Developing apparatus with elastic regulating member urged to a developer carrying member

A developing apparatus for developping an electrostatic latent image includes a movable developer carrying member facing toward or contacted with an image bearing member in a developing zone. An elastic regulating member for forming a regulated developer layer on the developer carrying member is elastically urged toward the developer to form a nip therebetween, through which the developer is conveyed to the developing zone. Fine particles different from particles constituting the developer are arranged on the surface of the regulating member comprising the nip.

FIELD OF THE INVENTION AND RELATED ART 
The present invention relates to a developing apparatus for developing an 
electrostatic latent image, more particularly to a developing apparatus 
having a developer carrying member and an elastic developer regulating 
member elastically urged to the developer carrying member. 
U.S. Pat. Nos. 4,458,627 and 4,356,245 disclose a developing apparatus 
wherein an elastic blade made of rubber or the like is elastically urqed 
to a developer carrying sleeve to form a nip therebetween, through which 
one component developer not containing carrier particles is passed, by 
which a thin layer of the developer is formed on a developer carrying 
sleeve. In such an apparatus, the developer is actively rubbed in the nip, 
and therefore, the developed image as a sufficient image density. 
However, since the elastic blade is press-contacted to the sleeve in such 
an apparatus, the driving torque required for rotating the sleeve is large 
during an initial stage after the start of use of the developing 
apparatus. Sometimes, the sleeve does not rotate smoothly. If this occurs, 
the developed image is not uniform. 
In addition, during the initial stage, for example, until 300 sheets are 
printed from the start of the use of the developing apparatus, the density 
of the developed image gradually increases from relatively low density. 
The reason is considered to be that during the initial stage, the motion 
of the developer in the nip is relatively inactive with the result of 
insufficient triboelectric charge to the developer. In fact, the 
triboelectric charge distribution of the developer on the sleeve is wide, 
and the average charge amount is low, as show in FIG. 1, during the 
initial stage. 
After approximately 300 sheets are processed, the triboelectric charge 
distribution becomes sharp, and the average triboelectric charge becomes 
high, as shown in FIG. 2. This is because, the developer is circulated and 
stirred adjacent the sleeve, and the developer particles are sufficiently 
triboelectrically charged by the friction with the sleeve and the blade. 
On the other hand, with the repeated operations, the nip between the 
developing sleeve and the developer regulating blade is clogged with the 
developer, and the developer is coagulated, by which the triboelectric 
charging action becomes instable, and therefore, the conveyance of the 
developer on the developing sleeve becomes also instable. 
Furthermore, with repeated operation, the developer is repeatedly rubbed 
with the developing sleeve and the developer regulating blade, and as a 
result, the material such as pieces of the resin materials which are not 
consumed for the developing action are fused on the developer regulating 
blade, or the binder resin of the developer is fused on the developer 
regulating blade, which form a film covering it. Therefore, the surface 
properties of the developer regulating blade are deteriorated. 
For the reasons stated above, the developed image involves stripes and 
non-uniformity. 
SUMMARY OF THE INVENTION 
Accordingly, it is a principal object of the present invention to provide a 
developing apparatus wherein a developer carrying member is smoothly moved 
from the initial stage immediately after the start of the use of the 
developing apparatus. 
It is another object of the present invention to provide a developing 
apparatus wherein the developer can be properly triboelectrically charged 
from the initial stage after the start of the use of the developing 
apparatus so that the developed image has sufficient image density from 
the initial stage. 
It is a further object of the present invention to provide a developing 
apparatus in which fusing and accumulation of a component of the developer 
on the elastic regulating member can be prevented. 
It is a yet further object of the present invention to provide a developing 
apparatus wherein a nip formed between a elastic developer regulating 
member and a developer carrying member is protected from being clogged 
with the developer. 
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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 4, there is shown a developing apparatus according to an 
embodiment of the present invention. Designated by a reference numeral 1 
is an electrophotographic photosensitive drum carrying an electrostatic 
latent image. The photosensitive drum 1 is rotated in a direction 
indicated by an arrow A, during which it is negatively charged by a 
primary charger to a potential, for example, Vd=-650 V, uniformly. 
Thereafter, the photosensitive drum 1 is exposed to a laser beam or the 
like modulated in accordance with an image to be recorded, by which the 
image portion potential (light potential) V1 is attenuated to -100 V, for 
example, so that a negative electrostatic latent image is formed. 
