JPH06324522A - Electrophotographic carrier - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a carrier for electrophotography, which is capable of uniformly forming a high-definition image over a long period of time by uniformly coating a resin on the surface of a core material. [Structure] The core material is ferrite particles containing strontium, barium or lead, and the coercive force of the ferrite particles is 300 under a magnetic field of 10 K oersted.
Gauss or more, the resin coating the core material surface has a styrene-acrylic copolymer and a fluorine-containing resin, the monomer ratio of the acrylic component in the copolymer is 30 to 90 wt%, Mw is about 30,000 to 7
Has a distribution of 0000, Mw / Mn of 2 to 10,
The mixing ratio of the fluororesin to the copolymer is 5: 9 by weight (weight of the fluororesin: weight of the copolymer).
It is characterized by being 5 to 95: 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier for electrophotography which is mixed with a toner to form an electrostatic image developer.

[0002]

2. Description of the Related Art US 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 this is deposited on 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, a method of developing such an electrostatic latent image with toner is roughly classified and a small amount of the toner is dispersed in a medium called a carrier. There are a method of using a so-called two-component type developer and a method of using a so-called one-component type developer which uses a toner alone without using a 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 the triboelectrification property to the toner is unstable in the developer containing the iron powder carrier as a component, and depending on the developer. There is a problem that fog occurs in the formed visible image. That is, with the use of the developer, the toner particles adhere to the surface of the iron powder carrier particles, so that 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.

As the insulating carrier, generally, a carrier obtained by uniformly coating the surface of a carrier core material made of a ferromagnetic material such as iron, nickel and ferrite with an insulating resin is typical. 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, and the durability is excellent and the service life is long. It has the advantage of being suitable.

However, in this insulating carrier, the coating layer for coating the surface of the carrier core material has sufficient wear resistance and strong adhesion to the core material, and the toner is fused to the carrier surface, so-called toner spent. Does not occur, and it is required to impart a desired sufficient triboelectric charge amount to a specific toner used 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 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, an attempt has been made to form a thin film of a fatty acid metal salt on the surface of a carrier core material to improve the toner spent resistance and 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, not only iron oxide powder but also ferrite particles are not suitable for a developing system for applying a bias voltage due to current leakage or adhesion of carriers onto the photoconductor. Is.

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 fluoropolymer 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 the fluoropolymer,
A method of coating by mixing with a polymer having a relatively good film-forming property is also described in US Pat. No. 4,297,427 and JP-A-54.
-110839. However, since all of them are composed of a fluoropolymer having a strong negative property in terms of charging characteristics, they can be advantageously used for a positive toner, but have 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. To be

On the other hand, in order to form a high quality image, Japanese Patent Laid-Open No. 2-8
No. 8429, an attempt is made to control the characteristics of a magnetic brush by using a carrier made of a hard magnetic ferrite material. However, it is important to control the conductivity of the carrier, and even if it is coated with a resin, it must be thin enough to maintain appropriate conductivity, and the durability of the film is sufficient. It is difficult to get sex. Furthermore, in general, when obtaining fine particles using a hard ferrite material, the sintering temperature cannot be sufficiently increased in the manufacturing process so as to have a high coercive force in terms of magnetic characteristics, and therefore,
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 a conventional resin, and even if it can be applied, there is no peeling or loss of the coating when used as a developer. However, it is difficult to obtain a resin-coated carrier that has durability and is capable of stably imparting an appropriate amount of charge to the toner over a long period of time.

[0011]

The main object of the present invention is to:
In the carrier whose surface is coated with a resin as described above, while excellent in durability and toner spent resistance, a good electric charge is stably applied to the toner for a long period of time, and a magnetic brush per unit area on the sleeve. Another object of the present invention is to provide an electrophotographic carrier capable of forming a high-definition image with a high density of "brushing".

A further object of the present invention is to have a suitable resistance,
Even if a bias voltage is applied, current leakage or
An object of the present invention is to provide a carrier for electrophotography, which is less likely to adhere to the photoreceptor.

