JP5473291B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus in which a charge eliminating unit for improving the separation of a recording material is disposed downstream of a transfer unit, and more specifically, a charge eliminating unit for setting transfer conditions during image formation prior to image formation. Regarding control.

  2. Description of the Related Art Image forming apparatuses that transfer a toner image onto a recording material by superimposing the toner image carried on an image carrier (photosensitive body or intermediate transfer body) and passing the recording material through a transfer unit are widely used.

  In such an image forming apparatus, in order to increase the curvature separation performance from the image carrier downstream of the transfer unit by eliminating the charge excessively injected into the recording material in the process of passing through the transfer unit, There are cases in which a static elimination means is disposed downstream.

  For example, Patent Document 1 discloses a charged particle generated by corona discharge on a recording material immediately after exiting a transfer portion by disposing a charge eliminating unit using a corona discharger downstream of a transfer portion using a transfer roller. An image forming apparatus that irradiates is shown.

  On the other hand, in an image forming apparatus that applies a constant voltage to a transfer portion and transfers a toner image onto a recording material, prior to image formation, a voltage is applied to the transfer portion to measure the current flowing through the transfer portion, In some cases, the voltage condition used in the transfer portion is set.

  For example, Patent Document 2 discloses ATVC control (Active Transfer Voltage Control). Here, a constant current corresponding to the current value necessary for the transfer of the toner image is applied to the transfer portion through which the recording material does not pass, and the output voltage value is measured. Based on the measurement result, the output voltage value is measured. A constant voltage applied to the transfer roller is set.

For example, Patent Document 3 discloses PTVC control (Programmable Transfer Voltage Control). Here, a plurality of stages of constant voltages are applied to the transfer portion through which the recording material has not passed, and the current value flowing through the transfer member is measured at each stage. An output voltage corresponding to a current value necessary for transferring the toner image is interpolated from a plurality of levels of voltage-current data, and a constant voltage used for image formation is set based on the calculation result.

JP 2002-372874 A JP-A-2-123385 JP-A-5-181373

  However, in the configuration shown in Patent Document 1, it has been found that if the voltage condition used in the transfer portion at the time of image formation is set using the control shown in Patent Documents 2 and 3, an appropriate voltage condition may not be set. did.

In other words, in the configuration shown in Patent Document 1, the static elimination member is installed quite close to the transfer member , and the static elimination member has a voltage (reverse polarity) having a large potential difference with respect to the voltage applied to the transfer member. Applied.

Therefore, at the time of image formation becomes a leakage current flows some of the charged particles generated by the charge removing member to the transfer member, and a portion of the current to be involved in the transfer of the toner image flows to the transfer unit would otherwise be impaired End up.

In particular, the component life end of the resistance value of the image bearing member and the transfer member is increased, because also increases the voltage applied to the transfer member during image formation in accordance with the increased resistance, the potential difference between the charge removing member and the transfer member Increases and leakage current increases remarkably.

For this reason, when a voltage is applied to the transfer member and a voltage to be applied to the transfer member at the time of image formation is set without applying a neutralization voltage to the charge removal member , the voltage may be set too low. In particular, when the voltage level set at the transfer section becomes high at the end of the component life, the leakage current increases rapidly, resulting in a shortage of current that should actually flow through the transfer section and participate in the transfer of the toner image. May cause.

An object of the present invention is to provide an image forming apparatus capable of reducing transfer defects caused by a set transfer voltage even when a voltage is applied to a charge removal member during image formation.

The image forming apparatus of the present invention includes an image bearing member, a toner image forming means for forming a toner image on said image bearing member, a transcription member you transferred to the transfer material a toner image formed on said image bearing member rolling than the transfer member in the direction of movement of Utsushizai positioned downstream, rolling and discharging member for neutralizing the Utsushizai, a transfer power supply for outputting a voltage to be applied to the transfer member, applied to the charge removing member A neutralizing power source that outputs a voltage to be applied, a test voltage is applied to the transfer member, a setting unit that sets a transfer voltage to be applied to the transfer member during image formation, and a basis weight of a transfer material to be used is determined a judgment means, wherein the setting unit, when the basis weight of the transfer material used is a predetermined value or less of the thin paper, before Symbol transfer member in a state where the neutralization power is applied a voltage to the charge removing member applying a test voltage set preferences of the transfer voltage, the use If the basis weight of the transfer material is greater than the predetermined value is the one in which the charge removing power to set the transfer voltage in a state where no voltage is applied to the charge removing member.

According to the present invention, even if a voltage is applied to the charge removal member during image formation, transfer defects caused by the set transfer voltage can be reduced.

  Hereinafter, some embodiments of the present invention will be described in detail with reference to the drawings. The present invention is also implemented in another embodiment in which a part or all of the configuration of the embodiment is replaced with the alternative configuration as long as a voltage corresponding to the voltage applied to the transfer unit is applied to the static elimination unit. it can.

  In the present embodiment, only main parts related to toner image formation / transfer will be described. However, the present invention includes a printer, various printing machines, a copier, a fax machine, a composite machine, in addition to necessary equipment, equipment, and a housing structure. It can be implemented in various applications such as a machine.

<Image forming unit>
FIG. 1 is an explanatory diagram of the configuration of the image forming apparatus according to the first embodiment, and FIG. 2 is an explanatory diagram of the configuration of the image forming unit.

