Developer for developing electrostatic image, image forming method and heat fixing method

A developer for developing an electrostatic image is disclosed which has a toner including toner particles each containing a polymer, a copolymer or a mixture thereof and from 5 to 30% by weight of a low softening point material, and each having a plurality of concavities on its surface; the toner particles being prepared by suspension polymerization. Also, an image forming method and a heat fixing method using the developer are disclosed.

BACKGROUND OF THE INVENTION 
1. Field of the invention 
The present invention relates to a developer for developing an 
electrostatic image, an image forming method, and a heat fixing method for 
fixing a toner image. 
2. Related Background Art 
A number of methods as disclosed in U.S. Pat. No. 2,297,691, etc. are 
hitherto known as method for carrying out electrophotography, which, in 
general, is a process in which copies are obtained by forming an 
electrostatic latent image on a photosensitive member by various means 
utilizing a photoconductive material, developing the latent image by the 
use of a toner, and transferring the toner image to a transfer medium such 
as paper if necessary, followed by fixing by the action of heat, pressure, 
heat-and-pressure, or solvent vapor. Methods for development using toners 
or methods of fixing toner images have been hitherto proposed in variety, 
and methods suited for any respective image-forming processes have been 
employed. In recent years, on such electrophotography, there is a demand 
for higher-speed copying and higher image quality. 
As methods of producing toners, it is commonly known to use a process 
comprising melt-kneading a thermoplastic resin, a colorant such as a dye 
or a pigment and additives such as a charge control agent to effect their 
uniform dispersion, thereafter cooling the melt-kneaded product, 
pulverizing the cooled product by means of a pulverizer, and classifying 
the pulverized product by means of a classifier to give a toner having the 
desired particle diameter. 
In the toners produced through the step of such pulverization, there is a 
limit in faithfully reproducing the latent image since in general their 
particles lack definite form, i.e., are amorphous. In order to achieve a 
high image quality using the toners produced by such pulverization, it is 
necessary to pulverize particles in a smaller diameter. However, making 
particle diameter smaller makes it necessary to use more energy and tends 
to make poor the yield of toner. 
In addition, in the toners produced by such pulverization, there are 
limitations when a release material (a material with release properties) 
such as wax is added. For example, in order to make the release material 
have a dispersibility on a satisfactory level, there are limitations such 
that i) the material is not dissolved into a liquid state in the range of 
the temperature at which it is kneaded together with the resin, and ii) 
the release material must be contained in an amount not more than a given 
amount. Because of such limitations, there is a limit in improving the 
fixing performance of the toners produced by pulverization. 
To cope with the problems in such amorphous toners, spherical toners have 
been proposed. For example, Japanese Patent Publication No. 56-13945 
discloses a method of obtaining a spherical toner by melt-spraying. 
Japanese Patent Publication No. 57-51676 discloses a method of obtaining a 
spherical toner by adding to an amorphous toner an organic solvent in a 
small quantity followed by stirring under cooling. Japanese Patent 
Publication No. 36-10231 and Japanese Patent Applications Laid-open No. 
59-53856 and No. 59-61842 also disclose a method of obtaining a spherical 
toner by suspension polymerization. 
These spherical toners have uniform particle shapes and hence can readily 
adhere faithfully to the latent image. In particular, no minute 
irregularity occurs at the edges of the latent image to give a high image 
quality. In the case when the spherical toner is obtained by suspension 
polymerization, the toner particles can be readily made to have a smaller 
particle diameter and can be more suitable for achievement of a higher 
image quality. 
The toner obtained by suspension polymerization (hereinafter "polymerized 
toner"), when compared with amorphous toners obtained by pulverization, 
can readily have a function of a capsular structure and hence can 
encapsulate wax in a large quantity, so that a good fixing performance and 
anti-offset properties can be expected. 
As for the spherical toners, they tend to cause a deterioration of their 
performance even if various additives are used, making it difficult to 
obtain toners with a satisfactory durability. They also so strongly adhere 
to a photosensitive member that the toner cleaning after the transfer step 
tends to become insufficient. Several reports are seen on such problems. 
In the method using suspension polymerization, toner particles are formed 
by dispersing in a dispersion medium as typified by water a polymerizable 
monomer composition substantially incompatible therewith, followed by 
polymerization. In order to obtain a toner with a sharp particle size 
distribution, it is a very important subject how stably droplets of the 
polymerizable monomer composition having been suspended in this aqueous 
dispersion medium, i.e., polymerizable monomer composition particles, are 
kept constant in diameter in the course of the polymerization. 
To settle this subject, it is very important to make researches on 
dispersion stabilizers capable of imparting an appropriate surface tension 
to the interfaces between the droplets of a polymerizable monomer 
composition and the dispersion medium without adversely affecting 
environmental properties of toners as exemplified by moisture resistance. 
It is also very important how to conduct a post-treatment. 
In recent years, copying apparatus or printers are not only used as a 
copying machine for office work to merely take copies of originals, but 
also has begun to be used in the field of printers serving as outputs of 
computers and in the field of personal copying of private use. 
Under such circumstances, the apparatus are severely sought to be made 
small-sized, lightweight and of low power consumption, and copying 
machines have now been formed of more simple components. For example, as 
methods of developing electrostatic latent images, there are the 
two-component development, which makes use of a mixture comprised of a 
toner and a carrier, and the one-component development, which makes use of 
only a toner. 
Non-magnetic one-component development as disclosed in Japanese Patent 
Applications Laid-open No. 58-116559, No. 60-120368 and No. 63-2711371 
have attracted notice as development methods that can solve the problems 
discussed above. 
In such non-magnetic one-component development, a developer is coated on a 
developer carrying member by means of a blade or the like to form a coat 
layer. The developer is electrostatically charged as a result of its 
friction with the blade or the surface of the developer carrying member. 
If the developer is coated in a thick layer, part of the developer can not 
be sufficiently charged, which causes fogging or toner scatter, and hence 
the developer must be coated in a thin layer. For this reason, the blade 
must be brought into pressure contact with the developer carrying member 
at a sufficient pressure. The force the developer receives at this time is 
larger than the force a developer receives in the two-component 
development or the one-component development making use of a magnetic 
toner. Hence the developer tends to be deteriorated and image 
deterioration such as fogging or density decrease tends to occur. 
The developer used in the non-magnetic one-component development is 
required to have a large mechanical strength and thermal strength. 
However, an attempt to merely increase these strengths results in an 
increase in the heat energy required for the fixing, which is 
contradictory to the demand for the low power consumption. Thus, in the 
non-magnetic one-component development, higher performances are sought in 
both developing performance and fixing performance. 
As a method of fixing a visible toner image to a recording medium, a 
heat-roll fixing system is widely used, in which a recording medium 
holding thereon a visible toner image having not been fixed is heated 
while it is held and carried between a heat roller maintained at a given 
temperature and a pressure roller having an elastic layer and coming into 
pressure contact with the heat roller. A belt fixing system is also known, 
as disclosed in U.S. Pat. No. 3,578,797. 
The heat-roll fixing, however, has the following disadvantages: 
(1) A time during which an image-forming operation is prohibited, i.e., 
what is called a waiting time, is required until the heat roller reaches a 
given temperature. 
(2) The heat roller must be maintained at an optimum temperature in order 
to prevent poor fixing caused by the variations of the heat-roller 
temperature that may occur when the recording medium is passed or because 
of other external factors, and also to prevent the transfer of toner to 
the heat roller, i.e., what is called the offset phenomenon. This makes it 
necessary to make large the heat capacity of the heat roller or a heater 
element, which requires a large electric power and also causes in-machine 
temperature rise in the image forming apparatus. 
(3) After the recording medium has been passed over the heat roller, the 
recording medium and the toner on the recording medium are slowly cooled 
because of a high temperature of the heat roller, resulting in a state in 
which a high adhesion of the toner is maintained. Thus, conjointly with 
the curvature of the roller also, there may often occur offset, or paper 
jam caused by the winding of the recording medium around the roller. 
(4) A protective member must be provided on account of safety since there 
is a possibility of direct touch to the high-temperature heat roller. 
The above problems (1) and (2) in the heat-roll fixing are not 
fundamentally solved also in the belt fixing system disclosed in U.S. Pat. 
No. 3,578,797. 
Japanese Patent Application Laid-open No. 63-313182 discloses an image 
forming apparatus with a shorter waiting time and a low power consumption, 
comprising a fixing unit in which a visible toner image is heated via a 
movable heat-resistant sheet by means of a heating element having a low 
heat capacity, pulsewise generating heat by electrification, and is thus 
fixed to a recording medium. Japanese Patent Application Laid-open No. 
1-187582 discloses a fixing unit for heat-fixing a visible toner image on 
a recording medium via a heat-resistant sheet, wherein said heat-resistant 
sheet comprises a heat-resistant layer and a release layer or a 
low-resistant layer, thereby effectively preventing the offset phenomenon. 
In addition to the factors in the above fixing apparatus, however, 
achievement of both the excellent fixing performance of a visible toner 
image to a recording medium and the prevention of offset and simultaneous 
realization of a fixing method with a shorter waiting time and a low power 
consumption are greatly concerned with the properties of a toner. Thus, it 
is sought to provide a toner suited therefor. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a developer for developing 
an electrostatic image, an image forming method and a heat fixing method 
that have solved the problems as discussed above. 
Another object of the present invention is to provide a developer for 
developing an electrostatic image, that may cause less deterioration of 
external additives, may cause less changes in performance and has a 
superior durability, even in long-term running. 
Still another object of the present invention is to provide a developer for 
developing an electrostatic image, containing a toner having superior 
fixing performance and anti-blocking properties. 
A further object of the present invention is to provide a developer for 
developing an electrostatic image, containing a toner having a superior 
charge stability and storage stability. 
A still further object of the present invention is to provide a developer 
for developing an electrostatic image, containing a toner that can achieve 
a high image density, a superior fine-line reproduction and a superior 
highlight reproduction. 
A still further object of the present invention is to provide a developer 
for developing an electrostatic image, capable of preferably matching the 
higher copying speed. 
A still further object of the present invention is to provide a developer 
for developing an electrostatic image, that can be preferably used in a 
full-color image forming method or multi-color image forming method. 
A still further object of the present invention is to provide a developer 
for developing an electrostatic image, that does not tend to cause carrier 
wear. 
A still further object of the present invention is to provide an image 
forming method that can achieve a high image density, causes no image 
deterioration such as fogging and can also achieve a superior fixing 
performance, even in long-term use in the non-magnetic one-component 
development. 
A still further object of the present invention is to provide a heat fixing 
method that requires substantially no, or only a very short, waiting time 
and also a low power consumption, causes no offset phenomenon and can 
achieve good fixing of a toner image to a recording medium. 
A still further object of the present invention is to provide a heat fixing 
method that employs no high-temperature revolving roller, thus requiring 
no heat-resistant special bearing. 
A still further object of the present invention is to provide a heat fixing 
method using a fixing device so constituted as to prevent direct touch to 
high-temperature parts, thus achieving higher safety or requiring no 
protective members. 
To achieve the above objects, the present invention provides a developer 
for developing an electrostatic image, comprising a toner comprising toner 
particles each containing a polymer, a copolymer or a mixture thereof and 
from 5 to 30% by weight of a low softening point material, and each having 
a plurality of concavities on its surface; said toner particles being 
prepared by suspension polymerization. 
As another embodiment of the developer, the present invention provides a 
developer for developing an electrostatic latent image, comprising a toner 
comprising toner particles; said toner particles being prepared by 
suspension polymerization, each containing at least two components 
comprised of a high softening point resin-A and a low softening point 
material-B, and each having a structure separated into a phase-A mainly 
composed of said resin-A and a phase-B mainly composed of said material-B, 
said phase mainly composed of said material-B being absent in the vicinity 
of the toner particle surface ranging from its surface to a depth 0.15 
time a toner particle diameter; and a dispersion stabilizer being present 
on the surfaces of said toner particles in an amount of not more than 0.2% 
by weight based on the weight of said toner. 
The present invention also provides an image forming method comprising; 
forming on a developer carrying member a magnetic brush layer formed of a 
developer; said developer comprising toner particles and magnetic 
particles; said toner particles each being prepared by suspension 
polymerization, containing at least two components comprised of a high 
softening point resin-A and a low softening point material-B, and each 
having a structure separated into a phase-A mainly composed of said 
resin-A and a phase-B mainly composed of said material-B, said phase 
mainly composed of said material-B being absent in the vicinity of the 
toner particle surface ranging from its surface to a depth 0.15 time a 
toner particle diameter; 
applying across said developer carrying member and a latent image bearing 
member, a bias electric field formed of an alternating current component 
and a direct current component; and 
forming in a developing zone defined by said latent image bearing member 
and said developer carrying member, a magnetic brush in such a manner that 
said magnetic particles are in a volume percentage of from 10% to 40%. 
As another embodiment of the image forming method, the present invention 
provides an image forming method comprising; 
feeding a toner to a developer carrying member by means of a feed roller; 
said toner comprising non-magnetic toner particles; said non-magnetic 
toner particles being prepared by suspension polymerization, each 
containing at least two components comprised of a high softening point 
resin-A and a low softening point material-B, and each having a structure 
separated into a phase-A mainly composed of said resin-A and a phase-B 
mainly composed of said material-B, said phase mainly composed of said 
material-B being absent in the vicinity of the toner particle surface 
ranging from its surface to a depth 0.15 time a toner particle diameter; 
forming a toner layer on said developer carrying member by means of a 
developer coating blade provided downstream said feed roller; and 
developing with said toner an electrostatic image formed on a latent image 
bearing member set opposingly to said developer carrying member. 
The present invention still also provides a heat fixing method comprising; 
carrying a visible image of a toner onto a recording medium; said toner 
comprising toner particles; said toner particles being prepared by 
suspension polymerization, each containing at least two components 
comprised of a high softening point resin-A and a low softening point 
material-B, and each having a structure separated into a phase-A mainly 
composed of said resin-A and a phase-B mainly composed of said material-B, 
said phase mainly composed of said material-B being absent in the vicinity 
of the toner particle surface ranging from its surface to a depth 0.15 
time a toner particle diameter; and 
bringing said recording medium into close contact with a heating element by 
means of a pressure member with a film interposed between them, to 
heat-fix said visible image of said toner onto said recording medium.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
According to a discovery made by the present inventors, in the toner 
produced by suspension polymerization, each toner particle may be provided 
on its surface with concavities and may be made to have a capsular 
structure that encapsulates a low-melting wax, so that an improvement in 
fixing performance, blocking resistance, and durability to copying on a 
large number of sheets can be improved; and the quantity of a dispersion 
stabilizer remaining and adhering on the toner particle surfaces may be 
controlled, so that a toner having a superior charge stability and storage 
stability can be obtained. 
According to another discovery made by the present inventors, the 
deterioration of durability and the poor cleaning performance in instances 
in which various external additives are used in spherical toners are 
mainly caused by the shapes of toner particles. More specifically, in the 
case when toner particles have spherical shapes, the friction, e.g., 
between toner particles, between a toner and a carrier or between a toner 
and a sleeve tends to take place more than in the case of amorphous 
toners, and hence any additives adhering to the surfaces of toner 
particles and freely movable tend to be embedded in the toner particle 
surfaces to tend to inhibit their functions, and tend to bring about a 
lowering of durability and cleaning performance. 
On the basis of such discoveries, the present inventors made further 
studies to accomplish the present invention. That is, they have discovered 
that deterioration of various external additives can be prevented by 
forming a plurality of appropriate concavities on the surface of each 
toner particle, and the cleaning can be efficiently carried out by counter 
blade cleaning. Moreover, the toner of the present invention can give a 
high-quality image. 
In the present invention, as the external additive, it is preferable to use 
at least one of a fluidity-providing agent, a lubricant and an abrasive. 
Use of a fluidity-providing agent makes it possible to weaken the van der 
Waals force applied to the toner, so that the toner behaves faithfully to 
the Coulomb force. As a result, the toner can readily move from a 
developer carrying member such as a developing sleeve to the latent image 
formed on a photosensitive member, so that a high image density can be 
obtained. Since also the latent image can be faithfully developed, it is 
possible to obtain a fog-free developed image. Moreover, use of the 
fluidity-providing agent makes it easy to feed the toner. In the case of 
two-component developers, its use improves mixing properties of magnetic 
particles, so that the toner becomes well chargeable. 
