Tube having holes and method for manufacturing the same

Abstract: A tube having holes formed at precise positions is obtained by preparing a tube in which a substantially black synthetic resin film portion (1) and a synthetic resin film portion (2) having a color other than substantially balck are formed alternately in its circumferential direction and then drilling the black synthetic resin film portion (1) by a laser beam (3).

Description: The present invention relates to a tube having holes, and a method for manufacturing such a tube, more particularly, which is suitable for use in irrigation or sprinkling. Conventional tubes having holes have a large number of small holes formed in the longitudinal direction on a half side thereof. Such tubes having holes are widely used for sprinkling water or spraying liquid fertilizer over vegetables, fruits or flowers. Manufacture of such a tube is not very difficult; it can be easily manufactured by forcing a synthetic resin through the cylindrical orifice of a die. However, drilling small holes only on one side of the continuous tube manufactured is not easy. Conventionally, a tube having holes is manufactured by preparing a first synthetic resin tape with a large number of holes drilled in it and a second synthetic resin tape having the same shape but no holes in it and then by sticking the edges of the first tape to the edges of the second tape to form a continuous tube. The first tape is drilled mechanically by punching or using a laser beam. However, the tube having holes manufactured in the above-described method has a disadvantage in that it may rupture at its seams when a hydraulic pressure is applied thereto. Furthermore, it is not easy to mass produce the above-described type of tube. Accordingly, it has been proposed to drill a seamless tube manufactured by the extrusion by folding the seamless tube into two and then notching the folded edge of the tube in a semicircular form at predetermined intervals. The semicircular notches formed become circular holes when the seamless tube is unfolded. However, it is very difficult to notch the edge of the folded tube in the same semicircular form, and this makes it difficult for substantially circular holes to be formed in an unfolded tube, causing the areas of the openings of the individual holes to vary from each other. According to US-4028525, a small hole may be formed in a wall of a flexible member or structure such as a tube of a thermoplastic material by an apparatus including a rotating wheel by a laser beam source directed towards the wheel, and rotating reflecting means for reflecting the beam from this source so as to direct the beam towards a specific area of the flexible member. Preferably the flexible member is held against a surface of the wheel as the beam is directed so as to engage only a single point on the surface of the flexible member. In view of the aforementioned problems of the prior technique, an object of the present invention is to provide a tube with precise holes, and a method and an apparatus for manufacturing such a tube. According to the present invention, there is provided a method of manufacturing a tube having holes, comprising the steps of: molding a seamless tube in which a black synthetic resin film portion and a synthetic resin film portion having a color other than black are provided so that any cross-section perpendicular to the length of the tube has alternate black and non-black portions; and drilling at least one hole in each black synthetic resin film portion by a laser beam focussed thereon. The present invention also provides a seamless tube of a synthetic resin having holes characterized in that said tube has a black synthetic resin film portion and a synthetic resin film portion having a color other than black so that any cross-section perpendicular to the length of the tube has alternate black and non-black portions and each black synthetic resin film portion has at least one through-hole. From the viewpoint of drilling using a laser beam, it is preferable for a synthetic resin that forms the black synthetic resin film portion to contain 0.5 to 10 wt% of carbon black as a coloring agent. Fig. 1 is a cross-sectional view of a tube from which a tube having holes according to the present invention is manufactured; and Fig. 2 is a cross-sectional view of another tube from which the tube having holes according to the present invention is manufactured. A tube having holes and a method of manufacturing such a tube according to the present invention will be mainly described below with reference to Figs. 1 and 2. A tube having holes according to the present invention is a seamless tube in which a black synthetic resin film portion and a synthetic resin film portion having a color other than black are alternately formed in a circumferential direction of the tube. The black synthetic resin film portion and the synthetic resin film portion having a color other than black may be formed of a thermoplastic resin. Suitable thermoplastic resins include polyolefines such as polyethylene, polyamide and polyester. Both the black film portion and non-black film portion may be colored using coloring agents. Any known coloring agent may be used. Examples of coloring agents for the non-black film portion include titanium white, cyanine green, chrome yellow, cyanine blue and quinacridone red. No coloring may be performed on the non-black film portion. However, it is preferable for the non-black film portion to be colored white or in a color as close to white as possible. Preferably, titanium white may be employed to color such a white film portion. In a case where titanium white is used as a coloring agent, the coloring agent may be mixed in a ratio of 0.8 wt parts or above relative to 100 weight parts of synthetic resin. The black film portion may be colored using carbon black. Carbon black may be contained in a ratio ranging from 0.5 wt % to 10 wt %, and preferably, from 2 wt % to 6 wt%, relative to the overall weight of the synthetic resin compound containing carbon black. If the ratio of carbon black is 0.5 wt% or less relative to the overall weight of the synthetic resin compound that forms the black film portion, a laser beam absorption rate is low, making drilling difficult. If the ratio of carbon black exceeds 10 wt %, the properties of the resultant film, such as tenacity or elongation thereof, are deteriorated. When a tube is to be manufactured from a thermoplastic resin, two extruders and one tube molding die connected to the two extruders may be employed to mold the thermoplastic resin. More specifically, black molten resin containing carbon black in a ratio ranging from 5 wt% to 10 wt% may be forced out from one of the two extruders, whereas non-black molten resin may be forced out from the other extruder, the two molded resin portions being fitted with each other later by a tube molding die to form a seamless tube such as that shown in Fig. 1 in which a black portion and a non-black portion are alternately formed in its circumferential directions. The seamless tube may also be formed such that it has a plurality of black portions and a plurality of non-black portions alternately, as shown in Fig. 2. In this invention, laser beam machining is performed on the tube obtained in the above-described manner by irradiating a laser beam on the black portion of the tube. Generally, a laser beam emitted from yttrium aluminum garnet crystals using neodymium ions may be employed. A laser beam may be output at 0.1 to 40 J/P, and preferably, at 0.3 to 2 J/P. If the output is less than 0.1 J/P, it is difficult to obtain an energy level sufficient to drill the tube. If the output exceeds 40 J/P, a laser beam may penetrate the tube, forming two holes in the tube or damaging the non-black portion, even if the tube employed is one in which two color portions are alternately formed. When the laser beam irradiates the black portion, most of the laser beam is absorbed by the dyestuff contained in the black portion where it is converted into thermal energy, by means of which a hole is formed from the outer side of the tube toward the inner side thereof. After having passing through the hole, the laser beam proceeds further and reaches the inner side of the opposite side of the tube. However, since the opposite portion of the tube is in a color other than black, most of the laser beam is irregularly reflected by that portion while the remaining portion of optical energy is converted into thermal energy, thus preventing a hole from being formed from the inner side of the tube toward the outer side thereof. This enables the tube to be drilled in a flat state by a laser beam. An example of the method of manufacturing a tube having holes will be described below with reference to Figs. 1 to 2. <Example> A tube having holes was manufactured by the manufacturing method in the manner described below. A tube molding die and two extruders connected to this tube molding die were employed. 96 weight parts of transparent pellet of polyethylene and 4 weight parts of carbon black were put in one of the extruders where they were kneaded. 98 weight parts of transparent pellet of polyethylene and 2 weight parts of titanium white were put in the other extruder where they were kneaded. The two molded resin portions extruded from the respective extruders were fitted with each other by the tube molding die so as to form a seamless tube in which a black synthetic resin film portion 1 and a white synthetic resin film portion 2 were formed, as shown in Fig. 1. Next, the black portion 1 of the thus-obtained tube was irradiated by a YAG laser beam 3 for drilling. The laser beam 3 was output at 0.8 J/P. An accurate hole was formed in the tube at a precise position. No damage was made on the white portion 3 of the tube by the laser beam 3. In the method of manufacturing a tube having holes according to the present invention, the tube prepared can be drilled using a laser beam, facilitating drilling. Furthermore, since the tube can be drilled by a laser beam in a flat state, the precise holes can be formed in the tube at precise positions. The resultant tube has no fitted portion and, hence, there is no decrease in the strength thereof. These eliminate provision of defected tube having holes.

