Abstract:
A method of attaching a gasket to a plastic surface includes providing a plastic material having a surface; applying sufficient heat to the surface to melt the surface while other portions of the plastic material remain solid; providing a liquid gasket material on the heated surface while the heated surface is melted; and allowing the liquid gasket material and the surface to cool so the gasket is welded to the plastic material.

Description:
RELATED APPLICATIONS AND PRIORITY 
     This application claims priority of PCT/US2008/071369, filed 28 Jul. 2008 which claims priority of Provisional Patent Application 60/952,397, filed 27 Jul. 2007, both of which are incorporated herein by reference. 
    
    
     FIELD 
     This patent application generally relates to a bond between plastic closures and sealing gaskets. More particularly, it relates to a system for improving bonding between plastic of the closure and the gasket. 
     BACKGROUND 
     Synthetic rubber compounds have been used to form a gasket inside a plastic closure for a container. The gasket has improved the seal between the closure and the container. The seal has been used to prevent leakage of the product out of the container and to prevent contamination of the product from outside air coming into the container. 
     The synthetic rubber compounds have been heated to a predetermined melting temperature before applying the molten synthetic rubber to the closure. In some prior systems the synthetic rubber has been mixed with an inert gas, such as nitrogen, to form a foamed gasket upon application to the closure. A Nordson Foam Melt model No. FM200 is an example of such a synthetic rubber and nitrogen gas applicator. 
     One suitable synthetic rubber compound that has been used is Foremelt 517/C, available from Foreco srl. (Marcallo Con Casone, Italy). Foremelt 517/C has a suggested application temperature of 175-180° Celsius. 
     The application has typically involved rotating the closure around a stationary applicator gun. The liquid synthetic rubber compound is applied from the gun to the closure. The closure is usually close to room temperature (20° C.) while the liquid synthetic rubber compound is applied. The synthetic rubber compound material may include a gas, such as nitrogen, to cause it to later become a foam. Because the closure is rotating during application of the liquid melted synthetic rubber compound, a ring shaped bead of foamed gasket forms all around the inside of the closure. Since the Foremelt 517/C is cold curing no further curing steps have been required, such as with a heated oven or microwave type oven. The closure with its gasket has then been applied to the container with the gasket providing the seal between closure and container. 
     However, product leakage has often been caused by inadequate bonding of the gasket to the closure. For food and beverage items, a gasket that separates from the closure after opening has not been acceptable. In some cases the gasket has fallen back into the container. In larger water cooler bottles gaskets with poor adhesion have shifted to one side allowing for leakage. In pressurized products, such as carbonated beverages, the pressurized gas has crept between the gasket and closure causing further gasket separation, escape of gas, and product spoilage. Thus, further improvement has been desired to more securely bond the gasket to the closure, and this solution is provided by the following. 
     SUMMARY 
     One aspect of the present patent application is a method of attaching a gasket to a plastic surface. The method includes providing a plastic material having a surface; applying sufficient heat to the surface to melt the surface while other portions of the plastic material remain solid; providing a liquid gasket material on the heated surface while the heated surface is melted; and allowing the liquid gasket material and the surface to cool so the gasket is welded to the plastic material. 
     Another aspect of the present patent application is a method of attaching a gasket to a plastic surface. The method includes providing a plastic material having a surface; applying sufficient heat to the surface to melt the surface while other portions of the plastic material remain solid, wherein the applying heat involves applying at least one from the group consisting of hot air, heat lamp, laser, and flame; providing a liquid gasket material on the heated surface while the heated surface is melted; rotating the plastic material while applying the heat to the surface and while providing the liquid gasket material; and allowing the liquid gasket material and the surface to cool so the gasket is welded to the plastic material. 
     Another aspect of the present patent application is a method of attaching a gasket to a plastic surface. The method includes providing a plastic material having a surface, wherein the plastic material is part of a closure, wherein the closure has a ring shaped planar surface; applying sufficient heat to the surface to melt the surface while other portions of the plastic material remain solid, wherein the heat is applied exclusively to the ring shaped planar surface; providing a liquid gasket material on the heated surface while the heated surface is melted; allowing the liquid gasket material and the surface to cool so the gasket is welded to the plastic material; and providing a container and placing the closure on the container, wherein the gasket provides sealing between the closure and the container. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1   a  is a cross sectional view of a snap on closure latched to a one gallon plastic milk container with a gasket of the present patent application there between; 
         FIG. 1   b  is an enlarged cross sectional view of a portion of  FIG. 1   a;    
         FIG. 1   c  is a side view of the closure and milk container of  FIG. 1   a;    
         FIG. 2   a  is a cross sectional view of a friction fit closure latched to a 5 gallon water bottle of a water cooler with a gasket of the present patent application there between; 
         FIG. 2   b  is an enlarged cross sectional view of a portion of  FIG. 2   a;    
         FIG. 2   c  is a side view of the closure and 5 gallon water bottle of  FIG. 2   a;    
         FIG. 3   a  is a side view of a hot air gun heating and applying liquid synthetic rubber compound to a one gallon milk container closure; 
         FIG. 3   b  is a cross sectional view of the hot air gun and milk container closure of  FIG. 3   a;    
         FIG. 3   c  is an enlarged cross sectional view of a portion of  FIG. 3   b  showing the hot air nozzle applying hot air and the synthetic rubber applicator gun nozzle applying liquid synthetic rubber to the one gallon milk container closure; 
         FIG. 3   d  is an enlarged cross sectional view of a portion of  FIG. 3   e  showing the hot air nozzle melting the surface of the one gallon milk container closure and the synthetic rubber applicator gun nozzle applying liquid gasket compound; 
         FIG. 3   e  is a three dimensional view of a hot air gun heating and applying synthetic rubber compound to the one gallon milk container closure; 
         FIG. 4   a  is a side view of a hot air gun heating and applying liquid synthetic rubber compound to a 5 gallon water bottle closure; 
         FIG. 4   b  is a cross sectional view of the hot air gun and 5 gallon water bottle closure of  FIG. 4   a;    
         FIG. 4   c  is an enlarged cross sectional view of a portion of  FIG. 4   b  showing the hot air nozzle heating and the synthetic rubber applicator gun nozzle applying liquid synthetic rubber to the 5 gallon water bottle closure; 
         FIG. 4   d  is an enlarged cross sectional view of a portion of  FIG. 4   e  showing the hot air nozzle melting the surface of the 5 gallon water bottle closure and the synthetic rubber applicator gun nozzle applying liquid gasket compound. 
         FIG. 4   e  is a three dimensional view of a hot air gun heating and applying synthetic rubber compound to the 5 gallon water bottle closure; and 
     
