Method and apparatus for coating and curing containers

Abstract

 The invention relates to the coating of plastic containers for foods, beverages, cosmetics and the like to make them less perme­able and give them a longer shelf life. The object of the invention is to obtain proper coating and curing in a fast and efficient man­ner. The containers (22) are gripped by their necks with a gripping member (46), which moves the containers through a coating chamber (14), in which an exterior barrier coating is applied such as by spraying onto the containers while they are rotated, which rotation is continued after the coating operation. The containers are there­upon moved to a curing chamber (16), where the coating is cured.

Description

BACKGROUND OF THE INVENTION

[0001] Soft drinks such as carbonated sodas are commonly packaged in plastic containers known as PET containers. Additionally, other plastic containers are being used or developed for packaging beer, salad dressing, and other foods and for packaging cosmetics, pharma­ceuticals, and other items. The plastic containers have a relatively short shelf life so that the carbonated soda or other product loses its carbonation or freshness within a relatively short period of time after which they cannot be sold to consumers. There are barrier coatings available for coating the exterior of PET containers such that they become less permeable and are able to retain the beverage in pressurized condition for longer periods of time thus extending the shelf life of the package. Other barrier coatings are being used or are being developed for other types of plastic containers for the purpose of extending package shelf life.

[0002] The present invention is directed to a method and apparatus for coating and curing plastic containers and includes systems for handling plastic containers and moving them through coating and curing equipment in a fast and efficient manner thus ensuring proper coating and proper curing of the containers so that the resulting coated and cured container receives the full advantage of extended shelf life provided by the outside barrier coating.

SUMMARY OF THE INVENTION

[0003] The method and apparatus for coating and curing containers according to the present invention preferably forms part of a container operating line including equipment for forming, washing, coating, curing, printing or labelling, and filling the container with the product being packaged. Such equipment is interconnected by container conveyors, single filers, and handling equipment to achieve high operating speeds necessary for economic and efficient production.

[0004] In the case of the present invention, containers are prefer­ably delivered to the coating and curing apparatus by a container transfer system described in copending application Serial No. 647,297 filed September 4, 1984. Such transfer system generally includes a conveyor for delivering uncoated plastic containers to a flighted transfer conveyor in a substantially horizontal position moving in timed relationship to a series of carrier devices. Suitable carrier devices are described in copending application Serial No. 657,244 filed October 3, 1984 entitled Rotational And Retractable Container Holding Device and Conveyor Therefor. The carrier devices engage each container by its neck or mouth for carriage through the coating and curing system and for delivery of the coated and cured containers to a takeaway conveyor. The carrier devices effectively close the mouth of each container so that the application of the barrier coating is limited to the exterior surface of the container. The carrier devices then move as they are carried along by their conveyor to position the containers within the coating chamber, rotating the containers within the coating chamber to assure full and uniform coating of the containers and to provide sufficient rotational movement so that the coating does not sag or drip but is evenly distributed. After the coating is applied, the containers are carried through a curing oven, still mounted on the carrier devices, in a serpentine path so that the curing becomes complete.

[0005] In a further aspect of the present invention, the containers after being coated are carried through the curing oven and subjected to a combination of radiant and convection curing of the exterior barrier coating. The carrier devices move the containers up and down through the oven in a serpentine path. Each vertical pass forms a separate chamber for projecting selected radiation on the entire coated surface of the container for curing. Additionally, each vertical pass provides heated air for convection curing the containers. The curing oven may have one or more vertical passes according to production rates required and the dwell time necessary to cure the coating.

[0006] In a preferred form, each vertical pass is provided with a source of radiant heat at the lower portion of each pass for radiation curing. Convection air is recirculated through each pass and is heated by the radiant source to a preselected temperature for convection curing of the containers in the upper portion of each pass. A control system is provided for regulating the velocity and quantity of curing air to assure proper curing.

[0007] The oven may include one or more zones having different curing conditions for temperature and humidity to provide a curing profile particularly suited to the requirements of various kinds of containers and barrier coating materials.

[0008] Each zone may be provided with a humidification system where moisture is necessary for proper curing of a particular coating.

