WO2010054188A1

WO2010054188A1 - Co-injection molding process and parts formed thereby

Info

Publication number: WO2010054188A1
Application number: PCT/US2009/063541
Authority: WO
Inventors: Frank J. Villari; Glenn Poyer
Original assignee: Illinois Tool Works Inc.
Priority date: 2008-11-10
Filing date: 2009-11-06
Publication date: 2010-05-14

Abstract

A co-injection molding system incorporating two or more injection gates feeding a common mold cavity to provide multiple cores surrounded by a skin material within the final finished part. An injection molding system including one or more slug traps disposed along the conveyance path between the injection nozzle and the injection gate and/or at remote portions of the mold cavity to collect and retain vestigial slugs that may form at the injector nozzle and/or at injector gates.

Description

CO-INJECTION MOLDING PROCESS AND PARTS FORMED THEREBY

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of and priority to Unites States Provisional Application No. 61/113,016 filed November 10, 2008, the contents of which are hereby incorporated by reference in their entirety as if fully set forth herein.

TECHNICAL FIELD

[0002] The present invention relates generally to co-injection molding in which a melt-processable skin material is injected into a mold followed by the injection of a second melt-processable material in following relation to the first material. The second material pushes the first material outwardly towards the perimeters of the mold cavity such that the second material forms a core with a surrounding skin of the first material.

[0003] The present invention is more particularly directed to improved arrangements of core structures relative to the surrounding skin in co-injection molded parts and/or for practices aiding in the capture of undesirable vestigial slugs of blended solidified material that may form at the injector nozzle and at injection gates. More particularly, the present invention may incorporate multiple injection gates used to form corresponding core elements arranged in spaced relation within the molded part with skin material disposed in surrounding relation to the core elements to define an "I" beam arrangement or other cross-sectional structure as may be desired. One or more vestigial slug capture cavities may be disposed along the polymer injection path and/or in fluid communicating relation to a distal portion of the mold cavity to capture and retain vestigial slug material at locations removed from the final molded part.

BACKGROUND OF THE INVENTION

[0004] Molded polymeric parts such as automotive door handles or the like may be formed using a co-injection molding process such as a so-called "twin-shot" process incorporating a single gate location for injection of a first thermoplastic material which forms the outer skin of the part followed closely by the injection of a second thermoplastic material which forms the core of the part. Specifically, during the molding operation, the skin-forming first thermoplastic material is injected into the mold cavity in leading relation to the core-forming second thermoplastic material. The injection of both the skin material and the core material takes place through a common gate feeding into the mold cavity. As the core-forming second material is injected into the mold cavity, the skin-forming first material is pushed distally and outwardly towards the perimeter walls of the mold cavity. The core-forming second material thereby occupies a core zone at the interior of the mold cavity which is surrounded by the skin material. The selection of the skin material and the core material permits manipulation of physical characteristics within the finished molded parts based upon the properties of the material selected. In this prior practice the single injection gate typically is located along the parting line of the mold so as to promote a substantially symmetrical arrangement of skin material surrounding a unitary core.

[0005] In prior twin-shot processes, a so called "vestigial slug" of the blended thermoplastic materials tends to form and solidify at the injection gate and at the nozzle of the upstream injection press during transitions when flow is shifting from one material to the other and/or between injection events. The presence of such vestigial slugs in the finished molded part may cause an irregularity in the part and is considered generally undesirable. By way of example only, the vestigial slugs may form at the injection gate and/or at the nozzle of the injection press supplying the thermoplastic materials during periods when the molded parts are being removed and/or other periods when flow of the thermoplastic materials has been curtailed. When the flow of thermoplastic materials is re-initiated, the formed vestigial slugs may be pushed into the mold cavity without melting thereby forming undesired irregularities in the final molded product.

SUMMARY OF THE INVENTION

[0006] The present invention may provide advantages and alternatives over prior constructions and practices by incorporating two or more injection gates feeding a common mold cavity to provide multiple cores arranged in spaced relation to one another within the final finished part. The selection of the core material and the skin material in combination with the orientation of the cores within the final part provides a substantial degree of freedom in providing desired performance characteristics.

[0007] The invention may provide further advantages and alternatives over the prior art by incorporating one or more slug traps to collect and retain vestigial slugs that may form at the injector nozzle and/or at the injector gates. Specifically, one or more cavities are placed in branched relation along the conveyance path between the injection nozzle and the injection gate and/or at remote portions of the mold cavity. Since the slugs are pushed ahead of the molten material, the slugs tend to enter and be trapped within these cavities rather than collecting within the molded part itself. The material within these cavities can then be allowed to solidify to form a button which can be removed and discarded.

