TPU Material for Making Soles and Its Foaming Process

Abstract

This case involves a TPU material for making shoe soles and its foaming process, including: thermoplastic polyurethane TPU, ethylene-vinyl acetate copolymer EVA, functional additives, foaming agents, cross-linking agents, and foaming accelerators; among them, the functional additives include styrene-acrylic resin, EVA grafted maleic anhydride, and modified SiO2. In this case, the SiO2 nanoparticles are modified to have stable dispersibility in the material, which can act as a reinforcing agent in the material and endow the foamed material with excellent reinforcing effects; in this application, the SiO2 nanoparticles are mixed with styrene-acrylic resin and EVA grafted maleic anhydride to form functional additives, which not only significantly improves the fusion degree of TPU and EVA, making the product have both the wear resistance and resilience of TPU and the light weight and softness of EVA; at the same time, it also further synergistically improves the mechanical strength of the foamed material, and can better meet the requirements for material properties when it is used as a shoe sole material.

Description

Technical Field

[0001] The present invention relates to the technical field of sole materials, and particularly to a TPU material for making soles and its foaming process. Background Art

[0002] One of the most important components of shoes is the sole. The sole, also known as the outsole, is the bottom part that directly contacts the ground when the shoes are in motion. Therefore, its "life" decreases rapidly during use. According to the styles and uses of shoes, soles are made of many different materials. The materials are very diverse, for example, including: natural rubber, vulcanized rubber, leather, polyurethane (PU), ethylene vinyl acetate (EVA), block polyether amide (PEBA), etc.

[0003] As the main material for current sports shoe soles, foamed EVA has the advantages of light weight, softness, and comfortable wearing. However, the EVA sole foaming material with a high foaming ratio has the problem of poor abrasion resistance and a large loss of resilience after long-term wearing. TPU is a thermoplastic polyurethane, which can be divided into polyester type and polyether type. It has good abrasion resistance and elasticity, and is more environmentally friendly. However, when used as a sole material, it has a relatively hard feel. Therefore, developing a soft TPU material with excellent abrasion resistance and resilience is the goal pursued by many researchers in this field. Summary of the Invention

[0004] Aiming at the deficiencies in the prior art, the present invention provides a soft TPU material with excellent abrasion resistance and resilience.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A TPU material for making soles, by weight, includes:

[0007] 100 parts of thermoplastic polyurethane TPU;

[0008] 5 - 10 parts of ethylene-vinyl acetate copolymer EVA;

[0009] 3 - 8 parts of functional additives;

[0010] 0.1 - 10 parts of foaming agent;

[0011] 0.1 - 10 parts of crosslinking agent;

[0012] 0.1 - 2 parts of foaming accelerator;

[0013] In this solution, thermoplastic polyurethane (TPU) and ethylene-vinyl acetate copolymer (EVA) are relatively common materials in sole production. Their commercialization is very mature, and they can be directly obtained from the market and used directly. In some specific solutions of this case, the brand of TPU selected is Covestro Bayer of Germany or BASF of Germany; the brand of EVA selected is DuPont of the United States, and other brands can also be used interchangeably.

[0014] In this solution, the blowing agent is selected from one or more of azodicarbonamide, sodium bicarbonate, sodium citrate, and p-toluenesulfonyl hydrazide; the crosslinking agent is selected from one of dicumyl peroxide and bis(tert-butylperoxyisopropyl)benzene; the foaming accelerator is a mixture of stearic acid and zinc stearate. They are all commonly used additives in the art and can be purchased from the market.

[0015] In another solution, the functional additive includes: 10-40 wt% styrene-acrylic resin, 20-50 wt% EVA grafted maleic anhydride, and the balance of modified SiO2;

[0016] Among them, the styrene-acrylic resin is a styrene-acrylate copolymer, which has good processing fluidity and good compatibility with other polymer resins, and is a very good modifier. In some specific implementation cases, it can be purchased from the market. In an improvable solution, this application uses styrene as the hard monomer, butyl acrylate and ethyl methacrylate as the soft monomers, and glycidyl methacrylate and maleic anhydride as the functional monomers to prepare the styrene-acrylic resin; among them, the mass ratio of the hard monomer, soft monomer and functional monomer is 5-6:3-4:0.5. The introduction of the functional monomer makes it have good connectivity with EVA grafted maleic anhydride and modified SiO2, and avoids self-aggregation during the extrusion granulation process, so that the obtained functional additive has good stability.

