Patent Publication Number: US-5829613-A

Title: Snap-on/screw-off cap and neck configuration

Description:
This is a continuation-in-part of application Ser. No. 08/517,065 filed on Aug. 21, 1995 now U.S. Pat. No. 5,642,825. 
    
    
     FIELD OF THE INVENTION 
     The present invention is related to caps and neck-finishes for use in blow-molded plastic containers, specifically to caps and neck-finishes configured for snap-on assembly and screw-off disassembly. 
     BACKGROUND OF THE INVENTION 
     Blow-molded plastic containers having mating threaded caps and neck-finishes are well known. Blow-molded plastic containers having mating annular features for snap-on assembly and snap-off disassembly are also well known. 
     Threaded caps offer several advantages over snap-on caps in end use. Threaded caps are tightly sealable in spite of modest dimensional variations in the unpredictably blow-molded neck. Threaded caps may be removed and re-assembled repeatedly with sealing consistency dependent only on the twisting force applied by the user. The sealing strength and reliability of threaded caps is generally superior to that of snap-on caps. 
     Snap-on caps, however, are more easily adapted for automatic assembly during the bottling process, primarily because relative rotational pre-positioning of the cap and neck is not required, and because only direct axial application of the cap onto the neck without rotation is required to affix the cap onto the neck during bottling. Such cap and neck configurations are therefore desirable in automated bottling applications. 
     Several attempts have been made in recent years to provide a cap which provides the advantages of both cap attachment methods, allowing direct axial application without rotational pre-positioning to affix the cap during bottling, and allowing the sealing reliability and end-use advantages of threaded engagement, but to date none have been successful in combining the aforementioned advantages while eliminating the aforementioned disadvantages. 
     Caps providing tamper-indicators are also well known. Screw-off cap designs having frangible rings to rotationally interlock with the container neck and theoretically require removal for cap unscrewing and thereby also provide tamper-indication have been presented in many prior art patents and embodiments. 
     Prior art cap and neck configurations promising both snap-on/screw-off engagement and frangible tamper-indication have been offered in several prior art patents such as U.S. Pat. Nos. 5,174,465, 5,190,178, 5,285,912, and 5,307,946. Although these and many other prior snap-on/screw-off/tamper-indicating configurations have promised to allow reliably sealing snap-on engagement regardless of the pre-engagement relative rotational positioning of the cap and neck, and have promised to deny unscrewing so long as the indicating means is not actuated, no such configuration heretofore practiced is known to the inventor to have fulfilled such promises. 
     For instance, in U.S. Pat. No. 5,190,178, a cap and neck-finish configuration is disclosed which provides snap-on assembly, screw-off disassembly and re-assembly, and a tamper-indicating frangible lock ring. Buttress type threads comprised in the neck finish allow the threads of the cap to be axially forced thereover during bottling. Interlocking features comprising voids in the frangible ring and lugs in the neck-finish collar are provided which mate to prevent unintentional rotation and loosening of the cap. With only two allowable relative rotational relationships between the cap and container for direct axial assembly, an orientation feature is and must be provided to pre-align the voids with the collar lugs. During automated bottling, such pre-alignment would be performed by an automatic orientation machine which would be fed randomly positioned caps and would reposition each cap into a predetermined upright and rotational position aligned with the container neck by means of the orientation feature. Such a need for proper pre-alignment is a drawback to the disclosed configuration, as it represents an additional procedure during the bottling process. 
     Further, although the interlocking of the frangible ring and collar disclosed in U.S. Pat. No. 5,190,178 is intended to require removal of the ring for unscrewing of the cap, the non-continuous frangible engagement partially around the collar has proven in actual embodiment to allow rotational slippage during unscrewing without such frangible removal, thereby circumventing the intended tamper-indication. 
