JP2012108203A - Image forming apparatus and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus in which occurrence of image shift in a secondary transfer nip part may be prevented to the utmost for improving image quality.SOLUTION: An image forming apparatus of the invention comprises: a transfer belt 40 including an elastic layer 40b and carrying an image thereon; a backup roller 44 around which the transfer belt 40 is wound; a secondary transfer roller 61 that transfers the image carried on the image carrier onto a transfer material in a transfer nip including a pressure nip formed through pressure contact with the backup roller 44 via the transfer belt 40 and a contact nip formed through contact with a portion of the transfer belt 40 not wound around the backup roller 44; a storage part storing information on a type of the transfer material onto which the image is transferred in the transfer nip; and an adjustment part adjusting a length of the contact nip along a moving direction of the transfer material on the basis of the information stored in the storage part.

Description

  The present invention develops a latent image formed on a photoreceptor with toner, transfers the developed toner image onto a transfer belt, further transfers the toner image on the transfer belt onto a medium such as recording paper, and the transferred medium The present invention relates to an image forming apparatus and an image forming method for forming an image by fusing and fixing an upper toner image.

  Various wet image forming apparatuses have been proposed in which a latent image is developed using a high-viscosity liquid developer in which toner particles made of a solid component are dispersed in a liquid solvent to visualize the electrostatic latent image. The developer used in this wet image forming apparatus suspends solids (toner particles) in a highly viscous organic solvent (carrier liquid) having electrical insulation properties such as silicone oil, mineral oil, and edible oil. The toner particles are extremely fine with a particle diameter of around 1 μm. By using such fine toner particles, the wet image forming apparatus can achieve higher image quality than a dry image forming apparatus using powder toner particles having a particle diameter of about 7 μm.

  By the way, in an image forming apparatus using a liquid developer, in a printing method using a liquid developer, particularly in a method in which a plurality of colors are superimposed on an intermediate transfer belt and then transferred onto a sheet (transfer material) at a time. Decrease in transfer (secondary transfer) efficiency is a problem.

In order to deal with such a problem, for example, in the invention described in Patent Document 1 (Japanese Patent Laid-Open No. 2001-166611), a transfer belt is wound around the secondary transfer roller 81 to add to the pressure nip. A transfer nip is formed by forming a contact nip and increasing the nip length in the secondary transfer part to some extent, and increasing the time of contact between the transfer material and the visible image on the transfer belt and the transfer electric field. A method of enhancing has been proposed.
JP 2001-166611 A

  However, in the conventional method in which the contact nip is provided together with the pressure nip by winding the transfer belt around the secondary transfer roller, there is a problem that image misalignment such as dragging the image on the transfer material may occur during transfer. was there.

  The cause of such image shift may be a change in the belt surface speed at the nip portion. At the portion (pressure nip) where the transfer belt is wound around the backup roller (rollers 73 and 72 inside the belt), the surface of the transfer belt expands, but the portion (contact) where the transfer belt is wound around the secondary transfer roller (roller 81 outside the belt) Conversely, the surface of the transfer belt is compressed at the nip portion. Thereby, the transfer belt surface speed changes.

  In particular, in a belt in which an elastic layer is provided on a base material layer for preventing elongation, instead of a structure that prevents the belt from being stretched by providing an inelastic core wire in an elastic body as used in the conventional example, Since the belt surface speed increases and decreases depending on the belt bending direction with respect to the belt traveling speed determined by the material layer, the belt surface speed change due to the bending change becomes large, and the image shift tends to be noticeable.

In order to improve the transfer efficiency as described above, in the method in which the transfer belt is wound around the secondary transfer roller and the contact nip is provided together with the pressure nip, the transfer belt surface speed at the pressure nip, the transfer belt surface speed at the contact nip, As a result of the change, there is a problem that an image shift occurs and the image quality may be deteriorated.

  In order to solve the above problems, an image forming apparatus according to the present invention includes an image carrier belt that has an elastic layer and carries an image, a roller that winds the image carrier belt, The image at a transfer nip including a pressure nip formed in pressure contact with the roller through the image carrier belt and a contact nip formed in contact with the image carrier belt not wound on the roller A transfer roller that transfers the image carried on the carrier belt to a transfer material, a storage unit that stores information related to the type of the transfer material that is transferred at the transfer nip, and the information that is stored in the storage unit And an adjustment unit that adjusts the length of the contact nip in the moving direction of the transfer material.

  In the image forming apparatus according to the present invention, the length of the contact nip adjusted by the adjusting unit in the moving direction of the transfer material is shorter than the length of the pressure nip in the moving direction of the transfer material.

  In the image forming apparatus according to the present invention, the outer diameter of the transfer roller is larger than the outer diameter of the roller.

  In the image forming apparatus according to the present invention, the transfer roller has an elastic layer, and the thickness of the elastic layer of the transfer roller is larger than the length of the contact nip in the moving direction of the transfer material.

  In the image forming apparatus according to the present invention, the thickness of the elastic layer of the image carrier belt is smaller than the length of the contact nip in the moving direction of the transfer material.

  In the image forming apparatus according to the present invention, the transfer roller has a concave portion on a peripheral surface, and a transfer material gripping member for gripping the transfer material in the concave portion.

  In the image forming apparatus according to the present invention, the transfer roller has a nozzle hole that adsorbs or peels off the transfer material by air flow.

  Further, an image forming method according to the present invention includes a roller around which the image carrier belt is wound via an image carrier belt having an elastic layer based on information related to the transfer material gun stored in the storage unit. The contact nip of the transfer nip including a pressure nip formed by pressure contact with the transfer roller, and a contact nip formed by contact of the transfer roller with the image carrier belt not wound around the roller Adjusting the length of the transfer material in the moving direction, carrying an image on the image carrier belt, and transferring the image carried on the image carrier to the transfer material at the transfer nip. To do.

  As described above, according to the image forming apparatus and the image forming method of the present invention, the elastic layer is provided on the transfer roller side, and the pressure nip is formed so that the backup roller bites into the transfer roller side through the image carrier belt and the transfer material. Subsequently, the image carrier belt does not come into contact with the backup roller, and the contact nip is formed by being wound around the transfer roller. By appropriately controlling the length, the occurrence of image shift can be prevented as much as possible, and the image quality is improved.

1 is a diagram illustrating main components constituting an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a block diagram related to control of the image forming apparatus according to the embodiment of the present invention. FIG. 7 is a diagram illustrating an operation example of a contact nip adjusting mechanism in the image forming apparatus according to the embodiment of the present invention. It is a figure which shows a mode that only the pressure nip was formed by the contact nip adjustment mechanism. It is a figure which shows a mode that the contact nip of predetermined length was formed in addition to the pressure nip by the contact nip adjustment mechanism. FIG. 3 is a diagram illustrating a configuration example of a contact nip adjusting mechanism in the image forming apparatus according to the embodiment of the present invention. It is a figure which shows the cylindrical member with an eccentric hole used with a contact nip adjustment mechanism. It is a figure which shows the structural example of the contact nip adjustment mechanism in the image forming apparatus which concerns on other embodiment of this invention. It is a figure which shows the cylindrical member with an eccentric protrusion part with an eccentric hole used with the contact nip adjustment mechanism in other embodiment. It is a figure explaining operation | movement of the contact nip adjustment mechanism in other embodiment. FIG. 6 is a diagram illustrating a configuration of a secondary transfer nip portion in an image forming apparatus according to another embodiment of the present invention. It is a figure which shows the structure of the secondary transfer roller in the image forming apparatus which concerns on other embodiment provided with a transfer material holding | grip mechanism. It is a figure which shows the cross section of the secondary transfer roller 61 used with the image forming apparatus which concerns on other embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing main components constituting the image forming apparatus according to the embodiment of the present invention. The developing devices 30Y, 30M, 30C, and 30K are arranged in the lower portion of the image forming apparatus with respect to the image forming units of the respective colors arranged in the central portion of the image forming apparatus, and are transferred to the transfer belt 40, the secondary transfer unit (secondary transfer unit). The configuration of the transfer unit 60, the fixing unit 90, and the like is disposed in the upper part of the image forming apparatus. In the present embodiment, the transfer material S such as paper that has undergone secondary transfer by the secondary transfer unit 60 is transported to the fixing unit 90.

