JP2006091554A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing the occurrence of quality defects or the like due to defective cleaning in other members without sticking toner to a secondary transfer member and causing dirt on the rear face of a sheet in an intermediate transfer type image forming apparatus for secondarily transferring a toner image formed on an intermediate transfer belt to a sheet by a secondary transfer member. <P>SOLUTION: The image forming apparatus is provided with at least an image carrier, a latent image forming means, a developing means, a primary transfer member, and a secondary transfer member, wherein a brush is used as a cleaning member for a toner removing means, and when it is defined that the tip force of the brush to the intermediate transfer body is Fb(IBT) and the tip force of the brush to the secondary transfer member is Fb(BT), the Fb(IBT) and the Fb(BT) satisfy the following inequality (1) of Fb(IBT)>Fb(BT). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus applied to a copying machine, a facsimile machine, a printer, and the like. More specifically, the toner image formed on an image carrier is transferred to an intermediate transfer belt, and the toner image on the intermediate transfer belt is transferred to a recording medium. The present invention relates to an image forming apparatus to be transferred onto the upper side.

  In an image forming apparatus using electrophotography and a color image forming apparatus therein, the toner image on the image carrier is not directly transferred to the recording medium, but is temporarily transferred to the intermediate transfer belt (intermediate transfer member) once. After that, an intermediate transfer method is known in which secondary transfer to a recording medium is performed.

  In this intermediate transfer method, it is necessary to clean the toner remaining on the toner carrying surface of the intermediate transfer belt (so-called transfer residual toner) after the secondary transfer.

  In the intermediate transfer method, for example, a recording medium is electrostatically adsorbed on the surface of a transfer conveyance belt (secondary transfer member) and conveyed to a secondary transfer portion of the intermediate transfer belt to transfer a toner image to the recording medium. In this case, it is also necessary to clean the free toner adhering to the surface of the transfer / conveying belt due to the reverse bias applied at the secondary transfer portion.

  However, as the image quality is improved, the diameter of the toner has become smaller and spheroidized. With such toner, cleaning becomes difficult, and a cleaner (hereinafter referred to as “secondary transfer cleaner”) provided on the transfer conveyance belt is sometimes used. Occasionally, the back surface of the paper (recording medium) may be smeared due to the occurrence of slip-through toner. In color machines, there are registration bands, density control, and toner band creation to ensure the reliability of the cleaning process in the intermediate transfer belt. From this point as well, the cleaning performance of the secondary transfer cleaner should be ensured. Was an important issue.

On the other hand, in a cleaner (hereinafter also referred to as “primary transfer cleaner”) provided on an intermediate transfer belt that needs to clean an image patch created in the inter-image portion, more toner than the secondary transfer cleaner. A certain amount of cleaning performance is required.
Further, when a brush is used as a cleaning member for the primary transfer cleaner and the secondary transfer cleaner, the number of power supplies increases, so that it is required from the viewpoint of cost reduction that the power supplies can be used in common.

In contrast to this, for example, by applying a bias having both polarities (+) and (-) to the cleaning brush that contacts the intermediate transfer belt, residual toner on the intermediate transfer belt after the secondary transfer can be removed. An image forming apparatus having a cleaning device has been proposed (see, for example, Patent Document 1). However, in this image forming apparatus, since the transfer conveyance belt is not provided, toner cleaning on the transfer conveyance belt is considered. The optimized overall cleaning system has not yet been optimized.
JP 2003-66735 A

The object of the present invention is to solve the above-mentioned problems of the prior art.
That is, according to the present invention, in the intermediate transfer type image forming apparatus in which the toner image on the intermediate transfer member is secondarily transferred to the paper by the secondary transfer member, the toner adheres to the secondary transfer member and the back surface of the paper is stained. In addition, an object of the present invention is to provide an image forming apparatus in which image quality defects or the like due to poor cleaning do not occur in other members.

The above-mentioned subject is achieved by the following present invention. That is, the present invention
<1> At least an image carrier on which a latent image is formed on the surface, latent image forming means for forming a latent image on the image carrier, and developing the latent image formed on the image carrier with toner Thus, a developing means for forming a toner image on the image carrier, a primary transfer member for transferring the toner image formed on the image carrier to an intermediate transfer member, and the intermediate transfer member are formed. And a secondary transfer member that transfers the toner image onto a recording medium.
A brush is provided as a cleaning member for toner removing means provided in the vicinity of the intermediate transfer member and the secondary transfer member, and the tip force of the brush provided for the intermediate transfer member is expressed as Fb (IBT), secondary. An image forming apparatus characterized in that Fb (IBT) and Fb (BT) have the relationship of the following formula (1), where Fb (BT) is the tip force of the brush provided to the transfer member. is there.
Fb (IBT)> Fb (BT) Formula (1)

<2> When a blade is provided as a cleaning member of a cleaning unit provided in the vicinity of the image carrier, and the frictional force between the blade and the image carrier is F (PC), F (PC) and the above The image forming apparatus according to <1>, wherein Fb (IBT) has a relationship represented by the following formula (2).
F (PC)> Fb (IBT) (2)

<3> When the brush fiber diameter of the brush provided for the intermediate transfer member is D (IBT) and the brush fiber diameter of the brush provided for the secondary transfer member is D (BT), D The image forming apparatus according to <1> or <2>, wherein (IBT) and D (BT) have a relationship of the following formula (3).
D (IBT)> D (BT) (3)

<4> When the brush peripheral speed of the brush provided for the intermediate transfer member is Vb (IBT) and the brush peripheral speed of the brush provided for the secondary transfer member is Vb (BT), Vb The image forming apparatus according to any one of <1> to <3>, wherein (IBT) and Vb (BT) have a relationship of the following formula (4):
Vb (IBT)> Vb (BT) (4)

<5> When the brush resistance of the brush provided for the intermediate transfer member is R (IBT) and the brush resistance of the brush provided for the secondary transfer member is R (BT), R (IBT) ) And R (BT) have the relationship of the following formula (5), the image forming apparatus according to any one of <1> to <4>.
R (IBT)> R (BT) (5)

<6> The image forming apparatus according to any one of <1> to <5>, wherein the toner has a volume average particle diameter in a range of 2 to 9 μm.

