EP0474460B1 - Entwicklungsverfahren - Google Patents

Entwicklungsverfahren Download PDF

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Publication number
EP0474460B1
EP0474460B1 EP19910308055 EP91308055A EP0474460B1 EP 0474460 B1 EP0474460 B1 EP 0474460B1 EP 19910308055 EP19910308055 EP 19910308055 EP 91308055 A EP91308055 A EP 91308055A EP 0474460 B1 EP0474460 B1 EP 0474460B1
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EP
European Patent Office
Prior art keywords
developer
carrier
developing
photosensitive material
sleeve
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 - Lifetime
Application number
EP19910308055
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English (en)
French (fr)
Other versions
EP0474460A2 (de
EP0474460A3 (en
Inventor
Toshio Nishino
Shoji Tomita
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Kyocera Mita Industrial Co Ltd
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Mita Industrial Co Ltd
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Publication date
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Publication of EP0474460A2 publication Critical patent/EP0474460A2/de
Publication of EP0474460A3 publication Critical patent/EP0474460A3/en
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Publication of EP0474460B1 publication Critical patent/EP0474460B1/de
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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
    • G03G15/00—Apparatus for electrographic processes using a charge pattern
    • G03G15/06—Apparatus for electrographic processes using a charge pattern for developing
    • G03G15/08—Apparatus for electrographic processes using a charge pattern for developing using a solid developer, e.g. powder developer
    • G03G15/09—Apparatus for electrographic processes using a charge pattern for developing using a solid developer, e.g. powder developer using magnetic brush
    • G03G15/0921—Details concerning the magnetic brush roller structure, e.g. magnet configuration
    • G03G15/0928—Details concerning the magnetic brush roller structure, e.g. magnet configuration relating to the shell, e.g. structure, composition
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G2215/00—Apparatus for electrophotographic processes
    • G03G2215/06—Developing structures, details
    • G03G2215/0602—Developer
    • G03G2215/0604—Developer solid type
    • G03G2215/0607—Developer solid type two-component
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G2215/00—Apparatus for electrophotographic processes
    • G03G2215/06—Developing structures, details
    • G03G2215/0634—Developing device
    • G03G2215/0636—Specific type of dry developer device

Definitions

  • the present invention relates to a developing process having an excellent image reproducibility in the electrophotography. More particularly, the present invention relates to a developing process in which in the reproduction of multiple fine lines, a high-quality image can be formed without shortening the life of a developing device or a developer while preventing occurrence of so-called front end lacking or rear end lacking and keeping the width of each line uniform.
  • a two-component developer comprising a magnetic carrier and a toner is widely used in commercial electrophotographic copying machines.
  • a magnetic brush of this developer is formed on a developing sleeve having magnetic poles arranged in the interior thereof, and this magnetic brush is brought into sliding contact with a photosensitive material having the charged image.
  • Japanese Unexamined Patent Publication No. 59-172660 discloses a process in which a two-component developer comprising a ferrite carrier and an electroscopic toner is used and the photosensitive drum/developing sleeve peripheral speed ratio and the angle of the main pole in the developing sleeve are set within specific ranges, whereby an image having a high density and an excellent gradation can be obtained. Furthermore, Japanese Unexamined Patent Publication No.
  • 61-118767 teaches that in the development using a two-component developer, by setting the surface voltage, the distance D-S (the distance between the photosensitive drum and the developing sleeve) and the electric resistance value of the magnetic carrier, a uniform image having a high quality can be obtained.
  • PD developer packing ratio
  • Each of the former two proposals defines the characteristics of the developer and the developing conditions, independently, but the practical developing operation is not comprehensively grasped. Since the characteristics of the developer and carrier are defined under static conditions but not defined under practical dynamic conditions, a good applicability to the practical development in a copying machine is not attained.
  • the above proposal made by the present inventors is significant in the finding that an image having a high quality can be obtained by setting the frequency (k) defined by the product of the contact number of the carrier per unit area of the photosensitive material (n, number per mm2) and the developing length (L), in the practical contact state between the magnetic carrier and the surface of the photosensitive material, within a specific range.
