PLASTIC MOLDING PROCESS AND PRODUCTS PRODUCED THEREBY

Abstract: The invention utilizes the adhesive properties which plastic material exhibits while still hot combined with a multi stage molding operation wherein one side of an insert or core (3) located in one side of a mold (1) is coated with molten plastic (6) on a first closing of the mold, the mold is then opened with the plastic still hot to remove the insert or core (3) from the one mold site by virtue of its adherence by the hot plastic to the other mold side, a second charge (6') of plastic is then introduced into the said one mold side and the mold is closed again with the plastic in a molten state to complete the encapsulation of the insert (3) or core. The invention also relates to completely encapsulated inserts or cores produced by the method aforesaid.

Description: PLASTIC MOLDING PROCESS AND PRODUCTS PRODUCED THEREBY FIELD OF THE INVENTION This invention relates to plastic molding processes and products produced thereby and more particularly to a plastic molding process wherein insert members or cores inserted into a mold are completely encapsulated by the plastic introduced into the mold during the molding operation. BACKGROUND OF THE INVENTION Insert molding is a widely used method to incorporate functional components such as metal pins, screws, electrical contacts, etc. into a plastic injection molding. These functional components are typically inserted at predetermined locations in the open molding tool which comprises a core side and a cavity side which when brought together or closed define the desired mold shape. After the functional components have been inserted, the tool is closed, and the molten plastic is injection into the cavity. The molten plastic flows around these inserts and after appropriate cooling the part can be removed from the tool with these inserts partly incorporated in the plastic body. Similar insert molding techniques are used for compression molding of e.g. polyester based Sheet Molding Compound (SMC). Here the functional part is inserted in the core and/or cavity side while the tool, which is heated, is open. Next the SMC is loaded into the tool and, as the tool is closed, the polyester SMC starts to flow under heat and pressure, filling the cavity and flowing around the inserts. After appropriate curing time the part can be removed from the tool with the inserts partly incorporated in the plastic body. Another technique utilizes the insertion of a preformed metal or plastic skin into the cavity side of the mold and the insertion of devices by means of which the part to be molded is to be fastened to other parts into the core side of the mold. The skin and the fastening devices are then combined with the injection of e.g. structural foam to produce one integral piece such as automotive bumper guards. Other known techniques involve the molding of thermoplastic material onto or around another component, such as Outsert Molding. This process uses a technique where an object is placed at the parting line between the core and cavity of a tool and actually extends out of the tool. After closing of the tool molten material is injected into the cavity and the portion of the object which is inside the cavity is being covered with plastic. These known methods of insert molding mentioned above involve the placements of the inserts into the core or cavity side of the mold prior to molding resulting in only a portion of the insert being anchored into the plastic moldings. One example of actual encapsulation of almost 100% of a core into an injection molding is the so called "Lost Core" molding technique used to produce complicated hollow plastic components such as engine intake manifolds. In this method, a metal alloy is first cast into a shape which resembles the hollow interior of the plastic components to be produced. This metal component or core is then placed into an injection molding tool at a predetermined location and held in place by e.g. pins, moving side cores, or in certain locations by the tool parting line. The gap between the metal components and the cavity wall determines the wall section of the finished plastic part. Following the securement of the metal component, the tool is then closed and molten plastic is injected between the metal component or core and the walls of the cavity. After appropriate cooling the plastic part with a metal core is removed from the tool and placed into a hot oil bath. The metal core is melted by the hot oil and can escape through the openings formed during the injection molding process where the metal core was held in place in the tool prior to molding. The resulting plastic part is hollow, similar to a blow molding, however more complex and with very smooth inner walls. A technique for encapsulating prefabricated cores with an injected liquid resin is known under the name of Resin Transfer Molding (RTM). This technique involves the fabrication of e.g. a foam core surrounded by several fiberglass mats. This prefabricated core is placed into a tool. The tool is closed and a liquid resin such as epoxy resin is injected into the space provided between the fibers of the fiberglass mat to totally encapsulate the foam core. Sometimes vacuum is applied to the tool, assisting the