GB2192570A - Developing electrostatic latent images - Google Patents

Abstract

An apparatus for developing electrostatic latent images comprising, in operative relationship, a flexible imaging member (23), a toner transporting means (15) comprised of a moving shell (19) having incorporated therein rotating magnets (17). A development zone (25) is situated between the flexible imaging member means (23) and the toner transporting means (15), wherein a developer composition is agitated in the development zone. Developer particles (3) comprised of toner composition particles and carrier particles comprised of resin particles and magnetite are immediately available adjacent to the imaging member; with the distance between the imaging member and moving shell being from about 0.1 millimeter to about 1.0 millimeter; and wherein the imaging member is deflected in an arc of from about 10 DEG to about 70 DEG with respect to the toner transporting member. <IMAGE>

Description

SPECIFICATION Electrostatographic development apparatus and process This invention generally relates to a process and apparatus for enabling the development of images in electrostatographic systems. More specifically, the present invention is directed to an improved process and an improved apparatus for effecting the development at high speeds of electrostatic latent images by providing a means for transporting developer particles to a deflected flexible imaging member.

The development of images by electrostatic means is well known. In these processes, toner particles applied to electrostatic latent images by various methods including cascade, magnetic brush, powder cloud, and touchdown development. Cascade development and powder cloud development methods were found to be especially well suited for the development of line images common to business documents, however, images containing solid areas were not faithfully reproduced by these methods. Magnetic brush development processes, however, provide an improved method for producing both line images and-solid area.

In magnetic brush development processes it is usually desirable to attempt to regulate the thickness of the developer composition, which is transported on a roller by moving the roller past a metering blade. The adjustment of the metering blade is important since in the development zone the flow of developer material is determined by a narrow restrictive opening situated between a transport roller and the imaging surface. Accordingly, in order to provide sufficient toner particles to the imaging surface, it is generally necessary to compress the developer bristles thereby allowing toner particles adhering to the carrier particles near the ends of the bristle to be available for development.Any variation, or nonuniformity in the amount of developer, plus or minus about 10 percent metered onto the transport roller, or into the spacing between the transport roller and imaging member can result in undesirable developer flow, and nonuniform image development. Nonuniform development is usually minimized by carefully controlling developer runout on the transport roller and on the imaging member, and by providing a means for side-to-side adjustment in the relative positions of the metering blade, development roller and imaging member.

Moderate solid area development with magnetic brush is usually achieved by transporting the developer composition on a roller at a speed that exceeds the process speed of the image bearing member. At high process speeds the development-transport roller speed is limited by centrifugal forces, which forces cause the developer material to be removed from the roller. Thus to obtain satisfactory solid area development at high process speeds the use of multiple development rolls is required for increased developability.

The developer materials presently used in magnetic brush development differ widely in their electrical conductivity, thus at one extreme in conductivity these materials can be insulating in that a low electrical current is measured when a voltage is applied across the developer. Solid area development with insulating developer composition is accomplished by metering a thin layer of developer onto a development roll, which is in close proximity to an image bearing member, the development roll functioning as an electrode, and thus increasing the electrostatic force acting on the toner particles. In these systems, the spacing between the image bearing member and the development roller is controlled to ensure proper developer flow, and uniform solid area development, the minimum average spacing generally being typically greater than 1.5 millimeters.

Developer compositions can be rendered conductive by utilizing a magnetic carrier material which supports a high electric current flow in response to an applied potential.

Generally, the conductivity of developer compositions depends on a number of factors including the conductivity properties of the magnetic carrier, the concentration of the toner particles, the magnetic field strength, the spacing between the image bearing member and the development roll, and developer degradation due to toner smearing on the carrier particles. Also, when insulative toner particles are permanently bonded to a conductive carrier, the conductivity decreases to a critical value below which solid area development becomes inadequate; however, within certain limits the process and material parameters can be adjusted somewhat to recover the decrease in solid area developability.

When using developer materials in electrostatographic imaging systems, the development electrode member is maintained at a close effective distance from the image bearing member, and a high electrostatic force acts only on those toner particles which are adjacent to the image bearing member. Accordingly, since the electrostatic force for development in such systems is not strongly dependent on the developer layer thickness, the uniformity of solid area development is improved despite variations in the spacing between the image bearing member and the development roller member.More specifically, for example, in magnetic brush development systems with conductive developer materials, solid area deposition is not limited by a layer of net-charged developed near the imaging member providing that the gap is adequately filled to enable contact, since this charge is dissipated by conduction to a development roller. The solid area deposition is, however, limited by image field neutralization provided there is sufficient toner available at the ends of the developer brush, which toner supply is limited to the ends or tips of the bristles since toner cannot be extracted from the bulk of the developer mixture, wherein high developer conductivity collapses the electric field within the developer at any location, and confines it to a region between the latent image and the developer.

For either insulative or conductive developer, solid area deposition is limited by toner supply at low toner concentrations, and the toner supply is limited to a layer of carrier material adjacent to the image bearing member since the magnetic field stiffens the developer, and hinders developer mixing in the development zone.

In the above-described processes, undesirable degradation or deterioration of the developer particles results. This is generally caused by a variety of factors including, for example, the frequency and intensity of collisions between adjacent carrier particles contained in the developer composition, which collisions adversely affect the developer conductivity, and the triboelectric charging relationships between the toner particles and magnetic carrier particles.Thus, for example, a decrease in the triboelectric charge on the toner particles causes an increase in solid area development, and an increase in the amount of toner particles that are deposited in the background or normally white areas of the image; accordingly, to maintain the original image quality in such situations, the triboelectric charge on the toner particles is increased by reducing the concentration of such particles in the developer composition mixture. Also, when the toner charge and toner concentration decreases, the developer material must be replaced in order to obtain images with acceptable solid areas decreased background.

