Plastic and nonmetallic article shaping or treating: processes – With step of cleaning – polishing – or preconditioning...
Patent
1995-01-09
1997-05-27
Woo, Jay H.
Plastic and nonmetallic article shaping or treating: processes
With step of cleaning, polishing, or preconditioning...
264 12, 425 7, 425 722, 425186, 4251925, 4253782, 425464, D01D 514
Patent
active
056329385
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to meltblowing dies and specifically to a meltblowing die with a replaceable die tip, wherein the air-gap and set-back parameters may be adjusted as desired before replacement. In another aspect, the invention relates to a method of replacing the die tip of a meltblowing die.
2. Discussion of the Prior Art
Meltblowing is a process for manufacturing nonwoven products by extruding a molten thermoplastic polymer resin through a plurality of small orifices to form fine fibers while blowing converging sheets of air onto each side of the orifices to attenuate and draw down the fibers. The extruded fibers are blown onto a moving collector surface where they entangle in a random way to produce a nonwoven fabric or web. The newly formed web is directly withdrawn from the collector for further processing as desired. The overall process is carried out continuously. The webs may be further processed into a number of commercially important products such as filters, fabrics, and battery separators among others. Meltblowing dies are disclosed in U.S. Pat. Nos. 3,978,185, 4,818,463, and 4,986,743.
A key component of a meltblowing die is the die tip. The die tip is an elongate member having an outwardly protruding nosepiece of triangular cross-section terminating in an apex with a row of side-by-side orifices drilled through the apex. A polymer melt is forced through the orifices for extruding the polymer and discharged as side-by-side molten or semimolten fibers. The die tip is generally formed of high quality steel in a separate machining process and fastened to the face of the die body using bolts. Precise machining is required to achieve uniform polymer flow over the length of the row of orifices. The polymer is forced through the die tip orifices by applying very substantial pressure to the molten polymer inside the tip. The internal pressure induces tensile stress in the die tip which tends to concentrate near the apex of the tip and may cause the tip to fail in tension. U.S. Pat. No. 4,986,743 teaches a method for mounting the die tip on the die body with induced compression in the apex region to counterbalance the tensile stress, rendering the die tip more reliable in service. This patent is incorporated herein by reference.
Other important components of the meltblowing die are elongate plates referred to as air knives which, in combination with the die tip nosepiece, form converging air flows to attenuate and draw down the extruded fibers to microsized diameters. The air knives are generally thick elongate plates which have a longitudinal edge tapered to form a knife edge. Conventionally, two air knives are bolted to the die body on either side of the triangular nosepiece of the die tip. The tapered edges of the air knives are aligned with the confronting tapered surfaces of the nosepiece and spaced slightly therefrom to form two air flow channels converging at the apex of the nosepiece, so that the air flowing rapidly past the apex of the nosepiece tends to entrain the fibers being extruded therefrom, and draw the fibers down until they break. The air flow characteristics are determined by the shape and size of the passages formed between the die tip and the air knives, which are defined by parameters known in the art as the "air-gap", the spacing between the confronting surfaces of the triangular nosepiece of the die tip and the air knives, and the "set-back", the vertical distance between the tip of the nosepiece and the outer plane of the air knives. (As used herein, terminology such as "upward", downward", "vertical", and the like refers to the usual orientation of the die, in which the fibers are extruded downwardly; however, the invention is not to be so limited).
The air-gap and set-back determine the geometry of the converging air flow passages, and thereby influence the air flow properties and the degree of fiber-air interaction. Research has shown that controlling the air flow properties in relation to the polymer fl
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Accurate Products Company
Angeli Michael de
Leyson Joseph
Woo Jay H.
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