Polymer foam articles and methods of making polymer foams

Abstract

Molded polymer foam articles are described as having novel foam structures. These polymer foam articles comprise a continuous polymer matrix present throughout the article, the continuous polymer matrix defining a plurality of air pockets contained in a surface region extending 500 micrometers below the surface of the article. This surface region is further characterized as having compressible air pockets. This novel foam structure is achieved even when molding polymer foam articles comprising a thickness greater than 2 cm and a volume greater than 1000 cm³, or a volume greater than 1000 cm³ and a thickness greater than 2 cm. Methods for preparing these molded polymer foam articles are also described.

Description

Technical Field

[0001] This invention relates to polymer foam products and methods for preparing polymer foam. [Cross-reference to related applications]

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 867,516, filed June 27, 2019, entitled "Method for Molten Foam Injection Molding of Foamed Parts". U.S. Provisional Patent Application No. 62 / 867,516 is hereby incorporated by reference in its entirety, as if fully set forth herein. Prior Technology

[0003] Foamed polymer products are widely used in the industry because they offer the highly desirable properties of high strength associated with solid polymer articles, while also providing reduced density and thus reducing the amount of polymer used to form articles of a given volume. Furthermore, compared to their solid counterparts, the industry benefits from the reduced weight of foamed products while still obtaining the strength, toughness, and impact resistance inherent in the polymer itself.

[0004] Therefore, the industry has developed several now-known methods for incorporating gas into thermoplastic polymers to manufacture such foamed products. For gas molding of foamed thermoplastic polymer products, commercial guidelines and industry practice employ melt-mixing apparatuses operable to maintain a certain pressure to limit gas expansion within the apparatus, while further mixing the melt-mixed gas or gas source with the melt of the thermoplastic polymer at a temperature above the melting temperature of the thermoplastic polymer. Such methods and apparatuses are designed to minimize the formation of gas pockets or gas bladders, which would otherwise form within the molten thermoplastic polymer due to gas expansion. Therefore, when located within and arranged within a melt-mixing apparatus, the thermoplastic polymer may contain a gas source or the gas itself dissolved or dispersed therein, without containing gas pockets or substantially without gas pockets. A mixture of molten thermoplastic polymer and gas at or above a temperature at which it would form gas pockets at atmospheric pressure, without containing gas pockets or substantially without gas pockets, can be referred to as a melt-gas mixture. The temperature at which a gas or pneumatogen will form a gas pocket in a molten gas-containing mixture at atmospheric pressure is called the critical temperature. Therefore, melt mixing apparatuses well-known in this technology are designed and adapted to produce and dispense molten gas-containing mixtures. Additionally, such apparatuses are suitable for producing molten gas-containing mixtures by adding nascent, latent, or latent gases that are released at a characteristic temperature or formed by exothermic or endothermic chemical reactions at a characteristic temperature. The critical temperature of a nascent, latent, or latent gas is the temperature at which the reaction occurs or the gas is released into the thermoplastic polymer. All such materials and methods are well understood, and melt mixing apparatuses of various designs are widely available for this purpose. Commonly used melt mixing apparatuses are single-screw or twin-screw extruders adjusted to have a pressurized chamber at the distal end of the screw to receive a quantity of the molten gas-containing mixture or its "shot," which pushes the molten gas-containing mixture into the pressurized chamber by operating the screw during mixing.

[0005] After a certain amount of material is accumulated or injected into a pressurized chamber, the molten gas-containing mixture is dispensed from the melt mixing device and guided through fluid-connected pipes or conduits to the cavity of a mold to obtain the desired shape. Dispensing is typically performed by releasing pressure while the thermoplastic polymer is still molten, maximizing the amount of foaming (in the form of air pockets) within the mold cavity. The expanded foam in the cavity is then cooled to produce a foamed product. Foamed parts molded using this method are referred to as injection-molded foam parts in this technology. These techniques are generally limited to manufacturing parts with a thickness of approximately 2 cm or less.

[0006] The injection molding method that uses gas-generated materials to induce a foam structure in molded parts can be understood as the 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 disclosure, the process conditions commonly used for molding standard injection molding ISO test strips with a thickness of 4.1 mm are systematically changed to produce 16 different combinations of process settings and formulation variables (concentration of gas-generated material source, filler content, injection velocity, injection time, holding time, and holding pressure). The author demonstrates that the control process and formulation produce some changes in the foam structure in the resulting foam component, but all variables produce a component with a "surface," which is a term used in this technique to describe a highly characteristic region of the surface of an injection-molded foam article that is close to or substantially free of air pockets.

[0007] The surface of the injection-molded foamed article and the solid thermoplastic region extending approximately 500 micrometers below the surface in any direction are tested; that is, these regions are free of or substantially free of air pockets. Foam parts produced by injection molding according to conventional injection molding methods include surface features. Furthermore, depending on the method, apparatus, and materials used, the surface layer of most such parts is significantly thicker than 500 μm, and can be 1 mm, 2 mm, 3 mm, or even thicker.

[0008] For manufacturing larger foamed components (e.g., trays or trolley bodies), the conventional methods described above are insufficient because the large mold cavity induces an overpressure drop as the molten gas-containing mixture flows and expands during mold filling, and air pockets can form but subsequently coalesce or leak from the self-adhesive polymer flow during filling. Therefore, in some cases of “structural foam” molding, using multiple nozzles simultaneously can rapidly fill larger or thicker mold cavities. In other cases, significant back pressure can be applied within the mold cavity to prevent air pocket formation during filling; the pressure is then released after mold filling to allow substantial air pocket formation within the mold cavity. Both methods are typically used in a single process.

[0009] However, the aforementioned structural foam molding process does not solve the problem that actually prevents the industry from producing very large parts. It is well known that the area near the surface of molten material cools faster than its interior, creating a temperature gradient within the material. The deepest points within the material cool the slowest. In the case of large mold cavities filled with molten polymers or gas-containing mixtures, the slow cooling of the material's interior allows the viscous flow of the thermoplastic to allow gas pockets to coalesce, forming large, polymer-free pockets and disrupting the intended continuous polymer matrix defining such foams. This effect is exacerbated by the shrinkage of the polymer volume as it cools below its melt transition temperature. For larger foamed parts, this effect can even cause the foam structure to collapse completely within the part.

[0010] Without a continuous polymer matrix throughout the component, the reduction in combined strength and density associated with foamed articles is not achieved. Foamed components with large areas of no polymer or voids compromise the structural integrity of the component, rendering it unsuitable for its intended use. These serious technical problems limit the industrial application of polymer foams to many other highly useful and beneficial applications. Therefore, there is a continued need for improved methods for preparing foamed articles, especially larger or thicker ones. There is a continued need to obtain components with continuous foam structures. In particular, there is a need to obtain components with a thickness greater than 2 cm and containing continuous foam structures. The industry continues to require the use of conventional equipment and materials to meet these needs. Summary of the Invention

[0011] This document describes a method for preparing molten polymer foam. The method includes: adding a thermoplastic polymer and a gas-generating source to an extruder; heating and mixing the thermoplastic polymer and the gas-generating source in the extruder under pressure to form a molten gas-containing mixture, wherein the temperature of the molten gas-containing mixture exceeds the critical temperature of the gas-generating source; collecting a portion of the molten gas-containing mixture in a collection zone of the extruder; defining an expansion volume in the collection zone to cause a pressure drop in the collection zone; allowing a certain expansion period after definition; and dispensing molten polymer foam from the collection zone. In embodiments, the expansion volume is selected to provide a total expected molten foam volume between 10% and 300% in the collection zone. In embodiments, the expansion period is between 5 seconds and 600 seconds. In embodiments, the molten gas-containing mixture is undisturbed or substantially undisturbed during the expansion period.

[0012] In one embodiment, the dispensing is to a forming element; in some embodiments, the forming element is a mold. In one embodiment, there is a fluid connection between the collection area of ​​the extruder and the mold. In one embodiment, the dispensing is in the form of unobstructed flow of molten polymer foam. In one embodiment, the dispensing is in the form of a linear flow of molten polymer foam.

[0013] In an embodiment, the method further includes cooling the dispensed molten polymer foam to a temperature below the melt transition temperature of the thermoplastic polymer. In an embodiment, one or more additional materials are used in the extruder, wherein one or more materials are selected from colorants, stabilizers, brighteners, nucleating agents, fibers, granules, and fillers. In an embodiment, the gas generator source is a gas generator, and the addition is pressurized. In other embodiments, the gas generator source includes bicarbonates, polycarboxylic acids or their salts or esters or mixtures thereof.

[0014] This document also discloses a polymer foam article prepared using the methods, materials, and apparatus described herein. In an embodiment, the polymer foam article has a foam structure throughout its entirety, characterized by a continuous polymer matrix defining a plurality of air bladders therein. In an embodiment, the surface region of the polymer foam article includes the compressed air bladders. In an embodiment, the surface region is a region extending 500 micrometers from the surface of the article.

[0015] This document also discloses thermoplastic polymer foam articles having a foam structure throughout, the foam structure being a continuous polymer matrix defining a plurality of air bladders therein, wherein a surface region of the article includes compressible air bladders. In some embodiments, the surface region is a region of the article extending 500 micrometers from its surface. In some embodiments, the article includes compressible air bladders more than 500 micrometers from its surface. In embodiments, the polymer foam article includes a thickness greater than 2 cm; in other embodiments, the polymer foam article includes a volume greater than 1000 cm³, 1000 cm³ to 5000 cm³, or even greater than 5000 cm³; and in still other embodiments, the polymer foam article includes a volume greater than 1000 cm³ and a thickness greater than 2 cm, a volume between 1000 cm³ and 5000 cm³ and a thickness greater than 2 cm, or a volume greater than 5000 cm³ and a thickness greater than 2 cm.

[0016] In the embodiments, the materials used to prepare the polymer foam articles are not specifically limited and include those selected from polyolefins, polyamides, polyimides, polyesters, polycarbonates, poly(lactic acid), acrylonitrile-butadiene-styrene copolymers, polystyrene, polyurethanes, polyvinyl chloride, tetrafluoroethylene copolymers, polyether ethers, polyacetals, aromatic polyamides, polyphenylene ethers, polybutene, polybutadiene, polyacrylates and methacrylates, ionomers, polyether-amide block copolymers, polyaryl ether ketones, polyether ethers, polyphenylene sulfide, polyamide-amide copolymers, polybutylene succinate, cellulose materials, polysaccharides and their copolymers, complexes, mixtures and blends. In some embodiments, the thermoplastic polymer is a mixed plastic waste stream. The continuous polymer matrix may further include one or more additional materials selected from colorants, stabilizers, brighteners, nucleating agents, fibers, granules and fillers, depending on the situation.

[0017] Other objectives and features will be partially obvious and will be partially indicated below. Simple Explanation of the Diagram

[0018] [Figure 1] A-1B illustrates a melt mixing apparatus suitable for performing the methods described herein.

[0019] [Figure 2]-1 is an image of a component molded according to the standard foam molding process as described in Example 1. Figure 2-2 is an image of a component molded according to the fused foam injection molding (MFIM) process as described in Example 1. Figures 2-3 and 2-5 are images of parts cut from components manufactured according to the standard foam molding process as described in Example 1. Figures 2-2 and 2-3 are images of parts cut from components manufactured according to the MFIM process as described in Example 1.

[0020] [Figure 3] A is an image of the cross-section of component A, which is manufactured according to the standard foam molding process as described in Example 2 and cut into two pieces to expose the cross-section. Figure 3B is an image of the cross-section of component B, which is manufactured according to the MFIM process as described in Example 2 and cut into two pieces to expose the cross-section.

[0021] [Figure 4]A is an image of the cross-section of component C, which is manufactured according to the MFIM process and cut into two pieces to expose the cross-section, as described in Example 2. Figure 4B is an image of the cross-section of component D, which is manufactured according to the standard foam molding process and cut into two pieces to expose the cross-section, as described in Example 2.

[0022] [Figure 5] is a graph showing the component density versus decompression volume for various decompression times, including Experiment B as described in Example 3.

[0023] [Figure 6] is a graph showing the strain versus time for components manufactured in experiments A, B and C as described in Example 4.

[0024] [Figure 7] shows images of views of components A, B and C in different states as described in Example 4.

[0025] [Figure 8] shows a cross-sectional image view of components A', B', C' and D' as described in Example 4.

[0026] [Figure 9] is a diagram of the two components as described in Example 5.

[0027] [Figure 10] is an isometric image of a tomographic scan of a first component manufactured according to the MFIM process as described in Example 6.

[0028] [Figure 11] is an image of the cross-sectional plane shown in Figure 10 as described in Example 6.

[0029] [Figure 12] is a graph showing the average hole size and hole count relative to hole roundness of the first component prepared as described in Example 6.

[0030] [Figure 13] is a diagram of an X-ray tomographic image of the cross-section of the second (spherical) component as described in Example 6.

[0031] [Figure 14] is a graph showing the average hole size and hole count relative to the hole roundness of the second (spherical) component prepared as described in Example 6.

[0032] [Figure 15] is a micrograph of the fractured surface of a fractured three-inch diameter composite sphere fabricated according to the MFIM process described in Example 7.

[0033] [Figure 16] is a micrograph of the fractured surface of a fractured three-inch diameter composite sphere fabricated according to the MFIM process described in Example 7.

[0034] [Figure 17] is a micrograph of the fractured surface of a fractured three-inch diameter composite sphere fabricated according to the MFIM process described in Example 7.

[0035] [Figure 18] is a micrograph of the fractured surface of a fractured three-inch diameter composite sphere fabricated according to the MFIM process described in Example 7.

[0036] [Figure 19] shows a microscopic image of the cross-section of an ISO strip component prepared according to the 10th, 11th, 14th and 15th rounds of the standard foam molding process described in Example 8.

[0037] [Figure 20] shows a microscopic image of a cross section of an ISO strip component manufactured according to the 9th, 10th, 15th and 16th MFIM processes as described in Example 8.

[0038] [Figure 21] shows a cross-section of an ISO strip component manufactured according to the 9th round MFIM process as described in Example 8, and a stress-strain curve of a repeating component manufactured according to the 9th round MFIM process.

[0039] [Figure 22] contains a cross-section of an ISO strip component prepared according to the standard foam molding process of the 10th round as described in Example 8, and a stress-strain curve of a repeating component prepared according to the standard foam molding process of the 10th round.

[0040] [Figure 23] contains two X-ray tomographic images of an ISO strip component prepared according to the standard foam molding process of round 15, as described in Example 8.

[0041] [Figure 24] contains two X-ray tomographic images of an ISO strip component fabricated according to the 9th round MFIM process, as described in Example 8.

[0042] [Figure 25] is an X-ray scan image of a large stretch strip component prepared according to the MFIM process, as described in Example 9.

[0043] [Figure 26] shows a cross-section of eight large stretch strip components fabricated according to the MFIM process as described in Example 9.

[0044] [Figure 27] is an X-ray tomographic image of a large stretch strip component fabricated according to the MFIM process as described in Example 9.

[0045] [Figure 28] includes a series of X-ray tomographic images at different depths within a stretch strip component fabricated according to the MFIM process as described in Example 10, and a series of images at different depths within a stretch strip component fabricated according to the standard foam molding process.

[0046] [Figure 29] is a graph showing the hole count relative to depth for a stretch strip component fabricated according to the MFIM process as described in Example 10, and a graph showing the hole count relative to depth for a stretch strip component fabricated according to the standard foam molding process.

[0047] [Figure 30] is a graph showing the roundness of holes relative to depth for a stretched strip component prepared according to the MFIM process as described in Example 10, and the roundness of holes relative to depth for a stretched strip component prepared according to the standard foam molding process.

