Abstract:
A process for treating a pile material which is ultimately to be made into a toner removal brush used in association with electrophotographic printing which comprises treating the pile substrate material with a saturated aqueous solution of a chemical mixture comprising at various times a surfactant, an alkali metal salt, a source of borate ions and an optical dye, withdrawing excess solution by mechanical means and simultaneously orienting the pile, and preferably allowing the still wet material to dry at ambient or elevated temperature, forming an elongated pile-covered tubular structure with the resulting dried pile material, sizing the tube to desired lengths if necessary, subjecting the dried pile material to a further wetting either with water alone or a saturated aqueous solution of the same chemical mixture above defined, and then subjecting the pile-covered tube to a centrifugal force sufficient to hurl the pile fibers to an erect condition thereby forming a brush with uniquely superior toner removal properties, and the brush nap made by this method.

Description:
BACKGROUND OF THE INVENTION 
     1 Field of the Invention: 
     This invention relates generally to toner removal systems in electrophotographic printing machines and specifically to a method for making a new toner removal brush with improved properties. 
     Description of the Prior Art: 
     By definition, electrophotographic printing comprises the steps of (1) charging an electrophotographic surface, e.g. of selenium, tellurium, palladium, with a static voltage of about 3,000 volts (2) shielding the selenium surface, such as a plate, with a light pervious layer carrying an opaque image that is to be recorded (3) exposing the combination to a light source that is directed through the shield to the electrophotographic surface, photoreceptor, or drum or plate whereby all the parts of the surface not covered by the opaque image give up their charge (4) dusting (i.e., developing) the plate with carbon or other powder toner (the toner will adhere to the charged portions) and (5) transferring the toner image to paper through the application of an electrostatic field. 
     Thus it is well recognized that electrophotography or &#34;dry printing&#34; requires the application of a pigmented powder on to the surface of a charged plate (the photoconductor) in order to develop the latent electrostatic images thereon. Thus toner removal becomes quite important if one is to accomplish both the substantial removal of all the toner from the photoconductor drum and at the same time, protect the longevity of the photoconductor drum, as well as the life of the brush. 
     In the prior art for example, cleaning brushes or wipers are used in drycopying machines or duplicators where such wipers are in contact with the image transferring masters made out of or coated with photoconductive (i.e. photoreceptive) materials and such wipers or brushes attempt to serve the purpose of removing the residual latent image from the photoconductor without damaging or destroying the photoconductor itself. So far this has not been fully accomplished in the prior art and the brush fiber ends retain fused toner and/or either become clogged with toner material after relatively few turns of the brush against the photoconductor (the brush develops the same charge as the photoconductor, such charge arcing over toner particles and fusing the toner); or the brushes are made such that they scar and damage the photoconductor drum. Representative U.S. Patents in the art of electrophotography and toner removal, just to name a few include U.S. Pat. No. 2,297,691; 2,859,673; 2,911,330; 2,944,147; 2,959,153; and 3,093,039. 
     SUMMARY OF THE INVENTION 
     It is therefore among the principal objectives of this invention to provide a toner removal brush having a tremendously increased longevity in terms of the number of images produced by the copier before the brush becomes unusable and must be replaced and just as importantly, to provide a toner removal brush of improved properties such that it will not scratch or prematurely erode the sensitive surface of the photoconductor, and to improve system recovery speed resulting in total system improvements. 
     In accordance with the present invention, there is now provided a method for making a brush which will have these properties aforementioned. The brush made by the present invention is superior even to the one obtained by the method of making that brush disclosed in my copending application filed concurrently herewith entitled &#34;PROCESS FOR TREATING PILE MATERIALS MADE INTO ELECTROPHOTOGRAPHIC TONER REMOVAL BRUSHES&#34;, Ser. No. 625,050. Indeed, the pile substrate in the finished product of the instant invention is believed to have a chemically altered composition. The present method comprises treating a pile substrate material, which has been previously cut into elongated strips and back coated, e.g. latex, with a saturated aqueous solution of a chemical mixture comprising at various times a surfactant, an alkali metal salt, a source of borate ions and an optical dye, withdrawing excess solution by mechanical means and simultaneously orienting the pile, and preferably allowing the still wet material to dry at ambient or elevated temperature, forming an elongated pile-covered tubular structure with the resulting dried pile material, sizing the tube to desired lengths if necessary, subjecting the dried pile material to a further wetting either with water alone or a saturated aqueous solution of the same chemical mixture above defined, and then subjecting the pile-covered tube to a centrifugal force which resultingly hurls the nap to an erect condition to form a brush with uniquely superior toner removal properties, and the brush nap made by this method. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be hereinafter more fully described with reference to the accompanying drawing in which: 
     FIG. 1 shows diagrammatically the various stages of the pile material as it is treated according to the method of the invention. 
     FIG. 2 shows a strip of the invention treated pile material in strip form as shown partially wound around a tube core. 
     FIG. 3 shows in perspective a pile covered tube just before the centrifugal hurling treatment. 
