Method of removing impurities from a transport member during an electrostatic imaging process

An imaging apparatus including a device for transferring a toner image from an image-forming medium to a receiving material including an endless movable intermediate provided with a top layer which, in a first transfer zone, is in contact with the image-forming medium, a heating device for heating the toner image on the top layer of the intermediate, a pressure applying device which, in a second transfer zone, can be brought into contact with the intermediate, a transport device for transporting the receiving material through the second transfer zone, and a cleaning device following the second transfer zone, between the second and first transfer zones, brought into contact with the top layer of the intermediate, the cleaning device being provided with an impurity-absorbent material on its outer surface.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an electrostatic imaging system and more 
specifically to an apparatus for transferring a toner image from an 
image-forming medium to a receiving material via an intermediate transfer 
member and cleaning the intermediate transfer member. 
2. Discussion of Related Art 
U.S. Pat. No. 4,607,947 describes a contact fixing apparatus in which a 
toner image is transferred from an image-forming medium to a heated 
intermediate. In a fixing zone in which the intermediate is in contact 
with a pressure applying means, the toner image is then transferred to and 
simultaneously fixed on a receiving material transported through the 
fixing zone. However, impurities may also be transferred at the same time 
from the receiving material to the intermediate. Residues of toner 
material may also be left as impurities on the intermediate because of 
inadequate transfer of the toner image to the receiving material. If such 
impurities remain on the intermediate they may be transferred to the 
image-forming medium in the first transfer zone. This results in 
disturbance of the image formation and hence ultimately image errors in 
the copy on the receiving material. 
Various cleaning means have been proposed to remove these impurities from 
the intermediate before reaching the first transfer zone. For example, 
U.S. Pat. No. 4,607,947 discloses a cleaning means having a cleaning 
surface to which the toner has better adhesion than to the intermediate. A 
cleaning means of this kind operates satisfactorily for removing 
high-melting temperature impurities, such as toner residues. This cleaning 
means can also remove paper dust from the intermediate, but it has been 
found in practice that low-melting impurities from receiving materials, 
such as wax-like compounds, plasticizers, anti-foaming agents, plastic 
fillers which occur in receiving papers, and dust particles from plastic 
receiving materials and the like, are removed only partially, if at all, 
from the intermediate with the known cleaning means. After deposition on 
the intermediate in the second transfer zone, these impurities can also 
then be transferred to the image-forming medium in the first transfer 
zone, resulting in disturbance of the image formation and hence ultimately 
image errors in the copy on the receiving material. This necessitates 
regular and premature replacement of the intermediate and image-forming 
medium, and this involves high maintenance costs and equipment stoppage. 
For example, it has been found that the "alkaline" receiving papers 
increasingly used and based, inter alia, on cellulose, chalk and sizing 
agents such as alkyl ketone dimers, are a significant source of such 
impurity. Receiving papers of this kind are currently used because of the 
lower costs and better durability compared with the "acid" receiving 
papers based, inter alia, on cellulose, clay and modified or unmodified 
rosins. It has now been found that when alkaline receiving papers are used 
reaction products from the agents used in sizing are deposited from these 
receiving papers on the intermediate and penetrate into the top layer. 
These reaction products are then transferred to the image-forming medium, 
resulting in image disturbance. 
SUMMARY OF THE INVENTION 
Therefore, it is an object of the present invention to provide a 
toner-image transfer system which will overcome the above noted 
disadvantages. 
It is a further object of the instant invention to provide an image 
transfer apparatus which provides for the transfer of toner images to an 
image-receiving material without the deposition of impurities on the 
image-forming medium. 
Still, a further object of the present invention is to provide a toner 
image transfer system which substantially eliminates impurity deposits 
which result in the disturbance of image formation. 
The foregoing objects and others are accomplished in accordance with the 
present invention, generally speaking, by providing an image-forming 
apparatus including an image-forming medium, means of forming an image on 
the image-forming medium, a toner image development system and a 
configuration for transferring the developed toner image from the 
image-forming medium to a first image-receiving support member or sheet 
material. The image transfer configuration includes an endless movable 
intermediate member provided with a top layer which, in a first transfer 
zone, is contacted with the image-forming medium for the purpose of 
transferring the toner image developed to the surface of the intermediate 
member. A heating means is provided for heating the transferred toner 
image now on the top layer of the intermediate member. A pressure applying 
means is brought into contact with the intermediate member within a second 
transfer zone. A transport means transports a receiving material through 
the second transfer zone in which the toner image is transferred to the 
receiving material. A cleaning means provided with an impurity-absorbent 
material is positioned following the second transfer zone and between the 
first and second transfer zones to be brought into contact with the top 
layer of the intermediate member. 
