Meltblown die tip with capillaries for each counterbore

1. Field of the Invention

The present invention relates to die heads for extruded filaments and particularly die heads for extruding meltblown fabrics.

2. Discussion of the Related Art

A general overview of meltblown polymer filament technology may be had by referring to U.S. Pat. No. 3,825,380 (Harding et al.).

Generally a single deep polymer-distribution channel is formed in the die head and multiple capillaries are drilled in the so-called “knife edge”, or extrusion edge of the die tip to contact the distribution channel and provide the extrusion channels and orifices for the fine, or small, diameter, meltblown fibers. The reader is also referred to U.S. Pat. No. 4,486,161 (Middleton) and U.S. Pat. No. 4,013,816 (Sabee et al.).

The words “fibers” and “filaments” will be used interchangeably in this specification.

However, owning to physical constraints of the die head, such as the requirement for a fine edge at the point of extrusion, there have always been tradeoffs between extrusion pressure and meltblown die capillary density in the meltblown die head. Ideally the maker of meltblown fabrics would prefer to have options for utilizing both higher pressures and greater capillary density than were previously available from prior art designs.

In order to accomplish the object of higher die head pressures and greater capillary, or extrusion orifice, density in a meltblown fiber die head, the present invention provides a die head with bores communicating with a central polymer distribution channel and running in the extrusion direction to communicate with multiple capillaries. At least some, or all, of the bores will have multiple capillary extrusion outlets. By distributing multiple capillaries to a bore, more metal may be retained in the die head thereby allowing higher pressures in the extrusion process while permitting higher capillary density.

It is anticipated that the die tip of the present invention will withstand extrusion pressures that would cause other seals in the die head assembly to fail, resulting in no practical pressure limit on the die tip of the present invention.

These and other objects and features of this invention will be better understood from the following detailed description taken in conjunction with the drawings wherein:

FIG. 1 is a front elevation of a meltblown fiber die head according to the present invention.

FIG. 2 is a bottom view, along line II—II of FIG. 1, of a section of the knife edge of the die showing the in-line capillaries with regular spacing and counterbores in phantom.

FIG. 3 and FIG. 4 show cross-sectional views of a front elevation to illustrate various densities of the multiple capillaries.

It will be appreciated that the drawings may be highly schematic and not to scale for purposes of clear explanation of the principles of the present invention.

Referring to FIG. 1, the die tip 11 is shown with a polymer distribution channel 13 connected to multiple counterbores, collectively 15 , whose longitudinal axes are parallel to the extrusion direction 16 , and which in turn communicate with the capillaries, collectively 17 . The capillaries pass through the die head body 20 and serve as the extrusion orifices of the die head 11 at its knife edge 19 . While these counterbores 15 are shown as continuing across the width of the die head, as indicated by the three dots 21 , it will be appreciated by the person having ordinary skill in the art that various suitable arrangements of counterbores and capillaries may be arranged according to the dictates of the particular manufacturing situation within the teachings of the present invention.

While designated as being a straight-sided counterbore, the bore need not have parallel sides if machining techniques or design dictates otherwise. Neither must the longitudinal axis of a bore necessarily run parallel to the extrusion direction 18 , i.e. perpendicular to the knife edge 19 . The ordinary skilled artisan will further appreciate that various common arrangements and components of a working die head have been left unshown or unstated as they are unnecessary to an exposition of the present invention.

Referencing FIG. 2, a partial bottom view of the knife edge 19 , the outlets of the capillaries 17 can be seen with the counterbores 15 shown in phantom. While shown as being regular in spacing, alignment, and distribution, the capillaries of the present invention, and their counterbores, need not be so limited to regular forms.

Referencing FIG. 3, a partial cross-section at a front elevational view, there is shown a detailed view of these capillaries 17 a , 17 b , and 17 c communicating between a first counterbore 15 a and the knife edge 19 of the die. It will be noted that the capillaries which are off-center of the counterbore, 17 a , 17 c , will be drilled at slight angles to the longitudinal axis of the counterbore 15 a . The counterbore may include a conical countersink portion 23 at its juncture with the capillaries 17 .

FIG. 4 illustrates that even higher concentrations of capillaries may be achieved. In this case, five capillaries 17 are shown connecting to each counterbore 15 . Present conventional drilling can easily achieve one hundred holes per inch in an exemplary die tip by utilizing the present invention.

While in the foregoing specification this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purpose of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.