Note: Descriptions are shown in the official language in which they were submitted.
104;~7
BACKGROUND OF THE- INVEN~ION
1. Field of the Invention. The ~present invention is
directed to nonwoven mats having unique properties prepared by
melt-blowing a blend of thermoplastic resins. More particularly,
the present invention relates to the melt-blowing of a blend of
thermoplastic resins which can be pre~lended or premixed prior
to introduction into the melt-blowing die and the novel and
unusual nonwoven mats made by the process.
2. 'Pr'ior Art. A melt-blowing process is disclosed '~
in the article "superfine Thermoplastics", by Van A. Wente, in
Industrial- and ~ng-ineer-ing Che~istry, 48, No. 8 (1956), Pages
1342-134-6. In the melt-blowing process disclosed in the Wente
article, synthetic resins such as nylon, polystyrene, polymethyl-
methacrylate and polyethylene are illustrated. However, no blends
are disclosed.
U.S. 3,532,800 discloses the Wente melt-blowing process
and also discloses that fibers o~ different resins can be physi- '
cally mixed. But it does not disclose individual fibers made up
of blends of resins.
A melt--~pinning and blowing process is disclosed in
British Patents 1,055,187 and 1,215,537.
' BRIEF BUMMARY OF ~HE INVENTION
Blends of two or more thermoplastic resins in a single
feed to a melt-blowing die are used, resulting in nonwoven mats
of unusual and novel physical characteristics.
BRrEF DE9CRIPTION OF THE DRAWrNGS
Fig. 1 is a schematic view of the overall melt-blowing
process; and
' Fig. 2 is a cross sectional view of a die used in the
meIt-blowing process. ~
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1~)4'~67
DETAILED DESCRIPTION OF ~HE INYENTION
As a matter of necessity heretofore, only one thermo-
plastic resin has been used in any fiber-forming process at one
time. In those instances where more than one thermoplastic
resin has been employed, it has required entirely separate
handling of each thermoplastic resin. There is a very cogent
and well-recognized reason for this state-of-the-art attitude.
It can be easily understood when it is remembered that most con-
ventional melt-spinning processes are intended to develop fairly
long, continuous fibers. When blends were attempted, it was
found that the dissimilarities between the polymers caused weak
spots to develop in the fiber. Consequently severe fiber break-
age would result.
Thus, it became strongly established conventional
wisdom in the fiber industry that blending resins together to
make fibers was a completely unacceptable practice.
It has now been realized for the first time and forms
the conceptional substance of this invention that in a melt-blown
process, fiber blends can be used because the fibers are so short
anyway that breakdown at weak spots is not a controlling aspect.
The benefits and advantages of mats comprised of fibers
made up of blends of at least two different thermoplastic resins
are profound. A wide variety of combinations is possible to
produce mats having an endless number of special properties; -
usually depending on a particular use requirement.
There are some basic principles which have been dis-
covered and should be followed to achieve the best results.
At least one of the resins in the blend must be an
accepted fiber-former. When it is blended with a nonfiber-
forming material, generally not more than 10 weight percent,
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1C~4;~1ti7
preferably less than 5 weight percent of the latter based on thetotal blend should be used.
Otherwise the resins or other material can be blended
in the ranges of 0.5 to 99.5, preferably 2 to 80 and most prefer-
ably 40 to 60 weight percent.
The resins can be previously melt-blended together,
but that is not necessary. Crude physical blending of the resins,
i.e. mixing up pellets of two different resins can be introduced
into the extruder portion of the melt-blown sequence.
When the blend is in its liquefied, low viscosity
state, just as it is contacted by the gas of the melt-blown
process, there is usually good mixing of the component polymers.
When the fibers solidify, a wide range of physical
relationships of the constituent polymers within each individual
fiber will exist. This will be dependent on the polymer types
in the blend as well as the particular ambient environment of a
given fiber, during formation and subsequent cooling.
Although most blends will be of polymers alone, it
i8 also possible to blend one or more non-polymeric components
with a fiber-forming polymer in amounts not exceeding 5 weight
percent of the former, and usually not more than 1 weight percent
of the former.
A good example of this is the incorporation of dyes
into the fiber-forming material in order to obtain colored mats
made up of dyed fibers. Other additives could also be used such
as ~urfactants, plasticizers, stabilizers, and the like.
