US20200305545A1

US20200305545A1 - Midsole Structure for an Athletic Shoe

Info

Publication number: US20200305545A1
Application number: US16/820,923
Authority: US
Inventors: Kentaro Yahata; Yohei Yoshida; Akira Morita
Original assignee: Mizuno Corp
Current assignee: Mizuno Corp
Priority date: 2019-03-31
Filing date: 2020-03-17
Publication date: 2020-10-01
Also published as: JP2020163082A; DE102020108911A1

Abstract

The midsole structure for an athletic shoe includes a midsole body made of foamed resin, and a sheet composite extending at least from the ball of the foot portion to the toe portion in the midsole body and comprising a plurality of foamed rubber sheets that are overlapped and shifted in the longitudinal direction. The sheet composite comprises a single sheet at the toe portion and a plurality of sheets at the ball of the foot portion.

Description

BACKGROUND OF THE INVENTION

The present invention relates generally to a midsole structure for an athletic shoe, and more particularly, to an improvement in the midsole structure so as to improve cushioning property and a touch on a foot of a shoe wearer and enhance a propulsion force during exercises.
Japanese patent application publication No. 2001-149101 discloses a sole structure for a boot. The sole includes a rubber sole body, a core material disposed above the sole body and made of foamed rubber, and a rubber-made shape-keeping material sandwiched between the sole body and the core material. The publication describes that a favorable cushioning property can be exhibited by the relatively thick core material made of foamed rubber and rigidity can be improved by the rubber-made shape-keeping material (see paras. [0018] to [0022], FIG. 1).
In athletic shoes such as running shoes and the like, since a sole thickness of a toe is thin, it is difficult to insert the relatively thick core material (or insole board) made of foamed rubber according to the prior art into a tip end of the toe. On the other hand, in the case that the sole thickness of the toe is made thick such that the insole board can be inserted into the tip end of the toe, cushioning property of the other sole regions maybe decreased. Also, in the prior-art structure, since the rubber sole body is used, there is a deficiency that the weight of the entire sole is heavy.
The present invention has been made in view of these circumstances and its object is to provide a midsole structure for an athletic shoe that can improve cushioning property and a touch on a foot of a shoe wearer and that can enhance a propulsion force during exercises. Also, the present invention is directed to decreasing the weight of such a midsole structure.
Other objects and advantages of the present invention will be obvious and appear hereinafter.

SUMMARY OF THE INVENTION

A midsole structure for an athletic shoe according to one aspect of the present invention includes a midsole body made of foamed synthetic resin and a sheet composite extending at least from a ball of a foot portion to a toe portion in the midsole body and comprising a plurality of foamed rubber sheets that are overlapped and shifted in a longitudinal direction. The sheet composite includes a single sheet at the toe portion and a plurality of sheets at the ball of the foot portion.
According to the present invention, at the ball of the foot portion of the midsole body, a plurality of foamed rubber sheets of the sheet composite, that is, a thick sheet layer made of foamed rubber is disposed. Therefore, a touch on a foot of a wearer can be improved at the ball of the foot portion and cushioning property can be enhanced at the ball of the foot portion.
At the toe portion of the midsole body, a single foamed rubber sheet of the sheet composite, that is, a thin sheet layer made of foamed rubber is disposed. Thereby, as a load at the time of impacting the ground is transferred from the ball of the foot portion to the toe portion, a downward sinking movement of the foot is gradually decreased. During a push-off motion of the foot at the toe portion, a high repellent force can be obtained and thus a propulsion force during exercises can be increased. Moreover, according to the present invention, since the midfoot body is made of foamed resin, the total weight of the midsole structure can be reduced.
The midsole body may include a stepped concave portion that is open to a foot-sole-contact-surface side and that has a difference in level in the longitudinal direction. The sheet composite may be housed in such a concave portion. In this case, at a deeper concave portion, a plurality of sheets of the sheet composite are disposed and at a shallower concave portion, a single sheet of the sheet composite is disposed.
The midsole body may include a stepped concave portion that is open to a ground-contact-surface side and that has a difference in level in the longitudinal direction. The sheet composite may be housed in such a concave portion. In this case as well, at a deeper concave portion, a plurality of sheets of the sheet composite are disposed and at a shallower concave portion, a single sheet of the sheet composite is disposed.
The midsole body may include a stepped concave portion that passes through the midsole body in a thickness direction and that has a difference in level in the longitudinal direction. The sheet composite may be housed in such a concave portion. In this case too, at a deeper concave portion, a plurality of sheets of the sheet composite are disposed and at a shallower concave portion, a single sheet of the sheet composite is disposed.
The midsole body may include a stepped inner space that has a difference in level in the longitudinal direction. The sheet composite may be housed in such an inner space. In this case as well, at a deeper inner space, a plurality of sheets of the sheet composite are disposed and at a shallower inner space, a single sheet of the sheet composite is disposed.
The sheet composite may be disposed at a forefoot portion, or a heel portion of said midsole body. Alternatively, the sheet composite may extend from the heel portion through a midfoot portion to the forefoot portion of the midsole body. In either case, at a region where the sheet composite comprises a plurality of sheets, a touch on the foot of the wearer and cushioning property can be improved by the thick sheet layer made of foamed rubber, whereas at a region where the sheet composite comprises a single sheet, a high repellent force can be obtained and a propulsion force can thus be increased by the thin sheet layer made of foamed rubber.
The sheet composite disposed at the heel portion of the midsole body may be separated from the sheet composite disposed at the forefoot portion of the midsole body in the longitudinal direction.
A midsole structure for an athletic shoe according to another aspect of the present invention includes a midsole body made of foamed synthetic resin and a sheet composite extending at least from a ball of a foot portion to a toe portion in the midsole body and comprising a first sheet and a second sheet that are made of foamed rubber and that are overlapped and shifted in the longitudinal direction. Each of the first sheet and the second sheet has a front end disposed on a front side thereof and a rear end disposed on a rear side thereof in the longitudinal direction. The front end of the first sheet is located in front of the front end of the second sheet at the toe portion of the midsole body.
According to the present invention, at the ball of the foot portion of the midsole body, the first and second foamed rubber sheets of the sheet composite, that is, a thick sheet layer made of foamed rubber is disposed. Therefore, a touch on a foot of a wearer can be improved at the ball of the foot portion and cushioning property can be enhanced.
At the toe portion of the midsole body, the first foamed rubber sheet of the sheet composite, that is, a thin sheet layer made of foamed rubber is disposed. Thereby, as a load at the time of impacting the ground is transferred from the ball of the foot portion to the toe portion, a downward sinking movement of the foot is gradually decreased. Also, during a push-off motion of the foot at the toe portion, a high repellent force can be obtained and thus a propulsion force during exercises can be increased. Moreover, according to the present invention, since the midfoot body is made of foamed resin, the total weight of the midsole structure can be reduced.
The front end of the first sheet may contact the midsole body from above. Thereby, during the push-off motion of the foot at the toe portion, a greater repellent force can be obtained.
The rear end of the first sheet may extend to the rear of the rear end of the second sheet. Thereby, as a load is transferred from the rear end of the first sheet through the rear end of the second sheet to an overlapped region of the first and second sheets, cushioning property and a touch on the foot of the wearer can be gradually improved.
The first sheet may be disposed at a forefoot portion and a heel portion of the midsole body and the second midsole may comprise a forefoot sheet portion disposed at the forefoot portion of the midsole body and a heel sheet portion disposed at the heel portion of the midsole body. The forefoot sheet portion and the heel sheet portion may be separated from each other in the longitudinal direction.
In this case, at a region where the first and second sheets are overlapped with each other, a touch on the foot of the wearer and cushioning property can be improved by a thick sheet layer made of foamed rubber, whereas at a region where only the first sheet is disposed, a high repellent force can be obtained and a propulsion force can be increased by a thin sheet layer made of foamed rubber.
As explained above, according to the midsole structure of the present invention, since a plurality of foamed rubber sheets of the sheet composite, that is, a thick sheet layer made of foamed rubber is disposed at the ball of the foot portion of the midsole body, a touch on a foot of a wearer can be improved and cushioning property can be enhanced at the ball of the foot portion. Also, since a single foamed rubber sheet of the sheet composite, that is, a thin sheet layer made of foamed rubber is disposed at the toe portion of the midsole body, during a push-off motion of the foot at the toe portion, a high repellent force can be obtained and thus a propulsion force during exercises can be increased. Moreover, since the midfoot body is made of foamed resin, the total weight of the midsole structure can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the invention, reference should be made to the embodiments illustrated in greater detail in the accompanying drawings and described below by way of examples of the invention.

