JP2008145831A - Wet developer and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wet developer in which toner hardly sediments or aggregates but shows excellent redispersion property and air bubbles are easily vanished, and to provide an image forming apparatus. <P>SOLUTION: The wet developer contains a carrier liquid and toner, in which inorganic fine particles subjected to surface treatment so as to increase dispersibility and affinity to the carrier liquid are added. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wet developer containing a carrier liquid, a toner, and inorganic fine particles, and an image forming apparatus using the wet developer.

  An electrophotographic image forming apparatus that forms an electrostatic latent image on a photoconductor (photosensitive drum), attaches toner to the photoconductor, and transfers and fixes the image onto paper or the like is a copying machine, an MFP (multifunctional printer), Widely used in FAX, printers, etc. The developing system generally used in these image forming apparatuses is dry development using powder toner.

  However, the powder toner has a problem that the toner is scattered, and also has a problem in image quality that the resolution is poor because the toner particles are as large as 7 to 10 μm.

  Therefore, in image forming apparatuses that require higher image quality and higher resolution, such as office printers for mass printing and on-demand printing apparatuses, wet development in which toner is dispersed in a nonpolar organic solvent such as liquid paraffin. A wet development method using an agent is used. This is because the wet developer has toner particles as small as about 1 μm and a large charge amount, so that the toner image is hardly disturbed and high resolution can be realized.

  In a conventional wet image forming apparatus, a low-viscosity liquid in which toner is mixed in an organic solvent as a carrier liquid at a ratio of 1 to 2% as a wet developer (hereinafter also referred to as a liquid developer or simply a developer). Developer was used. However, since such a developer has a low toner concentration (hereinafter, also referred to as developer concentration or simply concentration), it is necessary to deposit a large amount on the paper and dry it at the time of fixing, and a large amount of vapor is generated. It had a big environmental problem. Further, only a low boiling point carrier liquid can be used for volatilization, and there is a big problem in safety such as a low flash point.

  Against this backdrop, high viscosity and high concentration, which is constituted by dispersing toner as solid content consisting of resin and pigment in high concentration in insulating liquid “carrier liquid” such as silicone oil. An image forming apparatus using a liquid developer has been proposed. When this liquid developer is used, the above-described problems are prevented from occurring, and since the toner concentration is high, there is an advantage that it is not necessary to use a large amount of developer.

  When developing with this liquid developer, the charged toner moves in the insulating liquid by electrostatic force to develop the electrostatic latent image. The developing efficiency is improved as the moving distance is shorter. For this purpose, a thin layer of a micron unit of developer is formed on a developer carrying member such as a developing roller, and development is performed by bringing the thinned developer into contact with the photoreceptor.

  The toner image formed on the photosensitive member by development is directly transferred to the recording material, or is primarily transferred to the intermediate transfer member and then secondarily transferred to the recording material.

  However, in general, a wet developer tends to cause image flow because of a decrease in electrical resistance due to the use of a metal ion-based dispersant and a small particle cohesion force when toner particles are gathered together in development and transfer. It has been a problem. Therefore, a technique has been proposed in which inorganic fine particles are added to improve the close cohesion between toners and improve image flow (see Patent Document 1).

  According to the technique described in Patent Document 1, by incorporating inorganic fine particles, excess ions that lower the electrical resistance of the liquid developer are adsorbed, and the toner cohesive force at the time of close assembly is increased by interaction with the toner particles. It is said that the image flow can be prevented.

  However, on the other hand, in situations other than wet development and close-packed toner image formation during transfer, toner agglomeration may have a negative effect.

  For example, toner particles dispersed in a liquid developer tend to settle. When the toner particles settle, the toners easily adhere to each other, and unnecessary aggregation occurs there. If the toner starts to adhere and aggregate, re-dispersion becomes difficult and adversely affects the development and transfer processes. For this reason, the image quality is deteriorated due to image density unevenness.

  The technique described in Patent Document 1 shows an example in which a relatively small amount of inorganic fine particles are added to a liquid developer having a relatively low toner concentration. However, as described above, particularly in recent years, a liquid developer having a high concentration and high viscosity is often used.

In a liquid developer having a high concentration and high viscosity, there is a problem that image defects occur when bubbles generated in the developer are taken into the development nip. If the liquid developer has a low toner concentration, it is possible to increase the supply of developer to the development nip and make it difficult for air bubbles to stay, but for high-concentration and high-viscosity liquid developers, it is necessary to take other measures. There is.
JP-A-6-118726

  As described above, in a high-concentration, high-viscosity wet developer used for wet image formation, toner easily settles, adheres and aggregates with each other, reduces redispersibility, and adversely affects the image forming process. There's a problem. In addition, when bubbles are generated, it is difficult to eliminate the bubbles, and there is also a problem that the image is adversely affected.

  An object of the present invention is to solve the above-described problems, and to provide a wet developer and an image forming apparatus in which toner hardly settles and aggregates, has excellent redispersibility, and easily eliminates bubbles.

  In order to solve the above problems, the present invention has the following features.