flow of the resin and the complete wet out of the fiberglass mat. After curing of the epoxy resin, the part can be removed from the tool. This technique is used, for example, to produce lightweight and stiff automotive hoods. These known techniques directed at encapsulating a core or insert involve a mechanical means to keep the core in a predetermined distance from the cavity walls by means of e.g. pins (Lost Core) or a fiberglass mat (RTM) which enables the core to be almost completely encapsulated. It is the object of the present invention to enable the complete encapsulation of a core or insert without the use of pins or other locating means. SUMMARY OF THE INVENTION The present invention resides in providing a molding operation which enables the total encapsulation of a core or an insert or inserts in a surrounding plastic material by the utilization of the plastic material itself to secure the core or insert in position within the enveloping plastic during the molding operation. In this respect, the invention utilizes the adhesive properties which plastic material exhibits while still hot combined with a multi stage molding operation wherein a core or insert is placed in one side of a mold. A first charge of plastic material is introduced between the core or insert and the other side of the mold and the mold is closed with the plastic material in a molten state to coat the exposed surfaces of the core or insert with a plastic layer. The mold is then opened while the plastic layer is still hot causing the core or insert which is adhered to the other side of the mold by the hot plastic layer to be removed from the one mold side. A second charge of plastic material is then introduced into the mold side from which the core or insert has been removed. The mold is then closed with the plastic in a molten state to coat the remainder of the insert or core. In the preferred form of the invention, the charges of plastic material are charges of thermoplastic material introduced into the mold while in a molten state. However, it will be understood that thermoset plastic material may also be used and that, through the use of heated tooling, the plastic charges can be heated in the mold as part of the molding operation. It will be understood that the quantity of plastic introduced into the mold in each of the plastic charges will determine the thickness of the surrounding or encapsulating layer of plastic. It will also be understood that the molding steps can be repeated to encapsulate two or more inserts. The molding process of the invention in which inserts or cores are totally encapsulated with a continuous plastic film or layer gives rise to novel totally encapsulated products and structures which heretofore could not be produced and the invention further relates to such novel products and structures. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view of an open mold in which an insert or core has been placed on the core side of the mold and a first charge of plastic, which in the preferred embodiment of the invention is a viscous molten thermoplastic, has been introduced into the mold on top of the insert or core, that is, between the insert and the cavity side of the mold preparatory to the closing of the mold. Figure 2 shows the mold of Figure 1 in the closed position showing the molten plastic charge compressed to flow and cover the upper surface and the periphery of the insert or core as enabled by the spacing between the perimeter of the mold and the perimeter of the insert. Figure 3 shows the next step in which the mold is open while the plastic material is still hot causing the plastic material through its adhesion to the insert or core and to the cavity side of the mold to carry the insert or core off the core side of the mold and showing a second charge of viscous molten plastic introduced into the mold on the core side of the mold, that is, between the insert or core and the mold core side. Figure 4 shows the further step in which the mold has been closed again causing the second charge of molten plastic to spread and cover the underside of the insert or core and to meet the still hot plastic of the first charge around the perimeter of the insert or core to complete the encapsulation of the insert or core. Figure 5 is a view showing the mold open again and the completely encapsulated insert or core being removed after the plastic material has cooled sufficiently to harden. Figures 6 through 12 illustrate the molding steps corresponding to those shown in Figures 1 through 5 for encapsulating two inserts or cores. Figure 6 corresponds to Figure 1 showing a first insert or core placed on the core side of the mold and the first charge of viscous molten plastic material introduced into the open mold on top of the first insert or core. Figure 7 corresponds to Figure 2 and shows the mold closed. Figure 8 is similar to Figure 3 but in this case a second insert or core has been placed on the core side of the mold and a second charge of viscous molten plastic has been placed on top of the second insert or core. Figure 9 shows the mold closed and showing the first insert or core fully encapsulated and the second insert or core having its top surface and perimeter covered with the compressed and