JPH07146592A - Two-component developer for developing electrostatic charge image - Google Patents

Abstract

PURPOSE:To suppress the dependency of the charge amt. of a developer using magnetite on humidity by specifying the concn. of the alkali metal salt present on the surface of magnetite. CONSTITUTION:Fine magnetite particles are mixed with appropriate solvent and binder (aq. PVA, etc.) by a ball mill, etc., and slurried, the slurry is sprayed and granulated by a spray drier, and the granulated material is heat-treated in a calcination furnace such as an electronic furnace to produce the developer. The surface concn. of an alkali metal salt is controlled to <=0.15mug/cm<2> in this production process. Accordingly, the solvent and binder not contg. alkali metal salt impurities are used in the slurrying stage, or the produced core particle is washed with ion-exchanged water. The core particle is preferably coated with a silicone resin layer. A carrier with the resin coating layers provided on the magnetite core having an excellent characteristic as the carrier core and high environmental stability is used, and a two-component developer with the difference in triboelectric chareg amt. between under high-temp. and high- humidity conditions and under low-temp. and low-humidity conditiones reduced is obtained.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art So-called dry two-component type developers for electrostatic latent image development, which are composed of a mixture of carrier particles and toner particles, have been well known. This dry two-component type developer (hereinafter sometimes simply referred to as "developer") has a structure in which small toner particles are held on the surface of a relatively large particle by the electric force generated by the friction between the particles, When approaching the latent image, the attraction force in the latent image direction on the toner particles due to the electric field formed by the electrostatic latent image overcomes the binding force between the toner particles and the carrier particles, and the toner particles are transferred onto the electrostatic latent image. The electrostatic latent image is visualized by being attracted and adhered to. Then, the developer is repeatedly used while replenishing the toner consumed by the development. Therefore, during long-term use,
The carrier particles must always tribocharge the toner particles to the desired charge.

Metal oxides such as magnetite and ferrite are widely used as carrier materials for two-component developers, and have a smaller apparent density than iron powder carriers and can be made lighter as developers. Therefore, when the developer is stirred in the developing device, there is an advantage that the stirring resistance becomes small. Furthermore, magnetite,
Ferrite has excellent magnetic properties as a carrier material compared to iron. Further, since magnetite, ferrite and the like are oxides, they are chemically stable and have an advantage that chemical changes due to ozone, NOx, etc. generated in the copying machine are hard to occur. Further, in recent years, environmental safety of developers has become one of the important qualities due to increasing interest in ecology, and magnetite is becoming more superior than ferrite containing heavy metal oxides.

However, the developers using these metal oxides as carriers can solve the problem of the iron powder carrier, namely, the weight to some extent, but the developer particles collide with each other by high-speed development or copying of a large number of sheets, or development. Due to mechanical collision such as collision between developer particles and developing machine, a toner film is formed on the surface of the carrier, so-called spent formation occurs, the charging property of the carrier decreases with use time, toner scattering, background fog, etc. There was a drawback that it occurred. In order to prevent such spent-forming, a method of coating the surface of the core particles with various resins has been conventionally proposed. For example, a method of coating with a material having a low surface energy such as a styrene-methacrylate copolymer, a styrene resin, a fluorine resin, and a silicone resin has been devised.

[0005]

On the other hand, as a carrier having magnetite as a core particle, for example, a carrier having a resin coating layer is formed by partially reducing spherical magnetite to form metallic iron in its surface layer and having a magnetite inside. (JP-A-61-284774) and a carrier (JP-A-62-238580) in which spherical particles of magnetite containing hematite are coated with a resin have been proposed. However, these carriers have a problem that the triboelectric charge amount under high temperature and high humidity and under low temperature and low humidity is largely changed, and images of stable quality cannot be maintained.

Therefore, an object of the present invention is to use a carrier having a resin coating layer on a magnetite nucleus which has excellent properties as a carrier nucleus and is highly environmentally stable, and is used under high temperature and high humidity and low temperature and low humidity A two-component developer having a small difference in triboelectric charge amount is provided.

[0007]

The present invention is a two-component developer comprising carrier particles having a resin coating layer on the surface of magnetite core particles, and toner particles.
The concentration of the alkali metal salt existing on the surface of the magnetite is 0.15 μg / cm ² or less. 0.15 μg of alkali metal salt on the surface of magnetite
By setting it to be / cm ² or less, it is possible to suppress the humidity dependency of the charge amount of the developer using magnetite.