Coloring of the nonwoven material obtained by flowing
polymer through small orifices presents difficulties with the
usual pigments used in coloring plastics. At the high spin
temperature of 500 to 700F. the viscosity is low and pigment
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settles out, agglomerates, and plugs screens and passages.
Heat stable dyes, with low melting points, good
stability and fastness properties have been used to obtain
coloration with no processing difficulties. The dyes give
transparent colors where pigmentation results in opaque colors
that are not always desirable.
Some commercial dyes such as
Latyl Blue 46 FS
Latyl Blue BCN
DuPont Milling Blue BL C. I. No. 50315
Latyl Yellow GFS
have given good colored melt blown nonwoven materials with 0.25%
dye added to the polymer pellets prior to melt blowing into
fiber. These dyes in concentrations to 0.5% by weight can be
applied easily by heating the polymer pellets to 100 to 250 F.
and tumbling with a small amount of a silicone fluid for 10
minutes. The fine ground pure dye without filler is then added
and tumbled to obtain occlusion and penetration into the pellet.
The dye-containing polypropylene pellets are spun to a
nonwoven fiber by heating to temperatures as high as 700 F. and
blown with air through a spinning head to obtain an interlaced,
nonwoven mat that is collected on a revolving screen drum and
wound onto a roller.
The colors are of good quality with no evidence of
deterioration during spinning.
One aspect of the present invention may be briefly
de~cribed a~ a nonwoven mat of fibers comprised of a blend of
two or more thermoplastic resins wherein the fibers within the
mat have a two directional randomness and the fiber size may be
between about 0.5 and 5 microns. In most instances, the fibers
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are produced from a well mixed blend of the two or more thermo-
plastic resins, and thus appear as a mixed blend of resins across
essentially the entire cross section of the fiber formed in the
melt-blowing process.
The present invention may more fully be described as a
melt-blowing process for producing nonwoven mats of fibers con-
sisting of a blend of two or more thermoplastic resins. The
process comprises blending two or more thermoplastic resins,
preferahly as a salt and pepper blend of pellets into the hopper
of an extruder wherein the thermoplastic resins are thermally
treated, if necessary. The thermally treated thermoplastic resin
blend is then extruded through a plurality of die openings into
a heated gas stream, preferably air, to attenuate the thermoplas-
tic blend of resins into fibers.
The gas stream is produced by jets which are adjacent
to and on either side of the die opening. The attenuated fibers
are collected on a moving take-up device which is from one to
thirty inches from the die opening. The fibers in the nonwoven
mat can be self bonded ranging from a highly bonded mat to one
having little self bonding. Highly bonded nonwoven mats are
used in a number of applications without the requirement of
further treatment, compacting or shaping.
A PREFERRED EMBODIMENT
Referring to Fig. 1 of the drawings, a 50/50 salt and
pepper blend of nylon and polypropylene thermoplastic resin
pellets is introduced into a pellet hopper 1 of an extruder 2.
The thermoplastic blend is thermally treated in the extruder 2
and/or die head 3. The thermal treatment of the thermoplastic
blend is carried out in the extruder 2 at temperatures in excess
of 500 F., and preferably within the range of 575 F. to 750 F.
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The degree of thermal treatment necessary varies
depending upon the specific thermoplastic resins used in the
blend as well as the molecular weight of the thermoplastic resins
in the blend or the amount of thermal treatment which has been
carried out on the thermoplastic resins prior to being intro-
duced as pellets into the extruder 2. It has been found, for
example, that all conventional polypropylene and other polyole-
fins require substantial thermal treatment before they can be
utilized in the melt-blowing process of the present invention.
The thermoplastic blend is forced through the extruder
2 by a drive 4 into the die head 3. The die head 3 may contain
a heating plate 5 which may also be used in the thermal treat-
ment of the thermoplastic resins before the blend is melt-blown.
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The thermoplastic resin blend is then forced out a row of die
openings 6 in the die head 3 into a gas stream which attenuates
the resins into continuous fibers 7 which are collected on a mov-
ing collection device 8 such as a drum 9 to form a continuous
nonwoven mat 10. The gas stream which attenuates the thermo- -
plastic resin blend is supplied through a gas jet ll and 12,
respectively. These gas jets or slots 11 and 12 are supplied
with a hot gas, preferably air, by gas lines 13 and 14, respect-
ively.
