GB2133375A - Thermoplastic, two part, food container - Google Patents

Abstract

A thermoplastics container for receiving hot-filled food (e.g. soups and juices) consists of two body sections 101 and 103 which are friction welded together at flange 109, the body sections being made of multi-layered thermoplastics material, at least one layer of which is a barrier polymer having a low gas permeability. There are vacuum compensating means at both ends of the container. The bottom closure has a central diaphragm 111 separated from rim 110 by a pair of alternating flex-grooves 112 and 113 which allow upward flexing of the bottom closure during cooling of the food. A metal foil top seal 114 engaging over top rim 105 also has a central section which collapses inwardly into the container in response to vacuum therein. The two body sections are tapered and have indentations 116, 117 so that several same body sections can be rested during stripping without jamming. The inner and outer layers of the container wall comprise structural polymer selected from polypropylene, propylene, polyethylene, polystyrene, polyvinyl chloride and copolymers thereof, and the inner, barrier layer is selected from ethylene vinyl alcohol, polyvinyl alcohol, polyvinylidene chloride, PVC/PVdC copolymers and styrene- acrylonitrile copolymers. The friction welding may be spin welding or oscillatory welding. <IMAGE>

Description

SPECIFICATION Thermoplastic food container and method of manufacture The present invention generally relates to thermoplastic containers for receiving food products and more particularly involves a thermoplastic container made from a multilayered thermoplastic material.

In the current state of food packaging many food products such as soups and juices are still being packaged primarily in metal cans. Because of the high acidity and high susceptibility to spoilation from oxygen encroachment, many food products may be packaged in metal containers which exhibit some added chemical resistance to the acidity as well as being tightly and hermetically sealed. This involves, in the case of metal cans, some interior coating on the metal can to prevent the acidity in the food product from attacking the metal in the can.

Other types of food packaging containers involve glass containers with metal caps. The glass container offers both chemical resistance to acidity and a highly impermeable barrier to oxygen ingress into the container. Unfortunately, the glass container is expensive to manufacture and is subject to breakage and the accompanying danger of glass injuries to the consumers. Both the metal can with interior coating and the glass container are measurably more expensive to manufacture and less desirable than thermoplastic containers for the same food products.

Current food product packaging which utilizes plastic containers suffers from the disadvantage that the majority of plastic materials accepted by the FDA for contact with products for human consumption do not offer all the desired characteristics for containers. For example, one highly desirable material for food product containers is polyethylene terephthalate (PET).

This polymer is a tough clear plastic material having good strength characteristics and moderate barrier characteristics. Unfortunately, the material does not offer the impermeability needed to protect the products which are susceptible to oxygen encroachment and spoilation therefrom. For example, soups and juices suffer rapid spoilation when placed in straight PET containers because of the relative porosity of PET to the ingress of oxygen molecules. Thus, PET as a food container package leaves much to be desired.

The present invention overcomes the disadvantages of prior art containers by providing a multi-layered, multi-segmented container which is highly impervious to the transmission of gasses such as CO2 and oxygen therethrough, is relatively tough and resilient, and is inexpensive to manufacture.

According to the present invention there is provided a composite thermoplastic container for receiving hot-filled material therein, said container comprising a tapered upper body section containing a filler opening at the top end thereof and an open bottom end larger than said filler section; and a tapered lower body section having a bottom closure and an open upper end adapted for snug-fitting relationship with said upper body portion; wherein at least one of said body sections comprises a multi-layered thermoplastic material, at least one layer of which comprises a barrier polymer having a low gas permeability; and, wherein said body sections are fricton welded together to form a single container.

The present invention discloses a two-piece food packaging container made of a multi-layered thermoplastic material comprising a desirable package polymer such as polyethylene terephthalate or polypropylene in which is contained a layer of a barrier polymer such as ethylene vinylalcohol (EVAL). The container of this invention is manufactured by coextruding the barrier polymer inside a "sandwich" of the container polymer into a sheet material and then thermoforming the container in two separate sections which are then joined by spin-welding.

The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is partial cross-sectional side view of one embodiment of the container made according to the present invention.

Figure 2 is an axial end view of the container of Figure 1 taken at line 2-2 thereof.

Figure 3 is an axial bottom view of the container of Figure 1.

Figure 4 is a partial cross-sectional side view of the container of Figure 1 after the container has been filled.

Figure 5 is a cross-sectional side view of an alternate embodiment lid closure for the container of Figure 1, and Figure 6 is a cross-sectional side view of the container of Figure 5 after hot filling.

