JP5232501B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus for a wet developer.

As a developing method in the electrophotographic system, a dry developing method using powder toner (dry developer) is generally used. In recent years, a wet developing method using a wet developer in which toner particles are dispersed in an insulating carrier oil has also been proposed.
Since the wet developer can prevent the agglomeration of the toner particles, toner particles having a smaller particle diameter than that of the dry developer can be used, and image formation with high resolution can be performed.
In addition, unlike the dry developer, the wet developer does not use a heavy carrier such as an iron powder carrier, so that the burden on the image forming apparatus is small and high-speed printing can be supported.

  On the other hand, in an electrophotographic image forming apparatus, the surface of the photoconductor is uniformly charged by a charging unit (charging process), and the surface of the photoconductor is exposed by an exposure unit to form an electrostatic latent image (latent image). Image forming step), toner is ejected onto the electrostatic latent image by the developing means to develop the electrostatic latent image as a toner image (developing step), and the toner image is transferred to a recording medium such as paper by the transferring means (transfer step) ), The toner image is fixed on the recording medium by the fixing means, and an image is formed.

Further, as one of image forming methods using the above-described image forming apparatus, a toner image formed on a photoreceptor is temporarily transferred to an intermediate transfer member (primary transfer), and then the toner image is transferred to a recording medium ( Secondary transfer) methods are known. The toner remaining on the intermediate transfer member without being subjected to the secondary transfer is removed by cleaning the intermediate transfer member with a cleaning blade or the like (cleaning step), and prepares for image formation by the next round.
This method is often used when performing full-color printing, such as a rotary developing device having a plurality of developing devices or a tandem developing device.

  In this way, when performing the secondary transfer after performing the primary transfer in the transfer step, in order to improve the primary transfer property and the secondary transfer property, the intermediate transfer member is likely to adhere toner in the primary transfer, In secondary transfer, conflicting performance is required such that the toner is easily released. Further, if the toner is easily released, even if the toner remains on the intermediate transfer body without being subjected to secondary transfer, it can be easily removed by a cleaning blade or the like, and the cleaning property is improved.

Therefore, as an intermediate transfer body having a contradictory performance such as high when the adhesion force between the toner and the intermediate transfer body is high and low when it is, for example, Japanese Patent Application Laid-Open No. H10-228707 discloses an intermediate transfer body attached to the toner by irradiation with excitation light. An intermediate transfer member provided with a surface layer that generates a photo-excited hydrophilization phenomenon with increased adhesion, and an image forming apparatus including the intermediate transfer member are disclosed.
According to Patent Document 1, a material that develops a photoexcited hydrophilization phenomenon is used, and toner adhesion is switched by light irradiation, so that the intermediate transfer member is imparted with the contradictory performance of high adhesion and low adhesion. Yes.

  However, as described in Patent Document 1, a method for increasing the adhesion of toner by utilizing hydrophilicity is effective for a dry developer, but is not effective for a wet developer. In addition, although the primary transferability is improved when the toner adhesion increases due to the hydrophilicity, the secondary transferability and the cleaning performance are lowered as they are, so that the hydrophilicity is reduced in order to reduce the adhesion during the secondary transfer. It was necessary to reduce it. For this reason, it is necessary to stop the light irradiation during the secondary transfer and wait until the photoexcited surface returns to the ground state.

By the way, when a wet developer is used, the intermediate transfer member is used because the photosensitive member and the intermediate transfer member are close to each other and the toner particles move quickly through the gap between the photosensitive member and the intermediate transfer member. The toner easily adheres to the toner and generally has good primary transferability.
However, since the ratio of carrier oil in the toner image is reduced during secondary transfer compared to during primary transfer, the toner particles are less likely to move smoothly onto the recording medium, and the toner is difficult to release from the intermediate transfer member. It was. Therefore, the secondary transfer property and the cleaning property are likely to be deteriorated.
Therefore, conventionally, the surface of the intermediate transfer member has been coated with a fluorine-based resin such as polytetrafluoroethylene (PTFE) to improve the releasability of the toner.
JP 2001-282004 A

  However, the wet developer has a low surface tension, and in the conventional method of coating the surface of the intermediate transfer member with a fluorine-based resin, it is not always sufficient to improve the releasability. Therefore, particularly in an image forming apparatus using a wet developer, further improvement in secondary transfer property and cleaning property is required.

