US3724161A

US3724161A - Closuring containers

Info

Publication number: US3724161A
Application number: US00184697A
Authority: US
Inventors: E Vermeulen
Original assignee: Sidaplax
Current assignee: Sidaplax
Priority date: 1971-09-29
Filing date: 1971-09-29
Publication date: 1973-04-03
Anticipated expiration: 1990-04-03

Abstract

Improvements in closuring a container with a sheet of biaxially oriented thermoplastic resin by shrinking a portion of the sheet overlying the container mouth to tightly mechanically engage portions of the sheet which had been previously crimped under a peripheral lip on the container. The container, which may be of the thin walled variety, is supported by a holder during closuring in the vicinity of the peripheral lip to minimize the vertical load applied thereto.

Description

O United States Patent H 1 [111 3,724,161 Vermeulen [4 1 Apr. 3, 1973 [54] CLOSURING CONTAINERS [56] References Cited [75] Inventor: Emile R. Vermeulen, Ghent, Belgi- UNITED STATES PATENTS um 3,017,729 1/1962 Cheeley ..53/30 X Asslgnw SldaPlaX Gembmgge, Belgmm 3,345,798 l0/1967 Sternau ..53 42 x 22 Filed: Sept. 29, 1971 Primary ExaminerTrav1s S. McGehee PP N04 184,697 Attorney.lames C. Logomasini et al.

Related US. Application Data ABSTRACT [63] Continuation-impart of Ser. No. 868,162, Oct. 21, v r

l969 Improvements m closurmg a container with a sheet of biaxially oriented thermoplastic resin by shrinking a [30] Foreign Application Priority Data portion of the sheet oyerlying the oontainer mouth to tightly mechamcally engage portions of the sheet June 29, 1971 Great Br ta n ..30,386/71 which had been previously crimped under a peripheral Oct. 28, 197! Great Britain ..5l,058l68 lip on h container The container which may be of the thin walled variety, is supported by a holder during [52] US. Cl ..53/42, 53/329 closul-ing in the vicinity of the peripheral hp to [51] hill. Cl. ..B65b 7/28 minimize the vertical d applied thereto [58] Field of Search ..53/42, 30, 329

11 Claims, 5 Drawing Figures PAHLNTEU'APR 3 I975 SHEET 1 or 4 FIG. I

INVENTQR EMILE R. VERMEULEN ATTORNEY PATHHED PR 3 I975 SHEET 3 BF 4 FIG. 3

INVENTOR EMILE R. VERME ULEN ATTORNt Y CLOSURING CONTAINERS This application is a continuation-in-part of copending application Ser. No. 868,162, filed Oct. 21 1969.

BACKGROUND OF THE INVENTION This invention relates to the closuring of containers, and particularly to a new apparatus for applying to a lipped container a closure of biaxially oriented thermoplastic resin. The invention also relates to the closured containers so produced.

There has recently been a vast increase in the employment of small packaging containers, particularly in the food industry, and a requirement has arisen for a simple closure device that can be rapidly and cheaply applied to the mouths of a series of filled containers. Cleanliness and the possibility of automatic operation are obvious desirable characteristics of any closuring system that is adopted; others, which are difficult to reconcile in practice, are ease of opening when required and sufficient strength to withstand the stresses of transportation. It is also normally required for the finished container to be liquid-tight and airtight. The requirement for ease of opening is particularly important where the container is intended to contain a potable liquid such as milk or squash and to be used as a drinking cup, because the cup rim needs to be clean and smooth without any residue from the closure material. Also, container-cups of this kind are often intended to be used by children, who require particularly easily openable closures in order to avoid spilling the contents.

