Abstract:
Disclosed are dispensers for volatile materials. There is a container in the form of a well having an internal cavity, a volatile chemical positioned in the cavity, and a multi-layer covering enclosing the cavity. The covering has a lower section that is gas permeable, and an upper section removably bound to the lower section that is not. Embodiments include when (a) the lower section has a top layer that is a blend of high density polyethylene and low density polyethylene; the upper section has a bottom layer that has a mixture of polypropylene and a propylene/ethylene copolymer; and/or the lower section has an upper layer that has low density polyethylene but the lower section does not contain ultra low density polyethylene. These features help prevent premature leakage at the bond between the upper section and lower section.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to coverings over containers that house volatile chemicals. More particularly it relates to multi-layer membranes which can divide into a gas permeable laminate that is permanently affixed to the container, and a peel-off gas impermeable layer. 
     A variety of volatiles are contained in containers that have a membrane closure. The closure is in the form of a multi-layer film structure configured such that a lower membrane section of the structure is permeable to the volatile when the volatile is in a gas phase, and is permanently affixed to an otherwise open end of the container. There is also an upper membrane section of the closure that is a peel-off type lid that is impermeable to the gas volatile. Before the lid is peeled off, the volatile is trapped in the container. When the lid is peeled off the volatile (to the extent in a gas phase) can begin to escape for its intended purpose. See e.g. U.S. Pat. Nos. 4,055,672, 4,849,606, 5,518,790 and 6,722,578, and U.S. patent application publication 2007/0183932. 
     The volatile is often an air treatment chemical such as insect control agents (insecticides, insect repellents, insect growth regulators, insect attractants, synergists, etc.), fragrances and deodorizers. However, it may also be a use-up indicator chemical whose volatilization rate has been coordinated with the use-up rate of an air treatment chemical that is also being volatized. Often the volatilization occurs when the container is heated by an external source of heat. However, the volatization may optionally occur even though no additional heat is applied. 
     Regardless, such systems are typically designed so that volatilization shouldn&#39;t begin prior to the consumer placing the product in use. Hence, it is important that a peel-off structure used to initiate these products have a sufficient seal to the permeable membrane so as to effectively prevent premature leakage of the volatile during storage prior to use. This is made somewhat more complicated by the need for the bond between the upper and lower sections of the structure to be sufficiently weak so that the upper section can readily be pulled off it without disturbing the bond between the lower section and the container. 
     Further complicating matters is that such structures are sometimes exposed to temperatures over 50° C. (e.g. in a transport truck in the desert during the summer). This can degrade certain bonds. Moreover, it has been learned that some preferred volatiles, especially under elevated temperature conditions, can act to further degrade the bond between the peel-off portion and the permanent permeable portion. 
     Thus, a need exists for improved multi-layer film coverings for volatizing dispensers, particularly where the coverings have a reduced risk of leakage prior to use. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention provides dispensers for volatile materials. In one form there is a container in the form of a well having an internal cavity, a volatile chemical positioned in the cavity, and a multi-layer covering bound to the well. The covering has a lower/inward section that is sufficiently permeable to permit a gas form of the volatile chemical to pass through it, and an upper/outward section removably bound to the lower section that is essentially impermeable to the volatile chemical. When the upper section covers the lower section the volatile chemical can be trapped in the cavity, and when the upper section is peeled off from the lower section the volatile chemical can escape through the lower section out of the dispenser. 
     Three key embodiments of this structure are when: 
     (a) the lower section has a top layer that comprises a blend of high density polyethylene (often less than 50% by weight) and low density polyethylene; 
     (b) the upper section has a bottom layer that comprises a mixture of polypropylene and a propylene/ethylene copolymer (the latter preferably less than 30% by weight); and/or 
     (c) the lower section has an upper layer that comprises low density polyethylene, but the lower section does not contain ultra low density polyethylene. 
     For example, preferred embodiments are where lower section has a top layer that comprises at least 5% (alternatively at least 20%) high density polyethylene. However, in those situations where a heater is to be used, the top layer can even be as high as 100% high density polyethylene. 
     In one aspect the volatile chemical is stored as a gel in the cavity, and is in the form of an indicator chemical, and the lower section is heat sealed to the well. The volatile could be one of a variety of air treatment chemicals and/or use-up cue indicator chemicals. Further, it can be a solid material prior to heating. 
