Background of the Invention

Nonwoven fabric laminates are useful for a wide variety of applications. Such nonwoven fabric laminates are useful for wipers, towels, industrial garments, medical garments, medical drapes, and the like. In heavier basis weights the laminates are used in recreational applications such as tents and as car covers. Disposable fabric laminates have achieved especially widespread use in hospital operating rooms for drapes, gowns, towels, footcovers, sterilization wraps, and the like. Such surgical fabric laminates are generally spunbonded/meltblown/spunbonded (SMS) laminates consisting of nonwoven outer layers of spun-bonded polyolefins and an interior barrier layer of melt-blown polyolefins. Particularly, Kimberly-Clark corporation, the assignee of the present invention, has for a number of years manufactured and sold SMS nonwoven surgical fabric laminates, sterilization wrap and recreational fabrics under the marks Spunguard* and Evolution* Such SMS fabric laminates have outside spunbonded layers which are durable and an internal melt-blown barrier layer which is porous but which, in combination with the spunbond layers, inhibits the strikethrough of fluids or the penetration of bacteria from the outside of the fabric laminate to the inside. In order for such a medical fabric to perform properly, it is necessary that the melt-blown barrier layer have a fiber size and a porosity that assures breathability of the fabric while at the same time inhibiting strikethrough of fluids. Personal care absorbent articles such as disposable diapers, training pants, incontinent wear and feminine hygiene products utilize nonwoven fabrics for many purposes such as liners, transfer layers, absorbent media, backings, and the like. For many such applications the barrier properties of

the nonwoven play an important role such as, for example, containment flaps described in coassigned U.S. Patent 4,704,116 to Enloe dated 3 November 1987, incorporated herein in its entirety by reference. It is also desirable for personal care products such as containment flaps that the nonwoven fabric be soft and conformable and that the porosity of the fabric provide a level of breathability for increased comfort. As cost is always a factor, the ability to provide these benefits at low cost is another consideration. Although nonwoven laminates having some combination of the properties desired have been available, they have not been widely utilized for applications such as the aforementioned flaps because one or more of the important considerations has been lacking or not present to a desired degree. The present invention is directed to improved nonwoven laminates satisfying those and other desired requirements.

Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings.

summary

The present invention is directed to improved lightweight nonwoven laminates including at least one fine fiber component layer and at least one continuous filament layer. The fine fiber layer includes fibers having an average diameter in the range of up to about 10 microns and a basis weight in the range of from about 3 gsm to about 26 gsm. The continuous filament web has filaments with an average diameter in the range of from about 12 microns to about 22 microns and a basis weight in the range of from about 10 gsm to about 30 gsm. The layers are bonded intermittently for a total basis weight not to exceed about 55 gsm and with the ratio of fine fibers to continuous filaments at least 20%. The resulting laminate has an improved combination of properties including softness and conformability as measured by a cup crush peak load test value no more than 150 g, cup crush test energy

value of no more than 2250g/mm, barrier as measured by hydrostatic head of at least 15 cm, and breathability as measured in terms of Frazier porosity of at least 50 scfm. Preferred embodiments include spunbond continuous filament webs and meltblown fine fiber webs as the respective layers.

Brief Description of the Drawings

Figure 1 is a schematic diagram of a forming machine which is used in making the nonwoven fabric laminate including the melt-blown barrier layer of the present invention;

Figure 2 is a cross-section view of the nonwoven fabric laminate of the present invention showing the layer configuration including the internal fine fiber barrier layer made in accordance with the present invention;

Figure 3 is a cross-section view of an alternative embodiment of the nonwoven fabric laminate of the present invention in a two layer configuration; and

Figure 4 is a cross-section view of a third embodiment of the nonwoven fabric laminate of the present invention with external fine fiber layers.

Detailed Description of the Invention

While the invention will be described in connection with a preferred embodiment, it will be understood that we do not intend to limit the invention to that embodiment. On the contrary, we intend to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

The present invention is directed to improved lightweight nonwoven laminates including at least one fine fiber component layer and at least one continuous filament layer. The fine fiber layer includes fibers having an average diameter in the range of up to about 10 microns and a basis weight in the range of from about 3 gsm to about 26 gsm. The continuous filament web has filaments with an average diameter

in the range of from about 12 microns to about 22 microns and a basis weight in the range of from about 10 gsm to about 30 gsm. The layers are bonded intermittently for a total basis weight not to exceed about 55 gsm and with the amount of fine fibers based on the laminate weight of at least 20%. The resulting laminate has an improved combination of properties including softness and conformability as measured by a cup crush test value no more than 150 g, barrier as measured by hydrostatic head of at least 15 cm, and breathability as measured in terms of Frazier porosity of at least 50 scfm.