[0013]

Means and Actions for Solving the Problems The present invention provides an electrophotographic carrier in which the surface of a core material is coated with an insulating resin, wherein the core material is ferrite particles containing strontium, barium or lead, And the coercive force of the ferrite particles is 300 Gauss or more under a magnetic field of 10 K Oersted, and the resin coating the surface of the core material has a styrene-acrylic copolymer and a fluorine-containing resin, and the styrene-acrylic resin The monomer ratio of the acrylic component in the copolymer is 30 to
90% by weight and a weight average molecular weight of about 30,000 to 7
The weight average molecular weight / number average molecular weight is from 2 to 10, and the mixing ratio of the fluororesin to the styrene-acrylic copolymer is a weight ratio (the fluororesin weight: Polymer weight) 5:95 to 95:
The carrier for electrophotography is characterized in that it is No. 5.

The present invention will be described in detail below. 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 has a remarkably excellent developability. Although the details are not clear, it is believed that the reason why a higher-definition image can be obtained is as follows.

That is, when the surface of the carrier of the present invention was observed with a scanning electron microscope, the resin used in the present invention was coated with a coating layer in such a state that it penetrates into the concave and convex portions of the core material surface. It was observed that the core material was formed and 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 proper resistivity without leakage when 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 dense and forms a soft magnetic brush, resulting in a high-definition image. Conceivable.

Next, the structure of the present invention will be described in detail.

Examples of the styrene-acrylic copolymer which can be used for the coating resin for the carrier core material of the present invention include a copolymer of a styrene derivative and acrylic acid ester and a copolymer of a styrene derivative and methacrylic acid ester. Refers to a polymer. 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, pn-butylstyrene, p-tert-butylstyrene, pn-hexylstyrene, pn-octylstyrene, p -N-
Nonylstyrene, pn-decylstyrene, pn-dodecylstyrene, p-methoxystyrene, p-chlorostyrene, 3,4-dichlorostyrene, m-nitrostyrene, o-nitrostyrene, p-nitrostyrene, etc. Is mentioned.

Examples of acrylates include methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, dodecyl acrylate, and the like.
2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate, phenyl acrylate and the like can be mentioned.

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, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate and the like can be mentioned.

Further, the weight average molecular weight of the above-mentioned copolymer which can be used for the coating resin of the carrier core material of the present invention is essentially about 30,000 to 70,000, and the weight average molecular weight / number average molecular weight is 2 to 2. It is indispensable to be 10. When the weight average molecular weight is less than 30,000, the strength with respect to the impact resistance of the carrier cannot be obtained, and 70
If it is more than 000, the coverage with respect to the carrier core deteriorates, and the strength of the carrier and the charging stability become poor. More importantly, at this time, even if the weight average molecular weight is within this range, the weight average molecular weight /
If the number average molecular weight is not within the range of 2 to 10, the effect of the present invention cannot be obtained. 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.

Further, as the fluorine-containing resin mixed with the above-mentioned styrene-acrylic copolymer which can be used as the coating resin for the carrier core material of the present invention, polyvinyl fluoride, polyvinylidene fluoride, polytrifluoro are available. ethylene,
Hello fluoropolymers such as polytrifluorochloroethylene, polytetrafluoroethylene, polyperfluoropropylene, copolymers of vinylidene fluoride and acrylic monomers, copolymers of vinylidene fluoride and trifluorochloroethylene, Copolymer of tetrafluoroethylene and hexafluoropropylene, Copolymer of vinyl fluoride and vinylidene fluoride, Copolymer of vinylidene fluoride and tetrafluoroethylene, Copolymerization of vinylidene fluoride and hexafluoropropylene Fluoroterpolymers such as terpolymers of terpolymers, tetrafluoroethylene and vinylidene fluoride and non-fluorinated monomers.

The mixing ratio of these fluorine-containing resin and styrene acrylic polymer is preferably 5:95 to 95: 5 in terms of weight ratio (weight of the fluorine-containing resin: weight of the copolymer). When the content is within the above range, desired charge stability can be obtained with both positive and negative polarity developers, but when the content of the fluorine-containing resin is less than 5% by weight, the development showing positive charging characteristics is achieved. When the content of the fluorine-containing resin exceeds 95% by weight, the charge stability of the developer is deteriorated, and on the other hand, the charge stability of the developer exhibiting negative charge characteristics is decreased and the wettability is also reduced. As a result, the uniform coating on the core material becomes difficult.

