GB2122922A - Coating of containers - Google Patents

Abstract

Plastics bottles are coated by use of apparatus which conveys the bottles seriatim first to an applicator (42) which pours coating agent onto each bottle while the bottle is rotated, and then to a drying oven in which the coatings are dried by a stream of warm air. The applicator (42) has spouts (45) Äsee also Fig. 5Ü from which pours coating material as the bottles are rotated about a vertical axis by a rubber band (50) whilst being conveyed on a chain conveyor by hooks (29). <IMAGE>

Description

SPECIFICATION Improvements relating to the coating of containers This invention relates to the coating of containers, bottles for example.

It is known to form containers, bottles and jars for example, of materials which are suitable in some essential respects, such as being capable of providing the required degree of strength and rigidity to the container, but which nevertheless do not possess or possess to a sufficient degree a characteristic which is desirable or essential having regard to a particular commodity which it is intended that the container should hold. Thus, for example, polyethylene terephthalate (PET) possesses advantages as a material for use in the blow moulding of bottles. PET is readily blow moulded at a comparatively low temperature to provide bottles which although being thin skinned, and thus economical in material utilisation, are strong. Also, the bottles although having good structural rigidity, can withstand substantial mechanical shock without being ruptured.When though PET bottles are used to hold gasified liquids, cordials containing dissolved carbon dioxide for example, it has been found that the gas diffuses out of the bottle through the walls thereof so that when the consumer opens the bottle, the product lacks the expected amount of gasification.

It is also possible for atmospheric oxygen to diffuse into the bottle, a phenomenon which can have a deleterious effect on the liquid within the bottle. Furthermore, liquid loss can be occasioned by migration of the liquid through the PET walls.

Bottles and other hollow containers formed of PET can be rendered impervious to gases and liquids by applying thereto, preferably on the exterior, a suitable barrier agent. One such agent is polyvinylidene chloride (PVDC). Another is polyvinyl chloride (PVC).

Among the other reasons for coating the exterior or interior of containers is to impart colour or decoration to them, to remove static electrical charge or to reduce the transmission of light through the container walls.

Heretofore problems have been met in attempting to apply coating agents to containers in a speedy and economical fashion whilst obtaining a final coating which is uniform and free of blemishes.

The present invention provides apparatus for applying a liquid coating agent to containers, said apparatus comprising applicator means, container transport means operable to transport containers to and from a location at which said containers are presented to said applicator means, and rotation means operable to rotate said containers about respective axes thereof relatively of said applicator means when at said location, said applicator means being operable to apply by pouring a liquid coating agent to said containers while said containers are being rotated by said rotation means relatively of said applicator means.

The present invention also provides a method of applying a liquid coating agent to containers, wherein said containers are transported to a location at which said containers are presented to applicator means operable to pour said coating agent on to said containers, said containers being rotated about respective axes thereof relatively of said applicator means during operation of said applicator means.

Conveniently, the liquid coating agent comprises a coating material in a liquid medium.

The containers are suitably rotated about an upwardly extending axis, whereby the liquid coating agent flows downwardly gravitationally over the surface of the container. The coating agent may be applied to an exterior surface and/or an interior surface of each container. The whole or a part(s) of the exterior or interior surfaces may be coated with the coating agent.

The liquid coating agent is not sprayed onto the containers but issues from the applicator means under a low head and thus flows gently onto each container. This results in a very smooth, uniform and blemish-free coating of the coating agent on the containers.

In order to preserve this high quality coating in the final product, after the coating process has been completed the containers are subjected to a carefully controlled drying process in a dust-free environment. If the coating agent used comprises a coating material in suspension in water, the drying process is advantageously carried out by bringing the coated containers into contact with a stream of warm, moist air. The temperature, humidity and flow rate of the air are selected with a view to avoiding over rapid drying of the coatings on the containers.

