KR101203677B1 - Ethylene vinyl acetate resin composition for MASAI SENSOR - Google Patents

Abstract

The present invention relates to an ethylene vinyl acetate resin composition, and more particularly to an ethylene vinyl acetate resin composition comprising two kinds of ethylene vinyl acetate copolymer, ethylene-propylene-diene rubber, blowing agent, crosslinking agent, metal oxide and stearic acid. will be. The ethylene vinyl acetate resin composition of the present invention can be usefully applied as a soft sensor for shoe midsoles, especially Masai walking shoe midsoles, while having low hardness (hardness) when molded into foams and excellent hydrolysis resistance and permanent compression yield. .

Description

Ethylene vinyl acetate resin composition for MASAI SENSOR}

The present invention relates to an ethylene vinyl acetate resin composition for shoe soles, the ethylene vinyl acetate resin composition of the present invention has a low hardness (hardness) when molded into a foam, but also has excellent hydrolysis resistance and permanent compression shrinkage, In particular, it can be usefully applied as a soft sensing body of the Masai walking shoe midsole.

The Masai Walking Shoe has a curved sole midsole as described in Korean Patent No. 10-0377822 so that the load is spread over the soles of the feet and the ankles when walking, such as when the Masai people walk naturally on the soft grassland barefoot. It is the shoes that can make a correct posture by the roll action of. In the case of ordinary shoes, the gait center of gravity omits the center of the sole and passes from the heel to the heel, so that the gait is distorted and deformed without absorbing the impact from the ground, which adversely affects the joints or the spinal column. In this case, the entire sole of the foot touches the ground, so the pressure applied to the foot is evenly distributed to relax the foot and reduce the impact and load on the knees and waist when walking. Also, when you walk, you start to reach from the outside of the heel, and the center of gravity moves through the outside of the foot in the order of the little toe and the big toe to create a straight gait.

The soft sensing body 3 corresponding to the heel portion of the masai walking shoe midsole 2 should be easily deformed to be in parallel with the ground when the heel portion touches the ground during walking, and should be cushioned by shrinkage. When the heel of the ship leaves the ground, the shrinkage must be restored, so a soft foam having proper hardness, elasticity and restoring force should be used. If the hardness is too low, the sensor does not act as a support, if the hardness is too high, there is a problem that does not act as an elastomer because it is hard. In addition, the soft sensing body should be excellent in permanent compression rate because it is subjected to continuous load.

A general shoe midsole is a porous foam material, and is divided into an ethylene vinyl acetate copolymer (EVA) foam and a polyurethane foam according to the polymer used. Most of them are ethylene vinyl acetate copolymer foams, accounting for over 80% of the midsole market.

However, the soft sensing body of the Masai Walking Shoe midsole has a low hardness of 35 or less, but it is thicker and has more load than the midsole of the normal shoe, so it has to have excellent permanent compression rate (Cs). Polyurethane foams are used. However, the polyurethane foam has a high specific gravity and has a urethane bond, so that the discoloration resistance is worse than that of the ethylene vinyl acetate copolymer foam, and since the hydrolysis resistance is weak, the midsole absorbed with water or water becomes crumbly and continuously during walking. As the load is applied, the sensor is tattered, which limits the life of the masai walking shoe. In particular, in the case of rainy day, the use of polyurethane foam as a sensing material is limited in the use of masai walking shoes.

Ethylene vinyl acetate copolymer foam has the advantages of free molding, low specific gravity, low discoloration, and low price, so if it can be applied as a soft sensor of Masai walking shoe midsole, it is expected to solve the disadvantage of polyurethane foam. . However, with the known ethylene vinyl acetate copolymer composition, it is difficult to produce a foam exhibiting excellent permanent compression rate characteristics at a low hardness of about 35 or less. Korean Patent No. 10-0139146 discloses a foam using a ethylene vinyl acetate copolymer grafted with a hydrolyzed modified ethylene vinyl acetate copolymer or a polymer, but the improvement in hardness and permanent compressive shrinkage was not as expected. . In addition, the Republic of Korea Patent No. 10-0931028 is a foam using a silane-grafted ethylene vinyl acetate copolymer, the Republic of Korea Patent Publication No. 10-2003-0078135 ethylene vinyl acetate copolymer and isoprene rubber, sulfonyl polyethylene rubber Although a foam prepared by mixing and the like is proposed, there is a problem that it is difficult to apply as a soft sensing body of the Masai walking shoe midsole due to its good compression set and good hardness.

