Thermoplastic polymer foam and method for producing the same

Abstract

The thermoplastic foam article contains a thermoplastic polyurethane composition. The thermoplastic polyurethane composition contains a blowing agent and a nucleating agent. The thermoplastic polyurethane foam article exhibits an average density reduction or a porosity exceeding 10%.

Description

[Technical Field]

[0001] (Cross-reference of related applications) This application claims priority to U.S. Provisional Patent Application No. 63 / 509,143, filed on 20 June 2024, which is incorporated herein by reference in its entirety.

[0002] This disclosure relates in general to thermoplastic foams. More specifically, this disclosure relates to injection molding processes and formulations for forming thermoplastic foams having certain preferred cellular structures, physical properties and mechanical properties. [Background technology]

[0003] Certain thermoplastic polymers, such as TPU (thermoplastic polyurethane), TPE (thermoplastic elastomer), and TPV (thermoplastic vulcanized material), possess the mechanical properties of rubber, yet these materials can be processed in injection molding processes similar to general plastic materials. For example, TPU is a randomly segmented copolymer containing hard and soft segments, forming a two-phase microstructure that functions as a "spring and dashpot" mechanism. This mechanism results in unique viscoelastic behavior. The hard segments act as physical crosslinks involving a large number of chain entanglements, functioning similarly to the chemical crosslinking of rubber and exhibiting elastomer behavior. The soft segments, on the other hand, are above their glass transition temperature at room temperature and exhibit rubber-like behavior. The hard phase is below its glass transition temperature at room temperature and plays a major role in determining permanent deformation, hysteresis, and high modulus. As a result, TPU exhibits high elasticity along with high abrasion resistance, and has a wide range of applications in industries such as aerospace, furniture, and footwear.

[0004] Thermoplastic materials can be "foamed" by introducing a foaming agent into a polymer matrix molten in an injection molding machine. Foamed thermoplastic materials typically have a cellular structure inside. Such cellular structures in articles formed from foamed thermoplastic materials, as well as the resulting mechanical and physical properties, are controlled by several parameters, including processing settings and formulations. Selecting formulations and corresponding process parameters to form thermoplastic foams with predictable and desirable properties is challenging. Articles formed from foamed thermoplastic materials often have inconsistent cellular structures and inconsistent and undesirable mechanical and physical properties. For example, conventional foamed thermoplastic articles may have large internal cavities that cause the article to break when a load is applied. The structure of conventional thermoplastic foam articles typically consists of two phases: a first phase containing the internal cellular structure, and a thick, solid "skin" layer located on the outer surface of the article that does not contain the cellular structure.

[0005] The methods, systems, and articles disclosed herein describe and illustrate thermoplastic foam formulations and processes that result in articles having desirable physical and mechanical properties controlled by a consistent cellular structure throughout the article. [Overview of the project] [Means for solving the problem]

[0006] This specification discloses thermoplastic foam articles and methods for manufacturing the same. In one example, the thermoplastic polyurethane foam article includes a thermoplastic polyurethane composition. The thermoplastic polyurethane composition includes a blowing agent and a nucleating agent. The thermoplastic polyurethane foam article has an average density reduction of more than 10%. The thermoplastic polyurethane article has a uniform cellular structure throughout the article, from one surface to all other surfaces of the article.

[0007] In another example, a method of forming a thermoplastic polyurethane foam article includes providing a thermoplastic polyurethane composition comprising a blowing agent and a nucleating agent. The method includes melting the thermoplastic polyurethane composition and shaping it into an article having a uniform cell structure.

[0008] The accompanying drawings, together with the following detailed description, illustrate the structure of exemplary embodiments of the disclosed systems, methods, and apparatuses. Like elements are appropriately labeled with the same or similar reference numerals. Elements shown as a single member may be replaced by multiple members. Elements shown as multiple members may be replaced by a single member. The drawings may not be to scale. For the sake of explanation, the ratios of certain elements may be exaggerated.

