JP2003533745A - Method for using hard magnetic carriers in electrographic processing - Google Patents

Abstract

SUMMARY A method is disclosed for developing an electrostatic image using a developer composition that includes a hard magnetic carrier composition that can increase development efficiency as well as reduce the amount of image carrier pickup. These methods comprise a hard magnetic carrier modified to have a specific level of resistivity, eg, about 1 × 10 ⁵ to about 1 × ^{10 10} Ωcm, and a charge to mass ratio of the carrier of greater than about 1.0 μC / g. Use particles. These carriers can increase development speed without an unacceptable amount of image carrier pickup. In some embodiments, these hard magnetic materials are doped with a polyvalent metal, ie, bulk-substituted, to adjust the resistivity, while in other embodiments, these hard magnetic materials comprise at least one multi-metal. Coated with a valent metal oxide.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION CROSS REFERENCE TO RELATED APPLICATIONS This application is incorporated by reference in its entirety into the present specification, and is hereby incorporated by reference in its entirety into this application. Claiming benefits under 35 USC § 119 (e) of 60 / 204,941. further,
The following related US patent applications, both filed on May 17, 2000
Also noted are US Application Serial No. 09 / 572,988 entitled "Magnetic Carrier Particles" and US Application Serial No. 09 / 572,989 entitled "Magnetic Carrier Particles". The entire disclosures of these are cited in the present invention.

TECHNICAL FIELD OF THE INVENTION The present invention relates to electrography, and more particularly to magnetic carrier particles and a developer for dry developing electrostatic images.

Prior Art In electrography, an electrostatic image is formed on the surface of a dielectric, typically a photoconductive recording element. Generally, the development of this image
It is carried out by contact with a two-component developer consisting of a mixture of colored resin particles known as toners and magnetically attractable particles known as carriers. The carrier particles act as a site where triboelectric charges opposite to the charges of the electrostatic image can be obtained by the collision of the non-magnetic toner particles. During contact between the electrostatic image and the developer mixture, the fairly strong electrostatic forces associated with the charged image cause (due to triboelectric forces) the toner particles to peel away from the carrier particles that were originally attached. In this way, toner particles are deposited on the electrostatic image so that the electrostatic image becomes visible.

It is common to apply a developer composition of the above kind to an electrostatic image with a magnetic applicator, also known as a magnetic brush, consisting of a cylindrical sleeve made of a non-magnetic material with a magnetic core installed inside. Are known. The core is usually composed of a plurality of parallel magnetic strips arranged around the surface of the core and alternatingly presenting magnetic fields of north and south pole orientation. These magnetic fields are spread radially through the sleeve and serve to attract the developer composition to the outer surface of the sleeve to form what is commonly referred to in the art as a "brush" or "nap." By rotating one or both of the cylindrical sleeve and the magnetic core with respect to each other, the developer is delivered to a position where it comes into contact with the electrostatic image to be developed. After the development, the carrier particles from which the toner is separated return to the above-mentioned purpose and replenish the toner.

Heretofore, carrier particles made of a soft magnetic material have been used to carry and distribute toner particles to an electrostatic image. U.S. Pat. No. 4,546,060, 4,473
, 029 and 5,376,492 teach the use of hard magnetic materials as carrier particles and devices for developing electrostatic images with such hard magnetic carrier particles. The teachings of the above patents are all incorporated herein.
In these patents, the carrier particles are at least 300 when magnetically saturated.
It is required to consist of a hard magnetic material that exhibits an Oersted coercivity and an induced magnetic moment of at least 20 EMU / gm in an applied magnetic field of 1,000 Oersteds. The terms "hard" and "soft" when referring to magnetic materials are given on page 18 of B. Dee Kriti's "Introduction to Magnetic Materials" published by Addison-Wesley Publishing Co. in 1972. Has its generally accepted meaning. These hard magnetic carrier materials are much more advanced than the use of soft magnetic carrier particles in that the development rate is significantly faster while the image remains well developed. It has been demonstrated up to 4 times the maximum speed with soft magnetic carrier particles.

In the method taught in the aforementioned patent, the developer is developed by high speed rotation of a multi-pole magnetic core within the sleeve with the developer present on the outer surface of the sleeve. It moves in the same direction as the electrostatic image. The rapid pole transition on the sleeve is mechanically resisted by the carrier due to the carrier's high coercivity. A nap of carrier particles (with toner particles present on the surface), also known as a "string" or "chain", quickly "flips" on the sleeve.
To accommodate the reversal of the magnetic field imposed by the rotating magnetic core, so that the toner on the sleeve stays in the development area in contact with or in close proximity to the electrostatic image on the photoconductor. Will move. This interaction between the developer and the charge image is referred to herein as "contacting" or "contacting" for convenience. See US Pat. No. 4,531,832 for a further description of such a process. The teachings of the above patents are also entirely incorporated herein.

The rapid pole transitions occur at a maximum of 467 times per second on the sleeve surface when the magnetic core rotates at a speed of, for example, 2,000 revolutions per minute (rpm), causing the developer to move through the development area. Makes the developer very vigorous and violent as it passes through. This vigorous operation constantly recirculates toner from the surface of the sleeve to the outside of the nap to supply toner for development. Also, this reversing action will constantly supply fresh toner particles to the image. As described in the aforementioned patents, this method provides high density, high quality images at relatively high development rates.

The aforementioned US patents encompass all hard magnetic materials having the properties described therein, but as described in US Pat. No. 3,716,630, BaF.
e ₁₂ O ₁₉ , SrFe ₁₂ O ₁₉ and a compound of the formula MO.2 in which M is barium, strontium or lead. Hard magnetic ferrites, which are compounds of barium and / or strontium, such as magnetic ferrites represented by 6Fe ₂ O ₃ , are preferred. While these hard ferrite carrier materials significantly increase the speed of development performed in electrostatographic machines, many users of such machines require higher development rates, thus further improving the carrier and development process. Is expected.

US Pat. No. 4,764,445 discloses hard magnetic ferrite carrier particles for electrostatic development applications that contain from about 1 to about 5 weight percent lanthanum.
Although the speed of development in electrographic processing with conventional hard magnetic ferrite materials, as described in this patent, is faster than methods using other techniques such as those using soft magnetic carriers, Limited by the specific resistance of various ferrite materials. The patent discloses that the addition of lanthanum to the hard magnetic ferrite crystal structure in the disclosed amount results in more conductive magnetic ferrite particles, which enhances development efficiency and / or development rate.

Furthermore, methods for producing electrically conductive carrier particles have also been proposed. For example, U.S. Pat. No. 4,855,206 discloses conducting by adding neodymium, praseodymium, samarium, europium or mixtures thereof, or a mixture of one or more of these elements and lanthanum to a hard magnetic ferrite material. It is disclosed to improve the sex. US Pat. No. 5,795,692, an electrically conductive carrier composition having a magnetic oxide core said to be coated with a layer of zinc metal which is the reaction product of zinc vapor and a magnetic oxide. Is disclosed.

Other carriers proposed for use in electrographic processing include US Pat. Nos. 4,855,205, 5,061,586, 5,104,761 and 5,
, 106,714, 5,190,841 and 5,190,842.

In US Pat. No. 5,268,249, a formula wherein M is strontium or barium and Me is a divalent transition metal selected from nickel, cobalt, copper, zinc, manganese, magnesium or iron. Single-phase W represented by MFe ₁₆ Me ₂ O ₂₇
Magnetic carrier particles having a hexagonal crystal structure are disclosed.

US Pat. No. 5,532,096 describes curing a partially hydrolyzed sol obtained from at least one alkoxide selected from the group consisting of silicon alkoxides, titanium alkoxides, aluminum alkoxides and zirconium alkoxides. Carriers whose surfaces are coated with the resulting layers are disclosed. Said carrier coated with such a layer is said to be more durable than carriers coated with conventional resin coatings such as resin coatings prepared with silicone resins, acrylic resins and styrene-acrylic resins. It is being appreciated.

While some of the aforementioned patented techniques may describe carriers with enhanced conductivity compared to conventional hard magnetic materials previously used to develop electrostatic images, carrier It is believed that the carriers deposited in the image cause imaging problems because of their very high conductivity. Although it is not clear, when the conductivity of the carrier is at a certain level, it promotes the flow of charge between the carrier and the shell on the nap, which induces charge reversal of the carrier and images the carrier particles. Electrically deposited on the substrate, hereinafter referred to as "image carrier pickup" or "I-
It is believed that it can be called "CPU". The presence of the I-CPU is color rendering (col
or rendition) and the image quality.

As will be appreciated, it is desirable to develop new carriers and / or new methods for using carriers that can be used in electrographic processes to develop electrostatic latent images. Furthermore, an electrographic method that can exhibit higher conductivity than a conventional hard magnetic material that has been used for such processing up to now, has higher development efficiency than before, and has reduced I-CPU is used. It is also desirable that a carrier that can be provided be developed.

DISCLOSURE OF THE INVENTION The above objects and advantages are realized by the present invention. In one aspect, the invention provides: (a) a rotating magnetic core having a preset magnetic field strength; (b) an external non-magnetic shell installed around the rotating magnetic core; (c) (i) charged toner particles. And (ii) about 1 × ^{10 10} to about 1 × 10 ⁵ Ωc
composed of hard magnetic carrier particles of opposite polarity, having a resistivity of m and a carrier (Q / m) above about 1 μC / g, and placed on said shell and in contact with an electrostatic image. A method for developing an electrostatic image comprising contacting the image with a development system comprising at least one magnetic brush comprising an electrographic developer composition comprising: depositing on the electrostatic image. It relates to the above method, wherein the density of the carrier is lower than about 0.01 g / in ² .

In another aspect, the invention provides: (a) a rotating magnetic core of preset magnetic field strength;
b) at least one magnetic brush comprising an outer non-magnetic shell disposed around the rotating core, and (c) an electrographic developer composition disposed on the shell and in contact with an electrostatic image. It relates to a method for developing an electrostatic image comprising contacting the images. The developer composition comprises charged toner particles and opposite polarity charged hard magnetic carrier particles, and the carrier particles are at least one multi-component of the formula M ^{n +,} where ⁿ is an integer of at least 4. It is composed of a hard magnetic material having a crystal structure substituted with a valent metal.

In a preferred embodiment, the carrier particles are of the formula PFe _12-x M _x O ₁₉ where P is selected from strontium, barium or lead and M is antimony, arsenic, germanium, hafnium, molybdenum. , Niobium, silicon, tantalum, tellurium, tin, titanium, tungsten, vanadium, zirconium, and mixtures thereof, and x is less than about 0.6. It is composed of a hard magnetic ferrite material having a single-phase hexagonal crystal structure.

In another aspect, the invention provides: (a) a rotating magnetic core of preset magnetic field strength;
b) an external non-magnetic shell placed around the rotating core, and (c) charged toner particles placed on the shell and in contact with the electrostatic image, and carrier particles of opposite polarity. A method for developing an electrostatic image comprising contacting said image with at least one magnetic brush comprising an electrographic developer composition comprising The carrier particles are (1) a core made of a hard magnetic material having an outer surface, and (2) M is at least one polyvalent metal represented by the formula M ^{n + in} which ⁿ is an integer of at least 4. It consists of a coating of metal oxide on the outer surface of the core, expressed as MO _{n / 2} . The outer surface further defines a transition zone extending from the outer surface and into the core of the hard magnetic material, and the hard magnetic material is at least represented by the formula ^{Mn +} , as described above. It has a crystal structure substituted with ions of one polyvalent metal in the transition zone.

In another aspect, the present invention provides: (a) a rotating magnetic core having a preset magnetic field strength;
b) an external non-magnetic shell placed around the rotating core, and (c) charged toner particles placed on the shell and in contact with the electrostatic image, and carrier particles of opposite polarity. A method for developing an electrostatic image comprising contacting said image with at least one magnetic brush comprising an electrographic developer composition comprising The carrier particles are single-phase hexagonal crystals represented by the formula: P _1-y La _y Fe ₁₂ O _19, where P is selected from strontium, barium or lead, and y is less than 0.1. It is composed of a hard magnetic ferrite material having a structure.

Further disclosed are carrier particles used in the development of electrostatic latent images, which consist of a hard magnetic ferrite material substituted with lanthanum as described in the preceding paragraph.

DETAILED DESCRIPTION OF THE INVENTION As described above in connection with US Pat. Nos. 4,546,060 and 4,473,029, the use of "hard" magnetic materials as carrier particles results in "soft" magnetic particles. The development speed is dramatically higher than that of carrier particles composed of. The preferred ferrite materials disclosed in these patents include those of the formula MO.I. where M is barium, strontium or lead. Barium ferrite, strontium ferrite, and lead ferrite represented by 6Fe ₂ O ₃ are included. The preferred ferrite is strontium ferrite. These materials have a single-phase hexagonal crystal structure. The speed at which the development takes place is much faster than conventional techniques, but they are limited by the resistivity of said ferrite material with the magnetic properties necessary to carry out said development method. It is generally known that the resistivity of the carrier particles has a direct effect on the development rate that can be used.

Although commonly referred to in the art as development rate, a more meaningful term is “development efficiency”. In the case of a magnetic brush development system, the percent development efficiency was 100 times the pre- and post-development potential difference of the photoreceptor in the developed image area divided by the pre-development photoreceptor and brush potential difference. Is defined as being. For example, in a charged area development configuration, the voltage on the photoreceptor film is-
If the magnetic brush is -50 volts at 250 volts, the potential difference before development is -20.
It is 0 volts. If the film voltage in the image area is reduced by 100 volts to -150 volts due to the accumulation of positively charged toner particles during development, the development efficiency is (-100 volts / -200 volts) x 100, which is 50%. Development efficiency can be obtained. It will be readily appreciated that as the efficiency of the developer material increases, the various parameters used in the electrostatographic process may change in response to changes in the efficiency. For example, as the efficiency increases, the same amount of toner can be deposited in the image area by lowering the voltage difference before development, as was done when the efficiency was low. The same is true for the exposure energy levels used to apply the electrostatic latent image to the photoreceptor film. The higher the efficiency, the higher the speed of the development step of the method, because under the same conditions more toner will accumulate in a shorter time. In this way, by improving the developing efficiency, various parameters used in the electrostatic method can be adjusted, and both energy and time are saved.

As mentioned above, the development efficiency when using a hard magnetic carrier is limited by the resistivity of the material itself. For example, the resistivity of these materials is about 1 × 10 ¹¹ Ωcm, so the efficiency that is usually obtained is about 50%. However, in order to obtain a high quality reproduction of the original image, while increasing the conductivity of the particles, they have high magnetic properties, namely a coercivity of at least about 300 Oersted when magnetically saturated, At least about 20 in an applied field of 000 oersteds
It is necessary to maintain the induced magnetic moment of EMU / gm.

Today's electrographic printing industry is faster (pages per minute-ppm)
) And high-quality development equipment. These two performance goals call for materials that have properties that oppose one another, namely developer compositions. The smaller the toner particles, the higher the image quality. Generally, a smaller toner size means a lower development efficiency (DE), thus limiting the speed of the apparatus. Adjusting hardware operating conditions such as core speed, shell speed, gap setting and toning bias gives considerable latitude for high speed / quality copying / printing, but manipulates material properties of the carrier component of the developer. You can also

Achieving an increase in development efficiency by applying a conductive carrier is limited by the image carrier pickup (I-CPU). This behavior is due to the charge reversal induced on the carrier particles in contact with the shell in the bias-affected brush. Carrier particles of opposite polarity are electrostatically attracted to the charge image on the photoconductor. In effect, these particles act as toner and deposit on the image. It is believed that conductive carriers are more susceptible to this charge reversal because the higher the conductivity, the higher the charge mobility. The carrier existing in the image area is not a problem in the case of a black and white document, but it confuses a monotonous black image with a white image, and has a strong influence on the rendering, the entire area and the density of a color document.

Without wishing to be bound by theory, it is believed that the I-CPU relies on carrier charge. In the case of a developer composition composed of carrier particles and toner particles, the charge of the carrier has the opposite polarity to the charge of the toner. For conventional non-conductive carriers,
Toner deposits on the image during development can deposit in the background areas of the image, usually in the densest areas immediately adjacent to the toned image area with the strongest fringe field. . In the case of a relatively highly conductive carrier, the developer composition causes the "toning nip", ie, the photoconductive surface (where the electrostatic latent image to be developed) and the (development), due to the aforementioned charge transfer properties. When in the electric field, in the region between the surfaces of the shell sleeve of the toning device (where the agent composition is present), charge can be transferred from the toning shell to the carrier particles. In the case of discharged area development (DAD), the bias voltage of the toning device has the same polarity as the toner, so the toning bias can charge the conductive carrier to the same polarity as the toner. If the carrier gains sufficient charge by conduction of charge from the shell in the toning nip, the carrier can actually spread to the image area on the photoconductor.

