EP0949060A1

EP0949060A1 - Leak resistant seamed structure, method of forming same, and heat processing device for same

Info

Publication number: EP0949060A1
Application number: EP96938514A
Authority: EP
Inventors: Masami Kamiya
Original assignee: Asahi Chemical Industry Co Ltd; Asahi Kasei Kogyo KK
Current assignee: Asahi Kasei Corp
Priority date: 1996-05-07
Filing date: 1996-11-20
Publication date: 1999-10-13
Also published as: JP3253305B2; NO311914B1; WO1997042024A1; NO985191L; NO985191D0; TW310302B; EP0949060A4

Abstract

A seamed structure formed with seams which are soak- and leak-resistant to be suitable for three-dimensionally shaped, processed products such as shoes and the like, and a method of forming the same. The seamed structure has a feature in that a face material and a back material are seamed along seam lines through a hot melt adhevise resin layer, sewing needle holes defining the seam lines are filled with a part of a resin of the hot melt adhesive resin layer, and the face material is water-proof. The seamed structure can be prepared by a method which includes the following processes: (A) a process of preparing a precursor seamed layer structure by sewing the water-proof face material and the back material at least along the seam lines with a specified hot melt adhesive resin sheet between them; (B) while pressing the seamed layer structure by means of surfaces of a specified pressure plate body, applying sufficient high-frequency voltage to melt the hot melt adhesive resin sheet, thus fluidizing only the hot melt adhesive resin sheet and having a part of the resin sheet enter and fill into the sewing needle holes which constitute the seam lines. An embodiment of a method of forming the seamed structure is disclosed together with a high-frequency heating processing device, which is suitable for processing of shoes.

Description

Field of the Invention

This invention relates to a waterproof sewn structure and a method for forming a waterproof sewn structure, especially to a sewn structure having a waterproof seam portion for making a three dimensionally shaped sewn article in which a waterproof joining seam structure is especially required such as, for example, footwear such as trekking shoes, hats or hood bodies, gloves, and rucksacks; and a method for forming the sewn structure and heat treating apparatus for the sewn structure.

Background Art

Shoes such as trekking shoes, footwears, hats or hood bodies, gloves, rucksacks are mostly made by laminating a plurality of flat sheet-like materials such as a natural leather, an artificial leather, a woven or knitted fabric, a foamed or non-foamed sheet with an appropriate softness, and joining them together by sewing at prescribed portions. Generally, these sewn products are often required to have a waterproof performance. For this reason, use is made of a waterproof sheet material for the sheet member.
In a case where a fabricated sewn article is in the form of shoes, for example, trekking shoes, a trekking shoe is a three dimensionally shaped sewn article with a specific structure and shape which is fabricated by laminating a plurality of sheet including waterproof sheet material and sewing them together. In most cases, a three dimensionally shaped sewn structure as exemplified by trekking shoes are further provided with a waterproof finish at the joining seam portion and patch seam portion. The following conventional waterproof finish have been employed singly or in combination:
(1) Application of latex or a flexible adhesive coating on the inside surface or outside surface of a joining seam portion
(2) Application of a water-leak preventive adhesive tape to the inner or outer surface of a joining seam portion
(3) Application of a water-repellent finish to the entire sewn structure.
However, none of the foregoing means does work for many situations. With application of the coating method, for example, the coated resin layer on the surface of an article such as shoes may spoil the appearance of the article, the resin layer formed inside of the shoes may spoil wears comfort. Further, the application of the coating is not advantageous because the end-use product lacks waterproofness and durability. With application of the adhesive taping technique, there is a problem similar to that encountered in the case where application of the coating is made on the inner surface of a shoe. With application of a water repellent finish, it is difficult to provide a seam portion in a shoe with a waterproof property as high as those exhibited by the sheet material for a shoe upper.
It is described in Japanese Unexamined Patent Publication (Kokai) No. 7-32510 that, in a method for providing a shoe with a seam structure with a waterproof property, the method comprises interposing a thermoplastic resin material between the laminated shoe material layers and melting the thermoplastic resin by application of heating means such as an iron, a pressing machine, a pair of rollers, a heating apparatus and the like so as to form a melted layer of adhesive resin between the laminated layers at the seam portion. The waterproof structure of the seam portion contains an intermediate layer of adhesive resin formed through melting when the whole seam portion is heated under a press after the intermediate layer adhesive resin has been sewn as it is interposed between two waterproof sheet pieces folded one on top the other. However, this method for producing a waterproof sewn structure is difficult to produce a uniform layer of melted resin along a curved surface configuration, because this method uses an iron for melting a meltable material interposed as an intermediate layer at a joining portion within the curved surface of a thick laminate structure, for example, an upper of a shoe. Besides, this method cannot produce a strong waterproof sewn structure by making the resin penetrate into the needle holes in the seam for filling the holes.
In Japanese Unexamined Patent Publication (Kokai) No. 4-269901, an attempt to prevent water penetration through shoe upper by filling the gaps formed around sewn thread holes is described. In the attempt, the shoe upper sheet is first prepared by treating with thermoplastic resin, the workpieces of the treated material are sewn together with use of a sewing thread of which the surface is treated with a thermoplastic resin, and subsequently the sewn portion is pressed. For one thing, however, the pressing by means of an electric iron in the method cannot melt the resin sufficiently, and for another thing, an amount of resin which can be applied to the surface of a thread is not sufficient to fill up the stitching needle holes of the sewn seam. It is practically impossible to fill the stitching needle holes of a seam with a sufficient amount of resin using a resin coated sewing thread, because the surface coated sewing thread will make stitching holes in the seam become large and consequently give rise to disadvantage in a practical sewing work.
With a view to obtain a variety of decorative effect on a shoe, fabrication of a shoe upper by sewing a plurality of materials as well as fabrication of shoe upper with a sewn decorative piece has become very much practised in the shoe making industry in recent years.
On the other hand, it has been widely practised that rain wear and bag are made by welding (or-fusion-bonding) material such as thermoplastic sheet, woven fabric, film and the like using a high frequency heating technique. In fusion-bonding according to a high frequency heating, it is necessary that a workpiece and the electrode are in close contact in order to attain uniform heating and fusion. Using a conventional high frequency heating technique, it is impossible to apply efficient high frequency heating to a sewn seam structure having many curved surfaces and unevenly thick walled portions.

