Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Patent
1992-09-24
1998-12-15
Clardy, S. Mark
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
428116, 428118, 428119, 428166, 428178, 428188, 428 73, 425577, 425572, 2643287, 264572, B29D 2200
Patent
active
058493778
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an injection-molded hollow article having a large hollow portion, a hollow injection molding method for molding the same, and a metal mold therefor. More specifically, the present invention relates to an injection-molded hollow article having hollow portions of widely variable sizes which is reinforced by forming support portions for partially supporting the hollow portions, a hollow injection molding method for molding the same, and a metal mold therefor.
BACKGROUND ART
Conventionally, when an injection-molded hollow article having hollow portions is molded by injecting a melted resin of an amount smaller than the volume of a metal mold cavity when under pressure a pressurized fluid (mainly composed of a gas) is injected into the metal mold cavity, a necessary strength is obtained by partial retaining webs (hereinafter, referred to as a web or rib) which is a structure partially connected to the skin portion of the molded article.
For example, U.S. Pat. No. 4,247,515 discloses that key stocks are attached to a metal mold cavity and the viscosity, elasticity and density of a melted resin, the interfacial tension between a pressurized fluid and the melted resin, and the like are adjusted. Since the portions of the metal mold cavity to which the key stocks are attached has a decreased thickness and thus the pressurized fluid is difficult to cross over, a plurality of hollow portions are formed around the boundaries of the key stocks attached and the resin remains in the vicinity of the key stocks and solid ribs are formed from this resin.
Further, Japanese Patent Kokoku (Post Exam. Publication) No. Sho 61-53208 discloses that a distribution is provided with the fluidity and amount of a melted resin in a metal mold cavity and a gas is introduced to the portion of the melted resin having a high fluidity and the portion containing a less amount of the melted resin in the metal mold cavity to make these portions hollow and the other portions remain as solid ribs. In addition, this patent discloses a method in which a melted resin and gas are introduced under pressure into a metal mold cavity provided with a portion having a different thickness and a method in which a melted resin and gas are introduced under pressure to a metal mold cavity while the metal mold cavity is partially enlarged, to thereby preferentially introduce the gas to the thick portion and enlarged portion of a metal mold cavity to make these portions hollow. The resins in the thin portions and the portions other than the enlarged portions of the metal mold are retained as solid ribs. Further, said invention discloses use of these methods in combination.
According to the method disclosed in U.S. Pat. No. 4,247,515, if high key stocks are attached to the metal mold cavity, a portion to which the pressurized fluid is supplied can be securely isolated. However, if a portion corresponding to the high key stocks is made in a deep recess of an injection-molded hollow article and making the wall thickness of a rib thinner, the strength of the molded product is thus lowered. Although this reduction of the strength can be prevented by lowering the height of the key stocks, this lowering of the height makes the separation of the portion to which the pressurized fluid is introduced inaccurate. Since the location and size of the ribs are liable to be controlled by chance, the position of the ribs cannot be designed in advance. Therefore, as shown in FIGS. 18 and 19, a molded article obtained has ribs 101 having an irregular location and shape and the ribs 101 having a necessary size cannot be securely placed at the location which is really required, and thus a molded article having a desired strength cannot be obtained. Further, a recess 102, which originally is not needed in consideration of an object for which an injection-molded hollow article is used, is formed in the molded article by the key stocks attached to the metal mold cavity.
Further, since various factors are concerned with the method of pr
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Patent Abstracts of Japan, vol. 14, No. 323 (M-997) 11 Jul. 1990 and JP-A-21 08 510 (Toyoda Gosei Co Ltd) 20 Apr. 1990.
Horikoshi Maki
Nishiura Keiji
Tanaka Yuji
Asahi Kasei Kogyo Kabushiki Kaisha
Clardy S. Mark
Williamson Michael A.
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