Patent Description:
In the packaging industry, there is a general need to make disposable packaging of recyclable material. Preferably, the packaging is made of a single recyclable material, such as PET or a polyolefin. There is also a general need to reduce the mass of thermoplastic material used for any given packaging article. The reduced mass not only reduces the cost of manufacturing the packaging article, but also reduces the volume of material to be recycled.

Efforts have been made in the industry to provide various disposable packaging articles. For example, <CIT>, <CIT> and <CIT> disclose the manufacture of a lightweight polypropylene cup which has expanded regions comprising a cellular foam.

However, despite this prior art disclosure there is still a need to produce thermoplastic containers, in particular containers for foodstuffs and/or beverages, which have even smaller wall thickness and even lower mass, yet high stiffness, as well as low cost. Typically, containers for foodstuffs and/or beverages are required to have a desired precise geometrical shape, yet nevertheless have high wall strength, and preferably are readily recyclable, most preferably being composed of a single recyclable material.

<CIT> discloses a container having the features of the pre-characterising portion of claim <NUM> as well as a method for manufacturing the same.

The present invention aims at least partially to overcome the problem of achieving even smaller wall thickness and even lower mass, a desired precise geometrical shape, yet nevertheless high stiffness and wall strength, in containers for foodstuffs and/or beverages, which preferably are composed of a single recyclable material.

The present invention provides a container according to claim <NUM>.

The present invention further provides a method of forming a container according to claim <NUM>.

Preferred features of the container and method are defined in the respective dependent claims.

The drawings are highly schematic and not necessarily to scale, and some dimensions may be exaggerated for the purpose of clarity of illustration.

Referring to <FIG>, there is shown a container in accordance with a first embodiment of the present invention. In this embodiment, the container is in the form of a tray <NUM>.

The container, i.e. tray, <NUM> comprises an annular sidewall <NUM> which comprises upper and lower annular peripheral edges <NUM>, <NUM>, and a base <NUM> which comprises an annular peripheral edge <NUM> which is integral with the lower annular peripheral edge <NUM> of the sidewall <NUM>. The annular peripheral edge <NUM> of the base <NUM> surrounds a base wall structure <NUM> which is integral therewith. The base wall structure <NUM> comprises at least one injection moulding sprue <NUM> at a central region <NUM> of the base wall structure <NUM>. The sidewall <NUM> and the base <NUM> are comprised in a single integral moulded body <NUM> composed of a thermoplastic polymer and define a central concavity <NUM> for packaging a product, such as a foodstuff (not shown). The single integral moulded body <NUM> is formed by injection moulding, and the thermoplastic polymer has been injected through the sprue <NUM> to fill an injection moulding cavity for moulding the single integral moulded body <NUM> as described hereinbelow.

In the preferred embodiments of the present invention, the thermoplastic polymer may comprise a polyolefin or blend of a plurality of polyolefins, optionally polyethylene or polypropylene; or a polyester, optionally polyethylene terephthalate or polybutylene terephthalate; or polylactic acid. In a particularly preferred embodiment, the polymer comprises polypropylene. Polypropylenes having a Melt Flow Index (MFI) of from <NUM> to <NUM> are most particularly preferred. The Melt Flow Index of a polymer can be measured according to ASTM D1238.

In this specification, the term "annular" means "generally ring-like", is not limited to geometrically circular shapes, and encompasses shapes that may be circular or other than circular, for example elliptical, polygonal, etc.. In the illustrated embodiment, the tray <NUM> is polygonal in plan, being substantially rectangular in plan but with angled, or cut-away, corners. However, the tray <NUM> may have any desired plan shape, which may be any other polygonal shape, for example square, rectangular, triangular, pentangular, hexagonal, etc., or may a curved or rounded shape, for example circular, elliptical, etc..

In this embodiment, the sidewall <NUM> has a polygonal shape in plan and comprises a plurality of wall elements <NUM> which are connected in series to form an endless wall member <NUM> extending upwardly from, and surrounding, the base <NUM>. Each wall element <NUM> is disposed between respective portions of the upper and lower annular peripheral edges <NUM>, <NUM>. Each wall element <NUM> is outwardly inclined and planar. However, in other embodiments the wall elements <NUM> may be vertical, and orthogonal to the base <NUM>, or inwardly or outwardly curved. Essentially, any desired three-dimensional design for the tray <NUM> may be employed.

The sidewall <NUM> comprises a lattice structure <NUM> of elongate ribs <NUM> interconnecting the upper and lower annular peripheral edges <NUM>, <NUM>. In the illustrated embodiment, the elongate ribs <NUM> extend between the upper and lower annular peripheral edges <NUM>, <NUM> of the sidewall <NUM>. The lattice structure <NUM> is an open framework <NUM> defining a plurality of sidewall openings <NUM>. The wall elements <NUM> are connected at respective corner portions <NUM> of the sidewall <NUM>. Accordingly, the elongate ribs <NUM> extend between the upper and lower annular peripheral edges <NUM>, <NUM> of the sidewall <NUM> and are located between the upwardly oriented corner portions <NUM> of the sidewall <NUM>. Each corner portion <NUM> has opposite upwardly oriented edges <NUM>. The elongate ribs <NUM> in the sidewall <NUM> extend upwardly along the sidewall <NUM> and in a plurality of the wall elements <NUM>, typically each of the wall elements <NUM> extending along the length or width of the endless wall member <NUM>, although optionally not at any wall element <NUM> located at an angled corner of the endless wall member <NUM>, each wall element <NUM> a plurality of the elongate ribs <NUM> are serially located in a mutually spaced configuration along a width of the wall element <NUM>.

