KR0139147B1 - Method for manufacturing midsoles - Google Patents

Abstract

The present invention relates to a shoe sole manufacturing method, and more particularly, based on a ethylene vinyl acetate copolymer, ethylene ethyl acrylate or a blend of various resins and aerosols in each of these resins, The present invention relates to a method for producing a crosslinked foamed shoe sole having a low specific gravity and improved various physical properties such as tear strength and compressive permanent shrinkage by injection molding with a foaming agent and other additives.

Description

Manufacturing method of shoe sole

The present invention relates to a shoe sole manufacturing method, and more particularly, based on a blend of ethylene vinyl acetate copolymer, ethylene ethyl acrylate or a blend of various resins and rubbers in each of these resins, The present invention relates to a method for manufacturing a crosslinked foamed shoe sole having a low specific gravity and improved various physical properties such as tear strength and compressive permanent shrinkage by injection molding with a crosslinking agent, a foaming agent and other additives.

Currently, in the footwear industry, foams having an independent bubble structure formed by a press molding method based on ethylene vinyl acetate copolymer are widely used as midsoles or outsoles for footwear. The process of manufacturing a conventional outsole is as follows.

First, a compound containing a crosslinking agent, a foaming agent, and other additives in a resin is prepared in a sheet, put into a closed mold, and processed using a press machine for 20 to 30 minutes under high temperature and pressure to decompose the crosslinking agent and the foaming agent. Next, the primary foaming agent having a soft independent bubble structure is obtained by undergoing a primary press step of rapidly expanding the pressure difference by removing the pressure by temporarily opening the mold. It is turned into a certain thickness and size using a skiving machine and a cutter, and then trimmed and grinded by a skilled worker and put back into a mold having a product shape. After hot pressing at ～ 160 ℃ for 5 to 20 minutes and cooling the mold for 10 to 20 minutes at a low temperature of about 10 to 20 ℃ with the mold closed again, the product is subjected to a repressing process to demold the product. You get a product.

However, the conventional manufacturing process as described above requires not only the first and second press molding processes but also complicated processing processes such as skiving, cutting, trimming and grinding, so that the loss of raw materials due to time loss and complicated processing processes is increased. In addition to being large, there is a problem that requires a lot of labor.

Accordingly, the inventors of the present invention have studied the manufacturing method of a new shoe sole that can reduce the time and economic loss by simplifying the conventional complicated processing process, the content of vinyl acetate is 9 to 33% by weight and the melt flow index is 1.5 Ethylene vinyl acetate copolymer alone having a content of 10 to 10 g / 10 minutes, ethylene ethyl acrylate having a content of 9 to 35% by weight of ethyl acrylate and a melt flow index of 2 to 30 g / 10 minutes, or another resin and rubber for each of these resins. Is based on the blended material, and the kneaded material mixed with other additives is introduced into the injection molding machine and injected into the mold at a high temperature. After simultaneously carrying out, the mold is opened rapidly and then three-dimensionally wound to obtain a shoe sole foam continuously. It was completed.

It is an object of the present invention to provide a method for producing a cross-linked foamed shoe sole having excellent physical properties including mechanical properties and having an independent bubble structure through a single step without remolding or other complicated processing processes.

Hereinafter, the present invention will be described in detail.

The present invention is an ethylene vinyl acetate copolymer having a vinyl acetate content of 9 to 33% by weight and a melt flow index of 1.5 to 10 g / 10 minutes, and an ethyl acrylate content of 9 to 35% by weight and a melt flow index of 2 to 30 g /. It is characterized by injecting, crosslinking and foaming a compound based on 10 minutes of ethylene ethyl acrylate or a blend thereof and adding a crosslinked product, a blowing agent and other additives.

Such a present invention will be described in more detail as follows.

The present invention is based on ethylene vinyl acetate copolymer (ethylene / vinyl acetate, hereinafter referred to as EVA), ethylene ethyl acrylate (ethlene ethyl acrylate, hereinafter referred to as EEA) or their respective blends and added by adding other additives The present invention relates to a shoe sole manufacturing method for injection molding a composition, wherein the material composition for shoe sole according to the present invention is an EEA alone or EVA blend having a vinyl acetate content of 9 to 33% by weight and an MFI of 2 to 30g / 10 minutes. Or based on EEA blends.

