JP3154086B2 - Charging roller and charging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging roller mounted on an electrophotographic image forming apparatus such as a copying machine or a laser beam printer for charging a member to be charged, and a charging device.

[0002]

2. Description of the Related Art Recently, a contact-type charging device has been used as a charging device in an electrophotographic image forming apparatus such as a copying machine or a laser beam printer. In this apparatus, a charging member is brought into contact with a surface to be charged on the surface of the member to be charged, and a charging voltage is applied to the charging member, thereby uniformly charging the surface to be charged. According to this, there are advantages such as a lower voltage required for charging and a smaller amount of ozone generated as compared with a corona charging device which is a non-contact type charging device.

FIG. 10 shows a roller-shaped charging member (hereinafter referred to as "charging roller") used as a charging member of a non-contact type charging device. FIG. 1 is a longitudinal sectional view in a direction perpendicular to the axis of the charging roller.

[0004] A charging roller 100 shown in FIG. 1 includes a conductive core (shaft core) 101 also serving as a power supply electrode and a core 10.
The elastic layer 102 surrounding the periphery of the first member 1 and the coat layer 103 covering the outer peripheral surface thereof are mainly formed in a cylindrical shape as a whole.

The above elastic layer 102 is made of styrene
Solid-type members such as butadiene rubber, isoprene rubber, and silicone rubber can be used.

[0006] The coat layer 103 is composed of 1 to 3 layers,
Hydrin rubber, urethane, silicone rubber and the like are used, and a nylon resin is particularly used for the uppermost layer.

When the charging roller is brought into contact with, for example, the surface of the photosensitive drum (the surface to be charged) to apply an AC bias to charge the surface of the photosensitive drum, the charging roller and the surface of the photosensitive drum are charged. It is known that noise (charging noise) is generated between the two.

As one of measures for reducing the level of the charging noise, there is known a measure for packing a weight or the like inside the photosensitive drum. However, there are disadvantages in that the configuration of the photosensitive drum itself is complicated, and the photosensitive drum is heavy and the driving torque is increased.

Therefore, as a measure to eliminate the charging noise without filling the photosensitive drum with a weight or the like, the elastic layer 102 is
A roller having a configuration in which a sponge layer is formed instead of a solid type member and the surface of the sponge layer is covered with a resin tube, a so-called soundless charging roller, has been developed and put into practical use.

This soundless charging roller is formed by foaming and vulcanizing a base rubber (foam base) when forming a sponge layer.

[0011]

However, the above-mentioned soundless charging roller, that is, a charging roller having a structure in which the surface of a sponge layer is covered with a resin tube, has a drawback that it is costly due to the large number of manufacturing steps. there were.

In order to solve this drawback, a method of extruding a base rubber and at least one coat layer at the same time without a resin tube and foaming and vulcanizing them in a mold to form a sponge layer has been studied. .

According to this method of forming the charging roller, although the number of steps can be reduced, the foaming and vulcanization of the base layer rubber in the mold, which has been a problem in the conventional example, is not possible. The problem that air bubbles accumulate and generate air bubbles cannot be solved.

For this reason, if the escape path of the gas is insufficient, the gas may accumulate between the sponge layer and the core metal and large bubbles may be generated. Insufficient power supply to the layer may cause poor charging on the surface of the photosensitive drum, and further, poor image quality.

Also, in order to secure a sufficient gas escape route,
When a groove is provided on the inner surface of the base rubber, if the groove is too deep, the flow velocity at the time of extruding the base rubber is different between the grooved part and the part without the groove, and the base rubber surface after the extrusion is Irregularities corresponding to the grooves are formed inside. These irregularities also remain on the surface of the sponge layer formed after foaming and vulcanization, and a coat layer is laminated to fill the irregularities.
For this reason, the thickness unevenness of the coat layer increases, and uneven charging tends to occur in the circumferential direction of the photosensitive drum surface. When the uneven charging occurs, black stripes (hereinafter, referred to as “banding”) are generated on the image.

Therefore, the first aspect of the present invention is simple to manufacture,
It is an object of the present invention to provide a charging roller capable of eliminating thickness unevenness of a coat layer.

Another object of the present invention is to eliminate uneven charging due to uneven thickness of the coating layer and prevent occurrence of image defects such as banding due to uneven charging when mounted on an image forming apparatus. It is an object of the present invention to provide a charging device adapted to perform the charging.

[0018]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a structure in which a conductive shaft core is surrounded by a conductive cylindrical foam member. In the charging roller, an exhaust groove is provided on an inner peripheral surface of the foamed base material before foaming and sulphidation, which becomes the foamed member after foaming and sulphidation, as an escape path for gas during foaming and sulphidation.

