Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Reexamination Certificate
1998-07-21
2001-02-27
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
C264S040400, C264S540000, C264S541000, C264S021000, C106S031150
Reexamination Certificate
active
06193913
ABSTRACT:
The present invention relates to a process for marking a thermoplastic article produced by extrusion-blow moulding, as well as to a procedure for checking the production of such an article by extrusion-blow moulding.
The production of thermoplastic articles by extrusion-blow moulding is widely known and developed on an industrial scale. At the present time, it applies especially to the production of hollow bodies, such as bottles or containers, which have complex shapes and must meet increasingly demanding specific criteria. Thus, in the particular case of fuel tanks, voluminous hollow bodies, which have complex shapes dictated by the precise location for which they are intended and a non-uniform thickness, but which must also meet precise requirements especially in terms of mechanical strength and impermeability, are produced by extrusion-blow moulding.
Before blow moulding, an extruded parison may be shaped at several points and in several directions by quite complex tooling so as to adapt it already to the profile of the article which has to be produced.
Before the mould is closed, the parison may also be preblown, which runs the risk of part of this parison being forced out of the mould upon closing it (lateral flash).
Finally, due to the variation in the rheological behaviour of thermoplastics, the parison may also be longitudinally shifted and its working part displaced (in the longitudinal flash) with respect to the mould during blow moulding.
In view of these aspects, it currently proves to be essential to ensure that the parison is optimally positioned, longitudinally and azimuthally, before it is blow moulded, to be able to check this positioning and, where necessary, to be able to modify it, at least for the subsequent production cycles.
One possible checking method consists in weighing the as-produced article, the various types of flash and the deflashed article. However, such checking provides only an overall picture of the process and does not allow precise analysis of the results or, consequently, a specific intervention to be made based on the causes of the disturbance.
According to document GB-A-2,178,361, it is known to affix, to an extruded parison of longitudinally variable thickness, before blow moulding, marks uniformly space along the length by the movement of a marker and by its contact with the parison. After blow moulding, the thickness of the article produced is measured at the affixed marks, the results are compared with the desired values and, if required, it is possible, as a consequence, to rectroact on certain operating parameters for the purpose of the following cycles.
However, in industrial production, this process proves in fact to be very difficult, if not impossible, to implement, in particular in that keeping the markers in a high-temperature environment, moving them every cycle and bringing them into uniform contact with the parison extruded in the molten state very rapidly renders them unusable.
Furthermore, moving the markers and contacting them with the parison, as described, are poorly suited to marking, in a large number of separate positions, voluminous hollow bodies of complex shapes produced by extrusion-blow moulding.
Consequently, the object of the present invention is to allow marking in a manner which is simple, reliable and suited to the industrial conditions of the production of thermoplastic articles by extrusion-blow moulding.
For this purpose, the invention relates to a process for marking a thermoplastic article produced by the extrusion of a parison and blow moulding of the said parison, in which the extruded parison is marked before blow moulding by at least one jet of an ink based on a compound which crystallizes in acicular form during drying.
By implementing the marking process according to the invention, it has been possible to observe that, even in an industrial environment, at high temperatures near the extrusion head and the parison, not only is the marking of the parison always of excellent quality but that the marking device and, in particular, the ink remain operational both in long periods of continuous use and after long periods during which the production has stopped.
Furthermore, it has been advantageously observed in the case of marking according to the invention using injectors that it was no longer required to move these injectors so that they are taken away from the parison when they are not in operation so as to prevent them being closed off by the ink drying. This is because, even in the case of partial drying of the ink in the injector, due in particular to the surrounding temperature, the shape of the crystals allows them to be ejected for the purpose of marking the article.
The ink-jet marking may be carried out in any known manner. Ink-jet is understood to mean here the sending, without substantial dispersion, of a predetermined quantity of ink (m) over a defined distance (d) and with a high and reproducible velocity (v). Beneficial results have been obtained when the d/v ratio i.e. the duration of the movement of the ink, does not exceed 5 milliseconds. The distance d is varied depending on the specific application of the process. Preferably, it does not exceed 30 cm. In particular, the injectors are opened and closed by the movement of a needle in the injector. For dosing the ink, solenoid valves having a short response time, particularly of the order of 10
−3
s, have advantageously been used. In general, the ink jet or jets is or are controlled by an interface adapted by those skilled in the art to the specific constraints of each production. Advantageously, this interface comprises an electronic unit which receives information coming, especially, from the extrusion-blow moulding device and generating pulses which produce the appropriate ink jet or jets. Preferably, the pulse time is of the order of a millisecond, more preferably still about 1 millisecond. Matrix control of the electronic unit has given excellent results, in particular using a matrix having up to 64 segments which can represent up to 64 opening or closing positions of each injector per production cycle, and therefore up to 64 marks per injector at different positions on the parison. Useful results have been obtained with a pressure in the ink circuit not exceeding 3.5 bar. Moreover, this pressure in the ink circuit is advantageously at least 0.7 bar.
The invention may be implemented in the use of one or more injectors. Advantageously, it allows the use of several injectors. The marking may thus be readily carried out at various azimuthal and/or longitudinal positions on the parison. Particularly useful results have been obtained with the use of a large number of injectors, especially up to 24 injectors. In the particular case of a marking device comprising 24 injectors, which is combined with 64-segment matrix control, it is therefore possible to affix up to 64×24 marks, i.e. 1536 marks, to the parison.
Each injector may be stationary or can move during each production cycle. Useful results have been obtained when each injector is stationary.
The ink is employed in any manner known by those skilled in the art and adapted, in particular, to the production in question. It has been observed that, for marking a parison, a solution based on a chlorinated solvent proved to be particularly advantageous. These chlorine-based solvents are first of all widely available and well accepted in an industrial environment for the application in question. Furthermore, they have the advantage of rapidly evaporating at the temperatures to which they are subjected when marking the parison. Thus, they allow the ink to dry rapidly, prevent the blowing mould from being marked by the parison and prevent any undesirable marking of the parison which is introduced during the next cycle. Finally, their diffusion within certain thermoplastics, such as especially polyolefins, in the molten state promotes attachment of the ink to these thermoplastics. Advantageously, the ink is consequently employed according to the invention in solution with
McDowell Suzanne E
Schneller Marina V.
Silbaugh Jan H.
Solvay S.A. (Societe Anonyme)
Venable
LandOfFree
Process for marking an article produced by extrusion-blow... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for marking an article produced by extrusion-blow..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for marking an article produced by extrusion-blow... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2600221