JP3424485B2 - Semiconductive roll - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductive roll, and more particularly to a charging roll for uniformly charging the surface of an image carrier in an electrophotographic copying machine, an electrostatic printer or the like, which is formed on the image carrier. Semi-conductive used for a transfer roll for transferring the formed toner image to a transfer medium, a toner transport roll for transporting the toner on the image carrier, and a cleaning roll for removing the toner on the image carrier. The present invention relates to a roll, and particularly to a semiconductive roll suitable for weight reduction and speedup.

[0002]

EPDM for semiconductive rolls
(Ethylene propylene diene rubber), NBR (nitrile butadiene rubber), SBR (styrene butadiene rubber), urethane rubber, silicone rubber, nosolex and other general elastomers (elastic bodies), carbon black, metal oxides, organic and inorganic Conductivity is given by dispersing a conductive substance such as an electrolyte, and the roll is formed by coating the outer periphery of a conductive metal core material with a conductive foam elastic body foamed by mechanical foaming with air or nitrogen or a chemical foaming agent. There is.

As a method for controlling the electric characteristics of the semiconductive roll, there is known a method of changing the compounding amount of the conductive particles in the conductive foamed elastic body, and the hardness and resistance of the conductive foamed elastic body are known. Therefore, it is difficult to balance the resistance. 1 for semiconducting rolls with electronic conductivity
It is difficult to control the medium resistance in the range of 0 ^{5 to 10} ohm · cm, and there is a large variation in resistance within and between the semiconductive rolls, and it is difficult to obtain a uniform image at a stable current because of large dependence on the measured voltage.

Further, an ion conductive type semiconductive roll to which an antistatic agent such as a quaternary ammonium salt or an organic or inorganic electrolyte such as an alkali metal is added has a very small resistance change distribution in the roll, which is desirable, It has a problem that the resistance value greatly changes with environmental changes such as humidity and humidity, and a problem that the change with time during long-term use due to the movement of ions is large.

It is known that the use of the electron conductive type additive reduces the change in resistance to environmental changes, but it is difficult to adjust the hardness and it is difficult to obtain a uniform nip. Therefore, for low hardness, a large amount of softeners such as process oil, aroma oil, paraffin oil, and plasticizers such as phthalate ester are dispersed and mixed in the roll to improve the dispersibility of carbon black, and to improve the semiconductivity. A stable image can be formed by increasing the adhesiveness between the conductive roll and the contacted object that comes into contact with the semiconductive roll.

However, according to this method, the surface of the image forming member is contaminated due to the bleeding of these additives in the nip portion after long-term storage, and the surface of the image forming member is moved to the photoconductor to cause black streaks and white streaks. Is likely to occur as a defect on the image. In order to prevent these phenomena, surface treatment or installation of a protective layer is required on the semiconductive roll, which is disadvantageous in terms of resistance adjustment and cost. If a large amount of a plasticizer or a softening agent is filled, the permanent set is deteriorated, and there is a problem that image unevenness is likely to occur due to roll deformation.

As a method for improving the dispersibility of carbon black to obtain uniform electric characteristics, the surface of cocoon black is subjected to a coupling treatment (see JP-A-1-101375).
JP-A-1-109376, JP-A-4-5105, a method of mixing and dispersing with insulating particles, a metal oxide, etc., or blending two kinds of polymers having different solubilities.
No. 6), a specific acetylene black is added to the conductive silicone rubber composition (Japanese Patent Application Laid-Open No. 5-116789).
No. 0), two types of elastic polymer having different affinities for the conductive pigment are used (Japanese Patent Laid-Open No. 196067/1993).
JP-A-6-17), in which a conductive black layer is mixed with channel black and furnace black in a specific ratio.
Technologies such as Japanese Patent No. 3939) have already been proposed.

[0008]

In the case of the above-mentioned prior art, in order to improve the dispersibility of carbon black, when the surface is subjected to a coupling treatment or mixed with insulating particles or metal oxides and dispersed, There are problems of cost increase due to adjustment of mixing amount, change of surface property, and complexity of manufacturing process. In particular, a semiconductive roll in which carbon black is dispersed in an elastic body has a resistance value of 10 ⁵ -10 ohm.
Since it rapidly changes in the cm region, it is very difficult to stably adjust the predetermined resistance value within one digit only by the addition amount of carbon black.

When two kinds of elastomers having different solubilities are blended, control in the medium resistance region is possible without depending on the amount of carbon black depending on the blending ratio, but NBR / EPDM blended products and silicone / EPD are available.
When a small amount of carbon black is blended in the M blend elastic body, the conductive chain of carbon black is cut when reaching the 10 ^7-8 ohm · cm region, and the sea-island structure collapses due to moisture absorption or heat fluctuation on the polar elastomer side. It was found that the environmental fluctuations and resistance fluctuations of No. 2 significantly changed, and in the case of using two types of incompatible elastic bodies, the semiconducting rolls showed environmental fluctuations of more than two digits in resistance value, hardness and hardness. Is difficult to adjust only by its blending ratio.

