Note: Descriptions are shown in the official language in which they were submitted.
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HIGH STRENGTH SPUNBOND FABRIC
FROM HIGH MELT FLOW RATE POLYMERS
BACKGROUND OF THE INVENTION
This invention relates generally to a nonwoven fabric or web which is formed from
spunbond fibers of a the" llopl~tic resin and laminates using such a web as a component.
Thel ",oplaslic resins have been extruded to form fibers, fabrics and webs for a number
of years. The most common thermoplastics for this application are polyolefins, particularly
polypropylene. Other ~ rials such as polyesters, polyetheresters, polyamides andpolyurethanes are also used to form spunbond fabrics.
Nonwoven fabrics or webs are useful for a wide variety of applications such as diapers,
feminine hygiene products, towels, and recreational or protective fabrics. The nonwoven
fabrics used in these applications are often in the form of laminates like spunbond/spunbond
(SS) laminates or spunbond/meltblown/spunbond (SMS) laminates.
One of the desired characteristics of nonwoven fabrics is that they be as soft as
possible. Previously, improving softness has generally involved a trade-off with other
desi, ''e properties of the web such as tensile strength. For example, polyethylene webs
are very soft but also quite weak.
It is an object of this invention to provide a spunbond polyolefin nonwoven fabric or web
which is softer than those conventionally produced but which has comparable strength
characteristics .
SUMMARY OF THE INVENTION
A soft and strong nonwoven spunbond polyolefin fabric is provided which is a multilayer
laminate of a first web of high melt flow polymer fibers and a second web of low melt flow
polymer fibers. The web of low melt flow polymer fibers is produced from polyolefin polymer
~ having a melt flow rate of below 50 grams /10 minutes according to ASTM D-1238-9Ob
condition L. The web of high melt flow polymer fibers is produced from polyolefin polymer
having a melt flow rate of at least 50 grams /10 minutes according to ASTM D-1238-9Ob
condition L wherein the polyolefin polymer is initially produced as a reactor granule through
the use of a Ziegler-Natta catalyst with a melt flow rate below 50 grams/10 minutes at 230~C
and subsequently modified by a method such as the addition of up to 1000 ppm of peroxide,
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the addition of up to 5 weight percent of an organo-metallic compound and the addition of up
to 5 weight percent of a transition metal oxide. This treatment increases the meit flow rate
of the polymer by a factor of at least two. Such a laminate has a tensile strength of at least
10% greater than a similar laminate made without a high melt flow rate web but instead with
5 a web of the same type as the second web. The fabric of this invention may also have
various layers disposed between the first and second webs.
The nonwoven fabric of this invention may be used in products such as, for example,
gar,l,ents, personal care products, medical products, protective covers and outdoor fabrics.
1 0 DEFINITIONS
As used herein the term "nonwoven fabric or web" means a web having a structure
of individual fibers or threads which are interlaid, but not in an identifiable manner as in a
knitted fabric. Nonwoven fabrics or webs have been formed from many processes such as
15 for example, meltblowing processes, spunbonding processes, and bonded carded web
processes. The basis weight of nonwoven fabrics is usually expressed in ounces of material
per square yard (osy) or grams per square meter (gsm) and the fiber diameters useful are
usually expressed in "~i~;,ons. (Note that to convert from osy to gsm, multiply osy by 33.91).
As used herein the term "microfibers" means small diameter fibers having an
average dian ,eter not greater than about 75 microns, for example, having an average
diameter of from about 0.5 microns to about 50 microns, or more particularly, microfibers
may have an average diameter of from about 2 microns to about 40 microns. The diameter
of, for example, a polypropylene fiber given in microns, may be converted to denier by
squaring, and multiplying the result by 0.00629, thus, a 15 micron polypropylene fiber has a
denier of about 1.42 (152 x 0.00629 = 1.415).
As used herein the term "spunbonded fibers" refers to small diameter fibers which
are formed by extruding molten thermoplastic material as filan~ents from a plurality of fine,
usually circular capillaries of a spinneret with the diameter of the extruded filaments then
being rapidly reduced as by, for example, in U.S. Patent no. 4,340,563 to Appel et al., and
U.S. Patent no. 3,692,618 to Dorschner et al., U.S. Patent no. 3,802,817 to Matsuki et al.,
U.S. Patent nos. 3,338,992 and 3,341,394 to Kinney, U.S. Patent nos. 3,502,763, and U.S.
