CN104849983B - Image forming apparatus - Google Patents

Abstract

A kind of image forming apparatus is disclosed, which is sequentially transferred to the toner image formed in multiple photosensitive drums in intermediate transfer element or transfer materials to form image.The image forming apparatus includes conductive intermediate transfer belt, and power supply, the power supply is for applying a voltage to the electric current supply part contacted with intermediate transfer belt the electric current from electric current supply part is transmitted to multiple photosensitive drums via intermediate transfer belt, to which the upstream side in each of primary transfer portion generates electric discharge.

Description

Image forming apparatus

The application be based on be September in 2011 30 application No. is the 201180047108.0, applying date, it is entitled The divisional application of the patent application of " image forming apparatus ".

Technical field

The present invention relates to the image forming apparatuses of such as duplicator and laser beam printer etc.

Background technology

In order to realize flying print, it is known that electro photography color image forming device includes the independence for each color Image forming unit, the image from the image forming unit for each color is sequentially transferred to intermediate transfer belt On, and the image from intermediate transfer belt is jointly transferred in recording medium.

Each of image forming unit for each color includes the photosensitive drums as image bearing member.Each figure Further include charging unit for charging to photosensitive drums and for the charge image developing toner image in photosensitive drums as forming unit Developing cell.The charging unit of each image forming unit is contacted with predetermined pressure contact force with photosensitive drums, with by using The charging voltage applied from the voltage source (not shown) for being exclusively used in charging is come with predetermined polarity and electric potential uniform to photosensitive drums It charges on surface.

Toner is applied to the electrostatic latent image being formed in photosensitive drums with aobvious by the developing cell of each image forming unit Tone toner image (visual picture).

In each image forming unit, via intermediate transfer belt towards primary transfer roller (the primary transfer portion of photosensitive drums Part) toner image after the development of photosensitive drums is transferred on intermediate transfer band.Primary transfer roller is connected to specially Voltage source for primary transfer.

The toner image of primary transfer from intermediate transfer belt is secondarily transferred to transfer materials by secondary transfer printing component On.Secondary transfer roller (secondary transfer printing component) is connected to the voltage source for being exclusively used in secondary transfer printing.

Japanese Patent Application Laid-Open the 2003-35986th discusses wherein each of four primary transfer rollers and is connected to It is exclusively used in configuring in each of four voltage sources of primary transfer.Japanese Patent Application Laid-Open the 2001-125338th is begged for Following control is discussed, the control is for logical according to the sheet material of intermediate transfer belt and primary transfer roller before image forming operation It crosses durability and changes the transfer voltage that be applied to each primary transfer roller according to the resistance variations caused by environmental change.

However, the conventionally known image forming apparatus using intermediate transfer belt has the following problems.

Just wherein toner image is reversely transferred to from the multiple photosensitive drums of arrangement in a row on intermediate transfer band For primary transfer configuration, the polarity of the toner image transferred on intermediate transfer band may be because being happened at primary transfer Electric discharge at portion and be inverted, which is formed by intermediate transfer belt and photosensitive drums.In this case, there is reversion Polar toner may be moved to photosensitive drums from intermediate transfer belt.This phenomenon is referred to as reversed transfer.

Specifically, during printing full-colour image, the toner image of the first color transferred on intermediate transfer band It is electrostatically attracted to intermediate transfer belt.However, when the first color toner image by intermediate transfer belt and the second color and When gap between the photosensitive drums of subsequent color, the toner image of the first color, which may be partly reversed, is transferred to photosensitive drums On.Reversed transfer will lead to uneven image, concentration reduction or other problems.Potential difference at primary transfer portion can pass through Reduction is applied to the voltage of primary transfer component to reduce, to prevent reversely transferring.However, there are such trend, that is, subtract The small potential difference at primary transfer portion can reduce primary transfer efficiency, so that being difficult to be arranged can be arranged to prevent instead To the primary transfer voltage of transfer.

Invention content

The present invention relates to can be while reducing the number for applying alive voltage source to primary transfer component Prevent or reduce the image forming apparatus reversely transferred.

According to an aspect of the present invention, a kind of image forming apparatus includes：Multiple images load bearing component is configured as carrying Toner image；Rotatable cricoid intermediate transfer belt, being configured as will be from the tune of multiple images load bearing component primary transfer Toner image is secondarily transferred on transfer materials；Electric current supply part is configured as contacting with intermediate transfer belt；And power supply, It is configured as applying a voltage to electric current supply part, wherein intermediate transfer belt has following electric conductivity, the i.e. electric conductivity Electric current is enough set to be transmitted in the rotation direction of intermediate transfer belt via intermediate transfer belt from the contact position of electric current supply part Multiple images load bearing component, and wherein, power supply applies a voltage to electric current supply part, to make electric current from electric current supply unit Part is transmitted to multiple images load bearing component via intermediate transfer belt, with multiple primary turns in the rotation direction of intermediate transfer belt The upstream end thereof of the contact position between the intermediate transfer belt and image bearing member at each primary transfer portion in print portion At the position of upstream side, electric discharge is generated between intermediate transfer belt and image bearing member so that the centre at contact position Potential difference between transfer belt and image bearing member is less than Paschen (Paschen) discharge threshold voltage value.

Exemplary embodiment according to the present invention, electric current is in direction circumferential direction (circumferential) of intermediate transfer belt On supplied from electric current supply part, generated and put with the upstream side in the primary transfer portion in the rotation direction of intermediate transfer belt Electricity, to reduce reversed transfer.

The detailed description of following exemplary embodiment is read by reference to attached drawing, more features of the invention and aspect will become It obtains cheer and bright.

Description of the drawings

Including in the description and the attached drawing of a constitution instruction part shows exemplary embodiment of the present invention, feature And aspect, and be used to illustrate the principle of the present invention together with the description.

[Fig. 1] Fig. 1 is the sectional view for schematically showing image forming apparatus according to an exemplary embodiment of the present invention.

[Fig. 2] Fig. 2A and Fig. 2 B be schematically show it is according to an exemplary embodiment of the present invention for measuring intermediate transfer belt Circumferential resistance method sectional view.

[Fig. 3] Fig. 3 A and Fig. 3 B are the curve graphs for the circumferential resistivity measurements for showing intermediate transfer belt.

[Fig. 4] Fig. 4 is to schematically show the transfer power supply having in each image forming unit for primary transfer Image forming apparatus sectional view.

[Fig. 5] Fig. 5 is the sectional view for the method for schematically showing the current potential for measuring intermediate transfer belt.

