Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/10—Developers with toner particles characterised by carrier particles
  • G03G9/113—Developers with toner particles characterised by carrier particles having coatings applied thereto
  • G03G9/1132—Macromolecular components of coatings
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/10—Developers with toner particles characterised by carrier particles
  • G03G9/113—Developers with toner particles characterised by carrier particles having coatings applied thereto
  • G03G9/1131—Coating methods; Structure of coatings

Definitions

• the present invention relates to a carrier for electrostatic image development, used in electrophotography, electrostatic recording and electrostatic printing.
• a toner image is formed by applying uniform electrostatic charges to a latent image supporting member, i.e., a photosensitive member, having a photosensitive laver comprising a photoconductive material, followed by imagewise exposure to form an electrostatic latent image on the surface of the photosensitive member, and developing the electrostatic latent image with a developer.
• the toner image thus formed is transferred to a transferring medium such as paper, and fixed thereon by heating or application of pressure to form a copy image.
• CMOS images referred as methods of developing the electrostatic latent image are wet developing and dry developing.
• developers used in the latter dry developing are, in general, a one-component developer comprised of only a magnetic toner which comprises a toner containing a magnetic material, and a two-component developer comprised of a non-magnetic toner containing no magnetic material and a carrier having magnetic properties.
• the latter two-component developer in which the toner and carrier are mechanically agitated so that the toner may be frictionally charged, enables considerably easy control of the charging polarity and amount of electrostatic charging of the toner by the selection of properties of the carrier and conditions for the agitating. It also allows a wide range for the selection of the colors that can be imparted to the toner. Thus, in view of these, the latter developer is more advantageous than the former one-component developer.
• a coated carrier comprising magnetic particles whose surfaces are coated with a resin has been used with appreciation because of the possibility of improving the durability of carriers, frictional electrostatic charging performance and so forth.
• a coated carrier Most widely used as such a coated carrier is a spray-­coated carrier obtained by spray-coating in a fluidized bed the surfaces of magnetic particles with a coating solution prepared by dissolving a coating resin in a solvent, followed by drying.
• the carrier particles may be mutually fused because of the solvent used, so that the carrier may have a large diameter, resulting in a great decrease in the yield of the carrier having the desired particle size distribution. It also requires a drying step, and also requires a reasonably long period of time for the manufacture of the carrier, bringing about the problem of a low productivity. The productivity may be further lowered with an increase in the coverage with resin and a decrease in the diameter of magnetic particles. To cope with this problem, the following countermeasures may be taken as a means for improving the productivity as a result of the shortening of time:
• the coating solution when adhered to the particles of the magnetic material, may not smoothly spread because of its high viscosity, only providing an uneven coating, resulting in a lowering of the durability of carrier.
• the particles of the magnetic material may also readily adhere and fuse to each other once they have come into contact, resulting in a great decrease in the yield of the carrier.
• the spray coating takes a long time for the coating, and requires the recovery and thermal disposal of the solvent, making the manufacture uneasy.
• Another problem is that fine holes are produced on the surface of the carrier when the solvent is evaporated, resulting in non-uniformity on the surface of the carrier.
• the fusion also tends to take place to make it difficult to obtain a carrier with the particle size fitted to the purpose, also resulting in a poor yield.
• Still another problem is that part of starting materials scattered as a result of spraying does not participate in the formation of a layer, so that the starting materials are wasted and the materials which are nor coated electrostatically adhere in the form of powder to the surface of the carrier to give ill influences in carrying out the developing.
• the coating disclosed in these publications comprises mixing a carrier core material and polymer fine particles by a mechanical means to electrostatically interlockingly cover the surface of the carrier core material with the polymer fine particles to form a covering, and thereafter fixing said polymer fine particles by melting them by heat or dissolving them using a solvent, thereby covering the surface of the carrier core material with a resin layer.
• the resin interlockingly covering the core material is melted in fixing the polymer fine particles, so that the resin particles may adhere to each other or core particles may adhere and fuse to each other through the resin particles, bringing about the problem that the yield to obtain a carrier with the desired particle size distribution is lowered.
• Another problem is that it takes much time for a cooling step since the surface of the core material is covered with the resin layer at temperatures close to the melting point or not lower than the melting point, and a disintegrating step is further required to loosen blocked coated carrier particles to separate them into unblocked carrier particles, resulting in a serious lowering of the production efficiency.
