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
2001-10-09
2004-09-21
Ortiz, 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, C264S328130
Reexamination Certificate
active
06793861
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a method of producing an in-mold coated thermoplastic workpiece. More specifically the process comprises the steps of forming a substrate by injection molding a thermoplastic polymeric material and thereafter injecting, as soon as the substrate falls below its melt point, a coating material into the closed mold containing the substrate which is maintained at a constant clamp pressure to coat at least a portion of one of the surfaces of the substrate with the coating material. The substrate and in-mold coating are introduced into the mold using known injection molding techniques.
BACKGROUND OF THE INVENTION
The in-mold coating, which is sometimes referred to as IMC, of molded plastic parts, particularly automobile and truck body panels, is a widely used commercially acceptable method of production. Up to the present these commercially accepted items have almost all been made by compression molding using a fiberglass reinforced plastic (FRP) substrate. The most widely used processes are those described in U.S. Pat. No. 4,076,788. The in-mold coating materials generally used therewith are of the type described in U.S. Pat. Nos. 5,658,672; 5,614,581; and 5,777,053.
The parts that have been manufactured using the above-described processes and materials have generally been relatively large and relatively flat. This is due in part to the inherent constraints of applying a coating to a compression molded part and has limited what might be a very useful method to relatively few parts.
Until relatively recently there have been no commercially acceptable in-mold coating injection molding techniques. More recently, however, an application describing an injection molding technique and the in-mold coating used in the process was developed by some of the inventors of this invention and is more fully described in pending U.S. patent application Ser. No. 09/614,953.
Another in-mold coating process which contemplates injection molding is described in U.S. Pat. No. 6,180,043B1. That in-mold coating method uses multi-stagewise variable clamping pressures. The scenario in changing pressures in this process is time consuming and, accordingly, decreases the throughput of the molding machine on which it is being practiced. In other words, machine throughput, i.e. number of articles produced per unit of time, is not maximized.
SUMMARY OF INVENTION
The present invention is a process for producing a thermoplastic workpiece having a coating bonded thereto, comprising the steps of injecting, using a filling pressure, into a closed mold which is maintained under a constant clamping pressure, a thermoplastic material, such as a polyolefin, heated to a temperature above its melting point, until said mold is substantially full, completely filling said mold with said material using a packing pressure to form a workpiece; maintaining said thermoplastic material, as it cools, under a mold pressure; injecting, immediately after the workpiece cools to its melt temperature or as it is sometimes referred to melting point, a coating composition into the closed mold to contact at least a portion of a surface of the workpiece. The mold is opened and the workpiece is removed after the coating composition has at least partially cured.
A process for the production of substrates of a thermoplastic having in-molded coatings thereon has been developed. In-mold coating of a substrate or workpiece, whereby the coating composition has good flow and coverage during molding, good adhesion, uniform color, good surface quality, and, if necessary, good paintability, may be successfully achieved by the practice of the process of the present invention.
It is an object of the present invention to provide an injection molding process by which substrates may be coated with in-mold compositions, to form finished workpieces which are suitable for use as is in end use applications or which require minimal surface post-treatment.
Another object is to maximize the output of expensive injection molding equipment.
It is a further object of the present invention to eliminate the time and cost of pretreating a workpiece to accept a paint or other coatings thereon.
A further object of the present invention is to provide a workpiece having an appearance in-mold coating thereon, which has paint-like properties, such as high gloss, hardness, good adhesion and good weatherability.
A further object of the present invention is to provide a workpiece having an in-mold coating thereon, which has good flow and coverage during molding, good adhesion, uniform color, durability, weather resistance, good surface qualities, and good paintability.
Injection Molding
Injection molding is a well known and probably the most widely used method of producing plastic parts. In a typical process pelletized, granular or powdered plastic material is fed from a hopper into a heating cylinder. There it is softened by being forced through the heated cylinder, usually by a screw. The softened plastic is then injected into a closed mold, most often by using the screw as a ram. Pressure is maintained on the mold and on the plastic until the plastic reaches a state where it can be removed from the mold without distortion.
The mold into which the plastic is injected is in two parts; one stationary, and the other movable. The mold cavity generally has a first surface on the first mold half, upon which a show or finished surface of the molded article will be formed, and a corresponding or opposite second surface on the second mold half. The mold is opened and closed either mechanically or hydraulically usually using a predetermined timing cycle. The stationary half normally houses the cavity section of the mold and is mounted on the stationary platen in contact with the injection section of the cylinder of the injection machine. The movable mold half usually holds the core and the ejector mechanism. The injection of the plastic material occurs under pressure when the mold is in a closed position. The clamping pressure, that is the pressure used to keep the mold closed during the injection of the plastic must be greater than the pressure used to inject the plastic.
Injection molding machines are often rated according to the maximum number of ounces of uniformly heated plastic that can be injected into the mold with one complete stroke of the injection ram. Shot sizes typically range from about ten to 260 ounces but may be smaller or larger. Another method of measuring machine capability is the clamp force, usually in tons, available to hold the mold closed during the high pressure injection. Usual injection molding pressures range from 10,000 to 30,000 psi.
Most injection molding machines are horizontal but some are of the vertical type. Another machine variation is a so called two stage injection unit.
Another essential component of the machine is the clamp assembly which opens and closes the mold and ejects the finished part and further prevents the mold from opening during the pressure build up resulting from the injection of the material to be molded into the mold cavity. The clamping devices used today may be either mechanical, hydraulic or hydromechanical. The type most often used is a toggle clamp. In this set up, prior to injection, mechanical links in the clamp are collapsed or untoggled and the mold is opened. Pressure is then applied forcing the links to extend and then close the mold and at its fullest extension the linkage is in a position such that pure mechanical pressure holds the mold closed. Hydroelectric clamps and hydromechanical clamps may also be used.
The invention may be practiced using any of the various types of injection molding machines provided that provision is made to inject the in-mold coating.
The practice of this invention requires the application of a second polymeric material generally referred to as an in-mold coating (IMC) onto at least a portion of the substrate which was molded as described above. The additional equipment needed to apply it is a second injector, the IMC injection nozzle of wh
McBain Douglas S.
Straus Elliott J.
Thompson John A.
Burleson David G.
Fay Sharpe Fagan Minnich & McKee LLP
Omnova Solutions Inc.
Ortiz Angela
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