     It will be appreciated that this covering includes a lower section that is sufficiently permeable to permit a gas form of the volatile to pass through it (while preventing passage of solid or liquid form of the chemical), and an upper section removably bound to the lower section that is essentially impermeable to the volatile. The upper section can be in the form of a peel-off strip. 
     It has been discovered that by carefully controlling polyethylene densities in specified layers of membrane(s) and/or by adding a particular type of copolymer at a facing layer, the tendency of the bond between upper and lower sections of the covering to degrade during storage can be reduced. This can be achieved while also retaining desirable permeation characteristics and appropriate peel-off characteristics. These advantages are achieved at relatively low additional cost, and without introducing significant manufacturing complexity. 
     The foregoing and other advantages of the present invention will be apparent from the following description. In that description reference is made to the accompanying drawings which form a part thereof, and in which there is shown by way of illustration, and not limitation, preferred embodiments of the invention. Such embodiments do not necessarily represent the full scope of the invention, and reference should therefore be made to the claims herein for interpreting the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a prior art air treatment device that has positioned on its outward end a use-up indicator cartridge unit; 
         FIG. 2  is a sectional view through that indicator unit, showing how a peel-off layer can be removed so as to initiate volatilization of that use-up indicator unit; 
         FIG. 3  is a view similar to  FIG. 2 , but after some of the indicator chemical has volatized; 
         FIG. 4  is an enlarged detailed schematic view of a prior art multi-layer film covering used with a variety of dispensing devices; 
         FIG. 5  is a view similar to  FIG. 4 , but of a device of the present invention; 
         FIG. 6  is another view similar to  FIG. 4 , but of a second embodiment of the present invention; 
         FIG. 7  is another view similar to  FIG. 4 , but of a third embodiment of the present invention; 
         FIG. 8  is another view similar to  FIG. 4 , but of a fourth embodiment of the present invention; 
         FIG. 9  is another view similar to  FIG. 4 , but of a fifth embodiment of the present invention; 
         FIG. 10  is another view similar to  FIG. 4 , but of a sixth embodiment of the present invention; and 
         FIG. 11  is another view similar to  FIG. 4 , but of a seventh embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  depicts a prior art air treatment device generally  10 . It has a housing  12  that contains a heater (not shown) powered by contact prongs  14 . The heater heats an impregnated substrate (not shown) to drive an air treatment chemical (e.g. an insect repellent or fragrance) out radial sides of the housing. 
     Mounted at the front of the device is a table  18  that can be snapped onto a front wall  20  of the structure. That device had a compact indicator unit  100  removably positioned in a recess of the table  18 . The unit  100  had a cup-shaped storage well  102  for holding a volatile indicator chemical  104  in a cavity defined by the well. 
     A permeable multilayer membrane  106  encloses the well  102 . By “permeable” it is meant that a gas phase of the volatile indicator chemical  104  can pass through the membrane  106 , even though if in a solid or gel form (e.g. during storage) it cannot. 
     On top of membrane  106  is positioned a peel-off, essentially impermeable, multilayer membrane  108 . This positioning is via a heat seal  110  or other conventional adhesive bond. By tugging at a tab portion  112  of membrane  108  that membrane  108  can be pulled off membrane  106 , notwithstanding seal  110 , while leaving membrane  106  securely bound to the well  102  (e.g. at a radial flange of the well). By “essentially impermeable” it is meant that when the seal  110  is in place a gas form of the chemical  104  cannot readily diffuse through membrane  108 . 
     The nature of the membrane  106  and the chemical  104  are such that the rate of disappearance of the chemical  104  as to be coordinated with the rate of disappearance of the air treatment chemical inside the housing  12 . This therefore provides a visual cue regarding when the air treatment chemical needs to be replaced. This is facilitated by making the wall of the well  102  transparent. For example, the well  102  can be made from heat-resistant polyethylene terephthalate in a transparent form. The indicator chemical could be volatile hydrocarbons such as Norpar brand normal paraffins like NORPAR™ 12, NORPAR™ 13, and NORPAR™ 15, or Isopar brand isoparaffinic hydrocarbons like ISOPAR™ L and ISOPAR™ M, or mixtures thereof. 
     Various other refinements have been proposed for such devices in the prior art, such as providing snap arms  114  to facilitate mounting of the unit  100 . For further descriptions of prior art systems of this type see U.S. patent application publication 2007/0183932. 
     As seen in  FIG. 4 , a gas permeable, permanently affixed membrane  106  covers a storage well  102  having an air treatment chemical  104  therein. The membrane  106  has a low density polyethylene layer  106 A (preferably 0.5 mil thick), under which is positioned an ultra low density polyethylene layer  106 B (preferably 2.5 mil thick), under which is positioned another low density polyethylene layer  106 C (preferably 1.0 mil thick). 
