JP3969910B2 - Electrophotographic developing apparatus and electrophotographic developing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus and method for electrophotographic development of a lithographic printing original plate on which an electrostatic latent image is formed, and more particularly to a developing apparatus and a developing method using reversal development.
[0002]
[Prior art]
A method of developing a lithographic printing original plate (hereinafter referred to as a printing original plate) on which an electrostatic latent image is formed while being immersed in a developing solution (for example, a toner solution) is a well-known technique as wet electrophotographic development. Many devices using the method have been developed. In this wet electrophotographic development, there is a method called reversal development, in which a uniformly charged printing original is exposed in an image form, and the printing original is immersed in a developer in an electric field. In other words, the toner particles in the developer charged to the same polarity as in the above are adhered to the printing original plate.
[0003]
FIG. 4 shows an example of a conventional wet electrophotographic developing device (hereinafter simply referred to as a developing device), which is a developing device using a reversal developing method. The developing device 11 mainly includes a rear guide 2 installed at an angle AN with respect to the horizontal plane, an electrode 15 installed with a predetermined gap so as to face the rear guide 2, and a rear guide. 2 is provided with a toner liquid supplier 3 disposed on the side of the inlet portion EN and above the back guide 2 and two squeezing rollers 4a and 4b disposed on the exit portion EX side of the back guide 2. . And the printing original plate P is conveyed toward the exit part EX from the entrance part EN side. An electrostatic latent image is formed on the upper surface of the printing original plate P before entering the entrance portion EN, and after entering the entrance portion EN, the lower surface is conveyed toward the exit portion EX while being in contact with the back guide 2. Is done. During this conveyance, a bias voltage V1 is applied to the electrode 15, and the printing original P is always grounded by two earths 6a and 6b. Then, a toner liquid (not shown in FIG. 4, refer to FIG. 5) is supplied from the toner liquid supply device 3 toward the developing area. After passing between the electrodes 15, the toner is discharged from the toner discharge portion TE in the vicinity of the exit portion EN.
[0004]
FIG. 5 shows a cross-sectional view of the developing device 11 when viewed from the direction of the arrow S in FIG. As shown in FIG. 5, the printing original plate P moves in the electric field generated by the electrode 15 while being immersed in the toner liquid TL. The printing original plate P that has passed through the electric field is conveyed to the next fixing step after the excessive droplets are squeezed by the squeezing rollers 4a and 4b.
[0005]
The state of development will be described with reference to FIG. FIG. 6 is a cross-sectional view showing an area near the printing original plate P, and the area is filled with the toner liquid TL. On the upper surface of the printing original plate P, a non-image part having a positive charge and an image part in which this charge is attenuated by exposure are formed. The surface of the non-image portion is charged to the potential V2. Further, a bias voltage V1 is applied to the electrode 15, and therefore the electrode 15 has a potential V1. The potential V1 of the electrode 15 is lower than the potential V2 of the non-image portion, and therefore an electric field is generated in the direction of the arrow E1 in the range of the non-image portion. The surface of the image portion is charged to a potential V3 (this is generally referred to as a residual potential), but this potential V3 is usually lower than the potential V1 of the electrode 15. Therefore, an electric field is generated in the direction of the arrow E2 in the range of the image portion. That is, the bias voltage V1 is set between the non-image portion potential V2 and the image portion potential (residual potential) V3. Further, the bias voltage V1 is set so as to have a sufficient potential difference between the non-image portion and the image portion.
[0006]
The toner liquid TL contains positively charged toner particles TG. Since the toner particles TG entering the region where the electric field exists due to the electrode 15 are attracted toward the lower potential, the toner particles TG are attracted to the electrode 15 in the electric field range of the non-image portion, and the printing original plate P in the electric field range of the image portion. Is attracted to and attached to it. In this way, the toner particles TG adhere to the electrostatic latent image, and are fixed thereafter. Further, in the elution step, the photosensitive layer to which the toner particles TG are not attached is chemically eluted to form an image.