  As shown in FIG. 1, an image forming apparatus 100 according to the first embodiment is a laser beam printer that forms a full-color image on a recording material (recording paper, OHP sheet, cloth, etc.) using an electrophotographic method. The image forming apparatus 100 is an intermediate transfer type tandem type in which image forming portions Pa, Pb, Pc, and Pd, which are yellow, magenta, cyan, and black toner image forming units, are arranged along an intermediate transfer belt 51.

  In the image forming portion Pa, a yellow toner image is formed on the photosensitive drum 1 a and is primarily transferred to the intermediate transfer belt 51. In the image forming portion Pb, a magenta toner image is formed on the photosensitive drum 1 b and is primarily transferred to the yellow toner image on the intermediate transfer belt 51. In the image forming portions Pc and Pd, a cyan toner image and a black toner image are formed on the photosensitive drums 1c and 1d, respectively, and similarly, the toner images on the intermediate transfer belt 51 are sequentially superimposed and sequentially transferred. In this embodiment, the photosensitive drum and the intermediate transfer belt have a role as an image carrier that carries a toner image.

  The four-color toner images primarily transferred to the intermediate transfer belt 51 are collectively transferred to the recording material P fed to the secondary transfer portion N2. The recording material P onto which the toner image has been secondarily transferred at the secondary transfer portion N2 is heated and pressurized by the fixing device 7, and the toner image is fixed on the surface, and then discharged to the outside.

  The recording material feeding device 8 separates the recording material P drawn from the recording material cassette 81 by the pickup roller 82 one by one by the separating device 83 and sends it to the registration roller 84. The registration roller 84 receives and waits for the recording material P in a stopped state, and sends the recording material P to the secondary transfer portion N2 in synchronization with the toner image on the intermediate transfer belt 51.

  The intermediate transfer unit 5 spans an intermediate transfer belt 51, which is an example of an image carrier, over a driving roller 52, support rollers 58 and 59, a tension roller 53, and a counter roller 54, and rotates it in the direction of arrow R <b> 2.

  The fixing device 7 presses a pressure roller 73 against a fixing roller 72 disposed around a lamp heater 71 to form a heating / pressure nip of the recording material P.

  The belt cleaning device 57 rubs the intermediate transfer belt 51 with a cleaning blade, passes the secondary transfer portion N2, and leaves the transfer residual toner and paper dust remaining on the surface of the intermediate transfer belt 51 from which the recording material P has been separated. Etc. are removed.

  The image forming portions Pa, Pb, Pc, and Pd are configured substantially the same except that the colors of toner used in the attached developing devices 4a, 4b, 4c, and 4d are different from yellow, magenta, cyan, and black. Hereinafter, the image forming unit Pa will be described with reference to FIG. 2, and the other image forming units Pb, Pc, and Pd will be described by replacing “a” at the end of the reference numerals with “b”, “c”, and “d”. Shall.

  As shown in FIG. 2, in the image forming section Pa, a charging roller 2a, an exposure device 3a, a developing device 4a, a primary transfer roller 55a, and a cleaning device 6a are arranged around the photosensitive drum 1a.

  The photosensitive drum 1a is formed with an organic photoconductor layer (OPC) having a negative polarity on the outer peripheral surface of an aluminum cylinder, and rotates in the direction of arrow R1 at a process speed of 200 mm / sec.

  The charging roller 2a, which is a charging member, is formed by covering a surface of a metallic central axis with a resistive elastic layer, and is driven to rotate while being pressed against the photosensitive drum 1a. The power source D3 applies a DC voltage superimposed with an AC voltage to the charging roller 2a to charge the surface of the photosensitive drum 1a to a uniform negative potential.

  The exposure device 3a scans the scanning line image data obtained by developing the yellow separated color image with a rotating mirror, and writes an electrostatic image of the image on the surface of the charged photosensitive drum 1a.

  The developing device 4a agitates a two-component developer in which nonmagnetic toner is mixed with a magnetic carrier, and charges the nonmagnetic toner to negative polarity and the magnetic carrier to positive polarity. The charged two-component developer is carried on the developing sleeve 41a rotating around the fixed magnetic pole 42a in the counter direction with the photosensitive drum 1a, and rubs against the photosensitive drum 1a. The power source D4 applies a developing voltage obtained by superimposing an AC voltage to a negative DC voltage to the developing sleeve 41a, and moves the toner to the exposed portion of the photosensitive drum 1a that has a relatively positive polarity relative to the developing sleeve 41a. Then, the electrostatic image is reversely developed.

  The primary transfer roller 55a, which is a primary transfer member, is pressed against the photosensitive drum 1a so as to sandwich the intermediate transfer belt 51, thereby forming a primary transfer portion N1a between the photosensitive drum 1a and the intermediate transfer belt 51. The power supply D1a is a transfer output unit that applies a voltage to the primary transfer roller 55a, and applies a positive DC voltage of +900 V to the primary transfer roller 55a as a primary transfer bias. As a result, the toner image charged negatively and carried on the photosensitive drum 1a is primarily transferred to the intermediate transfer belt 51 passing through the primary transfer portion N1a.

As the primary transfer roller 55a, a semiconductive roller having a resistance value of 1 × 10 ² to 10 ⁸ Ω when 2000V was applied was used. Specifically, an ion conductive sponge roller formed by blending a nitrile rubber and an ethylene-epichlorohydrin copolymer and having an outer diameter of φ16 mm and a core metal diameter of φ8 mm was used. The resistance value of the primary transfer roller 55a is about 1 × 10 ⁶ to 10 ⁸ Ω at an applied voltage of 2 kV in an environment of a temperature of 23 ° C. and a humidity of 50% RH.

