JP2002123043A - Two-component developing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a two-component developing method and two-component developer, in which electrifying performance, carrying ability, stress resistance are excellent and high image quality and a long life are ensured, with respect to the two-component developing method using a two-component developing machine having two or more magnet rolls that are used in a printer which is operated at high speed, for example a linear velocity of >=370 mm/sec, preferably >=500 mm/sec. SOLUTION: In the two-component developing method that uses the two-component developing device having two or more magnet rolls and uses the two component developer including toner and carrier, ferrite carrier that satisfies the following conditions (a) and (b) is used: (a) magnetization measured when a magnetic field of 1 kOe is applied is 45 to 75 emu/g; and (b) a ratio between magnetization A measured when 1 kOE is applied and magnetization B calculated by a primary approximate expression (measured magnetization A/calculated magnetization B) is <=0.90, in which a relationship between magnetization measured when a magnetic field of -0.5 to 0.5 kOe is applied and the applied magnetic field is expressed by the primary approximate expression passing through an original point. The two-component developer is used for the two-component developing machine having the two or more magnetic rolls, and contains the ferrite carrier.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-component developing method and a two-component developer used for developing an electrostatic latent image formed in electrophotography, electrostatic recording, electrostatic printing, and the like.

[0002]

2. Description of the Related Art In the field of high-speed printers, a two-component developing method is mainly used from the viewpoints of charging performance, transportability, stress, and the like given to toner. In order to further improve the chargeability and transportability of toner. In many cases, the number of magnet rolls in a developing machine is two or more.

[0003] The use of a plurality of magnet rolls improves the stirring efficiency of the developer and increases the contact area / frequency with the photoreceptor to obtain a stable charging property. On the other hand, the developer tends to be clogged between the magnet rolls. Therefore, the stress applied to the developer is increased, and toner spent on the carrier surface is easily caused. As a result, fluctuations in charging are caused, which is a factor of shortening the life of the developer. In particular, since the transportability is improved, stress on the photoreceptor is also increased, and filming is likely to occur, resulting in a reduction in the life of the photoreceptor.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to achieve a linear velocity of 370 mm / sec or more, preferably 500 mm / sec.
In a two-component developing method using a two-component developing machine having two or more magnet rolls used for high-speed printers of c or higher, two-component developing with excellent charging performance, transportability, stress, etc., high image quality and long life It is to provide a method and a two-component developer.

[0005]

Means for Solving the Problems The present invention provides: [1] a two-component developing machine having two or more magnet rolls and a two-component developing method using a two-component developer comprising a toner and a carrier, A two-component developing method using a ferrite carrier satisfying the following conditions (a) and (b), and (a) magnetization measured when a magnetic field of 1 kOe is applied:
45-75 emu / g (b) When 1 kOe is applied when the relationship between the magnetization measured when a magnetic field of 0.5-0.5 kOe is applied and the applied magnetic field is expressed by a first-order approximation formula passing through the origin. (Measured magnetization A / calculated magnetization B): 0.90 or less [2] Used in a two-component developing machine having two or more magnet rolls A two-component developer comprising the ferrite carrier described in (1) above.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The two-component developing method of the present invention has a great feature in that a carrier having specified magnetic properties is used. Generally, magnetic powder exhibits magnetic hysteresis in the relationship between magnetic field and magnetization. Therefore, the carrier used in the two-component developing method is also a magnetic powder and thus has magnetic hysteresis, but the degree of hysteresis is extremely small.
Therefore, the magnetization of the carrier in the low magnetic field region changes as a linear linear function with respect to the magnetic field. However, in the magnetic field range close to 1 kOe, the behavior deviates from the linear linear function seen in the low magnetic field range, and the magnetic field tends to be saturated.

On the other hand, in a two-component developing method using a two-component developing machine having two or more magnet rolls, if the followability of the carrier to the rotation of the magnet roll is poor, the developer is clogged between the rolls, and the image quality characteristics are reduced. make worse. However, by using a carrier that is in a magnetically saturated region in the magnetic field formed by the magnet roll, the carrier follows the movement of the magnet roll, forming a good ear and improving the transportability and developability of the developer. It is expected to improve.

Accordingly, the present invention uses carriers whose transition to magnetic saturation occurs from a low magnetic field. Specifically, it is considered that a magnet roll having characteristics close to magnetic saturation at 1 kOe or less is preferable from the magnetic characteristics of a magnet roll used in an electrophotographic system, and a carrier satisfying the following conditions (a) and (b) is used. .