[0007]
[Problems to be solved by the invention]
Incidentally, in the developing device 11, as described above, the toner liquid TL is supplied by the toner liquid supply device 3, and the supplied toner liquid TL is discharged by the toner discharge portion TE. When comparing the toner supply amount per unit time and the toner discharge amount, if the supply amount from the toner liquid supply device 3 is larger than the discharge amount from the toner discharge portion TE, the toner liquid TL is transferred to the rear guide 2 ( Alternatively, it is accumulated in the region between the printing original plate P) and the electrode 15 and finally accumulates upstream (left side in FIG. 5) from the toner liquid supply device 3.
[0008]
For example, when developing a large printing original plate, the toner discharge port TE is smaller than when developing a narrow printing original plate, so that the developer is relatively difficult to discharge. For this reason, if the same amount of developer as the supply amount suitable for developing a narrow printing original plate is supplied even in the case of a large printing original plate, the supply amount will exceed the discharge amount. As the liquid accumulates, the developer accumulates further upstream than the toner supplier 3 as described above. And since the printing original plate P and the electrode 15 do not oppose in the said upstream, the electric field by the electrode 15 does not exist.
[0009]
In the toner liquid TL, positively charged toner particles TG and counter ions CI are present. Since the counter ion CI is negatively charged, the counter ion CI is attracted to the positively charged non-image portion and is electrodeposited on the upstream side where the electric field due to the electrode 15 does not exist. As a result, the potential V2 on the surface of the non-image portion is lowered. Therefore, the potential difference from the bias voltage V1 decreases and, in some cases, falls below the bias voltage V1. In this state, when the latent image enters the electric field, the toner is more likely to be electrodeposited on the non-image portion because the potential difference from the bias voltage V1 is small, and the image is disturbed or blurred. It will occur.
[0010]
In order to avoid such a situation, it is considered to adjust the supply amount per unit time of the toner liquid Tl from the toner liquid supply device 3 so that the toner liquid TL does not accumulate to the upstream side. However, this depends on the size of the printing original plate P to be developed and the adjustment itself requires a device such as a flow rate sensor, which greatly increases the cost.
[0011]
An object of the present invention is to provide an electrophotographic developing apparatus and an electrophotographic developing method for a printing original plate capable of preventing the occurrence of image disturbance and blurring as described above without significantly increasing the cost.
[0012]
[Means for Solving the Problems]
An object of the present invention is to provide a lithographic printing plate precursor having an electrostatic latent image formed of a non-image portion in which the surface potential remains by exposure after the photosensitive layer is uniformly charged and an image portion in which the surface potential is attenuated. And a bias voltage lower than the surface potential of the non-image portion and higher than the surface potential of the image portion while facing the back guide with a gap. In an electrophotographic developing apparatus, comprising: an electrode to which the developer is applied; and a developer supply device that supplies a developer containing toner particles charged to the same polarity as the electrode from above the electrode toward the gap. have a porous holes for the electrodes passing the developer, a constant amount of the developer is supplied to the developing region, the surplus of the developing solution passes through the porous pores in the electrode this is possible outflow onto the electrode by It is achieved by an electrophotographic developing apparatus according to claim.
[0013]
Another object of the present invention is to provide a lithographic printing method in which an electrostatic latent image is formed which comprises a non-image portion in which the surface potential remains by exposure after the photosensitive layer is uniformly charged and an image portion in which the surface potential is attenuated. In an electrophotographic development method in which an original plate is developed by a reversal development method, a certain amount of developer is supplied to a development region, and an excess of the developer passes through a porous hole in the electrode and onto the electrode. It is also achieved by an electrophotographic development method characterized by being capable of flowing out.
[0014]
In the electrophotographic developing apparatus and the electrophotographic developing method according to the present invention, surplus developer can flow onto the electrode, so that the developer is upstream of the position where the means for supplying the developer is installed. Therefore, it is avoided that the developer stays at a position where the electric field due to the electrode does not exist. As a result, the counter ions in the developer are prevented from being electrodeposited on the charged portion (non-image portion) on the printing original plate, and accordingly, image disturbance and bleeding caused by a decrease in the potential of the charged portion are prevented. be able to.
[0015]
Furthermore, the electrophotographic developing apparatus and the electrophotographic developing method according to the present invention allow an excess developer to flow onto the electrode, so that a certain amount of the developer necessary for good development may be supplied. It is not necessary to adjust the supply amount of the toner liquid per unit time. Therefore, there is no need to provide a flow sensor or the like, so there is no worry of an increase in cost due to this.
