JP2008076602A - Electrifying roller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrifying roller which can obtain a uniform electrifying property over a long period of time while being a roller type with light-weight and flexible two-layered structure and by which white dots or black dots are not caused even when a half tone image is printed. <P>SOLUTION: The electrifying roller 16 is provided with: a first conductive elastic layer 54 supported on a metal core 53 in a center; and a second conductive elastic layer 55 provided on the first conductive elastic layer 54. The first conductive elastic layer 54 is composed of a nitril-based foamed rubber and conductive carbon black. The second conductive elastic layer 55 is composed of epichlorohydrin-based rubber and the conductive carbon black and is provided with a surface treated layer subjected to surface treatment with a surface treatment liquid containing isocyanate on the surface. A relationship of "-0.30≤D2-D1≤-0.15" exists between an average outer diameter D1 (mm) of the first conductive elastic surface 54 and an average inner diameter D2 (mm) of the second conductive elastic layer 55. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a charging roller that prevents discharge that causes white spots and black spots that are likely to occur in a halftone image while being a simple and lightweight double roller type.

  2. Description of the Related Art Conventionally, an electrophotographic printer that forms characters and images on a sheet by transferring and fixing a toner image formed on a photoreceptor onto the sheet is known. Usually, the above photoreceptor is a drum type, and an electrostatic latent image is formed on the peripheral surface by an exposure head, the electrostatic latent image is converted into a toner image by a developing device, and the toner image is transferred by a transfer device. Transferred onto paper.

  Prior to this formation of the electrostatic latent image, initialization charging by a charging device is always performed. In this initialization charging, discharge-type non-contact chargers and brush-type contact chargers were used in the past, but the discharge type has an adverse effect on the surrounding environment, and the brush type achieves uniform charging. Each of them is problematic in that it is difficult, and at present, almost all roller-type contact chargers, that is, charging rollers, are used.

In the method using this charging roller, the roller is usually a rubber roller type composed of a conductive thick rubber layer fitted on a shaft (core metal). However, since this is expensive, the roller is configured at low cost. For this purpose, a lightweight, double-structured charging roller constructed by covering a conductive foam roller that is externally fitted to a shaft with a conductive tube and bonding them together with an adhesive in the non-image forming areas at both ends. The method used is known. (For example, refer to Patent Document 1.)
Generally, as the conductive foam used for the charging roller, conductive foam made of polyurethane, silicone rubber, nitrile rubber or the like has been used. However, since the charging roller is required to have a non-contaminating property to the photosensitive drum and its own conductivity, various coating layers and surface treatment layers are formed on the surface of the elastic layer made of the conductive foam. Alternatively, a double structure using a coated tube or the like is employed.

Further, in the above-described lightweight dual structure charging roller, when both ends of the charging roller are urged toward the photosensitive drum to enhance the charging property, pressure is applied to both ends rather than the center, and the center and both ends are charged. In order to eliminate the occurrence of unevenness in charging property at the portion, a method is known in which an adhesive is applied from the end portion to a predetermined range from the image forming region to increase the electrical resistance of the end portion. (For example, see Patent Document 2.)
Further, among these double structure types, a conductive foam layer made of nitrile rubber as a first conductive elastic layer on a core metal as a charging roller having a small discharge sound and excellent chargeability A charging roller has been proposed in which a coating layer made of epichlorohydrin rubber is formed as a second conductive elastic layer. (For example, refer to Patent Document 3.)
JP-A-11-125956 (paragraphs [0031] to [0033], FIG. 5) JP 2001-22251 (paragraphs [0054] to [0058], FIG. 5) Japanese Patent Laying-Open No. 2005-292600 ([Summary], FIG. 1)

  By the way, in recent years, electrophotographic printers using toner as described above have various technical aspects in which the printing speed was about 13 sheets / second when A4 size paper was laid down at the beginning. Due to the improvement, a printing speed of 29 sheets / second has become normal, and the printing speed has been increased to more than double the original printing speed.

  However, when the printing speed is increased in this way, there is no problem with the rubber roller type having a thick rubber single layer structure. However, the conductive foam roller and the conductive tube as described in Patent Documents 1 to 3 described above. In the case of the lightweight double structure, since only the both end portions are bonded, there arises a problem that even when used for a long time, the conductive tube on the surface layer portion is twisted or wrinkled and uniform chargeability cannot be obtained.