     An essentially impermeable, removable/peel-off membrane  108  has a layer of polyester material  108 A (used for reverse printing), under which is positioned a low density polyethylene material  108 B (seal or adhesive layer), under which is positioned aluminum foil  108 C (creating impermeability to the solvent), under which is positioned a layer of polypropylene material  108 D, under which is positioned a cast form layer of polypropylene material  108 E. 
     Turning now to  FIGS. 5-11 , there are disclosed a number of embodiments of the present invention. To better understand the terms being used in describing these embodiments the following definitions should be understood: 
     (a) A “polyester material” means a polymer which contains the ester functional group in its main chain. Although there are many polyesters made by replacing part of the terephthalic acid in the polymerization process with another acid, or part of the diol with another diol to produce polyester copolymers, the term “polyester” as a specific material most commonly refers to polyethylene terephthalate (PET) type materials. Polyesters include naturally-occurring chemicals, such as in the cutin of plant cuticles, as well as synthetics. 
     (b) An “ultra low density polyethylene material” (“ULDPE”) means a form of polyethylene defined by a density range of 0.860 g/cm 3 —just below 0.90 g/cm 3 . 
     (c) A “linear low density polyethylene material” (“LLDPE”) means a form of polyethylene defined by a density range of 0.90 g/cm 3 —just below 0.94 g/cm 3 . 
     (d) A “low density polyethylene material” (“LDPE”) means a form of polyethylene defined by a density range of 0.91 g/cm 3 —just below 0.94 g/cm 3 . 
     (e) A “high density polyethylene material” (“HDPE”) means a form of polyethylene defined by a density range of 0.94 g/cm 3 -0.97 g/cm 3 . Particularly desirable HDPE for mixing with conventional LDPE (as will be described below) are the high density polyethylene resins UNIVAL DMDA-6200NT7, 8007NT7 and 9804NT7. 
     (f) See generally for other polyethylene definitions, A. Peacock, Handbook of Polyethylene: Structures, Properties, and Applications, page 16, Marcel Dekker, Inc., New York, (2000). 
     In a first form of the invention (as depicted in  FIG. 5 ) the impermeable membrane  108 , and the well  102  are as shown in  FIG. 4 . However, the permanent membrane  106  now is a single 3 mil thick layer of LDPE, as distinguished from a thicker structure of  FIG. 4 , but without use of ULDPE. 
       FIG. 6  depicts a structure identical to  FIG. 5 , albeit in  FIG. 6  we have made layer  108 E a layer that contains 75% polypropylene blended with 25% of a propylene/ethylene copolymer. Suitable propylene/ethylene copolymers for use in this invention include the VERSIFY® family of copolymers available from Dow Chemical. This helps the bond resist degradation during storage, yet does not unduly interfere with the peel-off nature of the bond. 
       FIG. 7  depicts a structure identical to  FIG. 6 , except that layer  108 E now is either: 
     (a) a layer that contains 50% polypropylene blended with 50% propylene/ethylene copolymer; or 
     (b) a layer that contains 25% polypropylene blended with 75% propylene/ethylene copolymer. 
     The layers  108 E in  FIGS. 6 and 7  are preferably 1 mil thick. It should be noted that the  FIG. 6  construction is much preferred as compared to the  FIG. 7  constructions. Less than 30% propylene/ethylene copolymer is preferred in the facing layer. 
     In the  FIG. 8  embodiment the membrane  108  is the same as in  FIG. 5 . However, here the membrane  106  is altered. The top layer  106 A is now a structure which is a 90% LDPE/10% HDPE blend layer  106 A approximately 3.0 mil thick. Positioned underneath that is a LDPE layer  106 B that is 1.0 mils thick. Surprisingly, the higher density at layer  106 A retards leakage, yet does not unduly affect permeation when desired. 
       FIG. 9  is identical to  FIG. 8 , albeit the layer  106 A of the permeable membrane  106  comprises a 50% LDPE/50% HDPE material, and is again 3.0 mil thick. Increasing HDPE levels retards leakage, and correspondingly reduces permeation rates of solvent through the permeable layer  106 . 
     In the  FIG. 10  embodiment both membranes  106  and  108  are modified somewhat from the  FIG. 5  structure. In this regard, the layer  106 A is now split into a somewhat thicker layer  106 A/ 106 B structure. The layer  106 A is normal blown film LDPE at 1.0 mil thick, and the layer  106 B is a cast film of LDPE that is 3.0 mil thick. 
     However, here the membrane  108  is analogous to a structure having only layers  108 A,  108 B and  108 C, except that the layer  108 C is now metalized PET at 0.92 mils thick. This is a metalized polyethylene terephthalate (PET) material. 
     The  FIG. 1  embodiment is identical to the  FIG. 10  one, except that the layer  108 B is now a more linear LLDPE, such as SABIC® LLDPE  118 N. 
     The membranes  106  and  108  of the invention may be manufactured by many of various methods common in the art of making polymeric membranes. In one process, the layers may be coextruded. See also U.S. Pat. No. 6,902,817 for various other techniques of producing multi-layer laminates. 
     The two membranes  106  and  108  may be brought together over the storage well  102  with a heated die being applied to form heat bonds that bond the membrane  106  to the well, and assist in holding membrane  108  to membrane  106 . 
     Test Results 
     The following table provides results of elevated temperature storage testing conducted at 54° C. for two weeks to illustrate the concepts of the present invention. A solvent mixture of hydrocarbons was stored in a well covered with varied combinations of permeable membranes covered by impermeable peel-off membranes. Leakage was evaluated after the two weeks. 
     
