JP2006221066A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent microgap discharge under no influence from the existence of potential difference between a developed image portion and a background portion, and to eliminate failures such as toner spattering in transfer, faulty reproduction of a dot image, toner flying-off and reverse transfer of toner to a photoreceptor. <P>SOLUTION: In an image forming apparatus equipped with an intermediate transfer belt 10 whose volume resistivity ρ<SB>V</SB>is set to 10<SP>7</SP>-10<SP>15</SP>Ω cm to which a toner image on an image carrier 1 is transferred and a secondary transfer means to secondarily transfer the toner image on the image carrier 1 to a transfer material, on or near a surface of the intermediate transfer belt 10 on a side opposite to the image carrier, a material whose volume resistance is different from that of the peripheral material is made to exist so as to establish the relation: D≤L≤P<SB>MIN</SB>(μm) when a dispersion pitch average L not more than a minimum pixel diameter P<SB>MIN</SB>and not less than a volume average particle diameter D of the toner is represented as an average of distances each from an isolated dispersed material existing probability center to an identical and adjacent isolated dispersed material existing probability center in cross sections at the same depth from the surface of the intermediate transfer belt. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and more particularly to a configuration for preventing abnormal images during transfer.

As is well known, in an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a printing machine, a toner image obtained by developing an electrostatic latent image formed on a photosensitive member that is a latent image carrier is recorded on a recording medium. A transfer process of transferring to a sheet which is one of the above is executed.
In the transfer process, the toner image may be transferred directly from the photoconductor to the sheet as in the case of a monochrome image, and an image for each color is formed as in the case of a full color image. The image for each color is directly transferred to the sheet passing through the position of the photoconductor and superimposed on the sheet, and the image for each color formed by each photoconductor is sequentially transferred to the intermediate transfer body (primary). In some cases, the images superimposed and transferred onto the intermediate transfer member are collectively transferred (secondary transfer) to the sheet.

  In a combination of primary transfer and secondary transfer used as a transfer method for forming a full-color image, a toner image is generated by an electric field formed by applying a voltage from the back side of the intermediate transfer member by an electric field forming unit. A structure for electrostatically adsorbing is known.

On the other hand, the image transferred from the photosensitive member to the intermediate transfer member is deteriorated due to part of the toner in the image diffusing to the periphery in the process of moving to the transfer position formed between the photosensitive member and the intermediate transfer member. May cause.
Causes of image deterioration include transfer dust and transfer failure, and transfer dust means that toner is not transferred to the position where it should be transferred but is diffused and transferred to the periphery. It means being blurred. In particular, the sharpness at the thin line portion is impaired. As a cause of the occurrence, it is considered that a part of the toner is transferred by starting discharge in a minute gap between the photosensitive member and the intermediate transfer member due to the action of an electric field at the entrance of the transfer position. Moreover, if the discharge is started at the entrance of the transfer position, the charge amount (Q / M) of the toner affected by the discharge is reduced, the electrostatic adhesion is reduced, and the coulomb repulsion force between the toners is overcome. As a result, a part of the toner is scattered, and this also increases transfer dust.

  Apart from the transfer dust, the toner with a reduced charge amount remains on the photoconductor because the force due to the electric field cannot overcome the adhesion force between the photoconductor and the toner, which causes transfer defects. It will be.

The following configuration has been proposed as a measure for preventing transfer defects such as transfer dust described above.
An intermediate transfer body that temporarily carries a toner image and then transfers the toner image onto a transfer material, and is in contact with the back surface of the intermediate transfer body upstream from the transfer nip and is not electrically grounded. A configuration in which a member is provided and the charging means and the charge supply device are controlled so that the potential (Va) of the conductive member is zero or the same polarity as the charging polarity of the photosensitive member during transfer (for example, a patent) Reference 1).
The first electric field forming means provided on the upstream side in the moving direction of the image carrier at the transfer position gives an electric field in which the toner in the image moves toward the image carrier, and is provided on the downstream side in the moving direction. An electric field in which the toner in the image moves toward the intermediate transfer member is formed by the second electric field forming unit, and movement of the toner toward the intermediate transfer member is prevented on the upstream side in the moving direction of the image carrier. Thus, the generation of transfer dust is prevented, and the movement of toner to the intermediate transfer member is promoted on the downstream side in the movement direction to prevent the transfer efficiency from being lowered (for example, Patent Document 2).
In the moving direction of the intermediate transfer member, an electric field is provided upstream of the position where the transfer unit is provided and in contact with the intermediate transfer member, and the toner flies by an electrode that regulates the transfer electric field by the transfer unit. The structure which prevented that generation | occurrence | production arises (for example, patent document 3).

Patent 3205274 ("Claims") JP 2004-205969 A (paragraph “0044” column) JP 2000-122444 A (paragraph “0056” column)

By the way, there is a surface potential difference between the image portion and the non-image portion of the toner visible image on the photoreceptor immediately upstream of the primary transfer nip, and the toner charge amount distribution of the toner visible image is a normal polarity overcharge level to a normal polarity suitability level. ~ Normal polarity insufficiency level ~ Reverse polarity level is generally spread, and even when proper primary transfer electric field that does not cause minute void discharge phenomenon is applied to normal polarity appropriate charge level toner (The gap between the photosensitive member surface and the intermediate transfer member surface becomes wider than the toner adhesion portion), and the potential difference between the photosensitive member surface becomes larger. For this reason, it is difficult to completely prevent the above-described background portion discharge in the vicinity of the toner adhesion portion in the minute gap portions existing upstream and downstream of the primary transfer nip.
In other words, from this point of view, the configuration disclosed in the patent document only takes into account the configuration related to the transfer electric field control, and measures against the phenomenon caused by the surface potential difference on the photoconductor side are taken. As described above, it is difficult to completely prevent the increase in the low charge level toner and the transfer to the intermediate transfer body due to the minute gap discharge, and problems such as transfer dust, poor dot image reproduction, and toner scattering May not be completely resolved.

  In view of the problems in the conventional transfer process described above, the object of the present invention is to cause micro-gap discharge on the upstream side and downstream side of the transfer nip portion to be affected by the surface potential distribution on the photoconductor side that is the image carrier, that is, the visible image. High quality by eliminating defects such as transfer dust, dot image reproduction failure, toner scattering, and reverse transfer of toner to the photoreceptor. Another object of the present invention is to provide an image forming apparatus having a configuration capable of forming a multicolor image.

According to the first aspect of the present invention, an image carrier, a toner image forming means for forming a toner image on the image carrier, and a volume resistivity ρ _V to which the toner image on the image carrier is transferred are measured according to JIS. An intermediate transfer belt set to 10 ⁷ to 10 ¹⁵ Ω · cm as a value measured based on K69115.13.1 or JIS 3256, and a toner image on the image carrier is secondarily transferred to a transfer material 2 In the image forming apparatus including the next transfer unit, on the surface of the intermediate transfer belt facing the image carrier or in the vicinity of the surface, the minimum pixel diameter is less than _PMIN and the toner has a volume average particle diameter of D or more. When the average distance L between the dispersion centers is expressed as the average of the distance from the intermediate transfer belt surface to the adjacent dispersive material existence probability center, which is the same quality as the isolated dispersion material existence probability center in the same depth cross section,
D ≦ L ≦ P _MIN (μm)
It is characterized by the presence of a material having a volume resistance different from that of the surrounding material so as to satisfy the relationship.