FIG. 1 is a top plan schematic view of a midsole structure for an athletic shoe according to a first embodiment of the present invention.

FIG. 2 is a sectional view of FIG. 1 taken along line II-II illustrating a longitudinal sectional view along a longitudinal centerline of the midsole structure of FIG. 1.

FIG. 3 is a cross sectional view of FIG. 1 taken along line.

FIG. 4 is a cross sectional view of FIG. 1 taken along line IV-IV.

FIG. 5 is a top plan schematic view of a midsole structure for an athletic shoe according to a second embodiment of the present invention.

FIG. 6 is a sectional view of FIG. 5 taken along line VI-VI illustrating a longitudinal sectional view along a longitudinal centerline of the midsole structure of FIG. 5.

FIG. 7 is a cross sectional view of FIG. 5 taken along line VII-VII.

FIG. 8 is a cross sectional view of FIG. 5 taken along line VIII-VIII.

FIG. 9 is a top plan schematic view of a midsole structure for an athletic shoe according to a third embodiment of the present invention.

FIG. 10 is a sectional view of FIG. 9 taken along line X-X illustrating a longitudinal sectional view along a longitudinal centerline of the midsole structure of FIG. 9.

FIG. 11 is a cross sectional view of FIG. 9 taken along line XI-XI.

FIG. 12 is a cross sectional view of FIG. 9 taken along line XII-XII.

FIG. 13 is a top plan schematic view of a midsole structure for an athletic shoe according to a fourth embodiment of the present invention.

FIG. 14 is a sectional view of FIG. 13 taken along line XIV-XIV illustrating a longitudinal sectional view along a longitudinal centerline of the midsole structure of FIG. 13.

FIG. 15 is a cross sectional view of FIG. 13 taken along line XV-XV.

FIG. 16 is a cross sectional view of FIG. 13 taken along line XVI-XVI.

FIG. 17 is a top plan schematic view of a midsole structure for an athletic shoe according to a fifth embodiment of the present invention.

FIG. 18 is a sectional view of FIG. 17 taken along line XVIII-XVIII illustrating a longitudinal sectional view along a longitudinal centerline of the midsole structure of FIG. 17.

FIG. 19 is a cross sectional view of FIG. 17 taken along line XIX-XIX.

FIG. 20 is a cross sectional view of FIG. 17 taken along line XX-XX.

FIG. 21 is a top plan schematic view of a midsole structure for an athletic shoe according to a sixth embodiment of the present invention.

FIG. 22 is a sectional view of FIG. 21 taken along line XXII-XXII illustrating a longitudinal sectional view along a longitudinal centerline of the midsole structure of FIG. 21.

FIG. 23 is a cross sectional view of FIG. 21 taken along line XXIII-XXIII.

FIG. 24 is a cross sectional view of FIG. 21 taken along line XXIV-XXIV.

FIG. 25 is a top plan schematic view of a midsole structure for an athletic shoe according to a seventh embodiment of the present invention.

FIG. 26 is a sectional view of FIG. 25 taken along line XXVI-XXVI illustrating a longitudinal sectional view along a longitudinal centerline of the midsole structure of FIG. 25.

FIG. 27 is a cross sectional view of FIG. 25 taken along line XXVII-XXVII.

FIG. 28 is a cross sectional view of FIG. 25 taken along line XXVIII-XXVIII.

FIG. 29 is a top plan schematic view of a midsole structure for an athletic shoe according to an eighth embodiment of the present invention.

FIG. 30 is a sectional view of FIG. 29 taken along line XXX-XXX illustrating a longitudinal sectional view along a longitudinal centerline of the midsole structure of FIG. 29.

FIG. 31 is a cross sectional view of FIG. 29 taken along line XXXI-XXXI.