The at least one injection moulding sprue <NUM> is connected to the upper annular peripheral edge <NUM> of the annular sidewall <NUM> by the base wall structure <NUM>, the annular peripheral edge <NUM> of the base <NUM>, the lower annular peripheral edge <NUM> of the sidewall <NUM> and the lattice structure <NUM> of the sidewall <NUM>.

In this embodiment, the base wall structure <NUM> also comprises a base lattice structure <NUM> of elongate ribs <NUM> connected to the annular peripheral edge <NUM> of the base <NUM>. The base lattice structure <NUM> is an open framework <NUM> defining a plurality of base openings <NUM>. In the illustrated embodiment, the elongate ribs <NUM> intersect with one or more other of the elongate ribs <NUM> at rib junctions <NUM> to form an intersecting rib network <NUM>. At least some of the elongate ribs <NUM> extend radially outwardly from the central region <NUM> of the base wall structure <NUM> of the base <NUM>, which comprises a central rib junction <NUM>.

In an alternative embodiment, the lattice structure <NUM> in the sidewall <NUM> may additionally be provided with one or more elongate ribs which extend in a circumferential direction around at least a fraction of the annular periphery of the sidewall <NUM>, and/or at least some of the elongate ribs intersect with one or more other of the elongate ribs at rib junctions to form an intersecting rib network. In another alternative embodiment, the base <NUM> may comprise a solid layer of the thermoplastic polymer and is not provided with a lattice structure.

In the illustrated embodiment, the lattice structure <NUM> in the sidewall <NUM> and the lattice structure <NUM> in the base <NUM> are polygonal and the openings <NUM>, <NUM> between the elongate ribs <NUM>, <NUM> are polygonal. As illustrated, the lattice structures <NUM><NUM> are rectangular and the openings <NUM>, <NUM> between the elongate ribs <NUM>, <NUM> are rectangular or triangular. However, other shapes of openings may be provided in the sidewall <NUM> or base <NUM>.

The container further comprises a flexible sheet <NUM> which is bonded to the lattice structure <NUM> in the sidewall <NUM>, and when present the lattice structure <NUM> in the base <NUM>, to cover the sidewall openings <NUM>, and when present the base openings <NUM>, and form a sealed sidewall surface <NUM>, and a sealed base surface <NUM>, of the tray <NUM>.

In the preferred embodiments, at least one or both of the outer surface <NUM> and the inner surface <NUM> of the flexible sheet <NUM> is printed and/or embossed. Such printing and embossing enable the flexible sheet <NUM> cosmetically to function as a label in the tray <NUM>, as well as structurally functioning to provide the sealed sidewall surface <NUM>, and the sealed base surface <NUM>, of the tray <NUM>.

In the illustrated embodiment, an outer surface <NUM> of the flexible sheet <NUM> is bonded to an inner surface <NUM> of the lattice structure(s) <NUM>, <NUM>. An inner surface <NUM> of the flexible sheet <NUM> forms the interior surface <NUM> of the sidewall <NUM> and the base <NUM>.

In alternative embodiments of the present invention, the flexible sheet <NUM> may be bonded to an outer surface <NUM> of the lattice structure(s) <NUM>, <NUM>. The inner surface <NUM> of the lattice structure(s) <NUM>, <NUM> and exposed regions of the inner surface <NUM> of the flexible sheet <NUM> within the sidewall and base openings <NUM>, <NUM> form the interior surface <NUM> of the sidewall <NUM> and the base <NUM>.

In the illustrated embodiment, the sidewall <NUM> and the base <NUM> comprise or consist of an unfoamed layer of the thermoplastic polymer.

As recited in claim <NUM> and illustrated in <FIG>, in at least one of lattice structures <NUM> in the sidewall <NUM> and optionally the base <NUM> at least some, preferably all, of the respective elongate ribs <NUM>, <NUM> comprise elongate foam ribs <NUM>, <NUM>. Each foam rib <NUM>, <NUM> comprises opposed outer and inner unfoamed solid skins <NUM>, <NUM> of the thermoplastic polymer on opposite sides of a central cellular foam core <NUM> of the thermoplastic polymer. The inner unfoamed solid skin <NUM> is bonded to the flexible sheet <NUM>. Typically, in each foam rib <NUM>, <NUM> at least the outer unfoamed solid skin <NUM> of the thermoplastic polymer comprises a convexly curved surface <NUM>. Preferably, the convexly curved surface <NUM> is continuously convexly curved between opposite elongate longitudinal edges <NUM>, <NUM> of the elongate foam rib <NUM>, <NUM>.

The upper and lower annular peripheral edges <NUM>, <NUM> of the sidewall <NUM> may also be comprised of a solid skin/foam core/solid skin structure when foam ribs <NUM> are provided in the sidewall <NUM>. The annular peripheral edge <NUM> of the base <NUM> may also be comprised of a solid skin/foam core/solid skin structure when foam ribs <NUM> are provided in the base <NUM>. The foam ribs <NUM>, <NUM> may intersect at foam junctions located within the sidewall <NUM> or the base <NUM>.

The tray <NUM> further comprises an upper annular peripheral rim <NUM> which is integral with the upper annular peripheral edge <NUM> of the sidewall <NUM>. The rim <NUM> extends laterally outwardly circumferentially around the tray <NUM>. The rim <NUM> comprises or consists of an unfoamed layer of the thermoplastic polymer. Typically, when packaging a foodstuff a sealing film (not shown) is sealed to the upper surface of the rim <NUM>.

In an alternative embodiment, which is not illustrated, the upper annular peripheral rim <NUM> comprises an annular edge of unfoamed thermoplastic polymer reinforced by an integral annular foam hoop reinforcement, wherein the foam hoop reinforcement comprises opposed unfoamed solid skins of the thermoplastic polymer on opposite sides of a central cellular foam core of the thermoplastic polymer.

