More specifically, the present invention is directed to an airbag for shoe soles comprising a part exhibiting a shock absorption function according to externally applied force and an elastic part restored by resilience, which is advantageous in terms of excellent shock absorption function and high functionality.

PRIOR ART With improvement of living conditions, variously designed shoes have been produced as demands of users have changed. In addition, diverse shoes suitable for use in special purposes have been prepared. However, structures of most shoes are substantially the same.

Referring to Fig. 1, there is shown a shoe 1 comprising a shoe sole and an upper leather 4 attached to an upper portion of the shoe sole. The shoe sole includes an outsole 3 forming a bottom piece of the shoe, and a midsole 2 forming a middle layer of the shoe sole. The outsole 3 is made of rubber material for wear resistance and traction, and the

midsole 2 comprises a foamed structure of various synthetic resin materials.

In order to keep pace with the trends of the times, kinds of the shoes are varied and shoe materials for performing specific functions are under development. For instance, the midsole 2b should be excellent in shock absorption and restoring functions to reduce shock transferred to the human body upon stepping on the ground.

Further, upon wearing the shoe for a long time, such a midsole should be light to decrease fatigue of the user.

Accordingly, various materials satisfying the above conditions have been developed. With the aim of performing the above functions, an additional member may be inserted into the shoe. In this regard, members such as an airbag are used for shoes requiring high functionality.

The airbag, which is formed to a bag shape having air filled therein, is disposed inside the shoe sole and functions to absorb shock according to externally applied force. However, currently used airbags have the following problems.

First, a shock absorbing function is inferior.

Generally, an airbag should be sufficiently strong relative to external force so that shock applied during physical exercise is uniformly distributed. Additionally, the airbag should be made of high hardness material at least 1 mm in

thickness to prevent breakage of the airbag due to shock.

Thus the airbag made of material having such hardness and thickness may not break by the applied force, but is lowered in shock absorption function.

Second, the airbag having increased shock absorption function is decreased in resilience, and thus resistance to external force is weak and the airbag may be easily broken.

So, such an airbag is difficult to use for a long-term period.

DISCLOSURE OF THE INVENTION Accordingly, it is an object of the present invention to alleviate the problems encountered in the prior art and to provide an airbag for shoe soles, which is advantageous in terms of increased shock absorption function, ventilation function practicable even with no additional pumps, and enhanced elastic force with high resistance to external force.

To accomplish the above object, there is provided an airbag for shoe soles, as a cushion member mounted into a shoe sole, comprising a dual structure of an external airbag having air filled therein, and at least one internal airbag, coming in contact with a top face and a bottom face of the external airbag in a longitudinal direction of the external airbag, forming a separate internal space and having an internal air pressure lower than that of the external airbag.

Preferably, a plurality of perforated vents are formed through the top face of the external airbag coming in contact with the internal airbag, and the wall of the internal airbag is thicker than that of the external airbag.

Therefore, a dual airbag structure having different internal air pressures provides increased shock absorption and resilience.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side view showing a perspective view of a general shoe ; Fig. 2 is a perspective view showing each part for use in preparation of a cushion member according to a primary embodiment of the present invention; Fig. 3 shows schematically the cushion member according to the primary embodiment of the present invention; Fig. 4 shows the cushion member of the present invention; and Fig. 5 shows schematically a cushion member according to a secondary embodiment of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION With reference to Fig. 2, there is shown each part

forming a cushion member according to a primary embodiment of the present invention and associated state thereof. In addition, Fig. 3 shows schematically an inner structure of the cushion member. Fig. 4 is a perspective view of a cushion member of the present invention having fine vents formed therethrough. As shown in the drawings, the present invention is characterized by a dual airbag structure. That is to say, a separate internal airbag 10 is disposed within an external airbag 20, thus exhibiting a unique function of the internal airbag. The reason why such a dual airbag structure is used is that a conventional single airbag structure performs only a main function. In general, an airbag member should have a function of absorbing external shock to distribute such shock and be resilient for restoring to its original state. However, a shock absorption function is contrary to a restoring function by resilience, and thus a conventional single airbag structure cannot exhibit such two functions at the same time. In the present invention, a separate functional part in addition to a conventional single airbag structure is provided.

Thus, the inventive airbag is formed to have a dual structure of an internal airbag 10 for shock absorption, and an external airbag 20 for resilience.