Negatively charged toner will be considered in the following description. Assuming that the toner particles and the carrier particles are electrically neutral, when the externally applied electric field (E) is 0, the charge of the carrier and the charge of the toner in the developer composition are the same as the toner concentration (TC). There is a relationship according to the following formula (1). During _{Q T / M T x TC +} Q C / M C x (1-TC) = 0 (1) formula, Q _T and Q _C, respectively, represent the toner charge and the carrier charge,
M _T and M _C represent the mass of the toner and the mass of the carrier, respectively, and x is (
Means (rather than a variable), and TC is the fractional toner concentration based on the total weight of the composition, ie toner concentration in wt% divided by 100.
Therefore, the charge-to-mass ratio (μC / g) of the initial carrier can be expressed by the following equation (2). Q _Ci / M _C = −Q _T / M _T x TC / (1-TC) (2) As the developer composition enters into the electric field of the toning nip region, the carrier becomes It is believed that the mechanism loses the initial positive charge and makes the charge more negative. Provided that the dwell time in the toning nip area is sufficient, the carrier can obtain a large enough negative charge to develop with the toner in the image area.

Although not bound by theory, the initial charge of the carrier is estimated by the equation (2). For example, as shown by the following equation (3), the charge of the carrier in the toning nip region is an exponential time. It is reasonable to assume that the dependency is followed. Q _Ct / M _C = Q _Ci / M _C x e ^-kt + Q _Cf / M _C x (1-e ^-kt ) (3) where Q _Ct / M _C is the charge of the carrier as a function of time. Mass vs. Q _Ci /
M _C is the initial charge-to-mass of the carrier, the rate constant k is 1 / ρε (unit: sec ⁻¹ ), x means multiplication (not a variable), and t is within the toning nip. Dwell time in seconds and the maximum final charge of the carrier is given by Q _Cf / M _C.

In equation (3), quantitatively, ρ is the resistivity of the developer composition, and ε is the dielectric constant of the developer composition. The developer specific resistance ρ can be measured as described in Examples 43 to 52 below. The dielectric constant ε is influenced by the volume of the developer composition occupied by the toner. When the toner particles become large, the carrier particles withdraw, and the dielectric constant of the developer composition also decreases accordingly. Due to this effect, ε∝1 / D _T ³ holds. In the above formula, D _T is the average particle size (diameter) of the toner particles.

The maximum charge-to-mass ratio Q _Cf / M _C of the carriers depends on the voltage difference between the electrostatic image on the photoconductive surface and the shell sleeve of the toning device. When the potential difference is 400 V and the carrier is "bare carrier" (without toner), Q _Cf / M _C is about -2 μC
It can be reasonably assumed to be / g. In the presence of toner, the potential difference between the shell sleeve and the photoconductive surface at the end (exit) of the toning nip region is reduced by the charge of the toner particles developing in the image. The partial development efficiency (DE) can be estimated as a part of the initial toning potential difference removed by the development of the toner and is equal to the development efficiency in% divided by 100. When the toning potential is 400 V, Q _Cf / M _C ∝-2x (1-DE) holds in μC / g unit. This equation shows that the higher the development efficiency, the smaller the potential for sending charges into the carrier, and the proportionally smaller maximum charge-to-mass ratio of the carrier. Example 43 described later
The data obtained in connection with ˜52 and Comparative Example E are used in conjunction with the model described above. The data demonstrate that the I-CPU relies on the charge the carrier gets in the toning nip region.

Furthermore, the present invention relates to materials and hardware parameters that provide an operating space for further enhancing development efficiency without increasing I-CPU. Development efficiency is improved without the need for more I-CPUs at the same time, provided the specific materials and hardware operating conditions are met.

FIG. 1 shows a typical such operating space relationship in terms of toner charge to mass (Q / m) and toner concentration (TC) for different toner particle sizes. FIG. 1, provided for purposes of illustration, shows that smaller particle toners preferably operate at lower toner concentrations and tend to exhibit higher toner charge to mass. These relationships hold for toners of any polarity.

In tabular form, in addition to the associated change in development efficiency and the implied carrier conductivity for regaining development efficiency, the relationship is shown as follows: Toner size Toner Q / m Development efficiency Required carrier conductivity ↓ ↑ ↓ ↑ In the above table, arrows indicate increase / decrease in related parameters. To prevent the expected reduction in development efficiency by using smaller toners, a carrier with higher conductivity can be used, as indicated by the upward arrow under the heading "Required carrier conductivity". It is desirable to use.

The demand for higher quality and faster systems requires smaller toner particles. Due to the miniaturization of toner particles, the development efficiency is reduced. In order to regain the developing efficiency, the conductivity of the carrier must be further increased as the size of the toner becomes smaller (in other words, the specific resistance of the carrier must be lowered).
. To be feasible, an increase in development rate must occur without a significant I-CPU.

To address the I-CPU reduction, the toner size / concentration / charge region shown in FIG. 1 is awkward and cumbersome to generalize over all expected operating ranges. . For each toner size, for example, using each of the three toner sizes shown in FIG. 1, the uniqueness necessary to maintain development efficiency in a preferred range for a limited I-CPU. A table can be prepared with a data set showing the resistance range. Another approach used in connection with Examples 43-52 below is the main merit parameter: carrier charge versus mass (Q / m) carrier (μC / g) and developer composition specific. The resistance (Ωcm) characterizes the developing performance of the developer composition.

In general, the data show that the developer with the highest I-CPU has the lowest (Q / m) calculated carrier value determined by electrical neutrality. For example, as the toner concentration increases, the toner charge decreases at a small rate, but the net (Q / m) carrier value may double or triple. The higher the net (Q / m) carriers, the more difficult it is to cause charge reversal of the carriers to the I-CPU. When the size of the toner particles becomes smaller, the I-CPU may decrease due to the increased toner Q / m, but the decrease in the toner concentration may cause the I-CPU. As a result, the (Q / m) carrier has a value greater than about 1 μC / g, preferably greater than about 2 μC / g, more preferably greater than about 3 μC / g, and most preferably about 4.0 μC. It is desirable to maintain the value larger than / g. The (Q / m) carrier parameter can be controlled by adjusting the amount of toner in the developer composition, for example, as described in Examples 43-52 below.

As described above, since the present invention seeks to maintain at least the developing efficiency when the size of the toner becomes smaller, the (Q / m) carrier is, for example, about 1 μC / g as described above. Higher values, such as higher values, should be maintained, while the conductivity of the carriers should increase proportionally. Further, in order to obtain a high quality copy with a minimum amount of I-CPU, it is preferable to maintain the carrier resistivity at a value of about 1 × ¹⁰ 10 Ωcm to about 1 × 10 ⁵ Ωcm, and about 5 × 10 ⁹ Ωcm.
More preferably a value of about 1x10 ⁶ [Omega] cm, about 5x10 ⁹ Ωcm~1x10 ⁷ Ω
Values in cm are even more preferred. When the resistivity of the carrier is selected to be within the above range, the resistivity of the developer composition is desirably about 1 × 10 ¹² Ωcm-.
It will generally be in the region of 1 × ^{10 5} Ωcm, preferably 1 × ^{10 10} Ωcm to 1 × ^{10 7} Ωcm. Since the developer composition is mostly a carrier, the resistivity of the developer is generally very similar to that of the carrier.

The electrographic process can operate at a processing speed (defined as the speed at which a dielectric surface having a charge image on its surface passes through the development area) of at least about 5 inches / second. High capacity printing presses typically range from about 110 pages per minute (PPM) to 1
It can operate at speeds of 80 PPM and above, which corresponds to speeds of about 15 to about 30 inches / second. A processing speed of about 15 to about 50 inches / second is preferred. The lower resistivity of said range, ie less than about 1 × 10 ⁷ Ωcm, ie about 1 × 1
Carriers having a resistivity of from 0 ⁷ Ωcm to about 1 × 10 ⁵ Ωcm are particularly advantageous for use in electrographic processes operating at much higher processing speeds. This is due to the fact that the higher the processing speed, the proportionately the residence time of the carrier in the toning nip region decreases. The dwell time (seconds) is defined as the width of the toning nip (inches) divided by the processing speed (inch / s). For example, if a given carrier exhibits an I-CPU that is at or near an unacceptable level, i.e., an I-CPU, when the carrier is used in a developer composition at a given rate, By increasing the processing speed, the retention time of the carrier in the toning nip area can be reduced, and the I-CPU can be reduced. Alternatively, when the processing speed is increased 10 times, for example, from 5 inches / second to 50 inches / second, it is possible to use a carrier whose specific resistance is 1/10, for example, from 1 × 10 ⁶ Ωcm to 1 × 10 ⁵ Ωcm. To be able to
Similar I-CPU performance is obtained. Similarly, by changing the shape of the toning nip region, for example, the width of the toning nip region can be reduced. this is,
This is accomplished, for example, by placing the photoconductive surface on a cylindrical drum, or by reducing the diameter of this drum if it is already on the drum. Reducing the toning nip width to 1/2 means reducing the specific resistance to the carrier to 1/2 as well.

According to the invention, such a deposition density is less than about 0.01 g / in ² in terms of carrier deposition density (as described in Examples 43-52 below). Desirably, less than about 0.001 g / in ² , preferably about 0.00.
The I-CPU can be limited such that less than 0001 g / in ² is more preferable.

In a preferred embodiment, the present invention contemplates the use of certain hard magnetic materials as carriers in electrographic processing. The carrier has a high electrical conductivity with respect to conventionally used hard magnetic materials. In one embodiment, the carrier is
It is a hard magnetic material whose conductivity is enhanced by substitution with a polyvalent metal. In another embodiment, the conductive metal oxide composition is placed on top of a core made of hard magnetic material. Both of these embodiments are described below. Hereinafter, these embodiments will be described in some detail including Examples, but the present invention is not intended to be limited to these specific embodiments. Other hard magnetic materials may be used in the practice of the present invention provided they have the requisite conductivity and (Q / m) carrier parameters, and otherwise such materials are referred to herein. It should be understood that it can be used with the appropriate operating parameters for the disclosed method.

Conductive Carriers Substituted with Polyvalent Metals The present invention is directed, in one embodiment, to an embodiment wherein n is an integer of at least 4, ie 4,
Desirable by substituting an effective amount of at least one polyvalent metal ion corresponding to the formula M ^{n +} of 5 or 6 into the crystal lattice of a hard magnetic material, preferably a hard magnetic ferrite having a hexagonal crystal structure. We are investigating the use of carriers with reduced specific resistance while maintaining their magnetic properties. Therefore, the specific resistance of the hard hexagonal ferrite carrier material can be lowered from about 1 × 10 ¹¹ Ωcm to about 1 × 10 ⁵ Ωcm, and further, the specific resistance and (Q / m) carrier influence the high magnetic properties of the ferrite material. In order to suppress the I-CPU without doing so, it is preferable to be within the range specified above.

Without wishing to be bound by theory, considering the size and charge of the cations that are substituted, the mechanism by which the resistivity of the ferrite material decreases is that Sr ²⁺ between the lattices of the sublattice or hexagonal ferrite lattice, It is believed to be due to the substitutional introduction of the polyvalent metal ions into the iron lattice of the hexagonal ferrite crystal structure, rather than by the Ba ²⁺ or Pb ²⁺ substitution. In doing so, the M ^{n +} polyvalent metal ion substituent forces charge compensation into the trivalent iron (Fe ³⁺ ) lattice, ie, the cation form of divalent iron (Fe ²⁺ ). The Fe ²⁺ / Fe ³⁺ charge pair thus generated provides a semiconductive electron path, and a ferrite composition having higher conductivity is obtained.

In a preferred embodiment, the hard magnetic ferrite material doped with M ^{n +} polyvalent metal ions is of the formula PFe _12-x M _x O ₁₉ where P is selected from strontium, barium or lead and M is , Antimony, arsenic, germanium, hafnium, molybdenum, niobium, silicon, tantalum, tellurium, tin, titanium, tungsten, vanadium, zirconium and mixtures thereof, and x is greater than about 0.6. Small, can be represented by In a particularly preferred embodiment, P is selected from either strontium or barium, and more preferably strontium in terms of cost, magnetic properties and environmental issues. M is preferably selected from silicon, zirconium, tin or titanium mainly in terms of cost and availability. The amount of polyvalent metal ion used is preferably sufficient to obtain a value of x less than about 0.3, due to concerns over I-CPU, about 0.2.
More preferably, it is sufficient to obtain a smaller value of x. When the polyvalent metal ion is used in an amount of more than 0.6, the conductivity is not significantly improved as compared with the ferrite containing a smaller amount of the polyvalent metal ion. A further advantage associated with the hard magnetic ferrites of the present invention is the relatively light doping of polyvalent metal ions into the ferrite material, by the following examples as well as the co-pending application, which is incorporated herein in its entirety. US Patent Application No. 0
As shown in 9 / 572,988, it can be seen that the development efficiency is significantly improved. Furthermore, for the preparation of such hard magnetic materials, the introduction of substitution of such metal ions into the iron lattice is advantageous in terms of processing over the introduction of substitution into the Sr ²⁺ , Ba ²⁺ or Pb ²⁺ sublattice. Is believed to be.

With respect to the amount of M ^{n +} polyvalent metal ions substitutionally introduced into the hard magnetic material, the substitution amount increases the conductivity by at least about an order of magnitude, ie the resistivity is at least about 1 × 1.
It should be sufficient to reduce O ¹ Ωcm. Preferably, in terms of the aforementioned x value, the amount of metal substituted should be sufficient to obtain an x value of from about 0.01 to about 0.6, and from about 0.02 to about 0.02. Preferably, an amount is used that is sufficient to obtain an x value of less than about 0.3, and an amount that is sufficient to obtain an x value of from about 0.03 to less than about 0.2 is used. Is more preferable. The amount of ^{Mn +} polyvalent metal ions introduced by substitution into the crystal lattice is preferably limited so that the resulting structure consists essentially of a single-phase hexagonal crystal structure. The amount of ^{Mn +} polyvalent metal ion used may vary to some extent depending on the ^{Mn +} polyvalent metal ion used to prepare the ferrite particles and the sintering conditions, but ^{Mn +} polyvalent metal ion. Can generally be added in an amount of up to about 10% by weight of the ferrite material, and an amount within this range will have high magnetic properties sufficient to bring the developer nap into tight contact with the sleeve of the developer device. Can be kept. If the amount of M ^{n +} polyvalent metal ion added exceeds the above range, a further phase may be formed in the PO / MO _{n / 2} / Fe ₂ O ₃ phase diagram. A small amount of such additional phase, ie preferably 5 based on the total weight of the carrier.
Its presence in an amount less than 0% by weight does not adversely affect the beneficial properties of the substituted hexagonal crystal structure as described above.

The preparation of hard magnetic materials in a broad sense, specifically hard hexagonal crystal structure ferrites (Ba, Sr or Pb), is well documented in the literature. In preparing the hard magnetic particles, US Pat. Nos. 3,716,630, 4,623,603 and 4,0
42,518 (the teachings of which are incorporated herein by reference); European Patent Application No. 0086445; "Spray Drying" Kay Masters, Leonard.
Hilbucks London, pages 502-509 and "Ferromagnetic Materials," Volume 3, E.
Any suitable method may be used, such as the method described by P. Wolfers, North Holland Publishers, Amsterdam, New York, Oxford, page 315 et seq. (The teachings of which are also incorporated herein). .

The hard magnetic material containing at least one polyvalent metal ion substituted and introduced into the crystal lattice as described above has a structure in which the polyvalent metal ion of the polyvalent metal ion is doped so that the metal ion is doped into the crystal structure. It can be prepared as described in the previous paragraph by adding the source to the formulation. For example, the hard magnetic material to be prepared is about 1
~ 8 wt.% SrC for a hard magnetic strontium ferrite containing about 5 wt.% Polyvalent metal ions in the form of its oxide or oxide precursor.
O ₃ , about 1 to 5 parts of the source of the metal ions and 85 to 90 parts of Fe ₂ O ₃ are mixed with the dispersant polymer, gum arabic and the solvent water to form a slurry. The slurry is spray dried to remove solvent and the resulting raw beads are calcined in an oxidizing environment at about 1100 ° C to about 1300 ° C to form the desired hard magnetic material described above. . Then, by deagglomerating the obtained hard magnetic material, component carrier bead particles having a particle size generally required as carrier particles, that is, a particle size of less than about 100 μm, preferably about 3 to 65 μm. Is obtained. The resulting carrier particles are then permanently magnetized by being exposed to an applied magnetic field of sufficient intensity to induce a permanent magnetic hysteresis behavior.