[0009] In employing an oven of the present invention having radiant heat and convection air curing, the exterior barrier coatings are set and cured simultaneously. Additionally, the coating is cured from inside to outside to avoid "skinning" a condition which occurs when the outside sets and cures first and prevents curing of the coating subsurface. This condition leads to "mud-cracking" as the subsurface erupts. Containers improperly cured are unusable.

OBJECTS OF THE INVENTION

[0010] It is an object of the present invention to provide a method and apparatus for coating and curing containers particularly plastic containers including carrying containers to expose substantially their entire outer surfaces, applying an exterior barrier coating to the outer surfaces of the containers and thereafter curing the coating such that the container is ready to receive a consumer product.

[0011] A further object of the present invention is to hold, rotate, and move each container through coating and curing operations.

[0012] A further object is to grip each container at its open end so that the entire exterior surface of the container receives a barrier coating, while the neck and container interior are shielded from the coating, and that the applied coating may be cured.

[0013] A further object of the present invention is to provide a carrier system for receiving, holding, rotating and moving plastic containers in substantially horizontal orientation along a serpentine path through a coating chamber and a curing chamber.

[0014] A further object of the invention is to provide means for rotating the containers as they are carried through the coating and curing chambers.

[0015] Another object is to provide a method and apparatus for providing high speed rotation as the container is being sprayed in the coating chamber to assure uniform distribution of the coating in the coating chamber and thereafter lowering the speed of rotation substantially to maintain and control the thickness of the barrier coating without drip or sag.

[0016] A further object is to provide a system as described having a selectable line speed according to desired production rates, e.g., from twenty-five to one hundred fifty feet per minute.

[0017] Another object of the invention is to provide for curing the exterior barrier coating from inside to outside.

[0018] Another object of the invention is to provide radiant heat and convection air curing of the exterior coating.

[0019] Another object of the invention is to provide recirculating convection air heated to a preselected temperature by the radiation source.

[0020] Another object is to provide a curing oven with a plurality of zones for variation of curing conditions according to various types of containers and coatings.

[0021] Another object of the invention is to provide radiant heater panels at the bottom of each curing oven pass to provide a radiant curing profile to completely cover the bottle surfaces.

[0022] Another object is to provide a humidification system for particular coatings requiring elevated temperatures before beginning an evaporative curing process.

[0023] Another object of the invention is to provide an oven designed in standard modules for ease of fabrication, shipping, and assembly in a container operating plant.

[0024] Other and further objects will become apparent to those skilled in the art upon an understanding of the specification hereof, or will occur upon employment of the invention in practice.

DESCRIPTION OF THE DRAWING

[0025] A preferred embodiment of the invention has been chosen for purposes of illustration and is shown in the accompanying drawing in which:

FIGURE 1 is a schematic view of the method and apparatus of the present invention including a loading zone, a coating zone, a curing zone and a discharge zone all being connected by a conveying system shown in a dot-dash line.

FIGURE 2 is a fragmentary plan view showing a container transfer system including infeed conveyor, timing screw, transfer conveyor, and container holding device conveyor, with which the present invention may be used.

FIGURE 3 is a side elevational view of containers moving through a coating chamber and also illustrating the driving mechanisms for rotating the containers.

FIGURE 4 is a plan view in section of the container holding device as it carries a container through the coating chamber.

FIGURE 5 is a view corresponding to FIG. 4 and showing the relative position of a device having no container.

FIGURE 6 is a front elevation view of a curing oven comprising several modules according to the present invention.

FIGURE 7 is a side elevation view in section illustrating the interior layout of a curing pass and the recirculation path of convection air.

FIGURE 8 is a plan view of the interior of the module of FIG. 7 showing radiant heating panels arranged in profile for curing containers.

FIGURE 9 is a plan view of a module of FIG. 6 showing the profiles of radiant heating panels in adjacent oven passes.

DETAILED DESCRIPTION OF THE INVENTION

[0026] Referring to FIG. 1, the present invention is illustrated schematically and it includes an endless conveyor member 10 shown in broken line for receiving containers at a loading station 12, moving containers from the loading station into a barrier coating chamber 14 and then to a curing chamber 16 where the barrier coating is cured. The containers thereafter move to a discharge station 18 where they are taken away by conveyor for subsequent operations in filling them with consumable products such as carbonated beverages, or food products such as ketchup, salad dressing, and so forth. As more fully explained below, the containers are carried in a substantially horizontal orienta­tion by the endless conveyor member and travel serpentine paths through the coating and curing chambers.

