JP2009150962A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing image failure even if the surface of a transfer means which comes into contact with a transfer material is ≤7 μm in ten-point average roughness Rz<SB>JIS</SB>. <P>SOLUTION: The image forming apparatus has the transfer means 2 for sandwiching a transfer material P between an intermediate transfer body 1 and itself. The ten-point average roughness Rz<SB>JIS</SB>of the surface of the transfer means 2, which comes into contact with the transfer material P, is ≤7 μm. A toner image formed on the intermediate transfer body 1 is transferred to the transfer material P. In the image forming apparatus, an impedance Z1 between the surface of the intermediate transfer body 1 on which an image is formed and the reference potential of the image forming apparatus and an impedance Z2 between the surface of the transfer means 2 with which the transfer material P comes into contact and the reference potential of the image forming apparatus satisfy Z1≥Z2. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  In an image forming apparatus such as a copying machine, a printer, and a facsimile machine, an electrophotographic system that forms a toner image on an electrophotographic photosensitive member by an electrophotographic process, and transfers the toner image to a transfer material by a transfer unit. Is often used. In recent years, a contact-type contact transfer unit is often used as a transfer unit due to the trend toward ozone-free image forming apparatuses.

  However, when the image carrier and the transfer unit come into contact with each other, the non-image-part-attached toner on the image carrier, so-called “fogging toner”, is transferred to the transfer unit, which causes problems such as back contamination of the transfer material. Yes. In order to avoid this problem, for example, an image forming apparatus provided with a cleaning unit that cleans the transfer unit has been proposed (see, for example, Patent Document 1).

  FIG. 11 shows a schematic configuration of the conventional image forming apparatus.

  That is, the image forming apparatus 100 includes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 111 as an image carrier, and intermediately transfers a toner image formed by an electrophotographic process. The image is transferred to the intermediate transfer belt 101 as a body. The toner image on the intermediate transfer belt 101 is transferred to the transfer material P by the transfer unit 102. In order to prevent the transfer material P from being stained, the surface of the secondary transfer roller 102 is cleaned by a secondary transfer roller cleaner 122 serving as a cleaning unit (see, for example, Patent Document 2).

  Patent Document 2 proposes, for example, that the ten-point average surface roughness Rz of the transfer unit 102 be 3.5 μm or less in order to ensure good cleaning performance of the transfer unit 102.

  Furthermore, demand for marginless (marginless) printing is increasing due to diversification of printer demand in recent years. In particular, there is an increasing need for marginless printing for the purpose of simplifying the work of printing on a slightly larger transfer material and then cutting the margin to create a print with no margin.

For example, Patent Document 3 discloses an example of an electrophotographic image forming apparatus capable of printing without margins.
JP 9-305039 A JP-A-10-142956 JP 2004-5559 A

  The secondary transfer roller cleaner 122 in the conventional image forming apparatus 100 shown in FIG. 11 is provided with a release layer for blade cleaning the surface of the secondary transfer roller 102.

The inventor conducted an experiment using the secondary transfer roller 102 in which the ten-point average roughness Rz _JIS of the roller surface was 3.5 μm. In this experiment, an image defect (hereinafter referred to as “triasis”) that may be caused by discharge occurred in the secondary transfer process.

In the claims and specifications of the present application, the ten-point average roughness (Rz _JIS ) is based on the provisions of JIS B0601: '01, and is “Rz _JIS (JIS B0601: '01)”. Notation or simply “Rz _JIS ”.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of image defects even when the ten-point average roughness Rz _{JIS of} the surface contacting the transfer material of the transfer means is 7 μm or less. It is.

  Another object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of image defects even when a cleaning unit that comes into contact with the outer peripheral surface of the transfer unit is provided.

  Another object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of image defects even when printing without margins.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention supports an image carrier, an image forming unit that forms a toner image on the image carrier, a primary transfer unit that transfers the toner image to an intermediate transfer member, and the intermediate transfer member. A tenth-point average roughness Rz _{JIS of} a surface of the secondary transfer unit that contacts the transfer material, which is 7 μm or less; and a secondary transfer unit that sandwiches a transfer material between the support member and the intermediate transfer member In the image forming apparatus for transferring the toner image formed on the intermediate transfer member to the transfer material,
The impedance Z1 between the surface of the intermediate transfer member on which the toner image is formed and the reference potential of the image forming apparatus, and the surface between the surface of the secondary transfer unit where the transfer material contacts and the reference potential of the image forming apparatus. Impedance Z2 is
Z1 ≧ Z2,
The image forming apparatus is characterized by the above.

According to the present invention, even when the ten-point average roughness Rz _JIS (JIS B0601: '01) of the surface contacting the transfer material of the transfer unit is 7 μm or less, the occurrence of image defects can be suppressed.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
FIG. 1 shows a schematic configuration of a full-color electrophotographic image forming apparatus which is an embodiment of the image forming apparatus of the present invention. Next, the overall configuration of the image forming apparatus of this embodiment will be described first.

