JP7438687B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus such as a laser printer, a copying machine, or a facsimile machine using an electrophotographic method or an electrostatic recording method.

2. Description of the Related Art Conventionally, as an image forming apparatus using an electrophotographic method, for example, there is an intermediate transfer type image forming apparatus equipped with an intermediate transfer body. In this image forming apparatus, a toner image formed on a photoconductor (electrophotographic photoconductor) is primarily transferred to an intermediate transfer body at a primary transfer section, and then the toner image on the intermediate transfer body is transferred to a transfer material at a secondary transfer section. Secondary transfer is made to . As the intermediate transfer body, an intermediate transfer belt formed of an endless belt is widely used. Further, the secondary transfer is often performed using a secondary transfer roller, which is a roller-shaped secondary transfer member that comes into contact with the intermediate transfer body to form a secondary transfer portion.

In the secondary transfer section, the transfer material is conveyed while being sandwiched between the intermediate transfer body and the secondary transfer roller. At this time, a configuration in which the secondary transfer roller is driven by a gear and the transfer material obtains a conveying force by the frictional force between the intermediate transfer body and the secondary transfer roller (hereinafter referred to as "secondary transfer drive configuration") is adopted. be. On the other hand, from the perspective of cost control, there is a configuration in which a secondary transfer roller rotates following the rotation of an intermediate transfer body via a transfer material (hereinafter referred to as a "secondary transfer driven configuration") (Patent Document 1) ).

In addition, the conveyance speed of the transfer material by the registration roller pair is set so that the transfer material is loosened between the registration roller pair and the secondary transfer section, and the transfer material is aligned with the intermediate transfer body. A configuration for suppressing image defects that occur is also known (Patent Document 2). Note that the registration roller pair is a pair of rollers arranged upstream of the secondary transfer section in the conveyance direction of the transfer material and used to adjust (registration) the timing of conveyance of the transfer material to the secondary transfer section. It is.

Japanese Patent Application Publication No. 2016-194593 Japanese Patent Application Publication No. 2006-267656

In the secondary transfer driven configuration described above, the transfer material cannot receive the conveyance force from the secondary transfer roller, so the conveyance force that the transfer material receives in the secondary transfer section is due to the frictional force between the intermediate transfer body and the transfer material. Depends on. Therefore, in the secondary transfer driven configuration, the conveying force that the transfer material receives in the secondary transfer section is also affected by the surface properties of the transfer material and the presence or absence of toner. If the conveyance force of the transfer material in the secondary transfer section changes depending on the presence or absence of toner, the elongation (overall magnification) of the image may change depending on the image pattern formed on the transfer material, or There is a risk that the transfer material may be skewed while passing through.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to suppress skewing of a transfer material in a secondary transfer section in an image forming apparatus in which a secondary transfer rotating body rotates following rotation of an intermediate transfer body.

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides an image carrier that carries a toner image, a movable intermediate transfer member to which the toner image is primarily transferred from the image carrier, and a movable intermediate transfer member that is in contact with the intermediate transfer member. a secondary transfer rotary body that forms a secondary transfer portion that secondarily transfers the upper toner image onto a transfer material, the secondary transfer rotary body rotating in accordance with the movement of the intermediate transfer body; In the image forming apparatus, the surface of the intermediate transfer body has a plurality of grooves along the movement direction of the surface of the intermediate transfer body with respect to the width direction of the intermediate transfer body that intersects with the movement direction of the intermediate transfer body. are formed, the plurality of grooves are formed periodically at a predetermined period in the width direction , and the shape of the plurality of grooves in a cross section perpendicular to the movement direction is a rectangular wave shape, On the surface of the intermediate transfer body, the width of each groove in the width direction is less than the average particle diameter of the toner, and at the beginning of the preset life period of the intermediate transfer body and at the end of the life time. , the coefficient of kinetic friction between the surface of the intermediate transfer body and the predetermined transfer material is determined by determining the coefficient of kinetic friction between the intermediate transfer body and the predetermined transfer material, when no toner image is present between the intermediate transfer body and the predetermined transfer material , and when a predetermined toner image is present between the intermediate transfer body and the predetermined transfer material. The coefficient of dynamic friction when the toner image is not present is μ1, the coefficient of dynamic friction when the predetermined toner image is present is μ2 , and the difference between μ1 and μ2 (μ1−μ2). is the dynamic friction coefficient difference Δμ, the predetermined transfer material is coated paper with a Beck smoothness of 250 to 500 seconds, and the predetermined toner image is a halftone image in which the area ratio of the toner-covered portion is 50%. In the image forming apparatus, the intermediate transfer body is an endless belt satisfying Δμ<0.3 at the beginning of the life period and at the end of the life period.

According to the present invention, in an image forming apparatus in which a secondary transfer rotating body rotates following rotation of an intermediate transfer body, it is possible to suppress skewing of a transfer material in a secondary transfer section.

FIG. 1 is a schematic cross-sectional view of an image forming apparatus. FIG. 2 is a schematic top view and a schematic enlarged partial sectional view of an intermediate transfer belt. FIG. 3 is a schematic diagram of an image pattern used for evaluating skew. FIG. 3 is a schematic diagram for explaining skew. FIG. 3 is an enlarged schematic diagram of an image pattern used for evaluating skew. FIG. 2 is a schematic diagram of a device for measuring the coefficient of dynamic friction between an intermediate transfer belt and a transfer material. FIG. 7 is a schematic top view of another example of the intermediate transfer belt. FIG. 7 is a schematic enlarged partial sectional view of another example of the intermediate transfer belt.

Hereinafter, the image forming apparatus according to the present invention will be explained in more detail with reference to the drawings.

[Example 1]
1. Overall Configuration and Operation of Image Forming Apparatus FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment is a tandem laser beam printer that employs an intermediate transfer method and is capable of forming full-color images using an electrophotographic method.

The image forming apparatus 100 has four stations 10Y, 10M, 10C, and 10K that form yellow (Y), magenta (M), cyan (C), and black (K) images, respectively, as a plurality of image forming units. have For elements with the same or corresponding functions or configurations in each station 10Y, 10M, 10C, 10K, the suffix Y, M, C, K is omitted to indicate that the element is for one of the colors. I may give a general explanation. In this embodiment, the station 10 includes a photosensitive drum 1, a charging roller 2, an exposure device 3, a developing device 4, a primary transfer roller 5, a drum cleaning device 6, etc., which will be described later.

A photosensitive drum 1, which is a rotatable drum-shaped (cylindrical) photosensitive member serving as an image carrier carrying a toner image, is moved in the direction of arrow R1 (clockwise) by a drive motor (not shown) as a drive means. rotational direction) at a predetermined process speed (peripheral speed). The surface of the rotating photosensitive drum 1 is charged to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by a charging roller 2, which is a roller-shaped charging member serving as a charging means. During the charging process, a predetermined charging voltage (charging bias) is applied to the charging roller 2 by a charging power source (not shown). The charged surface of the photosensitive drum 1 is scanned and exposed according to image information by an exposure device 3 serving as an exposure means, and an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 1. In this embodiment, the exposure device 3 is composed of a scanner unit that scans laser light with a polygon mirror, and irradiates the photosensitive drum 1 with a scanning beam modulated based on an image signal corresponding to each image forming section 10. . The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) by supplying toner as a developer by a developing device 4 serving as a developing means, and a toner image (toner image) is formed on the photosensitive drum 1. be done.

An intermediate transfer belt 8, which is an endless belt and serves as a movable intermediate transfer member, is arranged so as to face the four photosensitive drums 1. The intermediate transfer belt 8 is stretched with a predetermined tension by a plurality of drive rollers 9a as support rollers (stretching rollers), a tension roller 9b, and a secondary transfer opposing roller (secondary transfer inner roller) 9c. There is. The intermediate transfer belt 8 is rotated by a drive roller 9a by a drive motor (not shown) serving as a drive means, and a driving force is transmitted to the intermediate transfer belt 8 to perform a predetermined process in the direction of arrow R2 (counterclockwise direction) in the figure. Moves (rotates) at speed (peripheral speed). Note that the intermediate transfer belt 8 will be described in more detail later. On the inner peripheral surface side of the intermediate transfer belt 8, a primary transfer roller 5, which is a roller-shaped primary transfer member serving as a primary transfer means, is arranged. The primary transfer roller 5 is urged toward the photosensitive drum 1 via the intermediate transfer belt 8 with a predetermined pressure, and forms a primary transfer portion (primary transfer nip) N1 where the photosensitive drum 1 and the intermediate transfer belt 8 are in contact with each other. do. The toner image formed on the photosensitive drum 1 as described above is primarily transferred onto the rotating intermediate transfer belt 8 by the action of the primary transfer roller 5 in the primary transfer portion N1. During the primary transfer, the primary transfer voltage (primary transfer bias) is applied to the primary transfer roller 5 by the primary transfer power source E1, which has the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner (the charging polarity during development). ) is applied. For example, when forming a full-color image, toner images of each color of Y, M, C, and K formed on each photosensitive drum 1 are sequentially transferred so as to be superimposed on the intermediate transfer belt 8 at each primary transfer portion N1. be done.