       
         
               
               
               
               
             
           
               
                   
               
               
                   
                   
                 Bottom Layer 
                 Passes 
               
               
                   
                 Top Layer Permeable 
                 Impermeable 
                 the Test 
               
               
                 Test Variable 
                 Membrane 
                 Membrane 
                 (Y/N) 
               
               
                   
               
             
             
               
                 Standard 
                 1 mil LDPE/1 mil 
                 1 mil PP 
                 No 
               
               
                   
                 ULDPE/1 mil LDPE 
               
               
                   
                 Blown Film 
               
               
                 1 
                 3 mil LDPE Cast Film 
                 1 mil 75% PP/25% 
                 Yes 
               
               
                   
                   
                 Versify 
               
               
                 2 
                 3 mil 50% LDPE/50% 
                 1 mil PP 
                 Yes 
               
               
                   
                 HDPE 
               
               
                 3 
                 3 mil 90% LDPE/10% 
                 1 mil PP 
                 Yes 
               
               
                   
                 HDPE 
               
               
                 4 
                 3 mil LDPE Cast Film 
                 92 ga MET PET/7# 
                 Yes 
               
               
                   
                   
                 LDPE 
               
               
                 5 
                 3 mil LLDPE Blown 
                 92 ga MET PET/7# 
                 Yes 
               
               
                   
                 Film 
                 LDPE 
               
               
                   
               
             
          
         
       
     
     While preferred embodiments of the present invention have been described above, it should be appreciated that the invention could be used in a variety of other embodiments. For example, membranes  106  and  108  may each have more or less layers, and varied thicknesses. Also, varied chemicals can be added to the layers to alter permeation rates (e.g. adding filler such as calcium carbonate or talc). 
     Thus, the principles of the present invention can be applied in a variety of other ways apart from those specifically noted herein and/or depicted in the drawings. Such other modifications may be made without departing from the spirit and scope of the invention. Thus, the claims (rather than just the preferred embodiments) should be reviewed in order to understand the full scope of the invention. 
     INDUSTRIAL APPLICABILITY 
     Disclosed are improved multi-layer covering structures for use in controlling volatilization of air treatment chemicals and associated use-up indicators, which have reduced risk of premature leakage.