Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FLASH-SPUN POLY ~ R
Field of the Invention
This invention relates to flash spinning polymer and particularly
to the products made from flash spinning polymer such as fibrous webs and
consolidated sheets and fabrics.
Back~round of the Invention
Flash-spun fibers were originally created by Herbert Blades and
James White, employees of E. I. du Pont de Nemours and Company
(DuPont), and disclosed in US Patent 3,0~1,510 on 19 March 1962. A
variety of polymeric materials were disclosed in the patent primarily
including linear polyethylene with some examples of polypropylene.
Further examples of polymeric materials which may be spun into
plexifilaments were described in a subsequent patent, US Patent 3,~27,784
on 4 January 1966, also to Blades et al. These included polyethylene
teraphthalate, polytetramethylbutadiene, polyhexamethylene adipamide,
polyformaldehyde resin, and perfluoroethylene/perfluoropropylene
copolymer in addition to further examples of linear polyethylene and
polypropylene.
Based upon the developments of Blades and White, and
subsequent work of others, DuPont has scaled up to commercial production
of flash-spun products under the trademark Tyvek(~) spunbonded olefin.
Tyvek~) spunbonded olefin has many uses for which its properties have
been adapted and engineered such as air infiltration barriers, banners,
envelopes, medical pack~ging, and protective apparel. DuPont has
developed t~vo basic styles of flash-spun nonwoven sheet products: area
bonded material and point bonded material. Area bonded material is
thermally bonded generally uniformly across the area of the sheet. Point or
pattern bonded matenal is thermally bonded at points or in a pattern where
the pattern creates portions which are more strongly bonded and not as
strongly bonded. As such, area bonded products are typically stiffer than
point bonded and have a paper-like feel. Point bonded flash-spun nonwoven
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products tend to have so~ter fabric-like feel. Point bonded flash-spun
material is most commonly used in protective apparel. Area bonded
products are used in envelopes, medical packaging and air infiltration
barriers in construction applications.
In several end uses, the tensile and elongation properties of the
flash-spun nonwoven fabrics are of considerable importance such as in
packaging and protective apparel. For example, the material for protective
apparel is preferably quite strong; however, if it were to fail, then it is
desired that it fail by stretching and deforming rather than ripping or
10 breaking. It is particularly desirable that both tensile strength and elongation
are high at the same time.
Thus, it is an object of the present invention to improve the tensile
and elongation properties of flash-spun products.
It is a further object to provide better quality flash-spun fibers and
15 sheet products made from flash-splm fibers.
Summary of the Invention
In the present invention, the foregoing objects are achieved by a
polyethylene flash-spun plexifilamentary film-fibril material having a BET
surface area of at least about two m2/gm and wherein the polymer has a
number average molecular weight of at least about 20,000 and a molecular
weight distribution of less the 4Ø
Brief Description of the Drawin~s
The invention will be more easily understood by a detailed
explanation of the invention including drawings. Accordingly, drawings
which are particularly suited for expl~inin~ the invention are attached
herewith; however, it should be understood that such drawings are for
explanation only and are not necessarily to scale. The drawings are briefly
described as follows:
Figure 1 is a schematic view of an apparatus suitable in the
process of flash spinning polymer into a plexifilamentary web and laying
down the plexifilamentary web to form a nonwoven sheet:
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Figure 2 is a fragmentary perspective view of the laydown of the
plexifilamentary web in Figure 1;
Figure 3 is an enlarged cross sectional view of the letdown
chamber and spin orifice in the apparatus in Figure l; and
S Figure 4 is a schematic view of a small scale test system for
making plexifilamentary yarn from polymer.
Detailed Description of the Preferred Embodiment
Referring now to the drawings, a preferred system and process for
flash spinning fibers and forming sheets is illustrated in Figures I and 2.
The basic system has been previously disclosed in U.S. Patent 3,860,369 to
Brethauer et al., which is hereby incorporated by reference. The process is
conducted in a chamber 1, sometimes referred to as a spin cell by those in
the industry, which has a vapor-removal port 2 and an opening 3 through
which non-woven sheet material produced in the process is removed.
Polymer solution (or spin liquid) is continuously or batch-wise prepared at
an elevated temperature and pressure and provided to the spin cell 1 via a
conduit 10. The pressure of the solution is greater than cloud-point pressure
which is the lowest pressure at which the polymer is fully dissolved in the
spin agent forming a homogeneous single phase mixture.
