Method for manufacturing TPU shoe sole mixed with hydrophobic nano-silica by using supercritical physical foaming

Abstract

The present invention proposes a method for manufacturing a TPU shoe sole mixed with hydrophobic nano-silica by using supercritical physical foaming, wherein hydrophobic nano-silica powder is contained as a foaming nucleating agent in order to uniformly form fine foam cells during a TPU shoe sole (midsole / insole) molding process by supercritical physical foaming, thereby implementing a comfortable wearing due to a soft tactile feel and high elasticity, excellent shape stability and durability, lightweighting of a product, and reduction of material costs.

Description

Method for manufacturing a TPU shoe sole blended with hydrophobic nanosilica by supercritical physical foaming

[0001] The present invention relates to a method for manufacturing a TPU shoe sole incorporating hydrophobic nanosilica by supercritical physical foaming, and more specifically, to a method for manufacturing a TPU shoe sole incorporating hydrophobic nanosilica by supercritical physical foaming that includes hydrophobic nanosilica powder as a foaming nucleating agent to uniformly form fine foam cells during the molding process of a TPU shoe sole (midsole / insole) by supercritical physical foaming, thereby enabling a soft touch, a comfortable fit with high elasticity, excellent shape stability and durability, as well as lightweighting of the product and reduction of material costs.

[0002]

[0003] Generally, various types of footwear, such as dress shoes, athletic shoes, and hiking boots, consist of an upper leather that forms the exterior, an outsole that contacts the ground, a midsole installed on the upper side of the outsole, and an insole that contacts the sole of the foot. Based on research results indicating that foot health is a very important factor for the human body, various functions are being added to the midsoles and insoles.

[0004] The aforementioned midsole is installed in the middle layer of the shoe and is formed with a structure that allows for comfortable walking by absorbing the weight exerted on the shoe by the human body during walking as elastic energy. The insole, located above the midsole, is molded into an ergonomic structure capable of effectively absorbing and dispersing shock to the soles of the feet, and many materials are used to provide sweat absorption, antibacterial, and deodorizing functions. Recently, technologies regarding midsoles and insoles with high-elasticity features are being developed, taking into account the diversity of materials.

[0005] These midsoles and insoles are typically manufactured in the form of foam sheets by foam molding materials such as polyurethane (PU), ethylene-vinyl acetate (EVA), polyethylene (PE), polypropylene (PP), latex, and Pebax, and are applied as various types of shoe sole materials.

[0006] In particular, thermoplastic polyurethane (TPU) resin is a non-toxic material with excellent elasticity and durability. As it is an eco-friendly material with excellent recyclability due to its ability to be plastically deformed by heat, foamed products made from this material maintain excellent performance while offering advantages such as low density, thermal insulation, soundproofing, and cushioning. Consequently, they are widely utilized in fields such as footwear, automobiles, and electrical and electronic industries, and can be applied to an even wider range of sectors.

[0007] Furthermore, the foaming methods for the TPU resin mentioned above include chemical foaming and physical foaming. Chemical foaming is a method that uses foaming agents such as azo-based foaming agents, CFCs, and low-boiling point solvents. Physical foaming is a method that generates bubbles by dissolving liquefied gas or supercritical fluid into the resin; since physical foaming does not use chemical foaming agents or Freons, it does not emit pollutants, resulting in low environmental hazard and the ability to produce recyclable foamed molded products.

[0008] For example, physical foaming using supercritical carbon dioxide is a highly effective and residue-free, environmentally friendly method for forming foam particles or molded products. This combination of foaming and subsequent molding steps is commercially implemented mainly for thermoplastic resins with a glass transition temperature (Tg) of less than 0°C, including thermoplastic polyurethane, ethylene vinyl acetate copolymer, polypropylene, and polyester elastomer. Conventional shoe soles, whether using chemical or physical foaming agents, have failed to overcome the limitations of high material costs and product properties, resulting in an overall heavy and hard texture that fails to meet the development trend of increasing lightweighting.

[0009] The aforementioned supercritical fluids (CO2, N2) possess the solubility of liquids and the diffusivity of gases under high temperature and high pressure conditions, offering the advantage of precise control over injection volume and the ability to dissolve large amounts of foaming agent into the resin. However, in the case of physical foaming using supercritical fluids, problems such as low foaming that fail to achieve the initially targeted specific gravity reduction, non-uniform foam cells, and the formation of pinholes on the product surface frequently occur.

