Polymeric foam articles and methods of making polymeric foams

Abstract

To provide polymer foam articles and methods of making polymer foams.SOLUTION: Molded polymer foam articles are described as having a novel foam structure. The polymer foam articles include a continuous polymer matrix defining therein a plurality of bubbles present throughout the article, including a surface region extending 500 microns beneath a surface of the article. The surface region is further characterized as having compressed bubbles. The novel foam structure is achieved even when the molded polymer foam article has a thickness exceeding 2 cm, a volume exceeding 1,000 cm3, or both a volume exceeding 1,000 cm3 and a thickness exceeding 2 cm. Methods of making the molded polymer foam articles are also described.SELECTED DRAWING: Figure 1A

Description

[Background technology]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Provisional Patent Application No. 62 / 867,516, entitled "Method for Molten Foam Injection Molding of Foamed Parts," filed June 27, 2019. U.S. Provisional Patent Application No. 62 / 867,516 is hereby incorporated by reference in its entirety as if fully set forth herein.

[0002] Foamed polymer articles have been widely adopted in industry due to the highly desirable attribute of providing the high strength associated with solid polymer articles while also reducing the density, and therefore the amount of polymer used to form an article of a selected volume. In addition, industry enjoys the benefits offered by the reduction in weight of a foamed article compared to its solid counterpart, while still obtaining the strength, toughness, impact resistance, etc., benefits provided by the polymer itself.

[0003] The industry has therefore developed several now-standard methods for entraining gas within thermoplastic polymers and creating such foam articles. To mold foamed thermoplastic polymer articles using gas, commercial guidelines and industry practices employ melt-mixing devices operable to melt-mix a gas or source of gas with a thermoplastic polymer while maintaining a pressure within the device to limit gas expansion, and also at a temperature above the melting temperature of the thermoplastic polymer. Such processes and devices are designed to minimize the formation of foam, i.e., pockets of gas, that would otherwise form due to the expansion of the gas within the molten thermoplastic polymer. Thus, while residing within and disposed within the melt-mixing device, the thermoplastic polymer may be foam-free or substantially foam-free, including the source of the gas or the gas itself dissolved or dispersed therein. A foam-free or substantially foam-free mixture of molten thermoplastic polymer and gas at or above a temperature that would form foam at atmospheric pressure may be referred to as melt-pneumatic mixing. The temperature at which a gas, i.e., a physical blowing agent, will form a foam upon melt-pneumatic mixing at atmospheric pressure can be referred to as the critical temperature. Melt-mixing devices known in the art are therefore designed and adapted to create and dispense melt-pneumatic mixtures. Furthermore, such devices are suitable for creating melt-pneumatic mixtures by adding nascent, latent, or latent gases that are released at a characteristic temperature or formed at a characteristic temperature by exothermic or endothermic chemical reactions. The critical temperature of a nascent, latent, or latent gas is the temperature at which a reaction occurs or the gas is released into the thermoplastic polymer. All such materials and processes are widely understood, and melt-mixing devices of various designs are widely commercially available for this purpose. A commonly employed melt-mixing device is a single-screw or twin-screw extruder having a pressurized chamber at the distal end of the screw, modified to receive a set amount of melt-pneumatic mixture, or "shot," that advances while the screw action mixes and forces the melt-pneumatic mixture toward the pressurized chamber.

[0004] In response to building a set amount, or shot, in the pressurized chamber, the molten pneumatic mixture is dispensed from the melt-mixing device and directed by fluidly connected tubes, pipes, etc. into a mold cavity, where it acquires the desired shape. Dispensing is generally performed to maximize the amount of foaming (foam formation) that occurs within the mold cavity upon release of pressure while the thermoplastic polymer is still molten. The expanded foam within the cavity is then cooled, resulting in a foamed article. Foam parts molded using this methodology are referred to in the art as injection-molded foam parts. This technique is generally limited to producing parts having a thickness in the range of about 2 cm or less.

[0005] An understanding of injection molding processes employing a physical blowing agent source to induce foam structure within molded parts can be seen in a recent peer-reviewed journal article by Bociaga et al., "The influence of foaming agent addition, talc filler content, and injection velocity on selected properties, surface state, and structure of polypropylene injection molded parts." Cellular Polymers 2020, 39(1) 3-30. In this publication, process conditions typically employed to mold standard injection-molded ISO test specimens 4.1 mm thick were systematically varied to generate 16 different combinations of process settings and formulation variables (physical blowing agent source concentration, filler content, injection rate, injection time, hold time, and hold pressure). The authors teach that while manipulating the process and formulation will produce some variations in foam structure in the resulting foam part, not all variables will produce a part with a "skin," a term in the art to describe a very characteristic region near the surface of an injection-molded foam article that is free or substantially free of bubbles.

[0006] Inspection of the surface of an injection-molded foam article and an area extending in any direction approximately 500 microns beneath the surface reveals solid thermoplastic regions, i.e., the regions are free of or substantially free of foam. Foam parts resulting from injection molding according to conventional injection molding processes contain a skin layer characteristic. In addition, the skin layer of most such parts is significantly thicker than 500 μm and may be 1 mm, 2 mm, 3 mm, or even thicker, depending on the method, equipment, and materials employed.

[0007] For making large foam parts (e.g., pallets or wheelbarrow bodies), the conventional processes described above are insufficient because large mold cavities induce excessive pressure drops as the molten pneumatic mixture flows and expands during mold filling, and foam may form but then coalesce or escape from the viscous polymer flow during filling. Therefore, in some cases of "structural foam" molding, multiple nozzles are used simultaneously to rapidly fill large or thick mold cavities. In other cases, significant back pressure may be applied within the mold cavity to prevent foam formation during filling. That is, releasing pressure after filling the mold acts to substantially allow foam formation within the mold cavity. Both approaches are often used in a single process.

[0008] However, the aforementioned structural foam molding process does not effectively solve the problems that have prevented the industry from making significant progress. As is widely understood, areas near the surface of a molten mass cool more rapidly than its interior, and a temperature cooling gradient develops within the mass. The cooling rate at the deepest point within the mass is slowest. From the perspective of a large mold cavity filled with a mass of molten polymer or pneumatic mixture, the interior regions of the mass may cool so slowly that the viscous flow of the thermoplastic allows foam coalescence, forming large polymer-free pockets and disrupting the intended continuous polymer matrix that defines such a foam. This effect may be exacerbated by polymer volume shrinkage as it cools below its melting transition. For large foam parts, this effect may even lead to complete collapse of the foam structure within the part.

[0009] The combined strength and density reduction associated with foamed articles cannot be achieved without a continuous polymer matrix throughout the entire part. Foamed parts with large polymer-free areas or voids compromise the structural integrity of the part, making such parts unsuitable for their intended use. These serious technical problems limit the industrial use of polymer foams to many otherwise very useful and beneficial applications. Thus, there is a continuing need to provide improved methods for making foamed articles, particularly large or thick foamed articles. There is a continuing need to obtain parts with a continuous foam structure throughout. There is a particular need to obtain parts with a thickness greater than 2 cm and with a continuous foam structure throughout. There is a continuing need in the industry to address such needs using conventional equipment and materials. Summary of the Invention [Means for solving the problem]

[0010] Described herein is a method for making a molten polymer foam. The method includes adding a thermoplastic polymer and a physical blowing agent source to an extruder; heating and mixing the thermoplastic polymer and the physical blowing agent source under pressure in the extruder to form a melt-pneumatic mixture, wherein the temperature of the melt-pneumatic mixture exceeds a critical temperature of the physical blowing agent source; collecting a quantity of the melt-pneumatic mixture in a collection area of ​​the extruder; defining an expansion volume in the collection area and allowing pressure to drop in the collection area; allowing an expansion time period to elapse after the definition; and dispensing the molten polymer foam from the collection area. In embodiments, the expansion volume is selected to provide 10% to 300% of the total expected molten foam volume in the collection area. In embodiments, the expansion period is 5 seconds to 600 seconds. In embodiments, the melt-pneumatic mixing is uninterrupted or substantially uninterrupted during the expansion period.

[0011] In embodiments, the dispensing step is dispensing into a forming element, and in some embodiments, the forming element is a mold. In embodiments, there is a fluid connection between a collection area of ​​the extruder and the mold. In embodiments, the dispensing step is an uninterrupted flow of the molten polymer foam. In embodiments, the dispensing step is a linear flow of the molten polymer foam.

[0012] In embodiments, the method further comprises cooling the dispensed molten polymer foam to a temperature below the melt transition temperature of the thermoplastic polymer. In embodiments, the method further comprises adding one or more additional materials to the extruder, the one or more materials being selected from colorants, stabilizers, brighteners, nucleating agents, fibers, particulates, and fillers. In embodiments, the physical blowing agent source is a physical blowing agent, and the addition is a pressurized addition. In other embodiments, the physical blowing agent source comprises a bicarbonate, a polycarboxylic acid or a salt or ester thereof, or a mixture thereof.

[0013] Also disclosed herein are polymeric foam articles made using the methods, materials, and apparatus described herein. In embodiments, the polymeric foam article has a foam structure throughout characterized as a continuous polymer matrix defining a plurality of bubbles therein. In embodiments, the surface region of the polymeric foam article comprises compressed bubbles. In embodiments, the surface region is a region extending 500 microns from the surface of the article.

[0014] Also disclosed herein are thermoplastic polymer foam articles, the article having a foam structure throughout that is a continuous polymer matrix defining a plurality of bubbles therein, and further, a surface region of the article comprises compressed foam. In some embodiments, the surface region is a region of the article extending 500 microns from its surface. In some embodiments, the article comprises compressed foam greater than 500 microns from its surface. In embodiments, the polymer foam article comprises a thickness greater than 2 cm, and in other embodiments, the polymer foam article comprises a thickness greater than 1,000 cm. 3 Exceeding 1,000cm 3 ~5,000cm 3 , or an additional 5,000 cm 3 and in yet other embodiments, the polymeric foam article has a volume greater than 1,000 cm 3 Volume greater than 1,000cm and thickness greater than 2cm 3 and ~5,000 cm 3 volume and thickness greater than 2cm, or 5,000cm 3 and a thickness of more than 2 cm.

[0015] In embodiments, materials used to make polymeric foam articles include thermoplastic polymers selected from, among others, but not limited to, polyolefins, polyamides, polyimides, polyesters, polycarbonates, poly(lactic acid), acrylonitrile-butadiene-styrene copolymers, polystyrene, polyurethanes, polyvinyl chloride, tetrafluoroethylene, polyethersulfones, polyacetals, polyaramids, polyphenylene oxides, polybutylenes, polybutadienes, polyacrylate and methacrylate copolymers, ionomeric polymers, polyether-amide block copolymers, polyaryletherketones, polysulfones, polyphenylene sulfides, polyamide-imide copolymers, poly(butylene succinate), cellulosics, polysaccharides, and copolymers, alloys, admixtures, and blends thereof. In some embodiments, the thermoplastic polymer is a mixed plastic waste stream. The continuous polymer matrix optionally further comprises one or more additional materials selected from colorants, stabilizers, brighteners, nucleating agents, fibers, particulates, and fillers.

[0016] Other objects and features will be partly apparent and partly pointed out hereinafter. The present invention provides, for example, the following. (Item 1) 1. A method comprising: adding a thermoplastic polymer and a source of physical blowing agent to an extruder; heating and mixing the thermoplastic polymer and a physical blowing agent source under pressure in the extruder to form a melt-pneumatic mixture, wherein the temperature of the melt-pneumatic mixture exceeds a critical temperature of the physical blowing agent source; collecting said amount of melt pneumatic mixing in a collection area of ​​said extruder; defining an expansion volume within the collection area and causing a pressure drop within the collection area; after said determination, allowing an inflation time period to elapse; dispensing molten polymer foam from said collection area; A method comprising: (Item 2) 2. The method of claim 1, wherein the expansion volume is selected to provide 10% to 300% of the total expected molten foam volume within the collection area. (Item 3) 3. The method according to claim 1, wherein the inflation period is 5 seconds to 600 seconds. (Item 4) 4. The method of any one of items 1-3, wherein the melt pneumatic mixing is substantially uninterrupted during the expansion cycle. (Item 5) 5. The method according to any one of items 1 to 4, wherein the dispensing is dispensing into a mold. (Item 6) 6. The method of claim 5, further comprising a fluid connection between the collection region of the extruder and the die. (Item 7) 7. The method of any one of items 1-6, wherein the dispensing comprises a linear flow of the molten polymer foam. (Item 8) 8. The method of any one of items 1-7, further comprising cooling the dispensed molten polymer foam to a temperature below the melting transition temperature of the thermoplastic polymer. (Item 9) 9. The method of any one of items 1-8, further comprising adding one or more additional materials to the extruder, wherein the one or more materials are selected from colorants, stabilizers, brighteners, nucleating agents, fibers, particulates, and fillers. (Item 10) 10. The method of any one of items 1-9, wherein the physical blowing agent source is a physical blowing agent and the addition is a pressurized addition. (Item 11) 10. The method according to any one of items 1-9, wherein the physical blowing agent source comprises a bicarbonate, a polycarboxylic acid or a salt or ester thereof, or a mixture thereof. (Item 12) A thermoplastic polymer foam article, the article having a foam structure throughout that is a continuous polymer matrix defining a plurality of bubbles therein, and further wherein a surface region of the article comprises compressed bubbles. (Item 13) Item 13. The polymeric foam article of item 12, wherein the surface region is the region of the article extending 500 microns from its surface. (Item 14) Item 14. The polymeric foam article of item 13, wherein the article comprises compressed foam greater than 500 microns from its surface. (Item 15) 15. The polymeric foam article of any one of items 12-14, wherein the thermoplastic polymer is selected from one or more of polyolefins, polyamides, polyimides, polyesters, polycarbonates, poly(lactic acid), acrylonitrile-butadiene-styrene copolymers, polystyrene, polyurethanes, polyvinyl chloride, tetrafluoroethylene, polyethersulfones, polyacetals, polyaramids, polyphenylene oxides, polybutylenes, polybutadienes, polyacrylate and methacrylate copolymers, ionomeric polymers, polyether-amide block copolymers, polyaryletherketones, polysulfones, polyphenylene sulfides, polyamide-imide copolymers, poly(butylene succinate), cellulosics, polysaccharides, and copolymers, alloys, admixtures, and blends thereof. (Item 16) 16. The polymeric foam article of any one of items 12-15, wherein the continuous polymer matrix further comprises one or more additional materials selected from colorants, stabilizers, brighteners, nucleating agents, fibers, particulates, and fillers. (Item 17) 17. The polymeric foam article of any one of items 12-16, wherein the continuous polymer matrix further comprises talc. (Item 18) 18. The polymer foam article of any one of items 12-17, wherein the continuous polymer matrix comprises a mixed plastic waste stream. (Item 19) 19. The polymeric foam article of any one of items 12-18, wherein the polymeric foam article has a thickness greater than 2 cm. (Item 20) The polymer foam article has a thickness of 1,000 cm 3 19. The polymeric foam article of any one of items 12-18, having a volume greater than (Item 21) The polymer foam article has a thickness of more than 2 cm and a thickness of 1,000 cm 3 19. The polymeric foam article of any one of items 12-18, having a volume greater than [Brief explanation of the drawings]

[0017] [Figure 1A] 1A-1B illustrate a melt mixing apparatus useful for carrying out the methods described herein. [Figure 1B] 1A-1B illustrate a melt mixing apparatus useful for carrying out the methods described herein.

[0018] [Figure 2] Figure 2-1 is a photographic image of a part molded according to a standard foam molding process, as described in Example 1. Figure 2-2 is a photographic image of a part molded according to a molten foam injection molding (MFIM) process, as described in Example 1. Figures 2-3 and 2-5 are photographic images of pieces cut from parts made according to a standard foam molding process, as described in Example 1. Figures 2-2 and 2-3 are photographic images of pieces cut from parts made according to the MFIM process, as described in Example 1.

[0019] [Figure 3]Figure 3A is a photographic image of a cross section of part A, made according to a standard foam molding process, as described in Example 2, cut into two pieces to reveal the cross section. Figure 3B is a photographic image of a cross section of part B, made according to the MFIM process, as described in Example 2, cut into two pieces to reveal the cross section.

[0020] [Figure 4] Figure 4A is a photographic image of a cross section of part C, made according to the MFIM process, as described in Example 2, cut into two pieces to reveal the cross section. Figure 4B is a photographic image of a cross section of part D, made according to a standard foam molding process, as described in Example 2, cut into two pieces to reveal the cross section.

[0021] [Figure 5] FIG. 5 is a graph containing plots of part density versus depressurization volume for various depressurization times for Prototype B, as described in Example 3.