[0048] [Figure 31] is a graph showing the hole size as a function of depth for a stretched strip component fabricated according to the MFIM process as described in Example 10, and a graph showing the hole size as a function of depth for a stretched strip component fabricated according to the standard foam molding process.

[0049] [Figure 32] is an image of sample 20 prepared according to the reverse MFIM process as described in Example 12.

[0050] [Figure 32] is an image of sample 20 prepared according to the reverse MFIM process as described in Example 12.

[0051] [Figure 33] is an image of sample 10 prepared according to the MFIM process as described in Example 12.

[0052] [Figure 34] is an image showing a cross-section of a sample 20 prepared according to the reverse MFIM process as described in Example 12.

[0053] [Figure 35] is an image showing a cross-section of sample 10 prepared according to the MFIM process as described in Example 12.

[0054] [Figure 36] is a graph showing the hole count versus depth (distance from the surface) for samples 10 (MFIM) and 20 (reverse MFIM) as described in Example 12.

[0055] [Figure 37] is a graph showing the hole size versus depth (distance from the surface) of sample 10 (MFIM) and sample 20 (reverse MFIM) as described in Example 12.

[0056] [Figure 38] is a graph showing the average stress versus strain of sample 10 (MFIM) as described in Example 12 and a graph of sample 20 (reverse MFIM) from the compression modulus measurement.

[0057] [Figure 39] is a graph showing the average stress versus strain of sample 10 (MFIM) as described in Example 12 and the curve of sample 20 (reverse MFIM) from the flexural modulus measurement.

[0058] [Figure 40] is a graph of stress versus strain curves measured by compression modulus of three metallocene polyethylene (mPE) materials with different densities, as described in Example 14, according to the MFIM process.

[0059] [Figure 41] illustrates the mold configuration applicable to the methods described herein.

[0060] Throughout the diagram, the corresponding component symbols indicate the corresponding parts. Implementation

[0061] While this disclosure provides reference to preferred embodiments, those skilled in the art will recognize that changes in form and detail may be made without departing from the spirit and scope of the invention. Various embodiments will be described in detail with reference to the accompanying drawings, wherein in several views, the same element symbols denote the same parts and assemblies. Reference to the various embodiments is not intended to limit the scope of the appended claims. Furthermore, any examples set forth in this specification are not intended to be limiting and are merely illustrative of some of the many possible embodiments for the purpose of illustrating the appended claims.

[0062] 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, this document (including definitions) shall prevail. Although the invention may be practiced or tested using methods and materials similar to or equivalent to those described herein, preferred methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated herein by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and are not intended to be limiting.

[0063] As used herein, “polymer matrix” including terms such as “continuous polymer matrix”, “thermoplastic polymer matrix”, “molten polymer matrix” and similar terms means a continuous solid or molten thermoplastic polymer phase or an amount of solid or molten thermoplastic polymer that defines a continuous phase.

[0064] As used herein, "melt mixture" means a molten thermoplastic polymer or a mixture of molten thermoplastic polymers, which may include one or more additional materials mixed with the molten thermoplastic polymer or a mixture thereof.

[0065] As used herein, a "molten gas-containing mixture" means a mixture of a thermoplastic polymer and a gas-generating source, wherein the polymer is at a temperature above its melting temperature and the temperature of the mixture exceeds the critical temperature of the gas-generating source, and wherein the mixture is characterized by the absence of air pockets or substantially the absence of air pockets. Molten gas-containing mixtures exist at pressures sufficient to prevent, or substantially prevent, air pocket formation, or to dissolve or disperse the gas-generating source in the thermoplastic polymer as a gas or supercritical fluid. Terms such as "substantially prevents air pocket formation" and "substantially absence of air pockets" for molten gas-containing mixtures mean that when pressure conditions are available to prevent air pocket formation in the molten mixture, unintentional pressure losses due to defects or wear of components in the processing equipment, and the like, do not generally interfere with obtaining and maintaining the pressurized molten mixture.

[0066] As used herein, the terms “foam,” “polymer foam,” “thermoplastic polymer foam,” “molten foam,” “molten polymer foam,” and similar terms generally refer to a continuous polymer matrix that defines a plurality of air bladders as a discontinuous phase dispersed therein.

[0067] As used herein, the term "airbag" means a discrete void defined and surrounded by a continuous thermoplastic polymer matrix.

[0068] As used herein, the term "gas product" refers to a gaseous compound that can define an air bladder within a molten thermoplastic polymer matrix.

[0069] As used in this article, the term "critical temperature" refers to the temperature at which a gas-generating source produces gas-generating products at atmospheric pressure.

[0070] As used herein, the term "gas-generating source" means a latent, potential, or primary gas-generating product added to or present in a thermoplastic polymer matrix (such as dissolved in the matrix and / or present therein in a supercritical fluid form); or in the form of an organic compound that produces gas-generating products by chemical reaction; or a combination thereof; or wherein the gas-generating source is a gas-generating product, becomes a gas-generating product, or produces gas-generating products at the critical temperature characteristics of the gas-generating source.

[0071] As used herein, the terms "comprising," "including," "having," "has," "may," "containing," and variations thereof are intended to be open-ended transitional phrases, terms, or words that do not preclude the possibility of additional actions or structures. Unless the context clearly specifies otherwise, the singular forms "a," "and," and "the" include the plural references. Whether explicitly stated or not, this disclosure also covers other embodiments, "comprising," "consisting of," and "substantially consisting of": the embodiments or elements presented herein.

[0072] As used herein, the terms “optional” or “as appropriate” mean that the events or circumstances described below may not occur, and the description includes both the circumstances in which the events or circumstances occur and the circumstances in which they do not occur.

[0073] As used herein, the term "about," used to describe the embodiments of this disclosure, refers to modifications such as the amount, concentration, volume, process temperature, process time, yield, flow rate, pressure, and similar values ​​and ranges of components in a composition. It means, for example, typical measurement and operating procedures used in the preparation of compounds, compositions, concentrates, or the use of formulations; unintentional errors in such procedures; variations in quantity due to differences in the manufacture, source, or purity of the starting materials or components used in the method, and similar similar considerations. The term "about" also covers amounts that differ from a particular initial concentration or mixture due to aging of the formulation, and amounts that differ from a particular initial concentration or mixture due to mixing or processing of the formulation. When modified by the term "about," the appended claims include equivalents of such amounts. Furthermore, unless specifically limited by the context, the use of any range of values ​​for "about," such as "about 1 to 5," means "1 to 5" and "about 1 to about 5," and "1 to about 5" and "about 1 to 5."

[0074] As used herein, the term "substantially" means "consistently of," as interpreted in U.S. patent law, and includes "composed of," as interpreted in U.S. patent law. For example, a composition that is "substantially free of" a specified compound or material may be free of that compound or material, or may have a small amount of that compound or material present, such as through unintended contamination, side reactions, or incomplete purification. "Small amount" can be trace, immeasurable, a amount that does not interfere with a value or characteristic, or some other amount provided in the context. A composition having a list of components that is "substantially only" provided may consist of only those components, or have trace amounts of some other components present, or have one or more additional components that do not substantially affect the characteristics of the composition. Additionally, the "substantially" modification used in describing embodiments of the invention (e.g., the type or amount, characteristic, measurable, method, value, or range of components in a composition) means a variation in the composition, characteristic, amount, method, value, or range that does not affect the overall description of the composition, characteristic, amount, method, value, or range in a manner that offsets the intended composition, characteristic, amount, method, value, or range. When modified by the term "substantially," the claims appended herein include equivalents according to this definition.

[0075] As used herein, any stated value range encompasses all values ​​within the range and should be interpreted as support for any subrange of the claims that has real values ​​at the endpoints of the stated value range. By way of hypothetical illustrative examples, the ranges 1 to 5 disclosed in this specification will be considered to support any of the following claims: 1-5, 1-4, 1-3, 1-2, 2-5, 2-4, 2-3, 3-5, 3-4, and 4-5.

[0076] In the embodiments disclosed herein, the method for extruding molten polymer foam includes, substantially, or comprises: adding a thermoplastic polymer and a gas generation source to an inlet located at a first end of an extruder; heating and mixing the thermoplastic polymer and the gas generation source in the extruder to form a molten gas-containing mixture, wherein the temperature of the molten gas-containing mixture exceeds the critical temperature of the gas generation source; collecting a portion of the molten gas-containing mixture in an extruder barrel region located near a second end of the extruder; forming an expansion volume in the barrel region, wherein the formation causes a pressure drop in the barrel region; allowing a certain period of time after the pressure drop; and dispensing molten polymer foam from the extruder.

[0077] In the embodiments, the extruder is any machine designed and adapted for melting, mixing, and dispensing thermoplastic polymers and mixtures thereof, and may have one or more additional materials, such as fillers, nucleating agents, diluents, stabilizers, brighteners, and the like; and further wherein the extruder includes a collection area for collecting a large quantity of mixed molten material and is further capable of forming an expanded volume in the collection area in relation to pressure drop. Extruders are well known in the industry and are widely used for melting, mixing, and manipulating molten thermoplastic polymers. In the embodiments, the extruder is adapted and designed for melting, mixing, and dispensing mixtures of thermoplastic polymers with a gas-generating source. Such extruders are adapted to obtain molten gas-containing mixtures at pressures sufficient to prevent or substantially prevent the formation of gas pockets in the molten gas-containing mixture.

[0078] In embodiments, the extruder suitable for carrying out the method of the present invention includes an internal volume, referred to in this art as the "barrel" of the extruder, designed and adapted to receive a solid thermoplastic polymer, further for melting and mixing it. In embodiments, the extruder defines an internal volume designed to receive a solid thermoplastic polymer and a gaseous product or gaseous product source, further for melting at least the polymer and for mixing the gaseous product or gaseous product source with the molten polymer to obtain a molten gaseous mixture. In embodiments, the extruder further includes a collection area for collecting a large quantity of the molten gaseous mixture material. In embodiments, the extruder further includes a component forming an expansion volume in the collection area in relation to pressure drop.

[0079] In this embodiment, the extruder is an injection molding machine. In this embodiment, the extruder is a SODICK™ molding machine sold by Plustech, Inc., Schaumburg, IL. In this embodiment, the extruder includes one or two components known in the art as a "screw" housed within an internal volume, referred to in the art as a "barrel." In this embodiment, the screw generally has a right-hand cylindrical shape and further includes one or more raised threaded components referred to as "threads." In some embodiments, the extruder is a single-screw extruder, defined as including a screw movably housed within the barrel for rotating a cylinder about its axis, for laterally moving along the axis of its cylinder, or including a combination of rotational and lateral movement. In other embodiments, the extruder is a twin-screw extruder, defined as comprising two screws disposed within a barrel in a substantially parallel and proximal relationship to each other, wherein each screw is movably disposed within the barrel for rotation of the barrel about its axis for lateral movement of the barrel along its axis, or a combination of rotational and lateral movement. The screws of the twin-screw extruder are further configured such that the operation of the screws, when rotating in opposite directions, defines the designed mixing and conveying mode of the molten thermoplastic polymer disposed within the barrel.

[0080] In this embodiment, the extruder is further adapted and designed to receive solid thermoplastic polymers. In this embodiment, the extruder barrel is further adapted and designed to receive solid thermoplastic polymers and to add solid thermoplastic polymers to the barrel via an inlet located near a first end of the extruder. The solid thermoplastic polymer is added to the inlet in any suitable form, such as beads, injection, powder, strip, or block, as is familiar to those skilled in the art. In this embodiment, the extruder includes a second, third, or even a fourth or higher number of inlets designed and adapted to add or introduce one or more additional materials comprising one or more solids, fluids, or gases into the internal volume of the extruder, further for mixing one or more additional materials with the thermoplastic polymer. The internal volume of the extruder is suitable for receiving, containing, and melting thermoplastic polymers and, as appropriate, one or more additional materials; and subjecting the thermoplastic polymers and, as appropriate, one or more additional materials to heating, shearing, and mixing to form a molten mixture, while simultaneously conveying the molten mixture generally from its first end to its second end. In embodiments where the extruder is a single-screw extruder or a twin-screw extruder, shearing, mixing, and conveying are achieved by rotating the screw or by two screws rotating in opposite directions.

[0081] In embodiments, the internal volume of the extruder, or a portion thereof, is surrounded or partially surrounded by one or more heat sources. In various embodiments, heat sources suitable for heating the internal volume of the extruder include heated water jackets, heated oil jackets, resistance heaters, open or jacketed flames, or another heat source. The heat source is operable to raise the temperature within the internal volume of the extruder. The temperature is appropriately selected by the operator to melt the thermoplastic polymer and / or maintain a desired temperature within a portion of the internal volume of the extruder. In embodiments, the extruder is adapted to include more than one heat source, wherein these heat sources can be operated independently to allow a person skilled in the art to provide a range of temperature "zones" within the internal volume. Additional temperature zones may be included in some extruders that add one or more materials to their inlet or dispense one or more materials from their outlet. In embodiments, the operator sets the temperature within one or more temperature zones to enhance the control and optimization of melting, mixing, shearing, and conveying of the thermoplastic polymer and, where appropriate, one or more additional materials.

[0082] Extruders are conventionally designed and adapted to apply and maintain pressure within their internal volume during the heating, mixing, and conveying of a molten mixture. In embodiments, the extruder is designed and adapted to apply and maintain a first pressure within its internal volume or barrel during the heating, mixing, and conveying of the molten mixture. In embodiments, the pressure within the barrel during the heating, mixing, and conveying of the molten gaseous mixture is sufficient to prevent or substantially prevent leakage of the molten gaseous mixture from the barrel. In embodiments, the pressure within the barrel is sufficient to prevent the formation of gas pockets in the molten gaseous mixture when the temperature within the barrel exceeds the critical temperature of the gaseous source. In embodiments, the pressure within the barrel is substantially sufficient to prevent the formation of gas pockets in the molten gaseous mixture when the temperature within the barrel exceeds the critical temperature of the gaseous source. In such embodiments described in this paragraph, "substantially" refers to unintentional leakage of material or unintentional loss of pressure from the barrel, as is familiar to those skilled in the art due to the manufacturing, aging, or use of extruders and / or screws. Additionally, in such embodiments, in the context of “sufficient to prevent the formation of air pockets in the molten gas mixture,” “substantially” means that when pressure is maintained on the molten gas mixture, a small percentage (such as up to 10% gas products) may inadvertently form air pockets; however, the objective is for operators to maintain sufficient pressure to prevent air pocket formation.

[0083] In one embodiment, the extruder barrel includes a collection area for collecting a quantity of molten mixture to prepare a self-dispensing molten mixture. The mass of the molten mixture is selected by the user. In one embodiment, the molten mixture is a molten gas mixture. In such embodiments, the technical term used to describe the collection of a large quantity of molten gas mixture in the collection area of ​​the extruder barrel is called "building injection". As those skilled in the art of injection molding will understand, for building injection, the molten gas mixture is conveyed from a first end of the extruder toward a second end, i.e., toward and into the collection area, by rotating one or more screws (or another mixing element) and further by accumulating the molten gas mixture in the collection area to collect a large quantity of molten gas mixture until all the required mass of molten gas mixture is collected and placed in the collection area of ​​the barrel. The collection area is located between one or more screws and the second end of the extruder and is in pressurized communication with the rest of the barrel.

[0084] In conventional injection molding for forming thermoplastic polymer foams, a molten gas-containing mixture is conveyed toward and into a collection area by the rotation of one or more screws (or another mixing element), where a large quantity of the molten gas-containing mixture, or "build charge," is collected. When the entire selected mass of the molten gas-containing mixture is contained within the collection area, it is referred to as build charge. Those skilled in the art will understand that the foregoing description of the mechanical components and features of melt mixing apparatus (such as extruders or other melt mixing devices) and the methods for producing and collecting molten gas-containing mixtures in the charge are consistent with conventional apparatus and methods for producing molten gas-containing mixtures and their build charges using such apparatus.