In general, such a fluidity-providing agent has a fluidity-providing 
ability which is higher with a decrease in particle diameter. When used in 
conventional spherical toners, the fluidity-providing agent tends to be 
embedded into the toner particles because of its small particle diameter, 
and hence tends to lose its fluidity-providing effect. 
As a countermeasure thereto, the present inventors have discovered that a 
toner not tending to cause deterioration of the fluidity-providing ability 
can be obtained when a toner produced by suspension polymerization and 
comprised of a particle with concavities on its surface is used in 
combination with the fluidity-providing agent. 
Making of toners having a small particle diameter so that a toner image 
with a high image quality can be obtained brings about a difficulty in 
toner cleaning and tends to result in an image with marks of faulty 
cleaning. In the present invention, toner particles are each provided with 
concavities on their surfaces. This makes it not liable for the additives 
to undergo deterioration and also makes it possible for toner particles to 
less adhere to the surface of a photosensitive member over a long period 
of time, so that the toner can be readily cleaned even when made to have a 
small particle diameter. 
As previously noted, each toner particle in the present invention has a 
plurality of concavities, which may preferably partially provided on its 
surface. More preferably, with respect to a projected area of the toner 
particle, its maximum inscribed circle corresponding to its radius r and 
minimum circumscribed circle corresponding to its radius R satisfy the 
expression: 
EQU 1.00&lt;R/r.ltoreq.1.20, 
and still more preferably satisfy the expression: 
EQU 1.02&lt;R/r.ltoreq.1.15. 
With an increase in the value of R/r, the particle tends to become less 
spherical. Its value more than 1.20 is not preferable since the particle 
become excessively less spherical. The toner comprised of such a particle 
may preferably have a weight average particle diameter of from 3 to 12 
.mu.m. 
In the present invention, circumferential length L and circumferential 
length 2.pi.r of a projected area of the particle may preferably satisfy 
the relationship of: 
EQU 1.01&lt;L/2.pi.r&lt;2.00, 
and more preferably satisfy the relationship of: 
EQU 1.02&lt;L/2.pi.r&lt;1.50. 
A particle with L/2.pi.r smaller than 1.01 results in a particle having few 
concavities. On the other hand, a value larger than 2.00 is not preferable 
since the particle comes to have a large number of minute or fine 
concavities, or have concavities with great differences in depth. In the 
case of the former, the concavities are too fine to readily give the 
operational effect. In the case of the latter, the particle becomes 
approximate to a substantially amorphous particle, making it difficult to 
obtain a high image quality and also tending to bring toner particles into 
a finely powdered state in a developing assembly. 
The projected area of the toner particle in the present invention refers to 
an image obtained by focusing the lens of an electron microscope on the 
contour of a toner particle at magnification of at least 2,000, and 
preferably 5,000. Using Luzex 5000, the radius r of its inscribed circle 
and the radius R of its circumscribed circle are also determined as shown 
in FIG. 3. The circumferential length L is also determined as shown in 
FIG. 4. 
These R, r and L are measured on at least 50, and preferably 100 or more, 
toner particle images, and average values thereof may preferably satisfy 
the relationships set out above. 
The toner particle of the present invention has the concavities on its 
surface. FIG. 1 shows an example of the surface shape. Such concavities 
bring about an increase in contact points between toner particles but 
instead bring about a decrease in pressure at every contact point, so that 
the additives can be hindered from being embedded into the toner particle 
and also the blocking resistance can be improved. 
In general, the addition of a fluidity-providing agent to a toner may bring 
about an improvement in blocking resistance because of the 
fluidity-providing agent serving as a spacer. As previously stated, 
however, when used in the conventional spherical toners prepared by 
suspension polymerization, the various external additives such as the 
fluidity-providing agent tend to fix on toner particle surfaces because of 
the stress produced by vigorous motion in a developing assembly and tend 
to cause a phenomenon of inhibiting the functions of the external 
additives. 
In the present invention, on the other hand, the concavities on the toner 
particle surface prevent the external additives from being deteriorated, 
and hence a good blocking resistance can be maintained for a long period 
of time. 
The toner particle of the present invention may also preferably have a 
surface layer portion 1 (phase-A) and a central portion 2 (phase-B) and 
may preferably be separated into two phases with a distinct boundary 
between them, as shown in FIG. 2. A capsular structure thus given to each 
particle, which functionally separates the particle into the surface layer 
portion 1 and the central portion 2, enables preferable toner designing. 
Stated specifically, a high softening point resin is used in the surface 
layer portion so that the toner can have a blocking resistance or a strong 
resistance to its vigorous motion in a developing assembly, and a low 
softening point material is used in the central portion so that the toner 
can have a superior fixing performance at the same time. In addition, a 
release material with a low melting point may have been incorporated in 
the center, which may be forced to exude therefrom by the application of 
pressure during fixing, so that the anti-offset properties can be 
remarkably improved. Charge control properties may be imparted to the 
surface layer portion. 
The particle in the present invention has a more definite double-layer 
structure than quasi-capsules disclosed in Japanese Patent Publication No. 
1-53786, and therefore the inside materials do not easily exude to the 
surface layer in the usual condition. Hence, a remarkable improvement is 
brought about also in preventing the phenomenon that the inside low 
softening point material contaminates a carrier or a developing sleeve. In 
particular, this function can be effective when the low softening point 
material is contained in a large quantity. 
Stated specifically, the toner particle contains at least two resin 
components, component-A and component-B, in a proportion A:B of from 50:50 
to 95:5, and has a structure separated in to a phase mainly composed of 
component-A and a phase mainly composed of component-B. The phase mainly 
composed of component-A forms a surface layer and the phase mainly 
composed of component-B is present at the center. As described above, a 
preferable combination is set up when the phase mainly composed of 
component-A has a high softening point and the phase mainly composed of 
component-B has a low softening point. Preferred is a combination which 
undergoes phase separation into the phase mainly composed of component-A 
and the phase mainly composed of component-B as the suspension 
polymerization proceeds. 
The component-A may preferably have a molecular weight of from 5,000 to 
200,000 as weight average molecular weight measured by gel permeation 
chromatography (GPC), and the component-A may preferably have melt 
properties such that it has a flow-out point (a point at which the resin 
begins to flow out) of from 65.degree. to 100.degree. C. when measured 
with a flow tester. 
The component-A that forms the surface layer of the toner particle may be 
produced from polymerizable monomers as exemplified by the following: 
Styrene; styrene monomers such as o-methylstyrene, m-methylstyrene, 
p-methylstyrene, p-methoxystyrene and p-ethylstyrene; acrylates such as 
methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 
n-propyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-ethylhexyl 
acrylate, stearyl acrylate, 2-chloroethyl acrylate and phenyl acrylate; 
methacrylates such as methyl methacrylate, ethyl methacrylate, n-propyl 
methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl 
methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl 
methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate and 
diethylaminoethyl methacrylate; and monomers such as acrylonitrile, 
methacrylonitrile and acrylamide. 
Any of these polymerizable monomers can be used alone or in the form of a 
mixture. Of the above polymerizable monomers, it is preferred in view of 
developing performance and durability to use styrene or a styrene 
derivative alone or to use styrene or a styrene derivative in combination 
with other monomer. 
The low softening point material (component-B) may preferably have a weight 
average molecular weight of from 300 to 10,000 as measured by GPC, and may 
preferably have a melting point of from 30.degree. to 130.degree. C., and 
more preferably from 60.degree. to 100.degree. C. A resin with a melting 
point lower than 30.degree. C. tends to increase the possibility of 
low-temperature offset during fixing. On the other hand, a resin with a 
melting point higher than 130.degree. C. tends to cause solidification of 
the component-B during the manufacture of the toner and also tends to make 
granulation properties poor. 
Use of a wax as the low softening point material makes the present 
invention more effective. The wax used in the present invention may 
include paraffin, polyolefin waxes and modified products of these as 
exemplified by oxides or grafted products, higher fatty acids and metal 
salts thereof, and amide waxes. 
The low softening point material may preferably be contained in an amount 
of from 5 to 30% by weight on the basis of the weight of the toner. 
The component-A and component-B may preferably be in a proportion A:B of 
from 50:50 to 95:5, and more preferably from 70:30 to 90:10. If the 
component-B is more than the proportion A:B of 50:50, it becomes difficult 
to retain the capsular structure, and if it is less than the proportion 
A:B of 95:5, it becomes difficult to obtain the operational effect 
attributable to the component-B. 
The main part of the phase B mainly composed of a low softening point 
material may be present in the center of the toner particle and the area 
of the phase-B in a cross section of the toner particle may hold from 10% 
to 45%. These are preferable in view of durability, fixing performance and 
anti-offset properties. 
In the toner of the present invention, the phase mainly composed of the 
component-B is preferably absent in the vicinity of the toner particle 
surface ranging from its surface to a depth 0.15 time a toner particle 
diameter. Stated conceptually, this means that the surface layer has a 
thickness 0.15 time or more the toner particle diameter. For example, even 
a configuration in which cracks are present and some parts of the surface 
layer do not have a thickness 0.15 times the toner particle is included in 
the scope of the present invention so long as the phase mainly composed of 
component-B is absent in the cracks. If the phase mainly composed of 
component-B is present in the vicinity of the toner particle surface 
ranging from its surface to a depth 0.15 time a toner particle diameter, 
the capsular structure may become unstable to tend to result in, for 
example, a poor blocking resistance. 
The concavities on the surface, which are one of the features of the 
present invention, can be preferably attained by dissolving in monomers a 
given amount of a specific polar resin soluble in the monomers capable of 
producing the component-A that mainly forms the surface layer, followed by 
granulation and suspension polymerization. 
The polar resin may include, for example, as cationic polymers, polymers of 
nitrogen-containing polymerizable monomers as exemplified by 
dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate, or 
copolymers of styrene or unsaturated carboxylates and nitrogen-containing 
polymerizable monomers; as anionic polymers, polymers of nitrile monomers 
such as acrylonitrile, halogen-containing monomers such as vinyl chloride, 
unsaturated carboxylic acids such as acrylic acid and methacrylic acid, 
unsaturated dibasic acids, unsaturated dibasic anhydrides or nitro 
monomers, or copolymers of any of these monomers and styrene or a styrene 
monomer. Examples are by no means limited to those set out here. 
Of these polar resins, it is particularly preferable to use those having a 
ratio of weight average molecular weight to number average molecular 
weight (Mw/Mn), as measured by GPC, of not more than 10, and more 
preferably not more than 5. Granulation and suspension polymerization 
carried out by adding such a polar resin to monomers promote the phase 
separation into the phase mainly composed of component-A (phase-A) and the 
phase mainly composed of component-B (phase-B). In other words, the 
boundary between phase-A and phase-B becomes distinct, and the 
concentration of the component-B contained in the phase-A becomes 
extremely low. As a result, the capsular structure of the toner particle 
itself becomes more remarkable, making it possible to achieve both the 
improvement in blocking resistance and the improvement in fixing 
performance. 
Such a tendency is more remarkable as the polar resin has a higher acid 
value, and the phase separation is promoted when its acid value is not 
less than 20, and preferably not less than 30. Moreover, the polar resin 
with a high acid value tends to be localized in the vicinity of the toner 
particle surface in the phase-A, so that this resin greatly affects the 
shape of the particle surface, making it possible to produce the toner 
particle with concavities in the form its surface has been caved in. 
Although details are unclear, it is presumed as follows: The polar resin 
with a high acid value is concentrated in the vicinity of the toner 
particle surface in the step of granulation and at the initial stage of 
the suspension polymerization, and, as the reaction of polymerization of 
monomers proceeds, comes to be present in the vicinity of the surface as a 
sort of an aggregate in which the polar resins have gathered. After a 
while, once the volume shrinkage of suspended particles begins to take 
place as a result of the polymerization of monomers, the degree of 
shrinkage becomes different depending on the manner in which the polar 
resin is localized, and soon after the shaped toner particles in the form 
that their surfaces are each concave in part and in plurality are 
produced. Such an effect can be obtained with difficulty when a polar 
resin with an acid value less than 20 is used. 
On the other hand, a polar resin with an excessively high acid value may 
bring the state of toner particle surfaces into disorder to cause a 
lowering of granulation properties. Hence, the polar resin should 
preferably have an acid value of from 20 to 100, and more preferably from 
30 to 80. Even with the acid value in the range of from 30 to 80, a polar 
resin with an Mw/Mn more than 10 may be accompanied with a difficulty in 
its uniform dispersion in monomers, tending to make it difficult to obtain 
the toner having the intended particle size distribution. Thus it is not 
preferable to use a polar resin having so extremely large Mw that it can 
not be uniformly dissolved in the monomers. The toner particle can not be 
concave also when the polymerization is carried out using, in place of the 
polar resin, polar monomers having a polar group. Polymerization carried 
out using a large quantity of such polar monomers rather tends to result 
in an extreme lowering of granulation properties. 
It is preferred to use a polar resin having an weight average molecular 
weight of from 10,000 to 200,000. 
The polar resin may be used in an amount of from 0.1 part by weight to 10 
parts by weight based on 100 parts by weight of polymerizable monomers. 
Use of the polar resin in an excessively small amount is not preferable 
since the toner particles may be less shaped. On the other hand, use of 
the polar resin in an excessively large amount makes it difficult to 
granulate a polymerizable monomer composition in an aqueous dispersion 
medium and makes it difficult to obtain toner particles with a sharp 
particle size distribution. 
In general, in the suspension polymerization, toner particles are formed by 
dispersing in a dispersion medium such as water a polymerizable monomer 
composition substantially incompatible therewith, followed by 
polymerization. In order to obtain a toner with a sharp particle size 
distribution, it is a very important subject how stably droplets of the 
polymerizable monomer composition having been suspended in this aqueous 
dispersion medium, i.e., polymerizable monomer composition particles, are 
kept constant in diameter in the course of the polymerization. 
To settle this subject, it is very important to find out dispersion 
stabilizers capable of imparting an appropriate surface tension to the 
interface between the droplets of a polymerizable monomer composition and 
the dispersion medium without adversely affecting environmental properties 
of toners as exemplified by moisture resistance. With regard to the 
dispersion stabilizers, the present applicant or assignee has proposed a 
method making use of a dispersion stabilizer that can make sharp the 
particle size distribution of toners and also may less affect the 
developing performance, which is a method of preparing a polymerized toner 
by using a slightly water-soluble inorganic dispersant and controlling the 
pH of a dispersion medium to give a toner with a preferable particle 
diameter (Japanese Patent Application Laid-open No. 63-198075). 
In the dispersion medium used in the present invention, a suitable 
dispersion stabilizer can be used. For example, as a dispersion stabilizer 
comprising a slightly water-soluble inorganic compound, it may include 
calcium phosphate, magnesium phosphate, aluminum phosphate, zinc 
phosphate, calcium carbonate, magnesium carbonate, calcium hydroxide, 
magnesium hydroxide, aluminum hydroxide, calcium metasilicate, calcium 
sulfate and barium sulfate. 
Such a slightly water-soluble inorganic compound may preferably have a 
particle diameter not larger than 3 .mu.m, and more preferably not larger 
than 2 .mu.m, as primary particles. 
These inorganic compounds may be in the form of powdered inorganic 
compounds, which may be used as they are. They may preferably be slightly 
water-soluble inorganic compounds produced in water in the presence of 
substances such as sodium phosphate and calcium chloride, which may be 
used as they are. The latter method is preferred in view of the advantage 
that inorganic compounds kept in the state of fine particles and having a 
good dispersibility can be readily obtained. 
In general, the agglomeration which the powdered, slightly water-soluble 
inorganic compounds undergo is usually in a strongly agglomerated state 
and also in such a state that the resulting agglomerates have non-uniform 
particle diameters. Hence, it is often necessary to carry out their 
dispersion in water with much care when such powder is used. However, use 
of the method in which the slightly water-soluble inorganic compound is 
produced in water as described above makes it possible to readily obtain a 
well dispersed state of the inorganic compound. 