[0010] Regarding the prior art for manufacturing TPU foam using the supercritical physical foaming method described above, Korean Patent No. 10-1609355 comprises the steps of: manufacturing a midsole by cutting after supercritical foaming injection of TPU resin (S100); and manufacturing an integrated shoe sole by inserting the midsole manufactured through the step S100 into an outsole mold and then injecting a specific 'dynamically cross-linked thermoplastic elastomer composition' into the outsole mold (S200); wherein the step S100 is characterized by supercritical foaming injection of TPU resin using a supercritical foaming injection machine, and injecting it as a foam with a specific gravity of 0.3 to 0.5.

[0011] In addition, Korean Patent No. 10-1856884 describes a method for manufacturing a low-density foamed article comprising the steps of: in an extruder, mixing a molten polymer selected from the group consisting of a thermoplastic polyurethane elastomer and a thermoplastic ethylene-vinyl acetate copolymer with (a) a physical or chemical blowing agent other than a supercritical fluid and (b) a supercritical fluid to form a mixture; and injecting the mixture into a mold including a porous tool at an injection pressure of 110 to 207 MPa to form a low-density foamed article, wherein the blowing agent (a) is present in an amount of 15 weight% or less based on the polymer weight, and the supercritical fluid comprises one of supercritical CO2 in an amount of 0.1 to 5 weight% based on the polymer weight or supercritical N2 in an amount of 0.1 to 4 weight% based on the polymer weight, and the foamed article has a density of 0.3 g / cm³ 3 A low-density foam having a density of less than [amount], a midsole, a shoe, and a method for manufacturing the low-density foam are disclosed.

[0012] In addition, the rigid polyurethane foam in Korean Patent No. 10-1867064 is manufactured by foaming and curing using a mixed polyether polyol main component comprising 1 to 50 parts by weight of a triethanolamine-based polyether polyol per 100 parts by weight of a polyether-based polyol, a curing agent comprising an amine-based catalyst and a polymerizable MDI having 2.5 to 2.9 NCO functional groups, and a mixed blowing agent comprising HFCs and supercritical carbon dioxide, wherein the mixed blowing agent is used in an amount of 1 to 40 parts by weight per 100 parts by weight of the polyol main component, and carbon dioxide in the mixed blowing agent is included in a ratio of 1 to 30 parts by weight per 100 parts by weight of HFCs.

[0013] And Korean Patent No. 10-2397310 comprises: an input step of introducing a polyurethane raw material into a reactor; a reaction step of reacting the polyurethane raw material by applying heat and pressure into the reactor; a constant temperature and constant pressure step of maintaining the temperature and pressure inside the reactor constant; and a step of foaming and curing the polyurethane raw material; wherein carbon dioxide is injected into the reactor in the reaction step and the density of the carbon dioxide is 0.127 to 0.200 g / cm³ 3 A method for manufacturing solvent-free high-foaming polyurethane foam, characterized by applying heat and pressure to achieve this, was proposed.

[0014] Meanwhile, the present invention has developed a method for manufacturing a TPU shoe sole incorporating hydrophobic nanosilica by supercritical physical foaming, wherein the inclusion of hydrophobic nanosilica powder as a foaming nucleating agent during the molding process of the TPU shoe sole (midsole / insole) by supercritical physical foaming results in the uniform formation of fine foam cells throughout, thereby improving not only the size variation of the foam pellets but also the density differences by region, which can enhance product quality and productivity.

[0015]

[0016] The objective of the present invention is to provide a method for manufacturing a TPU shoe sole incorporating hydrophobic nanosilica by supercritical physical foaming, wherein, by including hydrophobic nanosilica powder as a foaming nucleating agent during the molding process of a TPU shoe sole (midsole / insole) by supercritical physical foaming, fine foam cells are formed uniformly throughout, thereby enabling the production of a highly foamed product without size variations of foam pellets or differences in density by region, and furthermore, a soft touch and comfortable fit with high elasticity, as well as good shape stability and excellent durability, and the product can be made lighter and material cost reduced.