The weight average molecular weight of the fluorine-containing resin is preferably 50,000 to 400,000, more preferably 100,000 to 250,000. If it is less than 50,000, impact resistance tends to be insufficient, and if it is 40
If it exceeds 0000, uniform coating on the core material becomes unstable.

In the present invention, the molecular weight and molecular weight distribution of the coating resin that can be used as the coating resin for the carrier core material, and the molecular weight of the fluorine-containing resin are those of monodisperse standard by GPC (gel permeation chromatography). The value obtained by observing a calibration curve obtained by using polystyrene. The measurement conditions are shown below.

Equipment: GPC-150C (Waters) Column: Shoredex KF 7 stations (Showa Denko) Temperature: 40 ° C Solvent: THF (tetrahydrofuran) Flow rate: 1.0 ml / min Test material: 0. Inject 0.4 ml of 15% sample

It is essential that the magnetic material used for the carrier core material in the present invention contains at least one of Sr ferrite, Ba ferrite and Pb ferrite. Further, as other components, the periodic table IIIA, I
VA, VA, VIA, IB, IIB, IVB, VB, V
IB, VIIB and VIII elements may be included,
Other elements are preferably less than 1 wt%.

As described above, this increases the density of the "brushing" of the magnetic brush on the sleeve, and controls the resistance at which bias voltage leakage and carrier adhesion do not occur after resin coating to an optimum value. Is important for.

For the same reason, the carrier magnetic field 10 of the present invention is used.
The coercive force in K Oersted is preferably 300 Gauss or more, and more preferably 500 Gauss or more. In addition, the magnetic force in a magnetic field of 1K Oersted is 5
It is preferably emu / g to 59 emu / g, and more preferably 10 to 19 emu / g. The magnetic properties 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 less than m, carrier adhesion to the photoconductor is likely to occur, and if it exceeds 60 μm, the share of the developer in the developing device becomes large, resulting in deterioration of the developer, especially peeling of external additive of toner particles, shape. It causes changes and causes image deterioration. Furthermore, when the particle size is large, the specific surface area is small, so the amount of toner that can be held in the developer is small, and the image lacks fineness. The particle size of the carrier core of the present invention is randomly determined to be 500 by an optical microscope or a scanning electron microscope.
More than one piece was extracted, and the maximum chord length in the horizontal direction was measured as the carrier particle size.

The resistivity of the carrier of the present invention is 10 ⁸ to 10
A range of ¹⁴ Ω · cm is suitable. 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. On the other hand, when it exceeds 10 ¹⁴ Ω · cm, a charge-up phenomenon is caused under conditions such as low humidity, which causes image deterioration such as density unevenness, transfer failure, and fog.

In the present invention, the method of coating the surface of the carrier core material with the resin coating layer is carried out by dissolving or suspending the above resin material in an organic solvent such as toluene, xylene, tetrahydrofuran or acetone, and coating the carrier according to the present invention. The solution can be prepared and applied to the carrier core material by a general application device such as a spray method or a fluidized bed method.

The two-component developer for developing an electrostatic charge image of the present invention, which comprises an electrophotographic carrier and a toner, contains 10 to 100 parts by weight of the above resin-coated carrier per 10 parts by weight of the toner.
0 parts by weight, preferably 30 to 500 parts by weight are mixed and used.

The toner used in combination 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, in terms of resolution and toner consumption, the toner preferably has a particle size distribution within the following range.

That is, toner particles having a particle size of 5 μm or less are 17 to 60% by number of all particles, and 8 to 12.7 μm.
It is preferable that toner particles having a particle size in the range of 1 to 30% by number of the total number of particles and particles in the range of a particle size of 16 μm or more are less than 2.0% by volume of the total number of particles.

The weight average particle size and particle size distribution of the toner can be measured by various methods, but in the present invention, it is measured using a Coulter counter.

