Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – To produce composite – plural part or multilayered article
Reexamination Certificate
1998-05-14
2001-02-13
Oritz, Angela (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
To produce composite, plural part or multilayered article
C264S328800
Reexamination Certificate
active
06187241
ABSTRACT:
FIELD OF INVENTION
The present invention relates to the co-extrusion of two or more streams of plastic materials and the like, as for introduction into molding apparatus or similar applications; being more particularly directed to the problems of providing better controlling of such co-extrusion and enabling more uniform molding of the extruded materials and with greater flexibility of the use of a wide range of different-proposed materials, extruding temperatures and other conditions.
With specific reference to injection systems for co-injecting at least two materials, the present invention relates to an improved technique and apparatus for combining the different flow streams of materials, wherein a velocity profile of the combined stream is produced in the melt delivery system that is similar to the velocity profile of the combined stream in the injection mold cavity, for insuring uniformity in the resulting molded item.
BACKGROUND OF INVENTION
A common problem in the field of co-injection molding resides in the need to keep the leading edge of the core (interior) layer as uniform with respect to thickness as trailing portions of the core (interior) layer entering the mold cavity. A tapered leading edge will produce a molded part that is not uniform in its properties near the position of farthest penetration of the interior layer.
Usually, the leading edge of the core (interior) layer becomes tapered as it flows through a cylindrical central channel of prior art co-injection nozzles disposed downstream of the combining area of the nozzle and as it flows through the cylindrical gate portion of the mold cavity. Typical of such nozzles are those described, for example, in U.S. Pat. Nos. 4,895,504 and 4,892,699.
The amount of taper depends on the velocity profile of the combined flow which causes a gradient of velocity between the radially innermost portion and the radially outermost portion of the leading edge. The amount of taper also depends on the total axial distance of cylindrical flow between the area of combination and the cavity-end of the cylindrical gate.
To minimize the leading edge taper, such prior art nozzles have been constructed with a short axial flow distance between the area of combination and the cavity end of the cylindrical gate. Typically, this axial flow distance is between about 5 mm and 25 mm, and the resulting leading edge taper length is greater than about 1.8 mm for the shorter axial flow distance and 9 mm for the longer axial flow distance. This short axial flow distance requires that the combining means be part of the nozzle.
Another problem with the current art is that the outermost diameter of the co-injection nozzle close to the gate is larger than nozzle diameters used in single-material injection molding. This larger size requires a large clearance bore in the mold which makes it difficult to provide adequate cooling of the mold cavity near the gate. Some designs of current art use a combining means that has a conically or frustoconically-shaped portion to minimize the outermost diameter near the gate; even so, this diameter of the nozzle near the gate may be twice the size of a single material nozzle.
OBJECTS OF INVENTION
An object of the present invention is to provide a new and improved method of and apparatus for co-extrusion that shall not be subject to the above and other disadvantages of the prior art, but that, to the contrary, through a radically different conversion of the nozzle to a throttle-control extruder, provides for significantly improved, more uniform and more flexible operation.
Another object is to provide a novel extrusion apparatus in which a combined flow is produced having a velocity profile within and downstream of the area of combination of the extrusion materials which has a substantially zero gradient of velocity across the leading edge of the core (interior) layer, such velocity profile enabling the leading edge of the core (interior) layer to not become tapered, as in prior art nozzles, as it flows from the area of combination to the cavity end of the mold gate.
Still another object of the invention is to provide a novel apparatus in which the combining means is remote from the gate area of the nozzle so that mold design and mold cooling are not compromised.
A further object is the achievement of such novel results through radically converting prior art cylindrical nozzles designs into an extruder structure containing throttle or restrictor needles, rods or stems that force annular extrusion; and, in the case of inner core molding, create concentric outer and inner annular extrusion streams, with the core-forming annular stream encased within annular co-extruded outer and inner stream layers.
A further object is to provide such a novel extruder in which a gate vestige is left on the molded part which is as small as that which can be obtained by single material molding systems.
An additional object of the invention is to provide a novel co-extrusion method and apparatus wherein the velocity profile of the combined stream of the plastic materials downstream of the combining area is made substantially the same as the velocity profile of the combined stream in the cavity, so that improved part properties and improved cycle times are possible.
Other and further objects will be explained hereinafter and are more particularly delineated in the appended claims.
SUMMARY OF THE INVENTION
In summary, however, from one of its broader aspects, the invention embraces a method of co-extruding multiple plastic materials as for injecting through a gate region into a mold cavity to produce a molded product, that comprises combining streams of such flowing plastic materials with at least one internal stream that is to serve as an interior core of a resulting molded plastic product within internal and outer streams of plastic material to serve as covering plastic material layers; restricting the combined streams to flow along concentric annular flow paths within and along a longitudinally extending tubular extruder to the cavity gate region, with the annular core stream encased by inner and outer annular covering plastic material stream layers; at the gate region, splitting the concentric annular streams along opposite transverse directions to inject into corresponding opposite transverse sections of the cavity.
Preferred and best mode embodiments and apparatus designs for practicing the novel method of the invention are hereinafter more fully described.
REFERENCES:
patent: 3894823 (1975-07-01), Hanning
patent: 4174413 (1979-11-01), Yasuike et al.
patent: 4611987 (1986-09-01), Hahn et al.
patent: 4781572 (1988-11-01), Boring
patent: 5028226 (1991-07-01), De'ath et al.
patent: 5131830 (1992-07-01), Orimoto et al.
patent: 5510065 (1996-04-01), McFarlane
patent: 5556582 (1996-09-01), Kazmer
Kortec, Inc.
Oritz Angela
Rines and Rines
LandOfFree
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