Foaming thermoplastic polyurethane insole and preparation method thereof

Abstract

The invention discloses a foamed thermoplastic polyurethane insole and a preparation method thereof. The raw material composition of the foamed thermoplastic polyurethane shoe insole comprises thermoplastic polyurethane, the raw material composition of the thermoplastic polyurethane contains or does not contain a cross-linking agent, and when the raw material composition of the thermoplastic polyurethane does not contain the cross-linking agent, the raw material composition of the foamed thermoplastic polyurethane shoe insole further comprises the cross-linking agent; the cross-linking agent comprises one or more than two of polyisocyanate, a polyhydroxy compound and a polyamino compound; the polyisocyanate contains at least three isocyanate groups; the polyhydroxy compound contains at least three hydroxyl groups; the polyamino compound contains at least three amino groups. The preparation method can adopt a small blank foaming process. When the cross-linking agent is used for preparing the foamed thermoplastic polyurethane shoe midsole by a small blank foaming process, the shrinkage of a shoe wall during hot pressing can be prevented, and one or more than two properties of tensile strength, elongation at break and layered tearing strength of the foamed thermoplastic polyurethane shoe midsole can be improved.

Description

Technical Field

[0001] This invention relates to the field of polymer materials for footwear and footwear manufacturing processes, specifically to a foamed thermoplastic polyurethane shoe midsole and its preparation method. Background Technology

[0002] Foamed granules based on thermoplastic polyurethane (TPU), also known as beaded foam (or particle foam, granular foam, or pellet foam), and molded bodies made from them are existing well-known technologies. Relevant prior art includes CN101370861B, WO2013153190A1, CN112940488B, etc., and discloses various potential applications in packaging, industry, agriculture, transportation, military industry, aerospace industry, and daily necessities, especially in the field of shoe midsoles. According to consumer feedback and reviews on e-commerce platforms, problems such as easy breakage, shedding, and difficulty in cleaning due to dirt accumulation are observed during wear.

[0003] To address the issues of easy breakage, chipping, and difficulty in cleaning TPU foam granule molded shoe midsoles, the continuous advancement and innovation of supercritical foaming technology has led to the increasing application of small-scale foaming processes in high-end shoe materials for TPU shoe midsoles. These supercritical foaming processes result in TPU shoe midsoles with low microporous density, high specific strength, excellent rebound and shock absorption performance, a skin-like texture that resists dirt, and are environmentally friendly, making them popular among many well-known sportswear brands.

[0004] Foamed TPU shoe midsoles prepared using the preform foaming process present challenges. Firstly, controlling the uniformity of sole dimensions is difficult. Secondly, due to functional and aesthetic design requirements, midsoles typically feature three-dimensional surface textures. Secondary hot pressing is a commonly used method for creating these textures on the surface of foamed TPU shoe midsoles and is also an effective process for achieving dimensional uniformity in preform foamed shoe midsoles. However, due to the excellent elasticity and compressibility of foamed TPU materials, and their low permanent compression set, secondary hot pressing often yields poor results. It frequently requires high hot pressing temperatures, leading to significant shrinkage of the foamed TPU material and even collapse of the foam structure. This is especially true for complex structures with high sidewalls in foamed TPU shoe midsoles, where the shrinkage of the shoe walls is more severe during secondary hot pressing, significantly impacting the shoe's appearance and performance. Summary of the Invention

[0005] To address the aforementioned technical problems and shortcomings in the field, this invention provides a foamed thermoplastic polyurethane shoe midsole and its preparation method, solving the problem of shoe wall shrinkage during the secondary hot pressing of TPU shoe midsole preforms. In particular, for shoe midsoles with complex structures and high sidewalls, surprisingly, the foamed TPU shoe midsole prepared by this invention has superior physical properties.

[0006] The specific technical solution is as follows: In a first aspect, the present invention provides a foamed thermoplastic polyurethane shoe midsole, wherein the raw material composition of the foamed thermoplastic polyurethane shoe midsole includes thermoplastic polyurethane, wherein the raw material composition of the thermoplastic polyurethane may or may not contain a crosslinking agent, and when the raw material composition of the thermoplastic polyurethane does not contain a crosslinking agent, the raw material composition of the foamed thermoplastic polyurethane shoe midsole further includes a crosslinking agent. The crosslinking agent includes one or more of polyisocyanates, polyhydroxy compounds, and polyamino compounds; The polyisocyanate contains at least three isocyanate groups; The polyhydroxy compound contains at least three hydroxyl groups; The polyamino compound contains at least three amino groups.

[0007] In some preferred embodiments, when the raw material composition of the thermoplastic polyurethane contains a crosslinking agent, the raw material composition of the thermoplastic polyurethane also contains a polyol, a diisocyanate and a chain extender, and the mass of the crosslinking agent in the raw material composition of the thermoplastic polyurethane is 0.1%-5% of the total mass of the polyol, diisocyanate and chain extender.

[0008] In some preferred embodiments, the raw material composition of the foamed thermoplastic polyurethane shoe midsole includes thermoplastic polyurethane and a crosslinking agent, and the mass ratio of thermoplastic polyurethane to crosslinking agent in the raw material composition of the foamed thermoplastic polyurethane shoe midsole is 100:0.1-5.

[0009] The polyisocyanate preferably includes one or more of triphenylmethane 4,4',4''-triisocyanate, HDI trimer, HDI tetramer, and IPDI trimer.

[0010] The polyhydroxy compound preferably includes one or more of trimethylolpropane, trimethylolethane, glycerol, and 3,5-dihydroxy-4-methoxybenzyl alcohol.

