Thermoplastic elastomer bead as well as preparation method and application thereof

Abstract

The invention discloses thermoplastic elastomer beads as well as a preparation method and application thereof, and relates to the technical field of foaming materials. The thermoplastic elastomer bead provided by the invention is prepared from the following preparation raw materials in parts by mass: 80 to 99 parts of a thermoplastic elastomer a with the hardness of Shore A 90 to Shore D 75, 5 to 20 parts of a thermoplastic elastomer b with the hardness of Shore A 70 to Shore A 90 and 0.01 to 1 part of a cross-linking agent. The thermoplastic elastomers with different hardness are matched to serve as preparation raw materials, in the subsequent process of preparing a foaming part through the beads, the elastomer b with the low hardness can have the higher migration capacity, can gradually migrate to the surfaces of the beads and can play a role similar to a binder through melting of the elastomer b, and therefore the foaming performance of the beads is improved. The interface bonding between the beads is enhanced, the mechanical strength of the obtained foaming product is improved, and the migration of the thermoplastic elastomer b can promote the permeation of the foaming agent in the foaming process, so that the foaming efficiency and the foaming ratio of the obtained product are improved.

Description

Technical Field

[0001] This invention relates to the field of foaming materials technology, specifically to a thermoplastic elastomer bead, its preparation method, and its application. Background Technology

[0002] Foamed materials are widely used in footwear due to their ultra-low density and excellent elasticity. Currently, the mainstream preparation methods for foamed materials include autoclave bead foaming and molded sheet foaming, with high-ratio foamed materials primarily using bead foaming. However, the bonding between foamed beads is achieved through interfacial bonding during steam molding, typically resulting in low interfacial strength. This leads to lower tensile and tear strength in elastomer foamed materials, limiting the commercial application of thermoplastic elastomer molded products. In particular, when further increasing the foaming ratio and reducing the density of the elastomer foam is required, the tensile and tear strength of the parts decreases significantly, making it difficult for thermoplastic elastomer parts to meet the development requirements of high-quality footwear materials. Therefore, there is an urgent need for a foamed part production formula and process that balances high interfacial strength and excellent lightweight properties. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides thermoplastic elastomer beads, their preparation method, and their applications.

[0004] The above-mentioned objective of this invention is achieved through the following technical solution: A thermoplastic elastomer bead comprises the following raw materials in parts by weight: Thermoplastic elastomer a: 80-99 parts; thermoplastic elastomer b: 5-20 parts; crosslinking agent: 0.01-1 part; The thermoplastic elastomer a includes at least one of TPU, TPEE, and PEBA, with a hardness of Shore A 90-Shore D 75; The thermoplastic elastomer b includes at least one of TPU, TPEE, PEBA, EVA, SEBS, POE, and EPDM, with a hardness of Shore A70-Shore A90; the hardness of the thermoplastic elastomer b is lower than that of the thermoplastic elastomer a. The crosslinking agent includes a peroxide crosslinking agent, and the 1-minute half-life temperature T1 of the crosslinking agent satisfies: T sb +10℃ ≤T1≤T va -10℃, where: T sb T is the softening point of thermoplastic elastomer b. va is the flow point of thermoplastic elastomer a.

[0005] The thermoplastic elastomer beads provided by this invention employ different hardnesses and satisfy a specific softening / flowing temperature relationship (T). sb +10℃≤Tva When thermoplastic elastomers (-10℃) are used as raw materials, in the subsequent process of preparing foamed parts through foaming-molding or molding-foaming processes, thermoplastic elastomer b, which has lower hardness and softening point, has higher migration ability. It can gradually migrate to the surface of the beads and act as a kind of adhesive through its own melting, strengthening the interfacial bonding between the beads and thus improving the mechanical strength of the resulting foamed parts. Moreover, the improved migration ability allows thermoplastic elastomer b to promote the penetration of foaming agent during the foaming process, thereby simultaneously improving the foaming efficiency and the foaming ratio of the resulting parts. It should be noted that only a specific thermoplastic elastomer b with a hardness of Shore A70-Shore A90 can fully balance migration ability and bonding strength. On this basis, the matrix material thermoplastic elastomer a needs to be selected with a hardness of Shore A90-Shore D75, such as TPU, TPEE, and PEBA, so that thermoplastic elastomers a and b have different hardness and thermodynamic properties, ensuring that they have differentiated migration rates. Only in this way can a microstructure of "hard phase as bone and soft phase as rib" be constructed, and the preferential melting and fluidity of the soft phase be utilized during foaming to achieve rapid and high-strength fusion of the particle interface.

