A two-component developer includes a toner containing toner particles with a volume diameter of 8 .mu.m or less, and a carrier containing carrier particles, each carrier particle including at least one core particle and a carrier core coating layer, the carrier core coating layer being made of a silicone resin and a silicone oil, the carrier having a fluidity of 45 seconds or less.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a two-component developer for developing
 latent electrostatic images to toner images for use in electrophotography
 in a copying machine, facsimile apparatus or the like, and also for use in
 electrostatic recording, and electrostatic printing process.
 2. Discussion of Background
 Various electrophotographic methods are described, for instance, in U.S.
 Pat. No. 2,297,691, Japanese Patent Publication 42-23910, and Japanese
 Patent Publication 43-24748. In these methods, a photoconductive layer is
 irradiated with a light image corresponding to an original image to be
 copied, and a latent electrostatic image corresponding to the original
 image is formed on the photoconductive layer. In a normal development, a
 toner with an opposite polarity to that of the latent electrostatic image
 is deposited on the electrostatic image to develop the latent
 electrostatic image to a toner image on the photoconductive layer, and
 when necessary, the toner image is transferred to an image transfer
 material such as a sheet of paper, and the transferred toner image is then
 fixed thereto with the application of heat, pressure, heat and pressure,
 or a solvent vapor thereto, whereby a copied material can be obtained.
 In the step of developing the latent electrostatic image to the toner
 image, the toner image is formed, utilizing the electrostatic attraction
 between charged toner particles and the latent electrostatic image.
 Generally, in the above-mentioned development method of developing the
 electrostatic image with the toner, a two-component developer comprising
 toner particles and carrier particles is preferably employed in a copying
 machine for which high image quality is demanded.
 The carrier particles in the two-component developer are constantly stirred
 while in use for an extended period of time, so that the surface of the
 carrier particles is apt to be damaged and therefore it is difficult to
 attain stable triboelectric charging over an extended period of time.
 Furthermore, a photoconductor drum, which is disposed so as to face a
 development sleeve for carrying the two-component developer thereon, is
 also abraded with the two-component developer, and a cleaning blade is
 brought into pressure contact with the photoconductor drum, so that the
 surface of the photoconductor drum is caused to deteriorate with time, and
 the image quality is also caused to deteriorate.
 Japanese Laid-Open Patent Application 62-66268 discloses a carrier
 comprising carrier particles coated with a coating layer comprising a
 silicone-oil-containing silicone resin. In this prior art reference, it is
 stated that by the provision of the coating layer, the triboelectric
 charging characteristics of the carrier are improved, whereby images with
 such an image quality that is free of fogging can be obtained.
 However, the silicone-oil containing carrier disclosed in the
 above-mentioned prior art reference, however, has the problems that the
 fluidity of the carrier is caused to deteriorate due to the presence of an
 excessive amount of the silicone oil in the surface layer of the carrier
 particles and therefore the toner cannot be appropriately charged by the
 carrier, so that the fogging is apt to take place.
 Recently, in order to meet the demand for high quality image, an
 appropriate combination of the carrier and toner particles with a small
 particle diameter is essential. However, the above-mentioned prior art
 reference does not disclose anything about the combination of the carrier
 and a small-particle diameter toner, and conventionally, high quality
 images cannot be obtained when a small-particle diameter toner is
 employed.
 In the above-mentioned prior art reference, there is disclosed a
 two-component developer composed of the carrier and toner particles with a
 particle diameter as small as 6.5 .mu.m. The inventors of the present
 invention evaluated the developer. The result was that images obtained
 have such an image quality that has extreme fogging. The inventors of the
 present invention investigated the cause of the deterioration of the image
 quality with the extreme fogging and discovered that it is caused because
 the fluidity of the carrier is poor and the toner cannot be charged with
 an appropriate amount of triboelectric charges by the carrier. However, it
 is extremely difficult to provide a sharp charge quantity distribution by
 using small-particle diameter toners which are currently employed and the
 above-mentioned carrier because the triboelectric charging area in the
 small-particle diameter toners is large and the fluidity thereof is poor.
 SUMMARY OF THE INVENTION
 It is therefore an object of the present invention to provide a
 two-component developer free of the above-mentioned conventional problems,
 capable of providing high quality images with high precision and high
 reliability.
 The object of the present invention can be achieved by a two-component
 developer comprising (a) a toner comprising toner particles with a volume
 diameter of 8 .mu.m or less, and (b) a carrier comprising carrier
 particles, each carrier particle comprising at least one core particle and
 a carrier core coating layer, the carrier core coating layer comprising a
 silicone resin and a silicone oil, the carrier having a fluidity of 45
 seconds or less.