  The image forming apparatus 100, which is a tandem type intermediate transfer type color image forming apparatus of the present embodiment, includes four image forming units S (Sa, Sb, Sc, Sd) that form image forming means in the image forming apparatus main body 100A. ) Are juxtaposed in series in the image feed direction.

  Each image forming unit S (Sa, Sb, Sc, Sd) is a drum-shaped electrophotographic photosensitive member as a first image carrier, that is, first color (yellow), second color (magenta), first color Photoconductor drums 11a, 11b, 11c, and 11d for the third color (cyan) and the fourth color (black) are provided.

  Further, around each photosensitive drum 11, a charging device 12 (12a, 12b, 12c, 12d) as a charging unit and an exposure device 13 (13a, 13b, 103c, 13d) as an exposure unit are arranged. Thus, an electrostatic latent image is formed on each photosensitive drum 11.

  A developing device 14 (14a, 14b, 14c, 14d) as a developing unit is further disposed around each photosensitive drum 11, and the electrostatic latent image on the photosensitive drum 11 is visualized to form a toner image and a toner image. To do.

  Further, around each photosensitive drum 11, a primary transfer device 15 (15a, 15b, 15c, 15d) serving as a transfer roller as a primary transfer unit is provided, and a toner image on the photosensitive drum 11 is transferred. Then, the image is transferred by the intermediate transfer body 1 which is the second image carrier. The intermediate transfer body 1 is a belt-shaped or drum-shaped rotating body. In this embodiment, the intermediate transfer body 1 is an intermediate transfer belt that is a belt-shaped rotating body.

  The untransferred toner on the photosensitive drum 11 is cleaned by a cleaning device 17 (17a, 17b, 17c, 17d) having a cleaning blade as a photosensitive member cleaning means disposed around the photosensitive drum 11. .

  Further, it passes between the photosensitive drum 11 (11a, 11b, 11c, 11d) of each image forming unit S (Sa, Sb, Sc, Sd) and the primary transfer device 15 (15a, 15b, 15c, 15d). Further, an intermediate transfer belt 1 which is the belt-like intermediate transfer member is disposed. The intermediate transfer belt 1 is wound and stretched by support rollers 1a, 1b, and 1c, which are support members, and is movable in the direction of the arrow. Details of the intermediate transfer belt 1 will be described later.

  In the image forming apparatus 100 according to the present exemplary embodiment, the photosensitive drums 11 are arranged in order from the photosensitive drum 11a of the first color located at the most upstream side to the downstream side in the moving direction of the intermediate transfer belt 1. Photoconductor drums 11b, 11c, and 11c for the second color, the third color, and the fourth color are arranged.

  In this embodiment, the photosensitive drums 11a, 11b, 11c, and 11d have an outer diameter of 30.0 mm, and have a layer in which a photosensitive material is applied on an aluminum cylinder as a support member. The aluminum cylinder is electrically grounded to a reference potential (ground) of the image forming apparatus (not shown).

  The intermediate transfer belt 1 may be a resin film such as a urethane resin, a fluorine resin, a nylon resin, or a polyimide resin, or a resin film in which resistance is adjusted by dispersing carbon or conductive powder in these resins. it can. Furthermore, a sheet having a multi-layer structure in which a resin layer is formed as a release layer on the toner carrier surface side of a base layer sheet such as a resin film, urethane rubber, or NBR can also be used.

The intermediate transfer belt 1 used in this embodiment adjusts the volume resistivity ρv by adjusting the amount of carbon dispersed in the polyimide. In this embodiment, the intermediate transfer belt 1 is a single-layer endless belt having a circumferential length of 1000 mm and a thickness of 100 μm. The intermediate transfer belt 1 has a ten-point average roughness Rz _JIS of 1.0 μm from the viewpoint of ensuring good cleaning properties by an intermediate transfer member cleaner 4 described later and preventing image unevenness.

  The volume resistivity is measured in accordance with JIS-K6911. After obtaining good contact between the electrode and the belt surface by using conductive rubber as an electrode, the temperature is 23 ° C./50% R.D. H. In the environment, the measurement was performed using an ultrahigh resistance meter (R8340A manufactured by Advantest Corporation). The measurement conditions were applied voltage = 100 V and voltage application time = 30 s.

  As described above, the intermediate transfer belt 1 is suspended by three rollers, ie, a drive roller 1a, a support roller 1b, and a separation roller 1c, which are support members included in the intermediate transfer belt 1. The drive roller 1a, the support roller 1b, and the separation roller 1c are electrically grounded to a reference potential (ground) of the image forming apparatus.

The driving roller 1a is a roller having an outer diameter of 29.8 mm composed of an aluminum cored bar having a diameter of 24.0 mm and a hydrin rubber layer having a layer thickness of 2.9 mm, and the resistance of the roller is adjusted to 1 by adjusting the resistance of the hydrin rubber. × 10 ⁶ Ω. The support roller 1b is an aluminum roller having a diameter of 29.8 mm. The separation roller 1c is a roller having an outer diameter of 22.2 mm composed of an aluminum cored bar having a diameter of 16.4 mm and a hydrin rubber layer having a layer thickness of 2.9 mm. The roller resistance value is adjusted by adjusting the resistance of the hydrin rubber. is doing.

