JP4223978B2 - Non-magnetic one-component developing device - Google Patents

Description

  The present invention relates to a non-magnetic one-component developing device.

  In electrophotographic image forming apparatuses such as copying machines, printers, and electrostatic information recording apparatuses, the surface of a photoconductor containing a photoconductive material is uniformly charged, and the charged surface is exposed to form an electrostatic latent image. Then, the toner is attached to the electrostatic latent image to form a toner image, the toner image is transferred to the surface of the transfer material, and fixed by means such as heating and pressurization, whereby an image is formed on the transfer material. .

  In a conventional electrophotographic image forming apparatus, for example, a non-magnetic one-component developing device is used to form a toner image on a photoreceptor. The non-magnetic one-component developing device includes a developing roller disposed in contact with the photoreceptor and rotatably provided, and a toner thin layer disposed on the circumferential surface of the developing roller and disposed on the circumferential surface of the developing roller. A regulating blade for making the thickness uniform, a supply roller that is disposed in contact with the developing roller and supplies toner to the peripheral surface of the developing roller, a developing tank that is filled with toner, and a toner that is provided in and is filled in the developing tank And a stirring blade for stirring. In the nonmagnetic one-component developing device, nonmagnetic toner is used as the toner. According to the non-magnetic one-component developing device, the toner is charged by friction between the developing roller, the supply roller, the regulating blade, and the like, and the toner is attached to the electrostatic latent image on the photoreceptor.

  Such a non-magnetic one-component developing device has a drawback due to the material of the supply roller. That is, the supply roller is usually made of a foam to carry the toner, but the supply roller made of a single-bubble foam exists in a state of completely independent closed cells without connecting each bubble. Therefore, the amount of toner carried in the bubbles is small. As a result, the amount of toner supplied to the developing roller decreases, the followability of a high-print image such as a solid image deteriorates, and print defects such as blurring occur. Moreover, in the foam containing a closed cell, since the cell diameter of a bubble is generally small, the surface hardness is very high. For this reason, the contact pressure between the supply roller and the developing roller and thus the driving torque of each roller increase, and toner filming on the developing roller, toner deterioration, and wear of the supply roller are likely to occur. Furthermore, as a rubber material capable of forming a single-foam foam, a silicone rubber is exclusively used because a foam in which bubbles having a uniform size and shape are uniformly dispersed can be obtained. However, since silicone rubber is expensive, it greatly increases the manufacturing cost of the supply roller.

  On the other hand, a supply roller made of an open cell foam containing open cells is also known. In such a supply roller, since the bubbles are continuously connected to the shaft portion, the toner remains excessively in the bubbles, and the surface is hardened in a state containing the toner by using for a long time. As a result, the drive torque increases accordingly. The increase in the driving torque causes toner filming on the developing roller, toner deterioration, wear of the supply roller, and the like, similarly to the supply roller made of a single foaming foam. In the foam containing open cells, since the cell diameter of the bubbles is relatively large, the cell wall is destroyed as the driving time becomes longer, and the number of cells capable of holding the toner is remarkably reduced. This lowers the supply of toner onto the developing roller, so that the followability of a solid image is deteriorated, and it is unavoidable that printing defects such as blurring occur.

  Further, in order to prevent an increase in driving torque, for example, the peripheral speed of the supply roller is made equal to or smaller than the peripheral speed of the developing roller. However, even if the peripheral speeds of the supply roller and the developing roller are adjusted in this way, it is inevitable that the driving torque increases due to long-term use.

In view of the above problems, a supply roller made of a single foam rubber foam having a density of 0.18 to 0.28 g / cm ³ has been proposed (for example, see Patent Document 1). However, the supply roller made of such a rubber foam has insufficient durability, particularly long-term wear resistance, and its surface is easily worn by friction with a developing roller, a regulating blade, and the like. More specifically, due to long-term use, cells on the surface of the supply roller made of rubber foam are torn, and the rubber material is scraped off to reduce the outer diameter of the supply roller compared to the initial use. . As a result, poor toner scraping by the developing roller, a decrease in toner charge amount due to insufficient contact, a decrease in followability to the developing roller, and the like, and it is unavoidable that printing defects such as blurring occur. In particular, in a high-print image such as a solid image, the print blur after the consumption of toner for one rotation of the developing roller and one rotation of the supply roller is conspicuous. To do.

