Positively chargeable developer

A positively chargeable developer, comprising: positively chargeable toner particles, positively chargeable silicate fine powder having a positive triboelectric chargeability higher than that of the toner and a mean particle size of 3 microns or smaller, and a microdisperser having a triboelectric chargeability lower than that of the toner and a mean particle size which is larger than that of the silicate powder and smaller than that of the toner particles. The microdisperser has a function of disintegrating particularly the positively chargeable silicate fine powder and enhances the attachment thereof to the toner particles, whereby the developing characteristics including the triboelectric chargeability are stabilized from the initial stage of electrophotographic copying operation, and the storage stability is also improved.

FIELD OF THE INVENTION AND RELATED ART 
This invention relates to a developer for developing latent images using 
image forming methods such as electrophotography, electrostatic recording, 
electrostatic printing. More particularly, the present invention relates 
to a developer for electrophotography which is positively charged both 
uniformly and strongly and gives an image of high quality by visualizing a 
negative electrostatic image or visualizing a positive electrostatic image 
by reversal development in the direct or indirect electrophotographic 
developing method. 
It has been practiced in the prior art to form latent images by uniformly 
charging a photoconductive member and applying a light image exposure 
corresponding to an original thereby to extinguish the charges at the 
exposed portion, as described in U.S. Pat. Nos. 2,297,691; 3,666,363; and 
4,071,361. Development is carried out by attaching fine powdery 
electroscopic substance (so-called "toner") on the electrostatic latent 
image. The toner is attracted to the electrostatic image depending on the 
amount of charge on the photoconductive layer to form a shaded toner 
image. The toner image is optionally transferred onto the surface of a 
support such as paper, plastic film or cloth, and is permanently fixed 
onto the support surface by heating, pressurization or hot pressurizing 
rollers. When it is desired to omit the toner image transfer step, the 
toner image can be also fixed onto the photoconductive layer. Other than 
the fixing methods; mentioned above, it is also possible to use other 
means such as solvent treatment or overcoating. 
A large number of developing methods have been known in electrophotography, 
and the developing method such as the cascade developing method using a 
two-component developer of a mixture of carrier particles and a toner 
disclosed in U.S. Pat. No. 2,618,552 and the magnetic brush method 
disclosed in U.S. Pat. No. 2,874,063 have widely been practiced. 
All of these methods are excellent methods which can give good images 
relatively stably. On the other hand, they have common problems of 
deterioration of carrier and fluctuation in mixing ratio of toner and 
carrier which are inherent to the use of two-component developers. 
In order to circumvent the above problems, various developing methods 
employing one component developer have been proposed. Among them, many of 
the methods employing magnetic toner particles are known to be excellent. 
U.S. Pat. No. 3,909,258 proposes a developing method which develops 
electrically by use of a magnetic toner having electroconductivity. 
According to this method, electroconductive magnetic developer is 
supported on a cylindrical electroconductive toner carrier (sleeve) having 
an internal magnet, which developer is then permitted to contact an 
electrostatic image to effect development. During this operation, an 
electroconductive path is formed by the toner particles between the 
surface of a recording member such as a photoconductive layer and the 
sleeve surface in the developing instrument, and the charges are guided to 
toner particles through the electroconductive path from the sleeve, 
whereby the toner particles are attached on the image portion by the 
Coulomb force between the particles and the image portion of the 
electrostatic image to effect development. 
The developing method using electroconductive magnetic toner is an 
excellent method which has circumvented the problems inherent in the two 
component developing method in the prior art. On the other hand, since the 
toner is electroconductive, there is involved a problem that it is 
difficult to electrostatically transfer the developed image from a 
recording member to the final supporting member such as plain paper. 
As a developing method employing a high resistance magnetic toner capable 
of electrostatic transfer, there is a developing method utilizing 
dielectric polarization of toner particles. However, such a method has 
problems such that it is an inherently a slow developing method and that a 
sufficient density of the developed image cannot be obtained, thus 
involving a difficulty for practical use. 
As other developing methods using high resistance magnetic toner, there 
have been known the methods in which toner particles are charged by mutual 
friction between the toner particles or between the toner particles and 
the developer carrier such as a sleeve, and permitted to contact the 
electrostatic image-bearing member. However, these methods has the problem 
that triboelectric charge is liable to be insufficient due to minimal 
contact between the toner particles and the frictional member such as a 
sleeve, and the charged toner particles are enhanced in Coulomb force 
between the particles and the sleeve to be readily agglomerated on the 
sleeve. 
A research group to which we belong has previously proposed a novel 
developing method overcome the above problems in Japanese Laid-Open Patent 
Application No. 42141/1979 (U.S. Pat. No. 4,356,245). This method 
comprises applying an insulating magnetic toner in a very small thickness 
on a sleeve, triboelectrically charging the toner and bringing the toner 
to a position where it is closely opposed to an electrostatic latent image 
under the action of a magnetic field and is permitted to jump onto the 
electrostatic image thereby effecting development. According to this 
method, excellent image can be obtained because frequency of contact 
between the sleeve and the toner is increased by coating very thinly a 
magnetic toner on the sleeve, thereby enabling sufficient triboelectric 
charging; because the toner is supported by magnetic force and moved 
relative to the magnet to disintegrate the agglomeration between the toner 
particles, while being subjected to sufficient friction with the sleeve; 
and because ground fog is prevented by carrying out development with the 
toner on the sleeve being opposed to the electrostatic image without 
contact therewith while restraining the toner with magnetic force. 
