Rotatable member for fixing in which inorganic filler is contained in silicone rubber, and fixing device having the same

A fixing rotatable member for use in an image forming apparatus such as a copying apparatus or a laser beam printer is disclosed. The fixing rotatable member includes a base member and an elastic layer provided on the surface thereof. The elastic layer is addition type silicone rubber in which resin-like polyorganosiloxane and 0.1 to 2 percent by weight of inorganic fine powder are mixed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a rotatable member for fixing and a fixing device 
for application to an image forming apparatus such as a copying apparatus 
or a laser beam printer 
2. Related Background Art 
A fixing devices in an image forming apparatus of the electrophotographic 
type such as a copying apparatus or a laser beam printer is such that a 
recording medium having a toner image transferred thereto is nipped and 
conveyed by a pair of rollers of the fixing device and is heated and 
pressed to thereby fix the toner image on the recording medium and make it 
into a permanent image. 
The rollers used in such fixing device are coated with a material such as 
fluorine resin or silicone rubber which is good in parting property and 
rich in heat resisting property and wear resistance to thereby form the 
outer layer thereof. 
Particularly where the image forming apparatus of the electrophotographic 
type is a color copying apparatus which attaches importance to the quality 
of image, there is the tendency that use is made of fixing rollers having 
their surfaces coated with silicone rubber. 
However, silicone rubber only is low in strength and poses a problem in the 
use as rollers and therefore, reinforcing silica powder is mixed with it 
to thereby improve the physical strength thereof. 
However, when silicone rubber is reinforced by inorganic powder, 10 to 40 
percent by weight, practically 20 to 30 percent by weight of inorganic 
powder must be mixed with silicone rubber, and when a roller is made of 
thus reinforced silicone rubber, the problem has come out in which 
although physical strength is provided, the parting property of toner is 
extremely reduced and the life of the roller becomes shorter. 
In order to suppress such reduction in the parting property of toner, there 
is an example in which resin-like polyorganosiloxane as a reinforcing 
agent is mixed with silicone rubber to thereby improve physical strength 
and the parting property of toner (Japanese Laid-Open Patent Application 
No. 5-214250). 
In recent years, however, with the spread of color copying apparatuses, a 
tendency toward higher copying speeds has become remarkable and the set 
temperature for fixing has become higher. Further, with a requirement for 
a reduction in running cost, a longer life of fixing rollers has become 
desired. When the set temperature for fixing is thus relatively high, 
particularly 170.degree. C. or higher and the roller is used for a long 
time, the problem has become conspicuous that the fixing and pressing 
roller using as its surface layer the added type silicone rubber having 
the aforementioned reinforcing resin-like polyorganosiloxane mixed 
therewith becomes reduced in its strength by thermal deterioration and the 
life of the roller becomes remarkably shorter. 
Particularly, when a color both-side copying machine is considered, toner 
comes into contact also with the pressing roller and a high parting 
property is required also of the pressing roller and therefore, it is 
preferable that the added type silicone rubber having the aforementioned 
reinforcing resin-like polyorganosiloxane mixed therewith be used as the 
surface layer, but a member for removing any excess of silicone oil 
imparted to the fixing roller or for removing any toner and paper powder 
offset to the roller bears against the pressing roller, and when the 
strength of the roller is reduced by thermal deterioration, there has been 
the problem that when they frictionally contact with the pressing roller, 
they impart injuries to the pressing roller, which thus becomes shorter in 
life than the fixing roller. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a rotatable member for 
fixing and a fixing device which are excellent in the parting property of 
toner and physical strength. 
It is another object of the present invention to provide a fixing rotatable 
member having as its surface layer addition type silicone rubber in which 
resin-like polyorganosiloxane and 0.1 to 2 percent by weight of inorganic 
fine powder are mixed with each other. 
It is still another object of the present invention to provide a pressing 
rotatable member having as its surface layer addition type silicone rubber 
in which resin-like polyorganosiloxane and 0.5 to 8 percent by weight of 
inorganic fine powder are mixed with each other. 
It is yet still another object of the present invention to provide a fixing 
device having a fixing rotatable member having as its surface layer 
addition type silicone rubber in which resin-like polyorganosiloxane and 
0.1 to 2 percent by weight of inorganic fine powder are mixed with each 
other, and a pressing rotatable member having as its surface layer 
addition type silicone rubber in which resin-like polyorganosiloxane and 
0.5 to 8 percent by weight of inorganic fine powder are mixed with each 
other. 
It is another object of the present invention to provide a fixing device in 
which the amount of inorganic fine powder of a pressing rotatable member 
is greater than the amount of inorganic fine powder of a fixing rotatable 
member. 
Further object of the present invention will become apparent from the 
following detailed description.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Some embodiments of the present invention will hereinafter be described 
with reference to the drawings. 
