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
1998-11-23
2001-04-24
Silbaugh, Jan H. (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...
C264S540000, C264S541000, C425S525000, C425S526000, C425S535000
Reexamination Certificate
active
06221305
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to production of bottles by extrusion blow molding and, more particularly, to a method and apparatus for forming a neck finish in a wide range of plastic water dispenser bottles that has a smooth, straight inner diameter and is fully calibrated, not requiring any post trimming.
2. Description of the Related Art
Containers and other hollow articles are frequently formed by blow molding.
The blow molding process involves providing a tube of heated and softened plastics material (parison) about which a two-piece mold is closed. Air or another gas is introduced under pressure into the parison to expand it against the walls of the mold, forming the desired hollow article. Such blow molding machines can be of various types, the most common of which are extrusion-blow molding machines and injection-blow molding machines.
A requirement for the large bottles produced for the water bottle industry is a design that allows effective cleaning so that the bottles can be refilled and reused in a drinking water dispenser. An important feature with respect to the cleaning is a smooth, straight inner diameter for the neck of the bottle, so that there are no irregular surfaces that could retain bacteria or foreign matter. To ensure the desired surface for the inner diameter of the neck, the preferred method of the prior art has been to injection mold the desired neck geometry into a bottle preform that is subsequently reheated and blown to the final shape; i.e., form the bottles by the injection-blow molding process. While this process is very effective in producing bottles having the desired features, it tends to be relatively expensive due to the additional equipment and time associated with injection molding step.
Since extrusion-blow molding machines generally produce a less expensive container, they have also been used to some extent to form water bottles. However, they have not been well accepted because the inner diameter of the bottle neck lacks the desired smooth, straight geometry due primarily to variations in the geometry of the outer diameter. In extrusion-blow molding machines, plastics material is heated and softened in an extruder and is conveyed into a die head from which a tubular parison is extruded. The parison can either be continuous, whereby a plurality of molds are sequentially enclosed about successive, axially spaced portions of the parison, or individual parisons can be intermittently extruded into the mold area using an accumulator. In either case, the material is then ejected through an annular die to form a parison having the desired length, diameter, and wall thickness distribution.
More specifically, in the extrusion-blow molding process, the mold is closed over the parison pinching off (closing) the ends of the tubular parison. Air or another gas is injected inside the parison through a blow pin, expanding the parison to match the mold cavity. Obviously, the mold in this process controls only the shape of the outer surface of the bottle, including the neck. Since the outer surface of the neck has an irregular contour to facilitate use in dispensers or water coolers, the corresponding inner surface is also irregular since the material forming the inside wall is not constrained, resulting in varying wall thickness that further distorts as the bottle cools to ambient temperature.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method and apparatus for forming a water bottle that is economical to produce and will have a neck shape that will facilitate optimal cleaning of the bottle for reuse by the consumer. More particularly, it is an object of the present invention to provide a method and apparatus for forming a neck finish in a wide range of plastic water dispenser bottles that has a smooth, straight inner diameter and is fully calibrated, not requiring any post trimming.
In the preferred embodiment, the present invention accomplishes the stated objectives by a method and apparatus that enable the production of compression molded and finish-calibrated bottle neck from relatively a large range of plastic materials. More specifically, the invention involves the extrusion of a parison over a uniquely designed, fixed blow pin, which also serves as an inner mandrel for the neck. The parison wall thickness is programmed to provide the correct amount of material to fill the neck area and compression mold the neck body. During the clamp/mold closing, the area between the cutting ring and striker plate comes into contact to form a calibrated neck finish. Once the mold is closed the blow air enters the specially designed blow pin tip. The blow air is metered out the sides to help spread out material to reduce material push out and help cool lower neck area for a reduced blow air cycle time and distortion. This is achieved by a controlled orifice at the end of the blow air exit, metering the air through the lower side openings. The blow pin tip is also completely water cooled to the upper end. This gives a controlled shrinkage rate with optimum cooling to help reduce cycle time. The assembly is designed to be very rigid and thereby facilitate part de-molding.
In summary, the method and apparatus defined by the present invention facilitate production of economical, easily cleaned water bottles from a wide range of materials. Advantages to the water bottle industry are the wide range of plastic materials that can be used and the range of neck sizes that can be suitably formed. Another achievement is producing the straight inner diameter of the neck that facilitates total cleaning during bottle recycle. In particular, the invention eliminates inner grooves or voids in the bottle neck that would tend to retain stagnant water. This invention applies to both accumulator and continuous blow molding processes.
REFERENCES:
patent: 4116607 (1978-09-01), LeGrand
patent: 4234299 (1980-11-01), Kuenzig
patent: 4390338 (1983-06-01), Bowers et al.
patent: 4753591 (1988-06-01), Maes et al.
patent: 4954071 (1990-09-01), Austin
patent: 5449294 (1995-09-01), Spina
patent: 5749275 (1998-05-01), Dundas et al.
Friskney Stephen H.
McDowell Suzanne E
Milacron Inc.
Silbaugh Jan H.
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