阅读说明：本技术 一种聚氨酯微孔弹性体及其制备方法 (Polyurethane microporous elastomer and preparation method thereof ) 是由 王玉领 林芳茜 徐志磊 刘新建 王林瑞 沈沉 赵�怡 于 2019-08-21 设计创作，主要内容包括：本发明提供了一种聚氨酯微孔弹性体,所述弹性体采用聚醚多元醇作为反应原料,并与其他各组分配合,得到的聚氨酯微孔弹性体在具有较低密度的情况下,同时具有优异的拉伸强度、撕裂强度、断裂伸长率、耐磨、耐折性能。本发明还提供了所述弹性体的制备方法。(The invention provides a polyurethane microporous elastomer, which adopts polyether polyol as a reaction raw material and is matched with other components, and the obtained polyurethane microporous elastomer has excellent tensile strength, tearing strength, elongation at break, wear resistance and folding resistance under the condition of low density. The invention also provides a preparation method of the elastomer.)

1. A polyurethane microcellular elastomer, wherein said elastomer is obtained by reacting an isocyanate component and an isocyanate-reactive component; wherein the isocyanate-reactive component comprises a polyether polyol, a chain extender, a blowing agent, a catalyst; wherein the polyether polyol comprises polyether diol and polyether triol, and the chain extender comprises diol with side groups.

2. The elastomer of claim 1 wherein the isocyanate component is an isocyanate prepolymer.

3. An elastomer as claimed in claim 1 or 2, wherein the initiator of the polyether diol is one or more of ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, and 1, 4-butanediol, preferably one or more of ethylene glycol, propylene glycol, and 1, 4-butanediol, and has a number average molecular weight of 1000 to 8000, preferably 2000 to 5000; more preferably, the polyether glycol is prepared by polymerizing propylene oxide and blocking ethylene oxide, wherein the content of ethylene oxide is 10-70%, preferably 15-30%;

the initiator of the polyether triol is one or more of glycerol, trimethylolpropane, trimethylolethane, 1,2, 6-hexanetriol and triethanolamine, preferably one or more of glycerol, trimethylolpropane and triethanolamine, and the number average molecular weight is 3000-9000, preferably 5000-8000; more preferably, the polyether triol is prepared by polymerizing propylene oxide and blocking ethylene oxide, wherein the content of ethylene oxide is 10-70%, preferably 10-30%.

4. An elastomer as claimed in any one of claims 1 to 3 wherein the chain extender comprises a diol having pendant groups and a linear diol having no pendant groups; preferably, the diol with the side group is one or more of methyl propylene glycol, 3-methyl-1, 5 pentanediol and 2-ethyl-1, 3 hexanediol, and the linear diol without the side group is one or more of 1, 4-butanediol, diethylene glycol and 1,5 pentanediol.

5. An elastomer as claimed in any one of claims 1 to 4 wherein the mass ratio of the diol having pendant groups to the linear diol having no pendant groups is 1: 1-10, preferably 1: 2 to 6.

6. An elastomer as claimed in any one of claims 1 to 5 wherein said catalyst comprises a gel-type catalyst and an intumescent catalyst; preferably, the mass ratio of the foaming catalyst to the gel catalyst is 1: 3-10, preferably 1: 5 to 8.

7. An elastomer as claimed in any of claims 1 to 6 characterised in that the isocyanate reactive component further comprises an anti-wear agent; preferably, the anti-wear agent is one or more of polyethylene wax, polypropylene wax and polytetrafluoroethylene wax.

8. An elastomer as claimed in any of claims 1 to 7 wherein the molar ratio of isocyanate groups in the isocyanate component to hydroxyl groups in the isocyanate-reactive component is from 1: 0.9 to 1.1, preferably 1: 0.95 to 1.05.

9. An elastomer as claimed in any one of claims 1 to 8 characterised in that, based on the total mass of the isocyanate-reactive components:

the using amount of the polyether glycol is 10-40%, and the preferable using amount is 20-30%;

the using amount of the polyether triol is 45-75%, and preferably 55-65%;

the using amount of the chain extender is 8-20%, and the preferable using amount is 12-18%;

the amount of the foaming agent is 0.2-1%, preferably 0.5-0.7%;

the dosage of the catalyst is 1-4%, preferably 1-3%;

the dosage of the wear-resisting agent is 0-5%, preferably 0.5-3%.

