Patent Application
20090224439
The present invention is directed generally to injection molding apparatus and methods of making plastic preforms. More particularly, the present invention is directed to crystallizing a portion of a preform while cooling the preform.
Conventional manufacture of plastic (e.g. polyethylene terephthalate (PET)) containers employs an initial step of forming a substantially amorphous and unoriented parison or preform by an injection molding process. A process of crystallizing the finish of the preform is sometimes used to thermally stabilize the dimensions of the finish. This crystallization process is generally a separate operation performed between the injection molding process and a later blow molding process.
When performed as a separate operation, the crystallization process significantly increases the cost of production by way of increased equipment costs and operational expenses for each additional piece of equipment required (i.e., perform handling and transfer apparatus and crystallizer), increased further by the cost of custom tooling for each specific product undergoing this additional operation. As a further detriment, the additional handling increases the opportunities for damaging the preforms.
In accordance with various embodiments of the present invention, it is desirable to provide a process and apparatus for crystallizing a portion of a preform during cooling of the injection molded preform. Preferably, the crystallization can be accomplished without significantly increasing the cost of the container product and/or the operation (cycle) time for producing the preforms. This may be accomplished by crystallizing a portion of the preform while the preform is being cooled in a cooling, or take-off, tube. Preferably, the preform molding, cooling and crystallization is performed as a batch process on a plurality of preforms.
In accordance with one embodiment of the invention, a method of making a plastic preform comprises molding at least one preform in an injection molding apparatus, moving the at least one preform to a cooling tube while the at least one preform is in a deformable state, cooling the at least one preform from the deformable state to a temperature at which deformation of the at least one preform is resisted, and crystallizing a portion of the at least one preform during the cooling step.
According to another embodiment of the invention, a method of making a plastic preform comprises molding at least one preform in an injection molding apparatus, moving the at least one preform to a cooling tube while the at least one preform is in a deformable state, cooling the at least one preform from a deformable state to a temperature at which deformation of the at least one preform is resisted, heating at least a portion of a finish of the at least one preform to crystallize the finish portion during the cooling step, and inserting a sizing plug in the finish to reduce or eliminate shape deformation due to the crystallizing. The sizing plug may be inserted prior to, during, or after the heating (crystallizing) step.
In one embodiment, the sizing plug is cooled prior to and/or after insertion into the (amorphous or crystallized) neck finish. Crystallizing will generally stop when a cool plug is inserted. A hot finish will continue to crystallize, with or without the heater present, until cooled by air or the plug.
In accordance with other aspects of the invention, an apparatus for making performs comprises an injection molding apparatus configured to mold at least one preform, a cooling tube configured to receive the at least one preform in a deformable state and to cool the preform to a temperature at which deformation of the at least one preform is resisted, and a crystallizing member configured to crystallize a portion of the at least one preform while the at least one preform is in the cooling tube.
In various embodiments, at least a portion of the finish and more particularly the top sealing surface (TSS) of the preform is crystallized. The crystallizing may be accomplished by radiant heating or by directing heated air at the preform. The heating step may be followed by a sizing step in which a plug, preferably a cooling plug, is inserted into the warm neck finish to eliminate or reduce any shape deformation that may occur due to crystallizing.
These and other embodiments will be described in the following detailed description.
One exemplary embodiment of an injection molding apparatus and method according to the present invention is illustrated in
An injection molding and cooling apparatus 100 includes an array of injection mold cavities (not shown) and cores 104 configured to receive molten plastic from a source of molten plastic (not shown), as is well known in the art. Molten plastic is injected into each of the molds to form a plurality (batch) of injection molded preforms.
The injection molding and cooling apparatus 100 further includes an array of cooling tubes 110, also known as take-off tubes, configured to hold and cool the one or more preforms 150 formed by the injection molding apparatus 102. The cooling tubes 110 may comprise any known cooling tubes, as would be understood by persons skilled in the art. The cooling tubes receive the preforms 150 from the molds in a deformable state and cool the preforms down to a temperature at which deformation of the preforms is resisted. A robot (not shown) may be configured to move the cooling tubes 110 relative to the mold cores 104 (i.e., from a first position for receiving the hot performs from the cores, to a second position for cooling and/or transfer of the cooled performs to a conveyor or gaylord for collection of the cooled preforms.