In the illustrated embodiment, the base <NUM> has base openings <NUM>. In other embodiments, the base <NUM> may comprise a solid layer of the thermoplastic polymer and is not provided with a lattice structure <NUM>, in which case the flexible sheet <NUM> either may be bonded to an inner or outer surface of the base <NUM>, or may not be bonded or even cover the base <NUM>. In other words, in some embodiments the flexible sheet <NUM> may only cover the sidewall openings <NUM> and may not cover the base <NUM> when a solid base is provided.

In the illustrated embodiment, as shown in <FIG> the flexible sheet <NUM> is a single cross-shaped or star-shaped sheet element <NUM> which has been <NUM>-dimensionally pre-cut to have a shape and dimensions to fit the flexible sheet <NUM>, after bending and/or folding the <NUM>-dimensional sheet element <NUM> into a <NUM>-dimensional shape, to the single integral moulded body <NUM> which comprises the sidewall <NUM> and base <NUM>. The flexible sheet <NUM> therefore has a base-covering central part <NUM> and a plurality of sidewall-covering extending parts <NUM> connected to the central part <NUM> which extend away from the central part <NUM>, each extending part <NUM> being configured to cover a respective wall element <NUM>. Each extending part <NUM> has a peripheral end edge <NUM> and opposed peripheral side edges <NUM> which connect the end edge <NUM> to the central part <NUM>. The peripheral end edges <NUM> and the peripheral side edges <NUM> form an entire outer peripheral edge <NUM> of the flexible sheet <NUM>.

Thereafter the flexible sheet <NUM> is configured into a <NUM>-dimensional shape which, in the final tray <NUM>, covers the base <NUM> and extends upwardly to cover the sidewall openings <NUM>. Each sidewall opening <NUM>, and each base opening <NUM> is covered by a respective portion <NUM>, <NUM> of the flexible sheet <NUM>. The central part <NUM> covers the base <NUM> and the extending parts <NUM> cover a respective wall element <NUM> of the sidewall <NUM>.

The outer peripheral edge <NUM> of the flexible sheet <NUM> may be bonded to the inner or outer surface of the sidewall <NUM>. However, preferably the outer peripheral edge <NUM> of the flexible sheet <NUM> is sealed within the thickness of the sidewall <NUM> which provides an enhanced sealing bond between the flexible sheet <NUM> and the moulded body <NUM>. Such a sealing structure means that if the flexible sheet comprises a foam layer, or a recycled polymer layer, the foam or recycled polymer layer is prevented from coming into direct contact with the contents, e.g. foodstuffs, which may be packaged within the container <NUM>.

The peripheral end edges <NUM> of the flexible sheet <NUM> are bonded to the upper annular peripheral edge <NUM> of the sidewall <NUM>. The extending parts <NUM> are bonded to the lattice structure <NUM> of the elongate ribs <NUM> and to the corner portions <NUM>.

At each corner portion <NUM> of the sidewall <NUM>, each of the opposite upwardly oriented edges <NUM> of the corner portion <NUM> has bonded thereto a respective peripheral side edge <NUM> of the respective opposite extending part <NUM>. At the corner portions <NUM> the peripheral side edges <NUM> may abut or overlap. However, it is preferred that at the corner portions <NUM> the peripheral side edges <NUM> of the opposite extending parts <NUM> are spaced from each other by a spacing <NUM> extending along the corner portion <NUM>.

In the illustrated embodiment, each portion <NUM>, <NUM> is under tension. This tension may have been formed, as described hereinafter, by providing that the flexible sheet <NUM> is composed of a heat-shrinkable material and during the bonding of the flexible sheet <NUM> to the moulded body <NUM>, which comprises the sidewall <NUM> and base <NUM>, the flexible sheet <NUM> is heat-shrunk. This heat shrinking step can provide that the flexible sheet <NUM> is shrunk in dimensions, in at least one shrinkage direction, more than the moulded body <NUM> during a moulding process in which the flexible sheet <NUM> is bonded to the moulded body <NUM> in an in-mould labelling (IML) process.

In alternative embodiments, each portion <NUM>, <NUM> may be slack and thereby not under tension.

The flexible sheet <NUM> may be composed of a thermoplastic polymer film comprising a single polymer layer. The single polymer layer may comprise an oriented polymer film or a heat-shrunk polymer film. Alternatively, the flexible sheet <NUM> may be composed of a multilayer laminate. For example, the multilayer laminate may comprise a barrier layer comprising a metal or polymer. The flexible sheet <NUM> may alternatively be composed of any suitable sheet material for use in packaging, for example cardboard, metal or metallised plastics material. In other embodiments, the flexible sheet <NUM> may be composed of a woven or non-woven thermoplastic polymer fabric, preferably which is porous to air. In further embodiments, the flexible sheet <NUM> may be composed of a foamed thermoplastic polymer layer comprising opposed unfoamed solid skins of the thermoplastic polymer on opposite sides of a central cellular foam core of the thermoplastic polymer. Any of these alternative compositions for the flexible sheet <NUM> may be used with any structure of the sidewall and base and any shape and configuration of the moulded body <NUM> and the flexible sheet <NUM>. The selection of any desired composition for the flexible sheet <NUM> primarily depends upon the end use of the container and the product to be packaged therein.

In a particularly preferred embodiment, the injection moulded body <NUM> and the flexible sheet <NUM> are composed on the same thermoplastic polymer so that the entire container, which comprises the flexible sheet <NUM> bonded to the injection moulded body <NUM>, can be recycled without having to separate the flexible sheet <NUM> from the injection moulded body <NUM>. For example, the flexible sheet <NUM> and the injection moulded body <NUM> can both be composed or a polyolefin, such as polypropylene. Preferably, the polypropylene for the flexible sheet <NUM> comprises an oriented, preferably biaxially oriented or alternatively uniaxially oriented, polypropylene film, typically having a thickness of from <NUM> to <NUM> microns, for example from <NUM> to <NUM> microns.