Moreover, when the slightly water-soluble inorganic compound is produced in 
water in this way, a water-soluble neutral salt formed together with the 
slightly water-soluble inorganic compound is effective for both preventing 
polymerizable monomers from dissolving in water and making larger the 
specific gravity of the aqueous medium. 
Examples of the reaction to produce the slightly water-soluble inorganic 
compound are shown below. Examples are by no means limited to these. 
EQU 2Na.sub.3 PO.sub.4 +3CaCl.sub.2 .fwdarw.Ca.sub.3 (PO.sub.4).sub.2 +6NaCl(1) 
EQU 2Na.sub.3 PO.sub.4 +Al.sub.2 (SO.sub.4).sub.3 .fwdarw.2AlPO.sub.4 
+3Na.sub.2 SO.sub.4 (2) 
EQU 2Na.sub.3 PO.sub.4 +3ZnSO.sub.4 .fwdarw.Zn.sub.3 (PO.sub.4).sub.2 
+3Na.sub.2 SO.sub.4 (3) 
EQU Na.sub.2 PO.sub.3 +Zncl.sub.2 .fwdarw.ZnCO.sub.3 +2NaCl (4) 
EQU Na.sub.2 PO.sub.3 +ZnSO.sub.4 .fwdarw.ZnCO.sub.3 +Na.sub.2 SO.sub.4(5) 
In the method described above, the slightly water-soluble inorganic 
compound may optionally be used in combination of two or more kinds. Such 
a slightly water-soluble inorganic dispersant may preferably be used in an 
amount of from 1 to 20% by weight, and more preferably from 1 to 10% by 
weight, on the basis of the weight of the polymerizable monomer 
composition. 
Satisfactory results can be obtained in respect of the particle size 
distribution, toner particle shape and toner particle internal structure 
when calcium phosphate is used as the dispersion stabilizer, making the 
present invention more effective. 
The calcium phosphate may be in the form of powder, which may be used as it 
is. As previously described, it may preferably be calcium phosphate 
produced in water in the presence of substances such as sodium phosphate 
and calcium chloride, which may be used as it is. The latter method is 
preferred. 
Use of the latter method makes it possible to obtain a very fine salt to 
give a stable suspended state, resulting in good granulation properties. 
In respect of the toner particle shape, it becomes also possible to give a 
preferable size and number of concavities on the surface. Moreover, 
because of stable particles of the polymerizable monomer composition, the 
phase separation into component-A and component-B can be accelerated to 
greatly contribute the formation of the internal structure of toner 
particles and the promotion of the double-phase structure, as in the 
present invention. 
In the present invention, employed is a method in which, after it has been 
confirmed that the monomer composition particles thus formed have the 
desired particle size, the polymerization reaction is carried out while 
controlling the liquid temperature (for example, 55.degree. to 70.degree. 
C.) of the aqueous dispersion medium containing the particles, or a method 
in which the polymerization reaction is carried out simultaneously with 
the granulation and dispersion, while controlling the liquid temperature 
of the aqueous dispersion medium. 
After the polymerization reaction of the monomer composition has been 
completed, the reaction product may be post-treated by a conventional 
method using, for example, HCl, so that the toner produced by suspension 
polymerization (polymerized toner) can be obtained. For example, a 
Bronsted acid may be added to the system containing the polymer particles 
thus formed, to remove the powdery slightly water-soluble inorganic 
dispersant, and thereafter suitable means such as filtration, decantation 
and centrifugal separation may be carried out to collect the polymer 
particles, followed by drying. The toner can be thus obtained. 
The slightly water-soluble inorganic dispersant, which is soluble in the 
Bronsted acid used in the present invention, can be relatively readily 
removed from the toner particle surfaces upon the acid (or alkali) 
treatment mentioned above. 
Under existing circumstances, little study has been made on the correlation 
between hydrophilicization of toner particle surfaces which is 
attributable to the dispersion stabilizer remaining thereon, and charge 
performance of the toner. 
In the present invention, extensive studies made in this respect have 
revealed the following: The slightly water-soluble inorganic dispersant as 
described above can be removed by dropwise adding a Bronsted acid to the 
dispersion medium to lower the pH of the solution. If the acid is added in 
an isufficient amount or the post-treatment is in a short time, it can not 
be well removed, resulting in a lowering of charge performance to tend to 
make unstable the charge performance in a high-temperature and 
high-humidity environment. 
Especially when the polar resin is used, the dispersion stabilizer 
remaining has a remarkable influence. Although details are unclear, when 
the quantity of the remaining inorganic dispersant is varied by giving 
variety to the pH, the triboelectric charge performance of toners is 
lowered, in particular, the charge stability in a high-temperature and 
high-humidity environment is lowered in the case when the inorganic 
dispersant is present in a quantity more than 0.2% by weight on the basis 
of the weight of the polymerizable monomer composition. This tends to 
greatly occur in the case when the fluidity and charge performance are 
controlled using various external additives. This tendency is more 
remarkable in a system in which the inorganic dispersant is added in a 
little larger amount so that the toner can be made to have a smaller 
particle diameter. This is presumably because of water absorption in the 
remaining inorganic dispersant. 
On the other hand, complete absence of the inorganic dispersant on the 
toner particle surfaces results in an excessive quantity of 
triboelectricity of the toner when developing is carried out in a 
low-humidity environment, tending to cause charge-up. 
In the present invention, the inorganic dispersant or dispersion stabilizer 
remaining may preferably be controlled in an amount of from 0.005% by 
weight to 0.2% by weight, and more preferably from 0.01% by weight to 0.2% 
by weight, on the basis of the weight of the toner, by adding the acid 
such as HCl so as to adjust the pH of the dispersion medium to 3 or less 
(preferably 2.5 or less). 
The toner used in the present invention can be obtained, for example, by 
the following method. A release agent, a colorant, a charge control agent, 
a polymerization initiator and other additives are added to polymerizable 
monomers, which are then uniformly dissolved or dispersed using a 
homogenizer, an ultrasonic dispersion machine or the like to give a 
polymerizable monomer composition. The composition thus prepared is 
dispersed in an aqueous medium containing a dispersion stabilizer, using a 
conventional stirring machine or a high-shear mixer such as a homomixer or 
a homogenizer. Preferably the granulation is carried out by so controlling 
the stirring speed and time that the droplets of the monomer composition 
have the diameters corresponding to the desired particle diameters of 
toner particles, usually particle diameters of 30 .mu.m or less, e.g., 
from 1 to 20 .mu.m, and preferably from 4 to 10 .mu.m. Thereafter, the 
dispersion stabilizer acts to maintain the state of particles, where the 
stirring may be carried out to the extent that the particles are prevented 
from settling or floating. After the reaction has been completed, the 
dispersion stabilizer is removed, and the toner particles thus formed are 
washed and then collected by filtration, followed by drying. In the 
suspension polymerization, water may preferably be used as the dispersion 
medium usually in an amount of from 300 to 3,000 parts by weight based on 
100 parts by weight of the monomer composition. 
In the suspension polymerization described above, the polymerization may be 
carried out at a temperature of 40.degree. C. or higher, and preferably at 
a temperature set within the range of from 50.degree. to 90.degree. C. 
At this time, the polymerization temperature may be controlled in such a 
way that it is further raised by 5.degree. to 30.degree. C. during, i.e., 
at some time in the course of, the polymerization. Raising the temperature 
during the polymerization is effective for increasing the degree of 
concavities on the toner particle surfaces. Raising the temperature is 
also presumed to be contributory to the acceleration of the phase 
separation into phase-A and phase-B. 
The polymerization initiator may include, for example, azo or diazo type 
polymerization initiators such as 2,2'-azobis(2,4-dimethylvaleronitrile), 
2,2'-azobisisobutylonitrile, 1,1'-azobis(cyclohexane-1-carbonitrile), 
2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile, and 
azobisisobutylonitrile; and peroxide type polymerization initiators such 
as benzoyl peroxide, methyl ethyl ketone peroxide, diisopropyl 
peroxycarbonate, cumene hydroperoxide, 2,4-dichlorobenzoyl peroxide, and 
lauroyl peroxide. Any of these polymerization initiators may be used in an 
amount of from 0.5 to 20% by weight on the basis of the weight of the 
polymerizable monomers. 
In the present invention, a cross-linking agent may be added to the monomer 
composition. It may be added preferably in an amount of from 0.001 to 15% 
by weight on the basis of the weight of the polymerizable monomers. 
In the present invention, a charge control agent may preferably be 
previously added to the toner for the purpose of controlling charge 
performance of the toner. Among known charge control agents, those having 
little polymerization inhibitory action and little aqueous-phase shifting 
properties are used the charge control agent. For example, a positive 
charge control agent may include Nigrosine dyes, triphenylmethane dyes, 
quaternary ammonium salts, and amine or polyamine compounds. A negative 
charge control agent may include metal-containing salicylic acid 
compounds, metal-containing monoazo dye compounds, a styrene/acrylic acid 
copolymer, and a styrene/methacrylic acid copolymer. 
As the colorant used in the present invention, known colorants can be used, 
which are exemplified by dyes such as carbon black, C.I. Direct Red 1, 
C.I. Direct Red 4, C.I. Acid Red 1, C.I. Basic Red 1, C.I. Mordant Red 30, 
C.I. Direct Blue 1, C.I. Direct Blue 2, C.I. Acid Blue 9, C.I. Acid Blue 
15, C.I. Basic Blue 3, C.I. Basic Blue 5, C.I. Mordant Blue 7, C.I. Direct 
Green 6, C.I. Basic Green 4, and C.I. Basic Green 6; and pigments such as 
chrome yellow, cadmium yellow, Mineral Fast Yellow, Navel Yellow, Naphtol 
Yellow S, Hanza Yellow G, Permanent Yellow NCG, Tartrazine Yellow Lake, 
molybdenum orange, Permanent Orange GTR, Benzidine Orange G, cadmium red, 
Permanent Red 4R, Watchung Red calcium salt, Brilliant Carmine 3B, Fast 
Violet B, Methyl Violet Lake, prussian blue, cobalt blue, Alkali Blue 
Lake, Victoria Blue Lake, quinacridone, Rhodamine Lake, Phthalocyanine 
Blue, Fast Sky Blue, Pigment Green B, Malachite Green Lake, and Final 
Yellow Green G. 
Since in the present invention the toner is obtained by suspension 
polymerization, care must be taken on the polymerization inhibitory action 
and aqueous-phase shifting properties inherent in colorants. The colorant 
should preferably be previously surface-modified, for example, treated to 
be made hydrophobic using a material having no polymerization inhibitory 
action. In particular, since most of dyes or carbon black have 
polymerization inhibitory action, care must be taken when they are used. A 
preferable method for the surface treatment of dyes may include a method 
in which polymerizable monomers are previously polymerized in the presence 
of any of these dyes, where the resulting colored polymer may preferably 
be added to the monomer composition. With regard to carbon black, it may 
be subjected to the same treatment as the above dyes, or, alternatively, 
to graft treatment using a material capable of reacting with surface 
functional groups of carbon black, as exemplified by polyorganosiloxane. 
In the present invention, a magnetic material may be added to the toner 
particles, which may preferably be used after application of similar 
surface treatment. 
The additives used in the present invention for the purpose of providing 
various properties may preferably have a particle diameter of not more 
than 1/10 of the weight average particle diameter of the toner particles 
in view of the durability required when added to the toner. The particle 
diameter of the additives refers to an average particle diameter 
determined by observing toner particle surfaces using an electron 
microscope. The additives used for the purpose of providing the desired 
properties can be exemplified by the following. Examples are by no means 
limited to these. 
1) The fluidity-providing agent may preferably include metal oxides such as 
silicon oxide, aluminum oxide and titanium oxide, carbon black, and 
fluorocarbon, all of which may more preferably having been subjected to 
hydrophobic treatment. 
2) The abrasive may preferably include metal oxides such as strontium 
titanate, cerium oxide, aluminum oxide, magnesium oxide and chromium 
oxide, nitrides such as silicon nitride, carbides such as silicon carbide, 
metal salts such as calcium sulfate, barium sulfate and calcium carbonate. 
3) The lubricant may preferably include fluorine type resin powders such as 
vinylidene fluoride and polytetrafluoroethylene, and fatty acid metal 
salts such as zinc stearate and calcium stearate. 
4) Charge control particles may preferably include metal oxides such as tin 
oxide, titanium oxide, zinc oxide, silicon oxide and aluminum oxide. 
These additives may be used in an amount of from 0.1 part by weight to 10 
parts by weight, and preferably from 0.1 part by weight to 5 parts by 
weight, based on 100 parts by weight of the toner. These additives may be 
used alone or in combination of plural ones. 
As previously described, the toner of the present invention has a plurality 
of concavities on the surface of its each particle. An example of the 
shape of the toner particle surface is shown in FIG. 1. Because of such a 
plurality of concavities, the carrier and the sleeve can be better 
prevented from being contaminated. The presence of the concavities on the 
surfaces of toner particles also contributes an improvement in cleaning 
performance. Moreover, since the toner particle is approximate to a 
sphere, a toner image with a high image quality can be obtained. Since 
also no pulverization or size reduction of toner particles tends to occur 
because of their vigorous motion in a developing assembly, any fogging or 
toner scatter due to fine powder does not occur. 
The image forming method of the present invention can be carried out using, 
for example, the developing apparatus shown in FIG. 5. In the developing 
apparatus shown in FIG. 5, a bias electric field comprised of an AC 
component and a DC component is applied across a developer carrying member 
(a sleeve) and a latent image bearing member (a photosensitive member). 
This brings toner and magnetic particles into a state of vigorous 
oscillation and flying. Such oscillation and flying of toner and magnetic 
particles bring about the following advantages. 
That is, development efficiency becomes very high since the developing is 
carried out by causing the toner to fly from both a magnetic brush and the 
surface of the developer carrying member. Hence the coating weight of 
developer can be relatively small, and the resolution of a developed image 
can be improved. Because of the high development efficiency, it is 
possible to make substantially equal the relative speed between the 
developer carrying member and the photosensitive member, and hence any 
sweep-up at a developed solid image area does not tend to occur, which may 
occur when a relative speed is made. There is another advantage that the 
sweep-up can be decreased even when the relative speed is made. 
Since the magnetic particles undergo oscillation attributable to the 
alternating electric field, no line marks of the magnetic brush does not 
occur and hence a developed image with a very high image quality can be 
obtained. Moreover, application of the alternating electric field 
necessary only for the magnetic particles to move across the space defined 
by the developer carrying member and the photosensitive member allows the 
magnetic particles to behave together with the toner at image areas when 
they fly in the manner stated above, so that development an be 
accelerated. At background areas, the magnetic particles behave conversely 
to the toner to become effective for separating the toner having adhered 
to the surface of the photosensitive member, so that fogging can be 
prevented. Furthermore, the magnetic particles having adhered to the 
surface of the photosensitive member can also be finally drawn back to the 
side of the developer carrying member by the magnetism and the mobile 
force attributable to the electric field thereby produced, so that the 
quantity of magnetic particles adhering to the photosensitive member can 
be decreased. Even when ears formed of magnetic particles are localized, 
they collapse in part when magnetic particles fly, to bring about an 
effect of leveling the magnetic particles. 
Now, the volume percentage of magnetic particles in the developing zone 
will be described with reference to FIGS. 6 and 7. The "developing zone" 
is meant to be an area in which a toner 5 (FIG. 5) is transferred or fed 
from a developer carrying member (a sleeve) 3 to a photosensitive drum (a 
latent image bearing member) 4. The "volume percentage" refers to 
percentage of the volume held by magnetic particles 6 present in this 
developing zone, with respect to the capacity of that zone. As a result of 
various experiments and examinations, it has been discovered that this 
volume percentage has an important influence in the above developing 
apparatus and that it is very preferable for the percentage to be set 
within the range of from 10% to 45%, and particularly from 15% to 28%. A 
volume percentage less than 10% is not preferable in view of the 
disadvantages that developed image density may decrease, sleeve ghost may 
occur, a remarkable density difference may occur between a portion at 
which ears are present and a portion at which they are absent, and the 
thickness of a developer layer formed on the sleeve surface may become 
uneven as a whole. On the other hand, a volume percentage more than 45% is 
not preferable in view of the disadvantage that the magnetic particles may 
shut up the sleeve surface to cause fogging. 
