JP2014182308A - Image forming apparatus - Google Patents

Abstract

An image forming apparatus capable of reducing the coefficient of friction between a blade and an image carrier and preventing turning without risk of toner slipping.
A toner supply means for supplying toner T including toner base Tm and at least one type of external additive Ta having a charging polarity opposite to that of toner base Tm during a lubrication imparting sequence is provided. Includes a conductive cleaning blade 91b and bias applying means 91V for applying a bias to the cleaning blade, and the bias applying means 91V is configured so that the toner T supplied by the toner supplying means during the lubrication imparting sequence When the vicinity of the contact position between the carrier and the cleaning blade 91b is reached, a bias having the same polarity as the charging polarity of the toner base is applied to the cleaning blade 91b.
[Selection] Figure 2

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer that employs an electrophotographic system or an electrostatic recording system.

  Conventionally, in an image forming apparatus using an electrophotographic method, the blade cleaning method is widely used as a technique that is the simplest and has high cleaning performance among methods for cleaning residual toner on an image carrier. The blade cleaning method is a cleaning method in which a cleaning blade is brought into contact with the image carrier in a counter direction of the rotation direction of the image carrier with a predetermined amount of penetration, and the residual toner on the image carrier is scraped off. However, in the blade cleaning method, when friction increases between the cleaning blade and the image carrier, a problem of so-called “turning” may occur in which the cleaning blade turns in the moving direction of the image carrier.

  The factor that increases the friction coefficient between the cleaning blade and the image carrier is that there are fewer particles intervening between the cleaning blade and the image carrier (blade nip), and the portion where the cleaning blade and the image carrier directly touch each other. It will be mentioned.

  Since the cleaning blade scrapes out minute toner on the image carrier, it is required to have a function of deforming without leaving a gap along the unevenness and inclination of the image carrier surface. Therefore, an elastic rubber blade is usually used. Is done. Generally, the friction coefficient of a rubber blade that is an elastic body is high, and the friction when the rubber blade and the image carrier are in direct contact with each other is large. This friction causes turning of the rubber blade. Therefore, normally, in the initial stage of use of the image forming apparatus, initial lubricants such as carbon fluoride fine particles and silicone resin fine particles previously applied to the blade surface are interposed in the blade nip portion, and between the cleaning blade and the image carrier. It works to lower the coefficient of friction. Further, after the start of use of the apparatus, the transfer residual toner that could not be transferred from the image carrier to the transfer target is supplied to the blade nip portion and functions as a lubricant.

  However, when images with a low image printing rate are continuously formed or in systems with very high transfer efficiency, the amount of toner supplied to the blade nip is reduced, so the particles intervening in the blade nip are reduced. As a result, the friction coefficient between the cleaning blade and the image carrier increases.

  Therefore, as in Patent Documents 1 and 2, a belt-like toner image that is unrelated to the original image is formed on the image carrier between image regions and before and after image formation, and the toner is fed into the blade nip portion and interposed. Do things. Thus, a method is known in which the friction between the cleaning blade and the image carrier is reduced to prevent turning in advance.

JP 2006-138925 A JP-A-2005-250215

  As described above, the method of supplying and interposing the toner to the blade nip portion at the time of non-image formation has the effect of reducing the friction coefficient between the cleaning blade and the image carrier and preventing turning. However, since a large amount of toner rushes into the blade nip portion at a stroke than normal transfer residual toner, the force that the toner enters the blade nip portion increases. As a result, the problem of so-called “toner slipping” that the toner slips between the cleaning blade and the image carrier is likely to occur. When toner slip occurs, the slipped toner moves to the transfer target, causing streak-like image defects, or causing contamination of each member such as a charging member disposed in the vicinity of the image carrier. The reliability will be significantly impaired. On the other hand, if the amount of the belt-like toner image to be supplied is reduced in order to avoid the above problem, the toner slipping is improved, but the amount of intervening particles is also reduced, so the effect of preventing the turning-up is reduced. End up. From the above, it is difficult for the conventional techniques to stably solve both the problems such as “turn over” and “toner slipping”.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of reducing the coefficient of friction between a cleaning blade and an image carrier and preventing turning without risk of toner passing through.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention is for image formation in which a transfer residual toner on the image carrier after the toner image formed on the image carrier according to image information is transferred to a recording medium is removed by a cleaning device. In the image forming apparatus capable of executing the image forming sequence and the lubricity imparting sequence for supplying toner to the cleaning device at the time of non-image formation excluding the image forming by the image forming sequence, in the lubricity imparting sequence, A toner base and toner supply means for supplying toner containing at least one external additive having a charge polarity opposite to that of the toner base. The cleaning device includes a conductive cleaning blade, and a cleaning blade. Bias applying means for applying a bias, and the bias applying means is provided during the lubrication imparting sequence. When the toner supplied by the toner supply means reaches the vicinity of the contact position between the image carrier and the cleaning blade, a bias having the same polarity as the charging polarity of the toner base is applied to the cleaning blade. An image forming apparatus is characterized in that application is performed.

