GB1558464A

GB1558464A - Method and apparatus for providing flame cured coatings

Info

Publication number: GB1558464A
Application number: GB3178275A
Authority: GB
Original assignee: Metal Box PLC
Current assignee: Crown Packaging UK Ltd
Priority date: 1975-07-29
Filing date: 1975-07-29
Publication date: 1980-01-03
Also published as: CA1103107A; JPS5217532A; JPS6111674B2

Description

(54) METHOD AND APPARATUS FOR PROVIDING FLAME CURED COATINGS (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 coating of container bodies using two or more coatings at least the first applied of said coatings is of a cross-linkage material in a solvent.

Containers are known, which are made by drawing sheet metal into thin-walled/cylindrical shapes having one end closed. Such containers are passed through dies which reduce the wall thickness by ironing and in so doing subject the container wall to stresses which could disrupt any surface coatings thereon. It is therefore customary to coat such containers after forming. The coating may be in the form of a base coating and subsequent printed coatings. It is customary to stove each coating in an oven to cure each coat completely before the application of the next coating.

In this specification the word "cured" is used in relation to a cross-linkable coating and deemed to indicate that no further cross linking of the coating material is possible; "partially cured" therefore means that further cross linking of the coating material is possible. The word "dried" is used in relation to a coating having solvents and indicates that the solvents have been driven off.

In a first aspect this invention provides method of coating a container body with at least two successive coatings, said method comprising the steps of applying a first coating of an organic coating material to a container body; passing the coated container body rapidly before at least one flame source to only partially cure the first coating but sufficiently to permit application of a second coating; applying a second coating of organic coating material to the only partially cured first coating; and thereafter fully curing the two coatings.

In a preferred embodiment of the method the first coating is of a base coating material and the second coating is of a printihg ink.

Tn a second aspect this invention provides apparatus for coating a container body, said apparatus comprising a first coating means for applying a first coating to a container body; a flame source, support means for exposing said container body having a first coating thereon to the flame with the flame directly impinging on the coating to partially cure the first coating; second coating means for applying a second coating to the first coating while it is only partially cured; and means for fully curing the first and second coatings simultaneously.

The support means may effect the container movement mechanically, pneumatically or electrically, along a linear or a curved path.

Various embodiments will now be described, by way of example, and with reference to the accompanying drawings in which: Fig. 1 is a block diagram illustrating a prior art method of coating; Fig. 2 similarly illustrates one embodiment of the invention; Fig. 3A is a side elevation of a first apparatus arranged for putting the method of Fig. 2 into effect and in which a container being coated is conveyed along a linear path; Fig. 3B is an end elevation of the apparatus, taken on line A-A1 in Fig. 3A; Fig. 4A is a side elevation of a second apparatus in accordance with the invention, in which the container being coated is conveyed along a linear path; Fig. 4B is an end elevation of the apparatus of Fig. 4A, taken on the line B-B1 of that Figure; Fig. 5A is a side elevation of a third apparatus in accordance with the invention, in which the container being coated is conveyed along a curved path; and Fig. 5B is a front elevation of the apparatus of Fig. 5A, taken on line C-C1 of that Figure.

Referring to Fig. 1, during the conventional manufacture of wall ironed cans the cans are first coated with a base coating material and then passed to an oven where the coating is cured. A second coating is then applied on top of the base coating whereafter the cans are passed to a second oven for curing of the second coating before any subsequent coatings are applied or additional operations performed as desired.

Typical gas fired ovens for such known stoving operations comprise a thermally insulated tunnel oblong in cross section. A chain having horizontal pegs, one for each can passes through the oven. Such ovens have a large volume and require considerable amounts of energy to heat them. A typical stoving cycle for can coatings or print would include a period of 2 minutes at 2050C, and time for raising and lowering the temperature of the can to make a total time in the oven of up to 6 minutes, dependent upon line speed. Such extended stoving results in fully cured coatings which are completely crosslinked.

Applicants have discovered that coating need only be dried or partially cured before the application of a further coating thereon.

In the method shown diagrammatically in Fig. 2 a first coating is applied to a can and then dried or cured to produce a surface stable enough to permit the application of a second coating. The drying or curing of the first coating may be induced by heat from a gas flame. The second coating may be dried or cured in readiness to receive further coatings (as shown by the continuous line) or alternatively the combination of first and second coatings may be stoved to completely dry or cure both coatings, (as indicated by the dashed line).

Suitable conditions for achieving the desired degree of drying or curing depend on the characteristics of the coating materials used (e.g. base coatings, printing inks, or varnishes or lacquers). However, it has been found that by using the method of Fig. 2 the drying or curing time required can be reduced to the order of seconds from the minutes required in the prior art method. Preferred coating materials will require less than 10 seconds.

The temperature of the flam= used to bring about the desired degree of drying or partial curing is high and in order to prevent scorching or ignition of the coatings, the coated surfaces of the cans are passed rapidly before the flame.