<7> The image forming apparatus according to any one of <1> to <6>, wherein the intermediate transfer member is an intermediate transfer belt having an elastic layer.

<8> The image forming apparatus according to any one of <1> to <7>, wherein the secondary transfer member is a transfer conveyance belt having an elastic layer.

  According to the present invention, in an intermediate transfer type image forming apparatus in which a toner image on an intermediate transfer member is secondarily transferred to a sheet by a secondary transfer member, toner adhesion to the secondary transfer member and backside contamination of the sheet are generated. In addition, it is possible to provide an image forming apparatus in which image quality defects or the like due to poor cleaning do not occur in other members.

Hereinafter, the present invention will be described in detail.
The image forming apparatus according to the present invention includes at least an image carrier on which a latent image is formed, a latent image forming unit that forms a latent image on the image carrier, and a latent image formed on the image carrier. Developing means for developing a toner image on the image carrier by developing the image with toner, a primary transfer member for transferring the toner image formed on the image carrier to an intermediate transfer member, and the intermediate transfer And a secondary transfer member that transfers a toner image formed on the body onto a recording medium. Cleaning of toner removing means provided in the vicinity of the intermediate transfer body and the secondary transfer member A brush is provided as a member, and Fb (IBT) is the tip force of the brush provided to the intermediate transfer member, and Fb (BT) is the tip force of the brush provided to the secondary transfer member. (IBT) and Fb (BT) down Characterized in that the relationship of Equation (1).
Fb (IBT)> Fb (BT) Formula (1)

FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus of the present invention. This image recording apparatus is used in electrophotographic copying machines, laser printers, and the like.
As shown in FIG. 1, the image recording apparatus 10 includes a photosensitive drum 12 as an image carrier having a photosensitive layer on the surface and having a drum shape. The photoconductor drum 12 is a so-called function-separated type photoconductor in which a charge generation layer and a charge transport layer are sequentially laminated on a metal support (drum) such as aluminum, and the outer diameter of the photoconductor drum 12 is 84 mm in diameter. And rotate in the clockwise direction (arrow A direction) in FIG. On the circumference surrounding the photosensitive drum 12, a charger 14, an exposure device 16, a developing device 18, a transfer belt 20, and a cleaning device 34 are sequentially arranged in the clockwise direction (arrow A direction) in FIG. Has been.

A charger 14 is disposed above the photosensitive drum 12 so as to face the photosensitive drum 12. The charger 14 forms an elastic layer made of SBR (styrene butadiene rubber) containing carbon on a metal core, and ECO (epichlorohydrin rubber) containing an ionic conductive material as a resistance layer on the elastic layer. A film is formed, and a surface layer made of PA (polyamide) containing carbon and SnO ₂ (conductive filler) is further formed thereon. The thickness of each layer is 2.8 mm for the elastic layer, 150 μm for the resistance layer, and 10 μm for the surface layer, and the resistance value of the entire layer including the surface layer is 10 ⁷ to 10 ⁸ Ω. When a DC voltage is applied to the core of the charger 14, the surface 12A of the photosensitive drum 12 is uniformly negatively charged. In this embodiment, the type of charger 14 that contacts the photosensitive drum 12 is used. However, a type of charger that does not contact the photosensitive drum 12 such as a scorotron or a solid discharge device may be used. .

  An exposure device (latent image forming means) 16 is provided on the downstream side of the charger 14. The exposure device 16 includes a light emitting element (LD), and the laser light from the light emitting element (LD) can be repeatedly scanned substantially perpendicularly to the rotation direction of the photosensitive drum 12. When the light emitting element (LD) is turned ON / OFF based on the image signal, an image is written on the surface 12A of the photosensitive drum 12 that is driven to rotate, whereby a latent image is formed on the surface 12A of the photosensitive drum 12. It is supposed to be formed.

  A developing device (developing means) 18 is provided on the downstream side of the exposure device 16. The developing device 18 attaches yellow, magenta, cyan, and black toners to the surface 12A of the photosensitive drum 12 to form toner images of the respective colors. The forming unit 18M, the C image forming unit 18C, and the BK image forming unit 18B are circumferentially arranged along the counterclockwise direction in FIG. The developing device 18 attaches toner to the latent image formed by the exposure device 16, so that a toner image (visible image) is formed on the surface 12 </ b> A of the photosensitive drum 12.

Here, the developer used in the developing device 18 will be described.
Examples of the method for producing the toner used for the developer in the present invention include a kneading and pulverizing method, a suspension polymerization method, an emulsion polymerization method, a dry granulation method in liquid, and the like. In order to obtain a low production cost, suspension polymerization, emulsion polymerization, and dry granulation in liquid are desirable, and toner production by emulsion polymerization is most desirable.

  A method for producing a toner using an emulsion polymerization method is described in JP-A-6-250439. In this method, a resin fine particle dispersion is prepared by emulsion polymerization using a surfactant. On the other hand, a colorant dispersion in which a colorant is dispersed is prepared. A surfactant having the opposite electrical polarity to the agent is added to agglomerate the fine resin particles and colorant until the desired particle size is reached (aggregation step), and then the aggregated particles are stabilized at the desired particle size. Then, the aggregated particles are fused at a temperature equal to or higher than the glass transition point (Tg) of the resin fine particles (fusion process) to produce a toner. The nonionic surfactant is added to ensure dispersion stability of the fine particles when preparing emulsion polymerization or a colorant dispersion.