Referring to Figure 1 , there is illustrated a thermoplastic container 101 which is particularly advantageous for packaging hot food products such as vegetable juice. The container 101 comprises an upper body portion 102 and a bottom portion 103. Upper body portion 102 comprises a tapered frustoconical wall section having at its upper end an indented neck section 104 and a peripheral rim 105. Rim 105 has located therein an indented lip section 106 defining a fill opening 107.

Base cup 103 comprises an upwardly extending frustoconical wall section 108 having at the upper end thereof a peripheral spin-weld flange 109 integrally formed thereon. Cup 103 has a bottom support rim 110 and a diaphragm bottom section 111.

Diaphragm bottom 111 comprises a central diaphragm disk 111 separated from rim 110 by a pair of alternating flex-grooves 112 and 113. The provision of disk 111 and grooves 11 2 and 11 3 allows a certain amount of flexibility in the volume content of the container 1 01.

A flexible metal cap 1 14 is provided for tight fitting engagement over fill rim 105. Top 114 preferably is made of a ductile material such as aluminum foil. A collapsabie centre section 11 5 slightly raised from top 114 is formed therein to provide flex space above the filled product in the container. A plurality of indentations 11 6 are formed in the upper portion of the conical section of the body 1 02 and preferably at least three indentations 11 6 are formed in the wall of the upper body portion. Likewise, a set of indentations 11 7 are formed in lower cup portion 103 and comprises at least three indentations therein.The indentations 116 and 11 7 are adapted for nested stack control so that several nested components of the same configuration do not jam or lock together prior to denesting and application.

The material preferred for forming the present container consists of a multi-layered thermoplastic sheet having inner and outer layers of polypropylene with an interior layer of EVAL bonded therebetween. This sandwich effect results in a waterproof layer on the interior of the container formed of polypropylene and a tough, decorative outer layer of polypropylene with a captured or "sandwiched" layer of EVAL between the two polypropylene layers. The layer of EVAL serves to provide an oxygen barrier for the container to prevent the ingress of oxygen and to protect the food product from early spoilage. In one preferred embodiment the multi-layered thermoplastic material was extruded in a sheet coextrusion die such as those disclosed in U.S.

Patent 4,100,237 and pending application S.N.

408,105, filed August 1 6, 1982, by Hahn and Rutledge, for "Multiple-Layered Sheeting Apparatus and Process Therefor"; and was thereafter thermoformed by means such as blow molding into the final upper and lower body portion. One method of thermoforming such containers which also offers the additional advantage of obtaining biaxial orientation in the containers is disclosed in pending patent application serial number 394,382, filed by Granville J. Hahn and Raleigh N. Rutledge on July 1, 1982, entitled "Apparatus for Forming Biaxially Oriented Thermoplastic Articles", which application is hereby incorporated by reference in its entirety into this application. Other methods of thermoforming the container portions such as vacuum molding and more conventional methods of blow forming can be utilized to form these container portions.After the upper portion 102 is thermoformed a stamping machine can be utilized to cut top opening 107 therein.

After the upper and lower container portions are formed from the composite sheet, each section is placed in its respective spin-welding mandrel and they are joined together by spinwelding means to form a hermetically sealed integral container 1 01. It is preferred that a slight interference fit be designed into the container sections between flange 109 and the lower skirt portion of conical wall 102. This allows for slight variations in sizing between the two respective container portions and further aids in their joining by spin-welding techniques. The provision of polypropylene or polyethylene terephthalate outer and inner layers in the two container sections insures a good solid friction weld between the two sections due to the susceptibility of these polymers to pin-welding techniques.

Referring now to Figure 4, a container 101 is illustrated in its filled and cooled state. One problem with prior art containers is the shrinkage invoived when material which has been heated or retorted to sterilization temperatures is placed in the food container (a process called "hot-filling").

The problem generally occurs when hot food products at temperatures in excess of 2000F are placed in the containers and the containers are then sealed. As the heated material and the air above it in the container cools it naturally contracts due to the change in temperature. In many instances this could cause buckling of the external walls or top and bottom of the containers. This is particularly troublesome in thermoplastic containers which have higher flexibility than glass and metal. In the present invention this is overcome by the provision of the unique diaphragm bottom section 111 containing expansion grooves 112 and 113 to allow flexing upward of the bottom portion. Likewise the top seal 11 4 has a provision for compensating for the shrinkage of the headspace air and of the products.As shown in Figure 4, section 11 6 of top 114 is ductile enough to be drawn downwardly into the container opening as the product shrinks in response to being cooled.

