JP2017003614A - Image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation apparatus which suppresses reduction in the color development property of a fixed image.SOLUTION: An image formation apparatus 10 comprises: first toner image formation units (for example, toner image formation units 20S, 20Y, 20M, 20C, 20K) which form a first toner image with first toner; a second toner image formation unit (for example, a toner image formation unit 20T) which forms a second toner image being the second toner image having the volume average particle diameter larger than that of the first toner and the low temperature side storage elastic modulus measured within a range of temperature between 30°C and 50°C larger than that of the first toner, and overlapped on the first toner image on a recording medium; and a fixation unit (for example, a fixation device 40) which fixes the toner image on the recording medium (for example, a sheet member P) with heat.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus.

Patent Document 1 discloses that “a storage elastic modulus (G1) of a color toner at 80 ° C. composed of at least one color toner selected from the group consisting of magenta toner, cyan toner and yellow toner and a transparent toner. Is 10 ⁴ Pa or more and 10 ⁶ Pa or less, the tangent loss (tan δ) of the color toner at 80 ° C. is 1.0 or more and 2.5 or less, the storage elastic modulus (G2) of the transparent toner at 80 ° C. and the color toner. Discloses a toner set that satisfies the following formula (1): 1.1 ≦ G2 / G1 ≦ 3.0 and a storage elastic modulus (G1) at 80 ° C., and an image forming apparatus using the toner set ” Yes.

JP 2010-79106 A

  An object of the present invention is a first toner image forming portion for forming a first toner image with a first toner, and a second toner image with a second toner having a volume average particle size larger than that of the first toner, An image forming apparatus comprising: a second toner image forming unit that forms a second toner image to be superimposed on a first toner image on a medium; and a fixing unit that fixes the toner image to a recording medium by heat. An object of the present invention is to provide an image forming apparatus that suppresses a decrease in color developability of a fixed image as compared with a case where a low temperature side storage elastic modulus is smaller than that of a first toner.

  The above problem is solved by the following means.

The invention according to claim 1
A first toner image forming unit for forming a first toner image with the first toner;
A second toner image with a second toner having a volume average particle size larger than that of the first toner and a low-temperature side storage elastic modulus measured in a temperature range of 30 ° C. or more and 50 ° C. or less. A second toner image forming unit for forming a second toner image to be superimposed on the first toner image on the recording medium;
A fixing unit for fixing the toner image to the recording medium by heat;
An image forming apparatus comprising:

The invention according to claim 2
The fixing unit includes a heating member that contacts one surface of the recording medium and heats the image; and a contact member that contacts the other surface of the recording medium;
When fixing the first toner image and the second toner image superimposed on the first toner image on one surface of the recording medium, the first toner image on which the second toner image is not superimposed is The image forming apparatus according to claim 1, further comprising a control unit configured to increase a heat amount applied to the toner image from the contact member as compared with a case where fixing is performed on one surface of the recording medium.

The invention according to claim 3
The fixing unit includes a heating member that contacts one surface of the recording medium and heats the image; and a contact member that contacts the other surface of the recording medium;
When fixing the first toner image and the second toner image superimposed on the first toner image on one surface of the recording medium, the first toner image on which the second toner image is not superimposed is The control unit according to claim 1, further comprising a control unit that reduces a difference between an amount of heat applied from the heating member to the toner image and an amount of heat applied from the contact member to the toner image as compared with a case where the image is fixed on one surface of the recording medium. Image forming apparatus.

  According to the first aspect of the present invention, the first toner image forming unit for forming the first toner image with the first toner and the second toner image with the second toner having a volume average particle diameter larger than that of the first toner are used. An image forming apparatus comprising: a second toner image forming unit that forms a second toner image superimposed on the first toner image on a recording medium; and a fixing unit that fixes the toner image to the recording medium by heat. There is provided an image forming apparatus that suppresses a decrease in color developability of a fixed image as compared with the case where the low temperature side storage elastic modulus of the second toner is smaller than that of the first toner.

  According to the second aspect of the present invention, when the first toner image and the second toner image superimposed on the first toner image are fixed to one surface of the recording medium, the second toner image is not superimposed. Provided is an image forming apparatus that suppresses a decrease in color developability of a fixed image when fixing the first toner image on one surface of a recording medium as compared with the case where the amount of heat applied to the image from the contact member is equal. The

  According to the invention of claim 3, when the first toner image and the second toner image superimposed on the first toner image are fixed on one surface of the recording medium, the second toner image is not superimposed. When fixing the first toner image on one side of the recording medium, compared to the case where the difference between the amount of heat applied from the heating member to the image and the amount of heat applied from the contact member to the image is equal, the color of the fixed image There is provided an image forming apparatus that suppresses deterioration of the property.

FIG. 2 is a schematic side view showing a photosensitive drum and the like provided in the image forming apparatus according to the first embodiment. FIG. 3 is a schematic configuration diagram illustrating an image forming unit provided in the image forming apparatus according to the first embodiment. 1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment. 6 is a graph showing a relationship between storage elastic modulus and temperature of a colored toner (an example of a first toner) and a transparent toner (an example of a second toner). FIG. 6 is a schematic configuration diagram illustrating a fixing device provided in an image forming apparatus according to a second embodiment. FIG. 6 is a schematic configuration diagram illustrating a fixing device provided in an image forming apparatus according to a second embodiment. FIG. 10 is a state diagram illustrating a state in which a plurality of sheet members are conveyed to a fixing device in a fixing device provided in an image forming apparatus according to a fifth embodiment. FIG. 6 is a schematic diagram for explaining a phenomenon in which a reduction in color developability of a fixed image occurs.

  Embodiments that are examples of the present invention will be described below. In addition, the same code | symbol is provided to the member which has the substantially the same function and effect | action through all the drawings, and the overlapping description may be abbreviate | omitted.

<< First Embodiment >>
An example of the image forming apparatus according to the first embodiment will be described with reference to FIGS. In addition, the arrow H shown in each figure is the vertical direction and indicates the apparatus vertical direction, and the arrow W is the horizontal direction and indicates the apparatus width direction.

<Overall configuration of image forming apparatus>
FIG. 3 is a schematic diagram illustrating an overall configuration of the image forming apparatus 10 as viewed from the front side. As shown in this figure, the image forming apparatus 10 includes an image forming unit 12 that forms an image on a sheet member P as a recording medium by an electrophotographic method, a medium conveying device 50 that conveys the sheet member P, and an image formed. And a post-processing unit 60 that performs post-processing and the like on the sheet member P.

  Further, the image forming apparatus 10 includes a control unit 70 that controls the above-described units and a power source unit 80 described later, and a power source unit 80 that supplies power to the units including the control unit 70.

  Further, the image forming unit 12 is transferred to the toner image forming unit 20 that forms a toner image, the transfer device 30 that transfers the toner image formed by the toner image forming unit 20 to the sheet member P, and the sheet member P. And a fixing device 40 (an example of a fixing unit) that fixes the toner image on the sheet member P.

  The medium conveyance device 50 includes a medium supply unit 52 that supplies the sheet member P to the image forming unit 12 and a medium discharge unit 54 that discharges the sheet member P on which the toner image is formed. The medium conveying device 50 includes a medium returning unit 56 that is used when images are formed on both surfaces of the sheet member P, and an intermediate conveying unit 58 that will be described later.

  The post-processing unit 60 includes a medium cooling unit 62 that cools the sheet member P to which the toner image has been transferred by the image forming unit 12, a correction device 64 that corrects the curvature of the sheet member P, and an image formed on the sheet member P. And an image inspection unit 66 for inspecting. Each unit constituting the post-processing unit 60 is disposed in the medium discharge unit 54 of the medium conveyance device 50.

  In the image forming apparatus 10, each part is accommodated in a housing 90 except for the discharged medium receiving part 541 constituting the medium discharging part 54 of the medium conveying apparatus 50. The housing 90 in this embodiment has a two-part structure composed of a first housing 91 and a second housing 92 that are adjacent to each other in the apparatus width direction. Thereby, the conveyance unit of the image forming apparatus 10 is downsized in the apparatus width direction.

  The first housing 91 accommodates a main part of the image forming unit 12 excluding the fixing device 40 described later, and a medium supply unit 52. The second casing 92 includes a fixing device 40 constituting the image forming unit 12, a medium discharge unit 54 excluding the discharge medium receiving unit 541, a medium cooling unit 62, an image inspection unit 66, and a medium return unit 56. The control unit 70 and the power supply unit 80 are accommodated. The 1st housing | casing 91 and the 2nd housing | casing 92 are couple | bonded by fastening means, such as a volt | bolt and a nut which is not illustrated as an example. In this coupled state, between the first housing 91 and the second housing 92, a communication opening 90C1 of the sheet member P from a transfer nip NT to a fixing nip NF, which will be described later, of the image forming unit 12, and a medium return unit A communication path 90C2 for the sheet member P from 56 to the medium supply unit 52 is formed.