In order to solve the problems described above, the inventors of the present invention use a ethylene vinyl acetate copolymer only because the permanent compression rate is high, so that the permanent compression rate is not good, so that the ethylene-propylene-diene rubber is improved. The method of blending was studied. However, as a blend of ethylene vinyl acetate copolymer having 15 to 28% by weight of vinyl acetate used for shoe soles and ethylene-propylene-diene rubber only, the content of ethylene-propylene-diene rubber is increased. The compressive shrinkage characteristics are improved, but the hardness is increased, and it was found that the low hardness of 35 or less for use as a soft sensor of the Masai walking sole is not satisfied. In the case of a foam prepared by further blending an ethylene vinyl acetate copolymer having a vinyl acetate content of 33 to 45% by weight, it was found that the foam had a low hardness value and a low permanent compression shrinkage.

Therefore, an object of the present invention is to provide an ethylene vinyl acetate resin composition for shoe soles having low hardness and excellent hydrolysis resistance and permanent compression shrinkage.

The present invention

20 to 40% by weight of ethylene vinyl acetate copolymer with vinyl acetate content of 12 to 28% by weight, 20 to 40% by weight of ethylene vinyl acetate copolymer with 33 to 45% by weight of vinyl acetate and ethylene-propylene-diene rubber 30 to Based on 100 parts by weight of the polymer mixture containing 55% by weight;

3 to 7 parts by weight of blowing agent;

0.5-1 weight part of crosslinking agents;

3 to 5 parts by weight of the metal oxide; And

0.5 to 2 parts by weight of stearic acid;

It characterized by an ethylene vinyl acetate resin composition comprising a.

Ethylene vinyl acetate resin composition according to the present invention can solve the hydrolysis resistance problem, which is a disadvantage of polyurethane foam when molded into a foam, showing a low hardness of 35 or less and excellent permanent compression rate characteristics, shoe midsole, especially masai walking It can be usefully applied as a soft sensor for shoe midsole.

1 is a basic structural diagram of a masai walking shoe.

Hereinafter, the present invention will be described in more detail.

The present invention uses a mixture of two kinds of ethylene vinyl acetate copolymer and ethylene-propylene-diene rubber having different vinyl acetate content as a base polymer, and has low hardness and low permanent compression shrinkage when molded into a foam. It relates to a composition.

The ethylene vinyl acetate copolymer having a vinyl acetate content of 12 to 28 wt% may use a melt flow index (Melt index) of 2 to 8 g / 10 minutes. If the content of vinyl acetate is less than 12% by weight may increase the crystallinity of ethylene vinyl acetate may have a problem of increasing the hardness, if it exceeds 28% by weight may have a problem that the hardness is too low. The content of the ethylene vinyl acetate copolymer having a vinyl acetate content of 12 to 28% by weight of the polymer mixture is preferably 20 to 40% by weight. If the content is less than 20% by weight, the vinyl acetate content is 33 to 45% by weight. There may be a problem that the hardness of the foam is too low to increase the content of the ethylene vinyl acetate copolymer (%) is difficult to serve as a support, and when the content exceeds 40% by weight, the hardness is increased to use as a soft sensor of the Masai walking shoe midsole it's difficult.

The ethylene vinyl acetate copolymer having a vinyl acetate content of 33 to 45% by weight may use a melt flow index of 2 to 8 g / 10 minutes. If the content of vinyl acetate is less than 33% by weight may have a problem that the hardness of the foam rises, on the contrary, if the content exceeds 45% by weight may increase the adhesive force may have a problem in workability. The content of the ethylene vinyl acetate copolymer having a vinyl acetate content of 33 to 45% by weight in the polymer mixture is preferably 20 to 40% by weight. If the content is too low, the vinyl acetate content is 12 to 28% by weight. There may be a problem that the content of the ethylene vinyl acetate copolymer is increased to increase the hardness, and if the content is too large, the hardness may be too low.