  1. A wet developer comprising an insulating carrier liquid, toner particles that are incompatible with the carrier liquid, and inorganic fine particles dispersed in the carrier liquid, wherein the carrier liquid is a hydrocarbon solvent, and the inorganic fine particles Is a wet developer modified with an alkyl group.

  2. 2. The wet developer according to 1, wherein the inorganic fine particles are modified with an alkyl group having 8 or more carbon atoms.

  3. A wet developer comprising an insulating carrier liquid, toner particles that are incompatible with the carrier liquid, and inorganic fine particles dispersed in the carrier liquid, wherein the carrier liquid is a silicone-based solvent, A wet developer treated with silicone oil.

  4). A wet developer comprising an insulating carrier liquid, toner particles that are incompatible with the carrier liquid, and inorganic fine particles dispersed in the carrier liquid, wherein the carrier liquid is a hydrocarbon solvent, and the inorganic fine particles Is a wet developer treated with silicone oil.

  5. 5. The wet developer according to any one of 1 to 4, wherein the inorganic fine particles have a volume average particle size of 10 nm or more and 1 μm or less.

  6). The wet developer according to any one of 1 to 5, wherein the addition amount of the inorganic fine particles is 0.1% by mass or more and 15% by mass or less.

  7. 7. The wet developer according to any one of 1 to 6, wherein the toner concentration is 10% by mass or more and 40% by mass or less.

  8). 8. An image forming apparatus for developing a latent image on an image carrier with a developer carried on a developer carrier to form a toner image, wherein the developer is any one of 1 to 7. An image forming apparatus using a wet developer.

  According to the present invention, in a wet developer containing a carrier liquid and a toner, by adding inorganic fine particles having good dispersibility to the carrier liquid, the toner is less likely to settle and aggregate and has excellent redispersibility. In addition, it is possible to provide a wet developer that easily eliminates bubbles, and an image forming apparatus that uses the wet developer to suppress toner aggregation and image quality degradation due to bubbles.

  Embodiments according to the present invention will be described with reference to the drawings.

  2. Description of the Related Art Wet image forming apparatuses that develop using a thin layer of a liquid developer are used in copying machines, simple printing machines, printers, and the like. In general, an electrophotographic image forming process is commonly used for these. The configuration and functional operation of the electrophotographic wet image forming apparatus and the liquid developer according to the present invention used therein will be described.

  Hereinafter, embodiments of a wet image forming apparatus using a liquid developer according to the present invention will be described with reference to the drawings.

(Example of overall configuration and operation of image forming apparatus according to this embodiment)
FIG. 1 shows an example of the overall configuration of an image forming apparatus according to this embodiment. The overall configuration of the image forming apparatus will be described with reference to FIG. However, only the components related to the image forming process are shown. The components related to the feeding, transporting and discharging of the recording medium are omitted or simplified.

  In the image forming apparatus 10 of FIG. 1, the image forming unit includes a photosensitive drum 1 as an image carrier, a charging device 2, an exposure device 3, a liquid developing device 4, and a first cleaning device 6.

  In FIG. 1, only one liquid developing device 4 is disposed, but a plurality of liquid developing devices 4 may be disposed for color image formation. The color development method, the presence / absence of intermediate transfer, and the like may be set arbitrarily, and an arbitrary arrangement according to it can be taken.

  The photosensitive drum 1 has a cylindrical shape with a photosensitive layer (not shown) formed on the surface thereof, and is driven to rotate in the direction of arrow A in FIG. On the outer periphery of the photosensitive drum 1, a first cleaning device 6, a charging device 2, an exposure device 3, a liquid developing device 4, and an intermediate transfer roller 5 are sequentially arranged along the rotation direction of the photosensitive drum 1. ing.

  The charging device 2 charges the surface of the photosensitive drum 1 to a predetermined potential.

  The exposure device 3 irradiates the surface of the photosensitive drum 1 with light to lower the charge level in the irradiated area, thereby forming an electrostatic latent image.

  The liquid developing device 4 develops the latent image formed on the photosensitive drum 1. That is, the liquid developer is conveyed to the development area of the photosensitive drum 1, and the toner contained in the liquid developer is supplied to the electrostatic latent image on the surface of the photosensitive drum 1 to form a toner image.

  In the developing process, a developing bias voltage having the same polarity as the toner is applied to the developing roller 41 of the liquid developing device 4 from a power source (not shown). Similarly, a difference in electric field is formed by the balance between the toner and the potential of the latent image on the photosensitive drum 1 having the opposite polarity, and the toner in the developer is electrostatically adsorbed to the photosensitive drum 1 according to the latent image, and the photosensitive drum. The latent image on 1 is developed.

  The intermediate transfer unit includes an intermediate transfer roller 5 as an intermediate transfer member, a secondary transfer roller 7, and a second cleaning device 11.

  The intermediate transfer roller 5 is disposed so as to face the photosensitive drum 1 and rotates in the direction of arrow B while being in contact with the photosensitive drum 1. Primary transfer from the photosensitive drum 1 to the intermediate transfer roller 5 is performed at the nip portion between the intermediate transfer roller 5 and the photosensitive drum 1.