The invention according to claim 2 is the image forming apparatus according to claim 1, wherein the volume resistance average value R _V between the primary transfer bias application electrode and the intermediate transfer belt surface is
10 ⁷ ≦ R _V ≦ 10 ¹³ (Ω)
The average value R _{S of the} intermediate transfer belt surface resistance is R _S > R _V.
(However, the volume resistance R _V and the surface resistance R _S are values measured based on “JIS K6911 5.13.1” or “JIS 3256”)
It is characterized by being set to

  According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the electrode shifted to a different polarity side from the primary transfer bias is disposed in contact with or close to the back surface of the intermediate transfer belt upstream from the primary transfer nip. It is a feature.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the electrode shifted to a different polarity side from the primary transfer bias is disposed in contact with or close to the back surface of the intermediate transfer belt downstream from the primary transfer nip. It is a feature.

The invention according to claim 5 is the image forming apparatus according to claim 1, wherein the contact pressure N between the image carrier and the intermediate transfer belt is
5 × 10 ⁻⁴ ≦ N ≦ 5 × 10 ⁻² (MPa)
It is characterized by being set in the range.

  According to a sixth aspect of the present invention, in the image forming apparatus according to the first aspect, the surface of the intermediate transfer belt has elasticity.

  According to a seventh aspect of the present invention, in the image forming apparatus according to the first aspect, the intermediate transfer belt has an elastic layer having compressibility in the thickness direction, which means a characteristic that the thickness is apparently reduced by pressurization. It is characterized by that.

According to an eighth aspect of the present invention, in the image forming apparatus of the first aspect, the static friction coefficient μ ₁ measured by the Euler belt method of the intermediate transfer belt is not less than the static friction coefficient μ ₂ of the image carrier (μ ₁ ≧ μ ₂ ).

  According to a ninth aspect of the present invention, in the image forming apparatus according to the first aspect, the toner has an average circularity (a value obtained from a perimeter of a circle having the same area as the projected area of the particle / a perimeter of the projected particle image). Is a toner of 0.90 to 0.99.

  According to a tenth aspect of the present invention, in the image forming apparatus according to the first aspect, the toner contains a release agent in the base toner.

  According to an eleventh aspect of the present invention, in the image forming apparatus according to the first aspect, inorganic fine particles are externally added to the toner.

  According to a twelfth aspect of the present invention, in the image forming apparatus according to one of the first to eleventh aspects, a portion of the intermediate transfer belt is made of a homogeneous porous material.

  According to a thirteenth aspect of the present invention, in the image forming apparatus according to any one of the first to twelfth aspects, a part of the intermediate transfer belt is made of a plurality of dense projections of the same quality.

  According to a fourteenth aspect of the present invention, in the image forming apparatus according to the twelfth or thirteenth aspect, the intermediate transfer belt has a structure in which a part or all of the surface thereof is covered with a different resistance member.

  According to the first aspect of the present invention, the volume resistance of the intermediate transfer belt differs from that of the peripheral material so that the average dispersion center distance of the toner sets a predetermined relationship between the minimum pixel diameter and the volume average particle diameter of the toner. Since the material is present, a large number of minute fringe electric fields (fine closed electric fields, so-called microfields relating to electric fields (references: Electrophotographic Society Journal 34, 4, P329, Iwata, Suzuki) are present on the surface of the intermediate transfer belt. As a result, the high resistance portion and the low resistance portion are mixed in the intermediate transfer belt, and the potential difference relaxation phenomenon due to the charge transfer between the resistance portions is more likely to occur than the discharge phenomenon. As a result, the discharge phenomenon between the image carrier and the intermediate transfer belt in the gap before and after the primary transfer nip is suppressed, and toner flying is prevented. Rukoto can, it is possible to prevent the transfer dust efficiently.

  According to the second aspect of the present invention, the average surface resistance value of the intermediate transfer belt is larger than the average volume resistance value of the primary transfer bias application electrode and the intermediate transfer belt surface. When a potential shift (for example, setting of the same polarity low potential, ground potential, and different polarity potential) is performed before and after the nip, the member used for this shift is the primary transfer of the intermediate transfer belt. Even if it is in contact with or close to the nip, it affects the transfer nip, that is, the high surface resistance of the belt prevents charge movement, and applies a sufficient transfer bias necessary for high-efficiency transfer. As a result, the increase in the surface potential at the time of the transfer is suppressed, and it becomes possible to prevent the transfer dust from being deteriorated and to suppress the deterioration of the transfer efficiency due to the inadvertent increase in the surface potential during the transfer bias.

  According to the third aspect of the present invention, the surface potential of the intermediate transfer belt can be shifted to a different polarity side from the transfer nip portion upstream of the primary transfer nip, so that discharge in the transfer upstream gap can be prevented and transfer dust in the portion can be prevented. It becomes possible to do.

  According to the fourth aspect of the invention, the surface potential of the intermediate transfer belt can be shifted to a different polarity side from the transfer nip portion downstream of the primary transfer nip, and discharge in the downstream gap can be prevented, thereby preventing transfer dust in the portion. it can. Also, in the primary transfer of multiple colors, the primary transfer bias voltage level during the primary transfer of the next color can be lowered by the intermediate neutralizing effect that attenuates the surface potential of the surface belt of the intermediate transfer member. It is possible to improve the transfer dust problem.

According to the fifth aspect of the present invention, a transfer nip necessary for primary transfer can be formed with the lower limit of the contact pressure, and the toner image and the image carrier at the time of primary transfer can be formed with the upper limit of the contact pressure. The increase in non-electrostatic adhesion can be prevented, and high-efficiency transfer of primary transfer and prevention of transfer leakage can be achieved.
According to the sixth aspect of the present invention, it is possible to prevent the transfer pressure from being concentrated on the toner image portion at the transfer nip of the primary transfer, and to increase the non-electrostatic adhesion force between the toner image and the image carrier during the primary transfer. This makes it possible to prevent the transfer of primary transfer from being lost.

  According to the seventh aspect of the present invention, it is possible to prevent the transfer pressure from being concentrated on the toner image portion at the transfer nip of the primary transfer, and to increase the non-electrostatic adhesion between the toner image and the image carrier during the primary transfer. This makes it possible to prevent the transfer of primary transfer from being lost.

  According to the eighth aspect of the present invention, it is possible to suppress a non-electrostatic adhesion force increase between the toner image and the image carrier during the primary transfer, and to prevent the primary transfer from being lost.

  According to the ninth aspect of the present invention, it is possible to suppress the increase in non-electrostatic adhesion between the toner image and the image carrier during the primary transfer, and it is possible to prevent the primary transfer from being lost.

According to the tenth aspect of the present invention, it is possible to suppress a non-electrostatic adhesion force increase between the toner image and the image carrier during the primary transfer, and it is possible to prevent the primary transfer from being lost.
According to the eleventh aspect of the present invention, it is possible to suppress the increase in non-electrostatic adhesion between the toner image and the image carrier during the primary transfer, and it is possible to prevent the primary transfer from being lost.

  According to the twelfth aspect of the present invention, the transfer omission is prevented in the intermediate transfer primary transfer. The foreign material can be easily and stably disposed in the pores of a part of the porous material of the intermediate transfer member, and the performance of the intermediate transfer belt can be easily stabilized.