FIG. 32 is a cross sectional view of FIG. 29 taken along line XXXII-XXXII.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference to embodiments thereof as illustrated in the accompanying drawings. Here, a running shoe is taken for an example as an athletic shoe.
In the following explanation, “upward (upper side/upper)” and “downward (lower side/lower)” designate an upward direction and a downward direction, or vertical direction, of the shoe, respectively, “forward (front side/front)” and “rearward (rear side/rear)” designate a forward direction and a rearward direction, or longitudinal direction, of the shoe, respectively, and “a width(or lateral) direction” designates a crosswise direction of the shoe.
For example, in FIG. 1, a top plan schematic view of the midsole structure of the shoe, “upward” and “downward” designate “out of the page” and “into the page” in FIG. 1, respectively, “forward” and “rearward” designate “upward” and “downward” of FIG. 1, respectively, and “a width direction” designates “left to right direction” in FIG. 1.
Also, in FIG. 2, a longitudinal sectional view and in FIGS. 3, 4, cross sectional views, only the sheet composite constituting the midsole structure according to the present embodiment is shown by hatching and hatching of a midsole body and an outsole is omitted for illustration purposes. In the drawings, reference characters H, M and F designate a heel region, a midfoot region and a forefoot region of the midsole structure, respectively, which are adapted to correspond to a heel portion, a midfoot portion or a plantar arch portion and a forefoot portion of a foot of a shoe wearer, respectively.

