TECHNICAL FIELD

The invention relates to a stackable carton lid. In particular the invention relates to improved stacking properties of such a lid. The invention also relates to a device for a method of manufacturing a stackable carton lid.

STATE OF THE ART

Stackable carton lids, for example for food containers, are known from e.g. DE 4429057 and EP 639509. Such lids are made of a carton material and comprise i.a. a lid surface and a downward directed collar extending along the periphery of the lid surface and encircling and engaging with the container when the lid is put in place. The lid according to DE 442957 also comprises an upper collar extending along the periphery of the lid mirror on the top side of the lid surface.

Stacking of lids according to EP 639509 is possible in that the lower collar is angled outwards so that the inner side of the collar on an upper lid can abut against the, at the outer side folded/bent, lid surface of a lower lid, whereby the upper lid overlaps the lower lid at stacking. The lids according to DE

4429057 are also provided with an outward directed lower collar which allows overlap of stacked lids. In this case, at stacking the inner side of the lower collar on the upper lid abuts against the outer side of the upper collar on the lower lid. In certain variants the overlap is longer so that the inner side of the lower collar also abuts against parts of the outer side of the lower collar of the lower lid.

The stacking properties of the lids according to DE 4429057 are stated to be good, both as regards stability and possibility of removing one lid at a time from the stack without underlying lids tagging along. However, it has turned out that nevertheless these lids tend i.a. to stick to each other at stacking, which causes problems in automated industrial handling where the lids are to be attached onto filled containers. Thus, there is a need for further improving the stacking properties of carton lids.

In this connection it is remarked that it is considerably more difficult to give carton lids a suitable design for stacking than plastic lids since carton lids are formed by assembling and shaping one or more flat carton parts, whereas, by casting, plastic lids can be given, in principle, any shape at all. Furthermore, plastic lids can subsequently be thermo-shaped plastically to a considerably higher degree than carton lids since a carton material tends to crack in case of too strong deformation.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a stackable carton lid having improved stacking properties as compared with existing lids of such type. This object is obtained by a lid according to claim 1. The dependent claims constitute advantageous embodiments, developments and variants of the invention.

The invention relates to a stackable carton lid comprising: an essentially flat lid element intended for covering an opening in a container when the lid is attached onto the container, the said lid element having a top side and a bottom side, where the bottom side is intended for facing the container when the lid is attached; a lower collar extending along the outer edge of the lid element and at least partially downwards from the bottom side of the lid element in order to allow interaction with the container when the lid is attached; and an upper collar extending along the outer edge of the lid element on the top side of the lid element, the lid being arranged in such manner that the lower collar of a first lid overlaps at least part of the upper collar of a second lid when the first and the second lids are stacked on top of each other.

The invention is characterized in that the distance between the outer periphery of the upper collar and a hypothetical centre line through a centre point on the lid element is, at least over the stretch where the lower collar of the first lid overlaps at least a part of the upper collar of the second lid at stacking, essentially equal to or smaller than the distance between the inner periphery of the lower collar and the said centre line in an arbitrary position along the outer edge of the lid element, where the height of the upper collar above the top side of the lid element and the form and extent of the lower collar from the bottom side of the lid element are adapted in such manner that the lower collar is not appreciably pressed against a corresponding lower collar on an adjacent lid at stacking of a plurality of lids. This means that the upper collar of a lower lid can be fitted within the lower collar (skirt) of an upper lid without getting stuck. Furthermore, this means that the lower collar (skirt) of the upper lid goes free, in principle, of the lower collar (skirt) of the lower lid at stacking. In other words, the upper and lower collars of the lid are arranged in such manner that when placing a first lid on a second lid, where the bottom side of the lid element (lid surface) of the first lid faces the top side of the lid element (lid surface) of the second lid, the bottom side of the lid surface of the first upper lid gets into such position that the said bottom side abuts against the upper collar of the second lower lid. Thus essential contact between stacked lids takes place only between the bottom side of an upper lid and the upper side of the upper rim of the lower lid. Thereby it is avoided that the lower collar of the first upper lid gets stuck in the upper collar of the second lower lid when the upper lid is lifted away.

Furthermore, a stable stack of lids is formed since the weight rests on the upper side of the upper collar, and not on an angled lower collar, as e.g. in DE 4429057 where there is great risk that increased stack weight entails an increased tendency for the lids to get stuck in each other as well as risk that the stack keels over.