[0017]

[0018] A method for manufacturing a TPU shoe sole incorporating hydrophobic nanosilica by supercritical physical foaming according to a first embodiment of the present invention comprises manufacturing a TPU shoe sole using a thermoplastic polyurethane resin composed of a polyol, an isocyanate, and a chain extender as raw materials, wherein the thermoplastic polyurethane resin contains hydrophobic nanosilica powder, having a primary particle size of 1 to 100 nm, in a range of 0.1 to 5 phr (Parts per Hundred Resin) as a foaming nucleating agent, wherein the hydrophobic nanosilica powder forms nanosilica aggregates with an average size of 100 to 1200 nm within the thermoplastic polyurethane resin, and a supercritical fluid is injected into the thermoplastic polyurethane resin at a temperature of 120 to 180°C to obtain a specific gravity of 0.05 to 0.25 or less The method is characterized by manufacturing a foamed pellet and then compression molding the foamed pellet.

[0019] A method for manufacturing a TPU shoe sole blended with hydrophobic nanosilica by supercritical physical foaming according to a second embodiment of the present invention comprises manufacturing a TPU shoe sole using a thermoplastic polyurethane resin composed of a polyol, an isocyanate, and a chain extender, wherein the thermoplastic polyurethane resin contains hydrophobic nanosilica powder, having a primary particle size of 1 to 100 nm, in a range of 0.1 to 5 phr (Parts per Hundred Resin) as a foaming nucleating agent, wherein the hydrophobic nanosilica powder forms nanosilica aggregates with an average size of 100 to 1200 nm within the thermoplastic polyurethane resin, and injecting a supercritical fluid into the thermoplastic polyurethane resin at a temperature of 160 to 220°C to achieve a specific gravity within 0.05 to 0.25. It is characterized by molding.

[0020]

[0021] The TPU shoe sole incorporating hydrophobic nanosilica produced by supercritical physical foaming according to the manufacturing method of the present invention contains a certain amount of hydrophobic nanosilica powder as a foaming nucleating agent during the molding process of the TPU shoe sole (midsole / outsole), thereby ensuring that fine foam cells are formed uniformly throughout, so there is no variation in the size of the foam pellets or differences in density between parts. Furthermore, it has the effect of achieving a soft touch and a comfortable fit with high elasticity, as well as excellent shape stability and durability, and also enables product lightweighting and material cost reduction.

[0022]

[0023] FIG. 1a is a drawing showing a photograph of the surface of a TPU resin blended with hydrophobic nanosilica according to the present invention, measured at 50,000x magnification using SEM.

[0024] FIG. 1b is a drawing showing a photograph of the surface of a TPU resin blended with hydrophobic nanosilica according to the present invention, measured at 100,000x magnification using SEM.

[0025] FIG. 2a is a drawing showing an actual photograph of a TPU foam pellet (containing 1 phr of hydrophobic nanosilica) manufactured according to the first embodiment of the present invention.

[0026] FIG. 2b is a drawing showing an actual photograph of a TPU foam pellet without hydrophobic nanosilica.

[0027]

[0028]

[0029] A method for manufacturing a TPU shoe sole incorporating hydrophobic nanosilica by supercritical physical foaming according to a first embodiment of the present invention comprises manufacturing a TPU shoe sole using a thermoplastic polyurethane resin composed of a polyol, an isocyanate, and a chain extender as raw materials, wherein the thermoplastic polyurethane resin contains hydrophobic nanosilica powder, having a primary particle size of 1 to 100 nm, in a range of 0.1 to 5 phr (Parts per Hundred Resin) as a foaming nucleating agent, wherein the hydrophobic nanosilica powder forms nanosilica aggregates with an average size of 100 to 1200 nm within the thermoplastic polyurethane resin, and a supercritical fluid is injected into the thermoplastic polyurethane resin at a temperature of 120 to 180°C to obtain a specific gravity of 0.05 to 0.25 or less The method is characterized by manufacturing a foamed pellet and then compression molding the foamed pellet.

