Abstract:
A heat seal blister package having an improved moisture vapor transmission barrier hindering penetration of moisture into the blister package from the surrounding environment to support and protect a product therewithin, and a method for forming same. The blister package includes a substantially paperboard substrate, a coating having moisture vapor transmission barrier properties and heat seal capabilities and a plastic blister attached to at least one side of the substrate over a coated portion of the substrate by a heat seal, to create an enclosed pocket isolated from the surrounding environment, in which to house a product. The coating imparts a moisture vapor transmission barrier to the paperboard substrate to reduce penetration of moisture through the substrate, while simultaneously imparting heat sealing capabilities to the coated portion of the substrate to make the coated portion of the substrate susceptible to a heat seal.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to a heat seal blister package for housing a product and, more particularly, to a heat seal blister package having improved moisture vapor transmission properties to house a product which is moisture sensitive. 
     2. Background Art 
     Blister cards and blister packages have been known in the art for many years. Typically, a clear plastic blister made of PVC or other similar material is adhered to a paperboard card or backing panel to form an enclosed pocket to house a product therein. The plastic blister provides an airtight seal to protect the product, while allowing a potential consumer to view the product through the clear plastic blister. The paperboard card or backing panel typically provides an opportunity for labeling, identifying or advertising the product. 
     It has been a common practice in the art to attach the plastic blister to the backing card via a heat seal. In particular, heat seal coatings, such as polyurethane-based coatings, are typically used to coat one side of the backing card. The heat seal polyurethane coatings are typically applied to the backing card in an off-set printing process. Upon coating the backing card, the plastic blister is then applied to the card with heat to bond the plastic blister to the underlying backing card. 
     Although these and other prior art heat seal blister packages employing a heat activated sealing coat, including those polyurethane-based heat seal coats, have worked well for the packaging of a wide variety of articles, conventional heat seal coatings can often provide little or no barrier to prevent or impede the transmission of moisture vapor from the surrounding environment through the paperboard backing card and into the enclosed pocket where the product is typically housed. While the plastic blister usually forms an impermeable barrier to moisture transmission, moisture from the surrounding environment can often penetrate through the paperboard backing card. 
     Thus, although moisture vapor transmission barrier properties may be unimportant for the housing of certain products in blister packages, such as inedible ones, or products not affected by exposure to humidity, etc., other products are moisture sensitive. For instance, moisture vapor penetration into the blister package may be particularly troublesome in the context of edible products, which can be highly moisture sensitive. For these and other types of moisture-sensitive products, the penetration of moisture vapor through the paperboard backing card can lead to degradation or destruction of the product contained within the blister package. 
     Moreover, coatings which possess moisture vapor transmission barrier properties are also known. In particular, these coatings have been employed in paperboard products to prevent moisture infiltration into various moisture sensitive products. For example, coatings having moisture vapor barrier properties have been used to coat detergent boxes, as moisture vapor penetration into powder detergent has been known to cause clumping or other degradation of the detergent. However, these moisture vapor transmission barrier coatings are not known to have been used in a context of heat sealing plastic to paperboard—particularly in the environment of forming a blister package. 
     Accordingly, it is desirable to provide a blister package in which the coating applied to the paperboard card or backing panel possesses not only the capability of forming a heat seal bond with a plastic blister, but also the moisture vapor transmission barrier properties to hinder penetration of moisture vapor through the backing card and into the interior of the blister package. 
     It is likewise desirable to provide a process for forming a heat seal blister package having improved moisture vapor transmission barrier properties. As part of this process, it is desirable to employ a rotogravure process for application of the heat seal coating, to closely control the weight range of the coating as applied to the paperboard backing card. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a heat seal blister package having an improved moisture vapor transmission barrier hindering penetration of moisture into the blister package from the surrounding environment to support and protect a product therewithin. The blister package includes a substantially paperboard substrate having a first side and a second side, a coating having moisture vapor transmission barrier properties and heat seal capabilities, and at least one plastic blister attached to the substantially paperboard substrate over a coated portion of the substantially paperboard substrate to create an enclosed pocket isolated from the surrounding environment in which to house a product. The plastic blister is preferably attached to the substantially paperboard substrate by a heat seal. The product is maintained in position between the blister and the substantially paperboard substrate, until the pocket is opened. 