  In addition, when the charging roller disclosed in Patent Documents 1 to 3 is prototyped and tested, it turns out that there is a problem that white spots and black spots are generated when a halftone image is printed. did.

  In view of the above-described conventional situation, the object of the present invention is to obtain a uniform chargeability over a long period of time while being a lightweight and flexible dual structure roller type, and even when a halftone image is printed, both white spots and black spots are obtained. It is to provide a charging roller that does not occur.

  The charging roller of the present invention includes a first conductive elastic layer supported on a central core metal, and a second conductive elastic layer provided on the first conductive elastic layer. In the roller, the first conductive elastic layer is made of nitrile foam rubber and conductive carbon black, and the second conductive elastic layer is made of epichlorohydrin rubber and conductive carbon black. It has a surface treatment layer surface-treated with a surface treatment liquid containing isocyanate on the surface, the average outer diameter of the first conductive elastic layer is D1 (mm), and the average inner diameter of the second conductive elastic layer Where D2 (mm) is “−0.30 ≦ D2−D1 ≦ −0.15”.

  According to the present invention, the outer diameter of the first conductive elastic layer of the double-structured charging roller is made 0.15 to 0.30 mm larger than the inner diameter of the second conductive elastic layer, and both ends are bonded, Since the first conductive elastic layer and the second conductive elastic layer are not simply misaligned, but the entire contact surface of the outer diameter and the inner diameter is firmly adhered, the surface layer portion can be used even for long-term use. To provide a contact-type charging device in which no twisting or wrinkling occurs in the conductive tube, and thus uniform chargeability can be obtained over a long period of time and no white or black spots are generated even when a halftone image is printed. Is possible.

Embodiments of the present invention will be described below with reference to the drawings.
(Embodiment 1)
FIG. 1 is a side sectional view showing an internal configuration of an image forming apparatus provided with a charging roller in an embodiment, and shows a tandem type color image forming apparatus as an example.

  A color image forming apparatus 1 shown in FIG. 1 is a small color image forming apparatus that can be mounted on a desktop personal computer rack, for example, and is opened and closed on the front surface (right side of the figure) of the main body base 2. A paper feed tray 3 is provided, and a paper cassette 4 is detachably provided at the bottom. A large number of sheets P are placed and stored in the sheet cassette 4.

  The upper lid 5 forms a paper discharge tray 6 together with the upper surface of the rear part of the main body base 2, on which an image-formed paper discharged from the upper paper discharge port 7 is stacked. An operation panel 9 including a liquid crystal display device, a power switch, a plurality of data input keys and the like is disposed on the upper surface of the main body base 2 on the front side of the upper lid 5.

  Inside the color image forming apparatus 1, a paper transport belt (hereinafter simply referred to as a belt) 11 is arranged in a flat loop shape at the front and rear at substantially the center. The both ends of the sheet conveying belt 11 are held by the driving roller 12 and the driven roller 13 and circulate in a counterclockwise direction indicated by an arrow A in the drawing.

  In the upper circulation portion of the belt 11, four photosensitive drums 14 (14a, 14b, 14c, and 14d) are arranged in a multistage manner in the paper transport direction (from the right to the left in the drawing). Then, each of the photosensitive drums 14 is surrounded (hereinafter, only the peripheral devices around the photosensitive drum 14d are represented by reference numerals), and the cleaner 15, the charging roller 16, the writing head 17, and the developing device. 18 and a transfer sheet 19 are arranged.

  From the developing device 18 corresponding to the photosensitive drum 14a to the developing device 18 corresponding to the photosensitive drum 14d, each developing device 18 has M (magenta: red dye) and C (cyan: greenish) which are three primary colors of subtractive color mixing. Blue (with blue) and Y (yellow: yellow) toners, and K (black: black) toner dedicated to printing of black portions of characters and images are accommodated.

  The four write heads 17 are supported by the upper lid 5 via support members 21. The transfer sheet 19 is disposed as a member belonging to the belt unit. As will be described in detail later, the photosensitive drum 14, the cleaner 15, and the charging roller 16 constitute a drum sub unit, and the developing unit 18 includes members inside to constitute a developing sub unit. These sub units are combined to form an image forming unit.

  The belt 11 is always urged downward as indicated by an arrow B in the figure by a tension roller 22 that presses against the downstream side rear surface of the lower circulation portion, and maintains an appropriate tension. A suction roller 23 is pressed against the upstream end of the upper circulation portion of the belt 11 to form a paper carry-in portion.

