U.S. patent application number 17/294303 was filed with the patent office on 2022-01-13 for spinneret block with unitary spinneret body and nozzles for use in the manufacturing of spun-blown fibers.
This patent application is currently assigned to TEKNOWEB MATERIALS S.R.L.. The applicant listed for this patent is TEKNOWEB MATERIALS S.R.L.. Invention is credited to Fabio Zampollo.
Application Number | 20220010458 17/294303 |
Document ID | / |
Family ID | 1000005911910 |
Filed Date | 2022-01-13 |
United States Patent
Application |
20220010458 |
Kind Code |
A1 |
Zampollo; Fabio |
January 13, 2022 |
SPINNERET BLOCK WITH UNITARY SPINNERET BODY AND NOZZLES FOR USE IN
THE MANUFACTURING OF SPUN-BLOWN FIBERS
Abstract
The present invention relates to a particular execution for a
die block for spun-blowing process for forming a fibers or
filaments that may further form a spun-blown web or nonwoven
comprising such a formed fibrous web, e.g. as a layer in a
multi-layer composite web. The die block comprises a spinneret
block with unitary spinneret body and nozzles.
Inventors: |
Zampollo; Fabio; (Cremona,
IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TEKNOWEB MATERIALS S.R.L. |
Palazzo Pignano |
|
IT |
|
|
Assignee: |
TEKNOWEB MATERIALS S.R.L.
Palazzo Pignano
IT
|
Family ID: |
1000005911910 |
Appl. No.: |
17/294303 |
Filed: |
November 5, 2019 |
PCT Filed: |
November 5, 2019 |
PCT NO: |
PCT/EP2019/080293 |
371 Date: |
May 14, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D01D 4/04 20130101; D01D
4/025 20130101; D01D 13/00 20130101; D01D 5/0985 20130101 |
International
Class: |
D01D 4/02 20060101
D01D004/02; D01D 5/098 20060101 D01D005/098; D01D 4/04 20060101
D01D004/04; D01D 13/00 20060101 D01D013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 16, 2018 |
GB |
1818689.0 |
Apr 12, 2019 |
GB |
1905253.9 |
Aug 5, 2019 |
GB |
1911165.7 |
Claims
1. A die block for forming meltblown filaments comprising: wherein
said spinneret block, said air distribution plate, said exterior
air plate, and said cover strip mounted in this order and secured
by said securing means such that said nozzles protrude through
corresponding openings in said air distribution plate and further
through corresponding openings in said exterior air plate, and such
that polymer passageways are formed for molten polymer passing from
said polymer supply side of said spinneret body through said
nozzles; and such that air passageways are formed for air passing
from said air supply through openings in said air distribution
plate and said exterior air plate; whereby said openings in said
exterior plate and said nozzles are adapted so as to allow molten
polymer exiting said nozzles and air flowing through the openings
of said exterior air plate are essentially parallel, wherein said
spinneret body and said nozzles are unitary.
2. A die block according to claim 1, satisfying one or more of the
conditions selected from the group consisting of the inner diameter
of the nozzle being less than about 1.25 mm; the outer diameter of
the nozzle being less than about 2 mm; the nozzle exhibiting a
length of less than about 50 mm; the nozzle exhibiting a length of
more than about 10 mm; the nozzle exhibiting a L/d ratio of less
than about 50; the die block exhibiting a CD width of more than 250
mm.
3. A die block according to claim 1, further comprising pre-holes
in said block, said pre-holes extending from the upper surface
positioned towards the supply of the molten polymer towards said
capillaries in the form of countersinks to the capillaries of said
nozzles.
4. A die block according to claim 1, wherein the transition of said
nozzles to the base of said block exhibits a radius of more than
about 0.1 mm.
5. A die block according to claim 1, wherein said array of nozzles
comprises at least two sub-arrays comprising nozzles differing from
nozzles of a different sub-array in at least one of the dimensions
selected from the group consisting of inner diameter of the nozzle;
outer diameter of the nozzle, length of the nozzle.
6. A die block according to any of the preceding claim 1, wherein
further said array of nozzles comprises at least two sub-arrays,
each of said sub-arrays being connected to a separate polymer
supply system adapted to supply molten polymer to said sub-array
differing in at least one of the features selected from the group
consisting of polymer type; polymer flow rate; polymer pressure;
polymer temperature.
7. (canceled)
8. A method for the manufacture of a die block comprising a
spinneret block comprising a spinneret body and a plurality of
nozzles, an air distribution plate, and an exterior air plate,
comprising: providing a single piece of die block precursor;
machining from said single piece of die block precursor a spinneret
block comprising nozzles; air inlet and distribution chamber; an
air distribution plate; an exterior air plate, wherein said
machining is high precision CNC treatment.