It is preferable that the exhaust groove is formed along the axial direction of the shaft core, and is opened at an end face of the foam base material.

It is further preferable that the exhaust groove is formed along the axial direction of the shaft core, and is opened at both end surfaces of the foamed base material.

[0021] A plurality of the exhaust grooves may be formed along the circumferential direction of the inner peripheral surface of the foamed base material.

Next, in a charging roller constituted by surrounding a conductive shaft core with a conductive cylindrical foam member, a gas escape path at the time of foaming sulfuration is formed on the outer peripheral surface of the shaft core. An exhaust groove is provided.

It is preferable that the exhaust groove is formed along the axial direction of the shaft core and is opened at an end face of the foam base material.

[0024] It is further preferable that the exhaust groove is formed along the axial direction of the shaft core and is opened at both end surfaces of the foam base material.

[0025] A plurality of the exhaust grooves may be formed along the circumferential direction of the outer peripheral surface of the shaft core.

To increase the surface roughness of the outer peripheral surface of the shaft core;
You may do so.

[0027] It is also possible to provide a coat layer surrounding the surface of the foamed member after the foamed sulfurization.

The shaft core is arranged at the center of a cylindrical mold having a rough inner peripheral surface, and the foamed base material or the foamed base material is coated between the mold and the shaft core. After extruding the layer, the foamed substrate may be foamed and sulfurized in the mold to form the foamed member.

With respect to the thickness D of the coat layer after the foaming and sulfurization, a relation of D _max <2D _min is established between the thickness D _max of the thickest portion and the thickness D _min of the thinnest portion of the coat layer. May be formed so that

It is preferable that the depth H of the exhaust groove and the thickness D of the coating layer are formed so as to satisfy a relationship of 2H <D.

As the thickness D of the coat layer, the average thickness D _{A of} the coat layer or the thickness D of the thinnest part of the coat layer
can be _min .

[0032] The foamed member may be constituted by a sponge.

Next, the charging device includes any one of the above-described charging rollers, and a power supply that applies a superimposed voltage obtained by superimposing an AC voltage and a DC voltage of 1000 Hz or more to the charging roller.
Wherein the charging roller is disposed in contact with the surface to be charged of the member to be charged, and the superposed voltage is applied to the charging roller to uniformly charge the surface to be charged.

[Operation] The main operation of the above configuration will be described.

By providing exhaust grooves on the inner peripheral surface of the foamed base material or on the outer peripheral surface of the shaft core, gas generated during foam vulcanization of the foamed substrate can be released through these exhaust grooves. To prevent bubbles from accumulating and forming bubbles, resulting in uneven resistance.

Further, by making the surface roughness of the outer peripheral surface of the shaft core and the inner peripheral surface of the mold rough, gas can be released from these uneven portions.

If the depth of the groove formed on the inner surface of the base rubber is set so as to maintain the thickness unevenness of the coat layer under the above conditions, uneven charging caused by the uneven thickness of the coat layer is controlled, and banding is prevented. Can be prevented.

[0038]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic configuration of a laser beam printer as an image forming apparatus to which a charging roller and a charging device according to the present invention are applied.

The image forming apparatus shown in FIG. 1 includes a drum-type photosensitive member (hereinafter referred to as "photosensitive drum") 11 as a member to be charged (image carrier). The photosensitive drum 11 is formed by providing a photosensitive layer 11b of, for example, OPC on an outer peripheral surface of a conductive base 11a formed in a cylindrical shape.
The image forming apparatus is rotatably supported by an image forming apparatus main body (not shown), and is rotationally driven in a direction of an arrow R1 by a driving unit (not shown).

Around the photosensitive drum 11, a charging roller (contact charging member) 12, an exposure unit 13, a developing device 14, a transfer roller 15, and a cleaner 1 are arranged in this order along the rotation direction.
6 are provided. Further, a fixing device 17 is disposed downstream of the transfer roller 15 in the transport direction (the direction of the arrow K1) of the transfer material P such as paper. Further, a charging power source 18 for applying a superimposed voltage of a DC voltage and an AC voltage is connected to the charging roller 12, and the developing device 14
Is connected to a developing power supply 19 for applying a superimposed voltage of a DC voltage and an AC voltage, and a transfer power supply 20 for applying a DC voltage to the transfer roller 15. On the upstream side and the downstream side of the transfer roller in the transport direction of the transfer material P, transport guides 21 and 22 for guiding the transfer material P are disposed, respectively. The charging roller 12 according to the present invention will be described later in detail.