  A standby roller pair 24 is disposed upstream of the belt 11 in the conveying direction, a paper feed guide path 25 is disposed below the standby roller pair 24, and a feed roller pair 26 is disposed at the lower end thereof. A paper feed end of the paper cassette 4 is positioned below the pair of feed rollers 26, and a paper feed roller 27 is disposed above the paper feed end.

  On the other hand, on the downstream side of the belt 11 in the sheet conveyance direction (left side in the figure), from a pressure roller, a heat roller, a separation claw, a peripheral surface cleaner, an oil application roller, a temperature measuring device and the like assembled in a heat insulating casing. A fixing device 28 is provided.

  A pair of carry-out rollers 29 is disposed behind the fixing device 28, and a paper discharge path 31 is formed above the pair of discharge rollers 28. The end of the paper discharge path 31 opens above the rear of the discharge tray 6 and is there. A paper discharge roller pair 32 is arranged.

  In addition, an electrical component 33 having an appropriate circuit board mounted thereon is disposed between the belt 11 and the paper cassette 4, and a control device composed of a plurality of electronic components is mounted on the circuit board. The control device includes a controller unit and an engine unit (not shown).

  The controller unit comprises a CPU (Central Processing Unit), ROM (Read Only Memory), EEPROM (Rewritable Read Memory), Frame Memory, Image Data Transfer Circuit, etc., and print data input from a host computer etc. Is analyzed, print data is created and transferred to the engine unit.

  The engine unit includes a CPU, a ROM, and the like. Data and command signals from the controller unit, an output of a temperature sensor (not shown), an output of a paper detection sensor, etc. are input to the input side, and a motor (not shown) is input to the output side. A motor driver that drives the motor, a clutch driver that switches a drive system that transmits the drive of the motor to each part, a print driver that drives the write head 17 based on the print data, a charging roller 16, a transfer sheet 19, and a developing roller that will be described later Are connected to a bias power supply driver for supplying a predetermined bias current.

The engine unit drives and controls each unit based on data and command signals from the controller unit, outputs from various sensors, and the like.
FIG. 2A is an external perspective view showing only the above-described image forming unit, and FIG. 2B is a side sectional view showing the internal configuration thereof. In FIGS. 4A and 4B, the same parts as those shown in FIG. 1 are denoted by the same reference numerals as those in FIG.

  As shown in FIGS. 2 (a) and 2 (b), the image forming unit 35 is constructed by assembling the developing sub unit 18 and the drum sub unit 36 integrally. One drum sub-unit 36 includes the photosensitive drum 14, the cleaner 15, and the charging roller 16 shown in FIG. 1, and further includes a drum cover 37 movably back and forth (left and right in FIG. 2B). A waste toner delivery pipe 38 is provided inside the unit.

  As the upper lid 5 (see FIG. 2) is closed, the writing head 17 descends along an arcuate locus as shown by an arrow C in FIG. The upper portion of the drum unit 36 is positioned by being fitted into a long slot 39 (see FIG. 2A) formed along the axial direction of the photosensitive drum 14.

  The other developing unit 18 includes a support portion 41 (41a, 41b) that supports the drum sub unit 36, a developing casing 42 that contains developer (toner) 40, and an opening portion of the developing casing 42 that has a circumferential surface. A developing roller 43 with an exposed portion, and a toner stirring member 44, a toner supply roller 45, a doctor blade 46, a scooping sheet 47 and the like so as to be buried in the toner 40 inside the developing casing 42. Yes. In addition, a waste toner receiving pipe 48 is disposed at the upper portion, and a collection bag 49 for storing the waste toner is attached to the waste toner receiving pipe 48.

  A bearing hole 51 (see FIG. 2 (a)) is formed in one support portion 41a of the developing sub unit 18, and the other support portion 41b is not clearly visible in the figure formed by cutting out from above. Is provided with a bearing groove. In addition, a fixing lever 52 is attached in the vicinity of the opening so as to be rotatable about 90 degrees up and down.

  One end portion of the support shaft 43-1 of the developing roller 43 protrudes from the side surface of the support portion 41a of the developing sub unit 18, and one end portion of the support shaft 14-1 of the photosensitive drum 14 extends from the bearing hole 51. It protrudes.