9. (canceled)
10. Process for forming a nonwoven web comprising meltblown fibers,
comprising the steps of providing equipment according to claim 1,
providing a thermoplastic polymer for forming MB fibers, exhibiting
a MFI from 30 to 2000, forming filaments by applying a pressure of
less than 70 bar.
11. A die block according to claim 3 comprising pre-holes in said
block, wherein said pre-holes exhibit a chamfering angle of between
30.degree. and 60.degree..
12. A die block according to claim 3 comprising pre-holes in said
block, wherein said pre-holes exhibit a diameter of between 1.5 to
4 times the inner diameter of said capillaries.
13. A die block according to claim 3 comprising pre-holes in said
block, wherein said pre-holes exhibit a length of more than about 2
mm.
14. A die block according to claim 3 comprising pre-holes in said
block, wherein said pre-holes exhibit a length of less than about
20 mm.
15. A die block according to claim 3 comprising pre-holes in said
block, wherein said pre-holes exhibit a length of less than about
14 mm.
16. A die block according to claim 3 comprising pre-holes in said
block, wherein said pre-holes exhibit a length of less than about 8
mm.
17. A process for forming a nonwoven web according to claim 10,
wherein the operation of forming filaments is executed at a
pressure of less than 50 bar at the polymer supply.
18. A process for forming a nonwoven web according to claim 17
wherein the operation of forming filaments is executed at a
pressure of less than 45 bar at the polymer supply.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an equipment adapted to
create filaments of the spun-blown type for forming nonwoven
materials of superior quality, as well as methods to manufacture
and operate such an equipment.
BACKGROUND
[0002] Spunmelting is a process where fibers are spun from molten
polymer through a plurality of nozzles in a die block, also
referred to as die head, connected to one or more extruders for
being formed into web, such as nonwoven webs or as components
thereof. The spunmelt processes are well known in the art, and
include meltblowing, see e.g. U.S. Pat. No. 8,017,534 (K-C), and
spunbonding, see e.g. U.S. Pat. No. 5,935,512 (K-C).
[0003] From such technologies, a "hybrid" technology, often
referred to as "spun-blowing" has been developed and described in
e.g. U.S. Pat. No. 9,303,334 (Biax). This technology provides a
number of benefits with regard to the fiber and web properties, but
also with regard to the equipment and process for the
manufacturing. However, when implementing such technology, several
hurdles have been encountered. As will be discussed in more detail
herein below, it is difficult to precisely align the individual
nozzles, first, relative to other nozzles, which results in
difficulties at the assembly stage, but also with regard to air
blowing holes, such that an annular shrouding air flow may become
eccentric and deteriorate filament and further web properties, such
as by undesired bundling of adjacent filaments.
[0004] Henceforth, it is an object of the present invention to
overcome problems of the spun-blowing technology.
SUMMARY
[0005] In a first aspect, the present invention is a die block for
forming meltblown filaments, this die block comprising [0006] at
least one molten polymer supply; [0007] air supply; [0008] a
spinneret block comprising [0009] a spinneret body comprising a
polymer supply side, and [0010] a plurality of nozzles forming an
array of nozzles; [0011] an air distribution plate comprising
openings; [0012] an exterior air plate comprising openings; [0013]
a cover strip [0014] securing means, wherein the spinneret block,
the air distribution plate, the exterior air plate, and the cover
strip mounted in this order and secured by the securing means such
that [0015] the nozzles protrude through corresponding openings in
the air distribution plate and further through corresponding
openings in the exterior air plate, and [0016] such that polymer
passageways are formed for molten polymer passing from the polymer
supply side of the spinneret body through the nozzles; and [0017]
such that air passageways are formed for air passing from the air
supply through openings in the air distribution plate and the
exterior air plate; whereby the openings in the exterior plate and
the nozzles are adapted so as to allow molten polymer exiting the
nozzles and air flowing through the openings of the exterior air
plate are essentially parallel and wherein the spinneret body and
the nozzles are unitary.
[0018] The die block may satisfy one or more of the conditions
selected from the group consisting of [0019] the inner diameter of
the nozzle being less than about 1.25 mm, preferably less than
about 0.8 mm; [0020] the outer diameter of the nozzle being less
than about 2 mm; [0021] the nozzle exhibiting a length of less than
about 50 mm; [0022] the nozzle exhibiting a length of more than
about 10 mm; [0023] the nozzle exhibiting a L/d ratio of less than
about 50; [0024] the die block exhibiting a CD width of more than
250, preferably more than 1500, even more preferably of more than
about 2000 mm or even more than 5000 mm.