Although several improved types of toner and carrier materials as well as processes have been developed for the purpose of developing images, difficulties continue to be encountered in the design of a simple, inexpensive, and reliable two-component development system which will provide a high solid area development rate, low background deposition, and long term stability. The present magnetic brush systems can be inefficient primarily since only a small fraction of the toner transported through the development zone is accessible for deposition onto the image bearing member. For insulative developer, the solid area deposition is limited by a layer of netcharged carrier particles produced by toner development onto a precharged imaging member.Since the developer entering the development zone has a neutral charge, deposition of charged toner onto the imaging member- produces a layer of oppositely charged developer which opposes further toner deposition. Also, the net electrostatic force due to the charged image member, and the net-charged developer layer becomes zero for that toner between the developer and the electrostatic latent image; and a collapse in the electrostatic force, or the electric field acting on the charged toner, occurs even though the toner charge deposited on the photoreceptor does not neutralize the image charge.Image field neutralization can be approached however, if there is a sufficiently high developer flow rate and multiple development roller. Image field neutralization results when the potential due to a layer of charged toner deposited on the imaging member is equal but opposite to the potential due to the charged imaging member. In the absence of a bias on the development roller, image neutralization produces a zero development electric field; and since the toner layer is of finite thickness, the charge density of the toner layer is less than the image charge density. Should the thickness of the charged toner layer be much less than the imaging member, image field neutralization occurs when the toner charge density neutralizes the image charge density.

Many of the disadvantages illustrated hereinbefore have been eliminated with development of the imaging apparatus and process disclosed in US-A-4,394,429 and US-A4,368,970. In these patents there is described an imaging process and apparatus containing a development means which is comprised of a tensioned deflected flexible imaging member, and a transporting means with a development zone situated between the imaging means and the transporting means. The development zone can contain therein electrically insulating toner particles and electrically insulating magnetic carrier particles. Movement of the flexible imaging member means and the transporting means in opposite directions at different speeds causes the developer particles contained in the development zone to desirably agitate. In this process, however, a magnetic field is not present and furthermore a synthetic developer composition is not selected for use in the system.

Furthermore, there is described in US-A4,376,813 an improved reversal development method which involves forming a magnetic brush around an outer circumferential surface of a developing sleeve accommodating a magnet therein by the use of a developer composition comprised of high resistivity magnetic toner, and rubbing a surface of the electrostatic latent image with the magnetic brush. Additionally, US-A-4,345,014 discloses a magnetic brush development method wherein there is selected a dual component development material which includes electrically insulating magnetizable particles as carrier substances, and electrically insulating nonmagnetic particles as a toner composition.Accordingly, in this patent there is illustrated a developer composition which is comprised of carrier particles of, for example, magnetite, ferrite, or pure iron containing therein a bonding material, such as heat hardening resins including phenolic resins, reference column 3, beginning at line 60 of the '014 patent.

Moreover, there is described in US-A4,344,694 a development apparatus wherein there is selected as developing component, toner particles containing a ferromagnetic material in powder form, or a mixture of toner and carrier particles which may contain iron particles or other ferromagnetic material, reference column 2, beginning at around line 40.

In EP-A-O 132 932 there is disclosed an apparatus in which a rotating developer roller containing both fixed and moving magnetic members transports developer material into contact with a flexible member in a development zone so as to develop a latent image recorded thereon. The developer material being transported through the development zone on the developer roller is magnetically agitated by the moving magnetic member to improve development of the latent image.

Additionally, there is illustrated in EP-A-O 145 300, a process for causing the development of eletrostatic latent images on an imaging member comprising providing a development zone encompassed by an imaging member, and a stationary transporting member containing therein transporting magnets causing the imaging member to move at a speed of from about 5 cm/sec to about 50 cm/sec causing the transporting magnets to rotate at a speed of from about 200 to about 2,000 revolutions per minute, maintaining a distance between the imaging member and the stationary member of from about 0.10 millimeters to about 1.5 millimeters, adding developer particles to the development zone, which particles are comprised of toner particles and carrier particles containing resin and magnetite particles, whereby the toner particles migrate from one layer of carrier particles to another layer of carrier particles in the development zone.

In one specific process embodiment disclosed in EP-A-O 145 300, there is provided an improved process for developing electrostatic latent images which comprises (1) providing a development zone situated between an imaging member and a transporting member, (2) providing in close proximity to the development zone a stationary shell containing rotating magnets therein, (3) transporting a synthetic developer composition into the development zone by causing the magnets in the stationary shell to rotate, (4) causing movement of the imaging member, the imaging member moving in a direction opposite to the direction of movement of the rotating magnets, wherein the developer particles are desirably agitated in the development zone by magnetic means, and wherein developer particles are available immediately adjacent the imaging member, which developer particles are comprised of toner resin particles and carrier particles comprised of resin particles and magnetite, the distance between the imaging member and stationary shell being from about 0.1 millimeter to about 1.5 millimeters. As an example of an imaging member selected for the development process of EP-A-O 145 300, there is disclosed a layered flexible photoresponsive device.In contrast, with respect to the present invention there is selected a moving shell enabling a number of advantages with the development process and apparatus of the present invention as compared to that described in the aforementioned application, which advantages are illustrated hereinafter inclusive of, for example, subbstantially preventing the carrier beads from stagnating at the rotating charging roll surface, and substantially eliminating excess bead carry out which can result in low developability. Further, with the process and apparatus of the present invention, restricted developer flow at the entrance to the development nip is substantially eliminated.

Also, the art of xerography continues to advance and there continues to be a need for improved processes and apparatuses for enabling the development of images in an efficient and economical manner. Additionally, there continues to be a need for improved development processes wherein there is obtained images of high quality and excellent resolution at speeds up to 120 copies per minute. Furthermore, there continues to be a need for high speed development systems wherein only one toner transporting developer roller is required.

Also, there is a need for improved development processes and apparatuses wherein there is selected as developer compositions toner resin particles and carrier resin particles; and wherein this developer composition is rapidly agitated or tumbled in a development permitting toner particles to be available for development on a continual and immediate basis. Moreover, there is a need for improved development processes and apparatus wherein background development is substantially eliminated and wherein the life of the developer composition is increased. Also, there is a need for an improved development process and apparatuses wherein the carrier particles are within a size range that prevent bead carry out or consumption of the carrier particles during the electrophotographic process.By bead carry out in accordance with the process of the present invention is meant the sticking of carrier particles to the deflected flexible photoreceptor during development, which beads are moved out of the development subsystem and, for example, consumed either on the output copy or in the cleaner assembly.