Furthermore, this means that the upper collar is sufficiently high and that the lower collar is adequately well-designed in order to avoid that the lower collars grip each other at stacking of lids, i.e. in order to avoid that the lower collar of an upper lid grips the lower collar of an underlying lid. This can be achieved by i) making the upper collar so high relatively to the lower collar that the lower collars do not at all overlap at stacking of lids; ii) designing the lower collar in such manner at to obtain a distance between the inner side of the lower collar of an upper lid and the outer side of the lower collar of a lower lid at stacking of lids; iii) designing the lower collar in such manner that the inner side of the lower collar of an upper lid abuts only very lightly against the outer side of the lower collar of a lower lid at stacking of lids, i.e. so lightly that the lower lid does not tag along when the top lid is lifted; and/or iv) giving at least a part of the lower collar a certain angle to the centre line/vertical line, said angle, together with the height of the upper collar, entailing that the lower collars of the lids never rest on each other or just so lightly that they do not get stuck even if they are partially overlapping each other. In a preferred embodiment of the invention, the lid is arranged in such manner that a lower part of the lower collar of a first lid overlaps an upper part of the lower collar of a second lid when the first lid is stacked on top of the second lid, the distance between the inner periphery of the said lower part of the lower collar of the first lid and the hypothetical centre line through the centre point being essentially equal to or greater than the distance between the outer periphery of the said upper part of the lower collar of the second lid and the said centre line.

Such a design entails that even when the lower collars overlap at stacking, the lids do not grip each other as the upper lid rests on the upper rim of the lower lid.

In a preferred embodiment of the invention, the lid is provided with a projection extending circumferentially outside the upper collar, where the outer edge of the projection passes into the lower collar. Thus, the upper collar is somewhat retracted in relation to the centre point of the lid surface as compared with the lower collar so that a distance is created between the respective bases of the upper and the lower collars. Hereby an improved passage is created between the lower collar of an upper lid and the upper collar of a lower lid at stacking of lids.

In a preferred embodiment of the invention, the lower collar is provided with a bulge extending circumferentially on the inner side of the lower collar, the said bulge being intended for interacting with an upper part in the container when the lid is attached onto the container.

In a preferred embodiment of the invention, the lid is composed of a first, flat unit and a second, annular unit, the first unit constituting the lid element and the second unit constituting at least a part of both the lower and the upper collars.

In a preferred embodiment of the invention, the first unit is provided with a folded up rim along its outer edge, an upper part of the second unit being formed around and against the said rim, and the upper collar being composed of the upper part of the second element and the said rim. In a preferred embodiment of the invention, the upper collar has, circumferentially, wave shape or folded shape. Thereby an increased amount of excess material can be handled.

In a preferred embodiment of the invention, the upper collar is essentially flat and extends essentially perpendicularly up from the top side of the lid element.

The invention also relates to a device for and a method of manufacturing a stackable carton lid of the above mentioned type.

DESCRIPTION OF FIGURES

In the following, the invention will be described in more detail with reference to the following figures, where:

Figure 1 shows a perspective view, obliquely from below, of a preferred embodiment of a carton lid according to the invention,

Figure 2 shows a view, from below, of the embodiment according to

Figure 1 ,

Figure 3 shows a section A-A, with enlargement, according to Figure 2, Figure 4 shows a section B-B, with enlargement, according to Figure 2, and

Figure 5 shows a number of carton lids according to Figure 1 , stacked on top of each other.

PREFERRED EMBODIMENTS

Figure 1 shows a perspective view, obliquely from below, of a preferred embodiment of a stackable carton lid 1 according to the invention. The lid 1 comprises an essentially plane lid element 2 intended for covering an opening in a container (not shown) when the lid 1 is attached onto the container. The lid element 2 has a top side 2a and a bottom side 2b, where the bottom side is intended for facing the container when attaching the lid 1. A point C indicates a centre point on the lid element 2.

The lid 1 also comprises a lower collar 3 (skirt) extending along the outer edge of the lid element 2 and essentially downwards from the bottom side 2b of the lid element 2 in order to allow interaction with the container when the lid 1 is attached. The lid 1 is also provided with an upper collar 4 extending along the outer edge of the lid element 2 on the top side 2a of the lid element 2. Circumferentially, the upper collar 4 has undulated shape, i.e. waves or folds 5 are provided in the upper collar 4 in a direction essentially perpendicularly to the top side 2a of the lid element.