In the case of shoe sole manufacturing of the present invention, when EVA is used alone as a substrate, if the content of vinyl acetate is less than 9% by weight, the melting point of the resin is increased, resulting in premature decomposition of the crosslinking agent or foaming agent during injection crosslinking, and the flexibility, cushioning properties, and The powderiness of the compounding agent is poor, and if it exceeds 33% by weight, the specific gravity of the foam is increased, and wear resistance, formability, and the like are reduced. And if the MFI of EVA is less than 1.5g / 10min, the flowability of the resin decreases and the temperature rise inside the mixture may occur due to frictional heat during injection molding.If it exceeds 10g / 10min, the flowability of the mixture is excellent, but the mechanical properties of the foam There is a disadvantage that the physical properties are lowered.

In addition, when EEA is used alone, when the content of ethyl acrylate is less than 9% by weight, the rubber elasticity, flexibility, cushioning properties, and dispersibility of the compounding agent are lowered. There is. If the MFI of the EEA is less than 2g / 10min, the flowability of the mixture is reduced during injection molding as in the case of EVA, and if it exceeds 30g / 10min, the flowability of the mixture is improved, but the mechanical properties of the foam are deteriorated.

In addition, the EVA blend has a vinyl acetate content of 9 to 33% by weight and an MFI of 1.5 to 10.0 g / 10 minutes to 95 to 50 parts by weight of EVA, and a blend of rubber, resin and vinyl acetate to 10 to 55%. 5 to 50 parts by weight of at least one selected from EVA having a weight% of 6 to 150 g / 10 min is blended. In the case of blend EVA used in the manufacture of EVA blends, when the MFI value is less than 6 g / 10 min, the flowability of the resin can not be improved through the blend. If the blend exceeds 150 g / 10 min, the flow characteristics of the resin during injection are remarkable. There is a disadvantage that it is improved but the mechanical properties of the obtained foam are lowered. In addition, when the vinyl acetate content of the blend EVA is less than 10% by weight, the elasticity of rubber, flexibility, cushioning properties, and phase separation of the compounding agent are lowered. When the content of the vinyl acetate exceeds 50% by weight, the rubber elasticity, flexibility cushioning properties are improved, but the specific gravity of the foam It becomes high, and abrasion resistance, shape retention, bubble density, etc. fall.

In addition, the EEA blend contains 95 to 50 parts by weight of EEA containing 9 to 35% by weight of ethyl acrylate and 2 to 30 g / 10 minutes of MFI, and 10 to 55% of rubber, resin and ethyl acrylate for the blend. 5-50 parts by weight of at least one selected from EEA having a weight% of 6 to 150 g / 10 min. In the case of the blended EEA used in the preparation of the EEA blend, when the MFI value is less than 6 g / 10 minutes, the effect of improving the flow of the resin cannot be expected, and when the blend ratio exceeds 150 g / 10 minutes, the mechanical properties of the foam are deteriorated. When the content of ethyl acrylate in the blended EEA is less than 10% by weight, the rubber elasticity, flexibility and cushioning properties of the foam cannot be expected to be improved. If the content exceeds 55% by weight, the specific gravity of the foam is increased.

In addition, the amount of blended EVA, blended EEA, blended rubber or resin is preferably 5 to 50 parts by weight when the amount of the EVA blend or EEA blend is added. If the amount is less than 5 parts by weight, it is difficult to see the blend effect. If more than 50 parts by weight is added, the specific gravity of the foam is increased, and various physical properties including flexibility are deteriorated, and a stable bubble cannot be obtained.

Rubbers and resins for blends used in the manufacture of EVA blends and EEA blends of the present invention include isoprene rubber, natural rubber, styrene-butadiene rubber, ethylene-propylene rubber, ethylene-propylene-diene copolymers, 1,2- Polybutadiene rubber, liquid isoprene rubber, liquid rubber chloride, liquid polybutadiene rubber, liquid ethylene-propylene-diene rubber, silicone rubber, butyl rubber, styrene-isoprene-styrene copolymer, liquid chloroprene, ionomer resin, polyethylene , Chlorinated polyethylene, chlorosulfonated polyethylene, and millable polyurethane.

In the preparation of the shoe sole of the present invention, a filler, foam, crosslinking agent and metal oxide are added to a substrate composed of the above components and, if necessary, a foaming aid, a crosslinking aid, a stabilizer and other additives.

