Process for single-step forming and filling of containers

Abstract

A process for the manufacturing and filling of plastic containers, the process comprising the steps of: positioning a preform with relation to a mold assembly of two or more components, the preform generally being fabricated from a plastic and being provided with a longitudinal axis and presenting a stretchable portion and a non-stretchable portion; stretching the preform along its longitudinal axis; injecting a fluid into the interior volume of the preform, the fluid being under such pressure as to cause the preform to plastically deform until achieving the desired size and shape; and releasing the container from the mold assembly and sealing the container, and in which at least a portion of the stretchable portion of the perform is at a temperature below its vitreous transition temperature (Tg) and, preferably, at ambient temperatures.

Claims

1. A process for the manufacturing and filling of plastic containers comprising the steps of: heating a localized zone of a stretchable portion of a preform to a temperature closer to its vitreous transition temperature (Tg) than to ambient temperature while maintaining at least a portion of the stretchable portion of the preform at a temperature closer to ambient temperature than to the vitreous transition temperature (Tg); positioning the preform in a mold assembly of two or more components while still having the heated localized zone and a portion of the stretchable portion at a temperature closer to ambient temperature, the preform being fabricated from a plastic and being provided with a longitudinal axis and including the stretchable portion and a non-stretchable portion; after positioning the preform in the mold assembly while still having the heated localized zone and a portion of the stretchable portion at a temperature closer to ambient temperature, initially stretching the preform along its longitudinal axis; injecting a fluid into the interior volume of the preform, the fluid being under such pressure so as to cause the preform to plastically deform until achieving a container of a desired size and shape; and releasing the container formed from the preform from the mold assembly and sealing the container.

2. The process of claim 1, wherein the fluid is an incompressible fluid.

3. The process of claim 1, wherein the preform is fabricated from a thermoplastic resin.

4. The process of claim 1, wherein the step of stretching the preform and injecting the fluid are performed substantially sequentially.

5. The process of claim 1, wherein the step of injecting the fluid starts before the end of the step of stretching the preform.

6. The process of claim 1, wherein the steps of stretching the preform and injecting the fluid are performed substantially simultaneously.

7. The process of claim 1, wherein the fluid which is injected into the preform to form the container is enclosed within and distributed with the container.

8. The process of claim 1 wherein the fluid is at ambient temperature.

9. The process of claim 1, wherein at least 50% of the stretchable portion of the preform is at a temperature closer to ambient temperature than to its vitreous transition temperature (Tg).

10. The process of claim 1, further comprising the step of monitoring of a stretching element position, volumetric flow rate of the fluid, fluid pressure, stretching element force, and deformation pattern during the molding process; and adjusting the stretching element position and the volumetric flow rate of the fluid according to a predetermined relationship, the relationship being configured to optimize manufacture of the particular variety of container being manufactured.

11. The process of claim 10, wherein the fluid is an incompressible fluid.

12. The process of claim 1, further comprising the step of maintaining the portion of the stretchable portion that is at a temperature closer to ambient temperature than to the vitreous transition temperature (Tg) at a temperature closer to ambient temperature than to the vitreous transition temperature (Tg) during the entire manufacturing and filling process.

13. The process of claim 1, wherein the portion of the stretchable portion that is at a temperature closer to ambient temperature than to the vitreous transition temperature is at about and above ambient temperature.

14. A system for the manufacturing and filling of plastic containers, the system comprising: a mold assembly of two or more components; a preform positioned in the mold assembly, the preform being fabricated from a plastic and including a non-stretchable portion and a stretchable portion defining a longitudinal axis, while positioned in the mold assembly the preform having a localized zone in the stretchable portion at a temperature closer to a vitreous transition temperature (Tg) of the preform than to ambient temperature, while positioned in the mold assembly the preform also having at least a portion of the stretchable portion at a temperature closer to ambient temperature than to the vitreous transition temperature (T.sub.g); a stretching element moveable to initially stretch the preform along its longitudinal axis while the preform has the localized zone at a temperature closer to the vitreous transition temperature (Tg) than to ambient temperature and has the portion of the stretchable portion at the temperature closer to ambient temperature than the vitreous transition temperature (T.sub.g); a nozzle configured to inject a fluid into the preform, the fluid being under such pressure as to cause the preform to plastically deform until achieving a container of a desired size and shape; a release member for releasing the container from the mold assembly; and a sealing member for sealing the container.

15. The system of claim 14, wherein the fluid is an incompressible fluid.

16. The system of claim 14, wherein the portion of the stretchable portion that is at a temperature closer to ambient temperature than to the vitreous transition temperature is at about and above ambient temperature.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a diagram of a preform for use in the invention, including an indication of separate detailed views in FIGS. 2 & 3;

(2) FIG. 2 is a detailed view of a deformation zone on the preform of FIG. 1, where the zone is comprised of curved geometry;

(3) FIG. 3 is an alternative detailed view of a deformation zone on the preform of FIG. 1, where the zone is comprised of angular geometry; and

(4) FIG. 4 is a diagram of an apparatus in which the invention may be implemented.

(5) FIG. 5 is a depiction of a finished container produced by the process according to the invention.