Figure 2 shows a view, from below, of the embodiment according to Figure 1 , Figure 3 shows a section A-A, with enlargement, according to Figure 2; and Figure 4 shows a section B-B, with enlargement, according to Figure 2. As apparent above all from the enlargement in Figure 4, the lid 1 is composed of a first, flat unit and a second annular unit, the first unit constituting the lid element (lid surface) 2, and the second unit constituting the lower collar 3 and a part of the upper collar 4. The first unit is provided with a folded up rim 6 along its outer edge, where an upper part 40 of the second unit is formed around and against the said rim 6. Thus, the upper collar 4 is composed of the upper part 40 of the second unit and the said rim 6.

The upper part 40 of the second unit is glued to the rim 6, and the upper collar 4 thus formed is pressed flat by wave shaped (undulated) tools, which gives rise to the waves/folds 5. In this flattening moment, the upper collar 4 is passed inwards towards the centre point C so that a projection 9 is formed. The projection 9 extends circumferentially outside the upper collar 4, the outer edge of the projection 9 passing into the lower collar 3. Thus, this projection 9 defines a distance between the base of the upper collar 4 and the base of the lower collar 3. Thereby it is avoided that the lower collar 3 of an upper lid sticks on/to the corresponding collar 3 on a lower lid at stacking, without it being necessary to give the lower collar 3 a too extreme shape, which could entail formation of cracks.

Because of the undulated shape (waves/folds 5), more excess material can be taken up in the upper collar 4, which is thereby, as a matter of course, moved inwards in the corners of the lid 1 and becomes more rigid and more form stable also on the straight sides of the lid 1. The tools for the flattening moment may be heated to about 160-250 °C in order to make the carton material more formable and to make it stay re-formed when it cools. The flattening entails that the upper collar 4 gets an essentially flat shape and that it extends essentially perpendicularly up from the top side 2a of the lid element 2.

The lower collar 3 is provided with a bulge 7 extending circumferentially on the inner side of the lower collar 3 (and a corresponding concaveness 8 on the outer side of the lower collar 3). The bulge 7 is intended for interacting with an upper part in the container, for example a lip, in order to retain the lid 1 in position when the lid is attached onto the container.

Figure 2 shows i.a. that a lower part 30 of the lower collar 3 (see Figure 4) exhibits a larger angle outwards from the lid 1 at the sides of the lid than at the rounded corners of the lid.

Figure 5 shows a number of carton lids 1a-1d according to Figure 1 , stacked on top of each other. The lids 1a-1d are provided i.a. with corresponding lower and upper collars 3a-3d, 4a-4d. Furthermore, there is shown a lid element 2d for lid 1d. As is seen from Figure 5, each lid 1a-1d, according to the preferred embodiment, is arranged in such manner that the lower collar 3b of a first lid 1 b completely overlaps the upper collar 4c of a second lid 1c, seen in the height direction of the stack, when the first and the second lids 1 b, 1 c are stacked on top of each other.

As is apparent from Figure 5 together with e.g. Figure 4, the distance between the outer periphery of the upper collar 4, i.e. the outer side of the upper collar 4, and a hypothetical centre line through the centre point C on the lid element 2 is smaller, at least over the stretch where the lower collar 3b of the first lid 1 b overlaps the upper collar 4c of the second lid 1c at stacking, than the distance between the inner periphery of the lower collar 3, i.e. the inner side of the bulge 7 in the preferred embodiment (for example bulge 7b on lid 3b) and the said centre line in an arbitrary position along the outer edge of the lid element. In other words, the upper collar 4c of a lower lid 1c can be accommodated within the lower collar 3b (skirt) of an upper lid 1 b without getting stuck. This can be achieved also if the lower collar 3 has a different shape so that the inner periphery of the lower collar 3 within the overlapping stretch does not coincide with the inner side of the bulge 7. The hypothetical centre line passes through the centre point C and has a direction perpendicularly to the lid element 2. The distances compared above thus correspond to hypothetical radial stretches, being parallel to the lid element 2, between the hypothetical centre line and the outer periphery of the upper collar and the inner periphery of the lower collar, respectively. In

Figure 5, these hypothetical stretches are horizontal while the hypothetical centre line is vertical. Thus, the distance referred to is the radial distance.