[0027] A container transfer system suitable for use with the present invention is described in the aforesaid patent application Serial No. 647,297 and generally includes, as shown in FIG. 2, an in-feed conveyor 20 for moving containers 22 through an orienting chute 24 to timing screw 26 and transfer conveyor 28. The transfer conveyor includes an entry conveyor 30 for receiving individual containers in position bet­ween subsequent flights 32 and a container conveyor 34 which is flighted, for supporting and positioning containers after they have been reoriented from the vertical to horizontal positions by a neck engaging guide 36. The shape and arrangement of these flighted conveyor members is suitable for the container configuration illustrated in FIG. 2. It is to be understood that the configuration of the transfer conveyor flight sections may be modified as desired to conform with different container configurations including cylindrical containers as disclosed in copending application Serial No. 647,297.

[0028] The container carrier conveyor 10 moves in timed relation with the transfer conveyor 28 and includes carrier devices 38 for engaging and gripping each container at its open end and for carrying them in a substantially horizontal orientation through the coating and curing chambers. Each container carrier device travels in timed and spaced relationship and along a path A parallel to the path B travelled by containers on the transfer conveyor. Additionally the container carrier devices are aligned with individual containers such that by extending the devices across the space between parallel paths, each device engages and grips a container by the neck. After the container is securely gripped, the transfer conveyor and carrier conveyor follow diverging paths and the container carrier device carries its container through a subsequent coating and curing operations.

[0029] The container carrier devices are described in detail in copending application Serial No. 647,297 and for purposes of this application it is sufficient to understand that each device is mounted to endless conveyor 10, has an inner housing 40, and outer housing 42 rotatably mounted to the inner housing at roller joint 44, and a head or chuck 46 for engaging each container at its open end. The inner and outer housings are slidable axially with respect to their central mounting pin 48. A cam follower 50 on the inner housing provides for this axial movement in cooperation with a cam member 52.

[0030] For loading containers on to carrier devices 38, the cam follower 50 engages the surface 54 of cam member 52 and extends the device in an axial direction against the compression force of internal spring 56 (FIG. 4). As the gripping head 46 and container 22 are moving in timed relation and in registry with one another, the head engages and secures the individual containers shown at the left hand side of FIG. 2. Container holding devices 38A (FIG. 2) not engaging a container will be retracted by the force of their internal spring 56 through the cam gap 58 (FIG. 2) and follow a separate path than container bearing carriers throughout the coating and curing operation.

[0031] FIGS. 4 and 5 respectively illustrate the position and operation of container holding devices which have received a container and travel along an active path in engagement with cam surfaces 54. In FIG. 4, the device 38 has positioned container 22 within a coating chamber 14 to receive a barrier coating 60 sprayed by nozzles 62. The position of the container within the chamber is determined by location of cam surfaces 54 acting on cam follower 50. A drive belt 64 on drive wheel 66 located on the side of the holding device is driven by shaft 68. The drive belt engages belt member 70 for the purpose of rotating the outer housing 42 and container 22 within the coating chamber. Such container rotation is desirable to assure even reception of the coating by the container during spraying, and to prevent dripping of coating by the container during spraying, and to prevent dripping or sagging of the coating before it is cured.

[0032] It will be observed that by virtue of the neck gripping of the container, the entire outer surface of the container is available for reception of the barrier coating. Additionally the neck itself and the container interior are shielded from the coating which would be unwanted in these areas.

[0033] An antechamber 72 houses pipes 74 which direct a water mist 76 into the coating chamber to achieve desired humidity levels in the chamber and to prevent coating material from entering the ante­chamber. In FIGS. 4 and 5, the container holding device is oriented horizontally and is travelling vertically through the coating chamber with cantilever support from rails 78 and 80 affixed to brackets 82.

[0034] The container holding device 38 of FIG. 5 is inactive in that it has not received a container from the transfer conveyor. Consequently the device is fully retracted with head 46 travelling within the antechamber 72 without rotation, and with cam follower 50 disengaged from cam surfaces 54.