On the outer peripheral surface side of the intermediate transfer belt 8, at a position facing the secondary transfer opposing roller 9c, there is a secondary transfer member, which is a rotatable roller-shaped secondary transfer member (secondary transfer rotating body) serving as a secondary transfer means. A transfer roller (secondary transfer outer roller) 11 is arranged. The secondary transfer roller 11 is urged toward the secondary transfer opposing roller 9c via the intermediate transfer belt 8 with a predetermined pressure, and the secondary transfer roller 11 is in a secondary transfer portion ( Form a secondary transfer nip (secondary transfer nip) N2. The secondary transfer roller 11 contacts the intermediate transfer belt 8 directly or via the transfer material P, and rotates as the intermediate transfer belt 8 rotates (secondary transfer driven configuration). The toner image formed on the intermediate transfer belt 8 as described above is conveyed while being sandwiched between the intermediate transfer belt 8 and the secondary transfer roller 11 by the action of the secondary transfer roller 11 in the secondary transfer portion N2. Secondary transfer is performed onto the transfer material that is used. During the secondary transfer, a secondary transfer voltage (secondary transfer bias) having a polarity opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 11 by the secondary transfer power source E2. The secondary transfer opposing roller 9c is electrically grounded (connected to the ground). A secondary transfer voltage having the same polarity as the normal charging polarity of the toner is applied to the roller corresponding to the secondary transfer counter roller 9c of this embodiment, and the roller corresponding to the secondary transfer roller 11 of this embodiment is electrically charged. It may be grounded.

Transfer materials (recording materials, sheets) P such as recording paper are loaded in a transfer material storage section (cassette, etc.) in a feeding/conveying device (not shown), and are transported from this transfer material storage section by a feeding roller or the like. It is sent out and conveyed to the registration roller pair 13 by a conveyance roller or the like. Then, this transfer material P is temporarily stopped and the skew is corrected by the registration roller pair 13, and is then conveyed to the secondary transfer section N2 in synchronization with the toner image on the intermediate transfer belt 8. . At this time, the moving speed (peripheral speed) of the surface of the registration roller pair 13 is adjusted so that the transfer material P is conveyed in at least a slack state between the registration roller pair 13 and the secondary transfer portion N2. It is set to be larger than the moving speed (peripheral speed) of the surface of No. 8. In this embodiment, the moving speed of the surface of the pair of registration rollers 13 is set to be +1% larger than the moving speed of the surface of the intermediate transfer belt 8. Note that the rotation of the registration roller pair 13 may be controlled so that the amount of slack in the transfer material P between the registration roller pair 13 and the secondary transfer portion N2 is approximately constant.

The transfer material P onto which the toner image has been transferred is conveyed to a fixing device 14 as a fixing means. The fixing device 14 heats the transfer material P in the process of sandwiching and conveying the transfer material P carrying an unfixed toner image by an endless fixing film 14a containing a heat source and a pressure roller 14b. Then, pressure is applied to fix (melt and fix) the toner image on the surface of the transfer material P. The transfer material P on which the toner image is fixed is discharged (output) to the outside of the apparatus main body 110 of the image forming apparatus 100.

Further, toner remaining on the photosensitive drum 1 during the primary transfer (primary transfer residual toner) is removed from the photosensitive drum 1 and collected by a drum cleaning device 6 serving as a photosensitive member cleaning means. The drum cleaning device 6 uses a cleaning blade 61 as a cleaning member disposed in contact with the surface of the photosensitive drum 1 to scrape off primary transfer residual toner from the surface of the rotating photosensitive drum 1 and clean it inside the cleaning container 62. to be accommodated. Further, on the outer circumferential surface side of the intermediate transfer belt 8, a belt cleaning device 20 as intermediate transfer body cleaning means is arranged at a position facing the tension roller 9b with the intermediate transfer belt 8 interposed therebetween. In other words, the belt cleaning device 20 is located downstream of the secondary transfer section N2 and at the primary transfer section N1 (the most upstream primary transfer section) in the moving direction of the surface of the intermediate transfer belt 8 (hereinafter also referred to as "belt conveyance direction"). N1Y) is located upstream. Toner (secondary transfer residual toner) and paper powder remaining on the intermediate transfer belt 8 during the secondary transfer are removed from the intermediate transfer belt 8 by the belt cleaning device 20 and collected. The belt cleaning device 20 uses a cleaning blade 21 as a cleaning member disposed in contact with the surface of the intermediate transfer belt 8 to scrape secondary transfer residual toner and the like from the surface of the intermediate transfer belt 8 that is moving around. , housed in the cleaning container 22. The toner collected by the drum cleaning device 6 and the belt cleaning device 20 is sent to a waste toner box (not shown) and stored therein by a collected toner conveying means (not shown).

In this embodiment, in each station 10, a photosensitive drum 1, a charging roller 2, a developing device 4, and a drum cleaning device 6 as process means that act on the photosensitive drum 1 are integrally formed into a cartridge to form a process cartridge P. are doing. The process cartridge P is removably attached to the apparatus main body 110. The process cartridge P is replaced with a new one when the toner in the developing device 4 runs out or when the photosensitive drum 1 reaches the end of its life.

Further, the intermediate transfer belt 8 supported by the three tension rollers 9a, 9b, and 9c, each of the primary transfer rollers 5, the belt cleaning device 20, etc. are integrated into a unit to constitute the belt unit 12. The belt unit 12 is removably attached to the apparatus main body 110. The belt unit 12 is replaced with a new one when the intermediate transfer belt 8 reaches the end of its life. Note that the period of use (life span) of the intermediate transfer belt 8 is an index that correlates with the amount of use of the intermediate transfer belt 8, such as the number of images formed, the number of rotations, and the rotation time from the initial use of the intermediate transfer belt 8 (when new). It is preset based on.

Further, in this embodiment, the developing device 4 uses a non-magnetic one-component developer as the developer. The developing device 4 includes a developing roller 41 as a developer carrying member, a developing container 42 containing developer, a developing blade 43 as a developer regulating means, and the like. In this embodiment, the charged polarity of the photosensitive drum 1 (in this embodiment, a negative toner charged to the same polarity as the color (reverse development). The toner in the developer container 42 is negatively charged by the developer blade 43 and applied onto the developer roller 41 . During development, the developing roller 41 carrying toner is brought into contact with or close to the photosensitive drum 1, and a predetermined negative developing voltage (developing bias) is applied to the developing roller 41 by a developing power source (not shown). Ru.

Further, the toner used in this example is constructed by externally adding silica fine particles having an average particle size of 20 nm to toner particles having an average particle size of 6.4 μm manufactured by an emulsion polymerization aggregation method. The average particle size refers to, for example, the weight average particle size, and can be measured by the Coulter method. The measurement was carried out using "Coulter Counter Multisizer 3" (manufactured by Beckman Coulter, Inc.) and the attached dedicated software "Beckman Coulter Multisizer 3 Version 3.51" (manufactured by Beckman Coulter, Inc.) for setting measurement conditions and analyzing measurement data. (manufactured by the company). Note that the method for producing toner particles is not limited to the emulsion polymerization aggregation method, and toner particles can be produced by other methods such as a pulverization method, a suspension polymerization method, and a dissolution/suspension method.

Further, in this embodiment, the cleaning blade 21 of the belt cleaning device 20 is configured by adhering an elastic blade made of an elastic material to a support plate serving as a support member. In this embodiment, a substantially rectangular galvanized steel plate was used as the support metal plate. Further, in this embodiment, as the elastic blade, a substantially rectangular plate-shaped urethane rubber blade using urethane rubber (polyurethane) as an elastic material was used. This cleaning blade 21 is arranged so as to be in a counter direction (a direction in which the tip of the free end side faces upstream in the belt transport direction) with respect to the belt transport direction, and the edge portion of the free end is located on the intermediate transfer belt 8. is in contact with the surface of

2. Intermediate Transfer Body Next, the intermediate transfer belt 8 in this embodiment will be explained. FIG. 2A is a schematic top view of the surface of the intermediate transfer belt 8 viewed from above. Further, FIG. 2(b) shows the surface layer of the intermediate transfer belt 8 when cut in a direction substantially perpendicular to the belt conveyance direction (hereinafter also referred to as the "belt width direction") (as viewed along the belt conveyance direction). FIG. 3 is a schematic enlarged partial sectional view of the vicinity.

The intermediate transfer belt 8 is an endless belt member (or film-like member) consisting of two layers, a base layer 81 and a surface layer 82. The base layer 81 is the thickest layer among the layers constituting the intermediate transfer belt 8 . The surface layer 82 constitutes the surface (outer peripheral surface) of the intermediate transfer belt 8 and supports the toner transferred from the photosensitive drum 1.