Ideally, it is only necessary to heat the coating and not the can so less heat should be necessary than in prior art methods where the whole can is heated.

EXPERIMENTAL EXAMPLE.

The principle of the invention can be demonstrated by means of a simple apparatus (not shown) in which a rotatable mandrel or fixed peg adapted to receive a container is used to present the container before a gas burner.

A can having a wet base coating (for example an acrylic coating No. W758 sold in the United Kingdom by Ault and Wiborg Ltd.) was placed on the mandrel and rotated at a high speed, e.g. 900 revolutions per minute.

Flames from the burner bar were brought to impinge upon the surface of the base coating for a period of 1.3 seconds to dry or partially cure the coating. The coating so produced was capable of receiving a subsequent coating of printed ink (such as a red printing ink No.

GP 25 sold in the United Kingdom by Edward Marsden Ltd).

Figs. 3A, 3B, 4A, 4B, 5A and 5B show apparatus to illustrate, by way of non-limiting examples, ways in ehich the coatings on a can body may be presented to a flame.

Referring to Figs. 3A it will be seen that the apparatus has can carrying mandrels (such as that denoted at 1) which are each carried on the arm 2 of a chain link 3. Linear movements of the chain 4 moves the mandrels along and above a burner 5. Guides 6, best seen in Fig.

3B, are provided to control the spacing of the mandrels above the burner bar. Each mandrel 1 is rotated about its axis which is substantially parallel with the burner bar 5. Rotation is derived from a stationary rack 7 and pinions such as 8, which are attached'to a shaft 9 on each of the arms 2. Suitable bevelled gears attached to the shaft 9 are used to rotate each mandrel 1. The temperature to which the coating is raised is governed by the characteristics of the flames from the burner 5 and the time of impingement. The time of impingement is controllee either by the rate of linear passage of the mandrels over the burner or the length of the burner, or combination of these parameters.

Referring to Figs. 4A, 4B, a can body 10 is shown carried by an air conveyor 12. Such conveyors are known in which the cans are carried by air issuing from an elongate orifice 11 above a plenum chamber of the conveyor 12. By suitable adaption of the conveyor it is possible to not only convey each can along the conveyor but also rotate it before impinging upon it flames from a burner 5, thereby providing the conditions for the required degree of drying or partial curing according to the invention as already described. Hot air may be used to not only convey the cans but also assist in partially curing the coating. The degree of curing is controlled by controlling the temperature of the flame, hot air and the time the coating is exposed to the heat.

Referring to Fig. 5A, a rotary apparatus is shown in which a plurality of mandrels, such as the two denoted 14 and depicted, are rotatably mounted on a rotating hub 15 which is mounted on a shaft 16, driven by known means. As the hub rotates, as shown in Fig.

5B, each mandrel passes a feed position F at which a coated can body is fed onto it. As rotation of the hub 15 continues each can is therefore carried to pass, while rotating on its axis before a burner having a plurality of bars 5. In Fig. 5B the burner has a main supply pipe 17 through which gas is fed to the burner bars such as those denoted at 5. It is thought that there may be some advantage in the cyclic heating and cooling applied to the cooling applied to the coating on a can as it passes from bar to bar. As described previously the parameters of temperature and time of exposure are controlled to achieve partial curing.

After heating to effect the desired degree of drying or partial cure of the coating, the can body may optionally be carried through a cooling location in which cold air is directed onto the surface of the can body from a nozzle 18.

Thereafter each can is removed from the mandrel and ejected from the machine at a position E, and one or more further coatings are applied and dried or completely cured as described in relation to the method of Fig. 2.

In Fig. 5A, each mandrel 14 is carried by a shaft 29 mounted on the hub 15 and carrying a pinion 28 which coacts with a gear wheel 19 fixed to the machine frame 20, so that as the hub 15 rotates, each mandrel is rotated continuously, so permitting the entire surface coating of each can carried thereon to be presented, by rotation, to the burners. A flue 21 is provided to conduct the fumes, if any, away from the machine.

The coating materials used may be known materials or alternatively may be modified by the addition of a high level of lubricant incorporated to produce a high degree of slip in the coating which aids subsequent conveying of the cans.

When base coatings having high levels of lubricant are stoved in the manner of the prior art, the lubricant residing on the surface after the relatively low temperature curing interferes with the deposition of further coatings.

However, if the methods shown in Fig. 2 is used any residual lubricant in or near the surface of the base coating is driven off so leaving the surface receptive to a second coating of, for instance, a printing ink. The subsequent final stoving of the combined coating reblooms the surface to a lustrous quality and satisfactory slip.

While the invention has been described in terms of rotating mandrels to carry the coated article, where rotation is not essential, a known peg chain may be used to carry the article before the flame.