  Further, between the agglomeration step and the fusion step, a step of forming adhering particles by adding a fine particle dispersion in which fine particles are dispersed to the agglomerated particle dispersion and adhering the fine particles to the agglomerated particles (adhesion) Step) may be provided. In this adhesion step, the fine particle dispersion is added to and mixed with the aggregated particle dispersion prepared in the aggregation step, and the fine particles are adhered to the aggregated particles to form adhered particles. Since it corresponds to newly added particles as seen from the aggregated particles, they may be added fine particles.

  As the additional fine particles, in addition to resin fine particles, release agent fine particles, colorant fine particles and the like may be used singly or in combination. The method of additionally mixing the fine particle dispersion is not particularly limited, and may be performed gradually, for example, or may be performed stepwise by dividing into a plurality of times. In this way, by adding and mixing fine particles (additional fine particles), the generation of fine particles can be suppressed, and the particle size distribution of the resulting toner particles can be sharpened, contributing to higher image quality. It becomes.

  In addition, by providing an adhesion step, a pseudo shell structure can be formed, and the toner surface exposure of internal additives such as colorants and release agents can be reduced, resulting in improved chargeability and life. In addition, it is possible to maintain the particle size distribution during fusion in the fusion process, to suppress fluctuations, and to add a stabilizer such as a surfactant or base or acid to enhance stability during fusion. This is advantageous in that it can be eliminated or the amount of addition can be minimized, and costs can be reduced and quality can be improved. Therefore, when using a release agent, it is preferable to add additional fine particles mainly composed of resin fine particles. Furthermore, if this method is used, the toner shape can be easily controlled by adjusting the temperature, the number of stirring, the pH and the like in the fusing step.

The toner used in the present invention preferably has a volume average particle diameter D _50v in the range of ₂ to 9 μm. A range of ˜5.0 μm is more preferable. When the volume average particle diameter of the toner exceeds 9.0 μm, the ratio of coarse particles increases, and the reproducibility and gradation of fine lines and fine dots of an image obtained through the fixing process are deteriorated. On the other hand, when the volume average particle size of the toner is less than 2.0 μm, the powder fluidity, developability, or transferability of the toner deteriorates, and the cleaning property of the toner remaining on the surface of the image carrier decreases. Various problems occur in other processes due to the deterioration of powder characteristics.

The volume particle size distribution index GSDv of the toner in the present invention is preferably 1.3 or less, and more preferably 1.25 or less. The number particle size distribution index GSDp is preferably 1.4 or less, and more preferably 1.3 or less.
If GSDv is greater than 1.3, the amount of coarse powder in the toner increases and image scattering may occur. When GSDp is larger than 1.4, the amount of fine powder in the toner increases, and toner contamination in the machine due to toner scattering may increase.

The volume average particle diameter, GSDv, and GSDp are determined as follows. First, for example, based on the particle size distribution measured by a measuring instrument such as Coulter Counter TAII (manufactured by Beckman-Coulter), the volume and number are each subtracted from the small particle size side, and the cumulative 16% particle diameter D _16v composed, D _16p, the particle size (and which the volume average particle diameter) D _50v at a cumulative 50%, D _50p, defines the particle diameter at a cumulative 84% D _84v, and D _84p .
The volume particle size distribution index GSDv is calculated as (D _84v / D _16v ) ^1/2 , and the number average particle size distribution index GSDp is calculated as (D _84p / D _16p ) ^1/2 .

Furthermore, the toner shape factor SF1 in the present invention is preferably in the range of 105 to 160. If the shape factor SF1 is smaller than 105, the shape is very close to a sphere, so that it has fluidity like water, and the transportability may deteriorate. When the shape factor SF1 is larger than 160, the fluidity of the toner is lowered, and a strong stress is partially applied, and it is necessary to increase the conveyance force and the stirring force, thereby promoting the deterioration of the developer.
The SF1 is more preferably in the range of 110 to 145.

Here, the shape factor SF1 is obtained by the following equation (6).
SF1 = (ML ² / A) × (π / 4) × 100 (6)
In the above formula (6), ML represents the absolute maximum length of the toner particles, and A represents the projected area of the toner particles.

  The SF1 is quantified mainly by analyzing a microscope image or a scanning electron microscope (SEM) image using an image analyzer, and can be calculated as follows, for example. That is, an optical microscope image of the toner dispersed on the surface of the slide glass is taken into a Luzex image analyzer through a video camera, the maximum length and the projected area of 100 or more toner particles are obtained, calculated by the above formula (6), and the average Obtained by determining the value.

  To the obtained toner particles, inorganic particles and organic particles can be added as a flow aid, cleaning aid, abrasive, etc. to obtain a toner. Examples of inorganic particles include silica, alumina, titania, calcium carbonate, magnesium carbonate, tricalcium phosphate, cerium oxide, and all the particles that are usually used as external additives on the toner surface. Examples of the body include all particles usually used as an external additive on the toner surface, such as vinyl resin, polyester resin, silicone resin, and fluorine resin.

The carrier is a resin-coated carrier having a resin coating layer in which a conductive material such as carbon black is dispersed on the surface of a ferrite core material, and has a volume average particle size of 45 μm.
As the two-component developer in which the toner and the carrier are mixed, for example, a toner concentration (TC: Toner Concentration) of 8% by mass and a toner charge amount in the developer of 20 to 30 μC / g in absolute value is applied. can do. Here, TC is obtained by the following equation.