The developing apparatus of this embodiment, as shown in FIG. 4, comprises 
a developer container 7 containing toner T which is a one component 
developer of insulating and magnetic nature and a developing sleeve 4 
which is faced to the photosensitive drum 1 in a developing zone. The 
developing sleeve 4 is made of non-magnetic and electrically conductive 
material such as aluminum, and the surface thereof has been roughened by 
sandblasting or the like. The developing sleeve 4 carries thereon the 
toner T in the developer container 7 by the magnetic force provided by a 
magnet roll 3 within the developing sleeve 4. The developing sleeve 4 
rotates in a direction B to carry the toner T to the developing zone where 
the photosensitive drum 1 and the developing sleeve 4 are faced to each 
other. 
An elastic blade 5 is supported on a supporting plate 6 and is 
press-contacted to the developing sleeve 4 elastically by its only 
elasticity. That is, the blade 5 is elastically urged to the sleeve 4 to 
form a nip therewith. In this embodiment, the elastic blade 5 is made of 
urethane rubber having a thickness of 1.0 mm and a hardness of 65 degrees 
and is press-contacted to the developing sleeve 4 with a line pressure of 
15 g/cm along the length of the sleeve. The thickness of the toner layer 
on the developing sleeve 4 is regulated by the nip to form a layer 8 of 
the toner T which is smaller than the minimum gap between the 
photosensitive drum 1 and the developing sleeve 4 in the developing zone. 
Thus, a so-called non-contact type developing operation is carried out in 
the developing zone. The toner layer 8 on the developing sleeve 4 is 
erected by a developing magnetic pole of the magnet roll 3. 
The toner is mainly triboelectrically charged to a negative polarity by the 
friction with the sleeve, so that the latent image is reverse-developed. 
When the toner passes through the nip, the toner is rubbed with the sleeve 
and the blade 5 to be triboelectrically charged to such an extent as to 
provide sufficient image density of the developed image. 
The developing sleeve 4 is supplied with a developing bias voltage from a 
bias source 2. The developing bias is a DC biased AC voltage, for example, 
having a peak-to-peak voltage of 1400 V and a frequency of 1800 Hz in the 
form of a rectangular wave, the DC component being -500 V, for example. By 
the application of such a voltage, a vibratory electric field is formed in 
the developing zone to develop the electrostatic latent image on the 
photosensitive drum with the toner T from the toner layer 8 on the 
developing sleeve 4. In this embodiment, since the reverse-development is 
effected, the toner is deposited to the region of the photosensitive drum 
1 which has the potential of V1. 
In this embodiment, the developing bias voltage has a positive phase and a 
negative phase periodically and alternately. However, the developing bias 
may periodically changes within a negative polarity or within a positive 
polarity. Further alternatively, the voltage may be constant, that is, a 
DC bias voltage. 
In this embodiment, the magnetic toner comprises: 
______________________________________ 
Styrene-butyl methacrylate copolymer 
100 parts 
(copolymerization weight ratio = 8:2) 
(Mw = 270,000) 
Magnetic particles 50 parts 
(magnetite, BET = 8.0 m.sup.2 /g) 
Low molecular weight polypropylene 
4 parts 
(Mw = 6,000) 
Negative charge controlling agent 
2 parts 
(chrome complex of monoazo dye) 
______________________________________ 
Those materials are mixed, needed, roughly pulverized, finely pulverized 
and classified, so that classified toner having a volume average particle 
size of 10 microns is produced. To the toner powder (100 parts by weight) 
is mixed with silica fine particles (0.9 part by weight) treated with 
dimethylsilicone oil for the purpose of increasing fluidability of the 
toner and for the purpose of controlling the electric charge of the toner, 
the silica particles being triboelectrically charged to the sam polarity 
as the toner. In this specification, the average particle size means a 
volume average particle size. 
That surface of the elastic blade 5 which is contacted to the developing 
sleeve, that is, the surface of the elastic blade 5 cooperative with the 
developing sleeve 4 to form the nip, is coated with resin particles 9 
electrically chargeable to a positive polarity which is the opposite from 
the polarity of the toner, when they are rubbed with the toner. The 
coating is effected prior to the initial start of the operation of the 
developing apparatus. For example, the fine resin particles are applied on 
paper or cloth, for example, and are applied to the surface of the elastic 
blade while rubbing with the surface. The images were produced using the 
developing apparatus of this embodiment. It was confirmed that the image 
density of the solid black image was 1.42, and the density of a black 
image having a regular square configuration of 5.times.5 mm (5 mm square 
density) was 1.45 (both from the initial stage of the start of the use). 