Patent no. 3,542,615 to Dobo et al. Spunbond fibers are generally continuous and larger
than 7 microns, more particularly, they are usually between about 15 and 50 microns.
As used herein the term "meltblown fibers" means fibers formed by extruding a
molten thermoplastic material through a plurality of fine, usually circular, die capillaries as
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molten threads or rilc""enls into a high velocity gas (e.g. air) stream which attenuates the
rilarnenl~ of molten thermopl-~tic "~aterial to reduce their diameter, which may be to
microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas
stream and are deposited on a collecting surface to form a web of randomly disbursed
meltblown fibers. Such a process is disclosed, for example, in U.S. Patent no. 3,849,241 to
- Butin. Meltblown fibers are microfibers which are generally smaller than 10 microns in
dian~et~r. The term meltblowing used herein is meant to enco" ,pass the meltspray process.
As used herein the term "polymer" generally includes but is not limited to,
ho",opolymers, copolymers, such as for example, block, graft, random and alternating
copolymers, terpolymers, etc. and blends and modifications thereof. Furthermore, unless
otherwise specifically limited, the term "polymer" shall include all possible geometrical
configuration of the material. These configurations include, but are not limited to isotactic,
syndiotactic and random s~" "r"el, ies.
As used herein the term "bicol"ponent fibers" refers to fibers which have been
formed from at least two polymers extruded from separate extruders but spun together to
form one fiber. The polymers are arranged in sul)~tanlially conslanlly positioned distinct
zones across the cross-section of the bico" ,ponent fibers and extend continuously along the
length of the bicol"~onent fibers. The configuration of such a bicomponent fiber may be, for
example, a sheath/core arrangement wherein one polymer is surrounded by another or may
be a side by side arrangement or an "islands-in-the-sea" arrangement. Bicomponent fibers
are taught in U.S. Patent 5,108,820 to Kaneko et al., U.S. Patent 5,336,552 to Strack et al.,
and European Patent 0586924. The polymers may be present in ratios of 75/25, 50/50,
25/75 or any other desired ratios.
As used herein the term "b ~nsLiluent fibers" refers to fibers which have been
formed from at least two polymers extruded from the same extruder as a blend. The term
"blend" is defined below. Biconstituent fibers do not have the various polymer components
arranged in relatively constantly positioned distinct zones across the cross-sectional area of
the fiber and the various polymers are usually not continuous along the entire length of the
fiber, instead usually forming fibrils which start and end at random. Biconstituent fibers are
sometimes also referred to as multiconstituent fibers. Fibers of this general type are
discussed in, for example, U.S. Patent 5,108,827 to Gessner. Bicomponent and
biconstituent fibers are also discussed in the textbook Polvmer Blends and ComDosites by
~ John A. Manson and Leslie H. Sperling, copyright 1976 by Plenum Press, a division of
Plenum Publishing Corporation of New York, IBSN 0-306-30831-2, at pages 273 through
277.
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As used herein the term "blend" means a mixture of two or more polymers while the
term "alloy" means a sub-class of blends wherein the components are immiscible but have
been compatibilized. "Miscibility" and "immiscibility" are defined as blends having negative
and positive values, respectively, for the free energy of mixing. Further, "compatibili~ation"
5 is defined as the process of modifying the interfacial properties of an immiscible polymer
blend in order to make an alloy.
As used herein the term "prodey~adanr refers to materials which promote the
degradation of the melt flow of a polymer from low melt flow rate to high melt flow rate.
As used herein, the term "garment" means any type of apparel which may be worn.
10 This includes industrial work wear and coveralls, undergarments, pants, shirts, jackets,
gloves, socks, and the like.
As used herein, the term "medical product" means surgical gowns and drapes, facemasks, head coverings, shoe coverings wound dressings, bandages, sterilization wraps,
wipers and the like.
As used herein, the term "personal care product" means diapers, training pants,
absorbent underpants, adult incontinence products, and feminine hygiene products.