In this embodiment, the base layer 81 is a layer with a thickness of about 70 μm, which is made of polyethylene naphthalate resin and dispersed with, for example, carbon black as an electrical resistance adjuster. Examples of the material for the base layer 81 include thermoplastic resins such as polycarbonate, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polystyrene, polyamide, polyarylate polyethylene naphthalate, polybutylene naphthalate, and thermoplastic polyimide. These can also be used in combination of two or more types. Note that as the electrical resistance adjuster (conductive agent), an ionic conductive agent may be used in addition to an electronic conductive agent.

Further, in this embodiment, the surface layer 82 is a layer having a thickness of about 3 μm and is made of an acrylic resin as a base material and dispersed with, for example, zinc oxide as an electrical resistance adjuster. As the material for the surface layer 82, from the viewpoint of strength such as wear resistance and crack resistance, resin materials (curable resins) are preferable among curable materials. Among curable resins, acrylic materials containing unsaturated double bonds are preferable. Acrylic resins obtained by curing polymers are preferred. The unsaturated double bond-containing acrylic copolymer is available, for example, as Lucifral (trade name, manufactured by Nippon Paint Co., Ltd.), which is an acrylic ultraviolet curable hard coat material.

A conductive material (conductive filler, electric resistance adjuster) can be added to the surface layer 82 for the purpose of adjusting electric resistance. As the conductive material, an electronically conductive material or an ionically conductive material can be used. Examples of the electronic conductive material include particulate, fibrous, or flake carbon-based conductive fillers such as carbon black. Further, particulate, fibrous, or flake metallic conductive fillers such as silver, nickel, copper, zinc, aluminum, stainless steel, and iron may also be used. Further, examples thereof include particulate metal oxide-based conductive fillers such as zinc antimonate and tin oxide. Examples of the ionically conductive material include ionic liquids, conductive oligomers, and quaternary ammonium salts. One or more of these conductive materials may be selected as appropriate, and a mixture of electronically conductive materials and ionically conductive materials may be used.

Further, a solid lubricant may be added to the surface layer 82. The solid lubricant can be appropriately selected from polytetrafluoroethylene (PTFE) resin powder, vinyl fluoride resin powder, fluorine-containing particles such as fluorinated graphite, and copolymers thereof. In this example, in addition to the uneven surface shape described later, 40 parts by weight of PTFE resin powder is added to the material of the surface layer 82 (the base material of the surface layer 82 is 100 parts by weight; the same applies hereinafter). , the frictional resistance on the surface of the intermediate transfer belt 8 is reduced.

Note that by adding a conductive material, a solid lubricant, etc. to the material of the surface layer 82 described above, the ease with which the surface layer 82 wears (hereinafter also referred to as "wear rate") changes. The wear rate of the surface layer 82 of the intermediate transfer belt 8 of this embodiment in the durability evaluation described later is about 0.26 μm per 100K sheets (A4 size equivalent; the same applies hereinafter). Note that passing the transfer material P through the secondary transfer portion N2 is also referred to as "paper passing" here.

In this embodiment, the surface of the intermediate transfer belt 8 is subjected to fine unevenness processing to provide an uneven shape. In this embodiment, a plurality of grooves (groove shapes, groove portions) 83 are arranged regularly (periodically in this embodiment) in the belt width direction on the surface of the intermediate transfer belt 8 along the belt conveyance direction. It is formed. In this embodiment, the grooves 83 are present over substantially the entire circumferential direction (belt conveyance direction) of the intermediate transfer belt 8 . Further, in this embodiment, the grooves 83 are present over substantially the entire width direction of the intermediate transfer belt 8 (belt width direction). Note that in the belt width direction, the groove 83 corresponds to an area on the intermediate transfer belt 8 that can come into contact with the transfer material P at the secondary transfer portion N2 (approximately corresponds to an image forming area on the intermediate transfer belt 8 where a toner image can be formed). ) may be formed over substantially the entire area.

Generally, polishing processing, cutting processing, imprint processing, etc. are known as means for forming the fine unevenness shape. In this embodiment, from the viewpoint of shape stability, processing cost, and productivity, the means for forming the fine unevenness is made of acrylic resin, which is the base material of the surface layer 82 of the intermediate transfer belt 8 on which the fine unevenness is formed. We adopted imprint processing that takes advantage of photocurability.

In the imprint process, a mold (not shown) having fine irregularities that are opposite to the irregularities desired to be formed on the surface of the intermediate transfer belt 8 is pressed against the surface of the surface layer 82 of the intermediate transfer belt 8 . In this embodiment, the mold has a substantially cylindrical shape, and a convex portion is formed substantially parallel to the rotation direction of the cylinder. Thereby, by transferring the fine unevenness of the mold onto the surface of the surface layer 82 of the intermediate transfer belt 8, a desired unevenness can be formed on the surface of the intermediate transfer belt 8. The surface shape of the intermediate transfer belt 8 can be measured using, for example, a laser microscope VK-X250 manufactured by Keyence Corporation.

Here, the recess width (groove width) Wsc of the uneven shape on the surface of the intermediate transfer belt 8 is the width of the opening of the groove (recess) 83 in the belt width direction. In this embodiment, the recess width Wsc is approximately 1 μm. It is desirable that the recess width Wsc is sufficiently smaller than the toner particle diameter. Specifically, the recess width Wsc is preferably less than the average particle diameter of the toner, and more preferably less than half the average particle diameter of the toner. By making the recess width Wsc smaller than the average particle diameter of the toner, toner can be prevented from entering the groove 83 and passing through the cleaning blade 21. Further, from the viewpoint of suppressing the collapse of the convex portion of the mold, the concave portion width Wsc is preferably 0.5 μm or more. In the configuration of this embodiment, the width Wsc of the recessed portion of the intermediate transfer belt 8 is preferably in the range of 0.5 μm or more and 6 μm or less, and more preferably in the range of 1 μm or more and 3 μm or less.

Further, the depth (groove depth) d of the concave portion of the uneven surface of the intermediate transfer belt 8 is defined as the depth (groove depth) from the opening (position of the outermost surface 84) of the groove (concave portion) 83 in the thickness direction of the intermediate transfer belt 8. It is the depth to the bottom of 83. In this embodiment, the depth d of the recess is approximately 0.5 μm at the initial stage of use of the intermediate transfer belt 8. The depth d of the recess is preferably 0.2 μm or more and the thickness of the surface layer 82 or less at the initial stage of use of the intermediate transfer belt 8 . If the recess depth d is too small, the recesses may easily disappear due to abrasion of the surface layer 82 of the intermediate transfer belt 8, or cleaning defects may occur more easily. Further, by setting the depth d of the recess to be equal to or less than the thickness of the surface layer 82, the grooves 83 are formed so as not to reach the base layer 81 but to exist only in the surface layer 82. Here, the thickness of the surface layer 82 of the intermediate transfer belt 8 is typically about 1 μm or more and 5 μm or less, from the viewpoint of reducing durability due to being too thin and preventing cracking of the surface layer 82 due to being too thick. The thickness is about 1 μm or more and 3 μm or less.

Further, the width Wsv of the convex portion of the uneven shape on the surface of the intermediate transfer belt 8 is the width of the surface where the grooves 83 are not formed between adjacent grooves (concave portions) 83 in the belt width direction. In this embodiment, the convex portion width Wsv is approximately 19 μm. The convex portion width Wsv can be set so that the concave portion interval (groove interval, pitch) I of the uneven shape on the surface of the intermediate transfer belt 8 is set to a desired value. The recess interval I is the interval between one ends of the openings of adjacent grooves 83 in the belt width direction, and corresponds to the sum of the recess width Wsc and the convex width Wsv. In this embodiment, the grooves 83 are formed at a uniform pitch of approximately 20 μm (substantially the same recess interval I) over substantially the entire belt width direction, so that the average recess interval I is approximately 20 μm. The average recess interval I can be selected as appropriate from the viewpoint of reducing the frictional resistance of the intermediate transfer belt 8 as described later, but it is preferably in the range of 2 μm or more and 30 μm or less, and preferably in the range of 3 μm or more and 20 μm or less. It is more preferable that the range is within the range. If the average recess interval I is too small, it may become difficult to form a uniform uneven shape. Furthermore, if the average recess interval I is too large, it may become difficult to reduce the frictional resistance of the intermediate transfer belt 8, as will be described later.

Here, in the uneven shape formed by imprint processing, the width of the bottom of the groove (recessed portion) 83 may become small. Therefore, the width of the opening of the recess in the belt width direction (the above-mentioned recess width) Wsc is different from the width of the bottom of the recess Wbc, and the width of the top of the convex part (the above-mentioned convex width) Wsv and the width of the base of the convex part Wbv are different. may be different.

As described above, in this embodiment, the surface of the intermediate transfer belt 8 has a protrusion width Wsv of approximately 19 μm, a recess width Wsc of approximately 1 μm, and a recess depth d of approximately 0.5 μm along the belt width direction. The uneven shape is repeatedly formed at a predetermined period (approximately constant interval I between the recesses).

