JP6540246B2 - Image forming device - Google Patents

Description

  The present invention relates to an image forming apparatus.

Patent Document 1 discloses that “the storage elastic modulus (G1) of color toner at 80 ° C. is composed of“ transparent toner and at least one color toner selected from the group consisting of magenta toner, cyan toner and yellow toner ”. Is 10 ⁴ Pa to 10 ⁶ Pa, and the tangent loss (tan δ) of the color toner at 80 ° C. is 1.0 to 2.5, and the storage elastic modulus (G 2) of the transparent toner at 80 ° C. and the color toner Disclosed is a toner set that satisfies the relationship of the following formula (1): 1.1 ≦ G2 / G1 ≦ 3.0 with the storage elastic modulus (G1) at 80 ° C., and an image forming apparatus using the same There is.

JP, 2010-79106, A

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

  The above-mentioned subject is solved by the following means.

The invention according to claim 1 is
A first toner image forming unit for forming a first toner image by the first toner;
A second toner image by a second toner having a volume average particle diameter larger than the first toner and having a low temperature storage elastic modulus measured at a temperature of 30 ° C. to 50 ° C. greater than the first toner. A second toner image forming unit for forming a second toner image to be superimposed on the first toner image on a recording medium;
A fixing unit that fixes a toner image to a recording medium by heat;
An image forming apparatus comprising:

The invention according to claim 2 is
The fixing unit includes a heating member that contacts one side of the recording medium to heat the image, and a contact member that contacts the other side of the recording medium,
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 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 to be applied to the toner image from the contact member as compared with the case of fixing on one surface of the recording medium.

The invention according to claim 3 is
The fixing unit includes a heating member that contacts one side of the recording medium to heat the image, and a contact member that contacts the other side of the recording medium,
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 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 configured to reduce a difference between the heat amount applied to the toner image from the heating member and the heat amount applied to the toner image from the contact member as compared with fixing on one surface of the recording medium. Image forming device.

  According to the first aspect of the present invention, the first toner image forming portion 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 the first toner An image forming apparatus comprising: a second toner image forming unit for forming a second toner image to be superimposed on a first toner image on a recording medium; and a fixing unit for fixing the toner image on the recording medium by heat. An image forming apparatus is provided which suppresses the decrease in the coloring property 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 invention of claim 2, when the first toner image and the second toner image superimposed on the first toner image are fixed on one side of the recording medium, the second toner image is not superimposed. An image forming apparatus is provided which suppresses a decrease in color development of a fixed image as compared with the case where the heat amount applied to the image from the contact member is equalized when fixing the first toner image on one side of the recording medium. Ru.

  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 to one side of the recording medium, the second toner image is not superimposed. When fixing the first toner image on one side of the recording medium, coloring of the fixed image is made as compared with the case where the difference between the heat amount applied from the heating member to the image and the heat amount applied from the contact member to the image is equal. There is provided an image forming apparatus which suppresses the deterioration of image quality.

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. 2 is a schematic configuration view showing an image forming unit provided in the image forming apparatus according to the first embodiment. FIG. 1 is a schematic configuration view showing an image forming apparatus according to a first embodiment. It is the graph which showed the relationship of the storage elastic modulus and temperature of colored toner (an example of the 1st toner) and transparent toner (an example of the 2nd toner). FIG. 6 is a schematic configuration view showing a fixing device provided in an image forming apparatus according to a second embodiment. FIG. 6 is a schematic configuration view showing a fixing device provided in an image forming apparatus according to a second embodiment. FIG. 18 is a state diagram showing a state in which a plurality of sheet members are conveyed to the fixing device in the fixing device provided in the image forming apparatus according to the fifth embodiment. It is a schematic diagram for demonstrating the phenomenon which the color development fall of a fixing image produces.

  Hereinafter, an embodiment which is an example of the present invention will be described. In addition, the same code | symbol may be provided to the member which has a substantially the same function and 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 according to FIGS. 1 to 3. In addition, the arrow H shown to each figure is a perpendicular direction, and shows an apparatus up-down direction, and the arrow W is a horizontal direction and shows an apparatus width direction.

<Overall Configuration of Image Forming Apparatus>
FIG. 3 is a schematic view showing the entire 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 electrophotography, a medium conveyance device 50 that conveys the sheet member P, and an image. And a post-processing unit 60 that performs post-processing and the like on the sheet member P.

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

  The image forming unit 12 further includes a toner image forming unit 20 that forms a toner image, a transfer device 30 that transfers the toner image formed by the toner image forming unit 20 to a sheet member P, and the sheet member P. And a fixing device 40 (an example of a fixing unit) for fixing the toner image to 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. In addition, the medium conveyance device 50 is configured to include a medium return unit 56 used when forming an image on both sides of the sheet member P, and an intermediate conveyance unit 58 described later.

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

  In the image forming apparatus 10, the components are accommodated in a housing 90 except for a discharge medium receiving unit 541 that constitutes the medium discharge unit 54 of the medium conveyance device 50. The housing 90 in this embodiment has a two-split structure including a first housing 91 and a second housing 92 adjacent in the device width direction. Thereby, the transport unit of the image forming apparatus 10 is miniaturized in the apparatus width direction.

  In the first housing 91, the main part of the image forming unit 12 excluding the fixing device 40 described later and the medium supply unit 52 are accommodated. In the second housing 92, the fixing device 40 constituting the image forming unit 12, the medium discharge unit 54 excluding the discharge medium receiving unit 541, the medium cooling unit 62, the image inspection unit 66, and the medium return unit 56. , A control unit 70 and a power supply unit 80 are accommodated. The first housing 91 and the second housing 92 are coupled by fastening means such as a bolt and a nut (not shown) 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 the transfer nip NT to the fixing nip NF of the image forming unit 12 described later, and a medium return portion A communication path 90C2 of the sheet member P from 56 to the medium supply unit 52 is formed.

