Thermoplastic polymer foam and preparation method thereof

Abstract

A thermoplastic foam article comprising 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 or porosity greater than 10%.

Description

Cross-reference to related applications

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 509,143, filed June 20, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure generally relates to thermoplastic foams. More specifically, this disclosure relates to injection molding processes and formulations for forming thermoplastic foams having particularly preferred cell structures, physical properties, and mechanical properties. Background Technology

[0003] Some thermoplastic polymers (such as thermoplastic polyurethane (TPU), thermoplastic elastomers (TPE), and thermoplastic vulcanizates (TPV)) exhibit rubber-like mechanical properties, but these materials can be processed using injection molding processes like typical plastics. For example, TPU is a random block copolymer containing hard and soft segments, forming a two-phase microstructure that behaves as a "spring and damper" mechanism, resulting in unique viscoelastic behavior. The hard segments act as physical cross-links, containing numerous chain entanglements and exhibiting chemical cross-linking similar to that in rubber, thus producing elastic behavior; while the soft segments, at room temperature above their glass transition temperature, produce rubber-like behavior. The hard phase, at room temperature below its glass transition temperature, plays a major role in determining permanent deformation, hysteresis, and high modulus. Therefore, TPU exhibits a combination of high elasticity and high abrasion resistance, making it widely used in industries such as aerospace, furniture, and footwear.

[0004] Thermoplastics can be "foamed" by introducing a foaming agent while melting the polymer matrix in an injection molding machine. Foamed thermoplastics typically contain an internal cellular structure. Multiple parameters, including process settings and formulation, control this cellular structure and the final mechanical and physical properties of articles formed from foamed thermoplastics. Selecting the formulation and corresponding process parameters to form a thermoplastic foam with predictable and desired properties is difficult. Typically, articles made from foamed thermoplastics have a uniform cellular structure and non-uniform and undesirable mechanical and physical properties. For example, prior art foamed thermoplastic articles may contain large internal cavities, leading to article failure under load. The structure of prior art thermoplastic foam articles typically comprises two phases: the first phase contains the internal cellular structure, while a thick, solid "skin" layer on the outer surface of the article contains no cellular structure.

[0005] This paper discloses methods, systems, and articles that describe and illustrate the formulation and processing of thermoplastic foams to produce articles with desired physical and mechanical properties controlled by a uniform cell structure throughout the article. Summary of the Invention

[0006] This document discloses thermoplastic foam articles and methods for preparing the same. In one example, the thermoplastic polyurethane foam article comprises a thermoplastic polyurethane composition. The thermoplastic polyurethane composition comprises a foaming agent and a nucleating agent. The average density of the thermoplastic polyurethane foam article is reduced by more than 10%. The thermoplastic polyurethane article has a uniform cell structure throughout the entire article (including from one surface of the article to all other surfaces of the article).

[0007] In another example, a method for forming a thermoplastic polyurethane foam article includes adding a foaming agent and a nucleating agent to a thermoplastic polyurethane composition. The method includes melting the thermoplastic polyurethane composition and forming it into an article having a uniform cell structure. Attached Figure Description

[0008] The accompanying drawings illustrate structures and, together with the detailed embodiments provided below, describe exemplary implementations of the disclosed systems, methods, and apparatus. Where appropriate, similar elements are identified using the same or similar reference numerals. Elements shown as a single component may be replaced by multiple components. Elements shown as multiple components may be replaced by a single component. The drawings may not be drawn to scale. For ease of illustration, the scale of some elements may be exaggerated.

[0009] Figure 1 The structure of a thermoplastic foam product is illustrated schematically.

[0010] Figure 2 The structure of a thermoplastic foam article with ellipsoidal cells is schematically shown.

[0011] Figure 3 It is an image depicting a cross-section of a thermoplastic foam product formed from a formulation using a mixture of GPPS and HIPS as the matrix resin.

[0012] Figure 3A It is a description Figure 3 Enhanced image of the cross-section of the article shown.

[0013] Figure 4 It is an image depicting a prior art thermoplastic foam product formed from a formulation using polyolefin as the matrix resin.

[0014] Figure 5A An exemplary thermoplastic foam article formed by a cylindrical mold is shown schematically.

[0015] Figure 5B This is an example image of the internal cross-section of a TPU foam product.

[0016] Figure 6-8It is a cross-sectional image of a TPU foam product formed according to the molding conditions shown in the corresponding figure, wherein each TPU formulation contains a foaming agent but not a nucleating agent.

[0017] Figure 9 yes Figure 6-8 The summary shown is of TPU foam products.

[0018] Figure 10-14 Images of TPU foam products and / or cross-sectional images of each product are formed according to the molding conditions shown in the corresponding figures, wherein each TPU formulation contains a foaming agent and a nucleating agent.

[0019] Figure 15 These are cross-sectional images of TPU foam products formed using various formulations and molding conditions to control dimensional stability.

[0020] Figure 16 and 17 These are cross-sectional images of TPU foam products formed using various formulations and molding conditions to control the flexibility of the product.

[0021] Figure 18-20 These are scanning electron microscope (SEM) images of TPU foam products formed using various formulations and molding conditions to control the product's shape.

[0022] Figure 21-24 It is a description Figure 18-20 A chart showing the quantitative analysis results of SEM images.

[0023] Figure 25 This is an image of an exemplary apparatus used for testing the compression of TPU foam products.

[0024] Figure 26 This is an exemplary cross-sectional image of a low-density TPU foam product formed according to the molding conditions shown in the figure.

[0025] Figure 27 It is an image depicting the average compressive stress-strain curve of a low-density TPU foam product.

[0026] Figure 28-31 These are SEM images of the cell structure of low-density TPU foam products before and after compression tests, showing the superimposed analysis of horizontal and vertical cross-sectional samples.

