Disposable semi-durable nonwoven fabric
FIELD OF INVENTION 
     This invention generally relates to nonwoven wiping cloths having industrial, hospital and household applications, and more particularly, fluid entangled semi-durable wipes which are absorbent, abrasion resistant, and conform to wiping surfaces. 
     BACKGROUND ART 
     Nonwoven wipes fabricated by fluid entangling processes are well known in the prior art. In conventional entangling processes, webs of nonwoven fibers are treated with high pressure fluids while supported on apertured patterning screens. Typically, the patterning screen is provided on a drum or continuous planar conveyor which traverses pressurized fluid jets to entangle the web into cohesive ordered fiber groups and configurations corresponding to void areas in the patterning screen. Entanglement is effected by action of the fluid jets which cause fibers in the web to migrate to void areas in the screen, entangle and intertwine. 
     Prior art hydroentangling processes for producing patterned nonwoven fabrics which employ high pressure columnar jet streams are represented by U.S. Pat. Nos. 3,485,706 and 3,498,874, respectively, to Evans and Evans et al., and U.S. Pat. No. 4,379,799 to Holmes et al. 
     The art has fabricated nonwoven wiping cloths by conventional entangling processes employing isotropic webs of blended rayon and polyester fibers which have application for use in disposable wipes. Rayon and polyester respectively impart absorbency and tensile strength to the wipe. Variations in the percentage blend of these fibers provide wipes for diverse food service, medical and industrial applications. Abrasion resistance in such wipes is enhanced by application of adhesive binders to the entangled fabric. U.S. Pat. No. 4,612,226 to Kennette et al. discloses a representative prior art wipe. 
     In the selection of specifications for wipes, the art has recognized that there is an inverse correlation between absorbency and strength in nonwoven wipes. Fabric voids provide surface areas for absorption of fluids, however, increased void area dimininishes the tensile strength of the fabric. The present invention is directed to a process and fabrics which are absorbent and have greater tensile strength than achieved in the prior art. 
     Accordingly, it is a broad object of the invention to provide an improved disposable semi-durable wipe having absorption and tensile strength features which advance the art. 
     A more specific object of the invention is to provide an improved hydroentangling process which yields a durable, nonwoven wipe which is characterized by conformability to wiping surfaces, supple drape, dimensional stability, and abrasion resistance. 
     Another object of the invention is to provide a hydroentangling process which produces a rayon/polyester blend nonwoven wipe having characteristics improved over the prior art. 
     DISCLOSURE OF THE INVENTION 
     In the present invention, these purposes, as well as others which will be apparent, are achieved generally by providing a disposable semi-durable wipe fabricated by fluid entanglement of a composite web including carded and randomized layers of blended rayon and polyester fibers. The composite web includes top and bottom sides which are respectively supported and fluid entangled on formacious entangling members. Two sided entanglement of the web enhances interstitial binding of web fibers to provide a durable fabric in which void areas are well defined for improved conformability and absorbency. 
     A preferred fabric of the invention is fabricated of a composite web including 70% 1.5 inch denier staple hemicellular free rayon and 30% non-optically brightened polyester. The fabric includes a lattice structure of spaced approximately parallel machine direction (&#34;MD&#34;) oriented fibrous bands, and spaced cross-direction (&#34;CD&#34;) oriented fibrous bands which intersect the MD bands. The CD bands each have a generally sinusoidal configuration and are arranged in an array in which each band is 180° out of phase with respect to adjourning bands in the array. Void areas defined by the areas of nonintersection of the MD and CD bands occupy approximately 36% of the entangled fabric to provide for enhanced fabric absorbency. The fabric has a basis weight in the range of 45-70 gsy, uniform cohesive MD and CD grab tensile strengths of approximately 25 lbs/inch, and MD/CD fiber ratio in the range of 1.5:1 to 2.5:1. 
     Further advantage is obtained by saturating the fabric with an adhesive resin binder to enhance fabric abrasion resistance. The preferred fabric is coated with an acyrlic binder including a wetting agent and a pigment fixative. 
