Abstract:
Systems and methods for preventing and/or inhibiting toner scatter inside of laser printer toner cartridges including a shield that is adjacent to the toner regulating member, extends over and adjacent the developing roller, includes triboelectric material of a polarity corresponding to the polarity of the laser printer cartridge during operation and that functions as a physical barrier and as an electrical barrier to direct toner particles that scatter away from the developer roller back toward the developer roller.

Description:
FIELD OF INVENTION 
     The present system and process relates to the field of laser toner cartridges, specifically to preventing toner scatter in the developing section of a laser toner printer cartridge. 
     BACKGROUND OF INVENTION 
     Electro photo printing technology is an evolving technology that changes with time as market demands, especially the computer market and the imaging market, evolve and change. The main features of the printer/cartridge technology that are presently evolving include: 
     A. Printer Speed 
     As time passes printer manufacturing firms try to design faster printing machines. The speed of a printing machine is usually defined by the number of pages the printer can print per minute (also known as ppm). In today&#39;s market, there are office laser printers that can go up to 60 pages per minute. 
     B. Print Resolution 
     As the imaging market evolves more and more customers expect higher print quality. Where in the past, laser printers used to print simple graphics, in today&#39;s market the printers can print in relatively high resolutions, around 1200 dots per inch (dpi). 
     C. Demand for Color 
     The laser toner color printer market share is growing every year relative to that of the black and white laser toner printer market. 
     In order to accommodate for the market&#39;s demands, new toner formulations and toner making technologies have been developed to comply with the evolving demands for speed, resolution and use of colors. Higher printing speed printers require toner resins with lower melting points to accommodate for the faster fusing speed. Higher resolution printers require smaller average particle size toner in order to achieve the small details in high resolution images and color toners inhibit the use of magnetic toner system. Hence, most color toners are mono-component, non-magnetic toners. Moreover, the need for color, non-magnetic toner significantly limits the variety of materials that can be used as resins. Those changes and others known in this field but not specifically described herein are responsible for a number of side effects in the functionality of toner cartridges such that they create print defects and reduce print quality. The present system and method are directed to solving a common problem found in high speed, non-magnetic toner printer systems and color toner systems. This problem is usually called “toner scatter” or “dusting”. Toner scatter refers to toner particles that disengage from the developing system and accumulate inside of the laser toner cartridge, and typically create local print defects on the printed media, such as toner stains or continuous haze. Continuous haze is also known as “background” on the printed media. 
     In one preferred embodiment of the present system and method a toner shield is installed inside of the laser toner cartridge in order to prevent the toner scatter phenomenon. When installed the toner shield minimizes or prevents toner from scattering and/or accumulating inside of the cartridge, thus eliminating the aforementioned print defects. The shield described below can be used in a new laser toner cartridge or in a remanufactured laser toner cartridge. 
     SUMMARY 
     The toner shield system and method described herein overcomes the drawbacks of known toner scatter phenomena by providing physical and electrical shields that prevent and/or inhibit accumulation of toner in unwanted areas inside the toner cartridge and force the scattered toner back to its original course toward the developer roller, thus preventing or minimizing print defects or problems caused by scattered toner. 
     The present system and method relates, for the most part, to a single component, non magnetic toner system. In the case of a non-magnetic toner system, a relatively soft developing roller is used. The roller is generally made of polyurethane and includes a regulating member made of polyurethane or a metal. The regulating member is often referred to in this field as a “doctor bar”. In some laser printer systems the regulating member is made in the shape of a rigid metallic rod. 
     As is well known the toner particles are in a size distribution, with some particles of relatively small size, some of relatively large size and some of intermediate size. It is believed that high printing speed and use of non-magnetic toner causes smaller and larger particles within the toner particle size distribution to disengage from the developing roller and accumulate primarily on top of the regulating member. This toner accumulation is believed to create or lead to various defects or problems, such as hazing, local staining of the printed media and/or dusting inside of the printer. This scattered toner can contaminate printer and cartridge components such as the transfer belt, pick-up rollers, fuser rollers and so forth. 
