Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Production of continuous or running length
Reexamination Certificate
1999-03-26
2001-02-06
Simmons, David A. (Department: 1724)
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Production of continuous or running length
C264S103000, C264S210800, C264S211140, C425S066000, C425S464000
Reexamination Certificate
active
06183684
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to an apparatus, process, and the product produced therefrom for constructing a spunbond, non-woven web from thermoplastic polymers producing filaments of reduced diameter and improved uniformity at an increased production rate, and specifically, to an apparatus and process for heating and extruding thermoplastic materials through a spinneret, forming filaments of desired deniers by strategically positioning the drawing unit below the spinneret at a critical distance to increase filament velocity by reducing filament air drag and increasing form drag on the filaments by selective drawing unit slot length and air turbulence below the drawing unit slot to produce a filament of a desired diameter and molecular orientation and at an improved production rate, and the resultant spunbond product. A water spray for cooling may also be employed.
2. Description of the Prior Art
Devices for producing non-woven thermoplastic fabric webs from extruded polymers through a spinneret that form a vertically oriented curtain with downward advancing filaments and air quenching the filaments in conjunction with a suction-type drawing or attenuating air slot are well known in the art. U.S. Pat. No. 5,292,239 discloses a device that reduces significant turbulence in the airflow to uniformly and consistently apply the drawing force to the filaments, which results in a uniform and predictable draw of the filaments. U.S. Pat. No. 3,802,817 discloses a sucker apparatus positioned in a selected distance below the spinneret using jet streams having velocity in the range of turbulent flow to produce fine non-woven fleeces. U.S. Pat. No. 4,064,605 and European Patent Application No. 0230541 disclose examples of the formation of non-woven fabrics.
Conventionally, thermoplastic polymers such as polypropylene, polyethylene, polyester, nylon, and blends thereof are utilized. In the first step, the polymer is melted and extruded through a spinneret to form the vertically oriented curtain of downwardly advancing filaments. The filaments are then passed through the quench chamber where they are cooled down by chilled air, reaching a temperature at which the crystallization of the filament starts, resulting in the solidification of the filaments. A drawing unit located in a fixed position below the quench chamber acts as a suction having an air slot where compressed air is introduced into the slot creating a downward force on the filaments in the slot, and a rapidly moving downstream of air in the slot. This air stream creates a drawing force on the filaments, causing them to be attenuated or stretched above the drawing unit and exit the bottom of the slot where the filaments are deposited on a moving conveyor belt to form a continuous web of the filaments. The filaments of the web are then joined to each other through conventional techniques.
Providing for conventional construction of the filaments, typically filaments of 1.5 to 6 deniers or higher were produced. Using conventional methods, the hot filaments leaving the spinneret typically were immediately cooled to ambient temperature and solidified and then subjected to the drawing unit. According to a prior proposal, when the length of the filament traveling through the air is shorter than a specified value selected based on the throughput (gram per hole per minute) used, the extruded filaments will contact with a solid constituent of the drawing unit in advance of solidification of the filaments, resulting in development of filament breakage or damage. In other words, even though the prior art produces suitable non-woven webs, their production is limited by the ability to cool down and solidify the filaments in a predetermined length at appropriate throughput. The filament spinning speed reached in the prior art is in the range of 3,000 to 3,500 meters per minute.
Although the conventional method and apparatus produce suitable non-woven webs, the final product could be greatly improved and better fabric can be produced for any given polymer consisting of lower denier filaments. A thinner filament for any given throughput produces more surface area and more length per unit weight. A polypropylene spunbonded fabric with filaments of 0.1 to 5.0 or higher deniers would be desirable.
It is also desirable that a uniformity of filament denier and tensile properties be consistent so that the resulting fabric web has a uniform quality. Applicant has also determined that stress-induced crystallization in the spinning process (before solidification by cool-down) results in a stronger, higher tensile strength filament. The present invention provides for a higher rate of stress-induced crystallization.
Examples of end uses for the fabric web could be but are not limited to filtration materials, diaper covers and medical and personal hygiene products requiring liquid vapor barriers that are breathable and have air permeability.
With the present invention, a process for producing a superior quality non-woven web at much higher production and lower cost can be achieved. The core of the invention is to create an optimum situation wherein a much higher filament velocity (compared with that of conventional technologies) is achieved by selecting a minimum distance from the spinneret to the drawing unit based on the operating variables determined by such basic factors as the materials processed, the filament denier required, the throughput used, therefore resulting in a reduced air viscous friction drag associated with the length of filaments traveling with high velocity between the spinneret and the drawing unit and hence a reduced spin line tension, coupled with a higher drawing force created by the drawing unit with an optimal short slot vertical length to maximize the combination of the forces in terms of both the friction drag between air stream and filaments within the slot and the form drag underneath the slot.
The fiber velocity in the spunbond process is ultimately determined by the spin line force balance which, in the case of high speed spinning, can be reduced to the equation as follows:
F
ext
=F
inert
+F
drag
The force F
ext
is the external inert force pulling down the filaments. The force F
inert
is the inertia force which opposes the acceleration of the filaments and the force F
drag
is the air resistance produced by skin friction of the filaments traveling with high velocity in the air. Based on the spin line force balance, there are two ways to increase the filament spinning speed, that is, by increasing the force F
ext
and/or decreasing the force F
drag
. The force F
drag
is linearly proportional to the length of the spin line, therefore shortening the distance between the spinneret and the drawing unit will reduce the air resistance accordingly.
As to the F
ext
, unlike the fiber production where the F
ext
is supplied by a mechanical take-up reel or bobbin, the downward pulling force in the spunbond process on the filaments is created by the drawing unit which employs one or more streams of high velocity air directed downwardly inside the drawing unit slot in the direction of filament travel and interaction between the air stream generated inside the drawing unit and in accordance with the invention, the air flow below the drawing unit and the filaments. There are two types of such interaction: The first type arises from the viscous friction resulting from the differences in velocity between the filaments within the drawing unit and the drawing unit air stream in that the air stream with higher velocity pulls the filaments of slower speed downwardly. Therefore, the filament speed will always be lower than that of the air stream. The pull frictional force by viscous friction has almost a linear relationship with the generated air stream nozzle air velocity. The second type is the so-called “form” drag caused by the filaments “flapping” or “waving” in the airflow field below the drawing unit. It is very clear from the discussion above that the effectiveness of
Ason Engineering, Ltd.
Hopkins Robert A.
Malin Haley & DiMaggio, P.A.
Simmons David A.
LandOfFree
Apparatus and method for producing non-woven webs with high... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method for producing non-woven webs with high..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method for producing non-woven webs with high... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2567829