Toner for electrophotography with the change controlling agent dispersed therein

A toner for use in electrophotography comprising thermoplastic resin core particles (A) or colorant-embedded thermoplastic resin core particles (A') each having an average particale size of 1 to 15 .mu.m, a charge-controlling agent (B) and carrier particles (C) having an average particle size of 0.05 to 2.0 .mu.m, the charge-controlling agnet (B) being carried on the carrier particles (C), and the carrier particles (C) with the agent (B) carried thereon being embedded in the surfaces of the resin core particles (A) or the colorant-embedded resin core particles (A').

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to toners used for the dry development of an 
electrostatic latent image in electrophotography. 
2. Description of the Prior Art 
There have heretofore been known several dry developing methods including a 
method using a two-component developer composed of toner particles mixed 
with carrier particles such as glass beads or magnetic powder, and a 
method using a one-component toner composed of toner particles imparted 
with magnetism. In addition, there has recently been proposed a method 
using a one-component nonmagnetic toner which is excellent in environment 
resistance, e.g. temperature, humidity and the like. 
These conventional toners have been, in most cases, prepared by methods 
which comprise mixing, heating and melting thermoplastic resins, colorants 
such as pigments or dyes and additives such as wax, plasticizers, 
charge-controlling agents and the like, kneading the pigments or 
charge-controlling agents, changing the form of secondary agglomeration 
under the application of intense shearing force to primary particles, 
uniformly dispersing, if necessary, magnetic powder in the mixture to 
obtain a uniform composition, cooling and comminuting the composition and 
then classifying the resulting particles to obtain the toner particles. 
However, the conventionl methods have problems that they require a large 
amount of energy in the step of milling the pigment and charge controlling 
agent, provide the toner particles in a low yield as low as about 85% 
because finer toner particles are cut or removed in the step of 
classification, and exhibit an inevitably low productivity of toner 
particles although part of the removed toner particles are reused in the 
next production. Further, in cases where particulate toners which are 
different from each other in kind, particularly hue, are each produced by 
any conventional method using an apparatus including devices such as a 
kneader, grinder and dispenser, such devices must beforehand be thoroughly 
cleaned every time each of the toners is produced. Since the devices used 
in the conventional methods are considerably large in scale, the cleaning 
is a heavy burden to the workers. 
Moreover, the toner particles so obtained are qualitatively disadvantageous 
in that they have the charge-controlling agent insufficently dispersed 
therein and are non-uniform in size and shape and generally amorphous 
whereby they are individually different in frictional charging 
characteristics thus causing them to be stained and scattered within the 
copying devices. In addition, the toner particles have so low flowability 
that it becomes difficult to supply them smoothly with many troubles being 
undesirably involved. 
To avoid this, there have been proposed attempts to obtain spherical toners 
by a spray drying or suspension polymerization process. However, the 
former process requires proper selection of resins which are soluble in 
the solution used and raises a problem as to an offset phenomenon on a 
fixing drum. The latter process raises problems as to blocking and offset 
phenomena and is therefore not industrially used. 
Further, other methods proposed include a method in which binder resin 
particles and coloring material particles are treated in a hot air stream 
(Japanese patent application Laid-Open No. 37553/1984) and a method in 
which a binder resin and a coloring material are deposited on the surface 
of a spherical resin (Japanese patent application Laid-Open No. 
210368/1986). However, these methods involving heat treatment tend to 
cause the formation of coarse particles due to the fusion of fine 
particles and have not yet been put to practical use. 
Conventional toners have the common disadvantage that the colorant and 
charge controlling agent, which exhibit their characteristic properties on 
the toner surface and are relatively expensive as starting materials for 
the toners, are not economically contained not only in the surface portion 
of the toner but also in the interior. 
