JP2011242646A - Developing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device and an image forming apparatus capable of preventing density unevenness and performing an excellent printing.SOLUTION: The developing device comprises: a developer carrier 13 for sticking developer to an electrostatic latent image carrier 11; and a developer supply member 14 for supplying the developer to the developer carrier 13. The developer carrier 13 comprises: a shaft 131 having conductivity; an elastic layer 132 formed on the outer peripheral surface of the shaft 131 and formed of conductive urethane rubber containing an ion conductive agent or an electronic conductive agent; and a surface modified layer 133 formed by impregnating the surface of the elastic layer 132 with carbon black of which a structure is not developed and an isocyanate group-containing substance to modify the surface of the elastic layer 132.

Description

  The present invention relates to a developing device and an image forming apparatus using the developing device.

  Conventionally, the elastic layer of the developing roller used in the developing device has no nip marks because other members (for example, a regulating blade that regulates the thickness of the toner layer on the developing roller) are pressed against the surface of the elastic layer. Thus, it is formed of a material (high hardness urethane rubber) having a small compression set.

  Further, it is known that a surface-cured layer is formed by subjecting the surface of the elastic layer of the developing roller to a surface treatment using an isocyanate solution to which carbon black (acetylene black) having high conductivity is added ( For example, see Patent Document 1).

Japanese Patent No. 4041455

  However, when printing is performed using the above-described conventional developing roller, toner adheres to the surface of the developing roller as the number of printed sheets increases. When the fixing of the toner further proceeds, a filming phenomenon occurs and the function of the developing roller cannot be exhibited, and the density unevenness occurs in the printed image.

  This is because the surface of the developing roller is subjected to electrical stress due to application of a high voltage and mechanical stress due to contact with the regulating blade, so that the surface of the developing roller (surface-hardened layer) is solidified with carbon black. This is considered to be because the structure was destroyed, and the π-electrons that should have conductivity were relatively reduced, resulting in a decrease in conductivity. The decrease in conductivity on the surface of the developing roller leads to an increase in residual charge, and the charged toner is less likely to be separated from the surface of the developing roller having an increased degree of polarization (not easily transferred to the photosensitive drum).

  Another reason is that since the elastic layer of the developing roller is formed of high-hardness urethane rubber, a large mechanical stress acts on the toner passing between the developing roller and the regulating blade, and as a result, the toner It is conceivable that the toner is liable to be crushed and is liable to adhere to the surface of the developing roller and to cause filming.

  These problems become more prominent as the processing speed of the printer increases.

  The present invention has been made in view of the above problems, and an object thereof is to provide a developing device, an image forming apparatus, and a developer carrier that can suppress uneven density and enable good printing. .

  A developing device according to the present invention includes a developer carrying member for attaching a developer to an electrostatic latent image carrying member, and a developer supplying member for supplying the developer to the developer carrying member. The developer carrying member includes a conductive shaft, an elastic layer formed on the outer peripheral surface of the shaft and made of conductive urethane rubber containing an ionic conductive agent or an electronic conductive agent, and a surface of the elastic layer. And a surface modified layer formed by impregnating and reforming an undeveloped carbon black and an isocyanate group-containing material.

  According to the present invention, the carbon black having no developed structure used for the surface modification treatment of the elastic layer exhibits stable conductivity, thereby suppressing density unevenness and obtaining a good printed image. .

1 is a diagram illustrating a basic configuration of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a diagram illustrating a basic configuration of a process unit including a developing device according to the first embodiment of the present invention. It is a perspective view which shows the developing roller of the developing device in the 1st Embodiment of this invention. It is a schematic diagram showing a method for measuring the residual potential of the developing roller of the developing device according to the first embodiment of the present invention. It is a schematic diagram for demonstrating the image unevenness evaluation method in the 1st Embodiment of this invention. It is a figure which shows each measurement result and the result of a printing test of the developing roller of the Example in the 1st Embodiment of this invention, and a comparative example. It is a figure which shows each measurement result and the result of a printing test of the developing roller of the Example in the 2nd Embodiment of this invention, and a comparative example.

First embodiment.
FIG. 1 is a diagram showing a basic configuration of an image forming apparatus 10 according to the first embodiment of the present invention. In FIG. 1, an image forming apparatus 10 includes process units 1B, 1Y, 1M, and 1C for forming black, yellow, magenta, and cyan images. The process units 1B, 1Y, 1M, and 1C are also referred to as image forming units or photosensitive drum units. The process units 1B, 1Y, 1M, and 1C are arranged in a line from the left side to the right side in the horizontal direction along the paper P (medium) conveyance path defined in the image forming apparatus 10.

  FIG. 2 is a diagram illustrating the configuration of the process units 1B, 1Y, 1M, and 1C. Since the process units 1B, 1Y, 1M, and 1C have the same configuration except for the toner to be used, the process unit 1 will be described here.