In addition, when the melt flow index of the two kinds of ethylene vinyl acetate copolymer is too low, there may be a problem of workability deterioration due to high melt viscosity, on the contrary, if too high, there may be a problem of deterioration of physical properties of the foam 2 ~ 8 g / 10 minutes It is good to use the thing of the said range which is.

The ethylene-propylene-diene rubber is used to impart elasticity to the foam, ethylene 50 to 70% by weight, propylene 25 to 45% by weight and diene 3 to 8% by weight and melt flow index of 0.3 to 2 g / 10 minutes It is good to use that. If the ethylene content and propylene content are out of the above range and the ethylene content increases and the propylene content is relatively decreased, the crystallinity may be increased to increase the hardness of the foam and the elastic resilience may be deteriorated. As the content of propylene increases, there may be a problem of mechanical property deterioration due to an increase in the amorphous region. If the diene content is too low or high, there may be problems in crosslinking efficiency and weather resistance, so it is preferable to use the above range. In addition, when the melt flow index is out of the above range, there may be a problem in processability and mechanical properties of the foam, so it is preferable to use 0.3-2 g / 10 minutes. Ethylene-propylene-diene rubber is preferably used at 30 to 55% by weight in the polymer mixture. If the ethylene-propylene-diene rubber in the polymer mixture is less than 30% by weight, it is difficult to obtain an elastic foam that can be used as a soft sensor, and when it is used in more than 55% by weight, the foam having uniform foaming due to the high melt viscosity is used. Hard to get

As the blowing agent, at least one of azo compounds such as azodicarbonamide and modified azodicarbonamide having a decomposition temperature of 130 to 150 ° C may be used in an amount of 3 to 7 based on 100 parts by weight of the polymer mixture in consideration of the expansion ratio and specific gravity of the foam. It is preferable to use by weight part. If the amount is less than 3 parts by weight, the foaming ratio is small, the hardness is high and the specific gravity is increased. If the amount is more than 7 parts by weight, the foaming ratio is increased, thereby decreasing the mechanical properties of the foam and forming an unstable foaming cell because it is difficult to achieve uniform dispersion of the foaming agent. There can be.

The crosslinking agent uses a peroxide crosslinking agent capable of imparting high temperature viscoelasticity to sufficiently withstand the gas pressure generated above the decomposition temperature of the blowing agent. For example, benzoyl peroxide (BPO) and dicumyl peroxide (DCP). ) Or mixtures thereof. It is preferable to use 0.5-1 weight part with respect to 100 weight part of polymer mixtures for a crosslinking agent. If the content of the crosslinking agent is less than 0.5 parts by weight, insufficient crosslinking may not have a melting point that can withstand the gas pressure caused by decomposition of the blowing agent during the foaming of the composition. The gas produced by decomposition cannot expand and can be difficult to use for shoes due to its high hardness.

The metal oxide is used to promote the crosslinking and foaming by improving the thermal conductivity of the raw material when manufacturing the foam, for example, at least one selected from cadmium oxide, zinc oxide, magnesium oxide, mercury oxide, tin oxide, lead oxide and calcium oxide Can be used. It is preferable to use the amount of 3 to 5 parts by weight based on 100 parts by weight of the polymer mixture. If the amount is less than 3 parts by weight, the foaming property of the blowing agent may be weak. The characteristics may deteriorate.

The stearic acid was used to improve the dispersing and processing properties when preparing the blowing agent, it is preferable to use 0.5 to 2 parts by weight based on 100 parts by weight of the polymer mixture. If the amount of stearic acid is less than 0.5 parts by weight, there may be a problem in the workability due to the high melt viscosity, on the contrary, too much may have a problem of poor mechanical properties of the foam.