 In the above two-component developer, it is preferable that the carrier
 particles have a weight-average particle diameter of 60 .mu.m or less.
 DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The inventors of the present invention studied the improvement of the
 fluidity of the carrier to improve the image quality even when used in
 combination with a small-particle diameter toner.
 More specifically, as mentioned above, the fluidity of the carrier can be
 improved by use of the carrier comprising carrier particles, each carrier
 particle comprising at least one core particle and a carrier core coating
 layer, the carrier core coating layer comprising a silicone resin and a
 silicone oil.
 In other words, in the present invention, in order to impart excellent
 surface releasability to the carrier, the silicone oil is added to the
 carrier core coating layer, and the amount of the silicone oil in the
 surface layer of the carrier particles is controlled so as to exhibit
 excellent fluidity of the carrier, whereby the above-mentioned
 conventional problems have been decisively solved. To be more specific, a
 carrier comprising carrier particles coated with a carrier coating layer
 comprising a silicone oil in general use exhibits a stable charging
 performance for an extended period of time. Furthermore, a photoconductor
 drum is less abraded by the above-mentioned carrier, and the transfer
 performance of a toner tends to be improved when used in combination with
 the above-mentioned carrier. As a result, high quality images can be
 obtained in a stable manner.
 Why the above can be attained when used the above-mentioned carrier has not
 yet been completely clarified, but it can be assumed that the above
 advantages are attained by the releasability and the lubricating
 properties of the silicone oil which oozes from the carrier core coating
 layer. In other words, it can be assumed that the silicone oil contained
 in the carrier core coating layer serves as a lubricant when the developer
 is stirred, and protects the carrier from the stress applied thereto when
 the developer is stirred, so that the charging performance of the
 developer can be maintained in a stable manner for an extended period of
 time.
 The photoconductor drum is always in frictional contact with the developer,
 so that it is considered that an extremely small amount of the silicone
 oil is constantly applied to the surface of the photoconductor. As a
 result, a thin releasing layer made of the silicone oil is considered to
 be formed on the surface of the photoconductor drum. It is also considered
 that the photoconductor drum may be abraded mainly by (1) the developer
 which is in frictional contact with the photoconductor drum, and also by
 (2) the cleaning blade which is in pressure contact with photoconductor
 drum. However, the abrasion of the photoconductor drum is extremely
 reduced, when the silicone oil releasing layer is present on the surface
 of the photoconductor drum. Furthermore, the surface of the photoconductor
 drum can be protected from being scratched by the silicone oil releasing
 layer which serves as a protective layer even when some additives are
 externally applied thereto.
 Furthermore, the silicone oil applied to the surface of the photoconductor
 drum is considered to have some effect on the toner transfer performance
 of the photoconductor drum. Conventionally, when toner is transferred from
 the surface of the photoconductor drum to an image transfer sheet, a small
 amount of the toner inevitably remains on the surface of the
 photoconductor drum, and the remaining toner reduces the image transfer
 ratio. However, in the present invention, since the silicone oil releasing
 layer is present on the surface of the photoconductor drum, the toner,
 substantially in its entirety, is transferred to the transfer sheet, so
 that an extremely high image transfer ratio can be secured. However, when
 an excess silicone oil is present on the surface of the photoconductor
 drum, the toner on the photoconductor drum is apt to be trapped by the
 silicone oil, so that the image transfer ratio is reduced on the contrary.
 The fluidity of the carrier of the present invention can be controlled by
 adjusting the mixing ratio of the silicone oil and the silicone resin in a
 coating liquid for the formation of the carrier core coating layer, and
 controlling the heating conditions for heating the coated coating liquid
 coated on the core particles to form the carrier core coating layer.
 It is preferable that the amount of the silicone oil be in the range of 2
 to 10 wt. % of the entire weight of the coated coating liquid. Although it
 depends upon the curing temperature for the carrier core coating layer,
 when the amount of the silicone oil is less than 2 wt. %, the amount of
 the silicone oil that oozes from the carrier core coating layer is too
 small to obtain the above-mentioned advantageous effects of the silicone
 oil, while when the amount of the silicone oil is more than 10 wt. %, the
 amount of the silicone oil that oozes from the carrier core coating layer
 is excessive, so that improper triboelectric charging is apt to take
 place.
