Plastic article or earthenware shaping or treating: apparatus – Continuous filament forming or film casting means with...
Reexamination Certificate
1999-06-09
2002-04-30
Nguyen, Nam (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Continuous filament forming or film casting means with...
C425S072200, C425S083100, C425S463000
Reexamination Certificate
active
06379136
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a new sub-denier spunbonded nonwoven web product produced by a unique spunbond apparatus and its unique operating process for the continuous production of thermoplastic synthetic resin filaments at unusually high filament speeds. More particularly the invention relates to the production of such nonwoven webs by this spunbond apparatus utilizing extremely high fiber speeds, generally of the order of 80 m/sec and more typically exceeding 100 m/sec. resulting in fibers on the order of 1.0 denier and less. In another important aspect, the invention relates to a nonwoven fabric possessing a more uniformly random web structure with sub-denier fibers created by the inventive apparatus and method. This web structure results in a narrower ratio of machine direction to cross direction tensile properties in addition to significantly improved cover and greater opacity.
2. Prior Art
It is well known to produce nonwoven webs from thermoplastic materials by extruding the thermoplastic material through a spinneret and drawing the extruded material into filaments by eduction to form a random web on a collecting surface. U.S. Pat. No. 3,802,817 to Matsuki et al describes a full width eductor device and method which requires high pressures, however it is limited to lower speeds for practical operation. U.S. Pat. No. 4,064,605 to Akiyama et al similarly describes apparatus employing high speed air jet drafting with the same inherent limitations. U.S. Pat. No. 5,292,239 to Zeldin et al discloses a device that significantly reduces turbulence in the fluid flow in order to uniformly and consistently apply the drawing force to the filaments, which results in a uniform and predictable draw of the filaments. This system limits the magnitude of attenuation because of insufficient draw forces due to the extremely shallow jet angle. U.S. Pat. No. 5,814,349 to Geus et al discloses a device which combines quench fluid flow with below the belt suction. However, this arrangement requires a decoupling device in order to prevent skein forming deceleration which negates the original advantages of the U. S. Pat. No. 5,032,329 to Reifenhauser.
Polypropylene is the only thermoplastic resin that is commonly utilized in conventional air drawn spunbond processes. It is important to note that due to the limitations of existing spunbond spinning systems it is virtually impossible to process resin entities in equipment designed for polypropylene where flow and spinning characteristics deviate significantly from polypropylene.
As a first step, the resin is melted and extruded through a spinneret to form a vertically oriented cascade of downwardly advancing molten fibers. The filaments are fluid cooled to quench and uniformly cool the filament curtains for optimum drawing and development of the desired high crystallinity which provides the goal of high fiber strength. A fiber drawing system having a fluid draw jet-slot, into which a controlled volume of high velocity fluid is introduced, draws additional fluid into the upper open end of the drawing slot and creates a rapidly moving downstream of fluid within the slot. This fluid stream creates a contiguous drawing force on the filaments, causing them to be attenuated. After the filaments are attenuated they exit the bottom of the slot where they 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 calendering and point bonding techniques.
Forming filaments in the well known conventional spunbond systems results typically in filaments of 2.5 denier to 12 denier and higher. Using conventional methods, the molten filaments leaving the spinneret typically are immediately cooled at their surfaces to ambient temperature and then subjected to the typical drawing system. This conventional method and apparatus produce adequate non-woven fabrics however their properties, especially tensile strength, high machine direction to cross direction strength ratio, non-chemically enhanced hydrophobicity, drape, softness and opacity are poor.
When conventional spunbond systems attempt to make sub-denier fiber the resin output per hole drops precipitously reducing spunbond fabric production to less than half of the production when forming spunbond of typical denier range.
The instant invention through the use of a unique new apparatus and process, provides a greatly improved spunbond fabric consisting of a narrow range of low denier filaments which improves all of the aforementioned properties.
The low-denier filaments with their smaller diameter produces more surface area and more length per unit weight, reduces light transmission and improves light dispersion (greater opacity) and softness (lower unit fiber deflection forces). Using the instant invention spunbonded fabrics can be made from a wide range of resins, in addition to polypropylene, such as polyethylene, polyester, polyamides, polycarbonate, polyphenylene sulfide, liquid crystal polymers, fluropolymers, polysulfone and their copolymers as well as other extrudable synthetic resins. Providing narrow ranges of filament sizes from 0.1 denier to 1.0 denier with a wide range of polymers is extremely desirable because of their improved performance properties as indicated above. A further process benefit of the instant invention is that resin throughput per hole per minute is not reduced below existing commercial rates.
Examples of end uses for the instant invention are filtration materials, diaper covers and medical and personal hygiene products requiring liquid and particulate barriers that are breathable and provide good vapor transport with significant air permeability. Because of the low denier the spunbond fabrics produced by the instant invention have physical and performance properties comparable to SMS (Spunbond-Meltblown-Spunbond), SMMS (Spunbond-Meltblown- Meltblown-Spunbond) and SM (Spunbond-Meltblown) fabrics. This is an important result since it suggests that a single die head or beam can produce a material which now requires from two to four die beams.
Prior conventional spunbond art is almost completely concerned with the use of polypropylene. An important limitation of prior art is the inadequacy of conventional spunbond systems to extrude and highly draw common resins such as polyester, polyethylene or more unusual resins such as polyamides, polycarbonate, polysulfone and polytetrafluoroethylene.
The instant invention teaches apparatus and processes that are designed with intrinsic accommodations to extrude and draw fibers with an extreme range of extrusion temperatures, wide variations in glass transition temperatures, wide ranges of melt viscosities and other variable resin properties important to filament extrusion, forming, quenching and drawing, thereby widening the application of the spunbond arts.
Objects Of The Invention
It is the principal object of the present invention to provide an improved system for the production of spunbonded nonwoven webs of thermoplastic synthetic resin filament which allows:
1. significant increase in filament velocity and attenuation over a wide range of filament diameters.
2. significant decrease in fiber denier or diameter at lower operating costs without sacrificing mass through-put.
3. capability of spunbonding a wide variety of resins using one apparatus having a wide degree of adjustment in the extrusion, forming, quenching, drawing and laydown operations.
4. stronger fibers through improved crystallization kinetics based on improved attenuation and quench control.
5. higher nonwoven fabric opacity and cover.
6. increased fiber and nonwoven fabric uniformity (narrower filament diameter range).
7. significant increase in collector speeds with resultant higher mass throughput.
8. production of webs with filament deniers of less than 1.0.
9. production of light weight webs at collector speeds in excess of 600 meters per minute.
10. production of nonwoven material at mass rates of greater than 400 to
Najour Gerald C.
Ward Gregory F.
Leyson Joseph
Nguyen Nam
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