FIGS. 1 to 3 are schematic cross-sectional views of rotatable members for 
fixing (a fixing roller and a pressing roller) having as their outer 
layers addition type silicone roller which is the elastic layer of the 
present invention. 
Referring to FIG. 1 which is a schematic cross-sectional view of the 
rotatable member for fixing when it is a single-layer roller, the 
reference numeral 100 designates the addition type silicone rubber which 
contacts with toner, the reference numeral 200 denotes a mandrel using 
aluminum or the like as a base material, and the reference numeral 300 
designates a heater for heating. 
Referring to FIG. 2 which is a schematic cross-sectional view of the 
rotatable member for fixing when it is a two-layer roller, the reference 
numerals 100 to 300 designate the same members as those in FIG. 1, and the 
reference numeral 400 denotes the silicone rubber of a lower layer. 
Referring to FIG. 3 which is a schematic cross-sectional view of the 
rotatable member for fixing when it is a three-layer roller, the reference 
numerals 100-400 denote the same members as those in FIG. 2, and the 
reference numeral 500 designates an oil barrier layer formed of fluorine 
metamorphic silicone rubber provided between the addition type silicone 
rubber which contacts with toner and the silicone rubber 400 of the lower 
layer. 
Description will now be made of some embodiments of the addition type 
silicone rubber which is the surface layer shown in FIGS. 1 to 3. For the 
comparison of the heat resisting property of the silicone rubber, the 
degree of thermal deterioration of the silicone rubber has been measured 
from the rate of variation in dynamic viscoelasticity (tan.delta.) and the 
values thereof are also described below. 
(Embodiment 1) 
Addition type silicone rubber (composition) in which 0.1 percent by weight 
of silica powder (R-972 produced by Nippon Aerosil Co., Ltd.) as a heat 
resistance imparting agent which is inorganic minute powder was mixed with 
a polysiloxane mixture comprising 40 percent by weight of normal 
chain-like polydimethylsiloxane having its distal end enclosed by vinyl 
radical of which the viscosity at 25.degree. C. is 10000 Pa.multidot.s, 
and 60 percent by weight of reinforcing resin-like 
organopolydimethylsiloxane composed of a block polymer of which the 
viscosity at 25.degree. C. is 35 Pa.multidot.s and which has trifunctional 
and tetrafunctional resin segments and a bifunctional oil segment in one 
and the same molecule was hardened at 150.degree. C. in 10 minutes, 
whereafter it was subjected to secondary vulcanization at 200.degree. C. 
for 4 hours to thereby obtain addition type silicone rubber. This addition 
type silicone rubber was made into a silicone rubber sheet of 150 
mm.times.150 mm.times.1 mm, and this sheet was left in an oven of 
200.degree. C. and thermal shock was applied thereto for a predetermined 
time, whereafter a test piece of 40 mm.times.5 mm.times.1 mm was punched, 
and the measurement of tan.delta. was effected by a rheospectrometer 
produced by Rheolozy, Inc. 
When the degree of thermal deterioration of the silicone rubber was 
evaluated from the rate of variation with respect to the initial value of 
this tan.delta., the rate of Variation in tan.delta. at 200.degree. C. was 
-31% after 120 hours and -36% after 240 hours. 
(Embodiment 2) 
When the degree of thermal deterioration of the addition type silicone 
rubber was examined by the use of the same technique as Embodiment 1 with 
the exception that the amount of mix of silica powder (R-972 produced by 
Nippon Aerosil Co., Ltd.) was 0.5 percent by weight, the rate of variation 
in tan.delta. was -20% after 120 hours and -27% after 240 hours. 
(Embodiment 3) 
When the degree of thermal deterioration of the addition type silicone 
rubber was examined by the use of the same technique as Embodiment 1 with 
the exception that the amount of mix of silica powder (R-972 produced by 
Nippon Aerosil Co., Ltd.) was 1 percent by weight, the rate of variation 
in tan.delta. was 0% after 120 hours and -7% after 240 hours. 
(Embodiment 4) 
When the degree of thermal deterioration of the addition type silicone 
rubber was examined by the use of the same technique as Embodiment 1 with 
the exception that the amount of mix of silica powder (R-972 produced by 
Nippon Aerosil Co., Ltd.) was 2 percent by weight, the rate of variation 
in tan.delta. was +7% after 120 hours and +2% after 240 hours. 
(Embodiment 5) 
When the degree of thermal deterioration of the addition type silicone 
rubber was examined by the use of the same technique as Embodiment 1 with 
the exception that the amount of mix of silica powder (R-972 produced by 
Nippon Aerosil Co., Ltd.) was 3% by weight, the rate of variation in 
tan.delta. was +21% after 120 hours and +18% after 240 hours. 