In order that the invention may be clearly understood and readily carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which: Figure 1 shows a plan view of a bottle coating machine and a blow moulding machine; Figures 2-5 show detail views of parts of the bottle coating machine; and Figure 6 shows a coating agent flow circuit and a rinsing water flow circuit of the bottle coating machine of Figure 1.

The bottle coating machine shown diagrammatically in Figure 1 comprises a casing generally designated 1 comprised of a base wall 2, side walls 3-9 and a cover wall which has been removed in the view shown in Figure 1 for the purpose of illustrating parts of the machine within the casing 1. The casing 1 is supported by a support framework (not shown) disposed beneath the base wall 2. Secured at side wall 4 of the casing 1 is a control unit 10 housing a process controller (not shown). Abutting side wall 6 of the casing 1 is an air conditioning unit 11.

Outside of the casing 1 of the bottle coating machine there is disposed an input conveyor 1 2 arranged to receive freshly blow moulded bottles from an output conveyor 1 3 of a blow moulding machine 14. Pivotally connected to the conveyor 13 is a piston-and-cylinder unit 1 5 operable to slew the conveyor 1 3 to a position, indicated by chain line, in which bottles passing from the moulding machine 14 are directed to a store facility (not shown) instead of being transferred to the input conveyor 12.Thus if during operation of the blow moulding machine 14 the bottle coating machine stops, either manually by operation of a stop button or under action of a signal emitted from the process controller of control unit 10, the piston-and-cylinder unit 1 5 is activated to slew the conveyor 1 3 to its store position.

In a space bounded by the walls 4, 5 and 9 of the casing 1 there is positioned an applicator unit generally designated 1 6 and described in detail hereinbelow. A drip tray 1 7 lies between partition walls 18 and 19 of the casing 1. The region within the casing 1 which is bounded by the partition wall 19 and the outer wall 7 constitutes a drying oven generally designated 20.

Referring now to Figure 2, there are there depicted delivery end portions of the input conveyor 12 and a transfer head 21. The conveyor 12 comprises two laterally spaced elastomeric conveyor bands, only one of which (22) is shown, trained about pulley 23 and a second pulley (not shown) at the other end of the conveyor 12. The transfer head 21 comprises a block 24 having mounted at each of four faces thereof a suction cup 25. When a bottle is moved on the upper run of conveyor 12 towards the head 21, the base of the bottle is received in one of the cups 25 facing the conveyor 12 where it is held under vacuum, applied to the cup 25 by vacuum application means (not shown), while the head is indexed 900 to bring the bottle into an upright position. A bottle A at such latter position is indicated in chain line.

Mounted at a pivot location below the upper run of the conveyor 12 is a restraining arm 26 which under the action of a piston-and-cylinder unit 27 can be moved to the position thereof depicted in Figure 2, in which position the arm 26 projects above the upper run of the conveyor 12.

When the restraining arm 26 is in such projecting position a bottle being conveyed towards the transfer head 21 is held by the arm 26 against the drive force of the conveyor 1 2. The piston-andcylinder unit 27 may be activated to place the arm 26 momentarily in the projecting position to ensure synchronization of the presentation of a bottle with the indexing rotational movement of the transfer head 21. The process controller of the control unit 10 senses the position of the head 21 and emits signals to activate the piston-andcylinder unit 27 as required. Parts of a bottle B held by the arm 26 are shown in chain line.

When a bottle is brought into an upright position by the transfer head 21, a neck flange 28 of the bottle is supportively engaged by a pair of spaced-apart parallel support bars (not shown) extending beneath a conveyor chain 31 trained about chain wheels 33 and 34. The vacuum applied to the cup 25 holding the bottle is then released. Attached to the chain 32 are pusher elements (also not shown) which serve to engage the bottle necks and thereby cause the bottles to be moved with the chain 32.

In the vicinity of the chain wheel 33 the support bars are discontinued and each bottle is transferred to a main conveyor chain 56 as the chain passes about a chain wheel 55. The neck flange 28 of the bottle (see Figure 3) is supportively engaged by a bifurcated lower portion 29 of a bottle hook 30 forming part of the chain 56. Lower portions 29 of the bottle hooks 30 can be seen in plan view in Figure 4.