     Preferably, the coating is applied to at least a portion of at least one of the first and second sides of the substantially paperboard substrate to, in turn, impart a moisture vapor transmission barrier to the substantially paperboard substrate to reduce transmission of moisture through the substantially paperboard substrate, while simultaneously imparting heat sealing capabilities to the coated portion of the substantially paperboard substrate to make the coated portion of the substantially paperboard substrate susceptible to a heat seal. 
     In one embodiment, the coating includes a vinylidene chloride polymer component. The coating preferably includes at least component selected from the group consisting of a vinylidene chloride polymer, a vinylidene dichloride polymer and a vinylidene chloride/vinylidene dichloride copolymer emulsion. In this embodiment, the coating may be predominant in a vinylidene chloride polymer selected from the same group consisting of a vinylidene chloride polymer, a vinylidene dichloride polymer and a vinylidene chloride/vinylidene dichloride copolymer emulsion. 
     In another embodiment, the coating further includes a wax component. In one particular embodiment, the coating includes approximately 95% by weight of a component selected from the group consisting of a vinylidene chloride polymer, a vinylidene dichloride polymer and a vinylidene chloride/vinylidene dichloride copolymer emulsion and approximately 5% by weight of a wax component. 
     In one particular embodiment, the coating includes approximately 80%–95% by weight of a vinylidene chloride/vinylidene dichloride copolymer emulsion and approximately 3%–10% by weight of wax component. In still another particular embodiment, the coating includes approximately 82.5%–87.5% by weight of a polyvinylidene dichloride/polyvinylidene chloride copolymer emulsion, approximately 3.0%–7.0% by weight paraffinic wax, approximately 5.0%–7.0% isopropyl alcohol and approximately 0.5%–1.0% by weight of a carboxylated amine. 
     The coating preferably has a weight ratio, as applied to the substantially paperboard substrate, ranging from approximately 0.75 lbs. dry weight coating/msf of the substantially paperboard substrate to approximately 1 lb. dry weight coating/msf of the substantially paperboard substrate. Once formed, the heat seal created between the plastic blister and the substantially paperboard substrate may be broken primarily by tearing fibers in the substantially paperboard substrate. 
     In one preferred embodiment, the plastic blister includes a tray portion and a flange portion surrounding at least a portion of the tray portion. The flange portion is preferably heat sealed to the underlying paperboard substrate. In an embodiment where the flange portion completely surrounds the tray portion, the flange portion is heat sealed to the substantially paperboard substrate to isolate and enclose the pocket between the substantially paperboard substrate and the tray portion of the plastic blister. 
     In another preferred embodiment, the plastic blister further includes a pull tab for breaking the seal between the at least one plastic blister and the substantially paperboard substrate. At least a portion of the pull tab is preferably, initially unaffixed to the substantially paperboard substrate, to allow easier access by a consumer. The pull tab may also include a dimple to help separate at least a portion of the pull tab from the substrate surface. 
     In a preferred embodiment, the portion of the substantially paperboard substrate positioned adjacent the enclosed pocket is substantially entirely covered with the coating, to provide a moisture vapor barrier preferably protecting the entirety of the paperboard substrate adjacent the enclosed pocket from moisture penetration. In one preferred embodiment, the side of the substantially paperboard substrate attached to the plastic blister is completely covered with the coating. It is preferred that a product housed within the pocket is positionable directly adjacent at least one coated portion of the substantially paperboard substrate. 
     The blister package may further include a sleeve or other outer packaging for housing the plastic blister after it is heat sealed to the substantially paperboard substrate. In one embodiment, the sleeve includes a window for viewing the contents of the blister package. 
