JP2648221B2 - Magnetic brush development method using white toner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to a static toner formed on a positively charged organic photoreceptor using a two-component magnetic developer composed of a white toner and a resin-coated ferrite carrier. The present invention relates to a magnetic brush developing method for developing an electric image.

(Prior Art) In the field of commercial electronic copying, a two-component magnetic developer comprising a toner and a magnetic carrier is used, and this developer is transported in the form of a magnetic brush to form an electrostatic image. A magnetic brush developing method for developing an electrostatic image by rubbing a magnetic member with a photoreceptor that has been used is widely used. Recently, a ferrite carrier has been widely used as a magnetic carrier in the developer because it forms a soft magnetic brush and has good halftone reproducibility.

An apparatus for forming an image by magnetic brush development as described above has a structure as shown in FIG. The developing mechanism section 2 is provided with a box-shaped toner supply mechanism 4.
The toner 6 is supplied from above. The toner 6 is supplied to a lower developing unit 10 through a supply port 8 with a feeder, and is stirred by a stirrer 12 with a carrier in the developing unit 10 to form a two-component developer 14.

A developing sleeve (developer carrier) 16 having a large number of magnetic poles is arranged in the developing device 10, and the developer 14 is conveyed by the developing sleeve 16 in the form of a magnetic brush 18. The spike length of the magnetic brush 18 is adjusted by an ear-cutting mechanism 20, and the magnetic brush 18 is transported to a nip position with a surface photosensitive layer 24 of a photosensitive drum (image carrier) 22. The photosensitive drum 22 is provided at a fixed distance DD-S from the developing sleeve 16. The photoreceptor drum 22 is rotatably provided, and is driven in the nip position so that it is usually in the same direction (rotational directions are mutually opposite) with respect to the moving direction of the magnetic brush 18.

Around the photoreceptor drum 22, a corona charger 26 and an exposure optical system 28 connected to a variable high-voltage power supply 24 are arranged upstream of the developing device 10 to form an electrostatic image having a predetermined surface potential. It is possible to do.

A bias power source 33 having a voltage adjusting mechanism 30 is connected between the photosensitive drum 22 and the developing sleeve 16, so that a bias voltage can be applied. That is, the photosensitive layer 24
By applying a bias voltage to the developing sleeve 16 to have the same polarity as the main charging potential of the toner, the toner in the magnetic brush is transferred to an electrostatic image while mitigating the influence of the residual potential of the photoconductor, and A toner image corresponding to the image is formed. Further, a transfer mechanism 34 for transferring the toner image to a transfer material such as paper is provided downstream of the developing device 10.

In such a mechanism, the developer 14 is
The magnetic brush 18 is formed thereon, and contacts the photosensitive layer 24 at the nip position to form a toner image 36. The formed toner layer 36 is transferred to a transfer material by a transfer mechanism 34, and then a toner image is fixed to form an image. After the transfer of the toner image, although not shown, the toner remaining on the photosensitive layer 24 is removed by a cleaning device known per se,
Further, the charge removal device erases the remaining charges, and the next image forming cycle is performed.

(Problems to be Solved by the Invention) By the way, as a ferrite carrier of a two-component magnetic developer, in order to prevent the generation of so-called spent toner in which toner adheres to the surface thereof, the surface is coated with an acrylic resin or a silicone resin. Is now widely used. Such a resin-coated ferrite carrier has the advantage that the deterioration of the surface oxidation and the like is effectively prevented, so that toner contamination (for example, toner discoloration) due to the surface oxide of the carrier does not occur. Such an advantage is extremely significant especially when a white toner is used.

However, since the white toner has a colorant such as titanium oxide, which has a lower conductivity than carbon black, dispersed in the fixing resin, the electric resistance is lower than that of the black toner containing carbon black or the like. High quality. That is, when such a white toner is used, the amount of toner charge given by frictional charge with the carrier becomes unnecessarily high, which is caused by the number of toner particles transferred to the photoreceptor surface by a constant electric force. Is reduced, in other words, the image density is reduced.