[0025] The present invention also relates to a die block comprising
a unitary spinneret body and nozzles, further comprising pre-holes
in the spinneret block, the pre-holes [0026] extending from the
upper surface positioned towards the supply of the molten polymer
towards the capillaries [0027] in the form of countersinks to the
capillaries of the nozzles, [0028] preferably with a chamfering
angle of between 30.degree. and 60.degree., [0029] preferably
exhibiting a diameter of between 1.5 to 4 times the inner diameter
of the capillaries, [0030] preferably exhibiting a length of more
than about 2 mm, preferably more than about 4 mm, [0031] preferably
exhibiting a length of less than about 20 mm, preferably less than
about 14 mm more preferably less than about 8 mm, and most
preferably a length of about 6 mm.
[0032] In a preferred embodiment, the transition of the nozzles to
the base of the spinneret block exhibits a radius of more than
about 0.1 mm, preferably more than about 0.3 mm.
[0033] The array of nozzles in the die block may comprise at least
two sub-arrays comprising nozzles differing from nozzles of a
different sub-array in at least one of the dimensions selected from
the group consisting of [0034] inner diameter of the nozzle; [0035]
outer diameter of the nozzle, [0036] length of the nozzle.
[0037] The array of nozzles may further comprise at least two
sub-arrays, each of the sub-arrays are connected to a separate
polymer supply system adapted to supply molten polymer to said
sub-arrays differing in at least one of the features selected from
the group consisting of [0038] polymer type; [0039] polymer flow
rate; [0040] polymer pressure; [0041] polymer temperature.
[0042] In another aspect, the present invention is a method for the
manufacture of a die block comprising a spinneret block comprising
a spinneret body and a plurality of nozzles, an air distribution
plate, and an exterior air plate, comprising the steps of [0043]
providing a single piece of die block precursor, preferably steel;
[0044] machining from the single piece of die block precursor
[0045] a spinneret block comprising [0046] nozzles; [0047] air
inlet and distribution chamber; [0048] an air distribution plate;
[0049] an exterior air plate [0050] wherein the machining is high
precision CNC treatment.
[0051] In another aspect, the present invention is a method for the
manufacturing of a spinneret block comprising a spinneret body and
a plurality of nozzles for being used in a die block, comprising
the steps of [0052] providing a single piece of spinneret block
precursor, preferably steel; [0053] machining from the single piece
of spinneret block material [0054] nozzles; [0055] air flow
channels; [0056] wherein the machining is high precision CNC
treatment.
[0057] In yet a further aspect, the present invention is a process
for cleaning a melt blowing apparatus, comprising the steps of
providing a spinneret or a die clock as described, burning of
polymer residues, ultrasonically removing burnt residues, blowing
pressurized water/steam through the nozzles.
[0058] In yet a further aspect, the present invention relates to a
process for forming a nonwoven web comprising meltblown fibers,
comprising the steps of [0059] providing equipment as described in
the above, [0060] providing a thermoplastic polymer for forming
meltblown fibers, exhibiting a MFI from 30 to 2000, [0061] forming
filaments by applying a pressure of less than 70 bar, preferably
less than 50 bar more preferably less than 45 bar at the polymer
supply.
BRIEF DESCRIPTION OF THE FIGURES
[0062] FIG. 1 shows a spun-blowing equipment according to prior
art.
[0063] FIG. 2 A to H depict particular features of the present
invention.
[0064] FIG. 3 4A to D and 5 depict further features of the present
invention.
[0065] Same numerals in the figures depict same or equivalent
features. Figures are schematic and not to scale.
DETAILED DESCRIPTION
[0066] The present invention relates to a particular execution of a
die block for a spun-blowing process for forming a fibers or
filaments that may further form a fibrous web or nonwoven
comprising such a formed fibrous web, e.g. as a layer in a
multi-layer composite web. Spunmelt is a process where fibers are
spun from molten polymer through a plurality of nozzles in a die
head connected to one or more extruders. The spunmelt process may
include meltblowing, spunbonding and the hybrid process as
described hereinafter in more detail, also referred to as
spun-blowing.
[0067] Meltblown is a process for producing very fine fibers
typically having a diameter of less than about 10 microns, where a
plurality of molten polymer streams are attenuated using a hot,
high speed gas stream once the filaments emerge from the nozzles.
The attenuated fibers are then collected on a flat belt or drum
collector. A typical meltblowing die has around 35 nozzles per inch
and a single row of nozzles. The typical meltblowing die uses
inclined air jets at each side of the row of nozzles for
attenuating the filaments. Spunbond is a process for producing
strong fibrous nonwoven webs directly from thermoplastics polymers
by attenuating the spun filaments using cold, high speed air while
quenching the fibers near the spinneret face. Individual fibers are
then laid down randomly on a collection belt and conveyed to a
bonder to give the web added strength and integrity. Fiber size is
usually below 250 .mu.m and the average fiber size is in the range
of from between about 10 microns to about 50 microns. The fibers
are very strong compared to meltblown fibers because of the
molecular chain alignment that is achieved during the attenuation
of the crystallizing (solidifying) filaments. A typical spunbond
die has multiple rows of polymer holes and for a conventional
polymer of the polypropylene type the polymer melt flow index (MFI)
is usually below about 500 grams/10 minutes at 2.16 kg load.