[0017] The EVA grafted maleic anhydride can improve the compatibility of TPU and EVA, and preferably the brand of DuPont of the United States.

[0018] The preparation process of the modified SiO2 is as follows:

[0019] 1) Preparation of hyperbranched carrier

[0020] First, methyl acrylate and diethylenetriamine are used to carry out a Michael addition reaction, and then transferred to 150 °C for polycondensation polymerization reaction to obtain a multi-amino hyperbranched polymer;

[0021] 2) Preparation of carboxylated SiO2

[0022] Disperse SiO2 nanoparticles in ethanol by ultrasonic treatment, add KH-550 dropwise, and stir overnight at room temperature to obtain amino-modified SiO2 nanoparticles. Subsequently, redisperse them in THF by ultrasonic treatment, add succinic anhydride under stirring, stir overnight at room temperature, centrifuge, wash with water, and dry to obtain the product.

[0023] 3) Preparation of modified SiO2

[0024] Dissolve and dilute the hyperbranched polymer with multiple amino groups in an ethanol solution. Subsequently, disperse the carboxylated SiO2 in it by ultrasonic treatment to obtain a mixture. Bubble nitrogen into the mixture to remove air, and then heat and react under a nitrogen atmosphere, stir and reflux overnight. After cooling to room temperature, centrifuge, wash with water, and dry to obtain the product.

[0025] First, the hyperbranched carrier is a hyperbranched polymer containing abundant amino functional groups prepared from diethylenetriamine, which can be used as a bridging agent to improve the binding property with nanoparticles and other additives. Carboxyl functional groups are formed on the surface of SiO2 nanoparticles by using a silane coupling agent, and then react with the amino groups in the hyperbranched carrier. The organic bond has high stability, and the dispersibility of SiO2 nanoparticles in the organic resin is also improved. After mixing the modified SiO2 with styrene-acrylic resin and EVA grafted maleic anhydride and granulating, a functional additive integrated as a whole is formed, which contains benzene rings and SiO2. The rigid structure makes the functional additive not easily detached from the two phases of TPU and EVA during the strong shear reaction process, and it acts as a compatibilizer and enhances the effect at the same time, so that the prepared foamed material has the advantages of both TPU and EVA.

[0026] Furthermore, in the preparation process of the modified SiO2, the mass ratio of the hyperbranched polymer with multiple amino groups to the carboxylated SiO2 is 1:0.05 - 1.

[0027] Furthermore, the functional additive is obtained by mixing and extruding and granulating styrene-acrylic resin, EVA grafted maleic anhydride, and modified SiO2.

[0028] The second object of the present invention provides a foaming process for the TPU material used for making shoe soles as described above, including the following steps:

[0029] Weigh the TPU, EVA, and functional additive, mix them thoroughly in a mixer, and then add the measured blowing agent, blowing aid, and crosslinking agent and continue mixing to obtain a mixture. The temperature of the mixer is set to 120 - 140 °C, and the mixing time is 10 - 20 min.

[0030] Press the mixture into a thin sheet through an open two-roll mixer, then make it into particles through a granulator, and enter an injection molding machine for molding, with the temperature set to 170 - 180 °C.

