Patent Grant
8802345
This disclosure relates to a set of electrophotographic toners which are used for electrophotographic machines such as electrostatic copying machines and laser printers.
In electrostatic copying machines (hereinafter referred to as copying machines) which utilize a binary developer comprising an electrophotographic toner (hereinafter referred to as a toner) and a carrier, an initial supply toner is contained together with a carrier in a developing apparatus from the beginning of the copying process, while a supplementary toner is contained in a toner hopper. The toner contained in the developing apparatus is mixed with the carrier in this apparatus, resulting in a developer. The developer formed in this way is supplied either to a photosensitive drum by magnetic rollers or to a donor roll, from which a toner layer is presented to a photosensitive drum. The toner contained in the toner hopper is supplied to the developing apparatus when a decrease in toner concentration in the developer contained in the developing apparatus is observed by a sensor for detecting toner concentration. Thereafter, the toner supplied to the developing apparatus is mixed with a carrier to form a developer which is then supplied to the photosensitive drum in the same way as mentioned above. The toner contained in the developer is adsorbed by an electrostatic latent image which has been formed on the photosensitive drum, and then transferred to paper, resulting in a desired toner image thereon.
The toner remaining on the surface of the photosensitive drum after the transfer to paper is scraped off the surface of the photosensitive drum by a cleaning blade in a cleaning apparatus.
In conventional copying machines, the supplementary toner contained in the toner hopper is the same as that contained in the developing apparatus from the beginning of the copying process. Usually, the toner mentioned above is composed of toner powder and additives adhering to the surface of the toner powder. This toner powder is obtained by mixing the material used, kneading the mixture, grinding the mixture into powder, and sizing the resulting powder to have a desired mean particle size. An alternative manufacturing method involves a chemical process to aggregate and coalesce smaller particles to form toner of the correct final size. As the additives to be used for the toner, there can be mentioned, for example, charge-controlling agents and cleaning agents.
The present disclosure is generally directed to toner and developer compositions, and more specifically, is directed to processes for controlling developer aging characteristics. In embodiments to be described hereinafter, the present disclosure relates to development wires in printing platforms that are sensitive to the state of the developer material. The state of the material can change or age over time. To mitigate the changes to the developer state, bare carrier can be added to the developer housing at a constant rate. This process is known as carrier dispense. Carrier dispense is costly; and therefor it is desirable to reduce the amount of carrier dispensed while maintaining the same level of developer performance.
In addition to the benefits of adding new carrier to developer, it is also known that dispensing small amounts of fresh toner can improve performance after extended runs of low area coverage. The benefit is due to the toner additives on the surface of the fresh toner.
The toner and developer compositions of the present disclosure, in embodiments thereof to be described hereinafter, provides for the current carrier dispense system to be used to transport toner additives directly into the developer housings to maintain developer performance. The additives could be attached to the surface of carrier beads. The toner and developer compositions of the present disclosure can be selected for electrophotographic, especially xerographic imaging and printing processes, including color processes.
To be described in more detail hereinafter, the present disclosure provides for the use of the surface area of carrier beads as a vehicle to transport additives directly into a developer housing using an existing carrier dispense mechanism.
In one aspect of the present disclosure, a process is provided for the preparation of developer compositions comprising: providing a first developer comprised of carrier and toner comprised of resin, pigment, polyolefin, compatibilizer, charge control agent, and metal oxide surface additive, and adding thereto a second developer comprised of carrier, and second compatibilizer, charge control agent, and metal oxide surface additive. The second developer is directly dispensed into a developer housing.
In another aspect of the present disclosure, a process is provided for the preparation of developer compositions comprising: providing a developer comprised of carrier and a first toner comprised of resin, pigment, polyolefin, wax compatibilizer, charge control agent, and metal oxide surface additive, and adding thereto a second developer comprised of carrier, compatibilizer charge control agent, and metal oxide surface additive. The second developer comprises the surface of carrier beads.