[0022] [Figure 6] FIG. 6 is a graph containing plots of strain versus time for parts made in prototypes A, B, and C, as described in Example 4.

[0023] [Figure 7] FIG. 7 shows photographic images of views of different sides of parts A, B, and C as described in Example 4.

[0024] [Figure 8] FIG. 8 shows a photographic representation of the cross sections of parts A′, B′, C′, and D′ as described in Example 4.

[0025] [Figure 9] FIG. 9 is a depiction of two components as described in Example 5.

[0026] [Figure 10]FIG. 10 is a conformal image of a tomographic scan of a first part fabricated according to the MFIM process, as described in Example 6.

[0027] [Figure 11] FIG. 11 is an image of the cross-sectional plane shown in FIG. 10, as described in Example 6.

[0028] [Figure 12] FIG. 12 is a graph containing a plot of average cell size and cell count versus cell circularity for a first part made as described in Example 6.

[0029] [Figure 13] FIG. 13 is a depiction of an X-ray tomography image of a cross section of the second (spherical) part, as described in Example 6.

[0030] [Figure 14] FIG. 14 is a graph containing plots of average cell size and cell count versus cell circularity for the second (spherical) part, made as described in Example 6.

[0031] [Figure 15] FIG. 15 is a photomicrograph of the fracture surface of a fractured 3-inch diameter composite sphere made according to the MFIM process as described in Example 7.

[0032] [Figure 16] FIG. 16 is a photomicrograph image of the fracture surface of a fractured 3-inch diameter composite sphere made according to the MFIM process as described in Example 7.

[0033] [Figure 17] FIG. 17 is a photomicrograph image of the fracture surface of a fractured 3-inch diameter composite sphere made according to the MFIM process as described in Example 7.

[0034] [Figure 18] FIG. 18 is a photomicrograph image of the fracture surface of a fractured 3-inch diameter composite sphere made according to the MFIM process as described in Example 7.

[0035] [Figure 19] FIG. 19 shows photomicrograph images of cross sections from ISO specimen parts made according to standard foam molding process steps 10, 11, 14, and 15, as described in Example 8.

[0036] [Figure 20] FIG. 20 shows photomicrograph images of cross sections from ISO specimen parts made according to MFIM process steps 9, 10, 15, and 16, as described in Example 8.

[0037] [Figure 21] FIG. 21 shows a photomicrograph of a cross section of an ISO specimen part made according to the MFIM process of step 9, as described in Example 8, and a stress-strain plot of a replicate part made according to the MFIM process of step 9.

[0038] [Figure 22] FIG. 22 includes a photomicrograph of a cross section of an ISO specimen part made according to the standard foam molding process of step 10, as described in Example 8, and a stress-strain plot of a replicate part made according to the standard foam molding process of step 10.

[0039] [Figure 23] FIG. 23 contains two images from an X-ray tomography of an ISO specimen part made according to the standard foam molding process of step 15, as described in Example 8.

[0040] [Figure 24] FIG. 24 includes two images from an X-ray tomography of an ISO specimen part made according to the MFIM process of step 9, as described in Example 8.

[0041] [Figure 25] FIG. 25 is an image from an X-ray scan of a large tensile specimen part made according to the MFIM process as described in Example 9.

[0042] [Figure 26] FIG. 26 includes cross sections of eight large tensile specimen parts made according to the MFIM process as described in Example 9.

[0043] [Figure 27] FIG. 27 is an X-ray tomography image of a large tensile specimen part made according to the MFIM process as described in Example 9.

[0044] [Figure 28] FIG. 28 includes a series of X-ray tomography images at different depths within a tensile specimen part made according to the MFIM process, as described in Example 10, and a series of images at different depths within a tensile specimen part made according to a standard foam molding process.

[0045] [Figure 29] FIG. 29 is a graph including a plot of cell count versus depth for tensile specimen parts made according to the MFIM process, as described in Example 10, and a plot of cell count versus depth for tensile specimen parts made according to a standard foam molding process.

[0046] [Figure 30] FIG. 30 is a graph including a plot of cell circularity versus depth for tensile bar parts made according to the MFIM process, as described in Example 10, and a plot of cell circularity versus depth for tensile bar parts made according to a standard foam molding process.

[0047] [Figure 31]FIG. 31 is a graph including a plot of cell size versus depth for tensile specimen parts made according to the MFIM process, as described in Example 10, and a plot of cell size versus depth for tensile specimen parts made according to a standard foam molding process.

[0048] [Figure 32] FIG. 32 is a photograph of Sample 20, made according to the reverse MFIM process, as described in Example 12.

[0049] FIG. 32 is a photograph of Sample 20, made according to the reverse MFIM process, as described in Example 12.

[0050] [Figure 33] FIG. 33 is a photograph of Sample 10, made according to the MFIM process as described in Example 12.

[0051] [Figure 34] FIG. 34 is a photograph showing a cross section of Sample 20 made according to the reverse MFIM process as described in Example 12.

[0052] [Figure 35] FIG. 35 is a photograph showing a cross section of Sample 10 made according to the MFIM process as described in Example 12.

[0053] [Figure 36] FIG. 36 is a plot of cell count versus depth (distance from surface) for Sample 10 (MFIM) and Sample 20 (reverse MFIM), as described in Example 12.

[0054] [Figure 37] FIG. 37 is a plot of cell size versus depth (distance from the surface) for Sample 10 (MFIM) and Sample 20 (reverse MFIM), as described in Example 12.

[0055] [Figure 38] FIG. 38 is a graph including an averaged stress versus strain plot for Sample 10 (MFIM) and a plot for Sample 20 (inverse MFIM) from compressive modulus measurements, as described in Example 12.

[0056] [Figure 39] FIG. 39 is a graph including an averaged stress versus strain plot for Sample 10 (MFIM) and a plot for Sample 20 (inverse MFIM) from flexural modulus measurements, as described in Example 12.

[0057] [Figure 40] FIG. 40 is a graph of stress versus strain plots from compressive modulus measurements made from three metallocene polyethylene (mPE) materials of different densities and made according to the MFIM process, as described in Example 14.

[0058] [Figure 41] FIG. 41 illustrates a mold configuration useful for carrying out the methods described herein.

[0059] Corresponding reference characters indicate corresponding parts throughout the drawings. DETAILED DESCRIPTION OF THE INVENTION

[0060] Detailed Description While this disclosure provides reference to preferred embodiments, those skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. Various embodiments will now be described in detail with reference to the drawings, in which like reference numerals represent like parts and assemblies throughout the several views. Reference to various embodiments does not limit the scope of the claims appended hereto. Additionally, any examples described herein are not intended to be limiting, but merely to describe some of the many possible embodiments for the appended claims.

[0061] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present specification, including definitions, will control. Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and are not intended to be limiting.

[0062] As used herein, "polymer matrix," including "continuous polymer matrix," "thermoplastic polymer matrix," "molten polymer matrix," and similar terms, refers to a continuous solid or molten thermoplastic polymer phase, or a quantity of solid or molten thermoplastic polymer that defines a continuous phase.

[0063] As used herein, "molten mixture" means a molten thermoplastic polymer or a mixture of molten thermoplastic polymers, optionally including one or more additional materials mixed with the molten thermoplastic polymer or mixture thereof.

[0064] As used herein, a "melt-pneumatic mixture" refers to a mixture of a thermoplastic polymer and a physical blowing agent source, wherein the polymer is at a temperature above its melting temperature, the temperature of the mixture exceeds the critical temperature of the physical blowing agent source, and the mixture is characterized as being foam-free or substantially foam-free. The melt-pneumatic mixture is under sufficient pressure to prevent foam formation, or to substantially prevent foam formation, or to dissolve or disperse the physical blowing agent source as either a gas or a supercritical liquid within the thermoplastic polymer. "Substantially prevents foam formation," "substantially foam-free," and similar terms relating to melt-pneumatic mixtures mean that while pressure conditions can be used to prevent foam formation in the molten mixture, defects, wear of parts, and the like within processing equipment can cause unintentional pressure losses that do not generally interfere with obtaining and maintaining a pressurized molten mixture.

[0065] As used herein, "foam," "polymer foam," "thermoplastic polymer foam," "melt foam," "molten polymer foam," and similar terms generally refer to a continuous polymer matrix defining a plurality of bubbles as intermittent phases dispersed therein.

[0066] As used herein, the term "foam" means discrete voids defined by and surrounded by a continuous thermoplastic polymer matrix.

[0067] As used herein, the term "physical blowing agent" means a gaseous compound capable of defining a foam within a molten thermoplastic polymer matrix.

[0068] As used herein, the term "critical temperature" means the temperature at which a physical blowing agent source produces a physical blowing agent at atmospheric pressure.

[0069] As used herein, the term "physical blowing agent source" refers to a covert, latent, or nascent physical blowing agent in the form of an organic compound, or combination thereof, that is added to or present in a thermoplastic polymer matrix, such as dissolved in the matrix and / or present therein as a supercritical fluid, or that produces a physical blowing agent by chemical reaction, or the physical blowing agent source is, becomes, or produces a physical blowing agent at a critical temperature characteristic of the physical blowing agent source.

[0070] As used herein, the terms "comprise," "include," "having," "has," "can," "contain," and variations thereof are intended to be open-ended transitional phrases, terms, or words that do not exclude the possibility of additional acts or structures. The singular forms "a," "and," and "the" include plural references unless the context clearly dictates otherwise. The present disclosure also contemplates other embodiments "comprising," "consisting of," and "consisting essentially of" the embodiments or elements presented herein, whether explicitly stated or not.

[0071] As used herein, the term "optional" or "optionally" means that the subsequently described event or circumstance may, but need not, occur, and that the description includes instances in which the event or circumstance occurs and instances in which it does not occur.

[0072] As used herein, the term "about," employed in describing embodiments of the present disclosure to modify, for example, the amount, concentration, volume, process temperature, process time, yield, flow rate, pressure, and similar values ​​and ranges of ingredients in a composition, refers to variations in numerical quantities that may arise, for example, through typical measuring and handling procedures used to make a compound, composition, concentrate, or use formulation, through inadvertent errors in these procedures, through differences in the manufacture, source, or purity of the starting materials or ingredients used to carry out the method, and through similar proximate considerations. The term "about" also encompasses amounts that differ due to aging of a formulation with a particular initial concentration or mixture, and amounts that differ due to mixing or processing a formulation with a particular initial concentration or mixture. When modified by the term "about," the claims appended hereto include equivalents of these quantities. Furthermore, when "about" is employed to describe a range of values, e.g., "about 1 to 5," the recitation means "1 to 5" and "about 1 to about 5" and "1 to about 5" and "about 1 to 5" unless specifically limited by context.

[0073] As used herein, the term "substantially" means "consisting essentially of" as the term is interpreted in U.S. patent law, including "consisting of" as the term is interpreted in U.S. patent law. For example, if a specified compound or material is "substantially free," the composition may be free of that compound or material, or may have a small amount of that compound or material present through unintended contamination, side reactions, incomplete purification, or the like. A "minor amount" may be a trace amount, an immeasurable amount, an amount that does not interfere with value or properties, or some other amount as provided within the context. With a provided list of components "substantially only," the composition may consist only of those components, or may have trace amounts of certain other components present, or may have one or more additional components that do not significantly affect the properties of the composition. Additionally, "substantially," employed in describing embodiments of the present disclosure to modify, for example, the type or amount, property, measurable amount, manner, value, or range of an ingredient in a composition, refers to a variation that does not affect the entire recited composition, property, amount, manner, value, or range in a manner that eliminates the intended composition, property, amount, manner, value, or range. When modified by "substantially," the claims appended hereto include equivalents in accordance with this definition.

[0074] As used herein, any recited range of values ​​shall be construed as supporting a claim that contemplates all values ​​within the range and recites any subranges with endpoints that are real values ​​within the recited range. As a hypothetical illustrative example, the disclosure herein of a range of 1 to 5 shall be considered to support a claim to any of the following ranges: 1 to 5, 1 to 4, 1 to 3, 1 to 2, 2 to 5, 2 to 4, 2 to 3, 3 to 5, 3 to 4, and 4 to 5.

[0075] In embodiments disclosed herein, a method of extruding a molten polymer foam comprises, consists essentially of, or consists of: adding a thermoplastic polymer and a physical blowing agent source to an inlet mounted on a first end of an extruder; heating and mixing the thermoplastic polymer and the physical blowing agent source in the extruder to form a melt-pneumatic mixture, wherein the temperature of the melt-pneumatic mixture exceeds a critical temperature of the physical blowing agent source; collecting a quantity of the melt-pneumatic mixture in a barrel region of the extruder located proximate a second end of the extruder; forming an expanded volume in the barrel region, wherein the forming step involves allowing a pressure drop in the barrel region; allowing a period of time to pass after the pressure drop; and dispensing the molten polymer foam from the extruder.

[0076] In embodiments, an extruder is any machine designed and adapted to melt, mix, and dispense a thermoplastic polymer and mixtures thereof, optionally with one or more additional materials such as fillers, nucleating agents, diluents, stabilizers, brighteners, and the like, and further includes a collection area for collecting a mass of the mixed molten material and is capable of forming an expansion volume within the collection area coupled with a pressure drop. Extruders are well known in the industry and are broadly used to melt, mix, and manipulate molten thermoplastic polymers. In embodiments, the extruder is adapted and designed to melt, mix, and dispense a mixture of a thermoplastic polymer and a physical blowing agent source. Such an extruder is adapted to obtain a molten pneumatic mixture under a pressure sufficient to prevent or substantially prevent foam formation in the molten pneumatic mixture.

[0077] In embodiments, an extruder useful for carrying out the present method includes an internal volume, referred to in the art as the "barrel" of an extruder, designed and adapted to receive the solid thermoplastic polymer and further melt and mix it. In embodiments, the extruder defines an internal volume designed to receive the solid thermoplastic polymer and a physical blowing agent or source thereof, further melt the polymer, and mix the molten polymer with the physical blowing agent or source to obtain a molten pneumatic mixture. In embodiments, the extruder further includes a collection area for collecting a mass of the molten pneumatically mixed material. In embodiments, the extruder further includes a means for forming an expansion volume within the collection area coupled with a pressure drop.

[0078] In an embodiment, the extruder is an injection molding machine. In an embodiment, the extruder is a SODICK extruder sold by Plustech Inc. (Schaumburg, IL). TMIn some embodiments, the extruder is a molding machine. In embodiments, the extruder includes either one or two elements, known in the art as "screws," disposed within an internal volume known in the art as a "barrel." In embodiments, the screw has a generally right-handed cylindrical shape and further includes one or more protruding threaded elements, referred to as "steps." In some embodiments, the extruder is a single-screw extruder, defined as including one screw movably positioned within the barrel for rotation of a cylinder about its axis, for lateral movement of a cylinder along its axis, or for combined movement including both rotation and lateral movement. In other embodiments, the extruder is a twin-screw extruder, defined as including two screws movably positioned within the barrel in a generally parallel and adjacent relationship relative to each other, and further defined as including two screws movably positioned within the barrel for rotation of a cylinder about its axis, for lateral movement of a cylinder along its axis, or for combined movement including both rotation and lateral movement. The screws of the twin screw extruder are further arranged such that the action of the screws, when orbited in a counter-rotating manner, defines a designed mixing and transport pattern of the molten thermoplastic polymer disposed within the barrel.

[0079] In embodiments, the extruder is further adapted and designed to receive a solid thermoplastic polymer. In embodiments, the barrel of the extruder is further adapted and designed to receive a solid thermoplastic polymer by including an inlet mounted near the first end of the extruder and adapted to add the solid thermoplastic polymer to the barrel. The solid thermoplastic polymer is added to the inlet in any suitable format, such as beads, pellets, powder, ribbon, or block, all formats familiar to those skilled in the art. In embodiments, the extruder includes a second, third, or even fourth or higher inlet designed and adapted to add or introduce one or more additional materials, including one or more solids, liquids, or gases, into the internal volume of the extruder, and further to mix the one or more additional materials with the thermoplastic polymer. The interior volume of the extruder is adapted to receive, contain, and melt a thermoplastic polymer and, optionally, one or more additional materials, and to expose the thermoplastic polymer and, optionally, one or more additional materials to heat, shear, and mixing to form a molten mixture while simultaneously transporting the molten mixture generally in a direction proceeding from its first end to its second end. In embodiments where the extruder is a single-screw or twin-screw extruder, the shearing, mixing, and transporting are accomplished by rotating the screws or counter-rotating the two screws.

