Preparation method of POE (Polyolefin Elastomer)-based sneaker insole material capable of accurately regulating and controlling crosslinking strength

Abstract

The invention discloses a preparation method of a POE (Polyolefin Elastomer)-based sneaker insole material capable of accurately regulating and controlling crosslinking strength. The method comprises the following steps: blending insole materials containing an ethylene / alpha-olefin copolymer and a peroxide crosslinking agent, extruding and foaming. According to molecular structure parameters of an ethylene / alpha-olefin copolymer (POE) base material, the cross-linking strength of the shoe material is accurately controlled within an optimal interval, excessive / insufficient cross-linking is avoided, particularly, the gel content is controlled within the optimal range of 60-80%, and a high rebound rate and a low compression permanent deformation rate are brought to a foaming insole.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of shoe materials, and particularly relates to a preparation method of a POE-based sports shoe midsole material with precise crosslinking strength regulation. BACKGROUND

[0002] The core performance of a sports shoe midsole includes shock absorption, resilience and durability, and the realization of the above performance highly depends on the synergistic matching of the crosslinking network structure and the cell morphology of the base material. In actual application, there is a key technical bottleneck in the regulation of crosslinking strength: when the crosslinking strength is too low, the midsole material is prone to permanent deformation, and the compression permanent deformation rate is usually more than 15%; and when the crosslinking strength is too high, the toughness of the material will decrease significantly, the brittleness increases, and cracks are prone to appear after 100,000 times of compression fatigue test, which seriously affects the service life of the midsole.

[0003] At present, the preparation process of the POE-based sports shoe midsole has three major technical pain points, which leads to poor performance stability of the midsole and cannot meet the high quality requirements of industrial mass production.

[0004] 1. Blindness of crosslinking regulation: the existing technology only regulates the crosslinking strength by fixing the amount of crosslinking agent (usually 1-2%), and does not establish a correlation matching mechanism between the amount of crosslinking agent and the molecular structure parameters of the POE base material. It is found in the research process that this blind regulation method leads to great performance fluctuations of the midsole: for example, when the crystal size of POE is ≤15 nm, the molecular chain packing density is high, and at this time, the use of a fixed amount of crosslinking agent (such as DCP) for crosslinking is easy to cause overcrosslinking in the amorphous region, which makes the impact absorption performance of the midsole decrease to below 65%, and the shock absorption effect significantly decreases; and when the α-olefin insertion rate of POE is ≥35%, the proportion of amorphous region increases significantly, and a fixed amount of DCP cannot form enough crosslinking points in the base material, which leads to incomplete crosslinking network, and the compression permanent deformation rate of the midsole is more than 18%, which cannot meet the shape stability requirements in use.

[0005] 2. Instability of POE raw material parameters: the POE base material prepared by the traditional catalytic synthesis process has significant fluctuations in key molecular parameters: the deviation range of the crystal size is ±3 nm, the fluctuation amplitude of the α-olefin insertion rate is ±5%, and the molecular weight and molecular weight distribution also have uncontrollable fluctuations. Since the existing technology does not establish a self-adaptive regulation mechanism for the fluctuations of raw material parameters, even if the amount of crosslinking agent is adjusted artificially, it is difficult to compensate for the influence of fluctuations of raw material parameters, which leads to more than 15% difference in performance of the midsoles produced in different batches, and cannot meet the strict requirements of industrial large-scale production on product performance consistency.

[0006] In summary, the preparation technology of the existing POE-based shoe midsole has the problem of performance imbalance between shock absorption, resilience and durability of the midsole, and poor batch stability due to lack of systematic design of POE molecular structure parameters and crosslinking strength control. SUMMARY

[0007] To solve the above technical problems, the present application provides a preparation method of POE-based shoe midsole material with precise crosslinking strength control. This method can precisely control the crosslinking strength of the shoe material within the optimal range according to the molecular structure parameters of ethylene / alpha-olefin copolymer (POE) substrate, avoiding over / under crosslinking, especially controlling the gel content within the optimal range of 60-80%, which brings higher resilience and lower compression permanent deformation rate to the foamed midsole.

