WO2014067927A1

WO2014067927A1 - Container for temperature sensitive materials

Info

Publication number: WO2014067927A1
Application number: PCT/EP2013/072574
Authority: WO
Inventors: Valérie GEISER; Patrick Couzens
Original assignee: Nestec S.A.
Priority date: 2012-11-01
Filing date: 2013-10-29
Publication date: 2014-05-08

Abstract

The present invention relates to packaging. In particular the invention relates to a container having at least one wall and enclosing a storage volume. The at least one wall may comprise at least one enclosed region within its structure, the enclosed region containing phase change material. The enclosed region may have at least two dimensions smaller than 50 mm. Further aspects of the invention are the use of the container to contain foodstuffs and/or to keep the foodstuff warm or cool, as well as processes for manufacturing the container.

Description

Container for temperature sensitive materials

The present invention relates to packaging. In particular the invention relates to a container having at least one wall and enclosing a storage volume. The at least one wall may comprise at least one enclosed region within its structure, the enclosed region containing phase change material. The enclosed region may have at least two dimensions smaller than 50 mm. Further aspects of the invention are the use of the container to contain foodstuffs and/or to keep the foodstuff warm or cool, as well as processes for manufacturing the container. Many materials are heat or cold sensitive and must typically be stored and transported within a narrow range of temperatures. Foodstuffs are often sensitive to temperature changes. A box of chocolates or an ice cream may have been in perfect condition when it was purchased from the supermarket, but after a drive home in a hot car it is disappointing to find that the chocolates have bloomed or the ice cream has melted. Once at home, the quality of the ice cream rapidly deteriorates if it is not kept in the freezer. It is enjoyable to share a large tub of ice cream while watching television, but the longer the ice cream sits out of the freezer, the more its texture will suffer when it is eventually re-frozen. Even the temperature variations from repeated opening and closing of the freezer may cause quality loss of frozen products. In addition, keeping food at the correct temperature may not just be important for the eating quality, for some foodstuffs it is critical to avoid the growth of spoilage organisms.

Insulated containers and packaging materials are often used to slow the temperature equilibration between a foodstuff and the environment. For example, insulated shopping bags are used to keep frozen food cold on the journey home from the shop, and pizza delivery firms use insulated bags and boxes to keep the food hot on the way to the consumer. However, there is a limit to the time for which such insulation can maintain the foodstuffs temperature in the desired range. To increase the time the foodstuff is maintained within the correct tennperature range the insulation can be made thicker, but a significant increase in time requires materials which are inconveniently bulky. Vaccines, antibiotics and other temperature critical materials are often stored and transported in vacuum-panel insulated shipping containers. US5943876 describes such insulated vacuum panels, but vacuum insulation is relatively expensive and so finds only applications where containers are extensively reused. Application for foodstuffs are therefore very limited, such as vacuum flasks for small quantities of hot drinks. Another approach is to combine insulation with some means of passive cooling or heating the contents of the package. Cool boxes, used for example to transport food for picnics, have insulated walls. They are often sold together with blocks, usually made of plastic, filled with a liquid or paste of phase change material. These blocks, sometimes called freeze-packs are placed in the interior of the cool box. Phase change materials store and release large quantities of energy in melting and freezing. In the case of a cool box, the freeze-packs take heat from the contents of the cool box as the solid phase change material within them melts, and so the contents of the box are maintained at a desired cool temperature for longer. The same effect can also work in reverse with a phase change material which solidifies at a critical lower temperature of the food, maintaining the food at the phase change material's freezing point for longer when the box is subjected to a cold environment.

A problem encountered with blocks filled with phase change material is that the contents may start to leak, or "ooze" out. This may occur after repeated thermocycling or after physical damage. Leaks cause a mess, and may contaminate the items the blocks are intended to protect. To reduce the risk of this, some phase change materials are formed into gels with silica, microencapsulated into polymer shells, or mixed into a compound together with a structural polymer. US6765031 describes filling an open cell foam such as polyurethane with a phase change material and then sealing the foam in an impermeable film envelope. The sealed foam blocks are then packed around the temperature sensitive material within an insulated container. For best results, an insulated container should be tightly packed, which requires careful selection of the appropriate shapes and sizes of blocks containing phase change material and the need to provide additional padding and spacers to prevent the contents from moving. Movement of the phase change blocks can create temperature variations; thus some of the food in the box may be cool while other food is warm. WO2005/016635 discloses thermal packs containing phase change material which can be locked together to prevent the packs from moving. This protects the temperature sensitive products against shock and vibration during transit. It also allows for an equal distribution of temperature within an outer container used to house the phase change material and the products. However, selection of the appropriate insulated container, blocks and spacers for different product shapes is time consuming, and maintaining a stock of all the possible materials can be costly.

