BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to nonwoven fabrics made by thermally bonding fibrous webs made from certain types of multiconstituent fibers, and to laminates incorporating said fabrics. Thermal bonding of the nonwoven fabrics may be accomplished by calender or `through air` techniques or ultrasonically. The multiconstituent fibrous webs may contain other fibers in addition to the thermoplastic multiconstituent fibers. The nonwoven fabrics produced according to the present invention may be optimized as to softness and strength characteristics. 
     2. Description of the Prior Art 
     Structured multicomponent fibers--made by coextrusion of different polymers in a variety of structured configurations--have long been well-known. Some relevant references are: Davies (U.S. Pat. No. 3,595,731), Gerlach (U.S. Pat. No. 4,361,609), Kiriyama (U.S. Pat. No. 4,568,506), and Uchikawa (U.S. Pat. No. 4,770,925). 
     A few references cite fibers and nonwoven fabrics made from polymer blends wherein the dominant continuous phase is lower melting than is the dispersed noncontinuous phase; see Kubo (European Patent Application No. 0277707), Wincklhofer (U.S. Pat. No. 3,620,892) and Vassilatos (U.S. Pat. No. 4,632,861). By definition, to thermally bond such fibers, portions of the continuous fiber phase are raised to temperatures where partial molecular relaxation of the continuous lower melting phase occurs. Relaxation occurs not only at the bond site proper but also in the fiber region surrounding the bond site which is responsible for distributing a load or strain throughout the bonded fiber network. Although thermally-bonded nonwoven fabrics can be made from these materials, strength is compromised. 
     Some instances are also known wherein blends of different polymers are extruded from the orifices of spinnerets in order to make fibers containing &#34;free form&#34; microfibrils which can then be separated from the matrix polymer: Breen (U.S. Pat. No. 3,382,305), Twilley (U.S. Pat. No. 3,369,057), and Allan (U.S. patent application Ser. No. 07/220,203). 
     Finally, Graham U.S. Pat. No. (4,769,279) refers to meltblown fibers and fabrics made from blends of ethylene/acrylic copolymer with a second fiber-forming polymer such as a polyvinyl, a polyamide, and a polyolefin. Graham does not disclose thermally-bonded nonwoven fabrics from engineered fibers, however. Furthermore, the Graham disclosure is limited to blends based upon low viscosity ethylene/acrylic copolymers. 
     SUMMARY OF THE INVENTION 
     The present invention provides nonwoven fabrics made of engineered multiconstituent fibers. By &#34;engineered&#34; fibers, we mean oriented fibers made by melt-spinning blends of two or more immiscible polymers that are highly dispersed and that contain a dominant continuous phase which is substantially higher in melting point than the discontinuous phase or phases. 
     The present invention provides a thermally-bonded nonwoven fabric having a basis weight in the range of 5 through 100 g/m 2  that is made from a web which comprises from 100 to 5 percent by weight of a multiconstituent fiber having a fineness of 5 to 50 microns and up to 95 percent by weight of other fibers. Said multiconstituent fiber is composed of a highly dispersed blend of at least two different immiscible thermoplastic polymers and has a dominant continuous polymer phase and at least one noncontinuous phase dispersed therein. The noncontinuous phase exists as an elongated fibrillar polymer domain oriented generally in the direction of the fiber axis. The mean of the polymer domain cross-sections of said noncontinuous phase or phases is less than 0.1% of the cross-sectional area of said fiber. The polymer of the noncontinuous phase or phases has a Polymer Melt Temperature (PMT) at least 30° C. below the PMT of said continuous phase. The fiber is configured such that said noncontinuous phase or phases occupy a substantial portion of the fiber surface. 
     In addition to the fabrics described above, laminates--made by combining nonwoven fabrics made from the materials and processes as described herein with films, paper, tissue, woven fabrics, or nonwoven fabrics such as meltblowns--are also contemplated. The fabric according to the invention readily bonds to other materials of the sorts mentioned, and is therefore suitable for use in filtration media, medical and clean room garments, CSR wrap, absorbent article backsheets, and other barrier structures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a photomicrograph of a cross-section of a 20-micron-diameter fiber enlarged 25,000 times. 