In order to solve this problem, one of the present inventors proposed a 
toner produced by mixing a toner for use in electrophotography with a 
charge controlling agent while applying mechanical strain force to embed 
the charge controlling agent in the surface of the toner (Japanese patent 
application No. 51481/1986). However, it was found that, even with this 
improved method, the desired charge control cannot be often attained 
depending on the formulation of the toner and the conditions of 
production. Specifically, when the surface of the core particles (A) is 
preliminary coated with an electrically conductive material such as carbon 
black or a surfactant, difficulties are encountered in controlling the 
charges even when the charge controlling agent (B) is embedded in the 
surface of the core particles (A) by the above-mentioned method. The 
reason for this has not yet been fully elucidated. In any way, as is 
apparent from the foregoing description, the conventional toners still 
present problems to be solved. 
SUMMARY OF THE INVENTION 
An object of the present invention is to solve the above-mentioned problems 
and to provide a toner which can be prepared with excellent productivity 
and can produce a clear image free from fogging. 
The present inventors have made extensive and intensive studies. As a 
result, the present inventors have found that a toner for use in 
electrophotography, which is superior in productivity and sharpness in 
charge distribution to the conventional toners, can be stably obtained by 
mixing thermoplastic resin core particles (A) with carrier particles (C) 
having an average particle size of from 0.05 to 2.0 .mu.m, preferably 0.08 
to 2.0 .mu.m and carrying a charge controlling agent (B) on the surface 
thereof while applying mechanical strain force under such conditions that 
the resulting toner particles have an average particle size of from 1 to 
20 .mu.m, thereby embedding the carrier particles (C) in the surface of 
the core particles. The present invention is based on this finding. 
Specifically, in accordance with the present invention, there is provided 
a toner for use in electrophotography comprising thermoplastic resin core 
particles (A) or (A') and carrier powders (C) which carry a charge 
controlling agent (B) on the surface thereof and are embedded in the 
surface of said core particles (A) or (A'), said toner being produced by 
mixing the core particles (A) having an average particle size of from 1 to 
15 .mu.m or the core particles (A') having an average particle size of 
from 1 to 15 .mu.m and containing colorant particles embedded in the 
surface thereof, with carrier particles (C) having an average particle 
size of from 0.1 to 2.0 .mu.m and carrying a charge controlling agent (B) 
on the surface thereof while applying mechanical strain force to the 
resulting mixture under such conditions that the resulting toner particles 
have an average particle size of from 1 to 20 .mu.m. The state wherein 
"carrier particles (C) which carry a charge controlling agent (B) on the 
surfaces thereof are embedded in the surface of core particles (A)" as 
described herein refers to such a state that part of the carrier particles 
(C) are exposed on the surface of the core particle (A) without being 
completely buried in the core particles (A). In this state, part of the 
charge controlling agent (B) carried on the carrier particles (C) are 
exposed on the surfaces of the core particles (A). However, it is not 
necessary that all of the carrier particles (C) be exposed on the surfaces 
of the core particles (A). 
In the present specification, the particle size was measured with a Coulter 
Counter Model TAII (a product of Coulter Electronics Co., Ltd.) and 
expressed on the volume basis. 
DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION 
The core particles used in the present invention may be those obtained by 
conventional methods, i.e., by mixing a thermoplastic resin with a 
coloring material and, if necessary, additives such as a lubricant, 
followed by being subjected to a series of procedures such as melting, 
kneading, allowing to cool, coarse grinding, grinding, and then 
classification. Alternatively, the core particles may be those obtained by 
embedding a coloring material substantially as a primary particle in the 
surfaces of resin particles through the mixing operation under the same 
mechanical strain force as that of the present invention. Although the 
colorant such as pigment exists as a secondary agglomeration, since the 
colorant thus obtained by mixing operation is embedded to the surface of 
the core particle substantially as a primary particle, colorant core 
particle having tinting power and brightness is obtained (see U.S. patent 
application No. 020,585). 
