JP2007178588A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of stably charging a photoreceptor all the time by using a charging roller by maintaining a stable cleaning performance over long time even while using the highly durable photoreceptor. <P>SOLUTION: In the image forming apparatus, an image carrier as photoreceptor has an HU (universal hardness value) of 150 N/mm<SP>2</SP>to 220 N/mm<SP>2</SP>and an elastic deformation rate We of 40 to 65% upon the pressing at the maximum load 6 mN in the hardness test using a Vickers quadrangular diamond indenter and has a surface on which the ruggedness comprising a plurality of globular trace hollows are formed and satisfies such conditions that diameter R of the globular trace hollows is 1 to 50 μm, mean interval Sm-d of surface ruggedness is 10 to 100 μm and surface roughness Rz-d is 0.3 to 2.5 μm, and a contact charging member has a surface roughness Rz-c of 1 to 20 μm, has mean interval Sm-c of surface ruggedness is 10 to 500 μm, has Asker C hardness of 30 to 90° and satisfies 0.2≤(Sm-c)/(Sm-d)≤10. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile that forms an image using an electrophotographic system.

  In general, in an image forming apparatus that records an image on a recording medium such as paper such as a copying machine, a printer, and a facsimile, an electrophotographic system is employed as a system for recording the image on the recording medium. In an electrophotographic system, a photosensitive drum having a surface coated with a photosensitive material is used as an image carrier. First, after the surface of the photosensitive drum is uniformly charged, the surface of the photosensitive drum is irradiated with laser light, and a potential difference is given between the irradiated portion and the non-irradiated portion. Next, the charged toner contained in the developer adheres to the surface of the photosensitive drum, whereby a toner image is formed on the surface of the photosensitive drum. Thereafter, the toner image is transferred to a recording medium, and an image is formed on the recording medium.

  As means for uniformly charging the surface of the photosensitive drum, a corona discharge device or a contact charging device is generally used. The corona discharge device is effective as a means for uniformly charging the surface of an object to be charged such as an image carrier to a predetermined potential, but has problems such as requiring a high voltage power source and generating ozone. ing. In the contact charging device, a conductive charging member to which a voltage is applied is brought into contact with the surface of the object to be charged, whereby electric charges are directly injected into the surface of the object to be charged and charged to a predetermined potential. It has features such as lowering the power source, greatly reducing ozone generation compared to corona discharge devices, simple structure, and maintenance-free.

  Recently, demands such as higher image quality and lower running cost of output devices have increased, and the photosensitive drum as an image carrier used in the electrophotographic system has a higher photosensitive layer thickness because of the necessity of high resolution. Thin one is used. In addition, in order to reduce the running cost, it is necessary to increase the life of the photosensitive drum itself, so that the electrical and mechanical strength and wear resistance of the surface of the photosensitive member are improved.

  However, an image forming apparatus using such a photosensitive drum is not refreshed by scraping the surface of the photosensitive drum. As a result, electrical damage due to charging, surface deterioration due to adhesion of discharge products, mechanical damage due to rubbing with a cleaning blade, and the like accumulate for a long time. As a result, there arises a problem that slipperiness (especially the cleaning blade) on the surface of the photosensitive drum is lowered and chattering, squealing, and squeezing of the cleaning blade are likely to occur.

  An object of the present invention is to solve the above problems, and to maintain a stable cleaning performance for a long period of time while using a highly durable (high strength, high wear resistance) photoreceptor. It is another object of the present invention to provide an image forming apparatus having a long life, high image quality, and low running cost that can stably charge a photoconductor all the time using a simple charging roller as a charging device.

  The above object is achieved by an image forming apparatus having the following configuration according to the present invention.

Means for charging an image carrier having a photosensitive layer on a conductive support by a contact charging member; electrostatic latent image forming means for forming an electrostatic latent image on the charged image carrier; and toner for the electrostatic latent image In an image forming apparatus having a developing means for transferring and visualizing and a means for transferring a toner image formed on an image carrier onto a transfer material, the image carrier is subjected to a hardness test using a Vickers square pyramid diamond indenter, and the maximum An image carrier having an HU (universal hardness value) of 150 N / mm ² or more and 220 N / mm ² or less when pressed with a load of 6 mN, and an elastic deformation rate We of 40% or more and 65% or less, The image carrier has a surface on which irregularities due to a plurality of spherical trace depressions are formed, the diameter R of the spherical trace depressions is 1 to 50 μm, the average surface irregularity Sm-d is 10 to 100 μm, and the surface roughness Rz - Satisfies the conditions of 0.3 to 2.5 μm, the contact charging member has a surface roughness Rz-c of 1 to 20 μm, an average surface roughness Sm-c of 10 to 500 μm, and an Asker C hardness of 30-90 degrees,

の条件を満足することを特徴とする画像形成装置により目的は達成される。

The object is achieved by an image forming apparatus characterized by satisfying the following conditions.

  As described above, when using a high-hardness photoconductor with severe cleaning, the above configuration makes it easy to prevent image flow and chatter, squealing, and blurring of the cleaning blade over a long period of time. Stable image formation is performed while maintaining contact charging performance.