  In the primary transfer process, a transfer bias voltage having a polarity opposite to that of toner is applied to the intermediate transfer roller 5 from a power source (not shown). As a result, an electric field is formed between the intermediate transfer roller 5 and the photosensitive drum 1 at the primary transfer position, and the toner image on the photosensitive drum 1 is electrostatically adsorbed to the intermediate transfer roller 5, and the intermediate transfer roller 5 is transferred.

  When the toner image is transferred to the intermediate transfer roller 5, the first cleaning device 6 removes the residual toner on the photosensitive drum 1, and the next image formation is performed.

  The intermediate transfer roller 5 and the secondary transfer roller 7 are arranged so as to face each other with a recording medium 9 as a recording material interposed therebetween, and rotate in contact with each other via the recording medium 9. Secondary transfer from the intermediate transfer roller 5 to the recording medium 9 is performed at the nip portion between the intermediate transfer roller 5 and the secondary transfer roller 7.

  The recording medium 9 is conveyed in the direction of arrow C to the secondary transfer position in accordance with the secondary transfer timing.

  In the secondary transfer process, a transfer bias voltage having a polarity opposite to that of the toner is applied to the secondary transfer roller 7 from a power source (not shown). As a result, an electric field is formed between the intermediate transfer roller 5 and the secondary transfer roller 7, and the intermediate transfer roller 5 is transferred onto the recording medium 9 that has passed between the intermediate transfer roller 5 and the secondary transfer roller 7. The upper toner image is electrostatically attracted and transferred onto the recording medium 9.

  When the toner image is transferred onto the recording medium 9, the second cleaning device 11 removes the residual toner on the intermediate transfer roller 5, and the next toner image transfer is performed.

  The fixing unit includes a pair of fixing rollers 8a and 8b that are arranged to face each other and rotate in contact with each other. The fixing rollers 8a and 8b are provided with heat sources, respectively. When the recording medium 9 passes between the fixing rollers 8a and 8b, the recording medium 9 is pressurized at a high temperature. As a result, the toner that forms a toner image on the recording medium 9 is fused and fixed to the recording medium 9.

(Configuration and operation of the liquid developing device 4)
FIG. 2 shows a schematic configuration example of the liquid developing device 4. The configuration and operation of the liquid developing device 4 will be described with reference to FIG.

  The developer tank 44 contains a liquid developer.

  The supply roller 43 is disposed so as to be immersed in the liquid developer in the developer tank 44, and rotates to draw up the liquid developer from the developer tank 44. The high-viscosity liquid developer is conveyed while adhering to the surface of the supply roller 43 by its adhesive force.

  The regulating member 45 is a blade, and is disposed so as to face and abut the supply roller 43 as shown in the figure, and regulates the amount of developer that adheres to the surface of the supply roller 43 and is conveyed. As a result, a thin developer layer is formed on the surface of the supply roller 43 and is conveyed toward the next conveyance roller 42.

  The transport roller 42 is disposed to face the supply roller 43. At this nip portion, the developer thin layer formed on the surface of the supply roller 43 is copied onto the surface of the conveying roller 42 and conveyed toward the developing roller 41.

  The developing roller 41 is disposed to face the conveying roller 42. In this nip portion, the developer thin layer transported to the surface of the transport roller 42 is scraped off by the developing roller 41, and the developer thin layer is carried and transported to the surface of the developing roller 41.

  The developing roller 41 as the developer carrying member rotates in contact with the photosensitive drum 1 as the image carrying member, and the developer thin layer conveyed to the nip portion with the photosensitive drum 1, that is, the developing region is The latent image on the photosensitive member 1 is developed.

  The pre-developing charging device 47 assists the electrical movement of the charged toner to the latent image by applying a charge to the liquid developer on the developing roller 41.

  Even after the latent image on the photosensitive drum 1 is developed, a thin layer of developer remains on the surface of the developing roller 41. If the remaining developer is transported to the development area again as it is, the removal member 46 removes the remaining developer because it adversely affects the next development.

(Configuration of liquid developer)
The configuration of the liquid developer used for development will be generally described. The liquid developer according to the present invention further contains inorganic fine particles, which will be described later.

  In the liquid developer, colored toner particles are dispersed at a high concentration in a carrier liquid which is a solvent. In addition, additives such as a dispersant and a charge control agent may be appropriately selected and added to the liquid developer.

  As the carrier liquid, an insulating, non-volatile solvent at room temperature is used. The toner particles are mainly composed of a resin and a pigment or dye for coloring. The resin has a function of uniformly dispersing pigments and dyes in the resin and a function as a binder when being fixed to the recording material.

  The volume average particle diameter of the toner is suitably in the range of 0.1 μm or more and 5 μm or less. When the average particle diameter of the toner is less than 0.1 μm, the developability is greatly lowered. On the other hand, when the average particle diameter exceeds 5 μm, the quality of the image is degraded.