[0027] Figure 32 and 33 It is a description Figure 28-31 A chart showing the results of quantitative analysis of SEM images.

[0028] Figure 34 It is a description Figure 32 and 33 A chart showing the average values ​​of the morphological analysis results.

[0029] Figure 35 This is an exemplary cross-sectional image of a high-density TPU foam product formed according to the molding conditions shown in the figure.

[0030] Figure 35 It is a graph depicting the average compressive stress-strain curve of high-density TPU foam products.

[0031] Figure 37-40 These are SEM images of horizontal and vertical cross-sectional samples of high-density TPU foam products before and after compression tests.

[0032] Figure 41 and 42 It is a description Figure 37-40 A chart showing the quantitative analysis results of SEM images.

[0033] Figure 43 It is a description Figure 41 and 42 A chart showing the average values ​​of the morphological analysis results. Detailed Implementation

[0034] The thermoplastic formulations, thermoplastic foam articles, and methods and systems for manufacturing, testing, and characterizing thermoplastic foam articles disclosed herein will be described in detail through embodiments and in conjunction with the accompanying drawings. It should be understood that modifications can be made to the disclosed and described embodiments, arrangements, configurations, components, elements, devices, methods, materials, etc., and may be necessary depending on the specific application. In this disclosure, any description of a particular technique, arrangement, method, etc., is either related to the specific embodiment presented or is merely a general description of that technique, arrangement, method, etc. Unless expressly specified otherwise, the description of specific details or embodiments is not intended and should not be construed as mandatory or restrictive. The following will be combined with… Figures 1 to 43 This document discloses and describes in detail some embodiments of methods for testing and determining process parameters for forming TPU foams with specific preferred physical and morphological characteristics and mechanical properties.

[0035] A molten thermoplastic foam suitable for forming thermoplastic foam articles can be prepared by melting thermoplastic plastic in an injection molding machine and introducing a foaming agent and / or nucleating agent into the molten polymer within the injection molding machine. Subsequently, the molten thermoplastic foam can be injected into a mold cavity, and the mold cavity can be cooled until the thermoplastic foam solidifies, thereby forming a thermoplastic foam article. Based on the techniques, methods, and systems described in this disclosure, the physical and mechanical properties of thermoplastic foam articles can be controlled by controlling the cell structure of the thermoplastic foam article. Preferably, the cell structure of the thermoplastic foam article exhibits cell uniformity throughout the thermoplastic foam article. In one embodiment, cell uniformity includes the consistency of average cell size, cell density, average cell wall thickness, cell shape, roundness (if applicable), and other structural properties that directly affect the physical and mechanical properties of the thermoplastic foam article. As further described herein, consistency of more than one structural property of the cells can produce structural uniformity, which is beneficial to the mechanical and physical properties of the thermoplastic article.

[0036] As used herein, the term "bubble" refers to a cavitation formed in the molten thermoplastic polymer mixture in the injection molding machine and / or in the mold cavity before curing to form a thermoplastic foam article. The term "cell" as used herein refers to a cavitation formed by air bubbles in the final cured thermoplastic foam article. Figure 1 This is a schematic diagram depicting a cross-section of a thermoplastic foam product, illustrating the structural properties of the final cured thermoplastic foam product. Product 2 contains multiple cells 4, and the solid plastic between the cells 4 is called the cell wall 6. The term "cell size" typically refers to the diameter of the cell 4. Figure 1 As shown, the cell size of a product is typically assessed by cutting the product cross-section and measuring the diameter (D) of the cells 4 on a two-dimensional plane. These measurements can then be averaged to determine the average cell size of the product. When the cells are essentially spherical, as... Figure 1 As shown, regardless of how the diameter of each cell is measured, its diameter (D) is generally consistent, and the average of these diameter measurements from multiple cells can be used to calculate the average cell size of the product. However, the shape of cells in thermoplastic foam products can vary depending on the thermoplastic used in the formulation. For example, some thermoplastics form spherical cells after foaming, while others can form ellipsoidal, hexagonal, pentagonal, or generally irregularly shaped cells. Therefore, using a single diameter measurement or other single linear measurement for each cell to determine the cell size and average cell size will lead to inconsistent results. Therefore, for non-spherical cells, two measurements can be taken. For example, for approximately ellipsoidal cells, such as... Figure 2 As shown, the length of the major axis (A) can be measured and recorded. L ) and minor axis length (A SThese measurements can be used together to quantify cell size, as well as to calculate the average cell size.

[0037] As mentioned above, in some cases, when the cells are essentially spherical, it is appropriate to use the cell diameter to determine the cell size and assess the cell uniformity of thermoplastic foam products. Whether a cell is spherical is determined by its roundness value. The term "cell roundness" refers to the degree of roundness of a cell in a two-dimensional cross-sectional view, ranging from 0 to 1, where 1 represents a perfect circle and 0 represents a straight line. The term "cell wall thickness" refers to the distance between two cells (i.e.,...). Figure 1 (See figure 6 in the figure). The term "cell density" refers to the number of cells per cubic centimeter of thermoplastic foam. Figure 3 This is a cross-sectional image of a thermoplastic foam product formed using a formulation with a mixture of general-purpose polystyrene and high-impact polystyrene (GPPS / HIPS) as the matrix resin, employing the process parameters and techniques described herein. Figure 3A yes Figure 3 An enhanced image of the cross-section of the article shown further illustrates the cell structure of the article.

[0038] The formulation can be selected based on the intended application of the resulting thermoplastic foam product to optimize the cell structure specifications, thereby controlling its specific properties, such as physical, morphological, and mechanical properties. Specifically, the mechanical properties of the resulting thermoplastic foam parts can be controlled by adjusting the cell size and cell density of the cell structure.