     FIG. 2 is a graphic comparison of tensile strengths versus temperature for various fibers. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Biconstituent or multiconstituent fibers that may be used to make fabrics according to the present invention are those which are spun from an intimately-mixed blend of different polymers in which at least two of the polymers in the blend are immiscible. The choice of polymers is limited to those that are thermoplastic (including many elastomers) and that have a melt temperature below 350° C., preferably below 275° C. Examples of polymers that can be used are: 
     Polyethylenes: 
     Low density PE (0.90-0.940 g/cc) 
     Long-chain branched PE 
     LLDPE (made with C 3  -C 10  alpha-1-olefin copolymers or 4-methyl-1-pentene) 
     Medium and high density PE (0.940-0.960 g/cc) 
     Homopolymer or with copolymers described above 
     Atactic polypropylene 
     Polypropylene (at least 90% isotactic) 
     Block copolymers of ethylene and propylene 
     Random copolymers of ethylene and propylene 
     Polybutylene 
     Poly(4-methyl-1-pentene) [TPX] 
     Polycarbonate 
     Polyesters, e.g. poly(oxyethyleneoxyterephthaloyl) 
     Polyamides, e.g. poly(imino-1-oxohexamethylene) [Nylon 6] and poly(iminohexamethyleneiminoadipoyl) [Nylon 66] 
     Poly(oxymethylene) 
     Polystyrene 
     Styrene copolymers, e.g. styrene acrylonitrile [SAN] 
     Polyphenylene ether 
     Polyphenylene Oxide [PPO] 
     Polyetheretherketone [PEEK] 
     Polyetherimide 
     Polyphenylene Sulfide [PPS] 
     Poly(vinyl acetate) [PVA] 
     Poly(methyl methacrylate) [PMMA] 
     Poly(methacrylate) [PMA] 
     Ethylene acrylic acid copolymer 
     Polysulfone 
     The biconstituent or multiconstituent fibers that make up a significant portion of the webs to be thermally bonded according to the present invention must exhibit a high degree of dispersion. In principle, the mean of the cross-sectional areas of the noncontinuous phase or phases is less than 1/1000th of the cross-sectional area of the fiber. Factors which determine the level of dispersion and phase morphology of the dispersed phase or phases in blend fibers are discussed in detail by D. R. Paul in &#34;Polymer Blends&#34;, volume 2, chapter 16. Briefly, the dispersed-phase morphology of the blend fiber is dependent upon the relative rheologies of the blend components, the interfacial tension between the two or more phases, the polymer volume ratio, and the three stages of the blend melt preparation and processing: melt dispersion, extrusion, and extrudate draw-down prior to solidification. In general, the largest domains in the blend will exist when the polymer ratio is near 1.0; at this point the polymers are nearly co-continuous. The domain size of the discontinuous phase will decrease as the ratio deviates from 1.0, given that the quantity of work `mixered` into the blend and the melt-spinning conditions remain constant. 
     Thermal bonding work on fabrics made from biconstituent polyethylene/polypropylene staple fibers has demonstrated weak bonding at calender temperatures at and just above the melting point of the lower melting polyethylene constituent. One of the problems with biconstituents in general in thermal bonding can be that the lower melting component is distributed throughout the fiber matrix rather than being concentrated at the surface where it can be active in bonding. Therefore fibers according to the present invention are often preferably fibers with increased surface-to-volume ratios, with the ultimate being a ribbon-shaped fiber. High surface/volume fibers make more of the lower melting component available for bonding, which ultimately results in higher tensile strength fabrics and laminates. 
     FIG. 1 is a TEM photomicrograph of a RuO 4  -stained polyethylene/polypropylene fiber cross-section, enlarged 25,000 times. The dark domains are polyethylene (PE); the lighter domains are the continuous polypropylene (PP) phase. The photograph demonstrates how well the PE phase is dispersed in the PP phase. It is interesting to note how the PE phases become circumferentially elongated at the fiber surface. 
     Fibers used to make fabric in accordance with the present invention may be processed as follows: two or more polymers, selected to meet the melting point differential that characterizes the present invention, are combined and blended to form a dispersion. The dispersion is then emitter melt-spun into fibers, which may be formed into webs for instance by carding, airlaying, or wetlaying, or melt-spun directly into fibrous webs by a spunbonding process. The webs are then thermally-bonded to transform them into strong soft biconstituent-fiber nonwoven fabrics. The specific fabric characteristics will be dependent on the choice of precursor fiber and processing conditions. Said nonwoven fabrics may then be laminated into structures having a variety of desirable end-use characteristics. 