Therefore, when the white toner is used, it is necessary to set the appropriate triboelectric charge amount of the ferrite carrier to be smaller than that of the black toner. Although the frictional charge amount of the carrier and the frictional charge amount of the toner do not necessarily match, the frictional charge amount of the toner is determined according to the frictional charge amount of the carrier. The frictional charge of the toner is higher than the charge.) However, lowering the triboelectric charge amount of the carrier means that the resin coating amount is reduced accordingly, so that the ferrite carrier used in combination with the white toner has an amount sufficient to exhibit the above-mentioned advantages. It has been difficult to perform resin coating on the substrate. A similar problem is observed in color toners having low electrical conductivity as well as white toners. However, in the case of such color toners, even if discoloration occurs due to deterioration of the carrier, it is visually observed that the discoloration is not excessive. However, even if the resin coating amount of the carrier is set to a small amount, no significant problem occurs. On the other hand, in the case of a white toner, the discoloration (for example, yellowing) due to the deterioration of the carrier is immediately visually recognized. Therefore, if the carrier is not coated with a sufficient amount of resin, an image obtained due to the deterioration of the carrier is obtained. The color tone changes, making it difficult to use for a long period of time.

When a white toner is used as described above, there is a problem that it is extremely difficult to obtain a white image having a high density and no discoloration over a long period of time.

Also, recently, a positively charged organic photoreceptor has attracted attention. This is because the photoreceptor has the advantage that the degree of freedom in functional design is high and the cost is inexpensive, and that the photoreceptor does not generate a negative corona discharge that generates remarkable ozone during image formation. . However,
This positively charged organic photoreceptor has a disadvantage that the residual potential is larger than other photoreceptors, and therefore, a high bias voltage between the developing sleeve and the photoreceptor, for example, a bias voltage of 250 V or more, is applied. (The bias voltage in the case of the selenium photoreceptor is about 200 V).

However, since the difference between the main charging potential of the photoconductor and the bias potential corresponds to the developing potential, when a high bias voltage is applied, the developing potential decreases, making it difficult to obtain a high-density image. In addition, there is also a problem that so-called carrier pulling in which the carrier is transferred onto the photoreceptor easily occurs. To obtain a high-density image, the distance between the photoconductor and the developing sleeve (DD-S
It is preferable to increase the frequency of contact between the toner and the photoreceptor by reducing the width), but in this case, carrier pulling is more likely to occur. In addition, when a white toner is used, as described above, the charge amount of the toner is increased, and thus the charge amount of the carrier is also increased.
For this reason, the DD-S width can only be set to 1 mm or more, and it is actually difficult to obtain a high-density image.

Accordingly, an object of the present invention is to provide an electrostatic image formed on a positively charged organic photoreceptor by magnetic brush development using a two-component magnetic developer composed of a white toner having low conductivity and a resin-coated ferrite carrier. It is an object of the present invention to provide a developing method capable of effectively eliminating the problem of carrier pulling and the like, and capable of stably obtaining an image having a high density and a high whiteness without discoloration over a long period of time.

(Means for Solving the Problems) According to the present invention, a two-component magnetic developer composed of a white toner having a conductivity of 3.5 × 10 ⁻¹⁰ s / cm or less and a resin-coated ferrite carrier is magnetically charged by a developing sleeve. A magnetic brush developing method of transporting the magnetic brush in the form of a brush and rubbing the magnetic brush with a positively charged organic photoreceptor having an electrostatic image formed thereon to form a toner image; An amino group-containing silicone resin containing 0.1 to 10% by weight of a structural unit derived from a group-containing monomer component, and the resin coating amount is:
0.01 to 0.1% by weight per ferrite carrier, wherein the resin-coated ferrite carrier has a weight average particle size of
It has a particle size distribution such that the 50% diameter (D ₅₀ ) is 80 to 120 μm and the particle size of 250 mesh or less is 8% by weight or less, and the distance between the positively charged organic photoreceptor and the developing sleeve is 1m
m, and performing development while applying a development bias voltage of 280 V or more.