  The configuration and operation of an embodiment and an example of an image forming apparatus according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic view of a copying machine as an embodiment of an image forming apparatus according to the present invention. First, an outline of the entire copying machine will be described. A so-called reversal developing system is used in which a negatively charged organic photoreceptor is used for the photosensitive drum 1 as an image carrier and negatively charged toner is used as a developer. Is. Further, as a method for uniformly charging the photosensitive member, a roller charging method which is one of low-cost contact charging methods is used.

  The image forming process of this copying machine will be described. The photosensitive drum 1 is first charged to a uniform potential by a charging roller 2 constituting a charging device, and a laser beam L corresponding to image information is mainly emitted in the axial direction of the photosensitive drum 1 by an exposure optical system (not shown). Scanned and sub-scanned by rotation of the photosensitive drum 1. As a result, an electrostatic latent image corresponding to the image information is formed on the photosensitive drum 1. This electrostatic latent image is developed by the developing device 3 to become a toner image. The toner image is transferred to the recording medium P by the transfer device 4. The recording medium P to which this image has been transferred is separated from the photosensitive drum 1 and conveyed, and then fixed through pressurization and heating of the image by the fixing device 5 to complete printing. On the other hand, the toner remaining on the photosensitive drum 1 after the transfer is removed from the photosensitive drum 1 by the cleaning device 6. Thereafter, the charge remaining on the photosensitive drum 1 is neutralized by the neutralizing light from the neutralizing lamp 7, and the photosensitive drum 1 is prepared for the next image formation.

[Image carrier]
A photoconductor that is an image carrier in the present invention will be described below (hereinafter, the image carrier is referred to as a photoconductor or a photosensitive drum).

  The photoconductor used in the present invention is an electrophotographic photoconductor containing a compound in which at least the surface layer is polymerized or cross-linked and hardened, and the curing means is light such as heat, visible light, ultraviolet light, and radiation. Can be used. Therefore, as a means for forming the surface layer in the present invention, there is a coating method using a coating solution for melting or containing a compound that can be polymerized or crosslinked and cured for the surface layer. These include dip coating, spray coating, curtain coating, spin coating and the like. Next, it is a procedure of curing it by the curing means described above. The impregnation coating method is the best for efficient mass production of the photoreceptor, and the dip coating method is also possible in the present invention.

  As the constitution of the photoreceptor of the invention, first, a conductive substrate having an outer diameter of about 30 mm is used. On top of this, a single-layer type in which both the charge generation material and the charge transport material are contained in the same layer, or a charge generation layer containing the charge generation material and a charge transport layer containing the charge transport material, There is a stacked type in which the layers are stacked in order or in the reverse order. Furthermore, a surface protective layer can be formed on the photosensitive layer. In the present invention, it is sufficient that at least the surface layer of the photoreceptor contains a compound that can be polymerized or crosslinked and cured by heat, light such as visible light, ultraviolet light, or radiation. However, from the viewpoint of characteristics as a photoreceptor, particularly electrical characteristics such as residual potential and durability, a charge generation layer / charge transport layer is laminated in this order, or a functionally separated photoreceptor is laminated in this structure. A configuration in which a surface protective layer is formed on the photosensitive layer is preferable.

  In the present invention, the method of curing the compound such as polymerization or cross-linking of the surface layer uses radiation in that there is no deterioration in photoreceptor characteristics, no increase in residual potential, and sufficient hardness can be exhibited. Is preferred.

  At this time, the radiation used is an electron beam and a gamma ray. When irradiating with an electron beam, any of a scanning type, an electron curtain type, a broad beam type, a pulse type, and a lamina type can be used as an accelerator. In the case of irradiating an electron beam, the acceleration voltage is preferably 250 kV or less and optimally 150 kV or less, in order to develop the electrical characteristics and durability of the photoreceptor of the present invention. The irradiation dose is preferably in the range of 10 KGy to 1000 KGy, more preferably in the range of 30 KGy to 500 KGy. If the accelerating voltage exceeds the above, the electron beam irradiation damage tends to increase on the characteristics of the photoreceptor. In addition, it is necessary to be careful since curing is likely to be insufficient when the irradiation dose is less than the above range, and deterioration of the photoreceptor characteristics is likely to occur when the dose is large.

  The compound for the surface layer that can be polymerized or crosslinked and cured includes an unsaturated polymerizable functional group in the molecule from the viewpoint of high reactivity, high reaction rate, and high hardness achieved after curing. Those having are preferred. Among them, compounds having an acrylic group, a methacryl group, and a styrene group are particularly preferable.

  The thickness of the surface protective layer used in the present invention is preferably in the range of 0.5 to 10 μm, more preferably in the range of 1 to 6 μm.

  Further, the HU (universal hardness value) and elastic deformation rate in the present invention can be obtained by applying a continuous load to the indenter, directly reading the indentation depth under the load, and obtaining the continuous hardness. Measurement was performed using a measuring device Fischerscope H100V (manufactured by Fisher Instruments). The indenter used was a Vickers square pyramid diamond indenter with a face angle of 136 °. The load conditions were measured stepwise up to a final load of 6 mN (273 points with a holding time of 0.1 s for each point).