  The ratio of the toner particle mass to the liquid developer mass is suitably about 10 to 40 mass%. When the amount is less than 10% by mass, the toner particles are liable to settle, and there is a problem in stability over time during long-term storage. Further, in order to obtain a required image density, it is necessary to supply a large amount of developer, the carrier liquid adhering to the paper increases, and it must be dried at the time of fixing, and steam is generated, resulting in environmental problems. If it exceeds 40% by mass, the viscosity of the liquid developer becomes too high, making it difficult to manufacture and handle.

(Addition of inorganic fine particles, redispersibility, defoaming)
In the present embodiment, inorganic fine particles are further added to the liquid developer having the above configuration. As described above, the purpose of adding inorganic fine particles is to solve the problem that the toners easily settle, adhere to each other, aggregate, reduce the redispersibility, and adversely affect the image forming process. It is for improving. Further, in order to solve the problem that when bubbles are generated, it is difficult to eliminate the bubbles and adversely affect the image, that is, to improve the defoaming property.

<Surface treatment of inorganic fine particles>
In order to solve these problems, inorganic fine particles are used. In addition to simply adding inorganic fine particles, the inorganic fine particles to be added have a property of being easily dispersible and compatible with the solvent used as the carrier liquid. Need to be.

  In this embodiment, since a hydrocarbon solvent or a silicone solvent is generally used as the carrier liquid, inorganic fine particles subjected to surface treatment suitable for each solvent were selected.

  In order to make it easy to become familiar with the solvent as the carrier liquid, inorganic fine particles such as silicon oxide or titanium oxide are subjected to a surface treatment, and the inorganic fine particles whose surface is the same as the solvent used and has good dispersibility. Adopt as follows.

  For example, for hydrocarbon solvents, inorganic fine particles that have been treated so that the surface is modified with an alkyl group. Alternatively, inorganic fine particles that have been treated with silicone oil so that the surface has a low surface tension. In addition, inorganic fine particles that have been treated with silicone oil for silicone solvents.

  These surface treatments improve the dispersibility in the carrier liquid. The above-described problem, particularly the effect on redispersibility will be described with reference to FIG.

<Improvement of redispersibility>
FIG. 3 is a diagram illustrating a state of toner particle sedimentation in the liquid developer. 3 (a) to 3 (c) show a liquid developer (a) to which inorganic fine particles subjected to the surface treatment are added, a liquid developer (b) to which untreated inorganic fine particles are added, and inorganic fine particles, respectively. The state of the liquid developer (c) not added is shown.

  In FIG. 3A, the toner particles 31 exist in a dispersed state in the carrier liquid 32 while adsorbing the dispersant 33 on the surface in a timely manner. In addition, inorganic fine particles 34 are dispersed in the carrier liquid 32.

  The inorganic fine particles 34 are subjected to the above surface treatment. For example, when a hydrocarbon solvent is used as the carrier liquid 32, the surface of the inorganic fine particles 34 is modified with a long-chain alkyl group 34 a that is the same quality as the carrier liquid 32 and is easily dispersed.

  Due to the presence of these alkyl groups 34a, a carrier liquid (in this case, a hydrocarbon solvent) 32a is always held on the surface of the inorganic fine particles 34. Therefore, even if the toner particles 31 settle and try to approach each other, the inorganic fine particles 34 holding the carrier liquid 32 a are dispersed in the carrier liquid 32 and are held between the toner particles 31 together with the carrier liquid 32 a.

  The same applies when the surface of the inorganic fine particles 34 is treated with silicone oil. Since the surface is treated with silicone oil during the production of the inorganic fine particles, the bond between the silicone oil is cut by the influence of heat and acid, and the bond with the surface of the inorganic fine particles is formed. Thus, the inorganic fine particles 34 hold the carrier liquid 32a and are dispersed in the carrier liquid 32.

  Thus, the inorganic fine particles 34 are present between the toner particles 31 together with the carrier liquid 32 a, whereby a thick carrier liquid layer 32 is formed between the toner particles 31, thereby preventing contact between the toner particles 31.

  As described above, aggregation of the toner particles 31 when settled can be prevented, and redispersibility can be improved.

  Also in FIG. 3B, the toner particles 31 are present in a dispersed state in the carrier liquid 32 while adsorbing the dispersant 33 on the surface in a timely manner. Similarly, inorganic fine particles 34 are dispersed in the carrier liquid 32. However, the inorganic fine particles 34 are not subjected to the above surface treatment.

  Therefore, the inorganic fine particles 34 do not hold the carrier liquid 32a on the surface as in the case of FIG. When the toner particles 31 settle and try to come close to each other, the inorganic fine particles 34 do not form a thick carrier liquid layer 32 even if they are interposed between the toner particles 31, and sufficiently prevent the toner particles 31 from contacting each other. It is not possible.

  The presence of the inorganic fine particles 34 themselves between the toner particles 31 has a slight contact prevention effect. However, since the carrier liquid 32 cannot be interposed, a great effect cannot be expected.