In addition to introducing the polyvalent metal ions into the hard magnetic material crystal structure, it is possible for the present inventors to introduce a controlled amount of lanthanum into the hard magnetic ferrite material, and This results in the I-CP as shown in Examples 5-10 below.
It was also discovered that a carrier with good U performance can be obtained. Such a carrier comprises a hard magnetic ferrite material having a single-phase hexagonal crystal structure and has the formula P _1-y La _y Fe ₁₂ O ₁₉ where P is selected from strontium, barium or lead and y is Can be represented by less than 0.1.

Such carriers are generally source compounds for lanthanum metal ions according to the methods described in US Pat. No. 4,764,445, the aforementioned metal substitution methods and related teachings are incorporated herein by reference. Can be prepared by using.

For the substituted ferrite carrier, the resistivity of the carrier is about 1 × 1.
0 ¹⁰ Ωcm to about 1x10 ⁵ Ωcm, more preferably about 5x10 ⁹ Ωcm to about 1x.
10 ⁶ Ωcm, and even more preferably about 5 × 10 ⁹ Ωcm to about 1 × 10 ⁷ Ωcm.
It can be lowered to a value within the range. The reason why the specific resistance range is preferable is that
This is because the specific resistance value within this range can suppress the I-CPU or at least reduce the amount thereof without affecting the high magnetic properties of the hard magnetic material. Furthermore, it is preferable that the (Q / m) carrier of the carrier particles in the developer composition is larger than 1 μC / g as described above. Therefore, the carrier particles of the present invention, in such an embodiment, as illustrated by the examples below,
High development efficiencies (and thereby faster electrographic imaging processes) can be provided without producing a significant, or at least undesirable, amount of I-CPU.

Conductive Carrier Coated With Metal Oxide Coating Composition The present invention further contemplates, in another aspect, the use of a carrier consisting of a core made of hard magnetic material, preferably hard magnetic ferrite. A conductive metal oxide composition is deposited on the surface of the core, and the conductive metal oxide composition reacts with the hard magnetic material to maintain desired magnetic properties of the hard magnetic material. Can reduce the total specific resistance of the carrier. The composition is deposited on the core in a continuous or discontinuous state.

In a preferred embodiment, the outer surface of the hard magnetic core defines a transition zone extending into the interior of the magnetic core. That is, the transition zone is a region within the hard magnetic material near the outer surface of the core. For example, if the core is a spherical or nearly spherical particle, the transition zone can be recognized as a shell whose outer surface is mated with the outer surface of the particle. Within the transition zone, the crystal structure of the hard magnetic material preferably comprises a gradient of metal ions corresponding to the formula ^{Mn +} . In the above formula, M and n are as defined above for the metal oxide composition deposited on the core, and metal ions have been introduced by substitution into the crystal lattice of the hard magnetic material. What is meant by "gradient" is that the concentration of metal ions is highest near the outer surface of the core and decreases in the crystal lattice towards the center of the core. Without wishing to be bound by theory, considering the size and charge of the M ^{n +} cations disclosed herein, the polyvalent metal ion may be hexagonal instead of Sr ²⁺ , Ba ²⁺ or Pb ^2+. It is believed that the specific resistance of the hard magnetic ferrite can be lowered by substituting it into the iron lattice of the ferrite crystal structure.
In doing so, the aforementioned M ^{n +} polyvalent metal ion substitution imposes charge compensation on the trivalent iron (Fe ³⁺ ) lattice, ie, the cation form of divalent iron (Fe ²⁺ ). The Fe ²⁺ / Fe ³⁺ charge pair thus generated provides a semiconductive electron path, and a ferrite composition having higher conductivity is obtained. As a result, the conductive metal oxide compositions of the present invention generally deposit firmly on the core particles and do not easily flake off when used in electrographic processing.

Accordingly, by depositing the metal oxide composition on the surface of the core as described above, the resistivity of the hard magnetic carrier material is reduced from about 1 × 10 ¹¹ Ωcm to at least about one digit, ie, about 1 × ^{10 10} Ωcm. Can be lowered. The term "conducting" as used in connection with the carrier and / or its metal oxide composition means that the composition is provided on the surface of the core so that the composition is not deposited on the surface. It means that the specific resistance of the carrier can be reduced by at least about one digit as described above, based on the carrier made of magnetic material.

[0054] resistivity of the carrier is preferably lowered to a value within the range of about 1x10 ¹⁰ ~ about 1x10 ⁵ [Omega] cm, more preferably from about 5x10 ⁹ Ωcm~ about 1x10 ⁶ [Omega] cm, about 5x10 ⁹ Ωcm~ about 1x10 ⁷ Ωcm is even more preferable.
The reason why the specific resistance range is preferable is that the specific resistance value within the range can suppress or at least reduce the amount of I-CPU without affecting the high magnetic properties of the hard magnetic material. Is. Furthermore, it is preferable that the (Q / m) carrier of the carrier particles in the developer composition is larger than 1 μC / g as described above. Thus, the carrier particles of the present invention, in such embodiments, have high development efficiencies (without it) without enormous, or at least unfavorable, amounts of I-CPU, as exemplified by the examples below. It is possible to realize the speedup of the electrograph imaging process).

Using a qualitative method for measuring I-CPU performance of developers using magnetic carriers, it should be developed separately from the brush naps in the development area, as described in the examples below. The amount of carrier particles deposited on the electrostatic image can be explained. In many cases, the electrically conductive carriers of the present invention, when used in electrographic processing, show no clear image deposits, or weak to mild deposits (qualitative I-described in the examples. 2 or less at a level based on CPU measurements), or preferably no visual evidence of deposition on the photoconductor (level 0 in the qualitative test). By measuring the carrier deposition density (as described above) I
-A quantitative method of determining the CPU is described in detail below in connection with Examples 43-52.

In a preferred embodiment, the carrier has a core made of hard magnetic ferrite material with a single-phase hexagonal crystal structure. A metal oxide composition represented by the formula MO _{n / 2} is preferably deposited on the outer surface of the core. M in the above formula is n
Is at least one polyvalent metal represented by M ^{n +} , which is an integer of at least 4. n is preferably 4, 5 or 6, more preferably 4 or 5, and most preferably 4.

In a preferred embodiment, the metal of the conductive metal oxide composition is a metal capable of forming a polyvalent metal ion in the crystal structure of the hard magnetic material such that n in the above formula is 4 or more. It is an element. Examples of such metals include antimony, arsenic,
Germanium, hafnium, molybdenum, niobium, silicon, tantalum, tellurium,
Mention may be made of tin, titanium, tungsten, vanadium, zirconium and mixtures thereof. Preferably the metal is selected from silicon, zirconium, tin, titanium or mixtures thereof. Since these metals are more readily available than other metals, the raw material costs are much lower. Examples of metal oxides that can be used include GeO ₂ , ZrO ₂ , TiO ₂ , SnO ₂ and mixtures thereof.

The amount of the metal oxide composition used is such that the conductive carrier is obtained, that is, the specific resistance is based on the carrier made of a hard magnetic material on which the metal oxide is not deposited on the surface as described above. The amount should be at least about ¹ × 10 ¹ Ωcm reduction. The metal oxide composition is about 0.01 to about the total weight of the carrier.
It is preferably used in an amount of about 3% by weight. The metal oxide composition is preferably present in an amount of about 0.02 to about 2% by weight, based on the total weight of the carrier, and about 0.
． More preferably, it is present in an amount of 025 to about 1% by weight.

Optionally, the conductive metal oxide composition on the core does not contribute substantially to the conductivity enhancement of the carrier, but charge controllability and / or coating (deposition).
It may contain at least one other metal oxide, such as a glassy boron oxide (B ₂ O ₃ ) co-deposit that can provide integrity, but said other metal oxide is Be an oxide of an alkali metal such as lithium oxide, potassium oxide, sodium oxide or a mixture thereof that can enhance conductivity even when coated on a carrier without a co-deposit that is an oxide of a valent metal. preferable.

When other metal oxides are used in the conductive metal oxide composition, they are generally present in an amount of 0.01 to about 1% by weight, based on the total weight of the carrier.

Magnetic ferrite, hard hexagonal crystal structure ferrite (Ba, Sr or Pb)
The preparation of, has been well documented in the literature. To prepare the ferrite particles,
U.S. Pat. Nos. 3,716,630, 4,623,603 and 4,042,5
18 (the teachings of which are incorporated herein by reference); European Patent Application No. 0
0864445; "Spray Drying" Kay Masters, Leonard Hilbucks, London, pages 502-509 and "Ferromagnetic Materials," Volume 3, E.P.
Any suitable method may be used, such as those described by Wolfers Edit, North Holland Publishers, Amsterdam, New York, Oxford, page 315 et seq. (The teachings of which are also incorporated herein).

In general, the conductive carriers of the present invention can be prepared by solution coating and firing techniques. First, a granular hard magnetic material is prepared. The particulate hard magnetic material can be prepared by any method known in the art, such as the methods described in the aforementioned prior art references. The particulate material serves as the core for the carrier of the present invention. The particulate core material is then mixed with a solvent and a solution of at least one metal oxide precursor compound. The mixture is then heated, preferably with stirring, if necessary, to remove the solvent and form a coating of the at least one metal oxide precursor compound on the surface of the core particles. After forming the coating of the metal oxide precursor compound on the core particles, the coated particles at a temperature sufficient to form the desired metal oxide composition on the outer surface of the core particles. Is fired in an oxidizing atmosphere.

When mixing the particulate core material with the metal oxide precursor solution, the amount of solution used should be sufficient to at least wet the surface of the particulate ferrite material. Excessive amounts of this solution are undesirable, as the solvent in the solution must be removed in a subsequent processing step.

A solution of at least one metal oxide precursor compound can be prepared by dissolving at least one metal oxide precursor compound in a suitable solvent. In the method of preparation described herein, the solvent should be a solvent that evaporates readily, as the solvent is removed prior to the formation of the conductive metal oxide composition. Suitable solvents include water and other common organic solvents such as methanol, ethanol, isopropanol, toluene, hexane and the like. Preferred solvents are water, methanol and isopropanol. By the term "solution" it is believed that colloidal dispersions of metal oxide precursor compounds may also be used.

The compound used in the metal oxide precursor solution is a compound that produces a desired metal oxide when baked at a temperature described below in an oxidizing atmosphere. The compound is preferably a compound that can be easily dissolved in the solvent to form the metal. In general, metal salts, carbonates, halides and nitrates of organic acids are soluble and / or dispersible in common solvents and give good results.

The amount of at least one metal oxide precursor compound used in the coating solution is such that, upon firing, the weight as described above for the proportion of metal oxide composition in the finally obtained conductive carrier particles. The amount is selected such that a metal oxide composition in the range of% is obtained. Generally, it is sufficient if the amount of metal oxide precursor compound in the solution is from about 0.01 to about 5% by weight.

After mixing the ferrite core particles with the coating solution, excess solvent was removed by applying heat to the resulting mixture, and the dried or nearly dried particles were coated with a metal oxide precursor compound. Is obtained. This process is
Performing by gently heating the mixture at about 100 to about 150 ° C. for a time sufficient to remove the solvent without significantly converting the metal oxide precursor compound to its oxide form. it can. The temperature used in the drying step can be lowered by lowering the pressure used in the drying step.

After removal of the solvent, the coated core particles are calcined, ie, heated, in an oxidizing atmosphere at a temperature sufficient to substantially convert the metal oxide precursor compound to its oxide form. Bake. Generally, this step can be carried out in a high temperature furnace. The temperature at which the precursor compound pyrolyzes and converts to its oxide form depends on the precursor selected, but it is generally desirable that the firing temperature be at least about 250 ° C. The firing temperature is about 1,300 ° C. at the highest. As shown in the examples below and in FIG. 3, depending on the hard magnetic material selected, there is generally a firing temperature at which the resistivity of the resulting carrier drops significantly as the firing temperature increases. Without wishing to be bound by theory, it is believed that such a significant reduction in resistivity is the result of a vigorous reaction between the metal oxide and the magnetic material of the core. In the reaction, by introducing the metal oxide into the magnetic material,
A conductive region is formed within the transition zone previously described herein. Due to concerns about the I-CPU, it is preferable to select a firing temperature such that the resistivity of the finally obtained carrier is within the above-mentioned preferable range.

After firing, the conductive carrier obtained is deaggregated to give a carrier in the final form, ie a volume average particle size of less than 100 μm, preferably about 3 to 65 μm.
More preferably, beads of about 5 to about 20 μm are obtained. The resulting carrier particles are then magnetized by exposure to an applied magnetic field of sufficient intensity to cause magnetic hysteresis behavior.

Hard magnetic ferrites coated as described above are described in the examples below and co-pending US patent application Ser. No. 09/572, previously incorporated herein by reference.
As illustrated in the Example 989, the development efficiency is significantly improved.

The present invention involves the use of two types of carrier particles. One of these carriers is doped with at least one polyvalent metal ion as described above and / or has a conductive metal oxide composition on its surface, and has the required coercivity as described above. And a binder-free granular hard magnetic material exhibiting an induced magnetic moment. This type of carrier is preferred.

The other is heterogeneous and with a binder (also called matrix),
It consists of a composite of magnetic materials that exhibits the required coercivity and induced magnetic moment.
The hard magnetic material as described herein above is dispersed in the binder as discrete particles. However, as is well known to those skilled in the art, the binders used include vinyl resins such as polystyrene, polyester resins, nylon resins and polyolefin resins such as those described in US Pat. No. 5,256,513. Inherently highly resistant, as is the case with polymeric binders. Therefore, the decrease in conductivity of the magnetic material may be offset by the resistivity of the selected binder. It should be understood that the resistivity of these composite carriers must be comparable to the binder-free carrier to realize the aforementioned development efficiency-related advantages. It may be desirable to promote electrical conduction between the ferrite particles by adding conductive carbon black to the binder.

It is preferred that each piece of the magnetic ferrite material be relatively uniform in size and have a sufficiently smaller diameter than the composite carrier particles to be produced. Typically, the average diameter of the magnetic material should not exceed about 20% of the average particle size of the carrier particles.
Conveniently, a much lower average particle size ratio of magnetic component to carrier can be used. Excellent results are obtained when the average particle size of the magnetic particles is about 5 μm to 0.05 μm. Not only does the degree of subdivision not make unnecessary changes to the magnetic properties, and that the amount and nature of the binder selected produces sufficient strength, but the resulting carrier particles also have other desirable mechanical and electrical properties. Particles smaller than the above range may be used so long as they provide specific properties.

The concentration of magnetic material in the composite can vary widely. The amount of finely divided magnetic material used in the composite carrier may be from about 20 to about 90% by weight, so long as the resistivity of the particles is that of a ferrite particle as described above.

The induced moment of the composite carrier in the applied field of 1,000 Oersteds depends on the concentration of magnetic material in the particles. Therefore, it is understood that the induced moment of the magnetic material must be sufficiently greater than about 20 EMU / gm to compensate for the effect of dilution of the magnetic material in the binder on such induced moment. Will. For example, if the concentration of magnetic material in the composite particles is about 50% by weight, the induced magnetic moment in the applied field of 1,000 oersteds of the magnetic material achieves a minimum level of 20 EMU / gm for the composite particles. It will be appreciated that in order to do so, it must be at least about 40 EMU / gm.

The binder material used with the segmented magnetic material is selected to provide the required mechanical and electrical properties. The binder material is (
1) has good adhesion to magnetic materials, (2) promotes the formation of strong and smooth surface particles, and (3) preferably when the toner particles used in combination with the binder material are mixed with a carrier. The toner particles should be sufficiently different in terms of triboelectric properties so that the polarity and magnitude of the electrostatic charge between the toner and carrier is appropriate.

The matrix may be organic or inorganic, and examples thereof include a matrix made of glass, metal, silicone resin and the like. Organic materials such as natural or synthetic polymeric resins or mixtures of such resins with suitable mechanical properties are preferably used. Examples of suitable monomers (which can be used to prepare the resins thus used) include vinyl monomers such as alkyl acrylates and alkyl methacrylates, styrene and substituted styrenes, and basic monomers such as vinyl pyridine. . Copolymers prepared with these and other vinyl monomers such as acidic monomers such as acrylic acid and methacrylic acid can be used. Conveniently, such copolymers may contain minor amounts of multifunctional monomers such as divinylbenzene, glycol dimethacrylate, triallyl citrate and the like. It is also possible to use condensation polymers such as polyesters, polyamides or polycarbonates.