  According to the invention of claim 13. It is possible to easily and stably dispose a foreign material around a large number of dense protrusions in a part of the intermediate transfer member, and to easily stabilize the performance of the intermediate transfer belt.

  According to the fourteenth aspect of the present invention, the bonding with the other material contacting the different resistance member covering the surface or a part of the intermediate transfer member becomes strong and difficult to separate from each other, and the performance of the intermediate transfer belt is stabilized. It becomes possible to make it easy to convert.

  The best mode for carrying out the present invention according to the embodiment shown in the drawings will be described below.

  FIG. 1 is a schematic configuration diagram of a printer which is one of image forming apparatuses according to an embodiment of the present invention. Note that the present invention is not limited to a printer, and can also be applied to a copier, a facsimile machine, a printer, and a configuration in which these functions are combined.

In FIG. 1, around a drum-shaped photoconductor 1 as an image carrier rotating in the direction of an arrow, there are a photoconductor cleaning unit 2, a charger 4 as a charging means for uniformly charging the photoconductor, and image information. Correspondingly, an exposure unit 5 as exposure means for irradiating the photosensitive member 1 with light, developing means 6, 7, 8, 9 for developing the electrostatic latent image on the photosensitive member 1, an intermediate transfer belt 10, and the like are arranged. Yes.
As the toner image forming means for forming a toner image on the photoreceptor 1, the charger 4, the exposure unit 5, the developing means 6, 7, 8, 9 and the like are used.

The developing means includes four developing units, a yellow developing unit 6, a magenta developing unit 7, a cyan developing unit 8, and a black developing unit 9.
When forming a full-color image, a toner image (visible image) is formed in the order of the yellow developing device 6, the magenta developing device 7, the cyan developing device 8, and the black developing device 9, and the toner images of the respective colors are sequentially superimposed on the intermediate transfer belt 10. A full color image is formed by the transfer.
The surface of the photoreceptor 1 after the toner image is transferred to the intermediate transfer belt 10 is cleaned by the blade 3 of the photoreceptor cleaning unit 2.

The intermediate transfer belt 10 is stretched by a drive roller 13, a primary transfer bias roller 11, and driven rollers 12a and 12b, and is driven by a drive motor (not shown).
The pressure contact force of the primary transfer bias roller 11 is adjusted by a pressure contact spring 30.

The intermediate transfer belt 10 is formed by dispersing a conductive material such as carbon black in PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), or the like. A mixed / synthetic material with adjusted resistance, a conductive material, and an insulating material are used in combination of at least two materials, and the volume resistivity is set in the range of 10 ⁷ to 10 ¹⁵ Ωcm. As shown in FIG. 2, on the surface of the intermediate transfer belt 10 or near the surface, the minimum pixel diameter P _MIN (about 42 μm for 600 dpi, about 21 μm for 1200 dpi) or less, and the volume average particle diameter of the toner The above-mentioned two or more kinds of mixed / synthetic materials having different volume resistances from the surrounding materials with the average distance L between the dispersion centers of D or more are used. That.

  By mixing materials with different volume resistances with peripheral materials that have such a relationship, it corresponds to a fine fringe electric field that does not appear on the image due to the surface potential difference due to the resistance difference of the above multiple materials on the surface of the intermediate transfer belt. However, when the photoconductor 1 and the intermediate transfer belt 10 are separated from each other, it is difficult to act. However, in the almost contacted state, the electric field strength on the intermediate transfer belt 10 is difficult. The toner image on the photoconductor 1 can be attracted to the intermediate transfer belt and transferred by the strong electrostatic force of the microfield having a strong gradient. Thereby, transfer of toner from the photoreceptor 1 to the intermediate transfer belt 10 in a non-contact state can be prevented, and generation of transfer dust when the toner image is transferred (primary transfer) to the surface of the intermediate transfer belt 10 is prevented. it can.

  The microfield is disclosed, for example, in “Electrophotographic Society Journal 34, 4, P329, Iwata, Suzuki”.

  The developing method using such a microfield is applied to Ricoh's “IMAGEIO DA series” sold by the present applicant. The content corresponding to this principle is, for example, June 29, 1997. It is described in “Electronic Society Edition,“ Basics and Applications of Electrophotographic Technology ”, P264 (iii) column” issued by the first edition of the third edition.

3 to 5 show cases where the volume resistivity of the material A used in the configuration of the intermediate transfer belt 10 in this embodiment is different, including the case where the volume resistivity of the material B is low.
3A is a perspective view of an example in which a material B having a higher resistance than the surroundings is dispersed on the surface of the intermediate transfer belt, and FIG. 3B is a thickness of the intermediate transfer belt 10 shown in FIG. A direction sectional view is shown. In FIG. 3C, the surface of the intermediate transfer belt 10 is extremely thin (0 to D / 2 is preferable, preferably about 0.1 to 3 μm), is covered with a material B having higher resistance than the lower layer, and This is an example of a mode in which a part of the material B is finely cut into the material A having a lower resistance. Thereby, the boundary area of the material A and the material B is wide, and it can join firmly mutually.

4A is a perspective view of fine protrusions provided on the surface of the material A of the intermediate transfer belt 10, and FIGS. 4B and 4C are more resistant to the protrusions after the protrusions are provided. This is an example in which a high material B is applied.
In FIG. 4B, the material A is also exposed on the surface, but in FIG. 4C, the surface of the intermediate transfer belt is extremely thin (0 to D / 2 is preferable, and about 0.1 to 3 μm is preferable. ) It is an example of an embodiment in which the material B is covered with a material B having a higher resistance than the lower layer, and a part of the material B is finely cut into the material A having a lower resistance. Thereby, the boundary area of the material A and the material B is wide, and it can join firmly mutually.

FIG. 5A is a perspective view showing the form of the high resistance side material B of the intermediate transfer belt, which is connected to the mesh. Thereby, the role of preventing the expansion and contraction of the intermediate transfer belt and preventing the material A and the material B from being separated can be obtained.
In FIG. 5B, the material B does not completely cover the surface side of the material A (side facing the photoconductor), but in FIG. 5C, the material B is on the surface side of the material A (on the photoconductor). The facing side is very thin (0 to D / 2 is preferred, preferably about 0.1 to 3 μm). Thereby, the boundary area of the material A and the material B is wide, and it can join firmly mutually.

  If the volume resistivity of the intermediate transfer belt 10 exceeds the above upper limit value, the transfer bias necessary for transfer becomes high, resulting in an increase in power supply cost. Further, since the charging potential of the intermediate transfer belt 10 becomes high, it is necessary to repeat the static elimination process a plurality of times, resulting in a problem that the entire time of the image forming operation is prolonged and the mechanical life is shortened. On the other hand, if the volume resistivity of the intermediate transfer belt 10 is lower than the lower limit value, the charge potential decays faster, which is advantageous for static elimination. It was confirmed by experiments that toner splattered due to a large increase in the surface potential of the intermediate transfer belt at a location where there was a gap.