  According to the present invention, it is possible to provide an image forming apparatus capable of reducing the friction coefficient between the cleaning blade and the image carrier and preventing the turning without risk of toner slipping.

1 is a schematic sectional view illustrating an example of an image forming apparatus according to the present invention. FIG. 3 is a schematic sectional view showing an example of a cleaning device according to the present invention and an enlarged schematic sectional view showing a contact portion between a cleaning blade and an image carrier. FIG. 2A is a schematic sectional view of the cleaning device, and FIG. 2B is an enlarged schematic sectional view showing a contact portion between the cleaning blade and the image carrier. FIG. 2 is a schematic diagram of a toner and a developer according to the present invention and a schematic configuration diagram showing the behavior of the toner during development. 3A is a schematic diagram of the toner, FIG. 3B is a schematic diagram of the developer, and FIG. 3C is a schematic configuration diagram illustrating the behavior of the toner during development. It is a lubrication provision sequence in Examples 1, 2 and Comparative Examples 1-3. FIG. 4A is a diagram showing the timing of imparting lubricity, and FIG. 4B is a diagram showing the timing of applying the bias. It is an expansion schematic sectional drawing of the blade nip part of the blade cleaning means which concerns on this invention. 5 is a graph showing a relationship between a cleaning blade bias value and an external additive retention amount in a blade nip portion of the cleaning blade. 4 is a graph showing a relationship between a developing bias frequency and an external additive retention amount in a blade nip portion of a blade cleaning unit. 6 is an enlarged schematic cross-sectional view of a blade nip portion of a blade cleaning unit in Comparative Example 2. FIG. 10 is an enlarged schematic cross-sectional view of a blade nip portion of a blade cleaning unit in Comparative Example 3. FIG. 6 is a schematic sectional view of a cleaning device in Embodiment 3. FIG.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in the following examples are not intended to limit the scope of the present invention to those unless otherwise specified. Absent.

Example 1
(Overall image forming process)
First, the overall configuration of an embodiment of the image forming apparatus according to the present embodiment will be described.

  FIG. 1 shows a schematic cross-sectional configuration of the image forming apparatus 100. The image forming apparatus 100 is a tandem type electrophotographic laser beam printer.

  The image forming apparatus 100 includes first, second, third, and fourth image forming units (stations) S (SY, SM, SC, SK) as a plurality of image forming units. The first, second, third, and fourth image forming units SY, SM, SC, and SK form yellow (Y), magenta (M), cyan (C), and black (K) images, respectively. To do.

  In this embodiment, the configurations and operations of the image forming units SY, SM, SC, and SK are substantially the same except that the color of the toner used is different. Accordingly, in the following, when no particular distinction is required, the subscripts given to the reference numerals in the drawings will be omitted to indicate that they are elements provided for any color, and the description will be made comprehensively.

  The image forming unit S includes a drum-type electrophotographic photosensitive member, that is, a photosensitive drum 1 as an image bearing member that carries toner. The photosensitive drum 1 is rotationally driven in the direction of arrow R1 (clockwise) in the drawing. Around the photosensitive drum 1, a charging roller 2 as a contact charging member as a charging unit and a laser beam scanner 3 as an exposure device as an image information writing unit are arranged. Further, a developing device 4 as a developing means and a cleaning device 9 as a cleaning means are arranged. Further, an intermediate transfer belt 6 that is an intermediate transfer member is disposed so as to be in contact with the photosensitive drums 1 of all the image forming units S. The primary transfer roller 5 is sandwiched between the photosensitive drum 1 and the intermediate transfer belt 6. Has been placed.

  Next, the image forming operation in the image forming sequence will be described taking full color image forming as an example.

  First, the surface of the photosensitive drum 1 is uniformly charged to a predetermined potential having a predetermined polarity (negative polarity in this embodiment) by the charging roller 2. The photosensitive drum 1 rotates at a peripheral speed (surface movement speed) of 210 mm / sec in the arrow R1 direction in the figure. The peripheral speed of the photosensitive drum 1 corresponds to the process speed of the image forming apparatus 100.

  The charged surface of the photosensitive drum 1 is scanned and exposed by a laser beam scanner 3 with a laser beam L modulated by an image signal based on image information transmitted from a computer (not shown) or an image reading device. Since the charged charge on the photosensitive drum 1 is canceled at the portion irradiated with the laser beam L, an electrostatic image (latent image) is formed on the photosensitive drum 1.