It has been proposed to employ closures made of biaxially oriented thermoplastic resins, but although these have not been unsuccessful there is a need for improvement where the requirements for fluid-tightness and ease of opening exist. It has for example been proposed to employ the ability of the biaxially oriented resin to shrink by locally heating the edges of a closure cap so that these edges shrink under a lip around the edge of the container, and it has also been proposed to heat-seal such a closure to the container rim or to stick it by means of an adhesive, but such methods have not been entirely successful in that a certain percentage of failures occur with the consequent spoilage of contents or leakage onto other containers in close proximity to the offending one. For example a heat-seal or an adhesive can fail where a drop of the container contents has contaminated part of the sea] area. We have now also found that the temperatures necessary to effect shrinkage or a heat-seal can cause embrittlement of surrounding areas of the biaxially oriented resin with consequent danger of fracture in transportation. A heat-sealed closure is furthermore difficult to remove completely and a heat-seal lacquer can leave undesirable residues.

I In copending U.S. application Ser. No. 868,162 there is described an improved closuring method that gives a closure having both an excellent resistance to failure and the ability to be opened easily when required. The method is moreover simple and clean to carry out using inexpensive apparatus, and is amenable to automatic operation. The process and apparatus specifically exemplified in this copending application can place a degree of vertical compressive stress on the walls of the container, however, and to reduce any risk there might be of such stress damaging the container walls the modification described herein has been developed.

SUMMARY OF THE INVENTION In the process of closuring a lipped container with a sheet of biaxially oriented thermoplastic resin by placing said sheet over the open top of said container so that it overlaps the lipped edges thereof, pushing the overlapping portions of said sheet downwardly with a heated element without heat sealing the resulting heat softened sheet portions to the container while clamping to said container any heat softened portions of the sheet which contact the container to prevent such container contacting sheet portions from shrinking, crimping the pushed down sheet portions underneath and against the lipped edges of the container and shrinking thesheet portion overlying the open top of the container so as to pull the crimped portions tightly against the lipped edges of the container, the improvement which comprises supporting said container in the vicinity of the lipped edge to minimize the vertical stresses thereon during clamping.

The invention further contemplates improvements in apparatus for closuring a lipped container with a sheet of biaxially oriented thermoplastic resin which includes a heated element movable relative to the container to push down portions of the sheet overlapping the lipped edges of the container, means for clamping any heatsoftened parts of the sheet which contact the container tightly against the container, means for crimping without shrinking the pushed down sheet portions underneath and against the lipped edges of the container, means for shrinking the portion of the sheet overlying the open to of the container to pull the crimped pushed down portions underneath and against the lipped edges of the container by providing the improvement which comprises means acting in the vicinity of the lipped edges of the container for supporting the container during clamping.

The heated element for pushing down the overlapping portions of the sheet preferably comprises a frame having interior dimensions slightly larger than the lip of the container. Preferably these dimensions are so chosen that the frame clamps the small area of biaxially oriented sheet that abuts against the outer edge of the container lip. The frame thus needs to be designed to suit the particular container being used and it is therefore preferable that the apparatus as a whole should be so designed that interchangeable frames can be fitted. Preferably the part of the heated element that first meets the resin sheet is shaped or chamfered so that the overlapping portions are progressively bent down over the lip of the container; this part of the heated element can have ribs so that the sheet is heat softened at discrete areas spaced around the container rim, this assisting in the subsequent crimping operation by inducing the formation of evenly spaced crimps or pleats. Such ribs are not essential, however, as the pushed-down portions cockle and thus only contact even a smooth surfaced element at spaced areas.

BRIEF DESCRIPTION OF THE DRAWINGS In describing the overall invention, reference will be showing the first stage in an operation of closuring a container;

FIG..2 is a cross-section similar to that shown in FIG. 1 but showing the second stage in the closuring operatron;

FIG. 3 is a similar cross-section showing the third stage;

FIG. 4 is an enlarged portion of FIG. 3; and

FIG. is a timing diagram, showing the sequence of operations.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, the apparatus of the present invention comprises upper and lower assemblies 1 and 2 respectively, which are relatively movable in the vertical direction by means of a pneumatic cylinder A (see FIG. 5). In the lower assembly, a filled container 3 can be placed in a holder 4 which is movable (by means of pneumatic cylinders B) in a vertical direction on guides 5 fixed to a base plate 6. The upper rim of holder 4 is a reduced thickness so that it only contacts the part of the container lip that is adjacent to the container wall. This is shown most clearly in FIG. 4.