[0085] According to these known methods and apparatuses, when present in the barrel, during mixing, heating, conveying, and collection, and further when placed in the collection area, it is conventionally prevented or substantially prevented from forming air pockets in the injection of the molten gas-containing mixture. Conventionally, when collecting the desired injection in the collection area, a gate or valve located between the collection area and the outlet located at the second end of the extruder is opened to provide a fluid connection from the barrel to the outlet for dispensing the injection from the extruder. In some embodiments, when the gate or valve is opened, a mechanical plunger is applied to propel the molten gas-containing mixture from the barrel through the outlet. In embodiments, one or more screws are suitably configured for lateral movement in a direction toward the second end of the extruder, which in turn propels the molten gas-containing mixture from the collection area of ​​the barrel through the outlet.

[0086] We have found that after constructing the injection of the molten gas-containing mixture in the collection area of ​​the extruder, it is advantageous to form, provide, or define an expansion volume in the collection area of ​​the extruder, wherein this definition is accompanied by a pressure drop in the collection area; a certain period of time, referred to herein as the expansion period, is allowed after the definition; and the injection is dispensed from the extruder after the expansion period. In such embodiments, the injection is dispensed in the form of molten polymer foam. In embodiments, the expansion volume is defined as close to the injection disposed in the collection area of ​​the extruder. In embodiments, the injection is not mixed or subjected to applied shear or stretching while the expansion volume is in the defined process. In embodiments, the injection is not conveyed during the expansion period. In embodiments, the injection is allowed to remain stationary or undisturbed or substantially undisturbed in the collection area during the expansion period. In any of the foregoing embodiments, the injection may be heated during the expansion period; however, in some embodiments, no heat is added to the injection during the expansion period.

[0087] After the expansion period has passed or elapsed, molten polymer foam can be dispensed from the second end of the extruder. The molten polymer foam comprises a plurality of air pockets. Without being theoretically limited, it is generally believed that air pockets form when the molten gas-containing mixture undergoes an expansion volume and an accompanying pressure drop (secondary pressure). According to known principles of physics, air pocket formation may be caused by defining the expansion volume and accompanying pressure drop in the collection area of ​​the barrel, together with the expansion period by which air pockets are formed by the production of operating gas. In some embodiments, defining the expansion volume after the build-up produces desirable properties attributable to the dispensed molten polymer foam. In other words, it has been found that forming a molten gas-containing mixture under pressure, followed by depressurization and simultaneously forming a defined volume before dispensing the mixture (e.g., into a mold cavity), produces molten polymer foam, which, upon cooling, yields a cured polymer foam article with unexpectedly and highly beneficial physical properties.

[0088] We have discovered significant technical benefits from self-exploding molten polymer foams produced according to the aforementioned method. These benefits are observed in cured polymer foams and arise from cooling the molten polymer foam to a temperature below the melt transition temperature of the thermoplastic polymer. After the expansion period, articles prepared using self-exploding molten polymer foams exhibit macroscopic and microscopic structural differences compared to polymer foams prepared by conventional methods; and display excellent properties suitable for, for example, structural components. Polymer foam articles prepared using the methods, apparatus, and materials described herein are characterized by having a continuous thermoplastic matrix throughout and multiple air pockets distributed throughout the polymer foam article. This feature applies to articles with a thickness greater than 2 cm and a volume greater than 1000 cm³, or articles with a thickness greater than 2 cm and a volume greater than 1000 cm³, between 1000 cm³ and 5000 cm³, or even greater than 5000 cm³; and also to articles including articles with a volume greater than 1000 cm³ and a thickness greater than 2 cm, articles with a volume between 1000 cm³ and 5000 cm³ and a thickness greater than 2 cm, or articles with a volume greater than 5000 cm³ and a thickness greater than 2 cm.

[0089] In an embodiment, in a single-screw extruder, the expansion volume is appropriately defined by moving the screw toward the first end of the extruder and away from the collection area of ​​the extruder where the feed is collected. In an embodiment, in a twin-screw extruder, the expansion volume is defined by laterally moving the screw toward the first end of the extruder and away from the collection area of ​​the extruder where the feed is collected. Lateral movement is accompanied by rotation of one or more screws, depending on the situation. That is, one or two screws may be rotated during lateral movement, or rotation may be stopped during lateral movement. It should be understood that defining the expansion volume by the lateral movement of one or two screws is advantageously selectable by the extruder operator to provide the selected expansion volume. That is, the distance of lateral movement of one or more screws is appropriately selected by the operator to define the selected expansion volume.

[0090] Therefore, in this embodiment, the operator adds sufficient volume to the collection area to accommodate the total expected molten polymer foam volume, or a certain percentage thereof, with the expansion volume as the target. The total expected molten polymer foam volume of the injection can be calculated based on the amount of thermoplastic polymer and any additional materials added to construct the injection, further assuming that all gas generation sources will contribute to the formation of air pockets in the molten polymer foam to be obtained. Those skilled in the art will understand that industry-available gas generation source supplies have information suitable for calculating the total expected molten polymer foam volume based on the amount of gas generation source added to the manufacturing injection and other processing conditions. In this embodiment, the expansion volume is the difference between the injection volume and the expected molten polymer foam volume. In the embodiments, the target expansion volume is to provide 10% to 100% of the total expected molten polymer foam volume in the collection area, for example, 15% to 100%, or 20% to 100%, or 25% or 100%, or 30% to 100%, or 35% to 100%, or 40% to 100%, or 45% to 100%, or 50% 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% or 95%, or 10% or 90%, or 10% or 85%, or 10% to 80%, or 10% to 75%, or 10% to 70%, or 10% to 65%. The difference between the injection volume and the expected molten polymer foam volume, or 10% to 60%, or 10% to 55%, or 10% to 50%, or 10% to 45%, or 10% to 40%, or 10% to 35%, or 10% to 30%, or 10% to 25%, or 10% to 20%, or 10% to 15%, or 15% to 20%, or 20% to 25%, or 25% to 30%, or 30% 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 other embodiments, the expansion volume is between 100% and 300% of the difference between the injection volume and the expected molten polymer foam volume, such as 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 injection volume and the expected molten polymer foam volume.

[0091] After the expansion volume is defined, a certain period of time is elapsed before the molten polymer foam is dispensed from the extruder. In embodiments, this period is referred to as the expansion period. In some embodiments, during the expansion period, no mixing, conveying, shearing, or other physical operations or additional volume changes are performed in the collection area. Instead, in such embodiments, the filler is allowed to remain in 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 cooled to a temperature below the melt transition temperature of the thermoplastic polymer to obtain a cured polymer foam article.

[0092] In this embodiment, the expansion period is selected by the operator from approximately 5 to 600 seconds, depending on the sample quality, the source and amount of gaseous products, and any additional materials present in the injection. In this embodiment, the expansion period is 5 to 600 seconds, or 5 to 500 seconds, or 5 to 400 seconds, or 5 to 300 seconds, or 20 to 600 seconds, or 20 to 500 seconds, or 20 to 400 seconds, or 20 to 300 seconds, or 10 to 200 seconds, or 20 to 200 seconds, or 30 to 200 seconds, or 40 to 200 seconds, or 50 to 200 seconds, or 5 to 190 seconds, or 5 to 180 seconds, or 5 to 170 seconds, or 5 to 160 seconds, or 5 seconds... Up 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 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 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 to 140 seconds, or 140 seconds to 150 seconds, or 150 seconds to 160 seconds 0 seconds, or 160 to 170 seconds, or 170 to 180 seconds, or 180 to 190 seconds, or 190 to 200 seconds, or 200 to 250 seconds, 250 to 300 seconds, or 300 to 350 seconds, or 350 to 400 seconds, or 400 to 450 seconds, or 450 to 500 seconds, or 500 to 550 seconds, or 550 to 600 seconds.

[0093] The aforementioned method is used to form a molten polymer foam, which, when cooled to a temperature below the melting temperature of the thermoplastic polymer, yields several significant technical benefits described in the following sections to obtain a cured polymer foam. Polymer foam articles are generally characterized by a monomeric article having a continuous polymer matrix defining a plurality of air pockets dispersed throughout the article. In embodiments, the polymer foam article is particularly characterized by having a continuous polymer matrix defining a plurality of air pockets dispersed in a surface region of the article, wherein the surface region is defined as the area of ​​the article between the article surface (polymer foam-air interface) and a distance of 500 micrometers from the interior of the surface.

[0094] Figure 1A illustrates a representative embodiment of an apparatus effectively used to perform the aforementioned methods. Figure 1A is a schematic diagram of an exemplary single-screw injection molding apparatus 20 according to embodiments disclosed herein, suitable for performing the methods described herein to prepare molten polymer foams and polymer foam articles also disclosed herein. As shown in Figure 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 21a, a second end 21b, and a hollow internal barrel portion 22. The barrel portion 22 further defines a nozzle 36 adjacent to the second end 21b of the barrel. A screw 30 is disposed within the barrel portion 22 and includes a screw tip portion 34. The screw 30 is operatively coupled to the motor section 24 for rotation of the screw 30 about its central axis; or for lateral movement indicated by arrow Z. The screw 30 can be moved laterally in a direction generally from the first end 21a of the barrel toward the second end 21b of the barrel or in a direction generally from the second end 21b of the barrel toward the first end 21a of the barrel. Lateral movement of the screw 30 in either direction may be further coupled to rotational movement, as appropriate. The screw 30 further includes one or more threads 31, which are mixing elements for mixing and conveying materials present in the barrel portion 22 generally from the first end 21a of the barrel toward the second end 21b of the barrel. The screw 30 is positioned within the barrel portion 22 in a pressurized, sealed relationship such that pressure exceeding atmospheric pressure can be maintained within the barrel portion 22 by means of the screw threads 31 within the barrel 21 and further by means of the check valve 32. A shut-off valve 37 is connected to the barrel 21 near the second end 20b and is operable to control the fluid connection, pressurized connection, or both between the nozzle 36 and the mold section 26. The check valve 32, which is located within the barrel section 22 and surrounds the screw 30, is operable to prevent back pressure from pushing the material residing in the barrel section 22 toward the first end 21a of the barrel, and thus provides a pressurized seal, fluid seal, or pressurized fluid seal relationship between the shut-off valve 37 and the check valve 32.

[0095] Further relating to Figure 1A, mold segment 26 comprises two mold segments 38 as shown. The mold segments 38 are removably engaged together to define a cavity 39. In some embodiments, one or more of the mold segments 38 are movable to allow injection molding of a cured polymer foam article from them. In some embodiments, the mold segments 38 are positioned relative to each other in a contact manner; in other embodiments, the mold segments 28 are spaced apart by a gap.

[0096] In embodiments, the methods disclosed herein are suitably performed using an apparatus such as the system 20 shown in Figures 1A-1B. In Figure 1A, a mixture 42A comprising a selected amount of thermoplastic polymer, a gaseous source, and, where appropriate, one or more additional materials of a selected mass, is added to barrel section 22 through inlet 28, as indicated by arrow A. In some embodiments, the gaseous source is a gaseous material and inlet 28 or another inlet (not shown) is a pressurized air inlet connected to barrel section 22; and the gaseous material is added to the air inlet at a selected pressure while non-gaseous materials are 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. The rotation of screw 30 conveys and mixes mixture 42A to screw tip 34. A heat source (not shown) is suitably employed to add heat to mixture 42A within barrel section 22. Motor 24 rotates screw 30 generally from the first end 21a of barrel 21 toward the second end 21b until reaching screw tip 34 to convey mixture 42A present in barrel section 22. Additionally, the rotation of screw 30 provides mixing of mixture 42A during conveying. As mixture 42A is conveyed and mixed by the rotation of screw 30, heating elements or heating bands (not shown) near barrel section 22 are operated to heat mixture 42A. Multiple heating zones may exist near barrel section 22 to alter the internal temperature of barrel section 22 between the first end 21a and the second end 21b of barrel 21. During conveying, screw 30 rotating within barrel section 22 is operable to mix mixture 42A; and heat is added to the mixture during conveying, thereby raising the temperature of the mixture above the melting point of the thermoplastic polymer, so that mixture 42A is transformed into molten gas-containing mixture 42B at least by reaching the second end 21b of barrel 21. Additionally, a screw 30 is positioned within a barrel portion 22, wherein the thread 31 contacts the barrel 21 during screw 30 rotation; combined with a check valve 32, a shut-off valve 37 in the closed position, or both, provide a pressurized seal within the barrel portion 22, thereby allowing the molten gas-containing mixture 42B to exist within the barrel portion 22 at pressures exceeding atmospheric pressure. The pressure within the barrel portion 22 is sufficient to prevent or substantially prevent gas pocket formation, even if the gaseous source is above its critical temperature.

[0097] Furthermore, the rotation of the operating screw 30 delivers a pressurized molten gaseous mixture toward the screw tip 34, thereby delivering or accumulating a selected mass of the pressurized molten gaseous mixture 42B within the collection region 40 of the barrel section 22. The collection region 40 is defined as the area within the volume of the barrel section 22 extending between the check valve 32 and the shut-off valve 37 in FIG. 1A, and further defined as the area of ​​the barrel section 22 located along the X distance of the barrel 21. A selected mass of the pressurized molten gaseous mixture 42B or its "fill" is collected or accumulated in the collection region 40 of the barrel section 22. The pressure within the collection region 40 is sufficient to prevent or substantially prevent the formation of air pockets in the molten gaseous mixture. In an embodiment, the fill substantially fills the collection region 40.

[0098] The preparation of the molten gas-containing mixture 42B is achieved using conventional methods familiar to those skilled in the art. Conventional and known variations in the methods and materials used to prepare the mixture for injection molding are covered by the methods described herein. Once the mixture is prepared, it can be subjected to the methods disclosed herein to obtain all the technical benefits disclosed herein regarding the formation of polymer foams and polymer foam articles. For example, to form the mixture, a method such as the MUCELL® high-pressure process employed by Trexel, Wilmington, MA, is suitably used, in which a gas-generating source is added directly as a gas to the extruder, pressurized and mixed to prevent or substantially prevent air pocket formation, followed by mixture collection. Various patents and trade disclosures further describe specific melt mixing and conveying designs for obtaining molten gas mixtures and forming injections, such as specific screw designs for mixing and reflux modes and the like; any of these can be used effectively in conjunction with the aforementioned injection forming methods and apparatus to form injections as described herein, and to collect the injections under pressure in the collection area of ​​the melt mixing apparatus.

[0099] After the injection is formed and collected in the collection area, an expansion volume is defined therein, and the expansion is accompanied by a pressure drop in and near the injection area. Therefore, FIG1A depicts a molten gas mixture apparatus 20, wherein a screw 30 is positioned to collect the injection in a collection area 40. The injection comprises a selected mass of molten gas mixture 42B and is disposed within the collection area 40 under pressure. At this stage of the process, FIG1B further depicts the apparatus 20 relative to FIG1A, wherein the screw 30 is positioned to define an expansion volume 44 within the collection area 40. In slightly more detail, FIG1B shows the screw 30 in a position created by lateral movement of the screw 30 toward the first end 21a of the barrel; that is, retracted relative to FIG1A in FIG1B. The retraction of the screw 30 from the collection area 40 and the resulting partial displacement define the expansion volume 44 within the collection area 40 and further cause a pressure drop within the collection area 40. In some embodiments, the screw 30 is stopped rotating before retraction. In some embodiments, the screw 30 stops rotating during retraction or after retraction is complete. The retraction distance of the screw 30 (i.e., the lateral movement distance of the screw 30 toward the first end 21a of the barrel) is selected by the operator to provide a suitable expansion volume 44.