  The cleaning device 6a slides the cleaning blade against the photosensitive drum 1a to remove the transfer residual toner attached to the surface of the photosensitive drum 1a that has passed through the primary transfer portion N1a.

  In recent years, the number of types of recording materials has increased, and the thickness and electrical resistance of recording materials have become wide. Further, constant voltage control is employed in the transfer portion to the recording material in order to avoid a change in the amount of charge supplied to the toner image due to differences in image ratio, recording material width, and the like. Furthermore, the electrical resistance of the intermediate transfer belt and the transfer roller, the film thickness of the surface layer of the photosensitive drum, and the like change as the ambient environment such as temperature and humidity changes or as the image formation is accumulated. Along with these changes, in order to optimize the voltage applied to the transfer roller during image formation, ATVC determines a control value for constant voltage control (a constant voltage value applied to the transfer roller) prior to image formation. Control and PTVC control are executed.

  Further, when thin paper having a low basis weight is used as the recording material P, the rigidity of the material itself is low, so that separation failure from the intermediate transfer belt is likely to occur. For this reason, the separability of the recording material P in the secondary transfer portion N2 is improved by applying a high voltage to the static elimination needle 91 and removing the charged charge of the recording material P more efficiently.

<Secondary transfer section>
FIG. 3 is an explanatory diagram of the configuration of the secondary transfer portion and the static elimination needle.

  As shown in FIG. 3, the secondary transfer roller 56 as a secondary transfer member is urged by spring members at both ends and is pressed against the opposing roller 54 via the intermediate transfer belt 51, A secondary transfer portion N2 is formed between the secondary transfer roller 56 and the secondary transfer roller 56. The opposing roller 54 is connected to the ground potential.

  The transfer power supply D2 is a transfer output unit that applies a voltage to the secondary transfer roller 56, and applies a secondary transfer bias, which is an example of voltage conditions, to the secondary transfer roller 56, which is an example of transfer means, during image formation. . As a result, the toner image charged to the negative polarity and carried on the intermediate transfer belt 51 is secondarily transferred to the recording material passing through the secondary transfer portion N2. The secondary transfer bias is set by applying a voltage to the secondary transfer roller 56 prior to image formation, and is, for example, a positive DC voltage of +2.3 kV that is constant voltage controlled.

As the intermediate transfer belt 51, a semiconductive polyimide resin having a relative dielectric constant ε = 3 to 5 and a volume resistivity ρv = 1 × 10 ⁶ to 10 ¹¹ Ω · m was used.

The opposing roller 54 was a semiconductive roller having an outer diameter of 20 mm and a core metal diameter of 16 mm, in which conductive carbon was dispersed in EPDM rubber. The resistance value of the facing roller 54 is about 1 × 10 ¹ to 10 ⁵ Ω when the applied voltage is 10 V in an environment of a temperature of 23 ° C. and a humidity of 50% RH by the measurement method described above.

As the secondary transfer roller 56, an ion conductive sponge roller formed by blending nitrile rubber and ethylene-epichlorohydrin copolymer and having an outer diameter of φ24 mm and a cored bar diameter of φ12 mm was used. The resistance value of the secondary transfer roller 56 is about 1 × 10 ⁶ to 10 ⁸ Ω when the applied voltage is 2 kV in an environment of a temperature of 23 ° C. and a humidity of 50% RH by the measurement method described above.

  Even if a configuration in which the secondary transfer roller 56 is connected to the ground potential and a negative DC voltage is applied to the counter roller 54, which is an example of a transfer unit, is similarly applied from the intermediate transfer belt 51 to the recording material. The toner image can be secondarily transferred.

  As shown in FIG. 1, the image forming apparatus 100 can execute a black single color mode for forming a black single color image using only the image forming unit Pd. In the black monochrome mode, the above-described toner image forming process is performed only in the image forming unit Pd, and only the black toner image is carried on the intermediate transfer belt 51. Then, after the black toner image is transferred to the recording material P passing through the secondary transfer portion N2, it is fixed by the fixing device 7.

<Static elimination part>
On the downstream side of the secondary transfer roller 56 in the moving direction (conveying direction) of the recording material P, a static elimination needle 91 that is an example of a static elimination unit that neutralizes the recording material P is disposed. The static elimination needle 91 was obtained by processing a thin plate material of SUS304 having a thickness of 0.2 mm into a sawtooth shape, and the pitch of the adjacent sawtooth was 1 mm. The static elimination needle 91 is disposed at a height position where it is not in contact with the recording material P being conveyed so that the tip of the saw tooth faces the back surface of the recording material P.

  The static elimination needle 91 is connected to a static elimination power source D5 that is a static elimination output unit that applies a variable static elimination bias to the static elimination needle 91, and the static elimination bias can be applied to the static elimination needle 91 at a predetermined timing. The polarity of the neutralizing bias is set to a negative polarity that is opposite to the positive polarity secondary transfer bias applied to the secondary transfer roller 56.

  As shown in FIG. 3, the static elimination needle 91 is attached to the static elimination needle holder 92 and disposed. The static elimination needle holder 92 is an insulating member mainly composed of PBT (polybutylene terephthalate) whose insulation is ensured, and prevents high pressure from leaking directly between the secondary transfer roller 56 and the static elimination needle 91.

