Meltblown polyethylene fabrics and processes of making same

A nonwoven web of meltblown microfibers formed of a composition of polyethylene and at least one component added to provide processing stability to the polyethylene component. The meltblown web can be produced at high polymer throughputs and exhibits good barrier properties. The meltblown web is useful as a component of a composite fabric, which can be used for barrier application in medical and industrial applications.

FIELD OF THE INVENTION 
The invention relates to nonwoven fabrics and to processes for producing 
nonwoven fabrics. More specifically, the invention relates to nonwoven 
fabrics having barrier properties which are particularly suited for 
medical applications. 
BACKGROUND OF THE INVENTION 
Nonwoven fabrics and fabric laminates are widely used in a variety of 
applications, for example, as components of absorbent products such as 
disposable diapers, adult incontinence pads, and sanitary napkins; in 
medical applications such as surgical gowns, surgical drapes, 
sterilization wraps, and surgical face masks; and in other numerous 
applications such as disposable wipes, industrial garments, house wrap, 
carpets and filtration media. For example, nonwoven barrier fabrics have 
been developed which impede the passage of bacteria and other contaminants 
and which are used for disposable medical fabrics, such as sterilization 
wraps for surgical and other health care related instruments, surgical 
drapes, disposable gowns and the like. 
Barrier fabrics can be formed by sandwiching an inner fibrous web of 
thermoplastic meltblown microfibers between two outer nonwoven webs of 
substantially continuous thermoplastic spunbonded filaments. The fibrous 
meltblown web provides a barrier impervious to bacteria or other 
contaminants in the composite nonwoven fabric, and the spunbonded webs 
provide abrasion resistance and integrity to the laminate. Examples of 
such trilaminate nonwoven fabrics are described in U.S. Pat. No. 4,041,203 
and U.S. Pat. No. 4,863,785. 
Current industry standards require that laminate fabrics used for barrier 
purposes provide a predetermined level of protection against penetration 
of the fabric by air borne contaminants. The level of barrier protection 
required can depend upon the particular end use application of the fabric. 
Many laminate fabrics currently available cannot meet all of the 
requirements for a particular end use application. 
In addition, conventional trilaminate barrier fabrics can also be limited 
with regard to the types of sterilization procedures which can be used 
therewith. For some applications, it is desired that the fabric or garment 
be sterilized in the final stages of manufacture by exposure to gamma 
radiation. For example, the fabric or garment may first be sealed in a 
protective package, and then exposed to gamma radiation to sterilize the 
package and its contents. 
However, sterilization by gamma irradiation has been found to be unsuitable 
for many of the known medical barrier fabrics. Some of the polymers 
conventionally used in such medical barrier fabrics, such as conventional 
grades of polypropylene for example, are especially sensitive to 
degradation by gamma irradiation. Fabrics produced from such polymers tend 
to lose strength over time, becoming brittle as a result of the gamma 
irradiation. Also, the instability of the polymers to the irradiation 
results in the generation of distasteful odors in the product which are 
unacceptable to the consumer. 
Various attempts have been made to overcome these limitations. For example, 
efforts have been made to render the polypropylene polymers more stable to 
gamma irradiation, such as by incorporating certain additives in the 
polymer to reduce the amount of degradation. For example, U.S. Pat. No. 
4,822,666 describes a radiation stabilized polypropylene fabric in which a 
long-chain aliphatic ester is added to the polymer. U.S. Pat. No. 
5,041,483 discloses incorporating a rosin ester into the polypropylene to 
stabilize the polymer and reduce the tendency toward odor generation after 
gamma irradiation. However, the use of such additives adds expense to the 
manufacturing process. Further, polypropylene is difficult to render 
gamma-stable even with the use of additives or stabilizers. 
Other polymers have good stability upon exposure to gamma irradiation, such 
as polyethylene. However, there are problems associated with the use of 
polyethylene to form nonwoven webs, specifically as the meltblown 
component of a trilaminate fabric. For example, polyethylene generally 
exhibits poor spinnability, particularly at high spinning speeds. Yet high 
spinning speeds are highly desirable for successful commercial production 
of polyethylene fibers. Further, it is difficult to produce fine denier 
fibers at commercially feasible spinning speeds. This is especially true 
as fiber size decreases to the 1 to 50 micron range useful for imparting 
to a fabric the degree of barrier protection required by industry 
standards. 
SUMMARY OF THE INVENTION 
The present invention provides nonwoven meltblown webs which have excellent 
barrier properties and are flexible and soft. The meltblown webs of the 
invention can be used as components in any variety of nonwoven products, 
and are particularly useful as barrier components in medical fabrics, such 
as sterile wraps, surgical gowns, and the like. Further, the meltblown 
fabrics of the invention can be sterilized using gamma irradiation, 
without loss in strength and the generation of distasteful odors. 
The meltblown webs of the invention are formed of a blend or composition 
which includes polyethylene as the majority component thereof. Preferably 
the polyethylene is a linear low density polyethylene (LLDPE) having a 
melt flow rate of at least about 125, or higher. 
The blend also includes a polyethylene processing stabilizing component 
selected to stabilize the processing of the polyethylene resin. 
Advantageously, the polyethylene processing stabilizing agent is gamma 
irradiation stable. It is believed that the polyethylene processing 
stabilizing component acts to "stiffen" the soft, highly elongatable 
polyethylene resins sufficiently so that the resin can be meltblown 
without substantial formation of shot, polymer globules, and the like. 
Further, the polyethylene processing stabilizing agent provides improved 
web integrity and strength. 
The polyethylene can thus be meltblown at commercially desirable polymer 
throughputs without a corresponding significant increase in fiber size or 
denier, as determined by the resultant barrier properties of the meltblown 
web. Preferably, the polyethylene can be meltblown at polymer throughput 
rates of at least about 0.65 grams of polymer per capillary hole per 
minute ("g/h/m"), and up to about 1 g/h/m, and higher. In addition, the 
resultant polyethylene web can have good integrity and increased strength, 
particularly as compared to 100% polyethylene meltblown webs. 
