Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Including application of internal fluid pressure to hollow...
Reexamination Certificate
1999-08-02
2002-09-17
McDowell, Suzanne E. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Including application of internal fluid pressure to hollow...
C264S535000, C264S538000, C264S904000, C264S905000
Reexamination Certificate
active
06451243
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method of molding a heat-resistant container particularly from a synthetic resin such as polyethylene terephthalate (which will be called “PET”).
2. Description of the Prior Art
In general, a synthetic resin thin-walled packaging container known as biaxial stretching blow molded container is formed by positioning an injection-molded or extruded preform having an appropriate temperature for stretching within a mold and stretching the preform in its longitudinal direction corresponding to the longitudinal axis of the container while at the same time expanding the same preform in its lateral direction under the action of a pressurized gas blown into the mold.
Depending on selection of a material used to form the container, however, a problem was raised in that the container deformed when it was filled with a hot content such as a thermally sterilized fruit juice beverage.
To overcome such a problem, a proposal such as the applicant's Japanese Patent Application Laid-Open No. 3-205124 has been made in which the blow molding step to be executed after the temperature of the preform has been regulated is divided into primary and secondary sub-steps. In the primary blow molding sub-step, a primary molding is formed in the desired form of a container. The primary molding is thermally processed to shrink and then subjected to the secondary blow molding sub-step to form the final container.
Such a proposed molding process can provide a heat-resistant container which is improved in mechanical strength through the thermal treatment before the secondary blow molding sub-step.
More particularly, the thermal treatment before the secondary sub-step removes a strain produced at the primary blow molding sub-step or a residual stress due to stretching, and crystallizes the oriented walls to a higher level. This improves the heat resistance of the final product which may be placed under a severe temperature condition in markets.
To attain such a heat-resistant container, it is required that the temperature of the primary molding has been increased sufficiently to improve the crystallinity in the primary molding at its oriented walls.
However, the prior art could not smoothly increase the temperature of the molding since the necessary heat was only transmitted to the molding through radiation within an atmosphere.
Therefore, a long time is required until the temperature of the molding reaches a level that can provide the necessary crystallinity for the molding to have its sufficient heat resisting property. Thus, time for heating or conveying the molding must be prolonged. This may extend the molding cycle or increase the dimensions of the container molding apparatus including the heating conveyor path.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an inexpensive and compact apparatus and method of molding a heat-resistant container to be filled with a hot content such as a thermally sterilized fruit juice, which can increase the crystallinity of the container and also reduce the residual stress thereof in a reliable and short manner, resulting in improvement of the form stability at high temperature to avoid a thermal deformation.
Another object of the present invention is to provide a heat-resistant container molding apparatus and method of molding a heat-resistant container in an efficient blow molding manner without thermal loss.
Still another object of the present invention is to provide a heat-resistant container molding apparatus and method of molding a heat-resistant container, in which when a plurality of steps using clamping mechanisms are used, it can be prevented to increase the installation space due to a stroke required to open and close the respective mold.
A further object of the present invention is to provide a heat-resistant container molding apparatus and method of molding a heat-resistant container, in which a preform can be sufficiently cooled such that the blow molding step will not be influenced by the heat history of an injection molded preform.
To accomplish these objects, the present invention provides a heat-resistant container molding apparatus comprising:
a primary molding section for blow-molding preforms into primary moldings by using a primary blow mold having split molds;
a heat treatment section for heat treating the primary moldings to obtain intermediate moldings by bringing the primary moldings into contact with inner walls of a heat treatment mold having split molds while pressurizing an interior of each of the primary moldings within the heat treatment mold; and
a final molding section for blow-molding the heat treated intermediate moldings into final products within a heated final blow mold having split molds.
According to the present invention, the heat transfer is carried out by heating the primary molding in direct contact with the inner wall of the heat treatment mold while pressurizing the interior of the primary molding. Therefore, the temperature of the molding can efficiently be increased for a short time. At the same time, the apparatus can be compacted. In addition, the residual stress produced in the primary molding can reliably be removed for a short time to increase the crystallinity of the primary molding. As a result, the form stability can be improved at a raised temperature reliably to prevent a container from being thermally deformed when the container is filled with a hot content such as a thermally sterilized fruit juice beverage or the like.
Since the heat shrinkage and thus uneven wall thickness is prevented by pressurizing the interior of the primary molding within the heat treatment mold, an uneven wall thickness and irregular heat resistance can reliably be prevented at the final blow molding step. Thus, a desired heat can certainly be provided to the molding without variability. This can stabilize the shrinkage in the intermediate molding after being heat-treated. Consequently, the wall-thickness distribution of the final product can also be stabilized.
In the final molding section after the heat treating step, a strain in the final product can be removed by heat treating it within the final heated blow mold when the intermediate molding is blow-molded into the final product in the final heated blow mold. Thus, the heat stability can be improved to increase the heat resistance in the final product.
In the apparatus of the present invention, it is preferred that it comprises a receiving section for receiving the preforms to be primarily molded and a removing section for removing the final products and wherein the primary molding, heat treatment and final molding sections being located adjacent to one another.
Since the primary molding, heat treatment and final molding sections are sequentially positioned, the final blow molding step can be carried out immediately after the heat treating step while maintaining the heat in the heat treated molding. Thus, the blow molding step can efficiently be performed without heat loss.
It is also preferable that the apparatus of the present invention further comprises conveyor means for intermittently conveying a given number of preforms to be simultaneously molded to the primary molding section and a given number of moldings to be simultaneously molded to the heat treatment and final molding sections respectively, and wherein each of the primary molding, heat treatment and final molding sections includes a mold clamping mechanism for clamping the split molds, the primary molding, heat treatment and final molding sections are rectilinearly disposed in a transfer direction.
Such mold clamping mechanisms require a stroke of opening and closing the split molds and thus an increased installation space. If the mold clamping mechanisms are disposed opposed to one another, the spacing between the adjacent conveyor means will unnecessarily be increased. This will also increase the installation space.
When the primary molding, heat treatment and final molding
Kitamura Kazuya
Sakurai Atsushi
Sato Koichi
Takada Minoru
Yokobayashi Kazuyuki
McDowell Suzanne E.
Nissei ASB Machine Co. Ltd.
Oliff & Berridg,e PLC
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