  The electrostatic image formed on the photosensitive drum 1 is supplied with a developer toner T by the developing device 4 and developed as a toner image. In this embodiment, the developing device 4 develops the electrostatic image on the photosensitive drum 1 by a reversal development method. That is, the toner T charged to the same polarity (negative polarity in this embodiment) as the charged polarity of the photosensitive drum 1 is attached to the image portion (bright portion) where the charge is attenuated by exposure on the surface of the charged photosensitive drum 1. As a result, the electrostatic image on the photosensitive drum 1 is developed into a toner image.

  The toner images of the respective colors formed on the respective photosensitive drums 1 are transferred onto the intermediate transfer belt 6 at the primary transfer portion Nt1 where the primary transfer roller 5 and the photosensitive drum 1 face each other with the intermediate transfer belt 6 interposed therebetween. Are sequentially superimposed and transferred (primary transfer). At this time, a primary transfer voltage having a polarity opposite to the normal charging polarity of the toner T is applied to the primary transfer roller 5.

  The intermediate transfer belt 6 is rotationally driven by a driving roller 61, and the toner images superimposed on four colors on the intermediate transfer belt 6 are electrostatically transferred to a transfer material (recording medium) P such as paper by the secondary transfer member 7. Are collectively transferred.

  The transfer material P onto which the toner image has been transferred is separated from the intermediate transfer belt 6 and conveyed to a fixing device (heat roller fixing device) 8 as fixing means. The unfixed toner image on the transfer material P is fixed to the transfer material P by being heated and pressed by the fixing device 8. Then, the transfer material P on which the toner image is fixed is conveyed and discharged to an external discharge tray (not shown).

  Further, the toner remaining on the surface of the photosensitive drum 1 without being transferred to the intermediate transfer belt 6 after the primary transfer step (primary transfer residual toner) is removed from the surface of the photosensitive drum 1 by the cleaning device 9 and collected. .

  The schematic cross-sectional configuration of the cleaning device 9 is as shown in FIG. The cleaning blade 91b is in contact with the surface of the photosensitive drum 1 with a predetermined intrusion amount in a counter direction with respect to the traveling direction of the photosensitive drum 1. A blade nip portion N is formed in the vicinity of the contact position between the photosensitive drum 1 and the cleaning blade 91b. The scraped toner T is transported by a waste toner transport screw 92 to a waste toner box (not shown). The photosensitive drum 1 from which the primary transfer residual toner has been removed is repeatedly used for image formation.

  Further, the toner (secondary transfer residual toner) which is not transferred to the transfer material P after the secondary transfer process and remains on the surface of the intermediate transfer belt 6 is transferred to the surface of the intermediate transfer belt 6 by the intermediate transfer belt cleaner 10 (FIG. 1). Removed from and recovered. Similar to the cleaning device 9 for the photosensitive drum 1, the intermediate transfer belt cleaner 10 scrapes off the toner on the intermediate transfer belt 6 using a cleaning blade.

  Next, main components of the image forming apparatus 100 will be described.

(Developer)
In this embodiment, a two-component developing device 4 is used. 3A to 3C show the developer in the developing device 4. As shown in FIG. 3A, the toner T is composed of a toner base Tm and an external additive Ta. Further, as shown in FIG. 3B, the toner T and the carrier Tc are mixed well to form a developer Td. As shown in FIG. 3C, the developer Td is coated on a rotating sleeve 41 containing a fixed magnet 42. The developer Td on the rotating sleeve 41 forms a magnetic spike and contacts the photosensitive drum 1 while rotating. As shown in FIG. 3C, by applying an appropriate bias to the sleeve 41, the toner T leaves the carrier Tc and flies to the photosensitive drum 1 side and adheres to the image portion. The bias applied during development is obtained by superimposing an AC bias (rectangular bias, blank pulse bias, etc.) on the DC bias, and the frequency of the AC bias was 2 kHz.

(Cleaning device)
In the cleaning device 9 of the present embodiment, conductive blade cleaning means 91 in which a blade support metal plate 91a and a cleaning blade 91b are integrally formed as shown in FIG. 2A is used. A high voltage power supply 91V for applying a voltage to the blade support sheet metal 91a is provided, and an electric field can be applied to the blade nip N by applying a voltage to the blade support sheet metal part 91a. As a material of the cleaning blade 91b, for example, a material imparted with conductivity by kneading carbon black or an ionic conductive agent with polyurethane rubber may be used. In this embodiment, the cleaning blade 91b has an electrical resistance of 1 × 10 ⁸ Ωcm and a hardness of 75 degrees JIS-A hardness defined by JIS K 6253. The blade cleaning means 91 is in contact with the photosensitive drum 1 at a pressure of 35 g / cm. Further, as shown in FIG. 2B, the angle θ between the cleaning blade side face 91b-1 and the drum tangent line 1N at the cleaning blade contact point 91N is set to 27 °. The pressure of the blade cleaning unit 91 was measured by using a dedicated measuring device that reproduced the positional relationship between the photosensitive drum 1 and the blade cleaning unit 91 and enabled load measurement by a load cell. At the time of measurement, the bias is not applied to the blade cleaning unit 91 while the photosensitive drum 1 is stationary.

