JPH0619212A - Electrophotographic carrier - Google Patents

Abstract

PURPOSE:To provide an electrophotographic carrier with the surface coated with resin, excellent in durability and toner spending resistance, capable of stably impressing a good charge amt. to the toner over a long period and capable of forming a high-definition picture. CONSTITUTION:This electrophotographic carrier is obtained by coating a core with an insulating resin. The core consists of a ferrite grain contg. strontium, barium and lead, and the coercive force of the grain is controlled to >=300 Gauss in the magnetic field of 10kOe. A styrene-acrylate copolymer is used as the resin to coat the core, the copolymer contains 30-90wt.% acrylic monomer, and the weight average mol.wt. of the copolymer is controlled to about 30,000 to 70,000 and the ratio of the weight average mol.wt. to number average mol.wt. to 2 to 10.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to electrophotographic carriers which are mixed with toner to achieve an electrostatic image developer.

[0002]

2. Description of the Related Art U.S. Pat. No. 2,29 as an electrophotographic method
Various methods are described in Japanese Patent No. 7,691, Japanese Patent Publication No. 42-23910, Japanese Patent Publication No. 43-24748, etc., and all of these methods use a photoconductive layer in which light depending on the original is used. An electrostatic latent image is formed by irradiating an image, and then a colored fine powder called toner having a polarity opposite to that of the electrostatic latent image is adhered to the electrostatic latent image to develop the electrostatic latent image. The toner image is transferred onto a transfer material such as paper according to the requirements, and then fixed by heat, pressure or solvent vapor to obtain a copy.

In the step of developing the electrostatic latent image, toner particles charged to a polarity opposite to that of the latent image are attracted by electrostatic attraction and adhered to the electrostatic latent image (reversal development). In the case of, a toner having a triboelectric charge having the same polarity as that of the latent image is used). Generally, as a method for developing such an electrostatic latent image with toner, the toner is roughly classified and dispersed in a small amount in a medium called a carrier. There is a method of using the so-called two-component type developer, and a method of using the so-called one-component type developer using the toner alone without using the carrier. Generally, the carriers constituting such a two-component developer are roughly classified into conductive carriers and insulating carriers.

Oxidized or unoxidized iron powder is usually used as the conductive carrier, but in the developer containing the iron powder carrier, the triboelectric chargeability against the toner is unstable, and There is a problem that a visible image formed by the developer is fogged. That is, with the use of the developer, the toner particles adhere to the surface of the iron powder carrier particles, the electric resistance of the carrier particles increases, the bias current decreases, and the triboelectrification becomes unstable. The image density of the visible image is reduced and the fog is increased.

Insulating carriers are generally iron,
A typical example is a carrier in which the surface of a carrier core material made of a ferromagnetic material such as nickel or ferrite is uniformly coated with an insulating resin. In the developer using this carrier, toner particles are not significantly fused to the surface of the carrier as compared with the case of the conductive carrier, the durability is excellent, and the service life is long. There is an advantage that it is suitable for.

However, in this insulative carrier, the coating layer for coating the surface of the carrier core material has sufficient abrasion resistance and strong adhesion to the core material, and the toner is fused to the carrier surface. It is required that the spent is not generated and that a desired sufficient triboelectric charge amount be imparted to a specific toner used together with the carrier.
That is, the carrier is rubbed with other carrier particles and toner particles in the developing device, but if the carrier coating layer does not have sufficient film strength and adhesion to the core material, the coating peels off from the core material or The toner will be lost, and the ability to impart charge to the toner will be reduced. Further, even when toner spent occurs on the surface of the carrier, the original triboelectric charge imparting ability of the carrier coating layer cannot be exhibited and the charging characteristics become unstable.

Conventionally, as a technique for solving such a drawback, in a carrier which is not coated with an insulating resin, Japanese Patent Laid-Open No.
As disclosed in Japanese Patent No. 180563, a thin film of a fatty acid metal salt is formed on the surface of a carrier core material to improve toner spent resistance.
In addition, attempts have been made to improve the charge imparting property. However, when a developer using this carrier is left under high temperature and high humidity for a long period of time, the fatty acid metal salt on the surface of the carrier core material migrates to the toner resin layer having high affinity, and as a result, toner charging becomes unstable. However, there is a problem that image deterioration such as fogging and scattering occurs. Further, unless it is covered with an insulating resin to some extent, iron oxide powder as well as ferrite particles are unsuitable for a developing system for applying a bias voltage due to current leakage or adhesion of carriers onto the photoconductor. is there.

As a carrier coated with an insulating resin, a coated carrier coated with a fluorine-containing polymer is proposed in US Pat. No. 3,922,382. A carrier coated only with a fluorine-containing polymer has a poor film-forming property and can only partially cover the carrier surface, resulting in unstable charging characteristics. Further, in order to improve the film-forming property of a fluorine-containing polymer, a method of coating by mixing with a polymer having a relatively good film-forming property is also disclosed in US Pat. No. 4,297,427 and JP-A-54-110839. It is proposed in Japanese Patent Publication No. However, in both cases, since a fluorine polymer having a strong negative charge property is used as a constituent component, it is considered that it can be advantageously used for a positive toner, but it has a desired moderate size for a negative toner. It is expected that it will be difficult to obtain the amount of charge, and even if a sufficient value for the amount of charge is obtained, the rising speed of charge is slow and it is difficult to maintain stable chargeability. .