  The present invention has been made in view of the above circumstances, and an object thereof is to realize an image forming apparatus that can exhibit excellent releasability with respect to a wet developer at the time of secondary transfer.

  As a result of intensive studies, the present inventors have imparted oil repellency to the intermediate transfer member and repel the wet developer in which toner particles are dispersed in carrier oil, which is an oil component, so that the intermediate transfer member is separated from the wet developer. It was found that the moldability is improved. And it discovered that oil repellency could be provided by providing a hydrophilic surface layer in an intermediate transfer body, and came to complete this invention.

That is, the image forming apparatus of the present invention includes an image forming unit including a photoconductor on which an image is formed by a wet developer containing carrier oil, and an intermediate transfer body on which an image is transferred from the photoconductor. In the forming apparatus, the water contact angle of the surface of the intermediate transfer member is 10 ° or less.
Further, a water supply means for supplying water to the intermediate transfer member before the image is transferred from the photosensitive member to the intermediate transfer member is provided upstream of the image forming unit with respect to the driving direction of the intermediate transfer member. It is preferable.

According to the image forming apparatus of the present invention, an excellent releasability with respect to a wet developer can be expressed at the time of secondary transfer.
In addition, the image forming apparatus of the present invention is excellent in secondary transfer properties and cleaning properties.

Hereinafter, the present invention will be described in detail with reference to the drawings.
[Image forming apparatus]
FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus of the present invention. FIG. 1 shows a color printer adopting a tandem method, but the present invention is not limited to this, and can be suitably used for a copying machine, a facsimile, a laser beam printer, and the like.
The image forming apparatus 1 in this example includes an image forming unit 2 that forms an image using a wet developer, a paper feed cassette 3 that stores a recording medium (such as paper), and an image formed by the image forming unit 2. Secondary transfer means 4 for transferring onto the recording medium, fixing means 5 for fixing the transferred image on the recording medium, discharging means 6 for discharging the recording medium after fixing, and discharging means from the paper feed cassette 3 And a sheet conveying means 7 for conveying the recording medium up to six.

  The image forming unit 2 corresponds to the intermediate transfer member 20, the cleaning unit 21 that cleans the intermediate transfer member 20, and yellow (Y), magenta (M), cyan (C), and black (BK) colors, respectively. And an image forming unit F (FY, FM, FC, FB).

The intermediate transfer member 20 provided in the image forming apparatus 1 of the present invention has a surface water contact angle of 10 ° or less. Usually, the smaller the surface water contact angle, the more hydrophilic the surface, and the greater the water contact angle, the more water repellent. That is, if the surface is hydrophilic, it shows oil repellency, and if it has water repellency, it shows lipophilicity. When the water contact angle is 10 ° or less, the surface of the intermediate transfer member 20 is sufficiently hydrophilic, that is, oil-repellent. In the wet developer described later, since toner particles are dispersed in carrier oil, which is an oil component, the oil-repellent intermediate transfer member can easily repel the wet developer during the secondary transfer, and as a result, the releasability is improved. .
The upper limit of the water contact angle on the surface of the intermediate transfer member 20 is preferably 8 ° or less. On the other hand, the lower limit of the water contact angle is preferably 0 ° or more, and more preferably 2 ° or more.

The water contact angle on the surface of the intermediate transfer member is measured as follows.
At room temperature, pure water is dropped on the surface of the intermediate transfer member, and the tangent of the droplet drawn from the contact point of the three phases of the solid phase (intermediate transfer member), the liquid phase (droplet), and the gas phase (atmosphere) The angle on the droplet side formed by the surface of the intermediate transfer member is measured, and this is used as the water contact angle of the surface of the intermediate transfer member. As an apparatus for measuring the water contact angle, “OCA-40” manufactured by Data Physics can be used.
In the present invention, “room temperature” means 22 to 28 ° C.