TC (mass%) = ((mass of toner contained in developer (g)) / (total mass of developer (g)) × 100
If the charge amount of the toner when the toner and the carrier are mixed to form a developer is too high, the toner will not be developed because the adhesion force of the toner to the carrier becomes too high. On the other hand, if the charge amount is too low, the adhesion force of the toner to the carrier is weakened, a toner cloud due to free toner is generated, and the toner adheres to the non-image area that should originally be white at the time of printing and the density increases. (Fogging) occurs and becomes a problem. In order to perform good development by transferring the toner, the charge amount of the toner in the developer is preferably 5 to 50 μC / g in absolute value, more preferably 10 to 40 μC / g, In this embodiment, it was set to 30 μC / g.

  As shown in FIG. 1, an endless belt-shaped intermediate transfer belt (intermediate transfer member) 20 that contacts the photosensitive drum 12 is provided on the downstream side of the developing device 18 using such a developer. As the intermediate transfer belt 20, although not shown, for example, various laminated types in which an elastic layer and a surface layer are provided on a substrate can be preferably used. However, the intermediate transfer belt 20 is not limited thereto. A two-layer structure with the surface layer may be used, or a single-layer structure with only the substrate may be used. Further, the intermediate transfer member is not limited to the belt shape but may be a drum shape.

  Examples of the constituent material of the substrate of the intermediate transfer belt 20 include endless belts made of metal such as nickel and stainless steel, polyester, polyimide, polycarbonate, and the like, and metal pipes such as aluminum and stainless steel, and resin pipes such as polyimide. It may be a drum.

  The constituent material of the elastic layer of the intermediate transfer belt 20 includes ethylene propylene rubber (EPDM), nitrile rubber (NBR), styrene butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), chloroprene rubber (CR). And rubber materials such as acrylic rubber (ACM), silicone rubber and fluororubber; polystyrene, polyolefin, polyvinyl chloride, polyurethane, polyester and polyamide-based thermoplastic elastomer; urethane resin and urea resin. The elastic layer may be composed of a blend material of these constituent materials. The elastic layer may be composed of a blend material of these constituent materials. Furthermore, you may comprise with these foam materials (for example, urethane foam).

The constituent material of the surface layer of the intermediate transfer belt 20 is not particularly limited as long as it can achieve the purpose of improving the residual toner cleaning property by reducing the frictional resistance and the surface roughness.
In order to control resistance, the base and elastic layer of the intermediate transfer belt 20 are provided with conductive pigments such as quaternary ammonium salts, carbon black, and metal oxides, conductive materials such as polyaniline and polypyrrole, and these two types. It is preferable to disperse the above mixture. In particular, the elastic layer preferably has a volume resistivity adjusted to 10 ⁴ to 10 ¹⁴ Ω · cm.

The intermediate transfer belt 20 is held in a state of being stretched from the inside by the transport rollers 19A, 19B, 19C, and 19D, and can be driven in the counterclockwise direction (arrow B direction) in FIG. At a position inside the intermediate transfer belt 20 and facing the photosensitive drum 12, the intermediate transfer belt 20 is positively charged, and the toner on the surface 12 </ b> A of the photosensitive drum 12 is placed on the outer surface of the intermediate transfer belt 20. A primary transfer roll (primary transfer member) 22 for transferring the toner is disposed. The primary transfer roll 22 is formed by forming a urethane foam layer on a metal core, and the volume resistivity of the urethane foam layer is 10 ⁶ to 10 ⁷ Ωcm.
A positive voltage is applied to the primary transfer roll 22. Since the primary transfer roll 22 rotates while applying pressure to the intermediate transfer belt 20, the toner image formed on the surface 12 </ b> A of the photosensitive drum 12 is transferred to the intermediate transfer belt 20.

A secondary transfer member is disposed so as to face a part of the intermediate transfer belt 20. The secondary transfer member is composed of an endless transfer / conveying belt 32 and two stretching rolls 33a and 33b that stretch the endless transfer / conveying belt 32. The roll 33a also serves as a secondary transfer roll. That is, the transfer conveyance belt 32 is inserted between the intermediate transfer belt 20 and the stretching roll 33a, and at least one of the stretching rolls 33a and 33b also serves as a driving roll.
In the present invention, the secondary transfer member may be provided with a transfer roll for transferring the toner image on the intermediate transfer belt to the paper, or a transfer transport belt for transferring the toner image by transporting the paper. It may be provided.

As the transfer / conveying belt 32, various laminated types in which an elastic layer is provided on a substrate can be preferably used. Further, it is preferable that the transfer conveyance belt 32 sufficiently electrostatically attracts and restrains the recording medium P in order to convey the recording medium P to the transfer region and embed it in the elastic layer. For this reason, the electrical characteristics of the surface layer should be able to retain electric charge and not be charged up. From this viewpoint, the volume resistivity of the outermost surface layer should be in the range of 10 ⁷ to 10 ¹² Ω · cm. Is preferred. This volume resistivity can be adjusted, for example, by using a conductive resin material for the outermost surface layer or dispersing a conductive agent.

  As a constituent material of the substrate of the transfer conveyance belt 32, resin materials such as polyimide, polyarylate, polysulfone, polyetheretherketone, polyamide, polyamideimide, polycarbonate, polyester, polyvinylidene fluoride, and resin materials mainly composed of these are used. Can be mentioned. In particular, a polyimide resin is preferable from the viewpoint of satisfying the mechanical properties as a belt.

  The constituent material of the elastic layer of the transfer / conveying belt 32 includes ethylene propylene rubber (EPDM), nitrile rubber (NBR), styrene butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), chloroprene rubber (CR). And rubber materials such as acrylic rubber (ACM), silicone rubber and fluororubber; polystyrene, polyolefin, polyvinyl chloride, polyurethane, polyester and polyamide-based thermoplastic elastomer; urethane resin and urea resin, and the like.