Brief Description of the Drawings

[0009] [Figure 1] A diagram schematically showing the structure of a thermoplastic foam article. [Figure 2] A diagram schematically showing the structure of a thermoplastic foam article having elliptical cells. [Figure 3] An image showing a cross-section of a thermoplastic foam article formed from a blend of GPPS and HIPS as the base resin. [Figure 3A] An enlarged image showing the cross-section of the article of FIG. 3. [Figure 4] An image showing a prior art thermoplastic foam article formed from a formulation using a polyolefin as the base resin. [Figure 5A] A diagram schematically showing an example of a thermoplastic foam article formed from a cylindrical mold. [Figure 5B] An exemplary image of a cross-section inside a TPU foam article. [Figure 6] A cross-sectional image of a TPU foam article formed under the molding conditions shown in the figure, where the TPU formulation contains a blowing agent but no nucleating agent. [Figure 7] A cross-sectional image of a TPU foam article formed under the molding conditions shown in the figure, where the TPU formulation contains a blowing agent but no nucleating agent. [Figure 8] Cross-sectional image of a TPU foam article formed by the molding conditions shown in the figure, in which the TPU compound contains a foaming agent but does not contain a nucleating agent. [Figure 9] Figures 6-8 show an overview of the TPU foam articles. [Figure 10] Image and cross-sectional image of a TPU foam article formed by the molding conditions shown in the figure, in which the TPU compound contains both a foaming agent and a nucleating agent. [Figure 11] Image and cross-sectional image of a TPU foam article formed by the molding conditions shown in the figure, in which the TPU compound contains both a foaming agent and a nucleating agent. [Figure 12] Image of a TPU foam article formed by the molding conditions shown in the figure, in which the TPU compound contains both a foaming agent and a nucleating agent. [Figure 13] Cross-sectional image of a TPU foam article formed by the molding conditions shown in the figure, in which the TPU compound contains both a foaming agent and a nucleating agent. [Figure 14] Cross-sectional image of a TPU foam article formed by the molding conditions shown in the figure, in which the TPU compound contains both a foaming agent and a nucleating agent. [Figure 15] Cross-sectional images of TPU foam articles formed with various formulations and molding conditions to control dimensional stability. [Figure 16] Cross-sectional images of articles formed using various formulations and molding conditions to control the flexibility of TPU foam articles. [Figure 17] Cross-sectional images of articles formed using various formulations and molding conditions to control the flexibility of TPU foam articles. [Figure 18] SEM (scanning electron microscope) images of articles formed under various formulations and molding conditions to control the morphology of TPU foam articles. [Figure 19] SEM (scanning electron microscope) images of articles formed under various formulations and molding conditions to control the morphology of TPU foam articles. [Figure 20] SEM (scanning electron microscope) images of articles formed under various formulations and molding conditions to control the morphology of TPU foam articles. [Figure 21] Graphs showing the quantitative analysis results of SEM images in Figures 18-20. [Figure 22] Graphs showing the quantitative analysis results of SEM images in Figures 18-20. [Figure 23] Graphs showing the quantitative analysis results of SEM images in Figures 18-20. [Figure 24] Graphs showing the quantitative analysis results of SEM images in Figures 18-20. [Figure 25] Image of an exemplary configuration for a compression test to test a TPU foam article. [Figure 26] Exemplary cross-sectional image of a low-density TPU foam article formed under the molding conditions shown in the figure. [Figure 27] A graph showing the average compressive stress-strain curve of a low-density TPU foam article. [Figure 28] SEM image of a horizontal cross-sectional sample of a low-density TPU foam article before compression testing, with cellular structure analysis superimposed. [Figure 29] SEM image of a horizontal cross-sectional sample of a low-density TPU foam article after compression testing, with cellular structure analysis superimposed. [Figure 30] SEM image of a vertical cross-sectional sample of a low-density TPU foam article before compression testing, with cellular structure analysis superimposed. [Figure 31] SEM image of a vertical cross-sectional sample of a low-density TPU foam article after compression testing, with cellular structure analysis superimposed. [Figure 32] The table shows the quantitative analysis results of the SEM images in Figures 28-31. [Figure 33] The table shows the quantitative analysis results of the SEM images in Figures 28-31. [Figure 34] A table showing the average values ​​of the morphological analysis results in Figures 32-33. [Figure 35] Exemplary cross-sectional image of a high-density TPU foam article formed under the molding conditions shown in the figure. [Figure 36] A graph showing the average compressive stress-strain curve of a high-density TPU foam article. [Figure 37] SEM image of a horizontal cross-sectional sample of a high-density TPU foam article before compression testing. [Figure 38]SEM image of a horizontal cross-sectional sample of a high-density TPU foam article after compression testing. [Figure 39] SEM image of a vertical cross-sectional sample of a high-density TPU foam article before compression testing. [Figure 40] SEM image of a vertical cross-sectional sample of a high-density TPU foam article after compression testing. [Figure 41] The table shows the quantitative analysis results of the SEM images in Figures 37-40. [Figure 42] The table shows the quantitative analysis results of the SEM images in Figures 37-40. [Figure 43] A table showing the average values ​​of the morphological analysis results in Figures 41-42. [Modes for carrying out the invention]

[0010] Thermoplastic formulations, thermoplastic foam articles, and methods and systems for manufacturing, testing, and characterizing the thermoplastic foam articles disclosed herein are described in detail by examples with reference to the drawings. It will be understood that the examples, arrangements, configurations, components, elements, apparatus, methods, materials, etc. disclosed and described are modifiable and may be desirable for specific applications. In this disclosure, identification of specific techniques, configurations, methods, etc., is either related to the specific example described or merely a general description of such techniques, configurations, methods, etc. Unless otherwise specified, specific details or example identifications are not intended to be, and should not be interpreted, as essential or limiting. Selected examples of methods for testing and determining processing parameters for forming TPU foams having specific preferred physical and morphological and mechanical properties are disclosed and described in detail with reference to Figures 1-43.

[0011] A molten thermoplastic foam suitable for forming a thermoplastic foam article can be produced by melting a thermoplastic material in an injection molding machine and introducing a blowing agent and / or nucleating agent into the molten polymer in the injection molding machine. The molten thermoplastic foam is then injected into a mold cavity, and the mold cavity is cooled until the thermoplastic foam solidifies and a thermoplastic foam article is formed. The physical and mechanical properties of the thermoplastic foam article can be controlled by controlling the cellular structure of the thermoplastic foam article based on the techniques, methods, and systems described herein. The cellular structure of the thermoplastic foam article is desirable to have cellular uniformity throughout the thermoplastic foam article. In one embodiment, cellular uniformity includes consistency of average cell dimensions, cell density, average cell wall thickness, cell shape, roundness (if applicable), and other structural attributes that directly affect the physical and mechanical properties of the thermoplastic foam article. As further described herein, consistency of one or more cellular structural attributes can result in structural uniformity beneficial to the mechanical and physical properties of the thermoplastic article.

[0012] As used herein, the term “bubble” means a cavity formed in the molten thermoplastic polymer mixture in the injection molding machine and / or mold cavity before solidification into a thermoplastic foam article. As used herein, the term “cell” means a cavity formed from a bubble within the final solidified thermoplastic foam article. Figure 1 is a schematic diagram showing a cross-section of a thermoplastic foam article for examining the structural attributes of the final solidified thermoplastic foam article. Article 2 contains a number of cells 4, and the solid plastic between the cells 4 is referred to as the cell wall 6. The term “cell dimension” usually refers to the diameter of the cell 4. The cell dimension of an article is usually estimated by cutting a cross-section of the article and measuring the diameter (D) of the cell 4 in two dimensions, as shown in Figure 1. These measurements can be averaged to determine the average cell dimension of the article. If the cells are approximately spherical, as shown in Figure 1, the cell diameter (D) is approximately constant regardless of how the diameter of each cell is measured, and the average of these diameter measurements of multiple cells can be used to calculate the average cell dimension of the article. However, the cell shape of a thermoplastic foam article may vary depending on the thermoplastic material used in the formulation. For example, some thermoplastic materials produce spherical cells when foamed, while others may produce elliptical, hexagonal, pentagonal, or generally irregular shapes. Therefore, if cell dimensions and average cell dimensions are determined using a single diameter measurement or other single linear measurement of each cell, the results may be inconsistent. For this reason, two measurements can be used for non-spherical cells. For example, as shown in Figure 2, for a roughly elliptical cell, the length of the major axis (A) L ) and the length of the minor axis (A S These measurements can be taken and recorded, and these measurements can be combined to quantify cell dimensions and calculate average cell dimensions.