In particular, the present invention is not based on the fact that image 
quality is incrementally deteriorated or improved with an increase or 
decrease of the volume percentage, but based on the facts that a 
sufficient image density can be obtained when the volume percentage is in 
the range of from 10% to 45%, a lowering of image quality occurs when it 
is either less than 10% or more than 45%, and also neither sleeve ghost 
nor fogging occurs when it is within the above numerical range in which 
the image quality can be satisfactory. The former lowering of image 
quality is presumed to be due to negative properties, and the latter 
sleeve ghost or fogging is presumed to result from the fact that the 
magnetic particles become present in too large a quantity to open the 
sleeve surface and hence the quantity of toner fed from the sleeve surface 
greatly decreases. 
If the volume percentage is less than 10%, line-image reproduction may 
become poor and image density may greatly decrease. On the other hand, if 
it is more than 45%, problems may arise such that the magnetic particles 
may scratch the surface of the photosensitive drum and unwanted transfer 
and fixing may be caused by magnetic particles adhering to drum surface as 
part of an image. 
In instances in which the magnetic particles are present in a volume 
percentage close to 10%, there is a possibility (in a special environment) 
that uneven development partly occurs when a uniformly high-density image 
with a large area (a solid black image) is reproduced. Hence, it is 
preferable for the magnetic particles to be in a volume percentage not 
tending to cause such uneven development. 
This preferable value is such that the magnetic particles have a volume 
percentage of not less than 15% with respect to the developing zone. The 
range thereby defined is a more preferable range. In instances in which 
the magnetic particles are present in a volume percentage close to 45%, 
there is a possibility (at the time of a high developing speed) that the 
feeding of toner from the sleeve surface is delayed at the circumference 
of the part with which an ear formed of magnetic particles comes into 
contact, to cause scaly uneven density when a solid black image is 
reproduced. A sure range within which this possibility can be avoided is 
such that the magnetic particles have a volume percentage of not more than 
28%, which is a more preferable upper limit. 
So long as the volume percentage is in the range of from 10% to 45%, ears 
9, as shown in FIG. 6, can be formed in such a state that they are 
scattered to a preferable extent, so that the toner present on both the 
sleeve 3 and the ears 9 can be sufficiently open to the photosensitive 
drum 4 and the toner on the sleeve can also fly and transfer through the 
alternating electric field, bringing about the state that almost all the 
toner can be consumed for development. This makes it possible to achieve a 
high development efficiency (a proportion of the toner consumed for 
development, to the toner present in the developing zone) and a high image 
density. 
The volume percentage (%) of magnetic particles present in the developing 
zone can be determined according to the expression: 
EQU (M/h).times.(1/.rho.).times.[C/(T+C)].times..sigma..times.100 
wherein M represents a coating weight (g/cm.sup.2) of developer (a mixture, 
when no ear rises) per unit area of the sleeve, h represents a height (cm) 
of the space at the developing zone, .rho. represents a degree of true 
density (g/cm.sup.3) of magnetic particles, C/(T+C) represents a weight 
proportion of magnetic particles in the developer present on the sleeve, 
and .sigma. represents a ratio of peripheral speed of the photosensitive 
drum to that of the sleeve (sleeve peripheral speed/photosensitive drum 
peripheral speed). In the developing zone in the above definition, the 
toner may preferably be in an amount of from 3 to 40% by weight based on 
the weight of the magnetic particles. 
The magnetic particles used in the present invention may preferably have a 
narrow particle size distribution and be sharp-cut. A phenomenon in which 
the magnetic particles 6 adhere to the photosensitive drum 4 to adversely 
affect images or copying machines, i.e., what is called carrier adhesion, 
tends to occur when ultrafine magnetic particles are present. However, the 
magnetic particles used in the present invention are sharp-cut to have a 
400 mesh or less fine-powder content of not more than 20% by weight, and 
hence the carrier adhesion can be preferably prevented. The fine-powder 
content may more preferably be not more than 15% by weight. 
In the present invention, it is preferable to use magnetic particles having 
a uniform particle size, i.e., having a 250 mesh or more coarse-powder 
content of not more than 20% by weight, and more preferably not more than 
10% by weight. This brings about an improved fluidity required as 
developer, so that toner and magnetic particles can be swiftly blended 
when the toner is fed. As a result, the distribution of toner charge also 
becomes sharp, so that a fog-free high-quality image can be obtained and 
also no toner scatter occurs. Moreover, because of an improvement in 
development efficiency and transfer efficiency, waste toner percentage 
decreases to promise an efficient toner consumption. On the other hand, 
magnetic particles with a uniform particle size have so good a packing 
structure that the carrier-wear is accelerated. 
In the case of two-component developers, the toner particles each having a 
plurality of concavities on the particle surface may be used in 
combination, thereby making it possible to prepare a developer not tending 
to make the carrier worn out. 
An example of another image forming apparatus used in the present invention 
will be described below with reference to FIG. 8. In FIG. 8, reference 
numeral 21 denotes a latent image bearing member (a photosensitive drum), 
on which a latent image is formed through an electrophotographic process 
means or electrostatic recording means (not shown). Reference numeral 22 
denotes a developer carrying member (a developer sleeve), comprised of a 
non-magnetic sleeve made of aluminum, stainless steel or the like. Such a 
developer carrying member 22 may be comprised of a crude pipe of aluminum 
or stainless steel used as it is, whose surface may preferably be 
uniformly roughed by spraying thereon glass beads or the like, 
mirror-finished, or coated with resin or the like. It is more preferable 
to use a developer carrying member having a surface layer comprised of a 
resin layer in which fine particles with a lubricity as exemplified by 
graphite particles have been dispersed. Developer is reserved in a hopper 
23, and fed onto the developer carrying member 22 by means of a feed 
roller 24. The feed roller 24 is made of a foamed material such as 
polyurethane foam, and is rotated at a relative speed which is not zero in 
the normal or reverse direction with respect to the developer carrying 
member 22. This feed roller not only feeds the developer but also takes 
off developer (developer having not participated in development) remaining 
on the developer carrying member 22 after development. 
The developer fed onto the developer carrying member 22 is coated in a 
uniform and thin layer by means of a developer coating blade 25. It is 
effective for the developer coating blade 25 and the developer carrying 
member 22 to be brought into contact at a contact pressure of from 3 to 
250 g/cm, and preferably from 10 to 120 g/cm, as a linear pressure in the 
mother line direction of the sleeve. A contact pressure smaller than 3 
g/cm tends to make it difficult for the developer to be uniformly coated 
and tends to result in a broad distribution of charges of the developer to 
cause fogging or toner scatter. A contact pressure larger than 250 g/cm is 
not preferable since the developer tends to undergo agglomeration of 
particles because of a large pressure applied to the toner and a 
deterioration of external additives of the developer. Such a contact 
pressure is also not preferable since a large torque must be applied in 
order to drive the developer carrying member 22. 
As the developer coating blade 25, it is preferred to use a blade made of a 
material of a triboelectric series suited for the developer to be 
electrostatically charged in the desired polarity. For example, in order 
for the developer to be positively charged, silicone rubber, polyurethane, 
fluorine rubber or polychlorobutadiene rubber may be used and, in order 
for the developer to be negatively charged, styrene butadiene rubber or 
nylon may be used as the blade, whereby the triboelectric charge 
efficiency of the developer can be more improved. Silica or fine resin 
particles may also blended to control the properties of the blade that 
imparts triboelectric charge to the developer. Conductive powder such as 
carbon or titanium oxide may also be blended to provide the blade with an 
appropriate conductivity so that the developer can be prevented from being 
charged in excess. 
The toner heat fixing method according to the present invention can be 
carried out using a fixing device as shown in FIG. 9 or 10. In the fixing 
device shown in FIG. 9 or 10, a heater element has a smaller heat capacity 
than conventional heat rolls, and has a linear heating part. The heating 
part may preferably be made to have a maximum temperature of from 
100.degree. C. to 300.degree. C. A film, which is interposed between the 
heater element and a pressure member, may preferably comprise a 
heat-resistant sheet of from 1 to 100 .mu.m in thickness. The 
heat-resistant sheet that can be used therefor may include sheets of 
polymers having high heat-resistance, such as polyester, PET (polyethylene 
terephthalate), PFA (a tetrafluoroethylene/perfluoroalkyl vinyl ether 
copolymer), PTFE (polytetrafluoroethylene), polyimide and polyamide, 
sheets of metals such as aluminum, and laminate sheets comprised of a 
metal sheet and a polymer sheet. 
In an embodiment of the film according to the present invention, any of 
these heat-resistant sheets have a release layer and/or a low-resistance 
layer. The film may preferably have, as surface properties of its surface 
coming into pressure contact with a recording medium, a critical surface 
tension of not more than 30 dyne/cm and a surface electrical resistance of 
not more than 10.sup.10 .OMEGA./cm.sup.2. 
As the film applied to the present invention, it is more preferable to use 
a multi-layer coated film comprised of a heat-resistant material sheet 
comprising polyimide, polyetherimide, PES or PFA, with one side of which 
the heat element comes into pressure contact, and a low-resistance release 
layer provided at least on the side coming into contact with the image, 
comprising a binder resin such as PTFE or PFA having a critical surface 
tension of not more than 30 dyne/cm and to which a conductive material is 
added and dispersed to have a surface electrical resistance of not more 
than 10.sup.10 .OMEGA./cm.sup.2. The conductive material for controlling 
the surface electrical resistance, preferably used in the present 
invention, may include carbon black, graphite and inorganic oxides. 
If the film used in the heat fixing method of the present invention has a 
critical surface tension more than 30 dyne/cm on the side coming into 
pressure contact with a recording medium, what is called offset phenomenon 
may seriously occur, which is a phenomenon in which toner adheres to the 
film surface. Similarly, if its surface electrical resistance is more than 
10.sup.10 .OMEGA./cm.sup.2, a static offset phenomenon may seriously 
occur, which is a phenomenon in which toner electrostatically adhere to 
the film surface. The surface electrical resistance in the present 
invention can be measured according to the method as prescribed in JIS 
K6911. 
The critical surface on the side coming into pressure contact with a 
recording medium, referred to in the present invention, can be determined 
by measuring contact angles .theta. which various organic liquids of 
hydrocarbon types and other types having different surface tension .gamma. 
make on the film surface, and performing Zisman plotting. 
A preferred heat fixing unit or device used in the present invention will 
be described below with reference to the accompanying drawings. The 
following by no means limit the present invention. FIG. 9 illustrates a 
structure of such a heat fixing device. 
Reference numeral 36 denotes a low heat capacitance linear heater element 
stationarily supported in the device. An example thereof comprises an 
alumina substrate 37 of 1.0 mm in thickness, 10 mm in width and 240 mm in 
longitudinal length and a resistance material 38 coated thereon in a width 
of 1.0 mm, which is electrified from the both ends in the longitudinal 
direction. The electricity is applied under variations of pulse widths of 
the pulses corresponding with the desired temperatures and energy emission 
quantities which are controlled by a temperature sensor 39, in the 
pulse-like waveform with a period of 20 msec of DC 100 V. The pulse widths 
range approximately from 0.5 msec to 5 msec. In contact with the heater 
element 36 the energy and temperature of which have been controlled in 
this way, a fixing film 30 moves in the direction of the arrow shown in 
the drawing. An example of this fixing film is an endless film comprised 
of heat-resistant sheet of 20 .mu.m thick comprising, for example, 
polyimide or imide, with one side of which the heat element comes into 
pressure contact, and a release layer comprising PTFE to which carbon 
black is added as a conductive material, coated on the side coming into 
contact with the image to have a thickness of 10 .mu.m. This film has a 
critical surface tension of 20 dyne/cm and a surface electrical resistance 
of 1.times.10.sup.6 .OMEGA./cm.sup.2 on the side coming into pressure 
contact with a recording medium. In general, the total thickness of the 
film may preferably be less than 100 .mu.m, and more preferably less than 
40 .mu.m. 
The film is moved in the direction of the arrow in a wrinkle-free state by 
the action of the drive of, and tension between, a drive roller 31 and a 
follower roller 32. Reference numeral 33 denotes a pressure roller having 
on its surface an elastic layer of rubber with good release properties as 
exemplified by silicone rubber. This pressure roller is pressed against 
the heater element at a total pressure of 4 to 20 kg through the film 
interposed between them and is rotated in pressure contact with the film. 
Toner 35 having not been fixed on a transfer medium 34 is led to the 
fixing zone by means of an inlet guide 36. A fixed image is thus obtained 
by the heating described above. 
The above has been described with reference to an embodiment in which the 
fixing film comprises the endless belt. As shown in FIG. 10, a 
sheet-feeding shaft 47 and a wind-up shaft 48 may also be used, and the 
fixing film may not be endless. 
The image forming apparatus includes apparatus that form an image by the 
use of a toner, as exemplified by copying machines, printers, and 
facsimile apparatus, to all of which the present fixing device can be 
applied. 
When the temperature detected by the temperature sensor 39 in the low heat 
capacitance linear heater element 36 is T.sub.1, the surface temperature 
T.sub.2 of the film 30 opposed to the resistance material 38 is about 
10.degree. to 30.degree. C. lower than T.sub.1. The surface temperature 
T.sub.3 of the film on the part at which the film 30 is separated from the 
toner-fixed face is a temperature substantially equal to the above 
temperature T.sub.2. 
The particle size distribution in the present invention is measured in the 
following way. 
A Coulter counter Type-II (manufactured by Coulter Electronics, Inc.) is 
used as a measuring device. An interface (manufactured by Nikkaki) that 
outputs number average distribution and volume average distribution and a 
personal computer CX-I (manufactured by Canon) are connected. As an 
electrolytic solution, an aqueous 1% NaCl solution is prepared using 
first-grade sodium chloride. 
Measurement is carried out by adding as a dispersant 0.1 ml to 5 ml of a 
surface active agent, preferably an alkylbenzene sulfonate, to 100 ml to 
150 ml of the above aqueous electrolytic solution, and further adding 0.5 
mg to 50 mg of a sample to be measured. The electrolytic solution in which 
the sample has been suspended is subjected to dispersion for 1 minute to 3 
minutes in an ultrasonic dispersion machine. The particle size 
distribution of particles of 2 .mu.m to 40 .mu.m is measured on the basis 
of the number by means of the above Coulter counter Type TA-II, using an 
aperture of 100 .mu.m as its aperture, and then the volume average 
particle diameter and number average distribution are determined. 
From these volume average particle diameter and number average distribution 
thus determined, weight average particle diameter (D4) is obtained. 
The melting point of the low softening point material such as wax in the 
present invention is measured using a differential scanning calorimeter 
DSC-7 (manufactured by Perkin-Elmer Co.), at a rate of temperature rise of 
10.degree. C./min. In the DSC curve of the first temperature rise, the 
temperature corresponding to a maximum endothermic peak is regarded as the 
melting point of wax. 
The melt characteristics of the toner in the present invention is measured 
using an overhead-type flow tester (Shimadzu Flow Tester CFT-500 Type). A 
sample in a weight of 1.0 g molded using a pressure molder is extruded 
from a nozzle of 1 mm in diameter and 1 mm in length under application of 
a load of 20 kgf using a plunger at temperatures rising at a rate of 
5.0.degree. C./min, during which the fall quantity of the plunger of the 
flow tester is measured. Here, the temperature at which the sample begins 
to flow out in the plunger fall quantity-temperature curve of the flow 
tester is regarded as the flow-out temperature. 
The molecular weight in the present invention is measured by the method 
described below. 
(1) Preparation of sample: 
i) Standard sample: 
Commercially available standard polystyrenes shown below are used as 
standard samples. 
______________________________________ 
Molecular weight 
Manufacturer 
______________________________________ 
8.42 .times. 10.sup.6 
Toyo Soda Manufacturing Co., Ltd. 
2.7 .times. 10.sup.6 
Waters Co. 
1.2 .times. 10.sup.6 
Waters Co. 