It is, therefore, an object of the present invention to provide an improved development process and development apparatus which overcomes some of the above-noted disadvantages.

According to the present invention, there is provided an apparatus for developing electrostatic latent images comprising, in operative relationship, a flexible imaging member means, a toner transporting means comprised of a moving shell having incorporated therein rotating magnets; and a development zone situated between the flexible imaging member means and the toner transporting means, wherein a developer composition is agitated in the development zone, and developer particles comprised of toner composition particles, and carrier comprised of resin particles and magnetite are immediately available adjacent to the imaging member with the distance between the imaging member and moving shell being from about 0.1 millimeter to about 1.0 millimeter; and wherein the imaging member is deflected in an arc of from about 10 to about 70" with respect to the toner transporting member.

The invention also provides a process for the development of electrostatic latent images comprising (1) providing a development zone situated between a flexible imaging member and a toner transporting member, said transporting member being comprised of a moving shell having incorporated therein rotating magnets; (2) transporting synthetic developer composition into the development zone; (3) effecting movement of the imaging member in the direction opposite to the direction of movement of the rotating magnets, wherein the developer composition is desirably agitated in the development zone by the magnetic means, and wherein developer particles are available immediately adjacent the imaging member, which particles are comprised of toner resin, pigments, and carrier particles comprised of resin particles and magnetites with the distance between the flexible imaging member and the stationary shell being about 0.1 millimeter to about 1.0 millimeters, and wherein the imaging member is deflected in an arc of from about 10 to about 70" with respect to the transporting member.

The magnetically agitated development process and apparatus of the invention permits the generation of images of high quality at speeds in excess of 120 copies per minute.

The invention provides an apparatus and process for effecting the development of electrostatic latent images at high speeds wherein a synthetic developer composition is desirably agitated or tumbled in a development zone situated between a deflected flexible imaging member and a transporting means comprised of a moving shell containing therein rotating magnets.

Toner particles are continuously and immediately adjacent to the deflected flexible imaging member surface permitting full development of images including the development of all solid areas at high development speeds.

In one embodiment, the present invention is directed to a high speed development apparatus comprised of a housing means, a toner mixing means, a toner transporting means comprised of a moving shell with rotating magnets therein, a deflected flexible imaging member deflected in an arc of from about 10 to about 50 with respect to the toner transporting member, and situated between the toner transporting member and deflected flexible imaging member a development zone wherein developer particles are desirably agitated or tumbled permitting them to be continually and rapidly available for the development of images present on the deflected member.

The aforementioned apparatus is operable at various development speeds depending, for example, on the number of magnetic poles present in the moving shell. Additionally, and more importantly with the aforementioned apparatus the carrier particles tumble in the development zone thereby enabling toner particles on the outer surfaces of each of the carrier particles to be continuously available for electrostatic attraction to the flexible imaging member.

The imaging member in one process embodiment is moved at a speed of from about 5 cm/sec to about 50 cm/sec, while the transporting magnets are moving at a speed of from about 200 to about 2,000 revolutions per minute. Further, the shell is rotating at a speed of from about 100 to about 400 revolutions per minute.

There is also provided in accordance with the present invention an electrostatographic process wherein latent electrostatic images are developed with an apparatus containing an imaging means, a charging means, an exposure means, a development means, and a fixing means; the improvement residing in a development means comprising in operative relationship, a toner transporting means comprised of a moving shell and rotating magnets situated therein, a flexible imaging member deflected in an arc of from about 10 to about 70" with respect to the toner transporting means, a development zone situated between the deflected flexible imaging member means and the toner transporting means, the development zone containing therein toner particles and carrier particles comprised of resin particles and magnetic particles and wherein the imaging means is caused to move at a speed of from about 5 cm/sec to about 50 cm/sec, the transporting means moves developer particles at a speed of from about 30cm/sec to about 135 cm/sec, the means for imaging and the means for transporting toner having a distance therebetween of from about 0.10 millimeter to about 1.0 millimeter thus enabling high process development with a single toner transporting means.

For a better understanding of the present invention and further features thereof, reference is made to the following detailed description of various prefered embodiments wherein: Figure 1 is a partially schematic cross-sectional view of the development process and apparatus of the present invention; and Figure 2 illustrates an embodiment of the present invention in an electrostatographic imaging apparatus.

Illustrated in Fig. 1 is one apparatus and process embodiment of the present invention comprised of a container or housing means 1, developer particles 3, comprised of toner resin particles 5, and synthetic carrier particles 7, comprised of resin particles and magnetic particles, a paddlewheel means 9, with buckets thereon 11, a toner transporting means 15, comprised of rotating magnets 17, and a moving sleeve 19, moving in the direction depicted by the arrow 20, a developer trimmer bar means 21, a flexible imaging member 23 deflected in an arc of from about 10 to about 50 with respect to the toner transporting means 15, a development zone 25, and a stripper shim means 27.Generally, in operation the deflected flexible imaging member and the shell are moving at a relative speed and in opposite directions to the movement of the rotating magnets. This movement permits developer particles to be transported to development zone 25 situated between the imaging member and the toner transporting member whereby the toner particles contained in this zone are desirably agitated. The developer particles 3 are initially presented to the toner transporting means 15 by paddlewheel means 9 moving in the direction as depicted by the arrow 10. Additionally, the trimmer bar means 21 serves to maintain the thickness of the developer composition layer present on the toner transporting means.Further, stripper shim means 27 enables the developer particles, and particularly carrier particles, which are substantially depleted of toner particles, to be redirected to the developer housing 1 for admixing with toner particles.

Accordingly, thus the rotating magnets present in the moving shell of the toner transporting means provide a magnetic force permitting synthetic developer particles 3 to be transported, wherein they are initially contacted by the adjustable trim bar means 21 enabling a selected amount of developer particles to remain on the moving shell. While it is not desired to be limited by theory, it is believed that the synthetic developer particles which can be in the form of chains continually flip as a pole magnet pair rotates. These developer chains travel a distance of approximately one chain length and continuously flip and move along the moving shell providing high agitation at high rotation rates and, therefore, a continuous supply of toner particles enabling high speed development of images present on the flexible imaging member.Specifically, therefore, the carrier particles which are initially surrounded by toner particles are depleted of toner particles as they enter the development zone as a result of the electrostatic attraction generated by the latent image present on the deflected flexible imaging member. Without rotation or flipping, toner particles situated, for example, on the sides and bottom of the carrier particle would not be available for attraction to the imaging member.