However, even according to this method, the triboelectric charge possessed 
by the toner particles coated on the sleeve is smaller as compared with 
that possessed by the toner particles in the conventional two-component 
development. When a magnetic toner having only a weak charge is used in 
this method, such difficulties as lowered image density, scattering, 
blurring, and image irregularity are liable to occur and therefore 
improvement in image quality has been still desired. Particularly, the 
image density at the initial stage of copying (one to tens of sheets) is 
lower, and some hundreds of copies were generally necesssary before 
obtaining an image having good high density stably. This instability in 
rising or initial stage of copying is one of the great problems in 
one-component developing method. For solving the rising instability, one 
may consider to improve triboelectric chargeability of the toner. In a 
negatively chargeable developer it has been known to add silicate fine 
powder to the developer for overcoming the above problem. In that case, 
image density and image quality are improved, whereby an image with 
somewhat satisfactory stability in initial stage characteristic can be 
obtained. However, silicate fine powder is generally strongly negatively 
chargeable and it has been difficult to obtain good images if such 
negatively chargeable silicate fine powder is added to a positively 
chargeable toner or developer. In the magnetic toner or developer having 
positive chargeability, no satisfactory triboelectric charging 
characteristic is obtained by addition of negatively chargeable silica 
under the present situation. 
For the purpose of improving the positive triboclectric charging 
characteristic, it has been proposed to add a modified silica fine powder 
obtained by modifying silica fine powder which is inherently negatively 
chargeable to positively chargeable. For example, as disclosed in Japanese 
Patent Publication No. 22447/1978, Japanese Laid-Open Patent Application 
Nos. 185405/1983 or 34539/1984 (U.S. patent application Ser. No. 751,994), 
there has been proposed a method in which silicate fine powder treated 
with aminosilane is incorporated in the toner. Further, an attempt is made 
to incorporate silicate fine powder treated with a silicone oil having an 
amine in the side chain in the toner or developer (U.S. Pat. No. 
4,568,625). By addition of such positively chargeable silicate fine 
powder, sharp images with high density and relatively little fog can be 
obtained, but various problems caused by inappropriate triboelectric 
charging characteristic such as instability in rising cannot fully be 
solved and further improvement is expected. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a developer having stable 
and uniform positive chargeability. Another object of the present 
invention is to provide a toner yielding images with a high image density 
from the initial stage without rising (or fluctuation of) image density. 
Still another object of the present invention is to provide a toner 
excellent in storage stability which can maintain the initial 
characteristics even in prolonged storage. 
The present invention provides a positively chargeable developer, 
comprising at least a positively chargeable toner, positively chargeable 
silicate fine powder with a particle size of 3 microns or less having a 
higher triboelectric chargeability than said toner, and a microdisperser 
having a particle size greater than said silicate fine powder and smaller 
than said toner. 
We have found that positively chargeable silicate fine powder exhibits a 
charge controlling characteristic when it is contained in the developer, 
and further that the positive charging characteristic is improved and the 
toner characteristics can be maintained even after storage for a long term 
when a specific third fine powder (herein referred to as "microdisperser") 
is mixed into the developer. 
The microdisperser has a particle size which is greater than those of the 
positively chargeable silicate fine powder to be used in the developer of 
the present invention. The microdisperser alone shows no special transfer 
of charges to the toner single substance shown in Examples or the toner 
single substance available in a commercially available plain paper copying 
machine. Thus, a developer consisting of a toner and a microdisperser 
shows no effect of improving image quality, but can show no developing 
ability at all for development of electrostatic latent image in some 
cases. In contrast, when the microdisperser is added to the developer 
containing positively chargeable silicate fine powder, improvement in 
image density as a matter of course, cancellation of instability in 
initial stage characteristic and maintenance of the characteristics 
immediately after the toner production after storage for a long term can 
be recognized, thus accomplishing improvement in the toner developing 
characteristics to a great extent. When observed through a microscope, in 
the developer containing none of such a component, much agglomerated 
masses of positively chargeable toner and agglomerated masses of 
positively chargeable silicate fine powder can be observed. In contrast, 
substantially none or very little, if any, of such mass can be recognized 
in the developer containing a microdisperser. 
Since the developer containing a disperser exhibits very good flowability, 
it can be understood that the microdisperser has the function of 
dispersing well the positively chargeable silicate fine powder on the 
surface of the positively chargeable toner. In fact, depending on the 
presence of microdisperser, the amount of the silicate fine powder 
attached onto the toner surface or the state of attachment differ greatly. 
In the developer having a microdisperser, it can be recognized that 
agglomeration of the silicate fine powder existing on the toner surface is 
cancelled, simultaneously with good dispersion of the silicate fine powder 
well attached onto the toner surface. In contrast, in the developer 
containing no microdisperser, silicate fine powder exists locally at a 
part of the toner surface like an agglomerated mass. In the developer 
containing a microdisperser, it has been observed that some microdisperser 
particles have silicate fine powder attached therearound. From this fact, 
it may be estimated that the microdisperser has the roles of 
disintegrating and dispersing agglomerated masses of silicate fine powder; 
and behaving as a carrier for the silicate fine powder to supply the 
silicate fine powder to the toner. Accordingly, the microdisperser, in 
relation to the positively chargeable toner and the positively chargeable 
silicate fine powder, may be considered to act on the positively 
chargeable silicate fine powder to cancel its agglomeration simultaneously 
with supplying rapidly the positively chargeable silicate fine powder to 
the positively chargeable toner well against the electrostatic repelling 
force. The reason why the microdisperser acts preferentially on silicate 
fine powder rather than the toner may be considered to be probably because 
said silicate fine powder has potentially higher positively chargeable 
(Q/M) ability than said toner and at the same time the particle size of 
the silicate fine powder is approximate to the microdisperser. 
