JP7840029B2 - Soles and footwear equipped with them - Google Patents

Description

This invention relates to a shoe sole and footwear equipped therewith.

The sole is the part of the footwear that comes into contact with the ground. Because the sole is in contact with the ground, it affects the slip resistance of the shoe and how easily the footwear tires the wearer. As shown in Patent Document 1 below, soles with improved functionality have also been proposed.

Patent Document 1 describes a footwear sole made of a rubber composition in which cellulose fibers having a specific average fiber diameter and a specific average fiber length are blended with rubber in a specific proportion. This footwear sole is said to exhibit high slip resistance on floor surfaces contaminated with water or oil.

Patent Document 2 describes a rubber composition containing styrene-butadiene rubber, butadiene rubber, silica, a silane coupling agent, and a crosslinking agent, and comprising styrene-butadiene rubber and butadiene rubber in predetermined proportions, which is used to construct a shoe molding component. Patent Document 2 also states that incorporating a mercapto-silane coupling agent improves the abrasion resistance of the rubber while increasing its hardness.

Japanese Patent Publication No. 2018-15149 WO2015-151164 publication

Our inventors' research revealed that, as described in Patent Document 1, while shoe soles constructed by compounding cellulose fibers with rubber improve slip resistance, the abrasion resistance of the soles is sometimes insufficient, raising concerns that the soles may wear down easily due to friction.

Furthermore, the inventors' research revealed that in shoe soles constructed by compounding cellulose fibers with rubber, simply incorporating a mercapto-silane coupling agent sometimes resulted in insufficient abrasion resistance, leading to a tendency for the soles to wear down easily due to friction.

The present invention aims to provide a shoe sole with improved abrasion resistance, incorporating cellulose fibers. It also aims to provide footwear equipped with this shoe sole.

The above problems are solved by a shoe sole containing vulcanized non-foamed rubber, a filler, cellulose fibers, and a mercapto-silane coupling agent, wherein the abrasion resistance determined by the Williams abrasion test method B of JIS K 6264-2 is 470 ^mm³ /1000 rotations or less. Furthermore, the above problems are solved by footwear equipped with this shoe sole.

In the above-described shoe soles and footwear, the cellulose fibers preferably have an average fiber length of 1900 μm or less. Furthermore, the hardness of the shoe soles and footwear preferably has a hardness of 55 to 72. Furthermore, the filler in the above-described shoe soles and footwear preferably contains a hollow-structured filler. Furthermore, the specific gravity of the shoe soles and footwear preferably has a specific gravity of 1.3 or less.

According to the present invention, it is possible to improve the abrasion resistance of shoe soles containing cellulose fibers, and to provide footwear equipped with such abrasion-resistant shoe soles.

The following describes preferred embodiments of the present invention. However, the technical scope of the present invention is merely illustrative and not limited to the following embodiments.

The present invention relates to a shoe sole containing vulcanized non-foamed rubber, a filler, cellulose fibers, and a mercapto-silane coupling agent, and footwear equipped with the shoe sole. The shoe sole has an abrasion rate of 470 ^mm³ /1000 rotations or less, as determined by the Williams abrasion test method B of JIS K 6264-2.

The above-mentioned rubber can be those commonly used for shoe soles, and examples include one or more rubbers selected from the group consisting of natural rubber, styrene-butadiene rubber, butadiene rubber, urethane rubber, nitrile rubber, ethylene-propylene-diene rubber, and thermoplastic elastomers.

Examples of the thermoplastic elastomers mentioned above include styrene-based thermoplastic elastomers, olefin-based thermoplastic elastomers, urethane-based thermoplastic elastomers, ester-based thermoplastic elastomers, and amide-based thermoplastic elastomers. These thermoplastic elastomers may be used individually or as a mixture of two or more.