     Appropriate combinations of polymers combined to make the fibers used in accordance with the present invention are intimately blended before being melt-spun into fibers or fibrous webs. A high degree of mixing is necessary in order to prepare blends that will satisfy the degree of dispersion criteria that characterizes the fibers used according to the present invention. Among the commercially available mixers that can be used are the Barmag 3DD three-dimensional dynamic mixer supplied by Barmag AG of West Germany and the RAPRA CTM cavity-transfer mixer supplied by the Rubber and Plastics Research Association of Great Britain. 
     An example of an immiscible blend according to the present invention is a supermixed blend of linear low density polyethylene with polypropylene. 
     Thermally-bonded nonwoven fabrics according to the present invention exhibit advantages over similar homofilament-based nonwovens. A few of those advantages are higher tensile strength/basis weight ratio, and higher tear resistance/basis weight ratio. Many of these advantages are made possible by the fact that the lower melting component of the fibers used according to the present invention effects bonding at conditions that do not cause `relaxation` or loss of molecular orientation of the higher melting component. Typically, fiber used for thermally-bonded coverstock is not highly oriented. Highly oriented polypropylene, for example, is difficult to bond thermally without loss of molecular orientation in the individual filament. In addition, fabrics made from highly drawn polypropylene are harsh and possess poor `hand`. The filaments described by the present invention can be highly drawn to impart high tenacities and then thermally bonded into a nonwoven fabric with essentially no loss of individual filament tenacity. The retention of individual filament tenacity improves the strength properties of the fabric. Selection of the appropriate polymer (polyethylene for example) as the bonding constituent yields a fabric with greater softness than its homofilament counterpart. 
     The process for manufacturing the webs to be thermally or sonically bonded according to the present invention can be any of the known commercial processes for making nonwoven fabrics, including processes that use mechanical, electrical, pneumatic, or hydrodynamic means for assembling fibers into a web, for example carding, wetlaying, carding/hydroentangling, wetlaying/hydroentangling, and spunbonding. 
     EXAMPLE 1 
     Biconstituent staple fiber was prepared by dry blending 40% by weight of an ethylene/1-octene linear low density polyethylene [LLDPE] having a melt index of 26.5 and a density of 0.940 grams/cc with 60% by weight of controlled rheology polypropylene [PP] having a melt flow rate of 26. The dry blend [PP/LLDPE] was fed into a single-screw extrusion system equipped with a Barmag 3DD intensive mixer. Filaments were extruded and drawn to a final denier per filament of approximately 2.0. Line speeds and cold draw ratios were adjusted to produce two filament samples, one having 2X cold draw and another having 3.5X draw. Refer to Table I, samples 8319-2 and 8319-3, respectively. 
     One gram samples of each fiber type were formed into a web using a lab-scale carding device. The carded webs were then bonded on a Beloit-Wheeler lab top calender using a 16%-diamond-bond pattern and a nip pressure of approximately 400 PLI. Strip tensile strengths were determined for samples bonded over a range of temperatures. Carded webs made from Hercules T-185 polypropylene fiber served as a control. The biconstituent-based fabrics demonstrate superior tensile properties over the polypropylene homofilament-based fabric (see Tables II, III, and IV, and FIG. 2). 
     EXAMPLE 2 
     Both polypropylene and PP/LLDPE dry blend samples were (separately) fed into a single-screw extrusion system equipped with a Barmag 3DD intensive mixer. Filaments were extruded and drawn to a final denier per filament of approximately 2.0. Line speeds and cold draw ratios were adjusted to produce filament samples having 2X draw. Refer to Table I, samples 8319-1A and 8319-2, respectively. 
     Each fiber sample was separately carded and thermally bonded on a 36-inch-wide semicommercial line. Physical properties were then determined for the fabric samples. Data in Table V. The biconstituent fiber-based fabrics exhibited superior strip and grab tensiles, energies at yield (TEA), and tear values. 
     EXAMPLE 3 
     Staple biconstituent fiber containing 1% by weight of a substituted-sorbitol nucleating agent was prepared from dry blends of PP/LLDPE that was fed into a single-screw extrusion system equipped with a Barmag 3DD intensive mixer. Filaments were extruded and drawn to a final denier per filament of approximately 2.0. Line speeds and cold draw ratios were adjusted to produce filament samples having 3.5X draw. Refer to Table I, sample 8319-7. 
     The fiber was carded and thermally bonded on a 36-inch-wide semicommercial line. Data in Table VI. The strip and grab tensiles, energies at yield, and tear values were superior to a similar fiber sample without nucleating agent. 