     In accordance with the invention method, a composite web is provided which includes carded and randomized layers fabricated of a blend of at least 10% rayon with polyester fibers. Top and bottom sides of the web are respectively supported on formacious entangling members including void areas of approximately 39%, and traversed by first and second stage spaced entangling fluid jets. The fluid jets impact the web at pressures within the range of 400 to 2000 psi, and are preferably ramped, to impart energy to the web of approximately 0.7 to 1.2 hp-hr/lb of fabric. 
     Following entanglement, fluid is extracted from the fabric and an adhesive binder formulation, such as an acrylic resin polymer, may be applied to the fabric by conventional padding apparatus. The acrylic preferably has a low glass transition temperature (Tg) to provide a soft fabric finish. 
     It is a feature of the invention to employ entangling members which have a symmetrical pattern of void areas which correspond to preferred fabric patterns. Improved MD and CD tensile strengths are obtained by a two sided entanglement process which coacts with entangling member patterns. The preferred patterns include a 36×29 flat plain weave screen made of a plastic monofilament wire, and a 22×24 drum plain weave bronze wire screen which are, respectively, employed in the first and second entangling stages. 
     Other objects, features and advantages of the present invention will be apparent when the detailed description of the preferred embodiments of the invention are considered in conjunction with the drawings which should be construed in an illustrative and not limiting sense as follows: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a production line including high speed cards, hydroentangling modules, a vacuum dewatering roll, a padder, dry cans, and other apparatus for the production of nonwoven wipes in accordance with the invention; 
     FIG. 2 is a schematic illustration of the hydroentangling modules employed in the process of the invention; 
     FIG. 3 is a schematic illustration of the vacuum dewatering roll and padder employed in the process of the invention; 
     FIG. 4 is a plan view, partly in section, of a composite web employed in the invention including lower carded and upper randomized layers; 
     FIGS. 5A and B are photographs at 3.5× magnification of 36×29 and 22×24 mesh plain weave forming members, respectively, employed in the flat and drum entangling modules of FIG. 2; 
     FIG. 6 is a schematic illustration of a nonwoven fabric produced on the production line employing the forming members of FIGS. 5A and B; 
     FIGS. 7A and B are photographs at 2× and 11× magnification of nonwoven wipes produced as disclosed in Example 1; 
     FIGS. 8A and B are micro and open space light detection photographs at 7.5× magnification of the nonwoven wipe of FIGS. 7A and B showing void fiber pattern areas in the fabric; and 
     FIG. 8C is an inverse light detection photograph at 7.5× magnification of the nonwoven wipe illustrated in FIG. 8A. 
    
    
     BEST MODE OF CARRYING OUT THE INVENTION 
     With reference to the drawings, FIG. 1 shows a fabric production line 10 in accordance with the invention for production of nonwoven wipe fabrics including, a series of conventional carding apparatus C1-C6, a random web former 12, and pre-wet wire station 14 which feed a composite web 16 to hydroentangling modules 18, 20. At the output end of the entangling module 20, the line includes a deionized water rinse and vacuum slot extractor station 22, a conventional padder 24, and dry cans 26 which provide a finished nonwoven fabric 28 for stock rolling on a winder 30. An antistatic roll 32 and weight determination gauge 34 are also employed on the line. 
     Modules 18, 20 effect two sided entanglement of the composite web 16 which includes randomized and carded layers 36, 38 to provide a fabric with well defined interstitial fiber entanglement and structure. Particular advantage is obtained in the invention when the composite web 16 is anistropic and includes a blend of at least 10% rayon and polyester staple fibers. 
     The preferred composite web 16 is fabricated of a blend of AVTEX SN 6533 1.5 denier 1.5 inch staple hemicellular free rayon manufactured by Avtex Fibers Inc., Front Royal, Va, and a non-optically brightened polyester offered by Celanese Corporation, Charlotte, N.C. under product designation T-304. The AVTEX rayon and Celanese polyester fibers are processed in an open blender to provide web layers 36, 38 each having a 70/30 per cent rayon/polyester content, and weight of approximately 29 gsy. 
     Advantage in the invention is obtained by combining features of both carded and random web layers in the composite web 16 for use in hydroentangling modules 18, 20. As described hereinafter, layers 36, 38 coact to produce a fabric 28 which has improved uniformity and superior MD/CD strength characteristics. The composite web 16 and photomicrographs of a preferred fabric are respectively illustrated in FIGS. 4 and 7A and B. 
