Plastic article or earthenware shaping or treating: apparatus – Distinct means to feed – support or manipulate preform stock... – Extrusion shaping means
Reexamination Certificate
2000-01-27
2002-08-13
Davis, Robert (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Distinct means to feed, support or manipulate preform stock...
Extrusion shaping means
C118S420000
Reexamination Certificate
active
06431847
ABSTRACT:
FIELD OF USE
This invention relates generally to the field of mixing or compounding reinforcing fiber strands with thermoplastic resin.
The fiber strands may be of any predetermined length and are introduced into an admixture with thermoplastic resins for immediate use in molding machines at a product molding facility.
BACKGROUND OF THE INVENTION
Processes are known for combining reinforcing fiber strands with thermoplastic resin to form reinforced plastic composites. U.S. Pat. Nos. 4,439,387 and Re. 32,772 sharing common inventorship herewith disclose the embedding of thermoplastic resin in reinforcing fiber strands as they are drawn through a forming die having a convoluted passage, in the presence of molten thermoplastic resin introduced from an extruder. The extrusion product of that process comprises an elongated bar or rod having a continuous length of reinforcing fiber encased within thermoplastic resin. That preformed composite may be inserted into a die of an injection molding machine, and utilized as an insert in a compound, composite product comprising an additional layer of thermoplastic resin molded over the insert. It is also known to cut the extrudate rod from the aforesaid forming die into short lengths for use as molding pellets. In the process of the aforesaid United States patents, the extruded rod comprising a fiber/resin composite is immediately cooled, prior to final forming and cutting to desired lengths.
U.S. Pat. No. 5,185,117, also having identity of inventorship herewith, discloses a process for compounding thermoplastic resin and fiber strands in an extruding compounder. According to the process of that patent, melted thermoplastic resin is introduced into the compounding extruder along with reinforcing fiber strands. The resulting extrudate consists of a molten mass of thermoplastic resin having discrete lengths of fiber strands randomly dispersed therein. This hot mixture may then be fed directly into a preform device to produce a measured preform for use in a compression molding machine. In the disclosed process of the '117 patent, the fiber strands are precut to desired lengths, before being introduced into the extruding compounder. The process and apparatus further requires a loss-in-weight scale to accurately measure predetermined quantities by weight of reinforcing fiber strands to be controllably introduced into the compounding extruder in the presence of thermoplastic resin. A separate loss-in-weight feed scale assembly is required to accurately convey predetermined amounts by weight of the thermoplastic resin into the compounding extruder for mixing in the desired proportions with the reinforcing fiber strands. The loss-in-weight scales necessarily add to the cost and complexity of the compounding apparatus.
U.S. Pat. No. 4,616,989 discloses an apparatus for incorporating glass fiber strands into thermoplastic resins in which a premixing chamber is utilized to initially mix glass fiber strands with molten resin. This mixture is then fed into a two-stage screw-type extruder to complete the mixing of the fiber strands and resin. The resin-fiber mass as discharged from the final extruder is passed through a forming die having a plurality of orifices. This serves to form the material into elongated filaments of glass fiber reinforced resin which are then cooled, and then granulated for use as a molding compound.
U.S. Pat. No. 2,877,501 to Brandt discloses a process for forming granules comprised of glass fiber strands coated with a molding plastic, which are intended for use as feed stock for an injection molding machine. In the Brandt process, fiber strands are pulled through an orifice within which they are coated with a resin material.
None of the known prior art processes for formulating a mixture of fiber reinforced resin for molding purposes are operatively effective for preparing a molding material comprised of fiber reinforced resin for immediate introduction into a molding machine at the same site where the fiber-resin mixture is made. Nor can any of the known prior art processes for formulating a mixture of fiber reinforced resin for molding purposes operate in a controlled and accurate discontinuous manner. Either cumbersome and costly apparatus, including multiple stage mixing devices and loss-in-weight scales, are required in the prior processes, and/or the fiber-reinforced resin is extruded into lengths, cut and packaged for sale and transportation to separate molding facilities.
There thus exists a need for a compact, efficient apparatus and process for accurately formulating mixtures of fiber and resin and thereafter directly introducing that molding material directly into a molding machine, such as an injection molding machine, a compression molding press, a transfer mold, a blow mold, a profile extrusion machine or an inject compression molding machine. In addition, there also exists a need for an apparatus and process capable of operating in a discontinuous manner to allow the admixture of variously sized batches of fiber reinforced resin molding material.
SUMMARY OF THE INVENTION
This invention has as its primary objective the provision of a process and apparatus for interspersing fiber strands in a thermoplastic resin in a desired weight ratio, under a controlled, fiber-coating process, and thereafter introducing the coated fiber strands directly into a molding machine at the same site, without cooling of the fiber-resin mixture. Another objective lies in the provision of a process and apparatus as described which may be operated in a discontinuous manner so as to produce discrete and varying amounts of the fiber-resin mixture.
These basic objectives are realized by threading at least one fiber strand through a coating die passage having an outlet and introducing into that passage a thermoplastic resin in a molten, pressurized state so that the thermoplastic resin flows from the passage through the outlet, thereby entraining the fiber strand in the flow of thermoplastic resin and coating the fiber strand with thermoplastic resin.
The coating die passage comprises at least one orifice of predetermined size that is larger in cross-sectional area than the cross-sectional area of the fiber strand. The remaining annular space between the fiber strand and the orifice through which molten resin passes defines a predetermined area through which the thermoplastic resin may flow. The ratio of the cross-sectional area of the fiber to the cross-sectional area of the annular space being the means whereby the proportion of resin coating to fiber strand may be controlled.
The process for interspersing fiber strands in a thermoplastic resin comprises the steps of conveying at least one fiber strand through a coating die in the presence of molten thermoplastic resin, thereby coating the fiber strand with the resin; and thereafter directly introducing the resin-coated fiber strand in a heated state into a receiver for movement into a molding machine. The receiver may comprise an extruder barrel which houses a rotatable screw or simply a plate or tray utilized to convey a pliant mass of resin and fiber into the mold press of a compression molding machine.
This process may be run in a discontinuous manner to produce a desired quantity of the molding material. The thermoplastic resin is typically introduced into the passage at pressures of between 4,000 psi and 40,000 psi. By way of example, a coating die operating at pressures between 12,000 and 14,000 psi resulted in the resin coated fiber strand becoming entrained with the resin flowing through the coating die at velocities of between 80 and 250 feet per minute. The resulting fiber-resin mixture comprises between 20 to 60 weight percent fiber strands.
The apparatus for wetting and conveying fiber strands with a thermoplastic resin of the present invention comprises a housing having a passage with a fiber inlet and an outlet. This passage is arranged and constructed to permit a continuous strand of said fiber to be passed from the inlet through the housing and out of the outlet. A resi
Cross Paul C.
Hansen Craig N.
Hawley Ronald C.
Davis Robert
Moore & Hansen
Woodshed Technologies, Inc.
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