     By installing a shield on the top of the regulating member, the scattering and accumulation of the toner is prevented, inhibited and/or minimized. The preferred shield includes a film of double sided adhesive and a generally L-shaped, angled strip of insulating material having a high triboelectric value of the same polarity as the triboelectric value of the toner. Scattering and accumulation of the toner is prevented or minimized and as a result the related defects are prevented or minimized. The preferred shield functions as a physical barrier as well as an electrical barrier to flow of scattered toner to unwanted areas within the toner cartridge. The preferred shield creates a static electrical field with the same polarity as the charged toner, and thus repels the scattered toner particles, forcing them back to the developing roller. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view of a prior art laser toner cartridge developing section. 
         FIG. 2  is cross sectional view of the prior art laser toner cartridge of  FIG. 1  illustrating the toner scatter phenomenon. 
         FIG. 3  is a chart presenting a list of different materials and their relative triboelectric charge values. 
         FIG. 4  is a perspective view illustrating the position of a preferred embodiment shield inside of the toner hopper. 
         FIG. 5  is a cross sectional view of the  FIG. 4  preferred shield embodiment that prevents toner from accumulating in the developing section of the cartridge. 
         FIG. 6  is an exploded perspective view of the preferred toner shield of  FIG. 4 . 
         FIG. 7  is an exploded perspective view of the shield of  FIG. 4  shown attached by an alternative method to the regulating member. 
         FIG. 8  is a perspective view showing installation of the preferred shield of  FIG. 4  with a preferred tool. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a partial side view of a typical prior art laser toner cartridge development or developer section. The prior art laser toner cartridge contains a toner container  2  also known as “toner hopper”, toner powder  4 , photo-sensitive member  6 , developing roller  8 , regulating member  10 , a spring  12  that creates tension between the regulating member  10  and the developing roller  8 , the printing medium  18 . As the developing roller  8  rotates in the direction of the arrow  14 , it transfers toner  4  from the toner hopper  2  onto its surface  22 . As the toner at surface  22  passes through the narrow space, known in this field as a “nip”, between the developing roller and the regulating member  10  it acquires an electrical charge. The photo-sensitive member  6  rotates in the direction of the arrow  16 , and the toner is transferred only onto the areas were the laser formed the latent image over the surface of the photo-sensitive member at  24 . The toner at  24  is then transferred from the surface of the photo-sensitive member  6  onto the printing medium  18  as the printing medium moves in the direction of arrow  20 . The toner creates the image  26  on the printing medium. 
     Referring to  FIG. 2 , the toner scatter phenomenon is described. It is believed that as a result of the high rotational speed of the developing roller, some of the bigger or smaller toner particles have a high enough momentum to leave the surface of the developing roller  8  and accumulate on the surface of the regulating member  26 . It is also believed that small particle size toner powder cannot acquire sufficient electrical charge to keep them temporarily attached to the developing roller as it turns. As a result, those small size particles also accumulate over the surface of the regulating member  26 . Once the mass of the accumulated toner particles  26  is high enough, a portion of these particles  28  will fall onto the surface of the developing roller  8 . That portion of toner in turn will be transferred to the surface of the photo-sensitive member at  30 , and in turn fall directly onto the printing medium at  32 , or will turn with the photo-sensitive member and will be transferred to the printing medium, shown for example at  34 . Moreover, it is believed that some smaller toner particles from the toner accumulating on the regulating member  26  continuously disconnect from the toner accumulation at  26  and fall onto the developing roller, thus creating heavy hazing (background) on the printing media. 
     Referring to  FIG. 3 , examples of different materials with their relative triboelectric values are shown. Within the context of the present system and method the term triboelectric is used synonymously with the terms triboelectric effect and triboelectric charging, and means a type of contact electrification in which certain materials become electrically charged when they come into contact with another, different material, and are then separated, such as through rubbing or become electrically charged when they come into static contact with some other material that is electrically charged or biased and the charged is transferred to the triboelectric material. The polarity and strength of the charges produced differ according to the materials, surface roughness, temperature, strain and other properties. 