Disclosure of the Invention

The object of the invention is to provide a sewn structure containing joining seam portion which exhibits waterproof performance.
A further object of the invention is to provide a waterproof sewn structure of which outer surface has a curved configuration, and which afford a three-dimensionally shaped sewn product, for example, shoes such as trekking shoes, footwears, hats or hood bodies, gloves, rucksacks (backpacks).
A still further object of the invention is to provide an easy and simple method for forming a waterproof seam in a sewn structure having the above mentioned curved configuration, and to provide an apparatus for carrying out the foregoing method assuredly in a simple operation.
The object of the invention can be achieved basically by a waterproof sewn structure comprising a face sheet member and a back sheet member, the members being sewn together by a seam with a hot-melt resin interposed therebetween, the sewing needle holes forming the seam filled with a portion of the hot-melt resin so that the sewing thread is embedded in the hot-melt resin, and at least the face sheet member comprising a waterproof sheet material.
In the invention, a sewn structure refers to a sewn article made by sewing cut-out sheet members of materials, for example, leather, fabric and flexible synthetic resin sheet, which are used for manufacturing shoes, footwears, hats or hood bodies, gloves and rucksacks, and the cut-out sheet member constituting outer covering or outer shell should be a waterproof sheet material. Naturally, the face sheet member constituting an article of the sewn structure should be either waterproof finished or water-repellent finished when they are permeable or semi-permeable with water.
The face sheet member can be either a member for covering the whole surface of an article, or a decorative piece, depending on the embodied mode of an article. The face sheet member is a lining material corresponding to ground material, outer covering material or the like. For example, a sheet material constituting a back sheet member can be selected in accordance with an objective use. In the case where the sewn structure is a pair of shoes, for example, use is made of a material with due consideration of properties in moisture absorption, texture, resilience and hand touch. A laminated sheet in which a flex-foamed resin sheet is laminated with either a woven fabric or a knitted fabric, may be used.
In a sewn structure in accordance with the invention, joining of a face sheet member with a back sheet member is carried out by sewing using a sewing thread. A hot-melt adhesive resin film of which the melting point is at least 90°C up to 170°C is included in a seam portion, and is disposed in a sandwich-like form along the seam line between the face sheet and back sheet members within a laminate structure, and affords a watertight layer by an application of high-frequency heating in which the hot-melt adhesive resin is selectively melted to flow in the laminate. A portion of the hot-melt resin film layer penetrates into the sewing needle holes in the face and back sheet members filling the gapped spaces of the needle holes so that the resin wraps or embeds the sewing thread in the holes.
The hot-melt resin film is used in a minimum thickness so that the above mentioned functions can be attained. However, an appropriate dimension of the thickness is selected in a range where a sewn structure is not broken by a mechanical shock or impact, for example, mechanical bending or mechanical extension, encountered in an end use article. The thickness should be as small as possible as long as the watertight function is obtained. In this way, the sewn structure according to the invention is provided with a waterproof structure for preventing penetration of water through the stitching needle holes into the interior of the sewn structure and from the outer side to the reverse side of the structure and, further, through the lapped portion of face and back sheet members into the inner of the sewn structure.
The sewn structure according to the invention can be prepared basically by a method including the following steps:
(1) a step of sewing a laminate in which a hot-melt adhesive resin sheet is interposed along the seam line in a sandwich-like form between the face and the back sheet members made of waterproof sheet material to prepare a precursory sewn structure; a dielectric power factor of the hot-melt adhesive resin sheet being 1.7 times greater than those of the face and back sheet members; and
(2) a step of applying a high-frequency voltage to the above mentioned precursory sewn structure for melting the hot-melt adhesive resin while pressing the workpiece at least on one side thereof by an elastic sheet having a dielectric power factor of 0.002 to 0.02 and a product of dielectric constant and a dielectric power factor of 0.006 to 0.09 so that the melted thermoplastic resin sheet flow and penetrate into the stitching needle holes of the seam line where a portion thereof is filled.
The hot-melt resin sheet as referred to in the invention is a shaped article in the form of, for example, fabric and film, and is composed of a thermoplastic resin composition capable of developing an adhesive property to the face and back sheet members and the sewing thread, and can flow when it is melted in such a degree that the melted resin can penetrate into the stitching needle holes of the seam contained in the precursory sewn structure.
Further, the hot-melt adhesive resin should be a material which can be melted to flow at a temperature at which the face and back sheet members as well as a sewing thread will not be broken, or deteriorated in their mechanical properties and texture at normal temperature, and should be a material capable of being melted by means of application of a high-frequency current in a condition under which the face and back sheet members and the sewing thread are not melted.
The hot-melt resin sheet such as described above is selected from synthetic resins such as polyamide, polyesters, polyvinyl chloride, polyurethane, polyvinyl acetate and polyacrylics and the like which have a low melting point of from 90°C to 170°C. Besides, a value of dielectric power factor for the resin sheet is selected as about 1.7 times to 4.3 times greater than those of a face sheet member, a back sheet member and a sewing thread. Considering ease of handling and sewing work with hot-melt adhesive resin sheet, use is made of a hot-melt adhesive resin having a thickness of 50µ to 500µ and a basis of weight of 30 to 50 g/m² in the form of a tape or a cut-out piece having a shape similar to that of the face sheet member.
A precursory sewn structure is prepared by inserting a hot-melt adhesive resin sheet in a sandwich-like form between a face sheet member and a back sheet member, and subsequently sewing the three pieces together to form a desired seam using a sewing thread.
A precursory sewn structure (precursor of sewn structure) prepared as described above is set between a pair of flat plate electrodes disposed with the face opposing each other in parallel on a conventional high-frequency heating apparatus, and then a high-frequency voltage is applied to the electrodes in accordance with a conventionally known condition in order to make only the hot-melt adhesive sheet melt so that the melted resin penetrate into the stitching needles holes of a seam thereby forming a watertight layer along a seam line. The precursory sewn structure is preferably pressed at least on one of the surfaces in the direction of thickness by means of an interposition of an elastic pressing sheet of flexible sheet material having a dielectric power factor of 0.002 to 0.02 and a product of a dielectric constant and a dielectric power factor of 0.006 to 0.09. With the elastic pressing action of this elastic pressing sheet, the distance between the surface of the electrodes and the hot-melt adhesive resin sheet layer in the precursory sewn structure can be kept constant, and heat generation is caused to concentrate on the hot-melt adhesive resin sheet. In this way, occurrence of an uneven application of a high-frequency voltage along the rugged or rough seam line is prevented and as a result, film formation of the melted adhesive resin, penetration and filling of the melted resin flow into the stitching needle holes of a seam are promoted.
When the sewn structure of the invention is embodied in three dimensionally shaped product, for example, a shoe, it is advantageous that aforesaid step (b) includes a heating means which can finish the precursory sewn structure into a prescribed three dimensional shape. In the case where a precursory sewn structure is finished, for example, into a shoe, it is required that the precursory sewn structure is pressingly held between a conductive metal mold with the face curving along the line of a seam in a curved surface configuration of a shoe, for example, the shoe upper portion and heel portion, and a conductive metal clamp with the face opposed against the curving face of the mold, and that a high-frequency voltage is applied to the metal mold and the conductive clamp so that the an intermediate layer of hot-melt adhesive resin sheet is selectively heated to melt. In consequence, the seam line contained in the curving surface of the precursor of the sewn structure is evenly provided with an applied voltage and formation of a three dimensionally shaped sewn structure having a prescribed waterproof sewn structure can be attained without fail.

