Pipe of hard thermoplastic resin, pipe joint structure and methods of manufacturing the same

A pipe joint structure comprising a pipe main body made of a rigid thermoplastic resin, a release ring inserted from one opening of the pipe main body, an insertion mouth pipe portion made of a rigid thermoplastic resin which is molded separately from the pipe main body and allowed to coaxially abut the pipe main body to be integrally connected therewith, and a ring-shaped projection made of an elastic resin formed on an inner surface of the pipe main body for sealing a pipe to be connected that is inserted via the release ring,

• wherein the rigid thermoplastic resin of the pipe main body is a polyamide resin, a polybutylene terephthalate resin or a polyphenylene oxide resin,
• the elastic resin is a butadiene-acrylonitrile rubber or an ethylene-propylene rubber,
• the ring-shaped projection is thermoplastically integrated on the inner surface of the pipe main body by vulcanization of a molten material of the rubber,
• the release ring is formed of a rigid thermoplastic resin or a metal and includes a slip-off preventing protrusion on an outer circumferential surface of its insertion site, and
• a recess groove is formed on an inner circumferential surface of an abutting portion of the pipe main body and the insertion mouth pipe portion for engaging or engagingly stopping the slip-off preventing protrusion of the release ring,
• wherein the main body portion and the insertion mouth pipe portion are integrally connected by integrally molding or winding a ring-shaped connecting portion made of a rigid thermoplastic resin on an outer circumferential surface of their abutting portion.

A pipe joint structure comprising a pipe main body made of a rigid thermoplastic resin, a release ring inserted from one opening of the pipe main body, an insertion mouth pipe portion made of a rigid thermoplastic resin which is molded separately from the pipe main body and allowed to coaxially abut the pipe main body to be integrally connected therewith, and a ring-shaped projection made of an elastic resin formed on an inner surface of the pipe main body for sealing a pipe to be connected that is inserted via the release ring,

• wherein the rigid thermoplastic resin of the pipe main body is a polyamide resin, a polybutylene terephthalate resin or a polyphenylene oxide resin,
• the elastic resin is a butadiene-acrylonitrile rubber or an ethylene-propylene rubber,
• the ring-shaped projection is thermoplastically integrated on the inner surface of the pipe main body by vulcanization of a molten material of the rubber,
• the release ring is formed of a rigid thermoplastic resin or a metal and includes a slip-off preventing protrusion on an outer circumferential surface of its insertion site, and
• a recess groove is formed on an inner circumferential surface of an abutting portion of the pipe main body and the insertion mouth pipe portion for engaging or engagingly stopping the slip-off preventing protrusion of the release ring,
• wherein the main body portion and the insertion mouth pipe portion are integrally connected by integrally molding or winding a ring-shaped connecting portion made of a rigid thermoplastic resin on an outer circumferential surface of their abutting portion, and
• wherein the pipe main body has an injection hole for injecting a molten material of the butadiene-acrylonitrile rubber or the ethylene-propylene rubber from outside for forming the ring shaped projection made of the elastic resin, and the injection hole is closed by the ring-shaped connecting portion after the molten material of the rubber is injected.

A manufacturing method of a pipe joint structure in which a ring-shaped projection made of an elastic resin and having a sealing property is thermoplastically integrated on an inner surface of a pipe main body, comprising

• (1) a pipe main body portion molding step for molding a pipe main body portion made of the rigid thermoplastic resin by injecting a molten material of a polyamide resin, a polybutylene terephthalate resin, or a polyphenylene oxide resin-into a pipe-shaped cavity formed by splittable molds;
• (2) a ring-shaped projection forming step for injecting a molten material of a butadiene-acrylonitrile rubber or an ethylene-propylene rubber into a small cavity formed on the inner surface of the pipe main body portion by moving a part of an inner mold among the molds, and for thermoplastically integrating the ring-shaped projection made of the elastic resin and having the sealing property on an inner surface of the pipe main body portion while performing vulcanization;
• (3) an insertion mouth pipe portion molding step for molding an insertion mouth pipe portion by injecting a molten material of a rigid thermoplastic resin into a pipe-shaped cavity formed by other splittable molds;
• and
• (4) a pipe main body molding step for obtaining the pipe main body by coaxially and abuttingly disposing the molded insertion mouth pipe portion and the molded pipe main body portion, and injecting a molten material of a rigid thermoplastic resin into a cavity formed by still another mold on an outer circumferential surface portion of the abutting portion to mold a ring-shaped connecting portion to integrally connect the pipe main body portion and the insertion mouth pipe portion;
• and
• (5) a release ring inserting step for molding a release ring beforehand and inserting the molded release ring into the obtained pipe main body to obtain a pipe joint.