EP0257364B1 - Procédé pour développer des images latentes électrostatiques - Google Patents

Procédé pour développer des images latentes électrostatiques Download PDF

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Publication number
EP0257364B1
EP0257364B1 EP19870111197 EP87111197A EP0257364B1 EP 0257364 B1 EP0257364 B1 EP 0257364B1 EP 19870111197 EP19870111197 EP 19870111197 EP 87111197 A EP87111197 A EP 87111197A EP 0257364 B1 EP0257364 B1 EP 0257364B1
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EP
European Patent Office
Prior art keywords
resin
toner
developing
carrier
developer
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
EP19870111197
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German (de)
English (en)
Other versions
EP0257364B2 (fr
EP0257364A1 (fr
Inventor
Tadashi Konishiroku Photo Ind. Co. Ltd. Kaneko
Yuki Konishiroku Photo Ind. Co. Ltd. Okuyama
Mitsutaka Konishiroku Photo Ind. Co. Ltd. Arai
Yoko Konishiroku Photo Ind. Co. Ltd. Yamamoto
Satoru Konishiroku Photo Ind. Co. Ltd. Ikeuchi
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Konica Minolta Inc
Original Assignee
Konica Minolta Inc
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Priority claimed from JP61183423A external-priority patent/JPS6340171A/ja
Priority claimed from JP61183422A external-priority patent/JPS6340170A/ja
Application filed by Konica Minolta Inc filed Critical Konica Minolta Inc
Publication of EP0257364A1 publication Critical patent/EP0257364A1/fr
Publication of EP0257364B1 publication Critical patent/EP0257364B1/fr
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G13/00—Electrographic processes using a charge pattern
    • G03G13/06—Developing
    • G03G13/08—Developing using a solid developer, e.g. powder developer
    • G03G13/09—Developing using a solid developer, e.g. powder developer using magnetic brush
    • 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
    • G03G9/1133—Macromolecular components of coatings obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • G03G9/1134—Macromolecular components of coatings obtained by reactions only involving carbon-to-carbon unsaturated bonds containing fluorine atoms
    • 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
    • G03G9/1135—Macromolecular components of coatings obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
    • G03G9/1136—Macromolecular components of coatings obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds containing silicon atoms