The above-mentioned filler can be a powder or granule made of an inorganic substance, and for example, a solid filler selected from the group consisting of silica, talc, calcium carbonate, carbon, clay, and alumina can be used. Alternatively, as the above-mentioned filler, one or more hollow-structured fillers selected from the group consisting of glass balloons and fly ash balloons can be used. If a solid filler is used, for example, a shoe sole with a specific gravity of 1.3 or less can be manufactured. If a hollow-structured filler is used, a lightweight shoe sole can be obtained. For example, a shoe sole with a specific gravity of 1.1 or less can be obtained. The lower limit of the specific gravity is not particularly limited, but for example, it is 0.8 or higher. When silica is used as the filler, dry silica such as fumed silica or wet silica such as colloidal silica may be used. The particle size of the filler is not particularly limited, but for example, a BET specific surface area of 50 to 600 ^m² /g, more preferably 50 to 350 ^m² /g can be used.

As the cellulose fiber, any fiber with an arbitrary average fiber width can be used. For example, a fiber with an average fiber width of 500 μm or less may be used, a fiber with an average fiber width of 50 μm or less may be used, a fiber with an average fiber width of 30 μm or less may be used, or a fiber with an average fiber width of less than 1000 nm may be used. Using a cellulose fiber with an average fiber length of less than 1000 nm is preferable because it can improve strength while suppressing an increase in the hardness of the shoe sole. The average fiber length of the cellulose fiber is not particularly limited, but for example, a fiber with a length of 5 nm or more can be used.

The average fiber width or average fiber length of cellulose fibers is determined as follows: A suspension containing cellulose fibers is prepared, and the suspension is placed on a hydrophilic carbon-coated grid and observed with a transmission electron microscope. A scanning electron microscope may also be used for observation. Depending on the width of the cellulose fibers contained in the sample being observed, the sample is observed at one of the following magnifications: 1,000x, 5,000x, 10,000x, 20,000x, 50,000x, or 100,000x. However, the preparation and observation of the sample must satisfy the following two conditions.
1. When a straight line is drawn in the observed image, ensure that 20 or more fibers intersect with that line.
2. Draw a second straight line that intersects the straight line drawn in the image above, so that 20 or more fibers intersect with this second straight line.

For the image with the two lines drawn above, measure the length in the short direction (i.e., fiber width) and the length in the long direction (i.e., fiber length) of 20 or more fibers that intersect the first line. Next, measure the length in the short direction (i.e., fiber width) and the length in the long direction (i.e., fiber length) of 20 or more fibers that intersect the second line. Calculate the total fiber width by summing the subtotal of fiber widths for the 20 or more fibers read using the first line and the subtotal of fiber widths for the 20 or more fibers read using the second line. Divide this total by the number of fibers whose fiber width was read to calculate the average fiber width. Calculate the average fiber length in the same manner as the average fiber width.

As the cellulose fiber, cellulose fibers manufactured from plant materials may be used, or cellulose fibers manufactured from plant materials and chemically modified may be used. For example, commercially available cellulose fibers are produced by crushing, TEMPO-oxidizing, or finely processing plant-derived materials such as pulp, and these can be used. Cellulose fibers in powder form are preferably used.

Mercapto-silane coupling agents can, for example, use those having a silyl group (Si) and a mercapto group (SH) as a reactive group. For example, those in which the silyl group is substituted with an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a hydrogen atom are preferably used.

The mercapto group is known to undergo a thiourethane reaction with the cyanate group, producing a reaction product. Furthermore, the mercapto group is known to undergo an ene-thiol reaction with double bonds such as propylene, producing a reaction product. Examples of mercapto-silane coupling agents that can be used include those containing 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, 2-mercaptoethylmethyldimethoxysilane, 2-mercaptoethylmethyldiethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldiethoxysilane, 4-mercaptobutyltrimethoxysilane, or 4-mercaptobutyltriethoxysilane.

When vulcanizing rubber, a vulcanizing agent is used. The vulcanizing agent is not particularly limited and any suitable agent can be used. Examples of vulcanizing agents include sulfur, sulfur donors such as dithiodimorpholine or alkylphenol disulfide, and organic peroxides such as peroxides.

