Description

A SHOE AND MIDSOLE MANUFACTURING METHOD HAVING 2-STATE INSERT STRUCTURE

Technical Field

[1] The present invention relates to a health shoe including a midsole having a dual insert structure and a method of manufacturing the same, and, more particularly, to a health shoe including a midsole having a dual insert structure, in which the midsole is formed by joining low-hardness polyurethane and middle-hardness polyurethane together through a foaming process and thus the shoe is not hydrolyzed and has excellent cushioning properties, and to a method of manufacturing the same. Background Art

[2] Generally, in order to minimize the impact occurring when a shoe comes into contact with the ground, a shoe is provided with a sole assembly including a midsole which has relatively low hardness and which is formed at a predetermined thickness, and an outsole which has higher hardness than the midsole and which is placed beneath the midsole.

[3] The midsole is generally made of polyurethane foam or ethylene-vinyl acetate (EVA) foam in order to absorb impact, and the outsole is made of a rubber material in consideration of friction between the outsole and the ground and durability.

[4] However, since the conventional sole assembly chiefly depends on the midsole in order to absorb the impact occurring when a shoe comes into contact with the ground, when the ground is hard or uneven, this sole assembly does not suitably absorb the impact, so that the impact is directly transferred to a foot and knee, thereby negatively affecting an ankle or knee joint.

[5] In order to solve this problem, a method of absorbing impact by inserting a member functioning to absorb impact, such as an air bag, an air gel or the like, into the midsole in various shapes so that the member is integrated with the midsole, or a method of absorbing impact from the ground by forming a plurality of hollow portions in the midsole has been conducted.

[6] However, the former method is problematic in that the process is complicated, a process of preparing an air bag or air gel is additionally required, and additional costs are also required, and in that, when the midsole, air bag and air gel are used for a long period of time, they become deformed, and thus an inherent impact absorbing function is not suitably exhibited.

[7] Meanwhile, a method of preparing polyurethane foam for a midsole includes the steps of placing a polyurethane raw material into a mold and then closing the mold,

foaming the polyurethane raw material by heating the upper and lower plates of the mold using the upper and lower hot plate of a polyurethane molding machine to form polyurethane foam, and opening the mold and then separating the polyurethane foam from the mold.

[8] However, since a shoe is manufactured by joining polyurethane foam and different kinds of materials with an adhesive, as time advances, there is a problem in that the polyurethane foam is hydrolyzed by the adhesive. Disclosure of Invention Technical Problem

[9] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a shoe having excellent cushioning properties, which can overcome the problem of hydrolysis by enabling an inner polyurethane layer having low hardness and an outer polyurethane layer having middle hardness to be easily joined to each other without using an additional adhesive. Technical Solution

[10] In order to accomplish the above object, an aspect of the present invention provides a shoe including a midsole having a dual insert structure, the midsole including: a hard nylon injection piece layer; a low-hardness (30C) polyurethane layer covering the nylon injection piece layer; and a middle-hardness (55-60C) polyurethane layer covering the low-hardness polyurethane layer.

[11] Further, another aspect of the present invention provides a method of manufacturing a midsole having a dual insert structure included in a shoe, including: fabricating a hard nylon injection piece (SlO); inserting the hard nylon injection piece into a mold and then introducing a low-hardness polyurethane material into the mold to form a low-hardness polyurethane foam (S20); and inserting the low-hardness polyurethane foam covering the hard nylon injection piece into the mold and then introducing a middle-hardness polyurethane material into the mold to form a middle-hardness polyurethane foam covering the low-hardness polyurethane foam (S30). Brief Description of Drawings

[12] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. First, reference should now be made to the drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components. Further, in case it is judged that detailed description of the known functions and configuration thereof may obscure the gist of the invention, it should be understood that the detailed description is omitted.

[13] FIG. 1 is a perspective view showing a shoe according to the present invention;

[14] FIG. 2 is a schematic view showing a midsole according the present invention;

[15] FIG. 3 is a sectional view of a nylon injection piece layer of the midsole of the present invention;

[16] FIG. 4 is a sectional view of a low hardness polyure thane layer of the midsole of the present invention;

[17] FIG. 5 is a sectional view of a middle hardness polyurethane layer of the midsole of the present invention; and

[18] FIG. 6 is a flowchart showing a process of manufacturing the midsole according to the present invention. Best Mode for Carrying out the Invention

[19] As shown in FIG. 1, like a conventional shoe, a shoe of the present invention includes an upper 10 constituting a top part of the shoe, a midsole 20 constituting a cushion part of the shoe, and an outsole 30 covering the midsole and constituting a bottom part of the shoe.

[20] Further, the midsole 20 includes three layers, that is, a hard nylon injection piece layer 21, a low-hardness (30C) polyurethane layer 22 covering the hard nylon injection piece layer, and a middle-hardness (55-60C) polyurethane layer 23 covering the low- hardness polyurethane layer.

[21] Further, a method of manufacturing the midsole of the shoe includes the steps of: fabricating a hard nylon injection piece (SlO); inserting the hard nylon injection piece into a mold and then introducing a low-hardness polyurethane material into the mold to form a low -hardness polyurethane foam (S20); and inserting the low-hardness polyurethane foam covering the hard nylon injection piece into the mold and then introducing a middle-hardness polyurethane material into the mold to form a middle- hardness polyurethane foam covering the low-hardness polyurethane foam (S30).

[22] In this method, since the midsole of the shoe is manufactured by inserting the hard nylon injection piece into a mold and then introducing a low-hardness polyurethane material into the mold to form a low-hardness polyurethane foam, and then inserting the low-hardness polyurethane foam covering the hard nylon injection piece into the mold and then introducing a middle-hardness polyurethane material into the mold to form a middle-hardness polyurethane foam covering the low-hardness polyurethane foam, the human body is not influenced by discontinuous impact occurring when the shoe comes into contact with the ground.