     Method and Mechanism of the Entangling Modules 
     As illustrated in FIG. 1, following carding the upper web layer 36 is advanced on conveyor 40 to the random web former 12 to form an upper isotropic layer. Conveyors 42, which by-pass the web former 12, advance carded layer 38 to the pre-wet station 14 for combination with randomized layer 36 and feeding to the entanglement modules 18, 20. 
     FIG. 2 illustrates the entanglement modules 18, 20 which are utilized in a two staged process to hydroentangle, in succession, top and bottom sides 36a, 38a of the composite web 16. 
     Module 18 includes a first entangling member 44 supported on an endless conveyor means which includes rollers 46 and drive means (not shown) for rotation of the rollers. Preferred line speeds for the conveyor are in the range of 50 to 600 ft/min. 
     The entangling member 44, which preferably has a planar configuration, includes a symmetrical pattern of void areas 48 which are fluid pervious. A preferred entangling member 44, shown in FIG. 5A, is a 36×29 mesh weave having a 23.7% void area, fabricated of polyester warp and shute round wire. Entangling member 44 is a tight weave seamless weave which is not subject to angular displacement or snag. Specifications for the screen, which is manufactured by Appleton Wire Incorporated, P.O. Box 508 Kirby, Portland, Tenn. 37148, are set forth in Table I. 
     
                       TABLE I                                                     
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Forming Screen Specifications                                             
Property     36 × 29 flat                                           
                           22 × 24 drum                             
______________________________________                                    
Mesh         36 × 29 ± 1                                         
                           22 × 24 ± 1                           
Warp wire    .0157 polyester                                              
                           .025 ± .002 face x                          
(stainless steel                                                          
             round         .013 ± .002 height                          
or bronze)                                                                
Shute wire   .0157 polyester                                              
                           .018 ± .002                                 
(stainless steel                                                          
             round                                                        
or bronze)                                                                
Weave type   plain         plain                                          
Open area    23.7%         25.6% ± 1.5                                 
Plane difference           .008 ± .002                                 
Snag         none ± light                                              
Weave tightness (slay)                                                    
             no angular                                                   
             displacement                                                 
Edges        1/2&#34; reinforcement                                           
                           butted                                         
Seam         invisible/endless                                            
                           invisible/endless                              
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     Module 18 also includes an arrangement of parallel spaced manifolds 50 oriented in a cross-direction (&#34;CD&#34;) relative to movement of the composite web 16. The manifolds which are spaced approximately 10 inches apart and positioned approximately 1 inch above the first entangling member 44, each include a plurality of closely aligned and spaced jet nozzles (not shown) designed to impact the web with fluid pressures in the range of 400 to 2000 psi. Manifold pressures are preferably ramped in the machine direction so that increased fluid impinges the web as its lattice structure and coherence develop. Effective first stage entanglement in the invention is effected by energy output to the composite web 16 of at least 0.1 hp-hr/lb and preferably in the range of 0.1-0.5 hp-hr/lb. 
     Following the first stage entanglement, the composite web 16 is advanced to module 20 which entangles the bottom side 38a of the web. Module 20 includes a second entangling member, shown in FIG. 5B, which has a cylindrical configuration 52, and 26% symmetrical pattern of void areas 55. Entangling member 52 is a 22×24 plain weave, manufactured by Appleton Wire Incorporated, fabricated of stainless steel or bronze warp and round shute wire having the specifications set forth in Table I. 
     Module 20 functions in the same manner as the planar module 18. Manifolds 54 which carry jet nozzles are stacked in close proximity spaced from the entangling member 52 to impact the web with ramped essentially columnar jet sprays. The manifolds are preferably spaced 8 inches apart, 1 inch from the entangling member, and impact the web with fluid pressures in the range of 400 to 2000 psi. Effective second stage entanglement is effected by energy output to the composite web 16 of at least 0.4 hp-hr/lb and preferably in the range of 0.4-1.2 hp-hr/lb. 