A further problem with packing phase change blocks around foodstuffs within an insulated box is that the phase change material is not always in close proximity to the food. For example, if the food is stored in containers whose shape does not allow them to pack closely with the phase change blocks then there may be air gaps between the blocks and the food which prevent efficient heat transfer. Packing foods in insulated boxes and surrounding the food with phase change blocks is generally not suitable for presentation of the food in a retail environment as the presentation is not sufficiently attractive. Such a packaging arrangement is also not suitable for keeping food at the correct temperature during the time they are being consumed. It is not convenient to have to extract an ice cream carton from such an insulated box every time you want another spoonful.

There is therefore a need to provide packaging which can keep temperature sensitive foods within a desired temperature range for an extended period without the disadvantages described above.

The object of the present invention is to improve the state of the art and to provide a solution to overcome at least some of the inconveniences described above, or at least to provide a useful alternative. The object of the present invention is achieved by the subject matter of the independent claims. The dependent claims further develop the idea of the present invention.

Any reference to prior art documents in this specification is not to be considered an admission that such prior art is widely known or forms part of the common general knowledge in the field. As used in this specification, the words "comprises", "comprising", and similar words, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean "including, but not limited to".

Accordingly, the present invention provides in a first aspect a container, the container having at least one wall and enclosing a storage volume wherein the at least one wall comprises at least one enclosed region within its structure, the enclosed region containing phase change material and having at least two dimensions smaller than 50 mm.

Surprisingly, such a container having phase change material within its wall structure is effective at maintaining the temperature of the contents of the container. Furthermore, by limiting the size of the regions within the walls containing phase change material, the container remains physically strong. The container of the invention provides a much more attractive presentation of its contents than the combination of an insulated box with separate blocks containing phase change material. The container of the invention is ideal for situations where the consumer wishes to keep the food at a particular temperature and yet have easy access to it, for example the consumption of food "on the go", or having the food readily available for sharing.

The invention also relates to the use of the container of the invention to contain foodstuff. The container of the invention may be advantageously used to maintain the temperature of food, for example frozen foodstuff, chilled foodstuff or hot foodstuff. The container of the invention may be used to pack food products for transport by post, the container providing physical protection as well as protection from thermal damage.

A further aspect of the invention is a process for manufacturing the container of the invention comprising the steps of; forming the at least one wall with an indented surface; filling the indents with a phase change material; and affixing one or more additional layers of material to the at least one wall so as to cover the filled indents and form enclosed regions containing phase change material.

The invention also provides a further process for manufacturing the container of the invention comprising the steps of; forming the at least one wall with an indented surface where the indents are in the form of grooves; affixing one or more additional layers of material to the at least one wall so as to cover the grooves and form channels; filling the channels with a phase change material; and sealing the channels. Both these processes surprisingly provide efficient and practical manufacturing solutions. Brief description of figures:

Figure 1 shows the injection moulding of the box shaped container with grooves (8) on its inner surface of Example 1

Figures 2 and 3 show a thermoformed sheet (9) being affixed to the inner surface of the box shaped container of Example 1.

Figure 4 shows the filling of channels (11) in the container walls of Example 1 with phase change material.

Figure 5 shows the sealing of the channels (11) in the container walls of Example 1. Figure 6 shows the box shaped container (15) of Example 1, with one set of filled channels (11), being released from the mould (2).

Figure 7 is a schematic representation of the channels (11) in the side walls (16) and base (17) of the container of Example 1.

Figure 8 shows the grooved sheet (19) of Example 2 being thermoformed

Figure 9 shows the grooved thermoformed sheet (19) of Example 2 being affixed to the inner surface of the box shaped grooved container (7).

Figure 10 shows a thermoformed sheet (9) being affixed to the inner surface of the box shaped container (24) of Example 2.

Figure 11 shows the finished box shaped container (25) of Example 2, with two sets of filled channels (11), being released from the mould.

