1. Field of the Invention
This invention relates to pressurized containers and to methods for pressurizing and filling them. In accordance with a first aspect of the invention, the containers are completed by the container manufacturer and shipped ready to be filled. In a preferred embodiment a propellant is introduced into the completed container by the manufacturer before the container is shipped to a filler to be filled with product. According to a second aspect of the invention the container is pressurized and filled in a way to ensure that the container is not excessively pressurized during filling and an adequate pressure is maintained in the container until all or substantially all of the product is depleted during use.
2. Prior Art
Pressurized containers are used to dispense a variety of products, including paint, lubricants, cleaning products, food items, personal care products such as hair spray, and the like. Pressure for dispensing these products is provided by a propellant placed in the container. In some prior art systems the product and propellant are stored separately in the container, i.e., separated by a barrier, e.g. a piston or bag, commonly referred as a barrier pack system. In other systems the product and propellant are stored together under pressure in the container. Dispensing of the product occurs when a discharge valve or nozzle is opened, permitting the pressurized product to be forced out through the nozzle, usually as a spray, stream, or foam. As product is depleted from the container, the pressure exerted by the propellant decreases, especially evident when compressed gases are used as the propellant, and the propellant pressure may become diminished to the extent that all of the product cannot be dispensed from the container, or a desired characteristic, e.g., atomization, is not achieved.
In addition to the propellant component, many products, e.g., hair spray, require a carrier, e.g., alcohol, or combinations of alcohol with water or other volatile solvents that dry quickly upon discharge from the container. Other volatile solvents or propellants that can be used in these systems include volatile organic compounds (VOCs) such as propane, isobutane, dimethyl ether, and the like, but their use is limited due to environmental concerns. For instance, under some current regulations no more than 55% of the contents of the container can comprise a VOC. In an aerosol dispenser, as much as 25% of the VOC could be required for use as a propellant, leaving about 30% VOC in the product. The balance of the product would be the active ingredients and water, which does not dry as quickly as the VOC, resulting in a “wet” product when used.
Carbon dioxide (CO2) is useful as an aerosol propellant, but its use has been limited due to the fact that it is normally placed in the container as a pressurized or compressed gas, and in conventional systems the drop-off in pressure is excessive as the product is depleted and the volume occupied by the propellant increases. For example, in a typical situation the starting pressure might be 90-125 psig and the finishing pressure only 20 or 30 psig.
Conventional barrier pack systems typically comprise a can made of aluminum, steel, plastic, or other suitable material, with a barrier in the can between the product and the propellant. The barrier normally comprises a piston reciprocable in the can, or a collapsible bag in which the product is contained. In accordance with conventional practice, barrier pack cans are shipped empty from the manufacturer to a location where the can is to be filled, either with a piston in place in the can or a bag attached to the valve or the dome closing the end of the can. The filler adds the product, crimps and seals the valve in place in the opening provided for that purpose in the domed top of the can, and then injects the propellant.
If the barrier pack is of the type having a piston, the filler normally introduces product, e.g., a gel, through the opening in the domed top and into the can above the piston. The aerosol valve is then fitted and sealed to the can, and a propellant such as, e.g., isobutane, a VOC, is introduced under a predetermined pressure into the can beneath the piston through a sealing plug in the bottom of the can. If a liquefied propellant is used, some of it vaporizes until an equilibrium pressure is reached. The pressurizing propellant forces the piston up, placing pressure on the product so that it is discharged through the valve when the valve is opened.
In barrier packs utilizing a bag wherein the bag is affixed to the valve body on the bottom side of the valve cup with an undercup gasser, the filler introduces a propellant around the valve and into the can outside the bag, crimps the can, and then introduces product into the bag through the valve. Alternatively, a second method utilizes a plastic bag that is pre-inserted into the can and that has a formed one-inch neck shaped to fit the curl of the can, which allows product to be filled before the valve is applied and sealed. Propellant is then added through the sealing plug in the bottom of the can. The propellant exerts pressure on the bag, forcing product out through the valve when the valve is opened.
In those conventional systems wherein the propellant is mixed in the container with the product, the can manufacturer ships an empty container to the filler, who then places a desired quantity of product into the container, attaches and seals the valve, and then injects propellant through the valve to pressurize the product.
In order to promote dissolution of the propellant into the product as the propellant is being introduced, some prior systems shake the container, thereby reducing the pressure spike or over-pressurization that occurs when the propellant is first charged into the container and thus avoiding deformation of the can. However, these prior art systems have not been entirely satisfactory because of slower gassing and the shaking required.
Various other systems have been developed in the prior art for storing a reserve supply of propellant and adding it to the container as product is depleted, so that propellant pressure is maintained at a desirable level until a suitable amount of the product is dispensed from the container. Examples of such systems are described in applicant's prior issued U.S. Pat. Nos. 6,708,844 and 7,185,786, and applicant's prior copending U.S. application Ser. No. 11/250,235, filed Oct. 14, 2005, all of which are incorporated in full herein by reference.
Common to the foregoing systems is the need for the filler to provide machinery for completing manufacture and/or assembly of the final product, and in the case of pressurized aerosol dispensers to inventory propellants and solvents in addition to the product. For many small fillers, in particular, this is a burdensome requirement due to the cost of the necessary machinery to complete manufacture of the containers and to store propellant gases, and when applicable the cost of carrying insurance and maintaining appropriate storage facilities for required propellants and solvents.
It would be advantageous to have an economical, efficient, and environmentally safe system and method for filling and pressurizing containers, wherein completed containers are shipped by the container manufacturer to the filler so that the filler does not require the necessary equipment to complete the vacuum crimping, propellant gas injection, gas storage tanks, and pumping equipment to complete the manufacture of the pressurized product, and does not need to incur the cost of carrying insurance and maintaining manufacturing and appropriate storage facilities for required propellants. Moreover, it would be advantageous to have a system and method for filling and pressurizing containers wherein the initial starting pressure is not excessive and satisfactory pressure is maintained throughout the useful life of the container.