     Following entanglement the web 16 is rinsed with deionized water and passed through the vacuum slot extractor 22 to remove excess water and prepare the web for saturated application of an aqueous resin binder in the padder station 24. 
     Binder compositions for use in the invention are designed to enhance fabric tensile strength, abrasion resistance and resistance to staining. Acrylic latex binders have been found particularly suitable for use in wipe fabrics because of their stain resistance capabilities. A preferred acrylic composition employed in the invention is set forth in Table II. It will be recognized that the amount of binder applied to the fabric varies with fiber composition, weight and intended end use of the fabric. Typically, the acrylic binder saturates the fabric and comprises 1 to 5% of the finished resin treated fabric weight. The binder is cured in a conventional manner in stacks of dry cans 26 operated at steam pressures within the range of 80 to 200 psi. See FIG. 1. 
     Nonwoven fabrics produced by the dual entangling process of the invention are characterized by close knit fiber interstitial binding which enhances the fabric porosity and tensile strength. Preferred fabrics of the invention have a basis weight in the range of 45 to 70 gsy, and MD and CD grab tensile strengths of approximately 15 lbs/inch and 10 lbs/inch. Advantage is obtained through use of the composite web 16 which includes randomized and carded layers 36, 38 to yield fabrics which are uniform in fiber distribution and have MD/CD ratios in the range of 1.5:1 to 2.5:1. 
     
                       TABLE II                                                    
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               %                         Mix                              
               Active  pph    %    %     weight                           
Component      (solid) dry    dry  wet   (lbs)                            
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Water                              93.789                                 
                                         390.63                           
Acrylic resin polymer*                                                    
               45      100    97.6 6.070 25.28                            
(enhances fabric                                                          
durability)                                                               
Ethoxylated Alcohol                                                       
               50      .75    0.7  0.041 0.17                             
(nonionic wetting agent)                                                  
Polyethylene glycol                                                       
               38      .75    0.7  0.054 0.22                             
(softening agent)                                                         
Dioctyl Sodium Succinate                                                  
               60      1      1.0  0.046 0.19                             
(wetting agent)                                                           
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 *A preferred acrylic is marketed under the product designation National  
 Starch 254484 by National Starch and Chemical Corporation, 10 Sinderne   
 Avenue, Bridgewater, New Jersey 08807. National Starch acrylic has a low 
 glass transition temperature (Tg) and is also solvent resistant.         
 
    
     FIG. 6 schematically illustrates a preferred fabric structure of the invention which is obtained employing the entangling members 44, 52 of FIGS. 5A, B. Fluid entangled fibers are arranged in a symmetrical array including a lattice structure of spaced approximately parallel MD and generally sinusoidal CD bands 56, 58, respectively located in carded and randomized web layers 38, 36. The MD and CD bands 56, 58 intersect and entangle to define a cohesive structure. 
     MD bands 56 include parallel segments 56a, and cross-segments 56b which extend in the cross-direction between adjacent MD bands alternately spaced closer and farther apart in the machine direction. CD bands 58 are arranged in an array in which each band is 180° degrees out-of-phase with respect to adjourning bands. Out-of-phase CD bands have alternating sinusoidal peak and trough segments which overlie in alignment with the parallel and cross-segments 56a,b of the MD bands. Tensile strength in the fabric is enhanced by the arrangement of MD and CD bands in the carded and randomized web layers 38, 36 which are interstitially entangled in substantially all regions of interface. See FIGS. 6, 7A,B. MD and CD bands 56, 58 further define a symmetrical array of porous void areas 60, 62 which are disposed between aligned troughs and peaks of the CD bands and have generally rectangular configurations. FIGS. 8B and C illustrate this void pattern in open and inverse light detection photographs at 7.5× magnification of a preferred fabric. White and dark regions in the photographs respectively correspond to void areas 60, 62, and fibrous bands 56, 58 in the fabric. 
     Examples 1-3 and corresponding FIGS. 7A, B describe and illustrate representative fabrics produced by the method of the invention employing the entangling members 44, 52 and production line 10 of FIG. 1. 
