Plastic article or earthenware shaping or treating: apparatus – Means making particulate material directly from liquid or... – By means applying fluid jet or blast to unconfined liquid...
Reexamination Certificate
1998-08-28
2001-10-02
Nguyen, Nam (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Means making particulate material directly from liquid or...
By means applying fluid jet or blast to unconfined liquid...
C118S315000, C156S500000, C425S072200, C425S19200R
Reexamination Certificate
active
06296463
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to fiberization dies for applying hot melt adhesives to a substrate or for producing nonwovens. In one aspect the invention relates to a modular die provided with an internal rotary positive displacement pump. In another aspect, the invention relates to a segmented die assembly comprising a plurality of separate die units, each unit including a manifold segment and a die module and recirculation module mounted thereon.
The deposition of hot melt adhesives onto substrates by fiberization dies has been used in a variety of applications including diapers, sanitary napkins, surgical drapes, and the like. This technology has evolved from the application of linear beads such as that disclosed in U.S. Pat. No. 4,687,137, to air-assisted deposition such as that disclosed in U.S. Pat. No. 4,891,249, to spiral deposition such as that disclosed in U.S. Pat. Nos. 4,949,668 and 4,983,109. More recently, meltblowing dies have been adapted for the application of hot melt adhesives (see U.S. Pat. No. 5,145,689). As the term suggests, “fiberization” refers to a process wherein a thermoplastic melt is extruded into and set into fibers.
Modular dies have been developed to provide the user with flexibility in selecting the effective length of the fiberization die. For short die lengths only a few modules need be mounted on a manifold block. (See U.S. Pat. No. 5,618,566). Longer dies can be achieved by adding more modules to the manifold. U.S. Pat. No. 5,728,219 teaches that the modules may be provided with different types of die tips or nozzles to permit the selection of not only the die length but the deposition pattern.
U.S. Pat. No. 5,236,641 discloses a metering die which comprises a plurality of metering pumps which feed polymer to individual regions of a single elongated die tip. The tip is mounted on a single polymer manifold which has a plurality of side-by-side flow channels which feed a predetermined number of orifices of the tip. Each pump supplies polymer to a single channel. The pumps may be turned on or off so that polymer flow may be discontinued to some of the orifices of the integral elongate tip. In this design the length of the die is not variable because the manifold and die tip are of fixed length and are not formed from individual segments.
At the present, the most commonly used adhesive fiberization dies are intermittently operated air-assisted dies. These include meltblowing dies, spiral nozzles, and spray nozzles.
Meltblowing is a process in which high velocity hot air (normally referred to as “primary air” or “process air”) is used to blow molten fibers or filaments extruded from a die onto a collector to form a nonwoven web or onto a substrate to form an adhesive pattern, a coating, or composite. The terms “primary air” and “process air” are used interchangeably herein. The process employs a die provided with (a) a plurality of openings (e.g. orifices) formed in the apex of a triangular shaped die tip and (b) flanking air plates which define converging air passages. As extruded rows of the polymer melt emerge from the openings as filaments, the converging high velocity hot air from the air passages contacts the filaments and by drag forces stretches and draws them down forming microsized filaments. In some meltblowing dies, the openings are in the form of slots. In either design, the die tips are adapted to form a row of filaments which upon contact with the converging sheets of hot air are carried to and deposited on a collector or a substrate in a random pattern.
Meltblowing technology was originally developed for producing nonwoven fabrics but recently has been utilized in the meltblowing of adhesives onto substrates. Meltblown filaments may be continuous or discontinuous.
Another type of die head is a spiral spray nozzle. Spiral spray nozzles, such as those described in U.S. Pat. Nos. 4,949,668 and 5,102,484, operate on the principle of a thermoplastic adhesive filament being extruded through a nozzle while a plurality of hot air jets are angularly directed onto the extruded filament to impart a circular or spiral motion thereto. The filaments thus form an expanding swirling cone shape pattern while moving from the extrusion nozzle to the substrate. As the substrate moves with respect to the nozzle, a circular or spiral or helical bead is continuously deposited on the substrate, each circular cycle being displaced from the previous cycle by a small amount in the direction of substrate movement. The meltblowing die tips offer superior coverage whereas the spiral nozzles provide better edge control.
Other fiberization dies include the older non-air-assisted bead nozzles such as bead nozzles and coating nozzles.
SUMMARY OF THE INVENTION
The die assembly of the present invention may be viewed as a fiberization device for processing a thermoplastic material into fibers or filaments. (The terms “fibers” and “filaments” are used interchangeably herein.) The fiberization may be air-assisted as in meltblowing, spiral monofilaments, or melt spraying; or may be non-air-assisted as in bead or coating depositions.
The fiberization of hot melt adhesives is the preferred use of the die assembly of the present invention; but as will be recognized by those skilled in the art, it can be used in the meltblowing of polymers to form nonwoven webs.
The die assembly of the present invention features a number of novel features, but in a broad embodiment, it comprises three main components: a manifold segment; a fiberization die module; and a recirculation module. The manifold, in a preferred embodiment, includes an internal rotary positive displacement pump (e.g. gear pump) for receiving a polymer melt from a polymer delivering system (e.g. extruder) and discharging the same at a metered rate (constant rate) to one of the modules. Each module includes a valve for controlling the flow of the polymer melt therethrough. Controls are provided so that the flow from the gear pump is uninterrupted; that is, the pump discharge flows either to the fiberization die module or the recirculation module. This is achieved by selectively activating the valves of the fiberization die module and the recirculating module. Generally, the flow will be to one or the other module, but not both.
The preferred embodiment of the invention contemplates the use of a plurality of the manifold segments (with each having the two modules described above mounted thereon), interconnected in a side-by-side relationship. The number of segment/module units define the effective length of the die assembly. The side-by-side fiberization die modules form a row of nozzles (e.g. meltblowing die tips, spiral nozzles, etc.) for generating the fibers (or filaments) and depositing the same onto a substrate or collector. The driven rotary member of each internal gear pump rotates about an axis generally parallel to the row of nozzles. In a preferred embodiment, a motor driven shaft extends through the side-by-side manifold segments along this axis of rotation and is keyed to each driven rotary member. Thus, only one driven shaft is required for the entire assembly.
An alternate embodiment of the present segmented die includes a self-contained modular rotary pump in each segment, and wherein each pump comprises metering gears and a segmented drive shaft. The drive shaft of each pump has a tang at one end and a slot at the opposite end. In the assembled configuration, the tang of one pump shaft couples with the slot of the adjacent pump. The tang of the adjacent pump will couple with the slot of the pump adjacent to it; and so on along the die length. Thus in the modular pump embodiment, the integral drive shaft whereon all the driven pump gears are mounted is replaced with coupled drive shaft segments. This embodiment has the advantage that die segments may be removed or added without the need for disassembling the manifold, as well as eliminating the need for using integral drive shafts of various lengths to accommodate additional segments and pumps. The modular pumps may als
Leyson Joseph
Nguyen Nam
Nordson Corporation
Wood Herron & Evans L.L.P.
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