[0016]
Furthermore, since the electrophotographic developing apparatus and the electrophotographic developing method according to the present invention can distribute the toner liquid better than before, the fresh toner liquid is always supplied into the developing area (development time). Can do. Further, since more toner particles are present in the fresh toner liquid, the toner particles are easily electrodeposited on the image portion on the printing original plate, and more stable development can be obtained as compared with the conventional type. .
[0017]
Furthermore, in the electrophotographic developing apparatus and the electrophotographic developing method according to the present invention, since the electrode has a hole through which the developer can pass, the toner liquid can be supplied even if the toner liquid is supplied from directly above the electrode. The toner liquid can be caused to flow into a developing area where the electrode and the printing original plate are opposed to each other. As a result, an electric field always exists at the place where the printing original plate and the toner liquid are in contact with each other, and it is possible to prevent the inflow of the toner liquid to the range where there is no electric field due to the electrodes, which is a cause of the conventional problem. .
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0019]
FIG. 1 is a perspective model view of an electrophotographic developing apparatus (hereinafter referred to as a developing apparatus) 1 according to an embodiment of the present invention. The developing device 1 mainly includes a rear guide 2 installed at an angle AN with respect to the horizontal plane, an electrode 5a installed with a predetermined gap so as to face the rear guide 2, and an electrode. The toner liquid supply device 3 installed on 5a and two squeezing rollers 4a and 4b disposed on the exit portion EX side of the back guide 2 are provided. And the printing original plate P is conveyed toward the exit part EX from the entrance part EN side. An electrostatic latent image is formed on the upper surface of the printing original plate P before entering the entrance portion EN, and after entering the entrance portion EN, the lower surface is conveyed toward the exit portion EX while being in contact with the back guide 2. Is done. During this conveyance, a bias voltage V1 is applied to the electrode 5, and the printing original plate P is always grounded by two earths 6a and 6b. A constant amount of toner liquid (not shown in FIG. 1, see FIG. 2) is always supplied from the toner liquid supply device 3.
[0020]
2 shows a cross-sectional view of the developing device 1 when viewed from the direction of the arrow S in FIG. The toner solution TL, which is a developing solution, is supplied from the toner solution supply device 3, and the supplied toner solution TL passes through the electrode 5a and flows into the developing space where the electrode and the printing original plate face each other. The toner liquid that has flowed into the developing space passes between the back guide 2 and the electrode 5a, and is then discharged from the toner discharge portion TE in the vicinity of the exit portion EN in a direction as indicated by an arrow D2, for example. At the same time, the toner liquid TL passes through the electrode 5a again and flows out above the electrode, for example, in the direction indicated by the arrow D1.
[0021]
The developer TL that has flowed out above the electrode 5a may be discharged out of the developing device 1 or stored in that state. The stored developing solution TL automatically passes again through the electrode 5a and flows into the developing region when the developing solution TL becomes insufficient in the developing region between the electrode 5a and the printing original plate P.
[0022]
The printing original plate P transported to the developing device 1 includes a non-image portion in which the surface potential remains by exposure after the photosensitive layer is uniformly charged by corona discharge and an image portion in which the surface potential is attenuated. An electrostatic latent image is formed. Then, the developing device 1 exposes the printing original plate P to an electric field in the toner liquid TL, thereby causing toner particles, which are charged developing materials in the toner liquid TL, to be electrodeposited on the image portion to visualize the image. It is a device to let you. An electric field for promoting development is generated in a region where the electrode 5a to which the bias voltage is applied and the printing original plate P face each other with a gap. The developing device 1 is characterized in that the electrode 5a has a hole BO through which the toner liquid TL can pass. Below, the modification of the electrode 5a and an electrode is demonstrated.
[0023]
3A to 3D are plan views of first to fourth embodiments of electrodes provided in the developing device of the present invention. An arrow A represents the conveyance direction of the printing original plate (not shown in FIG. 3). The electrode 5a shown in FIG. 3A is made of a conductor in which a large number of holes (preferably micro holes) are randomly formed. For the electrode 5a, a porous metal such as a foam metal, a metal mesh, a punch metal, a sintered metal, a porous conductive plastic, or the like can be used. As the porous metal body, for example, Celmet (Sumitomo Electric Co., Ltd. product) can be used.