  Further, in FIG. 3C, the inorganic fine particles themselves are not dispersed in the carrier liquid 32. Therefore, when the toner particles 31 settle and try to approach each other, only the dispersant 33 interposed on the surface of the toner particles 31 prevents it.

  Although the dispersant is adsorbed to and desorbed from the toner particle surface at an appropriate time, it cannot prevent the proximity of the toner particle itself. Accordingly, it is considered that contact between the toner particles 31 cannot be prevented, and the toners are shifted to a very close state and easily cause aggregation.

<Improved antifoaming properties>
The carrier liquid used in the liquid developer generally has a problem that the surface tension is small and bubbles are likely to be mixed therein.

  In the case of using a conventional low-concentration liquid developer, the liquid developer can be excessively supplied to the development nip portion during development, so that even if bubbles are mixed, the bubbles remain in a fixed position. The possibility was small and it was possible to make it less susceptible to bubbles.

  However, when a high-concentration liquid developer of about 10% to 40% by mass is used as in this embodiment, the peripheral speed difference between the developing roller and the photosensitive member cannot be increased at the development nip portion. That is, the replacement of the liquid developer layer at the nip portion is slow, and when bubbles in the liquid developer are taken into the nip portion, the bubbles stay at a fixed position, and the image is developed without supplying the liquid developer to the bubble portion. Image defects may occur on the top.

  However, by adding inorganic fine particles that are easy to disperse in the carrier liquid as described above, even if bubbles are mixed in, the fine particles holding the carrier liquid on the surface in the liquid developer thin layer approach the bubbles. Becomes easy to break, and it is possible to suppress the occurrence of image loss due to bubbles.

<Addition of inorganic fine particles>
As described above, a hydrocarbon solvent or a silicone solvent is generally used as a carrier liquid for a liquid developer. Therefore, inorganic fine particles subjected to surface treatment suitable for each solvent should be selected. That's fine.

  Examples of the hydrocarbon solvent include Isopar and liquid paraffin, and examples of the silicone solvent include commercially available silicone oil.

  As for the inorganic fine particles subjected to the surface treatment, many such as alkyl group-modified inorganic fine particles and silicone oil-treated inorganic fine particles are available as commercial products (see Examples described later). Examples of the component serving as the base of the inorganic fine particles include silicon oxide and titanium oxide.

  As for the volume average particle diameter of the inorganic fine particles, the effect of improving the redispersibility is larger when it has a certain size. Specifically, the average particle diameter is preferably 10 nm or more.

  The larger the particle size of the inorganic fine particles, the larger the distance between the intervening toners, so that the dispersibility of the inorganic fine particles per se in the carrier liquid can be kept low.

  In order to further improve the dispersibility, for example, if alkyl group-modified inorganic fine particles are used for a hydrocarbon solvent, it is desirable to use an alkyl group having a long chain having 8 or more carbon atoms. More carrier liquid can be held on the surface of the inorganic fine particles.

  The volume average particle size of the inorganic fine particles is preferably 1 μm or less. If the particle size is not too large, the substantial toner layer thickness does not decrease due to the presence of the inorganic fine particles, and good developability can be maintained while preventing the occurrence of density unevenness. The average particle diameter of the inorganic fine particles is more preferably about 1/5 or less of the toner layer thickness.

  The inorganic fine particles are preferably added in an amount of 0.1% by mass or more and 15% by mass or less with respect to the liquid developer at the time of preparing the liquid developer. The inorganic fine particles may be added before or after the toner is pulverized.

  The larger the added amount, the more effective the redispersibility and the defoaming property, and preferably 0.1% by mass or more. Further, when the addition amount is 15% by mass or less, the developability is less likely to decrease due to an increase in the viscosity of the liquid developer.

  Examples in which these inorganic fine particles are added will be described below.

  Examples and comparative examples in which the liquid developer according to the present invention was prepared and redispersibility and antifoaming property were evaluated will be described.

(Preparation of liquid developer)
The liquid developer was prepared using a toner in which carbon is dispersed in a polyester resin and a hydrocarbon solvent or a silicone solvent as a carrier liquid. A small amount of a dispersant is added.

  Moresco White P-40 (manufactured by Matsumura Oil Research Co., Ltd.) was used as the hydrocarbon solvent, and silicone oil AK20 (manufactured by Asahi Kasei Wacker) was used as the silicone solvent.

  Wet pulverization was performed in a sand mill, and the pulverization time was adjusted to a toner volume average particle diameter of 2 μm. The toner content was 20% by mass with respect to the entire liquid developer. The viscosity of the liquid developer was 100 Pa · s to 400 Pa · s.

  As the inorganic fine particles, silicon oxide or titanium oxide as a base component, those having various particle diameters and subjected to various treatments were added after pulverization treatment by changing the addition amount. However, only Example 14 described later is added before pulverization.

  The amount added was changed from 0.1% by mass to 20% by mass on the basis of 8% by mass.

  The liquid developer preparation conditions (inorganic fine particles and solvent) for each example and comparative example will be described below (see Tables 1 to 5 below).