(A) The magnetization measured when a magnetic field of 1 kOe is applied is 45 to 75 emu / g, preferably 50 to 75 emu / g.
(B) When the relationship between the magnetization measured when a magnetic field of -0.5 to 0.5 kOe is applied and the applied magnetic field is expressed by a linear approximation passing through the origin, when 1 kOe is applied The ratio of the measured magnetization A to the value of the calculated magnetization B calculated by the first-order approximation (measured magnetization A / calculated magnetization B) is 0.90 or less, preferably 0.5 to 0.85.

In the condition (a), the magnetization is 45 emu /
If it is less than g, the carrier is less susceptible to the magnetic field, and the carrier cannot follow the movement of the magnet roll to form ears. If it is more than 75 emu / g, the amount of ears becomes excessive, A phenomenon occurs in which the developed image is scraped off to lower the image density.

In the condition (b), -0.5 to 0.5 k
The reason for the first-order approximation formula passing through the origin in the magnetic field of Oe is that the magnetic field formed by the magnet roll in the developing unit is usually as small as 1 kOe or less, and magnetic hysteresis of the carrier hardly occurs in this magnetic field region.
This is because, since there is no need to consider the residual magnetization and the coercive force, the magnetic field and the magnetization of the carrier behave as a linear linear function.

Carriers exhibiting the measured magnetization A / calculated magnetization B ≦ 0.90 mean that they have shifted to a magnetically saturated region at a relatively low magnetic field, and have a good magnetization response to the magnetic field. When the measured magnetization A / calculated magnetization B is greater than 0.90, the magnetic field at which the carrier reaches saturation magnetization is relatively high, so that the carrier does not reach magnetic saturation on the magnet roll, and the magnetic field followability of each carrier is reduced. Inadequate,
The developing characteristics become unstable.

Oe is a unit of magnetic field strength, and Ge
Auss is a unit of magnetic flux density. If a magnetic field of 1 Oe exists in a vacuum, a magnetic flux density of 1 Gauss is generated.
Generally, Oe and Gauss are used almost indiscriminately on a daily basis, but Gauss is mostly used when describing the characteristics of a magnet roll. When describing the magnetic properties of a magnetic powder or the like, the magnetic field strength Oe is used. The same applies to the present invention.

In the present invention, a ferrite carrier whose magnetization characteristics can be adjusted is used as the carrier.

The raw material of the ferrite carrier is F
e ₂ O ₃ , and MgO, Mn ₃ O ₄ ,
CuO, NiO, ZnO, SrCO ₃ , BaCO ₃ , M
nCO _{3 and the} like, and as additives, A1 ₂ O ₃ ,
SiO ₂ , Bi ₂ O ₃ , CaCO ₃ , V ₂ O ₅ , TiO
₂ , SnO ₂ , PbO, etc., but in the present invention,
From the viewpoints of adjustment of magnetic properties and ease of production, a ferrite carrier containing a magnesium compound and / or a manganese compound, more preferably a manganese compound, and mainly composed of iron oxide is preferable. The content of magnesium in the ferrite carrier is preferably 0.1 to 20% by weight, more preferably 0.5 to 10% by weight, and the content of manganese is preferably 0 to 40% by weight, more preferably 10 to 35% by weight.

In general, a ferrite carrier is prepared by mixing the above-mentioned raw materials and additives, calcining the mixture at about 1000 ° C., then pouring the mixture into water, and pulverizing the mixture to an average particle size of about 1 μm using a ball mill or the like. Polyvinyl alcohol or the like is added as a binder therein, and an antifoaming agent, a dispersant, and the like are further added to form a slurry. The slurry is granulated with a spray drier and dried with hot air. After that, it is baked at about 1200 ° C. or more, crushed, and then subjected to magnetic separation and classification to obtain a ferrite carrier.
The magnetic properties of the ferrite carrier can be adjusted by changing the additives to be mixed with the raw material mainly composed of iron oxide and the amount of the additives.

The surface of the carrier may be further coated with a resin from the viewpoints of chargeability, durability and the like. Examples of the coating resin include a fluorine resin, a silicone resin, an acrylic resin, a styrene-methacrylate resin, a styrene-acryl copolymer resin, a polymer resin, a polybutadiene resin, and a mixed resin thereof.
The resin coating can be performed by dissolving the resin in an organic solvent or the like, applying the resin to the carrier surface by dipping or spraying, and then drying or heating and curing to form a film.