Figure 12 shows a cross section through the side wall of the finished box shaped container (25) of Example 2, showing two sets of filled channels (11).

Consequently the present invention relates in part to a container, the container having at least one wall and enclosing a storage volume wherein the at least one wall comprises at least one enclosed region within its structure, the enclosed region containing phase change material and having at least two dimensions smaller than 50 mm. Optionally the container is to be used as a food container. Food in the context of the current invention includes beverages. "Wall" within the scope of the present invention refers to any structure enclosing the storage volume, so for a box shaped container it would include the base of the container, the front, back and side walls and any cover, closure or lid. A spherical container, for example, would have only one wall. The shape of the container may be selected from the group consisting of a rectangular box, a square box, a cylinder, a sphere, a hemisphere, a frustum of a pyramid or a frustum of a cone. An example of a shape for food containers is a frustum of a rectangular based pyramid, similar in shape to a rectangular box except that the sides slope inwards from top to bottom, making the box easier to form, fill and empty. Any corners and edges of the container may be curved to aid forming the container, cleaning it and, when in use, removing the contents. Containers with shapes close to rectangular or square box shapes generate less void volume when packed together. Spherical boxes and boxes with curved walls such as cylinder shapes reduce the surface to volume ratio of the container and so can reduce heat loss.

"Enclosed region" within the wall structure refers to a space within the wall itself. It is enclosed within the wall and not open to the exterior of the container or the storage volume. The enclosed region may be in one wall or many walls. For example, the enclosed region may only be in the lid. The enclosed region has at least two dimensions smaller than 50 mm. That is to say, at least two dimensions, measured perpendicularly to each other are smaller than 50 mm. For example, a rectangular- prism-shaped enclosed region with at least two dimensions smaller than 50 mm may have a width of 20 mm, a depth of 10 mm and a height of 100 mm. Two of the dimensions, in this case the width and depth, are smaller than 50 mm.

The enclosed region containing phase change material may have at least two dimensions smaller than 20 mm, for example smaller than 10 mm, for further example smaller than 5 mm. Narrow channels have the advantage that they do not weaken the structure of the wall. By having many narrow channels, phase change material may be widely distributed throughout the wall volume, without excessively weakening the structure.

A phase change material is a substance with a high heat of fusion which, melting and solidifying at a certain temperature, is capable of storing and releasing large amounts of energy. Heat is stored or released when the material changes from solid to liquid and vice versa. Examples of phase change materials include water; salt solutions, for example eutectic water based salt solutions; organic fatty acids; fatty acid esters; paraffins, for example octadecane; water/glycerol mixtures; and water/salt hydrate mixtures. Preferred phase change materials for use in the current invention are nontoxic and do not present a significant risk if they inadvertently come into contact with food.

The at least one enclosed region of the container of the present invention may occupy between 15% and 90% of the volume of the at least one wall, for example between 25% and 70%. The greater the total volume of the enclosed regions the more phase change material can be incorporated into the walls and so the capacity of the container to delay temperature changes of its contents increases. However, increasing the volume of the enclosed regions also reduces the amount of structural wall material, weakening the container and making it more prone to leaks. So there is a balance between increased effectiveness and reduced strength. The container may be a rigid container.

The phase change material may be present in the at least one wall of the container of the invention at a level of between 10% and 85% by volume, for example between 20% and 65%. Once again there is a balance between having large amounts of phase change material in order for the container to be more effective, and the potential for weakening the structure of the container walls. The appropriate level depends to some extent on the nature of the phase change material used. A more viscous material, such as one mixed with silica, can help to maintain a more rigid structure and so can be used at higher levels, whereas a material with a high specific latent heat is more effective and so less of it may be required. Those skilled in the art will understand that the amount of phase change material filled into the enclosed regions needs to allow for any volume change when the material changes phase and so leave room for expansion.

The at least one enclosed region of the container of the current invention may be distributed inhomogeneously. That is to say, some parts of the container's at least one wall may have an enclosed area within them, while others don't. Phase change materials may be expensive or add weight to the container. To make optimum use of a limited quantity of phase change material it may be an advantage to have more phase change material in some part of the container than in others. For example, for a container with a lid, the heat loss close to the opening may be greater than in the centre of a wall panel, so it makes best use of the phase change material to have more phase change material in the area close to the opening of the container to counter the heat loss. An inhomogeneous distribution of the enclosed regions advantageously allows for this targeted distribution of phase change material. The at least one enclosed region of the current invention may be a shallow cup shape. A shallow cup shape is that formed by a concave impression in a surface, the depth of the impression being small compared to the width of the impression. For example, the geometric shape called a "spherical cap" is a specific example of a cup shape, in this case having a circular cross-section. The advantage of having enclosed regions which are shallow cup shapes is primarily one of ease of manufacture. This is described later in the specification.