  • the earing length of the magnetic brush should be considerably reduced, which results in occurrence of another new problem.
  • the earing length of the magnetic brush is thus reduced, a considerably large stress is imposed on the developing sleeve or the brush-forming developer, which results in shortening of the life of the developing device or the developer. Furthermore, if the earing length of the brush is reduced, when the peripheral speed of the developing sleeve is kept constant, the developer delivery speed per unit time is reduced and hence, the image density is degraded. In order to overcome this defect, means causing degradation of the image quality, such as increase of the earing length of the brush or increase of the distance D-S, should be adopted. Therefore the image quality is inevitably sacrificed.
  • US-A-4018187 discloses a developing process in which toner is transferred from a magnetic brush comprising the toner and the magnetic carrier material on to a developing sleeve on a photosensitive drum by sliding contact between the brush and the sleeve.
  • the sleeve has axial grooves about its circumference and periodic variations in the thickness of the developing material on the sleeve resulting from these grooves.
  • Pitch, groove width and groove depth lie in the range of 15-25, 2-3 and 1-2 carrier diameters respectively, with a carrier diameter lying in the range of 100-400 microns.
  • Another object of the present invention is to provide a developing process which avoids shortening the life of the developing device or the developer.
  • a developing process having an excellent reproducibility which comprises forming a magnetic brush of a two-component developer comprising a magnetic carrier and a toner on a developing sleeve and bringing the magnetic brush into sliding contact with a photosensitive material having a charged image to form a toner image on the photosensitive material; wherein the developing sleeve has a plurality of axially extending grooves formed in the circumferential direction; wherein in advance of the sliding contact with the photosensitive material, developer sleeve portions having a high pack density of the developer are formed in the grooves and developer sleeve portions having a low pack density of the developer are formed at parts of the sleeve other than the grooves; characterized in that the depth of the grooves is 0.2 to 1.0 mm; in that the pitch of the grooves is 1.5 to 8 mm; in that the ratio of the width of the grooves to the width of the circumferential parts other than the grooves is in the range of from
  • n the contact number (per mm2) of the carrier per unit area of the photosensitive material, determined from a scanning electron microscope photo with respect to a collodion-fixed magnetic brush
  • Fig. 1 is a diagram illustrating the relation between the distance in the feed direction and the line density of congregated lines.
  • Fig. 2 is a diagram illustrating the relation between the contact frequency and the dispersion of the line width.
  • Fig. 3 is a side arrangement view illustrating the magnetic brush developing process.
  • Fig. 4 is a sectional view showing a grooved roll used in the present invention.
  • Fig. 5 is a diagram illustrating a method for measuring the resistivity of a carrier used in the present invention.
  • the present invention is based on the finding that if a magnetic brush of a two-component developer comprising a magnetic carrier and a toner is formed on a developing sleeve and in advance to the supply of this magnetic brush to a developing area of a photosensitive material, portions having a high pack density of the developer and portions having a low pack density of the developer are alternately formed on the developing sleeve, a proper frequency of the contact between the carrier and the photosensitive material drum can be obtained without drastically limiting the brush-cutting length or the distance D-S.
  • the problem of the life of the developer or the developing device is most serious at a brush-cutting part where the developer and the developing sleeve are most strongly rubbed with each other.
  • the carrier contact frequency (k) As the parameter having influences on the developing condition with respect to the reproducibility of fine lines or letters, there can be mentioned the carrier contact frequency (k), and as the factor having influences on this contact frequency, there can be mentioned the distance D-S and the delivery speed of the developer.
  • the delivery speed of the developer depends on the brush-cutting length and the speed of the sleeve, but since the change of the speed of the sleeve is naturally restricted, the brush-cutting length is generally changed.