[0100] In some embodiments, as illustrated in FIG1B, an operator selects an expansion volume 44 to provide a collection area 40 with a total volume matching the total expected molten polymer foam volume of the injection; in such embodiments, the total volume in collection area 40 after adding expansion volume 44 is the total expected molten polymer foam volume of the molten gas mixture 42B of FIG1B. In other embodiments, expansion volume 44 is selected by the operator to provide a collection area 40 with a total volume that is a percentage of the total expected molten polymer foam volume of the molten gas mixture or the injection present in collection area 40; that is, the total volume in collection area 40 after adding expansion volume 44 is equal to approximately 50% to 120% of the total expected molten polymer foam volume. In some embodiments, expansion volume is configured to provide a total volume in the collection area to accommodate 100% of the total expected molten polymer foam volume. The total expected molten polymer foam volume of the injection may be calculated based on the amount of thermoplastic polymer and any additional materials added externally to construct the injection, further assuming that all gas generation sources contribute to the formation of air pockets in the molten polymer foam to be obtained.

[0101] As shown in Figure 1B, after the retraction screw 30 defines the expansion volume 44, the filler material is allowed to be contained within the collection area 40 for a certain period of time (referred to as the "expansion period"), as shown in Figure 1B, specifically where the collection area 40 contains the expansion volume 44. The expansion period is selected by the operator between 5 seconds and 200 seconds. In embodiments, during the expansion period, the filler material is allowed to remain undisturbed or substantially undisturbed within the collection area 40. In embodiments, "undisturbed" means that the filler material does not undergo any processes that cause mixing, shearing, or conveying (flowing) of the filler material during the expansion period. In embodiments, "substantially undisturbed" means that mixing, shearing, or conveying processes performed during the expansion period do not intentionally disturb the filler material, but there may be other manufacturing problems such as thermal differences, leakage, and unintentional stress or strain on the filler material that may remain in the collection area during the expansion period.

[0102] After the expansion period has passed, the nozzle shut-off valve 37, as shown in FIG1B, opens and dispenses molten polymer foam from the barrel 22. In the embodiments shown in FIG1A-1B, the molten polymer foam flows into the cavity 39. In some embodiments, dispensing may be performed by mechanical means, such as pressurized dispensing using the lateral movement of a screw, or by applying pressurized gas to the collection area; however, in some embodiments, applying pressure is not necessary to dispense the molten polymer foam. In embodiments, during the dispensing of molten polymer foam, the pressure at nozzle 36, as shown in Figures 1A-1B, exceeds gravity by 1 psi to 20 psi, for example, 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 need for an external pressure source, such as by using additional lateral movement of screw 30 toward the second end 21b of the barrel in Figures 1A-1B to propel the molten polymer foam straight forward. In embodiments, dispensing is achieved by maintaining a fluid connection between nozzle 36 and cavity 39. In some such embodiments, the fluid connection is further a pressurized connection.

[0103] After being placed within the cavity 39 defined by the mold portion 38 shown in Figures 1A-1B, the molten polymer foam is cooled or allowed to cool until it reaches a temperature below the melt transition temperature of the thermoplastic polymer, such as the temperature present in the ambient conditions. In some embodiments where the expansion volume is configured to provide a total volume in the collection area less than 100% of the total expected molten polymer foam volume, the airbag may continue to nucleate and / or develop (size increase) after the molten polymer foam is dispensed and before the temperature is sufficiently cooled to reach the melt transition temperature of the thermoplastic polymer. Cooling of the molten polymer foam is achieved using conventional methods for cooling injection-molded articles, including immersing the mold in a fluid coolant having a set temperature, or spraying the mold with a fluid coolant such as fluid water; jetting air onto the mold; ambient air cooling; and similar methods without limitation.

[0104] In an alternative embodiment of the aforementioned method, the apparatus 20 configured as shown in FIG. 1B is used to form molten polymer foam. FIG. 1B shows the screw 30 in a position created by the lateral movement of the screw 30 toward the first end 21a of the barrel; that is, the screw 30 is retracted in FIG. 1B relative to FIG. 1A. The retraction of the screw 30 from the collection region 40 and the resulting partial displacement define the expansion volume 44 within the collection region 40 and further cause a decrease in pressure within the collection region 40. The apparatus 20 shown in FIG. 1B is configured to mix, heat, and deliver the molten gas-containing mixture 42B toward the second end 21b of the barrel 21 in substantially the same manner as described above. Additionally, a screw 30 is positioned within a barrel portion 22, wherein the thread 31 contacts the barrel 21 during screw 30 rotation; combined with a check valve 32, a shut-off valve 37 in the closed position, or both, provide a pressurizable seal within the barrel portion 22, thereby allowing the molten gas-containing mixture 42B to exist within the barrel portion 22 at pressures exceeding atmospheric pressure. The pressure within the barrel portion 22 is sufficient to prevent or substantially prevent gas pocket formation, even if the gaseous source is above its critical temperature. However, in this alternative embodiment, the molten gas-containing mixture is conveyed via the check valve 32 and further to a collection area 40 attached by an expansion volume 44.

[0105] The advantage of the method disclosed in this invention is that conventional materials and apparatus for extrusion and injection molding are suitable for performing these methods. No specialized equipment or material requirements are necessary to perform the disclosed methods. Therefore, any thermoplastic polymer or mixture thereof suitable for injection molding and / or for forming polymer foams can be effectively combined with conventional techniques (such as standard injection molding apparatus) along with one or more additional materials selected by the apparatus operator, as appropriate, and any industry-appropriate gas-generating source.

[0106] In the embodiments, the thermoplastic polymer used in conjunction with the methods, apparatus, and articles described herein comprises any thermoplastic or mixture thereof known in the industry as suitable for injection molding or injection molding polymer foam articles; and mixtures of such polymers. Suitable polymers are characterized by having a melt flow viscosity suitable for injection molding (such as in injection forming). Therefore, the thermoplastic polymer may comprise a degree of crosslinking that is thermally reversible or otherwise does not prevent sufficiently viscous melt flow for injection molding processes.

[0107] In the embodiments, the thermoplastic polymers that can be used in conjunction with the methods, apparatus, and articles described herein include olefin polymers, such as polyethylene, polypropylene, polyalphaolefins, and various copolymers and their branched / crosslinked variants, 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), etc.; polyamides (PA), polyimides (PI), polyesters, such as polyester terephthalate (PET) and polybutene terephthalate (PBT), polyhydroxyalkanoates (PHA), such as polyhydroxybutyrate (PHB), polycarbonate (PC), poly(lactic acid) (PLA), acrylonitrile-butadiene-styrene copolymers, etc. Polymers (ABS), polystyrene, polyurethanes, including thermoplastic polyurethane elastomers (PU, TPU), polycaprolactone, polyvinyl chloride (PVC), copolymers of tetrafluoroethylene, polyether ether (PES), polyacetal, aromatic polyamides, polyphenylene ether (PPO), polybutene, polybutadiene, polyacrylates and methacrylates (acrylic polymers), ionomers (SURLYN® and similar ionically functionalized olefin copolymers), polyether-amide block copolymers (PEBAX®), polyaryl ether ketones (PAEK), polyether, polyphenylene sulfide (PPS), polyamide-amide copolymers, polybutylene succinate, cellulose materials, polysaccharides and their copolymers, complexes, mixtures and blends may be effectively combined with the methods described herein without limitation.

[0108] Regarding the infinite uses of polymer blends and mixtures, we have found that the mixed stream of recycled plastics is suitable as a thermoplastic polymer in the examples. Therefore, in the examples, the marine waste plastic is a mixed stream of polymeric waste collected from the ocean and beaches, and has an illustrative content of 10%-90% polyolefin, 10%-90% PET, 1%-25% polystyrene, and 1% to 50% unknown polymer. Such mixed plastic streams and waste plastic streams (not limited to those collected from the ocean and beaches) are similarly effective for forming molten polymer foams and polymer foam articles using the methods and apparatus described herein.

[0109] Gas-generating sources are widely used in the industry, and the conditions for deploying gas-generating sources during melt mixing are well-known and widely reported. Therefore, any gas-generating source suitable for injection molding, reactant injection molding, or other methods of preparing polymer foams may be used herein to form molten polymer foams and solidified polymer foam articles according to the methods, apparatus, and polymer foam articles described herein. Gas-generating sources used in conjunction with the methods and apparatus described herein include air, CO2, and N2, encapsulated in thermoplastic materials, either in the form of beads, injection molding materials, or the like, or in a latent form, wherein a chemical reaction produces CO2 or N2 upon heating within the melt mixing apparatus. Such chemical reactions may be exothermic or endothermic, but are not limited to their use in conjunction with the methods and apparatus disclosed herein. Suitable gaseous source sources include sodium bicarbonate; polycarboxylic acid-based compounds (such as citric acid); or their salts or esters, such as sodium citrate or trimethyl citrate; mixtures of sodium bicarbonate and polycarboxylic acids (such as citric acid); sulfonamides comprising p-toluenesulfonamide (p-TSH) and 4,4'-oxybis-(benzenesulfonamide) (OBSH), pure and modified azodimethylamine, hemicarbazide, tetrazolium, and diazinon. In any of the foregoing, the gaseous source may be further encapsulated in a carrier resin, which is designed to melt during heating, mixing, and collection of the injection.

[0110] In the embodiments, useful gaseous product sources comprise commercially available components such as HYDROCEROL® BIH 70, HYDROCEROL® BIH CF-40-T, or HYDROCEROL® XH-901, all purchased from Clariant AG of Switzerland; FCX 7301 from RTP Company of Winona, MN; FCX 27314 from RTP Company of Winona, MN; CELOGEN® 780 from CelChem LLC of Naples, FL; ACTAFOAM® 780 from Galata Chemicals of Southbury, CT; and ACTAFOAM® from Galata Chemicals of Southbury, CT. AZ; ORGATER MB.BA.20 purchased from ADEKA Polymer Additives Europe in Mulhouse, France; ENDEX 1750TM purchased from Endex International of Rockford, IL; and FOAMAZOLTM 57 purchased from Bergen International of East Rutherford, NJ.

[0111] In some embodiments, the gas generator source is a gas generator, which is applied in gaseous form to a melt-mixing apparatus, such as an extruder similar to those shown in Figures 1A-1B. In such embodiments, the gas is dissolved in the thermoplastic polymer by introducing a pressurized additive into the melt-mixing apparatus and mixing within it. In some embodiments, the gas becomes a supercritical fluid by pressurizing it before or simultaneously with its dissolution in the molten thermoplastic polymer. The direct application of the gas generator to an injection molding apparatus is known in the industry as the MUCELL® process, as employed by Trexel, Inc. in Wilmington, DE. This process requires specialized equipment, such as a regulated pressurized fluid connection from a gas reservoir (tank, cylinder, etc.) to the inlet of the extruder apparatus to establish a pressurized relationship with the barrel when the thermoplastic polymer is also added to and melts. When such specialized equipment is available, the gas generator can be effectively used as a gas generator source by applying the gas generator directly to the thermoplastic polymer and one or more additional materials, in conjunction with the methods described herein, to form a molten gas-containing mixture.

[0112] Based on prior art relating to the desired polymer foam density and the operation of gas products and gas product sources, a gas product source is added to a thermoplastic polymer and any additional materials, selected as appropriate, in an amount targeted at a selective density reduction of the thermoplastic polymer to form a thermoplastic polymer foam. The amount of gas product source added to the thermoplastic polymer is not particularly limited; therefore, we have found that up to 85% density reduction can be achieved without the use of polymer or glass bubbles or the like, to provide polymer foam articles with the unique and striking characteristics reported below and further with a target density reduction of up to 85%. As used herein, "density reduction" compared to the same article without the addition of a gas product (source) means a percentage reduction in the mass of the polymer foam article used to prepare the article (i.e., a polymer article that does not contain or substantially does not contain air pockets). Therefore, in the embodiments, the molten polymer foams and polymer foam articles described herein suitably exclude glass or polymer bubbles while providing a density reduction of up to 85%, such as 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% selected. Including glass or polymer bubbles further expands the usable density reduction of the polymer foam articles prepared according to the methods herein. In some embodiments, a density reduction greater than 85% can be achieved. However, the polymer foam products that benefit from reduced density are characterized by having a continuous polymer matrix in which air pockets are dispersed throughout the product, including molded articles with a volume greater than 1000 cm3, 1000 cm3 to 5000 cm3 or even greater than 5000 cm3; and molded articles with a volume greater than 1000 cm3 and a thickness greater than 2 cm, a volume between 1000 cm3 and 5000 cm3 and a thickness greater than 2 cm, or a volume greater than 5000 cm3 and a thickness greater than 2 cm.

[0113] As mentioned above, the amount of gaseous source added to the thermoplastic polymer is not particularly limited; therefore, it has been found that up to 70% of the total volume of a polymer foam article includes air pockets. The percentage of the total volume of the air pockets to the total volume of the polymer foam article is referred to as the "void fraction" of the article; thus, achieving a void fraction of up to about 70% without containing polymer or glass bubbles or the like provides a polymer foam article with the unique and unexpected characteristics reported below and further with a target void fraction of up to 70% of the volume of the polymer foam article. Therefore, in the embodiments, the molten polymer foam and polymer foam articles described herein are suitably designed to exclude glass or polymer bubbles while providing a void fraction of up to 70%, such as 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%. The inclusion of glass or polymer bubbles further expands the available void fraction of the polymer foam articles prepared according to the methods herein. In some embodiments, a void fraction greater than 70% can be achieved. Nevertheless, a polymer foam article having a void fraction of 70% is characterized by having a continuous polymer matrix in which air pockets are dispersed throughout the article, comprising a molded article with a volume greater than 5000 cm³ and a thickness greater than 2 cm, or a volume greater than 5000 cm³ and a thickness greater than 2 cm.

[0114] In some embodiments, the thermoplastic polymer and the gaseous source are blended before the mixture is applied to the melt mixing apparatus for heating and mixing. In other embodiments, the thermoplastic polymer and the gaseous source are added to the melt mixing apparatus separately, such as through two different inlets or ports that can be used to add material to the melt mixing apparatus. In other embodiments, a solid mixture comprising both the thermoplastic polymer and the gaseous source is added as a single input to the melt mixing apparatus for heating and mixing.

[0115] In embodiments, one or more additional materials are included in or added to the melt-mixing apparatus along with the thermoplastic polymer and the gaseous source; such additional materials are suitably mixed or blended with the thermoplastic polymer, the gaseous source, or both; or one or more additional materials are added separately to the melt-mixing apparatus, such as through individual ports or inlets. Examples of suitable additional materials include colorants (dyes and pigments), stabilizers, brighteners, nucleating agents, fibers, granules, and fillers. Specific examples of some suitable materials include talc, glass bubbles or beads, thermosetting polymer particles, beads or bubbles, and fibers such as glass fibers, carbon fibers, or aramid fibers. Other examples of suitable additional materials are waste materials, further shredded or cut as needed, and include paper, sand, gravel, crushed stone, slag, recycled concrete, and geosynthetic aggregates and the like. Other examples of suitable additional materials include minerals such as calcium carbonate and dolomite; clays such as montmorillonite, sepiolite, and bentonite; mica; wollastonite; hydromagnesia / calcium-magnesium carbonate mixtures; synthetic minerals; silica agglomerates or colloids; aluminum hydroxide; alumina-silica composite colloids and particles; halloysite nanotubes; magnesium hydroxide; basic magnesium carbonate; precipitated calcium carbonate and antimony oxide. Other examples of suitable additional materials include carbon-containing fillers such as graphite, graphene, graphene quantum dots, carbon nanotubes, and C60 buckyballs. Other examples of suitable additional materials include thermally conductive fillers such as boron nitride (BN) and surface-treated BN.