The at least one enclosed region of the current invention may be a channel. A channel is a long narrow passage or tube along which a liquid can flow. Multiple channels may be spaced at different intervals within the walls depending on where there is the greatest need of temperature stabilization. Channels may also be aligned in such a way as to optimize the strength of the container in a desired direction. Where channels are aligned, running in approximately the same direction, the wall will be more resistant to flexing with a bend line parallel to the channels than a bend across the channels. Channels are also advantageous when manufacturing the container of the invention. The channels can be formed empty, and then subsequently filled by pumping the phase change material in a liquid state through the channels.

The channels may intersect. The channels may curl round to intersect with themselves or the channels may intersect with one another. Each channel intersection may connect no more than six ways. Such intersections can be helpful when filling the channels, allowing a better distribution of the phase change material. Intersections may also be used to form a network of channels within the container walls. However, multi-way intersections weaken the structure of the walls. Accordingly, each channel intersection may connect no more than six ways. An example of a six way intersection would be two channels crossing and connecting to each other at right angles, with a third channel crossing and connecting at the same point, perpendicular to the plane of the other two; thus there are six ways leading from the point of intersection.

The channels may have many intersections, forming a dense network. For example there may be at least 20 intersections per meter of channel length, for further example there may be at least 40 intersections per meter of channel length. The channels may be formed at different depths in the container wall. The container wall may be formed from multiple layers, with layers containing channels being separated by layers with no channels. For example, the container wall may comprise, in the direction of the wall thickness, an inner solid layer, a layer with channels, a second solid layer, a second layer with channels and an outer solid layer.

The phase change material of the container of the invention may be selected from the group consisting of organic fatty acids; fatty acid esters; water; salt solutions, for example eutectic water based salt solutions; paraffins, for example octadecane; water/glycerol mixtures; water/salt hydrate mixtures; and combinations thereof. For example, the phase change material may be a eutectic water based salt solution. The melting point of the phase change material determines its suitability for stabilizing food at different temperatures. For example, a frozen phase change material can be used to maintain temperatures below its melting point. As the temperature of the environment rises, the frozen phase change material initially also raises its temperature; storing heat according to its specific heat capacity. However, when the phase change material reaches its melting temperature it undergoes a phase transformation, during which it stores large amounts of heat without changing its temperature until all the material is transformed to the liquid phase. Having a phase change material in the enclosed regions of the walls of the container helps to prevent the temperature of the contents of the container from rising above the melting point of the phase change material until the phase change material has completely melted. The same works in reverse to prevent a drop in temperature; a liquid phase change material will maintain the contents of the container at temperatures above the phase change material's freezing point. As the phase change material crystallizes it liberates heat until it is completely solid. And again, during this phase transformation the temperature of the phase change material remains constant.

Eutectic aqueous salt solutions have melting points below 0°C and so may act as phase change materials suitable for stabilizing frozen food against temperature increases. A eutectic composition is a mixture of two or more constituents which solidify simultaneously out of the liquid at a minimum freezing point. Salt solutions are wel l known for forming eutectic com positions. For exam ple, a sol ution of 22.4 wt.% sod ium ch loride (NaCI) in water forms a eutectic composition which melts at -21.2 °C, whereas a 19.9 wt.% solution of potassiu m ch loride (KCI) in water has a eutectic melting point of -10.7 °C. Eutectic solutions such as these may be used in the container of the present invention. If a melting point needs to be adjusted, mixtures of salts in aq ueous sol ution can be used. Phase change materia ls are available with a wide range of melting points, for example Phase Change Material Products Ltd. of Hatfield, U K offer a range of eutectic salt solutions with melting points between - 46 °C and 0 °C, as wel l as salt hydrates covering the range 7 °C to 117 °C. Salt hyd rates utilise the abil ity of some salts to form complexes with water and to bind it up as water of crystall isation. This means that although the salt crystal is solid, it may contain over 50% water. When the crystal is heated it melts, releasing the water of crystal lisation and allowing the salt to dissolve in th is water. Th is melting process absorbs large amou nts of energy in the form of latent heat, which is released when the solution freezes. For exam ple, a salt hydrate such as sodiu m th iosul phate pentahydrate (Na₂S₂0₃-5H₂0) melts between 48 °C and 55 °C and so may be used in the container of the current invention to keep food above these tem peratu res. Paraffins may also be used in the container of the current invention, for example n-tetradecane (Ci₄H₃₀) melts at 6 °C and so may be used to prevent the contents of the container from freezing during transport in cold cl imates.