[0008] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0009] A preparation method of POE-based shoe midsole material with precise crosslinking strength control, characterized in that it comprises the steps of blending and extruding the midsole material containing ethylene / alpha-olefin copolymer and peroxide crosslinking agent, and then foaming.

[0010] The amount of the peroxide crosslinking agent satisfies the following formula:

[0011]

[0012] In the formula, P is the mass percentage of peroxide groups in the peroxide crosslinking agent to ethylene / alpha-olefin copolymer, with a value of 0.07-0.12, unit %; D is the crystalline size of ethylene / alpha-olefin copolymer, unit nm; I is the insertion rate of alpha-olefin in ethylene / alpha-olefin copolymer, unit %; Mw is the weight average molecular weight of ethylene / alpha-olefin copolymer, unit g / mol.

[0013] As a preferred example, in the formula, I has a value of 15-40, preferably 20-35, D has a value of 10-30, and Mw has a value of 20000-200000, preferably 40000-120000.

[0014] As a preferred example, the melting temperature Tm of the ethylene / alpha-olefin copolymer is 90℃ or lower, preferably 55-85℃.

[0015] For the raw material ethylene / alpha-olefin copolymer mentioned above, it generally refers to a copolymer obtained by polymerization reaction of ethylene and alpha-olefin in the presence of a catalyst system, and the present application does not make any limitation on its source. It can be purchased from commercially available products or prepared by any known synthesis method.

[0016] The kind of the feasible α-olefins is, for example, one or more selected from the group consisting of 1-olefins of C3-C 20 preferably propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-eicosene.

[0017] The catalyst system generally comprises a main catalyst and an aluminum-containing cocatalyst, and the main catalyst has a higher polymerization activity by using an appropriate amount of the aluminum-containing cocatalyst, which is beneficial to the insertion of the comonomer and the control of the chain segment structure.

[0018] The main catalyst can be any one or a combination of at least two selected from the group consisting of metallocene catalysts, non-metallocene catalysts, for example, dichlorobis cyclopentadiene zirconium, rac-ethylene bis(1-indenyl) zirconium dichloride, silyl(N-tert-butyl amido)(tetramethyl cyclopentadienyl) titanium dichloride, dimethylsilyl(N-tert-butyl amido)(tetramethyl cyclopentadienyl) titanium dichloride, dimethylsilyl(N-tert-butyl amido)(fluorenyl) titanium dichloride, (pentamethyl cyclopentadienyl) titanium trimethoxide, benzylidene(cyclopentadienyl)(9-fluorenyl) zirconium dichloride, dimethylsilyl bis(2-methyl-4-phenyl-1-indenyl) zirconium dichloride, meso dimethylsilyl bis(1-indenyl) zirconium dichloride, (bis(methyl cyclopentadienyl) zirconium dichloride, (bis(1,3-dimethyl cyclopentadienyl) zirconium dichloride, (cyclopentadienyl)(1,2-dimethoxy ethane) zirconium trichloride, diphenyl silyl(cyclopentadienyl)(9-fluorenyl) zirconium dichloride, rac dimethylsilyl bis(2-methyl-1-indenyl) zirconium dichloride, benzylidene cyclopentadienyl(2,7-di-tert-butyl-fluorenyl) zirconium dichloride, di-p-tolylidene cyclopentadienyl(2,7-di-tert-butyl-fluorenyl) zirconium dichloride, dimethyl bis(propyl cyclopentadienyl) hafnium dichloride, bis(n-butyl cyclopentadienyl) hafnium dichloride, dimethylsilyl bis(2-methyl-4-phenyl indenyl) zirconium dichloride, dimethylsilyl(N-tert-butyl amido)(fluorenyl) titanium dichloride and the compound represented by the following formula:

[0019]

[0020]

[0021] The aluminum-containing cocatalyst is, for example, one or more selected from the group consisting of alkyl aluminum, aluminoxane and their modifications, preferably one or more selected from the group consisting of methyl aluminoxane, modified methyl aluminoxane, trimethyl aluminum, triethyl aluminum, tripropyl aluminum, tri-n-butyl aluminum, triisobutyl aluminum, trioctyl aluminum, mono-chloroethyl aluminum, sesqui-ethyl aluminum chloride, di-chloroethyl aluminum;

[0022] Generally, the amount of the aluminum-containing promoter is 1-1000, preferably 50-500, in terms of the molar ratio of aluminum to metal M in the main catalyst.