The operation of the above-described image forming apparatus will be briefly described. The photosensitive drum 11 is driven by an arrow R1 by driving means.
It is rotationally driven at a predetermined process speed in the direction. The surface of the photosensitive drum 11 (the surface to be charged) is uniformly charged by applying a charging voltage from a charging power supply 18 to a charging roller 12 which is disposed in contact therewith and driven to rotate. The surface of the charged photosensitive drum 11 is exposed by exposure light from the exposure unit 13 in accordance with image information, and the charge of the light irradiation unit is removed to form an electrostatic latent image. The developing device 14 to which the developing voltage is applied by the developing power source 19
Toner is adhered to the toner and is developed as a toner image. The toner image on the photosensitive drum 11 is transferred to a transfer roller 15
By applying a transfer voltage by the transfer power supply 20,
The image is transferred onto the transfer material P conveyed while being guided by the conveyance guide 21.

The transfer material P after the transfer of the toner image is conveyed in the direction of arrow K1 along the conveyance guide 22, and the unfixed toner on the surface is heated and pressed by the fixing device 17 to be fixed.
Thereafter, the sheet is discharged outside the image forming apparatus main body. On the other hand, the transfer residual toner remaining on the surface of the photosensitive drum 11 after the transfer of the toner image is removed by the cleaner 16 and used for the next image forming process.

Next, FIG. 2 shows a charging roller 1 according to the present invention.
2 is shown. FIG. 3 is a longitudinal sectional view in a direction perpendicular to the longitudinal direction of the charging roller 12.

The charging roller 12 shown in FIG. 1 has a conductive core (shaft core) 12a having a diameter of 8 mm also serving as a power supply electrode, and ethylene propylene rubber and urethane so that the surface of the core 12a has a diameter of 14 mm. A sponge layer (foamed member) 12b formed by foaming and vulcanizing rubber, hydrin rubber, or the like. The appropriate value of the thickness of the sponge layer 12b is 2.0
When the layer thickness is large, the resistance value increases, and when the layer thickness is small, the hardness does not sufficiently decrease.

The coat layer (surface layer) 12c laminated on the surface of the sponge layer 12b has one to three layers and is made of hydrin rubber, urethane rubber, nylon resin or the like. The appropriate value of the thickness D of the coat layer 12c is 100 to 1000 μm, and the resistance value of the entire coat layer 12c is about 10 ⁵ to 10 ⁹ Ω · cm. Further, it is preferable that the resistance value of the coat layer 12c increases as approaching the surface layer. In the measurement of the resistance value of the above-mentioned coat layer 12c, first, a coat layer is formed in a film shape, and this is placed on an aluminum plate. Then, a DC voltage of 500 V is applied between the coat layer and the aluminum plate, and the resistance at that time is measured.

In general, the coat layer 12c has a function of protecting the surface of the charging roller 12 and a sponge layer 12b.
The sponge layer 12b has a function of preventing the oil from seeping out of the sponge layer 12b, eliminating the uneven resistance of the sponge layer 12b, and making the resistance uniform, and a function of increasing the pressure resistance against the photosensitive drum 11 at the time of contact.

In producing the charging roller 12, as described later, the base rubber and the coating layer 12c are extruded and then foamed and vulcanized in a mold. If the escape path of the gas generated during the foaming vulcanization is insufficient, a longitudinal sectional view in the longitudinal direction of FIG. 3 (however, the figure shows the core metal 12a and the sponge layer 12).
b shows only the upper half) as shown in FIG.
The bubble A remains as a gas reservoir between the a and the sponge layer 12b. Due to the bubbles A, a gap is formed between the cored bar 12a and the sponge layer 12b, so that a direct current is difficult to flow, and the surface potential of the photosensitive drum 1 at the time of charging is reduced. I do.

In order to prevent the generation of the bubbles A which cause the above-mentioned image defects, it is effective to secure a space for escaping gas generated in the mold during foam vulcanization. This space can be provided, for example, on at least one of the inner peripheral surface of the base rubber of the charging roller 12 before foam vulcanization, the outer peripheral surface of the cored bar 12a, and the inner peripheral surface of the mold. Details will be described later in Examples.

As a method of providing a space serving as the above-mentioned escape route, an exhaust groove is dug in the inner peripheral surface of the base rubber or the outer peripheral surface of the cored bar 12a, or the outer peripheral surface of the cored bar 12a or the inner peripheral surface of the mold is formed. A method of positively increasing the surface roughness can be considered.

First, when digging the former exhaust groove, the depth of the exhaust groove is preferably set to 0.1 to 1.5 mm. More preferably, it is 0.5 to 1.0 mm. The shape and the position of the exhaust groove will be described later in detail.