  HU (universal hardness value: hereinafter referred to as HU) is defined by the following formula (1) from the indentation depth under the same load when indented at 6 mN.

弾性変形率とは圧子が膜に対して行った仕事量（エネルギー）、即ち圧子の膜に対する荷重の増減によるエネルギーの変化より求めたものである。つまり、ＨＵを測定する際に圧子を特定の深さに進入させた際の全仕事量、及びこれが回復する仕事量を測定し、その回復する仕事量の全仕事量に対する割合が弾性変形率である。下記式（２）からその値は求まる。ここでＷｔ（ｎＷ）は全仕事量で、Ｗｏ（ｎＷ）は弾性変形（回復）の仕事量である。また、ＷｔはＨＵを測定する際の測定曲線により形成される面積を求めることにより算出され、Ｗｏは回復時に測定される曲線により形成される面積を求めることにより算出される。

The elastic deformation rate is obtained from the change in energy caused by the increase or decrease in the load of the indenter on the film, that is, the amount of work (energy) performed by the indenter on the film. That is, when measuring the HU, the total work amount when the indenter enters a specific depth and the work amount that this recovers are measured, and the ratio of the recovering work amount to the total work amount is the elastic deformation rate. is there. The value is obtained from the following equation (2). Here, Wt (nW) is the total work, and Wo (nW) is the work of elastic deformation (recovery). Wt is calculated by obtaining an area formed by a measurement curve when measuring HU, and Wo is calculated by obtaining an area formed by a curve measured at the time of recovery.

Elastic deformation rate We = Wo / Wt × 100 (%) (2)
As described above, the performance required for the organic electrophotographic photosensitive member includes improved durability against mechanical deterioration. In general, the hardness of the film is higher as the amount of deformation with respect to external stress is smaller, and it is considered that the electrophotographic photosensitive member having higher pencil hardness or Vickers hardness naturally improves durability against mechanical deterioration. However, the high hardness obtained by these measurements has not always been expected to improve durability.

As a result of intensive studies, we found that mechanical deterioration of the surface layer of the photoconductor hardly occurs when the values of HU and elastic deformation ratio are within a certain range, and the present invention has been achieved. It was found by performing a hardness test using a Vickers square pyramid diamond indenter. By using an electrophotographic photosensitive member that has an HU of 150 N / mm ² or more and 220 N / mm ² or less when pressed at a maximum load of 6 mN and an elastic deformation rate of 40% or more and 65% or less, the performance is dramatically improved. It was improved.

  The amount of wear on the surface of the photoreceptor, which is the image carrier used in this embodiment, is 2 mg or less in the Taber abrasion tester. As a test method for the Taber abrasion test, a sample is first mounted on a sample stage of a Taber abrasion tester (trade name: YSS Taber, manufactured by Yasuda Seisakusho Co., Ltd.). Next, a load of 500 gr of each rubber wear wheel (CS-0) with wrapping tape (trade name: C2000, manufactured by Fuji Photo Film Co., Ltd.) was applied to the two surfaces, and the sample after 1000 rotations was applied. This is a method of measuring weight loss with a precision balance.

  In the present invention, the surface shape of the electrophotographic photosensitive member is formed by irregularities (dimple shape) due to spherical trace depressions. Further, the surface roughness Rz-d is 0.3 μm or more and 2.5 μm or less, the surface unevenness average interval Sm-d is 10 to 100 μm, and the diameter R of the spherical trace depression is 1 to 50 μm. In the present invention, the surface roughness is a ten-point average roughness. It extracts the reference length from the roughness curve in the direction of the average line, and from the average line of the extracted part, the average value of the absolute values of the highest peak from the highest peak to the fifth and the fifth from the lowest valley It is the sum of the absolute value of the altitude of the valley bottom up to the average value. The smaller this value, the smoother the surface of the rotating body subjected to the evaluation. The average unevenness interval is obtained by extracting the reference length in the direction of the average line from the roughness curve and obtaining the sum of the lengths of the average lines corresponding to one peak and one adjacent valley. If this value is small, it is judged that the eye of processing is fine. When Rz-d is smaller than 0.3 μm, the contact area between the cleaning blade and the photoreceptor surface becomes too large, and problems such as blade chatter, blade wear and chipping occur, and good cleaning properties cannot be obtained. Similarly, even when Sm-d is larger than 100 μm, the adhesion between the blade and the surface of the photoreceptor becomes too high to perform good cleaning. On the contrary, when Rz is larger than 2.5 μm or Sm is smaller than 10 μm, the cleaning blade cannot follow the surface shape of the photoreceptor and the contact area is excessively reduced. As a result, the transfer residual toner cannot be blocked, and a cleaning failure such as slipping occurs. On the other hand, if Rz-d exceeds 2.5 μm, the resulting image may appear rough due to roughening.

