A BEVERAGE CAN BE EXTRACTED USING HOT WATER FIELD OF THE INVENTION

THIS INVENTION relates to capsules for containing coffee or another substance from which a beverage can be extracted using hot water. BACKGROUND TO THE INVENTION

Capsules containing coffee are widely used with "Nespresso" coffee extraction machines. "Nespresso" is the registered trade mark of Nestle. The capsules have a frustoconical body which has a transverse base at the smaller diameter end and an open mouth at the larger diameter end. After the capsule is filled, it is closed by a foil which is bonded to a flange which encircles the mouth of the capsule. The extraction machine includes a sleeve the free end of which, as the machine is closed for the purposes of extraction, presses on the face of the flange opposite that to which the foil is secured. Pins inside the sleeve penetrate the base of the capsule as the machine closes. Hot water is forced into the sleeve and this flows into the capsule between the outer surfaces of the pins and the edges of the holes that the pins have made.

The foil is pressed against a grid. When sufficient pressure has been created in the capsule, the foil bursts and a plurality of minute holes are formed in it through which the extracted beverage flows.

Another form of capsule is shorter than the capsule described above. This capsule is too short for the pins to reach it. Its base is in the form of a fine mesh through which the hot water in the sleeve enters the capsule.

In both forms of capsule it is essential that water not be able to leak between the flange of the capsule and the end of the pressing sleeve which is forced against the flange. Many forms of sealing structures have been proposed for the purpose of ensuring that there is a seal between the flange and the pressing sleeve which provides sufficient assurance that leakage will not take place. In practice there is some leakage but provided this is restricted to, say, less than 3 or 4 ml, it is acceptable. If excessive leakage does take place the requisite pressure to puncture the foil is not achieved. In this event a "short shot" may be delivered or water may be delivered to the cup before any coffee is delivered resulting in a weak beverage or no coffee at all may be delivered.

The present invention provides a sealing structure for a capsule which provides reliable sealing without the necessity of complex arrangements of ribs on the surface of the flange which faces the pressing sleeve.

BRIEF DESCRIPTION OF THE INVENTION According to the present invention there is provided a capsule for use in an extraction machine, the capsule having a frusto-conical side wall, a transverse base closing the smaller end of the capsule, an open mouth at the end of the capsule remote from the base and a peripheral flange encircling the open mouth of the capsule, characterised in that the side wall of the capsule is thickest over that section thereof which is closest to the flange, there being a single circumferentially extending sealing rib protruding from said flange in the direction towards the smaller end of the capsule and a circumferentially extending channel between said rib and said section. In one form the outer surface of the capsule's wall has a first step in it at which the conical angle increases and a second step spaced axially towards the flange from the first step at which the conical angle decreases thereby to form a shoulder between said steps which has a circumferentially extending skew surface. In this form the outer surface of the capsule is cylindrical between the skew surface and the flange. Further, in this form, there can be a circumferentially extending sealing rib protruding from said flange in the direction towards the smaller end of the capsule, the rib being of triangular cross section with its base integral with the flange and having an apex which, in use, is crushed by the leading end of the pressing sleeve. In a further form the conical angle of the outer surface of the side wall, over said section, is greater than the conical angle of the inner surface of said side wall over said section whereby said inner and outer surfaces diverge in the direction towards the flange and the wall thickness increases in the direction towards the flange. In this further form there can be a circumferentially extending sealing rib protruding from said flange in the direction towards the smaller end of the capsule, there being a circumferentially extending generally U-shaped channel between said rib and said section for receiving the leading end of the pressing sleeve. BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:- Figure 1 is a axial section through a capsule in accordance with the present invention;

Figure 2 is a radial section showing the relationship between the pressing sleeve of an extraction machine and the sealing structure of a capsule before the sleeve reaches the end of its travel towards the flange;

Figure 3 is a radial section showing the relationship between the pressing sleeve and the sealing structure when the sleeve is at the end of its travel; Figure 4 is a section showing the pressing sleeve of a coffee extraction machine and a further form of capsule before the sleeve reaches the end of its travel; and

Figure 5 is a section to a large scale illustrating the sealing zones which are created between the capsule and the pressing sleeve.