10. A method for preparing an elastomer according to any one of claims 1 to 9, comprising the steps of: mixing the isocyanate compound and the isocyanate reactive component, injecting the mixture into a mold for reaction, and obtaining an elastomer after the reaction is finished;

preferably, the temperature of the isocyanate compound and the isocyanate-reactive component is controlled to be 25 to 45 ℃, preferably 30 to 40 ℃ before being injected into the mold;

preferably, the temperature of the die is controlled to be 35-70 ℃, and preferably 40-60 ℃.

Technical Field

The invention relates to a polyurethane microporous elastomer, in particular to a polyether microporous elastomer applied to soles and a preparation method of the microporous elastomer.

Background

The polyurethane microporous elastomer is also called polyurethane microporous elastomer, and is a high polymer synthetic material with more carbamate groups on the main chain, the density is between that of foam and solid material, and the pore diameter of the pores is 0.1-10 μm. The polyurethane microporous elastomer has the advantages of light foam, good impact resistance, energy absorption and buffering performance, high strength and good wear resistance, and is particularly suitable for being used as a sole material. Polyurethane microcellular elastomers can be classified into two major types, polyester type and polyether type, according to the type of polyol used. The tensile strength, the tearing strength, the elongation at break, the wear resistance and the folding resistance of the polyester type microporous elastomer are superior to those of polyether type, but the polyester type microporous elastomer has poor low-temperature performance and is easy to hydrolyze and biodegrade; the polyether type microporous elastomer has better low-temperature performance, hydrolysis resistance and mildew resistance, has great advantages as a sole material in large rainfall, cold areas and humid working environments compared with polyester type, but greatly limits the popularization and application of the polyether type microporous elastomer as the sole material due to poor folding resistance and wear resistance.

Patent CN105492483A discloses hydrolysis-resistant polyurethane moldings which are based on polyester polyols and have improved stability against hydrolysis, but the stability against hydrolysis is still very different compared to polyether urethanes.

Patent CN1922235A discloses swelling resistance polyurethane integral foam, which uses polyether with high Ethylene Oxide (EO) content to improve the swelling resistance of the foam, but when the polyurethane foam is used as sole, the overall density is higher, and the current requirements for light weight and low cost cannot be satisfied.

Patent CN103483530A discloses a polyether polyurethane sole stock solution, in order to improve mechanical properties, polydiacid ethylene glycol diethylene glycol is introduced into isocyanate component, which increases product cost and process complexity; the adoption of the fluorine-containing physical foaming agent HCFC141B can affect the environment; in addition, the density of the product is high (0.5 g/cm)³) And does not meet the requirement of light weight.

Therefore, it is necessary to provide a technical solution to the problems in the prior art.

Disclosure of Invention

The invention provides a polyurethane microporous elastomer, which adopts polyether polyol as a reaction raw material and is matched with other components, and the obtained polyurethane microporous elastomer has excellent tensile strength, tearing strength, elongation at break, wear resistance and folding resistance under the condition of low density. The invention also provides a preparation method of the elastomer.

A polyurethane microcellular elastomer obtained by reacting an isocyanate component and an isocyanate-reactive component; wherein the isocyanate-reactive component comprises a polyether polyol, a chain extender, a blowing agent, a catalyst; wherein the polyether polyol comprises polyether diol and polyether triol, and the chain extender comprises diol with side groups.

