WO2010058876A1

WO2010058876A1 - Thermoplastic polyurethane foam film

Info

Publication number: WO2010058876A1
Application number: PCT/KR2008/007553
Authority: WO
Inventors: Hee-Dae Park
Original assignee: Hee-Dae Park
Priority date: 2008-11-20
Filing date: 2008-12-19
Publication date: 2010-05-27
Also published as: KR20100056629A; KR100995452B1

Abstract

The present invention develops a method for extruding a foam film through a T-die extruder, and can manufacture a single-layer foam film and a multi-layer film of two layers or three layers constituted of a foam layer and a non-foam layer. In particular, the single-layer film has troublesomeness requiring lamination of a non-foam film for actual use, but a top layer of a multi-layer foam film constituted of two layers or three layers is co-extruded as a non-foam layer, thus getting a lamination work unnecessary.

Description

THEBMOPIASTIC POLYURETHANE FOAM FILM

Technical Field

The present invention relates to a method for manufacturing a high frequency welding Thermoplastic

PolyUrethane (TPU) film used in the various industrial fields. More particularly, the present invention relates to a method for manufacturing a high frequency welding TPU foam film, for manufacturing a single-layer film constituted of a foam layer or a multi-layer film constituted of a foam layer and a non-foam layer in an extrusion method to realize the lightweight and surface uniformity of a TPU film, and a TPU foam film manufactured by the method.

Background Art

As well known in the art, the shoe industrial fields use various materials for ornament of shoes upper. Particularly, in recent years, a technology for screen printing a polyvinyl chloride or polyurethane film in various colors and then welding the printed film to shoes upper using a high frequency welding method has been widely used. This high frequency work enables a brilliant design of a shoe and enables a design of a three-dimensional effect, thus making a great contribution to advanced shoes. However, a polyvinyl chloride film has been much used by reason of a low manufacturing cost but, in recent years, its use is very strictly limited because of environmental regulation getting more serious. As a solution to this, Thermoplastic PolyUrethane (TPU) films have been much used. TPU is a very excellent material that makes it possible to manufacture films of various ranges of shoreness without using plasticizer and can keep excellent elasticity and durability even at very low temperature.

Such TPU is excellent in physical property, but its relatively high price is a burden to the cost of shoe manufacture. Also, polyurethane film materials have a high specific gravity of about 1.2 and thus, if a large quantity is used, it causes an increase of the whole weight of a shoe, having bad influence on the recent trend of shoe lightweight.

Meantime, in recent years, many attempts have been made to provide a solution to disadvantages of a price and specific gravity of a TPU film. Among them, attempts have been made to lower a specific gravity by foaming a film using a foam in a TPU film manufacturing process. In actual, these products have been manufactured and used. However, these are all limited to film manufacturing based on a calendar process. The thus manufactured foam film is not uniform in surface and thickness, thus involving many limitations of use in which direct use is difficult and a non-foam film should be necessarily laminated for use. In addition, in most high frequency welding processes, there is few case of using only a film itself, and its surface is screen printed and brilliantly ornamented and then only a defined part is welded and adhered through a high frequency work. If a TPU film has a coarse surface, a printing work is not smoothly performed and, even after a high frequency work, a surface is not clean, thus disadvantageously causing product defects in great quantities.

Description of Drawings FIG. 1 is a schematic diagram illustrating a cylinder, an adapter, and a dice of a construction of a T-dice extrusion device for manufacturing a multi-layer Thermoplastic PolyUrethane (TPU) foam film according to the present invention; FIG. 2 is a diagram illustrating a multi-layer TPU foam film according to an exemplary embodiment of the present invention; and

FIG. 3 is a diagram illustrating a construction of a multi-layer TPU foam film according to another exemplary embodiment of the present invention. Disclosure

Accordingly, the present invention is directed to a Thermoplastic PolyUrethane (TPU) foam film that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.

An object of the present invention is to manufacture a high frequency welding TPU film through T-die extrusion not a calendar process while foaming TPU using a foam for TPU lightweight, and provide not only a method for manufacturing a TPU film constituted of a single layer but also a manufacturing method of a high-frequency welding TPU foam film for foaming only a middle layer or bottom layer without foaming a top layer, thus being able to manufacture a multilayer foam film whose surface smoothness is very excellent, and a TPU foam film manufactured by the method.

