Apparatus for heat forming a continuous web of plastic

Abstract

Abstract A continuous web of heat-deformed plastic is drawn through apparatus wherein a succession of steps are performed in a repeated sequence to form blister or skin package elements. A segment of the web is clamped about a square periphery and heated to a moldable condition. A support is moved vertically to bring into contact with the softened segment either a mold surface for forming blister package segments, or articles of merchandise on supports to be skin packaged. The web clamping frame and vertically movable support are mounted on a horizontally reciprocating carriage which is moved to carry the molded segment of the web to a terminal position and bring a fresh segment into position for heating and forming. The molded segment of the web is cooled and thus assumes its final form as it is moved by the carriage, thereby reducing the overall cycle time. BACKGROUND OF THE INVENTION The present invention relates to plastic packageforming apparatus and, more specifically, to apparatus for treating a continuous web of thermo-plastic material to provide a component of either skin or blister packages. A wide variety of items are commonly sold in packages at least partly formed of transparent plastic through which the items may be viewed prior to purchase. Among the various types of packages in this category are those known as blister packages, wherein the plastic is formed in a rigid or semi-rigid covering for the item, and skin packages, wherein the plastic is heat-formed in direct contact with the item and/or a supporting element on which it is carried. In blister packages, the plastic is molded and cut to the proper form and later assembled with other portions of the package to enclose the item, usually without direct contact between the packaged item and the plastic. Skin packaging involves direct application of the plastic in a heat-softened state to the item which has previously been placed on a support. The latter commonly consists of a piece of stiff paperboard upon which the item has been laid, and the plastic is applied directly over the surface thereof upon which the item is placed. Such packaging operations are commonly performed by automatic or semi-automatic machinery. The cost of packaging is ultimately reflected in the cost of the packaged item. Therefore, it is obviously desirable to perform the packaging operation in the most economical manner consistent with the intended function and appearance of the package. A principal object of the present invention is to provide apparatus for heat forming plastic packaging from a continuous web of thermoplastic material in a more efficient and economical manner than prior art apparatus of the same general type. A further object is to provide plastic packaging apparatus operable in repeated cycles in such a manner that the overall cycle time is reduced, thereby providing more packages at the same cost. An additional object is to provide novel and improved plastic forming apparatus particularly directed to heat forming in repeated sequence a continuous web of material in either blister or skin packaging applications. Still another object is to provide apparatus adapted to perform a repeated heat forming cycle on longitudinal segments of a continuous plastic web according to a novel sequence of operations which allows more efficient utilization of the forming apparatus. Other objects will in part be obvious and will in part appear hereinafter. SUMMARY OF THE INVENTION In accordance with the foregoing objects, the invention comprises apparatus for operating upon a continuous web of plastic in a series of timed steps. Conventional timer apparatus controls the cycle time by actuating solenoid valves in pneumatic lines connected to air cylinders which move various portions of the apparatus. The plastic web is fed in a horizontal plane to a position directly beneath a radiant heater, also movable in a horizontal plane between operative and inoperative positions. Heat is applied for a predetermined time, sufficient to soften the plastic to a moldable condition. A movable carriage is mounted on supporting tracks and carries a vertically movable platen and a pivoted clamping frame. The latter is moved to grip the side edges and transverse portions of the plastic web about a generally square or rectangular periphery, corresponding to the portion softened by the radiant heater when in its operative position. At the end of the timed heat cycle, the platen is moved upwardly for the mold surface, or other material carried by the platen, to engage the softened portion of the web, which is drawn into forming engagement by vacuum applied through openings in the platen. The carriage is then moved horizontally, carrying with it the web, still engaged by the clamping frame and the surface to which it is molded. During such movement, the vacuum applied through the openings in the platen is changed to a positive flow of air out of the openings, thereby cooling the formed portion of the web and releasing it from the platen or mold surface. As the carriage reaches the end of its travel, the web is engaged by a pair of stationary grippers, the mold is moved vertically downward to its original position and the clamping frame is moved about its pivotal mounting to release the web. With the web held stationary by the grippers, the carriage is moved horizontally back to its original position, the heater again swings horizontally to its operative position above a fresh segment of the web and the cycle is repeated. The web is released by the grippers as the heater swings to the operative position. Certain portions of the above-described sequence are applicable only to blister package forming operation, but relatively slight modifications permit use of the apparatus as a skin packaging machine. Such modifications may be selectively made merely by changing the programming unit of the apparatus, thus permitting use of the same machine for either blister or skin packaging, as desired. In either mode of operation, the mold or package-forming portion of the apparatus is moved in the direction of web feed while part of the forming operation is in progress. This combination of the web feed and forming operations in the same time period reduces the overall cycle time, thus providing a greater output in any given time span.

Inventors

• 👤 William D. Birchenough

Bibliographic Details