JP2005221699A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which prevents deterioration in image with the lapse of time, and which relates to the image forming apparatus in which a protective agent is applied to the surface of an image carrier. <P>SOLUTION: The apparatus uses a toner such that the number of the toner ≥-0.1 fC/μm after stirring one minute is ≤10%, when the toner is stirred for a period (60 minutes) so that external additives remaining on the surface of the toner disappear and when uncharged toner is added so that the concentration of the toner is 7%. Thus, agglomeration of the toner with the lapse of time is prevented, and sharp electrification distribution can be maintained. As a result, because the amount of the existing weakly/reverse electrified toner ≥-0.1 fC/μm is maintained at ≤10% over a lapse of time, deterioration in the image such as a texture stain is restrained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus in which a protective agent is applied to the surface of an image carrier.

  2. Description of the Related Art Conventionally, an image forming apparatus that employs an electrophotographic process has a charging unit that charges the surface of a photoreceptor as an image carrier. One of the charging methods used in the charging means is a charging method using proximity discharge. This is a system in which a charging member is brought into contact with the surface of the photoconductor or brought close to it in a non-contact manner to charge the surface of the photoconductor by proximity discharge.

  Since the charging method using the proximity discharge directly exposes the surface of the photoreceptor to the proximity discharge, the surface of the photoreceptor is chemically deteriorated. Therefore, in order to protect the surface of the photoreceptor due to such proximity discharge, a method for forming a protective film such as zinc stearate on the surface of the photoreceptor is described in Patent Document 1.

JP 2002-229227 A

  However, as a result of forming the protective layer on the surface of the photoreceptor, the protective agent enters the developing device and adheres to the toner in the developing device. As a result, the toner is less likely to be frictionally charged and a sufficient charge amount may not be obtained for the toner. As described above, the toner that is not sufficiently charged causes deterioration of the image such as background stains. On the other hand, by increasing the toner agitation time, the ratio of weakly and reversely charged toner in the toner is reduced to suppress image deterioration such as background stains. However, even if the toner charge amount is controlled in this way, the toner deteriorates with time, and a toner that cannot obtain a sufficient charge amount is generated. This is because the external additive around the toner base resin is buried in the base resin due to mechanical stress over time such as stirring. As a result, toner aggregation easily occurs, fluidity is lowered, and the toner is less likely to be frictionally charged by stirring.

The progress of the amount of the external additive embedded in the toner varies depending on the stress applied to the toner. Parameters of stress applied to the toner include dynamic torque of the developing device, driving (stirring) time, and developer toner concentration. The inventors pay attention to these parameters and use the stress applied to the toner as an index as follows.
(Formula 1)
Stress index = (unit dynamic torque [kg · cm] × driving (stirring) time [min]) / (toner concentration [%] / 100)

  FIG. 9 shows the relationship between the stress index and the toner embedding rank when the same developer is stored in each developing unit. Here, the toner embedment rank is obtained by observing the toner surface with a field emission scanning electron microscope (FE-SEM) and visually categorizing the state of burying of the external additive into five levels. The toner rank 5 is a state where the toner is not buried, and the toner rank 4 is a state where a part of the external additive is buried. In toner rank 3, most of the external additives are embedded in the toner but remain on the toner surface. In toner rank 2, most of the external additives are embedded in the toner and remain on the surface. The toner rank 1 is a state in which all external additives are buried and do not remain on the surface. When the toner rank is 1, the external additive remaining on the toner surface disappears, the toner easily aggregates, the fluidity is lowered, and the toner is less likely to be frictionally charged by stirring. As can be seen from FIG. 9, when the stress index exceeds 500, the burial rank is 1 regardless of the characteristics of the developing unit. Generally, the dynamic torque of the developing unit is about 0.2 to 0.75 kg · cm. Therefore, in the case of a developer having a toner concentration of 5%, the stress index exceeds 500 after stirring for 60 minutes. The toner becomes a buried rank 1 toner.

  The toner after stirring for 10 minutes (initial stirring) shows a sharp charge distribution as shown by the dotted line in FIG. 10, but the toner after stirring for 60 minutes has an embedding rank of 1 and has a sharp charge distribution. As shown by the solid line in FIG. 10, weak and reversely charged toner of −0.1 fC / μm or more is present at 10% or more. As described above, as a result of the presence of 10% or more of weakly / reversely charged toner, there has been a problem in that image deterioration such as background stains appears remarkably.

  The present invention has been made in view of the above problems, and an object thereof is to provide an image forming apparatus that suppresses image degradation over time.

In order to achieve the above object, an invention according to claim 1 provides an image carrier that carries an electrostatic latent image, and a region that is provided at a position close to or in contact with the surface of the image carrier, and that is close to the surface of the image carrier. And a charging device that is charged by discharging in that region, and a developer composed of toner and a carrier is carried on the developer carrying member and conveyed to a developing region opposite to the image carrying member, on the image carrying member An image forming apparatus comprising: a developing device that develops a latent image into a toner image; and a cleaning device that removes transfer residual toner remaining on the image carrier after the developed toner image is transferred to a transfer material. A protective agent coating means for applying a protective agent to the surface of the image carrier and forming a protective layer on the surface of the image carrier is provided. As the toner, a developer with a toner concentration of 5% is stirred for 60 minutes after the initial stirring. After that, so that the toner density becomes 7%. In the charge amount distribution of the toner when the charged toner is added and stirred for 1 minute, the number of toners of −0.1 fC / μm or more is 10% or less of the total number of toners. To do.
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the average particle size of the toner is 3 μm or more and 6 μm or less.
The invention of claim 3 is characterized in that, in claim 1 or 2, the carrier has an average particle diameter of 20 μm or more and 40 μm or less.
According to a fourth aspect of the present invention, in the image forming apparatus of the first, second, or third aspect, the cleaning device is in contact with the image carrier in a rotatable manner, and the transfer residual toner remaining on the image carrier. The fur brush is a protective agent applying means for supplying a protective agent to the image carrier, and the rotation speed of the fur brush is set on the image carrier. Control means for controlling according to the area ratio of the toner image is provided.
According to a fifth aspect of the present invention, there is provided the image forming apparatus according to the fourth aspect, further comprising a homogenizing device for uniformly layering the protective agent on the image carrier applied by the fur brush on the surface of the image carrier. It is a feature.
According to a sixth aspect of the present invention, in the image forming apparatus of the first, second, third, fourth or fifth aspect, the toner charge amount after stirring the developer for 10 minutes is -30 μC / g or less. To do.
The invention according to claim 7 is the image forming apparatus according to claim 1, wherein the toner is produced by a dissolution suspension method involving a chemical reaction of a prepolymer. To do.
According to an eighth aspect of the present invention, in the image forming apparatus of the seventh aspect, the toner has irregularities on the surface.
The invention according to claim 9 is the image forming apparatus according to claim 8, wherein a part of the inorganic or organic fine particles is buried in the toner surface.
According to a tenth aspect of the present invention, in the image forming apparatus according to the seventh, eighth, or ninth aspect, the prepolymer is a branched polymer.
According to an eleventh aspect of the present invention, in the image forming apparatus according to the tenth aspect, the branched polymer is made of a urethane compound.
According to a twelfth aspect of the present invention, in the image forming apparatus according to the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth or eleventh aspects, a latent image is formed on the surface of the image carrier by a laser beam. The laser beam spot diameter of the laser light is 50 μm or less.
The invention of claim 13 is the image forming apparatus of claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, wherein a developing bias is applied to the developer carrying member. Applying means, and the developing bias is a DC voltage.