A crimping sleeve 7 is rigidly fixed to the tops of the guides 5 and has an upper edge 8 (shown in enlarged cross-section in FIG. 4), corresponding to the lower surface of the lip of the container.

The upper assembly 1 comprises an electrically heated frame 9. The inner dimensions of the frame are just larger than those of the lipped edge of the container, and its lower part is chamfered away as shown at 10. Slidably mounted within the frame 9 is a pressure plate 11. A compression coil spring 12 urges the pressure plate downwards with respect to the frame 9, such downward movement being limited by screws 13 and heads of which abut against the frame at the stroke limit. The pressure plate is not separately heated but becomes hot by conduction from the frame.

Referring to FIG. 5, cylinder A, which moves the upper assembly up or down, is controlled by solenoidoperated valve 14 and cylinders B, which move the container holder up or down, are controlled by solenoid operated valve 15. Cylinder A is double acting butcylinders B are single-acting, downward movement of the pistons being assisted by coil springs 16. A pressure regulator 17 limits the air pressure in cylinder A to one quarter that in cylinders B.

At the start of a closuring operation, both the upper assembly and the container holder are in their raised positions. A filled container 18 is placed in the holder and a sheet of biaxially oriented resin 19 over its open top (the latter movement can be either vertical or horizontal). This is the position shown in FIG. 1. The upper assembly is then brought down to the position shown in FIG. 2, from which it will be seen that the pressure plate 11 has first clamped the resin sheet against the container edge, holding it in position and physically preventing it from shrinking at this region, and that the frame 9 has pushed down the parts of the sheet overlapping the container edge. As the edges of the sheet are pushed down they become cockled, and alternate parts of the cockled edges are thus forced underneath the lip of the container as shown in FIG. 2. The cockled edge is also heated at the points of contact with the chamfered part but not sufficiently to cause them to shrink. This is Phase 0 of FIG. 5.

The position shown in FIG. 2 is quickly followed by that shown in FIG. 3 (Phase b in FIGiS Here both the upper assembly and container holder have moved downwards together, with the pressure plate still against the upper surface of the resin sheet and thus clamping it to the container lip, so as to bring the pushed-down portions of the sheet into tight contact with the fixed crimping sleeve 7 to crimp or pleat the pushed-down portions of the sheet against the underneath of the container lip. It is assisted in this by the spaced portions heated by the frame 9, but still no shrinkage of the resin takes place as the crimping sleeve is cold. The position of FIG. 3 is maintained for l or 2 seconds, during which the heat of the pressure plate 11 causes the central portion' of the sheet to shrink, giving the closure a smooth taut surface and building up tensions which, when the pressure plate is later retracted, pull the crimped edge portion into tight mechanical engagement with the container lip. The upper assembly is then moved upwards (Phase 0) and the container holder moves upwards almost immediately afterwards (Phase d). The position is then as in FIG. 1, permitting removal of the closured container and substitution of a new one.

When it is desired to open the container, a finger nail can be inserted under the crimped edge of the closure to pull the latter upwards and either tear it or spring it over the container lip; since the closure is not sealed or adhered to the container in any way it parts from the container without leaving residue.

Instead of supporting the container by its lip, an outwardly projecting shoulder, such as that sometimes employed as a stacking ring can sit on the top of the container holder. Such a holder might for example be about 0.2 to 0.5 inch below the lip, this comparatively small depth of wall being better able to resist deformation or damage by the stress of clamping than would the whole wall had the container been supported at its base. The double curvature that exists at such a shoulder also improves wall rigidity.

The above description and particularly the drawings are set forth for purposes of illustration only and. are not to be taken in a limited sense.