[0013] As mentioned above, under certain circumstances, if the cells are approximately spherical, it is appropriate to use the cell diameter to determine the cell dimensions and evaluate the uniformity of the cells in the thermoplastic foam article. Whether a cell is spherical or not is determined by the value of the cell's roundness. "Cell roundness" is a value between 0 and 1 that indicates how circular the cross-section of the cell is when viewed two-dimensionally, where 1 indicates a perfect circle and 0 indicates a line. The term "cell wall thickness" refers to the distance between two cells (i.e., reference numeral 6 in Figure 1). The term "cell density" refers to the number of cells per cubic centimeter of the thermoplastic foam article. Figure 3 is an image of a cross-section of a thermoplastic foam article formed from a mixture of general-purpose polystyrene and high-impact polystyrene (GPPS / HIPS) as the base resin using the processing parameters and techniques described herein. Figure 3A is a magnified image of the cross-section of the article in Figure 3, further illustrating the cellular structure of the article.

[0014] Based on the intended use of the resulting thermoplastic foam article, the formulation can be selected to optimize the specifications of the cellular structure of the thermoplastic foam article, thereby controlling specific properties such as physical properties, morphological properties, and mechanical properties. Specifically, the mechanical properties of the resulting thermoplastic foam member can be controlled by controlling the cell dimensions and cell density of the cellular structure.

[0015] Developing thermoplastic foam articles with desirable cellular structures that yield desirable physical, morphological, and mechanical properties is challenging. Indeed, even at the macro-scale level, thermoplastic foam articles with unoptimized injection molding formulations and parameters often exhibit undesirable characteristics such as sink marks and bubble coalescence. Bubble coalescence is a phenomenon in which multiple bubbles in the molten state of a thermoplastic foam combine to form much larger bubbles, ultimately resulting in the formation of large cavities (referred to as "coalition cavities") within the thermoplastic foam article. Such coalition cavities are typically significantly larger than the average cell of the thermoplastic foam. In one embodiment, a coalition cavity is defined as a cavity with a linear diameter at least four times larger than the average of the largest linear diameters of the other cells. In other embodiments, the ratio of the maximum diameter of a coalition cavity to the average of the remaining cells may be greater or less than four times, depending on the specific thermoplastic foam article being evaluated. Such coalition cavities can significantly impact the mechanical properties of a thermoplastic article compared to a thermoplastic foam article with few or no coalition cavities. Figure 4 is an image showing a conventional thermoplastic foam article 8 formed from a compound using polyolefin as the base resin. As shown in Figure 4, article 8 has several coalescing cavities that affect the mechanical and physical properties of article 8. Also noteworthy in the conventional article 8 in Figure 4 is the prominent presence of a region along the outer periphery 9 of article 8 that is essentially a thick skin layer without cells.

[0016] In this disclosure, thermoplastic foam articles are formed by adding a blowing agent and / or nucleating agent to a molten thermoplastic material in an injection molding machine. The blowing agent is used to introduce gas into the molten thermoplastic material through a physical and / or chemical system, and after an appropriate pressure drop rate is applied, the gas molecules form bubbles in the molten thermoplastic material. As the thermoplastic material cools and solidifies in the mold cavity to become an article, these bubbles become cells throughout the thermoplastic foam article. Nucleating agents are used to increase the number of bubbles by providing places for gas molecules to gather and form bubbles. By properly mixing and dispersing the nucleating agent, a thermoplastic article can be obtained in which a large number of cells are evenly dispersed throughout the thermoplastic foam article, which helps to form a uniform cellular structure throughout the article.

[0017] As described above, an article 10, such as the article schematically shown in Figure 5A (for example, a cylindrical body formed from a thermoplastic foam material), is formed by melting a thermoplastic compound and injecting it into a mold cavity. Figure 5B is an image of an exemplary internal surface 12, which is a cross-section of the article 10. This cross-section 12 is used to show and confirm the uniformity of the cellular structure of the article 10. The compound and molding conditions (temperature, injection speed, shot size, cooling time, etc.) are adjusted to control the quality of the article. The structural properties of the article can be evaluated by visually inspecting the article 10 and its cross-section 12.

[0018] While formulations are generally described as containing thermoplastic materials, they may specifically consist of TPU (thermoplastic polyurethane), TPE (thermoplastic elastomer), TPV (thermoplastic vulcanized material), or a mixture of these polymers. For example, thermoplastic polyurethanes include polyester TPU, polyether TPU, polycaprolactone TPU, aromatic TPU, and aliphatic TPU. For example, thermoplastic elastomers include TPE-E or TPE-S, which is a styrene-based block copolymer. For example, thermoplastic vulcanized material is a mixture of EPDM (ethylene propylene diene monomer) and PP (polypropylene). These thermoplastic materials and their formulations can be used in any suitable injection molding machine and mold cavity to form thermoplastic foam articles.

[0019] Furthermore, in addition to blowing agents and nucleating agents, additives may be added to the formulations described herein. For example, non-limiting examples of additives include fibers, pigments, flame retardants, antioxidants, ultraviolet absorbers, reinforcing additives, reinforcing agents, electrostatic dissipators, electrical conductors, thermal conductive materials, graphene, carbon black, and any combination or mixture of multiple additives.

[0020] By processing the described formulation using an injection molding process, structurally uniform thermoplastic articles can be manufactured. That is, when an injection-molded article manufactured as described herein is viewed in cross-section (i.e., when the article is cut open to reveal its internal structure), the article is characterized by the absence of unified cavities, structural uniformity of cell dimensions, cell density, cell wall thickness, cell shape and / or roundness (if applicable), and the cells extending from one surface of the article to all other surfaces of the article. Because the cells extend from one surface of the article to the other surfaces of the article, the article does not contain a "skin" layer on the surface of the article characterized by solid plastic without cells, as seen in the prior art.