  The static elimination needle 91 is applied with a static elimination bias to generate corona discharge, and irradiates the back surface of the recording material P with charged particles accompanying the corona discharge. The neutralizing bias neutralizes the charged charge of the recording material P downstream after passing through the secondary transfer portion N2, thereby reducing the electrostatic adsorption force to the intermediate transfer belt 51 and improving the separation property of the recording material P. .

<Example 1>
4 is a flowchart of control for setting the secondary transfer bias, FIG. 5 is an explanatory diagram of PTVC control for setting the secondary transfer bias, and FIG. 6 is an explanatory diagram of a transfer electric field when the static elimination bias is applied to the static elimination needle. . In the present embodiment, a static elimination needle 91 is used as a static elimination means for neutralizing a recording material as a transfer material.

As shown in FIG. 4 with reference to FIG. 3 , the control unit 110 applies a voltage to the secondary transfer unit N2 prior to image formation (S17) to the secondary transfer roller 56 during image formation. The secondary transfer bias to be applied is set (S14).

The transfer power supply D <b> 2 outputs a secondary transfer bias controlled at a constant voltage from the high voltage circuit 120 and applies it to the core metal of the secondary transfer roller 56 through the current detection circuit 121. The current detection circuit 121 outputs an analog voltage corresponding to the current value flowing from the current detection circuit 121 to the secondary transfer roller 56 to the control unit 110.

  The control unit 110 controls the high voltage circuit 120 to output a predetermined constant voltage, detects the output of the current detection circuit 121 at that time, and performs a secondary operation such that the current flowing through the transfer unit N2 becomes a predetermined value. It has a function of a setting unit that calculates the transfer bias and sets it in the high voltage circuit 120.

  The controller 110 performs PTVC control (S14) during pre-rotation (S11), which is an example of non-image formation.

As shown in FIG. 5 with reference to FIG. 3, the control unit 110 switches the output voltage of the transfer power supply D <b> 2 in multiple stages, and the current detection circuit 121 detects the output current value for the output voltage at each stage. As an example of the test voltage, the output voltage of the transfer power supply D2 is switched in three stages of a first voltage V1 = 2.5 kV, a second voltage V2 = 2 kV, and a third voltage V3 = 1.5 kV, but V3 <V2 <V1 There is no need to.

  The first voltage V1 is applied for one turn of the secondary transfer roller 56, and the current value at that time is detected by the current detection circuit 121 and averaged to obtain the current value I1 for the first voltage V1. Thereafter, using a similar procedure, a current value I2 for the second voltage V2 and a current value I3 for the third voltage V3 are obtained.

  The control unit 110 uses the applied voltages V1, V2, and V3 at the three measurement points and the current values I1, I2, and I3 detected by the current detection circuit 121, and uses the voltage-current characteristics (V of the secondary transfer unit N2). -I characteristics). In the interval between the three measurement points, the measurement data of the three measurement points are derived by a calculation process that linearly complements.

  The VI characteristic thus obtained is temporarily stored in a storage device (RAM or the like) 109 built in the control unit 110.

Here, in the storage device 109, a transfer current required in the secondary transfer unit N2 is determined in advance for each type of the recording material P, and stored in a table associated with the model name of the recording material P. . For example, 60 μA is stored in association with our recommended paper color laser copier paper (basis weight 81.3 g / m ² ).

  The control unit 110 reads the secondary transfer bias Vb applied to the secondary transfer roller 56 necessary for flowing a transfer current of 60 μA to the secondary transfer unit N2 from the storage device 109, and outputs the V of the secondary transfer unit N2. Obtained from -I characteristics.

When the transfer current necessary for transferring the toner image on the intermediate transfer belt 51 to the recording material P is Ib, for example, when Ib <I2, the reference voltage Vb is obtained from the following equation (1).
Vb = (Ib−I2) × (V3−V2) / (I3−I2) + V2 (1)

When Ib ≧ I2, the reference voltage Vb is obtained from the following equation (2).
Vb = (Ib−I1) × (V2−V1) / (I2−I1) + V1 (2)

As described above, the control unit 110 calculates the secondary transfer bias Vb and sets it to the charge removal power source D5 during image formation. At the time of image formation, the secondary transfer bias Vb set by the controller 110 is applied to the secondary transfer roller 56 by the transfer power source D2 , and a secondary transfer process of the toner image onto the recording material P is performed.

  As shown in FIG. 5 with reference to FIG. 3, the control unit 110 continues to apply a static elimination bias to the static elimination needle 91 in the process of measuring the current value at the three measurement points (S14) (S13). ).

When a basis weight of 63 g / m ² or less is specified (YES in S15), the control unit 110, which is an example of a determination unit, determines a constant voltage of −3 kV as a neutralization bias to the neutralization needle 91 during image formation (S17). A bias is applied (S16). However, in the case of thick paper to plain paper in which the separation property of the recording material P on the downstream side of the secondary transfer portion N2 is sufficiently secured (NO in S15), the static elimination needle 91 is connected to the ground potential.

  When image formation is performed on thin paper (YES in S12), the above-described PTVC control is executed in a state in which a static elimination bias of −3 kV is applied to the static elimination needle 91 (S13). However, in the case of thick paper to plain paper (NO in S12), the above-described PTVC control is executed by connecting the static elimination needle 91 to the ground potential. As a result, the secondary transfer bias Vb that offsets the change in leakage current due to the presence / absence of the neutralizing bias in the neutralizing needle 91 during image formation is set. Thus, in this embodiment, PTVC control is executed in the same state as the potential state of the charge eliminating needle 91 when the toner image is transferred to the transfer member.