[0031] Subsequently, it is placed in an autoclave for foaming with nitrogen at 33 MPa, carbon dioxide at 2 MPa, a temperature of 140 - 160 °C, and foaming for 6 - 10 h; then it is transferred to another autoclave, the temperature is controlled at 140 - 160 °C, nitrogen is at 0.5 - 2 MPa, and the time is 25 - 40 min. After cooling, the product is discharged.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] SiO2 nanoparticles themselves have relatively high strength. By modifying them, they have stable dispersibility in the material and can act as reinforcing agents in the material, endowing the foamed material with excellent reinforcement effects; in this application, SiO2 nanoparticles are mixed with styrene-acrylic resin and EVA grafted maleic anhydride to form a functional additive, which not only significantly improves the fusion degree of EVA and TPU, enabling the product to have the wear resistance and resilience of TPU while also having the light weight and softness of EVA; at the same time, it further synergistically improves the mechanical strength of the foamed material, better meeting the requirements for material properties when used as sole materials. Specific Embodiments

[0034] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0035] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0036] Embodiment: A TPU material for making soles, by weight, includes:

[0037] 100 parts of thermoplastic polyurethane TPU;

[0038] 5 - 10 parts of ethylene-vinyl acetate copolymer EVA;

[0039] 2 - 8 parts of functional additive;

[0040] 0.1 - 5 parts of blowing agent (azodicarbonamide, sodium bicarbonate, sodium citrate, p-toluenesulfonyl hydrazide);

[0041] 0.1 - 5 parts of crosslinking agent (dicumyl peroxide, bis(tert-butylperoxyisopropyl)benzene);

[0042] 0.1 - 2 parts of foaming accelerator (stearic acid and zinc stearate);

[0043] The metered TPU, EVA, and functional additives are thoroughly kneaded and mixed evenly in a kneader, and then the metered blowing agent, blowing aid, and cross-linking agent are added and kneaded continuously to obtain a mixture; the temperature of the kneader is set at 120-140 °C, and the kneading time is 10-20 min;

[0044] The mixture is pressed into a thin sheet by an open two-roll kneader, then made into particles by a granulator, and fed into an injection molding machine for molding under pressure, with the temperature set at 170-180 °C;

[0045] Subsequently, it is placed in an autoclave for foaming, with nitrogen at 33 MPa, carbon dioxide at 2 MPa, and the temperature at 140-160 °C for 6-10 h; then it is transferred to another autoclave, with the temperature controlled at 140-160 °C, nitrogen at 0.5-2 MPa, and the time at 25-40 min, and discharged after cooling.

[0046] The TPU foam material is prepared according to the above foaming process. Example

[0047] 100 parts of thermoplastic polyurethane TPU;

[0048] 5 parts of ethylene-vinyl acetate copolymer EVA;

[0049] 3 parts of functional additives;

[0050] 0.5 part of azodicarbonamide;

[0051] 0.5 of dicumyl peroxide;

[0052] 0.2 part of blowing promoter;

[0053] Among them, the functional additives include 20 wt% styrene-acrylic resin, 20 wt% EVA grafted maleic anhydride, and 60 wt% modified SiO2;

[0054] The styrene-acrylic resin is prepared with styrene as the hard monomer, equal amounts of butyl acrylate and ethyl methacrylate as the soft monomers, and equal amounts of glycidyl methacrylate and maleic anhydride as the functional monomers; the mass ratio of the hard monomer, soft monomer, and functional monomer is 5:3:0.5.

[0055] The metered monomers are mixed evenly with water and emulsifier to obtain a pre-emulsion. A part of the pre-emulsion is taken as the seed emulsion. Under nitrogen protection, ammonium persulfate is added and seed emulsion polymerization is carried out at 60 °C, and then ammonium persulfate and the remaining pre-emulsion are continuously added, and the reaction is stirred overnight to obtain a latex, and the latex is dried to obtain it.

[0056] The preparation process of the modified SiO2 is as follows:

[0057] 1) Preparation of hyperbranched carrier

[0058] Weigh equimolar amounts of methyl acrylate and diethylenetriamine. Dilute methyl acrylate with methanol and then dropwise add it to diethylenetriamine. After all the addition is completed, stir and react at room temperature for 4 h. Subsequently, transfer the reaction flask to an oil bath at 150 °C. Collect the methanol solvent during the heating process, and then carry out a polycondensation polymerization reaction at a constant temperature for 4 h to obtain a hyperbranched polymer with multiple amino groups;

