EXPANDABLE PRESSURIZED BARRIER CONTAINER

Abstract: A pressurized thin walled expandable can 10 from which a fluent pressurized product is dispensed is made from an expandable can wall 12 and a barrier 20, which may be a fully evertable bag having uniform thickness and flexibility and shaped to fit within the can wall 12. The open end of the bag is mounted to the can wall 12 by means which maintain a seal as the can wall expands and returns to its unexpanded condition. As product to be dispensed is introduced into the product chamber 30, the flexible bag is extended down into the lower end of the can. As the product is later expelled through a discharge opening, the flexible bag, which may be plastic, is fully everted into the upper end of the can to expel all the product. The can is thin walled, so that when pressurized, the can diameter expands by at least one-­ thousandth (1/1000) of its unexpanded value. In one embodi­ ment, the bag is mounted by a ring 24 inside the can. The ring 24 includes a portion which expands to maintain the seal 64 with the expanding can side wall. In another embodiment the ring 24 is rigid, but of slightly larger diameter than the can 10. This ring stretches the can, so as to maintain the sealing contact with the can as the can expands. In other embodiments, the bag may be mounted by a stretchable adhesive and, if the bag is slightly elastic, it may be mounted by an adhesive or by a melt seal process such as heat sealing.

Description: The invention relates to a pressurizable container according to the preamble of the claim. A container of this type is disclosed in US-A-2 815 152. A critical portion of a container of this type is the mounting means, which is intended to mount the edge of the flexible barrier to the can wall. An important draw back of this type of a container consists in a certain leakage of product as well as propellant past the edge of the barrier as the can wall expands and returns to the un-expanded condition. Besides in US-A-2 815 152 a flexible and extendible barrier is disclosed more in detail in US-A-3 225 965, particularly in column 1, lines 61 to 70, by the wording "moreover its elasticity permits the bag to be filled as it expands". The teaching of a ring with integral expansible-contractable means is disclosed in US-A-3 931 834. However, also these two further types of containers have the same draw back related to the mounting means, namely that the flexible barrier positioned in the can will remain sealed to the side wall of the can even as the pressure in the can causes its walls to expand, and that a seal is maintained as the can wall expands due to pressure. All these objects are provided by the characterizing features of the claim. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a cup shaped barrier assembled with a sealing ring prior to insertion into the can body. Fig. 2 shows the can body prior to the insertion of the barrier. Fig. 3 shows a sealing ring embodiment for the barrier for providing the seal between the product and propellant chambers of the pressurized can. Fig. 4 shows an alternate embodiment of pressurized can in which the barrier is mounted directly to the can wall. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Fig. 2, the pressurizable can according to the invention includes an outer can 10 comprising a cylindrical body, defined by a cylindrical peripheral side wall 12, an open top 14, and a closed bottom 16 shaped to allow the pressurized can to stably rest on a flat surface. For strength, the can bottom 16 includes a peripheral rounded ridge 17 on whose crest the can sits, and a rounded depression 18. Other bottom shapes can be used to increase the strength of the can, and a number of such shapes are generally known in the art. The top of the depression has a pluggable hole 19 through it into the can. A gaseous or liquified propellant is conventionally supplied (from a source not shown) through the hole 19 after the top opening 14 has been closed so that the can may be pressurized. Thereafter, a plug 21 is installed in the hole 19 to close it. The material of the can is typically metal. However, other materials like strengthened paper or plastic may be used, so long as it is strong enough to contain the pressure in a filled pressurized can. For safety, it is desirable often that the can be of metal. For economic reasons, that is to reduce the amount of materials required in can fabrication, it is desirable to have thin walled cans. The can wall according to the invention is sufficiently thin that it expands when the can chamber is pressurized. The dimension of the can wall across the can chamber, such as the diameter of a cylindrical can wall, will increase in length. For example, at the lower pressures described below, the can wall may be made by a drawn and ironed process from sheet steel or even sheet aluminum. It has been found that even a gap of 0,025 mm between the side wall of the can and a ring supporting a barrier in the can will permit leakage of propellant and/ or product past the ring and barrier, which is undesirable. Therefore, the container according to the invention includes means for mounting the edge of the flexible barrier to the can wall and for sealing the mounting for preventing the product and propellant from leaking past the edge of the barrier as the can wall expands and returns to its unexpanded condition. This means may take any of several forms, as described below. Because the propellant is not mixed with nor expelled with product from the can 10, the initial pressure and quantity of the propellant in the can need not be very high, and with some very fluent products and relatively larger discharge valve orifices, the can pressure can be quite low for low viscosity products, as compared with the conventional aerosol barrier can pressure. This lower pressure helps to avoid stress on the seal and can can wall, permitting use of thinner walls and simpler bottoms, but higher pressure could also be used with cans whose walls and