Abstract:
There is disclosed a substrate of layers of materials comprising ethylene vinyl alcohol copolymer layers having sandwiched therein between a metal foil layer and a paper layer all suitably adhered to one another. It is also contemplated that the substrate be employed in fabricating a dentifrice tube.

Description:
FIELD OF THE INVENTION 
     The present invention relates broadly to the container art, and is more particularly concerned with a collapsible dispensing container of laminated wall construction in the body portion thereof, whereby product permeation and absorption, and oxygen absorption are substantially prevented in all regions of the container structure susceptible thereto. 
     BACKGROUND OF THE INVENTION 
     Collapsible tubes formed of metallic and plastic materials have long been known in the packaging field. Extruded metal tubes are inherently brittle and repeated use not infrequently results in wall cracks so that product is exuded from a location other than the essentially rigid dispensing orifice. Of the prior art metal tubes, aluminum tubes, while probably being the least brittle, are somewhat limited in their applications since up to the present time it has not been possible to apply to the interior surfaces thereof a completely satisfactory coating, when required to prevent attack and corrosion of the metal by alkaline or acid contents and contamination of the contents by the reaction products. Notwithstanding the relatively brittle nature of a metal tube, the mentioned internal coating operation requires an additional processing step which necessarily increases the cost of the final article. 
     Tubes formed of polyethylene and other plastic materials have enjoyed wide commercial success in the packaging of many products; however, certain other products after a time have been noted to deteriorate when contained therein. Plastics as exemplified by polyethylene are permeable to a degree when employed in the wall thickness used in tubular containers, and the essential oils embodied in most dentifrices for flavoring purposes are reduced in volume during storage of the container, rendering the dentifrice less palatable. Also, the plastic container wall absorbs oxygen over a period of time and ultimately may decompose the product, which has actually been found to be the case with fluoride-containing toothpastes. A further disadvatage of a plastic tube resides in the inability of the surface to readily receive printing or decorative material. In addition, plastic tubes, as exemplified by polyethylene, have a memory effect; that is, they do not remain compressed when squeezed, a particular disadvantage for dentifrice tubes. 
     To counter the above problems, it has accordingly been proposed to provide a metallic foil barrier between the product and the polyethylene tube body. This would counter the compressibility problem in that the metal layer would impose its compressibility upon the plastic. In addition, the metallic foil barrier between the product and the polyethylene tube body would prevent the mentioned loss of essential oils and the absorption of oxygen. The metallic barrier has been suggested as an interlayer between facing sheets of polyethylene, and that a laminate be formed by heat with or without suitable adhesives. However, while a structure of this general character is effective to prevent some product permeation and oxygen absorption through the tube body, and particularly when the inner thermoplastic layer is a copolymer of ethylene olefin and a polar group containing monomer which is co-polymerizable therewith, there remains the possibility of product deterioration albeit to a much lesser extent. 
     PRIOR ART 
     Attention is directed to the following prior: 
     Brandt (U.S. Pat. No. 3,295,725) discloses a tube which combines above advantages of an aluminum tube with advantages of a plastic tube. This is a laminated collapsible dispensing container containing both a metallic barrier and a polyethylene inner wall. The thermoplastic layer is broadly described as polyolefin and copolymer of an olefin and a polar group containing monomer which is copolymerizable therewith. This laminate overcomes the above described limitations, except for absorption of the essential oils from the dentifrices. 
     Marchak (Can Patent No. 728,525) discloses a laminated tube containing an inner layer of polyethylene. He acknowledged the problem of absorption of flavor oil by the thermoplastic wall. 
