Image forming method and image forming apparatus

An image forming apparatus, comprises: an electrostatic image-bearing member for holding an electrostatic latent image; a developing means for developing the electrostatic latent image to form a toner image on the electrostatic image-bearing member, the developing means including a non-magnetic color toner developing means for development with a developer comprising a non-magnetic color toner and a magnetic toner developing means for development with a magnetic toner, wherein the non-magnetic toner has a volume-average particle size of 4 to 15 microns, the magnetic toner contains 17 to 60% by number of magnetic toner particles having a particle size of 5 microns or smaller, 1-23% by number of magnetic toner particles having a particle size of 8.0-12.7 microns and 2.0% by volume or less of magnetic toner particles having a size of 16 microns or larger, and the magnetic toner has a volume-average particle size of 4-9 micron and a degree of aggregation of 50-95%; a transfer means for transferring the toner image formed on the electrostatic image-bearing member to a transfer-receiving material; and a cleaning means for blade-cleaning the surface of the electrostatic image-bearing member after the transfer.

FIELD OF THE INVENTION AND RELATED 
The present invention relates to an image forming method such as an 
electrophotographic method or an electrostatic recording method wherein a 
magnetic toner and a non-magnetic toner are used, and an image forming 
apparatus therefor. 
Recently, as image forming apparatus such as electrophotographic copying 
machines have widely been used, their uses have also extended in various 
ways, and higher image quality has been demanded. For example, when 
original images such as general documents and books are copied, it is 
demanded that even minute letters are reproduced extremely finely and 
faithfully without thickening or deformation, or interruption. However, in 
ordinary image forming apparatus such as copying machines for plain paper, 
when the latent image formed on a photosensitive member thereof comprises 
thin-line images having a width of 100 microns or below, the 
reproducibility of thin lines is generally poor and the clearness of line 
images is still insufficient. 
Particularly, in recent image forming apparatus such as electrophotographic 
printer using digital image signals, the resultant latent picture is 
formed by a gathering of dots with a constant potential, and the solid, 
half-tone and highlight portions of the picture can be expressed by 
varying densities of dots. However, in a state where the dots are not 
faithfully covered with toner particles dots and the toner particles 
protrude from the dots, there arises a problem that a gradational 
characteristic of a toner image corresponding to the dot density ratio of 
the black portion to the white portion in the digital latent image cannot 
be obtained. Further, when the resolution is intended to be enhanced by 
decreasing the dot size so as to enhance the image quality, the 
reproducibility becomes poorer with respect to the latent image comprising 
minute dots, whereby there tends to occur an image without sharpness 
having a low resolution and a poor gradational characteristic. 
On the other hand, in image forming apparatus such as electrophotographic 
copying machine, there sometimes occurs a phenomenon such that good image 
quality is obtained in an initial stage but it deteriorates as the copying 
or print-out operation is successively conducted. The reason for such 
phenomenon may be considered that only toner particles which contribute to 
the developing operation are consumed preferentially as the copying or 
print-out operation is successively conducted, and toner particles having 
a poor developing characteristic accumulate and remain in the developing 
device of the image forming apparatus. 
Hitherto, there have been proposed some developers for the purpose of 
enhancing the image quality. For example, Japanese Laid-Open Patent 
Application (JP-A, KOKAI) No. 3244/1976 (corresponding to U.S. Pat. Nos. 
3942979, 3969251 and 4112024) has proposed a non-magnetic toner wherein 
the particle size distribution is regulated so as to improve the image 
quality. This toner comprises relatively coarse particles and most 
suitably comprises about 60% or more of toner particles having a particle 
size of 8-12 microns. However, according to our investigation, it is 
difficult for such a particle size to provide uniform and dense cover-up 
of the toner particles to a latent image. Further, the above-mentioned 
toner has a characteristic such that it contains 30% by number or less 
(e.g., about 29% by number) of particles of 5 microns or smaller and 5% by 
number or less (e.g., about 5% by number) of particles of 20 microns or 
larger, and therefore it has a broad particle size distribution which 
tends to decrease the uniformity in the resultant image. In order to form 
a clear image by using such relatively coarse toner particles having a 
broad particle size distribution, it is necessary that gaps between the 
toner particles are filled by thickly superposing the toner particles 
thereby to enhance the apparent image density. As a result, there arises a 
problem that the toner consumption increases in order to obtain a 
prescribed image density. 
Japanese Laid-Open Patent Application No. 2054/1979 (corresponding to U.S. 
Pat. No. 4284701) has proposed a non-magnetic toner having a sharper 
particle size distribution than the above-mentioned toner. In this toner, 
particles having an intermediate weight has a relatively large particle 
size of 8.5-11.0 microns, and there is still left a room for improvement 
as a toner for a high resolution. 
Japanese Laid-Open Patent Application No. 29437/1983 (corresponding to 
British Patent No. 114310) has proposed a non-magnetic toner wherein the 
average particle size is 6-10 microns and the mode particle size is 5-8 
microns. However, this toner only contains particles of 5 microns or less 
in a small amount of 15% by number or below, and it tends to form an image 
without sharpness. 
On the other hand, as a diversity of information is used, there has been 
desired an image forming method or image forming apparatus capable of 
recording image data of two colors or more than two colors, and various 
apparatus and recording methods have already been proposed. 
In a two-color image forming method, e.g., a two-color image forming method 
by the electrophotographic recording system known heretofore, an initial 
charge is uniformly provided to the surface of an electrostatic 
image-bearing member such as a photosensitive drum by a corona charger 
first of all, and the photosensitive drum surface is subjected to negative 
exposure corresponding to first color image data to form a first latent 
image. Then, the latent image is developed by a color toner developing 
apparatus using a two-component magnetic brush developer comprising a 
mixture of, e.g., a red non-magnetic toner and a magnetic carrier to form 
a red toner image, which is then transferred to a transfer-receiving 
material and is fixed thereon. The photosensitive drum after the transfer 
is cleaned and the surface thereof is charged to a prescribed potential by 
a charger. Then, the charged photosensitive drum surface is subjected to 
negative exposure corresponding to a second color image data to form a 
second latent image. Further, the second latent image is developed by a 
second magnetic toner developing apparatus using a one-component magnetic 
developer comprising e.g., a black one-component magnetic toner to form a 
second black toner image. Then, the toner image is transferred to a 
transfer-receiving material by using a transfer means, and the second 
color toner image transferred to the transfer-receiving material is fixed 
by a fixing means such as heat pressure roller fixing means to form a 
two-color image. 
In such a two-color developing system using a magnetic toner and a 
non-magnetic toner, there is liable to occur a problem that the 
non-magnetic toner passes by the cleaning step to remain on the 
photosensitive drum and provide an ill effect to the subsequent developing 
step. A magnetic toner, compared with a non-magnetic toner, is liable to 
damage the photosensitive drum surface, so that the blade cleaning 
condition therefore has to be relaxed relative to the optimum blade 
cleaning condition for the non-magnetic toner. Therefore, in case where a 
single cleaning blade is used for cleaning of both a magnetic toner and a 
non-magnetic color toner, the non-magnetic toner has a higher tendency of 
passing through the cleaning blade in the cleaning step. 
Hitherto, there have been proposed several methods for enhancing the 
cleaning characteristic. For example, it has been well-known to add a 
lubricating agent such as polytetrafluoroethylene, polyethylene, a higher 
fatty acid metal salt, molybdenum dioxide, and graphite. This method shows 
an effect but also a problem of filming on the photosensitive member which 
may be attributable to the toner or lubricant. In order to solve the 
problem, the kind and the addition amount of the lubricating agent have 
been considered, but no satisfactory results have been obtained. 
Japanese Laid-Open Patent Application No. 47345/1983 (corresponding to U.K. 
Patent No. 1402010) has proposed a method of using a friction-reducing 
substance and an abrasive substance. This method however involves a 
problem that the essential effects of the friction-reducing substance and 
the abrasive substance are cancelled by each other. Further, because such 
two substances which are not essential to a toner are contained in a 
toner, a highly skilled technique is required for providing an appropriate 
triboelectric charge and fixability which are essential to the toner. 
Therefore, the use of this method is practically serially restricted. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an image forming method 
and an image forming apparatus having solved the above-mentioned problems. 
A more specific object of the present invention is to provide an image 
forming method and an image forming apparatus capable of forming a toner 
image of two or more colors with little image soiling or contamination. 
Another object of the present invention is to provide an image forming 
method and an image forming apparatus for forming a toner image of two or 
more colors wherein the cleaning step is satisfactorily operated. 
A further object of the present invention is to provide an image forming 
method and an image forming apparatus using a specific magnetic toner and 
a non-magnetic color toner which provide a high image density and 
excellent thin-line reproducibility and gradational characteristic. 
A further object of the present invention is to provide an image forming 
method and an image forming apparatus using a magnetic toner and a 
non-magnetic color toner capable of providing a high image density with a 
small consumption. 
A still further object of the present invention is to provide an image 
forming method and an image forming apparatus, wherein the cleaning 
performance is improved, and the filming phenomena on a photosensitive 
member and its accompanying image defects, such as blurring, fading or 
flow, are prevented to stably provide good image for a long period. 
According to our investigation it has been found that toner particles 
having a particle size of 5 microns or smaller have a primary function of 
clearly reproducing the contour of a latent image and of attaining close 
and faithful cover-up of the toner to the entire latent image portion. 
Particularly, in the case of an electrostatic latent image formed on a 
photosensitive member, the field intensity in the edge portion thereof as 
the contour is higher than that in the inner portion thereof because of 
the concentration of the electric lines of force, whereby the sharpness of 
the resultant image is determined by the quality of toner particles 
collected to this portion. According to our investigation, it has been 
found that the control of quantity and distribution state of toner 
particles of 5 microns or smaller is effective in solving the problem in 
image sharpness. 
According to further study of ours, the use of a specific magnetic toner in 
a cleaning step is effective for stably providing good images for a long 
period. More specifically, the magnetic toner is caused to aggregate at a 
position where the photosensitive member and the cleaning member abut each 
other to provide an improved cleaning performance, and the non-magnetic 
color toner is prevented from passing by the cleaning action by the 
function of the magnetic toner particles per se aggregated to an 
appropriate degree, whereby the photosensitive drum is uniformly abraded 
to an appropriate degree to prevent the filming of the lubricating agent, 
the toner and others on the photosensitive drum and also the surface 
degradation of the photosensitive member, thus preventing blurring, fading 
or flow of images. Further, the abrading effect is stably shown for a long 
period even after repetitive image formation. 
The present invention is based on the above findings. 
Thus, according to the present invention, there is provided an image 
forming method, comprising: 
developing an electrostatic latent image on an electrostatic image-bearing 
member with a developer comprising a non-magnetic color toner having a 
volume-average particle size of 4 to 15 microns to form a non-magnetic 
color toner image; 
transferring the non-magnetic color toner image on the electrostatic 
image-bearing member to a transfer-receiving material; 
cleaning the electrostatic image-bearing member after the transfer with a 
cleaning blade; 
forming an electrostatic image on the electrostatic image-bearing member 
after the cleaning; 
developing the electrostatic latent image on the electrostatic 
image-bearing member with a developer comprising a magnetic toner to form 
a magnetic toner image, wherein the magnetic toner contains 17 to 60% by 
number of magnetic toner particles having a particle size of 5 microns or 
smaller, 1-23% by number of magnetic toner particles having a particle 
size of 8.0-12.7 microns and 2.0% by volume or less of magnetic toner 
particles having a size of 16 microns or larger, and the magnetic toner 
has a volume-average particle size of 4-9 microns and a degree of 
aggregation of 50-95%; 
transferring the magnetic toner image on the electrostatic image-bearing 
member to the transfer-receiving material; and 
cleaning the electrostatic image-bearing member after the transfer with a 
cleaning blade. 