  • portions having a high pack density and portions having a low pack density are alternately formed in the magnetic brush before the supply to the developing area, the supply of the developer to the developing area can be performed smoothly and sufficiently, rendering it possible to form a high-density image. Furthermore, there can be attained an advantage that the contact friction of the toner-loading carrier is maintained within an optimum range and the reproducibility of fine lines or letters is surprisingly improved.
  • the contact frequency (k, number/mm) having important influences on the reproducibility of fine lines or letters is defined by the above-mentioned formula (1), and according to the present invention, the contact frequency can be set within a range of 100 to 700, especially 100 to 300, on the average and in the development of congregated fine lines, a copied image having a high quality can be obtained while keeping the width of each line uniform and preventing occurrence of front end lacking or rear end lacking.
  • Fig. 1 illustrating top end lacking or rear end lacking caused in the development of congregated fine lines
  • the distance in the delivery direction of the fine lines is plotted on the abscissa and the reflection image density of a copied image of congregated fine lines, determined by a micro-densitometer, is plotted on the ordinate, and the relation between the above distance and the reflection image density is illustrated.
  • curve (i) shows the case where the width of each line is uniform and top end lacking or rear end lacking is not caused
  • curve (ii) shows the case where top end lacking is conspicuous
  • curve (iii) shows the case where rear end lacking is conspicuous.
  • Fig. 2 is a graph on which there is plotted the relation between the contact frequency (k) and the dispersion ( ⁇ ) of the line width, observed when three developers differing in the characteristics are used and developing conditions are variously changed to change the contact frequency (k) of the carrier. From the results shown in Fig. 2, it is clear that if the developer and the developing conditions are selected so that the contact frequency (k) is maintained within the above-mentioned range, the dispersion of the line width can be maintained at almost 100%. Generally speaking, if the contact frequency of the carrier (developer) is reduced, top end lacking (rear end thickening) appears, and if the contact frequency is increased, rear end lacking (top end thickening) becomes conspicuous. In contrast, by controlling the contact frequency within a specific range, appearance of these defects can be controlled. The tendencies shown in Fig. 2 are similarly observed when the contact frequency is changed by changing other developing conditions instead of the characteristics of the developer.
  • the contact frequency (k) of the carrier is represented by the product of the number n of contacts of the carrier per unit area of the photosensitive material and the developing length L, and since the developing length L is naturally determined within a certain range if a developing device is decided, the freedom of the developing length L is small, and therefore, the contact number n of the carrier is preferably adjusted.
  • Main factors having influences on the contact frequency n of the carrier are the properties of the developer, especially the magnetic carrier, and furthermore, there can be mentioned the distance dD-S between the developing sleeve and the photosensitive drum, and the pack density of the developer.
  • the frequency n becomes small, and in contrast, if dD-S becomes small, the value n becomes large. If dD-S is kept constant, the value n depends on the pack density of the developer and the characteristics, especially the saturation magnetization, of the developer, especially the magnetic carrier. If the pack density or the saturation magnetization increases, the value n becomes large, and if these values decrease, the value n becomes small.
  • the value of the contact frequency of the carrier can be set within a range of from 100 to 700, especially from 100 to 300, on the average, and in the development of congregated fine lines, the width of each line can be kept uniform and a copied image having a high quality can be obtained while preventing occurrence of front edge lacking or rear end lacking.
  • the carrier contact frequency (k) of portions having a high pack density be at least 500 and the carrier contact frequency (k) of portions having a low pack density be lower than 400 and that the former carrier contact frequency (k) be larger by at least 200 than the latter carrier contact frequency (k).
  • the characteristic value (m H/f) defined by the formula (3) is set within a range of 7,000 to 15,000, especially from 9,000 to 13,000, at the development of congregated fine lines, a copied image having a high quality can be obtained at a high density while keeping the width of each line uniform and preventing occurrence of top end lacking or rear end lacking.