Preferably the sheet has a thickness between 0.0005 and 0.02 inch, particularly between 0.00l and 0.008

inch. A sheet of thickness 0.001 or 0.002 inch is often convenient to use.

Biaxially oriented thermoplastic resins in sheet form are availabie commercially, and very suitable ones are the transparent sheets of bioriented polystyrene such as are sold under the name Polyflex (Registered Trade Mark). Other oriented resins can, however, be employed for instance polyacrylates; polymethacrylates; polycarbonates; polyvinylchloride, polyethylene terphthalates; is otactic polypropylene and styrene copolymers, for instance a styrene-acrylonitrile copolymer or a rubber-modified high-impact polystyrene. The translucent sheets of bioriented highimpact polystyrene sold under the name Bohips (Trade Mark) are also particularly suitable.

The sheet overlaps the lipped edges of the container, that is to say the flat sheet projects beyond the edges of the container, and the extent to which it does this depends on the depth of skirt that is required around the rim of the final closured container. For example,

where the container is intended to be used as a drinking cup, it is desirable for the skirt to be of Sufficient depth to give hygenic protection for the portion of the walls of the cup that will eventually come into contact with the lips of the user; for this purpose a skirt depth of about 0.25 to 0.5 inch is normally suitable. On the other hand, where the container is simply intended for packaging it is sufficient if the skirt is of sufficient depth to give a strong closure; for example the edge of the sheet can coincide with the junction between the sidewall and lip of the container. A slight downwardly extending skirt is, however, generally desirable since this assists in opening the package by inserting a fingernail under the closure. Another way of assisting opening, particularly where there is no skirt, is by the inclusion of a tear-strip of for example cellulose acetate film placed across the open top of the container before the sealing operation is performed and with its end protruding over the lipped container edges so that it remains trapped beneath the closure and can be pulled upwards to open the container when desired.

Where a ribbed frame is employed the spacing between the ribs is preferably chosen to that it is similar to the depth of the skirt, if any. Thus for example where the skirt is 0.35 inch deep the ribs can be about 0.25 to 0.5 inch apart. A smaller rib spacing, about 0.1 to 0.15 inch is usually preferable where there is no skirt.

The timing of the various operations of the method and the temperatures of the heated frame and pressure plate are interdependent and need to be chosen by means of experiment. They depend not only on the softening point of the biaxially oriented thermoplastic resin, but also on the thickness of the sheet, the heat capacity and temperature of the container contents and the proximity of the level of these contents to the container rim. In general the time/temperature cycle must be designed to ensure that the edge portions of the biaxially oriented resin are not permitted to shrink because otherwise the resin becomes embrittled and the closure fails in use. Nevertheless, the temperature employed needs to be sufficient to heat-soften these edge portions so they must be quickly clamped and crimped so that they are physically prevented from shrinking while in the heat-softened state. Another requirement is that the closure should not become heat-sealed to the container; otherwise embrittlement and consequent failure will again occur and the closure will not be easily removable. It is therefore necessary to decide the time/temperature cycle after a few experiments, and it is not possible to give comprehensive instructions here. However, as an example it has been found that when employing a biaxially oriented polystyrene sheet having a thickness from 0.001 to 0.003 inch, a temperature of 130 to 140 C., preferably from 133 to 137 C. is suitable for the heated frame, while the pressure plate reaches by conduction a temperature from 125 to 135 C. very often from 128 to 132 C. The time taken to push down the overlapping portions of the sheet and crimping them against the container edge is also preferably short, not more than 1.5 second and preferably from 0.2 to 1 second. After the crimping operation has been performed it is preferable to keep the crimping sleeve in position for a further period ranging from 1 to 5 seconds and very often from 1.5 to 3 seconds, during which shrinking of the central portion of the flat sheet takes place.

The crimping sleeve is cold, that is to say its temperature is less than softening point of the resin, for instance from 10 to 50C.; normally atmospheric cooling is sufficient to achieve this condition, otherwise cooling by water through appropriately disposed channels or air cooling by means of a fan is easy to achieve.