 The temperature at which the carrier core coating layer is cured depends
 upon the content of the silicone oil therein. However, it is preferable
 that the curing temperature be in the range of about 250.degree. C. to
 500.degree. C. For example, when the content of the silicone oil is about
 3 wt. %, it is preferable that the curing temperature be about 300.degree.
 C., while when the content of the silicone oil is about 10 wt. %, it is
 preferable that the curing temperature be about 400.degree. C. It is
 considered that by increasing the curing temperature, the bonding of the
 silicone oil and the silicone resin can be appropriately adjusted, whereby
 the amount of the silicone oil that oozes from the carrier core coating
 layer can be controlled. From the above, the inventors of the present
 invention have discovered that in order to maintain an appropriate amount
 of the silicone oil in the carrier core coating layer, it is required that
 the curing temperature be appropriately set so as to maintain the
 appropriate amount of the silicone oil in the carrier core coating layer.
 In the present invention, the fluidity is adjusted to 45 seconds or less
 per 50 g, preferably in the range of 20 to 45 seconds/50 g, by adjusting
 the amount of the silicone oil that oozes from the carrier core coating
 layer by the method as mentioned above. When the fluidity exceeds 45
 seconds/50 g, the toner cannot be smoothly charged by the carrier because
 of the poor fluidity thereof, so that image quality tends to become poor,
 while when the fluidity is less than 20 seconds/50 g, there is a tendency
 that the developer cannot be transported smoothly when transported by
 utilizing the frictional resistance of the developer.
 Some carriers coated with the carrier core coating layer comprising the
 silicone oil and the silicone resin have poor fluidity than the fluidity
 of a carrier coarse coating layer prepared without using the silicone oil.
 This indicates that an excessive amount of the silicone oil is present on
 the surface of the carrier particles of the former carriers. In such
 carriers, the amount of silicone oil that oozes from the carrier coating
 layer will have to be controlled by the above-mentioned method of the
 present invention.
 In order to cope with the recent demand for high quality images that can be
 obtained by image formation apparatus, the particle diameter of the toner
 particles is being reduced. However, as the particle diameter of the toner
 particles is reduced, the surface area of the toner particles per unit
 amount thereof increases and therefore, the blocking of the toner
 particles in a toner container is apt to take place, so that the
 developing performance and the image transfer performance are caused to
 deteriorate, and the image quality that can be obtained tends to become
 poor.
 Conventionally, in order to increase the fluidity of the toner, additives
 such as silica, titania and alumina are generally used and studies on the
 increasing of the amount of such additives to be added have been made.
 When the amount of such an additive added is increased, the fluidity of
 the toner can be surely improved and the image quality that can be
 obtained can also be improved. However, such additives tend to abrade the
 carrier core coating layer, or are apt to be deposited in the form of a
 film on the surface of the photoconductor, or scratch the surface of the
 photoconductor.
 In the present invention, as mentioned above, the toner transfer
 performance can be exceedingly improved by use of the silicone oil, so
 that the amount of the additives for use with the toner can be
 significantly reduced in comparison with a conventionally employed amount
 of more than 0.8 wt. %. Thus, according to the present invention, the
 amount of the additives for use with the toner is not more than 0.8 wt. %,
 so that there can be avoided the side effects of the additives, such as
 the environmental variations in the triboelectric charge quantity, the
 shaving of the carrier core coating layer, and the film-like deposition of
 the additives on the surface of the photoconductor.
 In the present invention, as the core particles, there can be employed
 particles substantially made of only a magnetic material such as magnetic
 ferrite, and magnetic-material-dispersed resin core particles composed of
 a number of finely-divided magnetic particles dispersed in a resin.
 As the magnetic material for the magnetic core particles, there can be
 employed magnetic metals such as iron, nickel and cobalt, alloys thereof,
 and alloys containing rare earth elements; soft ferrites such as hematite,
 magnetite, manganese-zinc based ferrites, nickel-zinc based ferrite,
 manganese-magnesium based ferrite and lithium based ferrite; iron based
 oxides such as copper-zinc ferrite, and mixtures thereof.
 Furthermore, there can be employed other iron based alloys such as
 iron-silicon based alloy, iron-aluminum based alloy, and permalloy.
 In the present invention, it is preferable to employ magnetic ferrite core
 particles containing at least one element selected from the group of the
 elements of IA, IIA, IIIA, IVA, VA, VIA, IB, IIB, IIIB, IVB, VB, VIB, VIIB
 and VIII, with the content of other elements being less than 1 wt. %.
