JP2993572B2 - Electrophotographic lithographic printing plate wet development method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for wet developing an electrophotographic lithographic printing plate.

[Conventional technology]

Many methods for preparing a lithographic printing plate are already known. For example, an original made of silver halide film is closely attached to the printing master,
The photosensitive layer of the original is directly exposed to ultraviolet light or the like, thereby forming a cured portion corresponding to the image portion of the document and a non-cured portion corresponding to the non-image portion, and washing and removing the non-cured portion with an alkali or water. This is a plate making method in which a cured portion is made ink-receptive. The printing plate obtained by this method is called a so-called PS plate, and is widely used.

On the other hand, with the development of mechanical image processing technology and memory development and transmission technology of large-capacity data, an electronic editing system has been adopted in the newspaper field and the like. With this system, image input, correction, editing, etc. of characters, figures, photographs, etc. can all be controlled by computer, and furthermore, output is high-speed communication network,
Alternatively, since a film can be instantly output to a remote terminal plotter by using satellite communication or the like, a printing plate can be manufactured in a shorter time than before. But,
In the printing field, such as newspaper printing, where this electronic editing system is currently used, it is an important issue to further reduce the time required for producing a printing plate. Therefore, there is a demand for a direct plate making system in which image information modulated light emitted from a light source of an output plotter is written directly on a PS plate instead of a silver halide film. However, currently used PS plates have low sensitivity, and require exposure with a light source having a short wavelength such as ultraviolet rays and having high energy, and the light source of the output plotter (for example, Ar laser, He-Ne laser, semiconductor With a long-wavelength laser light source such as a laser, a printing plate cannot be produced within a practical time. Therefore, an electrophotographic lithographic printing plate having higher sensitivity to the light source of the output plotter than the PS plate has been developed.

An electrophotographic lithographic printing plate is produced from an electrophotographic photosensitive member in which a photoconductive layer containing a photoconductive substance is adhered on a conductive support such as aluminum. The material constituting the photoconductor layer of the electrophotographic photosensitive member is described in JP-B-37-17162.
No. 38-7758, No. 46-39405, JP-A-52-2437
No. 57-161863, No. 58-2854, No. 58-28760,
Nos. 58-118658, 59-12452, 59-49555, 62
Organic photoconductive compound / binder resin materials as described in JP-A-217256, JP-A-63-226668 and JP-A-1-21659 are excellent in practical sensitivity, printing durability and the like.

In the plate making step of the electrophotographic lithographic printing plate, first, a predetermined charging step is performed on the photoconductor layer of the electrophotographic photosensitive member, and a uniform charge is applied. Next, an electrostatic latent image corresponding to the image is formed by exposure. Subsequently, development and fixing using an electrophotographic developer are performed, and a toner image corresponding to the electrostatic latent image is formed. The non-image area other than the toner image is dissolved and removed (eluted) by a solution containing an alkaline agent or the like, and then the apparent pH of the plate surface is adjusted by washing with water or an acidic rinsing liquid, and if necessary, Processing such as application of a plate surface protection liquid (protective gum liquid) is performed to obtain a final printing plate.

By the way, in such a plate making system utilizing the electrophotographic method, development using a liquid developer is advantageous from the viewpoint of high resolution. In the case of using the wet developing method, it is necessary to remove as much as possible and uniformly the excess liquid developer after forming an electrostatic latent image as an image with toner in order to obtain a high resolution. As a removing method, a squeezing roll method in which the plate is sandwiched between upper and lower rolls so that excess liquid developer present on the plate surface is not taken out of the developing device, and air is blown on the plate surface to push back the liquid developer Although there are a drawing method using an air knife and a drawing method using corona charging, a drawing roll method is effective from the viewpoint of simplicity, good drawing effect, uniformity in the drawing width direction, and the like. FIG. 1 is a schematic cross-sectional view of a main part showing an example of an electrophotographic lithographic printing plate wet developing apparatus employing an squeezing roll method. The electrophotographic lithographic printing plate 1 is carried into the developing section by the carrying roll pairs 2 and 3 with the plate surface 1a facing upward, and passes between the developing electrode 4 and the guide 8. At this time, the liquid developer is supplied from the developer supply port 5 to the surface of the printing plate 1a through the developer introduction pipe 7 and the developer rectifying chamber 6, and the developed printing plate 1 is moved through the nip of the pair of squeezing rolls 9, 10. Through which excess liquid developer is removed from the printing plate. Rubber rolls are extremely effective as the squeezing roll pairs 9 and 10.