(Image formation unit)
The image forming unit 12 includes the toner image forming unit 20, the transfer device 30, and the fixing device 40, as described above. A plurality of toner image forming units 20 are provided to form a toner image for each color. In this embodiment, a total of six toner image forming units 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 respective colors. The transfer device 30 transfers the toner images of the six colors onto the sheet member P at the transfer nip NT from the transfer belt 31 on which the toner images of the six colors are primarily transferred (the details will be described later) ).
Here, the toner image forming unit 20T that forms a toner image (an example of the second toner image) of each color of transparent (T) corresponds to an example of the second toner image forming unit, and the special color (S), yellow (Y) Toner image forming units 20S, 20Y, 20M, 20C, and 20K for forming toner images (one example of a first toner image) of each color of magenta (M), cyan (C), and black (K) It corresponds to an example of the image forming unit.

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

[Toner image forming unit]
The toner image forming unit 20 of each color is basically configured in the same manner except for the toner to be used. Therefore, hereinafter, the image forming units 14 of the respective colors 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 holder, a charger 22, an exposure device 23, and a developing which is an example of a developing device. It is configured to include the device 24, the cleaning device 25, and the charge removal device 26.

[Photosensitive drum]
The photosensitive drum 21 is formed in a cylindrical shape and grounded, and is rotationally driven about its own axis by a driving unit (not shown). On the surface of the photosensitive drum 21, as one example, a photosensitive layer exhibiting a negative charging polarity is formed. As shown in FIG. 3, the photosensitive drums 21 of the respective colors are arranged in a straight line along the apparatus width direction in a front view.

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

[Exposure system]
The exposure device 23 is configured to form 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 formed on the surface of the photosensitive drum 21 charged by the charger 22. It is supposed to irradiate. The irradiation of the exposure light L by the exposure device 23 forms an electrostatic latent image on the surface of the photosensitive drum 21.

[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 a developer G containing toner.

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

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

[Static charge]
The charge removal device 26 applies light to the photosensitive drum 21 after transfer to perform charge removal. As a result, the charging history of the surface of the photosensitive drum 21 is canceled.

[Transfer device]
The transfer device 30 superimposes and primarily transfers the toner image of the photosensitive drum 21 of each color on the transfer belt 31, and secondarily transfers the superimposed toner image to the sheet member P. The details will be 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 its posture. In this embodiment, the transfer belt 31 has a posture in the form of an inverse obtuse triangle that is long in the apparatus width direction in a front view. Among the plurality of rolls 32, a roll 32D shown in FIG. 2 functions as a drive roll that causes the transfer belt 31 to rotate in the direction of arrow A by the power of a motor (not shown).

  Further, among the plurality of rolls 32, the roll 32T illustrated in FIG. 2 functions as a tension application roll that applies tension to the transfer belt 31. Among the plurality of rolls 32, the roll 32B illustrated in FIG. 2 functions as an opposing roll of a secondary transfer roll 34 described later. The top of the lower end side forming the obtuse angle of the transfer belt 31, which is in the obtuse obtuse triangle shape as described above, is wound around the roll 32 </ b> B. The transfer belt 31 is in contact with the photosensitive drums 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 for transferring the toner image of each photosensitive drum 21 to the transfer belt 31, is disposed. Each primary transfer roll 33 is disposed opposite to the photosensitive drum 21 of the corresponding color with the transfer belt 31 interposed therebetween. Further, a transfer bias voltage having a reverse polarity to the toner polarity is applied to the primary transfer roll 33. The toner image formed on the photosensitive drum 21 is transferred onto the transfer belt 31 by the application of the transfer bias voltage.

[Secondary transfer roll]
The transfer device 30 also 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 disposed so as to sandwich the transfer belt 31 with the roll 32 B, and forms a transfer nip NT with 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 configured such that a transfer bias voltage having a polarity opposite to that of the toner polarity is applied 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 on the sheet member P passing through the transfer nip NT.

[Cleaning device]
The transfer device 30 further 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 for scraping the 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 on the sheet member P on which the toner image is transferred in the transfer device 30 by heat.

(Media 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 accommodated. In this embodiment, two containers 521 are arranged below the transfer device 30 along the device width direction.

  From the respective containers 521 to the transfer nip NT which is a secondary transfer position, a medium supply path 52P is formed by a plurality of transport roll pairs 522, a guide (not shown), and the like. The medium supply path 52P has a shape (generally “S” shape) reaching the transfer nip NT while being folded back and rising in the apparatus width direction at the two folds 52P1 and 52P2.

  A delivery roll 523 for delivering the uppermost sheet member P stacked in the container 521 is disposed above the respective containers 521. Among the plurality of transport roll pairs 522, the transport roll pair 522S on the most upstream side in the transport direction of the sheet member P separates the sheet members P which are overlapped and fed out from the container 521 by the delivery roll 5 Act as a role. Further, among the plurality of transport roll pairs 522, the transport roll pair 522R positioned immediately upstream of the transfer nip NT in the transport direction of the sheet member P is the transfer timing of the toner image on the transfer belt 31 and the transport timing of the sheet member P. It is supposed to be operated to match.

  In addition, the medium supply unit 52 includes a spare conveyance path 52Pr. The spare transport path 52Pr originates from an opening 91W opposite to the second housing 92 side of the first housing 91, and merges with the turn-back portion 52P2 of the medium supply path 52P. The preliminary conveyance path 52Pr conveys the sheet member P delivered from an optional recording medium supply device (not shown) disposed adjacent to the opening 91W of the first housing 91 to the image forming unit 12 It is considered to be a route.

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

  Air is suctioned (negative pressure suction) from the inside of the conveyance member 581 so that the conveyance belt circulates and conveys the sheet member P while suctioning the sheet member P against the surface of the conveyance belt.

[Media Discharger]
As shown in FIG. 3, the medium discharge unit 54 has the sheet member P on which the toner image is fixed by the fixing device 40 of the image forming unit 12, and the side opposite to the first case 91 in the second case 92. It discharges to the exterior of the housing | casing 90 from the discharge port 92W formed in the edge part of this.