  The roller resistance value is 23 ° C./50% R.D. H. In an environment, the measurement was performed using an ultrahigh resistance meter (R8340A manufactured by Advantest) while a roller to be measured was brought into contact with an aluminum cylinder having a diameter of 30 mm and rotated following the aluminum cylinder. Measurement conditions were applied voltage = 100 V, voltage application time = 30 s, contact force = 9.8 N, and aluminum cylinder surface rotation peripheral speed = 117 mm / s.

  The intermediate transfer belt 1 is rotated at a predetermined moving speed V1 (117.0 mm / s in this embodiment) by a driving device (not shown) in the direction of the arrow. Further, each of the photosensitive drums 11a, 11b, 11c, and 11d is rotated by a driving device (not shown) at V1 in the same direction as the moving direction of the intermediate transfer belt 1.

  The photosensitive drums 11a, 11b, 11c, and 11d are uniformly charged by the contact charging rollers 12a, 12b, 12c, and 12d, which are primary chargers. Thereafter, a laser beam scanner as the exposure device 13 is irradiated with laser light modulated by an exposure information signal from each of the scanners 13a, 13b, 13c, and 13d, and an electrostatic latent image is created.

  The image information signal sent from the host computer is processed by an image information processing means (not shown) so that the image finally formed on the transfer material can obtain a desired size and chromaticity based on the image information signal. As a result, an exposure information signal is obtained.

  The intensity of the laser beam and the irradiation spot diameter are appropriately set according to the resolution of the image forming apparatus and the desired image density. In this embodiment, the portion of each photosensitive drum 11 irradiated with the laser light is set to a bright portion potential VL (about −150 V). The portion that is not irradiated with the laser light is held at a dark portion potential VD (about −650 V) charged by each contact charging roller 12. Thereby, an electrostatic latent image is formed on each photosensitive drum 11.

  The electrostatic latent image reaches each of the developing units 14a, 14b, 14c, and 14d by rotation of the photosensitive drums 11a, 11b, 11c, and 11d, and has the same polarity as the surface of the photosensitive drum (in this example, Toner charged to negative polarity is supplied to be visualized to form a toner image.

  In this embodiment, the developing devices 14a, 14b, 14c, and 14d are developing devices that employ a two-component developing system. In this embodiment, the developing bias is a bias in which an AC voltage is superimposed on a DC voltage of DC component = −400 V, AC component = 1.5 kVpp, frequency = 3 kHz, waveform = rectangular wave.

  Further, as a two-component developer, a two-component developer of a color complex machine iR C3200 manufactured by Canon Inc. was used. The toner of this two-component developer has a spherical shape and a particle size of about 7 μm.

  The toner image formed on each photoconductor drum 11 is intermediately transferred at each primary transfer nip N1 (N1a, N1b, N1c, N1d), which is an area where the intermediate transfer belt 1 and the photoconductor drum 11 are in contact with each other. It is transferred onto the surface of the belt 1 (image carrier surface). In this specification, the “contact area” means a proximity or contact area in a contact state or a proximity state.

  The primary transfer rollers 15a, 15b, 15c, and 15d that are in contact with the back surface of the image carrying surface of the intermediate transfer belt 1 at each primary transfer nip N1 are primarily transferred from a primary transfer bias source 16 (16a, 16b, 16c, and 16d). A bias is applied. In this embodiment, the primary transfer bias is +400 V and is controlled at a constant voltage. When the intermediate transfer belt 1 passes through the primary transfer nip N1d with the photosensitive drum 11d, the formation of the four-color image on the intermediate transfer belt 1 is completed, and the primary transfer process is completed.

  On the other hand, the surface of each of the photoconductive drums 11a, 11b, 11c, and 11d after the primary transfer process is removed from the primary transfer residual toner by a drum cleaning device 17 (17a, 17b, 17c, and 17d) formed of a urethane rubber blade. To prepare for the next image forming process.

  Next, one transfer material P is taken out from the transfer material cassette 5. The transfer material P is inserted into a secondary transfer nip portion N2 which is an area where the separation roller 1c and the secondary transfer roller 2 as a secondary transfer unit are in contact with each other with the intermediate transfer belt 1 interposed therebetween. In the present specification, the “contact area” means a proximity or contact area in a contact state or a proximity state as described above.

  At this time, an optimal secondary transfer bias having a reverse polarity to the toner is applied to the secondary transfer roller 2 by the secondary transfer bias source 21, and the toner image is secondarily transferred from the intermediate transfer belt 1 to the transfer material P. The In this embodiment, the secondary transfer bias is +30 μA and is controlled at a constant current.

  The secondary transfer roller 2 in this embodiment will be described with reference to FIG.

  The secondary transfer roller 2 is an outer diameter 22.2 mm roller composed of an aluminum core 23 having a diameter of 14.0 mm, a silicon rubber layer 24 having a thickness of 4 mm, and a fluororesin layer 25 having a surface thickness of 100 μm. is there. The roller resistance value is adjusted by adjusting the resistance of silicon rubber and fluororesin. Further, by providing a fluororesin layer on the surface layer, the fog toner adhered to the secondary transfer roller 2 can be removed by a secondary transfer roller cleaner 22 described later.