By forming the grooves 83 regularly (periodically in this embodiment) in the belt width direction by imprint processing, the following effects can be obtained. First, by reducing the contact area between the intermediate transfer belt 8 and the contact object, the effect of lowering the frictional resistance on the surface of the intermediate transfer belt 8 can be obtained. Thereby, as will be described later, it is possible to reduce the difference in the conveying force of the transfer material P depending on the presence or absence of toner in the secondary transfer portion N2. Furthermore, since approximately the same shape is repeatedly formed on the surface of the intermediate transfer belt 8, the variation in pressure applied to each convex shape in the belt width direction is small, and the wear of the surface layer 82 of the intermediate transfer belt 8 progresses more uniformly. Effects can be obtained. Thereby, it is possible to suppress a difference in the conveying force of the transfer material P in the secondary transfer portion N2 in the belt width direction throughout the period of use of the intermediate transfer belt 8.

3. Transfer material conveyance in the secondary transfer section <Image elongation and transfer material skew>
In this embodiment, in the secondary transfer portion N2, the transfer material P obtains a conveying force due to the frictional force between it and the intermediate transfer belt 8. The conveying force changes depending on the presence or absence of toner in the secondary transfer portion N2. In other words, when the amount of toner between the intermediate transfer belt 8 and the transfer material P is small, typically when there is no toner (hereinafter also referred to as "solid white paper passing"), the transfer material P and the intermediate transfer The belt 8 is likely to come into close contact with the intermediate transfer belt 8, and the frictional force between the intermediate transfer belt 8 and the transfer material P is increased. On the other hand, if a certain amount of toner exists between the intermediate transfer belt 8 and the transfer material P, the toner acts as a lubricant, especially when forming a uniform halftone image (hereinafter also referred to as "halftone paper passing"). ), the frictional force between the intermediate transfer belt 8 and the transfer material P is significantly reduced.

When the frictional force between the intermediate transfer belt 8 and the transfer material P decreases, a sufficient conveying force for the transfer material P may not be obtained by the secondary transfer portion N2 alone. In this embodiment, the transfer material P is conveyed in a relaxed state between the registration roller pair 13 and the secondary transfer section N2. In other words, the rotational speed (rotational speed) of the registration roller pair 13 is set so that the peripheral speed of the registration roller pair 13 is greater than the peripheral speed of the intermediate transfer belt 8, and the stiffness of the transfer material P is used to transfer the transfer material. It assists the conveying force of P. As a result, when solid white paper is passed, that is, the greater the frictional force between the intermediate transfer belt 8 and the transfer material P, the lower the conveyance speed of the transfer material P in the secondary transfer portion N2. On the other hand, when halftone paper is passed, that is, the smaller the frictional force between the intermediate transfer belt 8 and the transfer material P, the faster the conveyance speed of the transfer material P in the secondary transfer portion N2 becomes. In the image forming apparatus 100 of the present embodiment, the registration rollers are arranged so that the elongation of the image (overall magnification) falls within a predetermined range, that is, so that the conveyance speed of the transfer material P in the secondary transfer portion N2 falls within a predetermined range. 13 rotation speeds have been determined. The conveyance speed of the transfer material P is adjusted to be slightly slower than the target when passing a solid white sheet, and is adjusted so that the conveyance speed of the transfer material P is slightly faster than the target when passing a halftone sheet. As a result, the image will shrink slightly when solid white paper is fed, and the image will be slightly stretched when halftone paper is fed.

When a uniform image is formed on substantially the entire surface of the transfer material P, differences in image patterns become apparent as image elongation (overall magnification). On the other hand, in a direction substantially orthogonal to the conveyance direction of the transfer material P (hereinafter also referred to as the "transfer material width direction"), one half side has a solid white image without toner image, and the other half side has a uniform halftone image. , consider the case of forming an image as shown in FIG. 3 (hereinafter referred to as a "one-sided halftone image"). In this case, since the frictional force between the intermediate transfer belt 8 and the transfer material P differs in the width direction of the transfer material, the transfer material P being conveyed may be skewed. In other words, as shown in FIG. 4, when forming a one-sided halftone image, even if the transfer material P is not skewed when it reaches the secondary transfer portion N2 (see FIG. This results in the transfer material P being skewed (FIG. 4(b)). This is because the frictional force between the transfer material P conveyed from the registration roller pair 13 and the intermediate transfer belt 8 on the halftone image side is smaller than that on the solid white side due to the presence or absence of toner. This is because the conveyance speed is relatively higher on the image side than on the solid white side. Even if the difference in image elongation between when solid white paper is passed and when halftone paper is passed is kept within a predetermined range, the skew of the transfer material P is easily visible to the naked eye as a tilt of the image. Therefore, in order to obtain high-quality printed matter, a higher target is set for the skew of the transfer material P in the secondary transfer portion N2 than the elongation of the image.

Here, the amount of skew is defined as "deviation in the width direction of the transfer material P per length of the transfer material P in the conveyance direction". For example, "1.0% skew" means that when A4 size paper with a length of 297 mm in the conveyance direction is passed through, the paper deviates by about 3 mm in the width direction during conveyance. . As a result, the image is formed with a tilt relative to the transfer material P than intended.

In the image forming apparatus 100 of this embodiment, the upper limit of the amount of skew (tolerable amount of skew) throughout the entire operation of forming and outputting an image on the transfer material P is 0.5% (when passing A4 size paper). The deviation in the width direction of the transfer material P: ±1.4 mm). In this embodiment, the upper limit of the skew amount (tolerable skew amount) in the secondary transfer portion N2 is set to ±0.25% even when forming a one-sided halftone image.

Note that the amount of elongation and skew of the image also differs depending on the density of the halftone image to be formed. The halftone image described in the following description is a 50% halftone image in which the phenomenon is most likely to occur. Here, the 50% halftone image in this embodiment is a binary image in which black and white images of 2 dots x 2 dots are dispersed in a checkered pattern as shown in FIG. The amount is approximately 0.2 mg/ ^cm2 . Further, the output resolution of the image forming apparatus 100 of this embodiment is 600 dpi, and one dot is 42.3 μm. In this embodiment, the above-described halftone image is used, but the image pattern, toner color, and applied amount are not limited thereto. For example, the image pattern may be a horizontal line pattern, a dithered halftone, or the like. It is sufficient that the halftone image has an amount of applied toner that is approximately 50% of the amount of applied toner of a solid image (image with maximum density level). In this embodiment, in order to determine the magnification of the image and the skew of the transfer material P, the image for determination (halftone image on one side) includes both the solid white part and the halftone part of the transfer material P. Two dot lines were formed in a grid pattern at 1 cm intervals in each of the transport direction and the transfer material width direction.

<Evaluation of oblique movement suppression ability>
Next, a method for evaluating the ability to suppress skewing of the transfer material P (skewing suppressing ability) will be described. The above-mentioned one-sided halftone image is an image that is most likely to cause skewing of the transfer material P in the secondary transfer portion N2. Here, the skew of the transfer material P is determined using a one-sided halftone image. Specifically, if the amount of skew is less than 0.25%, it is determined to be good (◯), and if the amount of skew is 0.25% or more, it is determined to be poor (×). Note that if the skew in the secondary transfer portion N2 can be suppressed, changes in the image elongation due to the image pattern can also be suppressed, as can be seen from the explanation of the causes of image elongation and skew of the transfer material P described above.

<Measurement of dynamic friction coefficient between intermediate transfer belt and transfer material>
Next, a method for measuring the coefficient of dynamic friction between the intermediate transfer belt 8 and the transfer material P will be described. The skew of the transfer material P in the secondary transfer section N2 when forming a one-sided halftone image is caused by friction between the intermediate transfer belt 8 and the transfer material P due to the presence or absence of toner, as well as the change in image magnification. The larger the difference in force, the more likely it is to occur. Here, HP Laser Glossy Brochure Paper 200gsm (hereinafter also referred to as "gloss coated paper"), which has a high surface smoothness, is used as the transfer material P where skewing is likely to occur, and the intermediate transfer belt 8 and the transfer material P are The coefficient of kinetic friction between the two was measured. The smoothness (Beck smoothness) of this gloss coated paper was 250 to 500 seconds. The smoothness was measured using a Beck smoothness tester manufactured by Kumagai Riki Kogyo in accordance with the JIS P 8119 paper pulp test method.