[0039] Developing thermoplastic foam articles with the desired cell structure that enables the desired physical, morphological, and mechanical properties is challenging. In fact, even at the macroscopic level, thermoplastic foam articles without optimized injection molding formulations and parameters often exhibit undesirable characteristics such as depressions and bubble coalescence. Bubble coalescence refers to the phenomenon where multiple bubbles coalesce to form a much larger bubble while the thermoplastic foam is in a molten state, ultimately resulting in a large open cavity (called a "coalesced pocket") within the thermoplastic foam article. Such coalesced pockets are typically much larger than the average cell size of the thermoplastic foam. In one embodiment, a coalesced pocket is any cavity whose linear diameter is more than four times larger than the average maximum linear diameter of the remaining cells. In other embodiments, depending on the specific thermoplastic foam article being evaluated, the ratio between the maximum diameter of the coalesced pocket and the average diameter of the remaining cells can be greater than or less than four times. Such coalesced pockets significantly affect the mechanical properties of thermoplastic foam articles compared to those with few or no coalesced pockets. Figure 4 This is an image depicting a prior art thermoplastic foam product 8 formed from a formulation using polyolefin as the matrix resin. (Example) Figure 4As shown, article 8 contains multiple fused cavities, which affects the mechanical and physical properties of article 8. It is also worth noting that... Figure 4 In the prior art product 8 shown, there is a large area of ​​non-porous region along the edge 9 of product 8, which is essentially a thick skin layer.

[0040] In this disclosure, thermoplastic foam articles are formed by adding a foaming agent and / or a nucleating agent to molten thermoplastic in an injection molding machine. The foaming agent is used to introduce gas into the molten thermoplastic via a physical and / or chemical system, whereby gas molecules form bubbles within the molten thermoplastic after an appropriate pressure drop rate is applied. These bubbles form cells throughout the thermoplastic foam article as the thermoplastic cools and solidifies in a mold cavity into an article. The nucleating agent is used to increase the number of bubbles by providing sites for gas molecules to aggregate and form bubbles. By dispersing the nucleating agent through appropriate mixing, the resulting thermoplastic article has a large number of cells uniformly distributed throughout the thermoplastic foam article, which contributes to the formation of a uniform cell structure throughout the article.

[0041] As described above, the thermoplastic formulation is melted and injected into the mold cavity to form article 10, for example... Figure 5A The article shown is schematic (e.g., a cylinder formed of thermoplastic foam material). Figure 5B This is an image of an exemplary inner surface 12, which is a cross-section of the article 10. This cross-section 12 is used to visualize and inspect the uniformity of the cell structure of the article 10. The formulation and molding conditions (e.g., temperature, injection speed, injection volume, cooling time, etc.) are adjusted to control the quality of the article. Visual inspection of the article 10 and its cross-section 12 allows for the evaluation of the article's structural characteristics.

[0042] While formulations are typically described as containing thermoplastics, they can specifically include thermoplastic polyurethane (TPU), thermoplastic elastomer (TPE), thermoplastic vulcanizate (TPV), or any mixture of these polymers. For example, thermoplastic polyurethane can include polyester TPU, polyether TPU, polycaprolactone TPU, aromatic TPU, or aliphatic TPU. For example, thermoplastic elastomers can include TPE-E or TPE-S (styrene block copolymers). For example, thermoplastic vulcanizates can be mixtures of ethylene propylene diene monomer (EPDM) and polypropylene (PP). These thermoplastics and their formulations are suitable for any suitable injection molding machine and mold cavity to form thermoplastic foam articles.

[0043] In addition to foaming agents and nucleating agents, other additives may be added to the formulations described herein. For example, non-limiting examples of additives may include fibers, pigments, flame retardants, antioxidants, UV absorbers, reinforcing additives, reinforcing materials, static dissipative agents, conductive materials, thermally conductive materials, graphene, carbon black, any combination or mixture of more than one additive, etc.

[0044] When processed using injection molding, the formulation produces thermoplastic articles with a uniform structure. That is, when a cross-sectional view is taken of an injection-molded article produced according to this document (i.e., the article is cut open to reveal its internal structure), the article has the following characteristics: no fused cavities exist; cell size, cell density, cell wall thickness, cell shape, and / or cell roundness (if applicable) are structurally uniform; and the cells extend from one surface of the article to all other surfaces. Because the cells extend from one surface of the article to the other surfaces, the article does not contain a solid plastic "skin" layer as seen in the prior art, which has no cells on the surface of the article.

[0045] Regarding structural uniformity, during the curing of molten thermoplastic foam into a thermoplastic foam product, the distance between the bubbles and the mold cavity wall affects the shape and size of specific cells as bubbles transform into pores. In other words, the portion of the product furthest from the mold cavity wall (i.e., the "core region") is unaffected by the mold cavity wall during curing. However, the portion of the product closest to the mold cavity wall is affected by it during curing (i.e., these pores experience a "surface effect"). The term "core region" primarily describes the internal portion of the product that is unaffected by the mold cavity wall. The shape of the core is not critical; the core simply refers to the portion of the product that is not close to the inner wall of the mold cavity during curing and is therefore not subject to the static effects of the molten formulation flowing and filling the mold cavity under injection force.

[0046] The static forces exerted by the mold cavity wall on the molten thermoplastic during the cooling and solidification process affect the morphology of the product at the mold cavity-product interface, as described below. It should be understood that when molten thermoplastic mixed with foaming agents and / or nucleating agents flows through the mold cavity, the mold cavity wall does not exert static forces on the forming bubbles in the core region; only the molten plastic surrounding the bubbles exerts dynamic and generally balanced forces. Bubbles can grow uniformly before solidifying into cells as gas gathers from various directions and interacts with nucleation sites or existing bubbles. Therefore, cells in the core region are more likely to share similar sizes and consistent shapes with other cells in that region. However, for molten thermoplastic flowing near the mold cavity wall, the mold cavity wall itself exerts static forces on the forming bubbles. Therefore, gas molecules cannot interact with nucleation sites or existing bubbles facing the mold cavity wall. This static force alters the aspect ratio of the bubbles, ultimately leading to longer or elliptical cells. Furthermore, fewer gas molecules interact with the growing bubbles. Therefore, on average, these bubbles are smaller and less uniform in shape than those in the core area of ​​the product.