First Embodiment

FIGS. 1 to 4 show a midsole structure for an athletic shoe according to a first embodiment of the present invention. As shown in FIGS. 1 and 2, the midsole structure 1 includes a midsole body 2 extending from the heel region H through the midfoot region M to the forefoot region H and a sheet composite (see hatched portions) 3 extending from the heel region H through the midfoot region M to the forefoot region H on a side of an upper surface (i.e. a foot-sole-contact-side surface) 20 of the midsole body 2. On a lower surface (i.e. a ground-contact-side surface) 22 of the midsole body 2, an outsole 4 is fixedly attached that has a ground-contact surface that contacts the ground. As shown in FIGS. 2 to 4, the midsole body 2 has an upraised portion 21 that extends upwardly from an outer circumferential edge portion of the upper surface 20. A bottom portion of an upper (not shown) of the shoe is to be fixedly attached to the upraised portion 21. In such a manner, the athletic shoe is assembled.
As shown in FIGS. 1 to 4, the upper surface 20 of the midsole body 2 has concave portions or concavities 2A, 2B formed therein to house the sheet composite 3. The concave portion 2A disposed on an upper side is open to the upper surface 20, and the concave portion 2B disposed on a lower side is open to the upper surface 20 through the concave portion 2A. None of the concave portions 2A, 2B are not open to the lower surface 22 of the midsole body 2.
A front-end wall portion 2A₁of the concave portion 2A is located in front of a front-end wall portion 2B₁of the concave portion 2B. A rear-end wall portion 2A₂of the concave portion 2A is located at the rear of a rear-end wall portion 2B₂of the concave portion 2B. A generally longitudinal length of the concave portion 2A is longer than that of the concave portion 2B. Thereby, between the concave portions 2A and 2B, there is formed a stepped surface 2Ab₁at the forefoot region F and a stepped surface 2Ab₂at the heel region H. Also, sidewall portions of the concave portions 2A, 2B have no stepped surfaces and are aligned with each other in the lateral direction (see FIGS. 1 to 3) and thus the sidewall portions of the concave portions 2A, 2B have straight surfaces in the vertical direction (see FIGS. 3, 4).
The sheet composite 3 comprises an upper sheet (or a first sheet) 30 disposed on an upper side and a lower sheet (or a second sheet) 31 disposed on a lower side. The upper sheet 30 is housed in the concave portion 2A and the lower sheet 31 is housed in the concave portion 2B. A lower surface 31B of the lower sheet 31 is fitted on a bottom wall surface 2B₀of the concave portion 2B, a front end 31 a of the lower sheet 31 faces the front-end wall portion 2B₁of the concave portion 2B, and a rear end 31 b of the lower sheet 31 faces the rear-end wall portion 2B₂of the concave portion 2B. A lower surface 30B of the upper sheet 30 is fitted on an upper surface 31A of the lower sheet 31, a front end 30 a of the upper sheet 30 faces the front-end wall portion 2A₁of the concave portion 2A, and a rear end 30 b of the upper sheet 30 faces the rear-end wall portion 2A₂of the concave portion 2A. An upper surface 30A of the upper sheet 30 forms a foot-sole-contact-side surface, which follows a contour of the foot of the wearer.
The sheet composite 3 has a two-layer structure at a region in which the upper and lower sheets 30, 31 are overlapped with each other, and the sheet composite 3 has a single-layer structure with only the upper sheet 30 at regions ahead of the lower sheet 31 and behind the lower sheet 31, i.e. at regions of the stepped surfaces 2Ab₁and 2Ab₂. That is to say, the front end 30 a of the upper sheet 30 is disposed in front of the front end 31 a of the lower sheet 31 and the rear end 30 b of the upper sheet 30 is disposed at the rear of the rear end 31 b of the lower sheet 31. In other words, the sheet composite 3 is so structured as to overlap the upper sheet 30 and the lower sheet 31 with the front and rear ends 30 a, 30 b of the upper sheet 30 shifted relative to the front and rear ends 31 a, 31 b of the lower sheet 31.
As shown in FIGS. 2 to 4, the upper sheet 30 has a uniform thickness in the longitudinal direction as well as in the lateral direction. The lower sheet 31 also has a uniform thickness in the longitudinal direction as well as in the lateral direction. In this example, the thickness of the upper sheet 30 is the same as the thickness of the lower sheet 31. The sidewalls of the upper sheet 30 are generally perpendicular to the upper surface 30A and the lower surface 30B. the sidewalls of the lower sheet 31 are also generally perpendicular to the upper surface 31A and the lower surface 31B.
As shown in FIG. 2, the thickness of the two-layer-structure portion of the sheet composite 3 relative to the midsole structure 1 occupies approximately half of the thickness of the midsole structure 1 at the heel region H, more than half of the thickness of the midsole structure 1 at a region from the midfoot region M to the forefoot region F, and the occupied thickness ratio gradually increases toward the toe of the foot. On the other hand, the thickness of a single layer portion of the sheet composite 3 relative to the midsole structure 1 occupies a very small part of the thickness of the midsole structure 1 at the heel region H, and the occupied thickness ratio in the forefoot region F gradually increases toward the toe of the foot.
As shown in a bone structure of the foot described in FIG. 1, the front end 30 a of the upper sheet 30 extends to a position of a proximal portion of a distal phalanx DP₁of a first toe, and the front end 31 a of the lower sheet 31 extends to a position of a proximal portion of a proximal phalanx PP₁of the first toe. Therefore, a thenar eminence portion or a ball of the foot TE, which includes a metatarsophalangeal joint MJ₁between the proximal phalanx PP₁and a metatarsus MB₁of the first toe and a bulged portion around the metatarsophalangeal joint MJ₁, is located at a region of the two-layer structure composed of the overlapped upper and lower sheets 30, 31.
The toe portion of the foot that includes a distal end portion of the proximal phalanx PP₁of the first toe and the proximal portion of the distal phalanx DP₁of the first toe is located at a region of a single-layer structure composed of only the upper sheet 30. The sheet composite 3 of the present embodiment extends from at least the ball of the foot portion TE to the toe. As shown in FIG. 2, the thickness of the midsole body 2 at the forefoot region F becomes gradually thinner toward the tip of the toe. A reference numeral 2 e in FIG. 2 designates the thinnest portion of the midsole body 2 disposed between a foremost end of the stepped surface 2Ab₁of the midsole body 2 and the lower surface 22 of the midsole body 2.
The midsole body 2 is formed of a foamed synthetic resin, more particularly, foamed thermoplastic resin such as foamed ethylene-vinyl acetate copolymer (EVA) and the like, or foamed thermosetting resin such as foamed polyurethane (PU) and the like. The sheet composite 3 is formed of foamed rubber, more particularly, foamed body of natural rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, nitrile butadiene rubber or the like. The hardness of the midsole body 2 is set at for example 50 to 60 C in Asker C hardness scale and the hardness of the sheet composite 3 is set at for example 10 to 40 C in Asker C hardness scale. As the sheet composite 3, a material of a low hardness and high repulsion is preferable. The outsole 4 is preferably formed of a harder elastic material than the midsole body 2, more specifically, thermoplastic resin such as ethylene-vinyl acetate copolymer (EVA) and the like, thermosetting resin such as polyurethane (PU) and the like, or rubber material such as butadiene rubber, chloroprene rubber and the like. The hardness of the outsole 5 is set at for example 50 to 90 A in Asker A hardness scale.
The, we will provide an additional explanation of the rubber foam that constitutes the sheet composite 3.
The rubber foam used in the present embodiment is formed of foaming rubber composition that includes rubber composition and foaming agent. The rubber foam is crosslinked foam in which the rubber composition is crosslinked and foamed.
The rubber composition is composed of at least one of either natural rubber or synthetic rubber. As synthetic rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber may be used. 1 kind in these rubbers may be solely used, alternatively, 2 or more kinds in these rubbers may be used together. Natural rubber and synthetic rubber may be used together. The content of the rubber composition relative to the entire rubber foam is preferably 40 to 90% by mass. That is because in the case of less than 40% by mass maintenance of repellant elasticity becomes difficult and in the case of more than 90% by mass processing sometimes becomes difficult due to occurrence of a crack during forming.
In addition, when using at least one of either natural rubber or isoprene rubber, the total content of the natural rubber and isoprene rubber relative to the entire rubber composition (i.e. total mass of the rubber composition) is preferably 60 to 100% by mass. That is because in the case of less than 60% by mass repellant elasticity cannot be maintained and processability or workability is deteriorated. Rubber composition is preferably mixed with nitrile butadiene rubber. Because nitrile group of nitrile butadiene rubber has polarity oil resistance of the rubber foam can be improved.
Foaming agents are not particularly limited if only it can generate gas necessary for foaming rubber composition by heating. 1 kind solely, or 2 kinds or more in combination may be used. The content of the foaming agents relative to the entire rubber composition is preferably 0.5 to 10% by mass, more preferably 2 to 5% by mass. That is because in the case of less than 0.5% by mass it is sometimes hard to foam stably and in the case of more than 10% by mass a problem occurs that the diameter of superficial or internal foamed cell varies due to excess-foaming.
The rubber foam according to the present embodiment is so formed as to add crosslinking agents, crosslinking assistant, foaming auxiliary agents, vulcanization accelerator, processing aid, reinforcing agents and the like to the above-mentioned rubber composite to crosslink and foam under a predetermined condition.
The crosslinking agents are not particularly limited, but sulfur that is common as crosslinking agents for rubber and organic peroxide that promotes peroxide crosslinking are used. These may be used by 1 kind solely, or by 2 kinds or more in combination. The content of the crosslinking agents relative to the entire rubber composite is preferably 1 to 7% by mass, more preferably 2 to 5% by mass. That is because in the case of less than 1% by mass repellent elasticity sometimes decreases due to an inadequate cross linking and in the case of more than 7% by mass foaming is sometimes inadequately performed due to an excessive crosslinking.
The crosslinking assistant is not particularly limited, but it may be used by 1 kind solely, or by 2 kinds or more in combination. The content of the crosslinking assistant relative to the entire rubber composite is preferably 1 to 10% by mass, more preferably 3 to 5% by mass. That is because in the case of less than 1% by mass repellent elasticity sometimes decreases due to an inadequate cross linking and in the case of more than 10% by mass weight reduction of a product becomes sometimes hard due to a great specific gravity of the rubber composite.
Foaming auxiliary agents are not particularly limited, but urea compound, zinc compound and the like may be used. These may be used by 1 kind solely, or by 2 kinds or more in combination. The content of the foaming auxiliary agents relative to the entire rubber composite is preferably 0.5 to 10% by mass. The foaming auxiliary agents are normally equal in quantity to the foaming agents. In the case that an addition of the foaming agents is less than an addition of the foaming auxiliary agents, some of the foaming agents produce formaldehyde or the like. Therefore, suitable adjustment is required according to the amount of addition of the foaming agents.
Vulcanization accelerator is not particularly limited, but it may be used by 1 kind solely, or by 2 kinds or more in combination. The content of the vulcanization accelerator relative to the entire rubber composite is preferably 0.2 to 3% by mass. That is because in the case of less than 0.2% by mass molding needs a long time to decrease productivity and repellent elasticity decreases due to an inadequate cross linking and in the case of more than 3% by mass the probability of blooming in the molding becomes higher.
From the point of improvement in fluidity and lubricity of rubber composite, restraint for attachment to kneading machines such as rollers, and improvement of mold-releasing effect, the content of processing aid relative to the entire rubber foam that may include processing aid is preferably 0 to 2% by mass. That is because in the case of more than 2% by mass rollers may slip relative to materials due to too greater lubricity and thus materials may become hard to be mixed at the time of processing rollers.
From the point of improvement in mechanical property such as tensile strength, wear resistance and the like of vulcanized rubber, rubber foam may contain reinforcing agents. The content of reinforcing agents relative to the entire rubber composite is preferably 5 to 50% by mass. That is because in the case of less than 5% by mass adequate strength may not be obtained and in the case of more than 50% by mass repellent elasticity may be deteriorated and specific gravity of the foam may become too great.
Then, a manufacturing method of rubber foam will be briefly explained.
Firstly, materials such as a rubber composition as a base material, a crosslinking agent and a foaming agent are casted into the kneading machine. By kneading these materials, a foaming rubber composition is manufacture (kneading process). In this case, rubber compositions, crosslinking aids, reinforcement agents, crosslinking agents, vulcanizing accelerators, foaming auxiliary and foaming agents are casted in this order into rollers heated to a predetermined temperature (for example, the surface temperature is 40-60° C.), and are kneaded. Thereafter, preforming such as sheeting and pelletizing is performed.
Secondly, the foaming rubber composite acquired in the kneading process is inserted into a metal mold and a heating process is conducted to promote foaming by the foaming agents. Thereafter, by performing a forming process and a mold-releasing process, a foaming rubber composition having a desired shape (foam molding process). In this case, the heating temperature in the heating process differs depending on the kinds of foaming agents and foaming aids, but the heating process is performed at a decomposition temperature or more (for example, 120-180° C.) of the foaming agents that are used.
The coefficient of repellant or rebounding elasticity or impact resilience coefficient of the rubber foam that was manufactured in the above-mentioned process is 72-84% according to the measurement method based on ASTM-D2632. In contrast, the impact resilience coefficient of an EVA foam of a high impact resilience is 63% according to the same method. The impact resilience coefficient of the rubber foam used in this embodiment has been found to be improved by 14-33% relative to the EVA of a high impact resilience. In the specific measurement, a foam sample (thickness: 10±1 mm) is prepared and VERTICAL REBOUND RESILIENCE TESTER_GT-7042-V of GOTECH is used. At the environmental temperature (23±3° C.), a metal plunger is dropped eight times at every 5 seconds. During five times in the later half, the indicator (%) at the standstill point (i.e. the rebounding height) of the metallic plunger after each rebounding is read and its average value is made the coefficient of rebounding elasticity.
In the midsole structure 1 structured as above-mentioned, when a load at the time of impacting the ground is transferred to the ball of the foot portion TE of the midsole body 2 during exercises, the two-layer-structured sheet composite 3 composed of upper and lower sheets 30, 31 made of foamed rubber, that is, a thick foamed-rubber sheet layer is disposed at the ball of the foot portion TE. Thereby, a touch on the foot of the wearer can be improved and cushioning property can be enhanced at the ball of the foot portion TE.
Next, when the load is transferred to the toe portion, a single-layered sheet composite 3 composed of only the upper sheet 30 made of foamed rubber, that is, a thin foamed-rubber sheet layer is disposed at the toe portion. Thereby, as the load on landing moves from the ball of the foot portion TE to the toe portion, a downward sinking movement of the foot is gradually lessened, a high repellent force can be obtained at the time of a push-off motion of the toe portion, and a propulsive force can thus be increased during exercises.
Especially, in the present embodiment, the thin portion 2 e of the midsole body 2 is formed between the frontmost end portion of the stepped surface 2Ab₁of the midsole body 2 and the lower surface 22 of the midsole body 2. Therefore, when the foot pushes off at the toe portion on the stepped surface 2Ab₁, a higher repellent force against the push-off force of the foot can be obtained from the stepped surface 2Ab₁. As a result, a higher propulsive force can be attained. Also, as foamed rubber composing the sheet composite 3, if the above-mentioned high rebounding rubber foam is used, a still higher rebounding force can be obtained and a much greater propulsive force can be attained. In addition, since the midsole body 2 is formed of foamed rubber, the entire weight of the midsole structure can be reduced.
Also, when the wearer impacts the ground at a heel rear end during exercises and the load is transferred from the heel rear end to a heel center, the load moves from a single-layer region to the double-layer region of the sheet composite 3. Thereby, a touch on the foot and cushioning property are improved gradually or in stages.