7.75 .times. 10.sup.5 
Toyo Soda Manufacturing Co., Ltd. 
4.7 .times. 10.sup.5 
Waters Co. 
2.0 .times. 10.sup.5 
Waters Co. 
3.5 .times. 10.sup.4 
Waters Co. 
1.5 .times. 10.sup.4 
Waters Co. 
1.02 .times. 10.sup.4 
Toyo Soda Manufacturing Co., Ltd. 
3.6 .times. 10.sup.3 
Waters Co. 
2.35 .times. 10.sup.3 
Waters Co. 
5.0 .times. 10.sup.2 
Toyo Soda Manufacturing Co., Ltd. 
______________________________________ 
These twelve standard polystyrenes are divided into the following three 
groups. 
(a) 8.42.times.10.sup.6, 7.75.times.10.sup.5, 3.5.times.10.sup.4, 
3.6.times.10.sup.3 
(b) 2.7.times.10.sup.6, 4.7.times.10.sup.5, 1.5.times.10.sup.4, 
2.35.times.10.sup.3 
(c) 1.2.times.10.sup.6, 2.0.times.10.sup.5, 1.02.times.10.sup.4, 
5.0.times.10.sup.2 
In a 30 ml sample bottle, four samples of each group are taken in an amount 
of about 3 mg (a quantity corresponding to a micro-spatula) for each, and 
15 ml of THF is added thereto, which are then left to stand at room 
temperature for 4 hours (during which the bottle is vigorously shaken for 
one minute at intervals of 30 minutes). Subsequently, its contents are 
filtered using a membrane filter (regenerated cellulose, 0.45 .mu.m; 
available from Toyo Roshi). Standard sample are thus prepared. 
ii) Unknown: 
Each sample weighed in an amount of 60 mg is put in a sample bottle, and 15 
ml of THF is further added. Extraction is carried out in the following 
way: The bottle is left to stand at room temperature for 24 hours, while 
it is shaken at intervals of 30 minutes for the first 3 hours. Ultrasonic 
treatment is further applied for 15 minutes to sufficiently effect 
extraction. Insoluble matters are sedimented by centrifugal separation 
(5,000 rpm/20 min.). The resulting supernatant is filtered using a 
membrane filter (regenerated cellulose, 0.45 .mu.m; available from Toyo 
Roshi). Sample are thus prepared. 
(2) GPC: 
Using 150C ALC/GPC (Waters Co.) as an apparatus, measured under the 
following conditions. 
i) Solvent: THF (special grade; Kishida Chemical Co., Ltd.) 
ii) Column: Combination of 4 columns, Showdex A-802, A-803, A-804, A-805 
(Showa Denko K. K.) 
iii) Temperature: 28.degree. C. 
iv) Flow velocity: 1.0 ml/min. 
v) Pour: 0.5 ml 
vi) Detector: RI 
(3) GPC data processing: 
i) Calibration curve: 
(a) Chromatograms of each standard sample are taken, and the retention time 
of a peak is read. In instances in which several peaks are present, the 
time of the main peak is read. 
(b) A calibration curve is prepared from the molecular weight of each 
standard sample and the peak retention time. 
ii) Unknown: 
Chromatograms of each unknown sample are taken, and its molecular weight is 
calculated form the peak retention time, using the calibration curve. 
The particle size distribution of the magnetic particles is measured by the 
method described below. 
1. About 100 g of a sample is weighed to a precision of 0.1 g. 
2. As sieves, 100 mesh to 400 mesh standard sieves (hereinafter "sieve(s)") 
are used and are overlaid one another in order of 100 mesh, 145 mesh, 200 
mesh, 250 mesh, 350 mesh and 400 mesh so that the 100 mesh sieve is 
uppermost. A dish is placed at the bottom. The sample is placed on the 
uppermost sieve, which is then covered. 
3. The sample is sieved using a vibrator for 15 minutes at a horizontal 
swing number of 285+6 per minute and and an impulse number of 150.+-.10 
per minute. 
4. After the sieving, iron powder on each sieve and the dish is weighed to 
a precision of 0.1 g. 
5. Size is calculated to two decimals in weight percentage, and 
calculations are rounded to one decimal. 
The frame of the sieves is 200 mm in inner diameter at the upper portion 
from the sieve surface and 45 mm in depth from the top to the sieve 
surface. 
The total weight of the iron powder on each part must be more than 99% of 
the mass of the sample initially taken. The average particle diameter is 
calculated according to the following equation, on the basis of the above 
measured values of particle size distribution. 
##EQU1## 
EXAMPLES 
The present invention will be described below in greater detail by giving 
Examples. 
Example 1 
In 709 parts by weight of ion-exchanged water 451 parts by weight of an 
aqueous 0.1M Ne.sub.3 PO.sub.4 solution was introduced, followed by 
heating to 60.degree. C. and then stirring at 12,000 rpm using a TK-type 
homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.). To the resulting 
mixture, 67.7 parts by weight of an aqueous 1.0M CaCl.sub.2 solution was 
added little by little to give a dispersion medium containing Ca.sub.3 
(PO.sub.4).sub.2. 
______________________________________ 
(by weight) 
______________________________________ 
Styrene 170 parts 
2-Ethylhexyl acrylate 30 parts 
Paraffin wax (m.p.: 75.degree. C.) 
60 parts 
C.I. Pigment Blue 15:3 10 parts 
Styrene/methacrylic acid/methyl methacrylate co- 
10 parts 
polymer (Mw: 51,000; Mw/Mn: 3.0; acid value: 70) 
Di-tert-butylsalicyclic acid metal compound 
3 parts 
______________________________________ 
Of the above materials, only C.I. Pigment Blue 15:3, di-tert-butylsalicylic 
acid metal compound and styrene were premixed using Ebara Milder 
(manufactured by Ebara Corporation). Next, all the above materials were 
heated to 60.degree. C., followed by dissolution and dispersion to give a 
monomer mixture. While the monomer mixture thus prepared was maintained at 
60.degree. C. 10 parts by weight of a polymerization initiator dimethyl 
2,2'-azobisisobutylate was added and dissolved. Thus a polymerizable 
monomer composition was prepared. 
The above monomer composition was introduced in the dispersion medium 
prepared in a flask of the TK homomixer. Using the TK homomixer, made to 
have an atmosphere of nitrogen, stirring was carried out at 60.degree. C. 
and at 10,000 rpm for 20 minutes to granulate the monomer composition. 
Thereafter, while stirring with a paddle agitating blade, reaction was 
carried out at 60.degree. C. for 3 hours, and then at 80.degree. C. for 
further 10 hours to complete polymerization. 
After the polymerization was completed, the reaction system was cooled, and 
27 parts by weight of 5N hydrochloric acid was added thereto, followed by 
further stirring with the paddle stirring blade for 2 hours. After the 
Ca.sub.3 (PO.sub.4).sub.2 was thus dissolved, filtration and washing with 
water were repeated several times, and finally the product was dried. A 
toner produced by suspension polymerization was thus obtained. 
The quantity of Ca.sub.3 (PO.sub.4).sub.2 remaining on toner particle 
surfaces was determined by X-ray fluorometry to reveal that it was in a 
quantity of 0.1% by weight based on the toner. 
Particle diameters of the resulting toner were measured with a Coulter 
counter to reveal that the toner had a weight average particle diameter of 
8.2 .mu.m and also had a sharp particle size distribution. Observation 
using an electron microscope confirmed that toner particles each had on 
their surfaces a plurality of concavities as shown in FIG. 1. The R/r of 
the toner particles was 1.10 and L/2.pi.r was 1.20. Cross sections of the 
toner particles were observed on a transmission electron microscope by a 
method using dyed ultra-thin sections. As a result, it was confirmed that 
the particles were each structurally separated into the surface layer 
mainly composed of styrene-acrylic resin and the center mainly composed of 
wax and that the phase mainly composed of wax was absent in the vicinity 
of each toner particle surface ranging from its surface to a depth 0.15 
time a toner particle diameter and was in the range of from 10% to 45% of 
the cross-sectional area of the particle. 
Based on 100 parts by weight of the toner obtained, 0.7 part by weight of 
hydrophobic silica having a specific surface area of 200 m.sup.2 /g as 
measured by the BET method was externally added. Next, 7 parts by weight 
of the toner to which the hydrophobic silica had been externally added and 
93 parts by weight of a Cu-Zn-Fe ferrite carrier having been 
surface-coated with a styrene/methyl methacrylate copolymer were blended 
to give a two-component developer. 
Using this developer, images were reproduced on a modified machine of a 
color copier (CLC-500; manufactured by Canon Inc.), which was so modified 
that no silicone oil was applied to its fixing roller. Results obtained 
are shown in Table 1. 
Examples 2 to 11 and 29 
Various toners were prepared in the same manner as in Example 1 except that 
their formulations were changed as shown in Table 1. Their performances 
were evaluated. Results obtained are shown in Table 1. 
Example 12 
A toner was prepared in the same manner as in Example 1 except that the 
polymerization reaction temperature was set constant at 60.degree. C. 
Results obtained are shown in Table 1. 
Comparative Example 1 
A toner was prepared in the same manner as in Example 1 except that the 
amount of paraffin wax was changed. Cross sections of toner particles were 
observed to reveal that the phase mainly composed of wax was more than 45% 
of the cross-sectional area of each toner particle. Results are shown in 
Table 2. 
Comparative Examples 3 to 6, 8 and 9 
Various toners were prepared according to the formulation shown in Table 2, 
and their performances were evaluated. Results obtained are shown in Table 
2. 
Comparative Example 7 
A toner was prepared in the same manner as in Example 1 except that the 
amount of paraffin wax was changed. Cross sections of toner particles were 
observed to reveal that the phase mainly composed of wax was less than 10% 
of the cross-sectional area of each toner particle. Results are shown in 
Table 2. 
Comparative Example 10 
Toner particles were obtained in the same manner as in Example 1 except 
that the post-treatment making use of the aqueous HCl solution was not 
made. The quantity of Ca.sub.3 (PO.sub.4).sub.2 remaining on toner 
particle surfaces was determined by X-ray fluorometry to reveal that it 
was in a quantity of 2.5% by weight based on the toner. 
Using this toner, images were reproduced. As a result, the developer showed 
so extremely poor a fluidity in a high-temperature high-humidity 
environment that the image reproduction was stopped halfway. It also gave 
so low a quantity of triboelectricity in a low-temperature low-humidity 
environment that the images obtained were much fogged and coarse. 
Example =b 30 
As a dispersion stabilizer 10 parts by weight of amino-modified colloidal 
silica (200 m.sup.2 /g) was used in place of Ca.sub.3 (PO.sub.4).sub.2, 
and was added to 1,200 parts by weight of water to give an aqueous 
dispersion medium. 
Suspension polymerization was carried out in the same manner as in Example 
1 except that the aqueous dispersion medium thus obtained was used. After 
the colloidal silica was removed using an aqueous NaOH solution, 
filtration and washing with water were repeated several times followed by 
drying to give a toner. Results are shown in Table 2. 
TABLE 1 
______________________________________ 
Low 
Polar resin softening 
Ex- Acid value point 
ample: 
Mw Mw/Mn (mgKOH/g) 
Amount material 
______________________________________ 
1 51,000 3.0 70 5* 30* 
2 102,000 4.5 50 5 20 
3 102,000 7.0 50 5 20 
4 102,000 4.5 25 5 20 
5 102,000 4.5 90 5 20 
6 20,000 2.0 50 5 20 
7 151,000 4.5 50 5 20 
8 51,000 3.0 70 5 8 
9 51,000 3.0 70 5 40 
10 51,000 3.0 70 0.5 30 
11 51,000 3.0 70 10 30 
12 51,000 3.0 70 5 30 
29 102,000 10.5 50 5 20 
30 51,000 3.0 70 5 30 
______________________________________ 
Par- Fix- 
Presence ticle Block- 
ing Dur- 
of size ing per- a- 
Ex- concav- distri- 
resis- 
form- bil- 
ample: 
ities R/r L/2.pi.r 
bution 
tance ance ity 
______________________________________ 
1 A 1.10 1.20 A AA A AA 
2 A 1.05 1.18 A AA A AA 
3 A 1.08 1.19 A A A A 
4 B 1.03 1.03 A A A B 
5 A 1.18 1.80 B AA A A 
6 B 1.06 1.10 B AA A B 
7 A 1.08 1.20 B AA A A 
8 A 1.09 1.15 A AA B AA 
9 A 1.10 1.20 A A A A 
10 B 1.05 1.11 A A A B 
11 A 1.11 1.21 B AA A A 
12 B 1.04 1.09 A A A B 
29 A 1.08 1.18 B B A B 
30 B 1.01 1.0 A B A B 
______________________________________ 
*part(s) by weight 
Evaluation: 
Presence of concavities: 
(Average number of concavities per toner particle in a visual field) 
A: 5 or more, B: 2 to 4, C: 0 to 1 
Particle size distribution: 
A: Very sharp distribution 
B: No difficulty in practical use 
C: Requires classification 
Blocking resistance: 
AA: 50.degree. C., 7 days or more all right 
A: 50.degree. C., 5 days or more all right 
B: 50.degree. C., 3 days or more all right 
C: 50.degree. C., less than 3 days 
Fixing performance: 
A: Very good 
B: No difficulty in practical use 
C: A difficulty in practical use 
Durability: 
AA: Very good 
A: Good 
B: No difficulty in practical use 
C: A difficulty in practical use 
TABLE 2 
______________________________________ 
Com- 
para- Low 
tive Polar resin softening 
Ex- Acid value point 
ample: 
Mw Mw/Mn (mgKOH/g) 
Amount material 
______________________________________ 
1 51,000 3.0 70 5* 60* 
3 102,000 4.5 10 5 20 
4 102,000 4.5 120 5 20 
5 8,000 1.5 50 5 20 
6 300,000 4.3 50 5 20 
7 51,000 3.0 70 5 3 
8 51,000 3.0 70 0.01 30 
9 51,000 3.0 70 20 30 
10 51,000 3.0 70 5 30 
______________________________________ 
Com- Par- Fix- 
para- Presence ticle Block- 
ing Dur- 
tive of size ing per- a- 
Ex- concav- distri- 
resis- 
form- bil- 
ample: 
ities R/r L/2.pi.r 
bution 
tance ance ity 
______________________________________ 
1 A 1.10 1.20 B C A B 
3 C 1.00 1.00 A AA A C 
4 C 1.25 2.03 C -- -- -- 
5 C 1.00 1.00 A AA A C 
6 C 1.21 2.01 C -- -- -- 
7 A 1.09 1.19 A AA C AA 
8 C 1.00 1.00 B B A C 
9 C 1.22 2.02 C -- -- -- 
10 A 1.10 1.20 A AA A C 
______________________________________ 
*part(s) by weight 
Evaluation: The same manner as Table 1. 
EXAMPLE 13 
In 709 g of ion-exchanged water, 451 g of an aqueous 0.1M Na.sub.3 PO.sub.4 
solution was introduced, followed by heating to 60.degree. C. and then 
stirring at 12,000 rpm using a TK-type homomixer (manufactured by Tokushu 
Kika Kogyo Co., Ltd.). To the resulting mixture, 67.7 g of an aqueous 1.0M 
CaCl.sub.2 solution was added little by little to give a dispersion medium 
containing Ca.sub.3 (PO.sub.4).sub.2. 
______________________________________ 
Styrene 170 g 
2-Ethylhexyl acrylate 30 g 
Paraffin wax (m.p.: 75.degree. C.) 
60 g 
C.I. Pigment Blue 15:3 10 g 
Styrene/methacrylic acid/methyl methacrylate co- 
5 g 
polymer (Mw: 50,000; Mw/Mn: 2.5; acid value: 50) 
Di-tert-butylsalicylic acid metal compound 
3 g 
______________________________________ 
Of the above materials, only C.I. Pigment Blue 15:3, di-tert-butylsalicylic 
acid metal compound and styrene were premixed using Ebara Milder 
(manufactured by Ebara Corporation). Next, all the above materials were 
heated to 60.degree. C., followed by dissolution and dispersion to give a 
monomer mixture. While the monomer mixture thus prepared was maintained at 
60.degree. C., 10 g of a polymerization initiator dimethyl 
2,2'-azobisisobutylate was added and dissolved. Thus a polymerizable 
monomer composition was prepared. 