  The developing devices 30Y, 30M, 30C, and 30K are photoconductors 10Y, 10M, 10C, and 10K, corona chargers 11Y, 11M, 11C, and 11K, and exposure units 12Y, 12M, such as an LED array, for forming an image using toner. , 12C, 12K, etc. The photoconductors 10Y, 10M, 10C, and 10K are uniformly charged by the corona chargers 11Y, 11M, 11C, and 11K, and the exposure units 12Y, 12M, 12C, and 12K perform exposure based on the input image signal. Then, electrostatic latent images are formed on the charged photoreceptors 10Y, 10M, 10C, and 10K.

  The developing devices 30Y, 30M, 30C, and 30K generally include liquid developers of respective colors including the developing rollers 20Y, 20M, 20C, and 20K, yellow (Y), magenta (M), cyan (C), and black (K). Developer containers (reservoirs) 31Y, 31M, 31C, 31K to be stored, and application rollers for applying liquid developers of these colors from the developer containers 31Y, 31M, 31C, 31K to the developing rollers 20Y, 20M, 20C, 20K. The anilox rollers 32Y, 32M, 32C, 32K and the like are provided, and the electrostatic latent images formed on the photoreceptors 10Y, 10M, 10C, 10K are developed with the liquid developers of the respective colors.

The transfer belt 40 (also referred to as “image carrier belt”) is an endless belt, and is stretched around a backup roller 44, belt stretching rollers 41 and 42, and a tension roller 52 that drive the transfer belt 40, and is subjected to primary transfer. The parts 50Y, 50M, 50C, and 50K are driven to rotate while contacting the photoreceptors 10Y, 10M, 10C, and 10K. The backup roller 44 is a drive roller having a drive unit such as a motor (not shown), and the transfer belt 40 is rotated by the rotation of the backup roller 44.

  In the primary transfer portions 50Y, 50M, 50C, and 50K, the primary transfer rollers 51Y, 51M, 51C, and 51K are arranged to face each other with the transfer belt 40 sandwiched between the photoreceptors 10Y, 10M, 10C, and 10K. Using the contact position with 10C and 10K as the transfer position, the developed toner images of the respective colors on the photoconductors 10Y, 10M, 10C and 10K are sequentially superimposed and transferred onto the transfer belt 40 to form a full-color toner image. To do.

  In the image forming apparatus according to the present invention, the backup roller 44 that drives the transfer belt 40 is provided immediately downstream of the developing device 30K, so that the toner images developed by the developing devices 30Y, 30M, 30C, and 30K are transferred. The primary transfer can be stably performed on the belt 40. In addition, the tension roller 52 absorbs a variation caused by the displacement of the belt stretching roller 41 or the like immediately downstream of the belt stretching roller 41 so that the variation is not transmitted to the primary transfer unit or each developing device. Yes.

  In the secondary transfer portion, a secondary transfer roller 61 is disposed opposite to the backup roller 44 with the transfer belt 40 interposed therebetween, and a cleaning device including a secondary transfer roller cleaning blade 62 is disposed. Then, at a transfer position where the secondary transfer roller 61 is disposed, transfer of a single-color toner image or a full-color toner image formed on the transfer belt 40 through a transfer material transport path L is performed. Transfer to material. The secondary transfer unit 60 has a configuration necessary for transferring a toner image formed on the transfer belt 40 to a transfer material at a nip formed between the transfer belt 40 and the secondary transfer roller 61. It contains everything. That is, the secondary transfer unit 60 includes a bias applying unit (not shown) that applies a potential difference between the secondary transfer roller 61 and the belt stretching roller 41 to promote the movement of the toner image.

  In the image forming apparatus according to the present invention, a pressure nip capable of applying a pressure between these two rollers to the transfer belt 40 and the transfer material S passing between the secondary transfer roller 61 and the backup roller 44. And a region (Nc) for forming a contact nip by winding the transfer belt 40 around the secondary transfer roller 61. As described in Patent Document 1, the transfer efficiency is improved. It can be raised. In the image forming apparatus according to the present invention, the length of the region (Nc) where the contact nip is formed (distance in the roller circumferential surface direction. Hereinafter, the definition of the nip length is assumed). Is adjusted according to the type of the transfer material S. With such an adjustment unit, the length of the contact nip (Nc) changes from zero to a predetermined length, but the length of the contact nip (Nc) is always set to be shorter than the pressure nip (Np). Yes. A specific configuration relating to the length adjusting portion of the contact nip (Nc) will be described later.

The secondary transfer roller 61 has a structure in which an elastic layer 61b having a predetermined thickness is disposed around the roller body 61a. That is, the elastic layer 61b of the secondary transfer roller 61 is provided, and further, a pressure nip (Np) is formed so that the backup roller 44 bites into the secondary transfer roller 61 side via the transfer belt 40 and the transfer material S. Subsequently, the transfer belt 40 does not come into contact with the backup roller 44, and the contact nip (Nc) is formed so as to be wound around the secondary transfer roller 61, thereby obtaining good transferability. Secondary transfer as described above The transfer material such as paper that has undergone secondary transfer in the unit 60 is conveyed to the fixing unit 90, and the fixing unit 90 transfers a single color toner image or full color toner transferred onto the transfer material such as paper. The image is fused and fixed to a transfer material such as paper.

A cleaning device comprising a transfer belt cleaning blade 49 for cleaning the transfer belt 40 is brought into contact with and disposed at a place where the transfer belt 40 is stretched on the belt stretching roller 42, and the remaining toner and carrier on the transfer belt 40 are removed. It is designed to be cleaned.

  The transfer material S is supplied to the image forming apparatus by a paper feeding device (not shown). The transfer material S set in such a sheet feeding device is sent to the transfer material conveyance path L one by one at a predetermined timing. In the transfer material conveyance path L, the transfer material S is conveyed to the secondary transfer position by the gate rollers 101 and 101 ′, and the single color toner developed image and the full color toner developed image formed on the transfer belt 40 are transferred to the transfer material. To do. The transfer material subjected to the secondary transfer is conveyed to the fixing unit 90. The fixing unit 90 includes a heating roller 91 and a pressure roller 92 urged to the heating roller 91 side with a predetermined pressure. A transfer material is inserted between the nips, and the transfer material is placed on the transfer material. The transferred single-color toner image or full-color toner image is fused and fixed to a transfer material such as paper.