  A recording paper supply device 26 that supplies the recording paper P to the transfer conveyance belt 32 is provided upstream of the transfer conveyance belt 32. The recording paper supply device 26 includes a pair of transport rollers 26A and 26A. A fixing device 28 for fixing the toner image on the recording paper P is provided on the discharge side of the recording paper P by the transfer conveyance belt 32. The fixing device 28 includes a pair of fixing rolls 28A and 28A for fixing the toner image by heating and pressing the recording paper P on which the toner image is transferred by the secondary transfer roller 24. A conveyance conveyor 28B that conveys the recording paper P toward 28A and a pair of discharge rolls 28C and 28C that discharge the recording paper P fixed by the fixing rolls 28A and 28A are provided. Note that the recording paper P is conveyed in the direction indicated by the arrow C in FIG. 1 by the recording paper supply device 26 and the fixing device 28.

  In the vicinity of the transfer conveyance belt 32 and at an intermediate position from the stretching roll 33a to the stretching roll 33b, a toner removing device (secondary removal device) that removes toner adhering to the conveyance transfer belt 32 that is released during secondary transfer. The transfer cleaner) 40 is also recorded by the transfer transfer belt 32 at an intermediate position from the transfer roll 19C to the primary transfer roll 22 in the vicinity of the intermediate transfer belt 20 and in contact with the transfer transfer belt 32. A toner removing device (primary transfer cleaner) 30 for removing the toner remaining on the intermediate transfer belt 20 after the toner image is transferred to the paper P is provided.

  Further, the surface of the photoconductive drum 12 is located at a position slightly advanced in the rotation direction of the photoconductive drum 12 (arrow A direction) from the position where the primary transfer roll 22 and the photoconductive drum 12 sandwich the intermediate transfer belt 20. A cleaning device 34 is provided for cleaning 12A to remove waste toner and the like remaining on the transfer.

Since the primary transfer cleaner and the secondary transfer cleaner have substantially the same configuration, these will be described below together with the primary transfer cleaner with reference to FIG.
As shown in FIG. 2, the toner removing device (primary transfer cleaner) 30 includes a conductive sheet 81, two brush rolls 83 and 86, a toner collection case 88, and a rotation support shaft 89. Swings as a shaft. By this swinging, the toner removing device 30 moves between a contact position where the conductive sheet 81 and the brush rolls 86 and 83 are in contact with the intermediate transfer belt 20 and a separation position where the conductive sheet 81 and the brush rolls 86 and 83 are separated from the intermediate transfer belt 20.

  The conductive sheet 81 is an example of a bias applying unit, and is configured by a sheet having elasticity and conductivity. One end of the conductive sheet 81 is fixed to the casing of the intermediate transfer device, and the other end is a portion wound around the transport roll 19D elastically with a predetermined contact pressure along the circulation direction of the intermediate transfer belt 20. The intermediate transfer belt 20 is in contact with the toner carrying surface. This contact pressure is set so that the conductive sheet 81 can be reliably brought into contact with the intermediate transfer belt 20 and does not cause excessive resistance (load) to the circulation of the intermediate transfer belt 20.

  A bias power supply 85 is connected to the conductive sheet 81, and a predetermined bias voltage (for example, 1700V) is applied. When the conductive sheet 81 comes into contact with the toner carrying surface of the intermediate transfer belt 20, the toner on the toner carrying surface is charged and the amount of charge is controlled.

  The toner removing device 30 includes two brush rolls (brushes), a front-stage brush roll 86 and a rear-stage brush roll 83, for cleaning the toner that remains on the surface of the intermediate transfer belt 20 and is conveyed.

  The pre-stage brush roll 86 has a cylindrical shape as a whole, and is disposed close to the intermediate transfer belt 20 and in parallel with the intermediate transfer belt 20. A cylindrical brush shaft 86A is provided as an axis of the front brush roll 86, and a large number of conductive fibers are radially planted on the peripheral surface of the brush shaft 86A via a conductive adhesive layer. To form a brush. A positive (for example, +300 V) DC voltage having the same polarity as the voltage applied in the primary transfer process is applied to the brush. As a result, an electric field is formed between the surface of the intermediate transfer belt 20 and the brush, and the negatively charged toner remaining on the intermediate transfer belt 20 is electrostatically attracted to the brush. Nylon etc. are used for the conductive fiber of a brush, for example.

  The pre-stage brush roll 86 is rotated counterclockwise (arrow D direction) in FIG. 2 by a motor (not shown), and scrapes the negatively charged toner remaining on the belt surface by rubbing the surface of the intermediate transfer belt 20. Can be taken. For example, a detoning roll or the like may be disposed at a position in contact with the pre-stage brush roll 86, and the toner scraped off by the brush may be removed.

  The post-stage brush roll 83 has a cylindrical shape as a whole, and is disposed close to the intermediate transfer belt 20 above the pre-stage brush roll 86 and in parallel with the intermediate transfer belt 20. A cylindrical brush shaft 83A is provided as an axial center of the rear brush roll 83, and a large number of conductive fibers are radially planted on the peripheral surface of the brush shaft 83A via a conductive adhesive layer. To form a brush. A negative DC voltage (for example, −300 V) having a polarity opposite to the polarity of the voltage applied to the brush of the front-stage brush roll 86 is applied to the brush. As a result, an electric field is formed between the surface of the intermediate transfer belt 20 and the brush, and the positively charged toner remaining on the belt surface is electrostatically attracted to the brush. Nylon etc. are used for the conductive fiber of a brush, for example.

The post-stage brush roll 83 is rotated in the counterclockwise direction (arrow D direction) in FIG. 2 by a motor (not shown), and scrapes off the positively charged toner remaining on the belt surface by rubbing the surface of the intermediate transfer belt 20. be able to. For example, a detoning roll as described above may be disposed at a position in contact with the subsequent brush roll 83 to remove the scraped toner.
In the present embodiment, the front-stage brush roll 86 and the rear-stage brush roll 83 are provided with the same outer diameter brushes made of the same material and rotate at the same rotational speed.

