Particulate developer containing inorganic scraper particles and image forming method using the same

A developer comprising colored resinous particles and inorganic fine particles having a BET specific surface area of 0.2 to 30 m.sup.2 /g as measured by nitrogen adsorption. The inorganic fine particles have an action of promoting removal of paper powder and other adherents during cleaning of the latent image-bearing member without sticking onto the latent image-bearing member. Accordingly, the developer containing the inorganic fine particles can give good images even after successive copying operation for a long term.

BACKGROUND OF THE INVENTION 
This invention relates to a novel developer adapted to electrophotography, 
electrostatic recording, magnetic recording, etc., and an image forming 
method using the same. 
In electrophotography, an electrostatic latent image is first formed 
through utilization of the photoconductors such as cadmium sulfide, 
polyvinylcarbazole, selenium, zinc oxide, etc., for example, by uniformly 
imparting charges on a photoconductor layer, and by applying an imagewise 
exposure to the photoconductor. The electrostatic latent image is 
developed with a powdery toner or developer charged to the opposite 
polarity to that of the electrostatic latent image and, if desired, the 
developed image is further transferred to a transfer sheet, followed by 
fixing. 
Of these processes, especially in the case of a device having the transfer 
step, it is generally practiced to remove the residual toner on the 
photosensitive member not transferred and use the photosensitive member 
repeatedly. 
For removing the residual toner on the photosensitive member, a cleaning 
member is generally brought into contact with the photosensitive member as 
practiced in the blade cleaning system, the fur brush cleaning system or 
the magnetic brush cleaning system. In this case, the cleaning member 
contacts the photosensitive member under an appropraite pressure, and 
therefore the photoconductive member may be damaged or the toner may stick 
onto the photosensitive member. In order to avoid sticking of the toner 
onto the photosensitive member, it has been proposed to add both a waxy 
friction-reducing material and an abrasive material into the toner, as 
disclosed in Japanese Laid-Open Patent Application No. 47345/1973. This 
method is indeed effective for avoiding sticking of toner, but involves 
the following drawback. That is, when a friction-reducing material is 
added in an amount enough to avoid toner sticking, it will become 
difficult to remove materials with low electric resistance such as paper 
powder, ozone-oxidation product, etc. formed on or sticking onto the 
surface of the photosensitive member after repeated uses. In particular, 
in an environment of high temperature and high humidity, a defect is 
observed that the latent image on the photosensitive member is damaged by 
the materials with low electric resistance. 
Also, it is difficult to control the amounts of the friction-reducing 
material and the abrasive material to be added, and therefore difficult to 
obtain a developer having stable characteristics. If the abrasive material 
is added in an amount sufficient to remove the sticking onto the 
photosensitive member, some troubles may be caused, such as damaging of 
the photosensitive member or damaging of the cleaning blade, whereby 
cleaning cannot satisfactorily be performed. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a developer free of the 
drawbacks as mentioned above, namely which scarcely sticks onto the 
surface of the photosensitive material while giving little damage to the 
photosensitive member and the cleaning member during cleaning. 
Another object of the present invention is to provide an image forming 
method using such a developer as mentioned above. 
The developer of the present invention comprises colored resinous particles 
and inorganic fine particles (A) having a BET specific surface area of 0.2 
to 30 m.sup.2 /g as measured by nitrogen adsorption. 
The image forming method of the present invention comprises developing a 
latent image on a latent image-bearing member with the above developer, 
transferring the developed image formed to a transfer material and 
removing the residual developer on the latent image-bearing member.

DETAILED DESCRIPTION OF THE INVENTION 
The inorganic fine particles having a BET specific surface area of 0.2 to 
30 m.sup.2 /g as measured by nitrogen adsorption to be used in the present 
invention (hereinafter referred to as "inorganic fine particles A") have 
the function of scraping off the materials with low electric resistance 
such as paper powder, ozone-oxidation product etc., and the toner sticking 
onto the surface of the photosensitive member. Particularly, the inorganic 
fine particles A form minute unevenness on the photosensitive surface, 
thereby effectively acting to alleviate the frictional resistance between 
the photosensitive surface and the cleaning member and prevent the 
sticking of toner. For this purpose, the inorganic fine particles A are 
also required to be harder than the photosensitive surface, particularly 
preferably to have a Mohs hardness greater than talc (Mohs hardness =1). 