[0011] The polyamino compound preferably includes one or more of 1,2,3-propanetriamine, triethylenetetramine (TETA), and 1,3,5-phenyltriamine.

[0012] In a second aspect, the present invention provides a method for preparing the foamed thermoplastic polyurethane shoe midsole described in the first aspect, comprising the steps of: (1) Obtain the shoe midsole preform through any one or more of the following methods: Method 1: 100 parts by weight of thermoplastic polyurethane and 0.1-5 parts by weight (e.g., 0.2 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.8 parts by weight, 1 part by weight, 3 parts by weight, etc.) of the polyisocyanate are mixed and then injection molded to obtain an unfoamed shoe midsole preform; Method 2: Add polyol, diisocyanate, chain extender, and crosslinking agent accounting for 0.1%-5% (e.g., 0.2%, 0.4%, 0.5%, 0.8%, 1%, 3%, etc.) of the total mass of polyol, diisocyanate, and chain extender into a twin-screw extruder, perform the extrusion reaction, and after passing through the die, granulate to obtain thermoplastic polyurethane granules. Inject the thermoplastic polyurethane granules into unfoamed shoe midsole preforms. (2) Obtain the initial blank of the foam shoe midsole through any one or more of the following methods: Method A: Place the unfoamed shoe midsole preform into a reactor containing high-pressure fluid, heat and impregnate it, then quickly depressurize and open the reactor to obtain the foamed shoe midsole preform; Method B: Place the unfoamed shoe midsole preform into a reactor with high-pressure fluid for low-temperature immersion, then slowly depressurize, open the reactor, remove the shoe midsole preform, and heat it to foam to obtain a foamed shoe midsole preform. (3) The foamed shoe midsole blank is placed into the shoe midsole mold for hot pressing, and then cooled and molded to obtain the foamed thermoplastic polyurethane shoe midsole.

[0013] In Method 1, the melting point of thermoplastic polyurethane is preferably 120-200℃, more preferably 120-180℃, and even more preferably 130-170℃.

[0014] In Method 1, the Shore hardness of the thermoplastic polyurethane is preferably 50A-98A, more preferably 70A-98A, and even more preferably 80A-98A.

[0015] Preferably, in Method 2, the polyol includes one or more of polyester polyol, polyether polyol, polyether ester polyol, and polycarbonate polyol.

[0016] Preferably, in Method 2, the diisocyanate includes one or more of hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), methylene diphenyl diisocyanate (MDI), 1,4-cyclohexane diisocyanate (CHDI), terephthalic diisocyanate (PPDI), and pentamethylene diisocyanate (PDI).

[0017] Preferably, in Method 2, the chain extender includes one or more of 1,2-ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, cyclohexanediol, and hydroquinone dihydroxyethyl ether.

[0018] In Method 2, the hard segment content of the thermoplastic polyurethane particles is preferably 20%-50%. The hard segment content in this invention is the percentage of the sum of the mass of diisocyanate and chain extender in the reaction raw materials to the total mass of the polyol, diisocyanate, and chain extender.

[0019] In Method 2, the melting point of the thermoplastic polyurethane particles is preferably 120-200℃, more preferably 120-180℃, and even more preferably 130-170℃.

[0020] In Method 2, the Shore hardness of the thermoplastic polyurethane particles is preferably 50A-98A, more preferably 70A-98A, and even more preferably 80A-98A.

[0021] In this invention, the melting point of thermoplastic polyurethane (granules) is obtained using differential scanning calorimetry (DSC). Specifically, a DSC 1 instrument manufactured by MetTLER is used, and data analysis is performed using STARe software. More specifically, 5-10 mg of thermoplastic polyurethane elastomer is heated from -10°C to 250°C at a heating rate of 20°C / min, then cooled from 250°C to -80°C at a rate of 10°C / min, held at -80°C for 2 min, and finally heated from -80°C to 250°C at a rate of 20°C / min. The peak melting point of the DSC curve obtained at the second heating is taken as the melting point of the thermoplastic polyurethane elastomer.

[0022] In this invention, the Shore hardness of the thermoplastic polyurethane (granules) is obtained by pressing for 15 seconds according to the standard ASTM D2240-15 (2021).

[0023] In Method 2, catalysts, antioxidants, UV resistant agents, hydrolysis resistant agents, pigments, inorganic nucleating agents, etc., can be optionally added when preparing thermoplastic polyurethane particles.

[0024] Preferably, in step (1), the injection temperature is 120-220℃.

[0025] In step (2), the high-pressure fluid preferably includes one or both of carbon dioxide and nitrogen.

[0026] Preferably, in method A, the temperature of the heating and impregnation is 100-200℃, the pressure is 5-30MPa, and the heat and pressure holding time is 0-6h.

[0027] Preferably, in method A, the pressure relief rate of the rapid pressure relief is 1-1000 MPa / s.

[0028] Preferably, in method B, the temperature of the low-temperature impregnation is 0-70℃, the pressure is 5-30MPa, and the time is 1-20h.

[0029] Preferably, in method B, the pressure relief rate of the slow pressure relief is 0.01-0.5 MPa / s.

[0030] Preferably, in method B, the heat source for heating and foaming includes one or more of water vapor, hot air, and microwaves.

[0031] Preferably, in method B, the heating and foaming temperature is 100-180℃ and the time is 5-200s.

[0032] Preferably, in step (3), the hot pressing temperature is 120-200℃ and the time is 2-30min.

