A composite supercritical foamed shoe material

Abstract

This invention provides a composite supercritical foamed shoe material, relating to the field of shoe material technology. The invention incorporates a first chain extender containing ester groups and benzene rings into the chain extender of rigid TPU, improving the affinity of rigid TPU for supercritical CO2 fluid, increasing the foaming ratio of rigid TPU to be close to that of flexible TPU, thereby resulting in better bonding between different structures in the composite supercritical foamed shoe material and obtaining a composite supercritical foamed shoe material with high mechanical strength.

Description

Technical Field

[0001] This invention belongs to the field of footwear material technology and relates to a composite supercritical foamed footwear material. Background Technology

[0002] Supercritical foaming technology has been widely used in shoe sole materials, such as midsoles. However, current shoe midsoles are generally made of only one supercritical foaming material, such as TPU. But having only one supercritical foaming material in the midsole presents the following problems: it's impossible to achieve both support and soft elasticity. Improving support requires increasing the hardness and strength of the shoe material, which reduces soft elasticity.

[0003] To address this, a composite shoe midsole with a composite structure is proposed, consisting of an outer frame support layer and an inner core cushioning layer. The outer frame support layer possesses high hardness and strength, while the inner core cushioning layer exhibits good soft elasticity. Both materials can be obtained by injection molding the outer frame support layer and the inner core cushioning layer, followed by supercritical foaming. Both materials can be TPU. However, the expansion ratios (i.e., different expansion proportions) of the two materials during supercritical foaming differ. For example, high-hardness TPU has a high content of hard segments (rigid segments formed by the reaction of diisocyanate monomers and chain extenders), making it difficult for supercritical fluid to penetrate into the hard segment region, resulting in a lower expansion ratio. Therefore, in the aforementioned composite shoe midsole, the bonding force between the two materials during supercritical foaming is insufficient, leading to easy detachment. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a composite supercritical foamed shoe material.

[0005] The technical solution of the present invention is as follows:

[0006] A composite supercritical foamed shoe material is obtained by combining a first TPU and a second TPU into one or more of the following structures: top and bottom structure, left and right structure, front and back structure, and inner and outer structure, and then supercritical foaming is carried out under supercritical CO2 fluid.

[0007] The hard segment content of the first TPU is at least 20% higher than that of the second TPU, and the chain extender of the first TPU includes a first chain extender.

[0008] The first chain extender has a molecular weight not exceeding 400 g / mol and contains ester groups and benzene rings;

[0009] The weight percentage of the first chain extender in the chain extender of the first TPU is not less than 20%.

[0010] Preferably, the weight percentage of the first chain extender in the chain extender of the first TPU is 30-70%.

[0011] Preferably, the first chain extender is selected from one or a combination of two or more of bis(2-hydroxyethyl) terephthalate, 1,3-propanediol bis(4-aminobenzoate), 2,5-bis(hydroxymethyl) terephthalate and di(1,3-propanediol) terephthalate.

[0012] Preferably, the chain extender of the first TPU further comprises C2-C6 alkyl diol.

[0013] Preferably, when the hard segment content of the second TPU is 20-25%, the hard segment content of the first TPU is 45-70%.

[0014] Alternatively, when the hard segment content of the second TPU is 25-35%, the hard segment content of the first TPU is 55-70%.

[0015] Preferably, the first TPU is obtained by reacting a first raw material component;

[0016] The first raw material component comprises a first diisocyanate monomer, a first polyester diol, and a chain extender for the first TPU;

[0017] The first polyester diol is selected from polycarbonate diol and / or polycaprolactone diol;

[0018] The number-average molecular weight of the first polyester diol is 600-1200 g / mol.

[0019] More preferably, the first diisocyanate monomer is selected from one or a combination of two or more of MDI, TDI, IPDI, HDI and HMDI.

[0020] More preferably, the first raw material component further comprises a nucleating agent accounting for 0.5-1% of the weight of the first raw material component;

[0021] The nucleating agent is selected from polyurethane microspheres with an average particle size of 0.05-5 μm.