[0080] In embodiments, the extruder internal volume, or a portion thereof, is surrounded or partially surrounded by one or more heat sources. Heat sources suitable for heating the extruder internal volume include, in various embodiments, a heated water jacket, a heated oil jacket, an electrical resistance heater, an open or jacketed flame, or another heat source. The heat source is operable to increase the temperature within the extruder internal volume. The temperature is suitably selected by an operator to melt the thermoplastic polymer and / or maintain a desired temperature within a portion of the extruder internal volume. In embodiments, the extruder is adapted to include more than one heat source, which are independently operable to allow one skilled in the art to provide a range of temperature "zones" within the internal volume. Additional temperature zones may be included in some extruders in association with adding one or more materials to their inlet or dispensing one or more materials from their outlet. In an embodiment, the temperature within one or more temperature zones is set by an operator for increased control and optimization of the melting, mixing, shearing, and transport of the thermoplastic polymer and, optionally, one or more additional materials.

[0081] Extruders are conventionally designed and adapted to apply and maintain pressure within their internal volume during heating, mixing, and transporting of the molten mixture. In embodiments, the extruder is designed and adapted to apply and maintain a first pressure within its internal volume or barrel during heating, mixing, and transporting of the molten mixture. In embodiments, the pressure inside the barrel during heating, mixing, and transporting of the molten pneumatic mixture is sufficient to prevent or substantially prevent leakage of the molten pneumatic mixture from the barrel. In embodiments, the pressure inside the barrel is sufficient to prevent the molten pneumatic mixture from developing a foam when the temperature inside the barrel exceeds the critical temperature of the physical blowing agent source. In embodiments, the pressure inside the barrel is substantially sufficient to prevent the molten pneumatic mixture from developing a foam when the temperature inside the barrel exceeds the critical temperature of the physical blowing agent source. In such embodiments described in this paragraph, "substantially" refers to inadvertent leakage of material or inadvertent loss of pressure from the barrel due to the manufacture, aging, or mode of use of the extruder and / or screw, as will be familiar to those skilled in the art. Further, in such embodiments, "substantially" in the context of "sufficient to prevent the molten pneumatic mixture from developing foam" means that a small percentage, such as up to 10%, of the physical blowing agent may inadvertently form foam while pressure is maintained on the molten pneumatic mixture, but it is the operator's goal to maintain sufficient pressure to prevent foam from forming.

[0082] In an embodiment, the extruder barrel includes a collection area for collecting a quantity of the molten mixture in preparation for dispensing the molten mixture from the extruder. The mass of the molten mixture is selected by a user. In an embodiment, the molten mixture is a molten pneumatic mixture. In such an embodiment, the term used in the art to describe the collection of a quantity of the molten pneumatic mixture into the collection area of ​​the extruder barrel is referred to as "building a shot." As will be understood by those skilled in the art of injection molding, to build a shot, a quantity of the molten pneumatic mixture is collected by rotating a screw or screws (or another mixing element) to transport the molten pneumatic mixture from a first end of the extruder toward a second end, i.e., toward and into the collection area, and by allowing the molten pneumatic mixture to accumulate in the collection area until the entire desired mass of the molten pneumatic mixture is collected and disposed within the collection area of ​​the barrel. The collection area is mounted between the screw or screws and the second end of the extruder and is in pressurized communication with the remainder of the barrel.

[0083] In conventional injection molding to form thermoplastic polymer foams, a mass of molten pneumatic mixture, or a "shot," is collected or "built" in a collection area by conveying the molten pneumatic mixture toward and into the collection area via rotation of a screw or multiple screws (or other mixing element). A shot is said to be built when the entire selected mass of the molten pneumatic mixture is disposed within the collection area. Those skilled in the art will understand that the foregoing description of melt-mixing equipment, such as the mechanical elements and features of an extruder or other melt-mixing equipment, as well as the foregoing description of methods for creating and collecting a molten pneumatic mixture into a shot, are in accordance with conventional equipment and methods of using such equipment to create a molten pneumatic mixture and build that shot.

[0084] According to these known methods and apparatus, the shot of molten pneumatic mixture is conventionally prevented or substantially prevented from developing foam while in the barrel, including during mixing, heating, transport, and collection, and while disposed in the collection area. Conventionally, once the desired shot is collected in the collection area, a gate or door installed between the collection area and an outlet installed on the second end of the extruder is opened to provide a fluid connection from the barrel to the outlet and dispense the shot from the extruder. In some embodiments, when the gate or door is opened, a mechanical plunger is applied to force the molten pneumatic mixture from the barrel through the outlet. In embodiments, a screw or multiple screws are preferably employed in a lateral movement in a direction toward the second end of the extruder, which in turn forces the molten pneumatic mixture from the collection area of ​​the barrel through the outlet.

[0085] We have found that after building a shot of molten pneumatic mixture in the collection region of the extruder, it is advantageous to form, provide, or define an expansion volume in the collection region of the extruder, the defining step involving a pressure drop in the collection region, allowing a time period, referred to herein as an expansion period, to pass after the definition, and dispensing the shot from the extruder after the expansion period. The shot, in such embodiments, is dispensed in the form of a molten polymer foam. In embodiments, the expansion volume is defined adjacent to the shot, disposed in the collection region of the extruder. In embodiments, the shot is not mixed or exposed to applied shear or elongation during the process in which the expansion volume is defined. In embodiments, the shot is not transported during the expansion period. In embodiments, the shot is allowed to rest or reside, uninterrupted or substantially uninterrupted, in the collection region during the expansion period. In any of the foregoing embodiments, the shot may be heated during the expansion period. However, in some embodiments, heat is not added to the shot during the expansion period.

[0086] After the expansion cycle has elapsed or is transient, the molten polymer foam may be dispensed from the second end of the extruder. The molten polymer foam comprises a plurality of bubbles. Without being limited by theory, it is believed that the bubbles form when the molten pneumatic mixture is exposed to an expanded volume and the accompanying pressure drop (second pressure). In accordance with known principles of physics, the formation of the bubbles is likely caused by the definition of an expanded volume and the accompanying pressure drop in the collection area of ​​the barrel, along with the expansion cycle, in which the bubbles are formed by the action of a physical blowing agent. In some embodiments, defining the expanded volume after building the shot results in superior properties attributed to the dispensed molten polymer foam. In other words, we have found that forming a molten pneumatic mixture under pressure, followed by a subsequent step of reducing the pressure and forming a concomitantly defined volume prior to dispensing the mixture (such as into a mold cavity), results in a molten polymer foam that, upon cooling, provides a solidified polymer foam article with unexpected and highly beneficial physical properties.

[0087] We have discovered that molten polymer foam dispensed from an extruder according to the aforementioned method obtains significant technical advantages. These advantages are observed in the solidified polymer foam resulting from cooling the molten polymer foam to a temperature below the melting transition temperature of the thermoplastic polymer. The structure of articles made using molten polymer foam dispensed from an extruder after an expansion cycle differs both macroscopically and microscopically from polymer foams made by conventional methods, exhibiting superior properties suitable for, for example, structural components. Polymer foam articles made using the methods, apparatus, and materials described herein are characterized as having a continuous thermoplastic matrix throughout and a plurality of bubbles dispersed throughout the polymer foam article. This characterization has been demonstrated for articles with thicknesses greater than 2 cm, 1,000 cm, and 1,000 cm. 3 or a thickness of more than 2cm, plus 1,000cm 3 Exceeding 1,000cm 3 ~5,000cm 3, or an additional 5,000 cm 3 and articles having a volume exceeding 1,000 cm 3 Volume greater than 1,000cm and thickness greater than 2cm 3 ~5,000cm 3 and a thickness of more than 2 cm, or a volume of more than 5,000 cm and a thickness of more than 2 cm.

[0088] In an embodiment, defining the expansion volume in a single-screw extruder is preferably achieved by moving the screw laterally toward the first end of the extruder and away from the collection area of ​​the extruder where the shot is collected. In an embodiment, defining the expansion volume in a twin-screw extruder is preferably achieved by moving both screws laterally toward the first end of the extruder and away from the area of ​​the extruder where the shot is collected. The lateral movement optionally involves rotation of the screw or screws. That is, one or both screws may be rotated during the lateral movement, or rotation may be stopped during the lateral movement. It should be understood that defining the expansion volume by lateral movement of one or both screws is advantageously selected by the extruder operator to provide a selected expansion volume. That is, the distance of lateral movement of the screw or screws is preferably selected by the operator to define the selected expansion volume.

[0089] Thus, in embodiments, the expansion volume is targeted by the operator to add a volume to the collection area sufficient to accommodate the total expected molten polymer foam volume, or a percentage thereof. The total expected molten polymer foam volume of the shot may be calculated based on the amount of thermoplastic polymer and physical blowing agent source plus any additional materials added to construct the shot, further assuming that all of the physical blowing agent source will contribute to the formation of bubbles within the molten polymer foam to be obtained. Those skilled in the art will understand that physical blowing agent sources available in the industry are provided with suitable information to calculate the total expected molten polymer foam volume based on the amount of physical blowing agent source added to create the shot and other processing conditions. In embodiments, the expansion volume is the difference between the shot volume and the expected molten polymer foam volume.In embodiments, the expansion volume is between 10% and 100% of the total expected molten polymer foam volume within the collection area, for example, between 15% and 100%, or between 20% and 100%, or between 25% and 100%, or between 30% and 100%, or between 35% and 100%, or between 40% and 100%, or between 45% and 100%, or between 50% and 60%, or between 60% and 70%, or between 70% and 80%, or between 80% and 90%, or between 90% and 100%, or between 10 ... % to 100%, or 55% to 100%, or 60% to 100%, or 65% to 100%, or 70% to 100%, or 75% to 100%, or 80% to 100%, or 85% to 100%, or 90% to 100%, or 10% to 95%, or 10% to 90%, or 10% to 85%, or 10% to 80%, or 10% to 75%, or 10% ~70%, or 10%~65%, or 10%~60%, or 10%~55%, or 10%~50%, or 10%~45%, or 10%~40%, or 10%~35%, or 10%~30%, or 10%~25%, or 10%~20%, or 10%~15%, or 15%~20%, or 20%~25%, or 25%~30%, or 30 Targeted to provide % to 35%, or 35% to 40%, or 40% to 45%, or 45% to 50%, or 50% to 55%, or 55% to 60%, or 60% to 65%, or 65% to 70%, or 70% to 75%, or 75% to 80%, or 80% to 85%, or 85% to 90%, or 90% to 95%, or 95% to 100%. In yet other embodiments, the expansion volume is 100% to 300% of the difference between the shot volume and the expected molten polymer foam volume, for example, 100% to 105%, or 100% to 110%, or 100% to 115%, or 100% to 120%, or 105% to 110%, or 110% to 115%, or 115% to 120%, or 120% to 125%, or 120% to 150%, or 150% to 200%, or 200% to 250%, or 250% to 300% of the difference between the shot volume and the expected molten polymer foam volume.

[0090] After the expansion volume is defined, a period of time is allowed to elapse or pass prior to dispensing the molten polymer foam from the extruder. In embodiments, the period of time is referred to as an expansion period. In some embodiments, no mixing, transport, shearing, or other physical manipulation or additional volume change is performed within the collection area during the expansion period. Instead, in such embodiments, the shot is allowed to rest within the collection area during the expansion period. At the end of the expansion period, the molten polymer foam is dispensed from the extruder outlet. In embodiments, the molten polymer foam is dispensed into a mold cavity, and the molten polymer foam is cooled to a temperature below the melting transition of the thermoplastic polymer to obtain a solidified polymer foam article.

[0091] In embodiments, the expansion period is selected by the operator to be about 5 seconds to 600 seconds, depending on the mass of the sample, the source of physical blowing agent, and the amount of any additional material present in the shot. In embodiments, the expansion period is 5 seconds to 600 seconds, or 5 seconds to 500 seconds, or 5 seconds to 400 seconds, or 5 seconds to 300 seconds, or 20 seconds to 600 seconds, or 20 seconds to 500 seconds, or 20 seconds to 400 seconds, or 20 seconds to 300 seconds, or 10 seconds to 200 seconds, or 20 seconds to 200 seconds, or 30 seconds to 200 seconds, or 40 seconds to 200 seconds, or 50 seconds to 200 seconds, or 5 seconds to 190 seconds, or 5 seconds to 180 seconds, or 5 seconds to 170 seconds, or 5 seconds to 160 seconds, or 5 seconds to 150 seconds, or 5 seconds to 140 seconds, or 5 seconds to 130 seconds, or 5 seconds to 120 seconds, or 5 seconds to 110 seconds, or 5 seconds to 100 seconds, or 5 seconds to 90 seconds, or 5 seconds to 80 seconds, or 5 seconds to 70 seconds, or 5 seconds to 60 seconds, or 5 seconds to 50 seconds, or 5 seconds to 40 seconds, or 5 seconds to 30 seconds, or 5 seconds to 20 seconds, or 5 seconds to 10 seconds, or 10 seconds to 15 seconds, or is 15 seconds to 20 seconds, or 20 seconds to 25 seconds, or 25 seconds to 30 seconds, or 30 seconds to 35 seconds, or 35 seconds to 40 seconds, or 40 seconds to 45 seconds, or 45 seconds to 50 seconds, or 50 seconds to 55 seconds, or 55 seconds to 60 seconds, or 60 seconds to 70 seconds, or 70 seconds to 80 seconds, or 80 seconds to 90 seconds, or 90 seconds to 100 seconds, or 100 seconds to 110 seconds, or 110 seconds to 120 seconds, or 120 seconds to 130 seconds, or 130 seconds ~140 seconds, or 140 seconds to 150 seconds, or 150 seconds to 160 seconds, or 160 seconds to 170 seconds, or 170 seconds to 180 seconds, or 180 seconds to 190 seconds, or 190 seconds to 200 seconds, or 200 seconds to 250 seconds, 250 seconds to 300 seconds, or 300 seconds to 350 seconds, or 350 seconds to 400 seconds, or 400 seconds to 450 seconds, or 450 seconds to 500 seconds, or 500 seconds to 550 seconds, or 550 seconds to 600 seconds.

[0092] The use of the aforementioned methods results in the formation of molten polymer foams that, when cooled to a temperature below the melting temperature of the thermoplastic polymer, yield a solidified polymer foam, obtain several significant technical advantages, as described in the following sections. Polymer foam articles are generally characterized as monolithic articles having a continuous polymer matrix that defines a plurality of bubbles dispersed throughout the article. In embodiments, polymer foam articles are specifically characterized as having a continuous polymer matrix that defines a plurality of bubbles dispersed throughout the surface region of the article, where the surface region is defined as the area of ​​the article between the article surface (polymer foam-air interface) and a distance of 500 microns inward from the surface.

[0093] A representative embodiment of an apparatus usefully employed to perform the aforementioned methods is shown in FIG. 1A. FIG. 1A is a schematic diagram of an exemplary single-screw injection molding apparatus 20 according to embodiments disclosed herein, which performs the methods described herein, also useful for making molten polymer foams and polymer foam articles disclosed herein. As shown in FIG. 1A, the injection molding system 20 includes a barrel 21 attached to a motor or drive section 24 and a mold section 26. The barrel 21 includes a first end 21 a and a second end 21 b and defines a hollow interior barrel portion 22. The barrel portion 22 further defines a nozzle 36 adjacent the barrel second end 21 b. A screw 30 is disposed within the barrel portion 22 and includes a screw tip portion 34. The screw 30 is operably coupled to the motor section 24 for rotation of the screw 30 about its central axis or for lateral movement, as indicated by arrow Z. The lateral movement of the screw 30 may be generally in a direction from the first end 21 a of the barrel toward the second end 21 b of the barrel, or from the second end 21 b of the barrel toward the first end 21 a of the barrel. Lateral movement of the screw 30 in either direction is optionally further coupled with rotational movement. The screw 30 further includes one or more steps 31, which are mixing elements for mixing and transporting materials present in the barrel portion 22 generally from the first end 21 a of the barrel toward the second end 21 b of the barrel. The screw 30 is disposed within the barrel portion 22 in a pressurizable sealed relationship therewithin, allowing a pressure above atmospheric pressure to be maintained within the barrel portion 22 by the screw steps 31 within the barrel 21 and, further, by the installation of a check valve 32. A shut-off valve 37 is connected to the barrel 21 near the second end 21 b and is operable to control fluid communication, pressurized communication, or both, between the nozzle 36 and the mold section 26.Check valve 32, located within barrel portion 22 and surrounding screw 30, is operable to prevent back pressure from forcing material resident within barrel portion 22 toward first end 21 a of the barrel, thus providing a pressurizable sealed, fluidly sealed, or pressurizable fluidly sealed relationship between closure valve 37 and check valve 32.

