GB2143773A - Improvements in the manufacture of insulating panels for portable containers - Google Patents

Abstract

A composite flexible plastics sheeting for use in making a thermally insulated container is made by backing a plastics sheet 14 faced with a reflective metal foil 12 is rendered capable of being made up into a liner for a thermally insulated container by bonding the plastics layer thereof to a larger layer 16 of plastics so as to leave a non-metallised margin 18 surrounding the edge of the foil. The latter is then used for making seam welds between panels so that the foil is substantially continuous over one surface of a prismatic liner and the resultant product used to make a heat-insulating container thermally insulated container. <IMAGE>

Description

SPECIFICATION Improvements in the manufacture of insulating panels for portable containers This invention relates to the manufacture of insulating panels for portable insulated containers such as are commonly used for the storage of food on personal journeys, picnics, etc., and the method of construction of such containers from such panels. It has become conventional to make these containers in the form of relatively deep, basically rectangular prismatic boxes having external walls of a suitable wear-resistant material which are lined with a thermally insulating material. Sometimes this material is of a spongy substance such as foamed plastics having a low density. Other materials include embossed plastics films and fibrous, low-density, high bulk substances.With few exceptions, all these conventional materials suffer from high local compressibility and ageing, both of which result in loss of heat insulating capacity.

It is a well-known physical phenomenon that heat is reflected by polished surfaces in the same way as light, and this principle has become universally accepted in flasks and jugs such as those sold under the Registered Trade Mark "Thermos". There is available on the market a metal foil faced flexible plastics sheeting the foil facing component of which can be polished and hence heat reflective. It could, therefore, form an effective insulator for such portable containers as are envisaged by the present invention. However, unless such containers can be manufactured by standard R.F. welding techniques, they cease to be economic.

R.F. welding depends on the insulating properties of the components to be joined. The abovementioned foil faced plastics sheeting has the foil facing continuous over its whole surface. Hence, two pieces of such sheeting cannot be welded by the R.F.

process because, even if the two plastics faces are lapped together between the electrodes, the R.F.

potential is reflected by the foil layer in contact with the live electrode so that not only does the heating effect not reach the plastics to plastics interface but serious damage is done to the welding machine. If, therefore, the foil faced sheeting is to be commercially successfully employed as heat-reflective linear, some method of welding two such sheets must be devised.

Foil faced plastics sheeting can be included in the work to be welded provided that there is only one layer of foil, and this is in contact only with the earthed electrode; in other words, so far as concerns the remainder of the components which make up the work to be welded, the foil becomes identified with, or effectively a substitute for, the earthed electrode.

This excludes the possibility of directly welding two or more pieces of foil faced plastics sheeting, but does not exclude the possibility of welding to the foil faced sheeting another sheet of non-metallic faced plastics. The present invention resides in the application of this fact to the manufacture of such a composite material and in the use of this material for the manufacture of portable thermally insulating containers.

According to the present invention, in order that a hollow three-dimensional article can be made up from plastics sheeting including metal faced sheet so that some, if not all, its internal wall surfaces are heat reflective, a flexible composite sheet of plastics is made by superposing a sheet of metal foil faced plastics on a larger plain or unfaced plastics backing sheet, plastics surfaces in contact, so that the margin of at least one edge of the composite sheet has no metallic facing, whereby the resulting composite sheet may be R.F. welded to a corresponding plain or metal-free margin on a similar composite sheet, or on a plain plastics sheet.

Ideally, the foil faced sheet is itself R.F. welded to the unmetallised backing sheet around the edges of the foil by placing the foil surface on the earthed electrode of an R.F. welding machine so that the edges of the foil register with the live electrode while the backing sheet overlaps the foil edges to provide the requisite plain margin; whilst the live electrodes is set to penetrate the combined thickness of the plastics material in both sheets to a depth of approximately 50% of that combined thickness during the welding stage.

Preferably, a thermally insulated container is made by forming the appropriate number of panels of composite sheeting to the respective sizes and shapes which, after welding them together into the desired form, will present inward-facing wall surfaces defined substantially completely by the heatreflective layers thereof.

Conveniently, a composite panel is wrapped on itself so that the originally opposite unmetallised margins overlap each other and are mutually outturned in register and are welded together to form a sleeve constituting the sides of the box; a flat panel to form the base is fitted to one end of the sleeve by overlapping the respective unmetallised margins as that the metal foil layers on the two components do not quite touch each other; a second flat panel similar to the base panel is attached to the other end of the sleeve by a hinge so as to constitute a lid, and a closure device is provided for releasably securing the lid in the closed position.