  Further, the other end of the support shaft 43-1 of the developing roller 43 protrudes from the side surface of the support portion 41b that cannot be seen in FIG. 2A, and other than the support shaft 14-1 of the photosensitive drum 14 from the bearing groove. The end is protruding.

  When the developing sub unit 18 and the drum sub unit 36 are assembled together and completed as the image forming unit 35 as shown in FIGS. 2A and 2B, the waste toner sending pipe 38 and the waste toner receiving pipe 48 are formed. Are connected by a transport pipe (not shown).

  Next, the operation of the tandem color image forming apparatus 1 having the above-described configuration will be described with reference to FIG. 1 and FIG. First, power is turned on to the apparatus main body 1 shown in FIG. 1, and printing (printing) is performed when the paper quality, number of sheets to be used, print mode, and other specifications are input as a key input or a signal from a connected host device. Be started.

  A sheet feeding roller 27 takes out one sheet of paper P placed and accommodated in the sheet cassette 4 and feeds the sheet P to the standby roller pair 24 through the feeding roller pair 26 and the sheet feeding guide path 25. The standby roller pair 24 temporarily stops its rotation, the front end of the paper P is brought into contact with the holding portion to stop the paper advance, the skew is corrected, and the conveyance timing is waited.

  The driving roller 12 rotates in the counterclockwise direction, and the driven roller 13 is driven to rotate in the same counterclockwise direction. As a result, the belt 11 is circulated and moved counterclockwise as a whole by the upper circulation portion coming into contact with the four photosensitive drums 14.

  At the same time, various devices arranged around the photosensitive drum 14 are sequentially driven in accordance with the printing timing. The photosensitive drum 14 rotates in the clockwise direction, and the charging roller 16 applies a uniform high negative charge to the circumferential surface of the photosensitive drum 14 to initialize the potential.

  The writing head 17 exposes the peripheral surface of the photosensitive drum 14 in accordance with the image signal to attenuate the potential. As a result, an electrostatic latent image is formed on the circumferential surface of the photosensitive drum 14 from the high negative potential portion by the initialization and the low negative potential portion attenuated by the exposure.

The developing roller 43 transfers the toner 40 of the developing casing 42 to the low potential portion of the electrostatic latent image to form a toner image on the circumferential surface of the photosensitive drum 14 (reverse development).
When the leading edge of the toner image on the peripheral surface of the most upstream photosensitive drum 14a is rotated and conveyed to the portion facing the belt 11, the standby roller pair is set so that the printing start position of the paper P coincides with the opposite portion. 24 starts to rotate and feeds the paper P to the paper carry-in section.

  The driven roller 13 and the suction roller 23 sandwich the conveyed paper P together with the belt 11 and convey it. The sheet P is attracted to the belt 11 and conveyed to the first transfer portion formed by the photosensitive drum 14 a and the transfer sheet 19.

  The transfer sheet 19 applies a transfer current (or transfer voltage) output from a transfer bias power source (not shown) to the paper P via the belt 11. As a result, the M (magenta) toner image on the photosensitive drum 14 a is transferred to the paper P.

  Subsequently, the C (cyan) toner image is transferred at the second transfer portion from the upstream formed by the photosensitive drum 14 b and the transfer sheet 19, and further from the upstream formed by the photosensitive drum 14 c and the transfer sheet 19. A Y (yellow) toner image is transferred at the third transfer portion.

Further, the K (black) toner image is transferred at the most downstream transfer portion formed by the photosensitive drum 14 d and the transfer sheet 19, and the four color toner images are sequentially overlaid on the paper P.
The paper P onto which the four color toner images have been transferred in this way is separated from the belt 11 and carried into the fixing device 28. The fixing device 28 fixes the toner image on the paper P by heat and pressure. After the image fixing, the paper P is discharged by the carry-out roller pair 29 via the paper discharge path 31 and the discharge roller pair 32 onto the paper discharge tray 6 with the toner image facing down.

  FIG. 3A is a front view showing the positional relationship between the charging roller 16 and the photosensitive drum 14 in the color image forming apparatus 1 of the present example that operates as described above, and FIG. It is sectional drawing of the diameter direction of these.

  The charging roller 16 of this example shown in FIGS. 4A and 4B includes a first conductive elastic layer 54 supported on a central core metal 53, and on the first conductive elastic layer 54. The second conductive elastic layer 55 is provided.

