Patent Grant
10996590
The present invention relates to an image forming apparatus adopting an electrophotographic system for forming an image using a liquid developer.
Hitherto, there has been known an image forming apparatus that develops an electrostatic latent image formed on a photosensitive drum as a toner image using liquid developer containing toner and carrier liquid, and primarily transferring the developed toner image to a transfer drum then secondarily transferring the primarily transferred toner image on the transfer drum to a recording material. In an apparatus using liquid developer, a cleaning roller abuts against the transfer drum to remove toner remaining on the transfer drum after performing secondary transfer (Japanese Patent Application Laid-Open No. 2011-158905). Toner moves from the transfer drum to the cleaning roller via the liquid developer according to an electric field formed by the application of voltage to a cleaning roller, which is so-called electrophoresis, at a nip portion formed by the cleaning roller abutting against the transfer drum. The toner moved to the cleaning roller is removed with the liquid developer by a cleaning blade that is rubbed against the cleaning roller.
Meanwhile, an image forming apparatus using a dry developer instead of a liquid developer is proposed, where a counter roller is arranged on an inner side of the belt and a cleaning roller is arranged on an outer side of the belt as a pair of rollers for removing the toner remaining on the intermediate transfer belt. In these apparatuses, the counter roller and the cleaning roller are arranged so that the intermediate transfer belt nipped by the counter roller and the cleaning roller is projected either toward the inner side or the outer side of the belt (Japanese Patent Application Laid-Open Nos. 2002-318493 and 2005-99361).
In the case of the image forming apparatus using liquid developer, it is desirable to use a metal roller as the cleaning roller for cleaning the intermediate transfer belt, since it has higher resistance than a rubber roller to deterioration by organic solvent and the like contained in the liquid developer. However, if the metal roller was used, there was a case where toner could not be moved from the intermediate transfer belt. In the image forming apparatus using a liquid developer, there was a demand to ensure a nip portion enabling toner to move by electrophoresis from the belt member such as the intermediate transfer belt, but there has been no proposal of such an apparatus.
According to a first aspect of the present invention, an image forming apparatus includes an endless belt member configured to bear a liquid developer including toner and carrier liquid on an outer circumferential surface and rotate, an outer roller configured to form a contact portion that is in contact with the outer circumferential surface of the belt member and receive toner moved from the belt member via the liquid developer, an inner roller configured to abut against the outer roller via the belt member, a power supply configured to apply voltage to the outer roller or the inner roller, a first roller adjacent to the outer roller and the inner roller on a downstream side in a direction of movement of the belt member and configured to tension the belt member, and, a second roller adjacent to the outer roller and the inner roller on an upstream side in the direction of movement of the belt member and configured to tension the belt member. At least a portion of at least one of the first and second rollers is provided on a same side as the outer roller with respect to a tangent passing an intersection of the inner roller and a straight line connecting a center of rotation of the outer roller and a center of rotation of the inner roller.
According to a second aspect of the present invention, an image forming apparatus includes an endless belt member configured to bear a liquid developer including toner and carrier liquid on an outer circumferential surface and rotate, an outer roller configured to form a contact portion that is in contact with the outer circumferential surface of the belt member and receive toner via the liquid developer from the belt member according to a potential difference generated between the belt member, a first roller adjacent to the outer roller and the inner roller on a downstream side in a direction of movement of the belt member and configured to tension the belt member, the first roller being positioned so that a position in which the first roller abuts against the belt member does not overlap with the contact portion with respect to a direction of movement of the belt member, and a second roller adjacent to the outer roller and the inner roller on an upstream side in the direction of movement of the belt member and configured to tension the belt member, the second roller being positioned so that a position in which the second roller abuts against the belt member does not overlap with the contact portion with respect to the direction of movement of the belt member. At least one of the first and second rollers is provided on a same side as the outer roller with respect to a tangent of the outer roller at a center position of the contact portion with respect to the direction of movement of the belt member.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Image Forming Apparatus
A first embodiment will be illustrated. First, a configuration of an image forming apparatus according to the present embodiment will be described with reference to
The intermediate transfer unit 20 includes an endless intermediate transfer belt 21 serving as a belt member, primary transfer rollers 22Y to 22K, a driving roller 23, a tension roller 24 and a secondary transfer inner roller 25. The intermediate transfer belt 21 is wound around and supported by rollers including the driving roller 23, the tension roller 24 and the secondary transfer inner roller 25 and driven by the driving roller 23 to rotate in a direction of arrow R2 of
The image forming units UY to UK are arranged along the direction of movement of the intermediate transfer belt 21, that is, in the direction of arrow R2 of
The image forming units UY to UK adopt a similar configuration except for the different toner colors of yellow, magenta, cyan and black used in developing apparatuses 4Y, 4M, 4C and 4K serving as supplied portions receiving supply of toner. Therefore, in the following description, the letters Y, M, C and K as suffixes indicating the distinction of image forming units UY, UM, UC and UK are omitted in illustrating the configuration and action of the image forming units UY to UK.
The image forming unit U includes a primary charger 12, an exposing unit 13, a developing apparatus 4 and a drum cleaning device 14 arranged in a manner surrounding a photosensitive drum 11 serving as a photosensitive member. The image forming unit U is arranged so that the photosensitive drum 11 opposes to a primary transfer roller 22 with the intermediate transfer belt 21 interposed therebetween so that a primary transfer portion T1 of toner image is formed between the photosensitive drum 11 and the intermediate transfer belt 21 by the primary transfer roller 22. The photosensitive drum 11 in which a photosensitive layer is formed on an outer circumferential surface of an aluminum cylinder is rotated in a direction of arrow R1 of
The primary charger 12 irradiates charged particles accompanying corona discharge to charge the photosensitive drum 11 to uniform negative dark potential. The exposing unit 13 scans an ON-OFF modulated laser beam of image data of scanning lines having developed separate color images of respective colors using a rotation mirror and writing an electrostatic latent image of an image on a charged surface of the photosensitive drum 11. The electrostatic latent image is developed into a toner image by the developing apparatus 4.