The isocyanate component refers to a class of compounds having isocyanate groups, examples of which include, but are not limited to, Toluene Diisocyanate (TDI), diphenylmethane diisocyanate (MDI), isophorone diisocyanate (IPDI), Hexamethylene Diisocyanate (HDI), dicyclohexylmethane diisocyanate (HMDI), Naphthalene Diisocyanate (NDI), p-phenylene diisocyanate (PPDI), 1, 4-cyclohexane diisocyanate (CHDI), Xylylene Diisocyanate (XDI), cyclohexanedimethylene diisocyanate (HXDI), trimethyl-1, 6-hexamethylene diisocyanate (TMHDI), tetramethylm-xylylene diisocyanate (TMXDI), norbornane diisocyanate (NBDI), dimethylbiphenyl diisocyanate (TODI), methylcyclohexyl diisocyanate (HTDI), etc., and polyisocyanates obtained by reacting the above isocyanate monomers, and the like, Isocyanate prepolymer, isocyanate dimer, isocyanate trimer and the like, and such isocyanate compounds may be used alone or in combination. Preferably, the isocyanate component is an isocyanate prepolymer. The isocyanate prepolymer refers to a compound which is formed by reacting polyether/polyester polyol with isocyanate according to a certain proportion and is terminated by isocyanate groups and has reactivity. The isocyanate prepolymer can improve the storage stability of the isocyanate component, and is convenient to transport and store; in addition, the use of the isocyanate prepolymer can improve the compatibility of the isocyanate compound and the isocyanate-reactive component, reduce the occurrence of side reactions, and improve the physical properties of the final product. Further preferably, the preparation of the isocyanate prepolymer does not use the polydiacid ethylene glycol diethylene glycol polyol, the hydrolysis resistance of the polydiacid ethylene glycol diol polyol is lower than that of the polyether polyol, and if the dimer ethylene glycol diethylene glycol polyol is mixed with the polyether polyol, the complexity of the production process is increased, the production cost is increased, and the product performance is further influenced. The polyether polyol is a compound polymerized by taking micromolecular alcohol as an initiator and taking alkylene oxide as a monomer.

Preferably, the initiator of the polyether diol is one or more of ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol and 1, 4-butanediol, preferably one or more of ethylene glycol, propylene glycol and 1, 4-butanediol, and the number average molecular weight is 1000-8000, preferably 2000-5000. More preferably, the polyether glycol is prepared by polymerizing propylene oxide and blocking ethylene oxide, wherein the content of ethylene oxide is 10-70%, preferably 15-30%.

Preferably, the initiator of the polyether triol is one or more of glycerol, trimethylolpropane, trimethylolethane, 1,2, 6-hexanetriol and triethanolamine, preferably one or more of glycerol, trimethylolpropane and triethanolamine, and the number average molecular weight is 3000-9000, preferably 5000-8000. More preferably, the polyether triol is prepared by polymerizing propylene oxide and blocking ethylene oxide, wherein the content of ethylene oxide is 10-70%, preferably 10-30%.

Polyether glycol reacts with an isocyanate component to generate a linear soft segment, which can play a role in increasing the flexibility of the elastomer and prolonging the elongation at break; in addition, the flexible soft segment has stronger moving capability, the speed of entering crystal lattices in the crystallization process is high, and the soft segment crystals are easy to form, so that the tensile strength and the tearing strength of the elastomer are improved. The polyether triol and the isocyanate compound react to generate a cross-linked bond to form a branched network structure, the structure can effectively limit slippage between molecular chains, the compressive stress is transmitted uniformly and stably under high strain, and the deformation resistance of the material is improved. The two polyols are used together within the range defined by the invention, and a crosslinking structure which is rich in flexibility and high in strength is formed in the elastomer, so that the performance of the polyurethane elastomer is more excellent.

The isocyanate-reactive component may also include polyester polyols, polycarbonate polyols, polymer polyols, biobased polyols, and the like.

In a preferred embodiment, the isocyanate-reactive component does not comprise a polyester polyol. The polyester polyol has high viscosity and is easy to crystallize, and needs to be heated before use, so that the operation cost is increased; in addition, polyester polyol is not resistant to hydrolysis, and the difference between the reactivity and polyether polyol is large, so that the reaction imbalance between isocyanate compounds and isocyanate reactive components is easily caused, and the mechanical property is deteriorated.

In a preferred embodiment, the isocyanate-reactive component does not comprise a polymer polyol. Although the polymer polyol is a polyol containing an organic filler and has the function of improving the hardness and carrying capacity of the polyurethane elastomer, the dispersed phase organic filler in the polymer polyol is attached to cell walls in the foaming process and has the function of weakening the cell walls, so that the cell walls are broken, the surface pores of the polyurethane elastomer are easily increased, and the appearance is poor.

In a preferred embodiment, the isocyanate-reactive component does not comprise a polyether monol.

The monofunctional degree in polyether monohydric alcohol reacts with isocyanate components to stop further growth of molecular chains, a linear long straight chain structure cannot be formed, cross-linking of the molecular chains is destroyed, and the strength and the elongation at break of the polyurethane elastomer are low.