Examples of thermoplastic resins for the core particles which may be used 
in the present invention include known binder resins, e.g., polystyrene 
resins, copolymer resins containing styrene, such as copolymer of styrene 
with acrylate, methacrylate, acrylonitrile or maleate, polyacrylate 
resins, polymethacrylate resins, polyester resins, polyamide resins, 
polyvinyl acetate resins, epoxy resins, phenolic resins, hydrocarbon 
resins, petroleum resins, and chlorinated paraffins. Further, it is 
preferred that the thermoplastic resins be solid at room temperature and 
have a heat softening temperature of 50.degree. C. or higher. These may be 
used alone or in the form of any mixture. With respect to other additives, 
coloring materials such as pigment and dye, magnetic powder, lubricants 
such as wax, fluidizers such as colloidal silica, and low-molecular weight 
polyolefins may be used in combination according to the purposes. When 
they are used in the form of fine particles, they can be also embedded in 
the same manner as that described above with respect to the carrier 
particles (C). It is preferred that the core particles (A) be 
substantially free from particles having a particle size of 25 .mu.m or 
more. Although it is generally believed that fine particles having a size 
of 1 .mu.m or less are unfavorable, it is not necessary in the present 
invention, as is mentioned later, that such fine particles be removed 
because the particle sizes are regulated by the mixing treatment. 
Examples of the coloring material include white and black pigments or dyes, 
such as zinc yellow, yellow iron oxide, hansa yellow, disazo yellow, 
quinoline yellow, permanent yellow, red iron oxide, permanent red, lithol 
red, pyrazolone red, watchung red calcium salt, watchung red manganese 
salt, lake red C, lake red D, brilliant carmine 6B, brilliant carmine 3B, 
prussian blue, phthalocyanine blue, metal-free phthalocyanine, titanium 
white, and carbon black. 
Examples of the carrier particles (C) include inorganic fine powders such 
as alumina, titanium dioxide, barium titanate, magnesium titanate, 
strontium titanate, zinc oxide, iron oxide, barium sulfate, silicon 
carbide, cerium oxide, silica, and carbon powder; fine particles of resins 
such as polyvinylidene fluoride, copolymers of vinylidene fluoride with 
vinyl fluoride, trifluoroethylene, ethylene, propylene, butene or the 
like, polystyrene, styrene-methyl methacrylate copolymer, xylene resin, 
polyamide, petroleum resins such as cumarone-indene resin, benzoguanamine 
resin, phenolic resin, melamine resin, epoxy resin, and unsaturated 
polyester resin; and fine particles of organic substances, e.g., waxes 
such as polyethylene wax and amide wax and metal salts of fatty acids, 
such as calcium stearate, aluminum stearate, and zinc stearate. It is 
preferred that these fine particles have a particle size of from 0.1 to 
2.0 .mu.m. When the particle size is too large, the carrier particles 
cannot be uniformly embedded in the core particles (A). On the other hand, 
the particle size is too small, the carrier particles (C) are completely 
embedded in the inside of the core particles (A), which makes it 
impossible to attain the main object. Further, it is preferred that the 
carrier particles (C) be solid at room temperature and have a heat 
softening temperature of 50.degree. C. or above. 
In the present invention, although the methods of carrying the charge 
controlling agent (B) on the surface of the carrier particles (C) are not 
particularly limited, it is preferred that the charge controlling agent be 
deposited to attain a sufficient strength. A preferable method for 
attaining this purpose comprises subjecting both components to wet mixing, 
drying the resulting mixture and, if necessary, grinding the dried 
mixture. Specifically, 1 weight part of the charge controlling agent (B) 
and 1 to 10 weight parts of the carrier particles (C) are milled using a 
ball mill, a sand mill or an attritor in the presence of a suitable 
medium, such as water or an organic solvent, followed by drying and 
grinding. The resulting product can be advantageously used in the present 
invention. 
