Discharging device and medium processing device

Abstract

The present invention provides a static eliminator and a medium processing device. The static eliminator includes: a first static elimination member that contacts a medium to be conveyed; a second static elimination member that sandwiches the medium between the second static elimination member and the first static elimination member; and a power source that applies a voltage to at least one of the first static elimination member and the second static elimination member, wherein at least one of the first static elimination member and the second static elimination member has an elastomer.

Description

Technical Field

[0001] The present disclosure relates to a static eliminator for removing static electricity from a medium and a medium processing apparatus. Background Art

[0002] As such a conventional static eliminator, for example, static eliminators described in Japanese Unexamined Patent Application Publication No. 2016-157011, U.S. Patent Publication No. US8,320,817B2, Japanese Unexamined Patent Application Publication No. 2017-111329, and Japanese Patent No. 6481219 are known.

[0003] Japanese Unexamined Patent Application Publication No. 2016-157011 discloses an image forming system having: a charge control unit that charges a medium on which an image is formed by an image forming unit in order to suppress adhesion between media; and a current application control unit that controls a current supplied to the charge control unit according to the temperature of the medium.

[0004] U.S. Patent Publication No. US8,320,817B2 discloses a static eliminator that removes static electricity from the surface of a charged sheet by a contact-type static elimination member and removes static electricity from the back surface of the charged sheet by a non-contact-type static elimination member.

[0005] Japanese Unexamined Patent Application Publication No. 2017-111329 discloses an image forming system having: a static elimination member that removes static electricity from a medium; a voltage application unit that applies a static elimination voltage to the static elimination member so that a static elimination current for removing static electricity from the medium flows through the medium; and a control unit that changes the conveyance speed of the medium when applying the static elimination voltage to the static elimination member, and changes the static elimination voltage according to the change in the conveyance speed, thereby changing the static elimination current flowing through the medium.

[0006] Japanese Patent No. 6481219 discloses a static eliminator configured to have: a plurality of first discharge electrodes that face one surface of a sheet, are arranged on a straight line substantially perpendicular to the moving direction of the sheet, and apply a DC voltage; and a plurality of second discharge electrodes that face the first discharge electrodes with the sheet therebetween, are arranged on a straight line substantially perpendicular to the moving direction of the sheet, and apply a DC voltage. The first and second discharge electrodes make the polarities of the adjacent discharge electrodes opposite to each other, and make the polarities of the opposing first and second discharge electrodes opposite to each other, so that positive ions and negative ions are mixed between the adjacent discharge electrodes. Summary of the Invention

[0007] The technical problem to be solved by the present disclosure is to provide an electrostatic elimination device and a medium processing device using the electrostatic elimination device that suppress electrostatic elimination unevenness in the cross direction intersecting the medium conveyance direction as compared with the case where the surfaces of the electrostatic elimination members for holding the medium are all made of metal products.

[0008] According to a first aspect of the present disclosure, there is provided an electrostatic elimination device including: a first electrostatic elimination member that contacts a medium to be conveyed; a second electrostatic elimination member that holds the medium between the second electrostatic elimination member and the first electrostatic elimination member; and a power source that applies a voltage to at least one of the first electrostatic elimination member and the second electrostatic elimination member, wherein at least one of the first electrostatic elimination member and the second electrostatic elimination member has an elastic body.

[0009] According to a second aspect of the present disclosure, both the first electrostatic elimination member and the second electrostatic elimination member have elastic bodies.

[0010] According to a third aspect of the present disclosure, at least one of the surfaces of the first electrostatic elimination member and the second electrostatic elimination member that contacts the medium has a curved surface portion.

[0011] According to a fourth aspect of the present disclosure, at least one of the first electrostatic elimination member and the second electrostatic elimination member is a rotating member.

[0012] According to a fifth aspect of the present disclosure, the medium is electrostatically eliminated in such a manner that the distribution of positive charges and negative charges on the surface after electrostatic elimination becomes uneven compared with that before electrostatic elimination.

[0013] According to a sixth aspect of the present disclosure, the medium is electrostatically eliminated in such a manner that the proportion of the charge that was dominant before electrostatic elimination in the distribution of surface charges after electrostatic elimination increases.

[0014] According to a seventh aspect of the present disclosure, the electrostatic elimination device has a control member that controls the applied voltage of the power source according to the surface potential of at least one of the medium before and after electrostatic elimination.

[0015] According to an eighth aspect of the present disclosure, the control member controls the applied voltage of the power source according to the surface potential of at least one of the medium before electrostatic elimination.

[0016] According to a ninth aspect of the present disclosure, the control member controls the applied voltage of the power source according to the surface potential of at least one of the medium after electrostatic elimination.

[0017] According to a tenth aspect of the present disclosure, the Asker C hardness of the electrostatic elimination member having the elastic body is 60 degrees or more and 80 degrees or less.

[0018] According to an eleventh aspect of the present disclosure, the volume resistivity of the electrostatic elimination member having the elastic body is 10 6Above Ω·cm and 10 8 Ω·cm or less.

[0019] According to the 12th aspect of the present disclosure, there is provided a charge removing device having: a contact type charge removing member having: a first charge removing part that contacts a medium to be conveyed; a second charge removing part that sandwiches the medium between the second charge removing part and the first charge removing part; and a power source that applies a voltage to at least one of the first charge removing part and the second charge removing part, at least one of the first charge removing part and the second charge removing part having an elastomer; and a non-contact type charge removing member that is disposed at a position downstream of the contact type charge removing member in the conveyance direction of the medium to remove the remaining charge of the medium that has been charge-removed by the contact type charge removing member in a non-contact state.

[0020] According to the 13th aspect of the present disclosure, the charge removing device has: a power source that applies a voltage to the non-contact type charge removing member; and a control member that controls the applied voltage of the power source that applies a voltage to at least one of the first charge removing part and the second charge removing part according to the surface potential of at least one of before and after charge removal of the medium, and does not control the applied voltage of the power source of the non-contact type charge removing member.

[0021] According to the 14th aspect of the present disclosure, there is provided a medium processing device having: a conveyance member that conveys a medium; a charging member that is disposed in the middle of the conveyance path of the medium to charge the medium; and a charge removing device that is disposed at a position downstream of the charging member in the conveyance direction of the medium to remove the charge of the medium charged by the charging member.

[0022] According to the 15th aspect of the present disclosure, the charging member is a transfer member that transfers an image by sandwiching the medium between paired transfer parts, and the contact pressure of the medium between the first charge removing part and the second charge removing part constituting the charge removing device is lower than the contact pressure of the medium between the paired transfer parts.

[0023] According to the 16th aspect of the present disclosure, the medium processing device has a medium turning member at a position upstream of the charge removing device in the conveyance direction of the medium, and the medium processing device has a switching member that switches the polarity of the applied voltage of the power source according to the presence or absence of turning of the medium by the medium turning member.

[0024] (Effect)

[0025] According to the 1st aspect, compared with the case where the surfaces of the charge removing parts that sandwich the medium are all made of metal, uneven charge removal in the cross direction intersecting the conveyance direction of the medium can be suppressed.

[0026] According to the second aspect, compared with the case where only one charge removal member has an elastic body, uneven charge removal in the cross direction of the medium can be more suppressed.

[0027] According to the third aspect, uneven charge removal in the cross direction of the medium can be suppressed without impairing the transportability of the medium.

[0028] According to the fourth aspect, the transportability of the medium can be maintained well, and uneven charge removal in the cross direction of the medium can be suppressed.

[0029] According to the fifth aspect, the surface potential of the medium during measurement using a surface potentiometer can be significantly reduced.

[0030] According to the sixth aspect, deviation in the distribution of charges on the surface of the medium after charge removal can be suppressed.

[0031] According to the seventh aspect, compared with the case of uniformly using the applied voltage of the power supply, the optimal voltage during charge removal can be set.

[0032] According to the eighth aspect, charge removal can be performed by feedback controlling the applied voltage of the power supply from the first sheet of the medium.

[0033] According to the ninth aspect, without using a surface potentiometer to measure the high potential, charge removal can be performed by feedback controlling the applied voltage of the power supply for the second and subsequent sheets of the medium.

[0034] According to the tenth aspect, the clamping state of clamping the medium by the first and second charge removal members can be stabilized, so that the charge removal characteristics in the cross direction of the medium are substantially uniform.

[0035] According to the eleventh aspect, compared with the case where the volume resistivity is less than 10 6 Ω·cm, the discharge between the first and second charge removal members can be stabilized, and compared with the case where the volume resistivity exceeds 10 8 Ω·cm, discharge can be implemented without excessive voltage.

[0036] According to the twelfth aspect, compared with the case of not using a non-contact type charge removal member, uneven charges on the medium generated during charge removal by the contact type charge removal member can be removed.

[0037] According to the thirteenth aspect, without complicating the control of the non-contact type charge removal member, good charge removal can be achieved by controlling only the contact type charge removal member that determines a larger charge removal effect.

[0038] According to the 14th aspect, a medium processing apparatus including a charge removing device can be constructed, which can suppress charge removal unevenness in a direction crossing the conveyance direction of the medium as compared with the case where the surfaces of the charge removing members holding the medium are all made of metal.

[0039] According to the 15th aspect, charge removal unevenness in the direction crossing the medium can be suppressed without degrading the image quality formed on the medium.

[0040] According to the 16th aspect, charge removal can be performed on the medium regardless of whether the medium is flipped by a medium flipping mechanism. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 FIG. (a) is an explanatory diagram schematically showing an embodiment of a medium processing apparatus using a charge removing device to which the present disclosure is applied. Figure 1 FIG. (b) shows Figure 1 FIG. (a) shows a main part of the contact type charge removing member shown in FIG. (a).

[0042] Figure 2 FIG. (a) is an explanatory diagram schematically showing an example of the charge distribution of a plurality of media stacked on a medium discharge receiving portion in a scheme where the charge removing device of the image forming apparatus according to Embodiment 1 is not used. Figure 2 FIG. (b) is an explanatory diagram showing the operation of the charge removing device. Figure 2 FIG. (c) is an explanatory diagram schematically showing an example of the charge distribution of a plurality of media stacked on a medium discharge receiving portion in a scheme where the charge removing device is used.

[0043] Figure 3 FIG. is an explanatory diagram showing the overall structure of the image forming apparatus according to Embodiment 1.

[0044] Figure 4 FIG. is an explanatory diagram showing a structural example around the secondary transfer portion and the charge removing portion of the image forming apparatus according to Embodiment 1.

[0045] Figure 5 FIG. (a) is an explanatory diagram showing a structural example of the contact type charge remover used in Embodiment 1. Figure 5 FIG. (b) is an explanatory diagram showing another structural example of the contact type charge remover used in Embodiment 1. Figure 5 FIG. (c) shows a state when the charge removing operation by the contact type charge remover shown in FIG. (b) is not performed. Figure 5 FIG. (b) is an explanatory diagram showing the state when the charge removing operation by the contact type charge remover shown in FIG. (b) is not performed.

[0046] Figure 6 FIG. (a) is an explanatory diagram schematically showing the charge removing operation by the contact type charge remover. Figure 6(b) is an explanatory diagram showing the tendency of the charging state of the medium accompanying the static elimination operation by this contact-type static eliminator. Figure 6 (c) is a schematic explanatory diagram showing the static elimination operation by the non-contact-type static eliminator. Figure 6 (d) is an explanatory diagram showing the tendency of the charging state of the medium accompanying the static elimination operation by the non-contact-type static eliminator.

[0047] Figure 7 (a) is an explanatory diagram showing an example of the charging state of the medium. Figure 7 (b) is an explanatory diagram showing the principle of the static elimination operation by the contact-type static eliminator. Figure 7 (c) is an explanatory diagram showing the principle of the static elimination operation by the non-contact-type static eliminator.

[0048] Figure 8 is a flowchart showing the imaging control processing procedure of the image forming apparatus according to Embodiment 1.

[0049] Figure 9 (a) shows Figure 8 an example of the "method for determining the static elimination method" shown. Figure 9 (b) is an explanatory diagram showing an example of measuring the surface resistance of the medium.