[0030] A method for manufacturing a TPU shoe sole blended with hydrophobic nanosilica by supercritical physical foaming according to a second embodiment of the present invention comprises manufacturing a TPU shoe sole using a thermoplastic polyurethane resin composed of a polyol, an isocyanate, and a chain extender, wherein the thermoplastic polyurethane resin contains hydrophobic nanosilica powder, having a primary particle size of 1 to 100 nm, in a range of 0.1 to 5 phr (Parts per Hundred Resin) as a foaming nucleating agent, wherein the hydrophobic nanosilica powder forms nanosilica aggregates with an average size of 100 to 1200 nm within the thermoplastic polyurethane resin, and injecting a supercritical fluid into the thermoplastic polyurethane resin at a temperature of 160 to 220°C to achieve a specific gravity within 0.05 to 0.25. It is characterized by molding.

[0031] Here, the hydrophobic nanosilica powder comprises one or more hydrophobic functional groups selected from alkyl groups, dimethyl groups, trimethyl groups, dimethylsiloxane groups, and methacrylate groups on the surface of the nanosilica particles, and the supercritical fluid is one or more gases selected from carbon dioxide (CO2) and nitrogen (N2) injected at a temperature and pressure above the critical point, and the product manufactured by the compression molding or injection molding is one of a shoe insole and a midsole.

[0032]

[0033] Hereinafter, a method for manufacturing a TPU shoe sole incorporating hydrophobic nanosilica by supercritical physical foaming according to the present invention will be described. This is intended to be an example sufficient to enable a person skilled in the art to easily practice the invention, and does not imply that the technical concept and scope of the present invention are limited thereby.

[0034] Generally, polyurethane resin is a resin produced based on urethane bonds generated by the reaction of isocyanate groups (-NCO) and hydroxyl groups (-OH) in the polymer, and its raw materials include polyol, isocyanate, chain extender, etc. By adjusting the ratio of soft segments and hard segments constituting the polyurethane, it is possible to design formulations with various molecular weights ranging from elastic products like rubber to hard products.

[0035] The characteristics of this polyurethane resin include excellent film strength and adhesive strength, which allows for the production of thin coating films; the coating film has abundant elasticity, which enables the production of porous film or sheet with a soft touch, thereby providing moisture permeability and breathability, as well as excellent cold resistance; and since it is processed without using plasticizers, there are fewer workability problems caused by plasticizers.

[0036] In addition, the above polyol is an active hydrogen compound used to produce polyurethane by reacting with isocyanate, and refers to one having two or more active hydrogen groups such as hydroxyl groups, carboxyl groups, and amine groups in its molecule, and the use of various types depending on molecular structure, molecular weight, functionality, and OH-value directly affects the physical properties of the polyurethane.

[0037] For example, compared to polyurethanes made with polyester polyols, polyurethanes made with polyester polyols have higher tensile strength, hardness, and elongation, as well as excellent flame retardancy and superior chemical and drug resistance, making them resistant to oxidation and providing excellent adhesion to various fabrics woven from polyester or nylon. However, a disadvantage is that they have poor water resistance due to their hydrolytic nature. On the other hand, polyurethanes made with polyether polyols exhibit excellent elasticity, can be used in high-temperature and high-humidity environments, and demonstrate excellent durability against acids and alkalis; therefore, it is desirable to use them individually or in combination depending on the application.

[0038] The above polyurethane (PU) resin is produced when a polyether made by the polymerization of ethylene oxide is mixed with a diisocyanate to produce polyurethane, and urethane is a mixed amide ester formed when an alcohol group reacts with an isocyanate, and if a triol is used instead of a diol, cross-linking occurs to produce thermosetting polyurethane.

[0039] Accordingly, the method for manufacturing a TPU shoe sole blended with hydrophobic nanosilica by supercritical physical foaming according to the first embodiment of the present invention comprises manufacturing a TPU shoe sole using a thermoplastic polyurethane resin composed of a polyol, an isocyanate, and a chain extender as raw materials, wherein the thermoplastic polyurethane resin contains hydrophobic nanosilica, having a primary particle size of 1 to 100 nm, in a range of 0.1 to 5 phr (Parts per Hundred Resin) as a foaming nucleating agent, wherein the hydrophobic nanosilica forms nanosilica aggregates with an average size of 100 to 1200 nm within the thermoplastic polyurethane resin, and a supercritical fluid is injected into the thermoplastic polyurethane resin at a temperature of 120 to 180°C to obtain a specific gravity of 0.05 to 0.25 The method is characterized by manufacturing a foamed pellet within a certain amount, and then compression molding the foamed pellet.