The charge controlling agent (B) used in the present invention may be one 
known in the art, and examples include dyes and metal-containing dyes such 
as Fettschwarz HBN, Nigrosine Base, Brilliant Spirit, Zapon Black X, Ceres 
Black RG, copper-phthalocyanine dye; other dyes such as C.I. Solvent Black 
1, 2, 3, 5, and 7, C.I. Acid Black 123, 22, 23, 28, 42, and 43, Oil Black 
(C.I. 26150) and Spiron Black; quaternary ammonium salt; metal salt of 
naphthenic acid; and metallic soaps of fatty acids and resin acid. In the 
present invention, in mixing the core particles (A) with the carrier 
particles (C) carrying the charge controlling agent (B) on the surfaces 
through the application of mechanical strain force under such conditions 
that the resulting toner particles have an average particle size of from 1 
to 20 .mu.m, it is necessary that the mixing be conducted so as not to 
cause unfavorable phenomena such as fusion of the core particles (A) to 
form a large mass and grinding into finely divided particles due to the 
application of excessive strain force and at the same time, so as to embed 
part of the carrier particles (C) carrying the charge controlling agent 
(B) on the surfaces in the surfaces of the core particles (A). In the case 
of commercial scale production, both of the above-mentioned requirements 
can be met by varying the operating conditions of a dispenser such as a 
ball mill or a sand mill etc. and conditions such as loading and 
dispersing medium so as to attain the above-mentioned purpose. 
However, the mixing step with a ball mill or a sand mill requires much 
time. In this respect, mixers preferable from the stand point of 
commercial scale production include one in which particles are fluidized 
together with an air stream at a high speed and one equipped with a blade 
or a hammer capable of applying percussions. Examples of such mixers 
include an SI mill (a product of Toyo Ink Mfg. Co., Ltd.; some description 
on an SI mill is given in Japanese patent application Publication No. 
43051/1982), an atomizer, a Jiyu Mill (a product of Nara Machinery Co., 
Ltd.), a grinder manufactured by Kawasaki Heavy Industries, Ltd. (KTM-1), 
and a Hybridizer (a product of Nara Machinery Co., Ltd.). These devices 
may be used as they are or used after they are modified according to the 
purposes of the present invention. If possible, it is preferred that a 
hermetically sealed device of circulation type, e.g., a Hybridizer, be 
used. 
Further, it is preferred that the core particles (A) be pre-mixed with the 
carrier particles (C) carrying the charge controlling agent (B) on the 
surfaces and other fine particles under stirring conditions milder that 
those of the above-mentioned mixing treatment, e.g., in a Henschel mixer. 
The pre-mixing causes the fine particles such as the particles (C) to be 
electrostatically deposited on the core particles (A), which contributes 
to the uniform embedding of the fine particles in the core particles (A). 
The reason why the mixing treatment causes such an effect that the carrier 
particles (C) carrying the charge controlling agent (B) on the surfaces 
are embedded on the surfaces of the core particles (A) is believed to 
reside in that these particles come into collision with each other or with 
the wall, blade or dispersing medium such as beads to instantaneously and 
partly generate a considerably high temperature, which leads to occurrence 
of a phenomenon similar to a mechanical reaction in the field of inorganic 
chemistry. Therefore, it is sometimes necessary that the system be allowed 
to cool. When the air stream temperature in the system is raised to around 
the T.sub.g (glass transition point) of the resin, the particles tend to 
fuse to each other. 
The above-mentioned phenomenon can be confirmed through examination of 
electron photomicrograph prior to mixing treatment, i.e., after 
pre-mixing, and after mixing treatment. Specifically, before the mixing 
treatment, the core particles (A) having a relatively broad particle size 
distribution and the carrier particles (C) carrying the charge controlling 
agent (B) on the surfaces are in a partly agglomerated state. On the other 
hand, after the mixing treatment, the core particles (A) are in a smooth 
state as a result of the removal of the angular portion thereof, and it is 
observed that the carrier particles (C) are embedded in the surface of the 
core particles (A). The resulting particles were hardly broken by the 
running test conducted within a copying device. Further, since the charge 
controlling agent (B) is present on the surface of the toner, the amount 
of the charge can be effectively regulated by the use of a small amount of 
the charge controlling agent (B). 
