CA1290517C - Nonwoven fabric with improved abrasion resistance - Google Patents

Nonwoven fabric with improved abrasion resistance

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Publication number
CA1290517C
CA1290517C CA000519563A CA519563A CA1290517C CA 1290517 C CA1290517 C CA 1290517C CA 000519563 A CA000519563 A CA 000519563A CA 519563 A CA519563 A CA 519563A CA 1290517 C CA1290517 C CA 1290517C
Authority
CA
Canada
Prior art keywords
web
fabric
fibers
square meter
veneer
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
CA000519563A
Other languages
French (fr)
Inventor
Larry Hughey Mcamish
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ethicon Inc
Original Assignee
Ethicon Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to US78284585A priority Critical
Priority to US782,845 priority
Application filed by Ethicon Inc filed Critical Ethicon Inc
Application granted granted Critical
Publication of CA1290517C publication Critical patent/CA1290517C/en
Anticipated expiration legal-status Critical
Application status is Expired - Fee Related legal-status Critical

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Classifications

    • DTEXTILES; PAPER
    • D04BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
    • D04HMAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
    • D04H1/00Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
    • D04H1/40Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
    • D04H1/54Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties by welding together the fibres, e.g. by partially melting or dissolving
    • D04H1/56Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties by welding together the fibres, e.g. by partially melting or dissolving in association with fibre formation, e.g. immediately following extrusion of staple fibres

Abstract

NONWOVEN FABRIC WITH IMPROVED ABRASION RESISTANCE

ABSTRACT

A melt-blown microfiber fabric having improved surface abrasion resistance is disclosed, having a surface veneer of melt-blown fibers with an average fiber diameter of greater than 8 microns and in which 75% of the fibers has a fiber diameter of at least 7 microns and a wet and dry abrasion resistance of greater than 15 cycles to pill. The method of producing the melt-blown microfiber fabric having improved abrasion resistance comprises forming at least one core web of thermoplastic melt-blown microfibers having a greater than 0.8N per gram per square meter tensile strength to weight ratio, a minimum Elmendorf tear strength, and a specific basis weight of 14 grams per square meter to 85 grams per square meter. At least one unreinforced surface veneer web of melt-blown thermoplastic fibers is formed on the core web. The veneer web has a high initial autogenous bonding and a greater than 8 microns average fiber diameter.
The veneer web also has a 3 grams per square meter to 10 grams per square meter basis weight range and a wet and dry surface abrasion resistance greater than 15 cycles to pill.
The veneer web is directly contiguous to the at least one core web.

Description

~90$~7 NONWOVEN FABRIC WITH IMPROVED ABRASION RESISTANCE

Field of the Invention The present invention relates to improved nonwoven fabrics made of microfiber web~, characterized by high ~urfa~e abrasion resi6tance, and especially suitable for u6e as medical fabric6.

Backaround of the Invention The pregent invention i~ directed to nonwoven fabrics and particularly to medical fabrics. The term l'medical fabric~l, as u6ed herein, refers to a fabric which may be used in 6urgical drapes, surgical gowns, instrument wraps, or the like. Such medical fabrics have certain required properties to insure that they will perform properly for the intended u6e. These properties include strength, the capability of resisting water or other liquid penetration, often referred to a~ ~trike-through re6istance, breathability, 60ftnes6, drape, 6terilizability, and bacterial barrier properties.

The use of microfiber webs in application6 where barrier propertie~ are desired is known in the prior art.
Microfiber~ are f~bers having a diameter of from le6s than 1 micron to about 10 microns. Microfiber webs are often referred to as melt-blown webs as they are u~ually made by a melt blowing proce6s. It is generally recognized that the use of relatively ~all diameter fiber~ in a fabric Btructure hould allow the achievement of high repellency or filtration properties without undue compromise of breathability. Microflber web fabric~ made heretofore, and intended for u6e as medical fabrics, have been composites of microfiber webs laminated or otherwise J~;U-61 ~90517 bonded to spunbonded thermoplastic fiber webfi, or films, or other reinforcing webs which provide the requisite stren~th.

Another important property for both nonwoven fabrics and ~edical ~abrics i~ abra~ion resistance. Resistance to surface abra6ion affects not only the performance of a fabric but may also affect the aesthetics of a fabric.
For example, linting of broken ~urface fibers is particularly undesirable in medical fabrics. In addition, surface abrasion can affect the strike-through resistance and bacterial barrier properties of a medical fabric.
Linting, a~ well as pilling or clumping of surface fibers i8 also unacceptable for many wipe applications. An outer lS layer of a spunbonded fiber web, film or other reinforcing web has been used to develop surface abrasion resistance in melt-blown fiber products.

U.S. Patent 4,041,203 discloses a nonwoven fabric made by combining microfiber webs and spunbonded webs to produce a medical fabric having good drape, breathability, water repellency, and surface abrasion resis~ance.

U.S. Patent 4,196,245 discloses combinations o~ melt-blown ~- 25 or microfine fibers with apectured films or with apertured films and spunbonded fabrics. Again, the apertured film and the spunbonded fabric are the components in the finished, nonwoven fabric which provide the strength and surface stability to the fabric.
U.K. Patent Application 2,132,939 discloses a melt-blown fabric laminate suitable as a medical fab~ic, comprising a melt-blown microfiber web welded at localized points ts a nonwoven reinforcing web of dificontinuous fibers, such as an air laid or wet laid web of staple fibers.

~SU-61 .~

1~905~

While ~he above-mentioned fabrics have the potential to achieve a better balance of repellency and breathability compared to other prior art technologies not using microfiber~, the addition of surface reinforcing layer6 of S relatively large diameter fibers limit6 their advantages.
U.S. Patent No. 4,436,780 to Hotchki~s et al. describe6 a melt-blown wipe with low linting, reduced ~reaking and improved absorbensy, comprising a middle layer of melt-blown fiber~ and on either ~ide thereof, a ~punbonded layer.

In order to improve surface abrasion re~istance and reduce lint of melt-blown web~ generally, it i6 al~o known to compact the web to a high degree, or add or increase the `_- 15 level of binder. Copending Canadian Patent, se~. No. 515,440-5 filedon August 6, 1986 provides a medical fabric f~om an unreinforced web or webs of microfine f~s. The fabric i6 unreinforced in that it need not be laminated or bonded to another type of web or film to provide adequate strength to be used in medical applications. The fabric also achieves a balance of repellency, strength, breathability and other aesthetics superior to prior art fabrics. However, as described in the application, in order to render the fabric especially effective for use in applications requiring high abra6ion ~, resistance, a ~mall amount of chemical binder may be ~~ applied to the surface of the fabric.

U.K. Patent 2,104,562 discloses surface heating of a melt-blown fabric to give it an anti-linting fini~h. It is also generally known to u6e a level of heat and compaction, e.g., embos6ing, of a microfiber web to improve abrasion re6i6tance.

The above fabric~ which have reinforcing web~ have to be a66embled using two or more web forming technologie6.