[0022] Preferably, the second TPU is obtained by reacting a second raw material component;

[0023] The second raw material component comprises a second diisocyanate monomer, a polyether diol and / or a second polyester polyol, and a second chain extender;

[0024] The number average molecular weights of the polyether diol and the second polyester polyol are both 1500-4000 g / mol.

[0025] More preferably, the second diisocyanate monomer is selected from one or a combination of two or more of MDI, TDI, IPDI, HDI and HMDI.

[0026] The beneficial effects of this invention are:

[0027] (1) Since the expansion ratio of supercritical foaming of high hardness and high strength rigid TPU (first TPU) is lower than that of soft elastic TPU (second TPU), the present invention introduces ester bonds in the first TPU through chain extender. Ester bonds have a high affinity for CO2 fluid, which is beneficial to improve the foaming performance and expansion ratio of the first TPU, approaching or reaching the expansion ratio of the second TPU, and improving the bonding force between the two supercritical foaming materials.

[0028] (2) In this invention, adding a nucleating agent to the first TPU can further optimize the performance of the first TPU after foaming, and improve the foaming ratio of the first TPU and the performance of the composite supercritical foamed shoe material. Detailed Implementation

[0029] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0030] This invention proposes a composite supercritical foamed shoe material, which is made by combining a first TPU and a second TPU into one or more of the following structures: top and bottom structure, left and right structure, front and back structure, and inner and outer structure, and then obtaining it by supercritical foaming under supercritical CO2 fluid.

[0031] The hard segment content of the first TPU is at least 20% higher than that of the second TPU, and the chain extender of the first TPU includes a first chain extender.

[0032] The first chain extender has a molecular weight not exceeding 400 g / mol and contains ester groups and benzene rings;

[0033] The first chain extender accounts for no less than 20% of the weight of the chain extender in the first TPU.

[0034] High-hardness thermoplastic polyurethane (TPU) contains a high proportion of crystalline hard segments. During supercritical foaming, the supercritical fluid has difficulty penetrating into these highly crystalline hard segments. Therefore, generally, the higher the hard segment content of the polyurethane (high hardness), the lower the foaming ratio. When supercritical foaming is performed on composite shoe materials composed of two TPUs with different hard segment contents, the foaming ratio of the TPU with the high hard segment content (first TPU) is significantly lower than that of the TPU with the low hard segment content (second TPU). This results in insufficient bonding between the two TPU materials after foaming, affecting the performance of the composite shoe material, such as lower tensile strength. In this invention, the first TPU in the composite supercritical foamed shoe material has a high hard segment content and provides support, while the second TPU has a low hard segment content and improves the soft and elastic effect. There are no particular restrictions on the structure of composite supercritical foamed shoe materials. For example, it can be an inner and outer structure, with the outer frame obtained by first TPU foaming and the inner core obtained by second TPU foaming, resulting in shoe materials with good flexibility and support; or it can be a front and back structure, with the forefoot area obtained by first TPU foaming and the heel area obtained by second TPU foaming.

[0035] In this invention, an ester group structure with good affinity for supercritical CO2 fluid is introduced into the first TPU by a first chain extender, which improves the permeability of supercritical CO2 fluid to the hard segment, resulting in a significant increase in the foaming ratio of the hard segment of the first TPU, thereby also significantly improving the overall foaming ratio of the first TPU, making it closer to the foaming ratio of the second TPU. This achieves good bonding between different layers and / or structures of the composite supercritical foamed shoe material, improving the performance of the composite supercritical foamed shoe material.