BEST MODE FOR CARRYING OUT THE INVENTION Resin-Coated Ferrite Carrier: In the present invention, it is extremely important to use an aminosilicon resin as a coating resin for a ferrite carrier. This aminosilicone resin is excellent in carrier deterioration prevention function by itself as compared with, for example, an acrylic resin, and by combining such a resin-coated ferrite carrier with a white toner, the aminosilicon resin can be used on a positively charged photoreceptor. Optimal toner charge for developing the electrostatic image of the photoconductor and developing sleeve gap (DD-S width)
Is less than 1 mm and high-density white images can be stably obtained without causing carrier pulling or the like by development under conditions of high bias voltage application.

FIG. 2 is a diagram plotting the amount of resin coating and the amount of carrier charge for a developer composed of a resin-coated ferrite carrier and a white toner, and one curve shows the use of an acrylic resin as the coating resin. Indicates the case,
The other curve shows the case where an amino silicone resin having an amino group content of 2.0% by weight (see Example 1 described later) was used. As is apparent from FIG. 2, it is understood that the carrier charge amount shifts to a lower level when the amino silicone resin is used than when the acrylic resin is used. That is, since the white toner has a higher resistance than the normal black toner, the toner charge amount becomes higher than necessary, and as a result, the image density is reduced. However, according to the present invention, the use of a ferrite carrier coated with an aminosilicon resin prevents an increase in carrier charge, that is, a tendency to increase the toner charge due to an increase in the resistance of the toner. It is also possible to prevent a decrease.

In addition, such an action of suppressing the charge amount of the amino silicone resin has an advantage of increasing the degree of freedom of the resin coating amount. That is, when a magnetic brush development is performed using a two-component magnetic developer using a white toner and a positively charged organic photoreceptor, the proper charge amount of the ferrite carrier that gives a proper charge amount to the white toner is as follows. About 8 to 15 per gram of toner
μC. In the case of using an acrylic resin-coated carrier, in order to set such a charge amount, the coating amount cannot be set to 0.05% by weight or more, and as a result, the effect of preventing the deterioration of the carrier by the resin coating is reduced. If the image formation is not sufficient, and the image formation is repeated, the obtained white image becomes yellowish. On the other hand, when the amino silicone resin is used according to the present invention, the coating amount can be reduced to 0.1% by weight. Therefore,
This makes it possible to set the toner at an appropriate charge amount and to enjoy a sufficient carrier deterioration preventing effect.

In the present invention, the amino group content of the amino silicone resin (that is, the amount of structural units derived from the amino group-containing silane monomer component) is in the range of 0.1 to 10% by weight, preferably 0.1 to 5% by weight. It is also important. For example, when the amino group content is less than the above range (for example, when a normal silicone resin containing no amino group is used), a sufficient negative negative charge is given to the white toner by triboelectric charging. When the amino group content is higher than the above range, the white toner is negatively charged far exceeding the proper charge amount. That is, in order to set an appropriate charge amount, the resin coating amount must be less than 0.01% by weight, and it becomes difficult to obtain an image having high whiteness over a long period of time. That is, the amino group in the amino silicone resin plays a role of a charge control agent, and the presence of a certain amount of the amino group enables the white toner to have a sufficient negative charge amount for image formation. Is performed.

In the present invention, the coating amount of the amino silicone resin is 0.01 to 0.1% by weight per ferrite carrier, particularly
The content is in the range of 0.02 to 0.1% by weight. When the coating amount exceeds 0.1% by weight, the charge amount of the carrier exceeds the appropriate charge amount,
If the charge amount of the white toner becomes too high, the image density is reduced. If the amount is less than 0.01% by weight, the function of preventing deterioration of the carrier is reduced, and it is difficult to obtain an image having a high whiteness over a long period of time. Would.