Further, during sulfur vulcanization, additives such as a vulcanization accelerator are prone to be biased due to remarkable phase separation, and are nonpolar EP.
Vulcanization of the DM phase and the like becomes insufficient, and permanent strain of 30 to 50% occurs in the NBR blend system.

Further, when EPDM having a low polarity is used alone, the interaction with the conductive particles such as carbon black is small and the dispersibility during mixing tends to become non-uniform, resulting in large resistance variation, resulting in excellent image density uniformity. The good image quality cannot be obtained.

Therefore, the present invention has been made in order to solve the problems so far, and an object of the present invention is to reduce variations in the resistance value in the medium resistance region and to prevent environmental fluctuations in a wide resistance region. An object of the present invention is to provide a semi-conductive roll having a stable resistance value and excellent manufacturing stability regardless of the applied voltage.

Another object of the present invention is that it does not contain a plasticizer such as process oil, can maintain a stable roller hardness with a low hardness, and is free from bleeding phenomenon and does not cause fatigue or contamination. To provide rolls.

Further, in the three-component system, the blending property of the incompatible elastic body is improved to suppress heat generation when carbon black is mixed, and improve the vulcanization uniformity by the compounding amount of the rubber in the middle position of the SP value, and Another object of the present invention is to provide a semi-conductive roll that can reduce permanent set and suppress deformation and resistance variation due to long-term storage in the nip portion.

[0015]

According to the present invention, in a semiconductive roll having a conductive core material coated with a conductive foam elastic body, the conductive foam elastic body is NBR or EPDM.
Solubility parameters intermediate to the solubility parameter values of these rubbers
And a CR having a meter value, the NBR, EPDM
And CR are mixed in a weight ratio of NBR / EPDM / C
R = 5/5/90 to 5/90/5 to 90/5/5
The semi-conductive roll is characterized in that two kinds of carbon blacks having different characteristics are dispersed therein. Further, the present invention provides a semiconductive roll having a conductive core material coated with a conductive foam elastic material on the outer periphery thereof, wherein
The foamed elastic body melts NBR and EPDM with these rubbers.
Has a solubility parameter value that is midway between the solution parameter values
SBR, including NBR, EPDM and SBR
The mixing ratio is NBR / EPDM / SBR = 5/5 by weight.
Within the range of / 90 to 5/90/5 to 90/5/5,
In addition, it is a semiconductive roll in which two types of carbon black having different characteristics are dispersed.

In the present invention, three rubbers ( NBR, EPDM, and EPDM) having different solubility parameter values are used as rubber components .
And SBR) or (NBR, EPDM and CR)
It is mixed at a predetermined ratio to improve the compatibility between rubbers, and carbon blacks with different characteristics are mostly distributed near the interface of the sea-island structure, mitigating the concentrated uneven distribution of carbon blacks. As a result, the dispersibility of carbon black as conductive particles is improved, and uniform charging and transfer are possible. Further, carbon black is composed of two types having different characteristics, and conductivity with little resistance variation can be obtained. In addition, since it is not necessary to use a plasticizer such as process oil, there is no need for bleeding of the plasticizer, it is not necessary to use an antistatic agent or other electrolyte, and the resistance value to environmental changes such as temperature and humidity can be reduced. Variations can be reduced and hardness and resistance can be easily adjusted.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the conductive foam elastic body formed on the outer periphery of the conductive core material has a sea-island structure of three kinds of rubbers having different solubility parameter values. These three rubbers include NBR (nitrile butadiene rubber) and EPDM (ethylene propylene diene rubber) and a third rubber (SBR or CR) having a solubility parameter value intermediate between those of these rubbers. Become.
The amount of acrylonitrile in NBR is 15 to 55%, preferably 15 to 35%. The styrene content of SBR is 15
˜55%, preferably about 25% (medium high nitrile). Examples of dienes in EPDM include ethylidene norbornene, 1,4-hexadiene,
Dicyclopentadiene and the like can be mentioned.

EPDM and NBR (SP value = 8.7 to 10.5) having greatly different solubility parameter values (SP values)
(SP value = 7.9 to 8.0) and solubility parameter value (SP value) located in the middle of these CR (chloroprene) as the third rubber (SP value = 8.1 to 9.4) or SBR (styrene butadiene rubber) (SP value =
In the case of the combination of 8.4 to 8.7), the increase in hardness due to the increase in the addition amount of carbon black such as Ketjen black can be reduced, and a stable resistance value can be obtained by adjusting the blend ratio and the copolymerization ratio. Can be maintained.