The bottle hooks 30 are so spaced along the chain 56 and drive means (not shown) are so operable that a bottle hook 30 is correctly positioned to receive a bottle from the chain 31 every time a bottle is conveyed by the chain 31 to the transfer location.

In order to guide and steady the bottle hooks 30 PTFE guide strips 35 and 36 are provided in the vicinity of the chain 56. Guide strip 35 is mounted on a bracket 37 attached to a stationary structural member 38 and guide strip 36 is mounted on a mounting strip 39 attached to a stationary structural member 40. Also mounted on the strip 39 is a bottle guard 41 which serves to prevent the bottles from becoming dislodged from the bottle hooks 30. The guard 41 is, of course, discontinued at the transfer location.

The applicator unit 16 further comprises an applicator head generally designated 42 (see Figures 4, 5 and 6). An upwardly extending cylindrical block 43 of the applicator head 42 is secured, via a bracket 44, to a chain wheel 58 of the conveyor chain 56 for rotation with the wheel 58. Mounted in and extending horizontally from the block 43 are four equi-angularly spaced tubular spouts 45. At its lower end the block 43 is received in a PTFE coupling 46 fixedly secured over the upper end of a pipe 47. A supply pipe 48 is integral with the pipe 47, the bore of pipe 48 communicating with that of pipe 47. The bore of the pipe 47 communicates with those of the spouts 45 via the coupling 46 and an axial bore in the block 43. The bore of the pipe 47 is extended downwardly with restricted diameter through a drain nippie 49. When liquid coating agent flows from the supply pipe 48 to the spouts 45 a small proportion of the liquid utilised to lubricate the coupling 46 issues from the upper end of the coupling 46.

Figure 4 shows a plan view of the applicator head 42, for the sake of clarity the chain wheel 58 and the chain 56 not being depicted. Reference numeral 50 designates a rubber band of 'O' section held in hooks 51 and 52 and passing about a peg 53.

In the direction of travel of the conveyor chain 56 the chain 56 passes from the chain wheel 55 around chain wheels 57 and 58 before entering between partition walls 17 and 19, where three runs of the chain 56 extend over the drip tray 1 7.

At the ends of these runs the chain 56 passes around chain wheels 59-61. The chain 56 then extends in a plurality of runs within the drying oven 20, the chain 56 passing within the oven 20 around chain wheels 62-72. From the chain wheel 72 the chain 56 extends to a chain wheel 73 and from chain wheel 73 back to chain wheel 55.

Disposed near to the chain wheel 73 is cam means (not shown) which acts to cause bottles to be transferred from the conveyor chain 56 to an upwardly inclined output conveyor belt 74.

The coating agent flow circuit (see Figure 6) comprises a reservoir tank 75 which may be replenished with liquid coating agent, PVDC for example, from a supply barrel connected to the tank 75 via a pipe 77 incorporating a remotely operable stop valve 78. Mounted on the tank 75 is a level detector 79 connected by a lead (not shown) to the process controller of the control unit 10. A peristaltic pump 80 is operable to draw coating agent from the reservoir tank 75 via a suction pipe 81 and to deliver the coating agent to a header tank 82 via a supply pipe 83 incorporating a filter 84. The header tank 82 is connected with the applicator head 42 via the supply pipe 48, the flow rate in the pipe 48 being controlled by means of a flow control valve 85.

From the header tank 82 there also extends a pipe 86, which pipe terminates within a small tank 87 provided with an orifice 88. A level detector (not shown) is located at the outlet end of the pipe 86 and is connected, by a lead (not shown), to the process controller of the control unit 1 0. Another level detector, designated 89, is mounted on the header tank 82.

