JPH09152747A - Carrier for two-component developer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration of initial characteristics over a long period of time by dispersing a specified amt. of high resistance magnetic powder having a specified resistivity in a resin having a specified wt. average mol.wt. SOLUTION: High resistance magnetic powder having >=1×10<5> Ω.cm resistivity is dispersed in a bonding resin having a wt. average mol.wt. of 80,000-150,000 in the mol.wt. distribution of the THF-soluble component by gel permeation chromatigraphy by 150-800 pts.wt. per 100 pts.wt. of the resin to obtain the objective carrier. When the wt. average mol.wt. of the resin is <80,000, the carrier becomes brittle and causes cracking. The cracked carrier sticks to an image, accelerates the wear of a photosensitive drum and damages the drum. In the case of >150,000, it becomes difficult to melt and knead the resin with other material in a producing process, pulverizability is deteriorated and production efficiency is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier for two-component developer, and more specifically, it has a small force required for stirring toner particles for charging and a small torque for carrying a magnetic brush. The present invention relates to a carrier for a two-component developer.

[0002]

2. Description of the Related Art As a carrier for a developer for developing an electrostatic charge image formed on an electrophotographic photosensitive member, a magnetic carrier made of iron powder, ferrite particles or the like is widely used. During development, this two-component developer mixes a magnetic carrier and toner to charge toner particles to a certain polarity, conveys this mixture to a photoconductor in the form of a magnetic brush, and the surface of the photoconductor is brushed with the magnetic brush. Rubbing to attract and hold the charged toner on the electrostatic charge image on the surface of the photoconductor to form a visible image.

However, in the conventionally known two-component developer, a large stirring force is required for mixing and stirring the magnetic carrier and the toner for charging the toner particles, and the developer is transferred to the photoconductor in the form of a magnetic brush. There are many device restrictions, such as a large torque being required for transportation. In addition, since the rubbing force of the magnetic brush on the photoconductor is large,
There is still room for improvement in terms of image quality, such as white streaks (sweep traces of the magnetic brush) occurring in the formed image.

In order to solve the above problems, Japanese Patent Laid-Open No. 54-
Japanese Patent No. 66134 discloses a so-called binder type carrier. The binder type carrier is one in which magnetic powder is dispersed in a binder resin, and has a smaller specific gravity than a conventionally known carrier using iron powder, ferrite or the like, and thus is lightweight. Therefore, the problems of the conventional carrier as described above can be solved.

However, since the binder type carrier binds the magnetic powder, which is an inorganic substance, with the resin, which is an organic substance,
If the binding property between the two is poor, there is a problem that the carrier is broken during the process of stirring and carrying. If broken carrier fragments adhere to the non-image area, secondary trouble such as fogging of the image may occur. JP-A-56-51755 proposes a carrier containing a titanium coupling agent. Although this carrier has improved binding property, when used for a long period of time, carrier cracking may occur. Since it contains a coupling agent more than that, its stability in an environment such as high temperature and high humidity is insufficient, and if it is used in such an environment, the insufficient amount of charge may cause Fogging occurs in the captured image.

[0006]

Therefore, an object of the present invention is to always exhibit stable performance even under a harsh environment such as high temperature and high humidity, and to improve mixing and stirring properties with a toner.
It is an object of the present invention to provide a carrier for a two-component developer having improved properties such as the transportability of the magnetic brush and the rubbing force of the magnetic brush.

Another object of the present invention is to provide a carrier for a two-component developer whose initial characteristics do not deteriorate even after long-term use. Another object of the present invention is to provide a carrier for a two-component developer in which the tendency of adhesion and aggregation on the surface of the photoreceptor is effectively improved.