  In addition, in image forming apparatuses such as copying machines, the guaranteed number of sheets (number of printable sheets) required without parts renewal or failure continues to increase, and the service life of the supply rollers is also increasing. Required. For this purpose, a supply roller made of rubber crosslinked with a plasticizer has been proposed. However, such a supply roller is not suitable for extending the life of the supply roller because the plasticizer disappears due to friction and heat caused by pressure contact with the developing roller and the cross-linked structure is lost.

JP-A-5-273848

  An object of the present invention is a supply roller made of a rubber foam, the surface of which has a foam structure capable of holding an appropriate surface hardness and an appropriate amount of toner, and the surface state is used even after long-term use. To provide a non-magnetic one-component developing device having a supply roller maintained at the same level as the initial stage and having a significantly long service life.

The present invention relates to a developing roller having a surface hardness of 45 ° to 65 ° (45 ° or more and 65 ° or less) as a spring hardness Hs (A), and rotating toner while being in pressure contact with the developing roller. A ratio of the peripheral speed Sa of the developing roller to the peripheral speed Sb of the supply roller (Sb), including a supply roller that is supplied above and a regulating blade that uniformly regulates the thickness of the toner thin layer formed on the developing roller. / Sa) in a non-magnetic one-component developing device having a ratio of 0.4 to 1.0,
In the pressure contact portion between the developing roller and the supply roller, the rotation direction of the development roller is opposite to the rotation direction of the supply roller.
The nip width between the developing roller and the supply roller is 2.0 to 4.0 mm (2.0 mm or more and 4.0 mm or less),
Feed rollers, the cell diameter of 300 to 500 [mu] m (300 [mu] m or more, 500 [mu] m or less) der is, the foaming ratio (porosity) is 0.75 to 0.85 (0.75 to 0.85 or less) of ethylene propylene is A non-magnetic one-component developing device comprising a continuous single-cell foam of a rubber material.

  According to the present invention, a developing roller having a surface hardness of 45 ° to 65 ° as the spring hardness Hs (A) is included, and the ratio (Sb / Sa) between the circumferential speed Sa of the developing roller and the circumferential speed Sb of the supply roller. ) Is a non-magnetic one-component developing device of 0.4 to 1.0, wherein at least the surface of the supply roller is a continuous monofoam foam of rubber material, and the cell diameter of the bubbles is 300 to 500 μm A non-magnetic one-component developing device constituted by a certain material and having a very long service life is provided.

  The supply roller used in the non-magnetic one-component developing device of the present invention has an appropriate surface hardness and a foam structure capable of holding an appropriate amount of toner, and is excellent in toner supply to the developing roller. Further, even after long-term use or storage, the surface hardness is maintained at the same level as in the initial use, so that the drive torque does not increase. Further, even when used for a long period of time, the walls of the bubbles in the foam structure are destroyed and the foam structure is hardly damaged, so that the toner supply to the developing roller is prevented from being lowered. In addition, it has excellent wear resistance.

  Therefore, in the non-magnetic one-component developing device of the present invention, the developing roller having the surface hardness in the specific range is used, the peripheral speed ratio of the supply roller to the developing roller is in the specific range, and the supply roller is By using it, image defects such as shading mainly due to the material of the supply roller, toner filming on the developing roller, toner deterioration, wear of the supply roller, etc. do not occur, and image defects over a very long period of time It is possible to form a high-quality image with no image.

  In this specification, “spring hardness Hs (A)” is an index representing surface hardness, and is a value measured by an A-type spring hardness tester defined in JIS K 6301.

Also, as the material of the continuous single foam rubber foam constituting the feed roller, by the use of ethylene propylene rubber (EPDM), and held for a long time, the elasticity of the supply roller surface to a preferred range, increasing the driving torque Therefore, it is effective to form an image with higher image quality.

Furthermore, as a continuous single foam rubber foam constituting the supply roller, the foamed rate by using those in the range of 0.75 to 0.85, the surface hardness of the supplying roller surface increases with time This is further prevented, and the occurrence of toner filming on the developing roller, toner deterioration, wear of the supply roller and the like due to an increase in driving torque is further reduced. In addition, the occurrence of image defects in which toner adheres to non-printing portions during image formation is further reduced.