The above-mentioned amino silicone resin is a known resin,
It can be produced in a manner known per se. That is, it can be obtained by subjecting a silane compound or an oligomer thereof such as an alkoxysilane or a halogenated silane or an amino group-containing silane such as an aminoalkylsilane or an oligomer thereof to a polycondensation reaction by cohydrolysis.

As the ferrite carrier to be coated with the aminosilicone resin, known sintered ferrite particles, for example, those exemplified below can be used alone or in combination of two or more.

Zinc iron oxide (ZnFe ₂ O ₄ ), yttrium iron oxide (Y ₃ Fe ₅
O ₁₂ ), iron cadmium oxide (CdFe ₂ O ₄ ), iron gadolinium oxide (Gd ₃ Fe ₂ O ₁₂ ), lead iron oxide (Pd ₃ Fe ₁₂ O ₁₉ ), nickel iron oxide (NiFe ₂ O ₄ ), iron oxide Neodymium (NdFe
O ₃ ), iron oxide copper (CuFe ₂ O ₄ ), barium oxide (BaFe ₁₂ O)
₁₉ ), magnesium iron oxide (MgFe ₂ O ₄ ), iron manganese oxide (MnFe ₂ O ₄ ), lanthanum iron oxide (LaFeO ₃ ) and the like.

Particularly preferably used are soft ferrites containing at least one metal component selected from the group consisting of Cu, Zu, Mg, Mn and Ni, particularly two or more, such as copper-zinc-magnesium ferrite. It is.

In the present invention, the resin-coated ferrite carrier particles are preferably spherical in terms of fluidity. The resin-coated carrier has a 50% diameter (D ₅₀ ) of the weight average particle diameter.
It is also important to have a particle size distribution in the range of 80 to 120 μm and a particle size of 250 mesh or less, 8% by weight or less, especially 5% by weight or less. In other words, since the toner has such a sharp particle size distribution and the content of the small particle size component is suppressed to a certain value or less, the rubbing force of the magnetic brush becomes appropriate, and the toner is uniformly rubbed. Since charging can be performed, carrier pulling and fogging can be effectively suppressed even under severe development conditions in which a high bias voltage is used and the DD-S width is small. For example, if D ₅₀ is less than 80 μm,
The rubbing force of the magnetic brush is higher than necessary, and carrier pulling and fogging are likely to occur. Further, if D ₅₀ is greater than 120 [mu] m, a specific surface area of the carrier is reduced, the frictional charging of the toner uniformly and sufficiently perform it becomes difficult (i.e.,
The amount of uncharged toner or low-charged toner is increased), and fogging tends to occur. The 50% diameter (D ₅₀ ) of the weight average particle diameter of the carrier indicates the particle diameter when the integrated value becomes 50% in the particle integrated distribution curve.

Also, when the particle size of 250 mesh or less is contained in a larger amount than 8% by weight, the carrier is easily drawn. This is because carrier particles having such a small particle size tend to cause carrier pulling. FIG. 3 shows a combination of a carrier having a particle size of 250 mesh or less and a resin-coated ferrite carrier having a content of 8% by weight or less according to the present invention and a carrier containing 8% by weight or less according to the present invention, respectively. FIG. 9 is a diagram illustrating a relationship between a bias voltage and a carrier pull (indicated by a carrier loss amount when performing 500 continuous copies) for a developer. As can be understood from this curve, when a carrier having a large content of small particles is used, carrier pulling tends to occur as the bias voltage increases.
It is understood that when the content of particles (0 mesh or less) is suppressed to 8% by weight or less, the tendency of carrier pulling to occur with an increase in bias voltage can be effectively suppressed.