[0008]

According to the present invention, at least a gel permeation chromatograph (GP) of a tetrohydrofuran (hereinafter referred to as "THF") soluble component is used.
In the molecular weight distribution of C), in a resin having a weight average molecular weight of 80,000 to 150,000, 150 to 800 parts by weight of high resistance magnetic powder having a specific resistance of 1 × 10 ⁵ Ω · cm or more per 100 parts by weight of the resin. There is provided a carrier for a two-component developer, which is characterized by being dispersed.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The binder resin used in the present invention has a weight average molecular weight of 80,000 to 150,000, preferably 90,000 to 13 in the molecular weight distribution of GPC of THF-soluble matter.
Whatever is used is used. If the weight average molecular weight is less than 80,000, the carrier becomes fragile and carrier cracks occur, and the broken carrier adheres to the image and the photoconductor drum is severely worn. In the worst case, the photoconductor drum is damaged. Or Further, when the carrier is crushed, a large amount of fine powder is generated, which lowers the production efficiency. On the other hand, when the weight average molecular weight exceeds 150,000, it is not preferable because not only the melt-kneading with other substances becomes difficult in the manufacturing process but also the pulverizability deteriorates, resulting in poor production efficiency.

The binder resin that can be used may be a conventionally known thermoplastic resin or a thermosetting resin in the form of an uncured or precondensate as long as the weight average molecular weight is within the above range. For example, vinyl such as polystyrene. Aromatic resins, acrylic resins, polyvinyl acetal resins, polyester resins, epoxy resins, phenol resins, petroleum resins, polyolefin resins, and copolymers of these resins are listed, among which styrene resins, acrylic resins or styrene-acrylic resins. Copolymer resins are preferably used.

Magnets used in the binder type carrier of the present invention
As a powder, the specific resistance is 1 × 10 ^FiveΩ · cm or more, special
1 × 10⁶~ 1 × 10⁷Ω · cm high resistance magnetic powder is used.
Used. Generally, as magnetic powder, triiron tetraoxide (Fe_Three
O_Four), Iron sesquioxide (γ-Fe_TwoO_Three), Zinc iron oxide (Z
nFe_TwoO_Four), Yttrium iron oxide (Y_ThreeFe_FiveO₁₂),
Iron cadmium oxide (CdFe_TwoO_Four), Iron oxide gadolinium
(Gd_ThreeFe_FiveO₁₂), Copper iron oxide (CuFe_TwoO_Four), Oxidation
Iron-lead (PbFe₁₂O₁₉), Iron oxide nickel (NiFe_Two
O_Four), Neodymium iron oxide (NdFeO)_Three), Iron oxide burr
Um (BaFe₁₂O₁₉), Iron magnesium oxide (MgF
e_TwoO_Four), Iron manganese oxide (MnFe)_TwoO_Four), Iron oxide
(LaFeO_Three), Iron powder (Fe), cobalt powder
(Co), nickel powder (Ni), etc. are widely known.
These are used as magnetic components in magnetic toner.
I have.

However, these have a specific resistance of 1 × 1.
0 ⁵ Omega · lower than cm, for example the resistivity of the tri-iron tetroxide (magnetite) is about 1 × 10 ³ Ω · cm. Therefore, in the present invention, it is necessary not to use these magnetic powders as they are, but to adjust the specific resistance within the above range by using, for example, surface oxidation treatment or removal of contaminant ions. Further, ferrite conventionally used as a magnetic carrier of a two-component magnetic developer has a high resistance and can be used without any special treatment.

Further, it is preferable that the particle diameter of the magnetic powder is usually 2 μm or less, particularly 0.05 to 1 μm. If the particle size is larger than this range, it may be difficult to adjust the particle size of the granular carrier in which the magnetic powder is dispersed in the resin to the above range. The magnetic powder may be surface-treated with, for example, a silane coupling agent or a titanium coupling agent as long as the specific resistance is within the above range, and the dispersibility in the resin may be improved.

As typical silane coupling agents,
For example, equation (1)

[0015]

Embedded image (In the formula, R represents a vinyl group, an amino group, an imino group, an epoxy group or a mercapto group, X represents a hydrolyzable group such as a lower alkoxy group or a halogen atom, and Y represents an alkyl group or a group X. , Particularly vinyltriethoxysilane, vinyltrichlorosilane and other vinylsilanes, aminopropyltriethoxysilane and other aminosilanes, γ-glycidoxypropyltriethoxysilane and other epoxysilanes, γ-isocyanatopropylethoxy Isocyanate functional silanes such as silanes may be mentioned.