[0006] To fully utilize the differences in thermodynamic properties between thermoplastic elastomers a and b, this invention requires selecting a 1-minute half-life temperature T1 that satisfies T... sb +10℃ ≤T1≤T va The peroxide crosslinking agent has a relationship of -10℃. The inventors of this application discovered through experiments that thermoplastic elastomer B, due to its lower hardness, begins molecular chain migration above its softening temperature; while thermoplastic elastomer A, with higher hardness, is difficult to migrate before reaching its flow temperature. Therefore, the 1-minute half-life temperature of the crosslinking agent is above the softening temperature of thermoplastic elastomer B, ensuring that while the crosslinking agent undergoes significant decomposition and initiates crosslinking, thermoplastic elastomer B has already begun to soften and migrate, and can be lightly crosslinked, enhancing interfacial adhesion strength. Conversely, this 1-minute half-life temperature is below the flow temperature of thermoplastic elastomer A, preventing it from melting and migrating prematurely when the crosslinking agent begins to work, thus avoiding premature crosslinking of elastomer A and affecting the foaming ratio. It should be noted that the 1-minute half-life temperature T1 of the crosslinking agent is related to T... sb and T va There needs to be a temperature difference of ≥10℃ between them; if the difference is too small, the crosslinking agent will not be able to play its full role.

[0007] It should be noted that the 1-minute half-life temperature T1 of the crosslinking agent described in this application refers to the temperature at which the peroxide crosslinking agent decomposes and its active oxygen content reaches half within 1 minute. The 1-minute half-life temperature is a value confirmed by dissolving the peroxide crosslinking agent at a concentration of 0.05~0.1 mol / L in a solvent inert to free radicals (such as benzene) and thermally decomposing the peroxide crosslinking agent solution under a nitrogen atmosphere.

[0008] In this application, the softening points of thermoplastic elastomers a and b were determined using a TMA (Thermomechanical Analysis) instrument, referring to standard ASTM E1545. The specific test method includes the following steps: A suitable amount of thermoplastic elastomer particles were taken and placed on the TMA sample stage. A constant load (recommended 0.05~0.5N, preferably 0.1N) was applied, and the sample was heated under a nitrogen atmosphere at a certain heating rate (recommended 5~10℃ / min, preferably 5℃ / min). The sample deformation-temperature curve was recorded. The temperature corresponding to the extrapolated starting point or the deformation reaching a specific value (5%) in the curve was defined as the softening point (T0) of the thermoplastic elastomer. s ).

[0009] In this application, the flow points of thermoplastic elastomers a and b were tested using a capillary rheometer, according to standard ASTM D3835. The specific test method included the following steps: thermoplastic elastomer granules were filled into the barrel of the rheometer, and the flow points were measured at a fixed shear rate (100~5000 s⁻¹). -1 Optimal 1200 s -1 The melt is extruded through a capillary die of a specific size (length-to-diameter ratio L / D = (10~40):1, preferably 20:1) by a piston. Multiple tests are conducted at different temperatures, and the apparent viscosity-temperature relationship of the extruded material is recorded. The temperature at which the apparent viscosity of the polymer melt decreases to a specific critical value (1000 Pa·s), or the temperature at which the melt begins to exhibit stable viscous flow by extrapolating the tangent of the viscosity-temperature curve, is defined as the flow point (T0) of the thermoplastic elastomer. v ).

[0010] Preferably, the hardness of the thermoplastic elastomer a is Shore A 95-Shore D 65.

[0011] Preferably, the softening point T of the thermoplastic elastomer a is... sa The temperature ranges from 120 to 180℃.

[0012] Preferably, the flow point T of the thermoplastic elastomer a is... va The temperature ranges from 180 to 230℃.

[0013] Preferably, the softening point T of the thermoplastic elastomer b is...sb The temperature ranges from 75 to 140℃.

[0014] Preferably, the flow point T of the thermoplastic elastomer b is... vb The temperature ranges from 140 to 190 degrees Celsius.

[0015] Preferably, the thermoplastic elastomer beads have a spherical structure.

[0016] This application does not restrict the distribution of thermoplastic elastomers a and b in the spherical structure beads. For example, thermoplastic elastomers a and b can be uniformly distributed at any position in the spherical structure, or thermoplastic elastomer b can be mainly distributed outside thermoplastic elastomer a, forming a spherical core-shell structure.

[0017] More preferably, the average particle size of the thermoplastic elastomer beads is 0.5-2 mm.

[0018] More preferably, the average particle size of the thermoplastic elastomer beads is 0.8-1.5 mm.

[0019] More preferably, the thermoplastic elastomer beads have a spherical core-shell structure, with the core layer having an average diameter of 0.3-1.995 mm and the shell layer having an average thickness of 5-200 μm.