The melt-blowing process is further understood by
considering the cross section of a die head 3 which may be used
in the process as set forth in Fig. 2. The die head 3 may be
made up of upper die plate 15 and a lower die plate 16. The
blend of thermoplastic resins may be thoroughly mixed in the
extruder 2 and may be introduced into the back of the die plates
15 and 16 through a single inlet 17. The blend of resins then
passes into a chamber 1~ between the upper and lower die plates
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15 and 16, respectively. In one possible die design for the
melt-blowing process, the facing of the die plate 16 may be
milled to have grooves 19 which terminate in die openings 6.
It is understood, of course, that the milled grooves may be in
the lower die plate 16, in the upper die plate 15, or the grooves
may be milled in both plates 15 and 16. An upper gas cover
plate 20 and a lower gas cover plate 21 are connected to the
upper die plate and lower die plate 15 and 16, respectively.
The hot gas is supplied through the inlet 22 in the
upper gas plate 20 and the inlet 23 in the lower gas plate 21.
Suitable baffling means (not shown) may be provided in both the
upper air chamber 24 and the lower air chamber 25 to provide a ~ -
uniform flow of air through the gas slots 11 and 12, respectively.
As shown in Fig. 1, the blend of thermoplastic resins is attenu- ;
ated by the air as attenuated fibers 7, each of which is com-
prised of the thermoplastic blend, and which are collected on a
collecting device such as the drum 9 which may be positioned ~ ~ -
from one to thirty inches from the die openings 6 in the die
head 3.
The nonwoven mats produced when the fibers are collect-
ed at a distance of one and one-quarter to two inches differ in
compactness and appearance from those produced at a distance of
five to eight inches, or those collected at a distance greater
than twelve inches. The primary difference is in the degree of
self bonding which occurs in the nonwoven mat. When the collect-
ing distance is very small, a compact and highly self bonded non- -
woven mat is produced. On the other hand, when the collecting
distance i~ greater than twelve inches, a soft web or mat is
produced which has greater tear resistance even though it may ;
not have quite the tensile strength of mats collected at shorter
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lU42167
distances.
In making a uniform mat or web, it is desirable to
eliminate the formation of "shot" and/or "rope". "Shot" is a
mass or glob of thermoplastic resin with a diameter many times
the average diameter of the fiber in the mat, and appears to be
the result of individual fibers breaking. "Rope" occurs when
the air rates are out of adjustment such that the attenuated
fibers come into contact one with the other and are not blown
away from the die head as individual fibers, but come into
contact and are laid down as collected aggregates of fibers.
Insufficient air pressure, or having either the upper or lower
gas slots out of control will produce "rope" in a nonwoven mat.
"Rope" can also be formed at long die head to collecting device
distances (two to three feet) where the fibers are entangled due
to the turbulence of the air jets. As the gas flow rates are
increased sufficiently so that "rope" is not formed, mats are
formed having essentially no "shot" or "rope". With increasing
gas flow rates, the amount of "shot" generally increases. As
the gas flow rates increase even further, the "shot" becomes
~maller and often elongated, and appears as very fine "shot" at
high gas flow rates. "Shot" is unacceptable when the masses or
globs of thermoplastic resin are relatively large (greater than
0.3 millimeters in diameter) and can be seen with the eye, or
when the web is calendered appear as an imperfection or fused
spot.
In the melt-blowing process involving a blend of two
or more thermoplastic resins according to the present invention,
the die temperature is maintained above about 500F. The pre-
ferred die temperatures range between 575 - 750F. The appro-
priate thermal treatment to be given to the blend of thermoplastic
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10421~i7
resins in the extruder 2 that feeds the melt-blowing die head 3
may be determined as follows. A die temperature is selected
from the preferred range and a polymer rate in terms of grams/
minute/die opening is selected, and then an air rate is set at
25 - 50 pounds/minute/inch2 of air slot. The nonwoven mat
produced is observed as the heating zones of the extruder 2 are
heated. At too low a temperature in the extruder 2, the nonwoven
mat contains many large globs of polymer and/or coarse ropy
material. As the temperature in the extruder is increased, the
nonwoven mat becomes finer fibered, softer, and has less and
smaller "shot". When the temperatures in the extruder 2 are too
high, the nonwoven mat produced ~ecomes extremely soft and fluffy,
but the air blast from the die causes extreme fiber hreakage,
and many short fibers to be blown through the air away from the
lay-down zone. The breakage of fibers and their being blown
away from the lay-down zone also occurs when the die temperature
is too high. Another indication that the thermal treatment is
adequate is the polymer pressure in the die head 3. When the
blend of thermoplastic resins is correctly thermally treated,
the pressure in the die head 3 lies in a small range independent
of the starting resin or the die temperature.