[Fig. 6] Fig. 6 A-6C are the curve graphs for the surface potential measurement result for showing intermediate transfer belt.

[Fig. 7] Fig. 7 A-7D show primary transfer according to an exemplary embodiment of the present invention.

[Fig. 8] Fig. 8 A-8C are to show relationship between the potential measurement result of intermediate transfer belt and primary transfer area of feasible solutions Curve graph.

[Fig. 9] Fig. 9 is the sectional view for schematically showing the electric current flowed in the rotation direction of intermediate transfer belt.

[Figure 10] Figure 10 A and Figure 10 B are to schematically show wherein Zener (Zener) diode or rheostat (varistor) It is connected to the sectional view of the state of each support member.

[Figure 11] Figure 11 A to 11C are the states for schematically showing wherein secondary transfer roller and being used as electric current supply part Sectional view.

[Figure 12] Figure 12 A are shown between photosensitive-member inflow current and transfer residual and the amount of the toner reversely transferred The curve graph of relationship, Figure 12 B are relationships between the voltage for showing to apply and transfer residual and the amount of the toner reversely transferred Curve graph.

[Figure 13] Figure 13 A and Figure 13 B are the amplification sectional views for showing primary transfer portion.

[Figure 14] Figure 14 A and Figure 14 B show the discharge condition at primary transfer portion.

[Figure 15] Figure 15 is the sectional view for schematically showing another image forming apparatus according to the present invention.

Specific implementation mode

Below with reference to each exemplary embodiment of attached drawing detailed description of the present invention, feature and aspect.

Fig. 1 shows that side-by-side type according to an exemplary embodiment of the present invention (in-line) color image forming device (has four A drum) configuration.Image forming apparatus includes four image forming units：It is used to form the image forming unit of yellow image 1a, the image forming unit 1b for being used to form carmetta (magenta) image, the image shape for being used to form cyan (cyan) image At unit 1c and it is used to form the image forming unit 1d of black image.This four image forming units are with fixed interval arrangement It is in a row.

Image forming unit 1a, 1b, 1c and 1d respectively include photosensitive drums 2a, 2b, 2c and 2d (image bearing member).At this In exemplary embodiment, each of photosensitive drums 2a, 2b, 2c and 2d by such as aluminium etc drum basal body (base) (not shown) and The photosensitive layer (not shown) as electronegative organic photo component on drum basal body is constituted.Photosensitive drums 2a, 2b, 2c and 2d are driven Moving cell (not shown) is rotatably driven with predetermined process speed.

Charging roller 3a, 3b, 3c and 3d and developing cell 4a, 4b, 4c and 4d are respectively disposed at photosensitive drums 2a, 2b, 2c And around 2d.Drum cleaning unit 6a, 6b, 6c and 6d are respectively disposed at around photosensitive drums 2a, 2b, 2c and 2d.Exposing unit 7a, 7b, 7c and 7d are arranged in above photosensitive drums 2a, 2b, 2c and 2d.Yellow toner, magenta toner, cyan toner It is respectively stored in developing cell 4a, 4b, 4c and 4d with black toner.Conventional toner band according to the present exemplary embodiment Electric polarity is negative polarity.

Intermediate transfer belt 8 (rotatable endless intermediate transfer component) is arranged to towards four image forming units.In Between transfer belt 8 by driven roller 11, secondary transfer printing counter roll 12 and jockey pulley 13 (these three rollers it is total be referred to as support roller or support portion Part) support, and the direction (side counterclockwise indicated with arrow by the driving force of the driven roller 11 driven by motor (not shown) To) rotation (movement).Hereinafter, the rotation direction of intermediate transfer belt 8 is referred to as the circumferential direction of intermediate transfer belt 8.Driven roller 11 are equipped with the superficial layer made of high frictional force rubber to drive intermediate transfer belt 8.It is 10 that rubber layer, which provides volume resistivity,⁵ Ω cm electric conductivity below.Secondary transfer printing counter roll 12 and secondary transfer roller 15 form secondary transfer printing via intermediate transfer belt 8 Portion.Secondary transfer printing counter roll 12 is equipped with superficial layer made of rubber to provide volume resistivity as 10⁵Ω cm are below to be led Electrically.Jockey pulley 13 is made of metallic roll, which gives the tension that gross pressure is about 60N to intermediate transfer belt 8 to pass through The rotation of intermediate transfer belt 8 drives and rotates.

Driven roller 11, secondary transfer printing counter roll 12, jockey pulley 13 are grounded via the resistor with predetermined resistance.This There are three types of the resistors of different resistance values 1G Ω, 100M Ω and 10M Ω using tool for exemplary embodiment.Because of driven roller 11 and two The resistance value of the rubber layer of secondary transfer counter roll 12 is much smaller than 1G Ω, 100M Ω and 10M Ω, so the electric effect of these rollers can It is ignored.

Secondary transfer roller 15 is that volume resistivity is 10⁷To 10⁹Ω cm and rubber hardness are 30 degree of (Asker C hardness Meter) resilient roller.Secondary transfer roller 15 is depressed into secondary transfer printing counter roll 12 with the gross pressure of about 39.2N via intermediate transfer belt 8 On.Secondary transfer roller 15 is driven and is rotated by the rotation of intermediate transfer belt 8.- 2.0 Dao 7.0kV from transfer power supply 19 Voltage can be applied to secondary transfer roller 15.

75 quilt of band cleaning unit for removing and collecting the transfer residual toner on the surface for staying in intermediate transfer belt 8 It is arranged on the outer surface of intermediate transfer belt 8.In the rotation direction of intermediate transfer belt 8, including fixing roller 17a and pressure roller The fixation unit 17 of 17b is disposed in the downstream side of secondary transfer section, at secondary transfer section, secondary transfer printing counter roll 12 and two Secondary transfer roll 15 contacts.

Image forming operation explained below.

When controller sends out the enabling signal for starting image forming operation, transfer materials (recording medium) are by from box It is singly sent out in (not shown) and is then conveyed to alignment roller (not shown).At this point, alignment roller (not shown) is Leading edges stop and transfer materials are awaited orders at the position before being close in secondary transfer section.When enabling signal is issued When, on the other hand, photosensitive drums 2a, 2b, 2c and 2d in image forming unit 1a, 1b, 1c and 1d are respectively with predetermined process speed Degree starts to rotate.In the present example embodiment, photosensitive drums 2a, 2b, 2c and 2d passes through charging roller 3a, 3b, 3c and 3d quilt respectively Uniform charging is negative polarity.Then, exposing unit 7a, 7b, 7c and 7d is respectively with laser beam irradiation photosensitive drums 2a, 2b, 2c and 2d To execute scan exposure, to be formed on electrostatic latent image.