The single phase polymer solution passes through a letdown
orifice 11 into a lower pressure (or letdown) chamber 12. In the lower
pressure chamber 12, the solution separates into a two-phase liquid-liquid
dispersion. One phase of the dispersion is a spin agent-rich phase which
comprises primarily spin agent and the other phase of the dispersion is a
polymer-rich phase which contains most of the polymer. This two phase
liquid-liquid dispersion is forced through a spinneret 13 into an area of much
lower pressure (preferably atmospheric pressure) where the spin agent
evaporates very rapidly (flashes), and the polyolefin emerges from the
spinneret as a yarn (or plexifilament) 20. The yarn 20 is stretched in a tunnel
14 and is directed to impact a rotating baffle 15. The rotating baffle 15 has a
shape that transforms the yarn 20 into a flat web 21, which is about 5-15 cm
wide, and separating the fibrils to open up the web 21. The rotating baffle
15 further imparts a back and forth oscillating motion having sufficient
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amplitude to generate a wide back and forth swath. The web 21 is laid down
on a moving wire laydown belt 16 located about 50 cm below the spinneret
13, and as best seen in Figure 2, the back and forth oscillating motion is
arranged to be generally across the belt 16 to form a sheet 22.
As the web 21 is deflected by the baffle 15 on its way to the
moving belt 16, it enters a corona charging zone between a stationary multi-
needle ion gun 30 and a grounded rotating target plate 31. The multi-needle
ion gun 30 is charged to a DC potential by a suitable voltage source 36. The
charged web 21 is carried by a high velocity spin agent vapor stream
through a diffuser consisting of two parts: a front section 32 and a back
section 33. The diffuser controls the expansion of the web 21 and slows it
down. The back section 33 of the diffuser may be stationary and separate
from target plate 31, or it may be integral with it. In the case where the back
section 33 and the target plate 31 are integral, they rotate together. Figure l
shows the target plate 31 and the back section 33 of the diffuser as a single
unit. Aspiration holes 34 and 35 are drilled in the back section 33 of the
diffuser to assure adequate flow of gas between the moving web 21 and the
diffuser back section 33 to prevent sticking of the moving web 21 to the
diffuser back section 33. The moving belt 16 is grounded through roll 17 so
that the charged web 21 is electrostatically attracted to the belt 16 and held
in place thereon. Overlapping web swaths collected on the moving belt 16
and held there by electrostatic forces are forrned into a sheet 22 with a
thickness controlled by the belt speed. The sheet 22 is compressed between
belt 16 and consolidation roll 18 into a structure having sufficient strength tobe handled outside the chamber 1 and then collected outside the chamber 1
on a windup roll 23.
Flash-spun nonwoven sheets made by a process similar to the
foregoing process are sold as Tyvek(~) spunbonded olefin sheets for air
infiltration barriers in construction applications, as packaging such as air
express envelopes, as medical packaging, as banners, and for protective
apparel and other uses. Tyvek(~ spunbonded olefin is quite strong and
lightweight with small interstices between the fibers to allow moisture vapor
and air to permeate the sheet but limit passage of liquid water.
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Thus, the properties of Tyvek(~) spunbonded olefin is of
considerable interest and importance for its various end uses. It should go
without saying that it is always desirable to improve the properties of flash-
spun products as long as there is not a sacrifice of other important properties.S As described in many prior patent applications on flash spinning, a myriad
of variations have been disclosed that lead to variations in properties of
flash-spun fabrics.
One particular important set of properties of Tyvek(~) spunbonded
olefin sheet are tensile strength, elongation and toughness. Tyvek(~)
10 spunbonded olefin has considerable tensile strength especially considering
that it is made of high density polyethylene. Flash spirming tends to provide
highly oriented polymer in the plexifilaments. While flash spinning
provides good tensile properties, improved tensile properties as well as
considerable elongation and toughness would be appreciated in the market
15 place. Elongation is a measure of the amount the product stretches before it
breaks. Work to Break (WTB) relates to both the elongation and tensile
strength. The WTB is the area under the stress-strain curve. Toughness is
the WTB normalized for the basis weight.
DuPont has relied solely upon high density polyethylene for all
20 commercial operations in its Tyvek business and, indeed, the polyethylene
used was specified from specific sources with very tight specifications.
Recently, however, DuPont has begun to add post consumer recycled high
density polyethylene to virgin polymer. The post consumer recycle is
primarily from recycled milk jugs. Considerable engineering has gone into
25 the system and process to accommodate the recycled materials, and the
company is quite proud of this accomplishment.
With its new-found ability to accommodate what would have
previously been considered very off-specification polyethylene, new types
of polymer are being considered with the belief that new polymers may
30 provide better economics of production or provide different product
properties. It has now been found that polymer having a narrower range of
molecular weight wil! actually provide considerably improved tensile
strength, elongation and toughness. Until recently, high density
s
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polyethylene was made by Ziegler-Natta heterogeneous solid catalyst
systems. New polymer science and single-site catalyst systems bring
opportunities and possibilities of polymers that have not been previously
available. Such polymers made with single site catalyst systems, may have
more consistent properties and perhaps specific molecular structures.
DuPont has been experimenting with systems to fractionate conventional
polymers into fractions having a very narrow molecular weight distribution
and thereby provide polymer to its flash spinning systems which are
relatively free of fractions which are less desirable in the final sheet
1 0 products.
Although running new polymers such as those described above
re~uire considerable adjustment in the flash spinning process, it certainly
appears that the polymer having a narrow molecular weight distribution may
be flash spun into products that have considerably better properties in the
very important areas of tensile strength, elongation and toughness.
