Method for making a nonwoven fabric
United States Patent Lofts et a1. Apr. 1, 1975 [5 METHOD FOR MAKING A NONWOVEN 3,185,582 5/1965 Alegre 117/140 X FABRIC 3,186,838 6/1965 Graff 6t :11. 3,706 595 12/19&#39;72 Drelich et [76] Inventors: Peter Frederick Lofts, 30 Winston 3,752,733 8/1973 Graham et al Ave, Cross Hills, near Keighley, 3,788,878 1/1974 Wheelock 117/140 X Yorkshire; John Elves, 45 Priory Gardens, Usk, Monmouthshire; P t B 7. S d i h Cl Primary E.raminer-Mayer Weinblatt Cl t B df d Y k hi Assistant Examiner-Edith L. Rollins BD146EB, all of England [22] Filed: May 11, 1973 21 Appl. No.: 359,399 1 ABSTRACT A xero raphic wi e com risin a bonded web of fibers [30] Forelgn Apphcauon Pnomy Data which l ias been tr eated \Bith ar i aqueous suspension of May 12. 1972 Great Britain inc stearate particles to provide a nonwoven fabric having zinc stearate particles attached to at least one 1 177/140 117/76 117/90, surface thereof. A method for making such a xero- 1 17H40 A graphic wipe comprising the steps of treating the non- [5 Int. Cl. woven fabric an aqueous uspension of inc tea- 1 Field of Search 117/76 FB, 90, 140 A, 140 R, rate particles and drying the thus treated web at a 1 17/161 F, 167 temperature below the melting point of the zinc stearate particles. [56] References Cited UNITED STATES PATENTS 17 Chims, N0 Drawings 3 l20.449 2/1964 Griswold 117/140 X METHOD FOR MAKING A NONWOVEN FABRIC This invention relates to a nonwoven fabric for use as a wipe in xerographic copying machines.  
  The quality of the reproductions obtained from a xerographic copying machine is determined, to a significant extent, by the cleanliness of the photoconductive surface used therein. Accordingly a wipe, hereinafter referred to as a xerographic wipe,&#34; is incorporated in the machine to clean unused electroscopic powder from the photo-conductive surface after a copy has been taken from an exposure. The wipe usually takes the form of a roll of rearranged (or *bundled) nonwoven fabric from which lengths of fabric are advanced as required to wipe against the photo-conductive surface and thereby clean it. A xerographic copying machine incorporating a wipe of this kind is described in U.S. Specification No. 3,186,838.  
  It is a main object of the present invention to provide a nonwoven fabric having improved wiping properties.  
  The present invention provides a nonwoven fabric, preferably a plain unrearranged nonwoven fabric, comprising a bonded web of fibers, which fabric or fibers has/have been treated with an aqueous suspension of zinc stearate particles to provide a nonwoven fabric having zinc stearate particles attached to the surfaces thereof.  
  Such a nonwoven fabric, when made into a xerographic wipe, improves the quality of the reproductions obtained from the xerographic copying machine. The clarity of the individual characters is sharper and the background is whiter than with a conventional wipe as referred to above.  
  Preferably the aqueous suspension contains a watersoluble viscosity modifier (which increases viscosity), even more preferably a film-forming viscosity modifier which has bonding properties, such as a modified cellulose thickener or a polyacrylate thickener.  
  Preferably, the fibers have already been formed into a nonwoven fabric when they are treated with the aqueous suspension of zinc stearate particles, although they may possibly be in the form of a suspension thereof in water as is used to form wet-laid nonwoven fabrics.  
  The present invention further provides a xerographic wipe comprising a roll of the nonwoven fabric described above. I  
  The present invention even further provides a method of making the nonwoven fabric described above, comprising the steps of treating the fabric, or the fibers, with an aqueous suspension of zinc stearate particles, and drying the nonwoven fabric at a temperature below the melting point of the zinc stearate particles. One preferred embodiment of the method comprises the step of treating a web of nonwoven fabric, preferably a plain unrearranged nonwoven fabric, with the aqueous suspension of zinc stearate particles referred to above, as by dipping the nonwoven fabric in the suspension. In another embodiment of the method, zinc stearate particles may be added to an aqueous suspension of the fibers, preferably a thixotropic aqeuous suspension prepared, e.g., as described in U.K. Specification No. 1,129,757, and the fibers are wet-laid to produce the nonwoven fabric. In both embodiments, the fabric is subsequently dried, at a temperature below the melting point of the zinc stearate particles.  