In order to set the water contact angle on the surface of the intermediate transfer member to 10 ° or less, for example, a hydrophilic surface layer may be provided on the surface of the substrate constituting the intermediate transfer member.
Here, an example of the configuration of the intermediate transfer member will be specifically described.
Examples of the material of the base material include resins such as polyimide, polyester, polyether, ether ketone, polyamide, polycarbonate, polyvinylidene fluoride, polyphenylene sulfide, polyfluoroethylene-ethylene copolymer, and resins mainly composed of these. It is done. Of these, polyimide is preferable. In the present invention, the “main raw material” means that the content is 50% by mass or more.
The base material is formed into an endless shape, that is, a loop shape by a method such as extrusion molding or inflation molding. As for the thickness of a base material, 100-150 micrometers is preferable.

The surface layer makes the surface of the intermediate transfer body oil-repellent, improves releasability with respect to a wet developer, and in particular, transfers an image (toner image) from the intermediate transfer body to the recording medium (secondary transfer). Although provided, the surface layer also serves to transfer an image satisfactorily from a photoconductor described later to an intermediate transfer member (primary transfer).
The surface layer can be formed by applying a surface layer coating solution containing inorganic particles and a resin medium to the surface of the substrate to form a coating film, and drying the coating film or curing it by light irradiation. Examples of the application method include known methods such as spraying, dipping, and brushing.
The thickness of the surface layer is preferably 3 to 10 μm.

Examples of inorganic particles include silica, titanium oxide, and alumina. Among these, silica is preferable from the viewpoint of versatility and cost reduction.
Examples of the resin medium include urethane-based, acrylic-based, phenol-based, melamine-based, alkyd-based, silicone-based, epoxy-based, and unsaturated polystyrene-based resins. Of these, urethane-based resins are preferable, and water-soluble urethane is particularly preferable from the viewpoint of hydrophilicity.
These inorganic particles and the resin medium may be used alone or in combination of two or more.

The surface layer coating liquid may contain components other than the inorganic particles and the resin medium described above.
Examples of other components include carbon black and barium titanate.

5-30 mass% is preferable in 100 mass% of coating liquids for surface layers, and, as for the compounding quantity of an inorganic particle, 10-25 mass% is more preferable. If the blending amount of the inorganic particles is within the above range, the inorganic particles are sufficiently exposed on the outermost surface of the surface layer and become a hydrophilic outermost surface. Therefore, a hydrophilic surface layer having a water contact angle of 10 ° or less is formed. It is formed. That is, an intermediate transfer member having a surface water contact angle of 10 ° or less is obtained.
Further, the water contact angle on the surface of the intermediate transfer member can be controlled by adjusting the blending amount of the inorganic particles in the surface layer coating solution. Specifically, as the blending amount of the inorganic particles increases, the hydrophilicity of the formed surface layer increases and the water contact angle on the surface of the intermediate transfer member tends to decrease. On the other hand, if the amount of inorganic particles is reduced, the water contact angle tends to increase.

In the present invention, an intermediate transfer member in which an elastic layer is provided between the substrate and the surface layer may be used. By providing the elastic layer, the adhesion with the recording medium is improved, so that the secondary transfer efficiency becomes better.
Examples of the material for the elastic layer include polyurethane rubber, chlorinated polyisoprene rubber, nitrile rubber, chloropyrene rubber, ethylene propylene rubber, butyl rubber, silicone rubber, and hydrogenated polybutadiene rubber.
The elastic layer can be formed by applying these materials to the substrate surface to form a coating film, and drying the coating film or curing it by light irradiation. Examples of the application method include known methods such as spraying, dipping, and brushing.
The thickness of the elastic layer is preferably 50 to 300 μm.

