Image forming apparatus

An image forming apparatus includes a draw-up member that draws a liquid developer containing oil and toner up from a storage part in which the liquid developer is stored while rotating; a cylindrical member that is disposed so as to face the draw-up member, receives the liquid developer from the draw-up member while rotating, and has a circumferential surface on which a film of the liquid developer is formed, the cylindrical member having an elastic part having a circular cross section and a coating film that covers the elastic part and is made of a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether; and a formation member having a circumferential surface on which an image is formed by the liquid developer received by the cylindrical member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2018-053955 filed Mar. 22, 2018.

BACKGROUND

(i) Technical Field

(ii) Related Art

A development roller described in Japanese Unexamined Patent Application Publication No. 10-123838 has a cylindrical permanent magnet having, on a surface thereof, magnetic poles of opposite polarities that are disposed in a circumferential direction at regular intervals and a coating layer that is made of a heat-shrinkable resin tube provided on the surface of the permanent magnet.

SUMMARY

In a conventional image forming apparatus using a liquid developer, a cylindrical member having a polyimide coating film is typically used as a cylindrical member that receives the liquid developer and as a cylindrical member on which an image to be transferred onto a recording medium is formed. However, polyimide has a high bending elastic modulus, and therefore sometimes the coating film of the cylindrical member is not deformed along a surface of an object which makes contact with the cylindrical member.

Accordingly, the cylindrical member that receives the liquid developer cannot sufficiently receive the liquid developer, and the cylindrical member on which an image to be transferred is formed fails to transfer part of the image onto a recording medium.

Aspects of non-limiting embodiments of the present disclosure relate to an image forming apparatus that uses a liquid developer that makes an output image less deteriorated than a case where a cylindrical member having a polyimide coating film is used as a cylindrical member that receives the liquid developer or as a cylindrical member on which an image to be transferred onto a recording medium is formed.

According to an aspect of the present disclosure, there is provided an image forming apparatus including a draw-up member that draws a liquid developer containing oil and toner up from a storage part in which the liquid developer is stored while rotating; a cylindrical member that is disposed so as to face the draw-up member, receives the liquid developer from the draw-up member while rotating, and has a circumferential surface on which a film of the liquid developer is formed, the cylindrical member having an elastic part having a circular cross section and a coating film that covers the elastic part and is made of a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether; and a formation member having a circumferential surface on which an image is formed by the liquid developer received by the cylindrical member.

DETAILED DESCRIPTION

An example of an image forming apparatus according to an exemplary embodiment of the disclosure is described with reference toFIGS. 1 through 13. In the drawings, the arrow H indicates a device height direction (vertical direction), the arrow W indicates a device width direction (horizontal direction), and the arrow D indicates a device depth direction (horizontal direction).

Overall Configuration

An image forming apparatus10is an apparatus that forms a toner image T on continuous paper P that is a long recording medium by using a liquid-type liquid developer G obtained by dispersing powder toner into volatile oil (carrier liquid). As illustrated inFIG. 5, the image forming apparatus10includes a transporting part20that transports the continuous paper P and an image processing part24that forms the toner image T.

Furthermore, the image forming apparatus10includes an oil removing part80that removes oil from the continuous paper P and a fixing device70that fixes the toner image T onto the continuous paper P.

In the present exemplary embodiment, for example, Isopar L (boiling point 184° C.) produced by Exxon Mobil Corporation is used as the oil.

The transporting part20is configured to transport the continuous paper P in a direction (hereinafter referred to as a “medium transporting direction”) indicated by the arrow A inFIG. 5at a predetermined constant transport speed and includes a pair of transporting rollers20A and20B.

Image Processing Part24

The image processing part24includes an image forming part26Y that forms a yellow (Y) toner image T, an image forming part26M that forms a magenta (M) toner image T, an image forming part26C that forms a cyan (C) toner image T, and an image forming part26K that forms a black (K) toner image T. The image forming part26K, the image forming part26C, the image forming part26M, and the image forming part26Y are aligned in this order in the device height direction from an upstream side in the medium transporting direction.

Hereinafter, “Y”, “M”, “C”, and “K” at the end of the signs are omitted in a case where these parts need not be distinguished from one another.

As illustrated inFIG. 3, each of the image forming parts26includes an image forming unit30that forms a toner image T by using the liquid developer G and a transfer unit32that transfers the toner image T formed by the image forming unit30onto continuous paper P. The liquid developer G used in the present exemplary embodiment is a liquid-type liquid developer G obtained by dispersing powder toner into volatile oil as described above. The “volatile” in the present exemplary embodiment means that a volatile portion of a substance is larger than 8% by weight after the substance is left in a 25° C. open system for 24 hours in a state where a flash point is less than 130° C. or is 150° C. The flash point is measured according to JIS K2265-4 (2007).