[0023] The polymerization reaction is generally carried out in the presence of an organic solvent, preferably C5-C 12 The alkane is preferably one or more of pentane, methylpentane, n-hexane, cyclohexane, methylcyclohexane, n-heptane, isoheptane, n-octane, iso-octane, n-decane, C6 mixed alkane, Isopar E.

[0024] The conditions of the polymerization reaction can be selected from a reaction temperature of 50-200°C and a reaction pressure of 0.5-2 MPa in terms of the gauge pressure, depending on the catalyst activity.

[0025] To obtain the ethylene / α-olefin copolymer meeting the above-mentioned parameter limits, the prior art provides many solutions for adjusting the α-olefin insertion rate, the crystalline size, and the weight average molecular weight (Mw), such as increasing the molar ratio of α-olefin to ethylene, or selecting a specific type of main catalyst (such as a symmetrical metallocene catalyst) to facilitate the increase of the α-olefin insertion rate; increasing the polymerization temperature to facilitate the formation of uniform small crystalline regions; and adjusting the weight average molecular weight (Mw) of the ethylene / α-olefin copolymer by introducing a chain transfer agent, etc. Based on the guidance of the known technology, the person skilled in the art can simply adjust the polymerization process to obtain the ethylene / α-olefin copolymer with the expected parameters.

[0026] As a preferred example, the peroxide crosslinking agent is selected from one or more of dicumyl peroxide (DCP), bis-tert-butyl peroxide diisopropylbenzene (BIPB), di-tert-butyl peroxide (DTBP), 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane (DBPH).

[0027] As a preferred example, the midsole material further comprises a foaming agent, an activator, a lubricant.

[0028] As a preferred example, the foaming agent is selected from one or more of azodicarbonamide (AC), N,N'-dinitrosopentamethylenetetramine (H), 4,4'-oxybisbenzenesulfonylhydrazide (OBSH).

[0029] Preferably, the amount of the foaming agent is 1-5% of the mass of the ethylene / α-olefin copolymer.

[0030] As a preferred example, the activator is selected from one or more of zinc oxide, magnesium oxide, zinc stearate, calcium stearate, urea, diethyl urea.

[0031] Preferably, the amount of the activator is 0.5-3% of the mass of the ethylene / α-olefin copolymer.

[0032] As a preferred example, the lubricant is selected from one or more of solid paraffin, polyethylene wax, stearic acid, organosiloxane;

[0033] Preferably, the amount of the lubricant is 0.5-2% of the mass of the ethylene / alpha-olefin copolymer.

[0034] As a preferred example, the blending conditions of the midsole material are: the ethylene / alpha-olefin copolymer, the activator, and the lubricant are added to an internal mixer, and the first mixture is obtained by mixing at 90-120℃ for 5-10min; then the crosslinking agent and the foaming agent are added to the first mixture, and the second mixture is obtained by continuing mixing at 110-130℃ for 3-5min;

[0035] Preferably, the extrusion conditions of the midsole material are: the second mixture is added to a single-screw extruder for extrusion granulation, and the blended particles are obtained by operating at a temperature of 90-120℃ and a main machine speed of 200-500rpm;

[0036] More preferably, the foaming conditions of the midsole material are: the blended particles are added to an injection foaming machine, and the shoe midsole blank is obtained by foaming and molding at 170-185℃ and 5-10MPa, with a pressure maintaining time of 6-10min.

[0037] As a preferred example, the midsole material further comprises a vulcanization step after foaming, and preferably the shoe midsole blank is subjected to secondary vulcanization treatment in an oven at 60-80℃ for 2-4h.