[0050] Figure 10 is a schematic explanatory diagram showing the static elimination operation process by the static eliminator in Embodiment 1.

[0051] Figure 11 (a) is an explanatory diagram showing the structure of the charging roller with a paired structure of the contact-type static eliminator according to Embodiment 1. Figure 11 (b) shows Figure 11 the contact state of the charging roller with a paired structure in part B of (a) in contact with the medium. Figure 11 (c) is an explanatory diagram showing the contact state of the charging roller with a paired structure in contact with the medium in the axial direction.

[0052] Figure 12 (a) is an explanatory diagram showing the significance of the contact between the charging roller with a paired structure and the medium and its contact pressure. Figure 12 (b) is an explanatory diagram showing an example of the measurement method of the volume resistivity of the charging roller.

[0053] Figure 13 (a) is an explanatory diagram showing an example of the setting of the surface potentiometer for measuring the surface potential of the medium. Figure 13 (b) is an explanatory diagram showing the positional relationship between the surface potentiometer and the medium.

[0054] Figure 14It is a flowchart showing an example of the charge removal bias control of a contact type charge remover.

[0055] Figure 15 (a) of is an explanatory diagram showing the charge change of the medium accompanying the charge removal operation by the contact type charge remover. Figure 15 (b) of is an explanatory diagram schematically showing the charged state of the medium surface before and after charge removal by the contact type charge remover.

[0056] Figure 16 (a) of is an explanatory diagram showing an example of the setting of the surface potentiometer relative to the contact type charge remover. Figure 16 (b) of is an explanatory diagram showing an example of a method for selecting the initial optimum value of the charge removal bias using a surface potentiometer set at a position downstream of the contact type charge remover in the conveyance direction of the medium. Figure 16 (c) of is an explanatory diagram showing an example of the measurement line obtained by this method.

[0057] Figure 17 (a) of is an explanatory diagram schematically showing the movement of charges from the discharge wire accompanying the corona discharge of the non-contact type charge remover. Figure 17 (b) of is an explanatory diagram showing an example of the voltage-current characteristics of the corona discharge. Figure 17 (c) of is an explanatory diagram schematically showing the ion balance of the AC corona tube (using an AC discharge bias).

[0058] Figure 18 (a) of is an explanatory diagram schematically showing an example of the ion generation operation in the non-contact type charge remover with a counter electrode. Figure 18 (b) of is an explanatory diagram schematically showing an example of the ion generation operation in the non-contact type charge remover without a counter electrode. Figure 18 (c) of is an explanatory diagram showing the charge removal process of the surface potential of the medium in the case of using an AC charge removal bias. Figure 18 (d) of is an explanatory diagram showing the charge removal process of the surface potential of the medium in the case of using a DC charge removal bias.

[0059] Figure 19 (a) of is a flowchart showing an example of the charge removal bias control of the non-contact type charge remover. Figure 19 (b) of is an explanatory diagram showing an example of a method for determining the frequency f of the charge removal bias Vd2.

[0060] Figure 20 is an explanatory diagram showing the main part of the image forming apparatus according to Embodiment 2.

[0061] Figure 21 is an explanatory diagram showing an example of the structure around the charge removal unit of the image forming apparatus according to Embodiment 2.

[0062] Figure 22 (a) of [Figure number] shows an explanatory diagram of the charge removal operation performed by a contact type charge remover without medium inversion. Figure 22 (b) of [Figure number] shows an explanatory diagram of the charge removal operation performed by a contact type charge remover with medium inversion.

[0063] Figure 23 (a) of [Figure number] shows an explanatory diagram of the main part of a non-contact type charge remover in Modification 1. Figure 23 (b) of [Figure number] shows... Figure 23 (a) of [Figure number] shows an explanatory diagram of an example of the shielding part observed from the B direction in Figure 23 (c) of [Figure number] shows an explanatory diagram of the function of the shielding part.

[0064] Figure 24 (a) of [Figure number] shows an explanatory diagram of the main part of a non-contact type charge remover in Modification 2. Figure 24 (b) of [Figure number] shows from Figure 24 (a) of [Figure number] shows a front view of the non-contact type charge remover observed from the B direction in Figure 24 (c) of [Figure number] shows... Figure 24 (c) of [Figure number] shows an explanatory diagram of a modification example of the non-contact type charge remover shown in (b).

[0065] Figure 25 (a) of [Figure number] shows an explanatory diagram of the waterfall development method for visualizing the surface charge distribution of the medium in Example 1. Figure 25 (b) of [Figure number] shows an explanatory diagram of an example of visualizing the surface charge distribution of the medium before charge removal, after passing through a contact type charge remover, and after passing through a non-contact type charge remover by the waterfall development method.

[0066] Figure 26 (a) of [Figure number] shows a graph of the relationship between the applied voltage based on constant voltage control and the potential after charge removal in the contact type charge remover related to Example 2. Figure 26 (b) of [Figure number] shows a graph of the relationship between the applied current based on constant current control and the potential after charge removal in the contact type charge remover related to Example 2.

[0067] Figure 27 (Figure number) shows an explanatory diagram of the relationship between the medium clamping variation of the charge removal roller based on the paired structure and the charge removal control stability in Example 3.

[0068] Figure 28 (a) of [Figure number] shows an explanatory diagram of the relationship between f / v as a charge removal parameter and its evaluation result in the non-contact type charge remover in Example 4. Figure 28 (b) of [Figure number] shows an explanatory diagram of an example of the assigned frequency f as a charge removal parameter. Figure 28(c) is an explanatory diagram showing an example of the distribution of the charge removal parameters f (frequency) / v (medium conveyance speed). Figure 28 (d) is an explanatory diagram showing an example of the distribution of the charge removal parameters f (frequency) / v (medium conveyance speed)*L (housing opening width).

[0069] Figure 29 (a) is an explanatory diagram showing the evaluation method of Example 4. Figure 29 (b) shows Figure 29 an explanatory diagram showing the relationship between the frequency and the tensile load in the evaluation method of (a).

[0070] Figure 30 (a) is an explanatory diagram showing an example of the surface charge distribution of the medium after charge removal when the charge removal parameters f (frequency) / v (medium conveyance speed) of the non-contact type charge remover according to Example 5 are above a specified value. Figure 30 (b) is an explanatory diagram showing an example of the surface charge distribution of the medium after charge removal when the charge removal parameter f / v is less than the specified value.

[0071] Figure 31 is an explanatory diagram showing the relationship between the electrode distance (corresponding to the distance between the discharge wire and the medium) and the charge amount (corresponding to the surface charge amount of the medium) in the non-contact type charge remover according to Example 6. Detailed implementation mode

[0072] ◎ Outline of the implementation mode

[0073] Figure 1 (a) shows an outline of the implementation mode of the medium processing device using the charge removal device applicable to the present disclosure.

[0074] In Figure 1 (a), the medium processing device includes: a conveyance member 13 that conveys the medium S; a charging member 14 that is provided in the middle of the conveyance path of the medium S and charges the medium S; and a charge removal device 10 that is provided at a position downstream of the charging member 14 in the conveyance direction of the medium S and removes the charge of the medium S charged by the charging member 14.

[0075] Here, the medium processing device is not limited to an image forming device having an image forming unit, and also includes a solution without an image forming unit. And the charging member 14 includes not only a transfer member that applies a transfer voltage, but also a conveyance member that charges the medium S by friction when conveying the medium S.

[0076] In this example, as Figure 1As shown in (b) of FIG. 0, the static eliminator device 10 includes: a contact-type static eliminator member 11 having a first static elimination member 1 that contacts the medium S to be conveyed, a second static elimination member 2 that sandwiches the medium S between the second static elimination member 2 and the first static elimination member 1, and a power source 3 that applies a voltage to at least one of the first static elimination member 1 or the second static elimination member 2. At least one of the first static elimination member 1 and the second static elimination member 2 has an elastomer 4; and a non-contact-type static eliminator member 12 that is disposed at a position downstream of the contact-type static eliminator member 11 in the conveyance direction of the medium S to eliminate the residual charge of the medium S that has been statically eliminated by the contact-type static eliminator member 11 in a non-contact state.

[0077] In such a technical component, the first static elimination member 1 and the second static elimination member 2 are not limited to rotating members (rollers), and widely include the following solutions: even if they are fixed members, for example, a contact surface with the medium S is formed on the curved surface portion to contact the medium S in a manner capable of conveying the medium S.

[0078] Moreover, the first static elimination member 1 and the second static elimination member 2 are non-contact when the medium does not pass through, but include the solution of contacting the medium S when the medium S passes through.

[0079] Furthermore, regarding the application voltage control of the power source 3, even though a static elimination effect can be obtained through constant current control, constant voltage control is preferably used. And a DC voltage is used as the applied voltage.

[0080] In addition, since at least one of the first static elimination member 1 and the second static elimination member 2 has an elastomer 4, when the medium S passes between the first static elimination member 1 and the second static elimination member 2, at least the first static elimination member 1 or the second static elimination member 2 having the elastomer 4 makes surface contact with the surface of the medium S and maintains the contact state with the surface of the medium S.

[0081] In particular, even in the crossing direction of the first static elimination member 1 and the second static elimination member 2 that crosses the conveyance direction of the medium S, the contact state with the medium S can be maintained through the elastic deformation of the elastomer 4, so that the static elimination unevenness in the crossing direction with respect to the medium S can be suppressed.

[0082] And in this example, the following effects are obtained: significant static elimination is performed by the contact-type static eliminator member 11, and the amount of static elimination is evenly leveled by the non-contact-type static eliminator member 12.

[0083] If we assume a case where the static elimination process by the static eliminator device (contact-type static eliminator member 11, non-contact-type static eliminator member 12) of this example is not performed, as Figure 2As shown in (a) of FIG. 0, for example, the surface potential of the high-resistance dielectric S such as a resin film has a - potential, and the back potential of the dielectric S becomes a reversed + potential due to dielectric polarization. If such dielectrics S are stored in a stacked state, there is a possibility that the dielectrics S adhere to each other due to electrostatic force.

[0084] However, if the static elimination treatment is performed by the static eliminator 10 (contact type static elimination member 11, non-contact type static elimination member 12) of this example, as Figure 2 shown in (b) of FIG. 0, even if a high-resistance dielectric S is used, it is possible to significantly eliminate the charging on the surface of the dielectric S by the contact type static elimination member 11 and the non-contact type static elimination member 12. Along with this, the charging on the back surface of the dielectric S is also significantly eliminated. Therefore, as Figure 2 shown in (c) of FIG. 0, even if the dielectrics S are stored in a stacked state, the concern that the dielectrics S adhere to each other due to electrostatic force can be eliminated.

[0085] Next, a representative or preferred embodiment of the contact type static elimination member 11 in particular among the static eliminators 10 according to this embodiment will be described.

[0086] First, regarding the preferred embodiments of the first static elimination member 1 and the second static elimination member 2, a case where both the first static elimination member 1 and the second static elimination member 2 have an elastomer 4 is cited. This is for the following reason: Compared with the case where only one static elimination member has an elastomer 4, it is easier to maintain the contact state with the two surfaces (corresponding to the front and back surfaces) of the dielectric S in the crossing direction of the dielectric S.

[0087] Moreover, it is preferably a case where at least one of the surfaces of the first static elimination member 1 and the second static elimination member 2 that contact the dielectric S has a curved surface portion. This is for the following reason: Since the sliding resistance between the curved surface portion of the first static elimination member 1 or the second static elimination member 2 and the dielectric S is small, there is less concern about impairing the transportability of the dielectric S transported by the transport member 13.

[0088] In terms of being able to maintain the transportability of the dielectric S well, a case where at least one of the first static elimination member 1 and the second static elimination member 2 is a rotating member is particularly preferred.

[0089] Furthermore, regarding the hardness of the first static elimination member 1 or the second static elimination member 2, it is preferably that the Asker C hardness of the static elimination member 1 or the static elimination member 2 having the elastomer 4 is 60 degrees or more and 80 degrees or less. This example is preferred in terms of stabilizing the clamping state of the dielectric S clamped by the first static elimination member 1 and the second static elimination member 2.

