KR0139143B1 - Method for manufacturing midsole - Google Patents

Abstract

The present invention is for shoe soles consisting of 100 parts by weight of ethylene-vinylacetate copolymer, rubber or iono, 0.5 to 20 parts by weight, 1 to 20 parts by weight of polyethylene, 0.1 to 5.0 parts by weight of crosslinking agent, 1 to 5 parts by weight of foaming agent and filler. After mixing the ethylene vinyl acetate copolymer composition at 80 to 120 ° C. to form pellets, the pellets are dried at 30 to 70 ° C. for 4 hours, and then put into an injection machine to maintain the temperature of the cylinder at 80 to 120 ° C. The present invention relates to a method for manufacturing shoe soles or outsoles having an average density of 0.15 g / cm 3 to 0.25 g / cm 3 by injection from a mold at 180 ° C., crosslinking and foaming, and the method of the present invention is made directly in a mold. Since there is no loss, it is not only economical but also greatly reduces the waste of raw materials, and the shoe midsole manufactured by this method is a machine for compressive strain, shock absorption, etc. The strength is excellent.

Description

Manufacturing method of shoe midsole by injection molding

1 is a chart showing the change in the ratio of the expansion ratio of the foam according to the change in the thickness of the mold.

The present invention relates to a method for manufacturing a shoe midsole by injection molding using a resin composition of ethylene vinylacetate copolymer (hereinafter abbreviated as EVA), and more specifically, EVA resin, polyethylene mixture, The present invention relates to a method for manufacturing a shoe midsole by injecting a resin composition comprising a blowing agent, a crosslinking agent and a rubber and / or an ionomer into a shoe midsole mold.

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, shoe 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 the raw materials and mixing in a short barrier, 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 physical properties such as compressive strain rate, shock absorbing ability, and mechanical strength, so that the basis weight, mixing, sheet manufacturing, press foaming, skiving, cutting, cold press forming, and cooling There are many improvements to the manufacturing process since more than 15 steps of manufacturing process and about 60% of raw materials are lost. Particularly, a large amount of scrap generated at this time causes pollution problems as waste plastics.

Accordingly, the present inventors in the manufacture of shoe midsole by foaming the EVA resin, by eliminating 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, permanent compression strain. A method for producing a polyolefin resin foaming agent including EVA by injection molding is described in Japanese Patent Publication Nos. 51-33944, 51-50978 and 52-49271. In Japanese Patent Publication No. 51-33944, only polyethylene or EVA, a foaming agent and a crosslinking agent are mixed to prepare a foam by injection molding. This method is a foam such as the size and arrangement of the cells of the foam and the connection to the side cells. It is known that it is difficult to control the structure of the cell, which has a great influence on the properties of.

Japanese Patent Laid-Open Publication Nos. 51-50978 and 52-49271 insert a space in which the resin can stagnate at the end of the cylinder of the injection machine so that preliminary foaming of the EVA resin does not occur in the cylinder and foaming occurs in the stagnant portion to some extent. A method of controlling the structure of a 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 method for manufacturing a shoe midsole that is economical as well as less susceptible to pollution due to fewer manufacturing process steps and fewer raw material losses.

Another object of the present invention is to provide a method for manufacturing a shoe midsole that is beautiful in appearance and excellent in physical properties such as compressive strain, shock absorbing ability, and mechanical strength.

The present inventors have completed a method for manufacturing a shoe midsole made of EVA foam by combining a raw material formulation and an injection method that can control the morphology of the foam cell in order to make the shoe midsole with light weight and excellent strength and resilience.

The method of the present invention can be used in a method of manufacturing shoe soles in addition to shoe soles.

In the present invention, 100 parts by weight of ethylene-butyl acetate 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, 1 to 5 parts by weight of foaming agent and filler, Provided is a method for producing a shoe midsole having an average density of 0.15 g / cm 3 to 0.25 g / cm 3 by maintaining the vinyl acetate copolymer composition at 80 to 120 ° C., injecting in a mold at a temperature of 140 to 180 ° C., and then crosslinking and foaming. .

As the polyolefin resin according to the present invention, EVA resin having a vinyl acetate content of 10 to 30% is mainly used and low density polyethylene (LDPE), high density polyethylene (HDPE), linear low density polyethylene (LLDPE), ultra low density polyethylene ( Polyethylene having a melting temperature of less than 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 a methylene monomer and an acrylic or methacrylic ester, acrylic or methacrylic acid monomer 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 temperatures such as p'-oxybisbenzelsulfonylhydrazide (OBSH), diphenylsulfone-3,3'-disulfohydrazide (DS-33) and p-toluenesulfonyl semicarbazide (TS) Above the plasticization temperature of the ethylene-based polymer may be used, and sodium bicarbonate, ammonium bicarbonate, sodium borohydrazide, etc. 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 such as (t-butylperoxy valerate) or more 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 melt viscosity, the foaming cell is stabilized and suppressed from excessively large. The high melt viscosity rubber is made of natural rubber, ethylene propylene rubber (EPR), ethylene propylene diene rubber (EPDM), Styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), polybutadiene rubber, polybutylene rubber, polyisoprene rubber, thermoplastic rubber, etc. can be used. Type ionomers can be used.