Liquid developer including powder toner serving as dispersoid dispersed in carrier liquid serving as dispersion medium is stored in the developing apparatus 4. Liquid developer supplied from a mixer (not shown) is supplied to the developing apparatus 4. Liquid developer supplied from the mixer to the developing apparatus 4 is coated, i.e., supplied, to a developing roller 4b by a coating roller 4a in the developing apparatus 4, which is used to develop an image. The developing roller 4b bears and conveys liquid developer on its surface, and the electrostatic latent image formed on the photosensitive drum 11 is developed using toner. Coating of liquid developer to the developing roller 4b from the coating roller 4a and developing of electrostatic latent image from the developing roller 4b on the photosensitive drum 11 are respectively performed using an electric field. Liquid developer that has not been used for developing image is returned to the mixer from the developing apparatus 4 to the mixer and reused.
The toner image formed on the photosensitive drum 11 is primarily transferred to the intermediate transfer belt 21 using an electric field at the primary transfer portion T1 formed by the primary transfer roller 22. Liquid developer, i.e., toner and carrier liquid, remaining on the photosensitive drum 11 after primary transfer is collected by the drum cleaning device 14.
The secondary transfer portion T2 is a transfer portion formed by abutting a secondary transfer outer roller 26 to the intermediate transfer belt 21 supported by the secondary transfer inner roller 25 for transferring toner image to the recording material P. By applying secondary transfer voltage to the secondary transfer outer roller 26 serving as a transfer member at the secondary transfer portion T2, toner image is secondarily transferred from the intermediate transfer belt 21 to the recording material P conveyed to the secondary transfer portion T2. Toner, i.e., residual toner, remaining on the intermediate transfer belt 21 after primary transfer is removed together with carrier liquid by a belt cleaning device 30. The belt cleaning device 30 will be described in detail later (refer to
The recording material P to which a toner image of four colors is secondarily transferred at the secondary transfer portion T2 is conveyed to a fixing unit and the like (not shown), and the toner image transferred to the recording material P is fixed by the fixing unit. The recording material P to which the toner image has been formed is discharged to an exterior of the apparatus body.
Liquid Developer
Next, liquid developer used in developing apparatuses 4Y to 4K will be described. Conventional liquid developer may be used as liquid developer, and a UV-curing liquid developer is used according to the present embodiment.
The liquid developer is a UV-curing liquid developer containing cation-polymerizable liquid monomer, photopolymerization initiator and toner particles insoluble to cation-polymerizable liquid monomer. Further, the cation-polymerizable liquid monomer is a vinyl ether compound and the photopolymerization initiator is a chemical compound represented by the following general formula (Chem. 1).
A more specific description follows. First, the toner particles contain toner resin enclosing a coloring material that generates color. Further, the toner particles may contain other materials such as a charge control agent in addition to toner resin and coloring material. A known technique such as a coacervation method in which coloring materials are dispersed and resin is caused to gradually polymerize and enclose the coloring materials or an internal pulverization method in which resin and the like is melted and the coloring material is caused to be enclosed in resin can be adopted as the manufacturing method of toner particles. Epoxy resin, styrene acrylic resin and the like can be used as toner resin. The coloring material for generating color may be general organic/inorganic pigments. Dispersing agent is used to enhance toner dispersibility during manufacture, but synergist may also be used.
Curing liquid serving as carrier liquid is composed of a charge control agent for charging the toner surface, a photopolymerization agent that generates acid by UV irradiation and a monomer bound by acid. The monomer is a vinyl ether compound that is polymerized by cation polymerization reaction. Further, a sensitizer may be contained in addition to the photopolymerization agent. Preservability is deteriorated by photopolymerization, so that 10 to 5000 ppm of cation polymerization inhibitor may be added. A charge controlling agent or other additives may also be added.
UV curing agent (monomer) of the above-described developer is a mixture containing approximately 10% (wt. %) of monofunctional monomer having one vinyl ether group represented by chemical formula (Chem. 2) and approximately 90% of difunctional monomer having two vinyl ether groups represented by chemical formula (Chem. 3).
An agent represented by chemical formula (Chem. 4) is mixed for 0.1% as a photopolymerization initiator. Unlike the case where an ionic photoacid generator is used, a high resistivity liquid developer may be obtained while ensuring preferable fixture, by using the photopolymerization initiator.
The cation-polymerizable liquid monomer should preferably be a chemical compound selected from a group consisting of dicyclopentadiene vinyl ether, cyclohexane dimethanol divinyl ether, tricyclodecane vinyl ether, trimethylolpropane trivinyl ether, 2-ethyl-1,3-hexanediol divinyl ether, 2,4-diethyl-1,5-pentanediol divinyl ether, 2-butyl-2-ethyl-1,3-propanediol divinyl ether, neopentyl glycol divinyl ether, pentaerythritol tetravinyl ether and 1,2-decanediol vinyl ether.
Further, a known charge control agent can be utilized. Specific chemical compounds include fats and oils such as linseed oil and soybean oil; metal soaps such as alkyd resin, halogen polymer, aromatic polycarboxylic acid, acid group-containing water soluble dye, oxidative condensate of aromatic polyamine, cobalt naphthenate, nickel naphthenate, iron naphthenate, zinc naphthenate, cobalt octylate, nickel octylate, zinc octylate, dodecyl acid cobalt, dodecyl acid nickel, dodecyl oxide zinc, aluminum stearate and 2-ethylhexanoic acid cobalt; sulfonic acid metal salt such as petroleum-based sulfonate metal salt and metal salt of sulfosuccinic acid ester; phospholipid such as lecithin; salicyclic metal salts such as t-butylsalicylate metal complex; and polyvinyl pyrrolidone resin, polyamide resin, sulfonic acid-containing resin and hydroxybenzoic acid derivatives.