In one embodiment of the invention, the polyethylene processing stabilizing 
agent is a "stiffening" polymeric component, such as, but not limited to, 
a polyolefin, polyester, polyamide, and the like. In this embodiment of 
the invention, preferably the polyethylene processing stabilizing agent is 
polyester. In this embodiment of the invention, the polyethylene 
processing stabilizing component preferably is present in the blend in an 
amount of about 1 to about 15 percent by weight based upon the weight of 
the polyethylene polymer. 
In another embodiment of the invention, the polyethylene processing 
stabilizing component is an agent which effects a change in the polymeric 
structure of the polyethylene, such as a polyethylene crosslinking agent. 
In this embodiment of the invention, the polyethylene processing 
stabilizing component is preferably present in the blend in an amount 
between about 0.05 to about 1 percent by weight based on the weight of the 
polyethylene polymer. 
The meltblown webs of the invention exhibit barrier properties, referred to 
as the "hydrohead" of the web, comparable to barrier properties exhibited 
by conventional polypropylene meltblown webs. Indeed, because the 
polyethylene blend is gamma irradiation stable, the resultant polyethylene 
meltblown webs can exhibit barrier properties superior to polypropylene 
webs after being treated with gamma irradiation. For example, the webs of 
the invention typically exhibit a hydrohead of at least about 40 
centimeters ("cm") when produced at polymer throughputs approaching 1 
g/h/m, and up to about 45 and 50 cm when produced at polymer throughputs 
of about 0.65 g/h/m. In contrast, although conventional polypropylene 
meltblown webs can initially exhibit good barrier properties (i.e., an 
initial hydrohead of 50 to 55 cm), the barrier properties of such webs 
decrease significantly after exposure to gamma irradiation and storage 
(i.e., a subsequent hydrohead of about 20 to 25 cm). This limits the shelf 
life of gamma treated polypropylene webs. 
In another aspect of the invention, laminate nonwoven fabrics are provided 
which include as a component thereof the polyethylene meltblown webs of 
the invention. An exemplary laminate nonwoven fabric includes the 
polyethylene meltblown web sandwiched between and bonded to outer nonwoven 
webs. Preferably, the outer nonwoven webs are also formed of a gamma 
irradiation stable polymer composition. At least one of the outer nonwoven 
webs can be a spunbonded web of substantially continuous thermoplastic 
filaments. The other of the outer nonwoven webs can also be a nonwoven web 
of spunbonded substantially continuous filaments. Alternatively, the other 
nonwoven web can be a nonwoven web of staple fibers. All of the layers are 
preferably thermally bonded together via a plurality of discrete thermal 
bonds distributed substantially throughout the length and width dimensions 
of the composite nonwoven fabric. The polyethylene meltblown layer 
provides good barrier properties, yet also imparts desirable aesthetic 
properties to the laminate fabric, such as improved flexibility and 
softness. 
Polyethylene meltblown webs of the invention, and laminate fabrics 
incorporating the same, can be readily manufactured according to another 
aspect of the invention. The polyethylene meltblown web can be 
manufactured at commercially feasible polymer throughput rates of at least 
about 0.65 g/h/m, and higher, by adding a polyethylene processing 
stabilizing component to the polyethylene resin, as described above. 
Processing parameters are selected based upon the physical properties of 
the components of the blend (i.e., melt flow rate of the polyethylene, the 
specific polyethylene processing stabilizing agent used and its 
properties, etc.). Advantageously the melt temperature of the polyethylene 
composition is increased at least about 10%, or higher, as compared to 
melt temperatures used in conventional polyethylene fiber production. This 
provides increases flowability of the polymer. Increasing melt temperature 
is also advantageous when the polyethylene processing stabilizing 
component is a polymer additive having a higher viscosity and/or higher 
melt temperature than the polyethylene component, such as a polyester, or 
is a crosslinking agent having an activation temperature at or greater 
than the melt temperature of the polyethylene. 
The polyethylene meltblown webs of the invention provide several desirable 
and yet apparently opposing properties in one fabric. The fabrics of the 
invention not only provide a barrier to the transmission of bacteria and 
other contaminants; they also provide desirable aesthetics such as a 
cloth-like feel and drapeability without the diminishment of the barrier 
characteristics. The webs of the invention are also gamma irradiation 
stable. Further, the meltblown webs can be produced at commercially 
feasible polymer throughput rates without a significant loss in barrier.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention will now be described more fully hereinafter with 
reference to the accompanying drawings, in which illustrative embodiments 
of the invention are shown. This invention may, however, be embodied in 
many different forms and should not be construed as limited to the 
embodiments set forth herein. Rather, this embodiment is provided so that 
the disclosure will be thorough and complete, and will fully convey the 
scope of the invention to those skilled in the art. Like numbers refer to 
like elements throughout. For purposes of clarity, the scale has been 
exaggerated. 
FIG. 1 is a fragmentary top view of a laminate fabric incorporating as a 
component thereof a meltblown polyethylene web of the present invention. 
The laminate is designated generally as 10. Laminate fabric 10 is 
partially cut away to illustrate the individual components thereof. The 
fabric is a three ply composite comprising an inner ply 12 sandwiched 
between outer plies 14 and 16. The composite fabric 10 has good strength, 
flexibility and drape and may be formed into various articles or garments 
such as sterile wraps, surgical gowns, surgical drapes and the like. The 
barrier properties of the fabric 10 make it particularly suitable for 
medical applications, but the fabric is also useful for any other 
application where barrier properties would be desirable, such as 
industrial garments, filtration media, and disposable wipes. 