[0116] In embodiments, one or more additional materials are included in or added to the melt mixing apparatus along with the thermoplastic polymer and the gaseous source, in an amount of about 0.1% to 50% of the mass of the thermoplastic polymer, for example 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% to 50%, 5% to 50%, 6% to 50%, 7% to 50%, 8% to 50%, 9% to 50%, 10% to 50%, 11% to 50%, 12% to 50%, 13% to 50%, 14% to 50%, 15% to 50%, 20% to 50%, 25% to 50%, 30% to 50%, 35% to 50%, 40% to 50%, 45% to 50%, 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 mass of thermoplastic polymer added to a melt mixing apparatus to form a casting.

[0117] Therefore, in melt mixing apparatuses other than extruders, those skilled in the art will understand that the following methods will produce molten polymer foams with the significant technical benefits described in the following sections. The method for forming and collecting molten polymer foams comprises: heating and mixing a thermoplastic polymer and a gas-generating source to form a molten gas-containing mixture, wherein the temperature of the molten gas-containing mixture exceeds the critical temperature of the gas-generating source, and the pressure applied to the molten gas-containing mixture is sufficient to substantially prevent air pocket formation; collecting a selected amount of the molten gas-containing mixture in a collection area; defining an expansion volume in the collection area near the molten gas-containing mixture where a pressure drop occurs; maintaining the expansion volume during the expansion period; and collecting the molten polymer foam from the collection area. In embodiments, the molten gas-containing mixture is undisturbed or substantially undisturbed during the expansion period.

[0118] In some embodiments, collecting molten polymer foam includes coating the molten polymer foam into a cavity defined by a mold; and cooling the molten polymer foam to below the melting temperature of the thermoplastic polymer to obtain a polymer foam article. In embodiments where molten polymer foam is coated into the cavity of a mold, the cooled polymer foam article obtains the shape and size of the mold, and wherein the polymer foam is characterized as a continuous polymer matrix having air pockets distributed throughout the article. In embodiments, molten polymer foam is coated into the mold cavity by allowing the molten polymer foam to flow and by gravity into the mold cavity; in some such embodiments, the flow is unimpeded and allows it to fall into an open cavity. In other embodiments, molten polymer foam is coated onto a molding element under pressurized flow. In embodiments, molten polymer foam is delivered into the mold cavity by other means, such as from a nozzle fluidly connected thereto or from a collection area of ​​a melt mixing device.

[0119] For example, in an embodiment, the extruder is adapted and designed to dispense a molten mixture from the outlet into a forming element, which is a mold defining a cavity therein, and is designed and adapted to receive a molten polymer mixture, such as a molten gas-containing mixture. In an embodiment, the forming element is a mold configured and adapted to receive molten thermoplastic polymer dispensed from the outlet, wherein the mold is further characterized by generally defining a gap or cavity having a desired article of selected shape and size.

[0120] In some embodiments, self-dispensing from the extruder is achieved by mechanical insertion, by applying gaseous pressure from within the extruder barrel, or a combination thereof. In other embodiments, only the outlet, valve, gate, nozzle, or door to the collection area is opened after the expansion phase, allowing the molten polymer foam to flow unimpeded through the outlet; the molten flow is then directed to cooling or other processing equipment, or allowed to be poured into a molding element. In other embodiments, the molding 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 molding element is fluidly connected to the extruder outlet such that pressure is maintained between the collection area, the outlet, and the molding element or mold. The molten polymer foam described herein can be molded using any known thermoplastic molding or forming process associated with the injection molding of polymer articles, such as polymer foam articles.

[0121] In embodiments, the molten polymer foam is allowed to flow unimpeded through an outlet or inserted under pressure from the outlet without further flow resistance, the molten flow ultimately illuminating a surface, such as a surface generally perpendicular to the direction of molten flow. It has been observed that in such cases the flow subsequently acquires generally cylindrical (rolled) and planar (folded) patterns during continued molten flow, such as those reported by Batty and Bridson, "Accurate Viscous Free Surfaces for Buckling, Coiling, and Rotating Liquids," Symposium on Computer Animation, Dublin, July 2008. In embodiments, the molten polymer foam is allowed to flow, or be "poured" unimpeded 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 molten polymer foam; in other embodiments, the open container mold is partially filled with molten polymer foam.

[0122] In some embodiments described above relating to coiled melt flow, a substantially shear-free melt flow, a substantially linear melt flow, or a substantially linear and shear-free melt flow is provided and enters the die cavity via a fluid connection between the extruder outlets. In some such embodiments, the melt flow can be coiled by impinging onto its vertical surface or by flowing downwards along the substantially vertical walls or sides of the die cavity and collecting at the bottom of the die cavity. A schematic representation of this embodiment is shown in FIG. 41, which shows a variation of the extruder of FIG. 1A-1B, wherein the die 26 of the device 20 is located on a substantially horizontal surface 100. Referring to the elements shown in FIG. 1A-1B, there is no shut-off valve 37 at the distal end 21b of the barrel 21; instead, in FIG. 41, the collection area 40 extends to a die valve 137 located close to the die cavity 39 defined within the die 26. Therefore, mold valve 137 is operable to define collection area 40 or provide an outlet for distributing molten polymer foam to mold cavity 39 via a substantially linear horizontal flow 110. Mold valve 137 is positioned at a height H above horizontal surface 100 and at a height H2 above the bottom layer or bottom 120 of mold 26 on horizontal surface 100. Referring to FIG. 41, mold valve 137 is selectively opened to provide fluid connection between collection area 40 and mold cavity 39. Therefore, mold valve 137 is selectively opened to provide a substantially linear horizontal flow 110 of molten polymer foam entering mold cavity 39. Upon entering mold cavity 39, the linear flow flows downward over a distance H2 and, in some embodiments, obtains a coiled melt flow as it continues to fill mold cavity 39. Other related variations of methods and apparatus are covered to provide the coiled melt flow as described herein.

[0123] In embodiments, after cooling and removal of the polymer foam article from an open container or mold positioned as shown in Figure 41, curled and folded flow patterns are visible on the surface of the article. Examples of this visible flow pattern can be seen, for example, in Figures 2-2 and 2-4. During cryogenic cracking and microscopic examination of the interior of a polymer foam article formed using curled and folded flow patterns, the interior of the article contains no or substantially no curled and folded flow patterns, interfaces, or other indications. For example, cryogenic cracking of such polymer foam articles does not occur at any identifiable interface between the coils and folds; and both macroscopic and microscopic examinations of the interior of such polymer foam articles yield a uniform appearance regarding the flow pattern. The physical properties of such polymer foam articles are consistent with those obtained by subjecting molten polymer foam to guided fluid flow, fluid connection between the outlet of the melt mixing device and the mold, or pressurized guided fluid flow.

[0124] In some embodiments, the method herein includes substantially filling a mold with molten polymer foam formed according to the foregoing described method, subsequently cooling the molten polymer foam to form a cured polymer foam; and in embodiments, further removing the cured polymer foam article from the mold. In embodiments, cooling is cooling to a temperature below the melt transition temperature of the thermoplastic polymer. In embodiments, cooling is cooling to a temperature equal to the ambient temperature of the surrounding environment. In some embodiments, during filling the mold with molten polymer foam, the mold further includes one or more vents for pressure equalization within the mold, but in other embodiments, no vents are present. After cooling, the polymer foam article can be removed from the mold for further modification or use.

[0125] According to any of the foregoing descriptions, Table 1 provides examples of suitable, but not limiting, processing conditions for preparing molten polymer foams using a conventional single-screw extruder type reaction injection molding apparatus, further by employing one or more representative thermoplastic polymers as indicated and a citric acid-based gaseous product source.

[0126] Table 1. Representative thermoplastic polymers and conditions suitable for the preparation and molding of molten polymer foams.

[0127] In the embodiments, the dimensions of the molds effectively used to form polymer foam articles prepared using these methods and the materials disclosed herein include molds that define cavities that can be filled by a single injection of molten polymer foam or a series of cavities that can be filled by a single injection of molten polymer foam. Therefore, the size of the mold cavity is limited only by the size of the injection that can be constructed in the melt mixing apparatus used by the user. Representative mold cavities with a volume up to 1 × 10⁵ cm³ are suitable for preparing larger parts, such as automotive cabins or exterior parts, I-beam structural parts, and other larger plastic articles suitably employing polymer foam. Furthermore, the shape of the mold cavity is not particularly limited and can be complex in terms of its overall shape and even surface pattern and features. For example, it can be identified as a dumbbell, tableware, a globe with raised geographical features; human, animal, or insect shapes; frame or shell shapes for framing or covering, such as electronic products, electrical equipment, automobiles, and the like; shapes for subsequently placing and mounting screws, bolts, and other non-thermoplastic articles into or through polymer foam articles; and so on are all suitable mold shapes for molding polymer foam articles as described herein. In some embodiments, the cavity includes a thickness gradient of up to 300% with respect to one or more regions of the cavity.

[0128] According to any of the foregoing descriptions, Table 2 provides applicable, but not limiting, examples of mold cavity volumes and dimensions suitable for molding molten polymer foam by pressurized or unimpeded flow into the mold. Additionally, larger mold volumes, such as up to or greater than 100,000 cm³, are suitable when the injection mass is appropriately increased.

[0129]

[0130] Any of the methods, processes, uses, machines, apparatuses, or individual features described above can be freely combined to form polymer foams and polymer foam articles with unique and unexpected characteristics. Therefore, in the embodiments, the aforementioned methods, materials, and apparatus are used to form polymer foam articles. Polymer foam articles are discrete monomeric objects and variations thereof prepared by forming or molding molten polymer foam according to any of the methods and materials disclosed above, which can be combined in any component and in any manner to form molten polymer foams as described above.

[0131] Therefore, the terms used below to refer to the methods, materials and apparatus described in the foregoing discussion are used to refer to articles prepared using one or more of the methods, materials and apparatus covered in the foregoing discussion.

[0132] In embodiments, any combination of the foregoing methods results in the formation of a polymeric foam article comprising, substantially comprising, or consisting of a continuous thermoplastic polymer matrix defining a plurality of air bladders. The continuous thermoplastic polymer matrix comprises, substantially comprises, or consists of a solid thermoplastic polymer, i.e., a thermoplastic polymer present below its melt transition temperature. In embodiments, the continuous thermoplastic polymer matrix further comprises one or more additional materials dispersed within the solid thermoplastic polymer.

[0133] Based on the density of the added thermoplastic polymer and any other materials, the polymer foam article achieves a density reduction to form a polymer foam having a selected percentage based on the amount of gaseous source added to the filler. In embodiments, density reductions of 30%, 40%, 50%, 60%, 70%, and even up to 80% to 85% are achieved, as selected by the user. In embodiments, up to 85% density reduction is achieved solely by the presence of discontinuously distributed air pockets within the polymer matrix. In embodiments, using the methods and apparatus described herein, the polymer foam article does not contain hollow particles, such as polymer or glass bubbles, added to the filler prior to its formation.

[0134] Furthermore, in conjunction with the reduced density, as mentioned above, the polymer foam articles described herein are characterized by having a continuous thermoplastic polymer matrix that runs through or substantially runs through the entirety of the article. It has been found that larger polymer foam articles can be suitably formed from the molten polymer foam disclosed herein to include a continuous polymer matrix defining a plurality of air pockets. "Larger" articles are those with a volume of 1000 cm³ or greater, such as 2000 cm³ or greater, 3000 cm³ or greater, 4000 cm³ or greater, or 5000 cm³ or greater, or any volume between 1000 cm³ and 5000 cm³; and include volumes of up to 10,000 cm³, up to 20,000 cm³, up to 50,000 cm³, or even up to 100,000 cm³ or greater. Therefore, larger polymer foam articles can be suitably formed to include a continuous polymer matrix defining a plurality of air pockets that runs through the entirety of the article. The volume of the article is limited only by the size of the mold cavity and the size of the injection that can be collected in the melt mixing device. In the embodiments, larger articles are formed by a single injection dispensed from a single outlet of the melt mixing device, that is, without diverting the molten polymer foam flow to multiple simultaneously distributed pipes, nozzles, or other methods that simultaneously guide multiple molten flows into a single mold cavity.

[0135] Furthermore, we have discovered that thick polymer foam articles can be suitably formed to include a continuous polymer matrix defining a plurality of air pockets. As used herein, thickness refers to the straight-line distance between any two points on its surface through the interior of the polymer foam article. A "thick" article is defined as having a thickness of 2 cm or greater, such as 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 greater. In some embodiments, polymer foam articles are formed using the methods and materials described herein, characterized by being larger and thicker, and further characterized by having a continuous polymer matrix defining a plurality of air pockets throughout the article. In embodiments, larger and thicker articles are formed by a single injection from a single outlet of a melt mixing apparatus, i.e., without diverting the molten polymer foam flow to multiple simultaneously distributed channels, nozzles, or other methods that simultaneously guide multiple molten flows into a single mold cavity.

[0136] The manufacture of larger, thicker, or larger and thicker polymer foam articles is problematic in the industry due to the cooling gradient of the molten foam after it is distributed into cavities of such sizes. The interiors of such articles tend to cool very slowly, and some of the thermoplastic polymer disposed within the mold cavity can remain above its melt temperature, allowing significant agglomeration of air pockets to occur before the thermoplastic material solidifies (reaches below its melt transition temperature). In contrast, we have found that larger, thicker, and larger and thicker articles can be appropriately formed using the methods, materials, and apparatus disclosed herein, and the polymer foam articles formed therein are characterized by a continuous polymer matrix with air pockets distributed throughout the article. During cooling, the slow cooling within larger articles exhibits minimal or no air pocket agglomeration. During the cooling of the molten polymer foam, the air pockets remain intact or substantially intact and do not agglomerate during cooling, resulting in a continuous polymer matrix, regardless of the size, thickness, or volume of the polymer foam article formed.

[0137] The characteristic of the polymer foam articles described herein is unexpected and surprising: during cooling, prior art methods produce foams that tend to undergo blister coalescence. Therefore, conventional molten polymer foam located within the internal volume of a mold can be cooled to allow the blister coalescence to fully coalesce, and thus the interior of larger or thicker articles formed using conventional polymer foaming methods can achieve a highly porous or even completely collapsed structure. In contrast, during the cooling of molten polymer foam, the molten polymer foam formed according to the method of the present invention does not undergo significant blister coalescence or collapse of the continuous polymer matrix. Therefore, larger and thicker polymer foam articles having a continuous polymer matrix can be achieved using the methods, materials, and apparatus described herein.

[0138] Due to the structural characteristics of polymer foam articles based on the aforementioned methods, apparatus, and materials, a continuous polymer matrix is ​​characterized as being present throughout the polymer foam article, including its surface region. The surface region can preferably be characterized as the internal region of the polymer foam article 500 micrometers or less from the surface. As defined herein, the surface region is a portion of the region of a foam article conventionally referred to as the "surface layer," which is the region in a polymer foam article prepared using conventional methods that is air-filled or substantially air-filled. Conventionally formed foam articles include a surface layer at least as thick as the surface region, i.e., 500 micrometers thick; however, the surface layer is often much thicker and can extend as far as 1 mm, 1.5 mm, 2 mm, 2.5 mm, or even 3 mm from the article surface. However, polymer foam articles formed using the methods disclosed herein achieve a true foam structure from their surface and throughout their thickness and volume. In the embodiments, microscopic examination reveals signs of air pockets on the surface of polymer foam articles formed using the conditions, processes, and materials disclosed herein. Therefore, in terms of the continuity of the polymer matrix structure throughout the polymer foam product, the method disclosed herein yields unexpected results in any direction and in each region, both within the interior of extremely large and / or extremely thick polymer foam products and on the surface regions of the product.