Belt Cleaning Device
The configuration of the belt cleaning device 30 according to the present embodiment will be described with reference to
The counter roller 40 serving as an inner roller is provided rotatably on an inner circumferential side of the intermediate transfer belt 21, and abuts against the inner circumferential surface, i.e., rear surface, of the intermediate transfer belt 21 between the secondary transfer inner roller 25 and the driving roller 23 (refer to
The present embodiment is configured to enable the physical nip T3b to be ensured by the counter roller 40 and the cleaning roller 31. The reason for adopting this arrangement is to suppress the generation of discharge that tends to occur near the nip portion T3 as much as possible. If discharge occurs near the nip portion T3, a stronger electric field is required to clean the toner on the intermediate transfer belt 21, which may lead to increased damaging of the intermediate transfer belt 21. The present embodiment adopts an elastic belt having an elastic layer as the intermediate transfer belt 21, as described later. Such an intermediate transfer belt 21 has a high electrical resistivity, so discharge especially tends to occur near the nip portion T3.
The cleaning roller 31 is driven to rotate by a motor 35 at a similar speed as the intermediate transfer belt 21 in a same direction (direction of arrow R3) as the direction of movement of the intermediate transfer belt 21 at the nip portion T3 with the intermediate transfer belt 21. By operation of electric field, the cleaning roller 31 electrically removes the toner remaining on the intermediate transfer belt 21 without being secondarily transferred, which is so-called electrophoresis. In the case of the present embodiment, the counter roller 40 is grounded and the cleaning roller 31 is connected to a power supply 36, and voltage having an opposite polarity as toner is applied to the cleaning roller 31 from the power supply 36. It is also possible to connect the power supply to the counter roller 40 and ground the cleaning roller 31. In that case, voltage having the same polarity as toner is applied to the counter roller 40. Then, toner remaining on the intermediate transfer belt 21 is moved from the intermediate transfer belt 21 to the cleaning roller 31 via a solution layer of liquid developer formed between the intermediate transfer belt 21 and the cleaning roller 31 at the nip portion T3.
The toner moved to the cleaning roller 31 is removed together with liquid developer by the cleaning blade 32. The cleaning blade 32 is a plate-like member made of metal such as stainless steel and abuts against the cleaning roller 31 at a downstream side of the nip portion T3 with respect to the direction of movement of the cleaning roller 31. Toner having been removed by the cleaning blade 32 flows down into the cleaning container 33 with liquid developer by gravity. The bottom surface of the cleaning container 33 is formed in an inclined shape, and a discharge port 34 is formed at a lowermost portion of the inclined bottom surface. Therefore, the liquid developer containing toner removed by the cleaning blade 32 flows along the bottom surface of the cleaning container 33 to the discharge port 34 and is discharged through the discharge port 34 to the exterior of the cleaning container 33.
Cleaning Roller
The above-described cleaning roller 31 will be described. In an image forming apparatus using liquid developer, it is preferable to form the cleaning roller 31 using a material that does not easily react to organic solvents and the like contained in the liquid developer. Durability of the roller is thereby enhanced by suppressing deterioration of the roller due to dissolution and alteration caused by the chemical compound contained in the carrier liquid. Generally, if the difference between solubility parameters (SP value) of the roller and the organic solvent is two or more, the roller tends to deteriorate, that is, roller degradation is advanced, compared to the case where the difference between SP values is less than two. In the present embodiment, a metal roller formed for example of stainless steel or aluminum is used as the cleaning roller 31 from the viewpoint of delaying deterioration of the roller. A metal roller having a thin surface coating of fluororesin and the like that is thin enough so that shape following property of the metal roller is not changed by deformation may be used. It is not always necessary to use a metal roller as the counter roller 40 since it has less opportunity to be in contact with liquid developer than the cleaning roller 31, so a rubber roller can be used as the counter roller 40. However, it is preferable to use a metal roller for the counter roller 40 from the viewpoint of roller deterioration.
In the case of an image forming apparatus using dry developer, it is difficult to adopt a metal roller as the cleaning roller 31. Toner contained in a dry developer is an insulator, and if the cleaning roller 31 is a metal roller having low electrical resistivity, discharge caused at the nip portion or a gap at the area close thereto may cause melting and adhesion of toner having opposite polarity. Thereby, the cleaning property is deteriorated. In contrast, in the case of the image forming apparatus using liquid developer, the polarity of toner will not be reversed even if discharge occurs. Since toner will move in the solution layer of liquid developer by electrophoresis, a metal roller may be used. However, the metal roller has very little shape followability by deformation compared to the rubber roller. Therefore, if a metal roller is used as the cleaning roller 31, a certain nip length of the nip portion T3, that is, the length of the nip in the direction of movement of the intermediate transfer belt 21, must be ensured to allow the toner to move by electrophoresis infallibly. As described in detail later (refer to
Intermediate Transfer Belt
We will now describe the intermediate transfer belt 21. The intermediate transfer belt 21 is formed in the shape of a film having a fixed thickness using resin such as polyimide or polyamide or an alloy thereof that contains an appropriate amount of antistatic agent such as carbon black. For example, the intermediate transfer belt 21 is a resin belt having a surface resistivity of 1E+9 to 1E+13 Ω/□ and a thickness of 0.04 to 0.1 mm
The intermediate transfer belt 21 is formed of a resin having a high Young's modulus (such as 300 MPa). In the case of the intermediate transfer belt 21 having a low Young's modulus and is easily deformed, a long nip length of the physical nip T3b can be obtained even if a metal roller is used. However, if the thickness of the intermediate transfer belt 21 is 1 mm or less, it is difficult to ensure a sufficient nip length to remove most of the toner unless a metal roller having a diameter larger than 40 mm is used. A nip length of 1.2 mm or more must be ensured, for example. However, considering the fact that the weight of the metal roller is increased in squares if the diameter is increased, it is preferable to use a metal roller having a diameter of 40 mm or less as the cleaning roller 31.