  • the dispersion of the line width can be maintained almost at a level of 100% while attaining an image density of at least 1.3. Namely, if the value m ⁇ H/f exceeds the above range, the reproducibility of a line image is reduced, and rear end lacking (top end thickening) is caused and the image density is generally degraded. If the value m ⁇ H/f is below the above range, top end lacking (rear end thickening) is caused, and the image density is reduced and troubles such as carrier dragging are brought about.
  • the numerator m ⁇ H/f is a value having a relation to the centripetal force acting on the carrier
  • the denomonator f is a value having a relation to the centrifugal force acting on the carrier. Accordingly, the ratio of these two values is a dimensionless number having a relation to the balance between the centripetal force and the centrifugal force.
  • the centripetal force is relatively small and since the carrier contacts strongly a latent image, the influence of dynamic scraping on a toner image is reduced and an image having a high density can be obtained.
  • the freedom of the carrier is large, neutralization and diffusion of counter charges are enhanced. For these reasons, it is considered that the reproducibility of fine lines is improved by a high electric field owing to an edge effect.
  • a magnet roll 11 having many magnetic poles N and S is contained in a developing sleeve 12 composed of a nonmagnetic material such as aluminum.
  • a photosensitive drum 15 comprising a substrate 13 and an electrophotographic photosensitive layer 14 formed thereon is arranged separately by a minute distance dD-S from the developing sleeve 12.
  • the developing sleeve 12 and the photosensitive drum 15 are rotatably supported on a machine frame (not shown) and are driven so that the moving directions (indicated by arrows) at the nip position are the same (the revolution directions are reverse to each other).
  • the developing sleeve 12 is arranged at an opening of a developing device 16.
  • a mixing stirrer 17 for a two-component developer (a mixture of a toner and a magnetic carrier) 18 is arranged in the interior of the developing device 16, and a toner supply mechanism 20 for supplying a toner is disposed above the mixing stirrer 17.
  • the two-component developer 18 is mixed by the stirrer 17 to frictionally charge the toner, and the developer is supplied to the developing sleeve 12 to form a magnetic brush on the surface thereof.
  • the earing length of the magnetic brush 21 is regulated by a brush-cutting mechanism 22, and the magnetic brush 21 is delivered to the nip position to the electrophotosensitive layer 14, that is, to a developing area 23, to develop an electrostatic latent image on the photosensitive layer 14 with the toner 19 and form a visible image.
  • portions having a high pack density and portions having a low pack density are formed in the magnetic brush 21.
  • the coarse-dense ratio between portions having a lowest pack density and portions having a highest pack density is in the range of from 1/1.1 to 1/2.5, preferably from 1/1.2 to 1/2, especially preferably from 1/1.3 to 1/1.8.
  • a developing sleeve having many grooves 24 extending in the axial direction, which are arranged in the circumferential direction, is used as the developing sleeve 21, and portions 25 having a high pack density of the developer are formed in the grooves 24 and portions 27 having a low pack density of the developer are formed at circumferential parts 26, other than the grooves 24, of the sleeve.
  • the flux density is high at grooves 24 of the developing sleeve 21 and therefore, the earing length of the brush is large and the pack density of the developer is high.
  • the flux density is low, and therefore, the earing length of the developer is small and the pack density of the developer is low.
  • the pitch P of the grooves 24 (the pitch of the circumferential parts 26 other than the grooves) should be such that along the above-mentioned developing length L, the unit latent image has at least one contact with the developer 25 having a high pack density on the groove 24 and at least one contact with the developer 27 having a low pack density on the circumferential part 26. It is generally preferred that the pitch P be from 1.5 to 8 mm, especially 2 to 5 mm.
  • the ratio between the width (l1) of the groove 24 and the width (l2) of the circumferential part 26 other than the groove is preferably in a range of from 1/3 to 3/1.
  • the depth of the groove 24 is such as giving a substantial difference of the pack density in the developer.
  • the depth of the groove 24 be 0.2 to 1.0 mm, especially 0.2 to 0.5 mm.
