Developer having specific spheriodicity

This invention relates to a two-components developer containing toners and carriers wherein the toners have spheroidicity of 150 or less, mean particle size of 14 .mu.m or less and coefficient of variation of 15% or less, and the carriers have mean particle size of between 20 .mu.m and 70 .mu.m and/or spheroidicity of 140 or more.

BACKGROUND OF THE INVENTION 
This invention relates to a developer for electrostatic latent images in 
electrophotography, electrostatic record or electrostatic printing, more 
particularly, to a developer that can duplicate images finely, in high 
quality, and without toner scattering. 
As a copying machine for electrophotography has become popular to be used 
generally, copied images are required to have higher quality and finer 
reproducibility, mesh pattern reproducibility or half-tone reproducibility 
than before. It is necessary to use toners with as small size and as sharp 
distribution as possible in order to meet the requirements. The sharp 
distribution of particle sizes improves line reproducibility, mesh pattern 
reproducibility or half-tone reproducibility and the like, and further 
effects sharp charge-distribution to result in the improvement of image 
quality such as texture and the like. Techniques that specify the 
distribution of particle sizes are known in the disclosures of, for 
example, Japanese patent application of published No. 24369/1982 and 
Japanese patent application of laid open Nos. 106554/1983, 275766/1986 or 
275767/1986 etc. 
However, to make particle sizes of toners small results in the decrease of 
fluidity of toners itself or developers. Therefore, it is desirable to 
make toners spherical as well as to make particle sizes of toners small in 
order to prevent the decrease of fluidity of toners or developers. 
When toners are made spherical, there arise other problems such as low 
contact-possibility and low chargeability because of the spherical shapes. 
That is, the use of ferrite type carriers which are used generally for 
toners of small sizes or spherical toners results in the formation of 
copied images with many fogs on account of poor electrification-build-up, 
broadening of charge distribution and flying of many toners and the like. 
SUMMARY OF THE INVENTION 
The object of the invention is to provide a developer containing small and 
spherical toners with narrow distribution of particle sizes, which is 
excellent in fluidity, electrification-build-up, prevention of toner 
scattering and prevention of fogs. 
The object is achieved by a two components developer containing toners and 
carriers wherein the toners have spheroidicity of 150 or less, mean 
particle size of 14 .mu.m or less and coefficient of variation of 15% or 
less, and the carriers have mean particle size of between 20 .mu.m and 70 
.mu.m and/or spheroidicity of 140 or more. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention provides a developer excellent in fluidity, 
electrification-build-up, charge stability, prevention of toner scattering 
and formation of copied images of high quality without fogs even if small 
and spherical toners with narrow distribution of particle sizes are used. 
The present invention has accomplished the above object by the combination 
of specified toners and specified carriers in sizes and shapes. 
A developer of the present invention comprises toners and carriers wherein 
toners have spheroidicity of 150 or less, mean particle size of 14 .mu.m 
or less and coefficient of variation of 15% or less, and the carriers have 
mean particle size of between 20 .mu.m and 70 .mu.m and/or spheroidicity 
of at least 140. 
From the view point of the formation of high quality copied images, it is 
preferable that the particle size of a toner to be smaller as well as the 
distribution of particle sizes of toner to be narrower. 
However, the use of spherical toners having small particle sizes of 14 
.mu.m or less, particularly 2 .mu.m-10 .mu.m in mean particle size, 15% or 
less, particularly 10% or less in coefficient of variation and 150 or 
less, particularly 140 or less in spheroidicity together with generally 
used carriers which do not have specified size and shape causes the 
problems such as toner scattering, toner-chargeability and the like. In 
practice, the combination of the above toners with the carriers does not 
effect the formation high quality copied images, resulting in the 
generation of fogs and the like. 
Fluidity is in general one of important properties of toners. However, the 
fluidity is much important for toners of small particle sizes, because the 
size is one of elements to achieve the formation of high quality copied 
images as shown in the invention. In general, the bigger, the size of 
toner is, or the sharper, the distribution of particle size is, or the 
more spherical, the shape of toner is, the better, the fluidity is. From 
the view point of copied image quality, it is necessary to make particle 
size small up to 14 .mu.m or less, preferably 2-14 .mu.m, more preferably 
2-10 .mu.m in mean particle size. The particle size required for fluidity 
conflicts with that required for image quality. However, although toners 
are small in particle size, mixing and stirring properties are maintained 
in practical use and good image quality can be achieved in the combination 
of toners having both spheroidicity (SF1) of 150 or less and coefficient 
of variation of 15% or less with a carrier having specified size and shape 
as described below. 