[0047] Depending on the dimensions of the product, surface effects can have a significant or negligible impact on the statistical data of cell uniformity. That is, the smaller the dimensions of the product (measurements from surface to surface, such as the product's thickness), the more significant the impact of surface effects on the overall statistical calculation of the product's cell structure. For example, for a product with a thickness of 3.2 mm, surface effects significantly affect the statistical data of the average cell size; while for a cubic product with a side length of 50 mm, the impact of surface effects on the statistical data of the average cell size is negligible.

[0048] In one embodiment, the terms "structural uniformity" and "structural homogeneity" as used herein refer to a certain percentage of cells in a thermoplastic foam article that are within a certain percentage of the overall average cell size of the article. However, the specific percentage depends on the significance of the surface effect. For example, for TPU foam articles with a small or negligible surface effect, structural uniformity means that approximately 75% of the cells are within 75% of the average cell size of the article. In another embodiment, for TPU foam articles with a large surface effect, structural uniformity means that approximately 50% of the cells are within 75% of the average cell size of the article. In any TPU foam article, structural uniformity of the core region means that approximately 75% of the cells in the core region are within 75% of the average cell size of that core region. As a general rule, a small surface effect is considered to be present if all dimensions of the article are greater than 50 mm. In other embodiments, structural uniformity also refers to a cell density deviation of no more than about 25% throughout the TPU foam article; and / or, for the TPU foam article, the wall thickness of about 75% of the cells in the article is 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 refers to the roundness of 75% of the cells in the article being in the range of 0.900 to 1.00. The parameters of structural uniformity are exemplary, and it should be understood upon reading this disclosure that other parameters can be set to achieve structural uniformity depending on the specific details and circumstances of the formulation, process, and resulting thermoplastic article. The basic principle is that a uniform cell structure leads to the desired mechanical and physical properties.

[0049] As described above, in some embodiments, the article prepared by the inventive method described herein is characterized by having a uniform structure. Specifically, in one embodiment, a uniform structure means that the article contains pores from one outer surface through the entire article to all other outer surfaces. That is, the edges of the outer surfaces also have a pore structure containing pores. However, as previously mentioned, due to the forces exerted on the article by the mold cavity wall during curing, the pores adjacent to the mold cavity wall and forming the outer surface of the article will inevitably be subjected to forces that are not experienced by the core region of the article. Therefore, although a uniform structure does give the entire article a consistent pore structure, the pores located at or near the edges may differ in shape, density, or size from the pores in the core region of the article. Nevertheless, these differences in the pore structure located on the outer surface of the article do not affect the overall performance of the article, and, with minimal surface effects, still meet the definition that approximately 75% of the pores in the entire article are within 75% of the average pore size. The differences in shape, density, or size of the cells located near the outer surface of the product are not actually "skin" because they are basically similar to the cells in the core area of ​​the product. However, as mentioned above, due to their direct contact with the mold cavity wall, they will inevitably be subjected to different physical forces.

[0050] Therefore, as described above, even taking surface effects into account, articles produced according to the method of the present invention have a remarkably uniform structure and can generally be described as having approximately 75% of the cells within 75% of the average cell size. As previously mentioned, this description of article uniformity may vary with the thickness of the article. That is, the considerations for an article with a thickness of 3.2 mm will necessarily differ from those for articles with a thickness of 25 mm or 250 mm. For articles with a maximum thickness of 3.2 mm, a more suitable definition of structural uniformity could be approximately 50% of the cells within 75% of the average cell size. For articles with a maximum thickness of 25 mm, a more suitable definition of structural uniformity could be approximately 50% to 75% of the cells within 75% of the article's average cell size. It should be understood that when the thickness of the article is on the order of millimeters rather than tens or hundreds of millimeters, the statistical effect of surface effects on cell characteristics is more significant, thereby reducing the percentage of cells within 75% of the average cell size.

[0051] Furthermore, for any article having a uniform structure and produced according to the inventive method described herein, regardless of thickness, it can be described as follows: approximately 50% to 75% of the cells are within 75% of the average cell size, or approximately 60% to 75% of the cells are within 75% of the average cell size, or any single value within this range, such as approximately 62.5% of the cells being within 75% of the average cell size. Structural uniformity can also be described as follows: the deviation between the cell density of any single region of the article and the cell density of any other region of the article does not exceed approximately 25%.

[0052] The formulations described herein are characterized by uniformity in cell size, cell density, cell wall thickness, and roundness (if applicable), regardless of the total number of cells. That is, the methods described herein provide articles with a uniform structure, ranging from approximately 5% to approximately 80% in weight reduction. In other words, regardless of the absolute number of cells in the article, the cells are uniformly distributed throughout the article. According to some embodiments, the weight reduction may be some value between 5% and 80%, such as 62%, or any subrange within the range of 5% to 80%, such as 5% to 20% or 65% to 80%. In other words, these embodiments describe an effective method for producing a wide variety of products, all of which possess the characteristic of structural uniformity in articles produced according to the methods described herein.

[0053] Articles produced by the formulations and methods disclosed herein exhibit structural uniformity, resulting in consistent performance in terms of stiffness or compressibility and density within individual articles and among multiple articles as a whole. This is because the method significantly reduces the possibility of fused cavities and produces a consistent and uniform cell distribution throughout the molded article. Cell size, cell density, and cell wall thickness work together to provide the desired properties of the article, and the structural uniformity of the entire article is a key advantage of the method described herein.

