Plastic article or earthenware shaping or treating: apparatus – Female mold and means to shape parison directly by internal... – With heating or cooling means
Reexamination Certificate
1999-05-11
2001-06-19
Davis, Robert (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Female mold and means to shape parison directly by internal...
With heating or cooling means
C425S529000, C425S533000, C425S534000
Reexamination Certificate
active
06247916
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an injection stretch blow molding apparatus and method wherein containers are stretch blow molded from preforms retaining heat from when they were injection molded. This invention also relates to an injection stretch blow molding apparatus and method wherein N (N≧2) preforms are simultaneously injection molded and n (1≦n<N) preforms among these are simultaneously blow molded into n containers. More particularly, the invention relates to an injection stretch blow molding apparatus and method with which while ample cooling time is provided the preforms can be molded with a shortened injection molding cycle time and furthermore the operation rate of the blow cavities can be increased. Also, this invention relates to constructions and methods for heating and adjusting the temperature of the preforms before they are blow molded. Also, this invention relates to an injection stretch blow molding apparatus and method with which it is possible when necessary to discharge the preforms to outside the apparatus instead of carrying them to the blow molding section.
Methods for blow molding a container from a preform (parison) include that known as the cold parison or 2-stage method and that which is known as the hot parison or 1-stage method. In both these methods, for injection molding the preforms required for the blow molding, at least an injection cavity mold which shapes the outer wall of the preform and an injection core mold which shapes the inner wall of the preform are necessary. Also, after the injection cavity mold and the injection core mold are clamped together and the preform is injection molded, with the molds still clamped together it is necessary to cool the preform down to a temperature at which the preform can be released from the molds.
Particularly in the case of the cold parison (2-stage) method, because this preform mold-release temperature has to be made quite low, the injection molding cycle time has been long and productivity has been poor. This is because when the preform is ejected by the injection cavity mold and the injection core mold being released from the preform and the preform being dropped or the like, it is necessary for the preform to be cooled to a mold-release temperature low enough for the preform not to be deformed when it makes contact with other members.
In the case of the cold parison method, because the preform molding step and the step in which a container is blow molded from this preform are completely independent, the blow molding cycle time is not affected by the injection molding cycle time. However, because the cold parison method involves reheating preforms which have been cooled to room temperature the cold parison method is inferior to the hot parison method in its energy efficiency.
In a hot parison (1-stage) method, an injection stretch blow molding machine blow molds bottles from preforms still containing heat from when they were injection molded. The cycle time of the overall apparatus is determined by the injection molding cycle time, which of all the cycles is the one requiring the most time. Consequently there has been the problem that when the time required for injection molding is long, the throughput of the whole apparatus is low.
In the case of the hot parison method, although the preform is mold-released at a higher temperature than in the cold parison method, there is a limit on this mold-release temperature and consequently it is not possible to greatly speed up the injection molding cycle. One reason for this is that when the preform mold-release temperature is high, when the injection core mold is released from the preform, a mold-release phenomenon called lifting, wherein the preform sticks to the core mold, occurs. Also, after the injection core mold is released from the preform, because there is no longer any member restricting deformation of the preform, deformation caused by temperature nonuniformity and thermal contraction and the like make it impossible for preforms conforming to the design to be ejected. Furthermore, when the cooling effected by the injection core mold is inadequate, crystallization caused by inadequate cooling occurs, particularly at the inner wall of the preform, and a preform of which the trunk portion is opaque is ejected.
Also, when preforms are ejected before they are completely cooled by the injection core mold and the injection cavity mold (with the preforms still at a temperature at which blow molding is possible) and blow molding is carried out thereafter, there have been the following problems:
(A) Unless the internal pressure (injection sustain pressure) is raised, shrink marks form at the injection cavity mold side of the preform and a preform with a uniform temperature distribution cannot be obtained. Consequently, when this preform is blow molded, a molded product with a uniform wall thickness distribution cannot be obtained.
(B) When the internal pressure (injection sustain pressure) is raised, a pressure differential forms between the gate portion and the preform end portion (for example the neck portion), and the resulting preform has large residual stresses at the preform bottom end where the pressure was high. Consequently, when the preform is blow molded, a molded product with a uniform wall thickness distribution cannot be obtained.
(C) When the preform is cooled by the injection core mold and the injection cavity mold, as the cooling progresses the preform contracts and tends to move away from the injection cavity surface. Because of this, there are some parts of the outer wall surface of the preform which are in contact with the injection cavity and some parts which are not in contact with the injection cavity, and consequently different parts of the preform cool at different rates and the temperature becomes uneven. As a result, when this preform is blow molded, a molded product of uniform wall thickness cannot be obtained.
Thus, in a conventional hot parison system, unless the preform is amply cooled by the injection cavity mold and the injection core mold it has not been possible to obtain good blowing characteristics or good bottle characteristics. Because of this, the injection molding of the preforms has required time, and the throughput of the apparatus has been low.
Various other problems have also been associated with injection stretch blow molding machines using the hot parison method, including the following:
When in order to increase the throughput the number N of preforms injection molded simultaneously is increased, the same number N of cavities conforming to the external shape of the bottles being manufactured have to be formed in the blow cavity mold. Of the molds used in a blow molding machine the blow cavity mold is the most expensive, and the cost of this blow cavity mold increases roughly in proportion to the number of cavities in it. Even if a mold is expensive, if its operation rate is high then it can be used cost-effectively. However, because as described above the cycle time of the overall apparatus depends on the injection molding cycle time and cannot be shortened, the operation rate of each cavity in the blow cavity mold has unavoidably been low. Also, when the number of bottles blow molded simultaneously increases, not only the number of cavities in the blow mold but also the number of drawing rods and blow core molds and mechanisms for supporting and driving these increases, and this has resulted in increases in the size and cost of the apparatus.
Another problem has been that conventionally it has not been possible to eject the preforms unless the injection core mold is completely pulled out of the preforms, and consequently with a rotary injection molding apparatus it has not been possible to carry the preforms from the injection molding section to the next stage. When on the other hand the injection core mold is completely pulled out of the preforms, there has been the problem that this pullout stroke is long and the overall height of the apparatus is high.
Another problem ha
Ogihara Shuichi
Sato Koichi
Takada Minoru
Yokobayashi Kazuyuki
Cislo & Thomas LLP
Davis Robert
Hoffman Esq. David L.
Nissei ASB Machine Co. Ltd.
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