Therefore, it is rather important to the process and apparatus of the present invention to effect the tumbling or flipping of the carrier particles permitting toner particles that would not otherwise be available for development to be presented to the imaging member by electrostatic attraction. It is in this manner that the process speed can be controlled depending on the number of magnetic poles present in the moving shell. Therefore, with the present invention there is enabled high process speeds, that is, wherein images of excellent resolution can be developed at speeds up to, or greater than 120 copies per minute.

With further regard to the high speed development process, developer agitation permits the toner particles adhering to the carrier particles to migrate towards the imaging member with the toner particles closest to the flexible imaging member being deposited thereon. Accordingly, the carrier particles adjacent to the imaging surface lose some of the toner adhering thereto, which toner particles must be replaced to permit the achievement of high quality development, and particularly solid area development. Movement or agitation of the carrier particles as indicated herein enables toner particles adhering to other portions of the carrier particles to be available for attraction to the electrostatic imaging member.Maximum agitation, which is preferred, is obtained when the development zone is thin, that is, the developer particles contained in the development zone range in thickness of from about 0.1 millimeter to about 1.0 millimeter, and preferably from about 0.3 millimeter to about 0.8 millimeter. Magnets of, for example, 16, 24, or 32 poles are secured to a moving support by a number of suitable means including, for example, the bonding of adhesives to a support or by a magnetizing cylinder. These magnets generally have a length of from about 200 millimeters to about 400 millimeters, a width of from about 5 millimeters to about 20 millimeters, and a thickness of from about 15 millimeters to about 30 millimeters. Additionallly, the magnets selected are commercially available and can be comprised of known materials such as ceramic magnetic materials including strontium ferrites.

The magnets can be moved at different speeds depending on, for example, the degree of agitation desired and the number of copies per minute to be generated. Generally, how ever, the magnets are moving at a speed of from about 200 revolutions per minute to about 2-,000 revolutions per minute, and preferably at a speed of from about 900 revolutions per minute to about 1,100 revolutions per minute. Additionally, each magnet generates a magnetic field of from about 450 gauss to about 1,000 gauss, and preferably magnets are selected so as to generate a field of from about 700 gauss to about 900 gauss.

With further respect to the apparatus of the present invention, the sleeve means 19 is generally comprised of a shell of aluminium having a circumference of from about 6 centimeters to about 25 centimeters, and preferably from about 10 centimeters to about 20 centimeters. This shell is generally of a thickness of from about 0.8 mm to about 2.4 mm.

Other suitable materials can be selected for the moving shell including, for example, stainless steel, brass, conductively coated formed plastics, and the like.

Illustrative examples of trimmer bars and stripper shims that may be selected for the process and apparatus of the present invention include aluminium, brass, and the like.

Examples of means for moving the synthetic developer composition to the toner transporting means include paddlewheels as illustrated with reference to Fig. 1, augers, chutes, and the like.

Illustrative examples of flexible imaging members include layered organic photoreceptors comprised of a substrate, a photogenerating layer, and a amine transport layer, such as those described in US-A-4,265,990. As examples of photogenerating layers for the aforementioned members, there can be selected metal phthalocyanines, metal free phthalocyanines, squarine compositions, vanadyl phthalocyanines, selenium, trigonal selenium, and the like, with vanadyl phthalocyanine and trigoiial selenium being preferred.

Examples of transport layer molecules include the diamine compositions as described in US A-4,265,990.

Generally, the photogenerating pigment and the amine transport molecules are dispersed in an inactive resinous binder composition in various effective amounts. Thus, for example, the photogenerating pigment vanadyl phthalocyanine is present in the photogenerating layer in an amount of from about 5 percent to 35 percent while the amine transport molecule is present in the resinous binder in an amount of from about 40 percent to about 80 percent.

Examples of resinous materials include those as described in US-A-4,265,990, such as polycarbonates, polyvinylcarbazole, polyesters, and the like.

With further regard to the imaging member, it is deflected in an arc of from about 10 to about 70 , and preferably in an arc of from about 10 to about 50 with respect to the toner transporting means. This deflection is provided primarily by the pressure exerted on the flexible imaging member by the developer particles present in the development zone. As a result of the presence of these particles, there is exerted on the imaging member pressures of from about 7x 10-4 kg. cm 2 to about 7x 10-2 kg. cm-2, and preferably from about 7 x 10--3 kg. cm-2 to about 7x10-2 kg.

cm-2. The pressure exerted on the imaging member is also dependent on the tension and arc radius of the member, thus the pressure P is obtained by dividing the belt tension, T expressed in a force per unit width of the deflected imaging member by the arc radius R of the imaging member as represented by the equation P=T/R.

A very important feature for the process and apparatus of the present invention resides in the use of synthetic developer compositions. This developer composition is identified as synthetic in that it contains as carrier particles, resin particles and magnetic particles as specifically illustrated hereinafter.

Various suitable toner compositions can be selected for the developers of the present invention. These compositions can include resin particles, pigment particles, an optional low molecular weight waxy material, and as a further optional component, a charge enhancing additive for the purpose of, for example, imparting a triboelectric charge to the toner particles. Thus, for example, a positively charged toner composition useful in the present invention is comprised of particles containing polyester resins, styrene butylmethacrylate resins, or styrene butadiene resins, pigment particles, a low molecular weight from about 1 ,000 to about 6,000, wax such as polyethylene or polypropylene, and a charge enhancing addi tive selected from the group consisting of akylpyridinium halides, organic sulfate, and organic sulfonate additives.Specific illustrative examples of akylpyridinium compounds include cetyl pyridinium chloride, reference for example US-A-4,298,672, and stearyl dimethyl phenethyl toluene sulfonate, reference US A-4,338,390.