  The surface shape required in the present invention is a shape having many isolated recesses that are as close to a circle as possible and can be expressed as a so-called dimple shape. This dimple shape preferably has no directionality in all directions on the surface of the photoreceptor.

  In the irregularities on the surface of the photoreceptor, when the valleys are continuous in stripes, low resistance substances such as charged products accumulate in the stripes, especially when used for a long time under high temperature and high humidity. A problem of streak-like image defects due to the shape is likely to occur. This streak-like image defect is a particularly significant problem in a photoreceptor that can achieve high durability as in the present invention. When the surface is roughened in a streak shape, since the concave portions are continuous, the surface can flow the electrostatic latent image in a streak shape, and a streak-like image defect occurs.

  In order to solve this problem, the dimple shape having an isolated recessed portion of the present invention is effective. Even if the charged product adheres to the surface, the recessed portion does not spread in a specific direction, so that the electrostatic latent image does not flow and disappear.

  The photoreceptor having the surface shape of the present invention is most effective when applied to a photoreceptor containing a curable resin in the outermost surface layer. Photoreceptors that contain a curable resin on the outermost surface layer have little surface wear when used for a long time, and the surface shape remains the same between the initial and endurance use, and the optimal surface shape formed initially is long-term. The initial cleaning characteristics can be maintained even when many sheets are used.

  As described above, it is important to appropriately set the surface shape of Rz-d, Sm-d, etc. in order to make full use of a drum with a low wear rate as in the present invention. Those having a large wear rate on the surface of the photoreceptor cannot be maintained even if the surface shape is determined in the initial stage, and thus do not contribute much to the cleaning performance after durability. Since the surface is always refreshed, discharge products and the like do not accumulate, and the friction coefficient between the cleaning blade and the photoreceptor surface does not increase so much. On the other hand, in the photoconductor having high durability as in the present invention, discharge products and the like accumulate and must be removed by the blade, which increases the load on the blade and causes problems such as blade wear, chatter, and sag. generate. Therefore, since the surface shape of a photosensitive drum having a very low wear rate is maintained even after long-term durability, it is important to determine the initial surface shape.

  In the present invention, the surface roughness of the surface of the electrophotographic photosensitive member is measured as follows using a contact type surface roughness measuring machine (trade name: Surfcorder SE3500, manufactured by Kosaka Laboratory Ltd.).

  Detector: R2 μm, 0.7 mN diamond needle, filter: 2CR, cut-off value: 0.8 mm, measurement length: 2.5 mm, feed rate: 0.1 mm, 10 points defined by JIS standard B0601 Data of average surface roughness Rz was processed. The average spacing Sm of the surface irregularities is an arithmetic average value obtained from the following equation measured under the same conditions.

Ｓｍｉ：凹凸の間隔
ｎ：基準長さ内で凹凸の間隔の個数

Smi: spacing of irregularities n: number of irregularities within the reference length

  In the present invention, any film forming method or roughening method may be used as long as the above dimple shape can be formed on the outermost surface layer. However, it is effective to use some mechanical roughening method to obtain the surface shape as required in the present invention. Among the various mechanical surface roughening methods, the dry blast method and the wet honing method are preferable as the method for forming the dimple shape. Furthermore, it is more preferable to use a dry blasting method because an electrophotographic photosensitive member sensitive to humidity conditions can be roughened without contacting with a solvent such as water.

  FIG. 4 shows a schematic view of abrasive grain discharging means for controlling the surface shape by a dry blasting method. It comprises an abrasive discharge device 9, a driving means (not shown) for rotating the electrophotographic photosensitive member 10 in the direction of arrow C, and an exhaust device (not shown). The abrasive grains are sprayed from the discharge device 9 onto the surface of the electrophotographic photosensitive member 10 rotated at a desired number of revolutions, and the discharge device 9 or the electrophotographic photosensitive member 10 moves in the thrust direction, whereby the electrophotographic photosensitive member. The entire surface of 10 is roughened. At that time, the abrasive grains discharged from the discharge device 9 are sucked by an exhaust device (not shown). The abrasive grains may be reused. The abrasive grains used in the roughening step are preferably metal, glass, resin or the like. Among them, a surface shape that can obtain the desired shape as described above may be selected as the surface shape of the electrophotographic photosensitive member. The shape of the abrasive grains is preferably spherical if it is indeterminate because deep recesses are likely to occur on the surface of the photoreceptor. In roughening, a plurality of particles having different particle diameters, shapes, and materials may be used.

[developing]
As a developing method used in the image forming apparatus of the present invention, there is a method of developing in a non-contact state with respect to a photosensitive drum (one-component non-contact development). Also, a method of developing in contact with the photosensitive drum (single component contact development), a mixture of toner particles and a magnetic carrier is used as a developer, and the developer is conveyed by magnetic force to the photosensitive drum. On the other hand, there is also a method of developing in a contact state (two-component contact development). Furthermore, there is a method of developing the two-component developer in a non-contact state with respect to the photosensitive drum (two-component non-contact development method), and any of them can be suitably used. In this embodiment, since the developing device can be simplified and low running cost can be achieved, the one-component non-contact development using magnetic toner is adopted.