Image Forming Unit30

The image forming unit30includes a photoconductor38having a circumferential surface on which a toner image T is formed, a charging member40that charges the photoconductor38, an exposure device42that forms an electrostatic latent image by irradiating the photoconductor38with exposure light, and a developing device44that develops the electrostatic latent image on the photoconductor38as a toner image T. Furthermore, the image forming unit30includes a collecting device56that collects the liquid developer G remaining on the photoconductor38from the photoconductor38. The photoconductor38is an example of a formation member.

As illustrated inFIG. 1, the developing device44includes a developing part50that delivers the liquid developer G to an electrostatic latent image formed on the photoconductor38and a supplying part48that supplies the liquid developer G to the developing part50.

The developing part50includes a development roller52that rotates (revolves) around an axis (in a direction indicated by the arrow R2) and a charging member54that is disposed so as to be opposed to the development roller52. Furthermore, the developing part50includes a charging member68that charges toner contained in the liquid developer G remaining on the development roller52without being supplied to the photoconductor38and a collecting device58that collects the liquid developer G remaining on the development roller52.

A developing voltage is applied to the development roller52by a power source (not illustrated), and an electric field for developing an electrostatic latent image formed on the photoconductor38is formed between the development roller52and the photoconductor38(in a nip part N1). Furthermore, an electric field for supplying the liquid developer G from a draw-up roller62to the development roller52is formed between the development roller52and the draw-up roller62that will be described later (in a nip part N2).

The charging member54is used to charge toner contained in the liquid developer G, for example, to a positive polarity. The charging member54is disposed so as to be opposed to the development roller52on a downstream side relative to the nip part N2and an upstream side relative to the nip part N1in a direction of rotation of the development roller52. The charging member68is used to charge toner contained in the liquid developer G remaining on the development roller52, for example, to a negative polarity. The charging member68is disposed so as to be opposed to the development roller52on a downstream side relative to the nip part N1and an upstream side relative to the collecting device58in the direction of rotation of the development roller52.

In this configuration, the charging member54changes toner contained in the liquid developer G supplied to the development roller52and held by the development roller52, and the liquid developer G containing the toner is delivered from the development roller52to an electrostatic latent image formed on the photoconductor38. In a case where the electrostatic latent image is developed as a toner image T by using the liquid developer G, oil also transfers to the photoconductor38. Furthermore, the charging member68changes toner contained in the liquid developer G remaining on the development roller52to a negative polarity. Charging the toner to a negative polarity makes it easier to collect the liquid developer G from the development roller52. Then, the collecting device58collects the liquid developer G remaining on the development roller52.

The supplying part48includes a storage part60in which the liquid developer G is stored and the draw-up roller62(an anilox roller) that draws the liquid developer G up from the storage part60and supplies the liquid developer G to the development roller52. Furthermore, the supplying part48includes a blade64that adjusts a layer film of the liquid developer G held by the draw-up roller62and a charging member66that charges toner contained in the liquid developer G held by the draw-up roller62, for example, to a positive polarity. Details of the development roller52, the draw-up roller62, and the collecting device58will be described later.

As illustrated inFIG. 2, the transfer unit32includes a holding roller34on which a toner image T held by the photoconductor38is transferred and is held. Furthermore, the transfer unit32includes a transfer roller36that is disposed on a side opposite to the holding roller34across the continuous paper P and a collecting device46that collects the liquid developer G remaining on the holding roller34. Details of the holding roller34, the transfer roller36, and the collecting device46will be described later.

In this configuration, a first transfer voltage is applied to the holding roller34that rotates in a direction indicated by the arrow R4inFIG. 2by a power source (not illustrated). This forms an electric field for transferring the toner image T on the photoconductor38onto the holding roller34between the holding roller34and the photoconductor38(in a nip part N3). This electric field causes the toner image T held by the photoconductor38to be transferred onto the holding roller34.

A second transfer voltage is applied to the transfer roller36by a power source (not illustrated). This forms, between the transfer roller36and the holding roller34, an electric field for transferring the toner image T on the holding roller34onto the continuous paper P. This electric field causes the toner image T transferred onto the holding roller34to be transferred onto the continuous paper P. The collecting device46collects the liquid developer G remaining on the holding roller34.

Oil Removing Part80

As illustrated inFIG. 5, the oil removing part80includes a melting part82that heats continuous paper P and an oil receiving part84that receives oil on the continuous paper P. The oil receiving part84includes plural pairs of heating rollers86each including a heater.

In this configuration, the melting part82heats the continuous paper P. The pairs of heating rollers86transport the continuous paper P while sandwiching the continuous paper P, and thus the heating rollers86that make contact with an image formation surface of the continuous paper P receive oil from the continuous paper P.

The fixing device70includes a fixing roller74that includes a heater and a sandwiching roller78that is disposed on a side opposite to the fixing roller74across the continuous paper P and includes a heater.

In this configuration, the fixing roller74heated by the heater and the sandwiching roller78heated by the heater transport the continuous paper P while sandwiching the continuous paper P, and thus a toner image T is fixed onto the continuous paper P.

Operation of Overall Configuration

In the image forming apparatus10, the continuous paper P supplied from a supplying device (not illustrated) is transported along a transport path28.