Referring to <FIG>, there is shown a container in accordance with a second embodiment of the present invention. In this embodiment, the container is in the form of a round pot <NUM>.

Again, as for the first embodiment, the round pot <NUM> has a sidewall <NUM> and an integral base <NUM>. The sidewall <NUM> has a lattice structure <NUM> but the base <NUM> is solid. In this embodiment, the sidewall <NUM> has a rotational shape in plan and comprises a single continuously curved endless wall member <NUM> extending upwardly from the base <NUM>. The elongate ribs <NUM> in the sidewall <NUM> extend upwardly along the sidewall <NUM> and are serially located in a mutually spaced configuration around a circumference of the single continuously curved endless wall member <NUM>. The sidewall is preferably also provided with one or more annular hoop ribs <NUM> around the sidewall <NUM> which connect at junctions <NUM> with the elongate ribs <NUM>.

The flexible <NUM> sheet is elongate and extends around the sidewall <NUM>. The flexible sheet <NUM> does not cover the base <NUM>. In particular, the flexible sheet <NUM> is an elongate strip <NUM> which is bent to extend circumferentially around the sidewall <NUM>. In this embodiment the flexible sheet <NUM> is bonded to the inner surface of the lattice structure <NUM> and forms the interior surface of the sidewall <NUM>. The flexible sheet <NUM> has opposite ends <NUM>, <NUM> which form a sealed joint <NUM> extending between the upper and lower annular peripheral edges <NUM>, <NUM> of the sidewall <NUM>. The opposite ends <NUM>, <NUM> are adjacent and are sealingly bonded to the lattice structure <NUM> to form the sealed joint <NUM>.

As shown in the Figures, the opposite ends <NUM>, <NUM> are preferably covered by an elongate rib <NUM> in the sidewall <NUM> so that the opposite peripheral end edges <NUM> of the ends <NUM>, <NUM> are sealed within the thickness of the sidewall <NUM>. Alternatively, the opposite ends <NUM>, <NUM> overlap and are sealingly bonded to each other to form the sealed joint <NUM>.

Referring to <FIG>, there is shown a container in accordance with a third embodiment of the present invention. In this embodiment, the container is in the form of a square pot <NUM>.

This embodiment is a modification of the round pot of the previous embodiment, and specifically the square pot <NUM> is not only square in plan, instead of round, but also square pot <NUM> further comprises a lid <NUM>. The lid <NUM> is also composed of the thermoplastic polymer used to form the moulded body <NUM> to form the sidewall <NUM> and integral base <NUM> as described for the previous embodiments. The lid <NUM> is removably fittable to the sidewall <NUM> and is connected to the sidewall <NUM> by the flexible sheet <NUM>.

The sidewall <NUM> and the base <NUM> each have a respective lattice structure <NUM>, <NUM>. The elongate ribs <NUM> in the sidewall <NUM> extend upwardly along the sidewall <NUM> and are serially located in a mutually spaced configuration around a circumference of sidewall <NUM>. The sidewall <NUM> is preferably also provided with one or more annular hoop ribs <NUM> around the sidewall <NUM> which connect at junctions <NUM> with the elongate ribs <NUM>. The ribs <NUM> in the base <NUM> are radial from a centre of the base <NUM>. As for the lattice structures of the previous embodiments, the sidewall and base lattice structures <NUM>, <NUM> are open frameworks <NUM>, <NUM> defining a plurality of sidewall and base openings <NUM>, <NUM>. The flexible sheet <NUM> is bonded to the sidewall and base lattice structures <NUM>, <NUM> to cover the sidewall and base openings <NUM>, <NUM> and form a sealed sidewall surface <NUM>, <NUM> of the square pot <NUM>.

As for the first embodiment, the flexible sheet <NUM> is a single cross-shaped sheet element <NUM> which has been <NUM>-dimensionally pre-cut to have a shape and dimensions to fit the flexible sheet <NUM>, after bending and/or folding the <NUM>-dimensional sheet element <NUM> into a <NUM>-dimensional shape, to the single integral moulded body <NUM> which comprises the sidewall <NUM> and base <NUM>. The flexible sheet <NUM> therefore has a base-covering central part <NUM> and a plurality of sidewall-covering extending parts <NUM> connected to the central part <NUM> which extend away from the central part <NUM>, each extending part <NUM> being configured to cover a respective wall element <NUM>.

The peripheral end edges <NUM> of the flexible sheet <NUM> are bonded to the upper annular peripheral edge <NUM> of the sidewall <NUM>. The extending parts <NUM> are bonded to the lattice structure <NUM> of the sidewall <NUM> and to the corner portions <NUM>.

As shown in <FIG>, at each corner portion <NUM> of the sidewall <NUM>, each of the opposite upwardly oriented edges <NUM> of the corner portion <NUM> has bonded thereto a respective peripheral side edge <NUM> of the respective opposite extending part <NUM>. At the corner portions <NUM> the peripheral side edges <NUM> may abut or overlap. However, it is preferred that at the corner portions <NUM> the peripheral side edges <NUM> of the opposite extending parts <NUM> are spaced from each other by a spacing <NUM> extending along the corner portion <NUM>. The peripheral side edges <NUM> are preferably embedded into the corner portions <NUM> so as to be sealed therein.

The flexible sheet <NUM> further comprises an integral extension part <NUM> which is connected to one of the sidewall-covering extending parts <NUM> of the flexible sheet <NUM> which is bonded to the sidewall <NUM>. The integral extension part <NUM> extends away from the sidewall-covering extending part <NUM> to form a lid portion <NUM> of the flexible sheet <NUM> which is bonded to the lid <NUM>, preferably the outer surface <NUM> of the lid <NUM>.