[0021] Regarding structural uniformity, the shape and dimensions of certain cells can be affected by the proximity of bubbles to the mold cavity walls as they transform into cells during the process of molten thermoplastic foam solidifying into a thermoplastic foam article. In other words, the portion of the article that is far from the mold cavity walls (i.e., the "core portion") is not affected by the mold cavity walls during solidification. However, the portion of the article that is close to the mold cavity walls is affected by the mold cavity walls during solidification (i.e., these cells experience a "surface effect"). With respect to the core portion, this term primarily refers to the interior of the article that is not affected by the mold cavity walls. The shape of the core is not necessarily important; it is simply the portion of the article that is not in close proximity to the inner wall of the mold cavity during the article's solidification and is therefore not subjected to the static forces acting on the molten compound that flows into and fills the mold cavity due to the injection force.

[0022] Static forces exerted on the molten thermoplastic by the mold cavity walls during the cooling and solidification of the article can affect the morphology of the article's structure at the interface between the mold cavity and the article, as described below. When molten thermoplastic mixed with a foaming agent and / or nucleating agent flows through the mold cavity, it is understood that for the core portion of the molten thermoplastic, no static forces act on the forming bubbles from the mold cavity walls; only the dynamic and approximately equal forces of the molten resin surrounding the bubbles act. As gases gather from all directions and interact with the nucleating sites or existing bubbles, the bubbles can grow uniformly before solidifying and becoming cells. Therefore, cells in the core portion are likely to have the same dimensions and uniform shape as other cells in the core portion. However, for molten thermoplastic flowing near the mold cavity walls, the walls themselves exert static forces on the forming bubbles. Therefore, gas molecules cannot bond with the nucleating sites or existing bubbles on the side facing the mold cavity walls. The static forces have the effect of altering the aspect ratio of the bubbles, ultimately resulting in more rectangular or elliptical cells. Furthermore, there are fewer gas molecules interacting with the growing bubbles. Consequently, on average, the bubbles are smaller and have less uniform shape than the bubbles in the core of the object.

[0023] Depending on the dimensions of the object, surface effects can have a significant or negligible impact on statistics regarding cell uniformity. In other words, the smaller the dimensions of the object (for example, dimensions measured from surface to surface, such as the thickness of the object), the more pronounced the impact of cells affected by surface effects on the overall statistical calculation of the object's cellular structure. For example, in the case of an object with a thickness of 3.2 mm, the statistics regarding average cell dimensions may be significantly skewed by surface effects, while in the case of an object where all three dimensions are 50 mm cubes, surface effects have a negligible impact on the statistics regarding average cell dimensions.

[0024] In one embodiment, the terms “structural uniformity” and “structurally uniform” as used herein mean that a certain percentage of cells in a thermoplastic foam article are within a certain percentage of the average cell dimensions of the entire article, provided that the specific percentage varies depending on the degree of surface effect. For example, in a TPU foam article with little or negligible surface effect, structural uniformity means that approximately 75% of the cells are within 75% of the average cell dimensions of the article. In another example, in a TPU foam article with a large surface effect, structural uniformity means that approximately 50% of the cells are within 75% of the average cell dimensions of the article. In a TPU foam article, structural uniformity of the core means that approximately 75% of the cells within the core are within 75% of the average cell dimensions of the core. As a general guideline, if all dimensions of an article are 50 mm or greater, the surface effect is considered small. In other embodiments, structural uniformity further means that the cell density deviation throughout the TPU foam article does not exceed about 25%, and / or, for a TPU foam article, about 75% of the cells in the article have a wall thickness within 75% of the average wall thickness of the entire article. In another embodiment, for a thermoplastic foam article having substantially spherical cells, structural uniformity means that the roundness of 75% of the cells in the article is within the range of 0.900 to 1.00. The parameters for structural uniformity are illustrative, and it can be understood from the description of this disclosure that other parameters can be set to obtain structural uniformity based on the specific details and circumstances of the formulation, process, and the resulting thermoplastic article. The basic principle is that desirable mechanical and physical properties are achieved because the cellular structure is uniform.

[0025] As described above, in some embodiments, articles manufactured by the methods of the present invention described herein are characterized by a uniform structure. In particular, in one embodiment, a uniform structure means that the article contains cells from one outer surface to all other outer surfaces. That is, even the outermost edges of the outer surfaces have a cellular structure containing cells. However, as described above, the forces applied to the article from the inner wall of the mold cavity during solidification inevitably cause the cells located near the mold cavity wall and forming the outer surface of the article to experience forces that are not present in the internal core of the article. Therefore, although a uniform structure actually forms a consistent cellular structure throughout the article, cells at or near the edges may differ in shape, density, or dimensions from the cells in the core of the article. However, differences in the cellular structure on the outer surface of the article do not impair the overall performance of the article, and furthermore, if the surface effect is small, the definition that approximately 75% of the cells in the entire article are within 75% of the average cell dimensions is satisfied. Differences in the shape, density, or dimensions of cells near the outer surface of the article do not actually constitute a skin. This is because, although these cells are inevitably subjected to different physical forces as they are in direct contact with the mold cavity walls as mentioned above, they are substantially similar to the cells in the core of the article.

[0026] Therefore, as mentioned above, even considering surface effects, articles manufactured by the method of the present invention have a remarkably uniform structure, and in many cases, it can be said that about 75% of the cells are within 75% of the average cell dimensions. As mentioned above, such an expression of uniformity of an article may vary depending on the thickness of the article. That is, an article with a thickness of 3.2 mm necessarily requires different considerations than an article with a thickness of 25 mm or 250 mm. For articles with a maximum thickness of 3.2 mm, it is more appropriate to define structural uniformity as about 50% of the cells being within 75% of the average cell dimensions. For articles with a maximum thickness of 25 mm, it is more appropriate to define structural uniformity as about 50% to 75% of the cells being within 75% of the average cell dimensions of the article. It is understood that when the thickness of an article is around a few millimeters, the statistical effect of surface effects on cell properties becomes more pronounced compared to when it is around tens or hundreds of millimeters, and as a result, the proportion of cells within 75% of the average cell dimensions decreases.

[0027] Furthermore, for any article having a uniform structure and manufactured according to the method of the present invention as described herein, regardless of thickness, it can be expressed that about 50% to 75% of the cells are within 75% of the average cell dimensions, or about 60% to 75% of the cells are within 75% of the average cell dimensions, or any single number within this range, for example, about 62.5% of the cells are within 75% of the average cell dimensions. Structural uniformity can be expressed as the cell density of any part of the article not differing by more than about 25% from that of any other part of the article.