  As shown in FIG. 1, the intermediate transfer member 20 is stretched around a drive roller 22 and a tension roller 23, and runs clockwise in FIG. In the running of the intermediate transfer member 20, the surface facing outward is referred to as the surface of the intermediate transfer member 20, and the other surface is referred to as the back surface.

The cleaning unit 21 includes a cleaning roller 211 and a cleaning blade 212.
Examples of the material of the cleaning roller 211 and the cleaning blade 212 include polyurethane rubber, silicone rubber, and ethylene-propylene-diene rubber.

Four image forming units F (FY, FM, FC, FB) are arranged near the intermediate transfer member 20 and arranged between the cleaning unit 21 and the secondary transfer unit 4. The order of arrangement of the image forming units is not limited to this, but the arrangement shown in FIG. 1 is preferable in consideration of the influence on the completed image due to the color mixture of each color.
Each image forming unit F includes a photoconductor 10, a charger 11, an exposure device 12, a developing device 13, a primary transfer roller 14, a cleaning device 15, a charge removal device 16, and a carrier liquid removal roller 17. Is provided.
Each image forming unit F is provided with a wet developer circulation device (not shown), and supplies and collects the wet developer corresponding to each color.

The photoreceptor 10 is a cylindrical member, and can carry an image containing charged toner on the surface thereof.
The charger 11 is a device that can uniformly charge the surface of the photoreceptor 10.
The exposure device 12 has a light source such as an LED, and irradiates light onto the uniformly charged surface of the photoconductor 10 in accordance with image data input from an external machine. As a result, an electrostatic latent image is formed on the surface of the photoreceptor 10. Note that the light source of the exposure device 12 may be the same type of light source as the light source of the charge removal device 16 described later.

  The developing device 13 holds the wet developer so as to face the electrostatic latent image on the photoconductor 10, thereby attaching the toner in the wet developer to the electrostatic latent image. As a result, the electrostatic latent image is developed as a toner layer. The developing device 13 includes a developing container 130, a developing roller 131, a supply roller 132, a drawing roller 133, a cleaning blade 134, and a developing roller charger 135. The wet developer 18 is accommodated in the developing container 130.

The primary transfer roller 14 is disposed on the back surface of the intermediate transfer member 20 so as to face the photoconductor 10. A voltage having a polarity opposite to that of the toner in the toner image is applied to the primary transfer roller 14 from a power source (not shown). That is, the primary transfer roller 14 applies a voltage having a polarity opposite to that of the toner to the intermediate transfer body 20 at a position where it is in contact with the intermediate transfer body 20. Since the intermediate transfer member 20 has conductivity, the applied voltage attracts toner to the surface side of the intermediate transfer member 20 and the periphery thereof.
The cleaning device 15 is a device for cleaning the wet developer remaining without being transferred from the photoconductor 10 to the recording medium, and includes a residual developer conveying screw 151 and a cleaning blade 152.

The static eliminator 16 has a light source for static elimination, and removes the wet developer by the cleaning blade 152 and removes the surface of the photoconductor 10 with light from the light source in preparation for the next round of image formation.
A known light source such as a light emitting diode (LED) can be used as the light source for static elimination.

  The carrier liquid removal roller 17 is a substantially cylindrical member that can rotate in the same direction as the photoconductor 10 around a rotation axis parallel to the rotation axis of the photoconductor 10. The carrier liquid removing roller 17 is disposed on the side where the secondary transfer unit 4 is disposed with respect to the position where the photosensitive member 10 and the intermediate transfer member 20 are in contact with each other, and removes carrier oil from the surface of the intermediate transfer member 20. It is a member to do.

The paper feed cassette 3 stores a recording medium (such as paper) on which a toner image is fixed.
The secondary transfer unit 4 transfers an image (toner image) formed on the intermediate transfer member 20 to a recording medium. The secondary transfer unit 4 is opposed to the drive roller 22 for driving the intermediate transfer member 20 and the drive roller 22. The secondary transfer roller 41 is arranged.