The soles may also contain other components such as vulcanization accelerators, anti-aging agents, and process oils. Examples of vulcanization accelerators, though not particularly limited, include 2-mercaptobenzothiazole, 2-benzothiazolyl disulfide, 1,3-diphenylguanidine, N-(tert-butyl)-2-benzothiazole sulfenamide, tetramethylthiuram monosulfide, hexamethylenetetramine, 1,3-diethyl-2-thiourea, and ethylenethiourea (2-mercaptoimidazoline). Examples of anti-aging agents, though not particularly limited, include 2,5-di-tert-butyl-hydroquinone, mono(or di, or tri)(α-methylbenzyl)phenol, 2-mercaptobenzimidazole, and 4,4'-bis(α,α-dimethylbenzyl)diphenylamine. It is also possible to use crack inhibitors in combination with anti-aging agents. Process oils are not particularly limited, but examples include naphthenic mineral oils, aromatic mineral oils, or paraffinic mineral oils.

If the sole is too hard, the shoes will be uncomfortable to wear and walk in, and your feet will tire easily. On the other hand, if the sole is too soft, it will wear down easily. Therefore, the hardness of the sole is preferably between 55 and 72 degrees. More preferably, the hardness of the sole is between 60 and 70 degrees. Note that the hardness referred to here is measured in accordance with JIS K 6253-3:2012 and measured using a Type A durometer.

According to the present invention, a shoe sole can be obtained in which the amount of wear determined by the William Abrasion Test Method B of JIS K 6264-2 is 470 ^mm³ /1000 rotations or less. The lower limit of the amount of wear is not particularly limited, but examples include an amount of wear greater than 0 ^mm³ /1000 rotations, or an amount of wear greater than 240 ^mm³ /1000 rotations.

The footwear to which the sole is fixed is not particularly limited. Examples include sneakers, tabi boots, leather shoes, and other low-cut footwear; work boots, leather boots, rain boots, and other long boots; or footwear without a heel cover, such as sandals and slippers.

While higher tear strength and tensile strength of shoe soles are desirable, for everyday wear, it is preferable to prioritize a lighter sole density over excessive tear or tensile strength. In such cases, a tear strength of 2.9 to 3.9 N/mm is acceptable, and a tensile strength of 5.0 to 9.0 MPa is acceptable. Here, tear strength refers to the value obtained by testing according to method B of JIS K 6252-1:2015, using an angle-shaped test specimen without cuts. Tensile strength refers to the value obtained by testing according to method JIS K 6251:2017, using a dumbbell-shaped No. 2 test specimen.

For example, in applications where tear strength is required for the soles of work boots, the tear strength is preferably 4.8 to 6.8 N/mm. Furthermore, in applications where tensile strength is required for the soles, the tensile strength is preferably 14.0 to 18.0 MPa.

Shoe soles tend to be more comfortable when they are more stretchable. Therefore, it is preferable that the 200% tensile modulus value be between 4.0 and 6.0 MPa. Here, 200% modulus refers to the tensile stress value at which 200% elongation occurs, as determined by testing according to the method of JIS K 6251:2017.

The amount of cellulose fiber added is not particularly limited, but it is preferable to add 5 to 30 parts by weight of cellulose fiber per 100 parts by weight of rubber. For solid fillers, it is preferable to add 35 to 65 parts by weight per 100 parts by weight of rubber. For fillers with a hollow structure, it is preferable to add 5 to 25 parts by weight per 100 parts by weight of rubber. For mercapto-silane coupling agents, it is preferable to add 0.5 to 5.0 parts by weight per 100 parts by weight of rubber.

The following describes embodiments of the present invention. The embodiments listed below are merely examples, and the technical scope of the present invention is not limited thereto.

[Example 1]
A rubber composition for shoe soles was manufactured using the raw materials listed in the composition column of Table 1. In Example 1, 100 parts by weight of a mixture of natural rubber (NR), styrene-butadiene rubber (SBR), and butadiene rubber (BR) was used as the uncrosslinked rubber. The cellulose fiber labeled "Cellulose Fiber 1" in Table 1 was 10 parts by weight of commercially available cellulose fiber (PDP-01, manufactured by Chuetsu Pulp & Paper Co., Ltd.). This cellulose fiber was prepared by mixing a dispersion of cellulose fibers with a dispersant, then removing the liquid and pulverizing it. The average fiber length of this cellulose fiber was 1.0 μm or more, and the average fiber width was 3 to 200 nm. The filler labeled "Filler 1" in Table 1 was 50 parts by weight of wet silica with a BET specific surface area of 50 to 350 ^m² /g according to the catalog value. The wet silica was a commercially available product with the liquid removed, and the blending amount is calculated on a solid content basis. In Table 1, the silane coupling agent labeled "Coupling Agent 1" was 2.5 parts by weight of a commercially available mercapto-silane coupling agent.