Various factors for attaining the above-mentioned effects may be mentioned. 
According to the studies conducted by the present inventors, the most 
important factor is the speed of the air stream of the mixing devices and 
it is preferred that the speed of the air stream be several tens to 
several hundreds m/sec. 
In the present invention, it is preferred that the toner particles have 
such a particle size distribution that they have an average particle size 
of from 1 to 20 .mu.m and are free from particles having a size of 0.5 
.mu.m or less and 25 .mu.m or more. The presence of a large amount of the 
toner particles having a size of 0.5 .mu.m or less brings about a lowering 
in the flow, which leads to the occurrence of staining of copied paper. On 
the other hand, the presence of a large amount of the toner particles 
having a size of 25 .mu.m or more leads to the formation of a roughened 
image, which brings about a reduction in the commercial value. However, 
the toner according to the present invention does not need any particular 
classification because the particles having a size of 0.5 .mu.m or less is 
regulated with respect to the particle size. 
In the present invention, when the production of a magnetic toner is 
intended, known thermoplastic resin core particles containing magnetic 
powders may be used. Alternatively, if necessary, core particles (A) 
having magnetic particles embedded therein obtained by the same procedures 
as those adopted in the present invention may be also used. The magnetic 
particles are not particularly limited. However, it is preferred that 
finely divided magnetic particles having an average particle size of 1 
.mu.m or less, preferably 0.5 .mu.m or less, be used when the magnetic 
toner is produced by the latter method. Examples of the magnetic particles 
known in the art, include various ferrites, magnetite, hematite, and 
alloys or compounds of iron, zinc, cobalt, nickel, and manganese. These 
magnetic particles may be those which were subjected to classification 
according to the purposes or known surface treatment, e.g., hydrophobic 
treatment or silane coupling agent treatment.

The present invention will now be described with reference to the following 
examples. In the examples, all the parts are by weight. 
REFERENCE EXAMPLE 1 
100 parts of carbon powder (Sevacarb MT-CI; trade name of a product of 
Columbia Carbon Co., Ltd.; an average particle size of 0.35 .mu.m), 20 
parts of a charge controlling agent (PNR-BE; trademark of a product of 
Orient Chemical Industries, Ltd.), and 200 parts of water were mixed with 
each other in a ball mill for 24 hours. The mixture was filtered and then 
dried at 100.degree. C. for 24 hours to obtain carrier particles (1) 
carrying a charge controlling agent on the surfaces of carbon powder. 
REFERENCE EXAMPLE 2 
Carrier particles (2) were produced in the same manner as that of Reference 
Example 1, except that Oil Black 1010 (trademark of a product of Chuo 
Synthetic Chemical Co., Ltd.) was used as the charge controlling agent. 
REFERENCE EXAMPLE 3 
Carrier particles (3) were produced in the same manner as that of Reference 
Example 1, except that 100 parts of barium sulfate (B-30; trade name of 
Onahama Sakai Chemical Co., Ltd.; an average particle size of 0.3 .mu.m), 
20 parts of a charge controlling agent (PNR-BE; trademark of a product of 
Orient Chemical Industries, Ltd.), and 140 parts of water were used. 
REFERENCE EXAMPLE 4 
Carrier particles (4) were produced in the same manner as that of Reference 
Example 3, except that precipitated barium sulfate 100 (trade name of a 
product of Onahama Sakai Chemical Co., Ltd.; an average particle size of 
0.6 .mu.m) was used as barium sulfate. 
REFERENCE EXAMPLE 5 
Carrier particles (5) were produced in the same manner as that of Reference 
Example 3, except that precipitated barium sulfate 300 (trade name of a 
product of Onahama Sakai Chemical Co., Ltd.; an average particle size of 
0.8 .mu.m) was used as barium sulfate. 
