WO 2007/021049 PCT/KR2005/002937 Description ODOR TRAP FOR DRAIN Technical Field 11] The present invention relates to a trap for preventing odor drifted back through a house drain or a road manhole drain, and more particularly, to an odor trap for a drain which is made in a long tube shape of synthetic resin, such as polyethylene, thin and flexible on the whole, comprises a drain mounting portion and a main body portion, the drain mounting portion being formed in a taper shape with an wide upper part and a narrow lower part so as to be easily mounted to a drain cover fixture and having a bonding portion formed at the upper end face, and the main body portion being integrally connected to a lower part of the drain mounting portion and having foldable portions longitudinally formed at both side faces in a length direction along the main body portion and a plurality of foldable strips formed in a transverse direction at pre determined intervals, whereby the system can smoothly discharge sewage water, being mounted inside the drain, and simultaneously can prevent odors or insects generated from inside a sewage pipe from being discharged to the outside through the drain after discharging the sewage water, with the inner faces of the main body kept in contact with each other. [2] Background Art [3] In general, regarding a drain, as shown in FIG.6, sewage water or the like is discharged through a sewage pipe 8' buried in the ground. A drain cover fixture 4' is installed inside an upper part of the drain, and a drain cover 9' is fitted to the upper end of the drain cover fixture 4' to serve to filter various kinds of impurities so as not to flow down through the drain. Below the drain cover fixture 4', an odor control pate 10' is installed spaced at a predetermined gap from the drain cover fixture 4', whereby odors generated from inside the sewage pipe 8' are drifted back to thus be discharged to outside of the drain or prevent various kinds of insects or the like from being released to the outside of the drain. [4] However, the odor control plate 10' installed at the drain in the prior art is problematic in that hairs, tiny impurities or sludge and so on are clogged in the spacing between the odor control plate 10' and the lower portion of the drain cover fixture 4' in the process of discharging various sewage waters through the drain. Accordingly, the discharge of sewage water is not done well and thus bad odors are generated to arouse an unpleasant feeling. [5] WO 2007/021049 PCT/KR2005/002937 Disclosure of Invention Technical Problem [6] The present invention is directed to solve the aforementioned problems and has for its object to provide an odor trap for a drain which can smoothly discharge sewage water through a sewage pipe and effectively prevent odors or insects generated from inside the sewage pipe from being released to the outside to thus keep clean, by naturally joining and adhering foldable portions, longitudinally folded along both side faces of a main body portion, to the main body portion of thin synthetic resin con stituting a long tube by the adhesive strength of moisture stained on the inner side of the main body portion. [7] Technical Solution 18] To achieve the above objects, there is provided an odor trap for a drain according to the present invention, which is made in a long tube shape of synthetic resin, such as polyethylene, thin and flexible on the whole, comprises a drain mounting portion and a main body portion, and is installed at an inner side of a drain to prevent odors generated from a house drain or road manhole, wherein the drain mounting portion is formed in a taper shape with an wide upper part and a narrow lower part so as to be easily mounted to a drain cover fixture, and has a bonding portion formed at the outer circumferential surface of the upper end of the drain mounting portion so as to be bonded and secured to an inner surface of the upper end of the drain cover fixture, and the main body portion is made in a long tube shape, is integrally connected to a lower part of the drain mounting portion, has a smaller diameter than the sewage pipe, and has foldable portions, longitudinally folded along a lengthwise direction of the main body portion, formed at both side faces of the main body portion, whereby after the discharge of sewage water along the main body portion, the inner sides of the main body portion are easily kept in close contact and stuck to each other, with a center on folded parts, by the adhesive strength of the moisture stained on the inner sides of the main body portion and its own elasticity of the foldable portions, thereby preventing odors generated from inside the drain from being drifted back. 19] Brief Description of the Drawings [10] These and other features, aspects, and advantages of preferred embodiments of the present invention will be more fully described in the following detailed description, taken accompanying drawings. In the drawings: [11] FIG. 1 is a perspective view showing an odor trap for a drain according to a preferred embodiment of the present invention; WO 2007/021049 PCT/KR2005/002937 [12] FIG.2 is a perspective view showing an odor trap for a drain according to another embodiment of the present invention; [13] FIG.3 is a schematic cross sectional view showing the odor trap for a drain of the invention being mounted to the drain of a straight sewage pipe; [14] FIG.4 is a schematic cross sectional view showing the odor trap for a drain of the invention which is opened as sewage water is discharged, being mounted to the drain of a L-shaped sewage pipe; [15] FIG.5 is a schematic cross sectional view showing the odor trap for a drain of the invention which is closed after sewage water is discharged, being mounted to the drain of the L-shaped sewage pipe; and [16] Fig.6 is a schematic cross sectional view of a conventional odor trap for a drain. [17] Best Mode for Carrying Out the Invention [18] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. [19] As shown in FIGs.1 to 5, the odor trap for a drain of the invention is installed at an inner side of a house drain or road manhole drain to prevent odors or insects. This odor trap for a drain is made in a long tube shape of synthetic resin, such as polyethylene, thin and flexible on