Illustrative examples of toner resins are polyesters, styrene/methacrylate or styrene acrylates, polyamides, diolefins, epoxies, polyurethanes, vinyl resins and polymeric esterification products of a dicarboxylic acid and a diol comprising a diphenol. Typical examples of vinyl monomers are: styrene, p-chlorostyrene vinyl napthalene, vinyl chloride, vinyl bromide, vinyl fluoride; ethylenically unsaturated mono-olefins such as ethylene, propylene, butylene, and isobutylene; vinyl esters like vinyl acetate, vinyl propionate, vinyl benzonate, and vinyl butyrate; esters of alphamethylene aliphatic monocarboxylic acids inclusive of methyl acrylate, ethyl acrylate, n-butlacrylate, isobutyl acrylate, didecyl acrylate, n-octyl acrylate, 2chloroethyl acrylate, phenyl acrylate, methylalpha-chloroacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate and the like; acrylonitrile, methacylonitrile, acrylamide, vinyl ethers; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, and rnethyl isopropenyl ketone; vinylidene halides like vinylidene chloride, and vinylidene chlorofluoride; styrene butadienes; and the like.

The prefered toner resins of the present invention are selected from polystyrene methacrylates; polyester resin such as those described in US-A-3,655,374; polyester resins resulting from the condensation of dimethylterephthalate, 1,3 butanediol, and pentaerythritol; and Pliolite resins. The Pliolite resins are believed to be copolymer resins of styrene and butadiene, wherein the styrene is present in an amount of from about 80 weight percent to about 95 weight percent, and the butadiene is present in an amount of from about 5 weight percent to about 20 weight percent. A specific styrene butadiene resin found highly useful in the present invention is comprised of about 89 percent of styrene, and 11 percent of butadiene.

Various suitable known colorants and/or pigments particles may be incorporated into the toner particles including, for example, carbon black, Nigrosine dye, magnetic particles such as Mapico Black, comprised of a mixture of iron oxides, and the like. The pigment particles are present in the toner in sufficient quantities so as to render it highly colored in order that it will form a visible image on the recording member. Thus, for example, the pigment particles, with the exception of magnetic materials, should be present in the toner composition in an amount of from about 2 percent by weight to about 15 percent by weight, and preferably from about 2 percent by weight to about 10 percent by weight.With regard to magnetic pigments such as Mapico Black, they are generally incorporated into the toner composition in an amount of from about 10 percent by weight to about 60 percent by weight, and preferably in an amount of from about 20 percent by weight to about 30 percent by weight.

While the magnetic particles can be present in the toner composition as the only pigment, these particles may be combined with other pigments such as carbon black Thus, for example, in this embodiment of the present invention, the other pigments including carbon black are present in an amount of from about 5 percent by weight to about 10 percent by weight with the magnetic pigment being present in an amount of from about 10 to about 60 percent by weight. Other percentage combinations of other pigments and magnetic pigments, may be selected provided the objectives of the present invention are achieved Low molecular weight waxy materials may also be incorporated into the toner composition in an amount of from about 1 percent by weight to about 10 percent by weight, and preferably in an amount of from about 2 percent by weight to about 5 percent by weight.

These waxes are generally of molecular weight of from between about 500 and about 20,000, and preferably are of a molecular weight of from about 1,000 to about 6,000.

Illustrative examples of low molecular weight waxy materials included within the scope of the present invention are polyethylenes commercially from Allied Chemicals and Petrolite Corporation; Epolene N-15, commercially available from Eastman Chemical Products Incorporated; Viscol 550-P, a low molecular weight available from Sanyo Kasei K.K.; and similar materials. The commercially available polyethylenes selected have a molecular weight of about 1,000 to 1,500 while the commercially available polypropylenes incorporated into the toner compositions of the present invention have a molecular weight of about 4,000.

Many of the polyethylene and the polypropylene compositions useful in the present invention are illustrated in GB-A-1,442,835.

Also, charge enhancing additives may be mixed into the developer composition so as to be present in an amount of from about 0.5 percent to about 20 percent by weight, and preferably from about 1 percent by weight to about 5 percent by weight, based'on the total weight of the toner particles. These charge control additives can either be blended into the developer mixture or coated onto the pigment particles such as carbon black. The preferred charge enhancing additives incorporated into the toner compositions of the present invention include cetyl pyridium chloride, reference US-A-4,298,672; and stearyl phenethyl ammonium para-toluene sulfonate.

Further, the toner resin is present in an amount to provide a toner composition which will result in a total of about 100 percent for all components. Accordingly, for non-magnetic toner compositions the toner resin is generally present in an amount of from about 60 percent by weight to about 90 percent by weight, and preferably of from about 80 percent by weight to about 85 percent by weight. In one embodiment, thus the toner composition can be comprised of 90 percent by- weight of resin particles, 5 percent by weight of pigment particles, such as carbon black, 3 percent by weight of the charge enhancing additive material, and 2 percent by weight of the low molecular weight wax.

One preferred toner resin material is comprised of about 67 percent by weight of a styrene butadiene copolymer containing about 88 to 91 percent by weight of styrene, and about 8 to about 12 percent by weight of butadiene; or 67 percent by weight of a branched polyester resin obtained from the reaction of bisphenol A, propylene oxide and fumaric acid; 25 percent by weight of a crosslinked styrene n-butyl methacrylate resin containing 58 percent by weight of styrene and 42 percent by weight of n-butyl methacrylate, 6 percent by weight of carbon black, and 2 percent by weight of a polypropylene wax of a molecular weight of from about 2,000 to about 7,000. The crosslinked resin contains about 0.2 percent of divinyi benzene.Another preferred toner composition is comprised of a polyester resin as disclosed in US-A3,655,374, which resin is present in an amount of about 80 percent by weight, and magnetic pigments, such as magnetite, including Mapico Black, present in an amount of about 20 percent by weight, with no carbon black being present in this composition.

Additionally, there can be incorporated into the toner composition various additives such as silica particles, including Aerosii R972, and various known fatty acids of metal salts including zinc stearate, reference US-A3,655,374; 3,720,617; and 3,900,588. These materials are incorporated primarily for assisting and providing a negative triboelectric charge to the toner particles.