[0033] Preferably, in step (3), the cooling and shaping includes one or both of water cooling and air cooling.

[0034] Preferably, in step (3), the cooling and shaping time is 50-600s.

[0035] As a general inventive concept, in a third aspect, the present invention provides the application of the crosslinking agent in the preparation of foamed thermoplastic polyurethane shoe midsoles using a preform foaming process. When used in the preform foaming process to prepare foamed thermoplastic polyurethane shoe midsoles, the crosslinking agent can prevent shrinkage of the shoe wall during hot pressing and improve one or more of the following properties of the foamed thermoplastic polyurethane shoe midsoles: tensile strength, elongation at break, and delamination tear strength.

[0036] The applications described in the third aspect can be further selected and optimized by referring to the technical solutions introduced in the first and second aspects.

[0037] Compared with the prior art, the beneficial effects of this invention are as follows: 1. In the injection molding process of unfoamed preforms, this invention adds polyisocyanate, which reacts the NCO groups of the polyisocyanate with the active hydrogen of the residual hydroxyl groups and / or urethane groups of TPU to form a micro-crosslinked network structure. This increases the temperature resistance of the foamed TPU shoe midsole preform and solves the problem of shoe wall shrinkage caused by high hot pressing temperature in complex high-sidewall shoe soles during the secondary hot pressing of TPU shoe midsole preforms, thus ensuring the appearance of the shoe midsole is qualified.

[0038] 2. In the synthesis of TPU, this invention involves adding polyisocyanates and / or polyhydroxy compounds and / or polyamino compounds. This allows the NCO groups of the polyisocyanates to react with the hydroxyl groups of the polyols, and / or the hydroxyl groups of the polyhydroxy compounds to react with the NCO groups of the diisocyanates, and / or the amino groups of the polyamino compounds to react with the NCO groups of the diisocyanates. This forms a micro-crosslinked network structure, increasing the temperature resistance of the foamed TPU shoe midsole preform. It also solves the problem of shoe wall shrinkage caused by high hot-pressing temperatures during the secondary hot-pressing of complex high-sidewall shoe midsole preforms, ensuring the appearance of the shoe midsole meets the required standards.

[0039] 3. The foamed TPU shoe midsole prepared by the method of the present invention has better physical properties, which greatly increases the wear life and wearing comfort of the shoe. Attached Figure Description

[0040] Figure 1 These are photographs of the midsole of Example 1 (right side) and the midsole of Comparative Example 1 (left side). Detailed Implementation

[0041] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer.

[0042] In the following examples: The thermoplastic polyurethane used in Examples 1-6 was purchased from Meiri New Materials Co., Ltd. The HDI trimer was purchased from Mirathane New Materials Co., Ltd., and its brand name was Mirathane® H300. Polyol 1 is PBA diol (poly(1,4-butanediol adipate) with the brand name Mirathane® P1110 of Mirathane New Materials Co., Ltd. and a number average molecular weight of 1000 g / mol. Polyol 2 is a PEA diol (polyethylene adipate diol) with the brand name Mirathane® P1215 of Mirathane New Materials Co., Ltd. and a number average molecular weight of 1500 g / mol. Polyol 3 is a BASF PTMEG diol (polytetrahydrofuran ether diol) with a number average molecular weight of 1000 g / mol. Chain extender 1 is commercially available conventional BDO (1,4-butanediol). Chain extender 2 is commercially available conventional HDO (1,6-hexanediol); Diisocyanate 1 is HDI from Meiri New Materials Co., Ltd.; Diisocyanate 2 is BASF's MDI; Polyisocyanate 1 is an HDI trimer of Mirathane® H300, manufactured by Mirathane New Materials Co., Ltd. Polyisocyanate 2 is a commercially available conventional triphenylmethane 4,4',4''-triisocyanate; Polyhydroxy compound 1 is commercially available trimethylolpropane (TMP); Polyamino compound 1 is commercially available conventional 1,2,3-propanetriamine; The catalyst is a commercially available organic bismuth catalyst.

[0043] Example 1: A method for preparing a complex structure high-sidewall foamed thermoplastic polyurethane shoe midsole, the specific steps of which are as follows: (1) 100 parts by weight of thermoplastic polyurethane with hardness 90A and melting point 155℃ and grade Mirathane® A190 and 1 part by weight of HDI trimer with grade Mirathane® H300 are mixed evenly with a mixer to obtain a mixture. The mixture is then injected through a disc injection molding machine to obtain an unfoamed shoe midsole preform. The injection molding machine temperature is set to 130-200℃. (2) Place the unfoamed shoe midsole preform from step (1) into the reactor, introduce high-pressure carbon dioxide fluid into the reactor, heat and impregnate it, maintain the temperature at 135°C, maintain the pressure at 10MPa, and the time at 0.5h, then depressurize rapidly at a rate of 3MPa / s, open the reactor, and obtain the foamed shoe midsole preform. (3) Place the foamed shoe midsole preform from step (2) into a complex structure high-sidewall shoe midsole mold for hot pressing. The hot pressing temperature is 150℃, and the hot pressing time is 10min. Then, water cool for 100s and demold to obtain the foamed thermoplastic polyurethane shoe midsole. See [link to relevant documentation]. Figure 1 .

[0044] The foamed thermoplastic polyurethane shoe midsole obtained in step (3) was placed at room temperature for 24 hours. The test data and observed appearance are shown in Table 1.