[0035] Referring now to FIGS. 1 and 3, the container carrier conveyor 10 is arranged over spaced sprockets 84 for passage through a serpentine path through the coating chamber 14 and the curing chamber or oven 16. The carrier conveyor with containers enters the coating chamber in a vertically downward path with the carrier devices engaging driving belt 64 for rotating the outer housing of each carrier device and the container 22 at the outer extremity of each device. The containers are rotated at considerable speed from 600 to 1,000 RPM and preferably at approximately 800 RPM as they enter and pass through the coating zone 86 within the coating chamber. The container spin allows for even distribution of the coating on the containers in the coating chamber. Continued spin of the containers thereafter at a slower spin rate assures the continuation of the even distribution of the coating without dripping or sagging.

[0036] The driving belt 64 as shown in FIG. 3 is mounted over suitable pulleys 88 and is driven by a drive motor and gear box 90.

[0037] As the carrier conveyor enters the curing chamber, the rotatable joint of the carrier devices engages the driving belt and rotates each of the containers at a substantial rate as, for example, 800 RPM for receiving the barrier coating. This rotation ensures even distribution of the coating on the containers. After emerging from the coating zone, the container carrier devices, at their rotatable joints, engage a rub rail 92 extending from point A to point B along the carrier conveyor path outside the coating chamber. Thereafter, the rotatable joints engage a second drive belt 94, suitably mounted over pulleys 96 and driven by motor 98 and belt 100, for the purpose of continuing the spin of the containers to preserve the integrity and distribution of the coating. A container speed of 40 to 100 RPM is suitable for this purpose. After emerging from the coating chamber, the containers once again engage a third drive belt 104 between points C and D of the conveying path and subsequently a driving belt 106 which rotates the containers 40 to 100 RPM as they travel a serpentine path through the curing oven.

[0038] As shown in FIGS. 1 and 6-9, the curing oven 16 in general arrangement comprises a series of upright units 110 each defining a module component of the curing oven. Typically, a curing oven will have left handed 112 and right handed modules 114 defining respectively container entrance and exit from the oven as well as initial and final curing passes of the oven together with intermediate modules 116 of similar design. The modular concept provides for ease of design, fabrication, final assembly, operation, maintenance and repair, as well as operating flexibility in different container operations at an operating plant. Preferably, the curing oven includes two or more zones with each having a curing environment for temperature and humidity particularly suited to a given container and coating composition and with each zone individually adjusted to provide the desired variations required of the curing process for such containers.

[0039] A preferred curing oven is illustrated in FIG. 6 and comprises a plurality of individual modules including right hand 114, intermediate 116, and left hand modules 112 joining at several interfaces 118. The left hand module provides downward pass 120 from the oven entrance 121 and upward vertical pass 122. Each intermediate module provides upward and downward passes 126, 128, and the right hand module a downward pass 124 and a upward pass 130 to oven exit 132.

[0040] Each module 110 is an enclosed upright boxlike structure with bottom 134 and roof 136 panels and front, rear, and side panels 138. The front panels of each module have elongated openings 140 providing access for the container carrier devices 38 and containers 22 into the curing chambers of each module. The openings 140 are continuous from module to module and define the sinusoidal or serpentine path travelled by the containers. The rear panel is provided with hinged 141 access doors 142 and latches 144 for entry to the interior of each vertical pass.

[0041] It is an aspect of the present invention to provide radiant curing and convection curing for coated containers. The nature of radiant energy required for curing depends on the composition of the coating and may be, for example, ultraviolet or infrared radiant energy. Additionally, convection curing is used wherein the curing medium, preferably air, is heated by the radiant source.

[0042] In a preferred embodiment of the invention for curing barrier coatings for PET containers infrared radiant energy and convection air are used in each vertical pass through the oven. The infrared source preferably occupies the lower half of each pass and the convection curing the upper half. In this way passing containers alternately encounter convection curing and infrared curing from entrance to exit of the oven.