Second Embodiment

FIGS. 5 to 8 show a midsole structure for an athletic shoe according to a second embodiment of the present invention. In these drawings, like reference numbers indicate identical or functionally similar elements to those in the first embodiment. In the first embodiment, an example was shown in which the concave portions 2A, 2B that house the sheet composite 3 are formed on the upper surface (i.e. the foot-sole-contact-side surface) 20 of the midsole body 2. In this second embodiment, the concave portions 2A, 2B that house the sheet composite 3 are formed on the lower surface (i.e. the ground-contact-side surface) 22 of the midsole body 2.
That is, the concave portion 2B disposed below is open to the lower surface 22 and the concave portion 2A disposed above is open to the lower surface 22 through the concave portion 2B. Neither of the concave portions 2A, 2B are not open to the upper surface 20.
Also, generally longitudinal lengths of the upper sheet 30 and the lower sheet 31 that constitute the sheet composite 3 of this second embodiment are opposite to generally longitudinal lengths of the upper sheet 30 and the lower sheet 31 that constitute the sheet composite 3 of the first embodiment. That is, the front end 30 a of the upper sheet 30 is disposed at the rear of the front end 31 a of the lower sheet 31 and the rear end 30 b of the upper sheet 30 is disposed in front of the rear end 31 b of the lower sheet 31.
In other words, the sheet composite 3 is so structured as to overlap the upper sheet 30 and the lower sheet 31 with the front and rear ends 30 a, 30 b of the upper sheet 30 shifted relative to the front and rear ends 31 a, 31 b of the lower sheet 31. Between the concave portions 2A and 2B, a stepped surface 2Bb₁is formed at the forefoot region F and a stepped surface 2Bb₂is formed at the heel region H.
In this case as well, in the same manner as the above-mentioned first embodiment, the two-layer-structured sheet composite 3 composed of upper and lower sheets 30, 31 made of foamed rubber, i.e. a thick foamed-rubber sheet layer, is disposed at the ball of the foot portion TE. Thereby, cushioning property can be improved at the ball of the foot portion TE.
Also, at the toe portion, a single-layered sheet composite 3 composed of only the upper sheet 30 made of foamed rubber, i.e. a thin foamed-rubber sheet layer, is disposed. Thereby, a high repellent force can be obtained at the time of a push-off motion of the foot at the toe portion, and a propulsive force can thus be increased during exercises.
Moreover, the thin portion 2 e of the midsole body 2 is formed between the frontmost end portion of the stepped surface 2Bb₁and the upper surface 20 of the midsole body 2. Therefore, when the foot pushes off at the stepped surface 2Bb₁, a higher repellent force against the push-off force of the foot can be obtained from the stepped surface 2Bb₁. As a result, a higher propulsive force can be attained. Also, as foamed rubber composing the sheet composite 3, if the above-mentioned high rebounding rubber foam is used, a still higher rebounding force can be obtained and a much greater propulsive force can be attained. Furthermore, as the load is transferred from the heel rear end to the heel central portion, cushioning property is improved gradually or in stages at the heel region H. In addition, the midsole body 2 is formed of foamed rubber, thus reducing the entire weight of the midsole structure.

