JPH0784459A - Wet type image forming device - Google Patents

Abstract

PURPOSE:To obtain high image quality stably over a long period by liquid development without unnecessarily deteriorating an org. photosensitive medium by a liquid developer. CONSTITUTION:The org. photosensitive medium having the extreme surface resin layer 4 into which a charge transfer material 5 of a low mol.wt. of <=1000 is not included is used as the photosensitive medium 1 of the wet type image forming device having the photosensitive medium 1, a latent image forming means 2 for forming an electrostatic latent image on the photosensitive medium 1 and a liquid developing means 3 or developing the electrostatic latent image on the photosensitive medium 1 by the liquid developer. More preferably, a curing resin is used for at least the extreme surface resin layer 4 of the photosensitive medium 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wet image in which a toner in a liquid developer is electrophoresed and an electrostatic latent image formed on a photosensitive medium such as a photoconductor or a photosensitive paper is wet-developed to obtain an image. The present invention relates to a forming apparatus, and more particularly, to a wet image forming apparatus having an improved photosensitive medium.

[0002]

2. Description of the Related Art Generally, in a wet image forming apparatus, an electrostatic latent image formed on a photosensitive medium is brought into contact with a liquid developer containing a toner and a dispersant and the toner is electrophoresed to form a toner on the electrostatic latent image. Is to be visualized by adhering, and after being visualized, a type in which it is transferred to paper and heated and fixed, a type in which it is dried and fixed on the photosensitive medium as it is, and the above steps are repeated using toners of respective colors, There are various applications such as a type that forms a color image.

In such a wet image forming apparatus, the dispersant which is one of the constituents of the liquid developer is a linear or branched aliphatic hydrocarbon, alicyclic hydrocarbon, aromatic hydrocarbon or halogen. It is known to consist of a hydrocarbon-based solvent such as a modified hydrocarbon and an organic solvent such as xylol, toluene and carbon tetrachloride. For example, octane, isooctane, decane, isodecane, dodecane, isododecane, nonane, isoper G, isoper L, norper 1
2, norper 13, norper 15 (isopar and norper are trade names of Exxon Corporation), sorbet 100, shell sol (shell company), I.S. P. Solvent (Idemitsu Petroleum) and the like.

The photosensitive medium which has been used in combination with the liquid developer containing the above dispersant has been an inorganic photoconductive material such as amorphous selenium, selenium-tellurium, selenium-arsenic, amorphous silicone, zinc oxide and titanium oxide. It was limited to sex substances. For example, Japanese Patent Application Laid-Open No. 4-1774 proposes a configuration in which amorphous silicone is used as a photosensitive drum (photosensitive medium) that is not easily deteriorated by a liquid developer.

[0005]

By the way, the organic photosensitive medium is superior to the inorganic type in that it is superior in transparency, film-forming property, flexibility and manufacturability. It could not be used in wet development because it deteriorates with long-term contact with a developer and its photoconductive properties change or disappear. One of the reasons for deterioration is the low molecular weight charge transport material (CTM) dissolved in the resin in the resin layer forming the outermost surface of the conventional organic photosensitive medium.
However, it may be dissolved by the dispersant of the liquid developer. Such a phenomenon occurs when a compound such as a dimer or trimer of a low molecular weight compound has high solubility and dispersibility in a solvent for adjusting a photosensitive medium to form a desired coating liquid. From the point of view, this is because the photosensitive medium was prepared by substantially dissolving and dispersing a compound having a molecular weight of 1000 or less. Therefore, it cannot be used in an electrophotographic copying apparatus or printer in which a photosensitive medium is reused many times.

Conventionally, an organic photosensitive medium has been used in combination with liquid development as an electrophotographic printing plate and an offset master for plate making. In this case, a toner image should be prepared only once. Therefore, the organic photosensitive medium is brought into contact with the liquid development after exhibiting photoconductivity, and deterioration of the organic photosensitive medium due to the dispersant does not pose any problem.