As the titanium-based coupling agent, for example, the following formula (2) is used.

[0017]

(R ¹ O) n-Ti- (OR ² ) ₄ -n · mHOP (OR ³ ) (2) (In the formula, R ¹ is a substituted or unsubstituted alkyl group or aryl group, and R ² is an acyl group, R ³ is a substituted or unsubstituted alkyl group or aryl group, and n is 1
When m is 0 or 1, and n is 2, R ¹ may be an alkylene group or an alkylenecarbonyl group. ), Particularly isopropyl triisostearoyl titanate, isopropyl trioctanoyl titanate, isopropyl dimethacryl isostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, isopropyl isostearoyl diacrylic titanate, isopropyl tricumyl phenyl titanate, isopropyl tri ( N-aminoethyl-aminoethyl) titanate, bis (dioctyl pyrophosphate) oxyacetate titanate, bis (dioctyl pyrophosphate) ethylene titanate, isopropyl tris (dioctyl pyrophosphate) titanate, tetraoctyl bis (ditridecyl phosphite) titanate, tetra (2,2-diallyloxymethyl-1-butyl) bis (di Li decyl phosphite) titanate, tetraisopropyl bis (ditridecylphosphite) such as titanates.

When the weight average molecular weight / number average molecular weight (Mw / Mn) is 3 or less in the GPC molecular weight distribution of the THF-soluble component of the binder resin, the object of the present invention can be more remarkably achieved. In the carrier of the present invention, the binder resin 1
It is necessary to contain 150 to 800 parts by weight of magnetic powder per 100 parts by weight. When the content of the magnetic powder is more than 800 parts by weight per 100 parts by weight of the binder resin, the magnetic force of the magnetic brush becomes high, so that the stirring force required for mixing and stirring becomes large, and the rubbing of the magnetic brush is performed. The power is also large and the image quality is unsatisfactory. On the other hand, when the content of the magnetic powder is less than 150 parts by weight per 100 parts by weight of the binder resin, the magnetic force of the magnetic brush becomes too small, and it is difficult to effectively carry the developer in the form of the magnetic brush. As a result, carrier scattering and the like occur, which contaminates the inside of the machine, and scattered carriers adhere to the image.

Unlike the carrier of the present invention, the conventional magnetic carrier having a resin-coated surface has a large magnetic component content in the carrier and has an extremely small particle size, so that the magnetic force of the magnetic brush is large. The magnetic brush described above is extremely inferior in terms of transportability and rubbing property. In order to prevent this, the carrier of the present invention has a particle size of 50 to 150 μm, preferably 70 to 12
It is preferably in the range of 0 μm. Further, the carrier of the present invention has a clearly smaller density than the conventional carrier in which the magnetic material surface is coated with a resin. Therefore, the stirring force required for mixing and stirring the carrier and the toner may be small,
Due to the charging of the toner, the mixing and stirring can be performed under mild conditions. Further, since it is a carrier with a large particle size, even though this carrier is one in which magnetic powder is dispersed in a resin, the aggregation tendency of the carriers is effectively suppressed,
The advantage that the magnetic brush development can be stably performed is also achieved.

For example, if the particle size of the carrier is smaller than 50 μm, the amount of fine powder increases, the density of the carrier increases, and a large stirring force is required for mixing and stirring the carrier and the toner for charging the toner. Therefore, the limitation on the device becomes large. Further, since the surface area of the carrier having a resin surface is large, the carriers are likely to aggregate with each other. On the other hand, if the particle size is larger than 150 μm, the surface area of the carrier becomes small, and the contact area with the toner cannot be sufficiently taken during mixing and stirring for charging the toner, and the toner is uniformly triboelectrified. Tends to be difficult.

