Home canning system
BACKGROUND OF THE INVENTION 
     This invention relates to home canning closure systems and more particularly it relates to an improved home canning closure system featuring a plastic ring and a metal lid combination which is adapted to allow excess pressure to escape while preventing the escape of the contents of the container. 
     Closure systems for a home canning jar have traditionally comprised a metal lid and a metal ring which fits over the metal lid and incorporates threads adapted to engage mating threads in the jar. The metal lid serves to seal or close the open mouth of the jar, and the metal ring serves to hold the metal lid in place until such time as a vacuum is created in the jar. The metal ring also provides a protective cover to prevent dislodging of the metal lid after the creation of a vacuum in the jar which holds the metal lid in place. 
     A sterilized home canning jar is filled with the product being canned while hot and then a sterilized metal lid is placed thereover and a metal ring is then threaded into engagement with the canning jar to hold the metal lid in sealing engagement with the jar. As the product cools, a vacuum is created in the headspace above the product in the jar which then holds the metal lid in sealing engagement with the jar. In the home canning of certain products, the jar is partially or fully immersed in boiling water after it has received the hot product and the closure system. This continued heating of the package creates increased pressure within the jar which must be allowed to escape. Thus, the metal lid and metal ring will flex slightly to allow some pressure to escape from the jar. 
     However, the metal rings have been found to have a rather short life span due to corrosion and rust. Even if they are re-used, they have a rather unpleasant appearance. 
     GENERAL DESCRIPTION OF THIS INVENTION 
     It is, therefore, an object of this invention to provide an improved home canning closure system which eliminates the defects and objections associated with the conventionally used metal lid and metal ring combination. 
     This invention provides an improved plastic ring which is utilized with a metal lid to provide an effective home canning closure system. The plastic ring does not corrode or rust and may be re-used many times without any deterioration of its appearance. In addition, a plastic ring, when presented in various colors, provides a far more attractive package than does a metal ring and facilitates denoting of the various products being canned by the use of certain color rings. 
     This improved plastic ring of this invention includes an annular top panel portion and a skirt portion depending downwardly from the outer periphery of the top panel portion. The skirt portion incorporates buttress threads on its inner surface to engage threads on the external neck of the home canning jar. The plastic ring features an upwardly and outwardly inclined ramp portion on its lower surface and a thin section at the junction of the top panel and skirt portions which combine to form a spring member to bias the metal lid into sealing engagement with the upper rim on the home canning jar. These features counteract the tendency of the plastic ring to expand under the influence of heat and pressure from the hot, product-filled jar. As the pressure builds up within the jar, the metal lid and plastic ring are adapted to flex slightly to release or vent some of the pressure from within the jar. But the unique combination of the ramp portion and spring member return the metal lid into sealing engagement with the upper rim on the jar to prevent loss of product from within the jar. 
    
    
     Other objects, features, and advantages of this invention will become obvious to one skilled in the art upon reference to the following detailed description and the drawings illustrating a preferred embodiment thereof. 
     IN THE DRAWINGS 
     FIG. 1 is a perspective view of the improved home canning closure combination of this invention including a plastic ring and a metal lid in assembled relationship. 
     FIG. 2 is a front view, with portions broken away in section, of the separated plastic ring and metal lid of this invention. 
     FIG. 3 is an enlarged, partial sectional view of the plastic ring and metal lid of this invention as applied to a home canning jar. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     Referring now to the drawings, FIGS. 1 and 2 show the unique plastic ring 10 and metal lid 12 of this invention. 
     The plastic ring 10 includes an annular top panel portion 14 and an annular skirt portion 16. The skirt 16 incorporates a plurality of raised ribs 18 around its outer surface which facilitate easy grasping by fingers. A plurality of buttress-style threads 20 are provided on the interior surface of the skirt 16. The annular top panel portion 14 has a tapered ramp portion 22 on its lower surface and a thin section 24 at the junction of the top panel 14 and the skirt 16. 
     The metal lid 12 incorporates a vacuum indicating button 26 in its center, an upwardly and outwardly inclined tapered portion 27, and annular sealing portion around its outer periphery which is filled with suitable sealing material, such as plastisol 28. 
     As can be seen in FIG. 3, metal lid 12 is adapted to be placed in engagement with the upper sealing rim 30 of a container neck 32 so that the sealing material 28 forms a seal with the rim 30. The metal lid 12 then effectively closes and seals the open mouth 34 of the container neck 32. The container neck 32 incorporates a plurality of threads 36 on its outer surface which are adapted to mate with buttress threads 20 on the plastic ring 10. 
     The unique ramp portion 22 and the thin section 24 create a spring action which provides a controlled pressure on the metal lid 12 during the cooling process. This controlled pressure ensures venting of the excessive pressure within the container to thereby avoid buckling of the metal lid 12. If such buckling were to occur, leakage or spoilage of the product may be experienced. 
     The use of the buttress thread design 20 provides a more constant vertical force between the plastic thread and top of the plastic ring 10, over a thread design which has a greater face angle (angle of the plastic thread where it contacts the glass thread). This force on the top of the metal lid is maintained as the plastic ring expands, due to the introduction of heat during the various canning processes.