The developing cell 4a for applying polarized and the identical developing voltage of charging polarity (negative polarity) of photosensitive drums 2a will be yellow Colour toners are applied to the electrostatic latent image formed on photosensitive drums 2a to be visualized as toner image.Charge volume and exposure Amount is adjusted so that each photosensitive drums in the current potential after being electrically charged roller charging with -500V and has after being exposed unit exposure There is the current potential (image section) of -100V.Developing bias is -300V.Processing speed is 250mm/sec.As perpendicular to transport The image formation width of length on the direction in direction (rotation direction) is arranged to 215mm.Toner charge volume is arranged to- 40μC/g.Amount in each photosensitive drums for the toner of solid (solid) image is arranged to 0.4mg/cm²。

This yellow toner image is transferred on the intermediate transfer belt 8 of rotation.Towards each photosensitive drums, at which Toner image is referred to as primary transfer portion from the part that each photosensitive drums are transferred on intermediate transfer belt 8.It is carried with multiple images The corresponding multiple primary transfer portions of component are arranged on intermediate transfer belt 8.The present exemplary embodiment by using from centre The electric current supply part of the outer surface contact of transfer belt 8, the electric current that is flowed in the rotation direction of intermediate transfer belt 8 executes Primary transfer.(electric current supply part will be then described in detail.)

As shown in Figure 1, electric current supply part be disposed in the rotation direction of intermediate transfer belt 8 with cleaning unit 75 Downstream side and the upstream side of the image forming unit 1a in the rotation direction of intermediate transfer belt 8.For turning for primary transfer Print power supply 33 is connected to primary transfer feed roller 31 (the electric current supply part for being used for primary transfer).Primary transfer feeds counter roll 32 are arranged to feed roller 31 towards primary transfer via intermediate transfer belt 8.

With reference to figure 1, opposite component 5a, 5b, 5c and 5d are arranged to form list towards image via intermediate transfer belt 8 respectively First 1a, 1b, 1c and 1d.Opposite component 5a, 5b, 5c and 5d pressed to via intermediate transfer belt 8 corresponding direction photosensitive drums 2a, 2b, 2c and 2d can keep nip portion (nip portion) that is wide and stablizing in this way to be formed.In this exemplary implementation In example, opposite component 5a, 5b, 5c and 5d are electrical isolations, i.e., they are not used as being connected to the voltage source for primary transfer Voltage application portion part.Because voltage application portion part as shown in Figure 4 it is conductive so that desirable electric current wherein Flowing, so resistance value adjustment is carried out for voltage application portion part, to increase cost.

The region transferred with yellow toner image on intermediate transfer belt 8 by intermediate transfer belt 8 rotation quilt It is moved to image forming unit 1b.Then, in image forming unit 1b, the magenta toner figure that is formed on photosensitive drums 2b As being similarly transferred on intermediate transfer belt 8 so that magenta toner image is added in yellow toner image.Class As, in image forming unit 1c and 1d, the cyan toner image that is formed on photosensitive drums 2c and subsequent it is formed in Black toner image on photosensitive drums 2d is transferred to respectively on intermediate transfer belt 8 so that cyan toner image is applied On to (yellow and carmetta) toner image of two kinds of colors and then black toner image is added to three kinds of colors (yellow, carmetta and cyan) toner image on, to forming full-color toner image on intermediate transfer belt 8.

Then, Timing Synchronization when secondary transfer section is moved to the leading edge of the full-color toner image on intermediate transfer belt 8 Ground, transfer materials P are aligned roller (not shown) and are transported to secondary transfer section.Full-color toner image on intermediate transfer belt 8 is logical Cross 15 quilt of secondary transfer roller for being applied with secondary transfer printing voltage (voltage with the polar opposite polarity of toner (positive polarity)) It is disposably secondarily transferred on transfer materials P.The transfer materials P for being formed with full-color toner image thereon is transported to fixing Unit 17.The fixing nip portion being made of fixing roller 17a and pressure roller 17b by heat and pressure be applied to full-color toner image with It is fixed on the surface of transfer materials P, and is then discharged to outside.

The present exemplary embodiment is characterized in that：For by toner image from photosensitive drums 2a, 2b, 2c and 2d are transferred to Between primary transfer in transfer belt 8 be primary transfer roller 55a, 55b, 55c and 55d as shown in Figure 4 are not applied it is alive In the case of execute.

In order to describe the feature of the present exemplary embodiment, volume resistivity, the surface electricity of intermediate transfer belt 8 explained below Resistance rate and circumferential resistance value.The definition of circumferential direction resistance value explained below and the method for measuring circumferential resistance value.

It is described below the volume resistivity and sheet resistance of the intermediate transfer belt 8 used in the present exemplary embodiment Rate.

In the present example embodiment, there is intermediate transfer belt 8 base layer, the base layer to be useful for resistance value adjusting by containing Polyphenylene sulfide (PPS) resin of 100 μ m-thicks of carbon of dispersion be made.Used resin can be polyimides (PI), gather Vinylidene fluoride (PVdF), polyethylene terephthalate (PET), polybutylene terephthalate (PBT) (PBT), gathers nylon Carbonic ester, polyether-ether-ketone (PEEK), polyethylene naphthalate (PEN) etc..

Intermediate transfer belt 8 has multi-layer configuration.Specifically, base layer is equipped with by 0.5 μm to 3 μ m-thicks of high resistance propylene Outer surface layer made of acid resin.The high resistance superficial layer is used for：By reducing the piece on the longitudinal direction of secondary transfer section Material by region and non-sheet material by the current difference between region, to obtain the effect for the secondary transfer printing performance for improving small size paper Fruit.

The method of manufacture band explained below.The present exemplary embodiment, which uses, is based on inflation (inflation) manufacturing method Method to manufacture band.The blending constituent (conducting material powder) of PPS (basis material) and such as carbon black etc is by using two Axis sand mixer and be melted and mix.Obtained mixture is extruded together by using ring mold, to form ring-type Band.

Ultraviolet hardening resin is sprayed onto on the surface of molding endless belt, and after resin drying, ultraviolet light quilt It is irradiated on belt surface so that hardening of resin, to form surface coating layer.Because blocked up coat is easily broken, apply The amount for covering resin is adjusted so that coat becomes 0.5 μm to 3 μ m-thicks.