[0040] The thermoplastic polyurethane (TPU) resin used in the present invention is obtained by polymerizing the raw materials, such as polyol and isocyanate, with the chain extender, such as low molecular weight glycol. Examples of the polyols used include polyester polyol, polyether polyol, and polycaprolactone; examples of the isocyanates include aromatic isocyanates and aliphatic isocyanates; and examples of the low molecular weight glycol include 1,4-butanediol.

[0041] In addition, the supercritical physical foaming referred to in the present invention is a technique for producing foamed pellets with a specific gravity of 0.05 to 0.25 by injecting a supercritical fluid as a foaming agent, wherein the supercritical fluid refers to injecting one or more gases selected from carbon dioxide (CO2) and nitrogen (N2) at a temperature and pressure above the critical point.

[0042] The aforementioned supercritical fluid refers to a fluid in which the temperature and pressure of the substance exceed the critical point, resulting in a state where it is impossible to distinguish between liquid and gas; it possesses properties such as density and solubility close to those of a liquid, while viscosity, diffusivity, and thermal conductivity are close to those of a gas.

[0043] In fact, no gas on Earth can become a liquid at room temperature no matter how much it is compressed. This is because the critical temperatures of nitrogen (N2) and oxygen (O2) are lower than room temperature. If nitrogen and oxygen are compressed at room temperature without cooling, they become supercritical fluids and not liquids. For reference, the critical point of nitrogen is -146.9°C and 3.39 MPa, the critical point of oxygen is -118.6°C and 5.05 MPa, carbon dioxide is 31°C and 7.38 MPa, and water is 374°C and 22.1 MPa. Supercritical carbon dioxide refers to carbon dioxide in a state that has a high density like a liquid but low viscosity like a gas under specific temperature and pressure conditions.

[0044] The amount of supercritical fluid used as the blowing agent is determined by considering the apparent density of the foamed pellet or product to be intended, the type of TPU resin, etc., but typically, the amount of physical blowing agent can be injected in a wide distribution ranging from 0.1 to 30 parts by weight per 100 parts by weight of thermoplastic polyurethane resin.

[0045] In the foam molding method using a supercritical fluid as described above, in order to obtain a foamed polyurethane with an excellent appearance without pinholes on the surface, the control of the supercritical fluid after the mixed polyurethane raw material is injected into the mold is a key point, and for this control, it is important to control the viscoelasticity of the raw material.

[0046] In addition to developing control technology for the process of injecting a supercritical fluid as described above, the present invention has invented that by including hydrophobic nanosilica powder, with a primary particle size of 1 to 100 nm, as a foaming agent for thermoplastic polyurethane resin in a range of 0.1 to 5 phr (Parts per Hundred Resin), fine foam cells are uniformly formed, thereby allowing the viscoelasticity of the TPU resin to be controlled, and thus, a lightweight TPU shoe sole (midsole / insole) with a specific gravity of 0.05 to 0.25 can be manufactured.

[0047] Based on the fact that the above hydrophobic nanosilica powder has excellent physical and chemical miscibility with TPU resin, it is dispersed into a particle size with the most suitable mixing properties, so the quality of the product, including moldability, homogeneity, elasticity, and durability, is very good.

[0048] The above-mentioned foaming nuclear agent plays a role in forming small cells by subdividing the gas around the nucleating agent during the process in which the thermoplastic polyurethane resin and the supercritical fluid (gas) are melt-mixed. Since such a nucleating agent is an indispensable and important additive in gas foaming with a high foaming ratio, it is an important additive that determines the physical properties of the foamed product, such as the size, elongation, strength, and appearance of the foamed cells, depending on the type and role of the nucleating agent; therefore, it goes without saying that it must be appropriately selected in consideration of the application and quality of the foamed product being produced.

[0049] The hydrophobic nanosilica powder used in the present invention can have its content controlled within a specified range according to the desired hardness and density of the molded body. If the content of the hydrophobic nanosilica powder relative to the TPU resin is less than 0.1 phr, the effect of forming a uniform foam is negligible, and it is difficult to expect an increase in the shape stability and elastic modulus of the product. Additionally, if the content of the hydrophobic nanosilica powder exceeds 5 phr, it becomes difficult to manufacture a foam molded body with the desired elasticity (cushioning) because there are constraints on the process conditions for forming the hardness of the molded body uniformly.