The hardness of the secondary transfer roller 2 is 45 ° (ASKER-C). The ten-point average roughness (Rz _JIS ) of the surface of the secondary transfer roller 2 that contacts the transfer material P is 3.5 μm.

In the claims and specifications of the present application, the ten-point average roughness (Rz _JIS ) is based on the provisions of JIS B0601: '01 as described above.

  The secondary transfer roller 2 is rotated by a driving device (not shown) in the same direction as the movement direction of the intermediate transfer belt 1 at the same speed V1 as the movement speed of the intermediate transfer belt 1.

  The transfer material P on which the unfixed toner image that has passed through the secondary transfer nip portion N2 reaches the fixing device 3 and is heated and pressurized to obtain a permanent fixed image. The transfer material P discharged from the fixing device 3 is discharged to a paper discharge tray 6 outside the device.

  After the transfer of the toner image onto the transfer material P, the surface of the intermediate transfer belt 1 is cleaned of secondary transfer residual toner by an intermediate transfer body cleaner 4 which is a cleaning unit having a cleaning blade made of urethane rubber.

  In this embodiment, since the intermediate transfer belt 1 and the secondary transfer roller 2 are in contact with each other, non-image-part adhering toner on the intermediate transfer member, so-called “fogging toner” adheres to the surface of the secondary transfer roller 2. Since this adhered toner can cause back contamination of the transfer material P, it is removed by the secondary transfer roller cleaner 22 in contact with the secondary transfer roller 2.

  The secondary transfer roller cleaner 22 in this embodiment will be described with reference to the schematic configuration diagram of the secondary transfer roller cleaner 22 shown in FIG.

  The secondary transfer roller cleaner 22 is configured such that the fur brush 22a is brought into contact with the secondary transfer roller 2 rotating in the direction of the arrow R2 at 15 N / m by a pressure member 22c with a constant load. Further, the fur brush 22a is driven to rotate by a driving device (not shown) at a predetermined process speed V1 in the direction of the arrow R3 (the counter direction is the arrow R2), so that the toner adhering to the secondary transfer roller 2 is efficiently removed. Can be removed.

  Next, the effect of the present embodiment will be described for three types of embodiment A1, embodiment B1, and embodiment C1.

  Referring to FIG. 4, an impedance between a surface 1f on which a toner image of intermediate transfer belt 1 serving as an image carrier is formed and a reference potential (ground) of image forming apparatus 100 is Z1. In addition, an impedance between a surface 2f of the secondary transfer roller 2 serving as a secondary transfer unit, which is in contact with the transfer material P, and a reference potential (ground) of the image forming apparatus 100 is Z2.

In Example A1, Example B1, and Example C1, the volume resistivity ρv of the intermediate transfer belt 1, the roller resistance value R1c of the separation roller 1c, and the roller resistance value R2 of the secondary transfer roller 2 are adjusted. Thereby, the relationship between the impedances Z1 and Z2 is
Z1 ≧ Z2,
Is set.

Moreover, as a comparative example, two types of comparative example A1 and comparative example B1 are shown. In the comparative example, the 10-point average roughness Rz _JIS of the surface 2f of the secondary transfer roller 2 that contacts the transfer material P is 3.5 μm. However, by adjusting the volume resistivity ρv of the intermediate transfer belt 1, the roller resistance value R1c of the separation roller 1c, and the roller resistance value R2 of the secondary transfer roller 2, the relationship between the impedance Z1 and the impedance Z2 is
Z1 <Z2,
Is set.

Furthermore, three types of configurations of Comparative Example C1, Comparative Example D1, and Comparative Example E1 were set as comparative examples. Comparative examples C1, D1, and E1 have the same volume resistivity ρv of the intermediate transfer belt 1 as the comparative example B, the roller resistance value R1c of the separation roller 1c, the roller resistance value R2 of the secondary transfer roller 2, and the impedance Z1 and impedance. The configuration was Z2. However, the ten-point average roughness Rz _JIS of the surface of the secondary transfer roller 2 that contacts the transfer material was changed.

Table 1 shows the ten-point average roughness Rz _JIS , ρv, R1c, R2, Z1, and Z2 of the surface 2f of the secondary transfer roller 2 that is in contact with the transfer material P in this example and the comparative example.

  A method for measuring the impedance Z1 between the surface on which the image is formed on the intermediate transfer belt 1 and the reference potential of the image forming apparatus will be described.

In the image forming apparatus of the present embodiment, the secondary transfer roller 2 is replaced with an aluminum pseudo secondary transfer roller 2 a having the same outer diameter of 22.1 mm as the secondary transfer roller 2. Then, in a state where the transfer material P is not inserted into the secondary transfer nip portion N2, 23 ° C./50% R.D. H. In the environment, the output voltage V1 [V] of the secondary transfer bias source when +30 μA was applied to the pseudo secondary transfer roller 2a by the secondary transfer bias source 21 was measured. The impedance Z1 is the following formula:
Z1 [Ω] = V1 [V] / (3 × 10 ⁻⁵ [A])
Ask from.