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

  The medium discharge unit 54 has a medium discharge path 54P for conveying 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 conveyance member 543, a plurality of roll pairs 542, a guide (not shown), and the like. Then, among the plurality of roll pairs 542, the roll pair 542E disposed at 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 unit]
The medium return unit 56 includes a plurality of roll pairs 561. The plurality of roll pairs 561 form a reverse path 56P to which the sheet member P having passed the image inspection unit 66 is fed when there is a request to form an image on both sides. The reverse path 56P has 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 transport path 56P2 feeds 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 transporting path 56P2, and is configured to reverse the front and back (switchback transporting) by turning the transporting direction of the sheet member P transported in the transporting path 56P2 in the opposite direction. .

(Post-processing unit)
The medium cooling unit 62, the correction device 64, and the image inspection unit 66, which constitute the post-processing unit 60, are upstream of the sheet discharging direction of the sheet member P with respect to the branch portion of the branch path 56P1 on the medium discharge path 54P of the medium discharge unit 54. In this order from the upstream side in the discharge direction.

[Media Cooling Unit]
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 heat absorbing device 621 includes an endless heat absorbing belt 6211, a plurality of rolls 6212 supporting the heat absorbing belt 6211, a heat sink 6213 disposed in the heat absorbing belt 6211, and a fan 6214 for cooling the heat sink 6213. It is configured.

  The heat absorbing belt 6211 makes heat exchange contact with the sheet member P on the outer peripheral surface. Among the plurality of rolls 6212, the roll 6212D functions as a drive roll that transmits a driving force to the heat absorption belt 6211. The heat sink 6213 is slidably in surface contact with the inner circumferential surface of the heat absorption belt 6211 in 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 supporting the pressing belt 6221. The pressing belt 6221 is wound around a plurality of rolls 6222. The pressing device 622 is configured to convey the sheet member P together with the heat absorbing belt 6211 while pressing the sheet member P against the heat absorbing 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 (curling) of the sheet member P received from the medium cooling unit 62.

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

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

  In addition to the control unit 70, the image forming apparatus 10 also 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 the operation display unit, the image processing unit, the image memory, the image forming unit, the storage unit, and the communication unit to control the respective units. Note that the image forming unit referred to here is the image forming unit 12 of the image forming apparatus 10, the medium conveyance device 50, and the post-processing unit 60.

<Image Forming Operation (Function) 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 post-processing process will be described.
The various operations of the image forming apparatus 10 are performed by a control program executed by the control unit 70. Here, in the image forming apparatus 10, for example, a control program for "image forming processing" is stored in advance in the ROM. The control program stored in advance is read by the CPU and executed using the RAM as a work area. Further, 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 non-volatile memory. The control program and various data may be stored in another storage device such as a ROM, a non-volatile memory, or a storage unit, or may be obtained from the outside via a communication unit.

  First, as shown in FIG. 3, the control unit 70 that has received an image formation command operates the toner image forming unit 20, the transfer device 30, and the fixing device 40. Thereby, as shown in FIG. 2, the photosensitive drum 21 of the image forming unit 14 of each color and the developing roller 242 of the developing device 24 are rotated, and the transfer belt 31 is circulated. In addition, the pressure roller 42 is rotated, and the fixing belt 411 is circulated. Furthermore, 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. Further, the control unit 70 sends the image data subjected to the image processing by the image signal processing unit to each exposure device 23. Each exposure device 23 emits each exposure light L according to 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 photosensitive drum 21 is developed by the developer supplied from the developing device 24. Thereby, the toner of the corresponding color among the transparent (T), the special color (S), the yellow (Y), the magenta (M), the cyan (C) and the black (K) on 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 circulating transfer belt 31 by application of a transfer bias voltage through the primary transfer rolls 33 of the respective colors. As a result, a superimposed toner image (or a single-layer toner image of the target color) on which the toner image of the target color is superimposed is formed on the transfer belt 31. The toner image is conveyed to the transfer nip NT by the rotation of the transfer belt 31.

  In this transfer nip NT, as shown in FIG. 3, the sheet member is synchronized with the conveyance of the superimposed toner image (or the single-layer toner image of the desired color) by the conveyance roll pair 522R of the medium supply unit 52. P is supplied. By applying a transfer bias voltage at the transfer nip NT, the superimposed toner image (or a single-layer toner image of a desired 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 passing through the fixing nip NF. Thereby, 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 toward the discharged medium receiving unit 541 outside the apparatus by the medium discharging unit 54. The sheet member P heated in the fixing process is first cooled in the medium cooling unit 62. Then, the sheet member P has its curvature corrected by the correction device 64. Further, in the toner image fixed on the sheet member P, the image inspection unit 66 detects the presence or absence and degree of toner density defect, image defect, image position defect and the like. Then, the sheet member P is discharged to the medium discharge unit 54.

  On the other hand, when forming an image on the non-image surface of the sheet member P in which the image is not formed (in the case of double-sided printing), the control unit 70 sets the conveyance path of the sheet member P after passing through the image inspection unit 66 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 through the reversing path 56P and fed to 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 above-described image forming process on the front surface. The sheet member P is discharged to the discharge medium receiving unit 541 outside the apparatus by the medium discharge unit 54 through the same process as the processing process after the image formation on the surface described above.

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

(toner)
The special color (S), yellow (Y), magenta (M), cyan (C), and black (K) toners (an example of the first toner: hereinafter also referred to as “colored toner”) S) To form toner images of each color of yellow (Y), magenta (M), cyan (C), and black (K) (an example of a first toner image: hereinafter also referred to as “colored toner image”) It is a toner.
On the other hand, a transparent (T) toner (an example of a second toner: hereinafter also referred to as “transparent toner”) is a transparent (T) image (an example of a second toner image: hereinafter also referred to as “transparent toner image”) . The transparent toner image is a toner image fixed in a state of being superimposed on the color toner image on the sheet member P for the purpose of protection of the image or provision of glossiness and the like.
The transparent toner has a volume average particle diameter larger than that of the colored toner, and has a lower temperature storage elastic modulus measured at a temperature in the range of 30 ° C. to 50 ° C. larger than that of the colored toner. That is, the color toner has a volume average particle diameter smaller than that of the transparent toner, and has a low temperature storage elastic modulus measured at a temperature in the range of 30 ° C. to 50 ° C. smaller than that of the color toner.