According to the present invention, there is further provided an image 
forming method, comprising: 
developing an electrostatic latent image on an electrostatic image-bearing 
member with a developer comprising a magnetic toner to form a magnetic 
toner image, wherein the magnetic toner contains 17 to 60% by number of 
magnetic toner particles having a particle size of 5 microns or smaller, 
1-23% by number of magnetic toner particles having a particle size of 
8.0-12.7 microns and 2.0% by volume or less of magnetic toner particles 
having a size of 16 microns or larger, and the magnetic toner has a 
volume-average particle size of 4-9 microns and a degree of aggregation of 
50-95%; 
transferring the magnetic toner image on the electrostatic image-bearing 
member to a transfer-receiving material; 
cleaning the electrostatic image-bearing member after the transfer with a 
cleaning blade; 
forming an electrostatic image on the electrostatic image-bearing member 
after the cleaning; 
developing the electrostatic latent image on the electrostatic 
image-bearing member with a developer comprising a non-magnetic color 
toner having a volume-average particle size of 4 to 15 microns to form a 
non-magnetic color toner image; 
transferring the non-magnetic color toner image on the electrostatic 
image-bearing member to the transfer-receiving material; and 
cleaning the electrostatic image-bearing member after the transfer with a 
cleaning blade. 
According to another aspect of the present invention, there is further 
provided an image forming apparatus, comprising: 
an electrostatic image-bearing member for holding an electrostatic latent 
image; 
a developing means for developing the electrostatic latent image to form a 
toner image on the electrostatic image-bearing member, the developing 
means including a non-magnetic color toner developing means for 
development with a developer comprising a non-magnetic color toner and a 
magnetic toner developing means for development with a magnetic toner, 
wherein the non-magnetic toner has a volume-average particle size of 4 to 
15 microns, the magnetic toner contains 17 to 60% by number of magnetic 
toner particles having a particle size of 5 microns or smaller, 1-23% by 
number of magnetic toner particles having a particle size of 8.0-12.7 
microns and 2.0% by volume or less of magnetic toner particles having a 
size of 16 microns or larger, and the magnetic toner has a volume-average 
particle size of 4-9 microns and a degree of aggregation of 50-95%; 
a transfer means for transferring the toner image formed on the 
electrostatic image-bearing member to a transfer-receiving material; and 
a cleaning means for blade-cleaning the surface of the electrostatic 
image-bearing member after the transfer. 
These and other objects, features and advantages of the present invention 
will become more apparent upon a consideration of the following 
description of the preferred embodiments of the present invention taken in 
conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
The magnetic toner used in the image forming method and the image forming 
apparatus of the present invention has a relatively large degree of 
aggregation of 50-95% and remains in an appropriate amount of the cleaning 
blade to show an excellent effect of cleaning a color toner remaining on 
the photosensitive member after the transfer. The magnetic toner also 
shows an appropriate abrasive function preventing the filming of a 
lubricating agent or toner on the photosensitive member, thus stably 
providing a high quality image for a long period. 
The reason why the magnetic toner shows such an effect in the present 
invention will be explained hereinbelow. 
The magnetic toner used in the present invention has a volume-average 
particle size of 4-9 microns and contains 17-60% by number of magnetic 
toner particles having a particle size of 5 microns or smaller, thus being 
smaller in particle size and containing more fine particles compared with 
most of the known magnetic toners. Corresponding thereto, a sufficient 
cleaning performance is provided by its aggregation characteristic in 
blade cleaning. The magnetic toner having a large aggregation 
characteristic of the present invention causes an appropriate degree of 
aggregation and compression of magnetic toner particles at the abutting 
position of the photosensitive member and cleaning member, so that the 
non-magnetic color toner is prevented from passing between the 
photosensitive member and cleaning member and is scraped from the 
photosensitive member by the cleaning member to be reliably recovered in 
the cleaner. Another advantage of the magnetic toner of the present 
invention is that the magnetic toner aggregated in the neighborhood of the 
abutting position between the photosensitive member and the cleaning 
member has an appropriate abrasive function by itself. As a result, the 
addition of an abrasive agent which can adversely affect development, 
transfer and fixing may be omitted or minimized to an extent of no harm 
while avoiding undesirable phenomena such as fading or flow due to filming 
on the photosensitive member or degradation of the photosensitive member 
surface to stably provide good images. 
In this way, the magnetic toner of the present invention provides a 
solution to the problems of the prior art based on an utterly different 
concept from the prior art and makes it possible to stably provide good 
images for a long period, which also satisfy a recent strict requirement 
of high quality. In the present invention, it is necessary that the 
non-magnetic color toner has a volume-average particle size of 4-15 
microns, preferably 5 to 15 microns, in relation to the magnetic toner. In 
view of the blade cleaning performance, it is preferred that the 
non-magnetic color toner has a volume-average particle size which is 
larger than that of the magnetic toner by 1 micron or more, more 
preferably 1-8 microns. 
The image forming method and apparatus according to the present invention 
will now be explained with reference to the accompanying drawings based on 
an example wherein a magnetic black toner and a non-magnetic color toner 
are used for two-color superposing copy operation. 
FIGS. 1 through 4 show an electrostatic image-bearing member (hereinafter 
called a "photosensitive drum") such as that formed from an organic 
photoconductive material, amorphous silicon photosensitive material, 
selenium photosensitive material or zinc oxide photosensitive material, 
and surrounding structure of a copying machine capable of superposing 
operation. Referring to FIGS. 1 through 4, a two-color superposing 
operation is explained. 
Adjacent to a photosensitive drum 1, a non-magnetic color toner developing 
unit 2 and a magnetic toner developing unit 3 are provided and are 
alternately pressed against the photosensitive drum 1 for development 
(FIGS. 1 and 2). For example, as a step 1, close to the photosensitive 
drum 1 having an electrostatic latent image formed thereon, the 
non-magnetic color toner developing unit 2 is disposed, and development is 
effected with a developer comprising a non-magnetic color toner and a 
magnetic carrier applied on a sleeve 6 in a thin layer by means of a blade 
4 for coating. Then, the resultant non-magnetic toner image is transferred 
to a transfer-receiving material at a transfer and separating position. 
Then, the toner remaining on the photosensitive member after the transfer 
is removed by a cleaning blade 12 and a cleaning roller 13 disposed in a 
cleaner unit 11 (FIG. 1), and the non-magnetic color toner image on the 
transfer paper is fixed by means of a heat-pressure roller fixing device 
(not shown). Subsequently, as a step 2, an electrostatic latent image is 
newly formed on the photosensitive drum 1, and a magnetic toner developing 
unit 3 is moved close thereto. The latent image is developed with a 
magnetic toner applied in a thin layer on a sleeve 7 by means of a blade 5 
for coating to form a magnetic toner image, which is then transferred to 
the transfer-receiving material having thereon the non-magnetic color 
toner image in advance at the transfer and separation position. The 
remaining toner on the photosensitive drum 1 after transfer is removed 
again by the cleaning blade 12 and the cleaning roller 13 in the cleaner 
unit 11 (FIG. 2). Two-color superposing operation can be effected 
continuously by repeating the above operations. In this instance, it is 
also possible to successively repeat the first step to accumulate a 
desired number of the transfer-receiving materials in the copying machine 
and then to repeat the second step to form a large number of two-color 
superposed copies. Further, as shown in FIG. 3, it is possible that a 
non-magnetic color toner developing unit 2 is disposed to effect the 
development, transfer, cleaning and fixing in the same manner as in the 
above first step, then the developing unit is replaced by a magnetic toner 
developing unit 3 to similarly effect the second step to effect two-color 
superposing operation. 
The cleaner unit 11 can be of various types and some of them are explained. 
Referring to FIGS. 4A and 4B, a cleaning blade 12 comprising an elastic 
material such as urethane rubber or silicone rubber is caused to contact 
the surface of the photosensitive drum 1 in a counter- or 
forward-direction to remove the remaining toner after transfer. As shown 
in FIGS. 1-3 and FIG. 4C, a cleaning roller 13 comprising an elastic 
material such as urethane rubber or silicone rubber is used for rubbing to 
enhance the effect of removal. Further, in case of a magnetic toner, a 
cleaning roller 13 is composed as a magnetic roller comprising a magnetic 
material and is disposed close to the photosensitive member to form years 
or brush of the magnetic toner on the magnetic roller, by which the 
surface of the photosensitive member is brushed. The cleaning blade used 
in the present invention may preferably be formed of polyurethane or 
silicone rubber and have a thickness of about 0.5 to 4 mm, preferably 
1.5-3 mm and a JIS-A rubber hardness of 50 degrees to 90 degrees. The 
blade pressure against the photosensitive member surface may preferably be 
5-40 g/cm. The cleaning roller used in the present invention may 
preferably be formed of polyurethane rubber or silicone rubber and have a 
JIS-A hardness of 20 degrees to 90 degrees. The cleaning roller may 
preferably be pushed against the photosensitive member to provide a 
depression of 0.5 to 2 mm and moved at a peripheral speed which is 50-200% 
of that of the photosensitive member. 
The magnetic toner used in the present invention can faithfully reproduce 
thin lines in a latent image formed on a photosensitive member, and is 
excellent in reproduction of dot latent images such as halftone dots and 
digital images, whereby it provides images excellent in gradation and 
resolution characteristics. Further, the toner according to the present 
invention can retain a high image quality even in the case of successive 
copying or print-out, and can effect good development by using a smaller 
consumption thereof as compared with the conventional magnetic toner, even 
in the case of high-density images. As a result, the magnetic toner of the 
present invention is excellent in economical characteristics and further 
has an advantage in miniaturization of the main body of a copying machine 
or printer. 
The reason for the above-mentioned effects of the magnetic toner of the 
present invention is not necessarily clear but may assumably be considered 
as follows. 
The magnetic toner of the present invention is first characterized in that 
it contains 17-60% by number of magnetic toner particles of 5 microns or 
below. Conventionally, it has been considered that magnetic toner 
particles of 5 microns or below are required to be positively reduced 
because the control of their charge amount is difficult, they impair the 
fluidity of the magnetic toner, and they cause toner scattering to soil or 
contaminate the machine. 
However, according to our investigation, it has been found that the 
magnetic toner particles of 5 microns or below are an essential component 
to form a high-quality image. 
For example, we have conducted the following experiment. 
Thus, there was formed on a photosensitive member a latent image, wherein 
the surface potential on the photosensitive member was changed from a 
large developing potential contrast at which the latent image would easily 
be developed with a large number of toner particles, to a small developing 
potential contrast at which the latent image would be developed with only 
a small number of toner particles. 
Such a latent image was developed with a magnetic toner having a particle 
size distribution ranging from 0.5 to 30 microns. Then, the toner 
particles attached to the photosensitive member were collected and the 
particle size distribution thereof was measured. As a result, it was found 
that there were many magnetic toner particles having a particle size of 8 
microns or below, particularly 5 microns or below. Based on such finding, 
it was discovered that when magnetic toner particles of 5 microns or below 
were so controlled that they were smoothly supplied for the development of 
a latent image formed on a photosensitive member, there could be obtained 
an image truly excellent in reproducibility, and the toner particles were 
faithfully attached to the latent image without protruding therefrom. 