Further, the inorganic particles A should preferably be shaped with round 
corners, since shapes with sharp corners may cause damaging of the 
photosensitive member and the cleaning blade. In this respect, the 
inorganic particles A should preferably be those formed by sintering. 
"Sintering" mentioned herein means an operation to heat the particles at a 
temperature not higher than the melting point thereof thereby to melt only 
the vicinity of the surfaces and agglomerate the particles, thereby 
forming bondings between the particles with substantially the same 
strength as in the internal portions. The shapes of the particles formed 
according to the sintering method have a morphological characteristic that 
they are rather round than having sharp corners. Such a morphological 
characteristic can also be maintained when a sintered product of wet or 
dry compressed particles or a sintered agglomerate is crushed to a desired 
particle size or specific surface area. 
The inorganic fine particles A should preferably be not readily soluble in 
water in order that the charging characteristics of the developer may not 
be lowered in an environment of high temperature and high humidity. More 
specifically, it is possible to use iron oxide, chromium oxide, calcium 
titanate, strontium titanate, barium titanate, magnesium titanate, cerium 
oxide, zirconium oxide, aluminum oxide, titanium oxide, zinc oxide and the 
like. These compounds can be used either singly or in mixture. 
The inorganic particles A have a BET specific surface area of 0.2 to 30 
m.sup.2 /g as measured by nitrogen adsorption. This is because desired 
effects cannot be obtained outside of this range. The inorganic particles 
A should desirably have a BET specific surface area of 0.5 to 15 m.sup.2 
/g, particularly preferably 1.0 to 6.0 m.sup.2 /g. The specific surface 
area as measured by nitrogen adsorption in the present specification is 
based on the values measured under the prescribed conditions by means of a 
commercially available device (Model 2200, produced by Micromeritics Co.), 
with proviso that the amount of sample was reduced in the case when the 
specific surface area exceeded 200 m.sup.2 /g. 
The above described inorganic fine particles A may be added in an amount 
preferably of 0.1 to 30 % by weight, more preferably of 0.2 to 10 % by 
weight, based on the total amount of the toner. 
Further, the inorganic fine particles A may be subjected to an organic 
treatment of the surfaces with the use of a known coupling agent. 
It is preferred to use finer inorganic particles having a BET specific 
surface area as measured by nitrogen adsorption of 40 to 400 m.sup.2 /g, 
preferably 50 to 350 m.sup.2 /g, particularly preferably 70 to 300 m.sup.2 
/g (hereinafter referred to as "inorganic fine particles B") in 
combination with the inorganic particles A. In this case, the inorganic 
fine particles A should preferably have a BET specific surface area of 0.5 
to 350 m.sup.2 /g. The inorganic fine particles B have also the function 
to scrape off the materials with low electric resistance such as paper 
powder, ozone-oxidation product, etc., and the toner sticking onto the 
photosensitive surface. However, co-use of the inorganic particles B may 
be considered to exhibit excellent effect, because they have a specific 
effect of removing minute adherents on the photosensitive surface. The 
inorganic particles B are also preferably not readily soluble in water, 
and may include, for example, iron oxide, magnesium oxide, siliceous 
powder, etc. It is also possible to use fine silica particles produced by 
the dry process and the wet process. 
The dry process herein mentioned refers to a process for production of fine 
silica particles formed by the vapor phase oxidation of silicon halides. 
For example, it is a process utilizing the pyrolytic oxidation in 
oxygen-hydrogen flame of silicon tetrachloride gas, and the basic reaction 
scheme may be represented as follows: 
EQU SiCl.sub.4 +2H.sub.2 +O.sub.2 .fwdarw.SiO.sub.2 +4HCl. 
Also, in this preparation step, it is possible to obtain a composite fine 
powder of silica and metal oxides by use of other metal halides such as 
aluminum chloride or titanium chloride together with the silicon halides, 
and such embodiments are also included within the present invention. 