  Here, an experiment was performed in which a toner image was transferred to a thin recording material P in a state where 1.7 kV was applied as a secondary transfer bias and −3 kV was applied as a neutralizing bias. At this time, when the total current amount and leakage current output from the static elimination power source D5 to the secondary transfer roller 56 and detected by the current detection circuit 121 were measured, the total current amount was about 85 μA. However, since a leakage current of about 5 μA flowed into the static elimination needle 91, the counter current amount used to transfer the toner image to the recording material P and flowed into the counter roller 54 was about 80 μA.

  On the other hand, with the charge eliminating needle 91 connected to the ground potential, the same toner image was transferred to the same recording material P, and the total amount of current flowing into the secondary transfer roller 56 and the leakage current were measured. At this time, when the secondary transfer bias is changed so that a current of 80 μA flows into the opposing roller 54, the total amount of current output from the static elimination power source D5 to the secondary transfer roller 56 and detected by the current detection circuit 121 is about. It was 83 μA. The leakage current flowing into the static elimination needle 91 was 3 μA.

  Therefore, in the case where the static elimination bias is applied to the static elimination needle 91, the secondary transfer bias to be applied to the secondary transfer roller 56 when transferring the same toner image to the same recording material in the secondary transfer portion N2. Is different. When image formation is performed by applying a charge removal bias to the charge removal needle 91, a slightly higher secondary transfer bias is required to compensate for the leakage current flowing into the charge removal needle 91.

  In other words, the secondary transfer bias set without applying the neutralization bias to the static elimination needle 91 increases the leakage current flowing into the static elimination needle 91 when the neutralization bias is applied to the static elimination needle 91 and the toner image is actually transferred. The voltage becomes insufficient as much as the amount.

  As shown in FIG. 6, since the electric field distribution in the secondary transfer portion N2 is different between when the static elimination bias is applied to the static elimination needle 91 and how the secondary transfer current flows.

  As shown in FIG. 6A, when no static elimination bias is applied to the static elimination needle 91, the equipotential surface inside the secondary transfer roller 56 is in contact with the opposing roller 54 via the intermediate transfer belt 51. It becomes parallel to the part N2. This is because the resistance of the counter roller 54 is low, so that the surface of the counter roller 54 can be regarded as an almost equipotential surface.

  Since the current flows in the direction perpendicular to the equipotential surface inside the secondary transfer roller 56, the current flows perpendicularly to the secondary transfer portion N2, and the nip of the secondary transfer portion N2 is reached. A uniform current distribution is formed in the plane.

  As shown in FIG. 6B, when a neutralization bias is applied to the neutralization needle 91, the neutralization needle 91 having a negative potential is present near the secondary transfer roller 56 having a positive potential. The potential on the downstream side is lower than that on the upstream side.

  For this reason, the equipotential surface inside the secondary transfer roller 56 is inclined in a direction parallel to the static elimination needle 91 as compared with the case (a) where no static elimination bias is applied. Since the current flows in the direction perpendicular to the equipotential surface inside the secondary transfer roller 56, the current is concentrated on the upstream portion of the secondary transfer portion N2.

Since the recording material P is conveyed to the secondary transfer portion N2 in an uncharged state, the potential difference between the secondary transfer roller 56 and the recording material P becomes the largest in the upstream portion of the secondary transfer portion N2. When the current concentrates on the upstream portion of the secondary transfer portion N2, the amount of charge moving from the secondary transfer roller 56 to the recording material P increases, and the secondary transfer current increases. Therefore, the appearance of the secondary transfer portion N2 is apparent. Impedance is low. Then, by applying the static elimination bias, the apparent impedance of the secondary transfer portion N2 is lowered, and the secondary transfer current output from the transfer power supply D2 is increased.

  This is because the total current amount was about 83 μA when no neutralization bias was applied, whereas it was about 85 μA when the neutralization bias was applied. When the neutralizing bias is applied, the apparent value of the secondary transfer portion N2 appears even though the resistance values of the members constituting the secondary transfer portion N2 such as the secondary transfer roller 56 and the intermediate transfer belt 51 do not change. It is thought that the impedance of fluctuates.

  Therefore, as shown in FIG. 4, in Example 1, the secondary transfer bias is applied in a state where the neutralizing bias is applied (S13) before image formation on the thin paper to which the neutralizing bias is applied (YES in S12). The PTVC to be set is performed (S14). Then, before image formation on plain paper to thick paper to which no neutralization bias is applied (NO in S12), PTVC control for setting a secondary transfer bias in a state where the neutralization bias is applied is performed (S14).

  This makes it possible to set the secondary transfer bias with higher accuracy and output a high-quality image without causing a transfer failure.

  Incidentally, it is preferable to apply a constant voltage bias to the static elimination needle 91 rather than a constant current bias. When a neutralization bias is applied to the static elimination needle 91 in the absence of the recording material P in the vicinity, the secondary transfer portion is in a state where a discharge is generated between the secondary transfer roller 56, the intermediate transfer belt 51 and the static elimination needle 91. The recording material P charged to the positive polarity is conveyed from N2.