The magnetic toner of the present invention is further characterized in 
that it contains 1-23% by number of magnetic toner particles of 8-12.7 
microns. Such a feature relates to the above-mentioned necessity for the 
presence of the toner particles of 5 microns or below. 
As described above, the toner particles having a particle size of 5 microns 
or below have the ability to strictly cover a latent image and to 
faithfully reproduce it. On the other hand, in the latent image per se, 
the field intensity in its peripheral edge portion is higher than that in 
its central portion. Therefore, toner particles sometimes cover the inner 
portion of the latent image in a smaller amount than that in the edge 
portion thereof, whereby the image density in the inner portion appears to 
be lower. Particularly, the magnetic toner particles of 5 microns or below 
strongly have such tendency. However, we have found that when 1-23% by 
number of toner particles of 8-12.7 microns are contained in a toner, not 
only the above-mentioned problem can be solved but also the resultant 
image can be made clearer. 
According to our knowledge, the reason for such phenomenon may be 
considered that the toner particles of 8-12.7 microns have suitably 
controlled charge amount in relation to those of 5 microns or below, and 
that these toner particles are supplied to the inner portion of the latent 
image having a lower field intensity than that of the edge portion thereby 
to compensate for the decrease in cover-up of the toner particles to the 
inner portion as compared with that in the edge portion, and to form a 
uniform developed image. As a result, there may be provided a sharp image 
having a high-image density and excellent resolution and gradation 
characteristic. 
In the magnetic toner of present invention, magnetic toner particles having 
a particle size of 16 microns or larger are contained in an amount of 2.0% 
by volume or below. The amount of these particles may preferably be as 
small as possible. 
It is preferred in the magnetic toner of the present invention that toner 
particles having a particle size of 5 microns or smaller contained therein 
satisfy the following relation between their percentage by number (N) and 
percentage by volume (V): 
EQU N/V=-0.04N+k, 
wherein 4.5.ltoreq.k.ltoreq.6.5, and 17.ltoreq.N.ltoreq.60. 
The region satisfying such a relationship is shown in FIG. 5. The magnetic 
toner according to the present invention which has the particle size 
distribution satisfying such region, in addition to the above-mentioned 
features, can attain excellent developing characteristic. 
According to our investigation on the state of the particle size 
distribution with respect to toner particles of 5 microns or below, we 
have found that there is a suitable state of the presence of fine powder 
in magnetic toner particles. More specifically, in the case of a certain 
value of N, it may be understood that a large value of N/V indicates that 
the particles of 5 microns or below (e.g., 2-4 microns) are significantly 
contained, and a small value of N/V indicates that the frequency of the 
presence of particles near 5 microns (e.g., 4-5 microns) is high and that 
of particles having a smaller particle size is low. When the value of N/V 
is in the range of 2.1-5.82, N is in the range of 17-60, and the relation 
represented by the above-mentioned formula is satisfied, good thin-line 
reproducibility and high resolution are attained. 
Hereinbelow, the present invention will be described in more detail. 
In the present invention, the magnetic toner particles having a particle 
size of 5 microns or smaller are contained in an amount of 17-60% by 
number, preferably 25-50% by number, more preferably 30-50% by number, 
based on the total number of particles. If the amount of magnetic toner 
particles is smaller than 17% by number, the toner particles effective in 
enhancing image quality is insufficient. Particularly, as the toner 
particles are consumed in successive copying or print-out, the component 
of effective magnetic toner particles is decreased, and the balance in the 
particle size distribution of the magnetic toner shown by the present 
invention is deteriorated, whereby the image quality is gradually 
degraded. On the other hand, if the above-mentioned amount exceeds 60% by 
number, the magnetic toner particles are liable to be mutually 
agglomerated to produce toner agglomerates having a size larger than the 
original particle size. As a result, roughened images are provided, the 
resolution is lowered, and the density difference between the edge and 
inner portions is increased, whereby an image having an inner portion with 
a somewhat low density is liable to occur. 
In the magnetic toner of the present invention, the amount of particles in 
the range of 8-12.7 microns is 1-23% by number, preferably 8-20% by 
number. If the above-mentioned amount is larger than 23% by number, not 
only the image quality deteriorates but also excess development (i.e., 
excess cover-up of toner particles) occurs, thereby to invite an increase 
in toner consumption. On the other hand, if the above-mentioned amount is 
smaller than 1%, it is difficult to obtain a high image density. 
In the present invention, the percentage by number (N %) and that by volume 
(V %) of magnetic toner particles having a particle size of 5 micron or 
below may preferably satisfy the relationship of N/V=-0.04 N+k, wherein k 
represents a positive number satisfying 4.5.ltoreq.k.ltoreq.6.5. The 
number k may preferably satisfy 4.5.ltoreq.k.ltoreq.6.0, more preferably 
4.5.ltoreq.k.ltoreq.5.5. Further, as described above, the percentage N 
satisfies 17.ltoreq.N.ltoreq.60, preferably 25.ltoreq.N.ltoreq.50, more 
preferably 30 .ltoreq.N.ltoreq.50. 
If k&lt;4.5, magnetic toner particles of 5.0 microns or below are 
insufficient, and the resultant image density, resolution and sharpness 
decrease. When fine toner particles in a magnetic toner, which have 
conventionally been considered useless, are present in an appropriate 
amount, they attain closest packing of toner in development (i.e., in a 
latent image formed on a photosensitive drum) and contribute to the 
formation of a uniform image free of coarsening. Particularly, these 
particles fill thin-line portions and contour portions of an image, 
thereby to visually improve the sharpness thereof. If k&lt;4.5 in the above 
formula, such a component becomes insufficient in the particle size 
distribution, the above-mentioned characteristics become poor. Further, in 
view of the production process, a large amount of fine powder must be 
removed by classification in order to satisfy the condition of k&lt;4.5. Such 
a process is disadvantageous in yield and toner costs. 
On the other hand, if k&gt;6.5, an excess of fine powder is present, whereby 
the resultant image density is liable to decrease in successive copying. 
The reason for such phenomenon may be considered that an excess of fine 
magnetic toner particles having an excess amount of charge are 
triboelectrically attached to a developing sleeve and prevent normal toner 
particles from being carried on the developing sleeve and being supplied 
with charge. 
In the magnetic toner of the present invention, the amount of magnetic 
toner particles having a particle size of 16 microns or larger is 2.0% by 
volume or less, preferably 1.0% by volume or less, more preferably 0.5% by 
volume or less. 
If the above amount is more than 2.0% by volume, these particles impair 
thin-line reproducibility. In addition, toner particles of microns or 
larger are present as protrusions on the surface of the thin layer of 
toner particles formed on a photosensitive member by development, and they 
vary the transfer condition for the toner by disordering the delicate 
contact state between the photosensitive member and a transfer paper (or a 
transfer-receiving paper) by the medium of the toner layer. As a result, 
there occurs an image with transfer failure. 
In the present invention, the volume-average particle size of the toner is 
4-9 microns, preferably 4-8 microns. This value closely relates to the 
above-mentioned features of the magnetic toner according to the present 
invention. If the volume-average particle size is smaller than 4 microns 
tend to occur problems such that the amount of toner particles transferred 
to a transfer paper is insufficient and the image density is low, in the 
case of an image such as graphic image wherein the ratio of the image 
portion area to the whole area is high. The reason for such a phenomenon 
may be considered the same as in the above-mentioned case wherein the 
inner portion of a latent image provides a lower image density than that 
in the edge portion thereof. If the volume-average particle size exceeds 9 
microns, the resultant resolution is not good and there tends to occur a 
phenomenon such that the image quality is lowered in successive use even 
when it is good in the initial stage thereof. 
The particle distribution of a toner is measured by means of a Coulter 
counter in the present invention, while it may be measured in various 
manners. 
Coulter counter Model TA-II (available from Coulter Electronics Inc.) is 
used as an instrument for measurement, to which an interface (available 
from Nikkaki K.K.) for providing a number-basis distribution, and a 
volume-basis distribution and a personal computer CX-1 (available from 
Canon K.K.) are connected. 
For measurement, a 1%-NaCl aqueous solution as an electrolytic solution is 
prepared by using a reagent-grade sodium chloride. Into 100 to 150 ml of 
electrolytic solution, 0.1 to 5 ml of a surfactant, preferably an 
alkylbenzenesulfonic acid salt, is added as a dispersant, and 2 to 20 mg 
of a sample is added thereto. The resultant dispersion of the sample in 
the electrolytic liquid is subjected to a dispersion treatment for about 
1-3 minutes by means of an ultrasonic disperser, and then subjected to 
measurement of particle size distribution in the range of 2-40 microns by 
using the above-mentioned Coulter counter Model TA-II with a 100 
micron-aperture to obtain a volume-basis distribution and a number-basis 
distribution. Form the results of the volume-basis distribution and 
number-basis distribution, parameters characterizing the magnetic toner of 
the present invention may be obtained. 
It is preferred for the magnetic toner of the present invention to have a 
degree of aggregation of 40-95%, more preferably 50-90%, further 
preferably 50-80%. If the degree of aggregation is below 40%, the cleaning 
function on the photosensitive member in cooperation with the cleaning 
member is insufficient to cause a low slippage of the non-magnetic color 
toner particles through the cleaning member, thus tending to cause 
cleaning failure resulting in contamination of images. The cleaning 
failure is liable to occur particularly in a low humidity condition, but 
in order to provide good images even under various conditions for a long 
period of time, the degree of aggregation may preferably be 50% or higher. 
With respect to the abrasive function, if the degree of aggregation is 
below 40%, the abrasive function attained by appropriate attachment of the 
aggregated magnetic toner to the cleaning member and utilized in the 
present invention becomes insufficient, so that image defects are liable 
to occur with elapse of time due to filming on the photosensitive member 
or the deterioration or soiling of the photosensitive member surface. 
If the degree of aggregation is above 95%, the toner is excessively 
aggregated in the cleaner, so that it becomes difficult to smoothly remove 
from the abutting position between the photosensitive member and the 
cleaning member to recover the toner in the cleaning unit. As a result, 
cleaning failure is liable to occur due to excessive accumulation of 
strongly aggregated toner. 
The magnetic toner having a specific particle size distribution of the 
present invention does not cause excessive coverage of toner particles at 
the edge portion of a latent image and is excellent in transferability 
compared with a magnetic toner having a conventional particle size 
distribution, so that the amount of the toner remaining on the 
photosensitive member surface after the transfer is small and the amount 
of toner recovered in the cleaning unit is also small. The total amount of 
the toner supplied to the abutting position between the photosensitive 
member and the cleaning member and in the neighborhood thereof is 
considerably less than before. This provides an advantageous condition in 
respect of improvement in cleaning performance and abrasive function due 
to an appropriate degree of aggregation of the magnetic toner particles of 
the present invention having a relatively large agglomeration 
characteristic. In case where a toner having a large agglomeration 
characteristic is excessively applied to the neighborhood for the abutting 
position between the photosensitive member and the cleaning member, it 
becomes difficult to remove the toner from the neighborhood of the 
abutting position between the photosensitive member and cleaning member to 
recover it in the cleaning unit so that there are caused inconveniences 
such as excessive abrasion of the photosensitive member, damage of the 
photosensitive member or cleaning failure due to accumulation of 
excessively aggregated toner. Thus, it is necessary that the amount of 
toner supplied to the neighborhood of the abutting position between the 
photosensitive member and the cleaning member is relatively less than 
before. 