[0094] 1A , mold section 26, as shown, includes two mold sections 38. Mold sections 38 are removably joined together to define cavity 39. In some embodiments, one or more of mold sections 38 are movable to allow injection of a solidified polymer foam article therefrom. In some embodiments, mold sections 38 are mounted in a touching relationship to one another, while in other embodiments, mold sections 28 are spaced apart by a gap.

[0095] In embodiments, the methods disclosed herein are preferably practiced using an apparatus such as system 20 shown in FIGS. 1A-1B. In FIG. 1A, a selected mass of mixture 42A comprising a thermoplastic polymer, a physical blowing agent source, and, optionally, a selected amount of one or more additional materials is added to barrel section 22 through inlet 28, as indicated by arrow A. In some embodiments, the physical blowing agent source is a physical blowing agent, and inlet 28 or another inlet (not shown) is a pressurized gas inlet relative to barrel section 22, with the physical blowing agent being added to the gas inlet at a selected pressure while a non-gaseous material is added to inlet 28. During the addition of mixture 42A to barrel section 22 through inlet 28, motor 24 is operable to rotate screw 30. Rotation of screw 30 transports and mixes mixture 42A to screw tip 34. A heat source (not shown) is preferably employed to add heat to mixture 42A within barrel section 22. Motor 24 rotates screw 30, transporting mixture 42A present in barrel section 22 generally in a direction progressing from first end 21 a to second end 21 b of barrel 21 until it reaches screw tip 34. Additionally, rotation of screw 30 provides mixing of mixture 42A during transport. A heating element or heating zone (not shown) proximate barrel section 22 operates to heat mixture 42A as it is transported and mixed by rotation of screw 30. Multiple heating zones may be present proximate barrel section 22 to vary the temperature inside barrel section 22 between first end 21 a and second end 21 b of barrel 21. During transport, the screw 30 rotating within the barrel portion 22 is operable to mix the mixture 42A, and heat is added to the mixture as it is transported, thereby raising the temperature of the mixture above the melting point of the thermoplastic polymer and converting the mixture 42A into a molten pneumatic mixture 42B, at least by the time it reaches the second end 21b of the barrel 21.Additionally, the positioning of screw 30 within barrel section 22, further including step 31 in contact with barrel 21 during rotation of screw 30, combined with check valve 32, shut-off valve 37 in the closed position, or both, provides a pressurizable sealed relationship within barrel section 22, whereby molten pneumatic mixture 42B exists within barrel section 22 under pressure above atmospheric pressure. The pressure within barrel section 22 is sufficient to prevent or substantially prevent foam formation, even when the physical blowing agent source is above its critical temperature.

[0096] Rotation of screw 30 further operates to transport the pressurized molten pneumatic mixture toward screw tip 34 and to transport or build a selected mass of pressurized molten pneumatic mixture 42B into collection area 40 of barrel section 22. Collection area 40 is defined as the area within the volume of barrel section 22 extending between check valve 32 and shut-off valve 37 in FIG. 1A and further as the area of ​​barrel section 22 located along distance X of barrel 21. The selected mass, or "shot," of pressurized molten pneumatic mixture 42B is collected, i.e., accumulated, within collection area 40 of barrel section 22. The pressure within collection area 40 is sufficient to prevent or substantially prevent foam formation in the molten pneumatic mixture. In an embodiment, the shot substantially fills collection area 40.

[0097] The construction of the shot of molten pneumatic mixture 42B is accomplished using conventional methods familiar to those skilled in the art. Conventional and known variations in methods and materials employed to construct shots for injection molding are encompassed by the methods described herein. Once constructed, the shot may be subjected to the methods disclosed herein to obtain all of the technical advantages disclosed herein for forming polymeric foams and polymeric foam articles. For example, to form the shot, a method such as the MUCELL® High Pressure Process employed by Trexel Inc. (Wilmington, MA) is preferably employed, which involves the direct addition of a physical blowing agent source as a gas to an extruder, with pressurized mixing to prevent or substantially prevent foam formation, followed by shot collection. Various patents and trademark publications further describe specialized melt mixing and delivery designs for obtaining the molten pneumatic mixture and forming the shot, such as specialized screw designs for mixing and counterflow patterns and the like. Any of these may be usefully employed in conjunction with the shot formation methods and apparatus described above to form a shot as described herein and collect the shot under pressure in a collection area of ​​a melt-mixing device.

[0098] Once the shot is formed and collected in the collection area, an expansion volume is defined therein, and the expansion is accompanied by a drop in pressure within the collection area and adjacent to the shot. Thus, FIG. 1A depicts melt-pneumatic mixing apparatus 20 with screw 30 positioned to collect the shot in collection area 40. The shot comprises a selected mass of molten pneumatic mixture 42B and is disposed under pressure within collection area 40. At this stage of the process, and still with reference to FIG. 1A, FIG. 1B depicts apparatus 20 with screw 30 positioned to define expansion volume 44 within collection area 40. In somewhat more detail, FIG. 1B shows screw 30 in a position resulting from lateral movement of screw 30 toward first end 21a of the barrel; i.e., screw 30 is retracted in FIG. 1B relative to FIG. 1A. The retraction of the screw 30 from the collection area 40 and the resulting partial displacement define an expansion volume 44 within the collection area 40 and further cause pressure to drop within the collection area 40. In some embodiments, rotation of the screw 30 is stopped prior to retraction. In some embodiments, rotation of the screw 30 is stopped during retraction or after retraction is complete. The retraction distance of the screw 30, i.e., the distance of lateral movement of the screw 30 toward the first end 21 a of the barrel, is selected by the operator to provide a suitable expansion volume 44.

[0099] In some embodiments depicted in FIG. 1B , the expansion volume 44 is selected by the operator to provide the collection area 40 with a total volume that matches the total expected molten polymer foam volume of the shot. In such embodiments, the total volume within the collection area 40 after the addition of the expansion volume 44 is the total expected molten polymer foam volume of the molten pneumatic mixture 42B of FIG. 1B . In other embodiments, the expansion volume 44 is selected by the operator to provide the collection area 40 with a total volume that is a percentage of the total expected molten polymer foam volume of the molten pneumatic mixture or shot residing within the collection area 40. That is, the total volume within the collection area 40 after the addition of the expansion volume 44 is equal to about 50% to 120% of the total expected molten polymer foam volume. In some embodiments, the expansion volume is set to provide a total volume within the collection area to accommodate 100% of the total expected molten polymer foam volume. The total expected molten polymer foam volume of the shot may further be calculated based on the amounts of thermoplastic polymer and physical blowing agent source, plus any additional materials added to construct the shot, assuming that all of the physical blowing agent source contributes to the formation of bubbles within the molten polymer foam to be obtained.

[0100] After retracting the screw 30 and defining the expansion volume 44, as shown in FIG. 1B, a time period, referred to as an "expansion period," is allowed to elapse or transition while the shot is held within the collection area 40, as shown in FIG. 1B. Specifically, the collection area 40 includes the expansion volume 44. The expansion period is selected by the operator to be between 5 and 200 seconds. In embodiments, the shot is allowed to rest uninterrupted or substantially uninterrupted within the collection area 40 during the expansion period. In embodiments, "uninterrupted" means that the shot is not exposed to any process that causes mixing, shearing, or transport (flow) of the shot during the expansion period. In embodiments, "substantially uninterrupted" means that the shot is not intentionally perturbed by the mixing, shearing, or transport processes performed during the expansion period, although, for example, thermal differentials, leakage, and other manufacturing issues may lead to inadvertent stresses or strains on the shot residing within the collection area during the expansion period.

[0101] After the expansion cycle has elapsed, nozzle shut-off valve 37, as shown in FIG. 1B, is opened and the molten polymer foam is dispensed from barrel 22. In the embodiment shown in FIGS. 1A-1B, the molten polymer foam flows into cavity 39. The dispensing step may be pressurized dispensing by mechanical means, such as pushing using lateral movement of a screw, or by applying pressurized gas to a collection area, although the application of pressure is not required to dispense the molten polymer foam in some embodiments. 1A-1B , the pressure at the nozzle 36 as shown in FIGS. 1A-1B during dispensing of the molten polymer foam exceeds gravity by 1 psi to 20 psi, e.g., 3 psi to 20 psi, 5 psi to 20 psi, 7 psi to 20 psi, 10 psi to 20 psi, 15 psi to 20 psi, 1 psi to 15 psi, 1 psi to 10 psi, 1 psi to 7 psi, 1 psi to 5 psi, 2 psi to 5 psi, 5 psi to 10 psi, 10 psi to 15 psi, or 15 psi to 20 psi, without the addition of an external pressure source, such as by using additional lateral movement of the screw 30 toward the second end 21 b of the barrel in FIGS. 1A-1B to force the molten polymer foam. In embodiments, the dispensing step is accomplished by maintaining a fluid connection between the nozzle 36 and the cavity 39. In some such embodiments, the fluid connection is further a pressurized connection.

[0102] Once placed within the cavity 39 defined by the mold sections 38 shown in Figures 1A-1B, the molten polymer foam is cooled or allowed to cool until it reaches a temperature below the melting transition temperature of the thermoplastic polymer, such as that present in the ambient conditions of the surrounding environment. In some embodiments, where the expansion volume is set to provide a total volume within the collection area that is less than 100% of the total expected molten polymer foam volume, the foam may continue to nucleate and / or develop (grow in size) after the molten polymer foam is dispensed and before the temperature has cooled sufficiently to reach the melting transition temperature of the thermoplastic polymer. Cooling of the molten polymer foam is accomplished using conventional methods for cooling injection-molded articles, including, but not limited to, immersing the mold in a liquid coolant having a set temperature, spraying the mold with a liquid coolant such as liquid water, impinging a stream of air onto the mold, cooling ambient air, and the like.

[0103] In an alternative embodiment of the foregoing method, an apparatus 20 configured as shown in FIG. 1B is employed to form a molten polymer foam. FIG. 1B shows the screw 30 in a position resulting from lateral movement of the screw 30 toward the first end 21 a of the barrel; i.e., the screw 30 is retracted in FIG. 1B relative to FIG. 1A. The retraction and resulting partial displacement of the screw 30 from the collection region 40 defines an expansion volume 44 within the collection region 40, further causing pressure to drop within the collection region 40. An apparatus 20 configured as shown in FIG. 1B is employed to mix, heat, and transport a molten pneumatic mixture 42B toward the second end 21 b of the barrel 21 in substantially the same manner as described above. Additionally, the positioning of the screw 30 within the barrel section 22, where the step 31 contacts the barrel 21 during rotation of the screw 30, combined with the check valve 32, the shut-off valve 37 in the closed position, or both, provides a pressurizable sealed relationship within the barrel section 22, whereby the molten pneumatic mixture 42B exists within the barrel section 22 under pressure above atmospheric pressure. The pressure within the barrel section 22 is sufficient to prevent or substantially prevent foam formation, even when the physical blowing agent source exceeds its critical temperature. However, in this alternative embodiment, the molten pneumatic mixture is transported through the check valve 32 into the collection area 40, which is further augmented by the expansion volume 44.

[0104] It is an advantage of the disclosed method that conventional materials and equipment for extrusion and injection molding are useful for carrying out the method. No special equipment or material requirements are required for carrying out the disclosed method. Thus, any thermoplastic polymer or mixture thereof useful for injection molding and / or for forming polymer foams can be usefully combined with any commercially available source of physical blowing agent using conventional techniques, such as standard injection molding equipment, optionally with one or more additional materials as selected by the equipment operator.

[0105] In embodiments, thermoplastic polymers useful in conjunction with the methods, apparatus, and articles described herein include any thermoplastic material or blends thereof, and blends of such polymers, known in the industry to be useful for injection molding or injection molding of polymer foam articles. Useful polymers are characterized as having a melt flow viscosity suitable for use in injection molding, such as shot molding. Thus, thermoplastic polymers may contain a degree of crosslinking that is thermoreversible or does not otherwise prevent sufficient viscous melt flow for the injection molding process.

[0106] In embodiments, thermoplastic polymers useful in conjunction with the methods, apparatus, and articles described herein include olefins, such as polyethylene, polypropylene, polyα-olefins and various copolymers and branched / crosslinked variations thereof, including, but not limited to, low density polyethylene (LDPE), high density polyethylene (HDPE), linear low density polyethylene (LLDPE), thermoplastic polyolefin elastomers (TPE), ultra-high molecular weight polyethylene (UHMWPE), and the like; polyamides (PA), polyimides (PI), polyesters, such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), polyhydroxyalkanoates (PHAs), such as polyhydroxybutyrate (PHB), polycarbonate (PC), poly(lactic acid) (PLA), acrylonitrile-butadiene-styrene copolymers (ABS), polystyrene, thermoplastic polymers, and the like. Polyurethanes, including thermoplastic polyurethane elastomers (PU, TPU), polycaprolactone, polyvinyl chloride (PVC), tetrafluoroethylene, polyethersulfone (PES), polyacetal, polyaramid, polyphenylene oxide (PPO), polybutylene, polybutadiene, polyacrylate, and methacrylate (acrylic) copolymers, ionomeric polymers (SURLYN® and similar ionically functionalized olefin copolymers), polyether-amide block copolymers (PEBAX®), polyaryletherketone (PAEK), polysulfone, polyphenylene sulfide (PPS), polyamide-imide copolymers, poly(butylene succinate), cellulosics, polysaccharides, and copolymers, alloys, admixtures, and mixtures thereof, without limitation, are usefully employed in conjunction with the methods described herein.

[0107] Regarding non-limiting uses of polymer blends and mixtures, we have found that mixed streams of recycled plastics are useful as thermoplastic polymers in embodiments. Thus, in embodiments, marine waste plastic is a mixed stream of polymer waste collected from oceans and beaches, with exemplary contents of 10%-90% polyolefin content, 10%-90% PET content, 1%-25% polystyrene content, and 1%-50% unknown polymer content. Such mixed and waste plastic streams, including but not limited to those collected from oceans and beaches, are also useful for forming molten polymer foams and polymer foam articles using the methods and apparatus described herein.

[0108] Physical blowing agent sources are widely available in the industry, and conditions useful for developing physical blowing agents during melt mixing are well understood and widely reported. Therefore, any physical blowing agent source useful for injection molding, reaction injection molding, or other methods of making polymeric foams is useful herein for forming molten polymeric foams and solidified polymeric foam articles in accordance with the methods, apparatus, and polymeric foam articles described herein. Physical blowing agents useful in connection with the methods and apparatus described herein include air, CO2, and N2, either in the form of beads, pellets, and the like, or in a covert form, encapsulated within a thermoplastic material, where a chemical reaction generates CO2 or N2 upon heating in a melt mixing apparatus. Such chemical reactions are preferably, but not limited to, exothermic or endothermic for their use in conjunction with the methods and apparatus disclosed herein. Suitable physical blowing agent sources include sodium bicarbonate, polycarboxylic acids such as citric acid or its salts or esters, e.g., compounds based on sodium citrate or the trimethyl ester of sodium citrate, mixtures of sodium bicarbonate and polycarboxylic acids such as citric acid, sulfonyl hydrazides including p-toluenesulfonyl hydrazide (p-TSH) and 4,4'-oxybis-(benzenesulfonyl hydrazide) (OBSH), pure and modified azodicarbonamide, semicarbazide, tetrazole, and diazinon. In any of the foregoing, the physical blowing agent source is optionally further encapsulated within a carrier resin designed to melt during heating, mixing, and collection of the shot.

[0109] In embodiments, useful physical blowing agent sources include commercially available compositions, such as those available from Clariant AG (Switzerland); HYDROCEROL® BIH70, HYDROCEROL® BIH CF-40-T, or HYDROCEROL® XH-901, available from RTP Company (Winona, MN); FCX7301, available from RTP Company (Winona, MN); FCX27314, available from CelChem LLC (Naples, FL); CELOGEN® 780, available from Galata Chemicals (Southbury, CT); ACTAFOAM® 780, available from Galata Chemicals (Southbury, CT); ACTAFOAM® AZ, available from ADEKA Polymer Additives Europe (Mulhouse, France); ORGATERMB.BA.20, available from Endex International (Rockford, IL); ENDEX1750 TM and FOAMAZOL, available from Bergen International (East Rutherford, NJ). TM Including 57.