Now, a test for examining the nip length while varying the belt thickness was performed to the nip length of the nip portion formed in a state where a metal roller is pressed against an endless belt. The result of the test is illustrated in
As illustrated in
Electrophoresis of Toner
Next, electrophoresis of toner at the nip portion T3 will be described with reference to
As described, the belt cleaning device 30 electrically removes toner F on the intermediate transfer belt 21 by the operation of an electric field, which is so-called electrophoresis. During the operation, a nip length L of the nip portion T3 must be ensured to more reliably move the toner F from the intermediate transfer belt 21 to the cleaning roller 31 by electrophoresis, and the nip length L (m) is a length that satisfies the following Expression 1.
(μ×E)×(L/P)>d Expression 1
In Expression 1, μ(m2/(V×s)) represents toner mobility, E (V/m) represents intensity of electric field that is generated at the nip portion T3 by application of voltage to the cleaning roller 31, P (m/s) represents rotational speed of the intermediate transfer belt 21, and d (μm) represents liquid thickness of liquid developer G at the nip portion T3. The nip length L refers to a length of toner remaining on the intermediate transfer belt 21 after secondary transfer by electrophoresis in a case where a so-called solid image where a solid toner image is formed on the whole surface of the recording material is secondarily transferred as toner image.
The left side of Expression 1 is a product of moving velocity of toner represented by (μ×E) and transit time for passing through the nip portion T3 represented by (L/P), in other words, the distance that toner can move by electrophoresis from the intermediate transfer belt 21 toward the cleaning roller 31. Meanwhile, the right side of Expression 1 is, as described above, the liquid thickness of liquid developer at the nip portion T3. In other words, if the nip length L according to which the left side of Expression 1 becomes greater than the right side is ensured, toner can move from the intermediate transfer belt 21 to the cleaning roller 31 via the liquid thickness of liquid developer while passing through the nip portion T3. As an example, toner mobility is 1.00−10 to 1.00−11 (m2/(V×s)). The electric field is 90 (V/μm). The rotational speed of the intermediate transfer belt 21 is 600 (mm/s). The liquid thickness d of liquid developer at the nip portion T3 is 2 (μm). In this case, the nip length L should be 1.5 (mm) or more. However, if the nip length L is elongated, a winding angle of the intermediate transfer belt 21 to the cleaning roller 31 is increased. This is not preferable from the viewpoint of belt life since the intermediate transfer belt 21 is repeatedly bent while rotating. Based on this viewpoint, the winding angle of the intermediate transfer belt 21 with respect to the cleaning roller 31 should preferably be less than 90°. More preferably, it should be less than 45°, or even more preferably less than 20°.
Now, the measurement of toner mobility, electric field, nip length and liquid thickness of liquid developer in Expression 1 will be described. The toner mobility μ may be expressed by following Expression 2.
μ=|v/E|=Q/(6π×η×α) Expression 2
In Expression 2, v (m/s) represents moving velocity of toner, and E (V/m) represents intensity of electric field that is generated at the nip portion T3 by application of voltage to the cleaning roller 31. Further, Q (C) represents amount of electric charge of the toner in the liquid developer, π represents circular constant, η represents viscosity of liquid developer (Pa·s), and α (μm) represents toner diameter. As an example, the viscosity of liquid developer is 4.0 (Pa·s), the toner diameter is 1.0 (μm) and the toner mobility can be calculated from these parameters. Further according to the present embodiment, the moving velocity of toner is approximately 9 to 90 (m/s). The amount of electric charge of toner can be calculated by the above-described various quantified parameters. Quantification of toner mobility is enabled by measurement using a measuring equipment such as a zeta potential measurement instrument Zeta-APS (product of Matec Applied Sciences Inc.).
The electric field is generally calculated by following Expression 3. In the expression, β (V) represents voltage applied to the cleaning roller 31, and d (μm) represents liquid thickness of liquid developer at the nip portion T3.
E=β/d Expression 3
The electric field can be calculated by modeling a path from the cleaning roller 31 via resistors of liquid developer and the intermediate transfer belt 21 to the counter roller 40 as a series circuit and performing circuit calculation thereof. As an example, the voltage applied to the cleaning roller 31 is 1000 (V), the electric resistivity of liquid developer is 6.0E+6 (Ω·cm), and the liquid thickness of the liquid developer is 2 (μm). Further, the electric resistivity of the intermediate transfer belt 21 is 1.0E+10 (Ω·cm) and the thickness of the intermediate transfer belt 21 is 100 (μm). In this case, the electric field is calculated to be approximately 90 (V/μm).
The nip length can be confirmed by momentarily stopping power such as by cutting off power supply during image forming operation and measuring the length of the nip portion T3 in the stopped state. The nip length is determined by the diameters of the cleaning roller 31 and the counter roller 40 and the deformation amount of the intermediate transfer belt 21. In the present embodiment, the diameter of the cleaning roller 31 is 28 mm and the diameter of the counter roller 40 is 21 mm. The surface roughness of the cleaning roller 31 and the counter roller 40 is less than 0.2 μm in accordance with JIS B 0031:2003 Standard. The surface roughness of these rollers can be measured using PU-OS400 (product of Kosaka Laboratory Ltd.)
The liquid thickness of the liquid developer is obtained by scraping off a portion of liquid developer from the surface of the intermediate transfer belt 21 having passed through the nip portion T3 using a scraper and the like and actually measuring the height difference of an area where liquid developer had been scraped off and an area where liquid developer had not been scraped off using a confocal microscope and the like. A value having doubled the actually measured height difference is set as the liquid thickness of liquid developer. That is, the liquid developer at the nip portion T3 is separated by and moved away from each other along the intermediate transfer belt 21 and the cleaning roller 31 after passing the nip portion T3. Thereby, the liquid thickness of the liquid developer on the surface of the intermediate transfer belt 21 after passing the nip portion T3 becomes half the liquid thickness of the liquid developer at the nip portion T3. Therefore, liquid thickness of liquid developer at the nip portion T3 can be calculated by doubling the height difference being actually measured as above. A confocal microscope VK8700 (product of Keyence Corp.) may be used as the confocal microscope, for example.