[0045] Example 2: A method for preparing a complex structure high-sidewall foamed thermoplastic polyurethane shoe midsole, the specific steps of which are as follows: (1) 100 parts by weight of thermoplastic polyurethane with hardness 85A and melting point 150℃ and grade Mirathane® A185 and 0.4 parts by weight of HDI trimer with grade Mirathane® H300 are mixed evenly with a mixer to obtain a mixture. The mixture is then injected through a disc injection molding machine to obtain an unfoamed shoe midsole preform. The injection molding machine temperature is set to 130-190℃. (2) Place the unfoamed shoe midsole preform from step (1) into the reactor, introduce high-pressure carbon dioxide fluid into the reactor, and perform low-temperature impregnation at a temperature of 30°C, a pressure of 9MPa, and a time of 20h. Then, slowly depressurize at a rate of 0.01MPa / s, open the reactor, take out the shoe midsole preform, and heat it with 130°C high-pressure steam for 30s to foam and obtain the foamed shoe midsole preform. (3) The foamed shoe midsole preform from step (2) is placed into a complex structure high sidewall shoe midsole mold for hot pressing. The hot pressing temperature is 145℃ and the hot pressing time is 5min. Then, it is water-cooled for 600s and demolded to obtain the foamed thermoplastic polyurethane shoe midsole.

[0046] The foamed thermoplastic polyurethane shoe midsole obtained in step (3) was placed at room temperature for 24 hours. The test data and observed appearance are shown in Table 1.

[0047] Example 3: A method for preparing a complex structure high-sidewall foamed thermoplastic polyurethane shoe midsole, the specific steps of which are as follows: (1) 100 parts by weight of thermoplastic polyurethane with a hardness of 98A and a melting point of 180℃ and a grade of Mirathane® A60D and 0.1 parts by weight of commercially available conventional triphenylmethane 4,4',4''-triisocyanate were mixed evenly using a mixer to obtain a mixture. The mixture was then injected through a disc injection molding machine to obtain an unfoamed shoe midsole preform. The injection molding machine temperature was set to 150-220℃. (2) Place the unfoamed shoe midsole preform from step (1) into the reactor, introduce high-pressure carbon dioxide fluid into the reactor, heat and impregnate, maintain the temperature at 170°C, maintain the pressure at 5MPa, and the time at 0h (during the heating process, when the temperature and pressure reach the limit, directly release the pressure to foam), and then release the pressure quickly at a rate of 1MPa / s, open the reactor, and obtain the foamed shoe midsole preform; (3) The foamed shoe midsole preform from step (2) is placed into a complex structure high sidewall shoe midsole mold for hot pressing. The hot pressing temperature is 175℃ and the hot pressing time is 30min. Then, it is water-cooled for 500s and demolded to obtain the foamed thermoplastic polyurethane shoe midsole.

[0048] The foamed thermoplastic polyurethane shoe midsole obtained in step (3) was placed at room temperature for 24 hours. The test data and observed appearance are shown in Table 1.

[0049] Example 4: A method for preparing a complex structure high-sidewall foamed thermoplastic polyurethane shoe midsole, the specific steps of which are as follows: (1) 100 parts by weight of thermoplastic polyurethane with hardness 80A and melting point 125℃ and grade Mirathane® A180 and 3 parts by weight of HDI trimer with grade Mirathane® H300 are mixed evenly with a mixer to obtain a mixture. The mixture is then injected through a disc injection molding machine to obtain an unfoamed shoe midsole preform. The injection molding machine temperature is set to 120-180℃. (2) Place the unfoamed shoe midsole preform from step (1) into the reactor, and introduce a high-pressure fluid mixture of carbon dioxide and nitrogen into the reactor (first introduce carbon dioxide to maintain a pressure of 10 MPa, then introduce nitrogen to maintain a pressure of 30 MPa) for impregnation, maintain a temperature of 102℃, maintain a pressure of 30 MPa, and a time of 6 hours. Then, depressurize rapidly at a rate of 100 MPa / s, open the reactor, and obtain the foamed shoe midsole preform. (3) The foamed shoe midsole preform from step (2) is placed into a complex structure high sidewall shoe midsole mold for hot pressing. The hot pressing temperature is 120℃ and the hot pressing time is 2min. Then, it is water-cooled for 50s and demolded to obtain the foamed thermoplastic polyurethane shoe midsole.

[0050] The foamed thermoplastic polyurethane shoe midsole obtained in step (3) was placed at room temperature for 24 hours. The test data and observed appearance are shown in Table 1.

[0051] Example 5 A method for preparing a complex structure high-sidewall foamed thermoplastic polyurethane shoe midsole, the specific steps of which are as follows: (1) 100 parts by weight of thermoplastic polyurethane with a hardness of 70A and a melting point of 145℃ and a grade of Mirathane® M70 and 5 parts by weight of commercially available conventional triphenylmethane 4,4',4''-triisocyanate were mixed evenly using a mixer to obtain a mixture. The mixture was then injected through a disc injection molding machine to obtain an unfoamed shoe midsole preform. The injection molding machine temperature was set to 130-190℃. (2) Place the unfoamed shoe midsole preform from step (1) into the reactor, introduce high-pressure carbon dioxide fluid into the reactor, and perform low-temperature impregnation at 0°C, 5MPa, and 20h. Then, slowly depressurize at a rate of 0.5MPa / s, open the reactor, take out the shoe midsole preform, and heat it with 120°C high-pressure steam for 5s to foam and obtain the foamed shoe midsole preform. (3) The foamed shoe midsole preform from step (2) is placed into a complex structure high sidewall shoe midsole mold for hot pressing. The hot pressing temperature is 140℃ and the hot pressing time is 5min. Then, it is water-cooled for 100s and demolded to obtain the foamed thermoplastic polyurethane shoe midsole.