In the preparation of the composite carrier particles according to the present invention, heat is used to soften the thermoplastic material, the thermosetting material is cured, and evaporation drying is used to remove the liquid vehicle, molding, Forming carrier particles using both pressure or heat and pressure in injection molding, extrusion, cutting or shearing, reducing the size of the carrier material to a suitable particle size, for example by milling in a ball mill, And, the particles can be classified by a shifting operation.

According to one preparation method, a magnetic material in powder form is dispersed in a solution of a binder resin. Then, the solvent is volatilized, and the obtained solid mass is pulverized and subdivided by sieving, whereby carrier particles having an appropriate size can be produced. According to another method, emulsion or suspension polymerization is used to produce uniform carrier particles with excellent smoothness and service life.

The coercive force of a magnetic material is defined as the remanence of the induced magnetic moment.
ce) value means the minimum external magnetic force required to reduce to zero. The coercivity remains constant not only in the external field, but also after the material has been magnetically saturated, ie after the material has been permanently magnetized. Various devices and methods can be used to measure the coercive force of the carrier particles of the present invention. For the present invention, the coercivity of powdered samples is measured using a Lakeshore Model 7300 Vibratory Sample Magnetometer available from Lakeshore Cliotronics, Inc., Westerville, Ohio. The magnetic ferrite powder is mixed with a non-magnetic polymer powder (90 wt% magnetic powder, 10 wt% polymer). The mixture is placed in a capillary tube heated to a temperature above the melting point of the polymer and allowed to cool to room temperature. Next, the loaded capillary tube is placed in the sample holder of the magnetometer, and the external field (unit: Oersted) vs. induced magnetism (unit: EMU /
Draw a graph of the magnetic hysteresis loop of gm). During this measurement, the sample is exposed to an external field of 0 to ± 8,000 Oersted.

Carrier particles may be coated in order to properly charge the toner particles of the developer. This forms a dry mixture of a hard magnetic material and a small amount of a powdered resin, such as about 0.05 to about 3.0 wt% of the resin, based on the total weight of the magnetic material and the resin, and the mixture. It is performed by heating to melt the resin.
Such low resin concentration forms a thin or discontinuous layer of resin on the particles of magnetic material.

Since the presence of the metal oxide coating is aimed at improving the conductivity of the carrier particles, the resin layer on the carrier particles is such that most of the particles can remain suitably conductive. Must be thin enough. This resin layer is because the exposed carrier locations on each particle allow for conductive contact.
It is preferably discontinuous.

Various resin materials can be used for coating the hard magnetic carrier particles. For example, U.S. Pat. Nos. 3,795,617, 3,795,6
18 and 4,076,857. The entire teachings of these patents are incorporated herein. The choice of resin depends on the triboelectric relationship with the toner of interest. When used with toners that are desired to be positively charged, preferred resins for coating the carrier include poly (tetrafluoroethylene), poly (vinylidene fluoride) and poly (vinylidene fluoride-co-tetrafluoroethylene). ) Such as fluorocarbon polymers. When used with a toner that is desired to be negatively charged, the preferred resins for coating the carrier are not only silicone resins, but also
There may be mentioned a mixture of resins such as a mixture of poly (vinylidene fluoride) and polymethylmethacrylate. Various polymers suitable for such coatings are also described in US Pat. No. 5,512,403. The entire teachings of said patent are incorporated herein by reference.

The developer is formed by mixing carrier particles and toner particles in a suitable concentration. A high-concentration toner can be used for the developer of the present invention.
Therefore, the developer of the present invention preferably contains about 70 to 99% by weight of carrier and about 30 to 1% by weight of toner, based on the total weight of the developer, and about 7 to 7.
More preferably, it will contain from 5 to 99% by weight of carrier and from about 25 to 1% by weight of toner.

The toner component of the present invention may be a powdered resin which may be colored. Normal,
It is a special mixture of a resin, a colorant or dye or pigment, and any other desired additives known in the art, pigment flash (pigment presscake and resins known in the art). ) Or pigment-resin masterbatch. If a low opacity developed image is desired, no colorant need be added. However, it is more common to add a colorant, which in principle
Any of the materials described in Index I, Volume II and Second Edition may be used. Carbon black is particularly useful. The amount of colorant can vary widely, for example from about 3 to about 20% by weight of the toner component. A plurality of colorants may be used in combination.

The colorant and other additives are dispersed in the resin by heating and milling the mixture of resin and colorant. The mass is cooled, ground into smaller masses and then milled. The resulting toner particles have a particle size of about 0.5 to about 25 μm and a volume average particle size of about 1 to about 16 μm, preferably less than 11 μm, more preferably less than 8 μm, even more preferably less than 6 μm. The average particle size ratio of carrier to toner particles is preferably in the range of about 15: 1 to about 1: 1. However, 50
High carrier to toner average particle size ratios such as: 1 are useful.

The toner resin can be selected from a variety of materials including, for example, natural and synthetic resins and modified natural resins as described in US Pat. No. 4,076,857. Particularly useful are US Pat. Nos. 3,938,992 and 3,941.
, 898. Particularly useful are crosslinked or non-crosslinked copolymers of styrene or lower alkyl styrene with acrylic monomers such as alkyl acrylates or alkyl methacrylates. In addition, condensation polymers such as polyesters are also useful. A number of polymers suitable for use as toner resins are introduced in US Pat. No. 4,833,060. US Patent No. 3
, 938,992, 3,941,898, 4,076,857 and 4,
The entire teachings of 833,060 are incorporated herein by reference.

The shape of the toner may be irregular as in the case of crushed toner, or may be spherical. Spherical toners are obtained by spray drying a solution of toner resin in a solvent. Alternatively, spherical particles can be used with Jay Ugerstad for 197
US Pat. No. 4,833,060, issued September 5, 1997, and the polymer bead swelling method described in US Pat. No. 4,833,060, previously incorporated. It can be prepared by turbid polymerization.

Further, the toner may contain a small amount of other components such as a charge control agent and an antiblocking agent, which are well known in the art. Particularly useful charge control agents are described in US Pat. Nos. 3,893,935 and 4,206,064 and British Patent 1,501,065. The entire teachings of these patents are incorporated herein. Research Disclosure, No. Two
Quaternary ammonium salt charge agents such as those described in 1030, 210, October 1981 (Industry Opportunities, Homewell, Havant, Hampshire, PO91EF, UK) are also useful.

In one embodiment of the method of the present invention, the electrostatic image is contacted with a rotating magnetic core, an external non-magnetic shell, and a magnetic brush developing device comprising a dry developer as described above. The electrostatic image thus developed may be formed by a variety of methods such as image-wise photoconductive decay of the photoreceptor, or application of an image-wise charge image on the surface of the dielectric recording element. it can. When an optical receptor is used, as in a high speed electrophotographic copying machine, halftone screening can be used to shape the electrostatic image, but by the combination of screening and development according to the method of the invention. , A high quality image with high Dmax and excellent tonal range is produced. An exemplary screening method, including using an optical receptor with an integrated halftone screen, is described in US Pat. No. 4,385,823.

A developer comprising magnetic carrier particles according to the present invention is disclosed in US Pat. No. 4,473,02.
When used in a device such as the device described in US Pat. No. 4,473,473.
, A traditional magnetic ferrite material, such as that used in US Pat. No. 029, shows a dramatic improvement in development efficiency compared to when operated under the same voltage difference between the magnetic brush and the photoconductive film. be able to. For example, when comparing the performance of a traditional strontium ferrite carrier particle, which is approximately the same in all respects except for the presence of the aforementioned polyvalent metal ions, with the carrier particles of the present invention, all other development conditions remain the same. , Development efficiency can be increased by at least about 50%, preferably up to 100% or even 200%. As described above, by using the carrier particles according to the present invention, the operating conditions such as the voltage difference, the exposure energy used for forming the electrostatic latent image and the developing speed are set in order to obtain the optimum conditions and the results.
Both can be diverse.

[0092]

【Example】

  The invention is explained in more detail by the following examples.

Specific Embodiments of the Invention In the following examples, all "parts" and "%" mean "parts by weight" and "% by weight" respectively, and the temperature is It shall be indicated in Celsius (° C).

Examples 1 to 4 Preparation and Use of Ge ⁴⁺ Substituted Strontium Ferrite Carrier A precursor mixture of strontium ferrite magnetic carrier is first prepared by the following method. A slurry of Fe ₂ O ₃ and SrCO ₃ (molar ratio: 5.7: 1) was added to 301.17 g of Fe ₂ O ₃ powder (α-phase-KFH-NA grade, manufactured by Toda Kogyo Co., Ltd. of Japan), 48. Prepared by charging 83 g of SrCO ₃ powder (Type D from Chemical Products, Cartersville, GA) and 350 g of aqueous binder solution into a 1,250 ml glass bottle. The binder solution is a sufficient amount of a gum arabic gum (Eastman Kodak Company, Rochester, NY) to obtain a solution containing 3.94 weight percent gum arabic and 0.33 weight percent ammonium polymethacrylate. Made acacia powder)
And ammonium polymethacrylate (DAXAD32 from WR Grace Co., Lexington, Mass.) Are each weighed and added. Then, the pH of the obtained slurry was adjusted to about 8-9 with concentrated NH ₄ OH.
Adjust to the value of.

For Examples 1-4, the strontium ferrite precursor mixture is doped with Ge ⁴⁺ ions using germanium oxide powder (from Eagle Pitcher Industries, Inc., Quapo, Okla.) As a source. However, in this case, Ge ⁴⁺ ions are not deliberately introduced into the crystal lattice by the stoichiometry of iron or strontium. In each example, the germanium oxide powder source weighed as shown in Table I is added as a dry powder to 100 parts of the strontium ferrite precursor mixture and the two are mixed together. Table I also shows the value of x in the formula PFe _12-x M _x O ₁₉ .

To this slurry is added 300 ml of 1 mm zirconium silicate media beads and the resulting mixture is milled on a roll mill for at least 24 hours. The resulting crushed material is loaded into a rotary atomizer rotating at a speed of at least 16,000 revolutions per minute (rpm) in a portable, laboratory spray dryer from Nero Atomizer, Copenhagen, Denmark. The spray dryer produces a dry product (“raw beads”) that is collected by a cyclone.

The firing of the raw beads is performed by allowing the raw beads to stand on an alumina tray and introducing them into a high-temperature box-shaped furnace. The temperature of the furnace is 50
The binder component of the raw beads is burned out by increasing the temperature to 0 ° C. at a rate of 7 ° C./min and maintaining the temperature at 500 ° C. for 1 hour. Then, the temperature of the furnace is raised to the final firing temperature at a rate of 5 ° C / min. The furnace at 1,250 ℃
After maintaining at the calcination temperature of 10 h for 10 h, it is allowed to cool to room temperature untouched (ie by “free fall”). The calcined charge is deagglomerated with a mortar and pestle and sieved with a 200 mesh screen to obtain Ge ⁴⁺ polyvalent metal ion doped strontium ferrite carrier particles.

[0098]   The measured resistivity values of each of the resulting carriers are shown in Table I below.

The electrostatic resistivity is measured using a cylindrical electrical cell. The cell used has a cylindrical chamber inside which is coaxial with the centerline of the cell. The cell is composed of two parts, namely, an upper part in which electrode pistons are concentrically arranged inside and arranged in parallel with the center line of the cylinder, and a lower part having an electrode base part. By connecting the upper part and the lower part, a cylindrical shape of the entire cell is formed. A circular bottom surface of the piston in the upper portion and a circular base portion of the lower portion define opposite ends of a cylindrical chamber in the cell. The piston is a small lever that extends radially outward from the cylinder,
It can be driven and extended downwards along the centerline of the cell. A small electrode is installed at the center inside the lower base of the cell. The piston in the top is itself an electrode and forms an electrode of opposite polarity. To use the cell, about 2.00 g of the carrier under test is placed on the cylindrical metal base in contact with the electrode. The upper part of the cell is placed on the lower electrode base and aligned. When the release lever is lowered, the upper piston electrode lowers and comes into contact with the powder. The depth of the powder is adjusted by physically rotating the top of the cell so that it is spaced 0.04 inches apart. Average specific resistance (
Ωcm) was determined by measuring the current flowing in the cell with a Keithley Model 616 ammeter (Kathley, Inc., Cleveland, Ohio) for three applied voltages in the range 10-250 volts. To be The resistivity is calculated using Ohm's law.

In each example, the resulting doped carrier was used to prepare substantially as described in US Pat. No. 4,833,060, the entire teachings of which are incorporated herein. A two-component developer using the prepared yellow polyester toner is prepared. The toner is 93% by weight of the total weight of the toner, a polyester resin binder (Kao P manufactured by Kao, Japan), and 1.0% by weight of an aluminum composite of di-t-butylsalicylic acid as a charge control agent (Japan. Orient Chemical's Bontron E-88) and 7.0 wt% yellow pigment 180 (BAS, Germany).
(Manufactured by Company F). The average particle diameter of the prepared toner measured by a Coulter counter is 7.1 μm. The developer consists of each carrier and toner concentration (
It is prepared by admixing with the above-mentioned toner having a TC) of about 6% by weight (the measured TC is given in Table I). In each example, the charge to mass ratio (Q / m) was measured and the measurements obtained are also shown in Table I.

The charge-to-mass ratio (Q / m) of the toner is measured in units of microcoulombs / gram (μC / g) in a “MECCA” device described below after a “motion period” described below.

During the first exercise period, 4-7 grams of developer was dosed into a 4-drum glass screw cap bottle, the bottle was capped, and about 2 Hertz (Hz), maximum amplitude about 11c.
The developer is vibrated violently by operating a "wrist movement type" robot shaker for 2 minutes under the condition of m to vibrate the developer, thereby charging triboelectricity.
The resulting charge is generally referred to in the table below as the "fresh" charge.

In addition, the developer is subjected to an additional 2 minutes and / or 10 minutes of motion on the rotating core magnetic brush. Fixing the bottle withdrawn from the robot shaker to the brush while the magnetic core is rotating at 2,000 rpm approximates the actual use of the developer in electrographic processing. In this way, the developer is moved as if it were directly on the magnetic brush, but since it is in the bottle, there is no reduction. The toner charge level after this movement is shown in the table below as "2 minute BB" or "10 minute BB".
Is shown. "

The toner Q / m ratio is ME which is composed of two electrode plates arranged in parallel with a space.
As measured by a CCA device, the two electrode plates apply both an electric field and a magnetic field to a sample of developer. Due to the combined effect of its electric and magnetic fields,
The two components, carrier particles and toner particles, are separated. A sample of 0.100 g of developer mixture is placed on the lower metal plate. Next, the sample is subjected to a magnetic field of 60 Hz and a potential of 2,000 V for 30 seconds between the two electrode plates to stir the developer. Toner particles are emitted from the carrier particles under the influence of the combination of the electric field and the magnetic field, and the emitted toner particles are attracted to the upper electrode plate and are deposited thereon, but the magnetic carrier particles are lower. It remains on the electrode plate. An electrometer measures the accumulated charge of the toner deposited on the upper electrode plate. The toner Q / m ratio, expressed in microcoulombs / gram (μC / g), is calculated by dividing the accumulated charge by the mass of deposited toner collected from the upper electrode plate.

[0105]

[Table 1]

As can be seen from Table I, the electrostatic specific resistances of Examples 1 to 4 are lowered by about two digits.

The performance of toners prepared with the carriers prepared in Examples 1-4 was as described in US Pat. No. 4,473,029, the entire teachings of which are incorporated herein by reference. Investigate using a different electrographic device. The device is equipped with two electrostatic probes, one in front of the magnetic brush development device and one behind the device to develop an electrostatic image on an organic photoconductive film. The voltage on the photoconductive film before and after is measured. The photoconductor voltage is set at -550 volts and the magnetic brush is maintained at -490 volts so that the total steady state deviation is +60.
It becomes a bolt. Place the shell and photoconductor with 0.020 inch spacing,
Rotate the core clockwise at a speed of 1,000 rpm and rotate the shell counterclockwise 1
Rotate at a speed of 5 rpm. In the charging device, the photoconductor is 2 inches /
The photoconductor is set to move at a speed of 2 seconds, and the photoconductor is set to move at a speed of 5 inches / second in the developing area. The nap density is 0.24 g / in ² . The carrier particles and the toner used are those prepared in Examples 1 to 4 above. The voltage of the photoconductor after charging and after exposure to a step wedge density target is measured by the first probe after development, and the voltage of the photoconductor film in the developed area is measured by the second probe. Development efficiency in the high density region is calculated by comparing the pre-exposure and post-exposure voltages of the photoconductor. After development, the development efficiency is calculated for each of the examples shown in Table II by measuring the voltage on the photoconductive film in the development area.