It is well known that the rubber roll used must have resistance to the components of the liquid developer used. However, the hardness of the roll is very important to enhance the drawing effect together with the presser pressure of the roll,
Further, it is not known that the quality of an image to be formed is also affected, and is not considered much. In the forward development method, Japanese Utility Model Publication No.
As disclosed in JP-A-2-47331, there is an example in which a hard material such as a metal roll or polycarbonate having no elasticity is used on the plate surface side of the squeezing roll.

As a result of various experiments, it has been found that the hardness of the roll easily affects the image quality, particularly when a halftone dot image having a high linear density is formed by reversal development.

In reversal development, the image area developed by the toner particles is the part where the surface potential has disappeared due to exposure,
The adhesive force of the charged toner particles to the plate surface is a Coulomb repulsion force from the surface potential mainly present in the non-image portion in the thin line portion. If the repulsion is reduced, the toner particles scatter from the image area. For example, when light is irradiated on the photoconductive layer after the development is completed, the charge held in the non-image portion is lost, and the electrical contrast with the image portion is also lost. As a result, the toner is held in the image portion. I lose my strength. Furthermore, if the dispersion medium is present more than necessary because the aperture is not good, there is a considerable repulsion between the charged toner particles, so that the toner necessarily moves and the image is distorted. Also, even if light does not strike, since the non-image portion potential may decrease due to dark decay of the photoconductive layer in relation to the time from the development process to the fixing process,
Development as described above may occur.

In the system for making an electrophotographic lithographic printing plate according to the present invention, the support of the electrophotographic lithographic printing plate is generally a surface-treated metal plate such as aluminum. Therefore, it is preferable to carry out linear horizontal transfer from the exposure to the elution step. In addition, even when a large number of sheets are processed, the temperature fluctuation of each plate can be set to a small value, and since the plate is not in contact with the toner-developed plate surface, it is advantageous to perform fixing by radiant heat which does not have a physical effect. However, in this case, there is a possibility that light from a halogen lamp or the like, which is a heat source of radiant heat, may be unnecessarily irradiated onto the image-formed plate immediately after development because the transport line is horizontal.

As described above, if the hardness of the roll itself is not appropriate, the excess liquid developer cannot be squeezed out even if the nip pressure of the roll is adjusted. Instead, an image with poor resolution is eventually formed. In particular, this is a very important problem in toner development for making a printing plate requiring high resolution, such as for color printing.

[Object of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic wet development method which is uniform and has high resolution in electrophotographic wet development processing, and particularly has excellent reproducibility of fine lines and halftone dots during reversal development.

[Means for solving the problem]

The present inventors have made intensive studies and as a result, the hardness of the squeezing roll in wet development of an electrophotographic lithographic printing plate using a metal support, particularly in reversal development, has a great influence on final image formation. I found something.

In other words, if the hardness is high, the drawability is reduced, causing image flow. If the roll pressing pressure is increased to improve the drawability, the formed toner image is crushed, resulting in an image with poor resolution. Further, if the nip width is too narrow, the end of the plate cannot be completely squeezed and the image at the rear end is disturbed.

If the hardness is too low, the contact area between the rolls, the so-called nip width, increases, and the rolls are deformed and stress is applied to the image, which again causes image collapse.