On the other hand, in order to form a high quality image, Japanese Patent Laid-Open No. 2-88429 attempts to control the characteristics of a magnetic brush by using a hard magnetic ferrite material and a carrier. However, in the carrier, it is important to control the conductivity, and even if it is coated with a resin, it must be thin enough to maintain an appropriate conductivity, and the strength of the coating is sufficient. It is expected that it will be difficult to obtain durability.

Further, generally, when obtaining fine particles using a hard ferrite material, the sintering temperature cannot be raised sufficiently in the manufacturing process so that the magnetic particles have a high coercive force. The surface of the obtained particles has a significantly uneven shape. Therefore, it is difficult to uniformly coat the particles having such a surface shape with the conventional resin, and even if it can be applied, there is no peeling or loss of the coating when it is used as a developer. It has been difficult to obtain a resin-coated carrier that has durability and is capable of stably imparting an appropriate amount of charge to the toner for a long period of time.

[0011]

SUMMARY OF THE INVENTION Therefore, the main object of the present invention is to provide a carrier whose surface is coated with a resin as described above, which is excellent in durability and toner spent resistance, and which is stable over a long period of time. To provide an electrophotographic carrier capable of imparting a good charge amount to a toner and having a high density of “brushing” of a magnetic brush per unit area on a sleeve and capable of forming a high-definition image. is there. A further object of the present invention is to provide a carrier having an appropriate resistance and having little current leakage or adhesion to the photoconductor even when a bias voltage is applied.

[0012]

The above object can be achieved by the present invention described below. That is, the present invention is an electrophotographic carrier comprising a core material surface coated with an insulating resin, wherein the core material is strontium, barium or lead-containing ferrite particles, and the coercive force of the ferrite particles is a magnetic field. 300 Ga under 10K Oersted
The resin having a uss or more and covering the surface of the core material has a styrene-acrylic copolymer, and the monomer ratio of the acrylic component in the copolymer is 30 to 90% by weight. Has a weight average molecular weight of about 30,000
The carrier for electrophotography is characterized in that it is 0 to 70,000 and the weight average molecular weight / number average molecular weight is 2 to 10.

[0013]

The carrier of the present invention improves various drawbacks of the conventional resin-coated carrier, is excellent in durability and stability of imparting charge to toner for a long period of time, and thereby the carrier of the present invention is remarkably excellent. It is considered that the reason why the high developability image can be obtained by exhibiting the above-mentioned developability is due to the following reason, although the details are unknown. That is, when the surface of the carrier of the present invention was observed by a scanning electron microscope, the resin used in the present invention formed a coating layer in such a state that it penetrated into the concave portions of the irregularities on the surface of the core material. Further, it was observed that the convex portions of the core material were finely exposed. Therefore, it is considered that the resin coating property allows the carrier of the present invention to have an appropriate specific resistance with no leak when a bias is applied and stability to impart charge to the toner, and further improve durability. Furthermore, since the ferrite particles constituting the carrier core material exhibit specific magnetic characteristics, the developer on the sleeve becomes finely packed to form a soft magnetic brush, resulting in a high-definition image. I'm guessing.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail with reference to the preferred embodiments. Examples of stearin-acrylic copolymers that can be used for the coating resin of the carrier core material of the present invention include copolymers of styrene derivatives and acrylic acid esters and copolymers of styrene derivatives and methacrylic acid esters. Point to. The following compounds can be mentioned as specific examples of the monomers constituting these styrene-acrylic copolymers. That is, as the styrene derivative, styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-phenylstyrene,
p-ethylstyrene, 2,4-dimethylstyrene, p-
n-butyl styrene, p-tert-butyl styrene,
pn-hexylstyrene, pn-octylstyrene, pn-nonylstyrene, pn-decylstyrene, pn-dodecylstyrene, p-methoxystyrene, p-chlorostyrene, 3,4-di Chlorostyrene,
Examples thereof include m-nitrostyrene, o-nitrostyrene, p-nitrostyrene and the like.

Examples of the acrylic acid esters include methyl acrylate, ethyl acrylate, -n-butyl acrylate, isobutyl acrylate, propyl acrylate, -n-octyl acrylate, dodecyl acrylate, acrylic acid. Examples include 2-ethylhexyl, stearyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, and the like.

Further, as the methacrylic acid esters,
For example, methyl methacrylate, ethyl methacrylate, propyl methacrylate, -n-butyl methacrylate, isobutyl methacrylate, -n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate. ,
Examples thereof include dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate.

The carrier core material coating resin used in the present invention preferably has a monomer ratio of the acrylic component in the styrene-acrylic copolymer of 30 to 90% by weight. If the amount is less than 30% by weight, the coating uniformity sufficient to contribute to the present invention cannot be obtained, and the toner has insufficient charge stability. On the other hand, if it is more than 90% by weight, uniform covering property is obtained, but the strength against impact resistance is insufficient.

Further, the weight average molecular weight of the above-mentioned copolymer which can be used for the coating resin for the carrier core material of the present invention is 30,000 to 70,000, and the weight average molecular weight / number average molecular weight is It is essential that it is 2 to 10. If the weight average molecular weight is less than 30,000, the strength with respect to impact resistance of the carrier cannot be obtained, and 7
If it is more than 10,000, the coverage of the carrier core is deteriorated, and the strength of the carrier and the charging stability are deteriorated. More importantly, at this time, even if the weight average molecular weight is within this range, the effect of the present invention cannot be obtained unless the weight average molecular weight / number average molecular weight is within the range of 2 to 10. When the weight average molecular weight / number average molecular weight is less than 2, the coating resin is uniformly coated, but the impact resistance is poor. If the weight average molecular weight / number average molecular weight is larger than 10, the uniformity of the coating on the carrier core becomes poor, and the strength of the carrier and desired charge stability cannot be obtained.

