BACKGROUND OF THE INVENTION
This invention concerns glazing particularly for automotive window panels. It has long been proposed to construct windows for automotive vehicles from synthetic resins, i.e., from plastic material. A suitable such material is polycarbonate, and use of this material of automotive windows has long been proposed. By hardcoating the surfaces by processes heretofore developed, sufficient scratch resistance can be achieved to produce automotive window panels performing well in service. Other coatings are also now available, such as UV blocking coatings to further improve the performance of plastic windows for automotive vehicles.
Molded plastic automotive windows offer a number of advantages over conventional glass glazing, including a significant reduction in vehicle weight and improved vehicle safety, as the polycarbonate panels better resist shattering as compared to glass, and in a crash fixed plastic windows keep the occupants from being ejected from the vehicle passenger compartment better than existing glass windows. Greater design freedom is afforded by plastic windows due to the ease in forming complex curved shapes.
One problem with polycarbonate panels used for automotive windows is a lack of edge stiffness, important for moving or “drop” windows. The edges of such plastic panels are insufficiently stiff tc reliably maintain registry with the window guides and seals, and can be pushed out by impact of an occupant with the window in a crash.
A requirement for existing fixed windows is a masking border to conceal the body and seal structure at the jointer of the window periphery to the body, which masking border requirement adds processing steps in manufacturing such window panels.
U.S. Pat. Nos. 5,339,584 and 5,035,096 both propose certain techniques in manufacturing synthetic resin windows for automotive vehicles in order to overcome the lack of stiffness in a molded plastic window panel.
U.S. Pat. No. 5,339,584 describes an insert molding technique for attaching a reinforced frame to an optical main glazing panel.
U.S. Pat. No. 5,035,096 describes producing a hollow frame portion extending about the perimeter of the main panel, the frame hollow portion formed by a gas assist technique, in which gas is injected into a cavity defining the frame portion, the gas expanding within the plastic to create the hollow shape of the frame portion.
In this approach, the hollow frame is molded as one piece with the optical panel and is thus formed from the same resin material, to be integrally molded therewith. In order to provide the masking border treatment, an extra painting or coating process is required. The hollow frame is an efficient way of achieving adequate perimeter stiffness, but there are several problems with the approach described in that patent.
Firstly, optical flaws are sometimes produced by the assist gas migrating into the main mold cavity where the main panel is formed. Also, stress riser cavities could be formed by such migrating gas. Other slight optical flaws can occur because of the two cavities inducing residual stresses in the optical portion.
The resin used in the optical panel does not itself form a particularly stiff material, and the use of the same material in the frame portion thus compromises the rigidity which could otherwise be achieved.
It is the object of the present invention to provide a manufacturing process for providing a hollow frame on the perimeter of a molded plastic main glazing panel which minimizes optical flaws in the main glazing panel.
It is a further object to provide such process in which the panel rigidity can be maximized by allowing the use of a different stiffer material in the frame portion.
Yet another object is to provide a process for manufacturing a glazing panel having a hollow perimeter frame which can eliminate other processing steps.
Still another object is to provide such process which allows many processing options to enhance manufacturing efficiency.
SUMMARY OF THE INVENTION
These and other objects which can be appreciated by a reading of the following specification and claims are achieved by utilizing a two shot process, in which the optical main glazing panel is separately molded from the hollow frame portion, the hollow frame portion formed by a conventional gas assist process.
The two shot molding process can be achieved by various options including overmolding (using movable cores, with either the frame or main molded panel first, using a second nozzle, for example), transfer molding, in which a separate mold is used for each part, or insert molding in which one or the other part is molded first, and inserted in a mold for the second part.
Separate molding of the main panel and the hollow frame portion eliminates many of the optical flaws resulting from gas migration, residual stresses and sink marks.
Separate molding also allows different draft angles for the hollow frame portion.
The frame portion may be molded from a stiffer material such as a filled resin to maximize the rigidity of the frame portion to maximize the rigidity of the window edge.
The frame portion material can also be rendered opaque to provide border masking without the need for a separate coating or painting step, or to necessitate the a difficult insert film molding step described in the above referenced patents.
Simplification of the complete window manufacturing process is also possible with the two shot molding approach, i.e., reinforcing ribs, latching and hinging features can be more easily molded into the frame portion to eliminate attachment of separate parts.