Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Nonwoven fabric – Including an additional nonwoven fabric
Reexamination Certificate
2000-09-27
2002-12-10
Juska, Cheryl A. (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Nonwoven fabric
Including an additional nonwoven fabric
C442S394000, C442S400000, C442S415000, C442S392000, C442S393000, C428S077000, C428S157000, C428S171000, C428S172000, C428S189000, C428S190000, C428S191000, C428S192000, C428S193000, C428S213000, C428S218000
Reexamination Certificate
active
06492286
ABSTRACT:
The present invention pertains to multilayer meltblown fibrous webs, methods of manufacturing such webs, and apparatus for manufacturing multilayer meltblown fibrous webs.
BACKGROUND
The manufacture of meltblown fibrous webs has been discussed in many references, including, Wente, Van A.,
Superfine Thermoplastic Fibers
, 48 Industrial Eng. and Chem. 1342-46 (1956); Report No. 4364 of the Naval Research Laboratories, published May 25, 1954, entitled
Manufacture of Superfine Organic Fibers
, by Wente, V. A., Boone, C. D., and Fluharty, E. L.; and U.S. Pat. No. 3,971,373 to Braun.
In making meltblown fibrous webs, a thermoplastic polymer or resin is commonly extruded through a row of small, side-by-side orifices into a high velocity gaseous stream that attenuates the emerging material into fibers. The gaseous stream creates turbulence that randomly entangles the fibers to form a coherent nonwoven web on a collector. The collector may be a moving flat belt or rotating cylindrical screen or drum. The resulting nonwoven web is transferred from the collector to a temporary storage roll.
Known processes have a couple drawbacks, namely, they can produce significant waste as a process by-product and they can produce non-uniformities across the web.
Waste (also referred to as weed) is commonly produced at the web edges when manufacturing meltblown fibrous webs. The waste or weed results because the web edges are typically “feathered”, meaning the edges taper off and do not have the same weight and density as the central portion of the web. The feathering stems from fiber dispersal at the web edges. To eliminate this variation in weight and density, the web edges typically are trimmed off and then discarded as waste, while the central portion of the web is retained for further processing. The wasted material adds to processing costs, especially when in-line web processing is desired.
Known meltblown fibrous webs are typically mono-layer webs that, by definition, have only a single layer. Mono-layer meltblown fibrous webs often suffer from non-uniformities over their cross-web dimension due, for example, to variations in orifice diameter. The variations in orifice diameter can cause non-uniform fiber deposition that, in turn, causes variations in the basis weight in the cross-web dimension. The basis weight is the weight per unit area of the mono-layer web, and it is commonly adjusted by varying the polymer extrusion rate or the collector speed or both. For example, if a higher basis weight web is desired, the collector speed can be reduced and/or the extrusion rate can be increased. Conversely, if a lower basis weight web is desired, the collector speed can be increased and/or the extrusion rate can be decreased.
One approach to overcoming variations in basis weight include laminating multiple webs together using agents such as adhesives or resins and/or by physical processing such as welding. The variations in the multiple webs then preferably average out the non-uniformities such that the minimum acceptable basis weight is achieved over the entire laminated web. One disadvantage to this approach is that some areas of the web can have an excessive basis weight and hence unnecessary amounts of web material. The unnecessary material, as well as the laminating agents and/or processing needed to laminate the webs to form the multi-web products adds to production costs and increases complexity. Furthermore, the agents and/or welds used to laminate the layers can adversely affect the resulting articles' conformability and flexibility.
Attempts to employ tubular fibrous web processes to achieve a flat web have typically involved forming the tubular meltblown fibrous web and compressing the tube to obtain a flat web without feathered edges. Alternatively, the tubular web may be slit longitudinally so that the tube is opened, thereby producing a flat web with two machine-cut edges. Two such approaches are described in U.S. Pat. Nos. 3,909,174 (Blair et al.) and 4,032,688 (Pall). A disadvantage of these processes is that variations in web thickness may often be helical in nature. As a result, slitting the web longitudinally often causes banded variations in the web density, which variations are located at an angle, commonly referred to as a “bias angle,” with respect to the web centerline.
SUMMARY OF THE INVENTION
The present invention is directed to overcoming the noted drawbacks in known methods for making meltblown fibrous webs. In one aspect, the present invention provides a new apparatus for manufacturing a meltblown fibrous web. The new apparatus includes (i) a collector that has a generally cylindrical forming surface and (ii) a source that is capable of directing meltblown fibers at the forming surface. The generally cylindrical forming surface can rotate about a longitudinal axis and can simultaneously move parallel to the longitudinal axis, such that a selected point on the forming surface can move in a helical pattern about and along the longitudinal axis from a first end of the collector to a second end of the collector. The helical pattern defines a helix angle relative to the longitudinal axis. The apparatus also includes (iii) a separator that can separate a tubular meltblown fibrous web formed on the forming surface in a direction generally parallel to the helix angle. The separator thus converts the tubular meltblown fibrous web into a non-tubular or flat meltblown fibrous web.
In a second aspect, the present invention provides a method of manufacturing a meltblown fibrous web using a collector having a generally cylindrical forming surface. The forming surface is rotated about a longitudinal axis and simultaneously moves longitudinally in the direction of the longitudinal axis such that a selected point on the forming surface moves in a helical pattern about and along the longitudinal axis from a to first end of the collector to a second end of the collector. The helical pattern defines a helix angle relative to the longitudinal axis. Meltblown fibers are directed at the forming surface as the forming surface rotates and moves longitudinally, such that a tubular meltblown fibrous web is formed on the forming surface. The tubular meltblown fibrous web is then separated along a direction generally parallel to the helix angle to convert the tubular meltblown fibrous web into a non-tubular or flat meltblown fibrous web.
In a third aspect, the present invention provides a multilayer meltblown fibrous web that has a plurality of interconnected layers that contain meltblown fibers. At least one of the fiber-containing layers has a feathered edge. The web also has two separated edges. The feathered edge is located between the separated edges, and the separated edges and the feathered edge are generally parallel to each other. The multilayer meltblown fibrous web may be used in a variety of articles such as filters for masks or respirators.
The multilayer meltblown fibrous webs of the present invention are produced on a collector having a forming surface in the general shape of a cylinder where the forming surface rotates about the longitudinal axis of the cylinder. While the forming surface rotates as such, it is simultaneously advanced parallel to and along the longitudinal axis. As a result, any particular point on the forming surface moves along a helical path during web manufacture.
A meltblown fiber source is directed at the forming surface along at least a portion of the longitudinal length of the collector, thereby forming a layer of meltblown fibers on the forming surface. The forming surface typically completes at least one rotation about the longitudinal axis in the time required to advance the forming surface along the length of the meltblown fiber source. Where the forming surface completes two or more rotations in the time required to advance the forming surface along the length of the collector, a multilayer tubular web is built-up on the forming surface.
Because the forming surface rotates about the longitudinal axis while simultaneously advancing parallel to the l
Berrigan Michael R.
Dyrud James F.
Erickson Luther E.
Erickson Stanley C.
3M Innovative Properties Company
Hanson Karl G.
Juska Cheryl A.
Salvatore Lynda
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