  The toner is stirred for a time (60 minutes) so that there is no external additive remaining on the toner surface. Further, uncharged toner is added so that the toner concentration becomes 7%, and after stirring for 1 minute, -0.1 fC / Check the number of toners of μm or more. The toner having no external additive remaining on the toner surface adheres to the carrier and aggregates. Even when a large amount of uncharged toner is added in a state where there is a large amount of the agglomerated toner, the toner and the carrier are agglomerated, so that the uncharged toner can rub against the toner and the carrier. Not fully charged. As a result, when the number of weakly charged / reversely charged toners of −0.1 fC / μm or more after adding the toner and stirring for 1 minute is examined, it becomes 10% or more of the whole. On the other hand, when the external additive remains on the toner surface, the toner does not aggregate with the carrier. Therefore, even if a large amount of uncharged toner is added, even if stirring is performed for 1 minute, the uncharged toner remains in contact with the toner or carrier. Rub enough. Therefore, the uncharged toner can be sufficiently frictionally charged even with stirring for 1 minute. As a result, the number of weakly charged / reversely charged toners of −0.1 fC / μm or more after stirring for 1 minute is 10% or less. In this way, by adding uncharged toner so that the toner concentration becomes 5% to 7% and examining the number of toners of −0.1 fC / μm or more after stirring for 1 minute, external addition of the toner surface is performed. The degree of burial of the agent can be determined quantitatively. At this time, the toner having the number of toners of −0.1 fC / μm or more of 10% or less can be determined as a stable toner in which the external additive on the toner surface is less likely to be buried over time as compared with the conventional toner. According to the first to thirteenth aspects, by using such a toner, aggregation of the toner is suppressed over time, and a sharp charge distribution can be maintained. As a result, the amount of weakly and reversely charged toner of −0.1 fC / μm or more is maintained at 10% or less over time, so that image deterioration such as background smearing can be suppressed. Therefore, there is an effect that a good image can be maintained for a long time.

FIG. 1 is a schematic configuration diagram showing a printer according to an embodiment of the present invention. This printer forms an image by an electrophotographic method. In the figure, the printer has four toner image forming units for forming images of each color of yellow (Y), magenta (M), cyan (C), and black (Bk) in parallel from the left side in the drawing. They are arranged side by side. These toner image forming portions have substantially the same configuration except for the color of the toner to be used. Taking a yellow toner image forming unit using yellow toner as an example, it is provided with a photosensitive drum 10Y, a charging roller 1Y, a developing device 2Y, an intermediate transfer bias roller 3Y, a cleaning device 4Y, a static elimination lamp, and the like. An optical writing unit 5Y (not shown) including a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like irradiates the photosensitive drum of each toner image forming unit while scanning the laser beam based on the image data. This scanning is performed based on single-color image information obtained by separating a full-color image into color information of yellow, magenta, cyan, and black. Therefore, on each photoconductive drum, electrostatic for single color of yellow, magenta, cyan, or black is used. A latent image is formed. The yellow electrostatic latent image formed on the photosensitive drum 10Y is developed into a yellow toner image by the developing device 2Y. An intermediate transfer unit 6 is disposed on the downstream side of the rotation of the photosensitive drum 10Y from the development position where the development is performed. This is because the intermediate transfer belt 6a stretched by the intermediate transfer bias rollers (3Y, M, C, Bk) for each color, the drive roller 6b, the secondary transfer backup roller 6c, the driven roller 6d, etc. Is rotated endlessly clockwise in the figure. The volume resistance of the intermediate transfer belt 6a is preferably 10 ⁶ Ω · cm or more. If the volume resistance of the intermediate transfer belt 6a is less than 10 ⁶ Ω · cm, transfer dust may occur and image deterioration may occur.

  The yellow toner image developed on the photosensitive drum 10Y moves to a contact position with the intermediate transfer belt 6a backed up by the intermediate transfer bias roller 3Y as the drum rotates. Then, intermediate transfer is performed on the intermediate transfer belt 6a while being influenced by the intermediate transfer bias applied to the intermediate transfer bias roller 3Y. The surface of the photosensitive drum 10Y after the intermediate transfer is neutralized by the neutralizing lamp 5Y after the transfer residual yellow toner is cleaned by the drum cleaning unit 4Y. Then, it is uniformly charged by the charging roller 1Y and prepared for the next image formation.

  Similarly, a magenta toner image, a cyan toner image, and a black toner image are formed on the photosensitive drums 10M, 10C, and 10B, respectively, and are sequentially superimposed and transferred onto the intermediate transfer belt 6a. By this superposition transfer, a four-color superposed toner image is formed on the intermediate transfer belt 6a.

  A paper transport unit 7 is disposed on the lower side of the intermediate transfer unit 6 in the drawing, and a fixing unit 8 is disposed on the left side of the intermediate transfer unit 6 in the drawing. The paper transport unit 7 moves the paper transport belt 7a stretched by the drive roller 7b, the driven roller 7c, the secondary transfer bias roller 7d, and the like endlessly in the counterclockwise direction in the figure by the rotational drive of the drive roller 7b. The four-color superimposed toner image formed on the intermediate transfer belt 6a moves to a secondary transfer position that is a contact position of the paper transport unit 7 with the paper transport belt 7a. On the other hand, a registration roller pair 9 is disposed on the right side of the paper transport unit 7 in the drawing, so that the recording paper P as an image forming body is superimposed on the four-color superimposed toner image on the intermediate transfer belt 6a. It is sent to the secondary transfer position at a possible timing.

  The intermediate transfer unit 6 is configured to be detachable from the apparatus main body in order to clean the surface contamination of the intermediate transfer belt 6a, replace the belt when the belt is deteriorated, or remove a paper jam.

  A secondary transfer bias is applied to the secondary transfer bias roller 7d of the paper transport unit 7 by a power source (not shown). At the secondary transfer position, a secondary transfer electric field is formed by the potential difference between the secondary transfer bias roller 7 d to which the secondary transfer bias is applied in this way and the secondary transfer backup roller 6 c of the intermediate transfer unit 6. . The four-color superimposed toner image on the intermediate transfer belt 6a is secondarily transferred onto the recording paper P under the influence of the secondary transfer electric field and nip pressure, and then sent to the fixing unit 8 to be transferred onto the recording paper P. To be established. The glossiness of the fixed image is preferably approximately the same as the glossiness of the transfer paper P. When the transfer paper P is plain paper, a high-quality image can be obtained by setting the glossiness of the fixed image to 20% or less.

  Next, the charging roller will be described. The charging roller 1Y charges the photosensitive drum using proximity discharge. As a method of charging the photosensitive member using proximity discharge, a contact charging method in which the charging roller 1Y is disposed in contact with the photosensitive drum, and a non-contact charging method in which the charging roller 1Y is disposed in a non-contact manner on the photosensitive drum. There is. In the case of the contact charging method, toner or paper dust or the like adhering to the surface of the photoconductor may be transferred and adhered to the charging roller due to poor cleaning, and when used for a long time, image deterioration is caused by charging failure due to contamination of the charging roller. May occur. Therefore, in the present embodiment, a non-contact charging method is employed in which the charging roller 1Y is disposed so as to face at least an image forming area on the surface of the photosensitive drum with a predetermined charging gap.

  A charging power source (not shown) is connected to the charging roller 1Y. As a result, the surface of the photosensitive drum 10Y is uniformly charged by the discharge in the charging gap between the surface of the photosensitive drum 10Y and the surface of the charging roller 1Y. Since the applied voltage bias method is difficult in practical use due to problems such as variation in charging potential due to charging gap fluctuation and discharge stability in the case of DC voltage, it is desirable to superimpose AC voltage.

The photosensitive drum 10Y has a wear resistance by forming a coating layer on the organic photosensitive layer in order to keep the photosensitive member surface potential at 30 V / μm (photosensitive member surface potential / photosensitive member film thickness) over time. Improves electrical durability. The coating layer improves the durability of the photoreceptor by dispersing an appropriate amount of inorganic particles in the binder resin. Examples of the inorganic particles include titanium oxide, silica, alumina, zirconium oxide, indium oxide, silicon nitride, and the like. In particular, titanium oxide and alumina are preferable because of excellent environmental stability.
On the other hand, the binder resin can be used by being dispersed in a polycarbonate resin, a polyethylene resin, a polyurethane resin, an acrylic resin, a polyamide resin, etc., but has no polarity dependence and has a moderately high resistance of 10 ¹⁶ to 10 ¹⁷ Ω · cm. Resins are preferred. Further, in order to keep the photosensitive member surface potential at 30 V / μm with time, a protective agent is applied to the surface of the photosensitive member by a protective agent applying means described later.