The carrier composition of the present invention, which has a diameter of from about 50 microns to about 250 microns, is comprised of resin particles, magnetic particles, and carbon black. Thus, for example, the carrier particles can be comprised of from about 20 percent to about 30 percent of the resin particles illustrated hereinafter, including styrene and butylmethacrylate polymers, polymethacrylates, and form about 50 percent by weight to about 70 percent by weight of magnetites including known magnetites, which are mixtures of iron oxides either of a cubic shape or an acicular shape, and from about 0 percent to about 10 percent by weight of carbon black, either in a conductive or non-conductive form.

Examples of resin particles useful for the carrier composition are polyamides, epoxies, diolefins, polyurethanes, vinyl resins, and polymeric esterification products of a dicarboxylic acid and a diol comprising a diphenol. Typical vinyl monomers are styrene, p-chlorostyrene vinyl napthalene, vinyl chloride, vinyl bromide, vinyl fluoride, ethylenically unsaturated monoolefins such as ethylene, propylene, butylene, and isobutylene; vinyl esters like vinyl acetate, vinyl propionate, vinyl benzoate, and vinyl butyrate; ester of alpha-methylene alipharic monocarboxylic acids inclusive of methyl acrylate, ethyl acrylate, n-butylacrylate, isobutyl acrylate dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methylalpha-chloroacrylate, ethyl methacrylate, butyl methacrylate and the like; acrylonitrile, methacrylonitrile, acrylamide, vinyl ethers; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, and methyl isopropenyl ketone; vinylidene halides like vinylidene chloride, and vinylidene chlorofluoride; styrene butadienes; and the like.

The preferred material for the carrier particles are comrpised of a styrene butadiene copolymer resin and a styrene n-butyl methacrylate copolymer resin.

As one preferred carrier resin there can be selected the esterification products of a dicarboxylic acid and a diol comprising a diphenol.

These materials are illustrated in US-A3,655,374, the diphenol reactant beginning of formula as shown in column 4, being at the line 5 of this patent, and the dicarboxylic acid being of the formula as shown in column 6.

Other preferred toner resins include styrene/methacrylate copolymers, and styrene/butadiene copolymers.

Other specific preferred resins selected for the carrier compositions of the present invention include polymethylmethacrylates, vinyl halide copolymers, particularly vinyl chloride copolymers, and the like.

Illustrative examples of magnetites included within the carrier resin particles are cubically shaped Mapico Black, commercially available from Cities Service; acicular magnetites, commercially available from Pfizer Corporation; and the like, with cubical Macipo Black being preferred. These magnetites are believed to be comprised of a mixture of iron oxides.

Conductive or non-conductive carbon black particles can be included in the carrier composition in the amount of from about 0 percent by weight to about 10 percent by weight. By conductive, in accordance with the present invention, is meant that the carrier particles with carbon black have a conductivity of from about 10 6 (ohm-cm) ' at 200 volts per millimeter to about 10 9 (ohms-cm) ' at 200 volts per millimeter, and preferably from about 10 7 (ohm-cm) l at 200 volts per millimeter to about 10 8 (ohm-cm) 1 at 200 volts per millimeter.

Developer compositions can be prepared by mixing in effective amounts of the toner composition described herein with the carrier composition comprised of resin particles, magnetite particles, and carbon black particles. More specifically, a developer compositon can be obtained by mixing about 98 parts of carrier particles with 2 parts of toner particles.

The process of the present invention is useful in many imaging systems, including electronic printers, and electrostatographic copying machines such as those utilizing known xerographic apparatuses. There is illustrated in Fig.

2 an electrophotographic printing machine with a deflected flexible imaging member 51 as described in US-A-4,265,990; 4,459,009 and EP-A-0 155 169, having a photoconductive surface deposited on a conductive substrate such as aluminized Mylar, which is electrically grounded and an overcoating amine transport layer.

The imaging member 51, can thus be comprised of numerous suitable materials, as described herein; however, for this illustration the photoconductive material comprised of a photogenerating layer of trigonal selenium, or vanadyl phthalocyanine overcoated with a transport layer containing small molecules of N,N,N'-tetraphenyl-[1,1'-biphenyl] 4,4'-diamine, or similar diamines dispersed in a polycarbonate resinous binder. With further reference to Fig. 2, deflected flexible imaging member 51 moves in the direction of arrow 57 to advance successive portions of the photoconductive surface sequentially through the various processing stations disposed about the path of movement thereof. The imaging member is entrained about a sheet-stripping roller 58 and drive roller 60.A tensioning system not shown includes a roller 61 having flanges on opposite sides thereof to define a path through which member 51 moves. Roller 61 is mounted on each end of guides attached to springs. The springs are tensioned such that roller 61 presses against the imaging belt member 51. In this manner, member 51 is placed under desired tension. The level of tension is relatively low permitting member 51 to be relatively easily deformed. With continued reference to Fig. 2, drive roller 60 is mounted rotatably and in engagement with member 51.

Motor 63 rotates roller 60 to advance member 51 in the direction of arrow 57. Roller 60 is coupled to motor 63 by suitable means such as a belt drive. Sheet-stripping roller 58 is freely rotatable so as to readily permit member 51 to move in the direction of arrow 57 with a minimum of friction.

initially, a portion of imaging member 51 passes through charging station H. At charging station H, a corona generating device, indicated generally by the reference numeral 64, charges the photoconductive surface of imaging member 51 to a relatively high, substantially uniform potential.

The charged portion of the photoconductive surface is then advanced through exposure station I. An original document 65 is positioned face down upon transparent platen 66.

Lamps 67 flash light rays onto original document 65. The light rays reflected from original document 65 are transmitted through lens 68 forming a light image thereof. Lens 68 focuses the light image onto the charged portion of the photoconductive surface to selectively dissipate the charge thereon. This records an electrostatic latent image on the photoconductive surface which corresponds to the informational areas contained within original document 65.