Inner ply 12 is a nonwoven fibrous web comprising a plurality of meltblown 
thermoplastic microfibers 18. The microfibers preferably have an average 
fiber diameter of up to about 10 microns with very few, if any, of the 
fibers exceeding 10 microns in diameter. Usually the average diameter of 
the fibers will range from 1 to 6 microns. The meltblown microfibrous 
layer 12 is preferably manufactured in accordance with the process 
described in Buntin et al U.S. Pat. No. 3,978,185, with modifications 
thereto as described in more detail below. The meltblown layer 12 may 
suitably have a basis weight in the range of about 10 to 80 gsm, and 
preferably in the range of about 10 to 30 gsm. 
The thermoplastic polymer used to form the microfibers of meltblown layer 
12 is selected for its stability to gamma irradiation. Specifically, the 
polymer is a blend or composition which includes polyethylene as the 
majority component thereof. The term "polyethylene" is used in a general 
sense, and is intended to include various homopolymers, copolymers, and 
terpolymers of ethylene, including low density polyethylene, low density 
polyethylene, linear low density polyethylene, with linear low density 
polyethylene (LLDPE) being the most preferred. 
LLDPE can be produced form any of the well-known processes. LLDPE is 
typically produced by a catalytic solution or fluidized bed process under 
conditions known in the art. Zieglar-Natta or single site metallocene 
catalyst systems have been used to produce LLDPE. The resulting polymers 
are characterized by an essentially linear backbone. Various alpha-olefins 
are typically copolymerized with ethylene in producing LLDPE. The 
alpha-olefins, which preferably have 4 to 8 carbon atoms, are present in 
the polymer in an amount up to about 10% by weight. The most typical 
comonomers are butene, hexene, 4-methyl-1-pentene, and octene. 
Various properties of LLDPE, such as density and melt flow rate, can be 
controlled by the level of comonomer incorporation into the otherwise 
linear polymer backbone. Density ranges for LLDPE are relatively broad, 
typically from 0.87 to 0.95 g/cc (ASTM D-792). 
Melt flow rate ranges are also relatively broad and can range from about 
0.1 to about 150 g/10 min. The polymer selected preferably has a 
relatively high melt flow rate, as compared to conventional polymers used 
in meltblowing processes, as explained in more detail below. Preferred 
melt flow rates are at least about 125, more preferably at least about 
150, or higher, although polymers having lower melt flow rates can be 
used. The higher melt flow rates are advantageous because of the increased 
flowability of such polymers, which can assist in increasing polymer 
throughputs. The MFR is determined according to ASTM test procedure D-1238 
and refers to the amount of polymer (in grams) which can be extruded 
through an orifice of a prescribed diameter under a mass of 2.16 kg at 
230.degree. C. in 10 minutes. The MFR values as used herein have units of 
g/10 min. or dg/min. 
Examples of suitable commercially available LLDPE polymers include those 
available from Dow Chemical Company such as the ASPUN polymers; the EXACT 
Series of polymers available from the Exxon Chemical Company; and the 
Affinity polymers available from the Dow Chemical Company. An exemplary 
LLDPE polymer is ASPUN Type 6831A (150 MFR) from Dow Chemical Company. 
Polyethylene resins typically exhibit high elongation and excellent 
softness due at least in part to low melt strength, which make their use 
as a minor component of a polymer blend desirable in the production of 
nonwoven webs. However, prior attempts to process polyethylene resins, 
either as a sole or majority component, including prior meltblowing 
attempts, have met with limited success. Polyethylene cannot be readily 
processed, particularly at high polymer throughput rates required for 
commercial feasibility and economies of manufacture. Further, fine denier 
fibers can be difficult to produce, and problems can be associated even 
with the low speed production of large denier polyethylene fibers, such as 
polymer breaks, the formation of shot (i.e., formation of large globules 
of resin in a web), low strength webs, and the like. 
The inventors have found that polyethylene can be meltblown quite 
effectively at relatively high throughputs by blending a polyethylene 
resin with at least one polyethylene processing stabilizing agent or 
component. Preferably, the polyethylene processing stabilizing agent is 
stable to gamma irradiation. The polyethylene processing stabilizing agent 
is selected to stabilize the processing of the polyethylene resin so that 
the blend can be meltblown at high polymer throughputs to produce fine 
denier polyethylene-based fibers, i.e., 1 to 50 micron microfibers, and 
preferably 1 to 10 micron microfibers. Further, by adding a polyethylene 
processing stabilizing component, meltblown webs can be produced which 
exhibit barrier properties comparable with and even superior to barrier 
properties associated with conventional polypropylene meltblown webs. In 
addition, the resultant polyethylene web has good integrity and increased 
strength. 
The term "polyethylene processing stabilizing component" is used herein to 
refer to any of the types of agents or components, which, when blended 
with polyethylene, provide a polyethylene composition capable of being 
meltblown at high polymer throughputs, i.e., at least about 0.65 grams of 
polymer per capillary hole per minute ("g/h/m"), and up to about 1 g/h/m, 
and higher, without a corresponding increase in fiber size or denier, as 
determined by the resultant barrier properties of the meltblown web. 
In this regard, the polyethylene meltblown webs of the invention exhibit 
superior barrier properties, as determined using standard hydrohead 
measurements. As the skilled artisan will appreciate, hydrohead 
measurements refer to the barrier protection of fabrics evaluated in terms 
of centimeters of water pressure which can be withstood by the fabric 
before compromising the barrier thereof. 
Current industry standards require barrier fabrics to have a hydrohead of 
at least about 40 cm. The meltblown webs of the present invention exhibit 
a hydrohead measurement of at least about 40 centimeters ("cm") when 
produced at polymer throughputs approaching 1 g/h/m, and up to about 45 
and 50 cm when produced at polymer throughputs of about 0.65 g/h/m. 