Thus as the product shrinks, the crown portion 115 of upper seal 114 is drawn downward into the lip area 106,107 of top portion 104.

Thus in Figure 4 it can be seen how top seal 114 has been drawn downward by cooling of the product and bottom diaphragm section 111 has flexed upward into the container to offset the shrinkage of the liquid. One of the principal advantages of the present invention is that these two effects are not obvious to the consumer. One of the significant disadvantages of previous thermoplastic container designs is that the shrinkage due to cooling usually caused an uneven flexing inward of the side walls or of the top/bottom sections. This flexing or "buckling" of the plastic container was often mistakenly perceived by the consumer as indicating a spoiled product. Thus the present invention, by providing the flex diaphragm bottom section and the collapsible top seal, compensates for the effect of the shrinkage in the container contents. The flexing of the bottom is indistinguishable to the average consumer and the downward drawing of the top seal apppears to be the natural sealed condition of the top.

Figures 5 and 6 illustrate the preferred embodiment of the invention wherein a different construction of the metal foil lid is utilized. In the lid illustrated in Figure 5, lid 214 comprises an outward circular flange section 21 5 and a concentric ribbed diaphragm section 21 6. The rib 216 and the dome 217 extend downward toward the container to eliminate most of the head space above the material in the container. This large reduction in the headspace gives a reduction in the vacuum effect when the contents and trapped air cool. This in turn will provide a more controlled downward flexure of the foil lid as the product in the container cools. Figure 6 illustrates the final downward position of the seal after total collapse into the fill opening of the container.

Thus the present invention discloses a thermoplastic food and beverage container manufactured from a composite thermoplastic sheet material having a barrier buried therein, which container is formed by thermoforming an upper and a lower section from the multi-layered sheet and then spin welding the two sections into a single integral container. The bottom section of the container comprises a disguised flexible diaphragm section and the top section receives a collapsible foil seal to compensate for the volume shrinkage due to cooling of the headspace air and of the hot-filled prdouct.

In addition to the advantages of the present invention enumerated above, the design of the container disclosed herein is particularly advantageous for shipping. Whereas most prior art conventional containers generally are formed in a single operation and must be either formed on location or shipped empty, the present invention discloses a container which is nestable and can be shipped at a fraction of the cost of conventional containers. Since most conventional containers which are shipped must be shipped empty the truck or railcar containing the conventional containers is filled primarily with air.

For example, the average semi-trailer load of normal products generally weighs about 20,000 pounds. A filled semi-trailer load of empty plastic containers might weigh only 2,000 pounds. Thus the shipper of the containers is paying for the cost of an entire truck load of containers but is primarily shipping air. With the present invention the containers may be shipped in separate parts, which due to the frustoconical nature can be nested in a very compact arrangement. The top sections 102 are nested together and shipped in one container and the bottom sections 103 may be nested together and shipped in a separate container. Thus the user of the containers realizes tremendous economies in shipping by the nestability of the various components.The filler or canner receives the nested portions and places them in a relatively simple and inexpensive spinwelding device to form the container sections into a single sealed integral container. Spin-welding systems which are particularly useful in welding the present container are disclosed in U.S.

Patents 3,800,400 to Mistarz et al; 3,799,821 to Jones; 3,708,376 to Mistarz; and RE 29,448 to Brown et al.

Although a specific preferred embodiment of the present invention has been described in the detailed description above, the description is not intended to limit the invention to the particular forms or embodiments disclosed therein since they are to be recognized as illustrative rather than restrictive and it will be obvious to those skilled in the art that the invention is not so limited. For example, whereas the container materials were cited as being polyethylene terephthalate (PET) or polypropylene, it is obvious that other known thermoplastic container materials can be utilized. For example, polyethylene, polyethylene terephthalate glycol (PETG), polyvinyl chloride, polystyrene, and various other poly olefins and polyesters can be utilized for the container material. Likewise other barriers can be utilized in the sandwich between the wall polymers, for example such as saran (PVDC) and barex. In addition, whereas the container is depicted as being generally cylindrical and is spin-welded together, it is also possible to use other geometrical cross-sectional shapes such as oval, elliptical or poiygonal, and to friction-weld them by means other than spinwelding, i.e. by oscillatory bonding or welding.

Oscillatory bonding techniques and apparatus are disclosed in our co-pending application Serial Number 371,363 by MacLaughlin and Fortuna, filed April 23, 1 982, and entitled: "Method of Oscillatory Bonding".