(Embodiment 6) 
When the degree of thermal deterioration of the addition type silicone 
rubber was examined by the use of the same technique as Embodiment 1 with 
the exception that the amount of mix of silica powder (R-972 produced by 
Nippon Aerosil Co., Ltd.) was 5 percent by weight, the rate of variation 
in tan.delta. was +39% after 120 hours and +46% after 240 hours. 
(Embodiment 7) 
When the degree of thermal deterioration of the addition type silicone 
rubber was examined by the use of the same technique as Embodiment 1 with 
the exception that the amount of mix of silica powder (R-972 produced by 
Nippon Aerosil Co., Ltd.) was 8 percent by weight, the rate of variation 
in tan.delta. was +45 after 120 hours and +50% after 240 hours. 
(Embodiment 8) 
When the degree of thermal deterioration of the addition type silicone 
rubber was examined by the use of the same technique as Embodiment 1 with 
the exception that the amount of mix of alumina (Aluminum Oxide C produced 
by Nippon Aerosil Co., Ltd.) as a heat resistance imparting agent was 1 
percent by weight, the rate of variation in tan.delta. was -5% after 120 
hours and -9% after 240 hours. 
(Embodiment 9) 
When the degree of thermal deterioration of the addition type silicone 
rubber was examined by the use of the same technique as Embodiment 1 with 
the exception that 1 percent by weight of silica powder (R-972 produced by 
Nippon Aerosil Co., Ltd.) as a heat resistance imparting agent was mixed 
with a mixture of 10 percent by weight of normal chain-like 
polydimethylsiloxane having its distal end enclosed by vinyl radical of 
which the viscosity at 25.degree. C. is 10000 Pa.multidot.s and 90 percent 
by weight of reinforcing resin-like organopolysiloxane composed of a block 
polymer of which the viscosity at 25.degree. C. is 35 Pa.multidot.s and 
which has trifunctional and tetrafunctional resin segments and a 
bifunctional oil segment in one and the same molecule, the rate of 
variation in tan.delta. was +10% after 120 hours and +11% after 240 hours. 
(Embodiment 10) 
When the degree of thermal deterioration of the addition type silicone 
rubber was examined by the use of a technique similar to Embodiment 1 with 
the exception that the ratio of mix of the normal chain-like 
polydimethylsiloxane and reinforcing resin-like organopolysiloxane used in 
Embodiment 9 was 20:80 and use was made of addition type silicone rubber 
having mixed therewith 1 percent by weight of silica powder (R-972 
produced by Nippon Aerosil Co., Ltd.) as a heat resistance imparting 
agent, the rate of variation in tan.delta. was +6% after 120 hours and +2% 
after 240 hours. 
(Embodiment 11) 
When the degree of thermal deterioration of the addition type silicone 
rubber was examined by the use of a technique similar to Embodiment 1 with 
the exception that the ratio of mix of the normal chain-like 
polydimethylsiloxane and reinforcing resin-like organopolysiloxane used in 
Embodiment 9 was 50:50 and use was made of addition type silicone rubber 
having mixed therewith silica powder (R-972 produced by Nippon Aerosil 
Co., Ltd.) as a heat resistance imparting agent, the rate of Variation in 
tan.delta. was -7% after 120 hours and -11% after 240 hours. 
Description will now be made of comparative examples for making comparison 
with the present invention. 
(Comparative Example 1) 
When the degree of thermal deterioration of the addition type silicone 
rubber was examined by the use of a technique similar to Embodiment 1 with 
the exception that the ratio of mixture of normal chain-like 
polydimethylorganosiloxane and reinforcing resin-like organopolysiloxane 
in the addition type silicone rubber was 40:60 and a heat resistance 
imparting agent was not mixed, the rate of variation in tan.delta. was 
-44% after 120 hours and -48% after 240 hours. 
(Comparative Example 2) 
When the degree of thermal deterioration of the addition type silicone 
rubber was examined by the use of a technique similar to Embodiment 1 with 
the exception that 10 percent by weight of silica powder (R-972 produced 
by Nippon Aerosil Co., Ltd.) as a heat resistance imparting agent was 
mixed with addition type silicone rubber of the same proportion as 
Comparative Example 1, the rate of variation in tan.delta. was +47% after 
120 hours and +54% after 240 hours. 
(Comparative Example 3) 
When the degree of thermal deterioration of the addition type silicone 
rubber was examined by the use of a technique similar to Embodiment 1 with 
the exception that use was made of addition type silicone rubber having 10 
percent by weight of silica powder (R-972 produced by Nippon Aerosil Co., 
Ltd.) as a reinforcing agent mixed with normal chain-like 
polydimethylsiloxane having its distal end enclosed by vinyl radical of 
which the viscosity at 25.degree. C. is 8000 Pa.multidot.s, the rate of 
variation in tan.delta. was +4% after 120 hours and +11% after 240 hours. 