, J: ~

1~9~5~7 re~ulting in increased proces6 complexity and c06t.
Furthermore, the bonding of relatively conventional fibrous webs to the microfiber~, the compaction or the addition of binder to a microfiber web can result in stiff fabrics, e6pecially where high strength is desired.

Brief SummarY of the Invention The pre6ent invention provid~s a melt-blown microfiber e~bos6ed web with improved wet and dry ~urface abra6ion resiRtance of greater than 15 cycle6 to pill. The abrasion resistance i~ achieved without the u~e of additional binder and doe6 not sacrifice the drape or hand of the material.
According to the pre6ent invention, surface abrasion reaistance is achieved with the addition of a surface veneer of melt-blown fibers having an average fiber diameter of greater than 8 microns, and in which 75% of the fibers have a fiber diameter of at least 7 microns.
The surface veneer may be bonded to a melt-blown core web, ~uch as that described i:n th~ aforelTentioned copending ~pplication, by heat embos6ing or other methods. The bondinq of the veneer to the core web and heat embossing of the core web may be achieved in one processing step. In addition, when the core web and veneer web are produced in one fabric making step using multiple die6, the veneer may be produced atop the core web, with high initial autogenous bonding, eliminating the need to bond the ~eneer to the core web.

By eliminating the need for additional binder, the present invention provides a method for making melt-blown microfiber web without the additional proce66ing steps of adding binder and dEying and/or curing the bindec. Also, 5~
.

potential heat damage during binder curing or drying which may adversely affect the drape and hand of a fabric i8 eliminated. Stiffening of the fabric through the use of binder solution i~ also eliminated, thereby permitting adjustment of proces6ing condition6 of the core web to maximize otheL propertie6.

In addition, the u~e of a surface veneer of melt-blown fibers pcovides a ~abric with a combination of drape and surface abrasion re~istance which cannot be achieved with the addition of binder materials. ~he u~e of melt-blown fibers tO form the surface veneer alco provide6 economic advantage6 and minimizes the technoloqies necessary to produce the fabric.
Thu6, the present inven~ion provides an improved melt-blown or microfiber fabric with improved surface abrasion resistance but without binder, which may be used as a medical fabric or wipe or in other applications where high surface abrasion resistance is required. In a preferred embodiment, the fabric of the present invention compri6es an unreinforced, melt-blown, microfiber fabcic with improved surface abrasion resi6tance, e.g., greater than 15 cycles to pill, suitable for use as a medical fabric, ~aid fabric having a minimum gtab tensile strength to weight ratio greater than 0.8 N per gram per square meter, and a minimum Elmendorf tear strength to weight ratio greater than 0.04 N per gram per ~quare meter. In a most preferred embodiment of the present invention, the embossed unreinforced fabrics described above have a wet abrasion resistance of at least 30 cycles to pill, and a dry abra~ion resistance of at least 40 cycle~ to pill.
The6e properties are achieved while also obtaining the properties of repellency, air permeability and e~pecially JSU-5~

~.~905i17 drapability -that are desired for -the use of the fabric in medical applications.

~ccording to a still further broad aspect of the present invention there is provided an improved unreinforced melt-blown microfiber fabric having improved surface abrasion resistance, the fabric comprises at least one unreinforced thermoplastic melt-blown microfiber core web having an average of length of greater than 10 cm, and an average diameter not exceeding 7 microns. The core web also has a minimum grab tensile s-trength to weight ratio greater than 0.8N per gram per square meter and a minimum Elmendorf tear strength to weight ratio greater than 0.04N per gram per square meter. The core web has a basis weight in the range of 14 grams per square meter to 85 grams per square meter, and at least one unreinforced surface veneer web on the core web. The veneer web is formed of melt-blown thermoplastic fibers having an average fiber diameter of greater than 8 microns in which 75% of the fibers have a diameter of at least 7 microns, a wet and dry surface abrasion resistance of greater than 15 cycles to pill and a basis weight in the range of 3 grams per square meter to 10 grams per square meter. At least one veneer web is directly contiguous to the at least one core web.

According to a still further broad aspect of the present invention there is provided a method of producing a melt-blown microfiber fabric having improved abrasion resistance.
The method comprises forming at least one core web of thermo-plastic melt-blown microfibers having a minimum grab tensile strength to weight ratio greater than 0.8N per gram per square meter, a minimum Elmendorf tear strength to weight ratio greater than 0.04N per gram per square meter, and a basis weight in the range of 14 grams per square meter to 85 grams per square meter. The method also comprises forming at least one unreinforced surface veneer web of melt-blown thermoplastic fibers on the core web. The veneer web has a high initial autoyenous bonding and an average fiber ~ ¢

1~0517 - 6a -diame-~er greater than 8 microns, in which 75~ of the fibers have a fiber diameter of at least 7 microns The veneer web has a basis weight in the range of 3 grams per square meter to 10 grams per square meter and a wet and dry surface abrasion resistance greater than 15cycles to pill. At least one veneer web is directly contiguous to the at least one core web.

Brief Description of the Drawings Figure 1 is an isometric view of the melt~blowing process.
Figure 2 is a cross-sectional view of the placement of the die and the placement of the secondaxy air source.
Figure 3 is a detailed fragmentary view of the extrusion die illustrating negative set back.
Figure 4 is a detailed fragmentary view of the extrusion die illustrating positive set back.

Detailed Description of the Invention In its broadest aspect, the present invention comprises providing a surface veneer of melt-blown fibers to a melt-blown microfiber web, said surface veneer having an average fiber diameter greater than 8 mlcrons in which at least 75% of the fibers have a diameter of at least 7 microns. For most fabric applications the surface veneer will be laminated to the remainder of web, e.g., by emboss bonding, or combined by other known methods. Thus, the surface veener may be formed separately from the remainder of the web and thermally bonded thereto, preferably at discrete intermittent bond regions.
Alternatively, the veneer may be formed with high initial autogenous bonding atop the remainder of the web eliminating the need to bond the veneer to the remainder of the web, though thermal embossing the fabric may be preferred. The fabrics of the present invention exhibit improved wet and dry surface abrasion resistance and are 1~9~)~;i17 especially applicable for use as wipes or medical fabrics.
In its broadest aspects, the process of the present invention may be carried out on conventional melt-blowing equipment which has been modified to providehigh velocity secondary air, such as that shown in the aforementioned co-pending application and shown in Figure 1. In the apparatus shown, a thermoplastic resin in the form of pellets or granules, is fed into a hopper 10. The pellets are then introduced into the extruder 11 in which the temperature is controlled through multiple heating zones to raise the temperature of the resin above its melting point. The extruder is driven by a motor 12 which moves the resin through the heating zones of the extrudex and into the die 13.
The die 13 may also have multiple heating zones.