Furthermore, as illustrated inFIG. 5, the photoconductor38of each of the image forming units30of the respective colors rotates, and the photoconductor38is charged by the charging member40. Next, the exposure device42exposes the charged photoconductor38to light in accordance with image data, and thus an electrostatic latent image is formed on the photoconductor38. Then, the developing device44visualizes the electrostatic latent image as a toner image T by developing the electrostatic latent image.

The toner image T formed on the rotating photoconductor38is first-transferred onto the holding roller34. The transfer roller36transfers, onto the transported continuous paper P, the toner image T that has been first-transferred onto the holding roller34. In this process, oil transfers to the continuous paper P together with the toner image T. This process is performed in each of the image forming parts26of the respective colors, and thus toner images T of the respective colors are transferred onto the continuous paper P.

Furthermore, the oil removing part80removes oil that has transferred onto the continuous paper P from the continuous paper P when the toner image T is transferred onto the continuous paper P. Furthermore, the fixing device70fixes the toner image T transferred onto the transported continuous paper P.

Configuration of Substantial Parts

Next, a development roller52, a draw-up roller62, and a collecting device58are described.

As illustrated inFIG. 1, the development roller52has an axial part102that forms a rotary axis and is made of a metal material, a cylindrical elastic part104which the axial part102penetrates, and a coating film106that coats the elastic part104. The development roller52is an example of a cylindrical member. In the present exemplary embodiment, an external diameter of the development roller52is 165 mm.

The elastic part104is made of a rubber material that is an elastic material containing an electrical conducting material. In the present exemplary embodiment, a hardness of the elastic part104is not less than 45 Hs and not more than 55 Hs according to JIS A hardness (JIS K 6253 type A). That is, the elastic part104is a member that is made of a material that is not less than 45 Hs and not more than 55 Hs according to JIS A hardness. Considering output image evaluations that will be described later, the hardness of the elastic part104is desirably not less than 48 Hs and not more than 52 Hs, more desirably 50 Hs according to JIS A hardness.

The coating film106is made of a copolymer (hereinafter referred to as a “PFA resin”) of tetrafluoroethylene and perfluoroalkyl vinyl ether that contains an electrical conducting material. A bending elastic modulus of the coating film106is set to not less than 0.4 GPa and not more than 0.7 GPa. Considering the output image evaluations that will be described later, the bending elastic modulus of the coating film106is desirably not less than 0.4 GPa and not more than 0.6 GPa, more desirably 0.4 GPa and not more than 0.5 GPa. The bending elastic modulus of the coating film106can be measured by peeling part of the coating film106off from the development roller52and evaluating this part according to JIS K 7171 or ISO0178.

A thickness of the coating film106is set to not less than 40 μm and not more than 150 μm. Considering the output image evaluations that will be described later, the thickness of the coating film106is more desirably not less than 40 μm and not more than 100 μm.

The draw-up roller62is made of a metal material, and grooves62A that extend in an axial direction are provided side by side in a circumferential direction on a circumferential surface of the draw-up roller62. That is, the circumferential surface of the draw-up roller62is a corrugated surface. The draw-up roller62is an example of a draw-up member. In the present exemplary embodiment, the draw-up roller62is pressed against the development roller52at a pressure of not less than 19.6 kPa and not more than 196 kPa. Furthermore, an external diameter of the draw-up roller62is set to 160 mm, and a depth of the grooves62A is set to 40 μm.

The collecting device58includes a removing blade90made of polyurethane rubber. That is, the removing blade90is made of an elastic material that can be elastically deformed. This removing blade90has a plate shape having a rectangular cross section, and an end of the removing blade90is in contact with a circumferential surface of the development roller52. The removing blade90is an example of a removing member.

In the present exemplary embodiment, a thickness of the removing blade90is set to 2 mm, and force by which the removing blade90is pressed against the circumferential surface of the development roller52is not less than 9.8×10−3N/mm and not more than 9.8×10−2N/mm. This keeps the liquid developer G remaining on the circumferential surface of the development roller52from passing the removing blade90and remaining on the circumferential surface of the development roller52.

In this configuration, the draw-up roller62that rotates in a direction indicated by the arrow R3inFIG. 1draws up the liquid developer G stored in the storage part60. Then, the blade64adjusts a layer film of the liquid developer G, and the charging member66charges toner contained in the liquid developer G. Furthermore, the liquid developer G drawn up by the draw-up roller62is supplied to the development roller52by an electric field formed between the draw-up roller62and the development roller52. This forms a film (layer) of the liquid developer G on the development roller52. Toner contained in the liquid developer G formed on the development roller52is delivered from the development roller52to an electrostatic latent image formed on the photoconductor38.

Furthermore, the removing blade90peels the liquid developer G remaining on the development roller52off from the development roller52, and thus the collecting device58collects the liquid developer G remaining on the development roller52.

Holding Roller34, Transfer Roller36, and Collecting Device46

Next, the holding roller34, the transfer roller36, and the collecting device46are described.