Another object of the present invention is to provide a method for manufacturing a TPU foam film by a single work by co-extruding, not laminating, a multi-layer film through a multi-layer film extruder, and a TPU foam film manufactured by the method.

A further object of the present invention is to provide a method for manufacturing a high frequency welding TPU foam film, for realizing not only lightweight of a TPU film but also uniformity of a surface and thickness of the film, and a TPU foam film manufactured by the method.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, there is provided a method for manufacturing a high frequency welding Thermoplastic PolyUrethane (TPU) film using a general T-die extruder having a plurality of chambers and having a cylinder, an adapter, and a dice installed in each chamber. The method includes filling each chamber with TPU, filling remaining chambers excepting one chamber among the chambers with auxiliary workability controlling resin such as Styrene-Butadiene- Styrene (SBS) copolymer, Ethylene-VinylAcetate (EVA) copolymer, and Styrene-AcryloNitrile (SAN) copolymer and a foam, foaming the TPU, simultaneously extruding the foam TPU and non-foam TPU by the T-die extruder, and forming a top layer as a non-foam layer and forming a bottom layer as a foam layer.

The high frequency welding TPU film may have a specific gravity of 0.6 to 1.1.

An auxiliary workability controlling resin such as SBS copolymer, EVA copolymer, and SAN copolymer may control a viscosity of extruded resin by 5 to 20 weight parts for 95 to 80 weight parts of the TPU. hereinafter, exemplary embodiments of the present invention will be described in detail with reference to accompanying drawings. In a detailed description below, a typical exemplary embodiment of the present invention will be provided to achieve the aforementioned technical solution. Other possible exemplary embodiments of the present invention are substituted with a description of a construction of the present invention. An exemplary embodiment of the present invention is to realize curing of a high frequency welding Thermoplastic PolyUrethane (TPU) film frequently used in a shoe manufacturing process, and also realize a method for manufacturing a high frequency welding TPU foam film, for manufacturing not only a single-layer film foamed and lighted but also a multi-layer foam film whose surface smoothness is very excellent by selectively foaming only a middle layer or bottom layer excepting a top layer, thus reducing a specific gravity of the whole film. For this, a foam for foaming TPU when manufacturing the TPU into a high frequency welding film should be disclosed in detail and in addition, a detailed composition constituting a TPU film together with the foam should be described. A detail of an extrusion condition for manufacturing a TPU foam film in an extrusion (i.e., co-extrusion) method using a general T-die extruder should be disclosed. Particularly, a composition of a TPU foam film constituted as a multiple layer as aforementioned should be disclosed in detail.

An exemplary embodiment of the present invention uses a general capsule type foam that is commercialized and is in use. The foam contains organic materials having a low boiling point at its interior and its exterior is protected with an acrylic or vinyl resin capsule. In general, the foam has a capsule size of a few microns or less, and a variety of foam products depending on a foaming start temperature and a foaming maximum temperature have been marketed. An exemplary embodiment of the present invention selects and uses a foam that can be used in a TPU film extruding process among the foam products. In detail, an exemplary embodiment of the present invention uses a foam whose foaming start temperature is 120 ⁰C or more and whose foaming maximum temperature is within 150 ⁰C to 180 ⁰C.

Also, a method for manufacturing a film according to an exemplary embodiment of the present invention manufactures a film in an extrusion method using a T-die extruder not in a film process using a conventional calendar, and uses a multilayer extruder for extruding a two-layer film as well as a single-layer film. In detail, an exemplary embodiment of the present invention uses a multi-layer extruder for co- extruding a maximum three-layer film. A conventional single- layer extruder is unreasonable in that extrusion and lamination should be repeated several times to manufacture a multi-layer film. A multi-layer extruder used in an exemplary embodiment of the present invention is a very efficient manufacturing device that can solve such repetitive extrusion at a time. That is, it is a multi-layer T-die extruder that can simultaneously extrude a film of each of layers having different functions and thus finally make a single film having a combined function of them. The multi-layer T-die extruder is well known in the art and thus, its detailed description is omitted in an exemplary embodiment of the present invention. In addition, a method for manufacturing a multi-layer film using the extrusion device has been disclosed in detail in Korean Patent Publication No. 10-2007-0113542 entitled "METHOD FOR MANUFACTURING MULTI-LAYER SHEET HAVING COLOR TPU LAYER AND MULTI-LAYER SHEET MANUFACTURED IN THE METHOD" filed on May 25, 2006 by this applicant and published on November 29, 2007.