- As shown in Figure 2, the resin passes from the extruder into a heater chamber 29 which is between the upper and lower die plates 30 and 31. The upper and lower die plates are heated by heaters 20 to raise the temperature of die and the resin in the chamber 29 to the desired level. The resin is then forced through a plurality of minute orifices 17 in the face of the die.
Conventionally, there are about 12 orifices per centimeter of width o the die.

An inert hot gas, usually air, is forced into the die through lines 14 into gas chamber 19. The heated gas, known as primary air, then flows to gas slots 32 and 33 which are located in either side of the resin orifices 17. The hot gas attenuates the resin into fibers as the resin passes out of the orifices 17.
The width of the slot 32 or 33 is referred to as the air gap. The fibers 1~90517 are directed by the hot gas onto a web forming foraminous conveyor or receiver 22 to form a mat or web 26. It is usual to employ a vacuum box 23 attached to a suitable vacuum line 24 to assi6t in the collection of the fibers.
The conveyor 22 i6 driven around rollers 25 so as to form a web continuously.

The outlets of the orifices 17 and ~he gas $10ts 32 and 33 may be in the same plane or may be offset. Fig. 3 shows the orifice 17 terminating inward of the face of the die and the slots 32 and 33. Thi~ arrangement iB ceferred to as negative ~etback. The setback dimension is shown by the space between the arrows in Fig. 3. Positive ~etback is illustrated in Fig. 4. The outlet of the orifice 17 -` 15 terminates outward of the face of the die and the slots 32 and 33. The setback dimen6ion is shown by the space between t~e arrows in Fig. 4. A negative setback is preferred in the present process as it allows greater flexibility in setting the air gap without adversely affecting the quality of the web produced.

The fabrics of the present invention comprise at least one surface veneer and a core web. Preferably, the fabric comprises a core web and surface veneers on both surfaces of the core web. As used herein, veneer means a web of -- fibers having a basis weight no greater than 50% of the total weight of the fabric. Preferably, the basis weight of the veneer web is about 25% of the weight of the total fabric, and most preferably, between about 15% to 25% of the total weight of the fabric. The veneer web(s) may be formed separately from the core web and then combined therewith in a face-to-face relationship. ~hen using this method, each veneer web must have a basis weight of about 6g~m2 to facilitate handling of the web to combine it with the core web. ~lternatively, the core and veneer ;, ¢
,... .;.

~90517 webs may be formed atop one another, e.g., by depositing the core web fibers atop the veneer web disposed on the conveyor 22 and acting as the receiver for the fibers of the core web. In this preferred method of the present invention, a veneer web of about 3g/m2 may be deposited on the conveyor and focm the receiver for the core web and/or a veneer web of about 3g/m may be deposited on the core web acting as a receiver. Alternatively, the fiber of the veneer webs may be deposited on both surfaces lo of t~e core web in ~eparate web forming step~. Thereafter the core web and veneer web(s) may be laminated, e.g., by heat embossing. When depo~iting the veneer web(s) on the core web, if the veneer web(s) is formed undec conditions which provide high initial interfiber oc autogenous bonding, including high die temperature, no secondary air and a short forming distance, (as described more fully below) it may not be necessary to laminate the veneer web(s) to the core as, e.g., by heat embossing, nor to emboss the veneer. The core web may be embossed or unembossed prior to the deposition of the fibers of the veneer web thereon. The embossed fabric laminates of the present invention exhibit a wet surface abrasion resistance of at least 30 cycles to pill and a dry surface abrasion resistance of at least 40 cycles to pill.

As stated hereinbelow, it is possible to form the fabric of the present invention according to the above m~thod6 with only one melt-blown die by increasing the polymer throughput and reducing the primary air to form the veneer web(s). In a most preferred method of making the fabrics of the present invention. multiple dies are used.

In its mo6t preferred aspect the present invention comprise6 an improved unreinforced melt-blown microfiber ~SU-61 1~''9()~17 fabric for use as a medical fabric. said fabric having a minimum grab ten6ile 6trength to weight ratio of at least 0.~ N per gram per 6quare meter and a minimum Elmendorf tear ~trength to weight ratio of at lea6t 0.04 N per gra~
per 6quare ~eter. The invention will now be further de~cribed in relation to thi6 preferred embodiment.

The cequirement6 for medical grade fabric~ are quite demanding. The fabric must have sufficient strength to lo resist tearing or ~ulling apart during normal u6e, for instance, in an operating room environment. Thi6 is especially true for fabric6 that are to be used for operating room apparel, such as surgical gowng, or scrub suits, or for surgical drapes. One measure of the ~trength of a nonwoven fabric i8 the grab tensile strength. The grab tensile strength is generally ~he load necessary to pull apart or break a 10 cm wide sample of the fabric.

The te6t for grab ten6ile strength of nonwoven ~abrics is described in ASTM D1117. Nonwoven medical fabrics must also be resistant to tearing. The tearing strength or re~istance is generally ~easured by the Elmendorf Tear Test a~ de~cribed in ASTM D1117. While the grab tensile strengths, measured in the weakest, normally cross machine direction, of the least strong commercially used medical fabric6 are in the Lange of 45 newton~ (N) with tear strengths in the weakest direction of approximately 2N, at the6e strength level6, fabric failure can occur and it is generally desired to achieve higher strength level~. Grab tensile ~trength levels of approximately 65 N and above and tear re6istance levels of approximately 6N and above would allow a particular medical fabric to be u ed in a wider range of application~. The preferred fabrics of the pre6ent invention have a high strength to weight ratio, such that at desirable weights, both geab tensile and tear strengths higher than the above values can be achieved, and generally have basis weights in the range of 14 to 85 g/m2 ~

Medical fabrics must also be repellent to fluids including blood, that are commonly encountered in hospital operating rooms. Since these fluids offer a convenient vehicle for microorganisms to be transported from one location to another, repellency is a critical functional attribute of ~edical fabrics. A measure of repellency that i influenced primarily by the pore structure of a fabric is the "hydrostatic head" test, AATCC 127-1977. The hydrostatic head test measures the pressure, in units of height of a column of water, necessary to penetrate a given sample of fabric. Since the ultimate resistance of a given fabric to liquid penetration is governed by the pore ~tructure of the fabric, the hydrostatic head test is an effective method to assess the inherent repellent attribute~ of a medical fabric. Nonwoven medical fabrics which do not include impermeable film6 or microfiber webs genecally possess hydrostatic head values between 20 to 30 cm of water. It is generally recognized that these values are not optimu~ for gowns and drapes, especially for those situations in which the risk of infection is high. Values of 40 cm or greater are desirable.
Unfortunately, prior art disposable fabrics which possess high hydrostatic head values are associated with low breathability or relatively low strength. The fabrics of the present invention can attain a high level of fluid repellency.

The breathability of medical fabrics is also a desirable property. This is especially true if the fabrics are to be u~ed for wearing apparel. The breathability of fabrics is related to both the rate of moicture vapor transmission (MVTR) and air permeability. Since most fibrous webs used for medical fabrics possess reasonably high levels of MVTR, the measurement of air permeability i6 an aperopriate discriminating quantitative te~t of breathability.