As used herein, the term "protective cover" means a
cover for vehicles such as cars, trucks, boats, airplanes, motorcycles, bicycles, golf carts,
etc., covers for equipment often left outdoors like grills, yard and garden equipment
20 (mowers, roto-tillers, etc.) and lawn furniture, as well as floor coverings, table cloths and
picnic area covers.
As used herein, the term "outdoor fabric" means a fabric which is primarily, though
not exclusively, used outdoors. Outdoor fabric includes fabric used in protective covers,
camper/trailer fabric, tarpaulins, awnings, canopies, tents, agricultural fabrics and outdoor
25 apparel such as head coverings, industrial work wear and coveralls, pants, shirts, jackets,
gloves, socks, shoe coverings, and the like.
TEST METHODS
Handle-O-Meter: The softness of a nonwoven fabric may be measured according to
the "Handle-O-Meter" test. The test used herein is the INDA standard test 1st 90.0-75 (R
82) with two modifications: 1. the specimen size was 4 inches by 4 inches and 2. five
specimens were tested rather than two. The test was carried out on Handle-O-Meter model
number 211-5 from the Thwing-Albert Instrument Co., 10960 Dutton Road, Phila. PA 19154.
The Handle-O-Meter reading is in units of grams.
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Tensile: The tensile strength of a fabric may be measured according to the ASTM
test D-1682-64. This test measures the strength in pounds and elongation in percent of a
fabric.
Melt Flow Rate: The melt flow rate (MFR) is a measure of the viscosity of a
5 polymers. The MFR is expressed as the weight of "laterial which flows from a capillary of
known dil "ensions under a specified load or shear rate for a measured period of time and is
measured in grams/10 minutes at 230~C accordi, lg to, for example, ASTM test D-1238-9Ob,
condilion L.
DETAILED DESCRIPTION
The il"poilanl properties of polyolefins used in the spunbonding process are known to
those skilled in the art. The melt flow rate and the viscosity are interrelated and are quite
important in characterizing a polymer. The melt flow rate is related to the viscosity of the
polymer with a higher number indicating a lower viscosity. The test for the melt flow rate is
defined above.
The spunbond process generally uses a hopper which supplies polymer to a heated
extruder. The extruder supplies melted poiymer to a spinneret where the polymer is
fiberized as it passes through fine openings arranged in one or more rows in the spinneret,
forming a curtain of rllanlenls. The rllal"e"ls are usually quenched with air at a low
pressure, drawn, usually pneumalically and deposited on a moving foraminous mat, belt or
"forming wire" to form the nonwoven fabric. Polymers useful in the spunbond process
generally have a process melt temperature of between about 400~F to about 610~F (200~C
to 320~C).
The fibers produced in the spunbond process are usually in the range of from about 15
to about 50 microns in diameter, depending on process conditions and the desired end use
for the fabrics to be produced from such fibers. For example, increasing the polymer
molecular weight or decreasing the processing temperature results in larger diameter fibers.
Changes in the quench fluid temperature and pneumatic draw pressure can also affect fiber
diameter. In this invention, the particular polymer used allows the fibers to be produced at a
smaller diameter than usual for spunbonding.
The fabric of this invention is a multilayer lan ,;"al~ incorporating the high melt flow
polymer fiber web and may be formed by a number of different techniques including but not
limited to using adhesive, needle punching, ultrasonic bonding, thermal calendering and any
other method known in the art. Such a multilayer laminate may be an embodiment wherein
some of the layers are spunbond and some meltblown such as a
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spunbond/meltblown/spunbond (SMS) laminate as disclosed in U.S. Patent no. 4,041,203 to
Brock et al. and U.S. Patent no. 5,169,706 to Collier, et al. or as a spunbond/spunbond
laminate. An SMS laminate may be made by sequentially depositing onto a moving
conveyor belt or forming wire first a spunbond fabric layer, then a meltblown fabric layer and
5 last another spunbond layer and then bonding the laminate in a manner described above.
Alternatively, the three fabric layers may be made individually, collected in rolls, and
combined in a separate bonding step.
Various pattems for calender rolls have been developed. One example is the
expanded Hansen Pennings pattern with about a 15% bond area with about 100
bonds/square inch as taught in U.S. Patent 3,855,046 to Hansen and Pennings. Another
common pattern is a diamond pattern with repeating and slightly offset diamonds.The fabric of this invention may also be laminated with films, glass fibers, staple fibers,
paper, and other commonly used materials known to those skilled in the art.