There is also a method in which an overcoat layer is provided on the surface of the organic photosensitive medium so that the organic photosensitive medium can be reused many times. However, the overcoat layer is not practical because it causes a decrease in sensitivity and accumulation of residual charges due to many uses. There is also a proposal in which a dispersant is devised in order to apply the organic photosensitive medium to liquid development. For example, JP-A-3-
No. 43749 describes that if a silicone oil is used as a dispersant, the organic photosensitive medium can be used with little deterioration, but since silicone oil is expensive, it is not suitable for practical use.

The present invention has been made in order to solve the above technical problems, and it is possible to carry out liquid development for a long period of time without unnecessarily degrading an organic photosensitive medium by a liquid developer. Provided is a wet image forming apparatus capable of obtaining stable high image quality.

[0009]

That is, the present invention is
As shown in FIG. 1, a photosensitive medium 1, a latent image forming means 2 for forming an electrostatic latent image on the photosensitive medium 1, and an electrostatic latent image on the photosensitive medium 1 are visualized with a liquid developer. In the wet image forming apparatus provided with the liquid developing means 3, an organic photosensitive medium in which the outermost resin layer 4 does not contain the charge transporting material 5 having a low molecular weight of 1000 or less is used as the photosensitive medium 1. And

The photosensitive medium 1 used in the present invention may have a function-separated multilayer structure or a single layer. The function-separated type (laminated) is mainly composed of a charge generation layer and a charge transport layer. There are two types of combinations depending on the order of stacking the two layers. In the charge generation layer, a charge generation material (CGM) is dispersed in resin. Known examples of compounds used as the charge generation material include bisazo pigments, pyrylium salts, indigo pigments, phthalocyanine pigments, and squarylium pigments.

The charge transport material 5 is dispersed in the charge transport layer. Examples of the compound used as the charge transport material (CTM) 5 include, for example, JP-A-4-257.
No. 866, No. 4-274434, No. 4-338964
The compounds described in Japanese Patent Publication No. 1994-242242 are known. For example, an oxazole compound as a low molecular weight hole transport material,
Known are triphenylamine compounds, pyrazoline compounds, hydrazone compounds, stilbene compounds, butadiene compounds, polyvinylcarbazole compounds as high molecular weight hole transport materials, and fluorenone compounds, diphenoquinone compounds, thiopyran compounds as low molecular weight electron transport materials. .

In a wet image forming apparatus for forming an image by visualizing with a liquid developer containing an organic solvent, a charge transport material 5 composed of a low molecular weight compound of 1000 or less is used as the uppermost layer of the photosensitive medium 1. A structure not provided in the surface resin layer 4, that is, a structure in which the charge transport layer is the lower layer and the charge generation layer is the upper layer is suitable.

As the single-layer photosensitive medium 1, a single-layer structure in which a pigment such as a phthalocyanine pigment, a rhodamine pigment, a crystal violet pigment, a perylene pigment, anthracene, or naphthacene is dispersed in a resin is suitable.

Further, it is preferable to use a curable resin which is not deteriorated by an organic solvent used as a dispersant for the liquid developer in at least the outermost surface resin layer 4 of the photosensitive medium 1. Generally, resins used for the charge generation layer and the charge transport layer are known to be polycarbonate resins, polyvinyl butyral resins, vinyl chloride-vinyl acetate copolymers, and polyester resins, but these resins are all thermoplastic resins. However, since it swells with the organic solvent used as a dispersant for the liquid developer, it is not preferable for wet development. As the curable resin used here, for example, melamine resin, phenol resin, urea resin, epoxy resin, xylene resin, aniline resin, diallyl phthalate resin, silicone resin, alkyd resin, unsaturated polyester resin, urethane resin, polyimide resin And so on. These can be used alone or mixed,
It may also be a copolymer. Examples thereof include melamine-acrylic resin, melamine-polycarbonate resin, polyester-melamine resin, epoxy-melamine resin, polyester-urea resin, urea-acrylic resin and epoxy-urea resin. The curing reaction may be any of heat curing, ultraviolet curing, room temperature curing and the like.