In the present invention, 5 to 40 parts by weight of calcium carbonate, magnesium carbonate, barium sulfate, calcium sulfate, silica, clay, carbon black, and modified substances thereof are used based on 100 parts by weight of the filler, and the amount thereof is 5 parts by weight. If less than it does not show a filling effect, if it exceeds 40 parts by weight, the specific gravity increases and the mechanical properties are lowered.

Examples of the blowing agent include azo compounds such as azodicarbonamide having a decomposition temperature of 130 ° C. to 200 ° C., nitroso compounds such as N, N′-dinitrosopentamethylene teramine, azobisisobutyronitrile and p-tololo. 2 to 10 parts by weight of ensulfonylhydrazine, p, p'-oxybis (benzelsulfonylhydrazide), diazoaminoazobenzene and the like are used based on 100 parts by weight of the substrate, and the amount of the foam is less than 2 parts by weight. If the hardness is high, the specific gravity is increased, and exceeds 10 parts by weight, uniform bubbles cannot be obtained due to the sudden expansion of the high temperature viscoelasticity of the resin beyond the limit.

In addition, 0.4 to 4 parts by weight of an organic ingot oxide crosslinking agent capable of sufficiently trapping the decomposition gas generated above the decomposition temperature of the foam and imparting high temperature viscoelasticity to 100 parts by weight of the substrate, which has a half-life temperature of 130 to 200 It is ℃. If the amount is less than 0.4 part by weight, the crosslinking is insufficient and the fine viscoelasticity of the resin is not maintained during decomposition of the foaming agent. If the amount is more than 4 parts by weight, the hardness is sharply increased and the foam becomes unstable. Examples of such crosslinkers include t-butylperoxyisopropylcarbonate, t-butylperoxylaurate, t-butylperoxyacetate, di-t-butyldiperoxyphthalate, t-dibutylperoxymaleic acid, cyclo Hexanonperoxide, t-butylsilicon peroxide, t-butylperoxybenzoate, dicumylperoxide, 1,3-bis (t-butylperoxyisopropyl) benzene, methylethylketone peroxide, 2,5-dimethyl -2,5-di (benzoylperoxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, di-t-butylperoxide, 2,5-dimethyl-2,5 (t-butylperoxy) -3-hexyne, n-butyl-4,4-bis (t-butylperoxy) valerate, (alpha), (alpha) 'bis (t-butylperoxy) diisopropyl benzene, etc. are mentioned.

On the other hand, metal oxides such as cadmium oxide, zinc oxide, magnesium oxide, mercury oxide, tin oxide, lead oxide, calcium oxide, and stearic acid, zinc stearate, zinc carbonate, calcium carbonate, and barium stearate are used to aid processing characteristics and improve the properties of the initiator. 1-4 weight part etc. can be used with respect to 100 weight part of base materials. In particular, the metal oxide also serves as a decomposition aid of the blowing agent.

In addition to the foaming aid, 0.5 to 8 parts by weight of urea and urea derivatives may be added to 100 parts by weight of the substrate. Examples of the crosslinking aid include a small amount of sulfur, triallyl cyanurate, triallyl isocyanurate, trimethylolpropane trimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, butylene glycol acrylate, Butylene glycol dimethacrylate, a metal-acrylate, a metal-methacrylate, etc. can use 0.1-5 weight part with respect to 100 weight part of base materials. Meanwhile, in order to increase the whiteness of the foam, titanium oxide may be used in an amount of 5 to 30 parts by weight based on 100 parts by weight of the substrate, and 0.001 to 5 parts by weight of a whiteness enhancer may be used in relation to 100 parts by weight of the substrate.

The mixture is kneaded sufficiently using a banbury mixer, an open roll mill or a kneader in the temperature range above the melting point of the substrate and below the decomposition point of the crosslinking agent and the blowing agent. After making it, it is sheeted appropriately for injection molding and fed into the injection machine in the form of ribbon or pellets with constant thickness and width. It is injected into the mold through the screw of the injection machine, and the temperature inside the screw is adjusted to 80 ~ 100 ℃, the mold temperature is set to 150 ~ 200 ℃ according to the decomposition temperature of the crosslinking agent and the blowing agent, and the mold pressure is 150 ~ 400kg / ㎠ After the time is set to 3 to 10 minutes, the mold is instantaneously opened and demolded and foamed at the same time to produce a shoe sole having a skin layer on the outside as desired by only one step.