(Comparative Example 4) 
When the degree of thermal deterioration of the addition type silicone 
rubber was examined by the use of a technique similar to Embodiment 1 with 
the exception that the ratio of mix of the normal chain-like 
polydimethylsiloxane and reinforcing resin-like organopolysiloxane used in 
Embodiment 9 was 60:40 and use was made of addition type silicone rubber 
having mixed therewith 1 percent by weight of silica powder (R-972 
produced by Nippon Aerosil Co., Ltd.) as a heat resistance imparting 
agent, the rate of variation in tan.delta. was -39% after 120 hours and 
-43% after 240 hours. 
The above results are shown in Tables 1 and 2 below. 
In Table 1, conditions are the same except the amount of silica. 
In Table 2, conditions are changed besides the amount of silica, and this 
table is given for reference. 
TABLE 1 
______________________________________ 
rate of variation in tan.delta. after 
heat history of 200.degree. C. 
after 120 hours 
after 240 hours 
______________________________________ 
Embodiment 1 -31 -36 
(silica 0.1%) 
Embodiment 2 -20 -27 
(silica 0.5%) 
Embodiment 3 0 -7 
(silica 1%) 
Embodiment 4 7 2 
(silica 2%) 
Embodiment 5 21 18 
(silica 34%) 
Embodiment 6 39 46 
(silica 5%) 
Embodiment 7 45 50 
(silica 8%) 
Comp. Ex. 1 -44 -48 
(silica 0%) 
Comp. Ex. 2 47 55 
(silica 10%) 
______________________________________ 
TABLE 2 
______________________________________ 
rate of variation in tan.delta. after 
heat history of 200.degree. C. 
after 120 hours 
after 240 hours 
______________________________________ 
Embodiment 8 -5 -9 
Embodiment 9 10 11 
Embodiment 10 
6 2 
Embodiment 11 
-7 -11 
Comp. Ex. 3 4 11 
Comp. Ex. 4 -39 -43 
______________________________________ 
As shown in Table 1, it is seen that the heat resisting property is 
improved by mixing silica. 
The addition type silicone rubber in the embodiments can be addition type 
silicone rubber provided by hardening a polysiloxane mixture having a heat 
resistant inorganic filler mixed with a polysiloxane mixture having 10 to 
50 percent by weight of normal chain-like polydimethylsiloxane having its 
distal end enclosed by vinyl radical of which the viscosity at 25.degree. 
C. is 8000 Pa.multidot.s or greater and 50 to 90 percent by weight of 
reinforcing resin-like polyorganosiloxane having two or more vinyl 
radicals and containing a resin segment of which the composition unit 
includes at least one of tetrafunctionality and trifunctionality and a 
bifunctional segment and of which the viscosity at 25.degree. C. is 1 
Pa.multidot.s or greater. 
Next, an experiment is effected with fixing and pressing rollers which were 
made on an experimental basis by the use of the silicone rubber in the 
present invention actually used in the fixing device of a full color 
both-side image forming apparatus. 
The full color both-side image forming apparatus and its fixing device will 
first be described here. 
FIG. 4 schematically shows the construction of an image forming apparatus 
as an embodiment. This apparatus is a color image forming apparatus of the 
electrophotographic type. 
The reference numeral 1 designates the outer housing of an apparatus body, 
and the letter A denotes an original scanning and reading portion disposed 
on the upper portion of the outer housing of the apparatus body. An 
original O is set on original supporting table glass 2 with its image 
bearing surface turned downward on a predetermined apparatus standard, and 
an original keep plate 3 is put thereon and reading is started, whereby a 
movable optical system 4 under the original supporting table glass is 
moved along the lower surface of the original supporting table glass from 
one side to the other side and the downwardly facing image bearing surface 
of the original set on the original supporting table glass 3 is 
illuminated and scanned, and the reflected light of the illuminating and 
scanning light reflected from the surface of the original is imaged on a 
photoelectric reading unit 5 and is color-resolved by a color resolving 
filter and also, each color-resolved component image of the original image 
is photoelectrically read as a color image signal (a time-serial 
electrical digital pixel signal) and is stored in a memory circuit. 
The reference numeral 6 designates an electrophotographic photosensitive 
drum as the image bearing member of an image forming portion. This 
photosensitive drum 6 has, for example, a diameter of 180 mm and is 
rotatively driven at a predetermined process speed (peripheral speed) in 
the clockwise direction indicated by arrow. 