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

  The storage elastic modulus of the toner is adjusted by the type and molecular weight of the binder resin, the type and amount of internal additives (coloring agent 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 serving as a metal ion source is added to the toner, The storage elastic modulus of the toner may be adjusted by ion crosslinking of the ester groups of the resin with metal ions.

Incidentally, the storage elastic modulus G ′ of the toner is measured using a rheometer (ARES) manufactured by TA Instruments Co., Ltd. Specifically, for measurement of storage elastic modulus of toner, a sample (toner) is set in a sample holder with a diameter of 8 mm, temperature rise rate 1 ° C./min, frequency 1 Hz, strain 1% or less, detection torque measured and guaranteed value Within the scope of And the change of the storage elastic modulus with respect to the temperature change is obtained. The analysis uses software that is the standard of the viscoelasticity measuring device.
And the low temperature side storage elastic modulus measured in the range of 30 to 50 degreeC in temperature is calculated | required as an average value of each storage elastic modulus calculated | required in 1 degree step in the range of 30 to 50 degreeC of temperature. That is, "the low temperature side storage elastic modulus is large or small" indicates that the 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, both the color toner and the transparent toner decrease in storage elastic modulus as the temperature rises, and in the temperature range of 30 ° C. to 50 ° C., the storage elastic modulus of the transparent toner is higher than that of the colored toner. Is high.

On the other hand, the difference (difference in absolute value) between the volume average particle diameter of the colored toner and the transparent toner is, for example, in the range of 0.3 μm or more and 2.7 μm or less from the viewpoint of suppressing the reduction in coloration 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, for example, preferably in the range of 3.5 μm to 5.1 μm. On the other hand, the volume average particle diameter of the transparent toner is preferably, for example, in the range of 5.4 μm or more and 6.2 μm or less from the viewpoint of the fixability of the toner.

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

The colored toner includes, for example, a binder resin such as a polyester resin or a polystyrene- (meth) acrylic copolymer resin, and a colorant that exhibits an intended color. The colored toner may optionally contain known internal additives such as a releasing agent. The colored toner may be an external additive 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 or a polystyrene- (meth) acrylic copolymer resin. The transparent toner contains no colorant or contains a colorant, and the content of the colorant is 0.01% by mass or less. The transparent toner may also contain known internal additives 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 part configuration>
Next, the operation of the main part configuration will be described.

First, in the image forming apparatus 10, a transparent toner image (an example of a second toner image) is formed by a transparent toner (an example of a second toner) in the 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), colored toner images (an example of a first toner image) are formed by colored toners of each color (an example of a first toner). When these images are formed, the transparent toner image formed by the upstream toner image forming unit 20T in the rotational direction of the transfer belt 31 is first transferred to the transfer belt 31, and the downstream toner image forming unit 20S, The color toners formed by 20Y, 20M, 20C, and 20K are 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 color toner image (see FIG. 8A). Then, in this state, the sheet member P to which the superimposed 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 passing through the fixing nip NF. Thus, 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 forming the transparent toner image is larger than the colored toner forming the colored toner image to be the lower layer of the transparent toner image, colored toner When a superimposed toner image in a state in which a transparent toner image is superimposed on an image is fixed, a phenomenon may occur in which the transparent toner of the upper transparent toner image breaks the toner layer structure of the lower colored toner image (FIG. 8B) ). For this reason, the coloring property of the fixed image (in the present embodiment, the fixed image of the colored toner image in the lower layer) may be reduced.

On the other hand, when the low temperature side storage elastic modulus of the transparent toner forming the transparent toner image is larger than that of the colored toner image underlying the transparent toner image, the transparent toner image is superimposed on the colored toner image. When the superimposed toner image in the state is fixed, melting of the color toner is likely to proceed ahead of the transparent toner, and in the color toner image, binding between the color toners also proceeds. Thus, even if 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 to be 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 makes it difficult to break the toner layer structure of the lower color toner image.
For this reason, in the image forming apparatus 10, the reduction in the coloring property of the fixed image (in the present embodiment, the fixed image of the color toner image of the lower layer) is suppressed.

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

Second Embodiment
Next, an example of the image forming apparatus according to the second embodiment will be described. The same members as those of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted, and parts different from the first embodiment will be mainly described.

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

(Fixing device)
As illustrated 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 the fixing module 120 and applies pressure. And 150. Further, between the fixing belt 122 and the pressure roll 150, a fixing nip NF in which the fixing belt 122 and the pressure roll 150 are in contact is formed.

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

  Although the fixing belt 122 is not shown, as an example, an elastic layer made of silicone rubber is formed on a polyimide base, and a fluorocarbon resin release layer is formed on the elastic layer. ing.

  The supporting member 124 has a fixing roll 128 as an example of a rotating member, and a peeling pad 130 as an example of a peeling member, and the fixing roll 128 and the peeling pad 130 are from the upstream side of the sheet member P in the transport direction. They are arranged in this order. The rotational force of a motor (not shown) is transmitted to the fixing roll 128 to rotate the fixing roll 128, whereby the fixing belt 122 revolves in the arrow C direction.

  Further, the peeling pad 130 is configured to have an outer side surface 130A in which a corner portion U for bending the fixing belt 122 is formed. When the leading end of the sheet member P passes through the corner portion U, the leading end of the sheet member P peels off the fixing belt 122.

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

  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.