  Further, the impedance Z2 between the surface of the secondary transfer roller 2 on which the transfer material contacts and the reference potential of the image forming apparatus was obtained by the following method.

In the image forming apparatus of the present embodiment, except for the intermediate transfer belt 1, the separation roller 1c is replaced with an aluminum pseudo separation roller 1c having the same outer diameter of 22.1 mm as the separation roller 1c. Then, in a state where the transfer material P is not inserted into the secondary transfer nip portion N2, 23 ° C./50% R.D. H. In the environment, the output voltage V2 [V] of the secondary transfer bias source when +30 μA was applied to the secondary transfer roller 2 by the secondary transfer bias source 21 was measured. The impedance Z2 is the following formula:
Z2 [Ω] = V2 [V] / (3 × 10 ⁻⁵ [A]),
Ask from.

  Table 2 shows the results of comparing the triacity generation levels using the secondary transfer roller 2 of Example 1 and Comparative Example.

The triacity occurrence level was determined as follows. That is, 15 ° C / 10% R.V. H. Canon color laser copier paper 81.4 g / m ² (A3 size) paper, which was dried by leaving it in the environment for 120 hours, was used. And 23 degreeC / 50% R. H. A sample printed with 10 full-color cyan images having an optical density of 0.4 in the environment was judged by sensory evaluation.

  The level of occurrence of triacity is “◯” for 0 out of 10 occurrences, “△” for occurrence of 1 to 2 out of 10 occurrences, and “Triple” for occurrence of 3 or more out of 10 occurrences. It is written as “×”.

As shown in Table 2, Z1 <Z2, which is not the configuration of the present embodiment, and the ten-point average roughness Rz _{JIS of} the surface that contacts the transfer material P of the secondary transfer roller 2 is 7.0 μm or less. In some cases, triacity has occurred.

  The triacities that the present inventors have confirmed in the comparative example will be described.

  Triacism is an image defect that occurs remarkably on paper that has been increased in resistance by being left in a low-humidity environment (for example, 15 ° C./10% RH) for about one week, and discharge downstream of the secondary transfer nip. This is considered to be an image defect that occurs with this.

  The mechanism by which the inventors consider triacity will be described with reference to FIG.

  FIG. 4 is an enlarged view of the vicinity of the secondary transfer portion in FIG. In FIG. 4, the separation roller surface 1cf, the toner carrying surface (front surface) 1f of the intermediate transfer belt, the non-toner carrying surface (back surface) 1r of the intermediate transfer belt, the toner carrying surface (front surface) Pf of the transfer material, the non-transfer material The toner carrying surface (back surface) Pr, the secondary transfer roller surface 2f, and the toner T.

  In this embodiment, the secondary transfer roller 2 is biased by a bias source 21 and an electric field for transferring the toner T to the transfer material P is formed in the secondary transfer nip N2. Due to this secondary transfer bias, in the gap near the secondary transfer nip N2, a discharge S1 in which a negative charge is applied to the transfer material surface Pf is generated between the intermediate transfer belt surface 1f and the transfer material surface Pf. Then, between the transfer material back surface Pr and the secondary transfer roller surface 2f, a discharge S2 is generated that imparts positive polarity to the transfer material back surface Pr. As a result, the transfer material P is charged.

  That is, the transfer material P after the secondary transfer process is charged, and the polarity thereof is the toner carried by the transfer material P (having a negative charge in this embodiment), the negative charge due to the discharge S1, and the discharge S2. Determined by the sum of the positive charges.

  The present inventors have confirmed that there is a correlation as shown in Table 2 between the polarity of the transfer material and the level of occurrence of triacity. That is, triacity occurs when the transfer material P is negative.

  The present inventors consider that the cause of the occurrence of triacity occurs as follows.

  That is, the transfer material having a negative polarity is separated from the intermediate transfer belt 1 and the secondary transfer roller 2, so that the negative polarity of the transfer material P is neutralized from the intermediate transfer belt 1 or the secondary transfer roller 2. Discharge occurs. As a result, it is considered that the toner moves due to a sudden change in the charge distribution of the transfer material P, and triacity occurs.

  A method for measuring the polarity of the transfer material will be described. An apparatus for measuring the polarity of the transfer material is shown in FIG.

The unfixed transfer material P before being inserted into the fixing device 3 after the secondary transfer process is taken out from the image forming apparatus and cut into a square (1 × 10 ⁻² m ² ) having a side of 100 mm. Thereafter, when the transfer material P is sandwiched between the electrode plate E1 and the electrode plate E2, a current having the same absolute value as the total charge amount and the opposite polarity of the transfer material P flows through the coulomb meter Q1. The polarity of the transfer material was measured from the polarity of the total charge amount of this current.

  Here, the electrode plate E1 and the electrode plate E2 are composed of E1a and E2a of a 100 μm thick insulating plate portion made of PET (polyethylene terephthalate), and E1b and E2b of a conductive layer formed by evaporating aluminum on the insulating plate. Become.