[0024]
The electrode 5b shown in FIG. 3B is made of a conductor having a slit SL. The slit SL preferably extends in the width direction perpendicular to the transport direction of the printing original plate P.
[0025]
The electrode 5c shown in FIG. 3C is made of a conductor having an elliptical hole or a slit. Shown is an elliptical hole mold. The elliptical holes or slits in this embodiment are arranged in a staggered manner, but they may be arranged randomly, and are preferably selected so that uneven development does not occur due to this arrangement.
[0026]
An electrode 5d shown in FIG. 3D is a combination of the first embodiment and the second embodiment, and no hole or slit is formed in the middle of the electrode. Since the electrode 5d has a non-porous range in the middle, it is possible to achieve stable development while achieving the object of the present invention.
[0027]
The electrodes used in the electrophotographic developing apparatus and the electrophotographic developing method according to the present invention are not limited to the above-described first to fourth embodiments, but the holes or slits formed in the electrodes are in the transport direction of the printing original plate P. Preferably it does not extend along. If the holes or slits extend along the conveying direction of the printing original plate P, the surface of the printing original plate P located under the holes or slits is hardly developed, and as a result, uneven development occurs. Absent.
[0028]
The conditions of the preferred embodiment of the present invention are described below in <1> to <10>.
<1> Celmet (product number # 6, size: 150 × 1100 × 30 mm) is used for the electrode 5a, and the number of micropores on the surface is 70 / inch.
<2> The squeezing rollers 4a and 4b are made of NBR rubber each having a diameter of 60 mm and a surface length of 1200 mm, and the nip pressure is set to 20 kgf (one side).
<3> For the rear guide 2, a glass plate (size: 150 × 1100 × 10 mm) having an uneven surface (0.5 mm pitch) is used.
<4> The gap between the electrode 5a and the back guide 2 is about 2 mm.
<5> Various supports can be used for the support of the printing original plate P. For example, a plastic sheet having a conductive surface, particularly a paper made of solvent-impermeable and conductive, an aluminum plate, a zinc plate, a copper-aluminum plate, a copper-stainless plate, a bimetal plate such as a chromium-copper plate, or chromium- A conductive substrate having a hydrophilic surface such as a trimetal plate such as a copper-aluminum plate, a chromium-lead-iron plate, a chromium-lead-stainless plate, etc. is used, and its thickness is preferably 0.1 to 3 mm, particularly 0. .1 to 0.5 mm is preferable. Among these supports, an aluminum plate is preferably used. This aluminum plate is a plate-like body such as pure aluminum containing aluminum as a main component or an aluminum alloy containing a small amount of foreign atoms, and its composition is not specified, and publicly known and publicly used materials should be used as appropriate. Can do. Furthermore, this aluminum plate can be used by graining and anodizing by a known method. Further, an aluminum plate described in Japanese Patent Publication No. 47-5125, which has been anodized and then immersed in an aqueous solution of an alkali metal silicate, is also preferably used. Silicate electrodeposition as described in US Pat. No. 3,658,662 is also effective. Treatment with polyvinyl sulfonic acid described in West German Patent No. 162214 is also suitable.
<6> A photoconductive material is used for the photosensitive layer of the printing original plate P, and many conventionally known compounds can be used for the photoconductive material. For example, triazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives, pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, N, N-bicarbazyl derivatives, oxazole derivatives, styrylanthracene derivatives In addition, low-molecular photoconductive compounds such as fluorenone derivatives, hydrazone derivatives, benzidine derivatives, and stilbene derivatives, and high molecular compounds such as polyvinyl carbazole and derivatives thereof can be used.
<7> The toner contained in the developer is not particularly limited as long as it has resist properties with respect to the etching solution used in the elution step. It is preferable that the resin component is contained. Examples of the resin component include acrylic resin using methacrylic acid, acrylic acid and esters thereof, vinyl acetate resin, copolymer resins such as vinyl acetate and ethylene or vinyl chloride, vinyl chloride resin, vinylidene chloride resin, polyvinyl butyral. Vinyl acetal resins such as polystyrene, copolymer resins such as polystyrene, styrene and butadiene, and methacrylic acid esters, polyethylene, polypropylene and chlorinated products thereof, polyester resins (for example, polyethylene terephthalate, polyethylene isophthalate, bisphenol A polycarbonate, etc.) , Phenol resin, xylene resin, alkyd resin, vinyl-modified alkyd resin, gelatin, cellulose ester derivatives such as carboxymethylcellulose, wax, polyolefin, wax, etc. It is.