In the present invention, the magnetic properties of the main magnetic pole of the magnet roll are preferably 1 kGauss or less on the sleeve of the magnet roll from the viewpoints of the developer transportability and the formation of appropriate ears.

The two-component developing method of the present invention takes account of the responsiveness of magnetization to a magnetic field, and the responsiveness of carrier magnetization is considered to be a very important factor in considering appropriate development characteristics.

The developing method of the present invention is particularly applicable to a two-component developing machine having two or more magnet rolls and a two-component developing method using a two-component developer comprising a toner and a carrier having the above-mentioned magnetic properties. Although not limited, when the number of magnet rolls is one, the effect of the carrier having the above-described characteristics is not seen. Although the reason is not clear, copiers and printers that use a single magnet roll development system are generally slow in process speed, and because of this process speed, the developer is relatively easy to stud, and toner This is probably due to the good transportability.

As a photosensitive member of a developing machine used in the developing method of the present invention, amorphous selenium, zinc oxide, cadmium sulfide, an organic photosensitive member, amorphous silicon or the like is used. Effective in combination with the body.

The two-component developer used in the two-component developing method of the present invention is not particularly limited as long as it contains the above-mentioned carrier.
An ordinary toner comprising a colorant or the like can be used without any particular limitation.

Examples of the binder resin include polyester, a polyester / styrene-acrylic polymer resin, a mixed resin of polyester and another resin, a hybrid resin, and a styrene-acrylic resin. From the viewpoint of colorant dispersibility, polyester and hybrid resins are preferred, and polyester is more preferred.

The polyester used in the present invention can be produced, for example, by using the compounds exemplified in JP-A-7-175260 and referring to the method described therein.

As a raw material monomer for the polyester, a divalent or higher valent alcohol component and a carboxylic acid component such as a divalent or higher carboxylic acid, carboxylic anhydride, or carboxylic ester are used.

Preferred dihydric alcohol components include bisphenol A alkylene (C2 or C3) oxide adduct (average number of moles added: 1 to 10), ethylene glycol, propylene glycol, 1,6-hexanediol, bisphenol A, hydrogenated bisphenol A and the like. Preferred trihydric or higher alcohol components are sorbitol, 1,4-sorbitan, pentaerythritol, glycerol, trimethylolpropane, and the like.

Examples of the divalent carboxylic acid component include various dicarboxylic acids, succinic acid substituted with an alkyl or alkenyl group having 1 to 20 carbon atoms, anhydrides of these acids, and alkyl (1 to 12 carbon atoms). ) Esters and the like;
Preferred are maleic acid, fumaric acid, terephthalic acid and succinic acid substituted with an alkenyl group having 2 to 20 carbon atoms. Preferred trivalent or higher carboxylic acid components are 1,2,
4-benzenetricarboxylic acid (trimellitic acid) and its anhydrides, alkyl (C1-12) esters and the like.

When polymerizing the raw material monomer of the polyester, a commonly used esterification catalyst such as dibutyltin oxide may be appropriately used in order to accelerate the reaction.

In the present invention, as described in JP-A-8-171231, a hybrid resin is obtained by using a mixture of two monomer monomers of a polymerization system having independent reaction paths as raw materials. Is obtained.

The two polymerization reactions proceed in independent reaction paths, and are preferably reactions that produce a condensation polymerization resin and an addition polymerization resin, respectively. As typical examples of the condensation polymerization resin, polyester, polyester
Polyamide, polyamide and the like are mentioned, and a typical example of the addition polymerization resin is a vinyl polymerization resin obtained by a radical polymerization reaction.

Of these, the polyester component can be obtained using the same divalent or higher alcohol component as described above and a carboxylic acid component such as a divalent or higher carboxylic acid, carboxylic anhydride, or carboxylic ester as the raw material monomers. .

Examples of the raw material monomer used to form the amide component in the polyester / polyamide or polyamide include various known polyamines, aminocarboxylic acids, amino alcohols, etc., preferably hexamethylenediamine and ε- Caprolactam.

The raw material monomers used to form the vinyl polymer resin obtained by the addition polymerization reaction include styrene; ethylenically unsaturated monoolefins such as ethylene and propylene; diolefins such as butadiene; ) Ethylenic monocarboxylic acid such as acrylic acid: alkyl (meth) acrylic acid (C1-18)
Examples include esters of ethylenic monocarboxylic acids such as esters.