With the developing apparatus wherein the resin particles were not 
applied, the solid black image density was 1.35, and 5 mm square density 
was 1.39. Until the density reached a satisfactory level, 300 sheets had 
to be processed. 
Therefore, the fine particles 9 are effective to improve the parting nature 
between the blade and the toner particles, the lubrication therebetween, 
thus enhancing the rolling of the toner particles in the nip. Therefore, 
the friction between the toner and the sleeve is activated to apply 
sufficient triboelectric charge to the toner. If the selection is made 
such that the blade 5 is triboelectrically charged to the polarity 
opposite from that of the toner, by which the toner is further charged by 
the friction with the blade 5. 
In addition, the fine particles applied to the elastic blade are such that 
they are triboelectrically charged to the polarity opposite from that of 
the toner by the friction with the toner particles in this embodiment, the 
toner particles are further charged by the friction with the fine 
particles, and therefore, it is further preferable. 
The fine particles 9 are effective to reduce the torque required for the 
rotation of the sleeve 4, and therefore, the sleeve 4 is smoothly rotated 
from the initial stage of the start of the use of the developing 
apparatus. This prevents non-uniform development attributable to the 
non-uniform rotation of the developing sleeve 4. The fine particles 9 are 
further effective to prevent the nip between the blade 5 and the sleeve 4 
from being clogged and are effective to prevent the binder of the 
developer from being fused on the blade 5. 
The effects of the fine particles 9 continue in this embodiment until 200 
sheets are printed. With the number of prints, the effects of the fine 
particles 9 relatively decreases. On the other hand, however, with the 
increase of the number of prints, the toner adjacent to the sleeve 4 in 
the container 7 come to be supplied with some level of electric charge by 
the friction with the sleeve 4, and in addition, that surface of the 
sleeve 5 constituting the nip with the sleeve 4 receives fine silica 
particles in the developer, and therefore, the motion of the toner in the 
nip is activated by the silica particles. Accordingly, the toner is 
triboelectrically charged by the friction with the sleeve 4 and the 
friction with the blade 5 to sufficient extent. 
After 300 sheets are printed, the fine silica particles in the toner are 
sufficiently applied to that surface of the elastic blade so as to 
constitute a layer of the silica particles. Mainly by the silica 
particles, the parting property between the blade 5 and the toner is 
enhanced, so that the rolling of the toner particles in the nip between 
the elastic blade and the sleeve is activated to accomplish the sufficient 
triboelectric charging. 
The positively chargeable fine particles 9 function to electrostatically 
attract the fine silica particles contained in the developer, thus 
promoting the formation of the silica layer on that surface of the elastic 
blade 5. 
The particles applied on the elastic blade preferably have a volume average 
particle size which is smaller than a volume average particle size of the 
toner particles, further preferably it is not more than on fifth the 
average particle size of the toner. The volume average particle size is 
measured by Coulter counter. 
The positively chargeable fine resin powder 9 is produced by spray-dry 
method, suspension polymerization method, emulsion polymerization method, 
seed polymerization method or the like. From the point of maintaining the 
configurations of the particles, the fine resin particles have a weight 
average molecular weight of 10,000-200,000 measured by GPC chromatography. 
Usable materials for the fine resin particles 9 include methyl 
methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl 
methacrylate, N-methyl-N-phenylaminoethyl methacrylate, diethylaminoethyl 
methacrylamide, dimethylaminoethyl methacrylamide, 4-vinylpyridine, 
2-vinylpyridine and other vinyl monomer or mixture of such monomers, which 
are polymerized. 
For the purpose of providing the resin particles with the positively 
chargeable property, a copolymerization initiator containing nitrogen is 
usable, and, monomer containing nitrogen-containing vinyl-monomer may be 
polymerized. 
The volume average particle size of the fine resin particles 9 is 
preferably 0.1-1.0 micron, and the amount of the triboelectric charge 
thereof is preferably 50-600 micro-coulomb/g. 
The next embodiment is intended to extend the effects of the fine resin 
particles. That surface of the elastic blade 5 which is contactable to the 
developing sleeve is roughened, and thereafter, the fine resin particles 
are applied. 
FIG. 5 shows the blade in this embodiment. The surface of the elastic blade 
5 contacted to the sleeve 4 has fine pits 26. The surface roughness is 
preferably smaller than the volume average particle size of the toner so 
as not to obstruct the rolling of the toner. It is further preferable that 
the surface roughness is smaller than the particle size of the toner 
contributable to the development, more particularly, the average roughness 
Ra (JIS) is preferably 0.1-5 microns. 