Extended runs of low area coverage increase the average time a toner particle spends in a housing. This allows the surface additives to become beaten or worn into the toner surface which ultimately reduces their effectiveness. In printing platforms that use fine wires to develop toner from a donor roll, a problem arises that leads to wire pollution in which small toner flats become highly charged and adhere to wires. This adherence to the wires causes non-uniform and low development. Currently, carrier dispense is used to mitigate this problem. A single reservoir of bare carrier can be used to supply all four developer housings. A steady supply of fresh carrier reduces wire pollution, although the exact mechanism for its effectiveness is unclear.
It is also known that toner additives are effective at reducing wire pollution. Small amounts of fresh toner dispensed into a housing are able to share their additives among the entire sump and rejuvenate a developer state that was susceptible to wire pollution. Additives are extremely small particles and are difficult to dispense in a controlled manner.
One embodiment proposed is to adhere toner additives to the surface of carrier beads and which can then be dispensed into developer housings. The result provides the benefits of the current carrier dispense system as well as providing a way to dispense fresh additives in a controlled manner. The realized benefits include a reduction in the carrier dispense rate while maintaining equivalent image quality and/or as in image quality improvement due to the extra additives dispensed with the current carrier dispense rate.
In one embodiment, additives were coated on the surface of carrier which was then dispensed at a 15% smaller rate than normal. Wire pollution performance was similar, indicating a potential to reduce the carrier dispense rate. The aforementioned method uses the surface of carrier beads as a vehicle to transport toner additives into a developer housing using the existing carrier dispense mechanism.
The amount of carrier dispensed, and the concentration and type of toner additives on the surface of the carrier beads can all be optimized for low run cost and image quality. The current carrier dispense system can be used and the rate of additive addition can be made uniform (i.e. constant rate). A uniform rate of addition can obviate the toner purge events used in systems heretofore cited. Toner purges are artificial events of large toner consumption used in many products. Large amounts of toner are developed to the photoconductor and subsequently end up in waste containers. The result of these toner purges is to reduce the average age of toner in the developer, hence improving its performance. Since many systems also dispense carrier mixed with the incoming toner, the rate of carrier dispensed into the developer also increases during these toner purges. A benefit of the proposed uniform rate of carrier addition is that it enables the total amount of additives to be reduced because of the constant rate of dispensing.
As described above, the surface of carrier beads are used as a vehicle to transport toner additives into a developer housing using an existing carrier dispense mechanism. The vehicle provides for a method to dispense small toner additives in a controlled manner. The vehicle also provides an additive dispense rate that can be more uniform than methods heretofore implemented. This results in achieving net cost reductions and/or image quality improvements by optimizing rates of carrier, toner, and additives.
The aforementioned provides a method of maintaining developer performance by dispensing toner surface additives from the fresh carrier dispense system where the carrier is pre-blended with the toner additives. Wire pollution was measured with carrier blended with toner additives and dispensed at 15% smaller rate than standard. The method results in a reduction in carrier consumption, and improved developer performance.
As mentioned above, the set of electrophotographic toners of this disclosure comprise an initial supply of toner particles and a supplementary supply of carrier beads, both of which comprise additives adhering to the surface of the particles. The weight ratio x of additives to toner particles in the initial supply toner is set to be greater than the weight ratio y of additives to carrier in the supplementary carrier beads. In one exemplary arrangement, the mass ratio of additives to toner in the initial toner supply was 0.062. The mass ratio of additives to carrier for the doped carrier that we dispensed was 0.0053. Thus, the useful ratio of additive mass to carrier mass would have a wide range. Some utility could be gained even for extremely small additive amounts. The maximum value would depend on the carrying capacity of the carrier surface, and would likely be equivalent a few monolayers on a perfectly spherical carrier. Real carriers are rougher than spherical and can hold more additives.
