so that the radiation passes through the gap between the cans. The radiation so applied may be delivered as a single flash or as pulsed flashes.

Single large intensity flashes are ineffective with low viscosity' free radical curing systems but do work with ionic curing systems. Pulsed lamps, pulsing between 50 and 100 Hertz initiate curing of both free radical and ionic curing lacquers but a Xenon tube is particularly suitable for low viscosity lacquers of the ionic curing type.

The source of radiation may be provided with a reflector (not shown) and guard means to protect people near the apparatus.

As the conveyor 4 carries each can body (such as 8) away from the body maker, past the ultra violet sources 5 or 6, the side stripe 3 inside each can receives two doses of irradiation: a first dose as it approaches the source, delivered through the leading opening in the body, and a second dose, as it moves away, delivered through the trailing end of the body.

Figure 2 shows the distribution of radiation from the tube 5 of Figure 1 onto a pair of can bodies 7 and 8 during a dose. As the cans 7 and 8 pass through the beam of irradiation the side strip 3 of each can becomes progressively irradiated.

In Figure 3A the intensity of irradiation (I) received at the side stripe is plotted as ordinate and the distance (d) along the stripes is plotted as abscissa. The curve 9 represents the dosage received by the stripe of can body 8 at the end of the first irradiation from tube 5 through the leading opening in the body.

Figure 3B shows the accumulated dose received by the side stripe of the body 8 after irradiation through the trailing opening in the body 8. The accumulated dose is indicated by the curve denoted 11 and the dose derived from the second period of irradiation is denoted 10. It will be noticed that the accumulated dose from two exposures is fairly evenly distributed and substantially uniform.

The location of the sources of radiation 5 and 6 outside the can bodies 7 and 8, as described with reference to Figure 1, permits the construction of simple apparatus in which the parts are conveniently accessible for wiring. However the radiation path length is at least equal to the diameter of the can body. The embodiments of Figures 4, 5 and 6 place the source of radiation inside the can body and therefore use the radiation more effectively, by virtue of the short radiation path.

Figure 4 shows the mandrel 19 of a bodymaker of the kind having a pair of welding wheels 16 which weld the side seam of a can body. Immediately after welding.

the can body 17 passes along the mandrel 19 to an applicator roll 12 which applies a stripe 13 of lacquer to the side seam. Each can body is pushed, by dogs on a conveyor 14, to the curing means which is in the form of a tube 15 supported in a reflector 26 which directs the radiation onto the stripe 13. The tube 15 is preferably a pulsed Xenon tube triggered to flash only when a can body 17 is present: however a continuously operating mercury vapour or other tubes may be used.

The tube may be cooled by a current of air.

delivered through conduits in the body maker mandrel 19, in a like manner to the wires 20 in the wiring conduits 18 actually depicted. However, a Xenon lamp operating at high long term average power may require water cooling of the electrodes.

After the side stripe has been irradiated, at least to initiate curing, the can body may optionally be passed to a source of heat such as the gas burner 21 shown to the right in Figure 4. The flames 22 from the burner 21 are directed onto the side seam of the body beneath so that further curing will be rapid.

Fumes from the burner are extracted up a flue 23. The gas burner of Figure 4 is mounted away from the tubes and body maker mandrel in contrast to the burner bar 24 of Figure 5, which is mounted as an extension to the mandrel of the body maker.

In the apparatus of Figure 5, the source of ultra violet radiation is a pair of tubes 15A, 15B mounted one each side of a reflector bar 27 of width substantially less than the diameter of the can body to be irradiated.

This arrangement is therefore able to irradiate the whole interior of a can body, such as that denoted 17, as it is carried on the conveyor 4 away from the body maker mandrel 25 in Figure 5. The need to irradiate the whole can interior is more likely to arise with extruded or wall ironed cans the interior of which is coated after the metal shaping operations, and this aspect of the invention will be discussed later with reference to modifications to the apparatus of Figure 6.

Figure 6 shows an entry conveyor 37, an irradiation apparatus and an exit conveyor 38. The irradiation apparatus shown in Figure 6 has a hub 30 revolving around a vertical central pivot 31. Four like spokes 32 extend radially fom the hub 30. At the end of each spoke 32, a holder plate 33 carries a reflector housing 34 which supports a Xenon tube 35 which serves as a source of ultra violet radiation. Each holder plate is adapted to receive, and releasably hold a can body such as that denoted 36 so that the Xenon tube 35 lies substantially parallel to the surface of the can 36 to be irradiated.