 The magnetic core particles for use in the present invention can be
 produced by a sintering method or an atomizing method, when necessary,
 with the particle diameter distribution of the magnetic particles being
 made sharp, or with predetermined magnetic characteristics being imparted
 theret by controlling, for instance, the sintering temperature, the
 temperature elevation rate, and the heat application time.
 There is no particular limitation to the specific resistance of the
 magnetic core particles for use in the present invention as long as the
 magnetic core particles satisfy desired magnetic characteristics. However,
 it is preferable to use ferrite particles or magnetite particles with a
 specific resistance in the range of 10.sup.5 .OMEGA..multidot.cm to
 10.sup.5 .OMEGA..multidot.cm.
 As the magnetic material for the magnetic-material-dispersed resin core
 particles, which magnetic material is dispersed in a resin, for example,
 there can be employed alloys and compounds of ferromagnetic metals such as
 iron, cobalt, and nickel.
 It is preferable that the carrier for use in the present invention have a
 weight-average particle diameter of 35 to 60 .mu.m. When the average
 particle diameter of the carrier is less than 35 .mu.m, a latent
 electrostatic image held on a latent electrostatic image bearing member is
 apt to be developed with the carrier, so that the latent electrostatic
 image bearing member, a cleaning blade and a charging roller are apt to be
 scratched by the carrier. On the other hand, when the average particle
 diameter of the carrier is more than 60 .mu.m, in particular, when used in
 combination with the small-particle diameter toner, the carrier's toner
 holding performance, which depends upon the surface area of the carrier
 particles on which the toner is held, and the carrier's toner charging
 performance are reduced, so that the density of solid toner image tends to
 be non-uniform, and the scattering of the toner and the fogging of toner
 images are apt to take place.
 As the material for the carrier core coating layer of the carrier for use
 in the present invention, silicone resins in general use can be employed.
 Specific examples of such silicone resins are straight silicone resins
 such as "SH804", "SH805" and "SR2400", made by Dow Corning Toray Silicone
 Co., Ltd., and silicone-modified organic resins such as "SR2107" and
 "SR2115", made by Dow Corning Toray Silicone Co., Ltd. it is considered
 that such silicone resins have excellent compatibility with the silicone
 oil, so that appropriate oozing of the silicone oil froms the carrier core
 coating layer can be attained.
 As the silicone oil for the carrier for use in the present invention, a
 commercially available dimethyl silicone oil, such as "SH20", made by Dow
 Corning Toray Silicone Co., Ltd., and a modified silicone oil, such as
 "SF8417" and "SF8421", made by Dow Corning Toray Silicone Co., Ltd., can
 be employed.
 In the present invention, it is preferable that about 1 to 60 parts by
 weight of the toner be mixed with 100 parts by weight of the carrier to
 use the mixture as the two-component developer.
 It is preferable that the toner for use in the present invention be
 prepared by kneading a mixture of a binder resin in an amount of 75 to 93
 wt. %, a coloring agent in an amount of 3 to 10 wt. %, a releasing agent
 in an amount of 3 to 8 wt. %, and other components in an amount of 1 to 7
 wt. %, and pulverizing the kneaded mixture. It is also preferable that as
 an additive, finely-divided particles of an inorganic material such as
 colloidal silica, be externally added to the toner, in an amount of 0.8
 wt. % or less in the entire amount of the toner.
 Abrasives, for example, metallic oxides such as titanium oxide and aluminum
 oxide, and silicon carbide; and a lubricant such as a fatty acid metallic
 salt, may also be added as the additives to the toner.
 Conventionally known resins can be used as the binder resins for use in the
 toner. In particular, as the binder resin, styrene resins such as a
 styrene homopolymer and copolymers of styrene monomer and other vinyl
 monomers are employed.
 Specific examples of the above-mentioned other vinyl monomer are ethylene
 unsaturated mono-olefins such as ethylene, propylene and isobutylene;
 halogenated vinyl monomers such as vinyl chloride, vinyl bromide and vinyl
 fluoride; vinyl esters such as vinyl acetate; acrylic esters such as
 methyl acrylate, ethyl acrylate and phenyl acrylate; vinyl ethers such as
 vinyl methyl ether and vinyl ethyl ether; vinylketones such as vinyl
 methyl ketone and vinyl hexyl ketone; N-vinyl compounds such as
 N-vinylpyrrole and N-vinylpyrrolidone; acrylonitrile; methacrylonitrile;
 acrylamide; and methacrylanide. These vinyl monomers can be employed alone
 or in combination.