Examples of additives which can be used are charge-controlling agents, cleaning agents, and the like. As a charge-controlling agent, fine powder can be used which is made of at least one material selected from the group consisting of hydrohobic silica, titanium dioxide, aluminum oxide, zinc oxide, magnesium oxide, calcium carbonate, magnesium carbonate, magnesium hydroxide, barium sulphate, calcium sulphate, magnesium sulphate, and metal salts of fatty acids. As a cleaning or lubricating agent, there can be used fine beads made of polystyrene or fine powder made of at least one material selected from the group consisting of polyfluoroethylene, zinc stearate, aluminum stearate, calcium stearate, and zinc laurate. Preferably, the fine bead or fine powder which is used for an additive such as a charge-controlling agent or a cleaning agent has a mean particle size of 2 .mu.m or less.
The toner particles mentioned above can be prepared, for example, from the components: a colorant by which the resulting toner is colored; a resinous binder by which the colorant is fixed on paper; a charge-controlling agent which gives a desired degree of electrification to the resulting toner; and an anti-tack agent which prevents the resulting toner from adhering to fixing rollers.
Examples of resinous binders which can be used are polystyrene, styrene copolymers such as styrene-butadiene copolymers and styrene-acrylate copolymers, polyethylene, ethylene copolymers such as ethylene-vinyl acetate copolymers and ethylene-vinyl alcohol copolymers, phenol resins, epoxy resins, diallyl phthalate resins, polyamide resins, polyester resins, and maleic resins.
Examples of colorants which can be used are carbon black, nigrosines, aniline black, chalco oil blue, chrome yellow, ultramarine yellow, methylene blue, du Pont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green, oxalate, lampblack, rose bengal, and mixtures thereof. The toner powder should contain a sufficient amount of colorant to form a distinct toner image.
Examples of charge-controlling agents which can be used are amino compounds, quaternary ammonium salts such as N-benzy-N,N-dimethyl-N-hexadecylammonium chloride and N-decyl-N,N,N-trimethylammonium chloride, and organic dyes, particularly basic dyes and salts thereof such as nigrosine, nigrosine hydrochloride, safranine, and crystal violet. Among these, nigrosine and nigrosine hydrochloride are sometimes used as a positive-charge controlling agent.
Examples of anti-tack agents which can be used are polypropylene, polyethylene, and paraffin wax. When used individually to prepare the toner, these anti-tack agents are quite useful in providing the improved release of the toner from the fixing rollers.
These and other objects of the present disclosure can be accomplished in embodiments thereof by providing toner compositions comprised of resin particles, and pigment particles, developer compositions thereof, and processes thereof. In embodiments, the present disclosure is directed to a process for the preparation of developer compositions comprising providing a first developer comprised of carrier and toner comprised of resin, pigment, a polyolefin, a polyolefin wax, compatibilizer, charge control agent, and surface additive, and adding thereto a second developer comprised of carrier, compatibilizer, charge control agent, and surface additive, and wherein the surface additive of the second developer is present in a lesser amount than the surface additive of the first toner; a process for the preparation of developer compositions comprising providing a developer comprised of carrier and a first toner comprised of resin, pigment, polyolefins, compatibilizer, charge control agent, and surface additive, and adding thereto a second developer comprised of carrier, compatibilizer, charge control agent, and surface additive, and wherein the additive of the second developer is present, in one exemplary arrangement, in an amount a factor of 10 to 40 weight percent lower than the additive of the first toner; and a process for the preparation of developers comprised of adding to a first developer comprised of carrier with a magnetite core, with a polymeric coating, or a plurality of coatings thereover and a first toner as indicated hereinbefore, to a second developer comprised of carrier beads of magnetite thereover, or a plurality of coatings thereover, wherein the second developer contains a smaller, or lesser amount of surface additive like titanium dioxide than the first toner.