     In U.S. Pat. Nos. 5,285,912 and 5,307,946, cap and neck-finish configurations are disclosed which provide snap-on assembly, screw-off disassembly and re-assembly, and tamper-indicating frangible lock rings. In both patents, mating seven-lead threads in the cap and neck are disclosed. Both patents promise to provide ease of automatic assembly by allowing direct axial application without pre-alignment of the cap to the neck, to provide more reliable sealing, and to provide true tamper-indication. However, in actual embodiment, the configurations are found prone to leakage and tamper-indication failure due to the potential rotational misalignment of up to one-seventh of a rotation from optimal and due to insufficient sealing of the container opening to allow for the effects of such misalignment. The particular thread configuration disclosed and practiced is found to provide insufficient sealing forces in some relative rotational positions of the cap and neck, and the non-continuous frangible ring engagement partially around the collar is found to allow rotational slippage during unscrewing, thereby circumventing the intended tamper-indication. The one-way rotatable engagement of the frangible rings with the collars of these disclosures and embodiments is imperative, as dictated by the need to allow additional cap tightening after axial assembly on containers found to be leaking during bottling. This ratchet interface allows tightening but not loosening of the cap, and is practically blow-moldable only partially around the collar. The one-way rotatable engagement offers an additional psychological drawback as well, in that end-users often notice that additional tightening is possible and believe that the particular cap was not fully tightened at bottling. Although these drawbacks have been well recognized in the bottling industry, no embodiment has yet been forthcoming which provides sealing reliable enough to obviate the need for the one-directional ratchet interlock and allow full circumferential interlocking. No embodiment has yet been forthcoming which maintains sealing integrity throughout the range of possible variations in the cap and container interface. 
     As a result of the drawbacks of these prior art cap and neck configurations, the bottling industry today suffers from the lack of an easily attachable and leak-proof cap with true tamper-indication, at great loss and risk. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     The present invention is a cap and neck-finish configuration for a blow-molded container adapted to allow more reliable sealing after direct axial assembly without post-tightening, to obviate the need for one-way rotatability of the cap relative to the neck, and to provide positive tamper-indication. Both the cap and neck threads are of the modified Buttress type and opposingly directed to provide improved slip-over during snap-on assembly and improved sealing strength thereafter. The cap and neck each include an eight-lead thread to ensure that the relative rotational position of the cap and neck at the initiation of axial engagement cannot vary more than forty-five angular degrees from optimal final engagement. Both the cap and neck threads are of the same pitch to allow proper thread mating. The eight-lead thread of the cap improves screw-on assembly starting for the user, while improving cap to neck squareness for improved sealing. The cap interior includes an annular wiper which sealingly engages an unthreaded portion of the neck&#39;s exterior and a reverse-tapered annular wall depending within and sealingly engaging the neck&#39;s opening to provide a sealing valve which cooperates with the wiper seal to capture the neck at both the neck&#39;s interior and exterior. The cap further comprises a frangible tamper-indicating ring with forty-five rotational locking lugs which interlock with mating ratchet teeth in the neck&#39;s collar. The lug tips are tapered to direct the lugs in-between the ratchet teeth and overcome slight misalignment during assembly, to ensure that the relative rotational position of the cap and neck at final engagement cannot be varied without activation of the tamper-indicator. This lug shape and the disposition of the lugs and teeth completely around the cap and collar facilitates proper interlocking regardless of the relative rotational positioning of the cap and neck. These interlock and thread arrangements provide that the axially assembled cap is not more than one forty-fifth of a revolution from maximum tightness, which is within a sealing range provided by the wiper/valve arrangement. This ensures that the dual interior/exterior sealing is fully engaged whether the cap is at maximum tightness or at maximum possible looseness, so will therefore function regardless of the cap&#39;s rotational position prior to assembly. Further, because the lugs and ratchet teeth are disposed completely around the cap and neck, a fully circumferential interlock between the frangible tamper-indicator and the neck collar is provided which yields a more positive interlock and a causes the frangible tamper-indicator to tear from the cap prior to unscrewing for true tamper-indication. As a result of the thread and interlock feature arrangement of the present invention, a snap-on assembly is provided which negates the need for an orientation feature in the cap or a one-way rotatable ratchet, and which provides tight and reliable sealing regardless of the cap&#39;s rotational position relative to the neck at assembly. 
     It is the object of the present invention to provide a cap and neck-finish configuration for a blow-molded plastic container which is more easily adapted for automatic assembly. 
     It is the further object to provide a snap-on screw-off cap and neck-finish configuration which provides a secure and reliable seal. 
     It is the further object to provide a snap-on screw-off cap and neck-finish configuration having improved tamper-indication. 
     It is the further object to provide a snap-on screw-off cap and neck-finish configuration which provides positive sealing, yet does not require or allow post-tightening of the cap. 