  The writing unit 5Y is arranged in four laser diode (LD) light sources prepared for each color, a pair of polygon scanners composed of a six-sided polygon mirror and a polygon motor, and an optical path of each light source. It is composed of a lens such as an fθ lens, a long WTL, or a mirror. Laser light emitted from the laser diode is deflected and scanned by a polygon scanner and irradiated onto the photosensitive member. The spot diameter of the laser beam is preferably 50 μm or less. Thus, as the laser beam spot diameter is reduced, a sharp latent image can be formed on the photosensitive drum 10Y.

Next, the developing device 2Y is shown in FIG. The developing device 2Y accommodates a two-component developer containing a magnetic carrier and non-magnetic toner in a developing case 21Y, and develops the developer agitating unit 22Y for agitating the two-component developer and the photosensitive drum 10Y. It is divided into a developing unit 23Y.
The stirring unit 22Y conveys the two-component developer while stirring and supplies and adheres the two-component developer to the developing sleeve 24Y, and is at a position lower than the developing unit 23Y. The stirring unit 22Y is provided with two parallel screws 25Y, and the two screws 25Y are partitioned by a partition plate 26Y except for both ends.

  The developing unit 23Y transfers toner of the two-component developer attached to the developing sleeve 24Y to the photosensitive drum 10Y. The developing sleeve 24Y faces the photosensitive drum 10Y through the opening of the developing case 21Y. Further, a developer regulating member 27Y that is held with a gap spaced apart from the surface of the developing sleeve 24Y by a certain distance is provided.

  The developing sleeve 24Y has a non-magnetic rotatable sleeve shape, and a plurality of magnets 28Y are disposed therein. Since the magnet 28Y is fixed, a magnetic force can be applied when the developer passes through a predetermined place. The developer forms a magnetic brush by the magnet 72 and is carried on the developing sleeve 24Y.

In the developing device 2Y configured as described above, the two-component developer is conveyed and circulated while being stirred by the two screws 25Y, and is supplied to the developing sleeve 24Y. The developer supplied to the developing sleeve 24Y is drawn up and held by the magnet 28Y to form a magnetic brush on the developing sleeve 24Y. The magnetic brush is trimmed to an appropriate amount by the developer regulating member 27Y as the developing sleeve 24Y rotates. The developer thus cut off is returned to the stirring unit 25Y.
On the other hand, of the developer on the developing sleeve 24Y, the toner is transferred to the photosensitive drum 10Y by the developing bias voltage applied to the developing sleeve 24Y, and the electrostatic latent image on the photosensitive drum 10Y is visualized. After the visualization, the developer remaining on the developing sleeve 24Y leaves the developing sleeve 24Y and returns to the stirring unit 25Y when there is no magnetic force of the magnet 28Y.

  A DC bias or a developing bias in which an AC bias is superimposed on the DC bias is applied to the developing sleeve 24Y from a power supply device (not shown). The developing bias is preferably one using only the DC bias rather than the one in which the AC bias is superimposed on the DC bias. By superimposing the AC bias on the DC bias, an oscillating electric field is formed in the developing region, and the oscillating electric field releases the binding of the toner to the carrier and makes it easier for the toner to move to the electrostatic latent image on the photoconductor. is there. However, it is difficult to optimize the frequency of the AC bias and the peak-to-peak value, which is the absolute value of the maximum value-the minimum value. If the value cannot be optimized sufficiently, the toner may scatter and stains may occur. May end up. However, by using only the DC bias as the developing bias, it is possible to suppress the scattering of the toner and the background stains, thereby forming a more precise toner image.

  Further, as shown in FIG. 3B, the developing device 2Y of the present embodiment fills the space a on the back side of the developer regulating member 27Y with resin 29Y. As shown in FIG. 3A, when there is a space a behind the developer regulating member 27Y, the developer blocked by the developer regulating member 27Y accumulates in this space. The developer remaining in the space on the back side of the developer regulating member 27Y presses the toner conveyed to the developer regulating member 27Y by the developing sleeve 24Y. By such pressing, the toner is subjected to great mechanical stress, and the external additive of the toner is buried in the base resin. As a result, the deterioration of the toner progresses, and a sufficient charge amount cannot be obtained, resulting in deterioration of the image such as background stains over time. Further, there are cases where sufficient developing ability cannot be obtained, for example, the torque of the developing sleeve 24Y increases or the developer moving speed decreases. On the other hand, as shown in FIG. 2, by filling the back side of the developer regulating member with resin 29Y, it is possible to prevent the developer from remaining in the space on the back side of the developer regulating member. As a result, the toner conveyed to the developer regulating member by the developing sleeve is hardly subjected to mechanical stress. Therefore, the external additive of the toner is suppressed from being buried in the base resin, and the toner can obtain a sufficient charge amount over time, and a high-quality image can be obtained over time.

  Next, the cleaning device 4Y will be described. As shown in FIG. 4, the cleaning device 4 </ b> Y of this embodiment uses a conductive fur brush to which an electric field is applied to remove toner on the photosensitive drum. The toner removed from the photosensitive drum 10Y by the conductive fur brush 41Y to which an electric field has been applied is electrostatically recovered to the recovery roller 42Y and scraped off from the recovery roller 42Y by the scraper 43Y in contact with the recovery roller 42Y. It is. As shown in FIG. 4, the voltage is applied to the conductive fur brush 41Y by contact with the collecting roller 42Y to which the voltage is applied by the cleaner power supply 44Y. Usually, the recovery roller 42Y is preferably made of a metal such as SUS or a fluorine-based resin coated or dispersed or subjected to eutectoid plating with the metal in order to reduce the coefficient of static friction of the surface. In addition, a urethane rubber blade is used as the scraper 43Y, but this is not a limitation. When spherical toner is used, the recoverability can be maintained by using an elastic roller as the recovery roller 42Y and bringing the metallic blade used in the scraper 43Y into contact with the bite amount. Further, the relationship between the outer diameter position tangential speed Vf of the fur brush 41Y and the outer diameter tangential speed Vk of the recovery roller 42Y is set to a desired recovery efficiency by setting conditions within a range where the relationship of Vk / Vf ≧ 0.8 is satisfied. Thus, by collecting the toner from the fur brush 41Y by the collecting roller 42Y, the fur brush 41Y can remove the toner from the photoreceptor drum 10Y on a fresh surface where the removed toner does not always remain. Therefore, the toner adhering to the photosensitive drum 10Y by the toner adhering to the fur brush 41Y and the image carrier wear due to the toner acting as abrasive particles between the fur brush 41Y and the photosensitive drum 10Y do not occur.

  Further, in conventional blade cleaning, there is a problem of abnormal photoconductor wear depending on an image pattern, a toner additive, and the like. However, since the toner is collected by the conductive fur brush 41Y, it is possible to prevent abnormal wear of the photoreceptor depending on the image pattern, toner additive, and the like.

  The cleaning device 4Y includes a protective agent coating unit that protects the photosensitive drum 10Y from proximity discharge and applies a protective agent for preventing film thickness reduction and resulting precipitation and separation of inorganic fine particles. Thus, by protecting the photosensitive drum 10Y and suppressing the decrease in film thickness, the surface potential of the photosensitive member can be kept at −30 V / μm with time, and a stable image can be obtained with time. The protective agent application means includes a protective agent 51Y molded into a bar shape, a conductive fur brush 41Y that scrapes off the protective agent and supplies and applies it to the photosensitive drum 10Y, and a pressure spring 52 that supports the protective agent 51Y. It is composed of

  As the protective agent 51Y, a metal soap such as zinc stearate, silicon, or wax is applied on the photosensitive drum 10Y. By applying a protective film on the photoreceptor drum 10Y, image carrier deterioration due to proximity discharge is suppressed.

  Next, a method for applying the protective agent on the photosensitive drum 10Y will be described. A protective agent 51Y formed into a bar shape constituting the protective agent application means is brought into contact with a fur brush 41Y as an application member, and is applied continuously or intermittently on the photosensitive drum 10Y via the brush. A supply method is preferred. As described above, in this embodiment, the toner is removed by the conductive fur brush 41Y, while the bar-shaped protective agent 51Y is scraped by the fur brush 41 and applied onto the photosensitive drum 10Y.