The polymers that can be used for this invention include ethylene
homo-polymers and copolymers, and blends of ethylene homo-polymers and
copolymers. These polymers can be prepared by using either Ziegler-Natta
type catalysts or single site catalysts. The polymers which are particularly
useful for this invention are high density polyethylene (HDPE) made from
ethylene homo-polymers or ethylene copolymers containing a relatively
small amount of polymerized co-monomer units. Alpha olefins such as
propylene, butene, hexene and octene are commonly used as a co-monomer
for commercially available high density polyethylene copolymers. For
purposes of clarity of me~ning, in this application and especially in the
claims, polyethylene shall mean a polymer comprised entirely or nearly
entirely of ethylene monomer with no more than to a small portion of
co-monomer units polymerized therein. High density polyethylene shall
mean polyethylene having a density greater than about 0.935 g/cc.
One additional benefit of flash spinning narrow molecular weight
distribution polymer is that much of the polymer that fouls the system is at
the lower molecular weight range of the polymer that is provided into the
system. Thus, it is anticipated that now that narrow molecular weight
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distribution polyethylene can be flash spun that it may provide the benefit
the system will suffer less fouling of the spin cell and possibly have longer,
more stable runs of the system. Certainly, more production time would
translate into better profit margins for the business.
Moreover, it has been found that tensile strength, elongation and
toughness may be further improved by changing the shape of the spin orifice
14. The shape of the spin orifice 14 of particular interest is the length to
diameter ratio. Referring to Figure 3, the spin orifice has a length identified
by the letter I and a diameter identified by the letter d. The ratio of the
length to diameter "I/d" for the standard arrangement has historically been
about one.
With the standard arrangement, the polymer concentration has
litt}e effect on elongation and tensile strength. However, if the length to
diameter ratio of the spin orifice 14 is sufficiently extended so that it is much
longer than its diameter, the elongation of the flash-spun material can be
substantially modified by adjustment of the ratio of polymer to spin agent in
the homogeneous mixture being fed to the spin cell 10. Quite notably, the
combination of spin orifice configuration, solution concentration and narrow
molecular weight distribution polymer combine to provide considerably
higher elongation and tensile properties.
Example cases were prepared to illustrate the effects of changing
the above described variables. However, it should be noted that other
process conditions must be modified to be able to spin well fibrillated yarns
which provide suitable sheets and sheet properties. In some situations, the
amount of polymer available to test was not enough to make sheets. A small
scale test device shown in Figure 4 is used to make flash-spun fiber which
can be tested and compared to polymer samples made into both fiber and
sheet.
Turning now to Figure 4, there is illustrated a twin cell test device
40 for mixing polymer and spin agent into a spin mixture. The device 40
comprises a block 41 which includes a primary cylinder chamber 44 and
second cylinder chamber 45. Measured quantities of polymer and spin agent
are provided into the primary cylinder chamber 44 through a suitable access
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such as port 48. The polymer and spin agent are directed back and forth
between the primary cylinder chamber 44 and the second cylinder chamber
45 through passage 50 which includes a static mixer element 51.
Pressurized fluid from a hydraulic pump 54 via hydraulic valve 55 and
5 hydraulic lines 56 and 57 causes pistons 64 and 65 to move the polymer and
spin agent between the two chambers 44 and 45. The mixture is heated to a
predetermined temperature and the pressure is monitored at sensor 67 until
the polymer and spin agent are adequately mixed. The hydraulic system is
then operated to direct the solution into the primary cylinder chamber 44
10 whereupon the valve 55 is closed to lock the secondary piston 65 closest to
the passage 50. The hydraulic valve 55 is also closed to preclude hydraulic
fluid from passing from line 56 back into the pump 54.
The spin solution now in the primary chamber 44 is spun through
a valve 71 using an accumulator 74 to maintain relatively constant spin
15 pressure. The accumulator 74 includes a relatively large cylinder 75
(compared to either of the primary and second cylinder chambers 44 and 45)
with a piston 76. Hydraulic fluid (preferably water) fills a large portion of
the accumulator cylinder 75, and pressurized gas fills the space inside
cylinder 75 on the other side of the piston 76. The pressurized gas provided
20 through a gas line 78 from a suitable source is controlled to create a nearlyconstant accumulator pressure during the spin which lasts a few seconds.
The accumulator pressure is monitored at sensor 79. With the hvin cell test
device 40, there are several items to consider when comparing the
operational parameters to the operation of the standard arrangement shown
25 in Figure 1. The pressure letdown chamber disclosed by Anderson et al.
(USP 3,227,794) was not used in the examples, and instead, the accumulator
pressure is set at the end of the mixing cycle to the desired spin pressure to
simulate the letdown chamber effect. Also, the valve 81 between the spin
cell and the accumulator and the spinneret orifice 71 are opened in rapid
30 succession. The resultant flash-spun product is collected in a stainless steel
open mesh screen basket. Because of the relatively small amount of material
and high pressure used, most of the spins in these Examples lasted for only
about one second.