In particular, CR forms a relatively low-viscosity and easily flowable layer in the vulcanization / foaming process of the other two blend rubbers due to its slow vulcanization, and has the effect of a polymer plasticizer. Is exerted to alleviate the phase separation state of NBR (sea) and EPDM (island) and stabilize the dispersed state of carbon black. Further, the rubber hardness of the semiconductive roll can be reduced without using an additive such as oil or a plasticizer that easily bleeds from the surface of the roll due to the effect of CR as a polymer plasticizer.

In the present invention, NBR having affinity with carbon black and EPDM having poor compatibility with this NBR
By blending CR or SBR having compatibility between the two, an elastic body in which a large amount of carbon black is distributed in the vicinity of the interface can be obtained. in this case,
By adjusting the blending ratio of these rubbers, the amount of acrylonitrile in NBR, the amount of styrene in SBR, and the amount of carbon black, the roll resistance value can be adjusted to 10 ⁵
It can be adjusted to about 10 ¹⁰ ohm · cm. The roller hardness (Asker C hardness) can also be controlled up to about 30 to 60 degrees with the vulcanization conditions kept constant, and the foamed state of the foamed elastic body is obtained by chemically or vacuum mechanically or mechanically foaming a blend of the three components. It can be used in either a closed cell or open cell state.

The semiconductive roll made of NBR, SBR and CR alone is combined with an EPDM component which is liable to suffer ozone deterioration due to a discharge phenomenon when used in an electrophotographic copying machine or an electrostatic printer and which has excellent ozone resistance. It can be used by. On the other hand, EPDM alone has a high rubber insulating property, and it is necessary to add a large amount of conductive pigment, which increases the hardness of the elastic body.

The mixing ratios of the above rubbers are NBR and EPD.
The mixing ratio of M and CR is NBR / EPDM /
CR = 5/5/90 to 5/90/5 to 90/5/5, and similarly, the mixing ratio of NBR, EPDM and SBR is NBR / EPDM / SBR = 5/5 / by weight ratio.
It is within the range of 90 to 5/90/5 to 90/5/5.

Low resistance rubber (1
In order to suppress the ozone deterioration resistance of NBR, SBR and CR which are 0 ¹¹ ohm · cm) and to control the conductivity of the elastic layer, the compounding amount of EPDM is 90% to 10%, preferably 30%.
% To 70%, the concentration of carbon black existing in the NBR layer can be increased, and a stable conductive path can be formed. The blending amount of NBR, SBR or CR is 90% to 5%, preferably 10 to 30%
By adjusting the amount to 1, the heat generation during kneading of carbon black can be suppressed and the compatibility between the two can be increased, whereby it becomes possible to impart processing stability during additive / filler blending. As a result, the effects of environmental changes in resistance and applied voltage dependence are also EP.
It is possible to obtain a semiconductive roller which has a smaller hardness and is stable as compared with the case where DM alone is compounded.

The carbon black used in the present invention is composed of two types of carbon black having different characteristics. As the two types of carbon black having different characteristics, a combination of two types of carbon black having different oil absorbency is particularly desirable. For example, it is desirable to use Ketjen Black, which has high oil absorption and excellent conductivity, and thermal black, such as soft carbon FT and MT, which has low oil absorption and excellent rubber reinforcement, in combination with these carbon blacks. It is possible to have a relatively small amount of conductivity with little resistance variation. Examples of Ketjen Black include Ketjen Black EC, Ketjen Black EC-600, and Ketjen Black EC-600JD (manufactured by Lion Akzo). FT for thermal black
Carbon, MT carbon (manufactured by Asahi Carbon Co., Ltd.), N990
ARO90 (manufactured by Harbor Company), HTC # 20 (manufactured by Chubu Carbon Company), MT N990 (manufactured by Degussa), Sev
acarb MT (manufactured by Colombia), # 3030B,
# 4013B (manufactured by Mitsubishi Chemical Corporation) and the like.

The use ratio of carbon black is, for example, Ketjen black: thermal black = 1: 1 by weight ratio.
˜1: 8, preferably 1: 2 to 1: 5. When these carbon blacks are used alone, it is possible to adjust in the low resistance region with Ketjen Black, which has high cohesiveness, but there are large variations in the resistance value depending on the location inside the roller and variations between lots during manufacturing. When using only the thermal black, the resistance cannot be adjusted to 10 ¹² ohm · cm or less and the resistance adjustment is difficult.

Further, when the use ratio of the above carbon black is out of the above range, the variation of the resistance value depending on the location or the variation between lots at the time of manufacturing becomes large, and it becomes difficult to control the predetermined resistance region. The blending ratio of carbon black varies depending on the blending ratio of NBR / CR or SBR / EPDM.
20 parts by weight, and the thermal black is preferably 10 to 40 parts by weight.