The degree of aggregation of a toner can be measured by various methods. 
The degree of aggregation used herein is based on the values measured in 
the following manner. Incidentally, the toner used herein referred to 
toners both with and without containing silica fine powder or alumina fine 
powder externally added. Generally, a toner sample is placed on a sieve 
and subjected to vibration, followed by measurement of a proportion of the 
toner remaining on the sieve. According to this method, a larger 
percentage of toner remaining on the sieve indicates a larger degree of 
aggregation of the toner so that the toner particles are more ready to 
behave as a mass. More specifically, the measurement is effected by using 
a powder tester (available from Hosokawa Micron Mellitics Laboratory 
K.K.). A 60-mesh sieve having an opening of 250 microns (upper), a 
100-mesh sieve having an opening of 149 microns (middle) and a 200-mesh 
sieve having an opening of 74 microns (lower) are arranged in this order 
from the above and set on a vibrating table. A toner in an amount of 2 g 
is placed on the 60-mesh sieve and is subjected to vibration for 40 
seconds by applying a voltage of 47 V to the vibration system. After the 
completion of the vibration. The toner weights remaining on the respective 
sieves are measured and multiplied by factors (weights) of 0.5, 0.3 and 
0.1, respectively, to provide a degree of aggregation in percentage. 
In the present invention, the true density of the magnetic toner may 
preferably be 1.45-1.70 g/cm.sup.3, more preferably 1.50-1.65 g/cm.sup.3. 
When the true density is in such a range, the magnetic toner according to 
the present invention having a specific particle size distribution 
functions most effectively in view of high image quality and stability in 
successive use. 
If the true density of the magnetic toner particles is smaller than 1.45, 
the weight of the particle per se is too light and there tend to occur 
reversal fog, and deformation of thin lines, scattering and deterioration 
in resolution because an excess of toner particles are attached to the 
latent image. On the other hand, the true density of the magnetic toner is 
larger than 1.70, there occurs an image wherein the image density is low, 
thin lines are interrupted, and the sharpness is lacking. Further, because 
the magnetic force becomes relatively strong in such a case, ears of the 
toner particles are liable to be lengthened or converted into a branched 
form. As a result, the image quality is disturbed in the development of a 
latent image, whereby a coarse image is liable to occur. 
In the present invention, the true density of the magnetic toner is 
measured in the following manner which can simply provide an accurate 
value in the measurement of fine powder, while the true density can be 
measured in various manners. 
There are provided a cylinder of stainless steel having an inner diameter 
of 10 mm and a length of about 5 cm, and a disk (A) having an outer 
diameter of about 10 mm and a height of about 5 mm, and a piston (B) 
having an outer diameter about 10 mm and a length of about 8 cm, which are 
capable of being closely inserted into the cylinder. 
In the measurement, the disk (A) is first disposed on the bottom of the 
cylinder and about 1 g of a sample to be measured is charged in the 
cylinder, and the piston (B) is gently pushed into the cylinder. Then, a 
force of 400 Kg/cm.sup.2 is applied to the piston by means of a hydraulic 
press, and the sample is pressed for 5 min. The weight (W g) of thus 
pressed sample is measured and the diameter (D cm) and the height (L cm) 
thereof are measured by means of a micrometer. Based on such a 
measurement, the true density may be calculated according to the following 
formula: 
EQU True density (g/cm.sup.3)=W/(.pi..times.(D/2).sup.2 .times.L) 
In order to obtain better developing characteristics, the magnetic toner of 
the present invention may preferably have the following magnetic 
characteristics: a remanences .sigma..sub.r of 1-5 emu/g, more preferably 
2-4.5 emu/g; a saturation magnetization .sigma..sub.s of 20-40 emu/g; and 
a coercive force Hc of 40-100 Oe. These magnetic characteristics may be 
measured under a magnetic field for measurement of 1,000 Oe. 
The binder constituting the toner according to the present invention, when 
applied to a hot pressure roller fixing apparatus using an oil applicator, 
may be a known binder resin for toners. Examples thereof may include: 
homopolymers of styrene and its derivatives, such as polystyrene, 
poly-p-chlorostyrene, and polyvinyltoluene; styrene copolymers, such as 
styrene-p-chlorostyrene copolymer, styrene-vinyltoluene copolymer, 
styrene-vinylnaphthalene copolymer, styrene-acrylate copolymer, 
styrene-methacrylate copolymer, styrene-methyl .alpha.-chloromethacrylate 
copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether 
copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl 
ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, 
and styrene-acrylonitrile-indene copolymer; polyvinyl chloride, phenolic 
resin, natural resin-modified phenolic resin, natural resin-modified 
maleic acid resin, acrylic resin, methacrylic resin, polyvinyl acetate, 
silicone resin, polyester resin, polyurethane, polyamide resin, furan 
resin, epoxy resin, xylene resin, polyvinylbutyral, terpene resin, 
coumaroneindene resin and petroleum resin. 
In a hot pressure roller fixing system using substantially no oil 
application, serious problems are caused by an offset phenomenon that a 
part of toner image on toner image-supporting member is transferred to a 
roller, and also in respect of an intimate adhesion of a toner on the 
toner image-supporting member. As a toner fixable with a less heat energy 
is generally liable to cause blocking or caking in storage or in a 
developing apparatus, this should be also taken into consideration. With 
these phenomenon, the physical property of a binder resin in a toner is 
most concerned. According to our study, when the content of a magnetic 
material in a toner is decreased, the adhesion of the toner onto the toner 
image-supporting member mentioned above is improved, while the offset is 
more readily caused and also the blocking or caking are also more liable. 
Accordingly, when a hot roller fixing system using almost no oil 
application is adopted in the present invention, selection of a binder 
resin becomes more serious. A preferred binder resin may for example be a 
crosslinked styrene copolymer, or a crosslinked polyester. Examples of 
comonomers to form such a styrene copolymer may include one or more vinyl 
monomers selected from: monocarboxylic acid having a double bond and their 
substituted derivatives, such as acrylic acid, methyl acrylate, ethyl 
acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, 2-ethylhexyl 
acrylate, phenyl acrylate, methacrylic acid, methyl methacrylate, ethyl 
methacrylate, butyl methacrylate, octyl methacrylate, acrylonitrile, 
methacrylonitrile, and acrylamide; dicarboxylic acids having a double bond 
and their substituted derivatives, such as maleic acid, butyl maleate, 
methyl maleate, and dimethyl maleate; vinyl esters, such as vinyl 
chloride, vinyl acetate, and vinyl benzoate; ethylenic olefins, such as 
ethylene, propylene, and butylene; vinyl ketones, such as vinyl methyl 
ketone, and vinyl hexyl ketone; vinyl ethers, such as vinyl methyl ether, 
vinyl ethyl ether, and vinyl isobutyl ethers. As the crosslinking agent, a 
compound having two or more polymerizable double bonds may principally be 
used. Examples thereof include: aromatic divinyl compounds, such as 
divinylbenzene, and divinylnaphthalene; carboxylic acid esters having two 
double bonds, such as ethylene glycol diacrylate, ethylene glycol 
dimethacrylate, and 1, 3-butanediol diacrylate; divinyl compounds such as 
divinyl ether, divinyl sulfide and divinyl sulfone; and compounds having 
three or more vinyl groups. these compounds may be used singly or in 
mixture. In view of the fixability and anti-offset characteristic of the 
toner, the crosslinking agent may preferably be used in an amount of 
0.01-10 wt. %, preferably 0.05-5 wt. %, based on the weight of the binder 
resin. 
For a pressure-fixing system, a known binder resin for pressure-fixable 
toner may be used. Examples thereof may include: polyethylene, 
polypropylene, polymethylene, polyurethane elastomer, ethylene-ethyl 
acrylate copolymer, ethylene-vinyl acetate copolymer, ionomer resin, 
styrene-butadiene copolymer, styrene-isoprene copolymer, linear saturated 
polyesters and paraffins. 
In the magnetic toner and the non-magnetic color toner of the present 
invention, it is preferred that a charge controller may be incorporated in 
the toner particles (internal addition), or may be mixed with the toner 
particles (external addition). By using the charge controller, it is 
possible to most suitably control the charge amount corresponding to a 
developing system to be used. Particularly, in the present invention, it 
is possible to further stabilize the balance between the particle size 
distribution and the charge. As a result, when the charge controller is 
used in the present invention, it is possible to further clarify the 
above-mentioned functional separation and mutual compensation 
corresponding to the particle size ranges, in order to enhance the image 
quality. 
Examples of the charge controller may include; nigrosine and its 
modification products modified by a fatty acid metal salt, quaternary 
ammonium salts, such as tributylbenzyl-ammonium-1 
hydroxy-4-naphthosulfonic acid salt, and tetrabutylammonium 
tetrafluoroborate; diorganotin oxides, such as dibutyltin oxide, 
dioctyltin oxide, and dicyclohexyltin oxide; and diorganotin borates, such 
as dibutyltin borate, dioctyltin borate, and dicyclo-hexyltin borate. 
These positive charge controllers may be used singly or as a mixture of 
two or more species. Among these, a nigrosine-type charge controller or a 
quaternary ammonium salt charge controller may particularly preferably be 
used. 
As another type of positive charge controller, there may be used a 
homopolymer of a monomer having an amino group represents by the formula: 
##STR1## 
wherein R.sub.1 represents H or CH.sub.3 ; and R.sub.2 and represent a 
substituted or unsubstituted alkyl group (preferably C.sub.1 -C.sub.4); or 
a copolymer of the monomer having an amine group with another 
polymerizable monomer such as styrene, acrylates, and methacrylates as 
described above. In this case, the positive charge controller also has a 
function of a binder. 
On the other hand, a negative charge controller can be used in the present 
invention. Examples thereof may include an organic metal complex or a 
chelate compound. More specifically there may preferably be used aluminum 
acetylacetonate, iron (II) acetylacetonate, and a 3,5-di-tertiary 
butylsalicylic acid chromium. There may more preferably be used 
acetylacetone complexes, or salicylic acid-type metal salts or complexes. 
Among these, salicylic acid-type complexes (inclusive of 
mono-alkyl-substituted compounds and di-alkyl substituted compounds) or 
metal salts (inclusive of mono-alkyl-substituted compounds and 
di-alkyl-substituted compounds) may particularly preferably be used. 
It is preferred that the above-mentioned charge controller is used in the 
form of fine powder. In such a case, the number-average particle size 
thereof may preferably be 4 microns or smaller, more preferably 3 microns 
or smaller. 
In the case of internal addition, such a charge controller may preferably 
be used in an amount of 0.1-20 wt. parts, more preferably 0.2-10 wt. 
parts, per 100 wt. parts of a binder resin. 
It is preferred that silica fine powder is externally added to the magnetic 
toner and the non-magnetic color toner of the present invention. 