  That is, in the cleaning device including the conductive fur brush 41Y, the collection roller 42Y, and the scraper 43Y, the conductive fur brush 41Y is placed in contact with the protective agent 51Y molded in a bar shape, and the conductive fur brush 41Y is interposed therebetween. Then, a protective agent 51Y is applied onto the photoreceptor 10Y to form a protective film. Further, a pressure spring 52Y is attached so that the protective agent 51Y can be stably supplied to the fur brush 41Y over time.

  The fur brush 41Y rotates in the same direction as the rotation direction of the photoconductor. That is, the photoconductor rotates clockwise in FIG. 4, and the fur brush 41Y also rotates clockwise. Thus, at a position where the fur brush 41Y and the photosensitive drum 10Y face each other, the fur brush 41Y moves in a direction opposite to the moving direction of the surface of the photosensitive drum. As a result, the protective agent can be applied to the surface of the photosensitive drum from which the toner has been removed. Further, the tips of many brushes come into contact with each other while the surface of the photosensitive drum 10Y passes through the region in contact with the fur brush 41Y. Therefore, the toner adhering to the surface of the photoconductor can be reliably collected and the protective agent can be reliably applied to the surface of the photoconductor.

  Further, the amount of the protective agent applied to the photosensitive drum is changed by controlling the rotation speed of the conductive fur brush 41Y based on the obtained image information. Specifically, in the case of an image having a high image area ratio, the rotational speed of the conductive fur brush 41Y is increased to increase the amount of the protective agent applied on the photosensitive drum. This increases the thickness of the protective layer formed on the photosensitive drum. In the case of an image with a high image area ratio, the amount of toner adhering to the photoconductor increases, and the surface of the photoconductor is easily scraped by the toner additive. Thus, the thickness of the protective agent on the photoconductor By increasing the thickness, the surface of the photoreceptor can be prevented from being scraped.

  The protective agent applied by the conductive fur brush 41Y is uniformly stretched by the blade 46Y, and the thickness of the protective agent attached to the surface of the photosensitive drum is adjusted. The thickness of the protective agent is adjusted so that at least the protective agent has a layer shape of 2 to 10 molecules. If the protective agent is a monomolecular layer, the surface of the photosensitive drum cannot be sufficiently protected. In addition, when the protective agent is a layer of 10 or more molecules, a sufficient charging potential cannot be obtained on the surface of the photosensitive drum, or the coefficient of friction on the surface of the photosensitive drum is reduced, so that the toner hardly adheres to the surface of the photosensitive drum. Or abnormal images may occur. The thickness of the protective agent is determined according to the potential difference between the AC bias peaks of the charging device. Thus, since the protective agent is stretched by the blade 46Y, the surface of the photosensitive drum can be completely covered with the protective agent. Moreover, since the thickness of the protective layer is adjusted, the occurrence of poor charging and abnormal images are suppressed.

The fixing device 8 preferably uses belt fixing as shown in FIG. In this fixing device, a fixing belt 81 that contacts a non-fixed toner image holding surface side of a sheet is rotated by a roller 83 with a built-in heater 82 and a support roller 84 disposed downstream of the roller 83 in the transport direction. Support movably. Further, the pressure belt 85 that contacts the surface of the sheet opposite to the unfixed toner image holding surface is similarly rotatably supported by a roller 87 and a support roller 88 built in the heater 86. Both belts 81 and 85 are configured to carry the paper with the sheet sandwiched between the extending portions in contact with each other. For example, each roller having a built-in heater is a drive roller. In the figure, 80 is a thermistor for driving the heater, and 88 is a paper discharge roller.
In the fixing device 8, the extending portions of the fixing belt 81 and the pressure belt 85 that are in contact with each other are over a predetermined distance on the paper conveyance path, and each belt is heated by a roller with a built-in heater. The sheet and toner can be heated by the contact between the belt portion of the extension portion and the sheet. Further, in the illustrated example, the support rollers 84 and 88 on the downstream side in the transport direction have a smaller diameter than the rollers 83 and 87 on the upstream side, and each belt surface wound around the support roller, particularly the surface of the fixing belt and the sheet. Increases separability. Further, the linear velocity difference between the fixing belt 81 and the pressure belt 85 is set to 10 mSec or less. Thereby, a high quality image can be obtained.

  Next, the developer used in this embodiment will be described. The developer of the present embodiment is composed of two components, a toner and a carrier. In order to achieve high image quality, the average particle diameter of the toner is 3 to 6 μm, and the average particle diameter of the carrier is 20 to 40 μm. In addition, the toner is preferably not in the form of a true sphere but has an uneven surface. Specifically, toners having shape factors SF-1 and SF-2 of 100 or more are preferable.

Here, the toner shape factors SF-1 and SF-2 will be described. FIG. 6 is an explanatory diagram of the shape factor SF-1, and FIG. 7 is an explanatory diagram of the shape factor SF-2.
First, the shape factor SF-1 will be described. As shown in FIG. 6, the shape factor SF-1 is a value indicating the ratio of the roundness of the shape of the spherical substance, and the maximum length MXLNG of the elliptical figure formed by projecting the spherical substance on the two-dimensional plane is It is expressed by a value obtained by dividing the square by the graphic area AREA and multiplying by 100π / 4. That is, the shape factor SF-1 is defined by the following equation 1.
(Formula 2)
SF-1 = {(MXLNG) ² / AREA} × (100π / 4)

  When the value of the shape factor SF-1 is 100, the shape of the substance becomes a spherical shape, and the larger the value of SF-1, the more irregular the shape of the substance.

On the other hand, as shown in FIG. 7, the shape factor SF-2 is a numerical value indicating the proportion of the unevenness of the shape of the substance. The value is obtained by dividing the square of the perimeter PERI of the figure formed by projecting the substance on the two-dimensional plane by the figure area AREA and multiplying by 100 / 4π. That is, the shape factor SF-2 is defined by the following equation 2.
(Formula 3)
SF-2 = {(PERI) ² / AREA} × (100 / 4π)

  When the SF-2 value is 100, there is no unevenness on the surface of the substance, and as the SF-2 value increases, the unevenness on the surface of the substance becomes more prominent.

  The shape factor was determined by randomly sampling a toner image 100 times using an FE-SEM (S-800) manufactured by Hitachi, Ltd., and introducing the image information into an image analyzer (LUSEX 3) manufactured by Nireco. Analyze and calculate from the above formula.

According to the study by the present inventors, it has been found that when the shape factors SF-1 and SF-2 both approach 100 and the shape of the toner approaches a spherical shape as much as possible, the transfer efficiency increases. This results in point contact between the toner particles and those that come into contact with the toner particles (toner particles, photoconductor, etc.) due to the shape effect. As a result, it is considered that the toner fluidity is increased or the attracting force (mirroring force) to the image carrier or the like is weakened so that the toner is easily influenced by the transfer electric field.
However, when the toner shape approaches a spherical shape, it is disadvantageous for mechanical cleaning (such as blade cleaning). This is because the toner fluidity is increased, or the adsorbing force (mirroring force) on the photosensitive member or the like is weakened, so that the toner easily passes through a slight gap between the cleaning member and the photosensitive member. Therefore, from the viewpoint of cleaning properties, the shape of the toner is somewhat irregular (in a direction in which the value of SF-1 is larger than 100) or uneven (in a direction in which the value of SF-2 is larger than 100). It is preferable that there is. According to experiments, in order to satisfy both transferability and cleaning properties, the shape factor SF-1 is 120 or more and 180 or less, and the shape factor SF-2 is 110 or more and 190 or less. Is desirable.

  Further, the toner of this embodiment is prepared by stirring toner for 5 minutes and toner for 60 minutes, adding uncharged toner so that the toner density becomes 7%, and stirring for 0 minute. The toner is preferably such that the result of examining the number of toners of 1 fC / μm or more is 10% or less. Therefore, it is preferable that the toner base resin is a material in which the external additive of the toner is less likely to be buried in the toner over time. There are several candidates for materials that are difficult to embed, but here, branched polymers are preferable from the viewpoint of charging characteristics, fixing characteristics, and cleaning characteristics, and among these branched polymers, urethane materials are more preferable. In order to produce toner with a uniform particle size, it is produced by a melt suspension method involving a chemical reaction using a urethane prepolymer, and the toner is produced using means for making the toner surface uneven during the production process. Is preferred. The production method of the toner is shown below.