(Lubricity imparting sequence)
In this embodiment, the lubricity imparting sequence for the blade nip portion N of the cleaning blade 91b according to the present invention is executed after a normal image forming sequence as shown in FIG.

  The lubricity imparting sequence in this embodiment is mainly formed by supplying a belt-like toner image from the developing device 4 and applying a cleaning bias in the cleaning device 9.

  FIG. 4B shows the bias application timing to the blade cleaning means 91 and other members. After the completion of the image forming sequence, the charging bias applied to the charging roller 2 is cut off, and then a bias is applied to the developing device 4 for a certain period of time during the lubrication imparting sequence, so that a belt-like toner image is formed on the photosensitive drum 1. . When the belt-like toner image passes through the primary transfer portion Nt1, the transfer bias of the primary transfer portion Nt1 is a bias at the time of image formation so that most of the toner image is sent to the cleaning device 9 without being transferred. Is significantly lower than.

  Immediately before the belt-like toner image reaches the cleaning device 9, -500V is applied to the blade support sheet metal 91a. After the trailing edge of the belt-like toner image reaches the blade nip portion N, it rotates for a while and then the bias applied to the blade cleaning unit 91 is cut off to 0V. Even after the belt-like toner image passes through the blade nip N, the toner base Tm and the external additive Ta once scraped by the cleaning blade 91b stay in the vicinity of the blade nip N for a certain period of time. For this reason, the bias is preferably turned off after the bias is continuously applied to the blade cleaning means 91 for an appropriate time. In this embodiment, after the belt-like toner image reaches the blade nip portion N, the bias is continuously applied to the blade cleaning unit 91 for the time that the photosensitive drum 1 rotates twice. In the figure, α corresponds to the time from when the belt-like toner image is formed by the developing device 4 until it reaches the cleaning device 9, and β in the drawing corresponds to the time for which the photosensitive drum 1 rotates twice.

  It is desirable that the bias applied to the blade cleaning unit 91 is set to a condition that does not cause a discharge between the cleaning blade 91b and the surface of the photosensitive drum 1. When the discharge occurs, the charging polarity of the toner base Tm and the external additive Ta is reversed and the surface of the photosensitive drum 1 is damaged. The presence or absence of discharge may be determined by measuring the current flowing through the cleaning blade 91b or by measuring the potential on the surface of the photosensitive drum 1.

  In this embodiment, the toner is supplied by the belt-like toner image after the image formation sequence. However, such a belt-like toner image supply sequence may be provided before or during the image formation sequence. Further, when image formation is performed over a large number of sheets, the image formation may be interrupted once in the middle, and a belt-like toner image supply sequence may be provided. That is, the lubricity imparting sequence including the belt-shaped toner image supply sequence is executed during the above-described so-called non-image formation.

  The belt-shaped toner image forming method is not limited to the above method. For example, after charging the photosensitive drum 1 with the charging roller 2, the belt-shaped toner image is exposed for a desired length with the laser beam scanner 3. You may form by drawing an electrostatic latent image. However, in this case, the bias applied to the blade cleaning unit 91 is adjusted so that the potential difference from the surface of the photosensitive drum 1 becomes −500 V, or exposure is performed using an LED lamp or the like upstream of the cleaning device 9 to perform photosensitivity. Means such as neutralizing the surface of the drum 1 are required.

(toner)
As shown in FIG. 3A, the toner T used in the present invention has a toner base Tm and an external additive Ta. A plurality of types of external additives Ta may be included, but at least one type has a charging polarity opposite to that of the toner base Tm.

(Toner base)
The toner particles used in the present invention may be produced using any method such as a pulverization method and a polymerization method.

  The charging polarity of the toner base Tm is determined by the characteristics of the polyester or styrene-acrylic resin as the main component of the toner base Tm and the charge control agent contained in the toner base Tm.

  Examples of the charge control agent for controlling the toner base Tm to be negatively charged include organometallic compounds and chelate compounds. The toner base Tm can contain the charge control agent alone or in combination of two or more kinds. You can also.

  In this example, a toner base Tm having an average particle diameter of 6 μm prepared by a pulverization method was used.

(External additive)
Toner particles in this embodiment are externally added as an external additive Ta for improving fluidity and transferability and for stably lubricating the cleaning blade 91b with respect to the photosensitive drum 1.

  Examples of the inorganic fine powder externally added to the toner particles include silica fine powder, titanium oxide fine powder, alumina fine powder, and double oxide fine powders thereof. The particle size of these inorganic fine powders is preferably 120 nm or less at most. It is preferable that the surface of these inorganic fine powders is subjected to a hydrophobization treatment and maintains stable charging characteristics against changes in temperature and humidity.