Preferred embodiments include spunbond continuous filament webs and meltblown fine fiber webs as the respective layers.

The foregoing objectives are preferably obtained by forming a melt-blown web in accordance with U.S. Patent 5,213,881 dated 25 May 1993, incorporated herein in its entirety by reference, from a propylene polymer resin having a broad molecular weight distribution and having a high melt flow rate which resin is modified by the addition of a small amount of peroxide prior to processing to achieve an even higher melt flow rate (lower viscosity). In general, the present invention involves starting with a propylene polymer in the form of reactor granules which polymer has a molecular weight distribution of 3.6 to 4.8 Mw/Mn, preferably 3.6 to 4.0 Mw/Mn and a melt flow rate of about 400 gms/10 in to 3000 gms/10 min at 230*C. Such a molecular weight reactor granule polymer is then modified to reduce and narrow the polymer's molecular weight distribution to a range from 2.2 to 3.5 Mw/Mn by the addition of up to 3000 parts per million (ppm) of peroxide. During the meltblowing process, the modified reactor granule polymer has an increased melt flow rate from 400 gms/10 min. to 3000, for example, to a range between 800 up to 5000 gms/10 min at 230'C.

Particularly preferred embodiments include a polypropylene resin in the form of a reactor granule having a starting molecular weight distribution of 3.6 to 4.8 Mw/Mn and a melt flow rate of from 600 to 3000 gms/10 min. at 230"C which is combined with a small amount of peroxide, less than

500 ppm, to produce a modified polypropylene having a very high melt flow rate of up to 5000 gms/10 min. at 230 ^β C and a narrower molecular weight distribution of 2.8 to 3.5 Mw/Mn. Alternatively, an improved fine fiber web for use as a barrier layer can be formed by utilizing a resin, particularly polypropylene, having a narrow molecular weight distribution and having a lower melt flow rate which resin is modified by the addition of a larger amount of peroxide prior to melt-blowing to achieve a high melt flow rate. The starting reactor granule polypropylene resin in this case has a molecular weight distribution between 4.0 and 4.8 Mw/Mn and a melt flow rate ranging from 400 to 1000 gms/10 min. at 230'C. The polypropylene resin is modified by adding peroxide in amounts ranging from 500 to 3000 ppm (the higher amounts of peroxide being used in connection with the lower initial melt flow rate) . The modified polypropylene resin has a melt flow rate, up to about 3000 gms/10 min. at 230*C and a narrow molecular weight distribution of 2.2 to 2.8 Mw/Mn, for example. Most preferably, the starting polypropylene resin for the fine fiber web of the lightweight nonwoven laminate of the present invention is a polypropylene reactor granule which resin has a molecular weight distribution between 3.6 and 4.8 Mw/Mn, has a melt flow rate of up to 3000 gms/10 min. at 230*C, and is treated with about 500 ppm of peroxide to produce a modified resin having a melt flow rate greater than 2000 gms/10 min. at 230*C and a molecular weight distribution of from 2.8 to 3.5 Mw/Mn. The broader molecular weight distribution at the high melt flow rate helps minimize production of lint and polymer droplets (shot) .

Turning to Figure 1, there is shown schematically a forming machine 10 which may be used to produce an improved nonwoven fabric laminate 12 having a fine fiber meltblown barrier layer 32 in accordance with the present invention. Particularly, the forming machine 10 consists of an endless foraminous forming belt 14 wrapped around rollers 16 and 18 so that the belt 14 is driven in the direction shown by the

arrows. The forming machine 10 has three stations, spun-bond station 20, melt-blown station 22, and spun-bond station 24. It should be understood that more than three forming stations may be utilized to build up layers of higher basis weight. Alternatively, each of the laminate layers may be formed separately, rolled, and later converted to the fabric laminate off-line. In addition the fabric laminate 12 could be formed of more than or less than three layers depending on the requirements for the particular end use for the fabric laminate 12. For example, for some applications it may be preferred to have at least two inner meltblown layers for improved performance and for extremely lightweight applications a two-layer laminate may be made.