In the latter case where the surface roughness is increased, it is preferable that the roughness (see JIS B0601) be 0.1 to 0.5 mm on a ten-point average.

However, even if the gas escape path between the cored bar 12a and the sponge layer 12b is eliminated by ensuring a sufficient gas escape path, as shown in FIG.
When unevenness occurs on the surface and uneven thickness occurs in the coat layer 12c, the resistance value differs between the thick portion and the thin portion of the coat layer 12c, and the AC resistance and the DC resistance of the charging roller 12 change due to the rotation. , And changes periodically, causing uneven charging.

In particular, when the AC voltage applied to the charging roller 12 is under constant current control, the effective value of the AC voltage of the charging roller is as shown in FIG. In the figure, T is a cycle of one rotation of the charging roller 12, and A
_max and A _min indicate the maximum value and the minimum value of the effective value, respectively. Maximum value A _max of the effective value corresponds to the thickest part of the coat layer 12c (hereinafter referred to as "thickest portion"), the minimum value A _min, the corresponding to the thinnest portion (hereinafter referred to as "the thinnest part") I do. The frequency of the effective value fluctuation is the same as the number of irregularities of the sponge layer generated when the base rubber is extruded and formed on the sponge layer 12c, and is determined by the number of irregularities. Thus, when the effective value of the AC voltage oscillates,
Since a direct current flowing through the photosensitive drum 11 changes due to a discharge generated between the charging roller 12 and the photosensitive drum 11, uneven charging on the surface of the photosensitive drum 11 becomes remarkable. For this reason, the drum potential fluctuates in accordance with the thickness unevenness of the coat layer 12c, and density unevenness and banding having the same cycle as the thickness unevenness of the coat layer 12c cause an image defect on an image after image formation. appear. Note that these image defects are 10
It becomes remarkable when a charging frequency of 00 Hz or more is applied and in a low-temperature and low-humidity environment.

In the present embodiment, the thickness of the coat layer 12c is appropriately set in order to prevent such defects.
That is, unevenness in the thickness of the coat layer 12c after foaming and vulcanization is reduced, and uneven charging is reduced. In particular,
When the thickness of the thickest portion of the coat layer 12c is D _max and the thickness of the thinnest portion is D _min , the coat layer 12c is formed so that the relationship of D _max <2D _min is satisfied.

For example, the transfer roller 12 having the above configuration is mounted on a laser beam printer,
When 0 Hz is applied, the coating layer 12 of the transfer roller 12
The thickness of c is, if a relationship of D _max = 2D _min, the deflection of the effective value of the AC voltage becomes approximately maximum 500V, became possible to generate a banding on the image.

If the relationship of 2H <D is not satisfied between the depth H of the exhaust groove provided at the time of extrusion and the thickness D of the sponge layer 12c after foaming and vulcanization, the base layer at the time of extrusion is not satisfied. Of rubber,
The difference in the flow velocity between the exhaust groove portion and the non-exhaust groove portion becomes large, which causes irregularities to be formed on the base rubber surface. Therefore, the coat layer 12c is extruded so as to fill the irregularities on the surface of the base rubber, and uneven thickness occurs. In order to prevent this, the above-mentioned relationship 2H <D is established between the depth H of the exhaust groove and the thickness D of the sponge layer 12c.

In this case, as the thickness D of the sponge layer 12c, the average thickness of the sponge layer can be applied, but more preferably, the thickness D _min of the thinnest portion is applied. <Embodiment 1> FIG. 6 further details the layer structure of the transfer roller 12 as the contact charging member described in the first embodiment. This figure is a longitudinal sectional view in a direction perpendicular to the cored bar 12a.

In this embodiment, the photosensitive drum of the organic photosensitive member (OPC) having a diameter of 30 mm was rotated at a process speed (peripheral speed) of about 30 mm / sec, and the charging roller 12 was brought into contact with the photosensitive drum. An AC voltage having a frequency of 360 Hz and a DC voltage of about -700 V were applied to the charging roller 12 in a superimposed manner.

The charging roller 12 shown in FIG. 6 has three layers. An elastic layer 12b and coat layers 12c ₁ and 12c ₂ were sequentially laminated on a conductive core metal 12a also serving as a power supply electrode, and were formed to have a diameter of 14 mm and a length of 310 mm as a whole. The charging roller 12 after simultaneous extrusion an elastic layer 12b and the coating layer 12c _1, foamed vulcanized in a mold,
After that, the coat layer 12c ₂ are roll coating.