As the additives to be added to the rubber, there are conductive fillers, vulcanizing agents, foaming agents, vulcanization accelerators, antioxidants,
Examples include softening agents, plasticizers, reinforcing agents, fillers, and the like, but conductive fillers, vulcanizing agents, blowing agents, other additives other than vulcanization accelerators may be added as necessary, In particular, it is desirable to avoid additives that tend to bleed, such as softening agents and plasticizers. Further, as the conductive filler, the above-mentioned carbon black is indispensable, and in addition, graphite, metal peroxide, etc. may be supplementarily used. Examples of the metal oxide include tin oxide and titanium oxide (on the surface of which is coated with tin oxide).

As the vulcanizing agent, for example, sulfur, organic sulfur-containing compounds, organic peroxides and the like can be used.
Examples of the organic sulfur-containing compound include tetramethylthiuram disulfide and N, N'-dithiobismorpholine. Examples of organic peroxides include dicumyl peroxide and benzoyl peroxide. The amount of the vulcanizing agent added is 0.3 to 4 parts by weight, preferably 1.0 to 4 parts by weight, based on 100 parts by weight of the rubber component.
3.5 parts by weight.

As the vulcanization accelerator, various conventionally used ones can be used, but in the present invention, it is particularly preferable to use a sulfenamide type vulcanization accelerator. That is, when compounded with three types of rubbers having different SP values, the sulfenamide-based vulcanization accelerator is concentrated and unevenly distributed in a specific rubber phase (for example, NBR phase). Has the effect of alleviating. It is desirable to add the vulcanization accelerator in an amount of 0.3 to 4 parts by weight, preferably 0.5 to 3 parts by weight, based on 100 parts by weight of the rubber component.

As the foaming agent, various conventionally used foaming agents can be used, but in the present invention,
The use of an azodicarbonamide (ADCA) type foaming agent which tends to delay the vulcanization rate of the entire rubber suppresses the rapid progress of vulcanization in a part of the rubber phase, and vulcanizes the entire rubber. It is preferable to make it uniform.

Examples of the antiaging agent include imidazoles such as 2-mercaptobenzimidazole, phenyl-α-naphthylamine, N, N'-di-β-naphthyl-.
Amine such as p-phenylenediamine, N-phenyl-N′-isopropyl-p-phenylenediamine, di-t
Examples include phenols such as ert-butyl-p-cresol and styrenated phenol.

The conductive core material is a semiconductive roll in which a conductive foamed elastic body is coated on the outer periphery of a metal core material (shaft) such as stainless steel (SUS), iron, Ni-plated iron or aluminum (A1). The volume resistance value is 10 ⁵ to 1
0 ¹⁰ ohm · cm, rubber hardness (Asker C hardness) 2
A roller in the range of 5 to 60 degrees, preferably 30 to 45 degrees can be used for transfer, cleaning roll, and the like.

Next, a suitable method for producing the semiconductive roll of the present invention will be described. First, three kinds of rubbers having different SP values are mixed, necessary additives such as carbon black are added thereto, kneaded, and then extruded into a cylindrical shape to have a predetermined length. Press-fit into a conductive core material such as
Vulcanize. Vulcanization is preferably can vulcanization, but may be pressureless oven vulcanization or the like. The vulcanization conditions vary depending on the rubber material used and the compounding amount, but are usually 140 to 170 ° C.
It is better to do this for 0.5 to 6 hours. Foaming is performed in the course of vulcanization to obtain a tube made of a conductive foamed elastic body.
The expansion ratio (volume%) is 140 to 400, preferably 2
The range is from 00 to 350.

Further, it is desirable to form a resistance layer on the above conductive foamed elastic body. The resistance layer is provided in order to prevent damage to the charging member and the photoconductor due to current concentration when a defect such as a pinhole occurs on the photoconductor, and is generally urethane. A polymer compound such as acrylic, nylon, or nylon is impregnated or coated with a coating material in which conductive fine particles such as carbon black or metal oxides (titanium oxide, tin oxide, etc.) are dispersed, and dried by heating and then cured. The curing of the coating film by heating and drying may be performed by drying and curing the laminated coating film, or by drying and curing each time when coating. Further, as the coating liquid for the resistance layer, not only an organic solvent-based emulsion but also a water-based emulsion which is relatively slow to dry may be used.

In the present invention, when the resistance layer is formed, the resistance layer coating liquid is applied onto the conductive foam elastic material at least twice, so that the wall surface and the surface of the pores of the conductive foam elastic material are surely conductive. It is possible to form a resistance layer having no pinholes on the surface by fixing and fixing the conductive coating film, and to prevent the pinhole leak of the charging member and the photoconductor due to the concentration of electric current. By applying a conductive coating film having different resistance or a conductive coating film having the same resistance a plurality of times, it is possible to reduce the weight, surface elasticity and smoothness of the conductive foamed elastic body.