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It usually takes about one to two seconds to open the spinneret
orifice 71 after opening the valve 81 between the spin cell and the
accumulator. When letdown chambers are used, the residence time in the
chamber is usually 0.2 to 0.8 seconds. However, it has been determined that
S residence time does not have too much effect on fiber morphology and/or
properties as long as it is greater than about 0.1 second but less than about
10 seconds. When the valve between the spin cell and the accumulator is
opened, the pressure inside the spin cell drops immediately from the mixing
pressure to the accumulator pressure. The spin cell pressure drops again
when the spinneret orifice 71 is opened because of the pressure drop in the
line 82. The pressure measured during spinning just before the spinneret
with a pressure transducer using a computer is entered as the spin pressure in
the examples. It is usually lower than the set accumulator pressure by about
100 to 200 psi. Therefore, the quality of the two phase dispersion in the spin
cell depends on both the accumulator pressure and the actual spin pressure,
and the time at those pressures. Sometimes the accumulator pressure is set
at a pressure higher than the cloud point pressure. In this case, the quality ofthe two phase dispersion in the spin cell will be determined primarily by the
spin pressure reached after the spinneret orifice is opened.
There are a number of tests and other measured parameters such
as the tensile strength, break elongation, and toughness on yarn and sheets.
Several measurements, tests and test methods are described hereafter to
provide a brief description of a number of the tests and measured
parameters.
Molecular Weight Distribution, Number Average Molecular Weight and
Weight Average Molecular Weight
Weight average molecular weight and number average molecular
weight were determined by gel permeation chromatography (GPC). The
GPC analyses were performed on a Waters 1 50-C chromatograph equipped
with three Polymer Labs Mixed B columns and a Viscotek viscosity
detector. The solvent used to prepare the polymer solutions and also used as
the mobile phase is 1,2,4-trichlorobenzene. Solution preparation and
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analysis are done at 140 C. The system is calibrated against a series of
narrow distribution polystyrenes.
Molecular weight distribution is the weight average molecular
weight divided by the number average molecular weight.
5 Melt Index
Melt index is measured according to ASTM D] 238-9OA, which
hereby incorporated by reference, at a temperature of 190~ C with a 2.16 kg
weight and is expressed in units of g/lO minllte~.
Concentration
Polymer/spin agent concentration is measured by weight percent
Surface Area
Surface area for flash-spun polyethylene typically is in the range
of 10 to 50 m2/gm. This is considerably higher than other fiber spinning
technologies and provides the high opacity typically desired in nonwoven
15 sheet products. The surface area of the plexifilamentary film-fibril strand is
measured by the BET nitrogen absorption method of S. Brunauer, P. H.
Emmett and E. Teller, J. Am. Chem. Soc., V. 60 p 309-319 ~1938), which is
hereby incorporated by reference, and is reported as m2/g. While surface
area was not measured for the samples discussed below, based on visual
20 observations by experienced personnel, it can be reported that all test belowwere within the typical surface area range for flash-spun polyethylene of l O
to 50 m~/gm.
Twin Cell Plexifilament Yarn Tensile Test Methods
Denier of the flash-spun strand is determined as follows: One 90
25 cm long strand of yarn is cut, and a weight of l OO grams is hung on one end
of the yarn for 3 minutes to remove bends and waviness. From the long
single yarn strand, five 18 cm individual pieces are cut, and denier is
deterrnined for each piece.
Tenacity, elongation and toughness of the strand are determined
30 with an Instron tensile-testing machine. The strands are conditioned and
tested at 70 F and 65 % relative humidity. The strands are then twisted to l O
turns per inch and mounted in the jaws of the Instron Tester. A t~vo-inch
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gauge length is used with an elongation rate of 2 inches per minute. The
tenacity at break is recorded in grams per denier (gpd). The elongation at
break is recorded as a percentage of the two-inch gauge length of the
sample. Toughness is a measure of the work required to break the sample
divided by the denier of the sample and is recorded in gpd. Modulus
corresponds to the slope of the stress/strain curve and is expressed in units ofgpd.
Basis Weight
Basis weight is determined by ASTM D3776, which is hereby
incorporated by reference, and is reported in oz/yd2 (g/m2). The basis
weights reported for the examples below are each based on an average of at
least six measurements made on the sheet.
Del~min~tion Stren~th
Del~min~tion strength of a sheet sample is measured using a
constant rate of extension tensile testing machine such as an Instron table
model tester. A 1.0 in. (2.54 cm) by 8.0 in. (20.32 cm) sample is
del~min~ted approximately 1.25 in. (3.18 cm) by inserting a pick into the
cross-section of the sample to initiate a separation and del~min~tion by hand.
