Barrier Can Prefill Seal

1. There are a number of special containers for dispensing products under pressure on the market in which the product and propellant are kept separated. There is the collapsible bag type, the expandable bag type using CO2 pellets, and the piston type. The piston may be of two types, the free piston and a piston which fits tightly with a well engaging skirt. In the piston can the container is divided into two chambers by an internal piston. The product is held on one side of the piston and the propellant on the other. Under pressure of the propellant, the piston forces the product from the container. This invention relates to a prefill method used in a container designed to dispense its contents under pressure. Particularly but not exclusively the invention is concerned with dispensing viscous material as well as liquids under pressure of a propellant. More specifically the invention relates to a free piston in which the piston is sealed with a secondary product other than the material dispensed.

2. Much emphasis has previously been placed on primary permeation which is gas going through the piston and secondary permeation which is gas going up between piston and can side wall. Pistons which use the product as the seal between can and piston are known in the art and are called free pistons. Pistons have been designed to minimize secondary permeation by only having minimal gap between piston and can side wall. Water based products such as shave gel, caulking compound and cheese have been successfully marketed for years with excellent shelf life using a free piston. Products with solvent contents like mineral spirits or III trichlorethane while forming a seal between piston and can also provide a path for the gas to be absorbed into the product. Solubilities of compressed gases in solvents are well documented as outlined in "Handbook of Aerosol Technology Second Addition". There are also products which although they do not contain a high percent of solvents, have by nature of the material, a high gas transmission rate. A material exhibiting this latter characteristic is silicone sealant. Each of these properties in products provide a continuous path for the gas to migrate up the side wall into the product side of the piston causing adulteration of products to be dispensed and giving them a foamy appearance. An object of the present invention is to provide a seal for a free piston with a material which will not absorb gas or transmit the gas into the product side. We will refer to this material as a pre-fill. Preferably the piston should be high barrier piston. These include a multi-layer material such as: polypropelene, eval, polypropelene, pressure formed into a piston which will create a barrier to gas transmission or an injection molded piston with high barrier properties. The piston should not be a tight piston, but free to move along the can side wall in order to permit the pre-fill material to flow into the gap between the piston and can. Preferably the material is a copolymer composed predominantly of high molecular weight mono-olefins. These materials are known to resist oxidation, are completely hydrophobic and are impermeable to water, vapor and gases. A product name for this copolymer is Polybutene, which can be used by itself or have paraffin added to form a paste. The material selected should be heated so to decrease its viscosity and cause it to flow. In the liquid stage the sealant will flow down and around the piston more easily forming a seal upon cooling. It should be noted that the seal, when cool, should be compatible with the material with which it comes in contact. The material should not be a liquid state when cool but should become a paste or slurry when sealing the piston.

The above material or combinations of materials is an example, since there are other polymers and sealants that could be used to prevent gas migration into the product. It should also be noted that the pre-fill may also be introduced as a paste and pushed down around the piston under pressure forming a seal.

FIG. 1 is a side elevation view of a container having a piston which is provided with a prefill sealant material.

FIG. 2 is a fragmentary view of the container of FIG. 1 being filled with compressed air.

FIG. 3 is a fragmentary enlarged view of FIG. 1 showing the prefill sealant in its nonflowing condition.

FIG. 4 is a fragmentary enlarged view of Figure showing the prefill sealant flowing between the piston and container wall.

FIG. 5 is a view analogous to FIG. 4 for an alternative embodiment of the piston.

Referring to the drawings, the reference number 10 denotes a pressurized container for dispensing materials, Container 10 is usable with materials of varying viscosities indepentent of piston sidewall clearance. FIG. 1 shows a container 10 which includes a substantially cylindrical body 11 closed at its dispensing end 12 by a cap 14 and at the other end by a bottom wall 16 all of which are secured together and sealed with liquid tight integrity. A dispensing nozzle 18 is carried in cap 14 and includes valve means (not shown) well known in the art. When nozzle 18 is depressed the contents of container 10 may escape through orifice 20 in nozzle 18.

A piston 22 is provided separating product 31 from propellant 35. Piston is longitudinally slidable within container 10. Piston 22 includes a generally annular sidewall 26 which is closed at its upper end by a barrier wall 24.

Piston 22 is formed with at least one annular step 28 on its sidewall 26 in which the prefill sealant 30 will flow in order to seal the piston. As the product is discharged from orifice 20 the piston will move up along the can side wall moving the prefill sealant 30 with it, thereby providing a continuous seal.

FIG. 2 shows a clamped can 10. Clamp 41 has a cylindrical lower portion for engaging can top wall 14. This portion being formed with opening 42 to introduce pressure. The clamp is connected by a rod 43 suitable means for moving it up and down. When the clamp engages can top wall 14 against support plate 38 fluid pressure 44 shown schematically in FIG. 2 such as compressed air is introduced into opening 42 and into can body 32, thereby forcing prefill sealant down around piston into sidewall 26.

FIG. 3 is a fragmentary enlarged view of piston 22 in can 10 showing prefill sealant 30 before being forced down between piston side wall 26 and container cylindrical body 11.

FIG. 4 is a fragmentary enlarged view of piston 22 in can 10 showing prefill sealant 30 forced down between piston side wall 26 and container cylindrical body 11.

FIG. 5 is a view analogous to FIG. 4 showing another embodiment of a sealed piston in accordance with the present invention.