<8> The toner liquid discharge port of the toner liquid supply device 3 is formed in a slit shape, and its width is about 2 mm. The toner liquid supply device 3 supplies about 40 liters of toner liquid per minute.
<9> A bias voltage of about 160 volts is applied to the electrode 5a. The potential of the non-image portion formed on the surface of the printing original plate P is about 360 volts.
<10> The inclination angle AN of the apparatus is about 7 °, and the conveyance speed of the printing original plate P is about 4 m per minute.
[0029]
Using the developing device 1 under the above conditions <1> to <10>, development of the printing original plate P having dimensions of 0.5 × 1 m ^{2 to} 1.0 × 1 m ² was performed. Even very good images could be visualized.
[0030]
The present invention can be implemented without being limited to the above-described embodiment.
[0031]
【The invention's effect】
As described above, the electrophotographic developing apparatus and the electrophotographic developing method of the present invention enable the electrode to which a bias voltage is applied to pass through the developing solution, thereby realizing a good distribution of the developing solution. Yes. As a result, the toner liquid does not accumulate to the upstream side of the position where the electrode is present, and therefore it is possible to avoid the toner liquid from staying up to a position where the electric field does not exist. As a result, it is possible to prevent the counter ions in the toner liquid from being electrodeposited on the charged portion (non-image portion) on the printing original plate. Therefore, image disturbance and bleeding caused by a decrease in the potential of the charged portion are generated. Can be prevented. At this time, there is no significant increase in cost.
[Brief description of the drawings]
FIG. 1 shows a perspective model view of an embodiment of an electrophotographic developing apparatus according to the present invention.
FIG. 2 is a cross-sectional view of an embodiment of an electrophotographic developing apparatus according to the present invention.
FIG. 3 shows an example of electrodes provided in the electrophotographic developing apparatus according to the present invention.
FIG. 4 is a perspective model view of a conventional electrophotographic developing apparatus.
FIG. 5 is a sectional view of a conventional electrophotographic developing apparatus.
FIG. 6 is a model diagram for explaining the theory of electrophotographic development.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Electrophotographic developing apparatus 2 Back surface guide 3 Toner liquid supply device 4a, 4b Diaphragm rollers 5a, 5b, 5c, 5d Electrodes 6a, 6b Earth AN Inclination angle BO with respect to the ground surface of the back guide
BS Elliptical hole (slit)
EN Rear guide inlet portion EX Rear guide outlet portion SL Slit TE Toner discharge portion V1 Bias voltage V2 Non-image portion potential V3 Image portion potential (residual potential)

Claims (2)

The lithographic printing original plate on which the electrostatic latent image formed of the non-image portion where the surface potential is left by the exposure after the photosensitive layer is uniformly charged and the image portion where the surface potential is attenuated is formed is in contact with the ground surface. A back guide inclined with respect to the back guide, and an electrode to which a bias voltage lower than the surface potential of the non-image portion and higher than the surface potential of the image portion is applied while facing the back guide with a gap. An electrophotographic developing apparatus comprising: a developer supplying device that supplies a developer containing toner particles charged to the same polarity as the electrode from above the electrode toward the gap. A certain amount of developer is supplied to the development area, and an excess of the developer passes through the porous hole in the electrode and onto the electrode. What outflow can der, the electrodes foam Electrophotographic developing device which is a genus. Development of a lithographic printing plate precursor with an electrostatic latent image composed of a non-image area in which the surface potential remains by exposure after the photosensitive layer is uniformly charged and an image area in which the surface potential is attenuated is developed by a reversal development method. in electrophotographic developing methods for a certain amount of the developing solution is supplied to the developing region, I outflow can der surplus of the developing solution passes through the porous holes in the electrode on the electrode, An electrophotographic developing method , wherein the electrode is a foam metal .

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