An exemplary embodiment of the present invention uses TPU materials including not only real TPU but also recycling TPU that is a recycle of a TPU film of a scrap state generated through a variety of paths after film processing. The recycling TPU has been described in detail in Korean Patent Application No. 10-2008-113102 filed on November 14, 2008 by this applicant. Further, a method for manufacturing the recycling TPU is briefly described below. After pulverizing scrap generated in a high frequency process, the method extrudes the pulverized scrap while eliminating foreign materials, thus manufacturing the pulverized scrap in a pellet form. After mixing the scrap pellet with TPU that is raw material, the method extrudes the mixture while eliminating foreign materials, thus manufacturing recycling TPU.

An exemplary embodiment of the present invention is described in detail below and does not intend to limit the scope of the present invention.

A first exemplary embodiment of the present invention provides a method for manufacturing a TPU foam film constituted of a single layer. Table 1 shows a detail of a composition and mixture ratio of each layer when manufacturing the TPU film.

Table 1

Top layer Middle layer Bottom layer

Here, SBS denotes Styrene-Butadiene-Styrene copolymer. The SBS is added to increase a viscosity of resin so as to prevent a problem resulting from low viscosity during a production process such as a problem of thickness control because a viscosity of resin is excessively reduced after foam reaction. For extrusion viscosity improvement, an input of SBS of 5 weight parts or more (at this time, TPU is of 95 weight parts or more) is required. When SBS exceeds 20 weight parts (at this time, TPU exceeds 80 weight parts) , product turbidity increases due to a failure of compatibility with TPU, thus causing poor appearance. 15 weight parts are most appropriate.

This is identically applied to each of exemplary embodiments of the present invention below. In addition to SBS, Ethylene-VinylAcetate copolymer (EVA) , Styrene- AcryloNitrile copolymer (SAN) , etc. can be used for the same purpose. Surely, a thickness control problem can be solved at the time of product production by using TPU itself having high viscosity without using SBS, EVA, SAN, etc. In more detail, the thickness control problem resulting from viscosity reduction can be solved by using TPU whose melt index is 7g/10min or less at 175 degrees and 2.16kg weight. That is, production is possible even without using SBS and, at a higher melt index, supplementary SBS is used, thus being able to achieve a viscosity increase effect.

An anti-yellowing master batch is of a Ultra-Violet (UV) absorber of 20%, an anti-oxidant of 20%, and TPU of 40%. Generally, the anti-yellowing master batch is used within a range of 1 to 5 weight parts and, most desirably, is used within 2 to 4 weight parts. The white-color pigment master batch is of TiO₂ of 40%, an anti-oxidant of 1%, and TPU of 59%. The anti-yellowing master batch and white-color pigment master batch constituted of such compositions are identically used in each of exemplary embodiments of the present invention below. A foam is of a capsule type as above. The foam is slightly yellowed in color because of its characteristic and thus, its final product appearance gives feeling as if it is yellowed. Thus, in order to reduce such a phenomenon, an exemplary embodiment of the present invention slightly adds a white-color master batch to a middle layer for improvement.

A mixture constituted of the above compositions is filled in each chamber installed in a general three-layer film extruder (i.e., a well-known multi-layer T-die extruder) . After that, the mixture is foamed while being simultaneously extruded, thus manufacturing a single-layer foam film. Table 2 shows an extrusion temperature condition of the extruder. Because a top layer, a middle layer, and a bottom layer of a TPU film have the almost similar mixing conditions, works are performed in the same temperature condition.

Table 2

Adapter

Cylinder (^c C) Dice (⁰C) (⁰C)

Top layer 170 175 180 185 185 185 180 180 180 180 180

Middle layer

Bottom layer Same temperature as top layer

As shown in FIG. 1, a cylinder, an adapter, and a dice have heaters installed in each section. In detail, the cylinder is divided into four parts for heater installation, the adapter is divided into two parts for heater installation, and the dice is divided into five parts for heater installation. The reason of installing a heater and differentiating temperature at each section is to improve workability. In detail, it is to prevent hardening of resin at both end parts, thus enabling a smooth extrusion of molten resin. A single-layer TPU film manufactured according to the above compositions and extrusion temperature condition is of a shape in which both surfaces are identically foamed and thus a surface is partially opened. The TPU film is difficult for single direct use and, desirably, a non-foam TPU film is laminated and is used after one surface is covered.