The hybrid resin is prepared by mixing a raw material monomer of a polycondensation resin, a raw material monomer of an addition polymerization resin, a polymerization initiator and the like. It is preferable to obtain an addition polymerization type resin component having a group, then raise the reaction temperature to 190 to 270 ° C., and then form the condensation polymerization type resin component mainly by a condensation polymerization reaction. A resin in which the compatibility of two kinds of resins is improved can be efficiently obtained by using such a mixture of raw material monomers as raw materials and allowing two independent reactions to proceed.

The weight ratio of the condensation polymerization resin to the addition polymerization resin, that is, the weight ratio of the raw material monomer of the condensation polymerization resin to the raw material monomer of the addition polymerization resin is usually 50 from the viewpoint of the dispersibility of the addition polymerization resin. / 50 to 95/5, preferably 60/40 to 95/5.

Further, the toner used in the present invention includes:
Additives such as coloring agents, release agents, charge control agents, conductivity regulators, fillers such as extenders, fibrous substances, reinforcing fillers such as antioxidants, antioxidants, fluidity improvers, and cleanability improvers. May be appropriately contained.

As the colorant, any of dyes and pigments used as colorants for toner can be used. Carbon black, phthalocyanine blue, permanent brown FG, brilliant fast scarlet, pigment green B, rhodamine- B base,
Solvent Red 49, Solvent Red 146, Solvent Blue 35, Quinacridone, Carmine 6B, Disazo Yellow and the like, and these can be used alone or in combination of two or more. The content of the colorant is preferably 1 to 10 parts by weight based on 100 parts by weight of the binder resin.

As the release agent, a low melting point wax having a melting point of 70 to 90 ° C. is preferable, and examples thereof include ester waxes and synthetic waxes such as Fischer-Tropsch wax.

Examples of the positively chargeable charge control agent include a nigrosine dye, a triphenylmethane dye containing a tertiary amine as a side chain, a quaternary ammonium salt compound, a polyamine resin, and an imidazole derivative. Nigrosine dyes are preferred from the viewpoints of stabilizing the dispersibility and the charge amount of the toner. Examples of the negative charge control agent include a metal-containing azo dye, a copper phthalocyanine dye, and a metal complex of an alkyl derivative of salicylic acid. In addition,
Both the positive charge control agent and the negative charge control agent may be contained.

The toner in the present invention is preferably a pulverized toner obtained by a kneading pulverization method or the like. For example, a binder resin, a colorant and the like are uniformly mixed by a mixer such as a ball mill, and then a closed kneader or a uniaxial or It can be manufactured by melt-kneading with a twin-screw extruder or the like, cooling, pulverizing, and classifying. Further, a fluidity improver such as hydrophobic silica may be added to the surface of the toner as needed. The volume average particle diameter of the toner thus obtained is preferably 3
１５15 μm.

[0041]

EXAMPLES Toner Production Examples Polyoxypropylene (2.2) -2,2-bis (4-hydroxyphenyl) propane 2000 g, polyoxyethylene (2.2) -2,2-bis (4-hydroxyphenyl) propane 800 g, 250 g of isododecenyl succinic anhydride,
800 g of terephthalic acid, 250 g of trimellitic anhydride,
A mixture of 0.5 g of dibutyltin oxide as an esterification catalyst was reacted at 220 ° C. under a nitrogen atmosphere until the softening point measured by ASTM E28-67 reached 145 ° C. After completion of the reaction, the mixture was cooled and pulverized to obtain a resin (polyester).

100 parts by weight of the obtained resin, 7 parts by weight of carbon black “Monarch 880” (manufactured by Cabot),
1.5 parts by weight of polypropylene wax "VISCOL 660P" (manufactured by Sanyo Chemical Industries, Ltd.) and charge control agent "Bontron
After premixing 2.0 parts by weight of "N-01" (manufactured by Orient Chemical Industries, Nigrosine Dye) using a Henschel mixer, the mixture was melt-kneaded with a twin-screw extruder, cooled, and then subjected to a usual pulverization and classification process. After that, 0.3 parts by weight of hydrophobic silica “HVK2150” (manufactured by Clariant) is mixed and adhered to the surface of 100 parts by weight of the obtained powder using a Henschel mixer, and a toner having a volume average particle diameter of 10 μm is added. Obtained.