In the configuration of FIG. 6, the shaft center 12a has a diameter of 8
mm nickel-plated steel rod, and the elastic layer 12b
The thickness is 2.5 mm, ethylene propylene rubber resistance foamed vulcanization of about 10 ⁶ Ω · cm, further coating layer 12c ₁ is a thickness 250 [mu] m, the resistance value of 10 ⁷ Omega ·
cm of hydrin, coat layer 12c ₂ is 10μm thickness
And a nylon resin having a resistance value of 10 ⁸ Ω · cm.

Here, the coat layer 12c ₁ is the elastic layer 12b
In addition to preventing the oil from seeping out of the elastic layer 12b, the resistance of the elastic layer 12b is eliminated and the resistance is made uniform. On the other hand, the coating layer 12c ₂ has a function of increasing the durability against the photosensitive drum, but also serve to protect the surface of the charging roller 12 while preventing the photosensitive drum contamination by coating layer 12c _1.

In this embodiment, the charging roller 12 is manufactured as follows. The core metal 12a is arranged at the center, and the cylindrical mold 30 is arranged at the outermost periphery. And therebetween, the foam vulcanization sponge layer (elastic layer) 12b and coating layer 12c ₁ and comprising a base layer rubber (foam substrate) 13b, and also the coating layer 12c ₂ foamed vulcanized coating layer 1
3c is foamed and vulcanized. At this time, the coat layer 13c is arranged close to the inner peripheral surface of the mold 30, and a large space is left between the inner peripheral surface of the base rubber 13b and the core metal 12a. Thereby, at the time of foam vulcanization, the base layer rubber 13b and the coat layer 13c
Expands in the direction of the arrow toward the center metal core 12a.
For this reason, the coat layer 13c can maintain a uniform state without receiving pressure during foaming, and the base layer rubber 13b can smoothly and uniformly foam without receiving the reaction of the coat layer 13c.

In this embodiment, an exhaust groove 51 having a depth H of about 1 mm is formed on the inner peripheral surface of the base rubber 13b before foaming and vulcanization.
The books were provided at equal intervals in the circumferential direction of the inner peripheral surface. This exhaust groove 51
Is formed along the axis 12a over the entire length of the base rubber 13b in the longitudinal direction, and is opened at both ends in the longitudinal direction of the base rubber 13b. That is, it penetrates the base rubber 13b in the longitudinal direction. In this embodiment, the thickness D (see FIG. 6) of the sponge layer 12b after foaming and vulcanization is 2.5 m.
m, the relationship 2H <D described above holds between the depth H of the exhaust groove and the thickness D of the sponge layer 12b, and the relationship between the exhaust groove portion and the non-exhaust groove portion of the base rubber 13b at the time of extrusion is obtained. The flow velocity difference between the base rubber 13b and the base rubber 13b after extrusion is reduced. In addition, the coat layer 1
The thickness D of the 2c _1, the thickness D _max of the thickest portion is 300 [mu] m,
The thickness D _min of the thinnest part has become a 180 [mu] m, the thickness of the thickest portion of the coating layer 12c ₁ D _max and thickness D _min of the thinnest portion
Between the, following relationship holds for D _max <2D _min.

Therefore, an escape path for gas generated during foam vulcanization was ensured, the generation of gas accumulation was prevented, and the close contact between the cored bar 12a and the sponge layer 12b was sufficiently achieved. Therefore, defective charging caused by gas accumulated in the gap between the cored bar 12a and the sponge layer 12b is prevented, and further, occurrence of defective images due to the defective charging is prevented. Further, since the thickness unevenness of the coat layer 12b is small, occurrence of banding due to uneven charging can be prevented. <Embodiment 2> In this embodiment, in the charging roller 12,
The exhaust groove 52, which serves as an escape path for gas during foam vulcanization, is
a on the outer peripheral surface. The other configuration except that the position of the exhaust groove 52 is different from that of the first embodiment is the same as that of the charging roller 12 of the first embodiment.
The detailed description of the configuration is omitted.

In this embodiment, an organic photoreceptor (OP
C), a photosensitive drum having a diameter of 25 mm
The photosensitive drum was rotated at a process speed (peripheral speed) of / sec, and the charging roller 12 was brought into contact with the photosensitive drum. The charging roller 12 has a frequency of 300 Hz and a peak-to-peak voltage of 1
A voltage was applied using a constant voltage controlled high voltage on which an AC voltage of 800 V _PP and a DC voltage of about -700 V were superimposed.