The resulting monomer composition was introduced in the dispersion medium 
prepared in a 2 lit. flask of the TK homomixer. Using the TK homomixer, 
made to have an atmosphere of nitrogen, stirring was carried out at 
60.degree. C. and at 10,000 rpm for 20 minutes to granulate the monomer 
composition. Thereafter, while stirring with a paddle agitating blade, 
reaction was carried out at 60.degree. C. for 3 hours, and then at 
80.degree. C. for further 10 hours to complete polymerization. 
After the polymerization was completed, the reaction system was cooled, and 
27 g of 5N hydrochloric acid was added thereto, followed by further 
stirring with the paddle stirring blade for 2 hours. After the Ca.sub.3 
(PO.sub.4).sub.2 was thus dissolved, filtration and washing with water 
were repeated several times, and finally the product was dried. A toner 
produced by suspension polymerization was thus obtained. 
The quantity of Ca.sub.3 (PO.sub.4).sub.2 remaining on toner particle 
surfaces was determined by X-ray fluorometry to reveal that it was in a 
quantity of 0.1% by weight based on the toner. 
Particle diameters of the resulting toner were measured with a Coulter 
counter to reveal that the toner had a weight average particle diameter of 
8.2 .mu.m and a sharp particle size distribution. Observation using an 
electron microscope confirmed that toner particles each had on their 
surfaces a plurality of concavities as shown in FIG. 1. The R/r of the 
toner particles was 1.07 and L/2.pi.r was 1.07. Cross sections of the 
toner particles were observed on a transmission electron microscope by a 
method using dyed ultra-thin sections. As a result, it was confirmed that 
the particles were each structurally separated into the surface layer 
mainly composed of styrene-acrylic resin and the center mainly composed of 
wax and that the phase mainly composed of wax was absent in the vicinity 
of each toner particle surface ranging from its surface to a depth 0.15 
time a toner particle diameter. 
Based on 100 parts by weight of the toner obtained, 0.7 part by weight of 
hydrophobic silica having a specific surface area of 200 m.sup.2 /g as 
measured by the BET method was externally added. Next, 7 parts by weight 
of the toner to which the hydrophobic silica had been externally added and 
93 parts by weight of a Cu-Zn-Fe ferrite carrier having been 
surface-coated with a styrene/methyl methacrylate copolymer were blended 
to give a two-component developer. 
Using this developer, images were reproduced on a color copier (CLC-500; 
manufactured by Canon Inc.). 
Developing conditions were as follows: 
Development contrast of 430 V in an environment of 20.degree. C./10% RH 
Development contrast of 320 V in an environment of 23.degree. C./65% RH 
Development contrast of 270 V in an environment of 30.degree. C./80% RH 
Under the respective conditions, images were reproduced on 10,000 copy 
sheets. 
As a result, no faulty cleaning occurred at all, and image densities were 
as very stable as from 1.4 to 1.6, where coarseness-free very sharp images 
were obtained. In any environments, the quantity of triboelectricity 
little changed before and after running, showing that the toner had a 
superior charge stability. 
Comparative Example 12 
Toner particles were obtained in the same manner as in Example 13 except 
that the treatment making use of HCl was not made. The quantity of 
Ca.sub.3 (PO.sub.4).sub.2 remaining on toner particle surfaces was 
determined by X-ray fluorometry to reveal that it was in a quantity of 
2.5% by weight based on the toner. 
Using this toner, images were reproduced. As a result, the developer showed 
so extremely poor a fluidity in a high-temperature high-humidity 
environment that the image reproduction was stopped halfway. It also gave 
so low a quantity of triboelectricity in a low-temperature low-humidity 
environment that the toner images obtained were much fogged and coarse. 
Comparative Example 13 
A toner was obtained in the same manner as in Example 13 except that the 5N 
HCl was added in an amount of 13.5 g, the stirring with the paddle 
stirring blade was carried out for 24 hours to dissolve the Ca.sub.3 
(PO.sub.4).sub.2. The quantity of Ca.sub.3 (PO.sub.4).sub.2 remaining on 
toner particle surfaces was determined by X-ray fluorometry to reveal that 
it was in a quantity of 0.33% by weight based on the toner. 
Using this toner, images were reproduced. As a result, although there was 
no particular problem in the low-temperature low-humidity environment, 
toner scatter gradually began to occur in the running in the 
high-temperature high-humidity environment, and the images obtained were 
much fogged and coarse. 
Comparative Example 14 
A cyan toner with a weight average particle diameter of 8.6 .mu.m was 
obtained in the same manner as in Example 13 except that the polar resin 
used was replaced with a styrene/butyl acrylate copolymer (Mw: 30,000; 
Mw/Mn: 3.8 acid value; 0.2). The quantity of Ca.sub.3 (PO.sub.4).sub.2 
remaining on toner particle surfaces was determined to reveal that it was 
in a quantity of 0.12 % by weight based on the toner. 
The resulting toner had no unevenness on its particle surfaces and was a 
true-spherical toner. Using this toner, a running test was made to find 
that a decrease in density greatly occurred and also the images obtained 
were much fogged and coarse. 
Comparative Example 15 
A cyan toner with a weight average particle diameter of 8.3 .mu.m was 
obtained in the same manner as in Example 13 except that the polar resin 
was not used. 
A developer was prepared in the same way, and images were reproduced. As a 
result, image density decreased as the running proceeds, and faulty 
cleaning occurred after running on about 3,000 copy sheets. The toner at 
the start of running was observed by FE-SEM (field emission scanning 
electron microscopy) to find that the toner had no surface concavities and 
was a true-spherical toner. 
Comparative Example 16 
Polymerization was carried out in the same manner as in Example 13 except 
that the Ca.sub.3 (PO.sub.4).sub.2 was replaced with polyvinyl alcohol as 
a dispersant. After cooling, washing with water was repeated several times 
to remove the polyvinyl alcohol. 
The toner obtained had a weight average particle diameter of 8.2 .mu.m, but 
had a reasonably broad particle size distribution. Moreover, it was 
impossible for this toner to have attained the wax-encapsulated 
double-layer structure characteristic of the present invention. 
This was presumed due to the fact that the stability of interfaces between 
toner particles decreased compared with that of toner particles provided 
with Ca.sub.3 (PO.sub.4).sub.2, resulting in a lowering of granulation 
properties. 
The above toner showed a poor blocking resistance and an inferior storage 
stability. 
Example 14 
A cyan toner with a weigh average particle diameter of 8.0 .mu.m was 
obtained in the same manner as in Example 13 except that the polar resin 
used therein was replaced with a styrene/methacrylic acid/methyl acrylate 
copolymer having an Mw of 100,000, an Mw/Mn of 3.5 and an acid value of 
70. The R/r of the toner particles was 1.08 and L/2.pi.r was 1.08. The 
quantity of Ca.sub.3 (PO.sub.4).sub.2 remaining on toner particle surfaces 
was determined to reveal that it was in a quantity of 0.06 % by weight 
based on the toner. 
A developer was prepared in the same manner as in Example 13, and a running 
test was made on 10,000 copy sheets. As a result, always stable images 
were obtained without variations in image density. No faulty cleaning was 
also seen. The toner after running was observed by FE-SEM to confirm that 
the toner particles each had a plurality of substantially the same 
concavities as those of the toner before running and a silica adhered the 
surface of the toner. 
Example 15 
In Example 13, 645 g of an aqueous 0.1M Na.sub.3 PO.sub.4 solution was 
introduced in 498 g of ion-exchanged water, followed by heating to 
80.degree. C. and then stirring at 10,000 rpm using a TK-type homomixer 
(manufactured by Tokushu Kika Kogyo Co., Ltd.). To the resulting mixture, 
96.7 of an aqueous 1.0M CaCl.sub.2 solution was added little by little to 
give a dispersion medium containing Ca.sub.3 (PO.sub.4).sub.2. 
The step of polymerization was completed in the same manner as in Example 
13, adding the same polymerizable monomer composition as used therein, 
except that the granulation and polymerization were carried out at 
80.degree. C. After cooling, 38.5 g of 5N hydrochloric acid was added to 
remove Ca.sub.3 (PO.sub.4).sub.2. A toner was thus obtained. 
Particle diameters of the resulting toner were measured with a Coulter 
counter to reveal that the toner had a weight average particle diameter of 
5.5 .mu.m and a sharp particle size distribution. The R/r of the toner 
particles was 1.06 and L/2.pi.r was 1.09. The quantity of Ca.sub.3 
(PO.sub.4).sub.2 remaining on toner particle surfaces was determined by 
X-ray fluorometry to reveal that it was in a quantity of 0.08% by weight 
based on the toner. 
Example 16 
A developer was prepared in the same manner as in Example 13 except that 
the amounts of silica and carrier were changed to 1.0 part by weight and 
94 parts by weight, respectively. 
Images were reproduced under development contrast made a little stronger. 
As a result, images with superior fine-line reproduction and highlight 
gradation were obtained. In particular, charge was stable also in the 
high-temperature high-humidity environment. No problem occurred also in an 
image reproduction test made after the developer had been left for a long 
period of time. 
Example 17 
An aqueous 0.1M Na.sub.3 PO.sub.4 solution and an aqueous 1M CaCl.sub.2 
solution were prepared. In a 2 lit. flask of a TK-type homomixer 
(manufactured by Tokushu Kika Kogyo Co., Ltd.), 451 g of the aqueous 0.1M 
Na.sub.3 PO.sub.4 solution and 709 g of ion-exchanged water were 
introduced, followed by stirring at 12,000 rpm. To the resulting mixture, 
67.7 g of an aqueous 1M CaCl.sub.2 solution was added little by little 
while the above stirring was carried out using the homomixer, heated to a 
temperature of 60.degree. C., to give an aqueous dispersion medium 
containing Ca.sub.3 (PO.sub.4).sub.2. 
______________________________________ 
Styrene 180 g 
2-Ethylhexyl acrylate 20 g 
Paraffin wax (m.p.: 75.degree. C.) 
60 g 
C.I. Pigment Blue 15:3 10 g 
Sytrene/methacrylic acid/methyl methacrylate copolymer 
5 g 
polymer (Mw: 48,000; Mw/Mn: 3.1; acid value: 50) 
Di-tert-butylsalicylic acid metal compound 
2 g 
______________________________________ 
Of the above materials, only C.I. Pigment Blue 15:3, di-tert-butylsalicylic 
acid metal compound and styrene were premixed using Ebara Milder 
(manufactured by Ebara Corporation). Next, all the above materials were 
heated to 60.degree. C., followed by dissolution and dispersion to give a 
monomer mixture. While the monomer mixture thus prepared was maintained at 
50.degree. C., 10 g of 2,2'-azobis(2,4-dimethylvaleronitrile) and 1 g of 
dimethyl 2,2'-azobisisobutylate as polymerization initiators were added 
and dissolved. Thus a polymerizable monomer composition was prepared. 
The resulting monomer composition was introduced in the aqueous dispersion 
medium prepared in a 2 lit. flask of the TK homomixer. Using the TK 
homomixer, made to have an atmosphere of nitrogen, stirring was carried 
out at 60.degree. C. and at 10,000 rpm for 20 minutes to granulate the 
monomer composition. Thereafter, while stirring with a paddle agitating 
blade, reaction was carried out at 60.degree. C. for 3 hours, and then at 
80.degree. C. for further 10 hours to complete polymerization. 
After the polymerization was completed, the reaction system was cooled, and 
hydrochloric acid was added to dissolve the Ca.sub.3 (PO.sub.4).sub.2, 
followed by filtration, washing with water and then drying to give a 
toner. 
Particle diameters of the resulting toner were measured with a Coulter 
counter to reveal that the toner had a weight average particle diameter of 
8.6 .mu.m and a sharp particle size distribution. Observation using an 
electron microscope confirmed that toner particles each had on their 
surfaces a plurality of concavities. The R/r of the toner particles was 
1.07 and L/2.pi.r was 1.05. 
Cross sections of the toner particles were observed on a transmission 
electron microscope by a method using dyed ultra-thin sections. As a 
result, it was confirmed that the particles were each structurally 
separated into the surface layer mainly composed of styrene-acrylic resin 
and the center mainly composed of wax and that the phase mainly composed 
of wax was absent in the vicinity of each toner particle surface ranging 
from its surface to a depth 0.15 time a toner particle diameter. 
Based on 100 parts by weight of the toner obtained, 0.7 part by weight of 
hydrophobic silica having a specific surface area of 200 m.sup.2 /g as 
measured by the BET method was externally added. 
Next, 7 parts by weight of the toner to which the hydrophobic silica had 
been externally added and 93 parts by weight of a ferrite carrier having 
been surface-coated with an acrylic resin, having an average particle 
diameter of 50 .mu.m, containing fine powder of 400 mesh or less in an 
amount of 12% by weight and containing coarse powder of 250 mesh or more 
in an amount of 3% by weight were blended to give a developer. 
Using the developer thus obtained, a 20,000 sheet running test was made 
using a color copier CLO-500, manufactured by Canon Inc. As a result, 
images having image density of 1.4 or higher, free from fogging and having 
very high resolution were stably obtained. Electron-microscopic 
observation of surfaces of carrier particles after the running test 
revealed that the carrier-spent was on the level of no problem. 
EXAMPLE 18 
An aqueous 0.1M Na.sub.3 PO.sub.4 solution and an aqueous 1M CaCl.sub.2 
solution were prepared. In a 2 lit. flask of a TK-type homomixer 
(manufactured by Tokushu Kika Kogyo Co., Ltd.), 451 g of the aqueous 0.1M 
Na.sub.3 PO.sub.4 solution and 709 g of ion-exchanged water were 
introduced, followed by stirring at 12,000 rpm. To the resulting mixture, 
67.7 g of an aqueous 1M CaCl.sub.2 solution was added little by little 
while the above stirring was carried out using the homomixer, heated to a 
temperature of 60.degree. C., to give an aqueous dispersion medium 
containing Ca.sub.3 (PO.sub.4).sub.2. 
______________________________________ 
Styrene 175 g 
2-Ethylhexyl acrylate 25 g 
Paraffin wax (m.p.: 75.degree. C.) 
60 g 
C.I. Pigment Blue 15:3 10 g 
Styrene/methacrylic acid/methyl methacrylate co- 
5 g 
polymer (Mw: 58,000; Mw/Mn: 3.1; acid value: 70) 
Di-tert-butylsalicylic acid metal compound 
3 g 
______________________________________ 
Of the above materials, only C.I. Pigment Blue 15:3, di-tert-butylsalicylic 
acid metal compound and styrene were premixed using Ebara Milder 
(manufactured by Ebara Corporation). Next, all the above materials were 
heated to 60.degree. C., followed by dissolution and dispersion to give a 
monomer mixture. While the monomer mixture thus prepared was maintained at 
60.degree. C., 10 g of 2,2'-azobis(2,4-dimethylvaleronitrile) and 1 g of 
dimethyl 2,2'-azobisisobutylate as polymerization initiators were added 
and dissolved. Thus a polymerizable monomer composition was prepared. 
The resulting monomer composition was introduced in the aqueous dispersion 
medium prepared in a 2 lit. flask of the TK homomixer. Using the TK 
homomixer, made to have an atmosphere of nitrogen, stirring was carried 
out at 60.degree. C. and at 10,000 rpm for 20 minutes to granulate the 
monomer composition. Thereafter, while stirring with a paddle agitating 
blade, reaction was carried out at 60.degree. C. for 3 hours, and then at 
80.degree. C. for further 10 hours to complete polymerization. 
After the polymerization was completed, the reaction system was cooled, and 
hydrochloric acid was added to dissolve the Ca.sub.3 (PO.sub.4).sub.2, 
followed by filtration, washing with water and then drying to give a 
toner. 
Particle diameters of the resulting toner were measured with a Coulter 
counter to reveal that the toner had a weight average particle diameter of 
8.5 .mu.m and a sharp particle size distribution. Observation using an 
electron microscope confirmed that toner particles each had on their 
surfaces a plurality of concavities. The R/r of the toner particles was 
1.07 and L/2.pi.r was 1.05. 