In the present invention, the molecular weight and molecular weight distribution of the coating resin and the molecular weight of the fluorine-containing resin which can be used as the coating resin for the carrier core material are determined by GPC (gel permeation chromatography) to be a monodisperse standard. The value obtained by observing a calibration curve obtained by using polystyrene. The measurement conditions are shown below. Equipment: GPC-150C (Waters) Column: Show Deluxe KF 7 stations (Showa Denko) Temperature: 40 ° C Solvent: THF (Tetrahydrofuran) Flow rate: 1.0 ml / min Reagent: 0.15% Inject 0.4 ml of sample

The magnetic material used for the carrier core material in the present invention must contain at least one of Sr ferrite, Ba ferrite and Pb ferrite, but as other components, the periodic table IIIA, IVA. , V
A, VIA, IB, IIB, VIB, VB, VIB, VIIB and V
The group III element may be contained, but the content of other elements is preferably less than 1% by weight. As described above, this is important for increasing the density of the "brushing" of the magnetic brush on the sleeve and controlling the resistance at which bias voltage leakage and carrier adhesion do not occur after resin coating to an optimum value. is there. For the same reason, the carrier magnetic field 10 of the present invention is used.
The holding power in K Oersted is 300 Gauss or more, preferably 500 Gauss or more. The magnetic force in a magnetic field of 1 K Oersted is 5 emu / g to 5
9 emu / g is preferable, and 10 to 19 e is more preferable.
mu / g. The magnetic characteristics described below are values measured by VSM manufactured by Toei Industry Co., Ltd.

The average particle size of the carrier particles of the present invention is from 10 to 10.
It can be preferably used in the range of 60 μm. 10μ
If it is smaller than m, carrier adhesion to the photoconductor tends to occur,
On the other hand, when it exceeds 60 μm, the share of the developer in the developing device becomes large, which causes deterioration of the developer, especially peeling of external additives of toner particles and change in shape, which causes image deterioration. Further, if the particle size is large, the specific surface area becomes small, so that the amount of toner that can be held in constituting the developer becomes small, resulting in an image lacking fineness.
The particle size of the carrier core of the present invention was randomly extracted by an optical microscope or a scanning electron microscope at 500 or more pieces, and the maximum particle length in the horizontal direction was measured as the carrier particle size.

The specific resistance of the carrier of the present invention is 10 ⁸ to 10
A range of ¹⁴ Ωcm is appropriate. When it is less than 10 ⁸ Ω · cm, in the developing method in which a bias voltage is applied, a current leaks from the sleeve to the surface of the photoconductor in the developing area, and a good image cannot be obtained. If it exceeds 10 ¹⁴ Ω · cm,
It causes a charge-up phenomenon under conditions such as low humidity,
This may cause image deterioration such as density density, transfer failure, and fog. The specific resistance of the carrier of the present invention was measured using the cell shown in FIG. That is, the cell A is filled with the carrier,
The electrodes 1 and 2 were arranged so as to be in contact with the filled carrier, a voltage was applied between the electrodes, and the current flowing at that time was measured to determine the specific resistance. The measurement conditions are as follows: the contact area of the filled carrier with the cell S = about 2.3 cm ² , the thickness d = about 1
mm, the load of the upper electrode is 275 g, and the applied voltage is 100V. Here, since the carrier is a powder, the specific resistance may change depending on the filling rate, so caution is required. As a method of coating the carrier core material surface with a resin coating layer in the present invention, the resin material is dissolved or suspended in an organic solvent such as toluene, xylene, or acetone to prepare a carrier coating solution according to the present invention. The carrier core material can be applied by a general application device such as a spray method or a fluidized bed method.

A two-component developer for developing an electrostatic image using the carrier of the present invention is prepared by using the above resin-coated carrier as a toner 1.
10 to 1000 parts by weight, preferably 30 to 500 parts by weight, may be mixed with 0 parts by weight and used. The toner used with the carrier of the present invention has a weight average particle diameter of 1 to 20 μm, preferably 4 to 13 μm, and more preferably 4 to 10 μm. Further, the toner has a toner particle size distribution in terms of developability and toner consumption.
It is preferably within the following range. That is, toner particles having a particle size of 5 μm or less account for 17 to 60% by number of all particles,
Toner particles having a particle size in the range of 8 to 12.7 μm account for 1 to 30% by number of the total particle number, and particles in the particle size range of 16 μm or more are less than 2.0% by volume of the total particle number. Is preferred.

The weight average particle size and particle size distribution of the toner can be measured by various methods, but in the present invention, it was measured using a Coulter counter. A Coulter counter TA-II type (manufactured by Coaster) is used as a measuring device, an interface (manufactured by Nikkaki) and a CX-1 personal computer (manufactured by Canon) for outputting number distribution and volume distribution are connected, and as an electrolyte, An about 1% aqueous sodium chloride solution is prepared using primary sodium chloride. As the measuring method, the electrolytic aqueous solution 100 to 1 is used.
To 50 ml, 0.1 to 5 ml of a surfactant, preferably an alkylbenzene sulfonate, is added as a dispersant, and 2 to 20 mg of a measurement sample is further added. The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes,
According to the Coulter Counter TA-II type described above, using a 100 μm aperture as an aperture, the particle size distribution of particles of 2 to 40 μm is measured based on the number,
Then, the value according to the present invention was determined.