The reference numeral 7 denotes a charger for uniformly charging the 
photosensitive drum 6 to a predetermined polarity and potential, and the 
reference numeral 8 designates image exposure means comprising a laser 
output portion, a polygon mirror, a lens system, a mirror, etc. The 
charged surface of the photosensitive drum by the charger 7 is scanned and 
exposed by a laser beam E modulated and outputted from the image exposure 
means 8 correspondingly to the time-serial electrical digital pixel signal 
from the memory circuit, whereby an electrostatic latent image 
corresponding to the scanned and exposed pattern is formed on the surface 
of the rotatable photosensitive drum 6. 
The reference numeral 9 denotes a compound developing device having a cyan 
developing device 9C containing a cyan toner therein, a magenta toner 
developing device 9M containing a magenta toner therein, an yellow toner 
developing device 9Y containing an yellow toner therein, and a black 
developing device 9K containing a black toner therein, and these four 
developing devices 9C, 9M, 9Y and 9K selectively act on the rotatable 
photosensitive drum 6, whereby the electrostatic latent image on the 
surface of the rotatable photosensitive drum 6 is toner-developed. 
The reference numeral 11 designates a transfer drum which, at a position 
next to the compound developing device 9, is in contact with the 
photosensitive drum and is rotatively driven at substantially the same 
peripheral speed as that of the photosensitive drum 6 in a forward 
direction relative to the rotation of the photosensitive drum 6. 
This transfer drum 11 has, for example, a diameter of 180 mm and in the 
opening area of the peripheral surface thereof, a recording medium 
carrying sheet 11a formed of a film-like dielectric material which is 
recording medium carrying means is cylindrically and integrally extended. 
There are also disposed an adsorbing corona charger 11b which is adsorbing 
charging means for adsorbing a recording medium to the outer peripheral 
surface of the transfer drum 11, an adsorbing (bearing) roller 11c as an 
electrode opposed thereto, a transferring corona charger 11d for causing 
the toner images on the photosensitive drum to be transferred to the 
recording medium adsorbed to the transfer drum 11, an inner corona charger 
11e, an outer corona charger 11f, a recording medium separating charger 
11g, a recording medium separating pawl 11h, etc. 
The reference numerals 12, 13 and 14 denote first to third automatic 
recording medium supply mechanisms, and the reference numeral 15 
designates a manual recording medium supply portion. Recording mediums 
(transfer mediums) P are supplied one by one from one of the first to 
third automatic recording medium supply mechanisms 12, 13 and 14, pass 
along a predetermined sheet path comprising a guide plate, a pair of 
conveying rollers, etc. and are conveyed to a pair of register rollers 16. 
Or, recording mediums are conveyed from the manual recording medium supply 
portion 15 to the pair of register rollers 16. 
The recording medium is then fed to the transfer drum 11 at predetermined 
timing by the pair of register rollers 16, is wound around the outer 
peripheral surface of the transfer drum 11, is electrostatically held 
thereon and is rotated with the transfer drum 11, and the toner images on 
the photosensitive drum 6 are transferred to the outer surface of the 
recording medium by the transferring corona charger 11d. After the 
transfer of the toner images to the recording medium P, the surface of the 
rotatable photosensitive drum 6 is cleaned by a cleaner (cleaning device) 
10, whereby any residual materials adhering thereto such as toners left 
after transfer are removed. 
In the case of the full color image forming mode, the following four image 
forming and transferring cycles (1)-(4) are successively executed with the 
rotation of the photosensitive drum 6 and transfer drum 11 continued: 
(1) Charging Of the rotatable photosensitive drum 6.fwdarw.image exposure E 
by a laser beam modulated by the cyan image signal of the aforedescribed 
color-resolved image signals of the desired color image.fwdarw.development 
by the cyan developing device 9C.fwdarw.transfer of the cyan toner image 
to the recording medium P.fwdarw.the step of cleaning the rotatable 
photosensitive drum 6; 
(2) Charging of the rotatable photosensitive drum 6.fwdarw.image exposure E 
by a laser beam modulated by the magenta image signal of the 
aforedescribed color-resolved image signals of the desired color image 
.fwdarw.development by the magenta developing device 9M .fwdarw.transfer 
of the magenta toner image to the recording medium P.fwdarw.the step of 
cleaning the rotatable photosensitive drum 6; 
(3) Charging of the rotatable photosensitive drum 6.fwdarw.image exposure E 
by a laser beam modulated by the yellow image signal of the aforedescribed 
color-resolved image signals of the desired color image 
.fwdarw.development by the yellow developing device 9Y .fwdarw.transfer of 
the yellow toner image to the recording medium P.fwdarw.the step of 
cleaning the rotatable photosensitive drum 6; and 
(4) Charging of the rotatable photosensitive drum 6.fwdarw.image exposure E 
by a laser beam modulated by the black image signal of the aforedescribed 
color-resolved image signals of the desired color image.fwdarw.development 
by the black developing device 9K.fwdarw.transfer of the black toner image 
to the recording medium P.fwdarw.the step of cleaning the rotatable 
photosensitive drum 6. 