[0054] In one embodiment, the injection molding machine includes a melting zone for mixing raw materials and hoppers for storing and conveying the raw materials to the melting zone. The injection molding machine can be configured to simultaneously deliver a thermoplastic polymer, a foaming agent, and / or a nucleating agent to the melting zone. Of course, "simultaneously" allows for slight differences in timing, as long as the foaming agent and nucleating agent have been added to and thoroughly mixed with the thermoplastic polymer before it reaches a temperature at which it is 100% melted. This process ensures that the raw materials are substantially homogeneous before the formulation is injected into the mold cavity to form the article. In some embodiments, the injection molding machine also includes multiple hoppers for storing different mixture components (e.g., thermoplastic polymer, foaming agent) separately and conveying them to the melting zone of the injection molding machine nearly simultaneously. Other raw materials injected into the melting zone of the injection molding machine include gaseous and liquid foaming agents. In one embodiment, the injection of gaseous and / or liquid foaming agents into the injection molding machine can be performed outside the melting zone, or both in the melting zone and at other locations.

[0055] One of the advantages of manufacturing articles using thermoplastic foam is the reduction in article weight. Several exemplary TPU foam articles are described below, along with cross-sectional images and an analysis of density reduction. Figure 6-8 In the illustrated embodiments, the TPU foam product is made from molten TPU and a foaming agent, the foaming agent content being from about 0.01 wt.% to about 2.5 wt.% (nucleating agents are not present in these embodiments). These raw materials are melted and mixed within an injection molding machine. The corresponding molding conditions are also shown in the figures. For example, the TPU formulation is fed into the injection molding machine through a feed inlet, flows through four different temperature zones (e.g., from zone 4 downstream to zones 3, 2, and 1), and then is injected into the mold cavity through a nozzle zone (e.g., from nozzle 2 downstream to nozzle 1). The temperature is controlled and varied at each stage or zone of the injection molding machine. Figure 6-8 This demonstrates the effect of foaming agent concentration on cell structure.

[0056] Figure 6A cross-sectional image of exemplary article 16 is shown. The TPU formulation of article 16 uses an appropriate amount of foaming agent, and article 16 has some wrinkling at its center. Article 16 has a slightly yellowish tint, which is likely due to phase separation. The cell structure near surface 18 (opposite to core portion 20) appears uniform.

[0057] Figure 7 A cross-sectional image of another exemplary article 22 is shown. The TPU formulation of article 22 uses a relatively low amount of blowing agent. Except for a few fusion cavities 23, article 22 has a relatively uniform cell structure. Article 22 shows slightly fewer signs of phase separation, which may be attributed to an excessively high blowing agent content or an excessively long residence time. The weld line 24 formed by the fusion of the flow front shows a finer and denser cell structure.

[0058] Figure 8 A cross-sectional image of another exemplary article 32 is shown. The TPU formulation of article 32 uses an appropriate amount of foaming agent. Except for a few fusion cavities 33, article 32 has a relatively uniform cell structure. Article 32 exhibits a low level of phase separation, which may be attributed to excessive foaming agent content, excessive residence time, or excessive moisture content. Article 32 does exhibit some degree of poor dimensional stability and may require a longer cooling time.

[0059] Figure 9 This paper summarizes products 16, 22, and 32, along with their corresponding molding conditions. Variations in formulation and molding conditions have a significant impact on the appearance and dimensional stability of TPU foam products.

[0060] exist Figure 10-14 The TPU foam articles shown are formed by adding approximately 0.01 wt.% to approximately 2 wt.% of a nucleating agent and approximately 0.01 wt.% to approximately 2.5 wt.% of a foaming agent to molten TPU in an injection molding machine. The corresponding molding conditions are also shown in the figures. These articles demonstrate the effect of using both a foaming agent and a nucleating agent simultaneously (compared to...). Figure 6-8 Compared to products that only use foaming agents.

[0061] Figure 10 Images of another exemplary article 38 formed according to the molding conditions shown in the figure, and an image of a cross-section 40 of the article, are displayed. Articles 38 and 40 exhibit a uniform cell structure, except for a few fused cavities. Although article 38 is over-expanded, it does not completely fill all corners of the mold.

[0062] Figure 11Images of another exemplary article 42 formed according to the molding conditions shown in the figure, and an image of a cross-section 44 of the article, are displayed. Both articles 42 and 44 exhibit a uniform cell structure. Articles 42 and 44 have excellent surface finish. Signs of expansion and a certain degree of indentation affect dimensional stability.

[0063] Figure 12 An image of another exemplary article 46 is shown, formed under the molding conditions illustrated in the figure. Article 46 exhibits a uniform cell structure. The surface finish is excellent. However, the lower melt temperature adversely affects density, and the article shows signs of depression (e.g., poor dimensional stability).

[0064] Figure 13 A cross-sectional image of another exemplary article 48 is shown, which is formed under the molding conditions illustrated in the figure. Article 48 exhibits a uniform cell structure. The surface finish is excellent. However, signs of expansion and some degree of indentation affect dimensional stability.

[0065] Figure 14 A cross-sectional image of another exemplary article 50 is shown, which is formed under the molding conditions illustrated in the figure. Article 50 exhibits a uniform cell structure. The surface finish is excellent. However, signs of expansion and some degree of indentation affect dimensional stability.