On the other hand, various known processes are applicable as the wet 
process. For example, there may be included the method according to 
decomposition of sodium silicate with an acid as generally shown by the 
following reaction scheme: 
EQU Na.sub.2 O.XSiO.sub.2 +HCl+H.sub.2 O.fwdarw.SiO.sub.2.nH.sub.2 O +NaCl 
or otherwise according to decomposition of sodium silicate with an ammonium 
salt or an alkali salt (hereinafter reaction schemes are omitted); the 
method wherein an alkaline earth metal silicate is formed from sodium 
silicate and decomposed with an acid, to form silicic acid; the method 
wherein a sodium silicate solution is converted with an ion-exchange resin 
into silicic acid; or the method in which natural silicic acid or silicate 
is utilized. 
For the fine siliceous particles herein mentioned, anhydrous silicon 
dioxide (silica) or otherwise any of silicates such as aluminum silicate, 
sodium silicate, potassium silicate, magnesium silicate, zinc silicate and 
the like may be applicable. 
The inorganic fine particles B including fine siliceous particles, should 
preferably be subjected to organic treatment of their surfaces such as the 
coupling treatment, the oil treatment or treatment with a fatty acid or a 
metal salt thereof. 
The inorganic fine particles B should preferably be employed in an amount 
of 0.01 to 20 % by weight, more preferably 0.03 to 5 % by weight, based on 
the total amount of the toner (namely, the total amount of the colored 
resinous particles and the inorganic particles A and B). 
These fine particles A and B should preferably exist in the form of being 
attached on the surfaces of the toner particles, namely the colored 
resinous particles. More preferably, the attachment should be a rather 
weak or triboelectric one as given by dry blending than by melt-blending. 
The colored resinous particles constituting the developer of the present 
invention in combination with the above inorganic fine particles A and the 
inorganic fine particles B (when used) comprise a binder resin and a 
colorant. 
The binder resin may be composed of homopolymers or copolymers of styrene 
and derivatives thereof such as polystyrene, poly-p-chlorostyrene, 
polyvinyltoluene, styrene-p-chlorostyrene copolymer, styrene-vinyltoluene 
copolymer; styrene-acrylate copolymers such as styrene-methyl acrylate 
copolymer, styrene-ethyl acrylate copolymer, styrene-n-butyl acrylate 
copolymer; styrene-methacrylate copolymers such as styrene-methyl 
methacrylate copolymer, styrene-ethyl methacrylate copolymer, 
styrene-n-butyl methacrylate copolymer; multi-component copolymers of 
styrene, acrylates and methacrylates; other copolymers of styrene with 
vinyl monomers such as styrene-acrylonitrile copolymer, styrene-vinyl 
methyl ether copolymer, styrene-vinyl ethyl ether copolymer, 
styrene-butadiene copolymer, styrene-vinyl methyl ketone copolymer, 
styrene-acrylonitrile-indene copolymer, styrene-maleic acid ester 
copolymer, etc.; polymethyl methacrylate, polybutyl methacrylate, 
polyvinyl acetate, polyester, polyamide, epoxy resin, polyvinyl butyral, 
polyacrylic acid resin, phenol resin, aliphatic or alicyclic hydrocarbon 
resin, petroleum resin, chlorinated paraffin, paraffin wax, etc. These 
binder resins may be used either singly or as a mixture. In particular, as 
the binder resin for the toner to be provided for use in the pressure 
fixing system, it is possible to use a low molecular weight polyethylene, 
a low molecular weight polypropylene, an ethylene-vinyl acetate copolymer, 
an ethylene-acrylate copolymer, a higher fatty acid, a polyamide resin, a 
polyester resin, etc. either singly or as a mixture. 
In the developer of the present invention, any known pigment or dye may be 
available as the colorant. For example, there may widely be used dyes and 
pigments such as carbon black, phthalocyanine blue, indanthrene blue, 
peacock blue, permanent red, lake red, rhodamine lake, hanza yellow, 
permanent yellow, benzidine yellow, etc. 