In order to prevent the above, the exit side squeezing roll is held down by at least a force that does not rise when entering the plate. In particular, the hardness of the squeezing roll is JIS (K6301)
In the range of 20 to 70 degrees, more preferably in the range of 40 to 60 degrees in hardness measurement with a spring type hardness tester type A specified in the paragraph, there is no so-called poor drawing, high resolution, high image quality. We found that a good plate-making product could be obtained.

That is, the present invention is a method of wet-developing a sheet-shaped electrophotographic lithographic printing plate using a metal support by passing it through a developing device having a pair of squeezing rolls, the method being formed by the development of the pair of rolls. The roll hardness of the roll in contact with the toner image forming surface of the lithographic printing plate must be at least 20 degrees with a spring-type hardness tester A type specified in JIS (K6301).
An electrophotographic lithographic printing plate wet developing method, wherein development is performed while maintaining the temperature within a range of 70 degrees or less.

In the practice of the present invention, the hardness of the pair of rolls that come into contact with the back surface of the lithographic printing plate of the squeezing roll is usually the same, but is not particularly limited.

In general, Barcoal hardness, Rockwell hardness, Vickers hardness and the like are known for measuring hardness of plastics. For the measurement of rubber rolls, blankets, etc., for printing machines, the above-mentioned spring type hardness tester type A, which is very simple and portable, is generally used. This was also used for measuring the roll hardness according to the invention.

As a method of measuring the roll hardness according to the present invention, a roll to be measured is installed horizontally, and a needle of a hardness tester is pressed vertically against a tangent line of the roll and a longitudinal direction of the roll, and pressed with a constant force. Read the maximum value indicated by the hardness meter.
The value at that time is defined as the roll hardness here. Preferably, this measurement is repeated several times at arbitrary points in the longitudinal direction of the roll, and the average value is defined as the hardness of the roll.

The nip pressure of the roll on the developing device varies depending on the weight of the roll, the material, the shape, and the thickness of the printing original plate, but within the above hardness range, 1 g / cm per length in the roll width direction. If it is in the range of ~ 100g / cm, there is no problem in practical use. According to this method, anyone can easily measure with a little training if calibration is performed because of its simplicity. Since the measurement can be performed with the squeezing roll incorporated in the developing device, the elasticity of the squeezing roll may change under various atmospheric conditions depending on the material used, such as rubber, when used for a long period of time. However, since the roll management is performed by measuring the roll hardness according to the present invention, it is possible to prevent the occurrence of image defects due to the deteriorated roll.

Further, the squeezing roll according to the present invention may be a material having elasticity in all of the cylindrical portions, for example, may be made of rubber,
A "core rod" made of metal or the like may be present at the center in order to increase the strength or increase the drawing pressure. The diameter of the entire roll, including the core rod, cannot be unconditionally determined because of the size of the developing device, the size of the electrophotographic lithographic printing plate, the amount of liquid, and many other factors. General. In such a roll, the so-called rubber range is not particularly limited, and it is sufficient that at least the roll surface layer is made of rubber and the hardness of the roll is in the above range.

As the elastic material of the squeezing roll according to the present invention, those having resistance to the components of the liquid developer and hardly swelling,
In addition, it is only necessary to have a certain degree of wear resistance, aging resistance, weather resistance, and the like. Preferred is a synthetic rubber made of a component having low solubility in hydrocarbons and solvents, and particularly preferred is an acrylonitrile-butadiene copolymer rubber (NB
R), isoprene-acrylonitrile copolymer rubber, chloroprene rubber (CR), acrylic rubber (ACM / ANM), chlorosulfonated polyethylene rubber (CSM), silicone rubber (Q), fluorine rubber (FKM), polysulfide rubber (TR) And the like. Among them, NBR containing a large amount of acrylonitrile is excellent in terms of processability, durability, solvent resistance, cost and the like. In addition, the rubbers include additives such as a reinforcing filler, a filler for increasing the amount, a dispersibility improver, an adhesion improver, a heat-resistant additive, an antioxidant, a colorant, a cross-linking agent, and a curing catalyst. It can be contained within a range that does not affect the solvent properties and the like.