     The present invention is also directed to a process for attaching a plastic blister to a substantially paperboard substrate to create a blister package having an improved moisture vapor transmission barrier hindering penetration of moisture into the blister package from the surrounding environment. The process includes the steps of providing a substantially paperboard substrate having at least one surface; applying a coating to at least a portion of the substantially paperboard substrate to impart a moisture vapor transmission barrier to said substantially paperboard substrate to reduce transmission of moisture through said substantially paperboard substrate, while simultaneously imparting heat sealing capabilities to the coated portion of the substantially paperboard substrate to make the coated portion of the substantially paperboard substrate susceptible to a heat seal; and heat sealing a plastic blister over a coated portion of the substantially paperboard substrate to create an enclosed pocket isolated from the surrounding environment in which to house a product. 
     In an embodiment, the step of applying a coating to at least a portion of the surface of the substantially paperboard substrate includes applying the coating on a gravure press. In one embodiment, the coating is applied to the substantially paperboard substrate in a weight ratio ranging from approximately 0.75 lbs. dry weight coating/msf of the substantially paperboard substrate to approximately 1 lb. dry weight coating/msf of the substantially paperboard substrate. 
     Also in an embodiment, the process further includes the step of cutting an oversized sheet or web of substantially paperboard substrate material into a plurality of substrate units—after applying the coating. Those smaller substrate units may be reduced in size even further to useable card blanks by a blanker station. 
     The process preferably further includes the step of heating the substantially paperboard substrate after applying the coating to assist in curing the coating onto the substantially paperboard substrate. Further, the process also may include the step of actively cooling the substantially paperboard substrate after the step of heating the substantially paperboard substrate to assist in curing the coating onto the substantially paperboard substrate. Cooling may be accomplished by passing the coated substrate over a chill roller. 
     In a preferred embodiment, the process includes the step of inserting a product between at least a portion of the plastic blister and at least a portion of the substantially paperboard substrate before the step of heat sealing the plastic blister to the substantially paperboard substrate to affect enclosure of the at least one product in the pocket of the blister package. The product may be positioned inside the plastic blister before the plastic blister is heat sealed to the substantially paperboard substrate to accomplish this purpose. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front elevational view of a blister package according to the present invention; 
         FIG. 2  is a left side elevational view of the blister package shown in  FIG. 1 ; 
         FIG. 3  is a perspective view of the blister package shown in  FIG. 1 ; 
         FIG. 4  is a front elevational view of an aperatured sleeve for housing a blister package; 
         FIG. 5  is a rear elevational view of the sleeve shown in  FIG. 4 ; 
         FIG. 6  is a side elevational view of the sleeve shown in  FIG. 4 ; 
         FIG. 7  is a perspective view of the sleeve shown in  FIG. 4 ; 
         FIG. 8  is a schematic view of a process for heat sealing a plastic blister to a substantially paperboard substrate to create a blister package having an improved moisture vapor transmission barrier; and 
         FIG. 9  is a block diagram schematic of the process shown in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While this invention is susceptible of embodiment in many different forms, there are shown in the drawings, and will be described in detail, several specific embodiments with the understanding that the present disclosure is to be considered as an exemplification of the principals of the invention and is not intended to limit the invention to the embodiments illustrated. 
     Blister package  20  is shown in  FIGS. 1–3  as comprising substantially paperboard card  22  and plastic blister  24 . At the outset, it must be noted that while card  22  is shown as having a substantially square configuration, card  22  may take any desired configuration which may be used in conjunction with a given blister, which also may take any desired configuration. Further, while card  22  is shown in the drawings as a single, two-sided piece of paperboard, the card may comprise any substantially paperboard substrate taking any number of shapes, dimensions or sizes. Indeed, the substantially paperboard substrate may comprise an envelope, a box, or any other object which contains a substantially paperboard surface. Moreover, while card  22  will be described as having a substantially paperboard composition, it is likewise contemplated that card may include other materials or sections, as long as at least a portion of the card is fabricated from paperboard. Throughout this description and the drawings, like parts will be designated by like reference numerals. 