A sump 90 extends below and around the applicator unit 16 and the tank 87 and from the lowest point of the sump 90 a pipe 91 extends to a two-position, remotely operable valve 92. A pipe 93 from the drip tray 1 7 extends to the pipe 91 intermediate its inlet and outlet ends. In one setting of the valve 92 the pipe 91 (and thus also the pipe 93) is put into communication with a pipe 94 which runs to the reservoir tank 75. In a second setting of the valve 92 the pipe 91 is put into communication with a pipe 95 which runs to a waste tank 96.

A rotary pump 97 is operable to draw water from a tank 98 via a suction pipe 99 and to deliver water to the header tank 82 via a supply pipe 100 incorporating a remotely operable stop valve 101.

The tank 98 may be replenished through a levelcontrolled valve (not shown) via a pipe 102 connected to a source of mains water 103.

Branching from the pipe 100 is a pipe 104, incorporating a remotely operable stop valve 105, which runs to a distribution pipe 106 extending within and for the full length of the drip tray 1 7.

In operation of the bottle coating machine, bottles freshly blow moulded, from for example PET, on the blow moulding machine 14 are received on the input conveyor 1 2 and are transferred one at a time by the transfer head 21 to the conveyor chain 31. As the chain 31 passes around the chain wheel 33 each bottle is transferred to the conveyor chain 56. As the bottles are conveyed on the chain 56 around the chain wheel 58 the bottles are each presented in a' vertical orientation to one of the spouts 45 of the applicator head 42 from which pours coating agent under the small head arising from the level of agent in the header tank 82. The head is typically 60 cm. The rubber band 50 contacts each bottle neck just below the neck flange 28 thereof and this causes the bottle to rotate about its axis several times while it is being presented to the spout 45.The bottle is first contacted by the liquid coating agent at a level just below the contact level of the band 50. As the coating agent flows smoothly onto each bottle without any splashing occurring, no drops of agent are deposited on the band 50. The coating agent flows downwardly over each bottle to provide a continuous, smooth and blemish-free coating over the whole exterior surface of the bottle below the initial application level.

Coated bottles are then conveyed over the drip tray 1 7 which serves to receive excess liquid coating agent which drops from the centre of the hemispherical base of each bottle. The conveyor chain 56 then conveys the bottles through the drying oven 1 7 where the bottles are brought into contact with a stream of clean, warm, moist air generated, at variable flow rate, by the air conditioning unit 11. The temperature of the air at entry to the oven 1 7 may be within a range of 40-700C and the air has an entry relative humidity of about 30%.The drying air leaves the oven 20 through an opening bounded by the wall 8 and one end of the wall 34 and then flows over the full length of the drip tray 1 7 before exhausting from the bottle coating machine via ducting (not shown) extending upwardly from the cover wall of the machine.

Bottles with fully dried coatings leave the drying oven 20 on the run of the conveyor chain 56 which extends between the chain wheels 72 and 73, being transferred to the output conveyor belt 74 before reaching the chain wheel 73. The thickness of the dried coating may be in a range of 6-10um.

If during operation of the bottle coating machine the level detector located at the outlet end of the pipe 86 emits a signal to the process controller indicative of the liquid level within the tank 87 having fallen below the level of the outlet end of the pipe 86, the process controller causes a signal to be displayed warning that the pressure head available at the spouts 45 has fallen.

If the level detector on the header tank 89 sends a low liquid level signal to the process controller, the process controller causes the machine to stop.

When the process controller receives a low liquid level signal from the level detector 79 mounted on the reservoir tank 75, the process controller causes the valve 78 to be opened for a sufficient time to replenish the tank 75.

During the coating operation of the bottle coating machine the sump 90 serves to receive surplus coating liquid which drops from the bottles during and immediately after presentation to the spouts 45, and coating liquid issuing from the upper end of the coupling 46, the drain nipple 49 and the orifice 88 of the tank 87. The liquid passes from the sump 90 via the r;pe 91. This liquid, together with that passing to pipe 93 from drip tray 17, flows through valve 92 into pipe 94 and thence to reservoir tank 75.