Carbon black is used as conducting material powder by the present exemplary embodiment.Resistance value for adjusting intermediate transfer belt 8 adds Add agent unrestricted.Exemplar conductive filler for resistance value adjusting includes the metal oxidation of carbon black and many other conductions Object.The preparation of resistance value adjusting for non-filler include various metal salts, the ion conductive material with low molecular weight (such as Ethylene glycol), include in the molecule ehter bond, hydroxyl etc. antistatic resin and organic polymer high-molecular compound.

Although the amount of carbon for increasing addition makes the resistance value of intermediate transfer belt 8 reduce, the carbon of addition excessively Amount makes the strength reduction of band to make it easier to rupture.In the present example embodiment, the resistance of intermediate transfer belt 8 is strong in band It spends in the allowable range that can be used for image forming apparatus and is lowered.

In the present example embodiment, the Young's modulus of intermediate transfer belt 8 is about 3000MPa.It is by using thickness 100 μm of detected materials are according to JIS-K7127, " Plastics--Determination of tensile properties " To measure Young's modulus E.

Table 1 shows the amount of the carbon of the addition for various matrixes (in terms of relative ratios).

【Table 1】

Table 1 is also shown surface coating layer and whether there is.For example, the amount of the carbon of the addition with B is 1.5 times of the amount with A, and And 2 times that the amount of the carbon of the addition with C is the amount with A.Band A, B and C have superficial layer, and band D and E is without superficial layer (single belt).Band B The amount of carbon of addition be equal to amount with D, and the amount of the carbon of the addition with C is equal to the amount with E.

The comparative sample band made of polyimides is by changing the amount (in terms of relative ratios) of the carbon added to adjust electricity Resistance value is formed.The amount (in terms of relative ratios) of the carbon of the addition of comparative sample band is 0.5 and volume resistivity is 10¹⁰It arrives 10¹¹Ω·cm.As intermediate transfer belt, this comparative sample band has common resistance value.

The result that volume resistivity explained below for comparative sample band and with A to E and surface resistivity measure.

Comparative sample band and volume resistivity with A to E and surface resistivity are to use MITSUBISHI CHEMICAL Hiresta UP (MCP-HT450) resistrivity meters of ANALYTECH measure.Table 2 shows volume resistivity and sheet resistance The measured value of rate (outer surface of each band).Volume resistivity and surface resistivity are to obtain electricity by using conductive rubber electrode According to JIS-K6911 it is " Testing method for thermosetting after preferred contact between pole and each belt surface Plastics " is measured.Measuring condition includes 30 seconds application times and the application voltage of 10V and 100V.

【Table 2】

When it is 100V to apply voltage, 1.0x 10 is presented in comparative sample band¹⁰The volume resistivity and 1.0x of Ω cm 10¹⁰The surface resistivity of Ω/sq..However, when it is 10V to apply voltage, the electric current flowing of comparative sample band is too small, to not Volume resistivity can be tested to obtain.In the case, resistrivity meter is shown " outranging (over) ".

When apply voltage be 100V when, there is excessive electric current flowing because of low resistance with B, C and D, from be unable to by Measure volume resistivity.In the case, resistrivity meter is shown " being less than range (under) ".When it is 100V to apply voltage, band 2.0x 10 is presented in B⁸The surface resistivity of Ω/sq., however can not be measured surface resistivity (" being less than range ") with C and D.

Reference table 2, when it is 10V to apply voltage, band A can not be tested to obtain volume resistivity and surface resistivity.When applying When making alive is 100V, surface resistivity more higher than comparative sample band is presented in band A.This phenomenon is because the influence of coat causes , that is, there is the band A of high resistance surface coating layer that there is resistance more higher than comparative sample band without surface coating layer.

With between B and D comparison and with the comparison between C and E show that coat provides high resistance value.With between B and C Compare and shows that the amount for increasing the carbon of addition makes resistance value reduce with the comparison between D and E.Too low resistance value is provided with E, Therefore all items can not be measured.

In the present example embodiment, it is necessary to use this volume with the display for being given in Table 2 " being less than range " The intermediate transfer belt 8 of resistivity and surface resistivity.Therefore, the volume resistivity and table in addition to being defined for intermediate transfer belt 8 Resistance value except surface resistivity is measured.It is above-mentioned circumferential resistance for another resistance value that intermediate transfer belt 8 defines.

Method explained below for obtaining the circumferential resistance of intermediate transfer belt 8.

In the present example embodiment, have the circumferential resistance of the intermediate transfer belt 8 of the resistance reduced by using Fig. 2A It is measured with method shown in Fig. 2 B.With reference to figure 2A, when fixed voltage (measuring voltage) (transfers power supply from high-voltage power supply 19) when being applied to outer surface roller 15M (the first metallic roll), this method is detected in the photosensitive drums for being connected to image forming unit 1d The electric current flowed in the ampere meter (current detecting unit) of 2dM (the second metallic roll).Based on the current value detected, this method obtains Obtain the resistance value between photosensitive drums 2dM and the contact portion of outer surface roller 15M of intermediate transfer belt 8.Specifically, this method is surveyed The electric current flowed in the circumferential direction (rotation direction) of intermediate transfer belt 8 is measured, the electricity that then will be measured voltage value divided by measure Flow valuve is to obtain the resistance value of intermediate transfer belt 8.In order to eliminate the shadow of the resistance other than the resistance of intermediate transfer belt 8 It rings, uses the only outer surface roller 15M and photosensitive drums 2dM made of metal (aluminium).For this reason, the label heel of the roller and band There is alphabetical M (metal).In the present example embodiment, the distance between photosensitive drums 2dM and the contact portion of outer surface roller 15M It is 370mm (in the upper surface side of intermediate transfer belt 8) and 420mm (in its lower face side).

Fig. 3 A show changing the resistivity measurements for applying band A to the E under voltage condition according to above-mentioned measurement method. According to this measurement method, the resistance in the circumferential direction (rotation direction) of intermediate transfer belt 8 is measured.In the present exemplary embodiment In, therefore, the resistance of the intermediate transfer belt 8 measured by this measurement method is referred to as circumferential resistance (in terms of Ω).

Resistance is all had with the trend applied alive increase and be gradually reduced with A to E.Resin includes dispersion wherein Carbon band in the case of find out this trend.

The method in method and Fig. 2A in Fig. 2 B differs only in ampere meter position.In the case, resistance measurement As a result almost consistent in Fig. 3 B, it means that measurement method according to the present exemplary embodiment is unrelated with ampere meter position.