     Card  22  includes blister side  30 , back side  32  and coating  34 . Once again, those with ordinary skill in the art with the present disclosure before them will appreciate that card  22  is one of many possible substrates; however, the present invention will be described relative to the card shown. Coating  34  covers at least a portion of one side of card  22 , and is shown as preferably covering the entirety of blister side  30 . Complete coverage of the blister side of card  22  ensures that plastic blister  24  may be sealed to any portion of the card, in any desired orientation, without specifically aligning the plastic blister with a particular coated area. Further, complete coverage likewise ensures that the entirety of the blister pocket, described below, will be adjacent to and protected from infiltration of moisture vapor which penetrates through unprotected areas of card  22 . 
     Of course, it is also contemplated that coating  34  may be applied only to select areas of card  22 , limited to those specific contact areas beneath blister  24 . However, coating  34  is preferably applied onto at least the entirety of card  22  proximate any portion of blister  24 , to ensure that the improved moisture vapor transmission barrier properties hinder penetration of moisture into the pocket of the blister package, and to protect the contents of that pocket from the surrounding environment. 
     Coating  34  may comprise any coating which has moisture vapor transmission barrier properties, while simultaneously possessing heat seal capabilities such that blister  24  may be bonded to card  22  through a heat seal. In particular, vinylidene chloride polymer-based coatings have been found to be effective in facilitating a strong heat seal between card  22  and plastic blister  24 , while substantially blocking moisture vapor transmission through the card. Such coatings may include a polyvinylidene chloride polymer, a polyvinylidene dichloride polymer, or co-polymer combinations thereof. Moreover, coating  34  may also include a wax component, such as paraffin wax. The wax component is believed to provide the coating with a non-stick property, to prevent the cards from sticking to one another during the manufacturing process. Notably, the wax component may not be needed in the coating formulation, depending on the blister package manufacturing process. 
     In one embodiment, the coating includes approximately 80%–95% by weight of a vinylidene chloride and/or vinylidene dichloride polymer component and approximately 3%–10% by weight of wax component. One such coating includes approximately 82.5%–87.5% by weight of a polyvinylidene dichloride/polyvinylidene chloride copolymer emulsion, approximately 3.0%–7.0% by weight paraffinic wax, approximately 5.0%–7.0% isopropyl alcohol and approximately 0.5%–1.0% by weight of a carboxylated amine. Suitable coatings are readily commercially available from a variety of sources, including Sun Chemical Corporation of Fort Lee, N.J. and Flint Ink Corporation of Ann Arbor, Mich. 
     Saran resin-based coatings manufactured by Dow Chemical Company are also contemplated for use with the present invention. The Saran coatings can also be mixed with a wax component. For example, the Saran component and the wax component may be mixed in a ratio of approximately 95 wt % Saran, and approximately 5 wt % of the wax component. An acceptable wax component is paraffinic wax. 
     Coating  34  is preferably applied to card  22  in a weight range of approximately 0.75 lbs. of dry weight coating/msf (thousand square feet of substrate) to approximately 1 lb. of dry weight coating/msf of substrate. Notably, while these weight ranges have been found to be suitable to coat card  22  shown and described, other weight ranges of the coating are likewise contemplated, depending on substrate thickness and construction. At this coating weight, coating  34  is typically less than a mil thick, although thickness may be varied according to the thickness of card  22  or other application surface. 