In this embodiment, the surface roughness Ra is approximately 1.0 micron, 
and the pits thereof exist along a direction substantially perpendicular 
to the peripheral movement of the rotatable developing sleeve 4 
(longitudinal direction of the blade). In this embodiment, the surface 
roughness is provided by integrally molding the rubber blade 5 and the 
blade supporting member 6 with rubber material. The molding surface has 
the corresponding roughness. In this specification, the surface roughness 
is the one defined in accordance with central average roughness Ra (JIS). 
By applying the fine particles 9 to the roughened surface of the elastic 
blade 5, the fine particles 9 are retained in the pits of the blade, as 
shown in FIG. 5. Therefore, the effects of increasing the image density 
can be continued. Accordingly, the images having sufficient image density 
can be stably provided from the initial stage for a long period of time. 
A developing apparatus has been proposed wherein the developing sleeve has 
a surface resin layer containing fine conductive carbon particles and fine 
graphite particles (solid lubricant) dispersed therein (Japanese Laid-Open 
Patent Application No. 277265/1989 and Japanese Laid-Open Patent 
Application No. 276174/1989 corresponding to U.S. Ser. No. 341,352). The 
developing apparatus prevents over charge of the toner on the developing 
sleeve to stabilize the charging of the toner, and therefore, it is 
excellent. However, the triboelectric charge amount of the toner at the 
initial stage of the start of the use of the developing apparatus is 
further lower. 
In referring to FIG. 6, the description will be made as to an embodiment 
wherein the present invention is applied to the developing apparatus 
having a developing sleeve provided with a surface layer made of 
conductive resin. 
As shown in FIG. 6, the sleeve 4 comprises a conductive sleeve 41 and a 
surface resin layer 42. The resin layer 42 is produced by mixing 50% by 
weight of phenol resin binder, 5% by weight of conductive carbon fine 
particles (CONDUCTEX 900, available from Columbia Ink) and 45% by weight 
of graphite fine particles (CSPE, available from Nihon Kokuen Kabushiki 
Kaisha) and diluting it with methyl cellosolve and methanol and then 
spraying it on the surface of the conductive sleeve 41 into a film 
thickness of 150 microns. The resin is heat-cured at 150.degree. C. for 30 
min. The average central roughness Ra of the surface is 0.3-5.0 microns, 
and the volume resistivity is 5.0.times.10.sup.0 ohm.cm. 
The other conditions other than those relating to the sleeve 4, are the 
same as in embodiment 1 (FIG. 4). The solid black image had the density of 
1.42 at the initial stage, and the 5 mm-square density was 1.45. With the 
time of use, the density changes, and the stabilized image without sleeve 
ghost was produced. 
When the elastic blade was not coated with the fine particles 9, the solid 
black image density was 1.30, and the 5 mm-square density of 1.35, at the 
initial stage. In addition, until the sufficient density is reached, 500 
sheets had to be processed. 
FIG. 3 is a graph showing the results of measurements of the triboelectric 
charge distribution of the toner in the initial stage of the start of the 
use of the developing apparatus according to the embodiment of FIG. 9 and 
a conventional developing apparatus. It will be understood that the 
distribution is sharper, and the amount of electric charge is higher in 
the apparatus of this invention than in the conventional apparatus. The 
present invention is particularly effective in the developing apparatus 
having a sleeve provided with conductive resin surface layer. The 
triboelectric charge of the toner is made higher from the start of the 
use, and the distribution thereof is made sharp to provide the high image 
density from the start of the use of the apparatus. 
In the foregoing embodiment, the elastic blade 5 is contacted to the 
surface of the sleeve 4 codirectionally with the rotational direction of 
the sleeve 4. That is, the free end of the blade 5 is disposed downstream 
of the fixed end of the holder 6 with respect to the rotational direction 
of the sleeve. However, as shown in FIG. 7 it may be contacted to the 
sleeve surface counter directionally with respect to the rotational 
direction of the sleeve 4. That is, the free end of the blade is upstream 
of the fixed end to the holder 6 with respect to the rotational direction 
of the sleeve. 
In the following embodiments, the elastic blade 5 has a resin layer 15 
containing dispersed solid lubricant particles at the contact surface to 
the developing sleeve 4, in order to prevent the toner T or the like is 
packed in the nip between the developing sleeve 4 and the elastic blade 5 
and from the toner T or the like from fusing on the elastic blade 5. 