Development efficiency is defined as the ratio of the potential difference of a photoreceptor in a developed image area before and after development with toner, divided by the potential difference of the photoreceptor before development. For example, in a discharge area development configuration where negatively charged toner is used, if the photoconductor film voltage is -100V and the magnetic brush is -500V, the pre-development potential difference is 400V. If negative toner particles accumulate during development and the voltage of the film in the image area drops by -200V to -300V, then the development efficiency is 200V / 400V, or 50%. Relative development efficiency (Rel DE)
Is a development prepared in substantially the same manner, except that the development efficiency measured for any of the examples was not treated such that Ge ⁴⁺ ions were substitutionally introduced into the strontium ferrite carrier for the carrier used. Calculated as the ratio of agent to development efficiency.

The criteria for I-CPU is a qualitative measurement of the extent to which carriers are trapped, or deposited, on the photoconductor, by visually inspecting high density areas of the step wedge image to determine the density of the deposited carrier particles. Is obtained by comparing. The numerical scale is assigned according to the degree of I-CPU deposition: 0-none, 1-very weak, 2-weak, 3-weak to moderate, 4-moderate, 5-moderate to high, 6-high, 7
-It is very expensive.

[0110]

[Table 2]

Comparative Example A In Comparative Example A, the electrostatic resistivity, triboelectric properties, development efficiency and I-CPU of a commercially available SrFe ₁₂ O ₁₉ hard ferrite carrier are substantially the same as those described in Examples 1 to 4 above. Was measured according to the same method. The commercial carrier is SrFe ₁₂ O ₁₉ hard ferrite manufactured by Powdertech, Inc. of Valparaiso, Indiana. Using this carrier, a developer containing the same toner as described in Examples 1 to 4 was prepared. The measured specific resistance of the carrier was 2.0 × ^{10 10} Ωcm, the toner Q / m was −71.1 μC / g, and the TC was 6.3% by weight.

Developers prepared with the commercial SrFe ₁₂ O ₁₉ hard ferrite carrier described above were tested for electrographic performance according to substantially the same procedure as described in Examples 1-4. All conditions, including toner concentration and charge, were essentially the same. The value of the relative development efficiency based on the definition of the development efficiency described in Examples 1 to 4 was 1.00. The I-CPU level is 0, which indicates no clear visible carrier build-up on the photoconductor.

Examples 5-10-Preparation of La ³⁺ Substituted Strontium Ferrite Magnetic Carriers In Examples 5-10, the procedure of Examples 1-4 was substantially repeated except for the following points. The strontium ferrite precursor mixture prepared as described in Example _{1~4, La 2 (CO 3)} 3 powder (Powder Tech Corp. in Indianapolis of Valparaiso) using as a source the La ³ Doped with ⁺ . In each example, dry powder weighted to give ay value of the formula P _1-y La _y Fe ₁₂ O ₁₉ shown in Table III was added to the precursor mixture prepared in Examples 1-4, Mix both. After crushing and spray drying as in Examples 1 to 4, the resulting mixture was allowed to stand in an alumina tray and fired in a high temperature box furnace at 1,255 ° C. at that temperature.
After holding for 0 hour, the furnace is allowed to cool to obtain La ³⁺ -doped strontium ferrite carriers.

In Examples 1-8, the resulting carrier was further coated with 1.5 parts of silicone resin per 100 parts of carrier. This coating was obtained by curing a silicone resin on carrier particles as follows. First, 20 ml of this methyltrimethoxysilane (98% Aldrich, Milwaukee, WI), 2.2 ml dimethoxydimethylsilane (95% Aldrich, Milwaukee, WI)
It was made by mixing 1 ml glacial acetic acid and 8 ml distilled water in a glass container. The mixture was stirred for 1 hour and then left overnight to complete the hydrolysis. After standing overnight, a 1.53 g portion of the solution was mixed with 15 ml of methanol and 50 g of the carrier in a suitable container and the resulting mixture was placed under an infrared heating lamp to remove excess. The free solvent is removed to yield substantially dry coated carrier particles. Then, the carrier particles are left to stand on a metal tray and heated in an oven at 230 ° C. for 2.5 hours to cure the silicone resin. The carrier thus coated is then removed from the oven and allowed to cool to room temperature.

[0115]   The resistivity measured for each of the resulting carriers is shown in Table III below.

In each example, the resulting doped carriers were used to prepare two-component developers using conventionally prepared powder cyan polyester toner. This toner contains 93 parts of polyester resin (Fineton 382 resin), 5 parts of copper phthalocyanine pigment, and 2 parts of 3,5-di-t-butylsalicylic acid charge control agent (Bontron E-88 manufactured by Orient Chemical Co., Ltd.). Was made using. The average particle size of the toner mixture after fine pulverization and classification was 8.0 μm as measured by a Coulter counter.

Developers were prepared by mixing each carrier with the above toner with a toner concentration (TC) of about 10 wt% (actual TC values shown in Table I). In each example, the charge-to-mass ratio (Q / m) of the toner was measured. The values obtained are also shown in Table III.

[0118]

[Table 3]

As can be seen from Table III, the electrostatic resistivity is reduced by about two orders of magnitude over the range of La ³⁺ added in Examples 5-10. When the amount of La ³⁺ ions is small, especially when y is smaller than 0.1, the amount of I-CPU is the I-CPU obtained when the amount of La ³⁺ doped into the ferrite crystal structure is large. Less than the amount of CPU. Silicone resin coating, compared to the developer prepared without resin coating,
It did not significantly change the performance of the developer.

Comparative Examples B and C For Comparative Examples B and C, the strontium ferrite material was mixed with a lanthanum source compound in an amount sufficient to give a y value of the formula P _{1 -y} La _y Fe ₁₂ O ₁₉ of 0.2. The procedure of Examples 5-10 was substantially repeated except that it was doped. The carrier of Comparative Example B was not coated with silicone resin, while the carrier of Comparative Example C was coated with silicone resin substantially as described in Examples 8-10. The electrostatic resistivity, triboelectric properties, development efficiency and I-CPU of La ³⁺ doped SrFe ₁₂ O ₁₉ hard ferrite carriers were measured substantially according to the same methods as described in Examples 1-4 above. did. Using this carrier, Examples 5-10
A developer containing the same toner as described in 1. was prepared. For comparison, the specific resistance,
Triboelectric properties, development efficiency and I-CPU were measured and the results are shown in Table III.

The obtained results show that with this amount of La ³⁺ , the relative development efficiency (R
el DE) is high, but the amount of I-CPU is large. 2 and 3 show the relationship between resistivity, Rel DE and I-CPU. A graph of the data of Examples 5-7 and Comparative Example B is shown in FIG. 2, where the large diamonds are Rel De data points and the small diamonds are I-CPU data points. FIG. 3 shows the data obtained for Examples 8-10 and Comparative Example C, with the meanings of the large and small diamonds being the same as in FIG. As can be seen, the carrier resistivity is about 1.0 × 10 ⁸
Below that, the value of Rel De increases significantly, but unfavorably, the value of I-CPU also increases at a considerable rate. Thus, FIGS. 2 and 3 reduce the carrier resistivity by introducing La ³⁺ into the ferrite material such that the resistivity is from about 1.0 × 10 ⁸ to less than the resistivity of the undoped ferrite material. And the Rel DE value (compared to undoped carriers) is significantly higher, I-
It also indicates that the amount of CPU can be obtained within a permissible range.

Examples 11-13-Preparation and Use of Strontium Ferrite Carrier Coated with GeO _{2 In} Examples 11-13, a commercially available SrFe ₁₂ O ₁₉ hard ferrite carrier was used with 1 part GeO ₂ (per 100 parts carrier). 0. to the total weight of the final carrier particles.
99% by weight) and varying the temperature at which this carrier is fired shows the effect of firing temperature on the resistivity and performance of the resulting carrier.

The coated carrier particles were prepared using SrFe ₁₂ O ₁₉ hard magnetic ferrite particles from Powdertech, Inc. of Valparaiso, Indiana. The slurry of ferrite particles was prepared by casting 400 g of SrFe ₁₂ O ₁₉ ferrite particles in a glass dish together with 66 ml of a solution of ammonium germanate and 122 ml of methanol. The ammonium germanate solution contained 120 g of GeO ₂ powder (Chemical grade-purity 99.999%) manufactured by Eagle Pitcher Co., Ltd., located in Cuapo, Oklahoma.
It was prepared by adding 2,000 ml of distilled water in an appropriately sized glass flask with stirring and then adding 33 ml of concentrated NH ₄ OH solution dropwise to the vessel to dissolve the GeO ₂ powder. The final pH of the obtained ammonium germanate solution was 8.5, and the germanium oxide content was 60 g / l (g / l
)Met.

The slurry was stirred under an infrared heating lamp until dry, then at 100 ° C.
The water was removed by heating overnight in an oven set to. At this point, the chemical species present in the ammonium germanate solution had not been pyrolyzed to the oxide form. Then, at least 20 g aliquots of the carrier particles thus coated were placed in an alumina tray, placed in a high temperature box furnace and fired to pyrolyze the ammonium germanate surface coating. The temperature of the furnace was raised at a rate of 7 ° C / min to a temperature of 250 ° C (Example 11) to 600 ° C (Example 13) (the firing temperature of each example is shown in Table IV below), and The temperature was maintained for 2 hours. After firing for 2 hours, the furnace was left to cool naturally to room temperature (ie, by "free-fall"). The calcined carrier charge was deaggregated with a mortar and pestle and sieved with a 200 mesh sieve to obtain strontium ferrite carrier particles having GeO ₂ deposited on the surface.

The specific resistance measured for each of the resulting carriers is shown in Table IV below. The electrostatic resistivity of the carrier was measured by the method described in Examples 1 to 4. FIG. 4 is a graph of the specific resistance of each carrier, showing specific resistance (Ωcm) vs. firing temperature (° C.).
Shown in. As can be seen from FIG. 4, the specific resistance of the carrier dropped sharply at a temperature higher than 600 ° C.

In each example, the resulting coated carrier was used to prepare Examples 1-4.
A two-component developer using the yellow polyester toner described in 1. was prepared. The developers were prepared by mixing each carrier with the above toner with a toner concentration (TC) of about 6% by weight (TC values found in Table IV). In each example, the toner charge-to-mass ratio (Q / m) toner and TC were measured as described in Examples 1-4, and the measurements obtained are also shown in Table IV.

The performance of the developers prepared for Examples 11-13 was investigated using the same electrographic equipment and operating conditions as described in Examples 1-4 above. The values obtained for relative development efficiency and I-CPU are also shown in Table IV.

[0128]

[Table 4]

As can be seen from Table IV, the relationship between electrostatic resistivity, development efficiency and ICU is clear. That is, as the conductivity increases, the developing speed and I-CPU also increase.
However, GeO ₂ coatings offer the opportunity to adjust the conductivity and performance of the resulting carrier when it is used as a carrier in electrographic processing by choosing the firing conditions. As can be seen in Table IV and FIG. 4, Example 13 and Comparative Example D (calcination temperatures of 600 ° C. and 7 respectively)
At 50 ° C.), the specific resistance decreases by about four orders of magnitude, and FIG. 4 schematically shows the tendency of the electrostatic specific resistance.

Comparative Example D In Comparative Example D, the procedure of Examples 11-13 was substantially repeated except that the GeO ₂ precursor compound coated ferrite material was fired at a furnace temperature of 750 ° C. All other procedures are substantially the same as in Examples 11-13. The electrostatic resistivity, triboelectric properties, development efficiency and I-CPU of the resulting coated ferrite carrier were measured substantially according to the same procedures as described in Examples 1-4 above. Using this carrier, a developer containing the same toner as described in Examples 11 to 13 was prepared. For comparison, the specific resistance, triboelectric properties, development efficiency and I-CPU were measured and the results are shown in Table IV. The results obtained are discussed above in connection with Examples 11-13 and shown in FIG. 4 for comparison.

Examples 14-17-Preparation and Use of Strontium Ferrite Carriers Coated with Mixed GeO ₂ / B ₂ O ₃ Coatings Examples 14-17 are commercially available SrFe ₁₂ O ₁₉ hard ferrite carriers according to the invention. Coated with mixed GeO ₂ / B ₂ O ₃ coating and used for electrographic processing. These carriers were the same as in Example 11 except for the following points.
Prepared using the procedure outlined in ~ 13.

In Example 14, a slurry of ferrite particles was prepared by pouring 50 g of SrFe ₁₂ O ₁₉ ferrite particles into a glass dish with 30 ml of ammonium germanate-boric acid solution. The ammonium germanate-boric acid solution was prepared by adding 10 ml of the ammonium germanate solution prepared as in Examples 11-13 together to 10 ml of distilled water and 10 ml of a methanolic boric acid solution. Was prepared. The methanol-based boric acid solution is 0.
22g of H ₃ BO ₃ was prepared by adding (USA Acros Co. reagent grade, NJ) in methanol 10 ml. By substantially repeating the procedure of Examples 11 to 13 at a furnace temperature of 900 ° C., GeO ₂ of 1.2 p is obtained.
ph (1.17% by weight based on the total weight of the carrier), B ₂ O ₃ is 0.5 pph (0
． A carrier coated with a mixed GeO ₂ / B ₂ O ₃ oxide coating having a stoichiometry of 487 wt%) was obtained.

In Example 15, a slurry of ferrite particles was prepared by charging 50 g of SrFe ₁₂ O ₁₉ ferrite particles together with 30 ml of ammonium germanate-boric acid solution into a glass dish. This ammonium germanate-boric acid solution was prepared by adding 10 ml of the ammonium germanate solution prepared as in Examples 11-13 to 10 ml of distilled water and 10 ml of methanolic boric acid solution. It was The methanol-based boric acid solution is 0.44 g
Of H ₃ BO ₃ was added to 10 ml of methanol. By substantially repeating the procedure of Examples 11-13 at a furnace temperature of 900 ° C., a mixed GeO ₂ / having a stoichiometry of 1.2 pph GeO _{2 and} 1.0 pph B ₂ O _3.
A carrier coated with a B ₂ O ₃ oxide coating was obtained.

In Example 16, a slurry of ferrite particles was prepared by pouring 50 g of SrFe ₁₂ O ₁₉ ferrite particles into a glass dish with 25 ml of ammonium germanate-boric acid solution. This ammonium germanate-boric acid solution was prepared by adding 5 ml of the ammonium germanate solution prepared as in Examples 11-13 to 10 ml of distilled water and 10 ml of methanolic boric acid solution. It was The methanolic boric acid solution was prepared by adding 0.44 g of H ₃ BO ₃ to 10 ml of methanol. Example 1
By substantially repeated at a furnace temperature of 900 ° C. 1 to 13 steps, GeO ₂
GeO ₂ / having a stoichiometry in which is 0.6 pph and B ₂ O ₃ is 1.0 pph
A carrier coated with a B ₂ O ₃ oxide coating was obtained.

In Example 17, a slurry of ferrite particles was prepared by charging 50 g of SrFe ₁₂ O ₁₉ ferrite particles with 35 ml of ammonium germanate-boric acid solution into a glass dish. This ammonium germanate-boric acid solution is prepared by adding 5 ml of the ammonium germanate solution prepared as in Examples 11-13 to 10 ml of distilled water and 20 ml of a methanolic boric acid solution. It was The methanolic boric acid solution was prepared by adding 0.88 g of H ₃ BO ₃ to 20 ml of methanol. Example 1
By substantially repeated at a furnace temperature of 900 ° C. 1 to 13 steps, GeO ₂
Mixed GeO ₂ / having a stoichiometry of 0.6 pph and B ₂ O ₃ 2.0 pph
A carrier coated with a B ₂ O ₃ oxide coating was obtained.

[0136]   The specific resistance measured for each of the resulting carriers is shown in Table V below.

In Examples 14 to 17, two-component developers were prepared by using the obtained carrier and a yellow polyester toner substantially using the method described in Examples 1 to 4. In each example, the charge-to-mass ratio (Q / m) (μC / g) and toner concentration (TC) (wt%) were measured as described in Examples 1-4. The measured values obtained are also shown in Table V.

[0138]

[Table 5]

In Examples 14 to 17, the developing efficiency and I-CPU were substantially the same as those in Examples 1 to 4.
Evaluation was performed according to the procedure as described in 1. The data obtained are shown in Table VI.