Using method shown in Fig. 2A and Fig. 2 B, brings using band A to E rather than comparative sample and complete resistance measurement.This is Because comparative sample band is connected with relevant voltage power supply (such as Fig. 4 for wherein primary transfer roller 55a, 55b, 55c and 55d It is shown) image forming apparatus band.

Image forming apparatus with the configuration in Fig. 4 is designed to provide the higher volume resistance of intermediate transfer belt 8 Rate and surface resistivity so that the electric current that neighboring voltage power supply does not flow wherein due to via intermediate transfer belt 8 and it is mutual It influences (interference).Once turn when voltage is applied to primary transfer roller 55a, 55b, 55c and 55d even if comparative sample band has The resistance of print portion also this degree not interfering with each other.Comparative sample band is designed to be not easy to generate electric current stream in circumferential direction It is dynamic.The band as comparative sample band is defined as high resistance band, and has electric current in circumferential direction as image-tape A to E The band of flowing is defined as conductive strips.

Fig. 3 B are the curve graphs formed by drawing the current value measured with the measurement method for Fig. 2A.Reference chart 3A, the resistance value for being assigned to the longitudinal axis are as obtained from will apply the current value measured in voltage divided by Fig. 3 B (in terms of Ω).

With reference to figure 3B, for comparative sample band, even when applying voltage and being 2000V also without electric current in circumferential side It flows up.However, for band A to E, even if having equal to or more than 50 μ if when applying voltage and being equal to or less than 500V The electric current flowing of A.The present exemplary embodiment is 10 using circumferential resistance⁴To 10⁸The intermediate transfer belt 8 of Ω.For being higher than 10⁸Ω Circumferential resistance, electric current is not easy to flow in circumferential direction and therefore desirable primary transfer performance cannot be ensured that.Cause This, the present exemplary embodiment uses circumferential resistance for 10⁴Ω to 10⁸The band of Ω, which is used as, is suitable for desirable primary transfer performance Band.

Circumferential direction resistance explained below is 10⁴To 10⁸The surface potential of the intermediate transfer belt 8 of Ω.Fig. 5 A and Fig. 5 B show to use In the method for the surface potential for measuring intermediate transfer belt 8.With reference to figure 5A and Fig. 5 B, by using four surface potential meters at four Potential measurement is carried out at different piece.Metallic roll 5dM and 5aM be used to measure.

Surface potential meter 37a and measurement probe 38a is used to measure the primary transfer roller 5aM (gold of image forming unit 1a Belong to roller) current potential.344 surface potential meters of MODEL from TREK JAPAN are used.Because metallic roll 5dM and 5aM have Current potential identical with the inner surface of intermediate transfer belt 8 can be used to the inner surface current potential for measuring intermediate transfer belt 8 in this approach. Similarly, surface potential meter 37d and measurement probe 38d are used to the primary transfer roller 5dM (metals based on image forming unit 1d Roller) current potential measure the inner surface current potential of intermediate transfer belt 8.

Surface potential meter 37e and measurement probe 38e is arranged to towards driven roller 11M to measure the outer of intermediate transfer belt 8 Surface potential.Surface potential meter 37f and measurement probe 38f is arranged to towards jockey pulley 13 to measure the outer of intermediate transfer belt 8 Surface potential.Resistor Re, Rg and Rf are connected respectively to driven roller 11M, secondary transfer printing counter roll 12 and jockey pulley 13.

When measuring the current potential of intermediate transfer belt 8 by this measurement method, potential difference is there's almost no between measuring part, And intermediate transfer belt 8 is presented in almost the same current potential.Although specifically, in the present example embodiment using Intermediate transfer belt 8 has a degree of resistance value, but it can be considered as conductive strips.

Fig. 6 A to 6C show the surface potential measurement result of intermediate transfer belt 8.Fig. 6 A are shown when resistor Re, Rf and Rg tool There is the result when resistance of 1G Ω.The longitudinal axis is designated as being applied to the voltage of transfer power supply 33, and horizontal axis is designated as intermediate transfer With 8 current potential.Fig. 6 A show the measurement result with A to E.

Similarly, Fig. 6 B show the result when the resistance that resistor Re, Rf and Rg have 100M Ω.Fig. 6 C are shown when electricity The result for hindering device Re, Rf and Rg when there is the resistance of 10M Ω.

For any one band, surface potential increases with alive increase is applied, and with resistor Re, Rf and Rg Resistance value reduction (being followed successively by 1G Ω, 100M Ω and 10M Ω) and reduce.Although resistor Re, Rf and Rg have identical Resistance, but it is known reduce any one resistor resistance the surface potential of each band will be made to correspondingly reduce.

Seeming the feelings for the intermediate transfer belt that resistance as comparative sample band so that electric current do not flow in circumferential direction Under condition, the surface potential of each band cannot be measured by the above method.In voltage primary transfer roller is applied to from power source special 9 In the case of the configuration (as shown in Figure 4) of 55a, 55b, 55c, 55d, potentiometric measuring probe cannot be arranged.Even if potential measurement Probe is arranged to towards support roller 11,12 and 13, and the surface potential of the intermediate transfer belt 8 at primary transfer portion can not be by It measures, because current potential is different at different location in circumferential direction.

Below with reference to Fig. 7 A to 7D descriptions, toner image can in the case of configuration according to the present exemplary embodiment The reason of intermediate transfer belt 8 being transferred to from photosensitive drums 2a, 2b, 2c and 2d.

Fig. 7 A show the electric potential relation at each primary transfer portion.The current potential of each photosensitive drums is in toner portion (image portion Point) at be -100V, and the surface potential of intermediate transfer belt 8 is+200V.The carried charge to develop in photosensitive drums is the toning of q Then agent is formed by the power F on the direction of intermediate transfer belt 8 by the current potential of current potential and intermediate transfer belt 8 by photosensitive drums Electric field E by primary transfer.

Fig. 7 B show that multiple transfer, multiple transfer refer to then toner is transferred to it on intermediate transfer belt 8 The toner of his color is further transferred to the processing on previous toner.Fig. 7 B show that wherein toner is negatively charged and turns The toner surface current potential of the toner of print is the state of+150V.In the case, the toner in each photosensitive drums is by centre Power F' on 8 direction of transfer belt, then by the electric field E' that is formed by the current potential of photosensitive drums and the surface potential of toner by one Secondary transfer.

Fig. 7 C show the state that wherein multiple transfer is completed.

The primary transfer of toner depends between charged toner amount and photosensitive drums current potential and the current potential of intermediate transfer belt 8 Potential difference.This means that a certain fixed current potential of intermediate transfer belt 8 is necessary, to ensure primary transfer performance.