     EXAMPLE 4 
     Biconstituent fiber 8342 was prepared from a dry blend of 40% by weight of an ethylene/1-octene copolymer [LLDPE] having a melt index of 50 and a density of 0.925 g/cc with 60% by weight of controlled rheology polypropylene [PP] having a melt flow of 35. Multiconstituent fiber 8343 was prepared from a dry blend of 40% by weight LLDPE having a melt index of 50 and a density of 0.925 g/cc with 55% by weight of controlled rheology PP having a melt flow of 35 and with 5% by weight of ethylene/acrylic acid copolymer [EAA] composed of low density polyethylene having a melt index of 300 and an acrylic acid content of 20%. Melt blends were then separately prepared and extruded and pelletized using a single screw extruder equipped with a 6 row Rapra cavity-transfer mixer (CTM) and a strand die cutter. The polymer-blend pellets were then separately re-extruded into filaments and melt-drawn to a final denier per filament of 1.9 and 2.7, respectively. 
     One gram samples of each fiber type were formed into webs, bonded, and tested as described in Example 1. Filament and fabric tensile properties are indicated in Table VII. 
     END-USE EXAMPLES 
     Example 5 
     8350-1A: PE film to PE/PP bicon fabric 8326-03 (1 osy) 
     8350-1B: PE film to PP fabric 8326-02 (1 osy) 
     To demonstrate the ability of multiconstituent fabric to form a fabric/film laminate, five-inch-wide fabric samples of a thermally bonded multiconstituent fiber-based nonwoven fabrics were `heat sealed` to polyethylene film. Laminate samples were prepared by heat-sealing a sandwich structure composed of carded fabric (8326-02 and 8326-03) (bottom)/polyethylene film (middle)/cover fabric (8326-02) (top). The cover fabric was used to insulate the low melting film from the sealing die. Fabric and film dimensions were 5&#34;×12&#34;. Time, pressure, and die-temperature conditions were chosen that insured optimum adhesion of the fabric to the film while maintaining the film integrity. The heat sealer used was a Hut-Theller Precision Instruments West, Model EB (Petaluma, Calif.). Multiple heat-sealed samples were prepared by sealing across the width of the laminate sample. The die dimensions were flat, 3/8&#34;×5&#34;, or 1.875 square inches. 
     Peel strengths were determined relative to a homofil fabric laminate control. Peel strengths are indicative of the level of adhesion between the fabric and film layers of the laminate. Peel strengths were determined using an Instron Model 4201 tensile tester. Strips 1-inch wide were cut from each sealed sample. The fabric was placed in the upper grip of the tensile tester and the film in the lower grip. A gauge length of 3-inches and a cross-head speed of 5-inches/minute were used. Peel strength properties are indicated in Table VIII. The level of adhesion was greater for the laminate which contained the multiconstituent fiber. 
     Examples 6 and 7 relate to breathable liquid barrier laminates with textile-like hand. Such laminates are suitable for use but not limited to use as medical and industrial garments, CSR wrap, surgical drape, and housewrap. The laminates are prepared from a layer or layers of microfibrous (for example meltblown) polymer, such as polypropylene, sandwiched between two layers of nonwoven fabric containing multiconstituent fiber according to the present invention. The discontinuous polymer phase of the multiconstituent fiber occupies a portion of the surface of the fiber such that both polymers of the blend are available for thermal or sonic bonding and/or lamination. The fabric can be bonded prior to lamination or can be directly deposited on either side of the microfibrous layer just prior to lamination. 
     The microfibrous layer can be composed of meltblown fibers, wet laid pulps, or webs prepared by other known means. The microfibrous layer can be formed prior to the lamination or extruded or formed directly onto the multiconstituent nonwoven fabric prior to lamination. The microfibrous layer must be composed of a polymer which adheres to either the continuous or discontinuous polymer component of the multiconstituent fiber upon thermal or sonic lamination. 
     Thus for instance, high melt flow isotactic polypropylene could be meltblown into a microfibrous web and then laminated to a fabric made from a polymer-blend fiber having polypropylene as one of the polymer constituents. Lamination can be with known calendering or sonic bonding technology. Bond pattern and processing conditions can be tailored to impart the desired combination of strength, barrier, drape, and textile aesthetics. 