     It can be observed from the  FIG. 3  listing of materials that in order to create an effective electrical shield, an insulating material with a negative triboelectric value has to be chosen for a negative toner system. In the context of the present system and method a negative toner system is a cartridge system that generates negative charge on the toner. Similarly, an insulative positive triboelectric value material has to be chosen for a positive toner system. From  FIG. 3 , PVC and polyethylene are good candidates for a negative toner system. It is believed that derivatives of polyethylene, such as polyethylene terephtalate (PET), for example, are also good candidates for a negative toner system. Also, acetate is a good example for a shield made for a positive toner system. With respect to usefulness as a shield, silicon and Teflon (fluorocarbons) are more negative than PVC (polyvinyl chloride), for example, but are harder to manage and less useful due to their mechanical properties, especially their stiffness, low adherence and their relative higher cost. With respect to positive toner system materials, such as glass, mica and asbestos, they are relatively less useful due to their hardness, which makes manufacturing shields to the required dimensions difficult. Also, these materials lack the physical stiffness and flexibility of the acetate polymer, another material listed on  FIG. 3  that is in the “more positive” category. 
     Referring to  FIG. 4 , a perspective view of the location of a preferred embodiment toner shield system is described. The shield shown in  FIG. 4  is intended for a particular toner cartridge. As will be appreciated by those skilled in this field, the structural details and configuration of toner shields of the present system and method will vary according the specific structure of the toner cartridge to which they will be coupled, and a wide variety of toner cartridge structures are known and commercially available. Also, while the  FIG. 4  embodiment shows a preferred shield to be adhered to the toner regulating member of a cartridge, a shield that functions to inhibit and/or prevent toner scatter may be placed at other locations within the printer. Thus, virtually any configuration and/or location of a toner shield is considered to be within the scope of the present system and method so long as it performs either or both function(s) of a physical barrier to toner scatter and/or an electrical barrier to toner scatter. Toner hopper  36 , a photo-sensitive member  6 , a developing roller  8 , a regulating member  10 , a tension leaf spring  12 , the printing medium  18  and the toner shield  38  are shown in  FIG. 4 . With respect to the toner cartridge shown in  FIG. 4 , the shield  38  is preferably located on the surface of the regulating member  10 . In the most preferred embodiment, as illustrated in  FIG. 4 , the toner shield  38  is spaced at about 0.005-0.5 inches from the bottom edge of the regulating member  10 . The included angle between the legs of the preferred angled toner shield preferably is in the range of about 70-130 degrees, as shown in greater detail in  FIG. 5 . The shield  38  does not touch the developing roller  8 . The shield  38  also functions to prevent the leaf spring  12  from disengaging as a result of vibration or impact. The shield  38  is preferably connected or fastened to the regulating member  10  with a double-sided, adhesive tape such as 3M 9495LE tape. As will be appreciated by those skilled in this field, other brands of tape, and other ways of positioning or attaching the shield to the toner cartridge may used without departing from the principles and functioning of the present system and method. 
