Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/10—Developers with toner particles characterised by carrier particles
  • G03G9/107—Developers with toner particles characterised by carrier particles having magnetic components
  • G03G9/108—Ferrite carrier, e.g. magnetite
  • G03G9/1085—Ferrite carrier, e.g. magnetite with non-ferrous metal oxide, e.g. MgO-Fe2O3
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
  • H01F1/34—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials non-metallic substances, e.g. ferrites
  • H01F1/36—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials non-metallic substances, e.g. ferrites in the form of particles
• • 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
  • G03G9/107—Developers with toner particles characterised by carrier particles having magnetic components
  • G03G9/1075—Structural characteristics of the carrier particles, e.g. shape or crystallographic structure

Definitions

• the present invention relates to a magnetic carrier powder. More particularly, the present invention relates to a magnetic carrier powder to be used for magnetic brush development.
• a magnetic carrier powder to be used for magnetic brush development there has been used an iron powder or a soft ferrite powder and it has been believed that the average particle size of the powder should preferably be from 30 to 1000 ⁇ m.
• a magnetic carrier powder which is capable of providing an image having an improved image quality such as the resolving power, graininess, black uniformity or gradation.
• the present inventors have conducted extensive researches and as a result, have found that the object can be attained by reducing the ferrite powder particlas to have an average particle size smaller than that of the conventional ferrite particles.
• the present invention has . been accomplished based on this discovery.
• the present invention provides a magnetic carrier powder composed of ferrite powder particles having a spinel structure and an average particle size of less than 30 ⁇ m.
• the magnetic carrier powder of the present invention is made of a ferrite having a spinel structure.
• the ferrite having a spinel structure there may be mentioned a so-called soft ferrite such as a 2-3 spinel or a 1-3 spinel, a magnetite (Fe 3 0 4 ) or a maghemite ( y -Fe 2 O 3 ).
• ferrites i) and ii) are particularly preferred in view of its magnetic characteristics.
• a spinel ferrite comprising at most 60 molar % of MO where M is Ni, Mn, Mg, Zn, Cu, Co or a combination thereof, as calculated as a divalent oxide, and at least 40 molar % of Fe 2 0 3 as calculated as a trivalent metal oxide.
• M is a combination of at least two kinds of metals
• their proportions may be optionally selected.
• ferrites i the following ferrites ia) and ib) are preferred.
• M is Ni, Mn, Mg, Cu, Zn or a combination thereof.
• M is a combination of at least two kinds of metals, . their proportions may be optionally selected.
• M is a combination of Ni, Mn, Mg, Cu, Zn or a combination thereof, with at most 20 atom % of Co.
• M is a combination of at least two kinds of metals selected from Ni, Mn, Mg, Cu and Zn, their proportions may be optionally selected.
• the saturation magnetization becomes extremely high, whereby the deposition of the carrier on the photosensitive material or scattering of the carrier from the magnetic brush can be minimized.
• the ferrite powder particles having the above-mentioned composition may further contain . at most 5 molar % of an oxide of Ca, Bi, Cr, Ta, Mo, Si, V, B, Pb, K, Na, or Ba.
• Such ferrite powder particles have an average particle size of less than 30 ⁇ m.
• the image quality particularly the resolving power, graininess, uniformity or gradation tends to be degraded. Further, the image quality tends to be of high contrast, which taxes the eyes of the observer.
• the average particle size should preferably be at least 5 ⁇ m. Particularly good results. are obtainable when the average particle size is from 5 to 25 ⁇ m.
• the particle size distribution is usually such that about 70% of the total particles have a particle size falling within the range of + 30% of the average particle size.
• Such ferrite particles are used as a carrier without being coated with a coating layer on the surfaces or without being dispersed in a resin. Therefore, the magnetic carrier powder of the present invention has great mechanical strength and hardly undergoes thermal degradation, whereby the degradation of its properties with time is minimum and its useful life is very long. Further, the reduction of the saturation magnetization due to the decrease of the volume occupying rate is minimum and its production is quite easy.
• the ferrite powder particles constituting the magnetic carrier powder of the present invention preferably have an electric resistance of from 10 4 to 10 14 ⁇ , more preferably from 10 5 to 10 12 n, when 100 V is applied in the following manner.
• the measurement of the electric resistance of the ferrite powder particles is conducted in the following manner in accordnace with a magnetic brush development system.
• An N-pole and a S-pole are arranged to face each other with a magnetic pole distance of 8 mm so that the surface magnetic flux density of the magnetic poles becomes 1500 Gauss and the surface area of the facing poles is 10 x 30 mm.
• a pair of flat non-magnetic electrodes are disposed in parallel to each other with an electrode distance of 8 mm.
• 200 mg of a test sample is placed and the sample is held between the electrodes by the magnetic force.
• the electric resistance is measured by an insulation resistance tester or an ampere meter.
• the image quality tends to be of high contrast.
• the saturation magnetization 0" m of the ferrite particles is preferably at least 35 emu/g, whereby the deposition of the carrier on the photosensitive material or the scattering of the carrier by repeated development operations can be minimized. In this case, better results are obtainable when the saturation magnetization ⁇ m is at least 40 emu/g.