The coefficient of dynamic friction between the intermediate transfer belt 8 and the gloss coated paper is calculated by the method described below using the apparatus shown in FIG. FIG. 6(a) is a sectional view of the dynamic friction coefficient measuring device, and FIG. 6(b) is a front view of the dynamic friction coefficient measuring device. First, the intermediate transfer belt 8 is stretched over an inner roller Rf made of stainless steel and having an axial length of 220 mm and an outer diameter of 18 mm. A rubber roller Rn whose rubber surface has an axial length of 212 mm and an outer diameter of 16 mm is pressed against the surface of the intermediate transfer belt 8 wound around the inner roller Rf with a pressing force of 44 N to form a nip portion. The rubber roller Rn is configured by providing a rubber layer with a thickness of 4 mm around a stainless steel core metal with an outer diameter of 8 mm. In the rubber roller Rn, both ends of the metal core are rotatably supported by bearings (not shown). The product hardness of the rubber roller Rn is approximately 30° (load: 4.9N) in terms of Asker-C hardness. The shaft of the inner roller Rf is fixed so as not to rotate, and the intermediate transfer belt 8 stretched around the inner roller Rf is also installed so as not to move. Gloss coated paper with a width of 216 mm is inserted into the nip. Then, the force required to pull this gloss coated paper in a direction substantially perpendicular to the nip portion at a speed of approximately 100 mm/sec (hereinafter also referred to as "pulling force") was measured using a force gauge (Nidec-Shimpo FGPX). -20). At this time, a reinforcing member (for example, a metal reinforcing plate (metal rod)) with a length longer than the width of the paper is wrapped around the tip of the gloss coated paper in the above-mentioned pulling direction to reinforce the gloss coated paper, and the reinforcing member is inserted into the nip. Pull it while keeping it approximately parallel to the part. Thereby, force is applied to the gloss coated paper substantially uniformly in the width direction of the paper via the reinforcing member. The reinforcing member may be made of a material and having a shape that is difficult to bend; here, a stainless steel rod with an outer diameter of 6 mm was used. In the rubber roller Rn, both ends of the core metal are held by bearings, and the effect on the pulling force is approximately zero. Therefore, the measured value obtained by the above measuring device is the force caused by the frictional resistance of the surface of the intermediate transfer belt 8 against the gloss coated paper. Note that the rubber roller Rn does not necessarily need to be held by a bearing; for example, a resin sliding bearing may be used as long as the influence of the rotational load of the rubber roller Rn on the measurement is understood in advance and subtracted from the measured value. good.

In order to calculate the difference in the dynamic friction coefficient between the intermediate transfer belt 8 and the transfer material P depending on the presence or absence of toner (hereinafter also simply referred to as "dynamic friction coefficient difference Δμ"), the following measurements are performed. First, the pull-out force (hereinafter also referred to as "solid white pull-out force") when there is no toner between the intermediate transfer belt 8 and the gloss coated paper is measured. Further, a 50% halftone image (unfixed halftone toner image) is formed in advance on gloss coated paper using black toner. Then, using the gloss coated paper on which the halftone image is formed, the pulling force (hereinafter also referred to as "halftone pulling force") when toner is present between the intermediate transfer belt 8 and the gloss coated paper is applied. Measure.

From the relationship between the pulling force F and the pressing force N, the dynamic friction coefficient μ between the intermediate transfer belt 8 and the gloss coated paper is calculated using the following equation (1). Here, it is assumed that the pulling force F under each condition (with toner, without toner) has the following value. That is, the average value of the pulling force in the latter half 100 mm of the paper where the pulling speed is stable is taken as the measured value per time, and the average value is obtained by repeating the measurement three times per condition. Note that, as described above, the pressurizing force N is 44N here.
μ=F/N (1)

When the dynamic friction coefficient corresponding to the solid white pulling force is "solid white dynamic friction coefficient μ1" and the dynamic friction coefficient corresponding to the halftone pulling force is "halftone dynamic friction coefficient μ2," the difference μ1 - μ2 is the dynamic friction coefficient described above. The difference is Δμ (Δμ=μ1−μ2).

Test results will be described later, but in this embodiment, the image forming apparatus 100 has a configuration that satisfies Δμ<0.3. This makes it possible to suppress the skew movement of the transfer material P when passing a halftone image on one side (typically to the above-mentioned "o" level). Furthermore, this makes it possible to suppress changes in image expansion due to the image pattern. If the image forming apparatus 100 is configured to satisfy Δμ<0.3 during at least part of the usage period (life span) of the intermediate transfer belt 8, a corresponding effect can be obtained. In this embodiment, the image forming apparatus 100 is configured to satisfy Δμ<0.3 at the beginning and end of the period of use of the intermediate transfer belt 8 (typically throughout the entire period of use). As a result, throughout the period of use of the intermediate transfer belt 8, the skew movement of the transfer material P in the secondary transfer portion N2 when passing a halftone image on one side is suppressed (typically to the above-mentioned "○" level). becomes possible. Furthermore, this makes it possible to suppress changes in image elongation due to the image pattern throughout the period of use of the intermediate transfer belt 8.

Note that the initial period of use (life span) of the intermediate transfer belt 8 corresponds to when the intermediate transfer belt 8 is new, but even if it is not immediately after starting to use it, it usually outputs about 10 to 100 images. Until then, it can be considered as new. Further, the end of the usage period of the intermediate transfer belt 8 typically corresponds to immediately before replacement due to the preset lifespan of the intermediate transfer belt 8, but is not limited thereto. The end of the period of use of the intermediate transfer belt 8 can be represented by a period from approximately the middle of the period of use to the time of replacement due to end of life, more specifically, a time closer to the time of replacement than approximately the middle of the period of use. For example, it may be possible to replace the intermediate transfer belt 8 based on the fact that the dynamic friction coefficient difference Δμ no longer satisfies the above-mentioned predetermined condition. In such a case, immediately before the intermediate transfer belt 8 is replaced, the dynamic friction coefficient difference Δμ may not satisfy the above-described predetermined condition.

<Evaluation test>
(Test method)
Below, the durability of the image forming apparatus was evaluated using intermediate transfer belts with different surface properties (this example, comparative examples 1 to 3), and the results of investigating the relationship between the skew feed suppression ability and the dynamic friction coefficient difference Δμ are presented. show. Specifically, the image forming apparatus 100 having the configuration of this embodiment was used, the intermediate transfer belt 8 manufactured by the above-mentioned manufacturing method was attached, and the OCE company A paper-running durability test was conducted using A4 paper manufactured by Extra, which has a basis weight of 80 g/m ² and printed intermittently on 4 sheets. Here, 4-sheet intermittent printing refers to a job that continuously passes 4 sheets (a series of operations to form and output an image on a single or multiple transfer materials that is started by one start instruction) at a predetermined interval. This is a repeated printing method. Note that the configurations of the intermediate transfer belt 8 and other image forming apparatuses 100 in each of the following comparative examples are substantially the same as in the present example except for the following points. In each comparative example, elements having the same or corresponding functions or configurations as those of the image forming apparatus 100 of the present embodiment will be described with the same reference numerals.

(Comparative example 1)
As Comparative Example 1, an intermediate transfer belt 8 was used in which 40 parts by weight of PTFE resin powder was added to the material of the surface layer 82, and the surface layer 82 was not subjected to surface roughening treatment, shape imparting treatment such as imprinting, etc. Durability evaluation was conducted. The additives and their amounts in the material of the surface layer 82 of the intermediate transfer belt 8 in Comparative Example 1 are the same as in this example. The wear rate in the durability evaluation of the intermediate transfer belt 8 of Comparative Example 1 is the same as that of this example, and is approximately 0.26 μm per 100K sheets of paper passed.

(Comparative example 2)
As Comparative Example 2, durability evaluation was performed using an intermediate transfer belt 8 in which 40 parts by weight of PTFE resin powder was added to the material of the surface layer 82 and the surface layer 82 was roughened. The surface roughening treatment of the surface layer 82 of the intermediate transfer belt 8 of Comparative Example 2 was performed as follows. A lapping film (Lapika #2000 (trade name), manufactured by KOVAX Corporation) containing aluminum oxide abrasive grains with a grain size of 9 μm was applied to the surface of the intermediate transfer belt 8 attached to the outer periphery of the cylindrical body at a surface pressure of 0.98 N/mm ^2. make contact with it. Then, by rotating the cylindrical body for 40 seconds, an intermediate transfer belt 8 was obtained in which grooves 83 were formed on the surface with a width W in the belt width direction of about 1 μm on average and a depth D of about 0.8 μm on average. . In Comparative Example 2, the surface shape obtained by roughening treatment using a wrapping film has large variations in the width of the unevenness and the depth of the concave part compared to Example 1, and the width of the convex part on the surface side is very small. There are also many. The additives and their amounts in the material of the surface layer 82 of the intermediate transfer belt 8 in Comparative Example 2 are the same as in this example. The wear rate in the durability evaluation of the intermediate transfer belt 8 of Comparative Example 2 is the same as that of this example, and is 0.26 μm per 100K sheets of paper passed.