As illustrated inFIG. 2, the holding roller34has an axial part122that forms a rotary axis and is made of a metal material, a cylindrical elastic part124which the axial part122penetrates, and a coating film126that coats the elastic part124. The holding roller34is an example of a cylindrical member. In the present exemplary embodiment, an external diameter of the holding roller34is set to 242 mm.

The elastic part124is made of a rubber material that is an elastic material containing an electrical conducting material. In the present exemplary embodiment, a hardness of the elastic part124is set to not less than 45 Hs and not more than 55 Hs according to JIS A hardness. That is, the elastic part124is a member made of a material that is not less than 45 Hs and not more than 55 Hs according to JIS A hardness. Considering the output image evaluations that will be described later, the hardness of the elastic part124is desirably not less than 48 Hs and not more than 52 Hs, more desirably 50 Hs according to JIS A hardness.

The coating film126is made of a PFA resin that contains an electrical conducting material. A bending elastic modulus of the coating film126is set to not less than 0.4 GPa and not more than 0.7 GPa. Considering the output image evaluations that will be described later, the bending elastic modulus of the coating film126is desirably not less than 0.4 GPa and not more than 0.6 GPa, more desirably not less than 0.4 GPa and not more than 0.5 GPa. The bending elastic modulus of the coating film126can be measured by peeling part of the coating film126off from the holding roller34and evaluating this part according to JIS K 7171 or ISO0178.

A thickness of the coating film126is set to not less than 40 μm and not more than 150 μm. Considering the output image evaluations that will be described later, the thickness of the coating film126is more desirably not less than 40 μm and not more than 100 μm.

The transfer roller36has an axial part132that forms a rotary axis and is made of a metal material and a cylindrical elastic part134which the axial part132penetrates. The transfer roller36makes contact with the transported continuous paper P and rotates so as to follow the transported continuous paper P. The transfer roller36is an example of a transfer member.

The elastic part134is made of a rubber material that is an elastic material containing an electrical conducting material. In the present exemplary embodiment, a hardness of the elastic part134is set to not less than 45 Hs and not more than 55 Hs according to JIS A hardness. Considering the output image evaluations that will be described later, the hardness of the elastic part134is desirably 50 Hs according to JIS A hardness.

In the present exemplary embodiment, an external diameter of the transfer roller36is set to 200 mm, and the transfer roller36is pressed against the holding roller34with the continuous paper P interposed therebetween at a pressure of not less than 98.0 kPa and not more than 392 kPa.

The collecting device46includes a removing blade92that is made of polyurethane rubber. That is, the removing blade92is made of an elastic material that can be elastically deformed. The removing blade92has a plate shape, and an end of the removing blade92is in contact with a circumferential surface of the holding roller34. In the present exemplary embodiment, a thickness of the removing blade92is set to 2 mm, and force by which the removing blade92is pressed against the circumferential surface of the holding roller34is set to not less than 9.8×10−3N/mm and not more than 9.8×10−2N/mm. This keeps the liquid developer G remaining on the circumferential surface of the holding roller34from passing the removing blade92and remaining on the circumferential surface of the holding roller34.

In this configuration, the transfer roller36and the holding roller34sandwich the continuous paper P, and thus the continuous paper P is pressed against the holding roller34. A second transfer voltage is applied to the transfer roller36by a power source (not illustrated). This forms, between the transfer roller36and the holding roller34, an electric field for transferring a toner image T on the holding roller34onto the continuous paper P. This electric field transfers, onto the continuous paper P, the toner image T transferred onto the holding roller34.

The removing blade92peels the liquid developer G remaining on the holding roller34off from the holding roller34, and thus the collecting device46collects the liquid developer G remaining on the holding roller34.

Operation

Next, operation of a substantial part of the image forming apparatus10is described. The following describes the operation of the substantial part of the image forming apparatus10in comparison with an image forming apparatus510according to a comparative embodiment. First, differences of a configuration of the image forming apparatus510from the image forming apparatus10according to the present exemplary embodiment are described below.

Image Forming Apparatus510

As illustrated inFIG. 12, a development roller552provided in an image forming unit530of the image forming apparatus510has an axial part102, a cylindrical elastic part104which the axial part102penetrates, and a coating film606that coats the elastic part104.

The coating film606is made of polyimide (hereinafter referred to as a “PI resin”) containing an electrical conducting material. A bending elastic modulus of the coating film606is set to 2 GPa, and a thickness of the coating film606is set to 40 μm. That is, the bending elastic modulus of the coating film606is higher than the bending elastic modulus of the coating film106. This means that the coating film606has a higher Shore hardness than the coating film106.

As illustrated inFIG. 13, a holding roller534provided in a transfer unit532of the image forming apparatus510has an axial part122, a cylindrical elastic part124which the axial part122penetrates, and a coating film626that covers the elastic part124.

The coating film626is made of polyimide (hereinafter referred to as a “PI resin”) containing an electrical conducting material. A bending elastic modulus of the coating film606is set to 2 GPa, and a thickness of the coating film606is set to 40 μm. That is, the bending elastic modulus of the coating film626is higher than the bending elastic modulus of the coating film126. This means that the coating film626is harder to deform than the coating film126.