  Next, a mechanism considered by the present inventors to suppress the occurrence of triacity in the configuration of this embodiment will be described.

  Due to the relationship of Z1 <Z2 which is the configuration of this comparative example, more charges reach the intermediate transfer belt surface 1f than the secondary transfer roller surface 2f, so that the discharge S1 is larger than the discharge S2, and the transfer material is Triacity occurs due to the negative polarity.

  On the other hand, by setting the relationship of Z1 ≧ Z2, which is the configuration of the present embodiment, the amount of charge reaching the secondary transfer roller surface 2f is equal to or greater than the amount of charge reaching the intermediate transfer belt surface 1f. The discharge S2 is equal to or greater than the discharge S1. For this reason, the transfer material becomes neutral or positive, and triacity does not occur.

  Further, the mechanism that the inventors consider that the occurrence of triacity is suppressed in Comparative Example E1 will be described with reference to FIG.

The secondary transfer roller 2 of Comparative Example E1 has a ten-point average roughness Rz _{JIS of} the surface in contact with the transfer material P of 9.0 μm. In FIG. 6, it is drawn as an uneven surface. Thus, a gap of about 9.0 μm exists between the non-toner carrying surface (back surface) Pr of the transfer material P and the secondary transfer roller surface 2 f.

  According to Table 2.4 of “Discharge Handbook (Electrical Society Discharge Handbook Publication Committee)”, the minimum value of the spark discharge gap length in the air of 760 Torr, which is obtained from the Paschen curve, is 7.2 μm.

  In Comparative Example E1, the gap between the non-toner carrying surface Pr of the transfer material and the secondary transfer roller surface 2f is wider than the minimum value of the spark discharge gap length, so that there is a gap between the transfer material back surface Pr and the secondary transfer roller surface 2f. The discharge S2 can also be generated in the secondary transfer nip N2. As a result, it is considered that the transfer material becomes positive and the generation of triacity is suppressed when the negative charge applied by the discharge S1 exceeds the positive charge applied by the discharge S2.

  As described above, the occurrence of image defects (triacities) can be suppressed by setting the relationship of Z1 ≧ Z2 that is the configuration of the present embodiment.

In this embodiment, the secondary transfer roller surface 2f has a 10-point average roughness Rz _JIS of 7 μm or less. Therefore, as described above, no discharge occurs in the gap between the non-toner carrying surface Pr of the transfer material P and the secondary transfer roller surface 2f. However, the secondary transfer roller surface 2f preferably has a 10-point average roughness Rz _JIS of 3.5 μm or less from the viewpoint of cleaning properties.

Example 2
Next, a second embodiment of the image forming apparatus of the present invention will be described with reference to FIG. The image forming apparatus according to the present embodiment is the same as the image forming apparatus 100 illustrated in FIG. 1 described in the first embodiment, and members having the same functions and functions are denoted by the same reference numerals. Will be omitted, and the re-explanation here will be omitted.

  The image forming apparatus 100 according to the second exemplary embodiment illustrated in FIG. 7 performs printing with no margin (no margin) on the transfer material P. That is, the image forming apparatus 100 according to the present exemplary embodiment has a function of performing image formation in the first image forming mode in which a toner image can be formed up to the edge of the transfer material P, and a toner image on any edge of the transfer material P. And a function of performing image formation in the second image forming mode that is not formed. Image formation in the first image formation mode and image formation in the second image formation mode are selected by the image formation mode selection unit 301. The image formation control means 300 constituting the image processing means drives and controls the image formation driver 302 based on the signal from the image formation mode selection means 301, and the image formation unit S performs predetermined image formation.

  Therefore, in the image forming apparatus of this embodiment, the mask area M for determining the printing area in the transfer material P in the conventional image forming apparatus is made larger than the transfer material P by the width of each additional area.

  That is, as shown in FIG. 8, the transfer material P is transferred for each of the added region widths Wlea, Wtre, Wref, and Wrig at each of the edge portions, that is, the front end portion, the rear end portion, the left end portion, and the right end portion. Make it larger than P. Thereby, in the first image forming mode, the image of the additional region B can be formed on the photosensitive drum.

  Therefore, in the image formation in the first image formation mode, a part of the toner in the added area outside the transfer material P during the transfer adheres to the secondary transfer roller 2. Since this adhered toner can cause back contamination of the transfer material P, it is removed by the secondary transfer roller cleaner 222 in contact with the secondary transfer roller 2.

  The secondary transfer roller cleaner 222 in Embodiment 2 will be described with reference to a schematic explanatory diagram of the secondary transfer roller cleaner 222 shown in FIG.

  The image forming apparatus according to the present exemplary embodiment is an image forming apparatus capable of performing printing without margins. The secondary transfer roller cleaner 222 according to the second exemplary embodiment includes a larger amount of the secondary transfer roller 2 as compared with the first exemplary embodiment. It is necessary to remove the toner adhering to the toner.