     Other coatings with a combination of moisture vapor transmission barrier properties and heat seal capabilities are likewise contemplated for use in the present invention as would be know by those with ordinary skill in the art with the present disclosure before them. Likewise, it is also contemplated that other films or substances outside of solvent-based or water-based coatings may be used to coat card  22 . For instance, a low-density polyethylene film may impart heat seal capabilities, while also functioning as a moisture vapor barrier. In particular, molten low-density polyethylene may be applied, such as by polyextruding, onto the card or other paperboard substrate, as would be known by those with ordinary skill in the art with the present disclosure before them. Indeed, other films may also be used. 
     Plastic blister  24  is shown in  FIGS. 1–3  as including tray portion  36 , flange portion  38  and pull tab  40 . Blister  24  is preferably made from a PVC plastic, thus rendering the blister clear. This allows a consumer to view a product contained in blister package  20  through clear blister  24 . Flange portion  38  of blister  24  is heat sealed to card  22 , thus forming a sealed ring around tray portion  36 , which extends outward from flange portion  38  to provide an enclosed, impermeable pocket  43 . Thus, as can be seen from  FIG. 1 , a continuous heat seal surrounds tray portion  36  of blister  24  to form pocket  43  between tray portion  36  of blister  24  and card  22 . Preferably, the heat seal bond formed between blister  24  and card  22  may only be broken by actually tearing the fiber of card  22 . This not only ensures impermeability of pocket  43 , but also shows evidence of tampering with blister package  20 . 
     Pull tab  40  is shown in  FIGS. 1–3  as extending from flange portion  38  of blister  24 . Pull tab  40  is not heat sealed to card  22 , thus leaving at least a portion of pull tab  40  unattached to card  22  to allow a consumer to easily grasp blister  24  and tear the blister away from the card to access the contents of blister package  20 . Moreover, pull tab  40  further includes dimple  42 , which causes pull tab to stick up and extend from card  22 , as shown in  FIG. 2 . This allows easier access to pull tab  40  for removal of blister  24  from card  22  to access the contents of pocket  43 . 
     Inasmuch as plastic blister  24  is itself impermeable to moisture, and the heat seal between plastic blister  24  and card  22  is likewise impermeable to moisture, the only way for moisture to enter the interior of blister package  20  is through card  22 . Coating  34 , however, with its moisture vapor barrier properties, reduces the moisture vapor transmission rate through the card, and hinders moisture vapor transmission from the surrounding atmosphere through the card into pocket  43  of the blister package. This improved moisture vapor transmission barrier property is particularly critical when a product to be housed within blister package  20  is moisture sensitive. For instance, items such as gum, breath strips, foods or other moisture sensitive items may degrade when exposed to a certain amount of moisture, such as the moisture which may permeate through a paperboard backing card. Certain moisture sensitive items require housing in an enclosed environment which allows little or no penetration of moisture from the surrounding environment. 
     As is shown in  FIGS. 4–7 , blister package  20  may be used in combination with a sleeve, jacket or carrier, such as sleeve  26 . In the particular embodiment shown in  FIGS. 4–7 , sleeve  26  includes front panel  44 , back panel  46 , top panel  48 , bottom panel  50  and open sides  52  and  54 . Blister package  20  may be slid into or out of sleeve  26  through either of open sides  52  and  54 . Moreover, front panel  44  further includes aperture  56  for displaying the contents of blister package  20 . However, it is likewise contemplated that blister package  20  may be used alone, or in combination with other sleeves, carriers or packages, as would be known by those of ordinary skill in the art with the present disclosure before them. Certainly, sleeve  26  is just one example of a multitude of packages which can be used in combination with blister package  20 , or another blister package made in accordance with the principals of the present invention. Further, as shown in  FIG. 1 , blister  36  can include a raised flange formation at the top of the tray portion for precise capture, and fitment of the blister, within sleeve aperture  56 . This, in turn, restrains the blister package within the sleeve. 
     The present invention likewise includes a process for forming a heat sealed blister package having an improved moisture vapor transmission barrier which hinders penetration of moisture into the blister package from the surrounding environment. In particular, and is shown in  FIGS. 8 and 9 , process  60  begins with a roll of paperboard  62  having a desired thickness and composition. Paperboard roll  62  determines the ultimate thickness and composition of card  22 . 