[0139] The following examples include analyses of surface regions of various polymer foam articles prepared using the methods disclosed herein and exhibiting this continuous foam structure. Macroscopically, polymer foam articles prepared using the methods disclosed herein may appear to have a surface layer: that is, the surface region of the article may appear different from the interior region of the article. However, it has been found that, in stark contrast to a surface layer characterized by the absence of air pockets, the surface region of polymer foam articles prepared by the methods of the present invention contains a plurality of compressed air pockets. Macroscopically, the compressed air pockets produce the appearance of a surface layer; however, microscopic examination reveals that the visually obvious difference arises from the "flattened" or compressed arrangement of the continuous polymer matrix near the surface of the article.

[0140] Therefore, for example, as seen in Figures 17 and 18, there exists a gradual transition from spherical to compressed air bladders towards the surface of a polymer foam article formed using the conditions, processes, and materials disclosed herein. Thus, in embodiments, the surface region of a polymer foam article prepared using the methods disclosed herein includes a plurality of compressed air bladders. In embodiments, compressed air bladders are present in the surface region of a polymer foam article prepared using the methods disclosed herein. In some such embodiments, compressed air bladders are present in the internal region of the polymer foam article at a distance of 500 micrometers or less from the surface. In some such embodiments, compressed air bladders are present in the internal region of the polymer foam article at a distance of up to 2 cm from the surface. A compressed air bladder is defined as an air bladder with a roundness value less than 1, where a roundness value of zero indicates a completely non-spherical air bladder, and a value of 1 indicates a completely spherical air bladder. In the embodiments, air bladders with a roundness of less than 0.9 were observed in the surface areas of the foamed polymer article, and air bladders in 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 surface areas had a roundness of 0.9 or less. In the embodiments, the average roundness of the surface region of the foamed polymer article is 0.70 to 0.95, such as 0.75 to 0.95, or 0.80 to 0.95, or 0.85 to 0.95, or 0.90 to 0.95, or 0.70 to 0.90, or 0.70 to 0.85, or 0.70 to 0.80, or 0.70 to 0.75, or 0.70 to 0.75, or 0.75 to 0.80, or 0.80 to 0.85, or 0.85 to 0.90, or 0.90 to 0.95.

[0141] In embodiments, the compression bladder is present in the polymer foam article at a distance of more than 500 micrometers from its surface. For example, in embodiments, the compression bladder is present at a distance of at most 1 mm from the surface of the polymer foam article, or at a distance of at most 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 1 cm or greater from its surface. In some embodiments, the area of ​​the compression bladder in the polymer foam article corresponds to 0.01% to 70% of the total volume of the article, for example 0.1% to 70%, or 0.5% to 70%, or 1% to 70%, or 2% to 70%, or 3% to 70%, or 4% to 70%, or 5% to 70%, or 6% to 70%, or 7% to 70%, or 8% to 70%, or 9% to 70%, or 10% to 70%, or 15% to 70%, or 20% to 70%, or 30% to 70%, or 40% to 70%, or 50% to 70%, or 6% to 70%. The total volume of the product is 0% 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%.

[0142] Figures 12 and 14 show graphs of average airbag size and average airbag count relative to average airbag roundness for two polymer foam products prepared using the method disclosed in this invention. Quantitative analysis of airbag size and distribution shows an inverse relationship between average airbag size and airbag roundness, and an inverse relationship between average airbag size and airbag number.

[0143] Figure 18 further illustrates the visible presence of air bladders on the surface of a polymer foam article formed using the methods, materials, and apparatus described herein. Figure 18 also illustrates the visible presence of a plurality of compressed air bladders substantially 500 micrometers from the surface of the polymer foam article formed using the methods, materials, and apparatus described herein. In this sense, the polymer foam article disclosed herein differs significantly from prior art foam articles. Although the “surface” or initial 500-micrometer thickness of foam articles prepared by conventional methods does not contain air bladders or substantially does not contain air bladders, prior art foam articles are generally characterized by being spherical regardless of the location of the air bladders. Therefore, in conventional foam articles where air bladders are observed, they are typically spherical with a roundness close to or approximately 1. Compressed air bladders are not formed using conventional methods to prepare foam articles, and therefore, the distribution of air bladder roundness is not observed in such conventional foam articles. Furthermore, the air bladder is not even formed in the first 500 micrometers of the thickness of the foam article prepared by conventional methods, therefore it is not possible to compare the surface areas of the foamed polymer article as described herein with those of the foamed article prepared using conventional injection molding methods regarding the air bladder.

[0144] Furthermore, depending on the intended end use or application, the conditions, processes, and materials disclosed herein are appropriately optimized to form polymer foam products with different physical properties. For example, the density of the polymer foam product is suitably varied with the expansion volume. By reducing the expansion volume, the density of the resulting polymer foam product decreases in a generally linear manner, as shown in Figure 5, for example. It can also be seen from Figure 5 that increasing the expansion period results in a denser polymer foam product. All such conditions and other variables within the scope of the conditions, methods, and materials disclosed herein are appropriately used to modify the physical properties of the resulting polymer foam products.

[0145] In one variation of the conditions, processes, and materials disclosed herein, molten polymer foam is suitably formed from a single injection molding process by dividing the molten polymer foam flow into two, three, four, or more paths leading to multiple molds or mold segments, thereby forming multiple polymer foam articles. In another variation of the conditions, processes, and materials disclosed herein, two injection molding processes are used to fill a single mold, wherein the first injection molding process differs from the second injection molding process in terms of thermoplastic polymer content or the ratio of mixed polymers, gaseous source, density included where applicable, void fraction of one or more additional materials, depth of the compressed air pocket region, or some other material or physical property difference.

[0146] In another variation of the conditions, processes, and materials disclosed herein, fastener pull-out tests according to ASTM D6117 were performed on polymer foam products prepared using the methods disclosed herein. The polymer foam products exhibited superior pull-out strength compared to foam products prepared using conventional foaming methods. Furthermore, polymer foam products formed using the materials, methods, and apparatus disclosed herein do not require pre-drilling, tapping, or engineering modifications to fastener locations.

[0147] Impact testing was conducted on polymer foam products prepared using the methods described herein, in yet another variation of the conditions, processes, and materials disclosed herein. Following the National Institute of Justice (NIJ) guidelines “Bulletproof Vest Performance NIJ Standard-0101.06,” a series of 3-inch thick polymer foam products were formed from polyether-amide block copolymer (PEBAX®), linear low-density polyethylene (LLDPE), and polypropylene using a citric acid-based gaseous source. The polymer foam products prepared using all three of these thermoplastic polymers were found to stop .22 LR pistol bullets, passing NIJ Level I; and were found to stop 9mm LLUGER® pistol bullets, passing NIJ Levels II and IIA.

[0148] [Experimental Section]

[0149] The following examples are intended to further illustrate the invention and are not intended to limit the scope of the invention in any way. Examples 1 and 11 were performed on an Engel Duo 550 Ton injection molding machine (available from Engel Machinery Inc. of York, PA, USA). Examples 2-4 were performed on a Van Dorn 300 injection molding machine (available from Van Dorn Demag of Strongsville, Ohio, USA). Unless otherwise stated, the remaining examples were performed on an Engel Victory 340 Ton injection molding machine (available from Engel Machinery Inc. of York, PA, USA).

[0150] In the examples in this article, "cc" means "cubic centimeter" or "cubic centimeters" (cm3), and "sec" means "second".

[0151] Standard foam molding and MFIM

[0152] In the examples presented herein, two direct injection expanded foam molding techniques are employed, referred to herein as "standard foam molding" and "molten foam injection molding" ("MFIM").

[0153] In standard foam molding, the following general procedure is used: A) A mixture is prepared by blending a polymer (which may be in the form of injection, powder, beads, granules, or the like) with a foaming agent and any other additives such as fillers. The mixture is introduced into the injection unit, and the screw of the injection unit is rotated to move the mixture forward in the barrel of the injection unit, thus forming a heated fluid material according to the normal injection molding process. B) A set volume of material is dispensed into the front of the barrel of the injection unit by rotating the screw, thus moving the set volume from the feed zone to the front of the screw. During this feeding step, the screw is rotated to move the molten mixture forward into the space in the barrel between the screw and the nozzle, thereby providing the set volume. C) The molten mixture is injected into the mold cavity by the forward movement and / or rotation of the screw.

[0154] In the molten foam injection molding (MFIM) process, the following general procedure is used: A) A mixture is prepared by blending a polymer (which may be in the form of pellets, fillers, powders, beads, granules, and the like) with a chemical foaming agent and any other additives such as fillers. The mixture is introduced into the injection unit, and the screw of the injection unit is rotated to move the material forward in the barrel of the injection unit, thus forming a heated fluid material according to the normal injection molding process. B) A set volume of material is dispensed into the front of the barrel of the injection unit by rotating the screw, thus moving the set volume from the feed zone to the front of the screw. During this feeding step, the screw is rotated to move the material between the screw and the nozzle, thereby providing the set volume. C) After the material has moved to the front of the screw, in a step referred to herein as "decompression," the screw is moved backward away from the nozzle without rotation or substantially without rotation to prevent further material from moving to the front of the screw.

[0155] A space is created within the barrel that does not contain the mixture between the screw and the nozzle; this defined space has a volume referred to herein as the "reduced pressure volume". D) The material is allowed to remain in the barrel between the screw and the nozzle for a certain period of time, referred to herein as the "reduced pressure time". During the reduced pressure time, the material foams due to the pressure drop created by the space added in step (C). E) The molten foam is injected into the mold cavity by the forward translation and / or rotation of the screw.

[0156] Example 1

[0157] Two parts were foamed and molded using a blend of low-density polyethylene and 2% by weight Hydrocerol® BIH 70 foaming agent, available from Clariant AG of Muttenz, Switzerland. Molding was performed using an Engel Duo 550 Ton injection molding machine (Engel Machinery Inc. of York, PA, USA). The mold cavity was (approximately) spherical in shape, with a diameter of six inches (15.24 cm). The first part was molded using a standard foam molding process, and the second part was molded using an MFIM process. An aluminum mold with a cold runner and runner system feeding into a 6-inch diameter spherical cavity was used for both parts. The melt delivery system for each part was the same as most of the processing conditions. The process settings for the MFIM process and the standard foam molding process, used as a comparison, are detailed in Table 3. For each process, the parts were made from approximately equivalent mass.

[0158]

[0159] The first and second components were photographed. Figure 2-1 is an image of the first component molded using a standard foam molding process. As can be seen in the image, the standard foam process did not produce a component that filled the mold cavity, and the component did not conform to the shape of the spherical cavity of the mold.

[0160] Figure 2-2 is an image of a second component molded using the MFIM process. As can be seen in the image, the MFIM process produces a component that completely or substantially fills the cavity of the spherical mold, and the component conforms to or substantially conforms to the shape of the spherical cavity of the mold.

[0161] The first component, molded using a standard foam molding process, is cut into two parts. Figures 2-3 and 2-5 are images of one of the parts of the component prepared according to the standard foam molding process. As can be seen in the images, the first component contains a larger hollow cavity.

[0162] The second component, molded according to the MFIM process, is cut into two parts. Figures 2-4 and 2-6 show images of one of the parts of the second component. As can be seen in the images, the second component lacks the large hollow cavity of a standard foam process component. It has a porous structure throughout the MFIM component.

[0163] Example 2

[0164] Two parts are formed by foam injection molding: part A is formed according to a standard foam molding process, and part B is formed according to an MFIM process. In both processes, LDPE / talc filler is dried and mixed with a foaming agent during loading into the molding machine.

[0165] For component B, a mixture of low-density polyethylene (LDPE), talc, and Hydrocerol® BIH 70 is formed and fed into a Van Dorn 300 injection molding machine to provide polymer injection into the barrel. After the injection accumulates at the front of the screw, the screw is moved backward away from the injection nozzle without rotation according to the MFIM process to create a space with a depressurized volume between the screw and the nozzle. The mixture is then foamed into this space before being injected into the mold.

[0166] Part A uses the same procedure, except that after the injection material accumulates at the front of the screw, the screw does not move away from the nozzle, meaning the depressurization volume is zero. Metered injection is used to fill the mold cavity under standard foam molding conditions, with the goal of reducing the weight of the solid part by 10%.

[0167] Table 4-7 below shows the polymer, mold, machine and processing setup used in Example 2.

[0168]

[0169]

[0170]

[0171]

[0172] Each of components A and B was cut in half to show its cross-section. Figures 3A and 3B show the resulting cross-sections of components A and B, respectively. As shown in Figure 3A, component A has a thicker outer region extending almost 0.8 inches (20.3 mm) from the surface, indicating that more than 50% of the molded component is completely solid. The density of component A is 0.84 g / cc.

[0173] Figure 3B shows a cross-section of component B molded using the settings shown in Tables 4 and 5 according to the MFIM process. As seen in Figure 3B, component B has a foam structure including the distribution of pore size and shape. There are almost no unfoamed external solid areas in component B. The density of component B is 0.35 g / cc.

[0174] A spherical cavity mold was used to form two other parts, C and D, manufactured by foam injection molding. Parts C and D were formed using the same mixture composition of LDPE, talc, and Hydrocerol® BIH 70. Part C was prepared using an MFIM process, and part D was prepared using a standard foam molding process. Both processes produced spherical or near-spherical parts with a diameter of six inches (15.24 cm). Parts C and D were cut in half from the middle (widest part) to expose their cross-sections. Figure 4A is an image of the cross-section of part C prepared using the MFIM process (471 g, required cooling time 160 sec). Figure 4B is an image of the cross-section of part D molded using a standard foaming process (1360 g, required cooling time 800 sec).

[0175] Similar results were obtained to those obtained using block molding. Part C, fabricated using the MFIM process, exhibits pores throughout the part, while part D, fabricated using the standard foam molding process, exhibits a region adjacent to the outer surface of the part that is pore-free or substantially pore-free ("solid"). Part C has a lower density than part D.

[0176] Example 3

[0177] In Example 3, MFIM process molded block components were used under various decompression volumes (Experiment A) and various decompression volumes and decompression times (Experiment B).

[0178] Table 8-10 shows the material composition, mold geometry information, and processing settings for tests A and B.

[0179]

[0180]

[0181] The composite LDPE / talc injection molding compound is mixed with a foaming agent just before molding.

[0182] Experiment A

[0183] In Experiment A, all variables remained constant, the only difference being the volume ratio of polymer to depressurized volume (empty space) in the barrel before injection. The sample run settings for Experiment A are shown in Table 10:

[0184] The volume of molten foam injected into the polymer cavity is constant, but the density of the molten foam is a function of the polymer injection / reduction volume ratio. Variations in the polymer injection / reduction volume yield components with different weights and densities, as shown in Table 11.

[0185] The results in Table 11 show that the density of the resulting component can be changed by reducing the mass and volume of the polymer in the molten foam injection while simultaneously increasing the decompression volume.

[0186] Test B

[0187] In Experiment B, molding was performed three times under the same conditions as in Experiment A: once at a decompression time of 20 seconds (same as in Experiment A), once at a decompression time of 70 seconds, and once at a decompression time of 120 seconds. Fifteen foam-molded parts were weighed, and their density was calculated using the volume of the mold cavity. The part density was plotted as a function of the decompression volume for each of the three decompression times. The graph is shown in Figure 5. As can be seen in Figure 5, the part density varies with the decompression volume. Furthermore, as shown in Figure 5, the longer the decompression time, the denser the part.

[0188] Example 4

[0189] In Example 4, two series of tests were conducted using the MFIM process, Series I and Series II. In Series I, a constant injection speed was used, but the mold closing height was varied. In Series II, the mold closing height increased with increasing injection speed. In Series II, all conditions remained constant except for the injection speed (cc / sec) and the mold closing height. In the tests, LDPE / talc filler was dried and mixed with a foaming agent during loading into the molding machine.