[0028] The formulations described herein are characterized by uniform cell dimensions, cell density, cell wall thickness, and, where applicable, roundness, regardless of the total amount of cells. In other words, the methods described herein provide structurally uniform articles, regardless of whether the weight loss is in the range of about 5% to about 80%. That is, cells are uniformly distributed throughout the article, regardless of the absolute amount of cells in the article. According to some embodiments, the range of weight loss may be a numerical value in the range of 5% to 80%, for example, 62%, or a smaller range within the range of 5% to 80%, for example, 5% to 20% or 65% to 80%, for example. In other words, these embodiments describe a useful method for producing a wide variety of articles, all characterized by the structural uniformity of the articles produced by the methods described herein.

[0029] The structural uniformity of articles produced by the formulations and methods disclosed herein results in consistent properties with respect to stiffness or compressibility and density throughout the article, both within a single article and across multiple articles. This is because the method significantly reduces the possibility of union void formation and achieves a consistent and uniform cell distribution throughout the molded article. Cell dimensions, cell density, and cell wall thickness all interact to achieve the desired properties of the article, and the uniform structure throughout the article is one of the advantages of the method described herein.

[0030] In one embodiment, the injection molding machine comprises a melting region for combining materials and a hopper for containing and delivering the materials to the melting region. The injection molding machine can be configured to deliver a thermoplastic polymer, a blowing agent, and / or a nucleating agent to the melting region of the injection molding machine simultaneously. Of course, simultaneous delivery allows for some timing differences, as long as the blowing agent and nucleating agent are added to the thermoplastic polymer and thoroughly mixed before the thermoplastic polymer reaches a temperature at which it is 100% melted. This process ensures that the materials are substantially homogeneous before the mixture is injected into the mold cavity to form an article. In some embodiments, the injection molding machine also includes multiple hoppers for not only containing different mixed components such as the plastic polymer and blowing agent separately, but also for supplying them to the melting region of the injection molding machine substantially simultaneously. Other materials injected into the melting region by the injection molding machine include gases and liquid blowing agents. In one embodiment, the injection of gases and / or liquid blowing agents into the molding machine may occur in a location other than the melting region, or in the melting region and additional locations.

[0031] One advantage of manufacturing articles from thermoplastic foams is the reduction in the weight of the article. Several exemplary TPU foam articles are described below, along with cross-sectional image analysis and density reduction analysis. In the examples shown in Figures 6-8, the TPU foam articles are manufactured from molten TPU (nucleating agents are absent in these examples) containing approximately 0.01 wt percent (W%) to approximately 2.5 wt percent of foaming agent, and the material is melted and mixed in an injection molding machine. Each figure also shows the corresponding molding conditions. For example, the TPU compound is fed into the injection molding machine from a feed port and flows through four different temperature zones (e.g., moving downstream from zone 4 to zone 3, zone 2, and zone 1), and the TPU compound is injected into the mold cavity through the nozzle region (e.g., moving downstream from nozzle 2 to nozzle 1). The temperature is controlled and varied at various stages or regions of the injection molding machine. Figures 6-8 show the effect of foaming agent concentration on the cellular structure.

[0032] Figure 6 shows a cross-sectional image of an exemplary article 16. The TPU compound of article 16 uses a moderate amount of foaming agent, resulting in slight shrinkage in the center of article 16. Article 16 is slightly yellowish, which is thought to be due to phase separation. The cellular structure near the surface 18 appears uniform (in contrast to the core 20).

[0033] Figure 7 shows a cross-sectional image of another exemplary article 22. The TPU formulation of article 22 contains a relatively small amount of foaming agent. Article 22 exhibits a relatively uniform cellular structure, except for the formation of several coalescing cavities 23. There is slightly less phase separation in article 22, which may be due to an excessive foaming agent content or residence time. The coupling line 24 formed by the leading portions of the converging flows appears to have a more finely condensed cellular structure.

[0034] Figure 8 shows a cross-sectional image of another exemplary article 32. The TPU compound of article 32 contains a moderate amount of foaming agent. Article 32 exhibits a relatively uniform cellular structure, except for a few coalescing cavities 33. Article 32 shows a low degree of phase separation, which may be due to excessive foaming agent content, residence time, or moisture content. Article 32 exhibits somewhat poor dimensional stability and is thought to require a longer cooling time.

[0035] Figure 9 shows an overview of articles 16, 22, and 32 and their respective molding conditions. Differences in formulation and molding conditions have a significant impact on the appearance and dimensional stability of the TPU foam articles.

[0036] In the articles shown in Figures 10-14, TPU foam articles are formed in an injection molding machine by introducing approximately 0.01% to 2.5% by weight of a foaming agent, along with approximately 0.01% to 2% by weight of a nucleating agent, into molten TPU. The corresponding molding conditions are also shown in each figure. These articles demonstrate the effect of using both a foaming agent and a nucleating agent (compared to the articles in Figures 6-8, which contain only a foaming agent).

[0037] Figure 10 shows an image of another exemplary article 38, along with an image of a cross-section 40 of an article formed under the molding conditions shown in the figure. Articles 38 and 40 exhibit a uniform cellular structure except for a few coalescing cavities. Article 38, despite being significantly bulging, does not fill all corners of the mold.

[0038] Figure 11 shows an image of another exemplary article 42, along with an image of a cross-section 44 of an article formed under the molding conditions shown in the figure. Articles 42 and 44 exhibit a uniform cellular structure. Articles 42 and 44 have excellent surface finish properties. Dimensional stability is compromised due to bulging and some degree of sink marks.

[0039] Figure 12 shows an image of another exemplary article 46 formed under the molding conditions shown in the figure. Article 46 exhibits a uniform cellular structure. It also has excellent surface finish properties. However, the low melting temperature negatively affects density reduction, resulting in sink marks (such as reduced dimensional stability) in the article.

[0040] Figure 13 shows a cross-sectional image of another exemplary article 48 formed under the molding conditions shown in the figure. Article 48 has a uniform cellular structure and excellent surface finish properties. However, dimensional stability is compromised by bulging and some degree of sink marks.