[0038] The present application constructs a technical system for quantitatively regulating the crosslinking strength of shoe midsoles based on the molecular parameters of POE, realizes the precise regulation and stable improvement of the performance of POE-based sports shoe midsole materials, makes up for the deficiencies of the prior art in this respect, and fundamentally solves the technical problems of poor batch stability and difficult stable regulation of crosslinking strength, thereby bringing higher rebound rate and lower compression permanent set to the foamed midsole. DETAILED DESCRIPTION

[0039] The present application will be further described by specific examples, and the examples of the present application are only used to illustrate the present application and do not limit the scope of the present application.

[0040] Unless otherwise specified, the raw materials and reagents in the following examples and comparative examples of the present application can be obtained by commercial channels, wherein:

[0041] Ethylene: Wanhua Chemical, purity 99.99%;

[0042] 1-butene: Yantai Mingtong Gas Co., Ltd., purity ≥99.0% (GC);

[0043] 1-hexene: Sigma-Aldrich, 99% purity;

[0044] 1-octene: Ineos, 98% purity;

[0045] 1-decene: Ineos, 98% purity;

[0046] Methylaluminoxane (MAO): Baoji Funokang Industry Co., Ltd;

[0047] Modified methylaluminoxane (MMAO): Nanon Chemicals (Ningbo) Co., Ltd, containing 10% trimethylaluminum, TMA;

[0048] Hydrogen: Airgas, 99.99% purity;

[0049] Methylcyclohexane: Aldrich, 99.0% purity.

[0050] Dichlorobis(cyclopentadiene)zirconium, Wuxi Yaode Xin Chemical Products Co., Ltd, 98% purity, denoted as main catalyst C1;

[0051] Dimethylsilyl(N-tert-butylamido)(fluorenyl) titanium dichloride, Jiangsu Xinnuo Catalyst Co., Ltd, 98% purity, denoted as main catalyst C2.

[0052] Dicumyl peroxide (DCP), Akzo, 11.84% mass peroxide group;

[0053] Di-tert-butyl peroxide isopropyl benzene (BIPB), Akzo, 18.91% mass peroxide group;

[0054] Di-tert-butyl peroxide (DTBP), Jiangsu Qiangsheng, 21.88% mass peroxide group;

[0055] 2,5-Dimethyl-2,5-bis(tert-butylperoxy) hexane (DBPH), Nanon, 22.04% mass peroxide group;

[0056] Azodicarbonamide, Innokem, 98% purity;

[0057] Zinc oxide, Innokem, 97% purity;

[0058] Magnesium oxide, Innokem, 95% purity;

[0059] Zinc stearate, Innokem, >95%;

[0060] Calcium stearate, Innokem, >95%;

[0061] Polyethylene wax, Honeywell;

[0062] Solid paraffin, China Petroleum and Natural Gas Co., Ltd.

[0063] Stearic acid, Ineos.

[0064] The performance test method related to the following embodiments of the present application is as follows:

[0065] (1) Molecular weight (Mw) and comonomer insertion rate are obtained by gel permeation chromatography (GPC). The specific conditions are as follows: chromatographic column: Agilent Olexis; solvent: 1,2,4-trichlorobenzene; flow rate: 1.0 mL / min; sample concentration: 1.0 mg / mL; injection volume: 200 μL; column temperature: 160 °C; detector: Agilent High Temperature RI detector; standard: polystyrene (modified with a cubic function)

[0066] (2) Melting temperature (Tm): obtained by using a differential scanning calorimeter (DSC6000) manufactured by PerkinElmer. Specifically, under a nitrogen atmosphere, the temperature of the copolymer is raised to 150 °C and maintained for 5 minutes, then cooled to -100 °C, and then the temperature is raised, and the DSC curve is observed, during which the heating rate and cooling rate are 10 °C / min, respectively;

[0067] (3) Gel content test: according to GB / T 2951.11-2008, the uncrosslinked small molecules in the foamed midsole are extracted by toluene Soxhlet, dried and weighed to calculate the gel content (mass after extraction / initial mass x 100%);