As the binder resin used for the toner used with the carrier of the present invention, the following binder resin for toner can be used when a heating and pressure roller fixing device having a device for applying oil is used. is there. For example, homopolymers of styrene and its substitution products such as polystyrene, poly-p-chlorostyrene, polyvinyltoluene; styrene-p-chlorostyrene copolymers, styrene-vinyltoluene copolymers, styrene-vinylnaphthalene copolymers. , Styrene-acrylic acid ester copolymer, styrene-methacrylic acid ester copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl Styrene-based copolymers such as ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer; polyvinyl chloride, phenol Resin, natural resin Phenol resins, natural resin modified maleic acid resin,
Acrylic resin, methacrylic resin, polyvinyl acetate, silicone resin, polyester resin, polyurethane resin, polyamide resin, furan resin, epoxy resin, xylene resin, polyvinyl butyral resin, terpene resin, coumarone indene resin, petroleum resin, etc. can be used. .

In the heating and pressure roller fixing method in which oil is hardly applied, offset development in which a part of the toner image on the toner image supporting member is transferred to the roller and adhesion of the toner to the toner image supporting member are important problems. Is. Toners that fix with less heat energy usually tend to be blocked or caked during storage or in a developing device, so these problems must be taken into consideration at the same time. Therefore, the selection of the binder resin is more important when the heating and pressure roller fixing method in which the oil is hardly applied is used in the present invention. Preferred binder resins include cross-linked styrene copolymers or cross-linked polyester resins.

Examples of the comonomer for the styrene monomer of the styrene type copolymer include acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate,
Dodecyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, acrylonitrile, methacrylonitrile, acrylamide, etc. A monocarboxylic acid having a heavy bond or a substituted product thereof; a dicarboxylic acid having a double bond such as maleic acid, butyl maleate, methyl maleate, dimethyl maleate and the like; a substituted product thereof; vinyl chloride, vinyl acetate, benzoic acid Vinyl esters such as vinyl; for example, ethylene-based olefins such as ethylene, propylene, butylene;
For example, vinyl ketones such as vinyl methyl ketone and vinyl hexyl ketone; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether and vinyl isobutyl ether; .

Here, as the cross-linking agent, a compound having two or more polymerizable double bonds is mainly used. For example, aromatic divinyl compounds such as divinylbenzene, divinylnaphthalene; ethylene glycol diacrylate, ethylene. Carboxylic acid ester having two double bonds such as glycol dimethacrylate and 1,3-butanediol dimethacrylate; divinyl compounds such as divinylaniline, divinyl ether, divinyl sulfide and divinyl sulfone; and 3 or more vinyl groups. Are used alone or as a mixture. The crosslinking agent is 0.01 to 10% by weight based on the binder resin.
It is preferable to use a binder resin (preferably 0.05 to 5% by weight) at the time of synthesis in terms of offset resistance and fixing property. When a pressure fixing method is used for fixing, a binder resin for pressure fixing toner can be used, and examples thereof include polyethylene, polypropylene, polymethylene, polyurethane elastomer, ethylene-ethyl acrylate copolymer, ethylene-acetic acid. Examples thereof include vinyl copolymers, ionomer resins, styrene-butadiene copolymers, styrene-isoprene copolymers, linear saturated polyester resins and paraffins.

For the toner used with the carrier of the present invention, it is preferable to use a charge control agent in the toner particles (internal addition) or mixed with the toner particles (external addition). The charge control agent makes it possible to control the optimum charge amount according to the developing system, and particularly in the present invention, it is possible to further stabilize the balance between the particle size distribution and the charge. As described above, it is possible to further clarify the function separation and the mutual complementarity for improving the image quality according to each particle size range. As a positive charge control agent,
Modifications with nigrosine and fatty acid metal salts; quaternary ammonium salts such as tributylbenzylammonium-1-hydroxy-4-naphthosulfonate, tetrabutylammonium tetrafluoroborate; dibutyltin oxide; dioctyltin oxide, dicyclohexyltin oxide. Organotin oxide; dibutyltin borate, dioctyltin borate, dicyclohexyltin borate can be used alone or in combination of two or more kinds. Among these, charge control agents such as nigrosine and quaternary ammonium salts are particularly preferably used.

General formula

[Chemical 1] [In the formula, R ₁ represents H or CH ₃ , and R ₂ and R ₃ are
A substituted or unsubstituted alkyl group (preferably C _{1 to} C ₄ ) is shown. ] A homopolymer of a monomer represented by the above or a copolymer with a polymerizable monomer such as styrene, acrylic acid ester and methacrylic acid ester as described above can be used as a positive charge control agent. In this case, these charge control agents also have an action as (the whole or a part of) the binder resin. As the negative charge control agent that can be used in the present invention, for example, organometallic complexes and chelate compounds are effective, and examples thereof include aluminum acetylacetonate, iron (II) acetylacetonate, and 3,5- Examples include chromium di-tert-butylsalicylate. Acetylacetone metal complexes (including monoalkyl-substituted and dialkyl-substituted), salicylic acid-based metal complexes (including monoalkyl-substituted and dialkyl-substituted) and salts are preferable, and salicylic acid-based metal complexes or salicylic acid-based metal salts are particularly preferable. Is preferred.