The rolls according to the present invention are desirably used as upper and lower pairs as squeezing rolls on the developing device outlet side in order to prevent generation of static electricity due to frictional charging. Of course, it can be used as a roll at the plate entrance of the developing device used.

The electrophotographic lithographic printing plate used in the present invention has at least one photoconductive layer on a conductive substrate.

As the conductive substrate, a metal plate such as an aluminum plate and a zinc plate is used, and its thickness is preferably 0.1 to 3 mm, and particularly preferably 0.1 to 0.5 mm. Among these substrates, an aluminum plate having an anodized film, which is anodized, is preferable. Further, the aluminum plate applied to the present invention is not limited in its composition, surface treatment and the like, and any conventionally known and publicly available printing plate material can be appropriately used.

A conventionally known electrophotographic photosensitive layer is provided on such a conductive substrate. Many conventionally known inorganic or organic compounds can be used as the photoconductive material used for the electrophotographic photosensitive layer. For example, inorganic photoconductive materials include selenium and selenium alloys, amorphous silicon, Cd, CdSe, CdSSe, ZnO, ZnS, and the like. Examples of the organic photoconductive material include: a) a triazole derivative described in U.S. Pat. No. 3,112,197, etc., b) an oxadiazole derivative described in U.S. Pat. No. 16096, etc .; d) U.S. Pat. Nos. 3,542,544, 3,154,022, 3,820,899, JP-B-45-555, JP-B-51-10983, JP-A-51-983.
No. 93224, No. 55-108667, No. 55-156953, No. 56-366
No. 56, etc., e) US Pat. Nos. 3,180,729 and 4,278,746;
No. 55-88064, No. 55-88065, No. 49-105537, No. 55-
51086, 56-80051, 56-88141, 57-45545
Pyrazoline derivatives and pyrazolone derivatives described in JP-A Nos. 54-112637 and 55-74546; f) U.S. Pat. No. 3,615,404, JP-B-51-10105,
Nos. 46-3712, 47-28336, JP-A-54-83435,
Phenylenediamine derivatives described in JP-A-54-110836 and JP-A-54-119925; g) U.S. Pat. Nos. 3,567,450, 3,180,703 and 3,240,597
No. 3658520, No. 42322103, No. 4159661, No. 40123
No. 76, West German Patent (DAS) 1110518, Japanese Patent Publication No. 49-
No. 35702, No. 39-27577, JP-A-55-144250, No. 56-
No. 119132, No. 56-22437, etc .; h) Amino-substituted chalcone derivative described in U.S. Pat. No. 3,352,501; i) N, N- described in U.S. Pat. No. 3,542,546, etc. A bicarbazyl derivative; j) an oxazole derivative described in U.S. Pat. No. 3,257,203; k) a styryl anthracene derivative described in JP-A-56-46234; 1) a styryl anthracene derivative described in JP-A-54-110837 M) U.S. Pat. No. 3,717,462, JP-A-54-59143 (corresponding to U.S. Pat. No. 4,150,087), JP-A-55-52063, and JP-A-55-52063.
-52064, 55-46760, 55-85495, 57-113
No. 50, Nos. 57-148749, No. 57-104144, etc .; n) U.S. Pat. Nos. 4,047,948, 4,047,949, 4,265,990
No. 4,273,846, No. 42,998, and No. 4,306,008, etc .; o) JP-A-58-19095, JP-A-59-95540, JP-A-59-97148.
Stilbene derivatives described in JP-B-59-195658, JP-B-62-36674 and the like; p) Polyvinylcarbazole and its derivatives described in JP-B-34-10966; q) JP-B-43-18674, 43 -Polyvinylylene, polyvinylanthracene, poly-2- described in JP-A-19192
Vinyl-4- (4'-dimethylaminophenyl) -5
Vinyl polymers such as phenyloxazole and poly-3-vinyl-N-ethylcarbazole; r) polymers such as polyacenaphthylene, polyindene and acenaphthylene / styrene copolymer described in JP-B-43-19193; ) Condensed resins such as pyrene / formaldehyde resin and ethyl carbazole / formaldehyde resin described in JP-B-56-13940, etc. t) Various triphenyls described in JP-A-56-90883 and JP-A-56-161550 Methane polymer, u) U.S. Pat. Nos. 3,397,866 and 4,466,802;
Nos. 827, 52-655643, JP-A-64-2061, 64-438
Metal-free or metal (oxide) phthalocyanines and naphthalocyanines described in No. 9 and the like, and derivatives thereof.