Under the above-mentioned condition of the present exemplary embodiment, needed for the toner image of the development in primary transfer photosensitive drums The current potential of intermediate transfer belt 8 is considered as 200V or higher.

Fig. 7 D are the passes between the current potential and the transfer efficiency for being assigned to the longitudinal axis of the intermediate transfer belt 8 for showing to be assigned to horizontal axis The curve graph of system.Transfer efficiency is to indicate that the toner image of the development of how much percentages in photosensitive drums has been transferred to centre Transfer performance index in transfer belt 8.Usually, when transfer efficiency is 95% or higher, toner is confirmed as by just Often transfer.Fig. 7 D show the current potential by 200V or higher intermediate transfer belts 8, good equal to or more than 98% toner It transfers well.

In this case, all image forming unit 1a, 1b, 1c and 1d each photosensitive drums and intermediate transfer belt 8 it Between potential difference having the same.More specifically, at all primary transfer portions of image forming unit 1a, 1b, 1c and 1d ,- The potential difference of 300V is formed between each photosensitive drums current potential of 100V and the current potential of the intermediate transfer belt 8 of+200V.For above-mentioned three kinds Different toner colors (assuming that monochromatic solid amount is 100%, then for 300% toner amount) multiple turn For print, this potential difference is needed, and this potential difference is nearly identical to when will be primary in the case where traditional primary transfer configures Transfer biasing is applied to the potential difference formed when corresponding primary transfer roller.Even if common image forming apparatus is set, there are four types of colors Toner, it without 400% toner amount execute image formed.Alternatively, image forming apparatus can utilize about 210% to 280% maximum toner amount forms sufficient full-colour image.

Therefore, the present exemplary embodiment by the circumferential direction of intermediate transfer belt 8 by electric current so that obtain in Between transfer belt 8 predetermined surface current potential, be enable to carry out primary transfer.In other words, transfer power supply 33 turns via centre Electric current is transmitted to photosensitive drums 2a, 2b, 2c by print band 8 from the primary transfer feed roller 31 contacted with the outer surface of intermediate transfer belt 8 And 2d, to realize primary transfer.In the present example embodiment, voltage is applied to primary transfer and feeds roller 31 so that energy Enough primary transfer is carried out using a transfer power supply.

Because primary transfer feed roller 31 be disposed in the rotation direction of intermediate transfer belt 8 under cleaning unit 75 Side is swum, so remaining toner or other stickums are not easy to be adhered to primary transfer feed roller 31.This means that in because Between the surface of transfer belt 8 cleaned so as not to toner or other stickums, so electric current by band cleaning unit 75 always Can stable supplying to the surface, to realize stable electric current supply.

Fig. 8 A to 8C show to realize condition when the current potential for the intermediate transfer belt 8 in Fig. 6 A to 6C considers primary transfer When the measurement result that is obtained.With reference to figure 8A to 8C, thick line A instructions execute the current potential of the intermediate transfer belt 8 needed for primary transfer. In the case of 1G Ω and 100M Ω resistance (being respectively Fig. 8 A and 8B), the application voltage equal to or more than predetermined value is applied to Intermediate transfer belt 8 is produced with the intermediate transfer belt equal to or more than predetermined voltage (being in the present example embodiment 200V) 8 surface potential, to realize preferred primary transfer.In the case of 10M Ω resistance (Fig. 8 C), application is needed to be higher than The application voltage of 3000V.Even if in the case of 10M Ω resistance, although increasing transfer voltage realizes good primary transfer, But the capacity for transferring power supply 19 needs practical increase to deliver current to support roller 11,12 and 13.In the case, from turn The primary transfer electric current for printing voltage source output is 20 μ A.Even if when transfer voltage is 2kV, because primary transfer feeds roller 31 Elastic layer resistance, so about 500V voltages below are also actually applied to intermediate transfer belt 8.In this case, such as Shown in Fig. 3 B, when hundreds of volt voltages are applied to intermediate transfer belt 8, enough electric currents are in the circumferential direction of intermediate transfer belt 8 Flowing.

When the application voltage of hundreds of volts is applied to primary transfer feed roller 31 and Transfer current is dozens of microampere, The circumferential resistance of band is 10⁴To 10⁸Primary transfer realizes that condition is satisfied in the case of Ω.

Fig. 9 schematically shows the electric current flowed from primary transfer feed roller 31 to intermediate transfer belt 8.With reference to figure 9, resistor Re, Rg and Rf are connected respectively to support roller 11,12 and 13.Heavy solid line arrows instruction feeds roller 31 to photosensitive drums from primary transfer The electric current of 2a, 2b, 2c and 2d flowing.The instruction of thick dashed line arrow flows into the electric current in support roller 11,12 and 13.As described above, this A little electric currents increase with the reduction of resistance value Re, Rg and Rf.Because image forming unit 1a, 1b, 1c and 1d are corresponding photosensitive There is almost the same potential difference, so almost the same electric current flows into photosensitive drums 2a, 2b, 2c between drum and intermediate transfer belt 8 In 2d.However, the thickness change of the photosensitive layer on photosensitive drums 2a, 2b, 2c and 2d of image forming unit 1a, 1b, 1c and 1d Cause capacitance variations, so as to cause to flow into the variation of the electric current in each photosensitive drums.In the present example embodiment, photosensitive The thickness of layer is 10 μm to 20 μm after sheet material is by the duration.

Secondary transfer printing is by the way that secondary transfer printing voltage is applied to secondary transfer printing from the voltage source 19 for secondary transfer printing Roller 15 is realized.Condition according to the present exemplary embodiment, high-quality paper (grammes per square metre 75g/m²) it is used as transfer materials, And the secondary transfer printing voltage needed for secondary transfer printing is 2kV or higher.

The timing of primary transfer explained below and secondary transfer printing.Just image forming apparatus according to the present exemplary embodiment For, primary transfer portion and secondary transfer section occupy the hemicycle of intermediate transfer belt 8, as shown in Figure 1.In other words, one page image It is formed in the range of hemicycle.Transfer power supply 33 for primary transfer starts at the startup timing of primary transfer to primary The voltage of transfer feed roller 31 applies, and stops voltage when completing primary transfer and apply.When primary on intermediate transfer belt 8 When the toner image of transfer reaches secondary transfer section, voltage source 19 with from the transfer materials that alignment roller (not shown) supplies to Secondary transfer printing voltage is applied to secondary transfer roller 15 in timing synchronization up to secondary transfer section.When completing secondary transfer printing, Voltage source 19 stops voltage and applies.