 In addition to the above-mentioned styrene resins, polyethylene resin,
 polypropylene resin, vinyl ester resin, rosin-modified phenol-formalin
 resin, epoxy resin, polyester resin, and polyol resin, and mixtures of the
 above-mentioned resins can also be used as the binder resins.
 As the coloring agents for the toner for use in electrophotography in the
 present invention, any conventional coloring agents can be employed.
 Examples of yellow coloring agents are C.I. Pigment Yellow 1 (Trademark
 "Symuler Fast Yellow GH", made by Dainippon Ink and Chemicals,
 Incorporated); C.I. Pigment Yellow 3 (Trademark "Symuler Fast Yellow
 10GH", made by Dainippon Ink and Chemicals, Incorporated); C.I. Pigment
 Yellow 12 (Trademark "Symuler Fast Yellow GF", made by Dainippon Ink and
 Chemicals, Incorporated, Trademark "Yellow 152" made by Arimoto Chemical
 Co., Ltd., Trademark "Pigment Yellow GRT", made by Sanyo Color Works,
 Ltd., Trademark "Sumikaprint Yellow ST-O", made by Sumitomo Chemical Co.,
 Ltd., Trademark "Benzidine Yellow 1316", made by Noma Chemical Industry
 Co., Ltd., Trademark "Seika Fast Yellow 2300", made by Dainichiseika Color
 & Chemicals Mfg. Co., Ltd., and Trademark "Lionol Yellow GRT", made by
 Toyo ink Mfg. Co., Ltd.); C.I. Pigment Yellow 13 (Trademark "Symuler Fast
 Yellow 5GR", made by Dainippon Ink and Chemicals, Incorporated); C.I.
 Pigment Yellow 14 (Trademark "Symuler Fast Yellow 5GR", made by Dainippon
 Ink and Chemicals, Incorporated); and C.I. Pigment Yellow 17 (Trademark
 "Symuler Fast Yellow 8GR", made by Dainippon Ink and Chemicals,
 Incorporated, and Trademark "Lionol Yellow FGNT", made by Toyo Ink Mfg.
 Co., Ltd.).
 Examples of magenta coloring agents are C.I. Pigment Red 5 (Trademark
 "Symuler East Carmine FB", made by Dainippon ink and Chemicals,
 Incorporated); C.I. Pigment Red 18 (Trademnark "Sanyo Toluidine Maroon
 Medium", made by Sanyo Color Works, Ltd.); C.I. Pigment Red 21 (Trademark
 "Sanyo Fast Red GR", made by Sanyo Color Works, Ltd.); C.I. Pigment Red 22
 (Trademark "Symular Fast Brill Scarlet BG", made by Dainippon Ink and
 Chemicals, Incorporated); C.I. Pigment Red 57 (Trademark "Symuler Brill
 Carmine LB", made by Dainippon Ink and Chemicals, Incorporated); C.I.
 Pigment Red 81 (Trademark "Symulex Rhodamine Y Toner F", made by Dainippon
 Ink and Chemicals, Incorporated); C.I. Pigment Red 112 (Trademark "Symuler
 Fast Red FGR", made by Dainippon Ink and Chemicals, Incorporated); C.I.
 Pigment Red 114 (Trademark "Symuler Fast Carmine BS", made by Dainippon
 Ink and Chemicals, Incorcorated); and C.I. Pigment Red 122 (Trademark
 "Fastogen Super Magenta RE 02", made by Dainippon Ink and Chemicals,
 Incorporated).
 Examples of cyan coloring agents are C.I. Pigment Blue 15 (Trademark
 "Fastogen Blue GS", made by Dainippon Ink and Chemicals, Incorporated, and
 Trademark "Chromofine SR", made by Dainichiseika Color & Chemicals Mfg.
 Co., Ltd.); C.I. Pigment Blue 16 (Trademark "Sunmitone Cyanine Blue LG",
 made by Sumitomo Chemical Co., Ltd.); C.I. Pigment Blue 15:3 (Trademark
 "Cyanine Blue GGK", made by Nippon Pigment Co., Ltd., and Trademark
 "Lionol Blue FG 7351", made by Toyo Ink Mfg. Co., Ltd.); C.I. Pigment
 Green 7 (Trademark "Phthalogcyanine Green", made by Tokyo Printing Ink
 Mfg. Co., Ltd.); and C.I. Pigment Green 36 (Trademark "Cyanine Green ZYL",
 made by Toyo Ink Mfg. Co., Ltd.).