  Here, the developing device will be described. Since the configurations of the image forming unit and the developing device for each color are the same, the description will be made based on the yellow (Y) image forming unit and the developing device.

  The image forming unit includes a photosensitive member cleaning blade 18Y, a corona charger 11Y, an exposure unit 12Y, a developing roller 20Y of the developing device 30Y, a first photosensitive member squeeze roller 13Y, and a second photosensitive member along the rotation direction of the outer periphery of the photosensitive member 10Y. A photoconductor squeeze roller 13Y ′ is disposed.

  The photoconductor cleaning blade 18Y that is in contact with the photoconductor 10Y cleans the liquid developer remaining without being transferred in the primary transfer portion on the photoconductor 10Y.

  A cleaning blade 21Y, an anilox roller 32Y, and a compaction corona generator 22Y are arranged on the outer periphery of the developing roller 20Y in the developing device 30Y. A regulating blade 33Y that adjusts the amount of liquid developer supplied to the developing roller 20Y is in contact with the anilox roller 32Y. An auger 34Y is accommodated in the liquid developer container 31Y. Further, a primary transfer roller 51Y of the primary transfer portion is disposed at a position facing the photoconductor 10Y so as to sandwich the transfer belt 40.

  The photoconductor 10Y is a photoconductor drum made of a cylindrical member having a photosensitive layer such as an amorphous silicon photoconductor formed on the outer peripheral surface, and rotates in the clockwise direction.

  The corona charger 11Y is disposed upstream of the nip portion between the photoconductor 10Y and the developing roller 20Y in the rotation direction of the photoconductor 10Y, and a voltage is applied from a power supply device (not shown) to corona-charge the photoconductor 10Y. The exposure unit 12Y is located on the photoreceptor 10Y charged by the corona charger 11Y, downstream of the corona charger 11Y in the rotation direction of the photoreceptor 10Y and upstream of the contact portion of the photoreceptor 10Y, the developing roller 20Y. Is irradiated with light to form a latent image on the photoreceptor 10Y. Note that, from the beginning to the end of the image forming process, the configuration of the rollers and the like arranged in the preceding stage is defined to be upstream from the configuration of the rollers and the like arranged in the subsequent stage.

  The developing device 30Y includes a compaction corona generator 22Y that performs a compaction action, and a developer container 31Y that stores a liquid developer in a state where toner is dispersed in a carrier at a weight ratio of approximately 20%.

Further, the developing device 30Y includes a developing roller 20Y that carries the liquid developer, an anilox roller 32Y that is a coating roller for applying the liquid developer to the developing roller 20Y, and a liquid developer amount that is applied to the developing roller 20Y. A regulating blade 33Y for regulating, an auger 34Y for feeding the liquid developer to the aniloc roller 32Y while stirring and transporting the liquid developer, a compaction corona generator 22Y for bringing the liquid developer carried on the developing roller 20Y into a compacted state, and a developing roller 20Y A developing roller cleaning blade 21Y that performs the above cleaning.

  The liquid developer contained in the developer container 31Y is a low-concentration (about 1 to 3 wt%) and low-viscosity volatile at room temperature using a conventionally used Isopar (trademark: exon) as a carrier. Is a non-volatile liquid developer having a high concentration and high viscosity and having non-volatility at room temperature. That is, in the liquid developer in the present invention, solid particles having an average particle diameter of 1 μm in which a colorant such as a pigment is dispersed in a thermoplastic resin are introduced into a liquid solvent such as an organic solvent, silicone oil, mineral oil, or edible oil. High viscosity (HAAKE RheoStress RS600, which is added together with a dispersant and has a toner solid content concentration of about 15 to 25%, and has a viscoelasticity of 30 to 30 at a shear rate of 1000 (1 / s) at 25 ° C. (About 300 mPa · s).

  The anilox roller 32Y functions as an application roller that supplies and applies a liquid developer to the developing roller 20Y. The anilox roller 32Y is a cylindrical member, and is a roller having a concave and convex surface formed by grooves engraved in a fine and uniform spiral shape on the surface so as to easily carry a developer on the surface. The anilox roller 32Y supplies the liquid developer from the developer container 31Y to the developing roller 20Y. During operation of the apparatus, as shown in FIG. 1, the auger 34Y rotates counterclockwise to supply the liquid developer to the aniloc roller 32Y, and the aniloc roller 32Y rotates counterclockwise to develop the developing roller 20Y. A liquid developer is applied to the substrate.

  The regulating blade 33Y is a metal blade having a thickness of about 200 μm, abuts on the surface of the anilox roller 32Y, regulates the film thickness and amount of the liquid developer carried and conveyed by the anilox roller 32Y, and is applied to the developing roller 20Y. Adjust the amount of liquid developer to be supplied. Then, the film thickness and amount of the liquid developer carried and conveyed by the anilox roller 32Y are regulated and adjusted, and the amount of the liquid developer supplied to the developing roller 20Y is adjusted.

  The developing roller cleaning blade 21Y is made of rubber or the like that contacts the surface of the developing roller 20Y. The developing roller 20Y is disposed downstream of the developing nip portion where the developing roller 20Y contacts the photoreceptor 10Y in the rotation direction of the developing roller 20Y. The liquid developer remaining on the roller 20Y is scraped off and removed.

  The compaction corona generator 22Y is an electric field applying means for increasing the charging bias on the surface of the developing roller 20Y. An electric field is applied from the compaction corona generator 22Y to the developing roller 20Y at the compaction site by the compaction corona generator 22Y. The The electric field applying means for compaction may use a compaction roller or the like instead of the corona discharge of the corona discharger shown in FIG.

  The developer carried on the developing roller 20Y and compacted is developed corresponding to the latent image on the photoconductor 10Y by applying a predetermined electric field at the developing nip portion where the developing roller 20Y contacts the photoconductor 10Y.

  The developer remaining after development is scraped off and removed by the developing roller cleaning blade 21Y and dropped into the collecting section in the developer container 31Y to be reused.

The photosensitive member squeeze device disposed upstream of the primary transfer is disposed downstream of the developing roller 20Y so as to face the photosensitive member 10Y, and collects excess carrier of the toner image developed on the photosensitive member 10Y. is there. This photoconductor squeeze device is composed of a first photoconductor squeeze roller 13Y and a second photoconductor squeeze roller 13Y ′ made of an elastic roller member that slides in contact with the photoconductor 10Y, and is developed on the photoconductor 10Y. It has a function of collecting excess carrier and originally unnecessary fog toner from the toner image and increasing the toner particle ratio in the visible image (toner image). A predetermined bias voltage is applied to the photoconductor squeeze rollers 13Y and 13Y ′.

  The surface of the photoreceptor 10Y that has passed through the squeeze device including the first photoreceptor squeeze roller 13Y and the second photoreceptor squeeze roller 13Y 'enters the primary transfer unit 50Y.

  In the primary transfer portion 50Y, the developer image developed on the photoreceptor 10Y is transferred to the transfer belt 40 by the primary transfer roller 51Y. In the primary transfer portion, the toner image on the photoconductor 10 is transferred to the transfer belt 40 side by the action of the transfer bias applied to the primary transfer backup roller 51. Here, the photoconductor 10Y and the transfer belt 40 are configured to move at a constant speed, and the driving load of rotation and movement is reduced, and the disturbance effect on the visible toner image of the photoconductor 10Y is suppressed.