As described above, the toner removing device (secondary transfer cleaner) 40 is also provided with two brush rolls with a similar configuration (not shown).
In the present invention, the tip force of the brush provided to the intermediate transfer belt (intermediate transfer member) 20 is Fb (IBT), and the tip of the brush provided to the transfer conveyance belt (secondary transfer member) 32 is used. When the force is Fb (BT), it is necessary that Fb (IBT) and Fb (BT) have the relationship of the following formula (1).
Fb (IBT)> Fb (BT) Formula (1)

  If there is a slight amount of toner passing through the toner removing means (secondary transfer cleaner) 40, even if one sheet has a level of contamination due to the toner adhering to the back surface of the paper, there is a slight amount of toner adhering to the back surface. Since toner accumulates on the paper transport path, a phenomenon occurs in which the accumulated toner adheres to the back side of the paper as the number of printed sheets advances. In particular, due to the influence of oil etc. that adheres to the paper that has passed through the fixing part in double-sided printing, etc., the adhesion force between the toner and the paper increases, so the accumulated toner is more likely to adhere to the paper and the paper backside stains occur. Resulting in.

Further, when brush cleaning is performed in the secondary transfer cleaner, toner is scattered and clouding easily occurs, and these adhere to the transfer conveyance belt 32.
Therefore, it is desirable that the brush tip force Fb (BT) in the secondary transfer cleaner be as small as possible without causing the toner to slip through, preferably in the range of 0.2 to 1.5 N / m, and 0.3 to 0. A range of 0.8 N / m is more preferable.

  On the other hand, even when brush cleaning is performed in the primary transfer cleaner, a small amount of toner that could not be cleaned by the brush is generated. Note that the polarity applied to the brush is determined so that the slipped toner returns to the photoconductor by the electric field at the primary transfer portion, but it is desirable that the return of the toner to the photoconductor is as small as possible.

  Therefore, the brush tip force Fb (IBT) in the primary transfer cleaner needs to be at least larger than Fb (BT). In this case, Fb (IBT) is preferably in the range of 1.5 to 4.0 N / m, and more preferably in the range of 2.0 to 3.0 N / m.

The tip force of the brush was measured with an apparatus as shown in FIG. 3A is a side view of a device for measuring the tip force of the brush, and FIG. 3B is a plan view of the device.
In the measurement, first, the tip of an aluminum plate 95 having a length of 50 mm and a width of 100 mm with one end fixed at a fulcrum 94 is inserted into a brush roll 92 having a diameter of 19 mm over 1 mm, and this brush roll 92 is rotated. Then, the deflection of the aluminum plate 95 at this time was measured with a load cell 96 fixed to an intermediate portion thereof, and this value was defined as a brush tip force Fb.

  There are various means for setting Fb (BT) and Fb (IBT) so as to satisfy the relationship of the above formula (1). For example, the brush roll brush in the primary transfer cleaner and the secondary transfer cleaner As appropriate, adjust and select brush bristles, brush fiber diameter, amount of interference of brush fibers with intermediate transfer belt, brush fiber flock density, Young's modulus of brush fibers, materials constituting brush fibers, etc. Alternatively, the rotation of the brush roll in the primary transfer cleaner and the secondary transfer cleaner may be controlled.

Particularly in the present invention, in order to satisfy the relationship of the above formula (1), the brush fiber diameter of the brush (the brush provided for the intermediate transfer belt) in the primary transfer cleaner is set to D (IBT), and the secondary transfer cleaner. When the brush fiber diameter of the brush (the brush provided for the transfer / conveying belt) is D (BT), D (IBT) and D (BT) may have the relationship of the following formula (3). preferable.
D (IBT)> D (BT) (3)

Here, the brush fiber diameter refers to the diameter per brush (one twisted state when the brush is a twisted yarn).
More specifically, D (IBT) is preferably in the range of 3.3 to 22 dtex (3 to 20 denier), and more preferably in the range of 4.4 to 11 dtex (4 to 10 denier). preferable. Moreover, it is preferable to make D (BT) into the range of 0.8-6.6 decitex (0.7-6 denier), and the range of 1.1-3.3 decitex (1.0-3 denier) More preferably.

  As a result of studies by the present inventors, it has been found that as D (IBT) is increased with respect to D (BT), the residual toner on the intermediate transfer belt for solid images decreases.

In the present invention, in order to satisfy the relationship of the formula (1), the brush peripheral speed of the brush provided for the intermediate transfer belt is Vb (IBT), and the brush provided for the transfer conveyance belt. When the brush peripheral speed is Vb (BT), it is preferable that Vb (IBT) and Vb (BT) have the relationship of the following formula (4).
Vb (IBT)> Vb (BT) (4)

Here, the circumferential speed is the speed at the tip of the brush roll.
More specifically, Vb (IBT) is -0.5 to -2.0 times the circulation speed (about 100 to 500 mm / sec) of the intermediate transfer belt (-is opposite to the circulation direction of the intermediate transfer belt). In the following, Vb (BT), which means the direction, is also preferably in the range, and more preferably in the range of -1.0 to -1.5 times. Vb (BT) is preferably in the range of −0.1 to −1.0 times the circulation speed (about 100 to 500 mm / sec) of the transfer conveyance belt, and is −0.2 to −0. More preferably, the range is 5 times.

  As a result of studies by the present inventors, as Vb (IBT) is made larger than Vb (BT), the residual toner on the intermediate transfer belt for the image background portion slightly increases, but for solid images. It was found that the untransferred toner was greatly reduced.

  As described above, the relationship between the formula (3) (D (IBT)> D (BT)) or the formula (4) (Vb (IBT)> Vb (BT)) is satisfied. Thus, it is possible to reduce the mechanical impact force of the toner, and to prevent the toner from adhering to the transfer / conveying belt due to the scattering of the toner and the back surface of the paper.