  Then, at the moment when the tip of the recording material P reaches the vicinity of the static elimination needle 91, the surrounding charged particles flow into the recording material P all at once, and the current that instantaneously flows into the static elimination needle 91 increases. For this reason, when a constant current is supplied to the static elimination needle 91, the potential of the static elimination needle 91 is suddenly lowered, and a sufficient neutralization / separation promoting effect cannot be exhibited with respect to the leading end of the recording material P.

On the other hand, when a constant voltage is supplied to the static elimination needle 91, the potential of the static elimination needle 91 does not decrease at the tip of the recording material P, so that necessary and sufficient charged particles are supplied to the tip of the recording material P. And a sufficient neutralization / separation promoting effect is exhibited. For thin paper having a basis weight of 63 g / m ² or less, since the rigidity of the recording material P is relatively low, the leading edge of the recording material P is attracted to the intermediate transfer belt 51 and is easily rotated. For this reason, by setting the static elimination bias to constant voltage control, the static elimination efficiency at the front end of the recording material P can be maintained high, and the separation of thin paper having a low basis weight can be improved.

  When image formation is performed by applying a charge removal bias to the charge removal needle 91, PTVC control of the secondary transfer bias applied to the secondary transfer roller 56 in a state where the charge removal bias is applied to the charge removal needle 91 is performed. As a result, the secondary transfer bias can be optimally controlled by taking into account the effect of the static elimination bias on the current flowing through the secondary transfer roller 56. The toner image on the intermediate transfer belt 51 can be satisfactorily transferred to the recording material P even when the static elimination needle 91 is disposed in the vicinity of the secondary transfer portion N2 and the static elimination bias is applied to the static elimination needle 91. As a result, a high-quality image free from transfer defects can be obtained.

  The storage device 109 stores a secondary transfer bias (recording material sharing) to be added when 60 μA is applied to the recording material P in association with the model name of the recording material P (including the width direction size corresponding to the feeding direction). The voltage Vp) may be stored in advance. Even if the secondary transfer bias applied to the secondary transfer roller 56 at the time of image formation is set by adding the recording material sharing voltage Vp read from the storage device 109 to the secondary transfer bias Vb obtained by PTVC control. Good.

<Example 2>
FIG. 7 is an explanatory diagram of the recording material feeding apparatus according to the second embodiment.

  As shown in FIG. 7, the recording material feeding device 8B is configured in the same manner as the image forming apparatus 100 shown in FIG. 1 except that the recording material cassette 81 includes a thickness detection sensor Sp. Therefore, in FIG. 7, the same reference numerals as those in FIG.

  A thickness detection sensor Sp attached to the recording material cassette 81 detects the thickness of the recording material P. The control unit 110 determines whether the recording material P on which an image is formed is thin paper according to the output of the thickness detection sensor Sp.

  As shown in FIG. 4, in the case of thin paper (YES in S12, YES in S15), the control unit 110 applies a static elimination bias to the static elimination needle 91 to perform PTVC control. Then, the secondary transfer bias set by the PTVC control is applied to the secondary transfer roller 56, and image formation is performed in a state where the static elimination bias is applied to the static elimination needle 91 (S17).

  However, if the paper is not thin (NO in S12, NO in S15), PTVC control is performed without applying a static elimination bias to the static elimination needle 91 (S14), and image formation is performed without applying the static elimination bias to the static elimination needle 91. (S17).

  As the detection sensor Sp, for example, a sensor having a mechanism as disclosed in JP-A-3-192050 can be used. Here, a mechanism is used in which a sensor arm is protruded toward the paper feed path, and the recording material P conveyed in the paper feed path detects the angle at which the sensor arm is swung to detect the recording material. The thickness of P is detected.

  Alternatively, as a detection device for the thickness of the recording material P, for example, a light emitting portion and a light receiving portion constituting a photosensor are arranged above and below the paper feed path to detect the intensity of light transmitted through the recording material P. Thus, it can be used as information on the thickness of the recording material P.

  In Example 2, only when it is determined that the recording material P is thin paper having a thickness of 50 μm or less, a neutralization bias of −3 kV is applied to the neutralization needle 91 in order to improve the separation at the secondary transfer portion N2. . On the other hand, if it is determined that the thickness of the recording material P exceeds 50 μm, the neutralizing bias is not applied to the neutralizing needle 91.

<Example 3>
FIG. 8 is an explanatory diagram of PTCV control in the third embodiment. In the third embodiment, a voltage condition at the time of image formation is set based on a voltage-current characteristic obtained by applying a plurality of stages of voltages to the transfer unit and measuring a current flowing through the transfer unit. Then, the current is measured when a predetermined voltage is applied to the static eliminator only with respect to the maximum voltage of the plurality of stages and when it is not applied.

  In the third embodiment, when a plurality of types of paper having different thicknesses coexist in the recording material cassette 81 of FIG. 7, the thickness detection sensor Sp is used to determine whether the recording material P is thin or not, thereby eliminating static electricity. Image formation is performed with bias ON / OFF.

  Alternatively, when thin paper is stored in one of the plurality of recording material cassettes and image formation on thin paper is started in the middle of continuous image formation on plain paper, whether the recording material P to be imaged is thin paper Corresponding to whether or not, image formation is performed by automatically turning on / off the static elimination bias. According to the distinction between the recording material cassettes that send out the recording material, the image forming is performed by automatically turning on / off the static elimination bias.

  In order to cope with such continuous image formation in which plain paper and thin paper are mixed, in the pre-rotation executed immediately before the start of continuous image formation, a case where a neutralization bias is applied to the static elimination needle 91 and a case where it is not applied. Both perform PTVC control.