  Accordingly, in the second embodiment, the blade type secondary transfer roller cleaner 222 having excellent cleaning performance is employed. The secondary transfer roller cleaner 222 rotates a urethane rubber sheet 222b having a thickness of 2.0 mm and a hardness of 40 ° (JIS-A) bonded to the support metal plate 222a in the direction of the arrow R2 at 30 N / m by the pressure member 222c. The secondary transfer roller 2 is in contact with a constant load.

In the present embodiment, the secondary transfer roller 2 has a ten-point average roughness Rz _JIS of 0.4 μm in order to obtain a good cleaning performance by a blade method.

  Next, the effect of the present embodiment will be described for three types of the embodiment A2, the embodiment B2, and the embodiment C2.

  As described in the first embodiment, the impedance between the surface of the intermediate transfer belt 1 on which the toner image is formed as the image carrier and the reference potential (ground) of the image forming apparatus 100 is Z1. In addition, an impedance between a surface of the secondary transfer roller 2 serving as a transfer unit that is in contact with the transfer material P and a reference potential (ground) of the image forming apparatus 100 is Z2.

In Example A2, Example B2, and Example C2, the volume resistivity ρv of the intermediate transfer belt 1, the roller resistance value R1c of the separation roller 1c, and the roller resistance value R2 of the secondary transfer roller 2 are adjusted. Thereby, the relationship between the impedances Z1 and Z2 is
Z1 ≧ Z2,
Is set.

Moreover, as a comparative example, two types of comparative example A2 and comparative example B2 are shown. In the comparative example, the ten-point average roughness Rz _JIS of the surface of the secondary transfer roller 2 that contacts the transfer material is 0.4 μm. However, by adjusting the volume resistivity ρv of the intermediate transfer belt 1, the roller resistance value R1c of the separation roller 1c, and the roller resistance value R2 of the secondary transfer roller 2, the relationship between the impedance Z1 and the impedance Z2 is
Z1 <Z2,
Is set.

Table 3 shows the ten-point average roughness Rz _JIS , ρv, R1c, R2, Z1, and Z2 of the surface of the secondary transfer roller 2 that is in contact with the transfer material in Example 2 and the comparative example.

  Table 4 shows the results of comparing the triacity generation levels using the secondary transfer rollers of Example 2 and Comparative Example. The method for determining the triacity occurrence level is the same as in the first embodiment.

From Table 4, even when the ten-point average roughness Rz _{JIS of the} secondary transfer roller 2 which is the configuration of the second embodiment is 0.4 μm, the image defect (triacity) is obtained by satisfying the relationship of Z1 ≧ Z2. It has been confirmed that the occurrence of the occurrence can be suppressed.

  As described above, the occurrence of image defects (triacities) can be suppressed by setting the relationship of Z1 ≧ Z2 that is the configuration of the present embodiment.

Example 3
In each of the above embodiments, a tandem type and intermediate transfer type color image forming apparatus has been described. Further, the relationship between the intermediate transfer member 1 as the toner image carrier, the secondary transfer roller 2 and the transfer material P has been described.

  The principle of the present invention is similarly applied to a direct transfer type image forming apparatus in which a toner image carrier as a toner image carrier is directly transferred to a transfer material by a transfer unit, and similar effects can be obtained.

  That is, the image forming apparatus 100 shown in FIG. 10 includes a drum-shaped photoconductor 211 in this embodiment, which is a drum-shaped or belt-shaped rotating body as an image carrier. Around the photosensitive member 211, a charging roller 212 as a charging unit and a scanner 213 as an exposure unit are arranged. The photoreceptor 211 has a layer in which a photosensitive material is applied on an aluminum cylinder that is a support member. The aluminum cylinder is electrically grounded to a reference potential (ground) of the image forming apparatus.

  Further, in this embodiment, four color developing devices 214 (214a to 214a) of yellow, magenta, cyan and black are provided as developing means. Further, around the photosensitive member 211, a transfer roller 2 as a transfer unit that contacts the photosensitive member and a photosensitive member cleaning blade 219 as a photosensitive member cleaning unit are provided. The transfer roller 2 is provided with a transfer roller cleaner 22 as transfer roller cleaning means. The transfer roller 2 and the transfer roller cleaner 22 can have the same configuration as in the first embodiment.

  With the above configuration, according to the present embodiment, the surface of the photosensitive member 211 as an image carrier is uniformly charged by the charging roller 212, and then, for each color based on the image data color-separated by the scanner 213. Laser light is scanned and exposed, whereby an electrostatic latent image is formed on the photoreceptor 211.

  Thereafter, a toner image is formed on the photoconductor 211 by switching the developing devices 214 (214a to 214a) of the respective colors arranged in the vicinity of the photoconductor 211 for each color.

  The above process is executed for each color, and a full-color toner image (or a single-color toner image may be formed) is formed on the photoreceptor 211.

  The toner image on the photoconductor 211 is transferred onto the transfer material by a bias applied to the transfer roller 2 when the transfer material passes between the transfer roller 2 as a transfer unit that contacts the photoconductor 211. . Note that unnecessary transfer residual toner on the photoconductor 211 after the transfer is cleaned by the photoconductor cleaning blade 219 that contacts the photoconductor 211. Since the image forming apparatus having such a configuration is well known to those skilled in the art, further detailed description is omitted.