In the present invention, the resin-coated ferrite carrier forms a soft magnetic brush,
It preferably has a saturation magnetization of 50 to 70 emu / g, particularly 55 to 65 emu / g, and desirably has a fluidity of 15 to 35 sec / 50 g, especially 20 to 30 sec / 50 g.

The above-described resin-coated ferrite carrier can be manufactured by a known method such as a so-called fluidized bed method in which an organic solvent solution of an aminosilicon resin is sprayed onto ferrite carrier particles floating in an air stream.
The particle size distribution may be adjusted by classifying the ferrite particles before coating or by classifying the particles after coating with the resin.

White Toner: In the present invention, the white toner used in combination with the resin-coated ferrite carrier is known per se, and a white colorant and a charge controlling agent or a toner compounding agent known per se in a fixing resin medium. It is a compound that is positively charged when mixed with a carrier. Since this white toner has a high resistance of the white colorant to be compounded, it is 3.5 × 10 ⁻¹⁰ s / cm or less, particularly 2.0 × 10 ⁻¹⁰ s / cm to 3.0
It has a conductivity of × 10 ⁻¹⁰ s / cm.

Examples of such a white colorant include white pigments such as zinc white, titanium oxide, antimony white, and zinc sulfide, and titanium oxide is particularly preferably used. The white colorant is used in such an amount that the electric conductivity of the toner falls within the above range, but is usually added in the range of 1% by weight to 20% by weight based on the fixing resin medium. .

As the fixing resin medium, styrene-based resin, acrylic resin or styrene-acrylic resin, polyester resin, polyurethane resin, silicone resin, polyamide, modified rosin, or the like is used. Among them, a styrene-acrylic copolymer resin is one of the preferable resin media, and in particular, a styrene monomer (A) and an acrylic monomer (B) are mixed in a ratio of A: B = 50: 50. Styrene-acrylic copolymer resins in the range of from 90 to 90:10, preferably from 60:40 to 85:15 are suitable. The fixing resin medium is generally 0 to
It preferably has an acid value of 25, and more preferably has a glass transition temperature (Tg) of 50 to 65 ° C from the viewpoint of fixability.

As the charge control agent, for example, nigrosine base (CI 5
0415), oil-soluble dyes such as oil black (CI 26150),
Any known positive charge control agent such as a naphthenic acid metal salt, a fatty acid, a soap, and a resin acid soap is blended, whereby the white toner is positively charged.

The particle diameter of the toner measured by a Coulter counter is 8 to 14 μm, particularly 10 to 12 μm on a volume basis median.
μm, and the particle shape should be
It may be an amorphous one produced by a pulverization method or a spherical one produced by a dispersion or suspension polymerization method. The surface of the toner may be coated with a known surface treatment agent such as hydrophobic silica fine particles or resin powder to improve the fluidity.

Two-component magnetic developer: The two-component magnetic developer used in the developing method of the present invention is obtained by combining the above-described resin-coated ferrite carrier with a white toner.
Generally, they are mixed in a weight ratio of 99: 1 to 90:10, especially 98: 2 to 95: 5, and their loose apparent specific gravity is generally
It is in the range of 1.7 to 2.1 g / cm ³ , especially 1.8 to 2.0 g / cm ³ .

In the present invention, since the two-component magnetic developer uses the resin-coated ferrite carrier described above, the initial charge amount of the white toner is −5 to −25 μC / g, particularly measured by a blow-off method, particularly It is set in the range of −10 to −20 μC / g.

Magnetic Brush Development: In the present invention, the two-component magnetic developer described above is used, and development is performed by a magnetic brush development method using a positively charged organic photoreceptor.

As the positively chargeable organic photoreceptor, those known per se can be used, and for example, those disclosed in JP-A-1-118143 (Japanese Patent Application No. 62-27158) are preferably used. Is done.

