Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Including application of internal fluid pressure to hollow...
Utility Patent
1998-06-01
2001-01-02
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...
C264S532000
Utility Patent
active
06168749
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a process for producing container, in which process a heated pre-form made of thermoplastic material is stretched and blown up with the aid of a gas under pressure and in which process the blowing up process is divided into a preliminary blowing phase with a gas under a lower pressure level and to a subsequent primary blowing phase with a gas under a higher level of pressure.
Such a process is described, for example, in DE-OS 43 40 291. Possibilities for controlling the varying pressure are given in DE-OS 41 13 874. A device for carrying out the process is described in DE-OS 42 12 583.
In such processes and with such devices variously shaped pre-forms, depending on the particular use intended, can be reshaped into containers and in particular into bottles. The contours of the container can be varied within very wide bounds.
One pre-form with a wall thickness changing by steps is known in the art from EP-OS 0 379 264. Here the outer limit of the pre-form wall thickness runs essentially parallel to a longitudinal axis and the interior wall thickness is thickened by steps in an area facing the ground. A pre-form with an essentially uniform wall thickness in the direction of its longitudinal extensions is described in DE-OS 40 33 531. A special variant for heating a pre-form with approximately uniform wall thickness is described in DE-OS 42 23 933.
Containers made from such pre-forms can have various characteristics and application. Known in the art are both single-use containers and refillable containers. In addition, containers are known in the art that can withstand increased temperatures when being filled, for example, during the washing processes.
Such a container can be shaped, for example, in such a manner that first a pre-form is produced from polyethylene terephthalate (PET) through injection molding, heated following an interstratification of the pre-form and then fed into the blowing station. But it is also known in the art to produce containers following the spray-blowing process, in which the pre-form, without an intervening heating up, can be fed into the blowing station immediately after being produced and after a sufficient stability has been achieved. Finally, it is also known in the art to produce pre-forms from tube segments, which are sealed off in the region of their end and are provided with a suitable mouth at their other end.
Common to all of the processes is that fact that the pre-form has essentially a smaller shape than the container to be produced. The pre-form for this reason inside the blowing station is charged with compressed air to transform it into the container intended to be produced. In this inflating process the material is oriented, in addition to a narrowing of the wall thickness owing to an expansion of the surface. This causes the thin wall of the container to have a very high wall stability, which makes the container suitable for a variety of uses.
Various processes for carrying out the blowing process are known in the art. For one thing, it is possible to use a uniform blowing pressure which is introduced into the pre-form to be inflated and which is deflated after being sufficiently formed from the finished container against surrounding pressure. It is also known in the art first to cause a preliminary expansion of the preforms which already approximates the form of the container to be produced relatively close with a lower pressure and only then to shape the finer contour of the container using a higher pressure. In this process the compressed air is also not deflated against surrounding pressure after the container has been produced.
The shaping of pre-forms previously known in the art cannot satisfy all requirements for the distribution of materials placed on manufactured containers. Geometry and tempering of the pre-form essentially influence the material distribution in blown containers. For reasons of costs, wall thickness' as slight as possible are striven for, which, owing to a very high bi-directional orientation still have a high tensile strength. In addition, it is attempted to have a uniform wall thickness in the area of the lateral wall of the container, and the goal is to have as little non-oriented material as possible in the area of the bottom of the container. Non-oriented material left in an amorphous tends to crack and thus impairs the durability of the container.
Material not required from a technical standpoint in the area of the bottom has the consequence of additional costs from the requisite use of materials, which with high production figures can run into large amounts. On the other hand, sufficient material must be present to allow for forming a standing ring or foot for the blown containers in the area of the foot of the pre-form and must be provided to shape the intended contour as conditioned by the maximum extension possible.
The process sequences known in the art for tempering the pre-form for carrying out the inflating and orientating process, especially in the production of small containers, can still not fulfill all requirements placed for long-lasting storage stability for the beverages filled into the containers. With smaller bottles there is a relatively unfavorable ratio between surface size to inner volume. Because of the material properties of many thermoplastic plastics, this causes carbon dioxide to escape from beverages containing this or oxygen to be absorbed by the fluid. Also, properties of permeability against other materials, as for example with aromatic materials, can be present.
Processes known in the art for improving barrier properties will employ, for example, multi-layer pre-forms, in which one or several layers will have special properties for lessening gas permeability. However, the multi-layer pre-forms are, for one thing, expensive and, for another, reduce the possibilities for recycling because of the combination of materials. It is also known in the art, for example to use co-polymers or blends of PET and PEN.
The task of the present invention, accordingly, is to improve a process of the type described above in such a manner that the properties of the containers produced can be improved in respect of the storage stability of the filling product without any significant increase in cost.
The task is solved in keeping with the present invention by selecting the ratio of the diameter of the container to the inner diameter of the pre-form to be more than 4.0; by letting the pre-form have a median wall thickness of greater than 3 millimeters, by providing a material temperature in the orientation area greater than 70 degrees Celsius, at least at the beginning of the preliminary blowing phase; by letting the pre-form, at least at the beginning of the preliminary blowing phase, have a medium temperature at its outer surface in the area to be oriented, which is equal to a medium temperature of the inner surface of the pre-form in the area to be oriented; by selecting a temporal duration of the preliminary blowing phase of less than 1.0 second and by expanding the pre-form to at least 50 percent of the volume intended for the finished blown container during the preliminary blowing phase.
The actual choice of the medium wall thickness of the pre-form is made in dependence on the actual size of the container and especially in dependence on the volume of the container.
The combination of pre-form dimensions selected in dependence on the dimensions of the container, the choice of temperature relative to the temporal sequence of the expansion process, the temperature distribution in the pre-form and the temporal coordination of the preliminary blowing phase and the primary blowing phase relative to the respective volume of an interim product causes the end product to show significantly improved properties because of the material properties achieved relative to the state of the art to reduce gas permeability. Significant improvements can be realized especially in combination with a suitable choice of thermoplastic m
Harness & Dickey & Pierce P.L.C.
Krupp Corpoplast Maschinenbau GmbH
McDowell Suzanne E.
Silbaugh Jan H.
LandOfFree
Method of manufacturing containers does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of manufacturing containers, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of manufacturing containers will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2500586