[0190] Tables 12-13 below show the material composition of the injection blends and basic molded configurations used in the experiments.

[0191]

[0192]

[0193] Series I

[0194] In Series I, an injection speed of 394 cubic centimeters per second was used, and three tests were conducted: Test A, which produced part A with a mold closing height of 1.02 mm; Test B, which produced part B with a mold closing height of 0.76 mm; and Test C, which produced part C with a mold closing height of 0.51 mm. The setup for the Series I tests is shown in Table 14.

[0195] During each molding cycle (each of Experiment A, Experiment B, and Experiment C), a strain gauge (Kistler surface strain sensor type 9232A) was used. The strain sensor (purchased from Kistler Holding AG, Winterthur, Switzerland) is mounted directly above or inside the molded cavity. It contains two piezoelectric sensors that measure the strain of the aluminum cavity over time during the molding cycle. The strain is measured as an indirect measure of the forces acting on the surface of the mold cavity caused by the injection of molten foam and any subsequent additional foaming occurring within the cavity. Cavity strain measurements are plotted in Figure 6 for test A (1.02 mm gap height, line A), test B (0.76 mm mold closure height, line B), and test C (0.51 mm mold closure height, line C). The strain (unit extension per unit length) is plotted in Figure 6 relative to time in seconds. The strain curves indicate that test C had higher pressure than test B, and test B had higher pressure than test A.

[0196] Figure 7 contains photographic images showing side, top, oblique, and bottom views of components A, B, and C. Components A and B show signs of collapse because they do not fully conform to the shape of the mold cavity. Component A shows more collapse than component B. Component C is more fully formed than either component A or B because its edges are better defined, it better conforms to the shape of the mold cavity, and its interior appears more uniform.

[0197] It is believed that if sufficient pressure is not supplied to stabilize the foam in the cavity during solidification, the part may partially collapse in the cavity during molding. Therefore, in Series II, the mold is closed more tightly at a slower injection rate to maintain sufficient pressure to prevent the part from collapsing during molding.

[0198] Series II

[0199] In Series II, the gap between the mold halves and the mold closing height systematically decrease as the injection rate decreases. The molding conditions used are the same as those in Series I, except that the injection rate and mold closing height used are as shown in Table 15.

[0200] Four components were generated in experiments A', B', C', and D', namely components A', B', C', and D'.

[0201] Each of components A', B', C', and D' is cut into two parts, and cross-sectional images are taken. The photographic images are shown in Figure 8. In order to produce components that do not collapse before solidification, as shown in Table 15, the mold halves must be gradually closed until they are actually pressed together (as indicated by the negative electrode dimension).

[0202] Parts A', B', C', and D' show no signs of collapse; their edges and surfaces are well-defined and appear quite uniform. Therefore, by controlling the pressure within the cavity during injection (e.g., by varying the mold closing height), significantly different injection rates were used to fabricate the parts using the MFIM process.

[0203] Example 5

[0204] In Example 5, the same LDPE composite material as in Examples 1-3 was used in two non-standard cavity molds with molding parameters as shown in Tables 16-18.

[0205]

[0206]

[0207]

[0208] Example 5 produces part 51 as shown in Figure 9. During injection, molten foam enters through runner 52 and is diverted into two separate channels to substantially simultaneously fill part 51. Therefore, the MFIM process can be used to form parts by dividing the melt into multiple paths in a mold.

[0209] Example 6

[0210] The first part was molded using a formulation of 15 wt% talc / 85 wt% polycarbonate composite material blended with 3 wt% Hydrocerol® XH-901 before being loaded into the injection molding machine. The first part was formed using an MFIM process. Process details are provided in Tables 19 and 20. The part was prepared using a 4×2×2 block mold (5.08×10.16×10.16cm) with a mold cavity volume of 524.4cc and a runner volume of 17.4cc. The runner was cut from the part, and the part was subsequently subjected to X-ray tomography to quantify the porous structure formed within the 5.08×10.16×10.16cm geometry.

[0211]

[0212]

[0213] X-ray tomography was performed using a Zeiss Metrotom 800 130kV imaging system (purchased from Carl Zeiss AG of Oberkochen, Germany). Instrument measurements were attributed to the attenuation of X-ray radiation due to the geometry, materials, and density of the components used. Data were calculated using the Feldkamp reconstruction algorithm (a standard industry technique). The instrument features a 1536 × 1920 pixel flat panel detector with a limiting resolution of 3.5 μm under these measurement conditions.

[0214] The isometric image of the first component obtained from a full Zeiss 3D tomographic scan is shown in Figure 10, where the solid polymer portion is shown as transparent, the aperture is shielded for observation, and a single cross-sectional cutting plane AA is specified. Figure 11 shows a single-plane cross-section AA selected from the X-ray data, where threshold analysis is applied to allow for precise aperture identification and subsequent quantitative analysis.

[0215] Obtain the roundness of the cross-sections of the holes. Use the roundness of these cross-sections as a measure of the sphericity of the holes. Therefore, in this example, roundness and sphericity are used interchangeably. The quantitative analysis shown in Figure 12 reveals the hole distribution as both the count and average size vary with the roundness of each hole. A roundness value of zero indicates a completely non-spherical hole, and a value of 1 indicates a completely spherical hole. The data shows the distribution of hole size and shape. Except for the holes with the most severe deformation (indicated by 0.1-0.2 in the roundness grade), there is an inverse relationship between the average hole size and the number of holes with a given roundness. Furthermore, there is an inverse relationship between the average hole size and the number of holes.

[0216] Using the MFIM process, a second spherical part with a diameter of six inches (15.24 cm) was molded from low-density polyethylene (LDPE) using the polymer formulations and processing parameters outlined in Tables 21 and 22. During loading into the molding machine, the LDPE / talc filler was dried, blended, and mixed with the foaming agent and Hydrocerol® BIH 70.

[0217]

[0218]

[0219] Figure 13 shows an X-ray tomographic image of a cross-section of the sphere. As seen in Figure 13, the outer region contains a large number of smaller apertures, while the central region contains larger apertures.

[0220] Figure 14 shows the curves of average hole size and average hole count relative to average hole roundness, and reveals the inverse relationship between average hole size and roundness, as well as the inverse relationship between average hole size and hole count.

[0221] Example 7

[0222] The MFIM process was used to mold 3-inch (7.62 cm) diameter LDPE composite spheres (92 wt% polymer, 5 wt% talc, and 3 wt% Hydrocerol® BIH 70) and the resulting foam pore structure detailed in Figures 15-18. Molding conditions are provided in Table 23. The part was molded in a custom-designed water-cooled aluminum mold on an Engel Victory 340 Ton injection molding press. The mold cavity volume was 15.38 in³ (252 cc), the injection volume was 5 in³ (82 cc), and the decompression volume in the barrel was 5 in³ (82 cc). The decompression time was 77 seconds. The molded part weighed 80.31 g, resulting in a final part density of 0.32 g / cc.

[0223]

[0224] After removal from the mold, the component was aged under ambient conditions for 24 hours, then scored and immersed in liquid nitrogen for two minutes. After removal from the liquid nitrogen, the sphere was fractured along the scored surface lines, and the fractured surface was imaged using an environmental scanning electron microscope (ESEM) (FEI Quanta FEG 650). The images shown in Figures 15-18 are micrographs of the fractured surface of the spherical component at various magnifications obtained using a large-area detector (5.0 kV and 40 Pa pressure).

[0225] The white box in Figure 15 indicates the area detailed in Figure 16. The white box in Figure 16 indicates the area detailed in Figure 17.

[0226] In Figure 17, the aperture on the left side of the image is larger and relatively spherical, while the aperture on the right side of the image gradually flattens as it approaches the surface of the sphere.

[0227] 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 a spherical shape to a "flat" shape or a compression hole moving towards the surface of the component.

[0228] Example 8

[0229] To determine baseline differences between standard thickness parts manufactured under standard foam molding conditions, a baseline of molding parameters was established using a recently published study on standard foam injection molding (Paultkiewicz et al., Porous Polymers 39, 3-30 (2020)) employing a 16-round Design of Experiments (DOE) method. Materials (standard molding grade polypropylene with 0 wt%, 10 wt%, and 20 wt% talc; and 0 wt%, 1 wt%, and 2 wt% Hydrocerol® BIH 70 (blowing agent)) were blended according to the specifications outlined in the publication to closely mimic the baseline study. The study was designed to investigate the effects of blower concentration, talc content, and processing conditions on selected properties of the injection-molded foam parts. A standard ISO stretch strip mold with a cavity size of 4.1 mm thickness, 10 mm gauge width, and 170 mm length was used. No special venting was developed for the ISO strip mold. After ensuring that the injection molding machine, material formulation, and process window could mimic the results published by Paultkiewicz et al., a second study was conducted using process variables specifically designed for MFIM, namely decompression volume and decompression time, while setting the pressure and holding time (important variables in the published study) to constant values ​​of zero kN and zero seconds, respectively.

[0230] Molding was performed 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.

[0231]

[0232] Each of the standard molding and MFIM molding studies required 16 treatment conditions / polymer formulation combinations (16 rounds). Each round was repeated multiple times to produce repeating parts for each round. Table 25 summarizes the variations between rounds in both the standard and MFIM design rounds. Rounds were performed in a random order to avoid bias. The L / T ratio for the ISO stretch strip was 40.5.

[0233]

[0234] After molding 32 unique process combinations from two 16-round DOE studies, the tensile strength and fracture surface images of five samples from each series were mechanically tested. Representative selections of ISO strip cross sections from rounds 10, 11, 14, and 15 of the standard foam molding process are shown in Figure 19, and representative selections of ISO strip cross sections from rounds 9, 10, 15, and 16 of the MFIM process are shown in Figure 20.

[0235] When examining cross-sectional images, the differences between the standard foam molding technique and the MFIM process, as adopted in recent literature, are readily apparent. The structure in the standard process strip consists of relatively few but well-defined spherical holes on all sides of a thicker region of the pore-deficient polymer. Cross-sectional images obtained from the standard foam molding process closely match those in the publications of Paultkiewicz et al., and represent the current industry standard. In contrast, a typical cross-section of an ISO strip molded with MFIM exhibits a pore structure with more asymmetrical, deformed holes.

[0236] The holes in the MFIM cross-section also extend to the area adjacent to the surface in almost all cases, similar to the previous examples described herein, and although for much thinner parts with a much larger L / T ratio (40.5) than previously described. The results clearly indicate that employing the decompression step in MFIM, combined with eliminating standard foam molding process variables of holding pressure and time, produces a significantly different hole structure in the molded part.

[0237] Tensile tests were performed on five repeating components from MFIM Round 9. Figure 21 shows representative cross-sections and a series of stress / strain curves of the five components tested from MFIM Round 9.

[0238] Tensile tests were performed on five repeating components from round 10 using a standard foam molding process. Figure 22 shows representative cross-sections and a series of stress / strain curves of the five components tested from round 10 of the standard foam molding process.

[0239] The average tensile strength of the five parts from the 9th round of MFIM was lower than that of the five parts from the 10th round of the standard foam molding process. However, the MFIM parts exhibited greater strain (elongation) at fracture.

[0240] The MFIM component from round 9 (102 holes) has more holes in its cross-section than the standard foam molding process component from round 10 (19 holes).

[0241] X-ray tomography scans were performed on randomly selected replicas from the 15th round of the standard foam molding process (shown in Figure 23) and on randomly selected replicas generated during the 9th round of the MFIM process (shown in Figure 24) (under the conditions described in Example 5). Figures 23 and 24 both show a "top" view and a "side" view taken at 50% depth.

[0242] In the hole structure developed in the standard foam molding process ISO strip (Figure 23), the cross-section is circular and the area near the surface of the strip does not contain holes.

[0243] In contrast, ISO strips produced by the MFIM process, as shown in Figure 24, contain a large number of elongated holes, with holes found in areas adjacent to the surface of the component.

[0244] Example 9

[0245] To investigate the dependence of the final pore structure on MFIM process conditions, eight stretched strips of LDPE were molded using the MFIM process on an Engel Victory 340 Ton injection molding machine. The mold contained cavities of aluminum-modified stretched strips with the following dimensions: a length of 24 cm, a thickness of 2.54 cm, a variable width gauge of 6 cm, and a standard width of 2.54 cm, tapering to a width of 3.5 cm on the side plates. Larger stretched strips were fed into the cold runner and runner system via a 1.0 cm diameter gate. The material formulation consisted of LDPE with or without talc, always containing 2% by weight of the foaming agent Clariant Hydrocerol® BIH 70. The melt temperature was set as detailed in Table 26, and the residence time in the barrel was 13 minutes before the build-up was used for injection. After the filler material is prepared, the screw is retracted to achieve a reduced volume of 4.0 cubic inches (66 cc) or 6.0 cubic inches (98 cc), and the LDPE foaming agent mixture is foamed into the empty barrel space for 15 or 45 seconds before injection. Studies were conducted on unfilled LDPE and LDPE filled with 15% talc. Detailed process conditions are shown in Table 26.

[0246]

[0247] Figure 25 shows an X-ray scan of one of the components from this study, revealing the overall shape of each component.

[0248] Figure 26 depicts the cross-sections of the test strips molded in the study, cut from the midpoint of the gauge length under the indicated variable parameters. The sample set comprises two main groups: samples prepared with talc and samples prepared without talc. In Figure 26, the sample set on the left depicts those components prepared without talc. These components exhibit a smaller pore structure in the core of the component, and the integrity of the developed pore structure is substantially unaffected by changes in the decompression ratio and decompression time, indicating that the decompression ratio and time are within acceptable ranges.

[0249] The sample set on the right depicts the equivalent containing 15% talc. Some blemishes on some surfaces are caused by tool damage on low-modulus LDPE and do not indicate part quality. The pore structure in the talc-treated part is consistently larger, and the pore roundness is slightly lower than that of the talc-free equivalent.

[0250] X-ray tomography images obtained from a cross-section of approximately 50% of the main surface were incorporated into an MFIM component prepared with 15% talc, a 6-in-3 (98 cc) decompression volume, and a decompression time of 15 seconds. The images are shown in Figure 27.

[0251] Example 10

[0252] Using the processing parameters described for Example 9, but without the decompression step of the MFIM process, a stretched strip component was prepared using a standard foam molding process from LDPE loaded with 15 wt% talc and 2 wt% Hydrocerol® BIH 70. This standard foam molded component was compared with the MFIM component prepared from Example 9 using 15% talc, a 6 in³ (98 cc) decompression volume, and a 15-second decompression time. X-ray tomography images of the central portion of each component (MFIM molding and standard foam molding) were obtained at various depths from the main surface using the method described in Example 6. Cross-sectional images were also recorded. The images are shown in Figure 28.

[0253] X-ray tomographic analysis was performed on the images of each tension strip component (MFIM and standard treated material) at various depths from the main surface to analyze hole count, hole roundness, average hole size (maximum hole size). Hole count, hole roundness, and average hole size were plotted relative to the depth of the cross section; and the individual curves are shown in Figures 29-31.

[0254] As shown in Figure 29, the hole count is high at all depths in MFIM molded parts. As can be seen throughout the example and diagrams, parts molded using standard foam molding processes appear to have no or substantially no holes in the area near the surface or in the "surface," for example, at a depth of about 2.5 mm from the main surface. However, in the area about 2.5 mm below the surface and between the surface and the surface, the MFIM process makes holes present in the molded parts.

[0255] As shown in Figure 30, the roundness of holes is generally greater in standard foam molding process samples than in MFIM molded parts, except towards the center of the MFIM part, where the roundness is also higher in the MFIM molded samples.