In the present invention, 1-20 parts by weight of polyethylene resin, preferably 3-15 parts by weight, and foaming agent is 1-5 parts by weight, preferably 2-5 parts by weight, and crosslinking agent of the ADCA organic foaming agent, based on 100 parts by weight of EVA resin. Is 0.1-5.0 parts by weight, preferably 0.4-2.0 parts by weight of organic peroxide, and 0.5-20 parts by weight of rubber or ionomer used for stabilizing the foaming cell to improve strength, resilience, etc., preferably 1- 15 parts by weight is used.

The resin blend of the present invention may be added as necessary dispersants, antioxidants, lubricants, etc. in addition to the above-mentioned essential components EVA and polyethylene resins, foaming agents, crosslinking agents, fillers, rubber or ionomers. 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 shoe midsole product 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 the injection, the molding agent expands to obtain a foaming agent of 3 to 6 times depending on the amount of the crosslinking agent and the blowing agent.

Since the crosslinked foam injection method of the present invention is filled with a high pressure in the injection molding machine, it is possible to fill a cavity of a complicated shape, thereby enabling a shoe sole bezo of a complicated shape. In addition, it is possible to control the foaming density by controlling the crosslinking and foaming by changing the heating temperature of each mold. In the case where the temperature of the mold is kept constant, the strength of the thin portion can be maintained by making the density of the thin portion and the shoe midsole rim rib higher than the thick portion. This is because when the temperature of the resin rises and the temperature of the resin rises in a thin cavity, bridging occurs actively and thus the foaming ratio decreases. 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 press for manufacturing the midsole, it is advantageous in terms of economics to use an injection machine or rotary injection machine in which multiple molds are attached to one injection machine.

EVA shoe midsole manufacturing by cross-linked foam injection molding of the present invention requires precise control of the filling amount suitable for the mold cavity and mold temperature must also be precisely controlled to produce a product of desired shape and dimensions. In particular, the shoe midsole made of the present invention is accompanied by a loss of raw material of about 60% of the shoe midsole made 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 and the process number Since it is made of four steps such as basis weight, dry blending, and mixed injection, 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

EVAA foaming agent [Kumyang, CELLCOM-JTR] 4.5 parts by weight, 0.8 parts by weight of crosslinking agent (DCP), 5 parts by weight of zinc 6 parts by weight of the ethylene ionomer, ions having a melt index, 55 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. The mixture mixed with the Henschel mixer was mixed at 250 rpm using a twin screw extruder controlled at 85-110 ° C. to prepare pellets. The pellets thus prepared are held at a temperature of 85 to 105 ° C. using a rotary injection molding machine with 10 molds, and the mold temperature is adjusted to 160 ° C. to inject a predetermined amount into the mold for 10 minutes, and then the mold is opened. At the same time the mold was opened, the shoe midsole was expanded. The density of the manufactured sole is measured in accordance with 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 measurement results are shown in Table 1.

Example 2-3

The vinyl acetate content was blended as shown in Table 1 using 100 parts by weight of EVA resin different from that of 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 containing a vinyl acetate content of 14% EVA and 25% EVA mixed 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 as a crosslinking agent and blended as shown in Table 1 and mixed and injected in the same manner as in Example 1 to measure the physical properties of the shoe midsole manufactured Table 1 shows.

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

The experiment was carried out in the same manner as in Example 1, but instead of the ionomer, EDPM rubber having 58% ethylene and 15% ethylidene norbornene as diene monomer (Example 11), and ethylene propylene rubber having 73% ethylene. (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 1-10

As shown in Table 2, the EVA resin, the crosslinking agent, and the foaming agent were blended. As shown in the table, the shoe sole was manufactured by mixing, injecting, crosslinking, and foaming in the same manner as in Example 1 without using rubber or ionomer. After the measurement of the physical properties is shown in Table 2.

In addition, in order to measure the expansion ratio of the thin rib portion, the result of measuring the expansion ratio by marking the rib portion of the mold is shown in FIG. Figure 1 shows the change in the foaming ratio by calculating the ratio of foaming ratio of the foam as the mold thickness changes. As a result, when the thickness of the mold is less than 6mm, the foaming ratio is greatly affected, and increases rapidly as the thickness is increased. 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 the shoe sole and tensile strength. 17-25 ㎏ / ㎠, permanent compression strain is 45-60% improved properties than the case without using rubber or ionomer, thick portion was able to make EVA foam with a high impact absorption capacity.

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 (7)

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 1 to 5 parts by weight of blowing agent and filler. A method for producing a shoe midsole having an average density of 0.15 g / cm 3 to 0.25 g / cm 3 by maintaining the coalescing composition at 80 to 120 ° C., injecting in a mold at a temperature of 140 to 180 ° C., and crosslinking and foaming. 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 low density polyethylene, linear low density polyethylene, ultra low density polyethylene and high density polyethylene. The rubber 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 Method for producing a shoe sole, characterized in that the sulfohydrazide, p-toluenesulfonyl semicarbazide, sodium bicarbonate, ammonium bicarbonate or sodium borohydrazide. The crosslinking agent according to claim 1, wherein the crosslinking agent is dicumylperoxide, 2,5-dimethyl-2,5-di (t-butyperoxy) hexane, 2,5-dimethyl-2,5- (y-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, characterized in that. The method of claim 1, wherein the foaming ratio is controlled by maintaining the overall temperature of the mold in a predetermined range in the foaming step by the difference in the thickness of the shoe midsole, so that when the thickness of the shoe sole is less than 1 cm, the density becomes larger as the thickness becomes smaller. Shoe sole manufacturing method.