     EXAMPLE 6 
     Samples of flat-calendered `sandwich-type` laminates were prepared from a polypropylene meltblown web weighing 20 grams per square meter and having a nominal filament diameter of 5 microns and two outer nonwoven layers composed of a multiconstituent fiber-based nonwoven fabric like that described in Example 1 and identified as Sample No. 8326-03 in Table V. The three webs were simultaneously unwound from a backstand and fed continuously into a heated calender nip. The lamination was effected using a 22&#34; lab calender equipped with a heated smooth rubber roll and a heated smooth steel roll. The samples were prepared at varied calender roll surface temperatures, ranging from 318° F. to 306° F. for the steel roll and from 300° F. to 284° F., for the rubber roll. Nip pressure was held constant at 150 pounds per linear inch (pli), and line speed was held constant at 22 feet per minute. 
     Physical properties were determined for the resulting laminate samples and are identified as sample numbers 8331-1A through 8331-1F in Table IX. It is apparent from these data (8331-1A through 8331-1F) that a breathable liquid-barrier laminate can be obtained with excellent fabric tenacity. 
     EXAMPLE 7 
     A helically-bonded `sandwich-type` laminate was prepared by a procedure similar to that described in Example 6, but wherein the smooth rolls were replaced with steel rolls engraved with a diagonal line pattern such that the angle between the crisscross bond lines of the diagonal bonds opening in the machine direction (MD) measures 120 degrees, each line measuring 60 degrees off the MD axis and such that the raised bonding surfaces of each roll are flat and approximately 1 mm wide, separated by a recessed area measuring approximately 1.5 mm wide. A laminate fabric was produced at 22 fpm, 150 pli, at a calender roll surface temperature of 290° F. to 294° F. 
     Physical properties were determined for the fabric which is identified as sample number 8331-04 in Table IX. It is apparent from a comparison of the thickness, tensile, and barrier properties of this fabric with those in the same Table which have been flat-calendered that significantly different properties can be obtained for laminates composed of identical starting materials. Thickness is greatly increased over the flat-calendered samples. The loft of a fibrous web contributes to its ability to filter airborne or liquidborne particles efficiently. Air permeability is equivalent to breathability, a property associated with comfort in disposable garments. Air permeability combined with liquid barrier properties defines a fabric which can be used as a protective garment in a medical or industrial end use. In addition, the range of properties exhibited by these laminates demonstrate the flexibility of multiconstituent fabrics in laminate applications. 
     EXAMPLE 8 
     By use of the isotactic polypropylene/linear low density polyethylene polymer blend fiber-based fabric described in Table V (Sample No. 8326-04C), laminates were prepared that demonstrate the flexible bonding character of these novel substrates. Film and meltblown fabric were acquired whose polymer compositions matched either that of the continuous phase or that of the noncontinuous phase of the polymer-blend fiber. The grades of each polymer were selected that suited the respective substrate manufacturing processes, and are therefore not the identical polymers used in the manufacture of the multiconstituent fiber. `Sandwich-type` laminates were prepared using the procedure described in Example 7. 
     Physical property data appears in Table X. It is apparent from examination of this data that laminates exhibiting excellent tensile and barrier properties can be prepared by bonding the multiconstituent fiber-based fabric to substrates composed of a polymer selected from the same polymer groups represented in the multiconstituent fiber. 
     From the above description and specific Examples of the invention, many variation in the webs, composites, useful products, and processes of this invention will be apparent to those skilled in the relevant arts. Such variations are within the scope of the present invention as measure by the apended claims. 