REFERENCE EXAMPLE 6 
Carrier particles (6) were produced in the same manner as that of Reference 
Example 3, except that 100 parts of the same barium sulfate as that used 
in Reference Example 3, 20 parts of a charge controlling agent (E-84; 
trademark of a product of Orient Chemical Industries, Ltd.), and 150 parts 
of water were used. 
REFERENCE EXAMPLE 7 
Carrier particles (7) were produced in the same manner as that of Reference 
Example 5, except that the amounts of barium sulfate and the charge 
controlling agent were 100 parts and 10 parts, respectively. 
REFERENCE EXAMPLE 8 
Carrier particles (8) were produced in the same manner as that of Reference 
Example 5, except that the amounts of barium sulfate and the charge 
controlling agent were 100 parts and 30 parts, respectively. 
REFERENCE EXAMPLE 9 
Carrier particles (9) were produced in the same manner as that of Reference 
Example 2, except that particles having a size of about 0.5 .mu.m obtained 
by classification of benzoguanamine resin particles (EP-S; trade name of a 
product of Nippon Shokubai Kagaku Kogyo Co., Ltd.) were used instead of 
the carbon powder. 
EXAMPLE 1 
96 parts of a styrene-acrylic resin (Nikalite NC-6100; trade name of a 
product of Nippon Carbide Industries Co., Ltd.) and 4 parts of 
low-molecular weight polypropylene (Viscol 550 P; trade name of a product 
of Sanyo Chemical Industry Ltd.) were mixed with each other in a Henschel 
mixer. The resulting mixture was molten, kneaded and allowed to cool in a 
twin-screw extruder. The kneading product was coarsely ground and then fed 
in a type I jet mill to obtain resin particles having a maximum particle 
size of 25 .mu.m or less and an average particle size of about 10 .mu.m. 
100 parts of the resin particles and 4 parts of carbon black (Monarch 880; 
trade name of a product of Cabot Corporation; a particle diameter of 16 m 
.mu.) were pre-mixed with each other in a Henschel mixer at a 
circumferential speed of 10 m/sec for 10 minutes to deposit carbon black 
on the surfaces of the resin particles. 100 g of the treated resin 
particles were fed into a Hybridizer (Model NHS-1). The Hybridizer was 
operated at 8,000 rpm for 2 minutes to obtain core particles in which the 
carbon black was embedded. During this step, the Hybridizer was cooled 
with water of 20.degree. C. 
100 parts of the core particles and 6 parts of the carrier powders (1) were 
subjected to the pre-mixing treatment and the mixing treatment in a 
Hybridizer in the same manner as that described above, thereby obtaining a 
toner having an average particle size of about 11 .mu.m and substantially 
free from particles having a size of 5 .mu.m or less and 25 .mu.m or more. 
The amount of blow-off electrification of the toner thus obtained was -20 
.mu.c/g, and the measurement with a particle change measuring device (a 
product of Hosokawa Micron Corporation) revealed that the toner was 
substantially free from toner particles having a reversed polarity. 
100 parts of the toner was added and mixed with 0.3 parts of finely divided 
silica (R-972; trade name of a product of Nippon Aerosil Co., Ltd.). The 
resulting mixture was further mixed with 900 parts of an iron powder 
carrier to prepare a two-component developing agent. The developing agent 
was set within a copying machine manufactured by Toshiba Corp. (trade 
name: BF-8411). The copying on plain paper was continuously conducted by 
making use of a test chart. 
In this copying test, the toner was excellent in charge stability, 
fixability, blocking resistance, and offset resistance and provided an 
image substantially free from scumming and fogging. Further, in a running 
test in which the copying operation was conducted while supplying the 
toner in a supply hopper of the copying machine, the toner was smoothly 
supplied, and the quality of the initial image was maintained until the 
image was duplicated on 60,000 pieces of plain paper. 