The above raw materials, along with 3 parts by weight of sulfur, 3 parts by weight of vulcanization accelerators (thiazole, sulfenamide, aldehyde ammonia, guanidine, and thiuram types), and 14 parts by weight of naphthenic process oil, were kneaded using a Banbury mixer and an open roll. The kneaded rubber composition was molded to dimensions suitable for the physical property tests described later, and the molded pieces were heated and vulcanized to produce test specimens for each physical property test according to Example 1.

[Examples 2 to 5]
As shown in Table 2, test pieces for each physical property test in Examples 2 to 5 were manufactured in the same manner as in Example 1, except that the mixing ratio of each raw material was changed. In Table 2, the cellulose fiber labeled "Cellulose Fiber 2" is a commercially available cellulose fiber (ARBOCEL FIF400) manufactured by Rettenmeyer Japan Co., Ltd., and the same applies to Table 1. Similarly, the cellulose fiber labeled "Cellulose Fiber 3" in Table 2 is a commercially available cellulose fiber (ARBOCEL BE600-30) manufactured by Rettenmeyer Japan Co., Ltd., and the same applies to Table 1. The silane coupling agent labeled "Coupling Agent 2" in Table 2 is a commercially available sulfide-based silane coupling agent, and the same applies to Table 1. The average fiber length and average fiber width of Cellulose Fiber 2 are 2000 μm and 35 μm, respectively. The average fiber length and average fiber width of Cellulose Fiber 3 are 30 μm and 18 μm, respectively.

[Comparative Examples 1 to 4, Comparative Examples 5 to 7]
As shown in Table 1, test specimens for Comparative Examples 1 to 4 for each physical property test were manufactured in the same manner as in Example 1, except that the mixing ratio of each raw material was changed. Similarly, as shown in Table 2, test specimens for Comparative Examples 5 to 7 for each physical property test were manufactured in the same manner as in Example 1, except that the mixing ratio of each raw material was changed.

[Examples 6 to 8, Comparative Examples 8 to 10]
As shown in Table 3, test specimens for each physical property test according to Examples 6 to 8 were manufactured in the same manner as in Example 1, except that the mixing ratio of each raw material was changed. Similarly, as shown in Table 3, test specimens for each physical property test according to Comparative Examples 8 to 10 were manufactured in the same manner as in Example 1, except that the mixing ratio of each raw material was changed.

The following physical property tests were performed on each test specimen manufactured using the method described above.

[Hardness measurement]
Hardness was measured according to the method of JIS K 6253-3:2012. Test specimens were prepared according to the method of JIS K 6250. A Type A durometer manufactured by Nishitokyo Seimitsu Co., Ltd. was used.

[Tear strength]
Tear strength was measured in accordance with the method of JIS K 6252-1:2015. Tear strength was determined using test method B with an angle-shaped test specimen without cuts.

[Tensile Test]
In accordance with the method of JIS K 6251:2017, the tensile elongation, 100% tensile modulus, 200% tensile modulus, 300% tensile modulus, and tensile strength were determined. A dumbbell-shaped specimen (Type 2) was used. The tensile elongation corresponds to the "elongation at break" in the JIS test, and the 100% tensile modulus corresponds to the "tensile stress at a given elongation" in the JIS test, and is the value obtained by dividing the tensile force when the specimen is given 100% elongation by the cross-sectional area of the specimen before the test. The 200% tensile modulus and 300% tensile modulus are obtained by replacing 100% with 200% and 300%, respectively. The tensile strength corresponds to the "tensile strength" in the JIS test.

[Abrasion test]
The abrasion resistance of each of the above test specimens was investigated using Method B with a Williams abrasion tester as specified in JIS K 6264-2:2005.