In exemplary embodiments, the surface additive for the first developer can be present in an amount from about 1.0 to about 5.0 weight percent of the toner, and the additive of the second developer can be present in an amount of from about a factor of 10 to 40 weight percent less than the additive of the first toner. Thus, when the additive of the first toner is present in an amount of 6.0 weight percent of the toner, the additive of the second developer can be present in an amount of about 0.15 to 0.60 weight percent of the carrier.
Illustrative examples of suitable toner resins selected for the toner, developer compositions and processes of the present disclosure include thermoplastics such as polyamides, polyolefins, styrene acrylates, styrene methacrylates, styrene butadienes, crosslinked styrenes, polyesters including extruded crosslinked polyesters, epoxies, polyurethanes, vinyl resins, including homopolymers or copolymers of two or more vinyl monomers; and polymeric esterification products of a dicarboxylic acid and a diol comprising a diphenol. Vinyl monomers include styrene, p-chlorostyrene, unsaturated mono-olefins such as ethylene, propylene, butylene, isobutylene and the like; saturated mono-olefins such as vinyl acetate, vinyl propionate, and vinyl butyrate; vinyl esters like esters of monocarboxylic acids including methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, and butyl methacrylate; acrylonitrile, methacrylonitrile, acrylamide; mixtures thereof; and the like. Examples of specific resins include styrene butadiene copolymers with a styrene content of from about 70 to about 95 weight percent; the esterification products of a dicarboxylic acid and a diol comprising a diphenol as illustrated in U.S. Pat. No. 3,590,000, the disclosure of which is totally incorporated herein by reference. Other specific toner resins include styrene/methacrylate copolymers, and styrene/butadiene copolymers; PLIOLITES®; suspension polymerized styrene butadienes, reference U.S. Pat. No. 4,558,108, the disclosure of which is totally incorporated herein by reference; polyester resins obtained from the reaction of bisphenol A and propylene oxide; followed by the reaction of the resulting product with fumaric acid, and branched polyester resins resulting from the reaction of dimethyl terephthalate, 1,3-butanediol, 1,2-propanediol, and pentaerythritol, styrene acrylates, and mixtures thereof. Also, polyolefins with a molecular weight M.sub.w of from about 1,000 to about 10,000, such as polyethylene, polypropylene, and paraffin polyolefins, can be included in, or on the toner compositions as fuser roll release agents.
Numerous well known suitable pigments or dyes can be selected as the colorant for the toner particles including, for example, carbon black, nigrosine dye, aniline blue, magnetite, or mixtures thereof. The pigment should be present in a sufficient amount to render the toner composition highly colored. Generally, the pigment particles are present in amounts of from about 1 percent by weight to about 20 percent by weight, and preferably from about 2 to about 10 weight percent based on the total weight of the toner composition; however, lesser or greater amounts of pigment particles can be selected providing the objectives of the present disclosure are achieved.
The toner surface additive can be a metal oxide such as aluminum oxides, cerium oxides, titanium dioxides, silicon oxides, especially fumed silicas, and the like. Titanium dioxide is preferred and is present in the amounts indicated herein, and wherein the second developer contains a smaller amount of the titanium dioxide than the first toner, for example about a factor of 10 to 40 weight percent (titanium dioxide weight divided by toner weight for the first toner and titanium dioxide weight divided by carrier weight for the second developer) less.
There can also be blended with the toner compositions of the present disclosure external additive particles including flow aid additives, which additives are usually present on the surface thereof. Examples of these additives include fumed silicas such as AEROSIL®, metal salts and metal salts of fatty acids inclusive of zinc stearate, and the like, which additives are generally present in an amount of from about 0.1 percent by weight to about 5 percent by weight, and preferably in an amount of from about 0.1 percent by weight to about 1 percent by weight. Several of the aforementioned additives are illustrated in U.S. Pat. Nos. 3,590,000 and 3,800,588, the disclosures of which are totally incorporated herein by reference.