Claims: A seamless tube of a synthetic resin having holes characterized in that said tube has a black synthetic resin film portion (1) and a synthetic resin film portion (2) having a color other than black so that any cross-section perpendicular to the length of the tube has alternate black and non-black portions and each black synthetic resin film portion has at least one through-hole. A tube according to claim 1, wherein said synthetic resin film portion (2) having a color other than black is white. A tube according to claim 2, wherein said white color is provided by titanium white. A method of manufacturing a tube having holes, comprising the steps of: molding a seamless tube in which a black synthetic resin film portion and a synthetic resin film portion having a color other than black are provided so that any cross-section perpendicular to the length of the tube has alternate black and non-black portions; and drilling at least one hole in each black synthetic resin film portion by a laser beam focussed thereon. A method according to claim 4, wherein each black synthetic resin portion contains 0.5 to 10 wt% of carbon black. A method according to claim 4 or 5 wherein said seamless tube is formed using an extruder apparatus consisting of one tube molding die and two extruders connected to said die, and wherein said seamless tube is formed by forcing black molten resin out of one of said two extruders while forcing molten resin having a color other than black from the other extruder. A method according to claim 4, 5 or 6, wherein said molten resin having a color other than black contains titanium white.

Inventors: OHE TATSUYA MITSUI PETROCHEMIC, OHE, TATSUYA MITSUI PETROCHEMICAL INDUSTRIES, LTD.
Applicants: MITSUI PETROCHEMICAL IND, MITSUI PETROCHEMICAL INDUSTRIES, LTD.
Application year: 1990
Main classification: A01G25
IPC codes: F16L11, B29C47, B23K26, A01G25