In particular, the toners for use in the present invention which are small 
in mean particle size and narrow in particle size distribution are 
accompanied with problems such as electrification-build-up and toner 
scattering. However those problems can be solved by use of carriers of 
20-70 .mu.m in mean particle size and/or 140 or more in spheroidicity. 
Carriers with the specified size and/or the specified shape as above 
mentioned can mix, stir and charge uniformly and quickly spherical toners 
of small sizes and narrow particle size distribution, resulting in 
effective electrification-build-up and prevention of toner flying, and can 
provide high quality copied images without fogs and the like, taking 
advantages of the benefits of toners of small particle sizes and narrow 
particle size distribution. 
The particle sizes of carriers particularly effect 
electrification-build-up, stability and prevention of toner flying. 
Carriers out of the range of 20-70 .mu.m in mean particle size can not 
achieve the foregoing effects sufficiently. 
The spheroidicity of carriers also effects electrification-build-up, 
stability and prevention of toner flying. Carriers with spheroidicity of 
less than 140 can not achieve the foregoing effects sufficiently. 
Most preferably carriers in the present invention have 20-70 .mu.m in mean 
particle size and 140 or more in spheroidicity. 
Spheroidicity is one of shape coefficients which specify shapes of 
particles, abbreviated to "SF1". SF1 is defined as; 
##EQU1## 
Wherein "area" means the projected area of a particle and "maximum length" 
means the longest length in the projected image of a particle. 
SF1 is used as a parameter which shows the difference between the long 
diameter and short diameter of a particle (distortability), shows the 
external surface area of a particle and the degree of roughness of a 
particle surface. The value of SF1 becomes near to the value of 100 as the 
shape is closer to a circle. 
Spheroidicity in the invention is expressed by the mean value measured with 
Image Analyzer (LUZEX 5000, made by Nihon Regulator K.K.), but, the value 
is limited to the one measured by the above Image Analyzer, because the 
value does not depend generally on a kind of measuring apparatus. 
Coefficient of variation in the present invention means variation measures 
(%) obtained as follows; a photograph is taken with a scanning electron 
microscope, one hundred of particles are taken at random for measurement 
of particle sizes to obtain a standard deviation value (.sigma.), the 
standard deviation value (.sigma.) is divided by the mean particle size 
(x), and one hundred times the divided value is the coefficient of 
variation (%). 
The standard deviation value is represented by the square root of the total 
values of the square of the difference between the mean particle size and 
each particle size represented by the following formula; 
##EQU2## 
Wherein x.sub.1, x.sub.2 ---, xn represent respective particle sizes of 
sample particles, x represents the mean value of the n particle sizes. 
The mean value of toners in the present invention is shown by a value 
obtained by measuring relative weight distribution of each particle size 
with Coulter Counter II (made by Coulter Counter Inc.,) equipped with 
aperture tube of 100 .mu.m. 
The mean value of carriers is shown by a value measured with Micro Truck 
Model 7995-10SRA (made by Nikkiso K.K.). 
As above mentioned, the specified size and shape etc. of carriers are 
significant elements in order to form high quality copied images without 
toner scattering, fogs and the like by using spherical toners which are 
narrow in particle size distribution and small in particle size 
Further, the aggregation properties of developers, spent phenomena of 
carriers, the density of images and carrier lines and the like have been 
found to be related to solid state properties such as the magnetic force 
of carriers and the specific gravity of carriers. 
That is, the magnetic force of carriers needs 900-3000 gauss, preferably 
1800-2800 gauss in the magnetic field of 1000 Oe. 
If the magnetic force is smaller than 900 gauss in the magnetic field of 
1000 Oe, carriers come to be developed, and copied images become 
deteriorated. If the magnetic force is bigger than 3000 gauss, ears of 
magnetic brushes become hard, resulting in the generation of carrier lines 
in solid parts etc. 