distributed plastic charge. Figure 10 shows the second opening of the mold this time while the plastic material is still hot and a third charge of viscous molten plastic material introduced into the mold between the underside of the second insert or core member and the core side of the mold by being deposited on the core side of the mold. Figure 11 shows the third closing of the mold to complete the encapsulation of the second insert or core. Figure 12 shows the final opening of the mold after the plastic material has hardened sufficiently on cooling that the multi insert or core encapsulated product can be handled and removed. Figures 13 to 17 correspond to Figures 1 to 5 inclusive but showing a different insert or core structure. Figure 18 is a broken away vertical section on an enlarged scale of the encapsulated insert or core produced by the molding operations of Figures 1 to 5 inclusive. Figure 19 is a broken away vertical section on a large scale of the encapsulated dual or multi-core product produced by the molding steps of Figures 6 to 12 inclusive. Figure 20 is a broken away vertical sectional view on an enlarged scale of the encapsulated insert or core produced by the molding steps " of Figures 13 to 17 inclusive. Figure 21 is a view similar to Figure 18 but showing the insert or core as comprising a composite sandwich of material. Figure 22 is a broken away perspective view illustrating where the products produced by Figures 1 to 5 inclusive and Figures 13 to 17 inclusive are being used to form a pallet with the pallet being in the process of being assembled. Figure 23 is a broken away vertical sectional view of the assembled pallet of Figure 22. DETAILED DESCRIPTION ACCORDING TO THE PREFERRED EMBODIMENTS OF THE PRESENT INVENTION Returning first to Figures 1 to 5, Figure 1 shows a molding tool or mold comprising a core side 1 and a cavity side 2 with the mold in the open position and an insert 3 which may, for instance, be a wafer board having a dimension slightly less than the dimension of the mold sides so that the edges 4 of the insert or core 3 stop short of the edges 5 of the core side 1. Placed on top of the insert 3 is a charge 6 of plastic material, preferably a viscous molten thermoplastic material, having a predetermined measured quantity so that, when the mold is closed under pressure to the position shown in Figure 2, the plastic material will be spread as a thin layer 7 covering the upper surface 8 and edges 4 of the insert or core with the plastic material being confined at the edges 4 of the insert by the perimeter walls or edges 9 of the cavity side 2 of the mold which telescopically engage the core side edges 5 as shown in Figure 2. Following closure of the mold under pressure to spread the plastic material 6 to cover the upper surface and edges of the insert or core 3, " the mold is then opened as illustrated in Figure 3 while the plastic material is still hot utilizing its viscosity or adhesive qualities to secure the material to the cavity side of the mold and to the core or insert 3 to remove the insert from the core side of the mold. Thus, the layer 7 of plastic material now forms the means of supporting the insert or core in the mold without requiring any pins or other support mechanism and the thickness of the plastic layer 7 determines the spacing between the cavity side of the mold and the core, that is, the location of the core. Also as shown in Figure 3 a second charge 6' of viscous molten plastic material as aforesaid is introduced into the mold by placing same on the core side 1 of the mold following which the mold is closed as illustrated in Figure 4 wherein the second charge 6' of the molten material is spread as a thin layer 7' to cover the undersurface 10 to complete the encapsulation of the core by uniting with the still hot plastic material of the layer 7 at the boundary or edges 4 of the core 3. Following cooling and hardening of the plastic layers 7 and T, the mold is opened as illustrated in Figure 5 and the encapsulated core removed. Figures 1 to 5 illustrate a molding operation carried out with the molding tool arranged conveniently in a horizontal position with the core side 1 oriented beneath the cavity side 2. It will be understood that the arrangement could be reversed with the cavity side 2 disposed beneath the core side 1 in which case the insert or core 3 would first be placed in the cavity side 2 of the mold and the first charge 6 of molten plastic material introduced into the cavity side of the mold on top of the core 3 and, in the sequence of molding steps, the roles of the cavity and core sides of the molds would be reversed throughout the sequence of mold steps to obtain the completely encapsulated insert or core 3. As illustrated in Figures 1 to 5, the core side 1 of the mold is formed with a pair of circular channels 11 having tapered center posts 12 into which material from the charge 6' is forced under pressure to provide the dependent annular hollow rings 13 on the underside of the encapsulated core as illustrated in Figure 22. It will be understood that the core side and as well the cavity side of the mold may be formed to provide ribs, grooves or designs as desired in the encapsulating plastic layers 7 and T. Figures 6 to 12 illustrate the