[0068] The present invention is related to spun-blowing, a hybrid
process between a conventional meltblown process and a conventional
spunbond process, using a multi-row spinneret similar to the
spinneret used in spunbonding except the nozzles are arranged to
allow parallel gas jets surrounding the spun filaments in order to
attenuate and solidify them. Each of the extruded filaments is
shrouded by pressurized gas and its temperature can be colder or
hotter than the polymer melt. Optionally, the periphery around all
of the filaments may be surrounded by a curtain of pressurized
gas.
[0069] In order to explain the general principles of the
spun-blowing equipment and process for forming filaments and
further webs, such as nonwoven webs or components of such webs,
express reference is made to U.S. Pat. No. 9,303,334 describing
such a technology in greater detail. Thus, FIG. 1 depicts a die
block for such a "hybrid" spun-blowing process.
[0070] Overall, a die block 26 comprises as elements a spinneret
body 52, an air distribution plate 70, an exterior plate 78, and a
cover strip 88. Further, nozzles 58 extend from the spinneret body
52 through openings of the distribution plate 70 and exterior plate
78, respectively, such that molten material can pass through the
capillary 60 of the nozzle 58 to form filaments 86 at the tip of
the nozzle 96.
[0071] Typically the order of the elements is such that the
spinneret body 52, the air distribution plate 70, the exterior
plate 78, and the cover strip 88 are arranged along gravity, and
for the purpose of the present explanation, the spinneret body 52
is positioned above and secured to the air distribution plate 70,
which is positioned above and secured to the exterior plate 78,
which is positioned above and secured to the cover strip 88, with
securing means not shown.
[0072] Whilst the present description has been explained by
referring to a positioning of the die block such that the nozzle
exhibits a vertical orientation, the skilled person will readily
realize that this is not essential, but the die block may be tilted
around a CD oriented axis such that nozzles may be oriented
relative to the vertical at more than 5.degree., or more than
15.degree., or more than 30.degree., or more than 45.degree. or
even more, though typically less than 90.degree. (i.e.
horizontal).
[0073] FIG. 1 shows a cross-sectional view of the die block 26.
When positioned into a manufacturing equipment for forming
nonwoven, this view corresponds to an x-z-directional view, with
the x-direction 12 denoting the manufacturing direction, i.e. the
direction of movement of the resulting web, and the z-direction 15
corresponding to the height (along gravity). In the execution as
depicted, the three nozzles 58 represent one "column" of the "multi
row" (here three-row) die block 26. The die block comprises a
plurality of columns positioned adjacently y-directionally 18 (i.e.
perpendicularly to the plane of drawing and indicated by the
circle) such that the columns and rows of nozzles form an array of
nozzles of a die block. A spinnerette body 52 can contain from as
few as ten nozzles 58 to several thousand nozzles 58. For a
commercial size line, the number of nozzles 58 in the spinneret
body 52 can range from between about 500 to about 10,000. The
number of rows can vary as well as the number of columns.
Typically, the number of rows will be more than 1, often more than
5, and will be less than about 30, or even less than 15. Typically,
the number of columns will be more than 50, but can be more than
about 200, and may be less than 3500.
[0074] As described in US'334, the nozzles 58 are formed of
capillary tubes that are inserted through openings in the spinneret
body 52 to form a passageway for the molten polymer. Each of the
nozzles 58 has an inside capillary diameter and an outside
diameter. The inside diameter can range from between about 0.125 mm
to about 1.25 mm. The outside diameter of each nozzle 58 should be
at least about 0.5 mm. The outside diameter of each nozzle 58 may
range from between about 0.5 mm to about 2.5 mm.
[0075] Typically, the length of a nozzle 58 ranges from between
about 0.5 to about 6 inches.
[0076] As the molten polymer needs to pass only through the
capillaries of the nozzles, US'334 describes the tubes to be
tightly fitted and typically welded to the spinneret body, which
represents an important difference, when compared to the present
invention, as will be described in more detail herein below.
[0077] The molten material 22, as may be a thermoplastic polymer of
the homopolymer type or a mixture of different polymers, is heated
to a temperature well above its melting point, in case of propylene
based polymers typically to at least about 170.degree. C., often to
about 210.degree. C., upstream of the die block 26, usually in an
extruder (not shown). Optionally, different polymers may be
directed to respectively different groups of nozzles.
