Coating apparatus – Projection or spray type – Plural projectors
Reexamination Certificate
2000-12-19
2003-04-01
Crispino, Richard (Department: 1734)
Coating apparatus
Projection or spray type
Plural projectors
C118S325000, C239S294000, C239S298000
Reexamination Certificate
active
06540831
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to material dispensing systems for applying material onto a substrate and, more particularly, to a material dispensing system having a modular die assembly for applying in a controlled manner patterns of fibrous material onto a moving substrate.
BACKGROUND OF THE INVENTION
Various dispensing systems have been used in the past for applying patterns of viscous material onto a moving substrate. In the production of disposable diapers, incontinence pads and similar articles, for example, hot melt adhesive dispensing systems have been developed for applying a laminating or bonding layer of hot melt thermoplastic adhesive between a non-woven fibrous layer and a thin polyethylene backsheet. Typically, the hot melt adhesive dispensing system is mounted above a moving polyethylene backsheet layer and applies a uniform pattern of hot melt adhesive material across the upper surface width of the backsheet substrate. Downstream of the dispensing system, a non-woven layer is laminated to the polyethylene layer through a pressure nip and then further processed into a final usable product.
In one known hot melt adhesive dispensing system, continuous beads or strands of adhesive are emitted from a multiple adhesive outlet die with multiple air jets oriented around the circumference of each material outlet. The multiple air jets drive air tangentially relative to the orientation of the adhesive strand as it emits from the die orifice, thereby attenuating each adhesive strand and causing the strands to swirl before being deposited on the upper surface of the moving substrate.
More recently, manufacturers of diaper products and others have been interested in small fiber technology for the bonding layer of hot melt adhesive in non-woven and polyethylene sheet laminates. To this end, hot melt adhesive dispensing systems have incorporated slot nozzle dies with a pair of angled air channels formed on either side of the elongated extrusion slot of the die. As the hot melt adhesive emits from the extrusion slot as a continuous sheet or curtain, pressurized air is emitted as a pair of curtains from the air channels to impinge upon, attenuate and fiberize the adhesive curtain to form a uniform fibrous web of adhesive on the substrate. Recently, fibrous web adhesive dispensers have incorporated intermittent control of adhesive and air flows to form discrete patterns of fibrous adhesive layers with well defined cut-on and cutoff edges and well defined side edges.
Meltblown technology has also been adapted for use in this area to produce a hot melt adhesive bonding layer having fibers of relatively small diameter. Meltblow dies typically include a series of closely spaced adhesive nozzles that are aligned on a common axis across the die head. A pair of angled air channels are formed on either side of the adhesive nozzles to extend parallel to the common nozzle axis. As hot melt adhesive emits from the series of aligned nozzles, pressurized air is emitted from the air channels as a pair of curtains that impinge upon, draw down and attenuate the fibers before they are applied to the moving substrate.
While meltblown technology has been used to produce fibrous adhesive layers on moving substrates, it has several drawbacks. As those skilled in the art will appreciate, meltblown technology typically uses a high volume of high velocity air to draw down and attenuate the emitted adhesive strands. The high velocity air causes the fibers to oscillate in a plane that is generally aligned with the movement of the substrate, i.e., in the machine direction. To adequately blend adjacent patterns of adhesive to form a uniform layer on the substrate, meltblow dispensers require the nozzles to be closely spaced. Moreover, the volume and velocity of the air must be high enough to sufficiently agitate and blend adjacent fibers.
However, the high volume of air used in meltblown dispensers adds to the overall operational cost as well as reduces the ability to control the pattern of emitted fibers. One byproduct of the high velocity air is “fly” in which the fibers get blown away from the desired deposition pattern. The “fly” can be deposited either outside the desired edges of the pattern, or even build up on the dispensing equipment which can cause operational problems that require significant maintenance. Another byproduct of the high velocity air and closely spaced nozzles is “shot” in which adjacent adhesive fibers become entangled and form globules of adhesive on the backsheet substrate. “Shot” is undesirable as it can cause heat distortion of the delicate polyethylene backsheet.
It will further be appreciated by those skilled in the art that the construction of the meltblow dies, with the continuous sheets of air formed on either side and parallel to the aligned nozzles, reduces the ability of manufacturers to modularize the meltblow dies in side-by-side fashion across the width of a moving substrate. The curtains of air are interrupted between adjacent melt blow dies which generally results in a less consistent fiber pattern on the substrate.
Additionally, the many closely spaced nozzles required in meltblow dies not only adds to manufacturing costs, but also forces lower material flow rates through each nozzle. Lower material flow rates per nozzle generally results in a greater variation of the fibers emitted from the nozzles. Moreover, the nozzles are typically more likely to clog at the lower material flow rates.
Thus, there is a need for a material dispensing system that improves control of dispensed material to form patterns on a moving substrate without “fly” or “shot”. There is also a need for a material dispensing system that reduces costs associated with operation and maintenance. There is yet another need for a material dispensing system that improves the ability to modularize the dispensing system to provide a wider range of uniform material pattern widths across a moving substrate.
SUMMARY OF THE INVENTION
The present invention overcomes the foregoing and other shortcomings and drawbacks of the material dispensing systems and methods heretofore known. While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention.
The present invention is directed to a material dispensing system and method for use in applying in a controlled manner a fibrous material in a desired pattern on a moving substrate. The material dispensing system has a source of fluid material to be applied and a source of pressurized air that are connected to a material dispensing head. The material dispensing head has a fluid manifold connected to the source of material, an air manifold connected to the source of pressurized air, and a dispensing module having an upper dispensing body and a lower modular die assembly mounted to one end of the dispensing body. The dispensing body is connected to the fluid manifold for delivering fluid in a controlled manner to the die assembly. The modular die assembly includes a series of aligned material outlets that emit the fluid in a series of spaced strands toward a substrate. The dispensing body is connected to the air manifold for delivering pressurized air in a controlled manner to the die assembly. The pressurized air is used to draw down and attenuate the strands to form fibers that oscillate in a generally transverse plane relative to the direction of travel of the moving substrate. The oscillation of the fibers provides a uniform pattern of fibrous material on the moving substrate. The pressurized air between the material outlets also separates the strands during the critical draw down phase to prevent entanglement of adjacent strands. The orientation of the air and material outlets in accordance with the principles of the present invention improves control of the dispensed material to form
Craine Andrew W.
Miller Scott R.
Schmidt Paul A.
Crispino Richard
Nordson Corporation
Tadesse Yewebdar T.
Wood Herron & Evans LLP
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