[0110] In some embodiments, the physical blowing agent source is a physical blowing agent, which is applied as a gas to a melt-mixing device, such as an apparatus similar to the extruder shown in FIGS. 1A-1B. In such embodiments, the gas is dissolved in the thermoplastic polymer by direct pressurized addition and mixing in the melt-mixing device. In some embodiments, the gas is made a supercritical fluid by pressurization, either prior to or simultaneously with dissolution into the molten thermoplastic polymer. The step of applying a physical blowing agent directly to an injection molding device is referred to in the industry as the MUCELL® process, as employed by Trexel Inc. (Wilmington, DE). Specialized equipment is required for this process, such as a regulated, pressurized fluid connection from a gas reservoir (tank, cylinder, etc.) to the inlet of the extruder device to form a pressurized relationship with the barrel as the thermoplastic polymer is also added to the barrel and melted. Where such specialized equipment is available, physical blowing agents are usefully employed as a source of physical blowing agent in conjunction with the methods described herein by direct application of the physical blowing agent to a thermoplastic polymer and one or more additional materials to form a molten pneumatic mixture.

[0111] The physical blowing agent source is added to the thermoplastic polymer and, optionally, one or more additional materials in an amount that targets a selected density reduction of the thermoplastic polymer according to conventional techniques associated with the desired polymer foam density and the operation of the physical blowing agent and physical blowing agent source to form a thermoplastic polymer foam. The amount of physical blowing agent source added to the thermoplastic polymer is not particularly limited. Thus, we have discovered that a density reduction of up to 85% can be achieved without the use of polymer or glass bubbles or the like, providing a polymer foam article having the unique and surprising properties reported below and further having a targeted density reduction of up to 85%. As used herein, "density reduction" refers to the percent mass reduction in a polymer foam article compared to the same article without the addition of a physical blowing agent (source) to create the article (i.e., a polymer article excluding or substantially excluding foam). Thus, in embodiments, the molten polymer foams and polymer foam articles described herein preferably provide a selected density reduction of up to 85%, e.g., 30% to 85%, e.g., 35% to 85%, 40% to 85%, 45% to 85%, 50% to 85%, 55% to 85%, 60% to 85%, 65% to 85%, 70% to 85%, 75% to 85%, 30% to 35%, 35% to 40%, 40% to 50%, 50% to 55%, 55% to 60%, 60% to 65%, 65% to 70%, 70% to 75%, 75% to 80%, or 80% to 85%, while excluding glass or polymer bubbles. The inclusion of glass or polymer bubbles further expands the available density reduction of polymer foam articles made according to the methods herein. In some embodiments, density reductions of greater than 85% may be achieved. Polymeric foam articles that benefit from density reduction may nonetheless be manufactured to a density of less than 1,000 cm. 3 Exceeding 1,000cm 3 ~5,000cm 3 , or an additional 5,000 cm 3 and molded articles with a volume exceeding 1,000 cm 3 Volume greater than 1,000cm and thickness greater than 2cm 3 ~5,000cm 3volume and thickness greater than 2cm, or 5,000cm 3 The foam is characterized as having a continuous polymer matrix throughout, including molded articles with a volume of more than 1000 sq ft and a thickness of more than 2 cm.

[0112] As noted above, the amount of physical blowing agent source added to the thermoplastic polymer is not particularly limited. Thus, we have found that up to 70% of the total volume of the polymeric foam article comprises foam. The total volume of foam as a percentage of the total volume of the polymeric foam article is referred to as the "porosity" of the article. Thus, a porosity of up to about 70% is achieved without the inclusion of polymer or glass bubbles or the like, providing a polymeric foam article having the unique and surprising properties reported below and further having a targeted porosity of up to 70% of the volume of the polymeric foam article. Thus, in embodiments, the molten polymer foams and polymer foam articles described herein suitably provide a porosity of up to 70%, e.g., 5% to 70%, 10% to 70%, 15% to 70%, 20% to 70%, 25% to 70%, 30% to 70%, 35% to 70%, 40% to 70%, 45% to 70%, 50% to 70%, 55% to 70%, 60% to 70%, 5% to 10%, 10% to 15%, 15% to 20%, 20% to 25%, 25% to 30%, 30% to 35%, 35% to 40%, 40% to 50%, 50% to 55%, 55% to 60%, 60% to 65%, or 65% to 70%, while excluding glass or polymer bubbles. The inclusion of glass or polymer foam further expands the available porosity of polymer foam articles made according to the methods herein. In some embodiments, sections of greater than 70% porosity can be achieved. Polymer foam articles with 70% porosity can nevertheless be 5,000 cm 3 volume greater than 2cm, thickness greater than 5,000cm 3 The foam is characterized as having a continuous polymer matrix throughout, including molded articles having both a volume greater than 100 mm and a thickness greater than 2 cm.

[0113] In some embodiments, the thermoplastic polymer and the physical blowing agent source are admixed prior to applying the admixture to a melt mixing device for heating and mixing. In other embodiments, the thermoplastic polymer and the physical blowing agent source are added separately to the melt mixing device, such as by two different inlets or ports available for adding materials to the melt mixing device. In still other embodiments, a solid mixture including both the thermoplastic polymer and the physical blowing agent source is added as a single input to a melt mixing device for heating and mixing.

[0114] In embodiments, one or more additional materials are included in or added to the melt-mixing device along with the thermoplastic polymer and the physical blowing agent source. Such additional materials are preferably mixed or blended with the thermoplastic polymer, the physical blowing agent source, or both, or the one or more additional materials are added separately, such as through individual ports or inlets to the melt-mixing device. Examples of suitable additional materials include colorants (dyes and pigments), stabilizers, brighteners, nucleating agents, fibers, particulates, and fillers. Specific examples of some suitable materials include talc, titanium dioxide, glass bubbles or beads, thermoplastic polymer particles, fibers, beads, or bubbles, and thermoset polymer particles, fibers, beads, or bubbles. Additional examples of suitable materials include fibers, e.g., glass fibers, carbon fibers, cellulose fibers and cellulose-containing fibers, natural fibers such as cotton or wool fibers, and synthetic fibers, e.g., polyester, polyamide, or aramid fibers, including microfibers, nanofibers, crimped fibers, crushed or chopped fibers, phase-separated and mixed fibers, e.g., bicomponent fibers comprising any of the aforementioned polymers, and thermosets formed from any of the aforementioned polymers. Further examples of suitable additional materials are waste materials, sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and other biological, organic, and mineral waste streams and mixtures thereof, optionally further crushed or shredded, including woven or nonwoven fabrics, textiles, or paper. Further examples of suitable additional materials are minerals such as calcium carbonate and dolomite, clays such as montmorillonite, sepiolite, and bentonite, mica, wollastonite, hydromagnesium / huntite mixtures, synthetic minerals, silica agglomerates or colloids, aluminum hydroxide, alumina-silica composite colloids and particulates, halloysite nanotubes, magnesium hydroxide, basic magnesium carbonate, precipitated calcium carbonate, and antimony oxide. Further examples of suitable additional materials are carbonaceous fillers such as graphite, graphene, graphene quantum dots, carbon nanotubes, and C 60Further examples of suitable additional materials include thermally conductive fillers, such as boron nitride (BN) and surface-treated BN.

[0115] In embodiments, the one or more additional materials, along with the thermoplastic polymer and the physical blowing agent source, comprise about 0.1% to 50% of the weight of the thermoplastic polymer, e.g., 0.1% to 45%, 0.1% to 40%, 0.1% to 35%, 0.1% to 30%, 0.1% to 25%, 0.1% to 20%, 0.1% to 15%, 0.1% to 10%, 0.1% to 9%, 0.1% to 8%, 0.1% to 7%, 0.1% to 6%, 0.1% to 5%, 0.1% to 4%, 0.1% to 3%, 0.1% to 2%, 0.1% to 1%, 1% to 50%, 2% to 50%, 3% to 50%, 4% of the weight of the thermoplastic polymer added to the melt mixing device. The amount of the molten or non-molten grease may be in the range of 0.1% to 2%, 2% to 5%, 5% to 10%, 10% to 15%, 15% to 20%, 20% to 25%, 25% to 30%, 30% to 35%, 35% to 40%, 40% to 45%, or 45% to 50% of the molten or non-molten grease may be included in or added to a melt mixing device to form a shot.

[0116] Thus, it will be appreciated by those skilled in the art that the following method, in a melt mixing device other than an extruder, will result in a molten polymer foam possessing significant technical advantages, as described in the following section. The method of forming and collecting a molten polymer foam includes the steps of: heating and mixing a thermoplastic polymer and a physical blowing agent source to form a molten pneumatic mixture, wherein the temperature of the molten pneumatic mixture exceeds the critical temperature of the physical blowing agent source and a pressure applied to the molten pneumatic mixture is sufficient to substantially prevent foam formation; collecting a selected amount of the molten pneumatic mixture in a collection region; defining an expansion volume in the collection region adjacent to the molten pneumatic mixture that creates a pressure drop; maintaining the expansion volume for an expansion time period; and collecting the molten polymer foam from the collection region. In an embodiment, the molten pneumatic mixture is uninterrupted or substantially uninterrupted during the expansion period.

[0117] In some embodiments, collecting the molten polymer foam includes applying the molten polymer foam to a cavity defined by a mold and cooling the molten polymer foam below the melting temperature of the thermoplastic polymer to obtain a polymer foam article. In embodiments where the molten polymer foam is applied to the mold cavity, the cooled polymer foam article acquires the shape and dimensions of the mold, and the polymer foam is further characterized as a continuous polymer matrix with bubbles dispersed throughout the article. In embodiments, the molten polymer foam is applied to the mold cavity by allowing the molten polymer foam to flow and enter the mold cavity by gravity; in some such embodiments, the flow is allowed to fall uninterrupted into the open cavity. In other embodiments, the molten polymer foam is applied to a forming element under pressurized flow. In embodiments, the molten polymer foam is delivered to the mold cavity by a fluid connection thereto from a nozzle or other means of delivering molten polymer foam from a collection region of a melt-mixing device.

[0118] For example, in embodiments, the extruder is adapted and designed to dispense the molten mixture from an outlet into a forming element, which is a mold, defining a cavity therein and designed and adapted to receive a molten polymer mixture, such as a molten pneumatic mixture. In embodiments, the forming element is a mold configured and adapted to receive the molten thermoplastic polymer dispensed from the outlet, and further, the mold is generally characterized as defining a void or cavity having a selected shape and dimensions of the desired article.

[0119] In embodiments, dispensing from the extruder is accomplished by mechanical pushing, by applying gaseous pressure from within the extruder barrel, or a combination thereof. In other embodiments, the outlet, valve, gate, nozzle, or door to the collection area is simply opened after the expansion cycle has finished, and the molten polymer foam is allowed to flow uninterrupted through the outlet, and the melt flow is then directed to cooling or other processing equipment, or the melt flow is allowed to be poured into a forming element. In other embodiments, the forming element is fluidly connected to the outlet and further designed and adapted to be filled with the molten mixture so that the molten mixture acquires a selected shape upon cooling and solidification. In some embodiments, the forming element is fluidly connected to the extruder outlet such that pressure is maintained between the collection area, the outlet, and the forming element or mold. Any conventional thermoplastic molding or forming process associated with injection molding of polymeric articles, such as polymeric foam articles, is suitably employed to mold the molten polymer foam described herein.

[0120] In embodiments where the molten polymer foam is allowed to flow uninterrupted through the outlet, or is forced under pressure through the outlet without further obstruction of flow, the melt flow eventually impinges on a surface, such as a surface that is generally perpendicular to the direction of the melt flow. We believe that flow under such circumstances then impinges on a surface that is generally perpendicular to the direction of the melt flow, as described by Batty and Bridson, "Accurate Viscous Free Surfaces for Buckling," As reported by the "Coiling, and Rotating Liquids" Symposium on Computer Animation, Dublin, July 2008, it has been observed that during continuous melt flow, the molten polymer foam acquires roughly cylindrical (coiled) and planar (folded) patterns. In embodiments, the molten polymer foam is allowed to flow uninterrupted, or "poured," from the outlet of the melt mixing device into a mold configured as an open container. In embodiments, the open-container mold is completely filled with the molten polymer foam; in other embodiments, the open-container mold is partially filled with the molten polymer foam.

[0121] In some embodiments, related to the coiled melt flow described above, a substantially shear-free melt flow, or a substantially linear melt flow, or a melt flow that is substantially linear and shear-free, is provided by the fluid connection between the extruder outlet and the interior of the die cavity. In some such embodiments, the melt flow may obtain a coiled melt flow either by impinging on a vertical surface thereof or by flowing down a substantially vertical wall or side of the die cavity and collecting at the bottom of the die cavity. A schematic diagram of one such embodiment is shown in FIG. 41, which shows a variation of the extruder of FIGS. 1A-1B, in which the die 26 of the apparatus 20 is mounted on a substantially horizontal surface 100. Referring to the elements as shown in FIGS. 1A-1B, the shut-off valve 37 is not present at the distal end 21b of the barrel 21; instead, in FIG. 41, the collection area 40 extends to a die valve 137 mounted adjacent to the die cavity 39 defined within the die 26. Mold valve 137 is thus operable to define collection area 40 or provide an outlet for dispensing molten polymer foam into mold cavity 39 via a generally linear horizontal flow 110. Mold valve 137 is mounted at a height H above horizontal surface 100, i.e., a height H2 above the floor or bottom 120 of mold 26 as mounted on horizontal surface 100. Referring to FIG. 41 , mold valve 137 is selectively opened to provide fluid communication between collection area 40 and mold cavity 39. Mold valve 137 is thus selectively opened to provide a generally linear horizontal flow 110 of molten polymer foam entering mold cavity 39. In response to entering mold cavity 39, the linear flow flows downward over a distance H2, and in some embodiments, acquires a coiled melt flow as it proceeds to fill mold cavity 39. Other related variations of methods and apparatus for providing a coiled melt flow as described herein are also contemplated.

[0122] In embodiments, upon cooling the polymeric foam article and removing it from the open container or mold in which it is mounted, as shown in FIG. 41 , coiled and folded flow patterns become visible on the surface of the article. Examples of such visible flow patterns can be seen, for example, in FIGS. 2-2 and 2-4. Upon cryogenic fracturing and microscopic inspection of the interior of a polymeric foam article formed using coiled and folded flow, the interior of the article is free or substantially free of flow patterns, interfaces, or other evidence of coils and folds. For example, cryogenic fracturing of such a polymeric foam article does not result in fracturing at any discernible interfaces between the coils and folds, and both macroscopic and microscopic inspection of the interior of such a polymeric foam article obtains a homogeneous appearance to the flow patterns. The physical properties of such polymeric foam articles are consistent with those obtained by exposing a molten polymeric foam to a directed fluid flow through a fluid connection between the outlet of a melt-mixing device and a mold, or by exposing a molten polymeric foam to a pressurized and directed fluid flow.

[0123] In some embodiments, the methods herein include substantially filling a mold formed according to the methods described above with molten polymer foam, then cooling the molten polymer foam to form a solidified polymer foam, and, in embodiments, further removing the solidified polymer foam article from the mold. In embodiments, the cooling step is to a temperature below the melting transition temperature of the thermoplastic polymer. In embodiments, the cooling step is to a temperature equilibrated with the ambient temperature of the surrounding environment. In some embodiments, the mold further includes one or more vents for pressure equalization within the mold while filling it with molten polymer foam, while in other embodiments, vents are absent. After cooling, the polymer foam article may be removed from the mold for further modification or use.

[0124] In accordance with any of the foregoing descriptions, Table 1 provides useful, but non-limiting, examples of processing conditions that may be employed to make molten polymer foams using conventional single-screw extruder-type reaction injection molding equipment by further employing one or more representative thermoplastic polymers and a citric acid-based physical blowing agent source, as indicated.

[0125] Table 1. Representative thermoplastic polymers and conditions useful for making and molding molten polymer foams. [Table 1]

[0126] In embodiments, mold dimensions usefully employed to form polymeric foam articles made using the methods and materials disclosed herein include molds that define a cavity, or a series of cavities, that can be filled with a single shot of molten polymer foam. Thus, the size of the mold cavity is limited only by the size of the shot that can be constructed in the melt mixing device employed by the user. Up to 1 x 10 5 cm 3Representative mold cavities having a volume of 100 psi or less are useful for making large parts, such as automobile interior or exterior components, I-beam structural components, and other large plastic items that suitably employ polymeric foams. Furthermore, the shape of the mold cavity may be particularly, but not exclusively, complex in terms of overall shape and even surface patterns and features, such as dumbbells, tableware, decorative globes with raised geographical features, human or animal or insect shapes, framework or packaging shapes for framing or encasing electronic items, appliances, automobiles, and the like, shapes for subsequently placing and fitting screws, bolts, and other non-thermoplastic items into or through the polymeric foam article, and similar recognizable shapes are all suitable mold shapes for molding polymeric foam articles as described herein. In some embodiments, the cavity includes a thickness gradient of up to 300% for one or more regions of the cavity.