A Coulter counter T is used as a measuring device.
Interface (made by Nikkaki) and CX that output number distribution and volume distribution using A-II type (made by Coulter)
-1 Connect a personal computer (made by Canon),
As the electrolytic solution, a 1% NaCl aqueous solution is prepared using first grade sodium chloride. As a measuring method, the electrolytic aqueous solution 100 to
To 150 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, and a particle size distribution of particles of 2 to 40 μm based on the number is used with the Coulter Counter TAII type using an aperture of 100 μm. Was measured, and the value relating to the present invention was then determined.

As the binder resin used for the toner, 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.

For example, homopolymers of styrene and its substitution products such as polystyrene, poly-p-chlorostyrene, polyvinyltoluene; styrene-p-chlorostyrene copolymers, styrene-vinyltoluene copolymers, styrene-
Vinyl naphthalene copolymer, styrene-acrylic acid ester copolymer, styrene-methacrylic acid ester copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-
Styrene such as vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer -Based copolymer; polyvinyl chloride, phenol resin, natural modified phenol resin, natural resin modified maleic acid resin, acrylic resin, methacrylic resin, polyvinyl acetate, silicone resin, polyester resin, polyurethane, polyamide resin, furan resin, epoxy resin , Xylene resin, polyvinyl butyral, terpene resin, coumarone indene resin, petroleum-based resin can be used.

In the heating and pressure roller fixing method in which oil is hardly applied, the offset phenomenon in which a part of the toner image on the toner image support member is transferred to the roller and the adhesion of the toner to the toner image support member are important. It's a problem.
Toners that fix with less heat energy usually tend to be blocked or caked during storage or in a developing device, and therefore 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 styrenic copolymers or cross-linked polyesters.

Examples of the comonomer for the styrene monomer of the styrene copolymer include acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate,
Double bond such as dodecyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, acrylonitrile, methacrylonitrile, acrylamide A dicarboxylic acid having a double bond such as maleic acid, butyl maleate, methyl maleate, and dimethyl maleate; and a substituted product thereof; for example, vinyl chloride, vinyl acetate, vinyl benzoate Vinyl esters such as ethylene; propylene; butylene; ethylene-based olefins such as vinyl methyl ketone; vinyl hexyl ketone; vinyl ketones such as vinyl methyl ether; Ether, such as vinyl ethers vinyl isobutyl ether; such vinyl monomers are used alone or two or more.

As the cross-linking agent, a compound having two or more polymerizable double bonds is mainly used, and examples thereof include aromatic divinyl compounds such as divinylbenzene and divinylnaphthalene; for example, ethylene glycol diacrylate and ethylene glycol diethylene. Methacrylate, 1,3
A double bond such as butanediol dimethacrylate
Carboxylic acid ester having one; divinylaniline, divinyl ether, divinyl sulfide, divinylsulfone divinyl compound; and a compound having three or more vinyl groups; 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 the pressure-fixing method is used, a binder resin for pressure-fixing toner can be used, and examples thereof include polyethylene, polypropylene, polymethylene, polyurethane elastomer, ethylene-ethyl acrylate copolymer,
There are ethylene-vinyl acetate copolymers, ionomer resins, styrene-butadiene copolymers, styrene-isoprene copolymers, linear saturated polyesters, and paraffins.

For the toner, it is preferable to use a charge control agent mixed with 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 depending on the particle size range. As the positive charge control agent, a modified product of nigrosine and a fatty acid metal salt; tributylbenzylammonium-1
-Quaternary ammonium salts such as hydroxy-4-naphthosulfonate, tetrabutylammonium tetrafluoroborate; diorganotin oxides such as dibutyltin oxide, dioctyltin oxide, dicyclohexyltin oxide; dibutyltin borate, dioctyltin borate, dicyclohexyltin borate Can be used alone or in combination of two or more. Among these, charge control agents such as nigrosine and quaternary ammonium salts are particularly preferably used.

General formula

[0048]

[Chemical 1] A homopolymer of a monomer represented by: 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 function as (all or part of) the binder resin.