The single-layer TPU film shows a physical property enough to avoid a problem of a use for high frequency- welding. This is shown in Table 3 in detail. In actual, upon extrusion, a non-foam film is laminated for use in a high frequency process, thus getting a surface smooth. On this surface, printing is performed and then high frequency work is performed. After the high frequency work, a very clean surface is maintained, thus providing excellent appearance.

Table 3

A second exemplary embodiment of the present invention provides a method for manufacturing a TPU foam film constituted of a single layer, and is to obtain the maximum foam rate by maximally increasing a quantity of foam compared to the first exemplary embodiment of the present invention. Table 4 shows a detail of a composition and mixture ratio of the single-layer TPU foam film.

Table 4

In the second exemplary embodiment of the present invention, extrusion is performed in the same extrusion temperature condition as in the first exemplary embodiment of the present invention, and its test result is shown in Table

5.

Table 5

A third exemplary embodiment of the present invention provides a method for manufacturing a TPU foam film constituted of a multiple layer, and is to selectively foam only a middle layer and a bottom layer without foaming a top layer. Table 6 shows a detail of a composition and mixture ratio of each layer when manufacturing the multi-layer TPU foam film.

Table 6

Table 7 shows an extrusion temperature condition for extruding a three-layer TPU foam film in the mixing condition of Table 6.

Table ^' 7

Cylinder (⁰C) Adapter (°C) Dice (° C)

Top layer 167 172 178 178 182 182 178 178 178 178 178

Middle layer 170 175 180 185 185 185 180 180 180 180 180

Bottom layer 170 175 180 185 185 185 180 180 180 180 180

As shown in Table 7, a mixture of a top layer is not much different from those of a middle layer and a bottom layer and thus, extrusion is performed within an almost similar range.

The thus manufactured multi-layer TPU foam film is already covered with a non-foam film and thus, a separate non-foam film laminating process is not required. A result of high frequency welding after a printing work on a top layer is a very clean surface and shows a very excellent appearance.

Meantime, as shown in FIG. 2, the multi-layer TPU foam film manufactured in the mixing condition and extrusion temperature condition has a construction in which the top layer is constituted of a non-foam layer and the middle layer and bottom layer are constituted of foam layers. Table 8 shows a detail of a physical property of the multi-layer TPU foam film.

Table 8

A fourth exemplary embodiment of the present invention also provides a method for manufacturing a TPU foam film constituted of a multiple layer, and is to about double increase a quantity of use of a foam compared to the third exemplary embodiment of the present invention, thus reducing a specific gravity a little more. Table 9 shows a detail of a composition and a composition ratio of the multi-layer TPU foam film, and extrusion is performed in the same extrusion temperature condition as in the third exemplary embodiment of the present invention.

Table 9

As above, a quantity of use of a foam increases, thus more reducing specific gravity, but a top layer also is not foamed and thus can keep a very clean state and its test result is shown in Table 10 in detail.

Table 10

<Fifth Exemplary Embodiment> A fifth exemplary embodiment of the present invention is to evaluate a minimum specific gravity producible with a maximum foam input. Table 11 shows a composition and mixing ratio of a multi-layer TPU foam film, and Table 12 shows a physical property of the multi-layer TPU foam film. An extrusion temperature condition is the same as in the third exemplary embodiment of the present invention.

Table 11

Table 12

As the test results of the first to fifth exemplary embodiments of the present invention, a conventional specific gravity of 1.20 of a film can reduce to 0.70, and more foam input leads to a failure of making excellent products because a difficulty to input raw materials into an extruder and a poor product appearance caused by excessive foam.

Each of exemplary embodiments below provides a detail of a composition and mixing ratio, an extrusion temperature condition, and a test result when manufacturing a multi-layer TPU foam film using the above recycling TPU.

In a sixth exemplary embodiment of the present invention, recycling TPU is polyurethane resin that is a collection and recycle of scrap generated in a high frequency welding process of a shoe manufacturing process. When being repeatedly used, polyurethane is deteriorated in its physical property due to yellowing and anti-hydrolysis because of its characteristic. Therefore, the polyurethane resin is separately manufactured by mixing real TPU at a predetermined rate. Because of the scrap characteristic, the recycling TPU contains foreign materials such as ink in large quantities and thus is in an opaque state. Thus, the trend has no yellowing when using real TPU, thus getting a use of a white- color master batch unnecessary.