(Image forming part)
As described above, the image forming unit 12 includes the toner image forming unit 20, the transfer device 30, and the fixing device 40. A plurality of toner image forming units 20 are provided so as to form a toner image for each color. In this embodiment, a total of six toner image forming portions 20 of transparent (T), special color (S), yellow (Y), magenta (M), cyan (C), and black (K) are provided. . (T), (S), (Y), (M), (C), and (K) shown in FIG. 3 indicate the colors described above. The transfer device 30 is configured to transfer a toner image for six colors onto a sheet member P at a transfer nip NT from a transfer belt 31 on which toner images for six colors are superimposed and transferred (details will be described later). ).
Here, the toner image forming unit 20T that forms a transparent (T) color toner image (an example of a second toner image) corresponds to an example of a second toner image forming unit, and includes special colors (S), yellow (Y ), Magenta (M), cyan (C), and black (K) toner image forming units 20S, 20Y, 20M, 20C, and 20K that form toner images (an example of a first toner image) are used as the first toner. This corresponds to an example of an image forming unit.

  A transparent toner image (hereinafter also referred to as “transparent toner image”) is a toner image made of transparent toner, and is a toner image having light transmittance (eg, light transmittance of 80% or more) in the visible range. On the other hand, the special color image is, for example, a toner image of a special color (S), which is a toner image of a user-specific corporate color toner that is used more frequently than other colors.

[Toner image forming section]
The toner image forming unit 20 for each color is basically configured in the same manner except for the toner to be used. Therefore, hereinafter, the image forming units 14 for each color will be described without particular distinction. As shown in FIG. 1, the image forming unit 14 of the toner image forming unit 20 includes a photosensitive drum 21, which is an example of an image carrier, a charger 22, an exposure device 23, and a developer which is an example of a developing unit. The apparatus 24, the cleaning apparatus 25, and the static elimination apparatus 26 are comprised.

[Photosensitive drum]
The photosensitive drum 21 is formed in a cylindrical shape and grounded, and is driven to rotate around its own axis by a driving unit (not shown). As an example, a photosensitive layer having a negative charging polarity is formed on the surface of the photosensitive drum 21. As shown in FIG. 3, the photosensitive drums 21 of the respective colors are arranged in a straight line along the apparatus width direction when viewed from the front.

[Charger]
As shown in FIG. 1, the charger 22 charges the surface (photosensitive layer) of the photosensitive drum 21 to a negative polarity. In this embodiment, the charger 22 is a corona discharge type (non-contact charging type) scorotron charger.

[Exposure equipment]
The exposure device 23 forms an electrostatic latent image on the surface of the photosensitive drum 21. Specifically, the exposure light L modulated according to the image data received from the image signal processing unit 71 (see FIG. 3) constituting the control unit 70 is applied to the surface of the photosensitive drum 21 charged by the charger 22. It comes to irradiate. An electrostatic latent image is formed on the surface of the photosensitive drum 21 by irradiation of the exposure light L by the exposure device 23.

[Developer]
The developing device 24 forms a toner image on the surface of the photosensitive drum 21 by developing the electrostatic latent image formed on the surface of the photosensitive drum 21 with the developer G containing toner.

  The developing device 24 is supplied with toner from a toner cartridge 27 that holds toner.

[Cleaning device]
The cleaning device 25 has a blade shape that scrapes off the toner remaining on the surface of the photosensitive drum 21 after the toner image is transferred to the transfer device 30 from the surface of the photosensitive drum 21.

[Staticizer]
The neutralization device 26 performs neutralization by irradiating the photosensitive drum 21 after the transfer with light. As a result, the charging history of the surface of the photosensitive drum 21 is canceled.

[Transfer device]
The transfer device 30 performs primary transfer by superimposing the toner image of the photosensitive drum 21 of each color on the transfer belt 31, and secondarily transferring the superimposed toner image to the sheet member P. This will be specifically described below.

[Transfer belt]
As shown in FIG. 2, the transfer belt 31 has an endless shape and is wound around a plurality of rolls 32 to determine the posture. In this embodiment, the transfer belt 31 has a reverse obtuse triangular posture that is long in the apparatus width direction when viewed from the front. Among the plurality of rolls 32, the roll 32D shown in FIG. 2 functions as a drive roll that rotates the transfer belt 31 in the arrow A direction by the power of a motor (not shown).

  Of the plurality of rolls 32, the roll 32 </ b> T illustrated in FIG. 2 functions as a tension applying roll that applies tension to the transfer belt 31. Among the plurality of rolls 32, the roll 32B shown in FIG. 2 functions as a counter roll of a secondary transfer roll 34 described later. As described above, the top of the lower end side forming the obtuse angle of the transfer belt 31 in the inverted obtuse triangular shape is wound around the roll 32B. The transfer belt 31 is in contact with the photosensitive drum 21 of each color from below at the upper side extending in the apparatus width direction in the above-described posture.

[Primary transfer roll]
Inside the transfer belt 31, a primary transfer roll 33, which is an example of a transfer member that transfers the toner image on each photosensitive drum 21 to the transfer belt 31, is disposed. Each primary transfer roll 33 is disposed opposite to the corresponding photosensitive drum 21 with the transfer belt 31 in between. The primary transfer roll 33 is applied with a transfer bias voltage having a polarity opposite to the toner polarity. By applying this transfer bias voltage, the toner image formed on the photosensitive drum 21 is transferred to the transfer belt 31.

[Secondary transfer roll]
Further, the transfer device 30 includes a secondary transfer roll 34 that transfers the toner image superimposed on the transfer belt 31 to the sheet member P. The secondary transfer roll 34 is arranged so that the transfer belt 31 is sandwiched between the secondary transfer roll 34 and the roll 32 </ b> B, and a transfer nip NT is formed between the secondary transfer roll 34 and the transfer belt 31. The sheet member P is supplied to the transfer nip NT from the medium supply unit 52 in a timely manner. The secondary transfer roll 34 is applied with a transfer bias voltage having a polarity opposite to the toner polarity by a power supply unit (not shown). By applying the transfer bias voltage, the toner image is transferred from the transfer belt 31 to the sheet member P onto the sheet member P passing through the transfer nip NT.

[Cleaning equipment]
Furthermore, the transfer device 30 includes a cleaning device 35 that cleans the transfer belt 31 after the secondary transfer. The cleaning device 35 is disposed downstream of the portion where the secondary transfer is performed (transfer nip NT) and upstream of the portion where the primary transfer is performed in the circumferential direction of the transfer belt 31. The cleaning device 35 includes a blade 351 that scrapes off toner remaining on the surface of the transfer belt 31 from the surface of the transfer belt 31.

[Fixing device: Overview]
The fixing device 40 fixes the toner image to the sheet member P to which the toner image has been transferred by the transfer device 30 by heat.

(Medium transport device)
As shown in FIG. 3, the medium conveyance device 50 includes a medium supply unit 52, a medium discharge unit 54, a medium return unit 56, and an intermediate conveyance unit 58.

[Media supply unit]
The medium supply unit 52 includes a container 521 in which the sheet members P are stacked and stored. In this embodiment, two containers 521 are arranged side by side along the apparatus width direction below the transfer apparatus 30.

  From each container 521 to the transfer nip NT which is the secondary transfer position, a medium supply path 52P is formed by a plurality of conveyance roll pairs 522, a guide (not shown), and the like. The medium supply path 52P has a shape (substantially “S” shape) that reaches the transfer nip NT while being folded and raised in the apparatus width direction at two folding portions 52P1 and 52P2.

  A delivery roll 523 that sends out the uppermost sheet member P stacked on the container 521 is disposed above each container 521. Among the plurality of conveyance roll pairs 522, the conveyance roll pair 522S on the most upstream side in the conveyance direction of the sheet member P separates the sheet members P sent from the container 521 by the delivery roll 523 one by one. Act as a role. Further, among the plurality of conveyance roll pairs 522, the conveyance roll pair 522R located immediately upstream of the transfer nip NT in the conveyance direction of the sheet member P is a movement timing of the toner image on the transfer belt 31 and a conveyance timing of the sheet member P. It is designed to work together.

  Further, the medium supply unit 52 includes a preliminary transport path 52Pr. The preliminary transport path 52Pr originates from the opening 91W on the opposite side of the first casing 91 from the second casing 92, and joins the folded portion 52P2 of the medium supply path 52P. The preliminary conveyance path 52Pr conveys when the sheet member P sent from an optional recording medium supply device (not shown) arranged adjacent to the opening 91W side of the first housing 91 is sent to the image forming unit 12. It is a route.

[Intermediate transport section]
As shown in FIG. 2, the intermediate conveyance unit 58 includes an endless conveyance belt that is disposed between the transfer nip NT of the transfer device 30 and the fixing nip NF of the fixing device 40 and is wound around a roll. A plurality of belt conveying members 581 are provided.

  The conveying belt circulates and conveys the sheet member P while sucking air (negative pressure suction) from the inside of the conveying member 581 and sucking the sheet member P onto the surface of the conveying belt.