The integral extension part <NUM> forms a hinge <NUM> for the lid <NUM> and/or a tamper evident connection <NUM>, shown in <FIG>, between the lid <NUM> and the sidewall <NUM>. A tamper evident connection <NUM> can be achieved by perforating the flexible sheet <NUM> during an earlier step of cutting the peripheral edge of the flexible sheet <NUM> to provide a tear line which is precisely positioned at the hinge <NUM> when the flexible sheet <NUM> is over-moulded. Alternatively, the flexible sheet <NUM> may extend beyond the lid <NUM> and include a tear line which is opposite to the hinge <NUM> when the lid <NUM> is closed, for example after an extending flap of the flexible sheet <NUM> has been bonded to the sidewall opposite to the hinge <NUM>.

The lid <NUM> may be a solid layer of the thermoplastic polymer. However, alternatively, as illustrated, the lid <NUM> comprises a lid lattice structure <NUM> of elongate ribs <NUM> integrally connected to an annular peripheral edge <NUM> of the lid <NUM>. As for the lattice structures of the previous embodiments, the lid lattice structure <NUM> is an open framework <NUM> defining a plurality of lid openings <NUM>. The flexible sheet <NUM> is bonded to the lid lattice structure <NUM> to cover the lid openings <NUM> and form a sealed lid surface <NUM> of the square pot <NUM>.

The container may be formed as a fresh produce container, e.g. a pot or punnet for berries or mushrooms, or a flower pot, and the container sidewall and/or base and/or lid, and optionally the flexible sheet, may be provided with air passage or drainage holes, as illustrated in <FIG> by holes <NUM> in the sidewall <NUM> aligned with openings <NUM>, holes <NUM> in the base <NUM> aligned with openings <NUM> and holes <NUM> in the lid <NUM> aligned with openings <NUM>.

The present invention also provides a method of forming a container, such as any of the containers of the previous embodiments. The flexible sheet can be incorporated into the container as an in-mould label (IML) using IML technology.

Referring to <FIG>, the method provides a mould <NUM> having a first mould part <NUM> and a second mould part <NUM>. The first and second mould parts <NUM>, <NUM> have respective first and second cavity-forming surfaces <NUM>, <NUM> for forming a sidewall, such as sidewall <NUM>, <NUM>, <NUM> of the previous embodiments, and a base, such as base <NUM>, <NUM>, <NUM> of the previous embodiments, of the container which define a central concavity for packaging a product in the container. The first and second cavity-forming surfaces <NUM>, <NUM> have respective first and second regions <NUM>, <NUM> for moulding the sidewall of the container.

In the illustrated embodiment, the first and second mould parts <NUM>, <NUM> are, respectively, outer and inner mould parts for moulding the outer and inner surfaces, respectively, of the container to be moulded.

An in-mould flexible sheet <NUM>, such as flexible sheet <NUM>, <NUM>, <NUM>, is provided between the first and second regions <NUM>, <NUM>.

The mould <NUM> is then closed, thereby defining a cavity <NUM> between the first and second cavity-forming surfaces <NUM>, <NUM>. The cavity <NUM> defines an annular sidewall-forming portion <NUM> and a base-forming portion <NUM> which is adjacent to the sidewall-forming portion <NUM>. The first region <NUM> of the first cavity-forming surface <NUM> comprises a lattice-forming portion <NUM>, comprising a latticed network <NUM> of concavities <NUM> in the first cavity-forming surface <NUM>. Therefore, in the illustrated embodiment, the lattice-forming portion <NUM> is in the outer mould part, whereas in other embodiments the lattice-forming portion <NUM> is in the inner mould part.

In one embodiment, the flexible sheet <NUM> is located within the cavity <NUM> adjacent to the lattice-forming portion <NUM> of the first cavity-forming surface <NUM>. In another embodiment, the flexible sheet <NUM> is located within the cavity <NUM> adjacent to the second cavity-forming surface <NUM> at a location opposite the lattice-forming portion <NUM> of the first cavity-forming surface <NUM>. Again, the lattice-forming portion <NUM> may be in the inner or outer mould part of the first and second mould parts <NUM>, <NUM>.

A plurality of opening-forming portions <NUM> of the mould <NUM> are provided adjacent to the concavities <NUM>. In the opening-forming portions <NUM> of the mould <NUM>, the flexible sheet <NUM> is held between the first and second cavity-forming surfaces <NUM>, <NUM>.

The lattice forming portion <NUM> is in the sidewall-forming portion <NUM> of the mould <NUM> to form a sidewall lattice structure, and may also be in the base-forming portion <NUM> of the mould <NUM> when a base lattice structure is to be formed.

Thereafter, a molten plastic composition <NUM> comprising the thermoplastic polymer is injected into the mould <NUM>. This fills the cavity <NUM> with the molten plastic composition. The sidewall-forming portion <NUM> of the mould <NUM> forms a sidewall of the container and the base-forming portion <NUM> of the mould <NUM> forms a base of the container, the sidewall and base having structures as described above.