     
                                           TABLE I__________________________________________________________________________BICONSTITUENT FILAMENT PROPERTIESPOLYBLEND  COLD DENIER FILAMENT                              ELONGATIONFIBER      DRAW PER    TENACITY                              AT BREAKDB # DESCRIPTION           RATIO                FILAMENT                       (g/den)                              (%)__________________________________________________________________________8319-1AHIMONT Z30S PP           2.2  2.10   3.12   51                (.10)  (.12)  (9.4)8319-1BHIMONT Z30S PP           3.5  1.95   4.72   27                (.10)  (.39)  (3.7)8319-240/60 PE(a)/PP           2    1.96   2.04   95                (.11)  (.09)  (40)8319-340/60 PE(a)/PP           3.5  1.98   3.29   33                (.11)  (.39)  (7)8319-440/60 PE(b)/PP           2    2.00   2.39   128                (.10)  (.11)  (32)8319-540/60 PE(b)/PP           3.5  1.99   3.98   39                (.12)  (.20)  (4.8)8319-6PE(a)/PP + .5% NA           2    1.96   1.85   59                (.12)  (.08)  (18.6)8319-7PE(a)/PP + .5% NA           3.5  1.94   3.75   35                (.10)  (.17)  (5.3)__________________________________________________________________________ # DENOTES STANDARD DEVIATION, WHERE n = 10. PE(a)  DOW ASPUN (R) 6811, octene1/ethylene copolymer, MI = 26 PE(b)  DOW ASPUN (R) 6815, octene1/ethylene copolymer, MI = 12 PP  HIMONT Z30S Controlled Rheology Grade Polypropylene, MF = 26 NA  MILAD 5L7110 Nucleating Agent. 10% conc. in LLDPE 
    
     
                       TABLE II______________________________________LAB TOP FABRIC PROPERTIES OF BICONSTITUENTBASED THERMAL BOND FABRICS(FIBER: 40/60 PE/PP, 8319-2, 2 × DRAW, TABLE I)CALENDERSURFACETEMPERATURE        STRIP         TEADATA   EMB.      SM.       TENSILE     (in/g/BOOK # F.        F.        (g/in)                            SD   % E  in2)______________________________________8324-1 240       244        819   87  11   1162      250       254       1263   55  17   2243      255       259       1811   86  15   3174      260       264       1594   48  19   3025      265       269       1817  185  20   3476      270       274       2058  184  22   4517      275       279       2292  100  23   4848      280       284       2829  141  21   5549      289       285       3571  177  28   82110     294       290       3938  215  27   80411     299       295       3747  355  32   93012     305       300       3360  272  27   686______________________________________ 
    
     
                       TABLE III______________________________________(FIBER: 40/60 PE/PP, 8319-3, 3.5 × DRAW, TABLE I)______________________________________8324-13      240    245     469  53    6     4914           245    249     625  42    9     7815           250    254     765  52    9    10016           255    259     977  58    9    12317           260    264    1115 216    10   15318           265    269    1067 185    7    12819           270    274    1351 186    9    16420           275    279    1368  93    8    15821           280    284    1568 147    7    18222           289    285    1868 121    12   24723           294    290    3230 173    11   38124           299    295    4228 181    14   55925           305    300    2704 211    26   644______________________________________ 
    
     
                       TABLE IV______________________________________(FIBER: HERCULES T-185)______________________________________8324-26      270    265     834 29     20   19627           280    275    1611 103    33   57328           290    285    2705 51     73   175729           300    295    2809 361    54   128930           310    305    2136 95     14   232______________________________________ NOTES: ALL SAMPLES PRODUCED AT 500 PLI, 22 FPM, 18% BOND AREA 
    
     
                                           TABLE V__________________________________________________________________________PHYSICAL PROPERTIES OF SELECTED STAPLE BICONSTITUENTS__________________________________________________________________________                                    STRIP TENSILES    FIBER SAMPLE               FIBER CALENDER       MD*        CD*    IDENTIFICATION               DENIER                     SURFACE °F.                             B.W.                                LOFT                                    (1 osy)    (1 osy)DATABOOK #    (TABLE I)  (dpf) E/S     (gsy)                                (mils)                                    (g/in)                                        % E TEA                                               (g/in)                                                   %__________________________________________________________________________                                                       E TEA                                                       78326-02  PP FIBER 8319-1               2     270/300 28.8                                15.9                                    1124                                        35  164                                               288 39   788326-03  FIBER 8319-2, 2×               1.95  270/295 32.6                                13.4                                    2098                                        24  415                                               501 59  2568326-04C SAME AS ABOVE               1.95  300/300 31.6                                13.3                                    1972                                        14  207                                               704 40  255__________________________________________________________________________                                            ELMENDORF                                GRAB TENSILES                                            TEAR                                MD    CD    MD   CD   SOFT.                       DATABOOK #                                (lbs)                                   % E                                      (lbs)                                         % E                                            (g)  (g)  (psu)__________________________________________________________________________                       8326-02  4.8                                   16 2.1                                         33 109  144  1.7                       8326-03  10.5                                   24 4.6                                         58 138  200  0.9                       8326-04C 9.2                                   15 6.1                                         46  72  149  -0.8__________________________________________________________________________ 
    
     