    
    
     DETAILED DESCRIPTION 
     The present applicant found that he could obtain substantially improved adhesion of the synthetic rubber gasket to the closure if he melted the surface of the closure in the contact region just before the liquid synthetic rubber compound was applied. One way he found to satisfactorily melt the surface of the closure in that region was with a hot air gun. He found that the bond between the synthetic rubber gasket and the closure was stronger than the bond holding together the synthetic rubber itself. 
     In one use of the present patent application, snap on closure  10  is latched to plastic milk container  14  with lower retaining ring  15  and upper retaining ring  16 , as shown in  FIGS. 1   a ,  1   b . Snap on closure  10  includes peel off portion  17   a  that is removed by pulling on tab  17   b , as shown in  FIGS. 1   b  and  1   c . Snap on closure  10  also includes gasket  25  of the present patent application that is firmly bonded to snap on closure  10  and that seals against rim  28  of plastic milk container  14  when snap on closure  10  is snapped on to plastic milk container  14 . 
     In another use of the present patent application, friction fit closure  30  is latched to five gallon plastic water bottle  33  with retaining ring  40 , as shown in  FIG. 2   b . Friction fit closure  30  includes valve  42  that fits to a stem on a water cooler for delivering water. Friction fit closure  30  also includes gasket  45  of the present patent application that is firmly bonded to friction fit closure  30  and that seals against rim  46  of five gallon plastic water bottle  33  when friction fit closure  30  is latched on to five gallon plastic water bottle  33 . 
     In one experiment, hot air was applied to form melted surface  50 ,  52  of plastic closure  10 ,  30  immediately before application of synthetic rubber compound  54  came from hot air tool  56  from Leister Process Technologies (Sarnen, Switzerland), model No. LE Mini 400, as shown in  FIGS. 3   a - 3   e  and  FIGS. 4   a - 4   e . The present applicant found that by placing hot air nozzle  58  in close proximity to sealing surface  60 ,  62  of closure  10 ,  30  hot air from gun  56  formed melted plastic surface  50 ,  52  to achieve a “wet” look. Before melted plastic surface  50 ,  52  cooled or resolidified, the applicant applied molten synthetic rubber compound  54  from applicator gun  66  through nozzle  68 . Because melted plastic surface  50 ,  52  and applied compound  54  were both in a molten state at the same time the resulting gasket  25 ,  45  was welded to plastic closure  10 ,  30 . Mixing of melted plastic surface  50 ,  52  with synthetic rubber compound  54  at their interface bonded them based on intermixing of the two materials at the interface, sometimes called an inter-dissolution bond, providing a much stronger bond than was achieved by just adhering compound  54  to the cold plastic closure. 
     Testing demonstrated that the gasket provided with the hot air surface treatment was virtually destroyed when applicant attempted to remove the gasket. Without hot air surface treatment the gaskets easily peels away intact from the plastic closure using, for example, a dental pick tool. Thus, the hot air surface treatment of the closure provided a much stronger bond. 
     Because sealing surface  60 ,  62 , of plastic closure  10 ,  30  was melted before application of molten synthetic rubber compound  54 , all portions of compound  54  contacting melted plastic surface  50 ,  52  of plastic closure  10 ,  30  were welded to melted plastic surface  50 ,  52  of plastic closure  10 ,  30 . 
     In addition to hot air, flaming, a heat lamp, a laser, or other methods can be used to melt sealing surface  60 ,  62  of plastic closure  10 ,  30  while leaving other portions of plastic closure  10 ,  30  cool to provide similar results. 
     Plastic closure  10 ,  30  can be any kind of cap or lid. The closure can be a snap-on type, a friction-fit type, or a screw-on type for milk containers, water bottles, or any other kind of container or bottle. This hot air concept can also be used on virtually any plastic substrate requiring an improved gasket bond. The gasket need not be round; it can be square, oval, or any other shape. In this case it may be desirable to move the applicator gun and the heat gun instead of rotating the closure. 
     Other compound formulations having similar properties as the Foremelt product can also be used. The gasket can also be formed of starch based material, a hot melt closure sealing compound, or any other material that melts. 
     The present applicants found that with hot air heating only the surface heated and melted to provide a wet look, and other portions of the plastic closure did not melt. The exclusively surface heating allowed the closure to retain its original shape after the heating process was complete. No deformation of the closure was observed as a result of this air heating process. 
     While several embodiments, together with modifications thereof, have been described in detail herein and illustrated in the accompanying drawings, it will be evident that various further modifications are possible without departing from the scope of the invention as defined in the appended claims. Nothing in the above specification is intended to limit the invention more narrowly than the appended claims. The examples given are intended only to be illustrative rather than exclusive.