[0059] 2) Preparation of carboxylated SiO2

[0060] SiO2 nanoparticles are prepared using tetraethyl orthosilicate as the raw material and ammonia water as the catalyst. Ultrasonically disperse the prepared SiO2 nanoparticles in ethanol, dropwise add KH-550, and stir overnight at room temperature to obtain amino-modified SiO2 nanoparticles. Subsequently, ultrasonically disperse them again in THF, and add succinic anhydride under stirring. Stir overnight at room temperature, centrifuge and separate, wash with water and dry to obtain;

[0061] 3) Preparation of modified SiO2

[0062] Dissolve and dilute the hyperbranched polymer with multiple amino groups in an ethanol solution. Subsequently, ultrasonically disperse 0.5 times the amount of carboxylated SiO2 in it to obtain a mixed solution. Bubble nitrogen into the mixed solution to remove air, and then heat and react under a nitrogen atmosphere, stir and reflux overnight. After cooling to room temperature, centrifuge and separate, wash with water and dry to obtain.

[0063] For the foaming material prepared in this example, its Shore hardness is 53, tensile strength is 5.2 MPa, elongation at break is 350%, resilience is 58%, and compression set is 30%. Example

[0064] 100 parts of thermoplastic polyurethane TPU;

[0065] 8 parts of ethylene-vinyl acetate copolymer EVA;

[0066] 5 parts of functional additive;

[0067] 0.7 part of azodicarbonamide;

[0068] 0.8 part of dicumyl peroxide;

[0069] 0.5 part of foaming accelerator;

[0070] Among them, the functional additive includes 20 wt% styrene-acrylic resin, 30 wt% EVA grafted maleic anhydride, and 50 wt% modified SiO2;

[0071] The styrene resin is prepared with styrene as the hard monomer, equal amounts of butyl acrylate and ethyl methacrylate as the soft monomers, and equal amounts of glycidyl methacrylate and maleic anhydride as the functional monomers; the mass ratio of the hard monomer, soft monomer and functional monomer is 5:4:0.5.

[0072] The measured monomers are mixed evenly with water and emulsifier to obtain a pre-emulsion. Take part of the pre-emulsion as the seed emulsion. Under nitrogen protection, ammonium persulfate is added and seed emulsion polymerization is carried out at 60 °C. Then, ammonium persulfate and the remaining pre-emulsion are continuously added, and stirring reaction is carried out overnight to obtain latex. The latex is dried to obtain the product.

[0073] The preparation process of the modified SiO2 is as follows:

[0074] 1) Preparation of hyperbranched carrier

[0075] Weigh equimolar amounts of methyl acrylate and diethylenetriamine. Dilute methyl acrylate with methanol and drop it into diethylenetriamine. After all the dropping is completed, stir and react at room temperature for 4 h. Then transfer the reaction flask to an oil bath at 150 °C. Collect the methanol solvent during the heating process, and then carry out polycondensation polymerization reaction at a constant temperature for 4 h to obtain a hyperbranched polymer with multiple amino groups;

[0076] 2) Preparation of carboxylated SiO2

[0077] SiO2 nanoparticles are prepared with tetraethyl orthosilicate as the raw material and ammonia water as the catalyst. The prepared SiO2 nanoparticles are ultrasonically dispersed in ethanol, KH-550 is dropped, and stirred overnight at room temperature to obtain amino-modified SiO2 nanoparticles. Then ultrasonically disperse them again in THF, and add succinic anhydride under stirring, stir overnight at room temperature, centrifuge and separate, wash with water and dry to obtain;

[0078] 3) Preparation of modified SiO2

[0079] Dissolve and dilute the hyperbranched polymer with multiple amino groups in an ethanol solution. Then ultrasonically disperse 0.5 times the amount of carboxylated SiO2 in it to obtain a mixed solution. Bubble nitrogen into the mixed solution to remove air, and then heat and react under a nitrogen atmosphere, stir and reflux overnight. After cooling to room temperature, centrifuge and separate, wash with water and dry to obtain.