• the carrier Since the resulting carrier is coated with the resin in part, there is still another problem that the carrier has a poor electrostatic charging stability at a high temperature and high humidity compared with a carrier entirely coated with a resin.
• the resin may undergo a change in properties because the core material is covered with the resin layer at temperatures close to, or not lower than, the melting point of the resin, and hence an inert atmosphere that may not cause the change in properties must be provided, making production apparatus very complicated.
• a first object of the present invention is to provide a carrier for electrostatic image development, that enables selection in a wide range, of the resin constituting the resin coating, and also enables firm fixing of the resin coating, may cause film peeling with difficulty, and is durable, having stable properties of imparting electrostatic charge.
• a second object of the present invention is to provide a method of preparing a carrier for electrostatic image development, that does not require any treatment for the recovery of solvents, can prepare the carrier through a simple means in a short time, and yet may cause fusion or fine holes with difficulty and can obtain in a high yield a carrier having the desired particle size distribution.
• a third object of the present invention is to provide a carrier for electrostatic image development, that may generate less out-of-coating matters which do not contribute the coating, and hence can prevent difficulties caused by adhesion of the out-of-coating matters on the carrier surface as a result of their liberation.
• a fourth object of the present invention is to provide a method of preparing a carrier for electrostatic image development, that requires no disintegrating step, and can prepare the carrier through a simple means in a short time and yet in a high yield.
• a fifth object of the present invention is to provide a carrier for electrostatic image development, that can achieve a stable electrostatic charging performance even at a high temperature and high humidity, and is free from environment dependence.
• a method of preparing a carrier for electrostatic image development comprising forming a uniform mixture comprised of magnetic material particles having a weight mean particle diameter of from 10 to 200 ⁇ m and resin particles having a weight mean particle diameter of less than 1/200 of that of said magnetic material particles, and repeatedly applying an impact force to said mixture in a mixing vessel having a material temperature set within the range of from 50 to 110°C, thereby coating said magnetic material particles with the resin material of said resin particles, and a carrier for electrostatic image development, prepared according to said method.
• said magnetic material particles may preferably have a circularity of not less than 0.7.
• the resin particles may also preferably have a BET specific surface area within the range of from 40 m2/g to 6,000 m2/g.
• the carrier for electrostatic image development can be prepared through a simple means in a short time and yet in a high yield, and has a superior durability, exhibiting a stable frictional electrostatic charging performance.
• the carrier can be obtained according to dry coating, using the magnetic material particles and resin particles both having a specific particle diameter, so that;
• magnetic material particles having a weight mean particle diameter of from 10 to 200 ⁇ m and a circularity of not less than 0.7, and resin particles having a weight mean particle diameter within the range of from 1/2,000 to 1/200 of that of said magnetic material particles and a BET specific surface area within the range of from 40 m2/g to 6,000 m2g are mixed and stirred to be brought into a uniformly mixed state, and an impact force is repeatedly applied to the resulting mixture.
• the resin particles are spread and adhered on the surfaces of the magnetic material particles.
• a coated carrier can be thus prepared.
• the resin particles may be used in an amount of from 0.1 to 10 parts by weight, and preferably from 0.5 to 4 parts by weight, based on 100 parts by weight of the magnetic material particles.
• the impact force applied to the mixture comprising the magnetic material particles and resin particles may be satisfactory if it is of the strength to the extent that the magnetic material particles are not crushed to powders.
• a size less than the lower limit results in an excessively small diameter of the resulting coated carrier, tending to cause adhesion of the carrier on a photosensitive member, resulting in a deterioration of image quality.
• the magnetic material particles As materials for the magnetic material particles, it is preferred to use substances capable of being strongly magnetized in the corresponding direction as a result of application of a magnetic field, as exemplified by metals such as iron, nickel and cobalt that show ferromagnetism, including iron, ferrites and magnetites, or alloys or compounds containing any of these metals.
• metals such as iron, nickel and cobalt that show ferromagnetism, including iron, ferrites and magnetites, or alloys or compounds containing any of these metals.
• the ferrites herein generically refer to magnetic oxides containing iron, including a ferrite represented by the chemical formula: MO ⁇ Fe2O3.
• M represents a divalent metal, and specifically represents nickel, copper, zinc, manganese, magnesium, lithium, or the like.