WHAT WE CLAIM IS:- 1. A method of coating a container body with at least two successive coatings, said method comprising the steps of applying a first coating of an organic coating material to a container body; passing the coated container body rapidly before at least one flame source to only partially cure the first coating but sufficiently to permit application of a second coating; applying a second coating of organic coating material to the only partially cured first coating; and thereafter fully curing the two coatings.

2. A method according to claim 1 wherein the first coating is presented to the gas flame for a period of time in the order of seconds as opposed to minutes.

3. A method according to claim 2 wherein the flame impinges simultaneously on the first coating for a period of time of less than 10.0 seconds.

4. A method according to any preceding claim wherein the container body is rotated to present the entire container body to a flame on a fixed burner.

5. A method according to any preceding claim wherein the first coating includes a lubricant, at least part of which is removed from the surface of the first coating by the flame, and the second coating also has a lubricant.

6. A method according to claim 1 wherein the first coating is a base coating and the second coating is a printing ink.

7. A method according to any preceding claim wherein the first and second coatings are fully cured after the application of the second coating and thereafter a further coating is applied.

8. Apparatus for coating acontainerbody, said apparatus comprising a first coating means for applying a first coating to a container body; a flame source, support means for exposing said container body having a first coating thereon to the flame with the flame directly impinging on the coating to partially cure the first coating; second coating means for applying a second coating to the first coating while it is only partially cured; and means for fully curing the first and second coatings simultaneously.

9. Apparatus according to claim 8 wherein the support means includes a rotatable mandrel and drive means for rotating said mandrel.

10. Apparatus according to claim 9 wherein the mandrel is carried on a chain link and said drive means includes a pinion, attached to a shaft in the link and which pinion coacts with a stationary rack.

11. Apparatus according to claim 8 wherein said flame source includes a plurality of burner bars disposed in adjacent relation, and said support means includes a hub mounted for rotation and carrying at least one shaft for movement past said burner bars, a mandrel rotatably mounted on said shaft, and means for effecting rotation of said mandrel.

12. Apparatus according to claim 11 wherein said burner bars are spaced apart.

13. Apparatus according to claim 8 wherein the support means is an air conveyor and includes a burner bar extending alongside the conveyor to direct flames therefrom onto the container body.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. pipe 17 through which gas is fed to the burner bars such as those denoted at 5. It is thought that there may be some advantage in the cyclic heating and cooling applied to the cooling applied to the coating on a can as it passes from bar to bar. As described previously the parameters of temperature and time of exposure are controlled to achieve partial curing. After heating to effect the desired degree of drying or partial cure of the coating, the can body may optionally be carried through a cooling location in which cold air is directed onto the surface of the can body from a nozzle 18. Thereafter each can is removed from the mandrel and ejected from the machine at a position E, and one or more further coatings are applied and dried or completely cured as described in relation to the method of Fig. 2. In Fig. 5A, each mandrel 14 is carried by a shaft 29 mounted on the hub 15 and carrying a pinion 28 which coacts with a gear wheel 19 fixed to the machine frame 20, so that as the hub 15 rotates, each mandrel is rotated continuously, so permitting the entire surface coating of each can carried thereon to be presented, by rotation, to the burners. A flue 21 is provided to conduct the fumes, if any, away from the machine. The coating materials used may be known materials or alternatively may be modified by the addition of a high level of lubricant incorporated to produce a high degree of slip in the coating which aids subsequent conveying of the cans. When base coatings having high levels of lubricant are stoved in the manner of the prior art, the lubricant residing on the surface after the relatively low temperature curing interferes with the deposition of further coatings. However, if the methods shown in Fig. 2 is used any residual lubricant in or near the surface of the base coating is driven off so leaving the surface receptive to a second coating of, for instance, a printing ink. The subsequent final stoving of the combined coating reblooms the surface to a lustrous quality and satisfactory slip. While the invention has been described in terms of rotating mandrels to carry the coated article, where rotation is not essential, a known peg chain may be used to carry the article before the flame. WHAT WE CLAIM IS:-

1. A method of coating a container body with at least two successive coatings, said method comprising the steps of applying a first coating of an organic coating material to a container body; passing the coated container body rapidly before at least one flame source to only partially cure the first coating but sufficiently to permit application of a second coating; applying a second coating of organic coating material to the only partially cured first coating; and thereafter fully curing the two coatings.

12. Apparatus according to claim 11 wherein said burner bars are spaced apart.

14. Apparatus according to claim 8

wherein the support means is a peg mounted on a chain.

15. A container body coated by the method according to any of claims 1 to 7.

16. A method substantially as herein before described with reference to Fig. 2 of the accompanying drawings.

17. Apparatus substantially as herein before described with reference to Figs. 3A and 3B of the accompanying drawings.

18. Apparatus substantially as herein before described with reference to Figs. 4A and 4B of the accompanying drawings.

19. Apparatus substantially as herein before described with reference to Figs. 5A and 5B of the accompanying drawings.