The charging roller 12 in this embodiment is the same as that shown in FIG.
As shown in the figure, twelve exhaust grooves 52 are provided on the outer peripheral surface of the cored bar 12a so as to equally divide it in the circumferential direction. Each exhaust groove 52 has a depth H of about 0.5 mm and is formed along the axial direction of the metal core 12a. In this case, unlike the case of the first embodiment, since the exhaust groove is not formed in the base rubber 13b, it is possible to prevent the occurrence of unevenness due to the flow velocity difference of the base rubber 13b at the time of extrusion. the thickness D of 12c _1, the thickness D _max of the thickest portion is 300 [mu] m, the thickness D _min of the thinnest part has become a 280 .mu.m, satisfy the relationship of the above, D _max <2D _min.

Therefore, a gas escape path during foaming vulcanization can be secured, so that the formation of a gas reservoir is prevented, the core 12a and the sponge layer 12b are sufficiently adhered to each other, and image defects due to poor charging occur. Was prevented. The thickness unevenness of the coating layer 12c _1, the occurrence of banding due to charging unevenness because they are suppressed was prevented. <Embodiment 3> In Embodiment 3, the core metal 1 of the charging roller 12 is used.
The surface roughness of the outer peripheral surface 12d of 2a (see FIG. 9) is positively increased. The configuration of the charging roller 12 after the foaming and vulcanization is the same as that of the first and second embodiments shown in FIG. 6, and the description is omitted. Further, the extruded position of the base rubber 13b is not the position shown in FIG.
And the position shown in FIG.

In this embodiment, a photosensitive drum 11 having a diameter of 30 mm and having an organic photoreceptor (OPC) on its surface is moved for about 90 m.
The photosensitive drum 11 was rotated at a process speed (peripheral speed) of m / sec. Then, a voltage obtained by superimposing an AC voltage of 900 Hz and a DC voltage of about -700 V was applied to the charging roller 12.

In the charging roller 12 of this embodiment, the outer peripheral surface 12d of the metal core 12a is roughened by an arbitrary method so that the ten-point average roughness is 500 μm. The unevenness of the outer peripheral surface 12d of the cored bar 12a serves as an escape route for gas during foaming vulcanization. Therefore, the occurrence of gas accumulation is prevented, and the cored bar 12a and the sponge layer 12b are sufficiently adhered to each other, resulting in poor charging. Can prevent the occurrence of image defects.

Also, in this case, unlike the case of the second embodiment, unlike the case where the exhaust groove is formed in the base rubber 13b, the base rubber 13b is not deformed. by it is possible to prevent the occurrence of unevenness, the thickness D of the coating layer 12c _1, the thickness D _max is 300μm in the thickest portion, the thickness D _min of the thinnest portion is 280μm
Becomes Since these values satisfy the relationship of the foregoing, D _max <2D _min, the thickness irregularity of the coating layer 12c ₁ is suppressed, the occurrence of banding due to charging unevenness was prevented. <Embodiment 4> In Embodiment 4, as shown in FIG. 9, the surface roughness of the inner peripheral surface 30a of the mold 30 is positively increased. The configuration of the charging roller 12 after the foaming and vulcanization is the same as that of the first and second embodiments, and therefore, the description thereof is omitted.

In the present embodiment, a photosensitive drum 11 having a diameter of 30 mm and having an organic photoreceptor (OPC) on its surface is moved for about 90 m.
The photosensitive drum 11 was rotated at a process speed (peripheral speed) of m / sec. Then, a voltage obtained by superimposing an AC voltage of 900 Hz and a DC voltage of about -700 V was applied to the charging roller 12.

The charging roller 12 used in this embodiment is composed of three layers, and the elastic layer 12b is formed of carbon-dispersed urethane rubber having a thickness of 3.0 mm and a resistance of about 10 ⁶ Ω · cm. coat layer 12c ₁ has a thickness 250 [mu] m, the resistance value 1
0 ⁷ Ω · cm of carbon-dispersed urethane acrylic, also coat layer 12c ₂ has a thickness 10 [mu] m, the carbon in the resistance 10 ⁸ Ω · cm, formed by a titanium oxide dispersion of the nylon resin.

In this embodiment, as shown in FIG.
The charging roller 12 is extruded between the metal core 12 a and the mold 30. The inner peripheral surface of the mold 30 has a ten-point average roughness of 100
The thickness is reduced to about μm, a gap is formed between the coat layer 13c and the mold 30, and gas between the coat layer 13c and the mold 30 is released. Note that any of the methods described in the first to third embodiments can be adopted as a method for venting the gas between the base rubber 13b and the metal core 12a.

In this case, after the foam vulcanization, the sponge layer 13b
Since the distance between the base rubber 13b and the metal core 12a forming the base rubber 13b is smaller than that in the above-described first and second embodiments, the first embodiment in which the base rubber 13b is provided with an exhaust groove for degassing.
Even when the method described above is adopted, the depth of the exhaust groove can be reduced. Accordingly, since the occurrence of unevenness can be prevented by the flow rate difference between the base layer rubber 13b during extrusion, eliminating thickness unevenness of the coating layer 12c ₁ of the foam after vulcanization of the thickest portion thickness D _max and the thinnest portion The thickness D _min can satisfy the relationship of D _max <2D _min .