The charge control agent (which does not function as a binder resin) described above is preferably used in the form of fine particles. In this case, the number average particle size of this charge control agent is
Specifically, it is preferably 4 μm or less (further, 3 μm or less). When internally added to the toner, such a charge control agent is preferably used in an amount of 0.1 to 20 parts by weight (more preferably 0.2 to 10 parts by weight) with respect to 100 parts by weight of the binder resin of the toner.
It is preferable to add silica fine powder to the toner used with the carrier of the present invention. When the toner and the silica fine powder are combined, the wear is remarkably reduced by the presence of the silica fine powder between the toner particles and the surface of the carrier or the sleeve. As a result, the life of the toner and / or the carrier and / or the sleeve can be extended, stable chargeability can be maintained, and a two-component developer having a toner and a carrier superior in long-term use can be obtained. Is possible.

Particularly, in the case of a toner having a weight average particle diameter of 10 μm or less, the specific surface area becomes larger than that of a toner having a weight average particle diameter of more than 10 μm, and the toner particles and the carrier are brought into contact with each other for frictional charging. In this case, the number of contact between the surface of the toner particles and the carrier is increased more than that of the toner having a weight average particle diameter of more than 10 μm, and the abrasion of the toner particles and the contamination of the carrier are likely to occur. By adding the fine powder, it becomes possible to obtain a good two-component developer.

As the silica fine powder, silica fine powder produced by a dry method or a wet method can be used, but from the viewpoint of filming resistance and durability, the silica fine powder by the dry method is used. Is preferred. The dry method mentioned here is, for example, a method for producing fine silica powder produced by vapor phase oxidation of a silicon halogen compound. On the other hand, as the method for producing the silica fine powder used in the present invention by the wet method, various conventionally known methods can be applied. For the silica fine powder referred to herein, anhydrous silicon dioxide (colloidal silica) and other silicates such as aluminum silicate, sodium silicate, potassium silicate, magnesium silicate and zinc silicate can be used. Among the above silica fine powders, those having a specific surface area of 30 m ² / g or more (particularly 50 to 400 m ² / g) by nitrogen adsorption measured by the BET method give good results. 0.01 to 8 parts by weight of fine silica powder, preferably 0.
It is preferable to use 1 to 5 parts by weight.

When the toner used in combination with the carrier of the present invention is used as a positively chargeable toner, the silica fine powder added for preventing the abrasion of the toner and the surface of the carrier and the sleeve is also negatively charged. Is preferable because it does not impair the charging stability when using a positively chargeable silica fine powder, and when used as a negatively chargeable toner, a negatively chargeable silica fine powder is used for the same reason. It is preferable. Since silica fine powder is generally negatively charged, a method for obtaining positively charged silica fine powder is to use the above-mentioned untreated silica fine powder as an organo group having at least one nitrogen atom in its side chain. And a method of treating with a nitrogen-containing silane coupling agent, or a method of treating with both of them. In the present invention, the positively chargeable silica refers to one having a positive triboelectric charge with respect to the iron powder carrier when measured by the blow-off method.

As the silicone oil having a nitrogen atom in the side chain used for treating the silica fine powder, silicone oil having at least a partial structure represented by the following formula can be used.

[0036]

[Chemical 2] (In the formula, R ₁ represents a hydrogen atom, an alkyl group, an aryl group or an alkoxy group, R ₂ represents an alkylene group or a phenylene group, R ₃ and R ₄ represent a hydrogen atom, an alkyl group or an aryl group, and R ₅ represents a nitrogen-containing heterocyclic group).

In the above formula, the alkyl group, the aryl group, the alkylene group or the phenylene group may have an organo group having a nitrogen atom, and may be substituted with halogen or the like as long as the chargeability is not impaired. It may have a group. The silicone oil is used in an amount of 1 to 50% by weight, preferably 5 to 30% by weight, based on the silica fine powder. The nitrogen-containing silane coupling agent used in the present invention generally has a structure represented by the following formula. R _m -Si-Y _n (R represents an alkoxy group or halogen, Y represents an amino group or an organo group having at least one nitrogen atom, m and n are integers of 1 to 3, and m + n = 4)

Examples of the organo group having at least one nitrogen atom include an amino group having an organic group as a substituent, a nitrogen-containing heterocyclic group or a group having a nitrogen-containing heterocyclic group. The nitrogen-containing heterocyclic group includes an unsaturated heterocyclic group and a saturated heterocyclic group, and known ones can be used. Examples of the unsaturated heterocyclic group include the followings.

[0039]

[Chemical 3]

Examples of the saturated heterocyclic group are shown below.