In the magnetic toner of the present invention having the above-mentioned 
particle size distribution characteristic, the specific surface area 
thereof becomes larger than that in the conventional toner. In a case 
where the magnetic toner particles are caused to contact the surface of a 
cylindrical electroconductive non-magnetic sleeve containing a magnetic 
field-generating means therein in order to triboelectrically charge them, 
the frequency of the contact between the toner particle surface and the 
sleeve is increased as compared with that in the conventional magnetic 
toner, whereby the abrasion of the toner particles or the contamination of 
the sleeve is liable to occur. However, when the magnetic toner of the 
present invention is combined with the silica fine powder, the silica fine 
powder is disposed between the toner particles and the sleeve surface, 
whereby the abrasion of the toner particle is remarkably reduced. 
Thus, the life of the magnetic toner and the sleeve may be extended and the 
chargeability may stably be retained. As a result, there can be provided a 
developer comprising a magnetic toner showing excellent characteristics in 
long-time use. Further, the magnetic toner particles having a particle 
size of 5 microns or smaller, which play an important role in the present 
invention, may produce a better effect in the presence of the silica fine 
powder, thereby to stably provide high-quality images. 
The silica fine powder may be those produced through the dry process or the 
wet process. A silica fine powder produced through the dry process is 
preferred in view of the anti-filming characteristic and durability 
thereof. 
The dry process referred to herein is a process for producing silica fine 
powder through vapor-phase oxidation of a silicon halide. For example, 
silica powder can be produced according to the method utilizing pyrolytic 
oxidation of gaseous silicon tetrachloride in oxygen-hydrogen flame, 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. 
In the above preparation step, it is also possible to obtain complex fine 
powder of silica and other metal oxides by using other metal halide 
compounds such as aluminum chloride or titanium chloride together with 
silicon halide compounds. Such is also included in the fine silica powder 
to be used in the present invention. 
Commercially available fine silica powder formed by vapor-phase oxidation 
of a silicon halide to be used in the present invention include those sold 
under the trade names of AEROSIL (Nippon Aerosil Co.) 130, 200 and 300. 
On the other hand, in order to produce silica powder to be used in the 
present invention through the wet process, various processes known 
heretofore may be applied. For example, decomposition of sodium silicate 
with an acid represented by the following scheme may be applied: 
EQU Na.sub.2 O.xSiO.sub.2 +HCl+H.sub.2 O.fwdarw.SiO.sub.2.nH.sub.2 O+NaCl. 
In addition, there may also be used a process wherein sodium silicate is 
decomposed with an ammonium salt or an alkali salt, a process wherein an 
alkaline earth metal silicate is produced from sodium silicate and 
decomposed with an acid to form silicic acid, a process wherein a sodium 
silicate solution is treated with an ion-exchange resin to form silicic 
acid, and a process wherein natural silicic acid or silicate is utilized. 
The silica power to be used herein may be anhydrous silicon dioxide 
(chloride silica), and also a silicate such as aluminum silicate, sodium 
silicate, potassium silicate, magnesium silicate and zinc silicate. 
Commercially available fine silica powders formed by the wet process 
include one sold under the trade name of Nipsil (Nippon Silica K.K.). 
Among the above-mentioned silica powders, those having a specific surface 
area as measured by the BET method with nitrogen adsorption of 30 m.sup.2 
/g or more, particularly 50-400 m.sup.2 /g, provide a good result. In the 
present invention, the silica fine powder may preferably be used in an 
amount of 0.01-5 wt. parts, more preferably 0.1-3 wt. parts, with respect 
to 100 wt. parts of the magnetic toner or the non-magnetic color toner, in 
view of improvement in fluidity and prevention of toner scattering. 
It is advantageous that the silica fine powder has a charge polarity equal 
to that of the toner to which it is added. For example, in the case where 
a positively chargeable silica fine powder is added to a positively 
chargeable magnetic toner or non-magnetic color toner, not only the 
transfer is advantageously effected because of the same charge polarity 
but also a part of the silica fine powder isolated from the magnetic or 
non-magnetic toner is also transferred so that the toner recovered in the 
cleaning unit tends to contain less silica fine powder and have an 
increased aggregation characteristic. This advantageously affects the 
enhancement of cleaning performance and abrasion function on the 
photosensitive member surface exerted by the aggregation of the toner 
particles per se in the present invention. 
On the other hand, in case where a silica fine powder having a charge 
polarity opposite to that the magnetic toner or non-magnetic color toner 
is added, the transfer of the silica fine powder becomes difficult so that 
the toner recovered in the cleaning unit is caused to contain more silica 
fine powder having a fluidity-imparting function to have a lower degree of 
aggregation. As a result, the effect of enhancing the cleaning performance 
and abrasive function exerted by the toner particles per se of the present 
invention can be weakened. 
In case where the magnetic toner of the present invention is used as a 
positively chargeable magnetic toner, it is preferred to use positively 
chargeable fine silica powder rather than negatively chargeable fine 
silica powder, in order to prevent the abrasion of the toner particle and 
the soiling of the sleeve surface, and to retain the stability in 
chargeability. 
In order to obtain positively chargeable silica fine powder, the 
above-mentioned silica powder obtained through the dry or wet process may 
be treated with a silicone oil having an organic group containing at least 
one nitrogen atom in its side chain, a nitrogen-containing silane coupling 
agent, or both of these. 
In the present invention, "positively chargeable silica" means one having a 
positive triboelectric charge with respect to iron powder carrier when 
measured by the blow-off method. 
The silicone oil having a nitrogen atom in its side chain to be used in the 
treatment of silica fine powder may be a silicone oil having at least the 
following partial structure: 
##STR2## 
wherein R.sub.1 denotes hydrogen, alkyl, aryl or alkoxyl; R.sub.2 denotes 
alkylene or phenylene; R.sub.3 and R.sub.4 denote hydrogen, alkyl, or 
aryl; and R.sub.5 denotes a nitrogen-containing heterocyclic group. The 
above alkyl, aryl, alkylene and phenylene group can contain an organic 
group having a nitrogen atom, or have a substituent such as halogen within 
an extent not impairing the chargeability. The above-mentioned silicone 
oil may preferably be used in an amount of 1-50 wt. %, more preferably 
5-30 wt. %, based on the weight of the silica fine powder. 
The nitrogen-containing silane coupling agent used in the present invention 
generally has a structure represented by the following formula: 
EQU R.sub.m SiY.sub.n, 
wherein R is an alkoxy group or a halogen atom; Y is an amino group or an 
organic group having at least one amino group or nitrogen atom; and m and 
n are positive integers of 1-3 satisfying the relationship of m+n =4. 
The organic group having at least one nitrogen group may for example be an 
amino group having an organic group as a substituent, a 
nitrogen-containing heterocyclic group, or a group having a 
nitrogen-containing heterocyclic group. The nitrogen-containing 
heterocyclic group may be unsaturated or saturated and may respectively be 
known ones. Examples of the unsaturate heterocyclic ring structure 
providing the nitrogen-containing heterocyclic group may include the 
following: 
##STR3## 
Examples of the saturated heterocyclic ring structure include the 
following: 
##STR4## 
The heterocyclic groups used in the present invention may preferably be 
those of five-membered or six-membered rings in consideration of 
stability. 
Examples of the silane coupling agent include: 
aminopropyltrimethoxysilane, 
aminopropyltriethoxysilane, 
dimethylaminopropyltrimethoxysilane, 
diethylaminopropyltrimethoxysilane, 
dipropylaminopropyltrtimethoxysilane, 
dibutylaminopropyltrimethoxysilane, 
monobutylaminopropyltrimethoxysilane, 
dioctylaminopropyltrimethoxysilane, 
dibutylaminopropyldimethoxysilane, 
dibutylaminopropylmonomethoxysilane, 
dimethylaminophenyltriethoxysilane, 
trimethoxysilyl-.gamma.-propylphenylamine, and 
trimethoxysilyl-.gamma.-propylbenzyl-amine. 
Further, examples of the nitrogen-containing heterocyclic compounds 
represented by the above structural formulas include: 
trimethoxysilyl-.gamma.-propylpiperidine, 
trimethoxysilyl-.gamma.-propylmorpholine, and 
trimethoxysilyl-.gamma.-propylimidazole. 
The above-mentioned nitrogen-containing silane coupling agent may 
preferably be used in an amount of 1-50 wt. %, more preferably 5-30 wt. %, 
based on the weight of the silica fine powder. 
The thus treated positively chargeable silica powder shows an effect when 
added in an amount of 0.01-8 wt. parts and more preferably may be used in 
an amount of 0.1-5 wt. parts, respectively with respect to the positively 
chargeable magnetic toner or non-magnetic color toner to show a positive 
chargeability with excellent stability. As a preferred mode of addition, 
the treated silica powder in an amount of 0.1-3 wt. parts with respect to 
100 wt. parts of the positively chargeable magnetic a non-magnetic toner 
should preferably be in the form of being attached to the surface of the 
toner particles. The above-mentioned untreated silica fine powder may be 
used in the same amount as mentioned above. 
The silica fine powder used in the present invention may be treated as 
desired with another silane coupling agent or with an organic silicon 
compound for the purpose of enhancing hydrophobicity. The silica powder 
may be treated with such agents in a known manner so that they react with 
or are physically adsorbed by the silica powder. Examples of such treating 
agents include hexamethyldisilazane, trimethylsilane, 
trimethylchlorosilane, trimethylethoxysilane, dimethyldichlorosilane, 
methyltrichlorosilane, allyldimethylchlorosilane, 
allylphenyldichlorosilane, benzyldimethylcholrosilane, 
bromomethyldimethylchlorosilane, .alpha.-chloroethyltrichlorosilane, 
.beta.-chloroethyltrichlorosilane, chloromethyldimethylchlorosilane, 
triorganosilylmercaptans such as trimethylsilylmercaptan, triorganosilyl 
acrylates, vinyldimethylacetoxysilane, dimethylethoxysilane, 
dimethyldimethoxysilane, diphenyldiethoxysilane, hexamethyldisiloxane, 
1,3-divinyltetramethyldisiloxane, 1,3-diphenyltetramethyldisiloxane, and 
dimethylpolysiloxane having 2 to 12 siloxane units per molecule and 
containing each one hydroxyl group bonded to Si at the terminal units. 
These may be used alone or as a mixture of two or more compounds. The 
above-mentioned treating agent may preferably be used in an amount of 1-40 
wt. % based on the weight of the silica fine powder. However, the above 
treating agent may be used so that the final product of the treated silica 
fine powder shows positive chargeability. 
An additive may be mixed in the magnetic toner or non-magnetic color toner 
of the present invention as desired. More specifically, as a colorant, 
known dyes or pigments may be used generally in an amount of 0.5-20 wt. 
parts per 100 wt. parts of a binder resin. Another optional additive may 
be added to the toner so that the toner will exhibit further better 
performances. Optional additives to be used include, for example, 
lubricants such as zinc stearate; abrasives such as cerium oxide and 
silicon carbide; flowability improvers such as colloidal silica and 
aluminum oxide; anti-caking agent; or conductivity-imparting agents such 
as carbon black and tin oxide. 
In order to improve releasability in hot-roller fixing, it is also a 
preferred embodiment of the present invention to add to the magnetic toner 
a waxy material such as low-molecular weight polyethylene, low-molecular 
weight polypropylene, microcrystalline wax, carnauba wax, sasol wax or 
paraffin wax preferably in an amount of 0.5-5 wt. %. 