Such an action is enhanced when the microdisperser is in combination with a 
stirring means. More specifically, when the developer is left to stand for 
a long term, the developer will cause deterioration, because the 
positively chargeable toner and the positively chargeable fine powder are 
generally liable to be separated from each other to effect agglomeration. 
For restoration of deterioration of the developer after standing, the 
toner and the silicate fine powder must be again stirred and mixed. Under 
the state when left to stand in a developing machine, gradual restoration 
by means of a stirring means in the developing device must be awaited. In 
the developer of the present invention containing a microdisperser, since 
the positively chargeable silicate fine powder is supplied more rapidly by 
the stirring device to the positively chargeable toner, restoration of the 
phenomenon of deterioration can be effected extremely rapidly. 
The above mentioned and other objects and features of the invention will be 
better understood upon consideration of the following detailed description 
concluding with specific examples of practice. 
DETAILED DESCRIPTION OF THE INVENTION 
In the present invention, the positively chargeable silicate fine powder 
which is one constituent of the developer should preferably be one with a 
charge provided under friction with iron powder carrier of +20 .mu.c/g or 
more. Particularly, it is preferred to exhibit +50 to +300 .mu.c/g and 
have a value greater than the positively chargeable toner free of said 
silicate fine powder and microdisperser. 
Measurement of a triboelectric charge in the present invention is carried 
out by mixing about 2 parts by weight of a substance to be tested with 
about 100 parts by weight of iron carrier having particle sizes of 200/300 
mesh (i.e., particles passing a sieve of 200 mesh and remaining on a sieve 
of 300 mesh). For this operation, the vessel for mixing may preferably be 
a vessel made of polyethylene, and it is preferred to charge a sample in 
amount of about 1/5 volume of the vessel and mix the sample by vigorous 
vertical manual shaking for about one minute. An amount of 0.5 to 1.5 g of 
the mixture after shaking is accurately measured, aspirated on a 400 mesh 
screen made of a metal connected to an electrometer under a pressure of 25 
cm.H.sub.2 O, and the charge per unit weight is determined from the weight 
of the substance to be tested separated by aspiration and the charge 
thereof as evaluated from the charge remaining on the iron powder carrier. 
The particle size of the silicate fine powder of the present invention 
(inclusive also of the agglomerated silicate fine powder) should 
preferably be 3 microns or less, particularly about 0.01 to 1 micron. 
These can be calculated by selecting 20 or more particles from the 
photography of a transmission type electron microscope and measuring their 
diameters. The mean particle size used herein is calculated as a 
number-average value based on the measured values. 
The silicate fine powder to be used in the present invention may be the 
silicate fine powder produce by the dry process or the wet process. 
Ordinarily, untreated silicate fine powder is negatively chargeable, and 
good result can not be obtained even when added as such to the developer 
of the present invention. 
The dry process as herein mentioned refers to the process for producing 
silica fine powder formed by vapor phase oxidation of a silicon halide. 
Examples of commercially available silica fine powder formed by vapor phase 
oxidation of silicon halides to be used in the present invention are shown 
below. 
______________________________________ 
AEROSIL 130 
(Nippon Aerosil Co.) 200 
300 
380 
OX50 
TT600 
MOX80 
MOX170 
COK84 
Ca-O-Sil M-5 
(CABOT Co.) MS-7 
MS-75 
HS-5 
EH-5 
Wacker HDK N 20 V15 
(WACKER-CHEMIE GMBH) N20E 
T30 
T40 
D-C Fine Silica 
(Dow Corning Co.) 
Fransol 
(Fransil Co.) 
______________________________________ 
Various known methods are applicable for production of silicate fine powder 
to be used in the present invention according to the wet process. 
Typical example of silicate fine powder is anhydrous silicon dioxide 
(silica), or otherwise silicates such as aluminum silicate, sodium 
silicate, potassium silicate, magnesium silicate, zinc silicate or the 
like may also be used. 
Examples of commercially available silicate fine powder synthesized 
according to the wet process are those sold under the trade names shown 
below. 
______________________________________ 
Carplex Shionogi Seiyaku K. K. 
Nipsil Nippon Silica K. K. 
Tokusil, Finesil 
Tokuyama Soda K. K. 
Vitasil Tagi Seihi K. K. 
Silton, Silnex Mizusawa Kagaku K. K. 
Starsil Kamijima Kagaku K. K. 
Himesil Ehime Yakuhin K. K. 
Siloid Fuji Davidson Kagaku K. K. 
Hi-Sil Pittsburgh Plate Glass Co. 
Durosil Fuelstroff Gesellschaft Marquart 
Ultrasil " 
Manosil Hardman and Holden 
Hoesch Chemische Fabrik Hoesch K-G 
Sil-Stone Stoner Rubber Co. 
Nalco Nalco Chemical Co. 
Quso Philadelphia Quartz Co. 
Imsil Illinois Minerals Co. 
Calcium Silikat 
Chemische Fabrik Hoesch K-G 
Calsil Fuelstoff-Gesellschaft Marquart 
Fortafil Imperial Chemical Industries Ltd. 
Microcal Joseph Crosfield & Sons Ltd. 
Manosil Hardman and Holden 
Vulkasil Farbenfabriken Bayer, A. G. 
Tufknit Durham Chemicals. Ltd. 
Silmos Shiraishi Kogyo K. K. 
Starlex Kamijima Kagaku K. K. 
Furcosil Tagi Seihi K. K. 