 Examples of black coloring agents are carbon black, spirit black and
 Aniline Black (C.I. Pigment Black 1).
 The toner for use in the present invention may further comprise a charge
 controlling agent. Various kinds of conventional charge controlling agents
 can be used, and specific examples thereof are a metal-containing monoazo
 dye, nitrohumic acid and salts thereof, salicylic acid, naphthoic acid,
 dicarboxylic acid complexes of metals such as Co, Cr and Fe, amino
 compounds, quaternary ammonium compounds, and organic dyes.
 The characteristics of the developer of the present invention were
 mneasured as follows:
 (1) Measurement of the Particle Diameter Distribution of the Toner:
 The particle diameter distribution of the toner of the present invention
 was measured by use of Coulter counter, although there are various kinds
 of methods for measuring the particle diameter distribution.
 (2) Measurement of the Fluidity of the Carrier:
 For the measurement of the fluidity of the carrier, each test sample was
 allowed to stand at a temperature of 23.degree. C..+-.3.degree. C., and a
 humidity of 60%.+-.5% for 24 hours, and then the fluidity of the sample
 was measured in accordance with the Japanese Industrial Standards (JIS-Z
 2502).

Other Features of this invention will become apparent in the course of the
 following description of exemplary embodiments, which are given for
 illustration of the invention and are not intended to be limiting thereof.
 EXAMPLE 1
 Preparation of Toner A
 A mixture of the following components was subjected to a preliminary mixing
 by sufficiently mixing the mixture in a Henschel mixer:

Parts by weight
 Unsaturated polyester resin 100
 Carbon black pigment 5
 Charge controlling agent 4.0
 (salicylic acid chrome complex)
 The above mixture was fused and kneaded in a double-screw extruder, and
 cooled. The cooled mixture was then roughly hammer milled to obtain
 particles with a diameter of about 1 to 2 mm, and then finely pulverized
 in an air-jet type mill The thus finely pulverized particles were then
 classified, using a multi-divided classifier, whereby classified toner
 particles with a particle diameter of 6.5 .mu.m (carbon-containing resin
 particles) were obtained. To 100 parts by weight of the thus obtained
 classified toner particles, 0.75 parts by weight of a commercially
 available hydrophobic silica (Trademark "R976" made by Nippon Aerosil Co.,
 Ltd.) were added, and the mixture was mixed in a mixer, whereby Toner A
 was prepared.
 Preparation of Toner A
 The above-mentioned procedure for preparing Toner A was repeated except
 that the amount of the hydrophobic silica "R976" was changed from 0.75
 parts by weight to 1.5 parts by weight, whereby Toner B was prepared.
 Preparation of Toner C
 The above-mentioned procedure for preparing Toner A was repeated except
 that instead of the classified toner particles with a particle diameter of
 6.5 .mu.m prepared in the procedure of the preparation of Toner A,
 classified toner particles with a particle diameter of 9.0 .mu.m were
 obtained by changing the fine pulverizing conditions and the
 classification conditions in the procedure of the preparation of Toner A,
 and to 100 parts by weight of the thus obtained classified toner
 particles, 0.75 parts by weight of a commercially available hydrophobic
 silica (Trademark "R976" made by Nippon Aerosil Co., Ltd.) were added, and
 the mixture was mixed in a mixer, whereby Toner C was prepared.
 Preparation of Toner D
 The above-mentioned procedure for preparing Toner C was repeated except
 that the amount of the hydrophobic Silica "R976" was changed from 0.75
 parts by weight to 1.5 parts by weight, whereby Toner D was prepared.
 Preparation of Carrier(a)
 Cu--Zn--Fe based ferrite core particles with a particle diameter of 50
 .mu.m were subjected to 10% coating, using a commercially available
 silicone resin (Trademark "SR2411", made by Dow Corning Toray Silicone
 Co., Ltd., in the form of a solution of silicone resin in toluene, with a
 solid component content of 20%). The 10% coating was conducted in such a
 manner that 100 parts by weight of the core particles were coated with 10
 parts by weight of the solid component contained in the silicone resin in
 the form of the toluene solution when dried.
 The Cu--Zn--Fe based ferrite core particles coated with the silicone resin
 were heated to 300.degree. C. for 2 hours, whereby Carrier (a) with a
 carrier core coating layer of 0.5 .mu.m was prepared.