Definitions

  • This invention relates to a developing method for electrostatic latent images and, more particularly, to a developing method for electrostatic latent images formed on a latent image carrying member in electrophotography, electrostatic recording, electrostatic printing and the like by making use of a two-component type developer.
  • the methods for forming a visible image from an image information the methods such as electrophotography, electrostatic recording and electroprinting are widely utilized, in which visible images are formed through electrostatic latent images.
  • developer used for developing the above-mentioned electrostatic latent images: one is the so-called two-component type developer comprising toners and carriers in the form of mixture (EP-A-0 160 503) and the other is a single component type developer comprising magnetic toners containing magnetic substances, which is used independently without mixing with carriers.
  • toners are frictionally charged by mechanically stirring the toners and carriers.
  • the above-mentioned non-contact developing system is a system in which a developer layer comprising toners and carriers, which is carried on a developer transport/carrying member, is fed into a developing area so as not to bring the developer layer into direct contact with the latent image carrying member.
  • the electrostatic and physical bonding strength of the carriers to a developer transport/carrying member is weakened and, similarly, the electrostatic and physical bonding strength of the carriers to the toner is also weakened.
  • the carriers are usually transported by magnetic force being adhered to the surface of the developer transport/carrying member, in the case of using small-sized carriers, the adhesion force of the carriers to the developer transport/carrying member is weak.
  • the carriers or toners will fly about in an apparatus to contaminate the inside thereof, and the toners or carriers will adhere to the non-image areas of the latent image carrying member to produce fog; and, further, the carriers will adhere to the latent image carrying member to make an image unclear.
  • a minimum gap that is a development gap, between a latent image carrying member and a developer transport/carrying member in a developing area.
  • the developability may be improved by generating a relatively greater oscillatory electric field in a development area as well as by making a development gap larger though, in the case of generating such a greater oscillatory electric field as the development gap is made wider, there is such a problem that toners will adhere increasingly to the non-image portions of a latent image carrying member to produce fog and carriers will increasingly fly about to contaminate the inside of an apparatus. Further, it is necessary to electrically insulate a developing unit satisfactorily from and the designing of the units is considerably complicated, because of the generation of the greater oscillatory electric field.
  • This invention is based on the circumstances mentioned above.
  • an object of the invention to provide a developing method in which no contamination is caused inside an apparatus by both toners and carriers flying about, no fog is produced, an excellent development can be performed with a two-component type developer comprising the toner and carriers and, resultingly, a sharp image can be formed so as to be excellent in both resolving power and gradation reproduction.
  • Another object of the invention is to provide a developing method capable of forming a sharp image without having any uneven imaging and imaging failure.
  • a further object of the invention is to provide a developing method in which a thin developer layer can stably be formed on a developer transport/carrying member even in repeating development processes many times and, resultingly, excellent images can stably be formed, extending over a long period of time.
  • the developing method of the invention is a developing method in which a two-component type developer layer comprising toner particles and magnetic carrier particles is formed on a developer transport member and the resulted developer layer is fed into a developing area where an oscillatory electric field is generated so as to develop an electrostatic latent image on a latent image carrying member.
  • the particular characteristic in that the developer layer formed on the developer transport member has a thickness of not more than 1000 /1.m and using resin coated carrier particles comprising the particles of magnetic substances coated with the resin containing silicone resin or fluoro resin in an amount of at least 30% by weight or more, for serving as the above-mentioned carriers.
  • the carrier surfaces are smoothed out, because the carriers forming two-component type developer are the resin-coated carriers comprising magnetic particles coated with a resin containing a silicone resin having a low surface energy as its property.
  • the so-called toner "filming phenomenon” will occur, that is a phenomenon that toner substances adhere to carrier surfaces to hinder the frictional chargeability of the carriers, in a frictional charge between toners and carriers. Therefore, the toners may be endowed stably with a frictional charge having proper polarity and charged volume.
  • the carriers forming a two-component type developer are resin-coated carriers comprising magnetic particles coated with resins containing fluororesins in an amount of not less than a specific proportion
  • the carrier surfaces are smoothed out, because a fluororesin is low in critical surface tension as its property.
  • toner filming phenomenon that is a phenomenon that toner substances including, for example, coloring agents such as Carbon Black and so forth, surface releasing agents, etc., adhere to carrier surfaces to hinder the frictional chargeability of the carriers, in a frictional charge between toners and carriers. Therefore, the toners may be endowed stably with a frictionally charge having proper polarity and charged amount.
  • the order of frictional chargeability of a fluororesin is the most negative among resins and, accordingly, the carriers coated with resins containing the fluororesin are also excellent in negative chargeability. Therefore, in the toners used with the carriers in combination, it is not particularly required to use any charge controller or fine grained additive such as dyes so as to provide the toners with a positive chargeability. Resultingly, the troubles caused when using the charge controllers and the like may be prevented. Besides, the frictional chargeability of toners may be controlled to a considerable degree by selecting a fluororesin content in the resins for coating carriers. It is, therefore, possible to prepare developers suitable for the developing method of the invention.
  • Satisfactory fluidity of developers may be obtained even when the carriers are made fine in size, because carrier surfaces are smoothed as mentioned above. Resultingly, a uniform and thin developer layer may be formed on a developer transport/carrying member. Further, the adhesion property of toners to a latent image formed on a latent image carrying member becomes excellent, because the thin developer layer is processed in a developing area where the above-mentioned oscillatory electric field is generated while applying the function of the oscillatory electric field. Resultingly, excellent images may be formed without any uneven imaging and imaging failure.
  • the surface releasing property of the carriers becomes excellent, because the carrier surface is smoothed.
  • a thin developer layer is formed, for example, by bringing a thin layer forming member such as a blade into pressure contact elastically with a developer transport/carrying member, it is possible to prevent carriers from adhering to the thin layer forming member so as to prevent the thickness regulating function of the thin layer forming member from being interfered by the carrier adhesion.
  • the developer transport member receives a strong pressure by the thin layer forming member, it is possible to prevent carriers from adhering physically and strongly to toners. Therefore, a thin developer layer may stably be formed on the developer transport member.
  • the toner filming phenomenon in which toner substances adhere to carriers may be prevented and an excellent frictional chargeability between toners and carriers may stably be displayed.
  • sharp images may be formed many times in repetition without any contamination caused in an apparatus by toner and carrier flying.
  • a developer layer having a two-component type developer comprising toners and carriers is formed on a developer transport/carrying member.
  • the developer layer is supplied to a developing area where an oscillatory electric field is generated and an electrostatic latent image on a latent image carrying member is developed.
  • the developer layer formed on the developer transport/carrying member is thin and a resin-coated carrier comprising magnetic particles coated with a resin containing a silicone resin is used for the carriers.
  • a developer layer on a developer transport/carrying member is thin.
  • the thickness of the thin layer is preferably not more than 1,000 /1.m and particularly from 10 to 500 /1.m.
  • a development process is carried out in such a manner that a developer layer, which is considerably thin as mentioned above, is transported into a developing area where an oscillatory electric field is generated so as to bring the developer layer into contact or, preferably, non-contact with a latent image carrying member and the oscillatory electric field is applied to the developer layer.
  • a minimum gap between the latent image carrying member and the developer transport/carrying member (hereinafter called a "development gap”) is desired to be as narrow as possible, provided that the developer layer may be transported into the developing area so that the developer layer may not come into contact with the latent image carrying member.
  • the development gap is preferably selected from the range of gap of from 100 to 1,000 /1.m, for example.
  • a developing area means an area to which toners transported by a developer transport/carrying member may be able to transfer when an electrostatic latent image on a latent image carrying member receives an electrostatic force.
  • a development gap means a closest space between a latent image carrying member and a developer transport/carrying member in the above-defined developing area.
  • the carriers used in the invention are resin-coated carriers comprising magnetic particles coated with a resin containing a silicone resin or a fluoro resin in an amount of more than 30% by weight.
  • the thickness of the coated layer is preferably from 0.1 to 10 ⁇ m on average, more preferably from 0.3 to 4 /1.m and particularly from 0.3 to 2 /1 .m.
  • the resin may be comprised of either only a silicone resin or both of the silicone resin and a highly compatible resin used in combination for further improving the properties of the silicone resin.
  • the developer transport/carrying members for transporting a thin developer layer to a developing area.
  • the developer transport/carrying members having the same construction as in the conventional types which are capable of applying a bias voltage, may also be used.
  • a developer layer carried on the surface of the developing sleeve is transported in undulations like waves by the rotation of the magnetic roll.
  • a developer layer formed on a developer transport/carrying member is thinned.
  • the non-contact and contact development systems may be used either.
  • the non-contact development system is preferably used.
  • the reasons are that a development gap may satisfactorily be narrowed, because a developer layer formed on a developer transport/carrying member is thinned as mentioned before so as to lower a bias voltage required for generating an oscillatory electric field by which toners are properly flown from the developer transport/carrying member to the latent image carrying member in a non-contact developing area, and that there are also the advantages of reducing undesirable toner flying about and preventing the bias voltage from leaking out of the developing sleeve surface, because a satisfactory oscillatory electric field may be generated by the relatively low bias voltage.
  • toners are present in a proportion of the order of at least 0.04 mg/cm 2 in a developer layer carried on a developing sleeve.
  • V s (mm/s) represents a linear velocity of a developing sleeve
  • V d (mm/s) represents a linear velocity of a latent image carrying member
  • m t (mg/cm 2 ) represents an amount of toners per unit area of a developer layer carried on the developing sleeve:
  • a ratio of A/B is from 0.5 to 2.
  • the toners contained in a developer layer carried on a developing sleeve may be made to efficiently adhere to an electrostatic latent image formed on a latent image carrying member and a stable development may be made and, resultingly, it is possible to reproduce images having extraordinarily excellent image qualities.
  • the means for forming such a thin developing layer as mentioned before on a developing sleeve there is no special limitation to the means for forming such a thin developing layer as mentioned before on a developing sleeve, and means having a variety of constitutions may be used.
  • the examples thereof include a means in which the thickness of a developer layer are regulated by bringing a thin layer forming member such as a blade into pressure contact elastically with the surface of a developing sleeve and, preferably, a means in which the thicknesses of a developer layer are regulated by arranging a regulating plate made of a magnetic substance and a developing sleeve so as to keep a specific gap between them, that is, for example, a means in which the thicknesses of a developer layer are regulated by arranging a magnetic bar close to a developing sleeve and then by generating a rotating magnetic field on the magnetic bar, or other means having been well-known.
  • a thin layer forming member having a pressure plate brought into pressure contact lightly and elastically with a developing sleeve.
  • the edge of the elastic pressure plate is brought into the developing sleeve toward the upper stream side of the rotation of the developing sleeve.
  • Fig. 4 is a diagram illustrating the relation of a gap between the edge of an elastic pressure plate and a developing sleeve (The gap sizes are in proportion to aperture areas) to a quantity per unit area of a developer carried on the developing sleeve, in the case of using the above-mentioned elastic pressure plate.
