Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Starting material is nonhollow planar finite length preform...
Reexamination Certificate
1999-12-02
2002-08-27
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Starting material is nonhollow planar finite length preform...
C264S553000
Reexamination Certificate
active
06440354
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a thermoforming method and apparatus for making a bowl-shaped container out of a thermoplastic resin sheet, a thermoforming female die, a method of thermoforming a bowl-shaped container, a thermoforming plug, a method of thermoforming a product with undercut and a thermoforming female die.
2. Description of the Prior Art
When a bowl-shaped container having a rim of a bottom is made of a thermoplastic resin sheet, the melted resin sheet is conventionally folded at the rim of the bottom.
FIG. 21
shows a section of the rim made in this conventional method. Also, when a body of the container is rendered rugged, the thermoplastic resin sheet is folded into folds.
FIG. 22
shows a section of the rugged body.
Japanese Patent Publication Nos. 50-87162A and 50-67370A disclose adjustment of thickness in the thermoforming by a plug. In the former, the plug is formed to be circumferentially split and each of split pieces is pivotally supported on an outer circumferential side of a base so that the diameter of an upper outer circumferential end can be spread and reduced. The plug in the reduced state is caused to abut against the thermoplastic resin sheet so that the sheet is pushed into a female die. Thereafter, the diameter of the plug is spread. This changes the degree of preliminary extension of a bottom wall of the thermoformed product, whereby the thickness is adjusted.
In the latter, the plug is supported on an elastic member such as a coil spring. While abutted against a thermoplastic resin plate, the plug is caused to strike against the female die so that the spring is contracted. As a result, the preliminary extension is carried out by the stroke of the spring in addition to the length of the plug regarding the circumferential wall.
In the thermoforming, the thermoplastic resin plate is heated so as to be plastic and then sucked into a die for the forming. The thermoplastic resin plate is thereafter removed from the die. Since the thermoplastic resin plate, even when hardened, has flexibility, a certain undercut can be performed.
In the aforesaid conventional method, an annular opening is formed in the bottom of the folded container so as to correspond to the rim. Accordingly, when poured into the container, soup or the like enters the annular opening. This results in no problem when the container is non-returnable. However, when the container is cleaned for re-use, it is difficult to wash away the soup or the like remaining in the annular opening. It is also difficult to wash away the soup or the like remaining in openings of the folds formed in the body of the container.
Further, the aforesaid thermoforming plugs have the following problems. Since the plug is split and pivoted in the former, the construction thereof becomes complicated. In the latter, the plug is caused to abut against the inner face of the female die. At this time, the thickness is reduced and accordingly, the plug cannot actually be employed.
Further, in the conventional method of thermoforming the product with an undercut, an allowed undercut is small. For example, when a rim of a bottom is made as a bowl for cupped noodle, a satisfactory result cannot be achieved.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a thermoforming apparatus and method, a thermoforming femele die, and a method of thermoforming a bowl-shaped container, which form the bowl-shaped container by folding a part of the resin sheet and yet which can prevent soup or the like from entering the opening formed in the bottom or the body thereof, a thermoforming plug, termoforming apparatus and method, which can provide a flexible thickness adjustment with a simple construction, a method of thermoforming a molding with an undercut and a thermoforming female die therefore, which can allow a large undercut to be stably removed from the die.
To accomplish the object, a first embodiment of the invention provides a thermoforming apparatus compressing a thermoforming female die and a plug moved forward and backward so that a softening thermoplastic resin sheet is thrust into the thermoforming female die. In the apparatus, the thermoforming female die includes a rim forming recess formed generally into a shape of a bowl-shaped recess, communicating with a bottom opening and of the bowl, an outer wall, a bottom wall and an inner wall of a rim of the bottom, and a bottom plate formed into a columnar shape similar to the bottom opening and supported to be moved forward and backward relative to the rim forming recess, the bottom wall being driven between a first position where the bottom plate is retreated inside the rim forming recess and a second stop position where the bottom plate is in the vicinity of the bottom opening. Further, the thermoplastic resin sheet heated to be softened is thrust by the plug while the bottom plate is held at the first stop position. The thermoplastic resin sheet is brought into close contact with an inner circumferential surface of the bowl-shaped recess and immediately thereafter, the bottom plate is moved to the second stop position so that a rim is formed.
In the invention of the first embodiment thus constructed, the thermoforming apparatus the thermoforming female die and the plug moved forward and backward so as to thrust the thermoplastic resin sheet into the thermoforming female die. The thermoforming female die is formed into a generally bowl-shaped recess. The female die has the rim forming recess communicating with a bowl bottom opening of the bowl-shaped recess so as to form the bottom wall of the bowl-shape and an outer form wall, bottom wall and inner wall of the rim. The bottom plate formed into the columnar shape similar to the bottom opening is supported to be moved forward and backward relative to the rim forming recess. The bottom plate is driven between the first stop position where the bottom plate is retreated inside the rim forming recess and a second stop position where the bottom plate is in the vicinity of the bottom opening.
Accordingly, the thermoplastic resin sheet heated to be softened is thrust by the plug into the female die while the bottom plate is held at the first stop position. When brought into close contact with the inner circumferential surface of the bowl-shaped recess, the thermoplastic resin sheet is expanded along the top of the bottom plate located inside the rim forming recess. However, immediately thereafter, the bottom plate is moved to the second stop position. Accordingly, the thermoplastic resin sheet on the top of the bottom plate is pushed up from the rim forming recess side to the bottom opening of the bowl-shaped recess. Then, a peripheral edge of the thermoplastic resin sheet turned up by the bottom plate and a part of the sheet positioned in the vicinity of the opening of the rim forming recess are welded together. More specifically, although the part of the sheet in the rim forming recess is expanded, the bowl bottom is immediately moved upward toward the bottom opening so that the parts of the sheet are welded together.
According to the first embodiment of the invention, when the bowl-shaped container with a rim is made out of the thermoplastic resin sheet, no gaps are formed inside, and re-use by cleaning can be rendered easy.
A second embodiment of the invention is constructed so that in the thermoforming apparatus of the first embodiment, the rim forming recess includes a first portion spread outward so as to be continuous from the bowl bottom and a second portion continuous from the first portion and having a reduced inner diameter, the first and second portions forming the outer wall and the bottom wall.
In the invention of the second embodiment thus constructed, the rim forming recess is spread out from the bowl bottom opening and its inner diameter is then reduced. Accordingly, a spread rim outer side wall surface is formed by this inclined portion. Further, a bottom wall of the rim is formed by a flat portion where the inner diameter is
Kikkawa Takashi
Maeda Tatsushi
Mizoguchi Kenichi
Takai Toshihiro
Yoshikoshi Akio
Armstrong Westerman & Hattori, LLP
Kabushiki Kaisha Asano Kenkyusho
Tentoni Leo B.
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