  • the shape of the groove 24 is not particularly critical. In general, there can be adopted a V-figured shape, a U-figured shape, a semicircular shape, a semi-ellipsoidal shape, a trapezoidal shape, a sine shape, a cycloidal shape and combinations of two or more of these shapes.
  • the circumferential part other than the groove may be a circumferential face or a plane. It is preferred that the groove be smoothly connected to the other part through a face of curvature, and it is preferred that the curvature radius (R) of this connecting part be 0.1 to 1.0 mm.
  • concavities and convexities of the magnetic brush are formed on larger concavities and convexities formed by the magnets arranged in the magnetic brush, but in the drawings, these larger concavities and convexities are omitted for facilitating the understanding of the function of the groove 24.
  • the carrier contact frequency (k) represented by the formula (1) is set within the above-mentioned range.
  • the flux density H of the magnetic pole located at the developing area, the saturation magnetization m of the magnetic carrier and the revolution frequency f of the developing sleeve are set so that the requirement represented by the formula (3) is satisfied.
  • the requirement of the formula (3) is satisfied and the carrier contact frequency (k) of the formula (1) is set within the above-mentioned range. This setting is accomplished, for example, in the following manner, though the following description by no means limits the scope of the present invention.
  • the saturation magnetization of the magnetic carrier is small, the ration m ⁇ H/f is reduced and the number of contacts of the carrier per unit area of the photosensitive material is reduced, and accordingly, the contact frequency (k) tends to lower. In the reverse case, a reverse tendency is observed.
  • the saturation magnetization of the carrier be 40 to 65 emu/g, especially 45 to 56 emu/g.
  • Ferrite carriers satisfying the above requirements, especially spherical ferrite carriers, are preferably used as the magnetic carrier. It is preferred that the particle size of the ferrite carrier be 20 to 140 ⁇ m, especially 50 to 100 ⁇ m.
  • sintered ferrite particles composed of at least one member selected from the group consisting of zinc iron oxide (ZnFe2O4), Yttrium iron oxide (Y3Fe5O12), cadmium iron oxide (CdFe2O4), gadolinium iron oxide (Gd3Fe5O12), copper iron oxide (CuFe2O4), lead iron oxide (PbFe12O19), nickel iron oxide (NiFe2O4), neodium iron oxide (NdFeO3), barium iron oxide (BaFe12O19), magnesium iron oxide (MgFe2O4), manganes iron oxide (MnFe2O4) and lanthanum iron oxide (LaFeO3).
  • ZnFe2O4 zinc iron oxide
  • Y3Fe5O12 Yttrium iron oxide
  • CdFe2O4 cadmium iron oxide
  • Gd3Fe5O12 gadolinium iron oxide
  • CuFe2O4 copper iron oxide
  • soft ferrites containing at least one member, preferably at least two members, selected from the group consisting of Cu, Zn, Mg, Mn and Ni, for example, a copper/zinc/magnesium ferrite, can be used. If these ferrites, those satisfying the above requirement are used.
  • the electric resistance of the ferrite carrier depends not only on the chemical composition thereof, but also on the particulate structure and preparation process thereof and the kind and thickness of the coating. It is preferred that the volume resistivity of the ferrite carrier be 1 x 1010 to 5 x 1011 ⁇ -cm, especially 4 x 1010 to 1 x 1011 ⁇ -cm.
  • the toner used in the present invention is prepared by incorporating a coloring agent, a charge-controlling agent and, optionally, known toner additives into a fixing resin binder. It is preferred that the volume resistivity, determined by the method described below, of the toner used in the present invention be 1 x 108 to 3 x 109 ⁇ -cm, especially 2 x 108 to 8 x 108 ⁇ -cm, and that the dielectric constant of the toner be 2.5 to 4.5, especially 3.0 to 4.0.
  • the fixing binder resin for the toner, the coloring agent, the charge-controlling agent and other toner additives are selected and combined so that the above-mentioned characteristics can be obtained.
  • a styrene resin, an acrylic resin and a styreneacrylic-copolymer resin are generally used as the fixing binder resin.