[Cleaning device]
As cleaning in the electrophotographic system, the surface of the photosensitive drum is repeatedly used for forming a toner image. Therefore, after the toner image is transferred to the recording medium, it remains on the surface of the photosensitive drum without being transferred to the recording medium. It is necessary to sufficiently remove the residual toner. As a method for removing the residual toner, many proposals have been made, but a method of scraping off the residual toner by contacting a cleaning blade, which is a counter blade made of an elastic material, with the surface of the photosensitive drum is preferable. . This is because the cost is low, the entire electrophotographic system can be made simple and compact, the toner removal efficiency is excellent, and it is widely put into practical use. As a material for the cleaning blade, urethane rubber having high hardness and high elasticity, and excellent in abrasion resistance, mechanical strength, oil resistance, ozone resistance and the like is generally used.

  FIG. 5 relates to a cleaning blade. The cleaning blade 8 is made of polyurethane rubber that is integrally held at the front end of the sheet metal, and is in contact with the photoreceptor 1 under conditions of a predetermined penetration amount δ and a set angle θ. As a result of repeating trial and error in this embodiment and finding optimum conditions, the rubber hardness is preferably 50 to 85 ° (JISA), and in this embodiment, a material of 70 ° (JISA) is used, θ = 22 °, δ = 1.2 mm, and the contact pressure to the photoreceptor 1 was about 30 g / cm.

[Charging]
FIG. 2 shows a front view a and a cross-sectional view b of the charging roller 2 and the photoreceptor 1. Here, it is important that the charging roller 2 as a contact charging member functions as an electrode. In other words, it is necessary to obtain sufficient contact with the photoconductor by providing elasticity, and at the same time to have a sufficiently low resistance to charge the moving photoconductor. On the other hand, it is necessary to prevent voltage leakage when a low breakdown voltage defect portion such as a pinhole exists in the photoreceptor 1. In order to obtain sufficient chargeability and leakage resistance, a resistance of 10 ⁴ to 10 ⁷ Ω is desirable. In this embodiment, 10 ⁶ Ω is used. The resistance value of the charging roller 2 was measured as follows. The photoconductor 2 of the printer is replaced with an aluminum drum. Thereafter, a voltage of 100 V was applied between the aluminum drum and the cored bar 2a of the charging roller 2, and the resistance value of the charging roller 2 was obtained by measuring the current value flowing at that time. The resistance measurement was performed in an environment at a temperature of 25 ° C. and a humidity of 60%.

  The charging roller hardness in the present invention is measured in an environment of 23.5 ° C./60% using an Asker C hardness meter. In the measuring method using the Asker C hardness tester, a charging roller is first placed on a metal plate, and a metal block is placed on the roller so that the roller does not roll. Next, the value after 5 seconds is read by pressing the Asker C hardness meter with a load of 1 kg so as to accurately hit the center of the charging roller from the vertical direction with respect to the metal plate. An average is calculated by measuring a total of nine points, three in the circumferential direction at both ends and the center at a position 40 mm from the rubber end of the charging roller. In the present invention, if the Asker C hardness of the charging roller is in the range of 30 to 90 ° C., good chargeability was obtained. If the hardness of the charging roller 2 is too high, the charging contact portion width (nip portion N) cannot be ensured between the charging roller 2 and the photosensitive member 1, and stable chargeability cannot be obtained. On the other hand, even if the hardness is too low, the shape is not stable, so that good charging performance cannot be obtained.

  The material of the charging roller 2 is not limited to the elastic foam as long as the above-described hardness and charging performance can be satisfied. In addition, as elastic materials, EPDM, urethane, NBR, silicone rubber, rubber materials in which conductive materials such as carbon black and metal oxides are dispersed to adjust resistance in IR, etc., and foamed these materials Can be mentioned. It is also possible to adjust the resistance using an ion conductive material without dispersing the conductive substance.

  Next, the surface shape of the charging roller will be described. According to the present invention, the surface roughness Rz-c of the charging roller is 1 to 20 μm, the surface unevenness average interval Sm-c is 10 to 500 μm, and the relationship with the photoreceptor surface unevenness average interval Sm-d is 0. By setting 2 ≦ Sm−c / Sm−d ≦ 10, good chargeability can be obtained. Here, as shown in FIG. 6A, when Rz-c is less than 1 μm, when the surface of the charging roller is partially soiled, the resulting charging failure is likely to appear in the image. This is presumably because the surface of the charging roller is smooth, so that the difference in the discharge state between the contaminated portion and the portion not so is directly received as the photosensitive member surface charging potential difference. On the other hand, if the charging roller surface is uneven as shown in FIG. 6B, the gap between the photosensitive member and the charging roller surface changes continuously even if the charging roller surface is slightly contaminated. It is difficult to receive a change as a charged potential difference on the surface of the photoreceptor. Accordingly, if the surface of the charging roller is moderately uneven, even if the surface of the charging roller is contaminated, image defects are less likely to occur. However, as shown in FIG. 6C, when the unevenness of the charging roller surface is made too large, the change in the gap with the surface of the photoreceptor becomes too rapid. Therefore, stable discharge is not performed and micro charge failure occurs. In the present invention, since the surface of the photoreceptor is roughened in a dimple shape in order to solve the problems such as the cleaning property and the image flow as described above, it is considered that the influence also relates to the charging property.