As the negative charge control agent, for example, an organometallic complex and a chelate compound are effective, and examples thereof include aluminum acetylacetonate, iron (II) acetylacetonate, and chromium 3,5-di-tert-butylsalicylate. There is. 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.

It is preferable to add fine silica powder to the toner. 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 carrier or the surface of the sleeve. As a result, the life of the toner and carrier or / and the sleeve can be extended, and the stable chargeability can be maintained, so that the two-component developer having a better toner and carrier can be used for a long period of time. It 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 and the abrasion of the toner particles and the contamination of the carrier are more likely to occur than the toner having a weight average particle diameter of more than 10 μm. Addition of the powder makes it 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, it is preferable to use the silica fine powder by the dry method.

The dry method referred to herein is a method for producing fine silica powder produced by vapor phase oxidation of a silicon halogen compound, for example.

On the other hand, various conventionally known methods can be applied to the method for producing the silica fine powder by the wet method.

As the silica fine powder referred to herein, anhydrous silicon dioxide (colloidal silica); silicates such as aluminum silicate, sodium silicate, potassium silicate, magnesium silicate and zinc silicate can be applied.

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. The fine silica powder is used in an amount of 0.01 to 8 parts by weight, preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the toner.

When the toner is used as a positively chargeable toner, the silica fine powder added to prevent the toner from being worn and the carrier and the sleeve surface from being soiled is positively charged silica rather than negatively charged. It is preferable to use fine powder without impairing the charging stability, and when used as a negatively chargeable toner, it is preferable to use negatively chargeable silica fine powder for the same reason.

Since the silica fine powder is generally negatively charged, the method for obtaining the positively-charged silica fine powder is the above-mentioned untreated silica fine powder with at least one nitrogen atom in the side chain. There is a method of treating with a silicone oil having an organo group contained therein, a method of treating with a nitrogen-containing silane coupling agent, or a method of treating with both of them.

Here, 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 fine silica powder, silicone oil having at least a partial structure represented by the following formula can be used.

[0063]

[Chemical 2]

(Wherein R ₁ represents hydrogen, an alkyl group, an aryl group or an alkoxy group, R ₂ represents an alkylene group or a phenylene group, and R ₃ and R ₄ represent hydrogen, an alkyl group or an aryl group. , R ₅ represents a nitrogen-containing heterocycle.) In the above formula, the alkyl group, aryl group, alkylene group, and phenylene group may have an organo group having a nitrogen atom, and do not impair the charging property. It may have a halogen substituent within the range. The silicone oil is used in an amount of 1 to 50% by weight, preferably 5 to 30% by weight, based on the fine silica powder.

The nitrogen-containing silane coupling agent generally has a structure represented by the following formula.

Rm-Si-Yn (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 =
It is 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. As the nitrogen-containing heterocyclic group, there are an unsaturated heterocyclic group and a saturated heterocyclic group, and known ones can be applied. Examples of the unsaturated heterocyclic group include the following.

[0067]

[Chemical 3]

Examples of the saturated heterocyclic group include the following.

[0069]

[Chemical 4]

The heterocyclic group is preferably a 5-membered ring or a 6-membered ring in view of stability.