The organic photoconductive compound is not limited to the compounds listed in a) to u), and any known organic photoconductive compound can be used. These organic photoconductive compounds are:
If desired, two or more kinds can be used in combination.

In addition, various pigments, dyes, and the like can be used in combination for the purpose of improving the sensitivity of the photoconductor and giving sensitivity to a desired wavelength region.

In photoreceptors for electrophotographic printing plates, the photoconductive compound itself may have film properties, but if the photoconductive compound alone does not have film properties, a binder resin may be used in combination. I can do it. In the electrophotographic photoconductive layer, it is necessary to finally remove the non-image part photoconductive layer. This step is based on the relative relationship between the solubility of the photoconductive layer in the eluate and the resistability of the toner image in the eluate. However, at least the binder resin is preferably a polymer compound soluble or dispersible in an eluate described later. A monomer-containing copolymer having an acid anhydride group or a carboxylic acid group and a phenol resin have a high charge retention when used as a photoreceptor for an electrophotographic printing plate, and can therefore be advantageously used.

As a monomer-containing copolymer having an acid anhydride group,
A copolymer of styrene and maleic anhydride is preferred. Examples of the monomer-containing copolymer having a carboxylic acid group include a copolymer of styrene and maleic acid monoester, and a copolymer of acrylic acid or methacrylic acid and their alkyl ester, aryl ester or aralkyl ester. Coalescence is preferred. Further, a copolymer of vinyl acetate and crotonic acid is also good. Particularly preferred phenolic resins include novolak resins obtained by condensing phenol, o-cresol, m-cresol, or p-cresol with methanal or ethanal under acidic conditions. The binder resin may be used alone or in combination of two or more.

The electrophotographic lithographic printing plate used in the present invention is obtained by coating a photoconductive layer on a conductive support according to a conventional method. In producing the photoconductive layer, a method of including the components constituting the photoconductive layer in the same layer, or a method of separately including two or more layers, for example, a charge carrier generating material and a charge carrier transporting material. A method of separating and using different layers is known, and any method can be used. The coating solution is prepared by dissolving each component constituting the photoconductive layer in an appropriate solvent, but when using a component insoluble in a solvent such as a pigment,
It is used by dispersing with an average particle size of 0.01 to 5 μm using a dispersing machine such as a ball mill, a paint shaker, and a dyno mill. The binder resin and other additives used in the photoconductive layer can be added during or after the dispersion of the pigment or the like. An electrophotographic lithographic printing plate can be obtained by applying the coating solution thus prepared on a support by a known method such as spin coating, blade coating, dip coating, rod bar coating, spray coating, and the like.

If necessary, in addition to the photoconductive compound and the binder resin, a plasticizer, a surfactant, and other additives may be added to the photoconductive layer for the purpose of improving the film properties such as the flexibility of the photoconductive layer and the shape of the coated surface. Can be added.

An intermediate layer may be provided between the conductive support and the photoconductive layer, if necessary, to improve adhesion, electrophotographic properties, and the like.

The electrophotographic lithographic printing plate thus prepared is cut into a desired size, and is used as a printing plate by the following plate making method. However, when a printing plate having a size larger than the printing plate is used, the printing plate is used. In order to prevent ink stains caused by the side portions of the electrophotographic lithographic printing plate, a layer that holds a potential in the charging step may be provided on the side portions of the cut electrophotographic lithographic printing plate. Further, in order to promote elution of the layer, an intermediate layer or the like having higher hydrophilicity than the potential holding layer can be provided below the potential holding layer.