  Further, the fixing module 120 is provided with an external heating roll 132 which is disposed on the outer peripheral side of the fixing belt 122 and which defines its circumferential path. 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, 139C as an example of heating means are disposed. The fixing roller 128 and the internal heating roller 126 contact the inner peripheral surface 122B of the fixing belt 122 to heat the fixing belt 122 from the inside, and the external heating roller 132 contacts the outer peripheral surface 122A of the fixing belt 122 for fixing The belt 122 is configured to be heated from the outside.

[Pressing roll]
The pressure roll 150 is configured, for example, by coating an elastic body layer 150B made of silicone rubber on the outer periphery of a cylindrical roll body 150A made of aluminum. Although not shown, on the outer peripheral surface of the elastic layer 150B, a peeling layer made of fluorine resin or the like with a film thickness of 100 μm is formed. The pressure roller 150 is configured to receive the rotational force of a motor (not shown) and rotate in the direction of arrow E at a peripheral velocity similar to that of the fixing belt 122.

[Others]
The fixing device 40 brings the pressure roller 150 into contact with the fixing belt 122 and brings the pressure roller 150 into contact with the fixing belt 122 (see FIG. 6), and separates the pressure roller 150 from the fixing belt 122. A position (see FIG. 5A) and a pair of support members 140 for movably supporting the pressure roll 150 are provided. The pair of support members 140 are respectively disposed on both sides of the pressure roll 150 in the device depth direction (depth direction in the drawing), and support the rotation shaft 151 of the pressure roll 150 via a bearing (not shown).

  Furthermore, a pair of cylinders 142 for moving the pressure roller 150 supported by the support member 140 to the contact position or the separated position is disposed on both sides of the pressure roller 150 in the device depth direction (the paper surface depth direction). ing. The cylinder 142 is configured to move the rotating shaft 151 of the pressure roll 150 via a bearing (not shown).

  The fixing device 40 also includes a fan 146 as an example of a blowing member that blows air on the pressure roller 150.

  The fixing device 40 further includes a temperature sensor 160 that detects the surface temperature of the fixing belt 122 in a noncontact manner, and a temperature sensor 162 that detects the surface temperature of the pressure roll 150 in a noncontact manner.

<Function 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 on which the superimposed toner image in a state in which the transparent toner image is superimposed on the colored toner image is transferred, and the superimposed toner image is transferred to the sheet member P.

  Here, the control unit 70 controls the fixing device 40 to fix the superimposed toner image in a state in which the transparent toner image is superimposed on the color toner image on the sheet member P (one side thereof), the transparent toner image Compared with fixing the color toner image (or the superimposed toner image on which the color toner images of the respective colors are not superimposed) on the sheet member P (one surface of the sheet member P), Increase the amount of heat to be applied.

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

  When the power of the image forming apparatus 10 is turned off, the pressure roll 150 is disposed at the separated position, as shown in FIG. 5A. When the image forming apparatus 10 is powered 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. In addition, the control unit 70 controls a motor (not shown) to rotate the fixing roll 128 to circulate (rotate) the fixing belt 122 at a predetermined peripheral speed (belt warm-up step).

  Further, the control unit 70 controls a motor (not shown) to rotate the pressure roll 150 at the same peripheral speed as the fixing belt 122. The control unit 70 also receives information of the temperature sensor 160. Then, when the fixing belt 122 reaches a predetermined surface temperature (for example, 170 ° C.), the cylinder 142 is controlled to move the pressure roller 150 from the separated position as shown in FIG. 5B. Move to the contact position. Then, the pressure roller 150 is brought into contact with the fixing belt 122 which circulates. 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. The pressure roller 150 is moved from the contact position to the separated position (see FIG. 5A).

  Furthermore, the control unit 70 controls the lighting of the halogen lamps 139A, 139B, 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. The surface temperature of the pressure roll 150 is maintained at a predetermined temperature (standby state).

  Here, when the superimposed toner image in a state in which the transparent toner image is superimposed on the colored toner image is fixed to the sheet member P, the control unit 70 maintains the surface temperature of the pressure roll 150 at, for example, 135 ° C. Do. In the case where a color toner image (or a superimposed toner image in which color toner images of respective colors are superimposed) on which a transparent toner image is not superimposed is fixed to the sheet member P (hereinafter sometimes referred to as "normal fixing") In addition, the control unit 70 maintains the surface temperature of the pressure roll 150 at 70 ° C., for example.

  That is, when the superimposed toner image in a state in which the transparent toner image is superimposed on the colored toner image is fixed to the sheet member P, the control unit 70 sets the surface temperature of the pressure roll 150 as compared with the normal fixing. Make it higher. 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 process and changing the time for which the pressure roll 150 and the fixing belt 122 are in contact. Specifically, when the superimposed toner image in a state in which the transparent toner image is superimposed on the colored toner image is fixed to the sheet member P, the control unit 70 includes the pressure roller 150 and the fixing belt 122 in the roll heating process. The contact time is made longer than the contact time of the pressure roll 150 and the fixing belt 122 in the roll heating step in the case of the normal fixing.

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

  Here, as described above, when the superimposed toner image in a state in which the transparent toner image is superimposed on the color toner image is fixed to the sheet member P, the control unit 70 applies pressure compared to the case of the normal fixing. The surface temperature of the roll 150 is raised. Thereby, when fixing a superimposed toner image in a state in which the transparent toner image is superimposed on the colored toner image on the sheet member P, the amount of heat to be applied to the toner image from the pressure roll 150 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 large, the transparent toner image is formed when the superimposed toner image in a state in which the transparent toner image is superimposed on the colored toner image is fixed on the sheet member P. Prior to the toner, melting of the color toner forming the color toner image tends to proceed, and in the color toner image, the binding property between the color toners also progresses. Thus, even if 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 to be 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 makes it difficult to break the toner layer structure of the lower color toner image.

  For this reason, in the image forming apparatus according to the second embodiment, as compared with the first embodiment (that is, when the superimposed toner image in a state in which the transparent toner image is superimposed on the colored toner image is fixed on the sheet member P) The amount of heat to be applied to the toner image from the pressure roll 150 is equal when fixing a color toner image (or a superimposed toner image on which color toner images of the respective colors are not superimposed) on which the image is not superimposed on the sheet member P. In the present embodiment, the reduction in the coloring property of the fixed image (in the present embodiment, the fixed image of the colored toner image in the lower layer) is suppressed.