[0041] Figure 14 shows a cross-sectional image of another exemplary article 50 formed under the molding conditions shown in the figure. Article 48 exhibits a uniform cellular structure. Surface finish characteristics are also excellent. However, dimensional stability is compromised by bulging and some degree of sink marks.

[0042] According to the experimental results, as the amount of the nucleating agent increases and as the cooling time lengthens, the dimensional stability improves, and as the amount of the foaming agent increases, the density reduction improves. FIG. 15 shows a juxtaposition of images of the cross-sections of articles 52, 54, 56, 58, 60, 62, and 64. All of the articles 52, 54, 56, 58, 60, 62, and 64 were prepared under molding conditions where the temperature of the supply port was 60° C., zone 4 was 200° C., zone 3 was 200° C., zone 2 was 210° C., zone 1 was 215.6° C., nozzle 2 was 221.1° C., nozzle 1 was 221.1° C., and the injection speed was about 16.387 cm 3 / second (1 cubic inch per second (in 3 / second)).

[0043] Article 52 was prepared with a shot size of about 294.967 cm 3 (18 cubic inches (in 3 )) and a cooling time of 220 seconds. It has excellent surface finish and has a uniform cell structure. However, it shows a swelling aspect and its dimensions are unstable.

[0044] Article 54 was prepared with a shot size of about 286.773 cm 3 (17.5 in 3 ) and a cooling time of 300 seconds. Article 54 has a uniform cell structure, excellent surface finish characteristics, and excellent dimensional stability.

[0045] Article 56 was prepared with a shot size of about 286.773 cm 3 (17.5 in 3 ) and a cooling time of 300 seconds. Article 56 shows a uniform cell structure, excellent surface finish characteristics, and excellent dimensional stability.

[0046] Article 58 was prepared with a shot size of about 278.580 cm 3 (17 in 3 ) and a cooling time of 300 seconds. Article 58 shows a uniform cell structure, excellent surface finish characteristics, and excellent dimensional stability.

[0047] Item 60 has a shot size of approximately 262.193 cm. 3 (16in 3 ) and prepared with a cooling time of 300 seconds. Article 60 exhibits a uniform cellular structure, excellent surface finish characteristics, and excellent dimensional stability.

[0048] Item 62 has a shot size of approximately 303.160 cm. 3 (18.5in 3 Article 62 is prepared with a cooling time of 220 seconds. Article 62 exhibits excellent surface finish properties and a uniform cellular structure. However, it shows signs of inconsistent flatness, suggesting a lack of dimensional stability.

[0049] Item 64 has a shot size of approximately 319.547 cm². 3 (19.5in 3 Article 64 is prepared with a cooling time of 300 seconds. Article 64 exhibits excellent surface finish properties and a uniform cellular structure. However, it shows signs of sink marks and suggests a lack of dimensional stability.

[0050] Figures 16 and 17 show cross-sectional images of articles 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, and 88, which have TPU formulations and molding conditions adjusted to achieve the desired flexibility of the articles. All articles 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, and 88 were prepared under molding conditions with temperatures of 60°C at the feed port, 200°C in area 4, 200°C in area 3, 210°C in area 2, 215.6°C in area 1, 221.1°C at nozzle 2, and 221.1°C at nozzle 1, with an injection speed of approximately 16.387 cm 3 / sec(1in 3 It is ( / second).

[0051] Item 66 has a shot size of approximately 360.515 cm². 3 (22in 3The material is prepared with a cooling time of 300 seconds. Article 66 exhibits excellent surface finish characteristics and a uniform cellular structure. However, it shows signs of inconsistent flatness, suggesting a lack of dimensional stability. The density reduction (decrease compared to the density of "solid" TPU manufactured without the use of foaming and nucleating agents) is 23%.

[0052] Item 68 has a shot size of approximately 360.515 cm². 3 (22in 3 The cooling time was set to 300 seconds. Article 68 exhibits excellent surface finish characteristics and a uniform cellular structure. However, it shows inconsistent flatness, suggesting a lack of dimensional stability. The density reduction is 27%.

[0053] Item 70 has a shot size of approximately 360.515 cm². 3 (22in 3 The material was prepared with a cooling time of 300 seconds. Article 70 exhibits excellent surface finish characteristics and a uniform cellular structure. However, it shows inconsistent flatness, suggesting a lack of dimensional stability. The density reduction is 27%.

[0054] Item 72 has a shot size of approximately 360.515 cm². 3 (22in 3 The material was prepared with a cooling time of 300 seconds. Article 72 exhibits excellent surface finish characteristics and a uniform cellular structure. However, it shows inconsistent flatness, suggesting a lack of dimensional stability. The density reduction is 27%.

[0055] Item 74 has a shot size of approximately 393.289 cm². 3 (24in 3 The cooling time is set to 300 seconds. Article 74 exhibits excellent surface finish characteristics and a uniform cellular structure. However, article 74 may be too dense to form a burr-free, flat article. The density reduction is 16%.

[0056] Item 76 has a shot size of approximately 393.289 cm². 3 (24in 3 The cooling time was set to 300 seconds. Article 76 exhibits excellent surface finish characteristics and a uniform cellular structure. However, article 76 does not have consistent flatness. The density reduction is 15%.

[0057] Item 78 has a shot size of approximately 385.096 cm². 3 (23.5in 3 The cooling time was set to 300 seconds. Article 76 exhibits excellent surface finish characteristics and a uniform cellular structure. However, article 76 does not have consistent flatness. The density reduction is 18%.

[0058] Item 80 has a shot size of approximately 376.902 cm². 3 (23in 3 The cooling time was set to 300 seconds. Article 76 exhibits excellent surface finish characteristics and a uniform cellular structure. However, article 76 does not have consistent flatness. The density reduction is 19%.

[0059] Item 82 has a shot size of approximately 372.805 cm². 3 (22.75in 3 The cooling time was set to 300 seconds. Article 76 exhibits excellent surface finish characteristics and a uniform cellular structure. However, article 76 does not have consistent flatness. The density reduction is 21%.

[0060] Item 84 has a shot size of approximately 364.612 cm². 3 (22.25in 3 The cooling time was set to 300 seconds. Article 76 exhibits excellent surface finish characteristics and a uniform cellular structure. However, article 76 does not have consistent flatness. The density reduction is 23%.