Furthermore, by the nip width is the width of the contact portion between the developing roller and the supply roller to the range of 2.0 to 4.0 mm, an increase of the driving torque is prevented, even less occurrence of disadvantages caused thereby Furthermore, the occurrence of image defects such as blurring is further reduced.

  FIG. 1 is a side view schematically showing a configuration of a main part of an electrophotographic image forming apparatus 1. The image forming apparatus 1 is supported so as to be rotatable in the direction of an arrow 10, and has a photosensitive member 2 on which an electrostatic latent image is formed, and faces the peripheral surface of the photosensitive member 2. And a non-magnetic one-component developing device 3 according to the first embodiment of the present invention, which is provided so as to extend in parallel with the extending direction.

  Around the photoreceptor 2, a charger, an exposure unit, a non-magnetic one-component developing device 3, which are not shown, face the circumferential surface of the photoreceptor 2 and from the upstream side to the downstream side in the rotational direction of the arrow 10, Non-transfer means and cleaning means are provided in this order.

  As the photoreceptor 2, a conventional photoreceptor having a photosensitive layer formed on the surface of a conductive support can be used. The photosensitive layer may be a single layer type including a charge generation material and a charge transport material in one layer, or a charge generation layer including a charge generation material and a charge transport layer including a charge transport material are laminated. A laminated type may be used. The photosensitive layer can further include an intermediate layer, an undercoat layer, a protective layer, and the like. The peripheral surface of the photoconductor 2 is uniformly charged with a single polarity by a charger (not shown) and then irradiated with light based on image information by an exposure unit (not shown) to form an electrostatic latent image.

The nonmagnetic one-component developing device 3 according to the first embodiment of the present invention includes a developing roller 4 that supplies toner to the peripheral surface of the photoreceptor 2 and develops an electrostatic latent image into a toner image, and a developing roller 4. A supply roller 5 that supplies toner, a doctor 6 that is a regulating blade that equalizes the thickness of the toner layer on the circumferential surface of the developing roller 4, a developing tank 7 that contains toner, and a developing tank 7. a stirring blade 8 for stirring the toner accommodated in the developing tank 7 including.

  The non-magnetic one-component developing device 3 includes a developing bias power source (not shown) that applies a developing bias voltage to the developing roller 4, a toner supply bias power source (not shown) that applies a bias voltage to the supply roller 5, and a doctor 6. A doctor bias power source (not shown) for applying a bias voltage is provided.

  The developing roller 4 is provided such that its peripheral surface is in contact with the peripheral surfaces of the photoreceptor 2 and the supply roller 5, and is supported rotatably in the direction of the arrow 11. The developing roller 4 includes a cylindrical shaft 4a made of a metal such as stainless steel, and an elastic layer 4b made of a rubber elastic body such as a urethane rubber elastic body formed with a uniform layer thickness on the peripheral surface of the shaft 4a. It is configured to include a cylindrical shape. The urethane rubber elastic body constituting the elastic layer 4b has a spring hardness Hs (A) of 45 to 65 °. If the spring hardness Hs (A) is less than 45 °, there is no particular problem in the initial stage of use, but the developing roller may be distorted or deformed by continuous use for a long time or leaving it for a long time. If the angle exceeds 65 °, the surface hardness of the developing roller increases, smooth rotation of the developing roller and the photosensitive member is not performed (banding), and image defects such as horizontal stripes (streaks) occur. In addition, the contact pressure between the photosensitive member and the developing roller increases, and the toner in the non-image forming portion tends to remain on the peripheral surface of the photosensitive member, thereby causing background fogging. Further, the toner is filmed on the peripheral surface of the photoconductor, causing an image defect. The urethane rubber elastic body constituting the elastic layer 4b contains a known conductive agent such as carbon black. Further, the surface roughness Rz of the urethane rubber elastic body is not particularly limited, but is preferably about 5 to 25 μm. Rz is a ten-point average roughness defined in JIS B 0601.

The developing roller 4 can be manufactured, for example, as follows. First, after adding 1 part by weight of conductive carbon to 100 parts by weight of polyesterol and uniformly dispersing, the temperature was raised to 140 ° C. and 1.33322 × 10 ^{3 to} 2.66644 × 10 ³ Pa (10 to 20 mmHg) The mixture is dehydrated and dried for 12 hours while stirring under reduced pressure. Under heating at 110 to 120 ° C., tolylene diisocyanate was added to this mixture to 7 parts by weight with respect to 100 parts by weight of polyesterol in the mixture, and vigorously mixed for 2 minutes, and then heated to 110 ° C. Pour and cure for 2 hours. When the cured product is taken out from the mold and further subjected to secondary crosslinking at 110 ° C. for 24 hours, a conductive rubber foam is obtained. The developing roller 4 is obtained by grinding the conductive rubber foam so as to have a desired diameter and surface roughness.

