Prior art plastic containers have included a unitary receptacle and a unitary cover that are secured to each other to close the container. Securement constructions previously utilized to securely hold the cover on the receptacle have not permitted easy opening and closing while still maintaining the cover securely closed on the receptacle. Also, there has not been any prior tamperproof design constructed as an integral part of a plastic container which has received any significant commercial acceptance.
Paint, varnish, stain and the like are conventionally sold at the retail level in metal cans which have an upper edge with a groove in which an annular edge of a metal cover is secured by a press fit. Opening of the cover is performed by prying the cover edge upwardly out of engagement with the can edge so that the stored contents can be used. Such metal cans are conventionally made from tin plated steel which has become more and more expensive in the recent past. Also, the ever increasing use of water-based latex paint with steel cans has necessitated the use of a special coating on the interior of the can in order to prevent the water from causing corrosion as the paint is stored. Another problem with metal paint cans is that they tend to dent when struck or dropped.
One prior attempt at making paint cans from other than metal utilized injection or blow molding of polypropylene pastic in order to overcome the corrosion problem when water-based latex paints are stored. This can require a molded bead on the inner surface at the upper end of the can in order to secure an associated cover with the required strength necessary to pass drop tests paint cans are subjected to before being accepted commercially by paint manufacturers.
U.S. Pat. Nos. 3,998,355 and 4,126,246 disclose plastic lids and pails which are secured to each other by engagement threads each of which extends about one-quarter of the circumference of the lid or pail. The size of the pails disclosed is relatively large, on the order of that required to hold five gallons of liquid or so. To date, this type of container has not found any widespread commerical acceptance as a paint container in the retail market. This lack of acceptance is probably a result of the fact that the pail wall thickness and cover wall thickness necessary to maintain engagement of the threads is so great as to make the construction impractical for paint containers which are normally sold at the retail level in a one gallon size or smaller. Also, the cover can only be secured to the pail by threading due to the cover, receptacle and thread construction involved.
U.S. Pat. Nos. 4,245,753 and 4,245,754 disclose plastic containers for paint wherein segmented buttress retainers secure a cover to a receptacle for storage while permitting removal of the cover upon rotation and subsequent upward movement. With this type of construction, the locations between the buttress retainers result in a spaced relationship between a side wall of the receptacle and an annular lip of the cover on which the segmented buttress retainers are supported. Such spacing between the receptacle side wall and the cover lip allows deflection therebetween in a manner that can disengage the buttress retainers such that opening of the cover can result in certain instances when the container is dropped.
My prior U.S. Pat. No. 4,453,647 discloses an improved plastic container having a receptacle and a cover which can be securely attached to each other by either threading rotation of the cover or downward cover movement onto the receptacle. The cover of this container can also be easily detached from the receptacle by unthreading rotation of the cover with respect to the receptacle. Such secure attachment of the cover to the receptacle is provided by at least one retainer on either the receptacle or the cover and is preferably provided by a retainer on both the receptacle and the cover. Each retainer has an annular shape and opens vertically, with the retainer of the receptacle opening upwardly, and with the retainer of the cover opening downwardly. Upon closing of the cover, the retainer of the receptacle receives the lower round edge of an annular lip on the cover and the retainer of the cover receives a round upper edge of the receptacle side wall to thereby maintain engagement of helical threads on the cover lip and the receptacle side wall. While this container construction securely holds the cover closed on the receptacle, there is no provision to prevent tampering of the closed container after filling with whatever goods are to be held by the container.