[Media discharge section]
As shown in FIG. 3, the medium discharge unit 54 is configured to place the sheet member P on which the toner image is fixed by the fixing device 40 of the image forming unit 12 on the side opposite to the first casing 91 side in the second casing 92. It discharges to the outside of the housing 90 from a discharge port 92 </ b> W formed at the end of the housing.

  The medium discharge portion 54 includes a discharge medium receiving portion 541 that receives the sheet member P discharged from the discharge port 92W.

  The medium discharge section 54 has a medium discharge path 54P that conveys the sheet member P from the fixing device 40 (fixing nip NF) to the discharge port 92W. The medium discharge path 54P is formed by a belt conveying member 543, a plurality of roll pairs 542, a guide (not shown), and the like. Of the plurality of roll pairs 542, the roll pair 542E disposed on the most downstream side in the discharge direction of the sheet member P functions as a discharge roll that discharges the sheet member P onto the discharge medium receiving portion 541.

[Media return section]
The medium return unit 56 includes a plurality of roll pairs 561. The plurality of roll pairs 561 form a reverse path 56P through which the sheet member P that has passed the image inspection unit 66 is sent when there is a request to form images on both sides. The reverse path 56P includes a branch path 56P1, a transport path 56P2, and a reverse path 56P3. The branch path 56P1 is branched from the medium discharge path 54P. The conveyance path 56P2 is configured to send the sheet member P received from the branch path 56P1 to the medium supply path 52P. The reversing path 56P3 is provided in the middle of the transport path 56P2, and the front and the back are reversed by turning back the transport direction of the sheet member P transported through the transport path 56P2 (switchback transport). .

(Post-processing section)
The medium cooling unit 62, the correction device 64, and the image inspection unit 66 constituting the post-processing unit 60 are upstream of the branching portion of the branch path 56P1 in the discharge direction of the sheet member P on the medium discharge path 54P of the medium discharge unit 54. Further, they are arranged in this order from the upstream side in the discharge direction.

[Medium cooling section]
The medium cooling unit 62 includes a heat absorbing device 621 that absorbs the heat of the sheet member P, and a pressing device 622 that presses the sheet member P against the heat absorbing device 621. The heat absorption device 621 is disposed on the upper side with respect to the medium discharge path 54P, and the pressing device 622 is disposed on the lower side with respect to the medium discharge path 54P.

  The endothermic device 621 includes an endless endothermic belt 6211, a plurality of rolls 6212 that support the endothermic belt 6211, a heat sink 6213 disposed in the endothermic belt 6211, and a fan 6214 for cooling the heat sink 6213. It is configured.

  The endothermic belt 6211 is in contact with the sheet member P so that heat exchange is possible on the outer peripheral surface. Among the plurality of rolls 6212, the roll 6212 </ b> D functions as a driving roll that transmits driving force to the heat absorbing belt 6211. The heat sink 6213 is slidably in surface contact with the inner peripheral surface of the endothermic belt 6211 within a predetermined range along the medium discharge path 54P.

  The pressing device 622 includes an endless pressing belt 6221 and a plurality of rolls 6222 that support the pressing belt 6221. The pressing belt 6221 is wound around a plurality of rolls 6222. The pressing device 622 conveys the sheet member P with the endothermic belt 6211 while pressing the sheet member P against the endothermic belt 6211 (heat sink 6213).

[Correction device]
A correction device 64 is provided on the downstream side of the medium cooling unit 62 in the medium discharge unit 54. The correction device 64 is configured to correct the curvature (curl) of the sheet member P received from the medium cooling unit 62.

[Image Inspection Department]
An inline sensor 661 that constitutes a main part of the image inspection unit 66 is disposed on the downstream side of the correction device 64 in the medium discharge unit 54. The in-line sensor 661 detects the presence and extent of a toner density defect, an image defect, an image position defect, and the like of the fixed toner image based on the light irradiated onto the sheet member P and reflected from the sheet member P. ing.

(Control part)
The control unit 70 is configured as a computer that controls the entire apparatus and performs various calculations. Specifically, the control unit 70 is not shown, but includes, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory) storing various programs, and a RAM used as a work area when executing the programs. (Random Access Memory), a nonvolatile memory for storing various information, and an input / output interface (I / O). Each of the CPU, ROM, RAM, nonvolatile memory, and I / O is connected via a bus.

  In addition to the control unit 70, the image forming apparatus 10 includes, for example, an operation display unit, an image processing unit, an image memory, an image forming unit, a storage unit, and a communication unit (not shown). The operation display unit, the image processing unit, the image memory, the image forming unit, the storage unit, and the communication unit are connected to the I / OE of the control unit 70. The control unit 70 exchanges information with each unit of the operation display unit, the image processing unit, the image memory, the image forming unit, the storage unit, and the communication unit, and controls each unit. The image forming units referred to here are the image forming unit 12 of the image forming apparatus 10, the medium transport device 50, and the post-processing unit 60.

<Image Forming Operation (Action) of Image Forming Apparatus>
Next, an outline of an image forming process on the sheet member P by the image forming apparatus 10 and a subsequent processing process will be described.
Various operations of the image forming apparatus 10 are performed by a control program executed in the control unit 70. Here, in the image forming apparatus 10, for example, a control program for “image forming processing” is stored in the ROM in advance. The control program stored in advance is read out by the CPU and executed using the RAM as a work area. In the image forming apparatus 10, for example, various data such as “image forming conditions (various process control values)” are stored in advance in a nonvolatile memory. These control programs and various data may be stored in other storage devices such as a ROM, a nonvolatile memory, or a storage unit, or may be acquired from the outside via a communication unit.

  First, as illustrated in FIG. 3, the control unit 70 that has received the image formation command operates the toner image forming unit 20, the transfer device 30, and the fixing device 40. As a result, as shown in FIG. 2, the photosensitive drum 21 of each color image forming unit 14 and the developing roll 242 of the developing device 24 are rotated, and the transfer belt 31 is circulated. Further, the pressure roll 42 is rotated and the fixing belt 411 is rotated. Further, in synchronization with these operations, the control unit 70 operates the medium transport device 50 and the like.

  As a result, the photosensitive drums 21 of the respective colors are charged by the charger 22 while being rotated. In addition, the control unit 70 sends the image data that has been subjected to image processing by the image signal processing unit to each exposure device 23. Each exposure device 23 emits each exposure light L according to the image data and exposes each charged photosensitive drum 21. Then, an electrostatic latent image is formed on the surface of each photosensitive drum 21. The electrostatic latent image formed on each photoconductor drum 21 is developed by the developer supplied from the developing device 24. As a result, the corresponding color toner among the transparent (T), special color (S), yellow (Y), magenta (M), cyan (C), and black (K) is applied to the photosensitive drum 21 of each color. An image is formed.

  The toner images of the respective colors formed on the photosensitive drums 21 of the respective colors are sequentially transferred onto the rotating transfer belt 31 by applying a transfer bias voltage through the primary transfer roll 33 of each color. As a result, a superimposed toner image (or a single-layer toner image of the target color) is formed on the transfer belt 31 by superimposing the toner image of the target color. This toner image is conveyed to the transfer nip NT by the rotation of the transfer belt 31.

  As shown in FIG. 3, the transfer nip NT has a sheet member in time with conveyance of a superimposed toner image (or a single-layer toner image of a target color) by a conveyance roll pair 522 </ b> R of the medium supply unit 52. P is supplied. By applying a transfer bias voltage at the transfer nip NT, a superimposed toner image (or a single-layer toner image of a target color) is transferred from the transfer belt 31 to the sheet member P.

  The sheet member P to which the toner image has been transferred is conveyed by the intermediate conveyance unit 58 from the transfer nip NT of the transfer device 30 toward the fixing nip NF of the fixing device 40. The fixing device 40 applies heat and pressure to the sheet member P that passes through the fixing nip NF. As a result, the toner image transferred to the sheet member P is fixed, and a fixed image is obtained.

  The sheet member P discharged from the fixing device 40 is processed by the post-processing unit 60 while being conveyed by the medium discharge unit 54 toward the discharge medium receiving unit 541 outside the apparatus. The sheet member P heated in the fixing process is first cooled in the medium cooling unit 62. Next, the curvature of the sheet member P is corrected by the correction device 64. Further, the toner image fixed on the sheet member P is detected by the image inspection unit 66 for the presence or absence of toner density defects, image defects, image position defects, and the like. Then, the sheet member P is discharged to the medium discharge unit 54.

  On the other hand, when an image is formed on the non-image surface of the sheet member P on which no image is formed (in the case of double-sided printing), the control unit 70 uses the conveyance path of the sheet member P after passing through the image inspection unit 66 as a medium. The medium discharge path 54P of the discharge unit 54 is switched to the branch path 56P1 of the medium return unit 56. As a result, the sheet member P is turned upside down via the reversing path 56P and fed into the medium supply path 52P. An image is formed (fixed) on the back surface of the sheet member P in the same process as the image forming process on the front surface described above. The sheet member P is discharged to the discharge medium receiving part 541 outside the apparatus by the medium discharge part 54 through the same process as the process after the image forming on the surface described above.