[0061] Item 86 has a shot size of approximately 364.612 cm². 3 (22.25in 3The cooling time was set to 300 seconds. Article 76 exhibits excellent surface finish characteristics and a uniform cellular structure. However, article 76 does not have consistent flatness. The density reduction is 23%.

[0062] Item 88 has a shot size of approximately 311.354 cm². 3 (19in 3 The cooling time was set to 300 seconds. Article 76 exhibits excellent surface finish characteristics and a uniform cellular structure. However, article 76 does not have consistent flatness. The density reduction is 36%.

[0063] Figures 18-20 are scanning electron microscope (SEM) images of articles (labeled samples 1-10) formed from TPU formulations containing approximately 0.01% to 2.5% by weight of foaming agent and approximately 0.01% to 2% by weight of nucleating agent. In particular, the flexibility of the foam is controlled by controlling the morphology, which is achieved by adjusting the amounts of foaming agent and nucleating agent.

[0064] Figures 21-24 show the morphology of samples 1-10, obtained by applying image analysis techniques, with the average cell dimensions (μm), average cell wall thickness (μm), average roundness, and cell density (cells / cm²), respectively. 3 This graph shows the results of a quantitative analysis from the perspective of (). Figure 21 shows the average cell dimension as a single diameter. Because the roundness is very high (see Figure 23, roundness is 0.97~0.99), a single diameter is used as the major axis (A L ) and minor axis (A S ) can be used instead.

[0065] Based on the results shown in Figures 6-24, it has been demonstrated that by changing the TPU formulation and mold injection conditions, cell nucleation and growth can be controlled to produce articles with different weight reductions while achieving structural uniformity. For example, by changing the formulation and / or molding conditions, a density reduction of 15% or more can be achieved. For example, by changing the formulation and / or molding conditions, a cellular structure with an average cell dimension of less than 900 micrometers (μm) can be obtained. For example, by changing the formulation and / or molding conditions, a cellular structure with an average cell wall thickness of more than 10 μm can be obtained. For example, by changing the formulation and / or molding conditions, an average cell density of 1000 cells / cubic centimeter (cells / cm) can be obtained. 3 A cellular structure exceeding ) can be obtained.

[0066] This disclosure investigates the quantitative characteristics of the flexibility and performance of TPU foam articles by performing uniaxial compression tests using the Instron 5985 model. From the molded TPU foam article, a rectangular parallelepiped sample of approximately 2.540 cm × 2.540 cm × 2.540 cm (1 × 1 × 1 inch) is cut out. Figure 25 is an image of an exemplary TPU foam article 90 undergoing compression testing. The test procedure is as follows: (1) Preloading: The sample is compressed in displacement mode at a rate of 10 mm / min until a force of 40 Newtons (N) is achieved. This step is to ensure that the moving side of the testing machine is in proper contact with the sample prior to the actual test. (2) Gradient step: The sample is compressed in displacement mode at a rate of 0.5 mm / min until a 50% compressive strain is reached. (3) Holding step: The sample is held at a 50% compressive strain for 60 seconds. (4) Gradient process: Reduce the pressure of the sample at a rate of 0.5 mm / min in displacement mode until 0% compressive strain is reached. (5) Repeat steps (2) to (4) to complete 6 cycles.

[0067] To ensure consistency of results, tests are performed on 3 to 5 samples from the same batch (e.g., TPU foam articles made with the same formulation and molding conditions). Before and after the compression test (24 hours after the sample is released from the stressed state), the sample is cut horizontally (e.g., along the XY plane of a rectangular sample) and vertically (e.g., along the XZ or YZ plane of a rectangular sample), and a complete morphological analysis and measurements (e.g., average cell dimensions, cell wall thickness, and cell density) are performed on these samples to evaluate the effect of periodic deformation on the sample morphology.

[0068] Figures 26–34 show images and results of tests on TPU foam articles (labeled sections A, B, and C) formed under the molding conditions shown in Figure 26. The cross-sectional images of article 92 are from any of sections A, B, and C. Sections A, B, and C consistently show a uniform cellular structure, excellent surface finish, and a 34% density reduction (relatively low density).

[0069] Figure 27 shows the average compressive stress-strain curves over 6 cycles for rectangular parallelepiped samples of sections A, B, and C. By changing the formulation and / or molding conditions, compressive stresses of less than 1.5 megapascals (MPa) can be achieved at approximately 50% compressive strain. In the first cycle, at 50% compressive strain, the average compressive stress is approximately 0.8 megapascals (MPa). Hysteresis loss due to plastic deformation from the second to the sixth cycle is acceptablely small.

[0070] Figure 28 shows examples of SEM images of horizontal sections of rectangular parallelepiped samples A, B, and C before the compression test. For comparison, Figure 29 shows examples of SEM images of horizontal sections of rectangular parallelepiped samples A, B, and C 24 hours after the compression test.

[0071] Figure 30 shows examples of SEM images of vertical cross-sections of rectangular parallelepiped samples A, B, and C before the compression test. For comparison, Figure 31 shows examples of SEM images of vertical cross-sections of rectangular parallelepiped samples A, B, and C 24 hours after the compression test.

[0072] When the cell contours of the uncompressed samples shown in Figures 28 and 30 are superimposed on the cell contours of the compressed samples shown in Figures 29 and 31, this superposition analysis reveals that these cellular structures possess excellent resilience / shape memory, and that the foam returns to a state close to its original structure when stress is removed. This shape memory / recovery ability is also reflected in the results of the following quantitative cellular structure analysis.

[0073] Image analysis techniques are applied to analyze the morphology of the SEM images shown in Figures 28-31. Figures 32-33 show the cell dimensions (μm) and cell density (cells / cm³) in the horizontal and vertical sections of parts A, B, and C of the rectangular parallelepiped sample before and after the compression test. 3 The following values ​​are shown: ) and roundness, respectively. The average cell size (μm) and cell density (cells / cm³) in the horizontal and vertical sections of parts A, B, and C of the rectangular parallelepiped sample before and after the compression test. 3 Figure 34 summarizes the cell dimensions and roundness. The values ​​for cell dimensions, cell density, and roundness of the compressed sample after 24 hours of recovery did not deviate significantly from the original values.