Generally the more open the structure of a fabric, the higher its air permeability. Thus, highly compacted, dense webs with very zmall pore structures result in lo fabrics with poor air permeability and are consequently perceived to have poor breathability. An increase in the weight of a given fabric would also decrea6e ies air permeability. A measure of air permeability i5 the Prazier air porosity test, ASTM D737. Medical garments made of fabrics with Frazier air porosity below 8 cubic meters per minute per square meter of fabric would tend to be uncomfortable when worn for any length of time. The fabric of the present invention achieve good breathability without sacrifice of repellency or strength.
Medical fabrics must also have good drapability, which may be measured by various methods including the Cusick drape test. In the Cusick drape test, a circular fabric sample is held concentrically between horizontal discs which are smaller than the fabric sample. The fabric i~ allowed to drape into folds around the lower of the discs. The shadow of the drap~d sample is projected onto an annular ring of paper of the same size as the unsupported portion of the fabric sample. The outline of the shadow i6 traced onto the annular ring of paper. The mass of the annular ring of paper is determined. The paper is then cut along the trace of the shadow, and the mass of the inner portion of the ring which represents the shadow is determined.
The drape coefficient is the mass of the inner ring divided by the ma~s of the annular ring times 100. The ~90~:i17 lower the drape coefficient, the more drapable the fabric. The fabric6 of the present invention demonstrate high drapability when measured by this method.
~rapability correlates well with softness and flexibility.
s In addition to the above characteristics, medical grade fabrics must have anti-6tatic properties and fire retardancy. The fabrics should also po~ses~ good resistance to abrasion, and not shed small fibrous particles, generally referred to as lint.

In addition to the characteristics mentioned above, the preferred fabric of the present invention differs from peior art melt-blown webs in that the average leng~h of the individual fibers in the web is greater than the average length of the fibers in prior art webs. The average fiber length in the core webs is greater than 10 cm, preferably greater than 20 cm and most preferably in the range of 25 to 50 cm. Also, the average diameter of the fibers in the core web should be no greater than 7 microns. The dictribution of the fiber diameters is such that at least 80t of the fibers have a diameter no greater ~han 7 micron6 and preferably at least 90% of the fibers have a diameter no greater than 7 microns.
In the description of the present invention the term "web"
refer6 to the unbonded web formed by the melt blowing process. The term "fabcic" refers to the web after it i6 bonded by heat embossing or other means.
The preferred fabric of the present invention comprises an unreinforced melt-blown embo6sed fabric having a core web of average fiber length greater than 10 centimeters and in which at least 80% of the fibers have a diame~er of 7 micron~ or les6, and a surface veneer provided on one or both 6urface6 of the core web, said surface veneers having 1~9~ 7 an average fiber diameter of greater than 8 micron~, and in which 75% of the fiber6 have a fiber diameter of at lea6t 7 micron6.

In the process of ~aking ~hi6 preferred fabric of the pre6ent invention, the fibers of the core web are contacted by high velocity 6econdary air immediately after the fiber6 exit the die. The fibers of the surface veneer may or may not be contacted by high velocity secondary air. The secondary air i6 a~bient air at room temperature or at outside air temperature. If desired, the secondary air can be chilled. The 6econdary air i~ forced under pre~sure from an appropriate 60urce through feed line6 15 and into di6tributor 16 located on each 6ide of the die.
The di~tributor6 are generally as long as the face of the die. The distributors have an angled face 35 with an opening Z7 adjacent the die face. The velocity of the secondary air can be controlled by increasing the pressure in feed line 15 or by the use of a baffle 28. The baffla would re6trict the size of the opening 27, theceby increasing the velocity of air exiting the di6tribution box, at constant volume.

The pre6ent nonwoven fabric differs from prior art microfiber-containing fabric6 in the utilization of the melt-blowing proce66 to produce a 6urface veneer of fibers with characteri6tics which differ from the chacacteristics of the microfibers of the core web and which re6ult in a fabric with high strength to weight ratios, good surface abra6ion resi6tance and drape if the fiber6 are formed into a core web and surface veneer and thermally bonded as de6cribed herein.

In the practice of prior art melt-blown technology for fabric related application6, it i6 typical to produce ~9()~1~

microfibers which cange in average diame~er from about 1 to 10 microns. While in a given web, there may be a range of fiber diameter~, it is often necessary to keep the diameters of these fibers low in order to fully exploit the advan~ages of microfiber structures as good filtration media. Thus, it is usual to produce webs or batts with average fiber diameters of le6s than 5 microns or at times even less than 2 microns. In such prior art proces~es, it is also typical for such fibers to be of average length6 between 5 tO 10 centimeters (cm). As discu~sed in the review of the prior art fabrics, the webs formed from such fibers have very low strength and abrasion resistance.
The tensile strength and abrasion resistance of such a web is primarily due to the bonding that occurs between fibers as they are deposited on the forming conveyor. Some degree of interfiber surface bonding can occur because in the conventional practice of melt-blown technology, the fibers may be deposited on the forming conveyor in a state in which the fibers are not completely solid. Their semi-molten surfaces can then fuse together at crossover points. This bond formation is sometimes referred to a~
autogenous bonding. The higher the level of autogenous bonding, the hiqher the integrity of the web. However, if autogenous bonding of the thermoplastic fibers is exces6ively high, the webs become stiff, harsh and quite brittle. The strength of such unembossed webs is furthermore not adequate for practical applications such a~ medical fabrics. Thermal bonding of these webs can generally improve strength and abrasion resi6tance.
However, as di~cu6sed in previous section6, without introduction of surface reinforcing elements or binder, it has heretofore not been possible to produce melt-blown microdenier fabric~ with high surface abrasion resistance, particularly for use as surgical gowns, scrub apparel and drapes.

~-~9t~S17 In forming the core webs of thi6 p~eferred fabric of the present invention, fibers are produced which are longer than fiber6 of the prior art. Fiber lengths were determined u~ing rectangular-shaped wire form6. The6e forms had 6pan length6 ranging from 5 to 50 cm in 5 cm increment6. Strip6 of double-faced adhe~ive tape were applied to the wire to provide adhe6ive sites to collect fibers from the fiber stream. Fiber lengths were determined by firs~ pas~ing each wire form quickly through the fiber stream, perpendicular to the direction of flow, and at a di6tance closer to the location of the forming conveyo~ than to the melt blowing die. Average fiber lengths were then approximated on the basis of the number of individual fibers spanning the wire forms at ~uccessive span lengths. If a 6ub6tantial portion of the fibers are longer than 10 cm, such that the average fiber length is at least greater than 10 cm and preferably greater than 20 cm, the webs, thus formed, can result in embossed fabrics with good strength, while maintaining other de6ired features of a medical fabric. Fabrics with highly desirable properties are produced when average fiber length~ are in the range of 25 to 50 cm. In order to maintain the potential of microdenier fibers to resist liquid penetration, it is necessary to keep the diameters of the fibers low. In order to develop high repellency, it i6 necessary for the average diameter of the fiber6 of the pre~ene core web to be no greater than 7 mic~ons. At least 80% of the fibers 6hould have diameter~ no greater than 7 micron6. Preferably, at least 90% of the fiber~
should have diameters no greater than 7 micron6. A narrow distribution of fiber diameters enhance6 the potential for achieving the unique balance of propertie6 of thi~
invention. While it is possible to produce fdbrics with average fiber diameters greater than 7 micron6 and obtain high 6~rength, the ultimate repellency of such a fabric ~05~ 7 would be compromi6ed, and it would then not be fea6ible to produce low weight fabrics with high repellency.