On the other hand, in this embodiment, the volume resistance average value R _V between the primary transfer bias application electrode and the intermediate transfer belt surface is 10 ⁷ to 10 ¹³ Ω, and the intermediate transfer belt surface resistance average value R _S is calculated from R _V. Thus, compatibility between high-efficiency transfer and transfer dust prevention can be improved. Further, an intermediate transfer belt back surface resistance average value R _S by greater than R _V, can be further improved compatibility of a high efficiency transcription and transfer dust prevention. Hereinafter, this reason will be described.
First, the measurement of electrical resistance will be described as follows.
The surface resistance and volume resistance were measured based on “JIS K6911 5.13.1”. That is, for the surface resistance, the insulation resistance measuring apparatus defined in “JIS K6911 5.12” was subjected to the test of the outer annular surface electrode and the inner disk-shaped surface electrode of the test piece according to the conditions of “JIS K6911 5.13”. Measured by connecting the two. The volume resistance was measured by connecting the surface electrode and the back electrode of the test piece according to the conditions of “JIS K6911 5.13” to the insulation resistance measuring apparatus. In addition, as another method for measuring electric resistance, it can be performed by a method defined in “JIS 3256”.

“JIS K6911 5.13.1” used for resistance measurement is shown below.
FIG. 6 shows the electrode arrangement of the resistivity test of “JIS K6911 5.13.1”, where (A) is the front electrode and (B) is the back electrode. In FIG. 6, the unit is mm. FIG. 7 shows an electrode connection method of “JIS K6911 5.13.1”, where (A) is a volume resistivity test and (B) is a surface resistivity test.
(1) Apparatus (1.1) Conductive rubber or moisture-permeable conductive paint cut into the shape of the hatched portion in FIG.
(1.2) Power supply, insulation resistance measuring instrument and switch from (1.1.2) to (1.1.4) of “JIS K6911 5.12.1”.
(1.3) Micrometer An outer micrometer specified in "JIS B 7502" or one having an accuracy equivalent to or better than this.
(1.4) Vernier caliper An outer micrometer specified in JIS B7507 or having an accuracy equivalent to or better than this.
(2) Test piece A test piece formed into a disk having a diameter of about 100 mm and a thickness of 2 mm is used.
(3) Pretreatment The test piece is pretreated at C-90 (+ 4-2) h / 20 ± 2 ° C./(65±5)% RH.
(4) Method The thickness of the test piece after treatment is accurately measured to 0.01 mm with an outer macrometer, and conductive rubber is disposed as shown in FIG. Moreover, as shown in FIG. 6, it can draw on a test piece with a moisture-permeable conductive paint, and can be set as an electrode.
In this case, the test piece is treated after drawing the electrode, and care is taken so that the moisture-permeable conductive paint does not peel off from the test piece during operation. The outer diameter of the inner circle of the surface electrode and the inner diameter of the annular electrode are measured to 0.02 mm with a caliper. When measuring the volume resistivity, as shown in FIG. 7 (A), when measuring the surface resistivity, they are connected as shown in FIG. 7 (B). This is further connected to the position of a test piece of a circuit similar to the above “JIS K6911 5.12,” and charged for 1 minute to measure volume resistance and surface resistance. In this case, the test is performed under conditions of a temperature of 20 ± 2 ° C. and a relative humidity (65 ± 5)%.
(5) Calculation The volume resistivity and the surface resistivity are calculated by the following equations.
ρ _V = (πd ² / 4T) × R _V ,
ρ _S = {π (D + d) / (D−d)} × R _S
Here, ρv: volume resistivity [MΩcm], ρs: surface resistivity [MΩ], d: outer diameter of inner circle of surface electrode, T: thickness of test specimen [cm], Rv: volume resistivity [ MΩ], D: inner diameter [cm] of the annular electrode on the surface, Rs: surface resistance [MΩ], and π: circumferential ratio = 3.14.

(1.1) of the above “JIS K6911 5.12.1” is shown below.
FIG. 8 is a diagram showing an insulation resistance measuring device according to (1.1) of “JIS K6911 5.12.1”.
(1.1) Insulation resistance measuring device A device having an electrode, a power source, a galvanometer, a universal shunt, a switch and the like as illustrated in FIG.
(1.1.1) A brass taper pin having a diameter of 5 mm as defined in the electrode “JIS B 1352” and having no scratch on the surface.
(1.1.2) A dry battery or a storage battery having a power supply DC voltage of 500V. However, a power source that has flowed alternating current may be used as long as it can be confirmed that a constant direct current voltage is maintained.
(1.1.3) Insulation resistance measuring instrument (1.1.3.1) When measuring an insulation resistance value of 1 MΩ or more and less than 10 ⁶ MΩ (comparative method) Standard resistance is 1 MΩ manganin or an accuracy equivalent to or better than that. The universal shunt shall be precise to adjust the galvanometer runout and measurement range. The galvanometer is highly sensitive with a stable 0 point, and if there is a 1 mm deflection at a distance of 1 m due to a current of 10 ⁻¹⁰ A, a resistance of less than 10 ⁶ MΩ with an accuracy of ± 10% Can be measured.
(1.1.3.2) When measuring an insulation resistance value of 5 MΩ or less, an insulation resistance meter specified in “JIS C 1302” is used.
(1.1.3.3) When measuring an insulation resistance value of 1 MΩ or more and less than 10 ⁸ MΩ Use a DC amplifier calibrated to an accuracy of ± 10%.
(1.1.4) Switch with appropriate insulation protection.

As another method for measuring electric resistance, “JISR3256 3” is shown below.
FIG. 9 is a diagram showing a surface resistance measuring method.
3. Measuring method at room temperature (3-1) Principle of measurement The surface of the test piece using a measuring circuit comprising an electrode-test piece system X, a DC power source E, a DC voltmeter V and an ammeter A as shown in FIG. The surface resistivity is calculated from the value of the surface resistance obtained by dividing the applied voltage by the current flowing on the surface of the test piece according to the formula defined in (3-5) described later. Note that a high insulation resistance meter is commercially available as a simple device for measuring the surface resistance in which the devices shown in FIG.
(3-2) Measurement conditions and applied voltage The test piece is measured after being left in an air-conditioned room at a temperature of 20 ± 2 ° C. and a relative humidity (50 ± 5)% for 16 hours or more. The applied voltage to the test piece is 1000 V or less, and 500 V is the standard voltage. The voltage application time is 1 minute as a standard, and is changed depending on the material of the substrate glass.
(3-3) Test piece preparation method The test piece adjustment method is as follows.
a) Shape and dimension The test piece is a rectangle with a side of 50 mm or more or a disk with a diameter of 50 mm or more.
b) Surface condition of the test piece The test piece should be mirror-polished or have a surface condition equivalent thereto.
c) Cleaning and drying The test specimen is first rubbed with a neutral detergent, then rinsed with tap water, and further ultrasonically cleaned in a solvent such as ultrapure water, acetone, ethanol, and the like. Drying may be performed using an oven or by natural drying.
d) Electrode formation method on test piece Electrode formation on the test piece is performed using a method such as vapor deposition or sputtering of a conductive material. Examples of the conductive material include gold and platinum. In this measurement method, it is desirable to use gold. Further, in this measuring method, since a high insulation resistance is measured, it is necessary to form a guard electrode in order to eliminate stray current of the electrode-test specimen system. FIG. 10 is a diagram illustrating an example of a method for applying an electrode to a test piece, in which (A) is a plan view and (B) is a front view.
e) The electrodes are arranged on concentric circles as shown in FIG. In this case, the size of the main electrode can be changed in the range of about 26 to 36 mm in consideration of the sensitivity of the measuring apparatus, and the size of the gap can be adjusted.
(3-4) Measurement procedure a) An electrode is formed on the test piece by the method shown in FIG. 10, and the caliper stipulated in “JIS B7507” for the diameter D _{1 of the} main electrode and the inner diameter D _{2 of the} counter electrode, or equivalent thereto. Measurement is performed with an accuracy of 0.05 mm using a measuring apparatus having the above accuracy.
b) The test piece is dried at about 120 ° C. for 2 hours or more and then cooled in a desiccator.
c) The surface resistance is measured by the surface resistance measurement method of FIG. 9 under the measurement conditions and applied voltage defined in 3.2. The measuring device is preferably held in a shielded ultra-high resistance measurement box.
(3-5) Calculation and number of measurements The electrical resistivity of the substrate glass surface is calculated by the following formula.
ρs [Ω] = (Dmπ / g) Rs
Here, ρs: surface resistivity [Ω], Rs: surface resistance [Ω], Dm: average diameter [D ₁ + D ₂ ] / 2 [mm], D ₁ : main electrode diameter [mm], D ₂ : the inner diameter of the counter electrode [mm], g: gap _{(D 2 -D 1) [mm} ]
The measurement is performed twice and the average value is taken as the surface resistivity measurement value.