The chain extender means a small molecule compound having two active hydrogen atoms capable of reacting with an isocyanate group in the molecule, and examples thereof include, but are not limited to, ethylene glycol, 1, 2-propylene glycol, 1, 3-propylene glycol, 1, 4-butylene glycol, 1, 3-butylene glycol, methyl propylene glycol, neopentyl glycol, pentanediol, 1, 6-hexanediol, 2, 4-diethyl-1, 5-pentanediol, 3-methyl-1, 5-pentanediol, diethylene glycol, dipropylene glycol, tripropylene glycol, etc., and such chain extenders may be used alone or in combination.

In a preferred embodiment, the chain extender comprises a diol having pendant groups and a linear diol having no pendant groups. Examples of such diols with pendant groups include, but are not limited to, methyl propylene glycol, neopentyl glycol, 2, 4-trimethyl-1, 3 pentanediol, 3-methyl-1, 5 pentanediol, butylethyl propylene glycol, 2, 4-diethyl-1, 5 pentanediol, 2-ethyl-1, 3 hexanediol, and the like; examples of the linear diol having no pendant group include, but are not limited to, propylene glycol, 1, 4-butanediol, diethylene glycol, 1, 5-pentanediol, 1, 6-hexanediol, and the like. Preferably, the diol with the side group is one or more of methyl propylene glycol, 3-methyl-1, 5 pentanediol and 2-ethyl-1, 3 hexanediol, and the linear diol without the side group is one or more of 1, 4-butanediol, diethylene glycol and 1,5 pentanediol. Preferably, the mass ratio of the dihydric alcohol with the side group to the linear dihydric alcohol without the side group is 1: 1-10, preferably 1: 2 to 6.

In the preferred technical scheme, the chain extender reacts with the isocyanate component to generate a polyurethane hard chain segment, and as a linear chain diol molecular chain without a side group is relatively regular, the generated chain segment is easy to crystallize, the chain segment is not easy to slide during stretching, and after the diol containing the side group is mixed into the chain segment, the regularity of the molecular chain segment is reduced, so that the crystallization tendency of the hard chain segment is reduced, and the elongation at break of the polyurethane elastomer is integrally improved. In addition, because the reaction speed has great influence on the cell structure, the polyurethane elastomer can keep high mechanical property and curing speed under the condition of maintaining high mechanical property and curing speed by optimizing the mass ratio of linear chain dihydric alcohol without side groups and dihydric alcohol containing side groups with different reaction activities, and simultaneously has good cell structure, thereby avoiding the problem of shrinkage or peeling of products.

The blowing agent refers to an additive capable of generating pores in the interior of the produced material during the reaction of the isocyanate group with the active hydrogen atom, and a blowing agent commonly used in the art, such as a physical blowing agent, a chemical blowing agent, etc., may be used. Preferably, the blowing agent is water.

The catalyst refers to a class of additives capable of catalyzing a reaction between an isocyanate group and an active hydrogen atom, and examples thereof include, but are not limited to, amine-based catalysts, organometallic-based catalysts, and the like, which may be used alone or in combination.

In a preferred embodiment, the catalyst comprises a gel-type catalyst and an intumescent catalyst. The gel-type catalyst refers to a type of catalyst mainly catalyzing the reaction of isocyanate groups with hydroxyl groups (gel curing), and examples thereof include, but are not limited to, triethylenediamine, N-methyldicyclohexylamine, tetramethylethylenediamine, N-bis (dimethylaminopropyl) isopropanolamine, 1, 2-dimethylimidazole, 1, 8-diazacycloundecene, N-dimethyl (hexadecyl) amine, tetramethyliminodipropylamine, stannous octoate, dibutyltin dilaurate, bismuth isooctanoate, potassium isooctanoate, and the like; the blowing catalyst refers to a type of catalyst mainly catalyzing the reaction of isocyanate groups with water (bubble formation), and examples thereof include, but are not limited to, bis (dimethylaminoethyl) ether, pentamethyldiethylenetriamine, trimethylhydroxyethylethylenediamine, N '-trimethyl-N' -hydroxyethylbisaminoethyl ether, dimorpholinyldiethyl ether, triethylamine and the like. More preferably, the mass ratio of the foaming catalyst to the gel catalyst is 1: 3-10, preferably 1: 5 to 8.