  The first conductive elastic layer 54 is composed of nitrile foam rubber and conductive carbon black. Further, the second conductive elastic layer 55 is composed of epichlorohydrin rubber and conductive carbon black, and a surface treatment layer is formed on the surface thereof by a surface treatment liquid containing isocyanate.

  Between the first conductive elastic layer 54 and the second conductive elastic layer 55, the average outer diameter of the first conductive elastic layer 54 is d (mm), and the second conductive elastic layer is used. When the average inner diameter of the layer 55 is D (mm), the relationship is “−0.30 ≦ D−d ≦ −0.15”.

  In other words, in the charging roller 16 having the double structure of this example, the outer diameter of the first conductive elastic layer 54 is 0.15 to 0.30 mm than the inner diameter of the second conductive elastic layer 55. Largely formed.

The reason for this will be described below.
First, as Example 1, a first conductive elastic layer 54 and a second conductive elastic layer 55 are formed by the following method.

  First, 100 parts by mass of a medium to high nitrile rubber (Mooney viscosity: ML1 + 4 (100 ° C.): 30) of 33% nitrile, 5 parts by mass of zinc white, 1 part by mass of stearic acid, conductive carbon (Toka Black) # 5500: manufactured by Tokai Carbon Co., Ltd., 25 parts by mass, DOP30 by mass, 1 part by mass of vulcanized material (sulfur), and 3.5 parts by mass of vulcanization aid are prepared.

  Next, a foaming agent (ADCA cell microphone CAP: manufactured by Sankyo Kasei Co., Ltd.) and 3 parts by mass of a foaming aid are added to each of these and kneaded with a roll mixer (first conductive material before foaming). The layer) is preformed by extrusion onto a core bar 53 having an outer diameter of 6 mm with a thickness of 1 mm.

  Thereafter, the first conductive elastic layer before foaming is foamed by heating in an electric furnace at 150 ° C. for 1 hour, polished so that the outer diameter D1 becomes 8.9 mm, and foamed first conductive The elastic elastic layer 54 is created.

  Subsequently, 100 parts by mass of epichlorohydrin rubber (ECO), 20 parts by mass of conductive carbon black (Toka Black # 4500, manufactured by Tokai Carbon Co., Ltd.), 5 parts by mass of zinc white, 2 parts by mass of stearic acid, and additive Add 1.5 parts by mass of the vulcanizing agent, knead with a roll mixer, and after injection molding, vulcanize at 170 ° C. for 30 minutes, thickness 0.7 mm, inner diameter D2 is 8.7 mm A rubber sleeve is formed.

  Further, 100 parts by mass of ethyl acetate, 20 parts by mass of isocyanate compound (MDI), 4 parts by mass of acetylene black (manufactured by Denki Kagaku), and 2 parts by mass of acrylic silicone polymer (Modipasa FS700: manufactured by Nippon Oil & Fats Co., Ltd.) A surface treatment liquid is prepared by time dispersion mixing.

  The rubber sleeve is immersed in the surface treatment solution at 23 ° C. for 60 seconds, and then heated in an oven at 120 ° C. for 1 hour to form a surface treatment layer on the rubber sleeve, so that the second conductive elasticity Layer 55 is created.

  After covering the first conductive elastic layer 54 thus formed with the second conductive elastic layer 55, the first conductive elastic layer 54 and the second conductive elastic layer are formed from both ends to 2 mm. Between 55, a urethane-based hot melt adhesive was applied with a dispenser, and both ends thereof were adhered to form a charging roller 16 (charging roller 16a of Example 1).

  In the charging roller 16a, a distance between the outer diameter D1 of the first conductive elastic layer 54 and the inner diameter D2 of the second conductive elastic layer 55 is “D2−D1 = 8.7−8.9 = -0.2 (mm) ".

  When the charging roller 16a produced by the above method was attached to a charging roller portion of a commercially available color printer (N5300: manufactured by Casio Computer Co., Ltd.), and a halftone image was printed and evaluated, a good image was obtained.

Next, as Example 2, a first conductive elastic layer 54 and a second conductive elastic layer 55 were formed by the following method.
The charging roller 16 (the charging roller 16b of Example 2) is the same as that of Example 1 except that the first conductive elastic layer 54 is foamed and then polished so that the outer diameter D1 is 8.85 mm. ) Was produced.

  In the charging roller 16b, the distance between the outer diameter D1 of the first conductive elastic layer 54 and the inner diameter D2 of the second conductive elastic layer 55 is "D2-D1 = 8.7-8.85 = -0.15 (mm) ".