[0090] In addition, regarding the volume resistivity of the first static elimination member 1 or the second static elimination member 2, it is preferably that the volume resistivity of the first static elimination member 1 or the second static elimination member 2 having the elastomer 4 is 106 Above Ω·cm and 10 8 Below Ω·cm. This is for the following reasons: When the volume resistivity is less than 10 6 Ω·cm, it is difficult to discharge, and if the volume resistivity exceeds 10 8 Ω·cm, an excessive voltage required for discharging is needed.

[0091] Moreover, as a preferable charge removal operation by the contact type charge removal member 11, a method of charging the dielectric S in such a manner that the distribution of positive and negative charges in the surface after charging becomes uneven compared to that before charging is cited. In this example, it is sufficient to apply a voltage with a polarity that cancels the surface potential of the dielectric S, but it is preferable to select the potential level so that the surface potential after charging approaches approximately 0.

[0092] More preferably, a method of charging the dielectric S in such a manner that the proportion of the dominant charge in the surface charge distribution after charging becomes larger is cited. Assuming that the charging is performed in such a manner that the proportion of the dominant charge before charging becomes smaller, a large amount of charges of different polarities are distributed, and the distribution of the charges on the surface of the dielectric after charging is likely to deviate.

[0093] Furthermore, although the applied voltage of the power supply 3 can be uniformly used, from the viewpoint of applying the optimal voltage during charging, a method having a control member 6 that controls the applied voltage of the power supply 3 based on the surface potential of at least one of before and after charging of the dielectric S can be cited. In this example, it is sufficient to provide a surface potentiometer 5 on at least one of before and after charging by the contact type charge removal member 11 and measure the surface potential of the dielectric S by the surface potentiometer 5.

[0094] At this time, the control member 6 can control the applied voltage of the power supply 3 based on the surface potential of at least one of before charging of the dielectric S or control the applied voltage of the power supply 3 based on the surface potential of at least one of after charging of the dielectric S. In the former method, the applied voltage of the power supply 3 can be feedback controlled from the first dielectric S, and in the latter method, the applied voltage of the power supply 3 can be feedback controlled from the second dielectric S. Since the surface potential of the dielectric S after charging is measured, it is not necessary to consider measuring a high potential as the surface potentiometer 5.

[0095] Moreover, regarding the control member 6, although the applied voltage of the power supply 15 of the non-contact type charge removal member 12 can be controlled, in this example, since the object of the charge removal operation by the non-contact type charge removal member 12 is the surface charge of the dielectric S remaining after charging by the contact type charge removal member 11, the surface potential of the dielectric S that is initially the object of charging is small, and the necessity of controlling the applied voltage of the power supply 15 by the control member 6 is small. Therefore, from the viewpoint of further simplifying the control system, a method of not controlling the applied voltage of the power supply 15 is adopted.

[0096] Further, regarding the contact type static eliminator member 11, for example, in a case where the charged member 14 is a transfer member that transfers an image by sandwiching a medium S between transfer members of a paired structure, the medium contact pressure (clamping pressure) between the first static eliminator member 1 and the second static eliminator member 2 can be set lower than the medium contact pressure between the transfer members of the paired structure. This is because, when it is a transfer member, as the medium contact pressure between the transfer members of the paired structure, image transferability is required, and accordingly, the medium contact pressure needs to be set relatively high to some extent. However, regarding the medium contact pressure between the first static eliminator member 1 and the second static eliminator member 2, there is no necessary condition such as a transfer member. As long as the contact state with the medium S is maintained, the static elimination operation can be performed. Therefore, the medium contact pressure can also be selected to be low. Moreover, by suppressing the clamping pressure between the first static eliminator member 1 and the second static eliminator member 2 to be lower than the medium contact pressure between the transfer members, excessive load on the first static eliminator member 1 or the second static eliminator member 2 can be suppressed, thereby suppressing wear or deformation.

[0097] Moreover, in a case where there is a medium turning member ( Figure 1 not shown in the figure) at a position upstream of the static eliminator device 10 in the conveyance direction of the medium S, it is preferable to have a switching member ( Figure 1 not shown in the figure) that switches the polarity of the applied voltage of the power supply 3 according to the presence or absence of turning the medium by the medium turning member.

[0098] Hereinafter, the present disclosure will be described in more detail based on the embodiments shown in the drawings.

[0099] ◎ Embodiment 1

[0100] Figure 3 The overall structure of the image forming apparatus according to Embodiment 1 is shown.

[0101] - Overall Structure of Image Forming Apparatus -

[0102] In Figure 3In [the device], the image forming apparatus 20 includes, within the image forming apparatus housing 21: an image forming unit 22 (specifically 22a to 22f), which forms images of multiple color components (in this embodiment, white #1, yellow, magenta, cyan, black, white #2); a belt-shaped intermediate transfer member 30, which sequentially transfers (primary transfer) and holds the images of the respective color components formed by each image forming unit 22; a secondary transfer device 50, which secondarily transfers the images of the respective color components transferred onto the intermediate transfer member 30 onto the medium S; a fixing device 70, which fixes the secondarily transferred images onto the medium S; and a medium conveyance system 80, which conveys the medium S to the secondary transfer area. Additionally, in this example, white #1 and white #2 use exactly the same white material, but different white materials may also be used depending on whether it is located in a position lower than the other color component images on the medium S or in a position higher than the other color component images, and for example, transparent color materials may be used instead of white #1 and white #2, and of course, other special color materials may also be used.

[0103] -Image Forming Unit-

[0104] In this embodiment, each image forming unit 22 (22a to 22f) respectively includes a drum-shaped photoreceptor 23, and the following devices are respectively disposed around each photoreceptor 23: a charging device 24 such as a corona tube or a transfer roller, which charges the photoreceptor 23; an exposure device 25 such as a laser scanning device, which writes an electrostatic latent image on the charged photoreceptor 23; a developing device 26, which develops the electrostatic latent image written on the photoreceptor 23 using toner of each color component; a primary transfer device 27 such as a transfer roller, which transfers the toner image on the photoreceptor 23 onto the intermediate transfer member 30; and a photoreceptor cleaning device 28, which removes the residual toner on the photoreceptor 23.

[0105] Moreover, the intermediate transfer member 30 is mounted on multiple tension rollers 31 to 33. For example, the tension roller 31 serves as a driving roller driven by a driving motor (not shown in the figure), and the intermediate transfer member 30 moves in a cycle through this driving roller. Also, an intermediate transfer member cleaning device 35 for removing the residual toner on the intermediate transfer member 30 after secondary transfer is provided between the tension rollers 31 and 33.

[0106] -Secondary Transfer Device-

[0107] Moreover, as Figure 3 and Figure 4 shown, the secondary transfer device 50 is configured such that a belt transfer module 51 with a transfer conveyor belt 53 tensioned and mounted on multiple tension rollers 52 (specifically 52a and 52b) contacts the surface of the intermediate transfer member 30.

[0108] Here, the transfer conveyor belt 53 is a semiconductive belt made of materials such as chloroprene, with a volume resistivity of 10 6 ~10 12 Ω·cm. One tension roller 52a is configured as an elastic transfer roller 55. The elastic transfer roller 55 is press-fitted and arranged in the secondary transfer area TR of the intermediate transfer body 30 via the transfer conveyor belt 53. And the tension roller 33 of the intermediate transfer body 30 is arranged opposite to the elastic transfer roller 55 as a relative roller 56 that constitutes the counter electrode of the elastic transfer roller 55. A conveyance path for the medium S is formed from the position of one tension roller 52a toward the position of the other tension roller 52b.

[0109] Moreover, in this example, the elastic transfer roller 55 has a structure in which an elastic layer containing carbon black or the like in foamed urethane rubber or EPDM is coated around a shaft made of metal.

[0110] Furthermore, the transfer bias voltage Vt from the transfer power supply 58 is applied to the relative roller 56 (which also serves as the tension roller 33 in this example) via the conductive power supply roller 57. On the other hand, the elastic transfer roller 55 (one tension roller 52a) is grounded via a metal shaft not shown in the figure. A specified transfer electric field is formed between the elastic transfer roller 55 and the relative roller 56. In addition, the other tension roller 52b is also grounded to prevent the transfer conveyor belt 53 from being charged. And when considering the peelability of the medium S at the downstream end of the transfer conveyor belt 53, it is effective to make the diameter of the downstream tension roller 52b smaller than the diameter of the upstream tension roller 52a.

[0111] -Fixing device-

[0112] The fixing device 70 includes: a heating fixing roller 71, which is arranged in contact with the image holding surface side of the medium S and can be driven to rotate; and a pressure fixing roller 72, which is press-fitted and arranged opposite to the heating fixing roller 71 and rotates following the heating fixing roller 71, so that the image held on the medium S passes through the press-fitting area between the two fixing rollers 71 and 72, and the image is heat-pressed and fixed. In addition, regarding the fixing method of the fixing device 70, it is not limited to the scheme shown in the embodiment, and fixing methods using non-contact and laser can also be appropriately selected.

[0113] -Medium conveyance system-

[0114] Further, the medium conveyance system 80 includes multi-stage (two-stage in this example) medium supply containers 81 and 82, and causes the medium S supplied from either of the medium supply containers 81 and 82 to reach the secondary transfer area TR via a vertical conveyance path 83 extending substantially in the vertical direction and a horizontal conveyance path 84 extending substantially in the horizontal direction. Thereafter, the medium S holding the transferred image reaches the fixing portion based on the fixing device 70 via the conveyance belt 85 and is discharged to a medium discharge receiving portion 86 provided on the side of the image forming apparatus housing 21.

[0115] In addition, the medium conveyance system 80 includes a branch conveyance path 87 that branches downward from a portion of the horizontal conveyance path 84 located downstream of the fixing device 70 in the medium conveyance direction and is capable of being turned over, causing the medium S turned over in the branch conveyance path 87 to return, and then returning to the horizontal conveyance path 84 from the vertical conveyance path 83 again via the conveyance path 88. The image is transferred to the back surface of the medium S in the secondary transfer area TR and is discharged to the medium discharge receiving portion 86 via the fixing device 70. Further, a medium turning mechanism 89 is provided in the middle of the branch conveyance path 87. The medium turning mechanism 89 turns over the medium S passing through the horizontal conveyance path 84 and discharges it to the medium discharge receiving portion 86. The medium turning mechanism 89 includes a branch return conveyance path 90 that branches from the middle of the branch conveyance path 87 and conveys the turned-over medium S to the side of the medium discharge receiving portion 86. Switching doors 91 and 92 are provided at the boundary between the horizontal conveyance path 84 and the branch conveyance path 87 and at the boundary between the branch conveyance path 87 and the branch return conveyance path 90, respectively, to turn over the medium S passing through the horizontal conveyance path 84 and discharge it to the medium discharge receiving portion 86.

[0116] Moreover, in the medium conveyance system 80, in addition to an alignment roller 93 that supplies the medium S to the secondary transfer area TR in an aligned manner, an appropriate number of conveyance rollers 94 are provided in each of the conveyance paths 83, 84, 87, and 88. Further, a manual feed medium supply device 95 capable of supplying manual feed medium to the horizontal conveyance path 84 is provided on the side of the image forming apparatus housing 21 opposite to the medium discharge receiving portion 86.

[0117] -Basic Structure of the Static Eliminator-

[0118] In the present embodiment, a static eliminator 100 is provided at a position on the horizontal conveyance path 84 from the fixing device 70 to the medium discharge receiving portion 86, upstream of the branch conveyance path 87 passing through the medium turning mechanism 89 in the medium S conveyance direction.

[0119] In this example, the static eliminator device 100 includes: a contact-type static eliminator 101 that contacts the medium S and eliminates more than half of the charges carried by the medium S; and a non-contact-type static eliminator 102 that is disposed at a position downstream of the contact-type static eliminator 101 in the conveyance direction of the medium S and eliminates the remaining charges of the medium S that has been static-eliminated by the contact-type static eliminator 101 in a non-contact state.

