KR0139144B1 - Method of manufacturing blowing preform for midsole - Google Patents

Abstract

The present invention relates to a foam preform for shoe soles by injection molding a resin composition based on an ethylene-vinylacetate copolymer, and a method for manufacturing a shoe sole using the same, wherein the ethylene-vinylacetate copolymer and ethylene-vinylacetate air 0.5-20% by weight of rubber and / or ionomer, 1-20% by weight of polyethylene, based on coalescence, comprising 0.1-5.0% by weight of crosslinking agent, 4-15% by weight of blowing agent and filler relative to the total amount of the resin The composition is injected into a mold at a temperature of 140-180 ° C. and maintained at a constant temperature to produce a foam preform for shoe soles and hot press molding it again to produce a shoe sole or an outsole. In this way, shoe soles are manufactured which are economical and cause less pollution and have excellent mechanical strength such as compression strain.

Description

Method for manufacturing shoe sole using foam preform

The present invention relates to a foam preform for shoe soles of ethylene vinyl acetate copolymer (abbreviated as EVA) using injection molding, and to a method for manufacturing shoe soles using foams. The present invention relates to a method for manufacturing a shoe sole by manufacturing a foam pre-form capable of making a shoe midsole by injecting a resin composition comprising a foaming agent, a crosslinking agent, and a rubber and / or an ionomer.

EVA resin, a thermoplastic resin, is flexible, excellent in flex resistance, easily crosslinked with organic peroxides, and can be made of foam having excellent physical properties. In particular, EVA foam is used in the manufacture of sandals, slippers, soles, strollers and children's bicycle wheels, toys, etc. because of its excellent resilience and elasticity even at low specific gravity. Conventional foam products using EVA resin is mainly prepared by weighing in a raw material, mixed with a short barley, roll mill, etc. and then foamed at a high temperature by a press. In particular, since the shoe midsole is complex in shape and beautiful in appearance, it must be excellent in characteristics such as compressive strain rate, impact absorption capacity, and mechanical strength. There are many improvements to the manufacturing process since more than 15 steps of manufacturing process and about 60% of raw materials are lost. In particular, most of the raw material loss occurs in the skiving and cutting processes up to preform manufacturing used in the secondary press molding, and a large amount of scrap generated at this time causes pollution problems as waste plastic.

Accordingly, the present inventors in the manufacture of shoe midsole by foaming the EVA resin, by omitting the skiving, cutting process and the related process by using the injection molding method can greatly reduce the manufacturing process step to improve economic efficiency and reduce the screen In addition, the method to improve the physical properties such as tensile strength, study compressive strain was studied.

The manufacturing method of a polyolefin resin foam including EVA by injection molding is described in Japanese Patent Laid-Open No. 51-33944, Japanese Patent Laid-Open No. 51-50978, and Japanese Patent Laid-Open No. 52-49271. In Japanese Patent Publication No. 51-33944, only polyethylene or EVA, a foaming agent, and a crosslinking agent were mixed to prepare a foam by injection molding. This method includes the size and arrangement of the cells of the foam and the connection diagram with the side cells. It is known that it is difficult to control the structure of the cell, which greatly affects the properties of the foam.

In Japanese Patent Laid-Open Publication Nos. 51-50978 and 52-49271, a space in which the resin can be stagnated is inserted into the cylinder end of the injection molding machine so that preliminary foaming of the EVA resin does not occur in the cylinder, and foaming occurs in the stagnant portion. A method of controlling the structure of a foam cell is disclosed. However, the foams produced by the above methods are not uniform in the size or shape of the cell has a very important properties such as elasticity, resilience, which is very important in the foam.

It is an object of the present invention to provide a process for producing foam preforms and shoe soles for shoe soles, which are economical as well as less raw material loss due to fewer manufacturing process steps. Still another object of the present invention is to provide a method for manufacturing foam preforms and shoe soles, which are beautiful in appearance and excellent in physical properties such as compressive strain, shock absorbing ability, and mechanical strength.

The present inventors have completed the method for manufacturing the soles of EVA foams by combining the raw material formulation and the injection method that can control the morphology of the foam cell in order to make a lightweight sole, excellent strength and resilience to the EVA foam.

