Plastic article or earthenware shaping or treating: apparatus – Air felting type shaping means – Means forming running length product
Reexamination Certificate
1997-12-31
2001-03-13
Cole, Elizabeth M. (Department: 1771)
Plastic article or earthenware shaping or treating: apparatus
Air felting type shaping means
Means forming running length product
C425S072200, C425S382200, C425S464000, C264S555000
Reexamination Certificate
active
06200120
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an improved die head assembly, apparatus, and process for meltblowing a thermoplastic polymer to form a fiber and a nonwoven fabric web, and more particularly relates to an improved die head assembly, apparatus, and process for meltblowing a fiber-forming thermoplastic polymer using an air flow through a removably securable passageway that is centrally-located within an extruded polymer flow, or using an extruded polymer flow through an elongated opening, to form meltblown fibers and a nonwoven fabric web.
Meltblowing techniques for forming very small diameter fibers, sometimes referred to as microfibers or meltblown fibers, from thermoplastic resins and polymers are well-known in the art. For example, the production of fibers by meltblowing is described in an article entitled “Superfine Thermoplastic Fibers”, appearing in
Industrial and Engineering Chemistry
, Vol. 48, No. 8, pp. 1342-1346. This article describes work done at the Naval Research Laboratories in Washington, D.C. Another publication dealing with meltblowing is
Naval Research Laboratory Report
111437
, dated Apr. 15, 1954. Generally, meltblowing techniques include heating a thermoplastic fiber-forming resin to a molten state and extruding the molten resin from a die arrangement having a plurality of linearly arranged small diameter capillaries as molten threads. The molten threads exit the die into a high velocity stream of gas, usually air, which is maintained at an elevated temperature, and which serves to attenuate the threads of molten resin to form fibers having a diameter which is less than the diameter of the capillaries of the die arrangement.
A typical apparatus and process for forming a meltblown fabric is shown in
FIG. 1
, in which a hopper
10
provides polymer material to an extruder
12
attached to a die
14
which extends across the width
16
of a nonwoven web
18
to be formed by the meltblowing process. Inlets
20
and
22
provide pressurized gas to die
14
.
FIG. 2
shows a partial cross-section of a portion of die
14
, including an extrusion slot
24
that receives polymer from extruder
12
and chambers
26
and
28
that receive pressurized gas from inlets
20
and
22
. Chambers
26
and
28
are defined by base portion
30
and plates
32
and
34
of die
14
.
The melted polymer is forced out of slot
24
through a plurality of small diameter capillaries
36
extending across tip
38
of die
14
. Capillaries
36
have a diameter on the order of 0.0145 to 0.0180 in., and are spaced from 9-30 capillaries per inch. The gas passes from chambers
26
and
28
through passageways
40
and
42
. The two streams of gas from passageways
40
and
42
converge to entrain and attenuate molten polymer threads
44
(see
FIG. 1
) as they exit capillaries
36
and land on a foraminous surface
46
, such as a belt. The molten material is extruded through capillaries
36
at a rate of from 0.02 to 1.7 grams/capillary/minute at a pressure of up to 300 p.s.i.g. The temperature of the extruded molten material is dependent on the melting point of the material chosen, and is often in the range of 125 to 335° C. The gas may be heated to 100 to 400° C. and pressurized up to 20 p.s.i.g.
The extruded threads
44
form a coherent, i.e. cohesive, fibrous nonwoven web
18
that may be removed by rollers
47
, which may be designed to press web
18
together to improve the integrity of web
18
. Thereafter, web
18
may be transported by conventional arrangement to a wind-up roll, pattern-embossed, etc. U.S. Pat. No. 4,663,220 discloses in greater detail an apparatus and process using the above-described elements, and is incorporated by reference herein.
U.S. Pat. No. 4,818,464, the disclosure which is also incorporated by reference herein, discloses a process and apparatus for meltblowing thermoplastic material using a different type of die head. In this patent, a centrally located gas jet passes through or between an opening or openings for extruding thermoplastic material.
FIG. 3
shows a partial sectional view of a die tip as taught in U.S. Pat. No. 4,818,464. As shown, gas inlet
48
and extrusion openings
50
and
52
are arranged such that the longitudinal axes
54
and
56
of openings
50
and
52
are disposed at an angle with longitudinal axis
58
of inlet
48
of about 30 degrees to less than about 90 degrees, and typically about 60 degrees. (See angles
60
and
62
).
While the above devices work well for their intended purposes, they are subject to a few minor drawbacks. For example, the small diameter capillaries used to deliver molten thermoplastic material in the above devices require very precise machining to properly locate and create the capillaries. Thus, die heads with extremely fine capillaries are expensive to create.
Also, the small diameter capillaries may be clogged if, for example, molten thermoplastic material were to char or degrade prior to reaching the capillary, forming a solid particle too large to fit through the capillary. Further, the addition of pigments and other additives, or the presence of impurities, could similarly cause clogging of capillaries. It is a time-consuming and expensive process to halt production of a meltblowing line, remove the partially clogged die head assembly, install a clean die head assembly, and clean the clogged die head assembly capillaries for future use.
Further, the small diameter capillary may require the molten thermoplastic material to be heated to an extremely high temperature in order to ensure a low enough viscosity to allow for smooth flow through the small diameter capillary. Also, a high pressure must be used to ensure the molten thermoplastic material is properly extruded through the small diameter capillaries at a flow rate high enough to justify commercial production. With the higher pressures and temperatures used, the entire apparatus must be larger and the energy usage must be higher. Alternately, a low molecular weight (high meltflow rate) material may be required to achieve a suitable low viscosity. Such low molecular weight polymers are often more expensive than materials than have not been treated to attain these characteristics.
Moreover, due to the small diameter of the capillaries, it is difficult to give the capillary any shape other than a circle. Thus, the shape of the fibers formed from such a die head assembly are limited to those attainable by extrusion through a circular capillary.
Also, typical commercial die head assemblies include one row of capillaries, rather than a large array of rows of capillaries, because of the need to have intimate contact between the primary air and polymer filaments to properly attenuate the filaments. The prior art does not permit the spacing of multiple rows of capillaries adjacent each other. Thus, commercial production is limited to the amount of polymer that can be extruded from a single row of extremely small capillary openings. In order to make commercial production feasible, high polymer velocity must be achieved through each hole, generally leading to larger fibers and
or harsher webs, which can be undesirable.
OBJECTS AND SUMMARY OF THE INVENTION
It is a principle object of the present invention to provide a die head assembly, apparatus, and process for meltblowing a thermoplastic polymer, and a meltblown fiber and a nonwoven fabric web that are easy and economical to construct, maintain, and run.
Another object of the present invention is to provide a die head assembly that is easier to clean and is less likely to clog than currently-available products.
Still another object of the present invention is to provide a die head assembly, apparatus, and process for meltblowing a thermoplastic polymer to create a nonwoven fabric web having a greater throughput and production rate than currently-available devices and processes.
Yet another object of the present invention is to provide a die head assembly, apparatus, and process using an array of openings for meltblowing a thermoplastic polymer.
Another object of t
Fish Jeffrey E.
Haynes Bryan D.
Lau Jark C.
Cole Elizabeth M.
Dority & Manning P.A.
Guarriello John J.
Kimberly--Clark Worldwide, Inc.
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