<Main part configuration>
Next, toner for forming transparent (T), special color (S), yellow (Y), magenta (M), cyan (C), and black (K) toner images will be described.

(toner)
Special color (S), yellow (Y), magenta (M), cyan (C), and black (K) toners (one example of the first toner: hereinafter also referred to as “colored toner”) are special colors ( S), yellow (Y), magenta (M), cyan (C), and black (K) toner images (an example of a first toner image: hereinafter also referred to as “colored toner image”) Toner.
On the other hand, the transparent (T) toner (an example of the second toner: hereinafter also referred to as “transparent toner”) is a transparent (T) image (an example of the second toner image: hereinafter also referred to as “transparent toner image”). . The transparent toner image is a toner image that is fixed in a state where it is superimposed (overlapped) on the colored toner image on the sheet member P for the purpose of protecting the image or imparting glossiness.
The transparent toner has a volume average particle size larger than that of the colored toner, and a low temperature storage modulus measured in the temperature range of 30 ° C. to 50 ° C. is larger than that of the colored toner. That is, the color toner has a volume average particle size smaller than that of the transparent toner, and has a low temperature side storage elastic modulus measured in the temperature range of 30 ° C. or more and 50 ° C. or less than that of the color toner.

Here, the difference in the low-temperature storage elastic modulus between the colored toner and the transparent toner (difference in absolute value) is, for example, 1.0 × 10 ⁸ Pa or more (preferably from the viewpoint of suppressing the decrease in color developability of the fixed image) Is 1.0 × 10 ⁸ Pa or more).
In addition, for both colored toners and transparent toners, the low-temperature side storage elastic modulus is preferably in the range of, for example, 3.0 × 10 ⁷ Pa or more and 1 × 10 ⁹ Pa or less from the viewpoint of toner fixability.
Furthermore, for both colored toners and transparent toners, the storage elastic modulus at 80 ° C. is preferably in the range of, for example, 3.0 × 10 ³ Pa to 7.0 × 10 ⁵ Pa from the viewpoint of toner fixing properties.

  The storage elastic modulus of the toner is adjusted by the kind and molecular weight of the binder resin, the kind and amount of the internal additive (colorant, etc.), and the like. In addition, after applying a resin having an ester group in the molecule (polyester resin, styrene- (meth) acrylic copolymer resin, etc.) as a binder resin, a metal complex that becomes a metal ion source is added to the toner, The storage elastic modulus of the toner may be adjusted by ionic crosslinking of the ester groups of the resin with metal ions.

The storage elastic modulus of the toner is measured using a rheometer (ARES) manufactured by TA Instruments Co., Ltd. for measuring the storage elastic modulus G ′. Specifically, the storage modulus of toner is measured by setting a sample (toner) on a sample holder with a diameter of 8 mm, a temperature rising rate of 1 ° C./min, a frequency of 1 Hz, a strain of 1% or less, and a detected torque that is a guaranteed value Within the range of And the change of the storage elastic modulus with respect to a temperature change is obtained. The analysis uses software that is a standard of a viscoelasticity measuring apparatus.
And the low temperature side storage elastic modulus measured in the temperature range of 30 degreeC or more and 50 degrees C or less is calculated | required as an average value of each storage elastic modulus calculated | required in the range of temperature 30 degreeC or more and 50 degrees C or less. That is, “the low temperature side storage elastic modulus is large or small” indicates that this average value is large or small.

  Here, an example of the relationship between the storage elastic modulus and the temperature of the color toner and the transparent toner is shown in FIG. As shown in FIG. 4, the storage elastic modulus of both the color toner and the transparent toner decreases as the temperature rises, and the storage elastic modulus of the transparent toner is higher than that of the color toner in the temperature range of 30 ° C. to 50 ° C. Is high.

On the other hand, the difference in volume average particle diameter between the color toner and the transparent toner (difference in absolute value) is, for example, in the range of 0.3 μm or more and 2.7 μm or less (preferably from the viewpoint of suppressing the decrease in color development of the fixed image) Is preferably in the range of 1.1 μm to 2.0 μm.
The volume average particle diameter of the colored toner is preferably in the range of 3.5 μm to 5.1 μm, for example. On the other hand, the volume average particle size of the transparent toner is preferably in the range of 5.4 μm to 6.2 μm, for example, from the viewpoint of toner fixability.

The volume average particle diameter of the toner is a value measured using Coulter Multisizer II (manufactured by Beckman-Coulter) and the electrolyte using ISOTON-II (manufactured by Beckman-Coulter).
In the measurement, 0.5 mg to 50 mg of a measurement sample is added as a dispersant to 2 ml of a 5% aqueous solution of a surfactant (preferably sodium alkylbenzenesulfonate). This is added to 100 ml or more and 150 ml or less of the electrolytic solution.
The electrolyte in which the sample is suspended is dispersed for 1 minute with an ultrasonic disperser, and the particle size distribution of particles having a particle size in the range of 2 μm to 60 μm is measured using a 100 μm aperture with a Coulter Multisizer II. taking measurement. The number of particles to be sampled is 50,000.
Then, a cumulative distribution is drawn from the small diameter side on the volume basis with respect to the particle size range (channel) divided based on the measured particle size distribution, and the particle size that becomes 50% cumulative is obtained as the volume average particle size D50v.

The colored toner includes, for example, a binder resin such as a polyester resin and a polystyrene- (meth) acrylic copolymer resin, and a colorant that exhibits a target color. The colored toner may contain a known internal additive such as a release agent, if necessary. The colored toner may be an externally added toner to which a known external additive such as silica particles is added.
On the other hand, the transparent toner contains a binder resin such as a polyester resin and a polystyrene- (meth) acrylic copolymer resin. The transparent toner does not contain a colorant, or even if it contains a colorant, the content of the colorant is 0.01% by mass or less. The transparent toner may also contain a known internal additive such as a release agent, if necessary. The transparent toner may also be an external additive toner to which a known external additive such as silica particles is added.

<Operation of main components>
Next, the operation of the main configuration will be described.

First, the image forming apparatus 10 forms a transparent toner image (an example of a second toner image) with a transparent toner (an example of a second toner) in a toner image forming unit 20T (an example of a second toner image forming unit). In the image forming units 20S, 20Y, 20M, 20C, and 20K (an example of a first toner image forming unit), a colored toner image (an example of a first toner image) is formed using colored toners (an example of a first toner) of each color. When these images are formed, in the rotation direction of the transfer belt 31, the transparent toner image formed by the upstream toner image forming unit 20T is first transferred to the transfer belt 31, and the downstream toner image forming units 20S, 20S, The colored toner formed by 20Y, 20M, 20C, and 20K is superimposed on the transparent toner image and transferred to the transfer belt 31.
Next, the superimposed toner image transferred to the transfer belt 31 is transferred from the transfer belt 31 to the sheet member P. At this time, the superimposed toner image on the sheet member P is in a state in which the transparent toner image is superimposed on the colored toner image (see FIG. 8A). In this state, the sheet member P to which the superimposed toner image is transferred is conveyed by the intermediate conveyance unit 58 from the transfer nip NT of the transfer device 30 toward the fixing nip NF of the fixing device 40. The fixing device 40 applies heat and pressure to the sheet member P that passes through the fixing nip NF. As a result, the superimposed toner image transferred to the sheet member P is fixed, and a fixed image is obtained.

  Here, in the superimposed toner image on the sheet member P, when the volume average particle diameter of the transparent toner that forms the transparent toner image is larger than the colored toner that forms the colored toner image that is the lower layer of the transparent toner image, the colored toner When the superimposed toner image in which the transparent toner image is superimposed on the image is fixed, a phenomenon may occur in which the transparent toner of the upper transparent toner image destroys the toner layer structure of the lower colored toner image (FIG. 8B). ). For this reason, the color developability of the fixed image (fixed image of the lower color toner image in this embodiment) may be lowered.

In contrast, when the low-temperature storage elastic modulus of the transparent toner that forms the transparent toner image is larger than that of the colored toner image that is the lower layer of the transparent toner image, the transparent toner image is superimposed on the colored toner image. When fixing the superimposed toner image in the state, the melting of the colored toner easily proceeds before the transparent toner, and the binding between the colored toners also proceeds in the colored toner image. As a result, even when the volume average particle diameter of the transparent toner forming the transparent toner image is larger than that of the colored toner forming the colored toner image serving as the lower layer of the transparent toner image, the transparent toner image of the upper layer is transparent at the time of fixing. The toner layer structure of the underlying colored toner image is not easily destroyed by the toner.
For this reason, in the image forming apparatus 10, a reduction in color developability of the fixed image (in this embodiment, the fixed image of the lower color toner image) is suppressed.

  In FIGS. 8A and 8B, TN1 indicates a color toner, TNL1 indicates a color toner image, TN2 indicates a transparent toner, and TNL2 indicates a transparent toner image.