                                           TABLE VI__________________________________________________________________________PHYSICAL PROPERTIES OF SELECTED STAPLE BICONSTITUENTS__________________________________________________________________________                                    STRIP TENSILES    FIBER SAMPLE               FIBER CALENDER       MD*        CD*    IDENTIFICATION               DENIER                     SURFACE °F.                             B.W.                                LOFT                                    (1 osy)    (1 osy)DATABOOK #    (TABLE I)  (dpf) E/S     (gsy)                                (mils)                                    (g/in)                                        % E TEA                                               (g/in)                                                   %__________________________________________________________________________                                                       E TEA                                                       18326-05  FIBER 8319-3               1.98  270/290 30.5                                12.9                                    1293                                        29  173                                               343 43   938326-07  FIBER 8319-6               1.93  270/290 31 14.1                                    1728                                        27  262                                               464 36  131__________________________________________________________________________                                            ELMENDORF                                GRAB TENSILES                                            TEAR                                MD    CD    MD   CD   SOFT.                       DATABOOK #                                (lbs)                                   % E                                      (lbs)                                         % E                                            (g)  (g)  (psu)__________________________________________________________________________                       8326-05  6.1                                   15 2.7                                         32 122  178  0.4                       8326-07  8.2                                   18 4  40 178  228  0.7__________________________________________________________________________ 
    
     
                       TABLE VII______________________________________FILAMENT AND FABRIC PROPERTIESOF SELECTED MULTICONSTITUENT FIBERSFILAMENT             FABRICPROPERTIES (1)       PROPERTIES (2)Fabric       Te-           Tough-            TEASample       nacity  Elong.                      ness  Tensile                                  Elong.                                        (in/g/No. (1) (dpf)  (gpd)   (%)   (gpd) (g/in)                                  (%)   in2)______________________________________8342-1 1.9    1.52    420   4.5   2808  74    993STD          (0.16)   (61) (1.0)  (251)                                  (17)DEV.8343-1 2.7    1.0     405   2.7   3276  30    727STD          (0.21)  (124) (0.8)  (377)                                   (6)DEV.______________________________________ STD DEV: N = 10 (1) 83421 Fabric: melt blend fiber composed of 40:60 wt % PE:PP 83431 Fabric: melt blend fiber composed of 40:55:5 wt. % PE:PP:EAA (2) Fabric properties normalized to 1.0 ounce/yd2 basis weight 
    
     
                       TABLE VIII______________________________________HEAT SEAL PEEL STRENGTHFOR BICONSTITUENT-FILM LAMINATE    Peel                  Peel    Strength    Elongation                          StrengthSample   pk load     at pk     TEANo.      (g/in)      (%)       (in/g/in2)______________________________________8350-1A  559         24        1758350-1B  443         27         86______________________________________ Die Geometry: 3/8&#34; × 5&#34;, flat Time: 500 msec Temp: top  245 F.; lower  245 F. Pressure: 550 psi 
    
     
                                           TABLE IX__________________________________________________________________________PE/PP BICONSTITUENT LAMINATES PHYSICAL PROPERTIES__________________________________________________________________________                    MODEL                    549  LAMINATION                                  STRIP TENSILES (2)SAMPLE DESCRIPTION               B.W. THICK.                         TEMP.    MD          CDDB # (1)            (gsy)                    (mils)                         (F.)     (g/in)                                      % E TEA (g/in)                                                  %__________________________________________________________________________                                                      E TEA                                                      08331-1AFC BICON./PPMB/BICON.               106  11.7 318/300  9078                                      15  1306                                              3940                                                  6   2508331-1B&#34;              102  9.2  316/297  9340                                      15  1078                                              4286                                                  8   2668331-1C&#34;              90   8.5  313/294  9508                                      16  984 3871                                                  8   2118331-1D&#34;              93   8.6  310/290  7963                                      11  674 4002                                                  6   1948331-1E&#34;              89   8.3  308/287  9189                                      14  855 4320                                                  8   2248331-1F&#34;              96   9.2  306/284  8440                                      14  1016                                              3796                                                  18  3068331-04HELIC. BIC./PPMB/BIC.               86   23.6 290/294  5863                                      15  625 3211                                                  17  353__________________________________________________________________________                              