     It is the further object to provide a snap-on screw-off cap and neck-finish configuration having tamper-indication which is easily accessed by both right-handed and left-handed users. 
     Further objects and advantages of the present invention will be best appreciated and more fully understood in reference to the herein described preferred embodiment and the appended drawings, of which the following is a brief description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of a cap and a container in accordance with the present invention; 
     FIG. 2 is an assembled perspective view of the cap and container of FIG. 1; 
     FIG. 3 is an assembled side view of the cap and container of FIG. 1; 
     FIG. 4A is a full sectional side view of the cap and container of FIG. 1; 
     FIG. 4B is a partial sectional side view of the cap and container of FIG. 1; 
     FIG. 5 is an top view of the cap of FIG. 1; 
     FIG. 6 is an bottom view of the cap of FIG. 1; 
     FIG. 7 is an bottom perspective view of the cap of FIG. 1; 
     FIG. 8 is an top view of the container of FIG. 1; 
     FIG. 9 is an assembled perspective view of the cap and container of FIG. 1 having the tamper-indicating ring partially removed; 
     FIG. 10A is a dimensioned side view of the neck of the container of FIG. 1; 
     FIG. 10B is a dimensioned top view of the neck of the container of FIG. 1; 
     FIG. 11A is a dimensioned top view of the cap of FIG. 1; 
     FIG. 11B is a dimensioned side view of the cap of FIG. 1; 
     FIG. 11C is a dimensioned sectional view of the cap of FIG. 1; 
     FIG. 11D is a dimensioned partial sectional side view of the threads and wiper of the cap of FIG. 1, drawn at a scale of ten-to-one; 
     FIG. 11E is a dimensioned partial sectional side view of the valve wall of the cap of FIG. 1, drawn at a scale of ten-to-one; 
     FIG. 11F is a dimensioned interior view of a lug of the cap of FIG. 1, drawn at a scale of ten-to-one; 
     FIG. 11G is a dimensioned partial sectional side view of a lug of the cap of FIG. 1, drawn at a scale of ten-to-one; 
     FIG. 11H is a dimensioned top view of a vertical tear grove of the cap of FIG. 1, drawn at a scale of ten-to-one; and 
     FIG. 11J is a dimensioned top view of a pull-tab of the cap of FIG. 1, drawn at a scale of five-to-one. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION 
     The preferred embodiment of the present invention is depicted in FIGS. 1 through 11J. 
     Cap 100 comprises a plano-circular top 101 having a cylindrical upper skirt 102 depending downwardly from the top&#39;s periphery 103. The upper skirt includes annular sealing bead 104 disposed adjacent the cap top and directed horizontally inward to the bead&#39;s inner diameter 105. A cylindrical lower skirt 106 is frangibly attached to the upper skirt at annular tear line 107. Also depending from the cap top is annular valve tube 110, having an outer diameter 111 concentric with and spaced inwardly from the upper skirt. The valve tube&#39;s outer surface is substantially spherical at it&#39;s lower end 112, as shown in FIG. 11E, and reverse-tapered at it&#39;s upper end 113, with it&#39;s maximum horizontal diameter 111 disposed below the annular sealing bead. The upper skirt 102 further includes eight helical internal threads 114, arranged equally about the inner diameter 115 of the skirt to form an eight-threaded screw-thread having each thread separated about the cap forty-five angular degrees. Reference to FIG. 11D shows that the threads approximate the Modified-Buttress type, each having steep lead surface 116, sloped fifty-three angular degrees below horizontal, and shallow engagement surface 117, sloped ten angular degrees above horizontal. The lower skirt 106 includes forty-five internal lugs 120 equally disposed about the skirt, each having tapered lower tips 121. The lugs are best understood by reference to FIGS. 11F and 11G. The lower skirt further includes three pull tabs 122, each adjacent a vertical tear groove 123, and equally disposed about the outer diameter 124 of the lower skirt. The preferred embodiment having three pull tabs provides that at least one pull tab will be convenient to the user regardless of the direction at which the cap is approached. This benefit adapts the cap well to both right-handed and left-handed users. The vertical tear grooves are somewhat stronger than the annular tear line 107, and the ring is thereby adapted so that pulling on a pull tab will first break the adjacent vertical tear groove, then break the annular tear line all around with the remaining vertical tear grooves remaining intact, as depicted in FIG. 9. 