[0008] In accordance with one exemplary aspect, the present invention provides an injection molded polymeric article including a first polymeric material defining a skin layer and two or more cores of a second polymeric material different from the first polymeric material. The cores have a length extending at least partially along the molded article. The cores are spaced apart from one another along at least a portion of their length with the first polymeric material disposed in spanning relation between the cores.

[0009] In accordance with another exemplary aspect, the present invention provides an injection molding system for forming a molded polymeric article. The system includes an injector adapted to sequentially inject a first polymeric material and a second polymeric material into a runner system in fluid communication with a mold cavity within a mold. At least one vestigial slug collection cavity is disposed in fluid communicating branched relation to the runner system or within the mold in fluid communicating relation to mold cavity. The vestigial slug collection cavity is adapted to collect and retain solidified vestigial slugs at a location remote from the molded polymeric article. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a schematic view illustrating an exemplary injection press feeding opposing mold cavities;

[0011] FIG. 2 is a schematic sectional view taken generally along line 2-2 of FIG. 1 illustrating an arrangement of injection gates in fluid communication with mold cavities in the form of door handles;

[0012] FIG. 3 illustrates schematically an arrangement of cores of thermoplastic material surrounded by a skin of a different thermoplastic material to form a substantially "I" beam construction;

[0013] FIG. 4 illustrates an exemplary handle structure molded by a co-injection process and including a sacrificial button at the distal end adapted to retain the vestigial slug material; and

[0014] FIG. 5 is a schematic view taken generally along section line 5-5 in Figure 4 illustrating an arrangement of two cores surrounded by skin material in the molded handle structure.

[0015] Before the embodiments of the invention are explained in detail, it is to be understood that the invention is in no way limited in its application to the details of construction and/or the arrangements of the components set forth in the following description or illustrated in the drawings. Rather, the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for purposes of description only and should not be regarded as limiting. The use herein of "including", "comprising", and variations thereof is meant to encompass the items listed thereafter and equivalents, as well as additional items and equivalents thereof. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Reference will now be made to the drawings wherein to the extent possible, like elements are designated by like reference numerals throughout the various views. Referring now to FIG. 1, a schematic view is shown illustrating an injection press 10 such as a twin-shot screw extruder or the like adapted to accept feedstock from two sources. As will be appreciated, such injection presses are well known to those of skill in the art. By way of example only, and not limitation, such exemplary injection presses are believed to be available from Spirex Corporation having a place of business in Youngstown, Ohio, USA. Such injection presses accept polymeric feed stock from two discrete sources and expel such materials in sequence such that a first polymeric material is expelled in leading relation to a second, different polymeric material.

[0017] As illustrated by the directional arrow, the press 10 feeds the polymeric materials outwardly through a nozzle 12 and into a diverging angled sprue 14. The sprue 14 intersects with a runner junction 16 with an arrangement of outlet lines 18 branching outwardly away from the runner junction to individual molds 22. As will be appreciated, the molds 22 include cavities for the acceptance of the injected polymer. Once the polymeric materials are injected into the molds 22 the polymeric materials are allowed to solidify and may be removed by opening the mold cavities. As will be appreciated, the mold cavities and the parts formed therein may have virtually any shape as may be desired. Accordingly, while the present description relates to the formation of handle structures, the molding operation may likewise be utilized in a formation of virtually any other structure as well.

[0018] As best illustrated through joint reference to FIGS. 1 and 2, in the illustrated exemplary system a first vestigial slug trap 24 in the form of a generally dome-shaped cavity is disposed in substantially aligned relation with the sprue 14 in overlying relation to the runner junction 16. In this arrangement, the first vestigial slug trap 24 will tend to collect and retain the leading portion of the polymer flow exiting the nozzle 12. Once the first vestigial plug trap 24 is filled, the remaining portions of the polymer stream can flow outwardly from the runner junction 16 through the outlet line 18 and towards the molds 22. [0019] As noted previously, in a twin-shot molding operation solidified vestigial slugs may tend to form at the exit of the nozzle 12 due to blending and solidification of the two polymeric compounds. This tends to occur during periods of transition from one polymer material to the other and/or between injection events. As flow is reinitiated, the solidified vestigial slug is pushed out of the nozzle 12 and ahead of the polymer flow stream. Since the vestigial slug moves in leading relation to the polymer flow stream exiting the sprue 14, the slug tends to be collected and retained in the first vestigial slug trap 24 rather than moving outwardly along the branched outlet lines 18. Thus, the occurrence of such vestigial slugs from the nozzle 12 within the final finished part may be reduced or eliminated. The collected material may be removed periodically by opening the mold and cleaning out the slug trap 24.