     Sugimoto (U.S. Pat. No. 4,261,482) discloses a laminated collapsible tube containing ethylene vinyl alcohol copolymer as the outside layer and an olefin as the inside layer. The function of the ethylene vinyl alcohol copolymer was to serve as an oxygen barrier resin. This tube differs from the present invention in two important manners. One is that it does not contain a metallic barrier as a center layer, and therefore does not have the above described advantages of a metallic layer. Secondly, it does not have ethylene vinyl alcohol copolymer as the layer contiguous to the dentifrice. Data below will demonstrate the value of ethylene vinyl alcohol copolymer as a flavor barrier when situated next to the dentifrice. 
     Other inventors also have used ethylene vinyl alcohol copolymers in laminates as an oxygen barrier, but they, too, have failed to recognize its efficacy as a flavor barrier. Furthermore, in none of these cases was the described article a collapsible laminated tube containing a metallic barrier layer. These include such U.S. patents as follows: Knott (U.S. Pat. No. 4,239,829), Schroeder (U.S. Pat. No. 4,254,169), Sakano (U.S. Pat. No. 4,182,457), Sugi (U.S. Pat. No. 3,620,435), Canio (U.S. Pat. No. 4,284,671), Farrell (U.S. Pat. No. 4,464,443), Farrell (U.S. Pat. No. 4,425,410), and Kushida (U.S. Pat. No. 3,958,721). 
     Additionally, inventors have also used ethylene vinyl alcohol copolymer as part of a laminate structure, but these also were not in the form of a collapsible tube containing a metallic barrier layer. Furthermore, the inventors also made no mention of this polymer&#39;s excellent flavor barrier properties. These include Christensen (U.S. Pat. No. 4,407,873), Christensen (U.S. Pat. No. 4,406,667), Bair (U.S. Pat. No. 4,400,428), Uehara (U.S. Pat. No. 4,352,850), Matsuo (U.S. Pat. No. 4,451,512), and Katayama (U.S. Pat. No. 4,410,595). 
     Ethylene vinyl alcohol copolymer has also been used as a thermal insulator by Sheptak (U.S. Pat. No. 4,284,674). This also was not in the form of a collapsible laminated tube. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an important aim of the present invention to provide a collapsible dispensing container of laminated wall construction in the body portion. 
     Another object of this invention lies in the provision of a tubular container having a plurality of adherent layers in the body portion thereof, one of said layers providing a barrier to product migration and oxygen absorption such as a metallic foil and another of said layers being ethylene vinyl alcohol copolymer or mixture thereof varying in density and crystallinity. The latter layer being innermost and preferably outermost with different additional laminae sandwiched therein between. 
     Such additional layers comprise paper and suitable adhesive and bonding agents such as copolymer of ethylene and acrylic acid. 
     The collapsible dispensing container of the present invention may be constructed from the laminated substrate of the present invention by conventional and known apparatuses. Exemplary of such equipment and method can be discerned from U.S. Pat. No. 3,832,964, which is incorporated herein by reference. 
     A further object of the instant invention is to provide a method of producing laminated tubes in which a tubular body is formed of a barrier layer and an ethylene vinyl alcohol copolymer laminated thereto; the laminated tube body is then located on a forming member in adjacency to a barrier member also positioned thereon. 
     Other objects and advantages of the invention will become more apparent as the description proceeds. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings wherein like numerals are employed to designate like parts throughout the same: 
     FIG. 1 is a cross-sectional view of a fragmentary portion of a laminated substrate of the present invention. 
     FIG. 2 is a side elevational view of a collapsible dispensing container embodying the novel concepts of this invention, with portions of the body walls being broken away to more fully illustrate the laminated structure. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The thermoplastic of the present invention is ethylene vinyl alcohol copolymer. 
     Referring now first to FIG. 1 of the drawings, a substrate 10 is shown in cross-section whereby to reveal the components of the sandwich that go to make up the laminated configuration. 
     It will be seen that the bottommost layer 11 is an ethylene vinyl alcohol copolymer. The second layer 12 thereabove is an adhesive layer which joins the ethylene vinyl alcohol copolymer layer 11 with third layer 13 which is a metal foil such as aluminum foil. The fourth layer 14 is another adhesive that adhesively secures the other surface of the metal foil layer 13 to a paper layer 15. The topmost layer 16 is ethylene vinyl alcohol copolymer. 
     The ethylene vinyl alcohol copolymer is particularly useful because it has very low flavor absorption characteristics as can be seen from the following tables where ethylene vinyl alcohol copolymer is compared with polyethylene where the thicknesses of the layers or coating are the same: 
     