<< Second Embodiment >>
Next, an example of an image forming apparatus according to the second embodiment will be described. In addition, about the same member as 1st Embodiment, the same code | symbol is attached | subjected, the description is abbreviate | omitted, and a different part from 1st Embodiment is mainly demonstrated.

  The image forming apparatus according to the second embodiment includes the following fixing device 40, and the fixing device 40 fixes the toner image on the sheet member P to obtain a fixed image.

(Fixing device)
As shown in FIG. 6, the fixing device 40 includes a fixing module 120 as an example of a heating member including an endless fixing belt 122, and a pressure roll as an example of a contact member that contacts and pressurizes the fixing module 120. 150. Further, a fixing nip NF in which the fixing belt 122 and the pressure roll 150 are in contact is formed between the fixing belt 122 and the pressure roll 150.

[Fixing module]
The fixing module 120 includes the above-described fixing belt 122, a support member 124, and an internal heating roll 126. The fixing belt 122 rotates and conveys the sheet member P to heat the toner image and fix the toner image on the sheet member P. The support member 124 is configured to support the fixing belt 122 by receiving the pressure of the pressure roll 150 at a position corresponding to the fixing nip NF inside the fixing belt 122. Further, the internal heating roll 126 is disposed on the inner side of the fixing belt 122 on the side opposite to the fixing nip NF, and the fixing belt 122 is wound around the inner heating roll 126.

  Although not shown, the fixing belt 122 has a configuration in which an elastic layer made of silicone rubber is formed on a polyimide base material and a fluororesin-based release layer is further formed on the elastic layer. ing.

  The support member 124 includes a fixing roll 128 as an example of a rotating member, and a peeling pad 130 as an example of a peeling member. The fixing roll 128 and the peeling pad 130 are from the upstream side in the conveyance direction of the sheet member P. They are arranged in this order. Then, the rotation force of a motor (not shown) is transmitted to the fixing roll 128 and the fixing roll 128 rotates, so that the fixing belt 122 rotates in the direction of arrow C.

  Further, the peeling pad 130 is configured to have an outer surface 130 </ b> A on which a corner portion U for bending the fixing belt 122 is formed. Then, when the leading end of the sheet member P passes through the corner portion U, the leading end of the sheet member P is separated from the fixing belt 122.

  Further, a support roll 134, a support roll 136, and a support roll 138 around which the fixing belt 122 is wound are disposed inside the fixing belt 122.

  The support roll 134 is disposed downstream of the peeling pad 130 in the circumferential direction of the fixing belt 122. Further, the support roll 136 and the support roll 138 are disposed between the fixing roll 128 and the internal heating roll 126 in the vertical vertical direction.

  In addition, the fixing module 120 includes an external heating roll 132 that is disposed on the outer peripheral side of the fixing belt 122 and defines a circulation path thereof. The external heating roll 132 is disposed so as to sandwich the fixing belt 122 with the support roll 138.

  Inside the fixing roll 128, the internal heating roll 126, and the external heating roll 132, halogen lamps 139A, 139B, and 139C as an example of a heating unit are arranged. The fixing roll 128 and the internal heating roll 126 come into contact with the inner peripheral surface 122B of the fixing belt 122 to heat the fixing belt 122 from the inside, and the external heating roll 132 comes into contact with the outer peripheral surface 122A of the fixing belt 122 for fixing. The belt 122 is heated from the outside.

[Pressure roll]
As an example, the pressure roll 150 is configured by covering the outer circumference of a cylindrical roll body 150A made of aluminum with an elastic body layer 150B made of silicone rubber. Although not shown, a release layer made of a fluorine resin having a film thickness of 100 μm is formed on the outer peripheral surface of the elastic layer 150B. The pressure roll 150 is rotated in the direction of arrow E in the drawing at the same peripheral speed as the peripheral speed of the fixing belt 122 by the rotational force of a motor (not shown) being transmitted.

[Others]
The fixing device 40 brings the pressure roll 150 and the fixing belt 122 into contact with each other, contacts the pressure roll 150 against the fixing belt 122 (see FIG. 6), and separates the pressure roll 150 away from the fixing belt 122. A pair of support members 140 that support the pressure roll 150 in a movable manner are provided at positions (see FIG. 5A). The pair of support members 140 are respectively arranged on both sides of the device depth direction (paper depth direction) with respect to the pressure roll 150, and support the rotating shaft 151 of the pressure roll 150 via a bearing (not shown).

  Further, a pair of cylinders 142 that move the pressure roll 150 supported by the support member 140 to a contact position or a separation position are arranged on both sides in the apparatus depth direction (paper depth direction) with respect to the pressure roll 150, respectively. ing. The cylinder 142 moves the rotary shaft 151 of the pressure roll 150 via a bearing (not shown).

  Further, the fixing device 40 includes a fan 146 as an example of a blowing member that blows air onto the pressure roll 150.

  Further, the fixing device 40 includes a temperature sensor 160 that detects the surface temperature of the fixing belt 122 in a non-contact manner, and a temperature sensor 162 that detects the surface temperature of the pressure roll 150 in a non-contact manner.

<Operation of Fixing Device 40>
Next, the operation of the fixing device 40 will be described.

  In the fixing device 40, heat and pressure are applied to the sheet member P onto which the superimposed toner image with the transparent toner image superimposed on the color toner image is transferred, and the superimposed toner image is transferred to the sheet member P.

  Here, when the control unit 70 controls the fixing device 40 to fix the superimposed toner image in which the transparent toner image is superimposed on the colored toner image on the sheet member P (one surface thereof), the transparent toner image Compared to the case where the colored toner image (or the superimposed toner image in which the colored toner images of the respective colors are superimposed) is fixed on the sheet member P (one surface thereof), the pressure roller 15 converts the toner image from the pressure roll 15 to the toner image. Increase the amount of heat applied.

  Hereinafter, the overall control of the fixing unit 40 by the control unit 70 will be described first, and then control for increasing the amount of heat applied to the toner image from the pressure roll 15 during fixing will be described.

  When the image forming apparatus 10 is powered off, the pressure roll 150 is disposed at a separated position as shown in FIG. When the image forming apparatus 10 is turned on, the control unit 70 turns on the halogen lamps 139A, 139B, and 139C disposed inside the fixing roll 128, the internal heating roll 126, and the external heating roll 132. Further, the control unit 70 controls a motor (not shown) to rotate the fixing roll 128 to rotate (rotate) the fixing belt 122 at a predetermined peripheral speed (belt warm-up process).

  Further, the control unit 70 controls a motor (not shown) to rotate the pressure roll 150 at the same peripheral speed as that of the fixing belt 122. Further, the control unit 70 receives information from the temperature sensor 160. When the fixing belt 122 reaches a predetermined surface temperature (for example, 170 [° C.]), the cylinder 142 is controlled to move the pressure roll 150 from the separated position as shown in FIG. Move to contact position. Then, the pressure roll 150 is brought into contact with the rotating fixing belt 122. Thereby, the pressure roll 150 is heated (roll heating process).

  Then, the control unit 70 receives information on the surface temperature of the pressure roll 150 from the temperature sensor 162, and when the surface temperature of the pressure roll 150 reaches a predetermined temperature, the control unit 70 controls the cylinder 142. Then, the pressure roll 150 is moved from the contact position to the separation position (see FIG. 5A).

  Further, the control unit 70 controls the lighting of the halogen lamps 139A, 139B, and 139C, maintains the surface temperature of the fixing belt 122 at a predetermined temperature, and controls the operation and non-operation of the fan 146, thereby The surface temperature of the pressure roll 150 is maintained at a predetermined temperature (standby state).

  Here, when fixing the superimposed toner image in which the transparent toner image is superimposed on the colored toner image on the sheet member P, the controller 70 maintains the surface temperature of the pressure roll 150 at, for example, 135 [° C.]. To do. In the case where a colored toner image (or a superimposed toner image in which colored toner images of respective colors are superimposed) is not superimposed on the sheet member P (hereinafter sometimes referred to as “normal fixing”). Moreover, the control unit 70 maintains the surface temperature of the pressure roll 150 at, for example, 70 [° C.].

  That is, when fixing the superimposed toner image in which the transparent toner image is superimposed on the colored toner image on the sheet member P, the control unit 70 sets the surface temperature of the pressure roll 150 as compared with the case of normal fixing. Make it high. The surface temperature of the fixing belt 122 is maintained at the same temperature in any case.

  The surface temperature of the pressure roll 150 can be changed by moving the pressure roll 150 to the contact position in the roll heating step and changing the time for which the pressure roll 150 and the fixing belt 122 are brought into contact with each other. Specifically, the controller 70 fixes the pressure roll 150 and the fixing belt 122 in the roll heating process when fixing the superimposed toner image in a state where the transparent toner image is superimposed on the colored toner image on the sheet member P. The contact time is made longer than the contact time between the pressure roll 150 and the fixing belt 122 in the roll heating process in the case of normal fixing.

  Then, when the toner image is fixed on the sheet member P, as shown in FIG. 6, the pressure roll 150 maintained at a predetermined temperature is moved from the separated position to the contact position, The fixing belt 122 is brought into contact (fixable state). Then, the toner image is fixed on the sheet member P by conveying the sheet member P between the fixing belt 122 and the pressure roll 150.