[0043] Accordingly, the interior of each module is provided with a radiant energy source 146 for projecting curing radiation toward the container coatings 148. As shown in FIGS. 7, 8, and 9 the radiant energy source preferably comprises a series of infrared panels 150 adjustably mounted by suitable brackets 152 to the oven interior. The infrared panels extend substantially through the lower half 153 of the oven passes and are arranged to project infrared radiation onto passing containers. As shown in FIG. 8, the panels 150 define a profile particularly suited to a given container configuration and extend in an arc following a one-half section of a container from the container centerline adjacent to the container base 154 around to the container neck 156. It will be understood that as each container rotates, its entire exterior surface is exposed to the infrared radiation and accordingly the infrared profile presents a most economical curing arrangement. Additionally, by this arrangement, the infrared radiation can be selectively directed to provide radiation intensity at optimum levels according to the curing demands of different portions of the container exterior. For example, the infrared panel nearest the container neck can be adjusted as to distance and direction of radiation toward the neck, generally considered a difficult to cure portion of the container.

[0044] The upper half 158 of each pass is provided with recirculating convection air for the purpose of curing container coatings. As best shown in FIG. 7, the convection air is circulated through a duct 160 fitted to and supported by a standard 162 at the rear face 164 of each oven zone. The recirculating duct is provided with a blower or fan 166 which forces air through a supply header 168 into the lower end of each pass for the purpose of being heated by the radiant source. A suitable control system such as a silicon control rectifier coopera­ting with a thermocouple (not illustrated) is provided for maintaining each radiation panel at a given temperature or radiation intensity in order to heat the recirculating air to a given curing temperature. The silicon control rectifier is set at a given temperature and in response to temperature variations sensed by the thermocouple will adjust the wattage to a radiant panel to maintain such given temperature. The convection air circulates upwardly in each pass curing entering containers and then returning through exhaust header 170 into the air circulation duct for continuous circulation into the curing chamber. The supply and exhaust headers of the air recirculating duct are provided with dampers 172 to control the volume and velocity of convection air. It is known that certain barrier coatings are sensitive to a relative velocity of air over the moving containers. This sensitivity may be taken into account in the present invention and the recirculating air by appropriate adjustment of the baffles be made to travel at various speeds as the containers move through the curing zone.

[0045] With certain coatings it is desirable to have a relatively high humidity so that the temperature of a barrier coating may be raised to an elevated level before significant evaporative curing of the coating begins. For this purpose a series of steam or water mist injection nozzles 174 may be provided for maintaining humidity at pre-selected levels within each air circulating chamber or in selected zones according to the desired curing cycle. High humidity will suppress evaporation of the coating until the coating reaches the proper temperature for curing.

[0046] The curing oven is preferably divided into separate zones having different conditions of temperature and humidity according to the particular stage of the curing process. Division of the oven into zones is accomplished by providing one or more vertical panels 176 or baffles to separate the interior in several chambers. A separate air recirculating system is then provided for each zone for circulating air of different temperature, humidity, and velocity.

[0047] In operation containers are carried on the carrier conveyor by individual holding devices through the serpentine path defined by each pass of the curing oven. As the containers enter the curing oven they are rotated by means of their carrier devices at a speed sufficient to maintain the even distribution of the coating on the container and also to continuously expose the outer surface of each container to the infrared curing profile in the infrared section of each pass. The containers first enter through the upper convection curing area and pass through the oven alternately receiving convection and radiation curing. After negotiating the lower sections of adjacent passes the containers rotating at 40 to 100 RPM emerge into the convection curing section and are cured in the upper portions of adjacent passes by means of convection air. The convection air is continuously recir­culated by means of an air circulation duct and maintained at an elevated temperature according to the infrared intensity setting for the infrared panels.

[0048] After passing through the curing oven the cured containers now pass along to a takeaway conveyor where they are further processed in the container operation, as for example, labelling, filling and so forth.

[0049] It will be apparent to those skilled in the art that various modifications can be made to the method and apparatus of the present invention without departing from the scope or spirit of the invention.

Claims

1. A method for coating and curing containers having neck and body portions with an exterior barrier coating comprising the steps of moving a line of containers to a transfer station, gripping each container by its neck with a gripping member in a manner that substantially the entire exterior surface of the body portion of each container is exposed, moving the containers to a coating chamber, applying an exterior barrier coating to each container, rotating the containers in the coating chamber as the barrier coat is applied to achieve even distribution of the coating over the container, rotating the containers after being coated to maintain uniform distribution of the coating without drip or sag, moving the containers to a curing chamber, and curing the coating.