The magnetic toner of the present invention contains a magnetic material, 
which may be one or a mixture of: iron oxides such as magnetite, hematite, 
ferrite and ferrite containing excess iron; metals such as iron, cobalt 
and nickel, alloys of these metals with metals such as aluminum, cobalt, 
copper, lead, magnesium, tin, zinc, antimony, beryllium, bismuth, cadmium, 
calcium, manganese, selenium, titanium, tungsten and vanadium. 
These ferromagnetic materials may preferable be in the form of particles 
having an average particle size of the order of 0.1-1 micron, preferably 
0.1-0.5 microns and be used in the toner in an amount of about 60-110 wt. 
parts, particularly 65-100 wt. parts, per 100 wt. parts of the resin 
component. 
The magnetic toner for developing electrostatic images according to the 
present invention may be produced by sufficiently mixing magnetic powder 
with a vinyl on non-vinyl thermoplastic resin such as those enumerated 
hereinbefore, and optionally, a pigment or dye as colorant, a charge 
controller, another additive, etc., by means of a mixer such as a ball 
mill, etc.; then melting and kneading the mixture by hot kneading means 
such as hot rollers, kneader and extruder to disperse or dissolve the 
pigment or dye, and optional additives, if any, in the melted resin; 
cooling and crushing the mixture; and subjecting the powder product to 
precise classification to form magnetic toner according to the present 
invention. 
The magnetic toner according to the present invention may preferably be 
applied to an image forming apparatus for practicing an image forming 
method using a magnetic toner developing means whereby a latent image is 
developed while toner particles are caused to fly from a toner-carrying 
member such as a cylindrical sleeve to a latent image carrying member such 
as a photosensitive member. 
The magnetic toner is supplied with triboelectric charge mainly due to the 
contact thereof with the sleeve surface and applied onto the sleeve 
surface in a thin layer form. The thin layer of the magnetic toner is 
formed so that the thickness thereof is smaller than the clearance between 
the photosensitive member and the sleeve in a developing region. In the 
development of a latent image formed on the photosensitive member, it is 
preferred to cause the magnetic toner particles having triboelectric 
charge to fly from the sleeve to the photosensitive member, while applying 
an alternating electric field between the photosensitive member and the 
sleeve. Examples of the alternating electric field may include a pulse 
electric field, or an electric field based on an AC bias or a 
superposition of AC and DC biases. 
A developing method using a one component magnetic developer is explained 
in more detail with reference to FIG. 7. 
Referring to FIG. 7, a one component-type developer 731 applied in a thin 
layer on the surface of a stainless steel-made cylindrical sleeve 707 
rotating in the direction of an arrow 736 by means of a magnetic blade 705 
and is carried through a clearance between the sleeve 707 and the blade 
705. The sleeve 707 contains inside therein a fixed magnet 735 as a 
magnetic field generating means, and the fixed magnet 735 formed a 
magnetic field in the neighborhood of the sleeve surface in a developing 
region where the sleeve surface faces close to a photosensitive drum 701 
comprising an organic photoconductive layer having a negatively charged 
latent image. Between the photosensitive drum 701 rotating in the 
direction of an arrow 737 and the sleeve 707, a biasing voltage formed by 
superposition of an AC bias and a DC bias is applied. 
The non-magnetic color toner of the present invention comprises a binder 
resin similar to that used in the above-mentioned magnetic toner and may 
further contain an additive as desired. The colorant contained in the 
non-magnetic toner may be a dye and/or a pigment known heretofore as a 
colorant and may for example be Phthalocyanine Blue, Peacock Blue, 
Permanent Red, Lake Red, Rhodamine Lake, Hansa Yellow, Permanent Yellow or 
Benzidine Yellow. The content of the colorant may be 0.5 to 20 wt. parts, 
and in order to provide an OHP (overhead projector) film having a good 
transparency, may preferably be 12 wt. parts or less, further preferably 
be 0.5 to 9 wt. parts, respectively per 100 wt. parts of the binder resin. 
The carrier usable in the present invention may for example be powder 
having a magnetism, such as iron powder, ferrite powder or nickel powder, 
or such powder further coated with a resin. The carrier may be used in an 
amount of 10 to 1000 wt. parts, preferably 30-500 wt. parts, per 10 wt. 
parts of the toner. The carrier may preferably have a particle size of 4 
to 100 microns, further preferably 10 to 60 microns, in view of the 
combination with a small particle size toner. 
The non-magnetic color toner for developing electrostatic image according 
to the present invention may be produced by sufficiently mixing a vinyl or 
non-vinyl thermoplastic resin, a pigment or dye as a colorant, and 
optionally a charge controller, another additive, etc., by means of a 
mixer such as a ball mill, etc.; then melting and kneading the mixture by 
hot kneading means such as hot rollers, kneader and extruder to disperse 
or dissolve the pigment or dye, and optional additive, if any, in the 
melted resin; cooling and crushing the mixture; and subjecting the powder 
product to precise classification to form a non-magnetic toner according 
to the present invention. 
In the non-magnetic color toner developing means according to the 
invention, a two-component type developer may be formed by the 
non-magnetic toner and magnetic particles and applied to an ordinary 
two-component type image forming method. It is particularly preferably 
applied to an image forming method, wherein a magnetic particle-confining 
member is disposed opposite to a toner-carrying member, a magnetic brush 
of magnetic particles is formed under the action of a magnetic force given 
by a magnetic field generating means inner region upstream of the magnetic 
particle confining member with respect to the moving direction of the 
surface of the toner-carrying member, to confine the magnetic brush by the 
magnetic particle-confining member, and form a thin layer of the 
non-magnetic toner on the toner-carrying member, and a latent image formed 
on a latent image-bearing member is developed with the non-magnetic toner 
under the application of an alternating electric field. 
The above-mentioned developing method is explained with reference to FIG. 
6A. Referring to FIG. 6A, the apparatus comprising a latent image-bearing 
member 601, a developer supplying container 621, a non-magnetic sleeve 
606, a fixed magnet 623, a magnetic or non-magnetic blade 604, a confining 
member for defining the region for circulating magnetic particles 626, 
magnetic particles 627, a non-magnetic toner 628, a scattering preventing 
member 630, a magnetic member 631, a developing region 632, and a biasing 
electric supply 634. The sleeve 606 rotates in the direction of B, and 
therewith, the magnetic particles 627 circulate in the direction of C. As 
a result, the sleeve surface contact and are rubbed with the magnetic 
particle layer to form a non-magnetic developer layer on the sleeve. While 
the magnetic particles circulate in the direction of C, a part thereof in 
a prescribed amount regulated by the clearance between the magnetic or 
non-magnetic blade 604 and the sleeve 606 is applied on the non-magnetic 
developer layer. As a result, the non-magnetic toner is applied on both 
the sleeve surface and the surface of magnetic particles, so that it is 
possible to obtain an effect substantially the same as given by an 
increase in sleeve surface area. In the developing region 632, one 
magnetic pole of the fixed magnet 623 is directed to the latent image 
surface to form a clear development pole, and the non-magnetic toner is 
caused to fly for development from the sleeve and the magnetic particles 
under the action of an alternating electric field. After the development, 
the magnetic particles and yet unused developer are moved along with the 
rotation of the sleeve to be recovered in the developer container. 
The development phenomenon is explained in more detail with reference to 
FIG. 6B. The electrostatic latent image is composed by a negative charge 
(dark image part) to form an electric field in the direction of an arrow 
a. The electric field direction given by the alternating electric field 
alternates with time, but in a phase when a positive component is applied 
to the sleeve 606 side, the electric field direction given thereby 
coincides with the electric field direction given by the latent image. At 
this time, the amount of charge injected to ears 651 by the electric field 
becomes the largest, so that the ears 651 assume the maximum standing 
position as shown in the Figure to reach the surface of the photosensitive 
drum 601. 
On the other hand, the non-magnetic toner 628 on the surfaces of the sleeve 
606 and the magnetic particles 627 is positively charged as described 
above, and is therefore transferred to the photosensitive drum 601 by the 
electric field formed in the space. At this time, the ears 651 stand in a 
coarse state, the surface of the sleeve 606 is exposed, and the toner 628 
is released from the surfaces of both the sleeve 606 and the ears 651. In 
addition, as the ears 651 are provided with charge of the same polarity as 
the toner 628, the toner 628 on the surface of the ears 651 is further 
easily released by the action of electric repulsion. 
In a phase when a negative component of the alternating voltage is applied 
to the sleeve 606, the electric field in the direction of an arrow b given 
by the alternating voltage is opposite to the electric field direction A 
given by the negative latent image. As a result, the electric field in the 
space is weakened and the amount of charge injection is decreased, so that 
the ears 651 form a contact state shrinked corresponding to the amount of 
charge injection. 
On the other hand, the toner 628 on the photosensitive drum 608 is 
positively charged as described above, and is therefore reversely 
transferred to the sleeve 606 or the magnetic particles 627 under the 
action of the electric field formed in the space. In this way, the toner 
628 is moved reciprocally between the photosensitive drum 603 and the 
sleeve 622 surface or the surface of the magnetic particles 627. 
Consequently, as the photosensitive drum 601 and the sleeve 606 rotate, 
the space between these members is expanded and the electric field is 
weakened to complete the developing action. 
The ears 651 are provided with a charge such as triboelectric charge or 
mirror-image charge given by the toner 628, a charge given by the 
electrostatic latent image on the photosensitive drum 601 and the charge 
injected by the alternating electric field between the photosensitive drum 
601 and the sleeve 606, and the charge state is changed according to the 
time constant of charge and discharge determined by the material of the 
magnetic particles 627 and other factors. 
As described above, the ears 651 of the magnetic particles 627 assume a 
minute but vigorous vibrating state under the action of the alternating 
electric field as described above. 
After the development, the magnetic particles and yet unused toner 
particles are carried along with the rotation of the sleeve and recovered 
in the developer container. 
The sleeve 606 can be formed from a cylinder of paper or a synthetic resin. 
By treating the surface of such a cylinder to provide an 
electroconductivity or by using a cylinder of an electroconductive 
material such as aluminum, bronze or stainless steel, a development 
electrode roller may be provided. 
Incidentally, in the present invention, the thin-line reproducibility may 
be measured in the following manner. 
An original image comprising thin lines accurately having a width of 100 
microns is copied under a suitable copying condition, i.e., a condition 
such that a circular original image having a diameter of 5 mm and an image 
density of 0.3 (halftone) is copied to provide a copy image having an 
image density of 0.3-0.5, thereby to obtain a copy image as a sample for 
measurement. An enlarged monitor image of the sample is formed by means of 
a particle analyzer (Luzex 450, mfd. by Nihon Regulator Co. Ltd.) as a 
measurement device, and the line width is measured by means of an 
indicator. Because the thin line image comprising toner particles has 
unevenness in the width direction, the measurement points for the line 
width are determined so that they correspond to the average line width, 
i.e., the average of the maximum and minimum line widths. Based on such a 
measurement, the value (%) of the thin-line reproducibility is calculated 
according to the following formula: 
##EQU1## 
Further, in the present invention, the resolution may be measured in the 
following manner. 