  • a quantity per unit area of a developer carried on a developing sleeve shows a stable value regardless of the sizes of a gap, when the gap between the edge of an elastic plate and the developing sleeve exceeds a specific size.
  • toners sufficient for developing an electrostatic latent image may be transported into a developing area.
  • a gap between the edge of the elastic plate and the developing sleeve that is, a gap of not wider than 5 mm. If exceeding 5 mm, there is some fear of making the thickness of a developing layer uneven.
  • Fig. 1 is an illustration showing an example of a developing unit suitable for performing the developing method of the invention.
  • reference numeral 20 is a latent image carrying member of, for example, a rotary drum type; 2 is a housing; 3 is a developing sleeve; 4 is a magnetic roll having a magnetic polarity of eight-pole type in total arranged N and S poles alternately around the circumference of the roll; and a developer transport/carrying member is comprised of the developing sleeve 3 and the magnetic roll 4.
  • 5 is a thin layer forming member
  • 6 is a member for fixing thin layer forming member 5
  • 7 is a primary stirring member
  • 8 is a secondary stirring member
  • 9 and 10 are the shaft for rotating the above-mentioned stirring members 7 and 8, respectively
  • 11 is a vessel of replenishing toners
  • 12 is a roller of replenishing toners
  • 13 is a developer reservoir
  • 14 is a bias power source
  • 15 is a developing area
  • T is a toner
  • D is a developer.
  • developer D is well stirred and mixed up in developer reservoir 13 by both of primary stirring member 7 rotating in the direction of the arrow and secondary stirring member 8 rotating in the direction opposite to the rotation of primary stirring member 7 so as to overlap the stirring areas of the both stirring members without colliding against each other and the developer D is then made to adhere to the surface of developing sleeve 3 by the transportation force produced by both of developing sleeve 3 rotating in the direction of the arrow and magnetic roll 4 rotating in the direction opposite to the rotation of the developing sleeve 3.
  • Plate-like thin layer forming member 5 comprising an elastic material brings one side of the plate close to the edge into pressure contact with the surface of developing sleeve 3.
  • This thin layer forming member 5 is held by fixing member 6 extended from housing 2.
  • fixing member 6 extended from housing 2.
  • the developer layer thinned in this manner is transported into developing area 15 as the layer is facing to an electrostatic latent image formed on latent image carrying member 20 rotating in the direction of the arrow, preferably through a narrow gap, so to say, so as not to come into contact with each other.
  • developing area 15 while the thin developer layer is being subjected to the oscillatory electric field generated by bias power source 14 containing a.c. components, only the toners held in the developer layer selectively and statically adhere to the electrostatic latent image, so that a toner image is formed.
  • a thickness of a developer layer may be measured in the following manner, for example.
  • a "Nikon Profile Projector” manufactured by Nippon Kogaku Co.
  • the position of the image of a developing sleeve projected on a screen and the position of the image of a thin developer layer formed on the developing sleeve projected on the screen are compared with each other to obtain the thickness of the developer layer.
  • Thin layer forming member 5 may be made of, for example, a magnetic or non-magnetic metal, a metal compound, a plastic, rubber and so forth. This member 5 is endowed with elasticity by fixing one end of the member 5 with fixing member 6. It is preferable that the thickness of this member 5 is very thin and uniform in thickness, that is from 50 to 500 /1.m.
  • An amount of carrier transported is regulated in such a manner that the above-mentioned thin layer forming member 5 brings one side close to the edge thereof into contact elastically with developing sleeve 3 and, preferably, the carriers may be passed one after another through the contact position of the thin layer forming member 5 with developing sleeve 3.
  • the impurities remaining in developer D, aggregates of carriers or toners and so forth are prevented from stealing into developing area 15 by the thin layer forming member 5. Therefore, every developer layer transported into developing area 15 becomes thin, uniform and stable in thickness.
  • the developing method of the invention uses a resin-coated carrier which is coated with a resin containing a silicone resin or a resin containing a fluororesin in a specific proportion or more. Therefore, the surface of the carrier is excellently smoothed even if the carrier is small-sized, because of the coated layer. The fluidity of the carrier is thereby improved. Accordingly, the thickness regulating function of the thin layer forming member 5 is satisfactorily displayed and, resultingly, every developer layer transported into developing area 15 may be satisfactorily uniformed and thinned in thickness. Further, the surface lubricity of the carrier is also excellent because of the coated layer. Therefore, the so-called filming phenomenon, that is, an adhesion of toner substances to carriers, may be prevented, even if the developer layer is applied with a strong pressure by thin layer forming member 5.
  • An amount of developer transported into developing area 15 may satisfactorily be controlled by changing the pressure and contact angles applied from thin layer forming member 5 to developing sleeve 3.
  • toners and carriers forming a developer it is generally advantageous that they are small-sized, because an image obtainable is high in resolving power and excellent in gradation reproduction.
  • a two-component type developer comprising toners having a weight average particle size of not larger than 5 /1.m and carriers having a weight average particle size of not larger than 50 /1.m and further not larger than 30 ⁇ m, any impurities, particle aggregates and so forth may automatically be removed from the developer so as to form a uniformed and thinned developer layer.
  • any impurities may be prohibited from stealing into the resulting developer layer by thin layer forming member 5 similar to the above-mentioned example, so that a uniformed and thinned developed layer may be formed.
  • a carrier having a weight average particle size of the order of from 50 to 100 /1.m it is advantageous to use a carrier having a weight average particle size of the order of from 50 to 100 /1.m.
  • a satisfactorily uniform and thin developer layer may be formed by thin layer forming member 5 and a carrier may also satisfactorily be prevented from adhering to latent image carrying member 20.
  • brush-like ears i.e., a magnetic brush
  • the carrier held in a developer layer are heightened and the layer is made coarse, so that the developability is lowered.
  • a magnetization of the carriers is preferably from 10 to 200 emu/g, more preferably from 10 to 100 emu/g and, particularly from 15 to 30 emu/g. If the magnetization of the carriers is too little, there may be some instance where none of excellent magnetic brushes may be formed. If the magnetization is too great, there may be some instances where an oscillatory electric field may not function well, so that an excellent image may hardly be formed.
  • Figs. 2(a) and 2(b) are a perspective view and a front view each for illustrating an example of the detailed unit structure of stirring members 7 and 8.
  • 7a, 7b and 7c are stirring blades of primary stirring member 7 and 8a, 8b and 8c are the stirring blades of secondary stirring member 8, respectively.
  • These stirring blades are arranged at an angle and/or position different from each other blades and fixed to rotating shafts 9 and 10, respectively.
  • These stirring members 7 and 8 are so arranged as to overlap each other member in a stirring area without colliding with the other blades. In Fig. 1, therefore, a stirring may satisfactorily be performed in the direction from right to left. At the same time, each stirring blade is slanted to the corresponding rotating shaft and fixed.
  • a stirring may also satisfactorily be performed in the direction of back and forth. Accordingly, toners T are replenished from toner replenishing vessel 11 through replenishing roller 12 so that they are uniformly mixed up with developer D within a short time.
  • Toners and carriers are frictionally charged well by the above-mentioned stirring members 7 and 8 and the resulting developers are allowed to adhere to and be held on developing sleeve 3 by magnetic force and a thin developer layer is then formed by thin layer forming member 5.
  • the thin developer layer While being transported toward a specific direction by the rotation of the developing sleeve 3, the thin developer layer receives a magnetic bias having an oscillatory component and derived from the reverse rotation of the magnetic roll 4 and performs a single motion, such as rolling, on the developing sleeve 3. Accordingly, the toner particles satisfactorily adheres to an electrostatic latent image formed on the latent image carrying member 20 especially if the thin developer layer transported to the developing area receives the influence of the oscillatory electric field on a non-contact basis in relation to the electrostatic latent image.
  • the thickness of developer layer is favorably set extremely small, or more specifically, at 10 to 500 /1.m.
  • This arrangement enables to narrow the development gap between the latent image carrying member 20 and the developing sleeve, for example, to 500 /1.m, and accordingly, ensures development in compliance with the so-called non-contact developing system.
  • Such a narrower development gap enhances the electric field strength in the developing area 15. This in turn enables satisfactory development operation even if the bias voltage applied onto the developing sleeve 3 is smaller, and, advantageously, reduces the leakage of bias voltage, and other disadvantages. Furthermore, the resultant greater contrast in the electrostatic latent image generally improves the resolution and quality of an image obtainable from the development operation.
  • the developing method of the invention may be favorably used for the multicolor development system in which the development process is repeatedly effected on an latent image carrying member where a toner image is formed.
  • the developer used in embodying the invention is a two-component developer comprising a toner, as well as a resin-coated carrier composed of magnetic particles each of which being coated with resin involving silicone resin or fluororesin in an amount of at least 30 % by weight.
  • a toner comprises fine particles each composed of binder resin containing a toner component such as a coloring agent.
  • the preferred binder resins used for toner include polyester resin, styrene-acryl resin, and the like.
  • the polyester resin favorably used as the binder resin of toner is prepared by the condensation polymerization of alcohol monomer and carboxylic monomer.
  • alcohol monomer examples include diols such as ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol and the like; etherified bisphenols such as 1,4-bis(hydroxymethyl) cyclohexane, bisphenol A, hydrogenated bisphenol A, polyoxyethylene bisphenol A, polyoxypropylene bisphenol A and the like; other bivalent alcohol monomers.
  • bivalent carboxylic monomer examples include maleic acid, fumaric acid, methaconic acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebatic acid, malonic acid; anhydrides, lower alkyl esters, and linolenic dimers of these acids; other bivalent organic acid monomers.
  • polyester resin favorably used as the binder resins of toner polymers having multifunctional monomeric components, larger than trifunctional ones, are also favorably used in addition to the polymers comprising the above bifunctional monomers.
  • multivalent alcohol monomers, or the above multifunctional monomers, whose valence being larger than trivalence are as follows: sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, saccharose, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,3,5-trihydroxymethylbenzene, and the like.
  • multivalent carboxylic monomers whose valence being larger than trivalence, are as follows: 1,2,4-benzenetricarboxylic acid, 1,3,5-benzenetricarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxylpropane, tetra (methylenecarboxy)-methan, 1,2,7,8-octanetetracarboxylic acid, empoltrimer acid; anhydrides of these acids; and others.
  • the resins not only having an Mw/Mn ratio, which is a ratio between weight-average molecular-weight Mw and number-average molecular-weight Mn, of more than 3.5 but containing a, ,8-unsaturated ethylene monomer, which was disclosed for example in Japanese Patent O.P.I. Publication No. 134652/1975, as a component are favorably used.
  • Mw/Mn ratio which is a ratio between weight-average molecular-weight Mw and number-average molecular-weight Mn, of more than 3.5 but containing a, ,8-unsaturated ethylene monomer, which was disclosed for example in Japanese Patent O.P.I. Publication No. 134652/1975, as a component are favorably used.
  • aromatic vinyl monomers such as styrene, o-methylstyrene, p-methylstyrene, a-methylstyrene, p-ethylstyrene, 2,4-dimethylstryrene, p-n-butylstyrene, p-tert-butylstyrene, p-n-hexylstyrene, p-n-oxtylstyrene, p-n-nonylstyrene, p-n-decylstyrene, p-n-dodecylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, 3,4-dichlorostyrene and the like; acrylic esters such as methyl
  • the values of number-average molecular-weight Mn and weight-average molecular-weight Mw in a specific polymer may be measured by various methods. Though the measured results differ depending upon a measuring method, the number-average molecular-weight Mn as well as the weight-average molecular-weight Mw in this specification are defined as the values determined by the following method.
  • each of these values is a value determined by a gel permeation chromatography with the following conditions; a solvent (tetrahydrofuran) is allowed to flow at a rate of 1.2 mî per minute with a temperature of 40 C, whereby 3 mg tetrahydrofuran solution of a density 0.2 g/20 m containing a sample is added for the measuring operation.
  • measuring conditions are selected so that the counted number of the molecular weight of the sample provides a linear relation with the logarithmic numbers on the analytical curve formed from the measuring results with various types of monodispersion polystyrene reference samples.
  • the reliability of the measuring result is confirmed when a NBS 706 polystyrene reference sample satisfies the following expressions under the above-mentioned measuring conditions.