  In the process unit 1, a toner cartridge 18 (developer container) is detachably attached to the unit main body 12. The process unit 1 includes a photosensitive drum 11 as an electrostatic image carrier in a unit main body 12. The photosensitive drum 11 rotates at a constant speed in the clockwise direction in the drawing, and light irradiation of an LED head 19 (attached to an upper cover (not shown)) as an exposure unit disposed on the upper side of the photosensitive drum 11 is opposed to the photosensitive drum 11. As a result, an electrostatic latent image is formed on the surface.

  The process unit 1 further develops the electrostatic latent image formed on the surface of the photosensitive drum 11 by the charging roller 15 as a charging unit that uniformly exposes the surface of the photosensitive drum 11 and the LED head 19 described above. And a developing roller 13 as a developer carrying member. The process unit 1 further includes a toner supply roller 14 as a developer supply member that supplies toner (developer) to the development roller 13, and a regulation blade 16 that regulates the thickness of the toner layer on the surface of the development roller 13. Prepare. The space from which the developing roller 13, the toner supply roller 14, and the regulation blade 16 are accommodated is supplied with toner from the toner cartridge 18.

  The process unit 1 further includes a cleaning blade 17 that scrapes off the toner (transfer residual toner) remaining on the photosensitive drum 11 and a storage space that stores the scraped waste toner. The waste toner stored in the storage space is conveyed to a waste toner collecting device (not shown).

  The photosensitive drum 11, the developing roller 13, and the supply roller 14 are each rotated in the direction indicated by the arrow by the power of a drive motor (not shown). Further, the charging roller 15 rotates following the photosensitive drum 11.

  In the process unit 1, a configuration including the developing roller 13, the toner supply roller 14, and the regulating blade 16 necessary for developing the electrostatic latent image formed on the photosensitive drum 11 is referred to as a “developing device”. .

  In FIG. 1, a transfer unit 20 is arranged on the side opposite to the process units 1B, 1Y, 1M, and 1C across the conveyance path. The transfer unit 20 passes through the four transfer rollers 22 arranged to face the photosensitive drums 11 of the process units 1B, 1Y, 1M, and 1C, and between the photosensitive drums 11 and the transfer rollers 22. The conveyor belt 21 is provided and a roller group (rollers 23, 24, 25, and 26) around which the conveyor belt 21 is stretched. The roller 23 is rotated by the power of a drive motor (not shown) to move the conveyor belt 21 in the direction indicated by the arrow in the figure.

  Below the transfer unit 20, a cassette 31 for storing paper P (medium) is disposed. Adjacent to the upper side of the cassette 31, a paper feed roller 32 is provided that feeds the paper P stored in the cassette 31 one by one and sends it to the conveyance path. Further, the transport roller group 33 that transports the paper P fed by the paper feed roller 32 toward the process units 1B, 1Y, 1M, and 1C, and the process units 1B, 1Y by correcting the skew (skew) of the paper P. , 1M, 1C and a registration roller pair 34 are arranged.

  A fixing device 35 including a fixing roller 35a and a pressure roller 35b is disposed on the downstream side of the process units 1B, 1Y, 1M, and 1C along the conveyance path of the paper P. Further, on the further downstream side of the fixing device 35, a paper discharge tray 36 on which the paper discharged from the fixing device 35 is placed is disposed.

The basic operation of the image forming apparatus configured as described above is as follows.
In each process unit 1 (FIG. 2), the surface of the photosensitive drum 11 is uniformly charged by the charging roller 15, and the LED head 19 exposes the surface of the photosensitive drum 11 based on the image data of each color. An electrostatic latent image is formed on the surface of the photosensitive drum 11. The electrostatic latent image on the surface of the photosensitive drum 11 is developed by the developing roller 13 to become a toner image.

  On the other hand, the paper P stored in the cassette 31 is fed out one by one by the pair of paper feed rollers 32 and is transported to the process units 1B, 1Y, 1M, 1C and the transfer unit 20 by the transport roller group 33 and the registration roller pair 34. Is done. The paper P is sucked and held on the transport belt 21 and transported, and passes through the process units 1B, 1Y, 1M, and 1C.

  When the paper P is transported to the transport belt 21 and passes through the process units 1B, 1Y, 1M, and 1C, the toner images of the respective colors formed on the surfaces of the photosensitive drums 11 are caused by the action of the transfer rollers 22. The images are sequentially transferred onto the surface of the paper P. As a result, a color toner image is transferred to the surface of the paper P. At this time, the toner image adheres to the paper P only with a weak electrostatic force.

  The sheet P on which the toner image is transferred is conveyed to the fixing device 35. The toner image is heated and melted at a high temperature between the fixing roller 35a and the pressure roller 35b, and fixed on the paper P by pressure contact. Thereafter, the paper P is discharged from the fixing device 35 and placed on the paper discharge tray 36.