Production Example of Carrier Iron oxide (Fe_TwoO_Three), Magnesium oxide (Mg)
O), manganese oxide (Mn) _ThreeO_Four), Magnesium and
And / or the content of manganese in the carrier is as shown in Table 1.
100 parts by weight of the resulting mixture
1.5 parts by weight of binder (polyvinyl alcohol)
And 0.5 parts by weight of a dispersant, and the slurry concentration was 50
Water was added to give a weight percent. This is made by Mitsui Mining Co., Ltd.
Wet grinding and mixing for 1 hour with an attritor
Made.

The slurry was granulated and dried with a spray drier, then fired in an electric furnace under a nitrogen atmosphere at about 1500 ° C., and classified with a vibrating sieve to obtain a carrier core material.
To 1000 parts by weight of the obtained core material, a fluororesin “H” was used.
Methyl ethyl ketone was added to 6 parts by weight of “YLAR301F” (manufactured by Ausimond) and 4 parts by weight of acrylic resin “Dianal BR-80” (manufactured by Mitsubishi Rayon Co., Ltd.) to prepare a resin solution for coating the core material. This resin solution was spray-coated on the core material using a fluid coating apparatus. Thereafter, a heat treatment is performed at 100 ° C. for 60 minutes in the fluidized bed to obtain a carrier A having an average particle diameter of 110 μm.
~ E was obtained. Note that the carrier B, C, and E have the same raw material composition, but are slightly affected by the firing temperature, impurities, and the like.
The different magnetic properties shown in Table 2 were shown. The carriers F and G are commercially available magnetite carriers.

[0045]

[Table 1]

The magnetic properties of the obtained carrier were measured by the following method. (1) The carrier is filled while tapping the plastic case with a lid having an outer diameter of 7 mm and a height of 5 mm, and the mass of the carrier is determined from the difference between the weight of the plastic case and the weight of the plastic case filled with the carrier. (2) Riken Denshi Co., Ltd. magnetic property measuring device "BHV-50"
A plastic case filled with a carrier is set in a sample holder of "H" (VS. MAGNETOMETER), and a magnetic field is applied while vibrating the plastic case using a vibration function to measure magnetic properties. The obtained value is converted into magnetic properties per unit mass in consideration of the mass of the filled carrier.

-10 kOe of carrier A and carrier E
A graph showing measured magnetization per unit mass in an applied magnetic field of ~ + 10 kOe and a first-order approximation line and a first-order approximation by a least square method obtained from the measured magnetization in an applied magnetic field of -0.5 to 0.5 kOe are shown in FIGS. 4 respectively.

For the carriers B to D, F, and G, a graph is created in the same manner as for the carriers A and E.
Table 2 shows the measured magnetization A at the time of application of kOe, a first-order approximation in a magnetic field of -0.5 to 0.5 kOe, the calculated magnetization B at the time of 1 kOe application, and the value of the measured magnetization A / calculated magnetization B calculated from the first-order approximation. Are shown below.

[0049]

[Table 2]

Examples 1 to 4 and Comparative Examples 1 to 39 39 parts by weight of the toner obtained in the above Production Example and 1261 parts by weight of a carrier shown in Table 3 were mixed with a Nauter mixer to obtain each developer. Was.

"Infoprint 4000ISl"
(Manufactured by IBM Japan, Ltd., linear velocity: 1066 m
m / sec, resolution: 240 dpi, number of magnet rolls of a developing machine: 3), and the printing pattern with a blackening ratio of 8% was continuously printed using 11 × 18 inch continuous paper. . As a result of the damage caused on the photoreceptor due to the stress caused by the developer and the filming of the toner, the number of white spots on the printed black solid portion is defined as the number of filming occurrences and the durability is measured. did. According to the following methods, the amount of charge, the image density, and the background fog at the end of life were measured when printing 50,000 sheets and at the end of life. Note that the maximum printing life is up to one million sheets. If filming does not occur even after printing one million sheets, the life end is the time of printing one million sheets. Table 3 shows the results.

[Charge Amount] Measured using a Q / M meter (manufactured by Epping Corporation). A specified amount of developer is charged into a cell attached to the Q / M meter, and only the toner is sucked through a sieve (twill) having a mesh size of 32 μm. The voltage change on the carrier generated at that time is monitored, and 90 minutes from the start of measurement.
The voltage after the second is converted into a charge amount to be a charge amount of the developer.