______________________________________ 
For the purpose of obtaining a developer exhibiting stable and uniform 
positive chargeability, it has been found effective to impart such a 
property to the developer by treating the above silicate fine powder with 
a silicone oil having an amine structure or unit in the side chain. 
As the above silicone oil having an amine unit in the side chain to be used 
for treatment of the silicate fine powder, silicone oils containing the 
constituent units represented by the formula (I) below ae generally 
available: 
##STR1## 
(wherein R.sub.1 represents hydrogen, alkyl, aryl or alkoxy; R.sub.2 
represents alkylene or phenylene; R.sub.3 and R.sub.4 each represents 
hydrogen, alkyl or aryl; with proviso that the above alkyl, aryl, alkylene 
or phenylene can contain an amine unit, and can also have a substituent 
such as a halogen atom as far as it does not impair chargeability). 
As the commercially available silicone oil having an amine unit in the side 
chain, amino-modified silicone oils represented by the following 
structural formula can be preferably used. 
##STR2## 
(wherein R.sub.1 R.sub.5 respectively represent alkyl or aryl; R.sub.2 
represents phenylene or alkyl containing an amine unit; R.sub.3 represents 
hydrogen, alkyl or aryl; l, m and n are integers of 1 or more). Typical 
examples of the above silicone oil are shown below. These may respectively 
be used individually or as a mixture of two or more kinds. 
______________________________________ 
Viscosity at 
Amine 
Trade name at 25.degree. C. (cps) 
equivalent 
______________________________________ 
SF8417 (Toray Silicone Co.) 
1200 3500 
KF393 (Shinetsu Kagaku Co.) 
60 360 
KF857 (Shinetsu Kagaku Co.) 
70 830 
KF860 (Shinetsu Kagaku Co.) 
250 7600 
KF861 (Shinetsu Kagaku Co.) 
3500 2000 
KF862 (Shinetsu Kagaku Co.) 
750 1900 
KF864 (Shinetsu Kagaku Co.) 
1700 3800 
KF865 (Shinetsu Kagaku Co.) 
90 4400 
KF369 (Shinetsu Kagaku Co.) 
20 320 
KF383 (Shinetsu Kagaku Co.) 
20 320 
X-22-3680 (Shinetsu Kagaku Co.) 
90 8800 
X-22-380D (Shinetsu Kagaku Co.) 
2300 3800 
X-22-3801C (Shinetsu Kagaku Co.) 
3500 3800 
X-22-3810B (Shinetsu Kagaku Co.) 
1300 1700 
______________________________________ 
In the present invention, "amine equivalent" refers to an equivalent amount 
per one amine unit (g/equiv.) which is a value obtained by dividing the 
molecular weight of a silicone oil with the number of amine units in one 
molecule. The silicone oil to be used in the present invention should 
preferably have an amine equivalent of 100 to 4000 for providing positive 
chargeability. 
The amount of the silicone oil having an amine unit in the side chain used 
for treatment in the present invention may be 0.2 to 70% by weight, 
preferably 1 to 60% by weight, of the total amount of the treated silicate 
fine powder. 
The silicone oil having an amine unit in the side chain should preferably 
have a viscosity at 25.degree. C. of 5000 cps or lower, particularly 3000 
cps or lower. If the viscosity is higher than 5000 cps, the silicone oil 
having an amine unit in the side chain can insufficiently be dispersed in 
the silicate fine powder, whereby poor images with much fog may be formed. 
Treatment of the silicate fine powder with the silicone oil having an amine 
unit in the side chain can be carried out as follows. While stirring 
vigorously silicate fine powder optionally under heating, the above 
silicone oil having an amine unit in the side chain or the silicone oil 
dissolved in an organic solvent is blown thereagainst by spraying or by 
vaporization, or alternatively the silicate fine powder is formed into a 
slurry, and the silicone oil having an amine unit in the side chain or its 
solution is added. 
The amount of the thus treated positively chargeable silicate powder 
applied may be 0.05 to 10% by weight based on the toner weight to exhibit 
the effect, particularly preferably 0.1 to 3% by weight. As another method 
for obtaining positively chargeable silicate fine powder in order to 
obtain a developer exhibiting stable and uniform positive chargeability, 
it is also effective to impart the above silicate fine powder treated with 
an aminosilane to the developer. 
The aminosilane to be used for the surface treatment of silicate fine 
powder is an amino-functional silane, which is represented by the 
following formula: 
EQU X.sub.m SiY.sub.n 
(wherein X is an alkoxy or a chlorine atom, m is an integer of 1 to 3, Y is 
a hydrocarbon group having a primary to tertiary amino group, and n is an 
integer of 3 to 1). For example, the following compounds may be included. 