~ Synthesis of resin fine particle emulsion ~
In a reaction vessel equipped with a stirrer and a thermometer, 683 parts by weight of ion-exchanged water, 11 parts by weight of sodium salt of ethylene oxide methacrylate adduct sulfate (Eleminol RS-30: manufactured by Sanyo Chemical Industries), 103 parts by weight of styrene, 60 parts by weight of methacrylic acid, 105 parts by weight of butyl acrylate, and 1 part by weight of ammonium persulfate were charged. And it stirred at 400 rotation / min for 15 minutes, and obtained the white emulsion. This emulsion was heated to raise the system temperature to 80 ° C. and reacted for 5 hours. Further, 30 parts by weight of a 1% ammonium persulfate aqueous solution was added dropwise, and the mixture was aged at 80 ° C. for 7 hours, followed by vinyl resin (styrene-methacrylic acid-butyl acrylate-methacrylic acid etherene oxide adduct sulfate sodium salt). Copolymer) aqueous dispersion [fine particle dispersion 1] was obtained. The volume average particle diameter of the [fine particle dispersion 1] measured by LA-920 was 0.09 μm. A portion of [Fine Particle Dispersion 1] was dried to isolate the resin component. The resin content Tg was 60 ° C.

-Adjustment of aqueous phase-
1000 parts by weight of ion-exchanged water, 83 parts by weight of [fine particle dispersion 1], 37 parts by weight of a 48.5% aqueous solution of dodecyl diphenyl ether disulfonate (Eleminol MON-7: manufactured by Sanyo Chemical Industries), 90 parts by weight of ethyl acetate The parts were mixed and stirred to obtain a milky white liquid. This is designated as [Aqueous Phase 1].

~ Synthesis of low molecular weight polyester ~
In a reaction vessel equipped with a condenser, a stirrer and a nitrogen introduction tube, 288 parts by weight of bisphenol A ethylene oxide 2-mole adduct, 550 parts by weight of bisphenol A propylene oxide 3-mole adduct, 233 parts by weight of terephthalic acid, 66 adipic acid 66 Part by weight and 2 parts by weight of dibutyltin oxide were added and reacted at 230 ° C. for 8 hours at normal pressure. Further, after 5 hours of reaction at a reduced pressure of 10 to 15 mmHg, 54 parts by weight of trimellitic anhydride was added to the reaction vessel and reacted at 180 ° C. and normal pressure for 2 hours to obtain [Low molecular weight polyester 1]. [Low molecular polyester 1] had a number average molecular weight of 2500, a weight average molecular weight of 6700, Tg of 48 ° C., and an acid value of 30.

~ Synthesis of prepolymers with isocyanate groups ~
In a reaction vessel equipped with a cooling pipe, a stirrer and a nitrogen introduction pipe, 698 parts by weight of bisphenol A ethylene oxide 2 mol adduct, 81 parts of bisphenol A propylene oxide 2 mol adduct, 283 parts by weight of terephthalic acid, trimellitic anhydride 22 parts by weight of acid and 5 parts by weight of dibutyltin oxide were added and reacted at 230 ° C. for 8 hours at normal pressure. Further, the reaction was carried out at a reduced pressure of 10 to 15 mmHg for 5 hours to obtain [Intermediate Polyester 1]. [Intermediate Polyester 1] had a number average molecular weight of 2,100, a weight average molecular weight of 9,500, Tg of 61 ° C., an acid value of 1, and a hydroxyl value of 54.
Next, 450 parts by weight of [Intermediate polyester 1], 80 parts by weight of isophorone diisocyanate, and 500 parts by weight of ethyl acetate were placed in a reaction vessel equipped with a cooling tube, a stirrer, and a nitrogen introduction tube, and reacted at 100 ° C. for 5 hours. [Prepolymer 1] was obtained. [Prepolymer 1] had a free isocyanate weight percentage of 0.98%.
Met.

~ Synthesis of ketimine ~
170 parts by weight of isophoronediamine and 75 parts by weight of methyl ethyl ketone were charged into a reaction vessel equipped with a stirrer and a thermometer, and reacted at 40 ° C. for 10 hours to obtain [ketimine compound 1]. The amine value of [ketimine compound 1] was 356.

-Adjustment of pigment master batch-
1200 parts by weight of water, 440 parts by weight of carbon black (Printex 60, manufactured by Dexa) and 1200 parts by weight of [low molecular weight polyester 1] are added and mixed with a Henschel mixer (manufactured by Mitsui Mining). This mixture was kneaded at 130 ° C. for 45 minutes using two rolls, rolled and cooled, and pulverized to 1 mmφ or less with a pulverizer to obtain [Masterbatch 1].

~ Creation of oil phase ~
In a container equipped with a stir bar and a thermometer, 400 parts by weight of [Low molecular polyester 1], 100 parts by weight of synthetic ester wax, 10 parts by weight of CCA (salicylic acid metal complex E-84: Orient Chemical Industry), 1000 parts by weight of ethyl acetate Prepare. And it heated up at 80 degreeC under stirring, and hold | maintained at 80 degreeC for 5 hours, Then, it cooled to 30 degreeC in 1 hour. Next, 500 parts by weight of [Masterbatch 1] and 500 parts by weight of ethyl acetate were charged in a container and mixed for 1 hour to obtain [Material solution 1].
1324 parts by weight of this [Raw Material Solution 1] was transferred to a container, and using a bead mill (Ultra Visco Mill, manufactured by Imex Co., Ltd.), a liquid feeding speed of 1 kg / hr, a disk peripheral speed of 6 m / sec, and 0.5 mm zirconia beads were 80. Under the condition of volume% filling and 3 passes, the dispersion of WAX was performed by the amount of carbon black and WAX. Next, 1324 parts by weight of a 65% ethyl acetate solution of [low molecular weight polyester 1] was added, and one pass was performed with a bead mill under the above conditions to obtain [Pigment / WAX Dispersion 1]. The solid content concentration of [Pigment / WAX Dispersion 1] (130 ° C., 30 minutes) was 50%.

~ Emulsification⇒Desolvation ~
[Pigment / WAX Dispersion 1] 700 parts by weight, [Prepolymer 1] 160 parts by weight, and [Ketimine Compound 1] 6.0 parts by weight are put in a container. Next, the mixture is mixed at 6,000 rpm for 1 minute with a TK homomixer (manufactured by Tokushu Kika). Thereafter, 1200 parts by weight of [Aqueous Phase 1] was added to the container and mixed with a TK homomixer at 13,000 rpm for 20 minutes to obtain [Emulsified Slurry 1].
[Emulsion slurry 1] is put into a container in which a stirrer and a thermometer are set, and the solvent is removed at 30 ° C. for 8 hours to form desired irregularities on the toner. By changing the solvent evaporation rate, the unevenness of the obtained toner changes. Then, aging was carried out at 40 ° C. for 8 hours to obtain [Dispersion Slurry 1].

~ Washing⇒Drying ~
[Emulsified slurry 1] After 100 parts by weight of the solution was filtered under reduced pressure,
A: 100 parts by weight of ion-exchanged water was added to the filter cake, mixed with a TK homomixer (rotation speed: 12,000 rpm for 10 minutes), and then filtered.
B: 100 parts by weight of 10% aqueous sodium hydroxide solution was added to the filter cake of A, mixed with a TK homomixer (30 minutes at 12,000 rpm), and then filtered under reduced pressure.
C: 100 parts by weight of 10% hydrochloric acid was added to the B filter cake, mixed with a TK homomixer (rotation speed: 12,000 rpm for 10 minutes), and then filtered.
D: C 300 parts by weight of ion exchange water was added to the filter cake, mixed with a TK homomixer (rotation speed: 12,000 rpm for 10 minutes), and then filtered twice to obtain [filter cake 1].
This [Filtered Cake 1] was dried at 45 ° C. for 48 hours with a circulating dryer, and sieved with a mesh of 75 μm. Thereafter, 100 parts by weight of toner particles, 0.5 part by weight of hydrophobic silica (hexamethyldisilazane surface-treated product, specific surface area: 200 m ² / g), and hydrophobized rutile titanium oxide (isobutyltrimethoxysilane surface-treated product) Toner A was obtained by repeating 0.5 cycles of 0.5 parts by weight (average primary particle size: 0.02 μm) with a Henschel mixer and stirring for 1 minute and allowing to stand for 5 minutes. The volume average particle size of the toner was 4.43 μm, Tg was 50 ° C., and the THF-insoluble content of the resin component was 8%.