[Chemical 4]

The above-mentioned heterocyclic group is preferably a 5-membered ring or 6-membered ring in view of stability. Examples of such treating agents include aminopropyltrimethoxysilane, aminopropyltriethoxysilane, dimethylaminopropyltrimethoxysilane, diethylaminopropyltrimethoxysilane, dipropylaminopropyltrimethoxysilane, dibutylaminopropyltrimethoxysilane,
Monobutylaminopropyltrimethoxysilane, dioctylaminopropyltrimethoxysilane, dibutylaminopropyldimethoxysilane, dibutylaminopropylmonomethoxysilane, dimethylaminophenyltriethoxysilane, trimethoxysilyl-γ-propylphenylamine, trimethoxysilyl-γ -Propylbenzylamine and the like, and the nitrogen-containing heterocycle having the structure described above can be used. Examples of such a compound include trimethoxysilyl-γ-propylpiperidine and trimethoxysilyl-γ-propylmonocycle. Examples include holin and trimethoxysilyl-γ-propylimidazole. The silane coupling agent is used in an amount of 1 to 50% by weight, preferably 5 to 30% by weight, based on the fine silica powder.

The applied amount of the treated positive or negative silica fine powder is 0.01 with respect to 100 parts by weight of the toner.
When 8 to 8 parts by weight, the effect is exhibited, and particularly preferably 0.
When added in an amount of 1 to 5 parts by weight, it exhibits positive or negative chargeability with excellent stability. With respect to the addition form, to describe a preferable mode, it is preferable that 0.1 to 3 parts by weight of the treated silica fine powder is adhered to the surface of the toner particle with respect to 100 parts by weight of the toner. The untreated silica fine powder described above can also be used in the same application amount.

The fine silica powder used in the above may be a silane coupling agent or a treating agent such as an organic silicon compound for the purpose of hydrophobizing, if necessary, and it reacts with the fine silica powder or is physically adsorbed. The treatment agent or various treatment agents may be used in combination. Examples of such a treating agent include hexamethyldisilazane, trimethylsilane, trimethylchlorosilane, trimethylethoxysilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, allylphenyldichlorosilane, and benzyldimethylchlorosilane. , Bromomethyldimethylchlorosilane, α-chloroethyltrichlorosilane, β-chloroethyltrichlorosilane, chloromethyldimethylchlorosilane, triorganosilylmercaptan, trimethylsilylmercaptan, triorganosilylacrylate, vinyldimethylacetoxysilane, dimethylethoxysilane, dimethyl Dimethoxysilane, diphenyldiethoxysilane, hexamethyldisiloxane, 1,3-divinyltetramethyldisiloxane, Examples include 1,3-diphenyltetramethyldisiloxane and dimethylpolysiloxane having 2 to 12 siloxane units per molecule and each terminal unit having a hydroxyl group bonded to Si per unit. These are 1
It is used as a mixture of two or more species. The treatment agent is
It is preferred to use from 1 to 40% by weight, based on the fine silica powder.

BET specific surface area of 5 instead of silica fine powder
It may be used 0~400m ² / g titanium oxide fine powder of the (TiO _2). Further, a mixed powder of silica fine powder and titanium oxide fine powder may be used. The toner may be a fine powder of a fluorine-containing polymer, which may be added internally or externally. As the fluorine-containing polymer powder, it is preferable to add, for example, fine powder of polytetrafluoroethylene, polyvinylidene fluoride or the like and tetrafluoroethylene-vinylidene fluoride copolymer. In particular, polyvinylidene fluoride fine powder is preferable in terms of fluidity and abrasivity. The amount added to the toner is 0.01 to 2.0% by weight,
In particular, 0.02 to 1.0% by weight is preferable.

As the colorant, conventionally known dyes and / or pigments can be used. For example, carbon black, phthalocyanine blue, peacock blue, permanent red, lake red, rhodamine lake,
Hansa yellow, permanent yellow, benzidine yellow and the like can be used. As its content,
0.1 to 20 parts by weight, preferably 0.5 to 20 parts by weight, relative to 100 parts by weight of the binder resin of the toner, and 12 to improve the transparency of the OHP film on which the toner image is fixed.
It is preferably not more than 10 parts by weight, more preferably 0.5 to 9 parts by weight. Toners used with the carrier of the present invention include
Low molecular weight polyethylene, low molecular weight polypropylene, microcrystalline wax, carnauba wax, sazol wax, for the purpose of improving releasability at the time of heat roll fixing.
0.5-5 wax-like substances such as paraffin wax
Addition of wt% is also one of the preferred forms of the present invention. If necessary, other additives may be added to the toner.

To prepare a toner to be used with the carrier of the present invention, a vinyl type or non-vinyl type thermoplastic resin, a pigment or dye as a coloring agent, a charge control agent, if necessary,
Other additives are thoroughly mixed by a mixer such as a ball mill, and then melted, kneaded and kneaded using a heat kneader such as a heating roll, a kneader and an extruder to make the resins compatible with each other. Toner particles can be obtained by dispersing or dissolving a pigment or dye, cooling and solidifying, and then pulverizing and strictly classifying. The toner particles can be used as a toner as they are, but if necessary, an external additive such as silica fine powder is added to the obtained toner particles, and the toner particles and the external additive are added using a mixer such as a Henschel mixer. A toner can be obtained by mixing and.