The meltblown webs of the present invention are particularly advantageous 
because of the gamma radiation stability of the webs. Conventional 
polypropylene meltblown barrier fabrics can have good barrier properties, 
typically hydroheads of about 50 to about 55 cm. However, as discussed 
above, conventional grades of polypropylene are sensitive to degradation 
by gamma irradiation. Fabrics produced from such polymers tend to lose 
strength over time, becoming brittle as a result of the gamma irradiation. 
Indeed, as a result of the polymer degradation, the barrier properties of 
the fabric can be compromised, as evidenced by reduced hydrohead 
measurements from 50 to 55 cm to about 20 to 25 cm for polypropylene webs 
treated with gamma irradiation and thereafter stored. Also, the 
instability of the polymers to the irradiation results in the generation 
of distasteful odors in the product which are unacceptable to the 
consumer. 
In contrast, polyethylene is stable to gamma irradiation and does not 
substantially degrade. As a result, the webs of the invention do not 
suffer a significant loss in barrier properties over time and do not 
generate distasteful odors. For example, meltblown webs of the invention 
having an initial hydrohead of at least about 40 cm can be exposed to 
gamma irradiation and then stored for several days, without a substantial 
loss in hydrohead properties (i.e. no greater than about 5%). In contrast, 
gamma irradiated polypropylene webs typically rapidly degrade 
significantly, even to the point that the fabric actually loses its 
cohesiveness or falls apart. 
In addition, the polyethylene webs have desirable aesthetics, as compared 
to polypropylene meltblown webs, i.e., the webs of the invention have 
improved softness, flexibility, and drapeability. 
Numerous agents can be employed as the polyethylene processing stabilizing 
component of the polyethylene composition or blend. The polyethylene 
processing stabilizing agent is selected to provide a stiffening effect to 
the polyethylene resin at low additive amounts. The polyethylene 
processing stabilizing component is added to the polyethylene resin in an 
amount sufficient to provide the desired degree of processing stability, 
and preferably is the minor component of the polyethylene/polyethylene 
processing stabilizing agent composition. One advantage of the invention 
is that small amounts of the additive can be used, so as to preserve the 
desirable qualities of the polyethylene resin, while concurrently 
enhancing its spinnability. This is also advantageous for purposes of 
economies of manufacture by minimizing costs associated with the use of 
additional resin components. 
In one embodiment of the invention, the polyethylene processing stabilizing 
agent is a polymer having a higher viscosity and/or a higher melt strength 
than the polyethylene resin component. Numerous polymers may serve as the 
polyethylene processing stabilizing agent, including, but not limited to, 
polyolefins, such as polypropylene, polymethyl pentene (TPX) copolymer, 
and ethylene-propylene copolymers; and polycondensate polymers such as, 
but not limited to, polyesters and polyamides. For the purposes of this 
embodiment of the invention, polyesters are preferred. 
In this embodiment of the invention, preferably the polymer is added to the 
polyethylene in an amount ranging from about 1 to about 15 percent by 
weight based upon the weight of the polyethylene polymer, and preferably 
from about 5 to about 10 percent by weight. The polymer can be added to 
the blend in an amount greater than about 15 percent by weight, but the 
inventors have found that the degree of improvement in polyethylene 
processing achieved by amounts of polymer above this level is minimal, as 
evidenced by the barrier protection achieved at a particular polymer 
throughput rate. 
As will be appreciated by those skilled in the art, polymers such as 
polyester are particularly advantageous in the manufacture of ply 12 
because this polymer has very good stability to gamma irradiation. 
However, polyolefins, such as polypropylene, may be employed in the 
manufacture of ply 12 as the component of a polymeric blend, so long as 
the composition is rendered gamma irradiation stable. 
Other additives conventionally used in the production of meltblown 
microfibers can also be incorporated in the polymer blend such as UV 
stabilizers, pigments, delusterants, lubricants, wetting agents, 
antistatic agents, nucleating agents, water and alcohol repellents, etc, 
in the conventional amounts, which are typically no more than about 10% by 
weight. Polymeric additives may also be used in conjunction with the 
blends which impart specific benefits to either processing and/or end use. 
For example, plastomers, compatibilizers, viscosity modifiers or diluents 
which affect phase domain size or crystallinity may be included. 
The components of the polyethylene composition can be combined in manners 
utilized in conventional extrusion processes. For example, the components 
can be dry blended in any acceptable form prior to being directed into the 
extruder and heated in the barrel of an extruder to form a melt blend. In 
some cases, sufficient mixing of the components may be achieved in the 
extruder as the components are converted to the molten state, although it 
may be preferable to use an additional mixing zone or step. 
Advantageously, meltblown web 12 is electrically treated to improve 
filtration properties of the web. Such electrically treated fibers are 
known generally in the art as "electret" fibrous webs. Electret fibrous 
filters are highly efficient in filtering air because of the combination 
of mechanical entrapment of particles in the air with the trapping of 
particles based on the electrical or electrostatic characteristics of the 
fibers. Both charged and uncharged particles in the air, of a size that 
would not be mechanically trapped by the filtration medium, will be 
trapped by the charged nature of the filtration medium. Meltblown web 12 
can be electrically treated using techniques and apparatus know in the 
art. 
Outer ply 14 of the composite fabric 10 is a nonwoven web of spunbonded 
substantially continuous thermoplastic filaments. The spunbonded web 14 
may be produced using well known spunbonding processes, and may suitably 
have a basis weight in the range of about 10 to about 100 gsm. The 
thermoplastic filaments of ply 14 can be made of any of a number of known 
fiber forming polymer compositions. Such polymers include those selected 
from the group consisting of polyolefins such as polypropylene and 
polyethylene, polyesters, polyamides, and copolymers and blends thereof. 
Preferably, the polymer is a gamma irradiation stable polymer or polymer 
composition, such as polyester or polyamide, but polymers such as 
polypropylene can also be used so long as steps are taken to impart gamma 
irradiation stability thereto. 