When the melt-blown fibrou~ core web is foImed in such a manner that autogenous bonding is very low and the webs have little or no integrity, the fabrics that re~ult upon thermal embossing the~e webs are much stronger and possegs better aesthetics than fabric~ made of web~ with high initial strength. That i8, the weakest unembo~6ed webs, with fiber dimension6 a~ described above, form the ~trongest embossed fabrics. The higher the level of initial interîiber bonding, the stiffe~ and more brittle the re~ulting fabric, leading to poor grab and tear strengths. As autogenous bonding is reduced, the resulting fabric develops not only good strength but becomes softer and more drapable after thermal embossing.
Becau6e of the relatively low levels of web integrity, it is useful to determine the strength of the unembossed web by the strip tensile strength method, which uses a 2.54 cm-wide 6ample and grip facings which are also a minimum 2.54 cm wide (ASTM D1117). In prior art melt-blown fabrics the machine direction (MD) strip tensile strength of the autogenously bonded web is generally greater than 30~ and frequently up to 70% or more of the strip tensile 6trength of the bonded fabric.
That is, the potential contribution of autogenous bonding to the 6trength of the embossed fabric is quite high. In the fabric of the pre6ent invention the autogenous bonding of the core web contributes le6s than 30%, and preferably less than 10%, of the strip tensile strength of the bonded fabric.

For example, a Nylon 6 melt-blown web with a weight of approximately 50 g/m2 made under prior art conditions may pos6e~s a ~trip tensile strength in the machine ~L',''P9~)51~7 direction of between 10 to 20 N. In this prefeered fabric of the invention, it i~ necessary to keep the strip tensile strength of the unembossed core web below 10 N and preferably below 5 N to achieve the full benefit6 of the invention. In other word6, when long fibers are produced and collected, in such a way that initial interfiber bonding i8 low, the individual fibers are stronger, and there i8 greater exploitation of the inherent strength of the fiber~ themselve~.
While it iz necessary to produce the fibers of the core web in such a way that initial interfiber bonding i6 low and 80~ of the fibers have a fiber diameter of no more that 7 microns, such webs when embossed do not exhibit high surface abra6ion resi~tance, and a chemical binder i8 often added to the surface of such fabrics to increa6e surface abrasion resistance. The addition of binder negatively impacts the drape of the fabric, therefore the amount of binder added mu6t be kept to a minimum, and, in Z0 practice, the amount of binder which can be added while maintaining adequate drape gives only satisfactory, but not high, abrasion resistance.

In the fabric of the present invention, the use of binder 2S and its negative impact on drape is avoided by providing the core web with a surface veneer of microfibers on one or both 6urfaces of the core web. The fibers of the 6urface veneer have an average fiber diameter of greater than 8 microns and 75% of the fibers have a fiber diameter of at least 7 microns. In addition, in a preferred embodiment, the surface veneer is formed with high initial interfiber bonding.

In summary, this preferred fabric of the present invention, in contra6t to conventional melt-blown webs of 9(~7 the prior ar~, is characterized by a core web of high average fiber length, low interfiber bonding, 6tronger individual fibers and low fiber diameters in a rslatively narrow distribution range to provide high resistance to fluid penetration, and at least one surface veneer of higher fiber diameters and, preferably, high interfiber bonding.

The method of producing the desired core web and ~urface 13 veneer characteristi~ of this ~referred fabric o~ the invention i8 ba~ed on the control of the key process variables and their interactions to achieve the desired fiber, web, and fabric properties. The6e process variables include extru6ion temperature6, primary air flow and temperature, 6econdary air flow, and forming length (distance from die to receiver). The influence of these variables on the key desired web and veneer properties i6 de~cribed below.

For both the core web and 6urface veneer, individual fiber 6trength can be enhanced 6ignificantly if the die melt temperature, for instance, can be maintained at levels generally 10 to 35C below temperatures recommended for prior art processe6. Generally, in the present proces6 Z5 the die melt temperature i6 no qreater than about 75C
above the melting point of the polymer.

In forming the core web, the velocity and temperature of the primary air, and the velocity and temperature of the secondaey air must be adjusted to achieve optimum fiber strength at zero span length for a given polymer. The high velocity secondary air employed in the p~esent process i6 in6trumental in increa~ing the time and ehe distance over which the fibers of the core web are attenuated adding ~o fiber strength. The u6e of 6econdary ~90~7 air in the process of producing the surface veneer fibers is not esRential, and secondary air is preferably omitted in forming the preferred surface veneer with high initial interfiber bonding.

The fiber length achievable in the core web and surface veneer is influenced by the primary and secondary air velocitie~, the level of degradation of the polymer and, of critical importance, air flow uniformity. It is important to maintain a high degree of air and fiber flow uniformity, avoiding large amplitude turbulence, vortices, streaks, and other flow irregularities. Introduction of high velocity secondary air may serve to control ehe air/fiber ~tream, by cooling and maintaining molecular orientation of the fibers 80 that stronger fibers are produced that are more resistant to possible breakage caused by non-uniform air flow.

In order to deposit the fibers of the core web on the forming conveyor as a web with low strip tensile strength, the forming air and forming distance are clearly important. In the present proces6, the forming distance is generally between 20 and 50 centimeters. First, in order for the core web to have minimal interfiber bonding, the fiber6 must arrive at the forming conveyor in a relatively solid state, free of 6urface tackines6. To allow the fibers time to solidify, it is possible to set the forming conveyor or receiver farther away from the die. However, at excessively long distances, i.e., greater than 50 cm., it is difficult to maintain good uniformity of the air/fiber stream and "roping" may occur. Roping is a phenomenon by which individual fibers get entangled with one another in the air stream to form coarse fiber bundles. Excessive roping diminishes the capacity of the resultant fabric to resi~t fluid ~J~0517 penetration, and al80 lead6 to poor ae6thetic attributes.
A primary air flow of high uniformity enhances the oppor~unity to achieve good fiber attenuation and relatively long di~tance forming without roping.

The primary air volume iB al80 an important factor.
Sufficient air volume must be used, at a given polymer flow rate and forming length, to maintain good fiber 6eparation in the air/fiber stream, in order to ~inimize the extent of roping.

