JP3335339B2 - Foam for midsole or inner sole of shoes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foam for a midsole or an inner sole of a shoe, which hardly changes in hardness due to a change in temperature.

[0002]

2. Description of the Related Art Midsole materials such as sports shoes are required to have characteristics such as cushioning, shock absorption and lightness. As a material satisfying such characteristics, a foam mainly composed of ethylene-vinyl acetate copolymer (EVA) and a foam mainly composed of polyurethane (PU) are used. Foams containing PU as a main component have a limit in weight reduction, and in addition, are strongly deteriorated by hydrolysis, which is not preferable in terms of quality assurance. For this reason, foams mainly composed of EVA occupy most of the products.

[0003]

However, these materials have the disadvantage that the hardness changes greatly with temperature. For example, in a high-temperature environment (temperature is about 30 ° C.), the material hardness of the midsole and the inner sole is greatly reduced, and causes trouble such as overpronation. On the other hand, under a use condition in a low-temperature environment (air temperature of 10 ° C. or less), the hardness increases, and the functional aspects such as cushioning property and shock cushioning property decrease.

[0004] As a means for solving this problem, the addition of a rubber material is effective. However, while many midsole and inner sole products are molded into a foam by primary processing and then subjected to secondary heat molding, there is a problem that the secondary heat molding cannot be performed with a compound containing a large amount of rubber material. is there. This is due to the low thermoplasticity of the rubber material. In addition, the addition and blending of the rubber material also causes problems such as a decrease in dimensional stability. For this reason, it has been desired to select a thermoplastic elastomer that can be subjected to secondary heat molding and is not easily affected by physical properties due to temperature, and / or to develop a combination of the thermoplastic elastomer with another material. The above-mentioned secondary heat molding means a molding method in which the material once crosslinked and foamed is heated again to soften, appropriately compressed, and then cooled. This molding method is performed mainly for design molding. This increases the value of the product and the degree of freedom in design.

It is an object of the present invention to provide a mid layer which has a small change in hardness due to temperature, has excellent cushioning properties and shock absorbing properties, and does not cause obstacles such as overpronation in any environment of high temperature environment and low temperature environment. An object of the present invention is to provide a foam for a sole or an inner sole. Another object of the present invention is to provide a foam for a midsole or an innersole that can be subjected to secondary heat molding.

[0006]

According to the present invention, the difference in surface hardness (JIS-C hardness) between a normal temperature atmosphere and a 40 ° C. atmosphere is 4%.
Surface hardness in 0 ° C atmosphere and normal temperature atmosphere (JI
The present invention relates to a foam for a midsole or an inner sole of a shoe having a difference of (SC hardness) within 5 degrees.

The foam of the present invention comprises, for example, a composition containing 30 to 100 parts by weight of a styrene-butadiene block copolymer having a styrene content of 60% or less and 0 to 50 parts by weight of a rubber material, It can be obtained by foaming in the presence of a foaming agent and other additives. Here, “parts by weight” is a compounding amount of each material when the total of raw materials (rubber, resin, thermoplastic elastomer) is 100 parts by weight.

[0008] Shoe materials having a composition similar to the composition of the present invention are known, for example, from JP-A-55-118944 and JP-A-58-216001. However, these known documents differ from the present case in the following points.

These documents all relate to compositions for footwear soles (outer soles). Here, there is a great difference between the outer sole and the midsole or the inner sole according to the present invention in terms of functions and performances to be fulfilled. That is, the outer sole is required to have a grip property, a bending property, and an abrasion resistance, whereas the midsole and the inner sole are required to have a light weight, a cushioning property, a shock absorbing property, and the like. In order to obtain these functional surfaces, the midsole and the inner sole preferably have a specific gravity of 0.45 or less and a surface hardness of 35 to 75 degrees (JIS-C hardness). Under these specific gravity and hardness conditions, it is extremely difficult to satisfy the required properties of the outer sole.