[0120] Hereinafter, the contact-type static eliminator 101 and the non-contact-type static eliminator 102 will be described.

[0121] <Contact-Type Static Eliminator>

[0122] As shown in (a) of Figure 3 、 Figure 4 and Figure 5 the contact-type static eliminator 101 arranges the paired static elimination rollers 111 and 112 in contact, transmits the driving force from the driving motor 113 to any one of the static elimination rollers via a driving transmission mechanism 114 such as a gear, and makes the static elimination roller 111 follow by contacting the static elimination roller 112, and clamps the medium S between the static elimination rollers 111 and 112 for conveyance.

[0123] Moreover, in this example, a static elimination power supply 115 is connected to one static elimination roller 111, and a static elimination bias voltage Vd1 (in this example, a positive-polarity DC voltage is used) is applied from the static elimination power supply 115, and the other static elimination roller 112 is grounded.

[0124] In addition, regarding the setting of the static elimination power supply 115, it can be either on the front side or the back side of the surface of the medium S. In the case of being arranged on the back side of the medium S, as long as the static elimination bias voltage and the static elimination current having polarities opposite to those of the static elimination bias voltage and the static elimination current used in the case of being arranged on the front side of the medium S are used.

[0125] In particular, as a solution different from this example, as shown in (b) of Figure 5 、 Figure 5 the contact-type static eliminator 101 is provided with a contact / separation mechanism 116 that makes one static elimination roller 111 contact or separate from the other static elimination roller 112. The contact / separation mechanism 116 used in this example has, for example, a swing arm 117 that swings around a swing fulcrum, supports the static elimination roller 111 at the end side far from the swing fulcrum of the swing arm 117 so as to be rotatable, and swings the swing arm 117 in the clockwise direction or the counterclockwise direction by a drive source 118 such as a driving motor, and arranges the static elimination roller 111 in a non-contact retracted position or a contact position with respect to the static elimination roller 112.

[0126] <Non-Contact-Type Static Eliminator>

[0127] In this example, as shown in Figure 4As shown, the non-contact static eliminator 102 has, for example, a static elimination housing 121 with a channel cross-sectional shape that opens to the surface side of the medium S conveyed along the horizontal conveyance path 84. A discharge wire 122 is installed along the length direction within the static elimination housing 121, and a static elimination power supply 125 is connected to the discharge wire 122. A static elimination bias voltage Vd2 is applied from the static elimination power supply 125 (in this example, an AC power supply 126 that outputs an AC voltage component and a DC power supply 127 that outputs a DC voltage component are used (refer to Figure 6 ). On the other hand, a ground electrode 123 composed of a grounded metal plate is disposed on the back side of the medium S.

[0128] In addition, in this example, a scheme using only one discharge wire 122 is adopted, but it is not limited to this. Multiple discharge wires 122 can also be used. In this example, the so-called corona tube method is adopted, but it is not limited to this. Of course, a scheme of attaching a grid plate as a control electrode to the opening-facing part of the static elimination housing 121 (the so-called back corona method) can also be adopted. Or, a scheme of providing a needle electrode described later instead of the discharge wire 122 can also be used. Regarding the setting of the static elimination power supply 125, it can be on either the surface side or the back side of the medium S, and it can also be set on both sides.

[0129] <Electrostatic elimination characteristics of each static eliminator>

[0130] Here, the electrostatic elimination characteristics of each static eliminator 101 and 102 will be briefly described.

[0131] Now, assume a case where the medium S is a high-resistance (dielectric) such as a resin film. For example, the medium S passing through the secondary transfer device 50 is charged by receiving a transfer electric field. At this time, as Figure 6 (a) of Figure 6 (b) of Figure 7 and (a) of

[0132] Figure 7 Figure 7As shown in (b), corona discharge is caused before and after the contact area (pinch area) CN between one charge removing roller 111 and another charge removing roller 112. In particular, in this example, since the medium S with a relatively high surface potential before charge removal enters the gap on the inlet side (equivalent to the upstream side in the conveyance direction of the medium S) of the contact area CN between the charge removing rollers 111 and 112, a large current discharge Hb is generated in the area far from the contact area CN, and a weak current discharge Hs is generated in the area close to the contact area CN. The two discharges coexist. Since the medium S with a relatively low surface potential after charge removal passes through the gap on the outlet side (equivalent to the downstream side in the conveyance direction of the medium S) of the contact area CN between the charge removing rollers 111 and 112, a weak current discharge Hs is generated in the area close to the contact area CN. As a result, a predetermined amount of positive charge is imparted to the surface of the charged medium S, and an amount of negative charge e- on the surface of the medium S corresponding to the imparted charge amount is eliminated. In this state, as the surface charge of the medium S decreases, the positive charge e+ polarized through the dielectric on the back surface of the medium S also decreases. Therefore, as shown in Figure 6 As shown in (b), the surface potential of the medium S decreases by ΔVc1 in absolute value from Vc1(-). However, since the contact type charge remover 101 can ensure a relatively large charge removal amount by taking the absolute value of ΔVc1 to a certain extent, there is a tendency that the deviation amount of the surface potential of the medium S after charge removal is large and the charge removal is likely to be uneven.

[0133] On the other hand, regarding the charge removal characteristics of the non-contact type charge remover 102, as shown in Figure 6 (c), Figure 6 As shown in (d), when assuming that the surface potential of the medium S is negative Vc2(-), the non-contact type charge remover 102 applies a charge removal bias voltage Vd2 (an AC voltage component superimposed on a DC voltage component) to the discharge wire 122. As shown in Figure 7 (c), AC corona discharge is caused between the discharge wire 122 and the charge removal housing 121, and positive ions (+) and negative ions (-) are generated around the discharge wire 122. As a result, the positive ions (+) and negative ions (-) generated by the corona discharge are attracted by the electric field between them and the medium S and supplied to the surface of the charged medium S, eliminating an amount of negative charge e- on the surface of the medium S corresponding to the supply amount of the positive ions (+), and eliminating an amount of positive charge e+ on the surface of the medium S corresponding to the supply amount of the negative ions (-). And since the back surface of the medium S becomes 0 V through the ground electrode 123, the charge e+ on the back surface of the dielectrically polarized medium S is easily released to the ground electrode 123. Therefore, as shown in Figure 6As shown in (d), the surface potential of the medium S decreases by ΔVc2 in absolute value from Vc2(-), but the non-contact static eliminator 102 cannot ensure the absolute value of ΔVc2 as large as the amount of static elimination. However, the deviation amount of the surface potential of the medium S after static elimination is small, and uniform static elimination can be achieved.

[0134] -Static elimination control system-

[0135] In the present embodiment, as Figure 4 shown, the static eliminator 100 (contact type static eliminator 101, non-contact static eliminator 102) determines whether static elimination is required by means of the static elimination control system 130. When static elimination is required, the static elimination method and conditions are determined, and the static elimination operation is performed.

[0136] In this example, as Figure 4 shown, the static elimination control system 130 includes, for example, a control device 131 composed of a microcomputer. An operation panel 140 of the image forming apparatus 20 and an environment sensor 145 for detecting environmental conditions (such as temperature and humidity) are connected to the control device 131. Further, the control device 131 is selectively connected to the static elimination power supplies 115 and 125 of the respective static eliminators 101 and 102 via selection switches 132 and 133.

[0137] Here, a start switch ( Figure 4 in, "SW" is used to mark "switch", the same applies hereinafter) 141 for starting the imaging process by the image forming apparatus 20, a mode selection switch 142 for selecting various imaging modes (single-sided / double-sided printing mode, standard / high image quality printing mode, etc.), and a physical property indication switch 143 for indicating the physical properties (resistance, thickness, basis weight, size, etc.) of the medium S are provided on the operation panel 140. In addition, regarding the physical properties of the medium S, of course, for example, detectors for detecting the physical properties (resistance, thickness, size, etc.) of the medium S may be provided in the medium supply containers 81 and 82 or the conveyance path, and the physical property information of the medium S is obtained through the detectors.

[0138] -Imaging process of the image forming apparatus-

[0139] Next, the imaging process of the image forming apparatus according to the present embodiment will be described with reference to the Figure 8 flowchart shown.

[0140] First, as Figure 3 and Figure 4As shown, when the start switch 141 is turned on, the image forming apparatus 20 starts printing operation. In this state, the medium S is supplied from the medium supply container 81 or 82 or the manual feed medium supply device 95. On the other hand, in the image forming unit 22, an image forming process of transferring an image to the medium S is performed, and the produced image is moved to the secondary transfer area TR by means of the intermediate transfer body 30.

[0141] After that, the medium S is conveyed to the secondary transfer area TR via the horizontal conveyance path 84, and a transfer operation by the secondary transfer device 50 is performed. After that, the medium S with the transferred image passes through the fixing device 70, and the image is fixed on the medium S. The medium S with the image fixed thereon faces the static elimination device 100.

[0142] In this state, the control device 131 reads the physical property information (such as the medium type) of the medium S according to the instruction information of, for example, the physical property instruction switch 143 from the operation panel 140, and determines whether static elimination based on the static elimination device 100 is required. As this determination method, for example, it is observed from the physical property information (such as the medium type) of the medium S whether the surface resistance of the medium S is at a level that requires static elimination (for example, 10 11 Ω / □) or more. In the case of the medium S at a level that requires static elimination, it can be determined that static elimination is required. However, it is not necessary to judge the surface resistance of the medium S as an internal process, and it can also be determined that static elimination is required only according to the information of the medium type.

[0143] In this example, in the above-described determination process of whether static elimination is required, if it is determined that static elimination is required, the medium S is conveyed after passing through the static elimination process based on the static elimination device 100. If it is determined that static elimination is not required, the medium S is not subjected to the static elimination process based on the static elimination device 100 and is conveyed to the medium discharge receiving portion 86.

[0144] Here, in the present embodiment, in the case of the scheme shown in (a) where the contact type static eliminator 101 is Figure 5 , the static elimination rollers 111 and 112 remain in a contact state regardless of whether static elimination is required. However, in this example, in the case where static elimination is required, a static elimination bias voltage Vd1 is applied, and in the case where static elimination is not required, the static elimination bias voltage Vd1 is not applied.

[0145] On the other hand, in the case of the schemes shown in (b) and Figure 5 (c) where the contact type static eliminator 101 is Figure 5 , in the case where static elimination is required, the paired static elimination rollers 111 and 112 remain in a contact state, and in the case where static elimination is not required, the paired static elimination rollers 111 and 112 are kept in a non-contact state by the contact separation mechanism 116.

[0146] Next, the processing in the case where static elimination is not required will be described.

[0147] In this example, when the control device 131 determines that static elimination is required, it determines the static elimination method and the static elimination conditions.

[0148] <Determination of the static elimination method>

[0149] In this example, the control device 131 identifies the physical property information (such as the medium type) of the medium S based on the indication information from, for example, the physical property indicating switch 143. For example, as shown in (a) of Figure 9 , it is determined whether the surface resistance (Ω / □) of the medium S is any one of low resistance, medium resistance, or high resistance. Here, the low resistance is 10 11 or more and less than 10 13 , the medium resistance is 10 13 or more and less than 10 15 , and the high resistance is 10 15 or more and less than 10 18 .

[0150] Moreover, in this example, from the viewpoint of suppressing the power consumption to the required minimum, the following method is adopted: when the surface resistance of the medium S is low resistance, both the selection switches 132 and 133 are turned off, and neither the contact type static eliminator 101 nor the non-contact type static eliminator 102 is selected. When the surface resistance of the medium S is medium resistance, the selection switch 132 is turned off and the selection switch 133 is turned on, and only the non-contact type static eliminator 102 is selected. When the medium S has high resistance, both the selection switches 132 and 133 are turned on, and both the contact type static eliminator 101 and the non-contact type static eliminator 102 are selected.

[0151] However, from the viewpoint of improving the static elimination accuracy of the static elimination device 100, in any case where the medium S has low resistance, medium resistance, or high resistance, both the contact type static eliminator 101 and the non-contact type static eliminator 102 can of course be used. And in this example, there is no method of only selecting the contact type static eliminator 101, but for example, when it is medium resistance, a method of only selecting the contact type static eliminator 101 can also be set.