  Here, as described above, when fixing the superimposed toner image in a state where the transparent toner image is superimposed on the colored toner image on the sheet member P, the control unit 70 applies pressure as compared with the case of normal fixing. The surface temperature of the roll 150 is increased. As a result, when the superimposed toner image in which the transparent toner image is superimposed on the colored toner image is fixed on the sheet member P, the amount of heat applied to the toner image from the pressure roll 150 side as compared with the case of normal fixing. Becomes larger.

  When the amount of heat applied to the toner image from the pressure roll 150 side is increased, the transparent toner image is formed when the superimposed toner image in which the transparent toner image is superimposed on the colored toner image is fixed on the sheet member P. Prior to the toner, the melting of the colored toner that forms the colored toner image easily proceeds, and the binding property between the colored toners also progresses in the colored toner image. As a result, even when the volume average particle diameter of the transparent toner forming the transparent toner image is larger than that of the colored toner forming the colored toner image serving as the lower layer of the transparent toner image, the transparent toner image of the upper layer is transparent at the time of fixing. The toner layer structure of the underlying colored toner image is not easily destroyed by the toner.

  Therefore, in the image forming apparatus according to the second embodiment, compared to the first embodiment (that is, when the superimposed toner image in which the transparent toner image is superimposed on the colored toner image is fixed on the sheet member P, and when the transparent toner image is fixed) The amount of heat applied to the toner image from the pressure roll 150 side is equal when fixing the color toner image (or the superimposed toner image in which the color toner images of the respective colors are superimposed) on the sheet member P to which the images are not superimposed. In comparison with this case, a decrease in color developability of the fixed image (fixed image of the lower-layer colored toner image in the present embodiment) is suppressed.

«Third embodiment»
Next, an example of an image forming apparatus according to the third embodiment will be described. In addition, about the same member as 1st and 2nd embodiment, the same code | symbol is attached | subjected, the description is abbreviate | omitted, and a different part from 1st and 2nd embodiment is mainly demonstrated.

  In the image forming apparatus according to the third embodiment, in the roll heating process of the fixing device 40, when the superimposed toner image in a state where the transparent toner image is superimposed on the colored toner image is fixed on the sheet member P, the pressure roll 150 is used. The time for contacting the fixing belt 122 with the fixing belt 122 is the same as the time for contacting the pressure roll 150 and the fixing belt 122 when the transparent toner is not used in normal fixing.

  In the image forming apparatus according to the third embodiment, regarding the surface temperature of the pressure roll 150, when the pressure roll 150 is rotated in contact with the fixing belt 122 in order to heat the pressure roll 150 in the roll heating step. It can be changed by changing the rotational speed (circumferential speed) of the fixing belt 122.

  Specifically, the control unit 70 normally fixes the rotation speed of the fixing belt 122 when the superimposed toner image in which the transparent toner image is superimposed on the color toner image is fixed on the sheet member P in the roll heating process. In this case, the rotational speed of the fixing belt 122 is faster. Similarly, the rotation speed of the pressure roll is also increased.

  That is, the area of the fixing belt 122 where the pressure roll 150 contacts the fixing belt 122 is increased per unit time. As a result, when the superimposed toner image in which the transparent toner image is superimposed on the colored toner image is fixed on the sheet member P, the surface temperature of the pressure roll 150 becomes higher than in the case of normal fixing. Other operations are the same as those in the first and second embodiments.

<< Fourth Embodiment >>
Next, an example of an image forming apparatus according to the fourth embodiment will be described. In addition, about the same member as 1st and 2nd embodiment, the same code | symbol is attached | subjected, the description is abbreviate | omitted, and a different part from 1st and 2nd embodiment is mainly demonstrated.

  In the image forming apparatus according to the fourth embodiment, in the standby state of the fixing device 40, at least one of the operation time of the fan 146 and the amount of air blown by the fan 146 (the amount of air blown to the pressure roll 150) is controlled. Thus, when the superimposed toner image in which the transparent toner image is superimposed on the colored toner image is fixed to the sheet member P, the surface temperature of the pressure roll 150 is increased as compared with the case of normal fixing.

  Specifically, the control unit 70 adds the surface temperature of the pressure roll 150 in the roll heating step when fixing the superimposed toner image in a state where the transparent toner image is superimposed on the colored toner image on the sheet member P. The surface temperature of the pressure roll 150 is set higher. Thereafter, the control unit 70 places the fixing device 40 in a standby state.

  In the standby state, the control unit 70 controls the fan 146 to lower the surface temperature of the pressure roll 150 to a predetermined surface temperature. And if the surface temperature of the pressure roll 150 falls, the control part 70 will make the fan 146 non-operation (it stops).

  Here, when fixing the superimposed toner image in a state where the transparent toner image is superimposed on the colored toner image on the sheet member P, the control unit 70 shortens the operation time of the fan 146 compared to the case of normal fixing. And at least one of control of reducing the amount of blowing by the fan 146. As a result, when the superimposed toner image in which the transparent toner image is superimposed on the colored toner image is fixed on the sheet member P, the surface temperature of the pressure roll 150 becomes higher than in the case of normal fixing.

  Note that, when the surface temperature of the pressure roll 150 disposed at the separated position becomes higher than a predetermined surface temperature due to heat received from the fixing belt 122 side, the control unit 70 causes the fan 146 to operate again. Then, the surface temperature of the pressure roll 150 is lowered to a predetermined surface temperature.

  Other operations are the same as in the second embodiment.

«Fifth embodiment»
Next, an example of an image forming apparatus according to the fifth embodiment will be described with reference to FIG. In addition, about the same member as 1st and 2nd embodiment, the same code | symbol is attached | subjected, the description is abbreviate | omitted, and a different part from 1st and 2nd embodiment is mainly demonstrated.

  In the image forming apparatus according to the fifth embodiment, a sheet member conveyed immediately before and after a superimposed toner image in which a transparent toner image is superimposed on a colored toner image is fixed on the sheet member P and in a case of normal fixing. The distance with P is changed. In the following description, the sheet member P to which the superimposed toner image in a state where the transparent toner image is superimposed on the colored toner image is fixed as “sheet member P1”, and the colored toner image in which the transparent toner image is not superimposed ( Alternatively, the sheet member P to which a superimposed toner image in which colored toner images of respective colors are superimposed is fixed may be referred to as “sheet member P2”.

  Specifically, when the toner image is continuously fixed on the sheet member P, the control unit 70 determines the distance between the sheet member P1 and the sheet member P conveyed by the fixing device 40 immediately before the sheet member P1 (see FIG. 7 is longer than the distance (S2 in FIG. 7) between the sheet member P2 and the sheet member P conveyed by the fixing device 40 immediately before the sheet member P2. The conveyance speed of the sheet member P is constant.

  Here, “continuously fixing the toner image on the sheet member P” means that the pressure roll 150 and the fixing belt 122 are brought into contact with each other to be able to fix the toner image, and this state is maintained and the toner image is maintained on a plurality of sheets. It is fixing continuously to the member P.

  That is, the pressure roll 150 is heated when the pressure roll 150 and the fixing belt 122 come into contact between the sheet members P that are continuously conveyed. That is, when the distance between the conveyed sheet members P is long, the degree of heating of the pressure roll 150 is increased and the surface temperature of the pressure roll 150 is higher than when the distance is short.

  Here, as described above, the control unit 70 determines the distance (S1 in FIG. 7) between the sheet member P1 and the sheet member P conveyed immediately before the sheet member P1 immediately before the sheet member P2 and the sheet member P2. The distance is longer than the distance (S2 in FIG. 7) from the conveyed sheet member P. As a result, when the superimposed toner image in which the transparent toner image is superimposed on the colored toner image is fixed to the sheet member P, the surface temperature of the pressure roll 150 becomes higher than in the case of normal fixing.

  As a method of increasing the distance between the sheet members P, the distance between the sheet members P is increased by changing the timing at which the toner image is transferred to the sheet member P. For example, the color toner image (or the color toner image of each color is superimposed) is set as the transfer interval when the superimposed toner image in which the color toner image is superimposed on the transparent toner image on the transfer belt 31 is transferred to the sheet member P. Superposed toner image) The distance between the sheet members P becomes longer by making the ratio between the transfer intervals when transferring a single toner image to the sheet member P twice.

  Other operations are the same as those in the second embodiment.

<< Sixth Embodiment >>
Next, an example of an image forming apparatus according to the sixth embodiment will be described. In addition, about the same member as 1st and 2nd embodiment, the same code | symbol is attached | subjected, the description is abbreviate | omitted, and a different part from 1st and 2nd embodiment is mainly demonstrated.

  In the image forming apparatus according to the sixth embodiment, the toner from the fixing belt 122 side is fixed in the case where the superimposed toner image in which the transparent toner image is superimposed on the color toner image is fixed on the sheet member P and in the case of normal fixing. The difference between the amount of heat applied to the image and the amount of heat applied to the toner image from the pressure roll 150 side is reduced.