[0066] According to the experimental results, the dimensional stability was improved with the increase of nucleating agent content and the extension of cooling time; at the same time, the density reduction was improved with the increase of foaming agent content. Figure 15 These are cross-sectional images of a series of articles 52, 54, 56, 58, 60, 62, and 64. All articles 52, 54, 56, 58, 60, 62, and 64 were manufactured under the following molding conditions: inlet temperature 60°C, zone 4 temperature 200°C, zone 3 temperature 200°C, zone 2 temperature 210°C, zone 1 temperature 215.6°C, nozzle 2 temperature 221.1°C, nozzle 1 temperature 221.1°C, and injection speed of 1 cubic inch per second (in). 3 / sec).

[0067] Product 52 uses 18 cubic inches (in) 3 It was prepared using an injection volume of [insert injection rate here] and a cooling time of 220 seconds. It exhibited excellent surface smoothness and a uniform pore structure. However, signs of expansion were observed, indicating poor dimensional stability.

[0068] Product 54 uses 17.5 in 3 The product was prepared using a specific injection volume and a cooling time of 300 seconds. Product 54 exhibits a uniform cell structure, excellent surface finish, and excellent dimensional stability.

[0069] Product 56 uses 17.5 in 3 The product was prepared using a specific injection volume and a cooling time of 300 seconds. Product 56 exhibits a uniform cell structure, excellent surface finish, and excellent dimensional stability.

[0070] Product 58 uses 17 in 3 The product was prepared using a specific injection volume and a cooling time of 300 seconds. Product 58 exhibits a uniform cell structure, excellent surface finish, and excellent dimensional stability.

[0071] Product 60 uses 16 in 3 The product was prepared using a specific injection volume and a cooling time of 300 seconds. Product 60 exhibits a uniform cell structure, excellent surface finish, and excellent dimensional stability.

[0072] Product 62 uses 18.5 in 3 The product was prepared using a specific injection volume and a cooling time of 220 seconds. Product 62 exhibited excellent surface finish and a uniform cell structure. However, inconsistencies in flatness were observed, indicating poor dimensional stability.

[0073] Product 64 uses 19.5 in 3 The sample was prepared using a specific injection volume and a cooling time of 300 seconds. Product 64 exhibited excellent surface finish and a uniform cell structure. However, signs of depressions were observed, indicating poor dimensional stability.

[0074] Figure 16 and Figure 17 The images show cross-sectional views of articles 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, and 88, for which the TPU formulation and molding conditions were adjusted to achieve the desired article flexibility. Articles 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, and 88 were prepared based on the following molding conditions: inlet temperature 60°C, zone 4 temperature 200°C, zone 3 temperature 200°C, zone 2 temperature 210°C, zone 1 temperature 215.6°C, nozzle 2 temperature 221.1°C, nozzle 1 temperature 221.1°C, and injection speed 1 in [time range]. 3 / Second.

[0075] Product 66 uses 22 in 3 The product was prepared using a specific injection volume and a cooling time of 300 seconds. Product 66 exhibited excellent surface finish and a uniform cell structure. However, inconsistencies in flatness were observed, indicating poor dimensional stability. The density was reduced by 23% (compared to the density reduction of "solid" TPU made without added foaming and nucleating agents).

[0076] Product 68 uses 22 in 3The product was prepared using a specific injection volume and a cooling time of 300 seconds. Product 68 exhibited excellent surface finish and a uniform cell structure. However, inconsistencies in flatness were observed, indicating poor dimensional stability. The density decreased by 27%.

[0077] Product 70 uses 22 in 3 The product was prepared using a specific injection volume and a cooling time of 300 seconds. Product 70 exhibited excellent surface finish and a uniform cell structure. However, inconsistencies in flatness were observed, indicating poor dimensional stability. The density decreased by 27%.

[0078] Product 72 uses 22 in 3 The product was prepared using a specific injection volume and a cooling time of 300 seconds. Product 72 exhibited excellent surface finish and a uniform cell structure. However, inconsistencies in flatness were observed, indicating poor dimensional stability. The density decreased by 27%.

[0079] Product 74 uses 24 in 3 The product was prepared using a specific injection volume and a cooling time of 300 seconds. Product 74 exhibits excellent surface finish and a uniform cell structure. However, product 74 may be too dense, making it difficult to obtain burr-free, flat parts. The density decreased by 16%.

[0080] Product 76 uses 24 in 3 The product was prepared using a specific injection volume and a cooling time of 300 seconds. Product 76 exhibited excellent surface finish and a uniform cell structure. However, the flatness of product 76 was inconsistent. The density decreased by 15%.

[0081] Product 78 uses 23.5 in 3 The product was prepared using a specific injection volume and a cooling time of 300 seconds. Product 76 exhibited excellent surface finish and a uniform cell structure. However, the flatness of product 76 was inconsistent. The density decreased by 18%.

[0082] Product 80 uses 23 in 3 The product was prepared using a specific injection volume and a cooling time of 300 seconds. Product 76 exhibited excellent surface finish and a uniform cell structure. However, the flatness of product 76 was inconsistent. The density decreased by 19%.

[0083] Product 82 uses 22.75 in 3 The product was prepared using a specific injection volume and a cooling time of 300 seconds. Product 76 exhibited excellent surface finish and a uniform cell structure. However, the flatness of product 76 was inconsistent. The density decreased by 21%.

[0084] Product 84 uses 22.25 in 3The product was prepared using a specific injection volume and a cooling time of 300 seconds. Product 76 exhibited excellent surface finish and a uniform cell structure. However, the flatness of product 76 was inconsistent. The density decreased by 23%.

[0085] Product 86 uses 22.25 in 3 The product was prepared using a specific injection volume and a cooling time of 300 seconds. Product 76 exhibited excellent surface finish and a uniform cell structure. However, the flatness of product 76 was inconsistent. The density decreased by 23%.

[0086] Product 88 uses 19 in 3 The product was prepared using a specific injection volume and a cooling time of 300 seconds. Product 76 exhibited excellent surface finish and a uniform cell structure. However, the flatness of product 76 was inconsistent. The density decreased by 36%.