As is well known in the art, the preforms 150 may be partially cooled in the molds before being ejected from the injection molds. According to various aspects, the preforms 150 may be in the mold cavities only long enough to form an exterior skin which enables their safe (relatively deformation free) transfer to the cooling tubes.
The injection and cooling apparatus 100 according to the disclosed embodiment of the invention includes a crystallizing member 120 configured to crystallize a portion of the preforms 150 while the preforms 150 are being cooled in the cooling tubes. In this embodiment, the portion of the preforms 150 to be crystallized is a portion of the finish 152 including the top sealing surface (TSS) 153. Thermal crystallization of the TSS (and optionally other portions of the finish) may be useful in later processing steps and/or during use, storage or handling of the container (e.g., blow molding of the container, hot filling, pasteurization, and/or hot caustic wash cleaning of refillable containers). A crystallized finish, which is more resistant to deformation, can improve the sealing engagement between the finish and closure (e.g., screw-on cap). In this embodiment, the crystallizing member 120 is configured to substantially complete the crystallization process (of the TSS) while the preforms are being cooled to a temperature at which deformation of the preforms is resisted (e.g., below the glass transition Tg temperature range of the polymer).
The crystallizing member 120 may comprise one or a series of heating elements movable relative to the cooling tubes 110 via, for example, a robot (not shown).
Alternatively, the crystallizing member 120 may comprise a hot air blower device 222, as illustrated in
As shown in
As shown in
In one embodiment, polyester beverage bottle preforms were made from Eastman 9921PET (available from Eastman Chemical Company, Kingsport, Tenn., USA). It was found sufficient to crystallize the TSS by positioning a flat panel radiant heater at a temperature of 1000° F. about ⅜ inches from the TSS for a time between 45 and 65 seconds. Different materials will require different times/temperatures/placement (distance from) the heater. Typical crystallizable polymer materials include polyesters (e.g., polyethylene terephthalate (PET) and polyethylene naphthalate (PEN)), polyolefins (e.g. polyethylenes and polypropylenes), and polyamides. Various preform materials, blends, layer structures, etc., may be used including one or more thermocrystallizable polymers. In various embodiments, particularly for treating polyester preforms, the heater may be positioned from about ⅜ to ½ inches from the preform portion to be crystallized, the heater may be in a temperature range of about 500° F. to 1250° F., and the crystallizing may take about 30 to 75 seconds. As used herein, PET includes PET homopolymers and copolymers as is well known in the art (i.e. generally including up to 10% of other monomers). Fillers, additives, colorants, etc., may also be present in the polymer material.
Referring to
In a further embodiment, after crystallizing a finish portion of the preforms, a plug may be inserted into the crystallized finish portion while still warm (deformable) to reshape the finish in order to reduce or eliminate any shape deformation which occurred during heating and crystallizing. For example,
The aforementioned apparatus and methods may increase the efficiency of producing a preform, and subsequently a container, with a crystallized portion. For example, performing the crystallization while the preforms are in the cooling tubes will reduce the handling of the preforms that would otherwise be necessitated by a separate operation and reduce the production time (compared to a separate crystallizing operation). The cost of crystallization may be kept to a minimum by using the already existing cooling tubes. Performing crystallization during the injection molding and cooling process may prevent damage to an otherwise uncrystallized portion of the preform that may occur between the injection molding and blow molding processes.
Various known preforms, injection molding apparatus and methods of making preforms may be used in the present invention, including single layer and multilayer, single material and multi-material, standard flat face multi-cavity injections molds, rotating turret molds, reciprocal shuttle molds, etc. The preform finishes may be of various types, with or without threads, optionally including a capping flange, and with or without a bead or snap-on mechanism for attaching a closure, dispensing spout, or the like.
It will be apparent to those skilled in the art that various modifications and variations can be made in the apparatus and methods of the present disclosure without departing from the scope of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only.