[0140]

[Table 6]

Examples 18-20-Preparation and Use of Strontium Ferrite Carriers Coated with Mixed GeO ₂ / Li ₂ O Coatings Examples 18-20 mix commercially available SrFe ₁₂ O ₁₉ hard ferrite carriers according to the invention. Coated with GeO ₂ / Li ₂ O coating and evaluated in electrographic processing. These coated carriers were prepared using the general procedure as described in Examples 11-13 above, except for the following.

In Example 18, a slurry of ferrite particles was prepared by charging 50 g of SrFe ₁₂ O ₁₉ ferrite particles with 20 ml of ammonium germanate-lithium acetate solution into a glass dish. This ammonium germanate-
The lithium acetate solution was prepared by adding 0.05 g of lithium acetate (98% grade manufactured by Aldrich Co., St. Louis, Missouri) to 11.7 ml of distilled water, and adding the resulting solution to 8.3 ml of Example 11. It was prepared by combining with an ammonium germanate solution prepared in the same manner as ~ 13. Examples 11-13
By repeating substantially the furnace temperature of the steps 600 ° C., GeO ₂ is 1.0
pph (0.99% by weight relative to the total weight of the carrier), Li ₂ O is 0.015 p
A carrier coated with a mixed GeO ₂ / Li ₂ O oxide coating with a stoichiometry of ph (0.015% by weight) was obtained.

In Example 19, a slurry of ferrite particles was prepared by pouring 50 g of SrFe ₁₂ O ₁₉ ferrite particles into a glass dish with 20 ml of ammonium germanate-lithium acetate solution. This ammonium germanate-
The lithium acetate solution contained 0.1 g of the lithium acetate used in Example 18 above.
It was added to 1.7 ml of distilled water and the resulting solution was added to 8.3 ml of Examples 11-13.
It was prepared by mixing with an ammonium germanate solution prepared as described in. By substantially repeating the procedure of Example 18, a carrier coated with a mixed GeO ₂ / Li ₂ O oxide coating having a stoichiometry of 1.0 pph GeO _{2 and} 0.029 pph Li ₂ O was prepared. Was obtained.

In Example 20, a slurry of ferrite particles was prepared by charging 50 g of SrFe ₁₂ O ₁₉ ferrite particles with 20 ml of ammonium germanate-lithium acetate solution into a glass dish. This ammonium germanate-
The lithium acetate solution was prepared by adding 0.15 g of the lithium acetate used in Example 18 to 11.7 ml of distilled water, and adding the resulting solution to 8.3 ml of Examples 11 to 1.
It was prepared by combining with an ammonium germanate solution prepared as described in 3. By substantially repeating the procedure of Example 18, a carrier coated with a mixed GeO ₂ / Li ₂ O oxide coating having a stoichiometry of 1.0 pph GeO _{2 and} 0.044 pph Li ₂ O was prepared. Was obtained.

The specific resistance measured for each carrier obtained in Examples 18-20 is shown in Table VII below.

[0146]

[Table 7]

In Examples 18 to 20, the obtained carrier was used, and substantially Examples 11 to 1 were used.
A two component developer was prepared using the yellow polyester toner and method as described in Section 3. In each example, the charge-to-mass ratio (Q / m) (μC / g) and toner concentration (TC) (wt%) were measured as described in Examples 1-4. The measured values obtained are also shown in Table VIII.

[0148]

[Table 8]

Examples 21-23-Preparation and Use of Strontium Ferrite Carrier Coated with Mixed GeO ₂ / Na ₂ O Coating Examples 21-23 used two different sources for the Na ₂ O component,
In accordance with the present invention, a commercially available SrFe ₁₂ O ₁₉ hard ferrite carrier is mixed with GeO ₂ /
Coated with Na ₂ O coating. These coated carriers were prepared using the general procedure as described in Examples 11-13 above, except for the following.

In Example 21, a slurry of ferrite particles was prepared by charging 50 g of SrFe ₁₂ O ₁₉ ferrite particles with 20 ml of ammonium germanate-sodium acetate solution into a glass dish. This ammonium germanate-sodium acetate solution was prepared by adding 0.05 g of sodium acetate (manufactured by Aldrich Co. in St. Louis, Missouri) to 11.7 ml of distilled water, and adding the resulting solution to 8.3 ml of Example. It was prepared by combining with an ammonium germanate solution prepared in the same manner as 11-13. By substantially repeating the procedure of Examples 1 to 4 at a furnace temperature of 600 ° C., GeO ₂ of 1.0 pph (
0.99% by weight based on the total weight of the carrier) and 0.023 pph of Na ₂ O (0
． A carrier coated with a mixed GeO ₂ / Na ₂ O oxide coating having a stoichiometry of 023 wt%) was obtained.

In Example 22, a slurry of ferrite particles was prepared by charging 50 g of SrFe ₁₂ O ₁₉ ferrite particles with 20 ml of ammonium germanate-sodium acetate solution into a glass dish. This ammonium germanate-sodium acetate solution was prepared by adding 0.10 g of the sodium acetate used in Example 21 to 11.7 ml of distilled water, and adding the resulting solution to 8.3 ml of Example 1.
It was prepared by mixing with an ammonium germanate solution prepared in the same manner as 1-13. By substantially repeating the procedure of Example 21, a carrier coated with a mixed GeO ₂ / Na ₂ O oxide coating having a stoichiometry of 1.0 pph GeO _{2 and} 0.046 pph Na ₂ O was prepared. Was obtained.

In Example 23, a slurry of ferrite particles was prepared by charging 50 g of SrFe ₁₂ O ₁₉ ferrite particles with 20 ml of ammonium germanate-sodium acetate solution into a glass dish. This ammonium germanate-sodium acetate solution was prepared by adding 0.15 g of the sodium acetate used in Example 21 above to 11.7 ml of distilled water, and adding the resulting solution to 8.3 ml of Example 1.
It was prepared by mixing with an ammonium germanate solution prepared in the same manner as 1-13. By substantially repeating the procedure of Example 21, a carrier coated with a mixed GeO ₂ / Na ₂ O oxide coating having a stoichiometry of 1.0 pph GeO _{2 and} 0.068 pph Na ₂ O was prepared. Was obtained.

The specific resistance measured for each carrier obtained in Examples 21-23 is shown in Table IX below.

[0154]

[Table 9]

In Examples 21-23, the resulting carriers were used to prepare two-component developers using the yellow polyester toner and method substantially as described in Examples 1-4. In each example, the charge-to-mass ratio (Q / m) (μC / g) and toner concentration (TC) (wt%) were measured as described in Examples 1-4. The measured values obtained are also shown in Table X.

[0156]

[Table 10]

Examples 24-33 Preparation and Use of Strontium Ferrite Carrier Coated with TiO ₂ Coating In Examples 24-33, a commercially available SrFe ₁₂ O ₁₉ hard ferrite carrier is coated with a TiO ₂ composition according to the present invention. did. These carriers were prepared using the general procedure as described in Examples 11-13 above, with the following exceptions.

In Example 24, a slurry of ferrite particles was prepared by charging 100 g of SrFe ₁₂ O ₁₉ ferrite particles together with 35 ml of a methanol-based tetrabutyl orthotitanate solution into a glass dish. This methanolic tetrabutyl orthotitanate solution was prepared by dissolving 1.065 g of tetrabutyl orthotitanate (Eastman Kodak Company, Rochester, NY) in 35 ml of methanol. Substantially repeating the procedure of Examples 11-13 at a furnace temperature of 600 ° C. yielded a carrier coated with 0.25 pph (0.25 wt% based on the total weight of the carrier) of TiO ₂ . .

In Example 25, a slurry of ferrite particles was prepared by charging 100 g of SrFe ₁₂ O ₁₉ ferrite particles together with 35 ml of a methanol-based tetrabutyl orthotitanate solution into a glass dish. This methanol-based tetrabutyl orthotitanate solution contained 2.13 g of the above tetrabutyl orthotitanate.
Prepared by dissolving in ml of methanol. By substantially repeating the procedure of Examples 11-13 at a furnace temperature of 600 ° C., 0.50 pph of TiO ₂
A carrier coated with was obtained.

In Example 26, a slurry of ferrite particles was prepared by charging 100 g of SrFe ₁₂ O ₁₉ ferrite particles with 35 ml of a methanolic tetrabutyl orthotitanate solution into a glass dish. This methanol-based tetrabutyl orthotitanate solution contained 4.26 g of the above tetrabutyl orthotitanate.
Prepared by dissolving in ml of methanol. Substantially repeating the procedure of Examples 11-13 at a furnace temperature of 600 ° C. resulted in a carrier coated with 1.0 pph of TiO ₂ .

In Example 27, a slurry of ferrite particles was prepared by introducing 100 g of SrFe ₁₂ O ₁₉ ferrite particles into a glass dish along with 35 ml of a methanol-based tetrabutyl orthotitanate solution. This methanol-based tetrabutyl orthotitanate solution contained 6.39 g of the above tetrabutyl orthotitanate.
Prepared by dissolving in ml of methanol. The procedure of Examples 1-7 is 60
Substantially repeating at 0 ° C. oven temperature resulted in a carrier coated with 1.5 pph of TiO ₂ .

In Example 28, a slurry of ferrite particles was prepared by introducing 100 g of SrFe ₁₂ O ₁₉ ferrite particles into a glass dish along with 35 ml of a methanol-based tetrabutyl orthotitanate solution. This methanol-based tetrabutyl orthotitanate solution contained 35 parts of 8.52 g of the above tetrabutyl orthotitanate.
Prepared by dissolving in ml of methanol. Substantially repeating the procedure of Examples 11-13 at a furnace temperature of 600 ° C. resulted in a carrier coated with 2.0 pph of TiO ₂ .

In Examples 29 to 33, Example 24 was repeated except that the furnace temperature was set to 900 ° C.
The procedure from ~ 28 was substantially repeated.

[0164]   The resistivity measured for each of the resulting carriers is shown in Tables XI and XII.

In Examples 24 to 33, the carrier thus obtained was used, and substantially any of Examples 11 to 1 was used.
A two component developer was prepared using the yellow polyester toner and method as described in Section 3. In each example, the charge-to-mass ratio (Q / m) (μC / g) and toner concentration (TC) (wt%) were measured as in Examples 1-4. The measured values obtained are also shown in Tables XI and XII. Relative DE and I-CPU are also the first to the first embodiments.
It was evaluated as in 4.

[0166]

[Table 11]

[0167]

[Table 12]

Examples 34-39-Preparation and Use of Strontium Ferrite Carriers Coated with ZrO ₂ Coating In Examples 34-39, commercially available SrFe ₁₂ O ₁₉ hard ferrite carriers were coated with ZrO ₂ coatings according to the invention. . These carriers were prepared using the general procedure as described in Examples 11-13 above, with the following exceptions.

In Example 34, 100 g of SrFe ₁₂ O ₁₉ ferrite particles were added to 35 ml of an aqueous colloidal zirconium acetate solution (manufactured by The P. Kew, Inc., Ashland, Mass., With a ZrO ₂ content of 20%). A slurry of ferrite particles was prepared by placing it in a glass dish with a certain NYACOL dispersion.
This zirconium acetate solution was prepared by adding 2.5 g of the zirconium acetate dispersion to 35
It was prepared by combining with ml of distilled water sufficient to prepare a solution of ml. Substantially repeating the procedure of Examples 11-13 at a furnace temperature of 900 ° C. resulted in a carrier coated with 0.5 pph of ZrO ₂ .

In Example 35, 100 g of SrFe ₁₂ O ₁₉ ferrite particles are placed in a glass dish along with 35 ml of an aqueous zirconium acetate solution prepared by combining 5.0 g of the zirconium acetate dispersion described above with distilled water. Thus, a slurry of ferrite particles was prepared. Substantially repeating the procedure of Examples 11-13 at a furnace temperature of 900 ° C. resulted in a carrier coated with 1.0 pph of ZrO ₂ .

In Example 36, 100 g of SrFe ₁₂ O ₁₉ ferrite particles were placed in a glass dish with 35 ml of an aqueous zirconium acetate solution prepared by combining 10 g of the zirconium acetate dispersion described above with distilled water. A slurry of ferrite particles was prepared. Substantially repeating the procedure of Examples 11-13 at a furnace temperature of 900 ° C. yielded a carrier coated with 2.0 pph of ZrO ₂ .

In Examples 37-39, the procedure of Examples 34-36 was substantially repeated, except that the furnace temperature was 1,150 ° C. in each example.

The resistivity measured for each of the obtained carriers is shown in Tables XIII and XIV.

In Examples 34 to 39, the obtained carrier was used, and substantially Examples 11 to 1 were used.
A two component developer was prepared using the yellow polyester toner and method as described in Section 3. In each example, the charge-to-mass ratio (Q / m) (μC / g) and toner concentration (TC) (wt%) were measured as in Examples 1-4. The measured values obtained are also shown in Tables XIII and XIV. Relative DE and I-CPU were also evaluated as in Examples 11-13.

[0175]

[Table 13]

[0176]

[Table 14]

Examples 40-42 Preparation and Use of Strontium Ferrite Carrier Coated with a SnO ₂ Coating In Examples 40-42, a commercially available SrFe ₁₂ O ₁₉ hard ferrite carrier was coated with a SnO ₂ coating according to an embodiment of the present invention. Coated with. These carriers were prepared using the general procedure as described in Examples 11-13 above, with the following exceptions.

In Example 40, a slurry of ferrite particles was prepared by introducing 100 g of SrFe ₁₂ O ₁₉ ferrite particles into a glass dish with 35 ml of an aqueous colloidal tin oxide solution. This tin oxide aqueous solution was 3.33 g of colloidal tin oxide dispersion (N made by The P. Kew, Inc., Ashland, Mass.).
yacol dispersion) was mixed with distilled water in an amount sufficient to prepare 35 ml of solution. Substantially repeating the procedure of Examples 11-13 at a furnace temperature of 900 ° C. resulted in a carrier coated with 0.5 pph of SnO ₂ .

In Example 41, a slurry of ferrite particles was prepared by charging 100 g of SrFe ₁₂ O ₁₉ ferrite particles together with 35 ml of an aqueous tin oxide solution into a glass dish. The solution was prepared by adding 6.67 g of the colloidal tin oxide dispersion of Example 40 to distilled water in an amount sufficient to make 35 ml of the solution. Substantially repeating the procedure of Examples 11-13 at a furnace temperature of 900 ° C. resulted in a carrier coated with 1.0 pph of SnO ₂ .

In Example 42, a slurry of ferrite particles was prepared by introducing 100 g of SrFe ₁₂ O ₁₉ ferrite particles into a glass dish with 35 ml of an aqueous tin oxide solution. The solution was prepared by adding 13.34 g of the colloidal tin oxide dispersion of Example 40 to distilled water in an amount sufficient to make 35 ml of the solution. Substantially repeating the procedure of Examples 11-13 at a furnace temperature of 900 ° C. yielded 2.0 pph of SnO ₂ coated carrier.

[0181]   The specific resistance measured for each of the resulting carriers is shown in Table XV below.

In Examples 40 to 42, the obtained carrier was used, and substantially Examples 11 to 1 were used.
A two component developer was prepared using the yellow polyester toner and method as described in Section 3. In each example, the charge-to-mass ratio (Q / m) (μC / g) and toner concentration (TC) (wt%) were measured as in Examples 1-4. The measured values obtained are also shown in Table XV. Relative DE and I-CPU were also evaluated as in Examples 11-13.

[0183]

[Table 15]

Example 43 In Example 43, a plurality of two-component developer compositions having different toner concentrations were mixed with commercially available Sr.
Prepared from a Fe ₁₂ O ₁₉ hard ferrite carrier (Powdertech, Inc., Valparaiso, IN). The carrier was prepared by substantially the method of Example 41, ie, coating the carrier with a 1.0 pph SnO ₂ coating followed by baking at an oven temperature of 900 ° C.
It is coated with nO ₂ coating. When the specific resistance of the carrier was measured according to the method described in Examples 1 to 4, it was 8 × 10 ⁷ Ωcm.

The toner used was prepared using 92% by weight of a conventional poly (styrene-co-butyl acrylate) polymer resin prepared by Eastman Kodak Company, Rochester, NY. The resin was blended with 1% by weight of an organic iron composite charge control agent (T-77 from Hodgaya, Japan) and 7% by weight of carbon black (430 Black Pearls from Cabot). The resulting unpurified toner mixture was ground and sieved to give a toner resin powder having an average particle size of 12.2 μm as measured with a Coulter counter.