  Further, as shown in FIG. 2, the electrode shifted to the different polarity side from the primary transfer bias is placed in contact with or in close proximity to the back surface of the intermediate transfer belt upstream from the primary transfer nip, so that intermediate transfer is performed upstream of the primary transfer nip. The belt surface potential can be shifted to a different polarity side from the transfer nip portion, discharge at the transfer upstream gap can be prevented, and transfer dust at the portion can be prevented.

  In addition, as shown in FIG. 2, an electrode shifted to a different polarity side from the primary transfer bias is disposed downstream of the primary transfer nip by contacting or in close proximity to the back surface of the intermediate transfer belt even downstream of the primary transfer nip. The surface potential of the intermediate transfer belt can be shifted to a different polarity side from the transfer nip portion, discharge in the transfer downstream gap can be prevented, and transfer dust and reverse transfer in the portion can be prevented.

Here, the contact pressure between the photoreceptor 1 and the intermediate transfer belt 10 generated by the pressure contact with the primary transfer bias roller 11 is preferably 5 × 10 ⁻⁴ Mpa or more and 5 × 10 ⁻² Mpa or less. . Within this range, transferability deterioration due to insufficient pressure contact force and toner aggregation due to overpressure contact can be prevented, transfer efficiency can be improved, and occurrence of void images can be prevented.
The surface of the intermediate transfer belt 10 has elasticity, and preferably the surface micro hardness is in a range of 30 to 70 degrees as measured by a micro rubber hardness meter (for example, MD-1 manufactured by Kobunshi Keiki Co., Ltd.) The transfer pressure can be prevented from concentrating on the toner image portion at the transfer nip of the primary transfer, and the non-electrostatic adhesion between the toner image and the image carrier during the primary transfer can be prevented. Can be prevented. Furthermore, regardless of the surface properties of the transfer paper, an intermediate transfer body that can perform transfer without white spots, voids, character crushing, color misregistration, etc., and a high-quality full-color image using the intermediate transfer body. Can be printed.

  In addition, the intermediate transfer belt is provided with an elastic layer that is compressible in the thickness direction, that is, has a characteristic that the thickness is apparently reduced by pressurization, and the surface micro hardness is preferably a micro rubber hardness meter (for example, a polymer By making the range of 30 degrees to 70 degrees as measured by Keiki Co., Ltd. MD-1), it is possible to prevent the transfer pressure from concentrating on the toner image portion at the transfer nip of the primary transfer, and the toner during the primary transfer. It is possible to prevent non-electrostatic adhesion between the image and the image carrier and to prevent primary transfer from being lost.

A small amount (about 0.1 to 1.0 part) of silicone oil SH200 (made by Toray Dow Corning Silicone Co., Ltd.) is present in the protective layer on the surface of the photoreceptor, or a lubricant such as zinc stearate is applied to the surface of the photoreceptor. If the static friction coefficient μ ₁ measured by the Euler belt method of the intermediate transfer belt is relatively larger than the static friction coefficient μ ₂ or more of the photoreceptor (μ ₁ ≧ μ ₂ ), The increase in non-electrostatic adhesion between the toner image and the image carrier during the next transfer can be suppressed, and the transfer failure during the primary transfer can be prevented.

  A near-spherical toner such as a polymerized toner, which uses a toner with an average circularity of 0.90 to 0.99, and suppresses the increase in non-electrostatic adhesion between the toner image and the photoreceptor, can suppress the primary transfer electric field strength. It is possible to prevent the transfer of primary transfer from being lost.

  In the base toner, a toner containing a release agent such as wax is used so that it is not necessary to apply oil at the fixing portion, and the toner image is made in a state where there is a slight release agent on the toner surface. If the increase in non-electrostatic adhesion force between the photosensitive member and the photosensitive member is suppressed, the primary transfer electric field strength can be suppressed and the transfer failure of the primary transfer can be prevented.

When hydrophobic inorganic fine particles are externally added to the base toner, and more preferably silica (SiO ₂ ) is externally added to improve the fluidity of the toner and suppress the increase in non-electrostatic adhesion between the toner image and the photoreceptor. The primary transfer electric field strength can be suppressed, and primary transfer transfer leakage can be prevented. The silica is more preferably hydrophobized on the surface with a silane coupling agent, silicone oil or the like.

  A part of the intermediate transfer belt is made of the same porous material (porous polyimide whose resistance is adjusted with carbon or the like) and the material does not expand or contract. The foreign material can be easily and stably disposed in the hole of the porous material, and the performance of the intermediate transfer belt can be stabilized.

  A part of the intermediate transfer belt is connected to each other in the same quality and has a large number of dense protrusions, and the material does not expand and contract in the rotation direction of the intermediate transfer belt, so that a foreign material is formed around the protrusions. Can be easily and stably disposed, and the performance of the intermediate transfer belt can be stabilized. Examples of a method for manufacturing the belt portion having the dense protrusions of the intermediate transfer belt include a casting method and a centrifugal molding method. The shape of the dense protrusions can be adjusted by adjusting the shape of the mold side corresponding to the surface of the belt portion having the dense protrusions. If necessary, the surface of the belt portion having the dense protrusions may be adjusted by blasting.

  As described above, when a part of the intermediate transfer belt 10 is made of the same porous material, or is connected to each other and has a large number of dense projections, a part or all of the belt surface is formed. Is thinly coated with different resistance members (preferably 0.1 to 1.0 μm), so that the bonding between the different resistance members can be made stronger, difficult to separate from each other, and the performance of the intermediate transfer belt can be stabilized. As the resistance member in this case, it is preferable to use the same material as the peripheral material located around the porous material or the projection material.

  Further, the surface of the intermediate transfer belt 10 may be coated with a release layer as necessary. Materials used for this coating include ETFE, PTFE (polytetrafluoroethylene), PVDF, PEA (perfluoroalkoxy fluororesin), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PVF (fluorine). Fluorine resin such as vinyl chloride) can be used, but is not limited thereto.

