TECHNICAL FIELD

The present invention refers to a container of the type having a cup body with an opening and a lid sealing the opening by a double seam.

BACKGROUND OF THE INVENTION

Containers such as cans are well known and widely used to contain materials such as retort food and chemicals. Taking retort food as an example, the food is normally canned in steel cans that are seamed up with lids by a double seam. The double seam is formed by mechanically interlocking five layers of material together: three layers of the lid and two layers of the cup body.

After seaming, the five layers are normally parallel with one another so as to have an increased overlap area and thus higher tightness.

US 4,526,290 discloses a container comprising a plastic body and a metal closure. The body has a flange that can be interfolded with a closure to form an interlocking double seam. The flange extends outwardly from a thin peripheral portion adjacent the open end of the body to a thicker terminal wedge-shaped portion. When bending and forming the double seam, the material of the thicker portion of the flange is displaced by compression into unfilled areas of the seam. This causes the formation of a continuous seal.

US 3,685,685 discloses a plastic-metal can with a double seam. The double-seam comprises at least two points where the plastic of the double seam is compressed to a thickness less than one-half of its original thickness before seaming.

However, with the conventional structure of the double seam, the cup body and the lid are easily broken or fractured during the seaming process in the case that the cup body and lid are made of different materials. Even minute fractures within the double seam may cause leakage and adulteration of the product therein.

SUMMARY OF THE INVENTION

The present invention is intended to overcome at least one of the above defects in the prior arts.

According to one aspect the invention, a container is provided which comprises comprising a cup body with an opening and a lid sealed tightly over the opening of the cup body by a double seam, wherein, said cup body is made of plastic and has a bottom wall, a side wall, an edge which defines the opening, and a flange which is connected to the edge of the opening and extends outwards and downwards from the edge of the opening, said lid is provided with a panel, a lid wall extending upwards from the panel, a curl portion extending outwards and downwards from the lid wall, and a hook portion extending inwards and upwards from the curl portion, and the lid wall, the edge of the cup body, the hook portion of the lid, the flange of the cup body and the curl portion of the lid form the double seam; in the double seam, the hook portion is compressed between the edge and the flange, and the hook portion and the lid wall form an over-hook angle between 20° and 40°.

With the hook portion inclined relative to the chuck portion, the edge and the flange of the side wall are bent less than a conventional double seam, thus the side wall is less likely to be broken or fractured; furthermore, because the hook portion is not parallel to the lid wall, the hook portion can engage or bite both the edge and the flange of the side wall more effectively when it is compressed between them. With the above configuration, a relatively small compressive force may be applied when forming the double seam of the present invention, and the double seam can achieve at least the same tightness as that of the metal-and-metal seam and can meet the requirement of National standards.

Preferably, the cup body may be made of a thermoplastic polymer such as polypropylene, and the lid may be made of metal, for example, aluminum alloy.

Preferably, the over-hook angle formed by the hook portion and the lid wall may be about 25° to about 35°, more preferably about 23° to about 34°, and most preferably about 30°.

Preferably, the thickness of the side wall may be greater than that of the lid.

According to another aspect the invention, a method for manufacturing a container for containing a food product is also provided, which method comprises the following steps:

a) providing a cup body with an opening, wherein said cup body is made of plastic and has a bottom wall, a side wall, an edge which defines the opening, and an outwardly extending flange which is connected to the edge;

b) providing a lid to be sealed tightly over the opening of the cup body, wherein said lid is provided with a panel, a lid wall extending upwards from the panel, and a peripheral curl extending outwards from the lid wall;

c) applying the lid to the flange of cup body; and

d) forming a double seam between the flange of the cup body and the lid by means of a chuck and at least one roller,

wherein during the step d), the flange of the cup body is forced to bend downwards, and the peripheral curl of the lid is also forced to bend downwards to form a curl portion covering the flange of the cup body, with the distal portion of the peripheral curl further extending inwards and upwards from the curl portion, so as to form a hook portion which bites the flange of the cup body; and

wherein in the double seam, the hook portion is compressed between said edge and said flange, and the hook portion and the lid wall form an over-hook angle (Θ) between 20° and 40°.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the examples of the invention will become apparent with reference to the embodiments and drawings, in which:

Fig. la shows a can with a conventional metal-metal double seam;

Fig. lb shows a cross-sectional view of a detail of the conventional metal-metal double seam in Fig. la; and

Fig. 2a shows a container with a metal-plastic double seam according to the present invention; and

Fig. 2b illustratively shows a cross-sectional view of a detail of the double seam in Fig. 2a.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will be described below with reference to the embodiments, which are shown in the drawings. It will be appreciated that the invention as claimed is not intended to be limited in any way by these embodiments.