Here, the alkali metal salt concentration is as follows:
It is the value obtained by the procedure of 2 and 3. 1. Quantification of alkali metal salt Weigh the sample and pure water in a beaker and calculate the total weight. Heat the beaker on a hot plate and bring to a boil. After cooling, the weight of the beaker is measured and pure water with a reduced weight is added. The above liquid is filtered, and the alkali metal in the filtrate is quantitatively analyzed by an atomic absorption method. (X μg / g = ppm) 2. Measurement of Specific Surface Area The sample is sieved with a low-tap (Ro-Tap) sieve shaker to calculate the weight average particle diameter. The specific area is calculated from the weight average particle diameter assuming that the shape is a sphere. (Ycm ² / g) 3. The surface concentration (c) of the alkali metal salt is calculated by the following formula. c = X / Y (μg / cm ² )

The present invention will be described in more detail below. Examples of the method for producing magnetite particles used in the present invention include the following methods. The magnetite fine particles are mixed with a ball mill etc. in an appropriate solvent and binder (PVA
Aqueous solution, etc.) to form a slurry, spray granulation with a spray dryer, and then heat treatment in a firing furnace such as an electronic furnace. In order to reduce the surface concentration of the alkali metal salt to 0.15 μg / cm ² or less in this manufacturing process, use a solvent / binder that does not contain an alkali metal salt impurity in the slurry forming process, or manufacture There is a method of washing the subsequent core particles with ion-exchanged water. The size of the magnetite core particles is 20
.About.200 .mu.m, preferably 40 to 100 .mu.m is suitable. The concentration of the alkali metal salt on the surface of the magnetite core particles is 0.15 μg / cm ² or less, preferably 0.1
It is 0 μg / cm ² . If the concentration of the alkali metal salt on the surface of the magnetite core particles is set to zero, the adhesiveness with the resin coating layer may deteriorate depending on the resin used. Therefore, 0.02 μg / cm ² or more is preferably present on the surface of the core particles. By satisfying such conditions, even when a toner using a polyester resin having a hydrophilic functional group and having a large fluctuation in triboelectricity due to humidity as a binder is used, stable charging characteristics are stable against fluctuations in humidity. Can be obtained.

Examples of the resin forming the coating layer (surface layer) with the carrier of the present invention include polyolefin resins such as polyethylene, polypropylene, chlorinated polyethylene and chlorosulfonated polyethylene; polystyrene, acrylic (eg polymethylmethacrylate), Polyvinyl and polyvinylidene resins such as polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether, and polyvinyl ketone; vinyl chloride-vinyl acetate copolymers; styrene-acrylic acid copolymers; Silicone resin composed of organosiloxane bond or its modified product (for example, modified product of alkyd resin, polyester resin, epoxy resin, polyurethane, etc.);
Fluorine resins such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride and polychlorotrifluoroethylene; polyamides; polyesters; polyurethanes; polycarbonates; amino resins such as urea-formaldehyde resins; epoxy resins and the like. Of these, silicone resins or modified products thereof, and fluororesins, particularly silicone resins or modified products thereof, are preferable from the viewpoint of preventing toner spent.

As the silicone resin, any conventionally known silicone resin may be used, and straight silicones and alkyds, polyesters, epoxies, urethanes consisting only of the organosiloxane bond represented by the following general formula (1). Silicone resin modified by, for example.

[Chemical 1](In the formula, R¹Is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.
Or phenyl group, R²And R³Is hydrogen atom, carbon number 1 to
4 alkoxy group, phenyl group, phenoxy group, carbon number
2-4 alkenyl groups, alkenyloxy having 2-4 carbons
Si group, hydroxy group, carboxyl group, ethyleneoxy
Group, glucidyl group or (R^FiveIs a hydroxy group, a carboxyl group, and a carbon number of 1 to 4
Alkyl group, C1-4 alkoxy group, C2
~ 4 alkenyl group, alkenyloxy having 2 to 4 carbon atoms
Group, phenyl group or phenoxy group), R^FourIs R^FiveSame as
is there. k, l, m, n, p, q are integers of 1 or more
You ) Each of these substituents is, in addition to an unsubstituted one, for example
Amino group, hydroxy group, carboxyl group, mercapto
Group, alkyl group, phenyl group, ethylene oxide group,
Has a substituent such as a glycidyl group and a halogen atom
May be.

