Abstract:
A method for manufacturing a plastic container which is substantially impervious to oxygen comprising the steps of corona treating a raw stock of polypropylene film; coating a first side of said raw stock of polypropylene film with an aqueous oxygen barrier solution; placing the film in an injection mold; and injection molding a polypropylene material into the mold to bring the polypropylene material in direct contact with the aqueous oxygen barrier solution. 
     An oxygen resistant container has a floor. A sidewall extends from the floor. An oxygen barrier material is disposed on a film. The film is disposed on the container so that the oxygen barrier material is in direct contact with the sidewall. The oxygen barrier material is one of a nano-silicate and a nano-clay.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention is related to molded plastic containers, and in particular, creating a molded plastic container which also acts as an oxygen barrier to products contained therein. 
         [0002]    It is well known in the art that plastic pails and containers are used for the storing of perishable items. The shelf life of perishable items such as foods, medicines and paints are affected by temperature, humidity and most importantly oxidation. In order to improve shelf life, many approaches have been taken including the formation of airtight seals, the use of better plastic materials, the use of plastic and foil seals across the opening of the container below the cap or lid of containers and even the use of labels about the container to prevent or slow down the rate at which the perishable item is exposed to oxygen. These prior art structures have been satisfactory, however, the plastic materials used for molding of containers still allow oxygen to pass there through and conventional labels do not envelope enough of the container surface to form an effective barrier. Therefore, over time, oxygen passes through the walls of injection, thermoformed and blow molded containers. 
         [0003]    It is known from the prior art to put oxygen barriers into the interior structure of a laminate and to affix the laminate to the container. It is also known to injection mold an oxygen barrier material, such as a second plastic within the container wall. Although these structures may prove satisfactory, they require complex structures and/or molding techniques. They also require extra materials as the laminate requires extra layers between which to sandwich the oxygen barrier. The molding technique requires molding a cavity to the oxygen barrier material within the container wall, and then molding the second material into the cavity. 
         [0004]    Accordingly, a structure and methodology for creating the containers which increases the impermeability of a molded plastic container wall, floor or lid to oxygen without significantly increasing cost, materials or complex is desired. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    A container is molded from a plastic. The container has at least a floor and a wall extending therefrom. A film is coated with an oxygen barrier solution and then applied to the molded container. The film may be formed of a multilayer structure including a deposit of nano-particles sprayed on at least one side of the film substrate. The film is applied to the container during an injection molding of the container by an injection mold label process so that when applied, the oxygen barrier material is in direct facing relation with a wall of the container. In a preferred embodiment, the nano-particles are silicate based and the film is corona charge treated. 
     
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         [0006]      FIG. 1  is a perspective partial exploded view of a container formed in accordance with the invention; 
           [0007]      FIG. 2  is a sectional view of the label constructed in accordance with the invention; 
           [0008]      FIG. 3  is a schematic diagram of a first step in the process for injection molding an oxygen barrier about a container in accordance with the invention; 
           [0009]      FIG. 4A  is a sectional view of an exemplary mold utilized for the application of an oxygen barrier to the container in accordance with the invention; 
           [0010]      FIG. 4B  is an enlarged view of the groove area of  FIG. 4 ; 
           [0011]      FIGS. 5A ,  5 B are before and after schematic diagrams showing the behavior of the bottom oxygen barrier film during the molding process in accordance with the invention; 
           [0012]      FIG. 6  is a partial sectional view of a container formed utilizing the mold of  FIG. 4  in accordance with the invention; 
           [0013]      FIG. 7A  is an exploded schematic view of a container formed prior to injection molding in accordance with another embodiment of the invention; and 
           [0014]      FIG. 7B  is a schematic view of a container after injection molding in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    As is known in the art, and is shown in  FIG. 1 , a container  10  constructed in accordance with the invention has enclosing side wall  12  and a floor  18  to provide a container having one open end  20 . A lid  22  may be fitted across open end  22  to close the container sealing contents therein. 
         [0016]    During manufacture to create container  10 , a shot of plastic, such as polypropylene material by way of non-limiting example, is injection molded to form container  10 , and/or lid  22 . 
         [0017]    Apart from the manufacture of the container itself, a thin film barrier  100  is manufactured. The label may be a multilayer structure. In a preferred embodiment, thin film  100  is applied as an in mold label. In a preferred example, as shown in  FIG. 2 , thin film  100  includes a first layer  102  which serves as a base layer. A tie layer  104  is disposed between first layer  102  and a gas barrier layer  106 . A second tie layer  108  is disposed between the gas barrier layer  106  and an outer layer  110 . At least one layer of the film is coated with, formed with, or includes within its structure an oxygen barrier solution to form oxygen barrier layer  112 . Oxygen barrier layer  112  is internal to the structure of thin film barrier  100   
         [0018]    Thin film barrier  100  is applied to sidewall  12 . A bottom film  14 , having a similar structure to film  100  is applied to bottom  18 . 
