Patent Application
20130193622
The invention relates to the manufacture of containers, particularly bottles, jars, by forming from blanks (generally preforms, although it can also include intermediate containers) of plastic material such as polyethylene terephthalate (PET).
The manufacture of containers involves two principal steps: a heating step during which the blanks are exposed to electromagnetic radiation from sources emitting in the infrared range, followed by a forming step during which a gas under pressure is injected into the blanks thus heated, to give them the final shape of the container.
Many containers are not symmetrical in revolution and have local impressions, recessed or in relief. Said impressions can be purely aesthetic, or they may have a particular function such as a handle (for example see American patent U.S. Pat. No. 4,123,217 in the name of Fisher), or reinforced feet (for example see French patent FR 2822804 or its American equivalent U.S. Pat. No. 7,051,889, in the name of the applicant, describing a petaloid bottom).
These containers are more difficult and more complex to form than ordinary containers due to a poor distribution of the material, which causes a deterioration of the physical properties of the container, or an opaque and whitish aspect of the material.
Thus, freedom of shapes is often limited by the desire of manufacturers to avoid locally stressing the material too much.
The invention seeks to facilitate the forming of containers having a recessed or relief impression.
To that end, the invention proposes a method of manufacturing a container having a local recessed or relief impression, from a blank of thermoplastic material, said method comprising:
Said method makes it possible to facilitate making an impression (recess or relief) at the level of a localized zone, the temperature of which is at an extremum, i.e., a maximum or a minimum. The result is greater facility of forming, better dimensional stability of the container, as well as greater freedom of possible container shapes.
According to one embodiment, the superheated zone is localized both axially and radially on the blank, for example on a bottom of the blank.
The infrared radiation, for example, is emitted by a matrix of monochromatic or pseudo-monochromatic radiation sources, subdivided into a main set of sources emitting a radiation of substantially identical average intensity, and a secondary set of sources emitting a radiation, the intensity of which is an extremum: either a maximum, or a minimum, with a difference of at least 10% with respect to the average intensity.
According to one embodiment, the secondary set comprises a series of groups of point sources, separated from each other and forming a periodic motif, which for example has a period equal to the distance covered by a blank during one complete revolution around a principal axis of said blank.
The sources of radiation are for example laser sources, and preferably laser diodes, particularly of the VCSEL type.
Other objects and advantages of the invention will be seen from the following description, provided with reference to the appended drawings in which:
Diagrammatically represented in
Each preform 2, produced from a thermoplastic material such as polyethylene terephthalate (PET), comprises a neck 3, which is not (or only slightly) heated, the shape of which is final, and a body 4 that terminates opposite the neck 3 in a hemispherical bottom 5.
At the junction between the neck 3 and the body 4, the preform 2 has a collar 6 by which the preform 2 is suspended in the various steps of manufacturing the container.
However, in the heating unit 1, the preforms 2 are attached to pivoting supports called spinners, which drive the preforms 2 in rotation around their principal axis A so as to expose the part below the neck (the entire body 4 and the bottom) to the heating. Each spinner comprises a pinion engaging a fixed rack, in such a way that each point situated on the circumference of the preform 1 describes on the trajectory of the preform 2 a cycloid C (drawn in dotted lines in
The heating unit 1 has a radiating wall 7 in front of which the preforms 2 travel. Said wall 7 is lined with a plurality of electromagnetic radiation sources 8 emitting both monochromatic (or pseudo-monochromatic) and directive electromagnetic radiation towards the preforms 2, in the infrared range.
In theory, a monochromatic source is an ideal source emitting a sinusoidal wave at a single frequency. In other words, its frequency spectrum is composed of a single ray of zero spectral width (Dirac).
In practice, such a source does not exist, a real source being at best quasi-monochromatic, i.e., its frequency spectrum extends over a band of spectral width that is small but not zero, centered on a principal frequency where the intensity of radiation is maximum. In common parlance, however, such a real source is called monochromatic. Moreover, a source emitting quasi-monochromatically over a discrete spectrum comprising several narrow bands centered on distinct principal frequencies is considered to be “pseudo-monochromatic.” This is also called multimode source.
In practice, the sources 8 are organized by juxtaposition and superposition to form a matrix 9. For example, this involves laser sources 8, and preferably laser diodes. According to a preferred embodiment, the matrix 9 is a matrix of vertical-cavity surface-emitting laser (VCSEL) diodes 8, each diode 8 emitting for example a laser beam 10 of rated individual power on the order of a milliwatt at a wavelength situated in the short and medium infrared range—for example on the order of 1 μm.
At the scale of the preforms 2, the diodes 8 can be considered as point sources, each emitting directive radiation, i.e., in the form of a conical light beam 10, the solid half-angle of which is closed at the top, and preferably between 10° and 60°. The beam 10 can be symmetrical in revolution (i.e., of circular cross-section), or non-symmetrical in revolution (for example elliptical cross-section).
The object of the present application is not to describe in detail the structure of the matrix 9 of diodes 8. For this reason, the matrix 9 is represented in a simplified manner, in the form of a plate, the diodes 8 appearing in the form of points.
The heating unit 1 is designed to enable a modulation of the power (also called intensity) of the radiation emitted by each diode 8, or by groups of diodes.
Such modulation can be performed electronically, the power of the diodes 8 being for example displayed on a control monitor. Said monitor can be a touch screen, and for a given group of diodes, can display a cursor, the movement of which causes the modulation of the power of the radiation emitted by the diodes 8 of the group to a value between a predetermined minimum value Pmin (for example zero) and a maximum value Pmax corresponding for example to the rated power of the diodes 8.