(Comparative example 3)
As Comparative Example 3, durability evaluation was performed using an intermediate transfer belt 8 in which 50 parts by weight of PTFE resin powder was added to the material of the surface layer 82 and the surface layer 82 was roughened. The surface roughening treatment of the surface layer 82 of the intermediate transfer belt 8 of Comparative Example 3 was performed as follows. A lapping film (Lapika #2000 (trade name), manufactured by KOVAX Corporation) containing aluminum oxide abrasive grains with a grain size of 9 μm was applied to the surface of the intermediate transfer belt 8 attached to the outer periphery of the cylindrical body at a surface pressure of 0.98 N/mm ^2. make contact with it. By rotating the cylindrical body for 40 seconds, an intermediate transfer belt 8 was obtained in which grooves 83 having an average width W of about 1 μm and a depth D of about 1 μm in the belt width direction were formed on the surface. The additives and their amounts in the material of the surface layer 82 of the intermediate transfer belt 8 of Comparative Example 3 are the same as in this example, except that the amount of PTFE resin powder was increased compared to this example. The wear rate in the durability evaluation of the intermediate transfer belt 8 of Comparative Example 3 was higher than that of this example due to the increased amount of PTFE resin powder, and was 0.33 μm per 100K sheets of paper passed.

(Test results)
The skew feeding suppression ability of the intermediate transfer belts 8 of this example and comparative examples 1 to 3 at the start of durability evaluation and at the time of 150K sheets passing, and the difference in the dynamic friction coefficient Δμ between the intermediate transfer belt 8 and gloss coated paper The measurement results are shown in Table 1. In addition, for both the intermediate transfer belt 8 of this example and Comparative Examples 1 to 3, the halftone pull-out force at the start of durability evaluation and when 150K sheets were passed was 7.8 N, and the halftone dynamic friction coefficient μ2 was 0.16. Met.

When the intermediate transfer belt 8 of this example was used, Δμ<0.3 was achieved both at the initial stage of durability evaluation and after passing 150K sheets, and the amount of skew when passing halftone images on one side It was also at the "○" level.

When the intermediate transfer belt 8 of Comparative Example 1 is used, since the surface layer 82 is not subjected to shape imparting treatment, the dynamic friction coefficient difference Δμ is larger than that of this example from the beginning of the durability evaluation, and the halftone image on one side is The amount of skew during paper feeding was also at the "x" level.

When the intermediate transfer belt of Comparative Example 2 was used, at the initial stage of durability evaluation, the dynamic friction coefficient difference Δμ was suppressed to less than 0.3 due to the effect of the surface roughening treatment, and the skew when passing halftone images on one side was suppressed to less than 0.3. The amount of work was also at the "○" level. On the other hand, the dynamic friction coefficient difference Δμ after passing 150K sheets was 0.3 or more, and the amount of skew when passing halftone images on one side was also at the "x" level. After the durability evaluation, most of the irregularities formed on the surface of the intermediate transfer belt 8 of Comparative Example 2 when roughened with a wrapping film had disappeared due to wear. As a result, it can be seen that as the convex portion wears out, the contact area between the intermediate transfer belt 8 and the transfer material P increases, the coefficient of dynamic friction increases, and the amount of skew increases.

When the intermediate transfer belt of Comparative Example 3 was used, at the initial stage of durability evaluation, the dynamic friction coefficient difference Δμ was suppressed to less than 0.3 due to the effect of increasing the amount of PTFE resin powder and roughening treatment, and The amount of skew when passing the tone image was also at the "○" level. On the other hand, the dynamic friction coefficient difference Δμ after passing 150K sheets was 0.3 or more, and the amount of skew when passing halftone images on one side was also at the "x" level. Further, the surface layer 82 of the intermediate transfer belt 8 of Comparative Example 3 has a higher abrasion rate, although the surface layer 82 is more easily roughened than the present example and other comparative examples due to the increased amount of PTFE resin powder. Therefore, on the surface of the intermediate transfer belt 8 of Comparative Example 3 after the durability evaluation, most of the irregularities formed when the surface was roughened with the wrapping film had disappeared due to wear. As a result, it can be seen that as the convex portion wears out, the contact area between the intermediate transfer belt 8 and the transfer material P increases, the coefficient of dynamic friction increases, and the amount of skew increases.

As described above, in this embodiment, the regular (periodic in this embodiment) grooves 83 are formed on the surface of the intermediate transfer belt 8, and the frictional force between the intermediate transfer belt 8 and the transfer material P is Reduce. As a result, in this embodiment, the dynamic friction coefficient difference Δμ depending on the presence or absence of toner in the secondary transfer portion N2 is suppressed to less than 0.3 throughout the period of use of the intermediate transfer belt 8. As a result, skewing of the transfer material P in the secondary transfer portion N2 can be suppressed for a long period of time.

Furthermore, according to the present embodiment, it is possible to reduce the difference in the conveying force of the transfer material depending on the presence or absence of toner in the secondary transfer portion N2, so it is also possible to suppress the difference in image magnification for each image pattern described above. Therefore, it is possible to suppress changes in image elongation due to the image pattern over a long period of time. Furthermore, the effect of improving the stability of the image magnification with respect to variations in the feed speed of the pair of registration rollers 13 can be obtained.

Here, the expression that the grooves 83 are regularly formed in the belt width direction typically means that the grooves 83 are formed periodically at a predetermined period (repeatedly formed at a predetermined pitch). Say something. However, this also includes a region where the grooves 83 are partially formed with a deviation from a predetermined period due to manufacturing reasons or on purpose. For example, a case may be considered in which the groove 83, which is formed periodically as a whole at a predetermined period, has a recessed portion width Wsc or a raised portion width Wsv changed in a portion in the belt width direction. Not only cases where the deviation follows a predetermined rule, but also cases where the deviation occurs irregularly (randomly) are included in the fact that the grooves 83 are regularly formed. In other words, the fact that the grooves 83 are formed regularly in the belt width direction does not mean that the grooves 83 are formed irregularly (randomly), but rather that the grooves 83 as a whole are formed in a predetermined manner according to common technical knowledge in the field. It is acceptable as long as it can be determined that it follows the rules.

Further, in this embodiment, a case has been described in which the cross-sectional structure of the intermediate transfer belt 8 is a two-layer structure including the surface layer 82. However, since the effect of this embodiment can be obtained by forming an uneven shape on the outermost layer (outermost surface), the layer structure of the intermediate transfer belt 8 is not limited. The intermediate transfer belt 8 may have a single layer structure or may have three or more layers.

Further, in this embodiment, the groove 83 was formed in a direction along the belt conveyance direction, which was substantially parallel to the belt conveyance direction (FIG. 2(a)). Further, in this embodiment, the groove 83 is formed continuously in a substantially straight line over one circumference of the intermediate transfer belt 8 in the circumferential direction (rotation direction). However, the direction along the belt conveyance direction only needs to extend along a direction intersecting the belt width direction, and may have an angle to the belt conveyance direction (FIG. 7). The angle formed by the longitudinal axis of the groove 83 with respect to the belt conveyance direction is preferably 45 degrees or less, more preferably 10 degrees or less. Typically, as in this embodiment, the belt conveyance direction and the longitudinal axis direction of the grooves 83 are substantially parallel. The groove 83 having an angle with respect to the belt conveyance direction may be formed by using a mold in which a convex portion is formed obliquely with respect to the rotating direction of the cylinder, or by using a mold having a convex portion formed approximately parallel to the rotating direction of the cylinder as in this embodiment. It can be formed by using a mold in which is formed obliquely with respect to the belt conveyance direction. As shown in FIG. 7, when the grooves 83 are formed diagonally, the cross section of the intermediate transfer belt 8 at the position of the straight line 15 drawn in a direction substantially perpendicular to the belt conveyance direction is similar to that in FIG. 2(b). Become. By setting the concave width Wsc, convex width Wsv, concave depth d, and concave interval I of the uneven surface of the intermediate transfer belt 8 in this cross section in the same manner as in this embodiment, the same effect as in this embodiment can be obtained. It is possible to obtain.

[Example 2]
Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of the first embodiment. Therefore, elements in the image forming apparatus of this embodiment that have the same or corresponding functions or configurations as those of the image forming apparatus of Embodiment 1 are given the same reference numerals as in Embodiment 1, and detailed explanations thereof will be omitted. .

<Configuration of this embodiment>
In Example 1, in addition to the effect of the uneven shape of the surface layer 82, the coefficient of dynamic friction between the intermediate transfer belt 8 and the transfer material P was kept low by adding a relatively large amount of solid lubricant to the material of the surface layer 82. . In this example, by making the average recess interval I smaller than in Example 1, it is possible to further improve the ability to suppress skew while suppressing the amount of solid lubricant added. Thereby, it is possible to further improve the durability of the intermediate transfer belt 8 while meeting the higher demands for image quality of graphic users, for example, while further improving the ability to suppress skew movement.