In the apparatus described above the pressure plate is heated by conduction from the heated frame, how ever it can be independently heated if desired; alternatively a suitable ring can be employed to clamp the heat-softened parts of the sheet, the central portion of the sheet being heated by means of a radiant heater or a blast of hot gas.

The apparatus can often with advantage be fitted with a knife tocut the sheet while it is in position on the container, or alternatively the sheet can be in the form of a pre-cut blank. This latter may be preferable since it is not always easy to cut a biaxially oriented resin without producing a certain amount of swarf and this might fall into the container and contaminate its contents if in-position cutting were employed.

For automatic operation there can be a number of lower assemblies, each holding a filled container, which cooperate with an upper assembly; the motion of the lower assemblies can be continuous or discontinuous and'in the former case the upper assembly would be designed to travelwith each other assembly for a shirt distance before being lifted and returned rapidly to intercept the next lower assembly.

In an alternative automatic arrangement, a number of pairs of upper and lower assemblies canbe positioned around a carousel or turntable apparatus, a series of containers being fed to these as they move passed a feed point. The filling and closuring operations can then take place as the containers move around the turntable until they reach a discharge station.

1 Containers that can suitably be closured by the process of the invention can be of virtually any material, for example a synthetic resin, thermoplastic or thermosetting, glass, paper cardboard, paper pulp, aluminum or sheet steel. Preferably however the container is of a thin walled (10 to 50 mils thickness) thermoplastic resin, particularly a polymeror copolymer of an olefinically unsaturated monomer such as ethylene, propylene, styrene, acrylonitrile or methyl methacrylate. Especially preferred are containers of polyethylene, polystyrene (including toughened polystyrene) or styrene-acrylonitrile copolymer. Containers of a thermoplastic resin can for example be made by injection molding or by vacuumor fluid-pressure forming. The containers need not have a circular mouth, the mouth can be of any desired shape, for example square, rectangular, hexagonal or oval.

The process of the invention is illustrated by the following Example.

EXAMPLE This Example describes a process according to the invention for closuring an injection-molded polystyrene cup containing milk.

The cup was injection-molded from polystyrene and had a capacity of 7 fluid ounces. It had a circular rim of diameter 72 mm with a lip 3 mm wide. The cup was filled nearly to the brim with milk at a temperature of l C. and placed in a holder of an apparatus as described above and illustrated in the drawings. A sheet of biaxially oriented polystyrene in the form of a flat circular blank of diameter 90 mm and thickness 0.001 mm was placed over the open top of the cup with the container holder in the raised position. The upper assembly was then brought down to contact the blank with the heated frame and pressure plate within 0.2 second. The temperature of the heated frame was l35 C. while that of the pressure plate was 130 C. and the temperature of the crimping sleeve was 20 C.

l .0 second after this the upper assembly and the container holder were lowered together with the pressure plate still in clamping contact with the blank, urged against the crimping sleeve and maintained in position for 2.75 seconds, during which time the heat of the pressure plate shrank the central portion of the sheet, pulling the sheet taut and developing tensions which on removal of the pressure plate acted to pull the crimped edge portions into tight mechanical engagement with the cup lip. At the end of this time the upper assembly was lifted up, followed after 0.2 second by the container holder, and when the container was removed from the apparatus it had been found to have been closed by a strong closure with a crimped skirt 8 mm deep covering the cup wall beneath the lip. The closure was easy to remove when required by lifting the skirt with a finger nail and tearing the sheet of resin away, leaving the cup edge clean and free from any residue derived from the closure. Tests of similarly closured containers by dropping them on to a concrete floor demonstrated an extremely good resistance to rupture, the injection molded container itself failing before the closure in some instances.

It is obvious that many variations may be made in the products, processes, and apparatus described herein without departing from the spirit and scope of this invention as hereinafter claimed.