Brief Description of the Drawings

Figure 1 (A) through Figure 1 (C) are schematic illustrations of a method for forming a sewn portion of a sewn structure according to the invention.
Figure 1 (A) illustrates that a face sheet member and a back sheet member are sewn together with a hot-melt adhesive resin sheet interposed in a sandwich-like form.
Figure 1 (B) illustrates that a three layered sewn structure is formed from the three materials by sewing and Figure 1 (C) illustrates a cross section of the three layered sewn structure.
Figure 2 is a schematic illustration of a cross sectional view of a sewn portion of the sewn structure according to the invention.
Figure 3 (A) and Figure 3 (B) present an embodiment of the invention in the form of a shoe; Figure 3 (A) shows an external view and; Figure 3 (B) shows the surface of the back sheet member before a sewn structure is formed.
Figure 4 (A) through Figure 4 (C) are schematic illustrations of a heat treating apparatus for treating a sewn structure of the invention according to high-frequency heating technique.
Figure 5 shows an explanatory view of a structure of a high frequency heat treating apparatus which is suitable for heat treatment of a shoe upper workpiece according to the invention, especially a cross-sectional view of an arrangement of heating means.
Figure 6 shows a perspective illustration of an arrangement of the main segments of the high-frequency heat treating apparatus shown in Figure 5.
Figure 7 is a perspective view illustrating an operational mode in which a high-frequency voltage is applied to a precursory sewn structure in the form of a shoe set on the mold of the treating apparatus shown in Figure 6.