  The developing roller 4 is applied with a voltage from a power supply for developing bias (not shown) via the shaft 4a, and thereby the toner supplied from the supply roller 5 is carried as a thin layer on the peripheral surface thereof. The toner thin layer is made uniform in thickness by the doctor 6 and then brought into contact with the portion where the electrostatic latent image is formed on the peripheral surface of the photoreceptor 2, and the electrostatic latent image is formed by contact development. The toner image is developed.

  The supply roller 5 is provided such that its peripheral surface is in contact with the peripheral surface of the developing roller 4, and is supported rotatably in the direction of the arrow 12. A bias voltage is generally applied to the supply roller 5 from a toner supply bias power source (not shown) in a direction in which the toner is pressed against the developing roller 4. If the toner is negative, a larger bias voltage is applied to the negative side. At least the surface of the supply roller 5 is made of a continuous single foam rubber foam having a cell diameter of 300 to 500 μm. The continuous single-foam rubber foam is a rubber foam in which closed cells and open cells are mixed. When such a continuous single-bubble rubber foam is used, the surface hardness of the supply roller 5 is obtained by mixing the closed cells and the open cells, which is the case of the closed cells alone, that is, like the single-bubble foam. Does not become too high, and various inconveniences caused by the surface hardness becoming too high do not occur. Further, in the case of open cells alone, that is, like the open cell foam, toner remains in the bubbles and the surface hardness of the supply roller 5 is not increased. Generation of toner, toner deterioration, wear on the supply roller 5 and the like is prevented. Even in the case of a continuous single foam rubber foam, if the cell diameter is significantly less than 300 μm, the surface hardness increases and the driving torque increases, resulting in various inconveniences. On the other hand, if the cell diameter greatly exceeds 500 μm, the wall between the cells is torn or broken on the peripheral surface of the supply roller 5 as the developing device is used (driven), and the amount of toner that can be carried becomes small. As a result, the toner supply performance to the circumferential surface of the developing roller 4 is lowered, the followability of the solid image is deteriorated, and image defects such as blurring occur.

  The continuous single-foam rubber foam constituting the supply roller 5 preferably has a foaming ratio of 0.75 to 0.85. When the foaming ratio is significantly less than 0.75, the density of the foam becomes too high, the surface hardness of the supply roller 5 becomes high, and the frictional force with the developing roller 4 becomes high, so that the driving torque increases, In addition, toner filming on the circumferential surface of the developing roller 4, toner deterioration, wear of the supply roller 5, and the like may easily occur. If the foaming ratio greatly exceeds 0.85, the surface hardness of the supply roller 5 becomes too small, and the force for scraping off the excessive amount of toner adhering to the developing roller 4 becomes insufficient, so that the toner on the photosensitive drum 2 is removed. Excessive supply of toner occurs, and toner adheres to the non-printing area, which may cause image defects such as background fogging. Furthermore, since the toner carrying amount increases more than necessary, the supply roller 5 may be cured with the elapse of the driving time.

  The rubber material that is the material of the continuous single foam rubber foam constituting the supply roller 5 is not particularly limited, but a rubber material that can be vulcanized and foamed without adding a plasticizer is preferable. Specific examples thereof include ethylene propylene rubber (ethylene-propylene-diene copolymer synthetic rubber, EPDM), chloroprene rubber, nitrile rubber, butadiene rubber, styrene-butadiene rubber, nitrile-butadiene rubber, isoprene rubber, isobutylene- Examples include isoprene rubber. Among these, EPDM is preferable. EPDM can be completely cross-linked without using a plasticizer, and can maintain moderate elasticity over a long period of time and does not increase the driving torque, so it is possible to stabilize the driving torque within an appropriate range. is there. When a synthetic rubber using a plasticizer is used, the plasticizer disappears due to friction between the developing roller 4 and the supply roller 5, heat, etc., so that the elasticity is lost and the surface is hardened and the drive torque is increased. Further, EPDM can be a foam having a fine cell diameter comparable to a urethane foam conventionally used as a material constituting the supply roller 5, and the toner scraping ability on the developing roller 4, the developing roller 4 is also advantageous in terms of the ability to supply toner to the toner.