Commercially available straight silicone resins include KR271, KR255, KR15 manufactured by Shin-Etsu Chemical Co., Ltd.
2. SR24 made by Toray Dow Corning Silicone
11, SR2405, etc. Moreover, commercially available modified silicone resins include KR206 (alkyd modified), KR5208 (acrylic modified), and ES manufactured by Shin-Etsu Chemical Co., Ltd.
1001N (epoxy modified), KR305 (urethane modified), Toray Dow Corning Silicone SR2
115 (epoxy modified), SR2110 (alkyd modified) and the like.

The electrically conductive fine powder dispersed in the coating layer may be conventionally known ones, and examples thereof include metal oxides such as silica, alumina and titania; pigments such as carbon black. Among them, particularly by using a mixture of furnace black and acetylene black, which is one of carbon black, it is possible to effectively adjust the conductivity by adding a small amount of conductive fine powder, and further to the abrasion resistance of the coating layer. It becomes possible to obtain an excellent carrier. These conductive fine powders preferably have a particle size of about 0.01 to 10 μm,
The amount of the conductive fine powder is 2 to 30 parts by weight, preferably 5 to 20 parts by weight, based on 100 parts by weight of the coating resin.

As the silane coupling agent contained in the coating layer, a compound represented by the following general formula (2) Y ¹ R ⁶ SiX ¹ ₃ (2) is effective. In the formula, X ¹ is a hydrolyzable group bonded to a silicon atom and is a chloro group, an alkoxy group, an acetoxy group, an alkylamino group, a propenoxy group or the like, and Y ¹ is an organic functional group which reacts with an organic matrix and is vinyl. Group, methacryl group, epoxy group, glycidoxy group, amino group, mercapto group and the like, and R ⁶ is an alkyl group having 1 to 20 carbon atoms or an alkylene group.
Among these silane coupling agents, an aminosilane coupling agent having an amino group in Y ¹ is preferable in order to obtain a developer having a negative charging property, and an epoxy group in Y ¹ is preferable in order to obtain a developer having a positive charging property. An epoxy silane coupling agent having is preferred. Specific examples of the silane coupling agent include those shown in Table 1 below.

[0015]

[Table 1- (1)]

[Table 1- (2)]

[Table 1- (3)]

As a method of forming the resin coating layer, the resin may be applied to the surface of the carrier core particles by a method such as a spraying method or a dipping method as in the conventional method.

As the toner which constitutes the developer together with the carrier, conventionally known toners can be used. Generally, a toner is obtained by melting and kneading a mixture of a binder resin, a colorant and a polarity control agent, and further, if necessary, any additives with a hot roll mill, cooling and solidifying the mixture, and pulverizing and classifying the mixture. Those having an average particle size of 5 to 30 μm are used.

As the binder resin, all known binder resins can be used. For example, polystyrene, poly p-
Styrene and homopolymers of styrene such as polyvinyltoluene and its substitution products, styrene-p-chlorostyrene copolymers, styrene-propylene copolymers, styrene-vinyltoluene copolymers, styrene-methyl acrylate copolymers, Styrene-ethyl acrylate copolymer, styrene-
Butyl acrylate copolymer, styrene-methylmethacrylate copolymer, styrene-ethylmethacrylate copolymer, styrene-butylmethacrylate copolymer, styrene-α-chloromethylmethacrylate copolymer, Styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-
Isoprene copolymer, styrene-maleic acid copolymer,
Styrene-based copolymers such as styrene-maleic acid ester copolymers, polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, polyurethane, polyamide, epoxy resin, polyvinyl butyral, polyacrylic Acid resins, rosins, modified rosins, terpene resins, phenol resins, aliphatic or aliphatic hydrocarbon resins, aromatic petroleum resins, chlorinated poraffins, paraffin waxes, etc. may be used alone or in combination. .

