Patent Application
20060255513
1. Field of the Invention
The present invention relates generally to a method and apparatus for blow-molding containers, and more particularly to an improved mold.
2. Related Art
Blow-molded plastic containers are commonplace in packaging beverages and other liquid, gel, or granular products. A large number of beverages, as well as a variety of food products, are packaged in plastic containers and/or containers. Plastic has proven to be readily adapted to being formed into a variety of shapes and sizes, and a variety of plastics can be used to form containers to package beverages, for example, non-carbonated, carbonated, refrigerated or pasteurized beverages, as well as containers for semi-solid food products, to include mayonnaise and peanut butter.
The plastics used to form these containers may include high density polyethylene (“HDPE”) used primarily for forming milk containers and for industrial applications, for example forming drums, flasks, and toys; polyvinylchloride (“PVC”), the pioneer polymer used in packaging non-carbonated or slightly carbonated beverages; and polyethylene terephthalate (“PET”), which is a lightweight transparent plastic material having superior resistance to impact, heat, and pressure, and which is 100% recyclable. PET is among the most commonly used plastics for packaging non-carbonated and carbonated liquids, to include water, fruit juices, soft drinks, cooking oil, household cleaning products, as well as liquids which may have required pasteurization or hot filling.
Biaxially oriented containers which are manufactured for use as containers for pressurized liquid are conventionally made using a blow molding process. In one type of blow molding process the preform is blown into conformance with a chilled mold. But in order to increase the dimensional stability of biaxially oriented containers to make them useful for “hot fill” operations, it is necessary to thermo-fix or “heat set” the biaxially oriented container in such a way that substantially relieves the remaining internal stresses.
A typical type of blow molding machine utilized to manufacture blow molded containers is a wheel blow molding machine which is vertically disposed and rotates about a horizontal axis. An example of such a machine is illustrated in FIG. 1 of U.S. Pat. No. 5,681,597 issued to Aguilar et al. and by the discussion provided in the Aguilar patent on column 2, line 52 to column 3, line 23. To this end, the blow molding machine has a plurality of molds positioned in a circular array following a circular path of motion. Each mold has a pair of mold halves which open to receive a parison or perform which can be formed by ejection molding. The mold halves then close so that the parison can be blown into conformance with the cavity defined by the mold. After the preforms are heated to the desired temperature, usually near the glass transition temperature (Tg) of the particular plastic from which the preform is molded, the preform is transferred into a blow-mold cavity. While in the blow-mold cavity, the preform is blown by means of compressed air into the shape of the mold cavity while preferably simultaneously being subjected to axial stretching to effect biaxial orientation of the container, all known in the art. The mold halves then open to release the blown article. All of these operations occur as the wheel continuously rotates at a constant speed, thereby forming and releasing blown articles in a continuous manner.
As the air is blown into the preform, the air between the cavity wall and the preform must be vented as the preform expands. If additional air is introduced into this area at a volume and supply that cannot be handled by the venting process, problems with the container may result. Interference with the venting process causes lack of container detail and definition and the overall heat set capabilities of the mold may be compromised. One source of additional air that may interfere with the venting process is air introduced by the blow nozzle via the gap between the mold halves and into the mold cavity. Existing blow molding apparatuses lack a proper seal at the parting line between the blow mold halves below the blow nozzle. Air may enter the mold via this opening. It is thought that the cooling effect resulting from the rapid traveling of air over the mold surfaces may contribute to ovality of the container in the area under the support flange. As containers are often conveyed or located by this area for labeling and capping, the ovality results in overall production line inefficiency.
The overall blow mold quality of a well-designed heat set blow molded container may be determined by a combination of factors directed to the economics of the process (impacted by the speed of blowing) and the surface temperature of the hot blow mold (limited by the amount of cooling gas which can be blown through the container). There is therefore a need to reduce or eliminate the amount of air introduced into the mold cavity via the mold gap.