Outer ply 16 may be either a web of spunbonded substantially continuous 
thermoplastic filaments or a web of staple fibers. In the embodiment 
illustrated, ply 16 is a nonwoven web of spunbonded substantially 
continuous thermoplastic filaments of a composition and basis weight 
similar to outer ply 14. The continuous filaments or staple fibers of 
outer ply 16 may be selected from the same polymers as described above for 
ply 14. Additionally, the staple fibers may be natural or synthetic fibers 
having hydrophilic properties to give one surface of the composite fabric 
absorbent characteristics. Examples of hydrophilic fibers include cotton 
fibers, wool fibers, rayon fibers, acrylic fibers, and fibers formed of 
normally hydrophobic polymers which have been treated or chemically 
modified to render them hydrophilic. When ply 16 is a nonwoven web of 
staple fibers, the nonwoven web can be a carded web or a wet-laid web of 
staple fibers. 
Layers 12, 14 and 16 of the laminate fabric of the present invention can be 
bonded together to form a coherent fabric using techniques and apparatus 
known in the art. For example, layers 12, 14 and 16 can be bonded together 
by thermal bonding, mechanical interlocking, adhesive bonding, and the 
like. Preferably, laminate fabric 10 includes a multiplicity of discrete 
thermal bonds distributed throughout the fabric, bonding layers 12, 14 and 
16 together to form a coherent fabric. 
In addition, as will be appreciated by the skilled artisan, laminate fabric 
10 can include one or more additional layers to provide improved barriers 
to transmission of liquids, airborne contaminants, etc., or additional 
supporting layers. 
Meltblown web 12 of the invention exhibits a variety of desirable 
characteristics, which make the web particularly useful as a barrier 
component in a laminate fabric, such as a sterile wrap. The microfibers of 
meltblown web 12 are formed of a gamma irradiation stable polymer 
composition so that the fabric does not substantially degrade upon 
treatment with gamma radiation. This can prevent a significant loss of 
barrier properties over time, as can result with the use of polypropylene 
barrier fabrics. Further, the fabrics do not suffer from objectional 
odors, as can result with polypropylene fabrics treated with gamma 
radiation. 
In addition, because the majority component of the microfibers is 
polyethylene, which is a relatively soft and elongatable polymer, the 
resultant fabric can exhibit significantly improved aesthetic properties 
such as a soft hand or feel, improved drape and flexibility, as compared 
to currently available commercial products. 
Referring now to FIG. 2, an illustrative process for forming the meltblown 
web 12 and the laminate fabric 10 of the present invention is illustrated. 
FIG. 2 includes a simplified, diagrammatic illustration of an apparatus, 
designated generally as 30, capable of carrying out the process of forming 
a meltblown web in accordance with the invention. Conventional meltblowing 
apparatus known in the art can be used. 
In meltblowing, thermoplastic resin is fed into an extruder where it is 
melted and heated to the appropriate temperature required for fiber 
formation. The extruder feeds the molten resin to a special meltblowing 
die. The die arrangement is generally a plurality of linearally arranged 
small diameter capillaries. The resin emerges from the die orifices as 
molten threads or streams into high velocity converging streams of heated 
gas, usually air. The air attenuates the polymer streams and breaks the 
attenuated streams into a blast of fine fibers which are collected on a 
moving screen placed in front of the blast. As the fibers land on the 
screen, they entangle to form a cohesive web. 
The technique of meltblowing is known in the art and is discussed in 
various patents, e.g., Buntin et al, U.S. Pat. No. 3,978,185; Buntin, U.S. 
Pat. No. 3,972,759; and McAmish et al, U.S. Pat. No. 4,622,259. 
In the present invention, process parameters of the meltblowing process are 
selected and controlled to form the microfine microfibers of the meltblown 
webs of the invention while minimizing or eliminating processing 
complications which can result form processing polyethylene resins. These 
complications include, for example, low polymer throughputs, excessive 
elongation and breakage of the polymer filaments, particularly at high 
polymer throughputs, formation of polymer globules in the web, high denier 
fibers, lack of structural integrity of the meltblown web, all of which 
can interfere with processing efficiency and cause defects in the 
meltblown web. In addition, the blend components which impart particular 
desired processing properties and end product characteristics can also 
further minimize or eliminate these and other undesirable processing 
conditions. 
It has been found that relatively high MFR polyethylene polymers, i.e., at 
least about 125 MFR, and preferably at least about 150 MFR or higher, can 
be attenuated in a heated high velocity air stream in such a way suitable 
for the stable production of microfine polyethylene microfibers and 
concurrent formation of a microfibrous nonwoven web. Further, the 
conditions can be controlled to achieve high polymer throughputs at 
commercially feasible rates, i.e., least about 0.65 g/h/m, and higher, 
without compromising the resultant fiber size and barrier properties of 
the webs. Specifically, these conditions include controlling polymer melt 
temperature, as well as selecting an appropriate MFR polymer, to promote 
formation of microfine polyethylene microfibers and high barrier webs at 
commercial throughputs without significantly impairing or adversely 
impacting the process conditions. 
The inventors have found that increasing the melt temperature of the blend 
can result in improved processability of the polyethylene component. 
Polyethylene resins are typically heated to a temperature of about 
510.degree. F. to about 520.degree. F. (about 265.degree. C.) to about 
270.degree. C.) in conventional meltspinning operations for fiber 
formation. In the present invention, advantageously the melt temperature 
of the blend is increased at least about 10%, relative to conventional 
processing parameters for polyethylene systems, i.e., to at least about 
580.degree. F. (300.degree. C.). This can be particularly advantageous as 
described in more detail below when the blend includes a polymer having a 
melt temperature and/or viscosity higher than the majority polyethylene 
component. 