     Referring to  FIG. 5 , the shielding effect of the toner shield and the prevention of toner accumulation by the toner shield will be described. The preferred shield has the general shape of an L, with an angle Φ included between the first leg and second leg, as shown in  FIG. 5 . The preferred angle Φ is 70 to 130 degrees. The developing roller  8  turns in the direction of the arrow  14  against the regulating member  10 . In case of a negative toner system, the developer roller  8  and the regulating member  10  are electrically connected to a conventional, negative bias  42 ,  44  respectively, so that a negative electrical charge is transferred to the surface of the shield. In this example the electrical shielding effect is shown with a negative toner system. The electrical bias on the developing member and on the regulating member creates a negative electrical field on their surface by induction. The toner  46  passes through the contact area  48 , also called the nip, and acquires a charge  50  of the same polarity of the bias  42  and  44 . As a result of the bias on the regulating member  10 , the toner shield  38  when connected to the regulating member with a double coated adhesive  39  develops a negative electrostatic field by induction, in a similar way an electrostatic field develops on a dielectric material inside of a capacitor when the capacitor is charged. The current applied on the regulating member generates an electrical field perpendicular to the face of the regulating member and that in turn induces an electrostatic field on the surface of the toner shield at  52 . It is believed that the magnitude of the electrostatic field developed in a direction perpendicular or orthogonal to the surface of the shield face, thus the effectiveness of the toner shield electrical barrier, depends on several factors. For example, the ability of the dielectric material, hence the toner shield to retain electrostatic charge on its surface is believed to be an important factor relating to shield effectiveness. Also, the dielectric constant of the polymer the shield is made of, the magnitude of the bias, the thickness of the shield, the thickness of the double-sided tape and the shape of the regulating member and the shape of the shield are all believed to be factors that play a role in shield effectiveness. Thus, it is believed that scattered toner particles  54  having the same polarity as the electrical field at  52 , encounter a physical barrier, i.e., the shield, as well as an electro-static barrier field at  52  due to the same polarity of the toner particles and the surface  52 . As a result the electrical forces cause the scattered particles  54 A and  54 B to be directed back onto the developing member  8  in the direction of the arrows  56 A and  56 B, thus preventing accumulation of the scattered particles  54 A and  54 B on unwanted areas inside the cartridge. In a positive toner system the biases  42 ,  44  will be positive and the electrical field  52  will be positive and the toner particles  50 ,  54 A and  54 B will be positive as well. 
     Referring to  FIG. 6 , the toner shield  38  includes shield face  58  and a regulating member face  60  that adheres to the surface of the regulating member preferably by adhesion with two-sided tape  64 . The two-sided tape  64  can be either insulated or conductive and, as referred to above the shielding effect depends on various factors such as the material and structure of the toner shield  38 . The shield  38  also preferably includes a notch  62  to accommodate the regulating member contact. The regulating member contact transfers the electrical bias, shown at  44  in  FIG. 5  to the regulating member, thus charging the regulating member, double-coated adhesive tape  64  and release film  66 . The two-sided tape and the release film are conventional and commercially available. During the process of application of the shield to the regulating member, the release paper is pealed off and the toner shield is placed in position using a positioning spacer tool, shown in  FIG. 8 , in order to assure the correct distance from the shield face  58  to the developing roller. The spacer tool is preferably a conventional, commercially available shim made of a soft flexible polymer in order to avoid damaging the developing roller during installation. A few examples for the spacer are polypropylene, polyethylene, PVC and acetate. 
     Referring to  FIG. 7 , an alternate preferred embodiment toner shield is shown. Instead of having one sheet of insulative material the toner shield  70  includes an insulative flat sheet  70 . The sheet  70  is made of a material with a high triboelectric value corresponding to the polarity of the bias. The shield  70  also includes a double or two-sided adhesive tape  72 . The preferred tape is 3M 9495E, but other tapes can be used so long as they function for its intended purpose. The shield  70  also includes a rod  74 , shown in  FIG. 7  as having a rectangular configuration. The rod  70  can be a rectangular rod, an angled rod or have an angled profile. A two-sided adhesive or double adhesive tape  76  connects the rod  74  to the regulating member. The rod  74  can be made of many types of material, electrically conductive or insulated, so long as it is structurally capable of functioning for its intended purpose of being a component of the toner shield. The tapes  72  and  76  can be any type of commonly used double sided adhesive tape, such as 3M 9495LE, which is preferred. 
     Referring to  FIG. 8 , the preferred method of installation of the toner shield on the regulating member is described, using a conventional, commercially available shim stock  78 . The shim stock is preferably made of a relatively soft material, preferably a polymer in order to avoid damaging the developing member  8 . The shim is inserted in the direction of the arrow  80 , preferably touching the developing member  8  at the bottom and the regulating member  10  at the same time. Then, once the release paper is pealed off the toner shield  38 , it is installed where the shield face  58  touches the upper surface of the shim stock  78 . In that manner the correct distance between the developing member and the toner shield is assured. 