  The configuration described in the first embodiment can be applied to the image forming apparatus having such a configuration.

  However, in the first embodiment, the image carrier is the intermediate transfer member 1, but in this embodiment, the image carrier is the photosensitive member 211.

  That is, as shown in FIG. 10, in this embodiment, instead of the secondary transfer roller 2, the intermediate transfer body 1, and the secondary transfer roller cleaner 22 shown in the first embodiment, the transfer roller 2, the photoconductor 211, The transfer roller cleaner 22 is replaced.

That is, the ten-point average roughness Rz _{JIS of} the surface of the transfer roller 2 that contacts the transfer material P is 7 μm or less. Preferably, it is 3.5 μm or less. Further, the impedance Z1 between the surface of the photosensitive member 211 on which the toner image is formed and the reference potential (ground) of the image forming apparatus, and the surface of the transfer roller 2 where the transfer material P contacts and the reference potential (ground) of the image forming apparatus. The impedance Z2 between
Z1 ≧ Z2,
It is said.

  Furthermore, as a matter of course, also in the present embodiment, as in the second embodiment, the image forming apparatus 100 shown in FIG.

  That is, the image forming apparatus 100 according to the present exemplary embodiment has a function of performing image formation in the first image forming mode in which a toner image can be formed up to the edge of the transfer material P, and a toner image on any edge of the transfer material P. And a function of performing image formation in the second image forming mode that is not formed. Then, image formation similar to that described in the second embodiment can be performed. Of course, in this case, it is preferable to use the cleaner 222 shown in FIG. 9 as the transfer roller cleaner.

  In each of the above embodiments, an intermediate transfer type or direct transfer type color image forming apparatus has been described. Of course, the image forming apparatus of the present invention is not limited to a color image forming apparatus. It may be a device.

  Since such an image forming apparatus is well known to those skilled in the art, further detailed description is omitted. The principle of the present invention as described in the first, second, and third embodiments can be similarly applied to the image forming apparatus having such a configuration, and similar effects can be obtained.

1 is a schematic configuration diagram of an embodiment of an image forming apparatus according to the present invention. It is a schematic block diagram of one Example of a secondary transfer roller. It is a schematic block diagram of one Example of the cleaning apparatus for a secondary transfer roller. It is a figure explaining the generation | occurrence | production mechanism of an image defect (triasis). It is a figure explaining the measuring method of a transfer material polarity. It is a figure explaining the mechanism in which generation | occurrence | production of the image defect (triacity) in the structure of the comparative example E1 is suppressed. It is a schematic block diagram of the other Example of the image forming apparatus which concerns on this invention. It is a figure explaining a mask area | region. It is a schematic block diagram of the other Example of the cleaning apparatus for a secondary transfer roller. It is a schematic block diagram of the other Example of the image forming apparatus which concerns on this invention. It is a schematic block diagram of the conventional image forming apparatus.

Explanation of symbols

1 Intermediate transfer member (first image carrier)
1c Separation roller (supporting member)
2 Transfer roller (transfer means)
11 (11a to 11d) Photosensitive drum (second image carrier)
12 (12a to 12d) Charging roller (charging means)
13 (13a-13d) Scanner (exposure means)
14 (14a-14d) Developing device (developing means)
21 Transfer bias source 22, 222 Transfer roller cleaner (cleaning means)
100 Image forming apparatus 211 Photosensitive member (image carrier)
212 Charging roller (charging means)
213 Scanner (exposure means)
214 Developing Device (Developing Unit)
219 photoconductor cleaning blade (photoconductor cleaning means)
300 Control Unit 301 Image Forming Mode Selection Unit 302 Image Forming Driver P Transfer Material S Image Forming Unit (Image Forming Unit)

Claims (3)

An image carrier, an image forming unit that forms a toner image on the image carrier, a primary transfer unit that transfers the toner image to an intermediate transfer member, a support member that supports the intermediate transfer member, and the intermediate transfer member Secondary transfer means for sandwiching a transfer material therebetween, the ten-point average roughness Rz _{JIS of} the surface of the secondary transfer means that contacts the transfer material is 7 μm or less, and the intermediate transfer member In the image forming apparatus for transferring the formed toner image to the transfer material,
The impedance Z1 between the surface of the intermediate transfer member on which the toner image is formed and the reference potential of the image forming apparatus, and the surface between the surface of the secondary transfer unit where the transfer material contacts and the reference potential of the image forming apparatus. Impedance Z2 is
Z1 ≧ Z2,
An image forming apparatus.   The image forming apparatus according to claim 1, further comprising a cleaning unit that cleans a surface of the secondary transfer unit that contacts the transfer material.   A function of forming an image in a first image forming mode capable of forming a toner image up to the edge of the transfer material, and an image forming in a second image forming mode in which a toner image is not formed on any edge of the transfer material. The image forming apparatus according to claim 1, wherein the image forming apparatus has a function to perform.

Images