The at least one wall of the container of the invention may be made from a thermoplastic material, for example selected from the grou p consisting of polyethylene, polypropylene, polystyrene, polyethylene terephthalate, thermoplastic starch, polylactic acid and com binations thereof. A thermoplastic material is a polymer that becomes soft, hence pliable or mouldable, above a specific temperatu re, and retu rns to a rigid state upon cooling. Scrap or defective shapes can be remelted and recycled . The easy formabil ity and economic recovery of recyclable material make the use of thermoplastics advantageous for packaging appl ications. Thermoplastics do not generally absorb water or oil (in contrast to a material such as cardboard) and they provide a lightweight container for food which can be easily cleaned. Thermoplastic materials used to form containers for foodstuff should be safe when in contact with the food, for example not leaching any harmful substances into the food. The container of the invention may be combined with an outer covering or sleeve. For example, the thermoplastic container may be enclosed within a corrugated card sleeve for additional protection.

The container of the invention may be used to control the temperature of a foodstuff. For example, the container may maintain the temperature of a foodstuff stored inside it to within ± 5°C of a target temperature for at least 6 hours. The container of the invention may be used to maintain the temperature of a chilled or frozen foodstuffs. The container may be used to maintain the quality of the food during transportation, for example during distribution to retailers, or from the retailer to the end consumer's home. The container of the current invention may also be used to directly serve the chilled or frozen foodstuff, retaining the foodstuffs desirable cold temperature. For example, the container can be placed on the dining table during the meal, allowing people to help themselves to second helpings without the food warming up too quickly, or a cold beverage may be kept at a pleasant cool temperature during consumption.

The container of the invention may be used to maintain the temperature of a hot foodstuff, for example a beverage or soup. The container may be sold filled with a beverage or soup, to be reheated in a microwave. With appropriate choice of phase change material, the container will extend the time during which the soup can be drunk hot.

The container of the invention may be used to maintain the temperature of chocolate products, beverages, dairy products or ice cream. Chocolate melts at around 30 °C, and when it cools and re-solidifies it often forms a white layer on its surface called fat bloom. Although not harmful, bloomed chocolates are not of a desired quality and are the cause of many consumer complaints. By using a phase change material which melts at 28 °C, for example n-octadecane, the container of the current invention can prevent or delay chocolate from melting in hot weather.

Fresh dairy products are also sensitive to temperature and should generally be maintained at temperatures below 8 °C, or ideally 4 °C to prevent growth of spoilage organisms. Water provides one option as a phase change material, melting at 0 °C. However, maintaining the container below 0 °C may be too cold for enjoyable consumption of the dairy product, or lead to a loss of product quality due to freezing. Another option is to use a phase change material with a higher melting point, for example n-tetradecane which melts at 6 °C. Ice cream should ideally be kept fully frozen until consumption. Allowing the ice cream to partially melt and then refreeze causes ice crystal growth, loss of air volume and water condensation inside the container which leads to undesirable ice crystal formation on the surface of the ice cream. This is known as heat shock. Every time the ice cream is removed from the freezer, allowed to warm up and then returned to the freezer, the quality of the remaining ice cream is reduced. The container of the current invention is able to maintain the ice cream at below a critical temperature for longer outside the freezer and so is ideal for transporting the ice cream home from the shops, eating ice cream "on the go", or for keeping the ice cream cold while it is being shared in front of the television for example. The container also protects ice cream stored in a freezer from the repeated small heat shocks caused by the freezer door being opened.