  In other words, prior to image formation, a secondary transfer bias Vb1 when a static elimination bias is applied to the static elimination needle 91 and a secondary transfer bias Vb2 when no static elimination bias is applied to the static elimination needle 91 are prepared by PTVC control. Thus, the static elimination power source D5 can be set.

  Then, the secondary transfer biases Vb1 and Vb2 are switched in accordance with the “result of determination as to whether or not the recording material fed to the secondary transfer unit N2 is thin paper” obtained during continuous image formation. Along with this, ON / OFF of the neutralization bias is switched so as to ensure equivalent recording material separation regardless of whether the paper is thin.

  As shown in FIG. 8 with reference to FIG. 3, the voltage for measurement controlled by the constant voltage output from the transfer power source D2 is switched to three stages of the first voltage V1, the second voltage V2, and the third voltage V3, The PTVC control applied to the secondary transfer roller 56 is executed.

  First, the first voltage V1, the second voltage V2, and the third voltage V3 are applied to the secondary transfer roller 56 for each round of the secondary transfer roller 56 in a state in which the neutralizing bias is not applied, and the current detection circuit 121 Each current is detected. The detected current is plotted with currents I1, I2, and I3 (marked with ● in the figure) detected when the first, second, and third voltages are applied in a state in which the neutralizing bias is not applied.

  Subsequently, with the neutralization bias applied to the neutralization needle 91, only the first voltage V1 is applied to the secondary transfer roller 56 for one round, and the current flowing into the secondary transfer roller 56 is measured by the current detection circuit 121. . A current I1n (circled in the figure) detected when the first voltage V1 is applied to the secondary transfer roller 56 in a state where the neutralizing bias is applied is plotted.

  In Example 3, the measurement voltages applied to the secondary transfer roller 56 were V3 = 1.5 kV, V2 = 2 kV, and V1 = 2.5 kV.

  At this time, voltage-current data at three points I1, I2, and I3 are interpolated and a secondary transfer bias Vb2 corresponding to a target current Ib that is a transfer current necessary for forming a toner image on the recording material P. Determine. The secondary transfer bias Vb2 is applied to the secondary transfer roller 56 at the time of image formation in which the charge removal bias 91 is not applied to the charge removal needle 91 because the thickness of the recording material P exceeds 50 μm.

  Further, the secondary transfer bias Vb1 corresponding to the same target current Ib is interpolated from three points I1n, I2, and I3. The secondary transfer bias Vb1 is a secondary transfer roller at the time of image formation in which the recording material P has a thickness of 50 μm or less and a neutralizing bias is applied to the neutralizing needle 91 in order to ensure separation of the recording material P in the secondary transfer portion N2. 56 is applied.

  As described with reference to FIG. 6, when a static elimination bias is applied to the static elimination needle 91, the apparent impedance of the secondary transfer portion N <b> 2 becomes lower than when no neutralization bias is applied. However, the behavior in which the apparent impedance of the secondary transfer portion N2 is lowered becomes more prominent when the potential difference between the secondary transfer roller 56 to which a positive voltage is applied and the static elimination needle 91 to which a negative voltage is applied is large. It is not noticeable if the potential difference is small.

  Therefore, when the current is detected in a state where the neutralizing bias is applied, even if only the current when the first voltage that is the maximum voltage is applied is detected, the accuracy in the PTVC control is not significantly reduced.

  According to the control of the third embodiment, an optimum secondary transfer bias can be set when the static elimination bias is frequently switched according to the thickness of the recording material. In addition, since the current-voltage characteristics can be measured by switching the detection voltage in three stages without applying the neutralizing bias, the optimum secondary transfer bias can be set. Furthermore, by limiting the current detection in a state where the neutralizing bias is applied to only one stage, it is possible to omit the voltage application and current measurement for the second rotation of the secondary transfer roller 56, and the time required for PTVC control. And the productivity of the image forming apparatus 100 is improved.

<Example 4>
In the first to third embodiments, the control for switching between the static elimination bias and the secondary transfer bias in accordance with the thickness of the recording material in the secondary transfer portion of the intermediate transfer type image forming apparatus has been described. However, the present invention can also be applied to a direct transfer type image forming apparatus.

  In the image forming apparatus according to the fourth exemplary embodiment, the black toner image formed on the photosensitive drum is directly transferred onto the recording material by the transfer unit in which the transfer roller is pressed against the photosensitive drum. Even in such a configuration, it is possible to dispose the charge eliminating needle downstream of the transfer unit and to turn on / off the charge eliminating bias applied to the charge eliminating needle in accordance with the separability of the recording material. When the transfer bias applied to the transfer roller during image formation is set by performing PTVC control prior to image formation, the charge removal bias is also applied in PTVC control in accordance with ON / OFF of the charge removal bias during image formation. Turn ON / OFF. Thereby, the transfer bias set by the PTVC control is optimized irrespective of the separation property of the recording material.

<Example 5>
FIG. 9 is an explanatory diagram of PTVC control in the fifth embodiment.

  In the first to fourth embodiments, image formation and PTVC control performed by applying a constant neutralization bias of −3 kV that is constant voltage controlled to the static elimination needle 91 have been described.

  On the other hand, in Example 5, the voltage applied to the static elimination needle 91 according to the measurement voltage so that the potential difference between the secondary transfer roller 56 to which the measurement voltage is applied and the static elimination needle 91 becomes constant. Is changed to execute PTVC control.