A total of five different developer compositions, one for each of the five runs in Example 43, were prepared by mixing the carrier with various amounts of the toner. The toner concentration (TC) based on the total weight of the applicable developer composition was 6.4, 8.6, 10.7, 13.1 and 15.1% by weight, respectively. For each of the above Examples 1-4 used to determine the resistivity of the carrier, except that 2.00 g of the developer mixture thus prepared was used in place of 2.00 g of carrier for each developer. The resistivity of the developer composition immediately after its preparation was determined by using substantially the same apparatus and method as described. The values obtained for the developer resistivity are given in Table XVI. For each developer mixture, the toner charge to mass ratio (Q / m) toner was measured according to the methods of Examples 1-4 above. The values obtained are shown in Table XVI. Then, for each developer, the charge-to-mass ratio (Q / m) of the carrier was calculated from the measured (Q / m) toner according to the following mathematical formula. In the above formula, TC is represented by weight%. (Q / m) carrier = (Q / m) toner x (TC / (100-TC)) (Q / m) carrier values are also shown in Table XVI.

The performance of each developer composition was then evaluated using the electrographic apparatus and method substantially as described in Examples 1-4, except for the following: To facilitate the quantitative I-CPU analysis procedure described below, the entire photoconductive film (having a 5.5 inch x 8.25 inch rectangular dimension as an exposed area of 45.375 in ² ) was bias developed. The grid voltage is about +6 when the potential on the photoconductive film is
An offset of -400V was set so that the potential from the shell to the photoconductive film was a constant + 400V. The development efficiency was calculated based on the degree to which the potential of + 400V decreased while developing the photoconductive film with each developer composition with reference to the original + 400V. The device is 1
It was equipped with a developing device using a rotating magnetic core with two magnetic poles and a magnetic strength of 1,000 gauss. Further, a shell is arranged around the rotating core of the developing device. The surface of the shell and the surface of the photoconductive film were installed with a spacing of 0.020 inch. The core rotated clockwise at 1,000 rpm and the shell rotated counterclockwise at 15 rpm. In the charging device, the photoconductive film was set to run at a speed of 2 inches / second, whereas in the developing device, the photoconductive film was run at a speed of 5 inches / second. Was set. The nap density was 0.24 g / in ² . The toning nip width was 0.375 inches.

The voltage of the photoconductor after charging was measured with a first probe, and the voltage of the developed area of the photoconductive film after development was measured with a second probe. After development, the development efficiency could be calculated for each run as shown in Table XVI by measuring the voltage in the developed area of the photoconductive film. Relative development efficiency (Rel DE)
No. of Example 47. Based on the developing efficiency obtained by using the developer in Example 3, it was determined as in Examples 1 to 4.

The I-CPU of each developer composition in each implementation was determined using the quantitative method described below. In each implementation, the I-CPU uses at least 15 ml of a solvent consisting of 50 wt% acetone and 50 wt% dichloromethane, based on the total weight of the mixed solvent, to remove toner (and All deposited carriers were determined by flushing. The mixed solvent was sufficient to dissolve the toner resin, but not enough to dissolve the carrier particles that could be deposited on the photoconductive film. The remaining carrier particles were magnetically recovered from the solvent, washed with the mixed solvent at least three times and then dried. Then, the dry carrier particles collected from the photoconductive film were weighed. The amount of carrier obtained in each run is shown in Table XVI. The carrier deposition density based on the above-mentioned exposed area of 45.375 in ² , that is, the I-CPU converted into the amount of carriers deposited per unit area of the photoconductive film is also shown.

[0190]

[Table 16]

The data in Table XVI show that by varying the level of TC in the developer composition, for example, when the average particle size of the toner is about 12 μm, the concentration of toner in the developer is compared to the total weight of the developer. To about 6 to 15% by weight, so that the (Q / m) carrier value of the developer composition can be adjusted and the I-CPU characteristics can be directly influenced. Shows. Therefore, a desirable range of TC for a developer composition comprising a carrier having a predetermined resistivity within the range described herein is desirably less than about 0.01 g / in ² , preferably about 0.001 g. / I
It is in the range sufficient to obtain a deposition density of less than n ² , more preferably less than about 0.0001 g / in ² . Further, the data is (Q / m), especially if the carrier resistivity is at or near a threshold value that would otherwise reach an amount outside the acceptable range.
) It shows that the I-CPU can be adjusted by the carrier value.

Example 44 In Example 44, the procedure described in Example 43 above was substantially repeated except for the following points. A commercially available SrFe ₁₂ O ₁₉ hard ferrite carrier was coated with a SnO ₂ coating by substantially following the procedure of Examples 41 and 43 above, except that the carrier was fired at an oven temperature of 875 ° C instead of 900 ° C. The resistivity of the resulting carrier was measured by substantially the same method as used in Example 43 and found to be 1.5 × 10 ⁸ Ωcm. That is, the obtained carrier was slightly higher in resistance than the carrier calcined at 900 ° C. used in Example 43. This is consistent with the general results obtained by Examples 11-13 above, as shown in FIG. The toner was substantially the same as that used in Example 43 except that it was milled and classified to a toner powder having an average particle size of 9.9 μm as measured by Coulter Counter.
The toner usage amounts are 5.1 and 6 based on the total weight of the applicable developer composition, respectively.
． Five developer compositions were prepared by substantially the same method except that they were sufficient to obtain TCs of 9, 9.1, 11.0 and 12.9% by weight. The data obtained is shown in Table XVII below.

[0193]

[Table 17]

The results obtained are consistent with Example 43. The data in Table XVII shows that by varying the level of TC in the developer composition, for example, when the average particle size of the toner is about 10 μm, the concentration of toner in the developer relative to the total weight of developer is About 5
˜13% by weight, with the result that TC is (Q /
m) It is shown that the carrier value can be adjusted to directly affect the I-CPU characteristics. The data shows that the I-CPU can be adjusted by the (Q / m) carrier value.

Example 45 In Example 45, the procedure described in Example 43 was substantially repeated except for the following points. The carrier used was a 1.0 pph SnO ₂ coated carrier prepared as described in Example 43. The toner used is substantially the same as described in Examples 1 to 4 above, and is substantially the same as in US Pat.
It was a yellow polyester toner prepared as described in No. 060. Further, the toner fluidity was enhanced by surface treating the toner with 0.89 wt% silica (relative to the total weight of the toner) (R972 from Degussa, Germany). The surface treatment was carried out by powder blending the crushed and sorted toner particles with R972 silica in a Henschel FM75 mixer, a high energy mixer manufactured by Thyssen Henschel Industry Technique Co. in Kassel, Germany. The toner and R972 silica were loaded into the mixer in sufficient amounts to obtain the weight percent silica. Thereafter, the mixer was operated for 2.5 minutes at a speed of 1,745 revolutions per minute (rpm). The resulting toner / silica mixture was then collected and sieved through a 325 mesh screen to
Aggregated silica particles were removed. Then, the developing agent described below was prepared using the toner which was sieved and surface-treated. The average particle size of the toner measured by a Coulter counter was 7.1 μm. The amount of toner used was sufficient to obtain TCs of 3.7, 4.8, 5.9, 6.3 and 8.0% by weight, respectively, based on the total weight of the applicable developer composition. Except for the above, five kinds of developer compositions were prepared by substantially the same method as described in Example 43. The data obtained is shown in Table XVIII below.

[0196]

[Table 18]

The results in Table XVIII show the same relationships as shown by Examples 43 and 44. The data in Table XVIII show that by varying the level of TC in the developer composition, for example, when the average particle size of the toner is about 7 μm, the concentration of toner in the developer relative to the total weight of developer is Can be about 4-8% by weight,
As a result, it is shown that TC can adjust the (Q / m) carrier value of the developer composition and directly affect the I-CPU characteristics.

Example 46 In Example 46, the procedure described in Example 43 was substantially repeated except for the following points. The carrier used was a 1.0 pph SnO ₂ coated carrier prepared as described in Example 43. The toner used was 100 parts of polyester resin binder and 1 part of di-t-butylsalicylic acid charge control agent (Bontron E-88 manufactured by Orient Chemical Co., Japan).
And 4 parts of carbon black (Cabot 330 from Cabot) were prepared by conventional methods well known in the art. The average particle size of the toner after pulverization and selection was measured by a Coulter counter device and found to be 5.9 μm. Furthermore, by surface-treating the toner with 1.5% by weight (based on the total weight of the toner) silica (R972 from Degussa, Germany) by substantially the same method as described in Example 45. Increased fluidity of toner.

The amount of toner used is 3.8 with respect to the total weight of the applicable developer composition, respectively.
Five developers were prepared in substantially the same manner as described in Example 43, except that 4.8, 5.6, 6.7 and 7.7 wt% TC were sufficient. A composition was prepared. The data obtained are shown in Table XIX below.

[0200]

[Table 19]

The results in Table XIX show the same results as shown by Examples 43-45. The data in Table XIX show that by varying the level of TC in the developer composition, for example, when the average particle size of the toner is about 6 μm, the concentration of toner in the developer is relative to the total weight of the developer. It can be about 4-8% by weight, and as a result TC is shown to regulate the (Q / m) carrier value of the developer composition and can directly affect the I-CPU properties.

Furthermore, each data set (that is, the data when the toner size is 12.2 μm, the data when the toner size is 9.9 μm, the data when 7.1 μm and the data of 5.9 μm).
It can be seen that the data for m) supports the above description with respect to FIG. (
For each toner used (with a specific average particle size), an operating window can be formed based on the developer resistivity and (Q / m) carrier that defines the relationship between development efficiency and I-CPU.

As shown by the above data, the TC is adjusted and the (Q / m) carrier parameter is preferably greater than 1 μC / g, more preferably 3.0 μC.
By maintaining a value greater than / g, most preferably greater than 4.0 μC / g, the amount of carrier deposition density in the resulting image can be reduced. The relationship between the I-CPU and the (Q / m) carrier is shown by FIG. 5, which shows the data obtained for the parameters in Examples 43-46. Very small amounts of I-CPU are generally obtained when the (Q / m) carrier parameter is greater than 2 μC / g, especially when the (Q / m) carrier parameter is greater.

Without wishing to be bound by theory, once the carrier has entered the area known as the "nip" between the photoconductive film and the core (with the developer on the surface), the carrier on the core is used. It is believed to have a positive charge level determined by the developer TC and (Q / m) toner. At the nip, the carrier begins to become negatively charged at a rate proportional to the toning bias and the developer resistivity. If the charge on the carriers in the nip region is maintained at a positive level then the I-CPU should be very low. Thus maintaining the (Q / m) carrier at a positive level, in particular the level mentioned above, in order to prevent the carrier from reaching a negative charge level in the nip region which can influence the I-CPU. Is important.

Example 47 In Example 47, the procedure described in Examples 43 to 46 was substantially repeated except for the following points. The carrier used was 1.0 pp prepared substantially as described in Example 43 except that it was baked at an oven temperature of 610 ° C.
hSnO ₂ coated carrier. The specific resistance of the carrier was 2.1 × ^{10 10} Ωcm. Although a plurality of developers having different TC levels were not prepared, each of the four types of toners from Examples 43 to 46 was used to prepare a developer.

Implementation No. The toner used in Example 1 was the black poly (styrene-co-butyl acrylate) toner described in Example 43. Implementation No. The toner used in No. 2 was the black poly (styrene-co-butyl acrylate) toner described in Example 44. Implementation No. The toner used in No. 3 was the yellow polyester toner described in Example 45. Implementation No. The toner used in No. 4 was the black polyester toner described in Example 46. The four developer compositions (carrier and toner described above) were prepared by substantially the same method as described in Example 43. The TC used for each developer composition is shown in Table XX along with electrographic performance data.

[0207]

[Table 20]

Example 48 In Example 48, the procedure described in Example 47 was substantially repeated except for the following points. The carrier used was 1.0 pph S, prepared substantially as described in Example 47 except that it was baked at an oven temperature of 825 ° C.
It was a carrier coated with nO ₂ . The specific resistance of the carrier is 8.
It was 0 × 10 ⁹ Ωcm. The TC used for each developer composition is shown in Table XXI, along with electrographic performance data.

[0209]

[Table 21]

Example 49 In Example 49, the procedure described in Example 47 above was substantially repeated except for the following points. The carrier used was prepared substantially as described in Examples 11-13 and calcined at an oven temperature of 750 ° C, 1.0 pph Ge.
It was a carrier coated with O ₂ . The specific resistance of the carrier is 5.2.
It was x10 ⁶ Ωcm. The TC used for each developer composition is shown in Table XXII along with electrographic performance data.

[0211]

[Table 22]

Example 50 In Example 50, the procedure described in Example 47 above was substantially repeated except for the following points. The carrier used was a strontium ferrite material doped with lanthanum metal, available as FXC4809 carrier from Powdertech. The specific resistance of the carrier was 2.8 × 10 ⁵ Ωcm. Although a plurality of developers having different TC levels were not prepared, Examples 43 to 46 were used.
Developers were prepared using each of the four toners from

Implementation No. The toner used in Example 1 was the black poly (styrene-co-butyl acrylate) toner described in Example 43. Implementation No. The toner used in No. 2 was the black poly (styrene-co-butyl acrylate) toner described in Example 44. Implementation No. The toner used in No. 3 was the yellow polyester toner described in Example 45. Implementation No. The toner used in No. 4 was the black polyester toner described in Example 46. The four developer compositions (carrier and toner described above) were prepared by substantially the same method as described in Example 43. The TC used for each developer composition is shown in Table XXIII along with electrographic performance data.

[0214]

[Table 23]

Comparative Example E In Comparative Example E, the procedure described in Example 47 was substantially repeated except for the following points. The carrier used was a conventional carrier substantially as described in Comparative Example A, except that it had a resistivity of 8 × ^{10 10} Ωcm. The TC used for each developer composition is shown in Table XXIV along with electrographic performance data.

[0216]

[Table 24]

Example 51 In Example 51, the procedure described in Example 44 was substantially repeated except for the following points. A commercially available SrFe ₁₂ O ₁₉ hard ferrite carrier was used by substantially following the procedure of Examples 41 and 43, ie said carrier was at 875 ° C.
Coated with SnO ₂ coating by baking at 900 ° C. oven temperature instead. The specific resistance of the obtained carrier was 8 × 10 ⁷ Ωcm. Although a plurality of developers were not prepared, the toner (9.9 μm) described in Example 44 was used.
A single developer composition having a TC of 8.9 wt% based on the total weight of the developer composition was prepared by using m) together with the carrier. The data obtained are: -42.1 μC / g Q / m toner, 4.1 μC / g Q / m carrier, 0.645 DE, (compared to the control carrier of Example 3 Example 3). ) 2.
Rel DE of 62, developer resistivity of 4.7x10 ⁷ Ωcm, and 0.00
The I-CPU was 5 g (1.10 × 10 ⁻⁴ g / in ² in terms of deposition density).

Example 52 In Example 52, the procedure described in Example 51 was substantially repeated except for the following points. The carrier was coated with a SnO ₂ coating by substantially following the procedure of Examples 41 and 43 except that the commercially available SrFe ₁₂ O ₁₉ hard ferrite carrier was fired at an oven temperature of 1025 ° C. instead of 900 ° C. . The specific resistance of the obtained carrier was 7.7 × 10 ⁵ Ωcm. A plurality of developers was not prepared, but by using the toner described in Example 44 (9.9 μm) together with the carrier, the total weight of the developer composition was 9.0.
A single developer composition having a wt% TC was prepared. The data obtained is -43.
． 1 μC / g Q / m toner, 4.2 μC / g Q / m carrier, DE 0.832, R 3.38 (compared to the control carrier of Example 3 Example 3).
el DE, developer specific resistance of 5.0 × 10 ⁵ Ωcm, and 0.0578 g (
When converted to a deposition density, the I-CPU was 1.27 × 10 ⁻³ g / in ² ).

FIG. 6 shows the relationship between the relative development efficiency (based on the average of the Rel DE data obtained for each toner particle size) versus the toner particle size data obtained by Examples 43-52 and Comparative Example E. In contrast, FIG. 7 shows (Q / m) toner to toner particle size data (based on the average of the (Q / m) toners obtained at each toner particle size). As can be seen, this data shows the effect of particle size on development efficiency and the general relationship between average toner particle size and (Q / m) carrier.

The data obtained by Examples 43 to 52 and Comparative Example E also show that the development efficiency is directly related to the carrier resistivity normalized to the toner particle size used. There is. This relationship is shown in FIG.