The u6e of the secondary air 6ystem also i6 important in achieving low interfiber bonding in the core web without roping. A6 noted previously, the high velocity 6econdary air is effective in improving the uniformity of the air/fiber 6tream. Thu6, it enhances the potential to increase the forming length without cau6ing undesirable roping. Furthermore, since the 6econdary air is maintained at ambient temperature, or lower if desired, it can serve also to cool and solidify the fibers in a 6horter time, thu6 obviating the need for det~imentally large forming length6. For the 6econdary air system to have an influence on flow uniformity and cooling, and the rate of deceleration of the fibers, it~ velocity should be high enough that its flow i6 not completely overwhelmed by the prima~y air flow. In the pre6ent proce66, a 6econdary air velocity of 30 m/sec to 200 m/6ec or higher i6 e~fective in providing the desired air flow characteristics. Obviously, there are variou approaches and co~binations of primary and 6econdary air flows, tempera~ure6, and forming lengths that can be used to achieve low interiber bonding in the unembossed core web. The ~pecific proce~s parameters depend on the polymer being used, the design of the die and its air systems, the production rate, and the desired product properties.

The unembossed core web or layer6 of unembo6sed core webs mu~t be bonded to form this preferred fabric of the pre~ent invention. It has been determined to be advantageous to use thermal bonding techniques. In a most preferred method of the present invention, the core web or webs are ~hermally bonded and the veneer thermally bonded and laminated to the core web in one thermal embossing step. ~ither ultrasonic or mechanical embossing roll 6yfitems using heat and pressure may be used. For the present invention, it is preferred to use a mechanical embossing system for point bonding using an engraved roll on one side and a solid smooth roll on the other side of the fabric. In order to avoid ~'pinholes~ in the fabric, it has also been found desirable to set a small gap, of the order of 0.01 to 0.02 mm, between the top and bottom rolls. For the intended use of the fabrics which can be produced by this invention, the total embossed area must be in the range of 5 to 30% of the total fabric surface, and preferably should be in the range of 10-20~. In the examples given to illustrate the invention, the embossed area is 18%. The embossing pattern is 0.76 mm x 0.76 mm diamond pattern with 31 diamond6 per square centimeter of roll surface. The particular embossing pattern employed i8 not critical and any pattern bonding between 5 and 30 of the fabric surface may be used.

The principles of this invention apply to any of the commercially available resins, ~uch as polypropylene, polyethylene, polyamides, polyester or any polymer or polymer blends capable of being melt-blown. It has been found particularly advantageous to use polyamides, and particularly Nylon 6 ~polycaprolactam), in ordec to obtain ~ ,905~'7 6uperior aesthetic6, low cusceptibili~y to degradation due to cobalt irradiation, excellent balance of properties, and overall ease of proc~s~ing.

A6 stated previously, the preferred fabrics of the pre6ent invention have a basis weight of fro~ 14 to B5 grams per &quare meter. The surface veneers when geparately formed, have a ba~is weight of from about 6 gram~ per square meter, and when co-formed, a basis weight of from about 3 grams per ~quare meter. Ba~is weight6 of the surface veneers are generally no greater than 10 to 15 grams per 6guare meter, as higher veneer base weight~ may require lower core web basis weights to achieve the de~ired overall ba6is weight of the fabric. The fabrics have a minimum grab tensile strength to weight ratio greater than 0.8 N per gram per square meter, a minimum Elmendorf tear strength to weight ratio gceater than 0.04 N per gram per square meter and wet and dry surface abrasion resistance of greater than 15 cycles to pill. For disposable medical fabrics where high 6trength and abrasion resistance are required, the preferred fabrics have basis weights no greater than 60 grams per square meter, a minimum grab tensile strength of not less than 65 N, a minimum Elmendorf tear strength not less than 6 N, and dry surface abrasion resistance of at least 40 cycles to pill and a wet surface abrasion resistance of at least 30 cycles to pill.

It is to be understood that the fiber~, webs or fabrics produced according to thi~ invention can be combined in various ways, and with other fiber~, webs, or fab~ics posse~6ing different characteri6tics to for~ products with specifically tailored properties.

The examples which follow are intended to clarify further ~905~7 the present invention. and are in no way intended to 6erve a6 the limits of the content or cope of thi6 invention.

ExamPle 1 In the following example, web6 1, 2 and 3 were produced under the condition6 6et forth in Table I below.
TABLE I

PROCESS CONDITIONS USED TO PRODUCE
MæLT-BLowN NYLON WEBS

Webs Proces6 Conditions 1 2 3 Extruder Temperature - Feed C 260 232 260 Extruder Temperature - Exit C 275 275 300 Screen/Mixer Temperature C 275 275 2a7 Die Temperature C 287 265 300 Primary Air Temperature C 2B7 287 335 Primary Air Velocity m~sec290 255 221 Polymer Rate g/min-hole 1 0.14 0.14 0.28 Die Air Gap mm1.14 1.14 1.14 Die Setback - Negative mml.02 1.02 1.02 Secondary Air Velocity m/6ec 30 30 30 8a6is Weight g~m2 52 44 6 Average Fiber Diam~ter microns 3.6 4.1 9.8 Web 1 was produced under condition~ similar to tho6e ~et fo~th in the aforementioned co~ending application for optimizing both barrier and 6trength propertie6 in the f~nal fabric.
Web 2 was produced under modified conditions to produce a fabric with enhan~ed fabric strength. but with a ~light 108s of barrier properties, achieved by lowering the die temperature and the primary air velocity relative to web 1 ~, . ~ , ....

o~

conditions. Web 3 was produced by increa6ing the polymer throughput rate and further decrea~ing primary air velocity to produce a fiber layer having an average fiber diameter of 9.8 micron6 and in which 80% of the fiberg have a fiber diameter greater ehan 7 micron6.
Additionally the die temperature was raised to increase the initial interfiber bonding of Web 3. Table II lists the physical propertie6 of embossed fabrics made from webs 1, 2 and 3. Table III ~ets forth the processing conditions for producing the embossed fabric6 who6e physical characteristic6 are li6ted on Table II.