Whenever the bottle coating machine is stopped, whether manually or under command of the process controller upon a fault condition being sensed by the process controller, a rinsing cycle is carried out automatically under command of the process controller. According to a rinsing cycle procedure, the pump 80 is stopped and after the elapse of a draining period of, for example, 3 minutes, the valves 101 and 105 are opened, the valve 92 is turned to its second setting and pump 97 is started and run for a period of, say, 1-10 minutes. The pump 97 is then stopped and the valves 101 and 105 closed. After the elapse of a water draining period, the valve 92 is put back to its first setting and the pump 80 is restarted.

When the bottle coating machine is stopped manually no more bottles are allowed to enter the machine, but the conveyor chains 31 and 56 continue in motion for a time sufficient for all of the bottles in the machine to pass out of the machine.

Immediately after a total stoppage occurs, an emergency stoppage for example, the air conditioning unit 11 acts, under command of the process controller, to rapidly reduce the temperature of the air entering the oven so as to prevent the coating agent on the stationary bottles therein, and the bottles themselves, being subjected to an over rigorous heating.

Bottles of material other than PET, those of PVC for example, may be coated on the above described coating machine.

The bottle coating machine is capable of coating 4,000 bottles per hour.

Claims (18)

1. Apparatus for applying a liquid coating agent to containers, said apparatus comprising applicator means, container transport means operable to transport containers to and from a location at which said containers are presented to said applicator means, and rotation means operable to rotate said containers about respective axes thereof relatively of said applicator means when at said location, said applicator means being operable to apply by pouring a liquid coating agent to said containers while said containers are being rotated by said rotation means relatively of said applicator means.

2. Apparatus according to Claim 1 , wherein said rotation means is operable to rotate each of said containers about an upwardly extending axis.

3. Apparatus according to Claim 1 or 2, and comprising supply means constructed and arranged to supply the coating agent to said applicator means under a low gravitational head.

4. Apparatus according to any one of Claims 1 to 3, wherein said applicator means comprises a pouring spout and drive means operable to drive said spout along a path which maintains said spout in coating application relationship with a container during the passage of the container through a portion of the path of travel along which the container is transported by said transport means.

5. Apparatus according to Claim 4, wherein said spout is one of a plurality of spouts each of which is drivable in the same manner by said drive means.

6. Apparatus according to any preceding claim, wherein said transport means comprises endless chain means carrying at regular intervals therealong a plurality of container support means.

7. Apparatus according to Claim 6 as appended to Claim 4 or 5, wherein said drive means comprises a rotary element drivable by said chain means.

8. Apparatus according to any preceding claim, wherein said rotation means comprises elongate means which is urged into frictional contact with the containers.

9. Apparatus according to any preceding claim, and further comprising an oven and air supply means operable to supply to said oven a stream of warm air, said transport means or further transport means being operable to transport coated containers through said oven.

10. A method of applying a liquid coating agent to containers, wherein said containers are transported to a location at which said containers are presented to applicator means operable to pour said coating agent on to said containers, said containers being rotated about respective axes thereof relatively of said applicator means during operation of said applicator means.

11. A method according to Claim 10, wherein the containers are formed of plastics material.

12. A method according to Claim 11, wherein the plastics material comprises polyethylene terephthalate or polyvinyl chloride.

13. A method according to any one of Claims 10, 11 and 12, wherein said coating agent comprises a coating material and a liquid medium.

14. A method according to any one of Claims 10 to 13, wherein said coating agent comprises polyvinylidene dichloride or poiyvinyl chloride.

1 5. A method according to any one of Claims 10 to 14, wherein said axes are upwardly extending axes.

1 6. A method according to any one of Claims 10 to 15, wherein the containers are bottles.

1 7. Apparatus for applying a liquid coating agent to containers, substantially as hereinbefore described with reference to the accompanying drawings.

18. A method of applying a liquid coating agent to containers, substantially as hereinbefore described with reference to the accompanying drawings.