  As treatment agents for the hydrophobic treatment of inorganic fine powder, unmodified silicone varnish, various modified silicone varnishes, unmodified silicone oil, various modified silicone oils, silane compounds, silane coupling agents, other organosilicon compounds, organotitanium Compounds. These treatment agents may be used alone or in combination.

  In this example, positively charged silica fine particles having been subjected to such a hydrophobic treatment were used as the external additive Ta. The shape of the silica fine particles was substantially spherical, and the particle size was about 110 nm. The amount of silica fine particles added to the toner base Tm was 2 parts. In addition, titanium oxide fine powder, ultrafine silica particles with a particle diameter of 20 nm, and the like were also externally added to impart fluidity.

  In this embodiment, the inorganic fine powder is used as the external additive Ta. However, the present invention is not limited to this, and an organic fine powder may be used.

(Measurement of charging polarity)
The charging polarity of each particle of the toner base Tm and the external additive Ta was measured by a blow-off method using the carrier used in the developing device of this example.

  After 9.0 g of a two-component developing carrier having an average particle size of 30 μm and 1.0 g of toner base Tm were well mixed in a plastic bottle, the carrier Tc and the toner base Tm were separated by a blow-off method to determine the charging polarity. In the case of the external additive Ta, since the particle size of the external additive Ta is very small with respect to the carrier Tc, the mixing ratio of the external additive Ta is decreased in order to reduce the proportion of the external additive Ta that cannot contact the carrier Tc. There is a need to. In this example, the mixture was mixed at a ratio of 9.9 g of carrier Tc and 0.1 g of external additive Ta, and measurement was performed in the same manner. It was confirmed by the above method that the toner base Tm used in this example has a negative charge polarity, while the hydrophobic silica as the external additive Ta has a positive charge polarity.

(Evaluation method)
The cleaning performance of the cleaning device 9 of this example was evaluated as follows.

  Using the image forming apparatus 100 of the present embodiment, an image having an image printing rate of 3% was output at intervals of 50 sheets, and the torque of the drive motor of the photosensitive drum 1 was measured while evaluating the output image. When a large amount of toner passes through, the charging roller 2 becomes more dirty as the number of durable sheets that have output images increases, and image defects such as fogging and streaks due to charging defects are observed. Whether or not the image defect is due to a charging defect was determined by observing the degree of contamination of the charging roller 2 and replacing the charging roller 2 with a new one and outputting the image again. Further, the torque measurement of the drive motor of the photosensitive drum 1 is performed for the purpose of evaluating the lubricity of the cleaning blade 91b with respect to the photosensitive drum 1, and the risk of turning the blade is lower as the torque is lower and more stable. The evaluation may be performed using one station S. In this embodiment, the evaluation was performed using only the black station SK. The transfer efficiency from the photosensitive drum 1 to the intermediate transfer member 6 always exceeds 95% during the evaluation time, and it has been confirmed that there is no problem in the evaluation of the present invention.

  The evaluation was performed in a high temperature and high humidity environment at a temperature of 32 degrees and a humidity of 85%.

(Evaluation results)
In this example, good images were continuously output up to 50,000 (50k). The torque of the drive motor of the photosensitive drum 1 was slightly varied but was within an allowable range.

  As described above, in this embodiment, stable image output can be performed over a long period of time with little risk of toner slipping and turning.

  The mechanism of this embodiment will be described below. FIG. 5 shows a state in the vicinity of the blade nip portion N of the cleaning blade 91b in this embodiment.

  A toner base Tm having a negative charging polarity and an external additive Ta having a positive charging polarity are supplied to the blade nip N as a belt-like toner image by a toner supply unit such as the developing device 4. At this time, a bias having the same polarity as the toner base Tm, that is, a negative voltage is applied to the cleaning blade 91b. Then, the external additive Ta receives a force (arrow B in the figure) in the direction of entering the blade nip portion N due to the electric field in the vicinity of the blade nip portion N of the cleaning blade 91b. The coefficient of friction between the cleaning blade 91b and the photosensitive drum 1 is lowered to prevent turning. The external additive Ta interposed in the blade nip N once is held there for a while by the pressure of the cleaning blade 91b. On the other hand, the toner base Tm receives a force in the direction away from the blade nip portion N (arrow A in the figure) due to the electric field, so that the toner slippage is hardly generated. In this way, in this embodiment, the supply of the belt-like toner image for preventing the blade curling can be effectively performed without risk of toner slipping, and both the problems of curling and toner slipping are solved. It is possible to do.

  In this embodiment, a bias is applied to the blade cleaning unit 91 only during image printing, that is, only when the toner T supplied during non-image formation reaches the blade nip N. A sequence in which no bias is applied to the blade cleaning unit 91 is provided during image printing other than that.