[0010] Further, all known documents are based on shoe soles obtained by injection molding. Materials containing a rubber material and materials having a high specific gravity of 0.45 or less cannot be injection-molded or have a very high rejection rate, and molding by injection is extremely difficult in practice. Have difficulty.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The styrene-butadiene block copolymer used in the present invention exhibits excellent elasticity like a vulcanized rubber at room temperature, and has a styrene content of 60% or less.
Preferably, it is a thermoplastic elastomer of 20 to 60%. If the styrene content exceeds 60%, the hardness will increase and the functionality will decrease. The styrene-butadiene block copolymer used has a melt flow rate of 2 g / 10 min or more (ASTM D1248 method:
190 ° C., 216 kg) is desirable. If the melt flow rate is lower than this value, the workability of the secondary molding decreases. MF
The upper limit of R is about 50 g / 10 min.

The rubber material used in the present invention includes diene rubbers such as natural rubber and styrene butadiene rubber;
Ethylene-propylene rubber (EPDM, EPM), urethane rubber, acrylic rubber and the like can be used. 1,2 syndiotactic polybutadiene resin having a crystalline structure is not included in the diene rubber of the present invention. In the present invention, the ratio of the styrene-butadiene block copolymer and the rubber material is 30 to 100 parts by weight of the former, more preferably 30 to 60 parts by weight, and 0 to 50 parts by weight of the latter, more preferably 20 to 50 parts by weight. It is good to use parts by weight. Styrene-
If the butadiene block copolymer is less than 30 parts by weight, the change in hardness under high and low temperature environments is large.

In the present invention, if necessary, ethylene-
Vinyl acetate copolymer (EVA), polyurethane (P
A thermoplastic resin such as U), polyethylene (PE), and high styrene resin may be blended. These are composition 1
It is preferable to use 0 to 70 parts by weight in 00 parts by weight.

In the present invention, in addition to the above components, fillers such as silica; stearic acid; antioxidants; vulcanization accelerators such as organic amines; zinc oxide;
Sulfur; a crosslinking agent such as dicumyl peroxide and dibutyl peroxide; and a foaming agent such as azodicarbonamide and dinitrosopentamethylenetetraamine can be added.

The foaming can be carried out by a generally known method, for example, by press molding at a temperature of about 145 to 160 ° C., usually about 150 ° C.
At this time, pressure and time can be appropriately adjusted so as to obtain a foam having a target hardness and specific gravity. The obtained foam is subjected to secondary heat molding to obtain the intended foam for the midsole or inner sole of the shoe of the present invention.

In the present invention, the specific gravity of the foam obtained is preferably 0.45 or less. Further, in order to respond to the demand for weight reduction from consumers, the specific gravity of the foam is preferably 0.40 or less, and particularly preferably in the range of 0.15 to 0.35.
Surface hardness of the foam of the present invention in a normal temperature atmosphere (JIS-C
(Hardness) is preferably from 35 to 75 degrees, particularly preferably from 40 to 60 degrees. When the specific gravity exceeds 0.45, lightness is lacking, and when the surface hardness is out of the range, the functions of the midsole and the inner sole are remarkably deteriorated in terms of impact buffering property and resilience.

In the foam of the present invention, the difference in surface hardness (JIS-C hardness) between the normal temperature atmosphere and the 40 ° C. atmosphere is within 4 degrees, more preferably within 3 degrees, and between the 0 ° C. atmosphere and the normal temperature atmosphere. It is important that the difference in the surface hardness (JIS-C hardness) is within 5 degrees, more preferably within 4 degrees.
The normal temperature described in the present case refers to a temperature of 23 ° C.

When the former hardness difference is within 4 degrees, more preferably within 3 degrees, it is effective for avoiding overpronation failure in a high temperature environment. On the other hand, if the hardness difference of the latter exceeds 5 degrees, characteristics such as impact cushioning and resilience as a midsole or an inner sole cannot be maintained.
Further, if the difference in hardness is within 4 degrees, the same performance as in a normal temperature state can be maintained even in a low temperature environment.

In the present invention, the foam may be partially used instead of the entire midsole or inner sole. For example, a foam may be used in the form of stripes, islands, or the like in the midsole or the inner sole, or may be discontinuously used in a streak shape, and the shape and mode are not particularly limited.

[0020]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples.