application of the method to provide a product having a multiple layers of inserts or cores which are completely encapsulated. As in the case of Figures 1 to 5, the method is illustrated with the mold tool in a horizontal position with the core side 1 below the cavity side 2. With this arrangement of the tooling, a first insert or core 14 is placed on the core side 1 of the mold and a first charge 15 of viscous molten thermoplastic material is placed on top of the core 14 as illustrated in Figure 6. Then, as illustrated in Figure 7, the mold is closed under pressure to spread the plastic material to cover the upper surface 16 and the edges 17 of the core 14. Again, as illustrated in Figure 8, the mold is open and the layer 18 of the plastic material adhering to the cavity side 2 of the mold and the first core 14 carries the first core 14 up away from the core side 1 of the mold at which time a second insert or core 19, shown in Figure 8 as having the same dimensions as the first core 14, is placed on the core side 1 of the mold and a second charge 20 of viscous molten thermoplastic material as aforesaid is placed on top of the second insert 19. The mold then is closed under pressure as illustrated in Figure 9 and a second charge of plastic material 20 is spread to complete the encapsulation of the first core 14 and to cover the upper surface 21 and the edges 22 of the second core 19 with plastic layer 18(a). Again, while the plastic material of both the first charge 15 and the second charge 20 are still hot, the mold is opened as shown in Figure 10 with the adhesive bond of the plastic with the cavity mold side 2 and the cores 14 and 19, the fully encapsulated core 14 and the partially encapsulated core 19, are removed from the core side 1 of the mold. A third charge 23 of viscous molten thermoplastic material as aforesaid is then placed on the core side 1 of the mold. The mold is again closed under pressure to complete the encapsulation of the second core 19 with a plastic layer 18(b) as illustration in Figure 11. Upon cooling, the mold is opened and the multiple core product 24 removed from the mold. Figures 13 to 17 illustrate the molding method being carried out to produce a pair of members having totally encapsulated cores which in the example given are to form the bottom members or runners of the pallet illustrated in Figure 22. In this case, a pair of inserts or core members 27 are placed in the correspondingly shaped dual wells 28 in the core side 29 of a molding tool arranged below the cavity side 30. Next a charge of viscous molten thermoplastic material 31 is placed on the core side 29 of the mold on top of the core members 27 and the mold closed under pressure to provide a layer 32 of plastic covering the exposed surfaces of the core members 27, the thickness of the layer being dependent upon the quantity of plastic material in the charge 31. Again, while the plastic material 31 is still hot, the mold is opened as illustrated in Figure 15 with the plastic material adhered to the cavity side of the mold and to the core members 27 to carry them away from the core side 29 of the mold. A second charge 31' of viscous thermoplastic material as aforesaid is introduced centrally into the core side 29 of the mold and the mold is again closed under pressure as illustrated in Figure 16 causing the second charge of plastic 31' to spread and complete the encapsulation of the core members 27 with a horizontal layer 33 extending across the bottom of the core members 27 and inclined layers 34 joining the bottom layer 33 with the layer 32. Again, the core side 29 of the mold is shown as having circular channels or grooves 35 with tapered center parts 36 to produce hollow mounting rings 37. After removal from the mold, the encapsulated core members 27, which comprise pallet runners 38, are separated and incorporated into a pallet designated at 39 ( Figures 22 and 23) comprising the upper platform 40, runners 38 (only one being shown) connected by spacers 41 which are welded, preferably by spin welding, into the annular rings or channels 13 and 37 of the pallet platform 40 and the pallet runner 38 as illustrated in Figure 23. Figure 18 is a cross-section of a corner portion of the product produced by the process of Figures 1 to 5 showing the core or insert 3 encapsulated by the layers 7 and 7' from the material of the plastic charges 6 and 6' respectively. While the core 3 may, for instance, be wafer board, it may be any other desired insert such as a foamed product or a composite product such as illustrated in Figure 21 which comprises a central foam layer 42 wrapped in a fiber glass mat 43 with the plastic layers 7 and 7' wetting the glass mat and penetrating open pores of the foamed central portion 42 of the composite insert. It will be understood that the plastic charges 6 and 6' may have different compositions or colours as desired so that the layers 7 and 7' can be coloured differently, have different compositions and different characteristics. Figure 19 illustrates a cross-section of a corner of the product produced by the process illustrated in Figures 6 to 12 where a pair of inserts 14 and 19 are encapsulated in plastic. Again, it will be appreciated that these inserts may be the same or different as