The del~min~ted sample faces are mounted in the clamps of the tester which
are set 1.0 in. (2.54 cm) apart. The tester is started and run at a cross-head
speed of 5.0 in./min. (12.7 cm/min.). The computer starts picking up force
readings after the slack is removed in about 0.5 in. of crosshead travel. The
sample is del~min~ted for about 6 in. (15.24 cm) during which 3000 force
readings are taken and averaged. The average del~min~tion strength is the
average force divided by the sample width and is expressed in units of Ibs/in
(N/cm). The test generally follows the method of ASTM D2724-87, which
is hereby incorporated by reference. The del~min~tion strength values
reported for the examples below are each based on an average of at least six
measurements made on the sheet.
Opacity
Opacity is measured according to TAPPI T-519 om-86, which is
hereby incorporated by reference. The opacity is the reflectance from a
11
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single sheet against a black background compared to the reflectance from a
white background standard and is expressed as a percent. The opacity
values reported for the examples below are each based on an average of at
least six measurements made on the sheet.
Grab Tensile
Tensile properties are determined by ASTM D1682, Section 19,
which is hereby incorporated by reference, with the following modifications.
In the test a 2.54 cm by 20.32 cm (1 inch by 8 inch) sample was clamped at
opposite ends of the sample. The sample was pulled steadily at a speed of
10 5.08 cm/min (2 in/min) until the sample broke. The tensile property values
reported for the examples below were each an average of six measurements
on specimens cut in the machine direction and six measurements on
specimens cut in the cross direction. The force at break was norm~li7ed by
dividing by the samples basis weight and was recorded in lb-yd2/(oz-in)
15 (N-m2/(g-cm)) as the breaking strength. The elongation at 13.34 Newtons (3
lb) load and the elongation at break were recorded as a percent of the
original sample length. The Work-to-Break (WTB), which is the area under
the stress-strain curve, was norrnalized by dividing by the sample basis
weight and the sample width and is reported as toughness in lb-yd2/oz
20 (N-m2/g)
Spencer Puncture
Spencer puncture is measured according to ASTM D3420-9 1
Procedure B, which is hereby incorporated by reference, with the exception
that an impact head with contact area of 0.35 square inches was used on a
modified Elmendorf tester having a capacity of 6400 gram-force. Results
are normalized by dividing the measured energy to rupture by the area of the
impact head and are reported in in-lbs/in2 (J/cm2). The results below are
each based on an average of at least six measurements on the sheet.
Elmendorf Tear
Elmendorftear strength is measured according to ASTM D1424,
which is hereby incorporated by reference. The Elmendorf tear values are
reported for the examples below.
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With the tv~in cell system 40 of Figure 4, a large numbe. of
polymer tests have been run providing data that can be used to predict
properties in the sheet products. In Examples Y-1 a through Y-D3, the spin
5 agent comprises 68% normal pentane and 32% cyclopentane. Focusing on
flash-spun yarn properties the following examples were run in the twin cell
system 40 with the following properties:
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Con. Y-la Con. Y-lb Con. Y-lc Con. Y-ld
Polymer
Number Average 22,000 22,000 22,000 22,000
Molecular Weight
Weight Average 124,000 124,000 124,000 124,000
Molecular Weight
Molecular Weight 5.5 5.5 5.5 5.5
Distribution
Melt Index (g/10 min) 0.67 0.67 0.67 0.67
Density (g/cc) 0.96 0.96 0.96 0.96
Spin Conditions
Concentration (%) 18 18 18 18
Temperature (~C) 186 185 185 185
Spin pressure (psig) 875 800 800 750
Accum. Pressure (psig)1100 1000 950 900
Properties
Denier 180 183 218 214
Modulus (gpd) 17.7 18.6 15.2 16.2
Tenacity (gpd) 4.82 5.75 5.08 5.27
Toughness (gpd) 1.62 2.91 2.82 2.58
Elongation ~%) 53.9 74.5 87.4 77.4
14
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Con. Y- 1 eEx. Y-A I Ex. Y-A2a Ex. Y-A2b
Polymer
Number Average22,000 47,000 27,80027,800
Molecular Weight
Weight Average124,00097,800 106,800106,800
Molecular Weight
Molecular Weight 5.5 2.08 3.84 3.84
Distribution
Melt Index (g/10 min) 0.67 0.77 1.56 1.56
Density (g/cc)0.96 0.953 0.959 0.959
Spin Conditions
Concentration (%) 18 18 18 18
Temperature (~C) 185 185 186 185
Spin pressure (psig) 650 1025 1000 950
Accum. Pressure (psig) 800 1100 1100 1000
Properties
Denier 185 152 164 185
Modulus (gpd) 14 12 12.3 10.9
Tenacity (gpd)4.43 3.71 4.33 3.88
Toughness (gpd) 2.37 3.88 3.43 3.17
Elongation (%)82.8 152 l 17 122