2. A method as defined in claim 1 including the step of shielding the neck and interior of the container for application of the coating.

3. A method as defined in claim 2 including the steps of rotating the containers at a higher speed as the barrier coating is applied, and at a lower speed to maintain uniform distribution.

4. A method as defined in claim 3 in which containers at the higher speed rotate at 600-1,000 RPM and at 40-100 RPM at the lower speed.

5. A method as defined in claim 1 including the step of providing a separate inactive path, through the coater, for any gripping member not receiving a container at the transfer station.

6. An apparatus for coating and curing containers having neck and body portions comprising means for moving containers along a first path uniformly spaced from one another and having a common axial orientation, means for moving container carriers along a second path parallel to the first with the carriers axially aligned and in spaced, timed relationship to the containers, the container carriers each having means for gripping a container by its neck and for rotating the containers about their axes, and means for moving the container carriers into engagement with the containers so each carrier grips a container by the neck, and container carrier moving means being arranged for travel along a path through a coating chamber, and through a curing chamber, means for rotating the containers as they are coated, and means for curing the containers.

7. An apparatus as defined in claim 6 in which the container carriers include a rotatable hub, and means for engaging and rotating the hub in the curing chamber.

8. An apparatus as defined in claim 7 in which the rotating means includes spaced drive belts for rotating the container carriers at speeds between 600 and 1,000 RPM and rub rails for rotating the container carriers at speeds from 40 - 100 RPM.

9. An apparatus as defined in claim 6 in which the container gripping means also shields the container necks and interior from receiving the coating.

10. An apparatus as defined in claim 6 including means for moving a container carrier along a second inactive path through the coating chamber in the event such container carrier does not receive a container.

11. A method for coating open ended containers with an exterior barrier coating and for curing the containers comprising the steps of moving a line of containers to a transfer station, gripping each container at its open end with a gripping member in a manner that substantially the entire exterior surface of the body portion of each container is exposed, moving the containers to a coating chamber, applying an exterior barrier coating to each container, rotating the containers in the coating chamber as the barrier coat is applied to achieve even distribution of the coating over the container, rotating the containers after being coated to maintain uniform distribution of the coating without drip or sag, moving the containers to a curing chamber, and curing the coating by exposing the containers to convection curing and radiation curing.

12. A method as defined in claim 11 including the step of rotating the containers during the curing step.

13. A method for curing barrier coating applied to the exterior surface of containers comprising the steps of moving the containers through a curing path, rotating the containers as they move, and alternately applying convection curing and radiation curing as the containers move through such path.

14. A method as defined in claim 13 in which the radiation curing is applied in a profile conforming to a one-half contour of the container.

15. A method according to claim 13 in which the convection curing is applied by heated air and the radiation by infrared heater panels.

16. A method according to claim 15 in which the curing air temperature is maintained by recirculation through the infrared radiation region.

17. A method according to claim 13 including the step of controlling the humidity of at least a portion of the curing path.

18. A curing oven for containers having an exterior barrier coating comprising a series of oven modules defining a continuous path through the oven, each module defining one or more passes together comprising the continuous path, means defining a convection curing section of each pass, means for providing a convection curing medium, means defining a radiation curing section of each pass, radiation means, means for profiling the radiation for projection along a one-half contour of each container, and means for moving and rotating said containers through said path.

19. An oven as defined in claim 18 in which the convection curing and radiation curing are positioned alternately along said path.

20. An oven as defined in claim 18 in which the passes are arranged vertically in a serpentine path through the oven and in which the convection curing sections occupy the upper portion of each pass and the radiation curing sections the lower portion of each pass.

21. An oven as defined in claim 18 which includes at least two zones along said path having different curing conditions.

22. An oven as defined in claim 21 in which separate sources of convection curing medium supply each zone.

23. An oven as defined in claim 22 in which one or more zones are humidified.

24. A radiation curing section for an oven for curing barrier coated containers moving in a path through the oven comprising a plurality of radiation panels adjustably mounted within said oven adjacent said path, said panels being arranged in a profile substantially conforming to the planar outline of a one-half section of the container.

25. A radiation curing section as defined in claim 24 in which each radiation panel is set to operate at a given output through the intermediation of a silicon control rectifier and a thermo­couple.

Drawing