  When the charging roller 16b produced by the above method was attached to a charging roller portion of a commercially available color printer (N5300: manufactured by Casio Computer Co., Ltd.), and a halftone image was printed and evaluated, a good image was obtained.

Furthermore, as Example 3, the first conductive elastic layer 54 and the second conductive elastic layer 55 were formed by the following method.
The charging roller 16 (the charging roller 16c of Example 3) was used in the same manner as in Example 1 except that the first conductive elastic layer 54 was foamed and then polished so that the outer diameter D1 was 9.00 mm. ) Was produced.

  In the charging roller 16 c, a distance between the outer diameter D 1 of the first conductive elastic layer 54 and the inner diameter D 2 of the second conductive elastic layer 55 is “D2−D1 = 8.7−9.00 = -0.3 (mm) ".

  When the charging roller 16c produced by the above method was attached to a charging roller portion of a commercially available color printer (N5300: manufactured by Casio Computer Co., Ltd.) and evaluated by printing a halftone image, a good image was obtained.

Further, as Comparative Example 1, a first conductive elastic layer 54 and a second conductive elastic layer 55 were formed by the following method.
The charging roller 16 (the charging roller 16x of Comparative Example 1) was prepared in the same manner as in Example 1 except that the first conductive elastic layer 54 was foamed and then polished so that the outer diameter D1 was 8.80 mm. ) Was produced.

  In the charging roller 16x, a distance between the outer diameter D1 of the first conductive elastic layer 54 and the inner diameter D2 of the second conductive elastic layer 55 is "D2-D1 = 8.7-8.80 = -0.1 (mm) ".

  When the charging roller 16x produced by the above method is attached to a charging roller portion of a commercially available color printer (N5300: manufactured by Casio Computer Co., Ltd.), and a halftone image is printed and evaluated, white dots are formed on the entire surface of the halftone image. A black spot was generated, which was not suitable as a halftone image.

  In summary, in the first to third embodiments, the average outer diameter D1 of the first conductive elastic layer 54 and the inner diameter D2 of the second conductive elastic layer 55 of the charging roller 16 (16a, 16b, 16c). Both layers are formed so that there is a relationship of “−0.15 ≦ D2−D1 ≦ −0.3”.

That is, the outer diameter D1 of the first conductive elastic layer 54 is formed to be greater than the inner diameter D2 of the second conductive elastic layer 55 by 0.15 mm or more.
Therefore, although the first conductive elastic layer 54 and the second conductive elastic layer 55 are bonded to each other by the hot-melt adhesive and not bonded to the other portions, the first conductive elastic layer 54 and the second conductive elastic layer 55 are substantially not bonded to each other. The elastic elastic layer 54 and the second conductive elastic layer 55 are pressure-bonded and are in good contact with each other.

  As described above, the first conductive elastic layer 54 and the second conductive elastic layer 55 are in close contact with each other by pressure bonding, and the surface treatment is added to the first conductive elastic layer 54 when a voltage is applied. And an abnormal discharge between the second conductive elastic layer 55 and the second conductive elastic layer 55 are prevented.

  As a result, in the initialization charging of the photosensitive drum 14 by the charging roller 16, charging unevenness on the photosensitive drum 14 is eliminated, and as a result, a good halftone image in which no white spot or black spot occurs is obtained.

  If the outer diameter D1 of the first conductive elastic layer 54 is 0.4 mm or more larger than the inner diameter D2 of the second conductive elastic layer 55, the first conductive elastic layer 54 has the second conductive property. Since it becomes difficult to insert into the elastic layer 55, it is not practical.

  In this example, a superimposed voltage of direct current and alternating current is applied to the charging roller 16. Specifically, the electric resistance of the first conductive elastic layer 54 described above is 9 × 10 5 Ω or less, and the surface electric resistance of the second conductive elastic layer 55 is 1 × 10 5 Ω / □ and 9 × 10. The superposed bias voltage DC-600 (V) and AC1650 (Vp-p) /1.3 KHz are applied to the charging roller 16 with a range of ^ 5Ω / □ and an overall product hardness ASKER-F of 90 ° or less.

  Thereby, for example, even if the toner from the photosensitive drum 14 adheres to the charging roller 16 and the electric resistance ground of the charging roller 16 has a resistance value unevenness of about four times, the uniform charging property with a sufficient margin is ensured. As a result of experiments, it has been proved that it can be ensured.

