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
1998-08-20
2001-04-24
Pyon, Harold (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...
C425S072200, C425S19200R
Reexamination Certificate
active
06220843
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to dies for applying hot melt adhesives to a substrate or producing nonwovens. In one aspect the invention relates to a modular die provided with at least one air-assisted die tip or nozzle. 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 mounted thereon.
The deposition of hot melt adhesives onto substrates 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).
Modular dies have been developed to provide the user with flexibility in selecting the effective length of the 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 also the deposition pattern.
At the present, the most commonly used adhesive applicators 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”) is used to blow molten 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 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.
The filaments extruded from the air-assisted die may be continuous or discontinuous. For the purpose of the present invention the term “filament” is used interchangeably with the term “fiber” and refers to both continuous and discontinuous strands.
Another popular 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 assume an expanding swirling cone shape pattern while moving from the extrusion nozzle to the substrate. As the substrate is moved in the machine direction 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 adhesive applications include the older non-air assisted bead nozzles such as bead nozzles and coating nozzles.
SUMMARY OF THE INVENTION
The segmented die assembly of the present invention is of modular construction, comprising a plurality of side-by-side and interconnected die units. Each die unit includes a manifold segment and a die module mounted on the manifold segment. The die module has mounted thereon an air-assisted die tip or nozzle. The die tip may be a meltblowing type and the nozzle may be a spiral nozzle or a spray nozzle. For convenience of description, the term “nozzle” is used herein in the generic sense, meaning any air-assisted die tip or nozzle; and the term “air-assisted” means a nozzle through which is extruded a molten thermoplastic filament or filaments, and air jets, air streams, or air sheets which contact the molten filaments to divert, attenuate or change the flow pattern of the filament(s) and impart a desired characteristic to the filaments, either in terms of the size of the filaments or the deposition pattern.
The main components of each die unit, the manifold segment and the module, are provided with (a) air passages for delivering air to the nozzles and (b) a polymer flow passage for delivering a polymer melt to the nozzle. In the preferred embodiment, the nozzle is a meltblowing die tip provided with a row of orifices and flanking air slits, so that as a row of filaments are extruded through the meltblowing die tip, they are contacted with converging sheets of hot air that attenuate or draw down the filaments to microsize. As described in detail below, the nozzle may also be a spiral or spray nozzle. In practice, the die assembly may include segmented units having different types of nozzles.
The segmented die units are assembled by interconnecting several identical manifold segments, wherein the air passages and the polymer flow passage of each segment are in fluid communication. In the assembled condition, the interconnected manifold segments function much in the manner of an integrated manifold. A die module is mounted on each manifold segment and, in combination with other die modules, form a row thereon. Thus, polymer melt is extruded as a row of filaments from the array of modules and deposited on a moving substrate positioned under the assembly.
In a preferred embodiment, each module is provided with an air-actuated valve to selectively open and close the polymer flow passage. The instrument air for activating the valve is delivered through each manifold segment to the module. The valves may be individually actuated or actuated as a bank, depending on the instrument air passages and the number of control valves used.
The segmented die assembly of the present invention offers several advantages over the prior art:
(a) Die modules may be replaced by merely removing an existing module from an assembled manifold segment, and replacing it with a new module. This feature not only permits the replacement of faulty modules, but also permits changing the die nozzle.
(b) The length of the die assembly determines the effective length of the die discharge (i.e. length of the row of nozzles). In prior art designs, the die length was determined by the manifold length which had to be preformed. For example, a manifold would be built to accommodate a maximum number of modules. Frequently, however, less than the maximum number would be required. This meant that several manifold sites (i.e. those without modules) would have to be sealed off. In the present invention, the manifold is made up of only the active manifold segments (i.e. those which have modules mounted thereon).
(c ) The manifold segments are substantially identical and interchangeable, and are simple in construction. The machining of the small segments is much easier than that required for bulky integrated manifolds.
(d) If a manifold segment becomes plugged or damaged, it can easily be replaced by a new manifold segment. In the prior art device, the entire manifold would have to be replaced.
(e) The solid block manifold of the prior art, in some operations, may include dormant polymer flow passages, as in situations where the active die le
Leyson Joseph
Nordson Corporation
Pyon Harold
Wood Herron & Evans L.L.P.
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