[0078] The polymer throughput through each nozzle 58 is stated in
"gram per hole per minute" ("ghm"). The polymer throughput through
each nozzle 58 can range from between about 0.01 ghm to about 4
ghm.
[0079] The die block 26 further comprises a cavity 30 and an inlet
28 connected to the cavity 30, positioned towards the polymer
supply, and typically at the upper part of the spinneret body (i.e.
against gravity). The molten material 22 is conveyed along the
polymer passageway from inlet 28 towards the upper portion of the
spinneret body 52, and further via the nozzles downwardly. The
spinneret body 52 also has one or more gas passages 32 formed
therethrough for conveying pressurized gas (air) to an air chamber
54, which is essentially formed between the spinneret body 52 and
the air distribution plate 70. The plurality of nozzles 58 extend
downwardly from the spinneret body allowing molten material to flow
through the capillaries 60 for exiting the nozzles and the die
block downward of the exterior plate at nozzle tip 96 in the form
of filaments 86.
[0080] Further, a plurality of stationary pins 62 may surround the
array of nozzles, affixed to the spinneret body and extending
through openings of the air distribution plate into the openings of
the exterior air plate.
[0081] Each of the stationary pins 62 is an elongated, solid member
having a longitudinal central axis and an outside diameter. Each of
the stationary pins 62 is secured to the spinneret body 52 and
usually they have a similar outside diameter to the polymer nozzles
58. The outside diameter of each of the stationary pins 62 should
remain constant throughout its length. The dimension of the outside
diameter can vary. The outside diameter of each of the stationary
pins 62 may be at least about 0.25 mm, or at least about 0.5 mm, or
at least about 0.6 mm, or even at least about 0.75 mm, and/or less
than about 5 mm, or less than about 2 mm.
[0082] An air distribution plate 70 is secured to the spinneret
body 52 having a plurality of openings. Each one of first openings
72 accommodates one of the nozzles 58. If stationary pins 62 are
employed, they are accommodated in second openings 74, and each of
the third openings 76 is located adjacent to the first and second
openings, 72 and 74 respectively. When operating the process,
pressurized gas, typically air, is flowing along air passageways
from the air chamber 54 through openings 72, which are a thin
annulus around the nozzles, openings 74, also a small annulus
around the stationary pins, if present, and third openings 76 as a
main passageway for the air.
[0083] An exterior air plate 78 is secured to the air distribution
plate 70, away from the spinneret body 52. The exterior member 78
has a plurality of first openings 80 surrounding the nozzle 58.
Second enlarged openings 82 surround each of the stationary pins
62, if present.
[0084] In operation, the molten material 22 (polymer) is extruded
through each of the nozzles 58 to form multiple filaments 86 which
are intended to be shrouded from the ambient air by the pressurized
gas (air) emitted through the first enlarged openings 80, formed in
the exterior member 78, at a predetermined velocity essentially
parallel to the axis of the capillaries 60 and hence the flow
direction of the filaments 86 at the nozzle tip 96.
[0085] The pressurized gas (air) flow exiting the second enlarged
openings 82 formed in the exterior member 78 around the stationary
pins, if present, forms a further shrouding air flow, which is also
oriented essentially parallel to the axis of the nozzles, and hence
also essentially parallel to the filaments exiting the nozzles,
aiming at isolating the filaments 86 from surrounding ambient air,
as indicated in FIG. 1 with the arrow 94.
[0086] Whilst the technology of US'334 can be employed well to
provide very useful nonwoven materials, it has been observed that
it carries certain limitations, mainly due to the inaccuracies
induced by the insertion of the nozzle tubes into the spinneret
body and the respective fixation. Even when adjusting the plurality
of nozzle tubes, as may be several thousands, with utmost
precision, at least the thermal dilatation upon inserting and
welding, as well as the welding itself, if applied, tend to cause
minute variations that can accumulate over the width of the
spinneret block and then induce deterioration in handling of the
equipment and/or quality of the resulting product:
[0087] If the capillaries are not exactly centered in the openings
82, the annular air passage way around the nozzles will be
eccentric and hence the shrouding effect of the air is uneven which
may disrupt the smooth airflow and result in bundling, i.e.
adjacent filaments are blown towards each other and then may stick
to each other, resulting in a larger fiber size distribution.
[0088] Further, even with sophisticated welding and machining
tools, there is a high probability of burrs that disturb the
smoothness of the flow into and through the capillaries.
[0089] As a consequence thereof, deposits of polymeric material may
form around the inlet of the capillaries, which may degrade over
time and require more frequent cleaning.
[0090] Considering the plurality of protruding capillaries and the
tightly fitting air distribution plate, the difficulty of proper
mounting increases with these variations, but also the number of
nozzles in one mounting step. Thus there is presently a practical
limitation of the y-directional extension of a single spinneret
body and consequently of the complete die block of about 500 mm
(approx. 20 in).