the whole, and comprises a drain mounting portion 2 and a main body portion 3. [20] The drain mounting portion 2 is a portion that is fixedly installed by fitting the odor trap for a drain 1 of the invention to a drain cover fixture 4 provided at an inner upper part of the drain, which is formed in a taper shape with a wide upper and a narrow lower part so as to be easily mounted to the drain cover fixture 4. A bonding portion 5 is projected on the outer circumferential surface of the upper end of the drain mounting portion 2 so as to be firmly bonded and secured to an inner surface of the upper end of the drain cover fixture 4 by epoxy resin or the like. [21] An upper outlet of the drain mounting portion 2 is made in a circular shape as shown in FIG. 1 or in a rectangular shape as shown in FIG.2 so as to cope with various shapes of drains. [22] Upon discharging sewage water, the main body portion 3 is kept opened by the weight of passing sewage water, while after discharging sewage water, it is kept closed because the inner sides are in close contact with each other due to the moisture stained on the inner side and due to foldable portions 6a and 6b and foldable strips 7, thereby effectively preventing odors or insects generated from inside the sewage pipe 8 from being released to the outside. The main body portion 3 is made in a long tube shape, integrally connected to a lower part of the drain mounting portion 2, and has a smaller WO 2007/021049 PCT/KR2005/002937 diameter than the sewage pipe 8. Therefore, the main body portion 3 is configured not to be stuck to the inner circumferential surface of the sewage pipe 8, being stretched in a circular fashion. Foldable portions 6a and 6b longitudinally folded along a lengthwise direction of the main body portion 3 are formed at both side faces of the main body portion 3. Therefore, after the discharge of sewage water along the main body portion 3, the inner sides of the main body portion 3 are easily kept in close contact and stuck to each other, with a center on folded parts, by the adhesive strength of the moisture stained on the inner sides of the main body portion 3 and its own elasticity of the foldable portions 6a and 6b, thereby preventing odors generated from inside the drain 8 from being drifted back. On the outer circumferential surface of the main body portion 3, a plurality of foldable strips 7 are formed along a circumferential direction at predetermined intervals, thus increasing the contact between the inner sides of the main body portion 3 by its own elasticity of the foldable strips 7 and preventing the main body portion 3 from being folded or twisted to thus be blocked upon discharging water. [23] The foldable portions 6a and 6b are formed by heat bonding or heat sealing by pressing both side faces of the main body portion 3 made in a tube shape of thin synthetic resin. At this time, it is most preferable that the width of the foldable portions 6a and 6b is about 1 to 5mm. [24] Meanwhile, in another embodiment according to the present invention, the main body portion 3 may be manufactured by forming only foldable portions 6a and 6b without forming a plurality of foldable strips 7 on the outer circumferential surface. [25] As shown in FIGs.3 to 5, the odor trap for a drain 1 of the invention can be easily installed on an L-shaped sewage pipe 8 as well as a straight sewage pipe 8. Preferably, the L-shaped sewage pipe 8 is installed in a manner that the foldable portions 6a and 6b formed on both sides of the main body portion 3 are placed in a transverse direction so that the inner sides of the main body portion 3 may be easily in close contact with each other after discharging sewage water. [26] Further, the odor trap for a drain 1 of the invention may be installed at an inner side of the inlet part of a road manhole, so that odors or the like may not be released to the ground through underground sewage piping. [27] The operation of the odor trap for a drain of the invention will be explained below. [28] Typically, the installation of the odor trap for a drain 1 of the invention is completed simply by bonding the bonding portion 5 of the drain mounting portion 2 to the top surface of the drain cover fixture 4 installed at the drain by epoxy resin and integrally securing them, and fitting the drain mounting portion 2 and the main body portion 3 so as to be located inside the sewage pipe 8. [29] Upon discharging sewage water, according to the properties of the main body WO 2007/021049 PCT/KR2005/002937 portion 3 made of synthetic resin, such as polyethylene, thin and flexible on the whole, the main body portion 3 is naturally stretched out by its own weight of sewage water passing through the inside of the main body portion 3, and thus sewage water is smoothly discharged to an inner lower part of the sewage pipe 8. After discharging sewage water, the inner sides of the main body portion 3 are easily kept in close contact and stuck to each other by the adhesive strength of the moisture stained on the inner sides of the main body portion 3 and its own elasticity of the foldable portions 6a and 6b formed on both sides of the main body portion and of the plurality of foldable strips 7 formed on the outer circumferential surface of the main body portion 3, thereby preventing odors or insects generated from inside the drain 8 from being released to the outside. [30] Industrial Applicability [31] As described above, according to the present invention, the drain mounting portion is simply and easily mountable at a typical house drain as well as a road manhole drain since it is made in a taper shape with a wide upper part and a narrow lower part, sewage water is not clogged or drifted back because the sewage water is smoothly discharged, and after the discharge of the sewage water, the inner sides of the main body portion are kept in close contact and stuck to each other by its own elasticity of the foldable portions folded at a predetermined width on both sides of the main body portion and the adhesive strength of the moisture stained on the inner sides of the main body portion, thereby preventing odors or insects generated from inside the sewage pipe from being drifted back and released to the outside through the drain and thus keeping the drain clean.