(6) FIG. 6 schematically illustrates experimental curves obtained through an example of a process according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

(7) The invention will be better understood from the description which follows, which relates to a preferred embodiment, given by way of non-limiting example, and explained with reference to the accompanying FIGS. 1-4 showing a preform and molding apparatus, according to this invention.

(8) The process for blow-molding containers from plastic, and more particularly from thermoplastic resin, e.g. PET, starts with the preform 1 shown in FIG. 1. In the preferred embodiment, the preform 1 is fabricated of PET resin in a conventional injection-molding process. Preform 1 is ideally axially symmetric about the longitudinal axis 17. The preform 1 is a tubular body of a generally elongated shape, composed of an upper portion 11 and a lower portion 13. The lower portion 13 of preform 1 is defined generally by an outer surface 3 and an inner surface 4, together forming a wall of thickness 5. Said thickness 5 is not necessarily fixed; it may vary slightly along the body of the preform 1 (in the longitudinal direction) as is needed to optimize the molding of the finished container. The upper portion 11 of preform 1 is provided with a shoulder 9, threading 10, and an opening 12, arranged in such a way as to provide a ready fitment for a cap. A neck 14 comprises the transition between upper portion 11 and lower portion 13.

(9) The upper portion 11 is a portion that is not stretched during the process of manufacturing the container and during the step of stretching the preform 1 along its longitudinal axis. It is therefore designated as a non-stretchable portion. On the contrary, the lower portion 13, is defined as a stretchable portion and is stretched and deformed until achieving the desired size and shape for the container.

(10) The preform 1 is further defined by a bottom portion 2, which comprises a hemispherical shell of inner radius 7 and outer radius 8. The effect of the combination of the bottom section 2 with the upper portion 11 and the lower portion 13 is to render the preform a tubular structure which defines an interior volume 6.

(11) The neck 14 is provided with a zone 16 that has a locally-reduced wall thickness 15 relative to the rest of the preform 1. Zone 16 is a concentrator of axial and radial stress in the wall of preform 1, serving to provide a consistent point of initiation of deformation during molding and thus facilitate the flow of preform 1 during molding. FIGS. 2 & 3 show two possible configurations of the decreased thickness 15. In FIG. 2, the decreased thickness 15 is accomplished by means of smooth curves 18, which may be of constant or variable radius. In FIG. 3, the preform is instead provided with angles 19 (sharp corners), which accomplish the same purpose as curves 18. While in the preferred embodiment only one such zone 16 is employed, multiple such zones may optionally be employed, depending on the properties of the material used and the geometry of the container being formed.

(12) Preferably the preform taken as a whole is at ambient temperature. More specifically, at least a portion of the stretchable portion of the preform is at ambient temperature and most preferably, at a temperature below the vitreous transition temperature (Tg) of the preform.

(13) As proposed, at least 30%, preferably at least 50%, more preferably at least 70%, most preferably 90% of the stretchable portion of the preform is at a temperature below its vitreous transition temperature (Tg) prior to stretching of the preform.

(14) However, to facilitate the stretching of the stretchable portion of the preform along its longitudinal axis, it is planned to locally heat the stretchable portion in some points. Advantageously, the preform can be heated at the location of zones 16 presenting the locally reduced wall thickness 15 to initiate the deformation of the stretchable portion during the molding. Zone 16 can be heated at a temperature approaching the vitreous transition temperature (Tg) or above the vitreous transition temperature (Tg) while the preform taken as a whole remains at a temperature below the vitreous transition temperature (Tg) and preferably at ambient temperature.

(15) FIG. 4 depicts the preferred embodiment of an apparatus to effectuate the molding process. The apparatus comprises a mold, having a base 20 and left and right halves 21 and 22 (collectively, the mold components), and a forming head 27 with a stretching element such as a stretching rod 25 driven by cylinder 26. The mold halves 21 and 22 meet along the mold centerline 35, and abut the mold base 20 along the mold base seam 34. The mold cavity 30 is thus defined by the inside surfaces 23 of the mold components. It is to be noted that a mold with a different number of components may alternatively be used. The mold may be further provided with one or more vent ports 38, to exhaust air displaced by the preform 1 during the molding operation.

(16) The mold halves 21 and 22 are provided with an upper orifice 36. The orifice 36 is of a size such that the preform neck 14 may pass through the orifice 36 while the preform shoulder 9 rests upon the upper surface of the mold halves 21 and 22. The result is that the preform's lower portion 13 is positioned within the mold cavity 30 while the preform's upper portion 11 rests outside the mold cavity.

(17) Before the molding operation, the preform 1 is prepared for the molding process. In the preferred embodiment, the preform is cleaned of any latent residues and sanitized to prevent spoilage of its future contents. Preferably, the preform is at ambient temperature. The prepared preform 1 is positioned relative to the mold components 20, 21, and 22 in such a way as to be enclosed as described above. In practical terms, the preform 1 is inserted into the assembled mold structure, or alternately the preform 1 may be held in position while the mold components are brought together and closed around it. Once properly positioned the mold components are held in position by means of clamps or locking devices. The apparatus together with the preform 1 form a system for the manufacturing and filling of plastic containers. The forming head 27 is then positioned about the mouth 28 of the preform 1 and held in position by the application of external force 41. The forming head 27 may optionally be provided with means for engaging the preform threads 10 for an improved connection and seal.