The container of the invention may be used to protect food products sent by post. In the scope of the invention the protection is against changes in temperature and protection against physical dannage such as may be caused by rough handling. The term "post" refers to the official service that delivers letters and parcels, as well as other parcel delivery services and couriers. The growth in the popularity of online shopping has greatly increased the number of foodstuffs being delivered by post. For example, dairy products such as cheese and clotted cream; smoked salmon; speciality meats and chocolates are all commonly sent by post and need to be kept cool to avoid deterioration in quality. The container of the invention is ideal for protecting products sent by post as it provides protection from both temperature and physical damage in one single container, making it quick and efficient to pack. The container of the invention is also light-weight compared to prior art packaging systems using insulated containers with individual blocks of phase change material. Having a lower weight reduces the cost of sending a parcel by post. The container of the invention, when empty, may have a weight of between 0.5 and 15 g per cm² of wall area; for example between 2 and 10 g per cm². The container also presents an attractive package to the consumer on delivery, without the need to open and dispose of multiple layers of packaging.

The container of the invention may be manufactured by a process comprising the steps of forming a first wall layer with an indented surface, filling at least some of the indents with a phase change material, and affixing one or more additional layers of material to the first wall layer so as to cover the filled indents and form enclosed regions containing phase change material. For example, a box-shaped container with a base and four sides may be manufactured by injection moulding; the mould core for the injection moulding having protrusions so as to form a series of indents on the inner surface of the box. Releasing the moulded box from the mould core with protrusions is facilitated by the box material being slightly flexible. In one example, the indents/protrusions are relatively shallow, with curved sides to help the removal of the mould core. An example of such an indent shape being a shallow cup shape. The indents are then filled with phase change material. For example, a phase change material may be made into a paste by mixing it, in its liquid state, with a suitable powder such as cellulose. The paste can then be spread into the indents and smoothed off level with the inner surface of the moulded box. Alternatively the phase change material may be sprayed into the indents. The indents are then covered by an additional layer of material, for example a thermoplastic sheet, heat formed into the inside of the box so as to heat weld to the original box material and seal the indents. Optionally, a tie or adhesive layer is incorporated between the inner surface of the moulded box and the thermoplastic sheet. A lid for the box, with enclosed regions containing phase change material, can be formed in a similar way. Together, the box and lid, each having a series of enclosed regions containing phase change material, form an example of the container of the invention. By way of further example, a box-shaped container may be manufactured by injection moulding with the outer female mould having protrusions so as to form a series of indents on the external surface of the moulded box. After release from the mould and filling the indents with phase change material, a thermoplastic sheet may be affixed to the external surface of the box, sealing the phase change material. In a yet further example, both the internal and external surfaces may have indents which, when sealed, provide phase change material under both the internal and external surfaces of the container walls.

The container of the invention may also be manufactured by a process comprising the steps of forming a first wall layer with an indented surface where the indents are in the form of grooves, affixing one or more additional layers of material to the first wall layer so as to cover the grooves and form channels, filling at least some of the channels with a phase change material, and sealing the channels. An example of such a process is described in more detail in Example 1. Having pre-formed channels makes it easier to fill the phase change material into the enclosed regions of the container walls when the phase change material is a flowable liquid.

The container may be manufactured from a series of wall layers with indented surfaces, providing multiple layers of enclosed regions within the at least one wall. Forming multiple wall layers, each comprising enclosed regions, increases the amount of phase change material which can be incorporated into the container's at least one wall. Not all the enclosed regions need be filled with phase change material. For example, the outer layer of enclosed regions may be left empty, the air in the enclosed regions providing additional insulation. A process for the manufacture of the container of the invention having a series of wall layers may comprise the steps of forming a first wall layer with an indented surface where the indents are in the form of grooves; affixing one or more additional layers of material to the at least first wall layer so as to cover the grooves and form channels, wherein the additional layers of material themselves have an indented surface on the opposite surface to that affixed to the first wall layer, the indents being in the form of grooves; affixing further additional layers of material to the indented layers so as to cover the grooves and form further channels; filling at least some of the channels with a phase change material, and sealing the channels. An example of such a process is described in more detail in Example 2.

An advantage of these manufacturing processes is that they may use thermoplastic forming equipment commonly found in industry, and so can be implemented on existing plastic container manufacturing lines, after appropriate re-tooling. The first wall layer with an indented surface and the one of more additional layers of material may be a thermoplastic material formed by injection moulding and/or thermoforming. A further advantage of these processes is that they are able to position the phase change material at an optimum depth in the container wall. For example, to efficiently keep the contents of the container cold, yet minimize the cold sensation for someone handling the container, the at least one wall may be formed so as to have the indents on the inner surface of the container, and the additional layer be sized so as to be relatively thin compared to the thickness of the wall material between the indents and the outer surface. The phase change material is thus positioned close to the product inside the container, with a relatively thick insulating wall between the phase change material and the outer surface of the container.