As in the apparatus of Figures 1, 4 and 5 the tubes of the apparatus shown in Figure 6 each require three wires to feed them, namely the anode, cathode and trigger wires. These wires led through each spoke to contacts in the hub where they are shown diagrammatically as three short lines denoted 'C'. After the entry conveyor 37 has delivered the can body 36 onto the holder plate 33 the hub 30 rotates about the pivot 31 until the contacts C in the hub 30 engage with the stationary contacts D as can be seen at the foot of the uppermost spoke 32A in Figure 6. Upon contact being made the tube emits ultra violet radiation to cure the internal coating on the can body 36A.

In the apparatus of Figure 6 it may be desirable to use a pulsed lamp rather than a "single flash" lamp. This is achieved by the provision of contacts (not illustrated) which would allow the lamp to irradiate for say one tenth of a second, during which time pulsing would be caused by any known means.

After which the hub 30 continues to rotate to carry the can body, with its cured coating, to the exit conveyor 38 where it is released from the holder plate. Continued rotation of the hub 30 takes the holder plate to receive another can body.

Whilst the embodiment shown in Figure 6 is particularly adapted for the curing of side seamed can bodies having a stripe of lacquer curable by ultra violet radiation it will be appreciated that minor modification of the tubes will enable the same apparatus to cure an overall internal coating on one piece containers having an end wall integral with a continuous side wall. Suitable modifications include the use of a "U" shaped tube or alternatively single cap tube on each holder plate. Alternatively the back to back tube arrangement with a central supporting reflector as shown in Figure 5 may be used.

Whereas the central supporting reflector may be able to give some mechanical protection to the tubes the single cap tube may need a simple array of rods or mesh to protect it.

WHAT WE CLAIM IS: 1. A method of coating an internal surface of a container body, said method including the steps of applying a coating material, curable by ultra violet radiation, to an internal surface of the container body; and exposing the coating to a source of ultra violet radiation.

2. A method according to claim 1 wherein the coating material is applied as a side stripe.

3. A method according to claim 1 or 2 wherein the radiation is of substantially steady intensity.

4. A method according to claim 1 or claim 2 wherein the radiation is pulsed.

5. A method according to any preceding claim wherein the source of radiation is controlled to fire when the internal surface of the container is suitably positioned in the path of the radiation.

6. A method according to any preceding claim wherein the container body is heated to effect further curing of the coating after irradiation.