There are formed ten species of original images comprising a pattern of 
five thin lines which have equal line width and are disposed at equal 
spacings equal to the line width. In these ten species of original images, 
thin lines are respectively drawn so that they provide densities of 2.8, 
3.2, 3.6, 4.0, 4.5, 5.0, 5.6, 6.3, 7.1, and 8.0 lines per 1 mm. These ten 
species of original images are copied under the above-mentioned suitable 
copying conditions to form copy images which are then observed by means of 
a magnifying glass. The value of the resolution is so determined that it 
corresponds to the maximum number of thin lines (lines/mm) of an image 
wherein all the thin lines are clearly separated from each other. As the 
above-mentioned number is larger, it indicates a higher resolution. 
Hereinbelow, the present invention will be described in further detail with 
reference to Examples, by which the present invention are not intended to 
be limited at all. In the following Examples, "parts" used for expressing 
a composition are by weight. 
EXAMPLE 1 
______________________________________ 
Styrene/butyl acrylate/divinylbenzene 
100 wt. parts 
copolymer (copolymerization wt. ratio: 
80/19.5/0.5, weight-average molecular 
weight: 320,000) 
Tri-iron tetraoxide 80 wt. parts 
(average particle size = 0.2 micron) 
Nigrosin 4 wt. parts 
(number-average particle size = about 
3 microns) 
Low-molecular weight propylene-ethylene 
4 wt. parts 
copolymer 
______________________________________ 
The above ingredients were well blended in a blender and melt-kneaded at 
150.degree. C. by means of a two-axis extruder. The kneaded product was 
cooled, coarsely crushed by a cutter mill, finely pulverized by means of a 
pulverizer using jet air stream, and classified by a fixed-wall type 
wind-force classifier (DS-type Wind-Force Classifier, mfd. by Nippon 
Pneumatic Mfd. Co. Ltd.) to obtain a classified powder product. Ultra-fine 
powder and coarse power were simultaneously and precisely removed from the 
classified powder by means of a multi-division classifier utilizing a 
Coanda effect (Elbow Jet Classifier available from Nittetsu Kogyo K.K.), 
thereby to obtain black fine powder (magnetic toner) having a 
number-average particle size of 7.4 microns. When the thus obtained black 
fine powder was mixed with iron powder carrier and thereafter the 
triboelectric charge thereof was measured, it showed a value of +8 
.mu.C/g. 
The number-basis distribution and volume-basis distribution of the thus 
obtained magnetic toner of positively chargeable black fine powder were 
measured by means of a Coulter counter Model TA-II with a 100 
micron-aperture in the above-described manner. The thus obtained results 
are shown in the following Table 1. Thus, the magnetic toner showed the 
values of N (value of % by number of particles having a size of 5 microns 
or smaller), V (value of % by weight of the particles having a size of 5 
microns or smaller) and ratio N/V as follows: N=35%, V=10%, and N/V=3.5. 
TABLE 1 
__________________________________________________________________________ 
Number of % by number (N) 
% by volume (V) 
Size (.mu.m) 
particles 
Distribution 
Accumulation 
Distribution 
Accumulation 
__________________________________________________________________________ 
2.00-2.52 
2374 2.3 2.3 0.0 0.0 
2.52-3.17 
4351 4.2 6.6 0.4 0.4 
3.17-4.00 
9556 9.3 15.9 1.9 2.3 
4.00-5.04 
20048 19.5 35.4 8.1 10.3 
5.04-6.35 
26486 25.8 61.3 19.7 30.0 
6.35-8.00 
25686 25.0 86.3 35.1 65.1 
8.00-10.08 
12200 11.9 98.2 27.2 92.3 
10.08-12.70 
1815 1.8 99.9 7.2 99.5 
12.70-16.00 
66 0.1 100.0 0.5 100.0 
16.00-20.20 
5 0.0 100.0 0.0 100.0 
20.20-25.40 
0 0.0 100.0 0.0 100.0 
25.40-32.00 
0 0.0 100.0 0.0 100.0 
32.00-40.30 
0 0.0 100.0 0.0 100.0 
40.30-50.80 
0 0.0 100.0 0.0 100.0 
__________________________________________________________________________ 
For reference, FIG. 8 schematically shows the classification step using the 
multi-division classifier, and FIG. 9 shows a sectional perspective view 
of the multi-division classifier. 
0.5 wt. part of positively chargeable hydrophobic dry process silica (BET 
specific surface area: 200 m.sup.2 /g) was added to 100 wt. parts of the 
magnetic toner of black fine powder obtained above and mixed therewith by 
means of a Henschel mixer thereby to obtain a positively chargeable 
one-component developer comprising a magnetic toner (a toner with silica 
externally added). 
The degree of aggregation of the magnetic developer was measured to be 65%. 
The above-mentioned magnetic toner showed a particle size distribution and 
various characteristics as shown in Table 3 appearing hereinafter. 
A non-magnetic color toner was prepared in the following manner. 
______________________________________ 
Styrene-butyl acrylate/dimethylaminoethyl 
100 wt. parts 
acrylate copolymer (copolymerization 
wt. ratio: 84/13/3, weight-average 
molecular weight: 230,000) 
Low-molecular weight polypropylene 
5 wt. parts 
Azo-type red pigment 5 wt. parts 
______________________________________ 
The above ingredients were well blended in a Henschel mixer and 
melt-kneaded at 150.degree. C. by means of a two-axis extruder. The 
kneaded product was cooled, coarsely crushed by a cutter mill, finely 
pulverized by means of a pulverizer using jet air stream, and classified 
by a wind-force classifier to obtain a classified red powder product 
(non-magnetic toner). The red powder (non-magnetic toner) showed a 
volume-average particle size of 12.5 microns, and 100 wt. parts thereof 
was blended with 0.5 wt. part of positively chargeable hydrophobic silica 
to obtain a non-magnetic color toner (with silica externally added). The 
non-magnetic color toner (with silica) showed a degree of aggregation of 
about 35%. Then, 9 wt. parts of the non-magnetic color toner was blended 
with 100 wt. parts of magnetic ferrite carrier coated with 
fluorine/acrylic resin (average particle size: about 55 microns) to obtain 
a two-component developer. 
The above prepared one-component developer and two-component developer were 
charged in an image forming (developing) device as shown in FIGS. 1 and 2, 
and a developing test was conducted. The developing conditions used in 
this instance are explained with reference to FIGS. 1 and 2. 
The two-component developer was used for development in the following 
manner. Referring to FIG. 1, the non-magnetic color toner developing unit 
2 was more specifically one shown in FIG. 6A, and the photosensitive drum 
1 (or 601) was rotated at a peripheral speed of 100 mm/sec. in the 
direction of an arrow a. The stainless sleeve 6 (or 606) having an outer 
diameter of 20 mm was rotated in the direction of an arrow b at a 
peripheral speed of 150 mm/sec. 
On the other hand, inside the rotating sleeve 6, a fixed magnet 623 (of 
sintered ferrite) was disposed to form a development magnetic pole 
providing a maximum surface magnetic flux density of about 980 Gauss. The 
magnetic blade 4 (or 604) was composed of a non-magnetic stainless steel 
plate having a thickness of 1.2 mm. The blade-sleeve spacing was 400 
microns. 
Opposite the sleeve 6 was disposed an OPC photosensitive drum having 
thereon an electrostatic latent image comprising a charge pattern having a 
dark part potential of -600 V and a light part potential of -150 V with a 
spacing of 350 microns from the sleeve surface. 
The development was effected by applying an alternating voltage with a 
frequency of 1800 Hz, a peak-to-peak value of 1300 V and a central value 
of -200 V. 
Then, the above-prepared one-component magnetic developer was used for 
development in the following manner. Referring to FIG. 2, the magnetic 
toner developing unit 3 was more specifically one shown in FIG. 7, and the 
one-component developer 3 was applied in a thin layer form onto the 
surface of a cylindrical sleeve 7 (or 707) of stainless steel as a 
toner-carrying means rotating in the direction of an arrow 736 by means of 
a magnetic blade 5 (or 705) as a means for forming the layer of the toner. 
The clearance between the sleeve 7 and the blade 5 was set to about 250 
microns. The sleeve 7 contained a fixed magnet 735 as a magnet means. The 
fixed magnet 735 produced a magnetic field of 1000 gauss in the 
neighborhood of the sleeve surface in the developing region where the 
sleeve 7 was disposed near and opposite to a photosensitive drum 1, as an 
electrostatic image-bearing means, comprising an organic photoconductor 
layer carrying a negative latent image. The minimum space between the 
sleeve 7 and the photosensitive drum 1 rotating in the direction of an 
arrow 747 was set to about 300 microns. In the development, a bias of 2000 
Hz/1350 Vpp obtained by superposing an AC bias and a DC bias was applied 
between the photosensitive drum 1 and the sleeve by an alternating 
electric field-applying means 736. The layer of the one-component 
developer formed on the sleeve 7 had a thickness of about 75-150 microns, 
and the magnetic toner formed ears having a height of about 95 microns 
under the magnetic field, due to the fixed magnet 735. By using the 
above-mentioned device, a negative latent image formed on the 
photosensitive drum 1 was developed by causing the one-component developer 
3 having a positive triboelectric charge to fly to the latent image. 
A developed red toner image was formed by the two-component developer on a 
half area of an A4-sized copying paper (plain paper) and fixed by 
heat-pressure rollers. Then, on the remaining half area, a black toner 
image was formed by the one-component magnetic developer and fixed by 
heat-pressure rollers. As a result, a fixed image of two-color images was 
formed on the copying paper. The above-image formation test was 
successively repeated 10000 times to form 10000 sheets of toner images. 
The results are shown in Table 4. 
As apparent from Table 4, both of the line portion and large image area 
portion of the letters formed by the magnetic toner showed a high image 
density. The magnetic toner of the present invention was excellent in 
thin-line reproducibility and resolution, and retained good image quality 
in the initial stage and also after 10,000 sheets of image formation. 
Further, the copying cost per one sheet was low, whereby the magnetic 
toner of the present invention was excellent in economical characteristic. 
Further, in the apparatus shown in FIG. 1, a felt pad was disposed in 
contact with the photosensitive drum between the cleaning blade 12 and the 
primary charger 10 so as to collect a toner leaked through the cleaning 
unit due to cleaning failure, whereby almost no color was observed on the 
pad and the weight increase was very small as 0.3 mg/1000 sheets. 
The cleaning blade was composed of polyurethane rubber and has a thickness 
of 2.0 mm and a JIS A rubber hardness of 65 degrees. The blade was pushed 
against the photosensitive drum at a pressure of 10 g/cm. The cleaning 
roller was composed of polyurethane rubber. 
Hereinbelow, the multi-division classifier and the classification step used 
in this instance are explained with reference to FIGS. 8 and 9. 
Referring to FIGS. 8 and 9, the multi-division classifier has side walls 
822, 823 and 824, and a lower wall 825. The side wall 823 and the lower 
wall 825 are provided with knife edge-shaped classifying wedges 817 and 
818, respectively, whereby the classifying chamber is divided into three 
sections. At a lower portion of the side wall 822, a feed supply nozzle 
816 opening into the classifying chamber is provided. A Coanda black 826 
is disposed along the lower tangential line of the nozzle 816 so as to 
form a long elliptic arc shaped by bending the tangential line downwardly. 
The classifying chamber has an upper wall 827 provided with a knife 
edge-shaped gas-intake wedge 819 extending downwardly. Above the 
classifying chamber, gas-intake pipes 814 and 815 opening into the 
classifying chamber are provided. In the intake pipes 814 and 815, a first 
gas introduction control means 820 and a second gas introduction control 
means 821, respectively, comprising, e.g., a damper, are provided; and 
also static pressure gauges 828 and 829 are disposed communicatively with 
the pipes 814 and 815, respectively. At the bottom of the classifying 
chamber, exhaust pipes 811, 812 and 813 having outlets are disposed 
corresponding to the respective classifying sections and opening into the 
chamber. 
