Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-06-13
2001-10-02
Sells, James (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S069000, C156S073500, C156S580000, C053S334000, C053S485000
Reexamination Certificate
active
06296726
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the sealing of plastic lids or closures to plastic containers and, more particularly, to the spin welding of lids and containers.
The process of spin welding is one in which the friction between relatively rotating lids and containers such as bowls and cups causes the synthetic resin at abutting surfaces to melt and bond the two surfaces upon cooling. Generally, many spin welding processes have involved spinning the lid or cover at a relatively high speed and then bringing it into contact with the container which produces the melting friction as the lid rotation is slowed and then stops. Exemplary of such a process is U.S. Pat. No. 3,297,504 to Brown et al.
The industry has been seeking ever shorter spin welding cycles to expedite the filling and sealing process, while obtaining a reliable weld over the entire circumference to ensure a good seal.
Hofuis et al U.S. Pat. No. 5,772,103 describes an alternate process in which the lid and container are first brought into contact under vertical load and then rotational force is applied for a preset small number of rotations to effect the desired fusion.
In any spin welding process, there is a problem in dealing with variables such as variations in surface characteristics and configuration, contamination of the abutting surfaces by the contents of the container during filling, etc.
Accordingly, it is an object of the present invention to provide a novel method of spin welding lids and containers which will accommodate surface variations and produce well sealed containers.
It is also an object to provide such a method which may be practiced easily and rapidly in high speed filling lines.
Another object is to provide novel apparatus for spin welding lids and containers which accommodates surface variations and produces well sealed containers.
SUMMARY OF THE INVENTION
It has now been found that the foregoing and related objects may be readily attained in a method of making sealed synthetic resin containers which comprises molding thermoplastic synthetic resin into bowls and lids which have substantially complimentary mating surfaces extending about the periphery thereof. One of the bowls is filled with product, and the opposed, generally horizontal mating surfaces of the lid and bowl are brought into contact under a predetermined axial pressure while gripping the bowl and lid securely. The lid is rotated to the bowl with rapidly accelerating rotation while maintaining substantially the axial pressure to produce melting of the mating surfaces until a desired torque value is attained. The rotation of the lid is then immediately decelerated to terminate the rotation and allow the mating surfaces to bond.
The rotation is effected at a high degree of acceleration and the termination of rotation is effected at a high degree of deceleration. The torque is monitored repeatedly during the step of accelerating rotation until a plateau is reached, and the rotation is continued for at least 50 milliseconds thereafter. The monitoring of the torque is conveniently effected by monitoring the power being drawn by a motor used for producing the accelerating rotation.
The predetermined axial pressure is preferably 200-500 p.s.i., and the acceleration and termination of rotation is effected in less than four relative rotations of the lid relative to the bowl. Both the acceleration and deceleration are at a rate of 35,000-250,000 rpm/sec.
Desirably, there is included the step of directing steam onto the mating surface of the bowl prior to bringing the lid into contact therewith, and nitrogen is preferably admixed with the steam. As a result, a partial vacuum is produced in the sealed container.
The apparatus for producing the spin welded containers comprises a holder for firmly gripping a bowl, a holder for firmly gripping a complimentary lid, and means for moving the holders relative to each other to bring mating surfaces into contact. Pressure applying means is provided to apply predetermined axial pressure on the abutting surfaces, and acceleration and deceleration means is provided for rapidly accelerating rotation of the holders relative to each other and for rapidly decelerating the relative rotation while maintaining substantially the predetermined axial pressure. Torque sensing means is included to sense the torque generated at the mating surfaces which is operative upon the acceleration and deceleration means to determine when the acceleration has reached a desired value indicative of the desired melting of the mating surfaces and then to effect the deceleration.
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Pepe & Hazard LLP
Sells James
Silgan Containers Corporation
LandOfFree
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