Thereby, the above-mentioned four toner images, i.e., the cyan toner image, 
the magenta toner image, the yellow toner image and the black toner image, 
are registered with one another in a predetermined manner relative to the 
outer surface (first surface) of the same recording medium P twining and 
held on the rotatable transfer drum 11 and superposedly transferred to the 
recording medium P, whereby a color toner image corresponding to the 
desired color image is formed on the recording medium P. 
When the superposition transfer of the four color toner images to the same 
recording medium P held on the rotatable transfer drum 11 is terminated, 
the recording medium has its charges removed by the separating charger 
11g, is separated from the transfer drum 11 by the separating pawl 11h as 
separating means, and is conveyed to a fixing device (in the present 
embodiment, a heat roller fixing device) 18 by conveying means 17, and the 
four color toner images are collectively fixed on the surface of the 
recording medium. 
In the case of the one-side image forming mode, a recording medium having 
left the fixing device 18 on one surface (first surface) of which the 
formation and fixing of an image have been finished is discharged onto a 
paper discharge tray 20 outside the apparatus through a paper discharge 
port 19. 
In the case of the both-side image forming mode, the recording medium 
having left the fixing device 18 on one surface of which the formation and 
fixing of an image have been finished is introduced into a reconveying 
sheet path a, passes along the route of a switchback sheet path b.fwdarw.a 
sheet path c, is reversed and is conveyed to an intermediate tray 21. It 
is then conveyed from this intermediate tray 21 to the pain of register 
rollers 16, is again fed to the transfer drum 11, and is wound and held on 
the transfer drum 11 with its first surface on which image formation has 
been finished turned inward and its second surface turned outward. 
Like the image formation on the first surface of the recording medium, the 
four color-resolved toner images of a color image for the second surface 
successively formed on the photosensitive drum 6 are successively 
transferred to the second surface of the recording medium, whereby a color 
toner image is formed thereon. 
The recording medium is then separated from the transfer drum 11 and is 
again conveyed to the fixing device 18, where the four color toner images 
formed on the second surface of the recording medium are collectively 
fixed, whereafter the recording medium on which full color both-side image 
formation has been finished is discharged onto the paper discharge tray 20 
through the paper discharge port 19. 
A recording medium on which one surface (first surface) image formation and 
fixing has been finished may be once discharged onto the paper discharge 
tray 20, whereafter the recording medium may be reversed so that its 
second surface may face upward, and may be again introduced from the 
manual paper supply portion 15 into the apparatus and image formation on 
the second surface may be executed. 
The order of the formation of the four color-resolved toner images is not 
limited to the order in the present embodiment. In the case of 
black-and-white image copying, the black developing device 9K alone 
operates. The both-side copy mode for black-and-white images and the image 
forming mode for forming a color image on one surface of a recording 
medium and forming a black-and-white image on the other surface of the 
recording medium can also be selectively executed. 
FIG. 5 is a schematic view showing an example of the fixing device of a 
full color image forming apparatus. The fixing device 18, as shown in FIG. 
5, is provided with a mixing roller 51 which is a fixing rotatable member 
having therein a halogen heater 56 which is a heating source, a pressing 
roller 52 which is a pressing rotatable member having therein a halogen 
heater 57 which is a heating source and rotatably urged against the fixing 
roller (in some cases, the pressing roller does not have the halogen 
heater 57 therein), silicone oil which is a parting agent an oil applying 
device 53 for applying to the surface of the fixing roller 51, and 
cleaning devices 54 and 55 for removing toners adhering to the surfaces of 
the fixing roller 51 and the pressing roller 52. 
Each of the fixing roller 51 and the pressing roller 52 is comprised of a 
lower layer formed of HTV (high temperature vulcanized type) silicone 
rubber on a mandrel made of aluminum, an intermediate layer formed of 
fluorine rubber for preventing the entry of oil outside of the lower 
layer, and a surface layer formed of LTV (low temperature vulcanized type) 
or RTV (room temperature vulcanized type) silicone rubber well concordant 
with silicone oil as parting agent further outside of the intermediate 
layer, and the fixing roller 51 and the pressing roller 52 cooperate with 
each other to form a nip portion for nipping and conveying a recording 
medium therebetween. Resin-like polyorganosiloxane and 1 percent by weight 
of silica powder are mixed with the addition type silicone rubber of the 
surface of the fixing roller, and resin-like polyarganosiloxane and 5 
percent by weight of silica powder are mixed with the addition type 
silicone rubber of the surface of the pressing roller. 