• the magnetic material particles may preferably have a circularity of not less than 0.7. Use of the magnetic material particles having such a high circularity brings about a high circularity also in the resulting coated carrier to increase the fluidity of the carrier. As a result, it becomes possible to steadily convey an appropriate quantity of toner to the developing space, so that a much superior development performance can be exhibited.
• This circularity can be measured, for example, with an image analyzer (a manufacture of Nippon Abionics Co.).
• the weight mean particle diameter of the resin particles may be within the range of from 1/20,000 to 1/200, and preferably from 1/2,000 to 1/400, relative to that of the magnetic material particles. From a practical viewpoint, however, used are resin particles having a weight mean particle diameter of from 0.001 to 1 ⁇ m, and preferably from 0.01 to 0.15 ⁇ m, and a BET specific surface area of from 40 m2/g to 6,000 m2/g. A weight mean particle diameter more than 1.0 ⁇ m or a BET specific surface area of less than 40 m2/g, of the resin particles makes the resin particles spread with difficulty on the surface of the magnetic material particles, resulting in a difficulty in the coating treatment under dry conditions. A weight mean particle diameter less than 0.01 ⁇ m or a BET specific surface area more than 6,000 m2/g may worsen the dispersibility, sometimes making it impossible to achieve uniform coating, also sometimes resulting in a lowering of the yield.
• the materials for the resin particles there are no particular limitations on the materials for the resin particles, and various resins can be used. Namely, in the present invention, the dry coating of a non-­solvent type can be employed and resins slightly soluble to solvents can also be used, so that the resins can be selected in a reasonably wide range. To describe specifically, it is possible to use resins as exemplified by styrene resins, acrylic resins, styrene-acrylic resins, vinyl resins, ethylene resins, rosin modified resins, polyamide resins, polyester resins, silicone resins, and fluorine resins. These resins may be used in combination.
• styrene-acrylic resins and acrylic resins can be particularly preferably used.
• This styrene-acrylic resins are resins obtained by copolymerization of styrene monomers with acrylic monomers.
• Specific examples of the styrene monomers may include, for example, styrene, o-­methylstyrene, m-methylstyrene, p-methylstyrene, ⁇ -­methylstyrene, p-ethylstyrene, 2,4-dimethystyrene, p-­butylstyrene, p-t-butylstyrene, p-hexylstyrene, p-­octylstyrene, p-nonylstyrene, p-decylstyrene, p-­dodecylstyrene, p
• acrylic monomers may include, for example, acrylic acids or esters thereof such as acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate, propyl acrylate, octyl acrylate, dodecyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, and methyl ⁇ -chloroacrylate; methacrylic acids or esters thereof such as methacrylic acid, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, isobutyl methacrylate, octyl methacrylate, dodecyl methacrylate, lauryl methacrylate, 2-­ethylhexyl methacrylate, stearyl methacrylate,
• the styrene monomers and acrylic monomers may preferably be in a compositional ratio of from 9:1 to 1:9 in weight ratio.
• the styrene component can afford to harden coating films and the acrylic component can afford to toughen coating films.
• the amount of the electrostatic charging attributable to the toner in the frictional electrostatic charging between the coated carrier and toner can also be controlled to a considerable extent by appropriately varying the compositional ratio of these components.
• the carrier may preferably have a weight mean particle diameter within an appropriate range corresponding with that of the magnetic material particles. That is to say, an excessively small weight mean particle diameter of the carrier tends to cause adhesion of the carrier on the photosensitive member, resulting in a deterioration of image quality. On the other hand, an excessively large weight mean particle diameter thereof results in a small specific surface area, so that it becomes difficult to achieve appropriate frictional electrostatic charging of the toner. It also becomes difficult for the carrier to be supported on the developer supporting member in a uniform state and also in a high density, resulting in a poor development performance.
• the carrier it is preferable for the carrier to have a narrow particle size distribution.
• the weight mean particle diameter ( r w) of the magnetic material particles is a value measured using "Microtruck, Type 7981-OX", manufactured by Lees & Northrup Co.; and the weight mean particle diameter ( r w) of the resin particles, measured using "Coulter, Model N4 Series", manufactured by Coulter Electronics Co.