  • Weight-average molecular-weight Mw 28.8 x 10 4
  • Number-average molecular-weight Mn 13.7 x 10 4
  • any columns may be used as for as they satisfy the above conditions. More specifically, a TSK GE, GMH (manufactured by Toyo Soda Mfg. Co., Ltd.) or the like may be used.
  • a preferred binder resin used for toner has a softening point Tsp of 80 to 150°C, or, more specifically, 100 to 140 C.
  • a glass transition point Tg of the similar resin is favorably 40 to 80 ° C, or in particular, 50 to 70 C.
  • the softening point Tsp refers to a temperature determined in the following manner: using a flow tester Model CFT-500 manufactured by Shimazu Seisakusho Ltd., the measurement was recorded with measuring conditions of 20 kg/cm 2 load, 1 mm nozzle diameter, 1 mm nozzle length, 80 ° C pre-heating for 10 minutes, 6 ° C/min heating rate, and 1 cm 3 (weight represented by intrinsic specific gravity x 1 cm 3 ), wherein, by assuming the height of S curve in the characteristic curve (softening fluidization curve) representing the correlation between the amount of plunger drop in the flow tester and the corresponding temperature is h, the softening point is determined by reading a temperature corresponding to h/2.
  • the glass transition point is a value determined in the following manner: using a differential scanning calorimeter Model Low-temperature DSC manufactured by Rigaku Denkisha Co., Ltd., a measuring operation is performed at a heating rate of 10°C/min, whereby the glass transition point is read from the temperature on an intersection, in a DSC thermogram, between the extension of baseline below the glass transition point and the tangent line representing a maximum slope from the initial rising portion to summit of a peak.
  • the toner used in the invention comprises binder resin particles containing a coloring agent, as well as other toner component added in compliance with a requirement.
  • the examples of useful coloring agent are as follows: Carbon Black, Nigrosine Dye (C.I. No. 50415B), Aniline Blue (C.I. No. 50405), Chalcoil Blue (C.I. No. Azoic Blue 3), Chrome Yellow (C.I. No. 14090), Ultramarine Blue (C.I. No. 77103), DuPont Oil Red (C.I. No. 26105), Quinoline Yellow (C.I. No. 47005), Methylene Blue Chloride (C.I. No. 52015), Phthalocyanine Blue (C.I. No. 74160), Malachite Green Oxalate (C.I. No. 42000), Lamp Black (C.I. No. 77266), Rose Bengal (C.I. No. 45435), and mixtures involving any of the above agents, and others.
  • a coloring agent is favorably incorporated into a toner so as to form a satisfactorily dense image.
  • the amount of such agent is usually 1 to 20 parts weight per 100 parts weight toner.
  • various surface releasing agents are favorably incorporated into the toner.
  • Such a useful surface releasing agent include polyolefin, metal salt of aliphatic acid, aliphatic ester, partially saponified aliphatic ester, higher alcohol, fluid or solid paraffin wax, amide wax, multivalent alcohol ester, silicone varnish, aliphatic fluoro carbon, and the like.
  • those preferred have a softening point, measured by a ring and ball test specified in JIS K2531-1960, of 80 to 180°C, in particular 70 to 160°C.
  • These surface releasing agents may be singly used, or more than two of them may be combinedly used.
  • the examples of above-mentioned useful polyolefin include resins such as polypropylene, polyethylene, polybutene and the like.
  • the examples of above-mentioned metal salt of aliphatic acid are as follows: salts of maleic acid and a metal such as zinc, magnesium, calcium and the like; salts of stearic acid and a metal such as zinc, cadmium, barium, lead, iron nickel, cobalt, copper aluminum, magnesium, and the like: lead salt of dibasic stearic acid; salts of oleinic acid and a metal such as zinc, magnesium, iron, cobalt, copper, lead, calcium and the like; salts of palmitic acid and a metal such as aluminum, calcium and the like; lead caprate, lead capronate, metal salts of linoleic acid and a metal such as zinc, cobalt and the like; salts of ricinoleic acid and a metal such as zinc, cadmium and the like; and the mixture of these salts.
  • the examples of the above-mentioned useful aliphatic ester include ethyl maleate, butyl maleate, methyl stearate, butyl stearate, cetyl palmitate, ethylene glycol montanate and the like.
  • a montanic ester whose calcium area is saponified may be used.
  • the examples of the above-mentioned useful higher aliphatic acid include dodecanic acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linolic acid, ricinoleic acid, arachic acid, behenic acid, lignoceric acid, ceracholeic acid and the like, and a mixture of these acids.
  • the examples of the above-mentioned useful higher alcohol include dodecyl alcohol, lauryl alcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol, aralkyl alcohol, behenyl alcohol and the like.
  • the examples of the above-mentioned useful paraffin wax include natural paraffin, microcrystalline wax, synthetic paraffin, chlorinated hydrocarbon and the like.
  • the examples of the above-mentioned useful amide wax include amide stearate, amide oleinate, amide palmitate, amide laurate, amide behenate, methylenebisstearoamide, ethylenebisstearoamide and the like.
  • the examples of the above-mentioned useful alcohol ester include glycerol stearate, glycerol ricinolate, glycerol monobehenate, sorbitan monostearate, propylene glycol monostearate, sorbitan triolate and the like.
  • the examples of the above-mentioned useful silicone varnish include methylsilicone varnish, phenyl- silicone varnish and the like.
  • the examples of the above-mentioned useful aliphatic fluoro carbon include lower polymers such as ethylene tetrafluoride and propylene hexafluoride, and a fluorine-containing surface active agent disclosed in Japanese Patent O.P.I. Publication No. 124428/1978, and other agents.
  • the proportion of these surface release agents to be used is favorably 1 to 10 part weight per 100 parts weight binder resin.
  • toner components are as follows: fluidizing agents such as fine silica powder, fine titania powder, fine alumina powder and the like; abrasive powder such as cerium oxide; lubricants such as zinc stearate and the like; charge controlling agents such as pigment or dye; and others.
  • the preferred toner used in the invention has a weight-average particle size of less than 20 /1.m, in particular, 1 to 15 ⁇ m.
  • the use of a toner having such a preferred weight-average particle size enables an image having extremely good image quality to be formed.
  • the use of a toner having an excessively large weight-average particle size readily decreases the image resolution and may sometimes decrease the gradation reproducibility.
  • the use of a toner having an excessively small weight-average particle size may cause the toner to fly around in an image forming apparatus, and this in turn may sometimes decrease the sharpness of resultant image.
  • a carrier composing a two-component developer together with a toner is, as mentioned previously, a resin-coated carrier whose individual particles comprise a magnetic particle coated with a resin containing silicone resin or fluororesin in an amount of at least 30% by weight thereof.
  • condensation-reaction type silicone resins the particularly favorable ones are those having a methyl substituent.
  • the coating layer composed of a methyl-substituted condensation-reaction type silicone resin provides a carrier having a satisfactory water-repelling property and excellent moisture-resistance.
  • a silicone resin used to form the coating layer of carrier particle whichever a thermosetting silicone resin or normal-temperature setting silicone resin may be used. Since a high temperature not being necessary to set a resin, the used of normal-temperature setting silicone resin simplifys the carrier preparation.
  • the normal-temperature setting silicone resin is a silicone resin which hardens, under a normal atmosphere, at a temperature of 20 to 25 °C, or a little higher, and accordingly, does not require a temperature exceeding 100°C.
  • the silicone resin used as the coating layer of carrier is prepared by singly or combinedly using the above-described silicone resins, or a resin having not only the above silicone resin but another resin may be used for this purpose.
  • Such another resin is favorably one having a high compatibility with a silicone resin.
  • the examples of such a resin include an acryl resin, styrene resin, epoxy resin, urethane resin, polyamide resin, polyester resin, acetal resin, polycarbonate resin, phenol resin, vinyl chloride resin, vinyl acetate resin, cellulose resin, polyolefin resin, copolymers of these resins, blend resins of these resins, and others.
  • fluororesins used for forming the coating layer of carrier is not specifically limited, however, the preferred fluororesin is one capable of being dissolved in solvent, and being applied onto the surface of magnetic particle by a conventional coating method.
  • the fluororesin used to form the coating layer of carrier is prepared by singly or combinedly using the above-described fluororesin, or a resin having not only the above fluororesin but another resin may be used for this purpose.
  • a resin having not only the above fluororesin but another resin may be used for this purpose.
  • Such another resin is favorably one having a high compatibility with a fluororesin.
  • the examples of such a resin include an acryl resin, styrene resin, epoxy resin, urethane resin, polyamide resin, polyester resin, acetal resin, polycarbonate resin, phenol resin, vinyl chloride resin, vinyl acetate resin, cellulose resin, polyolefin resin, copolymers of these resins, blend results of these resins, and others.
  • the content of fluororesin in the coating resin is at least 30 weight%, or more favorably, 40 to 100 weight%, or most favorably 50 to 100 weight%. Less than 30 weight% of fluororesin content does not fully provide the favorable property of fluororesin, often resulting in unstable triboelectric charging characteristic.
  • the magnetic particle serving as a core being coated with a resin is a particle made of a substance which is strongly magnetized in the direction of magnetic field.
  • a substance which is strongly magnetized in the direction of magnetic field.
  • the examples of such a substance are as follows: metals showing ferromagnetism such as ferrite, magnetite, as well as iron, nickel, cobalt and the like; alloys or compounds involving these metals; alloy not having ferromagnetic element but being endowed with ferromagnetism by an appropriate heat-treatment, and being typified by Heusler alloys such as manganese-copper-aluminum alloy, manganese-copper-tin,and the like; chromium dioxide and the like.
  • ferrite is a general term of a magnetic oxide involving iron and is not limited only to a Spinel structure ferrite represented by a formula MO.Fe 2 0 3 (M represents a bivalent metal atom).
  • MO.Fe 2 0 3 M represents a bivalent metal atom.
  • a ferrite is especially advantageous to prepare a carrier which best suits the object of the invention.
  • a ferrite powder has a specific gravity much smaller than metal powder such as iron powder or nickel powder. This feature allows easy mixing and blending with a toner, and advantageously contributes to the uniformity of toner concentration in the developer as well as to the optimization of triboelectrical potential formed in toner powder.
  • a further advantage is that, since having a resistivity of 10 8 to 10 12 ⁇ .cm, which is greater than that of iron powder, nickel powder or cobalt powder, the ferrite powder provides an insulative carrier satisfactorily used in a developing method in which a high bias voltage is applied to the developing gap, even when the layer thickness of resin forming the surface of carrier particle is extremely small, approximately 0.5 ⁇ m.
  • the above-mentioned ferrite favorably has a saturated magnetization of 10 to 40 emu/g and a coercive force of 0.1 to 100 Oe. Furthermore, the ferrite favorably has a resistivity of 1 x 10 6 to 1 x 10 11 ⁇ .cm, a specific gravity of 4.0 to 5.5, and a porosity of 1.0 to 10%.
  • the coating layer is formed in the following steps.
  • a solution prepared by dissolving silicone resin or fluororesin, and, if necessary, another resin, in a solvent is applied on the surface of individual magnetic particles by a dipping method, spray method, fluidized bed method or the like, whereby usually by heating, the solvent is allowed to vaporize and the solution is allowed to dry, then during or after the drying, the coat layer is allowed to set.
  • a solvent being used for this purpose is not specifically limited, as far as a silicone resin, fluororesin, and another additional resin can be dissolved in such a solvent.
  • the typical examples of such a solvent are as follows: aromatic hydrocarbons such as toluene, xylene and the like; ketones such as acetone, methylethyl ketone; tetrahydrofuran; dioxane; higher alcohol; and mixed solvents involving any of the above solvents.
  • thermosetting silicone resin In setting the coating layer, when a thermosetting silicone resin requires heating at 200 to 250 C. Though a normal-temperature setting silicone resin does not require heating with a high temperature, the heating with a temperature range of 150 to 250 ° C may be performed to accelerate the setting. Additionally, in the course of drying, a metal soap of octyl acid, nephthic acid or the like and lead, iron, cobalt, tin, manganese, zinc or the like may be used as a dryer. Also, an organic amine such as ethanol amine may be satisfactorily used as a dryer.
  • the preferred thickness of the formed resin coating-layer containing silicone resin is usually 0.1 to 20 ⁇ m.
  • the preferred heating temperature necessary for setting a coating layer comprising a resin containing fluororesin is usually 100 to 350 C.
  • a dryer or setter composed of, for example, an organic metal salt such as zinc octylate, dibutyl zinc oxide or the like may be used.
  • the preferred thickness of the formed resin coating-layer containing fluororesin is, for example, 0.1 to 10 ⁇ m, and more specifically, 0.3 to 4 ⁇ m, and most specifically, 0.3 to 2 /1 .m.
  • the individual particles of resin-coated carrier used in the invention are favorably spherical-shaped and have a weight-average particle size of less than 100 ⁇ m, and more favorably, 5 to 50 ⁇ m.
  • the use of a resin-coated carrier having such a favorable weight-average particle size improves the image resolution as well as the gradation reproducibility.
  • the use of a carrier having an excessively large weight-average particle size may sometimes make it difficult to form a thin developer layer on a developer bearing/carrying member, and possibly resulting in the deteriorated developability and decreased image quality.