In order to use the toner of the present invention in the form of a 
magnetic toner, magnetic powder may also be incorporated therein. The 
magnetic powder to be incorporated in the toner may be of a material which 
is magnetized when placed in a magnetic field, including powder of a 
ferromagnetic metal such as iron, cobalt or nickel, or alloys thereof, or 
compounds such as magnetite, hematite, or .gamma.-iron oxide ferrite. The 
magnetic powder also functions as a colorant and is contained in an amount 
of 15 to 70 wt.% based on the total amount of the so called toner 
components, excluding the carrier as hereinafter described. 
The developer of the present invention can be further mixed with other 
additives, if desired, as far as they do not impair the characteristics of 
the toner. Such additives may include agents for imparting free flowing 
property such as colloidal silica, lubricants such as Teflon, zinc 
stearate, polyvinylidene fluoride, or fixing aids (e.g. low molecular 
weight polyethylene, low molecular weight polypropylene, etc.) and further 
conductivity imparting agents such as tin oxide. 
In preparation of the developer of the present invention, any desired 
method may be applicable. For example, the above constituent materials may 
be well kneaded by means of a thermal kneading machine such as hot roll, 
kneader, extruder, etc., followed by mechanical crushing and 
classification. Alternatively, materials such as magnetic powder are 
dispersed in a solution of a binder resin, followed by spray drying. It is 
also possible to apply the toner preparation method according to 
polymerization technique by mixing necessary materials with the monomers 
for constituting the binder resin and then polymerizing the emulsion or 
suspension of the resultant mixture to obtain a toner. 
The developer of the present invention comprising the so called toner 
components as described above, if desired, can be used in the form of a 
mixture with carrier particles such as iron powder, glass beads, nickel 
powder, ferrite powder, etc. to be used as a developer for electrostatic 
latent images. 
The image forming method of the present invention comprises developing the 
latent image on a latent image bearing member with the use of the 
developer as described above, transferring the developed image formed to a 
transfer material and removing the residual developer on the latent 
image-bearing member. 
The latent image-bearing member to be utilized include photosensitive or 
insulating materials suitable for formation and holding of electrical 
latent images thereon, for example, those having organic polymer layer on 
the surface, photosensitive materials such as organic photoconductive 
material (OPC), amorphous Se, amorphous Si, zinc oxide, etc. In 
particular, one having an organic polymer layer on the surface and an 
amorphous silicon photosensitive material are preferred. 
The developer of the present invention is applicable to various developing 
methods. For example, it is applicable to the magnetic brush developing 
method, the cascade developing method, the method as disclosed in U.S. 
Pat. No. 3,909,258 in which conductive magnetic toner is used, the method 
as disclosed in Japanese Laid-Open Patent Application No. 31136/1978 in 
which high resistivity magnetic toner is used, the methods as disclosed in 
Japanese Laid-Open Patent Applications Nos. 42121/1979, 18656/1980 and 
43027/1979, the fur brush developing method, the powder cloud method, the 
touch down developing method, the impression developing method, and 
others. 
For transfer of the image developed with the developer of the present 
invention to a transfer material such as plain paper, the known methods 
such as corona transfer, bias roll transfer, heat transfer, magnetic 
transfer, etc. may be applied. 
For removing the residual developer on the photosensitive or insulating 
material, it is possible to apply known methods such as the blade cleaning 
method, the fur brush cleaning method, the magnetic brush cleaning method, 
etc. However, as is apparent from the foregoing explanation, the developer 
of the present invention has characteristics particularly adapted to the 
blade cleaning method. 
Further, fixing of the developer of the present invention onto a transfer 
member may be carried out according to any of the known methods such as 
oven fixing, hot roll fixing, pressure fixing, flush fixing, microwave 
fixing, etc. 
The present invention is further illustrated by referring to Preparation 
Examples for preparation of the inorganic particles A of the present 
invention, and Examples concerning preparation and evaluation of the 
developer using such inorganic particles A. In the following description, 
all "parts" and "parts by weight". 
PREATION EXAMPLE 1 
In a ball mill, 147.6 g of strontium carbonate and 79.9 g of titanium oxide 
were subjected to wet mixing for 8 hours, and then the mixture was 
subjected to filtering and drying. Twenty grams (20 g) of this mixture was 
molded under a pressure of 5 kg/cm.sup.2, followed by calcination at 1100 
.degree. C. for 8 hours to cause sintering. Then, the sintered product 
PG,16 was mechanically crushed into fine particles of strontium titanate 
with a BET specific surface area of 2.4 m.sup.2 /g. 