Also, there can be included in the toner compositions low molecular weight polyolefins, such as polypropylenes, polyethylenes, or mixtures thereof, for example from 10 to 90 and 90 to 10 of the first and second polyolefins, respectively, commercially available from Allied Chemical and Petrolite Corporation, EPOLENE N-15™, commercially available from Eastman Chemical Products, Inc., VISCOL 550-P™, a low weight average molecular weight polypropylene available from Sanyo Kasei K. K., 800P and P200 polyolefins from Mitsui Chemical Corporation, and the like. The commercially available polyethylenes selected have a weight average molecular weight of from about 1,000 to about 1,500, while the commercially available polypropylenes utilized for the toner compositions of the present disclosure are believed to have a weight average molecular weight of from about 4,000 to about 5,000. Many of the polyethylene and polypropylene compositions useful in the present disclosure are illustrated in British Patent No. 1,442,835, the disclosure of which is totally incorporated herein by reference.
Known charge additives can be selected for the toner in effective amounts, such as from about 0.5 to about 3 weight percent, examples of the additives including those as illustrated in the patents mentioned herein, P51, available from Orient Chemicals of Japan, and the like.
For the formulation of developer compositions, there are mixed with the toner particles carrier components, particularly those that are capable of triboelectrically assuming an opposite polarity to that of the toner composition. Accordingly, the carrier particles of the present disclosure can be selected to be of a positive polarity enabling the toner particles, which are negatively charged, to adhere to and surround the carrier particles. Illustrative examples of carrier particles include iron powder, steel, nickel, iron, ferrites, including copper zinc ferrites, magnetites, which are preferred, and the like. Additionally, there can be selected as carrier particles nickel berry carriers as illustrated in U.S. Pat. No. 3,847,604, the disclosure of which is totally incorporated herein by reference. The selected carrier particles can be used with or without a coating, the coating generally containing terpolymers of styrene, methylmethacrylate, and a silane, such as triethoxy silane, reference U.S. Pat. Nos. 3,526,533 and 3,467,634, the disclosures of which are totally incorporated herein by reference; polymethyl methacrylates; other known coatings; and the like. The carrier particles may also include in the coating, which coating can be present in one embodiment in an amount of from about 0.1 to about 3 weight percent, conductive substances such as carbon black in an amount of from about 5 to about 30 percent by weight. Polymer coatings not in close proximity in the triboelectric series can also be selected, reference U.S. Pat. Nos. 4,935,326 and 4,937,166, the disclosures of which are totally incorporated herein by reference, including, for example, KYNAR® and polymethylmethacrylate mixtures. Coating weights can vary as indicated herein; generally, however, from about 0.3 to about 2 and preferably from about 0.5 to about 1.5 weight percent coating weight is selected. Carrier coatings with a conductive component, such as carbon black, in an amount of from about 20 to about 40 percent can also be selected.
Furthermore, the diameter of the carrier particles, preferably approximately spherical in shape, is generally from about 3 microns to about 300 and preferably from about 20 to about 90 microns thereby permitting them to possess sufficient density and inertia to avoid adherence to the electrostatic images during the development process. The carrier component can be mixed with the toner composition in various suitable combinations, such as about 1 to 10 parts per toner to about 100 parts to about 200 parts by weight of carrier.
The toner and developer compositions of the present disclosure may be selected for use in electrostatographic imaging apparatuses containing therein conventional photoreceptors providing that they are capable of being charged negatively. Thus, the toner and developer compositions of the present disclosure can be used with layered photoreceptors that are capable of being charged negatively, such as those described in U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference. Illustrative examples of inorganic photoreceptors that may be selected for imaging and printing processes include selenium; selenium alloys, such as selenium arsenic, selenium tellurium and the like; halogen doped selenium substances; and halogen doped selenium alloys.
Other modifications of the present disclosure may occur to those skilled in the art subsequent to a review of the present application, and these modifications, including equivalents thereof, are intended to be included within the scope of the present disclosure.
It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
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