  Next, details of the developing device according to the first embodiment of the present invention will be described.

  The toner (developer) is a non-magnetic one-component negatively charged pulverized toner having an average particle size of 5.5 μm, and uses a polyester resin as a resin component. The saturation charge amount is -44 μC / g. The saturation charge amount was 4% by weight of toner and 96% by weight of silicone-coated ferrite carrier (manufactured by Kanto Denka Kogyo Co., Ltd., average particle size 90 μm) mixed for 1 minute by a ball mill, and a suction type small charge amount measuring device “ It measured using Q / M METER MODEL 210HS "(made by Trek Co., Ltd.).

  The regulating blade 16 is a plate-like member having a thickness of 0.08 mm made of stainless steel (SUS). The contact portion of the regulating blade 16 with the developing roller 13 is bent, the radius of curvature R of the bent portion is 0.5 mm, and the ten-point average roughness of the contact surface is Rz = 0.6 μm.

  FIG. 3 is a perspective view showing the configuration of the developing roller 13. The developing roller 13 has a semiconductive elastic layer 132 formed on the outer peripheral surface of a conductive shaft 131 and a surface modification layer 133 formed on the surface thereof. Here, the outer diameter of the conductive shaft 131 is 10 mm, and the outer diameter of the developing roller 13 is 16 mm.

  The elastic layer 132 can be made of urethane rubber, acrylonitrile butadiene rubber (NBR), styrene butadiene rubber (SBR), ethylene propylene diene rubber (EPDM), silicone rubber, or the like. In this embodiment, urethane rubber is used. . As a conductivity-imparting agent for imparting conductivity to the elastic layer 132, an electron conductive agent (carbon black, conductive filler, etc.) or an ionic conductive agent can be used. In this embodiment, an ionic conductive agent is used. (Lithium perchlorate) is used.

  The surface modification layer 133 can improve the chargeability of the toner, and the isocyanate layer-containing compound can be used to prevent the drum layer from being chemically reacted with the photosensitive drum 11 to cause drum contamination. It is formed by immersing in the above-mentioned solvent and modifying only the surface layer portion of the elastic layer 132.

  The surface modification treatment is different from the treatment for forming a coating layer on the surface of the elastic layer 132. The elastic layer 132 is immersed in the modification treatment liquid for a predetermined time or the modification treatment liquid is applied to the elastic layer 132. It means that the modified treatment liquid is permeated into the surface layer portion by a method such as coating or spray coating.

Next, a method for manufacturing the developing roller 11 will be described.
The elastic layer 132 made of urethane rubber is obtained by reacting a polyisocyanate that is a hard segment, a long-chain polyol that is a soft segment, a chain extender, a crosslinking agent, and the like. Polyisocyanates include aromatic polyisocyanates and aliphatic polyisocyanates. As the aromatic polyisocyanate, for example, tolylene diisocyanate (TDI), diphenylmethane isocyanate (MDI), polymethylene polyphenyl polyisocyanate, tolidine diisocyanate, naphthalene diisocyanate and the like can be used. As the aliphatic polyisocyanate, for example, hexamethylene isocyanate (HDI), isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, tetramethylhexamethylene diisocyanate and the like can be used.

  On the other hand, long-chain polyols include polyether-based polyols and polyester-based polyols. Examples of the polyether polyol include amines such as ethylene glycol, propylene glycol, ethylenediamine, diethyltriamine, and tolylenediamine, polypropylene glycol, polytetramethylene ether glycol, and the like. As the polyester-based polyol, for example, a low molecular polyol, a polycoupler, a polycarbonate polyol or the like can be used.

  The chain extender is a compound having two or more active hydrogens in a molecule having a molecular weight of less than 300, and for example, polyol, polyamine, amino alcohol, water, urea, and the like can be used. The cross-linking agent has a function of cross-linking between the hard segments to form a three-dimensional resin. For example, a resin-based cross-linking agent such as an isocyanurate of an organic isocyanate, or an amine resin. Can be used.

  As the conductivity-imparting agent, carbon black having high conductivity, such as acetylene black, furnace black, ketjen black, or the like can be used as a material that exhibits electronic conduction. Moreover, as a material (ionic conductive agent) that expresses ionic conductivity, sodium salts, potassium salts, lithium salts, and the like belonging to alkali metal salts can be used, and lithium salts are particularly preferable. Specific examples include halogen oxyacid salts, perhalogen oxyacid salts, thiocyanate salts, and phosphate salts. Perhalogen chloroxyacid salts are particularly preferable, and lithium perchlorate is more preferable.

  The surface modification layer 133 is prepared by first preparing a solution containing an isocyanate group-containing compound as a modification treatment liquid, immersing the elastic body 132 in the modification treatment liquid, and then performing a heat treatment, or a modification treatment. The liquid is applied to the elastic body surface, and then heated. Examples of means for applying to the elastic surface include a spray coating method and a roll coating method.