Areas in which the fabric of this invention may find utility are garments, medical
products, personal care products, and outdoor fabrics. More particularly, fabrics produced
according to this invention are useful in heavier basis weight applications such as protective
covers. Protective covers usually have basis weights ranging from about 2 osy (68 gsm) to
about 8 osy (271 gsm), according, a fabric produced according to this invention will
prefer~bly have basis weights ranging from about 0.2 osy (7 gsm) to about 3 osy (102 gsm).
A polyolefin polymer useful in this invention must have a high melt flow rate and low
viscosity. The melt flow rate desired for the polyolefin to be used in this invention is at least
50 gms/10 min according to ASTM D-1238-9Ob condition L, and preferably in the range from
about 50 gms/10 min to about 150 gms/10 min according to ASTM D-1238-9Ob condition L.
The viscosity of the polymer is measured at 180~C and must be at least 2.5 x 103dynes.sec/cm2 and preferably in the range of about 2.5 x 103 dynes.sec/cm2 to about 6.5 x
103 dynes.sec/cm2. The high melt flow rate and low viscosity allows the fibers to be drawn
more highly than otherwise, producing very fine spunbond fibers. Fibers produced with the
high melt flow polyolefin employed herein are in the range of about 11 to about 20 microns
in diar"eter.
One advantage of fine spunbond fibers may be seen in non-adhesive where energy is
applied to the web through various means to induce the fibers to melt together slightly. It is
believed by the inventors that smaller fibers made from lower viscosity polymers enable
more polymer to flow at the bond points during bonding, thus ensuring a strong bond, yet
the web retains the advantage of softness which smaller fibers also give.
The production of a high melt flow rate polyolefin may be achieved when starting with a
conventional low melt flow polyolefin through the action of free radicals which degrade the
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polymer from low to high melt flow. Such free radicals can be created and/or rendered more
stable through the use of a prudeg,adant such as a peroxide, an organo-metallic compound
or a transition metal oxide. Depending on the prodegradant chosen, stabilizers may be
useful.
One example of a way to make a high melt flow polyolefin from a conventional low melt
flow polyolefin is to incorporate a peroxide into the polymer.
Peroxide additiot1 to a polymer for meltblowing appl..,2t cns is taught in U.S. Patent
5,213,881 to Timmons et al. In Timmons, up to about 3000 ppm of peroxide is added to a
polymer which has been polymerized with a Ziegler-Natta catalyst. The polymer is in the
10 form of reactor granules and has a molecular weight distribution of 4.0 to 4.5 Mw/Mn and a
melt flow rate of about 400 gms/10 min according to ASTM D-1238-9Ob condition L prior to
modification. Such a polymer is modified by the peroxide to have a molecular weight
distribution in the range of about 2.2 to 3.5 Mw/Mn and a melt flow rate of about 800 to 5000
gms/10 min according to ASTM D-1238-9Ob condition L. Peroxide addition to polymer
pellets is also addressed in U.S. Patent 4,451,589 to Morman et al.
Peroxide addition to a polymer for spunbonding applications is done by adding up to
1000 ppm of peroxide to cor"lnercially available low melt flow rate polyolefin polymer and
mixing thoroughly. The resulting modified polymer will have a melt flow rate of
app,uki,,,ately two to three times that of the starting polymer, depending upon the rate of
20 peroxide addition and mixing time.
Another way to make a high melt flow pûlyolefin from a conventional low melt flow
polyolefin is to add an organo-metallic compound to the polyolefin. The organo-metallic
compound has the effect of increasing the stability of free radicals within the polymer which
allows them to remain active for a longer period of time, and thus to degrade the polymer
25 from low to high melt flow. Typically, the melt flow may be changed from about 35 to the
range of about 70 to 85 using this method.
The suitable organo-metallic compound is sodium bis(para-t-butylphenyl) phosphate.
An example of a suitable commercially available organo-metallic compound is that sold by
Witco Chemical Company of New Jersey under the trade name Mark 2180. When an
30 organo-metallic compound is used it may be used in an amount of from about 0.1 weight
percent to about 5 weight percent. Organo-metallic compounds have the added benefit of
giving the fabric enhanced ultraviolet light resistance, important in outdoor applications, as
well as giving color to the fabric, as most organo-metallic compounds are also pigments.