Next, the manufacturing method of a carrier is demonstrated.
7 wt% of carbon (manufactured by Lion Akzo, Ketjen Black EC-DJ600) is added to the solid content of the silicone resin (SR2411: manufactured by Toray Dow Corning Silicone) and dispersed for 10 minutes using a ball mill. This dispersion is diluted to a solid content of 10 wt% to obtain a dispersion. The above dispersion is applied at a rate of about 50 g / min in an atmosphere of 100 ° C. to 5 kg of the magnetite powder core material having an average particle size of 30 μm using a fluid bed type coating apparatus. Furthermore, it heated at 250 degreeC for 2 hours, and obtained the carrier with a film thickness of 0.5 micrometer. The film thickness was adjusted depending on the amount of the coating solution. The carrier had a volume resistivity of 4.3 × 10 ¹⁰ Ωcm. The obtained carrier was degassed for 30 minutes in the final step. The carrier resistance was measured by using a 4329A High Resistance Meter manufactured by Yokogawa Hewlett-Packard Co., Ltd., in which a core material was filled in a container having electrodes arranged in parallel at an interval of 2 mm, and the DC resistance at 1000 V between both electrodes was measured.

  FIG. 8 shows 5 parts by weight of toner A prepared by the above manufacturing method, 95 parts by weight of carrier A prepared by the above manufacturing method, 5 parts by weight of pulverized toner B, and 95 parts by weight of carrier prepared by the above manufacturing method. 6 is a graph obtained by examining the stress index and the toner burying rank using the developer B. As can be seen from FIG. 8, when the developer B using the conventional pulverized toner exceeds the stress index of 500 when stirred for 60 minutes with the dynamic torque of a general developing device, the burial rank becomes 1, The external additive is buried and does not remain on the surface. However, the developer A using the toner A prepared by the above-described manufacturing method has a buried rank of 3.5 even when the stress index shows a value close to 500, and there is a sufficient external additive on the toner surface. It can be seen that it is. This is presumably because the toner A of the present embodiment uses a urethane prepolymer, so that the external additive is hard to be buried.

  Next, an experiment was conducted to confirm the effects of the above-described image forming apparatus and toner. The experimental results are shown below.

(Example 1)
The image forming apparatus of Example 1 was modified using a Ricoh printer IpsioColor 8150 as a base machine. First, the developing unit of this base machine was replaced with a developing unit in which the doctor blade in the developing unit was modified. As shown in FIG. 2, the doctor blade was modified by filling the space behind the blade with the amount of resin agent and eliminating the space behind the doctor blade. The modified developing unit was arranged with a gap of 0.3 mm from the photoreceptor. Next, replace the cleaning unit with a modified cleaning unit. As shown in FIG. 4, this modified cleaning unit can be applied by scraping a protective agent made of zinc stearate formed into a bar shape with a conductive fur brush as a cleaning brush and supplying it onto the photoreceptor. It is what I did. Further, the blade pressure of the blade in the figure was set to 1000 ± 20 gf. As the developer, toner A manufactured by the above-described manufacturing method was used.
(Example 2)
The image forming apparatus of Example 2 was further improved over the image forming apparatus of Example 1 described above. First, the blade pressure was reset to 1000 ± 10 gf. Further, the intermediate transfer belt was changed from one having a volume resistance of 10 ⁸ Ω · cm to one having a volume resistance of 10 ⁹ Ω · cm. Further, toner B in which 0.5 part by weight of X-24 (manufactured by Aerosil) was added as inorganic fine particles to 100 parts by weight of toner A was used.
(Example 3)
The image forming apparatus of Example 3 was further improved over the image forming apparatus of Example 2. First, the developing bias was changed from a DC bias superimposed on an AC bias to a DC bias only. Further, the fixing device was changed to belt fixing in which the difference between the upper and lower linear velocity was 1 msec. Furthermore, the amount of toner attached to the transfer paper was controlled to be 0.41 mg / cm ² . The spot diameter of the laser beam of the writing unit was changed to 45 μm.
Example 4
The image forming apparatus of Example 4 was further improved over the image forming apparatus of Example 3 described above. The photoreceptor surface potential was changed from -650V to -450V.
(Comparative Example 1)
In the image forming apparatus of Comparative Example 1, IpsioColor 8150 was used in a standard state, and pulverized toner having a particle diameter of 6.8 μm to which a protective agent was added was used.
(Comparative Example 2)
In the image forming apparatus of Comparative Example 2, IpsioColor 8150 was used in a standard state, and the toner A manufactured by the above-described manufacturing method was used as the developer.
(Comparative Example 3)
In the image forming apparatus of Comparative Example 2, the cleaning device of IpsioColor 8150 was changed to a cleaning device similar to that of Example 1. Note that the toner in Comparative Example 1 was used as the toner in the developer.

  The toner used in the image forming apparatuses of Examples 1 to 4 and Comparative Examples 1 to 3 is stirred for 10 minutes, and the charge amount (Q / M) and charge amount distribution (q / d) of the charged toner at the time of initial stirring are determined. It was measured. Next, after the initially stirred toner was further stirred for 60 minutes, the toner was added and stirred for 1 minute so that the toner concentration increased by 2%. Then, the charge amount (Q / M) and charge amount distribution (q / d) of the toner at this time were measured. The rotation speed of the apparatus at this time was 30 rpm, and the initial toner concentration was 5%.

  The charge amount (Q / M) of the toner was measured using a blow-off method. In this blow-off method, a cylindrical conductor container (blow-off gauge) with a mesh that does not allow magnetic carrier to pass through on both sides is placed horizontally, and the charge carried away by the toner is measured by blowing compressed air. It is. The results are shown in Table 1.

For measurement of the charge amount distribution, E-SPART ANALYZER (analyzer manufactured by Hosokawa Micron Corporation, hereinafter referred to as “E-SPART analyzer”) was used. This E-SPART analyzer adopts a method using a dual beam frequency shift type laser Doppler velocimeter and an elastic wave that perturbs the movement of particles in an electrostatic field, and sprays air on the toner on the developing sleeve. The charge amount data of each toner can be obtained by skipping and capturing the movement in the electric field. In this confirmation experiment, 3000 toners were sampled to see the difference in distribution. From the charge distribution obtained by this E-SPART analyzer, the ratio of toner of -0.1 fc / μm or more was examined. In the state where the external additive is buried and the toner is agglomerated, even if a fresh non-charged toner is added and stirred, the embedded toner adheres to the carrier and agglomerates, so these fresh The toner is not easily triboelectrically charged with the carrier or toner. For this reason, agitation for 1 minute does not sufficiently charge the fresh toner and tends to be a weakly charged toner. On the other hand, when the external additive is sufficiently present on the toner surface, the toner is not aggregated. As a result, even if fresh uncharged toner is added and stirred, these toners rub against the carrier and the toner and are sufficiently charged even if stirring is performed for 1 minute. From this, by adding a large amount of fresh toner, increasing the toner concentration by 2%, and examining what percentage of the total number of weakly charged toners of −0.1 fc / μm or more after stirring for 1 minute is The degree of deterioration of the toner can be determined quantitatively. The results are shown in Table 1.

  Further, printing was performed with the image forming apparatuses of Examples 1 to 4 and Comparative Examples 1 to 3, and an initial image state after initial stirring and an image state with time after 180,000 sheets were evaluated. The state of the image was evaluated by graininess, sharpness, and gradation.

  Image graininess is defined as follows. In other words, “granularity” is defined as “subjective evaluation value indicating how rough an image that should be uniform” is, and the amount that objectively represents the granularity that is the subjective evaluation value is granularity. It is a measure of sex and is “granularity”. This granularity was calculated by the following method.