Cleaning Nip Portion
As described, toner is moved via liquid developer from the intermediate transfer belt 21 to the cleaning roller 31 by electrophoresis according to the present embodiment, so that the nip portion T3 must be formed to satisfy the nip length L stated in Expression 1. Therefore, the cleaning roller 31 and the counter roller 40 are arranged so that the intermediate transfer belt 21 is wound around the cleaning roller 31 according to the present embodiment. This arrangement will be described with reference to
As illustrated in
The cleaning roller 31 is fixed rotatably so as to press the intermediate transfer belt 21 from the outer side toward the inner side. Meanwhile, the counter roller 40 has bearings (not shown) that support both ends of the counter roller 40 which are urged by a pressurizing spring 41 so that the intermediate transfer belt 21 is pressed by the pressurizing spring 41 from the inner side toward the outer side. In the illustrated example, the cleaning roller 31 is fixed while the counter roller 40 is urged by the pressurizing spring 41, but any arrangement can be adopted as long as at least one of the cleaning roller 31 and the counter roller 40 is rotatably fixed and the other one of the rollers is urged by a spring.
The bending of the intermediate transfer belt 21 enables to increase the amount of winding of the intermediate transfer belt 21 around the cleaning roller 31 compared to a state where the intermediate transfer belt 21 is not bent. As described, the nip portion T3 includes the physical nip T3b and the tension nip T3a (refer to
In the present embodiment, the relationship between the nip length L and electric field E required to realize electrophoresis of toner can be expressed by Expression 4, which is a variation of Expression 1.
E>(d×P/μ)/L Expression 4
The relationship between nip length and intensity of electric field, i.e., electric field intensity, is illustrated in
In the present embodiment, the toner mobility may be set to 1.00−11 (m2/(V×s)). The toner mobility may drop by use, but if the toner mobility satisfies a minimum value, the cleaning performance by the belt cleaning device 30 can be ensured.
Next, a test was performed to compare cleaning performances between a case where the intermediate transfer belt 21 is bent by the cleaning roller 31 and the counter roller 40 formed of either a metal roller or a rubber roller and a case where the intermediate transfer belt 21 is not bent. The result of the test is shown in Table 1. The cleaning roller 31 used in the test had a diameter of 28 mm and the counter roller 40 used in the experiment had a diameter of 21 mm. The rubber roller had an elastic layer formed of urethane rubber with a thickness of 2 mm, and the Young's modulus thereof was 0.3 (MPa). First, second and fourth examples are comparative examples, and third and fifth examples correspond to the present embodiment.
As a first example, in a case where the cleaning roller 31 and the counter roller 40 are both rubber rollers, and the amount of projection of the cleaning roller 31 is “0 mm”, a nip portion T3 having a nip length of “1.5 mm” is formed. In this case, the amount of projection of the cleaning roller 31 is a distance between an external common tangent Z on the side of the intermediate transfer belt and an abutment position of the cleaning roller 31 and the intermediate transfer belt 21 which is the abutment position farthest from the external common tangent Z in the nip portion T3 (which is denoted by reference W in
As a second example, in a case where the cleaning roller 31 is a metal roller, the counter roller 40 is a rubber roller and the amount of projection of the cleaning roller 31 is “0”, the nip portion T3 having a nip length of “0.8 mm” is formed. In this case, as illustrated in Table 1, a satisfactory cleaning performance could not be obtained even if the electric field intensity was increased (115 (V/μm)) from that in the first example. This is because the metal roller is not easily deformed compared to the rubber roller and only a nip length shorter than that in the first example can be obtained, so that a nip portion T3 long enough for forming a solution layer having sufficient liquid developer for moving the toner by electrophoresis cannot be ensured. Therefore, as a third example, a nip length of “1.5 mm” which is equivalent to the first embodiment is ensured by arranging the cleaning roller 31 to be projected by an amount of projection of “5 mm”, that is, by bending the intermediate transfer belt 21. By ensuring a nip length of “1.5 mm”, a satisfactory cleaning effect can be obtained by an electric field intensity of 85 (V/μm), as shown in Table 1.
As a fourth example, in a case where both the cleaning roller 31 and the counter roller 40 are metal rollers and the amount of projection of the cleaning roller 31 is “0”, the nip portion T3 having a nip length of “0.3 mm” is formed. In this case, a satisfactory cleaning performance could not be obtained even if the electric field was increased significantly (300 (V/μm)) more than that in the first example, as illustrated in Table 1. This is because only a short nip length can be obtained between two metal rollers, and a nip portion T3 long enough for forming a solution layer having sufficient liquid developer for moving the toner by electrophoresis cannot be ensured. Further, the electric field intensity becomes too high and discharge may occur. Therefore, as a fifth example, the amount of projection of the cleaning roller 31 is set to “7 mm” which is greater than that of the third example. Thereby, a nip length of “1.5 mm” which is equivalent as the first example can be ensured, and a satisfactory cleaning performance can be obtained by an electric field intensity of 85 (V/μm), as shown in Table 1.
As described, according to the present embodiment, the intermediate transfer belt 21 is pressed inward from the outer side by the cleaning roller 31 so as to ensure the nip portion T3 long enough for forming a solution layer of liquid developer sufficient for moving toner by electrophoresis. Thereby, the amount of winding of the intermediate transfer belt 21 around the cleaning roller 31 is increased, and the tension nip T3a can be elongated. The tension nip T3a can be elongated to ensure the nip portion T3 having a nip length long enough to move the toner on the intermediate transfer belt 21 sufficiently by electrophoresis (refer to Expression 1). As described, the present embodiment enables to ensure a nip portion T3 enough to allow toner on the intermediate transfer belt 21 to be moved sufficiently by electrophoresis. Thereby, enhancement of durability of the cleaning roller 31 and improvement of cleaning performance can both be realized.