• the carrier for electrostatic image development according to the present invention can be prepared, for example, by the following procedure:
• the magnetic material particles having a weight mean particle diameter of from 10 to 200 ⁇ m, and resin particles having a weight mean particle diameter of less than 1/200 of that of said magnetic material particles and a BET specific surface area within the range of not less than 40 m2/g are mixed and stirred using, for example, an ordinary stirring apparatus until they are uniformly mixed.
• the resulting mixture is poured into, for example a high speed stirring mixing vessel or the like set to have a material temperature within the range of from 50 to 110°C, and an impact force is repeatedly applied to the above mixture for 10 to 60 minutes, and preferably 15 to 30 minutes.
• the resin particles are spread and adhered on the surfaces of the magnetic material particles.
• a coated carrier can be thus obtained.
• an excessively high material temperature may make higher the adhesion of the resin particles, so that a phenomenon may be caused in which the particles of the resin particle powder are agglomerated each other into a mass and also the magnetic material particles may be combined through the resin particles to cause fusion. This makes it difficult to uniformly adhere the resin particles to the surfaces of the magnetic material particles.
• polyester resin 100 parts of polyester resin, 10 parts of carbon black and 3 parts of a low molecular weight polypropylene were mixed, followed by kneading, pulverization and classification to obtain a toner with an average particle diameter of 11 ⁇ m.
• a carrier prepared in each Example and Comparative Example and the above toner particles were mixed so that the content of the toner particles may become appropriate corresponding with the particle diameter of the following each carrier. Electrostatic latent image developers were thus prepared.
• Example 1 Cu-Zn-based ferrite carrier (weight mean particle diameter r w: 80 ⁇ m) 5,000 parts Methyl methacrylate/butyl methacrylate copolymer (weight compositional ratio: 8/2; r w: 0.06 ⁇ m) 100 parts
• the above materials were mixed for 15 minutes using a high speed stirring mixing vessel to prepare an ordered mixture. Thereafter, hot water was circulated in the above mixing vessel, the material temperature was set to 70°C, and the main stirring blade was rotated to carry out coating for 15 minutes. A coated carrier was thus obtained.
• Example 1 was repeated under the same conditions to obtain coated carriers, except that the conditions as picked out and set out below were changed.
• Example 2 Cu-Zn-based ferrite carrier ( r w: 100 ⁇ m) 5,000 parts MMA/BMA (8/2)* ( r w: 0.06 ⁇ m) 75 parts * methyl methacrylate/butyl methacrylate (8/2) copolymer
• Example 3 Iron powder carrier ( r w: 100 ⁇ m) 5,000 parts MMA/BMA (8/2) ( r w: 0.06 ⁇ m) 60 parts
• Example 4 Mg-Cu-Zn-based ferrite carrier ( r w: 45 ⁇ m) 5,000 parts MMA/BMA (8/2) ( r w: 0.06 ⁇ m) 125 parts
• Example 5 Cu-Zn-based ferrite carrier ( r w: 80 ⁇ m) 5,000 parts MMA/BMA (8/2) ( r w: 0.10 ⁇ m) 100 parts
• Example 6 Mg
• Example 2 The same composition as Example 1. Temperature was raised to 120°C. Comparative Example 3 Mg-Cu-Zn-based ferrite carrier ( r w: 44 ⁇ m) 5,000 parts MMA resin ( r w: 0.4 ⁇ m) 150 parts Comparative Example 4 Cu-Zn-based ferrite carrier ( r w: 80 ⁇ m) 5,000 parts MMA/BMA resin (8/2) ( r w: 0.6 ⁇ m) 100 parts
• Example 1 was repeated but the material temperature was controlled to be 45°C.
• the distance between the drum and sleeve and the distance between the doctor blade and sleeve were set to appropriate conditions depending on the particle diameter of each carrier.
• the carrier is free from environment dependence, possessing a uniform and tough coating, so that a stable performance can be obtained under conditions including a high temperature and high humidity and a low temperature and low humidity.
• the coated carrier can also be prepared in a short time. Even when the coverage is changed, only the mixing ratio may be changed, where the coating time is not prolonged.

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• General Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Developing Agents For Electrophotography (AREA)

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• 1988
  • 1988-09-22 JP JP63239180A patent/JP2709943B2/ja not_active Expired - Lifetime
• 1989
  • 1989-09-13 DE DE68919313T patent/DE68919313T2/de not_active Expired - Lifetime
  • 1989-09-13 EP EP19890116985 patent/EP0360146B1/fr not_active Expired - Lifetime

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