[0020] The average thickness of the shell as described in this application refers to the difference between the outer diameter and the inner diameter of the shell.

[0021] More preferably, the content of thermoplastic elastomer a in the core layer is greater than the content of thermoplastic elastomer a in the shell layer, and the content of thermoplastic elastomer b in the shell layer is greater than the content of thermoplastic elastomer b in the core layer.

[0022] The spherical core-shell structure, with the core layer mainly composed of thermoplastic elastomer a and the shell mainly composed of thermoplastic elastomer b, can more effectively utilize the thermodynamic and hardness differences between thermoplastic elastomers a and b to construct a microstructure of "hard phase as bone and soft phase as rib". During foaming, the preferential melting and fluidity of the soft phase are utilized to achieve rapid and high-strength fusion of the particle interface, which can further improve the strength of the foamed part while taking into account the foaming ratio.

[0023] More preferably, the average diameter of the core layer in the core-shell thermoplastic elastomer beads is 0.8-1.5 mm, and the average thickness of the shell layer is 10-100 μm.

[0024] Preferably, the thermoplastic elastomer beads further include the following raw materials in parts by weight: Antioxidant 0.1-1 part, hydrolysis resistant agent 0.1-1 part.

[0025] Preferably, the thermoplastic elastomer beads comprise the following raw materials in parts by weight: Thermoplastic elastomer a 80-99 parts, thermoplastic elastomer b 5-20 parts, crosslinking agent 0.01-1 part, antioxidant 0.1-1 part, hydrolysis resistant agent 0.1-1 part.

[0026] More preferably, the crosslinking agent includes at least one of dicumyl peroxide (DCP) and di-tert-butyl peroxide (DTBP).

[0027] More preferably, the crosslinking agent includes at least one of hindered phenolic antioxidants and phosphite antioxidants.

[0028] More preferably, the hindered phenolic antioxidant includes pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010).

[0029] More preferably, the phosphite antioxidant includes tris(2,4-di-tert-butylphenyl) phosphite (antioxidant 168).

[0030] More preferably, the hydrolysis-resistant agent includes a carbodiimide-based hydrolysis-resistant agent. More preferably, the carbodiimide-based hydrolysis-resistant agent includes at least one of N,N'-bis(2,6-diisopropylphenyl)carbodiimide, poly(4,4'-dicyclohexylmethanecarbodiimide), or poly(1,3,5-triisopropylphenyl-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione).

[0031] Preferably, when the thermoplastic elastomer a and thermoplastic elastomer b are uniformly distributed in the spherical thermoplastic elastomer beads, the thermoplastic elastomer beads comprise the following parts by weight of raw materials: 80-90 parts of thermoplastic elastomer a, 10-20 parts of thermoplastic elastomer b, 0.05-0.5 parts of crosslinking agent, 0.1-0.5 parts of antioxidant, and 0.1-0.5 parts of hydrolysis resistant agent.

[0032] For thermoplastic elastomer beads with a uniform spherical structure, in order to ensure that the thermoplastic elastomer b (soft phase) is evenly distributed inside the beads and can effectively migrate to the interface during subsequent hot pressing and sintering, its dosage can be slightly increased to ensure a sufficient source of "binder phase".

[0033] Preferably, when the thermoplastic elastomer beads have a spherical core-shell structure and the content of thermoplastic elastomer a in the core layer is greater than the content of thermoplastic elastomer a in the shell layer, and the content of thermoplastic elastomer b in the shell layer is greater than the content of thermoplastic elastomer b in the core layer, the thermoplastic elastomer beads comprise the following raw materials in parts by weight: 90-99 parts of thermoplastic elastomer a, 1-10 parts of thermoplastic elastomer b, 0.01-0.3 parts of crosslinking agent, 0.1-0.5 parts of antioxidant, and 0.1-0.5 parts of hydrolysis resistant agent.

[0034] In core-shell thermoplastic elastomer beads, thermoplastic elastomer b coats the surface of the core layer with phase a as the core, forming a shell layer. Since this shell layer is located at the most critical foaming interface, and phase b is directly distributed at the foaming interface, the amount of phase b in core-shell thermoplastic elastomer beads can be slightly reduced.

[0035] This invention protects a method for preparing thermoplastic elastomer beads, comprising the following steps: Mix all the raw materials thoroughly, melt, extrude, and granulate to obtain the final product.

[0036] The thermoplastic elastomer beads prepared by the above method have a uniform spherical structure, wherein a and b are evenly distributed at any position within the spherical structure. The average particle size of the thermoplastic elastomer beads can be controlled by adjusting the pelletizing parameters.