EXAMPLE 2 
A flask was charged with 500 parts of purified water and 8 parts of 
polyvinyl alcohol and maintained at 80.degree. C. under a nitrogen gas 
stream. 50 parts of butyl acrylate and 1 part of benzoyl peroxide were 
added while stirring to the flask for about 30 minutes. The resulting 
mixture was maintained at that temperature for 30 minutes while stirring. 
Thereafter, 400 parts of styrene, 50 parts of butyl acrylate, and 4 parts 
of benzoyl peroxide were added thereto in about 2 hours. The stirring was 
further continued at 80.degree. C. for 4 hours, and the resulting product 
was dried at a low temperature, thereby obtaining pearl polymerization 
resin particles having an average particle size of 11.5 .mu.m. The same 
procedures as those of Example 1 were repeated to obtain a toner, except 
that the above-prepared pearl polymerization resin particles were used. 
The toner had an average particle size of about 12.5 .mu.m and an amount 
of blow-off electrification of - 17 .mu.c/g and exhibited excellent 
properties comparable to those of the toner as produced in Example 1. 
COMATIVE EXAMPLE 1 
A toner was produced in the same manner as that of Example 1, except that 1 
part of a change controlling agent (PNR-BE) which had been subjected to 
classification to obtain particles having a size of 1 .mu.m was used 
instead of the carrier particles (1). The toner thus obtained had an 
amount of blow-off electrification of -9 .mu.c/g. The toner was applied to 
the same test as that of Example 1. The above-obtained toner was inferior 
in resistance to scumming and fogging to the toners as produced in 
Examples 1 and 2. 
COMATIVE EXAMPLE 2 
A toner was produced using the same starting materials as those of Example 
1 by a conventional method. 
Specifically, 96 parts of a styrene-acrylic resin, 4 parts of low-molecular 
weight polypropylene, 4 parts of carbon black, and 3 parts of a charge 
controlling agent (used in an increased amount because of the 
incorporation method employed) were pre-mixed with each other in a 
Henschel mixer. The resulting mixture was molten, kneaded and allowed to 
cool in a twin-screw extruder, followed by coarse grinding. The coarse 
powders thus obtained were ground in a type I jet mill grinder and then 
subjected to classification to obtain a toner having a particle size of 
from 5 to 25 .mu.m. The toner was applied to the same test as that of 
Example 1. The above-obtained toner was inferior in resistance to scumming 
and fogging to the toners as produced in Examples 1 and 2 and further 
caused a bridging phenomenon within the toner hopper. 
EXAMPLE 3 
A toner was produced in the same manner as that of Example 1, except that 
the carrier particles (2) were used instead of the carrier particles (1). 
The amount of blow-off electrification of the toner was obtained was +19 
.mu.c/g, and the measurement with a particle charge measuring device (a 
product of Hosokawa Micron Co., Ltd.) revealed that the toner was 
substantially free from toner particles having a reversed polarity. 
100 parts of the toner was added and mixed with 0.1 part of finely divided 
silica (R-972; trade name of a product of Nippon Aerosil Co., Ltd.). The 
resulting mixture was further mixed with 900 parts of an iron powder 
carrier to prepare a two-component developing agent. The developing agent 
was set within a copying machine manufactured by Sharp Corporation (trade 
name: SF8100). The duplication of an image on plain paper was continuously 
conducted by making use of a test chart. 
In this copying test, the toner was excellent in charge stability, 
fixability, blocking resistance, and offset resistance and provided an 
image substantially free from scumming and fogging. Further, in a running 
test in which the copying operation was conducted while supplying the 
toner in a supply hopper of the copying machine, the toner was smoothly 
supplied, and the quality of the initial image was maintained until the 
image was duplicated on 60,000 pieces of plain paper. 
EXAMPLE 4 
The same procedures as those of Example 1 were repeated, except that 53 
parts of a styrene-acrylic resin (Himer SMB73; trade name of a product of 
Sanyo Chemical Industry Ltd.), 42 parts of magnetic particles (MAT-305 HD; 
trade name of a product of Toda Kogyo Corporation; a particle size of 0.2 
.mu.m), and 3 parts of low-molecular weight polypropylene (Viscol 550P; a 
product of Sanyo Chemical Industry Ltd.) were used, thereby obtaining 
resin particles having a maximum particle size of 25 .mu.m or less and an 
average particle size of 10 .mu.m. 