Next, the difference in characteristics between the conventional semiconductive roll and the semiconductive roll of the present invention will be described based on a graph.

FIG. 1 shows an ion conductive roll (urethane rubber containing 1.2% by weight of tetrabutyl quaternary ammonium salt).
Foamed roll added A) and the semiconductive roll of the present invention [NBR / CR / EPDM = 55/15/30 (wt%) relative to Ketjen Black / Thermal Black =
7 is a graph showing the relationship of the resistance change of the roll] B added with 7/25 (parts by weight).

FIG. 1 shows that when the primary transfer roll for color is running at 150 KPV, the semiconductive roll A of the present invention shows almost no increase in volume resistance even if the number of running times is increased, and is almost constant. The volume resistance is shown, and it is shown that a stable transfer current can be supplied. In the ion conductive roll B, the volume resistivity is gradually increased as the number of running times is increased, and the transfer failure is likely to occur. Is shown.

FIG. 2 shows current-voltage changes of the transfer current of the color primary transfer roll under low temperature and low humidity (10 ° C., 15% Rh). FIG. 2A shows the semiconductivity [N of the present invention.
BR / CR / EPDM = 55/15/30 (wt%), Ketjen Black / Thermal blank = 7/2
5 (part by weight)], FIG. 2 (B) shows a graph of current-voltage change for an ion conductive roll (foaming roll in which 1.2% by weight of tetrabutyl quaternary ammonium salt is added to urethane rubber). Shown respectively.

FIG. 2A shows that in the case of the semiconductive roll of the present invention, a power supply voltage of 2 KV or less can be applied at a current of 5 to 15 μA, and the cost can be reduced. 2 (B) shows that the conventional ion conductive roll requires a power source voltage of 2 KV or more at a current of 5 to 15 μA.

FIG. 3 shows a semiconductive roll [NBR of the present invention.
/ CR / EPDM = 55/15/30 (wt%) against Ketjen Black / Thermal blank = 7, 6, 5
/ 25 (parts by weight) in combination with three types] and an ion conductive roll (foaming roll in which 1.2% by weight of quaternary ammonium salt is added to urethane rubber) under low temperature and low humidity (10 ° C., The applied voltage current change of the transfer roll resistance value at 15% RH) is shown.

The semiconductive roll of the present invention has a roll resistance value in the range of 10 ⁵ to 10 ⁷ ohm · cm, while the conventional ion conductive roll has a resistance of 10 ^8.4 ohm · cm.

The conventional ion conductive roll has a thickness of 8 to 15 μm.
The transfer current of A requires a power supply voltage of approximately 3 kV or higher, while the semiconductive roll of the present invention has a thickness of 8 to 15 μm.
For the transfer current of A, a power supply voltage of 2 kV or less is sufficient, and it is shown that a low cost power supply can be used.

FIG. 4 shows a change in nip (Nip) resistance with respect to an applied voltage when the composition of the semiconductive roll of the present invention is varied within the following range.

NBR / CR / EPDM = 55-40 / 1
5-30 / 30 (wt%) CB (carbon black) ratio = Ketjenblack /
Thermal black = 4 to 6/19 to 28 (parts by weight) The nip resistance of the above semiconductive roll at an applied voltage of 10 V to 100 V was measured with different roll resistances and plotted.

From FIG. 4, in the semiconductive roll of the present invention,
The electric conductivity gradually decreases in the region of 10 ⁵ to 10 ⁸ ohm · cm, indicating that a hybrid state is formed.

FIG. 5 shows the environmental dependence and changes in the total nip (Nip) resistance of various rolls having the same composition as in FIG.

From FIG. 5, the influence of the ionic conductivity of the matrix itself contributes at 10 ^8.5 ohm · cm or more.
^{In the 7.5-8.5} ohm-cm region, it is possible to form a hybrid state in which both CB (carbon black) electrical conduction and NBR component ionic conductivity contribute to form stable transfer and charging current supply. ing.

FIG. 6 shows the dependence of the nip resistance value on the carbon black compounding amount when the composition of the semiconductive roll of the present invention is varied within the following range.

NBR / SBR / EPDM = 40/30 /
30 (wt%) CB (carbon black) ratio = Ketjen black /
Thermal black = 4 to 6/13 to 28 (parts by weight) Secondary vulcanization: 150 ° C. × 2 hours Third vulcanization: 160 ° C. ×
2 hours foaming In FIG. 6, the horizontal axis represents the blending amount of thermal black (parts by weight), where A is the blending amount of Ketjen black (4 parts by weight), and B is the blending amount of Ketjen black. (5 parts by weight) and C show the case of the compounded amount of Ketjen black (6 parts by weight), respectively.

