Pipes and tubular conduits – Flexible – Spirally wound material
Reexamination Certificate
2003-02-27
2004-02-10
Brinson, Patrick (Department: 3752)
Pipes and tubular conduits
Flexible
Spirally wound material
C138S137000, C138S140000, C138S130000, C138S144000
Reexamination Certificate
active
06688339
ABSTRACT:
BACKGROUND ART
Conventionally, high pressure pipes for transporting water, gas and like medium are served by steel pipes or resin pipes such as rigid polyvinyl chloride pipes and polyethylene pipes.
While steel pipes exhibit a high strength against internal pressure and an excellent creep resistance, they are deficient in having a poor earthquake resistance and developing rust and corrosion. Therefore, the recent trend is to employ synthetic resin pipes such as rigid polyvinyl chloride pipes and polyethylene pipes, or to use reinforced composite pipes. In particular, use of reinforced composite pipes has increased because of their superior rust resistance, corrosion resistance, pressure resistance, etc.
Reinforcements include metal fibers, glass fibers, carbon fibers, synthetic resin fibers, stretch-formed synthetic resin fibers, fiber bundles or braids of these fibers, and strips or stretch-formed strips of these fibers. To show their reinforcing effects, these reinforcements are arranged as an intermediate layer within the pipe wall layer of a synthetic resin pipe, or they are laminated on the outer layer or the inner layer.
Japanese Patent Laid-open Publication No. H10-19170 proposes an example of the reinforced high-pressure pipe. A reinforcing layer is formed by winding plural layers of metal sheets (steel strips) on the external circumferential surface of a synthetic resin pipe (an inner layer). In addition, a corrosion-resistant layer and a foamed layer (outer layers) are laminated on the external circumferential surface of the reinforcing layer. This high-pressure composite pipe is enhanced in pressure resistance against internal hydraulic pressure and also in pressure-resistant creep property.
This high-pressure composite pipe, however, is inferior in adhesive property (interface adhesion) between the reinforcing layer (the metal sheet) and the synthetic resin for the inner layer. Due to such deficiency, when the pipe is cut, the pipe may yield to water pressure on the pipe end. Then, water penetrates from the cut surface through between the reinforcing layer and the synthetic resin layer (i.e. inner layer) and causes weeping or so-called blister (bubbles of water generate on the surface of the reinforcing layer). In the end, contents may leak out of the pipe or block the pipe.
Therefore, with regard to the cutting and connection of the conventional high-pressure composite pipes, it is necessary to apply an adhesive to the widthwise end of each pipe or to remove the reinforcing layer at the connection part, before the pipes are connected. This preparation requires sophisticated work skills and higher working costs.
The present invention has been made to solve these problems. An object of the present invention is to provide high-pressure composite pipes which neither experience weeping due to penetration of water from a cut surface of the pipe nor suffer from fracture by blister, and which have a superior pressure resistance strength. Another object of the present invention is to provide a method for manufacturing these high-pressure composite pipes.
DISCLOSURE OF THE INVENTION
A high-pressure composite pipe of the present invention is characterized in comprising an inner layer pipe made of a synthetic resin, and a reinforcing layer formed by spirally winding a stretched polyolefin resin sheet on an external circumferential surface of the inner layer pipe, wherein the inner layer pipe and the stretched polyolefin resin sheet are fused together, and wherein the synthetic resin for the inner layer pipe is filled into a gap defined by the stretched polyolefin resin sheet which is wound on the external circumferential surface of the inner layer pipe.
In the context of the present invention, the gap defined by the stretched polyolefin resin sheet (the gap in the stretched polyolefin resin sheet) means, in principle, a spiral gap which is created between widthwise ends of adjacent turns of the polyolefin resin sheet, when the stretched polyolefin resin sheet is wound as the reinforcing layer on the external circumferential surface of the inner layer pipe.
Additionally, in the case where the stretched polyolefin resin sheet is wound in a plurality of layers, the gap in the stretched polyolefin resin sheet may include a gap which is created between a sheet layer contacting the inner layer pipe and another sheet layer overlying the former sheet layer (when an outer layer is coated, the term may also include a gap created between a sheet layer contacting the outer layer and another sheet layer underlying the former sheet layer) Besides, when the stretched polyolefin resin sheet is spirally wound such that its widthwise ends overlap on one another, the gap in the stretched polyolefin resin sheet may further refer to a gap which is created in the vicinity of the overlapping portion.
According to the high-pressure composite pipe of the present invention, the reinforcing layer made of a stretched polyolefin resin sheet is wound and laminated on an external circumferential surface of the inner layer pipe made of a thermoplastic resin. In this process, the inner layer pipe and the stretched polyolefin resin sheet are integrally fused together by heating.
At this stage, the heating temperature is raised to the neighborhood of the melting point of the synthetic resin for the inner layer pipe, so that the surface of the inner layer pipe can melt. Besides, the heat causes the stretched polyolefin resin sheet to shrink and generate a surface pressure. As a result, the resin for the inner layer pipe (the melted resin on the surface) is embedded into the gap in the stretched polyolefin resin sheet (the spiral gap between the sheet ends).
Thus, the high-pressure composite pipe of the present invention avoids penetration of water from a cut surface of the pipe, thereby preventing weeping or fracture by blister.
To give a specific example of the high-pressure composite pipe of the present invention, the inner layer pipe may be composed of a plurality of synthetic resin layers. A synthetic resin for at least the outermost layer of this inner layer pipe is filled into the gap in the stretched polyolefin resin sheet.
According to this structure, while the reinforcing layer made of the stretched polyolefin resin sheet is integrated with the inner layer pipe under heating, the outermost layer of the inner layer pipe swells and exudes into the gap in the stretched polyolefin resin sheet more effectively. Therefore, the synthetic resin for the inner layer pipe can be filled in a better condition.
If the inner layer pipe has a plurality of synthetic resin layers, these layers may be made of the same resin or different resins. For example, a polyethylene inner layer pipe may be constituted with an innermost layer of HDPE (high-density polyethylene), a middle layer of LLDPE (linear low-density polyethylene), and an outermost layer of LDPE (low-density polyethylene). To give another example, where an inner layer pipe is made of a polypropylene innermost layer and a polyamide outermost layer, an acid-modified middle layer may be provided between these layers in order to impart adhesive property.
In a preferable high-pressure composite pipe of the present invention, when the inner layer pipe has a plurality of synthetic resin layers, a synthetic resin for at least the outermost layer has a melt index (according to JIS K 6760) of 2 g/10 min or greater (including 2 g/10 min).
A synthetic resin with a high melt index, which is a synthetic resin showing high fluidity, enables the synthetic resin for the inner layer pipe to exude readily into the gap in the stretched polyolefin resin sheet. Hence, the synthetic resin can be embedded into the gap in a better condition. In the following description, the term “melt index” is mentioned as MI.
Concerning the above high-pressure composite pipe of the present invention, when the reinforcing layer made of the stretched polyolefin resin sheet is integrated with the inner layer pipe under heating, the stretched polyolefin resin sheet shrinks to cause exudation of the syn
Adachi Koichi
Matsuzaka Katsuo
Nogami Mitsuhide
Yamada Takehiro
Yamaguchi Koji
Brinson Patrick
Sekisui Chemical Co. Ltd.
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