Here, the first conductive elastic layer 54 will be described.
As described above, the first conductive elastic layer 54 provided on the core metal 53 of the charging roller 16 includes a nitrile rubber and a conductive carbon black, and is made of a foamed nitrile foam. Yes.

  In this configuration, in order to satisfy the predetermined conductivity, it is necessary to add conductive carbon black to the first conductive elastic layer 54, but if too much conductive carbon black is added, the hardness increases, There is a bias in the pressure bonding between the first conductive elastic layer 54 and the second conductive elastic layer 55.

On the other hand, when a plasticizer is added to reduce the hardness, the plasticizer may move to the outer surface of the charging roller 16 and contaminate the photosensitive drum 14 that is in contact therewith.
For this reason, when a medium-high nitrile or a high nitrile rubber is used as the nitrile foam rubber of the first conductive elastic layer 54, it can be highly foamed because of the low gas permeability of the nitrile rubber. , Low-fouling property and low-grade foam can be realized.

Further, since the nitrile rubber needs to have low gas permeability at the time of foaming, it is preferably a medium / high nitrile, a high nitrile or an extremely high nitrile rubber having a nitrile amount of 31% or more.
From the viewpoint of easiness of foaming, it is preferable to use one having a low Mooney viscosity, for example, one having a Mooney viscosity of ML1 + 4 (100 ° C.) of 40 or less.

  Furthermore, in order to satisfy the characteristics as the charging roller 16, the first conductive elastic layer 54 has an electric resistance value of DC-100V applied (-100V is applied to the core metal 53, and the surface layer of the charging roller 16 is grounded). Since it is necessary that the electric resistance value of the electrode) is 1 × 10 5 Ω or less, conductive carbon black is added as a conductivity imparting agent. For example, 20 parts by weight or more of conductive carbon black may be added to 100 parts by weight of nitrile rubber.

Moreover, the kind of conductive carbon black is not specifically limited. For example, Ketjen Black (manufactured by Lion), Toka Black (manufactured by Tokai Carbon Co., Ltd.) and the like can be mentioned.
The electrical resistance is measured by placing the charging roller 16 on a planar electrode made of SUS304 and applying a voltage (-100 V) between the core metal 53 and the planar electrode.

As this measuring instrument, it measures using ULTRA-HIGH-RESISTANCE-METER-R8340A (made by an advanced test company).
The expansion ratio of the nitrile rubber foam is preferably 2 to 4 times. The expansion ratio is determined by the mold volume of the first conductive elastic layer before foaming, the ratio of the amount of the first conductive elastic layer before foaming, the type, amount, and heating conditions of the foaming agent. Can do. The foam may be either closed cells or open cells.

Next, the second conductive elastic layer 55 will be described.
As described above, the second conductive elastic layer 55 deposited on the first conductive elastic layer 54 is composed of epichlorohydrin rubber and conductive carbon black, and the surface thereof includes isocyanate. The surface layer surface-treated with the process liquid is included.

  Examples of the epichlorohydrin rubber include epichlorohydrin homopolymers, epichlorohydrin-ethylene oxide copolymers, epichlorohydrin-allyl glycidyl ether copolymers, and epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymers.

  The surface treatment layer is formed by impregnating a surface treatment liquid containing isocyanate. As this surface treatment liquid, a solution obtained by dissolving an isocyanate compound in an organic solvent, or a solution obtained by adding a conductive car pump rack to this can be used.

  Moreover, you may use the surface treatment liquid which contains an at least 1 sort (s) of polymer chosen from an acrylic fluorine-type polymer and an acrylic silicone type polymer, and an electroconductivity imparting agent with an isocyanate component.

  Here, as the isocyanate compound, 2,6-tolylene diisocyanate (TDI), 4-4′-diphenylmethane diisocyanate (MDI), paraphenylene diisocyanate, 1,5′-naphthalene diisocyanate (NDI), and 3,3′- Examples thereof include dimethyldiphenyl-4,4′-diisocyanate (TODI) and the above-mentioned multimers and modified products.

  By providing the surface treatment layer as described above on the surface of the charging roller 16, the photosensitive drum 14 and the epichlorohydrin rubber of the second conductive elastic layer 55 are not in direct contact with each other. Contamination of the charging roller 16 due to the toner, toner additive, paper powder and the like can be prevented.