  • the use of a carrier having an excessively small weight-average particle size may sometimes deteriorate the developability, triboelectrical charging property, fluidity and the like, and may cause the carrier to fly around in an image forming apparatus.
  • a resin-coated carrier used in the invention is an insulative carrier having a resistivity of more than 10 8 ⁇ .cm, favorably, more than 10 13 ⁇ .cm, and more favorably, more than 10 14 ⁇ .cm.
  • the use of such a highly insulative carrier satisfactorily prevents, in the course of developing, a potential from being injected by a bias voltage and resulting in a filming of carrier on the surface of a latent image carrying member, or a potential to form an electrostatic latent image from being eliminated.
  • the weight-average particle sizes of toner and carrier are values determined with a Coulter Counter manufactured by Coulter Ltd.
  • the resistivities of magnetic particles as well as resin-coated carrier particles are determined by the following procedure: sample particles are poured into a container having a cross-sectional area of 0.50 cm 2 and tamped down, then a load of 1 kg/cm 2 is applied onto the tamped sample particles so as to make the thickness of sample to be approximately 1 mm, whereby an electrical field of 10 2 to 10 5 V/cm is applied to between the load and a bottom electrode and the value of current flowing is measured.
  • the preferred blending ratio between toner and carrier is a ratio where the total surface area of toner is approximately the same as the similar area of carrier. For example, if a weight-average particle size of toner is 10 /1.m and a weight-average particle size of carrier is 20 ⁇ m, the preferred toner concentration (weight ratio per total developer) is 5 to 40 weight%, in particular, 8 to 25 weight%.
  • the two-component developer used in embodying the invention by blending a toner and a fine particle carrier whose particle size being approximately the same as the toner at a ratio whre the total surface areas of carrier and toner are approximately the same with each other.
  • Fig. 3 is an explanatory diagram schematically illustrating one example of image forming apparatus being used in embodying the developing method of the invention.
  • the move of a draft table causes the optical draft image formed by an illuminating light source 21 to be focused on a latent image carrying member 20 via a mirror 22 and a lens 23, and an electrostatic latent image corresponding to an original draft is formed on the latent image carrying member 20.
  • a developing unit A has a constitution, for example, shown in Fig. 1.
  • the electrostatic latent image formed on the latent image carrying member is developed by the developing unit A to form a toner image.
  • a toner image obtained in such a manner is transferred onto a recording paper P with a transfer electrode 29 after being electrically neutralized for easy transfer by an exposure lamp 28.
  • the recording paper P is separated by a separation electrode from the latent image carrying member 20 and is fixed with a fixer 31 to form a fixed image.
  • the latent image carrying member 20 is electrically neutralized by a neutralization electrode 32 and its surface is cleaned by a cleaning mechanism 33.
  • the cleaning mechanism 35 in this example has a cleaning blade 34 for scraping off toner. Toner particles scraped off by the blade 34 are collected by a roller 36.
  • spherical copper-zinc ferrite particles having a weight-average particle size of 35 ⁇ m 100 parts spherical copper-zinc ferrite particles having a weight-average particle size of 35 ⁇ m (manufactured by TDK Corporation) were coated with 25 parts condensation-reaction type silicone resin solution SR-2411 (manufactured by Toray Silicone Co., Ltd.) at a temperature of 80 ° C, and were further heat-treated at a temperature of 200 ° C for one hour to obtain a carrier having individual particles being coated with a silicone resin layer.
  • the coating layer has a thickness of approximately 1 /1.m.
  • the carrier was designated carrier A.
  • the properties of the carrier A were as follows:
  • a carrier having particles individually being coated with a 1 ⁇ m thick silicone resin layer was prepared in a manner identical to that of carrier A except that silicone resin solution SR-2410 was used in the place of silicone resin solution SR-2411.
  • This carrier was designated carrier B.
  • the properties of the carrier B were as follows:
  • a carrier having particles individually being coated with a 1 ⁇ m thick silicone resin layer was prepared in a manner identical to that of carrier A except that thermosetting silicone resin solution (manufactured by The Sin-Etsu Chemical Co., Ltd.) was used in the place of silicone resin solution SR-2411. This carrier was designated carrier C.
  • the properties of the carrier C were as follows:
  • a carrier comprising copper-zinc ferrite particles identical to those of carrier A was designated comparison carrier a.
  • the properties of the comparison carrier a were as follows:
  • a carrier having particles individually have a coating layer of 1 an thick styrene was prepared in a manner identical to that of carrier A except that toluene solution (solid content, 10 weight%) containing styrene resin (weight-average molecular weight Mw, 71,000; number-average molecular weight Mn, 32,000; glass transition point Tg, 125°C) was used in the place of silicone resin solution SR-2411.
  • This carrier was designated comparison carrier b.
  • the properties of the comparison carrier b were as follows:
  • a carrier having particles individually being coated with a 1.5 ⁇ m thick methyl methacrylate resin layer was prepared in a manner identical to that of carrier A except that toluene solution (solid content, 10 weight%) containing methyl methacrylate resin (weight average molecular Mw, 73,000; number average molecular Mn, 33,000; glass transition point Tg:-121 ° C) was used in the place of silicone resin solution SR-2411.
  • This carrier was designated comparison carrier c.
  • the properties of the comparison carrier c were as follows:
  • black toner A To 100 parts weight of the black toner powder, 0.5 parts weight hydrophobic fine silica particles (R-812, manufactured by Nippon Aerozyl Co., Ltd.) was added, then thoroughly blended by a Henschel mixer to prepare black toner. This toner was designated black toner A.
  • the static bulk density of the black toner A was 0.44 g/cm 3 .
  • a yellow toner was prepared in a manner identical to that of black toner A except that yellow pigment, Pigment Yellow, was used in the place of Carbon Black. This toner was designated yellow toner B.
  • the static bulk density of the yellow toner B was 0.44 g/cm 3 .
  • magenta toner was prepared in a manner identical to that of black toner A except that magenta pigment, Permanent Carmine F-5B, was used in the place of Carbon Black. This toner was designated magenta toner C.
  • the static bulk density of the magenta toner C was 0.45 g/cm 3.
  • a cyan toner was prepared in a manner identical to that of black toner A except that cyan pigment, Copper Phthalocyanine, was used in the place of Carbon Black. This toner was designated cyan toner D.
  • the static bulk density of the cyan toner D was 0.44 g/cm 3 .
  • the above-mentioned carriers A through C were independently combined with the black toner A to prepare developers 1 through 3 individually having a toner concentration of 10 weight%.
  • the above-mentioned comparison carriers a through c were also combined with the black toner A to correspondingly prepare comparison developer 1 through 3 individually having a toner concentration of 10 weight%.
  • yellow toner B, magenta toner C and cyan toner D were independently combined with carrier A to correspondingly prepare color developers 1 through 3 individually having a toner concentration of 12 weight%.
  • a fixed image was inspected with human eye.
  • the surface of latent image carrying/transporting member was inspected with human eye.
  • a fixed image was inspected with human eye.
  • the toner demonstrated a proper triboelectricity, and a sharp image featuring high-resolution as well as excellent gradation reproducibility is formed without accompanying any of fog, carrier adhesion of the image carrying member, imaging failure, and uneven imaging.
  • the developing method of the invention using any of the developers 1 through 3 provides a sharp image, whose quality is comparable to that of the first copied image, even after 30000 sheet-copying operation. Additionally, inspection of the contamination in an image forming apparatus confirmed only an extremely limited contamination with toner and carrier. This is because the silicone resin to form the coating layer of the carrier used in embodying the invention has a smaller critical surface tension when compared to a resin used to prepare a comparison carrier, and accordingly, the toner substance does not easily adhere to the surface of individual carrier particles. Furthermore, the developing effects of bias voltage was satisfactorily demonstrated.
  • the comparison developer 1 incurred a smaller triboelectricity even in the initial stage of continuous 30000 sheet copying operation, and an obtained image was not sharp, showing considerable fog, imaging failure and uneven imaging. Also, the carrier adhesion on the latent image carrying member was found. In addition, the above problems further deteriorated after the completion of 30000-sheet copying operation, because of further decreased toner triboelectricity. Also, considerable adhesion of toner material on the surface of individual carrier particles also occurred.
  • comparison developer 2 incurred a smaller triboelectricity even in the initial stage of continuous 30000-sheet copying operation, and an obtained image was not sharp, showing minor fog, imaging failure and uneven imaging.
  • the above problems further deteriorated after the completion of 30000-sheet copying operation, because of further decreased toner triboelectricity. Also, considerable adhesion of toner material on the surface of individual carrier particles also occurred.
  • comparison developer 3 incurred imaging failure and uneven imaging on an obtained image during the initial stage of continuous 30000-sheet copying operation, and the carrier adhesion on the latent image carrying member was also found. After the completion of 30000-sheet copying operation, the toner triboelectricity further decreased, and accordingly, the obtained image is not sharp, showing minor fog, as well as imaging failure and uneven imageing. Also, considerable carrier adhesion on the latent image carrying member as well as considerable adhesion of toner substance on the surface of individual carrier particles also occurred.
  • test was performed in a manner identical to the above test 1 by actual copying operation except that the modified developing conditions below were used. The results similar to those of test 1 were obtained.
  • FIG. 5 schematically illustrates the constitution of another example of an image forming apparatus used in embodying the developing method of the invention, wherein an image input unit IN is unit-built and comprises an illuminating light source 1, a mirror 22, a lens 23 and one-dimensional color CCD image sensor 24.
  • the image input unit IN is shifted in the direction shown by an arrow x with an unshown driving mechanism, and the CCD image sensor 24 reads an original draft.
  • a draft table may be shifted to shift the original draft 25.
  • the image information read by the image input unit IN is converted into data suitable for recording at an image processing unit TR.
  • a laser optical system 26 forms a latent image on the image carrying member 20 in the following manner and based on the above-mentioned image data.
  • the surface of image carrying member 20 is uniformly electrified with a Scorotron electrification electrode 27.
  • image exposure light L with the recorded data incorporate is illuminated from the laser optical system 26 via a lens upon the image forming member 20. In this way, an electrostatic latent image corresponding to the original draft is formed on the latent image carrying member 20.
  • the electrostatic latent image is developed by a developing unit A containing yellow toner B.
  • the latent image carrying member 20 on which a toner image has been formed in again uniformly electrified by the Scorotron electrification electrode 27 and receives image exposure light L into which recorded data of another color element has been incorporated.
  • the formed electrostatic latent image is developed by a developing unit B containing magenta toner C.
  • a two-color toner image of yellow toner B and magenta toner C is formed on the image carrying member 20.
  • a cyan toner D image as well as a black toner A image are consecutively superposed on the two-color toner image to form a four-color toner image on the latent image carrying member 20.
  • the developing units A, B, C, and D respectively containing each color toner commonly have the constitution similar to that of the developing unit in Fig. 1.
  • a multicolor toner image obtained in such a manner is transferred on a recording paper P with a transfer electrode 29 after being electrically neutralized for each transfer by an exposure lamp 28.
  • the recording paper P is separated by a separation electrode 30 from the latent image carrying member 20 and is fixed with a fixer 31, thus forming a fixed image.
  • the triboelectricity on the image carrying member 20 is neutralized by a neutralization electrode 32, and the surface of which is cleaned by a cleaning mechanism 33.
  • the cleaning mechanism 33 in this example has a cleaning blade 34 and a fur brush 35 which are kept out of contact with the latent image carrying member 20 during formation of an image. Once a multicolor image is finally formed on the latent image carrying member 20, the cleaning blade 34 and the fur brush 35 come in contact with the latent image carrying member 20 and scrape off toner left untransferred on the member 20. Then, the cleaning blade 34 leaves the latent image carrying member 20, and, a little later, the fur brush also leaves the latent image carrying member.
  • the fur brush 35 functions to remove toner left on the latent image carrying member 20 after the cleaning blade 34 leaves the member 20.
  • Numeral 36 denotes a roller which collects toner scraped off by the blade 34.
  • FIG. 9 A typical example of laser optical system 26 is shown in Fig. 9.
  • numeral 37 denotes a semiconductor laser generator
  • numeral 38 a rotatable polygon mirror
  • numeral 39 a fe lens.