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Ex. Y-A3 Ex. Y-A4 Ex. Y-ASa Ex. Y-ASb
Polymer
Number Average40,20035,60046,50046,500
Molecular Weight
Weight Average127,800121,800 120,200 120,200
Molecular Weight
Molecular Weight 3.18 3.42 2.58 2.58
Distribution
Melt Index (g/10 min)0.8 0.7 0.75 0.75
Density (g/cc)0.955 0.954 0.955 0.955
Spin Conditions
Concentration (%) 18 18 18 18
Temperature (~C) 185 185 185 185
Spin pressure (psig)1100 1000 875 750
Accum. Pressure (psig) 1200 1100 1000 900
Properties
Denier 155 155 201 203
Modulus (gpd)12.1 16.1 11.9 9.85
Tenacity (gpd)5.36 5.39 4.5 4.01
Toughness (gpd) 3.29 3.37 3.65 3.51
Elongation (%)96 94 118 129
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Ex. Y-A5c Ex. Y-B l a Ex. Y-B l b Ex. Y-B l c
Polvmer
Number Average 46,500 49,500 49,500 49,500
Molecular Weight
Weight Average 120,200130,900 130,900130,900
Molecular Weight
Molecular Weight 2.58 2.65 2.65 2.65
Distribution
Melt Index (g/10 min) 0.75 0.75 0.75 0.75
Density (g/cc) 0.955 0.949 0.949 0.949
Spin Conditions
Concentration (%) 20 18 18 18
Temperature (~C) 184 185 186 185
Spin Pressure (psig) 600 l lO0 lOS0 950
Accum. Pressure (psig) 750 1250 1200 1050
Properties
Denier 194 162 195 174
Modulus (gpd) 10.8 8.79 9.09 8.88
Tenacity (gpd) 4.05 5.32 3.3 92.1
Toughness(gpd) 3.34 3.3 3.85 3.6
Elongation (%) 122 92.1 121 122
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Ex. Y-ClEx. Y-C2Ex. Y-C3Ex. Y-C4
Polymer
NumberAverage45 ooo29,90051,700 81.700
Molecular Weight
Weight Average172,000122,000 166,000 204,000
Molecular Weight
Molecular Weight 3.83 4.09 3.21 2.5
Distribution
Melt Index (g/10 min)0.14 0.66 0.24 0.12
Density (g/cc)0.95440.95820.95310.9477
Spin Conditions
Concentration (%) 18 18 18 18
Temperature (~C) 186 185 185 185
Spin Pressure (psig) 950 950 1125 1100
Accum. Pressure(psig)1050 1050 1250 1225
Properties
Denier 157 154 190 172
Modulus (gpd)14.1 11.3 9.29 12.1
Tenacity (gpd)5.4 3.9 5.5 5.66
Toughness (gpd) 3.11 3.3 5.03 3.14
Elongation (%)87 132 128 96
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Ex. Y-C5Ex. Y-C6Ex. Y-Dl
Polymer
Number Average36,30037,60045,000
Molecular Weight
Weight Average104,200105,200 80,800
Molecular Weight
Molecular Weight 2.87 2.8 1.79
Distribution
Melt Index (g/10 min)0.7780.778 nm
Density (g/cc)O.9S O.9S nm
Spin Conditions
Concentration (%) 18 18 18
Temperature (~C) 185 185 185
Spin Pressure (psig)lOS0 975 950
Accum. Pressure (psig) 1175 1050 lOS0
Properties
Denier 175 152 138
Modulus (gpd)14.2 11.3 6.42
Tenacity (gpd)5.39 4.81 1.68
Toughness (gpd) 3.31 3.46 3.4
Elongation (%)98 107 303
nm - not measured
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Ex. Y-D2Ex. Y-D3
Polymer
Number Average69,033128,900
Molecular Weight
Weight Average114,200242,800
Molecular Weight
Molecular Weight 1.65 1.88
Distribution
Melt Index (g/10 min)nm nm
Density(g/cc) nm nm
Spin Conditions
Concentration (%) 18 l S
Temperature (~C)185 185
Spin Pressure (psig) 975 1200
Accum. Pressure (psig) 1050 1350
Properties
Denier 124 150
Modulus (gpd) 1.5 10.6
Tenacity (gpd)3.52 4.29
Toughness(gpd)3.25 4.22
Elongation (%) 134 144
nm - not measured
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Tests have also been run on pilot line equipment to make sheet
products. On the pilot line for Example S-B 1 a, plexifilamentary
polyethylene was flash spun from a solution consisting of 18.1% of linear
high density polyethylene and 81.9% of a spin agent consisting of 32%
5 cyclopentane and 68% normal pentane. The polyethylene had a melt index
of 0.73 g/10 minutes ((~ 190~C with a 2.16 kg weight), a melt flow ratio
{MI(~ 190~C with a 2.16 kg weight)/MI (~190~C with a 21.6 kg weight)}
of 34, and a density of 0.96 g/cc. The polyethylene was obtained from
Lyondell Petrochemical Company of Houston, Texas under the tradename
10 ALATHON(~. ALATHON~) is currently a registered trademark of
Lyondell Petrochemical Company. The solution was prepared in a
continuous mixing unit and delivered at a temperature of 1 85~C, and a
pressure of about 13.8 MPa (2000 psi) through a heated transfer line to an
array of six spinning positions. Each spinning position has a pressure
15 letdown chamber where the solution pressure was dropped to about 7.0 MPa
( 1010 psi). The solution was discharged from each letdown chamber to a
region maintained near atmospheric pressure and at a temperature of about
50~C through a 0.871 mm(0.0343 in) spin orifice having a length to diameter
of about 0.9. The flow rate of solution through each orifice was about 136
20 kg/hr (299 lbs/hr). The solution was flash spun into plexifilamentary
film-fibrils that were laid down onto a moving belt, consolidated, collected
as a loosely consolidated sheet on a take-up roll as described above.