Third Embodiment

FIGS. 9 to 12 show a midsole structure for an athletic shoe according to a third embodiment of the present invention. In these drawings, like reference numbers indicate identical or functionally similar elements to those in the first and second embodiments. In the first embodiment, an example was shown in which the concave portions 2A, 2B that house the sheet composite 3 is open to the upper surface 20 and is not open to the lower surface 22 of the midsole body 2, and in the second embodiment, an example was shown in which the concave portions 2A, 2B is open to the lower surface 22 and is not open to the upper surface 20 of the midsole body 2.
In this third embodiment, the concave portions 2A and 2B are open to both of the upper and lower surfaces 20, 22 of the midsole body 3. Also, in this third embodiment, the lower sheets 31, 31′ composing the sheet composite 2 do not extend from the heel region H through the midfoot region M to the forefoot region F. The lower sheets 30, 31 are separated from each other in the longitudinal direction.
The concave portions 2A, 2B penetrate the midsole body 2 in the thickness direction (see FIGS. 10, 11). The lower sheet 31 extends from a front-end portion of the midfoot region M to the mid portion of the forefoot region F. The front end 31 a ₁of the lower sheet 31 faces the front-end wall portion 2B₁of the concave portion 2B and the rear end 31 b ₁of the lower sheet 31 faces the rear-end wall portion 2B₂of the concave portion 2B. The lower sheet 31′ is disposed at the heel region H. The front end 31 a ₂of the lower sheet 31′ faces the front-end wall portion 2B₁′ of the concave portion 2B and the rear end 31 b ₂of the lower sheet 30 faces the rear-end wall portion 2B₂′ of the concave portion 2B. The lower surface 30B.of the upper sheet 30 is in contact with the upper surface 31A of the lower sheet 31 and the upper surface 31′A of the upper sheet 31′.
The front end 30 a of the upper sheet 30 is disposed in front of the front end 31 a ₁of the lower sheet 31 and the rear end 30 b of the upper sheet 30 is disposed at the rear of the rear end 31 b ₂of the lower sheet 31′. At a region extending from the front end portion of the heel region H to the front end portion of the midfoot region M, the lower sheet is not provided and only the upper sheet 30 is provided. Between the concave portions 2A and 2B, a stepped surface 2Ab₁is formed at the forefoot region F, a stepped surface 2Ab₂is formed at the heel region H, and a stepped surface 2Ab₃is formed at the midfoot region M.
In this case as well, in a similar manner to the above-mentioned first and second embodiments, the two-layer-structured sheet composite 3 composed of upper and lower sheets 30, 31 made of foamed rubber, i.e. a thick foamed-rubber sheet layer, is disposed at the ball of the foot portion TE. Thereby, a touch on the foot and cushioning property can be improved at the ball of the foot portion TE.
Also, at the toe portion, a single-layered sheet composite 3 composed of only the upper sheet 30 made of foamed rubber, i.e. a thin foamed-rubber sheet layer, is disposed. Thereby, a high repellent force can be obtained at the time of a push-off motion of the foot at the toe portion, and a propulsive force can thus be increased during exercises.
Moreover, the thin portion 2 e of the midsole body 2 is formed between the frontmost end portion of the stepped surface 2Ab₁and the lower surface 22 of the midsole body 2. Therefore, when the foot pushes off at the stepped surface 2Ab₁, a higher repellent force against the push-off force of the foot can be obtained from the stepped surface 2Ab₁. As a result, a higher propulsive force can be attained. Also, as foamed rubber composing the sheet composite 3, if the above-mentioned high rebounding rubber foam is used, a still higher rebounding force can be obtained and a much greater propulsive force can be attained. Furthermore, as the load is transferred from the heel rear end to the heel central portion and also the load is transferred from the midfoot region M to the forefoot region F, a touch on the foot and cushioning property can be improved gradually or in stages. In addition, since the midsole body 2 is formed of foamed rubber, the entire weight of the midsole structure can be reduced.

Fourth Embodiment

FIGS. 13 to 16 show a midsole structure for an athletic shoe according to a fourth embodiment of the present invention. In these drawings, like reference numbers indicate identical or functionally similar elements to those in the first to third embodiments. In this fourth embodiment, an example is shown in which the concave portions 2A, 2B that house the sheet composite 3 are open to neither the upper surface 20 nor the lower surface 22 of the midsole body 2. That is, in this case, the upper and lower sheets 30, 31 that constitute the sheet composite 3 are housed in an interior space formed in the midsole body 2.
As shown in FIGS. 14 to 16, the midsole body 2 includes an upper midsole 2 ₁disposed on the upper side and a lower midsole 2 ₂disposed on the lower side. The upper sheet 30 is housed in the concave portion 2A formed on the lower surface 22 ₁of the upper midsole body 2 ₁and the lower sheets 31, 31′ are housed in two concave portions 2B formed on the upper surface 22 ₂of the lower midsole 2 ₂.
In this case too, in a similar manner to the above-mentioned first to third embodiments, the two-layer-structured sheet composite 3 composed of upper and lower sheets 30, 31 made of foamed rubber, i.e. a thick foamed-rubber sheet layer, is disposed at the ball of the foot portion TE, such that thereby a touch on the foot and cushioning property can be improved at the ball of the foot portion TE.
Also, at the toe portion, a single-layered sheet composite 3 composed of only the upper sheet 30 made of foamed rubber, i.e. a thin foamed-rubber sheet layer is disposed. Thereby, a high repellent force can be obtained at the time of a push-off motion of the foot at the toe portion, and a propulsive force can thus be increased during exercises.
Moreover, the thin portion 2 e of the midsole body 2 is formed between the frontmost end portion of the stepped surface 2Bb 1 and the lower surface 22 of the midsole body 2. Therefore, when the foot pushes off at the stepped surface 2Bb₁, a higher repellent force against the push-off force of the foot can be obtained from the stepped surface 2Bb₁. As a result, a higher propulsive force can be attained. Also, as foamed rubber composing the sheet composite 3, by adopting the above-mentioned high rebounding rubber foam, a still higher rebounding force can be obtained and a much greater propulsive force can be attained. Furthermore, as the load is transferred from the heel rear end to the heel central portion and also the load is transferred from the midfoot region M to the forefoot region F, cushioning property is improved gradually or in stages. In addition, since the midsole body 2 is formed of foamed rubber, the entire weight of the midsole structure can be reduced.