Those skilled in the art will understand that they can freely combine all features of the present invention disclosed herein. In particular, features described for the product of the present invention may be combined with the method of the present invention and vice versa. Further, features described for different embodiments of the present invention may be combined. Where known equivalents exist to specific features, such equivalents are incorporated as if specifically referred to in this specification. Further advantages and features of the present invention are apparent from the figures and non-limiting examples. Example 1

Process for manufacturing a container with phase change material in a single layer of wall channels.

A box shaped container with a grooved inner surface is injection moulded from polypropylene as shown in Figure 1. The mould cavity is formed between a lower platen (1) with a female mould (2) and an upper platen (3) with a mould core (4). The mould core has a series of ridges (5) on its surface, positioned to form the pattern of channels shown schematically in Figure 7. When the mould is closed, molten polypropylene is injected via an injection port (6). The polypropylene forms a moulded part (7) with walls 10 mm thick having grooves (8) on its inner surface corresponding to the ridges (5) on the mould core (4).

In the second step of the process, a polypropylene sheet (9) is heated and vacuum formed onto a vacuum plug (10) and held in position. The vacuum plug (10) then descends into the grooved moulded part (7), still held in the female mould (2), shown in Figures 2 and 3. The vacuum plug (10) and polypropylene sheet (9) are sized so that the formed sheet fits exactly into the grooved moulded part (7). The vacuum is maintained until the hot sheet bonds with the inner surface of the moulded part, preventing the sheet material from flowing into the grooves and closing them. This covers over the grooves to form channels (11). The channels have a depth of 4 mm and a width of 2 mm.

A 22.4 wt.% eutectic solution of sodium chloride in water (phase change material) is then injected into the channels (11), Figure 4. The channels are arranged so that they run from one side of the box, through the base and up the other side of the box, shown schematically in Figure 7. One set of nozzles (12) injects the phase change material, while a second set of nozzles (13) sucks the phase material through the channels, flushing the material through until the channels are full. To allow for expansion of the phase change material during the use of the container, this is performed with the salt solution at 60 °C.

The thermoplastic sheet (9) is then folded over the open channels and trimmed with cutters (14) as shown in Figure 5. The finished box (15) is then ejected from the female mould (2) shown in Figure 6. As the initial grooved moulded box (7) is thicker than the sheet (9), the channels (11) run closer to the inner surface of the container than the outer surface. A similar process is then repeated, with an appropriately shaped mould, to form a lid having channels filled with phase change material. The enclosed regions (the channels) occupy approximately 25% of the total wall volume; being the volume of the base, side walls and lid.

An alternative method of forming the initial box shaped container with a grooved inner surface would be to vacuum form a polypropylene sheet onto a vacuum plug with a ridged surface.

A schematic representation of the channels (11) in the side walls (16) and base (17) of a box shaped container is shown in Figure 7. There are many more channels than shown, with the minimum distance between channels running in the same direction in this example being 1.5 mm, but some channels are omitted to simplify the drawing. The channels on the side walls run in the same direction as that in which the ridged mould core (4) is inserted, making it easier to extract the mould core. The channels connect from one side to the other to aid filling. Some of the channels intersect with each other; a 4-way intersection (18) is shown.

To fill with ice cream, the container (including its lid) is first chilled and then soft ice cream is filled into the container before it is sealed. The container is then put into a freezer to freeze the ice cream to its ideal storage temperature and to solidify the salt solution in the channels. The container is able to increase the time that the ice cream remains frozen when the container is removed from the freezer and placed at 20 °C.

Example 2

Process for manufacturing a container with phase change material in multiple layers of wall channels.

In the first step, a box shaped container with a grooved inner surface is formed as in Example 1, in the same manner as shown in Figure 1. In the second step of the process (Figure 8), a trimmed polypropylene sheet is thermoformed between a ridged (21) vacuum plug (20) and a female mould (22), to form a sheet (19) having grooves (23) on its inner surface. The shaped grooved sheet is withdrawn from the female mould and held in position on the vacuum plug. The ridged vacuum plug (20) together with the shaped grooved sheet is then placed into the box shaped container formed in the first step (Figure 9). The ridged vacuum plug (20) and grooved polypropylene sheet (19) are sized so that the grooved sheet fits exactly into the grooved moulded part (7). The vacuum is maintained until the hot sheet bonds with the inner surface of the moulded part, preventing the sheet material from flowing into the first grooves (8) and closing them. The trimmed sheet covers over the first grooves (8) to form channels (11). When the ridged vacuum plug is withdrawn, it leaves a moulded part (24) containing channels (11), with grooves (23) on its inner surface.