  The supply roller 5 can be manufactured according to a known method. For example, an unvulcanized foaming rubber composition containing a rubber material, a foaming agent, a conductive agent, a filler, a softening agent, a vulcanizing agent, a vulcanization accelerator and the like is prepared. The blending amount of each component is not particularly limited, and is appropriately selected from a wide range according to the type and blending amount of other components, the vulcanization conditions of the vulcanizer used for vulcanization foaming, and the foaming rate is 0. What is necessary is just to mix | blend each component so that it may become about 1-0.8, Preferably it is about 0.2-0.6. Here, the expansion ratio is a value obtained by dividing the density of vulcanized and foamed rubber by the density of unvulcanized rubber. Each component is mixed by, for example, kneading with a general rubber kneader kneader and a roll. The unvulcanized foaming rubber composition thus obtained is extruded into a tube shape by an extruder, and the tube is continuously heated by a hot air vulcanizer, whereby the foam vulcanization proceeds. A conductive foam tube is obtained. The conductive foam tube is cut to a predetermined length. A core metal having an adhesive applied to the peripheral surface thereof is press-fitted into the tube to bond the tube and the core metal. Furthermore, pressure is applied to the tube by a pressure means such as a pressure roll to break some of the closed cells to convert them into open cells, and rubber foaming with the desired foaming rate (void ratio) and average cell diameter Let it be the body. Further, the bonded body of the rubber foam and the core metal is subjected to grinding and adjusted to a desired value such as its diameter and surface roughness. Thereby, the supply roller 5 having a structure in which a coating layer containing a rubber foam is formed on the peripheral surface of the cored bar is obtained.

  As an apparatus for vulcanizing and foaming an unvulcanized foaming rubber composition, a UHF continuous vulcanizing apparatus is preferable. In this apparatus, for example, the UHF output is set to 0.1 to 1.5 kW, the UHF tank temperature is set to 200 to 240 ° C., and the HAV tank is set to a range of 200 to 230 ° C., and vulcanization foaming is performed. By carrying out the pressure operation, it is possible to obtain a rubber foam having a mixture of open cells and closed cells and having a foaming rate (void ratio) and an average cell diameter in the above-mentioned range. In addition, when using a UHF continuous vulcanization | cure apparatus, the rubber-like foam used by this invention may be obtained even if it does not implement the pressurization operation after vulcanization foaming.

By observing the cross section of the foam obtained by the above method with a scanning microscope, it can be confirmed that the foam is a continuous single-cell rubber foam in which open cells and closed cells are mixed. In the rubber foam used in the present invention, the ratio between open cells and single cells is not particularly limited, and when the cut surface of the rubber foam is observed with a scanning electron microscope, open cells and single cells can be visually recognized. Although it is good, the open cell ratio indicating the ratio of open cells is preferably 5% or more, more preferably 10% or more, and particularly preferably 10 to 60%.
The foaming rate (void ratio) of the rubber foam is determined as follows.

A volume V (mm ³ ) rubber foam was submerged under the surface of a water tank having an inner dimension of 1000 mm in length × 1000 mm in width, and the height h (mm) at which the water surface rose was measured and calculated according to the following formula: .
Foaming rate (%) = [(V−1000 × 1000 × h) / V] × 100%

  The open cell ratio (%), which is the ratio of open cells, can be measured according to the air pycnometer (air comparison hydrometer) method (1-1 / 2-1 atmospheric pressure method) defined in ASTM D-2856. At that time, an air comparison type hydrometer manufactured by Toshiba Beckman Co., Ltd. is used.

  The peripheral speed Sb of the supply roller 5 is in the range of 0.4 to 1.0 with respect to the peripheral speed Sa of the developing roller 4. If it is less than 0.4, the toner supply property to the developing roller 4 is lowered, the followability of the solid image is deteriorated, and image defects such as blurring occur. If it exceeds 1.0, the driving torque of the developing roller 4 and / or the supply roller 5 increases, resulting in inconvenience.

