Functional and economical plastic can

A process for preparing a plastic can body, comprising the steps of:

• a. extruding a continuous parison of at least one layer of molten polymer;
• b. feeding said continuous parison into a series of continuously moving mold sections having an inside diameter on average about 1 to about 50% greater than the outer diameter of the continuous parison of molten polymer and an interior contour suitable to impart to the can body a plurality of circumferential beads extending over at least about 50 percent of the length of the can body, a non-beaded portion extending over at least about 5% of the length of the can body, and a radially outwardly directed flange at each end of the can body defining the end of the non-beaded portion, said sections advancing in the direction and at the approximate speed of the continuous parison of polymer and mating together about said continuous parison to form a series of cavities of the desired shape;
• c. applying a pressure differential outwardly from the interior of said continuous parison while said continuous parison is molten, whereby said continuous parison expands to provide a tube which conforms to the shape of said moving mold sections;
• d. cooling the inside and outside of the expanded tube to bring the polymer to below its solidification temperature;
• e. removing said moving mold sections from around the expanded tube;
• and
• f. severing the expanded tube transversely at an end of a non-beaded portion to form lengths comprising at least one can body of the desired shape.

A process for applying a metal lid to a plastic can body, comprising the steps of:

• a. selecting a plastic can body comprising
• i. a substantially cylindrical sidewall, wherein said sidewall includes a plurality of circumferential beads extending over at least about 50 percent of the length of the sidewall, said beads having a depth and spacing appropriate to permit compliance of the can body in a longitudinal direction of 0.5% when subject to 0.6-1.8 newtons of longitudinal force per mm of circumference of the can body at room temperature, and
• ii. a radially outwardly directed plastic flange at at least one end of the sidewall, said flange flange having a thickness which is about 0.28 to about 0.64 mm where it attaches to the sidewall and diminishes to a thickness of about 0.23 to about 0.58 mm at its outermost extent, said flange extending outwardly from the outer diameter of the can body for about 2.0 to about 2.5 mm;
• b. selecting a metal lid having a curl extending around the circumference of the lid and a countersunk center, said curl being about 0.20 to about 0.25 mm thick, the size of said lid being such that when superimposed on an end of the can sidewall having a flange, the curl extends about 0.75 to about 0.85 mm beyond the flange, and said countersunk center having a diameter about 0.025 to about 0.25 mm greater than the inside diameter of the can body so as to fit securely therein;
• c. placing said metal lid on said flanged end of the can sidewall such that the recessed center fits within the sidewall and the curl extends across the flange;
• d. applying pressure to said metal lid, whereby said lid is held against said flange;
• e. forming a seam between the curl of the lid and the flange of the can body by
• i. applying pressure against said curl by a first substantially cylindrical roller which moves progressively around the circumference of the lid, said first roller having a cut-out profile characterized by having a section sloping inwardly from top to bottom toward the axis of the roller at an angle of about 5 to about 25 degrees, the depth of said cutout profile being about 1.3 to about 1.5 mm, whereby the curl and flange are folded over each other;
• ii. thereafter applying pressure against the folded curl by a second substantially cylindrical roller which moves progressively around the circumference of the lid, said second roller having a cut-out profile characterized by having a section sloping outwardly from top to bottom away from the axis of the roller at an angle of about 3 to about 20 degrees,
• the depth of said cutout profile being about 0.6 to about 0.9 mm, whereby said curl and flange are further folded over each other and said seam is squeezed together and the sidewall is compressed between the end of the curl and the countersunk portion of the lid, thereby forming a seal.

A process for preparing a plastic can with at least one metal lid, comprising the steps of;

• a. extruding a continuous parison of at least one layer of molten polymer;
• b. feeding said continuous parison into a series of continuously moving mold sections having an inside diameter on average about 1 to about 50% greater than the outer diameter of the continuous parison of molten polymer and an interior contour suitable to impart to the can body a plurality of circumferential beads extending over at least about 50 percent of the length of the can body and a radially directed flange at each end of the can body, said sections advancing in the direction and at the approximate speed of the continuous parison of polymer and mating together about said continuous parison to form a series of cavities of the desired shape;
• c. applying a differential pressure from the interior to the exterior of said continuous parison while said continuous parison is molten, whereby said continuous parison expands to provide a tube which conforms to the shape of said moving mold sections;
• d. cooling the expanded tube to below its solidification temperature;
• e. removing said moving mold sections from around the expanded tube;
• and
• f. severing the expanded tube transversely to form lengths comprising at least one can body of the desired shape;
• g. precisely trimming said lengths to form can bodies of the desired size having a radially extending flange at each end thereof having a thickness which is about 0.28 to about 0.64 mm where it attaches to the sidewall and diminishes to a thickness of about 0.23 to about 0.58 mm at its outermost extent, said flange extending outwardly from the outer diameter of the can body for about 2.0 to about 2.5 mm;
• h. selecting a metal lid having a curl extending around the circumference of the lid and a countersunk center, said curl being about 0.20 to about 0.25 mm thick, the size of said lid being such that when superimposed on an end of the can sidewall having a flange, the curl extends about 0.75 to about 0.85 mm beyond the flange, and said countersunk center having a diameter about 0.025 to about 0.25 mm greater than the inside diameter of the can body so as to fit securely therein;
• i. placing said metal lid on said flanged end of the can sidewall such that the recessed center fits within the sidewall and the curl extends across the flange;
• j. applying pressure to said metal lid, whereby said lid is held against said flange;
• k. forming a seam between the curl of the lid and the flange of the can body by
• i. applying pressure against said curl by a first substantially cylindrical roller which moves progressively around the circumference of the lid, said first roller having a cut-out profile characterized by having a section sloping inwardly from top to bottom toward the axis of the roller at an angle of about 5 to about 25 degrees, the depth of said cutout profile being about 1.3 to about 1.5 mm, whereby the curl and flange are folded over each other;
• ii. thereafter applying pressure against the folded curl by a second substantially cylindrical roller which moves progressively around the circumference of the lid, said second roller having a cut-out profile characterized by having a section sloping outwardly from top to bottom away from the axis of the roller at an angle of about 3 to about 20 degrees, the depth of said cutout profile being about 0.6 to about 0.9 mm, whereby said seam is squeezed together and the sidewall is compressed between the end of the curl and the countersunk portion of the lid, thereby forming a seal.