A second embodiment will be described with reference to
As illustrated in
Unlike the first embodiment, the cleaning roller 31 and the counter roller 40 are arranged in an offset manner. That is, the cleaning roller 31 is arranged so that a first intersection N of the external common tangent Z and a perpendicular line passing a center of rotation M of the cleaning roller 31 is deviated in the direction of movement from a second intersection Q of the external common tangent Z and a perpendicular line passing a center of rotation O of the counter roller 40. However, according to the present embodiment, a center position in the direction of movement of the physical nip T3b is arranged downstream of the center position in the direction of movement of the nip portion T3 (refer to
The nip portion T3 having a nip length that satisfies Expression 1 described above can be formed by arranging the cleaning roller 31 and the counter roller 40 in an offset manner, without having to increase the amount of projection of the cleaning roller 31 compared to the first embodiment described earlier. That is, as illustrated in
According to the present embodiment, the cleaning roller 31 should preferably be arranged to abut against the intermediate transfer belt 21 upstream of the counter roller 40 in the direction of movement of the intermediate transfer belt 21, as illustrated in
The above-described discharge will be described based on
Meanwhile, discharge will not easily occur at the upstream side in the direction of movement if the cleaning roller 31 is arranged in an offset manner on the upstream side of a counter roller 402 in the direction of movement. In this case, current from the intermediate transfer belt 21 toward the counter roller 402 concentrates at the physical nip T3b after charge injection from the cleaning roller 31 to the intermediate transfer belt 21 occurs at the tension nip T3a. Then, the potential difference between the surface of the cleaning roller 31 and the surface of the intermediate transfer belt 21 will not be increased at the upstream side in the direction of movement of the intermediate transfer belt 21, and discharge will not occur easily. Further according to this case, even if discharge occurs at the physical nip T3b on the downstream side in the direction of movement of the intermediate transfer belt 21, a large portion of toner has already moved to the cleaning roller 31, so that there is very little impact on the cleaning performance.
Table 2 shows the result of having compared the cleaning performances of cases where the cleaning roller 31 and the counter roller 40 are offset upstream in the direction of movement and offset downstream in the direction of movement. Further, the cleaning performance of a case where the cleaning roller 31 is not offset with respect to the counter roller 40 is also shown for reference (center of Table 2).
As can be recognized from Table 2, if the cleaning roller 31 and the counter roller 40 are arranged in an offset manner, the cleaning performance is more preferable when the cleaning roller 31 is arranged in an offset position upstream of the counter roller 402 in the direction of movement. In contrast, when the cleaning roller 31 is arranged in an offset position downstream of the counter roller 402 in the direction of movement, discharge occurs upstream in the direction of movement as described earlier, and some remaining toner occurs. The density of remaining toner is measured by a densitometer manufactured by X-Rite, Inc., and the result was approximately 0.008. This shows that the cleaning performance has been deteriorated compared to a case where the density of the remaining toner is approximately 0.003 or less with the cleaning roller 31 arranged in an offset position upstream of the counter roller 402 in the direction of movement.
As described, according to the second embodiment, the nip portion T3 sufficient for moving the toner on the intermediate transfer belt 21 by electrophoresis can be easily ensured by arranging the cleaning roller 31 and the counter roller 40 in an offset manner. Specifically, a preferable cleaning performance can be realized by arranging the cleaning roller 31 in an offset position upstream of the counter roller 402 in the direction of movement (refer to
The first and second embodiments described above have illustrated an example of bending the intermediate transfer belt 21 by pressing the intermediate transfer belt 21 from the outer side toward the inner side by the cleaning roller 31, but the present disclosure is not limited to this example. For example, the intermediate transfer belt 21 can be bent by pressing the intermediate transfer belt 21 from the inner side toward the outer side by the counter roller 40. A third embodiment will be described with reference to
As illustrated in
The counter roller 40 presses the intermediate transfer belt 21 from the inner side toward the outer side by the pressurizing spring 41. Meanwhile, the cleaning roller 31 is rotatably fixed so as to press the intermediate transfer belt 21 from the outer side toward the inner side.
In the present embodiment, the amount of winding of the intermediate transfer belt 21 around the cleaning roller 31 is not increased by simply bending the intermediate transfer belt 21 outward. If the amount of winding of the intermediate transfer belt 21 is not increased, the tension nip T3a cannot be elongated, and the nip length of the nip portion T3 cannot be set to a length satisfying the above Expression 1. Therefore, according to the present embodiment, the cleaning roller 31 and the counter roller 40 must be arranged in an offset manner in a state where the physical nip T3b is formed. By arranging the cleaning roller 31 and the counter roller 40 in an offset manner, it becomes possible to ensure the nip portion T3 capable of enabling toner on the intermediate transfer belt 21 to be moved sufficiently by electrophoresis. Even according to this case, similar to the second embodiment described above (refer to
As described, even according to the third embodiment, the nip portion T3 capable of sufficiently moving the toner on the intermediate transfer belt 21 by electrophoresis can be ensured easily. Thereby, both enhancement of durability and improvement of cleaning performance of the cleaning roller 31 can be realized.