The object of the present invention described above is composed of 100 parts by weight of ethylene-vinylacetate copolymer, 0.5 to 20 parts by weight of rubber or ionomer, 1 to 20 parts by weight of polyethylene, 0.1 to 5.0 parts by weight of crosslinking agent, foaming agent and 5 to 15 parts by weight of filler. After mixing the ethylene vinyl acetate copolymer composition for shoe soles at 80-150 ° C. to make pellets, the pellets are dried at 30-70 ° C. for 4 hours, and then put into an injection machine to maintain the cylinder temperature at 80-120 ° C. , A foam preform having an average density of 0.08 g / cm 3 to 0.14 g / cm 3 by injection, crosslinking and foaming in a mold at a temperature of 140 to 180 ° C., and then adjusting the foam preform to 0.15 to It is achieved by a method for manufacturing a shoe sole, characterized in that hot pressing to have a density of 0.25g / cm 3.

In addition, an object of the present invention is achieved by a method of producing a shoe sole by hot pressing the foam preform obtained in the manufacturing method.

As the polyolefin resin according to the present invention, an EVA resin having a vinyl acetate content of 10-30% is preferable, and in order to increase the strength, low density polyethylene (LDPE), high density polyethylene (HDPE), linear low density polyethylene (LLDPE), ultra low density (VLDPE) Polyethylene having a melting temperature below the decomposition temperature of the blowing agent and the crosslinking agent may be used. In addition, copolymers polymerized using one or two or more of ethylene monomers and acrylic ester, acrylic or methacrylic acid monomers are also available. Meanwhile, as the blowing agent used in the present invention, an organic blowing agent or an inorganic blowing agent may be used alone or in combination, and as the organic blowing agent, azodicarbonamide (ADCA), N, N'-dinitrosopentamethylenetetramine (DPT), p Decomposition temperature such as, p'-oxybisbenzenesulfonylhydrazide (OBSH), diphenylsulfone-3.3'-disulfohydrazide (DS-33), p-toluenesulfonyl semicarbazide (TS) Above the plasticization temperature of the polymer may be used, and sodium bicarbonate, ammonium bicarbonate, sodium borohydrazide and the like may be used as the inorganic blowing agent. Examples of the crosslinking agent include dicumyl peroxide (DCP), 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne, 1,3-bis (t-butylperoxyisopropyl) benzene, 1,1'-bis (t-butylperoxy) 3,3 ', 5-trimethylcyclohexane, n-butyl-4,4'-bis The decomposition temperature (t-butyl peroxy valerate) and the like may be used above the plasticization temperature of the ethylene polymer. In particular, in the present invention, by using a rubber or ionomer having a high melting temperature, the foaming cell is stabilized and suppressed from excessively growing. The rubber having a high melt viscosity includes natural rubber, ethylene propylene rubber (EPR), and ethylene propylene diene rubber (EPDM). Butylene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), thermoplastic rubber and the like can be used as the ionomer can be used an ethylene ionomer having a low processing temperature.

In the present invention, 1-20 parts by weight of polyethylene resin, preferably 3-15 parts by weight, and foaming agent is 4-15 parts by weight, preferably 5-10 parts by weight, and crosslinking agent of the ADCA organic foaming agent, based on 100 parts of EVA resin. 0.1-5.0 parts by weight, preferably 0.4-2.0 parts by weight of organic peroxide, 0.5-20 parts by weight, preferably 1-15, of rubber or ionomer used for stabilizing the foaming cell to improve strength, resilience, etc. Parts by weight are used. When rubber or ionomer is excessively used, it is difficult to obtain a foam having excellent physical properties due to deformation in appearance.