Next, output image evaluations conducted on the image forming apparatus10and the image forming apparatus510are described. Specifically, a solid image evaluation, a missing dot evaluation, and an image unevenness evaluation are conducted as the output image evaluations. The evaluations are conducted by using an image forming apparatus obtained by modifying a development roller and a holding roller of MDP1260 manufactured by Miyakoshi Printing Machinery, Co., Ltd.

A rubber member having a hardness of 55 Hs according to JIS A hardness is used as the elastic parts104of the development rollers52and552, and a coating film having an elastic modulus of 0.7 GPa is used as the coating film106of the development roller52. The evaluations are conducted while changing the thickness of the coating film106.

A rubber member having a hardness of 55 Hs according to JIS A hardness is used as the elastic parts124of the holding rollers34and534, and a coating film having an elastic modulus of 0.7 GPa is used as the coating film126of the holding roller34. The evaluations are conducted while changing the thickness of the coating film126.

OK topcoat ±127.9 manufactured by OJI PAPER CO., LTD. is used as the continuous paper P. A surface of this continuous paper P has an allowable level of unevenness as the continuous paper P.

Evaluation Specifications

In Example 1, the development roller52having the coating film106having a thickness of 300 μm and the holding roller34having the coating film126having a thickness of 300 μm are used (seeFIG. 8).

In Example 2, the development roller52having the coating film106having a thickness of 200 μm and the holding roller34having the coating film126having a thickness of 200 μm are used.

In Example 3, the development roller52having the coating film106having a thickness of 200 μm and the holding roller34having the coating film126having a thickness of 150 μm are used.

In Example 4, the development roller52having the coating film106having a thickness of 150 μm and the holding roller34having the coating film126having a thickness of 200 μm are used.

In Example 5, the development roller52having the coating film106having a thickness of 150 μm and the holding roller34having the coating film126having a thickness of 150 μm are used.

In Example 6, the development roller52having the coating film106having a thickness of 100 μm and the holding roller34having the coating film126having a thickness of 100 μm are used.

In Example 7, the development roller52having the coating film106having a thickness of 40 μm and the holding roller34having the coating film126having a thickness of 40 μm are used.

In Example 8, the development roller52having the coating film106having a thickness of 300 μm and the holding roller34having a coating film made of a PI resin and having a thickness of 40 μm are used.

In Example 9, a development roller having a coating film made of a PI resin and having a thickness of 40 μm and the holding roller34having the coating film126having a thickness of 300 μm are used.

In a comparative example, the development roller552having the coating film606having a thickness of 40 μm and the holding roller534having the coating film626having a thickness of 40 μm are used.

The examples have similar specifications except for the above specifications.

Solid Image Evaluation

A solid image (area coverage 100%) is formed on the continuous paper P by using cyan (C), and uniformity of the solid image is evaluated by visually checking an output image. A case where there is no missing toner is expressed as “good”, a case where there is missing toner in an acceptable level as a product is expressed as “acceptable”, and a case where there is missing toner in an unacceptable level as a product is expressed as “unacceptable”.

Missing Dot Evaluation

A halftone dot image (area coverage 5%) is formed on the continuous paper P by using cyan (C), and dot missing is evaluated by visually checking an output image. A case where there is no missing dot is expressed as “good”, a case where there is a missing dot in an acceptable level as a product is expressed as “acceptable”, and a case where there is a missing dot in an unacceptable level as a product is expressed as “unacceptable”.

Image Unevenness Evaluation

A halftone image (area coverage 50%) is formed on the continuous paper P by using cyan (C), and image unevenness is evaluated by visually checking an output image. A case where the halftone image is formed without unevenness is expressed as “good”, a case where there is image unevenness in an acceptable level as a product is expressed as “acceptable”, and a case where there is image unevenness in an unacceptable level as a product is expressed as “unacceptable”.

Evaluation Results

As described in the table illustrated inFIG. 8, Examples 5 to 7 are evaluated as “good” in all of the evaluations, and Examples 1 to 4 are evaluated as “acceptable” in all of the evaluations. Meanwhile, the comparative example is evaluated as “unacceptable” in all of the evaluations.

DISCUSSION

Comparison Between Comparative Example and Examples 1 to 7

The comparative example is evaluated as “unacceptable” in the solid image evaluation, missing dot evaluation, and image unevenness evaluation. Meanwhile, Examples 1 to 7 are evaluated as “good” or “acceptable” in the solid image evaluation, missing dot evaluation, and image unevenness evaluation. This difference in evaluation result is discussed below.

In the comparative example, the coating film606of the development roller552and the coating film626of the holding roller534are made of a PI resin. The bending elastic modulus of each of the coating films606and626is 2 GPa. Meanwhile, the coating film106of the development roller52and the coating film126of the holding roller34according to Examples 1 to 7 are made of a PFA resin. The bending elastic modulus of each of the coating films106and126is 0.7 GPa. As described above, the bending elastic modulus of each of the coating films606and626in the comparative example is set higher than the bending elastic modulus of each of the coating films106and126in Examples. That is, the coating films606and626are harder to deform than the coating films106and126as described earlier.

