Method for manufacturing a film-covered article

Details Method for manufacturing a film-covered article Method for manufacturing a film-covered article

1998-09-14

2001-06-26

Silbaugh, Jan H. (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

Direct application of fluid pressure differential to...

Producing multilayer work or article

C264S516000, C264S267000, C264S275000, C264S294000, C425S127000, C425S129100, C425S577000

Reexamination Certificate

active

06251333

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a method of manufacturing a film-covered article. More specifically, the invention is directed to manufacturing an injection-molded article having a thermoformed decorative film covering in a single molding tool.
2. Description of the Related Arts
It is known to manufacture molded articles by a method called in-mold lamination. The method is described in U.S. Pat. No. 3,668,034 ('034). The '034 patent teaches placing a decorative laminate within a mold and then injection molding a polymeric material behind the laminate. The resin inlet is juxtaposed the laminate backing. The polymeric material heats, softens and finally fuses to the backing on the laminate.
This reference does not disclose forming the film, but illustrated are two relatively simple two-dimensional films. These films are easily positioned within a tool and molded into an article. Larger articles with three-dimensional surfaces are much more difficult to properly align within a tool. They must be precisely trimmed to the desired dimension. Because these articles are three-dimensional, it is difficult to precisely trim the article after it is molded. The films are easily trimmed while they are flat, but it is desirable to leave the films untrimmed to have excess material for the molding operation. The excess material is useful to retain the film during the thermoforming operation to enable the film to stretch over the mandrel. Films are normally trimmed after they have been formed.
U.S. Pat. No. 5,599,608, teaches a method of thermoforming a film on a mandrel and then trimming the film after it is removed from the mandrel. After the film is molded, it is trimmed. Removing the film from the forming mandrel eliminates the hard-point tooling references for the precise trimming location of the film. Because the film is flexible and formed in a three-dimensional shape, locating these areas precisely is difficult and time consuming.
These thermoforming references all relate to a two-step process whereby the film is first formed and trimmed into the rough shape of the final film-covered article and then transferred into an injection-molding machine. These methods suffer from a difficulty of thermoforming and trimming the film into precisely the desired shape needed for the finished article. The films are generally made from thermoplastic material such as ABS, thermoplastic olefin, and polycarbonate. The film is heated to pliability and then formed. After the film is formed it is cooled. This cooling causes the film to shrink. Unfortunately, this shrinkage is not uniform along the film. Because the film has been shaped into a three-dimensional surface by stretching, some areas are thicker than other areas. These thicker areas shrink more than the thinner areas. The result of the shrinkage is that the cooled part is shaped differently than the thermoforming tool and the injection-molding tool. It presently requires a great deal of effort to match the shape of the cooled thermoformed film to the injection mold surface.
Among the problems associated with matching the thermoformed film and the injection mold tool are differences between the film shape and the tool surface are wrinkles and plastic leakage between the tool surface and the decorative film surface. It is desirable to combine the thermoforming and injection molding operation to provide a low-cost and reliably in-mold lamination process. It is also desirable to utilize the injection mold surfaces to shape the film and to retain the film on the mold surface during injection molding to eliminate alignment difficulties.
These and other objects, features, and advantages of the present invention will become more readily apparent when viewed in connection with the accompanying drawings wherein like reference numbers correspond to like components.
SUMMARY OF THE INVENTION
The present invention is directed to a method of manufacturing a film-covered article by the following steps. A thermoplastic film is heated to become pliable. The film has a decorative surface and a backing surface. The heated film is positioned between an open mold. The open mold has a first mold surface, a sealing surface and a sealing member. The sealing surface contacts the sealing member and forms a chamber between the mold and the film. A fluid pressure is applied between the mold and the film to cause the film to conform to the first mold surface. A molten resin is injected adjacent to the film-backing surface to form the film-covered article. The invention may be practiced by either applying a positive pressure to push the film to conform to the first mold surface or a negative pressure to draw the film against a vacuum between the film and the first mold surface.
It is most preferred to utilize a stationary cavity and a moveable core for the mold part where the cavity has a cavity surface that acts as the first mold surface. Sliding sealing members adjacent to the movable core function to create a sealed cavity between the core surface and the film. A gas such as air or nitrogen is injected into the cavity through the core surface to force the film against the cavity surface.
After the film is forced against the cavity surface, a molten resin is injected adjacent to the backing surface. The resin fuses to the backing surface to form the rigid substrate underlying the film and forming the article body.
In one embodiment of the invention, the film is pierced by an injector nozzle so that molten plastic is injected through the film. In another embodiment, edge gating or core gating allows the substrate to be injection molded without puncturing the film.
The present invention greatly simplifies the process of making film-covered articles because it combines the thermoforming and injection molding operations into one apparatus. The film is thermoformed in the mold surface and remains on this surface during the injection molding operation, thus eliminating any transfer operation. This has the dual benefit of significantly reducing the process cost and improving the final part quality because the film is shaped directly on the cavity surface. The molten plastic resin is injected against the film-backing surface before the film is allowed to cool and shrink.
The final covered article is retained on the mold core, enabling existing unloading equipment to be utilized to remove the article from the mold.
These and other desired objects of the present invention will become more apparent in the course of the following detailed description and appended claims. The invention may best be understood with reference to the accompanying drawings wherein illustrative embodiments are shown.


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