     Due to the factors affecting the toner materials and formulation described in the background of the invention, i.e., high printing speed, high resolution and non-magnetic toner systems, the toner powder formulation and constituent materials have to comply in terms of flowability and chargeability. It is believed that the finer or smaller particles within the toner particle size distribution are most susceptible to scattering. It is believed that toner scatter occurs when toner particles that travel between the developing roller and the regulating member of the laser printer cartridge do not achieve sufficient charge to stick to the roller  8 . This is believed to be due to their size or the speed of the revolution or both. As a result, these toner particles get detached from the developing roller  8  and accumulate in unwanted areas inside the cartridge. It is also believed that larger toner particles within the toner particle size distribution, due to their mass, tend to drift off, and as a result of the roller motion disconnect themselves from the developing roller and accumulate in other areas. The accumulation of toner in unwanted areas within the cartridge is also referred to as contamination, and can cause minor to major problems with or defects in the printed media, depending on the extent of the scattered or contaminating toner and its location. Some typical problems or defects are described hereinafter. For example there can be toner build up on regulating member. In this problem the scattered toner builds up on top of the outer surface of the regulating member. This toner buildup creates haze on the printed media due to continuous dripping of un-regulated toner on the page or other print media. A second, frequently occurring problem occurs when a local buildup of toner on the regulating member becomes heavy enough, gravity causes it to fall down onto the printed media or onto the photo-sensitive member, with the result being a print defect or problem, as illustrated in  FIG. 2 . Third and fourth, in the event the volume of scattered toner powder that fell over the media is big enough, it can contaminate the fuser rollers as well create permanent damage to the fuser rollers inside of the printer. A fifth typical toner scatter defect or problem relates to scattered toner that leaves the cartridge and accumulates on different printer internal components, such as for example a transfer belt in a color laser printer, on pick-up rollers and/or on laser lenses. 
     The spacing between the shield face, shown at  58  in  FIG. 6 , of the toner shield and the bottom edge of the regulating member, shown at  48  in  FIG. 5 , was tested. The distance between the bottom face of the toner shield and the regulating member is measured as the distance between the bottom of the edge line of the shield, shown at  68  in  FIG. 6  and the center of the nip, shown at  48  in  FIG. 5 . It has been discovered that the lower edge of the toner shield cannot be touching the developing roller because that will prevent the toner from being transferred onto the drum. Testing to determine the largest, useable gap between the bottom surface of the toner shield and the outer surface of the developing member was determined for the cartridge of the  FIG. 5  embodiment. It was discovered that the spacing between the bottom surface of the toner shield and the developing roller should 0.1 inch or less. It is believed that the gap or space dimension depends on the following factors: 
     The Toner Shield Edge Angle 
     The smaller the angle Ø between the two faces, as shown in  FIG. 5 , the closer the shield has to be installed to the developing roller. 
     The Toner Shield Material 
     The more negative/positive the triboelectric value of the shield, the further away from the developing roller it can be placed. 
     The Location of the Regulating Member Contact 
     The location of the toner shield depends on the shape and location of the regulating member contact. In case the regulating member contact, shown at  40  in  FIG. 5 , is situated at the outer face of the regulating member, shown at  10  in  FIG. 4 , the notch, shown at  62  in  FIG. 6 , has to be cut in the right position in order to sustain electrical continuity between the regulating member contact and the regulating member. The thickness and weight of the toner shield can be varied as long as it does not fall off of the developing roller and so that it is not too thick to interrupt the cartridge&#39;s printing functionality. For example, the toner shield should not be so thick that it will block the laser beam path or touch other components in the cartridge. 
     Although specific embodiments of the invention have been described, various modifications, alterations, alternative constructions, and equivalents are also encompassed within the scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. It will, however, be evident that additions, subtractions, deletions, and other modifications and changes may be made thereunto without departing from the broader spirit and scope of the invention as set forth in the claims.