Standardized as this “granularity” is “RMS granularity” of the following equation, which is standardized by ANSI PH-2.40-1985.
(Formula 4)
RMS granularity (σD) = [1 / N Σ (Di−Da) ² ] ^1/2
Di: concentration distribution Da: average concentration (Da = 1 / NΣDi)

In addition, the granularity using the Wine Spectrum that is the power spectrum of the density fluctuation of the image is defined. Xerox Dooley and Shaw applied Winner Spectrum, and cascaded with visual spatial frequency characteristics (Visual Transfer Function: VTF) as shown in the following equation, and the integrated value was defined as granularity (GS). (For details, see RP Dooley, Rshaw: Noise Perception in Electrophotography, J. Appl. Photogr. Eng., 5, 4 (1979), pp 190-196)
(Formula 5)
GS = exp (−1.8 Da) ∫ (WS (f)) ^1/2 VTF (f) df
Da: Average concentration f: Spatial frequency (c / mm)
WS (f): Wine Spectrum
VTF (f): Visual spatial frequency characteristics

The “granularity” in this embodiment is defined by the following equation by further developing the granularity of the Dooley and Shaw.
(Formula 6)
Granularity = exp (aL + b) ∫ (WSL (f)) ^1/2 VTF (f) df
L: Average brightness f: Spatial frequency (c / mm)
WSL (f): power variation of brightness fluctuation VTF (f): visual spatial frequency characteristics a: coefficient (= 0.1044)
b: coefficient (= 0.8944)

  In this case, the lightness L * is used instead of the image density. The latter is characterized by excellent color space linearity and excellent adaptability to color images. The granularity described below is the granularity defined by this equation.

  The granularity represents the noise characteristics of the image based on its definition. By measuring the granularity of the output image by the above-described method, the noise characteristic (roughness) of the image can be quantified. As can be seen from the definition of the numerical value of the granularity, the value is small when the roughness is good, and the value becomes larger as the roughness becomes worse. The inventor calculated the granularity based on the above formula after reading the output image with a scanner (FT-S5000: manufactured by Dainippon Screen). This calculation result was divided into five stages to obtain a granularity rank.

  Next, the sharpness of the image is a psychological factor that represents the reproducibility of the contour and fine structure of the image. On the other hand, the sharpness is a physical factor obtained by physical measurement and quantification of an image. The sharpness evaluation includes a method for evaluating the resolution using a resolution chart such as a ladder chart or a bamboo shoot chart, and a method for obtaining a sharpness and an MTF (spatial frequency characteristic) of an image. The sharpness was evaluated based on the MTF, which has good psychological evaluation and correspondence.

The sharpness evaluation by MTF is performed by combining the MTF of an image and the visual spatial frequency characteristics. Specifically, it is obtained as a ratio of MTF-Fin of a sine wave signal as an input signal (image) and MTF-Out of a sine wave signal as an output signal (image).
(Formula 7)
MTF = MTF-Fin / MTF-Out

  By obtaining this MTF with respect to various spatial frequencies, the spatial frequency characteristics (transfer characteristics) of the image system to be evaluated can be obtained. The obtained MTF was used as a sharpness evaluation scale, and the sharpness was ranked.

The gradation of the image is a characteristic that expresses how the gradation of the image is reproduced. Whether the gradation of the output device is good or bad is the presence or absence of a sufficient dynamic range (solid density), the gradation reproduction characteristic, so-called gamma characteristic. Is determined by the smoothness, the lack of gradation skipping, and the like. Therefore, as a method for evaluating gradation, the following method is conceivable.
A. A method of measuring the brightness of the gray scale and evaluating the linearity of the gamma characteristic of the output characteristic (contribution rate or square error during linear regression).
B. Measure the brightness of 8-bit (256 gradations) gray scale, calculate how many times the brightness difference between each gradation is perceptible (JND = 0.27), and add this calculated value A method for evaluating the jump in gradation using the values obtained.
This time, the evaluation method of B was used. Then, the value obtained by the B evaluation method was divided into five stages to obtain gradation evaluation values.
The results are shown below.

  Looking at Comparative Example 1 in Table 1, although the charge amount Q / M after 70 minutes of stirring increased from the charge amount Q / M after 10 minutes after the completion of initial stirring, − The ratio of the toner of 0.1 fc / μm or more is higher than the ratio of the toner of −0.1 fc / μm or more after 10 minutes. This is because the toner charge distribution at the initial stage of Comparative Example 1 has a normal distribution centered on −16 μc / g, but the toner charge distribution after 70 minutes is a normal distribution centered on −25 μc / g. It wasn't. This is because a sufficient charge amount cannot be obtained even with stirring, and the proportion of deteriorated toner increased, so that the proportion of toner of -0.1 fc / μm or more increased despite a sufficient charge amount. it is conceivable that. This deteriorated toner is a toner in which an external additive of toner is buried during stirring. For this reason, the graininess, sharpness, and gradation of the image at the initial stage were good, but it has been remarkably lowered over time.

  On the other hand, in Comparative Example 2, the toner is changed from the pulverized toner to the toner prepared by the manufacturing method described in the embodiment of the present invention. Since this toner A is produced by a melt suspension method involving a chemical reaction using a urethane prepolymer, it is difficult for the external additive to be buried. For this reason, the proportion of toner of −0.1 fc / μm or more after 70 minutes is reduced as compared with Comparative Example 1. As a result, the graininess over time was improved as compared with Comparative Example 1. However, despite the use of a toner in which the external additive of the toner is difficult to be buried, the ratio of the toner of −0.1 fc / μm or more after 70 minutes is 10% or more. This is because, in the developing device of Comparative Example 1, the back side of the developer regulating member is a space as shown in FIG. ◯, and the developer accumulates in this space during the development process. Since the toner staying in this space stays without being stirred, the charge amount is gradually lost. As a result of a part of the toner that has accumulated and lost the charge amount adhered to the developing sleeve and conveyed to the developing region, the ratio of the toner of −0.1 fc / μm or more after 70 minutes is 10% or more. It is thought that it became. Further, as a result of the developer staying on the back side of the developer regulating member exerting a great deal of stress on the toner on the developing sleeve, the burying of the external additive of the toner has progressed. It is also considered that the ratio of toner of 1 fc / μm or more became 10% or more.

  Although Comparative Example 3 uses the same pulverized toner as Comparative Example 1, the granularity and gradation with time are improved. This is because a protective layer having a thickness of 2 or more molecules is formed on the surface of the photoconductor, so that the photoconductor is prevented from being deteriorated due to the discharge from the charging device or the influence of the external additive of the toner. It is thought that it was because it was done.

  In Example 1, the ratio of the toner of −0.1 fc / μm or more after 70 minutes was 10% or less, and the graininess, sharpness, and gradation were good values at the initial stage and over time. . In Example 1, as shown in FIG. 2, the back side of the developer regulating member is filled with resin. Thereby, since the developer does not collect on the back side of the developer regulating member, the toner on the developing sleeve is not subjected to great stress. Further, the toner that stays and loses the charge amount is not conveyed to the development area. For this reason, it is considered that the ratio of the toner of −0.1 fc / μm or more after 70 minutes became 10% or less, and the graininess over time was improved. In addition, since a protective layer having a thickness of two or more molecules is formed on the surface of the photosensitive member, deterioration of the photosensitive member due to discharge from the charging device and the influence of an external additive of the toner is suppressed. As a result, the surface potential of the photoreceptor was stabilized over time, and the image over time was improved.

In Example 2, since the toner B in which the volume resistance of the intermediate transfer belt is 10 ⁹ Ω · cm and 0.5 part by weight of inorganic fine particles are added to 100 parts by weight of the toner A is used, The graininess, sharpness, and gradation of the image were increased as compared with Example 1.

Further, in Example 3, since the developing bias was a DC bias, even if there was a toner whose charge amount dropped somewhat over time, it was difficult for background stains to occur. As a result, the graininess of the image was improved over time as compared with Example 2. Also, the fixing device is belt-fixed so that the linear velocity difference between the upper and lower sides is 1 msec, and the toner adhesion amount to the transfer paper is controlled to be 0.41 mg / cm ^2, and the spot diameter of the laser beam of the writing unit is set to 45 μm It has changed. As a result, the glossiness of the obtained image was 10%, and the gradation and sharpness of the image were improved as compared with Example 3.