Next, the case where the static friction coefficient is measured by the Euler belt method (Mechanical Engineering Handbook: Basic A3 Mechanics / Mechanical Mechanics P35 (issued in 1986) edited by the Japan Society of Mechanical Engineers) will be described with reference to FIG.
FIG. 11 is a diagram schematically showing a method of measuring the surface friction coefficient by the Euler method using the Euler belt method. First, a piece of paper (TYPE 6200 A4 T: manufactured by Ricoh Co., Ltd.) is cut into 297 mm × 30 mm, and a thread 201 is attached to both ends to create a measurement paper piece 100.
The properties of the paper pieces are as follows: weighing: 71.7 g / m2, thickness: 89 μm, density: 0.81 g / cm3, smoothness: table; 40 s, back: 37 s, volume resistance: 1.2E + 11 Ω · cm, friction coefficient: table / Back: (Rum with rubber) Tan θ, length: 0.64, width: 0.65. A piece of measuring paper 200 is placed on the photosensitive drum 1 supported by a support member 203 at one end of a table 202, a weight 204 of 0.98 N (100 g weight) is tied to one thread 201, and a digital push is applied to the other thread 201. The pull gauge 205 is connected. In this state, the digital push-pull gauge 205 pulls the measurement paper piece 200 through the thread 201, and reads the value of the digital push-pull gauge 205 when the measurement paper piece 200 starts to move. If the value at this time is F (N), the coefficient of static friction μ is
μ = (2 / π) × [ln (F / 0.98)]
Is required.

  Examples of the method for manufacturing the intermediate transfer belt 10 include a casting method and a centrifugal molding method. When reducing the surface roughness Rz, the value of the surface roughness Rz of the belt can be adjusted by reducing the surface roughness Rz on the mold side corresponding to the surface of the belt. Note that the belt surface may be polished and adjusted as necessary.

  In FIG. 1, the belt cleaning unit 19 that can come in contact with and separate from the intermediate transfer belt 10 includes a cleaning blade 18 and a contact / separation mechanism 26 that makes the cleaning blade contact and separate from the intermediate transfer belt 10. During the primary transfer of the second, third, and fourth colors after the primary transfer of the yellow image of the first color, the yellow image is separated from the surface of the intermediate transfer belt 10 by the contact / separation mechanism 26. The contact / separation mechanism 26 is in contact with an urging means (not shown) that urges the cleaning unit 19 so that the cleaning blade 18 contacts the surface of the photosensitive member 1 and a bottom surface portion of the cleaning unit 19 that swings. An eccentric cam that is rotationally driven based on a signal from a control unit (not shown) is used.

  In FIG. 1, a belt position detection mark 23 is provided at an end in the width direction of the outer peripheral surface of the intermediate transfer belt 10, and an image forming process for each color is started at the timing when the mark 23 is detected by the mark sensor 24. By doing so, accurate color superimposition of each color image becomes possible. The technique of the present invention is effective in preventing color misregistration because there is no stretching distortion or change in the rotation direction of the intermediate transfer belt.

As shown in FIG. 1, the secondary transfer unit 15 includes a secondary transfer bias roller 14 and a contact / separation mechanism 16 that contacts and separates the secondary transfer bias roller 14 from the intermediate transfer belt 10. .
The contact / separation mechanism 16 includes a spring member as a biasing unit that biases the secondary transfer unit 15 so that the secondary transfer bias roller 14 is separated from the intermediate transfer belt 10, and a bottom surface on which the secondary transfer unit 15 swings. And an eccentric cam that is rotationally driven based on a signal from a control unit (not shown) in contact with the unit.

The secondary transfer bias roller 14 is configured by coating an elastic body such as urethane adjusted to a resistance value of 10 ⁶ to 10 ¹⁰ Ω with a conductive material on a metal core bar such as SUS. The resistance value of the secondary transfer bias roller 14 is measured by installing the secondary transfer bias roller 14 on a conductive metal plate and measuring 4.9 N on one side (total of 9.8 N on both sides) at both ends of the core metal. It calculated from the electric current value which flows when the voltage of 1000V is applied between a metal core and the said metal plate in the state which applied the load.

  The secondary transfer bias roller 14 is given a driving force by a drive gear (not shown), and its peripheral speed is adjusted to be substantially the same as the peripheral speed of the intermediate transfer belt 10. The secondary transfer bias roller 14 is normally separated from the surface of the intermediate transfer belt 10, but collectively transfers four-color superimposed images formed on the surface of the intermediate transfer belt 10 onto a transfer sheet 22 as a transfer material. When the timing is pressed by the contact / separation mechanism 16 as the contact / separation means, a secondary transfer bias is applied to the secondary transfer bias roller 14 by the high-voltage power supply 100 as the secondary transfer bias application means. Transfer from the transfer belt 10 to the transfer paper 22 is performed.

In the printer according to this embodiment having the above-described configuration, the transfer paper 22 is fed by the paper feed roller 25 and the registration roller 21 at the timing when the leading end of the four-color superimposed image on the intermediate transfer belt 10 reaches the secondary transfer position. The paper is fed together. The four-color superimposed image transferred to the transfer paper 22 is fixed by the fixing unit 17 and then discharged.
The toner used in the printer preferably has a volume average particle size in the range of 4 to 10 μm. By reducing the particle size of the toner within the above range, toner scattering can be prevented and high-resolution image formation can be achieved. Deterioration of toner and toner aggregation can be prevented, and the occurrence of a void image can be effectively prevented.

  As the binder resin used for the toner, all those conventionally used as the binder resin for toner can be applied. Specific examples include polyol resins, styrene acrylic copolymers, styrene such as polystyrene, polychlorostyrene, and polyvinyltoluene, and homopolymers of the substituted products, styrene / p-chlorostyrene copolymers, and styrene / propylene copolymers. Polymer, styrene / vinyl toluene copolymer, styrene / vinyl naphthalene copolymer, styrene / methyl acrylate copolymer, styrene / ethyl acrylate copolymer, styrene / butyl acrylate copolymer, styrene / acrylic acid Octyl copolymer, styrene / methyl methacrylate copolymer, styrene / ethyl methacrylate copolymer, styrene / butyl methacrylate copolymer, styrene / α-chloromethyl methacrylate copolymer, styrene / acrylonitrile copolymer , Styrene / vinyl ethyl ether Styrene / vinyl methyl ketone copolymer, styrene / butadiene copolymer, styrene / isoprene copolymer, styrene / acrylonitrile / indene copolymer, styrene / maleic acid copolymer, styrene / maleic acid ester copolymer Styrene copolymers such as polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, polyvinyl butyl butyral, polyacrylic acid resin, rosin, modified rosin, terpene resin, Phenol resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin, chlorinated paraffin, paraffin wax and the like can be used, and these are used alone or in admixture of two or more.