     EXAMPLE I 
     A fabric designed for food service industry applications was produced employing a 50/50 carded and random web composed of 30% Celanese T304 1.5 inch, 1.45 denier, 5.5 gram/denier non-optically brightened polyester, and 70% AVTEX 6533 1.5 inch denier, 3.5 gram/denier hemicellular free rayon. The AVTEX rayon and Celanese polyester fibers were processed in an open blender to provide web layers 36, 38 having a 70/30 per cent rayon/polyester content and weight of approximately 29 gsy. Production speed on the line was ramped from 75 to reach 125 fpm to impart energy to the web at the rate 1 hp-hr/lb to produce a base fabric weighing 58 gsy ±4 gsy. 
     Table III sets forth energy specifications for production of the 58 gsy fabric of Example I at an average line speed of 100 fpm. Energy imparted to the web by each manifold in the entanglement modules is calculated by summing energy output for each manifold in accordance with the following equation: ##EQU1## where 
     
         ______________________________________                                    
E =  Hp-hr/lb         S =     line speed (ft/minute)                      
C =  jet orifice discharge coeffi-                                        
                      Wt =    basis weight at                             
     cient dimensionless)     winder (grams/yd.sup.2)                     
P =  manifold pressures (psi)                                             
                      Wj =    web width at each jet                       
N =  jet density (jets/inch)                                              
                      Ww =    web width at winder                         
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     The discharge coefficient (C) is dependent on jet pressure and orifice size. Coefficients for a jet having an orifice diameter of 0.005 inches and water temperature of 85° F. are as follows: 
     
         ______________________________________                                    
Pressure (psi)                                                            
            C           Pressure C                                        
______________________________________                                    
300         .77         900      .66                                      
400         .74         1000     .74                                      
500         .71         1100     .63                                      
600         .70         1200     .62                                      
700         .68         1300     .62                                      
800         .67         1400     .62                                      
                        1500     .62                                      
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                       TABLE III                                                   
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Hydroentangling Energy at 100 FPM                                         
Mani-  Pres-                                                              
fold   sure   Flow     Energy Total  Energy                               
No.    psi    gal/min  hp-hr/lb                                           
                              hp-hr/lb                                    
                                     distribution %                       
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Flatscreen - Module 18                                                    
1      400    68.895   0.023  0.023                                       
2      600    79.817   0.040  0.063                                       
3      700    83.749   0.049  0.112                                       
4      900    92.170   0.069  0.182                                       
5      1200   101.591  0.102  0.284                                       
6      1300   104.061  0.113  0.397                                       
Screen Total        0.397    39.5%                                        
Drum Screen - Module 20                                                   
7      600    79.817   0.040  0.040                                       
8      700    83.749   0.049  0.089                                       
9      800    88.215   0.059  0.148                                       
10     1100   98.810   0.091  0.239                                       
11     1200   101.591  0.102  0.341                                       
12     1400   107.989  0.127  0.468                                       
13     1500   111.779  0.140  0.608                                       
Screen Total        0.608    60.5%                                        
TOTAL ENERGY        1.005    hp-hr/lb                                     
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     Following entanglement, the base fabric was passed through the slot extractor station 22 for in line saturated padding with 2.8% acrylic binder mix having the composition set forth in Table II. Padder roll pressure settings were calibrated to effect an application rate of 1.6 gpm for a binder add-on of 2 ±1 gsy to yield a fabric having a weight of 60 gsy ±3 gsy. The binder was then cured in dry cans 26 to provide a finished fabric for converting. Tables IV and V respectively set forth dry can settings and physical characteristics of the fabrics of produced in Examples 1-3. 
     
                       TABLE IV                                                    
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Dry Can Settings                                                          
         Can Number:                                                      
Speed - FPM                                                               
           1     2       3   4     5-10  10-20                            
______________________________________                                    
75         20    80      80  90    40    90                               
100        25    80      80  90    100   105                              
125        30    80      80  95    110   115                              
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     EXAMPLES II-III 
     Nonwoven fabrics having application for use as automobile and hospital service wipes were produced employing the composite web and process conditions of Example I. Desired fabric characteristics were obtained in these applications through use of binder formulations set forth in Tables VI - A and B. 