  • Fig. 6 schematically illustrates the change in the surface potential of latent image carrying member having a positive triboelectrical polarity.
  • PH represents an exposure area in the latent image carrying member
  • DA a non-exposure area in the similar member
  • DUP an increase in potential due to the adhesion of positive-charged toner T 1 area PH caused by the first development.
  • the latent image carrying member is uniformly electrified with a Scorotron electrode, so as to have a specific positive surface potential E as shown in Fig. 6-(1
  • the first imagewise exposure is effected by an exposure light source such as a laser, cathode ray tube, LED or the like, whereby the potential of exposure are PH drops in proportion to the light amount as shown in Fig. 6-(2).
  • An electrostatic latent image formed in this way is developed by a developing unit to which a positive bias voltage approximately equal to the surface potential E on the non-exposure area is applied.
  • a positive-charged toner T 1 adheres to the exposure area PH having a relatively low potential as shown Fig. 6-(3), thus the first toner image is formed.
  • the surface of latent image carrying member where the first toner image has been formed is subjected to the second electrification by the electrifier, as a result, whichever the toner T 1 is present or not, uniform surface potential E is attained, as shown in Fig. 6-(4).
  • the surface of latent image carrying member is further subjected to the second imagewise exposure, which forms an electrostatic latent image, as shown in Fig. 6-(5).
  • the electrostatic latent image is, similarly to the above description, developed with a positive-charged toner T 2 whose color different from that of the toner T1. This step forms the second toner image shown in Fig. 6-(6).
  • a multicolor toner image is formed on the latent image carrying member. Then, the multicolor toner image is transferred onto a recording paper, which is heated or pressed to fix the image. Thus, the multicolor recorded image is finally formed. Toner and triboelectrical potential on the surface of latent image carrying member are removed, and the next sequence of multicolor image forming is prepared. Additionally, it is also possible to use a method to fix a multicolor toner image directly onto the latent image carrying member. In the developing method illustrated in Fig. 6, it is favorable that the processing step in Fig. 6-(6) be performed without allowing the developer layer to come in contact with the surface of latent image carrying member.
  • the toner when executing the developing method of the invention, demonstrated a proper triboelectricity, and a sharp color image featuring high-resolution as well as excellent gradation reproducibility is formed without accompanying any of fog, carrier adhesion of the image carrying member, imaging failure, and uneven imaging.
  • the developing method of the invention is capable of providing a sharp image, whose quality is comparable to that of the first copied image, even after 30000 sheet-copying operation. Additionally, inspection of the contamination in an image forming apparatus confirmed only an extremely limited contamination with toner and carrier.
  • FIG. 8 schematically illustrate the outline of another example of image forming apparatus used for embodying the developing method of the invention.
  • This image forming apparatus has a constitution, wherein a multicolor toner image is formed at once, while a latent image carrying members completes one rotation.
  • the image forming apparatus in Fig. 8 differs from the apparatus in Fig. 5 in that:
  • the image When forming, for example, a four-color image with this image forming apparatus, and even if the linear velocity of the latent image carrying member is set equal to that of the apparatus in Fig. 5, the image may be formed approximately four times swiftly than the latter apparatus.
  • a test operation to form 30000 sheets of copied image was performed so as to examine, respectively in the initial stage of image forming operation and after the completion of 30000-sheet copying operation, the triboelectricity on toner, fog, adhesion of carrier on a latent image carrying member, imaging failure, and uneven imaging.
  • the results were as satisfactory as those of the previously mentioned test 3 by actual copying operation.
  • the color development sequence may be modified; for example, (black) - (yellow) - (magenta) - (cyan).
  • the coating solution was applied to copper-zinc ferrite particles (particle size distribution, 15 to 60 ⁇ m; weight-average particle size, 35 ⁇ m), whereby heating with 100 ° C temperature was performed to prepared carrier having individual particles being coated with resin containing fluororesin.
  • the thickness of coating layer was 1.0 ⁇ m.
  • This carrier was designated carrier X.
  • a carrier having particles individually being coated with a 1.0 ⁇ m thick fluororesin layer was prepared in a manner identical to that of carrier X except that a polymer comprising monomer represented by the following general formula was used instead of the vinylidene fluoride-tetrafluoro ethylene copolymer.
  • the properties of the carrier Y were as follows:
  • This carrier was designated carrier Z.
  • Polymer (1) Vinylidene fluoride-tetrafluoro ethylene copolymer (copolymeric molar ratio, 80:200; intrinsic viscosity, 0.95 dt/g)
  • Polymer (2) Methyl methacrylate copolymer, Acrypet MF, manufactured by Mitsubishi Rayon Co., Ltd.
  • the properties of the carrier Z are as follows:
  • a carrier comprising copper-zinc ferrite particles identical to those of carrier X was prepared. This was designated comparison carrier x.
  • the properties of the comparison carrier x were as follows:
  • a carrier having particles individually have a coating layer of 1.0 ⁇ m thick styrene resin was prepared in a manner identical to that of carrier X except that styrene (weight-average molecular weight Mw, 71,000; number-average molecular weight Mn, 32,000; glass transition point Tg, 125°C) was used instead of vinylidene fluoride-tetarfluoro ethylene copolymer.
  • This carrier was designated comparison carrier y.
  • a carrier having particles individually have a coating layer of 1.0 ⁇ m thick styrene resin was prepared in a manner identical to that of carrier X except that methyl methacrylate resin (weight-average molecular weight Mw, 73,000; number-average molecular weight Mn, 33,000; glass transition point Tg, 121°C) was used instead of vinylidene fluoride-tetrafluoro ethylene copolymer.
  • This carrier was designated comparison carrier z.
  • black toner O To 100 parts weight of the black toner powder, 0.6 parts weight hydrophobic fine titania particles (T-805, manufactured by Nippon Aerozyl Co., Ltd.) was added, then thoroughly blended by a Henschel mixer to prepare black toner. This toner was designated black toner O.
  • the static bulk density of the black toner O was 0.38 g/cm 3 .
  • a yellow toner having a weight-average particle size of 11 ⁇ m was prepared in a manner identical to that of black toner O except that yellow pigment, Pigment Yellow, was used in the place of Carbon Black. This toner was designated yellow toner P.
  • the static bulk density of the yellow toner P was 0.28 g/cm 3 .
  • magenta toner having a weight-average particle size of 11 ⁇ m was prepared in a manner identical to that of black toner O except that magenta pigment, Permanent Carmine F-5B, was used in the place of Carbon Black. This toner was designated magenta toner Q.
  • the static bulk density of the magenta toner Q was 0.29 g/cm 3 .
  • a cyan toner having a weight-average particle size of 11 u.m was prepared in a manner identical to that of black toner O except that cyan pigment, Pigment Blue 1, was used in the place of Carbon Black. This toner was designated cyan toner R.
  • the static bulk density of the cyan toner was 0.27 g/cm 3.
  • the above-mentioned carriers X through Z were indepdendently combined with the black toner O to prepare developers 4 through 6 individually having a toner concentration of 12 weight%.
  • the above-mentioned comparison carriers x through z were also combined with the black toner O to correspondingly prepare comparison developer 4 through 6 individually having a toner concentration of 12 weight%.
  • yellow toner P, magenta toner Q and cyan toner R were independently combined with carrier X to correspondingly prepare color developers 4 through 6 individually having a toner concentration of 12 weight%.
  • the developing method of the invention using any of the developers 4 through 6 provides a sharp image, whose quality is comparable to that of the first copied image, even after 30000 sheet-copying operation. Additionally, inspection of the contamination in an image forming apparatus confirmed only an extremely limited contamination with toner and carrier. This is because the fluororesin to form the coating layer of the carrier used in embodying the invention has a smaller critical surface tension when compared to a resin used to prepare a comparison carrier, and accordingly, the toner substance does not easily adhere to the surface of individual carrier particles. Furthermore, the developing effects of bias voltage was satisfactorily demonstrated.
  • comparison developer 4 incurred a smaller triboelectricity even in the initial stage of continuous 30000-sheet copying operation, and an obtained image was not sharp, showing fog, and uneven imaging.
  • the above problems further deteriorated after the completion of 30000-sheet copying operation, because of further decreased toner triboelectricity. Also, considerable carrier adhesion on the latent image carrying member, as well as imaging failure were also found.
  • comparison developer 5 provided a relatively smaller triboelectricity even in the initial stage of continuous 30000-sheet copying operation, and an obtained image was not sharp, showing imaging failure and uneven imaging.
  • the above problems further deteriorated after the completion of 30000-sheet copying operation, because of further decreased toner triboelectricity. Also, large fog occurred, and minor carrier adhesion on the latent image carrying member was also found.
  • comparison developer 6 incurred imaging failure and uneven imaging on an obtained image during the initial stage of continuous 30000-sheet copying operation, and the carrier adhesion on the latent image carrying member was also found. After the completion of 30000-sheet copying operation, the toner triboelectricity significantly decreased, and accordingly, the obtained image is not sharp, showing great fog, as well as imaging failure and uneven imaging. Also, minor carrier adhesion on the latent image carrying member also occurred.
  • test was performed in a manner identical to the above test 5 by actual copying operation except that the modified developing conditions below were used. The results similar to those of test 5 were attained.
  • Example 2 Using the image forming apparatus illustrated in Fig. 5 and already described in Example 2, a test operation to form 30000 sheets of copied image was performed, in a manner identical to that of test 3 by actual copying operation, so as to examine, respectively in the initial stage of image forming operation and after the completion of 30000-sheet copying operation, the triboelectricity on toner, fog, adhesion of carrier on a latent image carrying member, imaging failure, and uneven imaging. The results are listed in Table 4 shown later.
  • the toner demonstrated a proper triboelectricity, and a sharp color image featuring high-resolution as well as excellent gradation reproducibility is formed without accompanying any of fog, carrier adhesion of the image carrying member, imaging failure, and uneven imaging.
  • the developing method of the invention is capable of providing a sharp image, whose quality is comparable to that of the first copied image, even after 30000 sheet-copying operation. Additionally, inspection of the contamination in an image forming apparatus confirmed only an extremely limited contamination with toner and carrier.
  • a test operation to form 30000 sheets of copied image was performed, in a manner identical to that of test 3 by actual copying operation, so as to examine, respectively in the initial stage of image forming operation and after the completion of 30000-sheet copying operation, the triboelectricity on toner, fog, adhesion of carrier on a latent image carrying member, imaging failure, and uneven imaging.
  • the results were as satisfactory as those of the previously mentioned test 7 by actual copying operation.
  • the color development sequence may be modified; for example, (black) - (yellow) - (magenta) - (cyan).
  • the developing method of the invention may be advantageously applied also to an apparatus being capable of forming a multicolor toner image with one imagewise exposure on a latent image carrying member.
  • a multicolor toner image is formed, for example, in the following manner.
  • the latent image carrying member is triboelectrically charged to smooth its potential pattern, and subjected to a specific color light different from the above-mentioned specific color light, so as to form a potential pattern on the filter layer of the latent image carrying member, whereby the potential pattern is developed by a developing unit containing a specific color toner different from the above-mentioned specific color.
  • This procedure forms the second color toner iamge as superposed on the first color toner image already formed on the latent image carrying member. Additionally, in performing this type of developing process, at least the second developing onwards should be effected in compliance with non-contact developing method.
  • Such a type of multicolor image forming apparatus completes a multicolor image forming with only one sequence of the imagewise exposure, and this in turn precludes the possibility of an image whose independent toner images are not misaligned to each other.
  • the latent image carrying member may either have a constitution (refer to Japanese Patent Application No. 199547/1984), wherein a filter is incorporated into the electroconductive substrate side, so as to perform the imagewise exposure as well as uniform exposing on the filter side, or another constitution (refer to Japanese Patent Application No. 201084/1984).
  • a photosensitive may either be made of a single layer or have a function-separating constitution comprising both a charge generating layer and a charge transporting layer (refer to Japanese Patent Application No. 245178/1985).
  • a latent image carrying member may have a constitution, wherein the photosensitive layer has color separation function (refer to Japanese Patent Applications Nos. 201085/1984 and 245177/1985).