[0037] Preferably, the melting and extrusion are carried out in a twin-screw extruder, wherein the temperature range of the extruder is set to 140-210℃, the screw speed is 200-400rpm, the length-to-diameter ratio is 36:1-48:1, and the screw diameter is 35-60mm.

[0038] More preferably, the granulation is underwater pelletizing.

[0039] Preferably, the method for preparing the thermoplastic elastomer beads includes the following steps: S1. Dissolve thermoplastic elastomer b in a solvent to obtain a thermoplastic elastomer b solution; S2. Mix the remaining raw materials, melt, extrude, and granulate to obtain precursor particles; S3. Immerse the precursor particles described in step S2 in the thermoplastic elastomer b solution obtained in step S1, then remove and dry them to obtain the final product.

[0040] The thermoplastic elastomer beads prepared by the above method have a core-shell structure. By adjusting the pelletizing parameters, the concentration of thermoplastic elastomer b in the impregnation solution, and the ratio between the solution and precursor particles, the core layer particle size, shell layer thickness, and overall particle size of the core-shell structure thermoplastic elastomer beads can be controlled. Impregnation coating treatment allows thermoplastic elastomer b to be completely distributed on the surface of thermoplastic elastomer a, forming core-shell structure thermoplastic elastomer beads with a lower hardness thermoplastic elastomer b as the shell and other raw materials as the core. This can more fully promote the migration of b during foaming and molding, thereby further improving the strength and foaming effect of the subsequently obtained foamed parts.

[0041] Preferably, the solvent in step S1 includes an organic solvent. More preferably, the organic solvent includes at least one selected from tetrahydrofuran, chloroform, acetone, and ethanol.

[0042] The preparation method provided by this invention requires the use of a solvent to dissolve the thermoplastic elastomer b in order to achieve its coating on the surface of the precursor particles. The aforementioned organic solvent has a low boiling point, which is beneficial for subsequent removal, and does not significantly corrode the thermoplastic elastomer a during the coating process.

[0043] More preferably, the mass fraction of thermoplastic elastomer b in the thermoplastic elastomer b solution in step S1 is 1%-20%.

[0044] Preferably, the melting and extrusion in step S2 are carried out in a twin-screw extruder, wherein the temperature range of the extruder is set to 150-205℃, the screw speed is 200-350rpm, the length-to-diameter ratio is 36:1-48:1, and the screw diameter is 35-60mm.

[0045] Preferably, the average particle size of the precursor particles in step S2 is 0.3-1.995 mm.

[0046] More preferably, the granulation in step S2 is underwater pelletizing.

[0047] Preferably, the mass ratio of the precursor particles to the thermoplastic elastomer b solution in step S3 is 1:(0.5-2).

[0048] This invention also protects the use of the thermoplastic elastomer beads in the preparation of foamed boards.

[0049] This invention also protects a method for preparing foamed boards, comprising the following steps: A1. Thermoplastic elastomer beads are injected into a mold and hot-pressed and sintered to obtain a precursor sheet; A2. The precursor board obtained in step A1 is immersed in a supercritical fluid until saturation, and then depressurized and foamed to obtain the foamed board.

[0050] The method for preparing foamed boards provided by this invention first involves injecting thermoplastic elastomer beads into a mold and hot-pressing and sintering them to obtain a precursor board with a certain porosity. During the subsequent supercritical fluid foaming process, the pores in the precursor board promote the diffusion of the supercritical fluid. Simultaneously, the plasticizing effect of the supercritical fluid increases the diffusion capacity of the polymer molecular chains, causing the low-hardness thermoplastic elastomer b to gradually migrate to the particle surface, further promoting the sintering of the particle interface. Therefore, this invention not only improves the production efficiency of foamed boards, but also, compared to the conventional batch foaming-steam molding process used for beads, the sintering-formation process allows for a more thorough utilization of the bead formulation and structure adjustments, increasing both the foaming ratio and the strength of the resulting foamed board.

[0051] Preferably, the hot pressing sintering temperature in step A1 is T. sb-T va .

[0052] The hot pressing sintering temperature described in this invention is lower than the flow point of thermoplastic elastomer a, but higher than the softening point of thermoplastic elastomer b.

[0053] More preferably, the hot pressing sintering temperature in step A1 is 140-180°C.

[0054] Preferably, the porosity of the precursor plate in step A1 is 3%-30%.

[0055] More preferably, the porosity of the precursor plate in step A1 is 5%-20%.