In particular, by using a polyester resin as the binder resin, an electrophotographic developer can be obtained which does not impair the vinyl chloride matt fusion resistance and the original color of the color material of the color toner. The polyester resin useful as a binder in the present invention is obtained by polycondensation of alcohol and carboxylic acid. The alcohol used therein is polyethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3. -Propylene glycol,
1,4-butanediol, neopentyl glycol,
Diols such as 1,4-butenediol, 1,4-bis (hydroxymethyl) cyclohexane, bisphenol A, hydrogenated bisphenol A, polyoxyethylenated bisphenol A, polyoxypropyleneized bisphenol A, and other etherified bisphenols, The divalent alcohol simple substance which substituted these with the C3-C22 saturated or unsaturated hydrocarbon group, and other divalent alcohol simple substance can be mentioned. Further, as the carboxylic acid,
For example, maleic acid, fumaric acid, mesaconic acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, malonic acid; 22 divalent organic acid monomers substituted with saturated or unsaturated hydrocarbon groups, acid anhydrides thereof, dimers of lower alkyl ester and linoleic acid, and other divalent organic acid monomers Can be mentioned.

In order to obtain the polyester resin used as the binder resin, not only the above-mentioned polymer containing only the bifunctional monomer but also the polymer containing the component containing the trifunctional or more polyfunctional monomer are used. Is also suitable. Examples of such polyfunctional trivalent or higher polyhydric alcohol monomers include, for example, sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaethritol, dipenta. Estritol, tripentaethritol, sucrose, 1,2,4-butanetriol, 1,2,5
-Pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,3,5-trihydroxymethylbenzene and the like. . Examples of trivalent or higher polyvalent carboxylic acid monomers include 1,2,4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid, 1,
2,4-cyclohexanetricarboxylic acid, 2,5,7-
Naphthalene tricarboxylic acid, 1,2,4-naltarene tricarboxylic acid, 1,2,4-butane tricarboxylic acid,
1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, tetra (methylenecarboxylic) methane, 1,2,
Examples thereof include 7,8-octanetetracarboxylic acid, embol trimer acid, acid anhydrides thereof, and the like.

The polarity controlling agent may be a conventionally known one, for example, a metal complex salt of a monoazo dye, nitrohumic acid and its salt, a metal complex amino compound such as salicylic acid, naphthoic acid or dicarboxylic acid such as Co, Cr and Fe, a secondary compound. Examples include quaternary ammonium compounds and organic dyes. Particularly, by containing the fluorine-containing quaternary ammonium salt represented by the following general formula (3), good chargeability can be obtained.

[Chemical 2]

Typical examples of the fluorinated quaternary ammonium salt include the exemplified compounds shown in Table 2 below.

[Table 2- (1)]

[Table 2- (2)]

[Table 2- (3)]

[Table 2- (4)]

[Table 2- (5)]

[Table 2- (6)]

[Table 2- (7)]

[Table 2- (8)]

[Table 2- (9)]

The amount of the polarity control agent used is determined by the type of binder resin, the presence or absence of additives used as necessary, and the toner production method including the dispersion method, and is uniquely limited. Although not limited, it is preferably used in an amount of 0.1 to 20 parts by weight, preferably 1 to 10 parts by weight, based on 100 parts by weight of the binder resin. If the amount is less than 0.1 parts by weight, the amount of charge of the toner is insufficient, which is not practical. On the other hand, when the amount exceeds 20 parts by weight, the amount of charge of the toner is too large and the electrostatic attraction with the carrier increases, resulting in a decrease in the fluidity of the developer and a decrease in the image density.

As the black colorant, for example, carbon black, aniline black, furnace black, lamp black and the like can be used. Examples of cyan colorants include phthalocyanine blue, methylene blue,
Victoria blue, methyl violet, aniline blue, ultramarine blue, etc. can be used. Examples of magenta colorants that can be used include rhodamine 6G lake, dimethylquinacridone, watching red, rose bengal, rhodamine B, and alizarin lake.
As the yellow binder, for example, chrome yellow, benzidine yellow, Hansa yellow, naphthol yellow, molybdenum orange, quinoline yellow, tartrazine and the like can be used.