The preferred specific gravity of carriers is 5 or less from the view point 
of the improvement of mixing and stirring properties and aggregation 
properties as developers. If the specific gravity of carriers is bigger 
than 5, the large difference of specific gravity between toners and 
carriers deteriorates mixing and stirring properties, the excessive stress 
to toners causes spent carriers resulting in the deterioration of the 
charging stability, and toners and/or carriers become liable to aggregate. 
Toners for use in the present invention may be prepared by a known method 
such as a suspension-polymerizing method, a encapsulizing method, a 
spray-drying method and the like so far as the toners may be applied to a 
developing system of two-components. Carriers for use in the present 
invention are not limited to specified ones by kinds of carriers and its 
production method etc., but exemplified by ferrite, coated iron particles, 
coated ferrite, granulated iron particles, binder-type carriers, 
surface-modified carriers.

Carriers and toners with specified sizes and shapes are mixed at the 
content of 1-20 wt% of toners for the preparation of a developer the 
present invention. 
Production Methods of toners 
Production examples of Toners a-c 
One hundred parts by weight of spherical monodisperse copolymer of styrene 
with n-buthyl methacrylate (8 .mu.m in mean particle size: 54 .degree. C. 
in glass transition temperature: 128 .degree. C. in softening temperature) 
prepared by seed polymerization, 8 parts by weight of carbon black (MA#8; 
made by Mitsubishi Kasei Kogyo K.K.) were set in Henshel Mixer with 
capacity of 10 liters, mixed and stirred for 2 minutes at the rotation 
speed of 1500 rpm, so that carbon black might be adhered to the surfaces 
of polymer particles. And then, the resultant particles with carbon black 
particles were treated at 7000 rpm for 3 minutes with the use of 
Hybridization System NHS-1 (made by Nara Kikai Seisakusho K.K.), so that 
the carbon black particles might be fixed to the surfaces of the copolymer 
particles. 
Then, 100 parts by weight of the resultant polymer particles treated with 
carbon black and 10 parts by weight of PMMA particles MP-1451 (0.15 .mu.m 
in mean particle size; 125 .degree. C. in glass transition temperature: 
made by Soken Kagaku K.K.) were mixed and stirred in a same manner as that 
of the above process, so that the surfaces of the polymer particles were 
coated with the PMMA resin. Furthermore, 100 parts by weight of the 
obtained PMMA-coated polymer particles, and 0.5 parts by weight of Spilon 
Black TRH of chromium-type dye (made by Hodoya Kagaku Kogyo K.K.) as a 
negative charge-controlling agent were mixed and stirred in the same 
manner as that of the above process, so that the particles of Spilon Black 
might be fixed to the surfaces of the polymer particles, to obtain Toner a 
of 8.3 .mu.m in mean particle size, 132 in spheroidicity and 8% of 
coefficient of variation. 
Toners b and c were prepared in a similar manner to the preparation of 
Toner a except that materials shown in the following Table 1 were used for 
toner productions. 
TABLE 1 
__________________________________________________________________________ 
seed polymer fine mean 
polymeriza- particles for 
charge particle 
sphero- 
efficient 
toner 
tion particle the formation 
controlling 
size of 
idicity 
of 
sample 
size (.mu.m) 
carbon black 
of coating layer 
agent toner 
SF1 variation 
__________________________________________________________________________ 
a 8 MA#8 MP-1451 Spilon Black 
8.3 132 8 
b 3 8 parts by weight 
10 parts by weight 
TRH 0.5 parts 
3.2 131 8 
c 12 made by Mitsubishi 
made by Soken 
by weight 
12.4 133 8 
Kasei Kogyo K.K. 
Kogaku K.K. 
made by Hodoya 
Kogaku K.K. 
__________________________________________________________________________ 
Production examples of Toners d-f 
______________________________________ 
ingredients parts by weight 
______________________________________ 
styrene 70 
n-butyl methacrylate 30 
2,2'-azobis(2,4-dimethylvaleronitrile) 
0.5 
carbon black MA#8 8 
(made by Mitsubishi Kasei Kogyo K.K.) 
Spilon Black TRH of chromium 
5 
complex-type dye 
(made by Hodoya Kagaku Kogyo K.K.) 