Therefore, an escape route for gas generated during foam vulcanization is ensured, and the generation of gas reservoirs is prevented.
Adhesion between the core bar 12a and the sponge layer 12b is sufficiently achieved, and it is possible to prevent the occurrence of defective charging due to the bubbles A, and further to the occurrence of defective images due to the defective charging. Further, since is also suppressed thickness unevenness of the coating layer 12c _1, the occurrence of black streaks due to charging unevenness (banding) was prevented.

Before foaming and vulcanization of the base rubber 13b, a method of bringing the core metal 12a into close contact with the base rubber 13b is also conceivable. In this case, the coat layer 13c is used as the base rubber 13b.
The base rubber 13b is also subjected to pressure during the foaming of the
Due to the reaction of c, the thickness of the coat layer 13c tends to vary. <Embodiment 5> A photosensitive drum having a diameter of 30 mm having an organic photosensitive member (OPC) on its surface was rotated at a process speed (peripheral speed) of about 110 mm / sec. Charging roller 12 (see FIG. 6)
The same charging roller as described above was contacted. Then, an AC voltage having a frequency of 1000 Hz and approximately -700
A DC voltage of V was superimposed and applied, and applied to a laser beam printer that performs constant voltage control at about 1400 μA.

At this time, the exhaust grooves cut in the inner peripheral surface of the base rubber have a depth H of about 0.5 mm and 20 pieces. In the charging roller 12 of the first embodiment, the depth H of the exhaust groove is 1
mm, and the number of exhaust grooves was 12. As mentioned above,
The depth H of the exhaust groove of the charging roller is 0.5 mm, and the number is 20.
In the case of a book, the thickness D of the coat layer is the thickness D of the thickest part.
_{The maximum} is 250 μm and the thickness D _min of the thinnest part is 220 μm, which satisfies the above-mentioned relationship of D _max <2D _min .

As described above, as the depth H of the exhaust groove is reduced, the thickness unevenness of the coat layer can be reduced.
When the depth of the exhaust groove is reduced, the number of exhaust grooves must be increased because the escape route between the cored bar and the sponge layer is insufficiently secured and the possibility of air bubbles increases. Ingenuity is needed.

According to this embodiment, no air bubbles are generated between the core metal and the sponge layer, and the unevenness of the thickness of the coat layer is reduced. Therefore, even in a low-temperature and low-humidity environment where the AC voltage tends to increase. The generation of black streaks (banding) due to unevenness can be prevented, and the occurrence of image defects due to defective charging caused by bubbles in the gap between the core metal and the sponge layer can also be prevented.

In the second embodiment, twelve exhaust grooves 52 having a depth H of 0.5 mm are provided on the outer peripheral surface of the cored bar 12a so as to equally divide the circumferential direction. Similarly to the fifth embodiment, when the depth H of the exhaust groove 52 is made shallower than that and the number is increased, almost the same effect as the fifth embodiment can be obtained.

[0082]

As described above, according to the charging roller of the first aspect of the present invention, the gas generated when the foamed base material is foamed and vulcanized to form the foamed member surrounding the shaft core is discharged to the exhaust grooves and the like. Since unevenness when the surface roughness is increased can be released by unevenness, it is possible to prevent non-uniform resistance from being generated due to accumulation of non-exhausted gas and bubbles.

According to the charging device of the second aspect of the present invention, it is possible to prevent uneven charging due to bubbles and uneven charging of the member to be charged due to uneven thickness of the coating layer. Therefore, when this charging device is mounted on an image forming apparatus such as a copying machine, it is possible to prevent black streaks (banding) due to uneven charging.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a laser beam printer equipped with a charging device according to the present invention.

FIG. 2 is a longitudinal sectional view of a charging roller according to the present invention in a direction perpendicular to an axis.

FIG. 3 is an axial longitudinal sectional view showing a state in which bubbles during foaming and vulcanization are accumulated between a cored bar and a sponge layer.

FIG. 4 is a longitudinal sectional view showing a state in which thickness unevenness occurs in a coat layer.

FIG. 5 is a view showing a periodic fluctuation of an AC voltage effective value when thickness unevenness occurs in a coat layer.

FIG. 6 is a longitudinal sectional view in a direction perpendicular to an axis, showing a configuration of the charging roller of the first embodiment.