As a processing method for producing a foam using the resin composition of the present invention, a conventional foam production processing method that is usually used can be used. As an example, the ethylene vinyl acetate resin composition is first kneaded using a kneader at 100 to 120 ° C., and then kneaded in an open roll mill in a range of 95 to 110 ° C. to prepare a mixture in the form of a sheet. After the mixture is aged at room temperature, an appropriate amount is added to the mold, and the press is pressed at a high temperature and a high pressure of 150 to 170 ° C and 140 to 150 kgf / cm ² using a hydraulic press, and then cooled to room temperature to prepare a foam. .

Ethylene vinyl acetate resin composition according to the present invention exhibits a low hardness and a low permanent compression shrinkage when molded into a foam, excellent hydrolysis resistance than polyurethane foam, it is useful as a soft sensor for shoe midsoles, especially Masai walking shoe midsole Applicable

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

[Example]

Example  1 to 3

The composition shown in Table 1 was first kneaded for 15 minutes using a kneader at 100-120 ° C., and then kneaded secondly in an open roll mill in the range of 95-110 ° C. to prepare a sheet-shaped mixture. . After the mixture was aged at room temperature for 24 hours, an appropriate amount was added to the mold, pressurized for 50 minutes at 150 to 170 ° C and 140 to 150 kgf / cm ² using a hydraulic press, and then cooled at room temperature to prepare a foam. .

Comparative Example 1

A foam was prepared in the same manner as in Example 1, using ethylene vinyl acetate copolymer having a vinyl acetate content of 12 to 28% by weight as the base polymer alone.

Comparative Example 2

In the same manner as in Example 1, a foam was prepared using a mixture of ethylene vinyl acetate copolymer having a vinyl acetate content of 12 to 28% by weight and ethylene-propylene-diene rubber as the base polymer.

division Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Base Polymer
(100 parts by weight) Ethylene Vinyl Acetate Copolymer (1) 25 wt% 30 wt% 35 wt% 100 wt% 60 wt% Ethylene Vinyl Acetate Copolymer (2) 35 wt% 30 wt% 25 wt% - - Ethylene-propylene-diene rubber 40 wt% 40 wt% 40 wt% - 40 wt% Foaming agent (parts by weight) 5 5 5 5 5 Crosslinking agent (parts by weight) 0.7 0.7 0.7 0.7 0.7 Metal Oxide (parts by weight) 3 3 3 3 3 Stearic acid (parts by weight) One One One One One Ethylenevinylacetate copolymer (1): [EVAFLEX 260, Du Pont-Mitsu polychemicals, (vinyl acetate content 28% by weight)]
Ethylene Vinyl Acetate Copolymer (2): [Elvax 40L, Dupont, (Vinyl Acetate Content 40 wt%)]
Ethylene-propylene-diene rubber: [EPDM 570P, Kumho Petrochemical, (70 wt% ethylene, 25.5 wt% propylene, 4.5 wt% diene)]
Foaming agent: Azodicarbonamide
Crosslinker: Dicumylperoxide
Metal Oxide: Zinc Oxide

Test Example: Property Measurement Experiment

Physical properties of the shoe foams prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were measured by the following methods, and the results are shown in Table 2 below.

1) Specific gravity: The specific gravity of the foam was measured using an automatic specific gravity meter (MS-2150, Ueshima) with the skin removed. At this time, the average value was obtained by measuring three times except the value exceeding 20% or more.

2) Hardness: After removing the skin of the foam, the smooth surface layer was measured in accordance with ASTM D 2240 with an Asker C type hardness tester.

3) Elongation rate: The prepared foam was made to a thickness of about 3 mm, and then the test piece was made with a dumbbell No. 3 cutter according to KS M 6518 to measure the elongation rate. At this time, the average value was calculated | required as three test pieces used for the same test.

4) Permanent Compression Shrinkage (Cs): A test piece prepared in the form of a cylinder having a diameter of 28.7 ± 0.05 mm having a thickness of about 10 mm was measured according to ASTM D-395-B. Insert the specimen between two chrome plated parallel metal plates, insert a spacer equal to 50% of the specimen thickness, compress it, and hold it for 6 hours in an air circulation oven maintained at 50 ± 0.1 ° C. The thickness was measured after taking out and cooling for 30 minutes at room temperature. Three identical specimens were used, and the permanent compression ratio was calculated by the following equation.