In this regard, a thermoplastic polyurethane resin which is generally used as an airbag material is cast in the

form of tube-shaped member opened at both ends. A preparation method of such members is widely known in this field and description thereof is omitted in the present invention. This resin is cast as an internal member 10 and an external member 20. In order to exhibit superior resilience after shock absorption, the wall of the internal member 10 has a thickness of about 1-1.5 mm, which is slightly thicker than that of the external member. The wall of the external member 20 is about 0.8-1.2 mm in thickness, which is the same as in conventional airbags. This external member determines a whole outline of the airbag and is formed in the same shape as in conventional airbags.

A description will be given of a preparation process of the cushion member including the internal and external members 10 and 20, below.

The internal member 10 is disposed to a hollow inside of the external member 20, and a conductive metal rod 30 made of brass or aluminum is placed in the internal member 10.

The reason why such a conductive metal rod 30 is used is that the external member 20 is bonded to the internal member 10 by high frequency when electric current is applied to the rod.

With the intention of sealing the inner face of the external member 20 and the outer face of the internal member 10 using a high frequency generator, both ends of the metal rod 30 in the internal member 10 are charged with external electric

current, whereby member faces coming in contact with the rod 30 are sealed together by high frequency. A portion of the members 10 and 20 sealed in a longitudinal direction by high frequency is shown as a slanted-lined region in Fig. 2. As seen in Fig. 3, the outer face of the internal member 10 is bonded to the inner face of the external member 20 by high frequency. As such, there are shown a first spacing region a'surrounded by the internal member 10 and two second spacing regions b'formed at right and left sides defined by the outer face of the internal member and the inner face of the external member.

After the above members 10 and 20 are sealed together by high frequency, the rod 30 is removed, thus forming a member shown in Fig. 3. To obtain an airbag of a desired size, thusly prepared member is cut to a suitable size.

Both opened ends of the cut member are sealed by high frequency and air is introduced into an inner space of the member at the same time, to form an airbag.

Based on the first spacing region a'surrounded by the internal member 10 and the second spacing regions b'formed externally at both sides of the internal member which have different air volumes and shapes, an airbag provided with a shock absorbing part and an elastic part, which is desirable in this invention, is realized.

The first spacing region a'surrounded by the internal

member 10 is filled with a small volume of air under the condition of not exceeding an atmospheric pressure, so as to act as a shock absorbing part. When external shock is applied to an airbag member, the airbag member should be deformed enough to absorb such shock. If too much air is filled in the member, this member is not sufficiently deformed, by which resilience is not exhibited. So, the first spacing region should be maintained at an atmospheric pressure. In some cases, fine vents p'may be formed through a wall of the first spacing region a'defined in the internal member 10 and external member 20 sealed by high frequency, through which air inside the internal member is ventilated, as shown in Fig. 4. Since air flows out of the inner space through such vents upon being subjected to external shock, the airbag member is smoothly deformed. The wall of the internal member 10 defining the first spacing region a'is slightly thick and thus is more easily restored due to its own elasticity. Since the elasticity of the internal member 10 depends on the thickness thereof, the above member is restored to its original state within a shorter time period after deformation thereof.

In addition, right and left second spacing portions b' defined between the outer wall of the internal member 10 and the inner wall of the external member 20 are filled to a pressure of 2-2.5 kg, which is the same as in conventional

airbags, to form an elastic part. Hence, elasticity of the above second spacing regions b'is maintained at the same level as that of conventional airbags.

Meanwhile, there exist several methods for introducing air into the first and the second spacing regions a'and b'.

As the simplest introduction method, after one end of such regions is sealed by high frequency, the other end is also sealed by high frequency, while only a vent having a size capable of introducing air is excluded from a high frequency sealing. Through such a vent, air required for each spacing region is introduced. After completion of air introduction, the vent is completely sealed by high frequency. Otherwise, both ends are firstly sealed, and air is introduced using a syringe into each spacing region, after which a through-hole perforated by the syringe is sealed by high frequency.

Moreover, since the first spacing region a'is preferably under an atmospheric pressure, it may be maintained at an atmospheric pressure even with no additional introduction of air. The introduced amount of air is controlled by the thickness of the internal member 10.

Turning now to Fig. 5, there is shown a schematic structure of a cushion member according to a secondary embodiment of the present invention.

In the case of the primary embodiment as mentioned above, the sealed portion between the internal member 10 and

the external member 20 is continuously formed, and the second spacing regions b'defined externally at both sides of the internal member are independently formed.

But, to form the structure of the secondary embodiment, a sealing process between an internal member 10 and an external member 20 by high frequency is discontinuously performed, and both of second spacing regions b'formed externally at right and left sides of the internal member may be mutually communicated.