Thus, in the case of a color image forming apparatus, it is necessary to 
sufficiently melt and mix toners and therefore, generally, soft rollers 
using an elastic material such as rubber are often used. Also, in the case 
of a fixing device in a both-side color image forming apparatus, the toner 
parting property is required of both the fixing roller 51 and the pressing 
roller 52 and therefore, silicone rubber is often used for the surface 
layers of the both rollers. 
The heating operation of the halogen heaters 56 and 57 is controlled by 
temperature control means (not shown). The temperature control means 
controls the operation of the halogen heaters 56 and 57 on the basis of 
the surface temperatures of the fixing roller 51 and pressing roller 52 
detected by thermistors 58 and 59. 
The oil applying device 53 is movable toward and away from the fixing 
roller, and moves silicone oil in an oil reservoir 53a toward an applying 
roller 501 by a draw-up roller 503 and applies the silicone oil to the 
surface of the fixing roller 51 by the applying roller 501. The movement 
of the oil applying device 53 toward and away from the fixing roller 51 is 
controlled by the ON/OFF of a solenoid, not shown. The amount of silicone 
oil applied to the fixing roller 51 is controlled by a control blade 502 
and is determined by the direction of contact, the angle pressure, etc. of 
this blade 502. 
Part of the oil applied to the fixing roller 51 is absorbed by the 
recording medium during fixing and the remainder of the oil shifts to the 
pressing roller 52 side and is scraped off by an oil scraping blade 70. 
The oil scraping blade 70 is made of fluorine rubber or the like, whereby 
excess oil on the surface of the roller is prevented from collecting in 
the nip portion to thereby cause OHP film or the like to slip in the nip 
portion. 
The cleaning devices 54 and 55 comprise heat-resistant unwoven fabric 
NORMEX (trade name) or webs 54a, 55a plated with nickel on this NORMEX by 
the electroless plating method, rollers 54b, 55b for urging these cleaning 
webs 54a, 55b toward the fixing roller 51 and the pressing roller 52, 
respectively, unwinding rollers 54c, 55c for letting out the cleaning webs 
54a, 55a, and take-up rollers 54d, 55d for taking up the cleaning webs 
54a, 55a. 
In such an apparatus, when a recording medium is conveyed to the fixing 
device 18, the fixing roller 51 and pressing roller 52 are rotated at a 
predetermined speed and the recording medium is pressed and heated from 
its both surfaces while passing between the rollers 51 and 52, and unfixed 
toners carried thereon are melted, whereby fixing is effected. Also, at 
this time, the toners adhering to the fixing roller 51 and pressing roller 
52 are removed by the cleaning devices 54 and 55. 
In order to examine the toner parting property and physical strength of the 
addition type silicone rubber made in Embodiments 1 to 7 and Comparative 
Examples 1 and 2 by the use of such an apparatus to which the present 
invention is applicable, the comparison of performance was made by the 
single-layer roller for fixing shown in FIG. 1. 
The roller for fixing used in the experiment was made in the following 
manner. 
DY39-051 (produced by Tore and Dowcorning Co., Inc.) as an adhesive layer 
was applied to an aluminum mandrel having an outer diameter of 58 mm and 
was heated and dried at 200.degree. C. On this mandrel, the abovedescribed 
addition type silicone rubber was hardened at 150.degree. C. for 40 
minutes, thereby making fixing rollers and pressing rollers each having 
the addition type silicone rubber of Embodiments 1 to 7 and Comparative 
Examples 1 and 2 on the surface layer of an outer diameter 60 mm (the 
thickness of the silicone rubber being 1 mm) which contacts with toners. 
These fixing and pressing rollers were used in the fixing device of the 
color copying apparatus capable of effecting both-side image formation 
shown in FIG. 5 by a forcible test of a set temperature 200.degree. C., 
and both-side image formation was done up to 20,000 sheets. 
The parting property of toners was examined by the number of copies during 
the occurrence of the offset of the toners to the rollers, and the heat 
resisting strength was examined by the number of copies for which the 
surfaces of the rollers were injured. 
The results are summarized in Table 3 below. 