______________________________________ 
The above ingredients were mixed sufficiently with the use of Sand-Stirrer 
to prepare a polymerizable composition. This polymerizable composition was 
mixed with an aqueous solution of arabic gum of a concentration of 3% by 
weight, and they were stirred at 4000 rpm with the use of T.K. AUTO HOMO 
MIxER (manufactured by Tokushukika Kogyo K.K.) to polymerize them at the 
temperature of 60.degree. C. for 6 hours, and they were heated to 80 
.degree. C. and further polymerized them. After their polymerization, the 
system of reaction was rinsed five times, then, filtered, dried, and 
air-classified resulting in spherical particles. 
The bigger particles among the spherical particles obtained by the above 
air-classification were further classified to obtain Toner d of 16.4 .mu.m 
in mean particle size, 118 in spheroidicity of toner, 13% in coefficient 
of variation of particle size distribution, 141.degree. C. in softening 
point (Tm) and 61.degree. C. in glass transition point (Tg). 
The smaller particles among the spherical particles obtained by the above 
air-classification were further classified to obtain Toner e of 8.1 .mu.m 
in mean particle size, 19% in coefficient of variation of particle size 
distribution. 
The above obtained toners were further classified repeatedly to obtain 
Toner f of 8.4 .mu.m in mean particle size, 117 in spheroidicity and 13% 
in coefficient of variation of particle size distribution. 
Production examples of Toners g and h 
______________________________________ 
parts 
ingredients by weight 
______________________________________ 
styrene-n-butyl methacrylate 
100 
(softening point of 132.degree. C.; glass transition point of 
60.degree. C.) 
carbon black 8 
(MA#8; made by Mitsubishi Kasei Kogyo K.K.) 
Spilon Black TRH of chromium complex-type dye 
3 
(made by Hodoya Kagaku Kogyo K.K.) 
______________________________________ 
The above-mentioned ingredients were sufficiently mixed by means of ball 
mills, thereafter being kneaded over a three-roller heated to 140.degree. 
C. The kneaded mixture was left to stand for cooling it, and coarsely 
pulverized by means of feather mills. Then, the obtained particles were 
further pulverized into fine particles under jet stream, following by 
being air-classified to obtain Toner g of 8.5 .mu.m in mean particle size, 
162 in spheroidicity and 18% in coefficient of variation of particle size 
distribution. 
The above obtained Toner g was further classified to obtain Toner h of 8.3 
.mu.m in mean particle size, 163 in spheroidicity, 12% in coefficient of 
variation of particle size distribution. 
Production example of Toner i 
Toner i was prepared in a similar manner to Production example of Toner a 
except that Nigrosine Base Ex (made by Orient Kagaku Kogyo K.K.) of 0.6 
parts by weight was used as a charge controlling agent. Toner i was 
positive-chargeable and had 8.2 .mu.m in mean particle size, 131 in 
spheroidicity and 8 in coefficient of variation. 
Production examples of Carriers A-H 
FeO.sub.3 was used as a main component of a carrier and mixed with CuO, 
NiO, ZnO, MuO, MgO so that the mixture might meet desired properties. The 
mixture was dispersed in an aqueous solution of polyvinyl alcohol to mix 
it by means of ball mills. Thus, a slurry of poly-vinylalcohol aqueous 
solution containing materials for carriers was prepared. The slurry was 
sprayed and dried with a spray-drier to obtain spherical particles of 
30-80 .mu.m. The particles were sintered for about 10 hours at the 
temperature of 1000.degree. C. under nitrogen atmosphere, followed by 
cooling them. On the other hand, styrene-acrylic resin of Hymer SBM 73 
(made by Sanyo Kasei Kogyo K.K.) was dispersed and stirred uniformly in 
toluene with the help of high shearing stirring. Then, the above obtained 
ferrite particles were added to the dispersion, followed by being 
subjected to spray-drying with a spray-drier, and they were cooled. Then, 
the resultant ferrite particles were sifted through sieve openings so that 
particles with desired particle size might be obtained. Thus, Carriers A-H 
having solid state properties shown in table 2 were prepared. 