[0068] (4) Resilience test: according to GB / T 6670-2008, a 16.6g steel ball is dropped from a height of 500mm onto the foamed midsole sample, and the rebound height is measured to calculate the resilience; verify whether the elasticity meets the standard;

[0069] (5) Compression set test: according to GB / T 6669-2008, the foamed midsole sample is tested at 50% compression rate at 50 °C for 6h, the clamp is removed after 30min, the recovery thickness is tested to calculate the deformation rate; verify the compression collapse resistance;

[0070] (6) Cell structure test: according to GB / T 12811-2021, freeze sectioning + SEM observation (100x), Image-Pro software statistics cell diameter and number;

[0071] (7) Fatigue resistance test: according to GB / T 3903.39-2021, test the sample of foamed midsole at 50% compression rate, 2Hz frequency to complete 100,000 cycles, and calculate the retention rate by the rebound rate before and after the test; verify the long-term wear resistance.

[0072] Preparation Example 1-5, Comparative Preparation Example 1-2

[0073] According to the following continuous process flow and the corresponding process parameters in Table 1, different ethylene / α-olefin copolymers were prepared:

[0074] First, replace the air in the kettle with nitrogen, then continuously introduce a certain flow of impurity-removed methylcyclohexane solvent, α-olefin monomer, main catalyst and aluminum-containing additive, while stirring, introduce ethylene gas and maintain a certain pressure. The heat released during polymerization is dissipated in time by the medium in the reaction kettle jacket, and the pressure is controlled by the pneumatic proportional regulating valve at the ethylene inlet and the reaction kettle outlet. The melt after the completion of the polymerization reaction is devolatilized and extruded into particles to obtain ethylene / α-olefin copolymer particles.

[0075] Among them, the type of α-olefin monomer, the flow rate ratio, the type and amount of catalyst, and the reaction conditions are shown in Tables 1 and 2. In Table 1, the main catalyst feed rate is in units of μmol·min-1. The amount of aluminum-containing additive is calculated based on the molar ratio of aluminum to metal M in the main catalyst.

[0076] The ethylene / α-olefin copolymers prepared in each preparation example were tested for performance according to the aforementioned method, and the corresponding P value was calculated. The results are shown in Table 3.

[0077] Table 1, catalyst type and feed amount

[0078]

[0079] Table 2, polymerization reaction conditions of each preparation example

[0080]

[0081] Note: C2, C4, C6, C8, C10 represent ethylene, 1-butene, 1-hexene, 1-octene, and 1-decene, respectively.

[0082] Table 3, test results of copolymers obtained in each preparation example

[0083]

[0084] The ethylene / α-olefin copolymers prepared in Preparation Example 1-5 were respectively marked as POE-1, POE-2, POE-3, POE-4, POE-5, and the comparative preparation examples were marked as POE-6, POE-7, and POE-based sports shoe midsoles were prepared by the following method, and the material formula is shown in Table 4 (the amount unit is g):

[0085] The ethylene / α-olefin copolymer, the activator, and the lubricant were added to the internal mixer, and the first mixture was obtained by mixing at 120℃ for 5 min; then the crosslinking agent and the foaming agent were added to the first mixture, and the second mixture was obtained by continuing to mix at 130℃ for 3 min; the second mixture was added to the single screw extruder for extrusion granulation, and the operating temperature was 110℃ and the main machine speed was 300 rpm, to obtain the blended particles; the blended particles were added to the injection foaming machine for foaming and molding under the conditions of 185℃ and 10 MPa, and the pressure maintaining time was 8 min, to obtain the shoe midsole blank. The shoe midsole blank was subjected to secondary vulcanization treatment in an oven at 80℃ for 2 h, to obtain the POE-based sports shoe midsole.

[0086] Table 4

[0087]

[0088] The POE-based sports shoe midsoles of each example and comparative example were subjected to the performance tests in Table 5, and the results were as follows:

[0089] Table 5

[0090]

[0091] The above only describes the preferred embodiments of the present application, and it should be noted that, for those skilled in the art, without departing from the method of the present application, several improvements and supplements can also be made, and these improvements and supplements should also be considered as the protection scope of the present application.