Preferably, a third and suitably stiffened flat panel of substantially the same size as those of the bottom and lid is provided for insertion into the finished container as an adjustable-level partition so that, say, food which is more sensitive to temperature change - such as ice cream - can be placed in the bottom of the container and covered by the partition to prevent transfer of heat by convection between the compartments above and below the partition. If the partition also has a reflective foil surface and is inserted with its surface downwards, it forms an almost totally internally reflective compartment above which may be placed less temperature sensitive substances. The partition separates the two categories of contents and the atrrospheres in which they are stored.Without such an adjustable partition, the insulation properties of the whole container in respect of special substances is much more difficult - if not impossible - to predict or control. The use of the adjustable partition means that it now becomes possible to calibrate the performance of the container, at least with a fair degree of accuracy.

if desired, the partition may have both surfaces reflective, but provision must be made for removal of the partition so that the reflective effectiveness of one surface of the adjustable partition may be reduced by the presence of an overlying strap handle or like manual gripping device.

The invention includes both the composite panel and a thermally insulated container when made by the process as defined above.

A practical illustration of the invention, and of one method of its use, will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic illustration ofthe formation of a composite panel (partly broken away) according to the present invention; Figure 2 is a cross-sectional view to an enlarged scale, of the foil faced plastics sheet of Figure 1, the section being taken on the line ll-ll of Figure 1; Figure 3 is a fragmentary schematic sectional view, on an enlarged scale, of the formation of a composite plastics sheet using the R.F. welding technique; Figures 4 and 5 are fragmentary sectional views, also on an enlarged scale, of different ways of joining composite sheets made by the method illustrated in Figure 1;; Figure 6 is a perspective view of a portable thermally insulated container made from composite sheets according to the methods illustrated in the preceding Figures; Figures 7and8 are perspective underplan and plan views, respectively, of a movable partition for a container as shown in Figure 6, and Figures 9 - 12 are perspective views, each partly cut away, illustrating movable partitions in use.

Throughoutthefollowing description, the metal foil faced plastics sheeting is assumed to be a proprietary product, and the present invention is not concerned with its manner of manufacture. Furthermore, in all Figures of the drawings, especially sectional views, the sizes and proportions are chosen purely for purposes of visual representation, and bear no relation to practical data.

Referring first to Figures 1 - 3, a metal foil faced plastics sheet 10, consisting of a reflective metal foil 12 (Figures 2 and 3) intimately bonded to a plastics base sheet 14, is offered up to a larger plain plastics backing sheet 16 (Figures 1 and 3) so as to leave a non-metallised or foil-free margin 18 around the edges of the foil. The long-dash lines 20 indicate the projection of the foil faced sheet 10 on the backing sheet 16 where it is superimposed in the position 10' marked by chain-lines 22. The loosely assembled sheets 10,16 are then located on the platen (represented in Figure 3 by the "Earth" symbol 24) with the foil layer 12 on the platen, and the conventional live electrode "rule" 26 is set to penetrate approximately to a depth of 50% of the total thickness of the plastics layers 14, 16.In Figure 3, the total plastics thickness is marked "r' and the depth of penetration is marked "d". When the working R.F. potential is applied across the composite assembly, the two plastics layers 14,16 are welded so that the resultant composite panel can be handled as an integral material.

Referring now to Figures 4 - 8, the invention will be described as applied to the manufacture of a "picnic" bag 30 (Figure 6). This comprises, essentially, a smooth outer shell or casing 32 of a wear-resistant plastics material and a liner 34 which provides the heat insulating property. The liner 34 consists of a side wall panel in the form of a tubular sleeve 36 to which is welded a base panel 38 (Figure 5) of the same composite sheeting and a lid panel 40 (Figure 6) also of the same composite sheeting. The bag is completed by the usual handles 42 and a separate adjustable - level partition 44 (Figures 7 and 8) which may or may not have one or both surfaces formed by heat-reflective composite sheeting.Its prime function is to act as a partition or baffle separating a lower compartment for more highly temperaturesensitive substances from the remainder of the internal volume. Its purpose can be achieved by merely preventing convection currents passing between the upper and lower compartments, so that the contents on opposite sides of the baffle or partition 44 can be stored, if desired, at different temperatures. The use of foil faced sheeting on one or both sides of the baffle will increase the thermal insulation of the compartment towards which it is directed, although the provision of some means of gripping and removing the partition 44 - such as the overlying strap handle 46 on the upper surface of the partition - will tend to reduce the heat-reflective characteristic of that surface.

Referring more specifically to Figure 4, the tubular wall panel 36 is formed by wrapping a composite sheet of the appropriate size on itself until the two originally opposite vertical foil-free margins 18 overlap and are turned out at 18' to be seam-welded in the conventional manner by electrodes indicated at 48. Similarly, the bottom margin 18 of the tubular sleeve 36 is out-turned to register with the margin 18 of the base panel 38 and seam-welded thereto.