[0052] The foamed thermoplastic polyurethane shoe midsole obtained in step (3) was placed at room temperature for 24 hours. The test data and observed appearance are shown in Table 1.

[0053] Example 6: A method for preparing a complex structure high-sidewall foamed thermoplastic polyurethane shoe midsole, the specific steps of which are as follows: (1) 100 parts by weight of thermoplastic polyurethane with hardness 95A and melting point 160℃ and grade Mirathane® A195 and 0.8 parts by weight of HDI trimer with grade Mirathane® H300 are mixed evenly with a mixer to obtain a mixture. The mixture is then injected through a disc injection molding machine to obtain an unfoamed shoe midsole preform. The injection molding machine temperature is set to 150-210℃. (2) Place the unfoamed shoe midsole preform from step (1) into the reactor, and introduce a high-pressure fluid mixture of carbon dioxide and nitrogen into the reactor (first introduce carbon dioxide to maintain a pressure of 10 MPa, then introduce nitrogen to maintain a pressure of 25 MPa) for low-temperature impregnation at a temperature of 70°C and a pressure of 25 MPa for 6 hours. Then slowly depressurize at a rate of 0.2 MPa / s, open the reactor, take out the shoe midsole preform, and heat it with high-pressure steam at 135°C for 40 seconds to foam and obtain a foamed shoe midsole preform. (3) The foamed shoe midsole preform from step (2) is placed into a complex structure high sidewall shoe midsole mold for hot pressing. The hot pressing temperature is 155℃ and the hot pressing time is 5min. Then, it is water-cooled for 600s and demolded to obtain the foamed thermoplastic polyurethane shoe midsole.

[0054] The foamed thermoplastic polyurethane shoe midsole obtained in step (3) was placed at room temperature for 24 hours. The test data and observed appearance are shown in Table 1.

[0055] Comparative Example 1: Compared with Example 1, no polyisocyanate was added, and some parameters in the preparation method were adapted and adjusted according to the materials.

[0056] A method for preparing a foamed thermoplastic polyurethane shoe midsole, the specific steps of which are as follows: (1) 100 parts by weight of Mirathane® A190 thermoplastic polyurethane with a hardness of 90A and a melting point of 155℃ were injection molded into an unfoamed shoe midsole preform by a disc injection molding machine. The injection molding machine temperature was set to 130-200℃. (2) Place the unfoamed shoe midsole preform from step (1) into the reactor, introduce high-pressure carbon dioxide fluid into the reactor, heat and impregnate it, maintain the temperature at 132°C, maintain the pressure at 10MPa, and the time at 0.5h, then depressurize rapidly at a rate of 3MPa / s, open the reactor, and obtain the foamed shoe midsole preform. (3) Place the foamed shoe midsole preform from step (2) into a complex structure high-sidewall shoe midsole mold for hot pressing. The hot pressing temperature is 145℃, and the hot pressing time is 10min. Then, cool it in water for 100s and demold to obtain the foamed thermoplastic polyurethane shoe midsole. See [link to relevant documentation]. Figure 1 .

[0057] The foamed thermoplastic polyurethane shoe midsole obtained in step (3) was placed at room temperature for 24 hours. The test data and observed appearance are shown in Table 1.

[0058] Comparative Example 2: Compared with Example 2, no polyisocyanate was added, and some parameters in the preparation method were adapted and adjusted according to the materials.

[0059] A method for preparing a foamed thermoplastic polyurethane shoe midsole, the specific steps of which are as follows: (1) 100 parts by weight of Mirathane® A185 thermoplastic polyurethane with a hardness of 85A and a melting point of 150℃ were injection molded into an unfoamed shoe midsole preform by a disc injection molding machine. The injection molding machine temperature was set to 130-190℃. (2) Place the unfoamed shoe midsole preform from step (1) into the reactor, introduce high-pressure carbon dioxide fluid into the reactor, and perform low-temperature impregnation at a temperature of 30°C, a pressure of 9MPa, and a time of 20h. Then, slowly depressurize at a rate of 0.01MPa / s, open the reactor, take out the shoe midsole preform, and heat it with 125°C high-pressure steam for 30s to foam and obtain the foamed shoe midsole preform. (3) The foamed shoe midsole preform from step (2) is placed into a complex structure high sidewall shoe midsole mold for hot pressing. The hot pressing temperature is 140℃ and the hot pressing time is 5min. Then, it is water-cooled for 600s and demolded to obtain the foamed thermoplastic polyurethane shoe midsole.

[0060] The foamed thermoplastic polyurethane shoe midsole obtained in step (3) was placed at room temperature for 24 hours. The test data and observed appearance are shown in Table 1.

[0061] Table 1 The preparation process of thermoplastic polyurethane in Examples 7-12 and Comparative Examples 3-4 is described as follows: The polyol, chain extender, diisocyanate, catalyst, and polyisocyanate, polyhydroxy compound, or polyamine compound are metered and added to the extruder feed inlet. The extruder temperature is 150-230°C. The melt is discharged from the extruder via a gear pump, and then the polymer melt is processed into granules by underwater granulation. The granules are then continuously dried in a heated fluidized bed at 40-90°C.

[0062] The usage of each raw material in Examples 7-12 and Comparative Examples 3-4 is summarized in Table 2 below.