[0127] In accordance with any of the foregoing descriptions, Table 2 provides useful, but non-limiting examples of mold cavity volumes and mold dimensions useful for shaping molten polymer foam, either by pressurized flow or by uninterrupted flow of the molten polymer foam into a mold. In addition, mold cavity volumes up to 100,000 cm are also suitable. 3 Larger mold volumes, such as 1000 or larger, are also useful if the shot mass is suitably increased.

[0128] Table 2. Representative mold cavity volumes and dimensions useful for molding molten polymer foams. [Table 2-1] [Table 2-2]

[0129] Any of the methods, processes, uses, machines, devices, or individual features thereof described above can be freely combined with one another to form polymeric foams and polymeric foam articles with unique and surprising properties. Thus, in embodiments, polymeric foam articles are formed using the methods, materials, and devices described above. The polymeric foam articles are discrete, monolithic objects made by forming or molding molten polymeric foam according to any of the methods and materials disclosed above and variations thereof, which can be combined in any part and in any manner to form molten polymeric foam as described above.

[0130] Thus, the terminology used to refer to the methods, materials, and apparatus in the foregoing discussion will be used below to refer to articles made using one or more of the methods, materials, and apparatus encompassed in the foregoing discussion.

[0131] In embodiments, any combination of the foregoing methods results in the formation of a polymeric foam article comprising, consisting essentially of, or consisting of a continuous thermoplastic polymer matrix defining a plurality of bubbles. The continuous thermoplastic polymer matrix comprises, consists of, or consists essentially of a solid thermoplastic polymer, i.e., the thermoplastic polymer is present at a temperature below its melting transition temperature. In embodiments, the continuous thermoplastic polymer matrix further comprises one or more additional materials dispersed in the solid thermoplastic polymer.

[0132] The polymeric foam article achieves a selected percentage density reduction based on the amount of physical blowing agent source added to the shot, based on the density of the thermoplastic polymer and any other materials added to form the polymeric foam. In embodiments, density reductions of 30%, 40%, 50%, 60%, 70%, and even up to 80%-85% are user-selectable. In embodiments, density reductions of up to 85% are achieved solely through the presence of bubbles intermittently dispersed within the polymer matrix. In embodiments, the polymeric foam article excludes hollow particulates, such as polymer or glass bubbles, that are added to the shot prior to forming the polymeric foam article using the methods and apparatus described herein.

[0133] Furthermore, in conjunction with reduced density, as noted above, the polymeric foam articles herein are characterized as having a continuous thermoplastic polymer matrix throughout, or substantially throughout, the entirety of the article. We have found that large-sized polymeric foam articles may be suitably formed from the molten polymeric foams disclosed herein to include a continuous polymer matrix defining a plurality of cells. A "large-sized" article is one having a size of 1,000 cm or greater. 3 More than, for example, 2,000 cm 3 More than 3,000cm 3 Over 4,000cm 3 or more than 5,000 cm 3 or more, or 1,000 cm 3 ~5,000cm 3 Any volume up to 10,000 cm 3 , up to 20,000cm 3 , up to 50,000cm 3 , or even up to 100,000 cm 3, or greater. Thus, large polymeric foam articles may be suitably formed to include a continuous polymer matrix defining multiple bubbles throughout. The volume of the article is limited only by the size of the mold cavity and the size of the shot that can be collected in the melt-mixing device. In embodiments, large articles are formed from a single shot dispensed from a single outlet of the melt-mixing device, i.e., without splitting the molten polymeric foam stream into multiple simultaneous distribution pipes, nozzles, or other methods of directing multiple melt streams simultaneously into a single mold cavity.

[0134] In addition, we have found that thick polymeric foam articles can be suitably formed to include a continuous polymeric matrix that defines multiple cells. Thickness, as used herein, refers to the linear distance through the interior of a polymeric foam article between any two points on its surface. A "thick" article is defined as having a thickness of 2 cm or more, e.g., 3 cm, 4 cm, 5 cm, 6 cm, 7 cm, 8 cm, 9 cm, 10 cm, 15 cm, 20 cm, 25 cm, 30 cm, 35 cm, 40 cm, 45 cm, or even 50 cm or more. In some embodiments, polymeric foam articles characterized as both large and thick are formed using the methods and materials described herein, and further, large, thick polymeric foam articles are nonetheless characterized as having a continuous polymeric matrix that defines multiple cells throughout the article. In embodiments, large, thick articles are formed from a single shot dispensed from a single outlet of the melt mixing device, i.e., without splitting the molten polymer foam stream into multiple simultaneous distribution pipes, nozzles, or other methods of directing multiple melt streams simultaneously into a single mold cavity.

[0135] The production of large, thick, or large and thick polymeric foam articles presents challenges in the industry due to cooling gradients of the molten foam after being dispensed into cavities of such dimensions. The interior of such articles tends to cool very slowly, and a portion of the thermoplastic polymer disposed within the mold cavity may remain above its melting temperature, allowing significant coalescence of the foam to occur before the thermoplastic solidifies (reaches a temperature below its melting transition temperature). In sharp contrast, we have found that large, thick, and large and thick articles are successfully formed using the methods, materials, and apparatus disclosed herein, and further, that the formed polymeric foam articles are characterized by a continuous polymer matrix with bubbles dispersed throughout the article. Cooling the interior of larger articles at slower rates shows little or no evidence of foam coalescence during cooling. The bubbles remain intact or substantially intact during cooling of the molten polymeric foam and do not coalesce during cooling, resulting in a continuous polymeric matrix regardless of the size, thickness, or volume of the polymeric foam article formed.

[0136] This feature of the polymer foam articles described herein is surprising and unexpected, as prior art methods result in foams that are prone to foam coalescence during cooling. Thus, prior art molten polymer foams placed within the interior volume of a mold may cool slowly enough to allow the foam to completely coalesce, resulting in the interior of large or thick articles formed using conventional polymer foaming methods having very large voids or even completely collapsed structures. In sharp contrast, molten polymer foams formed according to the present method do not undergo substantial foam coalescence or collapse of the continuous polymer matrix during cooling of the molten polymer foam. Thus, large and thick polymer foam articles with a continuous polymer matrix throughout are achieved using the methods, materials, and apparatus described herein.

[0137] The continuous polymer matrix as a structural feature of a polymeric foam article according to the aforementioned methods, apparatus, and materials is characterized as being present throughout the entire polymeric foam article, including its surface region. The surface region may be preferably characterized as the interior area of ​​the polymeric foam article from the surface down to 500 microns or less. The surface region, as defined herein, is the portion of the foam article's area, conventionally referred to as the "skin," which is the region of a polymeric foam article made using conventional methods that is free of or substantially free of foam. Conventionally formed foam articles include a skin layer at least as thick as the surface region, i.e., 500 microns thick, but in many cases the skin layer is much thicker, extending as far as 1 mm, 1.5 mm, 2 mm, 2.5 mm, or even 3 mm from the surface of the article. However, a polymeric foam article formed using the methods of the present disclosure achieves a true foam structure from its surface throughout its thickness and volume. In embodiments, microscopic inspection reveals evidence of bubbles on the surface of polymeric foam articles formed using the conditions, processes, and materials disclosed herein. Thus, the methods disclosed herein obtain unexpected results in terms of the continuous nature of the polymeric matrix structure throughout the entire polymeric foam article, in any direction and within the interior of very large and / or thick polymeric foam articles, and also in all of their regions, including the surface and surface regions of the article.

[0138] The following examples include analyses of the surface regions of several polymeric foam articles produced using the methods disclosed herein and exhibiting the present continuous foam structure. Macroscopically, polymeric foam articles produced using the methods disclosed herein may appear to have a skin layer, i.e., the surface region of the article may appear different from the interior region of the article. However, we have found that the surface region of polymeric foam articles produced by the present methods contains multiple compressed bubbles, in stark contrast to the skin layer, which is characterized by the absence of bubbles. Macroscopically, the compressed bubbles produce an appearance suggestive of a skin layer. However, microscopic inspection reveals that the visually apparent difference results from a "flattened" or compressed arrangement of the continuous polymer matrix near the surface of the article.

[0139] Thus, as seen, for example, in Figures 17 and 18, there is a gradual transition from spherical to compressed foam moving toward the surface of a polymeric foam article formed by employing the conditions, processes, and materials disclosed herein. Thus, in embodiments, the surface region of a polymeric foam article made using the methods disclosed herein comprises a plurality of compressed foams. In embodiments, the compressed foam is present within the surface region of a polymeric foam article made using the methods disclosed herein. In some such embodiments, the compressed foam is present within an interior area of ​​the polymeric foam article that is 500 microns or less from the surface. In some such embodiments, the compressed foam is present within an interior area of ​​the polymeric foam article as far as 2 cm from the surface. Compressed foam is defined as a foam having a circularity of less than 1, with a circularity value of zero representing a completely non-spherical foam and a value of 1 representing a perfectly spherical foam. In embodiments, bubbles having a circularity of less than 0.9 are observed within the surface region of the foamed polymer article, and further, 10% to 90%, or 10% to 80%, or 10% to 70%, or 10% to 60%, or 10% to 50%, or 10% to 40%, or 10% to 30%, or 10% to 20%, or 20% to 80%, or 20% to 70%, or 20% to 60%, or 20% to 50%, or 20% to 40%, or 20% to 30%, or 30% to 70%, or 30% to 60%, or 30% to 50%, or 30% to 40% of the bubbles within the surface region have a circularity of 0.9 or less. In embodiments, the average circularity within the surface region of the foamed polymer article is from 0.70 to 0.95, e.g., from 0.75 to 0.95, or from 0.80 to 0.95, or from 0.85 to 0.95, or from 0.90 to 0.95, or from 0.70 to 0.90, or from 0.70 to 0.85, or from 0.70 to 0.80, or from 0.70 to 0.75, or from 0.70 to 0.75, or from 0.75 to 0.80, or from 0.80 to 0.85, or from 0.85 to 0.90, or from 0.90 to 0.95.

[0140] In embodiments, the compressed foam is present within the polymeric foam article greater than 500 microns from its surface. For example, in embodiments, the compressed foam is present up to 1 mm from the surface of the polymeric foam article, or up to 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 1 cm, or more from its surface. In some embodiments, the compressed foam area within the polymeric foam article is between 0.01% and 70% of the total volume of the article, e.g., between 0.1% and 70%, or between 0.5% and 70%, or between 1% and 70%, or between 2% and 70%, or between 3% and 70%, or between 4% and 70%, or between 5% and 70%, or between 6% and 70%, or between 7% and 70%, or between 8% and 70%, or between 9% and 70%, or between 10% and 70%, or between 15% and 70%, or between 20% and 70%, or between 30% and 70%, or between 40% and 70%, or between 50% and 60%, or between 60% and 70%, or between 70% and 8 ...80% and 80%, or between 90% and 70%, or between 10% and 70%, or between 15% and 70%, or between 20% and 70%, or between 30% and 70%, or between 40% and This corresponds to 0.01% to 70%, or 60% to 70%, or 0.01% to 60%, or 0.01% to 60%, or 0.01% to 50%, or 0.01% to 40%, or 0.01% to 30%, or 0.01% to 20%, or 0.01% to 10%, or 0.01% to 9%, or 0.01% to 8%, or 0.01% to 7%, or 0.01% to 6%, or 0.01% to 5%, or 0.01% to 4%, or 0.01% to 3%, or 0.01% to 2%, or 0.01% to 1%, or 0.01% to 0.1%.

[0141] 12 and 14 show plots of average bubble size and average bubble count versus average bubble circularity for two polymeric foam articles made using the methods of the present disclosure. Quantitative analysis of bubble size and distribution reveals an inverse relationship between average bubble size and bubble circularity, and an inverse relationship between average bubble size and bubble count.

[0142] Figure 18 also shows visual evidence that bubbles are present on the surface of a polymeric foam article formed using the methods, materials, and apparatus described herein. Figure 18 also shows visual evidence that multiple compressed bubbles are present substantially 500 microns from the surface of a polymeric foam article formed using the methods, materials, and apparatus described herein. In this sense, the polymeric foam article of the present disclosure achieves a significant difference from prior art foam articles. While the "skin layer," i.e., the first 500 microns of a foam article's thickness made by conventional processes, is free of or substantially free of bubbles, prior art foam articles are characterized by the fact that the bubbles, regardless of their location, are generally spherical. Thus, at thicknesses within conventional foam articles where bubbles are observed, they generally have a spherical shape, with a circularity of approximately 1. Compressed bubbles are not formed using conventional methodologies for making foam articles, and therefore, a distribution of foam circularity is not observed in such conventional foam articles. Furthermore, foam is not even formed within the first 500 microns of foam articles made by conventional processes, and therefore no comparison with respect to foam is drawn with respect to the surface area of ​​foamed polymer articles as described herein and foam articles made using conventional injection molding methods.

[0143] Furthermore, the conditions, processes, and materials disclosed herein are preferably optimized to form polymeric foam articles with different physical properties depending on the targeted end use or application. For example, the density of the polymeric foam article is preferably varied as a function of expansion volume. By decreasing the expansion volume, the density of the resulting polymeric foam article decreases in a generally linear manner, as shown, for example, in FIG. 5. Also, as can be seen in FIG. 5, increasing the expansion time period results in the formation of a denser polymeric foam article. Such conditions and other variables, all within the scope of the conditions, methods, and materials disclosed herein, are preferably used to vary the physical properties of the resulting polymeric foam article.

[0144] In one variation of the conditions, processes, and materials disclosed herein, the molten polymer foam is preferably dispensed by splitting the molten polymer foam stream into two, three, four, or more paths toward multiple molds or mold sections for forming multiple polymer foam articles from a single shot. In another variation of the conditions, processes, and materials disclosed herein, two shots are used to fill a single mold, the first differing from the second shot in terms of thermoplastic polymer content or ratio of mixed polymers, source of physical blowing agent, optionally one or more additional materials, density, porosity, depth of compressed foam region, or some other material or physical property difference.

[0145] In another variation of the conditions, processes, and materials disclosed herein, polymeric foam articles made using the methods disclosed herein were subjected to fastener pull-out testing in accordance with ASTM D6117. The polymeric foam articles obtained superior pull-out strength to foam articles made using conventional foaming methods. Furthermore, polymeric foam articles formed using the materials, methods, and apparatus disclosed herein do not require pre-drilling, tapping, or engineering of fastener locations.

[0146] In yet another variation of the conditions, processes, and materials disclosed herein, polymeric foam articles made using the methods disclosed herein were subjected to impact testing. Using the guidelines of the National Institute of Justice (NIJ) "Ballistic Resistance of Body Armor NIJ Standard-0101.06," a series of 3-inch thick polymeric foam articles were formed from polyether-amide block copolymer (PEBAX®), linear low-density polyethylene (LLDPE), and polypropylene using a citric acid-based physical blowing agent source. Polymeric foam articles made using all three of these thermoplastic polymers were found to stop .22 caliber LR handgun bullets, passing NIJ Level I, and 9mm LUGER® handgun bullets, passing NIJ Level II and IIA. [Example]

[0147] Experimental Section

[0148] The following examples are intended to further illustrate the present invention and are not intended to limit the scope of the present invention in any way. Examples 1 and 11 were performed on an Engel Duo 550 Ton injection molding machine (available from Engel Machinery Inc., York, PA, USA). Examples 2-4 were performed on a Van Dorn 300 injection molding machine (available from Van Dorn Demag, Strongsville, Ohio, USA). Unless otherwise indicated, the remaining examples were performed on an Engel Victory 340 Ton injection molding machine (available from Engel Machinery Inc., York, PA, USA).

[0149] In the examples herein, "cc" stands for "cubic centimeter" (cm 3 ) and "sec" means "seconds." Standard Foam Molding and MFIM

[0150] In the examples herein, two direct injection expanded foam molding techniques were employed, referred to herein as "standard foam molding" and "molten foam injection molding" ("MFIM").

[0151] In standard foam molding, the following general procedure was used: A) A mixture was prepared by blending a polymer (which may be in the form of pellets, powder, beads, granules, and the like) with a blowing agent (expansion agent) and any other additives, such as fillers. The mixture was introduced into an injection unit, and a rotating injection unit screw moved the mixture forward within the injection unit barrel, thus forming a heated fluid material, typically according to an injection molding process. B) A set volume of material was dispensed into the front of the injection unit barrel by rotation of the screw, thus moving the set volume from the feed zone to the front of the screw. During this feed step, the screw was rotated, translating the molten mixture forward into the space within the barrel between the screw and the nozzle, thereby providing the set volume. C) The molten mixture was injected into a mold cavity by forward translation and / or rotation of the screw.