[0091] Thus, when employing such die blocks in large scale
operations, where an overall y-directional extension may be well
over 2 m, often 2.6 m, or even more 5 meter, multiple die blocks
need to be employed, which not only increase handling complexity
but that also can impact on the quality of the resulting product,
at least because of y-directional edge effects of each block.
[0092] Further, considering the cleaning process, the relevance of
which is aggravated by the increase in deposits around the
capillary inlets, it only can be executed in one direction, namely
along the normal process flow direction. Typically, the cleaning
process comprises a pyrolytic treatment followed by treatment with
pressurized steam or water. Also, ultrasonic cleaning, a generally
desirable process for removing such residues, cannot be properly
employed as it may very negatively interact with the connecting of
the capillary tubes to the spinneret body, i.e. the welding or
tight fitting.
[0093] Having thusly described the principle of the spun-blowing
process as known from US'334, FIG. 2A to F depict the principle of
the present invention, by showing a die block 126 comprising
spinneret block 152, air distribution plate 170, exterior air plate
178 and cover strip 188 arranged in the same way as described in
the context of FIG. 1. Further shown is one row of a plurality of
five nozzles 158, also arranged in columns and rows forming an
array of nozzles as described in the above. As described herein,
the nozzles are oriented vertically along gravity. However, the
orientation of the system may be such that the orientation of the
nozzles is angled relative to gravity, and the skilled person will
readily adapt relative positioning terms like "above" or "below"
accordingly.
[0094] Optionally, the array of nozzles may comprise sub-arrays.
Such a sub-array may include at least one row of nozzles,
preferably, though not necessarily extending over the full width of
a die block.
[0095] In a first execution of a die block comprising one or more
sub-arrays as shown in FIG. 2G, the nozzles of at least one of the
sub-arrays differ substantially from nozzles of a different
sub-array in at least one of the dimensions selected from the group
consisting of inner diameter of the nozzle, outer diameter of the
nozzle, and length of the nozzle. Within the present context, the
term "substantially different" refers to a difference in the
respective dimension of at least 5%, often more than 10%
thereof.
[0096] In a further execution as shown in FIG. 2H, not exclusive to
the other execution, the nozzles of one sub-array may be connected
to a first, separate polymer supply system adapted to supply molten
polymer to said sub-array differing from the molten polymer
supplied to a different sub-array in at least one of the features
selected from the group consisting of polymer type, polymer flow
rate, polymer pressure, and polymer temperature. Optionally, the
nozzles may be executed with co-axially positioned sub-capillaries
so as to create bi- or multi-component fibers, wherein such
sub-capillaries are supplied with different, respectively
immiscible polymer types.
[0097] Whilst FIG. 2A depicts the elements in an assembled state
(with securing means omitted), in FIG. 2B the spinneret block 152,
the air distribution plate 170 and the exterior air plate 178 are
shown in an exploded view, and FIG. 2C to 2F depict these
individual elements.
[0098] It is a key feature of the present invention that the
nozzles 158 are not formed separately as capillary tubes and
inserted into holes of the spinneret body, as described in US'334.
Rather, the spinneret body 153 and the nozzles 158 are "unitary"
forming the spinneret block 152 as made from a single piece of
material. This can conveniently achieved by modern CNC machining
technology, such as employing laser cutting, flame and plasma
cutting, hole-punching, drilling, milling, lathing, picking and
placing, sawing, and other such technologies as known in the art
for CNC treatments.
[0099] Referring to FIG. 2C, a piece of material, preferably
exhibiting a homogeneous composition, preferably a metal and more
preferably steel, is selected as a spinneret block pre-cursor 210,
depicted by the dotted line, circumscribing the spinneret body and
the nozzles to be formed integrally therefrom. It may be prepared
at a size generally corresponding to the overall dimension of the
later spinneret block, or its outer dimensions may be shaped
in-situ.
[0100] Then, parallel or consecutively, though not necessarily in
the listed order, the various features of the spinneret block are
formed, especially though not limiting [0101] an inlet cavity 130
for molten polymer 122; [0102] air inlet and distribution chamber
132 (the air supply means not being shown); [0103] the array of
nozzles 158, each exhibiting an inner diameter 157, corresponding
to the diameter of the capillary for the molten fluid flow, and an
outer diameter 159; [0104] optionally further securing holes
(199).
[0105] These elements may be machined with extreme precision, in
particular with regard to the size, positioning and orientation of
the nozzles 158. Further, once programmed, it is a well-known
manufacturing process, just mounting the spinneret block precursor
into the CNC machining tool and starting the machining program.