  In the developing devices 30M, 30C, and 30K, magenta (M), cyan (C), and black (K) toners are respectively formed on the photoreceptors 10M, 10C, and 10K by a process similar to the developing process of the developing device 30Y. Each image is formed. The transfer belt 40 passes through the nip of the primary transfer portion 50 for each color of yellow (Y), magenta (M), cyan (C), and black (K), and a developer (development image) on the photoreceptor of each color. Are transferred, color-superposed, and enter the nip portion of the secondary transfer unit 60.

  The transfer belt 40 that has passed through the secondary transfer unit 60 circulates again to receive the transfer image at the primary transfer unit 50, but on the upstream side where the primary transfer unit 50 is executed, the transfer belt 40 is a transfer belt cleaning blade. 49 or the like is performed for cleaning.

  The transfer belt 40 is composed of, for example, a flexible base layer 40a such as polyimide resin and an elastic layer 40b such as a rubber layer formed on the surface of the base layer 40a. Further, it is preferable to appropriately form a surface layer such as PFA on the surface of the elastic layer 40b. Such a transfer belt 40 is stretched by the backup roller 44 and the belt stretching roller 41 on the base material layer 40a side made of polyimide or the like so that the toner image is transferred on the surface layer side of PFA or the like. Used.

  Next, control of the image forming apparatus according to the present invention configured as described above will be described. FIG. 3 is a block diagram related to control of the image forming apparatus according to the embodiment of the present invention. In FIG. 2, reference numeral 200 denotes an image forming controller unit, 210 denotes a transfer material type information storage unit, 230 denotes a main control unit, and 250 denotes a contact nip adjusting mechanism control unit.

  The main control unit 230 is a main controller for performing each control of the image forming apparatus according to the present invention. As such a main control unit 150, a general-purpose information processing apparatus including a CPU, a RAM, a ROM, and the like is used, and a program for causing the CPU to execute an operation of outputting a command to a predetermined block based on input predetermined information Can be realized by storing in advance in the ROM.

The transfer material type information storage unit 210 is a storage unit that temporarily stores data relating to the type of transfer material on which an image is formed by the image forming apparatus. Such a transfer material type information storage unit 210 includes, for example, information from a determination sensor that determines the type of transfer material provided in the image forming apparatus, and a host device that outputs an image formation execution command to the image forming apparatus. Information from a sheet feeding device that supplies a transfer material to the image forming apparatus, or information from a control panel that is provided in a housing portion of the image forming apparatus and is operated by a user. Configured to store the information. The transfer material type information storage unit 210 stores what type of transfer material S is inserted into the pressure nip (Np) and the contact nip (Nc) to perform secondary transfer. The transfer material type data stored in the transfer material type information storage unit 210 is appropriately used for control in the main control unit 150.

  The image forming controller unit 200 generates data for image formation based on the image signal input to the image forming apparatus, and then appropriately outputs the generated data to the main control unit 150 side.

  The contact nip adjusting mechanism control unit 250 controls a mechanism that adjusts the length of the contact nip (Nc) formed in such a manner that the transfer belt 40 does not contact the backup roller 44 and is wound around the secondary transfer roller 61. Is. In the image forming apparatus according to the present embodiment, the contact nip adjusting mechanism control unit 250 adjusts the length of the contact nip (Nc) based on the data related to the transfer material S stored in the transfer material type information storage unit 210. By controlling the mechanism, an appropriate contact nip (Nc) length corresponding to the transfer material S is ensured to the minimum, the transfer efficiency is improved, and at the same time, the occurrence of image displacement is prevented as much as possible to improve the image quality. It is to make.

  By the way, a pattern in the case where data relating to the type of transfer material S stored in the transfer material type information storage unit 210 is input from the control panel will be described. For example, as a method of selecting coated paper or non-coated paper as the type of the transfer material S from the control panel, a method in which the user selects a paper type or product name built in the memory in advance from the control panel is conceivable. . In this case, as will be described later, each product name is recorded in the memory as to whether it corresponds to coated paper or uncoated paper.

  As a method for inputting data relating to the type of the transfer material S, a method in which the user directly selects either coated paper or non-coated paper from a control panel is conceivable.

  Moreover, when inputting the micro unevenness | corrugation of the transfer material S as data regarding the type of the transfer material S, it can be considered that the user selects a paper type or a product name from the control panel. At this time, the size of the unevenness for each product name is recorded in the memory.

  Further, as a method for inputting the minute unevenness of the transfer material S, a method in which the user inputs a value of the size of the unevenness (for example, Rz) from a control panel can be considered.

  Further, instead of selecting data relating to the type of transfer material S, the user may input the contact nip (Nc) length that the user wants to set directly from the control panel.

  How the transfer material S type and the contact nip (Nc) length set in the control panel are specifically used in the present embodiment as described above will be described later.

  An example of the operation of the contact nip adjusting mechanism controlled by the contact nip adjusting mechanism control unit 250 will be described. FIG. 3 is a diagram showing an operation example of the contact nip adjusting mechanism in the image forming apparatus according to the embodiment of the present invention. 4 is a view showing a state where only the pressure nip is formed by the contact nip adjusting mechanism, and FIG. 5 is a view showing a state where a contact nip having a predetermined length is formed in addition to the pressure nip by the contact nip adjusting mechanism. is there. FIG. 3 is a schematic view showing a configuration near the secondary transfer portion of the image forming apparatus, and FIGS. 4 and 5 are both enlarged views of the secondary transfer nip portion.

  In the operation example of the contact nip adjusting mechanism shown in FIG. 3, the length of the contact nip (Nc) is adjusted when the belt stretching roller 41 is displaced. The belt stretching roller 41 can take an arbitrary position between the position indicated by the solid line and the position indicated by the dotted line. At the position indicated by the solid line, the length of the contact nip (Nc) is zero, and the pressure nip (Np) only is formed (state shown in FIG. 4), and at the position shown by the dotted line, in addition to the pressure nip (Np), the maximum length contact nip (Nc) is formed (FIG. 5). State).

  As the transfer material S, there are types of coated paper with a predetermined coating on the surface, or non-coated paper without the coating, but when these are printed by an image forming apparatus, the coated paper is on the surface. The transfer efficiency in the secondary transfer part is relatively good with few minute irregularities, and uncoated paper is inferior to the transfer efficiency of coated paper.

  Therefore, in the image forming apparatus according to the present invention, when coated paper is used as the transfer material S, the length of the contact nip (Nc) is shortened or eliminated at all, and mainly the pressure nip (Np). ) To perform secondary transfer. In this case, since the contact nip (Nc) is relatively short, there is very little image displacement, and image quality is hardly deteriorated. Further, when coated paper is used, a transfer efficiency exceeding a predetermined level can be expected even with a nip configuration mainly composed of a pressure nip (Np).

  On the other hand, when uncoated paper is used as the transfer material S, a contact nip (Nc) of a certain length is taken, and this is used in combination with the pressure nip (Np) for secondary transfer. . In this case, since the contact nip (Nc) is set so as to secure the minimum necessary length, the resulting image misalignment is slight and the image quality is hardly deteriorated. Further, when using non-coated paper, even a nip configuration in which a contact nip (Nc) is provided together with a pressure nip (Np) provides good transfer efficiency.