##STR3## 
EQU H.sub.2 N--CONH--CH.sub.2 CH.sub.2 CH.sub.2 --Si--(OC.sub.2 H.sub.5).sub.3 
EQU H.sub.2 N--CH.sub.2 CH.sub.2 CH.sub.2 Si(OCH.sub.2 CH.sub.3).sub.3 
EQU H.sub.2 NCH.sub.2 CH.sub.2 NHCH.sub.2 CH.sub.2 CH.sub.2 Si(OCH.sub.3).sub.3 
EQU H.sub.2 NCH.sub.2 CH.sub.2 CH.sub.2 Si(OCH.sub.3).sub.3 
EQU H.sub.2 NCH.sub.2 CH.sub.2 NHCH.sub.2 CH.sub.2 NHCH.sub.2 CH.sub.2 CH.sub.2 
Si(OCH.sub.3).sub.3 
EQU H.sub.5 C.sub.2 OCOCH.sub.2 CH.sub.2 NHCH.sub.2 CH.sub.2 CH.sub.2 
Si(OCH.sub.3).sub.3 
EQU H.sub.5 C.sub.2 OCOCH.sub.2 CH.sub.2 NHCH.sub.2 CH.sub.2 NHCH.sub.2 
CH.sub.2 CH.sub.2 Si(OCH.sub.3).sub.3 
EQU H.sub.5 C.sub.2 OCOCH.sub.2 CH.sub.2 NHCH.sub.2 CH.sub.2 NHCH.sub.2 
CH.sub.2 NHCH.sub.2 CH.sub.2 NHCH.sub.2 CH.sub.2 CH.sub.2 
Si(OCH.sub.3).sub.3 
EQU NH.sub.2 C.sub.6 H.sub.4 Si(OCH.sub.3).sub.3 
EQU C.sub.6 H.sub.5 NHCH.sub.2 CH.sub.2 CH.sub.2 Si(OCH.sub.3).sub.3 
Alternatively, polyaminoalkyltrialkoxysilanes may be employed. These 
compounds can be used either singly or as a mixture of two or more 
compounds. 
The silicate fine powder to be used in the present invention may be further 
treated with a known treating agent for imparting hydrophobicity. Known 
treatment methods may be available and hydrophobicity can be imparted by 
treating chemically the silicate fine powder with an organic silicon 
compound which can react with or physically adsorbed onto the silicate 
fine powder. Such organic silicon compounds may be exemplified by 
hexamethyldisilazane, trimethylsilane, trimethylchlorosilane, 
trimethylethoxysilane, dimethyldichlorosilane, methyltrichlorosilane, 
allyldimethylchlorosilane, allylphenyldichlorosilane, 
benzyldimethylchlorosilane, bromomethyldimethylchlorosilane, 
bromomethyldimethylchlorosilane, .alpha.-chloroethyltrichlorosilane, 
.beta.-chloroethyltrichlorosilane, chloromethyldimethylchlorosilane, 
triorganosilylmercaptan, trimethylsilylmercaptan, triorganosilylacrylate, 
vinyldimethylacetoxysilane, dimethylethoxysilane, dimethyldimethoxysilane, 
diphenyldiethoxysilane, hexamethyldisiloxane, 
1,3-divinyltetramethyldisiloxane, 1,3-diphenyltetramethyldisiloxane, and 
dimethylpolysiloxanes having 2 to 12 siloxane units per molecule and 
containing hydroxyl group bonded to each one Si of the unit positioned at 
the terminal end. These can be used either singly or as a mixture of two 
or more compounds. 
The developer of the present invention comprises a microdisperser as 
another important constituent. The microdisperser should preferably be 
formed of a metalloid oxide or a metal oxide, particularly an oxide, 
including a double or complex oxide, of a metal element or a metalloid 
element positioned at the fourth period or higher in the periodic table. 
The microdisperser is about 0.1 to 5 microns in size, having a mean 
particle size smaller than the toner and greater than the silicate fine 
powder used in combination. The particle size of these microdispersers can 
be measured according to the same method as used for silicate fine powder. 
The amount of the microdisperser added sould preferably be about 0.5 to 10 
wt. % based on the toner. Particularly, preferable results can be obtained 
when the amount is more than the amount of the silicate fine powder added 
to the toner. Further, the microdisperser should preferably have a lower 
chargeability than the positively chargeable silicate fine powder and 
further a lower chargeability than the positively chargeable toner, in 
order to take in sufficiently the silicate fine powder and deliver it to 
the toner. 
In the positively chargeable developer of the present invention, it is 
preferred to formulate 0.1 to 3 parts by weight of the positively 
chargeable silicate fine powder and 0.5 to 10 parts by weight of the 
microdisperser with respect to 100 parts by weight of the toner in view of 
charging characteristic and durability. 
In the present invention, preferable results can be exhibited when the 
positively chargeable toner has a charging characteristic of +5 to +50 
.mu.c/g according to the measurement method as described above, while the 
microdisperser may have a value lower than that of the toner, which is 
generally about 10 .mu.c/g or lower, to give good results. The particle 
size and charging characteristic of the microdisperser as mentioned above 
are important in the action of the microdisperser on the silicate fine 
powder, and therefore should be selected carefully. 
Examples of the microdisperser include particles of oxides inclusive of 
bismuth oxide such as Bi.sub.2 O.sub.3, molybdenum oxide such as MoO.sub.2 
and MoO.sub.3, vanadium oxide such as V.sub.2 O.sub.3, nickel oxide such 
as NiO, and manganese oxide such as Mn.sub.2 O.sub.3. 
Known binder resins are available for the toner to be used in the present 
invention. For example, it is possible to use homopolymers of styrene and 
its substituted derivatives such as polystyrene, poly-p-chlorostyrene, 
polyvinyltoluene; styrene copolymers such as styrene-p-chlorostyrene 
copolymer, styrene-propylene copolymer, styrene-vinyl toluene copolymer, 
styrene-vinylnaphthalene copolymer, styrene-methyl acrylate copolymer, 
styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, 
styrene-octyl acrylate copolymer, styrene-methyl methacrylate copolymer, 
styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate 
copolymer, styrene-methyl .alpha.-chloromethacrylate, 
styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, 
styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone 
copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, 
styrene-acrylonitrile-indene copolymer, styrene-maleic acid copolymer, 
styrene-maleic acid half ester copolymer, styrene-maleic acid ester 
copolymer; polymethyl methacrylate, polybutyl methacrylate, polyvinyl 
chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, 
polyurethane, epoxy resin, polyvinylbutyral, polyamide, polyacrylic acid 
resin, rosin, modified rosin, terpene resin, phenol resin, aliphatic or 
alicyclic hydrocarbon resin, aromatic petroleum resin, chlorinated 
paraffin, paraffin, wax, either alone or as a mixture. Among them, styrene 
resins such as polystyrene or styrene copolymer, polyester resins and 
acrylic resins are preferable in view of thermal fixing characteristic, 
and developing durability or successive developing characteristic. For a 
pressure fixable toner, wax is preferred. 