Examples 1 to 5 and Comparative Examples 1 to 4 The materials shown in Tables 1 and 2 were kneaded for about 10 minutes in a kneader-sealed kneader, and the kneaded material was first heat-press molded at 140 ° C. (crosslinking, foaming). I do. Press conditions vary depending on the formulation,
Conditions were appropriately adjusted so that the internal hardness of the primary molded product was 35 to 50 degrees (JIS-C hardness). The primary molded product produced under these conditions was subjected to secondary molding (140 to 1) at a compression ratio of 30%.
Heating was performed at 60 ° C. for 7 minutes and cooling was performed for 15 minutes) to obtain a foam for the midsole or the inner sole of the shoe. Here, SBS-TPE is a styrene-butadiene block copolymer (styrene content 43%), RSS # 3
Is natural rubber, SBR1402 is styrene butadiene rubber, BR01 is butadiene rubber, PE is polyethylene,
JSR0061 is a high styrene resin having a styrene content of 76.8%, EVA is an ethylene-vinyl acetate copolymer, dicumyl peroxide was used as a crosslinking agent, and azodicarbonamide was used as a foaming agent. However, for Comparative Example 3 in Table 2, sulfur was used as a crosslinking agent.
Tables 3 and 4 show the performance evaluations.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Table 3]

[0025]

[Table 4]

The hardness at room temperature, the specific gravity, the change in hardness between normal temperature and 40 ° C., the change in hardness between normal temperature and 0 ° C., and the secondary heat processability are shown below. The hardness was measured after being left in each atmosphere for 30 minutes or more. The secondary heat moldability was examined based on the feasibility of the design design. O indicates that there is no problem, and X indicates that the unevenness is poor and the product is defective.

In all of Examples 1 to 5, the change in hardness due to the temperature change is small, and there is no problem in the secondary heat moldability. The hardness specific gravity at room temperature is a value that can satisfy the characteristics of the midsole and the inner sole.

Comparative Example 1 has a general EVA sponge composition. The hardness changes greatly under high and low temperature environments. As shown in Comparative Example 2, when the amount of SBS added was 30 parts by weight or less,
Hardness changes significantly in high and low temperature environments and does not reach the target level. As shown in Comparative Examples 3 and 4, only the rubber material was used.
Alternatively, when a rubber material is mainly used, the secondary heat processability is poor.

[0029]

As described above, the foam of the present invention is a foam for the midsole and the inner sole of shoes, and can exhibit the function of the midsole and the inner sole in any environment. The foam of the present invention is extremely effective as a foamed midsole material and an innersole material for shoes.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Satoshi Kiso 7-1-1, Minatojima-Nakamachi, Chuo-ku, Kobe City, Hyogo Prefecture Examiner, ASICS Co., Ltd. Toshicho Miyazaki (56) References JP-A-55-118944 (JP, A) JP-A-58-216001 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) A43B 13/38 A43B 17/00

Claims (5)

(57) [Claims] 1. The difference in surface hardness (JIS-C hardness) between a normal temperature atmosphere and a 40 ° C. atmosphere is within 4 degrees, and the difference in surface hardness (JIS-C hardness) between the 0 ° C. atmosphere and the normal temperature atmosphere is 5 degrees. Foam for midsole or inner sole of shoes that can be subjected to secondary heat molding processing within a degree. 2. The foam according to claim 1, which has a specific gravity of 0.45 or less and a surface hardness (JIS-C hardness) in a normal temperature atmosphere of 35 to 75 degrees. 3. The difference between the surface hardness (JIS-C hardness) between the normal temperature atmosphere and the 40 ° C. atmosphere is within 3 degrees, and the difference between the surface hardness (JIS-C hardness) between the 0 ° C. atmosphere and the normal temperature atmosphere is 4 degrees. The foam according to claim 1, which is within a degree. 4. The foam according to claim 1, comprising 30 to 100 parts by weight of a styrene-butadiene block copolymer having a styrene content of 60% or less and 0 to 50 parts by weight of a rubber material. 5. The foam according to claim 4, comprising 30 to 60 parts by weight of a styrene-butadiene block copolymer having a styrene content of 60% or less and 20 to 50 parts by weight of a rubber material.