[0256] As shown in Figure 31, for standard foam-molded stretch strip components, the hole size is generally large, but drops rapidly to zero in the region near the outer surface (e.g., within 2.5 mm of the surface). In contrast, in the deeper layers of MFIM-molded components, the hole size is more uniform, and the holes continue to extend towards the surface.

[0257] The same trend was observed by visual inspection of the cross-section shown in Figure 28. On any outer surface of 2.5 mm, the standard foam molded part was pore-free, while in the MFIM part, pores were visible all the way to the outer surface.

[0258] Example 11

[0259] Differential scanning calorimetry was used to analyze a large batch of recovered marine plastic samples, which were estimated to consist of approximately 85% by weight HDPE, with the remainder including polypropylene and contaminants.

[0260] Two parts, a 4"×4"×2" brick-shaped component and a sphere with a diameter of 15.24 cm, were successfully molded from Ocean Plastics using the MFIM process. Molding was performed using an Engel Duo 550 Ton injection molding machine (purchased from Engel Machinery Inc. of York, PA, USA). Both parts were center-gated and filled using a viscous coil folding flow.

[0261] The processing parameters and characteristics of the obtained components are listed in Tables 27 and 28, respectively:

[0262]

[0263] Example 12

[0264] A sphere with a diameter of nine inches (22.86 cm) was molded using the MFIM process described in this paper, "Sample 10". Additionally, a second sphere with a diameter of nine inches (22.86 cm) was molded using a variant process, "Sample 20". The variant process, referred to in this paper as the "reverse MFIM" process, is as follows:

[0265] A) A mixture is prepared by blending a polymer (which may be in the form of injection, powder, beads, granules, or the like) with a chemical foaming agent and any other additives (such as fillers). The mixture is introduced into the injection unit, and the screw of the injection unit is rotated to move the material forward in the barrel of the injection molding machine, thus forming a heated fluid material according to the normal injection molding process. B) The screw moves backward toward the funnel, thereby creating a predetermined space in the barrel between the screw and the nozzle. C) By rotating the screw, a set volume of material is dispensed to the front of the barrel of the injection unit, thus moving the set volume from the feed zone to the front of the screw and into the predetermined space created in step B. During this feed step, the screw is rotated to move the molten material into the space in the barrel between the screw and the nozzle, thereby providing the set volume. However, the set volume only occupies a portion of the predetermined space, thus providing volume for the injection to foam and for the depressurized volume to expand. D) The material is allowed to remain in the barrel between the screw and the nozzle for a certain period of time, referred to herein as the "depressurization time". During the decompression time, the material expands due to foaming to fill or partially fill the space created in step (B). E) Molten foam is injected into the mold cavity by the forward translation and / or rotation of the screw.

[0266] Therefore, the difference between conventional and reverse MFIM processes is that in the MFIM process, the screw is rotated to introduce material into the front of the barrel before the screw is reverse-translated to allow for decompression space; while in the reverse process, the screw is reverse-translated to allow for decompression space before the screw is rotated to introduce material into the predetermined space.

[0267] Samples 10 and 20 were both molded from virgin LDPE containing 2% Hydrocerol® BIH 70, 2% talc, and 1% yellow colorant. Molding was performed on an Engel Duo 550 Ton injection molding machine (purchased from Engel Machinery Inc. of York, PA, USA). The mold was a spherical cavity within an aluminum mold fed by cold runners and sprues.

[0268] The processing parameters are shown in Table 29:

[0269] The density of the components (both Sample 10 and Sample 20) was 0.214 g / cc, and the density decreased by 77% in both cases.

[0270] Figure 32 shows an image of sample 20 and Figure 33 shows an image of sample 10, with each spherical component mounted on a support. As can be seen in the figures, sample 20, prepared using the "reverse MFIM process," exhibits an inhomogeneous surface, while the surface of sample 10, prepared using the MFIM process, is much flatter. The average wrinkle depth was estimated using optical microscopy and X-ray tomography. The average wrinkle depth of sample 10 was measured at less than 50 micrometers, while that of sample 20 was measured at 565 micrometers.

[0271] Each of samples 10 and 20 was cut in half to provide a cross-section at its maximum diameter. Cross-sections of the four parts were photographed. Half of sample 20, prepared by the reverse MFIM method, is shown in Figure 34, and half of sample 10 is shown in Figure 35. Careful examination of the edges reveals that, unlike parts elsewhere in the example produced by the standard foaming method, holes are found on the right side of the surface of samples 10 and 20, for example, within 2.5 mm of the surface.

[0272] X-ray tomography was performed at a depth of one inch on samples 10 and 20, and the pore count and pore size at different distances from the surface of each sample were measured using the method described in Example 6. The curves are shown in Figures 36 and 37, where "MFIM" refers to sample 10 and "reverse MFIM" refers to sample 20.

[0273] Two other spherical components (component 6 and component 7) were prepared under the same conditions as sample 10 and using the same polymer / talc / colorant / foaming agent mixture (i.e., by MFIM method). Five cuboid components, each approximately 2 inches × 2 inches × 1 inch in size, were cut from each of components 6 and 7, and the compressive modulus (stress versus strain) was tested. The mean stress versus mean strain (MFIM method) was plotted and is shown in Figure 38.

[0274] Two other spherical components (components 22 and 24) were prepared under the same conditions as sample 20 and using the same polymer / talc / colorant / foaming agent mixture. Five cuboid components, each approximately 2 inches × 2 inches × 1 inch (approximately 5.1 cm × 5.1 cm × 5.1 cm), were cut from each of components 22 and 24, and their compressive modulus (stress versus strain) was tested. The average stress versus average strain (inverse MFIM method) is plotted and is also shown in Figure 38. As can be seen in Figure 38, the compressive modulus of the components prepared by the MFIM process (average of components 6 and 7) is similar to that of the components prepared by the reverse MFIM process (average of components 22 and 24).

[0275] Five strips were cut from each of components 6 and 7 (MFIM) and components 22 and 24 (reverse MFIM). Each strip was approximately 1 inch × 1 inch × 8 inches. The flexural modulus (stress versus strain) of all strips was tested, and the results from the ten MFIM strips and the ten reverse MFIM strips were averaged. The results are plotted in Figure 39.

[0276] Example 13

[0277] The components were manufactured using MFIM methods for various shapes and materials as described herein, as shown in Table 30. Each component was cross-sectioned. In all cases, the area closer to the surface contained smaller holes, but the hole size increased as the component moved away from the surface. Areas with smaller hole sizes closer to the surface further transitioned to larger hole sizes from the surface. Although there was a gradual change and therefore no smaller or larger dissimilar layers, the relative areas of smaller or "compressed" holes and larger holes were estimated visually and confirmed by optical microscopy using microscopy, and are shown in Table 30. Although the numbers are only estimates, examination of the images showed that the depth and percentage of area occupied by "compressed" holes varied widely, possibly depending on the component shape, material, and / or batch conditions.

[0278]

[0279] Example 14

[0280] The first part was molded using a formulation of 98% by weight metallocene polyethylene blended with 2% by weight Hydrocerol® BIH 70 before being loaded into the injection molding machine. The first part was formed using an MFIM process. Process details are provided in Tables 31 and 32. The part was prepared using a 2"×4"×4" block mold (5.08×10.16×10.16cm) with a mold cavity volume of 524.4cc and a runner volume of 17.4cc. The runner was cut from the part, and the part was subsequently subjected to a compression load test to quantify the compressive strength characteristics of the porous structure formed within the 2"×4"×4" geometry.

[0281]

[0282]

[0283] Compression tests were conducted on an Instron global testing system (purchased from Instron USA, Norwood, Massachusetts, USA). Each molded foam block was placed between the test plates and stabilized in an ambient chamber at 30°C for five minutes prior to testing. The instrument was equipped with a 250 kN force gauge. The compression test rate was 5 mm / min.

[0284] The results showed that the compressive modulus of sample A was 19 MPa (0.37 g / cm³), sample B was 39 MPa (0.45 g / cm³), and sample C was 55 MPa (0.57 g / cm³). As shown in Figure 40, the compressive strength of metallocene polyethylene (mPE) blocks increased with increasing density.

[0285] 20: Apparatus for molten gas mixture

[0286] 21: Machine barrel

[0287] 21a: First end of the barrel

[0288] 21b: Second end of the barrel

[0289] 22: Barrel Section

[0290] 24: Motor

[0291] 26: Mold

[0292] 28: Entrance

[0293] 30: Screw

[0294] 31: Thread

[0295] 32: Check valve

[0296] 34: Screw tip

[0297] 36: Nozzle

[0298] 37: Nozzle shut-off valve

[0299] 38: Mold Part

[0300] 39: Cavity

[0301] 40: Collection Area

[0302] 42A: Mixture

[0303] 42B: Gas-containing mixture

[0304] 44: Expansion Volume

[0305] 51: Components

[0306] 52:Note

[0307] 100: Horizontal surface

[0308] 110: Essentially linear horizontal flow

[0309] 120: Bottom or bottom layer

Claims

1. A polymer foam article having a continuous thermoplastic polymer matrix extending throughout the entire polymer foam article, the continuous thermoplastic polymer matrix defining a plurality of air pockets distributed throughout the entire polymer foam article, wherein a surface region of the polymer foam article extending 500 micrometers from its surface includes air pockets distributed throughout the entire surface region having a roundness of less than 0.9, further wherein the polymer foam article has a thickness greater than 2 cm or a volume greater than 1000 cm³, and the plurality of air pockets and the air pockets having a roundness of less than 0.9 together constitute 70% or less of the volume of the polymer foam article.

2. The polymer foam article of claim 1, wherein the polymer foam article further includes an air bladder having a roundness of less than 0.9 at a distance of more than 500 micrometers from the surface of the polymer foam article.

3. The polymer foam article of claim 1, wherein the thermoplastic polymer is selected from: polyolefins, polyamides, polyimides, polyesters, polycarbonates, poly(lactic acid), acrylonitrile-butadiene-styrene copolymers, polystyrene, polyurethanes, polyvinyl chloride, tetrafluoroethylene copolymers, polyether ethers, polyacetals, aromatic polyamides, polyphenylene ethers, polybutene, polybutadiene, polyacrylates and methacrylates, ionomers, polyether-amide block copolymers, polyaryletherketones, polyether ethers, polyphenylene sulfide, polyamide-amide copolymers, polybutylene succinate, cellulose materials, or polysaccharides, or any copolymers, complexes, mixtures or blends thereof.

4. The polymer foam article of claim 1, wherein the continuous thermoplastic polymer matrix comprises polyolefin, polyamide, ionically functionalized olefin copolymer or polyether-amide block copolymer.

5. The polymer foam article of claim 1, wherein the continuous thermoplastic polymer matrix comprises a mixed plastic waste stream.

6. The polymer foam article of claim 1, wherein the continuous thermoplastic polymer matrix further comprises one or more additional materials selected from colorants, stabilizers, brighteners, nucleating agents, fibers, particles and fillers.

7. The polymer foam article of claim 1, wherein the continuous thermoplastic polymer matrix further comprises talc or a colorant or both talc and a colorant.

8. The polymer foam article of any one of claims 1 to 7, wherein the polymer foam article includes a thickness of more than 5 cm.

9. A polymer foam article as claimed in any one of claims 1 to 7, wherein the polymer foam article includes a thickness of more than 10 cm.

10. A polymer foam article as claimed in any one of claims 1 to 7, wherein the polymer foam article comprises a volume greater than 5000 cm3.

11. The polymer foam article of any one of claims 1 to 7, wherein the polymer foam article has a thickness of more than 2 cm and a volume of more than 1000 cm3.

12. The polymer foam article of any one of claims 1 to 7, wherein the polymer foam article has a thickness of more than 5 cm and a volume of more than 1000 cm3.

13. The polymer foam article of any one of claims 1 to 7, wherein the polymer foam article has a thickness of more than 5 cm and a volume of more than 5000 cm3.

14. The polymer foam article of any one of claims 1 to 7, wherein the polymer foam article has a thickness of more than 10 cm and a volume of more than 5000 cm3.

15. A polymer foam article as claimed in any one of claims 1 to 7, wherein the polymer foam article has a density reduction of 30% to 85% compared with the density of the same article without such air pockets.

16. The polymer foam article of any one of claims 1 to 7, wherein the plurality of air bladders and the air bladders having a roundness of less than 0.9 together constitute between 5% and 70% of the volume of the polymer foam article.

17. A polymer foam article as claimed in any one of claims 1 to 7, wherein the polymer foam article is a sphere.

18. A polymer foam article as claimed in any one of claims 1 to 7, wherein the polymer foam article is a cuboid.

19. A polymer foam article as claimed in any one of claims 1 to 7, wherein the polymer foam article comprises a dumbbell shape, a tableware shape, an ornamental globe shape with raised geographical features, a human shape, an animal shape, or a shape suitable for placing a screw or bolt into the polymer foam article.

20. A polymer foam sphere having a diameter of six inches (15.24 cm), nine inches (22.86 cm), or eighteen inches (45.72 cm) and comprising a continuous thermoplastic polymer matrix extending throughout the polymer foam sphere, the continuous thermoplastic polymer matrix defining a plurality of air bladders distributed throughout the polymer foam sphere, wherein a surface region of the polymer foam sphere extending 500 micrometers from its surface includes air bladders distributed throughout the surface region having a sphericity of less than 0.9, wherein the plurality of air bladders and the air bladders having a sphericity of less than 0.9 together constitute 70% or less of the volume of the polymer foam sphere.

21. The polymer foam sphere of claim 20, wherein the polymer foam sphere has a density reduction of 50% to 85% compared to the density of the same sphere without such air pockets.

22. The polymer foam spheres of claim 20, wherein the thermoplastic polymer matrix comprises a mixed stream of plastic waste.

23. The polymer foam sphere of claim 20, wherein the polymer foam sphere is formed by injection molding.

24. The polymer foam sphere of claim 20, wherein the plurality of air bladders and the air bladders having a roundness of less than 0.9 together constitute between 5% and 70% of the volume of the polymer foam sphere.

25. A polymer foam cuboid having a thickness greater than 2 cm or a volume greater than 1000 cm³ and comprising a continuous thermoplastic polymer matrix extending throughout the entire polymer foam cuboid, the continuous thermoplastic polymer matrix defining a plurality of air pockets distributed throughout the entire polymer foam cuboid, wherein a surface region of the polymer foam cuboid extending 500 micrometers from its surface includes air pockets distributed throughout the entire surface region having a roundness of less than 0.9, wherein the plurality of air pockets and the air pockets having a roundness of less than 0.9 together constitute 70% or less of the volume of the polymer foam cuboid.

26. The polymer foam cuboid of claim 25, wherein the polymer foam cuboid has a density reduction of 50% to 85% compared to the density of the same cuboid without the air bladders.

27. The polymer foam cuboid of claim 25, wherein the thermoplastic polymer matrix comprises a mixed plastic waste stream.

28. The polymer foam cuboid of claim 25, wherein the polymer foam cuboid is formed by injection molding.

29. The polymer foam cuboid of claim 25, wherein the plurality of air bladders and the air bladders having a roundness of less than 0.9 together constitute between 5% and 70% of the volume of the polymer foam cuboid.

30. A method of forming a polymer foam article as claimed in any one of claims 1 to 19, the method comprising: forming a molten polymer foam in a barrel region of an extruder; and dispensing the molten polymer foam from the extruder into a cavity defined by a die, wherein the cavity is fluidly connected to the extruder and the dispensing comprises unimpeded flow of the molten polymer foam into the cavity, wherein the unimpeded flow is one or more of a coiled melt flow or a folded melt flow inside the cavity.

31. The method of claim 30, wherein the unimpeded flow is pressurized flow.

32. The method of claim 30 or 31, wherein the mold is an aluminum mold.