[0036] Hard segment content refers to the weight percentage of rigid hard segment structures in TPU. The hard segment content directly determines the number of hydrogen bonds, the degree of microphase separation, and the crystallinity of the TPU. Generally, as the hard segment content increases, the hardness and mechanical strength of the TPU increase, while its flexibility decreases. If the hard segment content of the first TPU is at least 20% higher than that of the second TPU, there will be a significant difference in hardness and strength between the two TPUs. This difference will also be evident after foaming. The first TPU will have high strength and high hardness after foaming, while the second TPU will have good flexibility. For example, this can be used to form a shoe midsole with good outer frame support and a soft, elastic inner core. For instance, the hard segment content of the first TPU can be 20%, 25%, 30%, 35%, or 40% higher than that of the second TPU. For example, if the hard segment content of the first TPU is 60% and that of the second TPU is 30%, then the hard segment content of the first TPU is 30% higher than that of the second TPU. In this invention, there are no particular restrictions on the testing method for hard segment content; differential scanning calorimetry (DSC) can be used for testing.

[0037] In some embodiments, the weight percentage of the first chain extender in the chain extender of the first TPU is 30-70%. By adopting the above technical solution, the good affinity of the first chain extender for supercritical CO2 fluid can be utilized, while avoiding the shortcomings of the first chain extender, such as poor solubility, uneven reaction, excessive hardness, and insufficient toughness. For example, the weight percentage of the first chain extender in the chain extender of the first TPU can be any value or any value between 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, and 70%, without particular limitation.

[0038] In some embodiments, the first chain extender is selected from one or a combination of two or more of bis(2-hydroxyethyl) terephthalate (BHET), 1,3-propanediol bis(4-aminobenzoate), 2,5-bis(hydroxymethyl) terephthalate, and di(1,3-propanediol) terephthalate (BHTT). The first chain extender contains hydroxyl or amino groups associated with NCO groups, enabling efficient chain extension. Furthermore, the presence of a benzene ring in the first chain extender provides high rigidity, which is beneficial for improving the mechanical strength of the first TPU foam and enhancing its support effect.

[0039] In some embodiments, the chain extender of the first TPU further comprises a C2-C6 alkyl diol. For example, the C2-C6 alkyl diol may be ethylene glycol, 1,4-butanediol, 1,6-hexanediol, etc. For the chain extension reaction of the first TPU, the chain extender may be added all at once, or the first chain extender may be added first, followed by the remaining chain extender (e.g., 1,4-butanediol).

[0040] In some embodiments, when the hard segment content of the second TPU is 20-25%, the hard segment content of the first TPU is 45-70%; for example, the hard segment content of the first TPU can be 45%, 50%, 55%, 60%, 65%, 70%, etc., and the hard segment content of the second TPU can be 20%, 25%, etc.

[0041] Alternatively, when the hard segment content of the second TPU is 25-35%, the hard segment content of the first TPU is 55-70%; for example, the hard segment content of the first TPU can be 55%, 60%, 65%, 70%, etc., and the hard segment content of the second TPU can be 25%, 30%, 35%, etc.

[0042] For example, the hard segment content of the first TPU can be 45%, 50%, 55%, 60%, 65%, 70%, etc., and the hard segment content of the second TPU can be 20%, 25%, 30%, 35%, etc.

[0043] In some embodiments, the first TPU is obtained by reacting a first raw material component;

[0044] The first raw material component includes a first diisocyanate monomer, a first polyester diol, and a chain extender for the first TPU;

[0045] The first polyester diol is selected from polycarbonate diol and / or polycaprolactone diol;

[0046] The number-average molecular weight (Mn) of the first polyester diol is 600-1200 g / mol.

[0047] In the first raw material component mentioned above, the molar ratio of the first diisocyanate monomer to the first polyester diol can be 1.8-2.9:1, and the R value (molar ratio of NCO / (OH+NH2)) can be 1.02-1.05. The soft segment uses the first polyester diol, which has high strength and hardness, and good affinity with supercritical CO2 fluid, which is more conducive to improving the hardness, strength, and foaming ratio of the first TPU. Furthermore, the first polyester diol has a lower Mn content, which can improve the hardness and strength of the first TPU. The hard segment content of the first TPU can be adjusted by changing the type of the first diisocyanate monomer, the type of the first polyester diol, and the molar ratio of the first diisocyanate monomer to the polyester diol.

