Plastic article or earthenware shaping or treating: apparatus – Means feeding fluent stock from plural sources to common...
Reexamination Certificate
2000-03-03
2001-07-17
Heitbrink, Tim (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Means feeding fluent stock from plural sources to common...
C425S564000
Reexamination Certificate
active
06261075
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to coinjection molding.
DESCRIPTION OF THE RELATED ART
Coinjection molding is the injection molding of two or more plastic materials in which an outer skin layer is formed surrounding one or more core layers. In coinjection molding the first material to enter the cavity is the skin material. Upon entering the cavity, the skin material will develop a flow front through the cavity towards the end wall of the cavity. The material flowing in the center of the cavity wall has the highest velocity. As the center flow reaches the flow front, it splits to the outer wall. The skin material contacts the cold mold wall and freezes developing a frozen layer. This frozen layer is the skin layer.
Before the skin material reaches the end of the cavity, the core material will be injected into the part to form the core of the part. The core material will develop a second flow front. The flow front will have a different velocity profile than the skin material. The core material pushes the skin material ahead of it, however, the center velocity of the core material will travel faster than the skin flow front. If the correct skin/core ratio is used, the skin material will reach the end of the cavity just ahead of the core.
An advantage of coinjection molding is the use of a core material having a different material than the skin material which appears visible on the molded part. Coinjection enables the use of less expensive materials as the core material, and can lower part costs substantially.
For example, in large automotive parts, especially a bumper fascia made of thermoplastic olefin (TPO), the molded parts are painted. The painted parts are often rejected for imperfections. The rejected parts do not have recycle value due to the paint in the reprocessed material, and are typically disposed of in landfills. With coinjection molding, it is possible to use the reprocessed reground painted fascia as the core of the part. New or virgin TPO is used as the skin layer. Thus, the coinjected molded part appears the same as a conventional part, while using a substantial amount of recycled material that otherwise would have been new TPO.
Other coinjection applications include fabrication of parts which require different properties of the skin and core materials, respectively. For example, expensive engineering resins may be needed on the outer surface of the part for special properties such as high strength, good heat deflection, or good weather resistance. Inexpensive core material can be used to reduce the part costs while maintaining the desired performance properties of the engineering resin. An example of this would be the use of Ultem as the skin material and polyethylene terephthalate (PET) as the core material.
Additionally, it may be desired to have a core material that has specific properties. An example is coinjection with a foamed core. A foamed core material with an unfoamed skin can be used to produce parts with a good appearance and with the benefits of light weight, large wall thickness, and good strength. Another example is using coinjection to produce PET food containers with ethylene vinyl alcohol (EVOH) in the core. EVOH prevents oxygen from discoloring the food. Lastly, molded in paint can be used to eliminate painting applications. With coinjection, a painted skin can be produced with an unpainted core to maintain low part costs.
Accordingly, it is an object of the present invention to provide an improved coinjection system.
It is a further object of the invention to provide an improved multiple gate coinjection system.
It is a further object of the invention to provide an improved valve pin actuator for a coinjection nozzle.
It is a further object of the present invention to provide an improved coinjection manifold system in which the manifold includes a skin shut-off.
SUMMARY OF THE INVENTION
In one illustrative embodiment of the invention, a valve pin actuator for a coinjection molding system is provided in which the valve pin actuator supports a valve pin adapted to control skin plastic flow and core plastic flow at a gate to a mold cavity. The valve pin actuator includes an actuator body, a first member movably mounted within said actuator body, and a second member movably mounted within said actuator body. The second member is adapted to support said valve pin such that movement of said second member causes movement of said valve pin, in which the first and second members are each movable to a plurality of positions to control movement of the valve pin to reciprocate to three separate positions. The three positions include a first position in which the valve pin closes the gate and neither skin nor core plastic flow is permitted; a second position remote from the gate relative to the first position, in which skin flow is permitted and core flow is not permitted through the gate; and a third position remote from the gate relative to the second position, in which skin flow and core flow is permitted through the gate.
In another illustrative embodiment of the invention, a coinjection molding system is provided for injecting first and second plastic materials into a mold cavity. The system includes a manifold having first and second channels therethrough for distributing said first and second plastic materials, and at least one nozzle coupled to the manifold for injecting said first and second plastic materials from said manifold into said mold cavity. The nozzle has first and second passages for receiving first and second plastic materials from the first and second channels of said manifold, respectively. The system also includes a shut-off in the first channel of said manifold for preventing a flow of said first material in said first channel.
REFERENCES:
patent: 4497621 (1985-02-01), Kudert et al.
patent: 4512730 (1985-04-01), Kudert et al.
patent: 4518344 (1985-05-01), Latreille et al.
patent: 4712990 (1987-12-01), Kudert et al.
patent: 4717324 (1988-01-01), Schad et al.
patent: 4775308 (1988-10-01), Schad et al.
patent: 4808101 (1989-02-01), Schad et al.
patent: 4863369 (1989-09-01), Schad et al.
patent: 4892699 (1990-01-01), Kudert et al.
patent: 4895504 (1990-01-01), Kudert et al.
patent: 4925100 (1990-05-01), Kudert et al.
patent: 4931234 (1990-06-01), Schad et al.
patent: 4931246 (1990-06-01), Kudert et al.
patent: 4932858 (1990-06-01), Gellert
patent: 4934915 (1990-06-01), Kudert et al.
patent: 4946365 (1990-08-01), Kudert et al.
patent: 5028226 (1991-07-01), De'ath et al.
patent: 5037285 (1991-08-01), Kudert et al.
patent: 5106284 (1992-04-01), Kobayashi et al.
patent: 5223275 (1993-06-01), Gellert
patent: 5286184 (1994-02-01), Nakayama
patent: 5374178 (1994-12-01), Nakayama
patent: 5523045 (1996-06-01), Kudert et al.
patent: 5545028 (1996-08-01), Hume et al.
patent: 5914138 (1999-06-01), Swenson
patent: 3632928 A1 (1988-03-01), None
patent: 0 378 138 A2 (1990-07-01), None
Injection Molding Magazine, Nov. 1996, “Coinjection hot runner basics”.
Lee Christopher W.
Moss Mark D.
Heitbrink Tim
Synventive Molding Solutions, Inc.
Wolf Greenfield & Sacks P.C.
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