In the injection molding, if the mold temperature is less than 150 ℃ or the processing time is less than 3 minutes, sufficient decomposition of the crosslinking agent and the blowing agent cannot occur, and if the mold temperature exceeds 200 ℃ or the processing time is more than 10 minutes, the foam part is discolored or An unstable form of foam is obtained.

When the shoe sole manufactured by the manufacturing method of the present invention as described above has a coating layer on the surface, the foaming ratio (specific gravity) was 10 to 3.3 times and the specific gravity was 0.1 to 0.3. In addition, the foam has excellent appearance without tearing or scratching, and has excellent adhesion to the outsole and upper, and has reduced rubber elasticity, tensile properties, abrasion resistance, tear resistance, and compressive permanentity than foam manufactured by conventional press molding. General physical properties such as yield were significantly improved.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited by the Examples.

Example 1

MgCO ₃ , stearic acid, oxidation as a filler using a roll with a surface temperature of 90 to 105 ° C in 100 parts by weight of vinyl acetate, 15 parts by weight of ethyl vinyl acetate (hereinafter referred to as EVA) having an MFI of 2.5 g / 10 min. Zinc, titanium oxide and other preparations were kneaded by the composition ratio shown in the following Table 1, and then documil peroxide as a crosslinking agent and azodicarbonamide as a blowing agent were kneaded for about 20 minutes, and the width was 30 mm and the thickness was 2 mm. Ribbon-shaped resin sheets or pellet-shaped resin particles having a degree were obtained. This is injected into the screw of 90 ~ 100 ℃ through the hopper of the injection molding machine, and it is injected into the mold having a temperature of 180 ℃ and mold pressure of kg / ㎠ and molded for 300 seconds. Got. After cooling this at room temperature, the physical properties of the foam were measured, and the results are shown in Table 2 below.

The obtained foam had a foaming ratio of 5 times and all physical properties were superior to the foam obtained by the conventional press molding method.

Example 2

Rolls with a surface temperature of 90-105 ° C. for 90 parts by weight of 15% by weight vinyl acetate, 2.5 g / 10 min of MFI and 10 parts by weight of vinyl acetate and 25 g / 10 min of MFI After blending using, and then kneaded in the same manner as in Example 1 by the composition ratio of the following Table 1 by injection cross-linking foam to prepare a foam. The results of measuring the physical properties of the foam are shown in Table 2 below.

The obtained foam had a foaming ratio of 5.6 times, MFI of the mixture increased about 3 times, hardness was decreased by blending EVA containing a large amount of vinyl acetate, and other various physical properties were superior to conventional press-formed foams. .

Example 3

Based on ethylene ethyl acrylate (hereinafter referred to as EEA) having a content of 30% by weight of ethyl acrylate and 3 g / 10 min of MFI, and kneading in the same manner as in Example 1 according to the composition ratio of Table 1 below, injection crosslinking The foams were prepared by presentation. The results of measuring the physical properties of the foam are shown in Table 2 below.

The foaming ratio of the obtained foam was 5.5 times, and it was possible to obtain a foam having lighter specific gravity and excellent tensile properties than when EVA was used alone, and was also superior to conventional press-molded foam.

Example 4

Ethyl acrylate content of 30% by weight and MFI blended 10 parts by weight of ethylene-propene rubber to 90 parts of EEA by injection crosslinking foaming in the same manner as in Example 2 to prepare a foam. The results of measuring the physical properties of the foam are shown in Table 2 below.

The foaming ratio of the foam was 5 times, and the tearing characteristics and compression set characteristics were significantly improved than the conventional press-molded foam and the injection molded foam of Example 3 using EEA alone.

Example 5

10 parts by weight of isoprene rubber was blended in 90 parts by weight of EEA having an amount of 30% by weight of ethyl acrylate and 3 g / 10 minutes of MFI, thereby preparing a foam by injection crosslinking foaming in the same manner as in Example 4. The results of measuring the physical properties of the foam are shown in Table 2 below.

The foaming ratio of the foam was 5.3 times, and the tearing characteristics and compression set reduction characteristics were significantly improved compared to the case of using EEA alone.

Example 6

10 parts by weight of natural rubber was blended to 90 parts by weight of EVA having a vinyl acetate content of 15% by weight and MFI of 2.5g / 10min to prepare a foam by injection crosslinking foaming in the same manner as in Example 2. The results of measuring the physical properties of the foam are shown in Table 2 below.