[0080] The foaming material prepared in this example has a Shore hardness of 52, a tensile strength of 5.7 MPa, an elongation at break of 380%, a resilience of 56%, and a compression set of 32%. Example

[0081] 100 parts of thermoplastic polyurethane TPU;

[0082] 10 parts of ethylene-vinyl acetate copolymer EVA;

[0083] 8 parts of functional additive;

[0084] 1.2 parts of azodicarbonamide;

[0085] 1 part of dicumyl peroxide;

[0086] 1 part of foaming accelerator;

[0087] The styrene-acrylic resin is prepared with styrene as the hard monomer, equal amounts of butyl acrylate and ethyl methacrylate as the soft monomers, and equal amounts of glycidyl methacrylate and maleic anhydride as the functional monomers; the mass ratio of the hard monomer, soft monomer and functional monomer is 6:4:0.5.

[0088] The metered monomers are mixed evenly with water and emulsifier to obtain a pre-emulsion. Take part of the pre-emulsion as the seed emulsion. Under nitrogen protection, ammonium persulfate is added and the seed emulsion polymerization is carried out at 60 °C. Then, ammonium persulfate and the remaining pre-emulsion are continuously added, and the reaction is stirred overnight to obtain a latex. The latex is dried to obtain the product.

[0089] The preparation process of the modified SiO2 is as follows:

[0090] 1) Preparation of hyperbranched carrier

[0091] Weigh equimolar amounts of methyl acrylate and diethylenetriamine. Dilute methyl acrylate with methanol and then drop it into diethylenetriamine. After all the dropping is completed, stir and react at room temperature for 4 h. Then transfer the reaction flask to an oil bath at 150 °C. During the heating process, collect the methanol solvent. After that, keep the temperature constant and react for 4 h to carry out polycondensation polymerization to obtain a hyperbranched polymer with multiple amino groups;

[0092] 2) Preparation of carboxylated SiO2

[0093] The SiO2 nanoparticles are prepared from tetraethyl orthosilicate as the raw material and ammonia water as the catalyst. The prepared SiO2 nanoparticles are ultrasonically dispersed in ethanol, and KH-550 is dropped. Stir overnight at room temperature to obtain amino-modified SiO2 nanoparticles. Then ultrasonically disperse them again in THF, and add succinic anhydride under stirring. Stir overnight at room temperature, centrifuge and separate, wash with water and dry to obtain the product;

[0094] 3) Preparation of modified SiO2

[0095] Dissolve and dilute the hyperbranched polymer with multiple amino groups in an ethanol solution. Then use ultrasound to disperse 0.5 times the amount of carboxylated SiO2 in it to obtain a mixed solution. Bubble nitrogen into the mixed solution to remove air. Then heat and react under a nitrogen atmosphere, stir and reflux overnight. After cooling to room temperature, centrifuge and separate, wash with water and dry to obtain the product.

[0096] The foamed material prepared in this example has a Shore hardness of 49, a tensile strength of 6.1 MPa, an elongation at break of 410%, a resilience of 52%, and a compression set of 33%.

[0097] Comparative Example 1:

[0098] 100 parts of thermoplastic polyurethane TPU;

[0099] 5 parts of ethylene-vinyl acetate copolymer EVA;

[0100] 3 parts of functional additive;

[0101] 0.5 part of azodicarbonamide;

[0102] 0.5 of dicumyl peroxide;

[0103] 0.2 part of foaming accelerator;

[0104] Among them, the functional additive includes 20wt% styrene-acrylic resin, 20wt% EVA grafted maleic anhydride, and nano-SiO2 particles; all are unmodified materials directly purchased from the market.

[0105] The foamed material prepared in this example has a Shore hardness of 55, a tensile strength of 4.8 MPa, an elongation at break of 320%, a resilience of 45%, and a compression set of 42%.

[0106] Comparative Example 2:

[0107] 100 parts of thermoplastic polyurethane TPU;

[0108] 10 parts of ethylene-vinyl acetate copolymer EVA;

[0109] 1 part of azodicarbonamide;

[0110] 1 part of dicumyl peroxide;

[0111] 0.5 part of foaming accelerator;

[0112] The foamed material prepared in this example has a Shore hardness of 55, a tensile strength of 4.2 MPa, an elongation at break of 290%, a resilience of 41%, and a compression set of 40%.