For this reason, the comparative example is considered to fail to sufficiently supply the liquid developer G to the development roller552in a state where the liquid developer G has been supplied from the draw-up roller62to the development roller552. Specifically, as illustrated in FIG.10A, a circumferential surface of the development roller552is recessed slightly in some cases. In such cases, as illustrated inFIG. 10B, the coating film606is not sufficiently deformed even in a case where the draw-up roller62is pressed against the development roller552, and therefore a gap550is created between the development roller552and the liquid developer G drawn up by the draw-up roller62. This is considered to be why the liquid developer G is not sufficiently supplied to the development roller552as illustrated inFIG. 10C.

Furthermore, the comparative example is considered to fail to transfer part of the toner image T onto the continuous paper P in a state where the toner image T has been transferred from the holding roller534to the continuous paper P. Specifically, a circumferential surface of the holding roller534is slightly recessed in some cases as illustrated inFIG. 11A. As described above, the surface of the continuous paper P is uneven. In such a case, as illustrated inFIG. 11B, the coating film626is not sufficiently deformed even in a case where the continuous paper P is pressed against the holding roller534by the transfer roller36, and therefore a gap554is created between the continuous paper P and the toner image T held by the holding roller534. This is considered why part of the toner image T is not transferred onto the continuous paper P as illustrated inFIG. 11C.

For the above reasons, the comparative example is considered to be evaluated as “unacceptable” in the output image evaluations.

Meanwhile, Examples 1 to 7 are considered to allow the liquid developer G to be sufficiently supplied from the draw-up roller62to the development roller52in a state where the liquid developer G has been supplied from the draw-up roller62to the development roller52. Specifically, the circumferential surface of the development roller52is slightly deformed in some cases as illustrated inFIG. 6A. In such cases, as illustrated inFIG. 6B, the coating film106is deformed in a case where the draw-up roller62is pressed against the development roller52, and therefore a gap is unlikely to be created between the development roller52and the liquid developer G drawn up by the draw-up roller62. This is considered to be why the liquid developer G is sufficiently supplied to the development roller52as illustrated inFIG. 6C.

Furthermore, Examples 1 to 7 are considered to allow almost whole of the toner image T to be transferred onto the continuous paper P in a state where the toner image T has been transferred from the holding roller34to the continuous paper P. Specifically, the circumferential surface of the holding roller34is recessed slightly in some cases as illustrated inFIG. 7A. As described above, the surface of the continuous paper P is uneven. In such a case, as illustrated inFIG. 7B, the coating film126is deformed in a case where the continuous paper P is pressed against the holding roller34by the transfer roller36, and therefore a gap is unlikely to be created between the continuous paper P and the toner image T held by the holding roller34. This is why almost whole of the toner image T is transferred onto the continuous paper P as illustrated inFIG. 7C.

For these reasons, Examples 1 to 7 are considered to be evaluated as “acceptable” or “good” in the output image evaluations.

Comparison Between Examples 1 to 4 and Examples 5 to 7

Examples 1 to 4 are evaluated as “acceptable” in the output image evaluations. Meanwhile, Examples 5 to 7 are evaluated as “good” in the output image evaluations. This difference in evaluation result is discussed below.

In Examples 1 to 4, the thickness of at least one of the coating film106of the development roller52and the coating film126of the holding roller34is 200 μm or more. Meanwhile, the thickness of the coating film106of the development roller52and the thickness of the coating film126of the holding roller34according to Examples 5 to 7 are set to 150 μm or less. That is, the thickness of at least one of the coating film106and the coating film126according to Examples 1 to 4 is larger than the thickness of the coating films106and126according to Examples 5 to 7.

Accordingly, in Examples 1 to 4, the circumferential surface of the development roller52sometimes does not follow the circumferential surface of the draw-up roller62because of the large thickness of the coating film106even in a case where the draw-up roller62is pressed against the development roller52. This is considered to prevent the liquid developer G from being sufficiently supplied to the development roller52.

Furthermore, in Examples 1 to 4, the circumferential surface of the holding roller34sometimes does not follow the surface of the continuous paper P because of the large thickness of the coating film126even in a case where the continuous paper P is pressed against the holding roller34by the transfer roller36. This is considered to prevent the toner image T from being sufficiently transferred onto the continuous paper P.

For the above reasons, Examples 1 to 4 are considered to be evaluated as “acceptable” in the output image evaluations.

Meanwhile, in Examples 5 to 7, the circumferential surface of the development roller52follows the circumferential surface of the draw-up roller62because of the small thickness of the coating film106in a case where the draw-up roller62is pressed against the development roller52. This is considered to allow the liquid developer G to be sufficiently supplied to the development roller52.