Furthermore, the data obtained according to Examples 43-52 and Comparative Example E are I-C
The PU clearly shows that the carrier depends on the charge it gets in the toning nip region. Using the data from these examples, Q _Ct / M _C was calculated from equation (3) above in the Detailed Description of Embodiments section and the confirmed I-CPU value was calculated as Q _Ct / M _C value plotted. The resulting graph of FIG.
It was prepared using measured data of C, Q _T / M _T (μC / g), ρ (Ωcm) and DE. The limit value of Q _Cf / M _C used is assumed to be about −2 μC / g and t
Was about 0.075 seconds = 0.375 inches nip width / 5 inches / second processing speed, and 1 / ε = 8 × 10 ¹⁷ Ω / (sec cm ² ) × D _T ³ . Where D _T (
The average particle size of the toner) was measured in centimeters (cm). Is a constant −
2 μC / g and 8 × 10 ¹⁷ Ω / (sec cm ² ) include adjustable parameters in this model. 9, I-CPU is a possible dependent on the charge to obtain a carrier toning nip region, Q _Ct / M that if Q _Ct / M _C is less that I-CPU is within the allowable range It indicates that there is a _C threshold.

Similar results are obtained when a carrier and developer composition comprising barium-containing ferrite and lead-containing ferrite, commonly referred to as magnetite ferrite, having the above-mentioned properties is used as an electrographic carrier material. Expected to be done.

As used herein, the terms "electrography" and "electrographic" are broad terms that also encompass the imaging process of developing an electrostatic charge pattern formed on a surface with or without exposure. Therefore, it also includes electrophotography and other similar processes.

Although the present invention has been described in considerable detail with a detailed consideration of the preferred embodiments, it should be understood that changes and modifications can be made to such embodiments within the scope of the invention. Is.

[Brief description of drawings]

FIG. 1 is a graph of toner charge versus mass (Q / m) versus toner concentration for a developer used in a method according to the present invention. This figure shows the operating window for three different toner particle sizes and the operating region for each that can result in the desired electrographic system performance.

FIG. 2 is a graph of both relative development efficiency (as previously defined) and I-CPU data obtained in connection with Examples 5-7 and Comparative Example B above.

FIG. 3 is a graph of both relative development efficiency (as previously defined) and I-CPU data obtained in connection with Examples 8-10 and Comparative Example C above.

FIG. 4 is a graph of carrier resistivity (Ωcm) versus firing temperature prepared and evaluated in connection with Examples 11-13 and Comparative Example D above.

[Figure 5]   I-CPU (grams deposited) vs. (Q / m) carrier associated with Examples 43-46 6 is a graph of the data and is described at the end of Example 46 above.

FIG. 6 is a graph of average relative DE data versus toner particle size associated with Examples 43-52, described at the end of Example 52 above.

[Figure 7]   Average (Q / m) Toner Data vs. Toner Particle Size Related to Examples 43-52 Is a graph of Figure 5 and is described at the end of Example 52 above.

8 is a graph of Log _e relative DE data pairs associated with Example 43-52 (magnitude of resistivity / toner particles of the carrier), which is described at the end of the above Example 52.

9 is a graph of I-CPU (g) vs. resulting charge of carrier (μC / g) related to Examples 43-52 and Comparative Example E, at the end of Example 52 above. It is explained.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 15/09 G03G 15/08 507L 21/00 350 9/10 351 352 354 341 (31) Priority claim number 09 / 572,989 (32) Priority date May 17, 2000 (May 17, 2000) (33) Priority claiming country United States (US) (81) Designated country OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, MZ, SD, SL, SZ, TZ, UG, ZW) , EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AG, AL, AM, AU, AZ, BA, BB, BG, BR, BY, BZ, C , CN, CR, CZ, DM, DZ, EE, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP, KE, KG, KR, KZ, LC, LK, LR, LS, LT, LV, MA, MD, MG, MK, MN, MW, MX, MZ, NO, NZ, PL, RO, RU, SD, SG, SI, SK, SL, TJ, TM, TR, TT , TZ, UA, UG, UZ, VN, YU, ZA, ZW (72) Inventor Patrick Lambert, New York, USA 14617 Biltmore Drive, Rochester 28 (72) Inventor Eric Sea Sterter, New York, USA 14534 Pittsford , Oak Meadow Trail 10 (72) Inventor William Kae Gobel 14607 Roger, Edgarton Sutri, New York, USA To 115 (72) Inventor Peter S Alexandrovich 14617 Rochester, Van Vollis Ave 324 F Term (Reference) 2H005 AA00 BA02 BA05 BA06 CB04 DA03 EA01 EA02 EA05 EA10 FA02 2H031 AC08 AC22 AC24 AD01 BA05 BA09 2H035 CG01 2H077 AD06 EA03

Claims (63)

[Claims] 1. (a) a rotating magnetic core having a preset magnetic field strength; (b) an outer non-magnetic shell installed around the rotating magnetic core; and (c) (i) charged toner particles, (Ii) About 1 × ^{10 10} to about 1 × 10 ⁵ Ωc
An electro-magnet consisting of hard magnetic carrier particles of opposite polarity, having a specific resistance of m and a carrier (Q / m) above about 1 μC / g and placed on said shell and in contact with an electrostatic image. A method for developing an electrostatic image comprising contacting the image with a development system comprising at least one magnetic brush comprising a graph developer composition, the method comprising:
The foregoing method of depositing a carrier density lower than n ² on an electrostatic image. 2. (a) a rotating magnetic core having a preset magnetic field strength, (b) an external non-magnetic shell installed around the rotating magnetic core, and (c) (i) charged toner particles, (Ii) About 1 × ^{10 10} to about 1 × 10 ⁵ Ωc
An electrograph consisting of oppositely charged hard magnetic carrier particles having a specific resistance of m and a carrier (Q / m) above about 1 μC / g and placed on said shell and in contact with an electrostatic image. A method for developing an electrostatic image comprising contacting the image with a development system comprising at least one magnetic brush comprising a developer composition, the method comprising:
The foregoing method of depositing a carrier density lower than in ² on an electrostatic image. 3. The hard magnetic carrier particles have: (i) a coercivity when magnetically saturated of at least about 300 oersteds, and (ii) an induced magnetic moment in an externally applied field of 1,000 oersteds. The method of claim 2, comprising a hard magnetic material that is at least about 20 EMU / gm. 4. The carrier has a specific resistance of about 5.0 × 10 ⁹ to about 1.0 × 1.
The method of claim 2, wherein the method is 0 ⁶ Ωcm. 5. The preset resistivity of the carrier is about 5.0 × 10 ⁹
The method of claim 2, wherein the method is about 1 × 10 ⁷ Ωcm. 6. The developer composition has a resistivity of about 1 × 10 ¹² to about 1 × 10 ^5.
The method of claim 2, wherein the method is Ωcm. 7. The resistivity of the developer composition is from about 1 × ^{10 10} to about 1 × 10 ^7.
The method of claim 2, wherein the method is Ωcm. 8. The method of claim 3, wherein the hard magnetic material is strontium or barium ferrite. 9. The method of claim 3, wherein the magnetic material has a coercivity of at least about 1,000 oersteds. 10. The method according to claim 2, wherein the volume average particle diameter of the toner is about 8 μm or less. 11. The method of claim 2, wherein the toner has a volume average particle size of about 6 μm or less. 12. The (Q / m) carrier is greater than about 2.0 μC / g. The method described in 2. 13. The (Q / m) carrier is greater than about 3.0 μC / g. The method described in 2. 14. The (Q / m) carrier is greater than about 4.0 μC / g. The method described in 2. 15. The method of claim 2, wherein the carrier deposition density is less than 0.0001 g / in ² . 16. The method of claim 2, wherein the image and the developer system make contact at a nip region between a dielectric surface having the image and the shell having the developer composition. 17. The method of claim 16, wherein the dielectric surface operates at a processing speed of at least about 5 inches / second. 18. The method of claim 16, wherein the dielectric surface operates at a processing speed of about 15 to about 50 inches / second. 19. The specific resistance of the hard magnetic carrier is about 1 × 10 ⁷ to about 1 ×.
The method according to claim 18, wherein the method is 10 ⁵ Ωcm. 20. (a) a rotating magnetic core having a preset magnetic field strength, (b) an external non-magnetic shell installed around the rotating magnetic core, and (c) (i) charged toner particles, (Ii) About 1 × 10 ⁷ to about 1 × 10 ⁵ Ωcm
Of an oppositely charged hard magnetic carrier particle having a specific resistance of 1 and a carrier (Q / m) greater than about 1 μC / g, wherein the developer composition is on the shell. Is located and is in contact with the image at a nip region formed between a dielectric surface having an electrostatic image and the shell having the developer composition, and the dielectric surface is from about 15 to about 50 inches. A method for developing an electrostatic image comprising contacting the image with a developing system comprising at least one magnetic brush comprising: operating at a processing speed of / sec. The above method wherein the density of the carrier is less than about 0.001 g / in ² . 21. (a) a rotating magnetic core having a preset magnetic field strength, (b) an external non-magnetic shell installed around the rotating core, and (c) an electrostatic image installed on the shell. In contact with, and comprises hard magnetic carrier particles charged with opposite polarity and charged toner particles, said carrier particles being of at least one type M ^{n +} of the formula M ^{n + in} which ⁿ is an integer of at least 4. Method for developing an electrostatic image, characterized in that said image is contacted with at least one magnetic brush consisting of an electrographic developer composition consisting of a hard magnetic material having a crystalline structure substituted with a valent metal. . 22. The hard magnetic material has a single phase hexagonal crystal structure.
The method according to 1. 23. The method of claim 21, wherein the hard magnetic ferrite material is strontium ferrite or barium ferrite. 24. The method of claim 21, wherein n is 4 or 5. 25. The method of claim 21, wherein n is 4. 26. The at least one metal is selected from the group consisting of antimony, arsenic, germanium, hafnium, molybdenum, niobium, silicon, tantalum, tellurium, tin, titanium, tungsten, vanadium, zirconium and mixtures thereof. 22. The method of claim 21, wherein 27. The at least one metal is silicon, zirconium,
22. The method of claim 21, selected from the group consisting of tin, titanium and mixtures thereof. 28. The carrier particles are of the formula PFe _12-x M _x O ₁₉ wherein P is selected from strontium, barium or lead, and M is antimony, arsenic, germanium, hafnium, molybdenum, niobium, A single phase represented by at least one metal selected from silicon, tantalum, tellurium, tin, titanium, tungsten, vanadium, zirconium and mixtures thereof, and x is less than about 0.6 Made of a hard magnetic ferrite material having a hexagonal crystal structure,
The method of claim 21. 29. The method of claim 28, wherein P is strontium. 30. The method of claim 28, wherein x is less than about 0.2. 31. The at least one metal is silicon, zirconium,
29. The method of claim 28, selected from the group consisting of tin, titanium and mixtures thereof. 32. The method according to claim 28, wherein the surface of the carrier particles is covered with a resin layer. 33. The method of claim 32, wherein the layers are discontinuous. 34. The method of claim 32, wherein the resin is a mixture of polyvinylidene fluoride and polymethylmethacrylate. 35. The method of claim 32, wherein the resin is a silicone resin. 36. The carrier has a resistivity of about 5.0 × 10 ⁸ to about 5.0 ×.
29. The method of claim 28, which is 10 ⁹ Ωcm. 37. The method of claim 28, wherein the magnetic material is strontium or barium ferrite. 38. The method of claim 21, wherein the contacting further results in a carrier deposition density of less than about 0.01 g / in ² . 39. The method of claim 21, wherein said contacting further results in a carrier deposition density of less than about 0.001 g / in ² . 40. The method of claim 21, wherein said contacting further results in a carrier deposition density of less than about 0.0001 g / in ² . 41. (a) a rotating magnetic core with a preset magnetic field strength, (b) an external non-magnetic shell installed around the rotating core, and (c) an electrostatic image installed on the shell. An electrographic developer composition in contact with and comprising charged toner particles and oppositely charged carrier particles, wherein:
The carrier particles include (1) a core made of a hard magnetic material having an outer surface, and (2)
A metal oxide disposed on the outer surface of the core, wherein M is of the formula MO _{n / 2} , which is at least one polyvalent metal of the formula M ^{n +} , where n is an integer of at least 4; A coating, the outer surface further defining a transition zone extending from the outer surface and into the core of the hard magnetic material, and the crystalline structure of the hard magnetic material within the transition zone is A method for developing an electrostatic image comprising contacting said image with at least one magnetic brush consisting of: at least one ion of a polyvalent metal of the formula M ^{n +} . 42. The method of claim 41, wherein the hard magnetic material is ferrite having a single phase hexagonal crystal structure. 43. The method of claim 42, wherein the hard magnetic ferrite material is strontium ferrite, barium ferrite or lead ferrite. 44. The method of claim 42, wherein the hard magnetic ferrite material is strontium ferrite. 45. The metal oxide coating is selected from the group consisting of germanium oxide, zirconium oxide, titanium oxide, tin oxide and mixtures thereof, and optionally the group consisting of boron oxide, lithium oxide and sodium oxide. 42. The method of claim 41, selected from the group consisting of another metal oxide selected from 46. The method of claim 41, wherein n is 4 or 5. 47. The method of claim 41, wherein n is 4. 48. M is antimony, arsenic, germanium, hafnium, molybdenum, niobium, silicon, tantalum, tellurium, tin, titanium, tungsten,
42. The method of claim 41, selected from the group consisting of vanadium, zirconium and mixtures thereof. 49. The method of claim 41, wherein M is selected from the group consisting of silicon, zirconium, tin, titanium, and mixtures thereof. 50. The method of claim 41, wherein the metal oxide composition further comprises an alkali metal oxide. 51. The method of claim 50, wherein the alkali metal is selected from the group consisting of lithium, potassium and sodium. 52. The method of claim 41, further comprising a layer of at least one polymeric resin overlying the layer of metal oxide. 53. The method of claim 52, wherein the resin layer is discontinuous. 54. The method of claim 52, wherein the at least one polymeric resin is a mixture of polyvinylidene fluoride and polymethylmethacrylate. 55. The method of claim 52, wherein the at least one resin is a silicone resin. 56. The carrier comprises: (i) a coercivity of at least about 300 Oersted when the hard magnetic material is magnetically saturated, and (ii) at least about when the material is in an externally applied field of 1,000 Oersteds. induced magnetic moment of 20 EMU / gm, and (iii) from about 1.0x10 ¹⁰ ~ about 1.0x10 ⁷ [Omega] cm method according to claim 41 having resistivity, the. 57. The method of claim 41, wherein the contacting results in a carrier deposition density of less than about 0.01 g / in ² . 58. The method of claim 41, wherein the contacting results in a carrier deposition density of less than about 0.001 g / in ² . 59. The method of claim 41, wherein the contacting results in a carrier deposition density of less than about 0.0001 g / in ² . 60. The resistivity of the carrier is from about 5.0 × 10 ⁸ to about 5.0 ×.
42. The method of claim 41, which is 10 ⁹ Ωcm. 61. (a) a rotating magnetic core having a preset magnetic field strength, (b) an external non-magnetic shell installed around the rotating core, and (c) an electrostatic image installed on the shell. An electrographic developer composition in contact with and comprising charged toner particles and carrier particles of opposite polarity, wherein the carrier particles are of the formula P _1-y La _y Fe ₁₂ O ₁₉ wherein , P is selected from strontium, barium or lead, and y is less than 0.1, consisting of a hard magnetic ferrite material having a single-phase hexagonal crystal structure represented by:
A method for developing an electrostatic image comprising contacting said image with at least one magnetic brush comprising 62. A single-phase hexagonal crystal represented by the formula P _1-y La _y Fe ₁₂ O ₁₉ wherein P is selected from strontium, barium or lead and y is less than 0.1. Carrier particles used for developing an electrostatic latent image, which are composed of a hard magnetic ferrite material having a structure. 63. (a) a rotating magnetic core having a preset magnetic field strength, (b) an external non-magnetic shell installed around the rotating magnetic core, (c) (i) an average particle size of about 8 μm or less. Charged toner particles, which is (ii) about 1
An electrographic developer composition comprising oppositely charged hard magnetic carrier particles having a resistivity of from x10 ⁷ to about 1x10 ⁵ Ωcm and a carrier of greater than about 1 μC / g (Q / m), wherein: A developer composition is provided on the shell and has an electrostatic image and a dielectric surface operating at a processing speed of about 15 to about 50 inches / second; and the developer composition. A method for developing an electrostatic image comprising contacting the image with a development system comprising at least one magnetic brush comprising: contacting the image in a nip region formed with a shell. Wherein the density of carriers deposited on the electrostatic image is less than about 0.001 g / in ² .