  • styrene type monomer constituting these resins there can be used monomers represented by the following formula: wherein R1 represents a hydrogen atom, a lower alkyl group (having up to 4 carbon atoms) or a halogen atom, and R2 represents a substituent such as a lower alkyl group or a halogen atom, such as styrene, vinylyoluene, ⁇ -methylstyrene, ⁇ -chlorostyrene and vinylxylene, and vinylnaphthalene.
  • R1 represents a hydrogen atom, a lower alkyl group (having up to 4 carbon atoms) or a halogen atom
  • R2 represents a substituent such as a lower alkyl group or a halogen atom, such as styrene, vinylyoluene, ⁇ -methylstyrene, ⁇ -chlorostyrene and vinylxylene, and vinylnaphthalene.
  • acrylic monomer there can be mentioned monomer represented by the following formula: wherein R3 represents a hydrogen atom or a lower alkyl group, and R4 represents a hydrogen atom or a substituted or unsubstituted alkyl group having up to 18 carbon atoms, such as ethyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate 2-ethylhexyl methacrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, aminoethyl (meth)acrylate, acrylic acid and methacrylic acid.
  • the acrylic monomer there can be used other ethylenically unsaturated carboxylic acids and anhydrides thereof, such as maleic anhydride, fumaric acid, maleic acid, crotonic acid and intaconic acid.
  • a styrene-acrylic copolymer resin is one of preferred resin binder, and the weight ratio A/B of the styrene type monomer (A) to the acrylic monomer (B)is preferably from 50/50 to 90/10, especially preferably from 60/40 to 85/15.
  • the acid value of the resin used is 0 to 25. From the viewpoint of the fixing property, it is preferred that the resin should have a glass transition temperature (Tg) of 50 to 65°C.
  • the coloring agent to be incorporated into the binder resin there can be used at least one member selected from the group consisting of inorganic and organic pigments and dyes, for example, carbon blacks such as furnace black and channel black, iron blacks such as triiron tetroxide, rutile titanium dioxide, anatase titanium dioxide, Phthalocyanine Blue, Phthalocyanine Green, cadmium yellow, molybdenum orange, Pyrazolone Red and Fast Violet B.
  • carbon blacks such as furnace black and channel black
  • iron blacks such as triiron tetroxide
  • rutile titanium dioxide such as furnace black and channel black
  • rutile titanium dioxide anatase titanium dioxide
  • Phthalocyanine Blue Phthalocyanine Green
  • cadmium yellow molybdenum orange
  • Pyrazolone Red and Fast Violet B for example, carbon blacks such as furnace black and channel black, iron blacks such as triiron tetroxide, rutile titanium dioxide, anatase titanium dioxide, Phthalo
  • charge-controlling agents can be used.
  • oil-soluble dyes such as Nogrosine Base (CI 50415), Oil Black (CI 20150) and Spilon Black, 1:1 or 2:1 type metal complex dyes, and metal salts of naphthonic acid, fatty acid soaps and resin acid soaps.
  • the particle size of toner particles is preferably such that the volume-based median diameter measured by a Coulter counter is 8 to 14 ⁇ m, especially 10 to 12 ⁇ m.
  • the particulate shape may be an indeterminate shape formed by melt kneading and pulverization, or a spherical shape formed by dispersion or suspension polymerization.
  • the carrier and the toner are used at a mixing weight ration of from 99/1 to 85/15, especially from 98/2 to 95/5, though the preferred mixing ratio is changed to some extent according to the physical properties of the toner and the magnetic carrier.
  • the resistivity of the developer as a whole be 5 x 109 to 5 x 1010 ⁇ -cm, especially 1 x 1010 to 4 x 1010 ⁇ -cm.
  • the carrier contact number per unit area of the photosensitive material be 100 to 300 per mm2, especially 100 to 200 per mm2.
  • the developing length L represented by the above formula (2) has relations to both of the contact frequency k and the image density.