  Specifically, the control unit 70 increases the surface temperature of the pressure roll 150 so that the difference between the amount of heat applied to the toner image from the fixing belt 122 side and the amount of heat applied to the toner image from the pressure roll 150 side. Make it smaller. Other operations are the same as those in the first and second embodiments.

≪Test example≫
Hereinafter, test examples supporting the effects of the image forming apparatus according to the present embodiment will be shown. The powder coating material according to the present embodiment is not limited to these test examples. In the following description, “part” and “%” are all based on mass unless otherwise specified.

<Production of developer>
(Preparation of cyan developer (C1))
-Synthesis of crystalline polyester resin (1)-
In a heat-dried three-necked flask, 100 mol% of decanedicarboxylic acid, 100 mol% of nonanediol, and 0.25% of dibutyltin oxide as a catalyst with respect to the total weight of these monomers were added. Under an inert atmosphere with nitrogen gas, the mixture was stirred and refluxed at 180 ° C. for 5 hours with mechanical stirring.

Thereafter, the temperature was gradually raised to 230 ° C. under reduced pressure, and the mixture was stirred for 2 hours. When it became viscous, it was cooled with air, the reaction was stopped, and a crystalline polyester resin (1) was synthesized. The weight average molecular weight (Mw) of the obtained crystalline polyester resin (1) was 24000 and the number average molecular weight (Mn) was 7600 by molecular weight measurement (polystyrene conversion) by gel permeation chromatography. The acid value was 10.5.
Further, the melting temperature (Tm) of the crystalline polyester resin (A) showed a clear endothermic peak, and the endothermic peak temperature was 72.3 ° C. In addition, the melting temperature of the crystalline polyester resin and the glass transition temperature (Tg) of the amorphous polyester resin are in accordance with ASTM D3418-8, a differential scanning calorimeter (manufactured by Mac Science: DSC3110, thermal analysis system 001). Was measured by measuring from 0 ° C. to 150 ° C. under a temperature rising rate of 10 ° C./min. The melting temperature was the peak temperature of the endothermic peak, and the glass transition temperature was the temperature at the intersection of the extension line of the base line and the rising line in the stepwise endothermic part.

-Synthesis of Amorphous Polyester Resin (1)-
-Bisphenol A ethylene oxide 2-mol adduct: 10 mol%
-Bisphenol A propylene oxide adduct: 90 mol%
・ Terephthalic acid: 40 mol%
・ Fumaric acid: 40 mol%
-Dodecenyl succinic acid: 20 mol%
The above monomer is charged into a 5 liter flask equipped with a stirrer, nitrogen inlet tube, temperature sensor, and rectifying column. The temperature is raised to 190 ° C. over 1 hour, and the reaction system is uniformly stirred. Then, 0.9% of tin distearate was added to the total weight of these monomers. Further, while distilling off the generated water, it took 6 hours from the same temperature to raise the temperature to 240 ° C., and continued the dehydration condensation reaction at 240 ° C. for another 3 hours, the glass transition temperature was 60 ° C., and the acid value was 13.6 mgKOH. / G, Amorphous polyester resin (1) having a weight average molecular weight of 16000 and a number average molecular weight of 6000 was obtained.

-Synthesis of Amorphous Polyester Resin (2)-
-Bisphenol A ethylene oxide 2-mol adduct: 50 mol%
-Bisphenol A propylene oxide adduct: 50 mol%
-Trimellitic anhydride: 7 mol%
・ Terephthalic acid: 65 mol%
・ Dodecenyl succinic acid: 28 mol%
The reaction was carried out using monomers other than trimellitic anhydride in the same manner as in the amorphous polyester resin (1) until the softening temperature reached 110 ° C. Next, the temperature was lowered to 190 ° C., and 7 mol% of trimellitic anhydride was gradually added, and the reaction was continued for 1 hour at the same temperature. The glass transition temperature was 56 ° C., the acid value was 11.3 mg KOH / g, and the weight average molecular weight was 78000. An amorphous polyester resin (2) having a number average molecular weight of 7800 was obtained.

-Preparation of resin particle dispersion (1)-
-Crystalline polyester resin (1): 100 parts-Methyl ethyl ketone: 60 parts-Isopropyl alcohol: 15 parts Charge methyl ethyl ketone into a 5 L separable flask, then gradually add the resin, and stir with a three-one motor. The oil phase was obtained by dissolving. The 5 L separable flask containing the oil phase was set to 65 ° C. with a water bath, and a 10% aqueous ammonia solution was gradually added dropwise to the stirred oil phase with a dropper so that the total amount became 5 parts. Further, 230 parts of ion-exchanged water was gradually added dropwise at a rate of 10 ml / min to phase-invert and emulsify, and the solvent was removed while reducing the pressure with an evaporator to obtain a resin particle dispersion (1) containing a crystalline polyester resin (1). ) The resin particles had a volume average particle size of 145 nm. (The resin particle solid content was adjusted to 20% with ion-exchanged water)

-Preparation of resin particle dispersion (2)-
-Amorphous polyester resin (1): 100 parts-Methyl ethyl ketone: 60 parts-Isopropyl alcohol: 15 parts Charge methyl ethyl ketone into a 5 L separable flask, and then gradually add the resin, and stir with a three-one motor. And completely dissolved to obtain an oil phase. The 5 L separable flask containing the oil phase is set to 40 ° C. with a water bath, and 10% aqueous ammonia solution is gradually added dropwise to the stirred oil phase with a dropper so that the total amount becomes 3.5 parts. Further, 230 parts of ion-exchanged water is gradually added dropwise at a rate of 10 ml / min to carry out phase inversion emulsification, and the solvent is removed while reducing the pressure with an evaporator, and the resin particle dispersion containing the amorphous polyester resin (1) is dispersed. A liquid (2) was obtained. The volume average particle diameter of the resin particles was 175 nm. (The resin particle solid content was adjusted to 20% with ion-exchanged water)

-Preparation of resin particle dispersion (3)-
In the preparation of the resin particle dispersion (2), the resin particle dispersion is the same as the preparation of the resin particle dispersion (2) except that the amorphous polyester resin (1) is changed to the amorphous polyester resin (2). A liquid (3) was obtained. The volume average particle diameter of the resin particles was 165 nm. (The resin particle solid content was adjusted to 20% with ion-exchanged water)

-Preparation of colorant particle dispersion-
Cyan pigment (Daiichi Seika Co., Ltd .: ECB-301): 50 parts Ionic surfactant Neogen RK (Daiichi Kogyo Seiyaku): 5 parts Ion-exchanged water: 195 parts After dispersion for 10 minutes by ultra turrax), dispersion processing is performed for 15 minutes at a pressure of 250 MPa using an optimizer (counter-impact type wet pulverizer: Sugino Machine), the central particle size of the colorant particles is 130 nm, and the solid content A 20% colorant particle dispersion was obtained.

-Preparation of release agent particle dispersion-
-Olefin wax (melting temperature: 88 ° C): 60 parts-Ionic surfactant Neogen RK (Daiichi Kogyo Seiyaku): 1.8 parts-Ion-exchanged water: 238 parts After dispersing with Ultra Turrax T50 manufactured, it was heated to 110 ° C. with a pressure discharge type gorin homogenizer and dispersed for 1 hour to obtain a release agent particle dispersion having a center diameter of 180 nm and a solid content of 20%.

-Production of cyan toner (C1)-
Resin particle dispersion (1): 100 parts Resin particle dispersion (2): 300 parts Resin particle dispersion (3): 300 parts Colorant particle dispersion: 50 parts Release agent particle dispersion: 50 parts or more were mixed and dispersed by stirring after adding 2.0 parts of the ionic surfactant Neogen RK in a round stainless steel flask. Subsequently, 1N nitric acid aqueous solution was dropped to pH 3.5, and then 0.40 part of polyaluminum chloride was added thereto, and the dispersion operation was continued with an ultra turrax. The flask was heated to 48 ° C. with stirring in an oil bath for heating. After holding at 48 ° C. for 40 minutes, a mixed solution of 100 parts of the resin particle dispersion (2) and 100 parts of the resin particle dispersion (3) was added thereto.
Thereafter, a 1N aqueous sodium hydroxide solution was added to bring the pH of the system to 7.0, and then the stainless steel flask was sealed and gradually heated to 90 ° C. while continuing to stir using a magnetic seal. Hold at 3 ° C. for 3 hours.

After completion of the reaction, the mixture was cooled, filtered, washed with ion exchange water, and then subjected to solid-liquid separation by Nutsche suction filtration. This was further redispersed in 1 L of ion exchange water at 40 ° C., and stirred and washed at 300 rpm for 15 minutes.
This was repeated five more times, and when the pH of the filtrate became 7.5 and the electric conductivity was 7.0 μS / cmt, solid-liquid separation was performed using No5A filter paper by Nutsche suction filtration. Next, vacuum drying was continued for 12 hours to obtain cyan toner (C1).