PREATION EXAMPLE 2 
Twenty grams (20 g) of zirconium hydroxide were molded under a pressure of 
50 kg/cm.sup.2 and calcined at 1800 .degree. C. for 8 hours to cause 
sintering. Then, the sintered product was mechanically crushed into 
zirconium oxide with a BET specific surface area of 2.0 m.sup.2 /g. 
PREATION EXAMPLE 3 
After wet mixing of 197.3 g of barium carbonate with 79.9 g of titanium 
oxide in a ball mill, the resultant mixture was subjected to filtering and 
drying. Twenty grams (20 g) of the mixture was molded under a pressure of 
5 kg/cm.sup.2 and calcined at 1200 .degree. C. for 8 hours. Then, 
mechanical crushing was effected to produce barium titanate particles with 
a BET specific surface area of 3.0 m.sup.2 /g. 
PREATION EXAMPLE 4 
Chromium hydroxide in an amount of 20 g was molded under a pressure of 5 
kg/cm.sup.2 and calcined at 1300 .degree. C. for 6 hours to cause 
sintering. The sintered product was mechanically crushed to produce 
chromium oxide particles with a BET specific surface area of 2.4 m.sup.2 
/g. 
PREATION EXAMPLE 5 
In a ball mill, 100.8 g of calcium carbonate and 71.7 g of titanium oxide 
were wet-blended, and the mixture was subjected to filtering and drying. 
Twenty grams (20 g) of the mixture was molded under a pressure of 5 
kg/cm.sup.2, calcined at 1350 .degree. C. for 6 hours, and mechanically 
crushed to produce calcium titanate having a BET specific surface area of 
1.9 m.sup.2 /g. 
PREATION EXAMPLE 6 
Zirconium hydroxide in an amount of 20 g was molded under a pressure of 5 
kg/cm.sup.2, calcined at 2000 .degree. C. for 10 hours, and mechanically 
crushed to produce zirconium oxide particles with a BET specific surface 
area of 6.7 m.sup.2 /g. 
PREATION EXAMPLE 7 
Cerium carbonate in an amount of 20 g was molded under a pressure of 5 
kg/cm.sup.2, calcined at 1600 .degree. C. for 10 hours, and thereafter 
mechanically crushed to produce cerium oxide particles with a BET specific 
surface area of 9.6 m.sup.2 /g. 
EXAMPLE 1 
Styrene-butadiene copolymer (weight ratio: 84:16): 90 parts 
Styrene-dimethylaminoethyl methacrylate copolymer (weight ratio 90:10): 10 
parts 
Low molecular weight polyethylene: 5 parts 
Magnetite: 60 parts 
The above materials were well blended and then melt-kneaded on a roll mill. 
After cooling, the mixture was coarsely crushed by a hammer mill, 
pulverized by means of a jet micropulverizer and further subjected to 
classification by use of a wind force classifier to obtain colored 
resinous particles of 5 to 20 microns in diameter. One hundred (100) parts 
of the colored resinous particles were blended with 1.5 parts of the fine 
powder of strontium titanate with a specific surface area of 2.4 m.sup.2/ 
g formed in Preparation Example 1 and 0.5 part of colloidal silica 
(specific surface area 90 m.sup.2 /g) to prepare a toner. 
On the other hand, an electrostatic latent image was formed on an OPC 
photosensitive member 1 having a surface layer of a methyl methacrylate 
copolymer and the above toner was applied to a developing device as shown 
in the drawing to effect development. The developer carrying member was 
made of a stainless steel cylindrical sleeve 2 with an outer diameter of 
50 mm. The surface magnetic flux density on the sleeve 2 was 700 Gauss, 
and the distance between the toner thickness-regulating blade 5 and the 
sleeve surface was 0.25 mm. The developing device having the rotating 
sleeve 2 and a fixed magnet 3 (sleeve circumferential speed being 66 
mm/sec and the same as that of the drum, with an opposite rotational 
direction) was set to give a distance of 0.25 mm between the surface of 
the above photosensitive drum 1 and the surface of the sleeve 2, and an 
alternate current of 1600 Hz and 1400 V and a direct current bias of -150 
to -300 V were applied to the sleeve. 