When the polyethylene processing stabilizing agent is a polymer additive 
having a higher melt temperature and/or higher viscosity as compared to 
the polyethylene resin, preferably the melt temperature of the 
polyethylene composition is selected to melt the polyethylene resin and 
also to melt and degrade the other polymer component sufficiently so that 
a flowable melt blend is formed. The degree and uniformity of mixing of 
the components can also be optimized by increasing the melt temperature of 
the composition. 
For example, when polyester is the polyethylene processing stabilizing 
agent, it is preferred to increase the melt temperature of the 
polyethylene composition to a temperature approaching the melt temperature 
of the polyester component, i.e., to at least about 580.degree. F. The 
temperature selected is sufficiently high to thermally soften and degrade 
the polyester additive and to obtain optimum mixing of the polyethylene 
and the minor polyester component of the blend. Further, as noted above, 
it is also believed that increasing the melt temperature of the blend 
improves the processability of the polyethylene component. Accordingly, 
the increase in melt temperature is adjusted in accordance with the 
characteristics of the blend system being processed. 
Accordingly, as will be appreciated by the skilled artisan, the melt 
temperature of the blend can be dependent upon a variety of factors, such 
as, for example, the specific polyethylene processing stabilizing agent 
used, the melting point and/or viscosity of the agent, the melt flow rate 
of the polyethylene majority component, and the like. 
It is noted that the as the melt flow rate (MFR) of the polyethylene 
increases, for example to levels above 150, and greater, the melt 
temperature of the blend does not necessarily have to increase as much as 
with polymers having a melt flow rates at or below this range to achieve 
the same end product. This does not, however, necessarily preclude the use 
of higher melt temperatures, particularly when the polyethylene processing 
stabilizing agent has a higher melt temperature. 
Referring again to FIG. 2, as shown, the polyethylene polymer and the 
polyethylene processing stabilizing agent are placed in a feed hopper 32 
of a screw extruder 34 where they are heated to a temperature sufficient 
to melt the polymer. Advantageously, the polyethylene polymer has a MFR of 
at least 125. Alternatively, as will be appreciated by the skilled 
artisan, polyethylene polymers having a MFR of less than 125 can be used 
in combination with a visbreaking agent, such as a peroxide, which 
degrades the polymer and reduces the melt flow rate thereof to form a 
polymer which exiting the extruder has a MFR of at least 125. Visbreaking 
agents and techniques are known in the art. 
The molten polymer composition is forced by the screw through conduit 36 
into a spinning block 38 and the polymer composition is extruded from the 
spin block 38 through a plurality of small diameter capillaries 40 into a 
high velocity gas stream, such as compressed air designated generally as 
42. The temperature and velocity of the air is controlled as described 
above to form microfine meltblown microfibers having an average fiber 
diameter between about 1 and 50 microns, preferably between 1 and 10 
microns. 
The meltblown microfibers are deposited onto a foraminous endless belt 44 
and form a coherent web 46 which is removed from the belt by a pair of 
consolidation rolls 48. The rolls optionally may include bonding elements 
(not shown) in the form of a relief pattern to provide a desired extent of 
point bonding of the microfibrous web. At these points where heat and 
pressure is applied, the fibers fuse together, resulting in strengthening 
of the web structure. 
The microfibrous web 46 can then be electrically treated to impart an 
electrical charge to the fabric, and thus improve its filtration 
capabilities. Techniques and apparatus for electrically treating a 
nonwoven web are known in the art. 
The microfibrous web can be removed from the assembly and stored on a roll. 
Alternatively, as illustrated, the microfibrous web can be passed on to 
additional manufacturing processes, as described in more detail below. 
As illustrated in FIG. 2, the microfibrous web 46 can be fed through 
consolidation rolls 48 and is combined with a pre-formed web 14 and 
preformed web 16, drawn from supply rolls 50 and 52, respectively, to form 
a laminate 54. 
As described above, at least one of preformed webs 14 and 16 can be 
spunbonded webs of continuous filaments. The spunbonding process involves 
extruding a polymer through a generally linear die head or spinneret for 
melt spinning substantially continuous filaments. The spinneret preferably 
produces the filaments in substantially equally spaced arrays and the die 
orifices are preferably from about 0.002 to about 0.040 inches in 
diameter. 
The substantially continuous filaments are extruded from the spinneret and 
quenched by a supply of cooling air. The filaments are directed to an 
attenuator after they are quenched, and a supply of attenuation air is 
admitted therein. Although separate quench and attenuation zones can be 
used, it will be apparent to the skilled artisan that the filaments can 
exit the spinneret directly into the attenuator where the filaments can be 
quenched, either by the supply of attenuation air or by a separate supply 
of quench air. 
The attenuation air may be directed into the attenuator by an air supply 
above the entrance end, by a vacuum located below a forming wire or by the 
use of eductors integrally formed in the attenuator. The air proceeds down 
the attenuator, which narrows in width in the direction away from the 
spinneret, creating a venturi effect and causing filament attenuation. The 
air and filaments exit the attenuator, and the filaments are collected on 
the collection screen. The attenuator used in the spunbonding process may 
be of any suitable type known in the art, such as a slot draw apparatus or 
a tube-type (Lurgi) apparatus. 
Alternatively, at least one of webs 14 and 16 can be a carded web formed of 
staple length textile fibers, or a wet-laid or air-laid web of staple 
fibers, including bicomponent staple length textile fibers. While 
pre-formed webs 14 and 16 are shown, it will be appreciated that the webs 
could be formed in a continuous in-line process and combined with 
meltblown web 46. It will also be understood that additional webs could be 
combined with meltblown web 46, on one or both sides thereof. 
The three-layer laminate 54 is conveyed longitudinally as shown in FIG. 2 
to a conventional thermal fusion station 56 to provide a composite bonded 
nonwoven fabric 10. The fusion station is constructed in a conventional 
manner as known to the skilled artisan, and advantageously includes 
bonding rolls. Preferably, the layers are bonded to provide a multiplicity 
of thermal bonds distributed throughout the laminate fabric. Because of 
the wide variety of polymers which can be used in the fabrics of the 
invention, bonding conditions, including the temperature and pressure of 
the bonding rolls, vary according to the particular polymers used, and are 
known in the art for differing polymers. 