-Preparation of externally added cyan toner (C1)-
Cyan toner (C1): 100 parts, 0.8 part of hydrophobic titania treated with decylsilane having a volume average particle diameter of 15 nm, 1.1 parts of hydrophobic silica (NY50, manufactured by Nippon Aerosil Co., Ltd.), volume After adding 1.0 part of hydrophobic silica (X24, manufactured by Shin-Etsu Chemical Co., Ltd.) having an average particle size of 100 nm and mixing for 10 minutes at a peripheral speed of 32 m / s using a Henschel mixer, using a sieve of 45 μm mesh Coarse particles were removed to obtain an externally added cyan toner (C1).

-Carrier production-
Ferrite (trade name EFC-35B, manufactured by Powdertech, weight average particle size; 35 μ): 100 partsToluene: 13.5 parts Methyl methacrylate / perfluorooctyl methacrylate copolymer (polymerization ratio 90:10, Weight average molecular weight 49,000): 2.3 parts, tin oxide-coated barium sulfate (trade name: Pastorlan type IV, manufactured by Mitsui Kinzoku Mining Co., Ltd.): 0.3 parts, Eposter S (melamine resin particles, manufactured by Nippon Shokubai Co., Ltd.): 0 .3 parts The above components except for ferrite were dispersed in a sand mill for 1 hour to prepare a resin coating layer forming solution. Next, this resin coating layer forming solution and ferrite were put in a vacuum degassing kneader and stirred for 20 minutes while reducing the pressure at a temperature of 60 ° C. to form a resin coating layer on the ferrite to obtain a carrier. The volume resistance (22 ° C., humidity 55% ° C.) was 2 × 10 ¹¹ Ωcm.

-Production of cyan developer (C1)-
Externally added cyan toner (C1): To 7 parts, 100 parts of a carrier was added and mixed for 5 minutes by a ball mill to obtain a cyan developer (C1).

(Transparent developer (T1))
In the production of the cyan toner (C1), the volume average particle size is the same as that of the cyan toner (C1) and the low temperature side storage elastic modulus is the same as that of the cyan toner (C1) except that no colorant particle dispersion is used. The same transparent toner (T1) was also prepared (from 30 ° C. to 50 ° C.). Then, using the transparent toner (T1), a transparent developer (T1) was produced in the same manner as the cyan developer (C1).

(Cyan developer (C2))
In the production of the cyan toner (C1), the volume average particle size is smaller than that of the cyan toner (C1), and the low temperature side storage is similar to that of the cyan toner (C1) except that the amount of polyaluminum chloride is reduced. A cyan toner (C2) having a low elastic modulus (30 ° C. or more and 50 ° C. or less) was produced. Then, using the cyan toner (C2), a cyan developer (C2) was produced in the same manner as the cyan developer (C1).

(Cyan developer (C3))
In the production of cyan toner (C1), the amount of polyaluminum chloride is reduced, and the temperature maintained before adding 100 parts of resin particle dispersion (2) and 100 parts of resin particle dispersion (3) is maintained. The volume average particle size is smaller than that of the cyan toner (C1) and the low temperature side elastic modulus (30 ° C. or more and 50 ° C. or less) is the same as that of the cyan toner (C1) except that the temperature exceeds 48 ° C. Produced the same cyan toner (C3). Then, using the cyan toner (C3), a cyan developer (C3) was produced in the same manner as the cyan developer (C1).

<Comparative Example 1, Test Examples 1-2, Reference Example 1>
An image forming apparatus “Color 1000 Press (manufactured by Fuji Xerox Co., Ltd.)” (provided with a fixing module (heating member) and a pressure roll (contact member)) in a combination of a cyan developer and a transparent developer according to Table 1. In the fixing device (see FIG. 6), a developing device for forming a cyan image and a developing device for forming a transparent toner image in a remodeled machine modified so that the heating temperature of the pressure roll can be changed were loaded.
Then, using this image forming apparatus, a superimposed toner image is formed by superimposing a transparent toner image having an image density of 100% on a cyan toner image having a size of 30 mm × 30 mm and an image density of 100% on A4 paper. Fixing was performed under the fixing conditions shown in 1. Further, a cyan toner image having a size of 30 mm × 30 mm and an image density of 100% was independently formed on A4 paper, and fixing was performed under the fixing conditions shown in Table 1.

Then, the color developability of the fixed image was examined. Specifically, the color difference (ΔE) between the fixed image obtained by fixing the superimposed toner image obtained by superimposing the transparent toner image on the cyan toner image and the fixed image of the cyan toner image alone was examined.
For image density measurement, X-rite 938 (manufactured by X-rite) was used, and the color difference (ΔE) was measured. The color difference (ΔE) is obtained by taking the square root of the square sum of the distance difference in the L * a * b * space in the CIE 1976 (L * a * b *) color system. The CIE 1976 (L * a * b *) color system is a color space recommended by the CIE (International Lighting Commission) in 1976, and is defined in “JIS Z 8729” in the Japanese Industrial Standards.

  Details and evaluation results of each example are listed in Table 1.

From the above results, Test Examples 1 and 2 in which a transparent toner having a volume average particle diameter larger than that of the cyan toner and having a low temperature side storage elastic modulus measured in the temperature range of 30 ° C. to 50 ° C. is larger than that of the cyan toner are as follows. It can be seen that, compared to Comparative Example 1 in which a transparent toner having a volume average particle size larger than that of the cyan toner and having the same low temperature side storage modulus as that of the cyan toner is applied, a decrease in color development of the fixed image is suppressed.
In Test Example 2 in which the heating temperature of the pressure roll (that is, the amount of heat applied to the toner image from the back side of the paper by the heating roll) is increased, the decrease in the generation of the fixed image is suppressed as compared with Comparative Example 1. I understand that.
As shown in Reference Example 1, it can be seen that when the volume average particle diameter and the low temperature side storage elastic modulus of the cyan toner and the transparent toner are the same, the color developability of the fixed image is hardly lowered.

Although the present invention has been described in detail with respect to specific embodiments, the present invention is not limited to the specific embodiments, and various other embodiments can be taken within the scope of the present invention. It will be apparent to those skilled in the art.
For example, in the above-described embodiment, a mode in which the toner image forming unit 20T that forms a transparent toner image with transparent toner is applied as the second toner image forming unit has been described. However, in the above-described embodiment, the second toner image forming unit is used as the second toner image forming unit. Alternatively, a color toner image forming unit that forms a color toner image with a color toner (for example, toner of orange, violet, green, etc.) may be applied. The colored toner image forming unit as the second toner image forming unit may be provided in place of the toner image forming unit 20T that forms a transparent toner image, or may be provided together with the toner image forming unit 20T that forms a transparent toner image. (For example, it may be provided as a toner image forming unit 20S that forms a special color toner image with a special color toner).

  Although not particularly described in the above embodiment, the fixing module 120 includes the fixing belt 122. However, for example, only the heating roll whose surface is heated without using the fixing belt 122 may be used. Good.

  In the above embodiment, the pressure roll 122 is heated by the fixing belt 122. However, a member for heating the pressure roll 122 may be provided separately.

  In the above-described embodiment, the pressure roll 150 is rotated by the rotational force of a motor (not shown) being transmitted. However, when the pressure roll 150 is in contact with the fixing belt 122 without using a motor, the rotation is performed. The fixing belt 122 may be rotated by following a pressure roll.

10 Image forming apparatus 20T Toner image forming unit (an example of second toner image forming unit)
20S, 20Y, 20M, 20C, 20K Toner image forming unit (an example of a first toner image forming unit)
40 Fixing device (an example of a fixing unit)
120 fixing module (an example of a heating member)
122 Pressure roll (contact member)

Claims (3)

A first toner image forming unit for forming a first toner image with the first toner;
A second toner image with a second toner having a volume average particle size larger than that of the first toner and a low-temperature side storage elastic modulus measured in a temperature range of 30 ° C. or more and 50 ° C. or less. A second toner image forming unit for forming a second toner image to be superimposed on the first toner image on the recording medium;
A fixing unit for fixing the toner image to the recording medium by heat;
An image forming apparatus comprising: The fixing unit includes a heating member that contacts one surface of the recording medium and heats the image; and a contact member that contacts the other surface of the recording medium;
When fixing the first toner image and the second toner image superimposed on the first toner image on one surface of the recording medium, the first toner image on which the second toner image is not superimposed is The image forming apparatus according to claim 1, further comprising a control unit configured to increase a heat amount applied to the toner image from the contact member as compared with a case where fixing is performed on one surface of the recording medium. The fixing unit includes a heating member that contacts one surface of the recording medium and heats the image; and a contact member that contacts the other surface of the recording medium;
When fixing the first toner image and the second toner image superimposed on the first toner image on one surface of the recording medium, the first toner image on which the second toner image is not superimposed is The control unit according to claim 1, further comprising a control unit that reduces a difference between an amount of heat applied from the heating member to the toner image and an amount of heat applied from the contact member to the toner image as compared with a case where the image is fixed on one surface of the recording medium. Image forming apparatus.