The fixing unit 5 fixes the image transferred on the recording medium, and includes a pair of fixing rollers 51. Examples of the fixing roller 51 include one that simply applies pressure to fix an image, and one that fixes heat using heat energy.
The discharge unit 6 discharges the recording medium on which the image has been fixed by the fixing unit 5, and is disposed on the upper part of the image forming apparatus 1.
The paper transport unit 7 includes a plurality of transport roller pairs, and transports the recording medium from the paper feed cassette 3 to the secondary transfer unit 4, the fixing unit 5, and the discharge unit 6.

The image forming apparatus of the present invention is preferably provided with water supply means 24 as shown in FIG. The water supply unit 24 supplies water to the intermediate transfer body 20 before the image is transferred from the photoreceptor 10 to the intermediate transfer body 20. By providing the water supply means 24, it is possible to positively form a water film on the surface of the intermediate transfer member 20, and as a result, it becomes easier to repel the wet developer and the releasability is further improved.
Here, “before the image is transferred from the photoreceptor to the intermediate transfer member” means before the first image is primarily transferred to the intermediate transfer member in a certain round of image formation. When the images corresponding to the respective colors are sequentially transferred from the four image forming units F to the intermediate transfer member 20 as shown, the images are primarily transferred from the image forming unit FY corresponding to yellow (Y) to the intermediate transfer member 20. Before that.

  Therefore, it is preferable that the water supply unit 24 is provided upstream of the image forming unit F with respect to the driving direction of the intermediate transfer body 20. Specifically, it is preferably provided upstream of the image forming unit FY corresponding to yellow (Y), and particularly preferably provided between the cleaning unit 21 and the image forming unit FY.

The water supply unit 24 includes a storage container 242 that stores the water 241 and a supply member 243 that supplies the water 241 from the storage container 242 to the intermediate transfer body 20.
Examples of the supply member 242 include a sponge roller, a sprayer, and a wet cloth.

Here, the wet developer used in the image forming apparatus of the present invention will be described.
<Wet developer>
The wet developer is obtained by dispersing toner particles containing a binder resin and a colorant in a carrier oil.
Examples of the binder resin constituting the toner particles include polyester resins, styrene resins, acrylic resins, styrene-acrylic copolymer resins, olefin resins (polyethylene, polypropylene, etc.), vinyl chloride resins, and polyamide resins. Thermoplastic resins such as resin, polyurethane resin, polyvinyl alcohol resin, vinyl ether resin, N-vinyl resin, styrene-butadiene resin; epoxy resin (bisphenol A type epoxy resin, hydrogenated bisphenol A type epoxy resin, novolak type) Epoxy resins, polyalkylene ether type epoxy resins, cycloaliphatic type epoxy resins, etc.), and thermosetting resins such as cyanate resins.

  Further, a charge control resin may be used as the binder resin. The charge control resin is colorless, and a wet developer having stable chargeability can be obtained even in color continuous printing at high speed. As the charge control resin, known negative charge control resins and positive charge control resins used in wet developers can be used, and they are appropriately selected according to the chargeability of the toner particles.

  A known pigment or dye can be used as the colorant. For example, black pigments such as carbon black, acetylene black, lamp black, spirit black, magnetite; I. Permanent Yellow 17, C.I. I. Pigment Yellow 3, Nephthol Yellow S, Hansa Yellow G, C.I. I. Yellow pigments such as vat yellow; I. Permanent Red 122, C.I. I. Red pigments such as CI Pigment Red 2 and Pigment Violet 19; I. Permanent blue, phthalocyanine blue, C.I. I. Bat Blue, C.I. I. And blue pigments such as acid blue.

  As the carrier oil, known carrier oils used for wet developers can be used, and specific examples include paraffin oil, isoparaffin oil, silicone oil, and naphthenic solvents.