Thereafter, imaging member 51 advances the electrostatic latent image recorded on the photoconductive surface to development station J described in detail hereinbefore. At development station J, a magnetically agitated development system illustrated herein, indicated generally by the reference numeral 69, advances the developer material into contact with the electrostatic latent image. The magnetically agitated development system 69 includes a developer roller or shell 70 on which a layer of synthetic developer material is transported comprising resin and magnetic carrier particles and toner particles into contact with the deflected flexible imaging member 51. As shown, developer roller 70 is positioned such that the blanket of developer material deforms imaging member 51 in an arc, such that member 51 conforms at least partially, to configuration of the synthetic developer material.The electrostatic latent image attracts the toner particles from the carrier granules forming a toner powder image on the photoconductive surface of member 51.

Imaging member 51 then advances the toner powder image to transfer station K. At transfer station K, a sheet of support material 74 is moved into contact with the toner powder image. The sheet of support material 74 is advanced to transfer station K by a sheet feeding apparatus (not shown). Preferably, the sheet feeding apparatus includes a feed roll contacting the uppermost sheet of a stack of sheets. The feed roll rotates so as to advance the uppermost sheet from the stack into a chute. The chute directs the advancing sheet of support material into contact with the photoconductive surface of member 51 in a timed sequence so that the toner powder image developed thereon contacts the advancing sheet of support material at transfer station K.

Transfer station K includes a corona generating device 76 which sprays ions onto the backside of sheet 74. This attracts the toner powder image from the photoconductive surface to sheet 74. After transfer, sheet 74 moves in the direction of arrow 78 onto a conveyor (not shown) which advances sheet 74 to fusing station L.

Fusing station L includes a fuser assembly, indicated generally by the reference numeral 80, which permanently affjxes the transferred toner powder image to sheet 74. Preferably, fuser assembly 80 includes a heated fuser roller 82 and a back-up roller 84. Sheet 74 passes between fuser roller 82 and back-up roller 84 with the toner powder image contacting fuser roller 82. In this manner, the toner powder image is permanently affixed to sheet 74. After fusing, a chute guides the advancing sheet to a catch tray for subsequent removal from the printing machine by the operator.

After the sheet of support material is separated from the photoconductive surface of imaging member 51, some residual particles remain adhering thereto, which particles are removed from the photoconductive surface of cleaning station M. Cleaning station M includes a rotatably mounted fibrous brush 86 in contact with the photoconductive surface. The particles are cleaned from the photoconductive surface by the rotation of brush 86 in contact therewith. Subsequent to cleaning, a discharge lamp (not shown) floods photoconductive surface 51 with light to dissipate any residual electrostatic charge remaining thereon prior to the charging thereof for the next successive imaging cycle.

The following specific examples are now being provided to illustrate preferred embodiments of the present invention, however, it is not intended to be limited to the process parameters disclosed. In these examples parts and percentages are by weight unless otherwise indicated; EXAMPLE I A synthetic developer composition comprised of 3 percent by weight of a positively charged toner composition containing 92.5 percent by weight of a styrene n-butyl methacrylate resin (58/42), 6 percent by weight of Regal' 330 carbon black, and 1.5 percent by weight of the charge enhancing additive distearyl dimethyl ammonium methyl sulfate, which toner has an average particle diameter 9.6 microns, and a carrier, 97 percent by weight consisting of 26 percent by weight of a styrene butadiene copolymer (89/11), 70 percent by weight of the magnetite Mapico Black, and 4 percent by weight of Vulcan carbon black, which carrier had an average particle diameter of from about 88 to about 177 microns, was incorporated into the apparatus of Fig. 1 wherein the photoreceptor wasXm- prised of an aluminium substrate, a photogenerating layer of trigonal selenium dispersed in a polyvinyl carbazole resinous binder, and thereover a charge transport layer of the aryl amine N,N,N'-tertraphyeny( 1 , 1 '-biphenyl]-4,4'- diamine, a polycarbonate resin, reference U.S.

Patent 4,265,990. With further reference to the apparatus of Fig. 1, the charging roll diameter was 6.3 cm, and the magnets which were rotating at a speed of 910 revolutions per minute were comprised of a ceramic material; and there were present 24 poles with each magnet generating a magnetic field of 900 gauss. Further, the shell which was comprised of stainless steel was rotating at a speed of 230 revolutions per minute, and the spacing between the charging roll and transporting means was 0.51 mm. The paddlewheel in the developer sump was rotating at 100 revolutions per minute. Also, the process speed was 45.7 cm per second.

Subsequent to charging of the toner particles and imagewise exposure of the imaging member, there were obtained images of excellent resolution with substantially no background deposits. Also, developed lines nongrainy with sharp edges, and the line aspect ratio was near 1, that is the partial line density divided by the perpendicular line density was nearly equal to 1 for the same input density. Additionally, half tones were of excellent resolution, and the densities thereof were faithfully reproduced.

EXAMPLE II The process of Example I was repeated with the exception that the process speed selected was 33.8 cm per second, the speed of the magnets was 420 revolutions per minute, the speed of the shell was 150 revolutions per minute, the paddlewheel speed was 120 revolutions per minute, and the carrier selected was comprised of 30 percent by weight of a styrene butadiene resin (89/11), and 70 percent of the magnetite Macipo Black, which carrier had an average particle diameter of from 75 to 120 microns. Further, the toner selected had an average particle diameter of 9.1 microns. Substantially similar results were obtained; and, for example, images of high resolutions with low background deposits. Also, solid areas were nongrainy and the lines possess sharp edges. As with the process of Example I, the line aspect ratio was near 1.

Claims (37)

1. An apparatus for developing electrostatic latent images comprising, in operative relationship, a flexible imaging member means, a toner transporting means comprised of a moving shell having incorporated therein rotating magnets; and a development zone situated bq tween the flexible imaging member meals and the toner transporting means, wherein a developer composition is agitated in the development zone, and developer particles comprised of toner composition particles, and carrier particles comprised of resin particles and magnetite are immediately available adjacent to the imaging member with the distance between the imaging member and moving shell being from about 0.1 millimeter to about 1.0 millimeter; and wherein the imaging member is deflected in an arc of from about 10 to about 70 with respect to the toner transporting member.

2. An apparatus in accordance with claim 1 wherein there is further included a developer housing means, a paddlewheel means, a toner trim bar means, and a developer stripping means.

3. An apparatus in accordance with claim 1 or claim 2 wherein from about 16 pole magnets to about 32 pole magnets are situated in the moving sleeve.