Accordingly, in at least the latticed network <NUM> of concavities <NUM> is injected a lattice-forming part <NUM> of the thermoplastic polymer. The lattice-forming part <NUM> defines a lattice structure <NUM>, such as the sidewall and optional base lattice structures of the previous embodiments. Each lattice structure is an open framework defining a plurality of sidewall openings formed by the plurality of opening-forming portions <NUM> of the mould <NUM>. As described above, the base wall structure <NUM> comprises at least one injection moulding sprue <NUM> at a central region <NUM> of the base wall structure <NUM> through which the molten plastic composition is injected through a gate <NUM> into the cavity <NUM>. The gate <NUM> is preferably on the opposite side of the mould cavity <NUM> from the side which receives the flexible sheet <NUM>, as shown in <FIG>; however, in an alternative embodiment the molten plastic composition could be injected through a hole in the flexible sheet <NUM> from a gate which is on the same side of the mould cavity <NUM> which receives the flexible sheet <NUM>. The at least one injection moulding sprue <NUM> is connected to the upper annular peripheral edge of the annular sidewall by the base wall structure, the annular peripheral edge of the base, the lower annular peripheral edge of the sidewall and the lattice structure of the sidewall, as described hereinbefore.

Thereafter, the molten plastic composition is cooled to solidify the thermoplastic polymer and bond the flexible sheet <NUM> to the lattice structure <NUM> to cover the sidewall openings and form a sealed sidewall surface of the container. The container may then be removed from the mould <NUM>.

Accordingly, the in-mould flexible sheet <NUM> may be located adjacent to an outer mould part of the first and second mould parts <NUM>, <NUM> which forms an outer surface of the container, and in the moulded container the flexible sheet <NUM> is bonded to an outer surface of the lattice structure <NUM>, and the inner surface of the lattice structure <NUM> and exposed regions of the inner surface of the flexible sheet <NUM> within the sidewall openings form an interior surface of the sidewall of the container.

Alternatively, the in-mould flexible sheet <NUM> may be located adjacent to an inner mould part of the first and second mould parts <NUM>, <NUM> which forms an inner surface of the container, and in the moulded container the flexible sheet <NUM> is bonded to an inner surface of the lattice structure <NUM> and an inner surface of the flexible sheet <NUM> forms the interior surface of the sidewall of the container.

In order to make the round pot container of the second embodiment, the in-mould flexible sheet <NUM> is an elongate strip, and the flexible sheet is located in the cavity <NUM> so as to extend circumferentially around the sidewall-forming portion <NUM> of the mould <NUM>.

As shown in <FIG>, in order to make the tray container of the first embodiment and the square pot container of the third embodiment, the in-mould flexible sheet <NUM> is additionally located in the base-forming portion <NUM> of the cavity <NUM>, and in the molded container the flexible sheet <NUM> is additionally bonded to a surface of the base.

As described above for the tray container of the first embodiment and the square pot container of the third embodiment, the base of the container may comprise a lattice structure. Accordingly, a base region of the first cavity-forming surface <NUM> may comprise a base lattice-forming portion, comprising a base latticed network of base concavities in the first cavity-forming surface <NUM>. The flexible sheet <NUM> is located within the cavity <NUM> adjacent to the base lattice-forming portion of the first cavity-forming surface or adjacent to the second cavity-forming surface <NUM> at a location opposite the base lattice-forming portion of the first cavity-forming surface <NUM>. This provides a plurality of base opening-forming portions of the mould <NUM> adjacent to the base concavities. In the base opening-forming portions of the mould <NUM>, the flexible sheet <NUM> is held between the first and second cavity-forming surfaces <NUM>, <NUM>. A base lattice-forming part of the molten plastic composition is injected into the base latticed network of base concavities. Accordingly, the base lattice-forming part defines a base lattice structure as described above. The flexible sheet is bonded to the base lattice structure to cover the base openings and form a sealed base surface of the container.

As described above, the flexible sheet <NUM> may be heat-shrunk during moulding in a heat shrinking step whereby each portion of the heat-shrunk flexible sheet <NUM> is under tension in the moulded container. The heat shrinking step may be an intrinsic part of the moulding process, so that the heat shrinking occurs when the flexible sheet <NUM> is exposed to elevated temperatures during moulding. Alternatively, an additional heat shrinking step may be added after the moulded container has been removed from the mould or the mould has been at least partly opened.

As described above for the third embodiment, the container may additionally comprise a lid, and the lid may be affixed to the remainder of the container, comprise the sidewall and base, by an extending part of the flexible sheet.

In order to make such a lid, as shown in <FIG>, in a further modification of the method of the present invention, the mould further comprises third and fourth cavity-forming surfaces <NUM>, <NUM> defining a lid-forming cavity <NUM> for forming a lid of the container. The in-mould flexible sheet <NUM> extends into the lid-forming cavity <NUM>. The molten plastic composition is injected into the lid-forming cavity <NUM> by a dedicated gate (not shown) to form a lid <NUM> composed of the thermoplastic polymer. The lid <NUM> is hingedly connected to the sidewall <NUM> by the flexible sheet <NUM>.

As described above, wherein the integral extension part forms a hinge for the lid and/or a tamper evident connection between the lid and the sidewall.

Referring to <FIG>, as described above, the sidewall <NUM> and optionally the base <NUM> comprises foam ribs <NUM>, <NUM> having a solid skin/foam core/solid skin structure. The foam ribs <NUM>, <NUM> are bonded to the flexible sheet <NUM> to close the openings in the lattice structure. The upper and lower annular peripheral edges <NUM>, <NUM> of the sidewall <NUM> may also be comprised of a solid skin/foam core/solid skin structure when foam ribs <NUM> are provided in the sidewall <NUM>. The annular peripheral edge <NUM> of the base <NUM> may also be comprised of a solid skin/foam core/solid skin structure when foam ribs <NUM> are provided in the base <NUM>. The foam ribs <NUM>, <NUM> may intersect at foam junctions located within the sidewall <NUM> or the base <NUM>.