Examples of such treating agents include aminopropyltrimethoxysilane, aminopropyltriethoxysilane, dimethylaminopropyltrimethoxysilane,
Diethylaminopropyltrimethoxysilane, dipropylaminopropyltrimethoxysilane, dibutylaminopropyltrimethoxysilane, monobutylaminopropyltrimethoxysilane, dioctylaminopropyltrimethoxysilane, dibutylaminopropyltrimethoxysilane, dibutylaminopropyltrimethoxysilane,
There are dibutylaminopropylmonomethoxysilane, dimethylaminophenyltriethoxysilane, trimethoxysilyl-γ-propylphenylamine and trimethoxysilyl-γ-propylbenzylamine. Furthermore, as the nitrogen-containing heterocycle, those having the above-mentioned structures can be used, and examples of such a compound include methoxysilyl-γ-propylpiperidine, trimethoxysilyl-γ-propylmorpholine, trimethoxysilyl-γ-propylimidazole. There is. 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 amount of the treated positive or negative silica fine powder applied was 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 silica fine powder may be treated with a silane coupling agent or a treating agent such as an organic silicon compound for the purpose of hydrophobizing, if necessary. It is processed. Examples of such a treating agent include hexamethyldisilazane, trimethylsilane, trimethylchlorosilane, trimethylethoxysilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, allylphenyldichlorosilane, and benzyldimethylchlorosilane,
Brommethyldimethylchlorosilane, α-chloroethyltrichlorosilane, β-chloroethyltrichlorosilane, chloromethyldimethylchlorosilane, triorganosilylmercaptan, trimethylsilylmercaptan,
Triorganosilyl acrylate, vinyldimethylacetoxysilane, dimethylethoxysilane, dimethyldimethoxysilane, diphenyldiethoxysilane, hexamethyldisiloxane, 1,3-divinyltetramethyldisiloxane, 1,3-diphenyltetramethyldisiloxane, and 1 There is a dimethylpolysiloxane having 2 to 12 siloxane units per molecule, with each terminally located unit containing a single Si-bonded hydroxyl group. These are used alone or in a mixture of two or more. The treating agent is 1 to 40 based on silica fine powder.
It is preferred to use weight percent.

BET specific surface area of 5 instead of silica fine powder
Titanium oxide fine powder (TiO ₂ ) of 0 to 400 m ² / g may be used. Further, a mixed powder of silica fine powder and titanium oxide fine powder may be used.

It is also possible to add fine powder of a fluorine-containing polymer (for example, fine powder of polytetrafluoroethylene, polyvinylidene fluoride or tetrafluoroethylene-vinylidene fluoride copolymer) to the toner. Particularly, fine powder of polyvinylidene fluoride is preferable in terms of fluidity and abrasivity. The amount added to the toner is 0.01 to 2.0 wt%, especially 0.02 to 1.5 w
t% (more preferably, 0.02 to 1.0 wt%) is preferable.

As the colorant, conventionally known dyes and / or pigments can be used. For example, carbon black, phthalocyanine blue, peacock blue,
Permanent red, rake red, rhodamine rake, Hansa yellow, permanent yellow, benzidine yellow, etc. can be used. The content thereof is 0.1 to 20 parts by weight, preferably 0.5 to 20 parts by weight, based on 100 parts by weight of the binder resin, and further 1 to improve the transparency of the OHP film on which the toner image is fixed.
It is preferably 2 parts by weight or less, more preferably 0.5 to 9
Good parts by weight.

For the toner, wax-like substances such as low molecular weight polyethylene, low molecular weight polypropylene, microcrystalline wax, carnauba wax, sazol wax and paraffin wax are added to the toner for the purpose of improving releasability at the time of heat roll fixing. Addition of ~ 5 wt% is also one of the preferable forms.

If desired, other additives may be added to the toner.

To prepare a toner, a vinyl-based or non-vinyl-based thermoplastic resin, and if necessary, a pigment or dye as a colorant, a charge control agent, and other additives are sufficiently mixed with a mixer such as a ball mill. After that, using a heat kneader such as a heating roll, a kneader, an extruder, a pigment or a dye is dispersed or dissolved in a resin in which the resins are mutually compatible by kneading and kneading, and kneading and crushing after cooling and solidifying. Toner particles can be obtained by performing strict classification. 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 for 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. 1 is an explanatory diagram of a triboelectric charge amount measuring device. A magnetic brush (deposited with toner) on the developer carrier for measuring the triboelectric charge amount in a metal measuring container 2 having a conductive screen 3 of 400 mesh at the bottom (which can be changed to a size that does not allow carrier particles to pass). The mixture 4) of the carrier of the present invention is put into the lid 4 made of metal. At this time, the weight of the entire measuring container 2 is weighed and designated as W ₁ (g). Next, in the suction device 1 (at least the portion in contact with the measurement container 2 is an insulator), suction is performed from the suction port 7 and the air volume control valve 6 is adjusted to set the pressure of the vacuum gauge 5 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 9 at this time is V (volt). Reference numeral 8 is a capacitor, and its 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.