 Preparation of Carrier(b)
 Cu--Zn--Fe based ferrite core particles with a particle diameter of 50
 .mu.m were subjected to 10% coating, using a mixture of the following
 components:

Parts by weight
 Silicone resin 500
 (Trademark "SR2411",
 made by Dow Corning
 Toray Silicone Co., Ltd.,
 in the form of a solution
 of silicone resin in toluene,
 with a solid component
 content of 20%)
 Silicone oil 10
 (Trademark "SH200",
 made by Dow Corning
 Toray Silicone Co., Ltd.,
 3000 cs)
 The 10% coating was conducted in such a manner that 100 parts by weight of
 the core particles were coated with 10 parts by weight of a mixture of the
 solid component contained in the silicone resin in the form of the toluene
 solution and the silicone oil in the above-mentioned mixture when dried.
 The Cu--Zn--Fe based ferrite care particles coated with the above-mentioned
 mixture of the solid component of the silicone resin and the silicone oil
 were heated to 200.degree. C. for 2 hours, whereby Carrier (b) with a
 carrier core coating layer of 0.5 .mu.m was prepared.
 Preparation of Carrier(c)
 Cu--Zn--Fe based ferrite core particles with a particle diameter of 50
 .mu.m were subjected to 10% coating, using a mixture of the following
 components:

Parts by weight
 Silicone oil 20
 (Trademark "SH200",
 made by Dow Corning
 Toray Silicone Co., Ltd.,
 3000 cs)
 Toluene 80
 The 10% coating was conducted in such a manner that 100 parts by weight of
 the core particles were coated with 10 parts by weight of the silicone oil
 in the above-mentioned mixture when dried.
 The Cu--Zn--Fe based ferrite core particles coated with tne silicone oil
 were heated to 400.degree. C. for 2 hours, whereby Carrier (c) was
 prepared.
 Preparation of Carrier(d)
 Cu--Zn--Fe based ferrite core particles with a particle diameter of 50
 .mu.m were subjected to 10% coating, using a mixture of the following
 components:

Parts by weight
 Silicone resin 500
 (Trademark "SR2411",
 made by Dow Corning
 Toray Silicone Co., Ltd.,
 in the form of a solution
 of silicone resin in toluene,
 with a solid component
 content of 20%)
 Silicone oil 3
 (Trademark "SH200",
 made by Dow Corning
 Toray Silicone Co., Ltd.,
 3000 cs)
 The 10% coating was conducted in such a manner that 100 parts by weight of
 the core particles were coated with 10 parts by weight of a mixture of the
 solid component contained in the silicone resin in the form of the toluene
 solution and the silicone oil in the above-mentioned mixture when dried.
 The Cu--Zn--Fe based ferrite core particles coated with the above-mentioned
 mixture of the solid component of the silicone resin and the silicone oil
 were heated to 300.degree. C. for 2 hours, whereby Carrier (d) with a
 carrier core coating layer of 0.5 .mu.m was prepared.
 Preparation of Carrier(e)
 Cu--Zn--Fe based ferrite core particles with a particle diameter of 50
 .mu.m were subjected to 10% coating, using a mixture of the following
 components:

Parts by weight
 Silicone resin 500
 (Trademark "SR2411",
 made by Dow Corning
 Toray Silicone Co., Ltd.,
 in the form of a solution
 of silicone resin in toluene,
 with a solid component
 content of 20%)
 Silicone oil 6
 (Trademark "SH200",
 made by Dow Corning
 Toray Silicone Co., Ltd.,
 3000 cs)
 The 10% coating was conducted in such a manner that 100 parts by weight of
 the core particles were coated with 10 parts by weight of a mixture of the
 solid component contained in the silicone resin in the form of the toluene
 solution and the silicone oil in the above-mentioned mixture when dried.
 The Cu--Zn--Fe based ferrite core particles coated with the above-mentioned
 mixture of the solid component of the silicone resin and the silicone oil
 were heated to 350.degree. C. for 2 hours, whereby Carrier (e) with a
 carrier core coating layer of 0.5 .mu.m was prepared.
 Preparation of Carrier(f)
 Cu--Zn--Fe based ferrite core particles with a particle diameter of 50
 .mu.m were subjected to 10% coating, using a mixture of the following
 components:

Parts by weight
 Silicone resin 500
 (Trademark "SR2411",
 made by Dow Corning
 Toray Silicone Co., Ltd.,
 in the form of a solution
 of silicone resin in toluene,
 with a solid component
 content of 20%)
 Silicone oil 12
 (Trademark "SH200",
 made by Dow Corning
 Toray Silicone Co., Ltd.,
 3000 cs)
 The 10% coating was conducted in such a manner that 100 parts by weight of
 the core particles were coated with 10 parts by weight of a mixture of the
 solid component contained in the silicone resin in the form of the toluene
 solution and the silicone oil in the above-mentioned mixture when dried.