In the present invention, the above-mentioned high-resistance magnetic powder is used, and as described above, the amount of the magnetic powder used with respect to the resin is considerably smaller than that of the conventionally known resin-coated carrier. The tendency of the carrier to adhere to the photoconductor due to the low resistance of the carrier is effectively prevented. (Carrier) As described above, the carrier of the present invention is GP
A resin having a molecular weight of 80,000 to 150,000 by C and magnetic powder are uniformly kneaded under heating, and fine powder is cut by pulverization and classification to adjust the particle diameter to a range of 50 to 150 μm, preferably 70 to 120 μm. It is manufactured by

Since the granular carrier thus obtained has a low density and the magnetic force of the magnetic brush is small, the mixing and stirring property and the transport property of the magnetic brush are good,
Further, the rubbing force of the magnetic brush on the photoconductor at the time of development is alleviated, and there are few restrictions on the apparatus, and it is extremely advantageous in obtaining an image of good quality. In addition, there is almost no aggregation of carriers or adhesion to the surface of the photoconductor. (Toner) Conventionally known toners can be used in the two-component developer of the present invention. Such toner is
For example, as the fixing resin, a resin having the fixing property and the electric detection property required for the toner, for example, a styrene resin, a styrene-acrylic resin, a polyester resin, a polyurethane resin, a silicone resin, a polyamide resin, a modified rosin, or the like is used. And preferably a styrene-acrylic resin is used.

A charge control agent may be used, and any charge control agent known per se, for example, nigrosine base (CI.50415), oil black (CI.261) may be used.
50), oil-soluble dyes such as spirone black, metal-containing azo dyes, naphthenic acid metal salts, alkylalicylic acid metal salts, fatty acid soaps, resin acid soaps and the like are used. The amount of these charge control agents blended is usually 0.1 to 10 parts by weight, particularly 0.5 to 5 parts by weight, per 100 parts by weight of the fixing resin.
Parts by weight.

In the toner, magnetic powder may be added internally or externally. That is, as described above, since the magnetic force of the carrier of the present invention is smaller than that of a normal carrier, the coupling between the toner particles and the carrier due to the Coulomb force is weakened, and the higher the speed of copying, the more the toner scattering. It is noticeable that the toner contamination in the copying machine and the fog density of the copy tend to increase.

In the toner, in order to compensate for this, a specific amount of magnetic powder is contained in the toner, and in addition to the Coulomb force of the toner-carrier, the magnetic attraction of the toner-carrier prevents the toner scattering. You can also As a result, it is possible to increase the apparent sensitivity during development while preventing toner scattering. That is, the smaller the amount of charge per toner particle, the greater the number of toner particles attached to the electrostatic latent image having a constant charge amount, so that the apparent developing sensitivity increases.

Such magnetic powder may be added internally or externally in a small amount such as 0.1 to 5 parts by weight, particularly 0.5 to 3 parts by weight, per 100 parts by weight of the resin medium. In the magnetic toner used in the conventional two-component developer, the magnetic powder is used in an amount larger than 10 parts by weight per 100 parts by weight of the resin medium, but the amount used in the present invention is considerably smaller than this. If the amount of the magnetic powder used is less than 0.1 parts by weight, toner scattering tends to occur, while if it is more than 5 parts by weight, the development density decreases.

As the above-mentioned magnetic powder, any one from low resistance to high resistance exemplified in the section of magnetic powder used in the carrier of the present invention can be used, but particularly preferable magnetic powder is It is fine-grained triiron tetraoxide (magnetite). The preferred magnetite has a regular octahedron shape and a particle size of 0.05 to 1 μm. The magnetite particles may be surface-treated with a silane coupling agent, a titanium coupling agent, or the like.