discussed in connection with Figure 21. Additionally, the method of encapsulating two inserts as illustrated in Figures 6 to 12 can be continued to encapsulate three or more separate inserts or cores to incorporate for instance a central insert of foamed material sandwiched between two separate wafer board inserts. Figure 20 is a cross-section of one of the corners of one of the encapsulated inserts 27. Again the insert or core 27 may take different forms including a composite core such as discussed with respect to Figure 21. While the preferred method for the method of the present invention is the use of a compression molding process using horizontally mounted tools with telescoping edges with either the core or cavity side facing upwards for easy placement of the core or cores, the method can be carried out using the injection or injection/compression molding process with either horizontally or vertically mounted tooling as long as telescoping edge tooling or other means such as moving side cores to contain the liquid plastic material is used. In this latter case, a system for securing the position of the core or prefabricated core materials must be provided during the first injection step, that is, until the process has proceeded until the hot plastic through it adhesive properties fixes the insert in position in the mold. When using the injection or injection/compression molding process with vertically mounted tooling in addition to the provision for the containment of the liquid material and for initially securing the position of the core or prefabricated cores in position until they are secured by the adhesive property of the plastic material, one or more apertures in the prefabricated core may be necessary to inject the first charge of molten material through the core into the core or cavity side of the tool. As mentioned, the preferred type of materials in carrying out the method of the invention are thermoplastic materials which can be used with water cooled tools. However, thermoset materials such as polyester S.M.C., epoxy and the like can also be used and rather than introducing the charges of plastic material into the mold in a molten state they may be brought to the molten state by heated molds or tools as part of the molding operation. Although various preferred embodiments of the present invention have been described herein in detail, it will be appreciated by those skilled in the art, that variations may be made thereto without departing from the scope of the appended claims.

Claims: THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS: 1. A method of completely encapsulating an insert or core in plastic material comprising placing said insert or core in one side of a mold tool having a core side and a cavity side whose perimeters are greater than the perimeter of said insert or core and means to confine plastic flow within said mold when the mold is closed, introducing a first charge of plastic between said insert or core and the other side of said mold, closing said mold with said plastic material in a molten state to cover exposed surfaces of said insert or core with a plastic layer, opening said mold while said plastic is still hot to utilize the adhesive properties of said plastic layer to fix said insert or core to said other mold side and spaced therefrom by said plastic layer, introducing a second charge of plastic material into said one mold side from which said insert or core has been removed, closing said mold with said second charge of plastic material heated to a molten state to complete the encapsulation of said insert or core, and removing said encapsulated insert or core after cooling. 2. A method as claimed in Claim 1 in which said first and second plastic charges are introduced into said mold in a molten state. 3. A method as claimed in Claim 2 in which said plastic material is a thermoplastic material. 4. A method as claimed in Claim 2 in which said plastic material is a thermoset material. 5. A method as claimed in Claim 1 in which said mold tool is a heated tool and said plastic material is heated to a molten state in said heated tool. 6. A method as claimed in Claim 4 in which said mold tool is a heated tool and said thermoset plastic material is heated to a molten state in said heated tooling. 7. A method of completely encapsulating a core in a thermoplastic material comprising introducing said core into one side of a mold having a core side and a cavity side and a perimeter greater than the perimeter of said core and means to confine plastic flow within said mold perimeter when the mold is closed, introducing a first charge of molten viscous thermoplastic material between one side of said core and the other of said mold sides, closing said mold to encapsulate said one side and perimeter of said core, opening the mold while said thermoplastic material is still hot to utilize its viscosity to adhere said core to said other mold side, to remove said core from said one side, introducing a second charge of viscous molten thermoplastic material into said one mold side, closing said mold to complete the encapsulation of said core, and removing said encapsulated core after cooling. 8. A method as claimed in Claim 7 in which said core is a rigid planar member. 