As shown in Figure 6, the lid panel 40 has a shallow skirt 50 attached around its periphery, and the rim of this skirt carries one track 52 of a sliding clasp fastener the other track 54 of which surrounds the top of the casing 32 at a depth below the rim equal to the depth of the shallow skirt 50. In this figure, although a visible gap is shown between the adjacent edges of the foil 12, it will be understood that in practice this would be effectively masked by the fullness of the liner.

Figures 7 and 8 show an adjustable-level partition 44 having its underface metallised but a plain upper face on which an overlying strap handle 46 is fixed.

The partition is dimensioned so as to be a snug fit, when horizontal, within the bag 30 and movable at will to any desired height above the base 38 so as to rest upon goods or packages - such as frozen foods whose temperature needs to be controlled within the limits of accuracy obtainable in a heat insulated container, and to isolate them thermally from the space above the partition. In Figure 9, the partition 44 is shown resting on top of packages or containers 60 of goods which are to be protected from an undesirable temperature change by exposure to the ambient temperature of the empty space above the partition 44.

In Figure 10, the space above the partition 44 is shown filled with goods whose temperature may be uncritical or which may be required to be stored at an elevated temperature - such as the ingredients of a hot meal. Thus, one or more hot courses may be stored at 62 while a cold dessert may be stored at 60.

In Figure 11, the entire contents 64 of the space within the bag 30 may be required to be kept at the same elevated or depressed temperature relative to ambient. Thus, a bag 30 according to the present invention and having a heat-reflecting metal foil faced partition 44 can be put to a wider range of uses than a conventional "picnic" bag having no heatreflecting internal wall surfaces.

It is to be understood that the upper surface of the partition 44 may be metallised as weli, while different handle patterns may be adoped - such as cord loops at each end -to minimise masking of the upper foil. Alternatively, all foil facings 12 can be omitted from the partition 44, although such treatment would greatly reduce the thermal insulation performance of the bag 30.

Figure 12 shows a variant of the arrangement of Figures 7 - 11. In Figure 12, the bag 30 is adapted for the transport of bottles, either solely - for example, wines - or in conjunction with other items -for example, bottle milk and other foodstuffs. In either case, it is convenient to pack bottles upright, and to thermally insulate one or more from other contents in the bag by an upright partition 66. Thus, red and white wines can be carried at their respective optimum temperatures, or cold milk can be separated from other foods at ambient temperature.

The upright partition 66 can be designed as a snug fit between opposite side walls of the bag 30 either on the shorter or the longer medial dimension of a bag shaped as shown in Figure 6. To accommodate these different widths, the partition 66 may be made to an overall width equal to the longer dimension of the bag but be formed with fold lines to accomodate the shorter span. In any case, the reflective composite material 10, 16 is not-rigid so that lateral deflections up to a certain limit are possible and will often facilitate the separation of items of unequal or irregular size and shape.

For maximum efficiency, the partition 66 must be provided with reflective surface on both sides. This can easily be achieved by R.F. welding two composite panels 10, 16 together around their plain plastics margins 18. Alternatively, a single composite panel of twice the desired width can be folded in half and the overlapping foil-free edges 18 can be seam welded.

A popular variant of the design shown in Figure 6 is a shoulder bag style. In this style, the hinged lid 40 of Figure 6 is replaced by an integral top wall having a sliding clasp fastener running thereacross between a pair of lugs or ears which are formed, as will be described later, by deformation of the top wall at each end of the fastener and constitute an anchorage for a shoulder strap which connects them. When the sliding clasp fastener is opened, an aperture is formed through which articles can be inserted or withdrawn. The lining of the bag can be thermally insulated by the use of foil faced plastics sheeting made up into a composite panel as illustrated in Figures 1 - 3.

A polished foil insulated shoulder bag according to the present invention is made by R.F. welding to each other a pair of equal-sized composite panels 10, 16 each of a length equal to the depth of the bag plus half its width when full. Two equal-sized plain panels of the external wall material are overlaid, one on the non-foil side of each composite liner panel, and all four panels are united at one end across their width by seam-welding to a sliding clasp fastener of a little less length than the common width of the composite liner panels and external wall panels. Thus, the sliding clasp fastener unites two similar pairs of panels, and these are then folded flat against each other about the line of the fastener, foil to foil, and the long edges are searn welded to each other down each side.The result is a double-walled, foil lined pocket open at the end remote from the fastener.

If desired, sheets of extra insulating material can now be inserted between each composite panel and its associated external wall panel. When this has been done, the pairs of liner and external panels are separate at the open end of the pocket and an oval composite base panel, already pre-formed, is registered with the rim of the open end of the pocket and R.F. seam welded thereto, in a manner generally similar to that of the attachment of the base panel 38 in Figure 5. The pocket is now sealed at what was its open end and closed at the other end by the sliding clasp fastener.