  The wet developer can be prepared by a known method. That is, a mixture of a binder resin and a colorant is kneaded to obtain a toner kneaded product, which is pulverized with a pulverizer or the like into toner particles, and the toner particles and carrier oil are mixed with a disperser or the like to obtain toner particles. A wet developer dispersed in a carrier oil is obtained.

Next, an image forming method will be described using the image forming apparatus 1 shown in FIG.
[Image forming method]
First, the surface of the photoreceptor 10 is charged by the charger 11. Next, the exposure device 12 exposes the surface of the photoreceptor to form an electrostatic latent image. Next, the developing device 13 attaches a wet developer to the electrostatic latent image on the photoreceptor 10 to develop the electrostatic latent image as a toner image (image). In this way, the image formed by each image forming unit F is transferred from the photosensitive member 10 to the intermediate transfer member 20 (primary transfer), and is superimposed on the intermediate transfer member 20 to form a color toner image.
Simultaneously with the formation of the color toner image, the recording medium accommodated in the paper feed cassette 3 is transported along the paper transport means 7 and sent to the secondary transfer means 4 in time with the primary transfer to the intermediate transfer body 20. The secondary transfer means 4 transfers the color toner image (image) on the intermediate transfer body 20 onto the recording medium (secondary transfer).

Next, the recording medium on which the image is transferred is conveyed to the fixing unit 5 and the image is fixed on the recording medium.
The recording medium on which the image is fixed is discharged to the outside of the image forming apparatus 1 by the discharge unit 6.

  After the secondary transfer, the wet developer remaining on the intermediate transfer member 20 is removed by the cleaning unit 21 of the intermediate transfer member 20. Further, the wet developer that is not supplied to the photoreceptor 10 and remains on the developing roller 131 is scraped off and collected by the cleaning blade 134. Further, after the wet developer remaining without being transferred is removed by the cleaning blade 152, the surface of the photoreceptor 10 is discharged by the discharging device 16 to prepare for image formation by the next round.

  Since the image forming apparatus of the present invention includes an intermediate transfer member having a water contact angle of 10 ° or less on the surface, it exhibits excellent releasability with respect to a wet developer during secondary transfer. This is because the surface of the intermediate transfer member is hydrophilic, that is, oil-repellent, and easily repels an oily wet developer. Therefore, the image forming apparatus of the present invention is excellent in secondary transferability. Further, since the intermediate transfer member is easy to repel the wet developer, even if an image remains on the intermediate transfer member without being subjected to the secondary transfer, it is easily removed by the cleaning unit. Therefore, the image forming apparatus of the present invention is also excellent in cleaning properties.

  In addition, by using an intermediate transfer member having a water contact angle of 10 ° or less on the surface, it is possible to express excellent releasability with respect to a wet developer. The toner easily adheres to the intermediate transfer member for reasons such as rapid movement, and the primary transfer property is good. Even if a specific intermediate transfer member as described above is used, the primary transfer property is affected. Primary transfer from the photosensitive member to the intermediate transfer member.

Further, when the image forming apparatus 1 includes the water supply unit 24 as illustrated in FIG. 1, the water supply is performed before the image formed by each image forming unit F is transferred from the photoconductor 10 to the intermediate transfer body 20. Water is supplied from the means 24 to the intermediate transfer member 20.
The amount of water supply is not particularly limited. For example, when a sponge roller is used as the supply member 243, an amount sufficient to wet the surface of the intermediate transfer member 20 when the wet sponge roller contacts the intermediate transfer member 20 is sufficient. is there. Since this amount is very small, there is almost no influence on the photoreceptor 10 or the recording medium. In addition, primary transfer from the photoconductor 10 to the intermediate transfer body 20 can be performed without affecting the primary transfer property, and a water film can be actively formed on the surface of the intermediate transfer body 20, resulting in wet development. It becomes easier to play the agent and the releasability is further improved. Therefore, secondary transfer properties and cleaning properties are improved.
When a sprayer is used as the supply member 243, it is preferable to supply water to the intermediate transfer body 20 at a spray amount of about 0.01 to 1 mL / min.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to a following example. In the following description, “part” indicates “part by mass”, and “%” indicates “% by mass”.
[Example 1]
<Manufacture of intermediate transfer member>
A polyamide resin was molded into a belt having a thickness of 100 μm by extrusion molding to obtain a base material.
Next, polyurethane rubber was coated on the outer peripheral surface of the base material with a spray coater so that the thickness after drying was 200 μm, and then dried to form an elastic layer.
Next, the surface layer coating solution containing 30 parts of silica and 70 parts of water-soluble urethane is coated on the outer peripheral surface of the elastic layer by a spray coater so that the thickness after drying is 10 μm, and then dried. A surface layer having a silica content of 30% was formed to obtain an intermediate transfer member.