The method of measuring the triboelectric charge amount of the toner with respect to the carrier in the present invention will be described in detail with reference to FIG. FIG. 2 is an explanatory diagram of the triboelectric charge amount measuring device. A magnetic brush (deposited with toner) on the developer carrier for measuring the triboelectric charge amount is placed in a metal measuring container 72 having a conductive screen 71 of 400 mesh at the bottom (which can be appropriately changed to a size that does not allow carrier particles to pass). The mixture 73 of the carrier of the present invention is put and the lid 73 made of metal is put. At this time, the total weight of the measurement container 72 is weighed and set as W ₁ (g). Next, suction device 74 (measurement container 7
At least the part that is in contact with 2 is an insulator), suction is made from the suction port 75 to adjust the air volume control valve 76, and the pressure of the vacuum gauge 77 is set to 70 mmHg. In this state, suction is sufficiently performed (for about 1 minute) to remove the toner by suction. The potential of the electrometer 78 at this time is V (volt). Reference numeral 79 is a capacitor, and the capacity is C (μF). The weight of the entire measuring container after suction is weighed and is W ₂ (g). This triboelectric charge amount Q (μC / g) is calculated by the following equation. Q (μC / g) = C × V / (W ₁ −W ₂ ) However, the measurement conditions are temperature / humidity of 23 ° C./65% RH.

[0048]

The present invention will be described below with reference to examples and drawings, but these do not limit the present invention in any way.
All percentages and parts in the following formulations are% by weight and parts by weight unless otherwise specified. Example 1 Sr ferrite (mol%; Fe ₂ O ₃ = 8) as a core material
7%, SrO = 13%, Hc = 1,700Gauss,
10 K Oersted, magnetic force 19 emu / g: 1 K Oersted) was used, and this surface was covered with a styrene-2-ethylhexyl methacrylate copolymer (monomer composition weight ratio = 4).
0:60, Mw = 42,000, Mw / Mn = 2.9)
Coated with. The styrene-based copolymer was dissolved in toluene at a concentration of 10% so that the coating resin amount was 0.8% of the core material to prepare a carrier coating solution. This carrier coating solution was applied to the above core material while being dried while being applied by an applicator (supplied by Okada Seiko Co., Ltd .: Spiracoater). The obtained resin-coated carrier after coating is dried at a temperature of 80 ° C. for 30 minutes to remove the solvent, and then heated at a temperature of 140 ° C. for 2 hours to obtain the resin-coated carrier of the present invention in which the core material surface is coated with a resin coating layer. Obtained. When the obtained resin-coated carrier was observed with an electron microscope, it was confirmed that the surface was uniformly coated in such a state that the resin penetrated into the irregularities of the core material. The physical properties of the obtained carrier are summarized in Table 1.

On the other hand, polyester resin obtained by condensing propoxylated bisphenol and fumaric acid 100 parts Phthalocyanine pigment 5 parts Di-tert-butylsalicylic acid chromium complex salt 4 parts The above materials were thoroughly premixed with a Henschel mixer. Then, the mixture was melt-kneaded three times with a three-roll mill, cooled, and coarsely pulverized with a hammer mill to a particle size of about 1 to 2 mm.
Then, it was pulverized by an air jet pulverizer. Further, the obtained finely pulverized product is classified to have a negatively chargeable cyan powder (toner) having a weight average diameter of 8.8 μm.
Got

100 parts of the cyan toner and 0.4 part of silica fine powder hydrophobized with hexamethyldisilazane were mixed by a Henschel mixer to prepare a cyan toner having silica fine powder on the toner particle surface. The cyan toner and the resin carrier have a temperature / humidity ratio of N / N.
Under a (23 ° C./60% RH) environment, a developer was obtained by mixing so as to have a toner concentration of 5%. 100 g of the obtained developer was put in a 250 cc plastic bottle and shaken with a tumbler mixer for 1 hour. After that, the developer was taken out and observed with an electron microscope. As a result, as shown in Table 2, peeling of the coating material from the carrier and filming by the toner were not observed.

Further, a cyan toner and the resin-coated carrier were mixed in an environment of temperature / humidity of N / N (23 ° C./60% RH) so that the toner concentration would be 5% to obtain a developer. Using this, under the same environment, using a Canon full-color laser copying machine CLC-500 modified machine, development contrast 350
An image output durability test was performed as V. The results are shown in Table 2.
As shown in, the reflection density of the solid image is 1.55 in the initial stage.
In addition, the reproducibility of the halftone portion and the fine line portion was good, and a high-definition image without carrier adhesion was obtained.
Also, the images obtained after 10,000 sheets of the durability test had good image quality as in the beginning of the durability test. Further, when the toner tribo of the developer was measured at the initial stage of the durability test and after 10,000 sheets, it was found to be −30.5 (μc / g) and −29.4 (μ
c / g) was almost unchanged.

Example 2 As a core material, Ba-ferrite (mol%; Fe ₂ O ₃ :
BaO = 85: 15, holding power 1300 Gauss; 10
K Oersted, magnetic force 18 emu / g: 1 K Oersted) was used, and this surface was covered with a styrene-methyl methacrylate-butyl acrylate copolymer (monomer composition weight ratio =
50:30:20, Mw / Mn = 4.5, Mw = 56,
000). This resin was added to the core material as 1.
A coating solution was prepared as a 10% xylene solution so as to be 0%. The carrier coating solution was applied to the core material by a coating machine (Okada Seiko Co., Ltd .: Spiracoater). The obtained coated carrier was heated at a temperature of 80 ° C. for 1 hour and then dried at 140 ° C. for 2 hours to obtain a carrier of the present invention in which the surface of the carrier core material was coated with a coating resin. Table 1 shows the physical properties of the obtained carrier. Further, when the same test as in Example 1 was conducted, the same good result as in Example 1 was obtained.