[0020] While the presence of the first vestigial slug trap 24 may be used to collect slugs formed at the nozzle 12, such slugs of solidified blended material may also form at injection gates 26 feeding into the mold cavities. In this regard, it is to be understood that while two injection gates 26 are illustrated as feeding into each mold cavity, a larger or smaller number of injection gates may likewise be utilized.

[0021] According to the illustrated exemplary practice, an arrangement of mold cavity slug traps 30 may be arranged in fluid communication with the mold cavity. As illustrated, the mold cavity slug traps 30 may be arranged at a substantially distal location relative to the injection gates 26. Thus, the leading portion of polymeric material entering the mold cavity will tend to flow through the mold cavity and into the mold cavity slug traps 30 as additional polymeric material is pushed from behind. Since the vestigial slugs tend to form at the injection gates 26 between injection events, such vestigial slugs tend to lead the polymeric flow stream and will thus enter and collect in the mold cavity slug traps 30. As illustrated, the mold cavity slug traps 30 may be oriented substantially along a parting line 32 of the mold to facilitate ease of removal of the finished part and the material collected in the mold cavity slug traps 30 following solidification.

[0022] By way of example only, and not limitation, FIG. 4 illustrates a handle structure 40 molded in fluid communication with a mold cavity slug trap 30 at a distal end. As shown, in the final molded arrangement a button 42 corresponding to the position of the mold cavity slug trap 30 is connected at a distal end of the handle structure 40. As will be appreciated, the button 42 contains the solidified vestigial slug material captured within the mold cavity slug trap 30. As previously explained, this button 42 will preferably include any vestigial slug material entering the mold cavity from the injection gate 26. Accordingly, the occurrence of such vestigial slug material within the handle structure 40 may be reduced or eliminated thereby enhancing the quality of the handle structure 40. Upon removal of the solidified structure from the mold, the button 42 may be cut away from the handle structure 40 and discarded or recycled.

[0023] As previously noted, the present invention also contemplates the formation of multiple substantially discrete cores in spaced relation within a co-injection molded part with a polymeric skin material surrounding the cores. Referring to FIG. 3, one exemplary cross-sectional arrangement for a co-injection molded part incorporating multiple cores is illustrated. In the configuration of FIG. 3, a first polymer defining a skin layer 50 is disposed in surrounding and separating relation to a pair of cores 52 formed from a second polymer. In this arrangement, the cores 52 and the skin layer 50 cooperatively define an "I" beam construction which may promote strength across the structure. Such an "I" beam structure may be useful in providing both horizontal and vertical load resistance.

[0024] The first polymer forming the skin layer 50 and the second polymer forming the cores 52 may be selected to provide desired physical characteristics across the final molded part. By way of example only, and not limitation, the skin layer 50 may be formed from a thermoplastic polymeric material having a relatively high flexural modulus while the cores 52 may be formed from lower modulus thermoplastic material. However, it is likewise contemplated that these materials may be reversed if desired. According to one exemplary construction, the structure may be formed with a skin layer 50 formed from a glass-filled polyester such as PBT (polybutylene terephthalate) with a foamed PBT core. In another construction a part may be formed with a skin layer 50 of glass or mica-filled polypropylene with cores 52 of foamed polypropylene. As will be appreciated, such skin layers may be painted or plated as may be desired. Of course, other thermoplastic polymer pairings of core materials which bond to skin materials may also be used.

[0025] While the use of a relatively high strength skin layer 50 in combination with cores 52 of lower strength material may be desirable, it is likewise contemplated that a substantially decorative skin material such as a high gloss skin or the like may be used around a high strength core material. Such a structure may be desirable when painting or other surface treatment is not desired.

[0026] It has been found that cross-sectional core and skin configuration substantially corresponding to the "I" beam construction of FIG. 3 may be achieved by using a pair of spaced-apart injection gates 26 feeding into the mold cavity. In this regard, the members of each injection gate pair may extend away from a common feed line connected to the runner junction 16 (FIG. 2). In such an arrangement, when the runner junction 16 is operatively connected to a twin- shot injection press 10 a substantially parallel flow circuit is established feeding each mold cavity. According to one contemplated practice, each of the injection gates may be oriented generally along the mold parting line 32 although other orientations may be used if desired.

[0027] In operation, a skin-forming first polymer is injected through each of the injection gates 26 to partially fill the mold cavity. A second-core forming polymer is then subsequently injected through the injection gates to form core structures within the skin-forming first polymer. Specifically, as the core-forming second polymer is injected, the skin-forming fist polymer is pushed distally and outwardly towards the edges of the mold cavity. Preferably, the core-forming second polymer is injected into the mold cavity simultaneously through each of the injection gates. In the finished structure, the cores 52 may extend substantially along the length of the finished structure. In this regard, it will be understood that while portions of the cores 52 may merge into one another, the cores 52 will preferably remain separate from one another over at least a portion of their length.