<Inorganic fine particles and solvent in each example>
In Example 1, TS720 (manufactured by Cabot Corporation) was used as the inorganic fine particles with respect to the hydrocarbon solvent. TS720 has silicon oxide as a base component and has an average particle size of 200 to 300 nm and is treated with octylsilane. The amount added was 8%.

  In Example 2, Aerosil R816 (manufactured by Aerosil) was used as the inorganic fine particles with respect to the hydrocarbon solvent. R816 has silicon oxide as a base component and has an average particle diameter of 12 nm and is treated with hexadecylsilane. The amount added was 8%.

  In Example 3, Aerosil R805 (manufactured by Aerosil) was used as the inorganic fine particles with respect to the hydrocarbon solvent. R805 is based on silicon oxide and has an average particle size of 12 nm and is treated with octylsilane. The amount added was 8%.

  In Example 4, Aerosil T805 (manufactured by Aerosil) was used as the inorganic fine particles with respect to the hydrocarbon solvent. T805 uses titanium oxide as a base component and has an average particle diameter of 21 nm and is treated with octylsilane. The amount added was 8%.

  In Example 5, Aerosil RY200 (manufactured by Aerosil) was used as the inorganic fine particles with respect to the hydrocarbon solvent. RY200 has silicon oxide as a base component, and has an average particle diameter of 12 nm and is treated with silicone oil. The amount added was 8%.

  In Example 6, Aerosil R972 (manufactured by Aerosil) was used as the inorganic fine particles with respect to the hydrocarbon solvent. R972 has silicon oxide as a base component and has an average particle size of 16 nm and is treated with dimethyldichlorosilane. The amount added was 5%.

  In Example 7, TS720 (manufactured by Cabot Corporation) was used as the inorganic fine particles with respect to the silicone solvent. TS720 has silicon oxide as a base component and has an average particle size of 200 to 300 nm and is treated with octylsilane. The amount added was 5%.

  In Example 8, TS720 (manufactured by Cabot Corporation) was used as the inorganic fine particles with respect to the hydrocarbon solvent. TS720 has silicon oxide as a base component and has an average particle size of 200 to 300 nm and is treated with octylsilane. The amount added was 0.1%.

  In Example 9, TS720 (manufactured by Cabot Corporation) was used as the inorganic fine particles with respect to the hydrocarbon solvent. TS720 has silicon oxide as a base component and has an average particle size of 200 to 300 nm and is treated with octylsilane. The amount added was 1%.

  In Example 10, TS720 (manufactured by Cabot Corporation) was used as the inorganic fine particles with respect to the hydrocarbon solvent. TS720 has silicon oxide as a base component and has an average particle size of 200 to 300 nm and is treated with octylsilane. The amount added was 10%.

  In Example 11, TS720 (manufactured by Cabot Corporation) was used as the inorganic fine particles with respect to the hydrocarbon solvent. TS720 has silicon oxide as a base component and has an average particle size of 200 to 300 nm and is treated with octylsilane. The amount added was 15%.

  In Example 12, TS720 (manufactured by Cabot Corporation) was used as the inorganic fine particles with respect to the hydrocarbon solvent. TS720 has silicon oxide as a base component and has an average particle size of 200 to 300 nm and is treated with octylsilane. The amount added was 20%.

  In Example 13, Aerosil RY50 (manufactured by Aerosil Co., Ltd.) was used as the inorganic fine particles with respect to the hydrocarbon solvent. RY50 has silicon oxide as a base component and has an average particle size of 40 nm and is treated with silicone oil. The amount added was 8%.

  In Example 14, Aerosil RY300 (manufactured by Aerosil) was used as the inorganic fine particles with respect to the hydrocarbon solvent. RY300 is based on silicon oxide and has an average particle size of 7 nm and is treated with silicone oil. The amount added was 8%.

  In Example 15, TS720 (manufactured by Cabot Corporation) was used as the inorganic fine particles with respect to the hydrocarbon solvent. TS720 has silicon oxide as a base component and has an average particle size of 200 to 300 nm and is treated with octylsilane. The amount added was 8%. However, the addition of inorganic fine particles is performed before pulverization.

<Inorganic fine particles and solvent of each comparative example>
In Comparative Example 1, inorganic fine particles are not added to the hydrocarbon solvent.

  In Comparative Example 2, Aerosil 200 (manufactured by Aerosil) was used as the inorganic fine particles with respect to the hydrocarbon solvent. Aerosil 200 is based on silicon oxide and has an average particle size of 12 nm and is not treated. The amount added was 5%.

  In Comparative Example 3, inorganic fine particles are not added to the silicone solvent.

  In Comparative Example 4, Aerosil 200 (manufactured by Aerosil) was used as the inorganic fine particles with respect to the silicone solvent. Aerosil 200 is based on silicon oxide and has an average particle size of 12 nm and is not treated. The amount added was 5%.

  In Comparative Example 5, Aerosil R816 (manufactured by Aerosil) was used as the inorganic fine particles with respect to the silicone solvent. Aerosil R816 is based on silicon oxide and has an average particle size of 12 nm and is treated with hexadecylsilane. The amount added was 5%.