Best Mode for Carrying Out of the Invention

In the following, the waterproof sewn structure, a method for forming the same and a preferred apparatus for the formation are described in detail referring to the drawings.
Figure 2 illustrates a vertical cross section of a sewn portion of a sewn structure according to the invention. Sewn structure (A₁) is of a laminate structure consisting of face sheet member (2), back sheet member (3) and hot-melt adhesive resin film layer (6) adhesively put between the sheet members, and the laminate structure is fixedly secured by sewing by means of sewing threads (5) and (5'). A portion of the resin constituting the hot-melt adhesive resin layer (6) fills up or chokes up at least the cross section of holes (7) formed by sewing needles and wraps or embeds the sewing threads so that flowing of water, for example, rain water through all the sewing needle holes and overlapped portion of the back sheet member is intercepted thereby providing the sewn structure with an excellent waterproof function.
In Figure 2, the seam is generally formed by lock stitch type seam. However, similar result can be attained with use of a type of seam called special lock seam, for example, a two-needled lock stitch seam, zigzag stitch seam, inseam sewing, twin chain stitches seams including twin zigzag stitch seam, covering chain, stitches and the like.
A sewn structure of the invention can be in various forms of fabricated products. For example, a sewn structure of the invention in which leather or fabric is used as the face sheet member can make a footwear, gloves for skier, a hat and a tent which contains a sewn portion having exceeding high waterproof function.
By way of an example, a trekking shoe fabricated from a sewn structure according to the invention is shown in Figure 3. The latest fashion of trekking shoes favors shoe upper finish designs, for example, in which a plurality of workpieces for a shoe upper are joined, or in which the shoe upper is partly constituted of a decorative sheet member having the seam appearing on the shoe upper. Figure 3 illustrates a sewn structure of a trekking shoe as seen in perspective according to the invention, and the trekking shoes is produced by joining leather decorative sheet members (As), (Bs) and (Cs) as portions of shoe upper face sheet members to a back sheet member by stitching lines of seams (7). In the trekking shoe illustrated in Figure 3 (A), the decorative workpieces (As), (Bs) and (Cs) are sewn to portions (Ab), (Bb) and (Cb) of back sheet member (3) as the lining member with interpositions of hot-melt adhesive resin sheet in the form of a tape put between by means of prescribed seam (7) to prepare a precursory sewn structure to which a high-frequency heat treatment hereinafter explained is applied for molding it into a prescribed form. The sewn portions are provided with a waterproof function along the seams by virtue of formation of films of the adhesive resin during the high-frequency heat treatment. In the example, the tapes of hot-melt adhesive resin sheet which are cut in a width of 10 mm to 15 mm in conformity with the line of seam for the decorative workpieces, and the tapes are inserted with the ends flushed with the edges of decorative sheet members, and the layers are sewn together. The seam (7) which is formed, for example, by a lock stitch type sewing machine (stitching pitch 3.5 needles/cm) consists of a couple of stitching lines; one is along 1.5 mm to 32.0 mm inside from the respective edges of respective decorative sheet and the other is along 2 mm to 5.0 mm inside.
A sewn structure of the invention is produced by a step of preparing a precursory sewn structure (1) mentioned above and a step of applying a high-frequency heat treatment to the precursory sewn structure.
As illustrated in Figure 1 (A) and Figure 1 (B), precursor sewn member (A₁) of the sewn structure is prepared by placing a face sheet member (2) over a back sheet member (3) with a hot-melt adhesive resin sheet piece (6) put between and subsequently joining the overlaid pieces together by a seam to produce a sewn laminated sheet structure.
In precursory sewn structure (A₁), the hot-melt adhesive resin sheet piece (6a) is secured fixedly along the line of seam in a sandwich-like form as illustrated in Figure 1 (C). In a preparation of precursory sewn structure (A₁), disposition of a seam may be optionally determined in accordance with an article which is the objective of a precursory sewn structure. Figure 1 (B) illustrates an example of a precursory sewn structure in which a face sheet member and back sheet member are joined en bloc by means of triple lines of seams 7₁, 7₂ and 7₃.
Figure 1 (C) illustrates that a cross sectional view of the sewn portion of the precursory sewn structure (A₁), and that the seam joining the face sheet member and the back sheet member is invariably formed confining the hot-melt adhesive resin sheet. The hot-melt adhesive resin sheet contains the seam in the face allowing a sufficient margin and is preferably laid in a band-like form along the seam. It is not necessary to sew together the hot-melt adhesive resin sheet together away from a seam.
The precursory sewn structure which has been prepared as above, is then set in place between a metal mold and a metal clamp of a high-frequency heating apparatus, and is charged with a high-frequency current while being pressed in the direction of the thickness so as to charge with an applied voltage sufficient to melt and make the hot-melt adhesive resin sheet to flow, and the resultant flow of the hot-melt adhesive resin produces a skin-like film layer between the face sheet member and back sheet member, and a portion of the resin penetrates and fill every sewing needle holes of the seam thereby a waterproof structure being formed.
The high-frequency heating can be done using a conventional heating apparatus, for example, a high-frequency welding apparatus. An application of high-frequency voltage make only the hot-melt adhesive resin in the precursory sewn structure flow under a condition corresponding to what is called, an interfacial adhesion heating method.