The organo-metallic compound may be added to the polyolefin to be spun prior to
35 entering the extruder. It is important that the organo-metallic compound and the polyolefin
be mixed as thoroughly as possible in order to provide as uniform a mixture as possible to
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the spinneret. Ullirul~lliLy in the co",posi~ion fed to the spinneret helps to ensure uniform
fiber production and to reduce broken fibers and shot. One suit~hle method of mixing the
polyolefin and organo-metallic compound is to add the organo-metallic compound, generally
a powder, to the polyolefin, generally in pellet form, in a large mixing vessel prior to addition
to the hopper as described previously. Alternatively, the organo-metallic compound may be
added to the polyolefin in the hopper.
Still another method is to add the organo-metallic compound in a controlled manner at
a number of points along the length of the extruder as the polyolefin is melted and moved
forward toward the spinneret. This method would allow the greatest conL~ ty of the
process yet also provides the least margin for error in the addition rate, as changes in the
addition rate would most immediately affect the unif~ r",iLy of the fibers produced.
Yet another way to make a high melt flow polyolefin from a conventional low melt flow
polyolefin is to add a llansition metal oxide to the polymer during processing. Suitable
l,~nsilion metal oxides are, for example, ferric oxides. An example of a suitable
commercially available transition metal oxide is that sold by Engelhard Corporation under
the trade name Fe-0301-P. When a l,~nsition metal oxide is used it may be used in an
amount of from about 0.1 weight percent to about 5 weight percent. Transition metal oxides
may be added to the polyolefin in the manner described above. Transition metal oxides
have the added benefit of giving the fabric enhanced ultraviolet light resistance, important in
outdoor applic~tions, as well as giving color to the fabric, as most transition metal oxides are
also pigments.
It is also believed that a combination of a number of the above techniques will also be
successful in producing polyolefin of the desired melt flow rate.
The polyolefin useful in this invention may be polyethylene, polypropylene, polybutylene
or copolymer and mixtures thereof. Polypropylene is preferred.
In addition to the above methods, high melt flow polypropylenes are commerciallyavailable from Shell Chemical Co., Houston, Texas as WRD5-1131, WRD5-1155 through
1157, WRD5-1160 through 1162, from Exxon Chemical Co., Baytown, Texas as PLTD-739,
PLTD-766, PLTD-782, PLTD 926, PLTD-927 and others, and from the Himont Corporation
of Wilmington, Delaware as X11029-20-1 and X1129-20-2. These materials have melt flow
rates of above 60 according to ASTM D-1238-9Ob, condition L. Commercially available
polymers may or may not have been chemically treated and/or modified in order to raise
their melt flow rates.
The polymers employed in the practice of this invention provide not only a high melt
flow rate, but are also believed to be responsible for the higher strength in the resulting
fabric after bonding. Thus, it has been surprisingly found that the fabric of this invention has
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a tensile ~ ngll, of at least 10% more than the fabric made from the same polymer without
modification to a high melt flow rate.
While the fabric made from the high melt flow rate polymer fibers described above may
be used in a laminate with only a low melt flow rate polymer web, it is preferred that the
5 fabric be laminated to other " ,dl~ri~ls as well. Such materials include meltblown webs, films
and other spunbond webs.
Films, and meltblown & spunbond webs may be made from any material known in the
art to be suitable for such applic~lions. This includes polyamides, polyethers,
polyellle,t:sh,:" polyurethanes, polyolefins and copolymers, terpolymers and mixtures
10 thereof. Webs may be made of fibers constructed in a bicomponent configuration as
defined above. Elastomeric thermopl~stic polymers may be used to form such films and
webs also. Elastomeric polymers are prererably selected from those made from styrenic
block copolymers, polyurethanes, polyamides, copolyesters, ethylene vinyl acetates (EVA)
and the like.