     FIG. 4 shows in perspective the toner removal brush formed after centrifugal hurling. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Describing the process now in further detail, a hollow multi or/monofilament natural or synthetic, preferably synthetic hollow filament, and preferably rayon, latex back coated pile substrate material is cut into elongated strips, e.g. about 15 to 30 yards in length and about 3-1/4 inches wide, but this is not critical and dimensions can vary. Each strip is then passed through a bath containing a saturated aqueous solution of a chemical mixture (Bath I, see Table I below) comprising at various times a surfactant, an alkali metal salt, e.g. sodium metasilicate, sodium phosphate, a source of borate ions, e.g. boric acid and sodium borate, the solution can also be sprayed on, thoroughly soaking it, and the strip is next passed over a source of suction such as a vacuum connected nap folding fixture head, as described in my copending application filed concurrently herewith, entitled &#34;COMBINATION NAP-FOLDING FIXTURE HEAD, Ser. No. 625,049.&#34; The purpose of the suction is two-fold. First, it removes loose fabric and excess solution from the strip, shortening ultimate drying time, and secondly, the pile nap is folded flat and oriented in one direction, and more importantly the fabric nap is edge-folded (lateral edges) for a reason which will be subsequently described hereinbelow. While vacuum suction is the preferred method of edge-folding the fabric nap, it is to be understood that this step can also be accomplished by streams of air directed at the edges. It is also to be understood that the edges can be vacuumed while a rotating brush combs the nap unidirectionally simultaneously. The strip is then allowed to dry at room temperature or slightly elevated for faster drying. This step can be omitted according to another specific embodiment of the invention, as will be discussed hereinbelow. 
     When the strip is dry, it is applied to a tubular core (preferably cylindrical), e.g. Kraft lined cardboard, by butt winding (edge to edge) or gap winding, or overlap winding, preferably butt winding. This is a critical step in that the core should be covered in a predetermined pattern. It can now be seen why the edge-folding step is so important. By this step clean straight lateral edges are obtained which will not be trapped in the winding seam. If the ragged edges were allowed to remain and become caught in the winding seam, the brush would not present a uniform nap and the seam windings would be visible through capillary seepage of the adhesive. Instead of winding strips a sleeve can also be made and fitted over the core. The sleeve or strip is bonded to the core by applying an adhesive to the core before fitting. As a precaution, a coloring agent is mixed in the adhesive, to contrast to the fabric color, whose purpose is to signal invasion of the adhesive to the brush which would have a serious deleterious effect on the uniformity of the brush nap and the adhesive would mar the photoconductor surface as well. Next, the adhesive is allowed to dry and following this, the pile covered core is cut to size. Of course, the cores can be pre-cut before pile covering. In the event, and this is preferable, the pile covered core is cut to size, it is important that it be cut at a 90° angle thereto and when cutting a vacuum force is applied in conjunction therewith to force the pile in an erect position. The angle of the cut and the vacuum associated therewith prevents the cutting across of fibers and partial loss of nap. 
     Thereafter, critically the pile on the core should be thoroughly wet, additionally wetting it with water or saturated aqueous chemical mixture (Bath II, Table I below), taking care not to wet the core ends and taking care that preferably the pile remains oriented, i.e. as originally uni-directional. In this retreated or rewetted condition the nap is hurled to an erect condition, thereby forming a brush, by subjecting it to a centrifugal force which results from a high speed rotation of the nap away from the core, i.e. each strand thus being positioned to be perpendicular to the rotational axis of the core. In this case, the core is inserted over a rotatable spindle and the wet nap is touched to a high speed rotating texturing brush. Since the highest degree of erectness of the nap which can be accomplished is a function of the accelerating centrifugal forces exerted on the liquid which is moving through the strands making up the nap, therefore the higher the degree of the acceleration the more prestressing of each strand is accomplished. Conversely, the core can be rotated at high speed in a plane perpendicular to the centrifugal hurling force. The centrifugal hurling time should be sufficient to bring the centrifugal force at the end of the nap to its full potential to bring the fibers erect, increase their density by imploding the fiber walls via the escape of the liquid solution caused by the centrifugal force, and resulting in the fibers having a prestressed state in the dry condition. Bath I and Bath II as previously indicated may vary and in order to more fully appreciate this feature, Table I immediately hereinbelow illustrates the bath variations: 
     
                                           TABLE I__________________________________________________________________________VARIATION    BATH I        vs.                        BATH II__________________________________________________________________________A      Water, sodium metasilicate,                     Water, sodium metasilicate,  optical dye, surfactant*                     optical dye, surfactant*B      Water, sodium phosphate,**                     Water, sodium metasilicate  Boric Acid, optical dye                     and sodium phosphate, optic                     dye, surfactantC      Water, Boric Acid, Sodium                     Water, sodium metasilicate  Metasilicate       and sodium phosphate,                     surfactantD      Water, Surfactant, Boric Acid                     Water, sodium metasilicate                     and sodium phosphate,                     surfactant, Boric AcidE      Water, Boric Acid  Water, Sodium Metasilicate                     and sodium phosphate,                     surfactantF      Water              Water, sodium metasilicate                     and sodium phosphate, sur-                     factant, boric acid, opticalG      Water, sodium metasilicate and                     Water  sodium phosphate, surfactant,  Boric Acid, Optical dye__________________________________________________________________________ *Contain same charge **Can be any one of the sodium phosphates, e.g. monobasic, dibasic, tribasic, etc. 
    