  Even if a bias is applied to the blade cleaning unit 91 during image printing, the effect of the present invention is exhibited. However, if an electric field is continuously applied to the external additive Ta interposed in the blade nip N, the cleaning blade 91b Charge injection may occur in the external additive Ta, and the retention of the external additive Ta in the blade nip N may be reduced.

  For this reason, by suppressing the bias application time to the blade cleaning means 91 to a minimum, the charge injection to the external additive Ta interposed in the blade nip portion N can be suppressed, and the effect of the present invention can be prevented from being lowered. .

(Cleaning blade bias value in lubrication sequence)
FIG. 6 shows the retention amount of the external additive Ta in the blade nip portion N with respect to the bias value applied to the blade cleaning means 91. The amount of retention of the external additive is that the external additive Ta retained in the blade nip portion N is adhered to the photosensitive drum 1 when the blade cleaning unit 91 is removed from the photosensitive drum 1. As observed, the amount of the external additive Ta is shown. The observation is performed after 1000 sheets are passed.

  As shown in FIG. 6, as the applied bias value increases, the external additive retention increases, and at -500 V, the external additive retention is substantially saturated.

  As described above, it has been confirmed that the torque of the drive motor of the photosensitive drum 1 is low and stable as the external additive retention amount increases.

Example 2
Since the overall configuration of the image forming apparatus 100 of the present embodiment is the same as that of the first embodiment, detailed description thereof is omitted.

  In the present embodiment, the frequency of the AC bias applied to the developing sleeve 41 when the belt-like toner image is formed on the photosensitive drum 1 from the developing device 4 after the end of the image forming sequence is increased to 10 kHz. Different from 1.

  The evaluation results of this example are shown below.

(Evaluation results)
When the same evaluation as in Example 1 was performed, no image defect due to charging failure was observed even when 100,000 images were output. The torque of the drive motor of the photosensitive drum 1 was low and stable throughout the evaluation time.

  Next, the mechanism of the effect of the present embodiment will be described below.

  Since the external additive Ta strongly adhering to the toner base Tm has a small absolute charge amount, it moves in the same manner as the toner base Tm under an electric field in the vicinity of the blade nip N. On the contrary, the external additive Ta separated from the toner base Tm moves in accordance with the electric field and easily intervenes in the blade nip portion N. That is, when the toner base Tm and the external additive Ta are separated and reach the blade nip portion N, the effect as shown in FIG. 5 can be made more conspicuous.

  When an electric field is applied to the toner T, the charging polarity of the toner base Tm and the external additive Ta are different, so that the electric field receives a force in a direction in which the toner T is separated from each other. By applying a high-frequency electric field, the number of times of receiving a force in the direction of separation increases, so that separation is promoted. In addition, there is an effect that separation of the toner T is promoted by a strong amplitude in a high frequency electric field.

  In this embodiment, the toner base Tm and the external additive Ta having different charging polarities are separated by applying an AC bias having a high frequency at the time of supplying the toner, and the effect of the first embodiment can be made more conspicuous.

(Frequency of belt-like toner supply bias in lubricity imparting sequence)
FIG. 7 shows the frequency of the developing bias applied to the developing device 4 and the retention amount of the external additive Ta in the blade nip N. The bias applied to the cleaning blade 91 is fixed at −500V. The retention amount of the external additive Ta is the same as in the first embodiment, and the external additive Ta adhered to the photosensitive drum 1 when the blade cleaning unit 91 was removed from the photosensitive drum 1 after passing 1000 sheets of durable paper. Shows the amount.

  As shown in FIG. 7, it can be seen that the amount of the external additive retained in the blade nip N increased as a result of the increase in the amount of the external additive Ta released from the toner base Tm with the increase in the frequency at the time of toner supply. . In this embodiment, it has been confirmed that a great effect can be obtained by setting the frequency of the developing bias to 10 kHz or more.

(Effect of Example 1 and Example 2)
The effects of the present invention will be verified by comparing the above-described Examples 1 and 2 with the following comparative examples.

Comparative Example 1
In this comparative example, a non-conductive blade was used as the cleaning blade 91b of the blade cleaning means 91. That is, no bias was applied to the non-conductive blade. Other configurations of the entire apparatus, the characteristics of the blade cleaning means 91, the belt-like toner supply sequence, the toner T, the external additive Ta, and the like are the same as those in the first embodiment.

(Evaluation results)
When the same evaluation as in Example 1 was performed, when 19,000 images were output, image defects due to charging defects began to be seen. It is considered that the charging roller 2 after use is dirty, and a minute amount of toner slipping often occurs when the belt-like toner image is supplied. The torque of the drive motor of the photosensitive drum 1 was within an allowable range although some fluctuation was observed.