Because the curing time, the appearance, the material temperature, the mold temperature and other process conditions of the polyurethane microporous elastomer are greatly influenced, and the production site can not be accurately controlled, the invention uses the foaming catalyst and the gel catalyst in a compounding way, limits the types and the use amounts of the two catalysts, and is more favorable for balancing two reactions of bubble generation and gel curing in the process, thereby effectively improving the tolerance of isocyanate compounds and isocyanate reactive components, expanding the production process conditions of the mold temperature, the material temperature and the like, and effectively reducing the rejection rate.

In a preferred embodiment, the isocyanate-reactive component further comprises an anti-wear agent, which refers to a class of adjuvants capable of enhancing the abrasion resistance of the microcellular elastomer, examples of which include, but are not limited to, micronized waxes and the like, more specific examples of which include, but are not limited to, polyethylene waxes, polypropylene waxes, polytetrafluoroethylene-modified polyethylene waxes, polyamide waxes, carnauba waxes, Fischer-Tropsch waxes and the like, preferably polyethylene waxes, polypropylene waxes, polytetrafluoroethylene waxes, and further preferably polyethylene waxes.

The isocyanate-reactive component may also optionally contain additives such as antistatic agents, antioxidants, light stabilizers, heat stabilizers, internal mold release agents, inorganic fillers, colorants, and the like, which in preferred embodiments are absent.

The molar ratio of isocyanate groups in the isocyanate component to hydroxyl groups in the isocyanate-reactive component is 1: 0.9 to 1.1, preferably 1: 0.95 to 1.05.

In a preferred embodiment, based on the total mass of the isocyanate-reactive components:

the using amount of the polyether glycol is 10-40%, and the preferable using amount is 20-30%;

the using amount of the polyether triol is 45-75%, and preferably 55-65%;

the using amount of the chain extender is 8-20%, and the preferable using amount is 12-18%;

the amount of the foaming agent is 0.2-1%, preferably 0.5-0.7%;

the dosage of the catalyst is 1-4%, preferably 1-3%;

the dosage of the wear-resisting agent is 0-5%, preferably 0.5-3%.

In a preferred embodiment, the elastomer has a density of 0.4 to 0.45g/cm³The hardness is 45-65 Shore A, the tensile strength is 2.5-3.5 MPa, the elongation at break is 300-500%, the tear strength is 10.0-14.5 KN/m, and the abrasion loss is 150-400 mm³。

The elastomer can be applied to the aspects of shock absorption materials, sealing, soles, solid tires, filtering, automobile steering wheels, motorcycle cushions, handrails and the like, and is preferably used as a sole material.

The preparation method of the elastomer comprises the following steps: and mixing the isocyanate compound and the isocyanate reactive component, injecting the mixture into a mold for reaction, and obtaining the elastomer after the reaction is finished.

It should be noted that the parts of the preparation method not described can be operated by referring to the techniques known in the art, without affecting the practice of the present invention, for example, refer to polyurethane foam (third edition) published by chemical industry publishers (ed by walteri, liu yi army, etc.).

Preferably, the temperature of the isocyanate compound and the isocyanate-reactive component is controlled to be in the range of 25 to 45 deg.C, preferably 30 to 40 deg.C, prior to injection into the mould.

Preferably, the temperature of the die is controlled to be 35-70 ℃, and preferably 40-60 ℃.

The invention has the beneficial effects that: the polyether triol and the polyether diol are matched for use, so that the defect of using single polyether polyol is overcome, the support property and flexibility of the elastomer macromolecular structure are more outstanding, and the tensile strength and the tearing strength are more excellent; the mixed chain extender is adopted, and the diol containing the side methyl reduces the regularity of a hard chain segment, so that the hard chain segment has certain flexibility while providing rigidity, and the bending fatigue performance of the elastomer is improved; the two catalysts are used in a compounding way to adjust foaming and gelling, so that a reaction system is more balanced, and generated foam holes are fine and uniform, and the wear-resisting agent is favorably migrated to the surface, so that the surface of the elastomer is bright and free of defects, and the friction-resisting effect of the surface is improved. The polyether polyol adopted by the invention is prepared by a conventional method, the raw materials are easy to obtain, the price is low, and the polyether polyol is very suitable for commercial application.

It should be noted that the beneficial effects of the present invention are all the result of the matching use of the components, and on the basis of the prior art, the beneficial effects of the present invention cannot be achieved by changing a single factor.