4. An apparatus in accordance with any one of claims 1 to 3 wherein the magnets are rotating at a speed of from about 200 revolutions per minute to about 2,000 revolutions per minute.

5. An apparatus in accordance with any one of claims 1 to 3 wherein the magnets are rotating at a speed of from about 900 revolutions per minute to about 1 ,100 revolutions per minute.

6. An apparatus in accordance with any one of claims 1 to 5 wherein the sleeve is rotating in a direction opposite to the direction of movement of the magnets at a speed of from about 100 revolutions per minute to about 400 revolutions per minute.

7. An apparatus in accordance with any one of claims 1 to 6 wherein the deflected flexible imaging member is moving at a speed of from about 5 cm/sec to about 100 cm/sec.

8. An apparatus in accordance with any one of claims 1 to 7 wherein the developer particles are caused to agitate in the development zone by movement of the rotating magnets, the sleeve means, and the imaging member means.

9. An apparatus in accordance with any one of claims 1 to 8 wherein development of images present on the flexible imaging member is accomplished at speeds of from about 60 cycles per minute to about 120 cycles per minute.

10. An apparatus in accordance with any one of claims 1 to 9 wherein the imaging member is comprised of a supporting substrate, a photogenerating layer; and a aryiamine charge transport layer.

11. An apparatus in accordance with claim 10 wherein the photogenerating layer is selected from the group consisting of metal phthalocyanines, metal free phthalocyanines, vanadyl phthalocyanines, squarylium pigments, and trigonal selenium optionally dispersed in an inactive resinous binder.

12. An apparatus in accordance with any one of claims 1 to 11 wherein the carrier particles are comprised of a styrene butadiene resin, or a styrene n-butylmethacrylate resin.

13. An apparatus in accordance with claim 12 wherein the resin particles are present in an amount of from about 20 percent by weight to about 40 percent by weight, and the magnetite particles are present in an amount of from about 60 percent by weight to about 80 percent by weight.

14. An apparatus in accordance with claim 13 wherein there is further included in the carrier particles from about 1 percent by weight to about 10 percent by weight of carbon black particles.

15. An apparatus in accordance with any one of claims 1 to 11 wherein the carrier particles are comprised of polymethacrylate resin particles from 20 percent by weight to about 80 percent by weight.

16. An apparatus in accordance with claim 1 5 wherein there is further included in the carrier particles carbon black particles.

17. An apparatus in accordance with any one of claims 1 to 16 wherein the carrier particles are of a diameter of 50 microns to 200 microns.

18. A process for the development of electrostatic latent images comprising (1) providing a development zone situated between a flexible imaging member and a toner transporting member, said transporting member being comprised of a moving shell having incorporated therein rotating magnets; (2) transporting synthetic developer composition into the development zone; (3) effecting movement of the imaging member in the direction opposite to the direction of movement of the rotating magnets, wherein the developer composition is desirably agitated in the development zone by the magnetic means, and wherein developer particles are available immediately adjacent the imaging member, which particles are comprised of toner resins, pigments, and carrier particles comprised of resin particles and magnetites with the distance between the flexible imaging member and the stationary shell being about 0.1 millimeter to about 1.0 millimeters, and wherein the imaging member is deflected in an arc of from about 10 to about 70 with respect to the transporting member.

19. A process in accordance with claim 18 wherein the imaging member is moved at a speed of from about 5 centimeters per second to about 100 centimeters per second, and the transporting means containing the rotating magnets is moved at a speed of from about 6 centimeters per second to about 100 centimeters per second.

20. A process in accordance with claim 18 or claim 19 wherein the imaging member is flexible and is comprised of a supporting substrate, a photogenerating layer, and an amine charge transport layer.

21. A process in accordance with claim 20 wherein the photogenerating layer is selected from the group consisting of metal phthalocyanines, metal free phthalocyanines, vanadyl phthtalocyanines, and trigonal selenium optionally dispersed in an inactive resinous binder.

22. A process in accordance with any one of claims 18 to 21 wherein the carrier resin particles are comprised of a styrene butadiene resin,or a styrene n-butyl methacrylate resin.

23. A process in accordance with claim 22 wherein the resin particles are present in an amount of from 20 percent by weight to about 40 percent by weight, and the magnetite particles are present in an amount of from about 60 percent to about 80 percent by weight.

24. A process in accordance with claim 22 wherein there is further included in the carrier particles from about 1 percent by weight to about 10 percent by weight of carbon black particles.

25. A process in accordance with any one of claims 18 to 21 wherein the carrier particles are comprised of polymethylmethacrylate resin particles, from about 20 to about 40 percent by weight, and magnetite particles, from about 60 percent by weight to about 80 percent by weight.

26. A process in accordance with claim 25 wherein there is further included in the carrier particles carbon black particles.

27. A process in accordance with any one of claims 18 to 26 wherein the magnets are rotating at a speed of from about 200 revolutions per minute to about 2,000 revolutions per minute.

28. A process in accordance with any one of claims 18 to 21 wherein the carrier resin particles are comprised of styrene polymer compositions.

29. A process in accordance with any one of claims 18 to 28 wherein the carrier particles are of a diameter of from about 50 to 250 microns.

30. A process in- accordance with any one of claims 18 to 29 wherein the toner resin particles are comprised of polystyrene polymers.

31. A process in accordance with any one of claims 18 to 29 wherein the toner resin particles are comprised of polyester compositions, or styrene butadiene copolymers.

32. A process in accordance with any one of claims 18 to 31 wherein the toner particles include therein a low molecular weight wax and charge enhancing additives.

33. A process in accordance with claim 32 wherein the wax is polypropylene, and the charge enhancing additive is cetyl pyrid)im chloride.

34. A process in accordance with any one of claims 18 to 33 wherein the sleeve is moving at a speed of from about 100 revolutions per minute to about 400 revolutions per minute.

35. A process in accordance with any one of claims 18 to 34 wherein from about 8 pole magnets to about 32 pole magnets are present in the moving shell.

36. An apparatus according to claim 1 substantially as hereinbefore described with reference to the accompanying drawings.

37. A process according to claim 18 substantially as hereinbefore described with reference to the accompanying drawings.