The purpose is to achieve a differential heating, i.e., selective and non-uniform, of each preform 2, in such a way as to obtain locally on said preform at least one localized zone 11, both axially (i.e., in the height of the preform 2) and radially (i.e., in the circumference of the preform 2), in which the temperature has an extremum (maximum or minimum) with respect to its vicinity. In other words, the purpose is to locally superheat, or on the contrary underheat, the preform 2.
According to a particular embodiment, the purpose is to obtain superheated zones 11, located for example on the bottom 5, particularly in order to facilitate the production of feet 12 during the forming of a container 13 with a petaloid bottom 14, as we will see hereinafter. Said zones 11 are located not only axially, but also radially on the bottom 5 of the preform 2.
To that end, the matrix 9 is subdivided into two sets of diodes, to wit:
The term “point” does not mean that each group 17 is necessarily reduced to a single diode 8 (although this is possible) or that each group 17 comprises a negligible number of diodes 8. It means on the one hand that each group 17 is related, its diodes 8 being adjacent, and on the other hand that the area occupied by each group 17 of diodes 8 is small with respect to the total area of the matrix 9.
The groups 17 of diodes 8 of the secondary set 16 are separated and dispersed along the trajectory of the preforms 2. They are separated from each other, while together forming a periodic motif depending on the configuration of the zone 11 (or zones) on the preform 2 to be superheated (or conversely underheated). Thus, in order to localize the intensity P2 of heating on zones 11 situated on the bottom 5 of the preforms 2, the secondary set 16 is formed by a linear horizontal series of groups 17 of diodes 8 situated at the height of and facing the bottom 5 of the preforms 2.
Each group 17 of diodes 8 defines a closed contour corresponding substantially to the contour of the localized zone 11. Thus, in the illustrated example, where the zones 11 are angular sectors located on the bottom 5 of the preform 2, the contour of the groups 17 of diodes 8 of the secondary set 16 is substantially triangular, with a peak of the triangle pointing downwards and towards the opposite side of the horizontal triangle.
To each localized zone 11, in the secondary set 16, there corresponds a subset of groups 17 of diodes 8 equally distributed along the trajectory (indicated by the arrow F1 in
In the configuration illustrated in
The adjustment of the shape and size of the point groups 17 of diodes 8 can be adapted according to various factors, in particular:
Moreover, because of the non-homogeneous nature of the heating, it is necessary to ensure that the angular orientation of the preform 2 is correct during its insertion into a mold upon completion of the heating. To that end, the preform 2 can be provided with an orientation reference mark (for example in the form of a notch made at the neck 3) capable of being detected by the mechanical (or optical) control means guaranteeing the proper angular orientation of the preform 2 at all times. According to a particular embodiment, the preforms 2 are transferred from the heating unit 1 to a mold by means of tongs provided with a projecting spur that lodges in the notch of the preform 2, in such a way that the correct orientation of each preform 2 is maintained throughout the transfer until the insertion of the preform 2 into the mold.
To heat the preforms 2, they are moved through the heating unit 1 while turning them around their axes A, in such a way as to expose their part beneath the neck (body 4 and bottom 5) to the radiation from the diodes 8. Because of the particular configuration of the matrix 9 as described above, localized zones 11 on the bottom 5 of the preform 2 are repeatedly and periodically exposed to the differential radiation from the groups 17 of diodes of the secondary set 16, and consequently undergo differential heating (in this instance superheating), while the other parts of the preform 2 (i.e., the remainder of the bottom 5 and all of the body 4 in the illustrated example) are exposed to the radiation from the diodes 8 of the main set 15 and consequently undergo heating of average intensity.
The temperature differential measured in the superheated (or on the contrary underheated) zones 11 and in the normally heated zones is illustrated in the thermogram of
Thus, upon completion of heating, the body 4 of the preform 2 has a substantially uniform wall temperature, and the bottom 5 of the preform 2 has normally heated angular sectors 18, the temperature of which is substantially equal to that of the body 4, alternating with superheated (or on the contrary underheated) angular sectors 11 (shown shaded in
The deformability of the localized superheated zones 11 is high, greater than that of the sectors 18, which facilitates the formation of relief impressions in the zones 11. The deformability of the underheated zones 11 is less, which allows—unlike the formation of relief impressions around the zones 11—the formation of recessed impressions in the zones 11.
Upon exiting from the heating unit 1, the preform 2 is transferred into the mold, its angular orientation being controlled as indicated above, in such a way that the angular sectors 11 of the preform 2 having undergone a differential heating are located in vertical alignment or in front of recessed (or, on the contrary, relief) parts of the mold. A fluid under pressure (for example a gas such as air) is injected into the preform 2 by means of a nozzle that is sealably applied around the neck 3 on the upper face of the mold.
In the example illustrated in
Following is a summary of the principal advantages of the method described above.
The heating of the preform 2 performed by means of infrared radiation from directive monochromatic sources (such as laser) is sufficiently precise to obtain marked temperature variations between the superheated (or underheated) localized zones 11 and the comparatively less heated (respectively more heated) surrounding zones. The high deformability of the localized superheated zones 11 makes it possible to facilitate the formation of relief impressions (such as the feet 12 on a petaloid bottom 14, as we have seen) or recessed impressions (for example by means of movable inserts, for example to form handles on the body of the container).
The results are:
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 03884 | Sep 2010 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR2011/052094 | 9/14/2011 | WO | 00 | 4/11/2013 |