[0083]

The present invention will be described below with reference to examples and drawings. This does not limit the invention in any way. still,
All percentages and parts in the following formulations refer to% by weight and parts by weight.

Example 1 Sr ferrite [Fe ₂ O ₃ : SrO = 87: 13 (molar ratio) as core material, Hc =
1700 Gauss; 10K Oersted],
This surface was coated with the following resin.

Styrene-2-ethylhexyl methacrylate copolymer 50% (monomer composition weight ratio = 40: 60, Mw 42000, Mw / Mn = 2.9) Vinylidene fluoride-tetrafluoroethylene copolymer 50% (monomer Composition weight ratio = 75: 25, Mw 210000)

10% of the above copolymer was dissolved in a mixed solvent of acetone and methyl ethyl ketone (mixing weight ratio = 1: 1) so that the amount of the coating resin was 0.8% from the above calculation formula, and the carrier was added. A coating solution was made. This carrier coating solution is applied by a coating machine (Okada Seiko Co., Ltd .: Spiracoater)
The core material was applied while being dried while being applied. The obtained coated carrier was dried at a temperature of 80 ° C. for 1 hour to remove the solvent, and then heated at a temperature of 140 ° C. for 2 hours to obtain a resin-coated carrier in which the core material surface was coated with a resin coating layer. Observation of the obtained resin-coated carrier with a scanning electron microscope showed that the resin was immersed in the irregularities of the core material and the surface was uniformly coated. They were scattered like islands on the polymer film and were uniformly dispersed.

The physical properties of the obtained carrier are summarized in Table 1.

On the other hand, polyester resin obtained by condensing 100 parts of propoxylated bisphenol and fumaric acid Phthalocyanine pigment 5 parts Di-tert-butylsalicylic acid chromium complex salt 4 parts

The above materials were sufficiently premixed with a Henschel mixer, melt-kneaded with a three-roll mill three times, 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 was classified to obtain a negatively chargeable cyan powder (toner) having a weight average diameter of 8.8 μm.

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.

This cyan toner and the above resin 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. 100 g of the obtained developer was put in a 250 cc plastic bottle and shaken with a Turbula 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.

Further, a cyan toner and the above resin-coated 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. Using this, under the same environment, using a Canon full-color laser copying machine CLC-500 modified machine, development contrast 3
An image output durability test was performed at 50V. This result is
As shown in Table 2, in the initial stage, a high-definition image having a sufficient reflection density of a solid image density of 1.53 and good reproducibility of a halftone portion and a thin line portion was obtained. The images obtained after 10,000 sheets of durability were also of good image quality as in the beginning of durability. In addition, when the toner tribo was measured at the initial stage of the durability test and after 10,000 sheets, each was −
30.1 (μc / g) and −28.8 (μc / g), which were almost unchanged.

(Example 2) Resin coating was carried out in the same manner as in Example 1 except that Ba-ferrite [Fe ₂ O ₃ : BaO = 85: 15 (molar ratio), coercive force 1300 Gauss; 10K oersted] was used as the core material. Got a career.
The surface of the obtained resin-coated carrier was observed by a scanning electron microscope, and it was confirmed that the surface of the core material was almost uniformly covered with the resin.

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 49 μm, coercive force 2.1 Gauss; 10 K Oersted) was used as the core material, 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 with a scanning electron microscope, some coating unevenness was found in the coating. Next, a shaking test using a Turbula mixer was carried out in the same manner as in Example 1 using this carrier, and it was found that the coating film was occasionally peeled off. Furthermore, in the same manner as in Example 1, CLC
A drawing durability test was performed using a -500 modified machine. At the initial stage of durability, the solid image had a reflection image density of 1.51, which was a sufficient density, but the halftone image was dull and the reproducibility of fine lines was insufficient. Further, after 10,000 sheets of durability, the reflection image density was reduced to 1.24, 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, coating treatment was performed with the following resin.