Fifth Embodiment

FIGS. 17 to 20 show a midsole structure for an athletic shoe according to a fifth embodiment of the present invention. In these drawings, like reference numbers indicate identical or functionally similar elements to those in the first to fourth embodiments. In this fifth embodiment, the concave portions 2A, 2B that house the sheet composite 3 are disposed at a region from the front end portion of the midfoot region M to the midportion of the forefoot region F of the midsole body 2, i.e. mainly at the forefoot region F. The concave portion is not provided at the heel region H. Therefore, the upper sheet 30 and the lower sheet 31 that compose the sheet composite 3 are disposed at the region from the front end portion of the midfoot region M to the midportion of the forefoot region F of the midsole body 2, i.e. mainly at the forefoot region F.
In this case as well, similar to the above-mentioned first to fourth embodiments, the two-layer-structured sheet composite 3 composed of upper and lower sheets 30, 31 made of foamed rubber, i.e. a thick foamed-rubber sheet layer, is disposed at the ball of the foot portion TE. Thereby, a touch on the foot and cushioning property can be improved at the ball of the foot portion TE.
Also, at the toe portion, a single-layered sheet composite 3 composed of only the upper sheet 30 made of foamed rubber, i.e. a thin foamed-rubber sheet layer, is disposed. Thereby, a high repellent force can be obtained at the time of a push-off motion of the foot at the toe portion, and a propulsive force can thus be increased during exercises.
Moreover, the thin portion 2 e of the midsole body 2 is formed between the frontmost end portion of the stepped surface 2Ab₁and the lower surface 22 of the midsole body 2. Therefore, when the foot pushes off at the stepped surface 2Ab₁, a higher repellent force against the push-off force of the foot can be obtained from the stepped surface 2Ab₁. As a result, a higher propulsive force can be attained. Also, as foamed rubber composing the sheet composite 3, by employing the above-mentioned high rebounding rubber foam, a still higher rebounding force can be obtained and a much greater propulsive force can be attained. In addition, since the midsole body 2 is formed of foamed rubber, the entire weight of the midsole structure can be reduced.

Sixth Embodiment

FIGS. 21 to 24 show a midsole structure for an athletic shoe according to a sixth embodiment of the present invention. In these drawings, like reference numbers indicate identical or functionally similar elements to those in the first to fifth embodiments. In this sixth embodiment, the concave portions 2A, 2B that house the sheet composite 3 are separated mainly at the forefoot region F and the heel region H. Thereby, the upper sheets 30 are separated mainly at the forefoot region F and the heel region H and similarly the lower sheets 31 are separated mainly at the forefoot region F and the heel region H.
In more details, the lower sheet 31 is disposed in the midportion of the heel region H and at the rear side part of the forefoot region F. At the heel region H, the rear end of the upper sheet 30 is disposed at the rear of the rear end of the lower sheet 31 and the front end of the upper sheet 30 is disposed in front of the front end of the lower sheet 31. Similarly, in a region from the midfoot region M to the forefoot region F, the rear end of the upper sheet 30 is disposed at the rear of the rear end of the lower sheet 31, and the front end of the upper sheet 30 is disposed in front of the front end of the lower sheet 31.
In this case as well, as with the above-mentioned first to sixth embodiments, the two-layer-structured sheet composite 3 composed of upper and lower sheets 30, 31 made of foamed rubber, i.e. a thick foamed-rubber sheet layer, is disposed at the ball of the foot portion TE, such that thereby a touch on the foot and cushioning property can be improved at the ball of the foot portion TE.
At the toe portion, a single-layered sheet composite 3 composed of only the upper sheet 30 made of foamed rubber, i.e. a thin foamed-rubber sheet layer, is disposed, such that thereby a high repellent force can be obtained at the time of a push-off motion of the foot at the toe portion and a propulsive force can thus be increased during exercises.
Moreover, the thin portion 2 e of the midsole body 2 is formed between the frontmost end portion of the stepped surface 2Ab₁and the lower surface 22 of the midsole body 2. Therefore, when the foot pushes off at the stepped surface 2Ab₁, a higher repellent force against the push-off force of the foot can be obtained from the stepped surface 2Ab₁. As a result, a higher propulsive force can be attained. Also, as foamed rubber composing the sheet composite 3, by adopting the above-mentioned high rebounding rubber foam, a still higher rebounding force can be obtained and a much greater propulsive force can be attained. Furthermore, as the load is transferred from the heel rear end to the heel central portion at the heel region H and also the load is transferred from the midfoot region M to the forefoot region F, a touch on the foot and cushioning property is improved gradually or in stages. In addition, since the midsole body 2 is formed of foamed rubber, the entire weight of the midsole structure can be reduced.

Seventh Embodiment

FIGS. 25 to 28 show a midsole structure for an athletic shoe according to a seventh embodiment of the present invention. In these drawings, like reference numbers indicate identical or functionally similar elements to those in the first to sixth embodiments. In this seventh embodiment, similar to the fifth embodiment shown in FIGS. 17 to 20, the concave portions 2A, 2B that house the sheet composite 3 are disposed at a region from the front end portion of the midfoot region M to the mid portion of the forefoot region F of the midsole body 2, i.e. mainly at the forefoot region F. Therefore, the upper sheet 30 and the lower sheet 31 that compose the sheet composite 3 are disposed at the region from the front end portion of the midfoot region M to the midportion of the forefoot region F of the midsole body 2, i.e. mainly at the forefoot region F.
However, this seventh embodiment differs from the fifth embodiment in that the width of the concave portion 2B of the seventh embodiment is smaller than the width of the concave portion 2B of the fifth embodiment (see FIGS. 25, 27 and FIGS. 17, 19). The width of the concave portion 2B is also smaller than the width of the concave portion 2A. On the medial side of the midsole body 2, the medial side surface 31 c of the concave portion 2B is vertically aligned with the medial side surface 30 c of the concave portion 2A (see FIG. 27), but on the lateral side of the midsole body 2, the lateral side surface 31 c of the concave portion 2B is not vertically aligned with and disposed laterally inwardly from the lateral side surface 30 c of the concave portion 2A (see FIG. 27).
In this case as well, similar to the above-mentioned first to sixth embodiments, the two-layer-structured sheet composite 3 composed of upper and lower sheets 30, 31 made of foamed rubber, i.e. a thick foamed-rubber sheet layer, is disposed at the ball of the foot portion TE, such that thereby a touch on the foot and cushioning property can be improved at the ball of the foot portion TE.
At the toe portion, a single-layered sheet composite 3 composed of only the upper sheet 30 made of foamed rubber, i.e. a thin foamed-rubber sheet layer, is disposed, such that thereby a high repellent force can be obtained at the time of a push-off motion of the foot at the toe portion and a propulsive force can thus be increased during exercises.
Moreover, the thin portion 2 e of the midsole body 2 is formed between the frontmost end portion, of the stepped surface 2Ab₁and the lower surface 22 of the midsole body 2 (see FIG. 26). Therefore, when the foot pushes off at the stepped surface 2Ab₁, a higher repellent force against the push-off force of the foot can be obtained from the stepped surface 2Ab₁. As a result, a higher propulsive force can be attained. Also, as foamed rubber composing the sheet composite 3, by adopting the above-mentioned high rebounding rubber foam, a still higher rebounding force can be obtained and a much greater propulsive force can be attained. Furthermore, in this embodiment, from the lateral side to the medial side of the forefoot region F, a touch on the foot and cushioning property is improved gradually or in stages. Conversely, on the lateral side of the forefoot region F, a higher repulsive force can be attained, thus preventing supination during running. In addition, since the midsole body 2 is formed of foamed rubber, the entire weight of the midsole structure can be reduced.