  • the nip width (Nip), the peripheral speed (VS) of the developing sleeve and the peripheral speed (Vs) of the drum are set so that the developing length L is 4 to 35 mm, especially 4 to 20 mm.
  • the developing nip width (Nip) is preferably 1 to 15 mm, especially preferably 2 to 8 mm.
  • the distance dD-S between the developing sleeve and the photosensitive layer has an important influence on the value n, and it is preferred that dD-S be 0.5 to 3.0 mm, especially 0.7 to 1.7 mm.
  • magnetic poles having a relatively small flux density are dispersed in the developing sleeve, so far as carrier dragging is not caused.
  • magnetic poles having a flux density of 400 to 1500 Gauss, especially 550 to 900 Gauss are preferably used.
  • a relatively large revolution speed of the developing sleeve is effective, and a revolution speed of the developing sleeve is effective, and a revolution number of 1.50 to 5.00 per second is preferably adopted, though the preferred revolution number depends to some extend on the sleeve diameter.
  • photosensitive material all of photosensitive materials used heretofore for the electrophotography, such as a selenium photosensitive material, an amorphous silicon photosensitive material, a zinc oxide photosensitive material, a cadmium selenide photosensitive material, a cadmium sulfide photosensitive material, and various organic photosensitive materials, can be used.
  • the bias voltage to be applied between the developing sleeve and the conductive substrate of the photosensitive material, as the other developing condition, is preferably such that the average intensity of the electric field is 100 to 1000 V/mm, especially 125 to 500 V/mn.
  • the resistivity and diectric constant of the toner used in the present invention are measured by using a parallel plate electrode type measuring device having an electrode area of 2.27 cm2 and an electrode spacing of 0.5 mm, packing a sample toner at a space ratio 25% and applying an alternating current voltage having peaks of +1 V and -1 V.
  • the resistivity of the carrier used in the present invention is measured by using a measuring device shown in Fig. 5 according to a method described below.
  • a carrier 33 is introduced into a developing device 32 equipped with a stirrer roller 31 to support the carrier 33 on a sleeve 34, and the thickness of the carrier layer 33 is adjusted to a predetermined value by an earing-regulating member 35 and is delivered in this state.
  • a detecting part 38 having a predetermined surface area is attached to a micrometer 37 arranged as the electrode spacing-adjusting means along an imaginary line 36 on the surface of a photosensitive material confronting the sleeve 34 separately therefrom by a predetermined distance.
  • an alternating current voltage having a predetermined frequency is applied to the sleeve 34 and a detection signal y from the detection part 38 is supplied to a parallel circuit comprising a dummy and an oscillogram 39, and wave pattern data on the oscillogram 39 are read by reading means 40 and the resistivity is computed at a computing unit 41.
  • reference numeral 42 represents a cleaning blade as the cleaning means for removing the carrier 33 left on the sleeve 34.
  • the distance between the sleeve 34 and the detecting part 38, that is, the electrode spacing d, is adjusted to 1.2 mm
  • the surface area of the detecting part 38, that is the electrode area S is set at 0.785 cm2
  • an alternating current voltage having a frequency of 50 Hz is applied.
  • the thickness of the layer of the carrier 33 supported on the sleeve 34 can be adjusted by the earing-regulating member 35 so that the pack ration of the carrier is about 15 to about 50%.
  • a magnetic brush of a two-component developer comprising a magnetic carrier and a toner on a developing sleeve and forming on the developing sleeve, alternately in the circumferential direction, and in advance of the supply of the magnetic brush to a developing area of a photosensitive material
  • portions having a high pack density of the developer and portions having a low pack density of the developer a proper frequency of contacts between the carrier and drum can be obtained without drastic limitation of the earing length of the magnetic brush or the distance D-S, and an image having a high quality and a high density can be obtained.
  • the reproducibility of Chinese characters is excellent and a high reproducibility is attained when a copy is reproduced from a copy.