[0152] And in this example, a method of determining the surface resistance of the medium S based on the indication information from the physical property indicating switch 143 is adopted, but it is not limited to this. For example, the resistance measurement circuit 150 shown in (b) of Figure 9 can also be used to actually measure and determine the surface resistance of the medium S. Figure 9The resistance measurement circuit 150 shown in (b) is arranged in a paired structure with measurement rollers 151 and 152 side by side along the conveyance direction of the medium S. One of the measurement rollers 151 in the paired structure of measurement rollers 151 located on the upstream side of the conveyance direction of the medium S is connected to a measurement power supply 153, and the other measurement roller 151 in the paired structure of measurement rollers 151 is grounded through a resistor 154. An ammeter 155 is provided between one of the measurement rollers 152 in the paired structure of measurement rollers 152 located on the downstream side of the conveyance direction of the medium S and the ground. Additionally, the conveyance members (alignment rollers 93 or conveyance rollers 94) of the medium S can be used as the measurement rollers 151 and 152, or they can be provided separately from the conveyance members.

[0153] In this example, for instance, it is assumed that a medium with any one of low resistance, medium resistance, or high resistance is used as the medium S. When the medium S has high resistance, even if the medium S is disposed across between the paired measurement rollers 151 and 152, the measurement current from the measurement power supply 153 flows in a manner that traverses the paired measurement roller 151, and there is almost no measurement current that reaches the ammeter 155 on the measurement roller 152 side along the medium S.

[0154] In contrast, when the medium S has medium resistance or low resistance, since the surface resistance of these media S is smaller than that of the high - resistance medium S, when the medium S is disposed across between the paired measurement rollers 151 and 152, a part of the measurement current from the measurement power supply 153 flows in a manner that traverses the paired measurement roller 151, and the remaining part of the measurement current reaches the ammeter 155 on the measurement roller 152 side along the medium S. The surface resistance of the medium S is calculated by operating based on the measurement current measured by the ammeter 155 and the applied voltage of the measurement power supply 153.

[0155] Furthermore, regarding such a resistance measurement circuit 150, of course, an ammeter can be provided, for example, between the elastic transfer roller 55 of the secondary transfer device 50 and the ground. The transfer current is measured by this ammeter, and the system resistance of the secondary transfer region TR is calculated based on the transfer bias and the transfer current, and the surface resistance of the medium S is obtained.

[0156] <Determination of the static - elimination conditions>

[0157] Next, the method for determining the static - elimination conditions in this example will be described.

[0158] In this example, as Figure 4 and Figure 9As shown, the control device 131 calculates the surface resistance of the medium S based on the transfer conditions of the secondary transfer device 50 (for example, correcting the transfer bias voltage Vt of the constant voltage control method according to the environmental information from the environmental sensor 145) and the indication information from the physical property indication switch 143 (such as the medium type), and predicts the charging potential of the medium S passing through the secondary transfer device 50. In addition, of course, the surface potential of the medium S charged by passing through the secondary transfer device 50 can also be actually measured by a potential probe (not shown).

[0159] Moreover, as the charge removal condition of the contact type charge remover 101, the charge removal bias voltage Vd1 is determined in such a way that the predicted or actually measured surface potential Vc of the medium S decreases by more than half in absolute value (in this example, the target surface potential is set to Vc1). And as the charge removal condition of the non-contact type charge remover 102, the charge removal bias voltage Vd2 is determined depending on the charge removal condition of the contact type charge remover 101 (the target surface potential Vc1 of the medium S), and it is sufficient to make the surface potential of the medium S become Vc2 (substantially 0 in this example).

[0160] In addition, in this example, the charge removal condition of the non-contact type charge remover 102 is made to depend on the charge removal condition of the contact type charge remover 101, but it is not limited to this. Of course, for example, the following method can be adopted: the charge removal condition of the non-contact type charge remover 102 is determined in advance, and the charge removal condition of the contact type charge remover 101 is made to depend on the charge removal condition of the non-contact type charge remover 102.

[0161] In this way, if the charge removal method and the charge removal condition are determined, an appropriate charge removal process is performed according to the surface resistance of the medium S.

[0162] For example, when the medium S is a high resistance such as a resin film, as shown in (a) of Figure 9 , both the contact type charge remover 101 and the non-contact type charge remover 102 are used as the charge removal method, and as shown in Figure 8 , the charge removal bias voltages Vd1 and Vd2 determined as the charge removal conditions are applied respectively.

[0163] In this state, as shown in Figure 8 and Figure 10 , the surface of the medium S is charged with negative charge e- by the secondary transfer device 50, and the back surface of the medium S is charged with positive charge e+ by dielectric polarization. However, first, the charge removal process by the contact type charge remover 101 is performed, and the surface potential Vc of the medium S decreases by more than half in absolute value to become Vc1. However, at this stage, the deviation amount of the surface potential Vc1 of the medium S is relatively large.

[0164] Then, the static elimination process is continued through the non-contact static eliminator 102 after the dielectric S has passed through the contact-type static eliminator 101, and the surface potential of the dielectric S reaches Vc2 (substantially 0) from Vc1. At this stage, the surface potential Vc2 of the dielectric S is uniformly eliminated.

[0165] Especially in this example, if the static elimination power of the contact-type static eliminator 101 is increased, the deviation of the charged potential of the dielectric S after the static elimination process through the contact-type static eliminator 101 is increased. Therefore, it is preferable to increase the static elimination power of the non-contact static eliminator 102.

[0166] Moreover, when the dielectric S has a medium resistance, as shown in (a) of Figure 9 , only the non-contact static eliminator 102 is used for the static elimination method, and the static elimination bias voltage Vd2 determined as the static elimination condition is applied to perform the static elimination process through the non-contact static eliminator 102. At this time, the surface potential of the dielectric S is eliminated from Vc to Vc2 (substantially 0). In addition, in this example, since the contact-type static eliminator 101 is not used, for example, in the cases of the schemes shown in (b) of Figure 5 and (c) of Figure 5 , the static elimination rollers 111 and 112 are arranged at positions retracted from the dielectric S.

[0167] Furthermore, when the dielectric S has a low resistance, as shown in (a) of Figure 9 , neither the contact-type static eliminator 101 nor the non-contact static eliminator 102 is used for the static elimination method, and no static elimination process is performed, but the surface potential of the dielectric S is naturally eliminated.

[0168] -Electrostatic elimination roller structure of contact-type static eliminator-

[0169] As shown in Figure 11 , in this example, both the static elimination rollers 111 and 112 have the following structure: an elastic layer 171 in which carbon black or the like is blended in foamed urethane rubber or EPDM is coated around a shaft 170 made of metal, and for example, the surface of the elastic layer 171 is coated with a protective layer 172 such as fluororesin. Moreover, the static elimination bias voltage Vd1 from the static elimination power supply 115 is applied to the shaft 170 made of metal.

[0170] In this example, from the viewpoint of the static elimination characteristics, the Asker C hardness of the elastic layer 171 is preferably 50 degrees or more and 90 degrees or less, and more preferably 60 degrees or more and 80 degrees or less. Here, the Asker C hardness refers to the resilience hardness under a 200 g load and is measured by the following method. In accordance with JIS-K7312 and JIS-S6050, a standard Asker C type hardness meter manufactured by Kobunshi keiki Co., Ltd. for measuring the hardness of soft rubber, sponge, etc. is used for measurement.

[0171] According to this embodiment, since the charge removal rollers 111 and 112 both have elastic layers 171, when clamping and conveying while sandwiching the medium S, the contact area CN in the axial direction contacts both surfaces of the medium S. Therefore, even if at least one of the charge removal rollers 111 and 112 is arranged obliquely with respect to the axial direction, as long as the inclination angle is small, the contact state with the surface of the medium S can be maintained between the charge removal rollers 111 and 112. Therefore, in the gap portions CNf and CNr before and after the contact area CN with the medium S between the two charge removal rollers 111 and 112, corona discharge is stably performed between the charge removal roller 111 and the surface of the medium S.

[0172] Moreover, as shown in Figure 11 (c) of, the charge removal rollers 111 and 112 contact both surfaces of the medium S through the elastic deformation of the elastic layer 171. Therefore, there is less concern that a part of the charge removal rollers 111 and 112 in the axial direction will be non-contact with the surface of the medium S. Therefore, when the charge removal rollers 111 and 112 clamp and convey the medium S, a non-contact portion will not be generated in a part of the contact area CN extending in the axial direction, and the contact area CN between the charge removal rollers 111 and 112 maintains the contact state with the medium S in the axial direction, and there is no concern about uneven charge removal with respect to the axial direction.

[0173] <Example of non-contact configuration of charge removal roller>

[0174] And, in this embodiment, the charge removal rollers 111 and 112 are in contact configuration even when the medium S does not pass through, but it is not necessarily limited thereto. For example, as shown in Figure 12 (a) of, when the medium S does not pass through, the charge removal rollers 111 and 112 can also be in non-contact configuration. However, the gap g between the charge removal rollers 111 and 112 only needs to be set narrower than the thickness ts of the medium S. When the medium S passes between the charge removal rollers 111 and 112, the charge removal rollers 111 and 112 contact both surfaces of the medium S, and the contact pressure Fd in the contact area CN ensures the conveyance property of conveying the medium S through the charge removal rollers 111 and 112 with respect to the medium S, and can also be appropriately selected as long as it is within the range that does not impair the charge removal action on the medium S.

[0175] In this example, the contact pressure Fd of the charge removal rollers 111 and 112 with respect to the medium S is selected to be lower than the contact pressure in the secondary transfer area TR of the secondary transfer device 50. Therefore, when the medium S passes through the contact type charge remover 101, there is no concern that the image formed on the medium S will be unnecessarily damaged, and the conveyance property and charge removal action property of the medium S are well maintained.

[0176] <Volume resistivity of elastic layer>

[0177] And, the volume resistivity of the elastic layer 171 is preferably 104 Above Ω·cm and 10 10 Below Ω·cm, more preferably 10 5 Above Ω·cm and 10 9 Below Ω·cm, further preferably 10 6 Above Ω·cm and 10 8 Below Ω·cm, most preferably limited to this range even when the environment changes.

[0178] Here, as a method for measuring the volume resistivity, it can be appropriately selected. However, for example, in Figure 12 An example is shown in (b).

[0179] In Figure 12 , place the conductive roller, which is either of the static eliminator rollers 111 and 112, on the metal plate 180, and apply a predetermined load (e.g., 500 g) to the portions of the arrows A1 and A2 at both ends of the metal shaft 170, which is the core material of the conductive roller. In this state, for example, in an environment of temperature 22°C and humidity 55% RH, apply a predetermined applied voltage (e.g., 1000 V) between the metal shaft 170, which is the core material, and the metal plate 180. Read the current value I (A) after 10 seconds using the current meter 181, and calculate the volume resistance R (Ω) using the formula "R = V / I". Rotate the conductive roller, which is either of the static eliminator rollers 111 and 112, circumferentially by 90° successively, and perform this measurement and calculation at 4 points. Take the average value as the volume resistance R of the conductive roller. Then, calculate the volume resistivity ρv (Ω·cm) of the elastic layer 171 based on the volume resistance R of the conductive roller using the following formula.

[0180] Formula ρv = D × W × R / t

[0181] In the above formula, D (cm) represents the axial length of the conductive roller, W (cm) represents the contact (clamping) width between the conductive roller and the electrode (equivalent to the metal plate 180), and t (cm) represents the thickness of the elastic layer. Calculate the volume resistivity using the above formula.

[0182] <Bias Voltage Control of Contact-Type Static Eliminator>

[0183] In this embodiment, the contact-type static eliminator 101 can also use a predetermined bias voltage Vd1. However, since the physical property values or the charged amounts of the medium S vary, it is preferably a method of controlling the bias voltage Vd1 according to the surface potential of the medium S.