[0106] Each of the nozzles 158 has an inside diameter 157 and an
outside diameter 159. The inside diameter may be more than about
0.125 mm and/or less than about 1.25 mm. The outside diameter of
each nozzle 158 is preferably more than about 0.5 mm, or more than
1 mm and/or less than about 2.5 mm. Typically, the length of a
nozzle 158 is more than about 20 mm and/or less than about 150
mm.
[0107] Thus, the spin block comprises a polymer passageway that
goes from the inlet cavity 130 through the capillaries of the
nozzles 158 towards the nozzle tip 196, where the filaments are
formed.
[0108] Further, because of this high precision, the nozzles 158 fit
accurately though the respective nozzle openings 172 of the air
distribution plate 170, and the nozzle openings in the 172 in the
air distribution plate can be made only slightly larger than the
outer diameter of the nozzle, down to an annular gap of less than
0.1 mm.
[0109] Thus, the air flow from the air chamber 132, which is
delimited by the spinneret block 152 and the air distribution plate
170, may be through the plurality of air flow openings 176, as may
be in a different row (i.e. not visible in the particular
cross-sectional plane shown in FIG. 2), see dotted lines in FIG.
2E, optionally staggered row (see dotted lines in FIG. 2A).
Further, the nozzle will also very precisely fit into the nozzle
openings 180 of the exterior air plate and provide a very accurate
and concentrically formed annulus around the nozzle 158. In
operation, this results in a very even annular air shroud
surrounding the filaments 186 as these exit the nozzle tip 196
essentially parallel to the filaments, thereby significantly
reducing, if not preventing, bundling of the filaments.
[0110] FIG. 2 A further depicts two options (alternatively or
jointly) for creating the outer perimeter curtain as described in
US'334. In a first option, air passage openings 183 in the exterior
air plate are positioned around the array of nozzles. In a second
option, stationary and solid pins 162 also machined from the same
spinneret block precursor extend from the spinneret body through
openings 174 the air distribution plate into openings 182 of the
exterior air plate 178, allowing also an annular air flow around
these pins in analogy to the approach as described in US'334.
[0111] Further, the present approach allows much easier
manufacturing when assembling the die block, by eliminating a
practical restriction for the y-directional size of a die block,
which now may well exceed the typical 500 mm of die block made
according to the teaching of US'334, and may now be more than 1000
mm, even more than 2600 mm (as a typical size of a non-woven
manufacturing unit into which such die block may be included) and
even more than 5000 mm can be reached.
[0112] With the present invention allowing to employ single piece
and unitary die blocks over much larger width, the fiber formation
and fiber laydown will be cross-directionally more homogeneous as
compared to having several less wide die blocks assembled together.
As depicted in FIG. 3, the present approach provides a further
advantage in that the transition from the capillaries to the
spinneret body may be executed with a radius 310, preferably of
more than 0.1 mm, more preferably of more than 0.3 mm. This will
increase the stability and hence also positioning of the nozzles
compared to executions according to US'334.
[0113] FIGS. 4A and C depict exemplary executions to reduce, if not
to avoid these negative impacts of the sharp edges around the
opening of the capillary of the nozzle.
[0114] In FIG. 4A as a first execution of a nozzle according to the
present invention, the nozzle 158 may be a nozzle as described in
general in the above cited US'647, exhibiting an inner capillary
diameter 157 of the capillary 160 for the molten fluid flow. This
inside capillary diameter can range from between about 0.125 mm to
about 1.25 mm. At its upper end, the capillary 160 is chamfering in
the chamfering section 333, preferably with a chamfering angle of
between 30.degree. and 60.degree., allowing a transition from the
capillary to chamfering opening diameter 337. This chamfering
opening diameter may range from more than about 2 mm or 4 mm to
less than about 20 mm, or 14 mm, or less than 8 mm. The outside
diameter 159 of the lower section 335 of the nozzle 158 should be
at least about 0.5 mm, and may range from between about 0.5 mm to
about 2.5 mm.
[0115] Typically, the overall length 330 of a nozzle 158 ranges
from between about 20 mm to about 150 mm. The length 334 of the
lower section 335 may be from about 10 mm to about 140 mm. The
length of the chamfering section from the first diameter to the
second diameter may range from about 2 mm to about 4 mm or
more.
[0116] Optionally, and as depicted in FIGS. 4B and C, the
transition from the capillary diameter to the chamfering opening
diameter may be executed as a radius or as another gradually
transitioning curve, such as an elliptic or a parabolic shape.
Within the present description, the term "chamfering" is intended
to include such executions mutatis mutandis, and the chamfering
angle is intended to correspond to the endpoints of the radius or
smooth curve. Another execution according to the present invention
is depicted in FIG. 4D, also showing a nozzle 158 with a capillary
160 exhibiting an inner capillary diameter 157 at the nozzle tip.