For example, as shown in FIG. 1, a magnetic brush development is performed around a photoconductor drum 22 having a positively charged photosensitive layer 24 on a conductive substrate, a corona jar 26 for main charging, and an optical system 28 for image exposure. This is performed using an apparatus in which the developing device 10 having the developing sleeve 16 and the transfer mechanism 34 are arranged. Although not shown in FIG. 1, the transfer mechanism 34 and the corona jar are usually used.
A static elimination mechanism and a cleaning device are disposed between the cleaning device and the cleaning device.

That is, the surface of the photosensitive drum 22 (photosensitive layer 24) is uniformly positively charged by the corona jar 26. This main charging potential is usually in the range of 750 to 850V. Then optical system 2
By the image exposure by 8, an electrostatic image is formed on the surface of the photosensitive drum 22. The electrostatic image is developed by rubbing the magnetic brush 18 of the two-component magnetic developer formed and conveyed by the developing sleeve 16 and the photosensitive drum 22 to form a white toner image 36. . The toner image 36 is transferred to a transfer material such as paper by a transfer device groove 34, and is fixed by a predetermined fixing mechanism (not shown) to form an image.

In the above-described magnetic brush development, a power supply 33 is provided on the developing sleeve 16 in order to reduce the influence of the residual potential of the photoconductor.
As a result, a bias voltage having the same polarity as the main charging potential of the photoconductor is applied. As described above, in the positive charging type photoconductor,
Since this residual potential is large, this bias voltage is increased,
In the present invention, it is 280 V or more.

When the bias voltage is increased, the development potential difference (corresponding to the difference between the main charging potential and the bias voltage) is reduced. Therefore, in the present invention, the distance (DD-S) between the photosensitive drum 22 and the development sleeve 16 is set to 1.0 mm. Set to less than.

Development area (nip position between drum 22 and sleeve 16)
The head length of the magnetic brush 18 supplied to the head is 0.5 to 1.5 mm, particularly 0.7 to 1.2 mm, depending on the DD-S width.
It is set in the range of mm.

(Effects of the Invention) According to the present invention, since a two-component magnetic developer composed of a ferrite carrier coated with an amino silicone resin and having a certain particle size distribution and a white toner is used, a positive charging type By developing the electrostatic image formed on the organic photoreceptor, it is possible to obtain a high-density white image without carrier pull, and even when used for a long time, a clear white image without discoloration can be obtained. can get. In particular, even when the developing bias voltage is set to a high voltage of 280 V or more and the spacing between the photoconductor and the developing sleeve is set as small as 1 mm or less, carrier pulling and the like are effectively suppressed. This is extremely advantageous in obtaining an image.

Examples Example 1 Preparation of Magnetic Carrier; Dimethyldichlorosilane, methyltrichlorosilane and N-β (aminoethyl) -γ-aminopropyltrimethoxysilane (hereinafter abbreviated as aminosilane) were used as monomers, and these were used. Amino silicone resin was prepared by condensation polymerization. The aminosilane was used at a ratio of 2.0% by weight based on all monomers.

This amino silicone resin was coated on a ferrite carrier in an amount of 0.1% by weight to prepare a magnetic carrier. Table 1 shows the dynamics such as saturation magnetization and the particle size distribution of the obtained magnetic carrier.

White toner; using titanium oxide as a coloring agent and dispersing it in a styrene-acrylic resin together with a positive charge control agent;
× 10 ⁻¹⁰ s / cm, and a white toner having an average particle size of 13 μm was prepared.

Two-component magnetic developer: The white toner described above and the magnetic carrier were mixed at a weight ratio of 4.5 / 95.5 to prepare a two-component magnetic developer. The initial charge amount of the white toner in this developer was measured by a blow-off method, and the results are shown in Table 1.

Experiment: Using the two-component magnetic developer described above, an image was formed by magnetic brush development using a positively charged organic photoreceptor under the following developing conditions, and the image was evaluated.

DD-S width: 0.8 mm Spike width: 0.7 mm Development potential difference: 460 V Bias voltage: 290 V Image evaluation was performed on carrier pull, image density, and image quality, and was performed by the following method. The results are shown in Table 1.