In order to produce such a foam core in a lattice structure in the sidewall and/or base, the molten plastic composition further comprises a physical blowing agent which is a gas dissolved in the thermoplastic polymer. During or after the injecting step, in which the molten plastic composition is injected at an injection pressure, as shown in <FIG> the injected plastic composition in contact with the first and second cavity-forming surfaces <NUM>, <NUM> is cooled to form first and second solid skins <NUM>, <NUM> respectively adjacent to and in contact with the first and second cavity-forming surfaces <NUM>, <NUM>. In the lattice-forming part <NUM> at least some of the plastic composition between the first and second solid skins <NUM>, <NUM> remains molten to form a molten core <NUM>. Therefore, the lattice-forming part <NUM> comprises opposed first and second solid skins <NUM>, <NUM> on opposite sides of a central core <NUM> of the molten plastic composition.

After the injecting step and before the final cooling step, the method further comprises a mould opening step as shown in <FIG> which is carried out before the molten plastic composition in the core <NUM> between the first and second solid skins <NUM>, <NUM> has solidified in the lattice-forming part <NUM>. The first mould part <NUM> is moved as shown by the arrow in <FIG>. The mould opening step exposes the molten plastic composition of the lattice-forming part <NUM> to an external pressure lower than the injection pressure, for example atmospheric pressure. This pressure differential allows the molten plastic composition between the first and second solid skins of the lattice-forming part <NUM> to expand by foaming to form an expanded cellular foam <NUM> as a result of the molten plastic composition beneath the first solid skin <NUM> expanding away from the second solid skin <NUM>. The expansion occurs because the blowing agent comes out of solution in the molten plastic composition at the reduced pressure and forms gas bubbles.

In the preferred embodiment, the mould opening step comprises removing the first mould part <NUM>, which is preferably the outer mould part, so that the first solid skin is no longer in contact with the first cavity-forming surface <NUM>. This causes the outer first solid skin to expand outwardly. However, the opposite configuration may be employed, and the second mould part <NUM>, which is preferably the inner mould part, is removed so that the second solid skin is no longer in contact with the second cavity-forming surface <NUM> to cause the inner second solid skin to expand inwardly.

In the final cooling step, the expanded cellular foam is cooled to cause the molten plastic composition between the first and second solid skins <NUM>, <NUM> of the lattice-forming part <NUM> to solidify and to form in the sidewall of the container the lattice structure <NUM> in which the elongate ribs <NUM> comprise opposed upper and lower unfoamed solid skins <NUM>, <NUM> of the thermoplastic polymer on opposite sides of a central cellular foam core <NUM> of the thermoplastic polymer, with the ribs <NUM> are bonded to the flexible sheet <NUM>. Correspondingly, a lattice structure of foam ribs can be formed in the base and/or lid of the container.

Preferably, in each elongate rib <NUM> the first solid skin is expanded to form a convexly curved surface <NUM>. The convexly curved surface <NUM> may be continuously convexly curved between opposite elongate longitudinal edges <NUM>, <NUM> of the elongate rib <NUM>.

Blowing agents which can be used in the embodiments of the present invention include physical blowing agents in the form of a gas dissolved in the molten plastic composition. Such a gas may comprise, for example, carbon dioxide. The gas may optionally further include a perfume composition (i.e. a scent) which remains present in the polymer material after expansion, to enhance the consumer experience.

When using carbon dioxide as the blowing agent, CO<NUM> gas is produced by the blowing agent in the extruder of the injection moulding machine, and the CO<NUM> gas then goes into solution during the injection phase (typically from <NUM> to <NUM> bar within the mould cavity) due to the relatively high pressure exerted on the material being greater than the pressure required (typically greater than <NUM> bar) to force CO<NUM> into solution within molten thermoplastic resin, such as polypropylene.

The molten plastic composition is injected at an injection pressure Pinjection. Typically, the injection pressure Pinjection is at least <NUM> bar. At the end of the injecting step, optionally a packing pressure, Ppacking, is applied to the cavity. Typically, packing pressure Ppacking is at least <NUM> bar.

During the injecting step, and any packing, the injection pressure Pinjection, and any packing pressure Ppacking, respectively, are above a minimum pressure threshold, Pthreshold, in the regions of the cavity to form unfoamed parts of the container. Typically, the minimum pressure threshold Pthreshold is <NUM> bar. This prevents the physical blowing agent from coming partly out of solution in the polymer so that cellular gas bubbles are not formed in those regions during the injecting step, and any packing step.

As described above, the base, sidewall and lid of the container are composed of thermoplastic polymer which is preferably injection moulded. The base, sidewall and lid may comprise respective lattice structures which are covered by the flexible sheet which is bonded thereto. The flexible sheet not only seals the lattice structures, and can function as a printed and/or embossed label, and can connect the lid to the remainder of the container and function as a hinge and/or tamper evident device, but also the flexible sheet can enhance the structural strength and integrity of the container.

Typically, any regions of the injection moulded thermoplastic polymer which are composed of a solid, unfoamed, layer of the thermoplastic polymer have a thickness of from <NUM> to <NUM>, optionally from <NUM> to <NUM>. Such solid, unfoamed regions of the thermoplastic polymer typically appear transparent to the naked eye. Even if a blowing agent is present which has been used to form foamed regions, the blowing agent, in the preferred embodiment CO<NUM> gas, can be under sufficient mould pressure to remain in solution in the polymer, in the preferred embodiment polypropylene, during manufacture of the container until the polymer has solidified throughout its thickness. After the molten polymer has solidified, it is not possible for cells to form as a result of any action of the blowing agent.

In contrast, typically any regions of expanded foam in the injection moulded thermoplastic polymer typically appear translucent to the naked eye because the expanded cellular foam includes cells that have cellular walls that reflect visible light. However, if a pigment is incorporated into the thermoplastic polymer at a high concentration, the expanded foam regions may typically appear opaque, with a solid colour. In contrast, the unexpanded regions have no cells, or if any cells are present, for example at a low concentration, they have a cell size of typically less than <NUM> microns and therefore are not visible to the naked eye, and consequently the unexpanded regions appear transparent to the naked eye.