(Evaluation methods and results)
The prepared liquid developer was used to evaluate redispersibility and antifoaming property. The evaluation methods and results are as follows.

<Redispersibility evaluation method>
Regarding redispersibility, the sedimentation state of the toner was evaluated. The evaluation was based on the fact that the adhesion and aggregation between the toners are less likely to occur, and the redispersion is easier, that is, the more the toner is less likely to settle, the easier it is to redisperse.

  In the evaluation method, the produced liquid developer was placed in a 300 ml glass bottle, stored at 40 ° C. for one week, and allowed to settle. Thereafter, the liquid developer was shaken with a red devil for 30 seconds and allowed to stand for 5 minutes, and then the amount of supernatant (depth of supernatant / total depth of liquid developer) was measured and evaluated. The smaller the amount of the supernatant, the better the redispersibility.

  Evaluation is ◎ (particularly good) when the amount of supernatant is less than 2%, ○ (good) when it is more than 5%, △ (also good) when it is more than 10%, and × (impossible) more than 10% It was. More than Δ is acceptable redispersibility.

<Defoaming evaluation method>
About the defoaming property, the bubble generation state was evaluated by an image. The liquid developer was subjected to a process in which bubbles are likely to be generated, and the evaluation was made that the smaller the number of image defects generated in an image after actually forming an image, the easier the bubbles generated in the liquid developer disappear.

  In the evaluation method, the liquid developer subjected to the redispersibility evaluation was used as it was, 20 g of alumina beads (φ6 mm) were added to the bottle, and the mixture was shaken with Red Devil for 2 minutes. Thereafter, a liquid developer was applied to the image forming apparatus shown in FIG.

  FIG. 4 shows a schematic configuration example of an image forming apparatus used for image output. Components having the same functions as those of the image forming apparatus shown in FIG. 1 are denoted by the same reference numerals. The explanation is omitted. However, the schematic configuration is different only in the liquid developing device and the point that the image is transferred directly to the recording medium 9 without the intermediate transfer roller 5.

  Unlike the case of FIG. 1, the liquid developing device of FIG. That is, there are only two rollers, a supply roller and a developing roller. The reason for adopting the two-roller configuration is that an image is formed and evaluated under conditions where bubbles are more likely to be affected during development.

  The image forming process conditions are a system speed of 400 mm / sec, the photosensitive member is negatively charged OPC, the charging potential is −700 V, the developing voltage is −450 V, the transfer voltage is +600 V, and the pre-developing corona charging is a needle applied voltage of −3. Adjusted appropriately at ˜5 kV.

  The output print image was visually observed to count the number of image defects caused by bubbles. The area of the visually evaluated image is 20 cm × 1 m wide. The number of image defects in that range was 0 (particularly good), 2 to 5 (good), and 6 or more x (impossible). ○ The above is acceptable defoaming property.

<Evaluation results>
The evaluation results in each example and comparative example are shown in Tables 1 to 5. The solvent HC represents a hydrocarbon solvent (P40), and Si represents a silicone solvent (AK20).

  Table 1 shows the contents of the treatment of the added inorganic fine particles and the effect on the hydrocarbon solvent. As a result, in all of Examples 1 to 5, the redispersibility ◎ or ◯ and the antifoaming property are all ◎. For Example 6, the redispersibility is Δ. About Comparative Examples 1 and 2, all are redispersibility x and defoaming property is also x.

  About Example 1, it has produced the effect that the dispersibility with respect to a hydrocarbon-type solvent is raised by performing an octylsilane process, and a particle size is large with 200 to 300 nm.

  Example 2 has a long-chain (C16) alkyl group and is easily compatible with a solvent.

  In Example 3, the alkyl group is C8, and a fine supernatant is seen in the toner sedimentation state, but there is no particular problem. This level has a sufficient effect compared to the comparative example.

  Example 4 is the same treatment as Example 3, but the particle size is slightly larger, indicating good results. The difference in surface properties between titanium oxide and silicon oxide appears to have no effect.

  Example 5 is a silicone oil treatment. This seems to be a slightly smaller particle size, but it is not a particularly problematic level. It has a sufficient effect compared with the comparative example.

  Example 6 shows an improvement due to modification with a methyl group, and is not a particularly problematic level. Compared with the comparative example, it is sufficiently effective.

  In Comparative Example 1, inorganic fine particles are not added.

  In Comparative Example 2, although inorganic fine particles are added, it is untreated and dispersibility in the solvent is not considered.

  Table 2 shows the addition of the added inorganic fine particles to the silicone solvent and the effect thereof. As a result, for Example 7, both the redispersibility and the antifoaming property are ◎. About Comparative Examples 3 to 5, all are redispersibility x.

  In Example 7, the effect of increasing the dispersibility in the silicone-based solvent by performing the octylsilane treatment and that the particle size is as large as 200 to 300 nm are effective.

  In Comparative Example 3, inorganic fine particles are not added.