[0028] It has been found that the inclusion of spaced cores 52 with a surrounding and separating skin layer 50 is readily adaptable to numerous geometries. By way of example only, and not limitation, FIG. 5 illustrates a cross-section of the molded handle structure 40 previously described. As illustrated, this structure has a skin layer 50 with a generally kidney-shaped cross-section surrounding cores 52 of generally oval cross- section to define a desired "I" beam construction. Of course, it is to be understood that while constructions with two cores 52 have been illustrated and may be desirable in many environments of use, constructions with three or more cores are also achievable by providing a corresponding number of injection gates. In the event that three or more cores are incorporated, such cores may be arranged in virtually any orientation relative to one another as may be desired.

[0029] Of course, variations and modifications of the foregoing are within the scope of the present invention. Thus, it is to be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention, the claims are to be construed to include alternative embodiments and equivalents to the extent permitted by the prior art.

[0030] Various features of the invention are set forth in the following claims.

Claims

CLAIMSWHAT IS CLAIMED IS:

1. An injection molded polymeric article comprising: a first polymeric material defining a skin layer; and a plurality of cores of a second polymeric material different from the first polymeric material, the cores having a length extending at least partially along the molded article, wherein the cores are spaced apart from one another along at least a portion of their length with the first polymeric material disposed in spanning relation between the cores.

2. An injection molded polymeric article as recited in Claim 1 , wherein the first polymeric material is characterized by a higher flexural modulus than the second polymeric material.

3. An injection molded polymeric article as recited in Claim 2, wherein the first polymeric material is glass-filled PBT and wherein the second polymeric material is foamed PBT.

4. An injection molded polymeric article as recited in Claim 2, wherein the first polymeric material is selected from the group consisting of glass-filled polypropylene and mica-filled polypropylene and wherein the second polymeric material is foamed polypropylene.

5. An injection molded polymeric article as recited in Claim 1, wherein the first polymeric material is characterized by a lower flexural modulus than the second polymeric material.

6. An injection molded polymeric article as recited in Claim 1 , wherein the article is an automotive door handle.

7. An injection molded polymeric article as recited in Claim 6, wherein the automotive door handle has a substantially kidney shaped cross-section, and wherein the cores are substantially oval in cross-section.

8. An injection molded polymeric article comprising: a first polymeric material defining a skin layer; and a pair of cores of a second polymeric material different from the first polymeric material, the cores being disposed in adjacent relation to one another and having a length extending at least partially along the molded article, wherein the cores are spaced apart from one another along at least a portion of their length with the first polymeric material disposed between the cores to define an "I" beam structure.

9. An injection molded polymeric article as recited in Claim 8, wherein the first polymeric material is characterized by a higher flexural modulus than the second polymeric material.

10. An injection molded polymeric article as recited in Claim 9, wherein the first polymeric material is glass-filled PBT and wherein the second polymeric material is foamed PBT.

11. An injection molded polymeric article as recited in Claim 9, wherein the first polymeric material is selected from the group consisting of glass-filled polypropylene and mica-filled polypropylene and wherein the second polymeric material is foamed polypropylene.

12. An injection molded polymeric article as recited in Claim 8, wherein the first polymeric material is characterized by a lower flexural modulus than the second polymeric material.

13. An injection molded polymeric article as recited in Claim 8, wherein the article is an automotive door handle.

14. An injection molded polymeric article as recited in Claim 13, wherein the automotive door handle has a substantially kidney shaped cross-section, and wherein the cores are substantially oval in cross-section.

15. An injection molding system for forming a molded polymeric article, the system comprising: an injector adapted to sequentially inject a first polymeric material and a second polymeric material into a runner system having one or more injection gates feeding a mold cavity within a mold; and at least a first vestigial slug trap comprising a slug collection cavity disposed in fluid communicating branched relation to the runner system or within the mold in fluid communicating relation to the mold cavity, the first vestigial slug trap adapted to collect and retain solidified vestigial slugs at a location remote from the molded polymeric article.

16. The injection molding system as recited in Claim 15, wherein the first vestigial slug trap is disposed at a runner junction in substantially aligned relation to a sprue feeding the runner junction.

17. The injection molding system as recited in Claim 16, wherein at least a second vestigial slug trap is disposed in fluid communicating branched relation to at a distal end of the mold cavity relative to the runner system.

18. The injection molding system as recited in Claim 17, wherein the second vestigial slug trap intersects the mold cavity at a parting line of the mold.

19. The injection molding system as recited in Claim 18, wherein the second vestigial slug trap defines a reservoir for collection and solidification of polymeric material in attached relation to the molded polymeric article.

20. The injection molding system as recited in Claim 19, wherein the runner system includes at least two injection gates feeding the mold cavity.