(Measurement of water contact angle)
The water contact angle of the surface of the obtained intermediate transfer member was measured using “OCA-40” manufactured by DataPhysics.
That is, pure water is dropped on the surface of the intermediate transfer member at room temperature (22 ° C.), and is drawn from the contact point of the three phases of the solid phase (intermediate transfer member), the liquid phase (droplet), and the gas phase (atmosphere). The angle between the tangent line of the droplet and the droplet side formed by the surface of the intermediate transfer member was measured, and this was used as the water contact angle of the surface of the intermediate transfer member. The results are shown in Table 1.

<Evaluation>
The wet transfer image forming apparatus shown in FIG. 1 was used as the image forming apparatus, and the obtained intermediate transfer member was provided. Further, a water supply unit is provided between the image forming unit and the cleaning unit. Further, a wet developer for black in which toner particles composed of a polyester resin (binder resin) and carbon black (colorant) are dispersed in paraffin oil (carrier oil) was used as a wet developer.

(Evaluation of secondary transferability)
Continuous printing was performed at a printing rate of 5%. Printing was interrupted immediately before the secondary transfer on the 10th sheet, and an adhesive tape was applied to the intermediate transfer member, and a part of the image on the intermediate transfer member was peeled off. The density of the image adhering to the adhesive tape was measured with a reflection densitometer (“Spectro Eye” manufactured by Gretag Macbeth Co., Ltd.), and this was taken as the density before transfer.
Next, printing was resumed, and the image was secondarily transferred onto the recording medium by the secondary transfer means. Immediately thereafter, the operation of the image forming apparatus was stopped, an adhesive tape was applied to the intermediate transfer body immediately after the secondary transfer, and the density of the image attached to the adhesive tape was measured, and this was used as the density after transfer. Secondary transferability was determined from the following formula (1). The results are shown in Table 1.
Secondary transferability (%) = {(image density before transfer−image density after transfer) / image density before transfer} × 100 (1)

(Evaluation of cleaning properties)
Continuous printing is performed at a printing rate of 5%, and after the second transfer on the 10th sheet, the operation of the image forming apparatus is stopped immediately before cleaning the intermediate transfer member in the cleaning section, and the adhesive tape is applied to the intermediate transfer member. The density of the image adhering to the film was measured and used as the density before cleaning.
Subsequently, the operation was restarted, and the intermediate transfer member was cleaned by the cleaning unit. Immediately after that, the operation was stopped, and an adhesive tape was affixed to the intermediate transfer member immediately after cleaning, and the density of the image adhering to the adhesive tape was measured, and this was taken as the density after cleaning. The cleaning property was determined from the following formula (2). The results are shown in Table 1.
Cleaning property (%) = {(Image density before cleaning−Image density after cleaning) / Image density before cleaning} × 100 (2)

(Image evaluation)
Continuous printing was performed at a printing rate of 5%, and the image on the 10th sheet was visually evaluated. The results are shown in Table 1.
“Good” means that the image density is 1.3 or more and no image unevenness is observed. “Image unevenness” means that the image density is 1.3 or more. This indicates a state where unevenness is recognized, and “low density” indicates a state where image unevenness is not recognized but the image density is less than 1.3.