In the nip configuration in which the contact nip (Nc) is provided in addition to the pressure nip (Np), the mechanism for improving the transfer efficiency is assumed as follows. That is, at the pressure nip (Np), the elastic layer 40b of the transfer belt 40 is deformed by the pressure load, so that the surface of the transfer belt 40 follows microscopic irregularities on the surface of the transfer material S. As a result, the adhesion between the toner image carried on the transfer belt 40 and the transfer material S is enhanced. Then, in the state in which the adhesion between the toner image and the transfer material S is high, an electric field is formed by the secondary transfer bias in the pressure nip (Np), so that the toner image carried on the transfer belt 40 becomes fine. Here, specific examples of coated paper and non-coated paper will be described. Examples of the coated paper that can be used in this embodiment include SA Kanto +, OK Kanto +, OK Top Coat +, OK Coat N Green 100, OK Top Coat Mat N, OK Coat L (above, Oji Paper Co., Ltd.). Made), Aurora Coat, Ultima Magros, MI Gloss, Pegasus, Ulite, Silver Diamond, Ultimax, Ulite L, Aurora LWX Matte, Piredera, Energy S, Pegasus Mat, Shirai Mat, Neptune, Ultima Silk, Aurora L , MI Silk, Aurora S, Pegasus Dull (Nippon Paper Industries Co., Ltd.).

  In addition, examples of uncoated paper that can be used in the present embodiment include OK Prince Fine, OK Prince Fine Eco G100, OK Everlight, OK Starlight, NEW Yamayuri R, White Yamayuri DX, Lilac (above, Oji Paper Co., Ltd.) Made, npi fine, Shirai, npi fine bulky, Highland, Justland, Alps, Whiteland, Andes, Andean Stuff, Highland Tough, Leaf Bulky White, Pyrene Tough, Cream Rocky Tough, White Rocky Tough, Hyper Pyrene There are tough, opera cream, alto cream (Nippon Paper Industries Co., Ltd.).

  By the way, when the toner image carried on the transfer belt 40 is transferred onto the surface of the transfer material S due to the secondary transfer nip configuration including only the pressure nip (Np), it adheres to the convex portion on the surface of the transfer material S. The toner is relatively easily peeled off from the transfer belt 40, but the toner attached to the concave portion on the surface of the transfer material S is less likely to peel from the transfer belt 40 than the toner attached to the convex portion of the transfer material S. The reason is considered as follows. When the contact nip (Nc) is not formed, the transfer material S is peeled from the transfer belt 40 at the exit of the pressure nip (Np) (the end of the pressure nip (Np) in the moving direction of the transfer material S). At this time, a relatively large physical adhesion force exists between the transfer belt 40 and the toner and between the transfer material and the toner due to the pressure applied at the pressure nip (Np). In the vicinity of the outlet of the pressure nip (Np), the pressure is suddenly released, and the deformation of the elastic layer 40b of the transfer belt 40 is recovered. Then, in the concave portion of the transfer material S, a minute gap tends to be generated between the concave portion of the transfer material S and the transfer belt 40, so that the cohesive force between the toners positioned in the concave portion of the transfer material S becomes small. On the other hand, since a large physical adhesion force exists between the transfer belt 40 and the toner near the outlet of the pressure nip (Np), the cohesive force between the toners causes the physical force between the transfer belt 40 and the toner. The toner film is broken in the film under the negative adhesion force. As a result, a part of the toner located in the concave portion of the transfer material S adheres to the transfer material S, but the remaining toner remains attached to the transfer belt 40, and it is considered that the toner remains untransferred.

In the secondary transfer portion as in this embodiment, the contact nip (Nc) is formed following the pressure nip (Np), so that the secondary transfer nip configuration is a transfer long nip. In the contact nip (Nc), the pressure contact between the backup roller 44 and the secondary transfer roller 61 via the transfer belt 40 is eliminated. Therefore, while the transfer material S is passing through the contact nip (Nc), almost no pressure is applied to the toner sandwiched between the transfer material S and the transfer belt 40. For this reason, the physical adhesion between the transfer belt 40 and the toner image carried on the transfer belt 40 is relaxed. In addition, a transfer current is generated in the pressure nip (Np) due to the secondary transfer bias, but the transfer belt 40 and the transfer material S are charged by the transfer current, so that an electric field also exists in the contact nip (Nc). . That is, while the transfer material S passes through the contact nip (Nc), an electric field acts on the toner in a state where the physical adhesion between the transfer belt 40 and the toner is relaxed. As a result, when the transfer belt 40 and the transfer material S are peeled off, the toner adhering to the concave portion on the surface of the transfer material S is affected by the electric field and the cohesive force between the toner adhering to the convex portion adjacent to the concave portion. As a result, peeling from the transfer belt 40 is facilitated. As described above, the contact nip (Nc) formed after the pressure nip (Np) causes the toner adhering to the concave portion of the transfer material S to be peeled off from the transfer belt 40 relatively easily, so that the transfer efficiency is improved. In the previous example, the length of the contact nip (Nc) is adjusted by the contact nip adjusting mechanism depending on whether the transfer material S is coated paper or uncoated paper. However, the length of the contact nip (Nc) can be adjusted according to other criteria, not depending on such criteria.

  For example, Rz is a parameter that defines the roughness of the surface of the transfer material S and the size of the microscopic unevenness. If this Rz is equal to or less than a predetermined value, there is little micro unevenness on the surface and secondary transfer is performed. The transfer efficiency in the area is relatively good. If the Rz is larger than a predetermined value, there are many irregularities and the transfer efficiency in the secondary transfer area is relatively poor.

  Therefore, when a transfer material S having an Rz of a predetermined value or less is used, the length of the contact nip (Nc) is shortened or eliminated at all, and the pressure nip (Np) is mainly used as the secondary material. Make a transfer. In this case, since the contact nip (Nc) is relatively short, there is very little image displacement, and image quality is hardly deteriorated. Further, when coated paper is used, a transfer efficiency exceeding a predetermined level can be expected even with a nip configuration mainly composed of a pressure nip (Np).

  On the other hand, when a transfer material S having an Rz larger than a predetermined value is used, a contact nip (Nc) having a certain length is taken, and this is used in combination with the pressure nip (Np) for secondary transfer. To do. In this case, since the contact nip (Nc) is set so as to secure the minimum necessary length, the resulting image misalignment is slight and the image quality is hardly deteriorated. Further, when using non-coated paper, even a nip configuration in which a contact nip (Nc) is provided together with a pressure nip (Np) provides good transfer efficiency.

  Next, the relationship between the contact nip (Nc) length and the pressure nip (Np) length will be described. In the image forming apparatus according to the present embodiment, even if the contact nip adjustment mechanism is adjusted so that the length of the contact nip (Nc) is maximized, the length of the contact nip (Nc) is equal to that of the pressure nip (Np). It is preferable to set the length to be shorter than the length. By setting in this way, the amount of winding of the transfer belt 40 wound around the secondary transfer roller 61 is reduced, so that the transfer belt 40 is compressed along the outer peripheral surface of the secondary transfer roller 61. Hardly bends. Therefore, since the bending direction of the surface of the transfer belt 40 hardly changes in the secondary transfer nip configuration, the change in the surface speed of the transfer belt 40 is suppressed between the pressure nip (Np) and the contact nip (Nc). As a result, it is possible to suppress the deviation of the image transferred to the transfer material during transfer.