Cross sections of the toner particles were observed on a transmission 
electron microscope by a method using dyed ultra-thin sections. As a 
result, it was confirmed that the particles were each structurally 
separated into the surface layer mainly composed of styrene-acrylic resin 
and the center mainly composed of wax and that the phase mainly composed 
of wax was absent in the vicinity of each toner particle surface ranging 
from its surface to a depth 0.15 time a toner particle diameter. 
Based on 100 parts by weight of the toner obtained, 0.7 part by weight of 
hydrophobic silica having a specific surface area of 200 m.sup.2 /g as 
measured by the BET method was externally added. Next, 7 parts by weight 
of this toner and 93 parts by weight of a ferrite carrier having been 
surface-coated with an acrylic resin were blended to give a developer. 
Using this developer, images were reproduced on a modified machine of a 
full-color copier (trade name: Color Laser Copia; manufactured by Canon 
Inc.). On the surface of the photosensitive member 4 set opposingly to the 
developing sleeve 3, a latent image with a dark portion (a laser power 
minimum) of -550 V and a light portion (a laser power maximum) a latent 
image portion) of -100 V was formed as an electrostatic latent image. The 
space between the surfaces of the sleeve and photosensitive member was set 
to be 400 .mu.m. Here, developing was carried out under conditions of -420 
V as DC component of the bias power source, 1.8 KHz as a frequency of AC 
component and 1.8 KVpp applied as a peak-to-peak voltage. At this time the 
volume percentage of the magnetic particles in the developing zone was 
20%. 
A 20,000 sheet running test was made under conditions as described above. 
As a result, images having image density of 1.4 or higher, free from 
fogging and having very high resolution were stably obtained. No faulty 
cleaning occurred and any toner scatter in the copier was not particularly 
seen. 
Example 19 
A toner with a weight average particle diameter of 8.8 .mu.m was prepared 
in the same manner as in Example 17 except that the monomer mixture was 
formulated as follows: 
______________________________________ 
Styrene 180 g 
2-Ethylhexyl acrylate 20 g 
Paraffin wax (m.p.: 65.degree. C.) 
80 g 
C.I. Pigment Blue 15:3 10 g 
Styrene/methacrylic acid/methyl methacrylate co- 
5 g 
polymer (Mw: 61,000; Mw/Mn: 6.6; acid value: 70) 
Di-tert-butylsalicylic acid metal compound 
3 g 
______________________________________ 
Particles of the resulting toner were confirmed each to have on their 
surfaces a plurality of concavities. The R/r of the toner particles was 
1.04 and L/2.pi.r was 1.03. Cross sections of the toner particles were 
also observed to confirmed that the phase mainly composed of wax was 
absent in the vicinity of each toner particle surface ranging from its 
surface to a depth 0.15 time a toner particle diameter. 
After a hydrophobic silica was externally added to this toner in the same 
manner as in Example 17, 5 parts by weight of this toner and 95 parts by 
weight of a ferrite carrier having been surface-coated with an acrylic 
resin, having an average particle diameter of 45 .mu.m, containing fine 
powder of 400 mesh or less in an amount of 16% by weight and containing 
coarse powder of 250 mesh or more in an amount of 1.0% by weight were 
blended to give a developer. 
Using the developer thus obtained, a running test was made in the same 
manner as in Example 17. As a result, images without any particular 
fogging and with very high resolution were stably obtained. Observation of 
surfaces of carrier particles revealed that the carrier-spent was a little 
poorer than that in Example 17, but on the level tolerable in practical 
use. 
Example 20 
A toner with a weight average particle diameter of 8.2 .mu.m was prepared 
in the same manner as in Example 18 except that the monomer mixture was 
formulated as follows: 
______________________________________ 
Styrene 180 g 
2-Ethylhexyl acrylate 20 g 
Paraffin wax (m.p.: 65.degree. C.) 
80 g 
C.I. Pigment Blue 15:3 10 g 
Sytrene/methacrylic acid/methyl methacrylate co- 
5 g 
polymer (Mw: 62,000; Mw/Mn: 5.5; acid value: 70) 
Di-tert-butylsalicylic acid metal compound 
3 g 
______________________________________ 
Particles of the resulting toner were confirmed each to have on their 
surfaces a plurality of concavities. The R/r of the toner particles was 
1.04 and L/2.pi.r was 1.04. Cross sections of the toner particles were 
also observed to confirmed that the phase mainly composed of wax was 
absent in the vicinity of each toner particle surface ranging from its 
surface to a depth 0.15 time a toner particle diameter. 
After a hydrophobic silica was externally added to this toner in the same 
manner as in Example 17, the same procedure as in Example 18 was repeated 
to give a developer. 
Using the developer thus obtained, a 20,000 sheet running test was made in 
the same manner as in Example 18. As a result, images having image density 
of 1.4 or higher, free from fogging and having very high resolution were 
stably obtained. 
Comparative Example 16 
To 1,200 ml of ion-exchanged water, 0.25 g of 
.gamma.-aminopropyltrimethoxysilane was added and 5 g of hydrophilic 
colloidal silica was further added. These were heated to 60.degree. C. and 
dispersed with stirring at 10,000 rpm for 15 minutes using a TK-type 
homomixer. An aqueous 1/10N HCl solution was further added to adjust the 
pH in the system to 6. Thus an aqueous dispersion medium was prepared. 
______________________________________ 
Styrene 180 g 
2-Ethylhexyl acrylate 20 g 
Paraffin wax (m.p.: 75.degree. C.) 
80 g 
C.I. Pigment Blue 15:3 10 g 
Sytrene/methacrylic acid/methyl methacrylate co- 
2 g 
polymer (Mw: 55,000; Mw/Mn: 10.2; acid value: 70) 
Di-tert-butylsalicylic acid metal compound 
3 g 
______________________________________ 
The above materials were heated to 60.degree. C. in a container, followed 
by dissolution and dispersion to give a monomer mixture. While the monomer 
mixture thus prepared was maintained at 60.degree. C., 1 g of dimethyl 
2,2'-azobisisobutylate and 10 g of 2,2'-azobis(2,4-dimethylvaleronitrile) 
as polymerization initiators were added and dissolved. Thus a 
polymerizable monomer composition was prepared. 
The resulting monomer composition was introduced in a 2 lit. flask holding 
the aqueous dispersion medium previously prepared. Using the TK homomixer, 
stirring was carried out in an atmosphere of nitrogen, at 60.degree. C. 
and at 9,000 rpm for 60 minutes to granulate the monomer composition. 
Thereafter, while stirring with a paddle agitating blade, polymerization 
was carried out at 60.degree. C. for 20 hours. After the polymerization 
was completed, the reaction system was cooled, and NaOH was added to 
dissolve the colloidal silica, followed by filtration, washing with water 
and then drying to give a toner. 
The toner thus obtained had a weight average particle diameter of 8.9 .mu.m 
and a sharp particle size distribution. It was also confirmed that toner 
particles each had been made a little amorphous. The R/r of the toner 
particles was 1.02 and L/2.pi.r was 1.03. However, observation of cross 
sections of the toner particles revealed that the phase mainly composed of 
wax was present also in the vicinity of each toner particle surface layer 
and that, of ten particles of wax, one was present in the surface region 
with a depth smaller than 0.15 time a toner particle diameter and also the 
boundary between phases was not so distinct as that of Example 18. 
After a hydrophobic silica was externally added to this toner in the same 
manner as in Example 18, the same procedure as in Example 18 was repeated 
to give a developer. Using the developer thus obtained, a running test was 
made in the same manner as in Example 18. As a result, the inside of the 
machine became soiled because of toner scatter as the running proceeds and 
also the image density became so high that it was difficult to make 
control. At this time the surfaces of carrier particles and the surface of 
the developer sleeve were observed to find that they were seriously soiled 
with toner compositions. 
Example 21 
A toner with a weight average particle diameter of 8.7 .mu.m was prepared 
in the same manner as in Example 17 except that the monomer mixture was 
formulated as follows: 
______________________________________ 
Styrene 175 g 
2-Ethylhexyl acrylate 25 g 
Paraffin wax (m.p.: 75.degree. C.) 
10 g 
C.I. Pigment Blue 15:3 10 g 
Sytrene/methacrylic acid/methyl methacrylate co- 
5 g 
polymer (Mw: 45,000; Mw/Mn: 3.0; acid value: 50) 
Di-tert-butylsalicylic acid metal compound 
3 g 
______________________________________ 
Particles of the resulting toner were confirmed each to have on their 
surfaces a plurality of concavities. The R/r of the toner particles was 
1.03 and L/2.pi.r was 1.03. Cross sections of the toner particles were 
also observed to confirmed that the phase mainly composed of wax was 
absent in the vicinity of each toner particle surface ranging from its 
surface to a depth 0.15 time a toner particle diameter. 
After a hydrophobic silica was externally added to this toner in the same 
manner as in Example 17, the resulting toner and the same carrier as used 
in Example 17 were blended to give a developer. Using the developer thus 
obtained, a running test was made in the same manner as in Example 17. As 
a result, images free from fogging and with very high resolution were 
stably obtained. Observation of surfaces of carrier particles revealed 
that the carrier-spent was on the same level as in Example 18, which was 
tolerable in practical use. 
Comparative Example 17 
To 1,200 ml of ion-exchanged water, 0.25 g of 
.gamma.-aminopropyltrimethoxysilane was added and 5 g of hydrophilic 
colloidal silica was further added. These were heated to 60.degree. C. and 
dispersed with stirring at 10,000 rpm for 15 minutes using a TK-type 
homomixer. An aqueous 1/10N HCl solution was further added to adjust the 
pH in the system to 6. Thus an aqueous dispersion medium was prepared. 
______________________________________ 
Styrene 180 g 
2-Ethylhexyl acrylate 20 g 
Paraffin wax (m.p.: 75.degree. C.) 
80 g 
C.I. Pigment Blue 15:3 10 g 
Sytrene/methacrylic acid/methyl methacrylate co- 
2 g 
polymer (Mw: 61,000; Mw/Mn: 10.2; acid value: 70) 
Di-tert-butylsalicylic acid metal compound 
3 g 
______________________________________ 
The above materials were heated to 60.degree. C. in a container, followed 
by dissolution and dispersion to give a monomer mixture. While the monomer 
mixture thus prepared was maintained at 60.degree. C., 1 g of dimethyl 
2,2'-azobisisobutylate and 10 g of 2,2'-azobis(2,4-dimethylvaleronitrile) 
as polymerization initiators were added and dissolved. Thus a 
polymerizable monomer composition was prepared. 
The resulting monomer composition was introduced in a 2 lit. flask holding 
the aqueous dispersion medium previously prepared. Using the TK homomixer, 
stirring was carried out in an atmosphere of nitrogen, at 60.degree. C. 
and at 9,000 rpm for 60 minutes to granulate the monomer composition. 
Thereafter, while stirring with a paddle agitating blade, polymerization 
was carried out at 60.degree. C. for 20 hours. After the polymerization 
was completed, the reaction system was cooled, and NaOH was added to 
dissolve the colloidal silica, followed by filtration, washing with water 
and then drying to give a toner. 
The toner thus obtained had a weight average particle diameter of 9.2 .mu.m 
and a sharp particle size distribution. It was also confirmed that toner 
particles each had been made a little amorphous. The R/r of the toner 
particles was 1.02 and L/2.pi.r was 1.03. However, observation of cross 
sections of the toner particles revealed that the phase mainly composed of 
wax was present also in the vicinity of each toner particle surface layer 
and that, of twenty particles of wax, three were present in the surface 
region with a depth smaller than 0.15 time a toner particle diameter and 
also the boundary between phases was not so distinct as that of Example 
17. 
After a hydrophobic silica was externally added to this toner in the same 
manner as in Example 17, the resulting toner and the same carrier as used 
in Example 17 were blended to give a developer. Using the developer thus 
obtained, a running test was made in the same manner as in Example 17. As 
a result, the inside of the machine became soiled because of toner scatter 
as the running proceeds, so that images became adversely affected, and 
accordingly the running test was stopped on 8,000 sheet coying. At this 
time, carrier particles surfaces were observed to confirm that the 
carrier-spent had greatly occurred. 
Example 22 
A toner with a weight average particle diameter of 8.3 .mu.m was prepared 
in the same manner as in Example 18 except that the monomer mixture was 
formulated as follows: 
______________________________________ 
Styrene 175 g 
2-Ethylhexyl acrylate 25 g 
Paraffin wax (m.p.: 75.degree. C.) 
10 g 
C.I. Pigment Blue 15:3 10 g 
Styrene/methacrylic acid/methyl methacrylate co- 
5 g 
polymer (Mw: 57,000; Mw/Mn: 3.3; acid value: 50) 
Di-tert-butylsalicylic acid metal compound 
3 g 
______________________________________ 
Particles of the resulting toner were confirmed each to have on their 
surfaces a plurality of concavities. The R/r of the toner particles was 
1.03 and L/2.pi.r was 1.03. Cross sections of the toner particles were 
also observed to confirmed that the phase mainly composed of wax was 
absent in the vicinity of each toner particle surface ranging from its 
surface to a depth 0.15 time a toner particle diameter. 
A hydrophobic silica was externally added to this toner in the same manner 
as in Example 18. Then, 6 parts by weight of the resulting toner and 94 
parts by weight of a ferrite carrier having been coated with a silicone 
resin were blended to give a developer. 
Using this developer, images were reproduced on a modified machine of a 
commercially available full-color copier (trade name: Color Laser Copia; 
manufactured by Canon Inc.). On the surface of the photosensitive member 4 
set opposingly to the developing sleeve 3, a latent image with a dark 
portion of -610 V and a light portion of -190 V was formed as an 
electrostatic latent image. The space between the surfaces of the sleeve 
and photosensitive member was set to be 400 .mu.m. Here, develooing was 
carried out under conditions of -500 V as DC component of the bias power 
source, 1.2 KHz as a frequency of AC component and 1.2 KVpp applied as a 
peak-to-peak voltage. At this time the volume percentage of the magnetic 
particles in the developing zone was 20%. 
A 20,000 sheet running test was made under conditions as described above. 
As a result, images having image density of 1.35 or higher, almost free 
from fogging and having very high resolution were stably obtained. 
Example 23 
An aqueous 0.1M Na.sub.3 PO.sub.4 solution and an aqueous 1M CaCl.sub.2 
solution were prepared. In a TK-type homomixer (manufactured by Tokushu 
Kika Kogyo Co., Ltd.), 451 g of the aqueous 0.1M Na.sub.3 PO.sub.4 
solution and 709 g of ion-exchanged water were introduced, followed by 
stirring at 12,000 rpm. 67.7 g of the aqueous 1M CaCl.sub.2 solution was 
heated to 70.degree. C. and added little by little while the above 
stirring was carried out using the homomixer to give an aqueous dispersion 
medium containing Ca.sub.3 (PO.sub.4).sub.2. 
______________________________________ 
(by weight) 
______________________________________ 
Styrene 170 parts 
Butyl acrylate 30 parts 
Paraffin wax (m.p.: 65.degree. C.) 
35 parts 
Styrene/methacrylic acid copolymer 
6 parts 
Phthalocyanine Blue 12 parts 
Di-tert-butylsalicylic acid metal compound 
3 parts 
______________________________________ 
A composition of the above materials was heated to 60.degree. C., and 
premixed using Ebara Milder (manufactured by Ebara Corporation). While the 
mixture thus prepared was maintained at 60.degree. C., 10 parts by weight 
of a polymerization initiator dimethyl 2.2'-azobisisobutylate was added 
and dissolved to give a polymerizable monomer composition. The monomer 
composition was introduced in the aqueous Ca.sub.3 (PO.sub.4).sub.2 
dispersion medium held in a 2 lit. flask of the TK homomixer. Here, the 
bath temperature was 60.degree. C. and the revolution number of the TK 
homomixer was 10,000 rpm. A granulated product of the monomer composition 
was obtained 20 minutes after its introduction. Thereafter, while stirring 
with a paddle agitating blade, reaction was carried out at 60.degree. C. 
for 3 hours, and then at an elevated temperature of 80.degree. C. for 
further 10 hours to complete polymerization. After the polymerization was 
completed, the reaction system was cooled, and 54 g of 5N hydrochloric 
acid was added to dissolve the Ca.sub.3 (PO.sub.4).sub.2, followed by 
filtration, washing with water and then drying to give a toner, toner-A. 