[0015]

According to the above technical means, since the outermost surface resin layer 1 does not contain a low molecular weight compound having a charge transport function, the outermost surface resin layer 4 of the photosensitive medium 1 and the dispersion constituting the liquid developer are formed. Even if the agent is contacted for a long time, the situation where the low molecular weight compound having the charge transport function is eluted is effectively avoided, and the photoconductive property of the photosensitive medium 1 is maintained for a long time.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the embodiments shown in the accompanying drawings. Example 1 FIG. 2 shows an example of a wet color image forming apparatus to which the present invention is applied. In the figure, reference numeral 11 is a photosensitive drum (see FIG. 4A) in which a photosensitive medium 13 is formed on a surface of a substrate 12 made of, for example, aluminum, and 14 is a charger for charging the surface of the photosensitive drum 11 (in this embodiment, a scorotron). ), 15 is a latent image writing unit for forming an electrostatic latent image corresponding to each color component image on the charged photosensitive drum 11, and in this embodiment, a laser scanning unit (ROS: Raster Output) as shown in FIG. Scanner) is used.
The laser scanning unit includes a semiconductor laser 151, a collimator lens 152 for collimating the beam from the semiconductor laser 151, a polygon mirror 153 for deflecting and scanning the beam from the collimator lens 152 along the axial direction of the photosensitive drum 11, and a polygon mirror 153. Light emission time control circuit 1 for controlling the light emission time of the image forming lens 154 and the semiconductor laser 151 for forming the beam from the image on the photosensitive drum 11.
The main part is composed of 55, and a gradation signal based on an image signal from an image reading device or a computer (not shown) is modulated by the emission time control circuit 155, and the semiconductor laser 151 emits a laser beam in accordance with the modulation signal. 1
56 is emitted, and the photosensitive drum 1 is passed through each of the above optical systems.
1 is exposed.

Reference numeral 16 is a liquid developing device for visualizing an electrostatic latent image for each color component formed on the photosensitive drum 11, and in this embodiment, cyan (C) and magenta (M). Developing units 16a containing liquid developers of yellow, yellow (Y) and black (BK) color toners
16d to 16d, one of the developing units 16a to 16d can be selected for each color component image forming cycle of the photosensitive drum 11. Further, reference numeral 17 is a cleaner for removing the residual toner on the photosensitive drum 11, and 18 is a static eliminator (for example, an erase lamp or an AC corotron) for removing the residual charge on the photosensitive drum 11.

Further, reference numeral 20 is an intermediate transfer belt for temporarily transferring and holding the toner images (developed images) of the respective color components on the photosensitive drum 11, and 21 is a transfer sheet for collectively transferring the toner images of the respective color components transferred to the intermediate transfer belt 20. Transfer device for transferring to 22, 23
Is a cleaner that removes residual toner on the intermediate transfer belt 20.

In particular, the photosensitive medium 13 on the photosensitive drum 11 according to this embodiment is adjusted as follows. X
Type metal-free phthalocyanine (Fastogen B manufactured by Dainippon Ink and Chemicals, Inc.
lue 8120B) 5 overlapping parts and polyvinyl butyral resin BM
-2 (manufactured by Sekisui Chemical Co., Ltd.) and 20 parts of tetrahydrofuran and 70 parts of tetrahydrofuran as a solvent were mixed with a ball mill to form 2 parts.
Stirring and dispersion were carried out for 4 hours to prepare a coating liquid. The obtained coating solution was applied to the surface of the aluminum base tube (substrate) 12 to form a thin film, and heat-treated (dried) at 120 ° C. for 1 hour to obtain a single-layer photosensitive drum having a thickness of about 20 μm. This photosensitive medium 1
The photosensitivity characteristic of No. 3 is as shown in (1) of FIG.

The liquid developer supplied to the liquid developing device 3 is Isopar G (Exxon Co.) as a dispersant.
The one containing is used.

The latent image formed on the photosensitive drum 11 is liquid-developed by the developing device 16a supplied with, for example, a cyan developer. The developed image is transferred onto the intermediate transfer belt 20. Subsequently, when forming a color image, the steps of charge elimination, charging, exposure corresponding to each color such as magenta, cyan, and black, development with toner of each color, and transfer are repeated to superimpose the image on the intermediate transfer belt 20 to form a color image. Form an image. Then, the toner images are collectively transferred to the transfer paper 22.