[0074] Figures 35-43 show images and test results of labeled sections D, E, and F of TPU foam articles formed under the molding conditions shown in Figure 35. The cross-sectional images are from one of sections D, E, and F. Sections D, E, and F consistently exhibit a uniform cellular structure, excellent surface finish, and a 24% density reduction (relatively high density).

[0075] Figure 36 shows the average compressive stress-strain curves over 6 cycles for rectangular parallelepiped samples of sections D, E, and F. By changing the formulation and / or molding conditions, compressive stresses of less than 1.5 megapascals (MPa) can be achieved at approximately 50% compressive strain. In the first cycle, at 50% compressive strain, the average compressive stress is approximately 1.35 megapascals (MPa). Hysteresis losses due to plastic deformation from the second to the sixth cycle are small enough to be acceptable.

[0076] Figure 37 shows examples of SEM images of horizontal sections of rectangular parallelepiped samples from sections D, E, and F before the compression test. For comparison, Figure 38 shows examples of SEM images of horizontal sections of rectangular parallelepiped samples from sections D, E, and F 24 hours after the compression test.

[0077] Figure 39 shows examples of SEM images of the vertical sections of the rectangular parallelepiped samples from sections D, E, and F before the compression test. For comparison, Figure 40 shows examples of SEM images of the vertical sections of the rectangular parallelepiped samples from sections D, E, and F 24 hours after the compression test.

[0078] When the cell contours of the uncompressed samples shown in Figures 37 and 39 are superimposed on the cell contours of the compressed samples shown in Figures 38 and 40, this superposition analysis reveals that the cellular structure possesses excellent resilience / shape memory, and that the foam returns to a state close to its original structure when stress is removed. This shape memory / recovery ability is also reflected in the following quantitative cellular structure analysis results.

[0079] Image analysis techniques are applied to analyze the morphology of the SEM images shown in Figures 37-40. Figures 41-42 show the cell dimensions (μm) and cell density (cells / cm³) in the horizontal and vertical sections of parts D, E, and F of the rectangular parallelepiped sample before and after the compression test. 3 The following values ​​are shown: ) and roundness, respectively. The average cell dimensions (μm) and cell density (cells / cm³) in the horizontal and vertical sections of the rectangular parallelepiped samples D, E, and F before and after the compression test. 3 Figure 43 summarizes the characteristics of the surface and roundness.

[0080] The cell dimensions, cell density, and roundness values ​​of the compressed sample after 24 hours of recovery did not deviate significantly from the original values.

[0081] The examples described above are presented for illustrative and illustrative purposes only. They are not exhaustive and do not limit the forms described. Numerous modifications are possible based on the above description. Some such modifications are described above, but others will be understood by those skilled in the art. The examples above have been selected and described to best illustrate the principles of various examples suitable for specific intended applications. Naturally, the scope of the present invention is not limited to the examples described herein and can be applied to any number of applications and equivalent devices by those skilled in the art.

Claims

1. A method for forming a foamed article, To provide a thermoplastic polymer, The thermoplastic polymer, a foaming agent in an amount of 0.01% to about 5% by weight, and a nucleating agent in an amount of about 0.01% to about 4.0% by weight are added to the molten region of an injection molding machine to form a mixture. The mixture is melted within the melting region of the injection molding machine, The mixture is injected into the mold cavity, To cool the mold cavity, This consists of removing the article from the mold cavity, A method for which the cellular structure of the foamed article has structural uniformity in terms of cell dimensions and cell density throughout the entire article.

2. The method according to claim 1, wherein the thermoplastic polymer is selected from thermoplastic polyurethane, thermoplastic elastomer, thermoplastic vulcanized product, or a mixture thereof.

3. The method according to claim 1, wherein the injection molding machine further comprises at least one hopper configured to contain at least one of the thermoplastic polymer, the blowing agent, and the nucleating agent, and to selectively deliver at least one of the thermoplastic polymer, the blowing agent, and the nucleating agent to the molten region of the injection molding machine.

4. The method according to claim 1, wherein at least one of the thermoplastic polymer, the blowing agent, and the nucleating agent is simultaneously delivered to the molten region of the injection molding machine and mixed in the molten region until the mixture reaches a homogeneous state.

5. The method according to claim 1, wherein the mixture is heated to a temperature of about 190°C to 245°C in the injection molding machine.

6. The method according to claim 1, wherein the mixture further contains an additive.

7. The method according to claim 1, wherein the cellular structure of the formed article is structurally uniform from one outer surface to another.

8. The method according to claim 1, wherein the cellular structure of the formed article is structurally uniform with respect to the wall thickness of the cells.

9. The method according to claim 1, wherein the cell dimensions of the foamed article are less than 900 μm.

10. The method according to claim 6, wherein the cell dimensions of the foamed article are 200 μm to 600 μm.

11. The method according to claim 1, wherein the cell density of the foamed article exceeds 1,000 cells / cubic centimeter.

12. The method according to claim 8, wherein the cell density of the foamed article is 1,000 cells / cubic centimeter to 60,000 cells / cubic centimeter.

13. The method according to claim 1, wherein the article is characterized by a consistent response over multiple cycles of compressive stress.

14. A thermoplastic polymer foam article, Thermoplastic polymers and A foaming agent in an amount of 0.01% to approximately 2.5% by weight, It contains a mixture of a nucleating agent in an amount of approximately 0.01% to approximately 2.0% by weight, The molding conditions for the aforementioned thermoplastic foam article include an injection temperature of 190°C to 245°C. The thermoplastic foam article formed by this process is characterized by structural uniformity in cell dimensions and cell density throughout the article, and is a thermoplastic polymer foam article.

15. The article according to claim 14, wherein the cell dimensions of the foamed article are 200 μm to 600 μm.

16. The article according to claim 14, wherein the cell density of the foamed article is 1,000 cells / cubic centimeter to 60,000 cells / cubic centimeter.

17. The article according to claim 14, wherein 75 percent of the cells have a roundness in the range of 0.900 to 1.

00.

18. The article according to claim 14, wherein the article is characterized by a compressive stress of less than 1.5 megapascals.

19. The article according to claim 4, wherein the article is characterized by a consistent response over multiple cycles of compressive stress.

20. The article according to claim 14, wherein the mixture further contains an additive.

Images