Claims

1. A method for preparing a POE-based sports shoe midsole material with precisely controllable crosslinking strength, characterized in that, The method comprises the steps of blending, extruding and foaming a midsole material containing ethylene / α-olefin copolymer and peroxide crosslinking agent; The amount of the peroxide crosslinking agent satisfies the following formula: In the formula, P is the mass percentage of peroxide groups in the peroxide crosslinking agent in the ethylene / α-olefin copolymer, and has a value of 0.07-0.12, unit %; D is the crystallization size of the ethylene / α-olefin copolymer, unit nm; I is the insertion rate of α-olefin in the ethylene / α-olefin copolymer, unit %; Mw is the weight average molecular weight of the ethylene / α-olefin copolymer, unit g / mol.

2. The method for preparing the POE-based sports shoe midsole material with precisely controllable crosslinking strength according to claim 1, characterized in that, In the formula, I has a value of 15-40, preferably 20-35, D has a value of 10-30, and Mw has a value of 20000-200000, preferably 40000-120000.

3. The method for preparing the POE-based sports shoe midsole material with precisely controllable crosslinking strength according to claim 2, characterized in that, The melting temperature Tm of the ethylene / α-olefin copolymer is 90℃ or lower, preferably 55-85℃.

4. The method for preparing the POE-based sports shoe midsole material with precisely controllable crosslinking strength according to claim 1, characterized in that, The peroxide crosslinking agent is selected from one or more of dicumyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane.

5. The method for preparing the POE-based sports shoe midsole material with precisely controllable crosslinking strength according to any one of claims 1-4, characterized in that, The midsole material further comprises a foaming agent, an activator, and a lubricant.

6. The method for preparing the POE-based sports shoe midsole material with precisely controllable crosslinking strength according to claim 5, characterized in that, The foaming agent is selected from one or more of azodicarbonamide, N,N'-dinitrosopentamethylenetetramine, and 4,4'-oxybisbenzenesulfonylhydrazide; Preferably, the amount of the foaming agent is 1-5% of the mass of the ethylene / α-olefin copolymer.

7. The method for preparing the POE-based sports shoe midsole material with precisely controllable crosslinking strength according to claim 5, characterized in that, The activator is selected from one or more of zinc oxide, magnesium oxide, zinc stearate, calcium stearate, urea, and diethyl urea; Preferably, the amount of the activator is 0.5-3% of the mass of the ethylene / α-olefin copolymer.

8. The method for preparing the POE-based sports shoe midsole material with precisely controllable crosslinking strength according to claim 5, characterized in that, The lubricant is selected from one or more of solid paraffin wax, polyethylene wax, stearic acid, and organosiloxane; Preferably, the amount of the lubricant is 0.5-2% of the mass of the ethylene / α-olefin copolymer.

9. The method for preparing the POE-based sports shoe midsole material with precisely controllable crosslinking strength according to any one of claims 5-8, characterized in that, The blending conditions of the midsole material are as follows: the ethylene / α-olefin copolymer, the activator, and the lubricant are added to a banbury mixer, and mixed at 90-120℃ for 5-10 min to obtain a first mixture; then the crosslinking agent and the foaming agent are added to the first mixture, and mixed at 110-130℃ for another 3-5 min to obtain a second mixture; Preferably, the extrusion conditions of the midsole material are as follows: the second mixture is added to a single-screw extruder for extrusion and granulation, and the operation temperature is 90-120℃, and the main machine rotation speed is 200-500 rpm to obtain blended particles; More preferably, the foaming conditions of the midsole material are as follows: the blended particles are added to an injection foaming machine, and foaming and molding are performed at 170-185℃ and 5-10 MPa, and the pressure maintaining time is 6-10 min to obtain a shoe midsole blank.

10. The method for preparing the POE-based sports shoe midsole material with precisely controllable crosslinking strength according to claim 9, characterized in that, The midsole material further comprises a vulcanization step after foaming, and preferably the shoe midsole blank is subjected to secondary vulcanization treatment in an oven at 60-80℃ for 2-4 h.

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