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Dry Development In Electrophotography (AREA)

Claims (15)

1. Procédé pour développer des images latentes électrostatiques sur un élément porteur d'image latente, un couche de développeur du type de deux composantes étant formé sur un élément de transport de développeur, ledit développeur du type de deux composantes comprenant des particules en toner et des particules porteur magnétiques, et ledit couche de développeur étant porté à une zone de développement entre ledit élément porteur d'image latente et ledit élément de transport de développeur, ladite zone de développement étant exposée à l'influence d'un champ électrique oscillatoire,
caractérisé en ce que
ledit couche de développeur a non plus de 1000 µm d'épaisseur et lesdites particules porteur sont couvertes d'un couche de résine contenant de la résine silicone ou de la fluororésine dans une quantité de plus de 30% du poids total de la résine.
2. Procédé selon la revendication 1, dans lequel l'épaisseur des particules de développeur est 10 à 500 um.
3. Procédé selon la revendication 1, dans lequel dans ladite zone de développement il y a un entrefer minimum entre ledit élément porteur d'image latente et ledit élément de transport de développeur de 100 à 1000 um.
4. Procédé selon la revendication 1, dans lequel ladite résine silicone est de la résine silicone du type de réaction de condensation.
5. Procédé selon la revendication 1, dans lequel ladite résine contenant de la fluororésine contient 40 à 100 % en poids de fluororésine.
6. Procédé selon la revendication 1, dans lequel ladite résine contenant de la fluororésine contient 50 à 100 % en poids de fluororésine.
7. Procédé selon la revendication 1, dans lequel l'épaisseur du couche couvert de résine est 0.1 à 20 um.
8. Procédé selon la revendication 1, dans lequel l'épaisseur du couche couvert de résine est 0.1 à 10 µm.
9. Procédé selon la revendication 1, dans lequel l'épaisseur du couche couvert de résine est 0.3 à 4 µm.
10. Procédé selon la revendication 1, dans lequel l'épaisseur du couche couvert de résine est 0.3 à 2 µm.
11. Procédé selon la revendication 1, dans lequel lesdites particules porteur couvertes de résine sont un porteur isolant ayant une résistance spécifique de plus de 108 Ω·cm.
12. Procédé selon la revendication 1, dans lequel lesdites particules porteur couvertes de résine sont un porteur isolant ayant une résistance spécifique de plus de 1013 Ω·cm.
13. Procédé selon la revendication 1, dans lequel lesdites particules porteur couvertes de résine sont un porteur isolant ayant une résistance spécifique de plus de 1014 Ω·cm.
14. Procédé selon la revendication 1, dans lequel lesdites particules porteur couvertes de résine sont des particules de forme sphérique.
15. Procédé selon la revendication 1, dans lequel lesdites particules porteur couvertes de résine ont un grandeur poids moyen de la particule de moins de 5 à 50 um.
EP19870111197 1986-08-06 1987-08-03 Procédé pour développer des images latentes électrostatiques Expired - Lifetime EP0257364B2 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
JP183422/86 1986-08-06
JP183423/86 1986-08-06
JP61183423A JPS6340171A (ja) 1986-08-06 1986-08-06 静電潜像の現像方法
JP61183422A JPS6340170A (ja) 1986-08-06 1986-08-06 静電潜像の現像方法