         [0019]    In a preferred embodiment, the barrier solution is formed from a nano-silicate solution or a nano-clay formed as an aqueous suspension as known from NanoLok PT MM manufactured by InMat Inc. A porous cylinder is used to dispose the aqueous nano-solution across at least one of the interior surface (facing towards layer  110 ) of first layer  102  or outer layer  110  of the film  100  by way of nonlimiting example. The barrier solution may also be disposed between layer  102  and  110  and an internally adjacent layer. The thickness of the nano-solution layer  112  is controlled by the diameter of the pores within the cylinder and the internal pressure of the cylinder. Other application methods such as cascade coating may be used. In a preferred embodiment, the thickness of the aqueous solution layer  112  is less than or equal to 3 microns. 
         [0020]    In a preferred, nonlimiting example, the first layer  102  and outer layer  110  are formed as plastic films, and more preferably polypropylene. However, first layer  102  may be formed of treated or untreated paper, foil or the like. 
         [0021]    The gas barrier layer  106  (preferably an oxygen barrier layer) may be formed from an EVOH. Layer  106  of thin film  100  could be replaced or coupled with PVDC (polyvinylidene chloride), aluminum, PVOH (polyvinyl alcohol), aluminum oxide, silicium oxide, a nano-clay or nano-crystalline cellulose alone or in any combination thereof. The properties of the various layers may enable film  100  to act as a moisture and/or light barrier. Furthermore, when thin film  100  is applied to an outer surface of container  10  such as sidewall  12  and bottom  18  as film  14 , in sections  202 ,  204 , thin film  100  may be printed upon with ink to form a label without affecting the use of the barrier&#39;s nano-particle layer  112 . The film may also be provided on the interior structure of container  10  such as the interior of sidewall  12 , floor  18  or lid  22 . 
         [0022]    Reference is now made to  FIGS. 7A ,  7 B wherein like numerals are utilized to indicate like structure, the primary difference between the embodiment of  FIG. 7B  and the embodiment of  FIGS. 2 ,  6  is that the barrier coating is applied directly between a film and the plastic container. 
         [0023]    In this embodiment, film barrier  600  includes a film substrate  504 . In a preferred embodiment, film substrate  504  is polypropylene. A first side of film  504  is coated with an oxygen barrier coating  502 . As with the previous embodiments, barrier coating  502  may be a nano-solution such as a nano-silicate solution or a nano-clay formed as an aqueous solution as known from NanoLok PT MM manufactured by InMat Inc. Artwork  506  such as indicia for labeling may be disposed on the opposed side of film substrate  504 . Additionally, as is known in the art as shown from the embodiment  FIG. 2 , additional oxygen barrier layers or outer layers of material may also be disposed on polypropylene film  504 . 
         [0024]    The indicia  506  may be provided as a layer of an ultraviolet primer, an ultraviolet ink and an aqueous top coat. 
         [0025]    The film barrier  500  is then affixed so that the oxygen barrier layer  502  is placed in facing relationship to what will become wall  12  of a container  10  during an injection mold labeling process (see  FIG. 7B ). In effect, the base layer  102  of the embodiment of  FIG. 2  and the oxygen barrier layer  106  have been transposed so that barrier coating  502  after injection molding is in direct contact with polypropylene container  12  as shown in  FIG. 7B . 
         [0026]    To facilitate the structure, in a preferred embodiment, film  504  is formed from a standard polypropylene such as ETH-57 manufactured by Treofan Group which is then corona treated to change the surface tension enabling the nano-silicate barrier coating  502  to better adhere to the polypropylene forming film  504 . During the process, by way of nonlimiting example, a  1  mil film is subjected to up to 10,000 W of current as a function of line speed. In one embodiment, 6,000 W is applied to a film being fed at 400 ft/min. 
         [0027]    Furthermore, barrier coating  502  may contain adhesion promoters such as the formulation known from NanoLok EXC 1007V-1 to adhere to the polypropylene container during the injection mold labeling process. 
         [0028]    In order to maximize the oxygen barrier nature of the present invention, it is preferred to encapsulate, i.e. substantially entirely cover the container with the barrier with any of the films discussed above so that a film covering at the bottom and about the sidewall of the container is desired. However, prior art molding processes resulted in the interference between the bottom film and the side film in the injection mold label formation process. 
         [0029]    In accordance with a preferred embodiment of the present invention, a bottom film  204  and a sidewall film  202  are carried by a formed mandrel  300  as shown in  FIG. 3 . Mandrel  300  includes a concave bottom portion  302 . Bottom film  204  has an area greater than the bottom surface of bottom portion  302 . Side film  202 , which is a wrap around film (in that it substantially wraps around the entire circumference of mandrel  300 ), has a length greater than mandrel  300 . 
