Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
1998-07-13
2001-11-27
Dye, Rena L. (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S036900, C428S122000, C428S188000, C280S848000, C296S198000, C296S901010, C293S120000
Reexamination Certificate
active
06322865
ABSTRACT:
TECHNICAL FIELD
This invention relates to hollow plastic articles and, in particular, to hollow plastic articles formed by gas-assisted injection molding systems.
BACKGROUND ART
It is often desirable to replace a conventional metal part with a plastic molded part for a number of reasons such as weight savings and ease of assembly.
In the plastic injection molding art, the usual challenges facing a product designer are to design an article having requisite strength for the product application and uniform surface quality for satisfactory appearance, but to avoid excessive weight, material usage and cycle time. A design compromise must often be made between strength and plastic thickness. A relatively thicker plastic section in the article, such as a structural rib, will incur greater weight, material usage, cycle time and induce sink marks and other surface defects due to thermal gradients in the area of the thickened section.
The exterior surface of the part may have to be “Class A” quality and be paintable in an automated line. Any surface degradation due to sink marks, blemishes or other imperfections were unacceptable for commercial standards as described in U.S. Pat. No. 5,344,596.
As described in U.S. Pat. Nos. 5,225,141, 5,069,858, and 5,447,762, it is known in the plastic molding art to use pressurized fluid in conjunction with the plastic molding of articles. The pressurized fluid is typically nitrogen gas which is introduced into the mold cavity at or near the completion of the plastic injection. The pressurized fluid serves several purposes. First, it allows the article so formed to have hollow interior portions which correspond to weight and material savings. Second, the pressurized fluid within the mold cavity applies outward pressure to force the plastic against the mold surfaces while the article solidifies. Third, the cycle time is reduced as the gas migrates through the most fluent inner volume of the plastic and replaces the plastic in these areas which would otherwise require an extended cooling cycle. Fourth, the gas pressure pushes the plastic against the mold surfaces, thereby obtaining the maximum coolant effect from the mold.
There have been practical limitations in the adaptation of gas injection in the plastic molding field. For example, oftentimes the gas channel will not be hidden as viewed from the “Class A” surface, especially where the “Class A” surface is concave or planar with the gas channel immediately behind the non-convex “Class A” surface.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a hollow plastic article formed by a gas-assisted injection molded system wherein a gas channel formed in the plastic article is hidden and a sink-free exterior surface (i.e. “Class A” surface of the article) is formed even if portions of the “Class A” surface in front of the gas channel are planar or concave.
In carrying out the above object and other objects of the present invention, a hollow plastic article of a one-piece construction being formed from a molten plastic resin by a fluid-assisted injection molding system is provided. The system includes a mold having an article-defining cavity and an injection aperture wherein the molten plastic resin is injected through the injection aperture and wherein pressurized fluid is communicated to the molten plastic resin in the article-defining cavity to at least partially distribute the molten plastic resin. The article includes a hollow body section having a front wall, a rear wall, and interconnecting top and bottom walls formed by the pressurized fluid to define a gas channel which extends at least partially through the hollow body section. The article also includes a solid wall section connected to the front wall and which extends downwardly from the front wall toward the rear wall immediately below the bottom wall of the hollow body section wherein the solid wall section and the front wall immediately adjacent the solid wall section define a convex, sink-free, exterior surface of the article to hide any gas channel read through.
Preferably, the top wall of the hollow body section also defines a sink-free exterior surface of the article.
Still, preferably, the rear wall includes a substantially planar attachment portion for securing the article to another article and an interconnecting portion connected to the attachment portion and which extends downwardly from the attachment portion and which is connected to the bottom wall. Preferably, the other article is a part of a motor vehicle.
The advantages accruing to an article constructed in accordance with the present invention are numerous. For example, a relatively lightweight, hollow, plastic part is provided having a Class A finish suitable for use as an interior or exterior automotive part even when the Class A finish includes non-convex (i.e. planar or concave) surface portions.
The above objects and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.
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J.C. Whitney Jan. 2000, “Everything Automotive”, p. 8, Items 6 (1973-1979 Ford) and H (1967-1972 Ford).*
The Chemical Condensed Dictionary, p. 699, col. 1-2, “plastic”, 1971.
Murphy John F.
Porter Randolph S.
Winget Larry J.
Brooks & Kushman P.C.
Dye Rena L.
Patent Holding Company
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