Publications (3)

Publication Number Publication Date
EP0257364A1 EP0257364A1 (fr) 1988-03-02
EP0257364B1 true EP0257364B1 (fr) 1992-10-21
EP0257364B2 EP0257364B2 (fr) 1997-10-15

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EP19870111197 Expired - Lifetime EP0257364B2 (fr) 1986-08-06 1987-08-03 Procédé pour développer des images latentes électrostatiques

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DE (1) DE3782300T3 (fr)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4904558A (en) * 1988-03-08 1990-02-27 Canon Kabushiki Kaisha Magnetic, two-component developer containing fluidity improver and image forming method
EP0363900B1 (fr) * 1988-10-13 1995-01-11 Daikin Industries, Limited Matériaux véhiculants pour le développement d'images électrostatiques
WO2020071486A1 (fr) * 2018-10-05 2020-04-09 Jsr株式会社 Composition pour capteurs optiques

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5927900B2 (ja) * 1979-02-07 1984-07-09 京セラミタ株式会社 磁性現像剤及びその製法
US4496643A (en) * 1984-03-23 1985-01-29 Eastman Kodak Company Two-component dry electrostatic developer composition containing onium charge control agent
JPS60201359A (ja) * 1984-03-27 1985-10-11 Ricoh Co Ltd 静電潜像現像剤用キヤリア
JPS61151551A (ja) * 1984-12-25 1986-07-10 関東電化工業株式会社 電子写真現像剤用キヤリヤ−

Also Published As

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DE3782300T2 (de) 1993-03-04
DE3782300T3 (de) 1998-02-19
DE3782300D1 (de) 1992-11-26
EP0257364B2 (fr) 1997-10-15
EP0257364A1 (fr) 1988-03-02

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