[0050] For reference, considering that the specific gravity of conventional EVA foam is 0.18 to 0.22, the specific gravity of PU foam is 0.25 to 0.38, and the specific gravity of Pebax (polyether block amide) foam is 0.13 to 0.17, the TPU foam blended with hydrophobic nanosilica by supercritical physical foaming of the present invention can be lighter and have better physical properties than EVA foam or PU foam, and even though it has physical properties with a specific gravity similar to Pebax foam, it has superior price competitiveness and enables the formation of a wider range of low-density TPU foams, thereby allowing the manufacture of various types of high-density foamed shoe soles.

[0051] As described above, when hydrophobic functional groups are introduced to the surface of nanosilica particles contained as a foaming agent in TPU resin, the dispersibility of the nanosilica is improved, and due to the hydrophobic action, the water resistance of the manufactured shoe sole is reinforced and tensile strength is increased, thereby improving physical properties such as moldability. The hydrophobic functional groups that can be introduced to the surface of the nanosilica particles may be alkyl groups, dimethyl groups, trimethyl groups, dimethylsiloxane groups, methacrylate groups, etc. For example, the nanosilica particles included in the thermoplastic polyurethane resin of the present invention are nanosilica obtained by controlling the temperature and pressure in a fumed silica manufacturing process, and then treated with an organosilane compound to include dimethyl groups on the surface of the nanosilica particles.

[0052] The nanosilica particles with the above-mentioned hydrophobic functional groups have an OH group density of 1.0 OH / nm 3 It is preferable that it be less than or equal to 0. The OH group density can be measured by known methods, such as reacting nanosilica particles with introduced hydrophobic functional groups with lithium aluminum hydride and measuring the molar absorbance (ε) of the OH group stretching vibration band in the free silanol group at 3750 cm using IR spectroscopy.

[0053] In the present invention, nanosilica particles with hydrophobic functional groups introduced exist in a nanosilica aggregate state, and are dispersed in an aggregate state that is difficult to separate within the TPU resin. It is preferable that the aggregates have an average aggregate size of 100 to 1200 nm, and more preferably, if they have an average aggregate size of 200 to 500 nm, the dispersibility becomes very good.

[0054] When the size of the above hydrophobic nanosilica aggregates is an average of 100 nm or more, the dispersion of nanosilica is well achieved, but when the average exceeds 1200 nm, the thickening effect decreases. The size of the above nanosilica aggregates refers to the length in the direction of the major axis of the nanosilica aggregates and can be measured using a transmission electron microscope, etc.

[0055] For example, Figures 1a and 1b present SEM images of the surface of a TPU resin containing 1 phr of hydrophobic nanosilica with a primary particle size of approximately 20 nm and containing a dimethyl group as a hydrophobic functional group on the surface. It was confirmed that the hydrophobic nanosilica powder dispersed in the TPU resin was well dispersed in the form of nanosilica aggregates having a certain size.

[0056] For the reasons mentioned above, the TPU shoe sole incorporating hydrophobic nanosilica produced by supercritical physical foaming according to the present invention is able to achieve lightweighting and material cost reduction, as fine foam cells are uniformly formed by dispersing a foaming nucleating agent composed of hydrophobic nanosilica aggregates within the TPU resin, thereby preventing variations in the size of the foam pellets and differences in density between different parts. Furthermore, it offers a soft touch and a comfortable fit with high elasticity, as well as excellent shape stability and durability.

[0057] The method for manufacturing a TPU shoe sole by supercritical physical foaming according to the first embodiment of the present invention involves injecting a supercritical fluid into a thermoplastic polyurethane resin mixed with hydrophobic nanosilica as described above at a temperature of 120 to 180°C to produce a foamed pellet with a specific gravity of 0.05 to 0.25, and then compression molding the foamed pellet to produce either a shoe insole or a midsole.

[0058] As shown in the actual photograph of FIG. 2a, the TPU foam pellets manufactured according to the first embodiment can produce a shoe sole with excellent physical properties such as lightness, elasticity, and tactile sensation, as foam cells of a size of 5 to 50 μm are uniformly formed throughout. On the other hand, as shown in the actual photograph of FIG. 2b, it was confirmed that the appearance and physical properties of the manufactured shoe sole are poor due to the TPU foam pellets not incorporating hydrophobic nanosilica, which not only have non-uniform size and an uneven surface condition but also clump together as foam pellets.