  Further, when the contact nip adjustment mechanism is adjusted so that the length of the contact nip (Nc) is minimized, the length is preferably set to be zero. In other words, in the image forming apparatus according to the present embodiment, it is preferable to set the secondary transfer nip including only the pressure nip (Np). As described above, the transfer speed of the transfer belt 40 can be changed by transferring the transfer material S with little microscopic unevenness on the surface to the transfer material S having a high secondary transfer efficiency without providing a contact nip (Nc). It is possible to eliminate the accompanying image shift.

Next, preferred configurations of the secondary transfer roller 61 and the backup roller 44 that constitute the secondary transfer nip portion will be described. In the present embodiment, it is preferable to configure the secondary transfer roller 61 so that the diameter of the secondary transfer roller 61 is larger than the diameter of the backup roller 44. With this configuration, the transfer belt 40 can be easily guided from the end of the pressure nip (Np) to the backup roller 44 side. As a result, the contact nip width (length in the roller circumferential direction) of the contact nip (Nc) can be reduced, and the bending of the surface of the transfer belt 40 along the outer peripheral surface of the secondary transfer roller 61 in the compression direction can be more effectively suppressed. Further, in the image forming apparatus according to the present embodiment, the thickness of the elastic layer 61b of the secondary transfer roller 61 is larger than the distance of the peripheral surface of the secondary transfer roller 61 in the contact nip (Nc). It is preferable to configure as described above. With this configuration, the belt stretching roller 41 can easily guide the transfer belt 40 from the end of the pressure nip (Np) to the backup roller 44 side. As a result, the contact nip (Nc) width (the length in the circumferential direction of the roller) can be reduced, and the bending in the compression direction of the surface of the transfer belt 40 along the outer circumferential surface of the secondary transfer roller 61 can be more effectively suppressed. It becomes.

In the image forming apparatus according to the present embodiment, the thickness of the elastic layer 40b of the transfer belt 40 is preferably configured to be smaller than the distance of the peripheral surface of the secondary transfer roller 61 of the contact nip (Nc). . With this configuration, the belt stretching roller 41 can easily guide the transfer belt 40 from the end of the pressure nip (Np) to the backup roller 44 side. As a result, the contact nip (Nc) width (the length in the circumferential direction of the roller) can be reduced, and the bending in the compression direction of the surface of the transfer belt 40 along the outer circumferential surface of the secondary transfer roller 61 can be more effectively suppressed. Next, a contact nip adjusting mechanism used for adjusting the length of the contact nip (Nc) will be described. FIG. 6 is a view showing a configuration example of a contact nip adjusting mechanism in the image forming apparatus according to the embodiment of the present invention, and FIG. 7 is a view showing a cylindrical member 140 with an eccentric hole used in the contact nip adjusting mechanism.

  The transfer belt unit frame 110 rotatably holds the rollers such as the backup roller 44 and the belt stretching roller 41 that stretch the transfer belt 40 from both ends in an image forming apparatus housing (not shown). There are two frames. Although not shown in FIG. 6, the transfer belt unit frame 110 is provided at both ends of each roller in the axial direction.

  A secondary transfer unit frame 120 is attached to the transfer belt unit frame 110 so as to be rotatable about a secondary transfer unit frame rotation center portion 122. The secondary transfer unit frame 120 has a secondary transfer roller 61 rotatably attached around a secondary transfer roller rotation center portion 123, and the secondary transfer roller 61 is also sandwiched between the secondary transfer roller 61 and the secondary transfer roller 61. One piece is arranged at each end.

  Also, one end of a biasing member 130 such as a spring is attached to the biasing member end fixing portion 121 of the secondary transfer unit frame 120. Further, the other end of the urging member 130 is attached to an urging member end fixing portion 111 provided on the transfer belt unit frame 110. Thus, the secondary transfer roller 61 attached to the secondary transfer unit frame 120 always presses the backup roller 44 via the transfer belt 40. Thus, a transfer load at the secondary transfer nip is secured, and the toner particles on the transfer belt 40 are efficiently transferred to the transfer material S side at the secondary transfer nip.

  The transfer belt unit frame 110 is provided with a hole 112, and the outer peripheral surface of the eccentric hole-attached cylindrical member 140 is fitted into the hole 112. The cylindrical member 140 with an eccentric hole is provided with an eccentric hole 141 having a central axis Or at a position eccentric from the central axis Oc. A shaft end portion of the belt stretching roller 41 is rotatably attached to the eccentric hole 141.

  Further, the cylindrical member 140 with an eccentric hole attached to the hole portion 112 rotates about the central axis Oc, so that the central axis Or revolves about the central axis Oc. The contact nip adjusting mechanism control unit 250 controls the rotation of the cylindrical member 140 with the eccentric hole so that the roller shaft of the belt stretching roller 41 is displaced and the length of the contact nip (Nc) can be adjusted. It has become.

  In FIG. 6, when the contact nip adjusting mechanism control unit 250 rotates the cylindrical member 140 with the eccentric hole in the direction (a), the length of the contact nip (Nc) is increased, and the contact nip adjustment mechanism control unit 250 rotates in the direction (b). Then, the length of the contact nip (Nc) is reduced.

  According to the image forming apparatus of the present invention configured as described above, the elastic layer 61b is provided on the secondary transfer roller 61 side, and the backup roller 44 is provided on the secondary transfer roller 61 side via the transfer belt 40 and the transfer material. Good by forming a pressure nip (Np) so as to bite in, and subsequently forming a contact nip (Nc) in such a manner that the transfer belt 40 does not contact the backup roller 44 and wraps around the secondary transfer roller 61 In addition to providing excellent transferability, the adjustment unit that adjusts the contact nip adjustment mechanism appropriately controls the length of the contact nip (Nc), thereby preventing image displacement as much as possible and improving image quality. .

Next, another embodiment of the contact nip adjusting mechanism used for adjusting the length of the contact nip (Nc) will be described. FIG. 8 is a diagram showing a configuration example of a contact nip adjusting mechanism in an image forming apparatus according to another embodiment of the present invention, and FIG. 9 is an eccentric protrusion with an eccentric hole used in the contact nip adjusting mechanism in another embodiment. It is a figure which shows the cylindrical member 145 with a part.

  Also in other embodiments, the transfer belt unit frame 110 rotates each roller such as the backup roller 44 and the belt stretching roller 41 that stretches the transfer belt 40 in an image forming apparatus housing (not shown). These are two frames that are freely clamped from both ends. Although not shown in FIG. 6, the transfer belt unit frame 110 is provided at both ends of each roller in the axial direction.

  The transfer belt unit frame 110 is provided with a transfer belt unit frame hole 115, and the protruding portion 147 of the cylindrical member 145 with an eccentric protruding portion is fitted into the hole 115. The cylindrical member 145 with an eccentric protrusion is provided with a cylindrical protrusion 147 having a central axis Or at a position eccentric from the central axis Oc of the main body 146.

  A secondary transfer unit frame hole 125 is provided in the secondary transfer unit frame 120 to which the secondary transfer roller 61 is rotatably attached, with the secondary transfer roller rotation center portion 123 as a center. It arrange | positions so that the outer peripheral surface of the main-body part 146 of the cylindrical member 145 with a protrusion part may be fitted by the said hole part 125. FIG. In addition, the operation | movement relevant to the cylindrical member 145 with an eccentric protrusion part is mentioned later.