ELMENDORF                                      GURLEY   HYDRO-                              TEAR    POROSITY STATIC                                                     MASON                              MD  CD  (sec)    HEAD  JAR                         DB # (g/in)                                  (g/in)                                      (20 oz)                                          (5 oz)                                               (cm)  (sec)__________________________________________________________________________                         8331-1A                              360 770 56  275  24.1  10                         8331-1B                              325 575 93  &gt;5 min.                                               25.6  70                         8331-1C                              290 490 120 &gt;5 min.                                               22.5  39                         8331-1D                              260 580 66  &gt;5 min.                                               22    26                         8331-1E                              310 520 65  &gt;5 min.                                               19.6  33                         8331-1F                              320 600 29  &gt;5 min.                                               18.9  28                         8331-04                              330 460 inst.                                          7    13.2   3__________________________________________________________________________ NOTES: (1) FC  FLAT CALENDERED HELIC.  CRISSCROSS BOND PATTERN FROM HELICAL ROLLS PPMB  POLYPROPYLENE MELT BLOWN (20 gsm) BICON.  POLYETHYLENE/POLYPROPYLENE BICONSTITUENT FIBER BASED FABRIC 832603 (2) TENSILES CORRECTED TO 3 OSY UNIT WEIGHT 
    
     
                                           TABLE X__________________________________________________________________________PHYSICAL PROPERTIES OF POLYETHYLENE/POLYPROPYLENEBICONSTITUENT FABRIC LAMINATES__________________________________________________________________________               CALENDER                      UNIT                          (3)   GRAB TENSILESSAMPLE              TEMP. (2)                      WT. CALIPER                                MD El.                                      CD El.NO.   DESCRIPTION (1)               (F.)   (gsy)                          (mils)                                (lbs)                                   (%)                                      (lbs)                                         (%)__________________________________________________________________________8333-05 BICON/PE FILM/BICON               252/263                      76.6                          28.1  22 27 11.7                                         388333-06 BICON/PP FILM/BICON               287/288                      70.9                          26.4  22.7                                   30 11.1                                         428333-04 BICON/PE-MB/BICON               268/260                      93.6                          26.8  23.1                                   24 10.2                                         348331-04 BICON/PP-MB/BICON               290/294                      86.3                          27.2  25.3                                   25 10.8                                         36__________________________________________________________________________                        (4)            ELM.        GURLEY   (5)  HYDRO-            TEAR  MULLEN                        POROSITY MASON                                      STATIC      SAMPLE            MD CD BURST (5 oz)                            (20 oz)                                 JAR  HEAD      NO.   (g)               (g)                  (psi) (sec)    (sec)                                      (cm)__________________________________________________________________________      8333-05            400               540                  21    NR  53.3 3.16 18.4      8333-06            330               430                  19    NR  98   163  23.7      8333-04            350               400                  20    1.57                            NR   inst.                                      16.1      8331-04            320               380                  19    7.1 NR   3    13.2__________________________________________________________________________ NOTES: ALL PE IS 1OCTENE, LINEAR LOW DENSITY POLYETHYLENE, UNLESS OTHERWISE STATED (1) BICON -- BICONSTITUENT FIBERBASED FABRIC (832604 CARDED THERMALBOND, 40:60, PE:PP), 1 OSY PE FILM -- LOW DENSITY POLYETHYLENE FILM OBTAINED FROM EDISON PLASTIC, 1 MIL. PPFILM -- POLYPROPYLENE FILM OBTAINED FROM EDISON PLASTIC, 1 MIL PEMB -- POLYETHYLENE MELTBLOWN FABRIC, 20 GSM (2) CALENDER -- HELICAL STEEL/HELICAL STEEL, NIP PRESSURE = 350 PLI, LINE SPEED = 12.5 FPM (3) FABRIC CALIPER MEASURED USING A 551M CALIPER TESTER (4) NR -- NO READING, PROCESS EITHER TOO FAST OR TOO SLOW FOR ACCURATE MEASUREMENT (5) INST -- INSTANTANEOUS
The present invention provides a thermally-bonded nonwoven fabric that is made from a web which comprises from 100 to 5 percent by weight of multiconstitutent fibers. The multiconstituent fibers are composed of highly dispersed blends of at least two different immiscible thermoplastic polymers and have a dominant continuous polymer phase with at least one noncontinuous phase dispersed therein. The noncontinuous phase exists as an elongated fibrillar polymer domain oriented generally in the direction of the fiber axis. No single polymer domain cross-section of said noncontinuous phase or phases is larger than 0.1% of the cross-sectional area of said fiber. The polymer of the noncontinuous phase or phases has a Polymer Melt Temperature (PMT) at least 30° C. below the PMT of the continuous phase. The fiber is configured such that the noncontinuous phase or phases occupy a substantial portion of the fiber surface. In addition to such fabrics, laminates--made by combining nonwoven fabrics made from the materials and processes as described herein with films, paper, tissue, woven fabrics, or nonwoven fabrics such as meltblowns--are also contemplated. The fabric according to the invention readily bonds to other materials of the sorts mentioned, and is therefore suitable for use in filtration media, medical and clean room garments, CSR wrap, absorbent article backsheets, and other barrier structures.