Further, in the present invention, in order to satisfy the relationship of the expression (1), the brush resistance of the brush provided for the intermediate transfer belt is R (IBT), and the brush provided for the transfer conveyance belt is When the brush resistance is R (BT), it is preferable that R (IBT) and R (BT) have the relationship of the following formula (5).
R (IBT)> R (BT) (5)

Here, the brush resistance is the electric resistance of the brush when a constant voltage is applied to the brush roll, and is obtained from the current value that flows when the voltage is applied by pressing the brush roll against a metal plate such as Al. Can do.
For example, in the case of a brush roll having a brush outer diameter of 17.5 mm, a shaft diameter of 12 mm, and a brush width of 320 mm, the amount of biting into the metal plate is set to 1.0 mm, and 300 V is measured by an ohm meter (advantest R8340A). It can be applied and measured.

  With a brush with low resistance, charge injection into the belt occurs, so when the same current is applied, the adsorption force between the brush and the belt becomes weaker when the resistance is low, so the impact force of the brush and belt when the resistance is low Can be reduced. Therefore, by setting the brush resistance to the relationship of the above equation (5), the suction force between the brush, the transfer / conveying belt, and the brush can be reduced.

  More specifically, R (IBT) is preferably in the range of 6 to 10 logΩ, and more preferably in the range of 5.5 to 7 logΩ. R (BT) is preferably in the range of 5 to 8 logΩ, and more preferably in the range of 5.5 to 7 logΩ.

  Next, a cleaning device (cleaning means) provided in the vicinity of the photosensitive drum (image carrier) (hereinafter also referred to as “photosensitive cleaner”) will be described.

  The surface of the photosensitive drum 12 is located slightly ahead in the rotational direction (arrow A direction) of the photosensitive drum 12 from the position where the primary transfer roller 22 and the photosensitive drum 12 in FIG. A cleaning device 34 is provided for cleaning 12A to remove waste toner T (see FIG. 4) remaining after transfer.

Details of the configuration of the cleaning device 34 are shown in FIG.
The cleaning device 34 includes a cleaner housing 36 that is disposed in the vicinity of the photosensitive drum 12 and opens to the side facing the photosensitive drum 12. A seal member 38 is fixed to the lower opening end of the cleaner housing 36. The seal member 38 substantially closes the gap between the photosensitive drum 12 and the cleaning device 34, and prevents waste toner T and the like in the cleaning device 34 from leaking to the outside.

  A cleaning blade (blade) 50 is provided downstream of the seal member 38 in the rotational direction (arrow A direction) of the photosensitive drum 12 so that the tip 50A abuts the surface of the photosensitive drum 12. The cleaning blade 50 is made of a plate-like rubber member such as urethane rubber having a thickness of 1.5 to 3.0 mm, and a base end portion 50B is bonded to a pressure application plate 52 made of a sheet metal having an L-shaped cross section. Yes. A holder 54 is arranged inside the bending of the pressure application plate 52. The pressure application plate 52 is fixed to the holder 54 with a set screw 56. The holder 54 includes a rotation shaft 54A and is rotatable about the rotation shaft 54A. A through hole 52A is formed at one end (the left end in FIG. 4) of the pressure application plate 52, and one end of the spring 58 is attached. The other end of the spring 58 is attached to the frame 60. .

  As shown in FIG. 4, a spiral auger 48 is provided below the cleaning device 34. The spiral auger 48 temporarily receives the waste toner T and the like that has floated and dropped from the cleaning blade 50 in the cleaning device 34, and then discharges the waste toner T and the like from the cleaning device 34.

  In the present invention, the cleaning member in the cleaning device 34 may be a blade, a brush as described above, or a magnetic brush. The frictional force between the cleaning member and the photosensitive drum 12 is not particularly limited as long as the tip force of the brush in the primary cleaner and the secondary cleaner satisfies the relationship of the expression (1).

  However, as described above, the polarity applied to the brush is determined so that the toner that has passed through the primary transfer cleaner returns to the photosensitive drum 12 by the electric field at the primary transfer portion. Therefore, it is necessary to clean the toner slipped from the primary transfer cleaner to a level that does not affect the next image by the photoconductor cleaner.

For this reason, in particular, when a blade is used as a cleaning member for the photoreceptor cleaner, F (PC) and Fb (IBT) are expressed as follows when the frictional force between the blade and the image carrier is F (PC). It is preferable to have the relationship of the formula (2).
F (PC)> Fb (IBT) (2)

  That is, even when a small amount of toner having a large adhesion force with the belt slips out of the secondary transfer cleaner, the toner returned to the photoconductor by the transfer electric field at the primary transfer portion is surely cleaned. By adopting a configuration in which the cleaning power for the photosensitive member is increased, cleaning can be performed even for small toner and spherical toner that are difficult to clean.

The F (PC) is represented by μN where the friction coefficient between the toner and the blade is μ and the pressure of the blade is N (N). By measuring, it can be measured as a frictional force F (PC) acting on the photosensitive member.
And in this invention, it is preferable that F (PC) is the range of 4-20 N / m, and it is more preferable that it is the range of 5-12 N / m.

  As described above, the image forming apparatus according to the present invention determines the magnitude relationship between the brush tip forces in the primary transfer cleaner and the secondary transfer cleaner. Prevents toner from adhering to the secondary transfer member and the back side of the paper from being stained, and further, by establishing a magnitude relationship with the blade friction force in the photoreceptor cleaner, a cleaning mechanism is provided for the intermediate transfer member and the secondary transfer member. Even in this case, it is possible to suppress the occurrence of defective cleaning as the entire apparatus, and it is possible to stably obtain high-quality images over a long period of time.