The above toner 4 was applied to this developing device to develop the 
above latent image, then the powder image was transferred while 
irradiating a direct current corona of -7 KV on the back of a transfer 
paper to obtain a copied image. Fixing was performed by means of a fixing 
device of a commercially available plain paper copying machine (trade 
name: NP-200, produced by Canon K.K.). The residual toner on the 
photosensitive member was removed by use of a blade cleaning system. The 
blade cleaning system comprised a blade of a polyurethane plate which was 
set at a counterwise position with respect to the rotating direction of 
the photosensitive drum and held to give a stationary pressure of 5 - 20 
g/cm against the photosensitive drum. 
As a result of the above practice, clear images without fog could be 
obtained. Also, when successive copying test was conducted for 3,000 
sheets, respectively, in environments of normal temperature-normal 
humidity (20 .degree. C., 60 %), low temperature-low humidity (15 .degree. 
C., 10 %) and high temperature-high humidity (30 .degree. C., 90 %), good 
images could be obtained in any of the environments, without occurrence of 
disturbance of the image or fog through toner sticking onto the surface of 
the photosensitive member. 
EXAMPLE 2 
Styrene-butyl acrylate copolymer (70/30): 100 parts 
Magnetite: 60 parts 
Nigrosine dye: 2 parts 
Low molecular weight polyethylene: 5 parts 
By use of the above materials, colored resinous particles of 5 to 20 
microns in diameter were obtained similarly as in Example 1. One hundred 
(100) parts of the colored resinous particles were mixed with 1 part of 
zirconium oxide with a specific surface area of 2.0 m.sup.2/ g obtained in 
Preparation Example 2 and 0.4 part of colloidal silica (specific surface 
area 90 m.sup.2/ g) to prepare a toner. This toner was employed similarly 
as described in Example 1 to give similarly good results. 
EXAMPLE 3 
Styrene-butyl acrylate copolymer (70/30): 100 parts 
Magnetite: 60 parts 
Gold-containing dye (Zapon Fast Black B): 2 parts 
Low molecular weight polypropylene: 3 parts 
By use of the above materials, colored resinous particles of 5 to 20 
microns were obtained similarly as in Example 1. One hundred (100) parts 
of the colored resinous particles were mixed with 1 part of barium 
titanate with a specific surface area of 3.0 m.sup.2/ g obtained in 
Preparation Example 2 and 0.4 part of colloidal silica (specific surface 
area 200 m.sup.2/ g) to prepare a toner. This toner was applied to a 
commercially available copying machine (NP-400 RE,, produced by Canon 
K.K.), and successive copying test was performed for 10,000 sheets in 
respective environments of normal temperature-normal humidity, low 
temperature-low humidity and high temperature-high humidity. Good results 
could be obtained from the beginning to the end in any of these cases. 
COMATIVE EXAMPLE 1 
Example 1 was repeated except that no strontium titanate prepared in 
Preparation Example 1 was employed. As the result, when successive copying 
test was conducted under high temperature and high humidity conditions, 
flaw-like irregularities occurred in the image after 1,000 sheets of 
copying, while marked toner sticking occurred after 3,000 sheets of 
copying under the low temperature and low humidity conditions. 
EXAMPLE 4 
A toner was prepared in the same manner as in Example 1 except for 
employing fine chromium oxide particles with a specific surface area of 
2.4 m.sup.2/ g in place of 1.5 part of the fine strontium titanate 
particles in Example 1. When successive copying test was conducted in the 
respective environments of normal temperature-normal humidity, low 
temperature-low humidity and high temperature-high humidity, good results 
substantially the same as in Example 1 could be obtained. 
When the colloidal silica with a specific surface area of 90 m.sup.2/ g 
synthesized according to the wet process was replaced with colloidal 
silica having specific surface area of 100 m.sup.2/ g, 170 m.sup.2/ g and 
210 m.sup.2/ g, respectively, synthesized according to the dry process, 
followed by treatment with an amine-modified silicone oil, good results 
were also obtained without occurrence of disturbance of image or fog 
through sticking of the toner onto the surface of the photosensitive 
member. 