Styrene-methyl methacrylate-methyl acrylate (monomer composition ratio = 80: 15: 5, Mw / Mn = 1
5, Mw = 320,000)

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 wt% with respect to the core material. When the surface of the obtained carrier was observed with a scanning electron microscope, unevenness was observed in the surface coating. Further, when a shaking test was conducted by using a Turbula mixer in the same manner as in Example 1, the peeling of the coating resin was remarkable. In addition, when image development durability was performed with a modified CLC-500 machine, image distortion occurred due to bias voltage leakage from the initial stage of durability.

Example 3 The same core material as in Example 1 was used, and this was coated with the following resin. Styrene-butyl acrylate copolymer 50% (monomer composition weight ratio = 50: 50 Mw = 56000, Mw / Mn = 4.5) Vinylidene fluoride-tetrafluoroethylene copolymer 50% (monomer composition weight ratio = 75 : 25, Mw = 210,000) was coated on the above core material in the same manner as in Example 1 using a carrier coating solution prepared by dissolving 10% in methyl ethyl ketone so that the coating resin amount was 1.2%. A dispersed resin carrier was obtained.

As the toner, styrene-2-ethylhexyl acrylate-100 parts dimethylaminoethyl methacrylate copolymer (monomer composition weight ratio = 80/15/5) copper phthalocyanine 4 parts low molecular weight polypropylene 5 parts

Using the same material as in Example 1, blue particles having a weight average diameter of 9.2 μm were obtained. This cyan particle 100
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 toner and the carrier are mixed with each other under a temperature / humidity N / N (23 ° C./60% RH) environment to have a toner density of 5
% To obtain a developer. Obtained developer 10
0 g was put into a 250 cc plastic bottle and shaken with a Turbula mixer for 1 hour. After that, take out the developer,
The developer was 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 toner and the carrier are mixed at a toner density of 5 under an environment of temperature / humidity of N / N (23 ° C./60% RH).
% To obtain a developer. Under the same environment, a modified copying machine NP-4835 manufactured by Canon Inc. was used and 10,000 sheets of images were printed and durable. As a result, the density of the solid image was sufficient even when images were printed on 10,000 sheets from the initial stage of durability, and the reproducibility of the halftone portion and the sharpness of the line image were good.

(Example 4) Pb-ferrite [Fe ₂ O ₃ : PbO = 90: 10 (molar ratio), coercive force 760 Gauss; 10K oersted] was used as the core material in the same manner as in Example 3 for resin coating. Got a career. The surface of the obtained resin-coated carrier was observed by a scanning electron microscope, and it was confirmed that the surface of the core material was almost uniformly covered with the resin.

When the same test as in Example 3 was conducted, good results were obtained as in Example 3.

Table 1 shows the carrier characteristics of the above Examples and Comparative Examples, and Table 2 shows the results of the image forming test.

[0107]

[Table 1]

[0108]

[Table 2]

[0109]

In the resin-coated carrier of the present invention, the surface of the core material is uniformly coated with the resin, and a good charge can be stably imparted to the toner over a long period of time. Also, the density of the "brushing" of the magnetic brush on the sleeve is high,
It is possible to form a high-definition image.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a method for measuring a triboelectric charge amount of toner with respect to a carrier.

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 ferrite particles have a coercive force of a magnetic field of 10K. 300 Gauss under Oersted
As described above, the resin coating the surface of the core material has a styrene-acrylic copolymer and a fluorine-containing resin, and the monomer ratio of the acrylic component in the copolymer of the styrene-acrylic copolymer is 30. To 90% by weight, the weight average molecular weight has a distribution of about 30,000 to 70,000, the weight average molecular weight / number average molecular weight is 2 to 10, and the fluorine-containing resin is mixed with the styrene-acrylic copolymer. Ratio is weight ratio (weight of the fluororesin: weight of the copolymer)
And a carrier for electrophotography, which is 5:95 to 95: 5. 2. The ferrite particles are IA and II of the periodic table.
A, IIIA, IVA, VA, VIA, IB, IIB,
2. At least one element selected from the group consisting of IVB, VB, VIB, VIIB, and VIII is contained, and the content of the other elements is less than 1% by weight. Carrier for electrophotography.