  In this comparative example, a large amount of toner T rushes into the blade nip N when supplying the belt-like toner image. For this reason, the toner T is present in the blade nip portion N, and although there is an effect of reducing the friction coefficient between the photosensitive drum 1 and the cleaning blade 91b, the toner slip easily occurs.

Comparative Example 2
In this comparative example, a positive bias (+500 V) opposite to the charging polarity of the toner base Tm is applied to the conductive cleaning blade 91b. Other configurations are the same as those of the first embodiment.
(Evaluation results)
When the same evaluation as in Example 1 was performed, streaky image defects were often seen in the output image when 3,000 images were output. The state of the blade nip portion N in this comparative example is shown in FIG. By applying a bias having a polarity opposite to that of the toner T to the cleaning blade 91b, the toner T receives a force (arrow A in the figure) in a direction in which the toner T is attracted to the blade nip portion N, and is interposed in the blade nip portion N. Although the lubricating properties of the cleaning blade 91b are good, it is considered that many toner slips occurred.

Comparative Example 3
In this comparative example, a toner in which the toner base Tm and the external additive Ta are both negatively charged is used. Other configurations are the same as those of the first embodiment.

(Evaluation results)
When the same evaluation as in Example 1 was performed, turning-up occurred when 6,000 images were output. A state of the blade nip portion N in this comparative example is shown in FIG. In the vicinity of the blade nip N, both the toner T and the external additive Ta receive a force in the direction away from the blade nip N (arrows A and B in the figure). It is considered that the intervening particles are insufficient, the friction coefficient between the cleaning blade 91b and the photosensitive drum 1 is increased, and turning is generated.

  Next, a cleaning device according to another aspect of the present invention will be described.

Example 3
This embodiment shown in FIG. 10 includes a fur brush 93 and a scraper 94 in the configuration of the cleaning device 9 and supplies toner for imparting lubricity from the fur brush 93 and does not form a belt-like toner image. This is different from the first and second embodiments.

  In this embodiment, as shown in FIG. 10, a conductive fur brush 93 is disposed inside the cleaning container 95 at a position upstream of the blade cleaning means 91 in the rotational direction of the photosensitive drum 1. 1 in contact with 1 while rotating in the counter direction. Most of the toner T scraped off by the blade cleaning means 91 is collected by the fur brush 93. If the toner T enters the fur brush 93 too much, the fur brush 93 is clogged and its function is deteriorated. Therefore, the scraper 94 is brought into contact with the fur brush 93 and the excessive toner T is transferred to the waste toner conveying screw 92. It is supposed to be ejected.

  Here, a power supply 93V for applying a voltage to the fur brush 93 is connected to the fur brush 93. By applying a voltage to the fur brush 93 by the power supply 93V, the collected toner T can be attached to the photosensitive drum 1 again. As a result, the fur brush 93 functions as a toner supply member that supplies toner to the image carrier, that is, to the photosensitive drum 1. Here, the overall configuration of the other devices, the blade cleaning means 91, the toner T, and the external additive Ta are the same as those in the first embodiment. However, as described above, the toner T collected by the fur brush 93 in the cleaning container can be supplied as a lubricant, so that a special belt-like toner image is supplied from the developing device 4 after the image forming sequence as in the other embodiments. I don't have to

The material of the fur brush 93 is a material in which conductive carbon black is dispersed in a nylon resin, the yarn resistance is 10 ¹⁰ Ωcm, and the fiber density is 240 KF / inch ² .

  In this embodiment, the fur brush 93 is used as the toner supply means in the cleaning container, but other members such as conductive rollers and sponges may be used as the toner supply means.

(Lubricity imparting sequence)
While the photosensitive drum 1 is rotating, the fur brush 93 is always rotating in the counter direction with respect to the photosensitive drum 1. At the time of non-image formation, for example, after the image formation sequence is completed, a 2 kHz AC bias is applied to the fur brush 93 by superimposing a DC bias of −300 V on the fur brush 93 by the power supply 93V. By applying a bias to the fur brush 93, toner is supplied to the blade nip portion N to impart lubricity. At the same time, -500V is applied to the blade cleaning means 91 by the power supply 91V. By applying a blade bias to the blade cleaning means 91, the external additive Ta stays in the blade nip portion N as in the above embodiment, and the lubricity is maintained.

(Evaluation results)
When the same evaluation as in Example 1 was performed, no image failure due to charging failure was observed until 80,000 images were output. The torque of the drive motor of the photosensitive drum 1 was low and stable throughout the evaluation time.

(Effect of Example 3)
Next, Example 3 is compared with the following comparative examples to verify the effect of the present invention.

Comparative Example 4
For comparison with Example 3, the same evaluation as in Example 3 was performed using a non-conductive blade as the cleaning blade 91b. That is, no bias was applied to the non-conductive blade. The bias conditions applied to the fur brush 93 and the fur brush 93 are the same.