[0059] In addition, the method for manufacturing a TPU shoe sole by supercritical physical foaming according to the second embodiment of the present invention enables the production of either a shoe insole or a midsole by injecting a supercritical fluid into a thermoplastic polyurethane resin mixed with hydrophobic nanosilica as described above at a temperature of 160 to 220°C and injection molding it to a specific gravity of 0.05 to 0.25.

[0060] At this time, the supercritical fluid is characterized by injecting one or more gases selected from carbon dioxide (CO2) and nitrogen (N2) at a temperature and pressure above the critical point. The supercritical fluid exhibits both gaseous and liquid properties, possessing the diffusivity of a gas and the solubility of a liquid, and has the advantages of being odorless, non-toxic, and non-flammable. Furthermore, once a specific temperature (critical temperature) and pressure (critical pressure) are exceeded, its state does not change no matter how much heat and pressure are applied thereafter. Accordingly, carbon dioxide is easier to bring into a supercritical state than other substances because its critical temperature and critical pressure are low; it is chemically stable and non-corrosive; it can be used as a solvent as a substitute for organic solvents; and it is environmentally friendly as it is non-toxic.

[0061] Below, we will specifically examine the method for manufacturing a TPU shoe sole (midsole / insole) incorporating hydrophobic nanosilica by supercritical physical foaming according to the present invention. The present invention will be explained through preferred embodiments that can be easily implemented by a person skilled in the art to which the present invention belongs.

[0062] [Example 1]

[0063] A method for manufacturing a shoe sole according to the first embodiment of the present invention comprises mixing a polyol, an isocyanate, a chain extender, and an additive as raw materials and polymerizing them to produce a thermoplastic polyurethane resin chip of size 1 to 2 mm, and mixing a hydrophobic nanosilica powder with a primary particle size of 1 to 100 nm as a foaming agent in a range of 0.1 to 5 phr, and then mixing and injecting N2 and CO2 as supercritical fluids into the thermoplastic polyurethane resin at a temperature of 120 to 180°C to produce a foamed pellet with an average particle size of 3 to 5 mm and a specific gravity of 0.05 to 0.25, and then compression molding the foamed pellet to produce a TPU midsole / insole.

[0064] [Example 2]

[0065] A method for manufacturing a shoe sole according to the second embodiment of the present invention involves mixing a polyol, an isocyanate, a chain extender, and an additive as raw materials and polymerizing them to produce a thermoplastic polyurethane resin, to which a hydrophobic nanosilica powder with a primary particle size of 1 to 100 nm is mixed as a foaming agent in a range of 0.1 to 5 phr, and then injecting a mixture of N2 and CO2 as a supercritical fluid into the thermoplastic polyurethane resin at a temperature of 160 to 220°C and injection molding to a specific gravity of 0.05 to 0.25 to produce a TPU middle sole / insole.

[0066] [Experimental Example]

[0067] When manufacturing shoe midsoles / insoles as in Examples 1 and 2 above, TPU shoe soles (Manufacturing Examples 1 to 4) according to the ratio of hydrophobic nanosilica powder included in the thermoplastic polyurethane resin were tested by comparing a TPU shoe sole containing 10 phr of hydrophobic nanosilica powder (Manufacturing Example 5) and a TPU shoe sole not containing hydrophobic nanosilica powder (Manufacturing Example 6) as comparative examples. The average values ​​of the results of evaluating the moldability, appearance, and elasticity several times are shown in [Table 1] below (◎: Very good, ○: Good, △: Average, ×: Poor).

