Adhesive bonding and miscellaneous chemical manufacture – Surface bonding means and/or assembly means therefor – Indefinite or running length flexible strand – rod – tube – or...
Reexamination Certificate
1999-04-28
2002-05-14
Johnstone, Adrienne C. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Surface bonding means and/or assembly means therefor
Indefinite or running length flexible strand, rod, tube, or...
C156S167000, C156S272600, C156S273100, C156S379600, C156S379800, C425S083100, C425S17480E
Reexamination Certificate
active
06386260
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for providing a web of thermoplastic filaments. In particular, the present invention relates to a method and apparatus whereby a slot member is combined with an accelerator gun type tube system.
BACKGROUND OF THE INVENTION
Through a typical spunbonding process, nonwoven fabrics are made by depositing spun filaments on a moving support to form a web followed by bonding the web. Generally, the thermoplastic filaments are first continuously extruded, quenched, drawn, and attenuated by exposure to a high velocity fluid, and then deposited on the moving support. The quality of the final web depends to a great degree on the relative arrangement and uniformity of the filaments in the deposited web. The method and apparatus used for drawing and attenuating the filaments will determine their uniformity and arrangement in the web.
Manufacturers of non-wovens have made many innovations regarding such drawing and attenuating methods and apparatuses. Generally, good separation between filaments in combination with a high velocity for high rates of production is desired. When separation between filaments is poor, strands undesirably become wrapped about one another; a condition referred to as “ropiness”. Ropiness in turn leads to poor uniformity in the resultant web.
Early spunbonding processes typically utilized round tubes for drawing and attenuating the filaments. High velocities of air were sent through the tubes to carry the filaments through and direct them for depositing on a moving support below to form a web. These tubes may be referred to as “Venturi tubes” or “attenuator guns”, with the “Lurgi” process one system of this type (use herein of any of these terms is generally intended to be interchangeable). Systems such as these have several problems associated with them. “Gun outs” can occur when one or more filaments break at the entry point of a tube due to the aggressive handling created by the air acceleration in the tube. When a gun out occurs, unattenuated fibers and polymer drips can fall directly onto the support below. This can result in an expensive total line stoppage for cleaning of the support.
Additional problems are also associated with Lurgi tube systems. Inside the tubes the filaments make contact with other filaments, which may result in them becoming stuck together or entangled, causing a defect referred to as “ropiness”. Additionally, the interior of the tubes can become partially or completely blocked due to polymer deposits resulting from drips or filaments contacting the tube inner surface. Finally, the high velocity of the air in the tubes is associated with a general non-uniform or splotchy appearance to the finished web, as the filaments are directed to the moving support with considerable force, providing little opportunity for spreading or randomization. These various problems tend to result in undesirable webs with low tensile strength.
Many attempts have been made to improve the performance of Lurgi tubes. For example, U.S. Pat. Nos. 3,163,753; 3,341,394; and 4,009,508 describe the use of corona electrodes for charging the filaments electrostaticly in combination with use of a Lurgi tube. Electrostatic charging tends to separate the filaments and thus to decrease ropiness and to otherwise result in a more uniform web. Although this method provides some improvement, it does not achieve fully satisfactory performance.
Alternate drawing and attenuation methods and apparatuses have also been developed. In particular, U.S. Pat. Nos. 4,340,563 and 4,405,297 describe slot draw processes which replace Lurgi tubes with an elongated slot extending across substantially the whole web cross section to draw and attenuate filaments. Further advancements to the slot draw system are described in U.S. Pat. Nos. 4,578,134; 5,397,413; 5,545,371. These patents describe modifications to the slot draw process that include, respectively, a complex directed air stream, a corona treatment, and an air stream with water dispersed in it. The slot draw system in its various forms has generally resulted in improved filament drawing and attenuating for more uniform and efficient non-woven web production.
Lurgi tubes, however, remain in use for economic and performance related reasons. Because of the high velocity of air that is developed through the tube, tube attenuation offers superior filament crystallinity and orientation over slot draw systems, which have a lower air velocity and resultant lower crystallinity. Low crystallinity can result in low filament tenacity, and in filament shrinkage during subsequent thermal bonding. Also, because of the large capital investment required to install a slot draw system, it is not practical for many manufacturers having existing Lurgi tube systems to take advantage of the advances offered by a slot draw system.
There is therefore a need for improved Lurgi tube systems.
Prior efforts at improving such systems have included deflecting the filaments off of a deflector plate mounted below the tube outlet. While this method broadened the laydown pattern of the filaments in the web, good uniformity was not realized. Another effort included mechanically oscillating one or more of the tubes, deflector plates, and/or the web. These methods, however, were found to depend on the operating frequency of the oscillating member(s), and also entailed numerous related maintenance problems.
Another proposed improvement to the Lurgi tube systems is described in U.S. Pat. No. 5,225,018 to Zeldin et al. Zeldin attaches a pair of tapered guide plates to a row of Lurgi tubes to form a slot at the outlet of tubes prior to depositing filament on the web. The plates are slanted at a precise angle so that turbulent air flow is developed in the tapered slot formed between the plates. As the filaments exit the tubes and enter the tapered slot, they are randomly spread by the turbulent air flow that exists in the slot. Zeldin further includes corona means below the outlet of the tapered slot for additional filament separation. Zeldin's device results in relatively randomly deposited filaments across the width of the web, with a high ratio of cross direction filament depositing to machine direction filament depositing.
The apparatus of Zeldin, however, leaves many problems with using Lurgi tubes unresolved. Due to the high cross direction/machine direction ratio that webs have when produced using the apparatus of Zeldin, for instance, Lurgi tubes are still unable to be used for production of a relatively uniform web with a high machine direction orientation and low machine direction elongation.
There is therefore an unresolved need in industry for an improved apparatus and method for producing a uniform web of continuous filaments with high machine direction strength, and high crystallinity.
OBJECTS OF THE INVENTION
It is an object of the invention to provide an apparatus and method for the production of a uniform web of filaments having high crystallinity, and high machine direction orientation.
SUMMARY OF THE INVENTION
The present invention generally comprises an apparatus and a method for providing a uniform web of non-woven filaments having high crystallinity, high machine direction orientation, and low machine direction elongation.
The apparatus of the present invention generally comprises filament transport means having an exit, with a confined zone of reduced turbulence adjacent to the transport means exit. The filaments exit the transport means and are conveyed through the confined zone where the conveying fluid velocity slows and turbulence is reduced, thus spreading the filaments in a cross direction.
The transport means preferably comprise a plurality of Lurgi tubes, while the preferred confined zone comprises a delivery slot defined by a slot member. The tube exits are located adjacent to the elongated delivery slot. The preferred delivery slot is defined by the substantially parallel first and second sideplates and substantially parallel endplates of the slot member. The side
Ferencz Richard
Weng Jian
Yamanouchi Brian
Polymer Group Inc.
Pyle & Piontek
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