Third Embodiment
Next, an example of the image forming apparatus according to the third embodiment will be described. The same members as those in the first and second embodiments are given the same reference numerals, and descriptions thereof will be omitted, and parts different from the first and second embodiments will be mainly described.

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

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

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

  That is, the area of the fixing belt 122 where the pressure roller 150 contacts the fixing belt 122 is increased per unit time. As a result, when the superimposed toner image in a state 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 is higher than that in the case of normal fixing. The other actions are the same as in the first and second embodiments.

Fourth Embodiment
Next, an example of the image forming apparatus according to the fourth embodiment will be described. The same members as those in the first and second embodiments are given the same reference numerals, and descriptions thereof will be omitted, and parts different from the first and second embodiments will be mainly described.

  In the image forming apparatus according to the fourth embodiment, at least one of the operating time of the fan 146 and the blowing amount (air blowing amount to the pressure roll 150) by the fan 146 is controlled in the standby state of the fixing device 40. When the superimposed toner image in a state 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 the normal fixing.

  Specifically, in the roll heating step, the control unit 70 adds the surface temperature of the pressure roll 150 to fix the superimposed toner image in a state in which the transparent toner image is superimposed on the color toner image on the sheet member P. The surface temperature of the pressure roll 150 is made higher. Thereafter, the control unit 70 sets the fixing device 40 in the 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. Then, when the surface temperature of the pressure roll 150 is lowered, the control unit 70 deactivates (stops) the fan 146.

  Here, when the superimposed toner image in a state in which the transparent toner image is superimposed on the colored toner image is fixed to the sheet member P, the control unit 70 shortens the operating time of the fan 146 as compared with the case of the normal fixing. And at least one control of reducing the blowing amount by the fan 146. As a result, when the superimposed toner image in a state 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 is higher than that in the case of normal fixing.

  When the surface temperature of the pressure roll 150 disposed at the separated position becomes higher than the predetermined surface temperature by the 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.

  The other actions are similar to those of the second embodiment.

Fifth Embodiment
Next, an example of the image forming apparatus according to the fifth embodiment will be described with reference to FIG. The same members as those in the first and second embodiments are given the same reference numerals, and descriptions thereof will be omitted, and parts different from the first and second embodiments will be mainly described.

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

  Specifically, when the toner image is continuously fixed to 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 made longer than the distance between the sheet member P2 and the sheet member P conveyed by the fixing device 40 immediately before the sheet member P2 (S2 in FIG. 7). The transport speed of the sheet member P is constant.

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

  That is, the pressure roller 150 is heated by contact between the pressure roller 150 and the fixing belt 122 between the sheet members P conveyed continuously. That is, when the distance between the sheet members P to be conveyed is long, the degree of heating of the pressure roll 150 is increased and the surface temperature of the pressure roll 150 is high, as compared with the case where the distance is short.

  Here, as described above, the control unit 70 sets the distance (S1 in FIG. 7) between the sheet member P1 and the sheet member P conveyed immediately before the sheet member P1 to the position immediately before the sheet member P2 and the sheet member P2. It is made longer than the distance to the sheet member P to be conveyed (S2 in FIG. 7). As a result, when the superimposed toner image in a state 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 higher than in the case of normal fixing.

  As a method of increasing the distance between the sheet members P, by changing the timing of transferring the toner image to the sheet member P, the distance between the sheet members P is increased. For example, the transfer interval in the case where the superimposed toner image in a state in which the colored toner image is superimposed on the transparent toner image on the transfer belt 31 is transferred to the sheet member P is a colored toner image (or a colored toner image of each color superimposed) Overlapping toner image) The distance between the sheet members P becomes long by doubling the ratio to the transfer interval in the case of transferring a single toner image to the sheet member P.

  The other actions are similar to those of the second embodiment.

Sixth Embodiment
Next, an example of the image forming apparatus according to the sixth embodiment will be described. The same members as those in the first and second embodiments are given the same reference numerals, and descriptions thereof will be omitted, and parts different from the first and second embodiments will be mainly described.

  In the image forming apparatus according to the sixth embodiment, the toner from the fixing belt 122 side in the case where 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 and in the 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 is reduced.

  Specifically, the control unit 70 increases the surface temperature of the pressure roll 150 to thereby differentiate the difference between the heat amount applied to the toner image from the fixing belt 122 side and the heat amount applied to the toner image from the pressure roll 150 side. Make The other actions are the same as in the first and second embodiments.

«Test example»
Hereinafter, test examples for supporting the effects of the image forming apparatus according to the present embodiment will be described. The powder coating material according to the present embodiment is not limited to these test examples. In the following description, "parts" and "%" are all based on mass unless otherwise noted.

<Preparation 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 are added. The reaction was purged with nitrogen gas under inert atmosphere and mechanically stirred at 180 ° C. for 5 hours under reflux.