[0184] In this example, as Figure 13As shown in (a) thereof, for example, a surface potentiometer 190 may be provided at an arbitrary position between the conveying rollers 94 to measure the surface potential of the medium S in a non-contact manner. Here, as the surface potentiometer 190, for example, an ESV (abbreviation for Electrostatic Voltmeter) using electrostatic measurement is used. In this example, as Figure 13 (a) of Figure 13 (b) shows, the surface potentiometer 190 is provided at a position corresponding to the center line CL in the width direction intersecting the conveying direction of the medium S (a position corresponding to 1 / 2 of the width dimension w of the medium S). A grounded counter electrode 191 is provided at a position opposite to the surface potentiometer 190, and the medium S passes while being in contact with the counter electrode 191. In addition, in Figure 13 (a), the symbol 192 is a support bracket for the surface potentiometer 190. Moreover, as the measurement value of the surface potentiometer 190, for example, the average value of the results obtained by measuring for a specified time may be adopted, or the average value of the results obtained by measuring a plurality of points may also be adopted. Alternatively, other calculation methods may also be used for measurement.

[0185] Figure 14 is a flowchart for implementing the charge removal bias control of the contact type charge remover.

[0186] In Figure 14 , it is confirmed whether it is the charge removal condition for using the contact type charge remover 101. In the case of using the contact type charge remover 101, the physical property information of the medium S is read, and the surface potential of the medium S is measured by the surface potentiometer 190.

[0187] Then, the charge removal bias Vd1 is determined, and the charge removal bias Vd1 may be applied to the charge removal roller 111.

[0188] <Regarding the layout of the surface potentiometer>

[0189] Regarding the layout of the surface potentiometer 190, relative to the contact type charge remover 101, it may be on the upstream side or the downstream side in the conveying direction of the medium S. Here, in the scheme where the surface potentiometer 190 is provided at a position upstream of the contact type charge remover 101 in the conveying direction of the medium S, the charge removal bias Vd1 of the contact type charge remover 101 can be feedback controlled from the first medium S.

[0190] On the contrary, in the case where the surface potentiometer 190 is provided at a position downstream of the contact type static eliminator 101 in the conveyance direction of the medium S, after measuring the surface potential of the first medium S for testing, the static elimination bias voltage Vd1 of the contact type static eliminator 101 can be feedback-controlled with respect to the second and subsequent media S. However, since the surface potential of the medium S after static elimination by the contact type static eliminator 101 is measured, it is not necessary to measure a large potential, and accordingly, the surface potentiometer 190 needs to be miniaturized.

[0191] In addition, in this example, the measurement result of the surface potentiometer 190 is not used for controlling the static elimination bias voltage Vd2 of the non-contact type static eliminator 102. The reason is that since the static elimination potential level based on the non-contact type static eliminator 102 is smaller than the static elimination potential level based on the contact type static eliminator 101, it is not necessary to specifically control the static elimination bias voltage Vd2 of the non-contact type static eliminator 102.

[0192] <Determination method of the static elimination bias voltage Vd1>

[0193] As a method for determining the static elimination bias voltage Vd1 of the contact type static eliminator 101, it can be appropriately selected. However, in this example, it is preferable to select the static elimination bias voltage Vd1 such that the distribution of positive and negative charges in the surface of the medium S after static elimination becomes non-uniform compared to before static elimination. In particular, in this example, it is preferable to statically eliminate the medium S in such a way that the proportion of the charge that was dominant before static elimination in the distribution of the surface charges after static elimination becomes larger.

[0194] As Figure 15 shown in (a) of [], it is now assumed that the surface potential of the medium S before static elimination is Vc1, and negative charges are dominant before static elimination.

[0195] At this time, as the static elimination bias voltage Vd1 of the contact type static eliminator 101, when the surface potential of the medium S after static elimination is Vc2, it is only necessary to select Vd1 such that |Vc2| decays to a value close to 0 and Vc2 has the same polarity as Vc1.

[0196] In this way, as Figure 15 shown in (b) of [], when the static elimination bias voltage Vd1 is selected, in the charge distribution of the medium S before static elimination, negative charges (marked with white circles in the figure) are dominant and uniformly distributed compared to positive charges (marked with × in the white circles in the figure), and the surface potential is Vc1. In the charge distribution of the medium S after static elimination, negative and positive charges are non-uniformly distributed in such a way that the proportion of negative charges changes, and |ΔVc1| is eliminated in such a way that the surface potential decays to Vc2. In addition, regarding the charge distribution of the medium S after static elimination, the part of the dotted white circle indicates the region of the decayed negative charges, and the part marked with × in the dotted white circle indicates the region of positive charges.

[0197] The reason for selecting such a charge-removing pattern is as follows: For example, the proportion of positive charges different from the dominant negative charges in the dielectric S before charge removal increases because the charge-removing bias voltage Vd1 is too strong and Vc2 is not close to 0, avoiding a potential with a polarity opposite to the potential before charge removal.

[0198] <Selection of the Initial Value of the Charge-Removing Bias Voltage of the Contact-Type Charge Remover>

[0199] As described above, when controlling the charge-removing bias voltage Vd1 of the contact-type charge remover 101, it is preferable to select the optimal initial value of the charge-removing bias voltage Vd1 with respect to the surface potential of the dielectric S. However, in order to select the initial value of the charge-removing bias voltage Vd1, it is necessary to apply multiple candidate charge-removing bias voltages Vd1 to the test dielectric S in a predetermined charged state, and measure the attenuation degree of the surface potential of the dielectric S due to each charge-removing bias voltage Vd1 by the surface potentiometer 190.

[0200] Therefore, in this example, as Figure 16 shown in (a) of [], it is necessary to have a scheme in which the surface potentiometer 190 is set at a position downstream of the contact-type charge remover 101 in the conveying direction of the dielectric S (corresponding to the scheme of setting the surface potentiometer 190 at the position shown by the double-dot dash line in the figure).

[0201] In this example, as Figure 16 shown in (b) of [], after applying different charge-removing bias voltages Vd1 (specifically Vd1(1) to Vd1(3)) to, for example, three patches PT1 to PT3 (all having the same surface potential under the same charging conditions) in the test dielectric S, the surface potential remaining on the dielectric S is measured. For example, when the surface potential remaining on the dielectric S is set to Vc2 (specifically Vc2(1) to Vc2(3)) for each charge-removing condition and this surface potential is plotted, as Figure 16 shown by the measurement line in (c) of [], it can be understood that as the charge-removing bias voltage Vd1 increases, the surface potential Vc2 remaining on the dielectric S decreases. At this time, as long as the charge-removing bias voltage Vd1 (specifically Vd1(0)) that makes the remaining surface potential Vc2 reach approximately 0 is linearly approximated from the Figure 16 measurement line in (c) of [].

[0202] In this way, since the optimal charge-removing bias voltage Vd1 (Vd1(0)) is calculated on the basis of removing the charge from the surface potential Vc1 of the predetermined dielectric S, it is possible to select the optimal charge-removing bias voltage Vd1 based on the initial value of the charge-removing bias voltage Vd1 when removing the charge from an arbitrarily charged surface potential Vc1. However, it is not necessary to linearly approximate from the measurement line. As long as the initial value of the charge-removing bias voltage Vd1 is obtained from multiple surface potentials remaining on the dielectric S after applying different charge-removing bias voltages Vd1, other methods are also possible.

[0203] -De-electrification parameters of non-contact type de-electrifier-

[0204] In this example, as Figure 17 shown in (a) of, between the discharge wire 122 and the de-electrification housing 121 of the non-contact type de-electrifier 102, a de-electrification power supply 125 that applies a de-electrification bias voltage Vd2 composed of an AC voltage component superimposed on a DC voltage component is connected.

[0205] In this example, since a de-electrification bias voltage Vd2 including an AC voltage component is applied between the discharge wire 122 and the de-electrification housing 121, positive ions (+) and negative ions (-) based on corona discharge are generated around the discharge wire 122 and coexist. In this example, positive ions (+) and negative ions (-) are alternately generated every half cycle of the frequency f (Hz) of the de-electrification bias voltage Vd2.

[0206] Here, when studying the de-electrification parameters of the non-contact type de-electrifier 102, it can be speculated that if the frequency f of the de-electrification bias voltage Vd2 becomes higher, the generation periods of the positive ions (+) and negative ions (-) become faster accordingly, and the amount of ion generation increases.

[0207] Moreover, when focusing on the conveyance speed v of the medium S, in the case where the conveyance speed v of the medium S is relatively fast, if the ion generation period (ion frequency) is not shortened, the ion balance deteriorates.

[0208] In this example, based on this, focusing on the de-electrification parameter f / v of the conveyance speed v of the medium S and the frequency f of the de-electrification bias voltage Vd2 including an AC voltage component, according to the evaluation based on the adhesion evaluation method of the medium S described later, the optimal range of the de-electrification parameter f / v is selected, and it is clarified that the preferred solution is to satisfy the following formula.

[0209] f / v ≥ 0.8...... (Formula 1)

[0210] In Formula 1, the solution that satisfies the following formula is particularly preferably listed.

[0211] f / v ≥ 1.5...... (Formula 2)

[0212] Moreover, in this example, as Figure 17 shown in (a) of, the opening 128 of the de-electrification housing 121 is formed to have an opening width L with respect to the conveyance direction of the medium S.

[0213] Here, the opening width L of the opening portion 128 of the charge removal housing 121 limits the ion emission region toward the medium S. If the opening width L is narrow, the ion emission region is narrow, and conversely, if the opening width L is wide, the ion emission region is wide. Therefore, the ion amount per unit length can be adjusted using the relationship between the ion amount and the ion emission region. Specifically, when the opening width L is long, if the ion generation period (ion frequency) is not shortened, the ion balance in the entire region of the opening portion 128 may deteriorate.

[0214] Thus, it can be speculated that the opening width L of the charge removal housing 121 affects the charge removal effect.

[0215] Based on this point, f / v*L is selected as the charge removal parameter, and it is clarified that a solution satisfying the following formula is preferably used.

[0216] f / v*L≥30……(Formula 3)

[0217] In addition, the reasons for adopting Formulas 1 to 3 will be described in detail in Example 4 described later.

[0218] Moreover, in this example, it can be seen that if the opening width L is narrow, charge removal may be insufficient unless a relatively high frequency is set. It is estimated that this is because, as the ion emission region becomes narrow, the ion amount received per unit length of the medium S passing through the non-contact type charge remover 102 decreases. On the other hand, if the opening width L is large, the ion emission region is wide, so the ion amount received per unit length of the medium S passing through the non-contact type charge remover 102 increases. Thus, even at a lower frequency, sufficient charge removal can be achieved compared to the case where the opening width L is narrow.

[0219] -Based on the corona discharge characteristics of the non-contact type charge remover-

[0220] In this example, as shown in (a) of Figure 17 , the charge removal bias voltage Vd2 applied to the discharge wire 122 is an AC voltage component Vac (having a peak-to-peak voltage Vpp and a frequency f) superimposed on a DC voltage component Vdc (a positive voltage is used in this example). At this time, corona discharge occurs around the discharge wire 122, and the voltage-current characteristics of the corona discharge are shown in (b) of Figure 17 .

[0221] In Figure 17 , the horizontal axis represents the applied voltage, and the vertical axis represents the corona discharge current. The absolute value of the applied voltage generated by negative corona (corresponding to negative ions (-)) is lower than the applied voltage generated by positive corona (positive ions (+)).

[0222] Here, in this example, since the AC voltage component Vac in the charge removal bias voltage Vd2 is superimposed on the DC voltage component Vdc, as shown inFigure 17 As shown by the solid line to the thin line in (c), it shows the change in the amount of displacement of the AC voltage component Vac toward the + side corresponding to the DC voltage component Vdc.

[0223] At this time, for example, it is assumed that Vpp is ±4 kV, Vdc is +0.3 kV, the positive corona discharge start voltage is +2 kV, and the negative corona discharge voltage is -1.7 kV. Figure 17 The slanted area in (c) is the ion generation area. Positive corona (+ ions) are generated in the ion generation area above +2 kV, and negative corona (- ions) are generated in the ion generation area below -1.7 kV. Therefore, compared with the case where the DC voltage component Vdc is not overlapped, the balance of the generation amounts of positive ions and negative ions becomes uniform.