Particle diameters of the resulting toner-A were measured with a Coulter 
counter to reveal that the toner had a weight average particle diameter 
(D4) of 8.1 .mu.m and a sharp particle size distribution. Observation 
using an electron microscope confirmed that toner particles each had on 
their surfaces a plurality of concavities. The R/r of the toner particles 
was 1.08 and L/2.pi.r was 1.16. Cross sections of the toner particles were 
observed on a transmission electron microscope by a method using dyed 
ultra-thin sections. As a result, it was confirmed that the particles each 
had a capsule structure separated into the surface layer mainly composed 
of styrene-acrylic resin and the center mainly composed of wax and that 
the phase mainly composed of wax was absent in the vicinity of each toner 
particle surface ranging from its surface to a depth 0.15 time a toner 
particle diameter. 
Based on 100 parts by weight of the toner-A obtained, 0.8 part by weight of 
hydrophobic silica was externally added to give toner-A to which the 
hydrophobic silica had been externally added. 
The toner-A was set in a copying machine obtained by modifying the 
developing device of a copier FC-2, manufactured by Canon Inc., to the one 
as shown in FIG. 8, and images were reproduced to make evaluation. A 
developer sleeve comprising an aluminum sleeve having on its surface a 
phenol resin layer in which fine graphite particles had been dispersed was 
used as the developer carrying member. 
As a result, no melt-adhesion of toner to the developer carrying member and 
to the photosensitive member was seen even after running of 5,000 sheet 
paper feeding. No image deterioration such as fogging or density decrease 
was also seen. Offset was also well prevented to give no background stain. 
The fixing device was set to a temperature of 140.degree. C. 
Example 24 
Toner-B was obtained in the same manner as in Example 23 except that the 
colorant used therein was replaced with 5 parts by weight of 
graft-modified carbon black and the amount of the di-tert-butylsalicylic 
acid metal compound was changed to 3.5 parts by weight. The toner had an 
average particle diameter of 8.3 .mu.m. 
Based on 100 parts by weight of the toner-B, 0.7 part by weight of 
hydrophobic silica was externally added to give toner-B to which the 
hydrophobic silica had been externally added. Using this toner-B and also 
using the same developing apparatus as in Example 23, images and running 
performance were evaluated. 
As a result, the same good images as those of Example 23 were obtained. 
Example 25 
Toner-C was obtained in the same manner as in Example 23 except that the 
amount of the styrene/methacrylic acid copolymer was changed to 4 parts by 
weight and the colorant was replaced with Permanent Yellow NCG. The toner 
had an average particle diameter of 8.7 .mu.m. The R/r of the toner 
particles was 1.05 and L/2.pi.r was 1.10. 
Based on 100 parts by weight of the toner-C, 0.65 part by weight of 
hydrophobic silica was externally added to give toner-C to which the 
hydrophobic silica had been externally added. Using this toner-C and also 
using the same developing apparatus as in Example 23, images and running 
performance were evaluated. 
As a result, the same good images as those of Example 23 were obtained. 
Comparative Example 19 
______________________________________ 
(by weight) 
______________________________________ 
Styrene/butylacrylate copolymer 
200 parts 
Paraffin wax (m.p.: 65.degree. C.) 
35 parts 
Styrene/methacrylic acid copolymer 
6 parts 
Phthalocyanine Blue 12 parts 
Di-tert-butylsalicylic acid metal compound 
3 parts 
______________________________________ 
A kneaded product of the above materials was prepared to give a toner 
prepared by pulverization. During its preparation, melt-adhesion of toner 
to the inside of a pulverizing machine occurred to make pulverization 
efficiency poor. The resulting pulverized product had so poor a fluidity 
that blocking occurred and it was difficult to make the product into 
toner. 
Comparative Example 20 
The amount of paraffin wax used in Comparative Example 19 was changed to 13 
parts by weight. Kneading, pulverization and classification were carried 
out to give a blue finely pulverized product (average particle diameter: 
8.3 .mu.m). Based on 100 parts by weight of the blue finely pulverized 
product, 0.8 part by weight of hydrophobic silica was externally added to 
give toner-D. Using this toner-D prepared by pulverization and also using 
the same developing apparatus as in Example 23, images were reproduced to 
make running evaluation. 
As a result, images were fogged to show deterioration. Melt-adhesion of 
toner also occurred on the developer carrying member in a 3,000 sheet 
running test. 
Example 26 
An aqueous 0.1M Na.sub.3 PO.sub.4 solution and an aqueous 1M CaCl.sub.2 
solution were prepared. In a TK-type homomixer (manufactured by Tokushu 
Kika Kogyo Co., Ltd.), 451 g of the aqueous 0.1M Na.sub.3 PO.sub.4 
solution and 709 g of ion-exchanged water were introduced, followed by 
stirring at 12,000 rpm. 67.7 g of the aqueous 1M CaCl.sub.2 solution was 
heated to 70.degree. C. and added little by little while the above 
stirring was carried out using the homomixer to give an aqueous dispersion 
medium containing Ca.sub.3 (PO.sub.4).sub.2. 
______________________________________ 
(by weight) 
______________________________________ 
Sytrene 170 parts 
Butyl acrylate 30 parts 
Paraffin wax (m.p.: 70.degree. C.) 
50 parts 
Styrene/methacrylic acid/methyl methacrylate co- 
6 parts 
polymer (Mw/Mn: 3.1) 
Phthalocyanine Blue 12 parts 
Di-tert-butylsalicylic acid metal compound 
3 parts 
______________________________________ 
A composition of the above materials was heated to 60.degree. C., and 
premixed using Ebara Milder (manufactured by Ebara Corporation). While the 
mixture thus prepared was maintained at 60.degree. C., 10 parts by weight 
of a polymerization initiator dimethyl 2,2-azobisisobutylate was added and 
dissolved to give a polymerizable monomer composition. The monomer 
composition was introduced in the aqueous Ca.sub.3 (PO.sub.4).sub.2 
dispersion medium held in a flask of the TK homomixer. Here, the bath 
temperature was 60.degree. C. and the revolution number of the TK 
homomixer was 10,000 rpm. A granulated product of the monomer composition 
was obtained 20 minutes after its introduction. Thereafter, while stirring 
with a paddle agitating blade, reaction was carried out at 60.degree. C. 
for 3 hours, and then at an elevated temperature of 80.degree. C. for 
further 10 hours to complete polymerization. After the polymerization was 
completed, the reaction system was cooled, and 54 g of 5N hydrochloric 
acid was added to dissolve the Ca.sub.3 (PO.sub.4).sub.2, followed by 
filtration, washing with water and then drying to give a toner, toner-E. 
Particle diameters of the resulting toner-E were measured with a Coulter 
counter to reveal that the toner had a weight average particle diameter of 
8.0 .mu.m and a sharp particle size distribution. Observation using an 
electron microscope confirmed that toner particles each had on their 
surfaces a plurality of concavities. The R/r of the toner particles was 
1.10 and L/2.pi.r was 1.18. Cross sections of the toner particles were 
observed on a transmission electron microscope by a method using dyed 
ultra-thin sections. As a result, it was confirmed that the particles were 
each structurally separated into the surface layer mainly composed of 
styrene-acrylic resin and the center mainly composed of wax and that the 
phase mainly composed of wax was absent in the vicinity of each toner 
particle surface ranging from its surface to a depth 0.15 time a toner 
particle diameter. 
Based on 100 parts by weight of the toner-E obtained, 0.8 part by weight of 
hydrophobic silica having a specific surface area of 200 m.sup.2 /g as 
measured by the BET method was externally added. Next, 7 parts by weight 
of this toner-E to which the hydrophobic silica had been externally added 
and 93 parts by weight of a ferrite carrier having been surface-coated 
with an acrylic resin were blended to give a developer. Using this 
developer toner, unfixed images were obtained using a full color copier 
CLC-500, manufactured by Canon Inc. 
The unfixed images were fixed using the fixing device as shown in FIG. 9. 
In this fixing device, the critical surface tension of the film on the 
side coming into pressure contact with a recording medium was 20 dyne/cm 
and the surface electrical resistance was 1.times.10.sup.6 
.OMEGA..multidot.cm. In this fixing device, the temperature sensor surface 
temperature T.sub.1 of the heater element was set to be 130.degree. C., 
the power consumption of the resistance material of the heating zone, 150 
W, the total pressure at the pressure roller, 5 kg, the nip between the 
pressure roller and film, 4 mm, and the fixing speed, 45 mm/sec. As the 
heat-resistant sheet, a 20 .mu.m thick polyimide film having a 
low-resistance release layer provided on the side coming into contact with 
a recording medium, comprising PTFE to which a conductive material (carbon 
black) had been added, was used. Here, the time taken for the temperature 
sensor surface temperature T.sub.1 of the heater element to reach 
130.degree. C. was about 0.5 second. The temperature T.sub.2 at this time 
was 126.degree. C. and the temperature T.sub.3, 126.degree. C. 
The fixed images obtained were free from penetration of toner to paper or 
strike-through. Fixing performance also was so good that good images were 
obtained without offset to the film. A 2,000 sheet continuous fixing test 
was also made under the same fixing conditions. As a result, fixing 
performance was so good that good images were obtained without causing the 
offset to the film. 
EXAMPLE 27 
Toner-F was obtained in the same manner as in Example 26 except that the 
colorant was replaced with Permanent Yellow NCG and the amount of the 
di-tert-butylsalicylic acid metal compound was changed to 4 parts by 
weight. The toner had an average particle diameter of 8.4 .mu.m. The R/r 
of the toner particles was 1.07 and L/2.pi.r was 1.17. 
Based on 100 parts by weight of the toner-F, 0.7 part by weight of 
hydrophobic silica was externally added to give toner-F to which the 
hydrophobic silica had been externally added. Next, 7.5 parts by weight of 
this toner-F and 93 parts by weight of a ferrite carrier having been 
surface-coated with an acrylic resin were blended to give a developer. The 
same fixing test as in Example 26 was made. As a result, the same 
offset-free good images as those of Example 26 were obtained. 
Example 28 
An aqueous dispersion medium was prepared in the same manner as in Example 
26. 
______________________________________ 
(by weight) 
______________________________________ 
Styrene 170 parts 
2-Ethylhexyl acrylate 30 parts 
Paraffin wax 40 parts 
Styrene/methacrylic acid copolymer (Mw/Mn: 3.0) 
6.5 parts 
Magnetic material (4% treated with a titanium 
140 parts 
coupling agent) 
Di-tert-butylsalicylic acid metal compound 
3 parts 
______________________________________ 
A composition of the above materials was heated to 60.degree. C., and 
premixed using Ebara Milder (manufactured by Ebara Corporation). While the 
mixture thus prepared was maintained at 60.degree. C., 10 parts by weight 
of a polymerization initiator dimethyl 2,2'-azobisisobutylate was added 
and dissolved to give a polymerizable monomer composition. The monomer 
composition was introduced in the aqucous Ca.sub.3 (PO.sub.4).sub.2 
dispersion medium held in a flask of the TK homomixer. Here, the bath 
temperature was 60.degree. C. and the revolution number of the TK 
homomixer was 10,000 rpm. A granulated product of the monomer composition 
was obtained 20 minutes after its introduction. Thereafter, while stirring 
with a paddle agitating blade, reaction was carried out at 60.degree. C. 
for and then at an elevated temperature of 80.degree. C. for further 10 
hours to complete polymerization. After the polymerization was completed, 
the reaction system was cooled, and 54 g of 5N hydrochloric acid was added 
to dissolve the Ca.sub.3 (PO.sub.4).sub.2, followed by filtration, washing 
with water and then drying to give a toner, toner-G. 
Particle diameters of the resulting toner-G were measured with a Coulter 
counter to reveal that the toner had a weight average particle diameter of 
9.0 .mu.m and a sharp particle size distribution. Observation using an 
electron microscope confirmed that toner particles each had on their 
surfaces a plurality of concavities. The R/r of the toner particles was 
1.07 and L/2.pi.r was 1.15. Cross sections of the toner particles were 
observed on a transmission electron microscope by a method using dyed 
ultra-thin sections. As a result, it was confirmed that the particles were 
each structurally separated into the surface layer mainly composed of 
styrene-acrylic resin and the center mainly composed of wax and that the 
phase mainly composed of wax was absent in the vicinity of each toner 
particle surface ranging from its surface to a depth 0.15 time a toner 
particle diameter. 
Based on 100 parts by weight of the toner-G obtained, 0.8 part by weight of 
hydrophobic silica having a specific surface area of 200 m.sup.2 /g as 
measured by the BET method was externally added. Next, 7 parts by weight 
of this toner-G to which the hydrophobic silica had been externally added 
and 93 parts by weight of a ferrite carrier having been surface-coated 
with an acrylic resin were blended to give a developer. 
Using this developer toner, unfixed images were obtained using a copier 
NP-1215, manufactured by Canon Inc. 
The unfixed images were fixed using the fixing device as shown in FIG. 9. 
In this fixing device, the critical surface tension of the film on the 
side coming into pressure contact with a recording medium was 20 dyne/cm 
and the surface electrical resistance was 1.times.10.sup.6 
.OMEGA..multidot.cm. In this fixing device, the temperature sensor surface 
temperature T.sub.1 of the heater element was set to be 140.degree. C., 
the power consumption of the resistance material of the heating zone, 150 
W, the total pressure at the pressure roller, 5 kg, the nip between the 
pressure roller and film, 4 mm, and the fixing speed, 45 mm/sec. As the 
heat-resistant sheet, a 20 .mu.m thick polyimide film having a 
low-resistance release layer provided on the side coming into contact with 
a recording medium, comprising PTFE to which a conductive material (carbon 
black) had been added, was used. Here, the time taken for the temperature 
sensor surface temperature T.sub.1 of the heater element to reach 
140.degree. C. was about 0.5 second. The temperature T.sub.2 at this time 
was 136.degree. C. and the temperature T.sub.3, 136.degree. C. 
The fixed images obtained were free from penetration of toner to paper or 
strike-through. Fixing performance also was so good that good images were 
obtained without offset to the film. A 5,000 sheet continuous fixing test 
was also made under the same fixing conditions. As a result, fixing 
performance was so good that good images were obtained without causing the 
offset to the film. 
Comparative Example 20 
______________________________________ 
(by weight) 
______________________________________ 
Styrene/butadiene copolymer (17:3) 
200 parts 
Paraffin wax (m.p.: 70.degree. C.) 
50 parts 
Styrene/methacrylic acid/methyl methacrylate 
6 parts 
copolymer 
Phthalocyanine Blue 12 parts 
Di-tert-butylsalicylic acid metal compound 
3 parts 
______________________________________ 
A kneaded product having the above composition (composition similar to 
toner-E) was pulverized to attempt to make the product into toner, but it 
was impossible to do so because of occurrence of melt-adhesion and 
blocking during its pulverization. In the pulverization method, it was 
impossible to use a large quantity of release agent. 
Comparative Example 21 
A toner prepared by pulverization was obtained in the same manner as in 
Comparative Example 20 except that the release agent was used in an amount 
of 15 parts by weight. Using this toner, a fixing test was made in the 
same manner as in Example 26. As a result, the offset occurred. Blocking 
resistance also was deteriorated. 
As having been described above, according to the present invention, it is 
possible to obtain a toner free from deterioration with time and having a 
superior durability. Because of its superiority in fixing performance, 
blocking resistance, charge stability, storage stability, etc., it is also 
possible to obtain very sharp images having a high image density and free 
from coarseness. 
According to the image forming method of the present invention, it is 
possible to obtain images with a high image density and a superior 
resolution, and to form stable images without changes in toner performance 
even in use for a long period of time. 
According to the image forming method and the heat fixing method, of the 
present invention, it is possible to obtain images free from image 
deterioration such as fogging. During fixing, it is also possible to make 
waiting time substantially zero or short, and to achieve a low power 
consumption and prevent offset from occurring.