The magnetic toner obtained by incorporating a magnetic material in a 
binder resin when formed into particles may have a particle size of 30 
microns or less, preferably 5 to 30 microns which is the toner particle 
size in general. When the mean particle size of the toner is 10 microns or 
less in terms of volume-average particle size, the developing 
characteristic of the positively chargeable developer of the present 
invention can be further improved. 
As the magnetic material to be contained in the toner, ferromagnetic 
elements, alloys containing these, for example, alloys or compounds of 
iron, cobalt, nickel, manganese, etc., such as magnetite, hematite, 
ferrite and other ferromagnetic alloys can be suitably used. The magnetic 
material also serves as a colorant. 
The particle size of the magnetic material may be 100 to 800 m.mu., 
preferably 300 to 500 m.mu., and it is preferably contained in an amount 
of 30 to 100 parts by weight, more preferably 40 to 90 parts by weight, 
per 100 parts by weight of the binder resin. 
Additives such as charge controlling agents, flow improvers, colorants, 
lubricants may be incorporated, if desired, without deviating from the 
present invention. 
When the positively chargeable toner according to the present invention is 
substantially nonmagnetic, the particle size of the toner should 
preferably be 30 microns or smaller, particularly 1 to 10 microns in terms 
of a volume-average particle size. 
As the colorant, it is possible to use dyes or pigments known in the art 
such as carbon black, iron black, Ultramarine Blue, Nigrosine dye, Aniline 
Blue, Phthalocyanine Blue, Phthalocyanine Green, Hansa Yellow G, Rhodamine 
6G lake, Chalcoil Blue, Chrome Yellow, quinacridone, Benzidine Yellow, 
Rose Bengal, triallylmethane, diallylmethane, anthraquinone, monoazo, 
disazo dyes or pigments, either alone or as a mixture. The colorant may be 
used in an amount of generally 0.5 to 30 parts by weight per 100 parts by 
weight of the binder resin. 
Illustrative of the positive charge controlling agent are nigrosine, azine 
dyes, quaternary ammonium salts, guanidine compounds, triazine compounds 
and dialkyltin oxides. The positive charge controlling agent is added in 
an amount of generally about 0.1 to 10 parts by weight based on 100 parts 
by weight of the binder resin. 
In preparation of the toner of the present invention, there may be adopted 
a method in which constituent materials are well kneaded by a hot kneading 
machine such as hot roll, kneader or extruder, then the kneaded product is 
cooled and crushed by means of a mechanical crushing means, and the 
crushed product is classified. 
It is also possible to apply the method of obtaining a toner in which a 
material such as magnetic powder is dispersed in a binder resin solution, 
and the dispersion is then spray dried, or the toner preparation method in 
which an emulsion or suspension containing the constituent materials 
dispersed in a polymerizable monomer providing the binder resin is 
polymerized to give a toner. 
Recently, for the purpose of separating the required functions of a toner, 
microencapsulated toner has been proposed. The present invention can also 
be applied to a developer containing a microcapsule toner. 
As the method for mixing positively chargeable silicate fine powder and 
microdisperser with said toner, rotary vessel type mixers such as a V type 
mixer and Turbula mixer; stationary vessel type mixers such as a 
ribbon-type, a screw-type, a rotary blade-type mixer may be used. 
The three components may be mixed at a time during mixing, or alternatively 
in a successive order in view of the properties of the toner. Further, a 
known fourth substance can be also added. For example it is possible to 
add polyethylene fluoride, polyvinylidene fluoride, aliphatic metal salts, 
various abrasives within an extent not adversely affecting the present 
invention.

The present invention is described in more detail by referring to the 
following Examples, in which "parts" indicate "parts by weight". 
EXAMPLE 1 
A toner of 5 to 20 microns (number-average size 15.3 microns) comprising 
100 parts of a polystyrene (D-125, produced by Hercules Inc.), 50 parts of 
magnetite (EPT-500, produced by Toda Kogyo K.K.) and 5 parts of nigrosine 
dye was obtained in a conventional manner including melt-kneading and 
crushing. A developer comprising 100 parts of the toner, one part of a 
treated silica (number-average size: 0.2 micron) obtained by treating 
colloidal silica (Aerosil #200, produced by Nippon Aerosil) with an 
amino-modified silicone oil (viscosity: 20 cps, amine equivalent: 320), 
and 5 parts of bismuth oxide (Bi.sub.2 O.sub.3, number-average size: 2.2 
microns) was prepared by mixing and applied to a commercially available 
plain paper copying machine (NP-150Z, produced by Canon K.K.). As a 
result, a very sharp image with a reflection density of 1.2 to 1.4 and 
free of fog could be obtained from the first sheet. When 200 sheets of 
copying were performed, the same good density as in the first sheet was 
obtained and no fluctuation in density was observed. Further, after the 
developer was left to stand for 40 days, copied image was again obtained 
and it was found to have the same image density of a reflection density of 
1.2 to 1.4 as the initial stage, thus providing a very sharp image free of 
fog. 