When the magnetic powder is added by external addition, it is effective in improving the fluidity of the toner and also in improving the transfer efficiency of the toner. The toner has a heat-fixing property, and therefore, it is necessary to impart releasability at the time of heat-fixing. However, the toner has a number average molecular weight of 7 as a release agent.
It is preferable to select polypropylene of 000 or more, preferably 7,000 to 30,000, and to mix this in an amount of 0.1 to 6 parts by weight per 100 parts by weight of the resin medium. As a result, it is possible to further improve the spent resistance of the toner while improving the offset resistance during heat fixing. The reason for this is that polypropylene having a number average molecular weight of less than 7,000 is less likely to be sheared because it melts and has a low viscosity during the kneading process for toner production, so that it is difficult to disperse it in the resin medium and is not easily dispersed in the carrier. On the other hand, polypropylene having a number average molecular weight of 7,000 or more has a high softening point, so that it is hard to melt during kneading, has a large share, and has a good dispersion in the resin medium, resulting in It is because the generation is suppressed.

When the compounding amount of the polypropylene is lower than the above range, the offset resistance at the time of heat fixing becomes insufficient. On the other hand, when it is more than the above range, the spent tendency becomes large, which is not preferable. The polypropylene having the above molecular weight range can be obtained, for example, under the trade name of "330P" (manufactured by Sanyo Kasei Co., Ltd., number average molecular weight: 15,000). (Colorant) In addition to the above-mentioned release agent, it is of course possible to add a compounding agent that has been conventionally compounded in a toner, for example, a colorant. Such colorants are usually used in an amount of 2 to 20 parts by weight, especially 5 to 15 parts by weight, per 100 parts by weight of the fixing resin medium.

Suitable examples of the colorant (pigment) are as follows. Black pigments Carbon black, acetylene black, run black, aniline black. Yellow pigment Yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, navels yellow, naphthol yellow S, Hansa yellow G, Hansa yellow 10G, benzidine yellow G,
Benzidine Yellow GR, Quinoline Yellow Lake, Permanent Yellow NCG, Tartrazine Lake. Orange pigments Red mouth lead, molybdenum orange, permanent orange GTR, pyrazolone orange, Vulcan orange, induslen brilliant orange RK, benzidine orange G, induslen brilliant orange GK. Red pigment Bengala, cadmium red, lead red, cadmium mercury sulfide, permanent red 4R, lithol red, pyrazolone red, watching red calcium salt, lake red D, brilliant carmine 6B, eosin lake, rhodamine lake B, alizarin lake, brilliant carmine 3B. Purple pigment Manganese purple, fast violet B, methyl violet lake. Blue pigment Navy blue, cobalt blue, alkali blue lake, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, partially chlorinated phthalocyanine blue, first sky blue, indaslen blue B
C. Green pigment chrome green, chromium oxide, pigment green B,
Malachite Green Lake, Fanal Yellow Green G. White pigment Zinc white, titanium oxide, antimony white, zinc sulfide. Extender barite powder, barium carbonate, clay, silica, white carbon, talc, alumina white.

The toner can be produced by a method known per se such as a pulverizing and classifying method, a melt granulating method, a spray granulating method and a polymerization method, but the pulverizing and classifying method is generally used. For example, each toner component is premixed with a mixer such as a Henschel mixer, and then kneaded with a kneading device such as a twin-screw extruder, and the kneaded composition is cooled, pulverized, and classified to obtain a toner. .

The particle size of the toner is generally such that the median diameter by a Coulter counter is 3 to 15 μm, and particularly 6 to 1.
It is preferable to be in the range of 2 μm. It is possible to improve the fluidity of the toner by externally adding a known fluidity-improving agent such as hydrophobic vapor-phase method silica to the surface of the toner particles, if necessary. The amount of the fluidity improver added by external addition is preferably 0.1 to 2% by weight based on the toner.

When the fluidity improving agent is externally added to the toner, it is preferable that the fluidity improving agent is previously intimately mixed under a pulverizing condition, and this mixture is added to the toner to sufficiently disintegrate it. (Two-Component Developer) The developer of the present invention is prepared by mixing the above-mentioned carrier and toner, and is used for development.

The mixing ratio of the magnetic carrier and the toner is generally 98: 2 to 90:10, preferably 97: 3 to 92: 8. In the electrostatographic copying method using the two-component developer of the present invention, the electrostatic latent image can be formed by any method known per se, for example, by uniformly charging the photoconductive layer on the conductive substrate. After that, imagewise exposure can be performed to form an electrostatic latent image.