FIG. 8 shows the vicinity of the surface layer of the intermediate transfer belt 8 of this embodiment when cut in a direction substantially perpendicular to the belt conveyance direction (hereinafter also referred to as "belt width direction") (viewed along the belt conveyance direction). FIG. 2 is a schematic enlarged partial sectional view of FIG. In Example 1, an uneven shape was formed on the surface of the intermediate transfer belt 8 so that the width of the concave portions Wsc was 1 μm and the width of the convex portions Wsv was 19 μm. In contrast, in this embodiment, as shown in FIG. 8, the surface of the intermediate transfer belt 8 has a concave width Wsc of 1 μm, which is the same as in Example 1, and a convex width Wsv of 2.5 μm, which is smaller than in Example 1. The uneven shape is formed so that As a result, in the present example, the effect of reducing the contact area due to the shape provision is more enhanced than in Example 1. On the other hand, in this example, the amount of PTFE resin powder, which is a solid lubricant, added is reduced compared to Example 1 to reduce the wear rate of the intermediate transfer belt 8 and further improve the durability of the intermediate transfer belt 8. We are trying to In this example, the amount of PTFE resin powder added to the material of the surface layer 82 of the intermediate transfer belt 8 is 20 parts by weight, and the wear rate in the durability evaluation described later is reduced to 0.13 μm per 100K sheets passed. .

Further, in this embodiment, as a means for further improving the durability of the intermediate transfer belt 8, the following configuration is adopted. That is, in this embodiment, the uneven shape of the cross section of the surface layer 82 of the intermediate transfer belt 8 in the belt width direction is made close to a rectangular wave shape. Thereby, even if the surface layer 82 of the intermediate transfer belt 8 is worn out, an increase in the contact area between the intermediate transfer belt 8 and the contact object can be suppressed. Specifically, in this embodiment, the surface of the intermediate transfer belt 8 has a recess depth d of 0.5 μm, a width Wsv of the convex portion near the surface of the surface layer 82 of 2.5 μm, and a convex portion near the bottom of the recess. The uneven shape is formed so that the width Wbv of the portion is 3.0 μm. Furthermore, in this embodiment, as a result, the width Wbc near the bottom of the recess is 0.5 μm. This suppresses an increase in the contact area between the intermediate transfer belt 8 and the transfer material P due to wear of the surface layer 82.

As in this embodiment, when the wear resistance of the intermediate transfer belt 8 is improved by reducing the amount of lubricant such as PTFE resin powder added, the transfer It is effective to reduce the contact area with material P. Therefore, in this embodiment, as described above, the surface layer 82 is formed with an uneven shape to increase the contact area ratio between the intermediate transfer belt 8 and the transfer material P at the secondary transfer portion N2 at the initial stage of use of the intermediate transfer belt 8 by 70. It has been reduced to about %.

Here, the above-mentioned contact area ratio is the contact area ratio between the intermediate transfer belt 8 and the transfer material with respect to the total area of the transfer material P located in the secondary transfer portion N2 (sandwiched between the intermediate transfer belt 8 and the secondary transfer roller 11). This is the ratio of the contact area with P. This contact area ratio can be determined from the ratio Wsv/I of the width Wsv of the convex portions to the interval I of the concave portions, taking as an example the initial stage of use of the intermediate transfer belt 8. According to the studies of the present inventors, in order to satisfy Δμ<0.3, more preferably Δμ<0.25, the contact area ratio is preferably 80% or less. On the other hand, if the width of the convex part is small, the contact area ratio should be 50% or more because of the reasons such as a decrease in manufacturing stability, a decrease in strength and the possibility of chipping, making it impossible to maintain the shape of the groove. It is preferable.

<Evaluation test>
(Test method)
Below, we evaluated the durability of an image forming apparatus using intermediate transfer belts with different surface properties (this example, comparative examples 4 to 6), and examined the relationship between the skew feed suppression ability and the dynamic friction coefficient difference Δμ. show. The test method is the same as described in Example 1. Note that the configurations of the intermediate transfer belt 8 and other image forming apparatuses 100 in each of the following comparative examples are substantially the same as in the present example except for the following points. In each comparative example, elements having the same or corresponding functions or configurations as those of the image forming apparatus 100 of the present embodiment will be described with the same reference numerals.

(Comparative example 4)
As Comparative Example 4, an intermediate transfer belt 8 was used in which 20 parts by weight of PTFE resin powder was added to the material of the surface layer 82, and the surface layer 82 was not subjected to surface roughening treatment, shape imparting treatment such as imprinting, etc. Durability evaluation was conducted. The additives and their amounts in the material of the surface layer 82 of the intermediate transfer belt 8 in Comparative Example 4 are the same as in this example. The wear rate in the durability evaluation of the intermediate transfer belt 8 of Comparative Example 4 is the same as that of this example, and is approximately 0.13 μm per 100K sheets of paper passed.

(Comparative example 5)
As Comparative Example 5, durability was evaluated using an intermediate transfer belt 8 in which 20 parts by weight of PTFE resin powder was added to the material of the surface layer 82 and the width Wsv of the convex portion of the uneven shape of the surface layer 82 was larger than that of this example. I did it. Specifically, in the intermediate transfer belt 8 of Comparative Example 5, the convex portion width Wsv was set to 9 μm. The additives and their amounts in the material of the surface layer 82 of the intermediate transfer belt 8 in Comparative Example 5 are the same as in this example. The wear rate in the durability evaluation of the intermediate transfer belt 8 of Comparative Example 5 is the same as that of this example, and is approximately 0.13 μm per 100K sheets of paper passed.

(Comparative example 6)
As Comparative Example 6, durability evaluation was performed using an intermediate transfer belt 8 in which 20 parts by weight of PTFE resin powder was added to the material of the surface layer 82 and the surface layer 82 was subjected to surface roughening treatment. The surface roughening treatment of the surface layer 82 of the intermediate transfer belt 8 of Comparative Example 6 was performed as follows. A lapping film (Lapika #2000 (trade name), manufactured by KOVAX Corporation) containing aluminum oxide abrasive grains with a grain size of 9 μm was applied to the surface of the intermediate transfer belt 8 attached to the outer periphery of the cylindrical body at a surface pressure of 0.98 N/mm ^2. make contact with it. By rotating the cylindrical body for 200 seconds, an intermediate transfer belt 8 is obtained in which grooves 83 are formed in the surface layer 82 with a width W of about 1 μm on average and a depth D of about 0.5 μm on average in the belt width direction. Ta. In Comparative Example 6, the surface shape obtained by roughening treatment using a wrapping film has larger variations in the width of unevenness and the depth of recesses than in Comparative Example 2, and the width of the protrusions on the surface layer side is very large. There are also many small ones. This is because in Comparative Example 6, the durability of the surface layer 82 was improved, making it difficult to give a shape. The additives and their amounts in the material of the surface layer 82 of the intermediate transfer belt 8 in Comparative Example 6 are the same as in this example. The wear rate in the durability evaluation of the intermediate transfer belt 8 of Comparative Example 6 is the same as that of this example, and is 0.13 μm per 100K sheets of paper passed.

(Test results)
The skew feeding suppression ability of the intermediate transfer belts 8 of this example and comparative examples 4 to 6 at the start of durability evaluation and at the time of 300K sheet passing, and the difference in the dynamic friction coefficient Δμ between the intermediate transfer belt 8 and the gloss coated paper The measurement results are shown in Table 2. Here, in comparison with the evaluation criteria described in Example 1, criteria for determining higher oblique travel suppressing ability were provided. Specifically, if the amount of skew is less than 0.20%, the ability to suppress skew is excellent (◎), if the amount of skew is 0.20% or more and less than 0.25%, it is good (○). If the line amount was 0.25% or more, it was determined to be defective (×). In addition, for any of the intermediate transfer belts 8 of this Example and Comparative Examples 4 to 6, the halftone pull-out force at the start of durability evaluation and when 300K sheets were passed was 7.8 N, and the halftone dynamic friction coefficient μ2 was 0.16. Met.

In the intermediate transfer belt 8 of Example 1 and Comparative Examples 1 to 3 described above, at least a portion of the surface layer 82 disappeared after 300K sheets were passed, causing problems such as image defects and cleaning defects.

When the intermediate transfer belt 8 of this example was used, Δμ<0.25 was achieved both at the initial stage of durability evaluation and after passing 300K sheets, and the amount of skew when passing halftone images on one side It was also at the "◎" level. As described above, in this embodiment, by providing the surface layer 82 of the intermediate transfer belt 8 with an uneven shape, the relationship between the intermediate transfer belt 8 and the transfer material P at the secondary transfer portion N2 at the initial stage of use of the intermediate transfer belt 8 is improved. The contact area ratio is about 70%. On the other hand, even after paper passing for 300K, the contact area ratio could be suppressed to about 80%.

When the intermediate transfer belt 8 of Comparative Example 4 was used, the surface layer 82 was not subjected to shape imparting treatment, and the amount of PTFE resin powder added was reduced compared to Comparative Example 1 described above. From the beginning of the durability evaluation, the dynamic friction coefficient difference Δμ was larger than that of this example and comparative example 1. Furthermore, from the early stage of the durability evaluation, the amount of skew when passing a halftone image on one side was also at the "x" level.

When the intermediate transfer belt 8 of Comparative Example 5 was used, the dynamic friction coefficient Δμ was larger than that of this example from the beginning of the durability evaluation. This is because although the shape of the recesses in the surface layer 82 of the intermediate transfer belt 8 is the same as in this example, the number of recesses is smaller than in this example, and the amount of PTFE resin powder added is smaller than in Example 1. It can be seen that this is due to the fact that it is decreasing. Furthermore, when the intermediate transfer belt 8 of Comparative Example 5 was used, the amount of skew when passing a halftone image on one side was also at the "x" level from the beginning of the durability evaluation.