bottoms are designed to withstand this stress. There are a variety of different propellants which may be placed in the pressure chamber, including various compressed gases or liquified gases. Where the propellant is a compressed gas, typically in an aerosol container, the compressed gas pressure chamber occupies in the range of 1/3-1/4 of the total volume of the entire can. On the other hand, where the propellant is in the form of a liquified gas, the pressure chamber occupies in the range of 1/10-1/50 of the total volume of the can. It is economically desirable to produce a standard can design which can include a barrier that is adapted for either type of propellant, that is where the propellant chamber can be relatively smaller in volume or where it must be larger. The invention permits this. Also, there is a wide variety of fluent products which may be contained in and expelled from the can 10, including quite fluent liquids of a viscosity of 10,000 cps or less and higher viscosity products like processed foods, e.g. cheese at a viscosity upwards of 300,000 cps or even higher, depending on the rheological properties of the product. Very low viscosity products, such as water and alcohol (1 cps or less) may also be contained and expelled. Referring to Fig. 1, there is a barrier 20 in the can, which is shown in the shape of a cup. The barrier is a sheet of greater cross-section than the can, and the barrier sheet may be cut and folded so that the cup shape may be defined. Further, the sheet may have a pocket or generally tubular shape or it may be flat, although its surface area and shape are preferably such that the sheet will extend to the closed cover of the can, as described below. The cup shaped barrier has a side wall 22 and a closed bottom. The barrier may simply be a flat sheet which is deformed in use. It may be a sheet with cut regions which enable the sheet to be shaped into a cup, and the cut regions of the sheet are attached to the can at their margins. The cup is of a flexible material so that the cup may be filled and later everted as described below. The cup may also be made by vacuum forming or blow molding. The material of the barrier 20 need merely be sufficiently ductile and flexible to evert as described below and be impervious to the product and to the propellant which contacts the barrier at its opposite sides. The material is preferably not a highly stretchable material like rubber, although some stretching may be desired. For example, an inexpensive plastic sheet or tube material of substantially uniform thickness and flexibility may be folded and heated to form a cup-shaped bag. Suitable plastics could include polyethylene, polypropylene, and so forth. The barrier may be made of a paper, e.g. a waxed paper. It may be of any appropriate fabric. It could even be a metallic barrier, such as an aluminum film, or metallized plastic, such as aluminum on Mylar or Saran. The means for mounting and sealing the barrier 20 to side wall 12 of can 10 may take several forms. In general, the mounting and sealing means must maintain the seal despite the expansion of the can. If can wall 12 is smooth and continuous, a seal may be more easily maintained, in most cases. The specific forms of the mounting and sealing means described below include ring seals as well as adhesives and melt sealing. Fig. 1 shows a general ring seal embodiment in which a barrier fastening ring 24 is inserted into the barrier 20 and is positioned in the region near the upper edge 26 of the cup shape. The barrier 20 with its ring 24 are inserted into the can 10 and are positioned a distance down from the open top 14 of the can. The dimensions of the ring 24 and the barrier are selected such that the ring 24 can snugly fit against the peripheral side wall 12 of the can 10, thereby securing the barrier cup 20 firmly in the can. In this manner, the can 10 is divided by the cup into the upper product chamber and the bottom propellant chamber. The size and shape of the barrier are coordinated with the height of the can 10 and with the position of the ring 24 along the height of the can intermediate the upper and lower ends so that when the barrier is sub stantially fully extended, it will extend toward the bottom of the can and be substantially fully in contact with the peripheral side of the can when the can is loaded with the product and it will extend toward the top of the can and be substantially fully in contact with the side of the can and with the cover over the can when all the product has been expelled. Although barrier 20 could be slightly larger than the upper region, it is preferable that the barrier substantially fill the upper region of the can when fully everted, barely leaving some unfilled space, so that it cannot be pinched off by islanding caused by the propellant and so that nearly all of the product may be expelled. This makes it unnecessary to use a tube or other device to prevent pinch-off. Any suitable type of valve may be used in the discharge opening. For use with liquified gas propellants, the initial volume of the upper product chamber may be much larger than that of the bottom propellant chamber, on the order of 15 or 20 to one, thereby utilizing the majority of the space within the can body for the product. For use with compressed gas propellants, the initial volume of the product chamber to the initial volume of the propellant chambers would typically be on the order of 2 or 3 to 1. To accommodate these different chambers of different volume in a can of a standard size, and to enable the two chambers to have a correct volume relationship it is desirable to be able to position the ring 46 (Fig 3) and the barrier at appropriate selected positions along the height of the can wall. As the invention is intended to assure complete expulsion of product in the product chamber, the barrier size and shape are selected so that the barrier will press against the inside of the can cover on eversion to expel product, and the barrier will not be folded or