  As the modification treatment liquid, those obtained by dissolving an isocyanate group-containing compound in an organic solvent, those obtained by dissolving an isocyanate group-containing compound and a polyol in an organic solvent, auxiliary agents commonly used in polyurethane formation reactions in these solutions, There is a solution to which a conductivity imparting agent or the like is added. The isocyanate group-containing compound can be selected from the aforementioned isocyanate compounds. The polyol can be selected from the polyols described above. Moreover, what has a siloxane bond can also be used. As the organic solvent, an aprotic polar solvent is preferable, and ethyl acetate, dimethylformamide or a mixture thereof is particularly preferable.

Carbon black, which is an electronic conductive material, is used as the conductivity-imparting agent to be added to the modification treatment liquid. Here, in the present embodiment, carbon black having low structure and low conductivity is used. As such carbon black, furnace black or channel black is suitable, the primary particle diameter is 15 to 40 μm, and the specific surface area by BET (Brunauer, Emmett and Teller) method is 50 to 300 m ² / g (more preferably, As will be described later, those having an oil absorption of 55 to 130 m ² / g) and DBP (dibutyl phthalate) in the range of 40 to 150 ml / 100 g are preferable.

  As a specific example of such a carbon black, no. 2300, no. 900, MCF88, No. 33, no. 44, no. 47, no. 52, MA7, MA8, no. 2200B (Mitsubishi Chemical Co., Ltd.), Raven 1255 (Columbian Carbon Co., Ltd.), REGAL400R, REGAL330R, REGAL660R, MOGUL-L (above, Cabot type), Color Black FW1, Color Black FW18, Color Black S170, Color Black S170, Examples include Black S150, Printex 35, Printex U (manufactured by Degussa).

  Hereinafter, a printing test using the developing roller 13 of each example in this embodiment and the developing roller 13 of each comparative example will be described. Here, for convenience, not only the developing roller of each embodiment but also the developing roller of the comparative example will be described as “developing roller 13”. First, a method for producing the developing roller 13 will be described.

<Formation of the elastic layer of the developing roller>
0.5 parts by weight of lithium perchlorate as an ionic conductive agent was added to 100 parts by weight of a polyether polyol (GP-3000, manufactured by Sanyo Chemical Industries, Ltd.), dispersed by stirring, adjusted to 80 ° C., and then decompressed. Under the conditions of defoaming and dehydration for 6 hours, liquid A was obtained. On the other hand, 70 parts by weight of prepolymer (Adiprene L100, manufactured by Uniroyal Chemical Co., Ltd.) was added and mixed with 20 parts by weight of isocyanate (Coronate C-HX, manufactured by Nippon Polyurethane Industry Co., Ltd.). Got.

  The liquid A and the liquid B were mixed and poured into an iron pipe mold having an inner diameter of 20 mm preheated to 110 ° C. In this pipe mold, a shaft 131 having a diameter of 10 mm is previously arranged in the center, and a polypropylene extruded tube (outer diameter 20 mm) is inserted so as to be in close contact with the inner wall surface. The mixture of the liquid A and the liquid B is poured into the pipe mold and heated at 110 ° C. for 120 minutes to obtain a molded body roll in which a conductive polyurethane layer is formed on the surface of the shaft 131 excluding both ends. It was. Subsequently, the compact roller was roughly polished to an outer diameter of 16 mm, and the surface roughness (JIS 10-point roughness Rz) was set to 8 μm by finisher polishing.

<Adjustment of reforming solution>
To 100 parts by weight of ethyl acetate, 10 parts by weight of carbon black (MA7, manufactured by Mitsubishi Chemical Co., Ltd., specific surface area 130 m ² / g) and 20 parts by weight of isocyanate compound (MDI) are added, mixed and dissolved, and modified. A liquid was prepared.

<Roller surface modification treatment>
In the state where the above-described modification treatment liquid is maintained at 23 ° C., the above-described polished roller is immersed for 30 seconds, and then heated in an oven maintained at 120 ° C. for 1 hour, whereby the surface of the elastic layer 132 is formed. The developing roller 13 of Example 1 in which the surface modification layer 133 was formed was obtained.

Example 2
Development of Example 2 was carried out in the same manner as in Example 1 except that the amount of isocyanate (Coronate C-HX, manufactured by Nippon Polyurethane Co., Ltd.) in the elastic layer 132 was changed from 20 parts by weight to 23 parts by weight. A roller 13 was obtained.

Example 3
Development of Example 3 was carried out in the same manner as in Example 1 except that the amount of isocyanate (Coronate C-HX, manufactured by Nippon Polyurethane Co., Ltd.) added to elastic layer 132 was changed from 20 parts by weight to 34 parts by weight. A roller 13 was obtained.