As used herein and in the appended claims, the singular form of a word includes the plural, and vice versa, unless the context clearly dictates otherwise. Thus, the references "a", "an", and "the" are generally inclusive of the plurals of the respective terms. For example, reference to "a container" includes a plurality of such "containers" . Similarly, the words "comprise", "comprises", and "comprising" are to be interpreted inclusively rather tha n exclusively. Likewise, the terms "include", "including" and "or" should all be construed to be inclusive, unless such a construction is clearly prohibited from the context. Where used herein the term "examples" particularly when followed by a listing of terms is merely exemplary and illustrative, and should not be deemed to be exclusive or comprehensive.

Fig. la shows a can with a conventional metal-metal double seam, a nd Fig. lb shows a cross- sectional view of a detail of the conventional metal-metal double seam in Fig. la . The can may comprise a side wall 5 and a lid 6 sealed together by the conventional double seam. I n order to form the double seam, the side wall 5 is configured to have an edge 51 and a flange 52; and the lid is provided with a lid wall 61 surrounding a panel 64, and also with curl portion 62 and hook portion 63. In the conventional double-seam structure, the above five layers are overlapped with each other and compressed together. In the compressed or tightened status, the hook portion, the edge and the lid wall are parallel with each other.

Referring to Fig. 2a, which shows a container with a metal-plastic double seam according to the present invention, and Fig. 2b which illustratively shows a cross-sectional view of a detail of the double seam in Fig. 2a, the container may comprises a cup body with an opening and a lid 2 sealed tightly over the opening of the cup body by a double seam. The cup body may be made of plastic, preferably a thermoplastic polymer (such as polypropylene) and has a bottom wall, a side wall 1, an edge 11 which defines the opening, and a flange 12 which is connected to the edge 11 of the opening and extends outwards and downwards from the edge 11 of the opening. The lid 2 may be provided with a panel 24, a lid wall 21 extending upwards from the panel 24, a curl portion 22 extending outwards and downwards from the lid wall 21, and a hook portion 23 extending inwards and upwards from the curl portion 22, and the lid wall 21, the edge 11 of the cup body, the hook portion 23 of the lid 2, the flange 12 of the cup body and the curl portion 22 of the lid 2 form the double seam; in the double seam, the hook portion 23 is compressed between the edge 11 and the flange 12, and the hook portion 23and the lid wall 21 form an over- hook angle Θ between 20° and 40°.

The lid at its central portion is provide with a panel (not shown) surrounding the panel, a lid wall 21 is formed which is nearly perpendicular to the panel in a cross-sectional view. For the engagement of the edge 11 and the flange 12 of the side wall, a curl portion 22 is formed which extends outwards and downwards from the lid wall 21, and a hook portion 23 is also formed which extends inwards and upwards from the lid wall. The double seam is formed by the lid wall, the edge, the hook portion, the flange and the curl portion from the inside to the outside. However, in this embodiment, the hook portion is not parallel to the lid wall, but forms with the lid wall an over- hook angle Θ between, for example, about 20° to about 40°.

The term "over-hook angle" according to the present invention means the angle which is formed by a hook portion and a lid wall of a double seam between an end unit (a lid) and a cup body of a container, and is measured in a normal plane of the lid passing through the geometric center of the lid. That means, if the lid is of a circular shape, the "over-hook angle" is measured in a normal plane (a vertical section) of the lid passing through the circle center of the lid. In accordance with the present invention, the over-hook angle Θ is between about 20° and about 40°, preferably between about 25° and about 35°, more preferably between about 23° and about 34°, and most preferably about 30°.

Comparing with Fig. lb, it can be seen from Fig. 2b that by virtue of the hook portion 23 inclined relative to the chuck portion 21, the edge 11 and the flange 12 of the side wall are bent less than a conventional double seam, which ca uses the side wall less likely to be broken or fractured. It also can be seen from Fig. 2b that the hook portion is biting the edge 11, with the end edge of the hook portion 23 embedded in the edge, thus the engagement between the hook portion and the edge is effectively improved. With above configuration, even a less compressive force is applied on the layers of the double seam, high tightness of the double seam ca n be achieved.