Thereafter, the temperature was gradually raised to 230 ° C. under reduced pressure and stirring was carried out for 2 hours. When it became viscous, air cooling was carried out to stop the reaction, and a crystalline polyester resin (1) was synthesized. In molecular weight measurement (in terms of polystyrene) by gel permeation chromatography, the weight average molecular weight (Mw) of the obtained crystalline polyester resin (1) was 24000 and the number average molecular weight (Mn) was 7600. Moreover, the acid value was 10.5.
Moreover, the melting temperature (Tm) of crystalline polyester resin (A) showed a clear endothermic peak, and the endothermic peak temperature was 72.3 ° C. The melting temperature of the crystalline polyester resin and the glass transition temperature (Tg) of the amorphous polyester resin are differential scanning calorimeters (manufactured by Mac Science, Inc .: DSC 3110, thermal analysis system 001) in accordance with ASTM D 3418-8. C. to 150.degree. C. under a condition of a temperature rising rate of 10.degree. C./min. The melting temperature was taken as the peak temperature of the endothermic peak, and the glass transition temperature was taken as the temperature at the intersection of the extension of the base line and the rising line in the step-like 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 rectification column, the temperature is raised to 190 ° C. in 1 hour, and the reaction system is uniformly stirred. After that, 0.9% of tin distearate was added to the total weight of these monomers. Further, while distilling off the water formed, the temperature is raised to 240 ° C. taking 6 hours from the same temperature, and the dehydration condensation reaction is continued at 240 ° C. for further 3 hours, glass transition temperature 60 ° C., acid value 13.6 mg KOH 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 until the softening temperature reached 110 ° C. in the same manner as the amorphous polyester resin (1) using monomers other than trimellitic anhydride. Then, the temperature is lowered to 190 ° C. and 7 mol% of trimellitic anhydride is gradually added, and the reaction is continued for 1 hour at the same temperature, glass transition temperature 56 ° C., acid value 11.3 mg KOH / g, weight average molecular weight 78000 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 Methyl ethyl ketone is charged into a 5 L separable flask, then the above resin is gradually charged, and stirring is performed with a three-one motor, Dissolve to obtain an oil phase. In a 5 L separable flask containing this oil phase, the temperature is set to 65 ° C. by a water bath, and a 10% ammonia aqueous solution is gradually dropped to a total of 5 parts by a syringe with a stirred oil phase. Furthermore, 230 parts of ion-exchanged water is gradually dropped at a rate of 10 ml / min to cause phase inversion emulsification, and solvent removal is carried out while reducing pressure with an evaporator, and resin particle dispersion liquid containing crystalline polyester resin (1) (1 Got). The volume average particle size of the resin particles was 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 Methyl ethyl ketone is charged into a 5 L separable flask, then the above resin is gradually charged, and stirring is performed by a three-one motor Completely dissolved to obtain an oil phase. In a 5 L separable flask containing this oil phase, the temperature is set to 40 ° C. by a water bath, and a dropper is gradually dropped so that a total of 3.5 parts of a 10% aqueous ammonia solution is added to the stirred oil phase. Further, 230 parts of ion-exchanged water is gradually dropped at a rate of 10 ml / min to cause phase inversion emulsification, and solvent removal is carried out while reducing pressure with an evaporator, and resin particle dispersion containing amorphous polyester resin (1) Liquid (2) was obtained. The volume average particle size 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), resin particles are dispersed in the same manner as the preparation of the resin particle dispersion (2) except that the amorphous polyester resin (1) is changed to the amorphous polyester resin (2). Liquid (3) was obtained. The volume average particle size 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 (manufactured by Dainichi Seika Co., Ltd .: ECB-301): 50 parts ionic surfactant Neogen RK (Daiichi Kogyo Seiyaku Co., Ltd.): 5 parts Ion exchange water: 195 parts The above components are mixed, and a homogenizer (IKA) After dispersion for 10 minutes with Ultra-Turrax, dispersion treatment is carried out for 15 minutes under pressure 250 Mpa using Ultimizer (counter collision type wet crusher: manufactured by Sugino Machine), and the center particle diameter of colorant particles is 130 nm, solid content Obtained a colorant particle dispersion of 20%.

-Preparation of releasing agent particle dispersion-
Olefin wax, (melting temperature: 88 ° C): 60 parts Ionic surfactant Neogen RK (Daiichi Kogyo Seiyaku Co., Ltd.): 1.8 parts Ion-exchanged water: 238 parts The above is heated to 100 ° C, IKA After dispersion with Ultra-Turrax T50 manufactured by Co., Ltd., the mixture was heated to 110 ° C. with a pressure discharge type Gorin homogenizer and subjected to dispersion treatment for 1 hour to obtain a release agent particle dispersion having a center diameter of 180 nm and a solid content of 20%.

-Preparation 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 Releasing agent particle dispersion: After adding 2.0 parts or more of the ionic surfactant Neogen RK in a round stainless steel flask, 50 parts or more of the above was mixed by stirring. Then, after 1N nitric acid aqueous solution was dropped to adjust to pH 3.5, 0.40 parts of polyaluminum chloride was added thereto, and the dispersing operation was continued with UltraTurrax. The flask was heated to 48 ° C. while stirring with a heating oil bath. 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.
After that, the pH of the system is adjusted to 7.0 by adding a 1 N aqueous solution of sodium hydroxide, and then the stainless steel flask is sealed and heated gradually to 90 ° C. while continuing stirring using a magnetic seal. Hold for 3 hours at ° C.

After completion of the reaction, the reaction solution is cooled, filtered, washed with ion exchange water, and subjected to solid-liquid separation by Nutsche suction filtration. This was further re-dispersed 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 was 7.5 and the electric conductivity was 7.0 μS / cmt, solid-liquid separation was performed using Nutsche-type suction filtration using No5A filter paper. Subsequently, vacuum drying was continued for 12 hours to obtain cyan toner (C1).

-Preparation of externally added cyan toner (C1)-
Cyan toner (C1): 100 parts of hydrophobic silica treated with decylsilane having a volume average particle size of 15 nm and 0.8 parts of hydrophobic titania, and 1.1 parts of hydrophobic silica (NY 50, manufactured by Nippon Aerosil Co., Ltd.) having a volume average particle size of 30 nm After adding 1.0 part of hydrophobic silica (X24, Shin-Etsu Chemical Co., Ltd. make) with an average particle diameter of 100 nm and mixing for 10 minutes at a peripheral speed of 32 m / s using a Henschel mixer, using a 45 μm mesh sieve The coarse particles were removed to obtain an externally added cyan toner (C1).