Furthermore it is seen from Figure 5 that the height of the upper collar 4 above the top side 2a of the lid element 2 and the shape and extent of the lower collar 3, i.e. for example length and angle, from the bottom side 2b of the lid element 2 are adjusted in such manner that the lower collar, e.g. 3b, is not appreciably pressed against a corresponding lower collar, for example 3c, on an adjacent lid at stacking of a plurality of lids. This can be expressed such that the lid 1 is arranged in such manner that a lower part of the lower collar 3b of a first lid 1 b overlaps an upper part of the lower collar 3c of a second lid 1c when the first and the second lids 1b, 1c are stacked on top of each other, where the distance between the inner periphery of the said lower part of the lower collar 3b of the first lid 1 b and the hypothetical centre line through the centre point C are essentially equal to or greater than the distance between the outer periphery of the said upper part of the lower collar of the second lid 1c and the said centre line. This applies in an arbitrary position in the overlap area formed where the said lower part of the lower collar 3b of the first lid 1 b overlaps an upper part of the lower collar 3c of the second lid 1c.

According to Figure 5, a small distance arises between the lower collars, for example between 3b and 3c, at stacking. In the corners of the lid 1 , where the lower collar has a smaller angle from the lid 1 , the collars 3b and 3c may abut lightly against each other, but without gripping each other so that removal of a lid from another in a stack is impeded.

The first and the second units constituting the lid 1 , i.e. the lid surface 2 and the annular unit constituting the two collars 3, 4, are both made of a carton material. Suitable carton materials in this connection are well-known to the skilled person. As an example it can be mentioned that the lid surface 2 can be made of Stora Ensos Cupforma Special 270 g/m ² with 13 g/m ² PE and that the annular unit can be made of spirally wound carton in three layers of Stora Ensos Cupforma Classic 230 g/m ² with a cover layer of paper MG 60 g/m ² .

It is remarked that the combination of having a relatively high upper collar 4 and that this collar 4 is retracted in relation to the centre point C of the lid element 2 makes possible very good stacking properties where problems with lids rubbing against each other and getting stuck are avoided.

A suitable machine for manufacturing a lid according to the invention in a carton material comprises heated squeeze or form trays adapted for folding and shaping the carton material to a lid with the shape described above. Hence, the form trays have a shape corresponding to the shape of the lid. It is possible to use unheated form trays, but the carton material becomes more formable and retains its new shape in a better way if the form trays are heated.

A suitable method of manufacturing a lid according to the invention in a carton material thus comprises the step of folding and shaping a carton material by using form trays, preferably heated, whereby the form trays have a shape corresponding to the shape of the lid.

The invention is not limited to the embodiment described above, but can be varied within what is defined by the appended claims. For example, it is not necessary that the lid 1 is essentially rectangular, or that the corners of the lid 1 are rounded in the way shown. Other conceivable shapes of the lid are annular, oval, or essentially square with more or less rounded corners.

Nor is it necessary to arrange a rim 6 in the periphery of the lid surface 2. The surface can be attached in a different manner, for example with its edge against the annular unit.

As regards the container onto which the lid is intended to be attached, this container may be contemplated for foodstuffs, but many other types of contents are also possible. Furthermore, the container may be made of a material different from that of the lid 1 , for example plastic. The distance between the outer periphery of the upper collar and the hypothetical centre line can, at least over the stretch where the lower collar of the first lid overlaps at least part of the upper collar of the second lid at stacking, be essentially equal to, and not necessarily smaller than, the distance between the inner periphery of the lower collar and the centre line. That the distance can be essentially equal to means that the distance can be the same and even that the distance between the outer periphery of the upper collar and the hypothetical centre line can be a bit longer than the distance between the inner periphery of the lower collar and the centre line. A skilled person knows that the lower collar on carton lids of the type described here is somewhat resilient, which means that the principle of the invention works even in these cases, i.e. when a lid is placed altogether loosely on another lid, the upper lid can stay in such position that a vertical gap is formed between the lid surface of the upper lid and the upper collar of the lower lid. Because of the resilient properties of the lower collar, this gap disappears, however, at a light pressure on the upper lid, for example when additional lids are placed on the stack so that the lid surface of the upper lid rests on the upper collar of the lower lid. Even when the gap is removed in this way can the lids be removed seamlessly from the stack one by one as the upper collar on underlying lids prevents the lids from getting too close and getting stuck firmly in each other.

Hence, it is possible, for example in order to save material, to allow a small (initial) gap between the upper collar and the overlying lid surface, which gap closes when load is applied as the lower collars flex and the lids thus engage with each other, which movement is stopped in that the lid surfaces land, at a comfortable level, on the upper collar of underlying lids without the forces between the lower collars increasing so much as to cause problems at separation. Hereby the lower collar can also stand on the projection as there is a gap between the upper collar and the next lid surface, which, when load is applied, closes so that the upper lid rests against the upper collar of the lower lid, and the resilience of the lower collar when it slides over the projection causes no locking effect impeding separation.