The triboelectric charges of the toner, the positively chargeable silicate 
fine powder and bismuth oxide were measured according to the method as 
described above to obtain the values of +15 .mu.c/g, about +200 .mu.c/g 
and about +3 .mu.c/g, respectively. 
EXAMPLE 2 
A toner of 5 to 20.mu. (number-average size: 15.3.mu.) comprising 100 parts 
of a polysyrene (D-125, produced by Hercules Inc.), 50 parts of magnetite 
(EPT-500, produced by Toda Kogyo K.K.) and 5 parts of nigrosine dye was 
obtained in a conventional manner. A developer comprising 100 parts of the 
toner, 0.5 part of a treated silica (number-average size: 0.08.mu.) 
obtained by treating colloidal silica (Aerosil #200, produced by Nippon 
Aerosil K.K.) with aminosilane and hydrophobic modifying agent in the 
manner as described above, and 2 parts of molybdenum oxide MoO.sub.2, 
number-average size: 2.2.mu.), was prepared and applied to a commercially 
available plain paper copying machine (NP-150Z, produced by Canon K.K.). 
As a result, a very sharp image with a reflection density of 1.2 to 1.4 
and free of fog could be obtained from the first sheet. When 200 sheets of 
copying were performed, the same good density as in the first sheet was 
obtained and no fluctuation in density was observed. Further, after the 
developer was left to stand for 40 days, copied image was again obtained 
and it was found to have the same image density of a reflection density of 
1.2 to 1.4 as the initial stage, thus providing a very sharp image free of 
fog. 
The triboelectric charge of the positively chargeable silicate fine powder 
was about +90 .mu.c/g. The triboelectric charge of molybdenum oxide was 
slightly lower than that of the toner. 
EXAMPLE 3 
A toner of 5 to 20 microns (number-average size: 11.5 microns) comprising 
100 parts of a styrene 2-ethylhexyl acrylate copolymer (produced by Sanyo 
Kasei K.K.), 50 parts of magnetite (EPT-500, produced by Toda Kogyo K.K.), 
and 5 parts of dibutyltin oxide was obtained in a conventional manner. A 
developer comprising 100 parts of the toner, 0.5 part of a treated silica 
(number-average size: 0.08 micron) of colloidal silica (Aerosil #200, 
produced by Nippon Aerosil K.K.) treated with aminosilane and hydrophobic 
modifying agent as described above and 0.8 part of vanadium oxide (V.sub.2 
O.sub.3, number-average size: 1.8 micron) was prepared by mixing and 
applied to a commercially available plain paper copying machine (NP-150Z, 
produced by Canon K.K.). As a result, a very sharp image with a reflection 
density of 1.2 to 1.4 free of fog could be obtained from the first sheet. 
When 200 sheets of copying were performed, the same good density as in the 
first sheet was obtained and no fluctuation in density was observed. 
Further, after the developer was left to stand for 40 days, copied image 
was again obtained and it was found to have the same image density of 
reflection density of 1.2 to 1.4 as the initial stage, thus providing a 
very sharp image free of fog. 
The triboelectric charge of the toner was about +25 .mu.c/g. The 
triboelectric charge of vanadium oxide was slightly lower than that of the 
toner. 
EXAMPLE 4 
A toner of 5 to 20 microns (number-average size: 11.5 microns) comprising 
100 parts of a styrene 2-ethylhexyl acrylate copolymer (produced by Sanyo 
Kasei K.K.), 50 parts of magnetite (EPT-500, produced By Toda Kogyo K.K.), 
and 5 parts of dibutyltin oxide was obtained in a conventional manner. A 
developer comprising 100 parts of the toner, 1 part of a treated silica 
(number-average size: 0.2 micron) obtained by treating colloidal silica 
(Aerosil #200, produced by Nippon Aerosil K.K.) with the amino-modified 
silicone oil and 3 parts of nickel oxide (NiO, number-average size: 0.5 
micron) was prepared by mixing and applied to a commercially available 
plain paper copying machine (NP-150Z, produced by Canon K.K.). As a 
result, a very sharp image with a reflection density of 1.2 to 1.4 and 
free of fog could be obtained from the first sheet. When 200 sheets of 
copying were performed, the same good density as in the first sheet was 
obtained and no fluctuation in density was observed. Further, after the 
developer was left to stand for 40 days, copied image was again obtained 
and it was found to have the same image density of a reflection density of 
1.2 to 1.4 as the initial stage, thus providing a very sharp image free of 
fog. 
The triboelectric charge of nickel oxide was slightly lower than that of 
the toner. 
EXAMPLE 5 
A toner of 5 to 20 microns (number-average size: 11.5 microns) comprising 
100 parts of a styrene 2-ethylhexyl acrylate copolymer (produced by Sanyo 
Kasei K.K.), 50 parts of magnetite (EPT-500, produced by Toda Kogyo K.K.), 
and 5 parts of dibutyltin oxide was obtained in a conventional manner. A 
developer comprising 100 parts of the toner, 2 parts of a treated silica 
(number-average size: 0.08 micron) obtained by treating colloidal silica 
(Aerosil #200, produced by Nippon Aerosil K.K.) with the aminosilane and 
the hydrophobic modifying agent as described above, and 8 parts of 
manganese oxide (Mn.sub.2 O.sub.3, number-average size: 4 microns) was 
prepared by mixing and applied to a commercially available plain paper 
copying machine (NP-150Z, produced by Canon K.K.). As a result, a very 
sharp image with a reflection density of 1.2 to 1.4 and free of fog could 
be obtained from the first sheet. When 200 sheets of copying were 
performed, the same good density as in the first sheet was obtained and no 
fluctuation in density was observed. Further, after the developer was left 
to stand for 40 days, copied image was again obtained and it was found to 
have the same image density of a reflection density of 1.2 to 1.4 as the 
initial stage, thus providing a very sharp image free of fog. 