The composition and physical property test results for each of the above examples and comparative examples are shown in Tables 1 to 3 below.

The test specimens for Examples 1 to 5 shown in Tables 1 and 2 contain rubber, cellulose fibers, a filler, and a mercapto-silane coupling agent. It can be seen that the abrasion resistance of these test specimens is improved compared to the test specimens for Comparative Examples 1 to 6.

Comparing the wear amount of the test specimen in Comparative Example 7 with the wear amount of Comparative Example 3, which had cellulose fibers added to the composition of Comparative Example 7, it can be seen that the wear resistance of the test specimen in Comparative Example 3, which only contained cellulose fibers, was reduced. The comparison of Comparative Examples 9 and 10 also shows that the addition of cellulose fibers reduces wear resistance.

A comparison of the test specimens from Example 1, Comparative Example 3, Comparative Example 4, and Comparative Example 5 reveals that by incorporating a mercapto-silane coupling agent, cellulose fibers, and filler into the rubber, the abrasion resistance of the test specimens is significantly improved compared to specimens containing cellulose fibers, filler, and rubber but no mercapto-silane coupling agent; specimens containing a mercapto-silane coupling agent, filler, and rubber but no cellulose fibers; and specimens containing a mercapto-silane coupling agent, cellulose fibers, and filler but with a small amount of filler.

Furthermore, a comparison of the test specimen from Example 1 with the test specimens from Comparative Example 1 or Comparative Example 2 reveals that the test specimen containing a mercapto-silane coupling agent, filler, cellulose fibers, and rubber exhibits improved abrasion resistance compared to the test specimens from Comparative Example 1 or Comparative Example 2, which contain a sulfide-silane coupling agent, filler, cellulose fibers, and rubber.

A comparison of the test specimens from Example 1 and Example 4 reveals that when the average fiber width of cellulose fibers exceeds 35 μm, while the abrasion resistance of the sole improves, the sole also becomes harder. Furthermore, a comparison of the test specimens from Example 1 and Example 5 shows that incorporating so-called nanocellulose fibers, with an average fiber width of less than 1000 nm, improves the abrasion resistance of the sole and prevents excessive hardening of the sole's flexibility compared to incorporating cellulose fibers with a medium fiber length, such as an average fiber width of 18 μm. Finally, a comparison of the test specimens from Example 1 and Example 4 or Example 5 indicates that incorporating nanocellulose fibers can improve the strength of the sole while suppressing the increase in hardness.

It is known that compounding glass balloons into rubber hardens the sole and significantly reduces its abrasion resistance. However, the test specimens in Examples 6 to 8 demonstrate high abrasion resistance despite the inclusion of glass balloons. The specific gravity of the test specimens in Examples 6 to 8 is lower than that of the test specimens in Examples 1 to 5. For example, a shoe sole made from the test specimen of Example 1 weighs approximately 142g. On the other hand, a shoe sole made from the test specimen of Example 1 weighs approximately 120g.

The wear results for Comparative Example 5 show that reducing the amount of filler reduces wear resistance. The wear results for Example 6 show that adding a filler with a hollow structure in addition to a solid filler can prevent a decrease in wear resistance.

Claims (5)

A shoe sole containing vulcanized non-foamed rubber, a filler, cellulose fiber powder, and a mercapto-silane coupling agent,
The following is a mixture containing 5 to 30 parts by weight of cellulose fiber powder per 100 parts by weight of the rubber:
The wear amount determined by the Williams wear test method B of JIS K 6264-2 is 470 ^mm³ /1000 rpm or less .
Shoe soles with a hardness of 60-72 as measured with a Type A durometer in accordance with JIS K 6253-3:2012 . The sole of a shoe according to claim 1, wherein the cellulose fiber has an average fiber width of 500 μm or less. The sole of a shoe according to claim 1 or 2 , wherein the filler contains a hollow-structured filler. The sole of the shoe according to any one of claims 1 to 3, wherein the specific gravity of the sole is 1.3 or less. Footwear comprising a sole according to any one of claims 1 to 4 .