The electrophotographic lithographic printing plate used in the present invention can be prepared by a known operation using the above-described electrophotographic lithographic printing plate. That is, it is charged substantially uniformly in a dark place, and forms an electrostatic latent image by image exposure. As the exposure method,
Reflection image exposure using a xenon lamp, a tungsten lamp, a fluorescent lamp, or the like as a light source, contact exposure through a transparent positive film, or scanning exposure using a laser beam, a light emitting diode, or the like. When performing scanning exposure, He-Ne laser, He-Cd laser, argon ion laser, krypton ion laser, ruby laser, YAG laser,
Nitrogen laser, dye laser, excimer laser,
Scanning exposure using a laser light source such as a semiconductor laser such as GaAs / GaAlAs or InGaAsP, alexandrite laser, or copper vapor laser, or scanning exposure using a light emitting diode or liquid crystal shutter (line using a light emitting diode array, liquid crystal shutter array, etc.) (Including a printer type light source).

Next, the electrostatic latent image is developed by a wet reversal developing method using a roll according to the present invention, which is capable of forming a fine image and producing a printing plate having good reproducibility. The range of the bias voltage to be applied cannot be unconditionally defined because it varies depending on the surface potential of the non-image portion of the printing original plate, the electrical properties of the toner to be used, and the like. It is suitable.

In the case of reversal development, the polarity of the toner to be used is the same as the polarity to which the printing original plate to be used is charged, and if the polarity of the applied bias voltage is also the same, it is possible to use both + and-without any problem. .

The toner image can be fixed by a known fixing method, for example, heat fixing, pressure fixing and the like. Using the toner image formed in this manner as a resist, the non-image portion photoconductive layer and the side surface potential holding layer are removed with an eluent, and a process such as gas blowing is performed to prepare a printing plate.

〔Example〕

Examples 1 to 3 and Comparative Examples 1 to 3 A JIS1050 aluminum sheet was immersed in a 10% NaOH aqueous solution at 60 ° C., and was etched so that the amount of aluminum dissolved was 6 g / m ² . After washing with water, it was immersed in a 30% nitric acid aqueous solution for 1 minute to neutralize, and sufficiently washed with water. Thereafter, electrolytic surface roughening was performed in a 0.7% aqueous nitric acid solution for 20 seconds, and the surface was washed by immersion in a 20% aqueous sulfuric acid solution at 50 ° C., followed by washing with water. In addition, 20%
An anodizing treatment was carried out in an aqueous sulfuric acid solution, followed by washing with water and drying to prepare a printing plate support.

The surface of the support is treated with a paint shaker.
The following photoconductive layer composition dispersed in time was applied with a bar coater, and dried at 90 ° C. for 5 minutes to prepare an electrophotographic lithographic printing plate. At this time, the coating amount of the photoconductive layer was 4.5 g / m ² .

Photoconductive layer coating liquid composition Butyl methacrylate / methacrylic acid copolymer (40% methacrylic acid) 18 parts Metal-free phthalocyanine 4 parts Butyl acetate 60 parts 2-propanol 18 parts The printing plate thus prepared is placed in a dark place. After applying a corona discharge to charge the surface potential (V ₀ ) so as to be about +300 V, scanning image exposure was performed using a semiconductor laser (780 nm), and immediately using the wet developing apparatus shown in FIG. Wet reversal development (developing bias voltage 90 V) was performed with a positively charged liquid developer (LOM-ED III, manufactured by Mitsubishi Paper Mills, Ltd.). At this time, stainless steel core rods 9b, 10 are used as the squeezing rolls 9, 10.
The peripheral surface of b is covered with a rubber coating layer 9a, 1 having the hardness shown in Table 1.
Six roll pairs with 0a (roll pressure 50 g / cm) were used.