[0224] -Regarding the charge removal effect of the non-contact type charge remover-

[0225] In this example, as shown in (a) of Figure 18 the non-contact type charge remover 102 is provided with the ground electrode 123 as a counter electrode grounded opposite to the discharge wire 122. When such a ground electrode 123 is provided, among the ions generated around the discharge wire 122, mainly positive ions (+) are attracted to the ground electrode 123 side and are used for removing the surface charge (mainly negative-polarity charge e-) of the dielectric S.

[0226] In contrast, as shown in (b) of Figure 18 in the scheme where the ground electrode 123 as a counter electrode is not provided opposite to the discharge wire 122, the ions generated around the discharge wire 122 only shoot out to the surroundings and are not actively attracted to the surface charge (mainly negative-polarity charge e-) side of the dielectric S and are not used for charge removal.

[0227] -Comparison between AC charge removal bias voltage and DC charge removal bias voltage-

[0228] In this example, as shown in (c) of Figure 18 the charge removal bias voltage Vd2 is an AC charge removal bias voltage composed of an AC voltage component with an overlapped DC voltage component as the charge removal power supply 125, and positive ions (+) and negative ions (-) coexist on the surface of the dielectric S and are used for charge removal. Therefore, both the negative-polarity charge e- and the positive-polarity charge e+ of the surface charge of the dielectric S are eliminated, and the surface potential of the dielectric S decays toward approximately 0.

[0229] In contrast, as shown in Figure 18As shown in FIG. (d), as the power supply 125' for discharging, it is assumed that a DC discharging bias voltage composed only of a DC voltage component is used as the discharging bias voltage Vd2, and only positive ions (+) are generated around the discharging wire 122. These positive ions (+) discharge the negative-polarity charges e- on the surface of the dielectric S, but negative ions (-) for discharging the positive-polarity charges e+ in the surface charges of the dielectric S are not generated, and the positive-polarity charges e+ on the dielectric S are not removed.

[0230] Thus, in this example, by adopting an AC discharging bias voltage, even if the surface charges of the dielectric S mix positive-polarity charges e+ and negative-polarity charges e-, both can be discharged.

[0231] -Discharging Bias Voltage Control of Non-Contact Discharger-

[0232] In this example, the non-contact discharger 102 can also fixedly use discharging parameters. However, in the case of a scheme where the conveyance speed v of the dielectric S changes, as Figure 19 shown in FIG. (b), it is preferable to control the frequency f of the discharging bias voltage Vd2 according to the conveyance speed v of the dielectric S.

[0233] That is, in this example, a speed sensor 200 for detecting the conveyance speed v of the dielectric S is provided in the middle of the conveyance path of the dielectric S, and the speed information from the speed sensor 200 is read into the control device 131, and the control device 131 controls the frequency f of the discharging bias voltage Vd2.

[0234] In this example, a discharging bias voltage control program for the non-contact discharger 102 is installed in the control device 131, and the discharging bias voltage control process shown in Figure 19 FIG. (a) is executed.

[0235] In Figure 19 FIG. (a), the control device 131 confirms whether it is the discharging condition for using the non-contact discharger 102. In the case of using the non-contact discharger 102, the physical property information of the dielectric S is read, and moreover, the conveyance speed v of the dielectric S is measured by the speed sensor 200.

[0236] Then, the frequency f of the discharging bias voltage Vd2 is determined, and the discharging bias voltage Vd2 is applied to the discharging wire 122.

[0237] In this example, as Figure 19 shown in FIG. (b), for example, when the conveyance speed v of the dielectric S is a speed v(fast) faster than the normal speed, the frequency f can be set to f(large). On the contrary, when the conveyance speed v of the dielectric S is a speed v(slow) slower than the normal speed, the frequency f can be set to f(small)+.

[0238] ◎Embodiment 2

[0239] Figure 20 Shows the overall structure of the image forming apparatus according to Embodiment 2.

[0240] In Figure 20 the image forming apparatus 20 includes: an image forming unit 210 incorporating an image forming section 22; and a static elimination unit 220 that receives the medium S discharged from the outlet portion of the horizontal conveyance path 84 of the image forming unit 210 and performs static elimination. Different from the image forming apparatus according to Embodiment 1, various elements other than the static elimination device 100 (image forming section 22, intermediate transfer member 30, fixing device 70, medium conveyance system 80) are assembled in the image forming unit 210, and the static elimination device 100 is assembled in the static elimination unit 220.

[0241] In addition, the same reference numerals as those in Embodiment 1 are assigned to the same components as in Embodiment 1, and their detailed descriptions are omitted.

[0242] In this example, as shown in Figure 20 and Figure 21 the static elimination unit 220 has a horizontal conveyance path 221 for conveying the medium S discharged from the image forming unit 210 in a substantially horizontal direction. A suitable number of conveyance rollers 222 to 224 are provided in the horizontal conveyance path 221, and a medium discharge receiving portion 86 is provided at the outlet portion of the horizontal conveyance path 221. In addition, a contact type static eliminator 101 is provided as the static elimination device 100 in the region between the conveyance rollers 222 and 223 in the horizontal conveyance path 221, and a non-contact type static eliminator 102 is provided on the downstream side of the contact type static eliminator 101 in the conveyance direction of the medium S.

[0243] In this example, a control device 240 is also assembled in the static elimination unit 220. For example, a surface electrometer 190 for measuring the surface potential of the medium S is provided in the region between the conveyance rollers 223 and 224, and a speed sensor 200 is provided in the region between the conveyance roller 222 and the contact type static eliminator 101 in the horizontal conveyance path 221.

[0244] Moreover, the basic structure of the contact type static eliminator 101 is substantially the same as that in Embodiment 1, but as the static elimination power supply 115, a positive polarity DC power supply 115a and a negative polarity DC power supply 115b are provided in parallel and selected by switching with a changeover switch 250.

[0245] Furthermore, the control device 240 switches and selects the positive polarity DC power supply 115a and the negative polarity DC power supply 115b of the static elimination power supply 115 by the changeover switch 250 based on whether the medium S is flipped by the medium flipping mechanism 89 in the image forming unit 210.

[0246] In addition, in substantially the same manner as in the first embodiment, the charge removal bias control (control corresponding to the surface potential of the medium S) of the contact type charge remover 101 and the charge removal bias control of the non-contact type charge remover 102 are implemented in the control device 240.

[0247] In this example, since the charge removal device 100 is provided at a position downstream of the medium turning mechanism 89 in the image forming unit 210 in the conveyance direction of the medium S, the positive-polarity DC power supply 115a and the negative-polarity DC power supply 115b of the charge removal power supply 115 are switched and selected according to the presence or absence of turning of the medium S.

[0248] For example, as Figure 22 shown in (a) of, when the medium S enters the charge removal unit 220 without passing through the medium turning mechanism 89, the control device 240 switches and selects the positive-polarity DC power supply 115a as the charge removal power supply 115. Therefore, the surface charges of the medium S are appropriately removed according to the charge removal bias Vd1 based on the charge removal power supply 115 (using the positive-polarity DC power supply 115a).

[0249] On the other hand, as Figure 22 shown in (b) of, when it is assumed that the medium S enters the charge removal unit 220 in a state of being turned by the medium turning mechanism 89, the control device 240 switches and selects the negative-polarity DC power supply 115b as the charge removal power supply 115. Therefore, the surface charges of the medium S are appropriately removed according to the charge removal bias Vd1 based on the charge removal power supply 115 (using the negative-polarity DC power supply 115b).

[0250] In addition, in this example, the polarity of the charge removal power supply 115 is switched according to the turning of the medium S, but it is not limited to this. For example, when the medium S is turned by the medium turning mechanism 89, the charge removal by the charge removal device 100 can also be not performed, and when the medium S is turned by the medium turning mechanism 89, it can also be set that the charge removal process by the charge removal device 100 cannot be selected on the UI (User Interface).

[0251] ◎ Modified Embodiment 1

[0252] Figure 23 (a) of shows a modified embodiment of the non-contact type charge remover 102.

[0253] In Figure 23 (a) of, the basic structure of the non-contact type charge remover 102 is as follows: The charge removal housing 121 is divided into two chambers by a partition member 260, and discharge wires 122 (122a and 122b in this example) are provided in each chamber, and a charge removal bias Vd2 including an AC voltage component is applied to each discharge wire 122 from the charge removal power supply 125 (having an AC power supply 126 and a DC power supply 127).

[0254] Moreover, in this example, as Figure 23 shown in (a) of Figure 23 a plate-shaped shielding member 270 is provided to shield the opening 128 of the de-electrification housing 121, and a through-hole 271 is formed in the shielding member 270.

[0255] Particularly in this example, the two discharge wires 122 (122a, 122b) extend along the width direction intersecting the conveyance direction of the medium S. However, as Figure 23 shown in (b) of Figure 23 and (c) of

[0256] shown in (c) of Figure 23 the through-hole 271 of the shielding member 270 intersects the plurality of discharge wires 122a, 122b in an inclined direction, and a plurality of them are arranged at a predetermined interval in the length direction of the plurality of discharge wires 122a, 122b. Here, the through-hole 271 may also continuously extend across the two discharge wires 122a, 122b. However, in this example, a partition portion 272 that divides the through-hole 271 into two is integrally formed in the shielding member 270 corresponding to the partition member 260.

[0257] Thus, in this embodiment, at least any one of the plurality of discharge wires 122a, 122b is exposed in an arbitrary region in the length direction. For example, in

[0258] shown in (c) of

[0259] ◎ Modified Mode 2

[0260] Figure 24Fig. (a) shows the non-contact static eliminator 102 related to the deformation mode 2.

[0261] In Figure 24 Fig. (a), the non-contact static eliminator 102 uses a needle electrode 300 instead of the discharge wire 122 which is a linear electrode used in the first and second embodiments and the deformation mode 1.

[0262] In this example, as shown in Figure 24 Fig. (a) and Figure 24 Fig. (b), the needle electrodes 300 are arranged at regular intervals on a long strip-shaped conductive support member 301 extending along the width direction of the medium S. A static elimination bias voltage Vd2 from a static elimination power supply 125 (including an AC power supply 126 and a DC power supply 127) is applied to the support member 301, and positive ions (+) and negative ions (-) are generated around the needle electrodes 300. A ground electrode 310 as a counter electrode is arranged on the side of the medium S opposite to the needle electrodes 300, and the positive and negative ions generated around the needle electrodes 300 are attracted to the surface charge portion of the medium S to eliminate the surface charge of the medium S.

[0263] In addition, regarding the number of the needle electrodes 300 arranged, it can also be appropriately selected in the entire region in the width direction of the medium S in a manner that enables the static elimination operation. And as shown in Figure 24 Fig. (c), a shielding member 270 can also be arranged between the needle electrodes 300 and the medium S, and through holes 271 are opened only at the portions corresponding to the needle electrodes 300 to prevent the medium S from touching the needle electrodes 300 and ensure the discharge operation through the needle electrodes 300.

[0264]

Example

[0265] ◎Example 1

[0266] Example 1 uses the static elimination device 100 (contact-type static eliminator 101, non-contact static eliminator 102) related to the first embodiment, and evaluates by visualizing the static elimination state based on the contact-type static eliminator 101 and the static elimination state based on the non-contact static eliminator 102.

[0267] Figure 25 Fig. (a) shows an example of spraying a negative charge toner (M: magenta toner) and a positive charge toner (C: cyan toner) onto the medium S and visualizing the charged charge distribution (electrostatic pattern) on the medium S.

[0268] In Figure 25In (a) of the figure, the symbol 330 is a toner spray chamber. Inside the spray chamber 330, a grounded metal plate 331 is provided. A medium S such as a resin film is placed on the metal plate 331, and air is sprayed toward the toner in the grid container 332 disposed in the spray chamber 330 to form a toner cloud state in the spray chamber 330. In this way, the clouded toner is attracted by the charges on the surface of the medium S, and the toner adheres to achieve visualization.