Feed powder to be classified is introduced into the classifying zone 
through the supply nozzle 816 under reduced pressure. The feed powder thus 
supplied are caused to fall along curved lines 830 due to the Coanda 
effect given by the Coanda block 826 and the action of the streams of 
high-speed air, so that the feed powder is classified into coarse powder 
811, black fine powder 812 having prescribed volume-average particle size 
and particle size distribution, and ultra-fine powder 813. 
EXAMPLE 2 
The same evaluation as in Example 1 was conducted except that the magnetic 
toner used in Example 1 was replaced by a magnetic toner which was 
prepared by changing the amount of magnetic powder and controlling the 
pulverization and classification conditions and showed various properties 
as shown in Table 3. As a result, no inconvenience such as cleaning 
failure or filming phenomena on the photosensitive member was observed, 
and as shown in Table 4, clear high quality images were stably obtained. 
The magnetic toner showed the following values: N=46%, V=14%, and N/V=3.3. 
EXAMPLE 3 
The same evaluation as in Example 1 was conducted except that the magnetic 
toner used in Example 1 was replaced by a magnetic toner showing various 
properties shown in Table 3. As a result, similarly as in Example 1 as 
shown in Table 4, clear high-quality images were obtained stably with good 
cleaning characteristics and durability. The magnetic toner showed the 
following values: N=20%, V=4%, and N/V=5.0. 
EXAMPLE 4 
The developing unit using the positively chargeable one-component magnetic 
developer prepared in Example 1 was applied to a digital copier NP9330 
(available from Canon K.K.) having an amorphous silicon photosensitive 
drum to effect development, and further was replaced by the developing 
unit using the two-component type developer used in Example 1 to effect 
development, whereby a positively charged electrostatic image was 
developed by the reversal development system in the manner shown in FIG. 3 
to effect 10,000 sheets of image formation. As shown in Table 4, clear 
images having a good gradation characteristic were produced with excellent 
thin line reproducibility and resolution. Further, good cleaning 
performance was obtained and substantially no cleaning failure with 
non-magnetic color toner was observed. 
EXAMPLE 5 
A black fine powder (magnetic toner) shown in Table 4 was prepared in the 
same manner as in Example 1, and 100 wt. parts of the black fine powder 
was mixed with 0.6 wt. part of a positively chargeable hydrophobic silica 
to form a positively chargeable one component magnetic developer (magnetic 
toner with externally added silica). The thus obtained one-component 
magnetic developer was evaluated in the same manner as in Example 1. The 
results are shown in Table 4. The magnetic toner showed the following 
values: N=57%, V=21.9%, and N/V=2.6. 
COMATIVE EXAMPLE 1 
Black fine powder (magnetic toner) as shown in Table 3 was prepared in the 
same manner as in Example 1 except that two of the fixed-wall type 
wind-force classifier used in Example 1 were used for the classification 
instead of the combination of the fixed-wall type wind-force classifier 
and the multi-division classifier as used in Example 1. The magnetic toner 
of Comparative Example 1 in the form of black fine powder showed the value 
of % by number of the magnetic toner particles having a particle size of 5 
microns or smaller which was less than the range defined by the present 
invention and a volume-average particle size which was larger than the 
range defined by the present invention, thus failing to satisfy the 
conditions defined by the present invention. 
The particle size distribution of the obtained magnetic toner is shown in 
Table 2. The magnetic toner showed the following values: N=9%, V=0.62%, 
and N/V=14.5. 
TABLE 2 
__________________________________________________________________________ 
Number of % by number (N) 
% by volume (V) 
Size (.mu.m) 
particles 
Distribution 
Accumulation 
Distribution 
Accumulation 
__________________________________________________________________________ 
2.00-2.52 
992 1.4 1.4 0.0 0.0 
2.52-3.17 
1035 1.4 2.8 0.0 0.0 
3.17-4.00 
1210 1.7 4.5 0.0 0.0 
4.00-5.04 
3093 4.3 8.8 0.6 0.6 
5.04-6.35 
3189 11.4 20.3 3.2 3.8 
6.35-8.00 
15353 21.4 41.7 10.8 14.7 
8.00-10.08 
19040 26.6 68.3 21.5 36.1 
10.08-12.70 
15920 22.2 90.5 33.7 69.9 
12.70-16.00 
6161 8.6 99.1 25.8 95.7 
16.00-20.20 
584 0.8 100.0 4.3 100.0 
20.20-25.40 
25 0 100.0 0.0 100.0 
25.40-32.00 
1 0 100.0 0.0 100.0 
32.00-40.30 
0 0 100.0 0.0 100.0 
40.30-50.80 
0 0 100.0 0.0 100.0 
__________________________________________________________________________ 
0.5 wt. part of positively chargeable hydrophobic dry process silica was 
blended with 100 wt. parts of the magnetic toner of black fine powder 
obtained above mixed therewith in the same manner as in Example 1 thereby 
to obtain a one-component developer. The thus obtained one-component 
developer was used together with the two-component developer containing a 
non-magnetic color toner used in Example 1 and subjected to image 
formation tests under the same conditions as in Example 1. 
As a result, soiling or contamination of images due to cleaning failure was 
observed during the image formation. The degree of soiling was measured in 
the same manner as in Example 1, whereby the increase in weight of the 
felt pad due to soiling was 19 mg/1000 sheets. 
Referring to FIG. 7, the height of ears formed in the developing region of 
the sleeve 707 was about 165 microns which was longer than that in Example 
1. In the resultant images, the toner particles remarkably protruded from 
the latent image formed on the photosensitive member, the thin-line 
reproducibility was 135% which was poorer than that in Example 1, and the 
resolution was 4.5 lines/mm. Further, after 1000 sheets of image 
formation, the image density in the solid black pattern decreased and the 
thin-line reproducibility and resolution deteriorated. Moreover, the toner 
consumption was large. 
The results are shown in Table 4 appearing hereinafter. 
COMATIVE EXAMPLE 2 
Evaluation was conducted in the same manner as in Example 1 except that a 
magnetic toner as shown in Table 3 was used instead of the magnetic toner 
used in Example 1. 
As a result, poorer results were obtained in all respects of image density, 
resolution and thin-line reproducibility. The ears of the toner on the 
sleeve as a toner-carrying member in the developing unit were long and 
coarsely present, so that when the toner was caused to fly onto the 
photosensitive member, the toner provided a tailing protruding out of the 
latent image and also caused other inconveniences inclusive of scattering 
of the toner and a decrease in image density due to coarse coverage with 
toner particles. 
After 2000 sheets of image formation, the soiling of images at the 
periphery of images was caused similarly as in Comparative Example 1, and 
after 1000 sheets of image formation, the image soiling was extended to 
the entirety to provide poor images. Further, similar cleaning failure as 
in Comparative Example 1 was observed. The magnetic toner showed the 
following values: N=12%, V=4.6%, and N/V=2.6. 
TABLE 3 
__________________________________________________________________________ 
(Properties of toner) 
Degree 
Particle size distribution of Magnetic properties 
% by % by % by volume-ave. 
aggrega- 
True 
Saturation Coercive 
number volume 
number 
size tion density 
magnifica- 
Remanence 
force 
.ltoreq.5 .mu.m 
.gtoreq.16 .mu.m 
8.0-12.7 .mu.m 
.mu.m % g/cm.sup.3 
tion .sigma.s emu/g 
.sigma.r emu/g 
Hc Oe 
__________________________________________________________________________ 
Ex. 1 
35 0.0 14 7.4 65 1.56 
27 3.2 91 
2 46 0.3 11 6.5 74 1.69 
38 4.2 92 
3 20 0.5 23 8.5 60 1.51 
25 2.8 90 
4 35 0.3 14 7.4 65 1.56 
27 3.2 91 
5 57 0.2 10 5.7 71 1.62 
31 3.7 90 
Comp. 
9 4.3 49 11.3 41 1.43 
22 2.3 90 
Ex. 1 
2 12 0.2 56 9.5 33 1.43 
24 1.4 49 
__________________________________________________________________________ 
TABLE 4 
__________________________________________________________________________ 
(Performances) 
Initial stage After 10000 sheets of image formation 
Toner 
Thin line 
Resolu- Thin-line 
Resolu- 
consump- 
Dmax Dmax reproduci- 
tion Dmax 
Dmax reproduci- 
tion tion 
5.phi. solid black 
bility 
lines/mm 
5.phi. 
solid black 
bility 
lines/mm 
g/sheet 
__________________________________________________________________________ 
Ex. 1 
1.32 
1.32 105% 6.3 1.36 
1.35 104% 6.3 0.032 
2 1.34 
1.32 102 6.3 1.37 
1.37 102 6.3 0.030 
3 1.31 
1.30 108 5.6 1.33 
1.32 110 5.6 0.033 
4 1.38 
1.38 100 7.1 1.40 
1.40 100 7.1 0.035 
5 1.34 
1.30 109 5.6 1.34 
1.29 115 5.6 0.030 
Comp 
1.31 
1.30 135 4.5 1.31 
1.25 150 4.0 0.055 
Ex. 1 
2 1.19 
1.12 135 4.0 -- -- -- -- -- *1 
__________________________________________________________________________ 
*1: In Comparative Example 2, image evaluation was difficult because of 
cleaning failure on the entire area. 
EXPERIMENTAL EXAMPLE 
A one-component developer prepared in Example 1 was charged in a developing 
unit as shown in FIG. 7, and a developing test was conducted. The 
developing conditions are explained with reference to FIG. 7. 
The one component developer 731 was applied in a thin layer onto the 
surface of a cylindrical sleeve 707 of a stainless steel rotating in the 
direction of an arrow 736 by means of a magnetic blade 705. The clearance 
between the sleeve 707 and the blade 705 was set to about 250 microns. The 
sleeve 707 contained a fixed magnet 735 as a magnetic field generating 
means inside thereof. The fixed magnet 735 produced a magnetic field of 
1000 Gauss in the neighborhood of the sleeve surface in the developing 
region where the sleeve 707 closely faced an OPC photosensitive drum 701 
comprising an organic photoconductive layer having a negatively charged 
latent image thereon. The photosensitive drum 701 rotating in the 
direction of an arrow 737 and the sleeve 707 were disposed to provide a 
minimum distance of about 300 microns. Between the OPC photosensitive drum 
701 and the sleeve 707, a biasing voltage of 2000 Hz/1350 Vpp formed by 
superposition of an AC bias and a DC bias. The one-component developer on 
the sleeve 733 was formed in a layer thickness of about 75 to 150 
microns, and the magnetic toner formed ears with a height of about 95 
microns in the developing region. 
A negatively charged latent image formed on the OPC photosensitive drum 707 
was developed by flying one-component magnetic developer 731 having a 
positive triboelectric charge. Such an image formation test was repeated 
10,000 times to form 10,000 sheets of toner images. 
As a result, line images such as characters and large area images both 
showed a high image density with excellent thin-line reproducibility and 
resolution. Even after the 10,000 sheets of image formation, no image 
defects due to cleaning failure or filming on the photosensitive member 
were observed, and the good image quality at the initial stage was 
maintained.