  Further, the developing roller 4 and the supply roller 5 rotate in the directions of the arrow 11 and the arrow 12, respectively, and in a portion (nip) where they are in pressure contact, the rotation direction is reverse and the sliding contact is made so as to face each other. . At this time, the nip width W is not particularly limited, but is preferably in the range of 2.0 to 4.0 mm. When the nip width is significantly less than 2.0 mm, the toner supply performance from the supply roller 5 to the developing roller 4 is lowered, and the followability of the solid image is deteriorated. If it greatly exceeds 4.0 mm, the friction between the developing roller 4 and the supply roller 5 increases, and accordingly, the driving torque increases, and toner filming on the peripheral surface of the developing roller, toner deterioration, the supply roller 5 It is easy for wear to occur.

  The supply roller 5 rotates in the direction of an arrow 12 under contact with the developing roller 4, carries the toner accommodated in the developing tank 7 on its peripheral surface, and supplies the toner to the peripheral surface of the developing roller 4. .

  The doctor 6 is located between the fixed end 6a fixed to the developing tank 7, the tip 6c inclined slightly in the direction away from the developing roller 4, and the fixed end 6a and the tip 6c, and is elastically deformed. And a contact portion 6b provided so as to be capable of being pressed against the peripheral surface of the developing roller 4. A predetermined bias voltage is applied to the doctor 6 from a doctor bias power source (not shown). That is, the bias voltage is applied in the direction in which the toner is pushed from the doctor 6 toward the developing roller 4 side. If the toner has a negative polarity, a larger bias voltage is applied to the doctor 6 on the negative electrode side.

  The contact portion 6b is made of an elastically deformable material having at least a surface opposed to the circumferential surface of the developing roller 4 and having a spring elasticity, and is in the vicinity of the tip 6c along the longitudinal direction (the rotational axis direction of the developing roller 2). A contact portion 6b facing the circumferential surface of the developing roller 4 is pressed against the circumferential surface of the developing roller 4 with a predetermined pressure.

  The doctor 6 is composed of a metal plate such as stainless steel having a plate thickness of about 0.07 to 0.15 mm, for example. The tip portion 6c can be formed by subjecting the metal plate to mechanical cutting, polishing, bending, or the like. In addition, the tip of the chip shaped into a desired shape in advance is attached to the metal plate with a conductive adhesive or the like, or a step is formed on the tip of the metal plate, and then the metal foil is applied with a conductive adhesive or the like from there. Can be formed by a processing method such as pasting.

The doctor 6 is in pressure contact with the circumferential surface of the developing roller 4 on the downstream side of the contact surface between the developing roller 4 and the supply roller 5 in the direction of the arrow 11, and determines the thickness of the thin toner layer carried on the circumferential surface of the developing roller 4. Make uniform. The toner thin layer having a uniform layer thickness is conveyed to a developing area where the developing roller 4 contacts the photoreceptor 2.
The developing tank 7 stores toner.

  The stirring blade 8 is provided in the developing tank 7 and is rotatably supported. The agitation blade 8 agitates the toner stored in the developing tank 7 to smoothly supply the toner to the supply roller 5 and also has a function of preventing solidification due to toner accumulation.

  The toner used in the nonmagnetic one-component developing device 3 of the present invention is not particularly limited, and conventional nonmagnetic one-component toner can be used. The non-magnetic one-component toner is obtained by adding and mixing an external additive such as silica to toner particles to remove aggregates and foreign matters. The toner particles are uniformly premixed with, for example, a binder resin, a colorant and an additive by a dry blender, a super mixer, a ball mill or the like, and the resulting mixture is mixed with, for example, a hand mixer, a roll, a single screw extruder, a twin screw It can be obtained by uniformly melting and kneading using a kneading apparatus such as an extrusion kneader, cooling and pulverizing the resulting kneaded product, and further classifying as necessary.

  In the nonmagnetic one-component developing device 3 of the present invention, the toner stored in the developing tank 7 is supplied to the developing roller 4 through the supply roller 5, and a thin toner layer is formed on the peripheral surface of the developing roller 4. . This toner thin layer is made uniform by the doctor 6 and then supplied to the photoreceptor 2, and the electrostatic latent image formed on the peripheral surface of the photoreceptor 2 is developed to form a toner image. .