There may be a case where the intermediate transfer belt 21 is wound around and supported by an idler roller in addition to the driving roller 23, the tension roller 24 and the secondary transfer inner roller 25. An idler roller may be arranged downstream of the secondary transfer inner roller 25 and upstream of a cleaning tip portion T3 with respect to the direction of movement of the intermediate transfer belt 21 to tension the intermediate transfer belt 21. In this case, the idler roller will affect the nip length of the nip portion T3 instead of the secondary transfer inner roller 25 described above. The image forming apparatus equipped which such an idler roller is illustrated in
As illustrated in
Cleaning Nip Portion
Also according to the present embodiment, similar to the embodiments described earlier, the nip portion T3 having the nip length L that satisfies Expression 1 described above must be formed to move toner from the intermediate transfer belt 21 to the cleaning roller 31 via liquid developer by electrophoresis (refer to
As illustrated in
The intermediate transfer belt 21 is pressed by the cleaning roller 31 with a predetermined contact pressure. If the contact pressure is too high, not only the deterioration of the intermediate transfer belt 21 mentioned earlier is hastened but also the driving load of the driving roller 23 may increase and wear of the bearing that supports each roller may be hastened by the increase of load to each roller tensioning the intermediate transfer belt 21. On the other hand, if the contact pressure is too small, the cleaning roller 31 may fluctuate while the intermediate transfer belt 21 is driven, and amount of winding of the intermediate transfer belt 21 around the cleaning roller 31 may be varied. That is, the size, i.e., contact area, of the nip portion may fluctuate during driving of the belt. Therefore, according to the present embodiment, the positional relationship of the three rollers is determined so that the contact pressure between the intermediate transfer belt 21 and the cleaning roller 31 is set to 30 N or greater and 300 N or smaller, as described earlier, and each roller is fixed to position. The adjustment of contact pressure between the intermediate transfer belt 21 and the cleaning roller 31 can be realized by the tension roller 24 (refer to
Since the intermediate transfer belt 21 is bent inward by three rollers, which are the cleaning roller 31, the idler roller 80 and the driving roller 23 according to the present embodiment, the contact pressure is stabilized, and the size of the nip portion T3 will not be varied while driving the belt. In other words, by fixing the three rollers, the intermediate transfer belt 21 will not return to a linear state even if force acts on the intermediate transfer belt 21 to return the belt from the approximately U-shaped bent shape to a linear shape while the intermediate transfer belt 21 is driven, so that the size of the nip portion T3 is not easily varied. For example, fluctuation or deviation of the intermediate transfer belt 21 caused by the recording material P entering the secondary transfer portion T2 is suppressed by the three rollers mentioned above, and the size of the nip portion T3 will not be easily varied. The fluctuation of the intermediate transfer belt 21 is further suppressed by the tension roller 24 according to the present embodiment, so that the variation of size of the nip portion T3 is even further suppressed by cooperation of the three rollers and the tension roller 24.
In a state where the intermediate transfer belt 21 is bent, the amount of winding of the intermediate transfer belt 21 with respect to the cleaning roller 31 is increased compared to a case where the intermediate transfer belt 21 is not bent. As described above, the nip portion T3 includes the physical nip T3b and the tension nip T3a (refer to
The present embodiment presses the intermediate transfer belt 21 from the outer side toward the inner side by the cleaning roller 31 so as to bend the intermediate transfer belt 21 and ensure the nip portion T3 capable of forming a solution layer of liquid developer sufficient to move the toner by electrophoresis. Thereby, the amount of winding of the intermediate transfer belt 21 with respect to the cleaning roller 31 is increased, and the tension nip T3a can be elongated. The tension nip T3a can be elongated so that the nip length of the nip portion T3 has sufficient length to move the toner on the intermediate transfer belt 21 by electrophoresis (refer to Expression 1). Further, the cleaning roller 31 is fixed to an outer circumferential side of the intermediate transfer belt 21 so that the intermediate transfer belt 21 is not displaced with respect to the idler roller 80 and the driving roller 23 which tensions the belt. Since the intermediate transfer belt 21 is bent by these three fixed rollers, the size, i.e., contact area, of the nip portion T3 is not easily varied while driving the belt. As described, according to the present embodiment, the nip portion T3 enough to move the toner on the intermediate transfer belt 21 by electrophoresis and suppressing variation of the contact area while driving the belt can be ensured easily.
According to the present embodiment, as illustrated in
The belt cleaning device 30 described above is applicable to a secondary transfer belt cleaning device for cleaning an endless secondary transfer belt serving as a belt member. This example will be described below. In the following description, configurations similar to the respective embodiments described earlier are denoted with the same reference numbers, and descriptions thereof are omitted or simplified.
Secondary Transfer Unit
As illustrated in
The secondary transfer belt 51 is an endless belt tensioned by the secondary transfer outer roller 26, the separation roller 53, the idler roller 54 and the belt driving roller 56. The secondary transfer belt 51 is rotated in the direction of arrow R4 in the drawing by the belt driving roller 56 in synchronization with the intermediate transfer belt 21, conveying the recording material P through the secondary transfer portion T2 to a fixing unit knot shown). The belt driving roller 56 tensions the secondary transfer belt 51 downstream of the idler roller 54 in the direction of movement of the secondary transfer belt 51. A resin belt is adopted as the secondary transfer belt 51. Specifically, the resin belt is formed of polyimide.
The secondary transfer outer roller 26 is in pressure contact with the secondary transfer inner roller 25 via the intermediate transfer belt 21 and the secondary transfer belt 51, and forms the secondary transfer portion T2 between the intermediate transfer belt 21 and the secondary transfer belt 51. A secondary transfer voltage having opposite polarity as that of the toner is applied to the secondary transfer outer roller 26 from a high voltage power supply knot shown), and a transfer electric field is generated at the secondary transfer portion T2 in accordance therewith. In response to this transfer electric field, yellow, magenta, cyan and black toner images borne on the intermediate transfer belt 21 are collectively secondarily transferred to the recording material P.
The separation roller 53 separates the recording material P from the secondary transfer belt 51 at a position downstream of the secondary transfer portion T2 in the direction of movement of the secondary transfer belt 51. Specifically, after reaching the separation roller 53, the recording material P on the secondary transfer belt 51 is self-stripped from the secondary transfer belt 51 on a curved surface of the secondary transfer belt 51 curved along the circumferential surface of the separation roller 53. According to the present embodiment, the separation roller 53 applies predetermined tension to the secondary transfer belt 51 by urging the secondary transfer belt 51 from the inner side toward the outer side by urging force of a pressure spring knot shown). In other words, the separation roller 53 also serves as a tension roller.