When a wet image forming apparatus using the photosensitive medium 13 of this embodiment was used to repeatedly output images a number of times over a long period of time, stable high image quality was obtained as shown in Table 1 below.

[0023]

[Table 1]

Example 2 The photosensitive medium 13 of the photosensitive drum 11 according to this example is adjusted as follows, unlike the first example. That is, X-type metal-free phthalocyanine (Fast manufactured by Dainippon Ink and Chemicals, Inc.
ogen Blue 8120B) 5 superposed parts and 20 parts by weight of polyester resin Almatex 645 (manufactured by Mitsui Toatsu) and 5 parts by weight of melamine resin U-Van 20-HS (manufactured by Mitsui Toatsu).
Further, 70 parts of a mixed solvent of cyclohexanone and tetrahydrofuran as a solvent was stirred and dispersed by a ball mill for 24 hours to prepare a coating liquid. The obtained coating liquid is applied to the surface of the aluminum base tube (substrate) 12 to form a thin film,
Heat treatment (drying) at 150 ° C for 3 hours, thickness about 2
A 0 μm single-layer photosensitive drum was obtained. The photosensitivity characteristic of the photosensitive medium 13 is as shown in (1) of FIG.

In the same manner as in Example 1 except for the above, a wet image forming apparatus using the photosensitive medium 13 of this example repeated a large number of image outputs over a long period of time.
As shown in Table 1, more stable image quality than that of Example 1 was obtained.

Example 3 The photosensitive medium 13 of the photosensitive drum 11 according to this example is adjusted as follows, unlike Examples 1 and 2. That is, the charge transfer agent represented by the following chemical formula 1 and the polycarbonate resin Iupilon Z-200 (manufactured by Mitsubishi Gas Chemical Co., Inc.)
It is completely dissolved in tetrahydrofuran at a ratio of / 10, and this solution is applied to the surface of an aluminum tube to form a thin film, which is then heat-treated (dried) at 110 ° C. for 1 hour to form a charge transport layer 13a (about 20 μm thick). 4 (b)) was obtained.

[0027]

[Chemical 1]

Next, an X-type metal-free phthalocyanine (Fastogen Blue 8120B manufactured by Dainippon Ink and Chemicals) and a polyester-modified silicone resin KR5221 (manufactured by Shin-Etsu Silicone Co., Ltd.) were used in a ball mill with a mixed solvent of cyclohexanone and tetrahydrofuran at a ratio of 7/10. The resulting coating solution is applied to the charge transport layer 13a to form a thin film and heat-treated (dried) at 120 ° C. for 30 minutes to obtain a charge generation layer 13b having a thickness of about 2 μm (see FIG. 4). (See (b)) was formed to obtain a desired photosensitive drum. The photosensitivity characteristic of the photosensitive medium 13 is as shown in (2) of FIG.

Except for the above, in the same manner as in Example 1, a wet image forming apparatus using the photosensitive medium 13 of this example repeated a large number of image outputs over a long period of time.
As shown in Table 1, stable image quality as stable as in Example 1 was obtained.

Example 4 The photosensitive medium 13 of the photosensitive drum 11 according to this example is adjusted as follows, unlike Examples 1 to 3. That is, the charge transfer agent represented by the above chemical formula 1 and the polycarbonate resin Iupilon Z-200 (manufactured by Mitsubishi Gas Chemical Co., Inc.) are used.
It is completely dissolved in tetrahydrofuran at a ratio of / 10, and this solution is applied to the surface of an aluminum tube to form a thin film, which is then heat-treated (dried) at 110 ° C. for 1 hour to form a charge transport layer 13a (about 20 μm thick). 4 (b)) was obtained. Next, 5 parts by weight of X-type metal-free phthalocyanine (Fastogen Blue 8120B manufactured by Dainippon Ink and Chemicals), 4 parts by weight of acrylic resin Almatex 762LV55A (manufactured by Mitsui Toatsu) and melamine resin U-VAN 20-HS (manufactured by Mitsui Toatsu). ) 1
By weight, 90 parts by weight of cyclohexanone as a solvent are dispersed by stirring for 24 hours by a ball mill, and the obtained coating solution is applied on the charge transport layer 13a to form a thin film.
After heat treatment (drying) at 0 ° C. for 1 hour and at 150 ° C. for 30 minutes, a charge generating layer 13b (see FIG. 4 (b)) having a thickness of about 1 μm is formed to obtain the desired photosensitive drum 11. It was The photosensitivity characteristic of the photosensitive medium 13 is as shown in (2) of FIG.