Comparative Example 1 Spherical iron powder (average particle size 52 μm, holding power 2.
1Gauss; 10K Oersted) was used and a resin coating layer was formed on this surface in the same manner as in Example 1. When the surface of the obtained resin-coated carrier was observed by a scanning electron microscope, coating unevenness was observed in the coating. Next, a shaking test using a tumbler mixer was conducted using this carrier in the same manner as in Example 1, and it was found that the coating film had partly peeled off. Furthermore, in the same manner as in Example 1, an image development durability test was performed using a CLC-500 modified machine. At the initial stage of the durability test, the solid image had a reflection image density of 1.53, which was a sufficient density, but the halftone image had peeling and the fine line reproducibility was insufficient.
Also, after 10,000 sheets of durability test, the reflection image density is 1.2.
The density was reduced to 7, and the halftone image was disturbed due to the leak of the bias voltage.

Comparative Example 2 Using the same core material as used in Example 2, a styrene-methyl methacrylate-methacrylic acid copolymer (monomer composition ratio = 80: 15: 5, Mw / Mn = 25, Mw =
380,000). A resin-coated carrier was obtained in the same manner as in Example 1 using a carrier coating solution in which 10% of this resin was dissolved in toluene so that the coating resin amount was 1.0% with respect to the core material. When observing the obtained carrier surface with a scanning electron microscope,
The surface coating was uneven. Further, a shaking test with a tumbler mixer was carried out in the same manner as in Example 1, and the peeling of the coating resin was remarkable. Also, CLC-5
When an image development durability test was carried out using a No. 00 remodeling machine, disturbance due to bias voltage leakage occurred from the beginning of the durability test.

Example 3 The same core material as in Example 1 was used.
Methyl methacrylate-2-ethylhexyl acrylate copolymer (monomer composition ratio = 40: 40: 20, Mw / M
(n = 12, Mw = 66,000).
10% of the above resin is added to the core material.
% Carrier solution was prepared as a solution of methyl ethyl ketone. Next, a resin-coated carrier of the present invention was obtained by the same method as in Example 1. When the surface of the obtained carrier was observed with a scanning electron microscope, a uniform coating layer was observed.

Further, as a toner, styrene-2-ethylhexyl acrylate-dimethylaminoethyl methacrylate copolymer (monomer composition weight ratio = 80/15/5) 100 parts copper phthalocyanine 4 parts low molecular polypropylene 5 parts the above materials In the same manner as in Example 1 with a weight average diameter of 9.2 μm.
Blue particles were obtained. To 100 parts of the particles, 0.6 part of positively chargeable colloidal silica treated with amino-modified silicone oil was mixed with a Henschel mixer to obtain a positively chargeable cyan toner. Next, the temperature and humidity of the toner and the carrier are N / N (23 ° C./60% RH).
Under the environment, a developer was obtained by mixing so as to have a toner concentration of 5%. 100 g of the obtained developer was put in a 250 cc plastic bottle and shaken with a tumbler mixer for 1 hour. After that, the developer was taken out and observed with an electron microscope. As a result, peeling of the coating material from the carrier and filming by the toner were not observed.

Next, the above toner and carrier were mixed in an environment of temperature / humidity of N / N (23 ° C., 60% / RH) so that the toner concentration was 5% to obtain a developer. Under the same environment, a copy machine NP-4835 manufactured by Canon Inc. was used as a modified machine, and a durability test was performed on 10,000 images. As a result, even after 10,000 images were printed from the initial stage of the durability test, the density of the solid image was sufficient, the reproducibility of the halftone portion and the sharpness of the line image were good.

[0058]

[Table 1]

[0059]

[Table 2]

[Table 3]

[0060]

[Effect] As described above, the carrier of the present invention improves the various drawbacks of the conventional resin-coated carrier and improves durability,
The stability of imparting charge to the toner over a long period of time is excellent, and thus the carrier of the present invention exhibits remarkably excellent developability, and a high-definition image can be obtained. Furthermore, again
The ferrite particles constituting the carrier core material exhibit specific magnetic characteristics, so that the developer on the sleeve becomes fine and forms a soft magnetic brush, so that a high-definition image is obtained.

[Brief description of drawings]

FIG. 1 is a diagram for measuring the specific resistance of a carrier.

FIG. 2 is an explanatory diagram of a triboelectric charge amount measuring device.

[Explanation of symbols]

 A: Cell 1,2: Electrode 71: Conductive screen 71 72: Measuring container 73: Lid 4: Suction machine 75: Suction port 76: Air flow control valve 77: Vacuum meter 78: Electrometer 79: Condenser

Claims (2)

[Claims] 1. An electrophotographic carrier having a core material surface coated with an insulating resin, wherein the core material is ferrite particles containing strontium, barium or lead, and the holding force of the ferrite particles is a magnetic field of 10K. Is 300 Gauss or more under Oersted, and the resin coating the surface of the core material has a styrene-acrylic copolymer, and the monomer ratio of the acrylic component in the copolymer is 30 to 90% by weight. The weight average molecular weight of the copolymer is about 30,000 to 70,000,
A carrier for electrophotography, which has a weight average molecular weight / number average molecular weight of 2 to 10. 2. Ferrite particles are IA, IIA,
IIIA, IVA, VA, VIA, IB, IIB, IVB, VB,
The electrophotographic carrier according to claim 1, which contains at least one element selected from the group consisting of VIB, VIIB, and VIII, and the content of other elements is less than 1% by weight.