[0056] The porosity of the board obtained in step A1 is mainly affected by the particle size of the thermoplastic elastomer beads, their filling amount in the mold, and the temperature and pressure of hot pressing and sintering. When the thermoplastic elastomer beads have a core-shell structure, the particle size of the core layer and the thickness of the shell layer both affect the porosity of the precursor board. An excessively thick shell layer results in high interfacial bonding strength but leads to a decrease in the porosity of the precursor board. Conversely, an excessively thin shell layer also reduces the interfacial bonding strength of both the precursor board and the subsequently obtained foamed board.

[0057] In this invention, the porosity of the precursor plate is calculated using the following formula: P = (m2 / m1) × 100%; Where P is porosity, m1 is the mass of the fully dense precursor plate under natural volume (by increasing the pressure and temperature of hot pressing sintering, a fully dense precursor plate with 0 porosity can be obtained, at which point its density and natural volume can be obtained, and then m1 can be obtained; the natural volume is calculated by measuring the length, width and height with measuring tools), and m2 is the actual mass of the precursor plate.

[0058] Preferably, the thickness of the precursor plate obtained in step A1 is 1-30 mm.

[0059] More preferably, the thickness of the precursor sheet obtained in step A1 is 2-20 mm.

[0060] Preferably, the supercritical fluid in step A2 includes at least one of supercritical CO2 and supercritical N2.

[0061] Preferably, the pressure of the supercritical fluid in step A2 is 10.0~20.0 MPa.

[0062] More preferably, the immersion time in the supercritical fluid until saturation in step A2 is 0.3~1.0h.

[0063] Preferably, step A2 is performed in a foaming mold, wherein the thickness ratio of the precursor sheet to the foaming mold is 0.3~1.0, the length ratio is 0.4~0.8, and the width ratio is 0.4~0.8.

[0064] More preferably, the thickness ratio of the precursor sheet to the foaming mold is 0.5~0.9, the length ratio is 0.5~0.7, and the width ratio is 0.6~0.8.

[0065] This invention also protects the use of the foamed board prepared by the said preparation method in the preparation of footwear materials.

[0066] Compared with the prior art, the present invention has the following beneficial effects: The thermoplastic elastomer beads provided by this invention are beneficial for improving the strength and lightweight properties of foamed parts, reducing the density of the resulting parts to 0.15 g / cm³. 3 The tensile strength and tear strength are as high as 2MPa and 20N / cm respectively, and the foaming is good, with a resilience of over 65% and a compression set of less than 25%. Detailed Implementation

[0067] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents. The raw material information used in each embodiment and comparative example is as follows (unless otherwise stated, the hardness of the raw materials mentioned below refers to Shore hardness): 1) Thermoplastic elastomer a: TPU-1: UT1-98AU20, Covestro Bayer, Shore A hardness 98A (60D), softening point Ts measured at 143℃, flow point Tv measured at 198℃.

[0068] TPU-2: Elastollan® 1164D (BASF), with a hardness of approximately 52D. Softening point (Ts) is 158°C, and flow point is 205°C.

[0069] TPU-3: Desmopan® 385E (Covestro), with a hardness of approximately 65D. Softening point (Ts) is 165℃, and flow point is 215℃.

[0070] TPU-4: Covestro Texin® 985AU, with a hardness of 45D, a softening point (Ts) of 153℃, and a flow point of 198℃.

[0071] TPU-5: Lerui NF75D, hardness 75D. Softening point (Ts) is 172℃, flow point is 225℃.

[0072] TPU-6: Lerui NF85D, hardness 85D. Softening point Ts is 175℃, flow point Tv is 230℃.

[0073] TPU-7: Lubrizol Estane® D91T80 NAT 01, hardness 90A (42D), softening point Ts is 140℃, flow point is 175℃.

[0074] TPU-8: Lubrizol TPU 11T92E, hardness ~95A (53D), softening point Ts is 152℃, flow point is 233℃.

[0075] PEBA: Pebax RNEW 35R53 SP01, Arkema, Shore hardness 53D (95A), softening point Ts measured at 170℃, flow point Tv measured at 203℃.

[0076] TPEE: Hytrel® 4556 (DuPont), hardness 55D. Softening point Ts is 165℃, flow point is 210℃.

[0077] 2) Thermoplastic elastomer b: TPU-9: S80A, BASF, Shore A hardness 81A (31D), softening point Ts measured at 132℃, flow point Tv measured at 186℃.

[0078] TPU-10: RxT70A, Covestro, Shore A hardness 70A, softening point Ts measured at 78℃, flow point Tv measured at 152℃.

[0079] TPU-11: S60A, BASF, Shore A hardness 60A. Softening point (Ts) is 65℃, and flow point (Tv) is 120℃.

