Background Art A Tube, such as a straw, is well known which is defined with a through hole therein and used to suck liquid, such as juice, contained in a container. When the user drinks liquid contained in a container using such a tube, he holds one end of the tube in a state, in which the other end of the tube is dipped in the liquid, and sucks the liquid through the tube. Typically, such a tube is made of synthetic resin such as polypropylene resin or vinyl resin and shaped into a desired elongated hollow structure.

However, such a tube, which is made of synthetic resin, is problematic in that it causes environmental pollution after usage thereof.

In order to solve such a problem, a tube made of a natural material such as starch is proposed. In this case, however, it is impossible for such a tube to have a through hole having a small diameter as in straws, in view of the manufacture thereof. Where a tube having a larger diameter is manufactured, facing portions of its inner surface defining a through hole may come into contact

with each other at an intermediate portion of the tube, thereby preventing a smooth flow of liquid through the tube.

Use of a natural material such as starch or wheat flour is well known in association with the manufacture of disposable products, such as dishes, trays, cups, spoons, packages of biscuits, or toothpicks, for the prevention of environmental pollution caused by disposal of such disposable products. In the manufacture of such disposable products, a natural material such as starch or wheat flour is kneaded using water and then aged at an appropriate elevated temperature. The resultant dough is forced to pass through an extruder under high pressure, so that it is shaped into a flat plate shape while being hardened by heat generated in the extruding process.

Thereafter, the hardened flat plate is cut and shaped into a desired shape. The resultant product is then dried.

The dried product is forced to pass through a starch solution containing starch at an appropriate density. The resultant product is finally freeze-dried. Thus, a desired disposable product is obtained.

As apparent from the above description, where a disposable product is manufactured using a natural material such as starch, a flat plate is first formed from a starch dough and then shaped into a desired shape.

Although une flat plate is in a hardened state, it is not in a comp-etely dried state. Under this condition, there is no problem in regard to the manufacture of disposable products such as dishes or cups. Where a disposable product having a severe topology is to be manufactured, however, it is impossible to maintain the shape of the product obtained after the shaping process. To this end,

it is necessary to use a support device for maintaining the shape of the product obtained after the shaping process. However, although such a support device is used, it is impossible to manufacture a tube defined therein with a through hole having a small diameter of 2 cm or less. Even when a tube having a larger diameter is manufactured, there is a problem in that facing portions of its inner surface defining a through hole may come into contact with each other at an intermediate portion of the tube, thereby clogging the through hole.' Disclosure of the Invention Therefore, the invention has been made in view of the above mentioned problems involved in the prior art, and an object of the invention is to provide a method for manufacturing a tube, such as a straw, which is defined with a through hole therein while having a desired length, using a natural material such as starch, thereby preventing the tube from being hazardous to the human body and from generating environmental pollution.

In accordance with the present invention, this object is accomplished by providing a method for manufacturing tubes, each defined with a through hole therein, comprising the steps of: pouring starch into water maintained at a temperature of 60 to 80°C, kneading the starch in a kneader, thereby forming a starch dough, and then aging the starch dough; feeding the aged starch dough to an extruder including a plurality of annular nozzles, each having a core, by a screw, thereby extruding tubes, each having a through hole, from the annular nozzles of the extruder; blowing air into the through hole of each of the tubes being extruded; feeding the extruded tubes to a

cutting stage by a conveyor belt while upwardly and downwardly blowing air toward the extruded tube, thereby cooling and drying the extruded tube; cutting the extruded tube into pieces, each having a desired length, at the cutting stage, and then slowly cooling the cut pieces in an aging room for 3 to 4 hours; and pre-cooling the cooled pieces in a freezing room at a temperature of 5 to-3°C, and then cooling the pre-cooled pieces at a temperature of -15 to-17°C for 3 to 4 hours.

Best Mode for Carrying Out the Invention The present invention provides a method for manufacturing a tube, such as a straw, using a natural material, such as starch, exhibiting a superior moldability and adherence, thereby preventing the tube from being hazardous to the human body and from generating environmental pollution. In accordance with the method of the present invention, water is first prepared which is in a state cooled to a temperature of 60 to 80°C after being boiled. Starch is then poured into the prepared water so as to form an agglomerate. The agglomerate is kneaded in a kneader and then aged. The resultant dough is forcibly fed by a screw so that it is extruded through an extruder having a plurality of, for example, 4 to 10 annular nozzles, each having a core. As a result, products, each having a tube shape, are formed. Since the tubes are in an incompletely dried state, it is necessary to prevent facing portions of the inner surface of each tube defining a through hole from coming into contact with each other in order to prevent the through hole from being clogged. To this end, air is blown into the through hole of each tube, being extruded, during the extruding process in accordance

with the present invention. The tubes emerging from the nozzles are then fed to a cutting stage by means of a conveyor belt. During the feeding, air is blown toward the tubes in a desired direction, for example, upwards and downwards, thereby causing the tubes to be cooled and dried while being fed to the cutting stage.

At the cutting stage, each tube is cut into pieces each having a desired length and then fed to an aging room. In the aging room, the tube is slowly cooled for 3 to 4 hours. In the slow cooling process carried out in the aging room, bubbles may be formed at the inner and outer surfaces of each tube. In order to remove bubbles possibly formed, each tube is subsequently pre-cooled at a temperature of 5 to-3°C in a freezing room. In order to achieve a convenient storage of the bubble-free tubes while preventing bacteria from penetrating those tubes, a cooling process is conducted for the pre-cooled tubes for 3 to 4 hours at a temperature of-15 to-7°C.

As mentioned above, in accordance with conventional methods adapted to manufacture disposable products using starch, it is possible to manufacture products only having a planar shape or a simply curved shape. Where a product having a cylindrical shape having a small diameter or a hollow shape defined therein with a through hole is manufactured in accordance with the conventional methods, there is a problem in that facing portions of the inner surface of the product come into contact with each other, thereby causing the through hole of the product to be clogged. In accordance with the present invention, however, such a problem involved in the conventional methods is avoided. In accordance with the present invention, it is also possible to achieve the formation of

the through hole in a simple, easy and reliable manner.

In accordance with the present invention, it is also possible to manufacture a tube having various shapes, for example, a twisted shape while maintaining the function of its through hole.

It will be appreciated that the tube manufactured in accordance with the present invention can be widely used because it can be substituted for tubes made of a chemical material such as polypropylene resin and adapted to be used as straws in accordance with the conventional methods.

Industrial Applicability As apparent from the above description, the present invention provides a method for manufacturing a tube, which is defined with a through hole therein, using a natural material such as starch or wheat flour. Since the tube is made of starch or wheat flour, it causes no hazard to the human body even when it comes into contact with the mouth during its use. After being used, the tube may be re-usable as feed or natural fertilizer. Also, the disposal of the tube does not result in environmental pollution because the tube can be naturally decomposed in that it is made of a natural material.

Although the preferred embodiments of the invention have beer. disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.