Detailed Description

The examples and comparative examples used the following starting materials:

the reaction mixture of a diphenylmethane diisocyanate and a diphenylmethane diisocyanate,MDI-100, Wanhua chemistry;

the modified MDI is prepared by carrying out the following steps,CDMDI-100L, Wanhua chemistry;

polyether polyol 1, propylene glycol is initiated and is prepared by propylene oxide polymerization and ethylene oxide end capping, wherein the ethylene oxide content is 15 percent, and the number average molecular weight is 4000;

polyether polyol 2, initiated by glycerol, is prepared by polymerizing propylene oxide and sealing ethylene oxide, wherein the content of ethylene oxide is 15 percent, and the number average molecular weight is 6000;

polyether polyol 3, initiated by diethylene glycol, is prepared by polymerization of propylene oxide and end capping of ethylene oxide, wherein the ethylene oxide content is 25 percent, and the number average molecular weight is 5000;

polyether polyol 4, initiated by triethanolamine, is prepared by polymerization of propylene oxide and end capping of ethylene oxide, the ethylene oxide content is 20%, and the number average molecular weight is 5000;

polyether polyol 5, propylene glycol is initiated and is prepared by propylene oxide polymerization and ethylene oxide end capping, wherein the ethylene oxide content is 20 percent, and the number average molecular weight is 2000;

polyether polyol 6, initiated by glycerol, is prepared by polymerizing propylene oxide and sealing ethylene oxide, wherein the content of ethylene oxide is 25 percent, and the number average molecular weight is 8000;

the polymer polyol 1, the acrylonitrile-styrene copolymer grafted polyether polyol, the hydroxyl value is 25-29 mgKOH/g, and the viscosity is less than or equal to 3500 mPa.s;

the polyester polyol 1 is synthesized by adipic acid, ethylene glycol and diethylene glycol, the acid value is 0.1-0.8 mgKOH/g, and the number average molecular weight is 2000;

a polydiacid ethylene glycol diethylene glycol polyol having a number average molecular weight of 2000;

chain extender: diethylene glycol, methyl propylene glycol, propylene glycol;

catalyst: bis (dimethylaminoethyl) ether (an intumescent catalyst), triethylenediamine (a gel-type catalyst);

micro powder wax:3620 polyethylene wax, particle size (D50)7.5-9.5 μm;9202F, polytetrafluoroethylene wax, particle size (D50)2.0-6.0 μm;6050M, polypropylene wax, particle size (D50)6.5-12.5 μ M;3920F, a polytetrafluoroethylene-modified polyethylene wax having a particle size (D50) of 5.0 to 7.0 μm, Claine, Germany;

the isocyanate component (1) is a mixture of,8618, polyether modified MDI, NCO content of 19.3%, Wanhua chemistry;

isocyanate component 2, self-made in laboratories, with NCO content of 19.3%, and the preparation method is as follows: adding 56 parts by mass into a reaction kettle in sequenceMDI-100, 5 partsCDMDI-100L, 31 portions of polyether polyol 1,8 portionsControlling the temperature of a reaction kettle at 70-80 ℃ to react for 3 hours, and finishing the reaction and discharging.

The amounts of the raw materials for examples and comparative examples are shown in Table 1 in parts by mass.

TABLE 1 (parts by mass)

The examples and comparative examples were prepared by the following method: according to the types and the amounts of the raw materials listed in Table 1, the isocyanate component and the isocyanate reactive component which is mixed in advance are preheated respectively, the temperature of the raw materials is controlled to be 35 ℃, then the raw materials are injected into a mold through a metering pump, the temperature of the mold is controlled to be 55 ℃ for reaction, and after the reaction is finished, the sample is taken out by demolding.

Examples 1 to 5 are preferable examples, and examples 6 to 9 are not preferable examples.

The examples and comparative examples were tested for hardness according to GB/T531.1-2008 standard, tensile properties according to GB/T528-.

In the "folding endurance" test, "Pass" indicates that the surface of the shoe sole sample has no cracks after 40000 cycles (cycles); "Fail" indicates that after 40000 cycles (cycles) of the sole sample, cracks appeared on the surface.

The test results are shown in Table 2.

TABLE 2

Note: the folding times of the sample of example 7 are 25000(cycles), which can meet the performance requirements of common soles.