1. Field of the Invention
This invention relates to apparatus for and a method of applying locking profile extrusions to a moving web of plastic film during the manufacture of plastic bags from the film.
2. Cross Reference to Related Applications
Application Ser. No. 433,588, filed Oct. 12, 1882, "Plastic Bags With Releasable Closure Which Resists Opening From Inside," Harrington, filed concurrently herewith, discloses and claims the plastic bag which is an example of the article which can be made by the present invention.
3. Description of the Prior Art
Various closure arrangements have been employed for closing plastic bags. U.S. Pat. No. Re. 28,969 Naito shows the Zip-loc storage bag in which a profile extrusion on one side of the bag mates with a profile extrusion on the other side of the bag to form an interlocking, reclosable, closure. The interlocking profiles of this closure are integral with the plastic film of the bag. The extrusion of the interlocking profiles is part of the plastic film making machinery. This adversely affects the speed of the film making machinery. Also, the interlocking profiles preferably extend from a heavier gauge film than would otherwise be required if the locking profiles were not extruded during the film making. This process restricts film gauge reduction which is a significant cost savings in the production of plastic bags. Another disadvantage of extruding the interlocking profiles during manufacture of the plastic film, is that the interlocking profiles must necessarily be of the same resin as the plastic film.
U.S. Pat. No. 3,226,787-Ausnit similarly shows apparatus for extruding the interlocking profiles during the fabrication of the plastic sheet, which adversely affects speed.
U.S. Pat. No. 4,212,337-Kamp shows a closure device made from a heat sealable material. This closure is attached to the heat sealable film in a separate step after the manufacture of the film. Heat is transferred through the film to produce melting at the interface of the film and the closure device to attach the closure to the film. This type of attachment is a slow process which cannot practically be performed in line with the extrusion and bag making. It is not possible to take advantage of in line bag manufacture which includes extrusion, folding, and bag making in a continuous in line process.
In practice the extruded interlocking closures of the prior art are integral with a narrow strip of film which is heat sealed to the plastic film. Making the closure on a separate strip of film for later attachment almost doubles the required amount of plastic material thereby increasing the cost of the bag greatly. These disadvantages are also inherent in other presently practiced manufacturing techniques wherein the closure is separately manufactured and then applied to the plastic film after it has been manufactured. Other techniques of attaching such separate locking profiles to the film include the use of ultrasonic seals which have the same disadvantages.
It is an object of the present invention to extrude locking profiles which are heat sealed to the plastic film during an in line bag manufacturing process.
It is another object of the present invention to provide a plastic bag manufacturing apparatus and process which do not have the aforementioned disadvantages of the prior art and which provide an efficient and economic bag manufacture.
It is another object of the present invention to maintain a temperature differential between a molten thermoplastic extruded locking profile and a moving web of film from which the bag is formed so that the molten thermoplastic adheres to the moving web upon contact and thereafter cools in a manner which prevents puckering of the moving web.