TABLE 2 
______________________________________ 
magnetization 
particle in-magnetic 
Carrier size field of specific 
sample spheroidicity 
(.mu.m) 1000 e (gauss) 
gravity 
______________________________________ 
A 132 75 3500 5.2 
B 131 75 800 5.1 
C 131 75 1200 5.2 
D 131 75 2800 5.2 
E 132 15 3500 5.2 
F 131 25 3500 5.2 
G 131 45 3500 5.2 
H 131 65 3500 5.2 
______________________________________ 
Production example of Carrier J 
Bigger particles among ferrite particles with the same composition as that 
of non-coated Carrier A in Production examples A-H were pulverized by use 
of Hybridization System NHS of Nara Kikai K.K. for 2 minutes at 6000 rpm 
to obtain ferrite particles. And then, obtained ferrite particles were 
coated with resin and classified in a manner similar to that of Production 
examples A-H to prepare Carrier J of 75 .mu.m in particle size, 157 of 
spheroidicity, 3500 gauss in magnetization in the magnetic field of 1000 
Oe, and 5.2 in specific gravity. 
Production example of Carrier K 
Carrier K was prepared in a similar manner to Production example of Carrier 
J except that ferrite particles with the same composition as that of 
non-coated Carrier D were used. Carrier D had 50 .mu.m in mean particle 
size, 156 in spheroidicity, 2800 gauss in magnetization in the magnetic 
field of 1000 Oe and 5.2 in specific gravity. 
Production examples of Carriers L and M 
Iron particles (KG series; made by Kanto Denka K.K.) were used as core 
particles, and coated with resin and classified in a similar manner to 
Production example of Carrier A-I to prepare Carriers L and M having solid 
state properties shown in Table 3. 
TABLE 3 
______________________________________ 
magnetization 
particle in-magnetic 
Carrier size field of specific 
sample spheroidicity 
(.mu.m) 1000 e (gauss) 
gravity 
______________________________________ 
L 145 50 4500 6.7 
M 146 75 4500 6.7 
______________________________________ 
Production examples of Carriers N and O 
______________________________________ 
parts 
ingredients by weight 
______________________________________ 
polyester resin 100 
(softening point of 123.degree. C.; glass transition point of 
65.degree. C., AV of 23, OHV of 40) 
Ferrite fine particles of Fe--Zn series 
500 
(MFP-2; made by TDK K.K.) 
carbon black 2 
(AM#8; made by Mitsubishi Kasei) 
______________________________________ 
The above ingredients were mixed and ground sufficiently in a Henshel 
mixer, followed by being fused and kneaded with a extrusion kneader in 
which the cylinder part was set at 180.degree. C. and the cylinder head 
part was set at 170.degree. C. The kneaded mixture was left to stand for 
cooling, and coarsely pulverized by means of feather mills. Then, the 
obtained particles were further pulverized into fine particles under jet 
stream, followed by being classified under different classifying 
conditions by a classifier to obtain carriers N and O; 
60 .mu.m (Carrier N) 
75 .mu.m (Carrier O) in mean particle size; 
165 in spheroidicity 
2400 gauss in magnetization in the magnetic field of 1000 Oe 
3.4 in specific gravity 
Production example of Carrier P 
______________________________________ 
ingredients parts by weight 
______________________________________ 
styrene-n-butyl methacrylate 
100 
(softening point of 132.degree. C., glass transition 
point of 60.degree.) 
inorganic magnetic particles 
500 
(EPT-1000; made by Toda Kogyo K.K.) 
Carbon black 2 
(MA#8; made by Mitsubishi Kasei Kogyo K.K.) 
______________________________________ 
The above ingredients were used to prepare Carrier P in a similar manner to 
the Production example of Carrier N. Carrier P had 35 .mu.m in mean 
particle size, 165 in spheroidicity, 2100 gauss in magnetization in the 
magnetic field of 1000 Oe and 2.5 in specific gravity. 
Production example of Carrier Q 
Carrier Q was prepared in a similar manner to the Production example N 
except that 100 parts by weight of ferrite fine particles of Fe-Zn series 
(MFP-2; made by TKD K.K.) were used and 400 parts by weight of 
non-magnetic ferrite of CuFe.sub.2 O.sub.4 -CuMn.sub.2 O.sub.4 composition 
(made by Dainichi Seika Kogyo K.K.) were used. Carrier Q had 75 .mu.m in 
mean particle size, 166 in spheroidicity, 800 gauss in magnetization in 
the magnetic field of 1000 Oe and 2.7 in specific gravity. 