[0080] TPU-12: Hailide HT09LPRG, Shore A hardness 90A, softening point Ts measured at 145℃, flow point Tv measured at 170℃.

[0081] SEBS: Kronen G1653VO, ​​Shore A hardness 70, softening point Ts measured at 90℃, flow point Tv measured at 140℃.

[0082] EVA: Elvax® 460 (DuPont), VA content approximately 18%, Shore A hardness 85A. Softening point (Ts) is 75°C, and pour point (Tv) is 130°C.

[0083] 3) Crosslinking agent: Crosslinking agent-1: Peroxide, dicumyl peroxide (DCP), with a 1-minute half-life temperature (T1) of 171°C (in a nitrogen atmosphere).

[0084] Crosslinking agent-2: 2,5-dimethyl-2,5-bis(tert-butylperoxide)-3-hexyne (DYBP), with a 1-minute half-life temperature (T1) of 195°C (in a nitrogen atmosphere).

[0085] Crosslinking agent-3: Sulfur.

[0086] Crosslinking agent-4: PEROCTA® ND, 1-minute half-life temperature (T1) of 92.4°C (in a nitrogen atmosphere).

[0087] 4) Antioxidant: Pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], Irganox 1010.

[0088] 5) Hydrolysis resistant agent: polycarbodiimide, Stabaxol® P (Lanxess).

[0089] Examples 1-9 and Comparative Examples 1-9 This embodiment and the comparative example provide a series of thermoplastic elastomer beads, and the raw materials for preparation are shown in Table 1-2 below.

[0090] The method for preparing the thermoplastic elastomer beads includes the following steps: S1. Dissolve thermoplastic elastomer b in tetrahydrofuran to obtain a 5 wt% thermoplastic elastomer b solution; S2. Mix the remaining raw materials, melt, extrude, and granulate underwater to obtain precursor particles; the melting and extrusion are carried out in a twin-screw extruder, the temperature zone of which is set to 150 / 170 / 180 / 175℃ (from the feed port to the die head), the screw speed is 280 rpm, the length-to-diameter ratio is 40:1, and the screw diameter is 40 mm; S3. The precursor particles described in step S2 are immersed in 500g of the thermoplastic elastomer b solution obtained in step S1, and then removed and dried to obtain the product; the mass ratio of thermoplastic elastomer a and thermoplastic elastomer b can be controlled by changing the mass of the precursor particles during immersion.

[0091] The thermoplastic elastomer beads obtained in Example 1 have a core-shell structure, with an average core diameter of 1.2 mm and an average shell thickness of 50 μm.

[0092] Table 1. Table 2. Example 10 A thermoplastic elastomer bead, which differs from Example 1 only in that: The method for preparing the thermoplastic elastomer beads includes the following steps: Mix all the raw materials thoroughly, melt, extrude, and granulate underwater to obtain the final product.

[0093] The melting and extrusion are carried out in a twin-screw extruder, the temperature zone of which is set to 160 / 185 / 200 / 195℃ (from the feed port to the die head), the screw speed is 280 rpm, the length-to-diameter ratio is 40:1, and the screw diameter is 40 mm.

[0094] The thermoplastic elastomer beads have a spherical structure, wherein thermoplastic elastomer a and thermoplastic elastomer b are uniformly distributed in the spherical structure; the average particle size of the thermoplastic elastomer beads is 1.25 mm.

[0095] Comparative Example 10 A thermoplastic elastomer bead, which differs from Example 1 only in that: The raw materials include 90 parts TPU-9, 10 parts TPU-10, 0.5 parts crosslinking agent-1, 0.5 parts antioxidant and 0.5 parts hydrolysis resistant agent.

[0096] Comparative Example 11 A thermoplastic elastomer bead, which differs from Example 1 only in that: The raw materials include 90 parts TPU-1, 10 parts TPU-4, 0.5 parts crosslinking agent-1, 0.5 parts antioxidant and 0.5 parts hydrolysis resistant agent.

[0097] Performance testing I. Performance Testing of Foamed Parts Sample preparation includes the following steps: A1. The thermoplastic elastomer beads obtained in the examples and comparative examples were injected into a mold and hot-pressed and sintered at 175°C to obtain a precursor plate with a thickness of 5 mm and a porosity of 15%. A2. Place the precursor board obtained in step A1 into a foaming mold with a thickness of 10 mm (the length ratio and width ratio of the board to the foaming mold are both 0.7), immerse it in supercritical CO2 at 168℃ and 15MPa for 0.6 h until saturation, and then depressurize and foam to obtain the foamed board.

[0098] Density: Calculated based on the mass and volume of the foamed board sample, referring to standard ASTM D3574.