Although a thermal fusion station in the form of bonding rolls is 
illustrated in FIG. 2, other thermal treating stations such as ultrasonic, 
microwave or other RF treatment zones which are capable of bonding the 
fabric can be substituted for the bonding rolls of FIG. 2. Such 
conventional heating stations are known to those skilled in the art and 
are capable of effecting substantial thermal fusion of the nonwoven webs. 
In addition other bonding techniques known in the art can be used, such as 
by hydroentanglement of the fibers, needling, and the like. It is also 
possible to achieve bonding through the use of an appropriate bonding 
agent as known in the art. 
The resultant fabric 10 exits the thermal fusion station and is wound up by 
conventional means on a roll 58. 
The present invention is subject to numerous variations. For example, the 
polymers used in the present invention may be specifically engineered to 
provide or improve a desired property in the composite. For example, any 
one of a variety of adhesion-promoting, or "tackifying," agents such as 
ethylene, vinyl acetate copolymers, may be added to the polymers used in 
the production of any of the webs of the composite structure, to improve 
inter-ply adhesion. Further, at least one of the outer webs may be treated 
with a treatment agent to render any one of a number of desired properties 
to the fabric, such as flame retardancy, hydrophilic properties, and the 
like. 
Additionally, the fibers or filaments used in any of the webs of the 
composite structure may comprise a polymer blend or bicomponent polymeric 
structure. For example, in one embodiment of the invention, fibers 
employed in the carded web can be sheath/core or similar bicomponent 
fibers wherein at least one component of the fiber is polyethylene. The 
bicomponent fibers can provide improved aesthetics such as hand and 
softness based on the surface component of the bicomponent fibers, while 
providing improved strength, tear resistance and the like due to the 
stronger core component of the fiber. Preferred bicomponent fibers include 
polyolefin/polyester sheath/core fibers such as a 
polyethylene/polyethylene terephthalate sheath core fiber. 
Additionally, although the process illustrated in FIG. 2 employs a 
meltblown web sandwiched between two spunbonded webs, it will be apparent 
that different numbers and arrangements of webs can be employed in the 
invention. For example, the composite nonwoven fabric of the invention may 
comprise a spunbonded/meltblown web composite. Alternatively, the 
meltblown web can be sandwiched between a spunbonded web and a carded web. 
Additionally, several meltblown layers can be employed in the invention 
and/or greater numbers of other fibrous webs can be used. Nonwoven webs 
other than carded webs are also advantageously employed in the nonwoven 
fabrics of the invention. Nonwoven staple webs can be formed by air 
laying, garnetting, and similar processes known in the art. 
The present invention will be further illustrated by the following 
non-limiting examples. 
EXAMPLE 1 
Meltblown webs were formed by meltblowing a composition comprising a 
polyethylene resin having a melt flow rate of 150 g/min. available from 
Dow Chemical Company under the trade designation ASPUN 6831A, with varying 
amounts (0%, 5%, 10% and 15% by weight based on the weight of the 
polyethylene) of a polyethylene processing stabilizing agent, specifically 
polyester available from Hoechst-Celanese Corporation under the trade 
designation 2000A (a polybutylene terephthalate, "PBT"). The composition 
was meltblown at varying polymer throughputs (0.65, 0.8, 0.9 and 1 grams 
per hole per minute or "g/h/m"). Hydrohead in centimeters was measured for 
each web. Specific processing parameters and hydrohead measurements of the 
webs including polyester are set forth below in Table 1; processing 
parameters and hydrohead measurements of 100% polyethylene webs are set 
forth below in Table 2. 
TABLE 1 
__________________________________________________________________________ 
PROCESSING CONDITIONS AND BARRIER PROPERTIES 
FOR MELOWN POLYETHYLENE WEBS WITH VARYING PERCENTAGES OF POLYESTER 
MELT AIR POLYMER BASIS HYDRO- 
SAM- 
% TEMP, 
TEMP, THROUGHPUT, 
WEIGHT, 
HEAD STD. 
SET AIR 
TABLE 
PLE.sup.1 
PBT.sup.2 
.degree.F. 
.degree.F. 
SCFM 
DCD G/H/M GSM (CM).sup.3 
DEV. 
BACK 
GAP 
VAC. 
__________________________________________________________________________ 
1A 5 580 410 550 5 0.65 27 41.85 2.85 
0.060 
0.080 
10.2 MPS 
2A 10 580 410 600 5 0.65 27 49.75 0.89 
0.060 
0.080 
10.2 MPS 
2XX 10 580 385 600 5 0.65 27 50.2 1.5 0.060 
0.080 
10.2 MPS 
3A 15 580 410 600 5 0.65 27 48.95 0.64 
0.060 
0.080 
10.2 MPS 
4A 5 580 410 600 5 0.8 27 47.25 1.55 
0.060 
0.080 
10.2 MPS 
5A 10 580 410 600 5 0.8 27 49.85 1.39 
0.060 
0.080 
10.2 MPS 
6A 15 580 410 600 5 0.8 27 49.45 1.61 
0.060 
0.080 
10.2 MPS 
7A 15 580 410 600 5 0.8 23 46.8 2.12 
0.060 
0.080 
10.2 MPS 
8A 10 580 410 600 5 0.8 23 45.9 2.24 
0.060 
0.080 
10.2 MPS 
9A 5 580 410 600 5 0.8 23 44.5 1.25 
0.060 
0.080 
10.2 MPS 
10A 5 580 410 600 5 0.9 23 36.5 2.07 
0.060 
0.080 
10.2 MPS 
11A 5 580 410 600 5 0.9 27 43.8 2.04 
0.060 
0.080 
10.2 MPS 
12A 10 580 410 600 5 0.9 23 42.4 1.58 
0.060 
0.080 
10.2 MPS 
13A 10 580 410 600 5 0.9 27 43.35 1.56 
0.060 
0.080 
10.2 MPS 
14A 15 580 410 600 5 0.9 23 43.7 1.87 
0.060 
0.080 
10.2 MPS 
15A 15 580 410 600 5 0.9 27 44.05 1.5 0.060 
0.080 
10.2 MPS 
16A N/A 580 410 600 5 N/A N/A N/A 0.060 
0.080 
10.2 MPS 
17A 5 580 410 600 5 1 27 37.05 4.28 
0.060 
0.080 
10.2 MPS 
18A N/A 580 410 600 5 N/A N/A N/A 0.060 
0.080 
10.2 MPS 
19A 10 580 410 600 5 1 27 40.85 1.68 
0.060 
0.080 
10.2 MPS 
20A N/A 580 410 600 5 N/A N/A N/A 0.060 
0.080 
10.2 MPS 
21A 15 580 410 600 5 1 27 41.15 2.32 
0.060 
0.080 
10.2 
__________________________________________________________________________ 
MPS 
.sup.1 Polyethylene is LLDPE 5831A from Dow Chemical. 