Production examples of Carriers R, S and T 
Carriers N, O and Q were treated by means of Angmill in order to make them 
spherical. Carriers R, S and T having properties shown in Table 4 were 
obtained. 
TABLE 4 
______________________________________ 
magnetiza- 
tion in 
particle magnetic 
Carrier 
spheroid- 
size field of specific 
sample icity (.mu.m) 1000 e (gauss) 
gravity 
comment 
______________________________________ 
R 137 60 2400 3.4 made 
spherical 
S 136 75 2400 3.4 made 
spherical 
T 136 75 800 2.7 made 
spherical 
______________________________________ 
The resultant toners and carriers were summarized in Table 5 and Table 6 
below. 
TABLE 5 
______________________________________ 
particle coefficient 
Toner size of evaluation 
production 
sample spheroidicity 
(.mu.m) (%) method 
______________________________________ 
a 132 8.3 8 
b 131 3.2 8 
c 133 12.4 8 
d 118 16.4 13 * 
e 118 8.1 19 * 
f 117 8.4 13 * 
g 162 8.5 18 ** 
h 163 8.3 12 ** 
i 131 8.2 8 
______________________________________ 
*suspension polymerized toner 
**pulverizing method 
TABLE 6 
__________________________________________________________________________ 
magnetization in 
carrier particle 
magnetic field 
specific 
sample 
spheroidicity 
size (.mu.m) 
of 1000 Oe (gauss) 
gravity 
comment 
__________________________________________________________________________ 
A 132 75 3500 5.2 coated ferrite 
B 131 75 800 5.1 coated ferrite 
C 131 75 1200 5.2 coated ferrite 
D 131 75 2800 5.2 coated ferrite 
E 132 15 3500 5.2 coated ferrite 
F 131 25 3500 5.2 coated ferrite 
G 131 45 3500 5.2 coated ferrite 
H 131 65 3500 5.2 coated ferrite 
J 157 75 3500 5.2 coated ferrite (pulverized) 
K 156 50 2800 5.2 coated ferrite (pulverized) 
L 145 50 4500 6.7 coated granular iron particle 
M 146 75 4500 6.7 coated granular iron particle 
N 165 60 2400 3.4 binder type 
O 165 75 2400 3.4 binder type 
P 165 35 2100 2.5 binder type 
Q 166 75 800 2.7 coated ferrite 
R 137 60 2400 3.4 binder type (made spherical) 
S 136 75 2400 3.4 binder type (made spherical) 
T 136 75 800 2.7 binder type (made spherical) 
__________________________________________________________________________ 
Evaluation for Properties 
One hundred parts by weight of each of the above-mentioned Toners a-i were 
subjected to surface treatment with 0.1 part by weight of Colloidal Silica 
R-972 (produced by Nippon Aerogile K.K.). The treated toners were used for 
evaluation of various properties. 
Two grams of the respective surface-treated toners, and 28 grams of the 
specified carrier shown in Table 7 were put in a poly bottle of a capacity 
of 50 cc, and were stirred respectively for 3 minutes, 10 minutes, and 30 
minutes. Then, the resultant charge amount and scattering amount were 
measured so as to examine the electrification-build-up properties of the 
Toners after the poly bottle was rotated on a rotating carriage at 1200 
rpm. 
The scattering amount was measured with the use of a digital dust measuring 
apparatus of P5H2 type (manufactured by Shibata Kagaku K.K.). The dust 
measuring apparatus was spaced 10 cm apart from a magnet roll, and two 
grams of the developer were set on the magnet roll, which was rotated at 
2,000 rpm. Then, the dust measuring apparatus detected the toner particles 
scattering about as dust, and displayed the resultant value in the number 
of counts per minute, i.e. cpm. The measured results of charge amount and 
scattering amount were shown in Table 7. 
TABLE 7 
__________________________________________________________________________ 
3 min. 10 min. 30 min. 
charging 
scattering 
charging 
flying 
charging 
flying image 
amount 
amount 
amount 
amount 
amount 
amount 
toner 
density 
image 
toner 
carrier 
(.mu.C/g) 
(cpm) 
(.mu.C/g) 
(cpm) 
(.mu.C/g) 
(cpm) 
fogs 
I.D. 
quality 
__________________________________________________________________________ 
Comparative 
Example 
1 a A -5 1368 -8 1277 -10 1239 x x x 
2 a B -5 881 -8 836 -10 821 x x x 
3 a E -7 797 -11 632 -13 588 .DELTA. 