The sheet was bonded on a Palmer bonder by passing the sheet
between a moving belt and a rotating heated smooth metal drum with a
25 diameter of about five feet. The drum is heated with pressurized steam and
the bonding temperature is controlled by adjusting the pressure of the steam
inside the drum. The pressurized steam heats the bonding surface of the
drum to approximately 133 to 141~C. The pressure ofthe steam is used to
adjust the temperature of the drum according to the degree of bonding
30 desired. The bonded sheet has the opacity, del~min~tion and other
properties as set forth in the following Table as Example S-B 1 a. Examples
S-B 1 b through C-Sheet were created manner similar to S-B 1 a with
differences as noted.
21
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W O9~ 9C~ PCTrUS97114513
It should be noted that properties of the sheet vary as the bonding
temperature is changed by adjusting the bonder steam pressure. Normally,
del~min~tion strength increases and opacity decreases as bonding
temperature is increased. The bonding temperature required to attain a
5 specified level of del~min~tion strength or opacity depends on the polymer
and spinning conditions used to make the unbonded precursor sheet. In
order to make meaningful comparisons among samples, each of the sheet
samples below were bonded over a range of temperatures yielding
del~min~tion strength values both less than and greater than 0.35 lb/in, and
10 the properties at 0.35 lb/in del~min~tion strength were then estimated using
linear regression.
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Ex. S-Bla Ex. S-Blb Ex. S-B2
Polymer
Number Average Molecular 25,033 25,033 49,500
Weight
Weight Average Molecular 143,467 143,467 130,900
Weight
MolecularWeight 5 73 5 73 2.65
Distribution
Melt Index (g/10 min) 0.73 0.73 0.75
Density (g/cc) 0.960 0.960 0.949
Spin Conditions
Concentration (%) 18.1 17.7 17.2
Temperature (~C) 185 185 185
Letdown pressure (psig) 1010 960 1100
SpinOrificeL/D Ratio 0.9 0.9 0.9
Bonding Pressure (psia) 49.8 49.4 48.4
Properties
Opacity (%) 96.9 97.5 97.5
BasisWeight(oz/yd2) 1.7 1.7 1.7
Break Strength (lb yd2/oz-in) 18.1 17.4 17.0
Break Elongation (%) 16.3 14.5 36.2
Toughness (lbs yd2/oz) 9.5 8.1 19.8
Elmendorf Tear (Ibs) 1.6 1.9 1.4
Spencer Puncture (in-lbs/in2) 22.0 27.1 51.3
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Ex. S-B3a Ex. S-B3b Ex. S-B4 Ex. S-B5
Polymer
Number Average Molecular 25 200 25,200 35,600 40,200
Weight
Weight Average Molecular 155,200 155,200 121,800 127,800
Weight
Molecular Weight 6.15 6.15 3.42 3.18
Diskibution
Melt Index (g/lOmin) 0.67 0.67 0.70 0.80
Density (g/cc) 0.961 0.961 0.954 0.955
Spin Conditions
Concentration (%) 17.8 18.2 17.8 17.5
Temperature (~C) 180 180 180 180
Letdown pressure (psig) 910 900 910 920
Spin Orifice L/D Ratio 0.9 0.9 0.9 0.9
Bonding Pressure (psia) 46.2 47.0 50.8 49.0
Properties
Opacity (%) 97.6 97.2 96.7 97.0
Basis Weight (oz/yd2) 1.7 1.7 1.7 1.8
Break Strength (lbs-yd2/oz) 17.3 18.9 19.8 16.7
Break Elongation (%) 17.4 15.7 27.3 22.7
Toughness (lbs yd2/oz) 9.8 9.7 16.7 12.2
Elmendorf Tear (Ibs) 1.6 1.5 1.7 1.9
Spencer Puncture (in-lbs/in2) 27.6 25.1 33.2 27.9
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Ex. S-B6 Ex. S-B7a Ex. S-B7b Ex. S-B8
Polymer
Number Average Molecular 47 ooo 24,700 25,400 41,400
Weight
Weight Average Molecular 97,760 156,400 153,000 94,400
Weight
Molecular Weight 2.08 6.34 6.03 2.28
Distribution
Melt Index (g/10 min) 0.77 .754 0.73 0.840
Density (g/cc) 0.953 0.9617 0.9615 0.9530
Spin Conditions
Concentration (%) 18.7 17.9 17.8 16.9
Temperature (~C) 180 185 185 185
Letdown pressure (psig) 900 980 1020 980
SpinOrificeL/DRatio 0.9 0.9 0.9 0.9
Bonding Pressure (psia) 44.9 47.9 48.4 47.5
Properties
Opacity (%) 97.3 97.6 97.9 96.7
Basis Weight (oz/yd2) 1.6 1.7 1.7 1.7
Break Strength (lbs-yd2/oz) 12.2 16.9 16.2 10.2
Break Elongation (%) 31.0 15.0 14.5 40.0
Toughness (lbs yd2/oz) 13.5 8.4 7.8 14.2
Elmendorf Tear (lbs) 1.7 1.5 1.7 1.3