[0048] In some embodiments, the first diisocyanate monomer is selected from one or a combination of two or more of MDI, TDI, IPDI, HDI, and HMDI. For the first diisocyanate monomer, to improve hardness and strength, a rigid diisocyanate monomer containing a cyclohexyl or aromatic group can be selected, such as TDI or MDI.

[0049] In some embodiments, the first raw material component further comprises a nucleating agent accounting for 0.5-1% by weight of the first raw material component. Adding a nucleating agent can improve the uniformity of the foaming of the first TPU and its foaming performance of the hard segments, making it closer to the foaming ratio of the second TPU, thereby improving the bonding force between different structures (first TPU and second TPU) in the composite supercritical foamed shoe material and the performance of the composite supercritical foamed shoe material, such as tensile strength and resilience. Commonly used nucleating agents include inorganic nucleating agents, such as nano-silica and nano-bentonite, as well as organic nucleating agents, such as polyurethane microspheres and polyamide microspheres. The nucleating agent is selected from polyurethane microspheres with an average particle size of 0.05-5 μm. This invention has found that, compared with other nucleating agents, polyurethane microspheres have a better effect on improving the foaming performance of the first TPU. Polyurethane microspheres are readily available from the market.

[0050] In some embodiments, the second TPU is obtained by reacting a second raw material component;

[0051] The second raw material component includes a second diisocyanate monomer, a polyether diol and / or a second polyester polyol, and a second chain extender;

[0052] The number average molecular weights of polyether diols and second polyester polyols are 1500-4000 g / mol.

[0053] In the second raw material component mentioned above, the molar ratio of the second diisocyanate monomer to the polyether diol and / or the second polyester polyol can be 1.1-1.2:1, and the R value can be 0.95-1.01. Using polyether diols and / or second polyester polyols with a higher Mn value in the soft segment is beneficial for improving the soft elasticity of the second TPU. The second TPU can be prepared according to existing technology or obtained directly from the market, such as commercially available soft TPU with a hardness of 55A-85A (Shore A hardness). Furthermore, using polyether diols in the soft segment of the second TPU results in better soft elasticity after foaming.

[0054] In some embodiments, the second diisocyanate monomer is selected from one or a combination of two or more of MDI, TDI, IPDI, HDI, and HMDI. For the second diisocyanate monomer, HDI, etc., can be selected to improve flexibility.

[0055] In this invention, the composite supercritical foamed shoe material combines the properties of the first TPU and the second TPU, providing better wearing and / or protective effects. Furthermore, the composite supercritical foamed shoe material can be used for modular midsoles, where different materials are injection molded into modular midsoles before supercritical foaming, achieving good bonding performance between different modules. For modular midsoles, those skilled in the art know that they are not limited to one of the following: top-bottom structure, left-right structure, front-back structure, or inner-outer structure; they can also be a combination of two or more. For example, taking a front-back structure as an example, both the front and back structures can be top-bottom structures, thus forming a modular midsole composed of four modules. The front lower structure and the rear upper structure can be the first TPU, and the front upper structure and the rear lower structure can be the second TPU. As another example, for an inner-outer structure, the inner core can be the second TPU, and the outer support layer can be composed of front and back structures, with the front structure being the second TPU and the back structure being the first TPU.

[0056] The technical solution of the present invention will be further described and illustrated below with reference to various embodiments. Unless otherwise specified, the parts mentioned in the following embodiments are parts by weight.

[0057] Preparation Examples 1-4: Preparation of the First TPU

[0058] Preparation Example 1

[0059] The molar ratio of MDI, polycarbonate diol (Mn=800), and chain extender is 2.2:1:1.15, and the weight of dibutyltin dilaurate is 0.15% of the sum of the weights of MDI and polycarbonate diol.

[0060] The chain extender is composed of BHET and 1,4-butanediol in a weight ratio of 1:9.