  Another effect brought about by unevenness on the surface of the charging roller is reduction of contamination due to external additives on the roller surface. When the roller surface is roughened, the adhesion to the surface of the photoconductor can be weakened compared to a smooth surface, and the pressure of the material adhering to the roller surface to be mechanically pressed against the surface of the photoconductor is reduced. Can weaken. Adhesive force is classified into electrostatic and non-electrostatic such as van der Waals force and liquid cross-linking force. Will be dominant. As the mechanical pressure on the deposit increases, these non-electrostatic adhesion forces increase and the contamination of the rollers worsens. This phenomenon is particularly remarkable in a high-humidity environment where the liquid crosslinking power becomes strong.

  Next, the relationship between Sm-c and Sm-d will be described. According to the present invention, if Sm-c and Sm-d are in the above ranges and 0.2 ≦ Sm-c / Sm-d ≦ 10 is satisfied, good chargeability can be obtained in the long term. When a fine irregularity interval such as Sm-c <10 μm was formed on the surface of the charging roller, it was as follows. That is, it is not certain whether it is due to the rapid change in the minute gap with the surface of the photosensitive member described above or has a charging property that reflects the shape of the photosensitive member dimple, but a microscopic charging failure has occurred. On the other hand, when a rough irregularity interval of Sm-c> 500 μm is formed on the surface of the charging roller, the contact with the surface of the photosensitive member is close to the state as shown in FIG. Therefore, a satisfactory level of contamination on the charging roller surface could not be obtained. That is, it was found that at least Sm-c must be in the range of 10 to 500 μm in order to charge the photoreceptor having the above surface satisfactorily. Furthermore, in the present invention, since the surface of the photoconductor has a special shape, it has been found that the relationship with the photoconductor surface Sm-d also contributes to the charging property. Table 1 shows the results of evaluating the chargeability under the conditions in which Sm-d is combined in the range of 10 to 100 μm and Sm-c in the range of 10 to 500 μm.

この結果より０.２＞Ｓｍ-ｃ／Ｓｍ-ｄとなる条件では良好な帯電性が得られなかった。これは図６-ｃで表されるように感光体のディンプル径に対して帯電ローラの凹凸間隔が非常に狭くなってしまうため、先にも述べたが感光体ディンプル形状を反映させてしまう帯電性を持つ為ではないかと考えられる。一方で、Ｓｍ-ｃ／Ｓｍ-ｄ＞１０となる条件においても良好な帯電性が得られなかった。これは感光体のディンプル径に対して帯電ローラの凹凸間隔が非常に広くなってしまうため、先に述べたように感光体表面との密着性が増し、帯電ローラ表面に凹凸を設けた効果が得られにくくなってしまう為だと考えられる。

From this result, good chargeability could not be obtained under the condition of 0.2> Sm-c / Sm-d. This is because, as shown in FIG. 6C, the unevenness of the charging roller becomes very narrow with respect to the dimple diameter of the photosensitive member. Therefore, as described above, charging that reflects the photosensitive member dimple shape is performed. It may be because of having sex. On the other hand, good chargeability was not obtained even under the condition of Sm-c / Sm-d> 10. This is because the unevenness of the charging roller becomes very wide with respect to the dimple diameter of the photoconductor, so that the adhesion to the surface of the photoconductor is increased as described above, and the effect of providing the unevenness on the surface of the charging roller is effective. It is thought that it is difficult to obtain.

  As described above, in the present invention, since a highly durable photoconductor having a dimple-like surface shape is used, it is necessary to optimize the surface shape of the charging roller in accordance with the high-sensitivity photoconductor and to make the charging property long-term.

  As a means for making the surface of the charging roller uneven, a method of adding particles such as resin balls to the surface of the charging roller, a method of polishing the surface of the charging roller, and the like are preferably used.

  In FIG. 2, the charging roller 2 is disposed in parallel with the photosensitive drum 1 while being supported by the bearing 2c at both ends in the longitudinal direction, and is also sensitized by a spring 2b as a pressure member attached to the bearing 2c. The drum 1 is pressed against the surface. In this embodiment, the contact pressure by the pressure spring 2b with respect to the surface of the photosensitive drum 1 at this time is set to about 40 g / cm. With this setting, a sufficient contact width N (nip width) between the photosensitive drum 1 and the charging roller 2 can be secured, and a stable charging property can be obtained. The contact pressure is not limited to those described above, and there is no problem as long as satisfactory charging properties, a surface of the photosensitive member, a surface of the charging roller, and the like can be obtained and satisfactory durability can be obtained.

  As a method for measuring the contact pressure, two sheets of SUS are inserted into the contact area between the photosensitive drum 1 and the charging roller 2, and the force required to pull out the sheet having a width of 1 cm is only a spring. The way to measure with was done. The charging roller 2 is driven to rotate along with the rotation of the photosensitive drum 1.