Further, the nozzle has the chamfering opening diameter 337 towards
the polymer supply, which chamfers towards a pre-hole diameter 341,
representing a pre-hole of the capillary over a pre-hole length
344, further chamfering towards the inner capillary diameter 157.
In this execution, the length of the nozzle is defined by the
length of the capillary, the length of the pre-hole, if present,
plus the length(s) of the chamfering section(s).
[0117] For one or both of the chamfering it may be executed as
described for FIG. 4A, or be executed as a radius as described in
FIGS. 4B and C.
[0118] Optionally, and often preferably, the spinneret block 152
may comprise pre-holes 340, see FIG. 4D showing one nozzle only.
These pre-holes are positioned upwardly and precisely aligned with
the axis of the capillary 160 of the nozzle 158. The pre-holes may
exhibit a diameter of 1.5 to 4 times the diameter of the capillary
and a length of from about 2 mm to about 20 mm Preferably, the
transition from the pre-hole 310 to the capillary 160 is executed
in a gradual way, e.g. at a chamfering angle of between 30.degree.
and 60.degree. at the inlet and at the transition towards the
capillary.
[0119] A pre-hole provides a smoother flow from the cavity with the
molten material into the capillary 160, which in turn will widen
the opportunity for a wider process window for the process.
[0120] Thus, in a second aspect, the present invention relates to
operating the equipment as described in the above in a process with
a wide process window, which is primarily dictated by [0121]
pressure of the molten polymer in the cavity; [0122] temperature of
the molten polymer; [0123] diameter of the capillary; [0124] length
of the capillary; [0125] material properties of the molten polymer,
as expressed by the Melt Flow Index (MFI), as may be determined by
ASTM D1238 and ISO 1133, and for polypropylene as a polymer that
suitably can be processed with the current equipment and process,
it is suitably expressed in units of gram per 10 minutes at
210.degree. C. and 2.16 kg load.
[0126] As a comparative example, the equipment and the process as
described in US'334 may exhibit [0127] a capillary inner diameter
of 0.46 mm, [0128] a capillary length of 24 mm, [0129] hence an L/d
ratio of about 52, and is preferably operated at a temperature of
about 210.degree. C. with a back pressure of 50 to 70 bar for a
molten polymer with an MFI of less than about 500 [g/10 min @ 2.16
kg load]. In order to achieve comparable fiber dimensions and
properties, the equipment of the present invention exemplarily
exhibited [0130] a capillary diameter of 0.46 mm; [0131] a
capillary length of about 18 mm: [0132] a pre-hole diameter of
about 1.2 mm: [0133] a pre-hole length (including a 60.degree.
chamfering at the inlet and at the transition to the capillary) of
about 6 mm; [0134] henceforth an L/d ratio for the capillary of
about 39, which will further allow to employ a polypropylene
polymer exhibiting an MFI of about 500 [g/10 min @ 2.16 kg load] of
a back pressure of significantly lower than 50 bar.
[0135] One benefit of subjecting the polymer to a lower
backpressure is that the reduction of the mechanical stress results
in allowing to produce stronger nonwovens.
[0136] In other terms, the present invention provides an equipment
that can exhibit a lower L/d ratio, which is for a given MFI
indicative of the flow resistance, and thusly allows to operate at
a wider process window for MFI and backpressure.
[0137] Further, the smoother flow from the cavity for the molten
polymer 130 to the pre-hole 340, preferably even more smoothed flow
of polymer in the chamfering, significantly reduces the turbulence
of polymer around the inlet and hence also polymer residue
deposition, allowing longer operating times without interruption
for cleaning.
[0138] In a further, and often highly preferred execution of the
present invention, as depicted in FIG. 5, all three elements
spinneret block 126, air distribution plate 170 and exterior air
plate 178 are manufactured from a single block of material,
indicated by dotted line 510, whereby in a first step slabs are
separated, from which the respective elements are formed by CNC
machining, as described in the above.
[0139] In a further aspect, the present invention allows simpler
maintenance of the equipment. First, as the spinneret block (152)
is now unitary and of the same material, it can readily withstand
ultrasonic treatment without risking damaging the connection of the
nozzles 158 and the spinneret body 153.
[0140] Second, as the nozzles and the spinneret body are much
sturdier than e.g. a design as described in US'334, the equipment
can also be cleaned with water and/or steam at a higher pressure
and also not only along manufacturing direction, but also in the
reverse direction (back-flushing).
[0141] Thus the cleaning of a spinneret block according to the
present invention may comprise the steps of [0142] burning
respectively pyrolyzing the residues; [0143] ultrasonically
loosening the pyrolyzed residues; [0144] flushing the
ultrasonically loosened pyrolyzed residues along the flow direction
of the molten polymer, and/or optionally in the opposite flow
direction with pressurized water or steam.
* * * * *