                       TABLE I______________________________________Flavor Content of Dentifricein Contact with Polymers*          DentifricePolymer        Flavor Concentration (%)**______________________________________None (control) 100Ethylene vinyl alcohol          100EF-F (Kurary)Low Density polyethylene          15-19Surlyn 1707    10-14Surlyn 1706    5-9Surlyn 1605    5-9______________________________________ *Fifteen minute contact time at 90° F. **Relative to control in which no polymer was in contact with the dentifrice; the greater the flavor concentration the more the inert polymer 
    
     
                       TABLE II______________________________________Polymer Absorption of Neat Flavor Oil(2 Week Total Immersion)Polymer          Weight Increase (%)______________________________________Ethylene vinyl alcohol            0.8EF-F (Kuraray)Low density polyethylene            10(USI)Surlyn 1707 (DuPont)            15Surlyn 1605 (DuPont)            19Surlyn 1706 (DuPont)            24______________________________________ 
    
     
                       TABLE III______________________________________Relative Flavor Absorption by PolymersAfter Contact with Dentifrice for 3 Months*             Flavor AbsorbedPolymer           by Polymer**______________________________________Ethylene vinyl alcohol              12EF-F (Kuraray)Low density polyethylene             100 ± 13(USI)Surlyn 1706 (DuPont)              893Surlyn 1707 (DuPont)             1557Surlyn 1605 (DuPont)             1672______________________________________ *at 90° F. **Relative to low density polyethylene which was arbitrarily set at 100; the lower the number the less flavor absorbed. 
    
     It is contemplated that within the purview of the invention the adhesives may be a copolymer of ethylene and acrylic acid or methacrylic acid, or sodium or zinc salts thereof in a diluent system. 
     The metal foil may be preferably aluminum foil. 
     The paper layer is desirably a kraft paper. 
     The thickness range of each of the layers is as follows: 
     Ethylene vinyl alcohol copolymer layer 11 0.5 mils to 3.0 mils, preferably 1.0 mils. 
     Adhesive layer 12--sufficient to assure adherence 
     Metal foil layer 13--0.5 mils to 2.0 mils, preferably 1.0 mils. 
     Adhesive layer 14--sufficient to assure adherence 
     Paper layer 15--1.5 mils to 2.5 mils, preferably 2.0 mils. 
     Ethylene vinyl alcohol copolymer layer 16--3.5 mils to 5.0 mils, preferably 4.0 mils. 
     The topmost ethylene vinyl alcohol copolymer layer 16 adheres to the paper layer 15 by means of the application of sufficient heat and pressure to the substrate. In the event the application of heat and pressure is not appropriate a suitable adhesive is to be employed. 
     FIG. 2 is an example of the laminated structure of a collapsible container with the layers being demonstrated as in FIG. 1 with layer 11 being inner most and the other layer being of the same materials and in the same order as shown. 
     It is believed manifest from the foregoing that applicant has provided a collapsible container structure which substantially reduces the problems heretofore unsolved by the prior art. The laminated substrate and laminated shoulder piece 20 substantially eliminates product permeation and oxygen absorption. 
     The outer layer of an ethylene vinyl alcohol copolymer is a thermoplastic capable of fusion during a side seaming step and granting adequate protection to the paper and metallic foil interlayer. The art of seaming of a collapsible dentifrice tube of the general type herein disclosed can be seen in U.S. Pat. No. 3,295,725, incorporated herein by reference. However, the outer layer of ethylene vinyl alcohol copolymer and paper may be eliminated if the foil barrier is of sufficient thickness to resist damage, and by flowing a thermoplastic material into the overlap side seam during the sealing thereof when such a system is employed. 
     Further, the outer layer may be paper in a three-ply laminate formed of paper, foil and an ethylene vinyl alcohol copolymer as described. As the outermost and innermost layers are preferably the same, the folded edges of the tube produced from the substrate is conveniently heat bonded. A suitable adhesive can be used when heat bonding is not possible. This modification is in addition to the aformentioned four-ply laminate comprised of from outside to in, ethylene vinyl alcohol copolymer, paper, foil and ethylene vinyl alcohol copolymer. It is contemplated that suitable adhesives will be employed between the laminae whenever necessary. 
     Ethylene vinyl alcohol copolymers can be employed for the shoulder piece, cap, neck, piston and in the construction of dispensing valves for other dentifrice particularly in conjunction with the interior portions dispensers, exposed to the contained dentifrice, and, again, where required, compatible adhesives would naturally be employed. 
     Additionally when cast as a film on the interior surfaces of fiber drums used for the storage of flavored dentifrice, the material will retard flavor loss into the drums, thereby extending storage life. 
     Various modifications of the invention have been disclosed herein, and these and other changes can of course be effected without departing from the novel concepts of the instant contribution.