In the lattice forming part, prior to opening the mould to cause expansion of the central molten polymer layer between the opposite solid skins, the rib-forming parts typically have a thickness of from <NUM> to <NUM>, optionally from <NUM> to <NUM>. In the final moulded container, the expanded foam ribs typically have a thickness of from <NUM> to <NUM>, optionally from <NUM> to <NUM>. Typically, rib-forming parts have increased in thickness by from <NUM> to <NUM> to form the expanded foam ribs.

In some embodiments of the present invention, the mechanical properties and dimensions of the in-mould flexible sheet can be selected to control the stretch ratio of any expanded foam regions in the container to which the in-mould flexible sheet is bonded. In this way, the in-mould flexible sheet can function to control the shape, dimensions and properties of the resultant container.

The present invention provides a container having a lattice structure in the sidewall, and optionally in the base and/or lid. The lattice structure defines openings which are sealed by the flexible sheet which is bonded to the sidewall, and optionally the base and/or lid. Typically, the surface area of a surface of the lattice structure is less than <NUM>% of the surface area of the associated wall, base or lid in which the lattice structure is provided. The provision of openings between ribs reduces the weight of, and thermoplastic material in, the container. However, the combination of the ribs and the flexible sheet bonded thereto provides a high strength structure for the container sidewalls, and optionally also for the base and/or lid. The container can be manufactured using an injection moulding apparatus having an in-mould labelling (IML) capability.

The configuration of the base and sidewall, in particular with respect to the injection moulding sprue in the base, enables containers of a wide variety of shapes and dimensions to be manufactured reliably using an injection moulding method and apparatus. The provision of the lattice structure(s) comprising elongate ribs enables rapid, controlled and reliable molten material flow from the sprue throughout the injection moulding cavity. Weak points of convergence can readily be avoided by the provision of the elongate ribs, and by selecting the rib dimensions and rib spacing, which enhance uniform material flow from the base, up the sidewall and to the rim. The reduced surface area of the lattice structure as compared to a continuous solid wall enables the clamp pressure of the injection moulding apparatus to be reduced.

In the method of the invention, the flexible sheet is bonded to the injection moulded container body, and optionally the lid, using an in-mould labelling (IML) technique, so that the bond between the flexible sheet and the injection moulded container is achieved by fusing the solidified thermoplastic polymer to the surface of the flexible sheet. However, the container of the invention can alternatively be manufactured by another method, in which the injection moulded container body, and optionally the lid, are formed independently of the flexible sheet, i.e. without using an in-mould labelling (IML) technique, to produce a bare skeleton of the injection moulded container body, and optionally separately the lid. Thereafter, the flexible sheet can be bonded to the injection moulded container, and optionally the lid, by bonding the separate flexible sheet to the surface of the injection moulded container body, and optionally the lid, to form any of the container structures of the various embodiments described hereinbefore. In this modification of the manufacturing method, the flexible sheet can be bonded to the injection moulded container body, and optionally the lid, by an adhesive layer. For example, the flexible sheet can be self-adhesive, with an inner surface of the flexible sheet being coated with a pressure-sensitive, hot melt or thermally activated adhesive. Typically, the adhesive would be provided in a pattern which corresponded to the lattice pattern and other surface patterns in the container body and lid to which the flexible sheet is to be adhered.

In the preferred embodiments of the present invention, the container may be designed or configured to package foodstuffs, but the container may be used for any purpose. The container may have heat resistance and may be suitable for warming foodstuff in an oven or microwave oven. The container may be disposable or reusable, and in either case is recyclable since the container is preferably composed of a single polymer, for example polypropylene.

Claim 1:
A container (<NUM>) comprising an annular sidewall (<NUM>) which comprises upper and lower annular peripheral edges (<NUM>, <NUM>) and a lattice structure (<NUM>) of elongate ribs (<NUM>) interconnecting the upper and lower annular peripheral edges (<NUM>, <NUM>), wherein the lattice structure (<NUM>) is an open framework (<NUM>) defining a plurality of sidewall openings (<NUM>), and a base (<NUM>) which comprises an annular peripheral edge (<NUM>) which is integral with the lower annular peripheral edge (<NUM>) of the sidewall (<NUM>), the annular peripheral edge (<NUM>) of the base (<NUM>) surrounding a base wall structure (<NUM>) which is integral therewith, wherein the sidewall (<NUM>) and the base (<NUM>) are composed of a thermoplastic polymer and define a central concavity (<NUM>) for packaging a product, and wherein the container (<NUM>) further comprises a flexible sheet (<NUM>) which is bonded to the lattice structure (<NUM>) to cover the sidewall openings (<NUM>) and form a sealed sidewall surface (<NUM>) of the container (<NUM>), characterised in that the base wall structure (<NUM>) comprises at least one injection moulding sprue (<NUM>) at a central region (<NUM>) of the base wall structure (<NUM>), wherein the at least one injection moulding sprue (<NUM>) is connected to the upper annular peripheral edge (<NUM>) of the annular sidewall (<NUM>) by the base wall structure (<NUM>), the annular peripheral edge (<NUM>) of the base (<NUM>), the lower annular peripheral edge (<NUM>) of the sidewall (<NUM>) and the lattice structure (<NUM>) of the sidewall (<NUM>), and in the lattice structure (<NUM>) in the sidewall (<NUM>) at least some of the elongate ribs (<NUM>) comprise elongate foam ribs (<NUM>), wherein each foam rib (<NUM>) comprises opposed outer and inner unfoamed solid skins (<NUM>, <NUM>) of the thermoplastic polymer on opposite sides of a central cellular foam core (<NUM>) of the thermoplastic polymer.