7. A method according to any preceding claim wherein the source of irradiation is within the container body.

8. A method according to any of claims 1 to 5 wherein the source of irradiation is outside the container body.

9. A method according to claim 7 wherein the coating is irradiated while

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. wires 20 in the wiring conduits 18 actually depicted. However, a Xenon lamp operating at high long term average power may require water cooling of the electrodes. After the side stripe has been irradiated, at least to initiate curing, the can body may optionally be passed to a source of heat such as the gas burner 21 shown to the right in Figure 4. The flames 22 from the burner 21 are directed onto the side seam of the body beneath so that further curing will be rapid. Fumes from the burner are extracted up a flue 23. The gas burner of Figure 4 is mounted away from the tubes and body maker mandrel in contrast to the burner bar 24 of Figure 5, which is mounted as an extension to the mandrel of the body maker. In the apparatus of Figure 5, the source of ultra violet radiation is a pair of tubes 15A, 15B mounted one each side of a reflector bar 27 of width substantially less than the diameter of the can body to be irradiated. This arrangement is therefore able to irradiate the whole interior of a can body, such as that denoted 17, as it is carried on the conveyor 4 away from the body maker mandrel 25 in Figure 5. The need to irradiate the whole can interior is more likely to arise with extruded or wall ironed cans the interior of which is coated after the metal shaping operations, and this aspect of the invention will be discussed later with reference to modifications to the apparatus of Figure 6. Figure 6 shows an entry conveyor 37, an irradiation apparatus and an exit conveyor 38. The irradiation apparatus shown in Figure 6 has a hub 30 revolving around a vertical central pivot 31. Four like spokes 32 extend radially fom the hub 30. At the end of each spoke 32, a holder plate 33 carries a reflector housing 34 which supports a Xenon tube 35 which serves as a source of ultra violet radiation. Each holder plate is adapted to receive, and releasably hold a can body such as that denoted 36 so that the Xenon tube 35 lies substantially parallel to the surface of the can 36 to be irradiated. As in the apparatus of Figures 1, 4 and 5 the tubes of the apparatus shown in Figure 6 each require three wires to feed them, namely the anode, cathode and trigger wires. These wires led through each spoke to contacts in the hub where they are shown diagrammatically as three short lines denoted 'C'. After the entry conveyor 37 has delivered the can body 36 onto the holder plate 33 the hub 30 rotates about the pivot 31 until the contacts C in the hub 30 engage with the stationary contacts D as can be seen at the foot of the uppermost spoke 32A in Figure 6. Upon contact being made the tube emits ultra violet radiation to cure the internal coating on the can body 36A. In the apparatus of Figure 6 it may be desirable to use a pulsed lamp rather than a "single flash" lamp. This is achieved by the provision of contacts (not illustrated) which would allow the lamp to irradiate for say one tenth of a second, during which time pulsing would be caused by any known means. After which the hub 30 continues to rotate to carry the can body, with its cured coating, to the exit conveyor 38 where it is released from the holder plate. Continued rotation of the hub 30 takes the holder plate to receive another can body. Whilst the embodiment shown in Figure 6 is particularly adapted for the curing of side seamed can bodies having a stripe of lacquer curable by ultra violet radiation it will be appreciated that minor modification of the tubes will enable the same apparatus to cure an overall internal coating on one piece containers having an end wall integral with a continuous side wall. Suitable modifications include the use of a "U" shaped tube or alternatively single cap tube on each holder plate. Alternatively the back to back tube arrangement with a central supporting reflector as shown in Figure 5 may be used. Whereas the central supporting reflector may be able to give some mechanical protection to the tubes the single cap tube may need a simple array of rods or mesh to protect it. WHAT WE CLAIM IS:

1. A method of coating an internal surface of a container body, said method including the steps of applying a coating material, curable by ultra violet radiation, to an internal surface of the container body; and exposing the coating to a source of ultra violet radiation.

4. A method according to claim 1 or claim 2 wherein the radiation is pulsed.

9. A method according to claim 7 wherein the coating is irradiated while

moving relative to the source of irradiation.

10. A method according to claim 8 wherein a first dose of irradiation is applied to the coating as it approaches the source and a second dose of irradiation is applied to the coating as it leaves the source.

11. Apparatus for coating an internal surface of a container body, said apparatus including means to apply a coating material, curable by ultra violet radiation, onto an internal surface of the container; a source of ultra violet radiation; and means to direct ultra violet radiation from the source onto the coating material.

12. Apparatus according to claim 11 wherein the means to apply a coating is adapted to apply a coating in the form of a side stripe.

13. Apparatus according to claim 11 or claim 12 wherein the source of ultra violet radiation is adapted to emit radiation of substantially steady intensity.

14. Apparatus according to claim 11 or claim 12 wherein the source of ultra violet radiation is adapted to emit radiation of pulsed intensity.

15. Apparatus according to any of claims 11 to 14 wherein the source is controlled to emit radiation only when a coating material is suitably positioned in the path of the radiation.

16. Apparatus according to claims 11 to 15 wherein the source is a Xenon tube.

17. Apparatus according to any of claims 11 to 15 having heating means adapted to further cure the coating material after irradiation.

18. Apparatus according to any of claims 11 to 17 wherein the source of radiation is within the container body during irradiation.

19. Apparatus according to any of claims 11 to 17 wherein the source of radiation is outside the container body.

20. Apparatus according to claim 19 having means to move the container body relative to the source of radiation.

21. Apparatus according to claim 20 wherein the means to move cylindrical container body is a conveyor adapted to convey each body to a signalling means which causes the source of radiation to deliver a first dose through a leading end of the cylinder as the cylindrical body approaches the source, and thereafter the conveyor conveys the body past the source to receive a second dose of irradiation through the trailing end of the cylinder.

22. A container body coated according to the method of any of claims 1 to 10 or by means of the apparatus of claims 11 to 21.

23. A method substantially as hereinbefore described with reference to Figures 1 to 3B of the accompanying drawings.

24. A method substantially as hereinbefore, described with reference to Figures 4, 5 or 6 of the accompanying drawings.

25. Apparatus substantially as hereinbefore described with reference to Figures 1 to 3B of the accompanying drawings.

26. Apparatus substantially as herein before described with reference to Figure 4, 5 or 6 of the accompanying drawings.