The spunbond stations 20 and 24 are conventional extruders with spinnerettes which form continuous filaments of a polymer and deposit those filaments onto the forming belt 14 in a random interlaced fashion. The spun-bond stations 20 and 24 may include one or more spinnerette heads depending on the speed of the process and the particular polymer being used. Forming spunbonded material is conventional in the art, and the design of such a spunbonded forming station is thought to be well within the ability of those of ordinary skill in the art. The nonwoven spunbonded webs 28 and 36 are prepared in conventional fashion such as illustrated by the following patents: Dorschner et al. United States Patent No 3,692,618; Kinney United States Patent Nos. 3,338,992 and 3,341,394; Levy United States Patent No. 3,502,538; Hartmann United states Patent Nos. 3,502,763 and 3,909,009; Dobo et al. United States Patent No. 3,542,615; Harmon Canadian Patent No. 803,714; and Appel et al. United States Patent No. 4,340,563. Other methods for forming a nonwoven web having continuous filaments of a polymer are contemplated for use with the present invention.

Spunbondedmaterials preparedwith continuous filaments generally have at least three common features. First, the polymer is continuously extruded through a spinnerette to form discrete filaments. Thereafter, the filaments are drawn

either mechanically or pneumatically without breaking in order to molecularly orient the polymer filaments and achieve tenacity. Lastly, the continuous filaments are deposited in a substantially random manner onto a carrier belt to form a web. Particularly, the spunbond station 20 produces spun-bond filaments 26 from a fiber forming polymer. The filaments are randomly laid on the belt 14 to form a spunbonded external layer 28. The fiber forming polymer is described in greater detail below. The meltblown station 22 consists of a die 31 which is used to form microfibers 30. The throughput of the die 31 is specified in pc nds of polymer melt per inch of die width per hour (PIH) . As the thermoplastic polymer exits the die 31, high pressure fluid, usually air, attenuates and spreads the polymer stream to form microfibers 30. The microfibers 30 are randomly deposited on top of the spunbond layer 28 and form a meltblown layer 32. The construction and operation of the meltblown station 22 for forming microfibers 30 and meltblown layer 32 is considered conventional, and the design and operation are well within the ability of those of ordinary skill in the art. Such skill, is demonstrated by NRL Report 4364, "Manufacture of Super-Fine Organic Fibers ¹¹ , by V.A. endt, E.L. Boon, and CD. Fluharty; NRL Report 5265, "An Improved Device for the Formation of Super-Fine Thermoplastic Fibers", by K.D. Lawrence, R.T. Lukas, and J.A. Young; and United States Patent No. 3,849,241, issued November 19, 1974, to Bun in et al. Other methods for forming a nonwoven web of microfibers are contemplated for use with the present invention. The meltblown station 22 produces fine fibers 30 from a fiber forming polymer which will be described in greater detail below. The fibers 30 are randomly deposited on top of spunbond layer 28 to form a meltblown internal layer 32. For a barrier flap fabric laminate, for example, the meltblown barrier layer 32 has a basis weight of preferably about 3 gsm to about 26 gsm, more preferably from about 6 gsm to -about 12 gsm.

After the internal layer 32 has been deposited by the meltblown station 22 onto layer 28, spun-bond station 24 produces spunbond filaments 34 which are deposited in random orientation on top of the melt-blown layer 32 to produce external spunbond layer 36. For a barrier flap fabric laminate, for example, the layers 28 and 36 each have a basis weight of preferably from about 10 gsm to about 30 gsm, more preferably about 15 gsm to about 25 gsm.

The resulting SMS fabric laminate web 12 (Fig. 2) is then fed through bonding rolls 38 and 40. The surface of the bonding rolls 38 and 40 are provided with a raised pattern such as spots or grids. The bonding rolls are heated to the softening temperature of the polymer used to form the layers of the web 12. As the web 12 passes between the heated bonding rolls 38 and 40, the material is compressed and heated by the bonding rolls in accordance with the pattern on the rolls to create a pattern of discrete areas, such as 41 shown in Fig. 2, which areas are bonded from layer to layer and are bonded with respect to the particular filaments and/or fibers within each layer. Such discrete area or spot bonding is well-known in the art and can be carried out as described by means of heated rolls Or by means of ultrasonic heating of the web 12 to produced discrete area thermally bonded filaments, fibers, and layers. In accordance with conventional practice described in Brock et al.. United States Patent No. 4,041,203, it is preferable for the fibers of the meltblown layer in the fabric laminate to fuse within the bond areas while the filaments of the spun-bonded layers retain their integrity in order to achieve good strength characteristics. For heavier basis weight laminates, for example, sonic bonding as described in United States Patent 4,374,888, incorporated herein by reference, is preferred.

Turning to Figs. 3 and 4, alternative embodiments are illustrated. Fig. 3 is a cross-section similar to Fig. 2 showing a two layer laminate 13 comprised of fine fiber layer 32 and continuous filament layer 36 combined by thermal bond 39. Fig. 4 is a similar view of an alternative three-layer

embodiment 15 comprising outer fine fiber layers 32 with inner continuous filament layer 36 combined by thermal bond 37.