From FIG. 6, the nip resistance is 10 ⁹ to 10 ¹¹ o.
It is shown that the reproducibility in the hm · cm region can be easily adjusted by adjusting the blending amount of two types of carbon black, Ketjen black and thermal black, and that the region in the range of 10 ⁷ to 10 ¹¹ ohm · cm can also be adjusted. ing.

FIG. 7 is a sectional view showing a transfer roll as an embodiment of the semiconductive roll according to the present invention.
In FIG. 11, 11 is a conductive core material, 12 is a conductive foam elastic layer, 13 is a first resistance layer, and 14 is a second resistance layer.

FIG. 8 is a schematic structural view showing an embodiment of an image forming apparatus in which the semiconductive roll according to the present invention is applied to a transfer roll. This image forming apparatus is a laser beam printer utilizing an electrophotographic process. Is configured as.

In FIG. 8, reference numeral 1 denotes a photoconductor drum using an organic photoconductor (OPC) or the like as an image carrier, and the photoconductor drum is driven in a predetermined direction by an unillustrated driving means along the arrow direction. Process speed (28mm / se
c and 56 mm / sec (two-step switching). The surface of the photoconductor drum 1 is primarily charged to a predetermined potential by the charging roll 2 that contacts the surface of the photoconductor drum 1.

For this charging roll 2, for example, a DCG, LV component having a voltage of -350 V and a frequency of 35 are supplied by a power source 3.
An oscillating voltage superimposed with a sinusoidal AC component of 0 Hz and a voltage of 2000 Vpp is applied, and the surface of the photosensitive drum 1 is uniformly charged by the charging roll 2 to −350 V which is equal to the DC component of the applied voltage. . Thereafter, the surface of the photosensitive drum 1 is subjected to image exposure (not shown) output from the laser writing device according to the image information, and an electrostatic latent image according to the image information is formed.

Next, after the electrostatic latent image formed on the photosensitive drum 1 is developed into a toner image by the developing roller 4a of the developing device 4 using a magnetic one-component developer or the like, it becomes a toner image.
This toner image is transferred onto the transfer paper 9 as a transfer medium that is fed at a predetermined timing by charging the transfer roll 6. The transfer roll 6 has a transfer current of 3 to
A constant-current controlled current is applied to 5 μA.

Thereafter, the transfer paper 9 on which the toner image is transferred
Is separated from the surface of the photoconductor drum 1 by being discharged by a discharging device (not shown) for discharging electricity, and is conveyed to a fixing device (not shown) to fix the toner image on the transfer paper 9 so that the toner image is transferred to the fixing device. The image is discharged to the outside, and the image forming process is completed.

The surface of the photosensitive drum 1 on which the toner image transfer step has been completed is cleaned of residual toner by the cleaning blade 8a of the cleaning device 8 to prepare for the next image forming step. Further, in the figure, 5 is a pressure spring for bringing the charging roll 2 into contact with the surface of the photosensitive drum 1, and 7 is a cleaning pad for cleaning the surface of the charging roll 2.

[0059]

【Example】

[Embodiment 1] A transfer roll is constructed by coating a foamed elastic body layer on a conductive core material made of iron plated with Ni. The foamed elastic layer was prepared by blending NBR / CR / EPDM at a weight ratio of 30/30/40 (Nippon Synthetic Rubber, NE71, Anka EM-30), and ketjen black (lion) as two types of carbon black. AKZO Co., Ltd., oil absorption 360 ml / g) 4 parts by weight and Asahi Thermal (Asahi Carbon Co., oil absorption 28 ml / g) 19 parts by weight were added, and further 1.5 parts by weight of sulfur and vulcanization accelerator Cz.
= 2 parts by weight, stearic acid 1 part by weight, foaming agent OBSH5
By adding the parts by weight to roll kneading, and extruding it into a cylindrical shape, a cylindrical conductive core material having a predetermined length is formed into a cylindrical shape.
It is press-fitted into an iron-plated iron conductive core material using an i-plated vulcanizing can (vulcanized molten steam heating and pressurizing device) at 160 ° C (5.5 k / c
After vulcanization and foaming for 30 minutes with m ² ), the surface was polished.

The transfer roll manufactured in this manner has a resistance value of 10 ^7.8 ohm · cm (roll outer diameter 18 mm) between roll nip when DC 1 kV is applied to the conductive core material.
The rubber hardness (Asker C hardness) was 35 degrees. Further, when the voltage applied to the transfer roll was changed between 1 and 5 kV, the voltage dependency of the roll resistance showed a decrease of 0.8 digits, but no dielectric breakdown occurred within this range. An image test of this semiconductive roll was carried out with the laser beam printer shown in FIG. 2, and a good image quality was shown.