[0063] Table 2 Example 7: A manufacturing process for a complex-structured, high-sidewall foamed thermoplastic polyurethane shoe midsole, comprising the following specific steps: (1) TPU 1 is injection molded into an unfoamed shoe midsole preform using a disc injection molding machine. The injection molding machine temperature is set to 130-200℃. (2) Place the unfoamed shoe midsole preform from step (1) into the reactor, introduce high-pressure carbon dioxide fluid into the reactor, heat and impregnate it, maintain the temperature at 130°C, maintain the pressure at 9MPa, and the time at 0.5h, then depressurize rapidly at a rate of 3MPa / s, open the reactor, and obtain the foamed shoe midsole preform. (3) The foamed shoe midsole preform from step (2) is placed into a complex structure high sidewall shoe midsole mold for hot pressing. The hot pressing temperature is 152℃ and the hot pressing time is 12min. Then, it is water-cooled for 100s and demolded to obtain the foamed thermoplastic polyurethane shoe midsole.

[0064] The foamed thermoplastic polyurethane shoe midsole obtained in step (3) was placed at room temperature for 24 hours. The test data and observed appearance are shown in Table 3.

[0065] Example 8: A manufacturing process for a complex-structured, high-sidewall foamed thermoplastic polyurethane shoe midsole, comprising the following specific steps: (1) TPU 2 is injection molded into an unfoamed shoe midsole preform using a disc injection molding machine. The injection molding machine temperature is set to 130-190℃. (2) Place the unfoamed shoe midsole preform from step (1) into the reactor, introduce high-pressure carbon dioxide fluid into the reactor, and perform low-temperature impregnation at a temperature of 30°C, a pressure of 10MPa, and a time of 20h. Then, slowly depressurize at a rate of 0.01MPa / s, open the reactor, take out the shoe midsole preform, and heat it with 125°C high-pressure steam for 30s to foam and obtain the foamed shoe midsole preform. (3) The foamed shoe midsole preform from step (2) is placed into a complex structure high sidewall shoe midsole mold for hot pressing. The hot pressing temperature is 132℃ and the hot pressing time is 5min. Then, it is water-cooled for 600s and demolded to obtain the foamed thermoplastic polyurethane shoe midsole.

[0066] The foamed thermoplastic polyurethane shoe midsole obtained in step (3) was placed at room temperature for 24 hours. The test data and observed appearance are shown in Table 3.

[0067] Example 9 A manufacturing process for a complex-structured, high-sidewall foamed thermoplastic polyurethane shoe midsole, comprising the following specific steps: (1) TPU 3 is injection molded into an unfoamed shoe midsole preform using a disc injection molding machine. The injection molding machine temperature is set to 150-220℃. (2) Place the unfoamed shoe midsole preform from step (1) into the reactor, introduce high-pressure carbon dioxide fluid into the reactor, heat and impregnate, maintain the temperature at 170°C, maintain the pressure at 5MPa, and the time at 0h (during the heating process, when the temperature and pressure reach the limit, directly release the pressure to foam), and then release the pressure quickly at a rate of 1MPa / s, open the reactor, and obtain the foamed shoe midsole preform; (3) The foamed shoe midsole preform from step (2) is placed into a complex structure high sidewall shoe midsole mold for hot pressing. The hot pressing temperature is 170℃ and the hot pressing time is 30min. Then, it is water-cooled for 500s and demolded to obtain the foamed thermoplastic polyurethane shoe midsole.

[0068] The foamed thermoplastic polyurethane shoe midsole obtained in step (3) was placed at room temperature for 24 hours. The test data and observed appearance are shown in Table 3.

[0069] Example 10: A method for preparing a complex structure high-sidewall foamed thermoplastic polyurethane shoe midsole, the specific steps of which are as follows: (1) TPU 2 is injection molded into an unfoamed shoe midsole preform using a disc injection molding machine. The injection molding machine temperature is set to 130-190℃. (2) Place the unfoamed shoe midsole preform from step (1) into the reactor, and introduce a high-pressure fluid mixture of carbon dioxide and nitrogen into the reactor (first introduce carbon dioxide to maintain a pressure of 9 MPa, then introduce nitrogen to maintain a pressure of 30 MPa) for impregnation, maintain a temperature of 108°C, maintain a pressure of 30 MPa, and a time of 6 hours. Then, depressurize rapidly at a rate of 100 MPa / s, open the reactor, and obtain the foamed shoe midsole preform. (3) The foamed shoe midsole preform from step (2) is placed into a complex structure high sidewall shoe midsole mold for hot pressing. The hot pressing temperature is 130℃ and the hot pressing time is 2min. Then, it is water cooled for 50s and demolded to obtain the foamed thermoplastic polyurethane shoe midsole.

[0070] The foamed thermoplastic polyurethane shoe midsole obtained in step (3) was placed at room temperature for 24 hours. The test data and observed appearance are shown in Table 3.

[0071] Example 11: A method for preparing a complex structure high-sidewall foamed thermoplastic polyurethane shoe midsole, the specific steps of which are as follows: (1) TPU 2 is injection molded into an unfoamed shoe midsole preform using a disc injection molding machine. The injection molding machine temperature is set to 130-190℃. (2) Place the unfoamed shoe midsole preform from step (1) into the reactor, introduce high-pressure carbon dioxide fluid into the reactor, and perform low-temperature impregnation at 0°C, 5MPa, and 20h. Then, slowly depressurize at a rate of 0.5MPa / s, open the reactor, take out the shoe midsole preform, and heat it with 127°C high-pressure steam for 5s to foam and obtain the foamed shoe midsole preform. (3) The foamed shoe midsole preform from step (2) is placed into a complex structure high sidewall shoe midsole mold for hot pressing. The hot pressing temperature is 130℃ and the hot pressing time is 5min. Then, it is water-cooled for 100s and demolded to obtain the foamed thermoplastic polyurethane shoe midsole.