The quantity of impurity on the intermediate member and its deposition on 
the image-forming medium are reduced as a result of the use of the 
impurity absorbent material, so that the life of the intermediate member 
and the image-forming medium, i.e. the period during which these media can 
be used without any image errors occurring, is lengthened. Preferably an 
impurity-absorbent rubber material is used. Particularly preferred is a 
rubber material which can absorb therein a distearyl ketone up to more 
than 5% of its weight. 
Good cleaning of the intermediate medium is obtained in an apparatus in 
which the impurity-absorbent material used is a rubber material selected 
from the group consisting of ethylene propylene diene rubber, ethylene 
propylene rubber, a mixture of ethylene propylene diene rubber and 
silicone rubber, ethylene vinyl acetate rubber, n-butyl rubber and 
mixtures of these rubbers. Particularly preferred rubber materials are 
those selected from the group consisting of ethylene propylene diene 
rubber, ethylene propylene rubber, n-butyl rubber, ethylene vinyl acetate 
rubber, silicone rubber and mixtures of these rubbers, containing more 
than 5% carbon black. Rubbers of this kind are resistant to high 
temperatures and have sufficient mechanical strength even after long 
periods of use.

DETAILED DISCUSSION OF THE INVENTION 
The image-forming apparatus illustrated comprises an endless 
photoconductive belt 1 advanced at uniform speed by means of drive and 
guide rollers 2, 3 and 4, respectively. The image of an original disposed 
on an exposure platen 5 is projected by flashlights 6 and 7, a lens 8, and 
a mirror 9, onto the belt 1 after the latter has been electrostatically 
charged up by a corona device 10. The latent charge image formed on the 
belt 1 after the flash exposure is developed with toner powder by means of 
a magnetic brush device 11 to give a toner image which in a first transfer 
zone is then brought into contact under pressure with an endless 
intermediate belt 12 provided with a top layer of soft resilient and 
heat-resistant material such as, for example, silicone rubber. In these 
conditions the toner image is transferred from the belt 1 to the belt 12 
by adhesion forces. 
After this image transfer, any remaining image residues are removed from 
belt 1 by means of a cleaning device 13, whereafter the photoconductive 
belt 1 is ready for re-use. The intermediate belt 12 is trained about 
drive and guide rollers 14 and 15, the intermediate belt 12 being heated 
to a temperature above the softening temperature of the toner powder, e.g. 
by means of an infra-red radiator 17, disposed inside roller 14. While 
belt 12 with the toner image thereon is advanced, the heating causes the 
toner image to become tacky. In a second transfer zone, under the 
influence of pressure, using a pressure means in the form of a belt 22 
trained about rollers 23 and 24, the tacky toner image is then transferred 
to and simultaneously fixed on a sheet of receiving material which is fed 
from reservoir 18 via rollers 19 and 20. Toner residues are removed by a 
first cleaning means 30 in the form of a roller 31 in accordance with U.S. 
Pat. No. 4,607,947. The resulting copy is then deposited by belt 22 in 
tray 25. 
To remove the impurities from the intermediate belt 12, the apparatus is 
provided with a second cleaning means 35, e.g. in the form of a freely 
rotatable roller 36 provided with a layer of peroxide hardened silicone 
rubber in which about 15% carbon black, having a specific surface of about 
900 m.sup.2 /g, is mixed. The choice of specific absorbent material 
depends on the type of impurity, the maximum amount of impurity which can 
be absorbed in the absorbent material, the absorption capacity, and the 
speed at which the impurity is absorbed in this material, i.e. the 
absorption speed. The absorption capacity and the absorption speed of a 
specific impurity can easily be determined by bringing such impurity into 
contact, in solid, liquid or dissolved form, with the absorbent material 
and monitoring the increase in weight of such absorbent material in the 
course of time. 
A model compound having an affinity comparable to that of the impurity for 
the top layer of the intermediate can also be used as an impurity. The 
absorption capacity for the low-melting impurities from alkaline papers is 
determined, for example, by bringing the absorbent material into contact, 
at about 100.degree. C., for 24 hours with distearyl ketone, a dialkyl 
ketone compound, and measuring the increase in weight. The absorption 
capacity of various materials is given in the following Table 1. 