EXAMPLE 5-8 
Preparation of toners and successive copying test were repeated according 
to substantially the same procedure as in Example 4, except that 2 parts 
of calcium titanate with a specific surface area of 1.9 m.sup.2/ g, 1.5 
parts of zirconium oxide with a specific surface area of 6.7 m.sup.2/ g, 1 
part of strontium titanate with a specific surface area of 2.0 m.sup.2/ g 
and 0.8 part of cerium oxide (purity: 70 %) with a specific surface area 
of 9.6 m.sup.2/ g were employed, respectively, in place of the chromium 
oxide in Example 4. In every case, good results could be obtained 
similarly as in Example 4. 
EXAMPLE 9 
Example 3 was repeated except for substituting fine chromium oxide 
particles having a specific surface area of 2.4 m.sup.2/ g for the barium 
titanate to obtain a toner. As the result of successive copying test for 
10,000 sheets, good results could be obtained similarly as in Example 3. 
EXAMPLE 10 
The toner of Example 3 was applied to a developing device as shown in the 
attached drawing having an amorphous silicon photosensitive member on 
which a latent image of +420 V was formed. The structure of the developing 
device was similar to that used in Example 1 but different conditions were 
adopted, i.e., a drum circumferential speed of 350 mm/sec, an alternating 
current of 1400 V and 1700 Hz and a direct current bias of 100 to 150 V 
applied to the sleeve. After the development, the resultant toner image 
was transferred while irradiating a direct current corona of 7 KV on the 
back of a transfer paper to obtain a copied image on the transfer sheet. 
Fixing was performed by means of a fixing device of a commercially 
available copying machine (NP-400 RE, produced by Canon K.K.). The 
residual toner on the photosensitive member was removed by use of the 
blade cleaning system as explained in Example 1. 
Successive copying test was coducted for 10000 sheets under the high 
temperature and high humidity conditions, whereby no disturbance of image 
or fog due to sticking of toner onto the photosensi-tive member was 
observed. 
EXAMPLE 11 
Styrene-butadiene copolymer: 80 parts 
Styrene-diethylaminoethyl methacrylate copolymer: 20 parts 
Magnetite: 55 parts 
Colored resinous particles of 5 to 20 microns in diameter were produced in 
substantially the same manner as in Example 1 except for using the above 
materials. The colored resinous particles in an amount of 100 parts were 
mixed with 1.5 parts of the strontium titanate particles of Preparation 
Example 1 produced through the sintering method and having a BET specific 
surface area of 2.4 m.sup.2/ g, to produce a toner. 
Imaging and heat fixing were performed by using a toner to obtain good 
images. As the result of successive copying test under the high 
temperature and high humidity conditions, no irregularity observed on 
copying 1000 sheets, while slight disturbance of image was observed on 
copying 3000 sheets. 
EXAMPLES 12 and 13 
Example 11 was substantially repeated except for using the zirconium oxide 
of Preparation Example 2 and the barium titanate of Preparation Example 3, 
respectively, in place of the strontium titanate of Preparation Example 1, 
whereby substantially the same results as in Example 11 were obtained. 
EXAMPLE 14 
Example 11 was repeated except for using cerium oxide particles having a 
specific surface area of 15 m.sup.2/ g produced without sintering in place 
of the strontium titanate of Preparation Example 1, whereby slight flaw 
was observed but no disturbance of image was observed on copying of 1000 
sheets, while disturbance of image was observed on copying of 3000 sheets. 
COMATIVE EXAMPLE 2 
Example 11 was substantially repeated except for using cerium oxide having 
a specific surface area of 50 m.sup.2/ g in place of the strontium 
titanate in Preparation Example 1, whereby disturbance of image was 
observed on copying of 1000 sheets. 
COMATIVE EXAMPLE 3 
Example 11 was substantially repeated except for using strontium titanate 
having a specific surface area of 42 m.sup.2/ g produced by the wet 
process in place of the strontium titanate of Preparation Example 1, 
whereby disturbance of image was observed on copying of 1000 sheets.