Styrenic block copolymers include styrene/butadiene/styrene (SBS) block
copolymers, styrene/isopr~ne/styrene (SIS) block copolymers, styrene/ethylene-
propylene/styrene (SEPS) block copolymers, styrene/ethylene-butadiene/styrene (SEBS)
block copolymers. For example, useful elastollleric fiber forming resins include block
copolymers having the general formula A-B-A' or A-B, where A and A' are each a
20 the", lopl ~ lic polymer endblock which contains a styrenic moiety such as a poly (vinylarene)
and where B is an elas~ol "eric polymer midblock such as a conjugated diene or a lower
alkene polymer. Block copolymers of the A-B-A' type can have different or the same
ther" lopl?stic block polymers for the A and A' blocks, and the present block copolymers are
intended to embrace linear, branched and radial block copolymers. In this regard, the radial
25 block copolymers may be designated (A-B)m-X, wherein X is a polyfunctional atom or
molecule and in which each (A-B)m- radiates from X in a way that A is an endblock. In the
radial biock copolymer, X may be an organic or inorganic polyfunctional atom or molecule
and m is an integer having the same value as the functional group originally present in X. It
is usually at least 3, and is frequently 4 or 5, but not limited thereto. Thus, in the present
30 invention, the expression "block copolymer", and particularly "A-B-A"' and "A-B" block
copolymer, is intended to embrace all block copolymers having such rubbery blocks and
thermoplastic blocks as discussed above, which can be extruded (e.g., by meltblowing), and
without limitation as to the number of blocks.
U.S. Patent 4,663,220 to Wisneski et al. discloses a web including "licluribers
35 comprising at least about 10 weight percent of an A-B-A' block copolymer where "A" and
"A"' are each a the""oplaslic endblock which comprises a styrenic moiety and where "B" is
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an elastomeric poly(ethylene-butylene) midblock, and from greater than 0 weight percent up
to about 90 weight percent of a polyolefin which when blended with the A-B-A' block
copolymer and subjected to an effective combination of elevated temperature and elevated
pressure condilions, is adapted to be extruded, in blended form with the A-B-A' block
5 copolymer. Polyolefins useful in Wisneski et al. may be polyethylene, polypropylene,
polybutene, ethylene copolymers, propylene copolymers, butene copolymers, and mixtures
thereof.
Commercial exa~ 'es of such elastomeric copolymers are, for example, those
known as KRATON~) materials which are available from Shell Chemical Company of
10 Houston, Texas. KRATON~ block copolymers are available in several different
formulations, a number of which are identified in U.S. Patent 4,663,220, hereby incorporated
by reference. Particularly suitable elastomeric polymers are elastomeric
poly(styrene/ethylene-butylene/styrene) block copolymers available from the Shell Chemical
Company of Houston, Texas under the trade designations KRATONO G-1657 and
15 KRATON~) G-2740.
In the laminate of this invention it has been found that an intermediate layer, such as a
meltblown layer, does not appreciably change the strength and softness properties of the
final laminate when compared to those without the intermediate layer.
Drape is a measure of the softness of a fabric and refers to how well the fabric20 conforms to an object over which it is laid. A soft fabric will drape more in conrur,l ,ance with
the outline of the obiect upon which it is draped than will a stiffer fabric. Drape is measured
by the Handle-O-Meter test which was previously defined.
The strength of a fabric is measured by the tensile test which was previously defined.
Fabrics made according to this invention have been found to have comparable drape
25 and superior tensile properties as fabrics made from conventional polypropylenes.
The following Control and Exd",ples show the characLeristics of fibers from polymers
which satisfy the requirements of this invention versus those that do not. All of the samples
were bonded with the expanded Hansen-Pennings pattern described above. The results
are shown in table 1.
CONTROL
A fabric was produced which was a spunbond/spunbond (SS) la~ Le. The basis
weight of the layers was 1 osy (34 gsm) and 1 osy (34 gsm). Both layers were made from
35 the same low melt flow rate polypropylene: Himont Chemical Co.'s PF-301. The fibers were
spun at a temperature of about 390-440~F (199-221~C). The spinneret hole size was 0.6
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mm with throughput between 0.5 and 0.7 grams/hole/minute (ghm) to produce fiber of 21
microns in diameter.