Referring to the schematic diagram shown in Figure 4 (A) through Figure (C), a high-frequency heating system for a precursory sewn structure is illustrated. Using a high-frequency heating apparatus which comprises a press-heating unit comprising an electro-conductive mold (10) having a mold face along the face sheet member of precursory sewn structure (A₁) and an upper conductive mold (11) (this may be called as conductive clamp) for supporting or pressing the precursory sewn structure on its opposing face; a high-frequency current generating device (13) and a cable (12) for connecting the press-heating unit and the high-frequency current generating device, the precursory sewn structure (A₁) is held under uniform pressure between conductive mold (10) and conductive upper mold (11). It is important that a voltage sufficient to cause only the hot-melt adhesive resin to melt and flow is applied. Holding a precursory sewn structure as described herein means that the precursory sewn structure is closely laid with the surfaces of the face sheet member and the back sheet member between conductive mold (10) and the upper conductive mold as shown in Figure 4 (see, arrow mark). This is invariably done regardless of whether the precursory sewn structure is to be shaped into a flat piece article (Figure 4 (A) shows heating by a flat mold.) or a three dimensionally shaped article which is to be shaped into an article with a curved surface configuration using a mold with a curving mold face as shown in Figures 4 (B) and (C). Since heat should be selectively generated only at a prescribed layer by applying a voltage on the precursory sewn structure which is held in place, an elastic pressing sheet (15) is provided removably for keeping the precursor in place so as to be set either on the surface of conductive mold (10) or on upper conductive mold (11).
In designing a high-frequency heating apparatus, attention should be paid particularly to the surface shape of conductive mold (10) for holding the precursor and upper conductive mold (11). Namely, the surfaces of conductive mold (10) for holding the precursory sewn structure and conductive upper mold (11) are required to have a shape corresponding to the contours or configuration of the objective article of a precursory sewn structure, especially to have a surface shape along the outer configuration of the objective article.
When an objective article of a precursory sewn structure is, for example, a shoe, the precursory sewn structure should be heat-treated while its shaped configuration of the shoe upper portion and peripheral portions around the heal as well as its designed form along the curving surfaces of the shoe upper portions and heel portions are secured. Accordingly, the configurations of conductive mold (10) and upper conductive clamp (12) should be designed, as illustrated in Figure 4 (A), Figure 4 (B) and Figure 4 (C), in order to provide molds having a configuration capable of holding or supporting a precursory sewn structure with a plane or curved face in conformity with the configurations of an objective article of the precursory sewn structure.
Referring to Figure 5, Figure 6 and Figure 7, a preferred structure of heating apparatus for shaping a precursory sewn structure into an solid shaped article is now explained. In Figure 5 through 7, a three dimensionally shaped article is represented in the form of a shoe, and especially a precursory sewn structure which is intended to be fabricated into the shoe upper member containing the vamp, heel, quarter, the counter and toe cap before the sole is joined thereto is set on a high-frequency heat finishing apparatus. As shown in Figure 5, the high-frequency heating apparatus comprises a conductive mold (10) for setting precursory sewn structure (A₁), conductive clamps (11a), (11b) and (11c) for pressing down the seam portions of the precursory sewn structure set on the conductive mold, manually operating handles (14a), (14b) and (14c) for moving the clamps, an elastic pressing sheet (15) disposed between the conductive mold and the conductive clamps so as to contact precursory sewn structure (A₁) when the precursory sewn structure being held with the clamp, metal plate (16), and a high-frequency generating unit (13) for melting a hot-melt adhesive resin sheet contained in precursory sewn structure (A₁) by applying a high-frequency voltage on the conductive mold and the conductive clamps. Additionally, the conductive mold and the like is mounted on the frame (17) with interposition of a insulating member of Teflon, Duracon and the like as described later in reference to Figure 7.
A material for making conductive mold (10) is not limitative, if it is a material capable of conducting electricity. The mold is preferably made of aluminum in view of workability and durability. The shape of the mold is adapted to a specific kind of precursory sewn structure (A₁). Specifically, use is made of a mold having a face shape with which a sewn part to be shaped into a curved contours contained in a precursory sewn structure can be brought in contact. Dimensions of conductive mold (10) is also determined in accordance with the shape and dimensions of a precursory sewn structure. The precursory sewn structure is to be shaped into the form of a shoe, for instance, use is made of a mold having a length of 20 - 40 cm, a width of 3 - 10 cm and a height of 10 - 30 cm.
The shape of conductive clamp (11) is determined in accordance with the shape of precursory sewn structure (A₁). It is preferable that the shape of the clamp is made in such U-shaped or doughnut-shaped configuration that a sewn part contained in precursory sewn structure (A₁) can be held under pressing by applying a pressure on the outer periphery of the precursory sewn structure. Specifically, in order to melt heat fusible resin sheet (6a) contained in the precursory sewn structure through single-time application of a high-voltage on the whole surface of the precursory sewn structure having a curved surface, the clamp has preferably a shape capable of holding the precursory sewn structure in place by grasping its peripheral surface at at least three sides. The conductive clamp (11) has dimensions enough to hold the sewn part in the outer surface of the precursory sewn structure.
In the example shown in Figure 5 in which precursory sewn structure (A₁) is a shoe, it is preferable that three pieces of horizontally movable clamps (11a), (11b) and (11c) are disposed in three directions around conductive mold (10) to make a U-shaped arm arrangement and that the clamps has a total length of 50 - 80 cm, a width of 3 - 5 cm and a height of 5 - 10 cm. Material for a conductive clamp is not limitative so far as it is an electrically conductive material. A clamp made of aluminum is preferred as in the conductive mold stated above.
