Patent Publication Number: US-2010108716-A1

Title: Aerosol for viscous products

Description:
TECHNICAL FIELD  
     The present invention relates to aerosol containers comprising an outer casing with a bag for product encapsulated therein. Such containers are commonly referred to in the art as bag-in-can aerosols. 
     In particular, the invention relates to adaptation of such bag-in-can systems to allow expulsion of viscous products, for example in the form of pastes or thick gels. Such products may include adhesives, sealants and fillers. 
     BACKGROUND ART  
     Bag-in can aerosol dispensers have been known from the prior art since the 1960′s. For example, GB 1030596 (ALLIED CHEM) May 22, 1966 describes the manufacturing method used for production of a nylon bag and its incorporation into such an aerosol container. 
     In later years, such systems were enhanced to provide various improvements to the bag structure and dispensing characteristics. For example, U.S. Pat. No. 3,539,083 (DART IND INC) Nov. 10, 1970 describes modification of the bag and can structure to ensure that the bag cavity fills the can and also the incorporation of a dip tube inside the bag to ensure that when the valve is opened, product being dispensed from the container does not itself throttle further product dispensing. U.S. Pat. No. 4,148,416 (METAL BOX CO LTD) Oct. 4, 1979 describes a loose core member within the bag, which prevents the formation of “pockets” within the product as the bag collapses and product is dispensed. 
     Whilst the disclosure in the prior art is suitable for many products, such aerosols are now being proposed for more challenging, viscous products. The viscosity of the products now being considered for such bag-in-can technology exacerbates the problems of throttling the product flow from the aerosol valve and the uneven or even lack of dispensing of some product from the container. 
     Where a product is very thick the bag-in-can system will tend to dispense the product nearest the valve adequately. However, as product is dispensed the bag tends to collapse near the valve, sealing the path between the remaining product and the valve. Thus, it becomes very difficult or impossible to expel some of the product, which remains trapped within the aerosol container. The viscosity of the product means that the use of a dip tub is impractical and a free-floating core will not provide a flow path necessary to dispense the product. 
     Historically, bags with pleats or folds created using only the material of the bag sidewall, “pleated bags”, have been a popular way of trying to control the collapsing of the product bag. The bags are typically made from a plastics material and are shaped using conventional blow-moulding techniques to introduce folds or pleats in the bag sidewall. These folds or pleats are usually ‘V’ or ‘U’-shaped in transverse cross-section and generally have a decreasing sidewall thickness as the diameter of the bag increases from its pre-shaped form due to stretching of the material. Their effect is to introduce an annular or circumferential weakening or bands in the bag, which permits the bag to collapse under applied forces. U.S. Pat. No. 3,471,059 A (J. L. MOLLER ET AL) Oct. 7, 1969 describes a dispensing container with such a pleated bag. The bag is formed from an integral piece of material and includes axially spaced primary fold sections and secondary fold bands collapsible subsequent to the collapse of the primary fold sections. The intention of the paneling is to regulate the collapse of the bag caused by the pressure forces acting on it radially and axially as product is dispensed. U.S. Pat. No. 4,062,475 A (HARRIS AND MONSON) Dec. 13, 1977 also describes in one particular embodiment a bag (flexible liner, 9) with horizontally pleated sides. Again, the Figures of U.S. Pat. No. 4,056,213 A (MARTIN PAINT) Nov. 1, 1977 show a pleated bag with the pleats or folds forming a collapsible bellows or piston. In GB 1116423 A (CONTINENTAL CAN) Feb. 28, 1967 such folds are used both to rigidify the bag (circumferentially extending first means,  25 ) and to regulate the collapse of the bag (circumferentially extending second means,  26 ). In practice however a pleated collapsible bag does not work very well; the inventor has found that pleated bags are prone to collapsing inwardly radially despite the teachings of Moller, Harris, Martin Paint and Continental Can. The decreasing bag sidewall thickness of the pleats or folds is insufficient, especially in combination with highly viscous products, to withstand the pressure of the propellants used these days and pleated bags still tend to collapse uncontrollably resulting in undispensed product. There remains the need to provide a strong product bag which will collapse predictably under the applied influence of propellant and the inventor has found that only extrinsic support means, i.e. those added to the bag, as opposed to intrinsic support means which are made out of the bag material such as folds or pleats, will suffice. 
     DISCLOSURE OF INVENTION  
     Accordingly, the present invention provides an aerosol dispensing container comprising a container body and a collapsible bag therein to separate a pressurised chamber defined between the container body and the bag from a product chamber defined by the bag, and an actuating valve carried by the container body and arranged in fluid communication with the product chamber, characterised in that the bag includes extrinsic support means adapted to prevent radial collapse of the bag to maintain flow of product to the valve whilst allowing axial collapse of the bag as the product is dispensed. 
     As product is dispensed from the aerosol container, the bag tends to collapse radially, but the support means keeps the walls of the bag at a defined distance, preventing further radial collapse and defining a flow path for the remaining product to the aerosol valve. 
     The inventor has used both a cage-like structure and subsequently a conventional spring as the support means with similar results. The cage or spring is preferably located inside the bag and it is therefore submerged in the product. Therefore, the material from which the cage or spring is made must be chosen carefully. The cage or spring must not be adversely affected by the product (e.g. it must not corrode) and neither must it adversely affect the product (e.g. by chemical reaction). The cage or spring should also be arranged so that it does not inhibit or prevent the flow of product to the actuating valve. 
    