In the case of continuous printing, charging and development timing are adjusted to make it possible to be formed in previous image secondary Transfer executes primary transfer after completing, to prevent primary and secondary be transferred at identical timing to be performed.Specifically, from Primary transfer feed roller 31 be supplied to intermediate transfer belt 8 electric current can be prevented from intermediate transfer belt 8 circumferential direction it is upper Enter into secondary transfer section.

As shown in figs. 10 a and 10b, constant voltage elements may be connected to each in support roller 11,12 and 13；And it transfers Power supply 33 and secondary transfer printing power supply 19 can output voltage simultaneously, to be performed simultaneously primary transfer and secondary transfer printing.Figure 10 A show it Middle Zener diode is connected to state in each of support member 11,12 and 13 as constant voltage elements.Figure 10 B show wherein to become Resistance device is connected to state in each of support member 11,12 and 13 as constant voltage elements.

However, in Zener diode or rheostatic, when the current potential of intermediate transfer belt 8 is beyond Zener diode electricity When position or rheostat current potential, electric current flowing is to maintain Zener diode current potential or rheostat current potential.Therefore, even if transfer power supply 33 With the output voltage simultaneously of secondary transfer printing power supply 19, the current potential of intermediate transfer belt 8 also less than reach or beyond Zener diode current potential or Rheostat current potential.The current potential of intermediate transfer belt 8 can be maintained in this way it is constant, to more stably maintain primary transfer Energy.Therefore, constant voltage elements each of support roller 11,12 and 13 is connected to make it possible to be performed simultaneously primary and secondary turn Print.In the present example embodiment, in the case where considering environment influence, Zener diode current potential or rheostat current potential are set It is set to 220V.

As shown in Figure 11 A, electric current can be supplied to primary transfer portion by secondary transfer printing power supply 19.In the case, two Secondary transfer roll 15 is used as the electric current supply part contacted with the outer surface of intermediate transfer belt 8.This configuration make it possible to by using One power supply supplies the voltage for being applied to execute primary and secondary transfer.Even in the case, constant voltage elements can also connect Each of to support roller 11,12 and 13, as shown in Figure 11 B and Figure 11 C.Constant voltage elements are connected to support roller 11,12 and 13 Each of make it possible to the surface potential of intermediate transfer belt 8 being maintained predetermined potential, to realize stable primary transfer Performance.

In addition, the image forming apparatus that conductive strips are used as to intermediate transfer belt 8 according to the present exemplary embodiment can be prevented The only reversed transfer at primary transfer portion.

Reversed transfer at primary transfer portion in order to prevent brings consideration to turn from centre by using conductive strips and high resistance The electric current (photosensitive-member inflow current) and reversely transfer it that print band 8 is flowed into photosensitive drums (specifically, the cores of photosensitive drums) Between relationship.

Figure 12 A show the relationship between photosensitive-member inflow current and transfer residual and the amount of reversed transfer toner.Ginseng Figure 12 A are examined, the longitudinal axis is designated as instruction by reversely transferring the reversed transfer toner for being moved to photosensitive drums from intermediate transfer belt 8 With the parameter of the amount of the transfer residual toner (not being transferred to the toner taken) on photosensitive-member.For reversely transferring tune The parameter of the toner measured value of the toner reversely transferred in photosensitive drums and the measurement without being obtained in the case of reversely transferring Difference between value indicates.In the case, the toner reversely transferred in photosensitive drums is by using Nichiban companies Scotch bands CT18 to collect from it, and adheres on transfer materials.Then, toner concentration by using X-Rite spectrum Concentration mensuration meter measures.Parameter for transfer residual toner measures in a similar manner.Figure 12 B show applying for transfer power supply Relationship between making alive and transfer residual and the amount of reversed transfer toner.

As shown in Figures 12 A and 12 B, in the case of high resistance band, the reversed amount for transferring toner is alive with applying Increase and increases.On the other hand, conductive to carry such trend：In the case of identical application voltage value, with high resistance band phase Than providing more a small amount of reversed transfer toners.Figure 12 A and 12B are indicated below a certain amount of photosensitive-member inflow current Occur almost without reversed transfer.

Reason explained below.Reversed transfer is considered as because the one of intermediate transfer belt 8 and corresponding photosensitive drums contact position Caused by the electric discharge occurred at secondary transfer section.Usually, it is known that Paschen's law is for discharging.With regard to photosensitive drum surface and intermediate transfer For the distance between band 8 (gap length) d, potential difference V is generated between photosensitive drums and intermediate transfer belt 8.When potential difference V is super When going out Paschen threshold voltage value V (d), electric discharge occurs.Otherwise, electric discharge does not occur.

Therefore, reversed transfer in order to prevent needs to make to be less than threshold voltage value V in relation to the potential difference V at primary transfer portion (d), to inhibit electric discharge and corresponding toner polarity reversion to occur.

Figure 13 A are the enlarged views in the primary transfer portion for showing image forming apparatus shown in FIG. 1.Figure 13 B are to show Fig. 4 Shown in image forming apparatus primary transfer portion enlarged view.

With reference to figure 13A, as described above, intermediate transfer belt 8 is conductive strips and therefore in the circumferential direction of intermediate transfer belt 8 It is upper that approximately equal surface potential is provided.Therefore, electric discharge is since the upstream side 8a' in primary transfer portion.In the case, upper The toner being transferred in trip image forming unit on intermediate transfer belt 8 forms unit in subsequent downstream image The upstream side experience electric discharge in primary transfer portion.Photosensitive drum surface is charged to negative polarity, and the surface of intermediate transfer belt 8 is electrically charged For positive polarity.Therefore, because the electronics with negative electrical charge is collided with the toner on intermediate transfer belt 8, therefore on intermediate transfer belt 8 Toner be charged to more negative polarity.Pass through downstream image as to the toner having transferred on intermediate transfer belt 8 The investigation result of the Q/M (quantity of electric charge/particle weight of=particle friction electrification) before and after the primary transfer portion of unit is formed, Confirm：Value before Q/M value of the toner after in relation to photosensitive drums is passed through higher than toner.

On the other hand, when photosensitive drum surface, which is undergone, to discharge, the current potential raising on photosensitive drum surface (is charged to anode Property), to reduce the potential difference between photosensitive drums and intermediate transfer belt 8.Therefore, it is until toner reaches primary transfer portion Only, the potential difference between intermediate transfer belt 8 and photosensitive drums reduces larger degree.Therefore, because the shape at primary transfer portion At potential difference be reduced to Paschen discharge threshold voltage value hereinafter, so electric discharge become difficult at primary transfer portion occur.Root According to the research of the present inventor, following potential value is obtained.Before experience is discharged, current potential on photosensitive-member is- Current potential on 500V and intermediate transfer belt 8 is+400V.After experience is discharged, the current potential on photosensitive-member becomes -100V and phase The potential difference between ground photosensitive-member and intermediate transfer belt 8 is answered to become+500V.The value is equal to or less than Paschen discharge threshold voltage Value.