In the resin blend of the present invention, in addition to the above-mentioned essential components of EVA and polyethylene resin, foaming agent, crosslinking agent, filler, rubber or ionomer, a dispersant, antioxidant, lubricant and the like may be added as necessary. As a blending method, each component is weighed and mixed using a conventional dry mixer such as a ribbon blender or a Henschel mixer. The melt mixing is performed by mixing a conventional one- or two-axis compressor or a kneader such as a kneader. The method of pelletizing by mixing at 80-120 ° C is used. The pellet is dried for 4 hours at 30-70 ° C., and then put into an injection machine to maintain the cylinder temperature at 80 to 120 ° C. and to be injected from a mold heated to 140 to 180 ° C. to decompose the crosslinking agent and the foaming agent in the mold. When the mold is opened after 3 to 20 minutes after injection, the molding agent expands to obtain a foaming agent of 6 to 10 times depending on the amount of the crosslinking agent and the foaming agent. The cross-linked foam injection molding method is a high pressure filling machine for injection molding, which allows filling into a cavity having a complex shape, which is about 1.05-1.5 times larger than a press mold for manufacturing secondary shoe soles, and has a convenient shape for compression molding. It is possible to manufacture. In terms of productivity, since injection resin is filled in the mold in the molten state, the crosslinking time is shorter than that of the conventional press foaming method, and the molding cycle can be reduced to 1/2 to 1/10 of the press method. Since the injection molding machine is more expensive than the midsole manufacturing press, it is advantageous to use an injection machine or a rotary injection machine in which several molds are attached to one injection machine.

In the production of preforms for shoe midsoles by cross-linked foam injection molding of the present invention, accurate control of the total amount appropriate for the mold cavity is required, and mold temperature must be precisely controlled to produce products of the desired dimensions. The preform for shoe midsoles can then be compression molded at high temperature by a conventional press method to produce shoe soles with excellent physical properties. In particular, the shoe midsole preform made of the present invention is a shoe midsole preform produced by the conventional press method, but the raw material loss of about 3 to 10% occurs depending on the design of the injection molding mold, compared to the raw material loss of about 60% In addition, since the process number is made of a simple process such as basis weight, dry blending, melt mixing, injection, etc., it has the advantage of being reduced to 1/2 to 1/4 of the conventional press method.

Examples and comparative examples of the present invention will be described in detail as follows.

Example 1

As the EVA resin, 8 parts by weight of ADCA-based blowing agent [Kumyang, Cellcom-JTR], 0.8 parts by weight of crosslinking agent (DCP), 100 parts by weight of vinyl acetate content of 19%, resin having a melt index of 2.5, and zinc. 6 parts by weight of ethylene ionomer, ion, melt index, 5 parts by weight of polyethylene having a softening point of 90 ° C., and 10 parts by weight of calcium carbonate were mixed at 300 rpm for 5 minutes using a Henschel mixer. Chemicals mixed with a Henschel mixer were pelletized by mixing at 250 rpm using a twin screw extruder controlled at 85-110 ° C. Using the rotary injection molding machine with 10 molds, the prepared pellets were maintained at a temperature of 85 to 105 ° C., and the mold temperature was adjusted to 160 ° C .. At the same time as the mold was opened, the foamed preform for the shoe midsole was expanded and hot pressed again to obtain the shoe sole. The density of the sole is measured according to ASTM D-3575, the hardness is measured by ASTM D-2240, Shore C, the tensile strength and elongation is ASTM D-412, and the permanent compressive strain is measured according to ASTM D-395. The results are shown in Table 1.

Example 2-3

The vinyl acetate content was mixed as shown in Table 1 using 100 parts by weight of EVA resin different from Example 1, and mixed and crosslinked foam injection was carried out in the same manner as in Example 1 to prepare foam preforms and shoe soles. Is shown in Table 1.

Example 4

Instead of using EVA alone, EVA resin having a vinyl acetate content of 14% EVA and 25% EVA mixed with 1: 1 was used. The other experiments were carried out in the same manner as in Example 1, and the results are shown in Table 1. It was.

Example 5-7

Using 100 parts by weight of the same EVA resin as in Example 1, varying the DCP content of the crosslinking agent and blended as shown in Table 1 and measured the physical properties of the shoe midsole manufactured by mixing, injection and compression in the same manner as in Example 1 The results are shown in Table 1.

Example 8-10

The experiment was carried out in the same manner as in Example 1 except that the blowing agent content was changed as shown in Table 1, and the results are shown in Table 1.

Example 11-17

Experiment was carried out in the same manner as in Example 1, but instead of ionomer, EPDM rubber having 58% ethylene and 15% ethylidene norbornene as diene monomer (Example 11), ethylene propylene rubber having ethylene content 73% (Example 12), styrene-butadiene thermoplastic rubber having a Shore A hardness of 58 (Example 13), styrene-butadiene rubber having a Mooney viscosity of 52 and having a styrene content of 23% (Example 14), and natural rubber (SMR L) (Example 15), polyisoprene rubber (Japanese synthetic rubber IR 2200) (Example 16), polybutadiene rubber (Japanese synthetic rubber, RB 820) (Example 17) were used, and the measured physical properties are shown in Table 1.