[0061] Under nitrogen protection, MDI was added to the reaction apparatus, followed by polycarbonate diol in batches. The mixture was stirred at room temperature for 2 hours, then BHET and dibutyltin dilaurate were added, and the mixture was heated to 115°C and reacted for 2 hours. 1,4-Butanediol was then added, and stirring continued for another 2 hours to obtain rigid TPU, designated as rigid TPU-1. The Shore D hardness of rigid TPU-1 was measured to be 54, and the hard segment content was 49%.

[0062] Preparation Example 2

[0063] The molar ratio of MDI, polycarbonate diol (Mn=800), and chain extender is 2.5:1:1.45, and the weight of dibutyltin dilaurate is 0.15% of the sum of the weights of MDI and polycarbonate diol.

[0064] The chain extender is composed of BHET and 1,4-butanediol in a weight ratio of 3:7.

[0065] A rigid TPU, designated as rigid TPU-2, was prepared according to the method described in Preparation Example 1. The Shore D hardness of rigid TPU-2 was measured to be 62, and the hard segment content was 55%.

[0066] Preparation Example 3

[0067] The molar ratio of MDI, polycarbonate diol (Mn=800), and chain extender is 2.8:1:1.7, and the weight of dibutyltin dilaurate is 0.15% of the sum of the weights of MDI and polycarbonate diol.

[0068] The chain extender is composed of BHET and 1,4-butanediol in a weight ratio of 7:3.

[0069] A rigid TPU, designated as rigid TPU-3, was prepared according to the method described in Preparation Example 1. The Shore D hardness of rigid TPU-3 was measured to be 73, and the hard segment content was 63%.

[0070] Comparative Preparation Example 1

[0071] The difference between this comparative example and Preparation Example 1 is that in Preparation Example 1, BHET in the chain extender was replaced with an equal weight of 1,4-butanediol, meaning that BHET was not added in this comparative preparation example. All other steps remained unchanged. A rigid TPU was obtained, designated as Rigid TPU-4. The Shore D hardness of Rigid TPU-4 was measured to be 51, and the hard segment content was 45%.

[0072] Preparation Example 4

[0073] The molar ratio of MDI, polycaprolactone diol (Mn=1000), and chain extender is 2.4:1:1.4, and the weight of dibutyltin dilaurate is 0.15% of the sum of the weights of MDI and polycaprolactone diol.

[0074] The chain extender is composed of BHET and 1,6-hexanediol in a weight ratio of 1:1.

[0075] A rigid TPU, designated as rigid TPU-5, was prepared according to the method described in Preparation Example 1. The Shore D hardness of rigid TPU-5 was measured to be 59, and the hard segment content was 50%.

[0076] In the following embodiments and comparative examples, the supercritical foaming process is as follows: supercritical CO2 fluid is used, foaming temperature is 120℃, foaming pressure is 10MPa, wetting time is 2h, and depressurization rate is 1.5MPa / s.

[0077] Soft TPU-1: Polyether-type TPU, Shore A hardness 71, hard segment content 26%.

[0078] Soft TPU-2: Polyether-type TPU, Shore A hardness 85, hard segment content 33%.

[0079] The preparation method of composite TPU is as follows: rigid TPU and soft TPU are selected respectively, and a composite layer with upper and lower layers is formed by injection molding. The upper layer is rigid TPU and the lower layer is soft TPU. The thickness of both the upper and lower layers is 1mm.

[0080] The foaming ratio is calculated as follows: Foaming ratio = Density before foaming / Density after foaming.

[0081] Tensile strength was tested using an electronic tensile testing machine.

[0082] The results of each embodiment and comparative example are shown in Table 1 below.

[0083] Table 1

[0084]

[0085] Therefore, as can be seen from the results in Table 1 above, the present invention introduces ester and phenyl structures into the hardness of rigid TPU through the first chain extender, which significantly improves the foaming ratio of supercritical foaming, making it closer to the foaming ratio of soft TPU, and also improves the mechanical strength of rigid TPU after foaming and the mechanical strength of composite TPU after foaming.

[0086] Example 9

[0087] In Preparation Example 1, 0.5% by weight of polyurethane microspheres with an average particle size of 1 μm were added to the rigid TPU-1 as a nucleating agent, and the mixture was mixed using a twin-screw extruder to obtain a composite rigid TPU, denoted as rigid TPU-6.