     The automobile service wipe is produced employing the binder formulation of Example I modified to include increased concentrations of ethoxylated alcohol, polyethlyne glycol, and dioctyl sodium. Crock resistant color pigments were also added to the binder for aesthetic effect to provide a uniform streak free wiping fabric that is solvent resistant. See Table VI - A. 
     The binder formulation for the hospital service wipe includes a antimicrobial agent of the type offered under the brand designation ULTRA-FRESH by Bio Dor Products Ltd., 1150 Fairfield Avenue, Bridgeport, Conn. 06604. The antimicrobial agent provides a fabric which is resistant to the growth of bacteria and fungi, and consequent rotting and mildewing of the fabric. Effective results are obtained when the antimicrobial is added to the formulation in the order of 1-10 pph on binder solids in the formulation. See Table VI - B. 
     
                       TABLE V                                                     
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Fabric Properties                                                         
                Example   Example  Example                                
Property:       I         II       III                                    
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Basis Weight (gsy)                                                        
With Binder     58-62     58-62    58-62                                  
Without Binder  56-60     56-60    56-60                                  
Tensile (lbs/inch)                                                        
MD              15-30     15-30    15-30                                  
CD              10-20     10-20    10-20                                  
Elongation (%)                                                            
MD              50-65     50-70    50-65                                  
CD              125-145   125-145  125-145                                
Thickness (mils)                                                          
                28-32     28-36    26-34                                  
Mullen Burst (psi)                                                        
                34-40     34-45    32-42                                  
Trapezoidal Tear (lbs/inch)                                               
                  7-10.5   8-12      7-10.5                               
Water Absorbency                                                          
                2.5-5.0   2.5-5.0  2.5-5.0                                
Sink Time/Second                                                          
Capacity (g fabric/g water)                                               
                 8-12      8-12     8-12                                  
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                       TABLE VI                                                    
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               %                         Mix                              
               Active  pph    %    %     weight                           
Component      (solid) dry    dry  wet   (lbs)                            
______________________________________                                    
A - Automobile Service Wipe                                               
Water                              93.411                                 
                                         389.06                           
Acrylic resin polymer                                                     
               45      100    84.7 5.273 21.96                            
Ethoxylated Alcohol                                                       
               50      2      1.7  0.095 0.40                             
Polyethylene glycol                                                       
               38      2      1.7  0.125 0.52                             
Dioctyl Sodium Succinate                                                  
               60      2      1.7  0.079 0.33                             
Pigment Yellow 28      10     8.5  0.847 3.53                             
Pigment Orange 28      2      1.7  0.169 0.71                             
B - Hospital Service Wipe                                                 
Water                              93.817                                 
                                         390.75                           
Acrylic resin polymer*                                                    
               49      100    87.7 5.013 20.88                            
Ethoxylated Alcohol                                                       
               50      .75    0.7  0.037 0.15                             
Polyethylene glycol                                                       
               38      .75    0.7  0.048 0.20                             
Dioctyl Sodium Succinate                                                  
               60      2.5    2.2  0.102 0.43                             
Antimicrobial  25      10     8.8  0.982 4.09                             
(ULTRA FRESH)                                                             
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     It will be recognized by those skilled in the art that the process of the invention has wide application for the production of a diversity of patterned nonwoven fabrics with characteristics determined by the design and specifications of the entangling members 18, 20, fiber blend of the composite web 16, as well as adhesive binder selection. 
     Thus, in the examples, food service and hospital wipes are differentiated by the chemical systems employed in the adhesive binder. The bacteria free hospital wipe includes an antimicrobial agent, while the food service wipe has larger binder concentrations of dioctyl sodium succinate for improved washability and soil release characteristics. All wipes are color pigmented and preferably include a pigment fixative, such as ethoxylated alcohol, which imparts solvent resistance to the binder formulation. 
     Numerous modifications are possible in light of the above disclosure. For example, the preferred process of the invention employs water as the entangling medium. Other media and chemical systems may be employed in the entangling process. Similarly, although selected entangling members 44, 52 are illustrated in the drawings, it will be recognized that other configurations are within the scope of the invention. 
     Therefore, although the invention has been described with reference to certain preferred embodiments, it will be appreciated that other nonwoven fabrics and processes may be devised, which are nevertheless within the scope and spirit of the invention as defined in the claims appended hereto.