What is claimed is:

l. [n the process .of closuring a lipped container with a sheet of biaxially oriented thermoplastic resin by placing said sheet over the open top of said container so that itoverlaps the lipped edges thereof, pushing the overlapping portions of said sheet downwardly with a heated element without heat sealing the resulting heat softened sheet portions to the container, while clamping to said container any heat softened portions of the sheet which contact the container to prevent such container contacting sheet portions from shrinking, crimping the pushed down sheet portions underneath and against the lipped edges of the container and shrinking the sheet portion overlying the open top of the container so as to pull the crimped portions tightly against the lipped edges of the container, the improvement which comprises supporting said container in the vicinity of the lipped edge to minimize the vertical stresses thereon during clamping.

2. The method of claim 1 which includes the step of verticxally reciprocating the supported container downwardly against a crimping sleeve subsequent to said clamping.

3. The method of claim 1- wherein shrinking is achieved by contactin the sheet portion overlying the open top of the con between 1 to 5 seconds.

4. In apparatus for closuring a lipped container with a sheet of biaxially oriented thermoplastic resin which includes a heated element movable relative to the container to push down portions of the sheet overlapping the lipped edges of the container, means for clamping any heat softened parts of the sheet which contact the container tightly against the container, means for crimping without shrinking the pushed down sheet portions underneath and against the lipped edges of the container, means for shrinking the portion of the sheet overlying the open top of the container to pull the crimped pushed down portions underneath and against the lipped edges of the container, the improvement which comprises means acting in the vicinity of the lipped edges of the container for supporting the container during crimping. 1

5. The apparatus of claim 4 wherein said means for supporting the container includes a holder vertically movable in guides fixed to a base plate.

6. The apparatus of claim 4 including means for moving the holder and the crimping sleeve relative to each other. I

7. The apparatus of claim 5 wherein the upper end of the holder is of reduced thickness relative to the remainder thereof.

8. The apparatus of claim 5 wherein the holder is reciprocably mounted within the crimping means.

9. The apparatus of claim 6 wherein said moving means comprises piston operated cylinders.

10. The apparatus of claim 8 wherein the crimping means comprises a crimping sleeve rigidly fixed to upper end portions of said guides.

11. The apparatus of claim 10 wherein the upper edge of the crimping sleeve corresponds in contour to the lower surface of the container lip.

ner with heating means for

Claims

1. In the process of closuring a lipped container with a sheet of biaxially oriented thermoplastic resin by placing said sheet over the open top of said container so that it overlaps the lipped edges thereof, pushing the overlapping portions of said sheet downwardly with a heated element without heat sealing the resulting heat softened sheet portions to the container, while clamping to said container any heat softened portions of the sheet which contact the container to prevent such container contacting sheet portions from shrinking, crimping the pushed down sheet portions underneath and againSt the lipped edges of the container and shrinking the sheet portion overlying the open top of the container so as to pull the crimped portions tightly against the lipped edges of the container, the improvement which comprises supporting said container in the vicinity of the lipped edge to minimize the vertical stresses thereon during clamping.

2. The method of claim 1 which includes the step of vertically reciprocating the supported container downwardly against a crimping sleeve subsequent to said clamping.

3. The method of claim 1 wherein shrinking is achieved by contacting the sheet portion overlying the open top of the container with heating means for between 1 to 5 seconds.

4. In apparatus for closuring a lipped container with a sheet of biaxially oriented thermoplastic resin which includes a heated element movable relative to the container to push down portions of the sheet overlapping the lipped edges of the container, means for clamping any heat softened parts of the sheet which contact the container tightly against the container, means for crimping without shrinking the pushed down sheet portions underneath and against the lipped edges of the container, means for shrinking the portion of the sheet overlying the open top of the container to pull the crimped pushed down portions underneath and against the lipped edges of the container, the improvement which comprises means acting in the vicinity of the lipped edges of the container for supporting the container during crimping.

6. The apparatus of claim 4 including means for moving the holder and the crimping sleeve relative to each other.