  As the colorant used in the toner, it is possible to apply all dyes and pigments that have been conventionally used as toner colorants. Specifically, carbon black, nigrosine dye, iron black, naphthol yellow S, Hansa yellow (10G, 5G, G), cadmium yellow, yellow iron oxide, ocher, yellow lead, titanium yellow, oil yellow, Hansa yellow, (GR, A, RN, R), Pigment Yellow L, Benzidine Yellow (G, GR), Permanent Yellow (NCG), Vulcan Fast Yellow (5G, R), Tartrazine Lake, Quinoline Yellow Lake, Anslagen Yellow BGL, Isoindolinone yellow, Bengala, red lead, lead red, cadmium red, cadmium mercury red, antimony red, permanent red 4R, para red, fire red, parachlor ortho nitroaniline red, risor fast scarlet G, brilliant Fast Scarlet, Brilliant Carmine BS, Permanent Red (E2R, F4R, FRL, FRLL, F4RH), Fast Scarlet VD, Belkan Fast Rubin B, Brilliant Scarlet G, Resol Rubin GX, Permanent Red F5R, Brilliant Carmine 6B, Pigment Scarlet 3B Bordeaux 5B, Toluidine Marine, Permanent Bordeaux F2K, Helio Bordeaux BL, Bordeaux 10B, Bon Marine Light, Bon Marine Medium, Eosin Lake, Rhodamine Lake B, Rhodamine Lake Y, Alizarin Lake, Thioindigolet B, Thioindigo Maroon, Oil Red, quinacridone red, pyrazolone red, chrome vermilion, benzidine orange, perinone orange, orange Le Orange, Cobalt Blue, Cerulean Blue, Alkaline Blue Lake, Peacock Blue Lake, Victoria Blue Lake, Metal-Free Phthalocyanine Blue, Phthalocyanine Blue, Fast Sky Blue, Indanthrene Blue (RS, BC), Indigo, Ultraviolet, Bituminous, Anthraquinone Blue, Fast Violet B, Methyl Violet Lake, Cobalt Purple, Manganese Purple, Dioxazine Violet, Anthraquinone Violet, Chrome Green, Zinc Green, Chrome Oxide, Pyridian Emerald Green, Pigment Green B, Naphthol Green B, Green Gold, Acid Green Lake, Malachite Green Lake, Phthalocyanine Green, Anthraquinone Green, Titanium Oxide, Zinc Hana, Litobon and it It is possible to use a mixture of these. In addition, generally the usage-amount of the said coloring agent is 0.1-50 weight part with respect to 100 weight part of binder resin.

  In this embodiment, four colors of toner are used, but toner of three colors, two colors, single color, or five colors or more may be used. The color used may be any color, but it is preferable to select a color that can reproduce a full color. In particular, as described above, it is preferable that the toner colors are black, yellow, cyan, and magenta because the number of developments can be reduced and a relatively wide color tone range can be covered.

  Further, the toner may contain a charge control agent as necessary. Any known charge control agent can be used. Specifically, nigrosine dyes, triphenylmethane dyes, chromium-containing metal complex dyes, molybdate chelate pigments, rhodamine dyes, alkoxy amines, quaternary ammonium salts (including fluorine-modified quaternary ammonium salts), alkyls It is possible to use amide, phosphorus simple substance or compound, tungsten simple substance or compound, fluorine-based activator, salicylic acid metal salt, metal salt of salicylic acid derivative, and the like.

  The amount of the charge control agent used is determined by the type of binder resin, the presence or absence of additives used as necessary, the toner production method including the dispersion method, etc. However, it is preferably used in the range of 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin. More preferably, the range of 2 to 5 parts by weight is good. Here, when the amount is less than 0.1 parts by weight, the toner is insufficiently charged and is not practical. On the other hand, when the amount exceeds 10 parts by weight, the chargeability of the toner is too high, and the electrostatic attraction force with the carrier, the developing sleeve or the like increases, and the image density is lowered due to spent or filming. If necessary, a plurality of charge control agents may be used in combination.

  The printer according to this embodiment may be developed by a so-called one-component developing method in which an electrostatic latent image is visualized by using toner alone as a developer, or a two-component developer obtained by mixing toner and a carrier. You may develop by the two-component developing method which visualizes an electrostatic latent image using. In the case of using the two-component development method, as the carrier to be used, conventional ones such as iron powder, ferrite and glass beads can be used. These carriers may be those coated with a resin, and as this resin, polyfluorinated carbon, polyvinyl chloride, polyvinylidene chloride, phenol resin, polyvinyl acetal, silicone resin, etc. can be used. . In any case, the mixing ratio of the toner and the carrier is generally about 0.5 to 6.0 parts by weight with respect to 100 parts by weight of the carrier.

  The toner may be mixed with an additive as necessary. Examples of the additives include fluidity imparting agents composed of inorganic fine particles such as hydrophobic silica, hydrophobic titanium oxide, and hydrophobic aluminum oxide, anti-caking agents, lubricants such as ethylene tetrafluoride resin and zinc stearate, carbon black, Conductivity imparting agents such as tin oxide, abrasives such as cerium oxide and silicon carbide, fixing aids such as low molecular weight polyolefins, and the like can be used. These may be used alone or in combination of two or more. The addition amount of these additives is desirably 0.1 to 5 parts by weight with respect to 100 parts by weight of the toner.

  In producing the toner, after mixing the constituent materials as described above in a mixer such as a Henschel mixer, the mixture is heated and kneaded in a kneader such as a continuous kneader or a roll kneader, and the kneaded product is cooled and solidified. A method of obtaining a desired average particle size by pulverization and classification is preferred. As other production methods, there are a spray drying method, a polymerization method, a microcapsule method and the like. The toner thus obtained can be sufficiently mixed with a desired additive with a mixer such as a Henschel mixer, if necessary, to produce a toner.

  The toner used in this embodiment uses a polyester-based resin as a binder resin and a zinc salicylate derivative as a charge control agent as materials common to all colors. This zinc salicylate derivative is contained in a ratio of 4 parts by weight to 100 parts by weight of the polyester resin. In addition, each color toner contains a colorant, and for 100 parts by weight of the polyester resin, 5 parts by weight of carbon black is used for black toner, and disazo yellow pigment (CI PIGMENTYELLOW17 for yellow toner). ) Is 5 parts by weight, cyan toner contains 4 parts by weight of copper phthalocyanine blue pigment (CI PIGMENTBLUE 15), and magenta toner contains quinacdrine magenta pigment (CI PIMGENTRED 184) at a ratio of 4 parts by weight. Yes.

  Hereinafter, image evaluation in which image formation was performed in Examples and Comparative Examples of the present invention will be described.

The image evaluation was performed with four types of generation of a dust image, generation of a hollow image, halftone granularity, and solid image density unevenness.
The generation of dust images and the occurrence of hollow images are evaluated by using OHP sheets and thick paper to evaluate print samples of characters and vertical and horizontal lines (both mixed patterns of single color, two colors, and three colors). , And the worst value of occurrence of a hollow image was evaluated according to the evaluation criteria shown in Tables 1 and 2, respectively.
Halftone granularity was evaluated by evaluating print samples when a full-color image was output, and evaluating the worst value of halftone density unevenness according to the evaluation criteria shown in Table 3.
The solid image density unevenness was evaluated by evaluating print samples when a full-color image was output, and the worst value of the solid image density unevenness was evaluated according to the evaluation criteria shown in Table 4. The evaluation results of all examples and comparative examples described later are shown in Table 6. Further, the volume average particle diameter of the toner is measured with a Coulter counter TA-II using a 100 μm aperture.

Hereinafter, the result of image evaluation will be described.
Table 5 is a table sequentially listing the characteristics relating to the materials A and B and the characteristics of the intermediate transfer belt 10 itself in this example and the comparative example, and the evaluation results of the images obtained by experiments based on the characteristics listed in this table. These are the results shown in Table 6. In Table 6, the result is shown based on the evaluation criteria shown in Tables 1 to 4.

  If the intermediate transfer belt having an elastic layer is composed of a single elastic layer, the belt is stretched when the belt is driven, and color misregistration or the like is caused. Therefore, it is preferable to provide an elongation preventing layer. The stretch prevention layer may be laminated on the intermediate transfer belt, or may be configured such that the stretch prevention layer and the elastic layer are the same in a form mixed with an elastic material in a single elastic layer. Further, a surface coating layer having a higher hardness but a thinner surface may be provided to prevent the surface from changing with time.