     The container 125 is a typical blow-molded bottle 126 having a centrally disposed neck 127. The neck is substantially cylindrical and includes circular opening 128 through the top thereof, such that inwardly directed annular flange 129 is formed. The neck opening is slightly smaller in diameter than the horizontal diameter 111 of the cap&#39;s spherical valve tube. Depending downwardly from the neck&#39;s upper periphery is a cylindrical stretch 132, then a threaded stretch 133, then a collar 134, the collar being adjacent the container bottle 126. The outer diameter 135 of the cylindrical stretch is slightly larger than the cap sealing bead&#39;s inner diameter 105. The threaded stretch includes eight helical external threads 136, arranged equally about the outer diameter of the stretch to form an eight-threaded screw-thread having the threads separated about the neck forty-five angular degrees. Reference to FIG. 10A shows the threads are of the Modified-Buttress type, each having steep lead surface 137 and shallow engagement surface 138, these surfaces being oppositely directed from those of the cap. The collar includes thirty-two ratchet teeth 139 grouped about the collar to accept and engage the cap&#39;s lugs 120. Clockwise ratchet teeth 140 retain the lugs from counter-clockwise rotation, and counter-clockwise ratchet teeth 141 retain the lugs from clockwise rotation. 
     Assembly of the cap and neck is accomplished by direct axial application of the cap onto the neck, and is depicted in FIGS. 2 through 4B. The lead-in surface of each cap thread slips past and snaps over the lead-in surface of each neck thread. The tapered lower tips of the lugs direct the lugs in-between adjacent ratchet teeth, and the lugs become fully engaged with the ratchet teeth as the valve tube is forced into the neck opening. The neck opening is firmly and sealingly stretched around the valve wall. Simultaneously, the sealing bead of the cap engages the neck&#39;s cylindrical stretch and the smaller inner diameter of the bead is firmly pulled over the larger diameter of the cylindrical stretch. The larger diameter of the valve tube interferes with and expands the smaller neck opening so that the upper periphery 144 of the neck&#39;s cylindrical stretch is enlarged slightly in diameter and further seals against the bead. 
     The sealing effect is enhanced by the cooperation of the valve tube/opening interference fit and the bead/cylindrical stretch interference fit. The outward pressure on the opening by the valve acts to enlarge the neck&#39;s upper periphery above the bead, improving sealing and engagement of the cap and neck. Inward pressure of the bead on the cylindrical stretch acts to reduce the opening diameter above the valve tube&#39;s maximum diameter, improving sealing and engagement of the cap and neck. 
     The vertical disposition of the bead ensures that it will always lie around the cylindrical stretch regardless of the rotational relationship between the cap and neck at assembly. The eight-thread configuration allows that the cap&#39;s rotational position relative to the neck may vary within forty-five rotational degrees. The lead of the eight-thread screw at two and one-half threads per inch is four-tenths of an inch, so that the pitch of the thread arrangement is fifty-thousandths of an inch. The caps axial position relative to the neck may thereby vary within that fifty-thousandths. The vertical disposition of the bead must therefore be no less than fifty-thousandths of an inch below the upper periphery of the cylindrical stretch in its intended position. The cylindrical stretch must be a minimum of fifty-thousandths of an inch tall to accomondate all possible dispositions of the bead. 
     Axial removal of the cap from the neck is denied by the mating of the neck&#39;s and cap&#39;s thread engagement at the respective engagement surfaces. Because rotation is also denied while the lower skirt and upper skirt are intact, by the engagement of the lugs and ratchet teeth, the cap cannot be removed and firm sealing is maintained. 
     Removal of the cap&#39;s lower skirt 106, as depicted in FIG. 9, allows rotation of the cap relative to the neck and the cap can be unscrewed and removed. Removal of the lower skirt further provides tamper-indication by alerting the user that the cap has likely been removed since initial assembly. 
     Re-attachment of the cap is accomplished by rotational screwing, wherein the sealing system re-engages with each subsequent re-attachment. 
     Those skilled in the art will recognize that there are many variations of the invention that are within the scope of the invention, therefore, the invention is to be defined only by the limitations and the equivalents thereof which the following claims set forth.