When the intermediate transfer belt 8 of Comparative Example 6 was used, at the initial stage of durability evaluation, the dynamic friction coefficient difference Δμ was suppressed to less than 0.3 due to the effect of the surface roughening treatment, and the The amount of skew was also at the "○" level. On the other hand, the dynamic friction coefficient difference Δμ after passing 300K sheets was 0.3 or more, and the amount of skew when passing halftone images on one side was also at the "x" level. After durability evaluation, most of the irregularities formed on the surface of the intermediate transfer belt 8 of Comparative Example 6 when roughened with a wrapping film had disappeared due to wear. As a result, it can be seen that the contact area between the intermediate transfer belt 8 and the transfer material P increases due to wear of the convex portions, the difference in the dynamic friction coefficient increases, and the amount of skew increases.

In this embodiment, a case has been described in which the convex width Wsv of the uneven shape on the surface of the intermediate transfer belt 8 is about 2.5 μm, the concave width Wsc is about 1 μm, and the concave depth d is about 0.5 μm. However, even after long-term use, if the contact area between the intermediate transfer belt 8 and the transfer material P can be kept within a predetermined range and Δμ<0.3, more preferably Δμ<0.25, the recess width and The depth of the recessed portion is not limited to the value of this example. For example, if the recess width Wsc can be made larger than in this example, or if the recess depth d can be made deeper than in this example, the contact area can be easily suppressed. On the other hand, as the convex width Wsv decreases and the concave depth d increases, the strength of the surface layer 82 of the intermediate transfer belt 8 decreases, and the risk of wear and chipping increases. Furthermore, if the recess width Wsc becomes large, cleaning failure may occur. Therefore, it is preferable that the concave width Wsc, the concave depth d, and the convex width Wsv are within the ranges described in Example 1. Especially when reducing the amount of solid lubricant added, the concavo-convex shape described in this example A shape close to that is desirable.

As explained above, according to the present example, the dynamic friction coefficient difference Δμ can be reduced more than in Example 1 for a longer period of time than in Example 1. Thereby, the skew movement of the transfer material P in the secondary transfer portion N2 can be suppressed more than in the first embodiment for a longer period of time than in the first embodiment. Further, according to the present example, the difference in image expansion due to the image pattern can be suppressed over a longer period of time than in the first example.

[others]
Although the present invention has been described above with reference to specific examples, the present invention is not limited to the above-mentioned examples.

The intermediate transfer member is not limited to a belt-like member, but may be a drum-like member (intermediate transfer drum) formed by, for example, stretching a sheet onto a frame, and the present invention may be applied to the intermediate transfer member as well. can be applied to obtain similar effects. Further, the image forming apparatus is not limited to an in-line type. For example, a plurality of developing devices are provided for one photoreceptor, and after the toner images sequentially formed on the photoreceptor are primarily transferred to an intermediate transfer member, the toner images are superimposed on the intermediate transfer member. The image forming apparatus may be of a type in which a combined toner image is secondarily transferred onto a transfer material. In other words, the intermediate transfer member may be one that transports a toner image that has been primarily transferred from an image carrier carrying a toner image to a transfer material for second transfer.

Further, in the above embodiment, the case where the secondary transfer rotating body is a roller has been explained, but the secondary transfer member is composed of a roller and an endless belt (or film) wrapped around the roller. Good too. That is, an endless belt stretched around a plurality of rollers is used, and this belt is brought into contact with the intermediate transfer belt (at least one roller may be brought into contact with the intermediate transfer belt via this belt). , a secondary transfer portion can be formed. The belt and roller can be configured to follow and rotate as the intermediate transfer belt rotates. The present invention can also be applied to such a configuration, and the same effects as in the above-described embodiments can be obtained. However, the present invention can be said to be particularly effective in a configuration in which the secondary transfer rotating body is a roller, in which stretching of the image and skewing of the transfer material in the secondary transfer section are relatively likely to occur.

Furthermore, in the above-described embodiments, the case where the conveyance means disposed adjacent to the secondary transfer section on the upstream side of the secondary transfer section in the conveyance direction of the transfer material is a pair of registration rollers. However, the present invention is not limited to such a configuration, and the conveying means may be composed of a roller and a non-rotating contact member such as a pad that comes into contact with the roller.

1 Photosensitive drum 8 Intermediate transfer belt 81 Base layer 82 Surface layer 83 Groove 84 Outermost surface

Claims (16)

an image carrier that carries a toner image;
a movable intermediate transfer member to which the toner image is primarily transferred from the image carrier;
A secondary transfer rotating body that forms a secondary transfer portion that comes into contact with the intermediate transfer body and secondarily transfers the toner image on the intermediate transfer body onto a transfer material, the secondary transfer rotating body forming a secondary transfer part that contacts the intermediate transfer body and secondarily transfers the toner image on the intermediate transfer body onto a transfer material, a secondary transfer rotating body that rotates in a driven manner;
In an image forming apparatus having
A plurality of grooves are formed on the surface of the intermediate transfer body along the movement direction of the surface of the intermediate transfer body with respect to the width direction of the intermediate transfer body that intersects with the movement direction of the intermediate transfer body, and The plurality of grooves are periodically formed at a predetermined period in the width direction,
In a cross section perpendicular to the movement direction, the plurality of grooves have a rectangular wave shape,
On the surface of the intermediate transfer body, the width of each groove in the width direction is less than the average particle size of the toner,
The coefficient of kinetic friction between the surface of the intermediate transfer body and a predetermined transfer material at the beginning of a preset life period of the intermediate transfer body and when the life reaches the end of the preset life period of the intermediate transfer body is determined by The coefficient of dynamic friction is μ1 when the toner image is not present , and when the predetermined toner image is present. The dynamic friction coefficient in the case is μ2, the difference between the μ1 and μ2 (μ1−μ2) is the dynamic friction coefficient difference Δμ, the predetermined transfer material is coated paper with a Beck smoothness of 250 to 500 seconds, and the predetermined transfer material is coated paper with a Beck smoothness of 250 to 500 seconds. When the toner image is a halftone image in which the area ratio of the toner-covered portion is 50%, the intermediate transfer body has the following characteristics at the beginning of the life period and at the end of the life period:
Δμ<0.3
An image forming apparatus characterized by being an endless belt that satisfies the following. The intermediate transfer body has the following characteristics at the beginning of the life period and at the end of the life period:
Δμ<0.25
The image forming apparatus according to claim 1, wherein the image forming apparatus satisfies the following. 3. The image forming apparatus according to claim 1, wherein the layer forming the surface of the intermediate transfer member is made of a curable resin. 3. The image forming apparatus according to claim 1, wherein the layer forming the surface of the intermediate transfer member is formed of an acrylic copolymer. 5. The image forming apparatus according to claim 1, wherein the layer forming the surface of the intermediate transfer body contains fluorine-containing particles. The image forming apparatus according to claim 5, wherein the fluorine-containing particles are polytetrafluoroethylene (PTFE). 7. The plurality of grooves are formed in substantially the entire region of the secondary transfer portion that can come into contact with the transfer material in the width direction, according to any one of claims 1 to 6. Image forming device. Conveying means for conveying the transfer material towards the secondary transfer section on the upstream side of the secondary transfer section with respect to the conveyance direction of the transfer material, the conveyance being faster than the conveyance speed of the transfer material in the secondary transfer section. Image forming according to any one of claims 1 to 7, further comprising a conveyance means that conveys the transfer material at a speed and loosens the transfer material between the secondary transfer section and the conveyance means. Device. The image forming apparatus according to any one of claims 1 to 8, wherein the secondary transfer rotating body is a roller. Claims 1 to 9, characterized in that a contact area ratio between the intermediate transfer body and the transfer material in the secondary transfer section is 50% or more and 80% or less at the beginning of the life period and at the end of the life period. The image forming apparatus according to any one of the above. The image according to any one of claims 1 to 10, wherein the width of each groove in the width direction on the surface of the intermediate transfer body is less than half the average particle diameter of the toner. Forming device. The image forming apparatus according to any one of claims 1 to 11, wherein a pitch of the plurality of grooves in the width direction is 2 μm or more and 30 μm or less. The image forming apparatus according to claim 12, wherein a pitch of the plurality of grooves in the width direction is 3 μm or more and 20 μm or less. 14. A difference between a width near the bottom of the groove and a width near the surface in the width direction is less than the thickness of a surface layer forming the surface of the intermediate transfer body. The image forming apparatus according to item (1). 15. The image forming apparatus according to claim 1, wherein the initial stage is when the intermediate transfer member is new. The image forming apparatus according to any one of claims 1 to 15, wherein the time when the life span is reached is a time when the intermediate transfer body needs to be replaced due to its life span.

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