  The elongation preventing layer may be composed of a core body layer using a resin such as PI (polyimide), PC (polycarbonate), PET (polyethylene terephthalate), or fibers. As fibers used for the core layer, natural fibers such as cotton, silk and hemp, recycled fibers such as chitin fibers and alginic acid fibers, semi-synthetic fibers such as acetate fibers, polyester fibers, nylon fibers, acrylic fibers, polyolefin fibers, Synthetic fibers such as polyurethane fiber, polyacetal fiber and aramid fiber, inorganic fibers such as carbon fiber and glass fiber, and the like can be used. In this example, an aramid fiber having a thickness of 100 μm was used in the form of a woven fabric.

  Materials used for the elastic layer include styrene-butadiene rubber, high styrene rubber, butadiene rubber, isoprene rubber, ethylene-propylene copolymer, nitrile butadiene rubber, chloroprene rubber, butyl rubber, silicone rubber, fluorine rubber, nitrile rubber, urethane. Examples thereof include rubber, acrylic rubber, epichlorohydrin rubber and norbornene rubber. In this example, a nitrile butadiene rubber having a hardness of 60 degrees (JIS-A) was used. The thickness of the elastic layer was 500 μm.

  As the material used for the surface coat layer, styrene-butadiene rubber, high styrene rubber, butadiene rubber, isoprene rubber, ethylene-propylene copolymer, nitrile butadiene rubber, chloroprene rubber, butyl rubber, silicone rubber, fluorine rubber, nitrile rubber, Examples thereof include urethane rubber, acrylic rubber, epichlorohydrin rubber, norbornene rubber, and thermoplastic elastomer. In the present example, polyurethane coated with a fluororesin was used. The coating thickness was several μm to several tens of μm (preferably 1 to 10 μm).

  In addition, this embodiment is described in order to make an understanding of this invention easy, and does not limit this invention. For example, in this embodiment, the photosensitive drum is used as the image carrier. However, the present invention is not limited to this and can be applied to all image carriers such as a photosensitive belt. In this embodiment, the photosensitive drum has a single form. However, the present invention can also be applied to a so-called quadruple tandem type full-color image forming system form using dedicated photosensitive drums for black, yellow, cyan, and magenta colors. It is. In this embodiment, the transfer roller is used as the primary transfer unit. However, a contact transfer system such as a transfer brush, a transfer blade, and a transfer plate is used as well as a rotary contact transfer system such as a rotary transfer brush. The present invention can be applied to any image forming apparatus.

1 is a diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. 2A and 2B are diagrams illustrating a configuration of a primary transfer unit among image transfer units in the image forming apparatus illustrated in FIG. 1. FIG. 2A illustrates a transfer structure, and FIG. FIG. FIG. 3 is a diagram illustrating an example of an intermediate transfer belt illustrated in FIG. 2. FIG. 4 is a diagram illustrating another example of the intermediate transfer belt illustrated in FIG. 2. FIG. 4 is a diagram illustrating another example of the intermediate transfer belt illustrated in FIG. 2. It is a figure which shows the electrode arrangement | positioning of the resistivity test by "JISK6911 5.13.1." It is a figure which shows the connection method of the electrode by "JISK6911 5.13.1". It is a figure which shows the insulation resistance measuring apparatus of (1.1) of "JIS K6911 5.12.1". It is a figure which shows the surface resistance measuring method by "JISR3256 3". It is a figure which shows an example of the electrode provision method to the test piece used for the resistance measuring method shown in FIG. It is a figure which shows typically the measuring method of the surface friction coefficient by the Euler method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 10 Intermediate transfer belt A One material B The other material

Claims (14)

An image carrier, a toner image forming means for forming a toner image on the image carrier, and a volume resistivity ρ _V to which the toner image on the image carrier is transferred are determined according to JIS K69115.13.1 or JIS. An image provided with an intermediate transfer belt set to 10 ⁷ to 10 ¹⁵ Ω · cm as a value measured based on 3256, and a secondary transfer unit that secondarily transfers a toner image on the image carrier onto a transfer material. In the forming device,
On the surface of the intermediate transfer belt facing the image carrier or in the vicinity of the surface, the average distance L between the dispersion centers is equal to or _smaller than the minimum pixel diameter P _MIN and greater than the volume average particle diameter D of the toner. In the same depth cross section, when expressed as the average of the distance from the isolated dispersive material existence probability center that is the same quality as the isolated dispersive material existence probability center,
D ≦ L ≦ P _MIN (μm)
An image forming apparatus characterized in that a material having a volume resistance different from that of a peripheral material is present so as to satisfy the following relationship. The image forming apparatus according to claim 1.
The volume resistance average value R _V between the primary transfer bias application electrode and the intermediate transfer belt surface is 10 ⁷ ≦ R _V ≦ 10 ¹³ (Ω).
And the intermediate transfer belt surface resistance average value R _S is R _S > R _V
(However, the volume resistance R _V and the surface resistance R _S are values measured based on “JIS K6911 5.13.1” or “JIS 3256”)
An image forming apparatus having the relationship of The image forming apparatus according to claim 1.
An image forming apparatus, wherein an electrode shifted to a different polarity side from a primary transfer bias is disposed in contact with or close to the back surface of an intermediate transfer belt upstream of a primary transfer nip. The image forming apparatus according to claim 1.
An image forming apparatus, wherein an electrode shifted to a different polarity side from a primary transfer bias is placed in contact with or close to the back surface of an intermediate transfer belt downstream from a primary transfer nip. The image forming apparatus according to claim 1.
The contact pressure N between the image carrier and the intermediate transfer belt is
5 × 10 ⁻⁴ ≦ N ≦ 5 × 10 ⁻² (MPa)
An image forming apparatus characterized by being set in a range of The image forming apparatus according to claim 1.
An image forming apparatus wherein the surface of the intermediate transfer belt has elasticity. The image forming apparatus according to claim 1.
An image forming apparatus, wherein the intermediate transfer belt has an elastic layer having compressibility in a thickness direction, which means a characteristic that the thickness is apparently reduced by pressurization. The image forming apparatus according to claim 1.
An image forming apparatus, wherein the static friction coefficient μ ₁ measured by the Euler belt method of the intermediate transfer belt is equal to or more than the static friction coefficient μ ₂ of the image carrier (μ ₁ ≧ μ ₂ ). The image forming apparatus according to claim 1.
The toner is an image having an average circularity (a value obtained from a circumference of a circle having the same area as the projected area of the particles / a circumference of the projected image of the particles) of 0.90 to 0.99. Forming equipment. The image forming apparatus according to claim 1.
An image forming apparatus characterized in that a toner contains a release agent in a base toner. The image forming apparatus according to claim 1.
An image forming apparatus, wherein inorganic fine particles are externally added to the toner. 12. The image forming apparatus according to claim 1, wherein:
An image forming apparatus, wherein a part of the intermediate transfer belt is made of a homogeneous porous material. The image forming apparatus according to claim 1, wherein
An image forming apparatus, wherein a part of the intermediate transfer belt is composed of a large number of closely spaced projections. The image forming apparatus according to claim 12 or 13,
The intermediate transfer belt has a configuration in which a part or all of the surface thereof is covered with a different resistance member.

Images