[0088] Example 10

[0089] In Preparation Example 1, 1% by weight of polyurethane microspheres with an average particle size of 1 μm were added to the rigid TPU-1 as a nucleating agent, and the mixture was mixed using a twin-screw extruder to obtain a composite rigid TPU, denoted as rigid TPU-7.

[0090] Example 11

[0091] In Preparation Example 1, 0.5% by weight of nano-silica with an average particle size of 100 nm was added to the rigid TPU-1 as a nucleating agent, and the mixture was mixed using a twin-screw extruder to obtain a composite rigid TPU, denoted as rigid TPU-8.

[0092] Example 12

[0093] In Preparation Example 1, 1% by weight of nano-silica with an average particle size of 100 nm was added to the rigid TPU-1 as a nucleating agent, and the mixture was mixed using a twin-screw extruder to obtain a composite rigid TPU, denoted as rigid TPU-9.

[0094] The results are shown in Table 2 below.

[0095] The tensile strength retention rate is calculated as follows: tensile strength of composite TPU / tensile strength of rigid TPU × 100%. A higher tensile strength retention rate indicates better bonding between the rigid TPU and flexible TPU in the composite TPU.

[0096] Table 2

[0097]

[0098] As shown in Table 2 above, adding a nucleating agent to rigid TPU can further improve the foaming ratio and mechanical strength of rigid TPU, as well as the mechanical strength of composite TPU after foaming. Moreover, compared with the use of inorganic nucleating agents (nano silica), rigid TPU has a higher foaming ratio when polyurethane microspheres are used.

[0099] As described above, the basic principles, main features, and advantages of the present invention have been shown and described. Those skilled in the art should understand that the present invention is not limited to the above embodiments, which are merely preferred embodiments and should not be construed as limiting the scope of the invention. All equivalent changes and modifications made in accordance with the scope of the patent and the description should still fall within the scope of the present invention. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A composite supercritical foamed shoe material, characterized in that, It is obtained by combining the first TPU and the second TPU into one or more of the following structures: top and bottom structure, left and right structure, front and back structure, and inner and outer structure, and then supercritical foaming is carried out in supercritical CO2 fluid. The hard segment content of the first TPU is at least 20% higher than that of the second TPU; The first TPU is obtained by reacting the first raw material component; The first raw material component comprises MDI, polycarbonate diol, chain extender, and dibutyltin dilaurate, wherein the molar ratio of MDI, polycarbonate diol, and chain extender is 2.8:1:1.7, and the weight of dibutyltin dilaurate is 0.15% of the sum of the weights of MDI and polycarbonate diol. The number-average molecular weight of the polycarbonate diol is 800; The chain extender is composed of bis(2-hydroxyethyl) terephthalate and 1,4-butanediol in a weight ratio of 7:

3.

2. The composite supercritical foamed shoe material according to claim 1, characterized in that, When the hard segment content of the second TPU is 20-25%, the hard segment content of the first TPU is 45-70%. Alternatively, when the hard segment content of the second TPU is 25-35%, the hard segment content of the first TPU is 55-70%.

3. The composite supercritical foamed shoe material according to claim 1, characterized in that, The first raw material component further comprises a nucleating agent accounting for 0.5-1% of the weight of the first raw material component; The nucleating agent is selected from polyurethane microspheres with an average particle size of 0.05-5 μm.

4. The composite supercritical foamed shoe material according to claim 1, characterized in that, The second TPU is obtained by reacting a second raw material component; The second raw material component comprises a second diisocyanate monomer, a polyether diol and / or a second polyester polyol, and a second chain extender; The number average molecular weights of the polyether diol and the second polyester polyol are both 1500-4000 g / mol.

5. The composite supercritical foamed shoe material according to claim 4, characterized in that, The second diisocyanate monomer is selected from one or a combination of two or more of MDI, TDI, IPDI, HDI and HMDI.

Images