Example 2 The elastic layer component composition ratio used in Example 1 is NBR / CR / EPDM = 55/15/30.
Ketjen Black as two types of carbon black (Lion Akzo, oil absorption 360 ml / g) 7.
A semiconductive roll as a charging roll was produced in the same manner as in Example 1 except that the ratio was 5 parts by weight / 28 parts by weight of Asahi Thermal (Asahi Carbon Co., Ltd., oil absorption 28 ml / g). The charging roll manufactured in this manner had a resistance value of 10 ^5.6 ohm · cm (roller outer diameter 14 mm) between the roll nips and a rubber hardness (Asker C hardness) of 32 degrees when a DC 100 V was applied to the conductive core material. It was

As a coating material, a water-based tin oxide-dispersed urethane paint SC0100 (manufactured by Nippon Bee Chemical Co., Ltd.)
Is applied onto the surface of the above charging roll by dip coating, and at 1400C for 1
After drying for an hour, a water-based tin oxide-dispersed urethane coating material SC-0101 (manufactured by Nippon Bee Chemical Co., Ltd.) was further applied by dip coating to form a resistance layer of 40 μm.

The resistance value of the semiconductive roll after forming the resistance layer is 10 ^6.3 ohm · cm and the rubber hardness (Asker C
The hardness) was 35 degrees. The semiconductive roll having the resistance layer formed has the cells of the underlying foam layer filled, and when mounted on the charging device shown in FIG. 2, a good image without image defects such as black spots and white spots can be obtained. It was

Example 3 The foam transfer member prepared in Example 2 was spray-coated with an organic solvent binder SC-801C (manufactured by Nippon Bee Chemical Co., Ltd.), dried and cured at 120 ° C. for 1 hour, and then further coated. The above coating is spray-coated on the foam and dried and cured at 120 ° C for 1 hour.
The resistance layer was formed to have a film thickness of. The resistance value of the foam transfer member after forming the resistance layer was 10 ^8.3 ohm · cm, and the rubber hardness (Asker C hardness) was 38 degrees. The foamed transfer member obtained in this example can form a transfer roll having a high cleaning property.

[Embodiment 4] A transfer roll is constructed by coating a foamed elastic layer on a conductive core material obtained by knee-plating iron. The foam elastic layer is NBR / SBR / E
PDM was blended at a weight ratio of 30/30/40 (Japan Synthetic Rubber, NE71, TRS1507) to 2
4 parts by weight of Ketjen Black (Lion Akzo, oil absorption 360 ml / g) and Asahi Thermal (Asahi Carbon, oil absorption 28 ml /)
g) 19 parts by weight were added, 1.5 parts by weight of sulfur, Cz = 2 parts by weight of a vulcanization accelerator, 1 part by weight of stearic acid, and 5 parts by weight of a foaming agent OBSH were roll-kneaded and extruded into a columnar shape. And press-fit it into a conductive core material of iron, which is obtained by plating a cylindrical conductive member with a Ni-plated conductive member to a predetermined length, and uses a vulcanizing can (vulcanized molten steam heating and pressurizing device) at 160 ° C.
After vulcanization and foaming at (5.5 k / cm ² ) for 30 minutes, surface polishing was performed.

The transfer roll manufactured in this manner has a resistance value of 10 ^7.8 ohm · cm (roll outer diameter 18 mm) between the roll nips when DC 1 kV is applied to the conductive core material.
The rubber hardness (Asker C hardness) was 35 degrees. Further, when the voltage applied to the transfer roll was changed between 1 and 5 kV, the voltage dependency of the roll resistance showed a decrease of 0.8 digits, but no dielectric breakdown occurred within this range. An image test of this semiconductive roll was carried out with the laser beam printer shown in FIG. 2, and a good image quality was shown.

[Embodiment 5] NBR, SBR, and EPDM
The blend ratio was changed to 30/15/55 by weight.
A transfer prepared in the same manner as in Example 1 except that the blended product was used.
10 for the photo roll ^7.5ohmcm, rubber hardness (Asker
The C hardness) was 38 degrees, and good image quality was obtained.

Comparative Example 1 A transfer roll manufactured in the same manner as in Example 4 except that the NBR / EPDM blend alone was used in a weight ratio of 7: 3 had a viscosity of 10 ^8.5 ohm · cm and a rubber hardness (Asker C hardness). It was 42 degrees. The resistance value of this roll at low temperature and low humidity (10 ° C, 15% RH) is 10 ^9.3 ohm.
It became m · cm, and transfer failure occurred.

[Comparative Example 2] In the semiconductive roll according to the above-mentioned Example 4, the transfer roll produced only by EPDM (Ep33 manufactured by Japan Synthetic Rubber Co., Ltd.) as a rubber material has a resistance value of 1
0 ^8.8 ohm · cm, rubber hardness (Asker C hardness) is 4
Although it was 5 degrees, dielectric breakdown occurred at an applied voltage of 3 kV.