In FIG. 9, which is an enlarged view of the nip formed between the elastic 
blade 5 and the developing sleeve 4, the elastic blade 5 has a thickness 
of t=1.0 mm and is provided with a resin layer 15 having a thickness a=20 
microns. The elastic blade 5 is made of urethane rubber having a rubber 
hardness of 60 degrees. 
An example of the resin layer 15 containing the solid lubricant is as 
follows: 
______________________________________ 
Resin:phenol resin (solid) 
30 parts by weight 
Conductive solid lubricant:artificial graphite 
25 parts by weight 
(average particle size of 7 microns) 
Diluent:methyl alcohol and 
200 parts by weight 
methylcellosolve 
______________________________________ 
The resin liquid containing the above components is applied onto the 
surface of the elastic blade 5 by spray or dipping method into a thickness 
of 5-100 microns, and then it is heat-cured at 150.degree. C. for 30 min. 
in a drying furnace to produce a resin layer 15 containing the solid 
lubricant on the elastic blade 5. The volume resistivity of the resin 
layer 15 was 1.0.times.10.sup.2 -1.0.times.10.sup.3 ohm.cm. 
In this embodiment, the elastic blade 5 thus produced is incorporated in 
the developing apparatus shown in FIG. 8, and the electrostatic latent 
image on the photosensitive drum 1 was developed, and a printed image was 
produced. As a result, the wearing of the resin layer 15 of the elastic 
blade 5 was approximately 3 microns even after 10,000 sheets were printed, 
and the resin powder component in the toner T did not fuse on the elastic 
blade 5. 
In the nip between the developing sleeve 4 and the elastic blade 5, the 
resin layer is effective to prevent coagulation of the toner T, and 
therefore, the resultant image was free from stripe or non-uniformity. 
This is because the solid lubricant in the resin layer 15 is effective to 
scrape the surface of the resin layer 15 with the printing operation, and 
therefore, to provide refreshed surface of the resin layer 15. Since the 
resistance of the resin layer 15 is small, the charging of the toner T is 
not influenced. 
In addition, the solid lubricant of the resin layer 15 is effective to 
reduce the resistance against the rotation of the sleeve 4 at the nip, and 
therefore, the sleeve 4 is able to rotate smoothly from the start of the 
use of the apparatus, and therefore, the image non-uniformity attributable 
to the non-uniform rotation can be prevented. 
Furthermore, the sliding is improved by the solid lubricant between the 
resin layer 15 and the toner. From the start of the use of the developing 
apparatus, the toner moves actively in the nip so that the toner is 
triboelectrically charge by the friction with the sleeve 4 and the blade 5 
to sufficient extent, and therefore, the high image density can be 
provided from the start of the use. 
The resin layer 15 is worn by the friction with the developing sleeve 4, 
and therefore, the surface roughness of the resin layer 15 and the 
configurations of the surface are not significant, and therefore, the 
formation of the resin layer 15 is easy. 
In this embodiment, the solid lubricant contained in the resin layer 15 was 
electrically conductive artificial graphite. Other usable materials 
include molybdenum disulfide particles, boron nitride particles, and 
silica particles with the same advantageous effects. The binder resin used 
in the resin layer 15 is not limited to the phenol resin. Other usable 
materials include thermo-curing resin such as epoxy resin or melamine 
resin. An ultraviolet-curing resin is also usable. The binder resin is 
preferably has a charging property to the polarity opposite from that of 
the toner. 
The resin layer 15 has been described as containing the solid lubricant 
only, but in order to reduce the electric resistance of the resin layer 
15, the resin layer 15 may contain conductive fine particles such as 
carbon. 
The elastic blade 5 may be made of resin elastomer such as polyethylene 
terephthalate (PET). 
An attempt has been made to use the resin elastomer as the elastic blade. 
The resin elastomer is advantageous in that the cost is lower than the 
rubber elastomer. However, the Young's modulus is larger by 2 -3 orders, 
and the hardness thereof is high, and therefore, when the elastic blade 
made of the material is contacted to the developing sleeve 2, it has been 
difficult to form a uniform nip between the elastic blade and the 
developing sleeve 4. 
According to the present invention, even if the elastic blade 5 is made of 
resin elastic material, the resin layer 15 containing the solid lubricant 
is formed, and therefore, the nip between the elastic blade 5 and the 
developing sleeve 4 becomes uniform. 