[0072] (4) The foamed thermoplastic polyurethane shoe midsole obtained in step (3) was placed at room temperature for 24 hours. The test data and observed appearance are shown in Table 3.

[0073] Example 12: A method for preparing a complex structure high-sidewall foamed thermoplastic polyurethane shoe midsole, the specific steps of which are as follows: (1) TPU 4 is injection molded into an unfoamed shoe midsole preform using a disc injection molding machine. The injection molding machine temperature is set to 150-220℃. (2) Place the unfoamed shoe midsole preform from step (1) into the reactor, and introduce a high-pressure fluid mixture of carbon dioxide and nitrogen into the reactor (first introduce carbon dioxide to maintain a pressure of 8 MPa, then introduce nitrogen to maintain a pressure of 25 MPa) for low-temperature impregnation at a temperature of 70°C and a pressure of 25 MPa for 6 hours. Then slowly depressurize at a rate of 0.2 MPa / s, open the reactor, take out the shoe midsole preform, and heat it with 140°C high-pressure steam for 40 seconds to foam and obtain a foamed shoe midsole preform. (3) The foamed shoe midsole preform from step (2) is placed into a complex structure high sidewall shoe midsole mold for hot pressing. The hot pressing temperature is 158℃ and the hot pressing time is 5min. Then, it is water-cooled for 600s and demolded to obtain the foamed thermoplastic polyurethane shoe midsole.

[0074] (4) The foamed thermoplastic polyurethane shoe midsole obtained in step (3) was placed at room temperature for 24 hours. The test data and observed appearance are shown in Table 3.

[0075] Comparative Example 3: A manufacturing process for a foamed thermoplastic polyurethane shoe midsole, comprising the following specific steps: (1) TPU 5 is injection molded into an unfoamed shoe midsole preform using a disc injection molding machine. The injection molding machine temperature is set to 130-200℃. (2) Place the unfoamed shoe midsole preform from step (1) into the reactor, introduce high-pressure carbon dioxide fluid into the reactor, heat and impregnate it, maintain the temperature at 127°C, maintain the pressure at 9MPa, and the time at 0.5h, then depressurize rapidly at a rate of 3MPa / s, open the reactor, and obtain the foamed shoe midsole preform. (3) The foamed shoe midsole preform from step (2) is placed into a complex structure high-sidewall shoe midsole mold for hot pressing. The hot pressing temperature is 150℃ and the hot pressing time is 12min. Then, it is water-cooled for 100s and demolded to obtain the foamed thermoplastic polyurethane shoe midsole.

[0076] The foamed thermoplastic polyurethane shoe midsole obtained in step (3) was placed at room temperature for 24 hours. The test data and observed appearance are shown in Table 3.

[0077] Comparative Example 4: A manufacturing process for a foamed thermoplastic polyurethane shoe midsole, comprising the following specific steps: (1) TPU 6 is injection molded into an unfoamed shoe midsole preform using a disc injection molding machine. The injection molding machine temperature is set to 130-190℃. (2) Place the unfoamed shoe midsole preform from step (1) into the reactor, introduce high-pressure carbon dioxide fluid into the reactor, and perform low-temperature impregnation at a temperature of 30°C, a pressure of 10MPa, and a time of 20h. Then, slowly depressurize at a rate of 0.01MPa / s, open the reactor, take out the shoe midsole preform, and heat it with 120°C high-pressure steam for 30s to foam and obtain the foamed shoe midsole preform. (3) The foamed shoe midsole preform from step (2) is placed into a complex structure high sidewall shoe midsole mold for hot pressing. The hot pressing temperature is 130℃ and the hot pressing time is 5min. Then, it is water-cooled for 600s and demolded to obtain the foamed thermoplastic polyurethane shoe midsole.

[0078] The foamed thermoplastic polyurethane shoe midsole obtained in step (3) was placed at room temperature for 24 hours. The test data and observed appearance are shown in Table 3.

[0079] Table 3 As can be seen, this invention solves the problem of shoe wall shrinkage caused by high hot-pressing temperatures in complex-structured, high-sidewall shoe soles during the secondary hot-pressing of foamed thermoplastic polyurethane shoe midsole preforms, ensuring the acceptable appearance of the shoe midsole. Surprisingly, the foamed thermoplastic polyurethane shoe midsole prepared by this invention exhibits superior physical properties, such as tensile strength and delamination tear strength, significantly increasing the shoe's lifespan and comfort.

[0080] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A foamed thermoplastic polyurethane shoe midsole, characterized in that, The raw material composition of the foamed thermoplastic polyurethane shoe midsole includes thermoplastic polyurethane, which may or may not contain a crosslinking agent. When the raw material composition of the thermoplastic polyurethane does not contain a crosslinking agent, the raw material composition of the foamed thermoplastic polyurethane shoe midsole also includes a crosslinking agent. The crosslinking agent includes one or more of polyisocyanates, polyhydroxy compounds, and polyamino compounds; The polyisocyanate contains at least three isocyanate groups; The polyhydroxy compound contains at least three hydroxyl groups; The polyamino compound contains at least three amino groups.