Development of the electrostatic image is facilitated by contacting the magnetic brush of the two-component developer with the substrate. The toner image formed by the development is transferred onto copy paper, and the toner image is fixed by bringing the toner image into contact with a heating roll. That is, the carrier of the present invention has, in addition to the characteristic of the binder type carrier that the magnetic force of the magnetic brush is smaller than that of the conventionally known iron powder or ferrite carrier, can prevent carrier adhesion due to induced charges, and has carrier cracking. It has a feature that it is unlikely to occur and can prevent carrier adhesion to the image.

[0036]

The present invention will be further described in the following examples. (Example 1) <Preparation of toner for test> (Toner composition) Resin styrene-acrylic copolymer 100 parts by weight Colorant 8 parts by weight carbon black Charge control agent Azo dye (manufactured by Orient Science) 2 parts by weight First, after premixing with a Henschel mixer, they were melt-kneaded with a twin-screw extruder. The obtained kneaded product was pulverized by a jet mill and classified by an air classifier to obtain toner particles having an average particle size of 9.8 μm.

Hydrophobic silica fine particles, Aerosil R972 (manufactured by Tegusa), as spacer particles, were added to the particles at a ratio of 0.5 parts by weight to 100 parts by weight of the toner particles, and mixed for 2 minutes with a Henschel mixer for testing. To obtain toner for use. <Production of Carrier 1> (Carrier composition) 100 parts by weight of styrene-acrylic copolymer (Mw: 100,000, Mw / Mn: 2.2) 400 parts by weight of magnetite (average particle size: about 0.3 μm) (resistivity 1 × 10 ⁶ Ω · cm) Carbon black 5 parts by weight Charge control agent 3 parts by weight First, the above composition is put into a Henschel mixer, and 300
The mixture was dispersed at a rotation speed of 0 rpm for about 10 minutes. Next, the mixture was melt-kneaded with a twin-screw extruder at a temperature of 200 ° C. The obtained kneaded product is pulverized by a PJM ultrasonic jet pulverizer,
By air classification and sieving, a carrier 1 having an average particle size of 90.5 μm was obtained.

The carrier strength of the obtained carrier 1 was measured by the following method and was 16.9%. <Carrier strength measurement method> After putting the carrier and stainless steel balls in a poly container and mixing at a rotation speed of 200 rpm for 2 hours, the carrier particle size before mixing and the carrier particle size after mixing are compared, and the central particle size is reduced. The ratio was calculated and used as the carrier strength.

The carrier 1 and the test toner were mixed so as to have a toner concentration of 5% by weight, and the mixture was used in an electrophotographic copying machine (DC2556 remodeling machine manufactured by Mita Kogyo Co., Ltd.).
A 10,000-sheet copy test was conducted. Each evaluation method is as follows. Table 1 shows the evaluation results. A) Image density (ID) The density of a black solid part in up to 50,000 copies of a predetermined number of copies was measured using a reflection densitometer (model number "TC-6D" manufactured by Tokyo Denshoku Co., Ltd.). . B) Fog density (FD) The density of the non-image area is measured with a reflection densitometer (model number "TC-6D" manufactured by Tokyo Denshoku Co., Ltd.), and the base paper (paper density before copying) is measured.
The difference is C) Adhesion of Carrier to Image Area The copied image after copying a predetermined number of sheets was visually observed and evaluated according to the following criteria.

◯: No carrier adhesion Δ: Little carrier adhesion ×: Many carrier adhesions (Example 2) <Production of Carrier 2> Mw: 100,000, Mw / Mn: 2.
Instead of the styrene-acrylic copolymer which is 2, Mw:
Carrier 2 having an average particle size of 80.5 μm was obtained in the same manner as in the preparation of Carrier 1 of Example 1 except that a styrene-acrylic copolymer having a Mw / Mn: 2.7 of 130,000 was used.