  The present invention still further provides an aqueous suspension of zinc stearate particles containing a water-soluble viscosity modifier, preferably a filmforming viscosity modifier, as described above. Such a suspension, once rendered homogeneous, retains its homogeneity for an extended period of time since the viscosity modifier reduces the tendency of the zinc stearate particles to sediment out. Thus a more uniform suspension is applied to the nonwoven fabric during sustained processing than would be applied in the absence of the viscosity modifier. Furthermore the viscosity modifier assists in bonding the zinc stearate particles to the fabric, especially when the viscosity modifier is one capable of forming a coherent film.  
  The binder used in the nonwoven fabric should be such that it is not unduly water-sensitive and does not give rise to harshness and rigidity in the fabric so that damage to the photo-conductive surface does not occur. Suitable binders include crosslinked acrylates, crosslinked vinyl acetate/acrylic ester copolymers, plasticised crosslinked polyvinyl acetate, crosslinked styrene-butadiene copolymers, and other homopolymers or copolymers containing any of, acrylates, vinyl acetate, ethylene, vinyl chloride, and vinylidene dichloride, etc. These binders each have substantial wet strength.  
  The amount of binder is generally from 1.5 to 25 percent by weight of the fabric, and preferably from 2 to 10 percent by weight of the fabric. The binder is preferably distributed uniformly throughout the fabric, e.g., continuously or in spaced areas. The binder may be applied to the unbonded web by, for example, a rotogravure print roller. Reference is also made to FIG. 5 of Specification No. 742,089 for suitable apparatus for carrying out the bonding step. The web is then dried, treated with an aqueous suspension of zinc stearate particles (if the web has not already been wet-laid from an aqueous suspension containing the fibers and the zinc stearate particles), wound up into a jumbo roll, slit into webs of a size suitable for use as xerographic wipes, and re-rolled.  
  The unbonded web of fibers constituting the precursor web of the bonded nonwoven fabric may be wetlaid, but preferably it is dry-laid. Preferably the web. is a carded web, although it may, for example, be air-laid using, eg a Rando-Webber random air-laying machine (produced by the Curlator Corporation). Natural and/or man-made fibers may be employed in the web which may comprise one or more plies. Preferably the web comprises cellulosic fibers, most preferably viscose rayon fibers and/or cotton fibers. A suitable manmade fiber in addition to viscose rayon is polyvinyl alcohol fiber, e.g., Kuralon&#34; from the Marubeni Corporation, Japan. Fibers having a length of 20 to 50 mm. and a denier of 1.5 to 3.0 are preferably used.  
  The range of strengths, weights per unit area, drape, handle, wettability and permeability of the nonwoven fabrics for use as xerographic wipes will be familiar to those skilled in the art. Preferred nonwoven fabrics of the present invention have a weight in the range 15 to 20 g/m A preferred embodiment of a nonwoven fabric in accordance with the present invention will now be described by way of example.  
 EXAMPLE A plain tenuous three-ply fibrous web comprising 13 g/m of 37 mm staple length, 1.5 denier viscose rayon fibers was produced from carding engines, and was then printed upon by means of a rotogravure roller with a self crosslinking plasticised vinyl acetate/butyl acrylate copolymer binder, the amount of binder (dry weight) being 3.1 g/m of the dry nonwoven fabric. The rotogravure roller employed was engraved with a pattern of wavy or saw-tooth&#34; lines, there being four lines per inch disposed circumferentially on the roller. The wet printbonded web was dried over steam-heated cans, although ovens may alternatively be employed.  