2. The foamed thermoplastic polyurethane shoe midsole according to claim 1, characterized in that, When the raw material composition of the thermoplastic polyurethane contains a crosslinking agent, the raw material composition of the thermoplastic polyurethane also contains a polyol, a diisocyanate and a chain extender, and the mass of the crosslinking agent in the raw material composition of the thermoplastic polyurethane is 0.1%-5% of the total mass of the polyol, diisocyanate and chain extender.

3. The foamed thermoplastic polyurethane shoe midsole according to claim 1, characterized in that, The raw material composition of the foamed thermoplastic polyurethane shoe midsole includes thermoplastic polyurethane and a crosslinking agent, and the mass ratio of thermoplastic polyurethane to crosslinking agent in the raw material composition of the foamed thermoplastic polyurethane shoe midsole is 100:0.1-5.

4. The foamed thermoplastic polyurethane shoe midsole according to claim 1, characterized in that, The polyisocyanate includes one or more of the following: triphenylmethane 4,4',4''-triisocyanate, HDI trimer, HDI tetramer, and IPDI trimer; The polyhydroxy compound includes one or more of trimethylolpropane, trimethylolethane, glycerol, and 3,5-dihydroxy-4-methoxybenzyl alcohol; The polyamino compound includes one or more of 1,2,3-propanetriamine, triethylenetetramine, and 1,3,5-phenyltriamine.

5. The method for preparing the foamed thermoplastic polyurethane shoe midsole according to any one of claims 1-4, characterized in that, Including the following steps: (1) Obtain the shoe midsole preform through any one or more of the following methods: Method 1: Mix 100 parts by weight of thermoplastic polyurethane and 0.1-5 parts by weight of the aforementioned polyisocyanate and then injection mold to obtain an unfoamed shoe midsole preform; Method 2: Add polyol, diisocyanate, chain extender, and crosslinking agent accounting for 0.1%-5% of the total mass of polyol, diisocyanate, and chain extender to a twin-screw extruder, extrude and react, and after passing through the die, granulate to obtain thermoplastic polyurethane granules. Inject the thermoplastic polyurethane granules into unfoamed shoe midsole preforms. (2) Obtain the initial blank of the foam shoe midsole through any one or more of the following methods: Method A: Place the unfoamed shoe midsole preform into a reactor containing high-pressure fluid, heat and impregnate it, then quickly depressurize and open the reactor to obtain the foamed shoe midsole preform; Method B: Place the unfoamed shoe midsole preform into a reactor with high-pressure fluid for low-temperature immersion, then slowly depressurize, open the reactor, remove the shoe midsole preform, and heat it to foam to obtain a foamed shoe midsole preform. (3) The foamed shoe midsole blank is placed into the shoe midsole mold for hot pressing, and then cooled and molded to obtain the foamed thermoplastic polyurethane shoe midsole.

6. The preparation method according to claim 5, characterized in that, In method one: The melting point of thermoplastic polyurethane is 120-200℃, preferably 120-180℃, and more preferably 130-170℃; The Shore hardness of the thermoplastic polyurethane is 50A-98A, preferably 70A-98A, and more preferably 80A-98A; In method two: The polyols include one or more of polyester polyols, polyether polyols, polyether ester polyols, and polycarbonate polyols. The diisocyanate includes one or more of hexamethylene diisocyanate, isophorone diisocyanate, methylene diphenyl diisocyanate, 1,4-cyclohexane diisocyanate, terephthalic diisocyanate, and pentamethylene diisocyanate. The chain extender includes one or more of 1,2-ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, cyclohexanediol, and hydroquinone dihydroxyethyl ether. The hard segment content of thermoplastic polyurethane particles is 20%-50%; The melting point of the thermoplastic polyurethane particles is 120-200℃, preferably 120-180℃, and more preferably 130-170℃; The thermoplastic polyurethane particles have a Shore hardness of 50A-98A, preferably 70A-98A, and more preferably 80A-98A.

7. The preparation method according to claim 5, characterized in that, In step (2), the high-pressure fluid includes one or both of carbon dioxide and nitrogen.

8. The preparation method according to claim 5, characterized in that, In method A: The temperature for the heating and impregnation is 100-200℃, the pressure is 5-30MPa, and the holding time is 0-6h. The rapid pressure relief rate is 1-1000 MPa / s; In method B: The low-temperature impregnation temperature is 0-70℃, the pressure is 5-30MPa, and the time is 1-20h; The slow pressure relief rate is 0.01-0.5 MPa / s; The heat source for heating and foaming includes one or more of water vapor, hot air, and microwaves. The heating and foaming temperature is 100-180℃, and the time is 5-200s.

9. The preparation method according to claim 5, characterized in that, In step (3): The hot pressing temperature is 120-200℃, and the time is 2-30 minutes; The cooling and shaping process includes one or both of water-cooled shaping and air-cooled shaping. The cooling and shaping time is 50-600 seconds.

10. The application of crosslinking agents in the preparation of foamed thermoplastic polyurethane shoe midsoles using a preform foaming process, characterized in that, The crosslinking agent includes one or more of polyisocyanates, polyhydroxy compounds, and polyamino compounds; The polyisocyanate contains at least three isocyanate groups; The polyhydroxy compound contains at least three hydroxyl groups; The polyamino compound contains at least three amino groups; When the crosslinking agent is used in the small-embryo foaming process to prepare foamed thermoplastic polyurethane shoe midsoles, it can prevent the shoe wall from shrinking during hot pressing and improve one or more of the following properties of the foamed thermoplastic polyurethane shoe midsoles: tensile strength, elongation at break, and delamination tear strength.

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