[0070]

EFFECT OF THE INVENTION In the semiconductive roll of the present invention, the electrically conductive foamed elastic body is a combination of NBR or EPDM and SBR.
It has a sea-island structure or a sea-island structure in which NBR and EPDM are combined with CR, and carbon black is dispersed at the interface between them, so that the increase in hardness due to crosslinking with a rubber component due to the addition of carbon black or the like increases. It is possible to reduce the amount, and it is possible to maintain a stable resistance value by adjusting the blend ratio.
The processing viscosity can be stabilized and the manufacturing variation can be suppressed.

Particularly, NBR having high polarity and low resin resistance,
By blending with SBR, dielectric breakdown at high voltage application can be prevented, and in the case of transfer roll, if there are defects such as pinholes on the photoconductor surface, excess current will flow and the current applied to the transfer roll will decrease. However, transfer defects are likely to occur, but in the semiconductive roll of the present invention, the voltage dependency is significantly improved as compared with the case of using EPDM alone, and a roller having a high dielectric breakdown voltage can be obtained. In addition, two components (NBR, E
In the case of a PDM blend), when the NBR component is large, it is easily affected by temperature and humidity and the resistance is likely to change greatly. By using a three-component system, the compatibility between the respective elastomers is increased, it is less susceptible to environmental changes, the dispersibility of the conductive particles is also improved, and uniform charging is possible.

[Brief description of drawings]

FIG. 1 is a graph showing changes in volume resistance of an ion conductive roll and a semiconductive roll of the present invention after repeated use.

FIG. 2 is a graph showing current-voltage changes of transfer current in an ion conductive roll and a semiconductive roll of the present invention.

FIG. 3 shows changes in applied voltage and current of transfer roll resistance in an ion conductive roll and a semiconductive roll of the present invention.

FIG. 4 is a graph showing a relationship between applied voltage and nip resistance in the semiconductive roll of the present invention.

FIG. 5 is a graph showing the relationship between environmental dependence and nip resistance in the semiconductive roll of the present invention.

FIG. 6 is a graph showing the carbon black dependence of the nip resistance value of the semiconductive roll according to the present invention.

FIG. 7 is a cross-sectional view showing a transfer roll as an embodiment of a conductive roll according to the present invention.

FIG. 8 is a schematic configuration diagram showing an embodiment of an image forming apparatus in which a semiconductive roll according to the present invention is applied to a transfer roll.

[Explanation of symbols]

1 photoconductor drum 2 charging roll 3 power supplies 4 Developing device 5 Pressure spring 6 Transfer roll 7 cleaning pad 8 cleaning device 9 Transfer paper 11 Conductive core material 12 Conductive foamed elastic layer 13 First resistance layer 14 Second resistance layer

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G03G 15/02 F16C 13/00 G03G 15/08 G03G 15/16 103 G03G 21/10

Claims (7)

(57) [Claims] 1. A semi-conductive roll having a conductive core material coated with a conductive foam elastic body, wherein the conductive foam elasticity is
The body has solubility parameters for NBR and EPDM and these rubbers.
CR with a solubility parameter value intermediate between the meter values
And the mixing ratio of NBR, EPDM and CR is high.
NBR / EPDM / CR = 5/5/90 to 5/9 in quantity ratio
A semiconductive roll characterized in that it is in the range of 0/5 to 90/5/5 and that two types of carbon black having different characteristics are dispersed. 2. A semi-conductive roll having a conductive core material coated with a conductive foam elastic body, wherein the conductive foam elasticity is
The body has solubility parameters for NBR and EPDM and these rubbers.
An SBR having a solubility parameter value intermediate between the meter values and
And the mixing ratio of the NBR, EPDM and SBR
Is NBR / EPDM / SBR = 5/5/90 by weight ratio
A semiconductive roll characterized in that it is in the range of 5/90/5 to 90/5/5 and that two types of carbon black having different characteristics are dispersed. 3. The semiconductive roll according to claim 1, wherein the two kinds of carbon black are composed of two kinds of carbon black having different oil absorbability. 4. The semiconductive roll according to claim 3 , wherein the two types of carbon blacks having different oil absorbencies are Ketjen black and thermal black. 5. The semiconductive roll according to claim 4 , wherein the mixing ratio of the Ketjen black and the thermal black is 1: 1 to 1: 8 by weight. 6. The semiconductive roll according to claim 1, further comprising a resistance layer on the conductive foamed elastic body. 7. The semiconductive roll according to claim 6 , wherein the resistance layer is formed by impregnating or coating a conductive paint and performing dry curing at least twice.