After the development, the dispersion medium of the liquid developer remaining on the plate surface was allowed to stand at room temperature until naturally dried, and then heat-fixed to obtain a toner image on the photoconductive layer. Table 1 shows the results of observation of the toner image.

In each of the rolls used in the examples and comparative examples, the elastic part is made of NBR, and the core rod (diameter 18 mm) is made of stainless steel.
Each roll hardness was measured by a rubber hardness tester (Teklock GS-706), which is a spring type hardness tester A type based on JIS K6301.

Note) "No collapse" in the toner image observation results in Table 1
Indicates that an image faithful to the exposed image was formed, and `` toner collapse '' indicates that a fogging state in which toner in the image portion was scattered around the image formed by the toner, "Image flow" is
This shows a state in which the toner image has collapsed from the rear end to the rear of the image.

As described above, there is a difference in the toner image formed due to the hardness of the squeezing roll of the developing device, and in any of the toner images formed in Examples 1 to 3, even after the treatment such as elution, the toner image collapses. Although a high-resolution printing plate without the like was obtained, any of the toner images formed in Comparative Examples 1 to 3 was disturbed in the same manner as the toner image, even after performing a process such as elution. Only a printing plate with poor resolution was obtained.

Comparative Examples 4 and 5 In the developing device shown in FIG. 1, the elastic layer 9a of the roll 9 was used in Comparative Example 4 with styrene-butadiene rubber (SBR) [roll hardness 50], and in Comparative Example 5 with ethylene-propylene rubber (EPD
M) Example 1 except that each [roll hardness 45] was used.
Using the same electrophotographic printing original plate as in
Performed continuously for hours. In the initial stage, an image without disturbance was obtained, but the occurrence of image defects such as toner collapse gradually increased, and the printing original plate made after 5 hours had severe image collapse and was not practically usable. Was. At this point, the roll was swollen and deformed, and the roll hardness was measured to be about 15.

Comparative Example 6 In the developing device of FIG. 1, toner development and fixing were performed in the same manner as in Example 1 except that the elastic layer 9a of the roll 9 was made of polycarbonate [roll hardness 97]. In the resulting toner image on the lithographic printing plate, image defects such as toner collapse occurred, and especially in the range of about 30 mm from the rear end of the plate, the image was very poor due to poor drawing of the liquid developer, and the plate-making printing was performed. The plate was not practical.

〔The invention's effect〕

According to the present invention, a halftone image having a high linear density can be developed at a high resolution in an electrophotographic wet development of a metal support, particularly in an electrophotographic wet reversal development process.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an example of a developing device to which the present invention is applied. 1 electrophotographic lithographic printing plate 1a electroplate lithographic printing plate 2 loading roll (a: elastic layer, b: core rod) 3 loading roll (a: elastic layer, b: core rod), 4: developing electrode, 5: developer supply port, 6: developer rectification chamber, 7: developer introduction pipe, 8: guide, 9: outlet side squeezing roll (a : Elastic body layer, b: core rod), 10 ... Outlet side squeezing roll (a: elastic body layer, b: core rod),

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-49-106834 (JP, A) JP-A-55-153971 (JP, A) Japanese Utility Model Showa 58-192657 (JP, U) Japan Rubber Association Ed., “Rubber Test Method”, reprint, The Rubber Association of Japan October 1, 1968, 263 (3.3.5 Relationship between measured values, especially Fig. 3.3-29)

Claims (1)

(57) [Claims] 1. A method for wet-developing a sheet-like electrophotographic lithographic printing plate using a metal support by passing it through a developing device having a pair of squeezing rolls, the method comprising: The development of a roll on the side that comes into contact with the toner image forming surface of a lithographic printing plate is maintained at a roll hardness of 20 degrees or more and 70 degrees or less using a spring-type hardness tester A type specified in JIS (K6301). An electrophotographic lithographic printing plate wet developing method.