  • the occurrence of front end lacking or rear end lacking can be prevented in the reproduction of multiple fine lines while keeping the width of each line uniform, and an image having a high density and a high quality can be obtained.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Magnetic Brush Developing In Electrophotography (AREA)
  • Dry Development In Electrophotography (AREA)

Claims (2)

  1. Ein Entwicklungsprozeß mit hervorragender Reproduzierbarkeit, der umfaßt Bildung einer Magnetbürste (21) aus einem einen magnetischen Träger und einen Toner umfassenden Zwei-Komponenten-Entwickler (18) auf einer einen magnetischen Pol enthaltenden Entwicklungshülse (12) und In-Gleitkontakt-Bringen der Magnetbürste mit einem lichtempfindlichem Material (14), das ein Ladungsbild aufweist, zur Bildung eines Tonerbilds auf dem lichtempfindlichen Material; wobei die Entwicklungshülse eine Vielzahl in Umfangsrichtung gebildeter sich axial erstreckender Furchen (24) aufweist; wobei vor dem Gleitkontakt mit dem lichtempfindlichen Material Entwicklungshülsenbereiche (27) mit hoher Packungsdichte des Entwicklers in den Furchen gebildet werden und Entwicklungshülsenbereiche (27) mit niedriger Packungsdichte des Entwicklers auf den von den Furchen verschiedenen Bereichen (26) der Hülse gebildet werden; dadurch charakterisiert, daß die Tiefe der Furchen 0.2 bis 1.0 mm beträgt; daß der Abstand der Furchen 1.5 bis 8 mm beträgt; daß das Verhältnis der Furchenbreite zu der Breite der von den Furchen verschiedenen Umfangsbereiche im Bereich von 1/3 bis 3/1 liegt; daß der Gleitkontakt zwischen der Magnetbürste und dem lichtempfindlichen Material so kontrolliert wird, daß die mittlere Frequenz (k), definiert durch die unten angegebene Formel, 100 bis 700 beträgt: K = L . n
    Figure imgb0011
     worin n die Kontaktzahl (pro mm²) des Trägers pro Flächeneinheit des lichtempfindlichen Materials darstellt, bestimmt aus einem Raster-Elektronenmikroskop-Photo einer Kollodium-fixierten Magnetbürste, und L die durch die folgende Formel definierte Entwicklungslänge darstellt: L = Nip Vd ( VS - Vd )
    Figure imgb0012
     worin Nip die Berührungslinienbreite (mm) des Entwicklers auf der Oberfläche des lichtempfindlichen Materials darstellt, VS die Bewegungsgeschwindigkeit (mm/sec) der Entwicklungshülse darstellt, und Vd die Bewegungsgeschwindigkeit (mm/sec) der Oberfläche des lichtempfindlichen Materials darstellt; und dadurch, daß die Entwicklungsbedingungen so festgesetzt sind, daß die durch die folgende Formel dargestellte Bedingung erfüllt wird: 15,000 ≧ m · H f ≧ 7,000
    Figure imgb0013
     worin f die Umdrehungszahl (pro Sekunde) der Entwicklungshülse darstellt, m die Sättigungsmagnetisierung (emu/g) des magnetischen Trägers darstellt, und H die Flußdichte (Gauss) des Magnetpols in der Entwicklungshülse darstellt.
  2. Ein Entwicklungsprozeß entsprechend Anspruch 1, worin die Trägerkontaktfrequenz der Bereiche (25) mit hoher Packungsdichte des Entwicklers mindestens 500 beträgt; worin die Trägerkontaktfrequenz (k) der Bereiche (27) mit niedriger Packungsdichte des Entwicklers niedriger ist als 400; und worin die erste Kontaktfrequenz (k) um mindestens 200 größer ist als die letztere Trägerkontaktfrequenz (k).
EP19910308055 1990-09-04 1991-09-03 Entwicklungsverfahren Expired - Lifetime EP0474460B1 (de)

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US20020078568A1 (en) * 1999-12-02 2002-06-27 Timothy M. Maggio Drawn, grooved stainless steel magnetic developer roll and process for making same
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