Example 18

The experiment was carried out in the same manner as in Example 1 except that 1/2 of the ionomer was replaced with the EPDM rubber used in Example 11, and the measured physical properties are shown in Table 1.

[Comparative Example 1-7]

Combination of EVA resin, crosslinking agent and foaming agent was as shown in Table 2, and as shown in the table, mixing, injection, crosslinking, foaming, and pressing were performed in the same manner as in Example 1 without using rubber or ionomer. Table 2 shows the results of measuring physical properties after manufacture.

Comparative Example 8

The experiment was carried out in the same manner as in Example 1, but was carried out using 20 parts by weight of ionomer. The measured physical properties are shown in Table 2.

As shown in the above examples and comparative examples, the shoe sole made in accordance with the present invention stabilizes the foaming cell by adding a rubber or ionomer having a higher melt viscosity than the thermoplastic resin, thereby facilitating the production of a shoe sole with a beautiful appearance. Tensile strength 20-25 ㎏ / ㎠ and permanent compression strain is 40-60% has improved properties than the product of the comparative example without the use of rubber or ionomer.

Compared to the press manufacturing method, the shoe midsole manufacturing method using the crosslinked foam injection molding method manufactured by the present invention has a merit that the number of manufacturing steps can be significantly shortened and raw material loss can be reduced to 1/6 or less.

While the present invention has been described in detail with respect to the embodiments described, it will be apparent to those skilled in the art that various modifications and variations are possible within the scope of the present invention and it is obvious that such modifications and modifications fall within the scope of the appended claims.

Table 1 Example

Table 2 Comparative Example

Claims (6)

Ethylene vinyl acetate copolymer for shoe sole consisting of 100 parts by weight of ethylene-vinylacetate copolymer, 0.5 to 20 parts by weight of rubber or ionomer, 1 to 20 parts by weight of polyethylene, 0.1 to 5.0 parts by weight of crosslinking agent, and 5 to 15 parts by weight of blowing agent and filler. After mixing the coalescence composition at 80 ~ 150 ℃ to make a pellet, the pellet was dried for 4 hours at 30 ℃ ~ 70 ℃, and then put into the injection machine to maintain the temperature of the cylinder at 80 ~ 120 ℃, 140 ~ 180 ℃ temperature The foam preform having an average density of 0.08 g / cm 3 to 0.14 g / cm 3 is produced by injection, crosslinking and foaming in a mold of the mold, and then the foam preform has a density of 0.15 to 0.25 g / cm 3 to control a specific shape or characteristic. Method of manufacturing a shoe sole, characterized in that hot pressing to have a. The method of claim 1 wherein the ethylene-vinylacetate copolymer is a mixture of one or more ethylene-vinylacetate copolymers in a vinyl acetate content ranging from 10 to 30% by weight. The method of claim 1 wherein the polyethylene is one or two or more mixtures selected from the group consisting of jubilido polyethylene, linear low density polyethylene, ultra low density polyethylene and high density polyethylene. The rubber composition according to claim 1, wherein the rubber is one or two or more mixtures selected from the group consisting of styrene-based thermoplastic rubber, styrene butadiene rubber, ethylene propylene rubber, ethylene propylene diene rubber, natural rubber, polyisoprene rubber and polybutadiene rubber. Method for producing a shoe midsole, characterized in that the ethylene ionomer. The blowing agent of claim 1, wherein the blowing agent is azodicarbonamide, N, N'-dinitrosopentamethylenetetramine, p, p'-oxybisbenzenesulfonylhydrazide, diphenylsulfone-3,3'-di A method for producing a shoe sole, characterized in that the sulfohydrazide, p-toluenesulfonyl semicarbazide, sodium bicarbonate, ammonium bicarbonate or sodium borohydrazide. The method of claim 1, wherein the crosslinking system is dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butyperoxy) hexane, 2,5-dimethyl-2,5- (t-butylperoxy) hexyne , 1,3-bis (t-butylperoxyisopropyl) benzene, 1,1'-bis (t-butylperoxy) 3,3 ', 5-trimethylcyclohexane or n-butyl-4,4'- Bis (t-butylperoxy valerate) method for producing a shoe sole.