Plastic and nonmetallic article shaping or treating: processes – With twining – plying – braiding – or textile fabric formation
Reexamination Certificate
2000-07-06
2002-11-12
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With twining, plying, braiding, or textile fabric formation
C028S245000, C264S210800, C264S211140, C264S211170, C264S237000, C425S072200, C425S104000, C425S377000, C425S378200, C425S379100, C425S382200, C424S464000
Reexamination Certificate
active
06478996
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method of producing a highly oriented yarn (HOY) from a thermoplastic material and a spinning apparatus for melt spinning a highly oriented yarn.
In the production of synthetic multifilament yarns from a thermoplastic melt in one process step, one distinguishes basically between partially drawn and fully drawn yarns. The partially drawn yarns, which are also described as preoriented yarns (POY), have a partially oriented molecular structure that requires a subsequent drawing in a second process step. In comparison therewith, fully drawn yarns (FDY) are suited for direct further processing without a subsequent drawing. The FDY yarns are drawn in the spinning process at a high ratio by means of draw systems, so that an aligned molecular structure is achieved in the polymer.
To produce a yarn with a highest possible orientation of the molecules of the polymer, methods are also known wherein the yarn is drawn at a high ratio while firming up directly before the solidification of the polymer. In these yarns, known as highly oriented yarns (HOY), a stress-induced crystallization leads to the orientation of the molecules in the polymer. In comparison with the FDY yarns, the known HOY yarns have a lower elastic limit. Depending on the method of further processing, this can lead, due to the force acting upon these yarns, to a permanent deformation and, thus, to an irregular dyeability. The known HOY yarns are totally unsuitable for methods of further processing, wherein major stress peaks act upon these yarns.
Although it is theoretically possible to increase the elastic limit of HOY yarns by increasing the withdrawal speed, there are physical limits set to this process, since in the melt spinning of HOY yarns, the filaments forming the yarn may have only a limited crystallinity during drawing to ensure a safe withdrawal without damage to the yarn. A too highly precrystallized filament is much too frozen in its structure to withstand, without being overstressed, the forces developing in the yield point.
EP 0 530 652 and U.S. Pat. No. 5,612,063, disclose an apparatus and a method for producing a synthetic yarn, wherein the filaments undergo a delayed cooling before their solidification. This further delays crystallization of the filaments, which leads to an increased elastic limit of the yarns. However, the known apparatus and method have the disadvantage that the length of the delayed cooling can be only very limited, since lacking stabilization of the filaments by the air flow represents within this region an increasing risk that the filaments stick together.
EP 244 217, and U.S. Pat. Nos. 5,141,700 and 5,034,182 propose to remove the filaments after passing through a pressurized cooling shaft from the cooling shaft by means of an air stream. This also achieves a delayed crystallization of the filaments. Likewise in EP 0 682 720, a delayed crystallization of the polymer is realized, in that an accompanying air stream is directed onto the filaments before solidification.
The apparatus and methods known in the state of the art are all aimed at producing a synthetic yarn at highest possible takeup speeds without its physical properties undergoing a substantial change. Thus, in these known methods, the decrease in elongation at higher withdrawal speeds is compensated by the delayed crystallization of the polymer in the spinning line. However, these methods are unsuitable for producing HOY yarns with higher elastic limits and with higher tenacities.
In the production of a highly oriented yarn, there exists the problem that the known yarns have too high elongation values and too low tenacity values. The elongation values of the yarn may be improved by increasing the withdrawal speed. An increase in the withdrawal speed, for example, in the apparatus disclosed in EP 0 530 652 and U.S. Pat. No. 5,612,063, is bound to lead to an increase in the withdrawal tension, which results, however, in that the filaments are overstressed during the drawing due to the low tenacity of the filaments.
It is an object of the invention to provide a method and a spinning apparatus for producing a highly oriented yarn (HOY), which exhibits elongation and tenacity values typical of a fully drawn yarn (FDY), and which can be produced with a high spinning reliability.
SUMMARY OF THE INVENTION
The above and other objects and advantages of the present invention are achieved by the provision of a method and apparatus wherein the melted thermoplastic material is extruded through a nozzle of a spinneret to form a plurality of downwardly advancing filaments, and such that the filaments solidify at a location spaced below the nozzle. The filaments are withdrawn from the nozzle under a withdrawal tension so as to cause the filaments to be drawn while being solidified, with the withdrawal tension being generated by a withdrawal speed of at least about 6500 m/min. In addition, the filaments are assisted in their advance before their solidification such that before their solidification the filaments are relieved from tensile stress and during solidification and drawing a reduced withdrawal tension is effective on the filaments. The filaments are also combined during their advance after their solidification, to form an advancing multifilament yarn, which is then wound into a package.
The invention is based on the recognition that overstressing of the filaments can occur in the process of the yarn formation. In high speed spinning, one observes no uniform rise of the yarn speed between the yarn exit from the spinneret and the solidification point of the filaments. After the filaments emerge from the spinneret, a relatively slow acceleration sets in initially, until the start of the stress-induced crystallization. Within few centimeters, the stress-induced crystallization leads to an acceleration of the filaments to the withdrawal speed. In this instance, the tenacity of the filaments must be greater than the forces necessary for the acceleration of the yarn, to avoid filament breakage. In accordance with the invention, the filaments are assisted in their advance before they solidify such that no significant additional tensile stresses resulting from frictional forces of the air act upon the filaments before they solidify. Thus, the filaments are relieved before their solidification, so that a reduced withdrawal tension is effective on the filaments while being drawn during their solidification. With that, one realizes on the one hand a high orientation of the molecules during drawing. On the other hand, a high withdrawal speed is made possible with a correspondingly high withdrawal tension. In this process, the withdrawal tension is generated by a withdrawal speed of at least 6,500 m/min. It has shown that it is thus possible to produce a highly oriented yarn with tenacity values greater than 4cN/dtex and an elongation in the range of 30%.
To assist the movement of the filaments before their solidification or to bring about a relief of the forces engaging on the filaments before their solidification, it is possible to apply basically two variants of the method according to the invention. In a first variant, the speed of the advancing yarns is increased before drawing by a higher injection speed in the extrusion of the filaments. In practice, this possibility can be used only to a certain extent due to the high pressure drops upstream of the spinneret.
In the second variant of the method, the air friction acting upon the filaments is influenced. To this end, the filaments advance after their extrusion through a cooling medium. Directly before the solidification of the filaments, a cooling medium stream is generated that assists the movement of the filaments. This measure effects a reduction of the air friction that exerts a braking effect on the filaments. The cooling medium in use is preferably air.
In a particularly advantageous embodiment of the method, the cooling medium stream has a flow velocity that is substantially the same as the speed of the advancing filaments bef
Meise Hansjörg
Schäfer Klaus
Schulz Detlev
Alston & Bird LLP
Barmag AG
Tentoni Leo B.
LandOfFree
Method and apparatus for producing a highly oriented yarn 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 and apparatus for producing a highly oriented yarn, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for producing a highly oriented yarn will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2952542