  In other embodiments as well, one end of a biasing member 130 such as a spring is attached to the biasing member end fixing portion 121 of the secondary transfer unit frame 120, and the other end of the biasing member 130 is The biasing member end fixing portion 111 provided on the transfer belt unit frame 110 is attached. Thus, the secondary transfer roller 61 attached to the secondary transfer unit frame 120 always presses the backup roller 44 via the transfer belt 40.

  Next, the operation of the contact nip adjusting mechanism configured as described above will be described. FIG. 10 is a diagram for explaining the operation of the contact nip adjusting mechanism in another embodiment. The contact nip adjusting mechanism control unit 250 is configured to control the rotation of the cylindrical member 145 with an eccentric protrusion.

  The protrusion 147 of the cylindrical member 145 with the eccentric protrusion is attached to the immovable transfer belt unit frame 110, whereas the main body 146 is attached to the movable secondary transfer unit frame 120. When the cylindrical member 145 with the eccentric protrusion is rotated, the center axis Oc of the main body 146 revolves around the center axis Or of the protrusion 147. Accordingly, when the contact nip adjusting mechanism control unit 250 rotates the cylindrical member 145 with the eccentric protruding portion, the main body portion 146 of the cylindrical member 145 with the eccentric protruding portion rotates around the protruding portion 147, and FIG. ) And a state as shown in FIG. When the contact nip adjusting mechanism control unit 250 sets the contact nip adjusting mechanism to the position as shown in FIG. 10A, the length of the contact nip (Nc) is reduced, and the position as shown in FIG. Then, the length of the contact nip (Nc) is increased.

  Next, another embodiment of the present invention will be described. FIG. 11 is a diagram illustrating a configuration of a secondary transfer nip portion in an image forming apparatus according to another embodiment of the present invention.

In the embodiments described so far, the structure in which the elastic layer 61b having a predetermined thickness is arranged around the secondary transfer roller 61 has been described. However, in the present embodiment, there is no elasticity around the secondary transfer roller 61. The elastic layer 44b is provided on the backup roller 44 side without providing a layer. That is, in this embodiment, the backup roller 44 has a structure in which an elastic layer 44b having a predetermined thickness is disposed around the roller body portion 44a. Even with such a structure, the pressure nip (Np) is formed so that the secondary transfer roller 61 bites into the backup roller 44 side via the transfer belt 40 and the transfer material S, and then the transfer belt 40 is connected to the backup roller 40. By forming the contact nip (Nc) so as to be wound around the secondary transfer roller 61 without contacting with the roller 44, good transferability can be obtained, and the length of the contact nip (Nc) is further increased. By adjusting by the method described above, it is possible to suppress the image shift.

  In another embodiment, the elastic layer 44 b is provided on the backup roller 44 side, but an elastic layer may be provided on both the secondary transfer roller 61 and the backup roller 44.

  Next, another embodiment of the present invention will be described. In another embodiment, the roller body 601 of the secondary transfer roller 61 is provided with a transfer material gripping mechanism. FIG. 12 is a diagram illustrating a configuration of the secondary transfer roller 61 in an image forming apparatus according to another embodiment including a transfer material gripping mechanism.

  Roller shaft portions 602 are provided at both ends of the roller body portion 601 of the secondary transfer roller 61, and the secondary transfer unit frame is configured such that the roller body portion 601 is rotatable about the roller shaft portion 602. It can be attached to the 120 side. The roller body 601 is provided with an opening recess 605 extending in the axial direction, and a transfer material gripping mechanism 610 is provided from one first opening edge 613 to the other second opening edge 614 of the opening recess 605. Is provided.

  The transfer material gripping mechanism 610 is a mechanism for gripping or releasing the transfer material S. The transfer material gripping mechanism 610 is generally composed of a plurality of pairs including transfer material gripping claws 611 and claw seat portions 612 provided discretely over the roller axis direction. The transfer material gripping claw 611 operates with the gripping claw rotation center 615 as the rotation center, thereby gripping the edge of the transfer material between the transfer material gripping claw 611 and the claw seat portion 612 or holding the transferred transfer material. Can be released.

  Also by the secondary transfer roller 61 having the transfer material gripping mechanism 610 as described above, it is possible to suppress image shift by adjusting the length of the contact nip (Nc) by the method described above.

  In the embodiment shown in FIG. 12, an elastic layer may be provided on the backup roller 44 side, or an elastic layer may be provided on both the secondary transfer roller 61 and the backup roller 44.

  Next, another embodiment of the present invention will be described. In the embodiment related to FIG. 12, the secondary transfer roller 61 is provided with an opening recess 605, and the transfer material gripping mechanism 610 is arranged in the opening recess 605 so as to grip the transfer material S. On the other hand, in the present embodiment, the transfer material S is gripped by air suction.

  FIG. 13 is a view showing a cross section of a secondary transfer roller 61 used in an image forming apparatus according to another embodiment of the present invention.

In the image forming apparatus of this embodiment, the roller body 61a of the secondary transfer roller 61 is formed in a cylindrical shape. One end of the cylindrical roller body portion 61a is closed by a disk-shaped end wall 61a ₁ having a rotating shaft 61d. The other end of the roller body portion 61a is partially closed by an annular end wall 61a ₂ having a rotational shaft 61e. The rotation shaft 61e of the other end with formed in a cylindrical shape, the axial direction of the air suction part connection hole 61f is provided extending through the end wall 61a ₂ and the rotary shaft 61e. Although not shown, the suction part connection hole 61f is selectively connected to an air supply part such as an air pump or an air blower and an air suction part via a switching valve.

  Further, the secondary transfer roller 61 is provided with a predetermined number of air flow nozzle holes 61g penetrating the cylindrical portion of the roller body portion 61a and the elastic layer 61b. These air flow nozzle holes 61 g are arranged along the axial direction of the secondary transfer roller 61. In that case, the air flow nozzle holes 61 g are arranged in a line along the axial direction of the secondary transfer roller 61. The air flow nozzle holes 61g are not limited to this, and a plurality of rows can be arranged in the circumferential direction along the axial direction of the secondary transfer roller 61. Thus, when providing the air flow nozzle holes 61g in a plurality of rows in the circumferential direction, they can be arranged in a staggered manner.

  In the image forming apparatus configured as described above, the switching valve is set so that the air suction part is connected to the air suction part connection hole 61f immediately before each air flow nozzle hole 61g reaches the secondary transfer nip 11c. At the same time, the air suction unit is activated. Thereby, the air inside the roller body 61a is sucked through the air suction part connection hole 61f, and the inside of the roller body 61a becomes a negative pressure. Then, the air in the vicinity of the outside in the air flow nozzle hole 61g forming portion of the secondary transfer roller 61 is sucked into the roller body 61a through each air flow nozzle hole 61g. In this state, when the transfer material S is fed from the gate roller 16 and the leading end portion 15a of the transfer material S reaches the air flow nozzle hole 61g forming portion of the secondary transfer roller 61, the leading end portion 15a of the transfer material S is It is sucked by each air flow nozzle hole 61g and adsorbed to the elastic layer 61b of the secondary transfer roller 61.