The polymer flow rate, or the rate at which polymer
is forced through the die opening 6, is dependent upon the
specific design of the die head 3 and extruder 2. The polymer
flow rate may be controlled by the speed of the extruder 2.
The gas flow rates are limited by process parameters.
However, suitable products have been obtained at air rates
between 0.5 to 225 pounds/min./inch of air slot. It has ~een
found that there are essentially two air rate regimes, a low to
moderate and a high regime, to produce good quality, nonwoven
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mats according to the melt-blowing process of the present
invention.
One of the advantages of the invention is that an
expensive polymer can be diluted to a certain degree with an
inexpensive polymer without detracting too much from the gross
properties of the expensive polymer.
In general the fibers of the invention are very small,
i.e. diameters of from 0.5 to 50, preferably 0.5 to 20, most ~ ,
preferably 0.5 to 10 microns in diameter.
The invention is further illustrated by the following
examples. Unless otherwise indicated the procedure for preparing
the mats of the Examples was generally that described above, but
the specific details were those described express-ly in each -
Example. The polyethylene used in the Examples was low density.
EXa~ple 1
Blends of 10%, 50% and 90% Firestone XN3I4 Nylon 6
were melt-blown with Enjay CD392 polypropylene resin~ These
blends were extruded from a four-inch melt-blowing die under
the following specific conditions, as set forth in TABLE I
hereinafter.
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TABLE I
Run46-1 46-3 46-4 46-5
Polypropylene100 90 50 10
% Nylon 6 - 10 50 90
Extruder Zone 1 - F 595
Extruder Zone 2 - F 620
Die Heaters - F640
Ave. Air Chamber - F 607 SAME SA~IE SAME
Ave. Die Tip Temp. - F 585
10 Screw RPM 4.5
Die to Collector
Dist. - In. 6
Polymer Rate-gm/min 8.1 8.9 9.3 12.5
Air Rate lb/min3.17 3.17 3.17 3.36
Air lb/lb Polymer 178 162 155 122
Die Pressure - PSl 115 135 140 125
Web AppearanceGood Good Good Fair (Shot)
No attempt was made during these runs to optimize blow-
ing conditions for each blend. The blends did process well at
the conditions used with the exception of 46-5 which had consider-
able ~hot.
Physical properties of the nonwoven webs or mats
produced above are liqted in TABLE II.
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1t)4Zltj7
TABLE II
Run 46-1 46-346-4 46-5
% Polypropylene 100 90 50 10
% Nylon 6 - 10 50 90
Ave. Basis Wt. 77 88 99 111
MD Zero Span Tensile-Meters 31222659 1856 1319
CD Zero Span Tensile-Meters 21111871 1425 817
Ave. Zero Span Tensile-Meters26172265 1641 1068
Ratio MD/CD Zero Span .68 .70.77 .62
MD Tear Factor-DM 184 163194 78
CD Tear Factor-DM 181 151245 76
The resulting mats, which were slightly compressed, had `
much better tear stren~th than comparable mats from 100% poly~
propylene or 100% nylon.