The recording material P self-stripped from the secondary transfer belt 51 is conveyed to a fixing unit (not shown), and the toner image is fixed to the recording material P at the fixing unit. The recording material P to which the toner image has been fixed is discharged to the exterior of the apparatus body. After the passing of the recording material P through the secondary transfer portion T2, toner on the secondary transfer belt 51 is removed by the secondary transfer cleaning device 30A. The secondary transfer cleaning device 30A will be described in detail later with reference to
A fifth embodiment will now be described with reference to
Regarding the external common tangents of the idler roller 54 and the belt driving roller 56, the secondary transfer belt 51 is projected inwardly of the external common tangent Z on the side of the secondary transfer belt. At least one of the rollers of the idler roller 54 and the belt driving roller 56 is provided on a same side as the cleaning roller 31 with respect to a tangent I that passes an intersection J of the counter roller 40 and a straight line H connecting a center of rotation of the counter roller 40 and a center of rotation of the cleaning roller 31. In the illustrated example, the positional relationship of the cleaning roller 31, the idler roller 54 and the belt driving roller 56 is determined so that both the idler roller 54 and the belt driving roller 56 are provided on the same side as the cleaning roller 31. The cleaning roller 31, the idler roller 54 and the belt driving roller 56 are fixed so as not to move from their positions. Thereby, the nip portion T4 long enough to allow the toner on the secondary transfer belt to move by electrophoresis and having suppressed the variation of contact area during driving of the belt can be ensured easily.
A sixth embodiment will be described with reference to
A seventh embodiment will be described with reference to
The cleaning rollers 31a and 31b are fixed rotatably to the outer circumferential side of the secondary transfer belt 51 so as not to be displaced with respect to the idler roller 54 and the tension roller 55. In the present embodiment, the positional relationship of four rollers, which are the cleaning rollers 31a and 31b, the idler roller 54 and the tension roller 55, is determined so that the secondary transfer belt 51 is projected inwardly of the external common tangent Z which is positioned on the side of the secondary transfer belt. The rollers are fixed so as not to move from their positions. Thereby, the effect described above of ensuring the nip portion T4 long enough to allow the toner on the secondary transfer belt to move by electrophoresis and having suppressed the variation of contact area during driving of the belt is obtained.
An eight embodiment will be described with reference to
According to the present embodiment, as illustrated in
In the seventh and eighth embodiments described above, the polarities of voltages applied from the power supply 36 to the cleaning rollers 31 of the secondary transfer cleaning devices 30A arranged on both the upstream side and the downstream side in the direction of movement of the secondary transfer belt 51 are the same.
Even according to the fifth to eighth embodiments described above, similar to the second embodiment described earlier, it is preferable to position the cleaning roller(s) 31 (31a and 31b) in an offset manner downstream of the counter roller 40 in the direction of movement.
Other Embodiments
In the first to eighth embodiments described above, an example of having applied the present invention to the belt cleaning device 30 and the secondary transfer cleaning device 30A have been illustrated, but the present disclosure is not limited thereto. The present disclosure is applicable to a primary transfer portion T1 for transferring toner to the intermediate transfer belt 21 from photosensitive drums 11Y to 11K. In this case, the photosensitive drums 11Y to 11K correspond to outer rollers and the primary transfer rollers 22Y to 22K correspond to inner rollers. Further, the embodiment is applicable to a secondary transfer portion T2 where the toner image is transferred from the intermediate transfer belt 21 to the recording material P. In this case, the secondary transfer inner roller 25 corresponds to an inner roller and the secondary transfer outer roller 26 correspond to an outer roller.
The first to eighth embodiments have been described assuming that the physical nip T3b is formed, but the present disclosure is not limited thereto. For example, the counter roller 40 may be offset further downstream so that only the tension nip T3a is formed between the cleaning roller 31 and the intermediate transfer belt 21 without forming the physical nip T3b. A belt cleaning device in which the physical nip T3b is not formed will be described with reference to
A tangent I′ of the cleaning roller 31 at a center position S of the nip portion T3 in the direction of movement of the intermediate transfer belt 21 is considered, as illustrated in
If the roller initially tensioning the intermediate transfer belt 21 downstream of the cleaning roller 31 in the direction of movement of the intermediate transfer belt 21 is set as a first roller, the first roller will be the counter roller 40. The counter roller 40 is arranged so that the position of abutment against the intermediate transfer belt 21 is at a position not overlapped with the tension nip T3a with respect to the direction of movement of the intermediate transfer belt 21 (refer to
The present image forming apparatus is especially preferably applied to an apparatus using liquid developer.
The present invention is not limited to the embodiments described above, and various changes and modifications are enabled without departing from the scope of the present invention. The following claims define the scope of the present invention, which is to be accorded the broadest interpretation.
Embodiment(s) of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-243646 | Dec 2017 | JP | national |
| JP2017-243647 | Dec 2017 | JP | national |
This application is a Continuation of International Patent Application No. PCT/JP2018/042175, filed Nov. 14, 2018, which claims the benefit of Japanese Patent Application No. 2017-243647, filed Dec. 20, 2017 and Japanese Patent Application No. 2017-243646, filed Dec. 20, 2017, which are hereby incorporated by reference herein in their entirety.
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| 20100046990 | Kamijo et al. | Feb 2010 | A1 |
| 20110182611 | Hofmann et al. | Jul 2011 | A1 |
| 20170108803 | Paul | Apr 2017 | A1 |
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| JP_2009244840_A_T MachineTranslation, Japan, Oct. 2009, Nishimura. |
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| Number | Date | Country | |
|---|---|---|---|
| 20200319576 A1 | Oct 2020 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2018/042175 | Nov 2018 | US |
| Child | 16904691 | US |