The foaming ratio of the foam was 5 times, tearing characteristics were greatly improved, and compression set was significantly improved.

[Comparative Example]

As an example manufactured by the press molding method currently used, based on 90 parts by weight of EVA and 10 parts by weight of isoprene rubber, 0.7 parts by weight of crosslinking agent, 3.3 parts by weight of foaming agent and other additives, 10 parts by weight of magnesium carbonate, 1.5 parts by weight of zinc stearate, 10 parts by weight of titanium oxide was kneaded well to obtain a mixture sheet, which was then introduced into a closed mold, and then processed at a pressure of 150 kg / cm 2 at 160 ° C. for about 20 minutes using a press machine, and then the mold was opened to obtain a primary foam. The foam was obtained by re-heating it to a thickness and size, and then trimming and grinding it, and putting it back into a mold having a product shape, pressing it at high temperature at 160 ° C. for 10 minutes, and cooling the mold at 10 ° C. for 10 minutes with the mold closed to produce a foam. It was. The results of measuring the physical properties of the foam are shown in Table 1 below.

TABLE 1

(Unit: parts by weight)

(1) The vinyl acetate content is 15% by weight, and the MFI is 2.5g / 10min.

(2) The vinyl acetate content is 28% by weight and the MFI is 25g / 10min.

(3) Ethyl acrylate content is 30 weight%, MFI is 3g / 10min.

(4) Ethylene-propylene rubber (Sprene 505A)

(5) isoprene rubber.

(6) Natural rubber (Standard Maleisian Rubber).

(7) Ultramarine Blue (manufactured by Daiichi Kaze, Japan).

(8) HAKKOL (manufactured by Hakko Chemical Co., Ltd.).

(9) Dicumylperoxide.

(10) Azodicarbonamide.

[Test Example]

Physical properties of the molded articles prepared according to Examples 1 to 6 and Comparative Examples were measured in the following manner.

[importance]

The specific gravity of the foam was measured five times using an automatic specific gravity measurement after removing the surface and the average value was taken.

[Hardness]

Hardness was measured in accordance with ASTM D-2240 by cutting an intermediate portion of the foam with an Asker C type hardness meter.

[The tensile strength]

After removing the surface layer of the foam and making a thickness of 3mm, a test piece was made with a Die A cutter to measure the tensile strength and elongation in accordance with ASTM-412.

[Tear strength]

The tear test was measured according to ASTM D-357 and ASTM-634, respectively, and the measurement speed was measured five times at 100 mm / min and the average value was taken.

[Compressed permanent rate]

The test piece manufactured in the form of a cylinder having a diameter of 28.7 ± 0.05mm by turning the foam up to 9mm in thickness was measured according to ASTM D-3574. Insert the specimen between two parallel metal plates, insert a spacer equal to 50% of the specimen thickness, compress it, and heat it in an air-circulating oven maintained at 45 ± 0.1 ° C for 6 hours, and then remove the specimen from the compression apparatus. After cooling for 30 minutes at the thickness was measured. Three test pieces were used in the same test, and the compressive shrinkage was calculated by the following equation (1).

… … (One)

Where Cs is the compressive permanent shrinkage, to is the initial thickness of the test piece, tf is the thickness of the test piece when cooled after heat treatment, and ts is the thickness of the spacer.

[Adhesion test]

The adhesion between the midsole prepared for the peel adhesion test and the rubber sheet used as the outsole was tested. After the surface of the test piece was washed with toluene and dried, a certain amount of adhesive was applied, and the resultant was repeatedly pressed five times in the longitudinal direction by using a hand roller. Three identical test pieces were used, and the tensile speed was measured at 20 ± 2 mm using a universal tensile tester.

TABLE 2

Claims (1)

In the production of shoe soles, the vinylacetate content is 9 to 33% by weight, the ethylene vinyl acetate and the ethyl acrylate content are 9 to 35% by weight and the melt flow index is 2 to 30g. Screw internal temperature of 80 to 100 ° C. by adding 0.1 to 5 parts by weight of crosslinking agent, 0.5 to 8 parts by weight of urea blowing agent and other additives to 100 parts by weight of the base containing any component selected from ethylene ethyl acrylate for 10 minutes. And then molding at a mold temperature of 150 to 200 ° C. for 3 to 10 minutes to simultaneously perform crosslinking and foaming, thereby obtaining a foam having a foam ratio of 3.3 to 10.