<Test example>
In order to confirm the operation of the above embodiment, the following comparative test was performed.
(Evaluation equipment)
The secondary transfer part of the Fuji Xerox color multifunction device DocuCenter Color 500 was equipped with a conductive brush on a transfer conveyance belt (thickness: 0.6 mm, resistance: 8 logΩ) using chloroprene rubber as shown in FIG. A structure in which a secondary transfer cleaner is provided and a belt (thickness: 0.7 mm, resistance: 9 logΩ) in which an epichlorohydrin rubber layer and a fluororesin surface layer are provided on a polyimide base material is used as an intermediate transfer belt. An image forming apparatus for evaluation was provided by providing a primary transfer cleaner provided with a conductive brush.

In the secondary transfer cleaner, the two conductive brushes rotate in the direction opposite to the rotation direction of the transfer conveyance belt. Here, as the brush, a 2-denier (2.2 decitex) nylon brush fiber obtained by making a nylon resin conductive into a brush having a density of 120,000 / inch was used. The outer diameter of the brush roll was 17.5 mm, the diameter of the shaft was 12 mm, and the amount of biting into the belt was 1.0 mm. The brush roll was rotated at a speed of 78 mm / sec in the opposite direction to the transfer conveyance belt rotating at a surface speed of 260 mm / sec, and the tip force of the brush was set to 0.4 N / m.
The brush resistance of the brush roll was 10 ⁶ Ω.

In the primary transfer cleaner, a brush roll having the same amount of biting as that of the brush roll used in the secondary transfer cleaner except that 6 denier (6.7 decitex) nylon brush fiber was used. The intermediate transfer belt is attached to the intermediate transfer belt and rotated at a surface speed of 260 mm / sec. The intermediate transfer belt is rotated at 390 mm / sec in the direction opposite to the belt, and the brush tip force is 2.2 N / m. Was set to be.
The brush roll had a brush resistance of 10 ⁷ Ω.

  Further, a urethane rubber blade having a thickness of 2 mm and a length of 320 mm was used as the cleaning blade (friction coefficient with respect to toner: 0.3), and the blade pressure was 29.4 N / m (3 gf / mm) (friction force: 8). .8 N / m).

The evaluation conditions were as follows.
(Developer)
As the toner, emulsion polymerization aggregation using resin fine particles made of styrene / n-butyl acrylate / β-carboxyethyl acrylate copolymer, colorant particles containing magenta pigment, and release agent fine particles containing polyethylene wax. Magenta toner (volume average particle size: 3.6 μm, shape factor SF1: 115 (spherical shape with a large stress on cleaning)), and silica black treated with carbon black on the ferrite particle surface. A two-component developer prepared by mixing a carrier having a volume average particle size of 45 μm coated with a polymethyl methacrylate copolymer dispersed as an agent so that the toner concentration (TC) is 8% by mass is used.

(Printing conditions)
As an apparatus, in order to add a stress condition for cleaning, a charger is made from a scorotron to a contact-type charging roll (an elastic layer is made of SBR containing carbon black, and an ECO containing an ionic conductive agent is formed on the surface thereof. Furthermore, the surface of the polyamide surface layer containing carbon black and SnO ₂ is replaced with a volume resistivity: 1 × 10 ⁸ Ωcm, and the voltage applied to the charging roll is 1.6 kV (Peak to Peak) as an AC voltage. ) The frequency was 2 kHz. Such contact-type charging increases the surface energy of the photosensitive member by discharging, thereby increasing the wettability and, as a result, improving the frictional force. Furthermore, the test environment was a high-temperature and high-humidity environment (28 ° C., 85% RH) in which the stress due to the cleaning by the discharge products is large.

Under the above conditions, the characteristics and conditions of the primary transfer cleaner brush and the secondary transfer brush are set as shown in Table 1, and after 500 images are continuously printed for a 4% halftone image, Then, it was run in the double-sided print mode and the cleaning property was evaluated.
As a result, under this condition, the paper back surface did not stain, and there was no image quality defect due to poor photoconductor cleaning.

  For comparison, the characteristics and conditions of the primary transfer cleaner brush and the secondary transfer brush were set as shown in Table 2, and the cleaning performance was evaluated in the same manner as described above. As a result, under these conditions, backside contamination occurred during double-sided printing.

It is a schematic block diagram which shows an example of the image recording device of this invention. 1 is a schematic configuration diagram of a toner removing device according to an embodiment of the present invention. The apparatus which measures a brush tip force is shown, (a) is a side view, (b) is a top view. It is a schematic block diagram of the cleaning apparatus which concerns on embodiment of this invention.

Explanation of symbols

10 Image recording device 12 Photosensitive drum (image carrier)
18 Developing device (developing means)
20 Intermediate transfer belt (intermediate transfer member)
22 Primary transfer roller 24 Secondary transfer roller 30, 40 Toner removing device 32 Transfer conveyance belt (secondary transfer member)
34 Cleaning device 50 Cleaning blade 81 Charge control sheet 83, 86, 92 Brush roll 88 Toner recovery case 89 Rotating spindle 95 Aluminum plate 96 Load cell T Waste toner

Claims (1)

At least an image carrier on which a latent image is formed, a latent image forming unit that forms a latent image on the image carrier, and developing the latent image formed on the image carrier with toner. Developing means for forming a toner image on the image carrier, a primary transfer member for transferring the toner image formed on the image carrier to an intermediate transfer member, and a toner image formed on the intermediate transfer member A secondary transfer member that transfers the image onto a recording medium,
A brush is provided as a cleaning member for toner removing means provided in the vicinity of the intermediate transfer member and the secondary transfer member, and the tip force of the brush provided for the intermediate transfer member is expressed as Fb (IBT), secondary. An image forming apparatus characterized in that Fb (IBT) and Fb (BT) have a relationship of the following formula (1), where Fb (BT) is a tip force of a brush provided on the transfer member.
Fb (IBT)> Fb (BT) Formula (1)

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