Eighth Embodiment

In each of the above-mentioned first to seventh embodiments, an example was shown in which the midsole structure of the present invention was applied to a running shoe, but the application of the present invention is not limited to such an example. The present invention also has application to various sports shoes such as walking shoes, tennis shoes, indoor shoes and the like. The present invention is also applicable to cleated shoes or spike shoes such as soccer shoes, baseball shoes and the like.
FIGS. 29 to 32 show a midsole structure for an athletic shoe according to an eighth embodiment of the present invention. In these drawings, like reference numbers indicate identical or functionally similar elements to those in the first to seventh embodiments. In this eighth embodiment, an example is shown in which the midsole structure 2 of the first embodiment is applied to a cleated shoe. Therefore, the midsole structure 2 of the eighth embodiment is functionally similar to the midsole structure 2 of the first embodiment, and thus the eighth embodiment has similar effects to those of the first embodiment with the exception that a plurality of cleats are provided on the bottom surface of the outsole 4. In this eighth embodiment too, by the thick two-layer-structured sheet composite 3 made of foamed rubber, an upward thrust from cleats 40 can be relieved with a favorable touch on the foot and cushioning property maintained at the ball of the foot portion TE. Also, a propulsion force can be further increased during exercises by the cleats provided directly below the stepped surface 2Ab₁.

Variant

In the above-mentioned first to eighth embodiments, an example was shown in which the sheet composite 3 has a two-layer structure that comprises the upper sheet 30 and the lower sheet 31, but the application of the present invention is not limited to such an example. The sheet composite 3 may have a multiple-layer structure that comprises three or more sheets.
As mentioned above, the present invention is useful for a midsole structure for an athletic shoe that can improve cushioning properties and a touch on the foot and that can enhance a propulsion force during exercises.
Those skilled in the art to which the invention pertains may make modifications and other embodiments employing the principles of this invention without departing from its spirit or essential characteristics particularly upon considering the foregoing teachings. The described embodiments and examples are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. Consequently, while the invention has been described with reference to particular embodiments and examples, modifications of structure, sequence, materials and the like would be apparent to those skilled in the art, yet fall within the scope of the invention.

Claims

What is claimed is:

1. A midsole structure for an athletic shoe comprising:

a midsole body that is made of foamed synthetic resin; and

a sheet composite extending at least from a ball of a foot portion to a toe portion in said midsole body and comprising a plurality of foamed rubber sheets that are overlapped and shifted in a longitudinal direction,

wherein said sheet composite includes a single sheet at said toe portion and a plurality of sheets at said ball of the foot portion.

2. The midsole structure according to claim 1, wherein said midsole body includes a stepped concave portion that is open to a foot-sole-contact-surface side and that has a difference in level in the longitudinal direction, and said sheet composite is housed in said concave portion.

3. The midsole structure according to claim 1, wherein said midsole body includes a stepped concave portion that is open to a ground-contact-surface side and that has a difference in level in the longitudinal direction, and said sheet composite is housed in said concave portion.

4. The midsole structure according to claim 1, wherein said midsole body includes a stepped concave portion that passes through said midsole body in a thickness direction and that has a difference in level in the longitudinal direction, and said sheet composite is housed in said concave portion.

5. The midsole structure according to claim 1, wherein said midsole body includes a stepped inner space that has a difference in level in the longitudinal direction and said sheet composite is housed in said inner space.

6. The midsole structure according to claim 1, wherein said sheet composite is disposed at a forefoot portion of said midsole body.

7. The midsole structure according to claim 6, wherein said sheet composite is disposed at a heel portion of said midsole body.

8. The midsole structure according to claim 1, wherein said sheet composite extends from a heel portion through a midfoot portion to a forefoot portion of said midsole body.

9. The midsole structure according to claim 7, wherein said sheet composite that is disposed at said heel portion of said midsole body is separated in the longitudinal direction from said sheet composite that is disposed at said forefoot portion of said midsole body.

10. A midsole structure for an athletic shoe comprising:

a midsole body that is made of foamed synthetic resin; and

a sheet composite extending at least from a ball of a foot portion to a toe portion in said midsole body and comprising a first sheet and a second sheet that are made of foamed rubber and that are overlapped and shifted in a longitudinal direction, each of said first sheet and said second sheet having a front end disposed on a front side thereof and a rear end disposed on a rear side thereof in the longitudinal direction,

wherein said front end of said first sheet is located in front of said front end of said second sheet at said toe portion of said midsole body.

11. The midsole structure according to claim 10, wherein said front end of said first sheet contacts said midsole body from above.

12. The midsole structure according to claim 10, wherein said rear end of said first sheet extends to the rear of said rear end of said second sheet.

13. The midsole structure according to claim 10, wherein said first sheet is disposed at a forefoot portion and a heel portion of said midsole body and said second sheet comprises a forefoot sheet portion disposed at said forefoot portion of said midsole body and a heel sheet portion disposed at said heel portion of said midsole body, said forefoot sheet portion and said heel sheet portion are separated from each other in the longitudinal direction.