The toner may further contain a magnetic material to be used as a magnetic toner. The magnetic material contained in the magnetic toner includes magnetite, hematite, iron oxide such as ferrite, metals such as iron, cobalt, nickel, or aluminum of these metals, cobalt, copper, lead,
Magnesium, tin, zinc, antimony, beryllium,
Examples thereof include alloys of metals such as bismuth, cadmium, calcium, manganese, selenium, titanium, tungsten, and vanadium, and mixtures thereof. It is desirable that these ferromagnetic materials have an average particle size of about 0.1 to 2 μm.
About 20 to 200 parts by weight, preferably 4
0 to 150 parts by weight.

Additives may be mixed with the toner as required. As the additive, for example, Teflon, a lubricant such as zinc stearate or cerium oxide, an abrasive such as silicon carbide, or a fluidity-imparting agent such as colloidal silica and aluminum oxide, an anti-caking agent,
Alternatively, examples thereof include conductivity-imparting agents such as carbon black and tin oxide, and fixing aids such as low molecular weight polyolefins.

The carrier and the toner of the present invention are preferably used in such an amount that the toner particles adhere to the carrier surface of the carrier particles and occupy 30 to 90% of the surface area of the carrier particles.

[0028]

EXAMPLES The present invention will be described in more detail by way of examples, but the present invention is not limited thereto. All parts here are parts by weight.

Examples 1 to 18 and Comparative Example 1 (Production of Toner) Production Example 1 Styrene-acrylic resin (Haimer 75: Sanyo Chemical Co., Ltd.) 88 parts Carbon black (# 44: Mitsubishi Kasei Co.) 10 parts Metal-containing metal Azo dye (Bontron S-34: manufactured by Orient Chemical Co., Ltd.) 2 parts A mixture of these formulations is melt-kneaded with a hot roll at 120 ° C., cooled and solidified, and then pulverized with a jet mill.
The toner was classified to obtain a toner a having an average particle size of about 10 μm. Production Example 2 Polyester resin (R6361: manufactured by Kao) 93 parts Carbon black (# 44: manufactured by Mitsubishi Kasei Co.) 5 parts Metal-containing azo dye (Bontron S-34: manufactured by Orient Chemical Co.) 2 parts A mixture of these formulations is used. A toner b having an average particle diameter of about 10 μm was obtained in the same manner as in Production Example 1. Production Example 3 Styrene-acrylic copolymer resin (Haimer 75: Sanyo Kasei Co., Ltd.) 88 parts Carbon black (# 44: Mitsubishi Kasei Co., Ltd.) 10 parts Fluorine-containing quaternary ammonium salt (Exemplary Compound 3-1) 2 parts These formulations A toner c having an average particle diameter of about 10 μm was obtained in the same manner as in Production Example 1 using the mixture of Production Example 4 Polyester resin (R-6361: manufactured by Kao) 93 parts Carbon black (# 44: manufactured by Mitsubishi Kasei) 5 parts Fluorine-containing quaternary ammonium salt (exemplified compound 3-1) 2 parts A mixture of these formulations is used. A toner d having an average particle diameter of about 10 μm was obtained in the same manner as in Production Example 1.

(Production Example of Magnetite Core Particles) 100 parts of natural mineral magnetite, 2 parts of polyvinyl alcohol and 60 parts of water were put into a ball mill and mixed for 12 hours to prepare a magnetite slurry. This slurry is spray-granulated with a spray dryer, and the average particle size is about 80 μm.
Spherical particles. 1000 these particles in a nitrogen atmosphere
After firing for 3 hours at a temperature of ° C, the mixture was cooled to obtain magnetite core particles (V) listed in Table 3. Then, 100 parts of the above-mentioned core particles (V) are mixed with 1000 parts of ion-exchanged water, stirred while heating to 100 ° C. in a glass flask, filtered and dried to obtain the core particles (IV) listed in Table 3. Got 100 parts of the above-mentioned core particles (IV) are mixed with 1000 parts of ion-exchanged water, stirred while heating to 100 ° C. in a glass flask, filtered and dried to obtain the core particles (II) shown in Table 3. It was 2 parts of polyvinyl alcohol and 60 parts of ion-exchanged water were put into a ball mill and mixed for 12 hours with respect to 100 parts of the natural mineral magnetite to prepare a magnetite slurry. This slurry was spray-granulated with a spray dryer to obtain spherical particles having an average particle size of about 80 μm. The particles were baked in a nitrogen atmosphere at a temperature of 1000 ° C. for 3 hours and then cooled to obtain magnetite core particles (I) listed in Table 3.
Next, 1 part of the above-mentioned core particles (I) is deionized water 1
000 parts were mixed, stirred in a glass flask while heating at 100 ° C., filtered and dried to obtain the core particles (III) listed in Table 3.