         [0030]    Bottom film  204  also has an area greater than an area of container bottom  10 . Side film  202  has a length greater than a length of sidewall  12 . In this way, bottom film  204  extends beyond the bottom  18  of container  10  by an overhang portion  204   a.  Similarly, side film  202  overhangs container wall  12  by an overhang portion  202   a.  In order to prevent interference between bottom film  204  and wrap around film  202  during the molding process, a bottom surface  302  of mandrel  300  is formed at least in part with a concave shape to arc bottom film  204  to take up any slack and prevent interference between wrap around film  202  and bottom film  204 . Each of wrap around film  202  and bottom film  204  are held to mandrel  300  by a vacuum pressure at mandrel  300  and/or a static charge of between 10 and 12 K volts. 
         [0031]    In a next step, mandrel  300  with films  202 ,  204  thereon are inserted into a mold steel cavity  400  (see  FIG. 4A ). Mold steel cavity  400  is formed with a groove  402  which extends below a floor  404  of mold steel cavity  400  much like the heel of a boot. Groove  402  receives the excess length of respective overhangs  202   a,    204   a  of both label  202  and label  204  therein. 
         [0032]    As seen in  FIG. 4A , a molded steel core  500  is inserted within mold steel cavity  400  with a gap h between the two as known in the art, to provide space for receiving the plastic shot during the molding process. The width of gap h being a function of the thickness of the desired container. 
         [0033]    As seen in  FIG. 4B , a gap j exists between an edge  204   c  of bottom film  204  and a planer surface of side label  202 . The gap is a function of the minimum distance required to separate a bottom label  204  having a section  204   a  sufficiently sized to cover an inner surface of the foot  30  (extend sufficiently across groove  402 ) without contacting side label  202 . In a preferred embodiment, gap j is about 0.005 inches. It should be noted that side label  202  is sufficiently longer than a side wall of container  10  so as to have sufficient material to cover the bottom and outside surface of foot  30 , all of the sidewall of container  10  and, in a preferred nonlimiting example, any overhanging lip  32  (see  FIG. 6 ). 
         [0034]    In another embodiment, a single film diper label may be used. A five faced diper label positioned at the bottom of mold  400  and used in an injection mold process would still cover 99.1% of the outer container surface. However, the preferred embodiment is the two label method which covers more than 99.4% of the surface. 
         [0035]    Because of the level of static charge, air flow from the mandrel forces the label to the mold and the fact that the mold is made out of steel, when mandrel  300  is inserted into mold cavity  400 , the attraction as a result of the static charge plus the air flow, between either of label  202 ,  204  and mold cavity  400  is greater than the attraction between either of film  202 ,  204  and mandrel  300 . Accordingly, once in sufficient proximity to mold cavity  400 , the labels  202 ,  204  are released from mandrel  300  and are held in place by the respective wall  402  and floor  404  of cavity  400 . 
         [0036]    As seen in  FIGS. 5A ,  5 B, film  204  is sufficiently rigid to maintain its shape across groove  402  ( FIG. 5A ). However, during the injection molding process, the plastic shot, as it takes form, moves into groove  402  and forces overhang  204   a  of bottom film  204  into groove  402  and in fact, pinned against a wall  402  by the plastic as it attaches to the plastic. Similarly, the shot pushes overhang  202   a  of film  202  against a floor  404  of groove  402  between the shot and the floor. 
         [0037]    As can be seen from  FIG. 6  in which a container molded from cavity  400  and core  500  is provided, because bottom label  204  has an area greater than the area of container bottom  18  including an overhang  204   a  sufficient to cover an inside surface of foot  30  of container  10 , and side label  202  encircles sidewall  12  of container  10  and has a length greater than sidewall  12  sufficient to extend at least partially into groove  402  and cover a bottom and side of foot  30 , and labels  202  and  204  are in close proximity at overhangs  204   a,    202   a,  to ensure that the encapsulation of plastic container  10  is optimized without interfering with each other. Also label  202  extends at the top of the container (the lip) to optimize covering lip  32 . 
         [0038]    It is understood that films  202 ,  204  may have the structure of film  100 . In another embodiment of the invention, a barrier solution is formed in a liquid or gel state. In a preferred embodiment, the solution is a nano-clay formed of an aqueous suspension of nano-dispersed silicate and polyester resin such as NanoLok PT MM manufactured by InMat Inc. The barrier may also be a resin which cures about the container. 
         [0039]    The aqueous gel may be applied as discussed above in connection with film  100  to an inner or outer surface of any of sidewall  12  or floor  18  by way of a dipping process, vapor deposition, an aqueous spray, or a fine particulate atomized spray. In a preferred embodiment, container  10  may be heat treated prior to the deposition of the aqueous barrier solution onto a surface of container  10 . 
         [0040]    Lid  22  may be treated in the same way as the body of the container to enhance the oxygen barrier properties of lid  22 . 
         [0041]    In an alternative embodiment, the polypropylene stock material may be treated with the aqueous barrier solution prior to injection molding to form container  10 . The raw stock of material such as polypropylene material may be dipped in a liquid or gel state of the barrier material, sprayed with the barrier material, or subject to vapor deposition of the barrier material or an atomized version of the solution. In this way, the injection molded lid  22  and/or container  10  are formed with an inherent oxygen barrier. 
         [0042]    While this invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention encompassed by the appended claims.