Except for the above, in the same manner as in Example 1, a wet image forming apparatus using the photosensitive medium 13 of this example repeated a large number of image outputs over a long period of time.
As shown in Table 1, more stable image quality than that of Example 3 was obtained.

Comparative Example The photosensitive medium of the photosensitive drum according to this comparative example is adjusted as follows. That is, the undercoat layer has a thickness of about 0.
5 μm Copolyamide Resin Laccamide 5003
X-type metal-free phthalocyanine (Fastogen Blue 8120B manufactured by Dainippon Ink and Chemicals) and polyvinyl butyral resin BM-2 (manufactured by Sekisui Chemical Co., Ltd.) were coated on the surface of an aluminum tube (substrate) coated with (Dainippon Ink). Was mixed and dispersed with methyl ethyl ketone at a pigment / binder ratio of 1/1 to form a thin film by forming a charge generation layer having a thickness of 0.3 μm. Next, the charge transfer agent represented by the above chemical formula 1 and the polycarbonate resin Iupilon Z-200 (manufactured by Mitsubishi Gas Chemical Co., Inc.) were completely dissolved in 78 parts by weight of tetrahydrofuran at a ratio of 7/10, and this solution was used as a charge generation layer. A thin film was coated on the above and heat-treated (dried) at 100 ° C. for 1 hour to form a charge transport layer having a thickness of about 20 μm, and a desired photosensitive drum was obtained. The photosensitivity characteristic of this photosensitive medium is as shown in (3) of FIG.

Except for the above, in the same manner as in Example 1, a wet image forming apparatus using the photosensitive medium of this comparative example repeated a large number of image outputs over a long period of time.
As shown in FIG. 5, streak-shaped image defects were found on the image.

[0034]

As described above, according to the first aspect of the invention, the outermost surface resin layer of the photosensitive medium does not contain a charge transporting material having a low molecular weight, and the constitutional components of the liquid developer are adopted. As the dispersant consisting of an organic solvent, which is one of the above, prevents the elution and modification of the low molecular weight charge transport material, it effectively suppresses the deterioration of the photosensitive medium due to the liquid developer, and long-term liquid development It is possible to obtain stable high image quality.

Further, according to the second aspect of the invention, since the outermost surface resin layer of the photosensitive medium is formed by the curable resin which does not swell by the dispersant which is one of the constituents of the liquid developer, the liquid development is performed. The deterioration phenomenon of the photosensitive medium due to the agent can be more reliably avoided, and stable high image quality can be obtained for a longer period of time.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a wet image forming apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing a first embodiment of a color wet image forming apparatus to which the present invention is applied.

FIG. 3 is an explanatory diagram showing a specific example of the image writing unit according to the first embodiment.

4A is an explanatory diagram showing a structure of a photosensitive medium according to Examples 1 and 2, and FIG. 4B is an explanatory diagram showing a structure of a photosensitive medium according to Examples 3 and 4. FIG.

FIG. 5 is an explanatory diagram showing the photosensitivity characteristics of the photosensitive media of Examples 1 to 4 and Comparative Example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photosensitive medium, 2 ... Latent image forming means, 3 ... Liquid developing means,
4 ... Outermost surface resin layer, 5 ... Charge transport material

Claims (2)

[Claims] 1. A photosensitive medium (1) and the photosensitive medium (1)
Wet image having a latent image forming means (2) for forming an electrostatic latent image thereon and a liquid developing means (3) for making the electrostatic latent image on the photosensitive medium (1) visible with a liquid developer. In the forming apparatus, as the photosensitive medium (1), an organic photosensitive medium in which a charge transporting material (5) having a low molecular weight of 1000 or less is not contained in the outermost surface resin layer (4) is used. apparatus. 2. The wet image forming apparatus according to claim 1, wherein at least the outermost resin layer (4) of the photosensitive medium (1) is made of a curable resin.