    
     
       BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS  
       Different embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  shows a cut away isometric drawing of a prior art aerosol container with bag and an expanded area of the top section of this container. 
         FIG. 2  shows a cross section view through an aerosol container according to the invention with a helical spring located inside the bag. 
         FIG. 3  shows a cross section through the same aerosol container as that shown in  FIG. 2 , after the contents of the bag has been dispensed and the helical spring is compressed. 
         FIG. 4  shows a cross section view through an aerosol container according to a second embodiment of the invention where ribs are situated within the product compartment and are adapted to define a bellows structure, which prevents radial collapse of the bag, whilst allowing axial compression of the bag. 
         FIG. 5  shows a cross section view through an aerosol container according to another embodiment of the invention, in which the bag sidewall incorporates ribs designed to prevent radial collapse of the bag, whilst allowing axial compression of the bag. 
     
    
    
     Referring to  FIG. 1 , a prior art aerosol container  1  comprises a body  30  having a base  20  and a cone  40 . The free edge of the cone  40  is finished with a curl  42 . The base  20  and cone  40  are connected to the body  30  using conventional joining methods, such as a double seam. The base  20  defines a charging port or aperture  25 , through which propellant is inserted into the aerosol container  1 , the propellant being used to drive any product in the aerosol container  1  out of the valve  5 , when it is opened. The propellant may either take the form of a liquidified propellant or a compressed gas. 
     The aerosol container  1  shown in  FIG. 1  is a conventional “bag in can” aerosol. A bag  50  is inserted into the body  30 . The inside of the bag  50  defines a product compartment and the space left outside the bag  50 , between the bag  50  and the body  30 , defines a propellant compartment into which propellant is introduced via the charging port  25 . Once propellant has been inserted into the propellant compartment, the charging port  25  is sealed with a grommet  26 . 
       FIG. 2  illustrates a first embodiment of the invention, in which a spring  54  is inserted into the neck  57  of the bag  50  in the vicinity of the valve  5 . The valve  5  is mounted in a valve cup  70  and is arranged in fluid communication with the product compartment inside the bag  50 . The spring  54  is arranged to brace the sidewall  53  of the bag against radial collapse, whilst allowing the base  52  of the bag to collapse axially. 
       FIG. 3  illustrates the same embodiment of the invention as  FIG. 2 , but this figure shows the spring  54  in its compressed configuration. As product is forced out of the valve  5 , by the propellant acting on the bag  50 , the spring  54  braces the bag  50  and prevents radial collapse. This ensures that the flow path of product to the valve  5  is maintained. As product is used up the spring  54  compresses axially, ensuring that most of the product is dispensed from the bag  50  through the valve  5 . 
     A disadvantage of this arrangement is that the spring  54  is submerged in the product inside the bag  50 . This may cause the spring  54  to become “clogged” by the product, thus restricting its effective operation. In order to overcome this problem, the spring  54  may need to be made of more expensive materials (such as stainless steel), which is uneconomic for many aerosol applications. Spring materials that are inert in the presence of a wide variety of products are prohibitively expensive, often costing many times the cost of the finished aerosol product on the supermarket shelf. 
     To avoid “clogging” of the spring, the inventor has designed an alternative bag arrangement (as shown in  FIG. 4 ), in which ribs  55  are provided around the circumference of the bag  50  in fluid communication with the product compartment, the sidewall  53  in between the ribs  55  acting as a flexible web. The ribs  55  and the flexible sidewall  53  therebetween form a bellows structure. The ribs  55  are adapted to prevent radial collapse of the bag  50  whilst the bellows structure allows axial compression of the bag  50 . The ribs  55  can be of any cross-section, for example, hexagonal, but preferably they have a circular cross-section. A disadvantage of this bellows structure is that it is difficult to manufacture and makes assembly of the bag  50  inside the aerosol body  30  complex. 
       FIG. 5  shows a third embodiment of the invention, which requires no spring or like component inside the bag  50  and no ribs  55 , which are difficult to assemble inside the aerosol body  30 . In this embodiment of the invention, one or more ribs  55  are provided integrally with the sidewall  53  of the bag  50 . The ribs  55  may be arranged to form a helix or may be provided as segments of a helix, i.e. they may be continuous or discontinuous. The ribs  55  are designed and arranged to restrict radial collapse of the bag  50 , whilst allowing axial compression of the bag  50  in much the same way as the spring  54  (shown in  FIGS. 2 and 3 ) and the ribs  55  shown in  FIG. 4 .