[0087] Figure 18-20 These are scanning electron microscope (SEM) images of articles (labeled as samples 1-10) formed using a TPU formulation containing approximately 0.01 wt.% to approximately 2.5 wt.% of a foaming agent and approximately 0.01 wt.% to approximately 2 wt.% of a nucleating agent. The content of the foaming agent and nucleating agent was specifically adjusted to control the morphology, thereby controlling the flexibility of the foam.

[0088] Figure 21-24 To display the graphs of the quantitative morphological analysis results of samples 1-10 using image analysis techniques, the analysis was performed on the average pore size (µm), average pore wall thickness (µm), average roundness, and pore density (pores / cm²). 3 This will be carried out in terms of ) aspect. For Figure 21 The average cell size is expressed as a single diameter. Due to the very high roundness (see...), Figure 23 (with a roundness of 0.97 to 0.99), therefore a single diameter can be used instead of the major axis (A). L ) and short axis (A S ).

[0089] based on Figure 6-24 The results show that by changing the TPU formulation and injection molding conditions, cell nucleation and growth can be controlled, thereby producing products with different weight reductions and achieving structural uniformity. For example, by changing the formulation and / or molding conditions, a density reduction of more than 15% can be achieved. For example, by changing the formulation and / or molding conditions, a cell structure with an average cell size of less than 900 micrometers (µm) can be obtained. For example, by changing the formulation and / or molding conditions, a cell structure with an average cell wall thickness greater than 10 µm can be obtained. For example, by changing the formulation and / or molding conditions, an average cell density greater than 1000 cells / cm³ can be obtained. 3 ) has a pore structure.

[0090] In this disclosure, uniaxial compression tests were performed using an Instron 5985 testing machine to quantitatively characterize the flexibility and properties of TPU foam products. 1×1×1-inch cuboid samples were cut from the molded TPU foam products. Figure 25 The image shows an exemplary TPU foam product 90 undergoing a compression test. The test procedure is as follows: (1) Preloading: The sample is compressed in displacement mode at a speed of 10 mm / min until a force of 40 Newtons (N) is reached. This step is to ensure that the moving side of the testing machine is in proper contact with the sample before the formal test; (2) Loading phase: The sample is compressed in displacement mode at a speed of 0.5 mm / min until 50% of the compressive strain is reached; (3) Holding phase: The sample is held at 50% of the compressive strain for 60 seconds; (4) Unloading phase: The sample is unloaded in displacement mode at a speed of 0.5 mm / min until 0% of the compressive strain is reached; (5) Repeat steps (2) to (4) for 6 cycles.

[0091] To ensure consistency of results, 3 to 5 samples from the same batch (e.g., TPU foam products made with the same formulation and molding conditions) were tested. Before and after the compression test (24 hours after removal from the stressed state), the samples were horizontally cut (e.g., along the XY plane of the cuboid sample) and vertically cut (e.g., along the XZ or YZ plane of the cuboid sample), and a comprehensive morphological analysis and measurement (e.g., average cell size, cell wall thickness, and cell density) were performed on these samples to assess the effect of cyclic deformation on the sample morphology.

[0092] Figure 26-34 Images and test results of TPU foam products are shown, which are based on Figure 26 The molding conditions shown are used to form the product, which is labeled as Part A, Part B, and Part C. A cross-sectional image of article 92 is taken from one of Part A, Part B, and Part C. Parts A, B, and C all exhibit a uniform cell structure, excellent surface finish, and a 34% density reduction (relatively low density).

[0093] Figure 27 The average compressive stress-strain curves for cuboid samples from parts A, B, and C are shown over six cycles. By changing the formulation and / or molding conditions, compressive stresses of less than 1.5 MPa can be achieved at approximately 50% of the compressive strain. In the first cycle, the average compressive stress at 50% of the compressive strain is approximately 0.8 MPa. From the second to the sixth cycle, the hysteresis loss due to plastic deformation is negligible.

[0094] Figure 28Example SEM images of the horizontal cross-sections of cuboid samples from parts A, B, and C before the compression test are shown. For comparison, Figure 29 Example SEM images of the horizontal cross-section of cuboid samples from parts A, B, and C 24 hours after the end of the compression test are shown.

[0095] Figure 30 Example SEM images of the vertical cross-sections of cuboid samples from parts A, B, and C before the compression test are shown. For comparison, Figure 31 Example SEM images of the vertical cross-section of cuboid samples from parts A, B, and C 24 hours after the end of the compression test are shown.

[0096] Will Figure 28 and Figure 30 The pore profile of the uncompressed sample shown is superimposed on... Figure 29 and Figure 31 As shown in the superposition analysis of the cell profiles of the compressed sample, these cell structures exhibit excellent recovery / shape memory properties; after stress removal, the foam recovers to a structure close to its original shape. This shape memory / recovery capability can also be observed in the following quantitative cell structure analysis results.

[0097] Analyze using image analysis techniques Figure 28-31 The shape of the SEM image shown. Figure 32 and Figure 33 The paper summarizes the cell size (µm) and cell density (cells / cm³) of the horizontal and vertical sections of the cuboid samples in parts A, B, and C before and after the compression test. 3 ) and roundness. Figure 34 The paper summarizes the average cell size (µm) and cell density (cells / cm³) of the horizontal and vertical sections of the cuboid samples in parts A, B, and C before and after the compression test. 3 The compressed sample, after 24 hours of recovery, showed no significant deviations in cell size, cell density, and roundness from the original values.

[0098] Figure 35-43 Images and test results of TPU foam products are shown, which are based on Figure 35 The products were manufactured under the molding conditions shown and are labeled as parts D, E, and F. The image of cross-section 94 is taken from one of parts D, E, and F. Parts D, E, and F all exhibit a uniform cell structure, excellent surface finish, and a 24% density reduction (relatively high density).