.sup.2 PBT is polybutylene terephthalate, 2000A, from Hoechst Colanese 
Corporation. 
.sup.3 Hydrohead measurement is the average of 10 samples. 
TABLE 2 
__________________________________________________________________________ 
COMATIVE MELOWING DATA FOR 100% POLYETHYLENE WEBS 
MELT AIR POLYMER HYDRO- 
SAM- 
TEMP, 
TEMP, THROUGHPUT, 
BASIS HEAD(CM).sup.2 / 
AIR 
TABLE 
PLE.sup.1 
.degree.F. 
.degree.F. 
SCFM 
DCD G/H/M WEIGHT, GSM 
STD. DEV. 
SET BACK 
GAP 
VAC. 
__________________________________________________________________________ 
MATERIAL PRODUCED AT .65 G/H/M 
7 578 396 550 5 0.65 27 GSM 44.8/2.3 
0.060 0.080 
9.4 MPS 
15 577 350 600 5 0.65 27 GSM 46.1/2.02 
0.060 0.080 
9.4 MPS 
MATERIAL PRODUCED AT .7 G/H/M 
6 580 420 450 5 0.70 20 GSM 34.4/1.71 
0.060 0.080 
8.2 MPS 
MATERIAL PRODUCED AT .8 G/H/M 
1 580 450 550 5 0.80 27 GSM 33.05/2.08 
0.060 0.080 
8.2 MPS 
10 577 395 550 5 0.80 27 GSM 39.2/2.66 
0.060 0.080 
9.4 MPS 
14 577 350 600 5 0.80 27 GSM 42.6/1.84 
0.060 0.080 
9.4 MPS 
MATERIAL PRODUCED AT .9 G/H/M 
2 580 430 550 5 0.90 27 GSM 36.05/2.2 
0.060 0.080 
8.2 MPS 
8 577 350 600 5 0.90 27 GSM 37.3/4.9 
0.060 0.080 
9.4 MPS 
12 577 397 550 5 0.90 27 GSM 38./2 0.060 0.080 
9.4 MPS 
MATERIAL PRODUCED AT 1. G/H/M 
3 590 410 550 5 1.00 27 GSM 36/1.33 0.060 0.080 
8.2 MPS 
4 590 421 450 5 1.00 18 GSM 29.25/4.29 
0.060 0.080 
10.2 MPS 
5 590 421 450 5 1.00 30 GSM 31.93/3.37 
0.060 0.080 
10.2 MPS 
9 577 350 600 5 1.00 27 GSM 36/1.94 0.060 0.080 
9.4 MPS 
11 577 397 550 5 1.00 27 GSM 35.2/1.23 
0.060 0.080 
9.4 MPS 
13 577 395 600 5 1.00 27 GSM 38.5/1.7 
0.060 0.080 
9.4 
__________________________________________________________________________ 
MPS 
.sup.1 Polyethylene is LLDPE 6831A from Dow Chemical. 
.sup.2 Hydrohead measurement is the average of 10 samples. 
Hydrohead is a measurement of the ability of a fabric to withstand water 
pressure applied to one surface of the fabric before breaching or 
impairing the barrier properties thereof. The barrier protection, or 
hydrohead, of the meltblown fabrics was evaluated in terms of centimeters 
of water pressure which can be withstood by the fabric before compromising 
the barrier thereof. A sheet of the fabric of the invention can exhibit 
hydro head measurements of up to about 50 cm at commercially feasible 
polymer throughputs of about 0.65 g/h/m, and up to about 40 cm at even 
higher throughputs up to about 1 g/h/m. For purposes of comparison, 100% 
polyethylene meltblown fabrics were also prepared and hydrohead measured. 
It is apparent from the data set forth in Tables 1 and 2 that as polymer 
throughput increases, the addition of a polyethylene processing 
stabilizing agent provides improved web barrier properties. In addition, 
as throughputs increase, the addition of the polyethylene processing 
stabilizing agent improved polyethylene processing, i.e., decreased shot, 
increased integrity, etc. 
EXAMPLE 2 
Trilaminate fabrics including outer spunbonded polyester and polyamide webs 
thermally bonded to samples of the meltblown webs as prepared above in 
Example 1 are prepared. The laminate fabrics are thermally bonded. The 
fabrics exhibit good barrier properties. Further, the laminate fabrics of 
the invention exhibit high flexibility (i.e., ease of handling) and 
superior softness. 
The foregoing examples are illustrative of the present invention, and are 
not to be construed as limiting thereof. The invention is defined by the 
following claims, with equivalents of the claims to be included therein.