[0031]

[Table 3]

(Production Example of Carrier Particles) Production Example 1 Acrylic resin (BR-83: manufactured by Mitsubishi Rayon Co., Ltd.) 100 parts Toluene 100 parts After mixing a coating layer forming solution having a formulation of 100 parts with a homomixer,
The particles were coated on magnetite core particles (I) using a fluidized bed coating apparatus and dried to obtain carrier particles A. Production Examples 2 to 8 Carrier particles B to H were obtained in the same manner as in Production Example 1 of the above-mentioned carrier particles with the formulations shown in Table 4 below. However, the amount of each core particle was 1000 parts, and toluene was 100 parts as a dispersion solvent of the coating layer forming liquid.

[0033]

[Table 4]

Then, carrier particles shown in Table 5 below:
A developer was prepared by mixing 97 parts and 3 parts of toner particles in a ball mill, and the developer was subjected to the following test. (Test) Developer is a commercially available electrophotographic copying machine (Ricoh F
T-6950) was used to print 200,000 images, and carrier adhesion, environmental change rate of charge amount, and transferability to vinyl chloride mat were examined. Also, at the start of the test and after 200,000 sheets,
The developer after 300,000 copies was sampled to measure the blow-off charge amount and the spent ratio. Each evaluation method is shown below. (Environmental stability) (1) Low temperature and low humidity charge amount Each developer is conditioned for 3 hours in an environment of 10 ° C. and 20% RH. Then, the carrier and the toner are put into a 120 ml stainless steel pot and stirred for 10 minutes, and the charge amount is obtained by the blow-off method. (2) High-temperature and high-humidity charge amount Each developer is conditioned for 3 hours in an environment of 30 ° C. and 80% RH. Then, the carrier and the toner are put into a 120 ml stainless steel pot and stirred for 10 minutes, and the charge amount is obtained by the blow-off method. Next, the environmental change rate was calculated by the following formula, and evaluated according to the judgment conditions. Environmental stability (%) = [(low-temperature low-humidity charge amount-high-temperature high-humidity charge amount) / low-temperature low-humidity charge amount] x 100 ◎: 0 to 5% ○: 5 to 10% △: 10 to 30% x: 30% <(Spent conversion rate) Toner is removed from the developer after the 300,000-sheet copy test by blow-off, and the weight of the remaining carrier is measured and designated as W ₁ . Next, this carrier is put into toluene to dissolve the fusion product, washed, dried, and then weighed to obtain W ₂
And Then, the percentage of spent was obtained from the following formula and evaluated. Spentification rate (wt%) = [(W ₁ −W ₂ ) / W ₁ ] × 100 ◎: 0 to 0.01 wt% ○: 0.01 to
0.02wt% △: 0.02-0.05wt% x: 0.05wt
% <(Vinyl chloride mat transfer property) The copied image was sandwiched with a commercially available vinyl chloride mat, a load of 200 g / cm ² was applied thereto, and the image was stored for 6 hours in an environment of 40 ° C to evaluate the presence or absence of toner transfer.

[0035]

[Table 5]

[0036]

According to the invention of claim 1, the alkali metal salt on the surface of the core particles is set to 0.15 μg / cm ² or less, and the coating layer is provided thereon to suppress the temperature dependence of the developer. be able to. According to the invention of claim 2, it is possible to effectively prevent the toner from being spent on the surface of the carrier. According to the invention of claim 3, the electric resistance of the carrier can be lowered, and a good image without edge effect can be obtained.

Claims (3)

[Claims] 1. A developer comprising toner particles and carrier particles having a resin coating layer formed on the surface of magnetite core particles, wherein the alkali metal salt concentration on the magnetite surface is 0.15 μg / A two-component developer for developing an electrostatic latent image, which is characterized by having a cm ² or less. 2. The two-component developer for developing an electrostatic latent image according to claim 1, wherein the coating layer of the core particles is a silicone resin. 3. A two-component developer for developing an electrostatic latent image according to claim 2, wherein the coating layer of the core particles contains conductive fine powder and / or a silane coupling agent.