  The charging roller is subjected to constant current control with a frequency of 1.8 kHz and a total current of 2000 μA from a high-voltage power supply for charging, and the photoreceptor potential is determined by the superimposed DC bias.

  Hereinafter, the present invention will be described more specifically with reference to examples. These examples are examples of the best mode of the present invention, but the present invention is not limited to these examples.

Example 1
In this example, a photoconductor having a universal hardness value of 200 N / mm ² and an elastic deformation rate We of 50% was used. For the roughening treatment, the surface of the surface was roughened by dry blasting using the apparatus shown in FIG. 4 at a rotational speed of the photosensitive member of 30 rpm and using abrasive grains: shaped glass beads (average particle size: 40 μm). The surface shape was Rz-d = 0.8 μm and Sm-d = 45 μm. A charging roller having an Asker C hardness of 60 degrees was used. The outer diameter of the charging roller was 14 mm, and the contact portion width between the charging roller and the photosensitive member was set to 2 mm. The charging roller surface roughness Rz-c was 5 μm. Rz-c was 50 μm. The cleaning blade uses urethane rubber with a hardness of 70 (Shore hardness HS), a 100% modulus of 25 kgf / cm ² and a resilience of 11%, a set angle θ = 25 °, an intrusion amount δ = 0.7 mm, The contact pressure was about 25 g / cm.

  Table 2 shows the results of evaluation of the durability of 100,000 sheets under high temperature and high humidity (30 ° C. 80%) and normal temperature and low humidity (23 ° C. 5%) with the above configuration. The evaluation items are as follows.

・ Charging property: ○: Good, ×: Poor charging, × Dirt: Charging failure due to contamination of charging roller ・ Cleaning property: ○: Good, ×: Cleaning failure, × chipping: Cleaning failure due to blade chipping

(Example 2)
In this example, the surface of the photoconductor roughening treatment was changed, and a photoconductor surface with Rz-d = 0.3 μm and Sm-d = 30 μm was prepared. Other conditions were the same as in Example 1, and the results of the same evaluation are shown in Table 2.

(Example 3)
In this example, the surface of the photoconductor roughening treatment was changed, and a photoconductor surface with Rz-d = 2.5 μm and Sm-d = 40 μm was prepared. Other conditions were the same as in Example 1, and the results of the same evaluation are shown in Table 2.

Example 4
In this embodiment, the charging roller roughening treatment conditions were changed, and the charging roller surface with Rz-c = 1.0 μm and Sm-d = 100 μm was prepared. Other conditions were the same as in Example 1, and the results of the same evaluation are shown in Table 2.

(Example 5)
In this embodiment, the charging roller roughening treatment conditions were changed, and the charging roller surface with Rz-c = 20 μm and Sm-d = 80 μm was prepared. Other conditions were the same as in Example 1, and the results of the same evaluation are shown in Table 2.

(Comparative Example 1)
In this comparative example, the photoconductor surface roughening conditions were changed, and the photoconductor surface with Rz-d = 0.15 μm and Sm-d = 20 μm was prepared. Other conditions were the same as in Example 1, and the results of the same evaluation are shown in Table 2.

(Comparative Example 2)
In this comparative example, the photoconductor surface roughening conditions were changed, and the photoconductor surface with Rz-d = 3.0 μm and Sm-d = 30 μm was prepared. Other conditions were the same as in Example 1, and the results of the same evaluation are shown in Table 2.

(Comparative Example 3)
In this comparative example, the charging roller roughening treatment conditions were changed, and the charging roller surface with Rz-c = 0.8 μm and Sm-d = 200 μm was prepared. Other conditions were the same as in Example 1, and the results of the same evaluation are shown in Table 2.

(Comparative Example 4)
In this comparative example, the charging roller roughening treatment conditions were changed, and the charging roller surface with Rz-c = 22 μm and Sm-d = 20 μm was prepared. Other conditions were the same as in Example 1, and the results of the same evaluation are shown in Table 2.

(Example 6)
In this embodiment, a member for cleaning the surface of the charging roller is provided. As a cleaning member, a sanderlon brush having a fineness of 100d / 10F, a fiber diameter of 35 μm, a fiber density of 570 fibers / 10 mm, and a fiber specific resistance of 100 to ^{−2 is} brought into contact with the charging roller, and is configured to reciprocate 5 mm in the thrust direction. .

  Other conditions were the same as in Example 1, and the results of the same evaluation are shown in Table 2.

  Even in the evaluation in the first embodiment, there is no practical problem, but the effect is further enhanced by combining a mechanism for cleaning the surface of the charging roller as in the present embodiment.

  When the contamination on the surface of the charging roller was observed, the level was better than that in Example 1.

(Example 7)
In this embodiment, as shown in FIG. 3, an intersection angle α of 0.15 ° is provided between the rotating shaft of the charging roller 2 and the rotating shaft of the photosensitive member 1. The purpose of providing the intersection angle is to diffuse as much as possible the local concentration of contamination of the charging roller from external additives or the like. This local concentration of contamination is likely to occur in response to continuous printing of the same image or local wear (chips) of the cleaning blade.