• the magnetic carrier powder composed of such ferrite powder particles may be prepared in such a manner as disclosed in U. S. Patent No. 3,839,029, No. 3,914,181 or No. 3,926,657.
• the corresponding metal oxides are mixed.
• a solvent such as water is added and the mixture is slurried, for instance, in a ball mill.
• Other additives such as a dispersing agent and a binder may be added as the case requires.
• the slurry is granulated and dried by a spray drier.
• the granules thereby obtained are burned at a predetermined burning temperature in a predetermined burning atmosphere.
• the burning is conducted in a fluidized furnace, a rotary kiln or a tunnel furnace, whereby particles having the above-mentioned average particle size is efficiently produced.
• the particles are pulverized or dispersed to obtain a desired particles size, whereby the magnetic carrier powder of the present inention is obtained.
• the magnetic carrier powder of the present invention is mixed with a toner to obtain a developer.
• the type of the toner to be used is not critical and any toner may be used.
• the magnetic brush development system and the photosensitive material to be employed to obtain an electrostatic copy image are not critical and an electrostatic copy image can be obtained in accordance with a conventional magnetic brush development method.
• an extremely good image quality is obtainable. Namely, the resolving power, graininess, black uniformity and gradation thereby obtained are extremely good.
• the image is of soft gradation, which does not very much tax the eyes of the observer.
• composition of the ferrite powder particles or the conditions for the burning may readily be varied to optionally change the quantity of magnetism or electric resistance so that images having various image densities and gradations may readily be obtained.
• the ferrite powder particles do not have a coating layer or they are not incorporated in a resin. Therefore, the degradation of the characteristics is minimum even when they are used for a long period of time, and they have good durability and a long useful life. They are free from the reduction of the magnetic characteristics which is likely to be led when incorporated with a resin component. Further, the number of the steps for their production can be minimized and the production is easy, whereby the production costs will be low.
• Metal oxides were mixed at various ratios (calculated as a divalent metal oxide and Fe 2 0 3 ) as shown in Table 1. One part by weight of water was added to one part by weight of each mixture and mixed in a ball mill for five hours to obtain a slurry. Appropriate amounts of a dispersing agent and a binder were added.
• the slurry was granulated and dried at a temperature of at least 150°C by a spray drier.
• Each granular product was burned in a fluidized furnace at the maximum temperature as shown in Table 1 in the atmosphere also as shown in Table 1.
• A represents an air atmosphere
• N represents a nitrogen atmosphere.
• the average particle size is an average particle size of 5000 particles randomly selected under observation by an electron microscope.
• the average particle size of 20 ⁇ m indicates that the particles have a particle size within a range of from 5 to 30 ⁇ m
• the average particle size 40 11 m indicates that the particles have a particle size within a range of from 25 to 55 ⁇ m
• the average particle size of 70 ⁇ m indicates that the particles have an particle size within the range of from 40 to 100 ⁇ m.
• each powder of the ferrite powder particles was subjected to an X-ray analysis, whereby it was confirmed that each powder had a spinel structure and the metal contents corresponding to the feed composition as shown in Table 1.
• the electric resistance was obtained by measuring electric resistance of the samples of 200 mg by application of 100 V in the aforementioned manner by an insulation resistance meter.
• Each ferrite powder thus obtained was used by itself as a magnetic carrier powder. Namely, it was mixed with a commercially available two-component toner(an average particle size of 11.5 ⁇ 1.5 ⁇ m) to obtain a developer having a toner concentration of 11.5% by weight.
• the surface magnetic flux density of the magnetic roller for the magnetic brush development was 1000 Gauss; the rotational speed of the magnetic roller was 130 rpm and the rotational speed of the sleeve roller was 30 rpm. Further, the space between the magnet roller and the photosensitive material was 3.0 + 0.3 mm.
• the photosensitive material a CdS photosensitive material of binder type was used and the maximum surface electric potential was 800 V.
• the resolving power was measured by means of a test chart made by Data Quest Company.
• the image of the test chart was observed by naked eyes to evaluate the graininess.
• the evaluation was made in accordance with five ratings A to E where A represents the best and E represents the worst.
• the gradation was evaluated by observation with naked eyes. The evaluation was made by means of a grade scale comprising 13 grades and the expressed by the grade numbers (1- 13 ).
• the soft gradation was evaluated also by observation with naked eyes. In this case, the order of superiority was expressed by a number.

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Citations (11)

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• 1982
  • 1982-02-13 JP JP57021923A patent/JPS58144839A/ja active Pending
• 1983
  • 1983-02-08 AT AT83101193T patent/ATE27380T1/de not_active IP Right Cessation
  • 1983-02-08 EP EP83101193A patent/EP0086444B1/fr not_active Expired
  • 1983-02-08 DE DE8383101193T patent/DE3371725D1/de not_active Expired
  • 1983-02-11 AU AU11360/83A patent/AU557231B2/en not_active Expired
  • 1983-02-11 DK DK060983A patent/DK161047C/da not_active IP Right Cessation

Patent Citations (11)

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