[0099] Tensile strength: Tested using a universal testing machine in accordance with standard ASTM D3574.

[0100] Tear strength: Test the ability of foam board samples to resist tear propagation according to standard ASTM D3574 (right angle).

[0101] Rebound rate: Tested according to standard ASTM D3574 using a ball rebound tester. A ball is dropped freely from a specified height onto the surface of the foam board sample, and the percentage of rebound height to fall height is measured.

[0102] Compression set: Referring to standard ASTM D3574, the foamed board sample was compressed to 50% of its original thickness and held at 70°C for 22 hours. The thickness recovery was then measured. A lower value indicates better fatigue resistance and durability of the material.

[0103] The performance test data is shown in Table 3 below: Table 3. As shown in Table 3 above, the thermoplastic elastomer beads provided by this invention are beneficial for improving the strength and lightweight properties of the foamed parts, reducing the density of the resulting parts to 0.15 g / cm³. 3 The tensile strength and tear strength are as high as 2MPa and 20N / cm respectively, and the foaming is good, with a resilience of over 65% and a compression set of less than 25%.

[0104] According to Examples 1 and 4-5, in this invention, thermoplastic elastomer a can be selected from at least one of TPU, TPEE, and PEBA, and thermoplastic elastomer b can also be selected from specific EVA, SEBS, TPU, etc.

[0105] According to Examples 1 and 6-7, the hardness of the thermoplastic elastomer a is Shore A95-Shore D65 (Example 1), which is preferred in this invention. The foamed part can obtain better overall performance, mainly because a more suitable hardness can reduce the impact on the foaming process while providing sufficient strength.

[0106] According to Examples 1 and 10, the thermoplastic elastomer beads prepared by conventional melt blending process, although having a spherical structure with thermoplastic elastomers a and b evenly distributed, can still achieve a relatively good foaming effect by combining thermoplastic elastomers a and b, and the foamed parts have excellent comprehensive performance.

[0107] According to Comparative Example 1, the excessively soft thermoplastic elastomer b has excessive fluidity and low bonding strength, which can cause the cells to easily merge during the foaming process, thus affecting the foaming effect and consequently the performance of the resulting parts.

[0108] According to Comparative Examples 2-3, an inappropriate ratio of a to b can lead to the inability to form a suitable bead structure, which in turn affects the performance of the foamed parts obtained later.

[0109] According to Comparative Example 4, although the overly stiff thermoplastic elastomer a can provide higher strength, it will affect the penetration of the foaming agent during the foaming process, resulting in a decrease in the performance of the foamed part (Comparative Example 4).

[0110] According to Comparative Example 5, the flow point of thermoplastic elastomer a is lower than the 1-minute half-life temperature of the crosslinking agent, which also leads to the inability to form a gradient melt structure, and thus the inability to obtain foamed parts with good overall performance.

[0111] According to Example 8 and Comparative Example 6, thermoplastic elastomers a and b need to satisfy the relationship that the hardness of thermoplastic elastomer b is lower than that of thermoplastic elastomer a in order to form a good microstructure of "hard phase as bone and soft phase as tendon".

[0112] Based on Comparative Examples 7 and 9 and Examples 2-3, the 1-minute half-life temperature satisfies T. sb +10℃ ≤T1≤T va Crosslinking agents with a temperature range of -10℃ can achieve the desired effect of this application. However, if the thermoplastic elastomers a and b are not selected appropriately, the same crosslinking agent may fail to meet the above relationship, thereby affecting the overall effect of the resulting foamed parts.

[0113] According to Comparative Example 8, sulfur does not have the concept of a 1-minute half-life temperature, which makes it unsuitable for the system of this application.

[0114] According to Comparative Examples 10-11, even if thermoplastic elastomers of different hardness can form a certain gradient melt structure, the comprehensive effect of this application cannot be obtained. This is mainly because a hardness of Shore A90-Shore D75 is a prerequisite for forming the hard phase support phase in this application, and a hardness of Shore A70-Shore A90 is also a prerequisite for the soft phase to obtain stronger fluidity and improve adhesion.

[0115] II. Research on Foaming Process Foamed boards were prepared using the foaming process provided by this invention and the conventional bead foaming process. The foaming effects of different processes were investigated, and the results are shown in Examples 1-2.

[0116] Example of an effect 1. A method for preparing foamed board includes the following steps: A1. The thermoplastic elastomer beads obtained in Example 1 were injected into a mold and hot-pressed and sintered at 175°C to obtain a precursor plate with a thickness of 5 mm and a porosity of 15%. A2. Place the precursor board obtained in step A1 into a foaming mold with a thickness of 10 mm (the length ratio and width ratio of the board to the foaming mold are both 0.7), immerse it in supercritical CO2 at 168℃ and 15MPa for 0.6 h until saturation, and then depressurize and foam to obtain the foamed board.