Example 4
10 parts by weight of carbon black (MA7, manufactured by Mitsubishi Chemical Corporation, specific surface area 130 m ² / g) to be added to the reforming treatment liquid is added 10 parts by weight of carbon black (MA33, manufactured by Mitsubishi Chemical Corporation, specific surface area 85 m ² / g). The developing roller 13 of Example 4 was obtained by the same method as that of Example 3 except that the surface modified layer 133 was formed.

Example 5 FIG.
10 parts by weight of carbon black (MA7, manufactured by Mitsubishi Chemical Co., Ltd., specific surface area 130 m ² / g) to be added to the reforming treatment liquid, 10 wt.% Of carbon black (MA25, manufactured by Mitsubishi Chemical Corporation, specific surface area 55 m ² / g) The developing roller 13 of Example 5 was obtained in the same manner as in Example 3 except that the surface modified layer 133 was formed.

Example 6
In addition to 10 parts by weight of the carbon black of Example 5 (MA25, manufactured by Mitsubishi Chemical Corporation, specific surface area 55 m ² / g), carbon black (acetylene black: Toka Black # 5500, Tokai Carbon Co., Ltd.) The surface-modified layer 133 was formed by adding 10 parts by weight of the product (specific surface area 225 m ² / g), and the developing roller 13 of Example 6 was obtained in the same manner as in Example 3 except that.

Comparative Example 1
10 parts by weight of carbon black (MA7, manufactured by Mitsubishi Chemical Corporation, specific surface area 130 m ² / g) to be added to the modification treatment liquid is added to carbon black (acetylene black: Toka Black # 5500, manufactured by Tokai Carbon Co., Ltd., specific surface area 225 m. ² / g) The surface modified layer was prepared by changing to 10 parts by weight, and a developing roller 13 of Comparative Example 1 was obtained in the same manner as in Example 3 except that.

Comparative Example 2
The addition amount of isocyanate (Coronate C-HX, manufactured by Nippon Polyurethane Co., Ltd.) in the elastic layer 132 was changed from 34 parts by weight to 38 parts by weight. A developing roller 13 was obtained.

Comparative Example 3
The addition amount of isocyanate (Coronate C-HX, manufactured by Nippon Polyurethane Co., Ltd.) in the elastic layer 132 was changed from 34 parts by weight to 20 parts by weight. A developing roller 13 was obtained.

  With respect to the developing rollers 13 of Examples 1 to 6 and Comparative Examples 1 to 3 thus prepared, the surface hardness and the residual potential were measured as follows.

  The surface hardness (micro rubber hardness: MD-1 hardness) of the developing roller 13 is automatically measured using a type A of a micro rubber hardness meter MD-1 manufactured by Kobunshi Keiki Co., Ltd., and the maximum value (peak hold value) is obtained. I read it.

  The residual potential of the developing roller 13 was automatically measured using a dielectric relaxation analysis system DRA-2000 manufactured by QEA. Specifically, as shown in FIG. 4, a measuring head 40 having a corona discharger 41 and a surface potential meter 42 is opposed to the developing roller 13 at a distance (C) of 1 mm, and the developing roller along the guide 43. 13 in the longitudinal direction. The surface at a predetermined position of the developing roller 13 is charged by the discharge of the corona discharger 41 of the measuring head 40, and after 0.1 second (by moving the measuring head 40), the potential (residual potential) at the position is changed to the surface. Measure with the electrometer 42. The larger the value of the residual potential, the easier the charge is accumulated and the stronger the dielectric property.

  Furthermore, a printing test was performed using the developing rollers 13 of Examples 1 to 6 and Comparative Examples 1 to 3.

  The printing test was performed using a MICROLINE 5900dn (resolution 600 DPI, manufactured by Oki Data Corporation) of an optical LED type color electrophotographic printer (image forming apparatus 10 shown in FIG. 1). As the developer, a non-magnetic one-component negatively chargeable pulverized toner having an average particle size of 5.5 μm was used. The printing environment was a temperature of 23 ° C., a relative humidity of 45% RH, plain paper was used as the paper P, and 10,000 sheets of 0.3% density solid images were continuously printed.

  After continuous printing of 10,000 sheets, the evaluation pattern of FIG. 5A including a 100% density portion and a 0% density portion was printed for evaluation of uneven image density. In FIG. 5A, the vertical direction (Y direction) coincides with the transport direction of the paper P, and the horizontal direction (X direction) coincides with the width direction of the paper P. In the evaluation pattern, the first pattern portion in which the 100% density portion is continuous over almost the entire region in the Y direction (excluding the peripheral portion), and the 100% density portion is continued in the middle of the Y direction (center portion). Thereafter, the second pattern portion in which the 0% concentration portion continues is provided alternately in the X direction. For convenience of illustration, in FIG. 5A, the 100% density portion is indicated by hatching.