JSU-~l 1~0517 TA~LE II

OF THERMALLY-EMBOSSED MELT-BLOWN NYLON

Fabric~
Characteri~tics 4 5 6 _ _ 7 Composition - Layer 1 Web 1 Web 2 Web 3Web 3 - Layer 2 - -Web 2 Web 2 - Layer 3 - - - Web 3 Total ~asis Weight (g~m2) 52 44 50 56 Grab Tensile Strength to Weight Ratio (N/g-m 2) MD 2.06 2.77 2.55 2.48 CD1.531.94 1.95 1.90 Hydro~tatic Pres~ure (cm of water) 49 36 39 39 Abrasion Re~istance (cycles) Side 1 Dry - to pill 15 15 40 50 - to fail 100 100 100 100 Wet - to pill 15 15 30 35 - to fail 100 100 100 100 Side 2 Dry - to pill 15 15 15 50 - to fail 100 100 100 100 Wet - to pill 15 15 15 35 - to fail 100 100 100 100 TA81,E III

PROCESS CONDITIONS FOR THERMAL EMBOSSING
OF M~LT-BLOWN NYLON

Fabrics ~Process Conditions 4 5 6 7 Percent Embossed Area (~) 18 18 18 18 10 Oil Temperature (C) Top Embos~ed Roll 126 122121 121 Bottom Smooth Roll 126 122122 L22 Nip Pressure Between Rolls (N~cm)685 685685 685 Web Speed (m/min) 15 9 9 9 As noted in Table II, Fabric 5 shows superior grab ten6ile strength than Fabric 4, but decrea6ed barrier properties as reflected in the hydrostatic pressure. The abrasion re6istance remains the same. Fabrics 6 and 7 illustrate ehe improved abrasion resistance achieved with the use Or ~urface veneers of web 3. Fabrics 6 and 7 show an increasing fall off of normalized grab tensile strengths due to the incorporation of the veneer layer(s) of web 3 which, while it adds to the weight of the fabric, it does not contribute a6 much grab tensile per unit weight as web 2. Veneer layers of web 3 add slightly to the hydrostatic head of Fabric~ 6 and 7, but add remarkable surface abrasion resistance.

The dry surface abrasion resi6tance was ~easured as follows. A ~ample of th~ ~abric to be ts3eed wa~ placed atop a ~oam pad on a boteom testing plate. A 7~6 cm by 12.7 cm ~ample of a 6tandard Lytron ~inishQd abrading eloth waa added to a top plate and placed in contact'with the fabric test sample, with the machine direction of the * Reg. TM

:

.. ~ . .. . ..

1;.'905i17 fabric te6t sample aligned with the machine directisn (length~ of the Lytron finished cloth. A 1.1 Kg weight was placed atop the top plate and the bottom plate rotated at a fixed 6peed of 1.25 revolution6 per minute, each rotation of the plate being recorded as one cycle. The fabric test sample wa~ inspected under magnification after each of the first five cycle6, and at five cycle intervals thereafter. The number of cycles to pill was recorded, as well as the number of cycles to create a hole in the fabric test sample. Pilling is defined as the breaking off of fibers which start to form clumps or beads. Four samples of the fabcic were tested and the average number of cycles to pill and to fabric failure was repoLted.

The wet 6urface abra6ion re6istance was measured under a similar testing procedure, with the following modifications; the fabric test sample, fastened to the bottom plate was wetted with 5 drops of purified water, and only a 0.2 Kg weight wa6 placed atop the top plate.
Example 2 In the following example webs 9, 9, 10, and 11 were produced under conditions set forth in Table IV below.

~'~90517 TABLE IV

PROCESS CONDITIONS USED TO PRODUCE
MELT-BLOWN NYLON BASE WEBS

Extruder Temperature - Feed C 246 232 232 260 Extruder Temperature - Exit C 274 274 274 301 Web~
Process Conditions 8 9 lo 11 Screen/Mixer Temperature C 274274 274 301 Die Te~perature C 274 265265 301 Primary Air Temperature C 309285 285 331 Primary Air Velocity mJ~ec299 252191 299 Polymer Rate g/min-hole 1 0.140.140.28 0.28 Die Air Gap mm1.141.141.14 1.14 Die Setback - Negative mm1.021.021.02 1.02 Secondary Air Velocity m/6ec 30 30 30 0 Basi6 Weight g/m2 52 42 6 6 Average Fiber Diameter microns 8.2 8.8 The proces6 conaitions for webs 8, 9, 10 and 11 fall within the proce66 conditions set forth in aforementioned 25 copending applica~ion. - . Web 8 was produced under condition6 for optimizing both strength and barr~er proper~ie~ in the final fabric. Web 9 was produced under modified conditions to produce a fabric with enhanced fabeic strengeh with a slight 1086 in barrier properties, by loweeing the die te~perature and primary air velocity relative to web B
condition~. Web 10 was produced by increa~ing the polymer throughout rate and further decreasing the primary air velocity to produce a fiber layer having an average fiber diameter of approximately 9 micron6, and in which ~0% of the fiber6 have a fiber diameter greater than 7 microns.

, ., . ~., 1~90517 The die temperature remained the same for web~ 9 and 10.
Web 11 was produced under conditions substantially similar to tho6e for producing web 3 but with no 6econdary air ~o as to increa~e initial interfiber bonding. The die temperatuIe for the production of web 11 wa6 al60 increa6ed over that u6ed to produce web 10 to increa~e initial interfiber bonding.

Table V, below, lists the phy6ical characteristic6 of embocsed fabrics made from webs 8, 9, 10 and 11 under the conditions set forth in Table III. Fabric 13 comprise Pabric 12 with 3 g/m of Primacor 4990* a 80/20 copolymer of ethylene and acrylic acid. manufactured by the Dow Chemical Company, added to each side of the fabric.
TABLE V

pESCRIPTION AND PHYSICAL PROPERTY CHARACTERISTICS
OF THERMALLY-EMBOSSED MELT-BLOWN NYLON
Fabric~
Characteristics 12 13 14 15 Composition - Layer 1 Web 8 Binder Web L0 Web 11 - Layer 2 - Web 8 ~eb 9 Web 9 - Layer 3 - 3inder Web 10 Web 11 Total Ba~is Weight (g/m2) 52 58 54 54 Grab Tensile Strength ~N) MD 94.1 103 94.0 108 CD 71.7 71.9 58.9 69.1 Hydrostatic Pres6ure (cm of water)41 38 37 38 * Reg. TM

1~,90~17 TABLE V
(Continued) DESCRIPTION AND PHYSICAL PROPERTY CHARACTERISTICS

Fabr iC5 Characteri~tics 12 13 14 15 10 Abra6ion Resi~tance (cycles) Side 1 Dry - to pill 5 15 40 45 - to fail 100 100 100 100 Wet - to pill 5 15 30 40 - to fail 100 100 100 100 Cusick Drape (%) 46 65 45 44 TABLE VI

PROCESS CONDITIONS FOR THERMAL EMBOSSING

Fabrics Process Conditions 12 14 15 Percent Embo6sed Area (~) 18 18 18 Oil Temperature (C) Top Embossed Roll 104 106 93 Bottom Smooth Roll 97 99 95 Nip Pressure Between Rolls (N/cm) 685 685 685 30 Web Speed (m/min) 9 9 9 1~9~)517 As shown in Table V, Fabric 13 shows an increase in surface abrasion resistance with a large increase in Cusick Drape. Further increase in binder level add-on will contribute to abrasion resi6tance but will continue to negatively impact the drape.

Fabric 14 exhibits far greater ~urface abrasion resistance than Fabric 13 with no attendant loss in drape. Fabcic ~5 exhibits an~even greater improvement in surface abrasion resistance over that shown by Fabric 14. The increase i8 believed to be due to the increase in initial interfiber bondinq of web 11.