In the third step of the process (Figure 10), a polypropylene sheet (9) is heated and vacuum formed onto a vacuum plug (10) and held in position. The vacuum plug (10) then descends into the grooved moulded part (24) containing channels, held in the female mould (2), shown in Figure 9. The vacuum plug (10) and polypropylene sheet (9) are sized so that the formed sheet fits exactly into the grooved moulded part (24) containing channels. The vacuum is maintained until the hot sheet bonds with the inner surface of the moulded part, preventing the sheet material from flowing into the grooves and closing them. This covers over the grooves to form a further set of channels (11).

A 22.4 wt.% eutectic solution of sodium chloride in water is then injected into both sets of channels and a thermoplastic sheet folded over the open channels and trimmed with cutters in the same way as for Example 1. The box shaped container (25) with two sets of channels is then released from the mould, Figure 11. The two sets of channels have a staggered arrangement so that they do not directly overlap. This maintains the strength of the container. Figure 12 shows a cross-section through a side wal l. The cha nnels (11) are encased between the grooved moulded part (7) the grooved polypropylene sheet (19) and the outer polypropylene sheet (9) in a staggered arrangement. Although the formation of only two sets of channels is described in Example 2, the skilled person will recogn ize that this method can be used to form containers with mu ltiple bonded layers, each enclosing chan nels.

Claims

1 . Container having at least one wall and enclosing a storage volume wherein the at least one wall comprises at least one enclosed region within its structure, the enclosed region containing phase change material and having at least two dimensions smaller than 50 mm.

2. A container according to claim 1 wherein the at least one enclosed region occupies between 15% and 90% of the volume of the at least one wall.

3. A container according to any one of the preceding claims wherein the phase change material is present in the at least one wall at a level of between 10% and 85% by volume.

4. A container according to any one of the preceding claims wherein the at least one enclosed region is distributed inhomogeneously.

5. A container according to any one of the preceding claims wherein the at least one enclosed region is a shallow cup shape or a channel.

6. A container according to claim 5 wherein the at least one wall comprises one or more channels and the channels intersect with themselves or one another and each channel intersection connects no more than six ways.

7. A container according to any one of the preceding claims wherein the phase change material is selected from the group consisting of organic fatty acids; fatty acid esters; water; salt solutions, for example eutectic water based salt solutions; paraffins, for example n-tetradecane; water/glycerol mixtures; water/salt hydrate mixtures; and combinations thereof.

8. A container according to any one of the preceding clainns wherein the at least one wall is made from a thermoplastic material, for example selected from the group consisting of polyethylene, polypropylene, polystyrene, polyethylene terephthalate, thermoplastic starch, polylactic acid and combinations thereof.

9. Use of a container according to any one of the preceding claims to maintain the temperature of a chilled or frozen foodstuff.

10. Use of a container according to any one of claims 1 to 8 to maintain the temperature of a hot foodstuff, for example a beverage or soup.

1 1 . Use of a container according to any one of claims 1 to 8 to maintain the temperature of chocolate products, beverages, dairy products or ice cream.

12. Use of a container according to any one of claims 1 to 8 to protect food products sent by post.

13. A process for manufacturing the container of claim 1 comprising the steps of: - forming a first wall layer with an indented surface,

- filling at least some of the indents with a phase change material, and affixing one or more additional layers of material to the first wall layer so as to cover the filled indents and form enclosed regions containing phase change material.

14. A process for manufacturing the container of claim 1 comprising the steps of: - forming a first wall layer with an indented surface where the indents are in the form of grooves,

- affixing one or more additional layers of material to the first wall layer so as to cover the grooves and form channels,

- filling at least some of the channels with a phase change material, and

- sealing the channels.

15. A process according to claims 13 or 14 wherein the first wall layer with an indented surface and the one of more additional layers of material are thermoplastic material formed by injection moulding and/or thermoforming.