  In Example 4, the photoreceptor surface potential was set to -450V. As a result, the surface potential of the photoreceptor can be set to −30 V / μm or less, and an image having good graininess, sharpness, and gradation can be maintained over time from the initial stage.

As described above, according to the image forming apparatus of the present embodiment, with conventional toner, the toner is stirred for a time (60 minutes) such that there is no external additive remaining on the toner surface, and the toner is uncharged so that the toner concentration becomes 7%. The toner is added so that the number of toners of −0.1 fC / μm or more after stirring for 1 minute is 10% or less. As a result, toner aggregation is suppressed over time, and a sharp charge distribution can be maintained. As a result, the amount of weakly and reversely charged toner of −0.1 fC / μm or more is maintained at 10% or less over time, so that image deterioration such as background smearing can be suppressed. Therefore, a good image can be maintained for a long time.
In addition, since the toner particle size is 3 to 6 μm, the toner charge amount distribution is uniform, a high-quality image with little background stain can be obtained, and the transfer rate is increased in the electrostatic transfer system. be able to. If the toner has a particle size smaller than 3 μm, background stains, toner scattering, etc. may occur during development, or fluidity may be deteriorated and toner replenishment and cleaning properties may be hindered. In addition, when the particle diameter is larger than 6 μm, dust in the image, deterioration of resolution, or the like may be a problem.
The particle size of the carrier is 20 to 40 μm. By setting the carrier particle size to 40 μm or less, the thickness of the developer spike (carrier chain) at the time of image formation can be uniformly thinned, and more precise toner can be delivered. In addition, since the density of developer spikes per unit area on the developing sleeve is increased, toner can be delivered to the latent image on the photoreceptor without any gap. Thereby, an image with more excellent dot reproducibility can be formed. If the carrier particle size is too smaller than 20 μm, carrier adhesion to the photoreceptor increases, so 20 μm or more is desirable.
Also, the amount of protective agent applied to the photoreceptor is changed by controlling the rotational speed of the conductive fur brush based on the obtained image information. Specifically, in the case of an image with a high image area ratio, the amount of toner adhering to the photoconductor is increased by increasing the number of rotations of the fur brush to suppress the effect of the toner surface being scraped by the toner additive. . As described above, since the rotation speed of the fur brush is controlled in accordance with the image area ratio, it is possible to suppress the influence of the abrasion of the photoreceptor surface due to the toner additive. As a result, a stable photoreceptor surface potential can be obtained over time, and a good image can be maintained over time.
In this embodiment, after the protective agent is applied to the photoreceptor, the protective agent is uniformly extended by the blade. Thereby, a protective layer having a thickness of two or more molecules can be uniformly formed on the surface of the photoconductor, and the surface of the photoconductor can be reliably protected.
In this embodiment, since the absolute value of the charge amount of the toner after the initial stirring is 30 μC / g or more, the reverse / weakly charged toner can be surely eliminated at the initial stage. As a result, a good image can be obtained at the initial stage.
Further, the toner of this embodiment is generated by a melt suspension method involving a chemical reaction using a urethane prepolymer. Thereby, the toner can be manufactured with a uniform particle size, and the particle size distribution and the charge distribution can be sharpened. Further, by using a urethane prepolymer, it is possible to obtain a toner in which the external additive is hardly buried. Therefore, it is possible to obtain a toner in which the charge amount does not decrease over time, and it is possible to suppress image deterioration such as scumming due to poor charging of the toner over time.
In addition, the toner of the present embodiment forms irregularities on the toner surface when the solvent is removed in the toner manufacturing process. As described above, by providing irregularities on the toner, it is possible to satisfy both transferability and cleaning properties.
Further, inorganic or organic fine particles such as silica and titanium oxide are present on the surface of the toner so as to be embedded in the toner to some extent. In this way, by burying the external additive to some extent, it is less likely to fall out of the toner as compared with the case where the external additive is physically attached to the toner. As a result, the toner can maintain stable performance over time.
Further, the spot diameter of the laser beam of the writing device is set to 50 μm or less. Thus, by scanning the surface of the photoreceptor with a small-diameter laser beam, a sharp electrostatic latent image composed of smaller dots can be formed, and a high-quality image can be formed.
In addition, by using a DC bias as the developing bias, it is possible to make it difficult to generate scumming or toner scattering even with toner whose charge amount has dropped slightly over time. Therefore, it is possible to suppress deterioration of the image over time.

1 is a schematic configuration diagram of an entire image forming apparatus according to an embodiment. FIG. 2 is a schematic configuration diagram of a developing device. (A) is the schematic of the conventional developing apparatus with the space a of the back side of a developer control member. FIG. 6B is a schematic diagram of a developing device in which a space a on the back side of the developer regulating member is filled with resin. The schematic block diagram of a cleaning apparatus. 1 is a schematic configuration diagram of a fixing device. The schematic diagram for demonstrating shape factor SF-1. The schematic diagram for demonstrating shape factor SF-2. The figure which shows the relationship between the embedding rank of the developer A and the developer B, and a stress index. The figure which shows the relationship between the burial rank and stress index in each developing unit. FIG. 6 is a diagram illustrating a charge distribution after stirring in a conventional toner.

Explanation of symbols

1Y, 1M, 1C, 1Bk Charging roller 2Y, 2M, 2C, 2Bk Developing device 4Y, 4M, 4C, 4Bk Cleaning device 5Y, 5M, 5C, 5Bk Writing device 6a Intermediate transfer belt 8 Fixing device 10Y, 10M, 10C, 10Bk Photosensitive drum 24Y Developing sleeve 27Y Development regulating member 29Y Resin 41Y Conductive fur brush 51Y Protective agent

Claims (13)

  An image carrier that carries an electrostatic latent image, and a charging device that is provided at a position close to or in contact with the surface of the image carrier, forms a region close to the surface of the image carrier, and is charged by discharging in the region. A developing device for carrying a developer comprising toner and a carrier on a developer carrying member and transporting the developer to a developing region facing the image carrying member to develop a latent image on the image carrying member into a toner image; In an image forming apparatus having a cleaning device that removes transfer residual toner remaining on the image carrier after the subsequent toner image is transferred to a transfer material, the surface of the image carrier is coated with a protective agent, and the image carrier A protective agent coating means for forming a protective layer on the body surface is provided. As the toner, a developer having a toner concentration of 5% is stirred for 60 minutes after the initial stirring, and then uncharged so that the toner concentration becomes 7%. When adding toner and stirring for 1 minute In the charge amount distribution of toner, it would like the image forming apparatus, characterized in that -0.1fC / μm or more of the number of toner is used not more than 10% of the total number of toner.   The image forming apparatus according to claim 1, wherein the toner has an average particle diameter of 3 μm to 6 μm.   3. The image forming apparatus according to claim 1, wherein the carrier has an average particle diameter of 20 μm to 40 μm.   4. The fur brush according to claim 1, wherein the cleaning device rotatably contacts the image carrier and electrostatically removes transfer residual toner remaining on the image carrier. The fur brush is a protective agent applying means for supplying a protective agent to the image carrier, and the rotation speed of the fur brush is controlled according to the area ratio of the toner image on the image carrier. An image forming apparatus provided with control means for performing   5. The image forming apparatus according to claim 4, further comprising a homogenizer for uniformly layering the protective agent on the image carrier applied by the fur brush on the surface of the image carrier.   6. The image forming apparatus according to claim 1, wherein a toner charge amount after stirring the developer for 10 minutes is −30 μC / g or less.   7. The image forming apparatus according to claim 1, wherein the toner is produced by a dissolution suspension method involving a prepolymer chemical reaction.   8. The image forming apparatus according to claim 7, wherein the toner has irregularities on the surface.   9. The image forming apparatus according to claim 8, wherein a part of the inorganic or organic fine particles is buried in the toner surface.   The image forming apparatus according to claim 7, wherein the prepolymer is a branched polymer.   The image forming apparatus according to claim 10, wherein the branched polymer is made of a urethane compound.   The image forming apparatus according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11, further comprising writing indenting means for forming a latent image on the surface of the image carrier with a laser beam, An image forming apparatus having a beam spot diameter of the laser light of 50 μm or less.   13. The image forming apparatus according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, further comprising application means for applying a developing bias to the developer carrying member. Is a direct current voltage.

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