(18) During preparation of the molding operation, the preform 1 is at ambient temperature or at least at a temperature below its vitreous transition temperature (Tg).

(19) Local zones 16 of the stretchable portion 13 of the preform can be heated at a temperature approaching its vitreous transition temperature (Tg) or above the vitreous transition temperature (Tg) of the preform 1 to help initiating plastic deformation of the preform 1 during the molding operation.

(20) The molding operation is commenced by the advancement of the stretch rod 25 into the interior volume 6 of the preform, causing it to plastically deform by stretching it along its longitudinal axis 17. The stretching rod 25 is driven by means of pneumatic cylinder 26, which is operated by compressed air supplied from source 32 and regulated by valves 33. Alternatively, other driving means may be used for driving the displacement of the stretching element. This deformation continues until the stretching rod 25 meets the mold bottom 20 at the bottom point 37, at which point the stretching rod 25 is halted and held in place until the completion of the molding operation.

(21) While the stretching rod 25 is deforming the preform by stretching, an incompressible fluid 29 under pressure, e.g. water, supplied from source 31 and regulated by valve 39 is injected into the preform interior volume 6. More particularly, the injection begins after the stretching has started and before it has come to an end. This makes it possible to obtain a regular distribution of cristallinity along the preform height. It is to be noted that stretching a PET preform that is initially rather in an amorphous form, induces cristallinity in the preform. However, heat generated by the stretching step breaks this induced cristallinity. The use of an incompressible fluid, in particular a fluid with good or even high heat conduction properties, such as water, makes it possible to evacuate heat produced by the stretching step and keep cristallinity at rather a high level, e.g. between 30 and 35%. Furthermore, for cristallinity purpose water is used at ambient temperature in the injection step. However, other fluids (e.g. liquid) may, alternatively, be used, and in particular fluid with any temperature between 0 and 100 C. A means for removing air from the inside of the preform 1 before the injection of the incompressible fluid 29 may optionally be provided. The longitudinal stress induced by the stretching rod 25 and the longitudinal and radial stresses induced by the pressure of the incompressible fluid 29 causes plastic deformations to be initiated at the stress concentrators found in the preform 1 at the zones 16.

(22) Once plastic deformation is initiated, the preform 1 continues to expand into the mold cavity 30 until it has assumed approximately the shape of the mold inside surfaces 23. This expansion is monitored by the apparatus' control systems by means of appropriately-located sensors 40. The exact number of sensors 40 required will vary according to the shape of the mold cavity 30; only two are depicted here for clarity. It is to be noted that control over the molding process is obtained by controlling the volume increase rate within the mold during the process. Controlling the volume of an incompressible fluid (e.g. water) injected into the preform (e.g. through a flow meter or another suitable means) is much easier than for a compressible fluid such as air. Controlling the volume increase rate makes it possible to control the surface increase rate during the expansion of the preform within the mold. The volume increase rate is monitored in such a way as to obtain a substantially constant PET bubble surface increase rate, thereby tending to obtain the maximum cristallinity as possible in the PET preform.

(23) As explained, during the manufacturing process, the container is performed with a preform 1. At least a portion of the stretchable portion 13 of said preform is at a temperature that is below the vitreous transition temperature Tg for the material of which it is produced and, preferably at ambient temperature.

(24) According to the proposed process, at least 30%, preferably at least 50%, more preferably at least 70% and most preferably 90% of the stretchable portion 13 of the preform 1 is at a temperature below its vitreous transition temperature (Tg), allowing a reduction in the energy required in the process.

(25) FIG. 6 illustrates schematic curves (a), (b), and (c) obtained in the course of implementation of an example of a manufacturing process according to the invention. Curve (a) represents the amplitude of the stretching position over time during the molding process. Curve (b) represents the amplitude of the volume of an incompressible fluid, e.g. water, which is injected into the preform while the latter is being stretched. As apparent from the drawing, the fluid starts to be injected while the preform stretching is in progress. Lastly, curve (c) in dotted lines represents the amplitude of a setpoint of water volume.

(26) Once the expansion has come to an end the mold halves 21 and 22 are then opened and the container is removed without emptying the incompressible fluid 29. The container is finally sealed with the incompressible fluid 29 inside (e.g. water or another liquid), preferably by means of a screw cap, and is then ready to be used by dispensing the fluid contained therein. A finished container produced by means of the preferred embodiment is depicted in FIG. 5 where the cap has been omitted for the sake of clarity.

(27) Of course, the invention is not limited to the embodiment described above and shown in the accompanying drawing. Modifications remain possible, particularly as to the construction of the various elements or by substitution of technical equivalents, without thereby departing from the scope of protection of the invention. Accordingly, the scope of this disclosure is intended to be exemplary rather than limiting, and the scope of the invention is defined by any claims that stem at least in part from this disclosure.