  As a result, the leakage current flowing from the secondary transfer roller 56 to the static elimination needle 91 is kept constant, and the error due to the difference in leakage current in the transfer current flowing through the secondary transfer portion N2 and involved in the transfer of the toner image is offset. Yes. Even when the voltage applied to the secondary transfer roller 56 at the time of image formation varies greatly, the secondary transfer bias 56 is applied to the secondary transfer roller 56 without any excess or deficiency while keeping the leakage current constant. .

  As shown in FIG. 9 with reference to FIG. 3, the constant voltage controlled measurement voltage output from the transfer power source D2 is switched to three stages of the first voltage V1, the second voltage V2, and the third voltage V3, The PTVC control applied to the secondary transfer roller 56 is executed.

  The first voltage V1, the second voltage V2, and the third voltage V3 are applied for each round of the secondary transfer roller 56, and the current detection circuit 121 detects each current. At this time, the neutralization biases Vc1, Vc2, and Vc3 are applied to the static elimination needle 91 so that the potential difference between the first voltage V1, the second voltage V2, and the third voltage V3 becomes a constant value. As the detection current, currents I1, I2, and I3 (marked with ● in the figure) detected when the first, second, and third voltages are applied are plotted.

  The secondary transfer bias Vb corresponding to the target current Ib is interpolated using the three pieces of V-I data V1-I1, V2-I2, and V3-I3. At the same time, the neutralization bias Vcb corresponding to the secondary transfer bias Vb is interpolated using the three V-Vc data of V1-Vc1, V2-Vc2, and V3-Vc3.

  At the time of image formation, the secondary transfer bias Vb is applied to the secondary transfer roller 56 with the static elimination bias Vcb applied to the static elimination needle 91, and the toner image is secondarily transferred to the recording material P.

  In Example 5, the voltages shown in Table 1 were applied to the charge removal needle 91 during PTVC control according to the first voltage V1, the second voltage V2, and the third voltage V3.

  In the control of the fifth embodiment, in order to deal with a wide variety of recording materials P, the optimum separation performance of the recording material P is achieved in the process in which the toner image is transferred and the recording material P is separated in the secondary transfer portion N2. Demonstrated.

It is explanatory drawing of a structure of the image forming apparatus of 1st Embodiment. It is explanatory drawing of a structure of an image formation part. It is explanatory drawing of a structure of a secondary transfer part and a static elimination needle. 6 is a flowchart of control for setting a secondary transfer bias. It is explanatory drawing of PTVC control which sets a secondary transfer bias. It is explanatory drawing of the transfer electric field at the time of applying a static elimination bias to a static elimination needle. FIG. 6 is an explanatory diagram of a recording material feeding device in Embodiment 2. It is explanatory drawing of ATCV control in Example 3. FIG. It is explanatory drawing of PTVC control in Example 5. FIG.

Explanation of symbols

1a, 1b, 1c, 1d Photosensitive drums 2a, 2b, 2c, 2d Charging rollers 3a, 3b, 3c, 3d Exposure devices 4a, 4b, 4c, 4d Developing device 7 Fixing device 8 Recording material feeding device 51 Image carrier ( Intermediate transfer belt)
52 Driving roller 53 Tension roller 54 Opposing rollers 55a, 55b, 55c, 55d Primary transfer roller 56 Transfer member (secondary transfer roller)
81 Recording material cassette 91 Static elimination needle 92 Static elimination needle holder D2 Transfer power supply D5 Static elimination power supply 121 Current detection circuit

Claims (4)

An image carrier;
Toner image forming means for forming a toner image on the image carrier;
A transcription member you transferred to the transfer material a toner image formed on the image bearing member,
Rolling than the transfer member in the direction of movement of Utsushizai positioned downstream, and neutralizing member for rolling neutralizes the Utsushizai,
A transfer power source for outputting a voltage applied to the transfer member;
A static elimination power source that outputs a voltage to be applied to the static elimination member ;
A setting unit for applying a test voltage to the transfer member and setting a transfer voltage to be applied to the transfer member during image formation;
Judging means for judging the basis weight of the transfer material used ,
The setting unit, when the basis weight of the transfer material used is a predetermined value or less of the thin paper, the applied test voltage before Symbol transfer member in a state where the neutralization power is applied a voltage to the charge removing member set preferences transfer voltage, if the basis weight of the transfer material to be used is larger than the predetermined value, characterized in that the neutralizing power to set the transfer voltage in a state where no voltage is applied to the charge removing member An image forming apparatus. Before Symbol setting unit claims, characterized in that the voltage applied to the charge removing member for each of a plurality of different test voltage applied to the transfer member to control the neutralization power to have a predetermined potential difference Item 2. The image forming apparatus according to Item 1 . The setting unit sets the transfer voltage when setting the transfer voltage based on a voltage-current characteristic obtained by measuring a current flowing through the transfer member when a plurality of different test voltages are applied to the transfer member. only the maximum voltage of the test voltage, and a current flowing through the transfer member when no voltage is applied to the charge eliminating member and the current flowing through the transfer member in the case of applying a voltage to the charge removing member, is measured The image forming apparatus according to claim 2 . The setting unit, an image forming apparatus according to any one of claims 1 to 3, characterized in that outputs the voltage of the charge eliminating power supply to be applied to the charge eliminating member in the constant voltage control.

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