[Example 2]
An intermediate transfer member was produced in the same manner as in Example 1 except that a surface layer coating solution containing 20 parts of silica and 80 parts of water-soluble urethane was used and a surface layer having a silica content of 20% was formed. Each evaluation was performed. Table 1 shows the water contact angle on the surface of the intermediate transfer member and the evaluation results.

[Example 3]
The image forming apparatus was provided with the same intermediate transfer member as in Example 1 except that no water supply unit was provided, and each evaluation was performed. The results are shown in Table 1.

[Comparative Example 1]
An intermediate transfer member was produced in the same manner as in Example 1 except that a surface layer coating solution containing 5 parts of silica and 95 parts of water-soluble urethane was used and a surface layer having a silica content of 5% was formed. Each evaluation was performed. Table 1 shows the water contact angle on the surface of the intermediate transfer member and the evaluation results.

[Comparative Example 2]
An intermediate transfer member was produced and evaluated in the same manner as in Example 1 except that a surface layer (thickness 10 μm) made of polytetrafluoroethylene (PTFE) was formed on the outer peripheral surface of the elastic layer. Table 1 shows the water contact angle on the surface of the intermediate transfer member and the evaluation results.

[Comparative Example 3]
An intermediate transfer member was produced in the same manner as in Example 1, except that a surface layer (thickness 10 μm) made of polytetrafluoroethylene (PTFE) was formed on the outer peripheral surface of the elastic layer. Each evaluation was performed in the same manner as in Example 1 except that the obtained intermediate transfer member was provided in an image forming apparatus and no water supply unit was provided. Table 1 shows the water contact angle on the surface of the intermediate transfer member and the evaluation results.

  As is clear from Table 1, in Examples 1 to 3 using an intermediate transfer body having a water contact angle of 10 ° or less on the surface, the surface of the intermediate transfer body was easy to repel the wet developer. Excellent cleaning performance. The obtained image was also good. In particular, in Examples 1 and 2 provided with water supply means, since a water film was easily formed on the surface of the intermediate transfer member, it was easier to repel the wet developer and the secondary transfer property was further excellent.

On the other hand, Comparative Example 1 using an intermediate transfer member having a water contact angle of 15 ° on the surface makes it difficult for the surface of the intermediate transfer member to repel the wet developer, and the secondary transfer property and the cleaning property are inferior to those of the examples. It was. In addition, image unevenness was observed in the obtained image.
In Comparative Example 2 using an intermediate transfer member having a surface layer made of PTFE and having a water contact angle of 110 ° on the surface, the surface of the intermediate transfer member is less likely to repel the wet developer, and the secondary transfer property is remarkably high. Declined. In addition, image unevenness was observed in the obtained image.
In Comparative Example 3 in which a surface layer made of PTFE was formed, an intermediate transfer body having a water contact angle of 110 ° on the surface was used, and no water supply means was provided, the surface of the intermediate transfer body was less likely to repel the wet developer. Secondary transferability was significantly reduced. Moreover, although the density unevenness was not recognized in the obtained image, the density was low and the image quality was inferior to that of the example.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus of the present invention.

Explanation of symbols

1: image forming apparatus, 2: image forming means, 3: paper feed cassette, 4: secondary transfer means, 5: fixing means, 6: discharge means, 7: paper transport means, 10: photoconductor, 18: wet development Agent: 20: intermediate transfer member, 21: cleaning unit, 24: water supply means, F: image forming unit.

Claims (1)

In an image forming apparatus comprising: an image forming unit including a photoconductor on which an image is formed by a wet developer containing carrier oil; and an intermediate transfer body on which an image is transferred from the photoconductor.
The water contact angle of the surface of the intermediate transfer member is 10 ° or less,
Before the image is transferred from the photosensitive member to the intermediate transfer member, water supply means for supplying water to the intermediate transfer member is provided upstream of the image forming unit with respect to the driving direction of the intermediate transfer member. An image forming apparatus.

Images