[Image density] "Model 938 Spectrodensito
meter "(X-Rite, aperture; 20 mm, measurement mode; Yxy, light source; D ₆₅ , viewing angle; 10 degree)
Is used to measure the solid black portion at the time of printing 5000 sheets and at the end of life, and the value of image density = log (1 / Y) is obtained.

[Undercoat Fogging] "Model 938 Spectrodensi
tometer "(X-Rite, aperture; 20 mm,
Measurement mode: Yxy, light source: D ₆₅ , viewing angle: 10degre
Using e), measure the Y value of the white part of the printed paper and the Y value of the unprinted paper, and obtain the value of base fog = Y value of the unprinted paper-Y value of the white part of the printed paper.

[0055]

[Table 3]

From the above results, in Examples 1 to 4, the charge amount, the image density and the background fog were all very good and stable, and the deterioration of the background fog and the occurrence of filming were observed even after 1,000,000 sheets of printing. Is not confirmed and has excellent durability. Although the behavior of the developer on the magnet roll was also observed on the way, very clean ears were formed, and very good follow-up performance to the rotation of the magnet roll was confirmed.

Further, with respect to the print quality, the formation of fine lines and the uniformity of solid black portions were very good. From these results, it is clear that, as shown in the present invention, in the magnetic properties of the carrier, it is better that the magnetic saturation occurs in a low magnetic field. , And a good spike can be formed, and the toner transporting property and the developing property can be improved.

On the other hand, in Comparative Examples 1 to 3, as shown in Table 2, since the magnetic saturation was located in the high magnetic field range, the magnetic characteristics did not reach the magnetic saturation on the magnet roll, so that the developing characteristics were unstable. It is considered that base fogging and filming occurred. Comparing the occurrence times of filming, the responsiveness of magnetization to a magnetic field is related irrespective of the core composition of the carrier. As the value of the measured magnetization A / calculated magnetization B at the time of applying 1 kOe is larger than 0.90, the occurrence of the filming occurs. The time is getting earlier.

[0059]

According to the present invention, the linear velocity is 370 mm / sec.
As described above, in a two-component developing method using two or more magnet rolls, which is preferably used for a high-speed printer of 500 mm / sec or more, a two-component developing method which is excellent in charging performance, transportability, stress, etc. and has high image quality and long life. A method can be provided.

[Brief description of the drawings]

FIG. 1 is a graph showing measured magnetization per unit mass of a carrier A prepared in an example in an applied magnetic field of −10 kOe to +10 kOe.

FIG. 2 is a graph showing a first-order approximation line and a first-order approximation by a least square method obtained from measured magnetization of a carrier A prepared in an example in an applied magnetic field of −0.5 to 0.5 kOe. .

FIG. 3 is a graph showing measured magnetization per unit mass of a carrier E prepared in an example in an applied magnetic field of −10 kOe to +10 kOe.

FIG. 4 is a graph showing a first-order approximation line and a first-order approximation by a least-squares method obtained from measured magnetization of a carrier E prepared in an example in an applied magnetic field of −0.5 to 0.5 kOe. .

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hidenori Tachi 1334 Minato, Wakayama-shi Kao Research Institute F-term (reference) 2H005 BA02 BA06 CA02 CA11 CB04 CB07 EA02 FA01 2H031 AC07 BA09 2H077 EA03 EA21 FA19

Claims (3)

[Claims] 1. A two-component developing machine having two or more magnet rolls and a two-component developing method using a two-component developer comprising a toner and a carrier, wherein the following conditions (a) and (b) are satisfied: A two-component developing method using a satisfactory ferrite carrier. (A) Magnetization measured when a magnetic field of 1 kOe is applied:
45-75 emu / g (b) When 1 kOe is applied when the relationship between the magnetization measured when a magnetic field of 0.5-0.5 kOe is applied and the applied magnetic field is expressed by a first-order approximation formula passing through the origin. Ratio between the measured magnetization A and the value of the calculated magnetization B calculated by the linear approximation (measured magnetization A / calculated magnetization B): 0.90 or less 2. The two-component developing method according to claim 1, wherein the ferrite carrier is a ferrite carrier containing a magnesium compound and / or a manganese compound. 3. A two-component developer for use in a two-component developer having two or more magnet rolls, the two-component developer containing the ferrite carrier according to claim 1 or 2.