Thus, in an exemplary embodiment of the present invention, a middle layer and a bottom layer have the fully same mixture. Surely, according to need, the middle layer and the bottom layer can have a different mixture without limit. Table 13 shows a detail of a mixing ratio when using recycling TPU.

The recycling TPU is slightly different from real TPU in extrusion temperature. However, the recycling TPU does not always have the same temperature condition as shown in Table 14, and a variation always exists more or less depending on a scrap state. Table 14 below provides an extrusion temperature condition when using the recycling TPU.

Table 14

When using the recycling TPU as above, there is a little change of a tensile strength or elongation of a foam film, but there is no problem in use for high frequency welding. Table 15 shows a detail of a physical property of a multi-layer TPU foam film according to the sixth exemplary embodiment of the present invention.

Table 15

A seventh exemplary embodiment of the present invention is to use recycling TPU and increase a content of foam. Table 16 shows a mixing ratio of each composition, and Table 17 shows a detail of a test result. Extrusion is performed in the same extrusion temperature condition as in the sixth exemplary embodiment of the present invention.

Table 16

Table 17

A TPU foam film extruded with the mixing ratio can more reduce specific gravity similarly with a case using real TPU of the fourth exemplary embodiment of the present invention. A product appearance is excellent because a top layer is covered with a non-foam layer.

In an eighth exemplary embodiment of the present invention, a multi-layer TPU foam film is manufactured using colorless recycling TPU and its mixing ratio is shown in Table 18. Extrusion is performed in the same extrusion temperature condition as in the third exemplary embodiment of the present invention.

Table 18

Among recyclable TPU materials, some uses colored scrap referred in the sixth and seventh exemplary embodiments of the present invention and other uses scrap being able to make a colorless film (i.e., a transparent or semitransparent film) because of more cleanness and no mixing of foreign materials. In the eighth exemplary embodiment of the present invention, such colorless scrap are used to make recycling TPU. In particular, this experiment uses recycling TPU manufactured with scrap generated for shoe shock-absorbing materials during an airbag manufacturing process.

The eighth exemplary embodiment of the present invention separately manufactures the colorless recycling TPU by, upon recycling, mixing a constant quantity of real TPU with scrap like the colored recycling TPU referred in the sixth and seventh exemplary embodiments of the present invention. Also, in the eighth exemplary embodiment of the present invention, yellowing tendency can be felt because of transparency or semitransparency as in the first exemplary embodiment of the present invention. Thus, a white-color master batch is added.

In the eighth exemplary embodiment of the present invention, recycling TPU uses scrap generated during an airbag manufacturing process. Polyurethane used herein is generally within a range of shoreness of 9OA or more or less. Thus, the polyurethane has much higher modulus than polyurethane having the shoreness of 85A or more or less of the above exemplary embodiments of the present invention. Also, a product appearance is very excellent as in the above exemplary embodiments of the present invention, and there is no particular problem even at a high frequency work after a printing work, and workability is excellent. Table 19 shows the test result of the eighth exemplary embodiment of the present invention.

Table 19

A ninth exemplary embodiment of the present invention is to co-extrude TPU whose only middle layer of the whole film is foamed and top layer and bottom layer are not foamed.

Table 20

As in the above exemplary embodiment, a top layer surface is not foamed and thus smooth, while a bottom layer surface is somewhat coarse because of a foam layer and its foamed state can be directly identified with the naked eye. Unlike this, in the ninth exemplary embodiment, a film manufactured keeps smoothness at its both surfaces.

Table 21

In the high frequency welding multi-layer foam films exemplified in the above exemplary embodiments of the present invention, lamination with a previously manufactured film having a different function for additional functionality in an extrusion step is possible. As an example, a high frequency welding multi-layer foam film in which a foam film coming out of a T-die is laminated with a previously manufactured hot melt film and thus a hot melt layer is added to a lowermost layer can be manufactured. In the actual spot of high frequency work, it is frequent that an adhesive is coated on one surface of a high frequency film to increase a high frequency adhesive force before high frequency work and then, the high frequency work is executed, thus improving the adhesive force. There is an advantage of being able to increase a high frequency adhesive force by laminating a hot melt to a lowermost layer of a high frequency film in an extrusion step and also, more save a process cost through lamination in the extrusion step than in a process of lamination after extrusion completion. While the present invention has been described and illustrated herein with reference to the preferred embodiments thereof, it will be apparent to those skilled in the art that various modifications and variations can be made therein without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention that come within the scope of the appended claims and their equivalents .