DETAILED DESCRIPTION OF THE DRAWINGS

The capsule shown in Figure 1 is designated 10 and includes a frusto-conical body 12, a transverse base 14 at the smaller end of the body 12 and a flange 16 at the wider, open end of the body 12. Long internal strengthening ribs 18 and short internal strengthening ribs 20 are provided in the angle between the body 12 and the base 14.

The flange 16, see particularly Figures 2 and 3, has a planar annular surface 22 which faces away from the smaller end of the body 12. The opposite surface of the flange 16 is designated 24. A bead 26 extends around the periphery of the flange 16 and protrudes above the surface 24 when the capsule is orientated as shown, that is, with its wide end lowermost. The bead 26 is provided for strengthening purposes and inhibits flexing of the thin flange 16. A sealing rib 28 is provided which protrudes above the surface 24 when the capsule is orientated as shown.

The rib 28 has a radially outer flat flank 30. Between the flank 30 and the radially inner flank 32 of the bead 26 there is a circular channel 34 which extends around the body 12. If the pressing sleeve is of the type which includes a sealing ring, this enters the channel 34 during extraction.

The radially inner flank of the rib 28 is designated 36 and slopes radially inwardly from the apex of the rib 28.

The flank 30 is of greater height, measured in the direction parallel to the longitudinal axis of the body 12, than the flank 36. The thickness "d" (Figure 2) of the flange 16 between the surfaces 22 and 24 is consequently less than the thickness "D" of the flange between the surface 22 and the bottom of a U-section channel 38 which is defined between the body 1 2 and the rib 28.

The wall 40 of the body 1 2 is not of uniform conical angle throughout its axial length from the base 14 to the flange 16. The angle changes a number of times over the section 42 of the wall 40 which lies between the planes P1 and P2 (Figure 1 ).

Over the section 42 the conical angles of the inner and outer surfaces of the wall 40 change in the same way. Hence the wall thickness remains the same.

At plane P2 the conical angle of the inner surface of the wall 40 and of the outer surface of the wall 40 both change as best seen in Figures 2 and 3. Over the wall section between the plane P2 and the plane P3, which is coincident with the beginning of the radially outer flank of the channel 38, the conical angle of the inner surface of the wall 40 differs from the conical angle of the outer surface. The conical angle of the outer surface of the wall 40 over the section closest to the flange is greater than the conical angle of the inner surface of the wall 40. Hence from the plane P2 to the plane P3 the wall thickness steadily increases. The maximum wall thickness is where the outer surface of the wall 40 curves outwardly to become the radially inner bounding flank of the channel 38.

The shape of the leading end of the pressing sleeve PS can be seen in Figures 2 and 3. In radial section it has a radially inner frusto-conical surface S1 , a rounded circumferentially extending protrusion R1 , a radially outer, circumferentially extending protrusion R2 and a circumferentially extending groove G between the protrusions R1 and R2.

As the leading end of the sleeve PS moves towards the sealing structure of the capsule, its inner surface S1 approaches the outer surface of the thicker part of the wall 40 of the capsule 10 (see Figure 2).

During the last part of the movement of the sleeve PS (see Figure 3) the surface S1 bears on the outer surface of the wall 40 of the capsule over the section which has the increasing wall thickness, the inner protrusion R1 enters the channel 38 and the rib 28 enters the groove G. The wall thickness of the section adjacent the flange is such as to resist any inward deformation of the wall.

In Figures 4 and 5 the pressing sleeve PS and a capsule 10.1 are illustrated. The inner and outer surfaces 12.1 , 12.2 of the capsule 10.1 are of constant conical angle between the plane P4 and the smaller diameter of the capsule. At plane P4 the conical angle of the outer surface 12.2 increases sharply, and then decreases again at plane P5, so as to provide a frusto-conical shoulder 42. The wall thickness of the capsule increases steadily over the extent of the shoulder 42. The part of the wall between the shoulder 42 and the bottom of the channel 38.1 is of constant thickness but is thicker than the part of the wall of the capsule between the shoulder 42 and the capsule's base. The rib 18.1 in this form is triangular in radial cross section with its base integral with the flange 16.1 .

As can be seen in Figure 5, the inner surface of the pressing sleeve PS bears on the capsule in the region of the shoulder 42, compressing the wall 40 of the capsule and forming a first radially inner sealing zone. The end of the pressing sleeve crushes the rib 28.1 thereby to form a second radially outer sealing zone.