[0269] In Figure 25 In (b) of the figure, the following states are shown in order from left to right: visualizing the medium S before static elimination; visualizing the medium S after static elimination by the contact type static eliminator 101 (after double-roller static elimination); visualizing the medium S after static elimination by the contact type static eliminator 101 and non-contact type static eliminator 102 (corona tube static elimination, electrode gap 3 mm); and visualizing the medium S after static elimination by the contact type static eliminator 101 and non-contact type static eliminator 102 (corona tube static elimination, electrode gap 0 mm).

[0270] According to Figure 25 It is confirmed from (b) of the figure that before static elimination, negative charges uniformly exist on the surface of the medium S. After static elimination by the contact type static eliminator 101, most of the negative charges are eliminated, but the negative charges exist as non-uniform blocks compared with before static elimination, and positive charges are generated in a smaller area compared with the negative charges. It can be understood from this that after static elimination by the non-contact type static eliminator 102, the surface charges of the medium S are almost eliminated.

[0271] ◎Example 2

[0272] Figure 26 (a) of the figure shows the relationship between the applied voltage and the potential after static elimination when constant voltage control is performed on the contact type static eliminator 101.

[0273] Figure 26 (b) of the figure shows the relationship between the applied current value and the potential after static elimination when constant current control is performed on the contact type static eliminator 101.

[0274] The experimental conditions are as follows.

[0275] · Environment: 22 degrees, 55%

[0276] · Medium: PET film, 100 μm, A3 size

[0277] · Medium conveyance speed: 546 mm / s

[0278] · Secondary transfer voltage: -3 kV

[0279] · Electrifier roller on the dielectric surface side: Asker C 65 degrees, diameter 20 mm, volume resistivity 10 6.5 Ω·cm

[0280] · Electrifier roller on the back side of the dielectric: Asker C 75 degrees, diameter 24 mm, volume resistivity 10 7 Ω·cm

[0281] In Figure 26 in the constant voltage control of (a), if it is below the discharge start voltage, the discharge is stopped, so the surface potential after static elimination is limited within a certain range regardless of the input surface potential.

[0282] In contrast, in Figure 26 the constant current control of (b), even if the roller resistance changes due to temperature rise or passage of time, the current value does not change, so it can withstand the change in system resistance. However, since a certain amount of charge is supplied to the dielectric S, the surface potential after static elimination may deviate due to the input surface potential.

[0283] ◎ Example 3

[0284] Figure 27 The influence of the clamping variation of the paired electrifier rollers 111 and 112 generated by the contact type static eliminator 101 was investigated.

[0285] The experimental conditions are as follows.

[0286] · Dielectric conveyance speed: 182 mm / s

[0287] · Constant voltage control

[0288] · Static elimination bias voltage: 1500 V

[0289] · Electrifier roller on the dielectric surface side: Asker C 70 degrees, diameter 20 mm, volume resistivity 10 6 Ω·cm

[0290] · Electrifier roller on the back side of the dielectric: Asker C 75 degrees, diameter 24 mm, volume resistivity 10 7 Ω·cm

[0291] In Figure 27 , the In-side bite amount refers to the bite amount of the shaft made of metal on the front side of the electrifier roller biting into the electrifier roller side on the opposite side of the shaft center position, and the Out-side bite amount refers to the bite amount of the shaft made of metal on the inner side of the electrifier roller biting into the electrifier roller side on the opposite side of the shaft center position.

[0292] In Figure 27In it, ○ indicates good conveyance property, clamping property, and charge removal operation property (Δ potential: charge-removable potential) with respect to the medium, and × indicates poor in all aspects.

[0293] Here, it is confirmed that different nip amounts on the In side and Out side of the charge removal roller indicate that the paired charge removal rollers are arranged inclined with respect to the axial direction. However, since it is a solution where the charge removal roller has an elastomer, there is a good range regarding the conveyance property, clamping property, and charge removal operation property with respect to the medium.

[0294] ◎ Example 4

[0295] Figure 28 (a) of shows the conveyance speed v of the medium, the frequency f of the charge removal bias Vd2, the value of the charge removal parameter f / v, and the adhesion evaluation result of the medium in the non-contact type charge remover. In addition, in the evaluation result, "○-" indicates a good charge removal result, "○" indicates a better charge removal result than "○-", and "×" indicates an insufficient charge removal result.

[0296] Figure 28 (b) of is an explanatory diagram showing the relationship between the frequency as the charge removal parameter and other parameters when a good charge removal result is obtained. Figure 28 (c) of is an explanatory diagram showing the relationship between the charge removal parameter f / v and other parameters when a good charge removal result is obtained. Figure 28 (d) of is an explanatory diagram showing the relationship between the charge removal parameter f / v*L (L is the opening width of the charge removal housing) and other parameters when a good charge removal result is obtained.

[0297] In this example, in Figure 29 (a) of shows an example of the adhesion evaluation method of the medium.

[0298] In Figure 29 (a) of, 5 sheets of the medium S made of resin film are laminated, the lower 4 sheets are fixed to the plate 401, and after 24 hours of placement after charge removal, the jig 402 is installed on the uppermost medium S, and the adhesion degree of the medium S is measured and evaluated based on the measured value.

[0299] Here, by observing the relationship between the frequency and the tensile load, the result shown in Figure 29 (b) of is obtained.

[0300] Using medium A (manufactured by OZK100, Heiwa Paper Industries Co., Ltd.) and medium B (manufactured by OZK188, Heiwa Paper Industries Co., Ltd.), adhesion evaluation of the media was carried out under the condition of no static elimination and under the condition of static elimination with the frequency f replaced by 100 Hz and 800 Hz. Although it was impossible to measure under the condition of no static elimination, after carrying out static elimination with an appropriately selected frequency, for either medium A or B, the tensile load became below the target, and the adhesion evaluation of the medium was good. In addition, it was confirmed that the target of the tensile load was specified as 1.4 N because if it was below the target level, after the medium was laminated on the medium discharge receiving part 86, it was easy to convey the medium to the post-treatment device by the normal medium conveying roller.

[0301] According to Figure 28 of (a) to (d), it can be understood that the following formula is good.

[0302] f / v ≥ 0.8......(Formula 1)

[0303] f / v ≥ 1.5......(Formula 2)

[0304] f / v * L ≥ 30......(Formula 3)

[0305] ◎ Example 5

[0306] Figure 30 (a) of is an explanatory diagram showing the static elimination effect of the medium when using a non-contact static eliminator and the static elimination parameter f / v is above a specified value.

[0307] Figure 30 (b) of is an explanatory diagram showing the static elimination effect of the medium when using a non-contact static eliminator and the static elimination parameter f / v is less than the specified value.

[0308] In either case, the charged state of the medium was visualized by the method used in Example 1.

[0309] According to Figure 30 of (b), it can be understood that when the static elimination parameter f / v is less than the specified value, the residual charge remains at each ion generation cycle. In contrast, it can be understood that if the static elimination parameter f / v is above the specified value, almost no residual charge remains on the medium and is eliminated.

[0310] ◎ Example 6

[0311] Figure 31 In a non-contact static eliminator, the static elimination effect based on the electrode distance (the distance between the discharge wire and the medium) was verified.

[0312] InFigure 31 The charge-removal state of the medium after passing through the contact-type charge remover after the double-roll charge removal is shown, and a large amount of the charge amount per sheet still remains.

[0313] After that, the charge removal through the non-contact type charge remover is performed while changing the electrode distance. It can be understood that if the electrode distance is within 3 mm, the charge removal effect through the non-contact type charge remover is good. In addition, in the example where the electrode distance is 9 mm, it can be understood that the distance between the discharge wire and the medium is too wide, and the charge removal effect through the non-contact type charge remover is insufficient.

Claims

1. An electrostatic elimination device, comprising: A first electrostatic elimination member that contacts the conveyed medium; A second electrostatic elimination member that clamps the medium between the second electrostatic elimination member and the first electrostatic elimination member; and A power source that applies a voltage to at least one of the first electrostatic elimination member and the second electrostatic elimination member, At least one of the first electrostatic elimination member and the second electrostatic elimination member has an elastomer, The medium is electrostatically eliminated in such a manner that the proportion of the dominant charge before electrostatic elimination in the distribution of the surface charges after electrostatic elimination increases.

2. The electrostatic elimination device according to claim 1, wherein Both the first electrostatic elimination member and the second electrostatic elimination member have elastomers.

3. The electrostatic elimination device according to claim 1, wherein The surface of at least one of the first electrostatic elimination member and the second electrostatic elimination member that contacts the medium has a curved surface portion.

4. The electrostatic elimination device according to claim 3, wherein At least one of the first electrostatic elimination member and the second electrostatic elimination member is a rotating member.

5. The electrostatic elimination device according to any one of claims 1 to 4, wherein The medium is electrostatically eliminated in such a manner that the distribution of positive charges and negative charges on the surface after electrostatic elimination becomes uneven compared to before electrostatic elimination.

6. The electrostatic elimination device according to any one of claims 1 to 4, wherein The electrostatic elimination device has a control member that controls the applied voltage of the power source according to the surface potential of at least one of the medium before and after electrostatic elimination.

7. The electrostatic elimination device according to claim 6, wherein The control member controls the applied voltage of the power source according to the surface potential of at least one of the medium before electrostatic elimination.

8. The electrostatic elimination device according to claim 6, wherein The control member controls the applied voltage of the power source according to the surface potential of at least one of the medium after electrostatic elimination.

9. The electrostatic elimination device according to any one of claims 1 to 4, wherein The Asker C hardness of the electrostatic elimination member having the elastomer is 60 degrees or more and 80 degrees or less.

10. The electrostatic elimination device according to any one of claims 1 to 4, wherein The volume resistivity of the charge removing member having the elastomer is 10 6 Ω·cm or more and 10 8 Ω·cm or less.

11. An electrostatic elimination device, comprising: A contact-type electrostatic elimination member, comprising: a first electrostatic elimination member that contacts the conveyed medium; a second electrostatic elimination member that clamps the medium between the second electrostatic elimination member and the first electrostatic elimination member; and a power source that applies a voltage to at least one of the first electrostatic elimination member and the second electrostatic elimination member, at least one of the first electrostatic elimination member and the second electrostatic elimination member has an elastomer, and the medium is electrostatically eliminated in such a manner that the proportion of the dominant charge before electrostatic elimination in the distribution of the surface charges after electrostatic elimination increases; and A non-contact-type electrostatic elimination member that is disposed at a position downstream of the contact-type electrostatic elimination member in the conveyance direction of the medium and electrostatically eliminates the remaining charges of the medium after electrostatic elimination by the contact-type electrostatic elimination member in a non-contact state.

12. The electrostatic elimination device according to claim 11, comprising: A power source that applies a voltage to the non-contact-type electrostatic elimination member; and A control member that controls the applied voltage of a power supply that applies voltage to at least one of the first static elimination member and the second static elimination member based on the surface potential of at least one of the medium before and after static elimination, and does not control the applied voltage of the power supply of the non-contact type static elimination member.

13. A medium processing apparatus, comprising: A conveyance member that conveys a medium; A charging member that is provided in the middle of the conveyance path of the medium and charges the medium; and The static elimination apparatus according to any one of claims 1 to 12, which is provided at a position downstream of the charging member in the conveyance direction of the medium and eliminates static electricity from the medium charged by the charging member.

14. The medium processing apparatus according to claim 13, wherein The charging member is a transfer member that transfers an image by sandwiching the medium between transfer members of a paired structure, The medium contact pressure between the first static elimination member and the second static elimination member constituting the static elimination apparatus is lower than the medium contact pressure between the transfer members of the paired structure.

15. The medium processing apparatus according to claim 13 or 14, wherein The medium processing apparatus has a medium turning member at a position upstream of the static elimination apparatus in the conveyance direction of the medium, The medium processing apparatus has a switching member that switches the polarity of the applied voltage of the power supply according to the presence or absence of turning of the medium by the medium turning member.

Images