As a method of holding precursory sewn structure (A₁) by conductive clamps (11a), (11b) and (11c), use is generally made of a method in which the precursory sewn structure is pressed by means of manually operated levers (14a), (14b) and (14c) which are attached to the respective conductive clamps. Considering operability, the holding can be carried out automatically by applying a pressure on the respective clamps by means of air cylinders connected with a compressor. Pressing force for holding the precursory sewn structure varies depending on kind of a precursory sewn structure; the pressing force may range preferably from 1.0 - 4.0 kg/cm² in the case of making a shoe.
An elastic pressing sheet (15) is disposed between conductive mold (10) and a precursory sewn structure, or between the precursory sewn structure and conductive clamps (11a), (11b) and (11c).
Precursory sewn structure (A₁) is fitted in conductive mold (10) and an elastic pressing sheet (15) is then disposed on or under the precursory sewn structure. By means of conductive clamps (11a), (11b) and (11c), elastic pressing sheet (15) is pressed so as to absorb curvature and roughness of the surface of the precursory sewn structure and thus can contact closely with the surface of the precursory sewn structure.
Material for elastic pressing sheet (15) is not specifically limitative so long as the material is not conductive, nor fusible upon an application of a high-frequency voltage. A preferred material is an elastic resin sheet having a dielectric constant of 3.2 - 4.7, a dielectric power factor of 0.002 - 0.02 and a product of dielectric constant and a dielectric power factor of 0.006 - 0.09. Such elastic resin includes, for example, a insulating rubber sheet such as a silicon rubber sheet, a polyurethane sheet and the like, or a foamed synthetic resin sheet. Of these materials, silicon resin sheet is especially preferred in point of its resiliency (stiffness) and excellence in compressive recovery which is in a range from 4/5 - 1/10, preferably 3/5 - 1/5 in terms of a thickness change ratio when the sheet is gripped by a clamp under a load of 2 kg/cm². Elastic resin sheet (15) is preferably of the same dimensions with mold 1 in view of ease of handling, and has preferably a thickness in a range of from 3 to 5 mm in view of formation of uniform melting of hot-melt adhesive resin sheet (6a).
Metal plate (16) is disposed between a precursory sewn structure fitted to conductive mold (10) and a set of clamps (11a), (11b) and (11c), and elastic sheet (15) is disposed so that it contact the surface of the precursory sewn structure.
A precursory sewn structure is fitted into conductive mold (10) with the peripheral surface in contact with elastic pressing sheet (15). Cramped by means of the conductive clamps, the elastic pressing sheet (15) can be brought into close contact with the precursory sewn structure while smoothing out the curvature or unevenness present in the surface of the precursory sewn structure. Since metal plate (16) which is in contact with elastic pressing sheet (15) is flexible, it also can be in close contact with the elastic pressing sheet which smooths out the curvature and unevenness present in the surface of the precursory sewn structure. On the other hand, metal plate (16) contacts conductive clamps (11a), (11b) and (11c), and is charged with a high-frequency electricity from high-frequency generating device (13) so that the precursory sewn structure is brought to be heated. So long as at least a portion of metal plate (16) is in contact with clamps (11a), (11b) and (11c), namely, even in a case where the metal plate is not fully in close contact with the clamps, a high-frequency voltage can be evenly charged to metal plate (16), and in consequence, hot-melt adhesive resin sheet (6a) can be melted within the precursory sewn structure which is closely held on metal plate (16) by an elastic sheet laid between. In other words, metal plate (16) is not necessarily kept in close contact with the entire surface of the conductive clamps. It is adequate that metal plate (16) is kept in contact with a portion of respective conductive clamps (11a), (11b) and (11c).
Material for metal plate (16) is not limitative if the material is electrically conductive. Preferred materials are copper, phosphor bronze or the like in view of fitability to a curved surface and ease of charging of electricity. For convenience of handling, the dimensions of metal plate (16) is preferably conformed to a conductive clamps. Further, the thickness of metal plate (16) is preferably in a range of 1 - 3 mm so that flexibility of the plate can be ensured.
As already stated, elastic pressing sheet (15) plays a role as buffering material to precursory sewn structure (A₁) having the curved surface and rough surface and metal plate (electrode), and smooths out the curved or rough contours occurring in the surface of precursory sewn structure (A₁), and conducts heat evenly to the sewn part of precursory sewn structure (A₁) thereby preventing occurrence of non-uniform melting of the hot-melt resin sheet (6).
Figure 6 illustrates an outward view of the aforementioned high-frequency heating apparatus in reference to Figure 5. Figure 7 illustrates an operation in which precursory sewn structure in the form of a shoe workpiece is fitted into conductive mold (10) of which structure is clearly shown in Figure 6. Both the surfaces of the shoe workpiece is pressed with an elastic pressing sheet (15) put between while a high-frequency voltage is applied to the precursory sewn structure. In Figures 6 and 7, base plate (17) is a support frame on which conductive mold (10), upper conductive molds or conductive clamps (11a), (11b) and (11c) and the like means are mounted with an insulating plate (not shown) made of a material such as Teflon, Duracon and the like interposed therebetween.
As a high-frequency heat-pressing apparatus used in a method of the invention, use can be made of a conventional apparatus, for example, high-frequency welder available from Seidensha Electronics Co., Ltd.
In order to charge a precursory sewn structure with a high-frequency electric charge by applying a high-frequency voltage to the conductive mold, upper conductive molds or conductive clamps, a voltage of 3 - 5 KW is applied to the conductive mold as input terminal (positive terminal) and the conductive clamp as output terminal (negative terminal). For attaining a sufficient melt adhesion by means of hot-melt adhesive resin sheet (6a), an electric current of normally, 0.4 - 0.9A, preferably 0.7 - 0.8A is charged for a period of 3 - 18 seconds, preferably 5 - 15 seconds, although it varies in accordance with an area of sewn portion.