[0068]

[0069] Classification Manufacturing Example ① Manufacturing Example ② Manufacturing Example ③ Manufacturing Example ④ Manufacturing Example ⑤ Manufacturing Example ⑥ Hydrophobic NS Powder (phr) 0.1135100 Moldability and Appearance ○◎◎○△× Elasticity ○◎◎○△○

[0070]

[0071] As shown in [Table 1] above, when comparing the experimental results for TPU shoe soles of Manufacturing Examples ① to ④ prepared according to Examples 1 and 2 and Manufacturing Examples ⑤ to ⑥ prepared in the same manner, it was found that Manufacturing Examples ① to ④ prepared according to the present invention had good moldability and appearance, and overall excellent tactile feel and elasticity. On the other hand, in the case of Manufacturing Example ⑤, where the content of hydrophobic nanosilica powder exceeded 5 phr, uniform foam cells were not formed, resulting in uneven moldability and appearance, and non-uniform elasticity. Furthermore, it was confirmed that Manufacturing Example ⑥, which did not contain hydrophobic nanosilica powder, had good elasticity but poor moldability and appearance, thus potentially reducing product productivity and shape stability.

[0072] As described above, the present invention includes hydrophobic nanosilica powder in the range of 0.1 to 5 phr as a foaming nucleating agent during the molding process of a TPU shoe sole (midsole / insole) by supercritical physical foaming, thereby forming fine foam cells uniformly throughout, resulting in a soft touch and a comfortable fit with high elasticity, as well as excellent shape stability and durability, and enabling the realization of lightweight products and material cost reductions, thus significantly improving the quality and productivity of shoes to which this is applied.

[0073]

[0074] The method for manufacturing a TPU shoe sole incorporating hydrophobic nanosilica by supercritical physical foaming according to the present invention is environmentally friendly and has the advantage of reducing defect rates and material costs in the manufacturing process. Therefore, it can be applied to various uses such as shoe soles requiring uniform moldability, as well as foam packages for shoe insoles or uppers (decorative), and molding materials, cushioning materials, and filling materials used inside clothing, bags, sports goods, household goods, and industrial goods made of fibers, natural and synthetic leather, plastics, etc.

Claims

1. In manufacturing a TPU shoe sole using a thermoplastic polyurethane resin composed of polyol, isocyanate, and a chain extender as raw materials, The above thermoplastic polyurethane resin contains hydrophobic nanosilica powder, having a primary particle size of 1 to 100 nm, as a foaming agent in a range of 0.1 to 5 phr (Parts per Hundred Resin), wherein the hydrophobic nanosilica powder forms nanosilica aggregates with an average size of 100 to 1200 nm within the thermoplastic polyurethane resin. A method for manufacturing a TPU shoe sole incorporating hydrophobic nanosilica by supercritical physical foaming, characterized by injecting a supercritical fluid into the above-mentioned thermoplastic polyurethane resin at a temperature of 120 to 180°C to produce a foamed pellet with a specific gravity of 0.05 to 0.25, and then compression molding the foamed pellet.

2. In manufacturing a TPU shoe sole using a thermoplastic polyurethane resin composed of polyol, isocyanate, and a chain extender as raw materials, The above thermoplastic polyurethane resin contains hydrophobic nanosilica powder, having a primary particle size of 1 to 100 nm, as a foaming agent in a range of 0.1 to 5 phr (Parts per Hundred Resin), wherein the hydrophobic nanosilica powder forms nanosilica aggregates with an average size of 100 to 1200 nm within the thermoplastic polyurethane resin. A method for manufacturing a TPU shoe sole incorporating hydrophobic nanosilica by supercritical physical foaming, characterized by injecting a supercritical fluid into the above thermoplastic polyurethane resin at a temperature of 160 to 220°C and injection molding to a specific gravity of 0.05 to 0.

25.

3. In either Paragraph 1 or Paragraph 2, A method for manufacturing a TPU shoe sole incorporating hydrophobic nanosilica by supercritical physical foaming, characterized in that the hydrophobic nanosilica powder comprises one or more hydrophobic functional groups selected from alkyl groups, dimethyl groups, trimethyl groups, dimethylsiloxane groups, and methacrylic groups on the surface of the nanosilica particles.

4. In either Paragraph 1 or Paragraph 2, A method for manufacturing a TPU shoe sole mixed with hydrophobic nanosilica by supercritical physical foaming, characterized by injecting one or more gases selected from carbon dioxide (CO2) and nitrogen (N2) into the supercritical fluid at a temperature and pressure above the critical point.

5. In either Paragraph 1 or Paragraph 2, A method for manufacturing a TPU shoe sole incorporating hydrophobic nanosilica by supercritical physical foaming, characterized in that the product manufactured by the above compression molding or injection molding is either a shoe insole or a midsole.

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