  When the toner adheres to the developing roller 13 (including the case where the filming has developed), as shown in FIG. 5B, the distance corresponding to the outer peripheral length (circumference) of the developing roller 13 from the Y-direction tip of the pattern Density reduction occurs behind the position separated by L (a region indicated by hatching in FIG. 5B). Therefore, here, in the first and second pattern portions, the density was measured using a spectral color densitometer X-Rite 528 (manufactured by X-Rite) at positions P1 and P2 behind the center of the sheet. When the density difference between the positions P1 and P2 is less than 0.05, the evaluation result is “good”, and when it is 0.05 or more, the evaluation result is “poor”.

  In addition, after the above-described continuous printing and printing of the evaluation pattern are completed, the color electrophotographic printer is left for a long time without performing the printing operation, and then the surface of the elastic layer 132 of the developing roller 13 is observed, and the regulating blade 16 The presence or absence of nip marks (concave portions) was examined.

  The measurement results of the developing rollers 13 of Examples 1 to 6 and Comparative Examples 1 to 3, and the results of printing tests using these developing rollers 13 are shown in FIG.

Examples 1-6.
The residual potential of the developing roller 13 in Examples 1 to 6 is as low as 1 to 8 V in the initial stage (before continuous printing) and 5 to 10 V after continuous printing, and suppresses electrical adsorption of toner to the developing roller 13. I was able to. Further, the MD-1 hardness was as low as 40 to 55 °, and the mechanical stress acting on the toner could be reduced.

  The evaluation results of the image density unevenness using the evaluation pattern (FIG. 5) were all “good”. That is, from the initial stage to after the continuous printing, the toner does not adhere to the surface of the developing roller 13, and an image having no density unevenness is obtained.

Such a result was obtained because carbon black MA7, MA33, MA25 (furnace black, specific surface area 55 to 130 m ² / g) used in the surface modification layer 133 of the developing roller 13 and not developed. However, it is considered that stable conductivity was developed from the initial stage to after continuous printing.

  Further, in Example 6, two types of carbon black are used for the surface modification layer 133, but one of them is carbon black (MA25) whose structure is not developed. Until later, it is considered that a stable image can be expressed and a good image without unevenness in density was obtained.

Comparative Example 1
In Comparative Example 1, the MD-1 hardness of the developing roller 13 was as low as 55 °, and mechanical stress acting on the toner could be reduced. However, the residual potential was 2 V in the initial stage, but became as high as 35 V after continuous printing, and the evaluation result of the image density unevenness was x (defect). This is because carbon black (acetylene black, specific surface area of 225 m ² / g) having a developed structure was used, so that the conductivity deteriorated with the destruction of the structure, thereby causing the toner to be electrically adsorbed to the developing roller 13. As a result, it is considered that toner adheres to the surface of the developing roller 13 and uneven image density occurs.

Comparative Example 2
The residual potential of the developing roller 13 of Comparative Example 2 was as low as 5 V at the initial stage and 6 V after continuous printing, and the electrical adsorption of toner onto the developing roller 13 could be reduced. However, the MD-1 hardness was as high as 57 °, and the evaluation result of the image density unevenness was x (defect). This is because, since the surface hardness of the developing roller 13 is high, the mechanical stress acting on the toner increases, and the toner adheres to the surface of the developing roller 13 as the toner is crushed, leading to uneven image density. It is thought that.

Comparative Example 3
The residual potential of the developing roller 13 of Comparative Example 3 was as low as 4 V at the initial stage and 5 V after continuous printing, and the electrical adsorption of toner onto the developing roller 13 could be reduced. Further, the MD-1 hardness was as low as 30 °, and the mechanical stress acting on the toner could be reduced. Further, the evaluation result of the image density unevenness was ○ (good). However, when the developing roller 13 of Comparative Example 3 is left for a long time without printing operation, the outer peripheral portion (elastic layer 132) that has been in contact with the regulating blade 16 is depressed, and printing is performed thereafter. As a result, a streak pattern corresponding to the period of the developing roller 13 occurred in the image. This is presumably because the compression set was insufficient due to the low surface hardness of the elastic layer 132 of the developing roller 13.

  As described above, the developing roller 13 according to the present embodiment exhibits stable conductivity from the initial stage to after the continuous printing of the carbon black having no structure used in the surface modification treatment. By doing so, the residual charge can be suppressed within the range of 1 to 10 V, and the electrical adsorption of the toner to the developing roller 13 can be suppressed.

  Further, by setting the MD-1 hardness of the elastic layer 132 of the developing roller 13 to 40 to 55 °, mechanical stress acting on the toner is reduced without impairing the compression set characteristic of the elastic layer (rubber) itself. Can be made.