FIG. 7 is a vertical cross-sectional view of the charging roller of Example 1 in a direction perpendicular to an axis, showing a configuration before foam vulcanization.

FIG. 8 is a vertical cross-sectional view of the charging roller of Example 2 in a direction perpendicular to an axis, showing a configuration before foam vulcanization.

FIG. 9 is a vertical cross-sectional view of the charging roller of Example 4 showing a configuration before foam vulcanization in a direction perpendicular to an axis.

FIG. 10 is a vertical cross-sectional view of a configuration of a conventional charging roller before foam vulcanization, taken in a direction perpendicular to an axis.

[Explanation of symbols]

11 a member to be charged (photosensitive drum) 12 charge roller 12a axial (metal core) 12b foamed member (sponge layer) 12c, 12c _1, 12c ₂ coat layer 12d axis peripheral surface 13 exposing unit 13b foaming base material (base rubber 13c Coat layer 14 Developing device 15 Transfer roller 16 Cleaner 17 Fixing device 18 Charging power supply 30 Mold 30a Inner peripheral surface of mold 51 Exhaust groove 52 Exhaust groove A Bubble D Coat layer thickness _{Dmax Thickest} portion of coat layer Thickness D _min Thickness of the thinnest part of the coating layer

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-121014 (JP, A) JP-A-7-92776 (JP, A) JP-A-7-43984 (JP, A) 320554 (JP, A) JP-A-2-110045 (JP, A) JP-A-60-256640 (JP, A) JP-A-54-88968 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/02 G03G 15/16 F16C 13/00-15/00

Claims (17)

(57) [Claims] 1. A charging roller in which a conductive shaft core is surrounded by a conductive cylindrical foam member, wherein the foamed base material before the foam sulfuration becomes the foam member after the foam sulfuration. A charging roller, characterized in that an exhaust groove is provided on the inner peripheral surface as an escape path for gas during foaming sulfurization. 2. The charging roller according to claim 1, wherein the exhaust groove is formed along an axial direction of the shaft core, and is opened at an end surface of the foamed base material. 3. The charging roller according to claim 1, wherein the exhaust groove is formed along an axial direction of the shaft core, and is opened at both end surfaces of the foamed base material. 4. The exhaust groove according to claim 1, wherein a plurality of the exhaust grooves are formed along a circumferential direction of an inner peripheral surface of the foamed base material.
Item. 5. A charging roller comprising a conductive shaft core surrounded by a cylindrical foam member having conductivity, wherein an outer peripheral surface of the shaft core has a gas escape path at the time of sulfurization. A charging groove provided with an exhaust groove. 6. The charging roller according to claim 5, wherein the exhaust groove is formed along an axial direction of the shaft core, and is opened at an end face of the foamed base material. 7. The charging roller according to claim 5, wherein the exhaust groove is formed along an axial direction of the shaft core, and is opened at both end surfaces of the foamed base material. 8. The method according to claim 5, wherein a plurality of the exhaust grooves are formed along a circumferential direction of an outer peripheral surface of the shaft core.
Item. 9. The method according to claim 1, wherein a surface roughness of an outer peripheral surface of the shaft core is increased.
Item. 10. The method according to claim 1, further comprising a coat layer surrounding a surface of the foamed member after the foaming and sulfurization.
Item. 11. The foam base, or the foam base, between the mold and the shaft center, wherein the shaft core is disposed at the center of a cylindrical mold having a rough inner surface. 11. The charging roller according to claim 1, wherein, after extruding the coating layer, the foamed base is foamed and sulfurized in the mold to form the foamed member. 12. . The thickness D of 12. The coating layer after the foaming sulfide, between the thickness D _min thickness D _max and the thinnest portion of the thickest portion of the coating layer, D _max <2D _min The charging roller according to claim 10, wherein the charging roller is formed to satisfy the following relationship. 13. The method according to claim 10, wherein the depth H of the exhaust groove and the thickness D of the coating layer are formed so as to satisfy a relationship of 2H <D. 14. The charging roller according to any one of 13). 14. The charging roller according to claim 13, wherein the thickness D of the coating layer is an average thickness of the coating layer. 15. The charging roller according to claim 13, wherein a thickness D of the coat layer is a thickness D _min of a thinnest portion of the coat layer. 16. The charging roller according to claim 1, wherein the foam member is a sponge. 17. The charging roller according to claim 1, further comprising: a power supply for applying a superimposed voltage obtained by superimposing an AC voltage and a DC voltage of 1000 Hz or more to the charging roller. A contact charging device, wherein a charging roller is disposed in contact with a surface to be charged of a member to be charged, and the superposed voltage is applied to the charging roller to uniformly charge the surface to be charged.