In Examples 5 to 7, the circumferential surface of the holding roller34follows the surface of the continuous paper P because of the small thickness of the coating film126in a case where the continuous paper P is pressed against the holding roller34by the transfer roller36. This is considered to allow the toner image T to be sufficiently transferred onto the continuous paper P.

For the above reasons, Examples 5 to 7 are considered to be evaluated as “good” in the output image evaluations.

Note that the thickness of the coating films106and126in Examples 5 to 7 is set to 40 μm or more in consideration of durability of the coating films106and126. Examples 8 and 9

Examples 8 and 9 are evaluated as “acceptable” in the solid image evaluation, missing dot evaluation, and image unevenness evaluation. This evaluation result is discussed below.

In Examples 1 through 7, the coating film of the development roller and the coating film of the holding roller are made of a PFA resin. This is considered to be why higher output image evaluations are obtained than a case where the coating film of the development roller or the coating film of the holding roller is made of a PI resin.

Next, a cleaning performance evaluation conducted on the image forming apparatus10is described. Specifically, cleaning performance of cleaning the liquid developer G remaining on the circumferential surface of the development roller52is evaluated. The evaluation is conducted by using an image forming apparatus obtained by modifying the development roller52and the removing blade90of MDP1260 manufactured by Miyakoshi Printing Machinery, Co., Ltd.

A rubber member having a hardness of 55 Hs according to JIS A hardness is used as the elastic part104of the development roller52, and a coating film having an elastic modulus of 0.7 GPa is used as the coating film106of the development roller52. Furthermore, a coating film having a thickness of 300 μm is used as the coating film106.

Force by which the removing blade90is pressed against the development roller52is set to 9.8×10−3N/mm.

The evaluation is conducted while changing a setting angle θ1of the removing blade90and filtered maximum waviness (JIS B0610) of the circumferential surface of the development roller52in an axial direction. As illustrated inFIG. 4, the setting angle θ1is an angle formed between a tangent L1to the development roller52at a tangent point T1between the removing blade90and the development roller52and the removing blade90.

Evaluation Specifications

In Example 10, the removing blade90disposed so that the setting angle θ1is 25 degrees and the development roller52configured such that the filtered maximum waviness (JIS B0610) of the circumferential surface in the axial direction is 3.0 μm are used (seeFIG. 9).

In Example 11, the removing blade90disposed so that the setting angle θ1is 30 degrees and the development roller52configured such that the filtered maximum waviness of the circumferential surface in the axial direction is 3.0 μm are used.

In Example 12, the removing blade90disposed so that the setting angle θ1is 35 degrees and the development roller52configured such that the filtered maximum waviness of the circumferential surface in the axial direction is 3.0 μm are used.

In Example 13, the removing blade90disposed so that the setting angle θ1is 40 degrees and the development roller52configured such that the filtered maximum waviness of the circumferential surface in the axial direction is 3.0 μm are used.

In Example 14, the removing blade90disposed so that the setting angle θ1is 45 degrees and the development roller52configured such that the filtered maximum waviness of the circumferential surface in the axial direction is 3.0 μm are used.

In Example 15, the removing blade90disposed so that the setting angle θ1is 25 degrees and the development roller52configured such that the filtered maximum waviness of the circumferential surface in the axial direction is 2.5 μm are used.

In Example 16, the removing blade90disposed so that the setting angle θ1is 25 degrees and the development roller52configured such that the filtered maximum waviness of the circumferential surface in the axial direction is 2.0 μm are used.

In Example 17, the removing blade90disposed so that the setting angle θ1is 25 degrees and the development roller52configured such that the filtered maximum waviness of the circumferential surface in the axial direction is 1.0 μm are used.

The examples have similar specifications except for the above specifications.

Cleaning Performance Evaluation

The liquid developer G that has passed the removing blade90in a case where a halftone image (area coverage 50%) is formed on the continuous paper P by using cyan (C) is visually checked. In other words, the liquid developer G that has not been removed from the circumferential surface of the development roller52by the removing blade90is visually checked. A case where the remaining liquid developer G does not pass the removing blade90and remain on the circumferential surface of the development roller52is expressed as “good”, and a case where the liquid developer G passes the removing blade90and remains on the circumferential surface of the development roller52is expressed as “unacceptable”.

Evaluation Results

As for evaluation results, Examples 10, 11, and 15 are evaluated as “unacceptable”, as described in the table illustrated inFIG. 9. Meanwhile, Examples 12, 13, 14, 16, and 17 are evaluated as “good”.

Discussion

Comparison Between Examples 10 and 11 and Examples 12, 13, and 14

Examples 10 and 11 are considered to cause a front end of the removing blade90that is in contact with the development roller52to be warped away from the development roller52since the setting angle θ1is smaller than the setting angle θ1in Examples 12, 13, and 14. Accordingly, the front end of the removing blade90is slightly away from the circumferential surface of the development roller52, and therefore Examples 10 and 11 are considered to be evaluated as “unacceptable” in the cleaning performance evaluation.