[0152] In the molten foam injection molding (MFIM) process, the following general procedure was used: A) A mixture was prepared by blending a polymer (which may be in the form of plastic particles, pellets, powder, beads, granules, and the like) with a chemical blowing agent and any other additives, such as fillers. The mixture was introduced into an injection unit, and a rotating injection unit screw moved the material forward within the injection unit barrel, thus forming a heated fluid material, typically according to an injection molding process. B) A set volume of material was dispensed into the front of the injection unit barrel by rotation of the screw, thus moving the set volume from the feed zone to the front of the screw. During this feed step, the screw was rotated, moving material between the screw and the nozzle, thereby providing the set volume. C) Once the material had been moved to the front of the screw, in a step referred to herein as "depressurization," the screw was moved backward, away from the nozzle, without rotation or substantially without rotation, to avoid more material moving to the front of the screw.

[0153] A mixture-free space between the screw and the nozzle was created in the barrel, the intentional space having a volume referred to herein as the "decompression volume." D) The material was placed in the barrel between the screw and the nozzle for a period of time referred to herein as the "decompression time." During the decompression time, the material foamed due to the pressure drop created by the space added in step (C). E) The molten foam was injected into the mold cavity by forward translation of the screw and / or rotation of the screw.

[0154] Example 1 Two parts were foam molded using a blend of low-density polyethylene blended with 2% by weight Hydrocerol® BIH70 blowing agent, available from Clariant AG (Muttenz, Switzerland). Molding was performed using an Engel Duo 550 Ton injection molding machine (available from Engel Machinery Inc., York, PA, USA). The mold cavity was approximately spherical, with a diameter of 6 inches (15.24 cm). The first part was molded using a standard foam molding process, and the second part was molded using the MFIM process. An aluminum mold with a low-temperature sprue and runner system feeding a 6-inch diameter spherical cavity was employed for both parts. The melt delivery system for each part was identical for the most part of the processing conditions. The process settings for the MFIM process, used as a control, and the standard foam molding process are detailed in Table 3. Parts were produced from each process of approximately equal mass. [Table 3]

[0155] The first and second parts were photographed. Figure 2-1 is a photographic image of the first part molded using a standard foam molding process. As can be seen in the image, the standard foam process did not result in the part filling the mold cavity, and the part did not conform to the shape of the spherical cavity of the mold.

[0156] Figure 2-2 is a photographic image of a second part molded using the MFIM process. As can be seen in the image, the MFIM process resulted in a part that completely or substantially filled the spherical mold cavity, and the part conformed or substantially conformed to the shape of the spherical cavity of the mold.

[0157] The first part, molded using a standard foam molding process, was cut into two pieces. Figures 2-3 and 2-5 are photographic images of one of the pieces of the part made according to the standard foam molding process. As can be seen in the images, the first part contained a large hollow cavity.

[0158] The second part, molded according to the MFIM process, was cut into two pieces. Figures 2-4 and 2-6 are photographic images of one of the pieces of the second part. As can be seen in the images, the second part lacked the large hollow cavities of the standard foam process part. The MFIM part had a cellular structure throughout.

[0159] Example 2 Two parts were formed by foam injection molding: Part A followed a standard foam molding process, and Part B followed the MFIM process. In both processes, the LDPE / talc pellets were dry compounded with the blowing agent and mixed during loading into the molding machine.

[0160] For Part B, a mixture of low-density polyethylene (LDPE), talc, and Hydrocerol® BIH70 was formed and fed into a Van Dorn 300 injection molding machine, providing a polymer shot inside the barrel. After the shot accumulated in front of the screw, the screw was translated backward, without rotation, away from the injection nozzle, according to the MFIM method, creating a space between the screw and the nozzle, which had a vacuum volume. The mixture was then foamed into the space prior to injection into the mold.

[0161] The same procedure was used for Part A, except that the screw was not retracted away from the nozzle after the shot accumulated in front of the screw, i.e., the vacuum volume was zero. The shot was timed to fill the mold cavity under standard foam molding conditions with a target of 10% weight reduction relative to the solid part.

[0162] Tables 4-7 below show the polymers, molds, machines, and processing settings used in Example 2. [Table 4] [Table 5] [Table 6] [Table 7]

[0163] Parts A and B were each cut in half to reveal the cross section. Figures 3A and 3B show the resulting cross sections of Parts A and B, respectively. As shown in Figure 3A, Part A had a thick outer region extending approximately 0.8 inches (20.3 mm) from the surface, indicating that over 50% of the molded part was completely solid. The density of Part A was 0.84 g / cc.

[0164] FIG. 3B shows a cross section of Part B, which was molded according to the MFIM process using the settings shown in Tables 4 and 5. As can be seen in FIG. 3B, Part B had a foam structure, including a distribution of cell sizes and shapes. Solid, non-foamed outer regions were nearly absent in Part B. The density of Part B was 0.35 g / cc.

[0165] A spherical cavity mold was used to form two additional parts, Part C and Part D, by foam injection molding. The same blend composition of LDPE, talc, and Hydrocerol® BIH70 was used to form Parts C and D. Part C was made by the MFIM process, and Part D by a standard foam molding process. Both processes produced spherical or near-spherical parts with a 6-inch (15.24 cm) diameter. Parts C and D were cut into two pieces through the center (widest part) to expose the cross-sections of the parts. Figure 4A is a photographic image of the cross-section of Part C (471 g, required 160 seconds of cooling time) made by the MFIM process. Figure 4B is a photographic image of Part D (1,360 g, required 800 seconds of cooling time), molded using a standard foam process target. This is a photographic image of a cross section of the requested

[0166] Similar results were obtained with the block mold. Part C, made according to the MFIM process, exhibited cells throughout the part, while Part D, made according to the standard foam molding process, exhibited regions adjacent to the outer surface of the part that were free of cells or substantially free of cells ("solid"). Part C was less dense than Part D.

[0167] Example 3 In Example 3, block parts were molded using the MFIM process at various vacuum volumes (Prototype A) and various vacuum volumes and vacuum times (Prototype B).

[0168] Tables 8-10 show the material compositions, mold geometry information, and processing settings used for Prototypes A and B. [Table 8] [Table 9]

[0169] The composite LDPE / talc pellets were mixed with the blowing agent just before molding.

[0170] Prototype A

[0171] In Prototype A, all variables were held constant except for the volume ratio of polymer to vacuum volume (empty space) in the barrel prior to injection. The sample run-by-run settings for Prototype A are shown in Table 10. [Table 10]

[0172] The volume of molten foam injected into the polymer cavity was constant, but the density of the molten foam was a function of the polymer shot / vacuum volume ratio, which was varied to give the parts the weights and densities shown in Table 11. [Table 11]

[0173] The results in Table 11 show that the density of the resulting part can be varied by decreasing the mass and volume of polymer within the molten foam shot with a corresponding increase in vacuum volume.

[0174] Prototype B

[0175] For Prototype B, five molds under the same conditions as Prototype A were performed three times: one using a 20-second decompression time (same as Prototype A), one using a 70-second decompression time, and one using a 120-second decompression time. The 15 resulting foam molded parts were weighed, and their densities were calculated using the mold cavity volume. Part densities were plotted as a function of decompression volume for each of the three decompression times. The plots are shown in Figure 5. As can be seen in Figure 5, part density varied as a function of decompression volume. Furthermore, as shown in Figure 5, the longer the decompression time, the higher the part density.

[0176] Example 4 In Example 4, two series of prototypes, Series I and Series II, were performed using the MFIM process. In Series I, a constant injection rate was used, but the mold closure height was varied. In Series II, the mold closure height was increased with increasing injection rate. In Series II, all conditions were kept constant except for the injection rate (cc / sec) and mold closure height. In the prototypes, LDPE / talc pellets were dry-blended with the blowing agent and mixed during loading into the molding machine.

[0177] Tables 12-13 below show the material composition of the composites to be injected and the basic mold configuration used for prototyping. [Table 12] [Table 13]

[0178] Series I

[0179] In Series I, an injection rate of 394 cubic centimeters per second was used and three prototypes were run: Prototype A had a mold closure height of 1.02 mm and produced Part A, Prototype B had a mold closure height of 0.76 mm and produced Part B, and Prototype C had a mold closure height of 0.51 mm and produced Part C. The settings for the Series I prototypes are shown in Table 14. [Table 14]

[0180] During each molding cycle (each of Prototype A, B, and C), a strain gauge (Kistler surface strain sensor type 9232A, available from Kistler Holding AG, Winterthur, Switzerland) was mounted directly above or inside the mold cavity. The strain sensor contained two piezoelectric sensors that measured the strain of the aluminum cavity as a function of time during the molding cycle. The strain measurements were used as an indirect measure of the forces acting on the mold cavity surface resulting from the injection of the molten foam and any subsequent additional foaming that occurred within the mold cavity. The cavity strain measurements are shown in Figure 6, where for Prototype A, there is a 1.02 mm gap height (line A), for Prototype B, there is a 0.76 mm mold closure height (line B), and for Prototype C, there is a 0.51 mm mold closure height (line C). In Figure 6, strain (unit extension per unit length) is plotted against time in seconds. The strain curves show that the pressure was higher in Prototype C than in Prototype B, which was higher than in Prototype A.

[0181] FIG. 7 includes photographic images showing side, top, perspective, and bottom views of parts A, B, and C. Parts A and B showed evidence of crushing because the parts did not adequately conform to the mold cavity shape. Part A showed more crushing than part B. Part C was more fully formed than either part A or B in that the edges of part C were better defined, part C conformed better to the mold cavity shape, and the interior of the part appeared more homogeneous.

[0182] It was believed that the part could partially collapse within the cavity during molding if sufficient pressure was not applied to stabilize the foam within the cavity during solidification. Therefore, in Series II, the mold was closed more tightly at a slower injection rate to maintain sufficient pressure to prevent part collapse during molding.

[0183] Series II

[0184] In Series II, the gap between the mold halves, i.e., the mold closure height, was systematically reduced as the injection rate was reduced. The molding conditions used were the same as in Series I, but the injection rates and mold closure heights used were as shown in Table 15. [Table 15]

[0185] Four parts were produced as parts A', B', C', and D' in prototypes A', B', C', and D', respectively.

[0186] Parts A', B', C', and D' were each cut in two and the cross sections were photographed. The photographic images are shown in Figure 8. To produce parts that would not collapse before solidification, the mold halves had to be gradually closed until they were actually pressed together (as indicated by the negative dimensions), as shown in Table 15.

[0187] Parts A', B', C', and D' showed no evidence of crushing and appeared fairly uniform with well-defined edges and surfaces. Thus, parts were made using the MFIM process using significantly different injection rates by controlling the pressure within the cavity during injection, for example, by varying the mold closure height.

[0188] Example 5 In Example 5, the same LDPE composite material as in Examples 1-3 was used in a non-standard two cavity mold with molding parameters as shown in Tables 16-18. [Table 16] [Table 17] [Table 18]

[0189] Example 5 produced part 51 shown in Figure 9. During injection, the melted molten foam enters through sprue 52 and splits into two separate channels, substantially simultaneously filling part 51. Thus, the MFIM process can be used to form parts by splitting the melt into multiple channels within the mold.

[0190] Example 6 The first part was molded using a 15 wt% talc / 85 wt% polycarbonate composite formulation and compounded with 3 wt% Hydrocerol® XH-901 prior to loading into the injection molding machine. The first part was formed using the MFIM process. Process details are provided in Tables 19 and 20. The part was made using a 4x2x2 block mold (5.08 x 10.16 x 10.16 cm) with a mold cavity volume of 524.4 cc and a sprue volume of 17.4 cc. The sprue was cut from the part, and the part then underwent X-ray laminography to quantify the cell structure formed within the 5.08 x 10.16 x 10.16 cm geometry. [Table 19] [Table 20]

[0191] X-ray tomography was performed using a Zeiss Metrotom 800 130 kV imaging system (available from Carl Zeiss AG, Oberkochen, Germany). The instrument measured the attenuation of X-ray radiation due to the component geometry and the density of the materials used. Column data were calculated using the Feldkamp reconstruction algorithm, which is a standard technique in the industry. The instrument had a 1,536 × 1,920 pixel flat panel detector for an ultimate resolution of 3.5 μm under the conditions of the measurements.

[0192] A conformal image of the full Zeiss 3D tomographic scan of the first part is shown in Figure 10, where the solid polymer section is shown as transparent, the cells are shaded for visualization, and the cutting plane AA for the single cross section is indicated. Figure 11 shows a single plane cross section AA selected from the X-ray data, where threshold analysis has been applied to enable discrete cell identification and subsequent quantitative analysis.

[0193] The circularity of the cell cross sections was obtained. These cross-sectional circularities were used as a measure of cell sphericity. Therefore, circularity and sphericity are used interchangeably in the examples. Quantitative analysis, shown in Figure 12, revealed the cell distribution of both count and average size as a function of each cell's circularity. A circularity value of zero represents a perfectly non-spherical cell, and a value of one represents a perfectly spherical cell. The data showed the distribution of cell size and shape. Except for the most deformed cells (indicated by 0.1 to 0.2 on the circularity scale), there was an inverse relationship between the average cell size and the number of cells for a given circularity. Furthermore, there was also an inverse relationship between the average cell size and the number of cells.

[0194] Using the MFIM process, a second 6-inch (15.24 cm) diameter spherical part was molded from low-density polyethylene (LDPE) using the polymer formulation and processing parameters as outlined in Tables 21 and 22. The LDPE / talc pellets were dry-blended with the blowing agent Hydrocerol® BIH70 and mixed during loading into the molding machine. [Table 21] [Table 22]

[0195] Figure 13 is an X-ray tomography image of a cross section of a sphere. As can be seen in Figure 13, the outer region contained numerous smaller cell sizes, with larger cells in the central region.

[0196] FIG. 14 shows a plot of mean cell size and mean cell count against mean cell circularity, revealing an inverse relationship between mean cell size and circularity, and an inverse relationship between mean cell size and number of cells.

[0197] Example 7 The MFIM process produced LDPE composite spheres (92 wt. % polymer, 5 wt. % talc, and 3 wt. % Hydrocerol®) with a diameter of 3 inches (7.62 cm). BIH70), and the resulting foam cell structure is detailed in Figures 15-18. Molding conditions are provided in Table 23. Parts were molded on an Engel Victory 340 Ton injection molding press in a custom-designed, water-cooled aluminum mold. The mold cavity volume was 15.38 in. 3 (252cc) and the shot size is 5 inches 3 (82cc) and the reduced pressure volume in the barrel is 5 inches 3 (82 cc). Decompression time was 77 seconds. The molded part weight was 80.31 g, resulting in a final part density of 0.32 g / cc. [Table 23]

[0198] After removal from the mold, the parts were aged under ambient conditions for 24 hours, then scored and submerged in liquid nitrogen for 2 minutes. After removal from the liquid nitrogen, the spheres were fractured along the scored surface lines, and the fracture surfaces were imaged using an environmental scanning electron microscope (ESEM) (FEI Quanta FEG650). The images shown in Figures 15-18 are photomicrographs at various magnifications taken from the fracture surfaces of the spherical parts using a large field detector, i.e., 5.0 kV and 40 Pa pressure.

[0199] The white boxes in Figure 15 indicate areas detailed in Figure 16. The white boxes in Figure 16 indicate areas detailed in Figure 17.

[0200] In Figure 17, the cells on the left of the image are larger and relatively spherical, while those cells on the right of the picture appear increasingly flattened as they approach the surface of the sphere.

[0201] The image in Figure 18 details the area indicated by the white box in Figure 17. As can be seen in Figure 18, there is a gradual transition from spherical to "flattened" or compressed cells moving towards the surface of the part.

[0202] Example 8 To establish baseline differences between standard thickness parts produced under standard foam molding conditions, a recently published study of standard foam injection molding (Paultkiewicz et al., Cellular Polymers 39, 3-30 (2020)) was used to establish molding parameter baselines using a 16-step statistical analysis design of experiment (DOE) approach. Materials (standard molding-grade polypropylene with 0, 10, and 20 wt% talc and 0, 1, and 2 wt% Hydrocerol® BIH70 (blowing agent)) were compounded to the specifications outlined in the publication to closely mimic the baseline study. This study was designed to investigate the effects of blowing agent concentration, talc content, and process conditions on selected properties of injection-molded foam parts. A standard ISO tensile specimen mold was used, with cavity dimensions of 4.1 mm thick, 10 mm wide at the gauge length, and 170 mm long. No special venting was developed for the O specimen mold. After ensuring that the injection molding machine, material formulation, and process window were capable of replicating the results published by Paultkiewicz et al., a second study was conducted using process variables specific to MFIM, specifically, decompression volume and decompression time, while pressure and hold time (critical variables in the published study) were set to constant values ​​of zero kN and zero seconds, respectively.