TABLE 3 
__________________________________________________________________________ 
fixing roller pressing roller 
number of copies 
number of copies 
number of copies 
number of copies 
till occurrence 
till occurrence 
till occurrence 
till occurrence 
of offset 
of injury 
of offset 
of injury 
__________________________________________________________________________ 
Embodiment 1 
not occurred up 
not occurred up 
not occurred up 
not occurred up 
(silica 0.1%) 
to to to to 
20,000 sheets 
20,000 sheets 
20,000 sheets 
20,000 sheets 
Embodiment 2 
not occurred up 
not occurred up 
not occurred up 
not occurred up 
(silica 0.5%) 
to to to to 
20,000 sheets 
20,000 sheets 
20,000 sheets 
20,000 sheets 
Embodiment 3 
not occurred up 
not occurred up 
not occurred up 
not occurred up 
(silica 1%) 
to to to to 
20,000 sheets 
20,000 sheets 
20,000 sheets 
20,000 sheets 
Embodiment 4 
not occurred up 
not occurred up 
not occurred up 
not occurred up 
(silica 2%) 
to to to to 
20,000 sheets 
20,000 sheets 
20,000 sheets 
20,000 sheets 
Embodiment 5 
occurred for 
not occurred up 
not occurred up 
not occurred up 
(silica 3%) 
10,000 sheets 
to to to 
or less 20,000 sheets 
20,000 sheets 
20,000 sheets 
Embodiment 6 
occurred for 
not occurred up 
not occurred up 
not occurred up 
(silica 5%) 
10,000 sheets 
to to to 
or less 20,000 sheets 
20,000 sheets 
20,000 sheets 
Embodiment 7 
occurred for 
not occurred up 
not occurred up 
not occurred up 
(silica 8%) 
10,000 sheets 
to to to 
or less 20,000 sheets 
20,000 sheets 
20,000 sheets 
Comp. Ex. 1 
not occurred up 
occurred for 
occurred for 
occurred for 
(silica 0%) 
to 16,000 sheets 
16,000 sheets 
9,000 sheets 
20,000 sheets 
or less or less or less 
Comp. Ex. 2 
occurred for 
not occurred up 
occurred for 
not occurred up 
(silica 10%) 
5,000 sheets 
to 12,000 sheets 
to 
or less 20,000 sheets 
or less 20,000 sheets 
__________________________________________________________________________ 
As shown in Table 3 in the case of the fixing roller, when the amount of 
silica was 0 percent by weight, injury occurred for 16,000 sheets or less. 
Also, when the amount of silica was 3 percent by weight or more, offset 
occurred for 10,000 sheets or less. Accordingly, it is seen that in the 
fixing roller, an amount of silica of 1 to 2 percent by weight is 
preferable from the viewpoints of parting property and heat resisting 
property. Also, in the case of the pressing roller, when the amount of 
silica was 0.1 percent by weight or less, injury occurred for 10,000 
sheets or less, and when the amount of silica was 10 percent by weight, 
offset occurred for 12,000 sheets or less. Accordingly, in the pressing 
roller, an amount of silica of 0.5 to 8 percent by weight is preferable 
from the viewpoints of parting property and heat resisting property. Thus, 
by applying the present invention to at least one of the fixing roller and 
the pressing roller, there can be provided a fixing device excellent in 
parting property and heat resisting property. Also, by a fixing roller and 
a pressing roller using the addition type silicone rubber of the present 
invention being used in the fixing device of a full color both-side image 
forming apparatus, there can be provided a fixing device capable of fixing 
both-side images and excellent in toner parting property, physical 
strength and heat resisting property. It has been found that particularly 
in a both-side image fixing device, the parting property is strongly 
required of the fixing roller and the physical strength and the heat 
resisting property are strongly required of the pressing roller. This is 
because as previously described, the oil scraping blade for scraping off 
any excess oil on the surface of the roller is in contact with the 
pressing roller, whereby when the number of copies becomes great, paper 
powder and toners adhering to the roller are liable to adhere to the oil 
scraping blade to thereby injure the pressing roller. Accordingly, by a 
roller using the addition type silicone rubber having a great amount of 
inorganic fine powder therein on the surface layer being used on the 
pressing roller side rather than on the fixing roller side, there can be 
provided a both-side image fixing device of long life in which the lives 
of the rollers for fixing can be adjusted to each other and which avoids 
waste. 
As reinforcing resin-like polyorganosiloxane to be mixed the polysiloxane 
mixture used in the aforedescribed construction, use can be made of one 
having a ladder polymer, or a block polymer having in one and the same 
molecule a segment including at least one of tetrafunctionality and 
trifunctionality and a normal chain-like oil segment having at least 100 
trifunctional construction units on end, and by the mixing of such 
reinforcing resin-like polyorganosiloxane, there can be obtained good 
physical strength and toner parting property. 
Also, the inorganic fine powder as the heat resistance imparting agent used 
in the aforedescribed instruction is inorganic fine powder of an average 
particle diameter of 10 to 1000 nm of silica (silicon oxide), alumina 
(aluminum oxide), titanium oxide, calcium carbonate or the like made by 
the wet method or the dry method. 
As such inorganic fine powder, use can also be made of one having is 
surface treated by an organic compound such as alkyl radical like methyl 
radical or alkoxy radical like methoxy radical, an organic silicon 
compound such as silanol radical, or an organic metal compound such as 
titanate, aluminate or zirconate to thereby enhance dispersibility and 
coupling property. 
While the embodiments of the present invention have been described above, 
the present invention is not restricted to the above-described 
embodiments, but all modifications are possible within the technical idea 
of the present invention.