The present invention will be specifically described below with reference to examples, comparative examples and test examples.
(Examples 1-2)
In a commercially available copying machine (trade name: AR260, manufactured by Sharp Corporation), a continuous single-bubble EPDM foam having a cell diameter of 500 μm (foaming ratio 0.82) or a continuous single-bubble EPDM foam having a cell diameter of 300 μm (foaming) An image forming apparatus including a non-magnetic one-component developing device 3 of the present invention shown in FIG. In the nonmagnetic one-component developing device 3, the surface hardness (spring hardness Hs (A)) of the developing roller 4 is 54 °, and the peripheral speed ratio of the supply roller 5 to the developing roller 4 is 0.9. The nip width W between the developing roller 4 and the supply roller 5 was 2.4 mm.

(Comparative Examples 1-4)
A supply roller (comparative example 1) made of continuous single-bubble EPDM foam having a cell diameter of 200 μm, a supply roller (comparative example 2) made of continuous single-bubble EPDM foam having a cell diameter of 700 μm, and a single-bubble EPDM foam An image forming apparatus was produced in the same manner as in Example 1 except that a supply roller (Comparative Example 3) or a supply roller (Comparative Example 4) made of open-cell EPDM foam was used.

(Test Example 1)
Using the image forming apparatuses obtained in Examples 1 and 2 and Comparative Examples 1 to 4, 10,000 photographs were taken in a normal temperature and humidity environment. Before and after that, a print test of an A3 black solid image was performed, and the solid followability and the surface hardness of the supply roller 5 were measured as follows. As the toner, a commercially available product (trade name: AR26-TB, manufactured by Sharp Corporation) was used. The results are shown in Table 1.

[Solid followability]
The density of the printing leading edge and trailing edge of the A3 black solid image was measured using an image density measuring device (trade name: X-rite, manufactured by X-rite), and the printing trailing edge was determined from the printing leading edge density value. The value obtained by subtracting the partial density value is defined as solid followability. If the solid followability is not 0.15 or less, it means that image defects such as blurring occur.

[Surface hardness]
An Asker FP spring hardness tester manufactured by Kobunshi Keiki Co., Ltd. was used. The surface hardness of the supply roller 5 was measured by fixing the surface of the supply roller 5 on a horizontal surface so that the supply roller 5 does not move, and placing an Asker FP spring hardness meter on the center of the supply roller 5. The surface hardness of the supply roller 5 is preferably 90 ° or less. When it exceeds 90 °, the wear of the supply roller 5 becomes remarkable.

  In Examples 1 and 2, the solid followability and the surface hardness of the supply roller 5 were 0.10 to 0.15 and the Asker FP hardness was 82 ° to 87 °, respectively, before and after the 10,000-sheet shooting test. Regarding image characteristics, solid followability is required to be 0.15 or less, and Asker FP hardness is required to be 90 ° or less in order to prevent wear of the supply roller. It is clear that the condition is met.

  In Comparative Example 1, an image failure occurred in the solid image after the 10,000 sheets were actually captured, and the solid followability was very poor at 0.28. This is presumably because the walls between the cells are broken as the driving time elapses, the apparent number of cells is reduced, and the toner supply performance is lowered.

  In Comparative Example 2, the surface hardness of the supply roller 5 exceeded 90 ° before 10,000 sheets were actually captured. Further, after 10,000 sheets were photographed, toner adhered to the developing roller 4 and the doctor 6, and the supply roller 5 was worn.

  In Comparative Example 3, an image defect occurred in the solid image before and after the actual shooting of 10,000 sheets, and the solid followability was about 0.25. This is presumably because the toner carrying amount of the supply roller 5 is small and the toner supply performance to the developing roller 4 is low.

  In Comparative Example 4, after 10,000 sheets were taken, the solid followability exceeded 0.15, and the surface hardness of the supply roller 5 exceeded 97 °. The driving torque was about 0.294 N · m (3.0 kgf · cm) or more. In order to prevent the supply roller 5 from being worn, the driving torque is required to be about 0.294 N · m or less. The driving torque was measured by attaching the developing device 3 to the SPEED CONTROL UNIT manufactured by ORIENTAL MOTOR, which was modified so that the developing device 3 was driven. The peripheral speed ratio during measurement was set to 0.9. The same shall apply hereinafter.

  In Comparative Example 4, as a result of the driving torque being about 0.294 N · m or more, toner adhesion occurred on the developing roller 4 and the doctor 6, and the supply roller 5 was worn. This is presumably because the toner soaks into the portion near the shaft of the supply roller 5 as the drive time elapses.