[0203] Molding was completed using an Engel Victory 340 Ton machine equipped with water cooling. The constant and variable process conditions used are shown in Table 24 for both the "standard" foam molding process and the MFIM molding process. [Table 24]

[0204] The designed studies called for 16 combinations of processing conditions / polymer formulations (16 runs) for each standard molding and MFIM molding study. Multiple replicates of each run were performed to produce replicate parts for each run. Table 25 outlines the variations between runs in both the standard and MFIM design runs. Runs were performed in a random order to avoid bias. The L / T ratio for the ISO tensile specimens was 40.5. [Table 25-1] [Table 25-2]

[0205] After molding the 32 unique process combinations of the two 16-step DOE studies, five samples from each series were mechanically tested for tensile strength and the fracture surfaces were imaged after fracture. A representative selection of ISO specimen cross sections from steps 10, 11, 14, and 15 of the standard foam molding process is shown in Figure 19, and a representative selection of ISO specimen cross sections from steps 9, 10, 15, and 16 of the MFIM process is shown in Figure 20.

[0206] The differences between standard foam molding techniques as adopted from recent literature and the MFIM process are apparent when examining cross-sectional images. The structure within the standard process specimen consists of relatively few, well-defined, spherical cells flanked on all sides by thick regions of polymer devoid of cells. Cross-sectional images obtained from the standard foam molding process are in good agreement with those in the publication by Paulkiewicz et al. and represent the current industry standard. In contrast, typical cross-sections of MFIM-molded ISO specimens reveal a cellular structure with more asymmetrically deformed cells.

[0207] The cells in the MFIM cross section also progress to regions adjacent to the surface in nearly all cases, despite being much thinner parts with a much larger L / T ratio (40.5) than previously described, similar to the previous examples described herein. The results clearly demonstrate that the employment of a decompression step in MFIM, combined with the elimination of the standard foam molding process variables of hold pressure and time, results in a significantly different cell structure within the molded part.

[0208] Tensile tests were performed on five replicate parts from MFIM process 9. Figure 21 shows a representative cross section and a series of stress / strain plots for the five tested parts from MFIM process 9.

[0209] Tensile tests were performed on five replicate parts from step 10 made using the standard foam molding process. Figure 22 shows a representative cross section and a series of stress / strain plots for the five parts tested from the standard foam process step 10.

[0210] The average tensile strength of the five parts from MFIM step 9 was less than the average of the five parts from the standard foam molding process step 10. However, the MFIM parts exhibited greater strain (elongation) at failure.

[0211] More cells were visible in the cross section of the MFIM part from step 9 (102 cells) than in the standard foam molding process part from step 10 (19 cells).

[0212] X-ray tomography scans (completed under conditions described in Example 5) were completed on randomly selected replica parts from step 15 of the standard foam molding process (shown in FIG. 23) and on randomly selected replica parts produced during step 9 of the MFIM process (shown in FIG. 24). Both FIG. 23 and FIG. 24 show a "top" view taken at 50% depth and a "side" view also taken at 50% depth.

[0213] In the developed cell structure of the standard foam molding process ISO specimen (Figure 23), the cells were circular in shape and the area adjacent to the surface of the specimen was devoid of cells.

[0214] In contrast, as shown in FIG. 24, the ISO specimens produced via the MFIM process contain multiple elongated cell populations, with the cells found in areas adjacent to the surface of the part.

[0215] Example 9 To explore the dependence of final cell structure on MFIM processing conditions, eight tensile specimens of LDPE were molded on an Engel Victory 340 Ton injection molding machine using the MFIM process. The mold contained an aluminum modified tensile specimen cavity with dimensions of 24 cm long, 2.54 cm thick, and variable width with a 6 cm gauge length and 2.54 cm gauge width tapering to a 3.5 cm wide flange. The large tensile specimens were fed from a cold sprue and runner system through a 1.0 cm diameter gate. The material formulation consisted of LDPE with or without talc, always containing 2 wt% blowing agent Clariant Hydrocerol® BIH70. The melt temperature was set to the profile detailed in Table 26, and the residence time in the barrel was 13 minutes before building the shot for injection. After building up the shot, the screw was backed off to give a vacuum volume of either 4.0 cubic inches (66 cc) or 6.0 cubic inches (98 cc), and the LDPE blowing agent mixture was allowed to foam into the empty barrel space prior to injection for either 15 or 45 seconds. Studies were completed on both unfilled LDPE and 15% talc-filled LDPE. Detailed process conditions are shown in Table 26. [Table 26]

[0216] Figure 25 shows an x-ray scan of one of the parts from this study, showing the overall shape of each part.

[0217] FIG. 26 depicts the cross-section of each specimen molded in this study and cut from the center of the gauge length, with the variable parameters indicated. The sample set includes two primary groups: samples made with talc and samples made without talc. In FIG. 26, the sample set on the left depicts those parts made without talc. These parts exhibit a smaller cellular structure within the core of the part, indicating that the integrity of the developed cellular structure was largely unaffected by changes in decompression ratio and decompression time, which were all within acceptable ranges.

[0218] The sample set on the right depicts those specimens containing 15 wt% talc. Some smearing on the part surface resulted from knife damage on the low modulus LDPE but is not representative of part quality. The cell structure in the talc parts was consistently larger, and cell circularity was slightly below that of the equivalents without talc.

[0219] X-ray tomography images of 15% talc, 6 inches 3 The image was taken from a cross section approximately 50% in from the major surface of the MFIM part, created using a (98 cc) vacuum volume and a 15 second vacuum time. The image is shown in FIG.

[0220] Example 10 Tensile specimen parts were made using a standard foam molding process from LDPE loaded with 15 wt. % talc and 2 wt. % Hydrocerol® BIH70 using processing parameters as described for Example 9, but without the decompression step of the MFIM process. The standard foam molded parts were made from the 15% talc, 6 inch foam from Example 9. 3 The results were compared with MFIM parts made using a 98 cc vacuum volume and a 15 second vacuum time. Using the method described in Example 6, X-ray tomography images were taken from the center of each part (MFIM molded and standard foam molded) at various depths from the major surface. Cross-sectional images were also recorded. The images are shown in FIG.

[0221] X-ray laminography analysis of cell count, cell circularity, and average cell size (longest dimension of the cells) was performed on images of each tensile specimen part (MFIM and standard process material) at various depths from the major surface. Cell count, cell circularity, and average cell size were each plotted against cross-sectional depth, and individual plots are shown in Figures 29-31, respectively.

[0222] As shown in Figure 29, cell counts are higher for MFIM molded parts at all depths. As can be seen throughout the examples and figures, parts molded using standard foam molding processes appear to have no, or substantially no, cells in the region or "skin" adjacent to the surface, for example, within about the first 2.5 mm depth from the major surface, while cells are present in parts molded using the MFIM process in the region between about 2.5 mm below the surface and the surface.

[0223] As shown in Figure 30, in general, cell circularity is higher in the standard foam molding process samples than in the MFIM shaped parts, except towards the center of the MFIM parts, where circularity is also higher in the MFIM molded samples.

[0224] As shown in Figure 31, cell size was generally larger for the standard foam molded tensile bar parts, but dropped sharply to zero in the region close to the outer surface (e.g., within 2.5 mm of the surface). In contrast, cell size was more uniform throughout the depth of the MFIM molded parts, with cells continuing right to the surface.

[0225] The same trend was observed by visual inspection of the cross-sections shown in Figure 28. Within 2.5 mm of any outer surface, standard foam molded parts appear to be devoid of cells, while cells are visible all the way to the outer surface in the MFIM parts.

[0226] Example 11 A large sample of the recovered marine plastic was analyzed using differential scanning calorimetry and estimated to consist of approximately 85% HDPE by weight, with the remainder comprising polypropylene and contaminants.

[0227] Two parts, a 4" x 4" x 2" brick and a 15.24 cm diameter sphere, were successfully molded from marine plastic using the MFIM process. Molding was performed using an Engel Duo 550 Ton injection molding machine (available from Engel Machinery Inc., York, PA, USA). Both parts were center-opened and filled by viscous coil-fold flow.

[0228] The processing parameters and properties of the resulting parts are listed in Tables 27 and 28, respectively. [Table 27] [Table 28]

[0229] Example 12 A 9 inch (22.86 cm) diameter sphere, "Sample 10," was molded using the MFIM process described herein. Additionally, a second 9 inch (22.86 cm) diameter sphere, "Sample 20," was molded using a modified process. The modified process, referred to herein as the "reverse MFIM" process, was as follows:

[0230] A) A mixture was prepared by blending a polymer (which may be in the form of pellets, powder, beads, granules, and the like) with a chemical foaming agent and any other additives, such as fillers. The mixture was introduced into an injection unit, and a rotating injection unit screw moved the material forward within the barrel of an injection molding machine, thus forming a heated fluid material, typically according to an injection molding process. B) The screw was moved backward toward the hopper, creating an intentional space within the barrel between the screw and the nozzle. C) A set volume of material was dispensed into the front of the barrel of the injection unit by the rotation of the screw, thus moving the set volume from the feed zone to the front of the screw and into the intentional space created in step B. During this feeding step, the screw rotated, moving molten material into the space within the barrel between the screw and the nozzle, thereby providing the set volume. However, the set volume occupied only a portion of the intentional space, thereby providing a volume for the shot to foam and expand, i.e., a decompression volume. D) The material remained in the barrel between the screw and the nozzle for a period of time, referred to herein as the "decompression time." During the decompression time, the material expanded due to foaming, filling or partially filling the space created in step (B). E) The molten foam was injected into the mold cavity by forward translation of the screw and / or screw rotation.

[0231] Thus, the normal and reverse MFIM processes differed from one another in that in the MFIM process, the screw was rotated to introduce the shot into the front of the barrel before being translated backward to allow for a vacuum space, while in the reverse process, the screw was translated backward to allow for a vacuum space before being rotated to introduce the shot of material into the intentionally created space.

[0232] Both Sample 10 and Sample 20 were molded from virgin LDPE containing 2% Hydrocerol® BIH70, 2% talc, and 1% yellow colorant. Molding was performed on an Engel Duo 550 Ton injection molding machine (available from Engel Machinery Inc., York, PA, USA). The mold was a spherical cavity within an aluminum mold fed by a cold runner and sprue.

[0233] The processing parameters are shown in Table 29. [Table 29-1] [Table 29-2]

[0234] The density of the parts for both Sample 10 and Sample 20 was 0.214 g / cc, a density reduction of 77% in both cases.

[0235] A photograph of Sample 20 is shown in FIG. 32, and a photograph of Sample 10 is shown in FIG. 33, with each spherical component mounted on a stand. As can be seen, Sample 20, fabricated using the "reverse MFIM process," exhibited an uneven surface, while the surface of Sample 10, fabricated using the MFIM process, was much more uniform. The average wrinkle depth was estimated using optical microscopy and X-ray tomography. The average wrinkle depth was measured to be less than 50 microns for Sample 10, but 565 microns for Sample 20.

[0236] Samples 10 and 20 were each cut in half to provide cross sections at their largest diameters. The cross sections of the four pieces were photographed. The half of Sample 20 made by the reverse MFIM method is shown in FIG. 34, and the half of Sample 10 is shown in FIG. 35. Close inspection of the edges showed that in Samples 10 and 20, unlike parts produced in any of the examples by the standard foam method, cells were found right up to the surface, e.g., within 2.5 mm of the surface.

[0237] X-ray tomography was performed on the first inch depth of the samples for Sample 10 and Sample 20 using the method described in Example 6, and cell counts and cell sizes were measured for different distances from the surface of each sample. The plots are given in Figures 36 and 37, where "MFIM" refers to Sample 10 and "reverse MFIM" refers to Sample 20.

[0238] Two additional spherical parts, Parts 6 and 7, were prepared using the same polymer / talc / colorant / blowing agent mixture under the same conditions as Sample 10, i.e., by the MFIM method. Five cuboid parts, each approximately 2 inches by 2 inches by 1 inch, were cut from each of Parts 6 and 7 and the compressive modulus (stress vs. strain) was tested. The average stress vs. average strain (MFIM method) was plotted and is shown in FIG. 38.

[0239] Two additional spherical parts, namely parts 22 and 24, were prepared under the same conditions as sample 20 and using the same polymer / talc / colorant / blowing agent mixture. Five cuboid parts, each approximately 2 inches by 2 inches by 1 inch (approximately 5.1 cm by 5.1 cm by 5.1 cm), were cut from each of parts 22 and 24, and the compressive modulus (stress vs. strain) was tested. The average stress vs. average strain (inverse MFIM method) was plotted and is shown in FIG. 38. As can be seen in FIG. 38, the compressive modulus of the parts made by the MFIM process (average of parts 6 and 7) and the parts made by the inverse MFIM process (average of parts 22 and 24) is similar.

[0240] Five strips were cut from each of parts 6 and 7 (MFIM) and 22 and 24 (reverse MFIM). Each strip was approximately 1 inch x 1 inch x 8 inches. The flexural modulus (stress vs. strain) was tested for all of the strips, and the results were averaged for the 10 MFIM-produced strips and the results were averaged for the 10 reverse MFIM strips. The results are plotted in Figure 39.

[0241] Example 13 Parts of various geometries and materials, as shown in Table 30, were processed using the MFIM method as described herein. The parts were cross-sectioned. In all cases, regions close to the surface contained smaller-sized cells, but cell size increased as one moved away from the surface. The reduced cell size region closer to the surface transitioned to larger cell sizes as one moved further away from the surface. The transition was gradual; therefore, distinct layers of smaller and larger sizes were not present; however, using microscopy, the relative areas of the smaller or "compressed" cells and the larger cells were estimated visually and confirmed by light microscopy, as shown in Table 30. While the numbers are estimates only, inspection of the images indicated that the depth of the area and percent area occupied by the "compressed" cells varied widely, likely depending on the part geometry, material, and / or process conditions. [Table 30]

[0242] Example 14 A first part molded using a 98 wt% metallocene polyethylene formulation was compounded with 2 wt% Hydrocerol® BIH70 prior to loading into an injection molding machine. The first part was formed using the MFIM process. Process details are provided in Tables 31 and 32. The part was fabricated using a 2 inch x 4 inch x 4 inch block mold (5.08 x 10.16 x 10.16 cm) with a mold cavity volume of 524.4 cc and a sprue volume of 17.4 cc. The sprue was cut from the part, and the part was then subjected to a compressive load test to quantify the compressive strength properties of the cellular structure formed within the 2 inch x 4 inch x 4 inch geometry. [Table 31] [Table 32]

[0243] Compression tests were performed on an Instron Universal Testing System (available from Instron USA, Norwood, Missachusetts, USA). Each molded foam block was placed between test platens and stabilized in an environmental chamber at 30°C for 5 minutes prior to testing. The instrument was equipped with a 250 kN load cell. The compression test rate was 5 mm / min.

[0244] The results showed that the compressive modulus was 19 MPa for Sample A (0.37 g / cc), 39 MPa for Sample B (0.45 g / cc), and 55 MPa for Sample C (0.57 g / cc). As shown in Figure 40, the compressive strength of the metallocene polyethylene (mPE) blocks increases with increasing density.

Claims

1. 1. A method of forming a polymeric foam article, the method comprising: forming a molten pneumatic mixture by heating and mixing a thermoplastic polymer with a physical blowing agent source, wherein the temperature of the molten pneumatic mixture exceeds a temperature at which the physical blowing agent source produces a physical blowing agent at atmospheric pressure, and wherein a pressure applied to the molten pneumatic mixture is sufficient to substantially prevent foam formation; collecting a selected amount of the molten pneumatic mixture in a collection area; forming a molten polymer foam from the molten pneumatic mixture by defining an expanded volume in the collection area adjacent to the molten pneumatic mixture; dispensing the molten polymer foam from the collection area into a cavity defined by a mold, wherein the molten polymer foam contacts a surface of the mold defining the cavity; cooling the molten polymer foam within the mold cavity to form a solidified polymer foam article; and A method comprising:

2. The method of claim 1 , wherein the dispensing comprises partially filling the mold cavity.

3. The method of claim 1 , wherein the dispensing comprises substantially filling the mold cavity.

4. The method of claim 1 , wherein the dispensing comprises completely filling the mold cavity.

5. The method of any one of claims 1 to 4, wherein the heating, mixing, collecting, defining and dispensing are performed using an injection molding machine.

6. The method according to any one of claims 1 to 5, wherein the source of the physical blowing agent is an organic compound, which produces the physical blowing agent by a chemical reaction.

7. The method of any one of claims 1 to 5, wherein the source of physical blowing agent is a physical blowing agent.

8. The physical foaming agent is CO ２ or N ２ The method according to any one of claims 1 to 7, wherein

Images