Stock material or miscellaneous articles – Hollow or container type article – Glass – ceramic – or sintered – fused – fired – or calcined metal...
Patent
1994-12-27
1998-06-02
Dye, Rena
Stock material or miscellaneous articles
Hollow or container type article
Glass, ceramic, or sintered, fused, fired, or calcined metal...
428 346, 428 347, 428 364, 428 358, 428 369, 428 3691, 428337, 428 1, 138DIG7, 425577, 2643287, 2643288, 74640, 3011241, B29C 4507, F16L 912
Patent
active
057596476
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a long tubular article made of a thermotropic liquid crystal resin, having a substantially uniform wall thickness, and serving advantageously in the field of electric and electronic parts, automobile parts, and machine parts and a method for the injection molding thereof. The term "long" used herein specifically means the fact that the ratio of the length (L) to the diameter (D) equivalent to cross section (hereinafter referred to as "equivalent diameter"), L/D, of the tubular article under consideration is not less than 2 and the term "equivalent diameter (D)" means the outside diameter of the circle of the tubular article when this tubular article is a cylindrical article having a circular cross section. When the tubular article has a triangular, tetragonal, or other similar angular cross section instead of a circular cross section, the equivalent diameter (D) is represented by the following formula: the tubular article and A for the peripheral length of the outer sides of the tubular article.
BACKGROUND ART
The tubular articles, particularly such long tubular articles as rolls and pipes (hereinafter referred to simply as "tubular article"), which are made of synthetic resins are now used in various fields. Most of them are formed by the method of extrusion. In recent years, the desirability of producing rolls in such office machines as copying devices and printers and pipes for machine parts in decreased weights has been finding enthusiastic recognition and the demands for tubular articles made of synthetic resins and enjoying high dimensional accuracy are growing.
The extrusion molding, however, does not easily achieve such dimensions as thickness and diameter with high accuracy. It is proper to adopt the injection molding method for the sake of high dimensional accuracy. The injection molding method, however, entails the following problems.
The ordinary injection molding machine uses an ejector pin for releasing a product from the mold and this ejector pin operates in the same direction as the direction of motion of the mold clamping mechanism of the machine. The direction in which the tubular article is disposed inside the mold, therefore, must be such that the direction of the central axis of this tubular article may coincide with the direction of motion of the mold clamping mechanism. Since it is desired that the size of the injection molding machine be proportionate to the size of the formed product thereof, the possibility that a tubular article formed by the injection molding machine will not be released from the mold owing to the limit of the transferring distance of the mold clamping mechanism which is undeniable.
When a tubular article having such a large L/D ratio as mentioned above is to be injection molded, it is desirable that the direction of the central axis of the tubular article be perpendicular to the direction of motion of the mold clamping mechanism.
The perpendicular relation of these two directions is at an economic disadvantage in complicating the mechanism for retaining a columnar member (drape mold) shaping the inner surface of the tubular article and the direction of release of the tubular article from the mold, though the central axis in this case may lie in a horizontal or a vertical direction or in a direction intermediate therebetween. To solve this problem, the idea has been conceived of using a method of injection molding which comprises shaping the columnar member (drape mold) shaping the inner surface of the tubular article in a structure releasable from the mold proper, injection molding a resin through a gate provided at one end in the longitudinal direction of the mold, removing the tubular article still mounting to the columnar member from the mold after the injection molding, and subsequently separating the columnar member and the injection molded tubular article in a separate process.
As a result, the injection molded tubular article to be produced by this method acquires veritable dimensional accuracy. In this case,
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Patent Abstracts of Japan: vol. 011, No. 350 (P-637) Nov. 17, 1987 & JP-A-62 128083 ( Sony Corp.) Jun. 10, 1987.
Injection molding Handbook, The Complete molding Operation Technology, Performance, Economics; Van Nostrand Reinhold Co, New York, Jan. 11, 1988.
Hashimoto Akio
Kuroda Rikio
Nishimura Sadahiro
Dye Rena
Nippon Petrochemicals Co. Ltd.
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