In accordance with the invention, the total basis weight of the laminate is in the range of up to about 55 gsm, more preferably up to about 34 gsm, most preferably up to about 29 gsm and the amount of fine fibers compared to continuous filaments is at least about 20%, more preferably at least about 25% based on total weight of fine fibers and continuous filaments. In accordance with the present invention, a preferred embodiment of a meltblown web formed in accordance with U.S. Patent 5,213,881 to Timmons, Kobylivker and oon dated 25 May 1993, incorporated herein by reference, is utilized as the fine fiber component or components. The resulting meltblown web 32 with its fine fibers and resulting small pore size distribution has superior barrier properties when incorporated into a fabric laminate. Particularly, the unla inated meltblown web 32 has an average fiber size of from 1 to 3 microns and pore sizes distributed predominantly in the range from 7 to 12 microns, with a lesser amount of pores from 12 to 25 microns, with virtually no pores greater than 25 microns, and with the peak of the pore size distribution less than 10 microns.

The present invention can be carried out with polyolefins including predominantly propylene polymer but which may include, polyethylene, or other alphaolefins polymerized with Ziegler-Natta catalyst technology, and copolymers, terpolymers, or blends thereof. Polypropylene is preferred for the continuous filament web.

EXAMPLE

A lightweight nonwoven laminate was produced generally in accordance with the teachings of U.S. Patent 4,041,203 to Brock and Meitner dated 9 August 1977, incorporated herein in its entirety by reference. An in-line process was utilized as shown in Fig. 1 where the initial layer of spunbond is laid

on the forming wire followed by the meltblown layer and finally the final layer of spunbond. The target total basis weight of the fabric was between 25 gsm and 34 gsm with the meltblown making up from between 6 gsm and 12 gsm of the total. For this Example, equal amounts of spunbond were on each side of the meltblown web although not essential to the invention.

The three-layer laminate material was then bonded using a thermal-mechanical bonder as in the above-mentioned U.S. Patent 4,041,203. As is preferred, a pattern bond roll with a percent bond area from 5 to 20%, target of 13%, and with a pin density from 50 to 350 pin /sq. in., target of 300/sq in was utilized. The temperature of the system was between 200*F to 300*F with a target of 250'F. Bonding pressure was set so that a uniform nip was maintained across the face of the unit.

In accordance with the foregoing an in-line SMS fabric was produced with a total weight of 29 gsm of which 25% was made up of meltblown. The spunbond polymer was Exxon PD3445 polypropylene and the meltblown was Exxon 3495G polypropylene, both of which are available from Exxon Chemical Company. The fabric was then bonded using a-"wire weave" pattern roll that had a bond area of 13% with a pin density of 300 pin/sq. in. and was operated at a temperature of 250'F.

Table 1 illustrates the combination of properties obtained with the nonwoven laminate material of the Example. Basis weight was determined in accordance with ASTM Standard Test D3775-9. Hydrostatic head was determined in accordance with Method 5514 Federal Test Methods STD No. 191A, also AATCC STD 127-1980. Frazier air porosity was determined in accordance with ASTM D737, also Federal Test Methods 5450 Standard No. 191A. Cup crush results were determined by measuring the peak load required for a 4.5 cm diameter hemispherically shaped foot to crush a 9"x9" piece of fabric shaped into an approximately 6.5 cm diameter by 6.5 cm tall inverted cup while the cup shaped fabric was surrounded by an approximately 6.5 cm diameter cylinder to maintain a uniform deformation of the cup shaped fabric. The foot and the cup

were aligned to avoid contact between the cup walls and the foot which could affect the peak load. The peak load was measured while the foot was descending at a rate of about 0.25 inches per second (15 inches per minute) utilizing a Model FTD-G-500 load cell (500 gram range) available from the Schaevitz Company, Tennsauken, New Jersey which provides the energy value.

TABLE 1

Fine Fiber Layer

Composition polypropylene

Average fiber diameter (microns) __3

Basis weight (gsm) 7.2

Continuous Filament Layers

Composition polypropylene

Average filament diameter (microns) 21

Basis weight (gsm-each) 10.8

Laminate

Basis weight (gsm) 28.82 Frazier Porosity (SCFM) 75 Hydrostatic head (cm water) 45 Cup Crush Peak Load (g) 70 Cup Crush Energy (g/mm) 1500

When incorporated into a personal care article as a barrier flap component, the laminate of the Example demonstrated highly desired functionality and perceived comfort.

Thus, in accordance with the invention there has been described an improved lightweight nonwoven laminate. Variations and alternative embodiments will be apparent to those skilled in the art and are intended to be embraced within the appended claims.