[23] Hereinafter, the method of manufacturing the midsole of the shoe according to the present invention is described in more detail as follows.

[24] First, a hard nylon injection piece layer 21 is inserted into a mold for low-hardness polyurethane, and then a low-hardness polyurethane layer 22 is inserted into the mold

to form low-hardness (30C) polyurethane foam.

[25] That is, the hard nylon injection piece layer 21 is inserted into the mold, and then a non foamed low-hardness polyurethane material is introduced into the mold, and then a foam- forming process is performed at a predetermined temperature and pressure to form the low-hardness polyurethane foam.

[26] The hardness of the material is adjusted by the control of foaming properties due to the change in the temperature and pressure of the mold. In the present invention, the "low hardness" means a hardness of about 30C in a Shore C type hardness meter.

[27] Subsequently, the low-hardness polyurethane foam is inserted into a mold for middle-hardness polyurethane, and then a middle-hardness polyurethane material is introduced into the mold, then a foaming process is performed to form middle- hardness polyurethane foam. The middle-hardness polyurethane foam is inserted into the mold and then foam-formed at a predetermined temperature and pressure. In the present invention, the "middle hardness" means a hardness of 55-60C in a Shore C type hardness meter.

[28] The shoe including the midsole manufactured by the above method has excellent elasticity and stability, and is very light and cushioned. Further, in the shoe, since the low-hardness (30C) polyurethane layer 22 is not joined to the middle-hardness (55-60C) polyurethane layer 23 with an adhesive, the hydrolysis of the shoe can be prevented, and the low-hardness polyurethane layer or middle-hardness polyurethane layer is 2/3 lighter than other polyurethane.

[29] Further, when the shoe comes into contact with the ground during walking, a part of the bottom of a foot partially presses the middle-hardness polyurethane layer 23 of the midsole. In this case, the impact strength applied to the low-hardness polyurethane layer 22 is inversely proportional to the area of the bottom of a foot, and is proportional to the weight of the human body pressing the ground.

[30] For this reason, the impact strength applied to the middle-hardness polyurethane layer 23 is dispersed to the low-hardness polyurethane layer 22, thus improving the cushioning property of the shoe.

[31] Accordingly, the impact occurring during walking is uniformly dispersed, and thus the impact transferred from the ground to the human body is decreased.

[32] Hereinafter, a method of preparing polyurethane used in the present invention is described as follows.

[33] First, polyurethane is formed by the addition polymerization reaction of alcohol having an active hydroxide group (-OH) and isocyanate having an isocyanate group (-N=C=O) while generating reaction heat. Isocyanates having one or more isocyanate groups (-N=C=O) and alcohols having one or more hydroxide groups (-OH) are referred to as polyfunctional groups. These polyfunctional groups are formed into

compounds having a structure of [-NHCOO-] , which is a urethane bond, while n generating high-temperature heat. Among the compounds, compounds having a molecular weight of 1000 or more are referred to as polyurethane.

[34] Side reactions in the formation of polyurethane are described below.

[35] Polyurea reaction: Isocyanate reacted with polyfunctional alcohol is reacted with water (H O) to form urea and carbon dioxide (CO ).

[36] Allophanate & Biuret reaction: The urea formed by the polyurea reaction and active hydrogen remaining in the urea are reacted with excess isocyanate under suitable conditions to form allophanate and biuret, which is a crosslinking reaction.

[37] Uretidinedion & Isocyanurate reaction: Isocyanates are reacted with each other in the presence of a basic catalyst to form uretidinedion as a dimer and isocyanurate as a trimer. The dimer is produced from aromatic isocyanate. For example, 4,4-diphenylmethane diisocyanate, which is monomeric MDI, is slowly dimerized at room temperature and thus formed into an insoluble polymer material at high temperature. Isocyanurate is formed by heating aliphatic and aromatic isocyanates, and this heating reaction is accelerated by a basic catalyst.

[38] Polyurethane raw materials: isocyanate and 4,4-diphenylmethane diisocyanate

(MDI). MDI is a material obtained by treating diphenylmethane diamine (MDA) formed by condensing aniline and formaldehyde with phosgene (COCl ). The reaction product includes various isomers and coenocytes, but pure MDI (crude MDI) is separated therefrom by refining the reaction product. Since monomeric MDI is a white solid at room temperature, it is modified into liquid MID, such as carbodiimide- modified MDI or uretonimine-modified MDI, and then used. Polymeric MDI is liquid at room temperature. The product has an average functional group number of about 2.3 ~ 3.0, and is characterized by viscosity, reactivity and NCO content. The viscosity of the product depends on its average molecular weight and NCO content. Monomeric MDI is chiefly used in nonfoamy polyurethane products such as Spandex, synthetic leather, elastomer, coating, sealant, and the like. Polymeric MDI is widely used to manufacture polyurethane foam used for insulation materials for refrigerators, containers, sprays and buildings, and interior materials for automobiles. Industrial Applicability

[39] The shoe according to the present invention is advantageous in that since a midsole includes two different polyurethane layers, that is, a polyurethane layer having low hardness and a polyurethane layer having middle hardness, the midsole can completely absorb the impact transferred from the ground when it comes into contact with the ground, and thus the impact is not transferred to an ankle or knee joint.

[40] Further, the shoe according to the present invention is advantageous in that, since the

midsole is formed by joining low-hardness polyurethane and middle-hardness polyurethane together without using an additional adhesive, the shoe is not hydrolyzed, thereby increasing the lifespan of the shoe.

[41] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the present invention as disclosed in the accompanying claims.