-Carrier preparation-
Ferrite (trade name EFC-35B, manufactured by Powder Tech, weight average particle diameter: 35 μ): 100 parts Toluene: 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: Pastelan Type IV, manufactured by Mitsui Mining & Smelting Co., Ltd.): 0.3 parts Eposer S (melamine resin particles manufactured by Japan Catalysts Co., Ltd.): 0 .3 parts The above components except ferrite were dispersed in a sand mill for 1 hour to prepare a solution for forming a resin coating layer. Next, the resin coating layer forming solution and the ferrite were placed in a vacuum degassing type 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 resistivity (22 ° C., humidity 55% ° C.) was 2 × 10 ¹¹ Ωcm.

-Preparation of cyan developer (C1)-
100 parts of carrier was added to 7 parts of externally added cyan toner (C1), and mixed for 5 minutes with a ball mill to obtain a cyan developer (C1).

(Transparent developer (T1))
The cyan toner (C1) has the same volume average particle diameter as the cyan toner (C1) in the same manner as the cyan toner (C1) except that the colorant particle dispersion is not used in the preparation of the cyan toner (C1), and the low temperature modulus The same transparent toner (T1) was prepared for (30 ° C. or more and 50 ° C. or less). Then, using the transparent toner (T1), a transparent developer (T1) was produced in the same manner as the cyan developer (C1).

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

(Cyan developer (C3))
In the preparation of the cyan toner (C1), the amount of polyaluminum chloride is reduced, and the temperature maintained before adding a mixture of 100 parts of the resin particle dispersion (2) and 100 parts of the resin particle dispersion (3) Similar to the cyan toner (C1) except that the temperature is higher than 48 ° C., the volume average particle diameter is smaller than that of the cyan toner (C1), and the low-temperature-side stored elastic modulus (30 ° C. to 50 ° C.) The same cyan toner (C3) was produced. Then, using a cyan toner (C3), a cyan developer (C3) was produced in the same manner as the cyan developer (C1).

<Comparative Example 1, Test Examples 1 to 2, Reference Example 1>
An image forming apparatus "Color 1000 Press (manufactured by Fuji Xerox Co., Ltd.)" (however, a fixing module (heating member) and a pressure roller (contact member) are provided by a combination of a cyan developer and a transparent developer according to Table 1 In the fixing device (see FIG. 6), the developing device for forming a cyan image and the developing device for forming a transparent toner image in a modified machine modified so that the heating temperature of the pressure roll is variable are loaded.
Then, using this image forming apparatus, a superimposed toner image in which a transparent toner image with an image density of 100% is superimposed on a cyan toner image with a size of 30 mm × 30 mm and an image density of 100% is formed 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 development 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.
Image density measurement used X-rite 938 (made by X-rite), and measured color difference (deltaE). The color difference (ΔE) is obtained by taking the square root of the sum of squares 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 Commission on Illumination) in 1976, which is defined in “JIS Z 8729” in the Japanese Industrial Standard.

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

From the above results, Test Examples 1 and 2 in which a transparent toner having a volume average particle diameter larger than that of cyan toner and having a low temperature storage elastic modulus measured at a temperature of 30 ° C. to 50 ° C. As compared with Comparative Example 1 in which the transparent toner having a volume average particle diameter larger than that of the cyan toner and having the same low temperature storage elastic modulus as that of the cyan toner is applied, it is understood that the decrease in the coloring property of the fixed image is suppressed.
Further, in the 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 sheet by the heating roll) is increased, the decrease in generation of fixed image is suppressed. I understand that.
As shown in Reference Example 1, 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, it is understood that the reduction of the coloring property of the fixed image hardly occurs.

Although the present invention has been described in detail with respect to particular embodiments, the present invention is not limited to the particular embodiments, and it is possible to take other various embodiments within the scope of the present invention. It will be apparent to one of ordinary skill in the art.
For example, in the embodiment described above, the embodiment in which the toner image forming unit 20T for forming a transparent toner image with transparent toner is applied as the second toner image forming unit has been described, but in the embodiment described above, the second toner image forming unit A mode may be applied in which a color toner image forming unit for forming a color toner image with a color toner (for example, toner of orange, violet, green, etc.) is applied. The color toner image forming unit as the second toner image forming unit may be provided instead of the toner image forming unit 20T for forming a transparent toner image, or may be provided together with the toner image forming unit 20T for forming a transparent toner image. For example, it may be provided as a toner image forming unit 20S for forming a special color toner image with a special color toner.

  Although the fixing module 120 is configured to include the fixing belt 122 in the above embodiment, the fixing module 120 may be, for example, only a heating roller whose surface is heated without using the fixing belt 122. Good.

  Further, although the pressure roller 122 is heated by the fixing belt 122 in the above embodiment, a member for heating the pressure roller 122 may be separately provided.

  Further, in the above embodiment, the pressure roller 150 is rotated by the transmission of the rotational force of a motor (not shown). However, when the pressure roller 150 contacts the fixing belt 122 without using a motor, the pressure roller 150 rotates. The pressure roller may be driven to rotate by the fixing belt 122.

10 Image forming apparatus 20T Toner image forming unit (an example of a 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 (example of fixing unit)
120 Fixing Module (Example of Heating Member)
122 Pressure roll (contact member)

Claims (3)

A first toner image forming unit for forming a first toner image by the first toner;
A second toner image by a second toner having a volume average particle diameter larger than the first toner and having a low temperature storage elastic modulus measured at a temperature of 30 ° C. to 50 ° C. greater than the first toner. A second toner image forming unit for forming a second toner image to be superimposed on the first toner image on a recording medium;
A fixing unit that fixes a toner image to a recording medium by heat;
An image forming apparatus comprising: The fixing unit includes a heating member that contacts one side of the recording medium to heat the image, and a contact member that contacts the other side of the recording medium,
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 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 to be applied to the toner image from the contact member as compared with the case of fixing on one surface of the recording medium. The fixing unit includes a heating member that contacts one side of the recording medium to heat the image, and a contact member that contacts the other side of the recording medium,
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 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 configured to reduce a difference between the heat amount applied to the toner image from the heating member and the heat amount applied to the toner image from the contact member as compared with fixing on one surface of the recording medium. Image forming device.