Stock material or miscellaneous articles – Hollow or container type article
Reexamination Certificate
1999-03-23
2002-02-05
Pyon, Harold (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
C428S036600, C428S036700, C425S130000, C264S328800
Reexamination Certificate
active
06344249
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multi-layered article such as a multi-layered container, a multi-layered parison which is a precursor of a multi-layered container, and a blow molded multi-layered container.
2. Description of the Related Art
In recent years, containers formed of thermoplastic resins are widely used as containers for cosmetics, foods, beverages and the like, from the viewpoints of light weight and safety for breaking. The development of containers formed of a polyethylene terephthalate resin (to be sometimes abbreviated as “PET resin” hereinafter) in particular is rapidly advancing owing to improvements in biaxial orientation blow molding technology. However, a container formed of a biaxially oriented thermoplastic polyester resin composed mainly of PET resin does not necessarily have complete performances. That is, when the content to be filled in a container is a food which requires high gas barrier properties of the container, the container formed of PET resin is insufficient in gas barrier properties against oxygen gas and carbon dioxide gas, and therefore, the container formed of PET resin has a defect that the taste of the content is impaired.
For satisfying the above requirement, JP-A-57-128520 (corresponding to U.S. Pat. No. 4,535,901) discloses a method in which an injection-molding apparatus having two injection cylinders for separately plasticizing and melting a thermoplastic polyester resin and an m-xylylene-group-containing polyamide resin (to be sometimes abbreviated as “MX nylon resin” hereinafter) which is a thermoplastic gas-barrier resin, respectively, and having a single mold is used, and in one molding cycle, the molten thermoplastic polyester resin is injected, the molten MX nylon resin is injected while the molten thermoplastic polyester resin is being injected, and the injection of the molten thermoplastic polyester resin is continued even after completion of injection of the molten MX nylon resin, to form a parison having a three-layer structure of the thermoplastic polyester resin layer/the MX nylon resin layer/the thermoplastic polyester resin layer. The above injection molding method is called a simultaneous-injection molding method.
Further, JP-A-60-240409 (corresponding to EP No. 161625/1985) discloses an injection-molding method similar to the above method, in which, for example, a molten thermoplastic polyester resin and a molten MX nylon resin are injected under specific conditions in the order of the molten thermoplastic resin, the molten MX nylon resin and the thermoplastic polyester resin, to form a parison having a five-layer structure of the thermoplastic polyester resin layer/the MX nylon resin layer/the thermoplastic polyester resin layer/the MX nylon resin layer/the thermoplastic polyester resin layer. The above method is called an alternate-injection molding method.
In recent years, further, a technique is being developed for pelletizing collected containers composed mainly of PET resin and recycling them as a recycled PET resin. When the above recycled PET resin (including a PET resin reclaimed from defective products in the production of parisons and a recycled PET resin once used in the production of parisons) is used to produce parisons for beverage containers, it is required to form a parison having a three-layer structure of the PET resin layer/the recycled PET resin layer/the PET resin layer or a five-layer structure of the PET resin layer/the recycled PET resin layer/the PET resin layer/the recycled PET resin layer/the PET resin layer.
The methods disclosed in the above Japanese Laid-open Patent Publications have enabled the production of multi-layered containers (bottles) having an appearance and mechanical performances equivalent to those of a container formed of a polyethylene terephthalate resin and having greatly improved barrier properties against oxygen gas and carbon dioxide gas, and thus-produced containers are now being used. Meanwhile, there are increasing demands for small-sized bottles in recent years. Since a small-sized bottle has a large surface area relative to a unit internal volume, the loss of carbon dioxide gas contained in a content generally increases, and oxygen gas permeates the contents to affect it to a greater degree. Small-sized bottles are therefore inevitably required to have higher gas-barrier properties.
Conventionally, when a multi-layered molded article (e.g., a multi-layered parison as a precursor of a multi-layered container) formed of two or more resins is produced by means of two or more injection cylinders, there is used an injection molding apparatus having a mold provided with a cavity and having two or more injection cylinders. For example, in an injection molding apparatus having two injection cylinders, resin-flow-passages (a first resin-flow-passage in which a first molten resin flows and a second resin-flow-passage in which a second molten resin flows) connecting the insides of the injection cylinders to the cavity are structured so as to meet with each other in a junction portion in the upstream of a gate portion opened to the cavity. Portions of the first and second resin-flow-passages positioned within the mold have a hot runner structure. Further, portions of the first and second resin-flow-passages upstream to the junction portion generally have the structure of a multiple tube. A screw provided in each injection cylinder is generally structured so as to move back when a pressure is exerted from the resin-flow-passage in any case other than the cases of injection of the molten resin and application of a dwell pressure, so that the molten resin in each resin-flow-passage flows back into each injection cylinder.
A multi-layered container (bottle) formed by biaxially stretch-blow molding a parison having the three-layer structure of PET resin layer/MX nylon resin layer/PET resin layer or the five-layer structure of PET resin layer/MX nylon resin layer/PET resin layer/MX nylon resin layer/PET resin layer has a problem that it is liable to undergo interlayer separation (delamination) when an impact is exerted thereon or when a sharp change occurs in internal pressure after carbonate beverage is filled therein. Further, when a multi-layered container (bottle) having an extremely bend portion is produced by a biaxially stretch-blow molding method, there is another problem that the bend portion is liable to undergo interlayer separation.
For example, JP-A-56-130351 discloses a method of improving the interlayer separation strength. It is described that the above method enables the production of a multi-layered article having high interlayer separation strength by forming an adhesive layer having a specific structure. Impractically, however, the method disclosed in the above Japanese Laid-open Patent Publication requires three injection molding apparatus, and at least there resins are required. Further, JP-A-57-128516 discloses a method of improving the interlayer separation strength, in which the injection of a molten resin for constituting the outermost layer (outer surface and inner surface) is completed before a resin for constituting no outermost layer is cooled to solidness, whereby each layer is brought into an amorphous state. However, the above method is not fully satisfactory for improving the interlayer separation strength.
As compared with a multi-layered container (bottle) having an MX nylon resin layer which extends from its body portion only to its neck portion, a multi-layered container having an MX nylon resin layer which extends from its body portion up to its spout or closure portion through its neck portion has improved barrier properties against oxygen gas and carbonate gas. Since, however, the spout portion is in a non-stretched state, the spout portion is whitened due to water absorption with the lapse of time (i.e., spherulite is formed), which is undesirable in appearance. Further, since gas-barrier resins including the MX nylon resin has a refractive index different from the refractive ind
Hara Takeshi
Maruyama Katsuya
Ota Takao
Terada Yoshihiro
Hon Sow-Fun
Mitsubishi Gas Chemical Company Inc.
Pyon Harold
Wenderoth , Lind & Ponack, L.L.P.
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