.DELTA. 
x 
Example 
1 a F -10 253 -12 241 -13 235 o o .DELTA. 
2 a G -10 267 -13 255 -13 252 .DELTA. 
o .DELTA. 
3 a H -9 271 -11 267 -12 259 .DELTA. 
o .DELTA. 
4 a J -10 363 - 12 337 -13 311 .DELTA. 
o .DELTA. 
5 a K -13 110 -13 103 -13 98 oo oo o 
6 a L -13 108 -13 100 -14 96 o oo o 
7 a M -10 345 -11 333 -11 317 .DELTA. 
o .DELTA. 
8 a N -14 87 -14 83 -14 81 oo oo oo 
9 a O -10 189 -12 173 -12 165 o o o 
10 a P -13 91 -14 90 -14 88 oo oo oo 
11 a Q -10 357 -12 341 -13 332 o o .DELTA. 
12 a R -10 251 -12 243 -13 237 .DELTA. 
o o 
13 b N -16 101 -17 96 -17 91 oo oo oo 
14 c N -13 96 -13 91 -14 88 oo oo oo 
Comparative 
Example 
4 d N -9 283 -10 278 -10 277 o o x 
5 e N -8 301 -11 236 -13 207 o oo .DELTA. 
Example 
15 f N -11 263 -11 231 -12 219 oo oo oo 
Comparative 
Example 
6 g N -11 198 -13 187 -15 172 o .DELTA. 
x 
7 h N -12 194 -14 183 -16 168 o .DELTA. 
x 
8 i A +4 1463 +7 1251 +8 1118 x x x 
9 i E +6 870 +9 694 +13 429 .DELTA. 
.DELTA. 
x 
Example 
16 i N +14 93 +14 89 +14 84 oo oo oo 
__________________________________________________________________________ 
It is understood from Table 7 that the combination of toners having 150 or 
less in spheroidicity, 14 .mu.m or less in mean particle size and 15% or 
less in coefficient of variation with carriers having 20-70 .mu.m in mean 
particle size or 140 or more in spheroidicity effected good and stable 
electrification-build-up of toners, low scattering amounts and practically 
good image quality such as toner fogs and image density as copied-image 
evaluations. Best results were obtained with the use of carriers having 
both 20-70 .mu.m in mean particle size and 140 or more in spheroidicity. 
Even though toners are positive-chargeable or negative chargeable, 
preferred toners are 14 .mu.m or less in mean particle size in order to 
get good image qualities. The small toners of 14 .mu.m or less in mean 
particle size need to have both spheroidicity of 150 or less and 
coefficient of variation of 15% or less so that solid state properties of 
particles, for example, fluidity, which are necessary to utilize the small 
toners as a toner itself or a component of a developer may be achieved, 
resulting in good chargeability, scattering properties etc. 
Evaluations on image formation properties 
Toners and carriers specified in Table 7-Table 9 were mixed at the mixing 
ratio of toners to carriers (toner/carrier) of 7/93 to prepare developers 
of two components system. The obtained developers were subjected to 
various kinds of evaluations on image formation properties of initial 
stage. Negative chargeable toners were evaluated with EP-570Z 
(manufactured by Minolta Camera K.K.) and positive chargeable toners were 
evaluated with EP-470Z (manufactured by Minolta Camera K.K.) 
The results were shown in Table 7-Table 9. 
(1) Evaluation on mixing and stirring properties of toner/carrier 
A developer above mentioned was stirred for 3 minutes in the developing 
machine of EP-570 or EP-470Z. The developing machine was only driven under 
practical conditions of EP-570 or EP-470Z. Then, a part of the developer 
was taken out from the developing machine to measure the mixing ratio of 
toner/carrier for evaluations on mixing uniformity. The mixing and 
stirring properties were ranked to show the symbols (oo, o, .DELTA., x). A 
developer needs the higher rank than .DELTA. for practical use, preferably 
the higher rank than o. 
