The present invention is directed to an apparatus for packaging articles using shrink-wrap film and, particularly, to an improved heat tunnel that can be used for various film configurations.
It is known in the art to overwrap articles in a web of heat shrinkable film to form a multipack package by separating a tube of such film wrapped around spaced groups of articles along a weakened zone by shrinking the tube adjacent the zone and then by shrinking the tube section formed thereby around the articles to form a package. See U.S. Pat. No. 3,545,165.
Previous methods of packaging such as the above have involved feeding the groups of articles into a heat tunnel in series, with the film wrapped around the articles from the leading edge of the group to the trailing edge of the group. FIG. 1 shows how this is typically accomplished. Groups G of articles A are placed spaced apart on a conveyor C. A layer L of film F (usually from a roll of film) is wrapped around the groups G with the film layer L continuously covering adjacent groups G.
The groups G are then fed on the conveyor into a heat tunnel T. Heat and (typically) forced air is applied to the junction J between adjacent groups G, causing the film layer L to soften at the junction J and pinch off between the groups G, at the same time shrinking tightly against the groups G as shown. This results in complete packages P of articles A, with the film shrunk about them. The closed ends E of the packages P (known as “bulls eyes”) are at ends of the packages P in the direction of travel of the conveyor C (shown by the arrow).
An extension to the above apparatus is shown in FIG. 2. Here, parallel conveyors C1, C2, C3, etc. carry article groups G1, G2, G3, etc. into the heat tunnel T, where the above-described heat-shrinking occurs. The parallelism improves total throughput.
The apparatus shown in FIGS. 1 and 2 has a number of disadvantages. In gathering of multiple articles A into the groups G (known as “pack patterns”), the continuous tube of film F creates design challenges to support the groups G from the underside while the tube of film F is formed around the product. This is further complicated by product size changeover requirements. Theoretically, the conveyor C that transports the product pack pattern into the heat tunnel T would have to change widths for each change in product size to accommodate the tube of film F around the pack pattern.
In yet another variation (which the Assignee has used in the past), cut sleeves of film F are used, one sleeve per article group, instead of a continuous layer of film F around the groups G1, G2, G3, etc. However, the groups G are fed serially into the heat tunnel T with the articles A in each group G oriented in such a manner that the film F will be shrunk around each group G with the resulting closed ends E (“bulls eyes”) oriented transverse to the direction of travel of the conveyor C. To improve throughput, multiple parallel streams of articles A may be fed into the heat tunnel T.
The present application discloses an improved heat tunnel for use with both pre-perforated and non-perforated shrink wrap film.
In the packaging industry, aesthetics has become an increasingly important issue, both for the package that is produced and the machine that produces it. When the film is shrunk around the end of a package, it should leave a circular opening, the “bulls eye”, and should be free of wrinkles. This should be consistent from package to package and over a variety of product sizes.
Many of the challenges in producing aesthetically pleasing “bulls eyes” stem from the way that current heat tunnels operate. Current heat tunnels often produce deformed bulls eyes due to uncontrolled airflow. That is, as the group of articles enclosed in shrink-wrap film enters the heat tunnel, the film is subjected to various disruptive air currents, causing the film to flutter as it is shrunk. This uncontrolled airflow results in the film wrinkling and shrinking non-uniformly, which in turn results in unaesthetically pleasing bulls eyes. Furthermore, current heat tunnels are not generally adjustable for various product sizes.
There is a need for a new heat tunnel capable of producing consistently good bulls eyes with controlled shrink and that is adjustable for a range of product sizes.
There is also a need for a new heat tunnel to reduce the heat transfer to the outer skin of the heat tunnel, increasing the operating efficiency and improving the working environment around the machine by lowering the temperature.
There is also a need for a more aesthetically appearing heat tunnel and one of reduced size.
All of the above needs are addressed by the present invention.