[0113] Although the embodiments of the present invention have been disclosed as above, it is not limited to only the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to specific details.

Claims

1. A TPU material for making a sole, characterized in that: By weight, including: Thermoplastic polyurethane TPU 100 parts; Ethylene-vinyl acetate copolymer EVA 5-10 parts; 3~8 parts of functional additives; Foaming agent 0.1~10 parts; Cross-linking agent 0.1~10 parts; 0.1~2 parts of foaming promoter; Wherein, the functional additives include styrene acrylic resin, EVA grafted maleic anhydride, and modified SiO2; the preparation process of the modified SiO2 is as follows: 1) Preparation of hyperbranched carriers First, methyl acrylate and diethylenetriamine are subjected to Michael addition reaction, and then the reaction is transferred to 150°C for polycondensation to obtain a hyperbranched polymer with multiple amino groups. 2) Preparation of carboxylated SiO2 The SiO2 nanoparticles were ultrasonically dispersed in ethanol, KH-550 was added dropwise, and the mixture was stirred overnight at room temperature to obtain amino-modified SiO2 nanoparticles. The particles were then ultrasonically dispersed in THF again, and succinic anhydride was added under stirring, and the mixture was stirred overnight at room temperature, centrifuged, washed with water, and dried to obtain the obtained particles. 3) Preparation of modified SiO2 The polyamino hyperbranched polymer is dissolved and diluted in an ethanol solution, and then the carboxylated SiO2 is dispersed therein by ultrasound to obtain a mixed solution, nitrogen is bubbled into the mixed solution to remove air, and then the mixture is heated to react under a nitrogen atmosphere, stirred and refluxed overnight, cooled to room temperature, centrifuged, washed with water, and dried to obtain the product.

2. The TPU material for making a sole according to claim 1, characterized in that: The percentage of each component of the functional additive is: 10-40wt% styrene acrylic resin, 20-50wt% EVA grafted maleic anhydride, and the remainder modified SiO2.

3. The TPU material for making a sole according to claim 1, characterized in that: The styrene acrylic resin is prepared by using styrene as a hard monomer, butyl acrylate and ethyl methacrylate as soft monomers, and glycidyl methacrylate and maleic anhydride as functional monomers; the mass ratio of the hard monomer, the soft monomer and the functional monomer is 5-6:3-4:0.

5.

4. The TPU material for making a sole according to claim 1, characterized in that: During the preparation of the modified SiO2, the mass ratio of the polyamino hyperbranched polymer to the carboxylated SiO2 is 1:0.05~1.

5. The TPU material for making a sole according to claim 1, characterized in that: The functional additive is obtained by mixing styrene acrylic resin, EVA grafted maleic anhydride and modified SiO2 and extruding and granulating them.

6. The TPU material for making a sole according to claim 1, characterized in that: The foaming agent is selected from one or more of azodicarbonamide, sodium bicarbonate, sodium citrate and p-toluenesulfonyl hydrazide.

7. The TPU material for making a sole according to claim 1, characterized in that: The cross-linking agent is selected from one of dicumyl peroxide and di-tert-butylcumyl peroxide.

8. The TPU material for making a sole according to claim 1, characterized in that: The foaming promoter is a mixture of stearic acid and zinc stearate.

9. The foaming process of TPU material for making shoe soles according to any one of claims 1 to 8, characterized in that: The steps include: The measured TPU, EVA and functional additives are fully and evenly mixed in an internal mixer, and then the measured foaming agent, foaming aid and cross-linking agent are added and continued to mix to obtain a mixture; the temperature of the internal mixer is set to 120-140°C, and the mixing time is 10-20 minutes; The mixture is pressed into sheets by an open twin-roll mixer, and then into particles by a granulator, and then enters the injection molding machine for molding, with the temperature set at 170-180°C; Then put it into a pressure autoclave for foaming, with nitrogen 33 MPa, carbon dioxide 2 MPa, temperature 140-160 ℃, and foaming for 6-10 hours; then transfer it to another pressure autoclave, with the temperature controlled at 140-160 ℃, nitrogen 0.5-2 MPa, time 25-40 min, and discharge after cooling.