The aforementioned structure is especially suitable for a can which comprises a plastic cup body and a metal lid, wherein the hook portion of the metal lid ca n easily bite or engage the edge of the plastic cup body.

For instance, the cup body may be made of polypropylene and the lid may be made of aluminum alloy. A series of tests have been carried out to verify the tightness of the double seams with different angles of over-hook Θ between the hook portion and the lid wall. The test results show that when the over-hook angle Θ ranges from about 20° to about 40°, the double seam meets the tightness requirement, i.e., at 180 kPa ^χ 1 minute and at ambient temperature, no air bubble occurs when the seamed container is immersed in a water tank.

Additional tests have also been undertaken by immersing PP (polypropylene) cups into boiling water (100°C) after an hour and then immediately applying tightness test at 180 kPa over longer periods up to 5 minutes. The results also show that when the over-hook angle Θ is between about 23° and about 34°, the overall mechanical resistance to the double-seaming treatment and the tightness of the double seam are highly improved.

The container according to the present invention may be manufactured by a method comprising the following steps:

a) providing a cup body with a n opening, wherein said cup body is made of plastic and has a bottom wall, a side wall 1, an edge 11 which defines the opening, and an outwardly extending flange 12 which is connected to the edge 11;

b) providing a lid 2 to be sealed tightly over the opening of the cup body, wherein said lid 2 is provided with a panel 24, a lid wall 21 extending upwards from the panel 24, and a peripheral curl extending outwards from the lid wall 21;

c) applying the lid 2 to the flange 12 of cup body; and d) forming a double seam between the flange 12 of the cup body and the lid 2 by means of a chuck and at least one roller.

During the step d), the flange 12 of the cup body may be forced to bend downwards, and the peripheral curl of the lid 2 may be also forced to bend downwards to form a curl portion 22 covering the flange 12 of the cup body, with the distal portion of the peripheral curl further extending inwards and upwards from the curl portion 22, so as to form a hook portion 23 which bites the flange 12 of the cup body. In the double seam, the hook portion 23 is compressed between said edge 11 and said flange 12, and the hook portion 23 and the lid wall 21 form an over-hook angle Θ between 20° and 40°.

A step of dosing the food product into the cup body may be performed between the above steps b) and c).

EXAMPLES

Comparative data with different angles of over-hook Θ of some examples of containers according to the present application is provided in Table 1. The cups are commercially available from, for example, Jiangsu Rotam Boxmore (JRB) Packaging Co., Ltd.

Table 1: Measurements for Double-seaming profiles for the examples of PP cups seamed with aluminum lids according to the present invention

Notes: I n Table 1: "OL1" refers to the overlap portion of hook portion and flange (see Fig. 2b); "HS1" refers to the hook spacing of the double seam (see Fig. 2b); and the "Overlapping" is a ratio of the overlap of hook portion and flange to the hook spacing.

I n Table 1, the value of the over-hook a ngle Θ ranges from 22.74 2 to 34.44, a nd the value of the double seam thickness Tl ranges from 1.88 mm to 2.06 mm.

The tightness results for 3-piece steel cans and PP cups with Aluminum 209 EOE (0 63 mm Easy-Open End) at ambient temperature is shown Table 2. Table 2: Tightness results for 3-piece steel cans and PP cups with Aluminum 209 EOE at ambient temperature

SST (Secure Seal Test, a type of pressure application test) has been performed with a n example of the container according to the present application, which consists of a 250 ml multilayer PP (polypropylene) cup and a lid of aluminum alloy, and the results in the following Table 3 and Table 4 show that the SST performance of the container examples is as good as that of metal cans. Table 3: SST performance test - tightness results with Aluminum 209 EOE

Although the invention has been described by way of example, it should be appreciated that variations and modifications may be made without departing from the scope of the invention as defined in the claims. Furthermore, where known equivalents exist to specific features, such equivalents are incorporated as if specifically referred in this specification. List of reference numbers

1. 5 side wall

11. 51 edge

12. 52 flange

2. 6 lid

21, 61 lid wall

22, 62 curl portion

23, 63 hook portion

24, 64 panel

Θ over-hook angle

Tl seam thickness

HS1 hook spacing

OL1 overlap portion of hook portion and flange