(Evaluation results)
When the same evaluation as in Example 3 was performed, an image failure due to a charging failure was observed when 20,000 images were output. When toner T is supplied from the fur brush 93 to the blade nip portion N, it seems that many toner slips occurred. The torque of the drive motor of the photosensitive drum 1 was within an allowable range although some fluctuation was observed.

  In this comparative example, when the toner T is supplied from the fur brush 93, a large amount of toner T rushes into the blade nip portion N, so that the toner T is interposed in the blade nip portion N, and the photosensitive drum 1 and the blade cleaning means. Although there is an effect of lowering the friction coefficient between 91, toner slip is likely to occur.

  Tables 1 and 2 collectively show the characteristics of the configurations and the evaluation results of the above examples and comparative examples. Table 1 summarizes the evaluation results of Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3, and Table 2 summarizes the evaluation results of Example 3 and Comparative Example 4.

  As described above, as the evaluation item, the image evaluation in which the number of good images obtained in the image output test and the result of examining the torque of the drive motor of the photosensitive drum 1 were shown as blade friction force.

  Regarding the image evaluation, 40k sheets were used as the evaluation standard, and less than that was evaluated as NG. Further, the blade friction force was turned over by the cleaning blade 91b only in Comparative Example 3 and was judged as NG only for this, and other than that, although there was a difference, there was no problem in practical use and it was made OK.

  From the above, it can be seen that in the embodiment to which the present invention is applied, the toner is effectively prevented without causing toner slip-through. As a result, the contamination of the charging roller 2 is reduced, and the number of sheets that can stably output a good image is greatly increased as compared with the comparative example.

  The present invention can be applied not only to a cleaning device using a blade cleaning method for the photosensitive drum 1 but also to a cleaning device using a blade cleaning method for the intermediate transfer body 6. In this case, the intermediate transfer member 6 serves as a second image carrier, and is transferred from the second image carrier to a recording medium (transfer material), and the transfer material toner is removed by a cleaning device.

  In each of the above embodiments, the toner base Tm is a negative polarity, the external additive Ta is a positive polarity, and the bias applied to the blade cleaning unit 91 is a negative polarity. Is demonstrated.

  On the other hand, the present invention can also be applied to an image forming apparatus that transfers a toner image on the photosensitive drum 1 directly to a recording medium (transfer material). Since such a direct transfer type image forming apparatus is well known to those skilled in the art, further detailed description thereof is omitted.

1 Photosensitive drum (image carrier)
4. Developing device (toner supply means)
6 Intermediate transfer member (image carrier)
DESCRIPTION OF SYMBOLS 9 Cleaning apparatus 91 Blade cleaning means 91a Blade support sheet metal 91b Cleaning blade 93 Fur brush (toner supply member)
100 Image forming apparatus T Toner Ta External additive Td Developer Tm Toner base

Claims (6)

An image forming sequence for image formation in which a transfer residual toner on the image carrier after the toner image formed on the image carrier according to image information is transferred to a recording medium is removed by a cleaning device;
Lubricity imparting sequence for supplying toner to the cleaning device during non-image formation except during image formation by the image formation sequence;
In an image forming apparatus capable of executing
A toner supply unit that supplies toner including a toner base and an external additive having a charge polarity opposite to that of the toner base during the lubrication imparting sequence;
The cleaning device includes a conductive cleaning blade and a bias applying unit that applies a bias to the cleaning blade,
The bias application unit is configured to apply the cleaning blade to the cleaning blade when the toner supplied by the toner supply unit reaches the vicinity of the contact position between the image carrier and the cleaning blade in the lubrication imparting sequence. An image forming apparatus, wherein a bias having the same polarity as the charging polarity of the toner base is applied. Developing means for forming a toner image corresponding to image information on the image carrier during the image forming sequence;
The toner supply means forms a belt-like toner image on the image carrier by the developing means during the lubricity imparting sequence,
The image forming apparatus according to claim 1, wherein the image forming apparatus is supplied to the cleaning device. A bias applying means for applying an AC bias to the developing means;
Supplying the toner from the developing means to the image carrier during the lubrication imparting sequence;
The frequency of the AC bias applied to the developing means during the lubricity imparting sequence is
The image forming apparatus according to claim 1, wherein the frequency is higher than a frequency of an AC bias applied to the developing unit during the image forming sequence. A cleaning container for collecting toner scraped off from the image carrier by the cleaning blade during the image forming sequence;
The image forming apparatus according to claim 1, wherein the toner supply unit includes a conductive toner supply member disposed in the cleaning container and a unit that applies a bias to the toner supply member.   The image forming apparatus according to claim 4, wherein a bias having the same polarity as the charging polarity of the toner base is applied to the cleaning blade at the same timing as the bias is applied to the toner supply member.   The image forming apparatus according to claim 1, wherein the image carrier is a photosensitive drum or an intermediate transfer member.

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