(2) Evaluation on spent carriers 
The same developer as used in (1) above was charged for 5 hours in the 
developing machine in a similar manner to (1). Then, the resultant 
developer was put into water for dispersion to separate carriers from 
toners. The separated carriers were taken out to dry them. The dried 
carriers were put into ethanol solvent for dispersion to dissolve charge 
controlling agents which adhered onto the surfaces of carriers transferred 
from toners. The amounts of charge controlling agents were measured by a 
spectrophotometer. The evaluations were ranked by the four symbols (oo, o, 
.DELTA., and x) according to the degree of measured amount. A developer 
needs the higher rank than .DELTA. for practical use, preferably the 
higher rank than o. 
(3) Fogs on copied images 
Copied images were formed in the foregoing combination of toners with 
carriers with EP-570Z or EP-470Z. Toner fogs around copied images on white 
paper were observed for the evaluation of fogs on copied images. The 
evaluations were ranked by the four symbols (oo, o, .DELTA., and x). The 
higher rank than .DELTA., preferably the higher rank than o are needed for 
practical use. 
(4) Carrier development, Image-density, Carrier-lines, Image-quality 
The standard chart of Dataquest company was copied under adequate exposure 
under the same condition aforementioned. 
The amounts of developed carriers were evaluated by the carrier amount 
existing on white parts of copying paper. The Image-Density was estimated 
on the density of solid parts with the use of Sakura reflection density 
measuring apparatus. The carrier lines were evaluated on the generating 
states of carrier lines in half-density parts of copied images. The image 
quality was totally evaluated on gradient, resolution power, line 
reproducibility, image-texture. The foregoing evaluations were ranked by 
the four symbols (oo, o, .DELTA., and x). The higher rank than .DELTA., 
preferably the higher rank than o, needed for practical use. 
(5) Durability with respect to copy 
The same developer as used in the example 8 was subjected to the durability 
with respect to repeating copy of 100,000 times. The charge amounts were 
stable and good properties at the initial stage of copy shown in Table 7 
were always kept. 
(6) Developer aggregation 
The same developer as used in the evaluation of spent carriers was charged 
for 5 hours in the developing machine in a similar manner to (1). When the 
resultant developer was sifted through sieve openings of 125 .mu.m. The 
easiness of passing was observed for the evaluation of developer carrier 
aggregation to be ranked by the four symbols (oo, o, .DELTA., x). The 
higher rank than .DELTA., preferably the higher rank than o, are needed 
for practical use. 
The results were shown in Tables 7-9. 
TABLE 8 
______________________________________ 
developer 
carrier carrier 
toner 
carrier development 
line 
______________________________________ 
Example 8 a N o o 
Example 9 a O o o 
Example 10 a P o o 
Example 12 a R o o 
Comparative Example 1 
a A o X 
Comparative Example 2 
a B X o 
Example 17 a C o o 
Example 18 a D o o 
Comparative Example 3 
a E X X 
Example 19 a S o o 
______________________________________ 
TABLE 9 
______________________________________ 
stirring 
and mixing 
properties 
aggregation 
developer 
of toner/ properties spent 
toner 
carrier carrier of developer 
carrier 
______________________________________ 
Comparative 
a A X X X 
Example 1 
Comparative 
a B X X X 
Example 2 
Comparative 
a E X .DELTA. .DELTA. 
Example 3 
Example 8 
a N oo oo oo 
Example 9 
a O o .DELTA. o 
Example 10 
a P oo oo oo 
Example 12 
a R o oo oo 
Example 19 
a S .DELTA. o .DELTA. 
Example 20 
a T o o o 
______________________________________ 
It was understood from Table 8 that when carriers were magnetized to the 
lower level than 900 gauss in the magnetic field of 1000 Oe, they were 
developed resulting in the deterioration of image quality. It was also 
understood that when carriers were magnetized to higher level than 3000 
gauss in the magnetic field of 1000 Oe, the hard ear of magnetic brush and 
the generation of carrier lines in the parts of solids caused the 
deterioration of image quality. 
It was understood from Table 9 that when the true specific gravity of 
carriers was 5 or less, the mixing and stirring properties of toners and 
carriers were improved, the excessive stress was not given to toners at 
mixing and stirring, carriers did not become spent, the chargeability was 
stabilized for a long time and toners themselves or a developer (toners 
and carriers) did not aggregate together.