Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Including application of internal fluid pressure to hollow...
Patent
1995-12-18
1998-01-27
Timm, Catherine
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Including application of internal fluid pressure to hollow...
264537, 264523, 425522, 425529, 425533, B29C 4928
Patent
active
057119139
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The present invention relates to biaxial oriented blow molding method for manufacturing a synthetic resin bottle by drawing a so called preform, a cylinder with a bottom preformed by synthetic resin, with a draw bar or air to biaxial orientation, and a structure of a preform holding jig used for the molding method.
DESCRIPTION OF PRIOR ART
Synthetic resin bottles formed by biaxial orientation blow molding, especially ones made of polyethylene teraphthalate resin are used in various fields, as they have many superior characteristics.
The synthetic resin bottle formed by biaxial oriented blow molding, in general, is made from a cylindrical preform with a bottom, using injection molding method. The bottle is shaped by drawing the preform axially and radially when it is heated to the temperature that it becomes elastic. The preform P has a cylindrical shape having a bottom, like a test tube, and a cylindrical mouth portion. Around the cylindrical mouth portion, normally, is a thread groove to screw on a cap. Further surrounding below the cylindrical mouth portion is an integrated jaw-like neck ring.
Such preform P is loosely fitted to a cylinder guide 10 of a preform holding jig 5, shown in FIG. 4 with the cylindrical mouth portion at the bottom. While held in this position, the preform P is heated to the temperature which the preform P becomes elastic. The heated preform P is then inserted to a blow metal mold 1 with the preform holding jig 5.
The blow metal mold comprises a cavity of the same shape of a bottle to be formed, an attaching concavity for the holding jig which has an insertion opening to insert the main body of the preform into the cavity, and a neck supporting jaw 3 inside the cavity and in contact with the neck ring P1 of the preform P for cooperating with the holding jig 5 in fixing the preform P to the metal mold.
The center of the holding jig 5 is provided with a draw bar insertion hole 11, penetrating the holding jig, therein. When the preform is set in the metal mold, a draw bar 16 is inserted through the draw bar insertion hole 11, presses with its tip the bottom of the preform, heated and now elastic deformable, and stretches the preform to the axial direction. Simultaneously, blow air will be forced in through the draw bar insertion hole 11 or through an air supply hole on the draw bar 16. The blow air draws the preform radially, thereby forming a bottle P'.
When molding the preform P into the bottle P' by biaxial oriented blow molding, a sealing will be necessary in order to prevent the blow air pressed inside the preform P from leaking from the metal mold. The sealing will be achieved according to the method stated below.
First, a seal ring 15 is installed to the base of a guide cylinder 10 of the holding jig 5. The preform held by the holding jig 5 is inserted into the cavity of the metal mold, and the holding jig 5 is attached to the attaching concavity 4 of the blow metal mold 1. Then force pushing the neck supporting law 3 downward pushes the preform P closely to an open end of the cylindrical mouth portion P2 of the preform P, thereby completing the sealing.
The blow pressure required for the biaxial oriented blow molding to mold the preform P into the bottle P', depending on the dimension of the preform P and/or on the percent of stretch to the bottle P' to be molded, generally is equals to or greater than 20 Kgf/cm2. In case of double stage blow molding where the blow molding of the preform P to the bottle P' is divided into 2 stages, the blow pressure required increases to 30-40 Kgf/cm2 or more.
As stated, a powerful blow pressure is applied to the preforms when molding the preforms into bottles using biaxial oriented blow. In regard to this point, the conventional technique has achieved the sealing by closely contacting the open end of the cylindrical mouth portion P2 of preform P to the seal ring; therefore, the enormous blow pressure is applied not only to the body of the preform but also to the cylindrical mouth portion. Thus, the size of the cylindr
Ichizawa Yoshiyuki
Kimura Masanori
Koshidaka Yukio
Seki Nobuichi
Timm Catherine
Yoshino Kogyosho Co. Ltd.
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