Examples

In the following, examples of the invention as well as a comparative example are explained. In the examples and comparative example, evaluations of the sewn structure and the like are made according to the following test methods:

(1) Measurement of water resistance

Measurement of water resistance was carried out according to the method described in JIS-L-1092 (Hydrostatic head test method).

(2) Measurement of water repellency

Measurement of water repellency was carried out according to the method described in JIS-L (Spray test method).

Example 1

Prepared are a cattle leather material finished with a fluorine-based water repellent (water resistance, 1,000 mm H₂O; water-repellency rating; 90) of a face sheet member and a waterproof laminated fabric (water resistance, 4,000 mm H₂O; water repellency, 85) for a back face sheet member. The laminated fabric was obtained by adhesively bonding a polyurethane-based resin film (50 micron thick), a polyurethane sponge (5 mm thick) and a spun-bonded fabric (trade name, Marique, available from Asahi Chemical Industry Co. Ltd.) composed of nylon 6 (50% by weight) and nylon 66 (50% by weight) having a basis of weight of 120 g/m² in the stated order, on the back side of a base fabric consisting of 100% nylon 66 fabric (fabric construction, mat weave; warp and weft yarn specification, 420d/70f × 2 ends; number of twist, 130 T/M; weave density, 50 ends/inch, 50 picks/inch).
Waterproof workpieces in prescribed shapes for making a shoe were cut out of the materials. When the waterproof fabric workpiece (back face sheet member) was laid under the cattle leather workpiece (face sheet member) for sewing together, a polyamide hot-melt resin tape (a product of Dicel Chemical Industries Co., Ltd.; Daiamid span [registered trade mark]; basis of weight, 300 g/m²) was interposed along the seam between the cattle leather workpiece (face sheet member) and the waterproof laminated fabric workpiece (back sheet member), and subsequently all the layers en bloc were sewn together using a lock-stitch sewing machine (sewing needle #20; sewing thread #8 [polyester filament yarn]; stitching pitch, 4 needles/cm). The polyamide-based hot-melt resin tape had a dielectric constant of 4.3, a dielectric power factor of 0.09 and a melting point of 100°C at an applied high frequency of 1 × 10⁶ HZ/20°C.
The sewn shoe upper sheet member (precursory sewn structure) was subsequently fitted in respective exclusive molds for the quarters (left and right sides), vamp and heal of the shoe upper, and a charge of 0.7A at a frequency of 40 MHZ was applied for a period of 12 second to the anode of a high frequency welder (a product of Seidensha Electronics Co. Ltd.) so that the hot-melt resin tape was forced to melt for bonding the seamed portion.
As a result, a shoe upper piece with a soft sewn portion which is capable of blocking off water such as rain water and the like passing through the needle holes and the gaps formed between the face material and the back face materials can be obtained. Regarding the water repellent finished cattle leather member and the waterproof laminated fabric member, no observable change was found in the resultant shoe upper piece. In the resultant shoe upper piece, only the hot-melt resin tape was perfectly, uniformly melted, and as shown in Figure 2, the portion of the melted resin tape chokes or fills at least the cross-sections of sewing needles of the seam embedding the sewing thread, and bonds adhesively the face and back sheet members. Water resistance of the seam portion contained in the shoe upper piece was 2300 mm H₂O.