9. A method as claimed in Claim 7 in which said core is a member formed of foam material. 10. A method as claimed in Claim 9 in which said foam member has open cells and said plastic material is forced into said open cells during said closings of said mold to encapsulate said core. 11. A method as claimed in Claim 7 in which said core has a composite structure comprising a central foamed member wrapped in a surrounding glass mat, and said plastic material is forced into the interstices of said glass mat and foam cells during said closings of said mold to impregnate said glass mat and enter said foam cells. 12. A method of encapsulating a core in plastic material comprising placing said core on one side of a mold having a core side and a cavity side with said core lying wholly within the perimeter of said one side, introducing viscous molten thermoplastic material into said mold between said core and the other of said mold sides, closing said mold to cause said molten plastic to envelope said core except for the portion thereof resting on said one mold side, opening said mold while said plastic is still hot to utilize the adhesion of said plastic to said core and to the other of said mold sides to remove said core from said one side, introducing a second charge of viscous molten thermoplastic material between said core and said one side, then said mold to complete envelopment of said core by said plastic. 13. A method as claimed in Claim 12 in which said mold sides have telescoping edges. 14. A method as claimed Claim 12 in which said core is a rigid planar member. 15. A method as claimed in Claim 12 in which said core is a composite structure. 16. A method of encapsulating multiple inserts or cores in plastic material comprising placing a first insert or core in one side of a mold having a core side and a cavity side and a larger perimeter than said first insert or core and means to confine outer flow around the perimeter of the mold when the mold is closed, introducing a first charge of viscous molten thermoplastic material between said first insert or core and the other side of said mold, closing said mold to spread said first charge of thermoplastic material over said first insert or core and around the perimeter thereof to partially encapsulate said first insert or core, opening said mold while said plastic material is still hot to utilize the adhesion of said plastic material to said first insert or core and said other mold side to remove said first insert or core from said one mold side, placing a second insert or core in said one mold side, introducing a second charge of molten viscous thermoplastic material between said second insert or core and said first insert or core, closing said mold again to spread said second charge of thermoplastic material to complete encapsulation of said first insert or core and to partially encapsulate said second insert or core including the perimeter thereof, opening said mold while said second charge of thermoplastic material is still hot to utilize the adhesion of said thermoplastic material to said other mold side to said first insert or core and to said second insert or core to remove said second insert or core from said one mold side, introducing a third charge of molten viscous thermoplastic material into said one side, closing said mold again to complete encapsulation of said second insert or core, and removing said encapsulated inserts or cores from said mold after said plastic material has cooled. 17. A molded product having an insert or core completely encapsulated in a continuous plastic material. 18. A molded product as claimed in Claim 17 in which said plastic material is a thermoplastic material. 19. A molded product as claimed in Claim 17 in which said plastic material is a thermoset material. 21. A molded product as claimed in Claims 18 or 19 in which said core is a composite planar structure. 22. A molded product having multi-layers of planar cores each totally encapsulated in plastic material. 23. A molded product as claimed in Claims 17, 18 or 19 comprising a substantially planar platform member in which said encapsulated core is a rigid substantially planar member. 24. A molded product as claimed in Claim 23 in which said planar member is a wafer board. 25. A molded product as claimed in Claim 23 in which said planar member is of a composite material. 26. A molded product as claimed in Claims 23, 24 or 25 in which said platform has a plurality of spaced support members secured to and projecting from one side thereof. 27. A molded product as claimed in Claim 26 in which said support members are hollow plastic cylinders. 28. A molded product as claimed in Claim 27 in which said support members are spin welded to said platform face. 29. A molded product as claimed in Claims 26, 27 or 28 in which said support members are secured to a base. 30. A molded product as claimed in Claim 29 in which said molded product is a pallet.

Inventors: COCKLE DAVE, HOEDL HERBERT K, MAURY EUFREDO, COCKLE, DAVE, HOEDL, HERBERT, K., MAURY, EUFREDO
Applicants: COCKLE DAVE, HOEDL HERBERT K, MAURY EUFREDO, ROYAL ECOPRODUCTS LTD, COCKLE, DAVE, HOEDL, HERBERT, K., MAURY, EUFREDO, ROYAL ECOPRODUCTS LIMITED
Application year: 1998
Main classification: B29C70
IPC codes: B29C43, B29C70