     Roll  62  is initially unwound such that a single flat web  63  of paperboard substrate first enters a gravure press  66 . Gravure press  66  preferably includes at least one printing station  64  and at least one coating application station  67 . While printing station  64  is shown in  FIG. 8  in an exemplary manner as comprising a single station with one set of rollers, those with ordinary skill in the art with the present disclosure before them will recognize that any number of printing stations may be employed as may be required for a specific application. Any necessary printing onto web  63  is performed before the coating is applied. Notably, if printing onto web  63  is not required, printing station  64  may be excluded from process  60 . 
     Upon exiting printing station  64  portion of gravure press  66 , web  63  proceeds to coating station  67 . Gravure press  66  preferably employs a rotogravure process to apply the coating, with an application cylinder that applies coating  34  onto web  63 . Again, the single roller shown in  FIG. 8  is merely exemplary of the rotogravure coating process, as would be know by those with ordinary skill in the art with the present disclosure before them. As was mentioned above, the application cylinder applies coating  34  in an approximate range of about 0.75 lbs. of dry weight coating/msf of substrate to approximately 1 lb. of dry weight coating/msf of substrate. The weight range of the coating can be important as a coating applied with too little weight may lead to difficulties with achieving a satisfactory heat seal between the web and the plastic blister later in the process. Likewise, a coating applied with too much weight can result in not only added material cost, but also a longer drying time. In particular, coating  34  is preferably a water-based coating; thus larger quantities of coating contain more water, and require a longer drying time. Of course, those with ordinary skill in the art with the present disclosure before them will appreciate that variations in the weight range of the coating applied by the gravure press may be necessary depending on the type of paperboard used. 
     After coating  34  is applied to web  63 , coated web  65  is heated by heater  68 . Heater  68  heats the surface of coated web  65  to evaporate the solvents in coating  34 , to facilitate the process of curing the coating to the paperboard web. Heater  68  may take the form of a pass-through oven, although coated web  65  may be heated by other conventional heating mechanisms as would be known by those with ordinary skill in the art with the present disclosure before them. 
     From heater  68 , the coated web  65  is passed to a cooling station  70 , where coated web  65  is passed over chill roller  71 . Chill roller  71  is preferably filled a refrigerant to facilitate completion of the coating curing process. Of course, cooling mechanisms other that a chill roller may be used to cool the coated web after removal of solvents from the coating in process  60 , as would be known by those with ordinary skill in the art with the present disclosure before them. 
     Coated web  65  subsequently proceeds to cutting station  72 , where coated web  65  is preferably cut into sheets  73 . A blanker  74  preferably follows cutting station  72  to cut coated sheets  73  into specific coated cards  75  of a desirable size. Of course, it is also contemplated that coated web  65  may be cut into the desired card blanks directly by one machine or at one station. Moreover, it is likewise contemplated that the web may be cut into larger sheets before the coating press, depending on process equipment and specifications. 
     Finally, coated cards  75  are forwarded to blister machine  76 . There, plastic blisters  24  are heat sealed to a targeted area of coated cards  75  to form blister packages  20 . While the insertion of a product into the blister package can be accomplished in several ways, the product is preferably housed in blister  24  before heat sealing blister  24  to coated card  75 . Specifically, the product is placed in tray portion  36  of plastic blister  24  before card  22  is positioned over blister  24  for heat sealing. However, any technique whereby the product to be included inside of blister package  20  is inserted between plastic blister  24  and card  22  before effecting a heat seal between the card and the plastic blister may be used, as would be known by those with ordinary skill in the art with the present disclosure before them. 
     The foregoing description and drawings merely explain and illustrate the invention, and the invention is not limited thereto except insofar as the appended claims are so limited as those skilled in the art having the present disclosure before them will be able to make modifications and variations therein without departing from the scope of the invention.