Thus, it is apparent that there has been provided, in accordance with the invention, a new, unreinforced, melt-blown, microfiber fabric having enhanced surface abrasion resistance that satisfies the objects, aims and advantages set forth above. While the invention has been described in conjunction with specific embodiment~
thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the above description.
Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

Claims (14)

1. An improved unreinforced melt-blown microfiber fabric having improved surface abrasion resistance, said fabric comprising at least one unreinforced thermoplastic melt-blown microfiber core web having an average length of greater than 10 cm and an average diameter not exceeding 7 microns, said core web also having a minimum grab tensile strength to weight ratio greater than 0.8N per gram per square meter and a minimum Elmendorf tear strength to weight ratio greater than 0.04N per gram per square meter, said core web having a basis weight in the range of 14 grams per square meter to 85 grams per square meter, and at least one unreinforced surface veneer web on said core web, said veneer web being formed of melt-blown thermoplastic fibers having an average fiber diameter of greater than 8 microns in which 75% of the fibers have a diameter of at least 7 microns, having a wet and dry surface abrasion resistance of greater than 15 cycles to pill, and having a basis weight in the range of 3 grams per square meter to 10 grams per square meter, said at least one veneer web being directly contigu-ous to said at least one core web.
2. The fabric of claim 1 in which the fabric is thermally embossed at intermittent discrete bond regions which occupy between 5 and 30% of the surface of the fabric.
3. The fabric of claim 1 having a wet abrasion resis-tance to pill of at least 30 cycles and a dry abrasion resistance to pill of at least 40 cycles.
4. The fabric of claim 3 wherein the basis weight is no greater than 60 grams per square meter and the minimum grab tensile strength is not less than 65N and the minimum Elmendorf tear strength is not less than 6N.
5. An improved unreinforced melt-blown microfiber fabric as in claim 1 wherein said surface veneer has an average fiber diameter of about 9 microns.
6. An improved unreinforced melt-blown fabric having improved abrasion resistance, said fabric comprising at least one unreinforced thermoplastic core web having an average length of greater than 10 cm and wherein at least 80% of the fibers have a diameter of 7 microns or less and in which the autogenous bonding of the fibers contributes no more than 30% of the strip tensile strength of the fabric, and at least one unreinforced surface veneer web on said core web, said surface veneer web being formed of melt-blown thermoplastic fibers having an average fiber diameter greater than 8 microns and in which 75% of said fibers have a diameter of at least 7 microns and having a basis weight in the range of 3 grams per square meter to 10 grams per square meter, said fabric being thermally embossed at intermittent discrete bond regions which occupy between 5 and 30% of the surface of the fabric, said core web having a minimum grab tensile strength to weight ratio greater than 0.8N per gram per square meter and an Elmendorf tear strength to weight ratio greater than 0.04N per gram per square meter, and said fabric having a wet surface abrasion resistance of at least 30 cycles to pill and a dry surface abrasion resistance of at least 40 cycles to pill, said at least one veneer web being directly contiguous to said at least one core web.
7. An improved unreinforced melt-blown fabric as in claim 6 wherein said surface veneer has an average fiber diameter of about 9 microns.
8. A method of producing a melt-blown microfiber fabric having improved abrasion resistance comprising:
(1) forming at least one core web of thermo-plastic melt-blown microfibers having a minimum grab tensile strength to weight ratio greater than 0.8N per gram per square meter, a minimum Elmendorf tear strength to weight ratio greater than 0.04N per gram per square meter, and a basis weight in the range of 14 grams per square meter to 85 grams per square meter, (2) forming at least one unreinforced surface veneer web of melt-blown thermoplastic fibers on said core web, said veneer web having high initial autogenous bonding and an average fiber diameter greater than 8 microns, in which 75% of the fibers have a fiber diameter of at least 7 microns, said veneer web having a basis weight in the range of 3 grams per square meter to 10 grams per square meter and a wet and dry surface abrasion resistance greater than 15 cycles to pill, (3) said at least one veneer web being directly contiguous to said at least one core web.
9. A method of producing a melt-blown microfiber fabric as in claim 8 wherein said veneer web has an average fiber diameter of about 9 microns.
10. The method of claim 8 further comprising thermally embossing said laminate at discrete intermittent bond regions.
11. A method of producing an unreinforced microfiber fabric having improved surface abrasion resistance wherein a fiber-forming thermoplastic polymer resin in molten form is forced through a row of orifices in a heated nozzle into a stream of inert gas to attenuate the resin into fibers, the fibers are collected on a receiver to form a web, and the web is thermally bonded to form a fabric comprising:
(a) at a first heated nozzle, maintaining the polymer melt temperature at a level which minimizes molecular degradation, controlling the primary air velocity, volume and temperature, resin throughput and exit temperature to produce a first layer of thermoplastic fibers having an average fiber diameter of greater than 8 microns, and in which 75% of the fibers have a fiber diameter of at least 7 microns, collecting the fibers on a receiver at a forming distance to form a first unrein-forced surface veneer web with good interfiber bonding and having a basis weight in the range of 3 grams per square meter to 10 grams per square meter and a wet and dry surface abrasion resistance of greater than 15 cycles to pill, (b) at a second heated nozzle, maintaining the polymer melt temperature at a level which minimizes molecular degradation, controlling the primary air velocity. volume and temperature to produce thermoplastic fibers at least 80%
of which have a diameter of 7 microns or less and having an average length of more than 10 centimeters, introducing a highly uniform high velocity secondary air stream in quantities sufficient to cool the fibers and maintain good fiber separation, collecting the fibers at a forming distance to form a core web with low interfiber bonding, prior to embossing the web to form a fabric, and collecting the fibers of said core web on said first surface veneer web such that said veneer web is directly contiguous to said core web.
12. The method of claim 11 further comprising:
(c) at a third heated nozzle producing a second surface veneer web of fibers similar to said first veneer web and collecting said second surface veneer web on the exposed surface of said core web.
13. A method of producing an unreinforced microfiber embossed fabric as in claim 11 or 12 wherein said veneer webs have an average fiber diameter of about 9 microns.
14. The method of claim 11 or 12 further comprising thermally embossing said webs.
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BR8604752A (en) 1987-06-30
DE3688771T2 (en) 1993-11-11
CN86106922A (en) 1987-04-01
AU583667B2 (en) 1989-05-04
EP0218473A3 (en) 1989-10-11
AU6321386A (en) 1987-04-09
JPH0320507B2 (en) 1991-03-19
JPS6290361A (en) 1987-04-24
EP0218473A2 (en) 1987-04-15
DE3688771D1 (en) 1993-09-02
ZA8607505B (en) 1988-05-25
CN1014156B (en) 1991-10-02
ES2042495T3 (en) 1993-12-16
EP0218473B1 (en) 1993-07-28
NZ217669A (en) 1990-03-27

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