Claims (21)

Claims

1. A composite thermoplastics container for receiving hot-filled material therein, said container comprising a tapered upper body section containing a filler opening at the top end thereof and an open bottom end larger than said filler section; and a tapered lower body section having a bottom closure and an open upper end adapted for snug-fitting relationship with said upper body portion; wherein at least one of said body sections comprises a multi-layered thermoplastic material, at least one layer of which comprises a barrier polymer having a low gas permeability; and, wherein said body sections are friction-welded together to form a single container.

2. A composite container as claimed in Claim 1, wherein the thermoplastic material comprises polypropylene and the barrier material comprises an ethylene-vinyl-alcohol.

3. A composite container as claimed in Claim 1 or 2, wherein the container comprises interior and exterior layers of a tough thermplastic coextruded with a barrier layer therebetween.

4. A composite container as claimed in Claim 1,2 or 3, further comprising vacuum compensating means at one end of the container adapted to flex inward in response to vacuum created in the container by cooling therein.

5. A composite container as claimed in Claim 4, wherein the vacuum compensating means comprises a flexible flanged diaphragm formed in the thermoplastic body closure.

6. A composite container as claimed in Claim 4, wherein the vacuum compensating means comprises a foil cap sealed on the filler opening, the cap having a collapsible diaphragm section formed therein.

7. A composite container as claimed in Claim 4, wherein the vacuum compensating means comprise a foil cap sealed on the filler opening and having a collapsible diaphragm section, and a flexible flanged diaphragm section formed in the bottom closure and arranged to flex inward in response to vacuum in the container.

8. A composite thermoplastics container as claimed in Claim 1, substantially as hereinbefore described with reference to the accompanying drawings.

9. A container for receiving hot-filled products, the container having nestable components and a vacuum compensating system, and comprising a thermoplastic nestable tapered upper section having a filler opening at one end and a frictionwelding end opposite said upper end; and, a thermoplastic nestabie tapered lower section having a bottom closure at one end and a frictionwelding opening opposite said bottom closure; the lower section being friction-welded to the upper section; the said bottom closure comprising an integral diaphragm, vacuum flexure section formed therein and adapted to flex inward in response to a vacuum in the container.

10. A container as claimed in Claim 9, further comprising a flexible top closure adapted for removable sealing engagement over said filler opening and having a collapsing diaphragm section designed to collapse inward into the container in response to a vacuum therein.

11. A container as claimed in Claim 10, wherein the flexible top closure comprises a metal foil seal cap.

12. A container as claimed in Claim 9, 10 or 11, wherein the bottom diaphragm comprises a generally circular disc with a peripheral U-shaped flange formed therearound.

13. A container as claimed in Claim 9 substantially as hereinbefore described with reference to the accompanying drawings.

14. A method of forming a barriered, nestable, composite thermoplastic container for receiving hot-filled products and having vacuum compensating ability, which method comprises: coextruding a composite thermoplastic sheet having at least one layer of a tough structural polymer material and at least one layer of a barrier polymer; thermoforming from said sheet a tapered upper body section having an open larger end and a narrower end with a filler opening, thermoforming from said sheet a tapered lower body section having a larger open upper end and a bottom closure, the bottom closure being thermoformed to contain a flanged, inwardly flexible diaphragm section arranged to flex inward in response to a vacuum in the container, and, friction-welding the upper and lower body sections together to form an integral container.

1 5. A method as claimed in Claim 14, further comprising the step of providing a sealable top closure for the container, having flexure means formed therein adapted to flex inwardly in response to a vacuum in the container.

1 6. A method as claimed in Claim 14 or 15, wherein the coextrusion step comprises coextruding at least three layers of polymer, with outer layers of structural polymer and an interior layer of a barrier polymer.

17. A method as claimed in Claim 16, wherein the structural polymer is selected from polypropylene, propylene, polyethylene, polyethylene terephthalate, polyethylene terephthalate glycol, polystyrene, polyvinyl chloride, and copolymers thereof.

18. A method as claimed in Claim 1 6 or 17, wherein the barrier polymer is selected from ethylene vinyl alcohol, polyvinyl alcohol polyvinylidene chloride, PVC/PVdC copolymers, and styrene-acrylonitrile copolymers.

1 9. A method as claimed in any one of Claims 14 to 18, wherein the friction welding step comprises spin-welding.

20. A method as claimed in any one of Claims 1 4 to 18, wherein the friction welding step comprises oscillatory welding.

21. A method as claimed in Claim 14, substantially as hereinbefore described with reference to the accompanying drawings.