Carrier pull: After making 500 copies continuously, collect the developer,
The evaluation was based on the amount of carrier loss.

Image density: Image formation was continuously performed on 500 sheets, and the image density of the 500th sheet was visually evaluated. Those that were found to have a sufficient concentration for practical use were indicated by ○, and those that were judged to be slightly lower were indicated by △.

Image quality: Continuous copying of 20,000 sheets was performed continuously, and the 20,000th image was visually judged for whiteness.

Example 2 An image was formed in the same manner as in Example 1 except that the aminosilicone resin-coated ferrite carrier shown in Table 1 was used, and the image was evaluated. Table 1 shows the results.

Comparative Example 1 An image was formed in the same manner as in Example 1 except that the acrylic resin-coated ferrite carrier shown in Table 1 was used, and the image was evaluated. Table 1 shows the results.

Reference Example A silicone resin was prepared in the same manner as in Example 1 except that aminosilane was not used and without using it at all.

Using this silicone resin, a resin-coated ferrite carrier having the following physical properties was prepared.

Coating resin: silicone resin (not containing amino groups) coverage (wt%): 0.49 saturation magnetization (emu / g): 65 fluidity (sec / 50g): 23 D 50 (μm): 80 250mesh path (wt% ): 8 This resin-coated ferrite carrier is used and contains CI Pigment Yellow as a colorant.
When a two-component magnetic developer was prepared by mixing with a yellow toner having an average particle diameter of 11 μm and a mixing ratio of 0 to ¹⁰ s / cm (the mixing ratio was Example 1
And the initial charge amount of the toner was −11 μC / g.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a developing mechanism, FIG. 2 is a diagram showing a relationship between a resin coating amount and a charge amount of a carrier, and FIG. 3 is a characteristic diagram showing a relationship between a bias potential and a carrier pull.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kyoya Taguchi 1-2-28 Tamazuki, Chuo-ku, Osaka, Osaka Inside Mita Industries Co., Ltd. (72) Inventor Hiroyuki Sako 1-2-2, Tamazuki, Chuo-ku, Osaka, Osaka No. 28 Mita Kogyo Co., Ltd. (72) Inventor Takeshi Higuchi 1-2-28 Tamatsukuri, Chuo-ku, Osaka-shi, Osaka No. 28 Mita Kogyo Co., Ltd. (72) Koji Honda 1-2-2 Takuma-zo, Chuo-ku, Osaka-shi, Osaka No. 28 Mita Kogyo Co., Ltd. (56) Reference JP-A-58-168056 (JP, A) JP-A-59-228261 (JP, A) JP-A-59-105652 (JP, A) JP-A-59-105652 JP-A-139056 (JP, A) JP-A-62-125370 (JP, A) JP-A-61-59361 (JP, A) JP-A-64-574 (JP, A)

Claims (1)

(57) [Claims] 1. A two-component magnetic developer comprising a white toner having a conductivity of 3.5 × 10 ⁻¹⁰ s / cm or less and a resin-coated ferrite carrier is transported by a developing sleeve in the form of a magnetic brush. In a magnetic brush developing method of forming a toner image by rubbing with a positively charged organic photoreceptor on which an electrostatic image is formed, the coating resin of the carrier includes a structural unit derived from an amino group-containing monomer component. An amino group-containing silicone resin containing 0.1 to 10% by weight, and the resin coating amount is 0.01 to 0.1% by weight per ferrite carrier. The resin-coated ferrite carrier has a weight average particle diameter of 50%.
% Diameter (D ₅₀ ) is 80 to 120 μm, the particle size is less than 250 mesh and the particle size distribution is 8% by weight or less, and the distance between the positively charged organic photoreceptor and the developing sleeve is 1 mm.
A magnetic brush developing method, wherein the developing is performed while applying a developing bias voltage of 280 V or more.