(Example 3)
Except for using the supply roller 5 made of a continuous single-bubble EPDM foam having a cell diameter of 380 μm (foaming ratio 0.81), the non-magnetic developing device 3 of the present invention is included in the same manner as in Example 1. An image forming apparatus was created.

(Comparative Examples 5-6)
Example 1 was used except that a supply roller (comparative example 5) made of continuous single-foam ester-based urethane rubber foam or a supply roller (comparative example 6) made of continuous single-foam ether-based urethane rubber foam was used. Thus, an image forming apparatus was created.

(Test Example 2)
Using the image forming apparatuses obtained in Example 3 and Comparative Examples 5 to 6, 20000 sheets were taken under normal temperature and humidity conditions, and before and after that, the surface hardness of the supply roller 5 was the same as in Test Example 1. Was measured. The results are shown in Table 2.

  In Example 3, it can be seen that there is almost no change in the surface hardness of the supply roller 5 before and after 20000 actual copying. On the other hand, in Comparative Example 5 and Comparative Example 6, the surface hardness of the supply roller 5 greatly increased after 20000 sheets were actually photographed, and the supply roller 5 was worn.

(Examples 4 to 7)
The nip width between the developing roller 4 and the supply roller 5 in the developing device 3 of the present invention is 1.5 mm (Example 4), 2.0 mm (Example 5), 4.0 mm (Example 6), or 4.5 mm (Example 6). An image forming apparatus was produced in the same manner as in Example 1 except that Example 7) was used.

  Using the obtained image forming apparatus, 10,000 sheets were photographed under a normal temperature and humidity environment, and before and after that, the solid followability was measured in the same manner as in Test Example 1. The driving torque was also measured. The results are shown in Table 3.

  In Example 4, although the driving torque was good, the solid followability was slightly insufficient. In Example 7, the solid followability was good, but the increase in driving torque was conspicuous. On the other hand, in Examples 5 and 6, both solid followability and driving torque were good.

(Examples 8 to 11)
As the supply roller 5, a continuous single-cell EPDM foam having a foaming ratio of 0.70 (Example 8), 0.75 (Example 9), 0.85 (Example 10) or 0.90 (Example 11) An image forming apparatus was produced in the same manner as in Example 1 except that a supply roller made of

  Using the obtained image forming apparatus, 10,000 sheets were photographed under normal temperature and humidity conditions, and before and after that, the surface hardness of the supply roller 5 was measured in the same manner as in Test Example 1. The driving torque was measured. The results are shown in Table 4.

In Example 8, both the driving torque and the surface hardness were slightly insufficient, and toner adhesion occurred on the developing roller 4 and the doctor 6, and the supply roller 5 was worn. In Example 11, the surface hardness was insufficient, and in the initial image, toner adhesion was observed on the non-image forming portion. This is presumably because the hardness of the supply roller 5 is 70 ° or less, which is a small value for scraping off the toner on the developing roller 4 at the initial stage, and excessive supply to the photosensitive member 2 occurs.
In Examples 9 and 10, both the driving torque and the surface hardness were good.

1 is a side view schematically showing a configuration of a main part in an electrophotographic image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrophotographic image forming apparatus 2 Photoconductor 3 Non-magnetic one-component developing device 4 Developing roller 4a Shaft 4b Elastic layer 5 Supply roller 6 Doctor 6a Fixed end 6b Contact part 6c Tip part 7 Developing tank 8 Stirring blade 10, 11, 12 Arrows

Claims (1)

A developing roller having a surface hardness of 45 ° to 65 ° as spring hardness Hs (A), a supply roller for supplying toner onto the developing roller by rotating while being pressed against the developing roller, and a developing roller formed on the developing roller And a regulating blade that uniformly regulates the thickness of the toner thin layer, and the ratio (Sb / Sa) of the peripheral speed Sa of the developing roller to the peripheral speed Sb of the supply roller is 0.4 to 1.0. In a magnetic one-component developing device,
In the pressure contact portion between the developing roller and the supply roller, the rotation direction of the development roller is opposite to the rotation direction of the supply roller.
The nip width between the developing roller and the supply roller is 2.0 to 4.0 mm,
Feed roller is a non-magnetic cell diameter Ri 300~500μm der, foaming ratio (porosity) is characterized in that it consists of continuous single froth foam of ethylene-propylene rubber is 0.75 to 0.85 One-component developing device.

Images