Example 2
Blends of 5% and 20% Polyethylene with Enjay CD 393
polypropylene resin were melt-blown. These blends were melt-blown
at both high and low air rates. TABLE III sets forth the melt-
blowing conditions using a four inch melt-blowing die~
TABLE III
Run 41-1 41-541-6 41-4 41-3
% Polypropylene100 95 100 95 80
% Polyethylene 0 5 0 5 20
Extruder Zone 1 - F 595615 615 615 615
Extruder Zone 2 - F 625650 648 650 650
Die Heaters - F640 680680 680 680
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104;~167
TABLE III - Continued
Run 41-1 41-5 41-6 41-4 41-3
Ave. Air Chamber - F 524 574 547 543 541
Ave. Die Tip. Temp - F 596 644 635 635 636
Screw RPM 28 28 28 28 28
Die to Collector Dist. -
In. 6 18 18 18 18
Polymer Rate-gm/min 22 22.6 22 22.8 22.8
Air Rate lb/min 3.51 3.38 .63 .67 .66
Air lb/lb Polymer 72 68 13 13 13
Die Pressure - psi 285 115 125125 200
Ave. Fiber Size - Microns 5 5 20 - 25
Web Appearance Good Good Good Good Good
Although optimum conditions were not established,
these runs illustrate that continuous nonwoven webs can be
made using polyethylene and polypropylene blends. Fine
fiber webs could not be made with the 20% polyethylene blend
but could be made at the 5% level. At the 20% polyethylene
level, using fine fiber processing conditions, only short
fibered, weak webs could be made. This type of behavior
has been observed using 100% polyethylene and is not observed
with polypropylene.
-13-
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1~4;~167
TABLE IV
Run 41-1 41-5 41-6 41-4 41-3
% Polypropylene 100 95 100 95 80
% polyethylene 0 5 0 5 20
ave. Basis Wt. 73 111 126 133 106
MD Zero Span Tensile-
meters 2015 1344 1006 963 962
CD Zero Span Tensile-
meters 1550 835 736 623 733
Ave. Zero Span Tensile-
Meters 1783 1090 871 793 848
Ratio mD/CD zero Span .77 .62 .73 .65 .76 --
MD Tear Factor-DM 72 77 56 50 450
CD Tear Factor-DM 91 77 48 35 333
Example 3
Pellet blends of 25%, 50% and 75% poly-4-methylpentene-1 (TPX)
were melt blown with Enjay* CD 392 polypropylene resin. These
blends were extruded at the following conditions from a four-
inch melt-blowing die at the following conditions, as set forth
in Table V.
TABLE V
Run 13-1 13-2 13-3 13-4 13-5
% Polypropylene 100 75 50 25 0
% TPX 0 25 50 75 100
Extruder Zone 1, F630
Sxtruder Zone 2, F635 ~
Die ~eaters, F 628 -~;
Avg. Air chamber, F 650 SAME SAME SAME SAME
Avg. Die Tip, F 665
Screw RPm 25
Die to Collector
Dist-Inches 12
-14-
* Trade Mark.
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lV421~7
TAsLE V - Continued
Run 13-1 13-2 13-3 13-4 13-5
Polymer rate gm/min. 15.7 15.7 14.7 14.1 12.1
air rate lb/min 3.3 3.3 3.3 3.3 3.3
Die Pressure, psi 100 100 50 75 175
Web Appearance Good Good Good Good Good
Very good quality webs were obtained for all samples
even though conditions were not changed during the run. Attempts
to optimize properties were not made in this run.
Physical properties for these blends are shown in
Table VI.
TABLE VI
Run 13-1 13-2 13-3 13-4 13-5
% Polypropylene100 75 50 25 0
% TPX 0 25 50 75 100
Avg. Basis Wt. g/met108 112 111 73 68
MD Zero Span Tensile,
Meters 2484 1707 1148 27182704
Strip Tensile Uncal., --
Meters 545 288 66 83 267
MD tear Factor, Dm2 203 51 70 151 124
CD Tear Factor, Dm 199 54 68 173 116
Electrical properties were also tested and found
to be excellent for all blends. The mats containing fibers
of a blend of polypropylene and poly-4-methylpentene-1 had
improved temperature resistance as the amount of poly-4-methyl-
pentene-l increased. Hence, a property which is deficient if
only a single thermoplastic resin is used to make a non-woven j~"~- -
mat may be overcome according to the present invention where a
blcnd of two or more thermoplastic resins are employed.
A blend of nylon and a polyolefin such as poly-
propylene yields a dyeable mat which is not possible with a ~ -
polyolefin alone. Polystryene blended with polyolefins yields
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1~42167
a stiffer mat. It is understood, however, that besides the
thermoplastic resin other additives may also be included in
the blend such as a dye pigment or the like.
The nature and object of the present invention
having been completely described and illustrated and the best -
mode thereof contemplated set forth, what we wish to claim as
new and useful and secure by Letters Patent is:
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