     After the centrifugal hurling thereby forming the final product the outside diameter of the brush can be sized by cutting to desired machine specifications, and allowed to dry before use, or preferably dried before sizing. 
     The requirement that the pile substrate material be formed of hollow monofilament fibers is of preference in this invention in that it is believed that the aqueous chemical mixture reacts with the rayon filament to form a new derivative thereof and moreover the residual chemicals remaining after centrifugal action have been forced up to the upper part of the hollow filament filling the hollow interior thereof to the tip of the nap. Thus, there is chemical change as well as molecular loading of the hollow fiber. It is further believed that the heavier components, e.g., the metallic ions, form the upper area of the brush nap whereas the lighter and more viscous components remain in the lower portions of the hollow filament. The heavier upper portion of the nap is the area of higher conductivity. Moreover, the fiber walls remain linked by capillary lock. When the aforesaid centrifugal force is applied, the fiber tends to stretch and there is an increased density taking place. Thus, the elastic memory of the individual nap fibers is increased, i.e. tendency to return to erect state. 
     The surfactant in the chemical mixture is anionic or cationic and can be any one of a number of commercially available surfactants; the latter is not critical. The optical dyes employed will vary depending on the charge on the photoconductor drum. For example, optical yellow has a shorter wave length and optical pink have a longer wave length and each would be used accordingly. Where the photoreceptor charge is positive, toner would have negative charge, or the photoreceptor charge is negative, toner would have positive charge, respectively. Thus, when the brush rubs against the photoconductor drum, the inter-strand spaces pick up the same charge as the toner and at the same time it carries the toner off the drum. Being of like charge as the brush end nap-spaces, the toner will be repelled thereby and will not foul or clog the brush. This phenomenon imparts &#34;self-adapting polarity&#34; to the brushes made by this invention and is a tremendous advance in the art. The repelled toner can be picked up in a filter using a vacuum as is conventionally done in present dry copy machines. 
     Table II immediately hereinbelow summarizes the method steps of the invention illustrating the various embodiments of the invention. 
     
                                           TABLE II__________________________________________________________________________STEPS1             2         3   4    5    6        7     8   9__________________________________________________________________________Substrate     Edging                                     SizingMethodWetting  Orienting Drying                       Winding                            Cutting                                 Wetting  Exploding                                                Drying                                                    (O.D.)__________________________________________________________________________Wetting with                     Yes, withA    Chemical Yes       Yes Yes  Yes  Chemical Yes   Yes YesBath I                           Bath IIB    Wetting with         Yes       Yes Yes  Yes  Yes, with                                          Yes   Yes YesChemical                         waterBath I and IIC    Wetting with         Yes       No  Yes  Yes  No       Yes   Yes YesChemicalBath I and II                                 Yes, wettingD    Wetting with         Yes       Yes Yes  Yes  with Chemical                                          Yes   Yes Yeswater                            Bath I and II                                 Yes, wettingE    Wetting with         Yes       No  Yes  Yes  with Chemical                                          Yes   Yes Yeswater                            Bath I and II__________________________________________________________________________ NOTE Comparing Table I with Table II it can be seen that the combinations of steps and bath variations are numerous. 
    
     Referring now to the figures of the drawing in terms of the method of invention just described hereinabove, there is shown in FIG. 1, a diagrammatic representation of a pile substrate strip at various stages of treatment: (a) the dry untreated substrate (b) immediately after wetting (c) edges folded by vacuum (d) pile oriented unidirectionally and flat. FIG. 2 shows a fragment of a wet (or dry) strip butt-wound around a core; note edges are folded in and pile is flat and unidirectional. FIG. 3 shows the pile on the brush before centrifugal hurling i.e., before subjection of tubular core to centrifugal force and FIG. 4 shows the pile strands in an erect position after hurling. 
     When employed in extant dry copying machines, the toner removal brushes made by this invention show a remarkable longevity over the prior art brushes providing a cleaner system extending the service life of the system. The invention brushes are stiff enough to clean more toner from the photoconductor yet soft enough not to damage the photoconductor drum. The brushes also remain toner clog free for many, many reproductions by the drum reducing significantly the number of service changes of brush and drum and providing more consistent copy quality. Indeed, the present brush is remarkably superior even to the brush described in the aforesaid copending application and remains in active service for tens of thousands more reproductions. By virtue of its &#34;self-adapting polarity&#34; the invention brush is still more prone to being and remaining toner clog free. It has also been found that improvements of the toner removal system, of which the brush is the critical component, afford the performance acceleration of the total system, extending service periods, resulting in reduced cost per copy.