Such discontinuous sealing between the members may be performed by inserting a metal rod 30 having a roughened surface into the internal member, thus depressed portions of the rod and the inner face of the internal member not coming in contact with each other.

Thusly prepared cushion member is advantageous in that even though air is introduced through only one inlet, the whole inner space including the second spacing regions is filled with air.

In addition, a further embodiment of a cushion member of the present invention is described, below.

This embodiment uses a blow molding process used in preparation of conventional airbags, instead of high frequency sealing of the internal and external members. In the blow molding process, a molten resin solution extruded in tube-shaped form is injected between the two halves of an

open blow mold provided with an airbag structure, followed by inflating the molten solution inside the mold cavity. As such, such a molten solution is instantaneously attached to right and left walls of the mold. After a cooling process, an airbag is obtained. A resin injection molding by a blowing process is generally used in preparation of airbags as well as hollow balls, plastic bottles, etc. In this embodiment, in order to form a first spacing region in an internal member and second spacing regions at external right and left sides of the internal member, a mold split into right and left spacing regions centering around a separate spacing region is provided, in which an inside of such a mold is designed to have a shape complementary to an outer shape of a desired airbag. As soon as a tube-shaped parison extruded from an extruder is injected into such a mold, it is inflated inside the mold. In the closed mold, while the hot parison is cooled, an airbag is formed in accordance with an inner shape of the mold. Thus, this blow method is advantageous in not requiring an additional high frequency sealing process.

The first and the second spacing regions are formed while being separately inflated in the mold, thereby producing an integrated airbag without using the internal member and the external member as stated above. A function of thusly prepared cushion member is described, below.

The cushion member, which is inserted into a midsole of a shoe, is subjected to shock according to physical exercise of a wearer. According to such shock, a first spacing region a'forming a shock absorbing part is deformed to distribute the shock. A relatively small volume of air is stored in the first spacing region a'for shock absorption. In the case where fine vents p'are formed, while the shock absorbing part discharges air through the vent, it is deformed.

Because of such deformation, shock applied to the foot of the wearer is absorbed.

The shock absorbing part a'comprising a thick wall exhibits elasticity to restore its original state within a short time. In addition, elastic parts formed externally at both sides of the shock absorbing part are restored by resilience. Thus, the shock absorbing part is elastically restored immediately after shock absorption, and second spacing regions acting as the elastic parts are restored by resilience. As such, the shock absorbing part is restored while air is again filled through fine vents. Air in the first spacing region acting as the shock absorbing part functions to ventilate the inside of the shoe whenever shock is applied, and thus may perform a pumping function even without an additional check valve.

A series of deformations of the shock absorbing part and restoring of the elastic part are repeatedly performed by

applied shock when the wearer engages in any physical activity. That is to say, through such a repeated procedure of shock absorption and elastic restoration, the applied shock is uniformly distributed, whereby external shock is not transferred to the wearer. Thus, the wearer feels much less fatigue.

Further, in the case where two airbags provided at each of a front portion and a rear portion of a shoe are connected, the shock absorbing part comprising the internal member of each airbag exhibits more desirable functions. In conventional airbags, each airbag is connected through an additional pump, to which a hose or check valve is attached to circulate air through the airbag. However, in the airbag of the present invention, air may be effectively circulated through the inventive airbag according to external shock even without an additional pump. So, the inventive airbag is advantageous in terms of low preparation cost due to not requiring hoses or check valves, and the use of the first spacing region functioning as a semi-permanent pump.

As described above, the present invention provides an airbag comprising one shock absorbing part, but is not limited thereto. Such an airbag according to the primary embodiment may be modified to have a plurality of the internal members within the external member, in order to provide multiple shock absorbing parts and elastic parts.

Also, in a blow molding process according to the secondary embodiment, airbags having various shapes of shock absorbing part and elastic part may be prepared by varying an inner structure of a mold upon performing the blow molding process.

INDUSTRIAL APPLICABILITY According to the present invention, an airbag equipped with a shock absorbing part and an elastic part is provided as a cushion member for shoe soles, and functions to effectively absorb and to distribute external shock.

The airbag of the present invention is advantageous in light of high functionality and reduced preparation cost due to a simple manufacturing process.

Further, regions constituting the shock absorbing part and the elastic part are separately formed in the airbag, which are visually confirmed with the naked eye, thus accomplishing a high class of finished articles.

The present invention has been described in an illustrative manner, and it is to be understood that the terminology used is intended to be in the nature of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.