TABLE 1 
______________________________________ 
ABSORPTION 
CAITY 
(% weight increase of 
MATERIAL the rubber) 
______________________________________ 
Addition-hardened silicone rubber 
4.4 
LIM 2600 (General Electric Co) 
Peroxide-hardened silicone rubber 
3.6 
(Wacker R300-50) 
EPDM Rubber (ethylene-propylene 
65.0 
ratio 40:60) 
Ethylene propylene rubber 
62.0 
Ethylene vinyl acetate rubber 
121.0 
EPDM/silicone blend (Shin Etsu 1411) 
68.0 
Silicone rubber mixed with 43% graphite 
4.0 
(specific surface graphite = 15 m.sup.2 /g) 
Silicone rubber mixed with 6% carbon 
7.0 
black with specific surface 265 m.sup.2 /g 
Silicone rubber mixed with 5% carbon 
9.8 
black with specific surface 900 m.sup.2 /g 
Silicone rubber mixed with 12% carbon 
10.7 
black 
Methyl phenyl silicone rubber 
&lt;0.6 
Fluorosilicone rubber 0.6 
(General Electric FSE 2120) 
n-butyl rubber 61.0 
______________________________________ 
In practice it has been found that materials which can absorb distearyl 
ketone to more than 5% of their own weight are very suitable as absorbent 
material on the cleaning means. Reasonably good results are obtained with 
aliphatic rubbers, preferably selected from the group consisting of 
ethylene propylene diene rubber, ethylene propylene rubber, ethylene vinyl 
acetate rubber, halogenated or non- halogenated n-butyl rubber, and 
ethylene propylene diene rubber/silicone rubber blend. Rubber materials 
which are compounded with more than 5% and preferably more than 10% of a 
highly structured carbon black are preferred. 
Examples of usable rubber materials are the above rubbers and condensation, 
peroxide and addition-hardened silicone rubbers. Suitable carbon blacks 
have a high specific surface, i.e. higher than 200 m.sup.2 /g and 
preferably higher than 500 m.sup.2 /g. Rubber materials which are 
compounded with such carbon blacks have sufficient absorption capacity and 
an absorption speed which is much higher (more than ten times as high) 
than with the previously mentioned rubbers. In addition, such 
rubber/carbon black mixtures have impurity-binding properties, thus 
preventing any carry back of impurities from the cleaning means to the top 
layer of the intermediate. 
PREFERRED EMBODIMENTS 
The invention is explained in detail with reference to the following 
examples, which are intended to illustrate, but not limit, the scope of 
the present invention. 
EXAMPLE 1 
In the apparatus according to FIG. 1, with an intermediate belt as 
described in EP-A-0 349 072, the cleaning means is in the form of a 50 mm 
thick metal cylindrical roller provided with a 10 mm thick layer of EPDM 
rubber. The concentration of dialkyl ketones, such as distearyl ketone, in 
the top layer of the intermediate after making 205,000 copies on alkaline 
paper, was less than 4 mg dialkyl ketones per g top layer rubber. There 
was no deposition on the photoconductive belt. 
The concentration of dialkyl ketones in the top layer after the same number 
of copies had been made, but without the use of the cleaning means, was 
about 6 mg/g top layer rubber. Impurities were also deposited on the 
photoconductive belt, resulting in image disturbance. 
EXAMPLE 2 
The apparatus according to FIG. 1 was provided with an intermediate belt 12 
in accordance with Example 1, the top layer of which contained about 2.5 
mg/g dialkyl ketones. This intermediate belt 12 was then brought into 
contact with a cleaning means 35 provided with a 2 mm thick layer of 
silicone rubber in which about 10% by weight of carbon black having a 
specific surface of 500 m.sup.2 /g had been mixed. After the intermediate 
belt 12 had operated for five hours against the cleaning means 35, during 
which time the intermediate belt 12 was kept at 100.degree. C. by means of 
the radiator 17, the concentration of ketones was halved. In similar tests 
in which the silicone rubber with carbon black was replaced by EPDM 
rubber, the ketone concentration after ten hours was still about 1.4 mg/g. 
In a similar test in which the cleaning means 35 was provided with 
ethylene vinyl acetate rubber, the ketone concentration in 15 hours 
dropped from 4.9 to 2.9 mg/g. The roller 36 can be heated internally or 
externally in order to accelerate the diffusion of impurities in the 
absorbent material. 
A cleaning means 35, as described immediately above, can be maintained 
continuously in contact with the intermediate 12. The cleaning means 35 
may also be provided with a mechanism (not shown) in order to lift the 
cleaning means from the intermediate during periods in which copying takes 
place. This obviates excessive heat dissipation during copying. In another 
embodiment, the cleaning means 35 may be formed by an endless belt trained 
about two shafts and having a layer of impurity-absorbent material. It is 
also possible to provide the outside of the absorbent material with a thin 
impurity-passing outer covering to improve the mechanical properties, to 
obviate charging and wear and to improve surface properties (non-stick and 
the like). 
The present invention being thus described, it will be obvious that the 
same may be varied in many ways. Such variations are not to be regarded as 
a departure from the spirit and scope of the invention, and all such 
modifications as would be obvious to one skilled in the art are intended 
to be included within the scope of the following claims.