  In this way, by suppressing the electrical adsorption of the toner to the developing roller 13 and further reducing the mechanical stress acting on the toner, the toner adheres to the surface of the developing roller 13 (and further the toner adheres). Filming due to the progress of the above-described process can be prevented, and a good printed image without density unevenness can be obtained.

Second embodiment.
In the first embodiment described above, the elastic layer 132 of the developing roller 13 contains lithium perchlorate as an ionic conductive agent. In contrast, in the second embodiment, the elastic layer 132 of the developing roller 13 contains conductive carbon black as an electronic conductive agent. The other components of the second embodiment are the same as those of the first embodiment.

  First, a method for producing the developing roller 13 of an example in the present embodiment and a developing roller 13 of a comparative example corresponding thereto will be described.

Example 7
When forming the elastic layer 132 of the developing roller 13, 5 parts by weight of conductive carbon black (Toka Black # 5500, manufactured by Tokai Carbon Co., Ltd.) as an electronic conductive agent is added instead of lithium perchlorate as an ionic conductive agent. Otherwise, the elastic layer 132 was formed by the same method as in Example 1. Further, the modification treatment liquid was prepared by the same method as in Example 1, and the surface modification treatment was performed by the same method as in Example 1 to obtain the developing roller 13 of Example 7.

Example 8 FIG.
Development of Example 8 was carried out in the same manner as in Example 7 except that the amount of isocyanate (Coronate C-HX, manufactured by Nippon Polyurethane Co., Ltd.) added to elastic layer 132 was changed from 20 parts by weight to 23 parts by weight. A roller 13 was obtained.

Example 9
The addition amount of the isocyanate (Coronate C-HX, manufactured by Nippon Polyurethane Co., Ltd.) in the elastic layer 132 was changed from 20 parts by weight to 30 parts by weight, and the others were the same as in Example 7 except that A developing roller 13 was obtained.

Example 10
10 parts by weight of carbon black (MA7, manufactured by Mitsubishi Chemical Corporation, specific surface area 130 m ² / g) to be added to the reforming treatment liquid is added by 10 weight of carbon black (MA33, manufactured by Mitsubishi Chemical Corporation, specific surface area 85 m ² / g). The developing roller 13 of Example 10 was obtained in the same manner as in Example 7 except that the surface modified layer 133 was formed.

Example 11
10 parts by weight of carbon black (MA7, manufactured by Mitsubishi Chemical Co., Ltd., specific surface area 130 m ² / g) to be added to the reforming treatment liquid, 10 wt.% Of carbon black (MA25, manufactured by Mitsubishi Chemical Corporation, specific surface area 55 m ² / g) In the same manner as in Example 7, the developing roller 13 of Example 11 was obtained.

Example 12
In addition to 10 parts by weight of the carbon black of Example 5 (MA25, manufactured by Mitsubishi Chemical Corporation, specific surface area 55 m ² / g), carbon black (acetylene black: Toka Black # 5500, Tokai Carbon Co., Ltd.) The surface-modified layer 133 was formed by adding 10 parts by weight of a specific surface area of 225 m ² / g, and a developing roller 13 of Example 12 was obtained in the same manner as in Example 3 except that.

Comparative Example 4
10 parts by weight of carbon black (MA7, manufactured by Mitsubishi Chemical Corporation, specific surface area 130 m ² / g) to be added to the modification treatment liquid is added to carbon black (acetylene black: Toka Black # 5500, manufactured by Tokai Carbon Co., Ltd., specific surface area 225 mm. ² / g) The developing roller of Comparative Example 4 was obtained in the same manner as in Example 7 except that the surface modified layer was formed by changing to 10 parts by weight.

Comparative Example 5
The amount of isocyanate (Coronate C-HX, manufactured by Nippon Polyurethane Co., Ltd.) added to the elastic layer 132 was changed from 20 parts by weight to 35 parts by weight. A developing roller 13 was obtained.

Comparative Example 6
The addition amount of isocyanate (Coronate C-HX, manufactured by Nippon Polyurethane Co., Ltd.) in the elastic layer 132 was changed from 20 parts by weight to 18 parts by weight, and the other methods were performed in the same manner as in Example 7 except that A developing roller 13 was obtained.

  As described in the first embodiment, each measurement and printing test were performed on the developing rollers of Examples 7 to 12 and Comparative Examples 4 to 6 produced as described above. The measurement results and test results are shown in FIG.

Examples 7-12.
The residual potentials of the developing rollers 13 of Examples 7 to 12 were as low as 1 to 7 V in the initial stage and 5 to 10 V after continuous printing, and the electrical adsorption of the toner to the developing roller 13 could be suppressed. Further, the MD-1 hardness was as low as 40 to 55 °, and the mechanical stress acting on the toner could be reduced. In addition, the evaluation results of the uneven density using the evaluation pattern (FIG. 5) were all good (good).