In this embodiment, the elastic blade has a thickness of 0.5 mm and is made 
of polyethylene terephthalate. On this elastic blade 5, a resin layer 15 
of approximately 50 micron thickness containing the solid lubricant was 
formed, similarly to the foregoing embodiments. The elastic blade 5 is 
incorporated in the developing apparatus of FIG. 8. The elastic blade 5 
was press-contacted to the developing sleeve 4 with the line pressure of 
20 g/cm. The same developing operation as in the foregoing embodiments was 
carried out to repeat the printing operations. 
As a result, the wearing of the resin layer 15 at the nip between the 
elastic blade 5 and the developing sleeve 4 was larger, but the uniform 
nip can be ensured throughout the repeated printing operations. In 
addition, the toner T did not fuse on the elastic blade 5. No stripes or 
non-uniformity was recognized on the resultant images. At the initial 
stage of the start of the use of the developing apparatus, the toner is 
sufficiently triboelectrically charged, and therefore, high density images 
could be produced. 
The developing sleeve 4 may be produced by coating the surface of the metal 
sleeve with conductive resin described in conjunction with FIG. 6, by 
impression molding with the conductive resin with or without the surface 
roughened. 
FIG. 10 shows a developing apparatus according to another embodiment. The 
one component developer in the developer container 7 is non-magnetic 
insulative toner T. A conductive sponge rubber roll 30 is contacted to the 
sleeve 4 made of metal such as stainless steel and is rotated in a 
direction C, by which the toner T is applied on the developing sleeve. 
This embodiment is the same as in the foregoing embodiments in the other 
respects. A voltage source 32 applies to the roller 30 a DC biased AC 
voltage or an AC voltage, by which the motion of the toner from the roller 
30 to the sleeve 8 is promoted. 
FIG. 11 shows another embodiment of the developing apparatus. The one 
component developer toner T in the developer container 7 is a non-magnetic 
insulative toner. A developing roll 42 is made of semiconductive elastic 
material (preferably rubber) and is rotated in a direction B in contact 
with the photosensitive member 1. A conductive sponge roll 30 functions to 
apply the toner T to the developing roll 42. An elastic blade 5 has at its 
bottom surface a resin surface layer 15 contacted to the developing roll 
42, the resin layer 15 comprising a solid lubricant. The elastic blade 5 
is contacted to the developing roll 42 perpendicularly. The elastic blade 
5 functions to regulate the toner T on the developing roll 42 to form a 
thin layer of toner. While the toner layer 8 on the developing roll 42 is 
in contact with the photosensitive drum 1 in the developing zone, a DC 
voltage or a DC biased AC voltage is applied as a developing bias to the 
developing sleeve 4 from the bias source 6, so that a developing operation 
is effected. 
In FIG. 12 embodiment, the elastic blade having the resin layer 15 is 
contacted to the sleeve 4 in the counter direction with respect to the 
peripheral movement of the sleeve 4. In this embodiment, the one component 
developer T in the developer container 7 is a magnetic toner, and the 
magnet roll 3 has N-poles and S-poles alternately, the magnet roll 3 being 
in the sleeve 4. The magnet roll 3 is located in the direction opposite 
form the rotational direction of the developing sleeve 4, by which the 
toner T is carried on the developing sleeve 4. With the photosensitive 
drum 1 and the toner layer 8 on the developing sleeve being contacted to 
each other in the developing zone, the bias voltage source 6 applies to 
the developing sleeve 4 as the developing bias a DC voltage or a DC biased 
AC voltage to effect the developing operation. 
The present invention is applicable to the developing apparatus using the 
magnetic developer or a non-magnetic developer. The charging polarity of 
the toner may be positive or negative. The development is not limited to 
the reverse-development wherein the right potential region of the latent 
image receives the toner, but also to a regular development wherein the 
dark potential region of the latent image receives the toner. As described 
in the foregoing, the present invention is applicable both to a so-called 
contact type development and to a so-called non-contact type development. 
The bias voltage applied to the developer carrying member is preferably an 
AC voltage, but may be a DC voltage. 
As for the elastic regulating member, silicone rubber blade, nitrile rubber 
blade, a thin phosphor bronze leaf spring or a thin stainless steel leaf 
spring or the like is usable. It is preferable that a blade having rubber 
elasticity is bonded to such a metal leaf spring to elastically urge the 
rubber elastic blade to the developer carrying member, from the standpoint 
of increasing the resistance against the plastic deformation of the blade. 
While the invention has been described with reference to the structures 
disclosed herein, it is not confined to the details set forth and this 
application is intended to cover such modifications or changes as may come 
within the purposes of the improvements or the scope of the following 
claims.