 The Cu--Zn--Fe based ferrite core particles coated with the above-mentioned
 mixture of the solid component of the silicone resin and the silicone oil
 were heated to 400.degree. C. for 2 hours, whereby Carrier (f) with a
 carrier core coating layer of 0.5 .mu.m was prepared.
 Preparation of Carrier(g)
 Cu--Zn--Fe based ferrite core particles with a particle diameter of 65
 .mu.m were subjected to 10% coating, using a mixture of the following
 components:

Parts by weight
 Silicone resin 500
 (Trademark "SR2411"
 made by Dow Corning
 Toray Silicone Co., Ltd.,
 in the form of a solution
 of silicone resin in toluene,
 with a solid component
 content of 20%)
 Silicone oil 3
 (Trademark "SH200",
 made by Dow Corning
 Toray Silicone Co., Ltd.,
 3000 cs)
 The 10% coating was conducted in such a manner that 100 parts by weight of
 the core particles were coated with 10 parts by weight of a mixture of the
 solid component contained in the silicone resin in the form of the toluene
 solution and the silicone oil in the above-mentioned mixture when dried.
 The Cu--Zn--Fe based ferrite core particles coated with the above-mentioned
 mixture of the solid component of the silicone resin and the silicone oil
 were heated to 300.degree. C. for 2 hours, whereby Carrier (g) with a
 carrier core coating layer of 0.65 .mu.m was prepared.
 Preparation of Two-component Developers
 By using Toners A to D, and Carriers (a) to (g) in such combnations as
 listed in TABLE 1, two-component developers were prepared, with 5 parts by
 weight of each toner and 95 parts by weight of each carrier being mixed in
 each of the two-component developers.
 Evaluation of Two-component Developers
 Each of the two-component developers was incorporated in a modified
 commercially available copying machine (Trademark "MF-200" made by Ricoh
 Company, Ltd.) and 200,000 copies at the maximum were made to test the
 durability of each of the two-component developers. The results are shown
 in TABLE 1.
 TABLE 1
 Comp. Comp. Comp. Comp.
 Comp. Comp. Comp.
 Ex. 1 Ex. 2 Ex. 3 Ex. 1 Ex. 2 Ex. 3 Ex. 4
 Ex. 5 Ex. 6 Ex. 7
 Carrier (d) (e) (g) (a) (a) (b) (c)
 (d) (d) (f)
 Fluidity sec/50 g 36.8 39.4 33.3 36.9 36.9 No No
 36.8 36.8 47.7
 flow flow
 Toner A A A A B A A C
 D A
 Life of Number 200 K 150 K 150 K 100 K 50 K 10 K 10 K
 200 K 120 K 75 K
 Developer of or
 or
 copies more
 more
 made
 Reproduc- Rank 5 5 4 2 4 3 3 2
 3 3
 tion of
 Thin Line
 Images
 Life of Number 200 K 200 K 200 K 75 K 40 K 200 K 200 K
 200 K 100 K 200 K
 OPC of or or or or or
 or or
 copies more more more more more
 more more
 made
 In TABLE 1, "No flow" denotes that the carrier did not indicate any
 fluidity, and "K" denotes 1,000, so that, for instance, 200 K indicates
 200,000.
 In TABLE 1, the life of each developer, the reproduction of thin line
 images, and the life of the OPC were evaluated as follows;
 Life of Developer:
 Maximum number of copies made at which the background deposition of the
 toner became too much to be used in practice.
 Reproduction of Thin Line Images:
 One dot line image was formed and the image quality thereof was evaluated,
 using 5 ranks, with respect to the blurring of the image, and the
 formation of a thinner or thicker line image than the original line image
 with reference to a limit sample. Rank 5 is the best, and Rank 1 (not
 shown) is the worst, and Ranks 2 to 4 are successively better between Rank
 1 and Rank 5.
 Life of the OPC:
 Evaluated by the maximum number of copes made at which the surface of the
 OPC began to be scratched.
 The results shown in TABLE 1 indicates that two-component developer of the
 present invention is capable of reproducing copied images with high
 quality, high precision and high reliability by electrophotography over an
 extended period of time.
 Japanese Patent Application No. 10-183281 is hereby incorporated by
 reference.