The carrier strength of the obtained carrier 2 was measured and found to be 15.8%. The carrier 2 and the test toner were mixed to prepare a two-component developer having a toner concentration of 5%. This developer was evaluated in the same manner as in Example 1. Table 1 shows the results. Comparative Example 1 <Production of Carrier 3> Mw: 100,000, Mw / Mn: 2.
Instead of the styrene-acrylic copolymer which is 2, Mw:
A carrier 3 having an average particle size of 91.0 μm was obtained in the same manner as in the preparation of the carrier 1 of Example 1 except that a styrene-acrylic copolymer having a weight ratio of 95,000 and Mw / Mn: 5.8 was used.

The carrier strength of the obtained carrier 3 was measured and found to be 31.9%. The carrier 3 and the test toner were mixed to prepare a two-component developer having a toner concentration of 5%. This developer was evaluated in the same manner as in Example 1. Table 1 shows the results. (Comparative Example 2) <Preparation of Carrier 4> Average particle size 0.3 μm, specific resistance 1
In place of the magnetite of 0 ⁶ Ω · cm, average particle size 0.
Except for using magnetite having a thickness of 3 μm and a specific resistance of 10 ³ Ω · cm, the carrier 1 of Example 1 was manufactured in the same manner as described above.
A carrier 4 having an average particle size of 81.8 μm was obtained.

When the carrier strength of the obtained carrier 4 was measured, it was 19.7%. The carrier 4 and the test toner were mixed to prepare a two-component developer having a toner concentration of 5%. This developer was evaluated in the same manner as in Example 1. Table 1 shows the results.

[0044]

[Table 1]

In Examples 1 and 2, no carrier adhered,
Good images were obtained through printing. In Comparative Example 1, the carrier strength was brittle, and the adhesion of the carrier increased during printing, causing a defect on the image. In Comparative Example 2, the carrier strength was sufficient, but the carrier had a low resistance, and due to the induced charges, carrier adhesion was large from the initial stage, and a defect occurred on the image. The copy test was terminated after 10,000 sheets.

[0046]

The carrier for a two-component developer of the present invention has a low density in which magnetic powder as a magnetic component is dispersed in a resin, and therefore the carrier and the toner can be mixed and stirred for charging the toner. Since the stirring force is low and the magnetic force of the magnetic brush is small, the conveying torque of the magnetic brush may be small. Therefore, there are few restrictions on the apparatus and it is extremely advantageous in terms of downsizing of the developing apparatus.

Further, since the magnetic force of the magnetic brush is small, the rubbing force of the magnetic brush on the surface of the photosensitive member is alleviated during development, and a good image is formed without forming an image such as a sweep of the magnetic brush. It is also excellent in that respect.
Further, since magnetic powder having a high resistance is used, the carrier is effectively prevented from adhering to the surface of the photoconductor, and there is no problem of carrier aggregation.

The carrier of the present invention is used as a resin for binding magnetic powder and has a weight average molecular weight of 80,000 to 15 in GPC.
Since all of them are used, the binding strength with magnetic powder and the strength as a carrier are both good.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Takuya Kadota Takuya Kadota 1-22-28 Mitsuko Kogyo, Chuo-ku, Osaka (72) Inventor Tadao Sumiyoshi 1-2-2 Tamazuku, Chuo-ku, Osaka Mita Within Kogyo Co., Ltd.

Claims (3)

[Claims] 1. At least gel permeation of tetrohydrofuran (hereinafter referred to as "THF") soluble matter.
In the molecular weight distribution of a chromatograph (GPC), a high resistance magnetic powder having a specific resistance of 1 × 10 ⁵ Ω · cm or more is contained in a resin having a weight average molecular weight of 80,000 to 150,000.
A carrier for a two-component developer, wherein 150 to 800 parts by weight are dispersed per part by weight. 2. The weight average molecular weight / number average molecular weight (Mw) in the GPC molecular weight distribution of the THF soluble component of the resin.
The carrier for a two-component developer according to claim 1, wherein / Mn) is 3 or less. 3. The carrier for a two-component developer according to claim 1, which is in the form of particles having an average particle diameter of 50 to 150 μm.