In an exemplary embodiment of the present invention, a blow molding apparatus is disclosed. The apparatus comprises a plurality of mold shells disposed adjacent to each other and having interior surfaces that define a mold cavity and a gap between adjacent ones of the mold shells. A barrier is arranged in the gap to at least partially block air from flowing via the gap into the mold cavity.
In another embodiment of the invention, the blow mold comprises a first mold shell having an interior surface defining a partial mold cavity and a border surface on the interior surface outside of the cavity. A second mold shell has an interior surface defining a partial mold cavity and a border surface on the interior surface outside of the cavity. The first and second mold shells form a mold cavity when their respective partial mold cavities and border surfaces are arranged opposite and interface with each other. A gap is arranged at the interface between the border surfaces of first and second mold shells. A barrier is formed in the gap to form a seal at least partially preventing air flow through the gap into the mold cavity.
In another embodiment of the invention, a mold is provided. The mold comprises two mold halves defining a mold cavity therein. The mold has a first end with an opening formed by the mold halves communicating with the mold cavity and adapted to receive a perform. A parting line is arranged between the mold halves at the first end, with a seal arranged in the parting line.
In another embodiment of the invention, a method of molding a container is provided. The method comprises bringing a plurality of mold shells together to define a cavity corresponding to the container therein; inserting a preform into the cavity; blowing air into the preform in order to expand the preform within the cavity; and substantially preventing the blow air from entering the cavity via a gap between the mold shells.
Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings.
The foregoing and other features and advantages of the invention will be apparent from the following, more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.
A preferred embodiment of the invention is discussed in detail below. While specific exemplary embodiments are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations can be used without parting from the spirit and scope of the invention.
Referring now to the drawings, in
As best shown in
Numeral 28 generally indicates a parison or preform which is substantially test tube shaped. The elongated tubular preforms 28 have a closed end and an opened end around which is generally formed a thread. The preforms are loaded onto a suitable blow nozzle for conveying the preforms into the mold via the opening 22 at the first end 6 of the mold for a blow molding operation. The present invention is described with reference to stretch blow molding. However, molds having a barrier according to the present invention can be used in other blow molding operations, for example, any of extrusion blow molding, and injection blow molding, which are well known to those of skill in the art. During the blow molding process, the mold shells are typically heated in order to heat set the container.
The blow nozzle 30 with the preform 28 mounted thereon is lowered towards the closed mold shells. The preform 28 is inserted into the mold via the opening 22 at the first end 6 of the mold. The blow nozzle 30 is lowered until the blow nozzle 30 contacts a striking plate 32 on top of the mold shells (
The preform 28 is expanded within the mold to form the desired container by the introduction of a blowing gas into the preform 28 through its open end. Thus, the preform 28 is stretched and continues to expand within the mold until the walls of the container conform to the shape of the mold cavity. When the blown container achieves contact with the surface 11 of the cavity within the mold, the container is maintained in contact with the mold cavity surface 11 by continued application of the blowing gas pressure for a time sufficient to cool the inner surface of the container sufficiently to maintain the shape of the container when the blowing pressure is stopped and the blow mold opens. The mold shells are moved to the open position to remove the molded article.
The mold shells may also include vents 36 as shown in
One such source of additional air may be air from the blow nozzle 30 that enters the cavity through the mold parting gap 20 during the blow molding process. If blow air from the blow nozzle 30 is allowed to enter the cavity, the blow air is of a volume and supply that can not be handled by the cavity vents 36. In order to prevent or minimize this or other air from being introduced into the cavity via the mold parting gap 20, a barrier, such as seal 40, for the mold parting gap 20 may be provided as shown in
In a further embodiment of the invention, as shown in
Accordingly, embodiments of the present invention provide an improved blow mold apparatus and method. For example, the barrier may prevent or substantially reduce the blow air from entering the cavity at the mold parting gap, increasing overall container definition, detail and heat set qualities.
While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should instead be defined only in accordance with the following claims and their equivalents.