  Other conditions were the same as in Example 1, and the results of the same evaluation are shown in Table 2.

  Even in the evaluation in the first embodiment, there is no problem in practical use. However, by providing a crossing angle between the rotating shaft of the charging roller and the rotating shaft of the photosensitive member as in the present embodiment, more stable durability can be obtained. can get.

  As a result of observing dirt on the surface of the charging roller, the local concentration of dirt was diffused and uniform as compared with that in Example 1.

(Example 8)
In this embodiment, the surface layer of the charging roller containing a fluororesin was used. Other conditions were the same as in Example 1, and the results of the same evaluation are shown in Table 2.

  Even in the evaluation in Example 1, there is no practical problem. However, as in this example, the surface of the charging roller contains a fluororesin, so that the releasability is improved and the surface of the charging roller is contaminated. It becomes difficult. When the contamination on the surface of the charging roller was observed, the level was better than that in Example 1.

Example 9
In this embodiment, the surface layer of the photosensitive member containing fluorine (PTFE) was used. Other conditions were the same as in Example 1, and the results of the same evaluation are shown in Table 2.

  Even in the evaluation in Example 1, there is no problem in practical use. However, by adding fluorine to the surface layer of the photoconductor as in this example, the friction between the surface of the photoconductor and the cleaning blade is reduced, and the durability is more improved. Stable cleaning becomes possible. When the wear (chip) of the cleaning blade was observed, the level was better than that of Example 1.

(Comparative Example 5)
The structure was the same as that of Example 1 except that an organic photoreceptor without a surface protective layer was used as the photoreceptor. The amount of wear on the surface of the photoreceptor used in Example 1 was 2 mg or less with the Taber abrasion tester as described above, but was 15 mg when the photoreceptor used in this comparative example was tested in the same manner. When the same evaluation as in Example 1 was performed using this photoconductor, the photoconductor was scratched with a durable number of about 80,000 sheets, and an image defect appeared.

以上述べてきた実施例は全て感光体表面上をクリーニングブレードによりクリーニングする系に関した。しかし、クリーニングブレード等のクリーニングシステムが無い画像形成装置を用いた場合においても、本発明によれば良好な帯電性が得られ、何ら問題なく適用することができる。

The embodiments described above all relate to a system for cleaning the surface of the photoreceptor with a cleaning blade. However, even when an image forming apparatus without a cleaning system such as a cleaning blade is used, according to the present invention, good chargeability can be obtained and the present invention can be applied without any problem.

Schematic cross-sectional view of an image forming apparatus suitable for the present invention Charger illustration Crossing angle diagram of charging roller Schematic diagram of abrasive discharge device Partial enlarged view explaining the cleaning blade A diagram showing the contact state between the photoreceptor surface and the charging roller surface

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 2a Metal core 2b Pressure spring 2c Bearing 3 Developing device 4 Transfer device 5 Fixing device 6 Cleaning device 7 Static elimination lamp 8 Cleaning device 9 Discharge device 10 Electrophotographic photosensitive member L Laser beam N Nip part P Recording medium

Claims (7)

Means for charging an image carrier having a photosensitive layer on a conductive support by a contact charging member; electrostatic latent image forming means for forming an electrostatic latent image on the charged image carrier; and toner for the electrostatic latent image In an image forming apparatus having developing means for transferring and visualizing, and means for transferring a toner image formed on an image carrier onto a transfer material,
The image carrier is subjected to a hardness test using a Vickers square pyramid diamond indenter, and the HU (universal hardness value) when pressed at a maximum load of 6 mN is 150 N / mm ² or more and 220 N / mm ² or less and is elastically deformed. An image carrier having a rate We of 40% to 65%,
The image carrier has a surface on which irregularities due to a plurality of spherical trace depressions are formed, the diameter R of the spherical trace depressions is 1 to 50 μm, the surface irregularity average interval Sm-d is 10 to 100 μm, and the surface roughness Rz-d satisfies the condition of 0.3 to 2.5 μm,
The contact charging member has a surface roughness Rz-c of 1 to 20 μm, a surface unevenness average interval Sm-c of 10 to 500 μm, an Asker C hardness of 30 to 90 degrees,

An image forming apparatus satisfying the following conditions:   The image forming apparatus according to claim 1, wherein the hardness test is performed in an environment of 25 ° C. and 50% humidity.   The image forming apparatus according to claim 1, wherein a member for cleaning the surface of the charging member is provided.   4. The image forming apparatus according to claim 1, wherein the charging member is provided with a crossing angle with respect to the image carrier.   The image forming apparatus according to claim 1, wherein the charging member surface contains fluorine.   6. The image forming apparatus according to claim 1, wherein the image bearing surface contains fluorine.   2. The image forming apparatus according to claim 1, wherein the image bearing member is formed with a spherical trace depression by subjecting the surface to a dry blasting process or a wet honing process.

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