With reference to figure 13B, intermediate transfer belt 8 is high resistance band, therefore is not provided closely in the circumferential direction of intermediate transfer belt 8 The surface potential of patibhaga-nimitta etc..Therefore, it for high resistance band, although electric discharge starts in the upstream side 8a of nip portion, discharges It is less likely to be reduced to Paschen electric discharge threshold to the potential difference between the current potential on the current potential and photosensitive drum surface on intermediate transfer belt 8 Threshold voltage value this degree below.When electric discharge occurs, the current potential on photosensitive-member accordingly increases.However, in the case, High resistance band provides the smaller raising of this current potential, because a small amount of electric discharges are happened at the upstream side of nip portion.Therefore, electric discharge also exists Continue at the downstream side 8c and primary transfer portion 8b in primary transfer portion.

Figure 14 A and 14B show the electric discharge of generation at the primary transfer portion of in conduction and high-resistance intermediate transfer belt Image.These images are captured using high speed camera.Figure 14 A show that the image captured on high resistance band, Figure 14 B are shown The image captured on conductive strips.So that intermediate transfer belt 8 is contacted with glass surface, then the image around nip portion by using The high speed camera of HOSOKAWA MICRON companies is captured.

With reference to figure 14A and 14B, the white portion in each image indicates the luminous component caused by electric discharge.With regard to high resistance band For, observe electric discharge on the upstream and downstream side both sides of the nip portion in primary transfer portion.For conductive strips, only pressing Observe electric discharge in the upstream side in portion.

Configuration according to the present exemplary embodiment, by using conductive intermediate transfer belt 8 and via intermediate transfer belt Transfer current is transmitted to photosensitive drums 2a, 2b, 2c and 2d from the electric current supply part contacted with the outer surface of intermediate transfer belt 8, Primary transfer is realized in this way.This configuration reduces the voltage source number for primary transfer, to reduce image The cost and size of forming apparatus.It is put in addition, conductive intermediate transfer belt 8 makes it possible to generate in the upstream side in primary transfer portion Electricity, to prevent reversed transfer.

Although the primary transfer feed roller 31 and two contacted in the present example embodiment with the outer surface of intermediate transfer belt 8 Secondary transfer roll 15 is used as electric current supply part, but electric current supply configuration is without being limited thereto.As shown in figure 15, primary transfer feeds roller 31 can contact with the inner surface of intermediate transfer belt 8.In addition, transfer power supply 33 may be connected to any of multiple support rollers.

Isobarically Control, current constant control or combination can be based on by being supplied to the voltage of electric current supply part, as long as figure As its sufficient primary transfer performance can be presented in forming apparatus.

Although in the present example embodiment, intermediate transfer belt 8 is made of the PPS of the carbon containing addition to provide electric conductivity, But the ingredient of intermediate transfer belt 8 is without being limited thereto.Even if using other resins and metal, those of with the present exemplary embodiment The similar effect of effect can be also expected, as long as equivalent electric conductivity is implemented.Although in the present example embodiment Single layer and the double-deck intermediate transfer belt are used, but the configuration of the layer of intermediate transfer belt 8 is without being limited thereto.Even if using for example including bullet Three layers of intermediate transfer belt of property layer, the effect similar with those of present exemplary embodiment effect can be also expected, as long as Above-mentioned circumferential resistance is implemented.

Although in the present example embodiment, with two layers of intermediate transfer belt 8 by being initially formed base layer and then It is formed on coat and is manufactured, but manufacturing method is without being limited thereto.It is, for example, possible to use casting (casting), as long as Relevant resistance value meets above-mentioned condition.

Although describing the present invention by reference to exemplary embodiment, it is to be appreciated that the present invention is not limited to disclosed Exemplary embodiment.The scope of the following claims is consistent with the explanation of widest range to include all modifications, equivalent structure And function.

This application claims the Japanese patent application submitted on October 4th, 2010 the 2010-224951st and in Septembers, 2011 The priority of the Japanese patent application submitted the 2011-212311st on the 28th, the full content of these Japanese patent applications pass through Reference is incorporated in this.

Claims (6)

1. a kind of image forming apparatus, including：

First image bearing member is configured as carrying toner image；

Second image bearing member is configured as carrying toner image；

Rotatable intermediate transfer belt, it is conductive；

Secondary transfer printing component is configured as toner image being transferred on transfer materials from intermediate transfer belt；

Power supply is configured to connect to secondary transfer printing component, and is configured as applying voltage to secondary transfer printing component,

Wherein, the second image bearing member is disposed in the downstream of the first image bearing member along the rotation direction of intermediate transfer belt Side,

Wherein, by the way that the voltage from power supply to be applied to via secondary transfer printing component on intermediate transfer band, toner image from First and second image bearing members are transferred on intermediate transfer band, and toner image from intermediate transfer belt by two It is secondary to be transferred on recording materials, and

Wherein, second image bearing member and intermediate transfer belt of the secondary transfer printing component in the rotation direction along intermediate transfer belt Between contact area upstream side, between the second image bearing member and intermediate transfer belt generate electric discharge so that contacting The potential difference between intermediate transfer belt and the second image bearing member at region is less than Paschen discharge threshold voltage value, and will Toner image is transferred to from the second image bearing member on intermediate transfer band at the contact area.

2. image forming apparatus according to claim 1, wherein the peripheral surface of secondary transfer printing component and intermediate transfer belt Contact.

3. the image forming apparatus according to any one of claim 1~2, further includes：

Multiple support members, are configured to support intermediate transfer belt,

Wherein, for by the surface potential of intermediate transfer belt be maintained predetermined potential or higher constant voltage elements be connected to it is described Multiple support members.

4. image forming apparatus according to claim 3, wherein the constant voltage elements are Zener diode or variable resistance Device.

5. image forming apparatus according to claim 1, further includes：

It is multiple at each position via intermediate transfer belt the first image bearing member of direction and the second image bearing member Opposite component,

Wherein, intermediate transfer belt connects via the multiple opposite component with the first image bearing member and the second image bearing member It touches.

6. image forming apparatus according to claim 5, wherein the multiple opposite direction component is electrical isolation.