Industry Using Possibility

A high frequency welding Thermoplastic Polyurethane (TPU) film according to an exemplary embodiment of the present invention can be lighted in weight 20% or more, and can completely solve' a problem of a conventional TPU foam film that is a surface non-uniformity phenomenon. By this, it is possible to manufacture a high frequency welding TPU foam film of a low specific gravity that is very suitable as a high-frequency shoe material.

Also, an exemplary embodiment of the present invention is a technology identically applicable to a recycling polyurethane resin as well as a real polyurethane resin, and has an advantage of being able to achieve remarkable cost saving and resource recycling.

Claims

1. A method for manufacturing a high frequency welding Thermoplastic PolyUrethane (TPU) film using a general T-die extruder, the method comprising: foaming TPU; extruding the TPU by the T-die extruder at a time; and manufacturing a foam TPU film.

2. The method of claim 1, wherein the film is comprised of a multiple layer, a top layer is formed as a non-foam TPU layer, and a bottom layer below the top layer is formed as a foam TPU layer.

3. The method of claim 2, wherein the top layer is formed by extruding TPU, and wherein the bottom layer is formed by mixing and extruding TPU, auxiliary workability controlling resin such as Styrene-Butadiene-Styrene (SBS) copolymer, Ethylene-

VinylAcetate (EVA) copolymer, and Styrene-AcryloNitrile (SAN) copolymer, and a foam.

4. The method of claim 3, wherein the foam contains organic materials having a low boiling point at its internal and its external is protected with an acrylic or vinyl resin capsule.

5. The method of claim 3, wherein the auxiliary workability controlling resin such as SBS copolymer, EVA copolymer, and SAN copolymer controls a viscosity of extruded resin by 5 to 20 weight parts for 95 to 80 weight parts of the TPU.

6. The method of any one of claims 1 to 5, wherein the film has a specific gravity of 0.6 to 1.1.

7. The method of any one of claims 1 to 5, wherein the film manufactured using recycling TPU or using together with the auxiliary workability controlling resin such as SBS copolymer, EVA copolymer, and SAN copolymer has a specific gravity of 0.6 to 1.1.

8. The method of any one of claims 1 to 5, wherein an additional layer is formed at a bottom layer or top layer by laminating a high frequency welding TPU foam film, which is extruded through a T-die in the T-die extrusion step, with a previously manufactured hot melt or TPU foam film.

9. A method for manufacturing a high frequency welding Thermoplastic PolyUrethane (TPU) film using a general T-die extruder having a plurality of chambers and having a cylinder, an adapter, and a dice installed in each chamber, the method comprising: filling each chamber with TPU; filling remaining chambers excepting one chamber among the chambers with auxiliary workability controlling resin such as Styrene-Butadiene-Styrene (SBS) copolymer, Ethylene- VinylAcetate (EVA) copolymer, and Styrene-AcryloNitrile (SAN) copolymer and a foam; foaming the TPU; simultaneously extruding the foam TPU and non-foam TPU by the T-die extruder; and forming a top layer as a non-foam layer and forming a bottom layer as a foam layer.

10. A high frequency welding Thermoplastic PolyUrethane (TPU) film, wherein a mixture of TPU, auxiliary workability controlling resin such as Styrene-Butadiene-Styrene (SBS) copolymer, Ethylene-VinylAcetate (EVA) copolymer, and

Styrene-AcryloNitrile (SAN) copolymer, and a foam, and TPU are simultaneously extruded, whereby a top layer is formed as a TPU layer and a bottom layer is formed as a foam TPU layer

11. A high frequency welding Thermoplastic PolyUrethane (TPU) film, wherein a mixture of TPU, auxiliary workability controlling resin such as Styrene-Butadiene-Styrene (SBS) copolymer, Ethylene-VinylAcetate (EVA) copolymer, and Styrene-AcryloNitrile (SAN) copolymer, and a foam, and TPU are simultaneously extruded, whereby a top layer and a bottom layer are formed as a TPU layer and a middle layer is formed as a foam TPU layer.