[0117] Example of effect 2. A method for preparing foamed board includes the following steps: A1. The thermoplastic elastomer beads obtained in Example 1 were injected into an autoclave and impregnated in supercritical CO2 at 168°C and 15MPa for 0.6 h until saturation. Then, the pressure was released and foaming was carried out to obtain foamed beads. A2. The obtained foamed beads were aged at room temperature (23±2℃) and normal pressure for 21 days to ensure that the foaming agent was evenly distributed inside the beads and that the pressure was stable. A3. Inject the foamed beads obtained in step A1 into the foaming mold, introduce saturated water vapor at a pressure of 0.3 MPa into the mold, maintain for 5 minutes, then cool with water to room temperature, open the mold and take out the foamed board.

[0118] A4. The foamed board is dried in a drying oven at 40℃ for 5 days to obtain the final foamed board.

[0119] The performance test results of the foamed boards obtained from the above examples are shown in Table 4 below: Table 4. As can be seen from Table 4 above, the thermoplastic elastomer beads provided in this application can be foamed to obtain parts with good lightweight properties and high strength, whether the process route of hot pressing and sintering followed by foaming is adopted or the conventional steam molding route is adopted. Among them, the foamed board produced by the process of hot pressing and sintering followed by foaming has better strength, and the process route has higher production efficiency.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A thermoplastic elastomer bead, characterized in that, The raw materials include the following parts by weight: Thermoplastic elastomer a: 80-99 parts; thermoplastic elastomer b: 5-20 parts; crosslinking agent: 0.01-1 part; The thermoplastic elastomer a includes at least one of TPU, TPEE, and PEBA, with a hardness of Shore A 90-Shore D 75; The thermoplastic elastomer b includes at least one of TPU, TPEE, PEBA, EVA, SEBS, POE, and EPDM, with a hardness of Shore A70-Shore A90; the hardness of the thermoplastic elastomer b is lower than that of the thermoplastic elastomer a. The crosslinking agent includes a peroxide crosslinking agent, and the 1-minute half-life temperature T1 of the crosslinking agent satisfies: T sb +10℃ ≤T1≤T va -10℃, where: T sb T is the softening point of thermoplastic elastomer b. va is the flow point of thermoplastic elastomer a.

2. The thermoplastic elastomer beads as described in claim 1, characterized in that, The softening point T of the thermoplastic elastomer a sa The temperature is 120~180℃; And / or, the flow point T of the thermoplastic elastomer a va The temperature ranges from 180 to 230℃.

3. The thermoplastic elastomer beads as described in claim 1, characterized in that, The softening point T of the thermoplastic elastomer b sb Temperatures range from 75 to 140℃. And / or, the flow point T of the thermoplastic elastomer b vb The temperature ranges from 140 to 190 degrees Celsius.

4. The thermoplastic elastomer beads as described in claim 1, characterized in that, The thermoplastic elastomer beads have a spherical structure; And / or, the average particle size of the thermoplastic elastomer beads is 0.5-2 mm.

5. The thermoplastic elastomer beads as described in claim 4, characterized in that, The thermoplastic elastomer beads have a spherical core-shell structure, with the core layer having an average diameter of 0.3-1.995 mm and the shell layer having an average thickness of 5-200 μm.

6. A method for preparing thermoplastic elastomer beads, characterized in that, Includes the following steps: Mix all the raw materials thoroughly, melt, extrude, and granulate to obtain the final product.

7. The method for preparing thermoplastic elastomer beads as described in claim 6, characterized in that, Includes the following steps: S1. Dissolve thermoplastic elastomer b in a solvent to obtain a thermoplastic elastomer b solution; S2. Mix the remaining raw materials, melt, extrude, and granulate to obtain precursor particles; S3. The precursor particles described in step S2 are immersed in the thermoplastic elastomer b solution obtained in step S1, and then removed and dried to obtain the final product.

8. The use of the thermoplastic elastomer beads according to any one of claims 1-5 in the preparation of foamed boards.

9. A method for preparing a foamed board, characterized in that, Includes the following steps: A1. Thermoplastic elastomer beads are injected into a mold and hot-pressed and sintered to obtain a precursor sheet; A2. The precursor board obtained in step A1 is immersed in a supercritical fluid until saturation, and then depressurized and foamed to obtain the foamed board.

10. The application of the foamed board prepared by the preparation method of claim 9 in the preparation of shoe materials.

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