The triboelectric charge of manganese oxide was slightly lower than that of 
the toner. 
COMATIVE EXAMPLE 1 
The same experiment as Example 1 was conducted except for adding no bismuth 
oxide. As a result, the initial image had a reflection density of 0.8 to 
1.0, was slightly fogged, and accompanied with some toner scattered around 
the letter images. When copying was further continued, the reflection 
density changed and became 1.2 to 1.4 after copying of about 50 to 150 
sheets. Further, after the developer was left to stand for 40 days, 
copying was performed again. The obtained copied image had a reflection 
density of 0.6 to 0.8, with more fog and inferior with excessive 
scattering of tone around letter images as compared with that obtained in 
Example 1. 
COMATIVE EXAMPLE 2 
The same experiment as Example 2 was conducted except for adding no 
molybdenum oxide. As a result, the initial image had a reflection density 
of 0.8 to 1.0, was slightly fogged, and accompanied with some toner 
scattered around the letter images. When copying was further continued, 
the reflection density changed and became 1.2 to 1.4 after copying of 
about 50 to 150 sheets. Further, after the developer was left to stand for 
40 days, copying was performed again. The obtained copied image had a 
reflection density of 0.6 to 0.8, with more fog and inferior with 
excessive scattering of toner around letter images as compared with that 
obtained in Example 2. 
COMATIVE EXAMPLE 3 
The same experiment as Example 3 was conducted except for adding no 
vanadium oxide. As a result, the initial image had a reflection density of 
0.8 to 1.0, was slightly fogged and accompanied with scattering of toner 
around the letter images. When copying was further continued, the 
reflective density changed and became 1.2 to 1.4 after copying of about 50 
to 150 sheets. Further, after the developer was left to stand for 40 days, 
copying was performed again. The obtained copied image had a reflection 
density of 0.6 to 0.8, with more fog and inferior with excessive 
scattering of toner around letter images as compared with that obtained in 
Example 3. 
COMATIVE EXAMPLE 4 
The same experiment as Example 4 was conducted except for adding no nickel 
oxide to obtain only the same result as in Comparative Example 3. 
COMATIVE EXAMPLE 5 
The same experiment as Example 5 was conducted except for adding no 
manganese oxide to obtain only the same result as in Comparative Example 
3. 
COMATIVE EXAMPLE 6 
The same experiment as Example 3 was conducted except for using colloidal 
silica (Aerosil #200) not treated with the amino-modified silicone oil for 
imparting positive chargeability. As a result, the initial image had a 
reflective density of 0.8 to 1.0, was slightly fogged, and accompanied 
with scattering of toner around the letter images. When copying was 
further continued, the reflection density remained low. 
COMATIVE EXAMPLE 7 
The same experiment as Example 2 was conducted except for adding no 
positively chargeable silicate fine powder. As a result, the initial image 
had a reflective density of 0.4 to 0.6, was slightly fogged, and 
accompanied with toner scattering around the letter images. When copying 
was further continued, the reflection density remained as low as about 0.5 
to 0.6 even after 2000 sheets of copying. Further, after the developer was 
left to stand for 40 days, copying was performed to give a copied image 
with a reflection density of 0.6 to 0.8, which was more fogged and 
inferior with excessive scattering of toner around the letter images than 
Example 2. 
EXAMPLE 6 
A toner of 1 to 15 microns (number average size: 7.3 microns; volume 
average particle size: about 9 microns) comprising 100 parts of a styrene 
butyl methacrylate copolymer (copolymerization weight ratio: 65:35, 
weight-average molecular weight: about 60,000), 50 parts of magnetite 
(mean particle size: about 0.13 micron) and 5 parts of nigrosine dye was 
obtained in a conventional manner. A developer comprising 100 parts of the 
toner, one part of a treated silica (number-average size 0.2 micron) 
obtained by treating colloidal silica (Aerosil #200, produced by Nippon 
Aerosil) amino-modified silicone oil (viscosity: 20 cps, amine equivalent: 
320), and 5 parts of bismuth oxide (Bi.sub.2 O.sub.3, length average size: 
2.2 microns), was prepared by mixing and applied to a commercially 
available plain paper copying machine (NP-150Z, produced by Canon K.K.). 
As a result, a very sharp image with a reflection density of 1.3 to 1.4 
and free of fog could be obtained from the first sheet. When 200 sheets of 
copying were performed, the same good density as in the first sheet was 
obtained and no fluctuation in density was observed. Further, after the 
developer was left to stand for 40 days, copied image was again obtained 
and it was found to have the same image density of a reflection denisty of 
1.2 to 1.4 as the initial stage, thus providing a very sharp image free of 
fog. When a fine line image of 250 lines per inch was copied, good copied 
image was obtained, whereby it was confirmed that excellent 
reproducibility of fine line image could be obtained. 
Further, due to presence of the microdisperser and the positively 
chargeable silica, appearance of toner agglomerated mass as ordinarily 
observed in small particle size toners was inhibited. 
The triboelectric charges of the toner, the positively chargeable silicate 
fine powder and bismuth oxide were measured according to the method as 
described above to obtain the values of about +48 .mu.c/g, about +200 
.mu.c/g and about +3 .mu.c/g, respectively.