Spencer Puncture (in-lbs/in2) 21.0 21.8 25.8 23.9
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Ex. B9aEx. B9b
Polymer
Number Average Mol~cular46,500 46,500
Weight
Weight Average Molecular120,200 120,200
Weight
Molecular Weight 2.58 2.58
Distribution
Melt Index (g/10 min) 0.75 0.75
Density (g/cc) 0.955 0.955
Spin Conditions
Concentration (%) 18.2 18.4
Temperature (~C) 185 185
Letdown pressure (psig) 1100 1030
Spin Orifice L/D Ratio 0.9 0.9
Bonding Pressure (psia) 47.5 48.5
Properties
Opacity(%) 97.2 97.9
Basis Weight (oz/yd2) 1.8 1.8
Break Strength (lbs yd2/oz) 13.4 14.2
Break Elongation (%) 21.1 20.8
Toughness (lbs yd2/oz) 9.3 9.9
Elmendorf Tear (lbs) 1.8 2.5
Spencer Puncture (in-lbs/in2) 23.8 32.8
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In the following example, the yarn was collected from the
unconsolidated sheet from the system described for m~king Example S-Bla.
Ex. C Yarn
PolYmer
Number Average Molecular49 500
Weight
Weight Average Molecular130,900
Weight
Molecular Weight 2.65
Distribution
Melt Index (g/10 min) 0.75
Density (glcc) 0.949
Spin Conditions
Concentration (%) 17.9
Temperature (~C) 185
Letdown pressure (psig) 1020
Spin Orifice L/D Ratio 4.1
Denier 279
Twisted Web
Modulus (gpd) 4.3
Tensile Strength (gpd) 2.6
Elongation (%) 205
Untwisted Web
Modulus (%) 3 .8
Tensile Strength (gpd) 1.4
Break Elongation (%) 74
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Ex. C Sheet
Polymer
Number Average Molecular 49 500
Weight
Weight Average Molecular 130,900
Weight
Molecular Weight 2.65
Distribution
Melt Index (g/10 min) 0.75
Density (g/cc) 0.949
Spin Conditions
Concentration (%) 17.9
Temperature (~C) 185
Letdown pressure (psig) 1020
Spin Orifice L/D Ratio 4.1
Properties
Del~min~t;on 0.35
Opacity (%) 95
Break Strength (lbs yd2/oz) 15
Break Elongation (%) 47
Toughness (lbs yd2/oz) 38
Elmendorf Tear (lbs) 1.1
Spencer Puncture (in-lbs/in2) 25
In summary, flash spinning narrow molecular weight distribution
5 polyethylene yields improved qualities, especially in tensile strength,
elongation and toughness. Additional improvements in elongation may also
be attained by changes in the spin orifice geometry and in the spin
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CA 02260881 1999-01-12
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concentration. Notably, each of these changes, polymer and spin conditions,
improve the properties of the product independently of the other. In other
words, each can be adjusted individually to improve the properties and both
can be adjusted together to improve them the most.
The foregoing description and drawings were intended to explain
and describe the invention so as to contribute to the public base of
knowledge. In exchange for this contribution of knowledge and
understanding, exclusive rights are sought and should be respected. The
scope of such exclusive rights should not be limited or narrowed in any way
by the particular details and preferred arrangements that may have been
shown. Clearly, the scope of any patent rights granted on this application
should be measured and deterrnined by the claims that follow.
.
CA 02260881 1999-01-12
_ 3 ~--
Table for Conver~ion to SI Units
1 denier = 1.1 decitex
1 pound per inch - 175.1 newtons per meter
1 pound-yard squared per ounce = .09 newton-meter squared
per gram
1 ounce per yard squared = 33.9 grams per meter squared
1 gram per denier = .091 gram per decitex
1 inch = 2.54 centimeters
1 inch squared = 6.45 centimeters squared
1 pound per inch squared (gage) = 6.89 kilo pascals
1 pound per inch squared (absolute) = 108.2 kilopascals
Breaking Strength - 1 pound-yard squared per ounce-inch =
5.2 x 10-2 newton-meter squared per gram-centimeter
Work-to-Break - 1 pound-yard squared per ounce = .09
newton-meter squared per gram
Spencer-Puncture - 1 inch-pound per inch squared = 1.7 x
10-2 newton-meters per centimeter squared
'ct~D'c~) S~
CA 02260881 1999-01-12
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