wrinkled there but will instead be fully extended. The two chambers are sealed off at the peripheral side wall of the can by the outward force exerted by the ring 46 on the wall 12. As the pressures in the product and propellant chambers are identical when the discharge valve 38 (Fig. 4) is closed and are nearly identical when that valve is open, the holding ring is not likely to move along the wall of the can. After the product has been loaded in the product chamber of the can 10 and the propellant has been loaded in the propellant chamber of the can 10, the can is pressurized. The internal pressure in the can causes the side wall of the can to bulge slightly in diameter. For example, if the can 10 is of aluminum with a 65 mm diameter and with a wall that is 0,13 mm thick, when the can is pressurized at normal room temperature of 70°C, its diameter will increase approximately 0.1 mm. If this expansion is not compensated for, a radial clearance will be created between the interior of the can wall and the exterior of the ring 24. The radial clearance will provide a leakage path between the product and propellant chambers allowing gas and/or product to bypass the barrier cup 20, resulting in a pressure reduction in the can, leakage of propellant out of the valve of the can and inability to properly expel all of the product from the product chamber. In the embodiment of Fig. 3 the ring 46 is a solid, annular body with an exterior peripheral channel 48 which opens radially outwardly. The channel receives and holds in it an elastic, resilient, compressible sealing element 50, illustrated as an O-ring. The diameter of the sealing element ring 50 is slightly greater than the internal diameter of the can, even when the can has stretched under pressure. When the ring 46 with the captive O-ring 50 in the channel 48 is installed in the can, the O-ring 50 is compressed through its engagement against the can wall. As the can wall expands under pressure, the resilient ring 50 tends to restore itself to its undeflected condition and is biased outwardly against the barrier and the can wall for maintaining the seal there. The above technique of maintaining a seal rely upon the elasticity of at least one of the can and ring for maintaining the seal, using the resilience of the ring to maintain the seal. The sealing effectiveness can be increased through the introduction of sealing compounds between the fastening ring and the barrier and/or between the barrier and the can wall. The invention simplifies production of the can and its product-propellant barrier and eliminates concern about close manufacturing tolerances for the barrier and for its attachment to the can. For example, in previous barrier pack cans, which employ a piston barrier system, or in the bag barrier system with folded or pleated bag side walls to enable the bag to collapse without pinch-off, the consistent predictable shape of the can 10 was critical to the operation of the barrier system. With a piston system, an indentation in the container above the piston would prevent the piston from traveling up the peripheral side wall of the can. With the present barrier system, however, the container can be of almost any size or shape. It is not even necessary that the peripheral side walls of the container be generally parallel to each other as with other known systems. Consequently, cans could be used with either esthetically pleasing shapes or other shapes which are designed in accordance with human factor engineering principles. It is preferred, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.

Claims: A pressurizable container (10) for containing a fluent product under pressure and for dispensing the product through a discharge opening (38), comprising: a can wall (12) defining a can chamber and having an upper end with the discharge opening and an opposite lower end; the can wall (12) being resilient and expanding slightly when the can chamber is pressurized and returning to an unexpanded condition as the pressure in the can chamber is reduced to zero; a flexible barrier (20) having an edge mounted to the can wall (12) in the can chamber, the barrier (20) dividing the can chamber into a product chamber (30) between the barrier (20) and the upper end of the can wall (12) and a propellant chamber (32) between the barrier (20) and the lower end of the can wall (12) the barrier (20) comprising material that is impervious both to the product and propellant; means for mounting the edge of the flexible barrier (20) to the can wall (12) in a manner that seals the barrier (20) to the can wall (12) for preventing the product and propellant from leaking past the edge of the barrier (20) as the can wall (12) expands and returns to the unexpanded condition; and the flexible barrier (20) being extendible toward the lower end when the product chamber (30) is initially filled with fluent product and being gradually extensible toward the upper end through pressure generated by propellant in the propellant chamber (32) to expel the fluent product out of the can chamber through the discharge opening (38), characterized in that the can wall (12) is cylindrical, and the mounting means comprises a ring (46) the periphery of which faces the can wall (12); the ring (46) having separate expansible-contractable means (50) at the periphery thereof for engagement with the can wall (12), and the ring (46) being of a size with respect to the diameter of the can that the expansible-contractable means (50) are deflected and contracted upon mounting of the ring (46) and the barrier (20) in the can chamber while the can chamber is unpressurized and the expansible-contractable means (50) being adapted for expanding to maintain the seal between the periphery of the ring (46) and the can wall (12) upon the can chamber being pressurized and the diameter of the can wall (12) increasing slightly.

Inventors: DIAMOND, GEORGE B.
Applicants: DIAMOND, GEORGE B.
Application year: 1985
Main classification: B65D83
IPC codes: B65D83, B05B11