The invention relates to a container for dispensing a product and, especially, containers which include a piston arrangement movably mounted within the container to dispense the product.

Dispensing containers are already known in which a piston arrangement which is slidably mounted within the container is used to dispense a product from the container by moving the piston towards the outlet through which the product is dispensed to push the product out of the outlet. Movement of the piston may be affected, for example, by using a pressurised gas to move the piston or by using mechanical means to move the piston.

One of the problems with the known type of piston arrangements is that in certain instances components of the product within the container may permeate through the piston and hence exit from the product chamber of the container. This can lead to deterioration of the product during storage.

Piston arrangements which include two pistons movably mounted within a container are already known for use with a container where pressurised gas is used as a propellant to move the piston.

However, these known types of double piston arrangements do not operate satisfactorily when used with mechanical operation, as it is possible that separation of the pistons may occur, especially if the mechanical actuator which moves the pistons is designed to be removable from the container, for example, to permit different types of products to be interchangeably dispensed using the same mechanical mechanism.

In accordance with the present invention, a container for dispensing a product therefrom comprises a composite piston movably mounted within the container and an outlet through which the product is dispensed, the container walls and the composite piston defining a product chamber within the container, and movement of the composite piston within the container towards the outlet expelling product through the outlet; the composite piston comprising a first piston, a second piston and a coupling means, the coupling means movably coupling the first and second pistons to each other and permitting limited relative movement between the first and second pistons in a direction substantially parallel to the direction of movement of the composite piston.

Preferably, the composite piston also includes a viscous substance which contacts the inside wall of the container adjacent the composite piston. The viscous substance may help to facilitate sealing of the

composite piston against the inside walls of the container and/or reduce friction between the composite piston and the inside walls of the container.

Typically, the viscous material is located between the first and second pistons and may be forced into engagement with the inside wall of the container by a compression force which acts between the first and second pistons to cause the second piston to move towards the first piston.

Preferably, the composite piston also includes a wall engaging skirt which abuts against an inside wall of the container. Preferably, a wall-engaging skirt is provided on both the first and the second pistons.

Preferably, the container is for use in combination with a mechanical actuating device which pushes the composite piston towards the outlet of the container. However, alternatively, the piston could be used in a pressure pack dispenser which comprises a propellant system which pushes the piston towards the outlet.

Preferably, the coupling means comprises a projection, on one of the first and second pistons, which engages with a recess in the other of the first and second pistons to couple the pistons to each other. Typically, the projection is of a smaller dimension than the recess to permit movement of the projection within the recess to facilitate the limited relative movement of the first and second pistons.

Typically, the recess extends circumferentially around one of the pistons and the corresponding projections on the other piston are disposed circumferentially on the

other piston to engage the recess.

Preferably, the first piston and/or the second piston may be elastically distorted to permit a push fit engagement of the projections in the recess. Typically, the pistons may be manufactured from a flexible material, such as plastic.

An example of a container for dispensing a product in accordance with the invention will now be described with reference to the accompanying drawings, in which:-

Fig. 1 is a cross-sectional view through a container showing the position of a composite piston within the container when the container is full with product; Fig. 2 is a cross-sectional view through a container showing the position of a composite piston within the container when the container has had the product dispensed; Fig. 3 shows a cross-sectional view through a lower piston for use in the composite piston shown in Figs. 1 and 2; Fig. 4 is a plan view of the lower piston shown in Fig. 3; Fig. 5 is a cross-sectional view through an upper piston for use in the composite piston shown in Figs. 1 and 2; and, Fig. 6 is a plan view of the upper piston shown in Fig. 5.

Fig 1 shows a cross-sectional view through a container 1 which contains a product 2 which is to be dispensed through an outlet 3 in the container 1. The outlet 3 has a closure cap 4 which is attached to the outlet 3

by means of complementary thread formations 5. At its lower end, the container 1 has a removable end cap 6 which is a push fit into the bottom end of the container 1. Typically, the end cap 6 is made of a plastic or rubber material and lip 7 of the end cap 6 is flexible to form a friction fit with the lower end of the can 1.

Located within the container 1 are two pistons 8, 9 between which a viscous material 10 is located.

Also located in the product 2 is a spherical ball 20.

In the example described shown in Fig. 1 the product 2 is paint and typically the container 1 is shaken by a user prior to use in order ensure the paint is thoroughly mixed. The presence of the spherical ball 20 helps to ensure that the paint is mixed properly during shaking and prior to use.

Fig. 1 shows the container 1 with the pistons 8, 9 at their lowermost position within the can 1. That is, when the can contains its maximum amount of product 2.

Fig. 2 shows the container when the pistons 8, 9 are at their uppermost position. That is when as much product 2 as possible has been dispensed from the container 1 through the outlet 3.

The pistons 8, 9 are shown in more detail in Figs. 3, 4, 5 and 6.

Figs. 3 and 4 show the piston 9 and it can be seen that the piston 9 comprises a central section 11 which is cone-shaped and a cylindrical wall-engaging skirt 12

which extends circumferentially around the outermost edge of the central section 11. On the inside surface of the wall engaging skirt 12 is an angled section 13 and a recess 14.

The piston 8 (see Figs. 5 and 6) has a central section 15 which is also cone-shaped and has six projections 16 which extend from the lower end of the edge of the central section 15. Below the projections 16 is a wall engaging skirt 17 which extends circumferentially around the lower end of the piston 8. It will be noted that the diameter of the wall-engaging skirt 17 is greater than the diameter of the outermost tips of the projections 16.

In use, inside portion 18 of the piston 9 is filled with a suitable viscous material which typically does not react with the product 2. The central section 15 of the piston 8 is then inserted into the interior 18 of the piston 9 until the projections 16 abut against the surface 13 on the lower end of the piston 9. Further pressure causes an elastic deformation of the projections 16 and skirt 12 and forces the projections 16 into the recess 14 in the wall engaging skirt 12, so that the piston 8 is coupled to the piston 9 and the sealant material is located between the pistons 8, 9, as shown in Figs. 1 and 2.

Hence, by means of the projections 16 and the recess 14, the pistons 8, 9 are coupled together and the gap between the central sections 11, 15 of the pistons 8, 9 is limited by virtue of the lower edge of the recess 14.

This helps to prevent separation of the pistons 8, 9

and also permits the pistons 8, 9 to move towards each other to ensure that there is a constant force of viscous material pressed against the inside wall of the container.

The presence of the viscous material 10 on the inside wall of the container reduces the frictional forces between the wall engaging skirts 17, 12 and helps to give a smooth movement of the pistons 8, 9 within the container 1. In addition or alternatively, the viscous material 10 may also be used as a sealing material to help prevent components of the product permeating either through the pistons 8, 9 or between the wall engaging skirts 12, 17 and the inside wall of the container 1.

In use, in the example shown in Figs. 1 and 2, the pistons are pushed towards the outlet 3 by inserting the container 1 into a mechanical device (not shown) which pushes the pistons 8, 9 towards the outlet 3 in order to dispense product 2 from the outlet 3 and desired by a user.

However, in an alternative example of the invention, the pistons 8, 9 could be incorporated into a conventional pressure pack dispenser to separate the product 2 from the propellant system and typically, the gas produced by the propellant system forces the pistons 8, 9 towards the outlet 3.

Modifications and improvements may be incorporated without departing from the scope of the invention.