98 parts of the resin particles and 2 parts of carbon black (Monarch 880; 
trade name of a product of Cabot Corporation; a particle size of 16 m.mu.) 
were subjected to the pre-mixing treatment and the mixing treatment with a 
Hybridizer in the same manner as that of Example 1 to obtain core 
particles having carbon black embedded on the surfaces thereof. 
100 parts of the core particles and 6 parts of the carrier particles (3) 
were subjected to the pre-mixing treatment and the mixing treatment with a 
Hybridizer in the same manner as that of Example 1 to obtain a toner 
having an average particle size of about 12 .mu.m and substantially free 
from particles having a size of 5 .mu.m or less and 25 .mu.m or more. 
The toner had an amount of blow-off electrification of -26 .mu.c/g and 
exhibited excellent charge distribution. 100 parts of the toner was added 
and mixed with 0.3 parts of finely divided silica (R-972; trade name of a 
product of Nippon Aerosil Co., Ltd.). The resulting mixture was set within 
a copying machine manufactured by Canon Inc. (trade name: NP300 Z). The 
duplication of an image on plain paper was continuously conducted by 
making use of a test chart. 
In this copying test, the toner was excellent in charge stability, 
fixability, blocking resistance, and offset resistance and provided an 
image substantially free from scumming and fogging. Further, in a running 
test, the toner was smoothly supplied, and the quality of the initial 
image was maintained until the image was duplicated on 50,000 pieces of 
plain paper. 
EXAMPLE 5 
Two kinds of toners were produced in the same manner as that of Example 4, 
except that the carrier particles (4) and the carrier particles (5) were 
used instead of the carrier particles (3). 
These toners were applied to the same test as that of Example 4. They 
exhibited excellent results comparable to those of Example 4. 
EXAMPLE 6 
100 parts of the resin as used in Example 1 and 4 parts of a red azo 
pigment were subjected to the pre-mixing treatment and the mixing 
treatment in a Hybridizer in the same manner as that of Example 1, thereby 
obtaining core particles having a red azo pigment embedded on the surfaces 
thereof. 
100 parts of the core particles and 6 parts of the carrier particles (6) 
were subjected to the pre-mixing treatment and the mixing treatment in a 
Hybridizer in the same manner as that of Example 1 to obtain a toner. 
The toner had an amount of blow-off electrification of -24 .mu.c/g and 
exhibited excellent charge distribution. 
100 parts of the toner was added and mixed with 0.3 parts of finely divided 
silica (R-972; trade name of a product of Nippon Aerosil Co., Ltd.). The 
resulting mixture was further mixed with 900 parts of an iron powder 
carrier and then set within a copying machine manufactured by Mita 
Industrial Co., Ltd. (trade name: DC-232). The duplication of an image on 
plain paper was continuously conducted by making use of a test chart. The 
toner exhibited excellent results comparable to those of Example 1. 
EXAMPLE 7 
A toner was produced in the same manner as that of Example 6, except that 
12 parts of the carrier particles (7) were used instead of the carrier 
particles (6). This toner was applied to the same test as that of Example 
6. The toner exhibited excellent results comparable to those of Example 6. 
EXAMPLE 8 
A toner was produced in the same manner as that of Example 6, except that 4 
parts of the carrier particles (8) was used instead of the carrier 
particles (6). This toner was applied to the same test as that of Example 
6. The toner exhibited excellent results comparable to those of Example 6. 
EXAMPLE 9 
A toner was produced in the same manner as that of Example 3, except that 4 
parts of the carrier particles (9) was used instead of the carrier 
particles (2). This toner was applied to the same test as that of Example 
3. The toner exhibited excellent results comparable to those of Example 3.