  Then, the toner image carried on the transfer belt 40 at the secondary transfer nip portion is transferred to the transfer material S in a state where the leading end portion of the transfer material S is adsorbed by each air flow nozzle hole 61g. Further, the transfer material S that has passed through the secondary transfer nip is reliably peeled off from the transfer belt 40 by adsorbing the leading end portion 15a of the transfer material S by the air flow nozzle holes 61g. Thereafter, the operation of the air suction unit is stopped, and the suction of the leading end portion of the transfer material S is completed. When the leading end of the transfer material S reaches the peeling position where the transfer material S is peeled off from the secondary transfer roller 61, the air supply unit is activated and the switching valve is switched so that the air supply unit is connected to the air suction unit connection hole 61f. Connected to. Then, positive pressure air is fed into the roller body 61a, and the positive pressure air flows out of the roller body 61a through the nozzle hole 61g. The transfer material S is easily peeled off from the secondary transfer roller 61 by the air that has flowed out.

  Also by the secondary transfer roller 61 having the transfer material gripping / peeling mechanism as described above, it is possible to suppress the image shift by adjusting the length of the contact nip (Nc) by the method described so far. . According to such an embodiment, the toner image carried on the transfer belt 40 is transferred to the transfer material S in a state in which the leading end portion of the transfer material S is sucked by the air flow nozzle holes 61g. S can be reliably peeled off from the transfer belt 40. Further, since the suction of the transfer material S through the air flow nozzle holes 61g is completed after the transfer, the transfer material S can be easily peeled off from the outer peripheral surface of the elastic layer 61b of the secondary transfer roller 61.

  In the embodiment shown in FIG. 13 as well, an elastic layer may be provided on the backup roller 44 side, or an elastic layer may be provided on both the secondary transfer roller 61 and the backup roller 44.

  As described above, according to the image forming apparatus and the image forming method of the present invention, the elastic layer is provided on the transfer roller side, and the pressure nip is formed so that the backup roller bites into the transfer roller side through the image carrier belt and the transfer material. Subsequently, the image carrier belt does not come into contact with the backup roller, and the contact nip is formed by being wound around the transfer roller. By appropriately controlling the length, the occurrence of image shift can be prevented as much as possible, and the image quality is improved.

10Y, 10M, 10C, 10K ... photoreceptor, 11Y, 11M, 11C, 11K ... corona charger, 12Y, 12M, 12C, 12K ... exposure unit, 13Y, 13M, 13C, 13K ... First photosensitive member squeeze roller, 13Y ′, 13M ′, 13C ′, 13K ′... Second photosensitive member squeeze roller, 14Y, 14Y ′, 14M, 14M ′, 14C, 14C ′, 14K, 14K ′,. Photoconductor squeeze roller cleaning blade, 18Y, 18M, 18C, 18K ... Photoconductor cleaning blade, 20Y, 20M, 20C, 20K ... Development roller, 21Y, 21M, 21C, 21K ... Development roller cleaning blade , 22Y, 22M, 22C, 22K ... compaction corona generator, 30Y, 3 M, 30C, 30K ... developing apparatus, 31Y, 31M, 31C, 31K ... developer container, 32Y, 32M, 32C, 32K ... anilox roller, 31Y, 31M, 31C, 31K ... developer Container, 33Y, 33M, 33C, 33K ... regulating blade, 34Y, 34M, 34C, 34K ... auger (supply roller), 40 ... transfer belt, 40a ... base material layer, 40b ... Elastic layer, 41 ... belt tension roller, 41c (belt tension roller) shaft, 42 ... belt tension roller, 44 ... backup roller, 44a ... roller body, 44b .. Elastic layer, 45... Developer collecting section, 46... Transfer belt cleaning roller, 47 .. transfer belt cleaning roller cleaning blade, 4 ... Transfer belt cleaning blade, 50Y, 50M, 50C, 50K ... Primary transfer part, 51Y, 51M, 51C, 51K ... Primary transfer backup roller, 52 ... Tension roller, 60 ... Secondary transfer unit 61 ... Secondary transfer roller 61a ... Roller barrel 61b ... Elastic layer 62 ... Secondary transfer roller cleaning blade 74 ... (Cleaning) Blade holding member 85 ... secondary transfer unit collection and storage unit, 90 ... fixing unit, 91 ... heating roller, 92 ... pressure roller, 95 ... first transfer roller, 96 ... second. Transfer roller, 101, 101 '... Gate roller, 110 ... Transfer belt unit frame, 111 ... Biasing member end fixing portion, 112 ... Hole portion , 115 ... transfer belt unit frame hole, 120 ... secondary transfer unit frame, 121 ... biasing member end fixing part, 122 ... secondary transfer unit frame rotation center part, 123 ...・ Secondary transfer roller rotation center, 125... Secondary transfer unit frame hole, 130... Biasing member, 140... Cylindrical member with eccentric hole, 141. Cylindrical member with eccentric protrusions 146... Body part 147... Protrusion part 200. , 250 ... Contact nip adjusting mechanism control unit, 601 ... Roller barrel, 602 ... Roller shaft, 605 ... Opening recess, 610 ... Transfer material gripping mechanism, 611 ... Transfer Material gripping claws, 612... Seat, 613 ... first opening edge, 614 ... second opening edge, 615 ... gripping claws pivot center

Claims (8)

An image carrier belt having an elastic layer and carrying an image;
A roller around which the image carrier belt is wound;
The image at a transfer nip including a pressure nip formed in pressure contact with the roller through the image carrier belt and a contact nip formed in contact with the image carrier belt not wound on the roller A transfer roller for transferring the image carried on the carrier belt to a transfer material;
A storage unit for storing information relating to the type of the transfer material transferred at the transfer nip;
An image forming apparatus comprising: an adjustment unit that adjusts a length of the contact nip in a moving direction of the transfer material based on the information stored in the storage unit. The image forming apparatus according to claim 1, wherein a length of the contact nip in the moving direction of the transfer material adjusted by the adjusting unit is shorter than a length of the pressure nip in the moving direction of the transfer material. The image forming apparatus according to claim 1, wherein an outer diameter of the transfer roller is larger than an outer diameter of the roller. The transfer roller has an elastic layer;
The image forming apparatus according to claim 1, wherein a thickness of the elastic layer of the transfer roller is larger than a length of the contact nip in a moving direction of the transfer material. 5. The image forming apparatus according to claim 1, wherein a thickness of the elastic layer of the image carrier belt is smaller than a length of the contact nip in a moving direction of the transfer material. 6. The image forming apparatus according to claim 1, wherein the transfer roller has a concave portion on a peripheral surface and a transfer material gripping member that grips the transfer material in the concave portion. The image forming apparatus according to claim 1, wherein the transfer roller has a nozzle hole that adsorbs or peels off the transfer material by a flow of air. Based on information relating to each transfer material gun stored in the storage unit, a pressure formed by press-contacting a roller around which the image carrier belt is wound and a transfer roller via an image carrier belt having an elastic layer The length of the transfer nip in the moving direction of the transfer nip of the transfer nip including the nip and the contact nip formed by the transfer roller contacting the image carrier belt not wound around the roller. Adjust
Carrying an image on the image carrier belt;
An image forming method, wherein the image carried on the image carrier is transferred to the transfer material at the transfer nip.

Images