  The web was then passed through a homogeneous aqueous suspension containing 15 percent by weight of zinc stearate particles and 0.25 percent by weight of a modified cellulose viscosity modifier. The fabric was then mangled to remove excess liquor, the pressure of the mangle being adjusted to leave 3.1 g/m of zinc stearate on the fabric, and dried over smooth releasecoated steam-heated drying cans, the temperature of which was below the melting point of the zinc stearate particles to avoid fusion of the particles. Commercial grades of zinc stearate melt at about 1 16 to 120C (the true melting point is 124C) and we prefer to dry the fabric at about l 10C. The particles soften at this temperature which may assist in bonding them to the fabric, as the fibers are partially impressed into the stearate particles as the fabric is dried over the cans. The web was rolled up for slitting into individual webs of a size suitable for use as xerographic wipes. The wipe was found to be more effective than conventional xerographic wipes as evidenced by the improvement in the quality of photocopies obtained using it over a sustained period.  
  The nonwoven fabric had particles of zinc stearate firmly attached to both surfaces thereof. Whilst we do not wish to be bound by theory we believe that the Zinc stearate particles are bonded&#39;in more than one way to the nonwoven fabric, namely by physical entrapment of the particles, by actual bonding of the particles by the viscosity modifier, and by sinteringof the particles to the nonwoven fabric.  
  We have found that the Zinc stearate particles are more firmly attached to the nonwoven fabric when the aqueous suspension contains a viscosity modifier. The zinc stearate particles thus do not dust off so copiously so that there is reduced health hazard from dust and substantially all of the zinc stearate particles are retained by the nonwoven fabric for effective use.  
  The zinc stearate particles may be applied to the nonwoven fabric using a rotary screen printing unit. A paste of zinc stearate, viscosity modifier and water is made up and deposited by the rotary screen printing unit on at least one surface of the fabric, e.g., in a pat tern of multitudinous dots, to give overall coverage of the fabric. The fabric is then dried below the melting point of zinc stearate as before.  
 What is claimed is:  
 1. A method for making a nonwoven fabric comprising:  
 a. providing a bonded web of fibers, said bonded web of fibers having substantial wet strength;  
 b. dispersing zinc stearate particles in water to form an aqueous zinc stearate suspension;  
 c. treating said bonded web by applying said aqueous suspension thereto; and  
 d. drying the treated bonded Web at a temperature below the melting point of the zinc stearate whereby there is formed a nonwoven fabric having zinc stearate particles attached to a surface.  
  thereof. 2. The method of claim 1 wherein said aqueous suspension contains a water soluble viscosity modifier- 3. The method of claim 2 wherein said viscosity modifier is film forming.  
  4. The method according to claim 3 wherein said viscosity modifier is a modified cellulosic thickener.  
  5. The method according to claim 3 wherein said viscosity modifier is a polyacrylate thickener.  
 6. The method according to claim 1 wherein the fibers comprising said bonded web are unrearranged.  
  7. The method according to claim 1 wherein the treated bonded web is dried at a temperature of about 1 l6-l20C.  
 8. The method according to claim 1 wherein the treated bonded web is dried at a temperature of about 1 10C.  
 9. A method according to claim 1 wherein the fibers comprising said bonded web have a length of from about 20 mm. to about 50 mm. and a denier of from about 1 /2 to about 3.0.  
  10. The method according to claim 9 wherein the fibers comprising said bonded web are rayon fibers.  
  11. The method according to claim 9 wherein the fibers comprising said bonded web are polyvinyl alcohol percent to about 10 percent by weight of said bonded web.  
 15. The method according to claim 1 wherein the I,  
 binder for said bonded web is uniformly distributed throughout said bonded web. i  
  16. The method according to claim 1 wherein said suspension is applied to said nonwoven fabric using a rotary screen printing unit.  
 17. The method according to claim 1 wherein said suspension is applied to said nonwoven fabric by passing said nonwoven fabric through said aqueous&#39;suspen 14. The method according to claim 1 wherein the. binder for said bonded web comprises from about 2