  In Comparative Example 4, although inorganic fine particles are added, it is untreated and dispersibility in the solvent is not considered.

  In Comparative Example 5, no improvement in redispersibility is observed with the hexadecylsilane treatment. Compared to the embodiment of the present invention, the level is still problematic.

  Table 3 shows the effect of changing the amount of inorganic fine particles added to the hydrocarbon solvent. As a result, for Examples 8 to 12, both redispersibility and antifoaming properties are ◎ or ま た は.

  Only in Example 8 where the addition amount is slightly smaller (addition amount 0.1%), the toner sedimentation state shows a slight supernatant, but it is a level having a sufficient effect as compared with the comparative example.

  In Example 12, the redispersibility and antifoaming property were ◎ or ○, but there was a tendency for the developed image density to decrease due to the increase in the viscosity of the liquid developer due to the addition of inorganic fine particles.

  Table 4 shows the effect when the particle size of the inorganic fine particles is changed with respect to the hydrocarbon solvent. As a result, in Examples 1, 13, 4 and 5, all of the redispersibility and antifoaming property are ◎ or ◯. For Example 14, the redispersibility is Δ.

  Only in Example 14 in which the particle size is slightly smaller (average particle size 7 μm), the toner sedimentation state is slightly clear, but it is at a level that has a sufficient effect as compared with the comparative example.

  Table 5 shows the effect of changing the addition time of the inorganic fine particles with respect to the hydrocarbon solvent. Example 1 is a standard post-grinding addition, and only Example 15 is added before grinding. As a result, in both Examples 1 and 15, the redispersibility and antifoaming properties are all ◎.

  It is presumed that since the inorganic fine particles have high dispersibility in the solvent, they are less likely to be adsorbed on the particle surface due to stress during pulverization.

  As can be seen from the above examples, according to the embodiment of the present invention, in the wet developer containing the carrier liquid and the toner, by adding inorganic fine particles having good dispersibility to the carrier liquid, To provide a wet developer in which toner does not easily settle and aggregate, has excellent redispersibility, and easily eliminates bubbles, and an image forming apparatus that uses the wet developer to suppress image aggregation due to toner aggregation and bubbles. Can do.

  The scope of the present invention is not limited to the above embodiment. Unless it deviates from the meaning of this invention, those changed forms are also included in the range.

1 is a diagram illustrating an overall configuration example of an image forming apparatus according to an embodiment. FIG. 2 is a diagram illustrating a schematic configuration example of a liquid developing device 4 in FIG. 1. (A) liquid developer to which surface-treated inorganic fine particles are added, (b) liquid developer to which untreated inorganic fine particles are added, and (c) toner particles in a liquid developer to which inorganic fine particles are not added. It is a figure which shows the state of sedimentation. It is a figure which shows the example of schematic structure of the image forming apparatus used for the image output for defoaming property evaluation.

Explanation of symbols

10 Image forming apparatus 1 Photosensitive drum (image carrier)
2 Charging device 3 Exposure device 4 Liquid developing device 5 Intermediate transfer roller (intermediate transfer member)
6 First cleaning device 7 Secondary transfer roller 8a, 8b Fixing roller 9 Recording medium 11 Second cleaning device 31 Toner particle 32 Carrier liquid 32a Carrier liquid held by inorganic fine particles 33 Dispersant 34 Inorganic fine particles 34a Inorganic fine particle surface Modifying groups (alkyl groups, siloxane groups, etc.)
41 Developing roller (developer carrier)
42 Conveying roller 43 Supply roller 44 Developer tank 45 Control member 46 Removal member 47 Pre-development charging device

Claims (8)

A wet developer comprising an insulating carrier liquid, toner particles incompatible with the carrier liquid, and inorganic fine particles dispersed in the carrier liquid,
The wet developer, wherein the carrier liquid is a hydrocarbon solvent, and the inorganic fine particles are modified with an alkyl group. The wet developer according to claim 1, wherein the inorganic fine particles are modified with an alkyl group having 8 or more carbon atoms. A wet developer comprising an insulating carrier liquid, toner particles incompatible with the carrier liquid, and inorganic fine particles dispersed in the carrier liquid,
The wet developer, wherein the carrier liquid is a silicone solvent, and the inorganic fine particles are treated with silicone oil. A wet developer comprising an insulating carrier liquid, toner particles incompatible with the carrier liquid, and inorganic fine particles dispersed in the carrier liquid,
The wet developer, wherein the carrier liquid is a hydrocarbon solvent, and the inorganic fine particles are treated with silicone oil. 5. The wet developer according to claim 1, wherein the inorganic fine particles have a volume average particle diameter of 10 nm or more and 1 μm or less. The wet developer according to claim 1, wherein the addition amount of the inorganic fine particles is 0.1% by mass or more and 15% by mass or less. The wet developer according to claim 1, wherein the toner concentration is 10% by mass or more and 40% by mass or less. An image forming apparatus for developing a latent image on an image carrier with a developer carried on the developer carrier to form a toner image,
An image forming apparatus using the wet developer according to claim 1 as the developer.

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