Meanwhile, Examples 12, 13, and 14 are considered to keep the front end of the removing blade90that is in contact with the development roller52from warping away from the development roller52since the setting angle θ1is larger than the setting angle θ1in Examples 10 and 11. Accordingly, contact between the front end of the removing blade90and the circumferential surface of the development roller52is maintained although the filtered maximum waviness of the circumferential surface of the development roller52is 3.0 μm, and therefore Examples 12, 13, and 14 are considered to be evaluated as “good” in the cleaning performance evaluation.

Comparison Between Examples 10 and 15 and Examples 16 and 17

In Examples 10 and 15, the filtered maximum waviness of the circumferential surface of the development roller52is set to 2.5 μm or more. Accordingly, in Examples 10 and 15, the front end of the removing blade90is slightly away from the circumferential surface of the development roller52. This is considered to be why Examples 10 and 15 are evaluated as “unacceptable” in the cleaning performance evaluation.

Meanwhile, in Examples 16 and 17, the filtered maximum waviness of the circumferential surface of the development roller52is set to 2.0 μm or less. Accordingly, contact between the front end of the removing blade90and the circumferential surface of the development roller52is maintained although the setting angle θ1of the removing blade90is 25 degrees. This is considered to be why Examples 16 and 17 are evaluated as “good” in the cleaning performance evaluation.

The cleaning performance evaluation is conducted by using the development roller52and the removing blade90that removes the liquid developer G remaining on the circumferential surface of the development roller52. Note, however, that similar evaluation results will be probably obtained even in a case where the holding roller34and the removing blade92that removes the liquid developer G remaining on the circumferential surface of the holding roller34are used.

SUMMARY

As described above, the coating film106of the development roller52is made of a PFA resin. As is clear from the results of the output image evaluations, an output image is less deteriorated than a case where a development roller having a coating film made of a PI resin is used.

The coating film126of the holding roller34is made of a PFA resin. As is clear from the results of the output image evaluations, an output image is less deteriorated than a case where a holding roller having a coating film made of a PI resin is used.

As is clear from the results of the output image evaluations, in a case where the bending elastic modulus of the coating film106of the development roller52is set to 0.7 GPa or less, an output image is less deteriorated than in a case where a coating film having a bending elastic modulus of 2 GPa is used.

As is clear from the results of the output image evaluations, in a case where the bending elastic modulus of the coating film126of the holding roller34is set to 0.7 GPa or less, an output image is less deteriorated than in a case where a coating film having a bending elastic modulus of 2 GPa is used.

As is clear from the results of the output image evaluations, in a case where the thickness of the coating film106of the development roller52is set to not less than 40 μm and not more than 150 μm, an output image is less deteriorated than in a case where a coating film having a thickness of larger than 150 μm is used.

As is clear from the results of the output image evaluations, in a case where the thickness of the coating film126of the holding roller34is set to not less than 40 μm and not more than 150 μm, an output image is less deteriorated than in a case where a coating film having a thickness of larger than 150 μm is used.

As is clear from the results of the cleaning performance evaluation, in a case where the setting angle θ1of the removing blades90and92is set to not less than 35 degrees and not more than 45 degrees, cleaning performance of removing the liquid developer G remaining on the circumferential surfaces of the development roller52and the holding roller34is higher than in a case where the setting angle θ1of the removing blades90and92is set to 30 degrees or less.

Furthermore, in a case where the filtered maximum waviness of the circumferential surface of the development roller52and the filtered maximum waviness of the circumferential surface of the holding roller34are set to 2.0 μm or less, cleaning performance of removing the liquid developer G remaining on the circumferential surfaces of the development roller52and the holding roller34is higher than in a case where the filtered maximum waviness is 2.5 μm or more.

Although a specific exemplary embodiment of the present disclosure has been described in detail, the present disclosure is not limited to the above exemplary embodiment, and it is clear to a person skilled in the art that other various exemplary embodiments are also encompassed within the scope of the present disclosure.

For example, although the bending elastic modulus of the coating films106and126is set to 0.7 GPa or less by using a PFA resin in the above exemplary embodiment, a bending elastic modulus of a coating film may be set to 0.7 GPa or less by using a tetrafluoroethylene/hexafluoropropylene copolymer (FEP resin) or polytetrafluoroethylene (PTEE). However, in this case, the effect produced in a case where the coating films106and126are made of a PFA resin is not produced.

Furthermore, although the bending elastic modulus of the coating films106and126is set to 0.7 GPa or less in the above exemplary embodiment, a bending elastic modulus of a coating film may be larger than 0.7 GPa. Although the effect produced by setting the bending elastic modulus of the coating films106and126to 0.7 GPa or less is not produced, a bending elastic modulus of a coating film is smaller and an output image is less deteriorated in a case where the coating films106and126are made of a PFA resin than in a case where a coating film is made of a PI resin.

Roller resistance of the holding roller34is not mentioned in particular in the above exemplary embodiment but is desirably not less than 10−7Ω and less than 109Ω in consideration of occurrence of a transfer defect caused by a voltage defect occurring between the photoconductor38and the holding roller34.