EXAMPLE 1
A fabric was produced which was a spunbond/spunbond (SS) laminate. One of the
layers was produced from a high melt flow rate polypropylene and the other from a
conventional low melt flow rate polypropylene. The basis weight of the layers was 1 osy for
the high melt flow rate layer and 1 osy for the low melt flow rate layer. The high melt flow
rate polypropylene was produced by the addition of 1000 to 1500 ppm of peroxide to
Himont's PF-301 polypropylene. The melt flow rate of the polymer after peroxide treatment
was about 110 according to ASTM D-1238-9Ob condilion L. The high melt flow rate fibers
were spun at a temperature of about 390-430~F (199-221~C). The spinneret hole size was
0.6 mm with throughput between 0.5 and 0.7 grams/hole/minute (ghm) to produce fiber of
15 microns in diameter.
The low melt flow rate polypropylene used was Himont's PF-301. The fabric was
produced by spinning fibers at the conditions of the Control.
The laminate was produced by first depositing the low melt flow layer onto a forming
wire and then depositing the high melt flow polymer layer directly onto the warm low melt
flow rate polymer layer.
EXAMPLE 2
A fabric was produced which was a spunbond/spunbond (SS) laminate. One of the
layers was produced from a high melt flow rate polypropylene and the other from a
conventional low melt flow rate polypropylene. The basis weight of the layers was the same
as in Example 1. The high melt flow rate polypropylene was produced by the addition of
0.65 weight percent of an organo-metallic compound to Himont's PF-301 polypropylene.
The melt flow rate of the polymer after organo-metallic treatment was 80 according to ASTM
D-1238-9Ob condition L. The organo-metallic compound used was pthalo-Fe2O3-cynanine
which is available commercially as a blue-grey pigment from the Standridge Chemical
Company of Social Circle, Georgia, as SCC6142. After addition, the polypropylene/organo-
metallic mixture was thoroughly mixed.
The high melt flow rate fibers were spun at the same conditions as in Example 1 to
produce fiber of 12 mE ons in diameter.
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The low melt flow rate polypropylene was Himont' PF-301. The fabric was produced by
spinning fibers at the same conditions as in Example 1 to produce fibers of 19.5 microns in
diameter.
The laminate was produced by first depositing the low melt flow layer onto a forming
5 wire and then depositing the high melt flow polymer layer directly onto the warm low melt
flow rate polymer layer.
EXAMPLE 3
10 A fabric was produced which was a spunbond/spunbond (SS) laminate. One of thelayers was produced from a high melt flow rate polypropylene and the other from a
conventional low melt flow rate polypropylene. The basis weight of the layers was the same
as in Example 1. The high melt flow rate polypropylene was produced by the adcliLion of
0.65 weight percent of an organo-metallic compound to Himont's PF-301 polypropylene.
15 The melt flow rate of the polymer after organo-metallic treatment was 80 according to ASTM
D-1238-9Ob condiLion L. The organo-metallic compound used is designated Fe2O3/Fe and
is available commercially from the Engelhard Corporation. After addition, the
polypropylene/organo-metallic mixture was thoroughly mixed. The high melt flow rate fibers
were spun at the same conditions as in Example 1 to produce fiber of 15 microns in
20 diar, leter.
The low melt flow rate polypropylene was a mixture of Himont' PF-301 and Exxon
Chemical Company's Escorene(g) 3445. The fabric was produced by spinning fibers at the
same conditions as in Example 1 to produce fiber of 19.5 microns in diameter.
The laminate was produced by first depositing the low melt flow layer onto a forming
25 wire and then depositing the high melt flow polymer layer directly onto the warm low melt
flow rate polymer layer.
CA 02249286 1998-09-17
WO 97/40225 PCT/US97106027
TABLE 1
Fiber-Size Elongation
Normalized Tensile Energy Handle-O-Meter
# Sample IdBW(", ~,uns) Cd Md Cd Cd Md
0 Control 2 19-25 30 60 54.3 82.8 97.7
Example 1 2 19-25 34 67 74 56.4 94.2
2 Example 2 2 19-25 39 78.5 78.6 89.8 82.6
3 Example 3 2 19-25 38.5 76 76 51.1 73
The results show that laminates made from fibers spun from polyolefin having thedesignated characteristics can have greater strength than those from unmodified
polymers. Strong polyolefin spunbond webs have not been produced as far as the
15 inventors are aware with comparable softness to that of conventional polyolefin spunbond
webs in the past.