The bag is now stood on its base panel and the side seams which run up the length of the bag are now pinched at either end of the fastener and the external surface flanking the fastener is depressed so that the top ends of the seams form the points of a pair of opposed lugs or ears. Each lug or ear is capped by an inverted U-shaped cap between the arms of which is inserted a metal D-ring or halfbuckle to which can be attached the ends of the shoulder strap. Each cap is then riveted to its lug or ear, and a linered shoulder bag according to the present invention is complete. A partition or baffle like that shown in Figures 7 and 8 is preferably also provided.

As has already been noted, the foil faced plastics sheeting is a proprietary article, and has a thickness of 0.005 in. (=0.125 mm). In practical tests, this material was welded by the process of Figures 1 - 3 onto a backing sheet having a thickness of 0.008 in.

(= 0.20mm). The use of the foil faced plastics sheeting was shown to be very effective as an insulator by placing a pan of boiling water direct from the boiling ring onto the polished foil facing 12, and after 2 minutes the temperature rise on the underside of the plastics base 14 was only just sensible to the touch. The pres - 7ce of the heat reflecting foil layer 12 imparts a iiigher overall heat resistance to the plastics base 14.

The deliberate avoidance of foil-to-foil contact at all R.F. welded seams is a precaution against arcing or like problems which are the reason for the design of a composite panel according to the present invention. The area of non-metallised plastics can be kept to 5% or less of the total wall surface of the liner and by suitable control of the panels during the welding process the natural resilience thereof will cause the welded panels to bulge sufficiently to bring the metallised layers into virtual or actual contact.

Instead of using foil faced plastics sheeting 14, foil faced polyethylene foam can be substituted.

Claims (15)

1. The method of making a composite flexible plastics sheet for use in making a thermally insulated container comprising backing a flexible plastics sheet faced with a reflective metal foil with another and larger flexible plastics backing sheet which is stitched, stuck or R.F. welded to the metal-faced sheet so that the latter provides a plain margin along one or more edges of the foil-faced sheet so as to expose a metal-free zone for the R.F. welding thereto of other metalfree margins on the same or other plastics sheets.

2. The method according to claim 1 wherein the foil-faced plastics sheet is initially located relative to the backing sheet with their plastics surfaces in contact between the electrodes of an R.F. welding machine; the electrodes are set to compress the plastics material to about 50% of its combined thickness and the R.F. voltage is applied for sufficient time to weld the plastics.

3. The method of making a thermally insulated bag comprising assembling the appropriate number of panels of a composite flexible sheet according to claim 1 or 2; and joining them at their respective metal-free margins so that no edge of the foil layer on each panel quite touches the neighbouring edge of the corresponding layer on the adjacent panel or panels.

4. The method according to claim 3 wherein a generally rectangular prismatic bag is made by wrapping a panel on itself so that originally opposite parallel metal-free margins overlap each other and are welded together to form a sleeve constituting the sides of the box; a flat panel made in accordance with the method of claim 1 or 2 to form the base is joined to one end of the sleeve by overlapping the respective metal-free margins and welding them together so that the metal foil layers on the two components do not quite touch each other; attaching a second flat panel similar to the base panel to the other end of the sleeve by means of a hinge; and providing a closure device for releasably securing the lid in the closed position.

5. The method according to claim 4 wherein the lid is provided with a shallow skirt adapted to fit over the top end of the sleeve in the closed position.

6. The method according to claim 4 or 5 wherein the sleeve and base constitute a liner which is secured within a larger outer casing, with the reflective metal foil layers ofthe liner facing inwards and with or without a stiffener or a layer of thermally insulating material between the liner and the outer casing.

7. The method according to any of claims 4 - 6 wherein a third flat panel comprising a composite sheet according to claim 1 or 2 is dimensioned for slidable insertion into the bag as a snug fit to form a partition to divide the space within the bag into separate mutually thermally insulated compartments.

8. The method according to claim 7 wherein the partition is similar in size to the base panel to divide the space within the bag horizontally, and is stiffened to provide a platform for resting on articles in the bottom of the bag and to support other articles on top of it.

9. The method according to claim 7 wherein the partition is adapted to divide the space within the bag vertically.

10. The method according to claim 8 or 9 wherein the partition has reflective metal foil on opposite surfaces.

11. The method according to claim 8,9 or 10 wherein a handle is attached to the partition to facilitate its removal from the bag.

12. The method of making a composite plastic sheet substantially as herein before described with reference to Figures 1 - 3 of the accompanying drawings.

13. A composite flexible plastics sheet when made by the method claimed in claim 1,2 or 12.

14. Athermally insulated bag when made by the method claimed in any of claims 3 - 11.

15. A thermally insulated bag substantially as hereinbefore described with reference to Figure 4 12 of the accompanying drawings.