[Equation 1]

Cs (%) = [(t ₀ -t _f ) / (t ₀ -t _s )] × 100

In Equation 1, Cs is a permanent compression shrinkage, t ₀ is the initial thickness of the test piece, t _f is the thickness of the test piece when cooled after heat treatment, and t _s is the thickness of the spacer.

5) Repulsive elasticity: The foams were measured in four strikes after three preliminary strikes in the form of cylinders of 29 mm diameter and 10 mm thickness using a Luffke type rebound elastic tester in accordance with Din 53512. The same test piece was made into three pieces.

division Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 importance 0.17 0.17 0.17 0.17 0.17 Hardness (asker C type) 32 32 33 34 42 Elongation (%) 269 261 265 253 270 Permanent Compression Decrease (%) 42 41 40 61 39 Resilience (%) 56 57 57 51 56

As shown in Table 2, in the case of Comparative Example 1 in which the foam was prepared based only on the ethylene vinyl acetate copolymer having a vinyl acetate content of 12 to 28% by weight, the permanent compressive shrinkage was not good, and thus the material was subjected to continuous load. It can be seen that it is difficult to use, in the case of Comparative Example 2 in which the foam was prepared by adding ethylene-propylene-diene rubber permanent compression shrinkage characteristics are improved, but the hardness was increased. The foams of Examples 1 to 3 using two ethylene vinyl acetate copolymers according to the present invention and ethylene-propylene-diene rubber together as base polymer mixtures had a hardness of 35 or less required for application as a Masai walking shoe midsole soft sensor. It can be seen that it has satisfactory but excellent permanent compression rate characteristics compared to Comparative Example 1.

After all, when molding the foam with the ethylene vinyl acetate resin composition of the present invention has a low hardness and low permanent compression rate difficult to implement in the existing ethylene vinyl acetate resin foam, it is to replace the polyurethane foam that is poor in hydrolysis resistance It was confirmed that the shoe can be applied as a soft sensor of the shoe midsole, especially the Masai walking shoe midsole.

1: insole 2: midsole
3: MASAI SENSOR 4: Outsole

Claims (8)

20 to 40% by weight ethylene vinyl acetate copolymer having 12 to 28% vinyl acetate content, 20 to 40% by weight ethylene vinyl acetate copolymer having 33 to 45% vinyl acetate content, 50 to 70% by weight ethylene, With respect to 100 parts by weight of a polymer mixture containing 25 to 45% by weight of propylene and 3 to 8% by weight of diene and 30 to 55% by weight of ethylene-propylene-diene rubber having a melt flow index of 0.3 to 2 g / 10 minutes;
3 to 7 parts by weight of blowing agent;
0.5-1 weight part of crosslinking agents;
3 to 5 parts by weight of the metal oxide; And
0.5 to 2 parts by weight of stearic acid;
Ethylene vinyl acetate resin composition comprising a.
According to claim 1, wherein the ethylene vinyl acetate copolymer having a vinyl acetate content of 12 to 28% by weight and the ethylene vinyl acetate copolymer having a vinyl acetate content of 33 to 45% by weight of each melt flow index (Melt index) 2 Ethylene vinyl acetate resin composition, characterized in that ~ 8 g / 10 minutes.
delete The ethylene vinyl acetate resin composition according to claim 1, wherein the blowing agent is azodicarbonamide, modified azodicarbonamide or a mixture thereof.
The ethylene vinyl acetate resin composition of claim 1, wherein the crosslinking agent is benzoyl peroxide (BPO), dicumyl peroxide (DCP), or a mixture thereof.
The ethylene vinyl acetate resin composition according to claim 1, wherein the metal oxide is at least one selected from cadmium oxide, zinc oxide, magnesium oxide, mercury oxide, tin oxide, lead oxide, and calcium oxide.
The foam molded from the ethylene vinyl acetate resin composition of any one of Claims 1, 2, and 4-6.
A shoe midsole made from the foam of claim 7.

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