This is because carbon black MA7, MA33, MA25 (furnace black, specific surface area of 55 to 130 m ² / g) used in the surface modification layer 133 of the developing roller 13 after the continuous printing from the initial stage is used. This is thought to be due to the fact that stable electrical conductivity was achieved.

  Further, in Example 12, two types of carbon black are used for the surface modification layer 133, but one of them is carbon black (MA25) having an undeveloped structure. Until later, it is considered that a stable image can be expressed and a good image without unevenness in density was obtained.

Comparative Example 4
In Comparative Example 4, the MD-1 hardness of the developing roller 13 was as low as 55 °, and the mechanical stress acting on the toner could be reduced. However, the residual potential was 3 V in the initial stage, but became as high as 41 V after continuous printing. The evaluation result of the image density unevenness was x (defect). This is because carbon black having a developed structure is used, so that the conductivity deteriorates with the destruction of the structure, and the electrical adsorption of the toner to the developing roller 13 is promoted. This is considered to be due to the occurrence of toner fixation and uneven image density.

Comparative Example 5
The residual potential of the developing roller 13 of Comparative Example 5 was as low as 4 V at the initial stage and 6 V after continuous printing, and the electrical adsorption of toner onto the developing roller 13 could be reduced. However, the MD-1 hardness was as high as 60 °, and the evaluation result of the image density unevenness was x (defect). This is because, since the surface hardness of the developing roller 13 is high, the mechanical stress acting on the toner increases, and the toner adheres to the surface of the developing roller 13 as the toner is crushed, leading to uneven image density. It is thought that it was because of.

Comparative Example 6
The residual potential of the developing roller 13 of Comparative Example 6 was as low as 4 V in the initial stage and 7 V after continuous printing, and the electrical adsorption of toner onto the developing roller 13 could be reduced. Further, the MD-1 hardness was as low as 35 °, and mechanical stress acting on the toner could be reduced. Further, the evaluation result of the image density unevenness was ○ (good). However, when the developing roller 13 of Comparative Example 6 is left for a long time in a state where there is no printing operation, a dent is generated in the outer peripheral portion (elastic layer 132) that has been in contact with the regulating blade 16, and printing is performed thereafter. As a result, a streak pattern corresponding to the period of the developing roller 13 occurred in the image. This is presumably because the compression set was insufficient due to the low surface hardness of the elastic layer 132 of the developing roller 13.

  From the above results, according to the present embodiment, as in the first embodiment, the carbon black having no developed structure used in the surface modification process of the developing roller 13 reaches from the initial stage to the continuous printing. In the meantime, by expressing stable conductivity, the residual charge can be suppressed within the range of 1 to 10 V, and the electrical adsorption of the toner to the developing roller 13 can be suppressed.

  Further, by setting the MD-1 hardness of the elastic layer 132 of the developing roller 13 to 40 to 55 °, mechanical stress acting on the toner is reduced without impairing the compression set characteristic of the elastic layer (rubber) itself. Can be made.

  In this way, by suppressing the electrical adsorption of the toner to the developing roller 13 and further reducing the mechanical stress acting on the toner, the toner adheres to the surface of the developing roller 13 (and further the toner adheres). Filming due to the progress of the above-described process can be prevented, and a good printed image without density unevenness can be obtained.

  1, 1B, 1Y, 1M, 1C Process unit, 10 image forming apparatus, 11 photosensitive drum (electrostatic latent image carrier), 12 unit body, 13 developing roller (developer carrier), 14 toner supply roller (development) Agent supplying member), 15 charging roller, 17 cleaning blade, 18 toner cartridge, 19 LED head, 20 transfer unit, 21 transport belt, 22 transfer roller, 31 cassette, 32 paper feed roller pair, 34 registration roller pair, 35 fixing device , 40 measuring head, 41 corona discharger, 42 surface potential meter, 131 conductive shaft (shaft), 132 elastic layer, 133 surface modified layer.

Claims (6)

A developer carrier for attaching the developer to the electrostatic latent image carrier;
A developer supply member for supplying a developer to the developer carrier,
The developer carrier is
A conductive shaft;
An elastic layer formed of a conductive urethane rubber formed on the outer peripheral surface of the shaft and containing an ionic conductive agent or an electronic conductive agent;
A developing device comprising: a surface modified layer formed by impregnating a surface of the elastic layer with carbon black having an undeveloped structure and an isocyanate group-containing substance.   2. The developing device according to claim 1, wherein a micro rubber hardness on an outer peripheral surface of the developer carrying member is in a range of 40 to 55 [deg.].   The developing device according to claim 1, wherein a residual potential of the developer carrying member is in a range of 1V to 10V. 4. The developing device according to claim 1, wherein the carbon black having no developed structure has a specific surface area in a range of 55 to 130 m ² / g by a BET method. 5.   The developing device according to claim 1, wherein the elastic layer contains carbon black as the electronic conductive agent. An image forming apparatus using the developing device according to claim 1.

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