Example 2

Fluorine-based water repellent finished full grain cattle leather (water resistance, 2,000 mm H₂O; water repellent rating, 95) as waterproof shoe material was cut out into a prescribed shape. Except that the cattle leather workpieces were sewn laying one on top the other, the workpieces were sewn together according to the method described in Example 1.
As a result, only the hot-melt resin tape was evenly melted, whereas no change was observed on the cattle leather member. The resultant shoe piece contained a soft seam portion. The seam portion contained in the shoe sheet member exhibited a water resistance of 2,200 mm H₂O.

Comparative Example 1

A precursory sewn structure in the form of a shoe upper piece which was prepared by a method similar to that in Example 1, was pressed under heat by ironing (temperature, 150°C; time, 20 seconds) so that the polyamide-based hot-melt resin tape is melted to obtain a waterproof sewn shoe. It was observed that the resultant shoe contained some partially melted portions. Water resistance of the sewn portion was 200 mm H₂O.

Industrial Applicability

A waterproof sewn structure according to the invention has a sewn structure exhibiting an extremely excellent waterproof performance. The water resistance of the sewn structure are not deteriorated even when the structure is subjected to an external force such as a bending force.
A waterproof sewn structure according to the invention has an extensively waterproof sewn structure even when the sewn portion is contained in an shaped article having a curved surface, because only the hot-melt adhesive resin sheet interposed in the sewn structure is melted by applying a high-frequency heating method.
Since a sewn structure of the invention is prepared by the aforementioned method, a uniform heating of the entire body of a three dimensionally shaped article containing a curved surface configuration and and rugged surface can be attained by a single-time application of electricity. Since a hot-melt adhesive resin containing structure of the invention can be produced with an excellent processability without impairing the waterproof fabric.
The method for making a three dimensionally shaped article having an excellent waterproof sewn structure according to the invention and the processing apparatus therefor can be suitably used, in order to afford a waterproof performance to a sewn structure portion having a curved configuration, for making a variety of waterproof sewn articles fabricated from a fabric and/or leather, for example, shoes, boots, trekking shoes, arctic boots, hats, hood bodies, gloves, skier's gloves, rucksacks and tent made of natural fiber and the like.

Claims

A waterproof sewn structure characterized in that a face sheet member and back sheet member are sewn together along a seam with a hot-melt adhesive resin layer interposed therebetween, the sewing needle holes forming the seam are filled up with a portion of the hot-melt adhesive resin layer in such a manner that a portion of the hot-melt adhesive resin embeds closely the sewing thread in the seam holes, and at least the face sheet member comprising a waterproof sheet material.
A waterproof sewn structure according to claim 1, wherein the sewing needle holes which pierce both the face sheet member and back sheet member are filled with the hot-melt adhesive resin in such a manner that the hot-melt adhesive resin embeds closely the sewing thread.
A waterproof sewn structure according to claim 1, wherein the hot-melt resin layer is composed of a polyamide hot-melt adhesive resin.
A waterproof sewn structure according to claim 1, wherein the sewn structure is a three dimensionally shaped article having a curved configuration containing a seam.
A waterproof sewn structure according to claim 1, wherein the sewn structure is in the form of a shoe.
A method for forming a sewn structure containing a waterproof seam characterized in that the process includes the following steps:

(a) preparing a precursory sewn structure by sewing a face sheet member of a waterproof material and a back sheet member together with a sheet of a hot-melt adhesive resin interposed along the seam in a sandwich-like form therebetween, the hot-melt adhesive resin having a 1.7 to 4 times greater dielectric power factor than those of the face materials; and

(b) applying a high-frequency voltage sufficient to force to melt the hot-melt adhesive resin sheet into flowing state to the precursory sewn structure while pressing it at least on one face with the face of an elastic pressing sheet having a product of a dielectric constant and dielectric power factor of 0.006 to 0.09 so that a portion of the hot-melt resin flows to penetrate into and fill the holes of the stitching needle of the seam.
A method for forming a sewn structure containing a waterproof seam according to claim 6, wherein the sewn structure is in the shape of a three dimensionally shaped article having a curved configuration containing a seam.
A method for forming a sewn structure containing a waterproof seam according to claim 6, wherein the hot-melt adhesive resin sheet is a polyamide-based adhesive resin sheet.
A method for forming a sewn structure containing a waterproof seam according to claim 6, wherein the elastic pressing sheet is a silicon resin sheet.
A method for forming a sewn structure containing a waterproof seam according to claim 6, wherein the sewn structure is in the form of a shoe.
An apparatus for finishing a seam contained in a precursory sewn structure comprising a conductive mold for molding the precursory sewn structure having a mold face along the curved contour of a finished article of the precursory sewn structure; another conductive mold or upper conductive mold for pressing the precursory sewn structure on the opposing side of the said mold to hold the precursory sewn structure in place; an elastic pressing sheet disposed on the molding face of either the said mold or conductive clamp for holding the precursory sewn structure; the elastic pressing sheet having a product of a dielectric coefficient and a dielectric power factor of from 0.006 to 0.09; and a means for applying a high-frequency current to either said mold or the conductive clamp.
An apparatus for finishing a seam contained in a precursory sewn structure according to claim 11, wherein a metal plate is interposed between the conductive mold or the upper conductive mold and the elastic pressing sheet.