  In this example, the diameters of the core metal 53, the first conductive elastic layer 54, and the second conductive elastic layer 55 used for the charging roller 16 are not particularly limited. The first conductive elastic layer 54 has a diameter of 8 to 14 mm, and the second conductive elastic layer 55 has a diameter of 10 to 16 mm.

  An example of the adhesive that bonds the first conductive elastic layer 54 and the second conductive elastic layer 55 is a hot-melt urethane adhesive. The bonding position of the adhesive is preferably about 1 to 5 mm from both ends of the conductive elastic layer of the charging roller 16.

  To summarize the above, in the production of the first conductive elastic layer, first, the core metal is positioned and held in the cylindrical mold. From such an injection port of the cylindrical mold, unfoamed and unvulcanized rubber to be the first conductive elastic layer before foaming is injected and extruded. The first conductive elastic layer before foaming is heated and foamed and vulcanized. The first conductive elastic layer after the foaming is polished and cut to have a predetermined outer diameter.

  Next, in the production of the second conductive elastic layer, the sleeve member to be the second conductive elastic layer is formed by transfer, injection or extrusion molding using a mirror-polished mold. Since a mirror-polished mold is used, the sleeve member has a highly accurate and smooth surface without particularly polishing the outer surface. Therefore, it is not necessary to polish the outer surface for dimension adjustment.

  The surface treatment liquid is applied to the surface of the sleeve member by spray coating or dip-coating with a core metal having the same diameter as that of the sleeve member, and then the surface treatment is performed on the outer surface of the sleeve member by heating. Form a layer.

  The second conductive elastic layer is coated on the first conductive elastic layer, and the both ends of the first conductive elastic layer and the second conductive elastic layer are bonded with an adhesive, thereby the present invention. The charging roller can be manufactured.

1 is a side sectional view showing an internal configuration of a tandem type color image forming apparatus including a charging roller according to an embodiment. (a) is an external perspective view showing only an image forming unit of a color image forming apparatus according to an embodiment, and (b) is a side sectional view showing an internal configuration thereof. (a) is a front view showing the arrangement relationship between the charging roller and the photosensitive drum of the color image forming apparatus in one embodiment, and (b) is a sectional view in the diameter direction of the charging roller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color image forming apparatus 2 Main body base 3 Opening / closing paper feed tray 4 Paper cassette 5 Top cover 6 Paper discharge tray 7 Upper paper discharge outlet 9 Operation panel 11 Paper conveyance belt (belt)
DESCRIPTION OF SYMBOLS 12 Drive roller 13 Driven roller 14 (14a, 14b, 14c, 14d) Photosensitive drum 14-1 Photosensitive drum support shaft 15 Cleaner 16 Charging roller 17 Writing head 18 Developer (development sub-unit)
19 Transfer Sheet 21 Support Member 22 Tension Roller 23 Adsorption Roller 24 Standby Roller Pair 25 Feeding Guide Path
26 Feeding roller pair 27 Feeding roller 28 Fixing device 29 Unloading roller pair 31 Paper discharge path 32 Paper discharge roller pair 33 Electrical unit 35 Image forming unit 36 Drum sub unit 37 Drum cover 38 Waste toner delivery pipe 39 Long groove hole 40 Development Agent (toner)
41 (41a, 41b) Support section 42 Developing casing 43 Developing roller 43-1 Developing roller support shaft 44 Toner stirring member 45 Toner supply roller 46 Doctor blade 47 Scoop sheet 48 Waste toner receiving pipe 49 Collection bag 51 Bearing hole 52 Fixed lever 53 Core metal 54 First conductive elastic layer 55 Second conductive elastic layer

Claims (1)

In a charging roller comprising a first conductive elastic layer supported on a central core metal, and a second conductive elastic layer provided on the first conductive elastic layer,
The first conductive elastic layer is composed of nitrile foam rubber and conductive carbon black,
The second conductive elastic layer is composed of epichlorohydrin rubber and conductive carbon black, and has a surface treatment layer surface-treated with a surface treatment liquid containing isocyanate on the surface thereof,
Assuming that the average outer diameter of the first conductive elastic layer is D1 (mm) and the average inner diameter of the second conductive elastic layer is D2 (mm), “−0.30 ≦ D2-D1 ≦ −0. 15 ",
A charging roller characterized by that.