[0099] Figure 36The average compressive stress-strain curves for cuboid samples from parts D, E, and F are shown over six cycles. By changing the formulation and / or molding conditions, compressive stresses of less than 1.5 MPa can be achieved at approximately 50% compressive strain. In the first cycle, the average compressive stress at 50% compressive strain is approximately 1.35 MPa. From the second to the sixth cycle, hysteresis losses due to plastic deformation are negligible.

[0100] Figure 37 Example SEM images of the horizontal cross-sections of cuboid samples from parts D, E, and F before the compression test are shown. For comparison, Figure 38 Example SEM images of the horizontal cross-section of cuboid samples from parts D, E, and F 24 hours after the end of the compression test are shown.

[0101] Figure 39 Example SEM images of the vertical cross-sections of cuboid samples from parts D, E, and F before the compression test are shown. For comparison, Figure 40 Example SEM images of the vertical cross-section of cuboid samples from parts D, E, and F 24 hours after the end of the compression test are shown.

[0102] Will Figure 37 and Figure 39 The pore profile of the uncompressed sample shown is superimposed on... Figure 38 and Figure 40 As shown in the superposition analysis of the cell profiles of the compressed sample, these cell structures exhibit excellent recovery / shape memory properties; after stress removal, the foam recovers to a structure close to its original shape. This shape memory / recovery capability can also be observed in the following quantitative cell structure analysis results.

[0103] Analyze using image analysis techniques Figure 37-40 The shape of the SEM image shown. Figure 41 and Figure 42 The paper summarizes the cell size (µm), cell density (cells / cm³), and roundness of the cuboid samples in parts D, E, and F before and after the compression test in both horizontal and vertical sections. Figure 43 The paper summarizes the average cell size (µm), cell density (cells / cm³), and roundness of the cuboid samples in parts D, E, and F before and after the compression test in both horizontal and vertical sections.

[0104] After 24 hours of recovery, the compressed sample showed no significant deviation from the original values ​​in terms of cell size, cell density, and roundness.

[0105] The above description of the embodiments is for illustration and explanation only. It is not intended to be exhaustive or to limit the forms described. Numerous modifications can be made based on the above teachings. Some of these modifications have been discussed herein, and others will be understood by those skilled in the art. These embodiments were chosen and described to better illustrate the principles of various embodiments to suit a particular intended use. Of course, the scope is not limited to the embodiments described herein, but can be applied by those skilled in the art to any number of applications and equivalent devices.

Claims

1. A method for forming a foamed article, the method comprising: Thermoplastic polymers are available; A thermoplastic polymer, a foaming agent in a content of 0.01 wt.% to about 5 wt.% and a nucleating agent in a content of about 0.01 wt.% to about 4.0 wt.% are added to the melting zone of an injection molding machine to form a mixture; The mixture is melted in the melting zone of the injection molding machine; Inject the mixture into the mold cavity; Cooling the mold cavity; as well as Remove the product from the mold cavity. The foamed product exhibits uniformity in cell size and density throughout the entire product.

2. The method according to claim 1, wherein, The thermoplastic polymer is selected from thermoplastic polyurethane, thermoplastic elastomer, thermoplastic vulcanized rubber, or mixtures thereof.

3. The method according to claim 1, wherein, The injection molding machine also includes at least one hopper for storing thermoplastic polymers, foaming agents and / or nucleating agents, and is configured to selectively deliver the thermoplastic polymers, foaming agents and / or nucleating agents to the melting zone of the injection molding machine.

4. The method according to claim 1, wherein, The thermoplastic polymer, foaming agent, and / or nucleating agent are simultaneously fed into the melting zone of the injection molding machine, where they are mixed until the mixture reaches a homogeneous state.

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

6. The method according to claim 1, wherein, The mixture also contains additives.

7. The method according to claim 1, wherein, The resulting product exhibits a uniform cell structure from one outer surface to the other.

8. The method according to claim 1, wherein, The resulting product exhibits uniform cell structure in terms of cell wall thickness.

9. The method according to claim 1, wherein, The foamed product has a pore size of less than 900 μm.

10. The method according to claim 6, wherein, The foamed product has a cell size of 200μm to 600μm.

11. The method according to claim 1, wherein, The foamed product has a cell density greater than 1000 cells / cm³. 3 .

12. The method according to claim 8, wherein, The foamed product has a cell density of 1000 cells / cm³. 3 Up to 60,000 bubbles / cm 3 .

13. The method according to claim 1, wherein, The article is characterized by its consistent responsiveness across multiple compressive stress cycles.

14. A thermoplastic polymer foam article comprising a mixture of the following components: Thermoplastic polymers; A foaming agent in a content of 0.01 wt.% to about 2.5 wt.%; and Nucleating agent in a content of about 0.01 wt.% to about 2.0 wt.%; in, The molding conditions for the thermoplastic foamed article include an injection temperature of 190°C to 245°C; and The thermoplastic foam products formed by this process are characterized by the uniformity of cell size and cell density throughout the product.

15. The article of claim 14, wherein, The foamed product has a cell size of 200μm to 600μm.

16. The article of claim 14, wherein, The foamed product has a cell density of 1000 cells / cm³. 3 Up to 60,000 bubbles / cm 3 .

17. The article of claim 14, wherein, 75% of the bubbles have a roundness of 0.900 to 1.

00.

18. The article of claim 14, wherein, The product is characterized in that its compressive stress is less than 1.5 MPa.

19. The article of claim 4, wherein, The article is characterized by its consistent responsiveness across multiple compressive stress cycles.

20. The article of claim 14, wherein, The mixture also contains additives.

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